Camshaft Actuator System Description: Notes

Fig 1: Identifying Camshaft Actuator System Components

Courtesy of GENERAL MOTORS CORP.

Callout	Component Name
1	Camshaft Position (CMP) Actuator Solenoid Valve - Exhaust
2	Camshaft Position (CMP) Actuator Solenoid Valve - Intake
3	Exhaust Camshaft Position (CMP) Sensor
4	Intake Camshaft Position (CMP) Sensor
5	Crankshaft Position (CKP) Sensor
6	CMP Actuator Assembly - Intake
7	CMP Actuator Assembly - Exhaust

The camshaft position (CMP) actuator system enables the powertrain control module (PCM) to change camshaft timing while the engine is running. The CMP actuators (6 and 7) vary camshaft position in response to directional changes in oil pressure. The CMP actuator solenoid valve controls the oil pressure that is applied to advance or retard the camshaft. Modifying camshaft timing under changing engine demand provides better balance between the following performance concerns:

Engine power output
Fuel economy
Lower tailpipe emissions

The CMP actuator solenoid valves (1 and 2) are controlled by the PCM. The crankshaft position (CKP) sensor (5) and the CMP sensors (3 and 4) are used to monitor changes in camshaft position. The PCM uses information from the following sensors in order to calculate the desired camshaft position:

The engine coolant temperature (ECT) sensor
The mass air flow (MAF) sensor
The throttle position (TP) sensors
The vehicle speed sensor (VSS)

Fig 2: Camshaft Position (CMP) Actuator Component View

Courtesy of GENERAL MOTORS CORP.

Callout	Component Name
1	Lock Pin
2	Vane Wheel
3	Intake Camshaft
4	CMP Actuator Housing

The CMP actuator assembly has an outer housing (4) that is driven by the engine timing chain. Inside the assembly is a wheel (2) with fixed vanes that is attached to the intake camshaft (3). The CMP actuator assembly also contains a lock pin (1) that prevents movement between the outer housing and the wheel vane assembly. The lock pin is released by oil pressure before any movement in the CMP actuator assembly takes place.

Fig 3: Camshaft Position (CMP) Actuator Solenoid Valve Component View

Courtesy of GENERAL MOTORS CORP.

Callout	Component Name
1	Spool Valve
2	Solenoid Plunger
3	Solenoid Coil
4	Oil Return During Retard
5	Oil Supply
6	Oil Return During Advance
7	Oil Supply to Camshaft Position Actuator for Advance
8	Oil Supply to Camshaft Position Actuator for Retard

The intake CMP actuator solenoid valve directs the oil flow that controls the camshaft phase movement. The PCM commands the intake camshaft CMP solenoid to move the solenoid plunger (2) and spool valve (1) until oil flows from the advance passage (7) or the retard passage (8). In most operating conditions the opposite oil return passage is open at the same time as the oil supply passage.

Fig 4: Camshaft Position (CMP) Actuator Solenoid Valve Component View

Courtesy of GENERAL MOTORS CORP.

Callout	Component Name
1	Spool Valve
2	Solenoid Plunger
3	Solenoid Coil
4	Oil Return During Retard
5	Oil Supply
6	Oil Return During Advance
7	Oil Supply to Camshaft Position Actuator for Retard
8	Oil Supply to Camshaft Position Actuator for Advance

The exhaust CMP actuator solenoid valve operates the same as the intake CMP actuator solenoid valve. One significant difference is that the oil flow that advances the exhaust camshaft is supplied from passage (8) and the oil flow to retard the camshaft is from passage (7). As with intake CMP solenoid, in most operating conditions the opposite oil return passage is open at the same time as the oil supply passage.