GB1424536A - Shoe expanding devices for internal shoe drum brakes adjustable speed projector - Google Patents

Abstract

1424536 Internal shoe drum brakes AUTOMOTIVE PRODUCTS Ltd 2 May 1973 [12 May 1972] 22374/72 Heading F2E A shoe expanding device for an internal shoe drum brake comprises a piston or pistons 11, 12 of a single or double acting wheel cylinder urged apart to apply a shoe or shoes of the brake by liquid pressure or by a wedge member 13 movable between a fixed abutment and the piston or between adjacent ends of the pistons 11, 12 and having rollers 26 located by a cage 29 mounted on the wedge member 13, stops being provided on the wedge member 13 and cage 29 which when engaged one with the other determine the relative positions of the wedge member 13 and cage 29 such that rollers 26 engage the thin end 23 of the wedge member. A spring 34 acts on one of the stops which spring yields to allow the wedge member 13 to be retracted in advance of the cage 29 if the stops engage before the wedge member is fully retracted. The cage 29 is U-shaped having two limbs 28 provided with a rectangular opening 31 in which are located washers 32, 33, slidable on the wedge member, the washer 32 co-operating with a shoulder 36 on the wedge member to constitute the stops. Wedge member 13 is moved by a stack of Belleville washers 17 to apply the shoes upon release of hydraulic pressure in a chamber 22 whereupon the rollers 26 roll in slots 27 between the wedge and piston surfaces 24 and shoulder 36 moves away from stop washer 32. If the brake shoes are partially applied by liquid pressure acting in wheel cylinder 10 and washers 17 are brought into action, wedge member 13, cage 29 and rollers 26 move together until rollers 26 contact piston surfaces 24 and only during further movement will the wedge member 13 move in advance of cage 29 and rollers 26. If liquid pressure in cylinder 10 is first released and pressure then restored to chamber 22 rollers 26 return to their idle position. Shoulder 36 then contacts washer 32, spring 36 yields allowing rollers 26 to roll until they come opposite to transverse grooves (37), Fig. 3 (not shown), at the thin edge of wedge member 13. The grooves ensure that the brake shoes are spaced from the drum when the rollers are engaged therein so that there is no load on the rollers. With the load released cage 29 returns to its normal position under the bias of a spring 35.