Schaeffler North America

 
 
 
 
 
 
Variable valve train systems

Switching valve

Switching valves are used to control the two-stage switching engine components. The oil pressure present in the engine oil circuit is used to activate the locking mechanism of the switching elements by means of a 3/2 way switching valve. The 3/2 way valve is controlled by a data map in the ECU as a function of various parameters such as speed, load, vehicle speed, operating temperature etc.

The switching valve is mounted directly in the cylinder head and integrated in the oil circuit. It consists of an electromagnet and a hydraulic mechanism. When the valve is fed with current, oil flows from the oil pump to the switching elements and switches the locking mechanisms of the switching engine components. When the valve is not fed with current, the passage from the oil pump to the switching elements is closed and the oil flows via a bypass through the switching gallery under low pressure back to the oil sump – the locking mechanisms return to their original position.

The switching times depend on the valve mechanism and the design of the hydraulic circuit. A highly decisive factor for good switching quality is also the valve lift variance occurring, i.e. the reproducibility of switching under varying operating conditions and system tolerances.