39396595-all-about-vvti.ppt
TRANSCRIPT
VVT-i 1
(Variable Valve Timing intelligent)
VVT-i
VVT-i 2
1. HERE’S WHAT I LOOK FOR IN AN ENGINE !
3. PROCESS OF DRAWING AIR-FUEL MIXTURE INTO CYLINDER 4. ENGINE RPM AND VALVE TIMNG5. VVT-i CONTROL6. VVT-i ADVANTAGE
INTRODUCTION
2. BASIC OPERATION OF THE FOUR-STROKE ENGINE
7. VALVE TIMING
VVT-i 3
“I wish it had bettergas mileage”
“I wish it had morepower”
“I don’t needto refuel yet”
“I wish engine performed smoothly even in heavy traffic”
“Even exhaustfumes are clean”
“I want engine that isenvironmentally
friendly”
“I wish they wouldn’t demand
so much”
1. HERE’S WHAT I LOOK FOR IN AN ENGINEWouldn't it be wonderful if your engine addressed all of your needs? Such as one that has plenty of power yet uses very little fuel and is friendly to the environment?
VVT-i 4
VVT-i
The VVT-i is an all-comprehensive engine control system that has achieved high levels of the seemingly opposing performance of "higher power output", "lower fuel consumption", and "cleaner exhaust gases".
VVT-i 52. BASIC OPERATION OF THE
FOUR-STROKE ENGINEBefore we learn how the VVT-i system operates, let us first review the basic operation of the four stroke engine.
Compression stroke
Combustion stroke
Exhaust stroke
Intake stroke
VVT-i 6
It takes me awhileto get moving.
Top-dead-center
Intake lag (1)
3. PROCESS OF DRAWING AIR-FUEL MIXTURE INTO CYLINDER
As the piston begins its descent from its top-dead-center, a vacuum is created in the cylinder, causing the pressure in the cylinder to become lower than that of the intake port. The air-fuel mixture that was standing by in the intake port does not move immediately when the vacuum that is created in the cylinder is ready to draw the air-fuel mixture into the cylinder.
The drawing of the air-fuel mixture into the cylinder is slightly delayed in relation to the descent of the piston, a phenomenon know as "intake lag".
VVT-i 7
There’s plenty of room for us
But they’re pushing harder!
Bottom-dead-center
Intake lag (2) Due to the "intake lag", even after the piston turns around at its bottom-dead-center and begins its descent, the pressure in the cylinder for sometime remains lower than that of the intake port.
Until this difference in pressure is eliminated by the further ascension of the piston, the air-fuel mixture continues to be drawn into the cylinder.
Engines are normally designed with these factors in mind.
Consequently, in order to draw in as much air-fuel mixture as possible during the intake stroke, it is important to take the "intake lag" into consideration when determining the timing of the opening and closing of the intake valve.
VVT-i 8
It’s not pulling me in very fast
I caught up with you
I’m coming down slowly
During low engine rpm (1)4. ENGINE RPM AND VALVE TIMING
Because the piston descends at a slow speed and the air-fuel mixture also flows at a slow speed, only a slight resistance is created against the drawing of the air-fuel mixture into the cylinder. Therefore, the air-fuel mixture in the intake port is drawn into the cylinder without lagging too far behind the movement of the piston.
The intake lag varies in accordance with the engine rpm because the piston's descent speed is proportionate to the engine rpm.
VVT-i 9
I’m fullNow.
Bottom-dead-center
During low engine rpm (2) Because the "intake lag" is short, the difference in pressure that is created in the cylinder and in the intake port at the piston's bottom-dead-center is only slight. Therefore, the pressure in the cylinder becomes higher than the pressure in the intake port as soon as the piston starts to ascend. Therefore, a larger amount of air-fuel mixture can be drawn in if the intake valve is opened near the piston's top-dead-center and closed near the bottom-dead-center.
VVT-i 10
It’s all the way down there already.
There’s noway to catch up.
During high engine rpm (1) Because the piston descends at a fast speed and the air-fuel mixture also flows at a fast speed, a considerable amount of resistance is created against the drawing of the air-fuel mixture into the cylinder. Therefore, the air-fuel mixture in the intake port is drawn into the cylinder lagging considerably behind, without being able to catch up with the movement of the piston.
VVT-i 11
There’splenty moreroom for me.
Bottom-dead-center
During high engine rpm (2) When the "intake lag" becomes long, even after the piston turns around at its bottom-dead-center and begins its ascent, the pressure in the cylinder for some time remains lower than that of the intake port. Thus, the air-fuel mixture continues to be drawn into the cylinder for quite some time after the piston has begun its ascent.Therefore, during high rpm operation, a larger amount of air-fuel mixture can be drawn into the cylinder when the intake valve is opened earlier than the top-dead-canter, and closed later than the bottom-dead-center.
VVT-i 125. VVT-i CONTROL
The VVT-i improves the engine's overall performance based on the engine rpm and the extent to which the throttle valve is opened. When greater power is needed, it changes the timing to that which enhances torque, and when less power is needed, it changes the timing to that which enhances fuel economy and cleaner exhaust gases.
Let us confirm how the VVT-i achieves "high power output", "low fuel consumption", and "clean exhaust gases" by using the various driving condition as the VVT-i control example.
VVT-i 13
It’s hard to get through.
Vacuum
Exhaustgas
I’m gettingpulled in!
Idling (1) Because the intake lag that occurs during idle minimal, it is not necessary to open the intake valve early. However, on a conventional engine in which the valve timing is fixed, the valves open early because they are designed with the intake lag in mind, which takes place during high-rpm operation.
When the air-fuel mixture is contaminated in this manner, it does not produce reliable combustion and results in an unstable engine rpm. For these reasons, in conventional engines that avoid valve overlap, it becomes necessary to raise the rpm at idle to a certain extent.
VVT-i 14
The exhaustgases are not coming in.
Idling (2)
During idle, the VVT-i delays the timing at which the intake valve opens to eliminate the valve overlap, thus preventing the exhaust gases from flowing back into the intake port.
VVT-i 15Light & medium load driving (1)
During normal driving, the VVT-i advances the valve timing to achieve a large valve overlap. During normal driving, when the throttle valve is not opened too widely, a vacuum is created in the intake port. Similar to when the engine is idling, when the valve overlap is large, this vacuum causes the exhaust gases to flow back into the intake side.
Why does the VVT-i increase the valve overlap, which could the state of the air-fuel mixture to worsen?
VVT-i 16
Now I can move moresmoothly!
Light & medium load driving (2)
As the exhaust gases are drawn in, the vacuum in the intake port becomes lower and reduces the resistance (the force that tries to pull the piston upward) during the descent of the piston during the intake stroke.
The engine's power loss is reduced and fuel economy is increased.
VVT-i 17
There’s less NOx because it doesn’t get too hot.
I’m clean!
Light & medium load driving (3)
The unburned fuel that is contained in the exhaust gases is re-introduced into combustion, resulting in a decreased amount of HC emissions and cleaner exhaust gases.
The mixing of the inactive gases into the air-fuel mixture lowers the combustion temperature, resulting in a decreased amount of NOx emissions and cleaner exhaust gases.
VVT-i 18
ClickI’m full now
Heavy-load with low & medium rpm (1)
Bottom-dead-center
When the driver is about to depress the accelerator pedal all the way to start accelerating, the engine rpm is low and the piston is operating at a low speed, so the intake lag of the air-fuel mixture is short.
Under such conditions, when the piston turns around at its bottom-dead-center, the pressure in the cylinder and the pressure in the intake port soon reach their equilibrium. Therefore, unless the intake valve is closed before the piston ascends, the air-fuel mixture gets pushed back. by advancing the timing of closing the intake valve, and enable the valve to close when the piston is near the bottom-dead-center, a sufficient amount of air-fuel mixture can be drawn in.
VVT-i 19
Overlap : Large
Heavy-load with low & medium rpm (2)
However, closing the intake valve early also means that the intake valve opens early, causing the valve overlap to increase. during idle, if the valve overlap is large, the exhaust gases flows back due to the vacuum that is present in the intake port. However, during sudden acceleration, in the intake port is low, and there is practically no back flow of the exhaust gases.
VVT-i 20
I’m going to delay it a little.
I can’t catch upwith the piston.
It’s getting graduallyearlier.
Heavy-load with high rpm
When the accelerator pedal continues to be depresses, the engine rpm increases, resulting in a longer intake lag.
Using sensors to monitor the engine rpm, the VVT-i gradually delays the timing to close the valve so that the maximum amount of air-fuel mixture can be drawn in according to the increase in the engine rpm.
VVT-i 21
(1)Stable combustion can be obtained even at a low rpm. Thus, with the lower idle rpm, the engine achieves better
fuel economy.
6. VVT-i ADVANTAGE
(2)The engine's power loss is reduced and fuel economy is increased.
The exhaust gases are cleaner.
(3)To maximize the potential of the engine.
VVT-i 22
TDC
BDC
IN
EX
Eliminated overlap
Amount of exhaust gas blowing-back to intake
port is contained
Stabilized combustion
Improved fuel economy
During Idling7. VALVE TIMING
VVT-i 23
Increased overlap
Internal EGR rate is
increased
Reduced pumping loss
Reduced NOxemission and
re-burning of HCImproved
fuel economy
During light & medium-load
VVT-i 24
Closing timing of intake valve is advanced
Amount of mixture blowing-back to intake
port is contained
Improved volumetric efficiency
Improved out put
During heavy-load, low & medium rpm
VVT-i 25
Closing timing of intake valve is retarded
according to engine speed.
Timing matched with inertia force of intake air
is set.
Improved volumetric efficiency
Improved output
During heavy-load, high rpm
VVT-i 26
Range Operation State
Valve timing
1Idling
2Light Load
3MediumLoad
4Medium rpm &Heavy Load
5High rpm& Heavy Load
TDC BDC
EXIN
EX
IN
EX
IN
EX
IN
EX
IN
Load
Engine rpm
Wide Open Throttle
Range 4 Range 5
Range 3
Range 1
Range 2
Summary
VVT-i 27
1. RELATED COMPONENTS2. OPERATION3. VVT-i CONTROL
D16D VVT-i SYSTEM
VVT-i 28
Cam angle sensor
Crankangle sensor
OCV
VVT-icontroller
1. RELATED COMPONENTS(1) VVT-i controller(2) OCV (Oil Control Valve)(3) Cam angle sensor(4) Engine revolution sensor
K3-VE
VVT-i 29
(Fixed on intake camshaft)
(Fixed on housing)
Lock pinHydraulicpressure Spring
force
During engine running When engine is In stopped state
RetardAdvance
(1) VVT-i controller (K3-VE)
VVT-i 30
Camshaft drive gear( Fixed on camshaft drive gear )
Rotor ( Fixed on exhaust camshaft )Vane
Housing
Lock pinHydraulicpressure Spring
force
During engine running When engine is In stopped state
(1) VVT-i controller (EJ-VE)
VVT-i 31
Drain DrainPump Spool valve
Advancechamber
Retardchamber
Operating direction of spool valve
Duty ratio
SmallLarge
(2) OCV (Oil Control Valve)
VVT-i 32
EJ-VE
Timing pin
Cam angle sensor
Two turns of engine
Cam angle sensor output
K3-VE
(3) Cam angle sensor
VVT-i 33(4) Engine revolution sensor
EJ-VE
K3-VE
VVT-i 342. OPERATION
(1) Advance operation(2) Retard operation(3) Retention operation
VVT-i 35
VVT-icontroller
Oil pressure
Rotatingdirection
Advance SignalDuty ratio : Large
EngineECU
DrainOperating direction
of spool valve
(1) Advance operation (K3-VE)
VVT-i 36
Intake camshaft
Exhaust camshaft
Engine ECU
DrainOil pressur
e
OCV
Advance SignalDuty ratio : Large
(1) Advance operation (EJ-VE)
VVT-i 37
Rotatingdirection
Oil pressure
Engine ECUVVT-i
controller
Operating directionof spool valve
Retard signalDuty ratio: Small
Drain
(2) Retard operation (K3-VE)
VVT-i 38
EngineECU
DrainOil pressure
Exhaust camshaft
Intakecamshaft
OCV
Retard signalDuty ratio: Small
(2) Retard operation (EJ-VE)
VVT-i 39
Engine ECU
Oil pressure
Retention signalDuty ratio : Middle
(3) Retention operation (K3-VE)
VVT-i 40
Exhaust camshaft
Intake camshaft
OCV
Oil pressure
Engine ECU
Retention signalDuty ratio :Middle
(3) Retention operation (EJ-VE)
VVT-i 413. VVT-i CONTROL
(1) Outline(2) Control(3) Valve timing
VVT-i 42
Each sensor
OCV
Oil pump
ECU
Cam angle sensorVVT-i controller
Intake cam shaft
Exhaust cam shaft
Engine revolution sensor
Retard
Advance
(1) Outline (K3-VE)
VVT-i 43
Cam angle sensorSignal rotor
Intake cam shaft
Exhaust cam shaft
Signal rotor
Engine revolution sensor
Each sensor
OCVOil pump
VVT-i controller
(1) Outline (EJ-VE)
VVT-i 44
OCV
Engine ECU
Compensation
Actual valve timing
Throttle sensor
Engine revolution sensor
Water temp. sensor
Pressure sensor
Cam angle sensor
Feedbackcontrol
Target valve timing
(2) Control
VVT-i 45
BDC
TDC
2°EX close12°30°
52°
10° 30°EX openIN close
IN open
Enginerotatingdirection
Valve TimingIntake :
Open : BTDC 30° ~ -12°
Close : ABDC 10° ~ 52°Exhaust :
Open : BBDC 30°Close : ATDC 2°
(3) Valve timing (K3-VE)
VVT-i 46
TDC
BDC
2°
6°
EX close
EX open44°
40
62°
20°
IN open
IN close
Valve TimingIntake :
Open : BTDC 40° ~ - 2°Close : ABDC 20° ~ 62°
Exhaust :Open : BBDC 44°Close : ATDC 6°
(3) Valve timing (EJ-VE)