U.S. patent application number 11/794011 was filed with the patent office on 2008-01-10 for linear compressor and corresponding drive unit.
This patent application is currently assigned to BSH Bosch and Siemens Hausgerate GmbH. Invention is credited to Alexander Schade, Jan-Grigor Schubert.
Application Number | 20080008607 11/794011 |
Document ID | / |
Family ID | 35708955 |
Filed Date | 2008-01-10 |
United States Patent
Application |
20080008607 |
Kind Code |
A1 |
Schade; Alexander ; et
al. |
January 10, 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, which are associated with respective readjusting
springs that counteract a deformation of the arm.
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 and Siemens Hausgerate
GmbH
Carl-Wery-Strasse 34
Munich
DE
81739
|
Family ID: |
35708955 |
Appl. No.: |
11/794011 |
Filed: |
November 30, 2005 |
PCT Filed: |
November 30, 2005 |
PCT NO: |
PCT/EP05/56359 |
371 Date: |
June 21, 2007 |
Current U.S.
Class: |
417/410.1 ;
417/417 |
Current CPC
Class: |
F04B 35/045
20130101 |
Class at
Publication: |
417/410.1 ;
417/417 |
International
Class: |
F04B 17/00 20060101
F04B017/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 23, 2004 |
DE |
10 2004 062 301.5 |
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 which engage the frame with a first end
and engage the oscillating body with a second end, wherein each
limb includes a readjusting spring which counteracts a deformation
of the limb.
14. The drive unit according to claim 13, wherein the limbs have a
curved path between the two ends.
15. The drive unit according to claim 14, wherein each arm has two
sections curved in different directions.
16. The drive unit according to claim 13, further comprising a
second diaphragm spring, the first and second diaphragm springs
engaging regions of the oscillating body that are spaced in the
direction of the oscillating movement.
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 oscillating body.
18. 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.
19. The drive unit according to claim 18, wherein the ends engaging
on the frame are connected by a frame integral with the limbs.
20. The drive unit according to claim 13, 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 13, wherein an effective
spring constant of the combination of diaphragm spring and
readjusting spring is adjustable.
22. The drive unit according to claim 13, 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
that is able to move 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 which engage the frame with a first end
and engage the oscillating body with a second end, wherein each
limb includes a readjusting spring which counteracts a deformation
of the limb.
Description
[0001] This invention relates to a linear compressor, in particular
for use for compressing refrigerant in a refrigerating device, and
in particular a drive unit for driving an oscillating piston
movement for such a linear compressor.
[0002] U.S. Pat. No. 6,506,032B2 discloses a linear compressor
whose drive unit comprises a frame and an oscillating body mounted
in the frame by means of a 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 moves 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. The limbs are more easily deformable, in the longitudinal
direction of the piston, than transversely to it, so that they
counteract a contact between the piston and the cylinder wall.
[0007] To achieve a desired throughout of the compressor the
oscillating frequency of the piston must not be too low. This
oscillating frequency is all the higher the stiffer the diaphragm
spring. However, there is a risk that too rigid a diaphragm spring
may result in fatigue at high oscillation amplitudes.
[0008] The object of this invention is to provide a 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 without risk of fatigue and
which is able to achieve a high throughput with a small piston
diameter.
[0009] To achieve a long stroke without the 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 just
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. In
order to achieve a natural frequency of the drive unit adequate for
a required throughput, a readjusting spring is therefore assigned,
according to the invention, to each limb, which spring counteracts
a deformation of the limb so that the diaphragm spring, together
with the readjusting springs, forms an elastic system whose
stiffness is considerably greater than that of the diaphragm spring
alone.
[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, so that together
with the back and forth movement a rotary oscillation of the
oscillating body is also excited. To prevent such a rotary
oscillation from having a disturbing effect, a rotationally
symmetrical structure of at least parts of the compressor may be
required.
[0011] However, pairs of limbs curved in opposite directions may
also be provided. In such a structure the torques induced on the
differently curved limbs are mutually compensating, so that the
oscillating body performs absolutely no or hardly any rotary
oscillation in connection with its back and forth movement.
[0012] 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.
[0013] 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.
[0014] 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.
[0015] The effective spring constant of the combination of
diaphragm and readjusting spring may be made adjustable so that the
natural frequency of the drive unit can be adapted as required.
[0016] A helical spring is preferably used as the readjusting
spring.
[0017] 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.
[0018] Further features and advantages of the invention are evident
from the following description of exemplary embodiments with
reference to the attached figures.
[0019] FIG. 1 shows a diagrammatic section through a linear
compressor;
[0020] FIG. 2 shows an elevation of a diaphragm spring for use in
the linear compressor in FIG. 1 according to the invention; and
[0021] FIG. 3 shows an elevation of a second design of a diaphragm
spring.
[0022] FIG. 1 shows a partially cut side view of a linear
compressor. The compressor has a frame with a central chamber 21,
in which openings are formed in two opposing walls, here with
reference to the representation in the figure designed as ceiling
22 and floor 23, for the sake of clarity, through which openings a
rod-shaped oscillating mass 24 extends with a certain clearance.
Chamber 21 is provided to accommodate electromagnets, not shown,
for driving a back and forth movement of a permanent magnet
inserted in oscillating mass 24.
[0023] The ends of oscillating mass 24 are fastened to central
regions 16 of two diaphragm springs 8 of by means of screws or
rivets 25
[0024] One of diaphragm springs 8 is shown in elevation in FIG. 2.
Diaphragm spring 8 has a closed outer ring or frame 13 which is
rectangular in shape, which is stabilised before installation in
the compressor and protects against distortion. 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.
[0025] Frame 13 of each diaphragm spring 8 rests on bridges 26
projecting from ceiling 22 or floor 23 of central chamber 21.
Diaphragm springs 8 are retained on bridges 26 by means of screws
or rivets 27, which each intersect a foot section 28 of the upper
and lower yoke 29, 30, respectively, and one of bores 20 in the
corners of frame 13 and engage in central chamber 21. The height of
bridges 26 determines the maximum stroke of the movement of
oscillating mass 24; if this maximum stroke is exceeded, the
central regions 16 of diaphragm spring 8 strike against ceiling 22
and bottom 23 respectively.
[0026] 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.
[0027] 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. 2, 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.
[0028] 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. Due to the movement of the piston on the inner wall of
cylinder 33, fluid is sucked in through a suction connection 24 of
cylinder 323, is compressed and is again ejected via a pressure
connection 35.
[0029] 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.
[0030] 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.
[0031] 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.
[0032] 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.
[0033] FIG. 3 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
protective 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. Here the limbs are wider,
given the same external dimensions of the diaphragm spring, and are
therefore stiffer than those of the spring in FIG. 2. The mode of
operation is no different to that of the diaphragm spring shown in
FIG. 3.
* * * * *