Abstract:
An apparatus and method for milling rumble strips into a pavement surface with a cutting wheel. The cutting wheel has rows of a cutting and non-cutting surface and is rotated to alternately present and withdraw a cutting surface and a non-cutting surface to the asphalt and cut a periodic rumble strip pattern as the apparatus moves forward. This alternating pattern is achieved without any up and down motion of the cutting wheel, and the apparatus can be operated a relatively rapid speed.

Description:
RELATED APPLICATIONS 
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     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
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     FIELD OF THE INVENTION 
     This invention relates to an apparatus for cutting rumble strips into asphalt or cement pavement. 
     BACKGROUND OF THE INVENTION 
     Rumble strips are typically installed in new asphalt pavement by pressing depressions perpendicular to forward direction of travel when it is still hot during installation of the pavement. This is accomplished by a roller with steel bars of suitable size and spacing with adequate weight to form the depressions. 
     It is often desirable to install rumble strips in asphalt that is already installed, or to increase the width of the rumble strip depressions to increase the magnitude of rumble effect. To this end, machines have been designed and built to mill wider depressions in cold asphalt pavement along the shoulder of roads. These rumble strip milling machines typically use the same type of cutting teeth used on large asphalt milling machines. The teeth are mounted on a cylindrical cutting head, with a diameter the same as the arch of the depressions to be milled. As the milling machine moves forward, the cutting or milling head is rotated at a rapid rate against the forward motion of the milling machine to cut into the pavement. Since the cutting must be periodic and not continuous to form a rumble strip, the cutting head is raised and lowered at regular intervals to leave unmilled areas between the milled depressions. Accordingly, during the forward travel of the milling machine it is necessary to continuously move the cutting head up and down in a regular periodic motion. This up and down motion must be carefully coordinated with the forward speed of the milling machine. This coordinated motion severely limits the forward speed of the milling machine. Typically the forward speed of these rumble strip cutters can be no greater than one or two miles per hour, making the process a relatively slow procedure. 
     The up and down motion of the cutting head not only limits the speed of the milling machine, but adds significantly to the mechanical complexity and cost of the machine. Accordingly, there is a continuing need in the art to a rumble strip cutting system that not only permits a faster cutting speed but also is a mechanically simpler method than existing systems. A desirable system would be mechanically simpler, and thus more reliable and allow for a faster forward speed of the milling machine. 
     Objects of the Invention 
     It is, therefore, an object of the invention to provide a rumble strip milling apparatus that can cut rumble strips while traveling significantly faster that prior-art systems. 
     Another object of the invention is a rumble strip milling apparatus that is mechanically simpler than existing systems. 
     Further objects of the invention will become evident in the description below. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention involves a milling machine and method for cutting rumble strips into pavement, such as asphalt and Portland cement. The present invention involves a cutting wheel with alternating rows of cutting teeth. The cutting wheel is mounted with the cutting rows transverse to the direction of travel and it is rotated at a fixed distance above the pavement to move the cutting rows in and out of cutting position as the milling machine moves forward. 
     As the teeth on the cutting wheel are rotated in and out of cutting position, the forward motion of the machine provides the cutting force as the row of cutting teeth are dragged along the pavement to cut a depression in the pavement. The cutting row is then rotated from cutting into the pavement, leaving an uncut portion as the machine continues its forward motion. In this manner periodic cut and uncut portions are provided, which together form a rumble strip. 
     The invention is contrary to prior-art practice where the cutting wheel is rotated rapidly to provide the cutting force for the wheel and the wheel is moved up and down as the machine moves forward. 
     Since the rotating of the cutting wheel enables the milling machine to form the periodic cuts, it is not necessary to move the cutting wheel up and down. Accordingly, the cutting wheel rotates at a fixed distance above the pavement, such that the cutting rows cut into the pavement when they are at the bottom of the cutting wheel, and an uncut portion is left when the non-cutting surface is at the bottom of the cutting wheel. 
     In order that the forward motion provide the cutting force for the teeth in the cutting rows, the teeth must be dragged across the pavement, i.e., the peripheral speed of the cutting wheel is slower than or opposite the speed of the pavement under a cutting row as it cuts. There are several ways of accomplishing this end. One method, as illustrated in Example I, is to provide a cutting wheel that turns at the same RPM rate and in the same direction as a drive wheel of the machine, but where the cutting wheel has a smaller diameter. In this instance the forward side of the wheel is turning down, like the drive wheel, but because the peripheral speed of the cutting wheel is lower, its cutting rows are dragged along the pavement when in cutting position. Another method, as illustrated in Example II, is to provide cutting wheels that turn opposite the forward motion. 
     In any case, it is important that the cutting wheels function to present and withdraw a cutting row for cutting. In addition, the arc and spacing of the depression must be correct. Accordingly, the cutting wheel diameter, the number of cutting rows on the cutting wheel, rotation speed and direction, must be chosen to achieve the desired ends. In addition, the peripheral speed of the cutting wheel and the forward motion must be proportionally coordinated in order to provide a strip of regular periodic cut depressions. 
     Coordinating the forward speed and cutting wheel speed together proportionally is mechanically simpler and more trouble free than coordinating the up and down motion of a cutting wheel and its drive mechanism. Without the requirement of a up and down motion of cutting wheels, it is possible for the apparatus of the present invention to travel much faster than prior-art systems, up to 20 to 30 miles per hour. The order of magnitude increase in speed, and the overall simplicity of the present system, over prior-art systems, allows for a significant savings in capitol and operating costs. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is schematic side view of an apparatus of the invention 
     FIG. 2 is a schematic of the cutting wheels of the apparatus in FIG. 1, illustrating the motion of the cutting wheels relative to the forward motion of the apparatus. 
     FIG. 3 is a schematic of an alternate apparatus of the invention. 
     FIG. 4 is a schematic showing in greater detail the cutting wheels of the apparatus of FIG.  3 . 
     FIG. 5 is a schematic illustrating the motion of the cutting teeth relative to the forward motion of the apparatus of FIG.  3 . 
    
    
     INDEX OF REFERENCE NUMBERS 
     FIGS. 1 and 2 
       101  apparatus of the invention 
       103  truck 
       105  rear drive axle 
       107  air bags 
       109  forward cutting wheel 
       111  rear cutting wheel 
       113  transfer case 
       115  drive wheels 
       117  cutting teeth 
       119  radius lines 
       121  center of cutting wheel 
       123  tip of cutter 
       125  pavement 
       127  wheel center locations 
       129  cutting tip locations 
     FIGS. 3,  4  and  5   
       301  apparatus of the invention 
       303  truck 
       305  rear drive axle 
       309  cutting wheel 
       310  cutting wheel 
       311  cutting wheel 
       312  cutting wheel 
       315  drive wheels 
       317  cutting teeth 
       319  radius lines 
       321  center of cutting wheel 
       323  tip of cutter 
       325  pavement 
       327  wheel center locations 
       329  cutting tip locations 
     DETAILED DESCRIPTION OF THE INVENTION 
     EXAMPLE I 
     Reference is now made to FIG. 1, which a schematic diagram of a rumble strip milling machine of the invention  101 . A large truck  103  with a suitable wheelbase and at least one rear drive axle  105  provides a forward motion to the apparatus. The truck is equipped with air bags  107  over the rear axle  105  to raise and lower the frame of the truck. Forward and trailing cutting wheels  109 ,  111  are mounted behind the drive axle. Two cutting wheels  109 ,  111  are mounted on two truck axles with the same gear ratios as the drive axle for the drive wheels of the truck. The cutting wheels  109 ,  111  are driven through a transfer case  113  to allow engagement or disengagement of the cutting wheels. The diameter of the cutting wheels  109 ,  111  is one half the diameter of the drive wheels, so that the peripheral speed of the cutting wheels  109 ,  111  is one-half of the drive tire or ground speed. 
     As an example, if the drive wheel is 42 inches in diameter, the diameter of the cutting heads (from the tips of the cutters) is 21 inches. Usually the spacing between rumble strips is 12 inches. Therefore, the spacing between the cutting teeth rows on the milling head must be 6 inches. The cutting head has a circumference of about 66 inches, thus 11 rows of cutting teeth are spaced around the circumference of the wheel, at about 6 inch intervals. 
     During operation of the milling machine the cutting wheels are lowered to the pavement surface by deflating the air bags  107  to dead axle. The apparatus is driven forward and the cutting wheels  109 ,  111  are dragged or pulled over the surface while being rotated forward, as indicated by the arrows. To provide weight in the cutters so that they will cut into the pavement, the vehicle may be weighted by any suitable means, for example, by a water tank. Auxiliary equipment used in pavement milling machines may also be provided, such as, for example, spray bars over the cutters, covers over the cutting wheels, compressed air for cleaning, noise suppression devices, and the like. 
     Reference is now also made to FIG. 2, which is a schematic illustrating the cutting wheels  109 ,  111 . The cutting wheels  109 ,  111  comprise rows of cutting teeth  117  (only one tooth in each row is shown for clarity) with spaces  119  without cutting teeth between the rows. To illustrate the motion of the cutting teeth rows as the wheel rotates and moves forward radius lines  119  are shown below between the center of the cutting wheel  109 ,  111  and the tip of a cutter  123  cutting into pavement  125 . The cutting wheel moves forward at a constant speed as shown by the equal spacing of the wheel center locations  127 . However, the speed of a cutting tip is less, by one-half in this example, when it is cutting into the pavement. This is shown by the spacing between the corresponding cutting tip locations  129 . As a result of the lower speed of the cutting wheel the cutting teeth are dragged along the pavement, which provides the cutting force for the milling of the depression by the teeth  117 . Thus, although the wheel is rotating forward side down, the cutting teeth  117  are set to cut up. 
     EXAMPLE II 
     Reference is now made to FIG. 3, which a schematic diagram of an alternate rumble strip milling machine of the invention  301 . A truck  303  with a suitable wheelbase and at least one rear drive axle  305  provides a forward motion to the apparatus. Four cutting wheels  309 ,  310 ,  311 ,  312  are mounted behind the drive axle. The truck is equipped with suitable means to raise and lower the cutting wheels (not shown). 
     With driving wheels  315  on the machine of about 30.56 inches in diameter, and the cutting wheel one-fourth of that diameter (from tips of teeth—7.64 inches) a ratio of 8:1 would turn cutting teeth on the cutting heads twice as fast as the forward motion of the milling apparatus. The circumference of the cutting heads is about 24 inches which means that the teeth would travel 24 inches in a circular motion for very 12 inches of forward motion. Using four cutting wheels mounting 15 inches part, each cutting wheel having one row of cutting teeth. In the four cutting wheels, the cutting rows are oriented 90° out of phase (e.g., 6, 9, 12, and 3 o&#39;clock). 
     During operation of the milling machine the cutting wheels are lowered, and the apparatus is driven forward and the cutting wheels  309 ,  310 ,  311 ,  312  are dragged or pulled over the surface while being rotated forward, as indicated by the arrows. 
     Reference is now also made to FIGS. 4 and 5, which are, respectively, a schematic illustrating the cutting wheels  309 ,  310 ,  311 ,  312 , and a schematic showing radius lines of a moving wheel. The cutting wheels comprise a row of cutting teeth  317  with a space  319  without cutting teeth. To illustrate the motion of the cutting teeth rows as the wheel rotates and moves forward (See FIG. 5) are radius lines  319 , i.e., the lines between the center  327  of a cutting wheel and the tip  329  of a cutter cutting into pavement  325 . The cutting wheel moves forward at a constant speed as shown by the equal spacing of the wheel center locations  327 . However, the speed of a cutting tip  329  is faster the wheel center when it is cutting into the pavement. This is shown by the corresponding cutting tip locations  329 . 
     While this invention has been described with reference to certain specific embodiments and examples, it will be recognized by those skilled in the art that many variations are possible without departing from the scope and spirit of this invention, and that the invention, as described by the claims, is intended to cover all changes and modifications of the invention which do not depart from the spirit of the invention. 
     For example, the cutting wheel could be mounted with its axis at an angle to the forward motion of the machine. The teeth would then be oriented in helical rows to cut the depressions straight across. The depressions would be similar to those of the above examples, but be parallelogram-shaped. 
     An apparatus of the invention may have one or a plurality of cutting wheels. A second cutting wheel may be used to cut in the same depression as a first cutting wheel to finish the shape and texture of the depression, as illustrated in the examples. In addition, a following cutting heads may be disposed to cut in between depressions cut by one or more leading cutting wheels. 
     Any system for providing and coordinating the peripheral speed of the cutting wheel and the forward motion is contemplated. Preferably, conventional power transfer systems that turn both the drive and cutting wheels at the same speed are used, using a smaller diameter for the cutting wheel. Other methods of coordinating these speeds is contemplated, using, for example, any combination of synchronized motors, gear boxes, electronic speed controllers and governors, and the like. The only requirement is that the peripheral speed of the cutting wheel be coordinated with the forward speed as recited in the claims. 
     In addition, the milling apparatus need not be on a motorized truck or be self propelled, as illustrated, but could be towed as a trailer, the requirements being that there by some motor or like for imparting forward motion and that the cutting wheel speed can be proportionally linked with the forward speed. The exact dimensions of the various components of the milling machine, in particular, the drive and cutting wheel diameters, the cutting row spacing, and the ratio between the speeds of the drive and cutting wheels, depends upon the dimensions of the rumble strip, the configuration of the drive mechanism, etc, The exact dimensions and configuration for any particular milling machine of the invention is well within the skill of an ordinary practitioner in the art to determine.