Electric vehicle (EV) driving mode optimization for a parallel hybrid electric vehicle

1. A method of operating a hybrid electric drive train, the drive train comprising an electric motor and an internal combustion engine, each capable of propelling a vehicle, the method comprising:

providing a manually selectable first mode, wherein the first mode includes an electric mode; and

after the first mode is selected, operating in the first mode, including:

detecting a battery state of charge;

comparing the battery state of charge to a threshold;

if the battery state of charge exceeds the threshold, entering the electric mode, the electric mode comprising:

propelling the vehicle using only the electric motor;

limiting an allowed vehicle acceleration to below a predetermined acceleration value; and

preventing an engine start; and

providing an override option, wherein the override option allows for starting the engine while otherwise maintaining operation in the electric mode, where maintaining operation in the electric mode includes not using the engine to propel the vehicle.

2. The method of claim 1 , wherein the first mode further includes increasing an amount of charge in a battery portion beyond a hybrid mode charging limit prior to the propelling the vehicle using only the electric motor, where the hybrid mode charging limit is an amount of charge above which the battery portion is not charged during operation in a hybrid mode.

3. The method of claim 2 , wherein increasing the amount of charge includes operating the internal combustion engine to drive the electric motor and operating the electric motor as a generator to charge the battery portion.

4. The method of claim 3 , wherein operating in the first mode further comprises notifying when a state of charge is below a first predetermined value.

5. The method of claim 4 , wherein when a battery state of charge is below a second predetermined value lower than the first predetermined value, operation in the electric mode is ceased, except that if the override option has been selected, operation in the electric mode is not ceased when the battery state of charge is below the second predetermined value and the engine is started and not allowed to propel the vehicle or to charge the battery.

6. The method of claim 5 , further comprising preventing a discharging of the battery below an approximately forty percent state of charge while in a hybrid mode, wherein the engine will automatically start to charge the battery during operation in the hybrid mode, and wherein the second predetermined value is less than or equal to thirty percent state of charge.

7. The method of claim 1 , wherein operating in the first mode further comprises notifying a user of an estimated vehicle availability value, the vehicle availability value including at least one of: a distance available for operation in electric mode, and a time remaining in electric mode.

8. The method of claim 1 , wherein the predetermined acceleration value may be selectively adjusted during operation in electric mode.

9. The method of claim 1 , wherein operating in the first mode further comprises at least partially recharging a battery portion with a regenerative brake.

10. The method of claim 1 , wherein detecting the battery state of charge includes estimating available battery power based upon an estimated discharge rate and battery state of charge.

11. A method of operating a hybrid electric drive train comprising:

receiving an indication of a manual selection of a first mode, wherein the first mode includes an electric mode that includes propelling a vehicle using only an electric motor; and

after receiving the indication:

comparing a battery state of charge to a threshold, and if the battery state of charge exceeds the threshold:

propelling the vehicle in the electric mode; and

preventing an engine start during operation in the electric mode while propelling the vehicle using only the electric motor; and

providing an option for a user override, wherein the user override allows an engine start while otherwise maintaining operation in the electric mode, where maintaining operation in the electric mode includes not using the engine to propel the vehicle.

12. The method of claim 11 , further comprising, when a user override option has been selected, preventing the engine from exceeding a rotational speed of approximately one-thousand revolutions per minute.

13. The method of claim 11 , further comprising preventing a discharge of a battery below an approximately forty percent state of charge while in a hybrid mode, wherein the engine will automatically start to charge the battery during operation in the hybrid mode.

14. The method of claim 11 , further comprising, when operating in the electric mode, limiting an allowed vehicle acceleration below a predetermined acceleration value wherein the predetermined acceleration value is less than a maximum acceleration value attainable by the vehicle and limiting the allowed vehicle acceleration does not require limiting a vehicle speed or load.

15. The method of claim 14 , wherein limiting the allowed acceleration includes limiting the rotational speed of the motor when in the electric only mode to a value below a speed permitted in a hybrid mode, wherein the electric motor and the engine are permitted to propel the vehicle during the hybrid mode.

16. The method of claim 11 , further comprising notifying the user of an estimated vehicle availability value, wherein the vehicle availability value includes at least one of: distance available for operation in electric mode, and time remaining in electric mode.

17. The method of claim 11 , wherein the first mode further includes increasing an amount of charge in a battery portion beyond a hybrid mode charging limit prior to the propelling the vehicle using only the electric motor, where the hybrid mode charging limit is an amount of charge above which the battery portion is not charged during operation in a hybrid mode.

18. The method of claim 17 , wherein increasing the amount of charge includes operating an internal combustion engine to drive the electric motor and operating the electric motor as a generator to charge the battery portion.

19. The method of claim 18 , further comprising, when operating in the first mode, notifying the user when a state of charge is below a first predetermined value.

20. The method of claim 19 , further comprising shutting down the motor when a state of charge of the battery portion is below a second predetermined value lower than the first predetermined value.

21. The method of claim 1 , further comprising notifying a user of a maximum acceleration rate available in electric mode.

22. The method of claim 11 , further comprising notifying the user of a maximum acceleration rate available in electric mode.