The VVTL-i system is based on the VVT-i system and employs a cam changeover mechanism to change the amount of the intake and exhaust valve lift. This makes it possible to attain high power without affecting the fuel economy or emissions performance. The basic construction and operation of the VVT-i mechanism is the same as that of the VVT-i system. Switching between two cams with different lift amounts is used to change the amount of the valve lift. For the cam changeover mechanism, the engine ECU switches between two cams using the oil control valve for VVTL based on the signals from the water temperature sensor and the crankshaft position sensor.`12Q
The VVTL-i system configuration components are nearly the same as those of the VVT-i system. The special components for the VVTL-i system are the oil control valve for VVTL and the camshafts and rocker arms.
1. Oil control valve for VVTL
The oil control valve for VVTL controls the oil pressure applied to the high-speed cam side of the cam changeover mechanism using the spool valve position control conducted by the engine ECU.
2. Camshafts and rocker arms
To change the amount of the valve lift, the camshaft has two types of cams, a low- and medium-speed cam and a high-speed cam, for each cylinder. The cam changeover mechanism is built into the rocker arm between the valves and cams. The oil pressure from the oil control valve for VVTL reaches the oil hole in the rocker arm, and this oil pressure pushes the lock pin below the pad. This fixes the pad and engages the high-speed cam. When the oil pressure is not being applied, the lock pin is returned by the spring force and the pad is freed. This makes the pad able to move freely in the vertical direction and disables the high-speed cam.
The intake and exhaust camshafts have cams with two different lift amounts for each cylinder, and the engine ECU switches these cams to the operating cam by oil pressure.
1. Low- and medium-speed (engine speed: below 6000 rpm)
As shown in the illustration at the top, the oil control valve opens the drain side. Therefore, the oil pressure does not act on the cam changeover mechanism. As shown in the illustration at the bottom, the oil pressure is not acting on the lock pin. Therefore, the lock pin is pushed by the spring in the lock release direction. In this manner, the pad repeats a disabling reciprocal movement. Therefore this lifts the valves by the low- and medium-speed cam.
2. High-speed (engine speed: over 6,000 rpm/coolant temp.: higher than 60