Patent GB-714339-A (GB)
Title: Friction contact type speed changer
IPC: F16H15/44
Filed: 1951-07-16
Abstract: 714,339. Variable-speed gearing. KRAUS, C. E. July 16, 1951 [Jan. 17, 1951], No. 16819/51. Class 80 (2) A torque-responsive continuously-variable change-speed friction gear in which the input torque is maintained at an adjustable value by a hydraulic device is combined, Fig. 6, with a constant-speed toothed epicyclic reverse gear, the output shaft being alternatively driven through forward or reverse hydraulically-operated friction clutches. The change-speed gear, Fig. 1, comprises a number, e.g. sixteen, of non- epicyclic balls 5 which are slidable on axles 14 carried by blocks 15 radially rockable about axial piris 16, the latter being mounted in a ring 17 secured to a stationary housing 18. Casings 7, 11 connected respectively to the driving and driven shafts 9, 13 carry respectively annular inner driving friction races 1, 2 end, outer driven friction races 3, 4, the axial positions of the races being controlled by four sets of torque-responsive wedging sprags 20, 23, Fig. 4, pinned between the races and end walls of the casings 7, 11. The radius of curvature of the races, Fig. 3 (not shown), is greater than that of the balls so' that each race contacts a ball at a point whose distance from the axle 14 is varied by the axial position of the race, i.e. by the amount of wedging action of the torque-responsive sprags 20, 23 which drivably inter-connect the races with their respective casings. The inner driving races 1, 2 have diametrically-opposite axial grooves engaged by a key 28 which is angularly movable in slots in the casing 7 and is secured to a pair of vanes 27 movable relatively to two vanes (not shown) fixed to the casing 7. A pump (not shown) driven by the shaft 9 supplies oil through an inlet 42 to the vanes at a pressure determined by an adjustable relief valve. To adjust the gear for a greater input torque the oil pressure is increased. thereby displacing the vanes 27 and races 1, 2 relatively to the casing 7, this displacement causing the sprags 23 to rock and move the races 1, 2 closer together to increase the speed ratio. In operation if the load should decrease the sprags cause the outer races 3, 4 to move apart and the inner races 1, 2 to move together to increase the speed ratio and thus automatically maintain a constant input torque. Two coil springs housed in circumferential grooves in the races 3, 4 are pinned at one end to the casing 11 and at the other end to the respective race to give a circumferential bias and hence, through the sprags 20, provide a light initial engaging pressure. Where the gear is applied to a vehicle the relief valve may be by-passed by a needle valve which operates to reduce rapidly the oil pressure to prevent stalling if the accelerator is released. Passages are provided in the balls 5, blocks 15, pins 16 and ring 17 for lubrication by the above-mentioned pump, the oil passing from the balls in a fog to lubricate the races 1 ... 4 and the sprags 20, 23. The oil is returned to a sump through a conduit 18i and a fixed relief valve maintains a predetermined pressure. A formula is given for designing the cam surfaces of the sprags so that the contact forces between the balls and races are' kept at a minimum for all positions of the races. ' In the modified change-speed and reverse gear shown in Fig. the friction ball axles 192 are rockably supported at one end on a fixed ring 194 and at the other end on a fixed gear ring 196 providing the reaction for an epicyclic reverse gear. A hydraulic control chamber 185, similar to that of Fig. 1, is supplied from a sump 210 by a pump 208 having an adjustable relief valve 218a to control the input torque. A further pump 209 supplies oil from the sump for lubrication and also for a spring-returned hydraulic piston 163 which is controlled by a slidable valve 165 and is mounted in the output shaft 164. The piston 163 is connected through a rod 172 to the common actuating plate of two clutches 161, 162 which connect the shaft 164 either with the driven casing 197 of the forward change-speed friction gear or with the oppositely-rotating planet carrier 202 of the epicyclic reverse gear whose sun 205 is keyed to an extension of the driving shaft. An adjustable relief valve 228 controlling the pressure in an annular passage 224 feeding both the lubrication system and the piston 163 is by-passed by an adjustable needle valve 236 which controls the speed at which the clutches are disengaged by their springs when the engine is slowed to idling. The rod 237 controlling the valve 165 is manually actuated by a three-position lever (not shown) having a neutral position when both clutches are disengaged. Rods 251 axially movable by a control 248 have tapered ends to provide adjustable stops for pins 252 on the outer friction races so that when the vehicle is driving the engine the displacement of the races may be limited, e.g. to a one-to-one ratio, by adjusting rod 248. In the extreme position of the rod ratchet teeth 255 are engaged to by-pass clutch 161 so that the engine may be started by pushing or rocking the vehicle even though pump 209 is inoperative.