Magnetic generator

A magnetic generator, or a so-called inner-rotor generator, provided with a rotor on the inside of a stator. The rotor has a ring-shaped yoke and a magnet integrally mounted in advance to the outer circumferential surface of the yoke. The rotor is mounted to a hub spindle of a rotating body.

FIELD OF THE INVENTION

The present invention relates to a magnetic generator provided with a magnet-equipped rotor on the inside of a coil-equipped stator and, more particularly, to a small generator for a general-purpose engine.

BACKGROUND OF THE INVENTION

General-purpose engines are predominantly gasoline engines having a spark plug. A generator is provided to a general-purpose engine due to a need to supply power to a spark plug and other electrical components. Since general-purpose engines are generally small, small generators are also used, as described in Japanese Patent Application Laid-Open Publication No. 2007-6594 (JP 2007-6594 A).

FIG. 5hereof shows a generator disclosed in JP 2007-6594 A. A generator100has a stator provided with a coil102, and a rotor provided with a magnet101which rotates relative to the stator. A flywheel104is mounted to an end of a crankshaft103. The flywheel104has a hub spindle105fitted to the tapered part of the crankshaft103, a disk part106extended radially outward from the hub spindle105, and an outer-mass part107formed integrally with the outer circumference of the disk part106. Since the outer-mass part107has a large mass and is distant from the center (rotational center) of the crankshaft103, the moment of inertia (the moment of inertia is proportional to mass×distance2) is also large, and the flywheel effect is considerable.

The magnet101is provided to the outer-mass part107. For this reason, the magnet101is a ring magnet having a large diameter. The magnet101is mounted to the outer-mass part107by holders108,108.

A disk-shaped iron core111wrapped in the coil102is secured to a crankcase113by bolts112,112.

When the crankshaft103rotates, electrical generation begins because the magnet101rotates relative to the coil102.

The magnet101must be fitted to the outer-mass part107and held in place by the holders108on both sides. The holders108are needed to prevent the magnet101from being separated from the outer-mass part107by vibration. However, the magnet101is fitted to the outer-mass part107and the holder108is then mounted, making it more complex to mount the magnet. A complex mounting process results in a greater number of assembly steps and is undesirable. In view of this, a simplified process for mounting the magnet is needed.

The magnet101has a large diameter, and hence a greater mass, making the magnetic generator100large and heavy. Considering that the generator is attached to a small general-purpose engine, a reduction in the size and weight of the generator is sought.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a small and lightweight generator in which a magnet can be easily mounted.

According to the present invention, there is provided a magnetic generator which comprises: a rotor having a rotary ring-shaped yoke and a magnet integrally mounted to an outer circumferential surface of the yoke; and a stator having a coil spaced a predetermined distance outwardly from an outer circumferential surface of the magnet.

The magnet is thus integrally formed with the yoke in advance in accordance with the present invention. The yoke can be easily secured to a rotating body such as a flywheel. For this reason, the magnet is very easy to mount. Also, the magnet is enclosed in a coil. In other words, the magnet has a small diameter since the rotor is disposed on the inside of the stator, and the main part of the rotor is the magnet. The magnet is therefore small and lightweight. It is thus possible to provide a small and lightweight magnetic generator in which a magnet can be easily mounted.

In a preferred form the generator is designed for use with a general-purpose engine while the yoke is mounted to a hub spindle of a flywheel mounted to a crankshaft. The coil may be mounted to a crankcase. The flywheel has a large outside diameter, but the hub spindle has a small diameter. Since the yoke is mounted to such a small-diameter hub spindle, the magnetic generator is small. A general-purpose engine provided with such a small magnetic generator can easily be made small and lightweight.

Preferably, the yoke has a ring-shaped flange mounted to an inner circumferential surface thereof, and the rotor is designed to be mounting to the hub spindle of the rotating body via the flange. Mounting the rotor to the rotating body is therefore simplified.

Desirably, the hub spindle has a stepped part on an end face thereof while the rotor is fitted into the stepped part of the hub spindle through a central hole formed in the flange. The movement of the rotor in a radial direction is therefore reduced by the stepped part, and the rotor can be stably mounted to the hub spindle.

The magnet may be integrally mounted in advance to an outer circumferential surface of the yoke by an adhesive. Mounting the rotor to the hub spindle is therefore simplified.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A stepped part27corresponding to a central hole26of the flange22is formed on a hub spindle25of a flywheel (rotating body)24.

The flange22is placed against the hub spindle25by fitting the stepped part27into the central hole26. Bolts29,29are subsequently passed through bolt holes28,28of the flange22and are threaded into threaded parts31,31provided in the hub spindle25of the flywheel24, making it possible to easily mount the magnet23to the rotating body that is the flywheel24.

Since the stepped part27is formed by machining, the diameter of the stepped part27can be finished with high precision. The central hole26of the flange22is also finished with high precision by machining. Merely fitting the flange22to the stepped part27allows the rotor20to be accurately assembled to the flywheel24.

Since the flange22is fitted to the stepped part27, the flange22is stably retained on the stepped part27even when a centrifugal force is applied to the rotor20, and there is no concern that the rotor20will move in a radial direction. As a result, a constant spacing can be maintained between the outer circumferential surface of the magnet23and the inner circumferential surface of an iron core41, and power can be generated as required.

The magnet23can be obtained, for example, by shaping a mixture of about 50 mass % of a magnetic powder and a solvent with about 50 mass % of a resin powder in a mold, drying the mixture, and subjecting the dried mixture to magnetic orientation, sintering, and magnetization. The magnetization process involves alternately aligning the north and south poles. Any method can be used to manufacture the magnet23, and a magnet manufactured by a commonly known method can be used.

The stator40has a toroidal iron core41composed by layering a plurality of thin silicon steel sheets, a bobbin42mounted to hold in the iron core41, coils43,43tightly wrapped to the bobbin42, and pipes44,44mounted through the iron core41. The stator40is secured to a crankcase46, which is a stationary body, by passing bolts45,45through the pipes44,44and threading the bolts into threaded parts47,47provided to the crankcase46.

In the coil43, twelve coils (eight large coils43L and four small coils43S) are aligned at a regular pitch so as to enclose the magnet23shown by the imaginary line inFIG. 2. The iron core41is secured by the four bolts45. The magnet23enclosed by such an iron core41is sufficiently small.

As shown inFIG. 3, the flywheel24has a disk part32extended radially outward from the central hub spindle25, and an outer-mass part33integrally formed with the outer circumference of the disk part32. Since the outer-mass part33has a large mass and is distant from the rotational center34, the moment of inertia is also large and the flywheel effect is considerable.

The rotor20is secured by two bolts29,29to the central hub spindle25. The magnet23and the yoke21, which are the main components of the rotor20, are rings disposed so as to enclose the rotational center34.

Referring toFIG. 4, a crankshaft53is rotatably supported in a crankcase46via a bearing51and a sealant52in a general-purpose engine50, and an end of such a crankshaft53protrudes from the crankcase46.

Before the flywheel24is mounted to the crankshaft53, the stator40is secured to the crankcase46by bolts45,45. Also, the rotor20is secured to the flywheel24in advance by the bolts29,29.

As an essential step in fitting a taper shaft54to a taper hole55of the hub spindle25, the flywheel24is mounted to the taper shaft54. The flywheel24is then secured to the crankshaft53using a key56, a washer57, and a nut58. A general-purpose engine50provided with a magnetic generator10such as the one shown in the drawing can thereby be obtained.

The flywheel24has a large outside diameter, but the hub spindle25has a small diameter. Since the yoke21is mounted to such a small-diameter hub spindle25, the magnetic generator10is small. A general-purpose engine50provided with such a small magnetic generator10can easily be made smaller and more lightweight.

The magnet23is integrally formed with the yoke21in advance in the unit of the magnetic generator10as well. The yoke21can be easily secured to a rotating body such as the flywheel24. For this reason, the magnet23is very easy to mount. The magnet23is enclosed in the coil43. Specifically, the coil43is disposed outside of the outer circumferential surface of the magnet23with a predetermined spacing. In other words, the magnet23has a small diameter since the rotor20is disposed on the inside of the stator40, and the main part of the rotor20is the magnet23. The magnet23is therefore small and lightweight.

The magnetic generator of the present invention is suitable for a small general-purpose engine but can also be used in engines for vehicles or industrial machinery, and the application of the generator can be chosen freely.

In the embodiment, the magnet-supporting yoke was mounted to the hub spindle of the flywheel using a flange and bolts, but since the yoke can be mounted to the hub spindle by press fitting, riveting, or bonding, any method can be used to mount the yoke.

Further, the flywheel was the object on which the yoke was mounted, but as long as the yoke is mounted to a rotating body, any rotating body can be used.