GB917175A - Improvements in or relating to brake systems for motor vehicles - Google Patents

Abstract

917,175. Hydraulic braking systems. FORD MOTOR CO. Ltd. March 14, 1961 [March 31 1960], No. 11444/60. Class 103 (1). [Also in Group XXIX] An hydraulically-operable braking system for a motor vehicle includes a device for varying the pressure supplied to a brake-applying means of either the front or rear wheels for a given pressure in a master cylinder and which comprises a differential area piston which is biased by a leaf-spring of variable effective stiffness to vary the output pressure corresponding to a given input pressure, e.g. in dependence on vehicle load. As shown, the pressure supplied to the front brakes is augmented by a differential piston 3 arranged to provide different pressures in chambers 2, 16 in dependence in part upon the difference in area of opposite faces of the piston and in part by the biasing effect of a leafspring 7 acting on a plunger 6 engaging an extension 4 of the piston. The biasing effect of the spring is variable by means of a link 21 having a roller 19 on its end which acts as a fulcrum for the spring, the link being movable axially by means sensitive to the load on the vehicle. Two rollers may be used in place of roller 19 (Fig. 2, not shown), one engaging the spring and the other the housing of the device. The link 21 is connected to a bell-crank 24 secured to shaft 25 of a damper 26 on the sprung part of the vehicle and connected via a rod 27 and springs 31, 32 to the front or rear axle, so that as the latter rises and falls with changes in the load the link 21 is moved to shorten or lengthen the effective length of the spring 7 to vary the force it exerts on the piston 3, and thereby vary the pressure supplied to the front brakes. The springs 31, 32 and damper 26 are arranged to prevent transient movements of the axle being transmitted to the link 21. A limiting valve 9, urged by a spring 10 to open a by-pass nullifies the effect of piston 3 when the pressure in the master cylinder falls below a predetermined value, so that initially or on light braking the pressure supplied to front and rear brakes is equal, the valve 9 closing with heavier braking so that pressure supplied to the front brakes is subsequently higher than that supplied to the rear brakes. Where the pressure varying device is used on a vehicle with pneumatic suspension, the link 21 may be moved by a piston acted on by the pressure of the air used to maintain a constant riding height.