Patent ID: 7472776
Filing Date: 2009-01-06
Classification: F16D

Abstract:
1. A drum brake for a vehicle including an adjuster arrangement with an extendable strut that is located between a first web of a first brake shoe and a second web of a second shoe through which a running clearance is established between the first and second shoes and a drum, said first and second brake shoes being retained on a backing plate that is fixed to the vehicle such that a first engagement end on each of the first and second webs is spaced apart by the extendable strut and a second engagement end of each of the first and second webs is aligned with an anchor on the backing plate, a first spring attached to the first web and connected to a pawl of the adjuster arrangement retained on the second web for urging the first engagement ends toward an actuator member and a second spring attached to the first and second webs for urging the second engagement ends toward the anchor such that in a position of rest the first and second brake shoes are positioned adjacent the drum with a minimum running clearance there between, said actuator member including first and second pistons that are responsive to an actuation input by respectively acting on the first and second webs and after overcoming the opposition to the first and second springs moving the first and second brake shoes from the position of rest through the running clearance and into engagement with the drum to effect a brake application, said adjuster arrangement including a first body that is connected to the first web and having a threaded bore therein, a second body that is connected to the second web and having a smooth bore therein and wherein the expandable strut is defined by a shaft with a threaded section that is mated with the threaded bore in the first body and a smooth section that is located in the smooth bore of the second body and a star wheel located between the threaded section and the smooth section, said pawl pivoting on said second web with movement of the first and second webs by the actuator member and when a predetermined pivotal movement occurs engaging the star wheel causing the threaded section to rotate with respect to the threaded bore and correspondingly lengthening the expandable strut to maintain the minimum running clearance, said first piston being characterized by a plunger that is connected through a resilient member to a linkage member connected to the first web, a rod that extends from the plunger and a lever arm that is pivotally retained on the first web, said rod engaging a first end of the lever arm and a second end of the lever arm engaging the first body of the adjuster arrangement, said operational input acting on said plunger and being communicated through the resilient member into the linkage member for moving the first web during a brake application, said resilient member resisting the operational input until a predetermined operational input overcomes the resilient member and allows the plunger to move toward the linkage member such that the rod acts on the first end of the lever arm causing the lever arm to pivot on the first web and apply a reactive force through the second end into the first body such that the pawl is held in a substantially stationary position and prevent the pawl from rotating the star wheel as a result of movement of the first web by the predetermined operational force to thereby retain a current running clearance.