Patent GB-1207043-A (GB)
Title: Pressure modulator assembly for anti-lock brake system
IPC: B60T8/74
Filed: 1968-10-03
Abstract: 1,207,043. Anti-skid brake control. GENERAL MOTORS CORP. 3 Oct., 1968 [11 Oct., 1967], No. 46894/68. Heading F2F. A pressure modulator for incorporation in a vehicle wheel brake system comprises a piston movable in accordance with variations in a sensed condition, e.g. of imminent skidding, to close sequentially primary and secondary check valves in a pressure supply inlet and to reduce pressure at a pressure apply outlet, and, conversely, to increase pressure at the pressure apply outlet and to open the secondary and primary valves sequentially, the secondary check valve being connected to the inlet by a restricted passage so that pressure equalization takes place through the restricted passage with the avoidance of surges. The lower end of the piston 88 which operates the hydraulic section 20, Fig. 2, of the modulator assembly 22 rests on a fastener 62 which secures a diaphragm 50, Fig. 1, to a power piston 48. Normally, the piston 48 is vacuum-suspended by connection of lower chamber 52 to vacuum source 94 (e.g. the vehicle engine intake manifold) at 56, and by connection of upper chamber 54 to the same vacuum source through conduit 38 and a valve of the anti-lock sensor and signal generator 34. Normally, also, the piston 48 is raised to the position shown by a spring 58. In operation, if the sensor 34 senses an incipient vehicle wheel brake locking condition, it operates to connect conduit 38 to the atmosphere at 92, whereupon piston 48 is forced downward. Piston 88, aided by hydraulic pressure in the inlet chamber 66 and by spring 86 acting on the primary check valve 74, also moves downward. The primary check valve 74 first seats on valve seat 72, and further slight movement of piston 88 (including pin 90) permits the secondary check valve 84 to seat on its seat 78. The rear brake apply pressure is now stabilized. Further downward movement of piston 88, as permitted by movement of piston 48, causes its disengagement from the valve mechanism, and increase in volume of outlet chamber 70, whereby rear brake apply pressure is decreased. If the signal from sensor 34 is such that piston 88 is moved down to a point where the rear brake apply pressure is zero (gauge), the piston will cease its movement, even though piston 48 may move down further. (Introduction of air into the rear brake system is thereby prevented.) When the wheel deceleration changes sufficiently to permit sensor 34 to reconnect conduit 38 with vacuum source 94, piston 48 rises, and lifts piston 88 with it, piston 88 thereupon lifting secondary check valve 84, thereby connecting inlet chamber 66 and outlet chamber 70 through a restriction in the form of a spiral passage 82 formed in the surface of a plug 80. Thus, if the mastercylinder-generated pressure in conduit 18 imposed in inlet chamber 66 is still substantially greater than the brake apply pressure in outlet chamber 70, a pressure surge to the wheel brake will be prevented. Further upward movement of piston 88 raises primary check valve 74. Also, if the master-cylinder-generated pressure is substantially decreased, while piston 88 is in its downward position, to a value less than that in outlet chamber 70, secondary check valve 84 will immediately open, and the pressures will be balanced through restrictive passage 82; if the pressure unbalance is sufficient, it will raise primary check valve 74 off its seat.