Chevrolet Equinox Service Manual: Camshaft Actuator System Description Valvetrain Camshaft

The camshaft (CMP) actuator system enables the engine control module (ECM) to changecamshaft timing of all camshafts while the engine is running. The CMP actuator assemblyvaries the camshaft position in response to directional changes in oil pressure. TheCMP actuator solenoid valve controls the oil pressure that is applied to advance orretard a camshaft. Modifying camshaft timing under changing engine demand providesbetter balancebetween the following performance concerns:

Engine power outputFuel economyLower tailpipe emissions

The CMP actuator solenoid valve is controlled by the ECM. The crankshaft position(CKP) sensor and the CMP sensors are used to monitor changes in camshaft positions.The ECM uses the following information in order to calculate the desired camshaftpositions:

The engine speedThe engine loadThe camshaft position (CMP) sensorsThe crankshaft position (CKP) sensorThe manifold absolute pressure (MAP) sensorThe throttle position (TP) sensorsThe barometric pressure (BARO)Operation

The CMP actuator assembly has an outer housing that is driven by an engine timingchain. Inside the assembly is a rotor with fixed vanes that is attached to the camshaft.Oil pressure that is applied to the fixed vanes will rotate a specific camshaft inrelationship to the crankshaft. The movement of the intake camshafts will advancethe intake valve timing. The movement of the exhaust camshafts will retard the exhaustvalve timing. Whenoil pressure is applied to the return side of the vanes, the camshafts will returnto 0-crankshaft degrees, or top dead center (TDC). The CMP actuator solenoid valvedirects the oil flow that controls the camshaft movement. The ECM commands the CMPsolenoid to move the solenoid plunger and spool valve until oil flows from the advancepassage. Oil flowing through the CMP actuator assembly from the CMP solenoid advancepassage appliespressure to the advance side of the vanes in the CMP actuator assembly. When the camshaftposition is retarded, the CMP actuator solenoid valve directs oil to flow into theCMP actuator assembly from the retard passage. The ECM can also command the CMP actuatorsolenoid valve to stop oil flow from both passages in order to hold the current camshaftposition.

The ECM operates the CMP actuator solenoid valve by pulse width modulation (PWM) ofthe solenoid coil. The higher the PWM duty cycle, the larger the change in camshafttiming. The CMP actuator assembly also contains a lock pin that prevents movementbetween the outer housing and the rotor vane assembly. The lock pin is released byoil pressure before any movement in the CMP actuator assembly takes place. The ECMis continuously comparingCMP sensor inputs with CKP sensor input in order to monitor camshaft position anddetect any system malfunctions. If a condition exists in either the intake or exhaustcamshaft actuator system, the opposite bank, intake or exhaust, camshaft actuatorwill default to 0-crankshaft degrees.

CMP Actuator System Operation

Driving Condition

Change in Camshaft Position

Objective

Result

Idle	No Change	Minimize Valve Overlap	Stabilize Idle Speed
Light Engine Load	Retard Valve Timing	Decrease Valve Overlap	Stable Engine Output
Medium Engine Load	Advance Valve Timing	Increase Valve Overlap	Better Fuel Economy with Lower Emissions
Low to Medium RPM with Heavy Load	Advance Valve Timing	Advance Intake Valve Closing	Improve Low to Mid-range Torque
High RPM with Heavy Load	Retard Valve Timing	Retard Intake Valve Closing	Improve Engine Output