| 摘要 |
PROBLEM TO BE SOLVED: To mechanically carry out automatic plowing depth control with a high accuracy irrespective of a change in a target plowing depth. SOLUTION: This controller for lifting and lowering of a tractor is obtained by composing a regulating lever 17 of a position control valve for lifting and lowering a lifting arm so as to be brought into contact and displaced to a lifting side with a position lever 20, installing an intermediate link mechanism 40 for bringing the front end of an inner wire 36a of a sensor wire 36 for detecting the vertical shaking of a rear cover in a rotary tillage device into contact and link with the regulating lever 17, composing the intermediate link mechanism 40 so as to change and regulate the reference contact state in the intermediate link mechanism 40 with an automatic lever 30, carry out setting of the plowing depth in the automatic plowing depth control and change the ratio of manipulated variables of the regulating lever 17 relatively to the unit shaking extent of a rear cover 32 according to the change in the reference contact state of the intermediate link mechanism 40.
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