Abstract:
Road milling machine ( 10 ) are employed to mill off defective or worn road surfaces ( 11 ) from the road bed. During operations some wheels may run along an already milled track ( 22 ), with the wheels running on the milled track ( 22 ) being disposed at a lower level. To compensate for this difference in height, known road milling machines ( 10 ) have a full-floating front axle. This causes the front wheels ( 14 ) to run at a tilt, which in particular hampers the steering properties in known road milling machines ( 10 ).  
     The invention proposes that the front wheels ( 14 ) be assigned to a parallelogram steering axle ( 23 ). The parallelogram steering axle ( 23 ) guides the front wheels ( 14 ) such that their wheel axles ( 48 ) remain in constant horizontal alignment even when the front wheels ( 14 ) run at different heights, thus avoiding any impaired steering of the road milling machine ( 10 ) even when a front wheel ( 14 ) runs on a lower, milled track ( 22 ).

Description:
DESCRIPTION  
         [0001]    The invention relates to a road milling machine pursuant to the preamble of claim 1.  
           [0002]    Road milling machines are employed to remove the entire paving surface of defective roads by means of milling. A milled street serves as the bed for a street to be repaired where only the application of a new road surface is required.  
           [0003]    Known road milling machines feature at least one milling drum driven by a horizontal shaft axle. The milling drum is mounted on the frame of a chassis. The chassis has at least one pair of front wheels and at least one pair of rear wheels. The front wheels are located in front of the milling drum, as seen in the direction of milling. The milling drum is aligned by adjusting the vertical spacing of the wheels to the frame. Milling of the road surface is usually conducted with a horizontally oriented milling drum. This is accomplished by setting the rear wheels at a corresponding vertical distance from the frame. The front wheel are mounted on the chassis in a manner that allows them to track uneven road sections and compensate for them automatically. For this purpose, the front wheels of known road milling machines are suspended on a full floating axle. When the full floating axle is skewed, the wheels roll on their edges, which not only results in non-uniform wear of the wheels&#39; solid rubber tread but also hampers the steering of the road milling machine, particularly on straight stretches of road. This is particularly evident when there is a considerable difference of height between the front wheels, such as when one of the two front wheels runs on a previously milled section which is deeper than the track of the neighboring front wheel running on an non-milled section.  
           [0004]    Proceeding from the above, the object of the invention is to create a mad milling machine with front wheels whose vertical distance to the frame are automatically adjustable such that the front wheels can compensate for uneven surfaces or for a previously milled track in the pavement without encountering the disadvantages stated above.  
           [0005]    A road milling machine for attaining this object is disclosed by the features of claim 1. By having the steerable wheels, in particular the front wheels, assigned to a parallelogram steering type axle, the wheel axles of these wheels retain their horizontal alignment even when the wheels, particularly the front wheels, are disposed at differing heights with respect to the frame. Even when a front wheel runs along a deeper track that has already been milled, the wheel, although disposed at a lower position with respect to the adjacent wheel as a result, remains constantly aligned by the parallelogram steering axle which can pivot in an approximately vertical place perpendicular to the longitudinal direction of the chassis, thus keeping the wheel axles of the wheels in horizontal alignment. The full width of the solid rubber treads of the wheels (solid-rubber wheels) thus contact the fundament of the street to be milled, thus ensuring a precise steering action of the road milling machine and avoiding uneven wear across the width of the wheel treads.  
           [0006]    The invention also provides for a parallelogram steering axle having two parallel levers arranged one above the other and mounted on the chassis frame, it being possible to pivot each lever in an approximately vertical plane about a central bearing or horizontal axis. The opposing ends of both levers therefore remain essentially above one another vertically in all pivoted positions. The superimposed ends of both levers are pin-jointed on each end of the lever by a respective coupling piece. A wheel bearing of each wheel, in particular a front wheel, is arranged at the respective coupling piece. Due to the fact that the superimposed ends on both sides of the levers remain vertically above one another in every position, the coupling pieces maintain a vertical alignment independently of the pivot position of the levers. Thus the direction of the wheel bearings do not change with respect to the wheels when the levers of the parallelogram steering axle pivot along a vertical plane perpendicular to the longitudinal direction of the chassis. The wheel bearings are merely moved up and down with the wheels in a vertical path so that when one wheel moves upwards, the opposite wheel moves approximately the same distance downwards.  
           [0007]    The coupling pieces are mounted at the end of the levers about a horizontal swiveling axis that run perpendicular to the horizontal wheel axles. This makes it possible to change the direction of the levers with respect to the coupling pieces during pivoting of the levers but still keep the coupling pieces in their vertical alignment. The invention also provides for linking the coupling pieces at the ends of the levers to vertical rotation axles in the longitudinal direction of the coupling pieces. This makes it possible to turn the front wheels about these vertical rotation axles along with the wheel bearings and at least parts of the coupling pieces. In this manner the vertical axles form steering axles for guiding the wheels. To ensure that the wheels on opposite ends of the levers can be steered parallel or synchronous to each other, the two coupling pieces at the opposite ends of the levers are preferably mechanically connected by a tie rod, for example. However, it is also conceivable to have the tie rods or the like mounted directly on the wheel bearings. It is also possible to synchronize the front wheels by means of pressure actuation or by cables or chains in order to achieve a steering angle of equal size.  
           [0008]    Further dependent claims relate to advantageous developments of the road milling machine. 
       
    
    
       [0009]    A preferred exemplary embodiment of the inventive road milling machine is described in more detail below by means of the drawing which shows:  
         [0010]    [0010]FIG. 1 a perspective view of part of the road milling machine (at a front angle),  
         [0011]    [0011]FIG. 2 a perspective view of the road milling machine in FIG. 1 (at a rear angle),  
         [0012]    [0012]FIG. 3 a side view of the road milling machine in FIGS. 1 and 2, and  
         [0013]    [0013]FIG. 4 a front view of the road milling machine. 
     
    
       [0014]    The figures show part of a road milling machine  10  for milling defective and/or deteriorated road surfaces  11 . The road milling machine  10  has an automotive design and is therefore provided with an appropriate drivetrain. The drivetrain is powered by an internal combustion engine  12  which drives a hydraulic pump, which in turn is used to drive hydraulic motors.  
         [0015]    The road milling machine  10  shown here has a chassis  13 , which in the shown exemplary embodiment features four wheels, specifically two front wheels  14  and two rear wheels  15 . Both the front wheels  14  and the rear wheels  15  are provided with solid-rubber tires. The treads  16  of the front wheels  14  and the rear wheels  15  are therefore also made of solid rubber. The front wheels  14  and preferably also the rear wheels  15  are driven separately, each by a hydraulic motor  37  configured as a drive motor.  
         [0016]    The chassis  13  has a frame  17  which bears a milling drum  18 . The cylindrical milling drum  18  can be driven about a centered horizontal rotation axis. The horizontal rotation axis  19  of the milling drum  18  runs perpendicular to a milling direction  20  of the road milling machine  10 . The front wheels  14  are located in front of the rear wheels  15  as seen in the milling direction  20 . When necessary, one of the rear wheels  15  can be swiveled so that it is located in front of the milling drum  18  as seen in the milling direction  20 . The figures show the road milling machine  10  with a rear wheel  15  disposed in front of the milling drum  18 . But the invention can also be utilized for road milling machines where both rear wheels  15  lie at opposite sides of the milling drum  18 . The two rear wheels  15  are themselves independently arranged in the known manner at the lower ends of upright lifting columns  21 . By virtue of the lifting columns  21  the rear wheels  15  can be moved up and down along a vertical axis independently of one another so that the vertical distance of the rear wheels  15  from the frame  17  is adjustable. This means that the road milling machine  10 , independent of the topography of the road surface  11  can always be aligned to ensure that the rotation axis  19  of the milling drum  18  remains horizontal. This applies in particular to the case shown in the figures, where a rear wheel  15 , namely the rear wheel  15  located next to an end face of the milling drum  18 , runs on a milled track  22  of the road surface  11  or of the road bed. This milled track  22  is lower than the yet non-milled road surface  11  on which the second rear wheel  15  runs (FIG. 1). The given difference in height between the non-milled road surface  11  and the milled track  22  is offset in that the lifting column  21  associated with the rear wheel  15  travelling on the milled track  22  is extended further than the lifting column  21  associated with the other rear wheel  15 . The lifting column  21  with the rear wheel  15  travelling on the milled track  22  is extended far enough until the rotation axis  19  of the milling drum  18  assumes an approximately horizontal alignment (FIG. 3).  
         [0017]    In a manner special to the invention, the front wheels  14  with solid rubber tires are coupled on the frame  17 . The front wheels  14  are namely connected to the frame  17  by a parallelogram steering axle  23  that can be pivoted in a upright plane. The parallelogram steering axle  23  essentially has two levers  24  and  25  arranged in a vertical plane running perpendicular to the milling direction  20 . The levers  24  and  25  run together in the manner of a parallelogram. Mounted on a bearing block  28  permanently fixed to the frame  17 , the superimposed levers  24  and  25  can be swiveled about a horizontal axis  26  and  27 , respectively, running along the milling direction  20 . The levers  24  and  25  have free ends  29 ,  30  and  31 ,  32 , respectively, located on either side of the bearing block  28  and which are respectively connected by means of a coupling piece. The identical coupling pieces in the shown exemplary embodiment are configured as coupling journal  33 ,  34 . Each coupling journal  33 ,  34  is permanently connected to a wheel bearing  35 ,  36  of the respective front wheel  14 . Each wheel bearing  35 ,  36  is assigned its own hydraulic motor  37  for driving the respective front wheel  14 . The hydraulic motors  37  propel the hubs  38  of the front wheels  14 . The hubs  38  are surrounded by a ring-like solid-rubber tire  39  with cylindrical tread  16 .  
         [0018]    Each coupling journal  33 ,  34  is hinge-mounted by means of an elongate core part  40  to the superimposed ends  29 ,  30  and  31 ,  32 , respectively, at each end of the two superimposed levers  24 ,  25 . The bearings of the core parts  40  are hinged at each end  29 ,  30  and  31 ,  32  so that the core parts  40  of the coupling journals  33 ,  34  can be pivoted with respect to the ends  29 ,  30  and  31 ,  32 , respectively, of the levers  24 ,  25  about a horizontal swiveling axis  41  running parallel to the milling direction  20 .  
         [0019]    The coupling journals  33 ,  34  can also be swiveled about their preferably vertical longitudinal axis  43 . To this end an outer sleeve  44  is rotatably mounted on the core part  40  of each coupling journal  33 ,  34 . The outer sleeve  44  on each core part  40  of the coupling journals  33 ,  34  extends between the ends  29 ,  30  and  31 ,  32  of the superimposed levers  24 ,  25 . The outer sleeve  44  cannot be displaced on the respective core part  40  in the longitudinal direction. The associated wheel bearing  35 ,  36  of the respective front wheel  14  is permanently attached to the outer sleeve  44  of each coupling journal  33 ,  34 . The front wheels  14  can be steered by rotating the outer sleeves  44  of the coupling journals  33 ,  34  about the (vertical) longitudinal axes  43  of the coupling journals  33 ,  34 . To ensure synchronous steering of both front wheels  14 , the outer sleeves  44  of the coupling journals  33 ,  34  preferably have lever arms  45  of equal length. The lever arms  45  of the front wheels  14  associated with the opposite ends  29 ,  31  and  30 ,  32  of the levers  24 ,  25  are connected to each other by means of a tie rod  46 . A steering drive  47  is assigned to a coupling journal  33  or to its associated wheel bearing  35  (FIG. 3). The preferably hydraulic-powered steering drive  47  is employed to swivel the two front wheels  14  uniformly about the vertical longitudinal axes  43  of the coupling journals  33 ,  34 , thus guiding the road milling machine  10  to follow the course of the road surface  11  to be milled.  
         [0020]    The parallelogram steering axle  23  is configured such that the front wheels  14  can be moved up and down along an imaginary rectilinear, vertical path. The center wheel axles  48  of the front wheels  14  thus run in a constant horizontal alignment, regardless of whether the distance of each front wheel  14  from the frame  17  is the same or different. When one front wheel  14  runs along a lower milled track  22  and the other front wheel  14  is located on the higher yet non-milled road surface  11 , as shown in particular detail in FIG. 4, the wheel axles  48  of the front wheels  14  run parallel to one another, with both wheel axles  48  being aligned horizontally. The consistently horizontal alignment of the wheel axles  48  of both front wheels  14  is achieved in that the two levers  24  and  25  of the parallelogram steering axle  23  are of the same length, the levers  24  and  25  are swivel-mounted on the bearing block  28  of the frame  17  and centered on the vertically superimposed axes  26  and  27 , both levers  24  and  25  run parallel to each other and all ends  29 ,  30 ,  31  and  32  of the levers  24  and  25  have the same distance from the center axes  26  and  27  of the levers  24 ,  25 . The described dimensions of the parallelogram steering axle  23 , in particular of the levers  24  and  25 , ensure that the longitudinal  43  of the coupling journals  33  and  34  are consistently held in vertical alignment by the levers  24  and  25  when the levers  24  and  24  are held horizontally as well as when the levers  24  and  25  they are swiveled out of the horizontal in uniform and parallel fashion. Consequently the wheel axles  48  of the wheel bearing  35  and  36  constantly remain in a horizontal position, regardless of whether the levers  24  and  25  of the parallelogram steering axle  23 , which are always disposed parallel to each other, assume horizontal positions or are more or less swiveled with respect to the horizontal. The wheel bearings  35 ,  36  with the front wheels  14  are merely moved up and down-specifically in opposite directions on parallel vertical paths by the same vertical displacement-by the levers  24 ,  25  of the parallelogram steering axle  23  which can be swiveled in a common vertical plane. The cylindrical treads  16  of the front wheels  14  therefore remain in contact the subsurface across their entire width even when one of the front wheels  14  runs on a lower, milled track  22 , as shown in particular detail in FIG. 4. The depth of the milled track  22  plays no role in this case. By virtue of the inventive parallelogram steering axle  23 , the wheel axles  48  of both front wheels  14  always run in horizontal alignment. Naturally the two front wheels  14  are also supported over their entire width by the road surface  11  when both front wheels  14  travel over the yet non-milled road surface  11  and both levers  24  and  25  assume a horizontal direction, with the wheel axles  48  also being in horizontal alignment. In this case (not shown) the wheel axles  48  of both front wheels  14  are aligned along a common horizontal axis.  
                                         List of designations                                10   road milling machine       11   road surface       12   internal combustion engine       13   chassis       14   front wheel       15   rear wheel       16   tread       17   frame       18   milling drum       19   rotation axis       20   milling direction       21   lifting column       22   milled track       23   parallelogram steering axle       24   lever (upper)       25   lever (lower)       26   axis       27   axis       28   bearing block       29   end       30   end       31   end       32   end       33   coupling journal       34   coupling journal       35   wheel bearing       36   wheel bearing       37   hydraulic motor       38   hub       39   solid-rubber tire       40   core part       41   swiveling axis       42   swiveling axis       43   (vertical) longitudinal axis       44   outer sleeve       45   lever arm       46   tie rod       47   steering drive       48   wheel axle