Studies on the Steering Characteristics of Tractor (Part II)

Frequency Response

Abstract

The frequency responses of the travelling tractor, with continuous steering control, were obtained from the experiments by means of the pulse method. From above results, the dynamic characteristics of the controllability and stability were discussed on the tractor.
(1) A tendency on the frequency responses relating between the course and the front wheel, is little recognized under any experimental conditions of the travel speeds and the distributions of the weight.
Therefore, within the extent of those experimental conditions, it seems that the responses of the tractor itself are not affected by the characteristics at high speed, and they depend on the characteristics at low speed.
(2) The frequency responses of the steering apparatus (the steering angle and the front wheel angle), relating directly with the control of the operators, show little differences of their characteristics wnder any experimental condition. Therefore, their transfer functions can be described approximately with the dead time element and the proportional constant, which is equivalent to the reduction gear ratio of the steering gear box.
(3) On the total characteristics of the frequency response, the gains decrease according to the increase of the frequency of the course, but they show some fluctuations from zero-db line in each test run. On the other hand, the phases show the lead and lag characteristics on the same conditions. It does not seen that the frequency responses have ang steady tendency under the various experimental conditions in this test.
(4) From above results, it was found that the responses of the operator-tractor control system mainly depend on the response characteristics of the operator. And the feedback control model of this system was composed with the first and secondary estimating operations.