Patent GB-1347734-A (GB)
Title: Control unit for the brake system of the trailer of a vehicle
IPC: B60T13/18
Filed: 1971-11-10
Abstract: 1347734 Brake systems ROBERT BOSCH GmbH 10 Nov 1971 [13 Nov 1970] 52163/71 Heading F2F A control unit for a brake system 10 of the trailer of a vehicle having an hydraulic circuit including an hydraulic load 18 supplied from a pressure medium source, comprises a valve 11 for controlling pressure medium to be supplied from the hydraulic circuit to a trailer brake line in dependence on the force applied to brake the vehicle, the valve having a main valve member 14 acted upon the force of a spring 32 and in use, control pressure acting in a control chamber 39, the valve also having an outlet 17 for connection to the hydraulic load 18 and an outlet 24 for connection to the trailer brake line. A return conduit is connected to an inlet 45 of the valve, a pilot valve 61 being included in the connection to the return conduit for influencing flow, in use, of pressure fluid therethrough in dependence of the force applied to brake the vehicle. The control chamber 39 of the valve is arranged to be put under a control pressure dependent on the flow, the pilot valve being arranged also to control a connection from the trailer brake line outlet to the return conduit. As shown, in a first braking position of a lever 57, pump 28 delivers pressure fluid to inlet port 27 and a small amount thereof flows through throttle 35 of slide valve 14 into control chamber 39, through duct 40, past control piston 46 and through duct 44 to return conduit 45, the difference in pressure at the throttle retaining the valve 14 against the force of the spring 32 and a large amount of pressure medium passing substantially unthrottled from the inlet 27 to the power-operated ram 18 on a vehicle; the control flow is kept low by the throttle effect of the control edge 38 of the valve. In this first braking position of the valve 61, the brake 25 is separated from the conduit 45 by the end 51 of a slide valve 50. To increase the braking force the lever is pivoted clockwise, as seen in Fig. 1, to cause the push rod 59 to displace the thrust member 54 and, through the spring 55, the control piston 46 together with the slide valve 50 into a second braking position wherein the collar 47 of the piston 46 interrupts the control line 62 comprising the connection between the inlet 27 and the conduit 45. The spring 32 pushes the valve 14 towards a stop ring 30 and the control edge 31 throttles the connection to the port 17, the control orifices at the same time opening a connection from the inlet port 27 to the annular chamber 16. A pressure builds up in the port 27 and, when high enough, a flow of pressure medium is branched off through the chamber 16, bores 19-23 and port 24 to the brake 25, such build up of pressure acting on the end 51 of the valve 50 to force the valve back together with the piston 46 into the first braking position and in this position the piston 46 again opens duct 40 while the connection from the port 24 to the conduit 45 remains closed and consequently a control flow can again flow from the inlet port 27 through the throttle 35 to the conduit 45 and the valve 14 can again occupy the first working position thereof as shown in Fig. 1 in which the valve closes the connection, the trailer brake connection and opens that to the load. When the lever 57 is pivoted anti-clockwise, the spring 55 is expanded and since braking pressure prevails the valve 50 is moved from the first braking position to the right into a starting position thereby connecting port 24 to the conduit 45, the trailer braking pressure then dropping until the spring moves the valve back to the first braking position thereof and so closes the connection. In a modification, Fig. 3, the main valve 71 includes a slide valve 77 and a pilot valve 93 actuated by hydraulic pressure fed to the connection 123 from the master cylinder of a traction vehicle hydraulic brake. With valve 71 in the starting position of the valve 96 the brake 25 is relieved through connections 88, orifices 111, groove 103, orifices 101 and groove 102 in the direction of return conduit 104 and in this position a control flow of pressure medium can flow from inlet 74 through duct 108, bores 107, groove 106 in valve sleeve 95, groove 115 and orifices 116 in control piston 97, and bores 105, 101 to the return. In the starting position, the valve 96 is retained by spring 118 which presses the valve against the pin 127 as with valve 11, Fig. 1. The valve 96 with the associated piston 97 takes up a first braking position wherein the connection from the brake 25 to the return conduit is closed while the connection for the control flow from inlet 74 to return 104 is open; the valve 96 can occupy a second braking position in which both connections are interrupted. When the maximum trailer brake pressure has been reached in the brake 25 and the corresponding control pressure in the connection 123 is exceeded, the bush 125 abuts the plate 121. If the trailer brake pressure acting on end 109 of valve 96 exceeds the permissible value, the valve is displaced against the force of the pre-stressed spring 126 and the piston 97 opens the connection for the control flow from the inlet 74 to the return conduit 104 and the valve 77 therefore opens the connection from inlet 74 to the load 18 and closes the connection from inlet 74 to the brake 25. In a further embodiment, a pressure limiting valve with an adjusting member is connected between the duct 108, Fig. 3, and the return duet 104 and is disposed inside or outside the valve body 72; pressure medium passing through the valve to the duct 104 produces a differential pressure at the throttling bore 82 so that the connection from the inlet 74 to the load 18 is opened and therefore the pressure in the brake 25 is unable to increase further. The valve can be adjusted so that manual or automatic adjustable maximum pressure limitation is possible, using loading sensors in dependence on the loaded state of the trailer; also when the trailer is uncoupled the valve is opened and therefore when the traction vehicle is braked pressure cannot build up in the connection 88 to the trailer brake.