Patent GB-1392484-A (GB)
Title: Vehicle drive system
IPC: F16H45/00
Filed: 1972-06-13
Abstract: 1392484 Clutch control; variable speed gear; clutches VOITH GETRIEBE KG 13 June 1972 [29 June 1971] 27657/72 Headings F2L F2D and F2C In a vehicle (such as a fork lift truck) drive system wherein an engine 10 drives the vehicle wheels via a clutch 20 and a torque converter 20 regulating means are provided (valves 52, 60) to vary the hydraulic pressure supplied to a piston 24 which actuates the clutch 20 so that for any position of a clutch pedal 50 a constant output torque is maintained, irrespective of engine speed, the engine 10 also driving a hydrostatic pump 15 for auxiliary services. A pump 40, driven by the engine 10, supplies a constant pressure (regulated by valve 41) through a pressure reduction valve 52 and a shut off valve 56 (open with the clutch pedal in position a) to the clutch actuating piston 24. Movement of the pedal 50 to position b diverts the flow through a valve 60 having a piston 64, one side of which being acted on by the pressure in line 43 (from valve 52) and the opposite side 61 being acted on by a piston 65 which is connected to measure the pressure difference across the impeller 34 of the converter through conduits 66, 67, the valve 60 is thus closed or opened in response to this pressure which is a measurement of the output torque. Further movement of pedal 50 past position b starts to close valve 52 and reduce the pressure to the clutch, and also the control pressure to one side of valve 60 so that this valve maintains the torque constant by variation of pressure. For very large amounts of slippage of clutch 20 the chamber 23 may only be partially filled and in this instance the valve 60 is acting as a flow control, rather than a pressure control valve, there being a constant flow through the chamber 23 (via throttle 27) to an oil reservoir. In a further embodiment the pedal 50 acts directly (through a spring) on-the left side of a valve equivalent to valve 60 (Fig. 2, not shown) and the opposite side of the piston of the valve is acted on by a pressure which reduces as torque increases (the opposite to the operation of Fig. 1). A yet further embodiment has the supply of fluid to the torque converter (through line 37 in Fig. 1) (Fig. 3, not shown) via a pressure relief valve so that the input side of impeller 34 is at constant pressure and the output side pressure may be taken as a measure of torque (this dispensing with the need for piston 65 of Fig. 1). The clutch 20 may be connected to the ring gear of planetary gearing (Fig. 3, not shown) whose planet carrier is directly connected to output and whose sun gear is connected to the converter impeller, the turbine (36 in Fig. 1) being interconnected with the planet carrier through further planetary gearing on the opposite side of the converter from the clutch. A stop 57. for the clutch pedal may be provided such that some torque is transmitted even with it fully depressed. The clutch may act opposite from that shown and be engaged by springs (instead of released) and disengaged by fluid pressure, this requiring a reversal of the operation of most of the control features.