Patent ID: 7588088

Claim:
A control system for a motor grader of the type having a blade for grading a surface, said motor grader further having first and second hydraulic cylinders for raising and lowering said blade adjacent first and second ends thereof, first and second hydraulic valves for controlling the flow of hydraulic fluid to said first and second hydraulic cylinders, respectively, and an inclinometer mounted for movement with said blade to provide an inclinometer output indicating the inclination with respect to horizontal of said blade along its length, comprising: a first hydraulic cylinder position sensor for determining the extended position of said first hydraulic cylinder, and a control, responsive to a control input specifying the desired height and cross slope of the blade, to said hydraulic cylinder position sensor, and to said inclinometer output, for providing valve control signals to said first and second hydraulic valves, wherein said control provides a first valve control signal to said first hydraulic valve in dependence upon said desired height specified by said control input, and said control provides a second valve control signal to said second hydraulic valve in dependence upon said inclinometer output and upon the cross slope specified by said control input, and wherein, during times when said blade is to be moved upward or downward, and said first hydraulic cylinder extended or retracted, said control provides said second valve control signal to said second hydraulic valve in dependence upon said first hydraulic cylinder position sensor which determines the extended position of said first hydraulic cylinder, such that said second hydraulic cylinder extends and retracts with said first hydraulic cylinder.