Shift control device for automatic transmission and shift control method thereof

1. A shift control device for an automatic transmission, which executes a shift from a current gear position to a target gear position by selectively engaging and disengaging a plurality of friction elements, comprising:

a thermal load prediction unit which predicts a thermal load state of the friction element upon completion of the shift from a current thermal load state of the friction element; and

a shift control unit which, when the thermal load state upon shift completion predicted by the thermal load prediction unit corresponds to a predetermined state, either performs the shift in a modified shift mode in which a heat generation amount of the friction element is smaller than the heat generation amount of the friction element when the predetermined state is not established, or prohibits the shift,

wherein the predetermined state is set at a different state in a case where the shift is an upshift and in a case where the shift is a downshift, and is set on the basis of a gradient of a traveling road.

2. The shift control device as defined in claim 1 , further comprising a driving force deficiency determination unit which determines, on the basis of at least the gradient of the traveling road, whether or not a possibility of a driving force deficiency due to uphill road travel exists,

wherein, when the driving force deficiency determination unit determines that the possibility of a driving force deficiency due to uphill road travel does not exist, the predetermined state is set as a state in which the thermal load of the friction element is equal to or greater than a first predetermined value in a case where the shift is an upshift and as a state in which the thermal load of the friction element is equal to or greater than a second predetermined value, which is lower than the first predetermined value, in a case where the shift is a downshift, and

when the driving force deficiency determination unit determines that the possibility of a driving force deficiency due to uphill road travel does exist, the predetermined state is set as a state in which the thermal load of the friction element is equal to or greater than a third predetermined value, which is higher than the second predetermined value, in a case where the shift is a downshift.

3. The shift control device as defined in claim 2 , wherein, when the driving force deficiency determination unit determines that the possibility of a driving force deficiency due to uphill road travel exists, the predetermined state is set as a state in which the thermal load of the friction element is equal to or greater than a fourth predetermined value, which is lower than the third predetermined value, in a case where the shift is an upshift.

4. The shift control device as defined in claim 1 , wherein the predetermined state is set as a state in which the thermal load of the friction element is equal to or greater than a first predetermined value in a case where the shift is an upshift and as a state in which the thermal load of the friction element is equal to or greater than a second predetermined value in a case where the shift is a downshift,

the first predetermined value is set at a higher value than the second predetermined value, and

the second predetermined value is set at a higher value as an upward gradient of the traveling road increases.

5. The shift control device as defined in claim 1 , wherein the predetermined state is set as a state in which the thermal load of the friction element is equal to or greater than a first predetermined value in a case where the shift is an upshift and as a state in which the thermal load of the friction element is equal to or greater than a second predetermined value in a case where the shift is a downshift,

the first predetermined value is set at a higher value than the second predetermined value, and

the first predetermined value is set at a lower value as an upward gradient of the traveling road increases.

6. The shift control device as defined in claim 1 , further comprising:

a current thermal load calculation unit which calculates the current thermal load state of the friction element; and

a heat generation amount prediction unit which predicts a heat generation amount of the friction element when the shift is performed before the shift begins,

wherein the thermal load prediction unit predicts the thermal load state of the friction element upon completion of the shift on the basis of the calculated current thermal load state and the predicted heat generation amount of the friction element.

7. A shift control method for an automatic transmission, which executes a shift from a current gear position to a target gear position by selectively engaging and disengaging a plurality of friction elements, comprising:

predicting a thermal load state of the friction element upon completion of the shift from a current thermal load state of the friction element;

when the predicted thermal load state upon shift completion corresponds to a predetermined state, either performing the shift in a modified shift mode in which a heat generation amount of the friction element is smaller than the heat generation amount of the friction element when the predetermined state is not established, or prohibiting the shift, and

setting the predetermined state on the basis of a gradient of a traveling road at a different state in a case where the shift is an upshift and in a case where the shift is a downshift.

8. The shift control method as defined in claim 7 , further comprising:

determining, on the basis of at least the gradient of the traveling road, whether or not a possibility of a driving force deficiency due to uphill road travel exists,

when it is determined that the possibility of a driving force deficiency due to uphill road travel does not exist, setting the predetermined state as a state in which the thermal load of the friction element is equal to or greater than a first predetermined value in a case where the shift is an upshift and as a state in which the thermal load of the friction element is equal to or greater than a second predetermined value, which is lower than the first predetermined value, in a case where the shift is a downshift, and

when it is determined that the possibility of a driving force deficiency due to uphill road travel does exist, setting the predetermined state a state in which the thermal load of the friction element is equal to or greater than a third predetermined value, which is higher than the second predetermined value, in a case where the shift is a downshift.

9. The shift control method as defined in claim 8 , further comprising:

when it is determined that the possibility of a driving force deficiency due to uphill road travel exists, setting the predetermined state as a state in which the thermal load of the friction element is equal to or greater than a fourth predetermined value, which is lower than the third predetermined value, in a case where the shift is an upshift.

10. The shift control method as defined in claim 7 , further comprising:

setting the predetermined state as a state in which the thermal load of the friction element is equal to or greater than a first predetermined value in a case where the shift is an upshift and as a state in which the thermal load of the friction element is equal to or greater than a second predetermined value in a case where the shift is a downshift,

setting the first predetermined value at a higher value than the second predetermined value, and

setting the second predetermined value at a higher value as an upward gradient of the traveling road increases.

11. The shift control method as defined in claim 7 , further comprising:

setting the predetermined state as a state in which the thermal load of the friction element is equal to or greater than a first predetermined value in a case where the shift is an upshift and as a state in which the thermal load of the friction element is equal to or greater than a second predetermined value in a case where the shift is a downshift,

setting the first predetermined value at a higher value than the second predetermined value, and

setting the first predetermined value at a lower value as an upward gradient of the traveling road increases.

12. The shift control method as defined in claim 7 , further comprising:

calculating the current thermal load state of the friction element; and

predicting a heat generation amount of the friction element when the shift is performed before the shift begins,

wherein the thermal load state of the friction element upon completion of the shift is predicted on the basis of the calculated current thermal load state and the predicted heat generation amount of the friction element.

13. A shift control device for an automatic transmission, which executes a shift from a current gear position to a target gear position by selectively engaging and disengaging a plurality of friction elements, comprising:

means for predicting a thermal load state of the friction element upon completion of the shift from a current thermal load state of the friction element,

means for, when the predicted thermal load state upon shift completion corresponds to a predetermined state, either performing the shift in a modified shift mode in which a heat generation amount of the friction element is smaller than the heat generation amount of the friction element when the predetermined state is not established, or prohibiting the shift, and

means for setting the predetermined state on the basis of a gradient of a traveling road at a different state in a case where the shift is an upshift and in a case where the shift is a downshift.

14. The shift control device as defined in claim 13 , further comprising means for determining, on the basis of at least the gradient of the traveling road, whether or not a possibility of a driving force deficiency due to uphill road travel exists,

means for, when it is determined that the possibility of a driving force deficiency due to uphill road travel does not exist, setting the predetermined state as a state in which the thermal load of the friction element is equal to or greater than a first predetermined value in a case where the shift is an upshift and as a state in which the thermal load of the friction element is equal to or greater than a second predetermined value, which is lower than the first predetermined value, in a case where the shift is a downshift, and

means for, when it is determined that the possibility of a driving force deficiency due to uphill road travel does exist, setting the predetermined state as a state in which the thermal load of the friction element is equal to or greater than a third predetermined value, which is higher than the second predetermined value, in a case where the shift is a downshift.

15. The shift control device as defined in claim 14 , further comprising means for, when it is determined that the possibility of a driving force deficiency due to uphill road travel exists, setting the predetermined state as a state in which the thermal load of the friction element is equal to or greater than a fourth predetermined value, which is lower than the third predetermined value, in a case where the shift is an upshift.

16. The shift control device as defined in claim 13 , further comprising means for setting the predetermined state as a state in which the thermal load of the friction element is equal to or greater than a first predetermined value in a case where the shift is an upshift and as a state in which the thermal load of the friction element is equal to or greater than a second predetermined value in a case where the shift is a downshift,

means for setting the first predetermined value at a higher value than the second predetermined value, and

means for setting the second predetermined value at a higher value as an upward gradient of the traveling road increases.

17. The shift control device as defined in claim 13 , further comprising means for setting the predetermined state as a state in which the thermal load of the friction element is equal to or greater than a first predetermined value in a case where the shift is an upshift and as a state in which the thermal load of the friction element is equal to or greater than a second predetermined value in a case where the shift is a downshift,

means for setting the first predetermined value at a higher value than the second predetermined value, and

means for setting the first predetermined value at a lower value as an upward gradient of the traveling road increases.

18. The shift control device as defined in claim 13 , further comprising:

means for calculating the current thermal load state of the friction element; and

means for predicting a heat generation amount of the friction element when the shift is performed before the shift begins,

wherein the means for predicting the thermal load state predicts the thermal load state of the friction element upon completion of the shift on the basis of the calculated current thermal load state and the predicted heat generation amount of the friction element.