Safety system for two-circuit brake installations of motor vehicles

Claim 1

A safety valve arrangement for controlling brake fluid flow from a plurality of brake fluid input lines to a corresponding plurality of brake fluid output lines which lead to a corresponding plurality of independently actuable wheel brake cylinders at a wheel to be braked; said arrangement comprising: first movable differential piston means having oppositely facing first and second differential piston pressure areas and a third differential piston pressure area facing in the same direction as said second differential piston pressure area, first and second independently supplied brake fluid input lines, first and second output lines for independently supplying brake fluid pressure to respective first and second independently actuable wheel brake cylinders at a wheel to be braked, first line means communicating the first input line to the first output line, first control piston means having oppositely facing first and second control piston pressure areas, said first control piston means being arranged in said first line means and being movable from a first control piston position permitting flow of brake fluid through said first line means to a second control piston position preventing said flow through said first line means, second line means communicating said first input line to said first differential piston pressure area, third line means communicating said first output line with said second differential piston pressure area, fourth line means communicating said third line means with said first control piston pressure area, and fifth line means communicating said second input line to said third differential piston pressure surface area; wherein said first differential piston means is constructed such that approximately equal fluid pressures in said second, third, and fifth line means maintains said first differential piston means in a first differential piston position with a maximum volume in said third line means, said first differential piston area being larger than said second differential piston area such that a substantial reduction in the fluid pressure in said fifth line means results in movement of said first differential piston means to reduce the volume in said third line means, and wherein said first control piston means is configured for movement to said second control piston position in response to a predetermIned reduction in pressure in said second input and output lines such that failure of the circuit containing said second input and output lines is automatically accommodated for by an increase in the pressure in said first output line by means of the closing of the first line means by the first control piston means and by means of the reduction in volume and corresponding increased pressure in said third line means caused by movement of the first differential piston means.