Fluid pressure and mechanical drum brake actuator

A drum brake assembly, comprising:

• a backing plate;
• a brake shoe attached to the backing plate and having two opposed and spaced ends, a first abutment at one end of the brake shoe and a second abutment at the other end of the brake shoe;
• a primary brake actuator comprising a piston-cylinder assembly that is movably supported on the two ends of the brake shoe so that the piston-cylinder assembly may move relative to said backing plate, said piston cylinder assembly having a piston part and a cylinder part, each of which is operable to coact with a respective one of said abutments;
• a secondary brake actuator comprising a member substantially fully contained in the brake assembly, said member having reaction means for coacting with said first abutment at an end portion thereof;
• and
• means connecting said member to one of said piston-cylinder assembly parts for relative movement about a pivot axis extending substantially parallel to the rotational axis of the brake drum, said pivot axis being spaced from said reaction means in a direction transverse to said pivot axis;
• wherein in a first mode of operation of said brake assembly said one piston-cylinder assembly part and said member cooperate to form a composite structure, said reaction means coacting with the first abutment, and said one piston-cylinder assembly part coacting with the second abutment so that said composite structure is operable to increase the spacing between said first and second abutments to cause radial expansion of the brake shoe when said member is moved in a first direction about said pivot axis;
• and
• wherein in a second mode of operation said piston-cylinder assembly is operable independent of said member and coacts with said first and second abutments to increase the spacing between the first and second abutments to cause radial expansion of the brake shoe.