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Eugenio,77
mail@toyota-club.net
© Toyota-Club.Net
Jan 2016
• Toyota Variable Valve Timing. Evolution
Type VVT-iW - timing drive by single chain for both camshafts, variable valve timing mechanism with a blade rotor in the sprockets of the intake and exhaust camshafts, an extended range of adjustment at the intake. Applied for engines: 6AR-FSE, 8AR-FTS, 8NR-FTS, 2GR-FKS...
VVT-iW system (Variable Valve Timing - intelligent Wide) allows to smoothly change the valve timing according to engine operating conditions. This is achieved by rotating the intake camshaft relative to the drive sprocket in the range of 75-80° (crankshaft rotation angle).
Extended range, compared with the conventional VVT, goes mainly on the retard side. At the second camshaft in this scheme traditional VVT-i drive is installed.
VVT-i system (Variable Valve Timing - intelligent) allows to smoothly change the valve timing according to engine operating conditions. This is achieved by rotating the exhaust camshaft relative to the drive sprocket in the range of 50-55° (crankshaft rotation angle).
Combined action of intake VVT-iW and exhaust VVT-i provides the following effect.
1. Starting (EX - advance, IN - intermediate). To ensure reliable starting two independent lock pins are used to hold the rotor in the intermediate position.
2. Partial load (EX - rertard, IN - retard). Allows engine operation over Miller / Atkinson cycle, reducing pumping losses and improves fuel efficiency. More details - see here.
3. Medium to high load (EX - retard, IN - advance). Provides so-called internal exhaust gas recirculation, and improved exhaust.
VVT-iW actuator
VVT-iW actuator with a bladed rotor is installed to the intake camshaft. Two lock pins hold the rotor at the intermediate position. Auxiliary spring torque applied in the advance direction to return the rotor to intermediate position for reliable locks operation. It provides normal engine start, stopped at retard position.
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VVT-iW actuator. 1 - central bolt, 2 - auxiliary spring, 3 - front cover, 4 - rotor, 5 - lock pin, 6 - housing (sprocket), 7 - rear cover, 8 - intake camshaft. a - locking groove. |
The oil control valve is integrated into the central bolt. Wherein the control oil passage has a minimum length to provide maximum response rate and normal response at low temperatures. The control valve is driven by VVT-iW solenoid plunger.
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a - reset, b - to advance chamber, c - to retard chamber, d - motor oil, e - to lock pin. |
Valve design allows independent control of the two lock pins separately for advance and retard circuits. It allows to fix the rotor in an intermediate position of VVT-iW control.
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1 - outer pin, 2 - inner pin. a - engaged, b - free, c - oil, d - locking groove. |
VVT-iW solenoid is einstalled to the timing chain cover and connected directly to the variable valve timeing actauator.
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1 - VVT-iW solenoid. a - coil, b - plunger, c - rod. |
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.
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1 - rotor, 2 - from ECM, 3 - VVT-iW solenoid. a - direction of rotation, b - retard chamber, c - advance chamber, d - to advance chamber, e - from retard chamber, f - drain, g - oil pressure. |
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.
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1 - rotor, 2 - from ECM, 3 - VVT-iW solenoid. a - direction of rotation, b - retard chamber, c - advance chamber, d - to advance chamber, e - from retard chamber, f - drain, g - oil pressure. |
Hold. ECM calculates the target angle according to the driving conditions, and after the set position achieved it switches the control valve to the neutral position until the next change of external conditions.
VVT-i actuator
VVT-i actuator with a bladed rotor is installed to the exhaust camshaft
(traditional or new type - with the oil control valve integrated in the central bolt). When the engine stopped the lock pin holds the rotor at maximum advance position for normal starting.
Auxiliary spring torque applied in the advance direction to return the rotor and reliable operation of the lock after switching off the engine.
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VVT-i actuator (AR). 1 - auxiliary spring, 2 - housing, 3 - rotor, 4 - lock pin, 5 - sprocket, 6 - camshaft. a - stop, b - operation. |
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VVT-i actuator (GR). 1 - central bolt, 2 - front cover, 3 - housing, 4 - rotor, 5 - rear cover, 6 - exhaust camshaft. |
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 advance angle.
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VVT valve (AR). 1 - solenoid. a - spring, b - sleeve, c - valve spool, d - to actuator (advance chamber), e - to actuator (retard chamber), f - drain, g - oil pressure. |
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VVT valve (GR). 1 - solenoid. a - drain, b - to actuator (advance chamber), c - to actuator (retard chamber), d - oil pressure. |
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.
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1 - rotor, 2 - VVT-i solenoid, 3 - from ECM. a - the direction of rotation, b - oil pressure, c - drain. |
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1 - rotor, 2 - ECM, 3 - VVT-i solenoid, 3 - from ECM. a - the direction of rotation, b - retard chamber, c - advance chamber, d - to advance chamber, e - from retard chamber, f - drain, g - oil pressure. |
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.
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1 - rotor, 2 - VVT-i solenoid, 3 - from ECM. a - the direction of rotation, b - oil pressure, c - drain. |
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1 - rotor, 2 - from ECM, 3 - VVT-i solenoid. a - the direction of rotation, b - retard chamber, c - advance chamber, d - from advance chamber, e - to retard chamber, f - drain, g - oil pressure. |
Hold. ECM calculates the target angle according to the driving conditions, and after the set position achieved it switches the control valve to the neutral position until the next change of external conditions.
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