Automatic Control of Rotary Tilling Tractor (I)

Automatic Travelling Speed Control by Detecting Engine Load

Abstract

An automatic travelling speed control system of a rotary tilling tractor in response to the load change was experimented. The deflection of the engine governor was detected by a differential transformer and the travelling speed was controlled by changing the swash-plate angle of the hydrostatic transmission with a three positional electromagnetic valve and a hydraulic cylinder.
(1) The control system was not stable when the setting value of the gain constant and the dead zone were not suitable, because the control system involved time delays in the load detector, the electromagnetic valve, the hydrostatic transmission and the rotary tiller.
(2) To make the system stable, a phase lead circuit and a negative hysteresis relay were provided. The negative hysteresis relay advanced the switching off of the electromagnetic valve. The effect of the phase lead circuit and the negative hysteresis relay were examined in the field tests and in the digital simulation.
(3) When the phase lead circuit and the negative hysteresis relay were provided, the system was stable. In the field tests, when the soil hardness changed the engine speed did not change considerably and the system was good enough. However the control system was not sufficient for the rapid change of the tilling depth.