The statements in this section merely provide background information related to the present disclosure and may not constitute the related art.
A hybrid electric vehicle (HEV) is a vehicle using two or more kinds of different driving sources and generally means a vehicle that is driven by an engine for generating a driving force by burning fuel and a motor generating a driving force with electric energy of a battery.
The hybrid electric vehicle is equipped with a hybrid control unit (HCU) that is an upper controller for controlling the overall operation of the vehicle and is also equipped with various controllers for controlling various kinds of devices of the vehicle.
For example, the hybrid electric vehicle is equipped with an engine control unit (ECU) configured to control the operation of the engine, a motor control unit (MCU) configured to control the operation of the motor, a transmission control unit (TCU) configured to control the operation of the transmission, a battery management system (BMS) configured to collect battery status information to be used for a charging and discharging control of the battery or provide the collected battery status information to other controllers and perform a control to manage the battery, a brake control unit (BCU) configured to perform a braking control of the vehicle, and the like.
The HCU and the respective controllers perform a cooperative control for the in-vehicle apparatuses while exchanging information with each other through CAN communication. Here, the upper controller transfers a control command to the lower controller while collecting a variety of information from the lower controllers.
Meanwhile, in the TMED hybrid electric vehicles (HEV and PHEV), to offset a shock occurring due to the sudden fluctuation in the torque on the output side of the transmission at the time of the shift, a torque intervention control is performed to reduce the motor torque transmitted to the input side of the transmission.
Further, the torque intervention control is performed even when the shift is made while a driver steps on a brake pedal to perform the regenerative braking, that is, the downshift to change a gear stage of the transmission downward during the regenerative braking.
Further, in the control for the downshift during the regenerative braking, the related art uses a torque control system of a conventional vehicle that does not perform the regenerative braking.
That is, control logic is implemented as a reference for controlling the conventional vehicle at the time of the downshift during the regenerative braking. Because the conventional vehicle does not use a negative (−) torque, the control logic is not suitable for the control of the hybrid electric vehicle performing the regenerative braking.
Further, the existing control system controls the intervention torque according to the shift progress state when the downshift is made, and thus, for example, an absolute value of the intervention torque gradually decreases along slopes by phase and slopes by actual shift progress rate.
At this point, because the torque at the time of the regenerative braking is the negative torque, the intervention torque is determined so that the absolute value thereof gradually decreases along a slope considering the shift progress state. As such, the intervention torque determined according to the shift progress state during the shift is used as a motor torque command to control the regenerative operation of the motor, such that the absolute value of the motor torque (negative torque) is reduced.
However, according to the above-mentioned related art, when the method for performing a feedforward control on the motor torque by the intervention torque determined based on the slopes by the shift phase and the slopes by the actual shift progress rate from the torque intervention entry timing for the shift, is applied, the torque may greatly fluctuate while the torque intervention is released at the end of the shift or after the completion of the actual shift, thereby deteriorating the braking linearity.