CMP System Operation

Fig 1: CMP Actuator

Courtesy of GENERAL MOTORS COMPANY

A CMP actuator dynamically changes valve timing events relative to piston timing by controlling camshaft position. This is sometimes referred to as variable valve timing or camshaft phasing. Variable valve timing or camshaft phasing does not change duration or lift.

• By advancing camshaft timing, an improvement in low end torque can be achieved.
• By retarding camshaft timing slightly, an improvement in high end power can be achieved.
• By retarding camshaft timing significantly, an improvement in light load fuel economy can be achieved.

There are 5 cavities divided by vanes within the CMP actuator.

• When oil is directed to the advance cavities (1), the camshaft timing is advanced.
• When oil is directed to the retard cavities (2), the camshaft timing is retarded.
• When oil is directed to both cavities, the camshaft is held stationary.

Fig 2: Timing Camshaft - 52 Degree Range Of Authority

Courtesy of GENERAL MOTORS COMPANY

The CMP actuator has a 52 degree range of authority. With the engine not running and no engine oil pressure to the CMP actuator, the high tension spring positions camshaft timing at the 7 degree advanced park position. During normal engine operation, and based on performance requirements, the ECM may adjust camshaft timing, as required, within a range from 7 degrees advanced to 45 degrees retard.