Engine start control device

1. An engine start control device that includes a motor and starts an engine using the motor in response to a start request, the motor being connectable to an engine output shaft and having power driving function, the engine start control device comprising:

an pass determination section that performs a pass determination process of determining, based on a rotation state of the engine output shaft, whether a piston in a cylinder of the engine can pass over a compression top dead center for a rotation drop period in response to an occurrence of the start request, the rotation drop period being a period until an engine rotational speed drops to zero after combustion of the engine is stopped;

a start control section that when it is determined that the piston cannot pass over the compression top dead center, starts driving of the motor in a low reaction force period to start the engine, the low reaction force period being a period in which a reaction force applied to the piston by a cylinder internal pressure in the cylinder is a predetermined value or less; and

a setting section that when it is determined that the piston cannot pass over the compression top dead center, sets a waiting time from a time point at the occurrence of the start request to a time point at which the low reaction force period will start, wherein

the start control section starts driving of the motor when the waiting time has elapsed.

2. The engine start control device according to claim 1 , wherein the setting section sets the waiting time on the basis of an engine rotational speed at the time point at the occurrence of the start request.

3. An engine start control device that includes a motor and starts an engine using the motor in response to a start request, the motor being connectable to an engine output shaft and having power driving function, the engine start control device comprising:

an pass determination section that performs a pass determination process of determining, based on a rotation state of the engine output shaft, whether a piston in a cylinder of the engine can pass over a compression top dead center for a rotation drop period in response to an occurrence of the start request, the rotation drop period being a period until an engine rotational speed drops to zero after combustion of the engine is stopped;

a start control section that when it is determined that the piston cannot pass over the compression top dead center, starts driving of the motor in a low reaction force period to start the engine, the low reaction force period being a period in which a reaction force applied to the piston by a cylinder internal pressure in the cylinder is a predetermined value or less; and

a period determination section that after it is determined that the piston cannot pass over the compression top dead center, acquires a rotational position of the engine output shaft and an engine rotational speed and determines, on the basis of the acquired rotational position of the engine output shaft and the acquired engine rotational speed, whether a current time is in the low reaction force period.

4. The engine start control device according to claim 1 , further comprising a rotation determination section that determines whether the engine output shaft is reversely rotating, wherein

when it is determined that the engine output shaft is reversely rotating, the start control section determines that a current time is in the low reaction force period, and starts driving of the motor.

5. An engine start control device that includes a motor and starts an engine using the motor in response to a start request, the motor being connectable to an engine output shaft and having power driving function, the engine start control device comprising:

an pass determination section that performs a pass determination process of determining, based on a rotation state of the engine output shaft, whether a piston in a cylinder of the engine can pass over a compression top dead center for a rotation drop period in response to an occurrence of the start request, the rotation drop period being a period until an engine rotational speed drops to zero after combustion of the engine is stopped;

a start control section that when it is determined that the piston cannot pass over the compression top dead center, starts driving of the motor in a low reaction force period to start the engine, the low reaction force period being a period in which a reaction force applied to the piston by a cylinder internal pressure in the cylinder is a predetermined value or less; and

a rotation determination section that determines whether the engine output shaft is reversely rotating, wherein

when it is determined that the engine output shaft is reversely rotating, the start control section determines that a current time is in the low reaction force period, and starts driving of the motor.

6. The engine start control device according to claim 1 , further comprising:

a storage section that stores a history of an engine rotational speed in the rotation drop period; and

a stop estimation section that estimates the engine rotational speed on the basis of the history of the engine rotational speed stored in the storage section, wherein

the pass determination section performs the pass determination process on the basis of the estimation by the stop estimation section.

7. An engine start control device that includes a motor and starts an engine using the motor in response to a start request, the motor being connectable to an engine output shaft and having power driving function, the engine start control device comprising:

an pass determination section that performs a pass determination process of determining, based on a rotation state of the engine output shaft, whether a piston in a cylinder of the engine can pass over a compression top dead center for a rotation drop period in response to an occurrence of the start request, the rotation drop period being a period until an engine rotational speed drops to zero after combustion of the engine is stopped;

a start control section that when it is determined that the piston cannot pass over the compression top dead center, starts driving of the motor in a low reaction force period to start the engine, the low reaction force period being a period in which a reaction force applied to the piston by a cylinder internal pressure in the cylinder is a predetermined value or less; and

a storage section that stores a history of an engine rotational speed in the rotation drop period; and

a stop estimation section that estimates the engine rotational speed on the basis of the history of the engine rotational speed stored in the storage section, wherein

the pass determination section performs the pass determination process on the basis of the estimation by the stop estimation section.

8. The engine start control device according to claim 1 , further comprising a temperature information acquisition section that acquires temperature information on at least one of the engine and the motor, wherein

the low reaction force period is corrected on the basis of the temperature information acquired by the temperature information acquisition section.

9. An engine start control device that includes a motor and starts an engine using the motor in response to a start request, the motor being connectable to an engine output shaft and having power driving function, the engine start control device comprising:

an pass determination section that performs a pass determination process of determining, based on a rotation state of the engine output shaft, whether a piston in a cylinder of the engine can pass over a compression top dead center for a rotation drop period in response to an occurrence of the start request, the rotation drop period being a period until an engine rotational speed drops to zero after combustion of the engine is stopped;

a start control section that when it is determined that the piston cannot pass over the compression top dead center, starts driving of the motor in a low reaction force period to start the engine, the low reaction force period being a period in which a reaction force applied to the piston by a cylinder internal pressure in the cylinder is a predetermined value or less; and

a temperature information acquisition section that acquires temperature information on at least one of the engine and the motor, wherein

the low reaction force period is corrected on the basis of the temperature information acquired by the temperature information acquisition section.

10. The engine start control device according to claim 1 , further comprising a remaining battery amount acquisition section that acquires a remaining battery amount of a battery that supplies electric power to the motor, wherein

the low reaction force period is corrected on the basis of the remaining battery amount acquired by the remaining battery amount acquisition section.

11. An engine start control device that includes a motor and starts an engine using the motor in response to a start request, the motor being connectable to an engine output shaft and having power driving function, the engine start control device comprising:

an pass determination section that performs a pass determination process of determining, based on a rotation state of the engine output shaft, whether a piston in a cylinder of the engine can pass over a compression top dead center for a rotation drop period in response to an occurrence of the start request, the rotation drop period being a period until an engine rotational speed drops to zero after combustion of the engine is stopped;

a start control section that when it is determined that the piston cannot pass over the compression top dead center, starts driving of the motor in a low reaction force period to start the engine, the low reaction force period being a period in which a reaction force applied to the piston by a cylinder internal pressure in the cylinder is a predetermined value or less; and

a remaining battery amount acquisition section that acquires a remaining battery amount of a battery that supplies electric power to the motor, wherein

the low reaction force period is corrected on the basis of the remaining battery amount acquired by the remaining battery amount acquisition section.

12. The engine start control device according to claim 1 ,

wherein the start control section is configured to

drive the motor, before the low reaction force period, to apply a first output torque of the motor to the engine output shaft in a reverse rotational direction of the engine output shaft; and

drive the motor, during the low reaction force period, to apply a second output torque of the motor to the engine output shaft in a forward rotational direction of the engine output shaft.

13. The engine start control device according to claim 1 , further comprising a rotation determination section that determines whether the engine output shaft is reversely rotating, wherein

when it is determined that the engine output shaft is reversely rotating, after the engine output shaft is reversely rotated until a compression reaction force applied to the piston reaches a minimum value, the start control section starts driving of the motor.

14. The engine start control device according to claim 13 ,

wherein in a case where it is determined that the engine output shaft is reversely rotating, the start control section is configured to:

drive the motor, before the compression reaction force reaches the minimum value, to apply a third output torque of the motor to the engine output shaft in a reverse rotational direction of the engine output shaft; and

drive the motor, after the compression reaction force reaches the minimum value, to apply a fourth output torque of the motor to the engine output shaft in a forward rotational direction of the engine output shaft.

15. The engine start control device according to claim 1 , wherein the start control section applies a field current before the low reaction force period.

16. The engine start control device according to claim 1 , wherein the pass determination section performs the pass determination process on the basis of the rotation state of the engine output shaft and a torque capable of being outputted by the motor.