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The electro-hydrostatic actuator (EHA) has a high energy density and a compact structure so it is widely used in all/more electric aircraft. To gain energy-saving capability, the hydraulic lock can be applied in the EHA system, which can overcome the change of load after the position control is complete, reducing the motor's need to work continuously. Due to the use of a hydraulic lock in the EHA system, there is a more significant position output delay compared with the EHA system. The delay would lead to a dynamic response error. Therefore, an electro-hydrostatic actuator with a bidirectional hydraulic lock (BHL-EHA) model is established that can reflect the position output delay and it can be used to analyze its influence factors. According to the analysis, the factors affecting the delay are pump speed, external load, hydraulic lock cracking pressure, friction load, pump displacement, fluid volume of the system, and effective bulk modulus; thus, an equation that can be used to calculate the delay is proposed. At the same time, the experimental system of the BHL-EHA system is established, and the parameters of the experimental facility are completely consistent with the simulation model. Finally, a delay compensation control method is proposed, and the control time parameter t 0 is calculated based on the equation proposed above. The results of the simulation and the experiment show that the method can compensate for the delay caused by the hydraulic lock. Combined with a feedforward control, the method can dismiss the dynamic response error of 0.6 Hz sinusoidal tracking characteristics. [ABSTRACT FROM AUTHOR]

The electro-hydrostatic actuator (EHA) has a high energy density and a compact structure so it is widely used in all/more electric aircraft. To gain energy-saving capability, the hydraulic lock can be applied in the EHA system, which can overcome the change of load after the position control is complete, reducing the motor’s need to work continuously. Due to the use of a hydraulic lock in the EHA system, there is a more significant position output delay compared with the EHA system. The delay would lead to a dynamic response error. Therefore, an electro-hydrostatic actuator with a bidirectional hydraulic lock (BHL-EHA) model is established that can reflect the position output delay and it can be used to analyze its influence factors. According to the analysis, the factors affecting the delay are pump speed, external load, hydraulic lock cracking pressure, friction load, pump displacement, fluid volume of the system, and effective bulk modulus; thus, an equation that can be used to calculate the delay is proposed. At the same time, the experimental system of the BHL-EHA system is established, and the parameters of the experimental facility are completely consistent with the simulation model. Finally, a delay compensation control method is proposed, and the control time parameter t0 is calculated based on the equation proposed above. The results of the simulation and the experiment show that the method can compensate for the delay caused by the hydraulic lock. Combined with a feedforward control, the method can dismiss the dynamic response error of 0.6 Hz sinusoidal tracking characteristics.

A spool valve of aerospace hydraulic breaks down because of uneven pressure distribution between sleeve and spool, which is called as hydraulic lock. The rectangular grooves on the spool surface can effectively weaken the lateral force, thereby preventing the hydraulic lock. So the mathematical model of spool valve with rectangular grooves is established according to the Navier-Stokes equations based on the cylindrical coordinate system. To verify the effectivity of the mathematical model, the numerical simulation is compared and used to modified the mathematical model.

We propose a unique flow meter that uses a lateral flow force generated on a pressure sensing bar in a rectangular flow channel. The mathematical model, based on laminar viscous flow analysis, has been previously described and the design criterion was established from the fundamental characteristics. The test flow meter has also been investigated experimentally to clarify the torque versus flow characteristics. Although the meter performed well in terms of linearity and repeatability in the low flow rate region, the results deviated from the analytical results at high flow rates. This paper presents a theoretical analysis of the flow meter based on CFD (computational fluid dynamics). The aim is to examine the flow behavior and the pressure distribution inside the meter. CFD analysis is conducted over a range of dimensional configurations and boundary conditions. The flow versus torque characteristics are derived from pressure distribution results and compared with the analytical model. On the basis of CFD analysis, we propose a revised configuration of the flow meter, and verify its performance experimentally. [ABSTRACT FROM AUTHOR]

The purpose of this article is to contribute to a more comprehensive overview of the lateral force on tapered pistons. Numerical analyses are carried out to evaluate the lateral force on a piston; the flow rate through the clearance is also calculated. The range of parameters, namely, length-to-diameter ratio, the taper and the eccentricity, covers almost all the applications that appear in fluid power engineering. The pressure distribution obtained by difference equations is verified using an iteration convergence test. The lateral force is obtained applying Simpson’s integral to the obtained pressure. Using the dimensionless lateral forces obtained using finite mesh sizes, an evaluation of the dimensionless lateral force for an infinitely fine mesh size is made. The numerical results coincide well with experiments reported in the literature. An approximate function is shown by expressing the dimensionless force with an accuracy of about 3% for a region of the taper and the length/diameter ratio appearing frequently in practice. Four types of difference equations that are derived from the laminar flow equation are compared with respect to necessary iteration numbers and accuracy of the results. [ABSTRACT FROM PUBLISHER]