Motor vehicle brake system

摘要

1,081,010. Fluid-pressure brakes; brake linings. FORD MOTOR CO. Ltd. Aug. 6, 1965 [Aug. 31, 1964], No. 33691/65. Headings F2E and F2F. The brakes of a road vehicle are adapted to be applied both hydraulically, for normal braking and mechanically, for parking, by depression of the same pedal, there being a lostmotion connection in the mechanical connection, whereby mechanical braking is not possible so long as the hydraulic system is functioning normally, and a by-pass valve being provided in the fluid circuit, opened by the driver pulling out a knob on the dashboard, to disable the hydraulic system, so as to permit mechanical braking by allowing travel of the pedal beyond the normal range. The dashboard control also places a locking pawl in operative position against a ratchet carried by the pedal, so that when the brake is thus applied mechanically it is locked on. In the embodiment shown in Fig. 1, the piston 41 of a master cylinder 42 is operated directly by pedal 12 through a link 38, an extension 14 of the pedal having a pin-and-slot connection, to provide lost-motion, with a plate 19 to which is attached a cable 15 for mechanical operation of the brakes (not shown). The master cylinder is connected to slave cylinders of the brakes, to operate them hydraulically, via a valve structure 45 which includes a by-pass valve for relieving pressure via a return pipe 43 to the master cylinder reservoir, this being operated by a pivoted plate 66 actuated by rods 34, 35 when a knob 37 on the dashboard of the vehicle is pulled out, so that fluid under pressure will then no longer flow via pipe 46 to the brakes. At the junction of rods 34, 35 is a lever 32 of J-shape (Fig. 2, not shown). A compression spring 29 is arranged between the bent-over end of lever 32 and a pawl 25 such that when the lever 32 is swung about pivot 26 as a result of knob 37 being pulled out the spring goes over-centre and urges the pawl 25 into engagement with a rack 23 carried by the pedal, for locking the brake. Similarly, spring 29 urges the pawl away from rack 23 when knob 37 is pushed in, i.e. when the bypass valve of structure 45 is re-closed. The valve structure 45 (Fig. 4, not shown), consists of a housing (47) which is bared to receive a hollow piston (61) acting as a closure member of the by-pass valve and normally seating on an 0-ring (62) carried by a block (53) under the action of a spring (63). When lever (66) is swung by rod (34) it moves a rod (57) which is slidable in a bore of block (53) and has flats (58) permitting fluid to pass from inlet (48), via grooves (61) in piston (59), into annular grooves (55) in the block and thence to return pipe (43) when the inner end of rod (57) has engaged and lifted the piston (61) from its seat, instead of passing to outlet pipe (46). In another embodiment (Figs. 5. and 6, not shown), the pedal (121) is connected via a vacuum servomotor (71) to the master cylinder piston (411), the mechanical brake linkage, comprising a cable (79) provided with a predetermined amount of slack, also being operated via the servomotor through a lever (75) pivoted at (76). The servomotor is controlled by initial movement of a rod (69) of the pedalactuated linkage (67), (68), (69), this opening a valve to communicate vacuum with one side of a diaphragm (72) to operate the servomotor. The locking mechanism (221) is as in the previous embodiment, but the by-pass valve is incorporated in the master cylinder (Fig. 6, not shown), the piston (591) when operated by the rod (571) allowing fluid to be by-passed to a chamber (91) which is connected by a passage (94) to the master cylinder reservoir, instead of pressurizing outlet pipe (87). Rod (571) is engaged by a T-shaped plate which is connected by a cable (89) to the lever (32).