Camshaft Reset Valve

Camshaft Reset Valve







5: Piston with slits
6: Return spring
A: Channel leading to chamber A1 in the CVVT unit
B: Channel leading to chamber B1 in the CVVT unit
C: Channel for oil (pressure)
D: Channel for oil (return)

The camshaft reset valve controls the oil flow to the continuous variable valve timing (CVVT) unit. The engine control module (ECM) uses a pulse width modulation (PWM) signal to control the valve.

Control takes place as follows when deploying the camshaft

HINT: The illustration is a view of the CVVT unit from the side and from the rear.







- The oil is forced from the engine lubrication system (C)
- The valve is grounded by the engine control module (ECM). The oil flows via the slits in the piston (5) to the oil channel (A) in the camshaft
- The oil flows via oil channels in the camshaft to the top of the lock pin (2). If the camshaft is in its 0 position, the lock pin will be forced in by the oil pressure and the rotor releases from the timing belt pulley
- The chamber (A1) fills with oil. The oil pressure will rotate the rotor (3)
- The oil in the chamber (B1) will be forced out of the chamber by the rotation of the rotor. The oil flows to the engine oil pan via the camshaft, channel (D) and the valve.

Control takes place as follows when returning the camshaft

HINT: The illustration is a view of the CVVT unit from the side and from the rear.







- The oil is forced from the engine lubrication system (C)
- The engine control module (ECM) breaks the ground connection for the valve. The piston (5) in the valve springs back (6) and the oil flows via the piston slits in the valve to the oil channel (B) in the camshaft
- The chamber (B1) fills with oil. The oil pressure in the chamber will rotate the rotor
- The rotor (4) reaches its limit position and the lock pin slides into a hole on the inside of the front end of the camshaft pulley
- The oil in the chamber (A1) will be forced out of the chamber by the rotation of the rotor. The oil flows to the engine oil pan via the camshaft, channel (D) and the valve.

The reset valve is controlled by the engine control module (ECM) at high frequency. The frequency changes for deployment and return. This ensures rapid and precise control. The extent of camshaft control (the angle of the camshaft) varies depending on the engine variant.

"Wide Range" concept







Ignition timing
The combustion of the fuel film on the cylinder walls is improved by retarding the ignition. Retarded ignition reduces the efficiency of the engine and the heat energy which is generated is released with the exhaust gases. This is used to heat the three-way catalytic converters (TWC).

Exhaust camshaft
By opening the exhaust valve late, combustion takes place over a relatively long period. The film of fuel on the cylinder walls combusts, reducing the exhaust emissions.

Intake camshaft
By opening and closing the intake valve late:
- so that there is little or no overlap, a predetermined pressure difference is maintained between the intake manifold and the combustion chamber/cylinder. The lower pressure in the cylinder ensures that all the injected fuel reaches the cylinder. This allows the Engine Control Module (ECM) to calculate and control the fuel quantity required in the combustion phase in advance
- maintains a high and stable pressure in the intake manifold (due to the upwards movement of the piston). Stable high pressure means that the vaporization of the fuel which has condensed on the walls of the intake manifold can be predicted.

Double continuous variable valve timing (CVVT)
The CVVT on both the intake camshaft and the exhaust camshaft means that the valve overlap can be changed to a greater degree than on engines where only one of the camshafts is controlled. Valve overlap is the extent to which the intake and exhaust valves (on the same cylinder) are open at the same time.

The advantages of continuous variable valve timing (CVVT) are used in different operating conditions:
- during cold starting and during the warm-up process when the intake camshaft and exhaust camshaft are set late. This reduces the emissions
- during idle and when the engine is at operating temperature when the exhaust camshaft is set to early and the intake camshaft is set to late. This results in small valve overlap, reducing exhaust gas recirculation (EGR) and ensuring stable idling
- at part load when both the exhaust and intake camshaft are set to relatively late, with greater valve overlap. Greater valve overlap results in internal exhaust gas recirculation (EGR) which reduces the release of nitrous oxide. This also limits the incoming fuel/air mixture to the cylinder. As a result, the throttle does not need to reduce the supply of air, thereby reducing "pump losses" and lowering the fuel consumption. At higher engine speeds (RPM), the camshafts are set for a smaller valve overlap. The exhaust camshaft is set earlier, the intake camshaft later. This provides an optimum fuel/air mixture to the cylinder. Reduces internal exhaust gas recirculation EGR).