Fluid pressure control device with a fluid failure alarm for a vehicle brake system

In a vehicle brake system of the type including two independent hydraulic lines extending from a dual type brake master cylinder to the front and rear wheel brakes, respectively, a fluid pressure control device positioned between the master cylinder and the front and rear wheel brakes, said fluid pressure control device comprising:

• a cylinder casing (1) defining therein a first cylinder chamber (2) and a second cylinder chamber (3) smaller in diameter than said first cylinder chamber and opening at one end into the latter in aligned relation therewith, a first pressure bearing piston (9) slidably fitted in said first cylinder chamber, a second pressure bearing piston (10) slidably fitted in said second cylinder chamber, a first core piston (18) slidably fitted in said first pressure bearing piston (9) and extending axially therethrough, a pressure adjusting spring (22) arranged between said first pressure bearing piston and said first core piston to bias the latter axially toward said second pressure bearing piston, a cylinder bore (15) formed in said second pressure bearing piston so as to open into said first cylinder chamber and having a diameter larger than that of said first core piston, means for placing said cylinder bore in fluid communication with the fluid chambers of the rear wheel brakes, a second core piston (19) slidably fitted in said cylinder bore and held in engagement with the adjacent end of said first core piston, a first fluid space defined in said first cylinder chamber (2) on the pressure bearing face of said first pressure bearing piston (9) and communicating on the one hand with one of the two output ports, (P.sub.1), of the dual brake master cylinder (M) and on the other hand with the fluid chambers of the front wheel brakes (B.sub.1), a second fluid space defined in said second cylinder chamber (3) on the pressure bearing face of said second pressure bearing piston (10) and communicating with the other output port (P.sub.2) of the dual brake master cylinder, a fluid passage formed in said second pressure bearing piston and communicating said cylinder bore with said second fluid space, valve means arranged in said fluid passage so as to be normally held open under the bias of said pressure adjusting spring acting thereon through the medium of said first and second core pistons and switch means on said cylinder casing and operatively associated with said second core piston to actuate an external alarm means in response to axial movement of said second core piston and second pressure bearing piston.