4RUNNER 4.0L V6
The VVT-i system used for the intake camshaft is adopted to realize excellent fuel economy, higher engine performance and reduce exhaust emissions.
Each cylinder has 2 intake valves and 2 exhaust valves. Intake and exhaust efficiency is increased by means of the larger total port areas. The intake camshafts are driven by the crankshaft via the primary timing chain. See Fig 1. The exhaust camshafts are driven by the intake camshaft of the respective bank via the secondary timing chain.
The VVT-i system uses an oil passage is provided in the intake camshaft in order to supply engine oil to the VVT-i system. A VVT-i controller has been installed on the front of the intake camshaft to vary the timing of the intake valves. See Fig 2. To detect the intake camshaft position, a timing rotor is provided in front of the VVT-i controller. This timing rotor, which is secured to the intake camshaft, is used by the VVT sensor to detect the actual position of the intake camshaft.
Camshaft timing oil control valve is an electrically controlled valve that receives oil pressure from the oil pump. The ECM uses input signals for engine speed, intake air volume, throttle position and engine coolant temperature to determine operation of camshaft timing oil control valve. See Fig 3. The ECM also uses input signals from variable valve timing sensors and crankshaft position sensor for determining the actual intake camshaft valve timing. See Fig 4. The ECM operates camshaft timing oil control valve by controlling position of spool valve. See Fig 5. This determines which side of variable valve timing controller the oil pressure will be applied on for advancing or retarding the valve timing by rotating the intake camshaft. See Figure.
When hydraulic pressure is not applied to the VVT-i controller immediately after the engine has been started, the lock pin locks the movement of the VVT-i controller to prevent a knocking noise. See Fig 6. When engine is idling, intake camshaft valve timing is set at the standard or hold position to stabilize the idle and obtain better fuel economy. During light engine load, intake camshaft valve timing remains retarded to provide stable engine operation. During medium engine load, intake camshaft valve timing is advanced to provide increased performance, fuel economy and improved emission control. During heavy engine load in low-to-medium-speed range, intake camshaft valve timing is advanced to provide increased torque. During heavy engine load in high-speed range, intake camshaft valve timing is retarded to provide improved high-speed range operation and better fuel economy. During cold temperatures, intake camshaft valve timing remains at the standard or hold position to stabilize fast idle speed and obtain better fuel economy. When engine is started or stopped, intake camshaft valve timing is set at retarded position to improve engine starting. If a problem exists in the VVT system, a Diagnostic Trouble Code (DTC) may be stored in ECM. See TESTING PROCEDURE under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article for retrieving of DTCs.