Abstract:
In an agricultural tractor system, an engine-cab unit and a front ground-drive part are combined to form one front assembly. The front assembly may be joined, in a modular fashion, to a first rear ground-drive part or to a second rear ground-drive part which is structurally different from the first rear ground-drive part, in order to form a driveable tractor.

Description:
CROSS-REFERENCE TO A RELATED APPLICATION 
       [0001]    The invention described and claimed hereinbelow is also described in German Patent Application DE 10 2008 059 467.9 filed on Nov. 28, 2008. This German Patent Application, whose subject matter is incorporated here by reference, provides the basis for a claim of priority of invention under 35 U.S.C. 119(a)-(d). 
       BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to an agricultural tractor, and focuses on, although is not limited to, a tractor comprising at least one crawler track assembly. 
         [0003]    Agricultural tractors which include a crawler track assembly are known in many forms, e.g., from EP 0 000 211 B1. In comparison to a ground drive comprising individual wheels, a crawler track assembly makes it possible to distribute the weight of the tractor over a large surface area of the ground, thereby allowing a heavy tractor to also be used on ground surfaces that are sensitive to high loads. Since the production of a crawler track assembly is much more complex than that of a ground drive comprising individual wheels, tractors which include a crawler track assembly are therefore more expensive than are machines which include a conventional ground drive. They therefore comprise only a small portion of all of the agricultural tractors in use. As a result, they are manufactured in small production series, which greatly increases the costs of these machines. 
       SUMMARY OF THE INVENTION 
       [0004]    The object of the present invention, therefore, is to create a concept for agricultural tractors that results in the largely uniform production of machines having a crawler track assembly and a conventional ground drive, thereby enabling the parts common to both machines to be manufactured in a uniform manner and, therefore in a larger production series, which has cost advantages. 
         [0005]    The object is attained via an agricultural tractor system in which an engine-cab unit and a front ground-drive part are combined to form one front assembly, and the front assembly may be joined, in a modular fashion, to a first rear ground-drive part or to the second rear ground-drive part which is structurally different from the first rear ground-drive part, in order to form a driveable tractor. The front assembly may therefore be manufactured identically and economically in large production runs for a large number of tractor types; the cost disadvantages associated with a smaller production series usually involve the rear ground-drive parts, and not the entire machine. 
         [0006]    The design differences between the at least two different rear ground-drive parts may be, in particular, that the first rear ground-drive part includes at least one wheel pair, and the second rear ground-drive part includes two track roller units. 
         [0007]    According to a first embodiment, the wheels or track roller units may comprise substantially all of the rear ground-drive parts, and they may be mountable on the same axle of the tractor. 
         [0008]    According to a second embodiment, the rear ground-drive parts may each include a carrier in addition to the wheels or track roller units; the wheels are rotatably mounted on the carrier of the first rear ground-drive part, and the two track roller units are mounted on the carrier of the second rear ground-drive part. 
         [0009]    It is also feasible to combine the two designs by making it possible to swap the wheels and track roller units on at least one of the carriers. It may also be possible for a swap of this type to be carried out by an operator, although joining the front assembly and the rear ground-drive part may be a substantially more complex procedure, which may possibly be so complex that it is carried out only when the tractor is manufactured or undergoes repair work. 
         [0010]    Preferably, each of the track roller units includes a central driven roller situated between non-driven front and rear deflection rollers. A track roller unit of this type is easily converted from crawler track operation to wheel operation by removing the crawler track, possibly removing the deflection rollers, and replacing the driven roller. 
         [0011]    There are various possibilities for steering a tractor of the system according to the present invention, one or two of which is/are preferably realized simultaneously in the same tractor:
       the front ground-drive part is steerable;   the wheels of the first rear ground-drive part and/or the roller track units of the second rear ground-drive part may be folded inward against their carriers;   the carrier of the first and/or second rear ground-drive part may be folded inward relative to the engine-cab unit;   the carrier of the first and/or second rear ground-drive part may be folded inward relative to the engine-cab unit.       
 
         [0016]    There are two variants, in particular, for the latter case: The rear ground-drive part may be connected to the front assembly such that it is pivotable about a vertical axis, i.e., the rear ground-drive part may be inherently rigid, or the rear ground-drive part includes, in addition to the carrier, a bridge part which is fixedly connected to the front assembly; the carrier is located underneath the bridge part, and it is pivotable about a vertical axis, toward the bridge part. 
         [0017]    Since the front ground-drive part of an agricultural tractor usually carries a lighter weight than does the rear ground-drive part, it is generally sufficient for the front ground-drive part to have a single axis. The front assembly is therefore not stable on its own, nor is it driveable. Only when it is combined with the rear ground-drive part is a driveable machine attained. 
         [0018]    Preferably, more than one axle may be provided on the rear ground-drive part, since it is usually loaded to a greater extent than is the front ground-drive part. 
         [0019]    An adapter for a device to be pulled is preferably provided on the rear ground-drive parts. Potential adapters include a trailer hitch, a hydraulic lift, and a saddle. 
         [0020]    When the rear ground-drive part includes a bridge part and a rotatable carrier installed underneath it, then the adapter is preferably located on the bridge part. 
         [0021]    The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1  shows a schematic side view of an agricultural tractor, according to the present invention, which includes a first type of rear ground-drive part; 
           [0023]      FIG. 2  shows a schematic side view of the tractor including a second type of rear ground-drive part; 
           [0024]      FIG. 3  shows a side view of the tractor including a third type of rear ground-drive part; 
           [0025]      FIG. 4  shows an example of the steering of the tractor; 
           [0026]      FIG. 5  shows a second example of the steering of the tractor; 
           [0027]      FIG. 6  shows a third example of the steering of the tractor; 
           [0028]      FIG. 7  shows a side view of the tractor including a fourth type of rear ground-drive part; 
           [0029]      FIG. 8  shows a side view of the tractor in  FIG. 7 , which includes a rear ground-drive part which has been converted from crawler track drive to wheel drive; 
           [0030]      FIG. 9  shows a side view of a variant of the tractor in  FIG. 7  during the conversion from crawler track drive to wheel drive; and 
           [0031]      FIG. 10  shows the tractor in  FIG. 9 , converted to wheel drive. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0032]      FIG. 1  shows a highly schematicized side view of an agricultural tractor according to a first embodiment of the present invention. The tractor is divided into two modules: a front module  5  and a rear module  4 . Front module  5  includes an engine housing  1 , a driver&#39;s cab  2 , and a front ground-drive part  3 . Front ground-drive part  3  includes an axle having wheels  6  which are steered via a steering knuckle and include air-filled tires. 
         [0033]    Rear module  4  includes a carrier block  7  having a rear axle on which wheels  6  comprising air-filled tires are mounted. The rear axle may be a rigid axle, or it may be steerable, like the front axle, in order to improve the maneuverability of the tractor, in particular to reduce its turning clearance circle and to enable travel in a “dog walking” manner. 
         [0034]    At an interface  8  between the modules, a drive shaft, e.g., extends from the engine in front module  5  to wheels  6  of rear module  4 . 
         [0035]    Rear module  4  is shown separately from front module  5  using solid lines, and it is shown connected to front module  5  using dashed lines, in order to indicate that modules  4 ,  5  are preassembled separately and are joined together in a subsequent phase of the tractor assembly. This makes it possible to use front module  5  in conjunction with rear modules having a design that differs from that shown in  FIG. 1 . 
         [0036]    An example of the combination of front module  5  with another type of rear module is shown in  FIG. 2 . In this case, rear module  4 ′ includes two axles  9 ,  10  comprising air-filled tires, in order to distribute a high load, e.g., of a trailer supported on rear module  4 ′, or a ground working tool that is carried in a freely hanging manner, over a larger ground surface area than is possible using the single axle of rear module  4 . 
         [0037]    Axles  9 ,  10  may be rigid axles. To improve the ability of tractor to travel around curves, preferably at least one rear axle  10  is steerable. Both axles  9 ,  10  must be steerable for dog-walking travel to be possible. Each axle  9 ,  10  may be controlled individually using steering knuckles, or a common carrier block of both axles  9 ,  10  may form a fifth wheel which is rotatable about a vertical axle and toward a bridge part—which is fixedly connected to front module  5 —of rear module  4 ′. 
         [0038]      FIG. 3  shows a tractor having the same front module  5  as that described above, and a modified rear module  4 ″. Rear module  4 ″ is composed mainly of a bridge part  11 , which extends in the longitudinal direction of the tractor, is oriented substantially horizontally, is rigidly attached to front module  5 , and includes a saddle  12  for a saddle support, and is composed of a crawler track assembly having a carrier block  7  which is located underneath bridge part  11  and is interconnected therewith via a flange joint  17 , and track roller units  13  located on either side of carrier block  7 . Each track roller unit  13  includes a front and a rear deflection roller  16 , a track belt  15  wound around deflection rollers  14 , and a support roller  16  which is located in an intermediate space between the two deflection rollers  14  in contact with a section of roller belt  15  lying on the ground, in order to distribute the weight resting on rear module  4 ″ as evenly as possible along the entire length of the section lying on the ground. Depending on the distance between deflection rollers  14 , it is also possible to eliminate the support roller  16 , or more than one support roller  16  per track roller unit  13  may be provided. 
         [0039]    In the case of front ground-drive part  3  and rear modules  4  and  4 ′, the extension of the ground-contact surface is determined mainly by the diameter and number of wheels  6 ; however, in the case of a crawler track assembly, such as that belonging to rear module  4 ″, the distance between deflection rollers  14  is the main determining factor of the extension of the ground-contact surface. As shown in  FIG. 3 , the diameter of deflection rollers  14  may therefore be smaller than the diameter of wheels  6 , and, in particular, it may be smaller than the ground clearance of bridge part  11 . When the crawler track assembly is turned for steering, it is therefore possible for deflection rollers  14  of the crawler track assembly to move unencumbered underneath bridge part  11 , and the steering angle is not limited by the possibility that the wheels may strike bridge part  11 , as could happen in the case of the embodiment shown in  FIG. 2 . 
         [0040]      FIG. 4  shows a top view of the tractor in  FIG. 3 , and is used to illustrate the mode of operation of its steering. Wheels  6 , which are steered using steering knuckles, are located on front module  5 . They are turned to the left relative to the longitudinal direction of the tractor; the longitudinal direction and rolling direction of wheels  6  are indicated using dash-dotted arrows. Carrier  7  is turned in the opposite direction, and so the crawler track assembly supports the travel around the curve. In an alternative operating mode, the carrier is turned in the same direction as wheels  6  of front module  5 ; in this operating mode known as “dog walking”, the tracks of wheels  6  and track roller unit  13  are offset in parallel to one another in order to distribute the machine load on the ground as evenly as possible. 
         [0041]    The rotational axis of flange joint  17  coincides with the center point of saddle  12 , and therefore braking forces applied by a trailer lying on the saddle do not affect the rotation of carrier  7 . A coupling  18  for a trailer drawbar  19  or a ground-working tool drawn behind is located on carrier  7 , since the rear end of bridge part  11  swivels outward when passing around a curve, and there is a risk that a trailer drawbar coupled thereto could tilt. 
         [0042]    An alternative design of the steering of the tractor is shown in  FIG. 5 . In this case, each track roller unit  13  may swivel individually about separate axes  20  relative to carrier  7 , and carrier  7  itself is stationary. In this design, the swing of track roller units  13  in the longitudinal direction of the tractor is less than it is in the case of the fifth-wheel design shown in  FIG. 4 , and so large turning angles are easier to realize. 
         [0043]    In the embodiment shown in  FIG. 6 , front and rear modules  5 ,  4 ″ are connected in a joint  21  to a vertical axis, and the machine is steerable by turning front wheels  6 , and via the swivel motion of both modules  4 ″,  5  opposite one another in joint  21 . 
         [0044]    Of course, rear module  4 ″ which includes a crawler track assembly and which is shown as an example may be replaced in the machines shown in  FIGS. 4 through 6  with rear modules having wheels, such as  4  and  4 ′, or with one of the rear modules  4 ′″,  4 ″″ to be described below. 
         [0045]      FIG. 7  shows the tractor according to a fourth embodiment of the present invention. In this case, rear module  4 ′″ of the machine is designed as a stacked crawler track, that is, each track roller unit  13  includes a central drive roller  22 , and it includes a non-driven deflection roller  23  in front (in the direction of travel) of it and one behind it, the diameters of which are much smaller than that of drive roller  22 . The diameter of drive roller  22  is greater than the ground clearance of bridge part  11 , but since the deflection rollers may move underneath bridge part  11  when swiveling, the pivot movement freedom of rear module  4 ′″ is not necessarily less than that of a module having wheels of the size of drive rollers  22 . 
         [0046]    In addition to the relative great pivot movement freedom, a further advantage of the stacked roller track is convertibility.  FIG. 8  shows a view of the tractor in  FIG. 7 , in which track belt  15  is open and lies flat on the ground. Deflection rollers  22  are offset on carrier block  7  in a raised position, and have no ground contact. When the tractor moves forward in this configuration, drive rollers  23  act as wheels. 
         [0047]    To improve the driving behavior when the wheels are used, drive rollers  22  may be provided with an elastic enclosure  24 . 
         [0048]    The operator may convert rear module  4 ′″ from roller track operation to wheel-driven operation and back as necessary. 
         [0049]    A further embodiment of a convertible rear module  4 ″″ is shown in  FIGS. 9 and 10 . In roller track operation, rear module  4 ″″ does not differ externally from module  4 ′″ in  FIG. 7 .  FIG. 9  shows an intermediate stage of the conversion from roller track operation to wheel-driven operation. Track belt  15  on both roller track units  13  has been opened, drive roller  22  has been removed, and a carrier flange of drive axle  25  is visible. Module  4 ″″ rests on deflection rollers  23 . The ground level at deflection rollers  23  is slightly higher than it is under drive axle  25 . It is therefore possible to mount a wheel  26 —which may include an air-filled tire—on the flange of drive axle  25 ; the diameter of wheel  26  is slightly greater than that of drive roller  22  which has been removed. When the machine moves, wheels  26  come in contact with the ground, and deflection rollers  23  become unloaded and may be easily removed. The configuration shown in  FIG. 10  attained, in which wheel-driven operation is possible. 
         [0050]    It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the types described above. 
         [0051]    While the invention has been illustrated and described as embodied in an agricultural tractor, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention. 
         [0052]    Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention.