Electricity: motive power systems – Field or secondary circuit control – Plural – diverse or diversely connected or controlled field...
Patent
1988-02-22
1989-12-19
Shoop, Jr., William M.
Electricity: motive power systems
Field or secondary circuit control
Plural, diverse or diversely connected or controlled field...
318 64, 318 71, 363 78, H02P 100
Patent
active
048885339
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a brushless DC motor which is to be used as a driving source of a refrigerant compressor of a refrigerating apparatus or a fan.
BACKGROUND ART
In a conventional brushless DC motor, three or more position detecting elements are required to switch current paths to a three phase coil.
FIG. 1 shows an example of the construction of a conventional brushless DC motor. The rotating position of a rotor 1 composed of a permanent magnet is detected by hall elements 2a, 2b and 2c. The electrical states of first driving transistors 4a, 4b, 4c and second driving transistors 5a, 5b, 5c are switched and controlled by a processing circuit 3 corresponding to the rotor detecting signals, and the current paths to the three phase coils 6a, 6b, 6c are switched. As mentioned above, in the case that hall elements 2a, 2b, 2c are used as the position detecting elements, the number of parts of the motor increases, and there is a disadvantage that the circuit is complicated. Moreover, in the case that such a brushless DC motor is used as a motor for a compressor, the hall elements are used in a high temperature and a high voltage state because a large amount of current flows, and therefore, reliability or life time is seriously diminished.
DISCLOSURE OF INVENTION
The present invention, by detection of a rotor position by using a terminal voltage appearing at input and output terminals for currents to three phase coils, purposes to provide a brushless DC motor which does not use at all any exclusive position detecting elements.
Furthermore, since the present invention enables stable detection of a rotor position by using the terminal voltage issuing on the input and output terminals of the three phase coils, any position detecting element (Hall element) which is exclusively used to detect position is not required, and, unstable phenomenon accompanied with detection of the terminal voltage including spike voltages is avoidable.
The above-mentioned object of the present invention, is realized by a construction mentioned below. Namely, the brushless DC motor of the present invention comprises: a rotor having N pairs (N is an integer) of magnetic poles, which is constituted by a permanent magnet, a group of three phase coils interlinking magnetic flux of the magnetic field of the above-mentioned rotor, a group of first driving transistors forming current paths from a direct current power source to the above-mentioned three phase coils, a group of second driving transistors forming current return paths from the above-mentioned three phase coils to the above-mentioned direct current power source, a group of first diodes in parallel across the input terminals and output terminals of the above-mentioned first driving transistors, a group of second diodes in parallel across the input terminals and output terminals of the above-mentioned second driving transistors, position detecting means for generating control signals by detecting terminal voltage of input and output terminals for the current to the above-mentioned three phase coils, and switching-driving means for outputting switching signals to the above-mentioned first driving transistors and second driving transistors on the basis of the control signal of the above-mentioned position detecting means and for switching and flowing current to the above-mentioned coils in turn. The above-mentioned position detecting means produces three kinds of smoothed signal from the terminal voltage of the respective terminals of the above-mentioned coils to produce three kinds of mixed signals from the respective smoothed signals and an output signal by comparing the smoothed signals with the mixed signals, to switch and to control the current flowing state of the above-mentioned first transistors and second transistors by using the generated signals as a control signal from the position detecting means.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is the starting circuit of the conventional brushless DC motor;
FIG. 2 is a block diagram showing a starti
Gotoh Makoto
Hamaoka Kouji
Romano Gary J.
Shoop Jr. William M.
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