GB1438579A - Wheel brake having two brake shoes - Google Patents

Abstract

1438579 Internal shoe drum brakes V KNOTT [trading as MASCHINENBAU KNOTT EGGSTATT Ing VALENTIN KNOTT] 28 Sept 1973 [30 Sept 1972] 45489/73 Heading F2E In a wheel brake comprising a brake drum (not shown) rotatable relatively to a brake shoe carrier 4, Fig. 1, and two brake shoes 1, 2, each of which bears at one end against the brake shoe carrier and co-operates at the other end with a floating expander 5, the brake lining 7 of at least one of the shoes (shoe 1, as shown) being mounted on a lining carrier 6 which can move relatively to the brake shoe 1 the relative movement between the lining carrier 6 and shoe 1 is guided, and spring 9 (one not shown) are provided for biasing the lining carrier 6 towards a first position of operation relative to the associated brake shoe 1. As shown, the brake shoes 1, 2, bear at their lower ends against a slack adjuster 3 associated with the shoe carrier 4 and co-operate at their upper ends with the floating expander 5. The lining carrier 6 is movably associated with shoe 1 by cam surfaces 13, 14, on carrier 6 engaging pins 10, 11, respectively on shoe 1. The respective cams and pins are retained in contact by the pre-stressed tension springs 9 (one only shown) extending on both sides of shoe 1 and carrier 6 between bores 15, 16, in carrier and shoe respectively. Cam surface 13, Fig. 3, begins with a partcircular recess 13A of radius substantially equal to that of pin 10, continues with a further recess 13B of at least twice that radius and ends with a straight line 13C perpendicular to the direction 8, Fig. 2, of the expanding force. Cam surface 14, Fig. 2, begins with a straight line which, produced, makes an angle of 36 degrees with the direction 8 of the expanding force, continues with a part-circular recess 14A of radius substantially equal to that of pin 11 and to which the first line is tangential, and ends with a further tangent to the recess, at right angles to the first straight line. In operation, with travel in the forward direction 12, Fig. 1, springs 9 maintain carrier 6 in the position of Fig. 1, and the brake when applied, behaves as a two-shoe non-servo brake. When the direction of rotation is reversed and the brake is applied, lining 7, being entrained by the drum, not shown, causes movement of the carrier 6 relative to the shoe 1 against springs 9 in an approximately clockwise direction until pins 10, 11, occupy the positions, relative to carrier 6, shown dotted in Fig. 2. Thus the brake is less forcefully engaged, and, if mounted on a trailer, permits reversing of the trailer. On resumption of forward movement, springs 9 restore carrier 6 to the Fig. 1 position without delay and without the necessity for relieving the action of expander 5, so forward braking power is immediately available. During reverse movement, the brake may be more forcefully engaged, despite the movement of carrier 6 by the drum, by further application of expander 5.