GB726760A - Tractor-trailer fluid pressure brake system - Google Patents

Abstract

726,760. Fluid pressure brakes. BENDIX AVIATION CORPORATION. Sept. 4, 1953 [Sept. 16, 1952], No. 24559/53. Class 103 (1). A vacuum servo-operated fluid pressure brake system for tractor-trailer vehicle combinations comprises a regulator valve such that the trailer brakes in addition to being applied in advance of the tractor brakes, may also be applied at a selected pressure appropriate to the loading or road surface conditions. As shown in Fig. 3, the regulator valve 40, which is similar to that described in Specification 678,474 includes a solenoid operated valve 53 which when de-energized allows communication between connection 38 to the engine intake manifolds and connection 19 linked by conduits 44 and 46 to a relay valve 36 governing the trailer brake pressure. When this solenoid is energized it opens valve member 19 and closes opening 23 thus connecting conduit 44 to a chamber 31 by opening 15, the pressure in the chamber 31 then governing also the trailer brake application pressure. The pressure in chamber 31 is regulated by a self lapping valve member 49 which controls communication with the atmosphere through tube 43 and filter 27 or with the vacuum source through tube 83, the action being governed by the compression of a spring 79. To provide different equilibrium pressures in the chamber 31, a handle 25 may be moved anti-clockwise thus carrying with it, by abutment with a flange 95, a ring 87. The handle 25 is integral with a member 75 having two cam slopes 77 engaged by the ends of a follower pin 63 which by pressing down tube 43 adjusts the compression of spring 79 so as to give the required pressure in chamber 31. The ring 87 which is moved by any counterclockwise movement of handle 25 has a tongue 15 which normally projects between an earthed spring pressed contact 113 carried by the ring 75 and a conductor strip 121 connected to the solenoid 55. The solenoid 55<SP>1</SP> may thus be energized at any time after the handle 25 and ring 87 have been rotated counter clockwise to set a pressure in the chamber 31, by a clockwise movement of the handle 28 back to its initial position so that the tongue 15 no longer prevents contact between the contact 113 and strip 121. Referring to Fig. 1, an initial advance braking of the trailer may thus be carried out at a brake pressure corresponding to the pressure set in chamber 31, either by a land operation as described above, or by initial movement of a brake pedal 60 and master cylinder 54 to close a further switch for engaging the solenoid 55<SP>1</SP>. At a later stage hydraulic pressure from the master cylinder 54, acting through the conduit 56 upon the governor valve 58 of a pneumatic servo device 30 for the tractor brakes provides a pressure in pipe 59 which operates a shuttle valve 42 to shut off the effect of the control valve 40 upon the trailer brakes, the brakes of both tractor and trailer then being applied in correspondence with the master cylinder pressure. This system constitutes an improvement on that described in Specification 629,225.