Patent GB-565814-A (GB)
Title: Improvement in vehicle brakes
IPC: B61H13/20
Filed: 1943-02-04
Abstract: 565,814. Transmitting-mechanism for brakes. SVENSKA AKTIEBOLAGET BROMSREGULATOR, and NILSSON, R. H. Feb. 4, 1943, No. 1897. [Class 103 (i)] In vehicle brake - operating mechanism wherein the fulcrum of a lever is changed at a predetermined position in the brake application stroke to increase the leverage when the brake shoes have been brought into contact with the wheels, the initial fulcrum comprises co-operating abutments carried respectively by the lever and by a support, and one of which is formed as a track upon which the other moves to permit engagement of the lever with the final fulcrum. The final leverage may be varied according to the loading of the vehicle. According to Fig. 1, which shows variable-leverage mechanism such as described in Canadian Specification 386,889, the lever 5 is pivoted to the operating piston-rod 3 at 4 and at 6 to the rod 7 connected to the brakes and it is guided by a link 33 connected to the pivot 4 and to a fixed pivot 32. The initial fulcrum of the lever is provided by an abutment in the form of a track 29, 31 having a bend at 30 and with which engages a roller 21 on a lever 22 pivoted at 23 on the lever 5. The other end of the lever 22 is normally held against an abutment 26 on the lever 5 by a spring 27. The abutment 29, 31 is carried by a fixed arm 28 on the frame member 11. The final fulcrum for the lever 5 comprises an abutment 8 pivoted in a block 9 slidable vertically on the member 11 and normally held in the lower position shown by the roller 21 acting through a lever 12, 14, 20 mounted on a fixed pivot 13 and connected to a two-part rod 15, 16 having an interposed spring 17. The other end of the rod 16 is connected to a normally fixed arm. In operation, the lever 5 having during its initial movement, fulcrumed about the track 29, the roller 21 reaches the bend 30 and traverses the track 31 while the lever moves further to contact the abutment 8 without further substantial displacement of the rod 7. Movement of the roller to the bend 30 permits movement of the lever 12, 20 by the spring 17, to slide the block 9 to its upper and effective position, this position and thus the final leverage being determined by the position of the rod 16, the end of which acts as a stop to the rod 15. The other end of the rod 16 is connected to a pivoted arm, the position of which and thus of the rod is adjusted by hand or automatically in accordance with the loading of the vehicle. An automatic slack-adjuster of the doubleacting type is preferably provided to maintain the correct brake-shoe clearance at release, but if such adjuster is not provided and should the clearance be too small so that the shoes contact the wheels while the roller is on the track 31, undue stresses which might arise in the parts are avoided by the spring 27 which permits the roller to yield. Fig. 4 shows the application of the invention to variable leverage mechanism of the type described in U.S.A. Specification 1,898,528, and comprising a floating lever 5 connected to the piston-rod 3, a lever 40 pivoted on the cylinder 1 and links 42, 43 connecting lever 40 to an auxiliary lever 41. The other parts shown correspond to parts bearing the same reference numerals in Fig. 1, the parts 8a, 29, 31, 12, 20, 24a, 33 being mounted on the triangular arm 28 of the lever 41 instead of on a fixed support as in Fig. 1, and the rod 15 being directly connected to abutment 8a. The track abutment 29, 31'may be provided on the lever 5 instead of upon the support 28.