Patent GB-1325329-A (GB)
Title: Overrunning and parking brakes for wheeled trailers
IPC: B60T7/10
Filed: 1970-11-26
Abstract: 1325329 Tractor-trailer over-run drum brakes; hand brakes; levers H O SCHROTER 26 Nov 1970 [27 Nov 1969] 56284/70 Heading F2E An anchorage, having limited freedom, for trailer brake shoes serves to release the brakes, or nearly so, (after initial application) during backing of the trailer by the tractor vehicle; the action of this anchorage is automatically nullified by application of the hand (parking) linkage. As shown, an over-running bar 1 is connected at the left to a tractor vehicle (not illustrated or described) and forward movement is to the left. Brake shoes 7 co-operate with a brake drum, not shown, rotatable about a wheel axle 10. The ends of shoes 7 remote from expanding mechanism 6 are supported by an anchorage 8 fixed to a disc 9 which is pivotally mounted on axle 10. In operation, if the tractor vehicle reduces speed, (over-run braking), the bar 1 is displaced to the right relative to the remaining mechanism, thereby pulling fork 18 to the left by means of reversing lever 2 having a fixed fulcrum at 3. Fork 18 via sheathed cable 4 actuates expanding mechanism 6 to apply the brakes. The torque consequentially exerted on pivoted disc 9 is counter-clockwise, so an arm 11 protruding from disc 9 is forced into contact with a fixed abutment 12, and an auxiliary linkage 14, 15A between the arm 11 and lever 2 is ineffective to release the brakes. When the trailer is backed by the tractor vehicle, the over-running bar, moving to the right, will again initiate a braking action. However, since the trailer is now moving to the right, the wheel is moving clockwise, the brake torque acting on disc 9 is clockwise, and arm 11 is pulled away from contact with abutment 12 against the force of a spring 13. Arm 11 via sheathed cable 14 thereupon pulls a fork 15A to the right until the left-hand end of slot 15 engages a pin 16 on reversing lever 2, tending to turn the lever counter-clockwise. The backing thrust of over-running bar 1 is thereby counteracted, or nearly so, with consequent substantial reduction of braking effect, so that the trailer can be backed by the tractor. If the trailer is braked by the hand lever 20, after having been uncoupled from the tractor vehicle or otherwise, a stop 26 on the lever 20, in the "apply" position of the lever, (not as shown), moves away from a locking lever 24, hinged about the same pivot as the lever 20. A spring 25 now pulls the locking lever 24 in a clockwise direction so that its hook-shaped free end engages behind a pin 27 on the fork 15A. Thereafter, if an attempt is made to back the trailer, and disc 9 consequently tends to pivot clockwise, the pull exerted by arm 11 cannot move fork 15A to the right because it is held by locking lever 24, so reversing lever 2 cannot be turned to release the brakes. Any forward movement of the trailer will tend to press arm 11 more firmly against abutment 12, the auxiliary linkage 14, 15A is ineffective to release the brakes as in the over-running situation, and the brakes consequently remain applied. Movement of the over-running linkage, during over-running and backing, is allowed for by the lost motion provided in the pin-and-slot connection 15, 16.