Downshift control method for hybrid DCT vehicle

A downshift control method for a dual clutch transmission for a hybrid vehicle, the method comprising the steps of:

• determining, by a controller, whether a vehicle travels on a slope having equal to or more than a predetermined reference gradient for a downshift;
• releasing, by the controller, a release-side clutch by reducing a torque thereof when the controller determines that the vehicle travels on the slope having equal to or more than the reference gradient;
• comparing, by the controller, a motor speed with a desired shift stage input shaft speed when the release of the release-side clutch is completed in the step of releasing the release-side clutch by reducing the torque;
• increasing, by the controller, a motor torque in a forward direction when the motor speed is lower than or equal to the desired shift stage input shaft speed in the comparing step;
• increasing, by the controller, the motor torque in a negative direction when the motor speed is determined to exceed the desired shift stage input shaft speed in the comparing step;
• checking, by the controller, whether the motor speed is synchronized with the desired shift stage input shaft speed in the step of increasing the motor torque in the forward direction or in the step of increasing the motor torque in the negative direction when gear engagement in the desired shift stage is completed;
• and
• completing, by the controller, gear shifting by controlling a torque of an engagement-side clutch and the torque of the release-side clutch when the motor speed is synchronized with the desired shift stage input shaft speed.