Fluid pressure controlling device for brake system of wheeled vehicle

Claim 1

A fluid pressure controlling device for a hydraulic brake system for a wheeled vehicle, the system being capable of developing independent and variable first and second fluid pressures for the front and rear brakes of the vehicle, the controlling device comprising: a housing having therein a stepped bore; a differential plunger axially movably received in said bore, a first inlet port for supplying said first fluid pressure to a first end face of said plunger; a second inlet port fluidly separate from said first inlet port for supplying said second fluid pressure to a middle portion of said plunger; an outlet port communicable with said second inlet port through said bore; a piston axially movably received in said bore opposite to a second end face of said plunger, said piston and said second end face being fluidly isolated from said first and second inlet ports; a first compression spring installed between said second end face and said piston to exert a force on said second end face; a third inlet port for supplying one of said first and second fluid pressures to an end face of said piston remoter from said plunger; a deceleration-responsive member movably received in said bore between said piston and said third inlet port; means to regulate the magnitude of a load on said compression spring resulting from said one fluid pressure acting on said piston; and a valve means to break the fluid communication between said third inlet port and said piston when said member is seated thereon; said bore and said plunger being shaped such, and said second inlet port and said outlet port being arranged such that said second fluid pressure at said second inlet port is transmitted to said outlet port without modulation when the magnitude thereof is below a critical value but modulated to a third fluid pressure when the magnitude thereof exceeds said critical value, the rate of increase in said third fluid pressure being lower than, inclusive of zero, the rate of increase in said second fluid pressure; the areas of said first and second end faces of said plunger being correlated with each other such that said critical value is raised when said first fluid pressure is not substantially supplied to said first inlet port; said member being seated on said valve means when the device is subjected to a deceleration larger than a predetermined magnitude to prevent said load from increasing as said one fluid pressure increases thereafter; said load being regulated such that said critical value is raised as the gross weight of the vehicle increases.