A R-gear removal system was developed for DCT TMED hybrid electric vehicles, which performs reverse driving by engaging the 1st gear and reversing the motor. Improved fuel efficiency, cost and weight reduction were obtained due to the R-gear removal system. In case of engine clutch related failure, reverse driving is prohibited because the engine rotates in reverse direction if the engine clutch is engaged. The engine reserve rotation can cause problems such as coolant backflow, piston noise, etc. However, since the state unknown failure which is one of the clutch related failure means that the clutch state cannot be determined, the engine clutch may actually be open. If the engine clutch is open under state unknown failure, reverse driving can be permitted because engine reverse rotation does not occur. In this paper, a strategy to predict engine clutch status under state unknown failure is developed and the driving strategies under these circumstances were proposed. In the TMED HEV, two power sources are disposed at both ends of the engine clutch. Therefore, when the one source rotates, the engine clutch state can be determined by whether the other source rotates. Strategies for predicting engine clutch status vary according to the drive mode which is EV and Idle. Basic conditions for these strategies are that state unknown failure is occurred, the car is stopped and P or N gear is engaged. In EV mode, neutral control of transmission is requested first in order to prevent the vehicle from moving. After neutral state of transmission is confirmed, the motor is forcibly driven. If the transmission is not neutral for a certain period of time, the process is stopped in order not to affect driving. A Proportional Integral(PI) controller was used to drive motor at the desired rpm. Engine clutch is judged to be open if the engine remains stopped for a certain period of time. And the engine clutch is judged to be not open if the motor is not stably controlled. In Idle mode, in which engine runs at idle speed and motor is stopped, the engine clutch is judged to be open if the motor is stopped for a certain period of time. A new driving strategies are developed under state unknown failure. When P gear is engaged, idle charge is performed after predicting the engine clutch status. When N gear is engaged, engine clutch state prediction is performed and the motor is turned off. When R gear is engaged, if the engine clutch is predicted to be open, reverse driving is allowed, and if not, reverse driving is prohibited and driver receives blinking notification. When D gear is engaged, as in the existing strategy, the vehicle is driven only in EV mode. The way of prohibiting reverse driving is also improved. Since the reverse driving is prohibited by controlling the torque to 0, engine reverse rotation occurs for quite a long time when the engine clutch is engaged during reverse driving. Therefore, neutral control of transmission is requested in addition to torque 0 control to reduce the reverse rotation time. Through this study, it is expected that the customer complaints can be reduced by decreasing the chance of not being able to drive in reverse. Moreover, by additionally requesting transmission neutral when reverse driving is prohibited, engine reverse rotation time is reduced by up to 50%, and vibration were also reduced which lead to benefits in engine durability and driving comfort. This development has been applied since the all-new Niro hybrid(SG2 HEV) model, and will be applied to all Gear R removal systems.
Ms. SUNYOUNG PARK, Research engineer, Hyundai Motor Company