GB1037608A - Improvements in or relating to brakes - Google Patents

Abstract

1,037,608. Internal shoe drum brakes. H. TEVES, E. A. TEVES, and M. TAUSEND, [trading as ALFRED TEVES MASCHINENUND ARMATURENFABRIK KOMM. GES.]. Oct. 23, 1964 [Nov. 23, 1963], No. 43315/64. Heading F2E. An internal shoe drum brake for a heavy motor vehicle is adapted to exhibit the characteristic of a " duo-duplex brake," i.e. one in which the shoes are anchored at either end according to the direction of rotation to give two-leading shoe brake in both directions, when hydraulically applied, and to operate as a "duo-servo" brake, i.e. with both shoes floating and anchoring one on the other, when mechanically applied, so that less manual force is required to operate the handbrake of the vehicle than is the case when a conventional " duo-duplex brake " is used, this result being obtained by arranging between the non- actuated shoe ends of a duo-servo type brake a transmission arrangement which comprises a lever engaged between the shoes and between a pair of cup spring assemblies which are also acted on by an hydraulic device arranged, when the brake is applied hydraulically, to pre-stress the cup springs, to apply a damping force to movement of the shoes. As shown, a pair of shoes 2, 3 are arranged within a drum 1 in association with an actuating cylinder 4 and a transmission arrangement comprising plungers 5, which incorporate slack-adjusters (Fig. 2, not shown) arranged between the non-actuated shoe ends for sliding in a fixed bush 6, a lever 9 having one end 9a located between the plungers and engageable with the sleeve 6 after an initial clearance 10 has been taken up, the other end 9b being located in a slot in a pin 12 slidable in pistons 13 against the centralizing force of cup springs 11, and cylinders 14 in which the pistons 13 operate, the chambers 15 being connected by a line 16 to the chamber of cylinder 4. In hydraulic operation the cup springs 11 are pre-stressed so that a damping force is applied to resist movement of the lower ends of the shoes and thereby reduce the force transmitted from one shoe to the other, so that the arrangement acts as a resilient anchor for these shoe ends with limited transmission of the drag force from the primary shoe to the secondary shoe. When the brake is manually applied, as by a lever and linkage 8 the cup springs 11 are not stressed, so that the end 9b of the lever 9 is free to move and substantially the whole of the drag force of the primary shoe is transmitted to the secondary shoe. Springs 17 ensure that the lever 9 is centralized after a manual application of the brake.