Patent GB-1487654-A (GB)
Title: Infinitely variable drive ratio hydromechanical transmission for vehicles or the like
IPC: B60K17/10
Filed: 1975-01-30
Abstract: 1487654 Hydromechanical variable-ratio gear CATERPILLAR TRACTOR CO 30 Jan 1975 [1 Feb 1974] 4164/75 Heading F2D  A hydromechanical transmission comprises an input shaft 29 coupled through epicyclic gearing 33, 34 and 36 to two transfer gears 19 and 24, variable delivery hydrostatic fluid transmitting devices 53 and 54, interconnected by pipes 58, and coupled to transfer gears 22 and 27 respectively and further epicyclic gearing 46 coupling two input transfer gears 21 and 26 to an output gear 31 of the transmission, an idler gear 23 interconnecting transfer gears 19, 22 and 21 and an idler gear 28 interconnecting transfer gears 24, 27 and 26, the transmission providing two forward and two reverse ranges with variation of hydrostatic devices 53 and 54 providing infinite variation in each range. In forward drive the lowest gear ratio (for maximum output speed) is obtained with a clutch 43 engaged, interconnecting ring gears 33R and 34R of epicyclic gears 33 and 34, the ring gear 33R rotating with the planet carrier of epicyclic gear 36, and with a brake 52 engaged to lock the ring gear 46R of epicyclic gear 46, other brakes 39 and 44 and clutch 51 being disengaged. The hydrostatic device 53 is at maximum displacement and device 54 is at zero displacement, which results in a stall condition with gear 22 stationary and so output gear 31 is stationary. Output speed is increased by increasing the displacement of hydrostatic device 54 and reducing that of device 53, the epicyclic gearing 33, 34 and 36 dividing the input from shaft 29 between two paths 61 and 62, through transfer gears 19 and 24 respectively and the hydrostatic devices 53 and 54 controlling the relative rates of rotation of gears 19 and 24 through gears 22 and 27 to control the proportion which passes along a path 63, through epicyclic gear 46 to the output gear 31. The maximum speed in the low gear is obtained with device 54 at maximum displacement and device 53 at zero displacement, which causes gear 27 to be stationary so that all the power passes through paths 61 and 63. The higher gear can now be selected by disengagement of brake 52 and engagement of clutch 51, both of these being stationary, and a continued increase in output speed (for a constant input speed) is obtained by decreasing the displacement of device 54 and increasing that of device 53, the power being divided along paths 61, 63 and 62, 64 to rotate the sun and ring gears respectively of epicyclic gear 46. The highest forward speed is obtained with device 53 at maximum displacement, device 54 at zero displacement and all the power passing along paths 62 and 63, with gears 19, 22 and 21 stationary. Low reverse gear is selected by engagement of brakes 39 and 52, clutches 43 and 51 and brake 44 being disengaged, and, as with forward gear, device 53 is reduced from its maximum displacement and device 54 increased from zero displacement to increase output speed, assuming a constant input speed, until device 54 is at its maximum, device 53 at zero displacement, gears 24, 26 and 27 are stationary, and the higher gear can be selected by engaging brake 44 and clutch 51 and disengaging brake 52. Speed is further increased by increasing the displacement of device 53 and reducing that of device 54.