Expanding wedge
The expanding wedge is that part of a drum brake which, through the hydraulic, pneumatic or mechanical pressure force F , caused by pressing the brake pedal, causes the brake shoes to expand against the brake drum.
Components and mode of operation
The brake shoes with the brake linings are pressed outward against the brake drum by the two brake pistons guided in an expanding housing. The spreading of the brake pistons is caused by the longitudinal movement of the expansion wedge, which presses two pressure transfer rollers freely mounted in a roller carrier against pressure wedges attached to the piston. The expanding wedge shape is cylindrical in the upper part and rectangular in the lower part with the wedge shape. The wedge shape also provides an effective brake force boost. The roller carrier is movably attached to the expanding wedge. Due to the spreading of the rollers, the brake works with very little friction, practically only rolling friction occurs.
The force introduced by the brake cylinder outside the brake drum takes place at the other end of the expanding wedge. In addition, drum brakes of this type have a guide roller which is supported on the one hand on the roller carrier and on the other hand on the expanding wedge and ensures exact guidance of the brake rollers.