Toyota Variable Valve Timing. VVT (gen.I)

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Jan 2016

Toyota Variable Valve Timing. Evolution

Conditional 1st gen. type - timing drive by belt for both camshafts, two-position variable valve timing mechanism with helical splines in the intake camshaft pulley. Applied for engines: 4A-GE type'91 silvertop and type'95 blacktop.

VVT system (Variable Valve Timing) allows to discrete change the valve timing according to engine operating conditions. This is achieved by rotating the intake camshaft relative to the drive pulley for 30° (crankshaft rotation angle).

VVT actuator housing (inner splines) is connected to the pulley, central gear (outer splines) is connected to the intake camshaft. There is a movable piston with inner and outer splines between them. During the axial movement of the piston the shaft rotates relative to the pulley.

1 - damper, 2 - helical splines, 3 - piston, 4 - camshaft, 5 - return spring.

ECM controls the oil flow to pulley chambers by solenoid, based on the signals of the sensors.

VVT control solenoid for silvertop (15330-16010) and blacktop (15330-16020).

ECM switches on solenoid to shift the spool. Engine oil under pressure is supplied to piston and moves it. When moving at helical splines, the piston turns the camshaft in the advance direction. When ECM switches off solenoid, the piston moves back and the camshaft returns to its basic position.

At high load and low to medium rpm, the early closing of the intake valves improves the volumetric efficiency. This increases the torque at low and medium rpm. At high rpm later closing of the intake valves (when VVT is off) helps to increase the maximum output.

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