Patent ID: 7258207

Claim:
An automatic shoe clearance adjusting apparatus for a drum brake of motor vehicles comprising: (a) a strut regulating a returning position of a pair of brake shoes and a driving member installed on the strut, said strut including (1) a rotatable nut member with a ratchet wheel, (2) a non-rotatable fitting member for supporting the nut member at one side portion of the nut member, and (3) a non-rotatable bolt member for making a screw engagement with the nut member at the other side portion of the nut member; and (b) the driving member, said driving member including (1) an arcuate leaf spring element having one end portion fixed to the fitting member and the other end portion rotatably engaged with the nut member and driving a resilient force urging the fitting member and the nut member away from each other in an axial direction of the strut and (2) a pawl element having one end integrated with the arcuate leaf spring element and the other end making a ratchet engagement with the ratchet wheel, said automatic shoe clearance adjusting apparatus has an automatic shoe clearance adjusting mechanism, for expanding the strut to adjust a shoe-to-drum clearance by unthreading the nut member out from the bolt member when the fitting member and the nut member are separated while the pawl element of the driving member makes a one-way-rotation of the nut member, due to the resilient force of the arcuate leaf spring element of the driving member, when strokes of the brake shoes exceed a predetermined value while releasing an axial force acting on the strut, wherein when a temperature of the arcuate leaf spring element of the driving member exceeds a predetermined degree, the temperature weakens the resilient force of the arcuate leaf spring element due to thermal deflection in the direction to reduce curvature of the arcuate leaf spring while keeping ratchet engagement of the pawl element against the ratchet wheel, thereby suspending an automatic shoe clearance adjusting operation.