Agricultural tractors have traditionally used hydro-mechanical draft control systems, wherein implement draft is sensed mechanically, and through appropriate linkage, a hydraulic valve is actuated to raise and lower the implement. Mechanical linkages have inherent limited flexibility, which has been further reduced by the implementation of environmentally isolated cabs.
The development of low cost, reliable microprocessors has allowed greater flexibility in the design of agricultural tractor control systems. For example, implement draft sensing need no longer be limited to top-link, lower-link or output torque monitor, but can be wheel slip, engine speed, engine load, etc.
The development reported herein involves a new concept of completely eliminating the mechanical draft sensors and instead using the engine speed to determine the draft load. The engine RPM is compared with the no load RPM expected at a given throttle setting. The draft is calculated as a function of the RPM deviation from no load.