Patent ID: 7306062
Filing Date: 2007-12-11
Classification: B62D

Abstract:
1. A tractor comprising: a tractor frame; an engine mounted on the tractor frame; a cab mounted on the tractor frame; 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, with the first hydraulic pump 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 including a first cam plate movable to vary the displacement of the pump to vary the volume of fluid generated as the pump is driven and the second hydraulic pump including a second cam plate movable to vary the displacement of the pump to vary the volume of fluid generated as the pump is driven; each of the first and second cam plates having a maximum position at which a maximum volume of fluid is generated, each maximum position being determined by an end stop; a manually operable steering control movable between left and right positions through a center position; a manually operable speed control movable between forward and reverse positions through a neutral position; the manually operable speed control being arranged to control a rate of supply of hydraulic fluid from the first hydraulic pump to the first drive motor and from the second hydraulic pump to the second drive motor to control a common speed of rotation of the driven wheels and thus a speed of movement of the tractor; the manually operable steering control being arranged to control a differential in rate of supply of hydraulic fluid from the first hydraulic pump to the first drive motor and from the second hydraulic pump to the second drive motor to control a relative speed of rotation of the driven wheels and thus a turning direction of the tractor; a linkage including a first link for controlling the first cam plate and a second link for controlling the second cam plate; the linkage including a speed control member operable by the manually operable speed control with the speed control member arranged, when actuated, to move both the first and second links for moving the first and second cam plates; the linkage including a steering member operable by the manually operable steering control with the steering member mounted relative to the speed control member so as, when actuated, to move the first and second links relative to the speed control member to effect differential movement of the first and second cam plates; the manually operable speed control including a manually operable lever defining a position input and a servo-cylinder arranged in response to the position input to move the speed control member to a position determined by the position input and to maintain the speed control member in the position by pressure in the servo-cylinder; the manually operable speed control being arranged so as to provide a maximum forward position of the speed control member in which the first and second cam plates are located in their maximum positions against the respective end stop and are maintained in the maximum position by pressure in the servo-cylinder; and a relief member operable, in the maximum forward position of the speed control member, on operation of the steering member by the manually operable steering control, to relieve pressure from the servo-cylinder to allow movement of the first and second links relative to the speed control member to effect differential movement of the first and second cam plates.