Automatic position control apparatus for ground working vehicle

An automatic position control apparatus for a ground working implement attached to a working vehicle vertically oscillatable by hydraulic means, the control apparatus being adapted to automatically control position of the working implement so that deviation of an actual draft value of the ground working implement from a preset optimum draft value is maintained within a permissible range, said control apparatus comprising:

• a draft setting unit for presetting said optimum draft value;
• a draft detector for detecting said actual draft value;
• subtracting means for calculating the deviation of said actual draft value from said optimum draft value;
• a sensitivity setting unit for setting a maximum permissible value and a minimum permissible value of said permissible range;
• comparing means for comparing said deviation with said maximum permissible value and minimum permissible value and for transmitting a lifting control signal to cause said hydraulic means to lift said working implement when said deviation is greater than said maximum permissible value and to transmit a lowering control signal to cause said hydraulic means to lower said working implement when said deviation is smaller than said minimum permissible value;
• a detector for detecting, when said deviation is greater than said maximum permissible value, whether or not said deviation is decreasing;
• and
• a lift preventing circuit responsive to detections by said detector for stopping said lifting control signal when said deviation is greater than said maximum permissible value and is at least decreasing;
• whereby said ground working implement is lifted only when said deviation is greater than said maximum permissible value of the permissible range and is increasing or remaining constant.