Patent GB-689876-A (GB)
Title: Improvements in or relating to slack adjusters for vehicle brakes and the like
IPC: F16D65/28
Filed: 1951-06-25
Abstract: 689,876. Brake slack adjusting mechanism. BENDIX-WESTINGHOUSE AUTOMOTIVE AIR BRAKE CO. June 25, 1951 [July 12, 1950], No. 15065/51. Class 103 (i). The invention comprises an improved method of automatic fluid-pressure operation for slack adjusting devices for vehicle brakes, of the kind comprising a worm 28. which is mounted on an arm 20 of the brake rigging linked to the brake actuator cylinder 10 and engages a wormwheel 22 rotatable with a shaft 24 coupled to the brake-applying transmission, the worm 28 being rotated one way or the other to increase or decrease the slack. As shown in Fig. 2, the worm shaft 26 may be rotated by an arm 42 to the end of which is pivotally connected a rod 40 from a piston 34 in a cylinder 32, the piston normally being maintained centrally in the cylinderby opposed springs 36 and 38 but being adapted to be moved one way or the other by fluid-pressure supplied at connections 65 or 66. A smaller adjacent cylinder 58 has a piston 60, normally maintained in the position shown by a spring 56, but which may be operated by fluid-pressure supplied at connection 64 to move a lever 48 pivoted on lever 42 so as to change over ratchet pawls 52 or 54, each of which is effective for a particular direction of rotation of the arm 42. Mounted on the rod 14 coupling the actuating cylinder 10 to the arm 20 is a cam device 90 having upper and lower cam slopes 94 and 116 operative to produce an automatic decrease or increase in slack, respectively. The mechanism being shown in the brakes released condition, a decrease in slack when necessary takes place as follows. If the slack is excessive the rod 14 in being moved to apply the brakes will carry with it the member 90 for a distance exceeding the flat surface 88 so that the slope 94 causes a valve spindle 80 to be moved upwardly. This causes the upper part of the spindle to engage a valve 72, thus closing off an exhaust outlet 82, 84, 76 and opening a valve 70 controlling a pressure supply from the main brake cylinder supply line by way of pipe 78 and a one-way valve 96. Pressure is thus supplied by pipe 65 to the left side of piston 34 of cylinder 32. No pressure is supplied to ratchet-operating piston 60, the extended condition of spring 56 corresponding to an engagement of pawl 54 being effective to produce a clockwise rotation of shaft 26 by lever 42. No adjustment of the slack can in fact take place until the brake shoes are released from engagement, whereupon the piston 34 is moved to the right. Although release of the brakes allows the 'spindle 80 to fall, re-opening the exhaust path 82, 84, 76, the size of the outlet 76 in combination with the one-way valve 96 is, however, such as to cause a residual pressure in the cylinder 32 sufficient to bring about the slack decreasing movement. When this pressure has been deposited, the springs 36, 38 return the piston 34 to central position. If the amount of slack is insufficient, increase will take place as follows. Due to the small amount of slack, the slope 116 on the cam member 90 will not have engaged the end of the valve spindle 106 when the brakes are fully applied. Pressure will therefore be supplied by pipe 110, open valve 100 and pipe 64, to ratchet-adjusting cylinder 58 and by pipe 66 to the right-hand side of piston 34 in cylinder 32. No increase in slack will, however, take place until the brake shoes are released, but when this occurs sufficient residual pressure is maintained to the right of piston 34 to be effective as a result of the restriction 108 at the connection of pipe 110 with the valve device 98. It should be noted that during a normal brake application, the engagement of cam slope 116 on the end of valve spindle 106 causes a closing of the valve 100 and an opening of the exhaust valve 102 which renders the cylinders 32 and 58 ineffective as far as a slack increasing operation is concerned.