Patent GB-687869-A (GB)
Title: Improvements in hydro-mechanical variable speed transmission gearing
IPC: F16H47/02
Filed: 1950-06-26
Abstract: 687,869. Hydromechanical variable speed gear. EBERT, H. June 26, 1950 [July 2, 1949], No. 15857/50. Class 80 (ii). [Also in Group XXIX] A countershaft toothed gear, on a vehicle, providing two stepped forward ratios and reverse, is driven through a hydrostatic gear of the variable-stroke piston type, primary and secondary elements (e.g. swash-plates 14, 15 or eccentrics) of which are mounted on a common shaft 10, to provide a ratio-range which is the same as that between the stepped countershaftratios, whereby the ratio-gaps are continuously bridged by the hydrostatic gear, and the arrangement is such that in at least one of the two limit positions of the hydrostatic gear there is no transfer of liquid between its primary and secondary cylinder-bodies 1, 2. The control is such that, during a shift in the countershaft gear, which is manually operated only by a ball mounted lever 43, the fluid gear is also changed through its extreme range so that output shaft speed initially remains the same in the new ratio and is subsequently changed gradually in the fluid gear, the overall shift thus being stepless, and also reverse being obtained without reversing the fluid gear. Change in the fluid gear, by varying the swash-plate inclination, is preferably automatic under the control of an engine driven centrifugal governor 54, Fig. 1, or the torque-responsive pressure in the fluid gear, Fig. 2 (not shown), conjointly with the vehicle accelerator and brake pedals 62, 63 and an additional manual control, Fig. 2 (not shown). A conventional main-clutch, e.g. 24, Fig. 3, may be used between the fluid and countershaft gears, or the fluid gear itself may be used as a main clutch. In Fig. 1, an intermediate shaft 10 drives a final aligned output shaft 26 through a simple countershaft gear having a synchronised directdrive and two-to-one reduced-speed dog-clutch 32 and sliding reverse wheel 33, controlled by a ball mounted shift lever 43. The intermediate shaft 10 is driven by a parallel input shaft 3 through a hydrostatic gear comprising variablestroke primary axial or radial pistons in a freely-mounted primary cylinder-body 1 delivering to the similar pistons of a freely-mounted secondary body 2 through a ported valve-block 16 integral with the intermediate shaft 10, the pistons being reciprocated by swash-plates 14, 15 (or eccentrics) fast rotationally with the shaft 10 and having their inclination simultaneously and oppositely varied through axiallyadjusted interconnected helically-slotted sleeves 20, 21. The primary and secondary cylinderbodies 1, 2 are both permanently geared to the input shaft 3 through gear-pairs 4, 5 and 6, 7 respectively, which provide one-to-one and twoto-one ratios, being the same as those of the countershaft gear. The fluid-gear control is such that in one limit position when the primary swash-plate 14 is at maximum inclination and the secondary 15 at minimum (as shown) the secondary unit cannot receive fluid so that there is no transfer of fluid between the primary and secondary bodies 1, 2 and the intermediate shaft 10 is driven through the primary unit and wheel-pair 4, 5 alone, providing one-to-one; whilst in the other limit position, when these inclinations are reversed, the shaft 10 is similarly driven at two-to-one through the wheel pair 6, 7 and secondary unit alone. Between these extreme ratio positions the intermediate inclinations of the swash-plates cause drive to pass from the primary body 1 to the secondary 2 by fluid interchange through the valve-block 16 in known manner, thus providing stepless change. Excess pressure in the fluid gear is relieved by a safety-valve 78 connecting the pressure and suction passages in the valveblock 16. Control of the swash-plate adjusting sleeves 20, 21 is by levers 47 operated simultaneously by a double-acting piston 45 to which pressureoil is supplied from a gear-pump 52 through a piston-valve 53 directly operated by an enginedriven centrifugal governor 54, the loading spring 59 of which is variably compressed by a cam 65 operated by the accelerator-pedal 62, and by the initial lost-motion in a rod operated by the service-brake pedal 63, so that enginebraking at reduced ratio precedes the application of the service brake. A clutch-pedal 73 operates a slide-valve 70, supplying pumped oil from an inlet 72 either to an inner space between, or to spaces on the outer sides of two pistons 51, which carry the pivots 48 of the swash-plate shift-levers 47 and are loaded inwardly by springs 49, 50. In the running position shown, pressure is supplied between the pistons 51 fixing the lever-pivots 48 in outer positions so that the main piston 45 exerts its normal control effect, whilst depression of the clutch pedal 73 urges both pistons inwardly to move both swash-plates 14, 15 to zero-stroke if either of them is not already in that position, thus preventing drive through both the primary and secondary units or, in effect, declutching the drive. The piston-loading spring 50 is stronger than spring 49 to ensure that movement of the secondary swash-plate 15 to zero position and its return to operative inclined position precedes movement of the primary swash-plate 14 during declutching and follows it during re-clutching, thus preventing racing of the engine. In operation, with the engine idling, to start the vehicle, the clutch-pedal is depressed and the manual shift lever 43 is moved from neutral to select the two-to-one reduced drive path through the wheel-pairs 24, 30, 35, 38. At this time the governor 54 is below fluid-gear upshift speed, and the main-piston 45 is at the left, inclining the secondary swash-plate 15 to its maximum and zeroising the primary 14, so that when the clutch-pedal is subsequently released the vehicle is driven through the two-to-one secondary wheel pair 6, 7 of the fluid-gear and the two-to-one countershaft path, giving fourto-one overall. As the vehicle accelerates, increasing engine-speed operates the governor 54 to move the main piston 45 to the right, causing a gradual upshift in the fluid gear from the two-to-one secondary wheel-pair 6, 7 to the primary one-to-one pair 4, 5, providing eventually two-to-one overall ratio. To make a further upshift, now possible only in the countershaft gear, the driver depresses the clutch-pedal 73, bringing the primary swash-plate 14 to zero inclination (the secondary being already in that condition), thus declutching and permitting manual selection of direct-drive in the countershaft unit by the shift-lever 43. During this action, the reduction of engine speed following accelerator-release and declutching, causes the governor 54 to downshift the fluid gear, so that, when the clutch-pedal 73 is again released, the fluid gear again drives through the secondary two-to-one wheel pair 6, 7, thus maintaining output shaft speed unchanged in a two-to-one overall ratio. As the vehicle accelerates, increasing engine-speed gradually upshifts the fluid gear by means of the governor 54, as before to an eventual one-to-one overall ratio. Downshifts in the fluid-gear, in addition to governorresponse, can be made by depressing the accelerator or brake-pedals 62, 63, which increases the governor-loading, as above described. In Fig. 2 (not shown), the valve-block of the hydrostatic unit comprises passages in the driving shaft on which latter the primary and secondary cylinder bodies 1, 2 are freely mounted and are geared to the intermediate shaft through the different ratio gear-pairs. In place of the governor-operated piston-valve 53, a similar valve slides axially inside the driving shaft, being moved in the one direction by fluid pressure derived from the pressure passages in the shaft connecting the primary and secondary cylinders, which pressure, being torque-responsive causes shifts in the fluid-gear to be controlled by torque instead of directly by engine speed. The control valve is biased in the downshift direction by a spring which is variably loaded by the accelerator and brake pedals and by an additional manual setting lever, all of which act independently on the valve-spring through interconnected floating levers. Automatic barometric and temperature-sensitive correction may be provided for this construction and the control valve series also as a pressurerelief valve for the fluid units. In the basically different fluid units shown in Fig. 3, the body 6 of the secondary unit is permanently fixed, its swash-plate 10 being of variable inclination as before, whilst the primary unit body 1 is fast to the input shaft 4 and its non-adjustable swash-plate 9 is fixed to the intermediate driven shaft 11, which latter drives the aligned input shaft 22 of the stepped countershaft gear through a friction-clutch 24 controlled by a pedal 25, in place' of the declutching control of the fluid-gear. Adjustment of the swash-plate 10 by its slotted sleeve 15 provides a ratio range of one-to-one to twoto-one, as before, control being by the speedgovernor 41, with variable loading by accelerator and brake pedals 42, 45. Fig. 4 (not shown) operates similar to Fig. 1, but uses multiple groups of simultaneously controlled small fluid units arranged in parallel on countershafts grouped around the input shaft and driving the aligned countershaft-gear input through a common wheel, this arrangement increasing the efficiency by reducing losses due to both fluid and mechanical friction. The pressure and suction passages of all units are interconnected for hydraulic equalisation in the units. Fig. 6 (not shown), uses similar multiple fluid units on countershafts but employs the Fig. 3 principle of stationary secondary units and non-adjustable primary swash-plates, with the exception that each primary and each secondary unit has two opposed sets of pistons and two opposed swash-plates. Fig. 5 uses primary and secondary units 12, 13 like those