Hybrid powertrain system using free piston linear alternator engines

1. Hybrid powertrain system, comprising:

an electrical energy storage device;

an electrically-powered torque machine configured to generate torque transferable to a driveline and react torque from the driveline;

a plurality of reciprocating free-piston internal combustion engines each including a linear alternator device configured to generate electric power when in an engine-on state, each reciprocating free-piston internal combustion engine configured to generate a rated output power differing from rated output powers of the other reciprocating free-piston internal combustion engines when operating at resonant speeds;

a power electronics circuit configured to transfer electric power between each of the linear alternator devices, the electrical energy storage device and the torque machine; and

a control module configured to

determine mechanical and electrical power demands responsive to an operator torque request and a state of charge of the electrical energy storage device,

command operation of the torque machine to generate an output torque responsive to the mechanical power demands, and

command operations of the reciprocating free-piston internal combustion engines to generate electric power responsive to the electrical power demands.

2. The hybrid powertrain system of claim 1 , wherein commanding operations of the reciprocating free-piston internal combustion engines to generate electric power responsive to the electrical power demands comprises a power management strategy including individually commanding operations of each of the reciprocating free-piston internal combustion engines over a range of output powers from a minimum electric power to a maximum electric power to generate electric power responsive to the electrical power demands.

3. The hybrid powertrain system of claim 1 , wherein commanding operations of the reciprocating free-piston internal combustion engines to generate electric power responsive to the electrical power demands comprises a power management strategy including commanding simultaneous operation of all of the reciprocating free-piston internal combustion engines in one of the engine-on state and an engine-off state.

4. The hybrid powertrain system of claim 1 , wherein commanding operations of the reciprocating free-piston internal combustion engines to generate electric power responsive to the electrical power demands comprises a power management strategy including commanding individual operation of each of the reciprocating free-piston internal combustion engines in one of the engine-on state and an engine-off state.

5. The hybrid powertrain system of claim 4 , wherein the individual operation of each of the reciprocating free-piston internal combustion engines includes individual operation in the engine-on state at the rated output power.

6. The hybrid powertrain system of claim 4 , wherein the individual operation of each of the reciprocating free-piston internal combustion engines includes individual operation in the engine-on state at the resonant speed and at the rated output power.

7. The hybrid powertrain system of claim 4 , wherein the individual operation of each of the reciprocating free-piston internal combustion engines includes individual operation in the engine-on state at a predetermined fraction of the rated output power.

8. The hybrid powertrain system of claim 4 , wherein the individual operation of each of the reciprocating free-piston internal combustion engines includes operation of selected ones of the reciprocating free-piston internal combustion engines to generate a total electric power that is greater than a required mechanical power associated with the operator torque request.

9. The hybrid powertrain system of claim 4 , wherein the individual operation of each of the reciprocating free-piston internal combustion engines includes operation of selected ones of the reciprocating free-piston internal combustion engines to generate a total electric power that is less than a required mechanical power associated with the operator torque request.

10. The hybrid powertrain system of claim 1 , wherein each reciprocating free-piston internal combustion engine configured to generate a rated output power differing from rated output powers of the other reciprocating free-piston internal combustion engines when operating at resonant speeds comprises a first of said engines configured to generate a rated output power of 10 kW, a second of said engines configured to generate a rated output power of 20 kW, a third of said engines configured to generate a rated output power of 30 kW, and a fourth of said engines configured to generate a rated output power of 40 kW.

11. The hybrid powertrain system of claim 1 , wherein each reciprocating free-piston internal combustion engine configured to generate a rated output power differing from rated output powers of the other reciprocating free-piston internal combustion engines when operating at resonant speeds comprises said engines configured with varying engine design factors including cylinder bore and stroke.

12. The hybrid powertrain system of claim 1 , wherein each reciprocating free-piston internal combustion engine configured to generate rated output power differing from rated output powers of the other reciprocating free-piston internal combustion engines when operating at resonant speeds comprises said engines configured with varying engine design factors including piston size and mass.

13. Hybrid powertrain system, comprising:

an electrical energy storage device;

a plurality of electrically-powered torque machines configured to generate and react mechanical torque;

a plurality of reciprocating free-piston internal combustion engines each including a linear alternator device configured to generate electric power, each reciprocating free-piston internal combustion engine configured to generate a rated output power differing from rated output powers of the other reciprocating free-piston internal combustion engines when operating at resonant speeds;

a power electronics circuit configured to transfer electric power between each of the linear alternator devices, the electrical energy storage device and the torque machines; and

a control module configured to

determine mechanical and electrical power demands responsive to an operator torque request and a state of charge of the electrical energy storage device,

command operation of the torque machines to generate torque responsive to the mechanical power demands, and

command operations of the reciprocating free-piston internal combustion engines to generate electric power responsive to the electrical power demands.

14. Hybrid powertrain system, comprising:

an electrical energy storage device;

an electrically-powered torque machine configured to generate torque transferable to a driveline and react torque from the driveline;

a plurality of reciprocating free-piston internal combustion engines each including a linear alternator device configured to generate electric power, each reciprocating free-piston internal combustion engine configured to generate a rated output power differing from rated output powers of the other reciprocating free-piston internal combustion engines when operating at resonant speeds;

a power electronics circuit configured to transfer electric power between each of the linear alternator devices, the electrical energy storage device and the torque machine; and

a control module configured to

determine electrical power demands responsive to an operator torque request and a state of charge of the electrical energy storage device, and

command operations of the reciprocating free-piston internal combustion engines to generate electric power responsive to the electrical power demands.

15. The hybrid powertrain system of claim 14 , wherein commanding operations of the reciprocating free-piston internal combustion engines to generate electric power responsive to the electrical power demands comprises a power management strategy including individually commanding operations of each of the reciprocating free-piston internal combustion engines over a range of output powers from a minimum electric power to a maximum electric power to generate electric power responsive to the electrical power demands.

16. The hybrid powertrain system of claim 14 , wherein commanding operations of the reciprocating free-piston internal combustion engines to generate electric power responsive to the electrical power demands comprises a power management strategy including commanding simultaneous operation of all of the reciprocating free-piston internal combustion engines in one of the engine-on state and an engine-off state during operation of the hybrid powertrain system.

17. The hybrid powertrain system of claim 14 , wherein commanding operations of the reciprocating free-piston internal combustion engines to generate electric power responsive to the electrical power demands comprises a power management strategy including commanding individual operation of each of the reciprocating free-piston internal combustion engines in one of the engine-on state and an engine-off state during operation of the hybrid powertrain system.

18. The hybrid powertrain system of claim 17 , wherein the individual operation of each of the reciprocating free-piston internal combustion engines includes individual operation in the engine-on state at the rated output powers.

19. The hybrid powertrain system of claim 17 , wherein the individual operation of each of the reciprocating free-piston internal combustion engines includes individual operation in the engine-on state at the resonant speed and at the rated output power.