System and method for controlling mild hybrid vehicle

1. A method for controlling a mild hybrid vehicle, comprising:

determining, by a controller, whether a first battery that supplies an electric power to a starter-generator of the mild hybrid vehicle is degraded; and

operating, by the controller, the starter-generator and a starter that receives an electric power from a second battery that stores a voltage less than a voltage of the first battery to start an engine within the vehicle when the first battery is degraded and an ambient air temperature of the engine exceeds a temperature reference value.

2. The method of claim 1 , wherein the determining of whether the first battery is degraded includes:

determining, by the controller, whether the mild hybrid vehicle satisfies a regenerative braking condition;

calculating, by the controller, a regenerative braking allowable amount based on a state of charge of the first battery when the regenerative braking condition is satisfied;

operating, by the controller, the starter-generator based on the regenerative braking allowable amount to charge the first battery;

determining, by the controller, whether a difference value between a target state of charge increase amount of the first battery that corresponds to the regenerative braking allowable amount and an actual state of charge increase amount of the first battery exceeds a difference reference value; and

determining, by the controller, that the first battery is degraded when the difference value exceeds the difference reference value.

3. The method of claim 2 , further comprising:

determining, by the controller, whether the regenerative braking condition is satisfied based on a speed of the mild hybrid vehicle, a position value of an accelerator pedal of the mild hybrid vehicle, and a position value of a brake pedal of the mild hybrid vehicle.

4. The method of claim 1 , further comprising:

determining, by the controller, whether the ambient air temperature of the engine exceeds the temperature reference value; and

operating, by the controller, the starter to start the engine in response to determining that the ambient air temperature of the engine is equal to or less than the temperature reference value.

5. The method of claim 1 , wherein the operating the starter-generator and the starter includes:

operating, by the controller, the starter-generator to rotate a crankshaft of the engine to move a piston of the engine to a top dead center of the engine; and

operating, by the controller, the starter-generator and the starter to start the engine after the piston of the engine is moved to the top dead center of the engine.

6. The method of claim 5 , wherein the starter-generator is connected to the crankshaft via a belt.

7. The method of claim 5 , wherein a drive shaft of the starter is connected to the crankshaft.

8. The method of claim 1 , further comprising:

operating, by the controller, a relay of the mild hybrid vehicle to apply a current greater than a current reference value to the starter to operate the starter to start the engine in response to determining that the first battery is degraded and the ambient air temperature of the engine is equal to or less than the temperature reference value.

9. A system for controlling a mild hybrid vehicle, comprising:

a memory configured to store program instructions; and

a processor configured to execute the program instructions, the program instructions when executed configured to:

determine whether a first battery that supplies an electric power to a starter-generator of the mild hybrid vehicle is degraded; and

operate the starter-generator and a starter that receives an electric power from a second battery that stores a voltage less than a voltage of the first battery to start an engine within the vehicle when the first battery is degraded and an ambient air temperature of the engine exceeds a temperature reference value.

10. The system of claim 9 , wherein the controller in determining whether the first battery is degraded is further configured to:

determine whether the mild hybrid vehicle satisfies a regenerative braking condition;

calculate a regenerative braking allowable amount based on a state of charge of the first battery when the regenerative braking condition is satisfied;

operate the starter-generator based on the regenerative braking allowable amount to charge the first battery;

determine whether a difference value between a target state of charge increase amount of the first battery that corresponds to the regenerative braking allowable amount and an actual state of charge increase amount of the first battery exceeds a difference reference value; and

determine that the first battery is degraded when the difference value exceeds the difference reference value.

11. The system of claim 10 , wherein the controller is further configured to:

determine whether the regenerative braking condition is satisfied based on a speed of the mild hybrid vehicle, a position value of an accelerator pedal of the mild hybrid vehicle, and a position value of a brake pedal of the mild hybrid vehicle.

12. The system of claim 9 , wherein the controller is further configured to:

determine whether the ambient air temperature of the engine exceeds the temperature reference value; and

operate the starter to start the engine in response to determining that the ambient air temperature of the engine is equal to or less than the temperature reference value.

13. The system of claim 9 wherein the controller in operating the starter-generator and the starter is further configured to:

operate the starter-generator to rotate a crankshaft of the engine to move a piston of the engine to a top dead center of the engine; and

operate the starter-generator and the starter to start the engine after the piston of the engine is moved to the top dead center of the engine.

14. The system of claim 13 , wherein the starter-generator is connected to the crankshaft via a belt.

15. The system of claim 13 , wherein a drive shaft of the starter is connected to the crankshaft.

16. The system of claim 9 , wherein the controller is further configured to:

operate a relay of the mild hybrid vehicle to apply a current greater than a current reference value to the starter to operate the starter to start the engine in response to determining that the first battery is degraded and the ambient air temperature of the engine is equal to or less than the temperature reference value.