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CROSS REFERENCES TO RELATED APPLICATIONS 
   None 
   STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT 
   Not Applicable 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to a rear blade mounting apparatus for a bulldozer. In particular, the invention relates to a blade apparatus and its control method, which blade is mounted to the rear of the bulldozer such that the rear blade can be operated in lift or tilt modes. 
   2. Brief Description of Prior Art 
   In the construction industry, labor and capital equipment costs are primary variables that effect the cost of a particular project. Large machinery is used to more efficiently handle tasks that were originally accomplished by hand, such as digging, lifting, and moving objects. For example, bulldozers are commonly used on construction job sites for digging, pushing and removing large amounts of earth for mining, grading and other tasks.  
   A bulldozer is typically a tractor-like machine having a forwardly mounted bucket that extends forward of the body of the bulldozer. The bulldozer further includes a pair of extending loader arms pivotally connected to the tractor, and said bucket pivotally mounted on free ends of the loader arms. Hydraulic cylinders, or the like, are mounted on the loader arms and controlled to cause the bucket to be positioned in various desired positions. The bucket can be lifted over the body or placed on the ground. Further, the orientation of the bucket can be controlled to hold dirt or the like or to dump the same. 
   The rear of the tractor may include an attachment that trails the body of the bulldozer such as a ripper, or a winch, or the rear of the tractor may not include any such accessory. 
   While these tractors in general, are effective in collecting and removing earth, especially large chunks of earth, these tractors have some limitations. In particular, a conventional bulldozer having said forwardly mounted bucket when collecting and removing earth from a mine pit for example, cannot pivot so that the bucket will collect the fine material remaining at or near the walls of such pit. Depending upon the size of the pit, there are often large volumes of such materials remaining. Often such remaining material must be shoveled by hand into a dump truck for transporting away. Such manual procedure requires additional manpower which is not only dangerous due to such manpower working near large machinery, but also costly, time consuming, and generally inefficient. The inventor herein is unaware of any attachment to the bulldozer available for collecting such materials at or near the walls of the mine pit work site.  
   As will be seen from the subsequent description, the preferred embodiments of the present invention overcome these and other shortcomings of prior art. 
   SUMMARY OF THE INVENTION 
   The present invention is designed to be mounted to the rear of a bulldozer that will effectively access and make collectable materials such as fine material remaining at or near the walls of a mine pit for example, that the front-end bucket of the bulldozer is unable to access. The preferred embodiment generally includes a frame that extends from the rear of the body of the bulldozer, said frame including a pair of extending loader arms pivotally connected to the rear of the bulldozer, and a blade pivotally mounted on free ends of the loader arms, and hydraulic cylinders, or the like, controlled to cause the blade to be positioned in various desired positions. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a side view of a bulldozer having rearwardly mounted the preferred embodiment of the present invention, where the blade is in a first position. 
       FIG. 2  is a side view of the bulldozer of  FIG. 1  where the blade is in a second position. 
       FIG. 3  illustrates a perspective view of the frame of the present invention. 
       FIG. 4  illustrates a perspective view of the blade of the present invention.  
       FIG. 5  illustrates a partial view of the bulldozer with the blade in a third position. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIGS. 1–5  illustrate a preferred embodiment of a bulldozer rear blade mounting structure  50  made in accordance with the present invention. With reference to  FIGS. 1–2 , a common bulldozer tractor  10  (also referred to as a tractor  10 ) having the prior art forwardly mounted bulldozer structure  12  having a bucket  15  secured to the front of the tractor  10  is disclosed. 
   As shown in  FIGS. 1–2 , attached to the rear of the tractor  10  is the rear blade mounting structure  50  made in accordance with the present invention. The structure  50  includes a frame  55 , said frame  55 , as best shown in  FIG. 3 , having first and second support arms  55 A and  55 B. The support arms  55 A and  55 B extend from the rear of the body of the tractor  10  and is pivotally mounted to the rear of the body of the tractor  10  in a manner using, connecting pivot points  57 A (not shown) and  57 B (shown in  FIG. 5 ). The opposite ends of support arms  59 A and  59 B of the support arms are coupled to midway end portions  65 A and  65 B of the inside of a blade  60 . The blade  60  having a blade edge member  61  and including upper end portions  62 A (not shown) and  62 B disposed at the approximate upper end of the blade  60  at opposing right and left ends thereof. The midway end portions  65 A and  65 B disposed at the approximate midway of the blade  60  at opposing right and left ends thereof. The blade  60  having a substantially rectangular configuration. 
   At the approximate midway of each of said arms  55 A and  55 B is disposed coupling joints  56 A and  56 B that attach to a pair of upper hydraulic cylinders   66 A and  66 B and a pair of lower hydraulic cylinders  67 A (not shown) and  67 B as will be further described. 
   Referring again to  FIG. 3 , the frame  55  further including support plates  70  and  72  disposed between support arms  55 A and  55 B, the plates  70  and  72  provided to support the functional elements of the frame  55 . 
   The rear of the tractor  10  having pairs of upper and lower end joints  58 A (not shown),  58 B and  58 C (not shown),  58 D, respectively, for attaching the hydraulic cylinders  66 A,  66 B and  67 A and  67 B. Specifically, the upper hydraulic cylinders  66 A and  66 B are removably and pivotally installed to the upper end joints  58 A and  58 B of the rear of the tractor  10 ; and the lower hydraulic cylinders  67 A and  67 B are removably and pivotally installed to the lower end joints  58 C and  58 D of the rear of the tractor  10 . The other end of the pair of upper hydraulic cylinders  66 A and  66 B removably and pivotally attached to the upper end portions  62 A and  62 B of the inside of the blade  60 ; and the other end of the pair of lower hydraulic cylinders  67 A and  67 B removably and pivotally attached to the coupling joints  56 A and  56 B of the support arms  55 A and  55 B. The attachment are of a conventional manner known in the art. 
   As shown in the drawings, said upper hydraulic cylinders  66 A and  66 B being longer than the lower hydraulic cylinders  67 A and  67 B in order to further extend the blade  60  from the tractor  10  and to give sufficient clearance between the blade  60  and the tractor  10 . As should be obvious, as a result of the extended length of the upper hydraulic cylinders  66 A and  66 B, and as a result of said cylinders  66 A and  66 B being pivotally attached to the upper end portions  62 A and  62 B at the approximate upper end of the blade  60 , the blade  60  is able to be positioned higher than the standard forwardly mounted bucket  15 .  
   As should be appreciated from the description herein, the rear blade mounting structure  50  is symmetrically constructed with pairs of elements on opposite sides of the tractor  10 . As such, only the elements found on one side of the tractor  10  is primarily discussed and shown in the  FIGS. 1–2 . It should be understood that the other set of elements are identical to those described, with the exception that the other set of elements are mirror images of the first set of elements described. 
   The application of the rear blade mounting structure  50  is generally operating means used for the conventional forwardly mounted bulldozer structure  12  known in the art. 
   In use, as shown in  FIG. 2 , the blade  60  may be moved substantially vertically by rotating the frame  55  about pivot arm  57 B and the blade  60  can be rotated about pivot point  65 B which forms a substantial horizontal axis. 
   Starting with the blade  60  in the position in  FIG. 1 , the user can retract upper cylinder pair  66 A, B to raise the blade  60  to the position shown in  FIG. 2 . This position allows the user to position the blade  60  above a pile of material to be moved. Once in position the user can extend cylinder pair  67 A, B to drop the frame  55  and extend cylinder pair  66 A, B to achieve a third position shown in  FIG. 5 . In this position, the blade edge  61  can dig in and by pulling the whole tractor  10  forward material in front of the blade  60  can be pulled forward. 
   With regard to rotation about a substantially horizontal axis, the user adjusts the blade  60  by selectively extending or retracting the upper hydraulic-cylinders  66 A and  66 B, and the lower hydraulic cylinders  67 A and  67 B. When said cylinders   66 A,  66 B and  67 A,  67 B are telescopically adjusted such to be shorter or longer, the blade  60  is shifted and rotates about said substantially horizontal axis. 
   If the user wishes the blade  60  to be oriented at a selected angle with respect to the longitudinal axis of the tractor  10  (as shown in  FIGS. 1–2 ), the user extends either the upper hydraulic cylinders  66 A and  66 B or the lower hydraulic cylinders  67 A and  67 B until the blade  60  is at the desired orientation. 
   In the configuration of the present invention, the tractor  10  uses the forwardly mounted bulldozer bucket  15  to collect and remove earth, from a mine pit work site for example. When the bucket  15  cannot pivot so that the bucket  15  will collect the fine material at or near the walls of such pit generally on an ascending slope, the user utilizes the rear blade mounting structure  50  mounted to the rear of the tractor  10  to move such material so that the forwardly mounted bucket  15  is then able to collect and remove such material. Specifically, the operator raises the upper hydraulic cylinders  66 A and  66 B causing the blade  60  to rotate as shown in  FIG. 2 , so that the blade  60  is positioned above the said material to be moved and on the approximate same vertical axis as the said wall of the pit. The operator then lowers the upper hydraulic cylinders  66 A and  66 B causing the blade edge member  61  of the blade  60  to lower and dig into the earth material as shown in  FIG. 5 . Once the blade  60  is lowered to a selected depth, the operator then drags the material by driving the tractor  10  in the direction away from the wall of the pit while the blade  60  is dug into the material. As a result, the blade  60  moves that material in contact with the blade  60 , that material approximately between the blade  60  and the rear of the tractor  10 . It has been found that such material should be moved the approximate length of the body of the tractor  10  in order to make available to the bucket  15  for collection. Once moved, such material is then  accessible to the bucket  15  and is collected and removed by the bucket  15  on the front of the tractor  10  in a conventional manner. 
   Although the description above contains many specificities, these should not be construed as limiting the scope of the invention but as merely providing illustrations of a presently preferred embodiment of this invention. 
   Though not shown, it would be possible to mount the upper cylinder pair  66 A, B with pivot point  55 B on the top edge of the frame  55  instead of on the tractor  10 . Such an arrangement would still allow the upper cylinder pair  66 A, B to pivot the blade  60  about pivot point  65 A, B to control the position of the blade  60  about the axis defined by pivot points  65 A, B. 
   Thus the scope of the invention should be determined by the appended claims in the formal application and their legal equivalents, rather than by the examples given.

Summary:
A rear blade mounting apparatus for a bulldozer. The mounting apparatus generally includes a frame that extends from the rear of the body of the bulldozer, the frame including a pair of extending loader arms pivotally connected to the rear of the tractor, and a blade pivotally mounted on free ends of the loader arms, and hydraulic cylinders, or the like, controlled to cause the blade to be positioned in various desired positions.