GB943504A - Improvements in or relating to braking systems for mechanically propelled vehicles - Google Patents

Abstract

943,504. Hydraulic brakes; dashpots. ROBERT BOSCH G.m.b.H. July 10, 1961 [July 8, 1960], No. 24817/61. Headings F2F and F2S. In a single-stroke master cylinder hydraulic brake system, see Fig. 1 (not shown), there is a control valve in the pipe-line to the rear brakes; two cylinders are connected to the pipe-line, one each side of the control valve, having their pistons connected by a balance lever so that after a predetermined pressure has been reached the pressure in the rear brake cylinders rises more slowly than that in the front ones. Pedal pressure is not affected when the device comes into operation. As shown in Fig. 2, the device comprises a control valve 51 connected by pipes 5, 7 to the master and rear brake cylinders respectively. Cylinders 14, 16 are connected to pipes 5, 7 by passages 10, 56 and their pistons 17, 18 are operatively connected through balls 27, 28 with a balance lever 39, with which they are maintained in contact by a tension spring 35. In the inoperative position the head 20 of the piston 18 raises the tail 49 of the control valve 51 to maintain the valve open. Initial depression of the brake pedal causes pressure to rise equally in the pipes 5 and 7 and hence in the front and rear brake cylinders. A further depression will cause the piston 18 to remove downwardly against the force of the piston 17 (the resultant downward force being a function of the lever ratio determined by engagement of the knife edge 36 with one of the teeth 43 of the balance lever) and the valve 51 will close. Thereafter each increase of pressure in the pipe-line 5 will depress piston 17 and raise piston 18 to open the valve 51, and pressure in line 7 will rise, but not so steeply as in line 5. The pressure at which the device first comes into operation may be adjusted by varying the compression of the spring 44 by means of the screw 46; and the ratio of pressures in the lines 5, 7 may be altered by moving the swinging lever 37 about the pivot 30 by means of the adjusting fork 38 to alter the lever ratio by engagement of the knife edge 36 with a different tooth 43. In another embodiment, Fig. 4 (not shown), the lever 37 is adjusted by means of a pneumatic ram which may be connected to the air suspension system of the vehicle to alter the lever ratio automatically with load. In a further embodiment, Fig. 5, the knife edge is received in a fixed seating in the centre of the balance lever, which may be moved sideways to vary the lever ratio between the cylinders by means of a cam connected to a lever 93 mechanically linked to the rear axle beam so that the pressure ratio between front and rear brake cylinders is again load dependant. The cam and lever 93 are clamped by hydraulic shock-absorber 100, the piston 101 of which is connected to the lever by engagement of the flattened end 99 of a pin 98 between the entrance surfaces 96, 97 of a recess 95 in the cam plate 94 mounted on the lever pivot 92. Liquid is displaced from one side to the other of the piston through an adjustable restriction 104.