Patent GB-1504910-A (GB)
Title: Pressure failure detector for a dual hydraulic system
IPC: B60T17/22
Filed: 1975-12-30
Abstract: 1504910 Dual circuit pressure failure detector; modulating valve; load responsive braking BENDITALIA SpA 30 Dec 1975 [9 Jan 1975] 53168/75 Heading F2F A detector for detecting failure of one of two hydraulic brake lines 20, 22 comprises a housing 10 with a bore 28 which receives a movable piston-forming assembly 40, 42, 44 which defines in the bore 28 pressure chambers 50, 52 connected respectively to lines 22, 20, switch means 74, 76 being provided to make electrical contact when the movable assembly 40, 42, 44 moves in either direction from a central idle position due to pressure difference denoting failure of one of the two lines 20, 22; the movable assembly 40, 42, 44 comprises a sleeve 40 slidable in bore 28 on a coaxial core 34 fixed relative to housing 10 and having the same axial length as sleeve 40, and two annular resilient discs 42, 44 being sealingly slidable along bore 28 and mounted in a fluid tight manner on two axial projections 36, 38 attached to opposite ends 45, 47 of the core 34, one face of each resilient disc 42 or 44 being partly in contact with one respective end of the sleeve 40 and partly in contact with one respective end of the core 34 when the movable assembly is in said central idle position. The discs 42, 44 may be urged on to the core 34 by compression springs. The detector illustrated shares its housing 70 with that of a dual master cylinder whose chambers 12, 14 are connected by the lines 20, 22 to rear brakes 24 and front brakes 26, the chamber 52 being connected to line 20 by way of a braking compensating valve. The bore 28 is stopped by a plug 30 to which is screwed the core 34. The switch means comprises a groove 74 in sleeve 40 and a terminal 76 which projects into the groove 74, the sleeve 40 and housing 10 being electrically conductive and the housing 10 being connected to vehicle's earth, and a circuit for a failure warning device is completed when the sleeve 40 moves from its idle position. A locking means is provided for locking, the sleeve 40 after movement from its idle positionthis locking means comprises a radially expansible ring 78 mounted in a groove 79 in core 34 and co-operable with a groove 80 in sleeve 40 which groove 80 contains two furrows connected by inclined surfaces to a central rib. The braking compensating valve comprises a differential piston 54 with an internal blind bore 56 slidable on a tube 58 attached to projection 38. The tube 58 contains a duct 59 connecting a compartment defined at the blind end of bore 56 with a source of control pressure which may be simply atmosphere or may be a pressure responsive to changes in the load on an axle of the vehicle. A valve member 64 attached to piston 54 is co-operable with an annular elastomeric member 62, but a spring 68 normally holds valve member 64 in its open position. However above a certain transition pressure in line 20 piston 54 moves the latter leftwardly to close valve 62, 64 and the pressure in a delivery chamber 66 will increase with the braking pressure in chamber 12 but proportionately less. A by-pass duct 70 in housing 10 communicates with line 20 downstream of the compensating valve and communicates with bore 28 through an orifice 72 normally closed by disc 44. Should one line, e.g. line 22 fail, sleeve 40 moves to operate the switch means and the resilient discs 42, 44 are deformed and ring 78 lodges in one of the furrows of groove 80. The deformation of disc 44 caused by failure of line 22 also allows orifice 72 to be opened and the compensating valve is by-passed. Where the compensating valve is load dependent the duct 59 may be connected to a fluid-type suspension apparatus in which the pressure prevailing responds to the load on an axle. In other vehicles, an hydraulic fluid transmission conducted to duct 59 is associated with a conventional mechanical suspension.