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Title: Fail-safe disc brake having a slack adjuster mechanism
Claims: We claim: 1. A brake actuator for a brake system having a friction element engageable against a rotatable braking surface and comprising: a housing presenting only a single brake control chamber for fluid under pressure; a piston reciprocal within the chamber and having a retracted position, said piston being the only piston for exerting brake forces; a main spring urging the piston forward away from its retracted position; an expansible linkage attached to the piston for imparting the forward translation of the piston to said friction element, said expansible linkage comprising an actuator nut and an actuator screw rotatably supported on the piston and threadedly received within the actuator nut, said actuator screw and nut having threads which lock together in response to forward movement of the piston to prevent rotation relative to one another; fluid pressure means for retracting the piston against the urging of the main spring; and slack adjuster means responsive to piston retraction causing an extension of the linkage to maintain a generally uniform spring expansion per brake application regardless of friction element wear, the last-named means comprising a one-way friction clutch member having a clutch surface effective to tenaciously grip and hold the actuator nut, permitting forward movement while preventing retracting movement of the actuator nut. 2. The actuator of claim 1 wherein the threads of the actuator screw and nut are generally uniform having wide inclined faces presenting friction surfaces and generally upright opposite faces; engagement of the friction surfaces locking the actuator screw and nut together in fixed angular relationship and disengagement thereof allowing generally free rotation therebetween. 3. The actuator of claim 2 further comprising a pre-load spring effective to urge the friction surfaces of the actuator screw and nut into mutual engagement. 4. The actuator of claim 1 further comprising a clutch stop member associated with the housing and cooperative with the clutch member to permit retraction of the actuator nut through a limited brake release distance and prohibit further retraction thereof. 5. The actuator of claim 4 wherein the one-way clutch member is pivotal about a point spaced radially from the actuator nut. 6. The actuator of claim 5 further comprising a clutch member spring urging the one-way clutch into engagement with the actuator nut. 7. The actuator of claim 5 further comprising a manual clutch release mechanism for disengaging the clutch surface from the actuator nut and thereby permitting retraction of the actuator nut. 8. The actuator of claim 1 wherein the expansible linkage further comprises a ball bearing nut slidably fitted within the actuator nut and precluded from rotation relative thereto and a ball screw rotatably carried by the piston and threaded into the ball bearing nut, said ball screw being axially aligned with the actuator screw and interlocked for integral translation and rotation therewith. 9. The actuator of claim 1 wherein the retracted position of the piston is adjustable to provide variations in the main spring compression incident to the retracted position of the piston. 10. The actuator of claim 1 wherein the main spring comprises a disc spring. 11. The actuator of claim 1 further comprising a manual brake release mechanism for manually retracting the piston against the urging of the main spring. 12. The actuator of claim 11 further comprising clutch release means effective to disengage the one-way clutch member in response to actuation of the manual brake release mechanism. 13. The actuator of claim 11 wherein the manual brake release mechanism comprises a release shaft rotatably mounted relative to the housing, a release pinion carried by the release shaft, a release gear encompassing the expansible linkage and driven by the release pinion, and a piston retraction device effective to cause retraction of the piston in response to rotation of the release gear. 14. The actuator of claim 13 wherein the piston retraction device comprises a release cam and a cam follower spider which spread apart in response to release gear rotation thereby engaging the piston and retracting the same. 15. Brake apparatus, for a brake system having a friction element engageable against a rotatable braking surface, comprising a housing, an expandable spring confined within the housing for applying the brake, said housing presenting a single brake control chamber for fluid under pressure, a piston within the housing having a retracted position for holding the spring in a state of compression, said piston being the only piston for exerting brake forces, means to supply fluid under pressure to said chamber for holding the piston in its retracted position, a decline in fluid pressure within said chamber releasing the piston and allowing the spring simultaneously to expand whereupon the piston is forced forwardly away from its retracted position, an expandable linkage for coupling the piston to the friction element such that forward movement of the piston is transmitted to said friction element and retracting movement of the piston elongates the expandable linkage forwardly to compensate for friction element wear, said expandable linkage comprising an actuator nut and an actuator screw attached to the piston, said actuator screw and nut having threads which lock together in response to forward movement of the piston to prevent rotation relative to one another, and a one-way friction clutch member having a clutch surface effective to tenaciously grip and hold the actuator nut, permitting forward movement while preventing retracting movement of the actuator nut. 16. The brake apparatus of claim 15 further comprising a pre-load spring urging the threads of the actuator screw and nut together. 17. The brake apparatus of claim 16 wherein the one-way clutch member is a pivotal member. 18. A disc brake caliper for forcing a brake pad against the braking surface of a rotating disc to restrain rotation thereof, comprising: a housing; an opening through the housing having a cylindrical portion presenting only a single brake control chamber for fluid under pressure; a piston reciprocative within the cylindrical portion and having a retracted position, said piston being the only piston for exerting brake forces; a spring urging the piston forward away from its retracted position; means for supplying fluid under pressure to said chamber to retract the piston against the urging of the spring, a decline in fluid pressure in said chamber releasing the piston and allowing the spring to expand; a back-up plate for supporting a brake pad, said plate overlying one end of the opening and being axially translatable relative thereto; a one-way screw mechanism, coupling the piston to said back-up plate, comprising an actuator nut slidably mounted within said opening for movement in unison with the back-up plate and an actuator screw rotatably carried by the piston and threaded into the actuator nut, and a one-way friction clutch member having a clutch surface tenaciously engageable with the actuator nut to grip and prevent retraction thereof while permitting forward movement thereof; forward movement of the piston causing the one-way screw mechanism to lock-up through the threads and thereby impart such forward motion to the back-up plate; and retraction of the piston causing engagement of the one-way clutch member with the actuator nut as aforesaid and separation of said threads allowing rotational retraction of the actuator screw rearward out of the actuator nut to compensate for brake pad wear, thereby maintaining a generally uniform spring expansion per brake application. Other info: Inventors: Jones, Roger D. (Ramsey, NJ, US) Buchholtz, Charles M. (New York, NY, US) Application Number: 550884 Filing Date: 1975-02-18 Publication_date: 1976-12-07 Assignee: Abex Corporation (New York, NY) Primary Class(es): 188/71.9 188/170, 188/196D Other Classes: US Patent Ref:
Other Refs:
Primary Examiner: Blix, Trygve M. Assistant Examiner: Kazenske, Edward R. Attorney: Kinzer, Plyer, Dorn & McEachran |
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