Speed and steering control of a hydraulically driven tractor

摘要

A tractor has hydraulically driven wheels at a cab end and castor wheels at an engine end. Each driven wheels is driven by a hydraulic motor with a continuous adjustment of the motor displacement, with the motor being driven by a pump also having continuous displacement. The motor displacement is controlled by an electronic controller in response to stroking of the speed control lever to manage the displacement to provide required drive torques at different points in the stroke. There is provided an automatic steering system having a guidance controller arranged to receive GPS position information which controls the steering by differentially adjusting the displacement of the motors so that the automatic steering is independent of the manual steering which controls the pumps.

主权项

1. A hydraulically driven tractor comprising:
a tractor frame; an engine mounted on the tractor frame; a cab mounted on the tractor frame for a tractor driver; a first and a second driven wheels of the tractor mounted at a driven end of the tractor, the first driven wheel including a first hydraulic drive motor for driving the first wheel and the second driven wheel including a second hydraulic drive motor for driving the second wheel; two non-driven castor wheels of the tractor mounted at a second end of the tractor; the driven end having mounting assemblies for supporting a crop cutting header at a position in front of the driven end and in front of the cab when the driven end is forwards; a first and a second hydraulic pump each driven by the engine for generating a source of hydraulic fluid under pressure; the first hydraulic pump being arranged for driving the first hydraulic motor of the first driven wheel and the second hydraulic pump arranged for driving the second hydraulic motor of the second driven wheel; the first hydraulic pump being operable to vary the displacement of the first hydraulic pump between a minimum and a maximum to vary the flow rate of fluid generated for supply to the first hydraulic motor as the first hydraulic pump is driven; the second hydraulic pump being operable to vary the displacement of the second pump between a minimum and a maximum to vary the flow rate of fluid generated for supply to the second hydraulic motor as the second pump is driven; the first hydraulic drive motor having a displacement control actuator which is operable by a control unit so as to provide continuous stepless adjustment of the displacement of the first hydraulic drive motor between a minimum and a maximum to vary a ground speed of the first driven wheel relative to a flow rate of the fluid supplied to the first hydraulic motor; the second hydraulic drive motor having a displacement control actuator which is operable by a control unit so as to provide continuous stepless adjustment of the displacement of the second hydraulic drive motor between a minimum and a maximum to vary a ground speed of the second driven wheel relative to a flow rate of the fluid supplied to the second hydraulic motor; a steering control operable to provide a steering output between left and right positions through a center position; a speed control operable to provide a speed output between forward and reverse positions through a neutral position; the speed control to vary the displacement of the first hydraulic pump and/or the first hydraulic motor to vary a ground speed of the first driven wheel; the speed control being arranged to vary the displacement of the second hydraulic pump and/or the second hydraulic motor to vary a ground speed of the second driven wheel; the speed control being arranged to vary the ground speed of the first and second driven wheels symmetrically to vary a common ground speed of the tractor; the steering control being arranged to vary the displacement of the first hydraulic pump and not the first hydraulic motor to vary a ground speed of the first driven wheel; the steering control being arranged to vary the displacement of the second hydraulic pump and not the second hydraulic motor to vary a ground speed of the second driven wheel; the steering control being arranged to vary the ground speed of the first and second driven wheels differentially to cause steering of the tractor to a desired direction.