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Methods and arrangements for controlling hybrid powertrains are described. In one aspect, an engine is alternatingly operated at different effective displacements. One displacement delivers less than a requested powertrain output and the other delivers more. A motor/generator system is used to add a

Methods and arrangements for controlling hybrid powertrains are described. In one aspect, an engine is alternatingly operated at different effective displacements. One displacement delivers less than a requested powertrain output and the other delivers more. A motor/generator system is used to add and subtract torque to/from the powertrain to cause the net delivery of the requested powertrain output. In some embodiments, energy added and subtracted from the powertrain is primarily drawn from and stored in a capacitor (e.g., a supercapacitor or an ultracapacitor) when alternating between effective displacements. In another aspect a hybrid powertrain arrangement includes an engine a motor/generator and an energy storage system that includes both a battery and a capacitor. The capacitor stores and delivers electrical energy to the motor/generator unit during operation of the engine in a variable displacement or skip fire mode.

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1. A method of controlling a hybrid powertrain to deliver a requested powertrain output, the method comprising alternatingly: operating an internal combustion engine in one or more first effective displacement modes that deliver less torque to the powertrain than the requested powertrain output and

1. A method of controlling a hybrid powertrain to deliver a requested powertrain output, the method comprising alternatingly: operating an internal combustion engine in one or more first effective displacement modes that deliver less torque to the powertrain than the requested powertrain output and controlling at least one motor to add torque to the powertrain to cause the delivery of the requested powertrain output wherein electrical energy used to drive the at least one motor during addition of torque to the powertrain is drawn from an electrical energy storage device; andoperating the engine in one or more second effective displacement modes that have a larger effective displacement than the one or more first effective displacement modes and that deliver more than the requested powertrain output and controlling at least one generator to subtract torque from the powertrain to cause the delivery of the requested powertrain output, wherein electrical energy generated by the at least one generator during subtraction of torque from the powertrain is stored in the electrical energy storage device; andwherein active working chambers in the engine are fired under substantially the same operating conditions in the first and second effective displacement modes and the motor and generator take the form of at least one selected from the group consisting of an integrated motor/generator and separate units. 2. A method as recited in claim 1 wherein: the electrical energy storage device includes a capacitor and energy added and subtracted from the powertrain is primarily drawn from and stored in the capacitor when alternating between the first and second effective displacement modes; andthe engine is one of (a) a variable displacement engine in which the first and second effective displacement modes correspond to different numbers of active cylinders, and (b) arranged to be operated in a skip fire mode in which the first and second effective displacement modes correspond to different firing fractions. 3. A method as recited in claim 2 wherein during regenerative braking electricity generated by the at least one generator is stored at least in part in both the capacitor and a battery. 4. A method as recited in claim 1 wherein: the engine working chambers that are fired in the first and second displacement modes are operated in a manner that provide substantially the maximum available energy efficiency; andany unfired working chambers are deactivated to thereby reduce pumping losses. 5. A method as recited in claim 1 wherein the effective displacements utilized in the first and second effective displacement modes may vary over time. 6. A method as recited in claim 1 wherein the engine transitions directly between the first and second effective displacement modes. 7. A method as recited in claim 1 wherein the engine is a variable displacement engine and the first and second effective displacement modes utilize different numbers of active cylinders and the specific number of active cylinders utilized in the first and second effective displacement modes may vary over time. 8. A method as recited in claim 1 wherein the engine is operated in a skip fire mode and the different first and second effective displacement modes utilize different firing fractions and the specific firing fractions utilized in the first and second effective displacement modes may vary over time. 9. A method as recited claim 1 wherein the energy added and subtracted from the powertrain is primarily drawn from and stored in a capacitor when alternating between the first and second effective displacement modes. 10. A method as recited in claim 9 wherein a motor/generator unit is used to add and subtract energy from the powertrain, the motor/generator being arranged to facilitate regenerative braking, wherein during regenerative braking electricity generated by the motor/generator unit is stored in at least in part in both the capacitor and a battery. 11. A method of controlling a hybrid powertrain to deliver a requested powertrain output, the method comprising alternatingly: operating an engine in a first effective displacement mode that delivers less torque to the powertrain than the requested powertrain output and controllably utilizing energy drawn from an energy storage device to add torque to the powertrain to cause the net delivery of the requested powertrain output; andoperating the engine in a second effective displacement mode that has a different displacement than the first effective displacement mode and that delivers more than the requested powertrain output and controllably subtracting torque from the powertrain to cause the delivery of the requested powertrain output, wherein excess energy subtracted from the powertrain is stored in the energy storage device, andwhereby the engine alternatingly transition back and forth between the first and second effective displacement modes such that the engine alternatingly supplies less torque and more torque than the requested powertrain output. 12. A method as recited in claim 11 wherein the energy added and subtracted from the powertrain is primarily drawn from and stored in a capacitor when alternating between the first and second effective displacement modes. 13. A method as recited in claim 12 wherein a motor/generator unit is used to add and subtract energy from the powertrain, the motor/generator being arranged to facilitate regenerative braking, wherein during regenerative braking electricity generated by the motor/generator unit is stored in at least in part in both the capacitor and a battery. 14. A method as recited in claim 11 wherein the engine working chambers that are fired in the first and second effective displacement modes are operated in a manner that provides substantially the maximum available energy efficiency. 15. A method as recited in claim 11 wherein the engine is a variable displacement engine and the first and second effective displacement modes utilize different numbers of active cylinders and the specific number of cylinders utilized in the first and second effective displacement modes may vary over time. 16. A method as recited in claim 11 wherein the engine is operated in a skip fire mode and the different first and second effective displacement modes utilize different firing fractions and the specific firing fractions utilized in the first and second effective displacement modes may vary over time. 17. A method as recited in claim 11 wherein unfired working chambers are deactivated to thereby reduce pumping losses. 18. A method as recited in claim 11 wherein active working chambers in the engine are operated under substantially the same conditions in the first and second effective displacement modes. 19. A method as recited in claim 11 wherein unfired working chambers are deactivated to thereby reduce pumping losses. 20. An arrangement comprising: an engine capable of applying torque to a powertrain, wherein the engine is arranged to operate in at least one of a variable displacement mode and a skip fire mode;an electric motor/generator unit arranged to add torque to and subtract torque from the powertrain during operation of the engine in the variable displacement mode or the skip fire mode;a battery arranged to store electrical energy, the battery being coupled to the electric motor/generator unit such that the battery may be charged and discharged by the motor/generator unit;a capacitor arranged to store electrical energy, the capacitor being arranged in a manner that facilitates the storage of electrical energy generated by the motor/generator unit and the delivery of electrical energy to the motor/generator unit during operation of the engine in the variable displacement or the skip fire mode to facilitate adding torque to and subtracting torque from the powertrain; anda controller arranged to direct the engine and motor/generator unit to cooperatively deliver a requested output. 21. An arrangement as recited in claim 20 wherein the controller is further arranged to operate the engine in a manner that provides substantially the maximum available energy efficiency during operation in the variable displacement mode or the skip fire mode. 22. An arrangement as recited in claim 20 wherein the controller is further arranged to deactivate unfired working chambers in the variable displacement mode or the skip fire mode to thereby reduce pumping losses. 23. An arrangement as recited in claim 20 wherein the controller is further arranged to alternatingly: operate the engine at a first effective displacement that delivers less torque to the powertrain than the requested output and operate the electric motor/generator to add torque to the powertrain to cause the net delivery of the requested powertrain output, during which the electric motor/generator draws electrical energy from at least one of the capacitor and the battery; andoperate the engine at a second effective displacement that is different than the first effective displacement and that delivers more torque to the powertrain than the requested output and operate the electric motor/generator to subtract torque from the powertrain to cause the delivery of the requested powertrain output, during which the electric motor/generator provides electrical energy to at least one of the capacitor and the battery wherein excess energy subtracted from the powertrain is stored in at least one of the capacitor and the battery. 24. An arrangement as recited in claim 23 wherein the engine is a variable displacement engine and the first and second effective displacements utilize different numbers of active cylinders and the specific number of cylinders utilized in the first and second effective displacement modes may vary over time. 25. An arrangement as recited in claim 23 wherein the engine is operated in a skip fire mode and the different first and second effective displacement utilize different firing fractions and the specific firing fractions utilized in the first and second effective displacement modes may vary over time. 26. An arrangement as recited in any claim 20 wherein the controller is further arranged to deactivate unfired working chambers during operation in a variable displacement mode or a skip fire mode to thereby reduce pumping losses. 27. An arrangement as recited in claim 20 wherein the controller is further arranged to alternatingly: operate the engine at a first effective displacement that delivers less torque to the powertrain than the requested output and operate the electric motor/generator to add torque to the powertrain to cause the net delivery of the requested powertrain output, during which the electric motor/generator draws electrical energy from at least one of the capacitor and the battery; andoperate the engine at a second effective displacement that is different than the first effective displacement and that delivers more torque to the powertrain than the requested output and operate the electric motor/generator to subtract torque from the powertrain to cause the delivery of the requested powertrain output, during which the electric motor/generator provides electrical energy to at least one of the capacitor and the battery wherein excess energy subtracted from the powertrain is stored in at least one of the capacitor and the battery. 28. An arrangement as recited in claim 27 wherein the engine is a variable displacement engine and the first and second effective displacements are different engine displacements. 29. An arrangement as recited in claim 27 wherein the engine is operated in a skip fire mode and the different first and second effective displacement utilize different firing fractions. 30. A hybrid powertrain controller suitable for use in a vehicle having an engine that drives a powertrain, at least one motor/generator unit arranged to add torque to and subtract torque from the powertrain and a capacitor arranged to store electrical energy, the hybrid powertrain controller comprising: an engine controller arranged to operate an engine in a manner that delivers a plurality of different effective displacements;a motor controller arranged to direct the operation of at least one motor/generator unit; andwherein the engine controller and motor controller are arranged to operate the engine and the motor/generator unit in a manner that delivers a requested powertrain output; andthe engine controller and motor controller are further arranged to be capable of causing the engine to alternatingly (i) operate the engine in a first effective displacement mode that delivers less torque to the powertrain than the requested powertrain output while operating the motor/generator unit as a motor to add torque to the powertrain using energy stored in the capacitor to cause the net delivery of the requested powertrain output, and (ii) operate the engine in a second effective displacement mode that has a different displacement than the first effective displacement mode and that delivers more than the requested powertrain output while operating the motor/generator unit as a generator to subtract torque from the powertrain to cause the net delivery of the requested powertrain output, wherein electricity generated by the generator is used to charge the capacitor during operation of the engine in the second effective displacement mode. 31. A hybrid powertrain controller as recited in claim 30 further arranged to: operate the engine in a manner that provides substantially the maximum available energy efficiency during operation in the plurality of different effective displacements; anddeactivate unfired working chambers during operation in the plurality of different effective displacements to thereby reduce pumping losses. 32. A hybrid vehicle powertrain comprising a motor, a generator, an engine capable of operating with at least one deactivated cylinder, an energy storage device, and a controller capable of directing operation of the powertrain in a manner in which activated cylinders of the engine are operated at substantially at their maximum energy efficiency during which time: (i) said engine sometimes operates, at a reduced output that is lower than the required total powertrain output by deactivating at least one cylinder, when said energy storage device's stored energy is sufficient to cause said motor to compensate for the difference between said required output and said reduced output; and(ii) said engine sometimes operates at an increased output exceeding the required total powertrain output when said energy storage device possesses enough available storage capacity to store the difference between said required output and any surplus output exceeding said required output. 33. A hybrid vehicle powertrain as recited in claim 32, wherein the energy storage device is a battery. 34. A hybrid vehicle powertrain as recited in claim 32, wherein the energy storage device is an ultracapacitor. 35. A hybrid vehicle powertrain as recited in claim 32, wherein the energy storage device is comprised of both a battery and an ultracapacitor. 36. A hybrid vehicle powertrain as recited in claim 35, wherein the ultra capacitor is partitioned from the battery.