Electricity: magnetically operated switches – magnets – and electr – Magnets and electromagnets – With magneto-mechanical motive device
Reexamination Certificate
2001-09-18
2004-06-29
Donovan, Lincoln (Department: 2832)
Electricity: magnetically operated switches, magnets, and electr
Magnets and electromagnets
With magneto-mechanical motive device
C310S105000, C310S181000
Reexamination Certificate
active
06756870
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a composite magnet of electromagnet and permanent magnet, comprising an iron core, a coil arranged to surround the outer peripheral surface of the iron core, and a permanent magnet mounted in the iron core in a manner that the magnetic pole is in agreement with the direction of magnetization of the iron core. The invention further relates to an eddy current retarder used for assisting the foot brake which is the main brake of a vehicle such as a truck, i.e., to an eddy current retarder equipped with the composite magnet of electromagnet and permanent magnet. The invention further relates to an eddy current retarder used for assisting the foot brake which is the main brake of a vehicle such as a truck, and to an eddy current retarder in which annular members made of a good conductor such as copper, a copper alloy or the like is coupled to the brake drum.
DESCRIPTION OF THE PRIOR ART
Japanese Examined Utility Model Publication (Kokoku) No. 44930/1988 discloses a composite magnet of electromagnet and permanent magnet comprising an iron core, a coil arranged to surround the outer peripheral surface of the iron core, and a permanent magnet mounted in the iron core in a manner that the magnetic pole is in agreement with the direction of magnetization of the iron core. A groove extending in the axial direction is formed in a part in the outer periphery of the iron core in the circumferential direction, the groove being formed at an intermediate portion in the axial direction or extending from one end to the other end in the axial direction. A permanent magnet is fitted into the groove.
A permanent magnet (e.g., ferrite magnet, rare-earth magnet) has a magnetic permeability smaller than that of the iron core (usually, a low-carbon iron material). In the above-mentioned composite magnet, since a permanent magnet having a low magnetic permeability is attached to a portion in the outer periphery of the iron core in the circumferential direction, the magnetic flux formed in the iron core cannot be sufficiently efficiently collected to one of the magnetic pole surfaces of the iron core when the iron core is magnetized by supplying a current to the coil. That is, since a permanent magnet having a low magnetic permeability is mounted on a portion in the outer periphery of the iron core in the circumferential direction, a portion in the outer periphery of the iron core in the circumferential direction is shut off in the direction of magnetization, the flow of magnetic flux formed in a portion of the outer periphery of the iron core is interrupted by the permanent magnet, and the magnetic flux formed in a portion in the outer periphery of the iron core is not efficiently guided as desired to one of the magnetic pole surfaces of the iron core. Further, the region of the iron core where the permanent magnet exists becomes remote from a portion of the coil in the radial direction, and the magnetic flux corresponding to the current supplied to the coil can not be efficiently generated. When the iron core is magnetized by supplying a current to the coil, therefore, the magnetic flux is not very efficiently generated in the iron core and hence, performance of the electromagnet is not utilized to a sufficient degree. Besides, since the permanent magnet is mounted on a portion of the outer periphery of the iron core in the circumferential direction thereof, it is not allowed to sufficiently increase the sectional area of the permanent magnet as desired and hence, the permanent magnet cannot be effectively utilized. Summarizing the foregoing, neither the electromagnet nor the permanent magnet is effectively utilized. Due to that neither electromagnet nor the permanent magnet is effectively utilized, the length of the electromagnet (iron core and coil) increases in the direction of magnetization, the composite magnet as a whole becomes of larger size, the weight increases, and the cost of production increases, too. The transverse sectional area of the iron core at a portion where the permanent magnet is mounted becomes considerably larger than the transverse sectional area of the permanent magnet. When the magnetizing force is applied for magnetization after the permanent magnet before magnetized has been incorporated in the iron core, therefore, much magnetic flux flows into the iron core, and the permanent magnet is not sufficiently magnetized as desired. To solve this inconvenience, the permanent magnet after magnetized must be mounted on the iron core, requiring a cumbersome assembling operation. Besides, due to the constitution in which the permanent magnet is mounted on a portion of the outer peripheral edge of the iron core in the circumferential direction, the permanent magnet cannot be formed in a simple transverse sectional shape such as a circular shape or a rectangular shape. Moreover, it is relatively difficult to form a groove in the outer periphery of the iron core, resulting in increase in the manufacture cost. In the above composite magnet, further, the permanent magnet which is a relatively long requires an increased cost for the material.
Typical examples of the eddy current retarder using a permanent magnet include the one in which a magnet support cylinder having plural permanent magnets arranged in the outer peripheral surface thereof is moved into or out of the brake drum to make a changeover between braking and non-braking (see Japanese Laid-open Patent Application (Kokai) No. 14782/1994 (JP-A 6-14782)) and the one in which a magnet support cylinder having plural permanent magnets arranged in the outer peripheral surface thereof is rotated forward or reverse inside the brake drum to make a changeover between braking and non-braking (see Japanese Laid-open Patent Application (Kokai) No. 83571/1994 (JP-A 6-83571))(both of these applications were developed and filed by Isuzu Motor Co.). These eddy current retarders require an actuator for moving the magnet support cylinder. As the actuator, there can be employed a pneumatic cylinder, a hydraulic cylinder, an electric motor or a linear motor. Therefore, the device as a whole becomes of larger size and heavy in weight and increases cost. In the eddy current retarder using an electromagnet (see Japanese Laid-open Patent Application (Kokai) No. 327227/1994 (JP-A 6-327227)), on the other hand, there is no need of moving the electromagnet; i.e., applying the brake and not applying the brake can be changed over by simply controlling the electric current supplied to the coil of the electromagnet and hence, the above-mentioned actuator is not required. However, the device becomes considerably large sized and heavy, compared with the eddy current retarder using the permanent magnet.
Japanese Laid-open Patent Application (Kokai) No. 243627/1998 (JP-A 10-243627) that was developed and filed by Isuzu Motor Co. Ltd. discloses an eddy current retarder in which a brake drum is equipped with annular members made of a good conductor such as copper, a copper alloy or the like. The eddy current retarder includes a brake drum coupled to a rotary shaft and a stationary guide cylinder arranged on the inside of the brake drum in the radial direction. The stationary guide cylinder formed chiefly of a nonmagnetic material constitutes a nearly rectangular inner space inclusive of an outer wall surface and an inner wall surface. Plural ferromagnetic plates are arranged at intervals on the outer peripheral wall of the stationary guide cylinder that is so disposed, maintaining a gap, as to be opposed to the inner peripheral surface of the brake drum. In the inner space of the stationary guide cylinder is supported a magnet support cylinder so as to be moved in the axial direction by the actuator. Plural permanent magnets are arranged on the outer peripheral portion of the magnet support cylinder at intervals in the circumferential direction so as to be opposed to the ferromagnetic plates. Magnetic pole surfaces of the permanent magnets are directed in the radial direction, and the permanent magnets neighbo
Donovan Lincoln
Isuzu Motors Limited
Rojas Bernard
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