Patent GB-578282-A (GB)
Title: Improvements relating to braking systems
IPC: B60T13/36
Filed: 1943-09-30
Abstract: 578,282. Differential braking for steering vehicles. TOMLINSON, A. V. (Bendix- Westinghouse Automotive Air Brake Co.). Sept. 30, 1943, No. 16063. [Class 79 (ii)] [Also in Group XXXIV] In a fluid-pressure braking system for tractortrailer vehicles in which differential braking of the tractor assists steering and arrangements are provided for individual control of the tractor brakes, the trailer brakes are each arranged to be operated to substantially the same pressure as that applied to the tractor brakes when the latter are applied equally and to substantially the same as'the lower of the two pressures applied to the tractor brakes when the latter are applied unequally for steering purposes. Mounted on the tractor in the fluid-pressure brake system shown are right and left brake actuators 4, 5 connected through conduits 11, 10, 9 and 13, 12, 9 with a fluid-pressure reservoir 6 supplied through a conduit 8 from a compressor 7, the conduits 11, 10 and 13, 12 being connected respectively by self-lapping brake valves 14, 15 constructed as described in U.S.A. Specification 2,204,530 which control the flow of fluid between the reservoir 6 and brake actuators and between the actuators and the atmosphere. Each brake valve is controlled by a lever 16 or 17, operation of'which either connects the conduits 10, 11 or 13, 12 so that fluid is supplied from the reservoir according to the amount of movement of the lever, or prevents communication between the conduits and connects the conduit 11 or 13 to atmosphere through the brake valve. The trailer is also provided with a fluid-pressure brake mechanism comprising a relay emergency valve mechanism 20 as described in U.S.A. Specification 2,018,212, a reservoir 18 supplied from the tractor reservoir 6 through a conduit 21, the valve mechanism 20 and a conduit 22, and brake actuators 19 to which fluid pressure is supplied from the reservoir 18 through conduit 22, valve mechanism 20 and conduits 23, 24. The valve mechanism 20 which consists of an emergency valve casing 25 and a relay valve casing 26, functions both as an emergency brake valve in the event of failure of one of the supply conduits add also as a pressure control for the trailer brake actuators 19. This control is variable by the operator since a part of the relay valve portion 26 of the mechanism 20 is connected through a conduit 41, a further relay valve mechanism 44 and a conduit 42 to the operator-controlled tractor brake valve 14 and through the conduit 41, valve mechanism 44 and conduit 43 to the tractor brake valve 15. Conduits 42, 43 are connected with the outlet chambers of the brake valves in the same manner as the conduits 11, 13 which lead to the tractor brake actuators 4, 5 so that the same fluid pressure occurs in the conduits 42, 43 as in the conduits 11, 13 on operation of the brake valves to control the tractor brakes. Operation.-With the parts in the positions shown, the valve mechanism 44 prevents communication between the conduits 42, 41 and 43, 41 and consequently either of the brake valves 14, 15 may be operated selectively by the operator for controlling the right or left tractor brakes without affecting the operation of the valve mechanism 20 to control the operation of the trailer brakes. For example, on operation of the valve 14, fluid pressure is supplied to the actuator 4 and also through conduit 42 to a chamber 47 in valve mechanism 44, thus opening an intake valve 50 which establishes communication between conduits 43, 41, but as the valve 15 is not being operated, there is no change in pressure in chamber 33 of the valve mechanism 20 and thus no operation of the trailer brake actuators. Similarly, on operation of the valve 15, the intake valve 50 remains closed and no change of pressure occurs in conduit 41 and chamber 33. If, however, .both valves 14, 15 are operated togetHer to actuate the tractor brakes, the pressure supplied to the chamber 47 opens the intake valve 50 and connects conduits 43, 41' and the resulting pressure supplied to the inlet chamber 45 of the valve mechanism 44 is passed through the conduit 41 to the chamber 33 of the valve mechanism 20, causing an inlet valve 38 therein to open and establish communication between an inlet chamber 31 and outlet chamber 29 so that the pressure is applied through the conduits 23, 24 to actuate the trailer brakes. When both the tractor and trailer brakes are partly applied and the operator increases the brake pressure on one side of the tractor in order to steer the vehicle on a down grade, the pressure in the trailer brake actuators corresponds to the lower of the two pressures on the tractor brakes. For example, with all the brakes partly applied, further operation of the control lever 16 increases the pressure in the chamber 47, but as the supply pressure to the inlet chamber 45 is unaltered, no increase in pressure is transmitted to the trailer brake actuators. Should the conduit 21 break, the pressure in the inlet chamber 27 -of the valve mechanism 20 is depleted and the greater pressure in the adjoining chamber 28 forces a diaphragm 36 downwardly to close the valve 37, thus preventing communication between the outlet chamber 29 and the atmosphere, while simultaneously establishing communication between the reservoir 18 and the chambers 28, 29 and brake actuators 19 which apply the trailer brakes.