Actuator for valve lift changeover, basic function

P05.00-A008-76

Overview

This document contains information on:

 General

 Function

General

The actuator for valve lift switchover controls axial adjustment of the camshaft. A switchover takes place between two different cam lifts. This adjustment optimizes the gas cycle in the partial-load range.

The actuator consists of a lift solenoid, which is in the form of a bistable double solenoid actuator. When the coil is actuated, this solenoid operates the two tappets, whereby only one tappet can extend depending on the position and shape of the curve on the camshaft. The respective tappet is reset mechanically by the shape of the curved track.

The current position of both tappets is recorded by the integral intake camshaft valve lift switching hall sensor.

Function

The actuator is actuated by the combustion engine control unit with a pulse width modulated signal depending on the characteristics map.

Both tappets are retracted in the initial position. The engine start takes place with long stroke of the intake valves.

The first changeover to a short stroke takes place at the end of the warm-up phase.

During the actuation of the actuator by the combustion engine control unit, the relevant coil in the actuator is energized and one of the two tappets moves into the relevant curved track. An axial shift of the camshaft takes places due to the design of the curved track, and the changeover to a smaller cam stroke occurs. The tappet is reset mechanically by an elevation in the curved track.

The camshaft is reset by means of reenergizing the coil. This time the other tappet extends and the camshaft is moved in the opposite direction to the position of the cam with a large stroke.