It is usual that fuel system of an aero-engine operates within a wide range of temperatures. As a result, this can have effect on both the characteristics and precision of fuel metering unit (FMU), even on the performance and safety of the whole engine. This paper provides theoretical analysis of the effect that fluctuation of fuel temperature has on the controllability of FMU and clarifies the drawbacks of the pure mathematical models considering fuel temperature variation for FMU. Taking the electrohydraulic servovalve-controlled FMU as the numerical study, simulation in AMESim is carried out by thermal hydraulic model under the temperatures ranged from −10 to 60 °C to confirm the effectiveness and precision of the model on the basis of steady-state and dynamic characteristics of FMU. Meanwhile, the FMU testing workbench with temperature adjustment device employing the fuel cooler and heater is established to conduct an experiment of the fuel temperature characteristics. Results show that the experiment matches well with the simulation with a relative error no more than 5% and that 0–50 °C fuel temperature variation produces up to 5.2% decrease in fuel rate. In addition, step response increases with the fuel temperature. Fuel temperature has no virtual impact on the steady-state and dynamic characteristics of FMU under the testing condition in this paper, implying that FMU can operate normally in the given temperature range.

When modeling an aeroengine control system, effects of fuel metering unit are neglected or oversimplified, which most probably leads to unreliable simulation or experimental results. In order to well understand influences of fuel metering unit on performance of an aeroengine and to enrich the component-level model of a turboshaft aeroengine, a stepping motor controlled fuel metering unit is examined by combining process-based modeling and object-oriented modeling and is employed in the component-level engine model. Performances of the engine with and without the fuel metering unit are compared by simulation. The component-level engine model with the fuel metering unit characteristics considered meets the simulation requirements on the steady precision and can describe dynamics of the engine more precisely. A semi-physical experimental verification is implemented to confirm the influence of the fuel metering unit. The results show that simulation using the component-level engine model with the fuel metering unit sub-model is in accordance with the experiment, and that comparing to the engine model without fuel metering unit, the model with a fuel metering unit can extend the performance parameter response dozens of milliseconds.

A direct drive servovalve has some inherent benefits over its conventional counterparts, but also has better reliability and output power. However, due to the rigid connection between the spool and the motor, which takes the place of interstage drive-by fluid, the spool oscillation is a long-standing unsolved problem. In order to study the oscillation mechanism and the influencing factors, a double-circuit direct drive servovalve was numerically simulated. An oil return valve cavity was concentrated on as the main flow domain and was used to analyze the fluid flow characteristics. Local cavitation fraction and surface average cavitation fraction were defined to evaluate the cavitation situation. The periodic growth process of bubbles in the valve cavity was obtained. The numerical results show that bubbles in the oil return valve cavity changes, although the occurrence, evolution, and collapse stages were certain. The intensity of pressure pulsation caused by bubble variation is highly related to the bubbles causing the cavitation, which suggests a workable way to inhibit the spool oscillation.

A compact and flexible hydraulic double-cylinder actuation scheme is proposed for use in applications, especially where power density is extremely demanding. In view of flexible amounting requirements, long and thin hoses were utilized to connect two cylinders. Affecting the actuation preciseness, volume variation of the hoses caused by pressurized oil and bubbles was the main problem the system encountered. In this study, an active disturbance rejection control (ADRC) strategy was adopted for the improvement of displacement control performance under uncertain external load. After the experimental verification of the necessity of a hose model for the system, a centralized-parameter hose model was constructed where the coefficients are determined on the basis of the experimental data. Additionally, the system and the controller proposed were mathematically modeled. Simulation results shows that the system using ADRC exhibited higher displacement accuracy and better dynamic performance than that using PID (Proportion-Integral-Derivative) or fuzzy PID. ADRC has a stronger disturbance rejection ability. ADRC is an effective solution to nonlinear control of systems with uncertain parameters or various loads.

For compact and efficient actuation, miniature hydraulic system has overwhelming superiority in power to weight ratio. However it always involves nonlinear interferences like variable hose volume or oil bulk modulus, which greatly restricts control performance for the actuation. In this paper, a miniature hydraulic volume-controlled actuation system is introduced and the problem of precise displacement control of the system in presence of variable hose volume caused by uncertain external load is investigated. A RBF-DOB(Radical Basis Function-Disturbance Observer) hybrid control strategy based on back-stepping theory is proposed. The system as well as the controller is mathematically modeled and simulation to demonstrate the validity of the RBF-DOB. Comparison to PID(Proportion-Integral-Differential) and SMC methods indicates that, the system using RBF-DOB has highest displacement precision and best dynamic performance. SMC(Sliding Model Control) is inclined to exhibit the best robustness but inferior jitter in control command output. As far as anti-disturbance capacity is concerned, RBF-DOB control strategy falls between other two counterparts. RBF-DOB hybrid control strategy can substantially solve the problems of nonlinear interferences resulted from uncertain system parameters and different load states in miniature hydraulic actuation systems.