Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1999-11-23
2001-10-09
Enad, Elvin (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S162000, C310S168000
Reexamination Certificate
active
06300703
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a construction of a rotor core of a reluctance motor utilizing reluctance torque.
BACKGROUND ART
Thanks to an advantage that secondary copper loss of a rotor is not produced in contrast with an induction motor, the reluctance motor attracts considerable attention as a driving motor for an electric vehicle, a machine tool or the like. However, this reluctance motor generally has poor power-factor and thus, requires improvement of the construction of the rotor core, a driving method, etc. in order to be used for industrial purposes. In recent years, a technology for improving the power-factor by providing flux barriers in a plurality of rows on a core sheet of the rotor core has been developed as described in a paper entitled Development of Multi-Flux Reluctance by Yukio Honda et al. in Proceedings No. 1029 published on Mar. 10, 1996 for a national meeting 1996 of the Electrical Society of Japan.
FIGS. 31
to
33
show an example of a construction of a rotor core of this improved known reluctance motor. In
FIG. 31
, a plurality of arcuate flux barriers
162
are provided on a circular core sheet
161
formed from an electromagnetic steel plate so as to convexly confront an axis
163
of the core sheet
161
. Each of the flux barriers
162
comprises a through-slit of about 1 mm in width, and is formed by a press. In order to impart strength to the core sheet
161
, against centrifugal force applied to the core sheet
161
during its rotation, an outer peripheral rim
164
having a predetermined width is provided at an outer periphery of the core sheet
161
.
By laminating several tens of the core sheets
161
on one another on a rotor shaft
165
, a rotor core
166
is obtained as shown in FIG.
32
. If this rotor core
166
is set in a stator
167
as shown in
FIG. 33
, a rotational magnetic field is given to the rotor core
166
by a plurality of field portions
168
of the stator
167
and thus, a reluctance torque T is produced. This reluctance torque T is expressed by the following formula (1).
T=Pn (Ld−Lq) id×iq (1)
In the above formula (1), “Pn” denotes the number of pairs of poles, “Ld” denotes a direct-axis inductance, “Lq” denotes a quadrature-axis inductance, “id” denotes a direct-axis current and “iq” denotes a quadrature-axis current. It is seen from the above formula (1) that performance of the reluctance motor relies on magnitude of (Ld−Lq). In order to increase (Ld−Lq), it has been a general practice that the above mentioned flux barriers
162
formed by the slits are provided on the core sheet
161
so as to impart resistance to a quadrature-axis magnetic path traversing the slits, while a direct-axis magnetic path interposed between the slits is secured.
In the above construction of the known rotor core
166
, the slits each having a width of about 1 mm are formed on the core sheet
161
by a press, and a strip is provided between neighboring ones of the slits such that the strips are coupled with each other at a predetermined width by the outer peripheral rim
164
.
However, in this construction of the known rotor core
166
, since the quadrature-axis magnetic flux penetrates each slit, the value of the quadrature-axis inductance Lq is increased and thus, the reluctance torque T decreases. On the contrary, if the width of each slit is increased so as to lessen the quadrature-axis magnetic flux, the width of each strip is also reduced, so that the value of the direct-axis inductance Ld is reduced and thus, the value of the reluctance torque T also decreases.
Meanwhile, in the construction of the known rotor core
166
, if the number of revolutions of the motor is increased, stress concentration may result, via centrifugal force in the vicinity of radially inner slits of the core sheet
161
, especially at the outer peripheral rim
164
at a radially innermost slit of the core sheet
161
. This possibly results in deformation of the rotor core
166
.
Large stress is applied to the outer peripheral rim
164
at the radially inner slits of the core sheet
161
for the following reason. The radially outer strips of the core sheet
161
, which are supported by the outer peripheral rim
164
, are short in length and thus, are light in weight. However, the radially inner strips of the core sheet
161
, which are supported by the outer peripheral rim
164
, become gradually larger in length and thus, become gradually heavier in weight. Therefore, centrifugal force produced by rotation of the rotor core
166
becomes gradually larger towards the radially innermost slit of the core sheet
161
along the outer peripheral rim
164
. Furthermore, by driving the rotor core
166
for its rotation, the strips projecting towards the center of the rotor core
166
are urged out of the rotor core
166
. As a result, the strips projecting towards the center of the rotor core
166
would depress the outer peripheral rim
164
outwardly so as to project out of the rotor core
166
. At this time, the strips become larger in size towards the radially innermost slit of the core sheet
161
along the outer peripheral rim
164
and therefore, produce larger force for depressing the outer peripheral rim
164
outwardly. Therefore, as location on the core sheet
161
approaches the stress concentration portions on the outer peripheral rim
164
at the radially innermost slit of the core sheet
161
, force for deforming the rotor core
166
becomes extraordinarily larger.
Hence, if width of the outer peripheral rim
164
is increased so as to prevent deformation of the rotor core
166
even at the time of high-speed rotation of the rotor core
166
, the outer peripheral rim
164
coupling the strips with each other is not subjected to magnetic saturation. Therefore, since quadrature-axis magnetic flux leaks through the outer peripheral rim
164
, the quadrature-axis inductance Lq becomes large and thus, the rotor core
166
cannot be driven for its rotation efficiently.
BRIEF DESCRIPTION OF THE INVENTION
Accordingly, the present invention has for its object to provide, with a view to eliminating the drawbacks of conventional rotor cores, a rotor core which is driven for its rotation by sufficient reluctance torque so as to improve performance of a motor.
In order to accomplish this object, the present invention provides a rotor core in which a plurality of core sheets are laminated on one another on a rotor shaft and a plurality of slits and a plurality of strips are alternately arranged in a radial direction of each of the core sheets so as to convexly confront a center of each of the core sheets such that an outer peripheral rim is formed between an outer peripheral edge of each of the core sheets and each of opposite ends of each of the slits. The rotor core comprises a stress concentration portion which is provided at a portion of the outer peripheral rim, and has a width larger than that of the remaining portions of the outer peripheral rim.
By this arrangement of the rotor core of the present invention, since the portion of the outer peripheral rim for the stress concentration portion subject ed to large centrifugal force has the large width, a rotor is not deformed even during high-speed rotations. Furthermore, since the remaining portions of the outer peripheral rim are made thin, magnetic flux flowing therethrough is saturated, so that durability of the rotor can be secured without lowering a ratio of a direct-axis inductance Ld to a quadrature-axis inductance Lq, i.e., (Ld/Lq).
REFERENCES:
patent: 3721844 (1973-03-01), Fong
patent: 5818140 (1998-10-01), Vagati
patent: 5903080 (1999-05-01), Nashiki et al.
patent: 10 43 488 (1959-04-01), None
patent: 0 289 075 (1988-11-01), None
patent: 7-274460 (1995-10-01), None
patent: 96/42132 (1996-12-01), None
A. Vagati: “The Synchronous Reluctance Solution: A New Alternative in A.C. Drives”, Proceedings of the International Conference on Industrial Electronic Control and Instrumentation, vol. 1, No. Conf.20, Sep. 5-9, 1994, pp. 1-13 XP000528562.
Yu
Honda Yukio
Kawano Shinichiro
Kiriyama Hiroyuki
Nishiyama Noriyoshi
Sawada Hiroshi
Dinh Le Dang
Enad Elvin
Matsushita Electric - Industrial Co., Ltd.
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