Variable Valve Timing Actuator: Description and Operation

TECHNICAL INFORMATION
Conventional 4G64-2.4L engine installed in vehicles is changed to new designed 4G69-2.4L engine. The primary improvement of 4G69-2.4L engine is the additional new valve timing and lift switching system.
This system is designed to improve power output performance and mileage and reduces emission gas (CO).

ACTUATOR

Engine Oil Control Valve







The engine oil control valve is a type of solenoid valve that is controlled with duty cycles. Mounted on the cylinder block, this valve is used for hydraulically controlling the switching of cams.
When the coil of the engine oil control valve is not energized (duty cycle: 0%), port B closes, and ports A and C open, allowing the oil that was acting on the cam switching control piston to be discharged from port C via port A. When the coil is energized (duty cycle: 100%), the spool valve moves, closing port A and opening ports B and C. The oil that has been pumped by the oil pump passes via ports B and C, and acts on the cam switching control piston.

VALVE TIMING AND LIFT SWITCHING CONTROL




At low engine speeds, a low-speed cam that is suited to low-speed operations actuates the intake valve. At high engine speeds, a high-speed cam that is suited to high-speed operations actuates the intake valve. Thus, both the low-speed torque and high-speed output have been further improved from the previous engine.

The low-speed cam has a shorter valve overlap and valve opening duration, characteristics that are suited to low-speed operations in which the intake inertia is small. The high-speed cam has a longer valve overlap and valve opening duration, characteristics that are suited to high-speed operations in which the intake inertia is large.

At low engine speeds (approximately below 3,500 r/min), the PCM turns the engine oil control valve OFF (duty cycle: 0%). As a result, the cam switching control piston discharges oil, and the low-speed cam actuates the intake valve. The low-speed cam, which consists of two cams with different valve lifts, and the two cams actuate one independent intake valve each. Consequently, the difference in the valve lifts between these intake valves strengthens the flow of the air/fuel mixture in the cylinder, thus stabilizing combustion. As a result, low fuel consumption, low exhaust gas emissions, and high torque have been realized.

At high engine speeds (approximately above 3,500 r/min), the PCM turns the engine oil control valve ON (duty cycle: 100% for 2 seconds during switching; 60% after 2 seconds have elapsed). As a result, the hydraulic pressure acts on the cam switching control piston, and the high-speed cam actuates the two intake valves altogether. By increasing the valve opening duration and the lift in this manner, the intake air volume has been increased and the output has been improved.

In addition, an engine oil pressure switch that is installed in the cam switching oil line detects system malfunctions. Under the conditions listed below, the low-speed cam constantly actuates the intake valve.
- Engine coolant temperature is 10 °C (50 °F) or less.
- Within 10 seconds after the completion of the starting of the engine.