Experimental Study on the Shift Control Characteristics of CVT using Embedded System

The continuously variable transmission (CVT), to implement speed ratio infinitely in the fixed range, has the characteristic of low fuel consumption and low exhaust gas due to operating the vehicle in a high efficiency range irrelevant to engine speed and vehicle speed. The speed ratio of belt type CVT is controlled by adjusting line pressure. The line pressure control prevents slip between the pulley and the belt by conserving optimal line pressure, which is implemented by controlling the thrust force of actuators of both the drive-shaft and the driven-shaft. The one of the line pressure control methods, mechanical-hydraulic control is usually adopting VDT's control method, in which the secondary solenoid valve has two functions both a regulator and a line pressure controller. However, this control method could not show the high performance of CVT with optimal driving capability because of the limitation of simple control algorithm, and it could not gain market share sufficiently in spite of the advantage of CVT with low fuel consumption. On the other hand, the electro-hydraulic control method gives the enhancement of power performance and low fuel consumption by implementing various driving mode using the proportional control or PWM control. The key of CVT technique is to develop a control algorithm of the electro-hydraulic solenoid valve in order to implement the speed ratio efficiently. In this paper, the line pressure control algorithm is proposed and the speed control characteristic is validated using metal belt type CVT test rig and the embedded ECU platform