Importance

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Abstract

A vehicle is described having a front pair of ground contacting wheels, a rear pair of ground contacting wheels, an internal combustion engine, hydraulic motors for driving each said ground contacting wheel, and a plurality of variable flow hydraulic pumps for driving the hydraulic motors. In such a vehicle the internal combustion engine (7) is arranged to drive directly first and second variable displacement pumps (12, 13) for driving the motors (46, 47) of the front pair of wheels (2) and the motors (47, 48) of the back pair of wheels (3) respectively as well as first and second boost pumps (14, 15), while a control valve (22) is supplied with hydraulic fluid from one of the boost pumps (14) and is arranged to give an output hydraulic pressure which is dependent on the speed of the engine (7). A further valve (33, 34) is positioned under the control of the output hydraulic pressure from the control valve (22) in the path of hydraulic fluid from each of the boost pumps (14, 15) to a respective operating piston and cylinder arrangement (35, 36; 37, 38) for adjusting the displacement of the hydraulic pumps (12, 13) in dependence on the speed of the engine (7).

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First Claim