The Camshaft Phase Regulater Is a Component of the Variable Valve Timing System (VVT)

The Camshaft Phase Regulater is a component of the Variable Valve Timing system (VVT) used to optimize the filling of the cylinders with working mixture. Shifting the closing timing of the intake valves enables better scavenging and vacuum generation at low engine speeds, while improving torque and power at high engine speeds. This is achieved by adjusting the opening time of the inlet camshaft according to the current load conditions of the engine via the injection computer.

The VVT system uses an electric machine, especially brushless DC electric motors or permanent magnet synchronous motors, as the actuator for the inlet camshaft. The electric machine is driven by a camshaft trigger wheel and connected to both the camshaft and crankshaft sprockets via a strain wave gearing. In steady-state operation the electric machine rotates at half of the engine speed. During the phasing event, the electric machine is controlled to accelerate or decelerate briefly with respect to the camshaft sprocket to shift the camshaft relative to the crankshaft sprocket.

For this purpose a sensor fusion approach is used where a Hall sensor and the camshaft position sensor are detected simultaneously at the same time with an integrated control unit. This allows for an optimal synchronization between the camshaft and crankshaft. The sensor fusion also improves the poor phase angle resolution of the camshaft trigger wheel and Hall sensor combination, especially at low engine speeds.

A comparison of the phasing duration related to the control target bandwidth of +-2degCA with and without communication delay shows that the sensor fusion reduces the overshooting and energy consumption significantly. With a six teeth trigger wheel the duration is reduced by up to 204 ms, whereas with a three teeth trigger wheel it increases to only 107 ms.

This is also due to the fact that the electronic control unit (ECU) transmits a signal to the electric motor controller that corresponds to the desired camshaft phasing angle, which it can then determine and compare with the actual phase angle of the camshaft. In this way, the ECU can also compensate for possible misalignments of the camshaft and crankshaft during a phasing event.

Another factor is the lower mechanical energy demand of the sensor fusion compared to the conventional method with a three teeth trigger wheel. The reason for this is the lower difference in velocity between the camshaft and crankshaft during the phasing event. The consequence of the lower difference in velocity is that there is a shorter recuperation period by the electric motor with the sensor fusion compared to the conventional approach.

Moreover, with the sensor fusion method the electrical power required for the control and drive of the camshaft phase regulator is also reduced significantly. This is mainly because the communication delay with the conventional camshaft phase regulator is eliminated.