Abstract
An optimal line pressure control algorithm was proposed for the fuel economy improvement of an AT-based parallel hybrid electric vehicle (HEV). By performing lever analysis at each gear step, the required line pressure was obtained considering the torque ratio of the friction elements. In addition, the required line pressure of the mode clutch was calculated. Based on these results, the optimal line pressure map at each gear step of the EV and HEV modes was presented. Using the line pressure map, an optimal line pressure was performed for the AT input torque and mode. To investigate the proposed line pressure control algorithm, a HEV performance simulator was developed based on the powertrain model of the target HEV, and fuel economy improvement was evaluated. Simulation results showed that as the gear step became higher, the optimal line pressure control could reduce the hydraulic power loss, which gave a 2.2% fuel economy improvement compared to the existing line pressure control for the FTP-72 mode.
Highlights
For the 2-shaft parallel hybrid electric vehicle (HEV), the development and control of a transmission that combines and separates the power of the engine and motor are the core technology
To investigate the proposed line pressure control algorithm, a HEV performance simulator was developed based on the powertrain model of the target HEV and fuel economy improvement was evaluated
When the input torque (TInput) acts on sun gear S3, the torque acting on each friction element is obtained from the lever analysis shown in Figure 3, and it is calculated as NBK1 = (a + 1)/c for brake BK1 and as NBK2 = a for brake BK2
Summary
For the 2-shaft parallel hybrid electric vehicle (HEV), the development and control of a transmission that combines and separates the power of the engine and motor are the core technology. For AT, hydraulic pressure, which is necessary for the friction elements (e.g., the clutch and the brake), should be continuously supplied to transmit the torque, and the required power causes to deteriorate the transmission system efficiency. The only way to reduce the power loss of MOP is to decrease the line pressure of the AT hydraulic control system. If the line pressure is too low, the torque transmission capacity of the clutch and brake, which is required for the torque transmission from the engine or motor, decreases, and a slip may occur in the friction elements. To reduce the power loss of the hydraulic control system, the optimal AT line pressure necessary for the torque transmission of the friction elements needs to be supplied. Theoretical model has been suggested for Advances in Mechanical Engineering
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