Slack adjusters for the shoes of vehicle shoe drum brakes of the duo servo type

A vehicle internal shoe drum brake comprising a rotatable drum, primary and secondary shoes located within said drum, said primary shoe being carried around with said drum with a servo-action when the brake is applied, and automatic slack adjustment means being located between adjacent ends of said shoes, wherein said automatic slack adjusting means comprises a housing, a thrust member slidably guided in said housing and having an adjustable effective length, two tappets slidable in said housing and protruding from opposite ends thereof for engagement by ends of said shoes so that the thrust on said primary shoe when the brake is applied is transmitted to said secondary shoe to augment the brake applying force applied to said secondary shoe, said thrust member having threaded engagements of opposite hands at its opposite ends with said tappets, sensing means for sensing movement of said shoes when the brake is applied, and adjuster means incorporated in said housing for automatically increasing the effective length of said thrust member to compensate for wear of friction linings carried by said shoes when the said movement exceeds a predetermined amount, said sensing means comprising a helically toothed pinion forming a part of said adjuster means, said thrust member comprising a body provided with helical gear teeth meshing with said teeth on said toothed pinion such that said pinion moves in response to sliding movement of said thrust member, at least beyond a given amount, during application of the brake, and energy-storing clutch means controlled by said sensing means located within said housing and connected to said adjuster means to operate said adjuster means to increase the effective length of said thrust member when the torque generated on said thrust member by stored energy force exceeds the torque generated by the force applied to said thrust member from said shoe ends, said energy-storing clutch means acting on said pinion so as to effect adjustment of the length of said thrust member, said energy-storing clutch means comprising energy-storing means, a one-way clutch connected to said energy-storing means, said one-way clutch being connected to said pinion, and lost motion being incorporated in the connection from said clutch through said pinion to said thrust member.