Shift control device and shift control method for hybrid vehicle

1. A shift control device for a hybrid vehicle in which an internal combustion engine configured to drive drive wheels, a rotating electric machine configured to drive the drive wheels as a motor and to supply power to an in-vehicle secondary battery as a power generator, and a multi-stage automatic transmission that is disposed between the internal combustion engine and the drive wheels and between the rotating electric machine and the drive wheels and that achieves one of a plurality of shift stages are installed, and in which an EV traveling mode that is selected in a low-drive region where a vehicle driving force is greater than zero and in which fuel is not supplied to the internal combustion engine and output from the rotating electric machine is transferred to the drive wheels, an HV traveling mode that is selected in a high-drive region where the vehicle driving force is greater than the vehicle driving force in the low-drive region and in which output from at least the internal combustion engine out of the internal combustion engine and the rotating electric machine is transferred to the drive wheels, and a regenerative traveling mode that is selected in a region where the vehicle driving force is smaller than zero and in which power obtained when the rotating electric machine is driven with rotation energy from the drive wheels is stored in the secondary battery when an accelerator is released while the vehicle is traveling are set, the shift control device comprising an electronic control unit, wherein:

the electronic control unit is configured to control switching between the shift stages in the multi-stage automatic transmission based on a vehicle speed and a parameter related to the vehicle driving force;

the electronic control unit is configured to control the switching between the shift stages in the multi-stage automatic transmission such that a gear ratio that is selected at a predetermined vehicle speed and is selected in the regenerative traveling mode that is a boundary region with respect to the EV traveling mode becomes greater than a gear ratio that is selected at the predetermined vehicle speed and is selected in the HV traveling mode that is a boundary region with respect to the EV traveling mode; and

the electronic control unit is configured to control the switching between the shift stages in the multi-stage automatic transmission such that a gear ratio of a shift stage that is selected in a case where a traveling mode is switched from the regenerative traveling mode to the EV traveling mode is greater than a gear ratio of a shift stage that is selected in a case where the traveling mode is switched from the HV traveling mode to the EV traveling mode under the same vehicle speed and the same parameter in a case where the traveling mode is switched from the regenerative traveling mode to the EV traveling mode and in a case where the traveling mode is switched from the HV traveling mode to the EV traveling mode.

2. The shift control device according to claim 1 , wherein the electronic control unit is configured to perform upshifting to a shift stage that is equal to or lower than a shift stage pertaining to a case where the traveling mode is switched from the HV traveling mode to the EV traveling mode after a shift stage is maintained for a predetermined time, in a case where the traveling mode is switched from the regenerative traveling mode to the EV traveling mode.

3. The shift control device according to claim 2 , wherein the electronic control unit is configured to perform the upshifting to the shift stage that is equal to or lower than the shift stage pertaining to the case where the traveling mode is switched from the HV traveling mode to the EV traveling mode without maintaining the shift stage for the predetermined time in a case where the traveling mode is switched from the regenerative traveling mode to the EV traveling mode and a rotation speed of the rotating electric machine is higher than a predetermined rotation speed.

4. The shift control device according to claim 1 , wherein the electronic control unit is configured to control the switching between the shift stages in the multi-stage automatic transmission such that a gear ratio of a shift stage that is selected in the EV traveling mode in the boundary region between the HV traveling mode and the EV traveling mode becomes equal to or greater than a gear ratio of a shift stage that is selected in the HV traveling mode under the same vehicle speed and the same parameter.

5. A shift control method for a hybrid vehicle in which an internal combustion engine configured to drive drive wheels, a rotating electric machine configured to drive the drive wheels as a motor and to supply power to an in-vehicle secondary battery as a power generator, and a multi-stage automatic transmission that is disposed between the internal combustion engine and the drive wheels and between the rotating electric machine and the drive wheels and that achieves one of a plurality of shift stages are installed, and in which an EV traveling mode that is selected in a low-drive region where a vehicle driving force is greater than zero and in which fuel is not supplied to the internal combustion engine and output from the rotating electric machine is transferred to the drive wheels, an HV traveling mode that is selected in a high-drive region where the vehicle driving force is greater than the vehicle driving force in the low-drive region and in which output from at least the internal combustion engine out of the internal combustion engine and the rotating electric machine is transferred to the drive wheels, and a regenerative traveling mode that is selected in a region where the vehicle driving force is smaller than zero and in which power obtained when the rotating electric machine is driven with rotation energy from the drive wheels is stored in the secondary battery when an accelerator is released while the vehicle is traveling are set, the shift control method comprising:

controlling switching between the shift stages in the multi-stage automatic transmission based on a vehicle speed and a parameter related to the vehicle driving force;

controlling the switching between the shift stages in the multi-stage automatic transmission such that a gear ratio that is selected at a predetermined vehicle speed and is selected in the regenerative traveling mode that is a boundary region with respect to the EV traveling mode becomes greater than a gear ratio that is selected at the predetermined vehicle speed and is selected in the HV traveling mode that is a boundary region with respect to the EV traveling mode; and

controlling the switching between the shift stages in the multi-stage automatic transmission such that a gear ratio of a shift stage that is selected in a case where a traveling mode is switched from the regenerative traveling mode to the EV traveling mode is greater than a gear ratio of a shift stage that is selected in a case where the traveling mode is switched from the HV traveling mode to the EV traveling mode under the same vehicle speed and the same parameter in a case where the traveling mode is switched from the regenerative traveling mode to the EV traveling mode and in a case where the traveling mode is switched from the HV traveling mode to the EV traveling mode.