Shift point strategy for hybrid electric vehicle transmission

1. A method for determining a shift point strategy, comprising:

providing at least two power sources;

selectively coupling a hybrid vehicle transmission having an input shaft to said at least two power sources, said hybrid vehicle transmission receiving power from said power sources;

defining a speed of said transmission input shaft to promote an acceleration as compared to a fuel economy;

defining a speed of said transmission input shaft to promote said fuel economy as compared to said acceleration;

determining driver intent to promote either of said acceleration and said fuel economy; and

setting a shift point based, in part, on at least said determining step, wherein said shift point is variable based on said determining step; and

wherein said setting of said shift point comprises setting an unscheduled up shift point and an unscheduled downshift point for an engaged gear of said hybrid transmission; and

wherein said determining driver intent to promote either of said acceleration and said fuel economy includes assessing a gear position indication to promote one of said acceleration and said fuel economy.

2. The method as recited in claim 1 , wherein said determining step comprises using driver demand torque as a fraction of total available torque.

3. The method as recited in claim 2 , wherein said total available torque comprises a sum of available torque from said at least two power sources.

4. The method as recited in claim 1 , further comprising:

determining an apparent inertia of a vehicle; and

using said determined vehicle apparent inertia as an indicator of a need to scale at least one shift point.

5. The method as recited in claim 4 , wherein said determining an apparent inertia of a vehicle comprises:

measuring an output shaft torque of said hybrid vehicle transmission;

determining an acceleration of said vehicle; and

dividing said output shaft torque by said vehicle acceleration.

6. The method as recited in claim 1 , further comprising the step of adding hysteresis after shifts to minimize a need for limit cycles.

7. The method as recited in claim 1 , wherein said setting a shift point based in part on at least said determining step comprises setting an up shift point and a downshift point for each gear in said hybrid transmission.

8. A method for determining a shift point strategy, comprising:

providing at least a first power source and a second power source, wherein said first power source is an internal combustion engine;

selectively coupling a hybrid vehicle transmission having an input shaft to said at least two power sources, said hybrid vehicle transmission being configured to selectively receive power from said at least first and second power sources;

defining a speed of said transmission input shaft to promote an acceleration as compared to a fuel economy;

defining a speed of said transmission input shaft to promote said fuel economy as compared to said acceleration;

determining driver intent to promote either of said acceleration and said fuel economy, said driver intent being determined using driver demand torque as a fraction of total available torque, an apparent inertia of a vehicle, and a transmission gear position indication; and

setting a shift point based, in part, on at least said determining step, wherein said shift point is variable based on said determining step; and

wherein said setting of said shift point comprises setting an unscheduled up shift point and an unscheduled downshift point for an engaged gear of said hybrid transmission.

9. The method as recited in claim 8 , further comprising adding hysteresis after shifts to minimize a need for limit cycles.

10. The method as recited in claim 8 , wherein said setting a shift point based in part on at least said determining step comprises setting an up shift point and a downshift point for each gear in said hybrid transmission.

11. A method for operating a hybrid vehicle comprising:

establishing a shift point strategy, wherein said establishing a shift point strategy includes providing at least two power sources, selectively coupling a hybrid vehicle transmission having an input shaft to said at least two power sources, said hybrid vehicle transmission receiving power from at least one of said power sources, defining a speed of said transmission input shaft to promote an acceleration as compared to a fuel economy, defining a speed of said transmission input shaft to promote said fuel economy as compared to said acceleration, determining driver intent to promote either of said acceleration and said fuel economy, and setting a shift point based, in part, on at least said determining step, wherein said shift point is variable based on said determining step;

determining an intermediate gear that falls within said shift point strategy; and

selecting said intermediate gear;

wherein said determining driver intent to promote either of said acceleration and said fuel economy includes assessing a gear position indication to promote one of said acceleration and said fuel economy; and

wherein said setting of said shift point based, in part, on at least said determining step comprises setting an unscheduled up shift point and an unscheduled downshift point for an engaged gear of said hybrid transmission.

12. The method for operating a hybrid vehicle of claim 11 , wherein said determining step comprises using driver demand torque as a fraction of total available torque.

13. The method for operating a hybrid vehicle of claim 12 , wherein said total available torque comprises a sum of available torque from said at least two power sources.

14. The method for operating a hybrid vehicle of claim 11 , further comprising:

determining an apparent inertia of a vehicle; and

using said determined vehicle apparent inertia as an indicator of a need to scale at least one shift point.

15. The method for operating a hybrid vehicle of claim 14 , wherein said determining an apparent inertia of a vehicle comprises:

measuring an output shaft torque of said hybrid vehicle transmission;

determining an acceleration of said vehicle; and

dividing said output shaft torque by said vehicle acceleration.

16. The method for operating a hybrid vehicle of claim 11 , further comprising the step of adding hysteresis after shifts to minimize a need for limit cycles.

17. The method for operating a hybrid vehicle of claim 11 , wherein said setting a shift point based in part on at least said determining step comprises setting an up shift point and a downshift point for each gear in said hybrid transmission.

18. A system for determining a shift point strategy in a hybrid transmission having a plurality of prime movers selectively coupled to an input shaft comprising:

a control unit configured to define a speed of said hybrid transmission input shaft to promote an acceleration as compared to a fuel economy, define a speed of said transmission input shaft to promote said fuel economy as compared to said acceleration, determine driver intent to promote either of said acceleration and said fuel economy based in part at least on driver demand torque as a fraction of total available torque, and set a shift point based in part on at least said determining step, where said shift point is variable based on said determining step; and

wherein said shift point comprises an unscheduled up shift point and an unscheduled downshift point for an engaged gear of said hybrid transmission.

19. The system of claim 18 , wherein said control unit is further configured to determine driver intent based at least in part on an automatic gear position indicator.

20. The system of claim 18 , wherein said control unit is further configured to determine an apparent inertia of a vehicle, and use said determined vehicle apparent inertia as an indicator of a need to scale at least one shift point.