Revolution speed control apparatus for an internal combustion engine

Abstract

A revolution speed control apparatus is provided. In particular, a variable valve drive apparatus for an internal combustion engine is provided, capable of continuously and variably setting a valve lift in conjunction with use of a three-dimensional cam. The apparatus provides a proper fail-safe system by setting an appropriate allowable engine revolution speed. An actual amount of adjustment in the position of a cam shaft, that is performed by a valve lift varying actuator, is detected by a shaft position sensor. Based on the actual amount of adjustment, the apparatus determines a cam profile of each intake cam contacting the corresponding cam follower. That is, the apparatus determines what portion of the oblique cam surface of each intake cam is providing a present valve lift. A valve lift is thus specified in addition to other parameters needed to determine an allowable revolution speed. These parameters include the valve spring load and the valve mass, for example. As a result, it becomes possible to set a precise allowable revolution speed. Based on the set allowable revolution speed, the apparatus determines whether the state of the actual revolution speed is appropriate. If the actual revolution speed is equal to or higher than the allowable revolution speed, the engine revolution speed can be properly reduced. This may be performed by implementing a fuel-cut.