Abstract: In an automatic draft control system for positioning a hitch, velocity feedback loop techniques are employed to control the rate of movement of the hitch. When the system is operating in an open loop position control mode, a switch mounted on a tractor fender enables an operator to manually control raising/lowering of the hitch for the purpose of attaching an implement. Hitch position is sensed and a microprocessor calculates the first derivative of the hitch position signal to determine actual hitch velocity. The actual velocity is subtracted from a desired velocity value to obtain a velocity error signal. The error signal is subjected to an integral control algorithm and the integrated value is used to energize raise or lower solenoids controlling a valve which raises or lowers the hitch. When the actual hitch velocity is equal to or greater than the desired hitch velocity, the integrated value is saved. When the next raise/lower sequence is initiated the integrator is reset to the saved value.

Abstract: A vehicle transmission system having shift lever control of synchronized couplers for selection of ranges of gears and electro-hydraulic powershift clutches for selection of a gear within the selected range is provided with controls for avoiding unexpected speeds or speed changes under certain conditions. On start-up, if the vehicle is stationary, a microprocessor automatically selects which powershift gear is effective, the selection being such that the start-up speed is as nearly uniform as possible within the limits imposed by the positions of the shift levers.

Abstract: A vehicle transmission system having shift levers mechanically linked to couplers for selection of ranges of gear speed ratios and electro-hydraulic powershift clutches for selection of a gear speed ratio within the selected range is provided with controls for avoiding unexpected speeds or speed changes under certain conditions. If the vehicle is moving at start-up as a result of a stall or accidental reset of the microprocessor, and the shift levers have not been moved since the stall or reset, the microprocessor retrieves from a nonvolatile memory an indication of the last selected powershift gear prior to the reset and uses it for the initial powershift gear selection. When an operator depresses a clutch, shifts a shift lever and then changes his mind and shifts the shift lever back to its original position before releasing the clutch above a threshold point, the microprocessor selects the powershift gear in effect at the time the clutch pedal was depressed.

Abstract: An automatic draft control for controlling the position of a tractor-mounted hitch includes a slip override circuit responsive to a wheel signal for modifying a hitch position command so that hitch draft is reduced by raising the hitch when the degree of tractor wheel slip exceeds a threshold value. The slip is determined by measuring theoretical (no-slip) ground speed with a sensor which senses the rate of rotation of the tractor rear axle, and measuring true ground speed with a radar unit mounted on one side of the tractor. Because the radar unit does not indicate the speed of the center line of the tractor as it turns, the slip signal is prevented from modifying the hitch position command if the hitch is raised since the hitch is usually raised when turning and there is no need to modify the position command with the slip signal when the hitch is raised.

Abstract: A non-volatile memory stores values defining a released position or a depressed position of a clutch pedal. A potentiometer mechanically linked to the clutch pedal produces an output signal whose value or magnitude represents the current position of the clutch pedal. When power is turned on, first and second end limit values which electrically define the depressed and released positions of the clutch pedal are read from the memory, a constant value is added to the first end limit value and subtracted from the second. Thereafter, each time the output signal is sensed for control purposes, the output signal is compared with the end limit values. If the output signal is less than the first end limit value it replaces that value in the memory and if the output signal is greater than the second end limit value it replaces that value. The sensor is thus calibrated in a manner transparent to the operator each time the system samples the sensor output signal for control purposes.