research trend of variable valve actuation technology

8/3/2019 Research Trend of Variable Valve Actuation Technology

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Sungsan Park2010.10.01

KAIST Engine Laboratory


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KAIST Engine Lab.

Introduction

Researches on VVA

VVA applied onconventional engine

Contents

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KAIST Engine Lab.

Introduction

Researches on VVA


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KAIST Engine Lab.

Variable Valve Actuation (VVA) : Any mechanism or method

that can alter the shape or timing of a valve lift event within aninternal combustion engine.

Variable Valve Actuation

4

[SAE Paper 2008-01-1359, Technische Universitat Braunschweig, Institute of Internal Combustion Engines]

Fully Variable Valve Actuation (FVVA) : Camless Valve Train


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Advantage of VVA

5

IVL and IVO points taken for 2000 rpm, 2.5 bars IMEP show sfc & NOx values.

The data is taken from Audi EA113 4-Cylinder Test bench engine.

[SAE Paper 2008-01-1353, Robert Bosch GmbH]


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Efficiency vs. Valve-train Technology

6

Cam profile

optimization

CamshaftPhasing

Cam profileSwitching

MechanicalVariable

Valve-train

CamlessElectro-Magnetic

Valve-train

CamlessElectro-Hydraulic& Pneumatic

Valve-train

Fully Variable Valve

Actuation

20101990

5%

10%

Year

Efficiency


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Introduction

Researches on VVA


7



VVT11

Mechanical

18

Electro-Magnet

ic10

Electro-Pneum

atic3

Electro-Hydraulic, 14

etc.5

Type of Valve Train

SAE Papers about VVA (2005~2010)

8

ValveTrain

Design25

Simulation13

Strategy10

Control6 etc. 7

Type of Research



Varieties of Valve Train Design (1)

9

[SAE Paper 2005-01-0767]

[SAE Paper 2007-01-1285]

Mechanical

[SAE Paper 2007-01-1290]

[SAE Paper 2008-01-1346]


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[SAE Paper 2005-01-0772]

[SAE Paper 2005-01-0773]


Electro-Magnetic

[SAE Paper 2006-01-0041]

Electro-Pneumatic


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[SAE Paper 2007-01-1295]

[SAE Paper 2008-01-1355]

Electro-Hydraulic


A B

M

P T

M

[, ,KAIST]



Points to be Considered when Designing

Actuator for Valve Train (1)

12[SAE Paper 2008-01-1359]

Acting Force of the Actuator

In case of exhaust valve, pgas

is very large.

FVVA = 852 N (intake valve)

FVVA = 852 N to 2265 N (exhaust valve)


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Opening time

ValveLift

Landing stage

Points to be Considered when Designing

Actuator for Valve Train (2)

Tappet Valve Sitting Velocity

Inadequate slowing down ofthe valve can cause significant

deterioration of the valve seatand other parts, or

NVH(Noise, Vibration, andHarshness ) problem.

Sitting Velocity 0.5 m/s


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KAIST Engine Lab.

Efficiency vs. Valve-train Technology

14

Cam profile

optimization

CamshaftPhasing

Cam profileSwitching

MechanicalVariable

Valve-train

CamlessElectro-Magnetic

Valve-train

CamlessElectro-Hydraulic& Pneumatic

Valve-train

Fully Variable ValveActuation

20101990

5%

10%

Year

Efficiency


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Pneumatic vs. Hydraulic

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Advantages of Pneumatics

Viscosity of working fluid isinsensitive to changes intemperature.

External leakage is not a factor.

Relatively safe when valve hitsthe piston head.

Disadvantages of Pneumatics

Pneumatic systems areconstrained to working with lowerpressure(2~9 bar) compared to

hydraulic systems(~275bar).

Compressibility of the workingfluid can make valve lift profileshaping and valve seatingdifficult.

A separate pneumatic supplysystem must potentially bepackaged for the engine.

[SAE Paper 2005-01-0771]


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A B

Servo valve

(Moog)

Engine valve

-Spring constant: 25 N/mm

- Preloaded force: 60 N

M

P T

~ 10 (LPM) Pressure relief valve

(150bar)

Motor(3hp)

M

Cooler

Return

filter

Suction filter

Pressure filter

* Operating pressure

: 50bar~100barGas type

accumulator

Engine

valve

12

50

80

[, , KAIST]


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Hydraulic snubber designCamless Engine valve position and velocity profile:(a) Simulation(AMESim), (b) Experimental result,(c) Experimental result(close up for landing stage)

[, , KAIST]


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Experimental and Numerical Study of an

Electro-Hydraulic Camless VVA System

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Analyze the opening phase of an exhaust valve

Numerical analysis to validate and update the model

Derive an estimation of the HVC system power demand potentiality

Objective

[SAE Paper 2008-01-1355, University of Perugia]


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HVC Starting : The ECU triggers the three-wayelectro-valve.

EV Opening : The supply port(S) opens and oil atthe supply pressure flows to the power pistonpushing down the engine valve.

EV Holding : Spool valve is designed in such away that the load port(L) closure and the arrivalof the engine valve at its maximum lift aresynchronized.

Given the value overshooting obtained duringthe EV opening, the oil volume trapped over thepower piston(P2) is compressed by the enginevalve spring well above the supply pressure.

19




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EV Closing : At the end of ET, the three-way electro-valve is discharged, so the spool valve is pushed backto its rest position.

Energy recovery : During the period in which theload port(L) is connected again to the supply

port(S)m the highly pressurized oil trapped in theactuator flows back to the supply line. Thisbackflow results in the recovery of energysupplied to move the engine valve.

Discharge : The supply port is closed and, the oil

remaining in the power piston volume is discharged. Landing : The use of a calibrated orifice ensures a

soft landing of the engine valve.

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Engine valve lift and duration can be modifiedby the ECU, by varying the supply pressure and

the energizing time duration respectively.


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The cylinder pressure increase significantly reduces the maximum valve lift.

This behavior is due both to a loss in the synchronization between the spool and the

engine valves, and to the aerodynamic direct braking effect of the engine valve. Consequently, the opening and closing phase durations are unchanged, hence the

global shape of the valve lift profile is not dramatically altered.

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Analysis of Back Pressure Effect


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For the analysis only the actuator was considered by measuring the oilconsumption (averaged over 5000 shots basis), which is supposed to be supplied

at a constant pressure.

At a given back-pressure level, the energy required by the HVC actuator remainsalmost constant for energizing times from 20 ms to 6 ms, due to the absence ofhydraulic energy requirements during the holding phase.

Energy Consumption Analysis


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Overall HVC System Power Demand Estimation

As a result, the HVC system compared well with other electro-hydraulic camlesssystems.

As far as the conventional valve train data are concerned, the HVC system FMEPat full load is higher than a conventional valve train.

However the part load HVC system values appear to be noticeable.


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Valve Actuation Strategies

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Miller/Atkinson Cycle (EIVC/LIVC) : Reduce pumping loss

Asymmetric Valve Lift : In-cylinder swirl Better A/F mixing

Cylinder Deactivation : Reduce fuel consumption in the partload operation.

Internal Exhaust Gas Recirculation : By second opening ofintake or exhaust valve.

Extending Operation Range of Alternative Combustion

Operation Mode Switching

Throttless (SI Engines)

2/4-Stroke Switching (SI Engines)

Exhaust Brake (Heavy Duty Vehicles)


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Late Intake Valve Closing as an Emissions Control Strategy

at Tier 2 Bin 5 Engine-Out Nox level

Examine the emissions, performance, and combustion characteristicsof the engine using late intake valve closing(LIVC) to determine thebenefits and limitations of this strategy to meet Tier 2 Bin 5 NOxrequirements without after-treatment

Objective

[SAE Paper 2008-01-0637]


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LIVC changes the path of the fuel parcel at the very beginning when fuel isinjected into the combustion chamber.

Due to the lower compression temperature, the ignition delay increases, whichprovides a longer mixing time prior to the start of ignition(A to B).

The local equivalence ratio is reduced, which contributes to soot reduction.

Lower combustion temperature also reduces the NOx formation.


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Effective Compression Ratio(CR)

Effective IVC volume is used rather than Cylinder volume at IVC for betterrepresentation of the actual in-cylinder compression process.

The volumetric CR decreases almost linearly with intake valve closing.

However, very little change was observed in the pressure based effective CR.

Significant changes in effective CR occurs when the IVC timing is retarded bymore than 50 CADs.


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Effects of Late Intake Valve Closing on Engine Performance and Emissions A1 LIVC Sweep, Constant EGR

Reducing the effective CR from 14.5 to 11.0 isequal to about 80 Celsius temperaturereduction near TDC.

When performing LIVC sweeps, injection timingis advanced to maintain the MFB50 at CAD after

TDC.

For both cases, cool flame combustion wasobserved before the main combustion.

Although the combustion phasing is maintained,LIVC results in lower peak heat release rate and

longer combustion duration due to the lowercombustion temperature.

LIVC reduces the temperature during the wholecompression and combustion process, which isthe key reason of the NOx reduction.


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EINOx was reduced by up to 50% wheneffective CR was reduced to lower than 12.

Although further retarding the intake valveclosing would result in lower NOx emissions,higher boost pressure was needed to offset thedecreasing volumetric efficiency, which mightresult in higher pumping losses depending on

the turbocharger efficiency

Combustion noise monotonically decreases withdecreasing effective CR due to the lower peakAHRR.

At the Tier 2 Bin 5 NOx emission level, LIVCgenerally increases the HC and CO emissionsdue to the sweet spot


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Effects of Late Intake Valve Closing on Engine Performance and Emissions A2 LIVC Sweep, Constant NOx

Cylinder pressures of LIVC are consistently lowerthan the baseline during the compression and

expansion stroke due to; Lower effective CR

Lower EGR percentage

Although less EGR is used, LIVC still needs higherboost pressure because of the significantly lower

volumetric efficiency. LIVC generates lower bulk gas temperature during

the compression stroke, which increases theignition delay.

After combustion, LIVC achieves higher bulk gastemperature because of the lower in-cylinder gas

density(less EGR).

C C S


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Advancing the fuel injection timing may reduce thesmoke emissions, but combustion noise increases.

LIVC reduces smoke emissions by more than 95%because of the longer ignition delay.

Not too much variation is observed for HCemissions, while CO emissions decrease withdecreasing effective CR, due to the sweet spot

Intake manifold pressure is determined based onthe air flow rate and the required EGR. Exhaustmanifold pressure is set so that the requiredturbocharger efficiency is maintained at 35%.

Both IMP and EMP increase with decreasingeffective CR. The pressure difference(dP) betweenEMP and IMP, which influences the pumpinglosses, also increases.

Although the LIVC results in higher combustionefficiency, NSFC increases by about 4% due to thehigher pumping losses.

L t I t k V l Cl i E i i C t l St t


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Effects of Late Intake Valve Closing on Engine Performance and Emissions A3 LIVC Sweep, Constant NOx

In order to reduce the combustion noise, themain injection timing is retarded to ATDC. Asmall pilot is injected before TDC to achievebetter smoke-noise trade-off and improve thecombustion stability.

The effects of LIVC on ignition delay, pressure,

bulk temperature are similar to A2 condition.

LIVC results in higher peak heat release ratethan the baseline IVC, due to the difference ofcombustion mode. (Diffusion burn)



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The baseline fuel injection timing is retarded.

As a result, ignition delay increases. The majority of the combustion starts after the

end of fuel injection.

Combustion is in the late PCCI mode.



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About 15% less EGR is needed to meet the sameNOx emissions if effective CR is reduced from 14.5to 11.0.

Smoke emissions are reduced by 40% at Bin 8level and 60% at Bin 5 level.

Both HC and CO emissions increase, but absolutequantities of HC and CO are very low at thisoperation condition.

Intake and Exhaust pressure difference(dP)increases with decreasing effective CR if therequired turbocharger efficiency is constant.

In average, LIVC increases NSFC by about 1.5%for both cases.



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Expanded Early PCCI Operation Range

The tests conducted at the A2 condition(1600rpm,540 kPa NMEP) show the potential of using LIVC toexpand the early PCCI operation range.

Both smoke and noise increase with increasingload, which is consistent with the HRR and ignitiondelay trends.

Figure 16 clearly presents the benefits of LIVC inreducing smoke and noise and shows how a higherload is achievable within the smoke and noiselimits.

Using LIVC80 expanded the noise and smokelimited load to about 635 kPa NMEP.

Pumping losses are the main concern of usingLIVC to expand the early PCCI operation range.

Manifold dP increases very quickly as loadincreases, resulting in higher fuel consumption.



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Summary and Conclusions

25%-50% NOx reduction attributable to LIVC depending on the operating conditions

and injection strategies if the combustion phasing, IMT, AFR, and EGR are fixed. For constant NOx emissions, LIVC can be used to reduce the EGR requirements.

LIVC reduces the EGR requirement by 25% at low loads, 15% at high loads.

LIVC significantly reduces the soot emissions at all operating conditions.


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Introduction

Researches on VVA


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KAIST Engine Lab.

MultiAir Technology (Fiat)

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A valve tappet (cam follower), moved by a mechanical intake cam, isconnected to the intake valve through a hydraulic chamber, controlled by anormally open on/off solenoid valve.

[Lucio Bernard, Andrea Ferrari, Damiano Micelli, Aldo Perotto, RinaldoRinolfi, Francesco Vattaneo, Electro-hydraulic Valve Control with MultiAir

Technology, ATZ autotechnology 06, 2009 Volume 9, pp.32-37]


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MultiAir technology is applied to Alfa Romeo MiTo 1.4L JTB Engine. Without MultiAir : 153 hp and 230 Nm while using 6.5 L/100km.

With MultiAir : 168 hp and 250 Nm while using 6.0 L/100 km.

research trend of variable valve actuation technology

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