Abstract:
In a self-propelled road milling machine for working road surfaces, comprising a machine frame, comprising a milling drum mounted to rotate and extending in axial direction transverse to the direction of travel, and a milling drum housing enclosing the milling drum, where the milling drum comprises multiple tools circumferentially preferably arranged in the shape of a helix, where the tools, except for the axial peripheral area, feature a specified mutual line spacing, it is provided for the following features to be achieved: an oscillation drive exercises an oscillation stroke on the axis of the milling drum moving to and fro in axial direction relative to the machine frame, where the rotating movement of the tools is superimposable with an axial movement parallel to the axis of the milling drum, the stroke of which is adjustable to the line spacing between two axially neighbouring tools.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates to a self-propelled road milling machine for working road surfaces and a method for working road surfaces. 
         [0003]    2. Description of the Prior Art 
         [0004]    Such road milling machines are already generally known. For small milling machines, in which the milling drum is located level with the rear axle of the chassis and between the rear wheels, it is known to provide a rear support wheel or tracked ground-engaging unit on the zero side of the machine which can pivot inwards behind the outer contour of the road milling machine for close-to-edge milling. 
         [0005]    Large milling machines are road milling machines, for example, in which the milling drum is mounted at the machine frame between the tracked ground-engaging units of the front axle and the rear axle, and at a distance to the same. EP 1 167 626 A1 (U.S. Pat. No. 7,644,994) describes such a large milling machine. 
         [0006]    The milling drums of such milling machines comprise multiple tools circumferentially preferably arranged in the shape of a helix. These are usually milling tools which are fixed in place in toolholders welded onto a cylindrically hollow drum body or in toolholder systems. The tools therefore exhibit a constant line spacing which corresponds to the axial distance between neighbouring tools and, as a rule, ranges between 3 mm and 25 mm. 
         [0007]    Due to the axial distance of the tools, a grooved texture is created on the milled surface during the milling process, wherein the mutual distance of neighbouring grooves corresponds to the line spacing. 
         [0008]    In the process, the selection of the line spacing depends on the particular milling application. For the removal of complete pavements, for example, a larger line spacing is usually selected than for fine milling which merely serves to roughen the pavement surface at a small milling depth. 
         [0009]    In simple terms, the reason for this is that milling drums with a small line spacing are not suitable for large milling depths due to the high tool density, whereas milling drums with a large line spacing do not achieve the desired texture for roughening the pavement as the grooved texture produced in the milled surface is too coarse. 
         [0010]    Furthermore, in addition to the milling depth and desired surface texture, a multitude of other factors play a role in the selection of the line spacing, such as the nature of the ground to be worked, which leads to a multitude of different milling drums with different line spacings being available for different applications. 
         [0011]    For milling contractors, this results in the necessity to maintain different milling machines and/or different types of milling drums for a milling machine for different applications. 
         [0012]    This results in additional costs for the acquisition of additional machines, or an additional amount of work and expenditure of time, respectively, for conversion of the machines with different milling drums. This is of disadvantage in particular in those cases where different requirements need to be met on a single construction site and, as a result, different machines need to be transported to the operating site or a single machine needs to be converted on site. 
       SUMMARY OF THE INVENTION 
       [0013]    It is therefore the object of the present invention to create a road milling machine for working road surfaces, as well as a method for working road surfaces, which enable a flexible usage for different milling applications, expand the possibilities of the milling operation, and can be used in a cost-saving and time-saving fashion. 
         [0014]    The invention advantageously provides for an oscillation drive to exercise an oscillation stroke on the milling drum moving to and fro in axial direction relative to the machine frame, in which arrangement the rotating movement of the tools is superimposable with an axial movement parallel to the axis of the milling drum, the stroke of which is adjustable to the line spacing between two axially neighbouring tools. 
         [0015]    The advantage according to the invention lies in the fact that large milling depths are now achievable and fine surface textures can also be created at the same time with a single roughing or standard drum. 
         [0016]    As a result of the milling drum exercising an oscillation stroke moving to and fro in axial direction relative to the machine frame, the linear texture on the road surface can be altered or entirely removed, respectively. As a result, it is also possible to achieve a road surface with a texture that is not directly dependent on the line spacing of the milling drum. It also eliminates the necessity to use a milling drum which creates a finer linear texture on the milled surface. A further advantage is offered in that the altered surface texture of the road surface can also be achieved at larger milling depths. In the process, the tools perform a rotating movement about the axis of the milling drum which is superimposed by an axial movement parallel to the axis of the milling drum. The stroke of the displacement of the milling drum in axial direction can be adjusted in accordance with the line spacing of two axially neighbouring tools so that the oscillation stroke is variably adjustable for milling drums with a different tool density. This eliminates conversion times, and the provision of a multitude of milling drums for different applications can be reduced considerably. 
         [0017]    In particular, the axial oscillation eliminates the need for fine and micro-fine milling drums which are cost-intensive due to the high tool density and high cutting tool wear per m 3 . 
         [0018]    In this way, both the complete removal of pavements and the removal of a surface course of a road surface only, or an increase of the skid resistance by means of roughening, can be performed effectively using, for example, a standard milling drum. 
         [0019]    The invention advantageously provides for time and costs to be saved because both coarse textures as well as fine textures can be created with a single milling drum. 
         [0020]    In so doing, advantages are furthermore also achieved in comparison to milling with conventional fine milling drums. The fine grooved texture created during fine milling may have a negative influence on the steering behaviour of, in particular two-wheeled, vehicles and lead to a self-steering behaviour. This formation of grooves parallel to the traffic lane is reduced due to the oscillation of the milling drum even if the oscillation stroke is smaller than the line spacing. 
         [0021]    It is understood that the oscillation stroke need not precisely correspond to the line spacing but may also be adjusted to be smaller or larger, or may alternatively be switched off altogether so that the road milling machine can be operated in the conventional fashion. 
         [0022]    It is preferably intended for the amplitude and/or the frequency of oscillation to be variably adjustable so that the type of texture created on the surface by the milling drum can be individually adapted to specific milling applications. 
         [0023]    In this arrangement, the oscillation stroke can be adjusted in the range between the 0.5-fold to 1.5-fold, preferably between the 0.9-fold to 1.1-fold, of the line spacing. Alternatively, the oscillation stroke may be adjustable in the range between 3 mm and 40 mm. 
         [0024]    The oscillation frequency may be adjustable, for example, between 0.1 and 20 Hz. 
         [0025]    It may preferably be intended for the relation of the average speed magnitude of the oscillation stroke to the circumferential speed of the milling drum tools to be in the range between 0.1 and 3, preferably between 0.25 and 2. 
         [0026]    In one embodiment, it is intended for the milling drum to comprise an axial support movable in axial direction. The movable axial support can be achieved in that the milling drum housing is displaced together with the milling drum, or in that the axial support is movable axially relative to the milling drum housing. 
         [0027]    In a further embodiment, it may additionally be intended for a movement moving to and fro in the direction of travel to be superimposable on the axial support. This means that the milling drum can oscillate both in axial direction and in the direction of travel. A further oscillation drive is preferably intended for this purpose. The displacement of the milling drum in the direction of travel can be effected not only linearly but also in the shape of an arc about an axis extending above the milling drum and parallel to the milling drum axis. 
         [0028]    A controller is preferably intended which controls or regulates the oscillation frequency and/or the amplitude of the oscillation stroke automatically in accordance with the milling drum speed and/or the advance speed and/or the milling depth of the milling drum. 
         [0029]    In a preferred embodiment, it is intended for the milling drum to oscillate in axial direction together with the milling drum housing, and for the oscillation drive to drive the milling drum housing relative to the machine frame. 
         [0030]    As an alternative to this, it may be intended for the oscillation drive to drive the milling drum in axial direction inside the milling drum housing. 
         [0031]    In this arrangement, the milling drum housing is longer in axial direction than the milling drum by, as a minimum, the maximum oscillation stroke. 
         [0032]    It is preferably intended for the axial support to be a fixed/floating support in which the fixed bearing is movable in axial direction. 
         [0033]    In this arrangement, the oscillation drive may act, on the side of the fixed bearing, axially on a drive shaft of the milling drum extending in the milling drum axis. 
         [0034]    The floating bearing allows a movement stroke which, as a minimum, corresponds to the oscillation stroke. 
         [0035]    The milling drum may comprise a rotary drive which, on the side of the fixed bearing, drives a drive shaft. If the entire milling drum housing can oscillate in axial direction, this is effected along no less than two linear guides extending in axial direction parallel to the milling drum axis. 
         [0036]    In all embodiments, it may be intended for the milling drum housing or the milling drum to be oscillatable in the direction of travel along no less than two linear or arc-shaped guides. 
         [0037]    All guides comprise a first guide which guides both vertically and horizontally, and no less than one further second guide extending parallel to the first guide which, as a minimum, guides in horizontal direction. 
         [0038]    In this way, it is ensured that the guides will not tension against one another. 
         [0039]    The object is also achieved by the method where during the operation an oscillation stroke moving to and fro in axial direction is exercised on the milling drum in axial direction, where the rotating movement of the tools is superimposed with an axial rotating movement parallel to the milling drum axis, the stroke of which is variably adjusted to the line spacing of two axially neighbouring tools. 
         [0040]    It is preferably intended for a milling drum rotation frequency in the range between 0.5 Hz and 3 Hz, corresponding to a milling drum speed in the range of 30 rpm to 180 rpm, preferably between 1 Hz and 2.5 Hz or 60 rpm to 150 rpm, respectively, to be combined with an oscillation frequency between 2 Hz and 40 Hz, preferably between 5 Hz and 15 Hz. 
         [0041]    Alternatively, the milling drum speed may be in the range between 180 rpm and 600 rpm, corresponding to a milling drum rotation frequency between 3 Hz and 10 Hz, preferably between 240 rpm and 360 rpm or the milling drum rotation frequency between 4 Hz and 6 Hz, respectively, and may be combined with an oscillation frequency of 0.1 Hz to 5 Hz, preferably between 1 Hz and 3 Hz. 
         [0042]    In a further development of the method, it may be intended for an oscillating movement in the direction of travel of the milling drum to be superimposed on the axial oscillation of the milling drum transverse to the direction of travel. 
         [0043]    Hereinafter, embodiments of the invention are illustrated in more detail with reference to the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0044]    The following is shown: 
           [0045]      FIG. 1  a perspective view of a road milling machine in the design of a large milling machine, 
           [0046]      FIG. 2 a    a milling drum with tools arranged in the shape of a helix in accordance with prior art, 
           [0047]      FIG. 2 b    the texture of a milled road surface, 
           [0048]      FIG. 2 c    the line spacing of the tools, 
           [0049]      FIG. 3  a conventional support of the milling drum, 
           [0050]      FIG. 4  a first embodiment of the invention, 
           [0051]      FIG. 5  a schematic representation in top view of an axially movable milling drum housing with a milling drum according to  FIG. 4  mounted in the same, 
           [0052]      FIG. 6  a schematic representation of the axial movement of the milling drum inside the milling drum housing according to a second embodiment, 
           [0053]      FIG. 7  a schematic representation of the linear movement of the milling drum housing in the direction of travel, and 
           [0054]      FIG. 8  a schematic representation of a linear movement of the milling drum axis in the direction of travel, 
           [0055]      FIGS. 9 and 10  a schematic representation of a pendulum movement of the milling drum housing or the milling drum, respectively, in the direction of travel, and 
           [0056]      FIG. 11  a cross-section through the linear guides. 
       
    
    
     DETAILED DESCRIPTION 
       [0057]      FIG. 1  shows a large milling machine as it is basically known from EP 2 011 921 A (U.S. Pat. No. 7,753,620). The road milling machine  1  comprises a machine frame  8  which is supported by a chassis comprising no less than three tracked ground-engaging units  20  or wheels. 
         [0058]    The milling drum housing  10  is arranged between the tracked ground-engaging units  20  as seen in the direction of travel  22 , with small milling machines, however, rather level with the rear support wheels or tracked ground-engaging units  20 . 
         [0059]    The milling drum  12  is rotatable, transverse to the direction of travel  22 , about a milling drum axis  24 , where the milling drum  12  is supported in side walls  11 ,  13  of the milling drum housing  10  or at the machine frame  8 . 
         [0060]    With its one front end, the milling drum  12  may reach up to the outer side of the machine frame  8  called the zero side, while a driving device for the milling drum  12  may be arranged at the opposite outer wall of the machine frame  8 . The driving device for the milling drum  12  may, for example, be a mechanical drive comprising a belt drive  38 , or a hydraulic or electrical drive. 
         [0061]    The operator&#39;s platform  14  with a seat for the machine operator is located above the milling drum  12 . 
         [0062]      FIG. 2 a    shows, by way of example, the arrangement of the tools  16  on the milling drum  12  as it is basically known from DE 102 03 732 (U.S. Pat. No. 7,422,391). In circumferential direction, the tools  16  feature a specified, mostly constant mutual distance. On each front end of the milling drum  12 , a number of tools  16  may be provided which are not arranged in the shape of a helix in order to create vertical milling edges. Since the tools  16  do not change their axial position during rotation of the milling drum  12 , they create grooves  18  on the road surface  2  which, in the direction of travel  22 , form indentations slot-shaped in cross-section on the road surface  2  as they can be discerned, for example, in  FIGS. 2 b    and  2   c.    
         [0063]    The distance  19  between two neighbouring grooves  18  is thus dependent on the line spacing of the milling drum, that is, the axial distance of the neighbouring tools  16  as seen in circumferential direction. 
         [0064]    Depending on the milling drum layout, line spacings preferably between 3 mm and 25 mm are common. 
         [0065]      FIG. 2 c    shows, in a schematic representation, the distance  19  between the grooves  18  resulting from the line spacing of the tools  16  arranged on the milling drum  12  in the shape of a helix. 
         [0066]    Preferably, two helices of tools  16  running in opposite directions are formed on the milling drum  12 , the task of which is to transport the milled material towards the drum centre or towards a specific axial position of the milling drum  12 . 
         [0067]      FIG. 3  shows, in a schematic representation, a conventional axial support of a milling drum  12  inside a milling drum housing  10  which is immovable axially relative to the machine frame  8 . The milling drum axis  24  is supported in the side walls  11 ,  13  of the milling drum housing  10  by means of a fixed bearing  30  and a floating bearing  32 . The floating bearing is, to a small degree, movable axially so that, for example, any thermal expansions of the milling drum axis  24  can be compensated for. 
         [0068]    The milling drum drive is usually arranged preferably on the side of the fixed bearing  30  and may be effected, for example, by means of a mechanical belt drive  38  but also hydraulically or electrically. 
         [0069]    The milling drum  12  which according to the invention is supported in the front end walls of the milling drum housing  10  has, aside from a radial support, an axial support movable in axial direction. In this arrangement, the fixed bearing (axial support) of the milling drum is moved relative to the machine frame  8  either with the entire milling drum housing  10  or relative to the same. 
         [0070]    Due to the relatively small oscillation stroke according to the invention, a mechanical drum drive is also realizable in this design as only a small axial movement of the belt drive  38  must be effected. 
         [0071]    In  FIGS. 4 and 5 , an embodiment is presented in which the axial movement of the milling drum is achieved in that the entire milling drum housing  10  with the milling drum  12  performs the oscillation stroke. In this arrangement, the oscillation drive  28  acts between the machine frame  8  and the milling drum housing  10 . 
         [0072]    As can be inferred from  FIGS. 4 and 5 , the milling drum housing  10  is movable transverse to the direction of travel  22  along no less than two linear guides  42   a,    44   a  and  42   b,    44   b  extending parallel to one another in order to enable an oscillation of the entire milling drum housing  10  with the milling drum  12  in axial direction parallel to the milling drum axis  24  in a ground-parallel plane. 
         [0073]    An oscillation drive  28 , especially a linear drive consisting of, for example, a piston-cylinder unit or a mechanical eccentric drive or a spindle drive, enables oscillation of the milling drum housing  10  relative to the machine frame  8 . 
         [0074]      FIG. 5  is a schematic top view of the embodiment shown in  FIG. 4  from which it can be inferred that the linear guides  42   a,    42   b  extend parallel to the linear guides  44   a  and  44   b  and to the milling drum axis  24 . 
         [0075]    As the milling drum housing  10  performs a short stroke only, the guides  42   a,    42   b,    44   a,    44   b  can be designed significantly shorter than in the schematic representation of  FIG. 5 . It is further understood that each linear guide  42   a,    42   b  and  44   a,    44   b,  respectively, may be of integral design. This means that the guiding elements  42   a,    42   b  and  44   a,    44   b,  respectively, may be connected to one another or may extend across the entire width of the milling drum housing  10 . 
         [0076]      FIG. 6  shows, in a schematic representation, a second embodiment in which the milling drum housing  10  is attached at the machine frame  8  in a rigid fashion and the milling drum  12  is supported in the side walls  11 ,  13  via floating bearings  32   a,    32   b.  The oscillation drive  28  acts between the milling drum  12  and the milling drum housing  10 . To this effect, the milling drum housing  10  is longer in axial direction than the milling drum  12  by, as a minimum, the maximum oscillation stroke. 
         [0077]    Alternatively, a non-depicted axially movable intermediate wall may also be arranged between the side wall  13  and the milling drum  12  in which the one end of the milling drum  12  is supported in a fixed bearing. In this case, the oscillation drive  28  acts between the intermediate wall and the side wall  13 . 
         [0078]      FIG. 7  shows, in a schematic representation, the oscillating movement of the milling drum housing  10  in the direction of travel  22 , while  FIG. 8  concerns an embodiment in which the milling drum  12  can oscillate in the direction of travel within the side walls  11 ,  13 . 
         [0079]    An additional oscillating movement parallel to the direction of travel  22  can be created by means of two additional linear guides  46 ,  48  depicted in  FIG. 7  which extend orthogonally to the linear guides  42 ,  44  so that not only an axial oscillating movement can be superimposed on the rotating movement of the tools  16  but also an additional oscillating movement parallel to the direction of travel  22 . 
         [0080]    In the embodiment shown in  FIG. 8 , the milling drum axis  24  is guided inside the milling drum housing  10  in a horizontal slot  25 . 
         [0081]    The linear guides  42 ,  44 ,  46 ,  48  may, for example, also be intended in the design of a compound slide. 
         [0082]    The amplitude and/or the frequency of the oscillation in axial direction as well as parallel to the direction of travel  22  are variably adjustable. For example, the oscillation stroke can be adjusted in a range between the 0.5-fold to 1.5-fold of the line spacing. The maximum oscillation stroke is preferably guided by the line spacing, however, and deviates only slightly from the same. 
         [0083]    For example, the oscillation stroke is adjustable in a range between 3 mm, preferably 5 mm, and 40 mm. 
         [0084]    The frequency of oscillation can be adjusted between 0.1 Hz and 40 Hz. 
         [0085]    Alternatively, the frequency may also be adjusted so that a specific relation is achieved between the average axial speed magnitude and the advance speed of the milling drum  12  or the circumferential speed of the tools of the milling drum  12  or the sum of the circumferential speed of the tools and the advance speed of the milling machine. 
         [0086]    According to a further alternative, it may be advantageous to combine a specific milling drum speed range with a range of the oscillation frequency adjusted to the same. 
         [0087]    For example, a relatively high milling drum speed in the range between 180 rpm to 600 rpm (or milling drum rotation frequency between 3 Hz to 10 Hz), preferably between 240 rpm to 360 rpm (or 4 Hz to 6 Hz), may be combined with a relatively low oscillation frequency between 0.1 Hz to 5 Hz, particularly preferably between 1 Hz to 3 Hz. 
         [0088]    In this arrangement, the oscillation frequencies refer to the specified range for the oscillation stroke. 
         [0089]    According to another, particularly preferred embodiment, a low milling drum speed may be combined with a high oscillation speed. 
         [0090]    In this case, the milling drum speed may be in the range between 30 rpm to 180 rpm (corresponding to a milling drum rotation frequency of 0.5 Hz to 3 Hz), preferably between 60 rpm to 150 rpm (corresponding to 1 Hz to 2.5 Hz), with an oscillation frequency in the range between 2 Hz to 40 Hz, preferably between 5 Hz to 15 Hz. 
         [0091]    As a general rule, this embodiment is to be preferred as it enables lower tool wear and tear to be achieved (lower circumferential speed of the cutting tools, that is, lower forces on the tool in the cut). 
         [0092]    The oscillation frequency should not correspond to an integral multiple of the rotation frequency of the milling drum (or vice versa), as this would enable the cut to always be performed in the same line extending in the direction of travel. This effect is, however, negligible in case of fast oscillation, for example, the fivefold drum rotation frequency. 
         [0093]    Integral multiples of half the rotation frequency must also be avoided in case of an oscillation stroke corresponding to the line spacing, as the cut will otherwise always be effected in the same line, or the neighbouring line, of the linear texture extending in the direction of travel. 
         [0094]    Finally, a variable oscillation frequency is also possible by superimposing with a harmonic wave of the rotation frequency of the milling drum, for example, with a frequency range of 30% around the oscillation frequency. 
         [0095]    The superimposed oscillation movement of the milling drum  12  parallel to the direction of travel  22  may also, instead of linear as illustrated in  FIGS. 7 and 8 , be effected in the shape of a circular arc about a pivoting axis  50  extending above and parallel to the milling drum axis  24 . 
         [0096]    In this context,  FIG. 9  shows an embodiment in which the milling drum housing  10  with the milling drum  12  can oscillate, in the direction of travel  22 , about the pivoting axis  50  in the shape of an arc. 
         [0097]      FIG. 10  shows an alternative embodiment in which the milling drum  12  can oscillate, in the direction of travel  22 , about the pivoting axis  50  inside the milling drum housing  10 . In this case, the slot  25  is arranged around the pivoting axis  50  in the side walls  11  of the milling drum housing  10  curved in the shape of an arc. 
         [0098]      FIG. 11  shows a cross-section of the longitudinal guides  42 ,  44 ,  46 ,  48 , from which it can be inferred that one each of the two guides  42 ,  48  extending parallel to one another features a single degree of freedom only, namely, in axial direction, and the other guide  44 ,  46 , respectively, features a degree of freedom in axial direction and a degree of freedom in horizontal direction. This design of the guides is suitable both for the linear guides  42 ,  44  acting in axial direction and for the linear guides  46 ,  48  acting in the direction of travel. 
         [0099]    The road milling machine may comprise a controller  14  which controls or regulates the oscillation frequency and/or the oscillation amplitude automatically in accordance with the milling drum speed and/or the advance speed of the milling machine and/or the milling depth of the milling drum. In addition, parameters of the road surface can be taken into account, for example, the consistency of the road surface.