Abstract:
A road marking has multiple depressions introduced into the road surface, the depressions comprising two lateral longitudinal walls, extending in the longitudinal direction of the road, that transition, proceeding from the road surface, continuously into a bottom region; and the depression being delimited by two transverse walls extending transversely to the longitudinal direction of the road. The road markings have improved utilization properties if provision is made that the longitudinal walls comprise a region convexly curved transversely to the longitudinal direction of the road. The invention further relates to a cutting unit for producing such road markings.

Description:
This application claims priority to German Patent Application No. 10 2009 034 766.6-25 filed on Jul. 25, 2009. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a cutting unit for producing a road marking, having a rotary unit, rotatable about a rotation axis, that can receive a plurality of cutting elements that define a cutting curve, the cutting curve forming a convex cutting region in the direction of the rotation axis. 
     The invention further relates to a road marking having multiple depressions introduced into the road surface, the depressions comprising two lateral longitudinal walls, extending in the longitudinal direction of the road, that transition, proceeding from the road surface, into a bottom region; and the depression being delimited by two transverse walls extending transversely to the longitudinal direction of the road. Such road markings are also referred to as “rumble strips.” 
     2. Description of the Prior Art 
     U.S. Pat. No. 6,547,484 B2 discloses a road milling machine having a cutting unit that comprises a tubular milling drum as a rotary unit. The drum surface is barrel-shaped and is curved convexly in the direction of the rotation axis. It receives cutting bit holders in which cutting bits can be replaceably received. The cutting bits are equipped with carbide metal tips that serve as cutting elements. Corresponding to the convex curvature of the drum surface, the carbide metal tips form a convex cutting curve in the direction of the rotation axis of the milling drum. This convex cutting curve results during rotation of the rotary unit. When the rotating cutting unit is advanced in the direction of the road surface to be processed, the cutting bits then cut a depression out of the road. Corresponding to the convex curvature of the cutting curve, a concave recess is correspondingly produced transversely to the longitudinal extension of the road. Because of the circular cross section of the rotary unit, the depression has a concave shape in the longitudinal extension as well. In order to produce a road marking, multiple depressions are milled into the road, distanced from one another at identical spacing. The road marking thus forms a deliberate geometrical irregularity in the road. When it is rolled over by a vehicle tire, noise and vibrations occur which are perceived by the driver and notify him or her, for example, of a departure from the road. 
     The road markings thus have the function and object of delivering an acoustic and haptic warning signal. This noise source is, however, on occasion perceived as disruptive by the surroundings adjacent to the road. A further disadvantage of the known road markings results when they are driven over by a two-wheeled vehicle. The two-wheeled vehicle is laterally offset in that context, which can then trigger dangerous steering corrections by the driver. When rainwater collects in the depressions, the driving situation of the two-wheeled vehicle can then additionally become unstable. 
     BREIF SUMMARY OF THE INVENTION 
     An object of the invention is to make available a cutting unit with which road markings having improved application properties can be produced. 
     A further object of the invention is to make available such road markings. 
     The object relating to the cutting unit is achieved in that a respective concave cutting region is indirectly or directly adjacent to the convex cutting region on both sides. 
     The object relating to the road marking is achieved in that the longitudinal walls of the depressions comprise a convexly curved region. 
     With the cutting unit according to the present invention, it is possible to mill depressions for road markings in which the road surface is caused to transition continuously via the convex region into the concave bottom. This has the advantage that the tires of a vehicle travel more smoothly into the depression. A reduction in noise generation is thereby achieved, although a sufficient sound level and, in particular, a sufficient haptic warning signal for producing attentiveness in the driver, are still produced. 
     The geometry of the road marking also enables a two-wheeled vehicle to drive over it with less difficulty, and diminishes a lateral offset that upsets the driver. In addition, the volume formed by the depression is decreased by the convex region of the depression. Less water can thus collect therein, which greatly decreases the risk of instability of a two-wheeled vehicle when the road is wet. 
     According to a preferred variant embodiment of the cutting unit, provision can be made that at least one of the concave cutting regions terminates, at the end facing away from the convex cutting region, in an end region parallel to the rotation axis. This produces in the depression a harmonious transition to the road surface that withstands mechanical stresses in particularly robust fashion. 
     If provision is made that the radius of the convex cutting region is between 200 mm and 400 mm, and/or that the radius of the concave cutting region is between 400 mm and 800 mm, this then results in corresponding geometries at the depression that allow sufficient noise production to occur with a decreased influence on tire guidance. 
     One conceivable inventive alternative is such that the rotary unit has a mounting surface on which are mounted tool holders that can replaceably receive the cutting elements; and that the mounting surface comprises a convex mounting portion associated with the convex cutting region and a concave mounting portion associated with the concave cutting region. With a rotary unit of this kind, the cutting curve can easily be produced using identical bit holders and cutting elements. 
     A cutting unit according to the present invention can be characterized in that a mounting flange is arranged in the hollow region enclosed by the rotary unit; and that the mounting flange is coupled onto the rotary unit on the inner wall portion associated with the convex cutting region. The mounting flange is thus secured in strength-optimized fashion in the thickened portion of the rotary unit formed by the convex cutting region. 
     In the context of the road marking according to the present invention, provision can be made that the convex region of at least one of the longitudinal walls is caused to transition into a concave region of the bottom, and/or that the convex region of at least one of the side walls is caused to transition into the road surface. The result of this is to produce depressions that have little negative influence on lateral guidance of the wheel. 
     It is also conceivable for the transverse walls to comprise a concave region that is caused to transition indirectly or directly into the road surface. Sufficiently high acoustic pressure then occurs as the wheel strikes the transverse wall. The depressions can be distanced from one another with a constant spacing pattern in order to form the road marking, or it is conceivable for the individual depressions to abut one another directly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be further explained below with reference to an exemplifying embodiment depicted in the drawings, in which: 
         FIG. 1  is a vertical section through a road and a cutting unit; 
         FIG. 2  is a vertical section through a road; 
         FIGS. 3 and 4  schematically depict various road markings; 
         FIG. 5   a  is a schematic side view of a cutting unit in accordance with the existing art; 
         FIGS. 5   b  and  5   c  show a road marking produced with a cutting unit in accordance with  FIG. 5   a;    
         FIG. 6   a  is a schematic side view of a cutting unit in accordance with the existing art; 
         FIGS. 6   b  and  6   c  show a road marking produced with a cutting unit in accordance with  FIG. 6   a;    
         FIG. 7   a  is a schematic side view of the cutting unit according to the present invention in accordance with  FIG. 1 ; 
         FIGS. 7   b  and  7   c  show a road marking produced with a cutting unit in accordance with  FIG. 7   a;    
         FIG. 8  shows, in a coordinate system, the contour of the road marking in accordance with  FIGS. 6   b  and  6   c;    
         FIG. 9  shows the first derivative of the curve resulting from  FIG. 8 ; 
         FIG. 10  shows, in a coordinate system, the contour of the road marking in accordance with  FIGS. 7   b  and  7   c ; and 
         FIG. 11  shows the first derivative of the curve resulting from  FIG. 10 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a cutting unit that comprises a drum-shaped rotary unit  10 . Rotary unit  10  is of tubular configuration and has a cylindrical internal receptacle that is formed by the enveloping surface of rotary unit  10 . Arranged in the internal receptacle is a mounting flange  11  having mounting receptacles  12  onto which the output shaft of a drive train can be flange-mounted. 
     The enveloping surface of rotary unit  10  forms a supporting part  13  having a barrel-shaped peripheral mounting surface  14 . Mounting surface  14  is assembled from a central convex mounting portion  14 . 2  and two concave mounting portions  14 . 1  respectively laterally adjacent thereto. Concave mounting portions  14 . 1  transition directly into convex mounting portion  14 . 2 . Installed on the two mounting portions  14 . 1  and  14 . 2  are bit holder changing systems made up of a base part and a bit holder  20  mountable replaceably thereon. The base parts are welded to mounting portions  14 . 1 ,  14 . 2 . The base parts are arranged in offset fashion from one another, resulting in spatial and load spirals that extend helically on mounting portions  14 . 1 ,  14 . 2 . 
     Also conceivable is a configuration of the invention in which bit holders  20  are welded directly onto mounting portions  14 . 1 ,  14 . 2 , so that base parts can be omitted. Bit holders  20  comprise bit receptacles in which bits  21 , preferably round-shaft bits, can be replaceably received. Bits  21  are equipped with cutting elements that, upon a rotation of rotary unit  10  about rotation axis R, define a cutting curve  15 . Cutting curve  15  forms, in this context, a kind of enveloping curve. 
     As  FIG. 1  illustrates, cutting curve  15  forms, correspondingly to the configuration of mounting portions  14 . 1 ,  14 . 2 , a convex cutting region  15 . 2  and, laterally adjacent thereto, concave cutting regions  15 . 1 . Radius R 2  of convex cutting region  15 . 2  is preferably between 200 mm and 400 mm; in the present case R 2 =300 mm. Radius R 1  of concave cutting regions  15 . 1  is preferably between 400 mm and 800 mm. The particularly preferred ratio R 1 :R 2  of approx. 2:1, for example, can thus be established. 
     Road markings, made up of depressions  31  arranged linearly behind one another, can be milled into road  30  using the cutting unit. 
     The geometry of depression  31  resulting in that context is depicted in enlarged fashion in  FIG. 2 . As this drawing indicates, depression  31  has transversely to the longitudinal direction of the road, in a manner complementary to cutting curve  15 , a concave bottom  31 . 2  from which two convex longitudinal walls  31 . 1  rise on both sides. Longitudinal walls  31 . 1  transition into road surface  32 . Transverse walls  31 . 3  extending transverse to the longitudinal extension of the road are curved concavely in accordance with the drum periphery. 
       FIGS. 3 and 4  depict different variant configurations of road markings that are respectively constituted by juxtaposed depressions  31 . Depressions  31  are generated by cutting units that correspond in principle to the design in accordance with  FIG. 1 . 
       FIG. 3  shows a variant configuration in which the cutting unit is advanced perpendicular to road surface  32  and, once the cutting unit has reached its deepest advance position, is retracted again before being offset in the longitudinal direction of the road by an amount equal to the desired spacing, and so forth. 
       FIG. 4  shows a procedure modified as compared with  FIG. 3 . Here the cutting unit is not retracted above the level of road surface  32 , but instead, during the feed movement, is continuously advanced along the longitudinal direction of the road to the deepest advance position and retracted back to the level of the road surface, so that depressions  31  are directly juxtaposed. The advance and retraction movement can be coordinated with the feed movement so as likewise to produce, in the longitudinal direction of the road, an alternating arrangement of convexly and concavely curved regions of the depression. The result that can thereby be achieved is that each individual depression of the series of depressions receives, in longitudinal section, a curve profile similar to the cross section. 
       FIG. 5   a  shows a cutting unit  10  in accordance with the existing art that generates, with its bits  21 , a cylindrical enveloping curve. As  FIG. 5   b  shows, road markings  31  having a partly cylindrical geometry can be correspondingly milled with this cutting unit  10 . The enlarged detail in accordance with  FIG. 5   c , taken from  FIG. 5   b , shows that in the case of these road markings  31 , an abrupt 90-degree transition results between road surface  32  and the adjacent longitudinal wall  31 . 1 . 
       FIG. 6   a  shows a further cutting unit  10  in accordance with the existing art (for example, in accordance with U.S. Pat. No. 6,547,484 B2). Here bits  21  generate a convex cutting curve. The road markings  31  that result with this cutting unit  10  have the shape shown in  FIG. 6   b.    
       FIG. 6   c  shows a detail taken from  FIG. 6   b . It is evident here that the transition from road surface  32  into longitudinal side walls  31 . 1  is considerably flattened as compared with the variant according to  FIGS. 5   b  and  5   c , but still forms a relatively steep transition. 
       FIG. 7   a  shows, for better comparison, cutting unit  10  in accordance with  FIG. 1 . 
       FIG. 7   b  corresponds approximately to  FIG. 2 , and  FIG. 7   c  shows the detail marked VIIc in  FIG. 7   b . It is clearly apparent that according to the present invention, an improved transition between road surface  32  and longitudinal wall  31 . 1  can be constituted. This advantage is further illustrated with reference to  FIGS. 8 to 11 . In  FIG. 8  the contour of road marking  31  resulting from the cross section in accordance with  FIG. 6   b  is plotted as a curve in a coordinate system. 
       FIG. 10  shows, analogously, the curve for the road marking in accordance with  FIG. 7   b.    
     If the first derivative of these curves (in accordance with  FIGS. 8 and 10 ) is then taken, the curves in accordance with  FIGS. 9 and 11  result. It is evident that with road marking  31  according to the present invention, a continuous transition from road surface  32  into longitudinal wall  31 . 1  can be effected, and this road marking  31  follows a sine curve in terms of its slope profile. 
       FIG. 9 , in contrast, illustrates the discontinuous transition between road surface  32  and longitudinal side wall  31 . 1 .