Patent GB-1390999-A (GB)
Title: Mechanical braking system for a vehicle trailer
IPC: B60T7/20
Filed: 1972-10-06
Abstract: 1390999 Overrun brakes; shoe-drum brakes; transmitting mechanisms H MERZ 6 Oct 1972 [8 Oct 1971] 46314/72 Heading F2E A mechanical braking system for a trailer has an over-run operating means and an auxiliary operating means the two means having common transmission members 14, 15, 16 to a pair of wheel brakes 18: each wheel brake 18 has at least two shoes 21, 22 and is contructed so that during forward rotation V a strong braking action is developed but during backward rotation R a weaker braking action is developed. In Fig. 1 is shown a trailer coupling 1 which is fixed to a draw bar 2. A force limiting means 6 includes a spring 7 which when compressed sufficiently will make face 3 of draw bar 2 bear on face 5 of casing 4 so that the resultant limiting force of spring 7 is transmitted via a lever 13 to members 14, 15, 16. A shock absorber 8 may be provided to damp the process. The auxiliary operating means comprises a hand lever 9 which acts on the lever 13 by way of a telescopic member 10, and an extension 11 of lever 9 may be connected to the towing vehicle by a break-away cable 12. In the arrangement of Fig. 2 (not shown) which is particularly envisaged for use with the wheel brakes shown in Figs. 11-14 the force limiting means 6 and the cable 12 are omitted and the telescopic member 10 is replaced by a link 17. Fig. 3 shows a wheel brake with a leading shoe 21 and a trailing shoe 22 which can be spread by a cam 39. The cam 39 is optionally mounted on an arm 40. A guiding arm 41 is connected to the cam 39, and the arm 41 carries a shoe 45 applicable to the end surface of a brake drum 20: the shoe is applied by a lever 42 connected to transmission member 16, and the cam 39 is turned in direction V or direction R by movement of the guiding arm 41 as soon as shoe 45 is applied to the brake drum 20. A compression spring 46 acts to form a force threshold so that it is only overcome by the limit set by the means 6, and below this limit only shoe 45 exerts a slight braking torque: shoes 21, 22 remain unactuated in the backward direction R and compression spring 46 can only be overcome by the auxiliary operating means. Fig. 3 has a sliding shoe support block 37 which may be replaced by a rotary mount. In the servo arrangement of Fig. 5 (not shown) stops (50, 51) fixed to the brake plate (19) act to brace the shoes in respective directions of rotation. In the servo arrangement of Figs. 6, 8 shoes 21, 22 are connected by a slide member 23 to adjusting means 24. Pressure pins 58, 56 brace the shoes 21, 22 respectively in the forward direction and the backward direction: in the forward direction the shoe 21 is actuated by means of an auxiliary shoe 52 acting through a lever 55 and pressure pin 56, and in the backward direction the shoe 22 is actuated by means of an auxiliary shoe 53 acting through a lever 57 and the pressure pin 58. The shoes 52, 53 are respectively actuated by levers 59, 60 with respective rollers 66, 67 but lever 60 is supported by a tension strap 63 and a lever 64 on a biased spring 65 which forms the force threshold. Lever 59 is connected by a tension mechanism 36 and the lever 60 by a tension mechanism 33 to a guide frame 34 acted on by member 16. In the embodiment of Figs. 9, 10 (not shown) there is only one auxiliary shoe (69) applied by a lever (70) with a roller (71): lever (73) which replaces lever 57 of Fig. 6 is acted on by springs (74) forming the force threshold. An adjusting means (75) for the auxiliary shoe is provided. The embodiment of Figs. 11, 12 incorporates a force limiting means consisting of a compression spring 82 operating in conjunction with a stop 19a. The particular embodiments using one or two auxiliary shoes are also applicable to brake shoes in a duplex or duo-duplex arrangement.