How the Camshaft Phase Regulater is Controlled

The Camshaft Phase Regulater is a component of the VVT system that adjusts the valve timing to optimize engine performance, fuel efficiency, reduce emissions and increase power and torque. The system enables the camshaft to open and close the intake and exhaust valves at different times during each piston stroke cycle. Advancing or “advancing” the camshaft will result in the valves opening earlier for milder performance, while delaying or "retarding" the camshaft will give the engine more power and faster response at higher RPM's.

Camshaft phasing is controlled by a hydraulic system that uses a solenoid valve to control oil flow to advance, retard or hold the camshaft position. An ECU (Engine Control Unit) calculates the phase angle between the crankshaft and camshaft and generates a pulse-width modulation (PWM) signal to follow a set phase angle. The control valve controls the flow of oil to advance or retard the camshaft position based on the calculated phase angle. The ECU also controls the actuation of the camshaft position sensor.

State-of-the-art automotive hydraulic camshaft phaser control systems have been developed that allow the actuation of the hydraulic actuator to be responsive to variation in control fluid temperature without the cost and complexity associated with direct measurement. These control systems utilize hybrid control methodologies that combine bang-bang control for significant position error, with PID control for relatively small position error and on-line calibration procedures to provide responsive, accurate phasing of the camshaft.

An example of such a control system is shown in FIG. 1. In general, an input set of signals is sampled at a step 402, which includes signals of a conventional type indicating engine operating parameters such as engine speed and signals Pcr and Pca of FIG. 1, which together indicate the actual position of the camshaft relative to the crankshaft. A counter, stored in a standard random access memory device of controller 32 of FIG. 1 is incremented at a step 330, which corresponds to the PID retard error band and indicates the number of cycles of the actual position signal.

After the initial command DCCMD is output at a step 210, if ERRORC is determined to be of sufficient magnitude to exceed a PID control deadband, then a counter is reset at a next step 212. The adjusted duty cycle command is then output at a step 214 as a pulse-width modulated command PWM to switch 30 of FIG. 1, and a delay of about 150 milliseconds is applied to the command, which is applied to the hydraulic actuator for responsive advance of the camshaft.

Alternatively, the camshaft phaser control system can be designed to be tolerant of a wide range of position errors by using sensor fusion with a resolver as an additional sensor and increasing the resolution of the camshaft trigger wheel from three teeth to six teeth or higher. This approach results in a massive reduction of the phasing duration to reach a target control bandwidth of +-2 degCA and significantly lower energy consumption than does the sensor fusion technique utilizing only three teeth.