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Toyota Variable Valve Timing. Dual-VVT

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Eugenio,77
mail@toyota-club.net
© Toyota-Club.Net
Jan 2016

Toyota Variable Valve Timing. Evolution

Type DVVT - as conditional 4th gen. type extension - timing drive by chain for both camshafts, variable valve timing mechanism with bladed rotor in the intake and exhaust camshaft sprockets. Applied for engines: series AR, ZR, NR, GR, UR, LR.


DVVT-i system (Dual Variable Valve Timing - intelligent) allows to smoothly change the valve timing according to engine operating conditions. This is achieved by rotating the intake and exhaust camshafts relative to the drive sprockets in the range of 40-60° (crankshaft rotation angle).

Timing drive (ZR series). 1 - VVT control solenoid (exhaust), 2 - VVT control solenoid (intake), 3 - camshaft position sensor (exhaust), 4 - camshaft position sensor (intake), 5 - water temperature sensor, 6 - crankshaft position sensor.

Variable valve timing actuator

VVT actuator with a bladed rotor are installed to the intake and exhaust camshafts. When the engine stopped the lock pin holds the rotor at maximum advance position for normal starting.

For some versions the auxiliary spring is used, that applied torque in the advance direction to return the rotor and reliable operation of the lock after switching off the engine.

VVT actuator (intake). 1 - housing, 2 - rotor, 3 - lock pin, 4 - sprocket, 5 - camshaft. a - stop, b - operation.

VVT actuator (exhaust). 1 - housing, 2 - rotor, 3 - lock pin, 4 - sprocket, 5 - camshaft, 6 - spring. a - stop, b - operation.

ECM controls the oil flow to advance and retard chambers by solenoid, based on the signals of the camshaft position sensors. When engine stopped the valve spool is moved by spring to ensure maximum retard angle for intake and maximum advance angle for exhaust.

VVT solenoid (intake). a - spring, b - sleeve, c - valve spool, d - to actuator (advance chamber), e - to actuator (retard chamber), f - drain, g - oil pressure.

VVT solenoid (exhaust). a - spring, b - sleeve, c - valve spool, d - to actuator (advance chamber), e - to actuator (retard chamber), f - drain, g - oil pressure.

Advance Retard Hold
The control signal from ECM to VVT solenoid (PWM)

Advance. ECM switches solenoid to an advance position and shifts the spool of the control valve. Engine oil under pressure is supplied to the rotor in advance chamber, turning it together with the camshaft in the advance direction.

Intake

Exhaust

Retard. ECM switches solenoid to an retard position and shifts the spool of the control valve. Engine oil under pressure is supplied to the rotor in retard chamber, turning it together with the camshaft in the retard direction.

Intake

Exhaust

Hold. ECM calculates the target angle according to the driving conditions, and after the set position achived it switches the control valve to the neutral position until the next change of external conditions.


Operation modes

Mode # Timing Condition Effect
Idling 1 Most late opening of the intake valves (maximum retard angle). Minimal valves overlap. Minimal exhaust gas amount by-pass to intake. Stable idle. Reduced fuel consumption.
Low load 2 Minimal valves overlap. Minimal exhaust gas amount by-pass to intake. Stable idle. Reduced fuel consumption.
Medium load 3 Valves overlap increases. Reduced pumping losses. Some exhaust gases are by-passed to intake (internal EGR). Reduced fuel consumption. Reduced emissions.
High load, low to medium rpm 4 Early closing of the intake valve to improve volumetric efficiency. Increased torque at low and medium rpm.
High load, high rpm 5 Late closing of the intake valve to improve volumetric efficiency. Increased maximal output.
Low temperature 6 Minimal valves overlap. Reduced fuel losses. Stable idle. Reduced fuel consumption.
Starting and stopping - Minimal valves overlap. Prevention of exhaust gases by-pass to intake. Improved starting conditions.

Valve timing (2ZR-FE)


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