Abstract:
Accurately measuring the payload weight of dump trucks, especially off highway trucks, is important to efficient operation of most applications, such as in the mining industry. An under-loaded truck decreases efficiency in a known manner. In addition, over-loading a truck can decrease efficiency in the long run by such things as shortening truck component life due to excessive wear, such as on the drive train. The present invention seeks a more accurate payload measurement by positioning the dump body between its travel position and its dumping position. In the payload measuring position, the dump body is supported at four points, which are preferably pins equipped with shear strain gauges. After measuring the payload weight, the dump body is returned to its travel position for transport.

Description:
TECHNICAL FIELD 
   The present invention relates generally to measuring the payload weight in a dump truck, and more particularly to measuring a dump truck payload weight when the dump body is between its travel position and its dumping position. 
   BACKGROUND 
   Many existing off highway truck payload measurement systems calculate payload weight by measuring the truck&#39;s four suspension strut pressures, and use a combination of formulas and empirical data to calculate the payload weight. For instance, co-owned U.S. Pat. No. 5,182,712 to Kyrtsos et al. teaches a dynamic payload monitor with the capability of measuring the compression condition of the truck&#39;s four struts while the truck is in motion, in order to produce an even more accurate measurement than that likely possible when the truck is in a stationary position. These strut pressure strategies can typically produce payload weight accuracies on the order of plus or minus 3-5%. While strut pressures provide a fairly good representation of the truck&#39;s weight, other factors such as strut seal friction and strut rod bending can reduce the accuracy of the payload measurement system. In addition, the suspension struts support most of the weight of the truck, and therefore, the sensors must be sized large enough to measure the truck weight plus the payload weight. The required large measuring range of the sensors can also tend to reduce the accuracy of the system. Thus, there remains room for improving the accuracy of measuring the payload weight of a dump truck. 
   The present invention is directed to one or more of the problems set forth above, and to improving accuracy in dump truck payload weight measurements. 
   SUMMARY OF THE INVENTION 
   In one aspect, a dump truck includes a dump body pivotally mounted on a chassis. The dump body is moveable to a payload weight measuring position that is between a travel position and a dumping position. At least one payload weight sensor is operably positioned between the chassis and the dump body when in the payload weight measuring position. 
   In another aspect, a bed support apparatus for a dump truck includes a rocker pad moveably attached to a base. The rocker pad is moveable between a first position in which a travel contact surface is exposed to contact with a dump body, and a second position in which a payload measuring contact surface is exposed to contact with a dump body. A payload weight sensor is operably positioned between the payload weight contact surface and the base. 
   In still another aspect, a method of operating a dump truck includes a step of moving a dump body to a payload weight measuring position that is between a travel position and a dump position. After measuring the payload weight, the dump body is moved to a travel position. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a side schematic illustration of a dump truck according to one aspect of the present invention; 
       FIG. 2  is a front view of a pair of rocker pad apparatuses for the truck of  FIG. 1  as viewed along line A—A, when the dump body is in its payload weight measuring position; 
       FIG. 3  is a view similar to  FIG. 2 , except showing the dump body in its travel position; and 
       FIG. 4  is a sectioned side view of a pin and payload weight sensor according to another aspect of the present invention. 
   

   DETAILED DESCRIPTION 
   Referring now to  FIG. 1 , a dump truck  10  includes a dump body  14  pivotably attached to a chassis  12 . Although dump truck  10  is illustrated as an off highway truck, those skilled in the art will appreciate that the present invention is applicable to virtually all dump trucks. Dump body  14  pivots about a pair of pivot pins  16  when moving from its travel position, as shown, toward its dump position as shown in shadow. This movement of dump body  14  is controlled by at least one dumping actuator  20  in a conventional manner. Each of the pivot pins  16  include at least one payload weight sensor  26 , which is preferably a strain gauge appropriately positioned within the pivot pin. Nevertheless, those skilled in the art will appreciate that other types of weight sensors could be substituted, such as a load cell, without departing from the present invention. When dump body  14  is in its travel position as shown in  FIG. 1 , the weight of dump body  14 , and hence its contents, are supported primarily by the pair of payload rail support pads  18 , and to a lesser extent by a pair of bed support rocker apparatuses  22  and a pair of dump pivot pins  16  in a conventional manner. The bed support rocker apparatuses  22  serve to help maintain proper centering of dump body  14 , such as to avoid side or twisting forces between dump body  14  and chassis  12 . Preferably, all of the payload weight sensors communicate their information to an electronic control module  24  in a conventional manner. Using techniques known in the art, such as formulas and empirical data, the electronic control module  24  calculates a payload weight based upon the information provided by the payload weight sensors. 
   Referring now to  FIGS. 2 and 3 , the bed support rocker apparatuses  22  are shown with the dump body  14  in its payload weight measuring position and travel position, respectively. Each rocker pad apparatus  22  includes a rocker pad  32  rotatably mounted on a base  34  via a pivot pin  33 . Base  34  is attached to chassis  12  in a conventional manner, such as by welding. Dump body  14  is shown with its centering pads  15  resting on rocker pads  32 . A hydraulic cylinder  40 , or other suitable actuator, is attached to each rocker pad  32  in order to provide the means by which it can be rotated between the positions shown in  FIGS. 2 and 3 . When rocker pads  32  are rotated to the position shown in  FIG. 2 , dump body  14  is supported on payload weight measuring contact surface  37 , and the dump body is at a slightly lifted position corresponding to a lift height h so that the entire dump body  14  is supported at four points. The payload weight measuring position is preferably 1.5-2 degrees away from the travel position. These four points include the two dump pivot pins  16  ( FIG. 1 ) and the rocker pad pivot pins  33 . Like the dump pivot pins  16 , rocker pad pivot pins  33  preferably have a hollow interior that includes a payload weight sensor  36 , preferably in the form of a strain gauge that communicates information to the electronic control module  24  of FIG.  1 . Thus, when the dump body  14  is in the position shown in  FIG. 2 , all of the payload weight sensors  26 ,  36  are operably positioned between dump body  14  and chassis  12 .  FIG. 3  shows the dump body  14  in its travel position such that dump body centering pads  15  are in contact with travel contact surface  38  of rocker pads  32 . In the preferred embodiment, payload weight measuring contact surface  37  and travel contact surface  38  are orthogonal to one another. Nevertheless, those skilled in the art will appreciate that any suitable angular configuration could be substituted without departing from the present invention. 
   Referring now to  FIG. 4 , the internal structure of a dump pivot pin  16  according to a preferred embodiment of the present invention is illustrated. As discussed, pivot pin  16  is received in bores through both dump body  14  and chassis  12 . The pivot pins  16  preferably include a hollow passage  17  within which a payload weight sensor, preferably in the form of a strain gauge, can be mounted. The strain gauge  26  communicates information to the electronic control module via communication lines  27  in a conventional manner. Preferably, the hollow passage  17  would be sealed on its ends in order to prevent debris and/or moisture from interfering with the proper functioning of payload weight sensor  26 . 
   INDUSTRIAL APPLICABILITY 
   When in operation, dump truck  10  arrives at a loading location with dump body  14  in its travel position as shown in FIG.  1 . Nevertheless, those skilled in the art will also recognize that the dump truck  10  could arrive at the loading location with dump body  14  already in its payload weight measuring position. Before being loaded, the dump body is raised by dump actuator  20  to a position that allows rocker pads  32  to be rotated from the position shown in  FIG. 3  to the position shown in  FIG. 2  without interference with dump body  14 . After positioning the rocker pads  32  in the position shown in  FIG. 2  such that payload weight measuring contact surfaces  37  are exposed to contact with dump body centering pads  15 , the dump body  14  is lowered onto rocker pads  32  via dumping actuator  20 . In order to prevent or minimize the influence of dumping actuator  20  on the loading and weight measuring process, hydraulic pressure in the dumping actuator(s)  20  and hydraulic cylinders  40  are preferably relieved so that the dump body  14  is supported on four pins, which include two dump body pivot pins  16  and a pair of rocker pad support apparatus pins  33 . If desired, or necessary, the payload weight measuring system can then be recalibrated since the weight of an empty dump body  14  should be known with relatively high precision. The dump truck  10  is then ready for loading in a conventional manner. As the truck is loaded, a payload monitoring aspect of the payload measurement system can be used to detect the payload weight increase with each shovel of material placed into dump body  14 . Preferably, the loading continues until the payload weight measurement system indicates that the payload weight is within a range that reflects a preferred payload weight for efficient operation of dump truck  10 . 
   After the desired payload weight is confirmed, the dumping actuator  20  preferably lifts the dump body  14  off of rocker pads  32  so that they may be rotated back to their travel position as shown in FIG.  3 . Thus, after dump body  14  is lifted clear of rocker pads  32 , the hydraulic cylinders  40  are employed to rotate rocker pads  32  from the position shown in  FIG. 2  to the travel position shown in FIG.  3 . Next, the dumping actuator  20  lowers dump body  14  to its travel position as shown in  FIG. 1  with the bulk of the weight now supported by payload support pad rails  18  and to a lesser extent by bed support rocker apparatuses  22  and dump pivot pins  16 . The truck  10  is then ready for travel to a dumping location. 
   The present invention provides a more accurate way to measure the weight of a payload by using strain gauged pins to support the truck body during the loading process. The strain gauged pins at each of the four support locations measure a shear load in the pin. However, in order to prevent damage to the dump body and chassis, the dump body is moved to a position that places much of its weight on the support rails  18  as shown in FIG.  1 . During travel, the rocker pads act the same as current rocker pad designs in that they support a portion of the dump body load and prevent lateral motion of the dump body. 
   An increase in accuracy can be achieved because the load pins are generally more accurate than strut pressure sensors. In addition, the capacity of the sensors can be made closer to the payload weight being measured. Finally, strut friction and bending do not affect the payload weight measurement. These advantages allow the payload weight measurement to be generally better than plus or minus 3%, and in many instances can be better than plus or minus 1%. Preferably, the strain gauged pins are put in tight fitting, lubricated joints so that the shear load measurement accurately represents the load supported by the pin. 
   Those skilled in the art will appreciate that many alternatives could be made to the illustrated embodiment without departing from the intended scope of the present invention. For instance, strain gauged pins could be substituted to support the opposite ends of dumping actuator(s)  20 . In that alternative, the dump body would be lifted to a payload weight measuring position such that the dump body were supported only by pivot pins  16  and pins associated with dumping actuator  20 . However, in order for this alternative to work, (i.e., accurately calculate payload weight) the angular position of the dump body  14  would likely need to be known with some relatively high degree of accuracy. But this information may already be available if the truck is equipped with a conventional body position sensor. In still another embodiment of the present invention, load cells could be substituted in place of strained gauged pins, especially in the area of rocker pad support apparatuses  22 . In addition, instead of rocker pads  32  being rotatable between their positions, the present invention also contemplates transitional movement to expose a payload weight measuring contact surface  37  to contact with dump body centering pads  15 . Thus, in all versions of the invention, the dump body  14  is placed in a payload weight measuring position that is between its travel position and its dumping position in order to perform the payload weight measuring function. In addition, the potential detrimental effects of vibrations and other jarrings that can occur when the dump truck  10  is in motion can be substantially relieved by the present invention by relieving stress on the payload weight sensors when the dump body is in its travel position. Those skilled in the art will appreciate that the present invention allows truck  10  to be operated measurably more efficient than trucks with payload weight measuring systems of the prior art. 
   It should be understood that the above description is intended for illustrative purposes only, and is not intended to limit the scope of the present invention in any way. Although the present invention has been illustrated in the context of an off highway dump truck, those skilled in the art will appreciate that the principals of the present invention are also applicable to virtually any dump truck, including those that do not support the dump body on rail pads when in its travel position. Thus, those skilled in the art will appreciate that other aspects, objects, and advantages of the invention can be obtained from a study of the drawings, the disclosure and the appended claims.