Electricity: electrical systems and devices – Safety and protection of systems and devices – Motor protective condition responsive circuits
Reexamination Certificate
1999-06-24
2001-07-03
Jackson, Stephen W. (Department: 2836)
Electricity: electrical systems and devices
Safety and protection of systems and devices
Motor protective condition responsive circuits
C361S051000, C361S115000
Reexamination Certificate
active
06256181
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a fan drive device for drive control of a fan drive motor and, more particularly, to the fan drive device having a detection circuit for detecting rotation of a fan drive motor caused by external air flow such as, for example, wind causing the fan drive motor in an outdoor unit of an air conditioner to turn.
2. Description of Related Art
Systems for detecting the wind-driven rotation of a fan drive motor in the outdoor unit of an air conditioning system are known in literature. A typical circuit diagram of a conventional fan drive device for controlling fan drive motor drive in such an outdoor unit is shown in FIG.
9
. As shown in
FIG. 9
, this fan drive device
100
comprises a drive circuit
102
for driving a fan drive motor
110
such as found in the outdoor unit of an air conditioning system in one direction; a control circuit
103
for controlling the drive circuit
102
; and a voltage monitoring circuit
104
for monitoring the output voltage of the dc power circuit
111
serving as a power source for the fan drive motor
110
. The drive circuit
102
has six n-channel MOS transistors, referred to below as simply MOS transistors. The control circuit
103
controls the rotational speed of the fan drive motor
110
by PWM control of the MOS transistors. The drive circuit
102
and control circuit
103
together form a so-called inverter.
When the fan drive motor
110
is not driven by the fan drive device
100
, the fan drive motor
110
can be driven by the wind in the direction opposite to the direction of normal rotation of the fan drive motor, that is, in reverse rotation. As the wind becomes stronger, the reverse rotation speed of the motor rises. If the wind is sufficiently strong, it is even possible without driving the fan drive motor
110
to achieve the air flow required for the heat exchange operation of the outdoor unit of the air conditioning system. It is also possible, however, to damage the fan drive device
100
and fan drive motor
110
when the electric power is supplied to the fan drive motor
110
to drive the latter in the direction of normal forward rotation while the fan drive motor
110
is being reverse-driven by the wind. This potential damage may be typically prevented by controlling the fan drive device
100
to not drive the fan drive motor
110
when the fan drive motor
110
is turning in the reverse direction at a speed exceeding a predetermined threshold.
A prior art method of detecting the direction of fan drive motor
110
rotation is described below.
When the fan drive motor
110
is driven by an external force, induction voltage is produced in the fan drive motor
110
. This induction voltage is then converted to dc by a diode in the drive circuit
102
. The voltage monitoring circuit
104
detects and monitors this converted dc voltage. If the voltage detected by the voltage monitoring circuit
104
exceeds a threshold value when the fan drive motor
110
is to be started, the control circuit
103
controls the drive circuit
102
so that the fan drive motor
110
is not started.
The fan drive motor induction voltage detected by the voltage monitoring circuit
104
in this method is, however, affected by the magnetization strength of the rotor magnet in the fan drive motor
110
, as well as variations in such components as the frequency dividing resistors used for frequency dividing the induction voltage in the voltage monitoring circuit
104
. This creates a problem with the induction voltage detection precision of the voltage monitoring circuit
104
, and the precision of fan drive motor speed detection.
The dc power circuit
111
supplies current to the compressor (not shown) as well as the fan drive motor
110
, and therefore uses high capacity electrolytic smoothing capacitors
115
. As a result, when the fan drive motor
110
is reverse-driven by the wind and produces an induction voltage, a relatively long period of time is required for the dc voltage detected by the voltage monitoring circuit
104
to stabilize because more time is required to charge these high capacity electrolytic smoothing capacitors
115
.
The reliability and efficiency of the voltage monitoring circuit
104
is also not optimal because high voltage is normally applied to the voltage monitoring circuit
104
and the internal frequency dividing circuit formed by the frequency dividing resistors. This is a particular problem when the voltage monitoring circuit
104
detects fan drive motor speed using the above-described method if the fan drive motor
110
is PWM driven with a high voltage.
SUMMARY OF THE INVENTION
The present invention is therefore directed to a fan drive device for resolving the aforementioned problems. More specifically, the present invention is directed to a fan drive device using a sensor for detecting the position of a rotor magnet to detect the wind-driven rotational speed of the fan drive motor, and thereby avoiding problems relating to the variation in rotor magnet strength and variation in the components of the circuit for detecting fan drive motor induction voltage.
A further object of the present invention is to provide a fan drive device capable of accurately detecting the wind-driven rotational speed in a high voltage PWM driven fan drive motor without adding component parts.
A fan drive device achieving these objects comprises a plurality of sensors for converting to and outputting as a two-value signal a change in magnetic pole position resulting from rotation of a fan drive motor rotor magnet; a drive circuit section for driving the fan drive motor; and a control circuit section for controlling the drive circuit section according to an output signal from each sensor in the fan drive motor. In this fan drive device, the control circuit section prohibits the drive circuit section from driving the fan drive motor when the fan drive motor is not driven and the fan drive motor speed is detected to as exceeding a specific speed due to an external force based on signals output from the plurality of sensors.
More specifically, the control circuit section determines the fan drive motor speed to be greater than or equal to the specific speed when, after a rectangular wave having a period less than or equal to a specific period is detected from any one of the plurality of sensors, the level of a signal applied from another of the plurality of sensors changes within a specific time. In this case, this specific time is preferably the time of one period of the detected rectangular wave.
Alternatively, the control circuit monitors signals from any two desired adjacent Hall ICs to detect the interval between signal level changes in these two signals. Whether the fan drive motor is turning at or above a specific speed can then be detected from this interval.
Further alternatively, the control circuit may monitor signals from all of the sensors to detect signal level changes in output signals from each two adjacent sensors, and detect the intervals between these signal level changes. The control circuit then determines if the fan drive motor is turning at or above a specific speed based on the time that all of these detected intervals continues below a specific level.
A fan drive device according to the present invention is therefore not affected by variations in the strength of the fan drive motor rotor magnet or the components of the circuit for detecting fan drive motor induction voltage, or by the capacitance of a high capacitance capacitor in the dc supply circuit, and can therefore detect with good precision and without adding components, the speed of a high voltage, PWM drive fan drive motor driven by an external force such as the wind.
REFERENCES:
patent: 5703459 (1997-12-01), Yasohara et al.
patent: 61-101738 (1986-05-01), None
patent: 62-46153 (1987-02-01), None
patent: 63-140688 (1988-06-01), None
patent: 63206187 (1988-08-01), None
Baba Toshinari
Chinomi Takahito
Matsushiro Hideo
Nitta Takehiko
Jackson Stephen W.
Matsushita Electric - Industrial Co., Ltd.
Wenderoth Lind & Ponack, LLP.
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