Patent Publication Number: US-9850628-B2

Title: Road milling machine for working road or ground surfaces

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a road milling machine for working road or ground surfaces. 
     2. Description of the Prior Art 
     Such road milling machines are known, for example, from EP 0 836 659. 
     With such road construction machinery, in particular small milling machines, good manoeuvrability of the road milling machine is of the essence. Such road milling machine must not only be suitable for straight-ahead travel and normal cornering procedures, for example, but must additionally be able to follow the course of narrow bends, for example, when negotiating around traffic islands or a manhole cover. 
     In the known small milling machines, the milling drum therefore ends nearly flush with one outer side of the machine frame, the so-called zero-clearance side. Due to this arrangement, it is possible to mill very close along obstacles. It has also already been known for this purpose to pivot the rear wheel located on the zero-clearance side inwards, relative to the zero-clearance side, from an outer end position to an inner end position in front of the milling drum. 
     The possibility to follow the course of very narrow bends on said zero-clearance side is of particular importance as it enables highly precise milling operations to be performed around very small obstacles. It has therefore already been known in such road milling machines to design differently large steering angles for a cornering procedure to the inside or to the outside respectively, relative to said zero-clearance side, in particular to design an especially large steering angle for a cornering procedure to the outside. 
     It is understood that, when the manoeuvrability is improved, the range of possible applications and the economic efficiency of such road milling machine can be improved. 
     SUMMARY OF THE INVENTION 
     It is therefore the object of the present invention to improve the manoeuvrability of a road milling machine, in particular of a small milling machine. 
     The above object is achieved, according to the invention, in that the wheel brackets of the wheels or crawler tracks of the front axle are coupled to one another via a connecting part for synchronous adjustment of the steering angles, and that said connecting part forms a steering tie rod together with an arm projecting from the connecting part, where the arm of said steering tie rod is coupled to the free end of at least one steering cylinder. 
     Such design of the connecting part enables an increase of the adjustable maximum steering angle of the wheels or crawler tracks while simultaneously allowing a compact machine design. 
     For a steering movement in which the zero-clearance side of the road milling machine is on the inside, it is intended for the wheel brackets to be coupled, via the connecting part, in such a fashion that, in the vertical plane of the rear axle or the extension of the same in the area of the rear wheel or crawler track, the center of rotation of both front wheels or crawler tracks is arranged as close as possible to the zero-clearance side. 
     As the milling drum axis lies in the same vertical plane as the rear axle of the rear wheels or crawler tracks, this arrangement enables the milling, with the front end of the milling drum on the zero-clearance side, of narrow bend radii, for example, around manhole covers. 
     The increase of the maximum possible steering angle enables the distance of the current center of rotation to the front end of the milling drum located on the inner side of the bend to be shortened, thereby allowing narrower bend radii to be driven. 
     In this design, it is intended for the arm of the steering tie rod to extend between the pivoting columns of the wheels or crawler tracks away from the connecting part, with the connecting part and the steering cylinder being arranged on opposite sides, as seen in the direction of travel, relative to an imagined connecting line of the pivoting axes. 
     It is preferably intended for the wheels or crawler tracks to be steerable between two steering angle end positions for a direction of travel to the left or to the right, where the connecting part exhibits curved sections or cut-outs in such a fashion that, in the end positions, the connecting part maintains a distance from the respective pivoting axis that is larger than the radius of the respective pivoting column. 
     In a preferred embodiment, the arm of the steering tie rod projects essentially centrally from the connecting part. The initially central arrangement of the arm offers the advantage that collision freedom relative to the pivoting columns is enabled for a larger area. In front of the area of the pivoting columns as seen in the direction of travel, the arm may be of curved or angled design. 
     It is preferably intended for the arm of the steering tie rod projecting from the connecting part to extend behind the pivoting columns in an approximately parallel fashion to the steering cylinder and, at the free end, to be connected in an articulated fashion to a single steering cylinder. In this way, the respective points of force application are located on opposite sides relative to the pivoting columns. 
     It is preferably intended for the arm projecting from the connecting part to feature a width that ranges between the 0.5-fold and 0.97-fold, preferably between the 0.75-fold and 0.95-fold of the difference between the distance of the pivoting axes and the twofold radius of the pivoting columns. 
     The steering levers may be arranged at the pivoting columns in different angular positions relative to the direction of travel in such a fashion that different maximum steering angles result for a steering direction to the right or left. 
     The pivoting columns of the front axle may be mounted in a cross member. 
     The fixed point of the steering cylinder is preferably arranged at the machine frame or at the cross member. 
     In a preferred embodiment, the cross member may be pivotable, relative to the machine frame, about a swing axle extending in the direction of travel. In this manner, it is also possible for the wheels or crawler tracks of the front axle to run on different planes. 
     It is preferably intended for the rear wheel located on the zero-clearance side to be pivotable inwards, relative to the zero-clearance side, from an outer end position in which the wheel is beyond the zero-clearance side and the rear axles of both rear wheels are in alignment, to an inner end position in front of the milling drum. 
     It may be intended, as a minimum, for the rear wheel on the zero-clearance side to be steerable. 
     The steerability, possibly of both rear wheels but as a minimum of the rear wheel located on the zero-clearance side, likewise improves the manoeuvrability of the road milling machine. It is particularly advantageous when crawler tracks are used. 
     A particularly preferred embodiment intends for the wheels or crawler tracks of the front axle as seen in the direction of travel to be arranged offset to one another in such a fashion that the wheel on the inside relative to the steering direction, or the wheel or crawler track on the zero-clearance side is arranged in front of the neighbouring wheel or crawler track as seen in the direction of travel. 
     The offset arrangement of the wheels or crawler tracks offers the advantage that, on account of the offset, the steering geometry permits larger maximum steering angles to be adjusted, which allows a narrow bend radius to be driven. This improvement is of major advantage in particular when performing a cornering procedure in which the zero-clearance side is located on the inside. 
     Ultimately, the offset arrangement of the front wheels allows the bend radii of both front wheels to be matched to one another while at the same time reducing the distance of the current center of rotation from the front end of the milling drum. Matching the bend radii of both front wheels enables a more precise cornering procedure, and shortening the distance of the center of rotation to, for example, the front end of the milling drum on the zero-clearance side allows extremely narrow bend radii of up to 130 mm and less to be achieved. As a result, the road milling machine can practically turn on the spot. 
     The invention also enables a better manoeuvrability of the road milling machine than before to be achieved in the event of a required lengthening of the wheelbase. 
     Lengthening of the wheelbase may become necessary, among other things, due to the use of a new and more complex engine technology or the integration of additional components, for example, for the after-treatment of exhaust gases. These components require additional construction space but are necessary in order to comply with emission directives. 
     It is preferably intended for the offset between the pivoting axes of the front axle as seen in the direction of travel to be between 50 mm and 350 mm, preferably between 100 mm and 250 mm. Such offset in the arrangement of the pivoting axes of the wheels or crawler tracks of the front axle allows a significant increase of the maximum steering angles. 
     It is preferably intended for the steering angle to the outside of the wheel or crawler track located on the zero-clearance side to be adjustable up to a maximum steering angle in excess of 70°, preferably between 70° and 90°. 
     A preferred embodiment intends for the offset of the wheels or crawler tracks of the front axle to be chosen in such a fashion that the wheels or crawler tracks in the steering direction to the outside relative to the zero-clearance side both run in a single track. 
     This offers the advantage that the road milling machine can be turned on the spot, that is, essentially around the current center of rotation, thus allowing the milling of extremely narrow bend radii. Furthermore, this arrangement allows a more precise cornering procedure. 
     In a further embodiment, it may be intended for the cross member to be pivotable about a vertical axis. This feature enables the offset of the front wheels to be optionally provided either on the zero-clearance side or on the side opposite the zero-clearance side so that, in each case, the wheel located on the inside relative to the steering direction can be arranged in front of the neighbouring wheel. In this way, it can be achieved that the bend radii of the front wheels are matched to one another even when steering to the left relative to the zero-clearance side, which enables the distance between the front end of the milling drum facing away from the zero-clearance side and the center of rotation in the form of an axis of rotation extending essentially orthogonally to the ground surface to be likewise reduced further. 
     It is preferably intended for the wheel brackets to be coupled via the connecting part in such a fashion that, when steering to the outside relative to the zero-clearance side, the center of rotation exhibits a distance from the outer front end of the milling drum of less than 250 mm, preferably less than 150 mm. 
     For a cornering procedure in which the zero-clearance side is on the outside, it is intended for the wheel brackets to be coupled via the connecting part in such a fashion that, when steering to the inside relative to the zero-clearance side, the center of rotation of both front wheels or crawler tracks exhibits, on the extension of the rear axle, a distance from the inner front end of the milling drum that is smaller than the wheelbase, preferably smaller than 2,000 mm. 
     In the following, embodiments of the invention are explained in more detail with reference to the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following is shown: 
         FIG. 1  a generic road milling machine in accordance with prior art, 
         FIG. 2  a top view of the road milling machine shown in  FIG. 1 , 
         FIG. 3  a top view of an embodiment of a steering tie rod, 
         FIG. 4  a side view of the front axle, 
         FIG. 5  a schematic illustration of the steering angles in a road milling machine according to  FIG. 1 , 
         FIG. 6  a schematic illustration of the adjustable steering angles in a first embodiment of the invention, and 
         FIG. 7  a schematic illustration of the adjustable steering angles in a further embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a road milling machine for milling off roadways with a self-propelled chassis comprising a steerable front axle  6  with two front wheels  10 ,  12  and two mutually independent rear wheels  14 ,  16 . It is understood that the wheels  10  to  16  may be substituted, wholly or in part, by crawler tracks. 
     The chassis supports a machine frame  8 , on which an operator&#39;s platform  4  is located on the so-called zero-clearance side  24  of the road construction machine in accordance with  FIG. 2 . The rear wheels  14 ,  16  are height-adjustable by means of lifting columns  48  in order to be able to use them to adjust the working depth of a milling drum  20 . 
     With its front end on the zero-clearance side, the milling drum  20  is nearly flush with the zero-clearance side  24  of the machine frame so that working close to the edge is possible on the zero-clearance side  24  of the road milling machine. To this effect, the wheel  16  is pivoted inwards, from an outer end position  26  beyond the plane of the zero-clearance side, in front of the milling drum and into a cut-out  18  of the machine frame  8  so that the outer edge of the wheel  16  can end flush with the zero-clearance side  24  or even assume an end position further inside relative to the zero-clearance side  24 . The rear wheel  16  or both rear wheels  14 ,  16  may be steerable. 
     As can best be inferred from  FIG. 1 , the milling drum axis  22  extends essentially in the same vertical plane as the axles  7  of the wheel  14  and of the wheel  16  in the outer end position  26 . 
     The circle of engagement of the milling drum  20  ends close to the rear end of the machine frame  8  so that milling close to the edge is possible right up into corners. 
       FIG. 3  shows a steering tie rod  30  with a connecting part  40  which connects the steering levers  36  of both front wheels  10 ,  12  in an articulated fashion. An arm  50  projects initially essentially centrally from and preferably orthogonally to said connecting part  40 . 
     The wheel brackets  32  are each connected with pivoting columns  34 , said pivoting columns  34  being mounted in a cross member  56  to pivot about one each pivoting axis  38 . 
     The steering levers  36  are connected with the wheel brackets  32  in a permanent fashion. 
     The arm  50  projecting essentially orthogonally from the connecting part  40  exhibits, on the sides facing the pivoting columns  34 , a curved contour  52 ,  54  that is adapted to the diameter of the pivoting columns  34  in order to be able to adjust maximum steering angles without causing any collision. 
     Above an imagined connecting line between the pivoting axes  38  of the pivoting columns  34 , the arm  50  may be angled or curved in order to be connected, at its free end, to a steering cylinder  44  which transfers the force required for steering to the steering tie rod  30 . The steering cylinder  44  is in turn directly or indirectly articulated at a fixed point  42  relative to the machine frame  4 . 
       FIG. 4  shows a side view of the front axle with wheels  10 ,  12  offset to one another, the pivoting columns  34  of said wheels  10 ,  12  being mounted in a cross member  56 . 
     The cross member  56  is articulated at a plate  58  attached to the machine frame  8  in such a fashion that the cross member  56  may be pivotable, relative to the machine frame  8 , about a swing axle extending in the direction of travel. 
     In an alternative embodiment, it may also be intended for the cross member  56  to be pivotable about a vertical axis  100  extending parallel to the pivoting axes  38  in such a fashion that the offset “d” can optionally be provided on the left or right as seen in the direction of travel so that, in each case, the wheel  10  or  12  located on the inside relative to the steering direction can be arranged in front of the neighbouring wheel as seen in the direction of travel. 
       FIG. 5  shows an embodiment according to prior art together with the geometrical distances relevant for the milling operation. The left-hand illustration of  FIG. 5  indicates the wheelbase “a” of the road milling machine. The middle illustration shows, as a characteristic relevant for the milling operation, the distance “b” of the center of rotation “D” from the front end of the milling drum  20  facing away from the zero-clearance side when adjusted to the maximum steering angle to the left. 
     The right-hand illustration of  FIG. 5  shows the same situation when adjusted to the maximum steering angle to the right in which the zero-clearance side  24  is located on the inner side of the bend. Not only the adjustable maximum steering angle of the front wheels  10 ,  12  is of great importance in this arrangement but also the distance “c” of the center of rotation D to the front end of the milling drum  20  on the zero-clearance side  24 . It is understood that a smaller distance “c” allows the milling of narrower bend radii. Moreover, a shortening of the distance “b”, or a possibly required extension of the wheelbase “a” and simultaneous reduction of the distances “b” and “c”, is also desirable. 
       FIG. 6  shows an embodiment of the invention in which the front wheels  10 ,  12  are arranged offset to one another. The wheelbase “a” of the front right wheel  12  has been maintained while the front left wheel  10  is moved back by an offset “d”. Said offset “d” may, for example, be in a range between 50 mm to 350 mm, preferably between 100 mm and 250 mm. 
     Firstly, said offset offers the advantage inferable from the middle illustration of  FIG. 6  that the steering angle of the front right wheel  12  can be increased, which allows the distance “b” between the center of rotation and the left front end of the milling drum  20  to be shortened significantly, thus also improving the manoeuvrability of the road milling machine to the inside relative to the zero-clearance side  24 . 
     It can be inferred from the right-hand illustration of  FIG. 6  that the maximum steering angle can be increased to, for example, 75° as a result of the offset arrangement of the front wheels  10 ,  12 , thus enabling the distance “c” of the center of rotation “D” to the front end of the milling drum  20  on the zero-clearance side  24  to be reduced significantly, that is, by approx. 20% in comparison with  FIG. 5 . 
       FIG. 7  shows the employment of a steering tie rod  30  in addition to the offset “d” of the front wheels  10 ,  12 , where said steering tie rod  30  allows a larger steering angle at least with regard to the left wheel  10 , as can be inferred from the middle illustration of  FIG. 7 , so that the distance “b” can be reduced further in comparison with  FIG. 4 . 
     When steering to the right, the steering angles of both front wheels  10 ,  12  can be increased further so that the distance “c” can be reduced by approx. 65% in comparison with  FIG. 5 , thus allowing extremely small bend radii to be milled when steering to the right relative to the zero-clearance side. The distance “c” achieves a dimension of less than 150 mm. A value of, for example, approx. 1700 mm is achievable for “b”. 
     The embodiments according to  FIGS. 6 and 7  offer a further advantage in that, when adjusted to the maximum steering angle to the outside as seen from the zero-clearance side, the front wheels  10 ,  12  can be driven in a more or less similar radius so that the wheels  10 ,  12  essentially run in the same track. 
     This arrangement offers the advantage of a more precise cornering procedure. 
     Maximum steering angles in excess of 70°, preferably between 70° and 90°, can be adjusted. 
     The embodiment in  FIG. 6  shows steering angles of the front wheels  10 ,  12  of between 55° and 75°, while steering angles of the front wheels of between 59° and 79° can be inferred from the embodiment in  FIG. 7 .