U.S. patent application number 09/863713 was filed with the patent office on 2002-11-28 for auto-centering linear motor.
Invention is credited to Redlich, Robert Walter.
Application Number | 20020175570 09/863713 |
Document ID | / |
Family ID | 25341626 |
Filed Date | 2002-11-28 |
United States Patent
Application |
20020175570 |
Kind Code |
A1 |
Redlich, Robert Walter |
November 28, 2002 |
AUTO-CENTERING LINEAR MOTOR
Abstract
Disclosed is a method of generating magnetic centering force on
the permanent magnets of a reciprocating permanent magnet motor or
generator, by allowing the ferromagnetic structure of the machine
to saturate magnetically when the permanent magnets are near the
ends of their travel.
Inventors: |
Redlich, Robert Walter;
(Athens, OH) |
Correspondence
Address: |
Frank H. Foster
KEMBLAS, FOSTER, PHILLIPS & POLLICK
7632 Slate Ridge Blvd.
Reynoldsburg
OH
43068
US
|
Family ID: |
25341626 |
Appl. No.: |
09/863713 |
Filed: |
May 23, 2001 |
Current U.S.
Class: |
310/15 |
Current CPC
Class: |
H02K 33/16 20130101;
H02K 35/02 20130101; H02K 7/09 20130101 |
Class at
Publication: |
310/15 |
International
Class: |
H02K 041/00; H02K
033/00; H02K 035/00 |
Claims
I claim:
1. An electromechanical transducer for converting reciprocating
motion to alternating voltage or for converting alternating voltage
to reciprocating motion, said transducer comprising the combination
a) through d) as follows, a) a permanent magnet in the shape of a
ring bounded by two circular cylinders and two parallel planes,
both cylinders coaxial about an axis A-A, both planes perpendicular
to axis AA, the permanent magnet being magnetized substantially
perpendicular to the surfaces of the cylinders, the permanent
magnet length being (S+L) measured in a direction parallel to axis
A-A, where S and L are defined below, b) a plurality of stationary
and substantially identical flux loop members composed of
ferromagnetic material, the flux loop members extending generally
radially outward from said axis A-A, each flux loop member having a
pair of air gaps separated by a distance S measured parallel to
axis A-A,, all said pairs of gaps being bounded by two cylindrical
surfaces, both surfaces coaxial with axis A-A, each air gap having
length L measured parallel to axis A-A, said permanent magnet ring
positioned within the plurality of air gap pairs and movable in a
direction parallel to axis A-A, the distance so moved, measured
from the location where the magnet ring is axially centered in the
air gaps, being denoted here by X, c) an armature coil wound to
encircle the central portions of all of said flux loop members, d)
one or more regions of said flux loop members where, for the
purpose of creating a magnetically generated axial centering force
on said magnet ring, the ferromagnetic material comprising said
region or regions is magnetically saturated when
.vertline.X.vertline.=L/2 and current in said armature coil is
zero, saturation being defined here as magnetic intensity H
exceeding 20 Oersteds.
Description
REFERENCES
[0001] 1. U.S. Pat. 4,602,174
[0002] 2. Disclosure Document no. 172295
TECHNICAL FIELD
[0003] The invention is in the general field of reciprocating
permanent magnet AC electric motors and generators. Specifically,
it is a means of generating magnetic centering forces to confine
reciprocating magnets within the air gaps of such machines.
BACKGROUND ART
[0004] Reference 1 discloses an AC electrical machine that can be
used either as a generator to convert reciprocating motion of a
permanent magnet ring to AC voltage, or as a motor to convert AC
voltage to reciprocating motion of a permanent magnet ring.
Referring to FIG. 4 of Reference 1, permanent magnets 50
reciprocate in a left-right direction, and if the machine is
conventionally designed, there will be no force on the permanent
magnets if there is no current in armature coil 56, provided the
magnets do not emerge from the air gaps. If the magnets do so
emerge, strong magnetic forces are generated that expel the magnets
further. To prevent emergence of the magnets and their subsequent
expulsion from the air gap, mechanical and/or magnetic centering
springs have been used in prior art. The latter are disclosed in
Reference 2. Centering springs introduce complication and increase
cost. The object of the present invention is to provide
magnetically generated centering force on the reciprocating magnets
without adding cost or complexity.
BRIEF DISCLOSURE OF THE INVENTION
[0005] In the invention, the ferromagnetic structure (60, 62, 64,
68 of FIG. 6, Reference 1) is designed unconventionally in that all
or part of it is allowed to magnetically saturate as permanent
magnets 50 of Ref. 1 approach the left or right extremes of the air
gap in which they reciprocate. Theory shows, and experiment
confirms, that magnetic saturation causes a force to be exerted on
the reciprocating magnets in a direction such as to confine the
magnets within the air gap. Conventional design avoids magnetic
saturation because it degrades performance by lowering efficiency,
and, in the case of generators, distorts output voltage waveform.
In a linear motion AC motor-generator of the type disclosed in Ref.
1 but modified according to the invention, it is found that useful
centering forces can be generated without incurring a significant
performance penalty.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIG. 1A is a cross sectional view of a linear, permanent
magnet motor or generator according to prior art. In FIG. 1A,
dimensions and magnetic quantities that are changed by the
invention are identified by symbols.
[0007] FIG. 1B is a cross-sectional view of a linear, permanent
magnet motor or generator, in which dimensions and magnetic
quantities that distinguish the invention from prior art are
identified by symbols.
[0008] FIG. 2 shows graphs of magnetic quantities in the iron
structure according to prior art and in the invention. These
quantities are plotted against displacement X of the magnets from
their centered position. The quantities graphed are magnetic
intensity H' (prior art), magnetic flux density B' (prior art), H
(invention) and B (invention).
[0009] FIG. 3 shows, for prior art and the invention, graphs of
magnetic force on the motor magnets plotted against displacement of
the magnets from their centered position.
DETAILED DESCRIPTION OF THE INVENTION
[0010] FIG. 1A is a cross-sectional view of a contemporary
embodiment of a reciprocating permanent magnet motor or generator
as disclosed in U.S. Pat. No. 4,602,174. The machine is
substantially axially symmetric about axis A-A. A permanent magnet
ring 1 is magnetized radially with magnetization M, and
reciprocates parallel to A-A in air gaps bounded by outer
ferromagnetic structure 2 and inner ferromagnetic structure 3. A
coil of wire 4 surrounds inner ferromagnetic structure 3. X denotes
axial displacement of the magnet ring from the position where it is
centered axially within the air gaps. With no current in coil 4,
the magnetic flux density B' and the magnetic intensity H' in the
inner and outer ferromagnetic structures are functions of X and of
the dimensions y' and Y', and are denoted in FIG. 1A by the
conventional functional notation B' (X), H' (X) respectively.
[0011] FIG. 2 shows graphs of H' (X) and B' (X) in a prior art
machine conventionally designed to avoid magnetic saturation. B'
(X) is a substantially linear function of X with a maximum value
typically less than 13000 Gauss, and H' (X) is typically below 10
Oersted for all X.
[0012] FIG. 1B is a cross sectional view of a linear permanent
magnet motor or generator according to the invention. FIG. 1B the
same as FIG. 1A except that one or both of dimensions y and Y are
made sufficiently smaller than their prior art counterparts y' and
Y' so that magnetic saturation occurs near X=L/2 and X=-L/2, which
are the values of X at which magnets 1 begin to emerge from the air
gap between iron structures 2 and 3.
[0013] FIG. 2 shows graphs of H(X) and B(X) in a motor or generator
according to the invention. Near .vertline.X.vertline.=L/2, H(X)
rises above 20 Oersted, exceeding typical saturation for electrical
steel, which is about 10 oersted. B(X) near
.vertline.X.vertline.=L/2 falls below a linear projection of its
values at small X, and reaches a maximum value exceeding 15000
Gauss.
[0014] The purpose of allowing parts of ferromagnetic structures 2
and 3 to saturate when magnet ring 1 nears either end of the air
gaps is to generate magnetic forces that prevent the magnet ring
from leaving the air gap. The existence of such forces is predicted
by the theory of electromagnetic energy, which teaches that, in
order to increase magnetic flux density B by a differential amount
dB in a differential volume dV, energy equal to
(H.times.dB.times.dV) is required. In the invention, the source of
such energy is mechanical work done on the magnet ring by an axial
force moving through a distance dX, from which it follows that the
force F on the magnet ring can be found from the following
equation;
F=-.intg.H.times.dB/dX.times.dV equation (1)
[0015] The minus sign in equation (1) means F is in a direction
opposite to dX. The integral must in principle be taken over all of
space, but in prior art and in the invention, the dominant
contribution to it is from the volume occupied by ferromagnetic
structures 2 and 3 of FIGS. 1A and 1B, provided the magnet ring
does not leave the air gaps. In prior art, magnetic saturation is
avoided by dimensioning the ferromagnetic structure so that H' is
considerably less than 10 Oersted for all X (5 Oersteds is
typical), and F is too low to be of practical use in confining the
magnet ring. In the invention, however, saturation typically raises
H(L/2) to above 20 Oersted, resulting in a much larger value of F
that will prevent magnet ring 1 from leaving the air gap.
[0016] FIG. 3 shows graphs of F in prior art and in the invention.
In both cases the magnets will be expelled from the air gap if
.vertline.X.vertline..gtoreq.L/2, as indicated by rapidly
increasing force for .vertline.X.vertline..gtoreq.L/2. In the
invention, but not in prior art, there is a relatively large
restraining force to prevent magnet ring 1 from reaching X=L/2 and
subsequently being expelled from the air gap.
[0017] Considerable variation is possible within the spirit of the
invention. For example, magnetic saturation could be confined to
outer ferromagnetic structure 2, or to inner ferromagnetic
structure 3, rather than existing in both structures.
* * * * *