Patent GB-1385180-A (GB)
Title: Vehicles having hydraulically operated braking systems
IPC: B60T8/26
Filed: 1970-11-04
Abstract: 1385180 Differential braking; load responsive braking JONAS WOODHEAD Ltd 4 Feb 1972 [4 Nov 1970] 52502/70 Heading F2F A vehicle hydraulic braking system with front and rear brakes has a spool valve 1 situated in a line leading to the rear brakes, and the spool 5 of the valve 1 is acted upon both by a force dependent on the loading of the rear wheel or wheels and by the pressure to the rear brakes, whereby the same hydraulic pressure is applied to the front brakes and the rear brakes until a certain brake pressure which is dependent on the instantaneous loading of the rear wheel or wheels is achieved and thereafter the pressure applied to the rear brakes varies with the instantaneous loading on the rear wheel or wheels. As shown in Fig. 1, the valve 1 acts to control communication between connections 2 and 3 which are respectively connected to the master cylinder front brake lines and the rear brakes and the spool 5 has a gallery 25 and bores 26, 27. The spool 5 is connected to a rigid inverted cup 6 in which is seated one end of a spring 7, the other end of which is seated in a sleeve 8: the sleeve 8 is pivoted at 9 to an arm 10 one end of which is pivoted at 11 to the body of the vehicle and the other end of which is connected by an adjustable link 12 to the rear axle. As pressure builds up during braking the pressure at the rear brakes is applied to spool 5 adjacent the connection 3, the force from this being opposed by the load of the spring 7, which load depends upon the instantaneous distance between the rear axle and a fixed point on the body of the vehicle. Thus at some stage during an increase in brake fluid pressure the spool 5 will move against spring 7 to isolate connection 3 from connection 2. If the rear wheels are now moved downwardly relative to the body due to high deceleration or a dip in the road, the valve spool 5 will move away from the connection 3 to reduce the pressure at the rear brakes; if the rear wheels move upwardly the spool 5 will move to increase the pressure in the rear brakes, and may restablish communication between the connections 2, 3 to further increase the pressure. When master cylinder pedal pressure is released fluid passes from connection 3 to connection 2 via passages (32, 33) and a non-return valve (29, 30, 31) as illustrated in Figs. 2, 3 (not shown). The embodiment of Fig. 4 illustrates a valve for use where at least part of the load of the vehicle is carried by adjustable fluid pressure operated devices having a self-levelling characteristic. The valve has an inlet 40 connected to the suspension devices and opens to a chamber 41 at the bottom of the valve spool 5. The chamber 41 contains a light spring 42 if the whole load of the rear axle is taken by the fluid pressure suspension devices but where this is not the case. the spring 42 is replaced by a compression spring of a strength related to the proportion of the load which is taken by the mechanical devices. A force proportional to the suspension pressure acts on the spool 5 and this pressure is proportional to the distance between the rear axle and a fixed point on the body. The spool 5 may be stepped.