Patent GB-341161-A (GB)
Title: Improvements in, and relating to, means for automatically retarding the speed of pit tubs and like railway vehicles and for automatically releasing them thereafter
IPC: B61K7/22
Filed: 1929-11-02
Abstract: 341,161. Brakes for pit tubs &c. SHEPPARD, H. B., 6, The Strand, Derby. Nov. 2, 1929, No. 33436. [Class 103 (i).] Apparatus for automatically retarding pit tubs and for automatically releasing them thereafter comprises a cylinder a, Fig. 2 [Provisional Specification Drawings] located in the rail track, the piston rod of which is provided with a mounting c slidable in guides c<1> and carrying a revolvable star wheel d with which the vehicle axles contact. The first axle of the vehicle partly rotates the star wheel and the second axle further rotates it to a rigid position whereupon the star wheel is longitudinally advanced by the moving vehicle until compression set up in the cylinder creates a retarding effect and at or near the end of the stroke of the piston the star wheel is freed for further rotation to allow the vehicle to pass and to reset the star wheel, the piston returning due to compression in the cylinder and retracting the star wheel to reset position. The first axle of the vehicle turns the arm s of the star wheel to bring the arm t in front of the second axle which turns the wheel until a pawl f on the mounting c engages one of two slots h in a cam e fixed to the star wheel which is thus held rigidly. The vehicle now takes the star wheel along with it. At the end of the stroke of the piston there is a rebound action caused by the air resistance at the front and the vacuum at the rear of the piston, which brings a pawl k mounted on an extension of the pawl f into engagement with a rack m between the guides c<1> and thereby raises the pawl f from engagement with the slot h. The star wheel is now free to rotate and the pawl f, having ridden along the cam e and being tilted thereby the pawl k is raised from engagement with the rack and is withdrawn by the spring p and the piston retracts the star wheel and the device resumes the normal set position. In the event of heavy vehicles where rebound action would be small the rack is adapted to be moved by an auxiliary cylinder controlled by hand or automatically by the tub. The rack is slidable on runwavs of such a contour that it is first thrust against the pawl k to release the pawlf and subsequently falls to release the pawl k. The rack is retracted by a spring in the auxiliary cylinder. As a further alternative the pawl f is formed with a face 3 adapted to engage a stop at the end of the stroke and thereby release the pawl f, the cam e and the spring p subsequently releasing the pawl k. Where compressed air is used in front of the piston a check valve is provided to prevent return of compressed air to the source of supply when compression is set up. Leakage passed the piston can escape by a relief valve in the return stroke. This leakage is made up by passage of air past an adjustable valve. A weight may be suspended by a wire rope &c. from the mounting c to assist the return stroke. In another modification the crosshead c, Fig. 1 [Complete Specification Drawings] is forked and the cam e is between the forks and a star wheel d on each side of the forks. A depending arm 11 on the pawl 8 is adapted to run idly over hanging ratchet teeth 12 on the first stroke, the rebound action at the end of the stroke bringing the arm 11 into reverse contact with one of the teeth which is restrained by a stop 13 and thus releases the pawl f from the slot h in the cam e. For heavy vehicles a pawl 14 is also provided connected by a rod 16 to the arm 11 and adapted to engage a stop at the end of the first stroke and release the pawl 8.