GB966692A - Vehicle propulsion - Google Patents

Abstract

966,692. Controlling vehicles. DOWTY HYDRAULIC UNITS Ltd. June 16, 1961 [June 21, 1960], No. 21769/60. Heading B7H. [Also in Division F2] Vehicle propulsion means wherein a pair of transversely spaced ground engaging elements are driven individually through separate infinitely variable speed ratio transmissions from a single mechanical power source, includes one or more devices operative, when overloading of the engine and/or one or both transmissions occurs, to reduce the speed ratios of both transmissions while maintaining the ratio between them. In this way, speed reduction to relieve overload will not affect steering obtained by driving the ground engaging elements at different speeds. In Figs. 1 and 2, the output gear 2 of an engine 1 drives variable displacement pumps 5 and 6 through gears 3 and 4, the pumps feeding hydraulic motors 7, 8, driving endless tracks or wheels, through pipe-lines 9, 11, 12 and 13. The displacement of the pumps is controlled by rods 14, 15, connected to bellcrank levers 18, 19, which are connected by links 23, 24, to a pivot slidable in a slot 26 in a lever 27. This lever is pivotable about an axis passing through the centre of the slot by an arm 29 connected by rod 31 to rack and pinion gear 32 operated by a steering wheel 33. In Fig. 1, the speed selection lever 39 (movable between full forward and full reverse speed positions) is pivoted at 58 and is attached to a cylinder 55, the piston 56 of which acts through rod 57 on a link 38 pivoted to one end of a lever 36 connected to move the pivot within slot 26, and affects the displacement of the two pumps equally and in the same sense, to control the speed of the vehicle. Zero speed is obtained with the pivot in the centre of slot 26. Rotation of the steering wheel from its datum position inclines arm 29 and slot 26, to move the pivot (if it is not in the centre of slot 26) so that the displacements of the two pumps are affected equally in opposite senses to drive the tracks or wheels on the two sides at different speeds and thus steer the vehicle, the sense of steering obtained being independent of the direction of travel of the vehicle. A Venturi 41 in the engine inlet manifold operates a diaphragm 44 acting on the fuel bar 45 of the engine fuel injection pump 46, to increase the fuel supply as the engine load rises. When overload occurs, detected by excessive fuel demand, bar 45 contacts a spring-biased spool valve 49 in a cylinder 48, having a port 52 connected to pressure, a port 53 connected to exhaust, and a port 51 connected to pressure through a restriction 62 and to one end of cylinder 55 through pipe-line 61. The other end of cylinder 55 is connected to pressure through pipe-line 59. Normally, port 51 is connected to exhaust through port 53, and the pressure drop across restriction 62 results in piston-rod 57 being withdrawn into cylinder 55, so that the velocity ratio between speed selection lever 39 and pivot 25 is a maximum. When overload occurs, valve 49 connects port 51 to pressure through port 52, so that full pressure acts on both sides of piston 56, which moves to extend rod 57 since the upper face of the piston has less effective area than the lower face. This reduces the velocity ratio between lever 39 and the pivot in slot 26, the latter moving nearer the centre of the slot to reduce the speed ratios of the two transmissions in the same proportion. This reduces the engine load, and valve 49 takes up an equilibrium position in which piston 56 is balanced' the piston then being in a position such that the transmission ratios are reduced just sufficiently to prevent overload of the engine. In Fig. 2, the speed selection lever 39 is connected to rod 38 through a doubleacting spring cage 65. The overload sensitive device detects excessive pump delivery pressure in pipe-lines 9 and 12 during forward travel, and in pipe-lines 11 and 13 during reverse travel, Pipe-lines 9 and 12 are connected by lines 67, 68 to a shutting valve 69 so that whichever line carries the higher pressure is connected to pipeline 72, the pressure acting on a plunger 81 in a bore 78 in a valve 66. Similarly, pipe-lines 11 and 13 are connected by lines 73, 74 to valve 75, the higher of the pressures in these lines acting through pipe-line 77 and plunger 82 in bore 79. The two plungers act on a piston 83 biased by a spring 84 variably stressed by a roller 85 co-operating with a cam 86 on rod 38. When the pressure in line 72 or 77 exceeds a datum, plunger 81 or 82 is moved to uncover a bore 87 or 88, to communicate that pressure to a jack 92 or 93, which extends and contacts an abutment 94 or 95 to move rod 38 towards (but not beyond) its central zero speed position, to relieve the excess pressure. The datum pressure is determined by the stressing of spring 84 by cam 86 and thus rises as the rod is centred until the operative jack is cut off. Each jack pipe-line is connected to exhaust through a restriction 96 or 97. Linkwork is described whereby the manual operation of two levers, one for controlling the drive speed on each side of the vehicle, is converted into appropriate movements of rods 31 and 38.