GB1277986A - Improvements in or relating to an electrohydraulic brake control system - Google Patents

Abstract

1277986 Electrohydraulic systems; disc brakes; adjusting brakes for wear WESTING- HOUSE ELECTRIC CORP 20 March 1970 13595/70 Headings F2E and F2F A spring applied electrohydraulically released brake system 10 for a vehicle disc brake assembly 38, 40, 42 comprises a master cylinder 24 and a slave cylinder 30 in communication, to form an hydraulic circuit, the master piston 22 in the master cylinder 24 incorporating a valve 50 for cutting off flow of fluid between a reservoir 26 and the circuit, and a solenoid 14 adapted to operate the master piston 22 to apply pressure to the hydraulic circuit to move brake shoe 40 away from brake disc 42 against the force of a load spring 44, and release the brake. The solenoid 14 acts on an armature 16 through a gap 18 to move a thrust pin 23 to the right; a metal skin 20 is situated in the gap 18; these components may be formed as in Fig. 2 (not shown). As the master piston 22 is moved to the right by the thrust pin 23 the valve 50 is closed and the circuit pressure builds up to release the brake: as the brake shoe 40 wears the amount of fluid trapped in the circuit is reduced by the slave piston 31 forcing fluid back into the reservoir 26. Between the master cylinder 24 and the slave cylinder 30 the circuit is split into two branch conduits 35, 36 each containing a respective unidirectional valve 33, 34, which valves 33, 34 allow fluid flow in one and respectively opposite directions to thereby maintain a minimum pressure in the slave cylinder 30. In the event of a loss of pressure in the system causing the brakes to be applied a warning light may give indication to the vehicle operator. Alternatively a recycling circuit 60 may be used to automatically replenish the circuit in the event of a pressure drop. A pressure sensing chamber 65 acts to close contacts 63, 64 of a pressure sensitive switch 62. Closure of contacts 63 causes illumination of a warning lamp 71, and closure of contacts 64 causes solenoid 74 of a time delay relay 76 to close normally open contacts 75 and solenoid 78 of a time delay relay 79 to open normally closed contacts 80. Current is thereby cut off from a brake control means 68 and from solenoid 14, and the master piston 22 moves to the left, the valve 50 opens and the hydraulic circuit is replenished. This recycling operation is continued until sufficient pressure is present in the system to hold the brakes released. Brake shoes 40 may be applied to both sides of the disc 42, and the system is described as being particularly applicable to track vehicles.