Patent GB-1366818-A (GB)
Title: Modulator for an adaptive braking system
IPC: B60T8/46
Filed: 1972-10-26
Abstract: 1366818 Modulators in compressed air adaptive braking systems BENDIX CORP 26 Oct 1972 [16 Nov 1971] 49412/72 Heading F2F [Also in Division G3] A compressed air adaptive vehicle braking system with a brake valve 20 and a brake chamber 22 includes an adaptive braking modulator 10 therebetween comprising a housing 12 defining a bore 24 having an inlet port 14 from the valve 20, an outlet port 16 to the chamber 22 and an exhaust port 18 to atmosphere and a pressure responsive self-lapping valve arrangement 32 within said bore 24 for controlling communication between the ports 14, 16, 18, the arrangement 32 including a piston 48 slidable in the housing 12 in response to differential pressure across the piston 48 to connect the outlet port 16 to the exhaust port 18 to relieve braking pressure; the attainment of such differential pressure across the piston 48 is achieved by energization of a solenoid valve 96 by an electronic control unit sensing an incipient skid condition of a vehicle wheel. As shown in Fig. 1 the solenoid valve 96 has an armature 98 carrying a resilient valve member 100 in a chamber between two valve seats 90, 92. In the unenergized condition of a coil 102 the valve member 100 engages valve seat 90 whereby uninhibited communication between an outlet chamber 30 below the piston 48 and a control chamber 54 above the piston 48, to provide substantially equal fluid pressures across the piston 48, is attained. However, when during a braking application with the components in the position illustrated, the coil 102 is energized the member 100 moves to engage the valve seat 92 to shut off communication between chambers 30, 54 and chamber 54 is communicated to a compartment 70 via a passage 84 and an inlet opening 86 which compartment 70 is communicated to atmosphere via a passage 76 in a plunger 60, a chamber 64, a flow restricting orifice 78, a passage 80 in a guide member 68 and the exhaust port 18. The pressure level in control chamber 54 therefore drops rather abruptly and piston 48 is moved upwardly to terminate communication between the inlet and outlet ports 14, 16 except via a flow restricting orifice 58 and to communicate port 16 to exhaust port 18 to release the brake. Pressure in chamber 64 acts to move plunger 60 downwardly to bring a seal 88 into momentary engagement with the inlet opening 86, but a stabilized position is reached when flow into chamber 64 is equal to the flow from it and pressure will exhaust from outlet chamber 30 at a controlled rate until a minimum pressure level is reached or until the wheel reaccelerates to initiate braking. The modulator 10 includes a quick release valve 104 comprising a diaphragm 106 and a valve seat 108 responsive to differences in pressure between the inlet port 14 and an inlet chamber 28-when the pressure in chamber 28 is greater than the pressure in port 14 the diaphragm 106 is deflected to connect chamber 28 to the exhaust port 18. In the embodiment of Fig. 2, a floating piston 312 defines compartments 314, 316 connected respectively to an exhaust port 218 via a passage 284 and an orifice 322 and to a control chamber 254. The pressure differential established across the piston 248 during an adaptive braking cycle will be proportional to the size of chamber into which the pressure in the chamber 254 is exhausted, and hence pressure in the outlet chamber 230 will be exhausted at a lesser rate when the initial pressure in outlet chamber 230 is high and at a greater rate when the initial pressure in chamber 230 is relatively low.