Power generation device and automobile

1. A power generation device, comprising:

a piston engine including a first piston, a second piston, a cylinder, a first crankshaft, and a second crankshaft, the first piston and the second piston reciprocating in the cylinder while facing each other, so that the first crankshaft rotates in a first rotation direction in accordance with the first piston and the second crankshaft rotates in a second rotation direction opposite to the first rotation direction in accordance with the second piston;

primary inertia bodies at least one of which is coaxially coupled to the first crankshaft and at least one of which is coaxially coupled to the second crankshaft; and

a secondary inertia body which is connected to each of the primary inertia bodies via a corresponding one of power transmission sections and rotates in conjunction with the primary inertia bodies at a speed increased at a basic step-up ratio of the power transmission sections,

the secondary inertia body including at least a power generator,

a total inertia moment is a sum of an inertia moment of the at least one of the primary inertia bodies and a product of an inertia moment of the secondary inertia body and the basic step-up ratio,

a total inertia moment in the first rotation direction and a total inertia moment in the second rotation direction being balanced with each other by not less than 50%.

2. The power generation device as set forth in claim 1 , wherein:

the primary inertia bodies include a first primary inertia body coupled to the first crankshaft and a second primary inertia body coupled to the second crankshaft;

the secondary inertia body includes a first power generator and a second power generator which are provided so as to be adjacent to each other;

the power transmission sections include a first power transmission section and a second power transmission section;

the first power generator is connected to the first primary inertia body via the first power transmission section and rotates in the first rotation direction, and the second power generator is connected to the second primary inertia body via the second power transmission section and rotates in the second rotation direction;

the first power generator includes a rotation shaft to which a first interlocking member is attached, and the second power generator includes a rotation shaft to which a second interlocking member is attached; and

the first interlocking member and the second interlocking member engage with each other so that the first power generator and the second power generator rotate in opposite rotation directions to each other.

3. The power generation device as set forth in claim 2 , wherein the first interlocking member and the second interlocking member which cause the first power generator and the second power generator to operate in conjunction with each other are each an anti-backlash gear.

4. The power generation device as set forth in claim 2 , wherein:

the first power transmission section includes a first power receiving section which is attached to the rotation shaft of the first power generator and receives power transmitted from the first crankshaft;

the rotation shaft of the first power generator is provided with a phase variable member which causes a phase angle of the first interlocking member and a phase angle of the first power receiving section to change relative to each other; and

a phase relationship between the first crankshaft and the second crankshaft is variable.

5. The power generation device as set forth in claim 2 , wherein:

the secondary inertia body further includes a mechanical supercharger;

the power transmission sections further include a third power transmission section;

the mechanical supercharger is connected to the second primary inertia body via the third power transmission section and rotates in the second rotation direction in conjunction with the second primary inertia body at a speed increased at a third step-up ratio of the third power transmission section;

the second power transmission section has a second step-up ratio smaller than a first step-up ratio of the first power transmission section; and

the first interlocking member and the second interlocking member have respective rotational speeds which are adjusted on the basis of the first step-up ratio and the second step-up ratio so that a rotational speed of the first power generator and a rotational speed of the second power generator are synchronized with each other.

6. The power generation device as set forth in claim 1 , wherein:

the primary inertia bodies include a first primary inertia body coupled to the first crankshaft and a second primary inertia body coupled to the second crankshaft;

the secondary inertia body includes a first power generator and a mechanical supercharger;

the power transmission sections include a first power transmission section, a second power transmission section, and a third power transmission section;

the first power generator is connected to the first primary inertia body via the first power transmission section and to the second primary inertia body via the second power transmission section and rotates in the second rotation direction at a speed increased at a first step-up ratio of the first power transmission section and at a second step-up ratio of the second power transmission section, the second step-up ratio being identical to the first step-up ratio; and

the mechanical supercharger is connected to the first primary inertia body via the third power transmission section and rotates in the first rotation direction in conjunction with the first primary inertia body at a speed increased at a third step-up ratio of the third power transmission section.

7. The power generation device as set forth in claim 6 , wherein:

the first primary inertia body has an inertia moment greater than that of the second primary inertia body; and

a product of the inertia moment of the first power generator and the first step-up ratio or the second step-up ratio is greater than a product of an inertia moment of the mechanical supercharger and the third step-up ratio.

8. An automobile in which a power generation device recited in claim 1 is provided, wherein

the power generation device is arranged such that:

a main body part of the piston engine is provided in a position closer to a front side of the automobile than an axis of a front wheel of the automobile or a position closer to a rear side of the automobile than an axis of a rear wheel of the automobile; and

(i) a rotation axis of the first crankshaft and a rotation axis of the second crankshaft each extend in a direction parallel to an entire length of the automobile and (ii) the power generator is provided on a side of the power generation device which side faces a center of the automobile.