Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1998-01-07
2001-03-06
Tamai, Karl (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310SDIG006, C337S169000
Reexamination Certificate
active
06198184
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a brushless motor that is mainly used in an air blower in an air conditioning system for vehicles.
Brushless motors in the prior, art include the one disclosed in Japanese Unexamined Utility Model Publication No. H2-139473. This brushless motor is provided with a rotor having a field magnet, a stator that generates a rotating magnetic field for the rotor, and a means for exciting the stator. Thus, in this brushless motor, a rotating magnetic field is generated by sequentially exciting a plurality of curved end portions arranged on the stator in a radial direction. The rotor is caused to rotate by the magnet provided on the rotor being repeatedly attracted and repulsed relative to the rotating magnetic field.
In this brushless motor, the means for exciting includes exciting coils that are wound around the stator core, and a means for switching the direction of the current running through the exciting coils. A plurality of field effect transistors (FETS) are normally used as the means for switching. These FETs control the direction of the current running to the exciting coils by controlling signals applied to the gate terminals of the individual FETs. Since a relatively large current runs through the exciting coils, a great quantity of heat is generated, normally reaching up to approximately 150° C., which necessitates that a heat radiator to be provided at each FET.
However, if a problem occurs in the brushless motor itself, e.g. an abnormality in the rotation rate, a circuit error or the like caused by excessive load, it is necessary to protect other normally operating portions from the problem. In particular, it is necessary to cut off communication between the source supply line and the exciting coils to stop the supply of power to the exciting coils so that the rotation of the brushless motor stops.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a brushless motor having a means for protection that protects the brushless motor by causing the means for switching to be cut off from the source supply line when heat is generated in a circuit due to an error and, in particular, when heat is generated at a field effect transistor, a power transistor or the like that is used as the means for switching.
Accordingly, the brushless motor according to the present invention comprises a rotating shaft, a rotor secured to the rotating shaft, a plurality of magnets provided at an internal circumferential surface of the rotor, a stator that generates a rotating magnetic field for the magnets, and exciting coil wound around the stator, a control circuit board having a plurality of means for switching the direction of the current supplied to the exciting coils, and a case housing that stores the control circuit. The brushless motor further comprises a means for protection provided on the control circuit board near the plurality of means for switching, which includes a connecting line between the source supply line and the means for switching, which connecting line melts and disconnects at a specific temperature to cut off the source supply line from the means for switching.
Thus, since the means for protection includes the connecting line that communicates between the source supply line and the means for switching, and is provided near the means for switching, the means for protection can sense heat generated at the means for switching with a high degree of sensitivity. Consequently, if the means for switching generates heat at or exceeding a specific level, causing the means for protection to become heated to a specific level, the communication between the source supply line and the means for switching is cut off, immediately stopping the operation of the brushless motor to achieve the object described above.
Moreover, according to the present invention, the case housing comprises a first case through which the rotating shaft passes, with the rotor and the stator mounted externally thereto. The control circuit board is mounted in the first case, and the means for heat discharge is located at the means for switching. The case housing further comprises a second case that interlocks with the first case to cover the control circuit board from below. The means for protection is provided on the control circuit board in the vicinity of the means for heat discharge and the means for switching, and extends toward the second case.
Thus, since the means for protection extends toward the second case, and is located on the control circuit board, the maintenance on the means for protection can be performed easily by simply removing the second case after the circuit is shut down by the means for protection.
Furthermore, according to the present invention, the means for protection includes a plate which is formed from an elastic conductive material and, in an elastically deformed state, the plate is fixed at its two ends to the source supply line and the side of the means for switching through solder that melts at a specific temperature.
Thus, when the solder is melted by the het generated at the means for switching, the plate cuts off communication between the source supply line and the means for switching due to the restoring force of the plate, thereby achieving the object described above. The plate is formed of a copper ally having a specific elastic coefficient, and it is desirable to use solder that melts within the range of approximately 160°~180° C.
Moreover, the means for switching is only required to be capable of turning on off the current by a specific signal. Normally, power transistors or field effect transistors are employed as the means for switching. It is particularly desirable to use field effect transistors. In addition, the means for heat discharge is a heat radiator of aluminum or an aluminum alloy to which the field effect transistors are bonded via silicon oil, and is provided in the vicinity of the rotating range of the fan located at the first case and is exposed to the outside from the first case.
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patent: 5592353 (1997-01-01), Shinohara et al.
patent: 6037726 (2000-03-01), Tabata et al.
patent: 6054818 (2000-04-01), Tabata et al.
patent: 195 21 557 (1995-12-01), None
Ando Kouji
Horiuchi Kazuyoshi
Ohi Shinichi
Ohsawa Hiroshi
Tamai Karl
Wenderoth , Lind & Ponack, L.L.P.
Zexel Corporation
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