Patent Publication Number: US-7588088-B2

Title: Motor grader and control system therefore

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not applicable. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to a motor grader and a control system for a motor grader of the type in which the vertical position of the grader blade is controlled by a pair of hydraulic cylinders. More particularly, the present invention relates to such a motor grader and control system in which the extension or retraction of one hydraulic cylinder of the pair follows that of the other hydraulic cylinder when vertical movement of the blade is to be effected, thereby maintaining the cross slope angle. 
     Motor graders are used to alter the contours of construction sites and road beds. Motor graders typically include a work implement, such as a surface-altering blade, that is movably connected to a frame of the grader by a structure including a pair of independently controlled hydraulic cylinders. The hydraulic cylinders are mounted on either side of the machine frame of the motor grader. The hydraulic cylinders are operated independently, and can be extended or retracted to lower or raise the respective ends of the blade relative to the corresponding sides of the machine frame. The blade height may be controlled manually or automatically. 
     In the manual mode, the operator controls the vertical position of one or both ends of the blade through a pair of control levers mounted in the cab of the motor grader. Each control lever modulates a corresponding control valve that is mechanically linked or electrically linked to the control lever. The manual control valves are connected between an hydraulic fluid supply and the hydraulic cylinders. The operator actuates the manual control valves to achieve the desired elevational position of the blade at one or both ends of the blade. In one variation of manual control, an inclinometer mounted for movement with the blade, provides an inclinometer output indicating the inclination of the blade along its length. The operator sets the desired inclination in the control system. The control system compares the measured inclination with the desired inclination and controls one control valve to extend or retract its associated cylinder at the same time that other cylinder is extended or retracted. This is accomplished while maintaining the slope of the blade at a desired inclination. 
     In the automatic mode, raising and lowering the blade by retracting and extending the cylinders is controlled based on the difference between desired blade height and measured blade height. The blade height may be measured in any of a number of ways, including the use of GPS-based and laser-based systems. The height of each end of the blade may be measured in this mode of operation. Alternatively, the height of one end of the blade may be measured, and the hydraulic cylinder at that end of the blade operated, based on the difference between the measured and desired height. The hydraulic cylinder at the other end of the blade is actuated based on the difference between the desired and measured inclination of the blade along its length. An inclinometer on or mechanically linked to the blade provides the measurement of blade inclination in this mode, as well. 
     Inclinometers are typically mechanically or electrically damped to reduce the rapid fluctuations and signal noise in the output that would otherwise result from vibration in the mechanical systems. However, damping produces a time delay in an inclinometer output in a motor grader system that degrades the operation of the system when a change in the elevation of the blade is to be effected. Because the hydraulic cylinder that is controlled manually or automatically is extended or retracted quickly in such a situation, the inherent time delay in the inclinometer results in one end of the blade being lowered or raised by a significant amount before the inclinometer provides an output indicating a change in inclination. This, in turn, results in an erroneous cross slope cut during those times when elevational change is effected. 
     It is seen, therefore, that there is a need for a motor grader, and control system for a motor grader, capable of changing the vertical blade position without introducing errors in the cross slope orientation of the motor grader blade. 
     SUMMARY OF THE INVENTION 
     This need is met by a motor grader and a control system for the motor grader in which the manner of controlling the blade position is different when the blade is moved upward or downward than when the blade is maintained at a desired height and inclination. The motor grader has a blade for grading a surface, and first and second hydraulic cylinders for raising and lowering the blade adjacent its first and second ends. First and second hydraulic valves control the flow of hydraulic fluid to the first and second hydraulic cylinders, respectively. An inclinometer is mounted for movement with the blade to provide an inclinometer output indicating the inclination of the blade along its length with respect to horizontal. The control system includes a first hydraulic cylinder position sensor for determining the extended position of the first hydraulic cylinder. The control system further includes a control that is responsive to a control input specifying the desired height and cross slope of the blade, to the hydraulic cylinder position sensor, and to the inclinometer output. The control provides valve control signals to the first and second hydraulic valves. The control provides a first valve control signal to the first hydraulic valve in dependence upon a desired height specified by the control input, and the control provides a second valve control signal to the second hydraulic valve in dependence upon the inclinometer output and upon the cross slope specified by the control input. However, when the blade is to be moved upward or downward, the control provides the second valve control signal to the second hydraulic valve in dependence upon the hydraulic cylinder position sensor such that the second hydraulic cylinder extends and retracts with the first hydraulic cylinder in a way that maintains the cross slope angle of the blade. When the second hydraulic cylinder is controlled in a closed loop manner, the control provides the second valve control signal to said second hydraulic valve in dependence upon the first and the second hydraulic cylinder position sensors. 
     The control provides the second valve control signal to the second hydraulic valve in dependence upon the hydraulic cylinder position sensor when the difference between the desired height and the measured height of the blade exceeds a predetermined threshold level. The control system further includes a manual control mechanism to permit the operator to control the control input manually, specifying the desired height and cross slope of the blade. The control system further includes an automated system that provides control signals to the valves in dependence upon the location of the motor grader. 
     A method of controlling a motor grader of this type comprises the steps of determining the inclination of the blade, raising or lowering the first end of the blade with a first hydraulic cylinder in response to a control input applied to a controller, and raising or lowering the second end of the blade. When the blade is to be maintained at a desired height, the inclination of the blade is monitored and the second end of the blade is raised or lowered with the second hydraulic cylinder so that the measured inclination of the blade remains constant. When the blade is to be moved upward or downward, however, the position of the first hydraulic cylinder is monitored and the second end of the blade is raised or lowered with the second hydraulic cylinder such that the second hydraulic cylinder moves with the movement of the first hydraulic cylinder. The second hydraulic cylinder may be controlled in either an open loop or a closed loop fashion. 
     The method further includes the step of monitoring the position of the first hydraulic cylinder with a sensor that monitors extension and retraction of the cylinder. The method further includes the step of monitoring the position of the second hydraulic cylinder with a sensor that monitors extension and retraction of the cylinder. The method may include the step of providing a control input to the control from a manually actuated control device. Alternatively, the method may include the step of providing a control input to the control from an automated system. The step of providing a control input to the control from an automated system may include the steps of projecting a reference plane of laser light, and a receiving the plane of laser light with a receiver, carried on the motor grader. The step of providing a control input to the control from an automated system may include the step of determining the position of the motor grader and determining the desired height of the first end of the blade and the desired inclination of the blade at the position of the motor grader. 
     It is an object of the present invention to provide a motor grader and a control for a motor grader that is capable of raising and lowering the grader blade with desired precision. Other objects and advantages of the invention will be apparent from the following description, the accompanying drawings, and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a perspective view of a motor grader, including a control system, constructed according to the present invention; 
         FIG. 2  is a diagram showing a first embodiment of a control system for a motor grader, constructed according to the present invention; and 
         FIG. 3  is a diagram showing a second embodiment of a control system for a motor grader, constructed according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Reference is made to  FIGS. 1 and 2  of the drawings which illustrate the invention. The motor grader  10  includes a control system  12 , shown in  FIG. 2 , for controlling the height of conventional grader blade  14 . Blade  14  is part of a blade sub-assembly, indicated generally at  16 , that is movably mounted to a frame  18  of the motor grader  10  through first and second individually controllable hydraulic motors or lift cylinders  20  and  21  that are connected between the machine frame  18  and the blade sub-assembly  16 . The blade sub-assembly  16  includes a circle and circle draw bar, indicated generally at  22 , and a grader blade  14  mounted to the circle. A selectively controllable circle drive (not shown) is mounted to the circle draw bar for rotating the circle and the blade about a generally vertical axis in a known manner. While the blade control system  12  will be described in detail below as applied to the motor grader of  FIG. 1 , it will be appreciated by those skilled in the art that other machines, such as bulldozers, compactors, pavers, profilers, scrapers and the like, equipped with suitable surface altering implements, are to be considered controllable by the control system, and are contemplated within the scope of the present invention. 
     With reference to  FIG. 2 , the control system  12  controls the orientation of the grader blade  14  of motor grader  10 . During operation of the motor grader  10 , the grade and cross-slope positions of blade  14  may be set and adjusted by manual or automatic control of the extension and retraction of the hydraulic cylinders  20  and  21  which are connected to the blade sub-assembly  16 . The pair of hydraulic lift cylinders  20  and  21  may be retracted and extended to raise and lower the corresponding ends of the blade  14  relative to the frame  18 . 
     In the manual control mode, the operator controls the vertical position of one or both ends of the blade  14  through a pair of manually actuatable control levers  30  and  31 , located in cab  32  of the motor grader  10 . Manually actuatable control lever  30  is connected to a first valve  32  including a manually actuatable control valve  34  unit and an electrically actuatable control valve  36 . Manually actuatable control lever  31  is connected to a second valve  33  including a manually actuatable control valve  35  and electrically actuatable control valve  37 . The control valves  34 ,  35 ,  36  and  37  are each connected between a hydraulic fluid supply (not shown), and a corresponding respective one of the hydraulic lift cylinders  20  and  21 . Movement of control levers  30  and  31  allows hydraulic fluid to flow under pressure through the manual control valves  34  and  35  to actuate the hydraulic lift cylinders  20  and  21 , extending or retracting the cylinders, depending upon the direction in which the control levers are moved. 
     Electrically actuatable or automatic control valves  36  and  37  are each connected between the hydraulic fluid supply (not shown) and a respective one of the hydraulic lift cylinders  20  and  21  to control extension and retraction of the corresponding hydraulic lift cylinders  20  and  21  in response to signals on lines  50  and  52 . The automatic control valves  36  and  37  are electrically coupled to the controller  28 . Controller  28  provides command signals to adjust the elevational position of corresponding blade ends through actuation of respective hydraulic lift cylinders  20  and  21 . The automatic control valves  36  and  37  are connected in parallel with the manual control valves  34  and  35 , respectively, and are operable independently from the manual control valves  34  and  35 , as described below. 
     The control system further includes a first hydraulic cylinder position sensor  40  for determining the extended position of the first hydraulic cylinder  20  and providing this information to the controller  28 . The sensor may be any of a number of known sensors that are suitable for this purpose. The controller  28  is responsive to a control input  45  that specifies the desired height and cross slope of the blade  14 . The controller  28  is responsive to control input  45  specifying the desired height, to the hydraulic cylinder position sensor  40 , and to the inclinometer  48 , for providing valve control signals to the first and second hydraulic valves  36  and  37 . In one automatic mode, the controller  28  provides a first valve control signal on line  50  to the first hydraulic valve  36  in dependence upon desired height specified by the control input  45 , and the control  28  provides a second valve control signal on line  52  to the second hydraulic valve  37  in dependence upon the inclinometer output on line  60  and upon the cross slope specified by the control input  45 . 
     A difficulty encountered with this arrangement occurs when the control input on line  50  calls for movement of cylinder  20 , or when the valve  36  is actuated in such a way as to call for movement of cylinder  20 . If the inclinometer output were to be used to determine the control signal on line  52 , no corresponding change in the extension or retraction of the cylinder  21  would be effected quickly, resulting in the blade  14  being inaccurately oriented. The present invention eliminates this problem by using the hydraulic cylinder position sensor  40 . During times when the blade  14  is to be moved upward or downward, the control  28  provides the second valve control signal  52  to the second hydraulic valve  37  in dependence upon the hydraulic cylinder position sensor  40  which determines the extended position of the first hydraulic cylinder  20 , such that the second hydraulic cylinder  21  extends and retracts in a manner corresponding to the extension and retraction of the first hydraulic cylinder  20 . The amount of extension or retraction of the hydraulic cylinder is a function of the geometry of the cylinders and blade support components and linkages, but is effected in such a way as to keep the cross slope angle cut by the blade  14  constant. It will be appreciated that this will eliminate the inaccuracies that have resulted from inclinometer damping and the resulting signal delay. 
     It will be appreciated that it may be desired that the second cylinder  21  be controlled in a closed loop manner, rather than being driven open loop. A control system using such closed loop control is shown in  FIG. 3 . In  FIG. 3 , elements which correspond to those shown in  FIG. 2  are designated by the same reference numerals. In the system of  FIG. 3 , the inaccuracies that might result from actuating valve  37  in an open loop drive are eliminated by the addition of hydraulic cylinder position sensor  62  to the hydraulic cylinder  21 , providing an indication to the controller  28  of the amount of extension of cylinder  21 . This permits closed loop control of cylinder  21  so that extension and retraction are measured, and are caused to track precisely the desired extension and retraction. 
     With reference to  FIG. 3 , the control system  12  controls the orientation of the grader blade  14  of motor grader  10 . During operation of the motor grader  10 , the grade and cross-slope positions of blade  14  may be controlled by manual or automatic extension and retraction of the hydraulic lift cylinders  20  and  21  connected to the blade sub-assembly  16 . The pair of hydraulic lift cylinders  20  and  21  may be retracted and extended to raise and lower the corresponding sides of the blade  14  relative to the frame  18 . 
     In the manual control mode, the operator can control the vertical position of one or both ends of the blade  14  through the pair of manually actuatable control levers  30  and  31 , which are connected to valves  34  and  35 , respectively. The automatic control valves  36  and  37  are electrically coupled to the controller  28 . Controller  28  provides command signals to adjust the elevational position of a corresponding blade side through actuation of a respective hydraulic lift cylinder  20  and  21 . 
     As with the previous embodiment, the control system includes a hydraulic cylinder position sensor  40  for determining the extended position of the first hydraulic cylinder  21  and providing this information to the controller  28 . The controller  28  is responsive to a control input  45  that specifies the desired height and cross slope of the blade  14 . The control  28  is responsive to control input  45  specifying the desired height, to the hydraulic cylinder position sensor  40 , and to the inclinometer  48 , for providing valve control signals to the first and second hydraulic valves  36  and  37 . In one automatic mode of operation, during periods when the grader blade  14  is to be maintained a constant height and inclination, the control  28  provides a first valve control signal on line  50  to the first hydraulic valve  36  in dependence upon desired height specified by the control input  45 , and the control  28  provides a second valve control signal on line  52  to the second hydraulic valve  37  in dependence upon the inclinometer output on line  60  and upon the cross slope specified by the control input  45 . 
     When the valve  34  or the valve  36  is actuated to call for movement of cylinder  20 , the inclinometer output is not used to determine the control signal on line  52 . Rather, the control  28  provides the second valve control signal  52  to the second hydraulic valve  37  in dependence upon the hydraulic cylinder position sensor  40  which determines the extended position of the first hydraulic cylinder  20  and in dependence upon the hydraulic cylinder position sensor  62  and the geometry of the cylinders  20  and  21  and cylinder linkage, such that the second hydraulic cylinder  21  extends and retracts with the first hydraulic cylinder  20  in a manner that keeps the cross slope cut of the blade  14  at a constant angle. It will be appreciated that this will eliminate the inaccuracies that might have resulted from the valve  37  being driven in an open loop fashion. 
     The control system includes an automated system for controlling the control input to provide valve control signals to the valves in dependence upon the location of the motor grader, which may include a laser or GPS based blade position sensor  64 . The system determines the x and y position of the motor grader blade as the motor grader moves across the construction site or along the road bed. The vertical position of the blade is then determined by either GPS or laser measurement and compared with the desired vertical position. The blade is then raised or lowered to bring this difference to null and the blade is tilted to the desired position by relative movement of the cylinders  20  and  21  and measurement of the inclination of blade  14  with inclinometer  48  with respect to horizontal. When the blade is to be raised or lowered, the cylinder  21  is driven in dependence upon the movement of the cylinder  20  without reference to the inclinometer output until a new steady state operating position is achieved. At this point the output of the inclinometer  48  is again to control the extension of cylinder  21 . 
     Other aspects, objects and advantages of the present invention can be obtained from a study of the drawings, the disclosure and the appended claims.