Variable Valve Timing Description and Operation Opel Agila B

General

The variable valve timing system consists of the following:

• Engine control module (ECM).
• Camshaft position actuator oil control valves.
• Camshaft position actuators.
• Camshafts.

The variable valve timing system improves the characteristics of the following factors by continuously adjusting both the intake and exhaust valve timing according to the engine operating condition.

• Engine power.
• Fuel efficiency.
• Exhaust emission control.

The valve timing is adjusted by the ECM, which controls each camshaft position actuator oil control valve to switch the hydraulic oil path between two circuits, one leading to the chamber for retarding the timing and the other to the chamber for advancing the timing. Because these chambers are formed inside the housing of each camshaft position actuator and separated by a rotor that is directly fixed to the camshaft, the phase between the housing of the camshaft position actuator and the rotor/camshaft unit can be changed by switching the hydraulic circuit as described above and thus the valve timing can be accordingly varied. The variable valve timing system can vary the valve timing within a range of 50° in crankshaft rotational angle for both the intake and exhaust camshafts.

1. Intake
2. Exhaust
3. 50° (variable angle)
4. Overlap of valves
5. Most advanced timing
6. Most retarded timing
7. 1. Housing
8. 2. Rotor
9. 3. Camshaft
10. 4. Oil passage to chamber for timing retarding
11. 5. Oil passage to chamber for timing advancing
12. 6. Chamber for timing retarding
13. 7. Chamber for timing advancing
14. 8. Oil filter
15. 9. Oil pump
16. 10. Oil pan
17. 11. Control signal from ECM
18. 12. Camshaft position actuator oil control valve
19. 13. Valve lift
20. 14. Crank angle
21. 15. Exhaust valve
22. 16. Intake valve

Camshaft Position Actuator Oil Control Valve

The camshaft position actuator oil control valve switches and adjusts the hydraulic pressure applied to the camshaft position actuator by moving the valve spool (1) according to the duty cycle pulses from the ECM. Through this control, the valve timing is continuously altered. The ECM sends a duty signal of approximately 240Hz to the camshaft position actuator oil control valve.

1. Intake
2. Exhaust
3. Seal

Camshaft Position Actuator

1. Intake
2. Exhaust
3. Seal

The camshaft position actuator has chambers for timing advancing (2) and retarding (3) which are separated by the rotor (5). The rotor turns according to a change in balance between the hydraulic pressures applied to both chambers. The sprocket (1) is installed on the housing (4) and the rotor is secured on the camshaft by bolts. Therefore, the rotation of the rotor changes the phase between the sprocket and camshaft.

Timing Advancing

When the duty ratio of the signal from the ECM to the intake camshaft position actuator oil control valve is high (or to the exhaust camshaft position actuator oil control valve is low), the valve spool (2) of the camshaft position actuator oil control valve moves to the left. By this valve spool movement, the pressurized oil (1) is led into the timing advancing chamber and the oil in the timing retarding chamber is drained. As a result, the rotor (3) turns in the timing advancing direction.

1. Intake
2. Exhaust
3. Drain

Timing Holding

When the ECM keeps the duty ratio of the signal sent to the camshaft position actuator oil control valve constant, the valve spool of the camshaft position actuator oil control valve is held in the same position. Because this condition creates no oil pressure change in both chambers, the rotor is fixed at a target position.

Timing Retarding

When the duty ratio of the signal from the ECM to the intake camshaft position actuator oil control valve is low (or to the exhaust camshaft position actuator oil control valve is high), the valve spool of the camshaft position actuator oil control valve moves to the right. By this valve spool movement, the pressurized oil is led into the timing retarding chamber and the oil in the timing advancing chamber is drained. As a result, the rotor turns in the timing retarding direction.

1. Intake
2. Exhaust