SE7500361L - - Google Patents

Abstract

1438930 Hydraulic brake boosters ROBERT BOSCH GmbH 14 Jan 1975 [15 Jan 1974] 1469/75 Heading F2F An hydraulic booster for connection between a brake pedal and a master cylinder comprises an actuating rod 4, an hydraulic piston 9 slidable in a cylinder 8, a valve 22 for controlling flow of fluid under pressure into and out of the cylinder, and a power transmission device 16 for controlling the valve and including rolling elements in the form of gear-wheels 17, 18 carried by the rod 4 and engaging linear members in the form of toothed racks 19, 20 on which the elements 17, 18 roll one rack 19 being secured to the piston 9 and the other being displaceable and coupled to the valve 22 which is a slide valve having a spool 23 acted upon by a spring 24. The spool 23 has an aperture 25 for receiving a collar 26 of a lever 27 pivoted in a screw 29, the other end 35 of the lever engaging in a groove 31 in the rack 20. On application of the brakes rod 4 moves into the booster rotating wheels 17, 18 and moving rack 20, the piston 9 being initially held by spring 10 and by the master cylinder. Spring 24 can then displace spool 23 to close an outlet port 33 and open communication between an inlet port 34 and a pressure chamber 6 the hydraulic pressure in which can then displace piston 9 and actuate the master cylinder. Rod 4 continues to move until the increasing hydraulic pressure on its end face produces a force equal to the foot pressure on the brake pedal, the piston 9 then moving spool 23 by way of rack 19 and gear-wheels 17, 18, rack 20 and lever 27 to close inlet 34. When the foot pressure is decreased, rod 4 moves to displace spool 23 until port 33 communicates with chamber 6 so that fluid can flow out and allow piston 9 to close port 33 again so that equilibrium prevails again at a lower level. If pressure at port 34 fails as a result of a defect in the system rod 4 mechanically displaces piston 9 and spool 23 is carried along by way of transmission device 16, the foot pressure being transmitted directly to the piston 9.