Startup assistance device for internal combustion engine

1. A startup assistance device which assists startup of an internal combustion engine in which fuel is supplied from an electronically controlled fuel injection device and ignition is performed by an ignition device, comprising:

a recoil starter which is driven by manpower and performs cranking for starting up the internal combustion engine;

an electric rotary machine which applies torque to a crankshaft of the internal combustion engine during at least one of a startup period of the internal combustion engine using the recoil starter and a standby period before the startup period;

a power source unit which supplies power to the electric rotary machine; and

a control unit which controls the magnitude and time of the torque output by the electric rotary machine,

wherein the control unit sets a predetermined magnitude of the torque as a maximum torque when a temperature of stored fuel is equal to or lower than a threshold value.

2. The startup assistance device for the internal combustion engine according to claim 1 , wherein

the control unit controls the power source unit so that the electric rotary machine outputs top-output torque of the magnitude obtained by subtracting torque obtained by driving the recoil starter from torque required fora piston of the internal combustion engine to reach top dead center during the standby period.

3. The startup assistance device for the internal combustion engine according to claim 2 , wherein

the power source unit includes a capacitor and a converter unit which converts output voltage of the capacitor into a multi-phase AC voltage, and

the control unit stops output of the top-output torque by the electric rotary machine when a temperature of the power source unit exceeds a predetermined value.

4. The startup assistance device for the internal combustion engine according to claim 1 , wherein

the control unit controls the power source unit so that the electric rotary machine outputs the predetermined magnitude of torque for a predetermined time after the recoil starter is driven.

5. The startup assistance device for the internal combustion engine according to claim 4 , wherein

the predetermined magnitude of the torque is the same as the top-output torque.

6. The startup assistance device for the internal combustion engine according to claim 4 , wherein

the predetermined magnitude of the torque is the maximum torque that the electric rotary machine can output by receiving power from the power source unit.

7. The startup assistance device for the internal combustion engine according to claim 4 , wherein

the predetermined magnitude of the torque is less than the top-output torque.

8. The startup assistance device for the internal combustion engine according to claim 4 , wherein

the predetermined time is shorter as the output voltage of the power source unit is lower.

9. The startup assistance device for the internal combustion engine according to claim 1 , wherein

the internal combustion engine includes a fuel tank in which the stored fuel is contained and a temperature sensor which is provided in vicinity of the fuel tank and configured to detect the temperature of the stored fuel.

10. The startup assistance device for the internal combustion engine according to claim 1 , wherein

the maximum torque is of a magnitude that is the highest the electric rotary machine can output.

11. The startup assistance device for the internal combustion engine according to claim 1 , wherein

the magnitude of the torque output by the electric rotary machine is controlled by the control unit so as to provide a maximum assistance when the recoil starter is driven during a low temperature fuel condition.