Motor vehicles – Steering gear – No mechanical connection between steering shaft and steering...
Patent
1997-10-06
1999-12-07
DePumpo, Daniel G.
Motor vehicles
Steering gear
No mechanical connection between steering shaft and steering...
180402, 180410, 180234, B62D 715
Patent
active
059967226
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a vehicle steering system for agricultural and other vehicles using implements which overhang the wheel base of the vehicle.
Implements fall broadly into two classes, namely those that are simply trailed behind the prime mover (referred to as the tractor), and those that are carried on a raising linkage. The invention is primarily concerned with linkage mounted implement/tractor combinations, although it can have applications to trailed implements.
Linkage mounted implements have numerous advantages. They can be lifted out of the ground when not in use, and the linkage mechanism can be used for height and depth control and also for transferring at least some of the weight of the implements onto the tractor to increase tractive effort.
A disadvantage of linkage mounted implements is that when they are in the ground, the implement prevents easy steering of the vehicle, since conventional steering action on the tractor attempts to move the implement sideways in the ground in a turn. This force impairs steering and may damage the implement, tractor or attaching linkage. Implements held on linkages which operate out of the ground also suffer from excessive sway or yaw due to the acceleration imparted to them on turning with conventional steering.
Current practice is to use swinging joints when joining implement and tractor. These are a partial solution in that they allow a limited amount of steering motion, restricted by the clearance that has to be maintained between the implement and the tractor rear wheels. This requirement for clearance means that the transport width of the tractor unit must be increased compared with what is required using a rigid linkage. When the implement is raised the swinging motion must be limited for safe transport. Another disadvantage of swinging links is that the lateral movement that they can allow can often exacerbate the problems of yaw and sway when in the raised position.
U.S. Pat. No. 4,798,393 (Honda) describes a tractor with various modes of steering. Its first embodiment has steerable front and rear wheels. They are mechanically linked so that, when the steering wheel is turned through a small angle, the front and rear wheels all turn in the same direction, although not by the same amount, to give a crabbing motion. But when the steering wheel is turned through a large angle, the rear wheels turn in the opposite direction to the front wheels, to give a tighter turning circle than that with just front wheel steer.
Although reference is made at one point to the rear wheels being "substantially not steered" there appears to be no provision for them to be held rigid while just the front wheels are steered in the small angle mode. Also, the transition between the rear wheels pointing one way and then the other over a very small arc of turn of the steering wheel must give an extremely awkward steering characteristic. It is a very inflexible system and is not known to have been put into practice.
The second embodiment of the Honda patent also relies on an entirely mechanical connection between the front and rear wheels. There is a lever which can be operated to change the nature of the connection, in one mode causing the front and rear wheels to turn in opposite directions (for tight cornering) and in another mode for the rear wheels to turn in the same direction as the front wheels. The geometry is then such that the vehicle turning circle is centered on a line transversely through an implement carried or towed at the rear. This enables the implement to follow a straight path, with no undue lateral forces. However, it is uncertain that the system maintains this throughout the full range of adjustment of the steering wheel, and it is too inflexible to cope in the same way with different implements with a different relationship to the wheelbase of the vehicle.
It is the aim of this invention to provide a steering system of much greater flexibility, able to accommodate easily to different implements, and to offer true front wheel only steering.
According
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