Electrical generator or motor structure – Dynamoelectric – Rotary
Patent
1992-06-15
1994-03-15
Skudy, R.
Electrical generator or motor structure
Dynamoelectric
Rotary
310 40MM, 310 71, H02K 1100
Patent
active
052948510
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a small-sized DC motor characterized in that a PTC (positive temperature coefficient) thermistor which is applied to a fixed-temperature heating resistor, a temperature sensor, a current limiting element, and so on, is incorporated into or circumscribed on the motor as the overload protection element for the motor.
BACKGROUND OF THE INVENTION
Mainly a bimetal, a PTC thermistor, etc. are known as over-current protection elements to be used as a counter measure an overload of a small-sized DC motor, and there is a tendency that those elements are particularly used in the automobile industry.
Of those elements, a bimetal is connected in series mainly to a motor having a diameter of 40 mm or more, that is, having an overload current of about 5 A or more, and usually used as the motor built-in type.
Generally, when an overload current is not larger than 5 A, the accuracy of switching operation of a bimetal is low so that the bimetal fails to perform stable operation. Accordingly, a PTC thermistor having a cost lower than that of the bimetal is broadly used.
As is known, a PTC thermistor is a resistor element having a positive temperature coefficient, and although the resistance value thereof is low at an ordinary temperature, the value suddenly increases to be 10.sup.4 -10.sup.7 times as large as the value at an ordinary temperature if the element reaches or exceeds a predetermined switching temperature because of self heating due to an over-current or heat transfer from a certain heat source.
A PTC thermistor made of BaTiO.sub.3 ceramics is most generally known, and a PTC thermistor of V.sub.2 O.sub.3 ceramic, a resin PTC thermistor in which conductive particles such as carbon black or the like are contained in polyolefin resin, and the like, are known in addition to the BaTiO.sub.3 PTC thermistor.
Conventionally, a PTC thermistor to be used in a small-sized DC motor is made of semiconductor ceramics containing BaTiO.sub.3 as the principal component. Because of limitation in the material characteristic that the resistivity of the material must be not lower than 8 .OMEGA.cm and the withstand voltage be in a range of 30-50 V, in use, a PTC thermistor is usually connected in series to a motor as a disk-like part provided with a lead wire having a diameter not thinner than 10-12 mm. Since a PTC thermistor cannot be incorporated into a motor because of its shape and its size, however, it is general that a separate PTC thermistor is mounted on the outside a motor through a printed wiring board or the like.
Consequently, there has been a problem that it takes a long time to mount a PTC thermistor, and development of a small-sized motor, even a small-sized motor having a diameter smaller than 40 mm, provided with an overload protection element is desired by a car industrial field, etc., who seek reduction in size and in weight.
In such a background, the inventors of this application previously proposed "A small-sized DC motor" (Japanese Patent Application No. Hei-1-292397) and "A small-sized DC motor (Japanese Patent Application No. Hei-1-292398). They are those structured fundamentally with materials having characteristics considerably improved than those of the conventional materials. Next, those motors will be described.
The first small-sized DC motor disclosed in Japanese Patent Application No. Hei-1-292397 is characterized in that a BaTiO.sub.3 ceramic in which the ratio (V.sub.B /.rho..sub.25) of the withstand voltage V.sub.B (V) to an ordinary-temperature resistivity .rho..sub.25 (.OMEGA.cm) is not smaller than 7 and not larger than 20 is connected in series to an armature winding and the PTC thermistor is incorporated in a motor casing. The BaTiO.sub.3 ceramic is formed of, as starting raw materials, a mixed crystal or a solid solution of BaTiO.sub.3, SrTiO.sub.3, PbTiO.sub.3, and CaTiO.sub.3 synthesized through a liquid-phase solution reaction method, and a valency control agent and Mn and Si which are added to the above principal components by predetermine
REFERENCES:
patent: Re31367 (1983-08-01), D'Entremont
patent: 4272714 (1981-06-01), Vind
patent: 4408244 (1983-10-01), Weible
patent: 4926077 (1990-05-01), Gauthier
patent: 5003208 (1991-03-01), Hama
patent: 5010264 (1991-04-01), Yamada
patent: 5140205 (1992-08-01), Baines
patent: 5170307 (1992-12-01), Nacewicz
Hinami Toshio
Nakahara Keisuke
Okano Yoko
Saito Hiromichi
Tajima Kazuo
NKK Corporation
Skudy R.
LandOfFree
Small-sized DC motor does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Small-sized DC motor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Small-sized DC motor will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1538055