Research on Hydro-Mechanical Shift System of Belt-CVT to Improve Both Efficiency and Performance

Abstract

A new-generation belt type Continuously Variable Transmission ranging up to 3.5 liter class engine is on the market. This CVT contributes to improvement in both efficiency and performance. This article describes a ‘control method’ newly developed for this CVT pulley ratio control. In the former control system, pulley ratio was controlled only by step-motor. Extra margin of line pressure was indispensable compared to primary pressure to accomplish target-ratio. If line pressure was not sufficient for primary pressure, pulley ratio couldn't be controlled accurately, and would be lower. On the other hand, in this new control, characteristics of hydro-mechanical shift system are utilized positively, and pulley ratio can be controlled by not only step-motor but also linear solenoid for line pressure. At this time, the most suitable line pressure is searched for by confirming the relation between command of step-motor and pulley ratio. In the result, line pressure can also be reduced a little less than primary pressure without causing unpleasant pulley ratio hunting.