Method and apparatus for controlling operation of an internal combustion engine for a multi-mode powertrain system

1. A method for controlling a powertrain system including an internal combustion engine and electric machines operative to transfer mechanical power through a gear train to an output member coupled to a driveline, wherein the electric machines electrically connect to a battery, the method comprising:

determining an audible noise-based maximum engine speed, wherein the engine generates an audible noise that is less than a threshold noise level when operating at a speed that is less than the audible noise-based maximum engine speed; and

controlling the electric machines and the engine responsive to an operator torque request including controlling the engine speed to be less than the audible noise-based maximum engine speed when battery power is greater than a minimum threshold, wherein controlling the engine speed to be less than the audible noise-based maximum engine speed when the battery power is greater than a minimum threshold comprises:

determining an input speed range between an idle speed and a maximum speed from the engine,

determining an engine torque range based upon the operator torque request and the battery power,

selecting a plurality of candidate input speeds within the input speed range,

selecting a plurality of candidate engine torques within the engine torque range,

executing a system torque determination scheme to determine preferred motor torque commands for the electric machines and an output torque when operating the powertrain system responsive to the operator torque request with the engine operating at each of the candidate input speeds and each of the candidate engine torques,

executing a cost model to determine a candidate cost for operating the powertrain system with the engine operating at each of the candidate input speeds and at each of the candidate engine torques and the electric machines operating at the corresponding preferred motor torque commands,

identifying, as a preferred input speed and a preferred engine torque, one of the candidate input speeds and one of candidate engine torques that achieve a minimum of the candidate costs and is responsive to the operator torque request, and

controlling the engine responsive to the preferred input speed and the preferred engine torque.

2. The method of claim 1 , wherein controlling the electric machines and the engine responsive to an operator torque request comprises controlling torque outputs from the electric machines and the engine responsive to the operator torque request.

3. The method of claim 1 , wherein executing the cost model to determine a candidate cost for operating the powertrain system with the engine operating at each of the candidate input speeds and at each of the candidate engine torques and the electric machines operating at the corresponding preferred motor torque commands comprises:

determining a cost associated with NVH (noise-vibration-harshness) for the candidate input speed; and

determining the candidate cost based upon the cost associated with NVH.

4. The method of claim 3 , wherein determining the cost associated with NVH for the candidate input speed comprises assigning zero cost associated with NVH when the candidate input speed is less than the audible noise-based maximum engine speed.

5. The method of claim 3 , wherein determining the cost associated with NVH for the candidate input speed comprises assigning an increasing cost associated with NVH when the candidate input speed is greater than the audible noise-based maximum engine speed.

6. The method of claim 1 , wherein executing the cost model to determine a candidate cost for operating the powertrain system with the engine operating at each of the candidate input speeds and at each of the candidate engine torques and the electric machines operating at the corresponding preferred motor torque commands comprises:

determining costs associated with hardware limits, output torque, a battery state of charge, efficiency and NVH for operating the powertrain system with the engine operating at each of the candidate input speeds and at each of the candidate engine torques and the electric machines operating at the corresponding preferred motor torque commands;

assigning weighting factors to each of the hardware limits, output torque, battery state of charge, efficiency and NVH; and

determining the candidate cost by combining the costs associated with hardware limits, output torque, battery state of charge, efficiency and NVH with the corresponding assigned weighting factor.

7. The method of claim 6 , wherein the weighting factor for NVH is assigned a high priority ranking when the battery power is greater than the minimum threshold.

8. The method of claim 6 , wherein the weighting factor for NVH is assigned a low priority ranking when the battery power is less than the minimum threshold.

9. The method of claim 1 , wherein the audible noise-based maximum engine speed comprises an engine speed at which generated engine noise is masked by an expected road noise generated by the driveline.

10. A method for controlling a powertrain system including an internal combustion engine, first and second electric machines, a gear train, and a battery supplying electric power to the first and second electric machines, the powertrain system operative to transfer mechanical power generated by one of the first and second electric machines through the gear train to an output member, the method comprising:

determining an audible noise-based maximum engine speed, wherein the engine generates an audible noise that is less than a threshold noise level when operating at a speed that is less than the audible noise-based maximum engine speed; and

controlling the engine speed to be less than the audible noise-based maximum engine speed when the electric power supplied from the battery to the first and second electric machines is greater than a minimum threshold, including:

determining an input speed range between an idle speed and a maximum speed from the engine,

determining an engine torque range based upon the operator torque request and the battery power,

selecting a plurality of candidate input speeds within the input speed range,

selecting a plurality of candidate engine torques within the engine torque range,

executing a system torque determination scheme to determine preferred motor torque commands for the electric machines and an output torque when operating the powertrain system responsive to the operator torque request with the engine operating at each of the candidate input speeds and each of the candidate engine torques,

executing a cost model to determine a candidate cost for operating the powertrain system with the engine operating at each of the candidate input speeds and at each of the candidate engine torques and the electric machines operating at the corresponding preferred motor torque commands,

identifying, as a preferred input speed and a preferred engine torque, one of the candidate input speeds and one of candidate engine torques that achieve a minimum of the candidate costs and is responsive to the operator torque request, and

controlling the engine responsive to the preferred input speed and the preferred engine torque.

11. The method of claim 10 , wherein executing the cost model to determine a candidate cost for operating the powertrain system with the engine operating at each of the candidate input speeds and at each of the candidate engine torques and the electric machines operating at the corresponding preferred motor torque commands comprises:

determining a cost associated with NVH (noise-vibration-harshness) for the candidate input speed; and

determining the candidate cost based upon the cost associated with NVH.

12. The method of claim 11 , wherein determining the cost associated with NVH for the candidate input speed comprises assigning zero cost associated with NVH when the candidate input speed is less than the audible noise-based maximum engine speed.

13. The method of claim 11 , wherein determining the cost associated with NVH for the candidate input speed comprises assigning an increasing cost associated with NVH when the candidate input speed is greater than the audible noise-based maximum engine speed.

14. The method of claim 10 , wherein executing the cost model to determine a candidate cost for operating the powertrain system with the engine operating at each of the candidate input speeds and at each of the candidate engine torques and the electric machines operating at the corresponding preferred motor torque commands comprises:

determining costs associated with hardware limits, output torque, a battery state of charge, efficiency and NVH for operating the powertrain system with the engine operating at each of the candidate input speeds and at each of the candidate engine torques and the electric machines operating at the corresponding preferred motor torque commands;

assigning weighting factors to each of the hardware limits, output torque, battery state of charge, efficiency and NVH; and

determining the candidate cost by combining the costs associated with hardware limits, output torque, battery state of charge, efficiency and NVH with the corresponding assigned weighting factor.

15. The method of claim 14 , wherein the weighting factor for NVH is assigned a high priority ranking when the battery power is greater than the minimum threshold.

16. The method of claim 14 , wherein the weighting factor for NVH is assigned a low priority ranking when the battery power is less than the minimum threshold.

17. The method of claim 10 , wherein the audible noise-based maximum engine speed comprises an engine speed at which generated engine noise is masked by an expected road noise generated by the driveline.

18. A powertrain system for a vehicle, comprising:

an internal combustion engine and first and second electric machines mechanically coupled to a gear train, wherein the gear train is coupled to a driveline of the vehicle;

a battery electrically connected to the first and second electric machines,

a controller operatively connected to the internal combustion engine and the first and second electric machines, the controller including an instruction set, the instruction set executable to:

determine an audible noise-based maximum engine speed, wherein the engine generates an audible noise that is less than a threshold noise level when operating at a speed that is less than the audible noise-based maximum engine speed, and

control the electric machines and the engine responsive to an operator torque request including controlling the engine speed to be less than the audible noise-based maximum engine speed when battery power is greater than a minimum threshold, which includes an instruction set executable to:

determine an input speed range between an idle speed and a maximum speed from the engine,

determine an engine torque range based upon the operator torque request and the battery power,

select a plurality of candidate input speeds within the input speed range,

select a plurality of candidate engine torques within the engine torque range,

execute a system torque determination scheme to determine preferred motor torque commands for the electric machines and an output torque when operating the powertrain system responsive to the operator torque request with the engine operating at each of the candidate input speeds and each of the candidate engine torques,

execute a cost model to determine a candidate cost for operating the powertrain system with the engine operating at each of the candidate input speeds and at each of the candidate engine torques and the electric machines operating at the corresponding preferred motor torque commands,

identify, as a preferred input speed and a preferred engine torque, one of the candidate input speeds and one of candidate engine torques that achieve a minimum of the candidate costs and is responsive to the operator torque request, and

control the engine responsive to the preferred input speed and the preferred engine torque.