Multiple step valve opening control system

摘要

A multiple step valve opening control system, particularly for an EGR control valve unit, having a plurality of valve lifts. The system comprises a valve member for opening a fluid passage in multiple steps, a first piston slidably housed in a housing, a second cylinder substantially coaxial with the first piston, a second piston fitted in the second cylinder and coupled to the valve member, and a first piston stroke regulating member which is moved selectively to a first position for regulating an allowable displacement of the first piston to a first predetermined extent (l1) or to a second position for regulating the allowable displacement of the first piston to the first predetermined first extent (l1) plus a third predetermined extent (l3). By changing the position of the first piston displacement regulating member, the valve member is opened by various valve lifts.