Patent GB-986732-A (GB)
Title: Improvements relating to hydraulic braking systems
IPC: B60T17/22
Filed: 1961-04-12
Abstract: 986,732. Hydraulic brakes; brake indicators. R. T. HAMILTON. April 12, 1962 [April 12, 1961], No. 13092/61. Headings F2E and F2F. In an hydraulically operated master cylinder braking system primarily for road vehicles a warning is given of a failure in the system prior to the operation of the system to apply the wheel brakes whereby a driver of the vehicle is warned of the failure before an emergency arises wherein an hydraulic pressure retaining means 27 is disposed between the master cylinder 12 and the wheel cylinders to retain a predetermined supra-atmospheric hydraulic pressure in the part of the system between the retaining means and the wheel cylinder and a pressure responsive indicator means 46, 49 disposed in the system and arranged to give indication of the collapse of the supra-atmospheric hydraulic pressure in that part of the system. In the braking system shown in Fig. 1 hydraulic pressure retaining means 27 is provided between the master cylinder 12 and the various pipe connections to the front brakes 10 and the rear brakes 11 of the vehicle. Although hydraulic pressure retaining means have been shown in all of the positions at which it may be desirable for them to be placed it is not necessary for them all to be used in the one system. Fig. 3 shows a form of the hydraulic pressure retaining means 27 comprising a body 28 formed with a chamber 29 adapted to be connected to a pipe connected with the master cylinder 12, the chamber 29 communicating with a further chamber 36 through a passage 32 and a primary non-return valve 33. The passage 36 is formed with a connection 38 to the wheel brake cylinders and a further passage 44 connects the passage 36 with the passage 29 through a secondary non-return valve 41. When hydraulic pressure is supplied to the bore 31 from the master cylinder the secondary valve 41 remains closed and the primary non-return valve 33 is opened to permit hydraulic pressure to pass through the union 38 to the wheel brake mechanism. Upon release of the hydraulic pressure the primary non-return valve 33 will close and the secondary non-return valve 42 will be opened by the supra-atmospheric pressure obtaining in the part of the system between the secondary valve 42 and the wheel brake cylinder. This return flow will continue until the pressure in that part of the system is reduced to such a supra-atmospheric pressure as will enable the secondary non-return valve 41 to be closed by the spring 43. Should a fault develop in the part of the system between secondary valve 42 and the wheel cylinder the supra-atmospheric pressure in that part of the system will collapse and a liquid pressure responsive electric switch 46 will operate to illuminate an electric lamp or buzzer 49 to warn the driver of a fault in the system. Alternative hydraulic pressure retaining means are disclosed in the Specification such as that shown in Fig. 4 wherein a primary non-return valve 33 is constituted by a sealing member 51 carried by a tubular valve member 50 which acts on a seat 52 formed at one end of a chamber 53 in the pressure retaining means 27. The secondary non-return valve 42 is formed by a spring-loaded ball 58 acting on a conical seat 57 formed in the tubular member 50. Fig. 2 (not shown) discloses a system with two hydraulic master cylinders; one actuating the front wheel brakes and the other actuating the rear wheel brakes of the vehicle.