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

In this report, pressure losses based on pipe arrangement of the hydraulic circuit used were computed using the two equations, i. e., the one is Weisbach's epuation which was applied in the field of hydraulics since a long time ago, and the other is Ito's equation. As to the latter an equation has been made and its achievements have been highly rated. From these calculation results the outlines of pressure loss were comprehended quantitatively. Moreover, these two old and new methods were compared and their adaptability to the hydraulic circuit were discussed.<br>The summary of results is as follows;<br>1. Constant loss elements, such as the low pressure line filter and the oil cooler were important in the hydraulic circuit. Therefore, extreme care must be taken to the selection of it.<br>2. As to the loss elements related to flow rate in a pipe, the more the load pressure increased, the more the pressure loss decreased, because the flow rate became smaller according to the control principle of this system. Judging from the aspects of presssure loss, it was evident from these results that our control method was desirable.<br>3. Concerning the relation between pump input speed and pressure loss, the loss tended to increase in proportion to the flow rate as the pump speed became higher. Especially, the rate of increase in low pressure range became larger. Therefore, such a countermeasure as to make the pump input speed smaller at the light operating load must be prepared.<br>4. Flow in a pipe was almost laminar flow except for a few combinations of high speed and light load in the high and low pressure pipe line. It was evident from these results that the design and layout of pipe line was proper.<br>5. As described in the paragraph 2. flow rate decreased inversely to the load pressure. Therefore, Reynolds number generally became smaller as the load pressure became larger. Consequently, comparing Weisbach's equation with Ito's one, there was no remarkable difference at the heavy load. From the facts described above, we may conclude that a rigorous treatment in the field of fluidmechanics is unnecessary in the case of this control system.<br>6. The calculation results of input shaft horsepower of the pump also agreed very well with the experimental one of the engine system which had been described in the previous report. Therefore, it was proved that the calculated values of pressure loss were quantitatively in the right range.<br>Considering above results on the basis of the equations to be used in this paper, we can generally make the following statement; the pressure loss in this circuit was smaller contrary to our initial estimates. This is based on the reason why we could design an ideal layout on account of the bench test But, in the case of mounting on farm tractor, we shall naturally encounter the space restrictions. Therefore, it seems that actual pressure loss becomes larger.