Permanent-magnet generator having protrusions for dissipating heat

1. A permanent-magnet generator comprising:

a flywheel having a ringlike portion and a bottom portion which closes off one end of the ringlike portion;

a plurality of magnets arranged on an inside surface of the ringlike portion of said flywheel;

a plurality of air passages formed in the bottom portion of said flywheel;

a plurality of protrusions bulging inward from the bottom portion of said flywheel; and

a coil disposed to face said magnets for generating electricity by virtue of electromagnetic induction caused by relative movement of said coil and said magnets;

wherein an irregular surface portion is formed in each of said protrusions, said irregular surface portion being configured so as to create a turbulent air flow when said flywheel rotates, said irregular surface portion being irregularly shaped along a circumferential direction of said flywheel, and

wherein the irregular surface portion of each of said protrusions comprises at least two steps on each side of said protrusions, in said circumferential direction of said flywheel, and

wherein each respective protrusion is located in between two respective adjacent air passages.

2. The permanent-magnet generator according to claim 1 , wherein a top surface of each of said protrusions slopes in a radial direction of said flywheel in such a way that the height of the top surface of each protrusion decreases from the outside to the inside of said flywheel.

3. The permanent-magnet generator according to claim 1 , wherein each of said protrusions is thickened at an outer end portion thereof where each protrusion connects to the ringlike portion of said flywheel.

4. The permanent-magnet generator according to claim 1 , wherein the irregular surface portion of each protrusion is situated against a conductor winding portion of said coil.

5. The permanent-magnet generator according to claim 1 , wherein said protrusions are formed of resin material.

6. The permanent-magnet generator according to claim 1 , wherein said protrusions constitute integral parts of a resin layer formed by filling resin material in areas around said plurality of magnets for fixing said magnets to said flywheel.

7. The permanent-magnet generator according to claim 1 , wherein said protrusions are formed as at least one discrete component which is fixed to said flywheel.

8. The permanent-magnet generator according to claim 1 , wherein each of said protrusions is formed of a base portion and at least one upper portion that is narrower in width than said base portion, in said circumferential direction of said flywheel, said at least one upper portion being substantially centered on said base portion, in said circumferential direction of said flywheel, such that said at least two steps are formed on each side of each of said protrusions.