Patent GB-1357697-A (GB)
Title: Over-run apparatus for trailers
IPC: F16D65/46
Filed: 1972-02-04
Abstract: 1357697 Trailer over-run brakes; internal shoe drum brakes HAHN FAHRZEUGBAU GmbH 4 Feb 1972 [24 Feb 1971 28 April 1971] 5214/72 Headings F2E and F2F The internal shoe-drum brake of a trailer overrun apparatus has two brake shoes 8, 9 operable by a spreading device 7, the brake shoe 9, which acts as the secondary shoe during forward movement and as the primary shoe during reverse movement, being resiliently supported by a spring 11 which is adapted to be compressed by an amount which is related to the displacement of the spreading device 7 as caused by maximum overrun displacement S. As shown in Fig. 1, the apparatus has a slide tube 2 slidable in a guide pipe 1 over a path length S and a brake lever 4 engages the end of the slide pipe 2; the lever 4 is attached to a cable 6 by a rod 5 and the cable 6 is attached to the spreading device 7. The brake shoe 8 at its end remote from the spreading device 7 is supported on an adjustable support bearing 10 secured on a brake carrier 19, and the shoe 9 engages in a slot of the bearing 10 at a distance from the bottom thereof. The spring 11 is yoked between holders 21, 22 mounted on the carrier 19 arid a plate 22 is mounted between the holder 21 and the spring 11 and is connected by means of an adjustment screw to an adjustable fork piece 14, which forms with the shoe 9 a joint 13. A draw spring 23 is yoked between holder 20 and shoe 8, and a spring 24 biases the shoes 8, 9 together. The bearing 10 has adjustment screws 12, 15. During forward rotation in direction A overrun braking by operation of the spreading device 7 will, if the power of spring 11 is exceeded, cause the shoe 9 to move towards the bearing 10 to prevent excessive braking resulting in the locking of the trailer wheels. On reversing the slide pipe 2 is pushed into the guide pipe 1 by a distance S, and the brake lever 4 is moved through an angle S 1 . A force exceeding the force of spring 11 causes the shoe 9 to be moved to rest against the bottom of the slot in the bearing 10, and only a very slight braking takes place. The distance travelled by the shoe 9 is related to the distance S. The apparatus also includes a hand brake lever 16 which is connected to a brake draw-rod 17 via a slot, the rod 17 being jointed on to the lever 4; by means of the lever 16 the brake lever 4 may also be pivoted through an angle S 2  to lock the brake. In the embodiment of Fig. 2 (not shown) the spring (11a) is yoked between a peg shaped holder (20a) mounted on the brake shoe (9a) and a plate spring (22a) disposed in a slot (26) defined by a wall part (21a) of the shoe (9a). Two springs (11a) may be disposed on each side of shoe (9a). In the embodiment of Figs. 3 and 4 the support bearing 10b has a bush 35 in which is mounted the pressure spring 11b between rings 20b and 22b. Adjustment nuts 14b and 15b project into the bush 35 and have adjusting screws 37, 43 screwed thereinto. A leaf spring 39 secures the rotational positions of the nuts 14b, 15b. The nut 15b is supported directly on the bush 35 but the nut 14b is movable against spring 11 by a distance related to the path S until it is supported against the bush 35.