Drum brake adjuster

Abstract

A drum brake adjustment mechanism is provided to maintain a running clearance between a pair of brake shoes and a rotatable member. The adjustment mechanism includes an extendible member which is disposed between the pair of brake shoes and engageable with a pawl which is pivotally mounted on one of the brake shoes. A .Iadd.single .Iaddend.resilient member encircles the extendible member and engages the other brake shoe and the pawl to bias the pair of brake shoes into engagement with a hydraulic actuator which is operable to urge the pair of brake shoes into engagement with the rotatable member. .[.Moreover, the.]. .Iadd.The single .Iaddend.resilient member cooperates with the pawl to extend the .[.extensible.]. .Iadd.extendible .Iaddend.member when the clearance between the pair of brake shoes and the rotatable member is greater than the running clearance. .Iadd.The pawl defines an arm in abutment with the extendible member and the single resilient member engages the pawl between the abutment and the pivotal mounting to bias the extendible member toward the other brake shoe. .Iaddend.

I claim: 
     
       1. An adjustment mechanism for a drum brake having a hydraulic actuator cooperating with a pair of brake shoes to urge the latter into engagement with a rotatable member for effectuating braking, said adjustment mechanism comprising: an extendible member engaging the pair of brake shoes, said extendible member being extendible to dispose the pair of brake shoes adjacent but slightly spaced from the rotatable member;   a pawl pivotally mounted on one of the brake shoes, said pawl engaging said extendible member to provide for extension of the extendible member when the pawl pivots relative to the one brake shoe; and   a resilient member extending from the other brake shoe to said pawl, said resilient member cooperating with the one brake shoe via the pivotal mounting with said pawl and the other brake shoe to bias the pair of brake shoes into engagement with the hydraulic actuator .[.and.]..Iadd., .Iaddend.said resilient member .[.also.]. cooperating with said pawl to pivot said pawl relative to the one brake shoe, .Iadd.and said resilient member also cooperating with said pawl to bias said pawl into abutting engagement with said extendible member to bias said extendible member away from the one brake shoe and into engagement with the other brake shoe and said pawl being pivoted about the abutting engagement with said extendible member by said resilient member in order to retract the one brake shoe away from the rotatable member upon termination of braking. .Iaddend. .[.2. The adjustment mechanism of claim 1 in which said resilient member surrounds said extendible member between the other brake shoe and said pawl..]. .[.3. The adjustment mechanism of claim 1 in which said resilient member cooperates with said pawl to bias said extendible member away from the one brake shoe and into engagement with the other brake shoe when said pawl is pivoting relative to the one brake shoe..].  .[.4. The adjustment mechanism of claim 1 in which said resilient member cooperates with said pawl to maintain said extendible member in engagement with the other brake shoe when the pair of brake shoes expand to engage the rotatable   
     
     
        member..]. 5. An adjustment mechanism for a drum brake having a hydraulic actuator cooperating with a pair of brake shoes to urge the latter into engagement with a rotatable member during braking, said adjustment mechanism comprising: an extendible member carried by the pair of brake shoes, said extendible member being extendible to dispose the pair of brake shoes adjacent but slightly spaced from the rotatable member;   a resilient member cooperating with the pair of brake shoes to urge the latter into engagement with the hydraulic actuator; and   a pawl pivotally mounted on one of the pair of brake shoes and cooperating with said resilient member to pivot relative to the one brake shoe, said pawl including a first arm engaging said extendible member and a second arm engaging said extendible member, said first arm cooperating with said extendible member to provide for extension of the latter and said second arm cooperating with said resilient member to move said extendible member away from the one brake shoe when said pawl pivots relative to the one brake shoe.Iadd., and said resilient member engaging said pawl between the pivotal mounting and said second arm.Iaddend..  .[.6. The adjustment mechanism of claim 5 in which said resilient member engages the other brake shoe and said pawl, said resilient member coiling around said extendible member and biasing the latter into engagement with the other brake shoe such that said extendible member moves with the other brake shoe when the pair of brake shoes are expanded into engagement with the rotatable member..].  .[.7. In a drum brake assembly having a hydraulic actuator for urging a pair of brake shoes into engagement with a rotatable member during braking and an extendible member for adjusting the clearance between the rotatable member and the pair of brake shoes, the improvement wherein a pawl pivots relative to one of said pair of brake shoes and engages the extendible member and a single resilient member cooperates with the pawl to provide for extension of the extendible member when the clearance between the pair of brake shoes and the rotatable member is above a predetermined value and said single resilient member also cooperates with said extendible member and said pawl to urge the pair of   
     
     
        brake shoes into engagement with the hydraulic actuator..]. 8. In a drum brake assembly having a hydraulic actuator for urging a pair of brake shoes into engagement with a rotatable member during .Iadd.braking .Iaddend.and an extendible member for adjusting the clearance between the rotatable member and the pair of brake shoes, the improvement wherein a pawl engages the extendible member and a single resilient member cooperates with the pawl to provide for extension of the extendible member when the clearance between the pair of brake shoes and the rotatable member is above a predetermined value, said single resilient member also cooperating with said extendible member and said pawl to urge the pair of brake shoes into engagement with the hydraulic actuator, said pawl being pivotally mounted on one of the brake shoes and being in abutment with the extendible member, said single resilient member engaging said pawl between the pivotal mounting and the abutment with the extendible member such that said pawl is pivoted about the abutment by said single resilient member to urge the one brake shoe into engagement with the hydraulic actuator via 
     
     
        the pivotal mounting. .Iadd.9.  In a drum brake assembly, the combination of a pair of brake shoes engageable with a rotatable member during a service brake application, a hydraulic actuator engageable with the pair of brake shoes to move the latter from a non braking position to a braking position in engagement with the rotatable member, a backing plate carrying the hydraulic actuator and defining an abutment to pivotally anchor the pair of brake shoes on the backing plate, an extendible assembly engageable with the pair of brake shoes and cooperating with the latter to substantially maintain a predetermined clearance with the rotatable member, one of the pair of brake shoes including a pin disposed on the one brake shoe between the engagement of the one brake shoe with the actuator and extendible assembly, a parking lever pivotally anchored on the pin and cooperating with the extendible assembly to move the pair of brake shoes to a braking position during a parking brake application, a pawl cooperating with the extendible assembly to increase the length thereof in response to the clearance between the rotatable member and the pair of brake shoes exceeding the predetermined clearance, the pawl pivoting relative to the one brake shoe via the pin and including a first arm engaging the extendible assembly to control extension thereof and a second arm in abutting engagement with the extendible assembly, and a single resilient member extending from the other brake shoe to the pawl, the single resilient member engaging the pawl at an intermediate location between the pin and the second arm to bias the extendible assembly via the pawl toward the other brake shoe and also to bias the one brake shoe via 
     
     
        the pawl to its non braking position. .Iaddend. .Iadd.10.  A drum brake assembly including a pair of brake shoes which are movably carried on a backing plate, a hydraulic actuator cooperating with the pair of brake shoes to move the latter from a non-braking position to a braking position in engagement with the drum during a service brake application, the backing plate including an anchor assembly about which the pair of brake shoes pivot during the service brake application, an extendible assembly engageable with the pair of brake shoes to substantially define the non-braking position, a pawl pivotally mounted on one of the pair of brake shoes, the pawl defining a first arm cooperating with the extendible assembly to control extension thereof and a second arm in abutment with the extendible assembly, the extendible assembly substantially maintaining a predetermined clearance between the pair of brake shoes and the drum, and a retraction and adjustment spring cooperating with the pair of brake shoes to retract the latter to the non-braking position upon termination of the service brake application, the improvement wherein the retraction and adjustment spring extends from the other brake shoe to the pawl, the retraction and adjustment spring engaging the pawl to pivot the latter about its abutment with the extendible assembly upon termination of the service brake application so that the one brake shoe is retracted to its nonbraking position as a result of the pawl pivoting about its abutment with the extendible assembly, the retraction and adjustment spring also pivoting the pawl about its abutment with the extendible assembly whereby the first arm of the pawl cooperates with the extendible assembly to extend the latter when the clearance between the pair of brake shoes and the drum is greater than the predetermined amount. .Iaddend. .Iadd.11. The drum brake assembly of claim 10 in which the retraction and adjustment spring is engageable with the pawl at an intermediate position on the pawl between the abutment with the extendible assembly and the pivotal mounting on the one brake shoe. .Iaddend. .Iadd.12. The drum brake assembly of claim 10 in which the retraction and adjustment spring is also engaging the other brake shoe such that the engagement of the retraction and adjustment spring with the pawl and the other brake shoe biases the pawl to urge the extendible member toward the other brake shoe which is in engagement with the retraction and adjustment spring. .Iaddend. .Iadd.13. The drum brake assembly of claim 10 in which the retraction and adjustment spring, upon termination of braking, simultaneously retracts the pair of brake shoes to the non-braking position and also cooperates with the pawl to extend the extendible member when the clearance between the pair of brake shoes and the drum is greater than the predetermined amount. .Iaddend.