Patent Abstract:
The entire right, title and interest in and to this application and all subject matter disclosed and/or claimed therein, including any and all divisions, continuations, reissues, etc., thereof are, effective as of the date of execution of this application, assigned, transferred, sold and set over by the applicant(s) named herein to Deere &amp; Company, a Delaware corporation having offices at Moline, Ill. 61265, U.S.A., together with all rights to file, and to claim priorities in connection with, corresponding patent applications in any and all foreign countries in the name of Deere &amp; Company or otherwise.

Full Description:
FIELD OF THE INVENTION 
   This invention relates generally to vehicles having all wheel steering, and more specifically to lawn and garden tractors and other similar off-road vehicles having all wheel steering. 
   BACKGROUND OF THE INVENTION 
   Lawn and garden tractors and other utility vehicles may include all-wheel steering mechanisms which serve to turn all four ground engaging wheels. This provides the capability of executing relatively tight, small radius turns. For example, a tight turning radius may be desirable when using a lawn tractor to mow close around obstacles such as trees, posts or similar obstructions. 
   All-wheel steering mechanisms typically include an arm that translates or shifts forward or backward as the steering shaft pivots in response to the steering wheel being turned. Examples of all-wheel steering systems are shown in U.S. Pat. Nos. 5,174,595, 6,131,689 and 6,684,974 assigned to Deere and Company of Moline, Ill. U.S. Pat. No. 5,174,595 entitled “Four Wheel Steering Mechanism” relates to a steering linkage extending along the left side of the vehicle, which includes front and rear rod members that pivot, and an intermediate rod member that shifts longitudinally, as well as slightly laterally and vertically. U.S. Pat. No. 6,131,689 entitled “All-Wheel-Steer Biasing Mechanism” relates to a steering linkage having a front link element and a rear link element, both of which shift fore or aft to turn the front and rear wheels, and a biasing mechanism for biasing the rear wheel steering linkage back to a position for straight forward travel. U.S. Pat. No. 6,684,974 entitled “Four-Wheel Steering System for Utility Vehicle” relates to a linkage assembly that transforms pivoting motion of the front steering arms to pivoting motion of the rear steering arms, and eliminates the need for a front center-pivot. 
   All wheel steering systems are relatively costly and complex to manufacture and assemble, and may require many more parts and components than two wheel steering systems. There is a need to reduce the cost, complexity and number of parts and components in an all wheel steering system. 
   All wheel steering systems also require considerable space under the vehicle frame for link elements that translate or shift forward or backward when executing a turn. For example, drag links and bell cranks in an all wheel steering system may transmit motion for turning the front and rear wheels, and consume space under the frame that may be desirable for other parts and/or functions. There is a need to reduce the space requirements for an all wheel steering system. 
   In the past, all wheel steering systems also may not offer an equal turning radius in both directions. For example, the arm and/or link rods may not swing forward as far as backward. There is a need for an all wheel steering system that provides a more equal turning radius in both directions. 
   SUMMARY OF THE INVENTION 
   An all wheel steering system for a utility vehicle includes a torque shaft between pairs of steerable front and rear wheels. The torque shaft pivots on a longitudinal axis parallel to the longitudinal axis of the vehicle. A front crank may be secured to the torque shaft adjacent its forward end, and left and right rear cranks may be secured to the torque shaft adjacent its rearward end. The torque shaft transmits rotation from the front crank to the left and right rear cranks when the steering wheel is turned to steer the pairs of front and rear wheels. 
   The all wheel steering system with torque shaft may be operated manually or hydraulically assisted. The torque shaft reduces or minimizes the space requirements for an all wheel steering linkage between the front and rear pairs of wheels. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of the all wheel steering system with torque shaft linkage according to a first embodiment of the invention. 
       FIG. 2  is a perspective view of the front steering linkage according to the first embodiment. 
       FIG. 3  is a perspective view of the rear steering linkage according to the first embodiment. 
       FIG. 4  is a perspective view of the all wheel steering system with torque shaft linkage according to a second embodiment. 
       FIG. 5  is a perspective view of the front steering linkage according to the second embodiment. 
       FIG. 6  is a perspective view of the rear steering linkage according the second embodiment. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring now to  FIGS. 1-3 , a first embodiment of the present invention is shown. Lawn tractor or other utility vehicle  10  includes a pair of front wheels  12 ,  13  and a pair of rear wheels  14 ,  15 . The rear wheels may be driven by an engine supported at the front of the vehicle. Steering wheel  24  may be mounted in an operator station in conventional fashion such that a seated operator can steer the vehicle by turning the steering wheel. 
   One embodiment of front steering linkage  26  will be described in greater detail. Steering shaft  28  may be coupled to and extend downwardly from steering wheel  24 . At the lower end of steering shaft  28  is a pinion gear in mesh with sector gear  34 . The sector gear may be pivotably supported by first support plate  36  which may be bolted or otherwise affixed to second support plate  37 . The first and/or second support plates may be bolted or secured to the tractor frame. A first end of sector pin  40  may be fixed with the sector gear and may define a first axis about which sector gear  34  pivots. Sector pin  40  may extend through openings in first support plate  36  and second support plate  37 . 
   In one embodiment, pivot pin crank  48  may be securely fixed by welds or other means at or near a second end of sector pin  40 . Pivot pin crank  48  may pivot along with sector pin  40  on a first generally vertical axis defined by the sector pin. Rod  47  may provide a link between pivot pin crank  48  and front crank  49 , and may be pivotably connected to cranks  48 ,  49  with threaded or other pivotable fasteners. Rod  47  may connect cranks  48 ,  49  such that pivotal movement of pivot pin crank  48  on the first generally vertical axis may be translated to pivotal movement of front crank  49  on a second generally horizontal axis transverse to the first axis. The second generally horizontal axis may be parallel to the longitudinal axis of the vehicle. 
   In one embodiment, left and right sector arms  61 ,  62  may be attached and secured to the opposing ends of sector gear  34  with bolts or other fasteners. Left and right front tie rods  42 ,  43  may pivotably attach left and right sector arms  61 ,  62  to left and right front steering arms  51 ,  52  respectively. Left and right front steering arms  51 ,  52  may be operatively fixed with left and right front wheel support assemblies or spindles  54 ,  55  for pivoting the left and right front wheels  12 ,  13  during execution of a vehicle turn. The front wheel support assemblies or spindles  54 ,  55  may be mounted to front axle  56 . In one embodiment, as the operator turns steering wheel  24 , steering shaft  28  causes sector gear  34  to pivot about the first axis defined by sector pin  40 . As a result, sector arms  61 ,  62  mounted to sector gear  34  also pivot, causing front tie rods  42 ,  43  to turn front steering arms  51 ,  52 . 
   In one embodiment, front crank  49  pivots on a second axis that may be parallel to the longitudinal axis of the vehicle. The second axis may be defined by torque shaft  21 . Torque shaft  21  may be an aluminum or steel bar or tube having an outer thickness or diameter of between about ½ inch and about 2 inches. The torque shaft may be positioned in the vehicle above the front axle center line and the rear axle center line. 
   In one embodiment, front crank  49  may be fixed by welds or other secure attachment to torque shaft  21  at or near the forward end of the torque shaft. Left and right rear cranks  58 ,  59  may be fixed by welds of other secure attachment to torque shaft  21  at or near the rearward end of the torque shaft. The forward end of torque shaft  21  may be supported for pivotal rotation by plate or bracket  67 , and the rearward end may be supported for pivotal rotation by plate or bracket  68 . Supporting brackets  67 ,  68  may be secured to the tractor frame, and may include bearings to facilitate rotational or pivotal motion of the torque shaft about its longitudinal axis. 
   Next, one embodiment of rear steering linkage  27  will be described in greater detail. Right rear crank  59  may be positioned on torque shaft  21  at an angle of between about 60 and 180 degrees from left rear crank  58 . Left rear tie rod and right rear tie rod may be positioned behind or rearwardly of rear axle  19 . Left rear tie rod  61  may be pivotably connected by use of fastener  81  between left rear crank  58  and left rear arm member  76 . Right rear tie rod  62  may be pivotably connected by use of fastener  82  between right rear crank  59  and right rear arm member  77 . Rear arm members  76 ,  78  may be pivotable for turning the left and right rear wheels  14 ,  15 . The left and right rear wheels may be supported at the opposing ends of rear axle  19 . 
   In one embodiment, as the steering wheel is turned, the sector gear and sector steering arms pivot, and the front tie rods cause the front wheels to turn. Pivoting the sector gear also causes torque shaft  21  to rotate about its longitudinal axis, so that left and right rear cranks  58 ,  59  pivot, thereby moving left and right rear tie rods  61 ,  62  so that the rear wheels also turn simultaneously with the front wheels. 
   In a second embodiment shown in  FIGS. 4-6 , steering shaft  128  may be coupled to and extend downwardly between steering wheel  124  and hydraulic power steering valve  145 . The hydraulic steering valve may be connected via hydraulic conduits  146  to cylinder  147 . Cylinder  147  houses a piston that extends or retracts from the cylinder to cause front wheels  112 ,  113  to turn. 
   In a second embodiment, front tie rod  142  may be pivotably attached between left and right front steering arms  151 ,  152 . Left and right front steering arms  151 ,  152  may be operatively fixed with left and right front wheel support assemblies or spindles  154 ,  155  for pivoting the left and right front wheels  112 ,  113  during execution of a vehicle turn. The front wheel support assemblies or spindles  112 ,  113  may be mounted to front axle  156 . 
   In a second embodiment, rod  148  may pivotably connect left steering arm  151  to front crank  149 . Front crank  149  may be securely fixed by welds or other means at or near the forward end of torque shaft  121 . Pivotal movement of front crank  149  causes torque shaft  121  to pivot on its longitudinal axis. As the operator turns steering wheel  124 , steering shaft  128  rotates, causing a piston in cylinder  147  to turn front steering arms  151 ,  152 . As a result, front crank  149  causes torque shaft  121  to pivot. 
   In a second embodiment, crank  149  and torque shaft pivot on an axis parallel to the longitudinal axis of the vehicle. This axis may be defined by torque shaft  121 . Front crank  149  may be fixed by welds or other secure attachment means to torque shaft  121  at or near its forward end. Left and right rear cranks  158 ,  159  also may be fixed by welds of other secure attachment means to torque shaft  121  at or near its rearward end. In the embodiment of  FIGS. 4-6 , the left and right rear cranks may form an integral one-piece structure that may be welded to the torque shaft at or near its rearward end. The forward end of torque shaft  121  may be supported for pivotal rotation by plate or bracket  167 , and the rearward end may be supported for pivotal rotation by plate or bracket  168 . Supports  167 ,  168  may be secured to the tractor frame, and may include bearings to facilitate rotational or pivotal motion of the torque shaft about its longitudinal axis. 
   In one embodiment, right rear crank  159  may be secured to torque shaft  121  at an angle of between about 60 and 180 degrees with respect to left rear crank  158 . Left rear tie rod  161  may be pivotably connected between left rear crank  158  and left rear arm member  176 . Right rear tie rod  162  may be pivotably connected between right rear crank  159  and right rear arm member  177 . Rear arm members  176 ,  177  may pivot to turn the left and right rear wheels  114 ,  115 . The left and right rear wheels may be pivotably supported at the opposing ends of rear axle  119 . 
   In one embodiment, the torque shaft linkage of the present invention may function in a smaller space than required by other all wheel steering systems. The torque shaft linkage includes fewer parts than other all wheel steering systems. The torque shaft linkage can better absorb shock loading through elastic strain in torsion. The torque shaft linkage offers a more equal turn radius in both directions, because the torque shaft may pivot either way without restriction. 
   Having described the preferred embodiment, it will become apparent that various modifications can be made without departing from the scope of the invention as defined in the accompanying claims.

Technology Classification (CPC): 1