In case of a low speed gearing in the automatic transmission, since the torque is increased, it is difficult to secure a good feeling on gear shift of transmission. It is possible to improve the shift feeling on transmission by applying a one-way clutch in case of the gear shift from the first stage to the second stage. But in case of the gear shift from the second stage to the third stage, it is difficult to secure a good feeling on gear shift of transmission because the hydraulic components are directly controlled simultaneously. In this study, a shift performance of an automatic transmission was investigated as a basic study to solve these problems. The subjects of this study are 2-3 step upshifting gearing process and the performance data such as the pressure characteristics and torque of the transmission according to the amount of the throttle valve opening are analyzed on basis of experiment with an actual vehicle. As a result, the transient time of the shift is closely related to the amount of the throttle valve, opening and the time point at which the shifting ends is shortened when the throttle valve opening reaches 30% of the opening amount.

In this paper, numerical investigation of transition characteristics in a square-sectional curved duct flow. Computational fluid dynamic(CFD) simulation was performed using the commercial CFD code FLUENT to investigate the transition characteristics. The flow development is found to depend upon Dean number and curvature ratio. The velocity profiles in center of the duct have lower value than those of the inner and outer walls.

이 연구에서는 정사각 단면을 갖는 덕트 내부에 원심력의 영향을 받는 유동의 천이특성을 실험 및 수치적으로 규명하였다. 실험적 연구로서 레이저도플러 속도계를 이용하여 축방향속도를 측정하였고, 상용소프트웨어인 플루언트를 이용한 전산유체 시뮬레이션으로 천이특성을 고찰하였다. 유동의 발달은 딘수와 굽힘각에 의존한다는 사실을 알 수 있었으며 덕트의 중앙에서의 속도분포는 원심력 때문에 내외벽보다 낮은 값을 나타내었다.