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You are an expert at summarizing long articles. Proceed to summarize the following text: 
FIELD OF THE INVENTION  
       [0001]     The invention relates to blade distance ratio as a factor in the grading ability of dozers. More specifically, it relates to a system and method for dynamically adjusting the blade distance ratio on a four track articulated dozer.  
       BACKGROUND OF THE INVENTION  
       [0002]     Current market trends indicate that crawler operators are using their machines for more finish grading work than has historically been done. Thus the need for dozers that can competently grade is growing. To support this trend, manufacturers continue to improve the machines ability to perform this work to the operators expectations.  
         [0003]     Key contributors of the dozers finish grading capability include such factors as machine balance, weight distribution, track length on ground, machine rigidity, and the location of the blade relative to the track. Locating the blade closer to the tracks increases the machine stability, and makes the machine easier to operate. The ability to minimize this distance is limited on dozers that have the ability to angle their blade because the blade must have adequate clearance to the tracks in all positions.  
         [0004]     The blade distance ratio is commonly used as an indicator of a dozers grading ability. The blade distance ratio is determined by dividing the distance from the rear track roller to the blade (RTBD) by the effective track length on ground (ETL), i.e. Blade Distance Ratio=RTBD/ETL.  
       SUMMARY OF THE INVENTION  
       [0005]     The exemplary embodiment of the invention described herein is applied to a crawler dozer with 4 independent tracks. In this configuration, the tracks are mounted such that they can move in a way that they can follow the contour of the ground. Each of the tracks pivots about a drive wheel. The blade distance ratio in this case would be best described as the (distance between the rear track pivot and the blade) divided by the (distance between the front and rear track pivots). In the case of a wheeled dozer, the latter term would be the wheel base.  
         [0006]     In order to have a uniform ground pressure for the tracks of the exemplary embodiment, the pivot to the frame is located near the fore-aft center of the track. The negative consequence of this arrangement is that the distance from the blade to the center of the front weight bearing member is greater than would be achieved with a conventional crawler.  
         [0007]     The invention improves the machine performance, i.e., the machine&#39;s ability to grade, by reducing the distance between the blade and the center of force under the front track system. This is accomplished by adding a hydraulic cylinder between the track frame and the track mounting frame which can increase the down-force on the front of the track frame. The cylinder is hydraulically connected to an accumulator and pressure regulating system so that the track can rotationally move around its mounting pivot and maintain contact with the ground.  
         [0008]     This system can be actuated by the operator from the operators station when desired. When this system is activated, the cylinder exerts a torque on the track frame that creates an increased downward force at the front of the track, and a reduced force at the rear of the track. This subsequently causes an increased ground pressure on the front of the track, and a reduced ground pressure at the rear of the track. The amount of force is approximately proportional to the hydraulic cylinder force which can be adjustably controlled by the operator, or preset by the manufacturer.  
         [0009]     An additional benefit of this system is that it enables the operator to artificially increase the downforce at the front of the track. In certain soil conditions, this can increase the tractive effort of the machine by forcing the track lug into the ground deeper than would be achieved without this feature enabled. The remainder of the track would then have a packed track to run in. This increased soil density under the track would enable the track to exert higher pull forces than would be otherwise achievable. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a side view of a work vehicle in which the invention may be used;  
         [0011]      FIG. 2  is an elevated oblique view of a rear of the vehicle illustrated in  FIG. 1 ;  
         [0012]      FIG. 3  is a schematic of a front track drive illustrated in  FIG. 1 ;  
         [0013]      FIG. 4  illustrates the track length for calculating the blade ratio without the activation of the invention; and  
         [0014]      FIG. 5  illustrates the track length for calculating the blade ration when the invention is activated. 
     
    
     DETAILED DESCRIPTION  
       [0015]      FIGS. 1 and 2  illustrate a vehicle in which the invention may be used. The particular vehicle illustrated in  FIGS. 1 and 2  is a four track articulated dozer  10  having a front portion  20  a rear portion  30 ; an articulation mechanism  40  between the front portion  20  and the rear portion  30 ; first track systems  50 ,  60 ; and second track systems  70 ,  80 . The front portion  20  includes a blade  22  and a blade mounting frame  23  as well as an operator cab  21 .  
         [0016]      FIG. 3  is a schematic of an exemplary embodiment of the invention. Included is an exemplary embodiment of the track system  50  which includes a track assembly  50 ′ and a hydraulic circuit  50 ″. The track assembly  50  is as illustrated in  FIG. 3 . A track frame  50   d  is pivotally mounted at track frame mounting pivot  50   d ′ to a mounting frame  200 . A drive wheel  50   a  is also pivotally mounted to the mounting frame  200  at drive wheel pivot  50   a ′. A first main idler  50   b  is pivotally attached to tension link  50   e  at first main idler pivot  50   b ′ and the tension link  50   e is pivotally attached to the track frame  50   d  on a first side of the track frame mounting pivot  50   d ′ at tension link pivot  50   b ″. A second main idler  50   c  is pivotally attached to the track frame  50   d  on a second side of the track frame mounting pivot  50   d ′ at second main idler pivot  50   c ′. A tensioning cylinder  57  is pivotally connected to the track frame  50   d  at tensioning cylinder pivot  57 ′ and pivotally connected to the tensioning link at cylinder link pivot  57 ″. A biasing cylinder  56  is pivotally mounted to the mounting frame  200  at biasing cylinder mounting pivot  56 ′ and pivotally mounted to the track frame  50   d  at track frame biasing pivot  56 ″.  
         [0017]     Minor idler rollers  50   g  and  50   h  are pivotally connected to minor rocker beam  50   k  at minor roller pivots  50   g ′ and  50   h ′ respectively. The minor rocker beam  50   k  is pivotally mounted to the track frame  50   d  at rocker beam mounting pivot  50   f . As illustrated in  FIG. 3 , the minor roller pivots  50   g ′ and  50   h ′ are mounted on first and second sides of rocker beam mounting pivot  50   f , respectively.  
         [0018]     A first side of a track  50   m  contacts the drive wheel  50   a , the first main idler  50   b , the second main idler  50   c , the first minor idler  50   g  and the second minor idler  50   h . A second side of the track contacts the ground for purposes of vehicle propulsion. As illustrated in  FIG. 3 , the track  50   m  assumes a triangular appearance as the first side contacts and conforms to the drive wheel  50   a  and the first and second main idlers  50   b  and  50   c  on front and rear portions of the track assembly, respectively.  
         [0019]     Controlling the biasing cylinder  56  is exemplary hydraulic circuit  50 ″ which includes: a hydraulic pump  51 ; a load sense actuating valve  52 ; a pressure reducing valve  53  in communication with the hydraulic pump  51  and fluid reservoir  59 ; a check valve  52 ′ in communication with the pressure reducing valve  53 ; an electrically adjustable pressure relief valve  54  in communication with the pressure reducing valve  53 ; a first gas charge accumulator  55  in communication with the biasing cylinder  56  as well as in communication with the adjustable pressure relief valve  54  and the pressure reducing valve  53 .  
         [0020]     The pressure relief valve  54  is adjustable. In this particular embodiment, it is adjustable from 70 bar to 140 bar. The pressure relief valve  54 , in practice, is set 10 bar above the setting of the pressure reducing valve  53 . The pressure reducing valve  53  and the pressure relief valve  54  may be adjusted from the operator&#39;s cab  21  via a switch control  53 ″ and a controller  53 ′.  
         [0021]     The biasing cylinder  56  is actuated when a signal from the controller  53 ′, prompted by a manipulation from the switch control  53 ″ activates the pump load sense valve  52  and shifts the pressure reducing valve  53  from position (1) to position (2), thus exposing the pressure relief valve  54 , the accumulator  55  and the biasing cylinder  56  to pressurized fluid from the pump  51 . The pump  51  is driven by conventional means well known in the art.  
         [0022]     The blade ratio is improved as it decreases and moves toward a value of 1.  FIG. 4  illustrates distances for blade distance ratio calculations for the vehicle of  FIG. 1  without the invention activated and  FIG. 5  illustrates distances for blade distance ratio calculations for the vehicle of  FIG. 1  after the invention is activated. As is clearly illustrated the effective track length (ETL) increases by at least a distance between the track frame pivot  50   d ″ and pivot  50   b ′ for the first main idler  50   b  when the biasing cylinder  56  is actuated. The maximum increase in distance (ΔDmax) is illustrated in  FIG. 5 . The increase in distance (ΔD) depends upon the fluid pressure applied to the biasing cylinder  56 . Such changes increase the grading ability of the dozer  10 . Activation of the invention tends to shift the weight seen by the track assembly  50 ′ toward the first main idler  50   b  the load seen by the ground is more concentrated which results in a greater amount of packing of the dirt under the track  50   m  and, consequently, greater traction.  
         [0023]     Having described the illustrated embodiment, it will become apparent that various modifications can be made without departing from the scope of the invention as defined in the accompanying claims.

Summary:
The blade ratio of an articulated work vehicle with multiple tracks is adjusted by shifting a load from the weight of the vehicle toward the front or rear of one or more of the tracks. The load may be shifted through the actuation of a hydraulic cylinder that applies a biasing load between a frame on which a track frame is mounted and a front or rear portion of the track frame.