Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2001-11-15
2003-09-30
Mullins, Burton (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S216006
Reexamination Certificate
active
06628037
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a power generator, electronic device using the power generator and a method of setting plate thickness in a magnetic circuit in electronically controlled timepiece and power generator. More specifically, it relates to a technique for reducing iron loss of a power generator to improve efficiency thereof.
BACKGROUND ART
Small-sized and portable electronic devices such as a timepiece, a cellular phone and a portable information tool are ordinarily driven by electric power supplied by a battery. However, electronic devices requiring no battery exchange and simultaneously improving usability and ecological friendliness have been known in recent years, in which a power generator having a rotor rotated by an oscillating weight or a main spring to generate power is installed.
Since various functions are installed in such portable electronic devices, increase in generated power is desired. However, enlarging the size of the power generator for increasing the generated power amount deteriorates portability of the electronic device and therefore cannot be employed.
Accordingly, in order to improve the efficiency of the power generator (increase the generated power amount), decrease in iron loss (hysteresis loss, eddy-current loss) of the magnetic circuit of the power generator is desired.
An object of the present invention is to provide a power generator capable of decreasing iron loss of the magnetic circuit of the power generator to improve the efficiency of the power generator, an electronic device having the power generator, an electronically controlled timepiece, and a plate thickness setting method of a magnetic circuit of the power generator.
DISCLOSURE OF THE INVENTION
A power generator according to an aspect of the present invention has: a rotor having a permanent magnet; a stator and a magnetic core of soft magnetic material constituting a magnetic circuit; and a coil wound around the magnetic core, in which the plate thickness d (m) of the soft magnetic material constituting at least one of the stator and the magnetic core is set at a value represented by the following formula of
d
=
k
h
k
e
ρ
·
f
-
0.375
B
m
-
0.175
(
1
)
where k
h
represents hysteresis loss coefficient, k
e
represents eddy-current loss coefficient, &rgr; (&OHgr;·m) represents resistivity, f (Hz) represents frequency and B
m
(T) represents maximum amplitude magnetic flux density of the soft magnetic material.
The principle of the formula (1) will be described below. Incidentally, PC permalloy material is taken as an example in the following explanation and a part of coefficients etc. is different in the other material. However, the principle and the formula based thereon are common irrespective of the material.
The iron loss W of the power generator is an addition of the hysteresis loss W
h
and the eddy-current loss W
e
. The hysteresis loss W
h
and the eddy-current loss W
e
can be obtained as follows.
(A) Hysteresis Loss W
h
With regard to the hysteresis loss for one cycle per unit area, Steinmetz experimentally deduces the following formula for electromagnetic steel plate.
W
h
≅k
h
B
m
&eegr;
In the above, W
h
: hysteresis loss (J/m
3
), k
h
: proportion constant, B
m
: maximum amplitude magnetic flux density (T), &eegr;: proportion constant.
It is generally well known that the size of grain of the material is substantially in inverse proportion to direct current coercive force, which shows that the hysteresis loss is in inverse proportion to the plate thickness. Considering the fact, following formula can be deduced, which can be defined as the hysteresis loss:
W
h
≅k
h
d
−1
B
m
&eegr;
In the above, k
h
: proportion constant, d: plate thickness (m).
(B) Eddy-Current Loss
The iron loss is formulated based on the concept of abnormal eddy-current loss coefficient. The eddy-current loss can be represented using the abnormal eddy-current coefficient as follows:
W
e
=
k
ae
1
6
ρ
π
2
fd
2
B
m
2
In other words, the eddy-current loss can be represented as the eddy-current loss formula of classical theory multiplied by the abnormal eddy-current loss coefficient k
ae
obtained by an experiment. In the above, k
ae
: abnormal eddy-current loss coefficient, W
e
: eddy-current loss (J/m
3
), &eegr;: resistivity (&OHgr;·m), f: frequency (Hz), d: plate thickness (m), B
m
: maximum amplitude magnetic flux density (T).
(C) Calculation of Proportion Constant
The hysteresis loss is calculated by measuring direct-current magnetic characteristics by assigning the plate thickness, base on the result of which the maximum amplitude magnetic flux density and the k
h
and &eegr; of the above W
h
formula can be approximately represented as in the following formula.
W
h
≅1.72×10
−3
d
−1
B
m
1.65
Further, alternating-current magnetic characteristics is measured by assigning plate thickness, the maximum amplitude magnetic flux density and the frequency, based on the result of which the k
ae
of the above W
e
formula can be approximately represented as in the following formula.
W
e
=
k
ae
1
6
ρ
π
2
fd
2
B
m
2
≅
(
1.6
×
10
-
3
d
-
1
f
-
0.25
)
(
π
2
d
2
fB
m
2
6
ρ
)
=
2.63
×
10
-
3
1
ρ
df
0.75
B
m
2
When the hysteresis loss coefficient k
h
=1.72*10
−3
, and the eddy-current loss coefficient k
e
=2.63*10
−3
in the above W
e
and W
h
formulae, the iron loss W=W
h
+W
e
can be represented as in the following formula (6).
W
≅
k
h
d
-
1
B
m
1.65
+
k
e
1
ρ
df
0.75
B
m
2
(
6
)
In the above, W
h
: hysteresis loss (J/m
3
), W
e
: eddy-current loss (J/m
3
), k
h
: hysteresis loss coefficient, d: plate thickness (m), B
m
: maximum amplitude magnetic flux density (T), k
e
: eddy-current loss coefficient, &rgr;: resistivity (&OHgr;·m), f: frequency (Hz).
The plate thickness d for minimizing the iron loss W can be obtained by the formula (6), which can be modified into a formula representing d as in the above-described formula (1).
According to the present invention, the plate thickness d for minimizing the iron loss W can be calculated by assigning the hysteresis loss coefficient k
h
, the eddy-current loss coefficient k
e
, the resistivity &rgr; (&OHgr;·m) determined by the material of the stator and the magnetic core made of soft magnetic material such as permalloy, and the frequency f (Hz) and the maximum amplitude magnetic flux density B
m
(T) determined based on design of the power generator into the above-described formula (1).
Accordingly, the iron loss of the power generator can be decreased by designing the stator and the magnetic core with the plate thickness d, thereby improving efficiency of the power generator (increasing the amount of generated power).
Though the hysteresis loss coefficient k
h
and the eddy-current loss coefficient k
e
have to be calculated in advance by experiment, usually four types of permalloy material (Supermalloy, PC permalloy, PD permalloy, PB permalloy) are used for the power generator and the hysteresis loss coefficient k
h
and the eddy-current loss coefficient k
e
can be obtained in advance per the respective types.
Accordingly, in designing the power generator, the hysteresis loss coefficient k
h
, the eddy-current loss coefficient k
e
, and the resistivity &rgr; defined by the selected soft magnetic material and the maximum amplitude magnetic flux density B
m
and the frequency f defined during design process in accordance with the required performance are assigned to the above-described formula (1), so that the appropriate plate thickness d for minimizing the iron loss W can be easily calculated and the highly efficient power generator can be easily designed and produced.
Therefore, increase in generated power amount and size reduction of the po
Mullins Burton
Seiko Epson Corporation
Watson Mark P.
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