Patent GB-1369181-A (GB)
Title: Tandem spring and serivce brace actuator
IPC: F16D65/28
Filed: 1973-02-22
Abstract: 1369181 Tandem spring and service brake actuators; compressed air brake systems BENDIX CORP 22 Feb 1973 [22 Feb 1972] 8769/73 Headings F2F and F2E [Also in Division H1] A tandem spring and service brake actuator comprises a service actuator part 14 and a spring actuator part 16 separated by a central wall 12, the service actuator part 14 having a service pressure chamber 18 and the spring actuator part 16 having a spring chamber 40 and a control cavity 36 separated by a piston 34, a sleeve 44 integral with piston 34 extending through an opening 48 in the wall 12 to abut a service diaphragm 22 which itself engages a push plate 24 and a brake applying push rod 26; a check valve 66 is carried by the sleeve 44 which valve 66 is open in the unactuated condition of the spring actuator part 16 to allow interconnection of chamber 40 and cavity 36 and closes when spring actuation moves piston 34 and diaphragm 22 rightwardly to a brake applying position. The check valve 66 comprises a valve head 68 positioned in a valve cavity 70, the valve head 68 being secured to a stem 72 which in the unactuated condition of the spring actuator part 16 abuts a fixed sleeve 52 integral with a housing wall 54 to hold the valve head 68 away from a valve seat 75 against the bias of a spring 74. An 0-ring seal 50 between wall 12 and sleeve 44 seals off chamber 18 and cavity 36 and the sleeve 44 includes one or more radial holes 76 which when uncovered by the seal 50 communicate any excess pressure in cavity 36 to chamber 40 via the valve cavity 70, open valve 66, a cavity 58, an annular passage 56 between sleeves 44, 52, and ports 60 in a rearward extension 62 of sleeve 44 the holes 76 thereafter being covered again. During a spring application fluid pressure is released from cavity 36 via a port 38 and piston 34 and sleeve 44 move rightwardly whereby holes 76 move to the right of seal 50 to communicate chamber 40 with chamber 18. Surplus pressure within the spring chamber 40 initially holds the valve 66 open until this pressure is dissipated via chamber 18 and an exhaust port 87 of a valve 78, whereupon check valve 66 closes. During release of a spring brake application any excess fluid pressure in chamber 40 flows out to chamber 18 until the components regain the position of Fig. 1. Fig. 4 illustrates a valve arrangement for controlling operation of the tandem actuator, the arrangement comprising valves 78, 80 respectively connected with one or more service actuator parts 14 by conduits 98, 100 and with one or more spring actuator parts 16 by conduits 104, 106. The valve 78 has an inlet port 82 connected to a brake valve, an exhaust port 87 and a pair of outlet ports 84, 86 connected to conduits 98, 100. The valve 80 has an inlet port 88 connected to a spring brake parking control valve, a pair of outlet ports 90, 92 connected to conduits 104, 106 and an exhaust port 94 connected to conduit 98 by a conduit 108. By means of this arrangement compounding of service and spring brake forces is preventedfor example with the spring actuator in its operative position, a service application will cause pressure build up in chamber 18 via valve 78 and conduit 100 and in cavity 36 via conduit 108, valve 78 and conduit 106. A differential pressure switch 110 is connected to the conduit 106 via a conduit 112 and to the spring chamber 40 via a conduit 114, and the switch 110 is included in a circuit comprising battery 118, ignition switch 120 and a signal 116 which may be a light or audible alarm, said signal 116 serving to indicate spring brake application and release, and also failure of spring 42 or diaphragm 32. The differential pressure switch 110 shown in Fig. 5, has contacts 136, 140 closed by a spring 142 to energize the signal 116 when conduit 112 is exhausted during spring actuation. During release of spring actuation a cavity 130 is pressurized and a piston 146 with a finger 148 is moved downwardly to open contacts 136, 140. Should spring 42 brake or diaphragm 32 fail the pressure in chamber 40 and cavity 36 will equalize and contacts 136, 140 close to energize signal 116.