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Torque Converter Launch and Lock with Multi-Input Multi-Output Control
ISSN: 0148-7191, e-ISSN: 2688-3627
Published April 14, 2020 by SAE International in United States
A torque converter is a type of fluid coupling device used to transfer engine power to the gearbox and driveline. A bypass clutch equipped in a torque converter assembly is a friction element which when fully engaged, can directly connect the engine to the gearbox. The torque converter is an important launch device in an automatic transmission which decouples engine speed from gearbox input speed while providing torque multiplication to drive the vehicle. During partial pedal launch, it is desired to engage the bypass clutch early and reduce the converter slippage in order to reduce power loss and achieve better fuel economy. However, engaging the bypass clutch early and aggressively may disturb the wheel torque and cause unpleasant driving experiences. This paper describes a multi-input multi-output (MIMO) control method to coordinate both engine and converter bypass clutch to simultaneously deliver desired wheel torque and reduce converter slippage. The proposed control method leverages a feedforward control derived from a standard converter hydrodynamic model and an LQR feedback control. It considers the desired gearbox input torque and converter slippage as two control targets and engine torque and bypass clutch capacity as two control inputs to achieve the targets. This method enables aggressive converter lock-up without degrading driveability and will potentially improve calibration efficiency.