U.S. patent application number 10/586735 was filed with the patent office on 2008-12-11 for compression device for gaseous media.
This patent application is currently assigned to BEHR GmbH & CO. KG. Invention is credited to Roland Burk.
Application Number | 20080304989 10/586735 |
Document ID | / |
Family ID | 34744967 |
Filed Date | 2008-12-11 |
United States Patent
Application |
20080304989 |
Kind Code |
A1 |
Burk; Roland |
December 11, 2008 |
Compression Device for Gaseous Media
Abstract
The invention concerns a device for compressing gaseous media
comprising at least one compression chamber (10) into which the
gaseous medium can enter and from which the gaseous medium can
exit, and comprising a first valve device (13, 7) having at least
one first opening (13) and at least one first covering device (7)
that essentially covers the first opening at least intermittently.
The first valve device permits the gaseous medium to enter the
compression chamber (10) and prevents, in essence, the gaseous
medium from exiting the compression chamber (10). The inventive
device also comprises a second valve device (4, 8) having at least
one second opening (4) and at least one second covering device (8)
that essentially covers the second opening at least intermittently.
The second valve device permits the gaseous medium to exit the
compression chamber (10) and prevents, in essence, the gaseous
medium from entering the compression chamber (10). To this end, the
narrowest free cross-section of one valve device considerably
exceeds the narrowest free cross-section of the other valve
device.
Inventors: |
Burk; Roland; (Stuttgart,
DE) |
Correspondence
Address: |
FOLEY AND LARDNER LLP;SUITE 500
3000 K STREET NW
WASHINGTON
DC
20007
US
|
Assignee: |
BEHR GmbH & CO. KG
|
Family ID: |
34744967 |
Appl. No.: |
10/586735 |
Filed: |
January 19, 2005 |
PCT Filed: |
January 19, 2005 |
PCT NO: |
PCT/EP2005/000496 |
371 Date: |
July 15, 2008 |
Current U.S.
Class: |
417/571 |
Current CPC
Class: |
F04B 39/1073 20130101;
F05C 2253/12 20130101; F04B 27/1009 20130101; F05C 2225/04
20130101 |
Class at
Publication: |
417/571 |
International
Class: |
F04B 39/10 20060101
F04B039/10 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 21, 2004 |
DE |
10 2004 003 137.1 |
Claims
1. A device for compressing gaseous media, comprising at least one
compression space into which the gaseous medium can enter and from
which the gaseous medium can discharge; a first valve means having
at least one first opening and at least one first covering means
essentially covering the first opening at least intermittently, the
first valve means allowing the gaseous medium to enter the
compression space and essentially preventing a discharge of the
gaseous, medium from the compression space; a second valve means
having at least one second opening and at least one second covering
means essentially covering the second opening at least
intermittently, the second valve means allowing a discharge of the
gaseous medium from the compression space and essentially
preventing the gaseous medium from entering the compression space;
wherein the narrowest free cross section of one valve means
considerably exceeds the narrowest free cross section of the other
valve means.
2. The device as claimed in claim 1, wherein the narrowest free
cross section of the first valve means considerably exceeds the
narrowest free cross section of the second valve means.
3. The device as claimed in claim 1 wherein the narrowest free
cross section of the one valve means exceeds the narrowest free
cross section of the other valve means at least by a factor of
2.
4. The device as claimed in claim 1 wherein the device has a piston
means arranged so as to be movable relative to the compression
space.
5. The device as claimed in claim 1 wherein at least one covering
means is designed as a reed.
6. The device as claimed in claim 1 wherein at least one valve
means is arranged in a valve plate, and preferably both valve means
are arranged in said valve plate.
7. The device as claimed in claim 1 wherein the first opening of
the first valve means is designed to be noncircular.
8. The device as claimed in claim 1 wherein the first valve means
has a plurality of first openings.
9. The device as claimed in claim 1 wherein the periphery of the at
least one first opening of the first valve means is greater than
the periphery of the at least one second opening of the second
valve means.
10. The device as claimed in claim 1 wherein the at least one
opening of the first valve means, compared with an imaginary
circular opening which has the same cross-sectional area as the at
least one first opening, has a periphery which exceeds the
periphery of said imaginary circular opening by at least 10%,
preferably by at least 20% and in particular preferably by at least
50%.
11. The device as claimed in claim 1 wherein at least one covering
means, preferably the covering means of the first valve means, has
at least one aperture.
12. The device as claimed in claim 1 wherein at least one covering
means, preferably the covering means of the first valve means, has
at least one projection.
13. The device as claimed in claim 1 wherein at least one covering
means is fastened to the valve plate.
14. The device as claimed in claim 1 wherein the configuration of
at least one covering means is adapted to the configuration of the
opening assigned to this covering means.
15. The device as claimed in claim 1 wherein the peripheral margins
of at least one covering means project beyond the peripheral
margins of the associated opening by between 0.5 mm and 5 mm,
preferably by 1 mm to 3 mm.
16. The device as claimed in claim 1 wherein at least one opening
has a peripherally encircling groove.
17. The device as claimed in claim 1 wherein the valve plate has at
least one surface section having a coating which is deformable at
least in sections.
18. The device as claimed in at claim 1 wherein at least one
covering means has at least one surface section having a coating
which is deformable at least in sections.
19. The device as claimed in claim 1 wherein the coating has a
material which contains Teflon.
20. The device as claimed in claim 1 wherein, in the open state of
the valve, at least a section of at least one covering means is at
a distance from its assigned opening which is greater than 0.5 mm,
preferably greater than 1.0 mm, and in particular greater than 1.5
mm.
21. The use of a device as claimed in claim 1 in an
air-conditioning system, in particular for a motor vehicle.
Description
[0001] The present invention relates to a device for compressing
gaseous media. The invention is described with regard to a
compressor, in particular for an air-conditioning system of a motor
vehicle; however, it is pointed out that the device may also be
used for other devices for compressing gaseous media.
[0002] Such compressors are known from the prior art for
air-conditioning equipment as a basic component of the same.
Likewise, it is known from the prior art that the compressors or
refrigeration compressors constitute a large loss source for the
air-conditioning system inasmuch as they lead to a significant,
additional energy consumption and thus fuel consumption.
[0003] The causes of these energetic losses are different
irreversibilities which on the one hand increase the compressor
driving power and on the other hand increase the thermal output
which is to be dissipated to the environment. Depending on the
refrigerant used, the losses in the compressor split up in
different ways into various loss processes. The most important loss
processes include the stroke-independent friction power, the
stroke-dependent friction power, the power loss due to internal
leakage, the throttling losses at the suction valve and the
throttling losses at the pressure valve. Opposed effects on the
individual loss processes can be produced by design changes to the
construction of the compressor.
[0004] For example, measures for improving the inner tightness
between a volumetric displacement means, in particular a piston,
and the wall assigned to it, in particular a cylinder wall, are at
the same time reflected in an increase in the friction power, which
again nullifies some of the improvements.
[0005] Intensive investigations have been able to show that in
particular throttling losses at the suction valve have an adverse
effect, in particular at high suction volumetric flows delivered,
that is to say at a high speed and at a high delivery efficiency of
the compressor, and when using a refrigerant having a relatively
low volumetric refrigerating capacity, such as R134a for
example.
[0006] The object of the present invention therefore consists in
improving the overall efficiency of a compressor, in particular at
high volumetric flows, by the pressure loss at the suction valve
being reduced by design measures. This is achieved according to the
invention by a device as claimed in claim 1. Advantageous
developments and embodiments are the subject matter of the
subclaims.
[0007] The device according to the invention for compressing
gaseous media has at least one compression space into which the
gaseous medium can enter and from which the gaseous medium can
discharge. Furthermore, at least one first valve means having at
least one first opening and at least one first covering means
essentially covering the first opening at least intermittently is
provided, the first valve means allowing the gaseous medium to
enter the compression space and essentially preventing a discharge
of the gaseous medium from the compression space.
[0008] In addition, a second valve means having at least one second
opening and at least one second covering means essentially covering
the second opening at least intermittently is provided, the second
valve means allowing a discharge of the gaseous medium from the
compression space and essentially preventing the gaseous medium
from entering the compression space.
[0009] According to the invention, the free cross section of one
valve means considerably exceeds the free cross section of the
other valve means.
[0010] The expression "the free cross section" or "the narrowest
free cross section" refers to the surface or the lateral area,
peripherally defining the opening, of the geometrical space or
volume whose height is defined by the distance of the covering
means (with open valve) from the opening and whose periphery is
defined by the periphery of the opening cross section of the valve.
In this case, the distance between the covering means and the
opening need not necessarily be constant.
[0011] The free cross section of the first valve means considerably
exceeds the free cross section of the second valve means. This
means that the free cross section of the valve means which enables
the gaseous medium to be drawn into the compression space
considerably exceeds the free cross section of the valve means
which enables the gaseous medium to be discharged from the
compression space. The corresponding cross sections at the suction
valve are thus designed to be larger than the cross sections at the
pressure valve of the compression device.
[0012] The expression "covering means" in this case refers to a
means which essentially completely covers, at least intermittently,
the opening assigned to it and therefore acts in a sealing manner
for the opening in this state.
[0013] In a further preferred embodiment, the free cross section of
the one valve means exceeds the free cross section of the other
valve means at least by a factor of 2; this means that the free
cross section of the suction valve exceeds the free cross section
of the pressure valve by at least a factor of 2. The free cross
section of the one valve means preferably exceeds the free cross
section of the other valve means at least by a factor of 2.5,
preferably at least by a factor of 3, and in particular preferably
at least by a factor of 4.
[0014] In a further preferred embodiment, the device has a piston
means arranged so as to be movable relative to the compression
space, one respective valve closing and one being opened at least
intermittently as a function of the direction of movement of the
piston.
[0015] In a further preferred embodiment, at least one covering
means is designed as a reed. Both covering means are preferably
designed as reeds. The latter, relative to the compression space,
depending on the direction of movement of the piston means, are
either at a distance from the openings assigned to them or bear
essentially against said openings, so that in this way the passage
of gas in one direction through the opening is prevented and is
essentially permitted in the other direction.
[0016] In a further preferred embodiment, at least one valve means
is arranged in a valve plate, and preferably both valve means are
arranged in said valve plate. The valve plate forms the closure of
the compression space. Thus the above-designated distance between
the opening and the covering means also refers to the distance
between the valve plate or that surface of the valve plate which
faces the covering means, on the one hand, and the covering means,
on the other hand.
[0017] In a further preferred embodiment, the first opening of the
first valve means, i.e. the suction valve means, is designed to be
noncircular.
[0018] As explained above, the free cross section of the valve
means results from the periphery of the valve opening cross section
and the distance between the opening and the covering means. In
this embodiment, therefore, by selecting a noncircular cross
section, the periphery of the opening is increased at the same
cross-sectional area or lateral dimension and thus with the same
space requirement. It is known that a circle has the smallest ratio
between circle periphery and circle area compared with other
two-dimensional geometrical figures. The modification of the
opening cross section from the circular profile therefore produces
an increase in the ratio of periphery and area of the opening. In
other words, a ratio between circle periphery and circle area is
selected which is greater than 2/r, where r is the radius of the
circle opening.
[0019] The advantage of this procedure is that the periphery of the
opening can be increased without at the same time the cross section
or the area of the opening increasing to a comparable degree, as a
result of which the areas available only to a limited extent on the
valve plate can be taken into account.
[0020] In a further preferred embodiment, the first valve means has
a plurality of first openings. In this way, too, the periphery of
the valve opening cross section in relation to its area can be
increased.
[0021] In a further preferred embodiment, the periphery of the at
least one first opening of the first valve means is greater than,
preferably markedly greater than, the periphery of the at least one
second opening of the second valve means. This means that the
suction valve has a larger, preferably considerably larger, opening
periphery than the pressure valve. In this way, as mentioned at the
beginning, the loss of the device for compressing gas can be
considerably reduced, even if an increase in slight losses at the
pressure valve are tolerated in the process.
[0022] In a further preferred embodiment, the at least one opening
of the first valve means, compared with an imaginary circular
opening which has the same cross section as the at least one
opening, has a periphery which exceeds the periphery of said
imaginary circular opening by at least 10%, preferably by at least
20% and in particular preferably by at least 50%. This means that
the actual opening is compared with an imaginary circular opening,
the imaginary opening having the same cross-sectional area as the
actual opening, and the actual opening on the other hand having a
larger periphery than the imaginary opening. As explained above,
this can be achieved, for example, by deviations, preferably
significant deviations, from the circular shape.
[0023] The specified increases in the periphery/area ratio with
regard to the circular opening by 10%, 20% or 50%, which are also
considered to be significant increases, produce a considerable
reduction in the power loss at the suction valve.
[0024] In a further preferred embodiment, at least one covering
means, preferably the covering means of the first valve means, has
at least one aperture. The expression "aperture" in this case
refers to an interruption in the covering means. Here, the aperture
may have any desired geometrical shapes, for example circular,
elliptical, polygonal and/or similar cross sections. In this case,
the apertures may be arranged in the regions where a long gas path
of narrow cross section would be produced if these apertures were
not present.
[0025] In a further preferred embodiment, at least one covering
means, preferably the first covering means of the first valve
means, has at least one projection. In contrast to the
abovementioned aperture, a recess refers to a formation which
projects from the remaining area, whereas the aperture is
surrounded essentially over the full periphery by the area of the
covering means.
[0026] In a further preferred embodiment, at least one covering
means is fastened to the valve plate; both covering means are
preferably fastened to the valve plate.
[0027] In a further preferred embodiment, the configuration of at
least one covering means is adapted to the configuration of the
opening assigned to this covering means. The expression "opening
assigned to this covering means" refers to that opening which the
relevant covering means is intended to cover. The peripheral
margins of at least one covering means preferably project beyond
the peripheral margins of the associated opening by between 0.5 mm
and 5 mm, preferably by 1 mm to 3 mm. This means that, if, for
example, the opening were to be of circular design with a radius of
20 mm, the covering means assigned to it would be arranged
concentrically relative to the opening with a radius of between
20.5 mm and 25 mm, preferably between 21 mm and 23 mm. In this
case, the covering means can project by an essentially constant
amount along the entire periphery beyond the opening assigned to
it; however, the amount of overlapping may also vary, so that the
covering means projects beyond the opening to a different extent at
different regions.
[0028] In a further preferred embodiment, at least one opening has
a groove encircling the opening cross section. The abovementioned
slight overlap has the advantage that the damping when the covering
means lifts and comes into contact due to the breakaway or the
displacement of the gas cushion and/or refrigerating-oil cushion in
the narrowest gap is minimized. In order to minimize this effect, a
groove encircling the opening cross section or specific roughening
of the valve plate may be additionally provided.
[0029] In a further preferred embodiment, the valve plate,
preferably on the side facing the covering means, has at least one
surface section having a coating which is deformable at least in
sections.
[0030] In a further preferred embodiment, at least one covering
means has at least one surface section, preferably on the side
facing the opening, having a coating which is deformable at least
in sections. In this case, in an especially preferred embodiment,
the coating has at least one material which contains Teflon
(PTFE).
[0031] The reason for this embodiment is that, due to the
significant increase in the periphery of the suction valve opening
and of the valve plate, the sealing area between the valve plate,
on the one hand, and the covering means, on the other hand, is also
increased and thus additional leakage cross sections may arise. Due
to the elastically and/or plastically deformable coating on the
valve plate and/or the covering means, these leakages can at least
be reduced. As stated, temperature-resistant polymers, such as
Teflon (PTFE), are suitable for the coating, but metallically soft
claddings are also able to compensate for microroughness by plastic
adaptation of the sealing members. In the latter case, however, it
is necessary to fix the covering means or reeds in position with
respect to the cylinder base, which, however, does not pose a
technical problem.
[0032] In a further preferred embodiment, in the open state of the
valve, at least a section of at least one covering means is at a
distance from its assigned opening which is greater than 0.5 mm,
preferably greater than 1.0 mm, and in particular greater than 1.5
mm. This preferably involves the covering means of the first valve
means.
[0033] As explained above, the narrowest free cross section of the
suction valve is to be increased, this cross section resulting from
the product of the periphery of the valve opening and the distance
of the covering means from the opening or the valve plate. Instead
of the periphery of the opening being increased, the distance can
therefore also be increased. However, an increase in this distance
also leads to the opening and closing times of the valve being
increased and as a result additional internal leakages may occur
due to the valve closing too late. However, it is possible to
improve an increase of the maximum permitted stroke of the covering
means relative to the valve plate in connection with an adaptation
of the spring rigidity and/or prestress of the covering means.
[0034] The invention also relates to the use of the device
according to the invention in an air-conditioning system, in
particular for a motor vehicle. However, it should be made clear
that such devices for compressing gas may also be used in other
refrigerating machines, such as domestic refrigerators for
example.
[0035] Further advantages and embodiments of the present invention
follow from the attached drawings, in which:
[0036] FIG. 1 shows a plan view of a valve plate of a device for
compressing a gaseous medium according to the prior art;
[0037] FIG. 2 shows a schematic section through the valve plate of
the device from FIG. 1;
[0038] FIG. 3 shows a diagram for illustrating the compressor power
losses in a device according to the prior art;
[0039] FIG. 4 shows a plan view of a first embodiment according to
the invention of a valve plate of a device for compressing a
gaseous medium;
[0040] FIG. 5 shows a plan view of the device according to the
invention in a further embodiment;
[0041] FIG. 6 shows a plan view of a device according to the
invention in a further embodiment;
[0042] FIG. 7 shows a plan view of a device according to the
invention in a further embodiment;
[0043] FIG. 8 shows an illustration of the power losses for the
device according to the invention;
[0044] FIG. 9 shows an illustration of the efficiency for a device
according to the prior art; and
[0045] FIG. 10 shows an illustration of the efficiency for a device
according to the invention for compressing a gaseous medium.
[0046] FIG. 1 shows a plan view of the piston-side surface of a
valve plate 2 of a compression device according to the prior art.
Provided in this valve plate is a pressure valve opening 4 which is
provided with a covering means (not shown). Also shown is a
covering means 7, a second (concealed) valve opening 13, which is
part of the suction valve.
[0047] In the compression device according to the invention, both
the opening 4 of the pressure valve and the opening 13 of the
suction valve have peripheries of similar size.
[0048] FIG. 2 shows a schematic detail of a compression device
according to the prior art. In this case, the designation 7
designates the covering means of the suction valve, which is open
in this state, the bottom end 7a of the suction valve reed coming
to lie at the left-hand stop of the notch 3 and thus being
prevented from moving further away from the opening 13. The top end
7b of the covering means of the suction valve is fastened between
the valve plate 2 and a cylinder wall 18. The designation 13
relates to the opening of the suction valve, this opening being
essentially covered by the covering means 7 in the closed state.
The designation 4 identifies the opening of the pressure valve,
this opening likewise being essentially covered by the covering
means 8 in the closed state shown here. The covering means 8 is
fastened with the bottom end between the valve plate 2 and a
separating web 14. This separating web 14 serves to seal off the
suction space 12 from the pressure space 11 in an essentially
gas-tight and/or liquid-tight manner. The compression space 10 or
its end region is closed off by the cylinder wall 18 and the valve
plate 2. A piston means (not shown) moves inside the compression
space 10, either the suction valve or the pressure valve being
closed, depending on the direction of movement of the piston
device. The designations 16a and 16b designate the annular grooves
around the respective valve openings 13 and 4. These annular
grooves serve to minimize the time delays when the respective valve
covering means lift or come into contact due to the breakaway or
the displacement of the gas cushion and/or refrigerating-oil
cushion.
[0049] An illustration of the compressor power losses for a
compression device according to the prior art is shown in FIG. 3.
This is based on defined pressures and on the original suction
valve at a high pressure ratio. The total power losses in relation
to the isentropic power, that is to say the power at constant
entropy, is shown in the y axis. Different respective compressor
speeds in the unit rev/min is shown in the x axis.
[0050] In this case, the loss proportions relate to the isentropic
work of compression, that is to say the loss-free work of
compression. The four diagrams show the respective power losses at
different delivery efficiencies, the designation A identifying a
delivery efficiency of 0.8, the designation B identifying a
delivery efficiency of 0.6, the designation C identifying a
delivery efficiency of 0.4 and the designation D identifying a
delivery efficiency of 0.2.
[0051] Here, the delivery efficiency is defined as the product of
the control efficiency and the volumetric efficiency. In this case,
the control efficiency .lamda..sub.control is defined as follows as
the ratio of the current geometric swept volume of the compressor
controllable in power output and the maximum geometric swept
volume:
.lamda..sub.control=V.sub.geo/V.sub.geo-max
[0052] The volumetric efficiency is defined in conventional manner
as the ratio of the actually delivered volumetric flow relative to
the volumetric flow theoretically delivered at the current swept
volume, according to the following equation:
.lamda..sub.volumetric=G.sub.R/(.rho..sub.suctionV.sub.geor.sub.c)
[0053] For the delivery efficiency, that is to say the product of
the volumetric efficiency and the control efficiency, the follow
ratio is thus obtained:
.lamda..sub.delivery=G.sub.R/(.rho..sub.suctionV.sub.geo-maxr.sub.c)
[0054] The quantitative determination of the individual loss
contributions to the total loss is complicated and requires
extensive measuring at the compressor, for example indication of
the compression behavior by means of a high definition measuring
technique.
[0055] In this case, compressor optimization which takes place by
"trial and error" is known from the prior art, only the effect on
the efficiency, which is easy to determine, and the volumetric
efficiency actually being determined. The way in which the
individual loss contributions are quantitatively split up under the
various operating conditions is not determined according to the
prior art. Such a resolution leads to an optimization potential for
the compressors which can be improved even further.
[0056] Thus, as mentioned at the beginning, design changes to the
compressor configuration possibly lead to opposed effects on the
individual loss processes, in which case the magnitude of these
effects may provide important hints for further optimization
steps.
[0057] However, the individual loss proportions can be quantified
by means of a computer analysis of measured data, as a result of
which conclusions can be drawn with regard to the dominating loss
mechanisms under various basic or operating conditions. However,
this optimization process is not the subject matter of the present
invention and is consequently not described in more detail. On the
contrary, the result of such a loss analysis is explained with
reference to an actual example and the conclusions are drawn which
can result in an increase in the overall efficiency in a R1349
compressor for a motor-vehicle air-conditioning system.
[0058] In this case, the designation 31a in FIG. 3 relates to the
relative stroke-independent friction power, the designation 31b
relates to the relative stroke-dependent friction power, the
designation 31c relates to the relative leakage loss, the
designation 31d relates to the relative pressure valve loss and the
designation 31e relates to the relative suction valve loss. It can
be seen that the relative stroke-independent friction power and the
relative stroke-dependent friction power are essentially
independent of the respective compressor speed. The relative
leakage loss 31c and the relative pressure valve loss 31d change as
a function of the compressor speed. In particular at high delivery
efficiencies, as shown in figs A and B, it can be seen that the
relative suction valve loss 31e greatly increases as a function of
the compressor speed toward high compressor speeds and, in
particular at high delivery efficiencies and high compressor
speeds, the relative suction valve loss 31e dominates the overall
power loss.
[0059] For this reason, the total power loss can be considerably
reduced, in particular at high compressor speeds, by a reduction in
the relative suction valve loss. In actual operating states of an
air-conditioning compressor, the suction power through the valve
gap of the suction valve reaches values of over 1000 W.
[0060] By a reduction in these losses at the suction valve, the
total loss can thus be reduced even if the pressure valve loss,
which has a less pronounced effect on the total loss compared with
the suction valve loss, is increased by the same measure.
[0061] A device according to the invention for compressing gaseous
media is shown in a first embodiment in FIG. 4. This device has one
pressure valve opening 4 and two suction valve openings 13a and
13b. The result of this is that the periphery of the suction valve
openings far exceeds the periphery of the pressure valve opening 4,
i.e. it is essentially twice the size in this exemplary embodiment.
The designation 7 identifies the covering means of the suction
valve, this covering means completely covering the valve openings
13a and 13b in the closed state.
[0062] As mentioned at the beginning, the largest proportion of the
pressure loss is produced at the narrowest cross section of the
respective valve. In the conventional design of the compressor
valves, this is generally the lateral area of the column-like
structure (cf. FIG. 2), the height of which is defined by the
distance of the covering means from the valve plate and the
periphery of which is defined by the periphery of the valve opening
cross section of the valve plate. This means that the narrowest
free cross section of the suction valve in relation to the
narrowest cross section of the pressure valve is defined by the
respective defined lateral areas in the product with the distances
of the covering means from the valve plate.
[0063] A further embodiment of a device according to the invention
is shown in FIG. 5. In this embodiment, the considerably larger
periphery of the suction valve relative to the pressure valve is
achieved by this valve opening having a substantially larger
circular cross section. It is to be noted in this case, however,
that a sufficiently wide web (not shown) remains between the
respective openings for the pressure valve and the suction valve,
this web permitting separation between the pressure space and the
suction space on that side of the valve plate which is opposite the
cylinder, in which or from which the gas to be compressed flows
(cf. FIG. 2).
[0064] A further embodiment of the device according to the
invention is shown in FIG. 6. In this case, the pressure valve or
its opening 4 remains essentially unchanged in comparison with the
embodiment shown in FIG. 5. The covering means 7 for the suction
opening has a multiplicity of apertures 27a, 27b, etc. These
apertures 27a, 27b serve to reduce the flow path at the narrowest
gap.
[0065] Since, in addition to the cross section of the respective
gap, the length of the gap between the opening 13 of the valve and
the covering means 7 is important, these apertures 27a, 27b can
ensure that the gas can discharge directly at the locations which
would result in a relatively long gas path of narrow cross section.
The respective apertures 27a, 27b may be arranged essentially
symmetrically, as in the embodiment shown in FIG. 6; however, an
arrangement of the respective apertures 27a, 27b which deviates
therefrom is also possible. In this embodiment, the opening 13 is
of star-shaped design, as a result of which a greatly increased
periphery is achieved. The apertures are arranged between the
projections 28a, 28b, etc. of the opening 13.
[0066] In the embodiment shown in FIG. 7, the covering means 13 has
recesses 29a, 29b, etc. instead of the apertures 27a, 27b from FIG.
6. In this embodiment, the suction opening 13 likewise has
projections 28a, 28b, etc. By means of this measure, firstly the
periphery of the suction opening 13 can be greatly increased, and
secondly flow paths which are far too long can also be prevented,
since the covering means 7 projects slightly beyond the opening in
each case only in the region of the respective projections. The
projections 39a, 39b, 39c (cf. FIGS. 6 and 7) of the covering means
7 preferably serve to limit the stroke of the covering means.
[0067] The advantages of the present invention result from the
avoidance of the abovementioned disadvantages (high energetic loss
contributions through the suction valve inside the compression
device). In particular, it is possible for the passage area of the
narrowest valve gap mainly responsible for the pressure loss, or
the passage area at the suction valve, to be increased by factors
compared with that of the pressure valve.
[0068] The compressor power loss for different control efficiencies
for the device according to the invention for the exchange of heat
is shown in FIG. 8. In this case, the sections A, B, C and D again
designate the individual ratios for the different control
efficiencies 0.8 (A), 0.6 (B), 0.4 (C), 0.2 (D). The power loss in
relation to the isentropic power is also plotted here against the
respective compressor speed.
[0069] It can be seen that, in the device according to the
invention for compressing gas, the relative stroke-independent
friction power 31a and the relative stroke-dependent friction power
31b also remain essentially constant over the compressor speed
range considered. On the other hand, in the device according to the
invention for compressing gas, with increasing compressor speed, a
considerably smaller increase in the relative suction valve loss
compared with the prior art takes place as a function of the
compressor speed, in particular at high control efficiencies and
high compressor speeds.
[0070] On the other hand, at low control efficiencies, the
improvement at the suction valve has only a relatively slight
effect.
[0071] The overall efficiency of an R134a compressor is shown in
FIGS. 9 and 10, FIG. 9 showing the effective cross section of a
compressor according to the prior art and FIG. 10 showing that of
the device according to the invention. Defined pressures are again
taken as a basis here. The respective speed of the compressor is
plotted over the x axis, the delivery efficiency is plotted over
the y axis and the calculated overall efficiency is plotted over
the z axis. It can be seen that, in the case of the device
according to the invention, in particular at high delivery
efficiencies and high speeds, the overall efficiency is
considerably higher than the comparable efficiency in the device
according to the prior art. The maximum overall efficiency in the
device according to the invention is also markedly higher than in
the device according to the prior art. Whereas for high delivery
efficiencies and high compressor speeds the calculated overall
efficiency in the device according to the prior art very quickly
drops to values below 0.25, the overall efficiency for the device
according to the invention is still about 0.35 at the comparable
speeds and delivery efficiencies.
[0072] As shown in FIG. 8, in comparison with FIG. 3, it was
possible to reduce the suction valve losses to about 30%. In this
case, it was possible for the effects on the overall
efficiency--shown in FIGS. 8, 9 and 10--defined as the ratio of
isentropic compression power and invested mechanical driving power,
in particular at average and high volumetric flows (that is to say
average and high speeds and average and high control efficiencies),
to be significantly improved, as can be seen from the comparison of
FIGS. 9 and 10. The result of this, in effect, is that lower
driving power is required for the operation of the air-conditioning
system, and in this way the fuel consumption required for the
air-conditioning system and the associated emission (greenhouse
effect) can be reduced.
[0073] In addition, it is possible to reduce the hot-gas
temperature. This leads to lower thermal loads on the coolant
hoses, to a reduction in the power requirements imposed on the
condenser, since less heat is to be dissipated to the environment,
and to a reduction in the refrigerant diffusion rate through the
elastomeric hose materials, which in turn leads to further
protection of the environment.
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