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.
Introduction The
Task Of Variable Valve Timing
Var iabl e valve timing has the task of setting the most advantageous valve timing for the par ticu lar eng ine for the operating modes idle, ma%imum power and tor&ue as well as e%haust gas r ecir culation.
Idle /t idle, the camshafts are set so that the inlet camshaft opens late and, conse&uently, closes late as well. he e%haust camshaft is set so that it closes well before 0-. 0ue to the minimal gas residue from combustion, this leads to sm ooth idling.
Power o achieve good power at high eng ine speeds, the e%haust valves are opened late. In this way, the e%pansion of the burned gases can act against the pistons longer . valves open after 0- and close well after +0-. In this way, the dynamic self#char ging effect of the enter ing air is used to incr ease ease power. he inlet
Torue
o achieve ma%imum tor&ue, a high degree of volumetric efficiency must be attained. his re&uires that the inlet valves be opened ear ly. +ecause they open ear ly, they close ear ly as well, which avoids pressing out the fresh gases.
he e%haust
camshaft closes 1ust before 0-.
!"haust gas recirculation Internal e%haust gas recirculation can be achieved by ad1usting the inlet and e%haust camshafts. In this process, e%haust gas flows f r om the e%haust port into the inlet port while the valves over la p 2inlet and e%haust valves are bo th open3. he amount of over la p determines the amount of r ecir culated e%haust gas . he inlet camshaft is set so that it opens well before 0- and the e%haust camshaft does not close until 1ust before 0-. /s a r esult, both valves are open and e%haust gas is r ec ir culated . he advantage of internal e%haust gas r ecir culation over e%ter nal e%haust gas recirculation is the fast reaction of the system and very even distri bution of the rec irculated e%haust gases
.
VARIAB#! VA#V! TI$I%& 'esign Of Variable Valve Timing he variable valve timing system consists of the following com pone nts4# Two
( lu te d Variators
variator for ad1 usting the inlet camshaft is fitted directly on the inlet camshaft. It ad1usts the inlet camshaft accor ding to signals from the engine contr ol unit. he fluted var iator for ad1usting the e%haust camshaft is fitted directly on the e%haust camshaft. It ad1usts the e%haust camshaft accor d ing to signals from the engine contr ol unit. +oth fluted variators are hydr aulically operated and ar e connected to the engine oil system via the contr ol housing. he fluted
illustr ation shows the arrangement of the var iabl e valve timing system on the V5 and V6 engines. he
The Control )ousing contr ol housing is attached to the cyl inder head. 7il galleries to both fluted variators are located in the contr ol housing. he
Two
Solenoid Valves are two solenoid valves located in the contr ol housing.
direct oil pressure to both fluted var iators accor ding to the signal from the engine contr ol unit. her e
hey
Inlet camshaft timing ad1ustment valve #!# 2 8(953 is responsible for the inlet camshaft, and e%haust camshaft timing ad1ustment valve #!# 2 8"!)3 is responsible for the e%haust camshaft. illustr ation shows the arrangement of the var iable valve timing system on one cylinder head of the :) and :!( engines. he
O*eration Of Variable Valve Timing eng ine contr ol unit contr ols the var iabl e valve timing. o ad1ust the camshafts, it r e&u ir es information about eng ine speed, engine load and temperature and the positions of the crankshaft and camshafts. he
o ad1ust the camshaft, the engine contr ol unit actuates the solenoid valves 8(95 and 8"!). hey in turn open oil galler ies in the contr ol housing. En gine oil flows through the contr ol housing and camshaft into the fluted variators. he fluted variators turn and ad1ust the cams haft according to the specif ications of the engine contr ol unit.
his section goes into more detail about the ad1ustment of the camshafts. parts, the design and the operation are the sub1ect of the following pages.
he
Inlet Camshaft Ad+ustment camshaft is regulated by the engine contr ol unit over the entir e speed range of the eng ine. he ma%imum ad1ustment is 5( -/. he ad1ustment is dependent on the ad1ustment map stored in the engine contr ol unit. he inlet
0esign of the fluted variator for the inlet cam shaft he ad 1usting m echanism consists of4
Inle t Camshaft )ow the camshaft is ad vanced inlet camshaft is set in the position =inlet valves open before 0-> for e%haust gas r ecir culation and for incr easing tor&ue. o change the position, the eng ine contr ol unit actuates inlet camshaft timing ad1ustment valve ! 2 8(953. :hen actuated, the valve moves the contr ol pist on. he
the contr ol housing, the oil galler y for tim ing advance is opened accor ding to the degree of ad1ustment. -onse&uently, the eng ine oil under pressure flows through the contr ol housing into the r ing channel 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 var iator . her e it presses against the flutes of the inne r rotor. he inner rotor turns r elative to the outer rotor 2and crankshaft3, turning the camshaft with it. -onse&uently, the camshaft turns further in the dir ection of cr ankshaft rotation and the inlet valves open sooner. In
)ow The Cam shaft Is Retarded :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 contr ol unit actuates inlet camshaft timing ad1ustment valve ! 2 8(953. solenoid valve opens the gallery for timing retardation by moving the contr ol piston. 7il flows through the contr ol housing into the ring channel of the camshaft. he oil flows thr ough drillings in the camshaft to the pocket hole of the secur ing bo lt for the camshaft ad1uster. 'rom there, it flows through 5 drillings in the cams haft ad1uster into the oil chamber for tim ing retardation behind the flutes of the inner r otor . he oil presses the inner rotor and the camshaft in the direction of camshaft rotation and the valves open later . he
/t the same time that the oil gallery for timing retardation opens, the contr ol piston opens the oil return for the gal ler y for timing advance, r elieving pressure in it. he rotation in the dir ection of retardation presses the oil out of the timing advance oil chamber which flows out through the timing advance oil galler y
)ow Regulation ,orks R egulation ena bles continuous variation of the inlet camshaft between advanced and r etar ded, whereby the total var iation is a m a%imum of 5( crankshaft ang le. 7n the basis of the
camshafts can then be ad1usted accor ding to the map saved in the eng ine contr ol unit. :hen actuated by the engine contr ol unit, inlet camshaft timing ad1ustment valve ! 2 8( 953 pushes the contr ol piston in the dir ection, for e%am ple, of advanced timing. 7il pr essur e travels through the contr ol housing into the camshaft ad1uster and presses the camshaft in the =advanced> position. ?ushing the contr ol piston in the =advanced> direction autom ati cally opens the oil return of the oil channel for r etar ding timing. :hen the desired angle of ad1ustment is attained , the contr ol piston is moved by the actuation of inlet camshaft timing ad1ustment valve ! 2 8(953 to a position in which the pressure is held in both chambers of the ad1uster. If the timing is later retarded, the process runs in the opposite dir ection. he
!"haust Camshaft !"haust Camshaft Ad+ustm ent /s you saw in the preceding pages, the inlet camshaft is regulated by the c ontr ol unit. In contrast to that, the e%haust camshaft can only be contr olled . he contr ol unit sets the var iator only to the basic position or the idle position. he ma%imum angle of ad1ustment is (( cr ankshaf t ang le.
'esign Of The (luted Variator (or The !"haust Camshaftfluted var iator for the e%haust camshaft is iden tical in design to the fluted variator for the inlet camshaft. 7nly the inner rotor is wider because the ad1ustment is only (( cr ank shaf t /ng le. he
Basic
Position
e%haust camshaft is in its basic position wh en the eng ine is starting and at engine speeds above idle. he e%haust valves then close shortly before 0- . he e%haust camshaft is in this position in the oper ating modes power, tor&ue and e%haust gas he
recirculation. he e%haust camshaft timing ad1ustment valve these ranges.
!
2 8"!)3 is not actuated in
)ow The Basic Position ,orks In the basic position, the e%haust camshaft is positioned so that the valves close shortly befor e 0-. he e%haust camshaft timing ad1 ustm ent valve ! 2 8"!)3 is not actuated by the engine contr ol unit. In this position, the oil galler y for timing retardation is open. hr ough oil galleries, oil pressure reaches the ring channel of the e%haust camshaft. 'rom there, it travels thr ough the f ro ntal 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. he camshaft remains in this position as long as the solenoid is not actuated.
Idle he e%haust
camshaft is set to the =advanced> position from idle to engine speeds
to abou t !,(99 rpm.
)ow The Idle Position ,orks camshaft timing ad1 ustment valve ! 2 8"!)3 is actuated by the engine contr ol unit. his pushes the contr ol pist on and opens another oil gallery in the contr ol housing. he eng ine oil now flows into the other r ing channel in the camshaft and through the dr illed camshaft into the camshaft ad1uster. her e it presses against the flutes of the inner r otor . he flutes are pressed in the direction of engine rotation, taking the camshaft with them, so that the e%haust valves open and close ear lier . he oil from the chamber in front of the flutes runs through the drilling in the camshaft ad1 uster , the pocket hole of the secur ing bo lt and the r ing channel of the camshaft back to the solenoid valve. In the solenoid valve it flows through the oil return in the contr ol bo% cover. he e%haust
Oi l S.stem following pages introduce the oil system. he var iabl e valve timing system operates at an oil pressure of 9.@ bar and above. he
Course of oil under *ressure
7il pressure created by the oil pump flows through the c ylinder block to the cylinder head and from there through an oil str ainer into the contr ol housing of the camshaft ad1 uster . hr ough galler ies in the contr ol housing, it reaches the r ing channel in the camshaft and from there it tr avels through f r ontal drillings in the camshaft into the camshaft ad1 uster. Course of oil without *ressure
7il from the chambers in the camshaft ad1 uster without pressure flows through the ring channel in the camshaft back to the contr ol housing. 7il flows from the contr ol housing back to the solenoid valve. 'rom the solenoid valve, it flows through the timing chain cover back to the s ump.
he
oil course to the e%haust camshaft is identical with that to the inlet camshaft.
S. ste m o ve rv ie w for V/ and V0 engin es
!ngine Control 1nit eng ine contr ol unit, the sensors which provide it with information and the final controls which ar e actuated by the contr ol unit are the sub1ect of the following pages . he des cr iptions of the f inal contr ols and sensors in this self#study programme refer to engines with one e%haust and one inlet camshaft each . Eng ines with more than one e%haust and one inlet camshaft r e&uir e, of course, a
contr ol unit is r es ponsi ble for contr olling camshaft ad 1ustment. o this end, maps for inlet and e%haust camshaft ad1us tment are stored in the engine c ontr ol unit. hese maps e%ist for each mode of eng ine operation in which camshaft ad1ustment is active. he engine
'or e%ample, these operating m odes4
engine warm#up phase or for the engine at operating temper atur e.
functional structure of the engine contr ol unit is based on engine tor&ue as the base value for all further engine management m easur es calculated by the E-A. he base value, tor&ue, is calculated directly in the eng ine contr ol unit. o calculate tor&ue, the contr ol unit uses the s ignals from the air mass meter and the engine speed sender. he new
#earning Abilit. Of The S.stem var iabl e valve timing system is adaptive. his adaptability compensates for component and assem bly toler ances as well as wear occurring during engine use. he engine contr ol unit automatically initiates adaptation when the engine is idling and the coolant temperature is greater than 69 -. 0uring adaptation at idle, the engine contr ol unit uses signals from the engine speed sender and the
Air $ass $eter &23 mass meter G@9 is located in the intake tract of the engin e. he air mass meter signal is used by the engine contr ol unit to calculate the volumetric efficiency. 7n the bas is of volumetric efficiency, the lambda 27(3 value and the ignition timing, the he air
eng ine contr ol unit calculates the tor &ue.
Ase of signal
-onse&uences of loss of signal
In the var iabl e valve timing system, the signal is used for load#dependent ad1ustment of the camshaft. If the air mass meter f ails, the eng ine contr ol unit creates a substitute signal. -amshaft ad1ustment continues to operate giv en operating accor ding to the conditions.
!ngine S*eed Sender &45 engine speed sender G() is located in the crankcase. It senses electr om agnetically the teeth 269 minus (3 of the sender rotor on the cr ankshaf t . :ith this signal, the eng ine contr ol unit can detect the engine speed and the 0- positi on of the crankshaft. +ut to ad1ust the camshaft, the eng ine contr ol unit r e&u ir es the precise location of the crankshaft . o detect pr ecisely the pos ition of the cr ankshaft , the engine contr ol unit uses the signals from the individual teeth of the sender rotor. he gap in the sender rotor serves as the ero point 20- 3 and each sender rotor tooth marks 6 cr ankshaf t ang le. he
Ase of signal
-onse&uences of loss of signal
In the var iabl e valve timing system, the signal is used for engine#speed#dependent ad1ustment of the camshaft. If this signal fails, the eng ine stops and cannot be started again.
)all Sender &63 And )all Sender 4 &708 +oth
Ase of signal
-onse&uences of loss of signal
Coolant Tem*erature Sender &04
eng ine contr ol unit uses the engine speed sender signal to detect the position of the crankshaft. :ith the signals for the camshafts in addition, the contr ol unit calculates the position of the camshafts relative to the crankshaft. he contr ol unit needs these positions for the pr ecise ad1ustment of the camshafts and to start the engine &uick ly. If only one
coolant temperature sender G6( is located in the thermostat housing. It informs the eng ine contr ol unit of the current engine temper atu r e. he
Ase of signal
-onse&uences of loss of signal
sender signal is used for temper ature# dependent start of camshaft ad1 ustm ent. if the signal fails, the contr ol unit uses a su bstitute temperature stored in it he
Inlet C am sha ft Timing Ad +ustment Valve %43/ Camshaft Timing Ad+ustment Valve %8759
And
! "ha us t
+oth valves are integrated in the camshaf t ad1ustment contr ol housing. hey have the task of dir ect ing oil pressure to the camshaft ad1 usters depending on the dir ection and distance of ad1ustment accor ding to specif ications from the contr ol unit. o ad1ust the camshafts, the valves are actuated with a variable duty cycle 2on#off ratio3 by the contr ol unit. Inlet camshaft timing ad1ustment valve 8(95 ad1usts the inlet camshaf t and e%haust camshaft timing ad1ustment valve 8"!) ad1usts the e%haust camshaft.
-onse&uences of loss of signal
If an electrical wire to the camshaft timing ad1uster is defective, or a camshaft timing ad1uster fails, camshaft ad1ustment will not be per f ormed
Automotive %omenclature Canufacturers use many different names to describe their implementation of the various types of variable valve timing systems. hese names include4
/V- 2ubaru3
•
/V$ 2ubaru3
•
-? 2?roton, Volvo3
•
-V- 28issan, Infiniti3
•
-VV 2/lfa Romeo, -itroDn, Geely,
•
0-V-? # dual continuous variable cam phasing 2General Cotors3
•
0VV 20aihatsu3
•
CIVE- 2Citsubishi3
•
8#V- 28issan3
•
#V 2Cada3
•
V/87 2+C:3
•
Vario-am 2?orsche3
•
V- 2'ord, Famaha3
•
i#VE- 2
•
VV- 2CG Rover3
•
VV$ 28issan3
•
Valvelift 2/udi3
•
VVE$ 28issan, Infiniti3
•
VV 2-hrysler, General Cotors, ?roton, uuki, Volkswagen Group3
•
VV#i 2oyota, $e%us3
•
VV 2
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.
R!(!R!%C! htt*-::en9wiki*edia9org:wiki:Variable;valve;timing htt*-::auto9howstuffworks9com:camshaft49htm htt*-::+alo*nik9com:how
