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CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority under 35 U.S.C. §119 of German Patent Application No. 10 2011 109 450.8, filed Aug. 4, 2011, the disclosure of which is hereby incorporated herein by reference in its entirety. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to a milling rotor for processing ground material, having a plurality of milling tools which are arranged in a distributed manner over the jacket surface spaced at predetermined distances and according to a predetermined pattern. 
       BACKGROUND OF THE INVENTION 
       [0003]    In the road construction industry, ground milling machines in form of road milling machines, stabilizers and recyclers are used which comprise a milling rotor. The milling rotor consists of a cylindrical tube, on the jacket surface of which the milling tools are arranged. Chisels or chisel-like apparatuses which are either welded directly onto the rotor or held in quick-change tool holders are used as milling tools. 
         [0004]    Ground milling machines of the generic kind are used for tearing open the respective surfaces over a wide area and in a continuous fashion, such as during the reconstruction of roads and paths, and for re-using the milling material subsequently for the production of a new base course. In the case of stabilizers and recyclers, stabilizing agents and so-called secondary raw materials and further building materials such as sand and the like are optionally mixed into the milling material within the rotor box in a continuous manner. They will be mixed with the detached milling material by a rotation of the milling drum in the rotor box. The mixture will remain locally as a relatively flat layer for further processing. The detached milling material and the mixture of detached milling material and aggregates will be referred to below simply as milling material. 
         [0005]    In known milling rotors, the milling tools are distributed on the rotor jacket in the manner that—as seen in the circumferential direction—a pattern with a V-like or W-like progression is produced which is symmetrical to the central line. It has been found, however, that depending on the milling depth, the rotor speed and the travelling speed of the ground milling machine, the milling material will be conveyed towards the center of the rotor or on both sides to the outside, and will be deposited in an inhomogeneous manner. Coarse fractions in particular form undesirable accumulations in the center of the milling track. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention is therefore based on the object of providing a milling rotor of the kind described above and a ground milling machine having such a rotor with which the distribution of the milling material is improved. 
         [0007]    This object is achieved in such a way that the milling tools are arranged in the circumferential direction of the milling rotor along imaginary lines which extend in parallel and are composed of at least one respective, equally long section of a left-handed and a right-handed helical line. 
         [0008]    The present invention offers the advantage that, as a result of the arrangement of the milling tools, there will not be any scooping effect and therefore no undesirable displacement and accumulation of the milling material by the milling tools. The arrangement of the milling tools in accordance with the present invention does not form any pattern causing a division within the jacket surface along the circumference, and no division towards the center of the rotor. The milling material rather remains approximately on the milling line when the rotor has turned once and forms a flat surface with homogeneous distribution. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The present invention will be explained below in closer detail by reference to an embodiment shown in the schematic drawings, wherein: 
           [0010]      FIG. 1  shows a perspective view of a milling rotor; 
           [0011]      FIG. 2  shows a top developed view of the cylinder jacket of the milling rotor according to  FIG. 1 ; 
           [0012]      FIG. 3  shows a side view of the milling rotor of  FIG. 1 ; and 
           [0013]      FIG. 4  shows a top developed view of the cylinder jacket according to  FIG. 2  with auxiliary lines. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]    In accordance with  FIGS. 1 and 2 , a circular-cylindrical milling rotor  10  of a ground milling machine (not shown) comprises a jacket surface  11 , on which a plurality of milling tools  12  are attached. The rotor axis is designated with reference numeral  8 . A component is designated here as a milling tool which consists of a chisel holder  13  with a chisel receptacle  14 , a clod breaker  15  and a chisel  16  which is only shown on a single milling tool  12   a . The milling tools  12  are arranged in lines  9  which extend along parallel dot-dash lines  17 ,  18  and which extend over the entire width of the milling rotor  10 . The lines  9  are disposed at the same angular distance a from one another and the milling tools  12  have the same lateral distance from one another within one line. From a spatial point of view, the lines  17 ,  18  concern sections of helical lines with a first, relatively large ascending gradient. The direction of rotation of the milling rotor  10  is illustrated with arrow  19 . 
         [0015]    As is shown in  FIG. 2  in conjunction with  FIG. 3 , the milling tools  12  are further arranged in the circumferential direction along imaginary further lines  20  which in a developed view of the jacket surface  11  in accordance with  FIG. 2  are shown as a zigzag line with four equally long, alternating sections A, B and A′, B′ and four direction changes C. In order to ensure clarity of the illustration, only one of these lines  20  is shown. The number n of the direction changes C along the further lines  20  therefore has an even number. From a spatial point of view, this concerns four alternating sections of left-hand and right-hand second and third helical lines with a second ascending gradient. The second ascending gradient is identical in the second and third helical line. It is much shorter in comparison with the first helical line. The arrangement of the milling tools  12  is repeated after half a jacket length, i.e., it is similar on each half of the milling rotor  10 .  FIG. 3  shows the first section A of a right-hand helical line and the first section B of a left-hand helical line, as shown in a view on one side of the milling rotor  10 . Each section A, B and A′, B′ has the same number of milling tools  12 . As an example, three milling tools  12  are respectively disposed along the line  20  in each of sections A, B and A′, B′. 
         [0016]    In order to provide more clarity as to the arrangement of the milling tools  12  on the jacket surface  11 , the developed view of the jacket surface  11  according to  FIG. 4  shows auxiliary lines in the form of a rectangular grid. Furthermore, the left-hand helical lines of the sections B and B′ are additionally labeled with an (*) for visually illustrating the arrangement in the figure. In all other respects,  FIG. 4  corresponds to the illustration of  FIG. 2 . The grid of the auxiliary lines shows that the milling tools  12  which are arranged in one line  9  are arranged with a first lateral offset a to each other within the line  9 . Furthermore, the milling tools which are arranged on further imaginary lines  20  in the circumferential direction are arranged in interstices, i.e., in the circumferential direction at least one other milling tool  12  is arranged at least in a partly lateral overlapping manner between two adjacent milling tools  12  or in a gap that is formed by two adjacent milling tools  12 . In the illustrated example, the milling tools  12  are arranged along the lines  20  within each section A, B and A′, B′ with the predetermined second lateral offset b. The milling tools  12  in sections of the line  20  with opposing helical lines, i.e., sections A, A′ on the one hand and sections B, B′ on the other hand, are further arranged in sections by the second lateral offset b in the manner that the milling tools  12  of the sections with opposing helical lines A, B and A′, B′ overlap partly by the second lateral offset b, as seen in the circumferential direction. Two further milling tools  12  are therefore disposed along the line  20  in connection with each milling tool  12 , which further milling tools are arranged in a partly overlapping manner by the second lateral offset b. The second lateral offset b is smaller than the first lateral offset a. In the illustrated example, the first offset a corresponds approximately to the width of three milling tools  12  and the second offset b approximately to half the width of the milling tool  12 . 
         [0017]    A respective channel  21  on either side of the lines  20  is obtained between the milling tools  12  of two adjacent lines  20  by the first lateral offset a, which channel has the same width as the first offset a. These channels  21  are free from milling tools  12  and extend along the entire circumference of the milling rotor  10 . Their progression corresponds to the progression of the lines  20 . Material detached by the milling tools  12  and optionally admixed material therefore reaches the adjacent channels  21  on both sides of the milling tools  12  on the lines  20 . The material is therefore merely provided with a lateral deflection which is not larger than the channel width or the first lateral offset a. The material processed by the milling tools  12  on two adjacent lines  20  reaches the channels  21  in the described manner. 
         [0018]    Milling tools  12  are provided having two different angular positions relative to the rotor axis  8 . One part of the milling tools is arranged with an angular orientation directed to the left with an angle γ on the one rotor edge and an equally large part is arranged with an angular orientation directed to the right with an angle γ′ on the other rotor edge. The angles γ and γ′ are equally large and mirrored on a circumferential line. They are disposed in the range of approximately 2° to 3°. The milling tools  12  with the one angular position are disposed on the sections A, A′ of the lines  20 , which corresponds to the one helical line. The milling tools  12  with the other angular position are disposed on the sections B, B′; the milling tools  12  on the sections with the left-hand helical line all have the same angular position and the milling tools  12  with the mirrored angular position are all disposed on the sections with the right-hand helical line. Furthermore, all milling tools on a line  9  respectively have the same angular position. 
         [0019]    The milling tools  12  are subdivided into equally large groups. Each group comprises the milling tools  12  which are arranged within one of the sections A, B, A′ and B′. It is therefore determined by a number m of the associated lines  9 . All milling tools  12  within one group further respectively have the same angular position of the milling tools  12 . The number of such groups is even. A total of four groups are provided in the illustrated example, with groups with milling tools  12  with opposing angular positions alternating along the jacket surface  11  in the direction of rotation. 
         [0020]    As a result of the angular position of the milling tools  12 , a wedge surface acting against the direction of rotation of the milling rotor  10  will be produced in each milling tool  12  especially by the chisel holders  13  and the clod breakers  15 , because the milling tools  12  form a body by the chisel holders  13  and the clod breakers  15 , which body is aligned with its longitudinal axis in an oblique manner in relation to the direction of rotation. The wedge surfaces produce a lateral deflection of detached or admixed material, which is also supported by the chisel tips because the chisels  16 , together with the chisel holders  13 , are likewise aligned in an angular fashion. 
         [0021]    While the present invention has been illustrated by description of various embodiments and while those embodiments have been described in considerable detail, it is not the intention of Applicants to restrict or in any way limit the scope of the appended claims to such details. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of Applicants&#39; invention.

Summary:
The present invention relates to a milling rotor for processing ground material, comprising a plurality of milling tools which are arranged in a distributed manner over the jacket surface spaced at predetermined distances and according to a predetermined pattern. In order to improve the distribution of the milling material, the milling tools are arranged in the circumferential direction of the milling rotor along parallel imaginary lines which are composed of at least one respective, equally long section of a left-hand and a right-hand helical line.