Variable Valve Timing System (VANOS)

Valve timing is changed on both the intake and the exhaust camshafts. This system, referred to as double VANOS, provides torque increase in the low to mid (1500-2000 RPM) range without power loss in the upper RPM range, less incomplete combustion when idling due to less camshaft overlap (also improves idle speed characteristics), internal Exhaust Gas Recirculation (EGR) in the part load range (reduces NOx and post-combustion of residual gasses in the exhaust), rapid catalyst warm up and lower raw emissions after cold start, and reduction in fuel consumption.

Double VANOS consists of intake and exhaust camshafts with helical gear insert, sprockets with adjustable gears, VANOS actuators for each camshaft, 2 three-way solenoid switching valves, 2 impulse wheels for detecting camshaft position, and 2 camshaft position sensors (Hall effect). Initial timing is set by gear positioning and the chain tensioner. Hydraulically controlled actuators move the helical geared cups to regulate camshaft timing. Angled teeth of the helical gears cause the pushing movement of the helical cup to be converted into a rotational movement. This rotational movement is added to the turning of the camshafts and cases camshafts to advance or retard. Adjustment rate is dependent on oil temperature, oil pressure, and engine RPM.

With extremely hot oil temperatures, VANOS is deactivated. If the oil is too thick (wrong viscosity) a fault could be set. When the engine is started, the camshafts are in failsafe position (deactivated). Intake camshaft is in retarded position, held by oil pressure from sprung open solenoid. Exhaust camshaft is in advanced position, held by a preload spring in actuator and oil pressure from sprung open solenoid. After 50 RPM (2-5 seconds) from engine start, PCM is monitoring exact camshaft position. PCM positions the camshafts based on engine RPM and the throttle position signal. From that point the camshaft timing will be varied based on intake air and coolant temperature. Double VANOS system is fully variable. When the PCM detects the camshafts are in the optimum positions, the solenoids are modulated (approximately 100-220 Hz) maintaining oil pressure on both sides of the actuators to hold the camshaft timing. See Fig 1.

On V8 engine, there is an inlet and exhaust solenoid for each camshaft. These solenoids are both installed on one side of the control piston. The engine control module regulates the solenoids through a pulse width modulated signal to apply or drain control oil pressure from the VANOS pistons. Camshaft adjustment is based on several characteristic maps stored in the control module. The main control parameters for camshaft adjustment are derived from the engine speed signal and the throttle valve position signal