Patent Abstract:
A road milling machine includes a rear wheel or track mounted on a pivot arm such that the wheel or track is movable between a first outer end position projecting laterally relative to the machine frame, and a second inner end position which permits milling close to an edge. A travel drive of the rear wheel or track provides a driving force to move the wheel or track between the end positions.

Full Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a road milling machine for the treatment of road pavements, as well as to a method for pivoting a travelling drive unit of a road milling machine. 
     2. Description of the Prior Art 
     A road milling machine is known, for example, from EP 916 004 A and U.S. Pat. No. 6,106,073. 
     Such road milling machine comprises a controller for the travelling, steering and milling operation, said controller being operated by an operator, and is provided with a machine frame adjustable in height via lifting columns. 
     Travelling drive units are arranged at the lower ends of the lifting columns which may be designed as wheeled travelling drive units or tracked travelling drive units. In this arrangement, it is also possible to have a mixture of wheeled and tracked travelling drive units. 
     A working drum revolving about an axis is arranged at the machine frame. 
     No less than one of the rear lifting columns with travelling drive unit attached thereto is pivotable by means of a pivoting arm from a first, outer end position projecting laterally relative to the machine frame to a second, inner end position wholly or in part within the machine frame. The inner position is required in order to be able to drive as closely along obstacles as possible with the so-called zero side of the road milling machine, where the zero side of a road milling machine is that side on which a front end of the working drum extends as closely as possible to the outer side of the road milling machine. 
     The pivotable travelling drive unit is also provided with a steering device which can adjust a steering angle for the travelling drive unit that deviates from straight-ahead travel. One driving device each is intended for driving the pivoting arm and for driving the steering device. 
     In such road milling machines, the travelling drive unit needs to be raised in order to move it from one end position to the other end position irrespective of whether the lifting column is guided by a single pivoting arm, or by two pivoting arms articulated in a parallelogram-like fashion, or in a different fashion. To this end, the machine frame needs to be raised in a first step, at least at the rear travelling drive units, until the working drum has a certain distance from the road surface. In order to protect the working drum, a wooden beam, for example, then needs to be pushed under the working drum so that the same does not rest on the ground and there is no possibility of damaging the milling tools when the pivotable travelling drive unit is raised in order to be able to pivot it without being in contact with the ground surface. 
     SUMMARY OF THE INVENTION 
     The object of the invention now is to specify a road milling machine and a method for pivoting a travelling drive unit of a road milling machine which is simplified in design on the one hand and is easier and quicker to operate on the other. 
     The invention advantageously provides for the travel drive of the pivotable travelling drive unit to form the first driving device for the pivoting movement of the pivoting arm. It is thus intended for the pivoting arm to not comprise a separate, own driving device and for the travel drive to be used for pivoting the pivoting arm with the lifting column and the travelling drive unit while the travelling drive unit is in contact with the ground surface. As a result, it is no longer necessary to raise the machine frame of the road milling machine and to arrange a protection device underneath the milling drum in order to then be able to bring the pivotable travelling drive unit out of contact with the ground surface. Rather, it is merely necessary for the working drum to no longer be in the cut, whereas contact with the ground surface of the pivotable travelling drive unit is maintained and is even required in order to be able to perform the pivoting movement. 
     The controller may coordinate the travel drive and the steering angle of the pivotable travelling drive unit in such a way that the travelling drive unit is transferable, on a circular arc, from the first outer end position projecting relative to the machine frame to the second inner end position and back while being in permanent contact with the ground surface. In the process, the controller for transferring the travelling drive unit from one end position to the other may drive the steering device automatically until the travelling drive unit is aligned essentially orthogonal to the pivoting arm. In this position, the controller operates the travel drive automatically in order to perform the pivoting movement of the pivoting arm to the other end position in order to then, in the other end position, drive the steering controller once again until the travelling drive unit is once more aligned for straight-ahead travel. 
     It is preferably intended for the pivotable lifting column to be coupled to the machine frame via a single pivoting arm. Such a solution requires fewer machine elements and can be implemented in a more torque-resistant fashion. 
     The pivoting axis of the travelling drive unit for adjustment of the steering angle may be coaxial or parallel to the longitudinal axis of the lifting column. 
     In a preferred embodiment, the pivotable lifting column is lockable in no less than one of the end positions. 
     The pivotable lifting column may comprise an upper part which in longitudinal direction is connected to the machine frame in a fixed position, and a telescopically extendable lower part with the travelling drive unit being attached to the lower end of said lower part. 
     In this arrangement, the steering device is coupled to the extendable lower part of the lifting column in a torque-resistant fashion. 
     The travelling drive unit, the lifting column or the steering device may comprise first locking mechanisms interacting with the machine frame in the inner end position, where said locking mechanisms fix the lateral distance of the travelling drive unit to the machine frame on the one hand, while allowing the adjustment of a steering angle on the other. 
     The travelling drive unit, the lifting column or the steering device may comprise second locking mechanisms interacting with the machine frame in the outer end position, where said locking mechanisms fix both the lateral distance of the travelling drive unit from the machine frame and the steering angle of the travelling drive unit orthogonal to the axis of the working drum. 
     It is thus possible in the inner end position to fix the lateral position of the lifting column relative to the machine frame but allow steering of the travelling drive unit nonetheless, while it is possible in the outer end position to fix not only the lateral distance to the machine frame but also the steering angle for an alignment parallel to the longitudinal axis of the machine frame or orthogonal to the axis of the working drum respectively. 
     The locking mechanism may particularly advantageously be arranged at a steering device. 
     The first and second locking mechanisms may comprise recesses in a steering ring of the steering device, in which arrangement no less than one each engagement element projecting from the machine frame, for example, a bolt, engages with said recesses, or may comprise no less than one engagement element attached to the steering ring, for example, a bolt, which engages with recesses of the machine frame. 
     In this arrangement, the recesses are open on one side so that the engagement elements, for example, bolts, are insertable into the recesses. 
     A particularly preferred embodiment intends for the first and second driving device to be able to transfer the travelling drive unit from the first outer end position to the second inner end position and back while maintaining the direction of travel of the travelling drive unit. To this end, the steering device is driven, in one of the end positions, in such a way that the direction of travel of the travelling drive unit is maintained. It is then no longer necessary to reverse the direction of rotation of the travel drive. 
     Transfer of the travelling drive unit from one end position to the other is effected by coordinating the steering angle and, as a minimum, the travel drive of the pivotable travelling drive unit, where the travelling drive unit can be transferred, along a circular arc having the radius of the pivoting arm, from the first outer end position to the second inner end position and back. 
     To this end, the travelling drive unit is first aligned, starting from the first end position, essentially orthogonal to the pivoting arm or the radius of the pivoting arm respectively, then the travel drive of, as a minimum, the pivotable travelling drive unit is driven in order to perform the pivoting movement of the pivoting arm to the other end position. In the other end position, the travelling drive unit is subsequently adjusted to its neutral straight-ahead position once again, namely, to an alignment parallel to the machine frame and orthogonal to the axis of the working drum. 
     In the end positions, the pivotable lifting column may be locked by pivoting the travelling drive unit about a steering axis for adjustment of the steering angle. The steering device may therefore also be used to lock the lifting column at the machine frame. 
     During the pivoting procedure of the pivotable lifting column, the travel drive of the pivotable travelling drive unit, as a minimum, can be driven in a coordinated fashion while in forward or reverse travel. 
     It is understood that the travel drives of the remaining rear travelling drive unit and/or the front travelling drive units may also be driven. 
     In the following, one embodiment of the invention is explained in greater detail with reference to the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following is shown: 
         FIG. 1  a side view of a road milling machine with pivotable travelling drive unit, 
         FIG. 2  a top view of the road milling machine in accordance with  FIG. 1 , 
         FIG. 3  a perspective view of a travelling drive unit in the form of a support wheel, 
         FIG. 4  the pivoting and steering movement of the support wheel in accordance with  FIG. 3 , and 
         FIG. 5  a section of the lifting column in the respective end positions. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  depicts an automotive road milling machine  1  with a machine frame  2  that is height-adjustable via lifting columns  3 . A working drum  5  is mounted at the machine frame  2  to rotate about an axis  7  of the working drum and is usually raised or lowered together with the machine frame  2 . Alternatively, the working drum  5  may also be height-adjustable itself vis-à-vis the machine frame  2 . 
     The lifting columns  3  may be intended both at the rear axle  8  and at the front axle  10 . The axis  7  of the working drum preferably extends in the same vertical plane as the rear axle  8  of the rear travelling drive units  4 . 
     In  FIGS. 1 to 5 , the travelling drive units  4  are shown as wheeled travelling drive units. They may be exchanged for tracked travelling drive units together or individually. The travelling drive units  4  may also be referred to as ground engaging units or as running gears. 
     The travelling drive units  4  are arranged at the lower ends  18  of the lifting columns  3 . In normal operating position, which can be inferred from  FIG. 2 , the rear axle  8  extends coaxially to the axes of the rear wheeled travelling drive units  4  and in the same vertical plane as the axis  7  of the working drum and the longitudinal axes  20  of the rear lifting columns  3 . 
     As can be inferred from  FIG. 2 , a total number of four wheeled travelling drive units are intended in the embodiment, said wheeled travelling drive units carrying the machine frame  2 . The front wheeled travelling drive units may also be substituted by a single central wheeled travelling drive unit. 
     The rear travelling drive unit  4  located on the right as seen in the direction of travel  9  may be pivoted, starting from the normal operating position as depicted in  FIG. 2 , from a first outer end position  12  to an inner second end position  14  in which the travelling drive unit  4  is located essentially within a recess  16  of the machine frame  2 . In the inner end position  14 , the road milling machine  1  can be guided closely along obstacles with its working drum  5 . 
       FIG. 3  shows a perspective view of the lifting column  3  with the wheeled travelling drive unit  4 , said lifting column  3  being articulated at a pivoting arm  6  at the machine frame  2 . At the lower part  18  of the lifting column  3 , the wheeled travelling drive unit  4  is mounted in a height-adjustable fashion. The wheeled travelling drive unit  4  is steerable about the longitudinal axis  20  of the lifting column  3  by means of a steering device  22 . The lower part  18  of the lifting column  3  is, therefore, rotatable and shiftable within the upper part  21  of the lifting column  3 . 
     The steering device  22  comprises a steering cylinder  24  which is arranged inside the pivoting arm  6  and may act on a steering ring  26  which may engage with a slot  28  of the lifting column  3  so that for steering the travelling drive unit  4  can be pivoted about the longitudinal axis  20  of the lifting column  3 . In the embodiments shown, the longitudinal axis  20  therefore forms the steering axis for the travelling drive unit  4 . 
     The pivoting arm  6  is pivotable about a pivoting axis  30  arranged at the machine frame  2 , said pivoting axis  30  extending parallel to the longitudinal axis  20  of the lifting column  3 . 
       FIG. 4  shows the motion sequence of the wheeled travelling drive unit from the first outer end position  12  to the second inner end position  14  in the recess  16  of the machine frame  2 . 
     As can be inferred from  FIG. 4 , pivoting of the travelling drive unit  4  is initiated in that the wheeled travelling drive unit is turned, by means of the steering device  22 , until it is orthogonal to the pivoting radius  34  of the pivoting arm  6 . Then, the travel drive  36  of the wheeled travelling drive unit is driven, and the wheeled travelling drive unit is moved along the circular arc  32  having the pivoting radius  34  into the second end position  14  in which the steering device  22  is operated once more in order to realign the wheeled travelling drive unit  4  with the direction of travel  9 . 
     If the direction of travel  9  of the wheeled travelling drive unit is maintained, reversing the direction of rotation of the travel drive  36  can be omitted. 
     Because of the coordinated or sequential operation of the controller of the steering device  22  and the travel drive  36 , pivoting of the travelling drive unit  4  is possible without a separate driving device for the pivoting arm  6  and with the travelling drive unit  4  maintaining contact with the ground surface. The movement may be effected in an either coordinated or sequential fashion, that is, first steer, then move (pivot) on the circular arc, and then steer once again. In case of coordinated control, the sequential steps mentioned may in part also occur simultaneously, that is, in an overlapping fashion. 
       FIG. 5  shows a section of the lifting column  3  in two different planes of the steering ring  26  which comprises first and second locking mechanisms  38 , 40  for the inner and outer end positions  12 , 14  respectively. 
     For the purpose of simplicity, both end positions are illustrated in  FIG. 5 . In the first outer end position  12 , coupling of the steering cylinder  24  to the steering ring  26  can be inferred from  FIG. 5 , where said steering ring  26  engages with the slot  28  in the lower part  18  of the lifting column  3  by means of a slot nut  29 . Operation of the steering cylinder  24  therefore enables the steering ring  26  to be turned. On its side facing the machine frame  2 , the steering ring  26  is provided with a recess  42  which may accommodate a first bolt  44  which is attached to the machine frame  2  in a fixed position. In this arrangement, the recess  42  is aligned in such a way that, when operating the steering device  22 , the bolt  44  may be accommodated in the recess  42 . When the bolt  44  is located at the end of the recess  42 , the travelling drive unit  4  is aligned and fixed parallel to the direction of travel  9 , in which case the wheeled travelling drive unit then also exhibits a laterally fixed distance A from the machine frame  2 . 
     In the inner second end position  14 , the second locking element  40  is arranged in a second plane extending orthogonal to the longitudinal axis  20  of the lifting column  3 , for example, arranged below the plane of the recess  42 , said locking element  40  comprising an arc-shaped recess  46  which is moulded at the steering ring  26  and which may be engaged with a bolt  48  projecting from the machine frame  2  in a fixed position. 
     By means of operating the steering device  22 , the bolt  48  may be inserted into the recess  46  also in the second end position  14 . The arc-shaped course of the recess  46  is such that, independent of the current position of the second bolt  48 , the travelling drive unit  4  always exhibits the same lateral distance B to the machine frame  2 . The recess  46  is therefore arranged in the shape of a circular arc, with a centre of the circle being in the longitudinal axis  20  of the lifting column  3 . 
     In the second inner end position  14 , it is therefore possible to maintain the lifting column  3  at a constant lateral distance from the machine frame  2  while simultaneously steering the travelling drive unit  4 .

Technology Classification (CPC): 4