Steering apparatus

Claim 1

A tractor comprising: a chassis: steering apparatus including: first, second, third and fourth wheels, each pivotably and rotatably mounted onto said chassis; first positioning means for selectably positioning said first, second, third and fourth wheels in first and second extreme positions and for selectably positioning said first and second wheels at predetermined angled positions intermediate said first and second extreme positions; second positioning means associated with said second and third wheels and operative to provide selectable steering of said second and third wheels, said first, second, third and fourth wheels being pivotably mounted at vertices of an imaginary rectangle, whereby said first and second wheels are separated by a first distance, said third and fourth wheels are separated by said first distance, said second and third wheels are separated by a second distance and said first and fourth wheels are separated by said second distance, said first distance being greater than said second distance, wherein first distance represents the tractor wheelbase for off-highway operation and said second distance represents the tractor wheelbase for highway operations, said first and second wheels being selected to be at the front leading end of said tractor for off-highway operations and said second and third wheels are selected to be at the front leading end of said tractor for highway operations, said first positioning means comprising first, second, third and fourth fluid operated piston and cylinder assemblies associated with said first, second, third and fourth wheels respectively for providing selectable pivotal positioning thereof, the stroke lengths of all of said first, second, third and fourth fluid-operated piston and cylinder assemblies each providing a 90 degree pivot range for an associated wheel, said second positioning means comprising a bidirectional piston assembly which is coupled to said second and third piston and cylinder assemblies in a series arrangement, said second positioning means also comprising means for locking said bidirectional piston assembly in a central position only when the tractor is operated for off-highway operations.