Abstract
To find the steering characteristics of 4 wheel tractor on the slope field, some tests were carried out on the idle running locus of each wheel under the condition of constant steering angle of front wheel.
The test results are summarized as follows:
A tractor aiming to travel along the contour line with constant steering angle δ must have an upward deflecting angle of the center line of tractor body α against the contour line.
The direction of the deflecting angle of tractor is different from the running direction of the tractor, and the different angle of them γ increse with the increasing of angle of the land inclination. Hence, difference γ represents (δ+β+toe in). The curvature K and the locus are decided by γ.
The skid angle β increases with the increasing of the angle of land inclination, that is, the skid is proportional to the downward tangential component of the tractor weight. The increasing rate of the skid angle of the front wheel is larger than that of the rear wheel. Substituting γ into eq. (9), (10), (15) and (16), the shapes of locus and the curvature are decided. And there is a steering angle at which the curvature becomes 0, that is, A is 0 on the eq. (17) “y=Ax2+Bx”, and then tractor will travel downward from the contour line, because of B<0. At the other steering angles, the travelling locus of tractor will show parabolic curve given by eq. (17). Hence, in order to operate the tractor along the contour line on the slope field, the steering angle of front wheel should be adjusted at all times.
