Modeling of a New Hydraulic Control System for a Belt-Type Continuously Variable Transmission

A new hydraulic control system for belt-type continuously variable transmissions (CVT) has been devised. The control scheme features a dual-pump configuration with one pump serving as the primary pump, providing minimum clamping pressure to each CVT pulley. The primary pump is also used to meet any additional transmission flow requirements. The second pump creates a pressure differential between the pulleys to generate the clamping-force ratio needed to achieve the desired speed-ratio. The system is designed to minimize ratio-transient flow requirements, allowing the flow capacity of the primary pump to be reduced while also permitting lower operating pressures, hence, improving vehicle fuel economy. The system allows CVT pulley pistons of identical area to be used. This simplifies the design and potentially reduces cost. In this paper, system operation and model-based estimates of fuel-economy gains are discussed and contrasted with existing control schemes.