STUDY OF A HYDRAULIC SERVO DRIVE WITH A JET AMPLIFIER

E. P. MIKHAEVICH, E. G. FRANK

(Presented by the Department of Mining Machines)

An effective means of automating modern machines is hydraulic power servo drives. At present, in servo hydromechanisms, spool-type amplifiers have found the widest application. However, spool-type amplifiers, along with their advantages, also have a number of known disadvantages, from which proportional-control amplifiers based on the interaction of submerged jets are free [1, 2, 3, 4]. Therefore, comprehensive studies of servo hydromechanisms with jet amplifiers contribute to the accumulation of useful information for developing methods of calculating elements of jet hydraulic automation.

In the present work, the basic diagram is given of a physical model of an open-loop hydraulic servo drive with a continuous-control jet amplifier and a rotary hydraulic motor for studying the static and dynamic characteristics of the jet amplifier and of the drive as a whole. Some static characteristics of the drive are presented. The diagram of the physical model of the drive with a two-stage hydraulic amplifier is shown in Fig. 1.

In the first stage of the amplifier, nozzle–flapper type elements are used, connected according to a differential scheme.

The second stage is based on the interaction of mutually perpendicular axisymmetric submerged turbulent jets. A rotary hydraulic motor MG153A is connected to the output of the amplifier. A load unit is mounted on the hydraulic-motor shaft, creating frictional \(M_{\mathrm{fr}}\) and inertial \(M_{\mathrm{in}}\) loads.

In the absence of a control signal, the differential control pressure \(\Delta P_y = P_{y_1} - P_{y_2} = 0\), and the jet emerging from the supply nozzle is distributed uniformly between two receiving nozzles and, consequently, the pressure drop across the hydraulic motor is \(\Delta P_m = P_1 - P_2 = 0\). Displacement of the \(x\)-flapper of the first control stage from the neutral position causes a change in the control pressures \(P_{y_1}\) and \(P_{y_2}\) (i.e., \(\Delta P_y \ne 0\)), which deflect the supply jet formed under the action of the supply pressure \(P_p\). Deflection of the supply jet causes a change in the pressures \(P_1\) and \(P_2\) at the output of the jet hydraulic amplifier (in the cavities of the actuator motor), which, in turn, cause motion of the hydraulic motor. Thus, continuous control of the hydraulic-motor speed \(\dfrac{d\varphi}{dt}\) is effected by displacement of the \(x\)-flapper of the first stage of the hydraulic amplifier.

The drive was supplied by axial-piston pumps NP-26 of adjustable delivery. The supply pressure \(P_p\) of the pump ...

was set by a GA124 safety valve and varied from 20 to 200 kg/cm². The control pressure \(P_{\mathrm{un}}\) was provided by a G52-12 overflow valve and varied in the range 10–60 kg/cm².

The drain from the GA124 and G52-12 safety valves is connected to the jet-interaction chamber in order to create in it a constant pressure \(P_{\mathrm{k}}\) by means of throttle Dr1.

The main parameters of the drive were varied over a fairly wide range. Thus, the distance \(L\) between the supply nozzle and the receiving channels, the distance \(l\) between the control nozzles, and the distance \(l_1\) between the cut of the supply nozzle and the point of jet interaction were varied continuously in the ranges \(L=0\div50\) mm, \(l=2\div40\) mm, and \(l_1=0\div20\) mm.

The diameters \(d_{\mathrm{p}}\), \(d_{\mathrm{u}}\), and \(d_{\mathrm{pr}}\) of the supply and control nozzles and of the receiving channels of the amplifier, respectively, were varied in the range 1–6 mm by simple readjustment.

For photography and visual observation of the jets, the jet-interaction chamber was made of an optically transparent material.

To study the transient regimes of the drive, a setting device (SD) was provided, making it possible to apply harmonic and step control signals to the input (displacement \(x\)) of the tracking system.

Registration of transient processes was carried out by means of an inductive displacement transducer (ID)—

Fig. 2. Dependence of the pressure \(P_{\mathrm{pr}}\) in the receiving channel on the distance \(L\) between the nozzles \(\left(P_{\mathrm{p}}=100\ \text{kg/cm}^2,\ d_{\mathrm{p}}=2.5\ \text{mm},\ P_{\mathrm{k}}=0,\ \text{AMG-10 fluid},\ T=45\text{–}50^\circ\text{C}\right)\).

Fig. 3. Force characteristics of the hydraulic amplifier with the hydraulic motor braked \(\left(P_{\mathrm{p}}=100\ \text{kg/cm}^2,\ P_{\mathrm{un}}=35\ \text{kg/cm}^2,\ d_{\mathrm{p}}=d_{\mathrm{u}}=1.5\ \text{mm},\ d_{\mathrm{pr}}=2.5\ \text{mm},\ L/d_{\mathrm{p}}=4.35,\ l/d_{\mathrm{u}}=3\right)\).

Fig. 4. External characteristics of the hydraulic mechanism (the amplifier parameters correspond to those given in Fig. 3).

displacement of the \(x\)-valve, strain-gauge pressure sensors and the torque on the motor shaft, a tachometric sensor for rotation of the hydraulic-motor shaft, and an N-700 loop oscillograph.

One of the important indicators of jet elements is the coefficient

\[ \frac{P_{\mathrm{p}}}{P_{\mathrm{pr}}} \]

of recovery of the supply pressure \(P_{\mathrm{p}}\) in the receiving channel connected with the closed cavity. The test scheme and the dependence of the pressure \(P_{\mathrm{pr}}\) in the receiving channel on the distance \(L\) between the feeding and receiving nozzles, for various values of the nozzle diameters, are presented in Fig. 2. It follows from Fig. 2 that the maximum value of the pressure \(P_{\mathrm{pr}}\) in the receiving channel reaches \(0.975 P_{\mathrm{p}}\), i.e., the minimum pressure losses in the jet converter amount to 2.5%.

Figure 3 presents the force characteristic of the hydraulic amplifier (Fig. 1) with the hydraulic motor braked, and its dependence on the pressure \(P_{\mathrm{k}}\) in the jet-interaction chamber.

The dependence of the speed of the actuating hydraulic motor on the load for various values of the control signal (external characteristics) is given in Fig. 4.

Experimental studies of the drive showed that continuous control of the hydraulic-motor speed by means of interacting turbulent jets is stable, the static characteristics are stable over time, and one of the important tasks in the study of jet elements is the synthesis of rational structures, compensating and feedback links, which make it possible to improve the characteristics of tracking hydromechanisms.

REFERENCES

1. L. A. Zalmanzon. Theory of Elements of Pneumatics. Moscow, Nauka, 1969.
2. Jet Technology. Proceedings of the Yablonna Conference. Translated from Polish, edited by L. A. Zalmanzon and I. V. Lebedev. Moscow, Mir, 1969.
3. Pneumatic Means and Control Systems. Moscow, Nauka, 1970.
4. E. G. Frank, E. P. Mikhaevich. “Experimental Stand for Investigating the Static Characteristics of a Hydraulic Tracking Drive with an Amplifier Based on the Interaction of Axisymmetric Submerged Jets.” Collection of papers of the conference Automation of Production Processes in Mechanical Engineering, Tomsk, Tomsk University Press, 1970.