Patent GB-1092316-A (GB)
Title: Continuously variable power transmission
IPC: F16H47/04
Filed: 1965-08-23
Abstract: 1,092,316. Hydro-mechanical variable-speed gear. G. M. DELALIO. Aug. 23, 1965, No. 36014/65. Headings F2C and F2D. A combined epicyclic and swashplate hydrostatic gear, particularly for buses, delivery vehicles, tractors and earth movers, comprises two rotatable cylinder barrels I, II connected in closed hydraulic circuit and having adjustable angle swash-plates in non-rotatable housings, and a torque-splitting input epicyclic gear having an engine-connected driving element, a driven element connected or connectible to a final output element, and two reaction elements, the barrel II being permanently mechanically connected to one epicyclic reaction element and the barrel I being selectively connectible to either the final output element, through an auxiliary speed reducing gear, for Low Range, or to the other epicyclic reaction element, for High Range. The gear shown is particularly suitable for " transaxle " units for rear engine drive and front wheel drive vehicles and vehicles with a long shaft connection between the engine and the gear. The input epicyclic gear comprises long planets 140 mounted on a driven carrier 135 and meshing a driving ring 132, a reaction sun 141 and, through idler planets 144, a reaction sun 145. The sun 141 is geared at 171, 170 to a countershaft 168 on which is splined the barrel II. The sun 145 is geared at 147, 175 to a countershaft 157 coaxial with a shaft 182 on which is splined the barrel I. A pinion 209 of a final drive hypoid bevel pair is connected to a carrier 206 on which are independently mounted planets 220, 226. A Low Range auxiliary epicyclic gear comprises the planets 220 meshing a ring 221 and a sun 193 geared at 189, 188 to the barrel I. A Reverse epicyclic gear comprises the planets 226 meshing a ring 228, through idler planets 227, and a sun 195 formed on a centre shaft 136 on which is splined the input epicyclic driven carrier 135. The shafts 157, 182 and the centre shaft 136 and the final output carrier 206 may be respectively connected by a High Range clutch 177 and a Forward Drive clutch 197; and the rings 221, 226 may be respectively stationed by a Low Range brake 222 and a Reverse brake 230. These clutches and brakes may be positive, combined friction and positive, or, as shown, of the fluid engaged, spring-released multiplate type. In operation, assuming constant input power and speed, with the High Range and Forward Drive clutches 177, 197 engaged, and the swashplates of barrels I, II respectively at full and zero tilt, the sun 145 is held by the hydraulically locked barrel I and transmission, at high output speed, is purely mechanical. To reduce speed, the tilts of the I, II swashplates are respectively reduced and increased, the transmission being then hydro-mechanical until the I, II swashplates are respectively at zero and full tilt as shown, at which stage the sun 141 is held by the hydraulically locked barrel 2 and transmission, at a lower output speed, is again purely mechanical. For further speed reduction, the High Range clutch and Low Range brake are respectively released and engaged, this changeover being effected under no-load conditions, the I swashplate being at zero tilt, and with full or part synchronization, the gearing being matched to this end. Retaining the II swashplate at full tilt, the I swashplate tilt is then increased so that the torque of the barrel I multiplied by the auxiliary epicyclic gear 220 is added to the output torque, while the output speed is reduced. To provide further speed reduction after both swashplates are at full tilt, the II swashplate tilt is reduced, thereby increasing pressure to the barrel I. Overdrive beyond the first-mentioned high output speed may be obtained by tilting the II swashplate over-centre, with the I swashplate at full tilt. For Reverse, the Low Range and Reverse brakes are engaged, the Forward drive clutch is disengaged, and the II swashplate is tilted at full displacement over centre; the shaft 136 then driving the carrier 206 reversely through the Reverse Epicyclic gear, and the barrel I, serving as a reversely driven motor, adding reverse torque to said carrier. In Fig. 1 (not shown), the barrels I, II and the input and auxiliary epicyclic gears are coaxial. The input epicyclic gear comprises freely mounted coaxial planets, on a free carrier, respectively meshing a driving ring and a fixed sun, and a driven ring, a sun connectible to the barrel I through the High Range clutch, and, through stepped idler planets, a sun permanently connected to the barrel II. In this embodiment the Reverse gear is dispensed with and the driven ring of the input epicyclic gear is permanently connected to output. In Fig. 5 (not shown), each of the barrels I, II, disposed on countershafts, comprises two barrel portions which are connected together for corotation, are disposed on opposite sides of a valve plate, and have co-tilting swashplates. The Reverse gear is dispensed with, the input epicyclic gear is similar to that shown, and the Low Range auxiliary epicyclic gear and brake are replaced by Low Range gear pair and clutch between the barrel I and the output. This embodiment is suitable for the connection of auxiliary power take-off devices. Control.-The control may be manual or automatic. An automatic control system (Fig. 6), particularly for the gear shown but adaptable for use with the gears of Figs. 1, 5 (not shown), comprises cam-slot plates 242, 243 respectively controlling the tilt of I, II swashplates and movable together by the piston 247 of a doubleacting servomotor 250 having a movable cylinder sleeve 248. The servomotor 250 is energized from an input driven pump 281 through an input speed responsive governor valve 260, the flyweights of which are loaded by a spring 285 variably loaded, independently, by a cam 288 shifted along with a Drive, Neutral, Reverse, control valve 295, and, in order that the governor valve may maintain a set engine speed for every throttle position, by a cam 289 connected to the engine throttle 291. A control cam 252, movable with the cam-slot plates 242, 243 and provided with reference pointer 254, acts on the plunger of a valve 300. An Engage valve 313 is arranged between hydrostatic pressure lines 153<SP>1</SP>, 153<SP>11</SP>. In operation, with the control valve 295 in Neutral, fluid pressure is directed through lines 316, 317, 318 to engage the Forward drive clutch, engage the Low Range brake through the valve 300, a line 308 and a shuttle valve a 309, and urge the cylinder sleeve 248 to its right-hand position. At the same time, pressure in a line 312 is released through a restrictor hole 326 in the Engage valve to allow a spring 325 to open the Engage valve to by-pass hydrostatic pressure. The Neutral position of the cam 288 so increases governor spring load that the servomotor piston 247 is forced to the left so that the reference pointer 254 indicates a point " C " and the swashplates are set for low ratio for initial vehicle acceleration. On shifting the control valve to Drive the line 312 is pressurized to close the Engage valve 313 and render the hydrostatic gear operative. During Drive, the governor valve 260 controls the movement of the servomotor piston 247 to move the  swashplates. At a point B the plunger of the valve 300 drops from an upper surface 303 to a lower surface 304 of the control cam 252 and redirects pressure from the Low Range brake to the High Range clutch through a line 307. For Reverse, the control valve is shifted to Reverse through Neutral thereby ensuring opening of the Engage valve and by-passing of hydrostatic pressure during such shift. In Reverse, the control valve 295 vents the lines 316, 317, 318, thereby releasing pressure from the Forward Drive clutch, the valve 300 and the left-hand side of the cylinder sleeve 248, pressurizes a line 315 to engage the reverse brake and, through a line 311 and the shuttle valve 309, engage the Low Range brake, and pressurizes the line 312 to close the Engage valve 313. The Reverse position of the cam 288 effects extreme leftward movement of the servomotor piston 247, the cylinder sleeve 248 being leftwardly movable, for over-centre tilting of the II swashplate. The Engage valve 313 is rendered input speed and load responsive to provide for differing starting conditions and for shifting from Forward to Reverse and vice versa, and to prevent stalling on overload. The spring chamber of the engage valve 313 is connected by a line 314 to the throat of a Venturi 280 through which pumped fluid is fed to the control and governor valve 295, 260, so that as input speed increases the pressures in lines 312, 314, respectively, increase and reduce and a differential force acting on opposite sides of the Engage valve spool increases. Differential land areas are provided on the Engage valve spool so that increasing hydrostatic pressure increases the input speed at which the Engage valve closes.