Patent ID: 7077220
Filing Date: 2006-07-18
Classification: B60B,B60Y,B62D,Y10T

Abstract:
1. An agricultural tractor comprising: a tractor frame for movement in a direction of forward working movement of the tractor across a field; the tractor frame having support members at a forward end of the frame, in respect of the direction of working movement, arranged for attachment to an implement to be moved across the ground with the implement supported across and in front of the forward end; a pair of first ground wheels mounted on the frame at the forward end of the frame at positions spaced transversely of the frame; the first ground wheels being mounted on the frame at fixed angles parallel to each other and parallel to a center line of the frame; a pair of second ground wheels mounted on the frame at a rearward end of the frame at positions spaced transversely of the frame; each of the second ground wheels being mounted on a respective castor assembly providing, for the respective wheel: each of the first ground wheels being driven by a respective drive motor which allows variable speed in both the first and second directions such that steering of the tractor is effected by a differential in speed between the first wheels with the second wheels following the steering in a castoring action; and a pair of damper cylinders each connected between the frame and a respective one of a pair of levers where each lever is arranged at a respective one of the castor assemblies so as to provide a damping force tending to restrict rotation of the respective second wheel about the respective vertical pivot axis; the damper cylinders and the levers being arranged such that the damping force for each castor assembly varies at different angles around the vertical pivot axis due to changes in mechanical advantage as the lever pivots around the vertical pivot axis and is at a maximum value when the second wheels are parallel to the center line and the tractor is moving in the direction of forward working movement and is at a maximum value when the second wheels are parallel to the center line and the tractor is moving in the opposite direction.