Patent GB-690539-A (GB)
Title: Wheel-slip prevention control mechanism for fluid pressure brakes
IPC: B60T8/32
Filed: 1951-11-05
Abstract: 690,539. Fluid-pressure brakes. TECALE MIT SOC. ANON. Nov. 5, 1951 [Nov. 7, 1950; Oct. 9, 1951], No. 25880/51. Class 103 (i). In fluid pressure braking apparatus for railway vehicles of the type in which the speeds of two wheel pairs of a bogie are compared so as to operate means which vent the brake cylinders so as to prevent wheel slip, the speed comparison device is arranged to be operative for either direction of movement of the vehicle. As shown in Fig. 1, two sheaves g and e of equal diameter mounted on a shaft d secured to the bogie frame, are driven at the same speed and in the same direction from sheaves i and m on the axles a and b. An intermediate sheawe f of larger diameter than sheaves g and e is mounted between g and e and is driven at a slower speed from a further sheave k on the axle b. As shown in Fig. 3, the sheave e is coupled through a friction clutch 10 to a member 9 having a follower 8 that projects through a slot 16 in sheave f and engages the base of a V -shaped recess in member 7 coupled by friction clutch 14 to sheave g. Operation is as follows. When both axles a and b are rotating at the same speed, the different speed of sheave f causes it to be rotated until a projection 19 thereon engages an abutment shoulder 6 on the member 13. Thereafter slip occurs in the clutches 10 and 14. As seen from Fig. 1, it is intended that axle a shall be more heavily braked than axle b, as indicated by the brake cylinder q being larger than the brake cylinder r. Assuming therefore that slip occurs on the axle a and not axle b, the sheave g will take an angular lag relative to the sheave f so that due to the camming action of follower 8 on slope 2 there is an axial movement of sheave e which causes opening of brake cylinder vent valve 12 which reduces the slip. If the direction of travel is reversed, the follower 8 is engaged instead by the end face of sheave f but remains in the bottom 3a of the double slope 1, 2 unless slip of the axle a also occurs in this direction. A ball rolling in a slot may be used instead of follower 8. In Fig. 5, an arrangement is shown which provides that the slip may be reduced in two stages, first by shutting off the fluid supply to the brake cylinders and then by venting the brake cylinders. Two sets of sheaves e, f, g are used but the cam slopes 1, 2 are such that for the shaft d the relief valve 57 is lifted at an angular slip ratio of the order of 4 per cent and the relief valve 12 at a ratio of about 8 per cent. The lifting of valve 57 allows pressure to escape from one side of piston 37 so that the supply pressure acting on the other side closes the supply valve 40 against the action. of spring 38 before the brake cylinder connected at 35 may subsequently exhaust past valve 12. In other arrangements the brake cylinders are of equal size and the forward tilting of the bogie is relied upon for loading one axle more heavily than the other. In another arrangement shown in Figs. 12 and 14 all three sheaves e, f, g are of different size, the centre sheave f having duplex cam slopes 100 and 101 co-operating with followers 107 and 106. Due to the equal angularlity of slopes 100 and 101, no axial displacement of valve 12 will be caused if the followers 106, 107 are displaced simultaneously in opposite directions and therefore this arrangement may also be used effectively for either direction of movement.