• Journal of the Korean Society for Precision Engineering
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• v.27 no.5
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• pp.27-35
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• 2010

A loader used for uploading materials into truck is a kind of construction equipment. Mainly, a wheel loader is applied to construction work. Recently, an automatic transmission for the wheel loader is used to help drivers get the repetitive works done comfortably. It is composed of geartrain, clutch pack, hydraulic control system and TCU. Especially, a high-performance proportional control valve and its control algorithm is demanded to achieve the shift quality during a change of speed. In this paper, the commercial package program was used in order to justify model of the proportional control valve and simulate it. Steady-state and dynamic characteristics of PCV were analyzed to classify attractive forces and hydraulic control characteristics. This model also was verified the validity compared to the experimental result. Using the developed model, performances of PCV were predicted as studying design parameters.

• Journal of Biosystems Engineering
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• v.27 no.6
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• pp.521-528
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• 2002

Rotary and plow implements are mainly utilized for the tillage operation in Korea, and a implement control system for agricultural tractors was designed and fabricated to improve the working accuracy and efficiency. The control system was composed of three units: 1) sensors fur detection of angle of liftarm, draft force, engine rpm, tillage depth and so on, 2) a controller, and 3) hydraulic circuits, which included solenoid valves and so on, for operation of three point linkage and implements. The control system can control the speed(high and low speed) of implements by adjusting input flow rates of the hydraulic cylinder which was controled by two speed valve, which was composed of a solenoid valve and a orifice. Indoor experiments were conducted to evaluate response characteristics of the designed implement control system under experimental conditions of various engine nm, two kinds of input flow rates of the cylinder and some input frequency. The results of experiments showed the response characteristics sufficient to use as the implement control system fur agricultural tractors.

• Journal of Drive and Control
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• v.14 no.1
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• pp.14-22
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• 2017

Flow force is the additional unbalanced force acting on the valve spool by fluid flow, excluding the static pressure force that is offset on the spool land wall at the same magnitude. When designing the valve spool, it is assumed that the same average value of static pressure is applied to the inlet and outlet spool land wall in one chamber. However, the high velocity of the fluid flow by the inlet or outlet metering orifice creates unbalanced pressure distribution and generates additional force in the opposite direction to that of the solenoid attraction force. This flow force has a negative effect on the control performance of the EPPR valve, which needs to develop uniform output pressure along the entire spool control range. In this study, we developed a 3D model of the EPPR valve and conducted flow force characteristic analysis using CFD S/W (ANSYS FLUENT). The alleviated flow force model was derived by adjusting the design parameters of the spool notch.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.04a
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• pp.213-217
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• 1997

The semi-active recoil system provides automatic hydraulic pressure and recoil length by an exteral impulse compared with the conventional recoil system. We developed the proto type of recoil system and validated the performance through simulation and experiment. The main issue of the system is how to adjust pressure and length simultaneously. The system consists of external pressure control valve and flow control valve outside of cylinder. The pressure control valve control the cylinder pressure and recoil length. The controlled system enhances the control performance.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.3
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• pp.485-501
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• 1997

Pressure control is possible driving a simple ON/OFF 3-way valve of hydraulic servo system by pulse width modulation signal. But the pressure varies according to the duty ratio and carrier frequency and repeated on-off action induces pressure fluctuation. So equations for mean pressure and ripple amplitude are theoretically derived as a function of on/off time, the system parameters which decide the pressure characteristics are arranged and they are verified by experimental study. As the result selection criteria for the major design parameters are established and the basic strategy to suppress the unnecessary fluctuation can be provided for a hydraulic pressure control system using these type of valves.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.10a
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• pp.569-572
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• 1995

In this study, a hydraulic modulator of solenoid-flow type ABS, the master sylinder, and the wheel cylinder are modeled and simulated for increasing pressure characteristics of the brake. Response can be predicted by external force of the the master sylinder and pulses to the solenoid valve as input. For a demonstration of simulation result, experiment is done under the same condition as simulation condition after experimental apparatus of 1/4 car model is constructed. When factors of flow control valve are changed, the effect of each factor to response, how to improve response, and the most critical factors are considered from simulated result of time constant.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.04a
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• pp.107-111
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• 1997

Pressure control is possible by pulse width modulation signal driving a simple ON/OFF 2-way valve of hydraulic servo system. But it indices pressure fluctuation due to repeated on-off action and the pressure varies according to the duty ratio and carrier frequency. So mean pressure and ripple amplitude are arranged by experimental study as the driving signal change which decides the pressure characteristics. As the result selection criteria of the major design parameters may be established and the basic strategy to suppress the unnecessary flucturion may be provided for a hydraulic pressure control system.

• Journal of Institute of Control, Robotics and Systems
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• v.7 no.4
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• pp.288-294
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• 2001

In this study, a new PWM method considering the actuation delay of high speed solenoid valves is proposed to improve the response characteristics of electro hydraulic servo systems controlled by high speed solenoid valves. In addition, the decision method for the system gain, the basic period of PWM, and the sampling time is proposed, Since the conventional system controlled by high speed solenoid valves is too slow to apply this method, a high speed driving circuit(Quick-Drive) which enables rapid switching of the high speed solenoid valve at a high speed sampling mode is applied to realize this method. The experimental result shows that it is possible to achieve precision and quiet control without occurrence of limit cycle and wide range dead band.

• Journal of the Korean Society for Precision Engineering
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• v.17 no.10
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• pp.162-169
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• 2000

A Direct Drive Valve(DDV) hydraulic actuation system which is commonly used as an aircraft's control surface driving actuator has multi-loop control structure to ensure its safety operation. However, because of not perfect matching of one self channel characteristics with the others, the servo valve driving current of each channel can be widely different. Therefore, the long-time use of DDV actuator without any correction of these channel current offsets will cause the problem of performance or life expectancy degradation due to unwanted heats in the linear motor. A current equalization loop structure which can minimizes current offsets between channels is introduced and designed. The performance of the current equalization loop is investigated and verified through the analytic and experimental ways.

• Journal of Power System Engineering
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• v.14 no.6
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• pp.102-108
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• 2010

In this study, the authors investigate the basic characteristics of a two stage directional control valve with pilot spool assembled in main spool coaxially. The step response characteristics and effects of major design parameters' values on valve performances arc clarified through numerical simulations. In addition, the authors examined the possibility of applying the object valve for this study as a proportional control valve. Based on the numerical simulation results, new design values for the reformed design as a proportional control valve were suggested.