The self-excited oscillation of a spool valve servomotor has been widely investigated by many researchers.
The author has clarified the condition of the occurrence of the oscillation which results from the load-dependent flow force acting on the spool.
In the course of recent experimental work, the author found a new important factor which influences the above condition. Namely, when the cylinder of the servomotor drives the load, the servomotor receives the reaction force which is equal in magnitude to the driving force. When the base of the servomotor is rigidly secured so that it will not move during operation, it is often caused to move slightly due to this reaction force. Consequently, the inertial force acts on the spool, having an important influence on the occurence of the self-excited oscillation.
Therefore, in this research the self-excited oscillation which is influenced by the movement of the base is clarified theoretically and experimentally.
The results show that, if the base is slightly movable, the stability of the servomotor is improved by setting the spool valve so that the spool displacement and resulting cylinder movement are in opposite directions.

View full abstract

It is necessary to have a good knowledge of the influence of the cutoff ratio on the characteristic performance of an air motor for the improvement in its performance. For this purpose, in this paper the influence of the cutoff ratio on the characteristics of the air motor was studied theoretically and experimental consideration was taken into such influence by means of a radial piston air motor under various driving conditions.
Conclusions from this study can be sumarized as follows:
(1) The theoretical analysis shows that the expansion efficiency at a constant pressure drop across the motor increases with a decrease in the cutoff ratio. However, the practical adiabatic efficiency increases little below a certain cutoff ratio.
(2) If the dearance volume is taken into account in the equation of a theoretical air consumption, the volumetric efficiency is little affected by a change in the cutoff ratio. However, if the air consumption in the clearance volume is regarded as the loss of flow, the volumetric efficiency increases with an increase in the cutoff ratio.
(3) The mechanical efficiency decreases with a decrease in the cutoff ratio.

View full abstract