vvt (variable valve timing)

8/9/2019 VVT (variable Valve Timing)

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ABSTRACT

Variable valve actuation in heavy duty diesel engines is not well documented,partly because of diesel engine nature, such as, unthrottled air handling, which gives

little room to improve pumping loss; a very high compression ratio, which makes the

clearance between the piston and valve is little when the piston reaches the top dead

center. It is a long time that diesel engines are running by EGR and VG. he goal of

this research work is addressed the issue about how much fuel benefit diesel engines

at !"#mode cycle could be achieved using variable valve timing in a heavy duty diesel

engine. $ate inlet valve closing strategy will be used. In order to see how much fuel

efficiency could improve in addition to EGR and VG, EGR and VG are fully

controlled in a closed#loop. his paper e%amines fuel improvement in different speeds

and tor&ues. 'inally, we could see that ".()* +'- benefit at !"#mode cycle could be

achieved. he reason of this benefit is that fi%ed valve lift engine makes a compromise

between high speed engine performance and low speed fuel economy, late inlet valve

closing optimies valve timing at each engine tor&ue and speed.


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Introduction

The T a s k O f V ariable V a lv e Timing

Variablevalve timing has the task of setting the most advantageous valve timing

for the particular engine for the operating modes idle, ma%imum power and tor&ue as

well as e%haust gas recirculation.

Idle

/t idle, the camshafts are set so that the inlet camshaft opens late and,

conse&uently, closes lateas well. hee%haust camshaft is set so that it closes well before

0-. 0ue to the minimal gas residue from combustion, this leadsto smooth idling.

Po wer

o achieve good power at high engine speeds, the e%haust valves are opened

late.In this way, the e%pansion of the burned gases can act against the pistons longer.

he inlet valves open after 0- and close well after +0-. In this way,the dynamic

self#charging effect of the enteringair is used to increasepower.

T orue

o achieve ma%imum tor&ue, a high degree of volumetric efficiency must be

attained. his re&uires that the inlet valves be opened early. +ecause they open early,they closeearlyas well, which avoids pressing out the fresh gases.


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hee%haust camshaft closes1ustbefore 0-.

! " haust g a s r ecirc ula tion

Internal e%haust gas recirculation can be achieved by ad1usting the inlet and

e%haust camshafts. In this process, e%haust gas flows from the e%haust port into the inlet

port while the valves overlap 2inlet and e%haust valves are both open3. he amount ofoverlap determines the amount of recirculatede%haust gas.he inlet camshaft is set so

that it opens well before 0-and the e%haust camshaft does not closeuntil 1ust before

0-. /s a result,both valvesare open and e%haust gas is recirculated.headvantage of

internal e%haust gas recirculation over e%ternal e%haust gas recirculation is the fast

reaction of the system and very even distribution of the recirculatede%haust gases

.


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V ARIAB#! V A # V ! TI$I%&

' e s ig n O f V ariable V a lv e Timing

he variable valve timing system consists of the following components4#

Two ( lu t e d Variators

he fluted variator for ad1usting the inlet camshaft is fitted directly on the inlet

camshaft. It ad1usts the inlet camshaft according to signals from the engine controlunit.

he fluted variator for ad1usting the e%haust camshaft is fitted directly on the e%haust

camshaft. It ad1usts the e%haust camshaft according to signals from the engine control

unit. +oth fluted variators are hydraulicallyoperated and are connected to the engine oil

system via the controlhousing.

he illustrationshows the arrangement of the variablevalvetiming system on the

V5 and V6 engines.


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The C ontrol )ousing

hecontrolhousing is attached to the cylinder head. 7il galleries to both fluted

variators are located in the controlhousing.

Two S o le n oid Valves

here are two solenoid valves located in the control housing. hey direct oil

pressure to both fluted variatorsaccordingto the signal from the engine controlunit.

Inlet camshaft timing ad1ustment valve #!# 28(953 is responsible for the inlet

camshaft, and e%haust camshaft timing ad1ustment valve#!#28"!)3 is responsible for the

e%haust camshaft.

heillustrationshows the arrangement of the variablevalve timing system on one

cylinderhead of the:) and :!( engines.


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O*e r at io n O f Varia bl e Valve T im ing

heenginecontrolunit controlsthe variable valve timing. o ad1ust the camshafts,

it re&uires information about engine speed, engine load and temperature and the

positions of the crankshaft and camshafts.

o ad1ust the camshaft, the engine controlunitactuates the solenoid valves8(95

and 8"!).hey in turn open oil galleriesin the control housing. Engineoil flows through

the control housing and camshaft into the fluted variators. he fluted variators turn and

ad1ust the camshaft according to the specificationsof the engine controlunit.

his section goes into more detail about the ad1ustment of the camshafts. he

parts, the design and the operation are the sub1ect of the followingpages.


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In le t Ca m s haf t Ad+ ustmen t

he inlet camshaft is regulated by the engine control unit over the entire speed

range of the engine.hema%imum ad1ustment is 5( -/. he ad1ustment is dependent on

the ad1ustment map stored in the engine controlunit.

0esign of the fluted variator for the inlet camshafthead1usting mechanism consists

of4


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Inle t Ca mshaft

) o w th e cam s haf t i s a dvanc ed

heinlet camshaft is set in the position =inlet valves open before 0-> for e%haust

gas recirculation and for increasing tor&ue. o change the position, the engine control

unit actuates inlet camshaft timing ad1ustmentvalve ! 28(953.:hen actuated, the valve

moves the controlpiston.

In the control housing, the oil gallery for timing advance is opened according to

the degree of ad1ustment. -onse&uently, the engineoil underpressure flows through the

controlhousing into the ringchannel in the camshaft. hen the oil flows through the five

drillings in the face of the camshaft into the five advance chambers of the fluted variator.

here it presses against the flutes of the inner rotor. he inner rotor turns relative to the

outer rotor 2and crankshaft3, turning the camshaft with it. -onse&uently, the camshaftturns further in the directionof crankshaft rotation and the inlet valves open sooner.


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) o w T h e C a m sh a ft Is R et ard ed

:hen the engine is idling or when a great deal of power is re&uired from the

engine, the inlet camshaft is rotated so that the inlet valves open late, that is, after 0-.

o retard the inlet camshaft, the engine control unit actuates inlet camshaft timing

ad1ustment valve ! 28(953.

hesolenoidvalve opens the gallery for timing retardation by moving the control

piston. 7il flows through the controlhousing into the ring channelof the camshaft. heoil

flows through drillings in the camshaft to the pocket hole of the securingbolt for the

camshaft ad1uster. 'rom there, it flows through 5 drillings in the camshaftad1uster into

the oil chamber for timing retardationbehind the flutes of the inner rotor. heoil presses

the inner rotor and the camshaft in the direction of camshaft rotation and the valves open

later.

/t the same time that the oil gallery for timing retardation opens, the control

piston opens the oil return for the galleryfor timing advance, relievingpressure in it. he

rotation in the direction of retardation presses the oil out of the timing advance oil

chamber which flows outthrough the timing advance oil gallery


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) o w Regul a t io n ,or ks

Regulation enablescontinuous variation of the inlet camshaft between advanced

and retarded, whereby the total variationis a ma%imum of5( crankshaft angle.7n the

basis of the position. ?ushing the control piston in the

=advanced> direction automatically opens the oil return of the oil channel for retarding

timing. :hen the desired angle of ad1ustment is attained, the controlpiston is moved by

the actuation of inlet camshaft timing ad1ustment valve!

28(953to aposition in which thepressure is held in both chambers of the ad1uster. If the timing is later retarded, the

process runs in the opposite direction.


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! " h a u s t C am sh aft

! " haust C a m s ha f t Ad+ustm ent

/s you saw in the preceding pages, the inlet camshaft is regulatedby the control

unit. In contrast to that, the e%haust camshaft can onlybe controlled.hecontrolunit sets

the variator only to the basic position or the idle position. he ma%imum angle of

ad1ustment is (( crankshaft angle.

'es i g n O f Th e ( lu te d V ar i a t o r (o r Th e !"haust Cam shaft-

he fluted variator for the e%haust camshaft is identical in design to the fluted

variator for the inlet camshaft. 7nly the inner rotor is wider because the ad1ustment is

only (( crankshaft/ng le.

Basi c Position

he e%haust camshaft is in its basic position when the engine is starting and at

engine speeds above idle.hee%haust valves then close shortly before 0-. hee%haust

camshaft is in this position in the operating modes power, tor&ue and e%haust gas


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recirculation. he e%haust camshaft timing ad1ustment valve ! 28"!)3 is not actuated in

these ranges.

) o w T h e Basi c Positio n ,or ks

In the basic position, the e%haust camshaft is positioned so that the valves closeshortlybefore 0-. hee%haust camshaft timing ad1ustment valve ! 28"!)3is not actuated

by the engine controlunit. In this position, the oil galleryfor timing retardation is open.

hroughoil galleries, oilpressure reaches the ring channel of the e%haust camshaft. 'rom

there, it travels through the frontal drillings in the camshaft to the oil chamber of the

camshaft ad1uster. 'rom there it presses against the flutes of the inner rotor. he flutes

turn to stop, turning the camshaft along with it. hecamshaft remains in this position as

long as the solenoidis not actuated.


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Id le

he e%haust camshaft is set to the =advanced>position from idle to engine speeds

to about!,(99 rpm.

) o w T h e Id le Po s it i o n ,orks

he e%haust camshaft timing ad1ustmentvalve ! 28"!)3 is actuated by the engine

control unit. his pushes the controlpiston and opens another oil gallery in the control

housing.heengineoil now flows into the other ring channelin the camshaft and through

the drilled camshaft into the camshaft ad1uster. here itpresses against the flutes of the

innerrotor.he flutes are pressed in the direction of engine rotation, taking the camshaft

with them, so that the e%haust valves open and close earlier.heoil from the chamber in

front of the flutes runs through the drilling in the camshaft ad1uster, the pocket hole of the

securingbolt and the ring channel of the camshaft back to the solenoid valve. In thesolenoid valveit flows through theoil return in the controlbo% cover.


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Oi l S.stem

he following pages introduce the oil system. he variable valve timing system

operates at an oilpressure of 9.@ bar and above.

C o u rse o f o il un d er *re ss ure

7il pressure created by the oil pump flows through the cylinder block to the

cylinder head and from there through an oil strainer into the control housing of the

camshaft ad1uster. hroughgalleriesin the controlhousing, it reaches the ringchannelin

the camshaft and from there it travels through frontal drillings in the camshaft into the

camshaft ad1uster.

C o u rse o f o il wi th o u t *r essure

7il from the chambers in the camshaft ad1uster without pressure flows

through the ring channel in the camshaft back to the controlhousing.7il flows

from the controlhousingback to the solenoid valve.

'rom the solenoid valve, it flows through the timing chain cover back to the

sump.

heoil course to the e%haust camshaft is identical with that to the inlet camshaft.


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S . st e m o v e r v ie w fo r V / a n d V 0 e ngin es


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!ngi n e C o n t r o l 1nit

heengine control unit, the sensors which provide it with information and

the final controls which are actuated by the control unit are the sub1ect of the

followingpages.

he

de

scriptions of the fina

lcontrols and sensors in this self#studyprogramme refer to engines with one e%haust and one inlet camshaft each.

Eng ineswith more than one e%haust and one inlet camshaft re&uire,of course, a


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#e a rning Abi l it. O f The S.stem

heentire variablevalvetiming system is adaptive. his adaptabilitycompensates

for component and assemblytolerancesas well as wear occurring during engine use.he

engine control unit automatically initiates adaptation when the engine is idling and the

coolant temperature is greater than 69 -.0uring adaptation at idle, the engine control

unit uses signals from the engine speed sender and the


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A ir $ a s s $ e t e r & 23

he air mass meter G@9 is locatedin the intake tract of the engine.he air mass

meter signal is used by the engine controlunit to calculate the volumetric efficiency. 7n

the basis of volumetric efficiency, the lambda 27(

3 value and the ignition timing, the

enginecontrolunit calculates the tor&ue.

Ase of signal In the variable valve timing system, the

signal is used for load#dependent

ad1ustment of the camshaft.

-onse&uences of loss of signal If the air mass meter fails, the engine

control unit creates a substitute signal.

-amshaft ad1ustment continues to operate

according to the given operating

conditions.


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! n g ine S* e ed S e nder &45

he engine speed sender G() is located in the crankcase. It senses

electromagneticallythe teeth 269 minus (3 of the sender rotor on the crankshaft.:ith this

signal, the enginecontrol unit can detect the engine speed and the 0- positionof the

crankshaft. +ut to ad1ust the camshaft, the engine control unit re&uires the precise

location of the crankshaft. o detect precisely the position of the crankshaft, the engine

control unit uses the signals from the individual teeth of the sender rotor. hegap in the

sender rotor serves as the ero point 20-3 and each sender rotor tooth marks 6

crankshaft angle.

Ase of signal In the variable valve timing system, the

signal is used for engine#speed#dependent

ad1ustment of the camshaft.

-onse&uences of loss of signal If this signal fails, the engine stops and

cannot be started again.


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)a l l S e nder & 63 A n d )all S end e r 4 &708

+oth


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he coolant temperature sender G6( is located in the thermostat housing. It

informs the engine controlunit of the current engine temperature.

Ase of signal he sender signal is used for temperature#

dependent start of camshaft ad1ustment.

-onse&uences of loss of signal if the signal fails, the control unit uses a

substitute temperature stored in it


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I n l et C a m s ha f t T im ing Ad+ u s t m ent Valve % 4 3/ And ! " ha u s t

Ca m s haf t Timi n g Ad+ustme n t Valve %8759

+oth valvesare integrated in the camshaft ad1ustment controlhousing. heyhavethe task of directingoilpressure to the camshaft ad1usters depending on the directionand

distance of ad1ustment according to specifications from the control unit. o ad1ust thecamshafts, the valves are actuated with a variable duty cycle 2on#off ratio3by the controlunit. Inlet camshaft timing ad1ustment valve 8(95 ad1usts the inlet camshaft and e%haustcamshaft timing ad1ustment valve8"!) ad1usts the e%haust camshaft.

-onse&uences of loss of signal If an electrical wire to the camshaft timingad1uster is defective, or a camshaft timing

ad1uster fails, camshaft ad1ustment will notbeperformed


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Automotive %omenclature

Canufacturers use many different names to describe their implementation of the various types of

variable valve timing systems. hese names include4


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VV- 2CG Rover3

VV$28issan3

Valvelift 2/udi3

VVE$28issan, Infiniti3

VV 2-hrysler, General Cotors, ?roton, uuki, Volkswagen Group3

VV#i2oyota, $e%us3

VV 2


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CO%C#1SIO%

Variable valve actuation in heavy duty diesel engines is not well

documented, partly because of diesel engine nature, such as, unthrottled air

handling, which gives little room to improve pumping loss; a very high

compression ratio, which makes the clearance between the piston and valve is

little when the piston reaches the top dead center.


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R!(!R!%C!

htt*-::en9wiki*edia9org:wiki:Variable;valve;timing

htt*-::auto9howstuffworks9com:camshaft49htm

htt*-::+alo*nik9com:how

vvt (variable valve timing)

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