• Journal of Drive and Control
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• v.15 no.3
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• pp.36-42
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• 2018

Agricultural tractors require frequent shifting to improve operation efficiency, and PST (Powershift Transmission) is considered as a suitable transmission. However, due to the inherent characteristics of the PST, shocks arise during shifting, which imparts a negative effect on the operator. Therefore, in order to improve the transmission performance of the tractor PST, researches on various methods including the hydraulic system circuit, the engine input speed control, and the mechanical system of the transmission are steadily being conducted. In this study, in order to reduce the impact of PST on a shift based on SimulationX software, we analyzed the characteristics of the input signal of PCV (Pressure Control Valve) through sensitivity analysis and verified the simulation model through actual vehicle test. Optimization was performed for minimizing the shift shock for some of the parameters of the input signal at constant temperature and RPM conditions.

• Journal of the Korean Society of Propulsion Engineers
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• v.9 no.3
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• pp.74-84
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• 2005

This paper include the investigation of finding the system characteristics of facility by simulating open-type turbo-pump fed system, which has commercial control valves, using AMESIM (Advanced Modeling Environment Simulation) commercial software. After developing a flight-type control valve on the basis of the results, the system characteristics of facility for control and valve tests is estimated. Especially, one of purposes of this paper is to find PID value of each commercial control valve in the facility for system test. To find suitable control logic, PI and PID modes are also compared. This paper also introduces design parameters of valve and equipment for thrust control and TDS simulation, which are using control valves.

• 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 Veterinary Clinics
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• v.14 no.2
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• pp.201-207
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• 1997

This study was carried out to investigate the changes of blood chemical values in 61 crossbred calves at 1 day, 1 week, 2 weeks, 4 weeks and 9 weeks of age, respectively. The blood chemical values of calves with diarrhea were compared with those of normal calves, and blood chemical values were compared for groups of calves with weight gain divided into four ranges; up to 0.9 kg/wk and over 7.0 kg/wk. The results obtained in this study show that the mean values and standard deviation of red blood cell (RBC) and packed cell volume (PCV) of normal calves at 1 day of age (806.7$\pm $56.5 10$^{4}$/$\mu$l and 33.8$\pm $5.2 %) decreased at 1 week of age and increased at 2 and 4 weeks of age. The PCV of normal calves at 9 weeks of age (32.6$\pm $2.3 %) was significantly lower than that at 2 and 4 weeks of age (p<0.05). Total protein of normal calves at 1 day of age (6.8$\pm $0.5 g/100 ml) decreased to 6.4$\pm $0.6 g/100ml at 1 week and increased to 7.0$\pm $ 0.7 g/100 ml at 2 weeks. After 2 weeks of age, total protein tended to decrease gradually to 9 weeks of age. Glucose of normal calves at 9 weeks of age (78$\pm $4 mg/100 ml) was significantly lower than that at 1 week (110$\pm $8 mg/100 ml) (p<0.01). At all ages, RBC, white blood cell (WBC), PCV and fibrinogen of calves with diarrhea were higher than those of normal calves. RBC and PCV of calves with diarrhea at 1 week of age (929.7$\pm $39.7 10$^{4}$/$\mu$ and 42.3$\pm $0.4 % were significantly higher than those of normal calves at 1 week (786.4$\pm $80.9 10$^{4}$/$\mu$l and 32.2$\pm $3.8 %) (p< 0.05), which suggest that diarrhea at this age can be dangerous. The weekly weight gain was an average of 4.2 kg/wk from birth to 9weeks. RBC, PCV, fibrinogen, total protein and vitamin E of calves with weight gain more than 4.0kg/wk. From the above results we obtained eledata support the importance of providing high quality feed from 4 weeks to 9 weeks of age for satisfactory weight gain of calves.

• The Journal of Korean Institute for Practical Engineering Education
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• v.3 no.1
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• pp.9-14
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• 2011

The expansion work that is wasted through the irreversible expansion through the PC valve of decompression process of the natural gas governor station can be recovered by replacing the process by an isentropic expansion. The energy and exergy analyses for the two decompression process models of power producing and current decompression process model are presented. Analysis results showed that the exergy by gas supply is 56.29%, the exergy by producing power is 32.12 % in case of preheating system and 22.52% in case of non-preheating system. The dead exergy at the PCV is generated much more network. As these results, the usefulness of exergy analysis is verified.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.2
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• pp.107-114
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• 2014

This paper proposes a common rail pressure control algorithm for passenger car diesel engines. For handling the parameter-varying characteristics of common rail systems, the quantitative feedback theory (QFT) is applied to the design of a robust rail pressure control algorithm. The driving current of the pressure control valve and the common rail pressure are used as the input/output variables for the common rail system model. The model parameter uncertainty ranges are identified through experiments. Rail pressure controller requirements in terms of tracking performance, robust stability, and disturbance rejection are defined on a Nichols chart, and these requirements are fulfilled by designing a compensator and a prefilter in the QFT framework. The proposed common rail pressure control algorithm is validated through engine experiments. The experimental results show that the proposed rail pressure controller has a good degree of consistency under various operating conditions, and it successfully satisfies the requirements for reference tracking and disturbance rejection.