• Journal of Drive and Control
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• v.11 no.4
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• pp.61-67
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• 2014

When a manual transmission equipped car stops on an incline where the nose of the car is higher than the rear, hill-start control or hill-holder could prevent the vehicle from rolling backward as the car moves forward. The easy-hill assist valve consists of a check valve and a needle type ON/OFF solenoid valve connected in parallel; it is a hydraulic actuator that can maintain brake pressure using an electrical signal from the ECU. As the EHA valve is a safety-related component of the brake system, high reliability as well as superior dynamic performance is required for it to be applied in commercial vehicles. This paper presents the design of the EHA valve as a piece of equipment that can simulate the brake actuation pressure with a pressurizing piston. Following specific test standards, the experimental results validate the implemented functions of the test equipment, proving the test stand to be effective for the performance and endurance of the EHA valve.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.11
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• pp.1483-1490
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• 2011

Electro-hydrostatic actuators(EHAs), which are usually composed of a direct motor-driven hydraulic pump and a cylinder, have been widely adopted as aircraft actuation systems because of their benefits in terms of improved efficiency, weight savings and the fact that they use a standalone power source. Since the recent trend in construction vehicles has been focus on energy savings in their hydraulic systems, EHAs are expected to be potential substitutes for conventional power transmission, since they are capable of energy recovery as well as highly efficient pump control. In this paper, the start and stop characteristics of EHAs were investigated through cracking pressure analysis of the pilot-operated check valve(PCV), which enables the cylinder to standstill against an external load with no holding effort from the hydraulic pump. A mathematical model that includes the load dynamics and the EHA's internal hydraulic circuit was derived for simulation with the MATLAB Simulink package. This model verified the PCV's opening and closing sequence, which in turn affects the EHA's start and stop characteristics.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.4
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• pp.316-322
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• 2007

The EHA(Electro-hydrostatic Actuator) reveals completely different characteristics from the conventional valve-controlled Electro-hydraulic actuators. In this paper, its mathematical model including nonlinear elements was derived to be verified by experiments. Based on this, a simulation program was developed for the EHAs consisting of an electric motor driven hydraulic pump, pipe lines and a cylinder. The influence of important design parameters such as peak motor torque and rotational inertia moment of the hydraulic pump on control performance was investigated, where the test condition was intentionally selected so that the motor torque was saturated during the transient phase. As a result, design requirements for improving the control accuracy under full speed operation conditions of the EHAs were investigated.

• Journal of the Korea Society for Simulation
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• v.23 no.2
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• pp.17-24
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• 2014

This study attempts to show an example of developing and applying thermal hydraulic simulation model for Aircraft-EHA. The overview of research procedure is as in the following. First, The unit hydraulic simulation model, which reflects physical quantity answering engineer's purpose is developed. Second, The unit hydraulic simulation model is combined, and then branched out to EHA hydraulic model. Third, a simulation model including flow thermal is developed, and then oil temperature rise time according to 'initial temperature and load' is examined. Finally, the master graph that can be used for designing EHA combined with thermal hydraulic analysis results in several cases is compiled, and suggested. AMESim, commercial software, is used through whole procedure.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.41 no.4
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• pp.291-298
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• 2013

In this paper a new hybrid-type control system is proposed which reduces the pump speed of an electro-hydraulic actuator consisting of a pressure-compensated variable displacement piston pump and a valve-controlled hydraulic cylinder, whenever the flow rate demand is low. In order to avoid interfering with the pressure regulator which also has an effect on swash plate angle, the pump speed is changed in proportion to the mean value of the speed component of position commands. Additionally a pressure switch is employed to prevent the system pressure from getting lower than a reference value. Based on computer simulation & experimental results, it is shown that the hybrid control can save the idling power up to 44% at a stand-by mode by reducing the pump speed from 1,800 rpm to 600 rpm without affecting the dynamic response of the electro-hydraulic actuator.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.3
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• pp.231-237
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• 2007

The torque ripple of the hydraulic pumps for the Electro-hydrostatic Actuators can disturb the cylinder position control under slewing speed operation condition. In principle, the periodic change of the reaction torque generated by a piston type pump is highly dependent on the waveform of its cylinder chamber pressure. In case of uni-directional pumps operating at constant speed, the transient overshoot and rising slope of the cylinder pressure can be adjusted by the precompression angle and notch shape of their valve plates. Therefore, the influence of the valve plate geometry on the torque ripple magnitude of a bent-axis type piston pump for EHA application was investigated in this study. The results showed that any improvement of the torque ripple of such a bi-directional pump can not be achieved by modifying the valve plate geometry, regardless of its operation speed.

• Journal of Drive and Control
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• v.13 no.3
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• pp.39-46
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• 2016

Flow and pressure ripple in swash plate type piston pumps is largely dependent on the design of notches(silencing grooves) in the valve plate. In uni-directional pumps, the basic design concept for notches in the valve plate could be said to be established. It is easily deduced that the design concept for notches in uni-directional pumps can not be simply applied to bi-directional pumps requested for EHA(electric hydrostatic actuators). To carry out systematic research on technological issues regarding notch applications to bi-directional piston pumps, five notch designs are devised. The effects of the notch designs on the characteristics of the pump are investigated by numerical simulations and experiments. Through this study, basic concepts about notch design for bi-directional piston pumps are suggested.

• Journal of Drive and Control
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• v.18 no.3
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• pp.8-15
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• 2021

A rear axle steering (RAS) system is attached to the rear of medium and large commercial vehicles that transport large cargo. The existing RAS systems are driven by electro-hydraulic actuator (EHA), and most commercialized EHAs consist of electric motors, hydraulic pumps, relief valves, prefill valves and cylinders. The prefill valve required for such EHAs is a type of check valve with extremely low cracking pressure that should not allow RAS to have noise or vibration, and the prefill valve prevents system negative pressure as well as unstable operation. Most papers on this topic rely on experiments to predict valve performance, and theoretically detailed modeling of valves or pipelines is performed, but it is very rare to evaluate hydraulic vibration characteristics by analysing everything from hydraulic pumps to valves comprehensively. In this study, we proposed an experimental circuit that can predict the performance of the prefill valve. The study also analysed the pressure-flow pulsation that is transmitted to the valve through the pipeline, and how the transmitted pressure-flow pulsation affects the valve vibration.