Cylinder apparatus for rack and pinion type power steering mechanism of motor vehicle

Claim 1

A cylinder apparatus for a rack and pinion type power steering mechanism, comprising: a gear housing including a power cylinder; a pinion disposed in said gear housing and operatively connected to a steering wheel; a rack shaft provided with a rack portion disposed in intermeshing relationship with said pinion, said rack shaft being axially movably inserted in said power cylinder with one end thereof extended out of one end of said power cylinder and coupled to a steering linkage, said rack shaft comprising a large-diameter section, an intermediate-diameter section constituting said rack portion and a small-diameter section, there being a stepped junction between said large-diameter section and said intermediate-diameter section and a stepped junction between said intermediate-diameter section and said small-diameter section; a first pressure chamber defined in said power cylinder in such a manner that pressure fluid can be introduced thereinto; a second pressure chamber defined in said power cylinder in such a manner that pressure fluid can be introduced thereinto; first means provided on said rack shaft in association with said first pressure chamber for providing a first effective pressure-applied area operative to urge said rack shaft in a first direction when said pressure fluid is introduced into said first pressure chamber; and second means provided on said rack shaft in association with said second pressure chamber for providing a second effective pressure-applied area substantially equal to said first effective pressure-applied area and operative to urge said rack shaft into a second direction when said pressure fluid is introduced into said second pressure chamber; said first means comprising a first power piston disposed in said power cylinder and fixedly mounted on said intermediate-diameter section of said rack shaft at the stepped junction between said large-diameter section and said intermediate-diameter section in such a manner that said first pressure chamber is defined between said first power piston and said one end of said power cylinder; said second means comprising a second power piston disposed in said power cylinder and fixedly mounted on said small-diameter section of said rack shaft at the stepped junction between said intermediate-diameter section and said small-diameter section in such a manner that said second pressure chamber is defined between said second power piston and the other end of said power cylinder.