pi rr4 0300 engine n74 en

Technical training.Product information.

Rolls-Royce

N74 engine.

General information

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The following symbol / sign is used in this document to facilitate better comprehension and to draw attention toparticularly important information:

contains important safety guidance and information that is necessary for proper system functioning and which it isimperative to follow.

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Vehicles made by Rolls-Royce Motor Cars Limited meet the highest demands with regard to safety and quality.Changes in terms of environmental protection, customer benefits and design make it necessary to develop sys-tems and components on a continuous basis. Consequently, this may result in differences between the content ofthis document and the vehicles available in the training course.

As a general principle, this document describes left-hand drive vehicles in the European version. Some controls orcomponents are arranged differently in right-hand drive vehicles than those shown on the graphics in this docu-ment. Further discrepancies may arise from market-specific or country-specific equipment specifications.

Additional sources of information

Further information on the individual topics can be found in the following:

• in the Owner's Handbook

• in the Integrated Service Technical Application.

Contact: [email protected]

©2009 Rolls-Royce Motor Cars Limited, United Kingdom

Reprinting, also of excerpts, only with the consent in writing of Rolls-Royce Motor Cars Limited,United Kingdom

The information in the document is part of the Rolls-Royce technical training course and is intended for its train-ers and participants. Refer to the latest relevant Rolls-Royce information systems for any changes/supplements tothe Technical Data.

Status of the information: July 2009VH-23/International Technical Training

mailto:[email protected]

N74 engine.Contents.

1. Introduction...................................................................................................................................................................................................................................................................................11.1. Highlights.....................................................................................................................................................................................................................................................................1

1.1.1. Technical data...............................................................................................................................................................................................................21.1.2. Full load diagram....................................................................................................................................................................................................31.1.3. Engine identification..........................................................................................................................................................................................4

2. Engine mechanical system.............................................................................................................................................................................................................................52.1. Engine housing...................................................................................................................................................................................................................................................5

2.1.1. Engine block...................................................................................................................................................................................................................52.1.2. Cylinder head...............................................................................................................................................................................................................62.1.3. Oil sump...............................................................................................................................................................................................................................62.1.4. Crankcase ventilation.....................................................................................................................................................................................6

2.2. Crankshaft drive.........................................................................................................................................................................................................................................142.2.1. Crankshaft......................................................................................................................................................................................................................142.2.2. Connecting rods.................................................................................................................................................................................................152.2.3. Pistons...................................................................................................................................................................................................................................15

2.3. Camshaft drive..............................................................................................................................................................................................................................................152.3.1. Chain tensioner....................................................................................................................................................................................................15

2.4. Valve gear..............................................................................................................................................................................................................................................................152.4.1. VANOS............................................................................................................................................................................................................................... 162.4.2. Camshafts........................................................................................................................................................................................................................172.4.3. Roller cam followers...................................................................................................................................................................................172.4.4. Valves......................................................................................................................................................................................................................................17

2.5. Belt drive................................................................................................................................................................................................................................................................172.5.1. Revolver tensioning system.............................................................................................................................................................19

3. Oil supply.........................................................................................................................................................................................................................................................................................213.1. Oil circuit...............................................................................................................................................................................................................................................................213.2. Oil pump.................................................................................................................................................................................................................................................................22

3.2.1. Advantage of the volumetric-flow-controlled oil pump...................................................................233.2.2. Function of the volumetric-flow-controlled oil pump........................................................................243.2.3. Pressure limiting valve.............................................................................................................................................................................. 24

3.3. Oil filter....................................................................................................................................................................................................................................................................243.4. Oil cooling...........................................................................................................................................................................................................................................................243.5. Oil spray nozzles......................................................................................................................................................................................................................................24

3.5.1. Oil spray nozzles for piston crown cooling.........................................................................................................243.5.2. Oil spray nozzles for timing chain lubrication.................................................................................................25

3.6. Oil level measurement....................................................................................................................................................................................................................25

4. Cooling...................................................................................................................................................................................................................................................................................................264.1. Engine cooling................................................................................................................................................................................................................................................26


4.1.1. Coolant pumps......................................................................................................................................................................................................274.1.2. Expansion tank.......................................................................................................................................................................................................28

4.2. Charge air cooling..................................................................................................................................................................................................................................284.2.1. Auxiliary coolant pump for charge air cooling...............................................................................................284.2.2. Charge air cooler.............................................................................................................................................................................................294.2.3. Engine control unit.........................................................................................................................................................................................294.2.4. Ventilation.......................................................................................................................................................................................................................29

5. Air intake and exhaust system.......................................................................................................................................................................................................305.1. Intake air duct...............................................................................................................................................................................................................................................315.2. Turbocharging................................................................................................................................................................................................................................................. 31

5.2.1. Exhaust turbochargers.............................................................................................................................................................................315.2.2. Charge air cooling...........................................................................................................................................................................................355.2.3. Load control..............................................................................................................................................................................................................36

5.3. Intake manifold.............................................................................................................................................................................................................................................385.4. Exhaust system.............................................................................................................................................................................................................................................39

5.4.1. Exhaust manifold................................................................................................................................................................................................ 395.4.2. Exhaust re-treatment..................................................................................................................................................................................395.4.3. Secondary air system.................................................................................................................................................................................40

6. Vacuum system.................................................................................................................................................................................................................................................................426.1. Structure..................................................................................................................................................................................................................................................................42

7. Fuel system................................................................................................................................................................................................................................................................................447.1. Basic principles of direct fuel injection..............................................................................................................................................................44

7.1.1. Homogeneous direct fuel injection....................................................................................................................................447.2. Direct fuel injection of the 2nd generation...............................................................................................................................................45

7.2.1. Overview and function............................................................................................................................................................................457.3. High pressure pump...........................................................................................................................................................................................................................47

7.3.1. Hydraulic circuit diagram.....................................................................................................................................................................497.4. Injectors....................................................................................................................................................................................................................................................................50

7.4.1. Structure of the piezo injector.................................................................................................................................................527.4.2. Fuel injection strategy...............................................................................................................................................................................557.4.3. Injector control and adaptation...............................................................................................................................................567.4.4. Injector adaptation..........................................................................................................................................................................................56

7.5. Emergency operation of the direct fuel injection............................................................................................................................57

8. Engine electrical system................................................................................................................................................................................................................................588.1. Control unit......................................................................................................................................................................................................................................................588.2. Sensors.......................................................................................................................................................................................................................................................................58

8.2.1. Exhaust gas oxygen sensors...........................................................................................................................................................58


8.3. Actuators................................................................................................................................................................................................................................................................588.3.1. Electric fan....................................................................................................................................................................................................................58

N74 engine.1. Introduction.

1

1.1. Highlights

The N74 engine is the successor to the N73 engine. It is a completely new development with a whole range ofnew technologies. It has a highly modern mixture preparation with exhaust-gas turbocharging and direct fuel in-jection of the 2nd generation.

Highlights of N74 engine


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Index Explanation

1 Camshaft drive with toothed sleeve-type chain

2 High pressure pump for high precision injection

3 Charge air cooling for indirect charge air cooling

4 Outward-opening piezo injector

5 Volumetric-flow-controlled oil pump

6 Exhaust turbocharger

7 Charging pressure control by means of wastegate valves

Other details such as a volumetric-flow-controlled oil pump or camshaft drive with an innovative toothed sleeve-type chain make this engine an extremely efficient, comfortable and still powerful drive source – quite simply ef-fortless performance.

1.1.1. Technical data

N73B68O2 N74B66U0

Type V12 60° V12 60°

Firing order 1-7-5-11-3-9-6-12-2-8-4-10

1-7-5-11-3-9-6-12-2-8-4-10

Displacement [cm³] 6749 6592

Bore / stroke [mm] 92/84.6 89/88.3

Power outputat engine speed

[kW/bhp][rpm]

338/460/4535350

420/570/5635250-6000

Torqueat engine speed

[Nm][rpm]

7203500

7801500-5000

Power output per litre [kw/l] 50.1 63.6

Cutoff speed [rpm] 6500 6500

Compression ratio [�] 11.0 10.0

Distance between cylin-ders

[mm] 98 98

Valves per cylinder 4 4

Diameter of intake valve [mm] 35 33.2

Diameter of exhaustvalve

[mm] 29 29

Diameter of main bear-ing journals of thecrankshaft

[mm] 70 65

Diameter of connectingrod bearing journals ofthe crankshaft

[mm] 54 54

Fuel specification [RON] 98 95


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N73B68O2 N74B66U0

Fuel [RON] 91-98 91-98

Engine control system 2 x MED 9.2.1 +1 x VALVETRONIC con-trol unit +2 high-pressure fuel in-jection valve controlunits (HPFI)

2 x MSD87-12

Exhaust emission stan-dard EURO

EURO 4 EURO 5

Exhaust emission stan-dard US

LEV II ULEV II

1.1.2. Full load diagram

Full load diagram of N74B66 engine in comparison with N73B66 engine


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1.1.3. Engine identification

Engine designation

In the technical documentation, the engine designation is used to ensure the unambiguous identification of en-gines.

For the market launch, the N74 engine is available in the following version: N74B66U0.

In the technical documentation, you will also find the short form of the engine designation - N74 - which only per-mits identification of the engine type.

The components of the designation mean the following:

Index Explanation

N New generation

7 12-cylinder engine

4 Direct fuel injection of 2nd generation and tur-bocharging

B Petrol engine

66 6.6 litres displacement

U Lower power stage

0 New development

Engine identification and number

To ensure unambiguous identification and classification, the engines have an identification mark on the crankcase.This engine identification is also necessary for approval by authorities. Decisive here are the first seven positions.The N74 engine has an engine identification that complies with the new standard, in which the first six positionsare the same as the engine designation. The seventh position is a consecutive letter that can be used for variousdistinctions, e.g. power stage or exhaust emission standard. A general assignment is not possible, but an "A" usual-ly means the basic model.

The engine number is a consecutive number that permits unambiguous identification of each individual engine.The engine designation and number are on the crankcase behind the bracket for the air conditioning compressor.

N74 engine.2. Engine mechanical system

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2.1. Engine housing

2.1.1. Engine block

The engine block of the N74 engine is a new design. Apart from the cover plate, the design corresponds to theconcept of the N73 engine and comprises:

• Monoblock made of an aluminium alloy (Alusil)

• Closed cover plate (closed deck) – N73 open deck

• Exposure-honed cylinder liners

• Lowered side walls (deep skirt) with main bearing caps

• Double main bearing screw connection with additional side wall connection.

Engine block, N74 engine

The closed-deck design and the screw connection of the cylinder heads in the floor plates of the cylinder housingensure high rigidity and low deformation of the exposure-honed cylinder liners. The crankcase with lowered sidewalls (deep skirt) has a double main bearing screw connection with additional side wall connection by means ofthreaded support sleeves and bolts to absorb the lateral forces from the crankshaft drive on a V-engine.

Between the cylinders in the hot zone, there are coolant bore holes for to cool the bridge. In order to keep thelosses due to pumping in the crankcase to a minimum, there are one to six ventilation bore holes in each of thebearing seats. Separated channels for the oil return from the cylinder heads and for crankcase ventilation have en-abled a reduction in the proportion of oil in the blow-by gases.

The torque converter is bolted onto the flywheel through an opening in the converter housing with six bolts at anangle of 30° in relation to the horizontal. This makes it easier to replace the transmission.


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2.1.2. Cylinder head

The structure of the cylinder head in the N74 engine features a central arrangement of the injection system andspark plug in the combustion chamber. The high-pressure fuel pumps are located above the intake camshafts (be-tween cylinder 1 and 2 or 7 and 8, as the case may be).

The intake port has a separation edge to generate a more intensive charge movement.

Coolant flows diagonally across the cylinder head (from the outer side of the engine towards the V chamber),whereby the inlet is at the outside rear and the outlet at the inside front. This is also referred to as diagonal cool-ing.

There is now only one non-return valve for the oil circuit integrated in the cylinder head. The two non-returnvalves that were responsible for the VANOS are now integrated in the VANOS units.

Cylinder head cover

The cylinder head covers are made of die-cast aluminium. They accommodate the oil separation of the crankcaseventilation. The oil separator is made of plastic.

2.1.3. Oil sump

The transmission oil sump is structured in two parts. The upper and lower sections of the die-cast aluminium oilsump have been optimised with regard to strength and acoustics. A two-part oil deflector also ensures particular-ly low oil foaming in extreme driving situations. A surge plate ensures that an adequate oil level is achieved in thecase of high longitudinal and lateral dynamics.

The thermostat for the engine oil cooler as well as the oil filter with an oil filter insert made of synthetic fleeceare integrated in the transmission oil sump. The lower section of the oil sump contains the oil level sensor thatenables electronic oil level measurement. There is no oil dipstick.

2.1.4. Crankcase ventilation

The turbocharging means that the crankcase ventilation has a special structure.

Standard function

Via the ventilation duct (2), the blow-by gas enters an oil separator (8) in which the engine oil is separated fromthis mixture. The separated engine oil flows back into the oil sump through an oil outlet (9). The cleaned blow-bygas passes through a volume-control device (7) via a duct through the intake pipe (6) into the clean air pipe of theair intake system.


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Crankcase ventilation, standard function

Index Explanation

1 Throttle valve

2 Ventilation duct

3 Oil return

4 Crank chamber

5 Oil sump

6 Duct to the intake pipe

7 Pressure control device

8 Oil separator

9 Oil outlet


8

Oil separator

Labyrinth and cyclone filters are used on the N74 engine. One labyrinth and four of the cyclones are integrated inthe oil separator housing of each cylinder bank.

Oil separation, N74 engine

Index Explanation

1 Duct to the intake plenum

2 Cylinder head cover

3 Labyrinth

4 Ventilation duct out of the cylinder head

5 Oil return

6 Oil separator housing

7 Cyclone

The oil mist drawn in from the crankcase is fed through the labyrinth. This is where an initial separation of the oiltakes place, as it attaches to the walls of the labyrinth and flows off. The flowing blow-by gas is swirled in the cy-clones. The centrifugal forces cause the heavy oil to be deposited on the walls of the cyclone and it drips fromthere into the oil outlet; the lighter blow-by gas is extracted from the centre of the cyclone. From there, thecleaned blow-by gases are delivered to the intake plenum.

Crankcase ventilation, naturally aspirated operation

The standard function can only be used also long as there is a vacuum in the air intake system, i.e. with naturallyaspirated engine operation.


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Crankcase ventilation, naturally aspirated operation

Index Explanation

A Excess pressure

B Vacuum

C Exhaust gas

D Oil


10

Index Explanation

E Blow-by gases

1 Air filter

2 Intake manifold

3 Oil separator

4 Oil drain

5 Ventilation duct

6 Crank chamber

7 Oil sump

8 Oil return duct


10 Clean air pipe

11 Line to clean air pipe

12 Non-return valve to air intake system

13 Throttle valve

14 Non-return valve to clean air pipe

15 Line to air intake system

16 Pressure restrictor

As soon as the pressure in the differentiated air intake system rises as a result of charging, it is no longer possibleto introduce the blow-by gases by this path. As there would be a danger that the charging pressure is introducedinto the crankcase, a non-return valve is fitted in the line to the air intake system.

As there is a risk with high vacuums that oil is drawn into the intake system via the crankcase ventilation, this areaof the crankcase ventilation must be fitted with pressure limitation. This is implemented in the N74 engine with arestrictor that limits the flow and therefore also the pressure level in the crankcase ventilation.

The ventilation during naturally aspirated operation takes place via a line from the cylinder head cover to the airintake system, as the following diagram shows. The restrictor for pressure limitation is integrated in the non-re-turn valve to the intake system. During naturally aspirated operation, ventilation is only via the separator in cylin-der bank 2. This is called register ventilation and it increases the extent of separation of the oil separator in par-tial load operation. The crankcase is ventilated in the counterflow via the separator of cylinder bank 1. This ven-tilation with fresh air removes water and fuel components from the crank chamber more effectively, increasingthe service life of the oil and reducing the moisture (emulsion formation) in the lines. It also reduces the dangerof freezing. The N74 engine does not require heating for the crankcase ventilation. The ventilation is implementedthrough a bore hole in the non-return valve towards the clean air pipe of cylinder bank 1.


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Crankcase ventilation, N74 engine

Index Explanation

1 Inlet from oil separator, bank 2

2 Non-return valve

3 Outlet to air intake system, cylinder bank 2

4 Outlet to air intake system, cylinder bank 1

5 Non-return valve

6 Inlet from oil separator, bank 1

7 Bore hole for ventilation in the counterflow


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Index Explanation

8 Non-return valve

9 Outlet to clean air pipe, cylinder bank 1

10 Connection to clean air pipe, cylinder bank 1

11 Oil separator, cylinder bank 1

12 Oil return ducts

13 Connection to air intake system, cylinder bank 1

14 Connection to air intake system, cylinder bank 2

15 Oil separator, cylinder bank 2

16 Connection to clean air pipe, cylinder bank 2

17 Inlet from oil separator

18 Non-return valve

19 Outlet to clean air pipe, cylinder bank 2

For normal engine operation, the crankcase ventilation ensures a vacuum of maximum 70 mbar in the crankcase.During catalytic converter heating, higher vacuums can also occur.

Crankcase ventilation, charged operation

During charged operation, the pressure in the air intake system rises, thus closing the non-return valve. As thereis a vacuum in the clean air pipe in this operating range, it opens the non-return valve to the clean air pipe and theblow-by gases are fed via the compressor of the exhaust turbocharger and charge air cooler into the air intakesystem.


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Crankcase ventilation, charged operation

Index Explanation

A Excess pressure

B Vacuum

C Exhaust gas

D Oil


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Index Explanation

E Blow-by gases

1 Air filter

2 Intake manifold

3 Oil separator

4 Oil drain

5 Ventilation duct

6 Crank chamber

7 Oil sump

8 Oil return duct


10 Clean air pipe

11 Line to clean air pipe

12 Non-return valve to air intake system

13 Throttle valve

14 Non-return valve to clean air pipe

15 Line to air intake system

16 Pressure restrictor

If blue smoke emerges from the exhaust system, it must be checked whether the engine is taking oil into the com-bustion chamber via the crankcase ventilation, which indicates a fault in the area of the crankcase ventilation. Aclear indication of this is oil contamination inside the clean air pipe.

2.2. Crankshaft drive

2.2.1. Crankshaft

This is a forged crankshaft with inductively hardened running surfaces. A central bore hole through the main bear-ing and bore holes in the crank pin contribute to reducing the weight. In the same way as in the predecessor 12-cylinder engines, 100% of the mass forces of the 1st and 2nd order are balanced out.

To reduce fuel consumption, the main bearing diameters of the crankshaft have been reduced from 70 mm to65 mm. This also enables the use of a double main bearing screwed connection without enlarging the crankcase.The oil pump is driven at the flywheel end by the crankshaft. The camshaft sprocket is directly integrated into thecrankshaft.

Crankshaft bearings

The main crankshaft bearings are two-component bearing shells.


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2.2.2. Connecting rods

The N74 has cracked, forged connecting rods with trapezoid gudgeon pin bosses. On the rod side, they havethree-component sputter bearing shells; three-component bearing shells are fitted on the cover side.

2.2.3. Pistons

The Alusil cylinder barrels mean the pistons are iron-coated. This is a common part for both cylinder banks.

2.3. Camshaft drive

A newly developed toothed sleeve-type chain is used on each cylinder bank to drive the camshaft. This combinesthe advantages of a toothed and a sleeve-type chain, namely high resistance to wear and low noise.

The chain tensioners, tensioning rails and slide rails are common components for both cylinder banks.

The N74 engine is disconnected at firing TDC, first cylinder. To disconnect, a special tool is applied to the tor-sional vibration damper, forming the reference for the alignment pin to the crankcase.

2.3.1. Chain tensioner

The N74 engine has a chain tensioner for each cylinder bank. These are hydraulic chain tensioners that affect thetensioning rail. Each is arranged within the chain track to save space.

Before removal, the chain tensioner must be fully retracted and secured with the special tool supplied for the pur-pose. In this connection, follow the procedure in the repair instructions.

The oil spray nozzles for timing chain lubrication are integrated in the chain tensioners.

2.4. Valve gear

The valve opening times have been optimised with regard to the change in charging for this mixture preparation.


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Valve stroke curves, N74 engine

Index Explanation

1 Valve lift [mm]

2 Crank angle [°CA]

3 Exhaust valve opens

4 Intake valve opens

5 Opening period, exhaust valve

6 Exhaust valve closes

7 Intake valve closes

8 Opening period, intake valve

2.4.1. VANOS

In the same way as the N73 engine, the N74 engine is also equipped with variable double VANOS. The VANOSunits have the following adjustment angles:

• VANOS unit intake: 50° CA

• VANOS unit exhaust: 50° CA

The VANOS units of the N74 engine differ from the VANOS units of the N73 engine. The function has remainedthe same, but some parts are no longer required and the VANOS unit has been optimised. The vanes of theVANOS unit on the N74 engine are no longer separate components, rather have been enhanced to create a tiltrotor. The torsion spring integrated in the N73 VANOS unit is now fitted as a coil spring on the front of the N74VANOS unit, protected by a plastic cover.


17

2.4.2. Camshafts

The camshafts in the N74 engine are thermally jointed and have forged cams, a steel flange for the VANOS units(including width across flats and mounting flats for the special tool) and a sintered camshaft sensor wheel as refer-ence for the camshaft position sensor. The intake camshafts each have an additional 3-way cam to drive the highpressure pumps. All components are shrunk onto the corrugated tubing.

2.4.3. Roller cam followers

Roller cam followers are also used in the N74 engine as transfer elements of the cam movement onto the valves.New is a directional oil splash bore hole in the contact surface of the roller cam follower on the hydraulic valveclearance compensating element. The oil from the hydraulic valve clearance compensating element splashes pre-cisely onto the contact surface between the camshaft and roller cam follower. This supplies the roller and the camwith oil for cooling and lubrication.

Roller cam followers, N74 engine

Index Explanation

1 Roller

2 Oil splash bore hole

2.4.4. Valves

The exhaust valves are sodium-filled and the valve stems are not chrome-plated.

2.5. Belt drive

The main belt drive, a drive belt with seven ribs, drives


18

• the power steering pump with the possible variant for Dynamic Drive

• the air-cooled 210 A alternator and

• the mechanical coolant pump.

Belt drive, N74 engine

Index Explanation

1 Coolant pump

2 Tensioning pulley

3 Deflection pulley

4 Alternator

5 Power steering pump

6 Poly-V belt

7 Torsional vibration damper

8 Elastic belt

9 Air conditioning compressor

The main belt drive has a mechanical tensioning pulley that applies the necessary tension to the poly-V belt. Theuse of a smooth belt pulley for the coolant pump drive enables a partial shift in the belt wear to the tips of thebelt ribs. This has a positive effect on the service life of the belt. A patented drainage system on the belt pulleys ofthe crankshaft and the power steering pump drains off water that enters between the belt and pulley if there areintense splashes of water or if the vehicle is driven through water.

The belt drive is driven by the primary side of the damper. This prevents the torsional vibration excitation fromthe secondary side, which is usually used for this function, from shortening the service life.


19

The belt drive is driven by the primary side of the torsional vibration damper. The belt pulley is thus rigidly con-nected to the crankshaft. This is a new feature: the belt pulley usually belongs to the secondary side, i.e. the sidethat is flexibly connected to the crankshaft. As a general principle, it is the task of the torsional vibration damperto counteract the torsional vibrations of the crankshaft. Here, the secondary side is also subjected to torsional vi-brations that have a greater amplitude than those on the crankshaft.

Now that the belt pulley is subjected to lower torsional vibration amplitudes, the load on the belts is reduced,which has a positive effect on the service life.

2.5.1. Revolver tensioning system

Here, the belt pulley can be shifted on the torsional vibration damper in a certain position towards the air condi-tioning compressor. This enables simple installation of the elastic belt without special tools.

Installation of the elastic belt


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Index Explanation

1 Installation position for the elastic belt

2 Rotation of the torsional vibration damper to tension the belt

3 Normal position

This is enabled by an eccentric elongated hole in the belt pulley that permits a radial shift towards the crankshaftwhen the four mounting bolts of the belt pulley have been removed. If the engine is now turned another 180°, thetension of the elastic belt pulls the belt pulley back to the central position above the crankshaft.

Follow the new procedure for elastic belt installation in the repair instructions.

N74 engine.3. Oil supply.

21

3.1. Oil circuit

Oil circuit, N74 engine

Index Explanation

1 Oil sump

2 Volumetric-flow-controlled oil pump

3 Pressure limiting valve

4 Oil filter

5 Filter bypass valve

6 Thermostat

7 Oil cooler, oil-air heat exchanger


22

Index Explanation

8 Oil pressure switch

9 Crankcase

10 Oil spray nozzles for piston crown cooling

11 Lubrication points, main crankshaft bearings

12 Lubrication points, shaft bearings of the exhaust turbochargers

13 Cylinder heads (2x)

14 Non-return valve

15 VANOS valve, intake camshaft

16 Non-return valve

17 Strainer

18 Solenoid valve

19 VANOS swivel motor

20 VANOS valve, exhaust camshaft

21 Non-return valve

22 Strainer

23 Solenoid valve

24 VANOS swivel motor

25 Oil spray nozzle for the timing chain

26 Chain tensioner

27 Lubrication points, camshaft bearings (10)

28 Lubrication points, high pressure pump

29 Hydraulic valve clearance compensating elements (8)

3.2. Oil pump

The N74 engine now has a volumetric-flow-controlled oil pump. It is driven at the flywheel end by the crankshaftand is a pendulum slide cell pump.


23

Oil pump, N74 engine

Index Explanation

1 Vanes

2 Pump shaft

3 Compression spring

4 Intake side

5 Sealing strip

6 Pendulum slide

7 Control oil chamber

8 Rotor

9 Pressure side

10 Rotational axis

3.2.1. Advantage of the volumetric-flow-controlled oil pump

The oil pump absorbs a substantial proportion of engine output. The VANOS in particular requires a high oil vol-ume to adjust the camshaft angle. However, if the VANOS maintains the camshaft angle, no oil flow is required forthe VANOS. The oil requirement therefore depends on the scale of the adjustment operations. Conventional oilpumps generate the required oil pressure for the greatest possible oil flow that can occur in the engine. At manyoperating points, this represents futile energy consumption via the oil pump and superfluous wear of the oil. Thevolumetric-flow-controlled oil pump only supplies the amount of oil required by each operating range of the en-gine. In ranges with lower loads, no superfluous oil quantity is delivered. This reduces the fuel consumption of theengine and slows down wear of the oil.


24

3.2.2. Function of the volumetric-flow-controlled oil pump

The pump used is a pendulum slide cell pump. The pump shaft is seated in the delivery off-centre in the housingand the vanes are displaced radially during rotation. This means that the vane chambers form different volumes.When the volume rises, the oil is taken in; when the volume decreases, oil is pressed into the oil ducts. The oilpressure in the system (after oil filter and cooler) pushes the pendulum slide against the force of a compressionspring in the control oil chamber. The pendulum slide can be turned around a rotational axis. If less oil is deliveredby the lubricating system than the pump delivers, the pressure in the system rises. This also increases the pres-sure in the control oil chamber, turning the pendulum slide in the direction where the pump shaft is seated morecentrally in the pendulum slide. This reduces the volume changes and the fuel delivery rate drops. If the oil re-quirement of the engine rises, for example due to an adjusting intervention by the VANOS, the pressure in the lu-bricating system falls and thus also in the control oil chamber. The compression spring moves the pendulum slideback in the direction where the pump shaft is seated off-centre. This means the volume changes and the fuel deliv-ery rate are greater.

3.2.3. Pressure limiting valve

The pressure limiting valve is integrated into the oil pump. Pressure is applied to it upstream of the filter and itopens at a pressure of approx. 18 bar. When it opens, it releases surplus oil directly into the oil sump.

3.3. Oil filter

The N74 engine has the usual full-flow oil filter. In the same way as the predecessor, the synthetic-fleece oil filteris bolted onto the oil sump from below. This arrangement means that neither a discharge valve nor a non-returnvalve is required. The filter bypass valve is located in the oil filter cover.

3.4. Oil cooling

The thermostat for oil cooling is also integrated into the oil sump. It only lets the oil flow over the oil cooler as ofa certain oil temperature, thus ensuring rapid heating of the engine oil. The oil coolers used are two engine oil-airheat exchangers. These are positioned behind the trim panel of the front bumper in the wheel arches.

3.5. Oil spray nozzles

Oil spray nozzles are always used when an oil duct cannot be routed directly to the lubrication and cooling point.In the N74 engine, these are the usual positions, namely the oil spray nozzles for piston crown cooling and the oilspray nozzles for timing chain lubrication.

3.5.1. Oil spray nozzles for piston crown cooling

In the same way as in the N73 engine, the pistons are cooled by an oil spray from the underside. However, thisnow involves six double oil spray nozzles that are arranged centrally. They only open (pressure-controlled) above1.5 bar, thus enabling an adequately high volumetric flow of oil to maintain the VANOS adjustment in hot-idlingmode.


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3.5.2. Oil spray nozzles for timing chain lubrication

The oil spray nozzles for timing chain lubrication are each integrated in the chain tensioners of the two cylinderbanks. They spray the engine oil directly onto the timing chains. A restrictor in the oil spray nozzle limits the oilquantity that emerges.

3.6. Oil level measurement

The familiar QLT (Quality Level Temperature) oil condition sensor is used in the N74 engine. This implements theelectronic oil level measurement. No oil dipstick is used.

N74 engine.4. Cooling

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The exhaust-gas turbocharging means that the N74 engine generates a great deal of heat. Accordingly, a greatdeal of significance is attached to cooling. Furthermore, indirect charge air cooling where the charge air is cooledacross an air-coolant heat exchanger has been developed for the first time. The engine and charge air cooling sys-tems have two separate coolant circuits.

4.1. Engine cooling

The engine cooling system performs the classical task of drawing heat off the engine and maintaining a certain op-erating temperature that is as constant as possible. The two exhaust turbochargers are also cooled.

Cooling circuit for engine cooling, N74 engine

Index Explanation

1 Radiator

2 Radiator for transmission cooling

3 Coolant temperature sensor at radiator outlet

4 Electric fan

5 Characteristic map thermostat

6 Electric auxiliary coolant pump for turbocharger cooling

7 Coolant pump


9 Heater matrix


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Index Explanation

10 Duo-valve

11 Electric auxiliary coolant pump for vehicle heating

12 Coolant temperature sensor at engine outlet

13 Filling canister

14 Expansion tank

15 Transmission fluid-to-coolant heat exchanger

16 Thermostat

On the N74 engine, the coolant routes have been integrated mainly in the crankshaft drive. Further optimisationsto the cooling circuit within the engine have enabled a significant reduction in the coolant quantity for the bypassmode, thus shortening the warm-up phase.

The coolant feed line downstream of the coolant pump is routed in the engine directly beside the main oil duct.The oil in the main oil duct flows in the opposite direction to the coolant. This means there is very good heat ex-change between the two media, which has a positive effect on the engine oil temperature. The effect is compara-ble with that of an engine oil-coolant heat exchanger.

The coolant flows through the cylinder heads diagonally from the outside to the inside, whereby it flows in at therear (outside) and flows out at the front (inside). This is also known as diagonal cooling.

4.1.1. Coolant pumps

Main coolant pump

The N74 engine has a conventional mechanical coolant pump driven by the belt drive. As this cannot be used tocontinue cooling the exhaust turbochargers after stopping the engine, an additional electric coolant pump is re-quired.

Auxiliary coolant pump for exhaust turbochargers

The electrical auxiliary coolant pump ensures that accumulated heat continues to be withdrawn from the tur-bochargers after stopping the engine. This coolant pump has an electrical power output of 20 W. It is also usedduring engine operation to support turbocharger cooling. The electric auxiliary coolant pump is activated takingaccount of the following factors:

• Coolant temperature at the engine exit

• Engine oil temperature

• Injected volume of fuel

The injected volume of fuel is used to calculate the heat contribution to the engine. The after-run of the electricalauxiliary coolant pump can last up to 30 minutes. To improve the cooling effect, the electric fan is also switchedon. As before, this will have an after-run of a maximum of eleven minutes, but this after-run will be requestedmore frequently.


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4.1.2. Expansion tank

For reasons related to space, the expansion tank could not be positioned in such a way that filling is possible inthe same way as usual. The expansion tank is located in the front side panel behind the wheel arch. A separatefilling canister enables filling. The expansion tank and filling canister are interconnected by an expansion and tankventilation line.

4.2. Charge air cooling

Indirect charge air cooling is used for the first time at Rolls-Royce in the N74 engine. Here, the heat is extractedfrom the charge air by means of an air-coolant heat exchanger. This heat is then released to the ambient air acrossa coolant-air heat exchanger. To achieve this, the charge air cooling has its own low-temperature cooling circuit.This is independent of the engine cooling circuit.

Cooling circuit for charge air cooling, N74 engine

Index Explanation

1 Radiator for charge air cooling

2 Electric coolant pump for charge air cooling

3 Engine control unit

4 Expansion tank

5 Charge air cooler

4.2.1. Auxiliary coolant pump for charge air cooling

The cooling circuit for charge air cooling is operated with a 50 W pump. It does not run automatically when theengine is switched on. The following values are used for activation:


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• Outside temperature

• Difference between charge-air temperature and outside temperature.

4.2.2. Charge air cooler

The charge air coolers are attached to the rear end of the cylinder heads. They operate according to the principleof countervailing influence and enable efficient cooling of the charge air.

4.2.3. Engine control unit

The cooling circuit for charge air cooling also cools the two engine control units. To achieve this, a cooling loopthat is connected to the low-temperature cooling circuit of the charge air cooling is located on the housing of thecontrol unit.

4.2.4. Ventilation

There is a separate ventilation procedure for ventilation of the low-temperature circuit. This can be found in therepair instructions.

N74 engine.5. Air intake and exhaust system.

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Air intake and exhaust system, N74 engine

Index Explanation

1 Unfiltered air intake

2 Unfiltered air pipe

3 Unfiltered air resonator

4 Connection for crankcase ventilation, charged operation

5 Intake silencer

6 Intake manifold

7 Charge air cooler

8 Charging pressure sensor

9 Throttle valve


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Index Explanation

10 Charge air pipe

11 Hot film air mass meter

12 Exhaust-gas turbocharger

13 Charge-air temperature sensor

14 Clean air pipe

5.1. Intake air duct

The air intake duct consists of two lines with engine-mounted intake silencers. The arrangement leads to mini-mum pressure losses on the intake and pressure sides. The air is drawn in on both sides at the side behind the ra-diator grille. An air intake resonator on each side optimises the acoustic characteristics of the system.

Hot film air mass meters are only used in the US and Korean versions (digital HFM 7). They are located in theoutlet of the intake silencer.

The throttle valves are located directly upstream of the charge air coolers. The N74 engine is equipped with indi-rect charge air cooling.

5.2. Turbocharging

5.2.1. Exhaust turbochargers

The exhaust turbochargers are positioned outside the N74 engine. In the case of a V12-cylinder engine with 60°cylinder angle, this is the optimal arrangement of the turbocharger system and of the entire peripherals.


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Exhaust turbochargers, N74 engine

These are conventional exhaust turbochargers (no variable turbine geometry, VNT, no twin scroll) in which vacu-um-controlled wastegate valves are used for charging pressure control.


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Turbocharger details, N74 engine

Index Explanation

1 Connection from exhaust manifold (turbine inlet)

2 Connection for coolant line

3 Connection to catalytic converter (turbine outlet)

4 Wastegate valve

5 Wastegate duct

6 Turbine wheel

7 Connection for overflow duct

8 Recirculating blow-off valve

9 Connection to charge air cooler (compressor outlet)

10 Connection from intake silencer (compressor inlet)

11 Impeller

12 Vacuum unit for wastegate valve activation

They are two relatively small exhaust turbochargers switched in parallel, ensuring quick response even at low en-gine speeds. The charging pressure control is via wastegate valves. Blow-off valves are also used.


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Functional principle

The exhaust turbocharger is driven by the exhaust gases of the engine. The hot, pressurised exhaust gases arefed through the turbines of the exhaust turbocharger, thus delivering the driving power for the compressor thatruns on the same shaft. The intake air is precompressed here, which means that a higher air mass enters the com-bustion chamber of the engine. This makes it possible to inject and combust a greater fuel quantity, leading toan increase in engine power output and torque. The speeds of the turbines and of the compressor can be up to175,000 rpm. The exhaust gas entry temperature can reach a maximum of 950 °C.

These high temperatures mean that the exhaust turbochargers of the N74 engine are not only connected to theengine oil system but are also integrated in the cooling circuit of the engine. In conjunction with the electricalauxiliary coolant pump of the N74 engine, it is possible to draw the residual heat out of the exhaust turbocharg-ers even after the engine has been switched off, thus preventing overheating of the lubricating oil in the transmis-sion housing.

The after-run function of the electrical auxiliary coolant pump draws the accumulated heat from the exhaust tur-bocharger, thus counteracting carbon build-up (coking) of the oil in the bearing positions. This is an importantfunction that protects components.

Bi-turbocharging

On the N74 engine, great deal of significance is attached to the response characteristics of the exhaust tur-bocharger. A delayed reaction to the driver's choice, i.e. the pedal sensor position, is unacceptable. The drivermust not perceive a so-called "turbocharge lag". This requirement is met on the N74 engine with two relativelysmall exhaust turbochargers switched in parallel. Each cylinder bank drives an exhaust turbocharger. Smaller ex-haust turbochargers have the advantage that when the exhaust turbocharger starts up the lower inertia torqueof the turbine means that lower masses are accelerated, enabling the compressor to reach a higher charging pres-sure more quickly.

Charging pressure control

The charging pressure of the exhaust turbochargers is directly dependent on the exhaust flow that enters the tur-bines of the exhaust turbocharger and it determines the speed of the exhaust turbocharger. Both the speed andthe mass of the exhaust flow are directly dependent on the engine speed as well as the engine load. The waste-gate valves are available to the Digital Motor Electronics to control the charging pressure. These are operated bymeans of vacuum units controlled by electro-pneumatic pressure converters (EPDW) via the Digital Motor Elec-tronics.

The vacuum is generated using the permanently driven vacuum pump of the engine and stored in two vacuumreservoirs. It is ensured that these consumer units do not have a negative influence on the function of the brakepower assistance.

The wastegate valves can influence how much of the exhaust flows through the turbine wheel. Once the charg-ing pressure has reached the desired level, the flap of the wastegate valve starts to open and a portion of the ex-haust flow is routed past the turbine wheel. Here, the increased exhaust flow prevents the speed of the compres-sor from increasing further.

This control possibility enables appropriate responses to a wide variety of operating situations. In the idle phase,the wastegate valves of both exhaust turbochargers are closed. The consequence of this is that the entire availableexhaust flow can be used even at these low engine speeds to accelerate the compressor. If engine power is thenrequested, the compressor can deliver the required charging pressure without any noticeable delay. In the full loadsituation, the charging pressure is kept at a consistent high level when the maximum permitted torque is reached


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by partially opening the wastegate valves. This means the compressors are only taken to the speed required in theoperating situation. Opening the wastegate valves takes driving power away from the turbines, limiting the exhaustturbocharger speed and protecting it against overspeed. There is also no further increase in charging pressure,which benefits fuel consumption.

In full load operation, the N74 engine works with an excess pressure of up to 0.7 bar in the intake pipe.

Blow-off control

The blow-off valves of the N74 engine reduce unwanted peaks in the charge air pressure that can arise when thethrottle valve is closed quickly. In doing so, they perform an important function with regard to engine acousticsand contribute to protecting the components of the exhaust turbochargers.

If the throttle valve is closed at high engine speeds, a vacuum is created in the intake pipe. High ram pressurebuilds up behind the compressor, and this is unable to escape because the path to the intake pipe is blocked. Thiswould lead to "pumping up" of the exhaust turbocharger. This means that

• a clearly noticeable pump noise occurs

• this pump noise is accompanied by a load being exerted on the exhaust turbocharger that can damagecomponents, as high-frequency pressure waves place a strain on the bearings of the exhaust turbocharg-er in an axial direction.

The blow-off valves are electrically operated valves.

Blow-off valve, N74 engine

If the throttle valve is closed, the charging pressure (before the throttle valve) and its rise are compared withstored nominal values. If the actual values are a certain value above the nominal values, the blow-off valves areopened. This diverts the charging pressure to the intake side of the compressor. The effect of this process is thatdisruptive pumping that can damage components does not occur.

5.2.2. Charge air cooling

So-called indirect charge air cooling is used for the first time in the N74 engine. The charge air is not routed di-rectly to an air-air heat exchanger. The charge air is cooled on an air-coolant heat exchanger. To achieve this, theN74 engine has a separate closed low-temperature cooling circuit.


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The charge air coolers are engine-mounted (bolted) on the cylinder head covers and directly connected to the airintake system.

The purpose of charge air cooling is to enhance performance and to reduce fuel consumption. The charge air thatis heated in the exhaust turbocharger by its component temperature and compression is cooled in the charge aircooler by up to 80 °C. This increases the density of the charge air, leading to better charging of the combustionchamber. This results in a low required charging pressure. The risk of knocking is also reduced and the engine op-erates with more favourable efficiency. The advantage of indirect charge air cooling is the low space requirement,as the system can be fitted directly on the engine. The installation position close to the engine means that the sig-nificantly shorter lengths of pipe for the charge air supply also have a positive effect. This enables significant reduc-tions in pressure loss, which improves the utilisation of power output and response characteristics of the engine.

5.2.3. Load control

The load of the N74 engine is controlled via the throttle valve and wastegate valves. The throttle valve is the pri-mary actuator here. Fine tuning of the charging pressure takes place by activating the wastegate valves. At fullload, the throttle valve is fully opened and load control is assumed by the wastegate valves. It can be seen in theload control diagram that the wastegate valves are integrated (map-controlled) in the load control in all operatingsituations of the N74 engine.

Load control, N74 engine


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Index Explanation

n Engine speed in rpm

p Absolute pressure in the intake pipe in mbar

1 Naturally aspirated operation

2 Charged operation

3 Dark = wastegate valve closed, Bright = wastegate valve opened

Control variables

The following variables (among others) are included in control of the charging pressure of the N74 engine:

• Intake air temperature

• Engine speed

• Throttle position

• Ambient pressure

• Intake pipe vacuum

• Pressure before the throttle valve (reference variable).

Based on these variables, activation of the electro-pneumatic pressure converter (EPDW) is specified by the en-gine control unit. The result of this activation can be checked on the basis of the charging pressure measured be-fore the throttle valve. A comparison of the charging pressure achieved with the nominal values of the character-istic map is run; if necessary, this can lead to a correction of the activation. This means the system regulates andmonitors itself during operation.

Emergency mode

If there are malfunctions, implausible values or failures in the sensors involved in control of the exhaust-gas tur-bocharging during operation, activation of the wastegate valves is shut down and the valve flaps are fully opened.Charging no longer takes place.

Components or functional groups of the N74 engine where a failure, malfunction or implausible values lead to de-activation of the charging pressure control are listed below. A fault of this nature is indicated to the driver by theemissions warning light.

• High pressure fuel system

• VANOS intake

• VANOS exhaust

• Crankshaft sensor

• Camshaft sensor


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• Charging pressure sensor

• Knock sensors

• Intake air temperature sensor.

A fundamental principle of vehicle repair is of special significance here: work on the causes and not on the effects!

With regard to the diagnosis and subsequent repair of the components involved in turbocharging, it must be en-sured that they are indeed identified as damaged components using the available diagnostic techniques. It mustalways be ensured that the fault cause is determined and remedied and that work is not carried out merely onthe consequences of the fault. For example, a leaking flange on the charge air cooler can have far-reaching conse-quences.

Three golden rules of handling also apply to the N74 engine:

1 Do not prematurely attribute power loss and malfunctions of the engine to the exhaust turbocharger. Itis often the case that faultlessly functioning exhaust turbochargers are removed and replaced unnecessari-ly. If blue smoke emerges from the exhaust system, check whether the air filter is contaminated or if wearmeans that the engine is consuming too much oil. Only then should the exhaust turbocharger be checked. Ifthe exhaust turbocharger runs noisily, examine all the connections on the pressure side of the exhaust tur-bocharger. If black smoke emerges or there is a power loss, first check the engine and the connection lineshere too.

2 Main causes of damage to an exhaust turbocharger:- Lack of lubrication leading to bearing failure. This causes the compressor and turbine wheel to grind in

the housings, the gaskets are damaged and the shaft can shear off.

- Foreign bodies damage turbines and the impeller. The resulting imbalance reduces efficiency and can leadto the rotors bursting.

- Contaminated lubricating oil forms score marks on the shaft journals and bearings. Oil holes and sealsclog up and cause high oil leaking losses. Matter entering from the outside such as sand, dirt, screws andsimilar is intercepted by a filter before the compressor. The filters are to be serviced at regular intervals(service intervals). The clean air section of the air filter and the air duct to the compressors are to becarefully kept clean and free of any particles.

3 Do not change anything on the exhaust turbocharger. Never attempt to adjust the control rod of the charg-ing pressure control. The exhaust turbocharger has been given the optimal configuration at the plant. If theexhaust turbocharger operates at higher charging pressures than permitted by the engine manufacturer, theengine can run hot and the pistons, cylinder head or engine mounts can fail or the safety functions of the en-gine electronics can respond and activate the emergency program of the engine.

5.3. Intake manifold

The air intake system (plastic) is located in the V chamber of the engine. The left and right-hand sides are sepa-rate. This is why there are also two charging pressure sensors at the rear end of the air intake system.


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5.4. Exhaust system

Exhaust system, N74 engine

Index Explanation

1 Position of exhaust gas oxygen sensor (monitoring sensor) after catalytic converter

2 Catalytic converter

3 Position of exhaust gas oxygen sensor (control sensor) before catalytic converter

4 Vacuum unit for wastegate valve activation


6 Recirculating blow-off valve

7 Exhaust manifold

5.4.1. Exhaust manifold

Air-gap-insulated exhaust manifolds that offer advantages with regard to faster heating up of the catalytic convert-ers are used. They have a 2 times 3 in 1 junction, optimised for the firing sequence.

5.4.2. Exhaust re-treatment

The catalytic converters are arranged near the engine directly behind the turbines of the exhaust turbochargers.This short exhaust gas duct ensures the catalytic converters reach their operating temperature quickly. The useof the latest exhaust recirculation sensors, the LSU ADV exhaust gas oxygen sensor and a secondary air systemmeans that the engine complies with the strict EURO 5 and ULEV 2 exhaust emission standards.


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5.4.3. Secondary air system

In the same way as the N73 engine, the N74 engine is equipped with a secondary air system. Blowing additionalair (secondary air) into the exhaust gas duct in the cylinder head during the warm-up phase initiates thermal post-combustion that leads to a reduction in the uncombusted hydrocarbons (HC) and carbon monoxide (CO) con-tained in the exhaust gas. The energy generated here heats up the catalytic converter more quickly in the warm-up phase and increases its conversion rate. The catalytic converter response temperature (light-off temperature)of approx. 300°C is reached only a few seconds after the engine is started.

What is new is that there is a pressure sensor before each secondary air valve. The function of the secondary airsystem is monitored by registering the pressure conditions.

Secondary air pump

The electrically operated secondary air pump is attached to the cylinder head of cylinder bank 1. During thewarm-up phase, the pump draws in fresh air from the engine compartment. This is cleaned by the filter integratedin the pump and delivered across the pressure line to the two secondary air valves.

After the engine start, the secondary air pump is supplied with vehicle voltage by the DME via the secondary airpump relay. The switched-on period is approx. 20 seconds and it depends essentially on the coolant temperatureat engine start. It is activated at a coolant temperature of +5 °C to +50 °C.

Secondary air valve

A secondary air valve is bolted onto the rear end of the cylinder heads for each cylinder bank. The secondary airvalve opens as soon as the system pressure generated by the secondary air pump exceeds the opening pressureof the valve. Secondary air is fed via the aerodynamic secondary air line into the elongated bore hole of the cylin-der head. From the elongated bore hole, 24 tap bore holes lead to the 12 exhaust ducts where the thermal post-combustion takes place.

The secondary air valve closes as soon as the secondary air pump switches off, thus preventing exhaust gas fromflowing back to the secondary air pump.

On-board diagnosis of secondary air system

Monitoring takes place with the help of the pressure sensors that are fitted before each of the secondary airvalves. The exhaust gas oxygen sensors are also used.

The overall diagnosis is divided into a rough diagnosis that begins immediately after the secondary air pump startsup and the fine diagnosis that begins around twelve to 14 seconds after the secondary air injection starts.

The rough diagnosis uses only the pressure signals. Every fault in the secondary air system is detected if there isa drop below a minimum pressure in the event of a leakage or if a maximum pressure is exceeded when a valve isclogged or jammed closed. However, under certain circumstances, it might not be possible to assign the fault cor-rectly, because the pressure sensors indicate the same pressure due to the connecting line.

The fine diagnosis uses the exhaust gas oxygen sensor signals in addition to the pressure signals. The combinationof exceeding or falling short of fault thresholds for the pressure and exhaust gas oxygen sensor values means thefault can be precisely assigned to the relevant cylinder bank. The fine diagnosis relies on the oxygen sensor readi-ness. The heat loss in the exhaust turbocharger means this is available much later than in naturally aspirated en-gines.


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There is also an electrical diagnosis for the secondary air pump relay and for the pressure sensors. These indicatethe usual electrical faults (line disconnection, short circuit to earth, short circuit to supply voltage). There is anadditional mutual plausibility check of the pressure sensors on initialisation with ambient pressure.

N74 engine.6. Vacuum system.

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6.1. Structure

To generate the necessary vacuum for the brake servo and for auxiliary consumer units, the N74 engine has avacuum pump. These auxiliary consumer units are the wastegate valves and the exhaust flaps.

Vacuum system, N74 engine

Index Explanation

1 Vacuum pump

2 Non-return valve for auxiliary consumer units

3 Non-return valve for brake servo

4 Non-return valve on brake servo

5 Brake servo

6 Electric changeover valve

7 Vacuum unit for exhaust flaps

8 Vacuum accumulator

9 Electro-pneumatic pressure converter

N74 engine.6. Vacuum system.

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Index Explanation

10 Vacuum unit for wastegate valve, cylinder bank 1

11 Vacuum accumulator

12 Electro-pneumatic pressure converter

13 Vacuum unit for wastegate valve, cylinder bank 2

In the same way as on the N73 engine, a two-stage vacuum pump where the main stage generates the vacuumfor the brake servo. The auxiliary stage generates the vacuum to activate the wastegate valves of the exhaust tur-bochargers and the exhaust flaps. Two vacuum reservoirs are used to ensure there is sufficient vacuum for thewastegate valves at all times. These are attached to the rear end of the intake system. Electro-pneumatic pressureconverters for the wastegate valves are mounted directly on the vacuum reservoirs.

N74 engine.7. Fuel system.

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The N74 engine is equipped with high precision injection, i.e. direct fuel injection of the second generation - inhomogeneous operation at all times.

7.1. Basic principles of direct fuel injection

With direct fuel injection, the fuel is injected under high pressure (between 50 and 200 bar) directly into the com-bustion chamber. As a general principle, the homogeneous or stratified mixture preparation enables two conceptsfor direct petrol injection, each of which has distinctive features with regard to consumption and emissions.

Comparison of mixture preparation

Index Explanation

1 Intake pipe fuel injection

2 Homogeneous direct fuel injection

3 Stratified mode direct fuel injection

The differences arise as a result of the different mixture preparation processes. The above diagram "Comparisonof mixture preparation" shows the time sequence of mixture preparation for direct fuel injection in the homoge-neous and stratified operating modes as well as in comparison with intake pipe fuel injection. The mixture compo-sition is shown as the air ratio for four points in time. The colours represent the local air ratio according to thecomparison scale.

7.1.1. Homogeneous direct fuel injection

With direct fuel injection, the fuel injector leads directly into the combustion chamber. The fuel evaporates in thecombustion chamber. The gas motion in the combustion chamber mixes the air with the injected fuel so that ahomogeneous (�=1) fuel-air mixture prevails at the ignition point. The mixture preparation - and therefore thecombustion process - is similar to that on a conventional engine with intake pipe fuel injection. As the fuel is in-troduced into the cylinder first of all and evaporates there, heat energy is withdrawn from the cylinder charge duethis evaporation. This improves the knock characteristics, which means that the compression ratio can be raised.In total, the efficiency rises by up to 10%.


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7.2. Direct fuel injection of the 2nd generation

7.2.1. Overview and function

Fuel preparation, N74 engine

Index Explanation

1 Quantity control valve

2 High pressure pump

3 High pressure line (pump - rail)

4 Rail pressure sensor

5 Rail

6 High pressure line (rail - injector)


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Index Explanation

7 Fuel feed from the electric fuel pump

8 Fuel pressure sensor

9 Feed line

10 Piezo injector

The fuel is delivered to the high pressure pump from the fuel tank by the electric fuel pump via the feed line at adelivery pressure of 5 bar. The delivery pressure is monitored by the fuel pressure sensor. The fuel is supplied bythe electric fuel pump in line with requirements. If this sensor fails, operation of the electric fuel pump continueswith a 100% delivery rate at terminal 15 ON. The fuel is compressed in the permanently driven single-piston highpressure pump and fed via the high pressure line into the rail. The fuel stored in this way under pressure in therail is distributed via the high pressure lines to the piezo injectors.

Fuel pressure diagram

Index Explanation

p Pressure

m Load

n Engine speed

The required fuel pressure is determined by the Digital Motor Electronics depending on the load and enginespeed. The pressure level that is reached is picked up by the rail pressure sensor and sent to the engine controlunit. Control takes place on the basis of a nominal / actual comparison of the rail pressure by the quantity con-trol valve. The configuration of the pressure aims to achieve the best possible fuel consumption and operationalsmoothness of the N74 engine. 200 bar is only required at high load and lower engine speed.


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Work on this fuel system is only permitted after the engine has cooled. The coolant temperature must not ex-ceed 40 °C. Compliance with this instruction is mandatory, as otherwise the residual pressure in the high-pres-sure fuel system represents a danger that fuel will be sprayed back.

When performing repair work on the high pressure fuel system, particular attention is to be paid to cleanlinessand the workflows described in the repair instructions. Even the smallest impurities and damage to the bolt con-nections of the high pressure lines can lead to leaks.

During work on the fuel system of the N74 engine, attention must be paid to ensuring that the ignition coils arenot contaminated with fuel. The resilience of the silicone material is greatly reduced by intensive contact with fuel.This can lead to flashovers on the spark plug head and thus to misfiring.

• Before making any modifications to the fuel system, make absolutely sure that the ignition coils are re-moved and that the spark plug bore is protected against fuel entering by means of a cloth.

• Before installing a new piezo injector, the ignition coils are to be removed and the greatest possiblecleanliness is to be ensured.

• Ignition coils that are heavily contaminated by fuel must be replaced.

7.3. High pressure pump

High pressure pump with quantity control valve, N74 engine


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Index Explanation

A Low-pressure connection

B High-pressure connection

1 Compensating chamber

2 High-pressure non-return valve


4 Pistons


6 Electrical connection of the quantity control valve

The fuel is delivered to the high-pressure pump via the inlet with delivery pressure generated by the electric fu-el pump. The fuel is then fed via the volume control valve into the compression chamber of the pump element. Inthis pump element, the fuel is placed under pressure by a plunger and supplied via the high-pressure non-returnvalve to the high-pressure connection. The high-pressure pump is bolted onto the cylinder head and is driven bythe camshaft via a triple cam. This means that, as soon as the engine is running, the triple cam continuously movesthe plunger to make its stroke. Fuel is placed under pressure until new fuel is delivered via the volume controlvalve into the high-pressure pump. The volume control valve is activated via the connection to the engine man-agement system; it specifies the delivered volume of fuel. Pressure regulation takes place via the volume controlvalve in that it is opened or closed by the pump element towards the fuel feed. When the quantity control valve isopened, most of the fuel drawn in by the piston is pressed back into the fuel feed.

The maximum pressure in the high-pressure area is restricted to 245 bar. If such a high pressure arises, the high-pressure circuit is relaxed to the low-pressure area by a pressure limiting valve via the connections. The pres-sure peak that arises is compensated for on introduction into the low-pressure area by the fluid volume there andpressure damper in the compensating chamber. The compensating chamber is integrated in the inlet towards thehigh pressure pump. This ensures that pressure peaks are lowered by connecting and disconnecting the high andlow-pressure areas. When the piston generates pressure, fuel flows between the piston and its guide. This is de-liberate, as it lubricates the pair of sliding elements. On downward movement of the pressure piston, a high pres-sure would arise at its rear side. This would lead to a danger that fuel would be pressed through the sealing of thepiston from the pump into the oil circuit of the engine. The connection to the compensating chamber means thatthere is never a higher pressure behind the piston than in the fuel feed. This prevents pressure fluctuations frombeing transferred into the low pressure fuel system, as the volume changes in front of and behind the piston arebalanced.


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7.3.1. Hydraulic circuit diagram

Hydraulic circuit diagram for fuel preparation, N74 engine

Index Explanation

1 Electric fuel pump

2 Fuel pressure sensor

3 Engine control unit

4 High pressure pump


6 High pressure pump element (piston)

7 High pressure non-return valve


9 Compensating chamber

10 Rail

11 Rail pressure sensor

12 Piezo injectors

The volume control valve controls the fuel delivery pressure in the rail. In the induction stroke with the quanti-ty control valve opened, the entire compression chamber is filled with fuel via the low-pressure area. In the com-pression stroke, the point in time when the quantity control valve closes determines how much fuel is pumped


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back into the low-pressure area and how much of the remaining stroke is used for the compression and the effec-tive high pressure delivery. In addition, the pressure limiting valve provides the possibility to reduce the pressurein the rail in that fuel is fed out of the high-pressure fuel system back into the pump element.

7.4. Injectors

Outward-opening PIEZO injectors are used.

Outward-opening piezo injector

The outward-opening piezo injector is what enables the overall innovation of high precision fuel injection. Onlywith this injector is it possible to ensure the injected fuel cone remains stable, also under the prevailing influencesof pressure and temperature in the combustion chamber. This piezo injector enables injection pressures of up to200 bar and extremely fast opening of the nozzle needle. This makes it possible to inject fuel into the combustionchamber regardless of the operating cycles restricted by the valve opening times.


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The piezo injector is integrated into the cylinder head together with the spark plug in the centre between the in-take and exhaust valves. This installation position prevents the cylinder walls or piston crown from being soakedwith injected fuel. An even formation of the homogeneous fuel-air mixture is achieved with the help of the gasmotion in the combustion chamber and a stable fuel cone. The gas motion is influenced by the geometry of theinlet ports on the one hand and by the shape of the piston crown on the other. The injected fuel is swirled in thecombustion chamber with the charge air until a homogeneous fuel-air mixture is available everywhere in the com-pression chamber at the ignition point.


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7.4.1. Structure of the piezo injector

Piezo injector

Index Explanation

1 Outward-opening nozzle needle

2 Piezo element

3 Thermal compensator

The injection system consists essentially of the three assemblies: The nozzle needle is raised from its valve seat tothe outside on expansion of the piezo element when current is applied. In order to be able to deal with the dif-ferent operating temperatures with comparable valve opening stokes, the piezo injector has a thermal valve clear-ance compensating element.

When the piezo injector is installed and removed, the Teflon sealing ring must be replaced. This also applies whena piezo injector that has just been installed has to removed again after an engine start.

A piezo injector fitted with new Teflon sealing ring should be fitted as quickly as possible, as the Teflon sealing ringcould swell up. The information in the repair instructions must be taken into account!

On installation, pay attention to ensuring that the piezo injector is seated perfectly.

The hold-down device for mounting the piezo injectors must make contact with both injector vanes, as otherwisethe required force is not applied to the piezo injector.


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The tip of the nozzle needle of the piezo injector must not be cleaned.

Piezo element

In the piezo injector, the movement of the nozzle needle is no longer created by means of a solenoid coil, ratherby a piezo element.

Characteristics of a piezo element

Index Explanation

1 Piezo crystal, without current

2 Piezo crystal, with current

3 Layer structure of the piezo element

A piezo element is an electromechanical converter, i.e. it consists of a ceramic material that converts electricalenergy directly into mechanical energy (force / path). A familiar use is the piezo cigarette lighter: pressure on apiezo crystal generates voltage until a spark jumps across and ignites the gas. With the piezo actuator, voltage isapplied so that the crystal expands. To achieve a greater path, a piezo element can be structured in a number oflayers. The actuator module consists of layers of the piezo ceramic material mechanically arranged in series andelectrically arranged in parallel. The deflection of a piezo crystal depends on the voltage applied. The result of thisup to a maximum deflection is: the higher the voltage, the greater the path.

Piezo injector compensation

On production of the piezo injector in the plant, a great deal of measured data is recorded at certain points. Thisdetermines the tolerance ranges for the injection quantity compensation, specified in a six-digit combination ofnumbers. Information on the stroke characteristics of the piezo injector is added for the injection voltage com-pensation. The injection compensation is required due to the individual voltage requirement of each piezo actua-tor. The piezo injector is assigned to a voltage requirement that is included in the combination of numbers. Thesedata are sent to the control unit. During engine operation, these values are used to compensate for deviations inthe metering and switching characteristics.

When a piezo injector is replaced, it is mandatory to run the injection compensation.


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Outward-opening nozzle needle

Outward-opening nozzle needle

The nozzle needle is pressed outwards from its cone-shaped valve seat, opening up a ring-shaped gap. The pres-surised fuel flows through this ring-shaped gap and forms a hollow cone where the injection angle is independentof the counter-pressure in the combustion chamber.

Injection cone of the outward-opening piezo injector

Index Explanation

1 Ideal cone

2 Permitted expansion of the injection cone

3 Non-permitted expansion of the injection cone


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The injection cone (1) of a piezo injector can expand during operation (2). To a certain extent, this is due in sootbuild-up within the engine and is normal and acceptable. However, if the injection expands so far that it soaks thespark plug, the spark plug can be damaged.

Spark plug patterns of the N74 engine:

• Chunking can occur in the insulator base of the spark plug.

• The electrode can burn off on one side.

When handling the spark plugs of the N74 engine, attention must be paid to the fact that there are patterns ofdamage that indicate faults in the piezo injectors. Simply renewing the spark plugs in such cases does not rectifythe problem.

7.4.2. Fuel injection strategy

The fuel injection of the mass of fuel required for the operating situation can take place in up to three individualinjections. The possibility that is used in each operating situation depends on the load and engine speed. Here, re-sulting from the engine speed, the actual time available for metering the fuel is an important parameter.

The following diagram shows the fuel injection strategy for an engine at operating temperature.

Fuel injection strategy, N74 engine

Index Explanation

n Engine speed

M Torque

1 Single injection

2 Double injection

3 Triple injection

A special situation during operation of any engine is the range in which a high load occurs at low engine speed, so-called "low end torque" operation. In this operating situation, the engine is metered the required mass of fuel inthree individual injections. This results in very effect mixture preparation which, all things considered, enhancespower output and saves fuel.


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Catalytic converter heating mode

In order to get the catalytic converters to operating temperature as quickly as possible, the catalytic converterheating is used when the cold N74 engine is started. In this operating mode, combustion heat is deliberately fedinto the exhaust tract and not used primarily for power development. The ignition point is shifted to 30° CA af-ter top dead centre (TDC). The main volume of the required fuel is injected before top dead centre (TDC) andmixed in with the charge air. After TDC, the piston is moving downwards, which means that the fuel-air mixtureis already expanding again, lowering the tendency of the fuel-air mixture to ignite. In order to ignite the fuel-airmixture reliably, a small residual amount of fuel is injected 25° CA after TDC, thus ensuring a fuel-air mixture atthe spark plug that will ignite. This small fuel quantity ensures that the remaining charge ignites in the combustionchamber. This operating mode is set for a maximum of 60 s after engine start by the Digital Motor Electronics,but it is aborted if the maximum reaches its response temperature earlier.

7.4.3. Injector control and adaptation

The mass of fuel required for the operating situation is injected by the piezo injector into the combustion cham-ber. This volume can be influenced with three adjusting values:

• the rail pressure

• the injector opening duration

• and the injector opening stroke.

The injector opening duration and injector opening stroke are activated directly at the piezo injector. The openingduration is controlled via the signal ti and the opening stroke is controlled via the amount of energy in the activa-tion of the piezo injector.

7.4.4. Injector adaptation

The masses of fuel and injection cycles determined from the load/engine speed map are included in a pilot map.The amounts of energy and the injector opening times required for activation of the piezo injector are specifiedhere, taking account of other general parameters. The N74 engine can be operated reliably with these mappedvalues.

To optimise:

• Emission levels

• Smooth performance

• Fuel consumption

• Power output

the control factors 'amounts of energy' and 'injector opening times' are continuously monitored. This is done ona cylinder-specific basis via the oxygen sensor control. The residual oxygen in the exhaust gas is measured in eachcase for cylinder bank 1 and cylinder bank 2. The new exhaust gas oxygen sensors permit assignment to the indi-vidual cylinders. This measuring result is compared with the values expected from the control variables that havebeen applied. A deviation leads to the injector opening signal being adapted. This adaptation is stored in the con-trol unit and is therefore available for continued engine operation. However, these stored values are lost when thesystem is flashed and they have to be learned once again.


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Depending on time and use, further adaptation of the fuel injector activation takes place. This cylinder-specif-ic adaptation involves a check of the residual oxygen content that indicates the cylinder that has made the adap-tation necessary. To achieve this, it is required that part of the exhaust flow is not swirled in the exhaust tur-bocharger. This is why the flap of the wastegate valve has to be fully opened, i.e. swivelled out of the exhaust flow.This position of the wastegate flap goes beyond the normal opening position during engine operation. Based onthe results of this cylinder-specific monitoring, the amount of energy for activation of the piezo injectors is adapt-ed if necessary. The cylinder-specific adaptation might also involve an adaptation of the injector opening signalbased the operational smoothness monitoring of the N74 engine. The total adaptation of the piezo injectors islimited to an additional amount of 15%.

7.5. Emergency operation of the direct fuel injection

If a fault is diagnosed in the system, e.g. failure of the rail pressure sensor, the quantity control valve is de-ener-gised; the fuel then enters the rail through a so-called bypass.

During emergency operation of the high precision injection, the exhaust-gas turbocharging is switched off byopening the wastegate valves.

Causes of emergency operation of the HPI can be:

• Implausible rail pressure sensor values

• Failure of the fuel pressure control valve

• Leak in the high-pressure fuel system

• Failure of the high pressure pump

• Failure of the rail pressure sensor.

N74 engine.8. Engine electrical system.

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8.1. Control unit

Two water-cooled MSD87-12 control units are used. The direct fuel injection of the 2nd generation and tur-bocharging in conjunction with twelve cylinders represent a great challenge for the control units. This is why avery powerful processor with 150 MHz is used. The control units have a new connector design with five cham-bers and functional assignment. This means that each chamber is assigned to a certain functional group. The fol-lowing list shows the assignment of the chambers in the corresponding order:

• Chamber 1 (8 pins): ignition

• Chamber 2 (59 pins): engine connector for cylinder bank 1 and some central engine functions

• Chamber 3 (40 pins): vehicle connector

• Chamber 4 (54 pins): engine connector for cylinder bank 2 and some central engine functions

• Chamber 5 (16 pins): fuel injection

The engine connector is for sensor / actuator connections on the engine, whereas the vehicle connector is the in-terface to the vehicle-specific components. The functions of the Digital Motor Electronics are described in the rel-evant systems.

In the same way as for the predecessor engine N73, a master-slave concept has been implemented with the twocontrol units. They have the same hardware, software and data records. The connected sensor system runs anautomatic master-slave identification. In this arrangement, the master is responsible for communication with thecomplete vehicle and the specified nominal values for the engine functions. The control unit is designed with thecurrent software for a vehicle network with FlexRay.

8.2. Sensors

8.2.1. Exhaust gas oxygen sensors

The familiar Bosch LSF4.2 sensors are used. New are the control sensors before the catalytic converter. The newLSU ADV sensors are used here for the first time. LSU stands for "Lambda Sensor Universal" and ADV for "Ad-vanced". This means they are enhanced broadband exhaust gas oxygen sensors. The new ADV exhaust gas oxygensensor features an extended measuring range as of Lambda value = 0.65. Other advantages of the new sensor arethe higher temperature resistance, shortened response times of under 30 milliseconds, as well as high signal accu-racy. Faster operating readiness, which is reached in less than five seconds, enables lower emission values in thewarm-up phase of the engine. Thanks to the high measuring dynamics of the sensor, the fuel-air ratio can be bet-ter determined and adjusted separately for each cylinder. This enables a homogeneous exhaust flow that lowersemission values and has a favourable effect on long-term emission behaviour. The service life of the sensor is con-figured for the service life of the vehicle.

8.3. Actuators

8.3.1. Electric fan

As usual, the electric fan has its own electronics and its speed is controlled by a pulse-width modulated signal. Theduty cycle in the normal operating mode (100 Hz) is converted into a speed signal.

N74 engine.8. Engine electrical system.

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• 7% duty cycle wakes up the fan electronics

• 11% duty cycle results in 33% of the maximum fan speed

• 93% duty cycle results in the maximum fan speed

• 97% duty cycle is a command for self-diagnosis of the fan electronics.

To output the fan after-run command, the output frequency of the DME is lowered to 10 Hz within the self-main-tained phase (terminal 15 off). The duty cycle is used to select the time and speed of the fan. New is that thepower supply is provided through terminal 30 via a relay from the Digital Motor Electronics.

Rolls-Royce Motor Cars LimitedAftersales Training UR-V-AThe DriveWesthampnettPO18 0SHUnited Kingdom

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