Abstract:
A suspension system for a vehicle includes a right front wheel, a left front wheel, a right rear wheel and a left rear wheel. A suspension system for the vehicle includes a first cylinder supporting the vehicle at the right front wheel in fluid communication with a second cylinder supporting the vehicle at the left front wheel, wherein the first and second cylinders form a virtual articulated front axle. The suspension system also includes a third cylinder supporting the vehicle at the right rear wheel and a fourth cylinder supporting the vehicle at the left rear wheel. The suspension system includes two spool valves in fluid communication with the first and second cylinders and intermediate the first and second cylinders. When one of the rear wheels is unweighted, an associate one of the spool valves closes and fluid flow between the first and second cylinders is blocked to create a virtual locked axle.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a vehicle and suspension system with an automatically locking front floating axle that locks when it detects that one of the rear wheels is unweighted and is directed to a control system for such a suspension. 
     2. Description of the Prior Art 
     Wheeled vehicles that operate on a slope and especially those that work on side slopes may require adjustable suspensions that reposition the vehicle frame with respect to the ground to maintain a level orientation. Such systems provide height adjustment while increasing stability and maintaining the vehicle at a substantially level operating orientation. Many types of agricultural vehicles such as over the row harvesters with a relatively high center of gravity require such adjustable suspension systems. 
     Systems are known that utilize hydraulic cylinders to maintain the vehicle at a level orientation for improved positioning relative to plants being treated or harvested. Typical prior art systems may have front and rear hydraulic cylinders that are interconnected to form a master/slave system. Systems are known that use interconnected front wheels or rear wheels to simulate a floating axle. Such systems shift fluid back and forth to extend and simultaneously retract opposed hydraulic cylinders at the front or rear to level the vehicle. Although such hydraulic suspension systems generally provide for a ride with improved leveling, such systems may suffer from lack of responsiveness or overcorrection in certain situations. Therefore, such vehicles may are subject to tipping over, especially when working on a hillside or when a hole is encountered by one of the wheels. 
     A system is needed that provides for large coverage to maintain stability when the center of gravity of the vehicle is over the supported area formed by the support points of the vehicle. Under various operating conditions with a floating axle, the suspension system has support points that change. An improved hydraulic suspension system would provide stable correction with a stability area that overlaps as it shifts and is not vulnerable to tipping over. Such a suspension system should also have the advantages of a floating axle to maintain a level operating orientation. Such a system should also be simple and reliable. The present invention addresses these as well as other problems associated with hydraulic suspension systems for vehicles operating on slopes. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a harvester and a hydraulic suspension system for a harvester that provides greater stability and improved ride. In particular, the present invention uses a hydraulic suspension system for a harvester that simulates a floating front axle that is automatically lockable to provide improved stability. 
     In one embodiment, the harvester vehicle is a harvester such as an over-the-row harvester. Such vehicles have a relatively high center of gravity and may travel on uneven terrain such as across the slopes of hills where stability and tipping are concerns. The suspension system for the vehicle is a hydraulic system with an extendable cylinder associated with each of the four wheels of the vehicle. The hydraulic cylinders may be extended or retracted to raise or lower the vehicle. In addition, the cylinders on one side are raised or lowered together to maintain the cab and chassis at a level orientation when traversing sides of hills. The front and rear hydraulic cylinder on each side of the vehicle are in a master-slave relationship with the rear cylinders extending and retracting so as to follow the front cylinders. 
     The front wheels are supported on hydraulic cylinders of the suspension system that are arranged and connected in parallel and simulate a virtual floating axle. When one of the front hydraulic cylinders extends, the other retracts in an equal and opposite amount due to the hydraulic fluid flow between the front cylinders. The fluid flow may also be locked so that the virtual front axle does not float. The floating axle provides improvements for ride and suspension while the locked axle generally provides a wider and more stable support base for the vehicle having four support points. 
     The present suspension system uses a spool valve associated with each rear hydraulic support cylinder. The spool valve has a sliding spool that blocks flow in an actuated position and a spring opens the valve when not actuated. When the spring force is overcome by hydraulic fluid pressure, the spool slides and the valve closes and flow stops. When both valves are in the open position, fluid flows freely between the front hydraulic cylinders and the virtual front axle behaves as a floating axle. When either of the valves is actuated, the parallel circuit between the front hydraulic cylinders is broken and the virtual front axle becomes a locked front axle. 
     With a locked virtual front axle, the vehicle is supported on all four wheels and provides a rectangular base of support that is stable as long as the center of gravity falls within the rectangle form by the four wheels. When the virtual front axle is in a floating mode, the stability base forms a triangle formed by the rear wheels of the vehicle and by the virtual pivot of the front axle intermediate the front wheels. As long as the center of gravity is maintained within this stability triangle, the vehicle is stable and will not tip. This is a normal operating condition and is achieved as long as neither of the spool valves associated with the rear cylinders are actuated. 
     Should the vehicle encounter uneven terrain and begin to tip, in a conventional hydraulic suspension system, the floating axle may pivot further and the vehicle tips. The vehicle operator may not be able to correct such a situation. However, with the present suspension system, when the vehicle begins to tip, one of the rear wheels may no longer support the vehicle. As this happens, the fluid pressure from the associated cylinder to the associated spool valve stops and the valve changes to its actuated mode wherein it is closed. When one of the spool valves closes and blocks fluid flow, the parallel circuit between the front support cylinders ends is broken and the virtual front axle is no longer floating and becomes a locked front axle. As the vehicle tips, the center of gravity also shifts to the lower side to which the vehicle is tipping. However, when the opposite rear hydraulic cylinder becomes unweighted and the front axle locks, a new virtual support zone is created as the vehicle is supported on a locked front axle rather than a virtual pivot. A triangle support zone is formed by the two front wheels and the still weighted rear wheel. This zone overlaps the triangle of the normal operating position and extends to the side to which the center of gravity shifts. Therefore, the vehicle remains stable and will not tip. The center of gravity is always maintained in a zone of stability with this configuration as the suspension system provides a support zone that changes and overlaps automatically if tipping begins. 
     The suspension system provides the advantages of a floating front axle as well as the stability provided with a locked front axle and provides the switch between the different modes automatically while maintaining stability. 
     These features of novelty and various other advantages that characterize the invention are pointed out with particularity in the claims annexed hereto and forming a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings that form a further part hereof, and to the accompanying descriptive matter, in which there is illustrated and described a preferred embodiment of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Referring now to the drawings, wherein like reference numerals and letters indicate corresponding structure throughout the several views: 
         FIG. 1  is a side diagrammatic view of a vehicle with a hydraulic suspension system; 
         FIG. 2  is an end view of the vehicle shown in  FIG. 1  on level ground; 
         FIG. 3  is an end view of the vehicle shown in  FIG. 2  moving along a side of a hill; 
         FIG. 4  is a diagrammatic top view of a vehicle and suspension system having a virtual front with a stability diagram overlaid on the vehicle axle locked according to the principles of the present invention; 
         FIG. 5  is a diagrammatic top view of the vehicle and suspension system shown in  FIG. 4  with a floating front axle with a stability diagram overlaid on the vehicle; 
         FIG. 6  is a diagrammatic top view of the vehicle and suspension system shown in  FIG. 4  with a stability diagram overlaid on the vehicle when no weight detected in a first rear wheel; and 
         FIG. 7  is a diagrammatic top view of the vehicle and suspension system shown in  FIG. 4  with a stability diagram overlaid on the vehicle when no weight detected in a second rear wheel; and 
         FIG. 8  is a diagrammatic view of the control system for the suspension system shown in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings and in particular to  FIG. 1 , there is shown a harvester vehicle, generally designated  100 . The harvester vehicle  100  generally includes a chassis  102  and is configured as an over the row type harvester as is more clearly shown in  FIGS. 2 and 3 . However, one of ordinary skill in the art would readily understand that other vehicle configurations could also be used. The harvester includes a cab  110  and a drive for the harvester  100 . The front wheels  112  and  114  define a virtual front axle  106  while the rear wheels  116  and  118  define a virtual rear axle  108 . It can be appreciated that if the vehicle  100  is configured as an over the row type harvester vehicle, it is not possible to have actual axles that extend between the associated left and right wheels. However, the hydraulic suspension system  104  provides a variable system that responds as either a locked front axle or floating front axle wherein the front wheels  112  and  114  raise and lower as if connected on an axle pivoting about a center pivot. 
     The suspension system provides for raising and lowering the entire chassis  102  depending on the needs of the operation being performed, the terrain and the crop being harvested. It can be appreciated that the harvester  100  may travel along the sides of hills, as shown in  FIG. 3 . In such situations, the wheels must be raised or lowered relative to the frame  102  on at least one side of the vehicle to provide leveling and prevent the vehicle  100  from tipping over. As shown in  FIG. 3 , the left side of the vehicle is raised relative to the right side of the vehicle, thereby maintaining the cab  110  and chassis  102  at a substantially level horizontal position on the side of the slope. To maintain the harvester  100  at this level horizontal position, telescoping hydraulic cylinders  124  and  128  on the left side of the vehicle are extended while corresponding hydraulic cylinders  122  and  126  on the right side of the vehicle  100  are retracted. When the harvester is traversing sideways on a hill with the right side of the vehicle on the downhill slope, the position is reversed from that shown in  FIG. 3  and hydraulic cylinders  122  and  126  are extended while hydraulic cylinders  124  and  128  are retracted. 
     Referring to  FIGS. 4-7 , the stability and support of the harvester vehicle  100  varies as the suspension system  104  is configured for different harvester orientations and situations. As shown in  FIG. 4 , when the suspension system  104  is locked and the hydraulic cylinders  122  and  124  associated with each front wheel cannot extend or retract, the suspension system  104  is substantially locked and the vehicle  104  is supported on all four wheels in a rectangular configuration as represented by stability rectangle A of  FIG. 4 . As long as the center of gravity of the vehicle  100  remains within the rectangular support area A, the vehicle  100  is stable and will not tip. 
     As shown in  FIG. 5 , to provide improved ride and to accommodate uneven terrain, the virtual front axle  106  is normally in a floating mode. The virtual floating front axle  106  performs as if there were a central pivot point intermediate the front wheels  112  and  114 . One of the hydraulic cylinders  122  or  124  extends while the other retracts in response to uneven terrain. When the suspension  104  is configured so that the virtual front axle  100  floats, the stability diagram is triangular as shown at B in  FIG. 5 . In the normal operating mode, the virtual front axle  106  floats. The vehicle  100  will remain stable as long as the center of gravity does not fall outside of the stability base B formed by the virtual pivot and the rear wheels. 
     It can be appreciated that prior suspension systems with a floating front axle would become unstable and may tip over if the center of gravity falls outside of the triangle B shown in  FIG. 5 . Such systems would become unstable when the floating front axle could not extend the proper cylinder quickly enough. In other situations, the front axle may retract the wrong hydraulic cylinder, compounding the tipping. 
     The present suspension system  104  provides for floating the virtual front axle  106  during normal operation while also providing the larger support base of a locked front axle. 
     As shown in  FIGS. 6 and 7 , the present suspension system  104  provides for locking of the virtual front axle  106  if there is a decrease in weight to below a predetermined level, or no weight on one of the rear wheels  116  or  118 . In such a situation, the front virtual front axle  106  locks and the stability diagram for the harvester  100  changes from stability triangle B as shown in  FIG. 5  to stability triangle C shown in  FIG. 6  when there is no weight on the left rear wheel. Similarly, when there is no weight on the right rear wheel  116 , the stability diagram changes from stability triangle B shown in  FIG. 5  to stability triangle D shown in  FIG. 7 . It can be appreciated that stability triangles C and D provide a base that accommodates movement of the center of gravity as it shifts, as would occur if one of the rear wheels is no longer supporting the vehicle  100 . The present suspension system  104  also returns to a floating virtual front axle once there is weight on both rear wheels  116  and  118  and the support base B is again achieved. It can be appreciated that when both rear wheels have weight on them, the center of gravity is shifted to a position within the stability triangle B shown in  FIG. 5 . 
     Referring now to  FIG. 8 , there is shown a flow diagram for the suspension system  104 . The suspension system  104  includes four extendible hydraulic cylinders  122 ,  124 ,  126  and  128 . Hydraulic cylinder  122  is mounted at the right front wheel  112 . Hydraulic cylinder  124  is mounted at the left front wheel  114 . Hydraulic cylinder  126  is mounted at the right rear wheel  116  and hydraulic cylinder  128  is mounted at the left rear wheel  118 . Hydraulic lines  132  and  134  extend from opposite ends of the cylinder  122 . When hydraulic fluid is increased through line  132 , the cylinder  122  retracts. When hydraulic fluid is increased through line  134 , the hydraulic cylinder  122  extends. Similarly, the left front hydraulic cylinder  124  includes hydraulic lines  136  and  138  and behaves in a same manner. 
     The right rear hydraulic cylinder  126  includes hydraulic lines  142  and  144 . When hydraulic pressure is increased through line  142 , the right rear cylinder retracts. When hydraulic pressure through line  144  increases, the right rear cylinder  126  extends. Similarly, the left rear cylinder  128  includes hydraulic lines  146  and  148  and operates in the same manner. The suspension system also includes control valves  172 A and  172 B on the right side of the vehicle  100 , control valves  174 A and  174 B for the side of the vehicle that act as load holding valves to prevent the machine from drifting down. The entire height of the vehicle  100  can be increased or decreased by control valves  172 A,  172 B,  174 A and  174 B. Valves  170 A and  170 B actuate to raise and lower the front wheels in case of tilting. The entire vehicle  100  can be raised or lowered by extending or retracting all support cylinders  122 ,  124 ,  126  and  128 . Even when one side is extended more than the other, the vehicle  100  may be raised or lowered. The suspension system  104  includes servo valves  180 ,  182  and  184  that control the speed and flow to ensure smooth extension and refraction and prevent a sudden shift of the vehicle  100 . 
     With the suspension system  104 , the respective front and rear cylinder pairs  122 - 126  and  124 - 128  for each side are in a master-slave relationship with the front cylinders  122  and  124  controlling the respective rear cylinders  126  and  128 . The front and rear cylinders  122 - 126  and  124 - 128  are connected in series so that a side of the vehicle  100  may be raised or lowered together to achieve configurations such as shown in  FIG. 3  by adjusting one of the cylinders  122  or  124 . The front cylinders  124  and  122  are connected in parallel and define a floating front axle in normal operation. Fluid lines  152  and  154  flow through and are connected to fluid line  150  through pilot valves  162  and  164 . The valves  162  and  164  are spool type valves that are biased so as to be normally open. In normal operation, there is weight on the rear wheels  116  and  118  and therefore on the rear cylinders  126  and  128 . Therefore, hydraulic pressure is applied through fluid lines  166  and  168  to the spool in each respective valve  162  and  164 . When there is force on the rear wheels, the fluid lines  166  and  168  deliver hydraulic pressure to the valves  162  and  164  and the inlet remains open. In this situation, the virtual front axle  106  is a floating axle and the suspension system  104  behaves with a stability diagram B as shown in  FIG. 5 . When the vehicle  100  begins to tip such that there is no pressure on at least one of the rear wheels, the hydraulic pressure to one of the valves  162  or  164  drops. Therefore, when the pressure drops relative to the fluid pressure of lines  176  and  178 , the valve  162  or  164  shifts to its actuated position and closes the inlet port. This blocks the parallel connection between the left and right front cylinders  122  and  124  and the virtual front axle  106  is locked automatically. When the left rear cylinder  128  has no pressure acting on it, the fluid pressure in line  148  drops and the valve  162  closes. In this position, the suspension system  104  has a triangular stability base shifted toward the front axle, which is locked and away from the unweighted wheel  116  as shown in  FIG. 6  with stability triangle C. In a similar manner, when the pressure in hydraulic line  144  drops, the force to the pilot spool valve  164  drops. When the fluid pressure relative to the pressure in line  176  drops, the valve  164  closes and the inlet is closed. Under these conditions, the virtual floating front axle  100  is a locked axle and the support configuration shifts to that shown in  FIG. 7  and stability triangle D. 
     When both of the rear wheels  116  and  118  again have pressure, the hydraulic force to valve  162  or  164  again increases relative to the pressure in lines  176  and  178 , the valve  162  or  164  opens and the virtual front axle  106  becomes a floating axle. When the front axle  106  becomes a floating axle, the suspension behaves with a stability base as shown in  FIG. 5  and stability triangle C. 
     It can be appreciated that with the suspension system  104 , the stability triangles B, C and D are overlapping. Therefore, as the vehicle  100  begins to tip, the center of gravity moves to a position within one of the stability frames as the vehicle  100  is tipping and therefore prevented from tipping further. The center of gravity never passes outside a stable supported zone. The suspension system  104  provides the ride and performance of a floating front axle while providing the stability of a locked front axle with a simple and reliable suspension system. 
     It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.