Patent GB-1451327-A (GB)
Title: Brake actuator mechanisms provided with automatic slack adjusters
IPC: F16D65/14
Filed: 1973-02-23
Abstract: 1451327 Brake actuators and slack adjusters; disc brakes GIRLING Ltd 21 Feb 1974 [23 Feb 1973] 8868/73 Heading F2E In an actuator mechanism for a vehicle braking system comprising an hydraulic actuator 15, 17, Fig. 1, an auxiliary mechanical actuator 27, 28, 29, 30, 36, and an automatic slack adjuster 25 operative between one, 17, of two components of the hydraulic actuator and the mechanical actuator, which is fitted to the other hydraulic actuator component, 15, the hydraulic actuator components being movable apart to apply an associated brake 12, 13 by fluid pressure applied between the components, the mechanical actuator is in the form of a reversible face cam as defined in the Specification aligned with the hydraulic actuator axis and comprising first and second cam members, 27, 29 respectively, having co-operative helicallyinclined surfaces thereon, the first cam member 27 being part of or, as shown, journalled in, the "other" hydraulic actuator component 15, one of the cam members (27, as shown) being turnable for mechanical actuation of the brake, and the slack adjuster comprises a first non-rotatable adjuster member 17 and a second rotatable adjuster member 24 in screwthreaded engagement therewith at 26, the first adjuster member being disposed to be axially abutted by or, as shown, being part of, the "one" hydraulic actuator component 17, the second adjuster member 24 being disposed to be axially abutted by the second cam member 29, and means being provided to enable the second cam member 29 to turn the second adjuster member 24 in one direction upon hydraulic operation when adjustment is required, but not in the opposite direction. On hydraulic operation, after brake-lining wear, member or strut 24 is drawn by piston 17 away from cam disc 29 until slotted flange 43 encounters and entrains slidable collar 41 and through it compresses spring 45. Fingers 42 of collar 41 (engaging the flange slots) moving to the right, are followed by cam disc 29, which is forced rightwards and rotated by torsion spring 44. Collar 41 is prevented from turning because thread connection 26 is under load. On brake release, brake retraction forces urge piston 17 and strut 24 to the left, thereby permitting spring 45 to urge collar 41 against cam disc 29 and in turn moving cam disc 29 towards cam disc 27 against the force of spring 44. Cam disc 29 is thereby rotated in the opposite direction to the previous direction (i.e. counter-clockwise as seen from the left), and because of the friction developed between fingers 42 and cam disc 29 under the force of spring 45, collar 41 and strut 24 are also rotated, strut 24 thereby being slightly unscrewed from piston 17 in the absence of axial load at screwthread connection 26. In Fig. 4 (not shown) the strut incorporates a spring-loaded piston to prevent over-adjustment on heavy braking. Fig. 6 (not shown) also has provision for preventing such over-adjustment; the normal adjustment mechanism includes a one-way pawl-and-ratchet between a cam disc equivalent to 29 and strut 24.