Studies on the Automatic Control of Hydrostatic Transmission Tractor (II)

Static Characteristics of Engine Output Power Constant Control System

Abstract

We report the results of experiments on the static characteristics of engine output power constant control system and discuss them in this paper. This control system consists of the closed circuit PV-MF hydrostatic transmission system and the torque constant type servo-control regulator being its control device. If pump input speed is constant, this system has such a function as keeps constantly the pump input power, namely, engine output power in spite of great and small sizes of the disturbance of torque. For further details the reader should refer to previous report (I).
A summary of the results is shown below.
1) It became evident that pump input torque had always a constant value regardless of great and small sizes of load pressure. But, it was difficult to find a certain relation between pump input torque and its speed. These results agreed approximately with the characteristics shown in design diagram. Thus, it have been proved that the pump output pressure detecting actuator acted successfully, but the pump input speed detecting one must be improved on a few points. (See. Fig. 3 (a))
2) Overall efficiency of the variable-displacement type axial-plunger pump was about 60-85% in the region of normal load, and the efficiency of the fixed-displacement type axial-plunger motor was more than 90% in the same region. Judging from these effects, it was evident that efficiency performance was affected remarkably by the displacement of pump or motor. (See. Fig. 3 (d), (e), (f) and Fig. 5 (d), (e))
3) In order to obtain quantitatively the optimum quantity for tractor operation about the control system used, we tried to represent the combination diagram of the engine governor setting and the pump stroke setting for pump output flow and motor differential pressure. As is evident from the design principle of this control system, it is shown that these combinations are the optimum setting values which give the best mechanical performances to engine and hydraulic system. This diagram is useful to simplify and speed up the tractor operations which were done by intuition and experiences up to this time. (See. Fig. 7)
4) In order to estimate effects of this control system, we compared the differences in following performances between the two cases of having the control action or not, i. e., transmission efficiency in the case of hydraulic system and power utilization rate (P. U. R) and specific fuel consumption (S. F. C) in the case of engine system. These experimental results proved that this control system was always operated under the optimum condition from the point of mechanical and economical performance, and that satisfied sufficiently the initial control purpose. (See. Fig. 9, Fig. 10 and Fig. 11)