Dual type hydraulic circuit in a vehicle brake system

Claim 1

A dual type hydraulic circuit for a vehicle brake system including (1) a dual master cylinder building up hydraulic braking pressure relative to the degree of depression of a brake pedal; (2) at least one wheel cylinder disposed at each of the right and left rear road wheels of the vehicle; (3) two mutually independent hydraulic piping systems which connect said dual master cylinder to said rear wheel cylinders; and (4) valve means incorporated in said two piping systems, said valve means comprising: (a) a housing having two mutually independent fluid passages therein each of which constitutes a portion of said two hydraulic piping systems respectively; (b) two valve seats formed one within each respective one of said one fluid passages; (c) two valve pistons each having a valve poppet adapted to contact said corresponding valve seat, and being axially movable for bringing said valve poppet thereof onto and off of said corresponding valve seat, said valve pistons being disposed in parallel to one another and both being exposed at respective one ends thereof to an air chamber formed within said housing, with a result that, as long as said valve poppets are held in contact with said valve seats, the pressure-receiving areas of said valve pistons exposed to a portion of said fluid passages in communication with said rear wheel cylinders are greater than those of said valve pistons exposed to another portion of said passages in communication with said master cylinder; (d) a compression spring urging said two pistons away from said air chamber; (e) transmission means interposed between said two valve pistons and said spring for transmitting the resilient force of said spring to said two valve pistons to make them operate together and, upon rising of the hydraulic pressure in said master cylinder beyond a predetermined upper limit, the hydraulic braking pressure in said rear wheel cylinders being controlled to rise at a lower gradient than the hydraulic pressure in said master cylinder, said transmission means including a first portion disposed within said housing and slidable in parallel with a line of movement of said two valve pistons to cause the resilient force of said spring to act in parallel with said line and further including a second portion fixed to said first portion, which second portion is a plate-like configuration and is in contact with one end of said spring at the middle thereof to receive the resilient force of said spring, and in contact with said two pistons at opposite end portions thereof to evenly deliver said resilient force to said two pistons at said opposite end portions thereof; said end portions of said second portion extending outwardly of said first portion of said transmission means; (f) said first portion of said transmission means comprising a hollow cylindrical member; (g) a movable seat member, means to mount said movable seat member in contact with the other end of said spring and so as to permit said seat member to move substantially in parallel with said line of movement of said transmission means, (h) said movable seat member comprising a bottom and a hollow cylindrical member, said movable seat cylindrical member being slidably mounted on the outside of and telescopically fitted to said transmission means first portion; (i) said movable seat member bottom and said transmission means first portion defining a space in which said compression spring is housed; and (j) means to move said movable seat member in response to variations of the load applied to said rear wheels; whereby the axial movements of said valve pistons are controlled in accordance with the varying magnitude of the load applied to said rear wheels.