Patent GB-980881-A (GB)
Title: Improvements in automatic slack adjusters for brakes
Inventor: SOBOL WOLDIMAR
IPC: B61H15/00
Filed: 1962-02-15
Abstract: 980,881. Automatic slack adjusters for brakes; friction clutches. WESTINGHOUSE BRAKE & SIGNAL CO. Ltd. Jan. 11, 1963 [Feb. 15, 1962], No. 5834/62. Headings F2C and F2E. In an automatic slack adjuster for vehicle brakes, first (1) and second (23) members are movable telescopically relative to each other to effect slack adjustment, the first member 1 being provided with a screw threaded portion threadedly engaged by first (48) and second (43) nuts, displacement of which on the screw threaded portion effects relative telescoping of the two members, a sensing member formed by a casing 26 and end plates 24 and 49 is located axially on the second member 23 and mounted for movement therewith towards a stop bracket 19 and compression of a strong spring 16 before the sensing member engages the stop permits the axial displacement by spinning of the two nuts 48, 43 on the first member 1 to move the members relative one to the other by axial movement of the second member only for as long as the sensing member does not engage the stop. Normal brake clearance.-Immediately a brake application commences by energization of a brake cylinder 63 (Fig. 2) a tubular pull rod 23 forming the second member starts to move to the right and the pull rod 23 carries with it a load transmitting ring 14 and a pull rod collar 8. A clutch e-e is disengaged and a clutch d-d engages such as to continue to prevent rotation of the load transmitting nut 43 due to the fact that a strong release spring 12 is not compressed and serves to maintain a housing 32 solid with the pull rod 23 by holding a plate 13 into engagement with the load transmitting ring 14 secured to the pull rod 23. Continuing movement of the pull rod 23 pulls the spindle 1 to the right and the load transmission nut 43 which, being prevented from rotation by engagement of the clutch d-d, is therefore not free to spin down the spindle 1 and pulls the spindle 1 with it. Should the resistance to movement of the rigging between the slack adjuster SA and the brake blocks 66 (Fig. 2) be insufficient to compress the main spring 16, the spindle 1 will still be moved to the right by movement of the pull-rod 23. At the moment at which the brake blocks 66 engage the wheel 67 the spring 16 is compressed by an amount sufficient to disengage the clutch e-e and prevent rotation of the load transmitting nut 43, by engagement of the clutch d-d. In the case of normal clearance such engagement by the brake blocks 66 will occur at the instant when a clutch k-k between the front end plate 24 of the sensing member and a fixed stop member 19 is engaged (the distance " N " corresponding to the distance " n " between the shoes 66 and the wheel 67. Once the brake blocks 66 engage the wheel 67, further movement of the brake cylinder rod will be resisted with an increasing force as pressure in the brake cylinder 63 increases. Increased force soon increases to a value sufficient to compress the release spring 12, the right-hand end of the spring 12 being held by the spindle 1 through the nut 43, the housing 32 and the stop plate 13, and the left-hand end tending to be moved to the right by the end bush 8 of the pull rod 23, the thrust race 10 and the extension 33 of the coupling bush 36. Thus the pull rod 23 will start to move to the right independently of the spindle 1 against the force exerted by the release spring 12 and by virtue of the load transmitting ring 14 being secured to it, the ring 14 will be moved to the right to disengage a clutch f-f. Disengagement of this clutch frees the mechanism of the slack adjuster for rotation but rotation will not occur by the engagement of the clutch k-k between the front end plate 24 and the stop bracket 19. During the compression of the spring 12 the coupling bush 36 will have moved to the right relative to the housing 32 and this relative movement of the bush 36 carries with it the coupling ring 7 the annular inclined face of which is engaged by balls 38 and the latter are forced outwardly against an encircling split ring 37 which is radially expanded to engage the stretched control tube 28. After the brake blocks 66 have engaged the wheel 67, any increase of force exerted by the brake cylinder 63 causes the brake blocks 66 to be applied with increasing effort. In order to avoid stretching of the brake rigging affecting the setting of the slack adjuster means is provided for permitting the slack adjuster to react to and compensate for this stretching without the setting of the slack adjuster being effected. Such movement of the various parts of the slack adjuster will continue all the time the ring stretches, the relative spacing between the two nuts 43 and 48 always being preserved by reason of a spacer member 4 until finally the force exerted by the brake cylinder 63 reaches its maximum and the brake blocks 66 are fully applied. Excessive brake clearance.-When this occurs the clearance between the front end plate 24 of the operating member and the stop bracket 19 will still be " N " but the clearance between the brake blocks 66 and the wheel 67 will be greater than " n." The various parts of the slack adjuster will be as shown in Fig. 1 as in the case of normal brake clearance. Upon the commencement of a brake application, the same operations occur as in the ease of " normal " brake clearance, but in this case when the front end plate 24 of the sensing member abuts the stop bracket 19 to engage the clutch k-k due to the brake clearance being excessive, the brake blocks 66 will not yet have engaged the wheels 67. Continued brake application will not exert sufficient force to overcome and compress the release spring 12. Consequently, no relative movement will occur between the bush 36 and the housing 32 and the expanding clutch 7, 37, 38 will not be operated to cause engagement of the split ring 37 with the stretch control tube 28. The sensing member 26, 24, 49 is also prevented from rotation and axial movement to the right by engagement of the clutch k-k, the pull rod 23 and the spindle 1 locked to it through the housing 32 and the low transmitting nut 43 will be pulled to the right through the casing 26 against the effort of the main spring 16 which will be compressed. As the spindle 1 moves to the right it will tend to carry with it the rod and nut 48 which is resiliently prevented from travelling with the spindle 1 by the spacer 4 acted upon by the return spring 17 of the tube 28 and the thrust bearing 47. The tendency for the nut 48 to be moved to the right by the movement of the spindle 1 relieves the pressure on the clutch a-a and the nut 48 spins to permit the spindle 1 to be drawn through it. The low transmitting nut 43 locked to the spindle 1 by the force required to move the brake ring passing through the clutch d-d travels with the spindle 1. The spacing between the two nuts 43 and 48 now starts to increase and the nut 43 will have moved away from the spacer 4. The separation of the nuts 43 and 48 continues until the brake blocks 66 engage the wheel 67 whereupon further application of the brakes generate sufficient force to compress the release spring 12. This causes displacement of the bush 36 and the housing 32 to expand the expanding clutch to cause the tube 28 to be engaged by the split ring 37. At this point in the brake application the separation of the nuts 43 and 48 will have increased by an amount corresponding to the excessive brake clearance. From this point the remainder of the brake application proceeds as in the case of the normal brake " clearance." That is to say that the brake ring will stretch as the brakes are applied with increasing pressure but this stretch will not affect the relative position of the nuts 43 and 48 on the spindle 1 as the stretch control tube 28 has been engaged by expansion of the expanding clutch by means of which the tube 28 will be carried along with the spindle 1 and the pull rod 23 against the effort of the return spring 17. Such movement of the tube 28 carries with it spacer 4 which permits the rider nut 48 to be carried to the right by the spindle 1 the braking pressure can now be increased to the maximum without disturbing the relative positions of the nuts 43 and 48 on the spindle 1. Manual adjustment.-Manual adjustment is provided for in the slack adjuster of Fig. 1 by inserting a tommy bar into recesses in the front end plate 24 and rotating the casing 26. An alternative embodiment is disclosed in the Provisional Specification wherein the stop bracket 19 merely provides an abutment for the front end plate 24 and the adjacent faces of these two parts do not constitute a clutch as they do in Fig. 1. Further, the load transmitting nut 43 is provided with another thrust bearing located on its left-hand end. The spring support 15 in this case does not provide the clutch h-h which slips in manual adjustment. Specification 980,582 is referred to.