Patent GB-1222882-A (GB)
Title: Improvements in or relating to vehicle braking systems
Inventor: HARRIES DAVID ANTONY
IPC: B60T11/10
Filed: 1968-01-04
Abstract: 1,222,882. Dual brake-pedal arrangements. GIRLING Ltd. 2 Jan., 1969 [4 Jan., 1968], No. 699/68. Headings F2E and F2F. A brake pedal arrangement for a braking system of the kind in which separate pressure lines feeding respective brakes on opposite sides of a vehicle, such as a tractor, are linked by a compensating device, comprises a pair of pedal components mounted for independent angular movement about a common axis, and a pair of co-operating cam surfaces each mounted to move angularly with a respective one of the pedal components, one of the cam surfaces being formed on a member movable longitudinally of the axis, relative angular movement of the two pedal components (and hence of the cam surfaces) causing axial displacement of the member. As shown in Fig. 1, a right pedal component R is keyed to a shaft 21 while a left pedal component L is journalled on the shaft. Each pedal component is arranged to actuate a master cylinder (not illustrated) for a pressure line on one side of the vehicle. A cylinder 22 is keyed to pedal component. L by a peg 28, while a cam plate 36, formed with a cam surface 34, is keyed to pedal component R by a peg 38. An annular piston 30, urged to the right in cylinder 22 by a spring 40, is formed with a cam surface 32, the surfaces 32, 34 being shown in their normal relative position of top-dwell. In operation, if one pedal component is angularly displaced relative to the other, in order to effect braking on one side of the vehicle only to facilitate steering, the interaction between the cam surfaces 32, 34, permits axial displacement of piston 30 to the right. In consequence hydraulic fluid is withdrawn through port 20 from the region to the right of a piston 16, the piston 16 being thereupon urged to the right by a spring 18. Piston 16 forms part of a valve element in a valve body 10, which element, in consequence of such movement, permits valve balls 14 to seat, thereby interrupting flow through line 12 which connects the two pressure lines each extending from one of the master cylinders to one of the brakes (right or left). Thus only one of the brakes is applied. If both pedals are depressed at the same time, pistons 30 and 16 are not actuated, so both brakes are applied, and furthermore the open valve 10 serves to equalize the pressures in the two lines. In Fig. 3 the piston 30 is replaced by a toroidal flexible bag 42, and relative angular displacement of the pedal components results in compression of the bag by the riding-up of balls 50 out of ramps 52, which moves a cam-plate 44 to the left. Movement of piston 16 is consequently effected by compression instead of suction. In Fig. 2 (not shown) a toroidal bag is likewise provided, but it is normally subjected to internal compression, and relative angular displacement results in movement of the cam-plate to the right, so the actuation of valve 10 occurs as described with respect to Fig. 1. In Fig. 4 (not shown), movement to the left of a spring-loaded cam-plate of the kind shown in Fig. 3 serves through a mechanical lever to move piston 16 in the appropriate direction against a spring. In Fig. 6 the valve 10 is replaced by a compensating device 10A comprising a floating piston having two heads 59, 59, between pressure spaces 56, 58. The piston is locked against axial movement, when appropriate, by cam-actuated engagement of a plunger 62 (having projections 64) with threads on the piston shank 60.