BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates generally to agricultural self-propelled windrowers, and more particularly to a rear axle suspension system for such machines.  
         [0002]     Self-propelled windrowers have been used in farming operations for several decades. Generally, the self-propelled windrower is designed to cut and process hay and other crops. More specifically, a windrower of the type under consideration here includes a tractor and a separate header. The tractor has a pair of drive wheels on the forward end and a pair of pair of tricycle-like wheels on the rear end. The wheels support a main frame that carries the engine between the wheel pairs and a drive train. A cab provides an enclosed environmentally controlled operator&#39;s platform generally above the drive wheels. A variety of crop-harvesting headers are selectively attachable to the forward end of the unit to provide the operator with a choice of tools with which to handle the crops.  
         [0003]     In past designs, the rear axle was a single beam (known as a “walking beam”) with very little suspension to ease the ride for the operator. Substantially every obstacle encountered by the rear wheels transmitted a “bounce” or vibration directly through the chassis to the operator&#39;s platform, making the ride uncomfortable and tiring, and thus resulting in lower field operation speeds. It is a unique characteristic of this type windrower that when driven without the significant weight of a header, the majority of the weight is shifted to the rear wheels. This causes the rear of the unit to squat and it becomes difficult to turn because the tail forks cannot freely pivot.  
         [0004]     It would be a significant advantage in this technology to solve the above-identified problems by providing a suspension system that provides a comfortable ride for the operator during field operation, with higher operation speeds, yet allows safe and effective operation when the unit is driven without a header.  
       SUMMARY OF THE INVENTION  
       [0005]     Accordingly, it is an object of the present invention is to provide a self-propelled windrower rear axle suspension system.  
         [0006]     Another object of the present invention is to provide a rear axle suspension system for an agricultural windrower that efficiently and effectively permits faster operating speeds than previously known.  
         [0007]     It is another object of the instant invention to provide a rear axle suspension system for a windrower that employs a split rear axle with an air spring associated with each side to independently absorb shocks.  
         [0008]     Yet another object of the present invention is to provide a rear axle suspension system for a self-propelled windrower with a split rear axle with an air spring associated with each side to absorb shocks, and a mechanism for selectively fixing the relationship between the split axle components.  
         [0009]     It is yet another object of this invention to provide a rear axle suspension system for a windrower that is durable in construction, inexpensive of manufacture, carefree of maintenance, facile in assemblage, and simple and effective in use.  
         [0010]     These and other objects are attained by providing a suspension system for the rear axle of a self-propelled agricultural windrower. The axle is split into two components, each having an air spring to absorb shocks. The two air springs are interconnected by a tube to equalize the internal pressure. A pair of pins can be inserted through the respective axle components and a structural member of the tractor to fix the components relative to the unit structure, thereby incapacitating the suspension and permitting effective steering of the tractor in the absence of a header. 
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0011]     The advantages of this invention will be apparent upon consideration of the following detailed disclosure of the invention, especially when taken in conjunction with the accompanying drawings wherein:  
         [0012]      FIG. 1  is a side plan view of a windrower, with header, showing portions of the suspension system herein discussed;  
         [0013]      FIG. 2  is partial rear view of the windrower of  FIG. 1 , without header, showing a partial break-away of the suspension system;  
         [0014]      FIG. 3  is a partial frontal perspective view of the suspension system; and  
         [0015]      FIG. 4  is a partial sectional view, taken along lines  4 - 4  of  FIG. 3 .  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0016]      FIG. 1  shows the two primary components of a self-propelled windrower  10 , i.e., tractor  12  and header  14 . Tractor  12  has a main frame  16 , with a longitudinal horizontal axis from front to back, that is supported by a pair of drive wheels  18  (only one shown) on the forward portion thereof and a pair of rear wheels  20 ,  21  (see  FIG. 2  for both wheels) adjacent the rear end. An engine, located under cowling  24 , a transmission and other components, all well known in the art, are supported on the main frame  16  and provide the power necessary for the machine to operate. A cab  26 , also supported on the main frame, encloses the operator&#39;s platform to provide an environmentally controlled location from which the windrower may be comfortably operated.  
         [0017]     Header  14  may be of several designs, but typically comprises a cutting mechanism, either a sicklebar or rotary cutter, a feeder mechanism and conditioning rolls. The header is supported by a hydraulic lift and flotation structure  28  that may be activated to selectively raise or lower the header between transport and operational positions. It is significant to note here that the rotary cutter operates at such speed and efficiency that operational speed of the windrower is limited not so much by the efficiency of the header, but more so by the comfort of the operator and the long term integrity of the windrower itself. The rear axle suspension system on the typical self-propelled windrower is such that bumps and irregularities in the field are directed through the chassis to the operator. The higher the speed of the windrower, the more stress the chassis is subjected to, and the more discomfort experienced by the operator. The rear axle suspension system to be described herein reduces this stress and discomfort, making it possible to operate the windrower at a higher ground speed and thus greater crop throughput.  
         [0018]      FIG. 2  shows a general rear view of the windrower  10 , with a depiction of the main elements of suspension system  30 . A split axle, comprised of two mirror image axle members  32 ,  34  interconnect rear wheels  20 ,  21  and main frame  16 . Each axle member is made up of two telescoping members  36 ,  38  (since one side is the mirror image of the other, only one will be described in detail, though the same reference numbers will be used when describing components of both axle members), each having horizontal front-to-back holes therein that can be aligned and pinned or bolted to fix the distance at which telescoping member  38  extends outwardly beyond member  36 . In this manner, the distance between wheels  20 ,  21  may be varied as required by the farming process being undertaken.  
         [0019]     Wheel  21  is bolted to the axle of tailfork  40  which in turn has a generally vertically extending stub axle (not shown) fixed in a bearing housing  42  at the outer end of telescoping member  38 . A flange  44  is affixed to the inner end portion of telescoping member  36  and is attached to main frame  16  by pin  46  for vertical pivotal movement thereabout. An air spring  50  is positioned toward the outward end of telescoping member  36  to work between main frame  16  and axle member  32 . This interaction can be seen well in  FIG. 4 . A spring cover  52 , affixed to main frame  16  where the inward side of the cover and the main frame are in contact, extends up and over and contacts the top of spring  50 , and extends downwardly past telescoping member  36 . Thus, the air springs absorb a great deal of the forces encountered by the wheels, and provide an independent suspension for the two axle members.  
         [0020]     The two air springs  50 ,  51  are interconnected by air tubes  54 ,  56  that are joined by T-connector  58 . The free leg of T-connector  58  is attached to second T-connector  60 . One leg of T-connector  60  is attached to a relief valve  62  and the other to a tank valve  64 . Tank valve  64  is used to pressurize the two air springs, and to adjust the pressure therein. Of course, it is not required for operation that the two air springs be interconnected; however, it filled individually, extra effort must be exerted to assure that they are at the same, or very nearly the same, pressure.  
         [0021]     When the tractor is supporting the header, the primary weight distribution is focused on the front wheels  18 . However, when the header is removed, as might be done for road transit, the rear wheels  20 ,  21  bear the greater weight. In fact, the weight is such that the axle members pivot substantially or fully to the maximum, causing the machine to “squat” at the rear end. Steering under these circumstances becomes difficult because the rear wheels cannot freely pivot within bearing housing  42 . To overcome this problem, a pin  70  is provided for manual selective insertion through tube  72  which is rigidly affixed to telescoping member  36  (see  FIGS. 3 and 4 ).  FIG. 4  further shows that spring cover  52  is located closely adjacent one end of tube  72 , such that pin  70  protrudes through tube  72  and a somewhat elongate slot  74  through the cover. Thus, insertion of pin  72  incapacitates the air spring and locks axle member  34  to main frame  16  in a generally horizontal position. The vertical location of pin  70  within the slot  74  also serves as a gauge to determine if the machine is level. If the pin is in the center of the slot, the windrower is substantially level. A snap or cotter pin  76  can be inserted through a hole in the end of pin  70  to hold it in position.  
         [0022]     It will be understood that changes in the details, materials, steps and arrangements of parts which have been described and illustrated to explain the nature of the invention will occur to, and may be made by those skilled in the art upon a reading of this disclosure within the principles and scope of the invention. The foregoing description illustrates the preferred embodiment of the invention; however, concepts, as based upon the description, may be employed in other embodiments without departing from the scope of the inventions. Accordingly, the following cairns are intended to protect the invention broadly as well as in the specific form shown.
A suspension system for the rear axle of a self-propelled agricultural windrower. The axle is split into two components, each having an air spring to absorb shocks. The two air springs are interconnected by a tube to equalize the internal pressure. A pair of pins can be inserted through the respective axle components and a structural member of the tractor to fix the components relative to the unit structure, thereby incapacitating the suspension and permitting effective steering of the tractor in the absence of a header.