U.S. patent application number 11/794009 was filed with the patent office on 2008-04-17 for linear compressor and corresponding drive unit.
This patent application is currently assigned to BSH Bosch und Siemens Hausgerate GmbH. Invention is credited to Alexander Schade, Jan-Grigor Schubert.
Application Number | 20080089796 11/794009 |
Document ID | / |
Family ID | 35814082 |
Filed Date | 2008-04-17 |
United States Patent
Application |
20080089796 |
Kind Code |
A1 |
Schade; Alexander ; et
al. |
April 17, 2008 |
Linear Compressor And Corresponding Drive Unit
Abstract
A drive unit for a linear compressor comprising a frame and an
oscillating body. The oscillating body is mounted in the frame via
at least one diaphragm spring and can be moved back and forth in
one direction. The diaphragm spring comprises a plurality of limbs,
fastened with one end to the frame and with the other end to the
oscillating body. Two limbs each have inversely curved sections
between the two ends.
Inventors: |
Schade; Alexander;
(Freiberg, DE) ; Schubert; Jan-Grigor; (Senden,
DE) |
Correspondence
Address: |
BSH HOME APPLIANCES CORPORATION;INTELLECTUAL PROPERTY DEPARTMENT
100 BOSCH BOULEVARD
NEW BERN
NC
28562
US
|
Assignee: |
BSH Bosch und Siemens Hausgerate
GmbH
Carl-Wery-Strasse 34
Munich
DE
81739
|
Family ID: |
35814082 |
Appl. No.: |
11/794009 |
Filed: |
November 30, 2005 |
PCT Filed: |
November 30, 2005 |
PCT NO: |
PCT/EP05/56356 |
371 Date: |
June 21, 2007 |
Current U.S.
Class: |
417/417 |
Current CPC
Class: |
F04B 35/045
20130101 |
Class at
Publication: |
417/417 |
International
Class: |
F04B 35/00 20060101
F04B035/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 23, 2004 |
DE |
10 2004 062 302.3 |
Claims
1-12. (canceled)
13. A drive unit for a linear compressor comprising a frame and an
oscillating body mounted in the frame by means of at least one
diaphragm spring and moving back and forth, the diaphragm spring
having a plurality of limbs engaging the frame with a first end and
the oscillating body with a second end, and a curved path between
the two ends, wherein two of the limbs have inversely curved
sections.
14. The drive unit according to claim 13, wherein each limb has two
sections curved in different directions.
15. The drive unit according to claim 13, further comprising a
second diaphragm spring, the first and second diaphragm springs
engaging on regions of the oscillating body that are spaced in the
direction of the oscillating movement.
16. The drive unit according to claim 13, wherein the limbs of the
same diaphragm spring are integrally joined together at their ends
engaging on the oscillating body.
17. The drive unit according to claim 13, wherein the limbs of the
same diaphragm spring are integrally joined together at their ends
engaging on the frame.
18. The drive unit according to claim 17, wherein the ends engaging
on the frame are connected by a frame integral with the limbs.
19. The drive unit according to claim 13, further comprising a
readjusting spring assigned to each limb and counteracting
deformation of the limb.
20. The drive unit according to claim 19, wherein the stiffness of
the diaphragm spring is lower in the direction of deformation than
that of the readjusting spring.
21. The drive unit according to claim 19, wherein an effective
spring constant of the combination of diaphragm spring and
readjusting spring is adjustable.
22. The drive unit according to claim 19, wherein the readjusting
spring includes a helical spring.
23. The drive unit according to claim 13, wherein the mass of the
oscillating body is greater than the mass of all the springs.
24. A linear compressor comprising: a working chamber; a piston
being movable back and forth in the working chamber for compressing
a working fluid; and a drive unit coupled to the piston for driving
the back and forth movement and comprising a frame and an
oscillating body mounted in the frame by means of at least one
diaphragm spring and moving back and forth, the diaphragm spring
having a plurality of limbs engaging the frame with a first end and
the oscillating body with a second end, and a curved path between
the two ends, wherein two of the limbs have inversely curved
sections.
Description
[0001] This invention relates to a linear compressor, in particular
for use for compressing refrigerants in a refrigerating device, and
in particular a drive unit for driving an oscillating linear piston
movement for such a linear compressor.
[0002] U.S. Pat. No. 6,506,032 B2 discloses a linear compressor
whose drive unit comprises a frame and an oscillating body mounted
in the frame by means of one diaphragm spring. The oscillating body
comprises a permanent magnet, a piston rod rigidly connected to the
permanent magnet and a piston articulated to the piston rod, which
piston can be moved back and forth in a cylinder. The movement of
the piston is driven by an electromagnet arranged around the
cylinder, which electromagnet interacts with the permanent magnet.
A disc-shaped diaphragm spring is screwed centrally to the piston
rod, and the outer edge of the diaphragm spring is connected to a
yoke which surrounds the cylinder, the electromagnet and the
permanent magnet.
[0003] The oscillating body and the diaphragm spring form an
oscillating system whose natural frequency is determined by the
mass of the oscillating body and the diaphragm spring, as well as
by the stiffness of the diaphragm spring. The diagram spring only
permits small oscillation amplitudes because any deflection of the
oscillating body is associated with an expansion of the diaphragm
spring. Due to the low oscillating amplitude it is difficult to
reduce the dead volume of the cylinder reliably. However, the
higher the dead volume the lower the efficiency of the compressor.
The short stroke also necessitates designing the cylinder with a
diameter that is proportional to the length in order to achieve a
given throughput. It is expensive to seal the correspondingly large
circumference of the piston sufficiently.
[0004] Since the oscillating body is only retained in the radial
direction by its connection to the spring, it is possible that the
head of the piston rod supporting the piston may oscillate back and
forth and grind against the cylinder wall. To prevent this a
compressed gas bearing is provided for the piston, i.e. the
cylinder wall covered by the piston has openings which are
connected to the high pressure outlet of the linear compressor to
form a gas cushion between the inner wall of the cylinder and the
piston. However, such a compressed gas bearing only functions if
the required excess pressure is present at the outlet of the linear
compressor, i.e. not when the compressor starts or stops. At these
times there is a risk that the piston will grind against the
cylinder wall, resulting in premature wear of the compressor.
[0005] A linear compressor is disclosed in U.S. Pat. No. 6,641,377
B2. In this double-piston linear compressor each piston is retained
by two two-armed diaphragm springs.
[0006] Due to the curvature of the limbs a longer piston stroke is
possible, but each diaphragm spring exerts a torque on the piston
when deflected. If this torque is not exactly compensated for, the
piston performs a rotary oscillation in addition to its linear
oscillating movement, and wobble movements of the piston may be
excited which may result in contact between the piston and cylinder
and consequently to increased wear.
[0007] The object of this invention is to provide a low-wear drive
unit for a linear compressor with a frame and an oscillating body
mounted by means of a diaphragm spring, in which the diaphragm
spring permits a long stroke of the oscillating body and which is
able to achieve a high throughput with a small piston diameter.
[0008] The object is achieved in that the plurality of limbs of the
diaphragm spring each engage with one end on the frame and with the
other end on the oscillating body, and in that the limbs have pairs
of sections with opposing curvature between the two ends. The limbs
do not therefore extend along the shortest path between the two
ends, so that when the oscillating body is deflected, they stretch
and my approach the rectilinear shape without the material of the
limbs having to be expanded for this purpose. Within the same
workpiece it is very easy to produce the limbs so that their
torques exactly compensate each other; if, as described in U.S.
Pat. No. 6,641,377 B2, two diaphragm springs are provided with
limbs covered in different directions, deviations in material
strength from one spring to another may prevent such compensation
or at least render it extremely difficult.
[0009] The diaphragm spring preferably has pairs of limbs with
sections curved in opposite directions.
[0010] In the simplest case each limb has an individual section
curved in one direction. Each such limb also exerts a torque on the
oscillating body supported by it when deflected, but this is
compensated for by the limb paired with it and curved in the
opposite direction.
[0011] Each limb preferably has two sections curved in different
directions. Since the differently curved sections also generate
torques in opposite directions in this case too, the torque of each
individual limb may therefore be made very small or caused to
disappear altogether.
[0012] It is also advantageous to provide at least a second
diaphragm spring whose limbs engage on a region of the oscillating
body which is distant from the region of engagement of the first
diaphragm spring in the direction of the oscillating movement. The
oscillating body is reliably guided linearly in the direction of
the desired oscillating movement by the two diaphragm springs, and
a lateral deflection movement, which could result in contact
between a piston supported by the oscillating body and a cylinder
surrounding the piston, can be avoided.
[0013] The limbs of the same diaphragm spring are preferably joined
integrally together at their ends engaging on the frame and/or at
their ends engaging on the oscillating body. The ends engaging on
the frame may also be connected by a frame integral with the leaf
springs.
[0014] To provide a long stroke without risk of material fatigue,
the limbs of the at least one diaphragm spring should be produced
from a very thin material. Its strength may be dimensioned so small
that it is only sufficient to prevent lateral deflection of the
oscillating body. However, such a weak diaphragm spring would
result in a low natural frequency of the drive unit and hence, at a
predetermined stroke, in a low throughput of a compressor driven by
the drive unit. To achieve a natural frequency of the drive unit
sufficient for the required throughput, each limb is preferably
assigned a readjusting spring which counteracts deformation of the
limb so that the diaphragm spring, together with the readjusting
springs, form an elastic system whose stiffness is considerably
higher than that of the diaphragm spring alone.
[0015] The effective spring constant of the correlation of
diaphragm and readjusting spring may be made adjustable so that the
natural frequency of the drive unit can be adapted as required. A
helical spring is preferably used as the readjusting spring.
[0016] A further subject matter of the invention is a linear
compressor with a working chamber, a piston that can be moved back
and forth in the working chamber to compress a working fluid, and a
drive unit of the type described above, coupled to the piston, for
driving the back and forth movement.
[0017] Further features and advantages of the invention are evident
from the following description of exemplary embodiments with
reference to the attached figures.
[0018] FIG. 1 shows a diagrammatic section through a linear
compressor;
[0019] FIG. 2 shows an elevation of a diaphragm spring for use in
the linear compressor in FIG. 1 according to the invention;
[0020] FIG. 3 shows an elevation of a second design of a diaphragm
spring;
[0021] FIG. 4 shows a partially cut side view of a linear
compressor with the diaphragm spring shown in FIG. 3; and
[0022] FIG. 5 shows a further design of a diaphragm spring.
[0023] The linear compressor shown in FIG. 1 for a refrigerating
device comprises a compressor chamber 1, which is delimited by a
moving piston 2 on the one hand and a cylinder 3 on the other,
joined together by a pipe section 4 and a cover 5. Cover 5, not
shown, incorporates in an intrinsically known manner a suction
connection, a pressure connection and valves which allow
refrigerant to flow into the compressor chamber only via the
suction connection and discharge only via the pressure
connection.
[0024] Pipe section 4 is surrounded concentrically by a second pipe
section 6 and is connected to it by a radial flange 7. The
circumference of a diaphragm spring 8 is fastened to the end of
pipe section 6 facing away from flange 7. An oscillating body 9,
which is composed of a piston rod 10, to which piston 2 is
articulated, a flange 11 fastened to piston rod 10 and a permanent
magnet 12, which is fastened to flange 11 and projects into the
interval between pipe sections 6, 4, is fitted in the centre of
diaphragm spring 8. Electromagnets, also accommodated in the
interval, for exerting a force in the direction of piston rod 10 on
permanent magnets 12, are omitted in the figure.
[0025] FIG. 2 shows an elevation of diaphragm spring 8. It
comprises a peripheral outer ring 13 and mirror image limbs 14
which are arranged in pairs and run spirally inwards from ring 13,
which limbs are connected to each other at their ends facing away
from ring 13. A central opening 15 is provided for screwing piston
rod 10.
[0026] Diaphragm spring 8 consists of spring steel or another
elastically deformable, but essentially non-expandable material.
The central region of diaphragm spring 8 can be elastically
deflected with little force in a direction perpendicular to the
plane shown in FIG. 2, the deflection causing the curvature of
limbs 14 to be reduced slightly in elevation and the central region
to be rotated slightly in the anticlockwise direction. The
resistance of diaphragm spring 8 against a displacement of the
central region in the plane shown in FIG. 2 is much greater than
the resistance against a deflection perpendicular to this plane, so
that the end of piston rod 10 fastened to opening 15 of diaphragm
spring 8 is reliably guided so that it moves in a linear
direction.
[0027] A second design of diaphragm spring 8 is shown in FIG. 3 in
elevation. This design also has a closed outer ring 13. Here this
ring is rectangular in shape, but this is insignificant as far as
the function of the diaphragm spring is concerned. Four limbs 14
extend from the corners of frame 13 towards central region 16, each
of them being formed from three rectilinear sections 17 and two
curved sections 18, 19 connecting sections 17. The two sections 18,
19 of each limb 14 are each curved in opposite directions. Four
bores 20 for fastening the diaphragm spring are located in the
corners of frame 13.
[0028] When central region 16 is deflected, this results in slight
upward bending of curved sections 18, 19. Because of the opposite
directions of curvature of the two sections 18, 19 of each limb,
the upward bending gives rise to opposing torques, so that the
torque exerted by each individual limb 14 on central region 16 is
small. Moreover, the torques of adjacent limbs 14 are mutually
compensating because each of them is the mirror image of the other
and the torques exerted by them are therefore inversely the same.
Central area 16, and consequently also a piston rod 10 fastened to
it, are therefore guided exactly linearly and free from
distortion.
[0029] FIG. 4 shows a partially cut side view of a linear
compressor in which diaphragm springs 8 of the type shown in FIG. 3
are used. The compressor has a frame with a central chamber 21, in
which openings are formed in two opposing walls, here denoted as
ceiling 22 and floor 23 with reference to the representation in the
figure, for the purpose of clear illustration, through which
openings a rod-shaped oscillating mass 24 extends with a certain
clearance. The chamber is provided to accommodate electromagnets,
not shown, for driving a back and forth movement of a permanent
magnet inserted in the oscillating mass.
[0030] The ends of oscillating mass 24 are fastened to central
regions 16 of two diaphragm springs 8 of the shape shown in FIG. 3
by means of screws or rivets 25. Frame 13 of each diaphragm spring
8 rests in turn on bridges 26 projecting from ceiling 22 and floor
23 of central chamber 221. The height of bridges 26 establishes the
maximum stroke of movement of the oscillating mass 24; if this
maximum stroke is exceeded, central regions 16 of diaphragm spring
8 strike against ceiling 22 and floor 23.
[0031] Diagram springs 8 are retained on bridges 26 by screws or
rivets 27, each of which intersect a foot piece 28 of an upper and
lower yoke 29, 30 and one of bores 19 in the corners of frame 13,
and engage in central chamber 21.
[0032] Lower yoke 30 supports two helical springs 31, each of which
is positioned so that free head piece 32 of these springs each
touch curved sections 18 of two limbs 14, as also denoted as a
dash-dot outline in FIG. 3, when they are deflected downwards and
therefore resist a downward deflection of oscillating mass 24.
Corresponding helical springs 31, which touch curved sections 18 of
limbs of upper diaphragm spring 8 and counteract an upward
deflection of the oscillating mass, are provided on upper yoke
29.
[0033] Upper yoke 29 also supports a cylinder 33 in which a piston
connected to oscillating mass 24 by means of a piston rod 10, not
shown in the figure, is able to move back and forth. Since
oscillating mass 24 is guided exactly linearly by the two diaphragm
springs 8, piston rod 12, and with it the piston supported by it,
cannot deviate transversely to the direction of movement and
grinding of the piston against the inner wall of cylinder 33 can be
avoided.
[0034] When oscillating mass 24 is located at one of the points of
inversion on its trajectory, its entire kinetic energy is stored in
the diaphragm springs 8 and the helical springs 31 in the form of
deformation energy, the distribution of the energy among the spring
types depending on their respective spring constants. The diaphragm
springs may therefore be made very thin and easily deformable so
that no material fatigue occurs even during protracted operation.
For the energy which the diaphragm springs are unable to store due
to insufficient stiffness may be absorbed by suitably dimensioned
helical springs 31.
[0035] Moreover, compressors with different throughputs can be
achieved with the same model of diaphragm spring if the diaphragm
springs are each combined with helical springs with different
spring constants, resulting in different natural frequencies of the
oscillating system.
[0036] It is also conceivable to render the natural frequency of a
drive unit adjustable by mounting helical springs 31 displaceably
on yokes 29, 30. The closer the region of limbs 14 touched by head
pieces 32 of helical springs 31 is to central region 16 of
diaphragm springs 8, the stiffer will be the entire system,
consisting of the diaphragm spring and helical springs, and the
higher will be the natural frequency of the resultant drive
unit.
[0037] In the extreme case it is possible to replace the two
helical springs 31 of each yoke 29, 30 by a single helical spring
which touches central region 16 directly.
[0038] FIG. 5 shows a modification of diaphragm spring 8 from FIG.
3, which can be used in its stead in the compressor shown in FIG.
4. In the case of the diaphragm spring shown in FIG. 5, outer frame
13 is omitted and instead only the three right and two left limbs
14 are connected at their ends facing away from central region 16
by a material strip 34. The mode of operation is no different to
that of the diaphragm spring shown in FIG. 3.
* * * * *