Es300 & RX300
The VVT system controls intake camshaft valve timing to provide improved torque, improved fuel economy and reduce exhaust emissions. VVT system consists of 2 oil control valves, 2 VVT controllers, crankshaft position sensor, oil pump, Engine Control Module (ECM) and associated wiring. See Fig 1.
The exhaust camshaft is driven by the timing belt and the intake camshaft is driven by a gear on the end of the exhaust camshaft. The intake camshaft drive gear is integrated with the VVT controller to vary intake camshaft valve timing. The VVT controller consists of a housing driven from the exhaust camshaft and a vane that is attached to the intake camshaft. See Fig 2. Oil pressure sent from the advance or retard side path at the intake camshaft causes rotation in the VVT controller resulting in a change in valve timing.
The oil control valve is an electrically controlled valve that receives oil pressure from the oil pump. See Fig 3. The ECM uses input signals for engine speed, intake air volume, throttle position and engine coolant temperature to determine the operation of the oil control valve. ECM also uses input signals from VVT sensors and crankshaft position sensor for determining the actual intake camshaft valve timing. The ECM operates the oil control valve by controlling position of spool valve in the oil control valve. Positioning of spool valve determines which side of the piston the oil pressure will be applied on. By applying oil pressure on the piston, the piston will move inward or outward, causing the intake camshaft valve timing to change.
During light load, intake camshaft valve timing is retarded to provide stable engine operation. During medium load, intake camshaft valve timing is advanced to provide increased fuel economy and improved emission control. During heavy load in low to medium speed range, intake camshaft valve timing is advanced to provide increased torque. During heavy load in high speed range, intake camshaft valve timing is retarded to provide improved high speed range operation.
If a problem exists in the VVT system, a Diagnostic Trouble Code (DTC) may be stored in the ECM. DTC may be retrieved from ECM for system diagnosis using a scan tool. See SELF-DIAGNOSTICS - INTRODUCTION article.