Fluid pressure controlling device

Claim 1

A fluid pressure control device for use in a vehicle fluid brake system comprising: a housing having a first bore including a valve chamber and a stepped bore including a small diameter portion and a large diameter portion; a stepped piston having a small diameter portion sealingly slidable in said small diameter bore portion and a large diameter portion sealingly slidable in said large diameter bore portion; an outlet pressure chamber defined by one end of said stepped piston within said small diameter bore portion; an inlet pressure chamber defined by the other end of said piston within said large diameter bore portion; a passage connecting said first bore with said outlet pressure chamber; a valve seat member in said first bore and separating said valve chamber and said passage; a deceleration responsive valve member in said valve chamber and moving toward said valve seat to interrupt a fluid communication between said valve chamber and said passage when the vehicle deceleration reaches a predetermined value; a first inlet connecting a source of fluid pressure with said valve chamber; a second inlet connecting said source of fluid pressure with said inlet pressure chamber; an outlet connecting said passage with a brake cylinder; spring means urging said piston in a direction enlarging the volume of of said outlet pressure chamber; and pin means extending from said one end of said piston into said passage, the end of said pin means passing through said passage and said valve seat to move said valve member away from said valve seat to permit said fluid communication between said valve chamber and said passage when fluid pressure in said source of fluid pressure reaches a predetermined value.