Patent GB-1409698-A (GB)
Title: Hydromechanical transmissions and controls
IPC: F16H47/04
Filed: 1974-03-21
Abstract: 1409698 Hydromechanical change-speed gear control GENERAL MOTORS CORP 21 March 1974 [14 May 1973] 12550/74 Headings F2D and F2W In a motor vehicle a variable displacement pump-motor hydrostatic transmission H, which drives the load through a series mechanical two-speed gear, controlled by ratio-establishing devices, such as a direct-drive clutch 24 and reduced drive brake 30, has its displacement controlled by a fluid pressure servo 14 controlled by a ratio-pressure control valve arrangement 41, which provides a variable pressure for selectively shifting the displacement control between minimum and maximum values, the pressure level being reduced by directing fluid pressure to the said valve arrangement by upshift from low to high ratio in the mechanical gear to return the displacement control to minimum and permit the variable pressure to be repeated for displacement shift from minimum to maximum in the high ratio. The arrangement is such that upshift in the mechanical gear downshifts the hydrostatic, resulting in no change in overall ratio. Function summary.-The speed ratio of the hydrostatic gear, and in Fig. 4 (not shown), also in the mechanical gear, is controlled automatically in response to engine speed and engine throttle setting, together with a manually operated operator request valve 38 for modifying the response. A manual selector valve 43 selects neutral N and drive ranges D1, D2 in the mechanical gear, the low range D1 selecting the low brake 30 only, whilst the high range selects the high clutch 24 only. Forced downshifts by selecting D1 from D2 range are prevented at excessive engine speeds by the speed responsive control. In one form, Fig. 5 (not shown), pressure in the usual service brake system on the vehicle downshifts the hydrostatic gear for increased engine braking, the downshift being restricted to safe engine speeds. A separate forward-reverse valve 163, operating on the hydrostatic gear, has its action inhibited by a valve group which prevents reversal at excessive engine speed and ratio setting and automatically downshifts the hydrostatic gear before the direction of drive can be changed. Establishment of drive from neutral is similarly inhibited. Trimmer valves 47, 48 of known type, cushion the engagement of the clutch and brake of the mechanical gear. Gear arrangement.-An engine 10 drives the pump P of the hydrostatic gear H, the motor M of which drives a parallel shaft 21, driving an output shaft 32, also parallel thereto, through a direct reduced sun-ring-planet gear with direct drive clutch 24 and reduced drive brake 30. The engine shaft 11, 15 also directly drives a parallel power-take-off shaft 18. The displacements of both the pump and motor are variable under control of a double acting servo 42, shiftable in opposite forward and reverse directions from zero. Servo pressure supply and regulation.-A single engine-driven pump 54, supplies line pressure to a system main 56, with pressure regulator 57 not described. Ratio control hydrostatic.-The displacement controlling servo 14 is actuated by a servo 42, moved in the appropriate direction from zero to produce progressive upshifts in accordance with the magnitude of the pressure supplied to the servo, such magnitude being determined by an engine-driven centrifugal governor valve 39, opposed at 79 by linkage to the engine throttle, and assisted by applying to a land d a request pressure 67 supplied by an operator request valve 38 which regulates this pressure 67 from line 56 in accordance with loading produced by the operator turning a cam 65, increased downward loading reducing the shift speeds. The governor 39 produces throttle-modulated engine-speed responsive pressure in a governor line 95 indirectly by supplying or relieving fluid pressure in lines 80, 81, leading to opposite ends of a double-acting servo 84, which, mechanically through a cam 90, loads a governor signal valve 40, which is a pressure regulator, regulating line pressure 56 into the governor pressure line 95 in accordance with the cam load. Governor pressure 95 loads a ratio pressure control valve 41, which is another pressure regulator regulating line pressure 56 to a final ratio control pressure line 69 in accordance with the governor pressure loading. This ratio control pressure 69 is fed to the hydrostatic shift servo 42 to produce ratio shift in accordance with the pressure magnitude, the direction of movement of the servo 42 for forward or reverse being determined by an interposed forward-reverse servo valve 50, described below. Hydrostatic-mechanical ratio interconnection.- This interconnection, referred to above, comprises a line 102, feeding line pressure from the direct-drive mechanical gear clutch 24 to below the ratio pressure control valve 41 to oppose the downward load by governor pressure 95, thus reducing ratio control pressure 69 and downshifting the hydrostatic gear to result in unchanged overall ratio on upshift in the mechanical gear and producing a less steep upshift response in the hydrostatic gear thereafter (Fig. 2, not shown). Ratio control mechanical.-The direct-drive clutch 24 and reduced drive brake 30 are engaged by supplying line pressure 56 to or from lines 139 and 132respectively under control of a shift valve 46 which, in the low range setting D1 of the manual selector valve 43, is spring-held in its upper position, shown, to supply line pressure 56 through the manual valve 43 and lines 113, 123 to the low brake line 132. The shift valve 46 is depressed to supply the high clutch line 139 from the same pressure line 113, 123, and exhaust 132 for upshift, when the manual valve 43 is moved to D2 setting, to supply line pressure 56, through a line 115, to a top chamber of the shift valve 46. Assisting the shift valve 46 is a shift signal valve 45, which, in D1 setting of the manual valve 43, is maintained in its upper position, shown, by low brake pressure 132. When D2 is selected the shift valve 46 is depressed through the line 115, low brake pressure 132 is exhausted and the shift signal valve 45 is depressed by governor pressure 95. Pressure 113, 124 is then supplied through a line 130 to hold the shift valve 46 depressed, supplying pressure 113, 123 to the high clutch line 139 completing the upshift. For forced downshift by selecting D1 range, the line 115 is exhausted but the shift valve 46 remains depressed by the high hold pressure 130, still selecting the high clutch 24, until governor pressure 95 falls sufficiently to permit the shift signal valve 45 to be lifted by its spring, exhausting the high hold line 130, to permit the shift valve 46 to be spring returned to its upper position pressurizing the low brake 30, pressure 132 in which then holds up the shift signal valve 45 preventing any upshift in this D1 setting. Inhibit and reverse controls.-Included in the pressure supply line 113, 123 to the mechanical gear shift valve 46 is a Neutral-Drive inhibit valve 44, which is depressed by governor pressure 95 to exhaust the supply line 123, thus preventing pressurization of either clutch 24 or brake 30 if engine speed is too high. Reverse is established by pressurizing the upper chamber and exhausting the lower of the hydrostatic servo 42 through lines 173, 172 respectively, ratio control pressure supply 69 being taken through a forward-reverse servo valve 50 which, for forward drive, is maintained in the upper position, shown, by a spring 166, and is depressed, or maintained depressed, for reverse when downward pressure is supplied to any of three lines 175, 177, 178 under control of a forward-reverse inhibit valve 51, a forwardreverse request valve 49, a manual forwardreverse valve 163 and two neutral shuttle valves 52, 53, acting as follows. In its forward setting, shown, the manual F-R valve 163 maintains the F-R request valve 49 in its upper position, shown, by line pressure 56, 159 and the F-R servo valve 50, also up, supplies ratio-control pressure 69 to the forward line 172 of the hydrostatic servo 42. Selection of reverse at the manual F-R valve 163 immediately depresses the F-R request valve 49 by line pressure 56, 160, causing line pressure 56 to be supplied through lines 162, 176 to the F-R inhibit valve 51, which, in its upper position, shown, pressurizes a line 178 to depress the F-R servo valve 50, changing over the supply of ratio control pressure 69 from line 172 to 173 to the hydrostatic servo which then produces reverse ratios. In the F-R servo valve 50 line 178 is now exhausted through line 176 and the F-R inhibit valve 51, but downward pressure is maintained through lines 162, 177. If engine speed, and hence hydrostatic ratio, are excessive for entering reverse, governor pressure 95 depresses the F-R inhibit valve 51, exhausting the line 178 to prevent depression of the F-R servo valve 50, so that line pressure 56 now passed through the already depressed F-R request valve 49, line 162, the F-R servo valve 50, line 176, the depressed F-R inhibit valve 51, line 186, both neutral shuttle valves 52, 53, and a line 70 to load upwardly the operator ratio request valve 38, exhausting the request pressure line 67 to remove the downward load on the governor valve 39, which reduces governor pressure 95 and hence, through the governor signal and ratio pressure valves 40, 41, reduces ratio control pressure 69, thereby downshifting the hydrostatic gear. The reduction in governor pressure 95 also permits the F-R inhibit valve 51 to rise, pressurizing the line 178 to depress the F-R servo valve 50 for reverse as above. Lines 174, 175 produce a similar but opposite action for entering forward from reverse, and a similar hydrostatic downshift action is produced when the manual selector valve 43 is set to neutral, the line 70 being then pressurized directly through a line 114 and the two neutral shuttle valves 52, 53. Modifications.-In Fig. 4 (not shown), the shift and signal valves (46a, 4