Patent GB-868736-A (GB)
Title: A variable speed power transmission device
IPC: B62M11/10
Filed: 1958-11-12
Abstract: 868,736. Variable-speed ratchet gear; changespeed control. USTAV PRO VYZKUM MOTOROVYCH VOZIDEL. Nov. 12, 1958 [Nov. 16, 1957], No. 36364/58. Class 80 (2). [Also in Group XXXI] In variable-speed ratchet gearing, driving eccentrics, cams or cranks are operatively connected to ratchets on the driven shaft by means of chains or flexible bands. As shown in Fig. 1 a driving crankshaft 1 has two cranks 2 (only one being shown) disposed at 180 degrees, over each crank roller 2a of which passes a chain 3 which is secured at one end to a pin 4 on an adjustable support 5, passes round a sprocket 10 forming the driving part of a ratchet on a driven shaft 12, and is secured at its other end to a band 13 which passes round a spring-mounted roller 15 and is secured at its far end to the other chain. The support 5 is formed with a toothed sector 6a engaged by a worm 6 rotatable to adjust the support 5 and hence vary the gear ratio. Worm 6 is pivotable about a pivot 9 and can be raised out of mesh with the toothed sector, whereupon the tension in chains 3, due to springs 17 of the roller 15, moves the support 5 anticlockwise to its neutral position in which the rollers 2a do not contact the chains in any position. In the embodiment of Figs. 3, 4, 5 two eccentrics 2, 180 degrees out of phase, each engage a rigid contact piece 3a fixed to a band 3 fixed to a driving part 10 of a ratchet on a driven shaft 12, the contact piece 3a being pivoted at 4 to an adjustable support 5. The contact piece is urged towards the eccentric by a spring 14 which gives the driving part 10 its return movement. The gear ratio is varied, as before, by means of a sector 6a and worm 6, but worm 6 carries a worm-wheel 22 engaging a worm 23 on a shaft 24 which also carries a sprocket 25 and a gear 26. Sprocket 25 engages, through a chain, a sprocket 27 fast with a driven part of a double clutch, and gear 26 meshes a gear 28 fast with the second driven part of the double clutch, the driving part of which rotates with the driving shaft 1 and which can be moved to selectively engage the driven parts either manually, through a shift collar 30, or automatically by a centrifugal governor 29 driven by the shaft 1, so that the rear ratio is changed manually or automatically. The ratchet gearing forms part of a transmission having an input shaft 34 carrying a double dog clutch member 36 movable to the left to drive a gear 37 which drives the shaft 1, and movable to the right to engage shaft 12 for direct drive. With gear 37 clutched to the input shaft, a gear 39 on the shaft 1 may be engaged with a gear 40 on the driven shaft 12 to give enforced low and engine braking; a double dog clutch member 41 on an output shaft 12a is normally in a left-hand position clutching shaft 12 to the output shaft 12a, but is movable to the right and a bevel pinion 42 simultaneously movable to engage bevel teeth on gear 40 and clutch member 41 to give reverse drive. Worm 6 pivots about the shaft 24 so as to disengage the adjustable support 5 which is thereupon moved to its neutral position due to the spring 14. This disengagement occurs on engaging direct drive and enforced low and on hard application of the vehicle brakes, by means of push members acting on rollers 21. In the embodiment of Fig. 14 the driving shaft is the engine crank shaft and rollers 2a on the piston con-rods engage contact pieces 3a of the ratchet gear. A chain or belt 3 is connected to one end of the contact piece which is pivoted at 4 to an adjustable sector 6a meshing a worm 6. Worm 6 is rotated by a second wormwheel and worm which is rotated by a pneumatic, hydraulic or electric motor 50 controlled manually and/or automatically. Three such ratchet gears may be provided in a transmission for a tracked vehicle, Fig. 16, one gear A being the main change-speed gear and interconnecting driving and driven shafts 1, 12, the other gears B, C being used during steering of the vehicle. A bevel pinion 65 on the shaft 12 meshes bevel gears 56, 58 alternatively clutchable to a shaft 59 to give forward and reverse. Shaft 59 is connected by dog clutches 61 to half shafts 1b fast with sprockets 64 driving the vehicle tracks. The shafts 1b are connected by the ratchet gears B, C to a shaft 12b which is connected by gears 62, 57 to the bevel pinion 56. When running straight ahead both clutches 61 are engaged and the gears B, C are set in neutral or a lower ratio than that of gears 57, 62. For turning to the right, say, the right-hand clutch 61 is disengaged and the right-hand ratchet gear set to a high ratio. The right-hand track is driven due to the vehicle's momentum and drives the righthand shaft 1b which therefore drives the shaft 12b faster than it is driven from the shaft 59. Shaft 12b therefore drives the shaft 59 and thus helps to drive the left-hand sprocket 64. In the embodiment of Fig. 17, which is for a bicycle, eccentrics 2 driven by the pedals engage contact pieces 3a connected to chains 3 driving the driving parts 10 of the ratchets which are formed as sprockets, the chains 3 being interconnected by a cable 13 passing round a spring- mounted roller 15. The contact pieces 3a are pivoted to a support 5 which is pivoted at 18 to the frame and is adjustable by a screw 6 and nut 6a. Alternatively support 5 may be adjusted by means of a cable fixed to a pulley having a ratchet or dog clutch arrangement so as to be held in various positions. In all the embodiments the adjusting means may carry means indicating the gear ratio. Ratchets.-The ratchets, Fig. 7, may comprise driving members 10 rotatably mounted on a driven shaft 12 on either side of a driven ratchet member 11. Each driving member is formed with a screw-threaded hub on which is mounted a ratchet member 10a which is screwed into engagement with the driven ratchet member for one direction of rotation of the driving member. The co-operating faces of members 10a, 11 are suitably toothed, and the members 10a may be subject to continuous light braking to assist engagement and disengagement.