U.S. patent application number 12/281998 was filed with the patent office on 2009-09-03 for multistage compressor.
This patent application is currently assigned to Deutsches Zentru, Fur Luft-und Raumfahrt e.v.. Invention is credited to Klaus Baumer, Dirk Grulich, Herbert Wiegand.
Application Number | 20090220357 12/281998 |
Document ID | / |
Family ID | 38042803 |
Filed Date | 2009-09-03 |
United States Patent
Application |
20090220357 |
Kind Code |
A1 |
Baumer; Klaus ; et
al. |
September 3, 2009 |
MULTISTAGE COMPRESSOR
Abstract
The invention relates to a multistage compressor for providing
high-pressure gas in filling stations, said compressor consisting
of a high-pressure compressor and a multistage booster compressor
(W). Both compressors comprise membrane pump chambers which are
controlled by camshafts. The booster compressor (VV) can contain a
plurality of stages (S.sub.1, S.sub.2, S.sub.3), the chambers in
each stage forming groups (G.sub.1, G.sub.2, G.sub.3) of chambers.
The chambers of a group are synchronously operated in phase. The
chambers of two successive stages are operated in opposition of
phase. The number of chambers in a group is approximately the same
as the pressure ratio .pi., so that the size of the chambers can be
standardised.
Inventors: |
Baumer; Klaus; (Bonn,
DE) ; Grulich; Dirk; (Siegburg, DE) ; Wiegand;
Herbert; (Koln, DE) |
Correspondence
Address: |
RENNER OTTO BOISSELLE & SKLAR, LLP
1621 EUCLID AVENUE, NINETEENTH FLOOR
CLEVELAND
OH
44115
US
|
Assignee: |
Deutsches Zentru, Fur Luft-und
Raumfahrt e.v.
|
Family ID: |
38042803 |
Appl. No.: |
12/281998 |
Filed: |
February 9, 2007 |
PCT Filed: |
February 9, 2007 |
PCT NO: |
PCT/EP07/51265 |
371 Date: |
May 11, 2009 |
Current U.S.
Class: |
417/244 |
Current CPC
Class: |
F04B 41/06 20130101;
F04B 25/00 20130101; Y02E 60/32 20130101; F04B 45/0533 20130101;
F04B 27/0414 20130101 |
Class at
Publication: |
417/244 |
International
Class: |
F04B 25/00 20060101
F04B025/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 7, 2006 |
DE |
10 2006 010 326.2 |
Oct 9, 2006 |
DE |
10 2006 047 657.3 |
Claims
1. A multistage compressor comprising a high-pressure compressor
(HD) having at least one periodically driven membrane pump chamber
(HD1), characterized in that a booster compressor (VV) is provided
upstream of the high-pressure compressor (HD), said booster
compressor having at least one booster compressor stage
(S.sub.1-S.sub.3), each booster compressor stage comprising a
plurality of chambers (11-14) combined into at least one group
(G.sub.1-G.sub.4), and that the chambers of a group are driven
together and synchronously.
2. The multistage compressor of claim 1, characterized in that the
number (n) of the chambers in a group (G.sub.1-G.sub.4) of the
booster compressor (VV) is substantially equal to the compression
ratio (.pi.) of this stage.
3. The multistage compressor of claim 1, characterized in that the
booster compressor (VV) includes at least two booster compressor
stages (S.sub.1-S.sub.3), each chamber of the second booster
compressor stage (S2) being fed by a group (G.sub.1-G.sub.4) of
chambers of the first booster compressor stage (S.sub.1).
4. The multistage compressor of claim 3, characterized in that a
third booster compressor stage (S.sub.3), where each chamber is fed
by a group of chambers of the second booster compressor stage
(S.sub.2).
5. The multistage compressor of claim 1, characterized in that the
chambers are operated by one or a plurality of synchronized
camshafts (52), and that, according two the two-stroke method, an
intake and a compression of the gas is performed in the chambers
(53) during one half of a rotation of a camshaft between 0.degree.
and 180.degree., which is completed at an upper dead centre at a
cam angle of 90.degree. and which is followed by an expulsion of
the gas into the next stage up to a camshaft angle of
180.degree..
6. The multiple compressor of claim 1, characterized in that, with
several chambers existing in a stage of the booster compressor
(VV), the compression of the gas is performed synchronized in time
and, when the compression is completed, the gas is delivered to two
or more chambers of the following stage of the booster compressor
also synchronized in time.
7. The multistage compressor of claim 1 characterized in that the
gas leaving two or more chambers of the last stage of the booster
compressor is introduced into the first stage of a high-pressure
compressor (HD) at the end of the compression stroke.
8. A multistage compressor of claim 1, characterized in that the
dimensions of the membrane chambers (53) of the booster compressor
(VV) are configured such that membranes (52) of equal diameter may
be used for different structural sizes of a membrane compressor
that cover a range of the multiple pressure increase and gas
delivery.
9. The multistage compressor of claim 1, characterized in that the
mass moment of inertia caused by the gas forces is balanced in an
even number of stages of the booster device (VV).
10. The multistage compressor of claim 1, characterized in that,
with an odd number of stages of the booster compressor (VV), the
mass moment of inertia, which is caused by the gas forces in a
stage and is not balanced, is balanced by a circumferential counter
weight at the camshaft.
Description
[0001] The invention refers to a multistage compressor for
compressing gases and in particular to a membrane compressor for a
gas filling system for fueling a motor vehicle operating on natural
gas, methane or similar gases as well as on hydrogen.
[0002] Gases used as a means of energy storage in a motor vehicle
are problematic because of the required storage volume that, for
natural gas, is larger by 3 orders of magnitude under ambient
conditions, compared to liquid energy carriers. For this reason, it
has been regulated that natural gas is available at filling
stations at a pressure of 250 bar, so that a pressure of 200 bar,
as defined by technical rules, is reached and not exceeded in a
pressure gas container of a vehicle at a reference temperature of
15.degree. C. Thus, only about three times the storage volume of a
petrol vehicle have to be made available in the car.
[0003] In gas filling stations for direct filling with a
compressor, the compression causes an undesirable heating of the
gas, whose effect is the greater, the greater the stage pressure
ratio X is. To achieve the desired end pressure, the pressure ratio
.pi. may be reduced by increasing the number of stages.
[0004] In gas filling stations, the pressing work to be done causes
a heating of the gas in the pressure gas container. The
Joule-Thomson effect (change in the gas temperature by throttling)
of the real gas generally counteracts this heating. However, it is
only under very favorable conditions, i.e. at sufficiently low
temperatures, that the Joule-Thomson effect and the heat
dissipation to the environment will be sufficient to compensate for
the heating caused by the work of pressing the gas. If these
favorable conditions do not exist, a short-filling of the pressure
gas container will occur in gas filling stations without a cooling
device during decanting or direct filling. This is due to the fact
that the pressing work causes a high temperature and thus a
correspondingly high-pressure in the pressure gas container,
whereby the differential pressure available for filling is reduced
so much that the filling operation takes long and is therefore
interrupted before the pressure gas container holds the gas volume
possible by technical specifications.
[0005] DE 197 05 601 A1 describes a natural gas filling method
without a cooling of the gas, wherein the operation of filling the
pressure gas container is carried on until the pressure in the line
to the pressure gas container exceeds a maximum pressure. Another
possibility provides that the filling operation is interrupted when
the mass flow exceeds a threshold value.
[0006] WO 97/06383 A1 describes a gas charging system for
high-pressure gas bottles. In this case, the gas is cooled by
flushing the high-pressure gas bottle to be filled, whereby two
connectors for the feed and return lines are required. In the
flushing circuit, the gas is cooled by a heat exchanger or by being
mixed with the gas in the supply container.
[0007] EP 0 653 585 A1 proposes a system for filling a pressure gas
container. It describes the execution of a testing impulse which is
evaluated using the thermal equation of state for the real gas.
Further, a switching to supply containers with higher pressure
(multi-bank method) during the filling is described. The filling
operation is executed intermittently. No cooling device for the gas
is provided.
[0008] DE 102 18 678 B4 describes a method and a device wherein the
gas to be filled into the pressure gas container is fed from a
high-pressure supply container via a cyclone tube as a cooling
device. The cyclone tube utilizes the existing differential
pressure in the filling system to separate the gas flow into a hot
gas flow and a cold gas flow. The latter will then be fed to the
pressure gas container.
[0009] DE 10 2005 006 751 A1 also proposes a device, wherein a
decrease in the temperature of gases is obtained through a cyclone
tube without providing for a separation into a hot gas flow and a
cold gas flow.
[0010] The operation of the two latter methods and devices is based
on the fact that the gas is fed to a swirling device at a
supercritical pressure ratio, which swirling device is arranged
axially between two pipes that have different inlet diameters. A
decrease in the temperature of gases by means of a cyclone tube
will be successful if, and only if, supercritical pressure
conditions prevail. At a critical pressure ratio for natural gas of
1/.pi.'<0.5427 and a pressure in the supply container of
p.sub.D=250 bar, which is typically under-run when a plurality of
vehicles are filled in short succession, a subcritical state is
reached when the pressure in the pressure gas container has risen
to P.sub.D=135 bar. This means that under the conditions set by the
technical specifications, the use of a cyclone tube will provide no
further decrease in the temperature of the gas when a pressure gas
container is filled with natural gas in the pressure range from
P.sub.D=135 bar to p.sub.D=200 bar.
[0011] In WO 01/27475 A1, a multistage membrane compressor of a
star-shaped structure is described, wherein the compressor chambers
are arranged in a star shape around a crankshaft. The compressor
chambers form individual stages of a multistage compressor and
therefore have different volumes. Thus, high compression ratios can
be realized, however, while producing substantial amounts of
compression heat.
[0012] Direct filling independent of a filling station is feasible
where installing public natural gas filling stations is
uneconomical. Vehicles--and not only those of individual
transport--could be filled where they are during their downtime.
This may be in industrial parks, garages or car boards. Numerous
households or buildings have natural gas at their disposal for
hating purposes. Using a compressor (natural gas compressor), this
natural gas could be compressed in a garage during the night from
the typical natural gas network pressure level of 50 mbar to 200
bar at a reference temperature of 15.degree. C. The motor vehicle
can be filled therewith.
[0013] Another possibility to use such a filling system is
envisaged in agriculture, where biological gas is produced in vast
amounts. Instead of feeding this biological gas into a public gas
network, the gas may be compressed in situ and be used to drive
agricultural vehicles and machines. Thus, it would be possible in
the future to replace biological diesel fuel in the field of
agriculture. One demand, among others, to be met by this compressor
is that the compressor has to be designed such that a full filling
can be achieved in one night (ca. 8 hours) at 200 bar and a
reference temperature of 15.degree. C.
[0014] The major problem of a multistage high-pressure compressor
is the heating of the gas between the individual compressor stages
and the cooling of the gas at the compressor outlet, which must
never exceed a temperature of 60.degree. C. when entering the
pressure gas container during the filling.
[0015] It is an object of the present invention to design a
multistage compressor such that it becomes possible to fill a
pressure gas container by direct filling such that a limit value of
the pressure, given by technical specifications, is reached in the
pressure gas container at a predetermined limit temperature.
[0016] The multistage compressor of the present invention is
defined in claim 1. According to the same, a booster compressor is
located upstream of the high-pressure compressor, which booster
compressor includes at least one booster stage, wherein each
booster stage comprises several chambers that are combined into at
least one group and the chambers of a group are operated in common
and synchronously.
[0017] The invention is based on the idea that, in a high-pressure
compressor of membrane structure, a reduction of the pressure ratio
should not be obtained by increasing the number of stages of the
high-pressure compressor, but that a single- or multistage booster
compressor should be provided upstream of the high-pressure
compressor.
[0018] With such a booster compressor, not only the pressure ratio
.pi. can be decreased, but--without changing the dimensions of the
high-pressure compressor--also the mass flow rate can be increased
proportionally to the increase of the boost pressure. The
combination of a booster compressor and a high-pressure
compressor--both realized as membrane structures--allows to
establish a gas filing system that meets a wide range of demands
with respect to the mass flow rate (filling time). This is achieved
with a single- or multistage compressor, if the membrane dimensions
thereof identically match the dimensions of the membrane of the
first stage in the high-pressure compressor. This is true
irrespective of the number of stages, if an integral value .pi.=2,
3, 4, . . . is chosen for the pressure ratio in the booster
compressor.
[0019] The invention allows to use standardized multiple membrane
pumps. In this case, the sizes of the different pump chambers may
be equal to each other. It is also possible, however, in a pumping
device with pump chambers in a star-shaped arrangement, to make the
pump chambers replaceable so that pump chambers of different sizes
are available which may optionally be mounted in the pumping
device.
[0020] In direct filling, it becomes possible with a multistage
booster compressor to maintain a supercritical pressure ratio until
the end of filling of a pressure gas container at a container
pressure of 200 bar. As already comprehensively described in DE 10
2005 016 114 A1, this allows to decrease the gas temperature
through the use of a cyclone tube or a spray-nozzle element
according to DE 100 31 155 C2 or only through adiabatic throttling,
so that an increase in temperature caused by the pressing work can
be compensated. In this manner, filling at a container pressure of
200 bar at a reference pressure of 15.degree. C. can be realized
even in direct filling, regardless of the ambient temperature.
[0021] If, according to the invention, the high-pressure compressor
is also realized as a membrane compressor, it may be operated at
the same speed via a common shaft with the upstream membrane
booster compressor.
[0022] A particularly suitable embodiment of the invention provides
that, with very large gas volume flows, the first and the following
stages of the booster compressor are divided into several membrane
chambers if the membrane diameter required for a large volume flow
can not be realized for material related reasons. For example, in a
single-stage booster compressor with a pressure ratio .pi.=2, the
first stage of the high-pressure compressor can be supplied with
twice the gas volume flow of a high-pressure compressor operated
without a compressor. To achieve this, the booster compressor has
to be provided with two membrane chambers of the same dimensions as
the first stage of the high-pressure compressor. Depending on the
boost pressure to be generated in the booster compressor and the
gas volume flow increasing proportionally thereto, different
variations can be made to the booster compressor design according
to the invention, which variations will be explained hereunder
using a simple mathematic consideration.
[0023] Applying the geometric series
I+x+x.sup.2+x.sup.n (1)
as the base, where the quotient of two successive members is
constant and, in the present case, the value x describes the
pressure ratio .pi. and the exponent n describes the number of
membrane chambers per stage, so that the above equation can be
represented in the following form:
I+.pi.+.pi..sup.2+.pi..sup.3+.pi..sup.n (2)
[0024] From equation (2), the following is obtained for a pressure
ratio of
.pi.=2:1+2+4+8+2.sup.n
.pi.=3:1+3+9+27+3.sup.n
.pi.=4:1+4+16+64+4.sup.n
wherein, in the practical implementation, first, only the
combinations listed in the table below may be realized.
TABLE-US-00001 pressure number of number of ratio .pi. stages z
chambers n 2 1 2 2 4 3 6 3 1 3 2 9 4 1 4
[0025] For a pressure ratio of .pi.=2, the dimensions of the two
membrane chambers of the last stage of the booster compressor have
to be the same as those of the first stage of the downstream
high-pressure compressor of membrane structure. For a pressure
ratio of .pi.=3, this is true for the three membrane chambers, and
for a pressure ratio of .pi.=4, this applies to the four membrane
chambers of the last stage of the booster compressor.
[0026] Provided that the booster compressor is operated at the same
speed of rotation as the downstream high-pressure compressor of the
membrane type and the stroke in the individual membrane chambers is
the same as the membrane stroke in the first stage of the
high-pressure compressor, it can be proven that the diameter of the
membrane chamber always corresponds to the membrane diameter of the
first stage of the high-pressure compressor. The pressure ratio
.pi. must always correspond to the number z of the membrane
chambers/stages and be an integral .pi.=2, 3, 4 that is independent
of the stage pressure ratio .pi..sub.HD in the high-pressure
compressor.
[0027] For a single-stage booster compressor with a pressure ratio
.pi.=4, a diameter D.sub.1 and [0028] 4 membrane chambers in the
1st stage: z.sub.1=4 it can be shown that [0029] 1st stage:
V.sub.1=z.sub.1D.sub.1.sup.2=4D.sub.1.sup.2 [0030] HD.sub.1:
V.sub.HD1=V.sub.1/.pi.=(4D.sub.1.sup.2)/4 [0031]
D.sub.HD1=(D.sub.1.sup.2).sup.0.5=D.sub.1
[0032] Here, V.sub.1 is the volume of the 1st stage, D.sub.1 is the
diameter of the 1st stage of the booster compressor, HD.sub.1 is
the diameter of the first stage of the high-pressure compressor,
V.sub.HD1 is the volume of the 1.sup.st stage of the high-pressure
compressor, D.sub.HD1 is the diameter of the 1.sup.st stage of the
high-pressure compressor, z.sub.n is the number of the membrane
pumps in the stage n.
[0033] For a two-stage booster with a pressure ratio .pi.=3, a
diameter D.sub.1 and [0034] 9 membrane chambers in the 1st stage:
z.sub.1=9 [0035] 3 membrane chambers in the 2nd stage: Z.sub.2=3
the following is obtained [0036] 1st stage:
V.sub.1=z.sub.1D.sub.1.sup.2=9D.sub.1.sup.2 [0037] 2.sup.nd stage:
V.sub.2=V.sub.1/.pi.=(9D.sub.1.sup.2)/3=3D.sub.1.sup.2 [0038]
D.sub.2=(3D.sub.1.sup.2/z.sub.2).sup.0.5=(3D.sub.1.sup.2/3).sup.0.5=D.sub-
.1 [0039] HD.sub.1: V.sub.HD1=V.sub.2/.pi.=(3D.sub.1.sup.2)/3
[0040] D.sub.HD1=(D.sub.1.sup.2).sup.0.5=D.sub.1 and for a
three-stage booster compressor with the pressure ratio .pi.=2, a
diameter D.sub.1, as well as [0041] 8 membrane chambers in the 1st
stage: z.sub.1=8 [0042] 4 membrane chambers in the 2nd stage:
z.sub.2=4 [0043] 2 membrane chambers in the 3rd stage: z.sub.3=2
the following is obtained [0044] 1st stage:
V.sub.1=z.sub.1D.sub.1.sup.2=8D.sub.1.sup.2 [0045] 2.sup.nd stage:
V.sub.2=V.sub.1/.pi.=(8D.sub.1.sup.2)/2=4D.sub.1.sup.2 [0046]
D.sub.2=(4D.sub.1.sup.2/z.sub.2).sup.0.5=(4D.sub.1.sup.2/4).sup.0.5=D.sub-
.1 [0047] 3.sup.rd stage:
V.sub.3=V.sub.2/.pi.=(4D.sub.1.sup.2)/2=2D.sub.1.sup.2 [0048]
D.sub.3=(2D.sub.1.sup.2/z.sub.3).sup.0.5=(2D.sub.1.sup.2/2).sup.0.5=D.sub-
.1 [0049] HD.sub.1:
V.sub.HD1=V.sub.3/.pi.=(3D.sub.1.sup.2)/2=D.sub.1.sup.2 [0050]
D.sub.HD1=(D.sub.1.sup.2).sup.0.5=D.sub.1
[0051] It is considered a particular advantage of a booster
compressor designed in this manner that like components can be used
in a cost-saving manner when subdividing the stages into individual
membrane chambers. These are, as essential parts of the booster
compressor, the membranes of the membrane chambers which all have
the same dimensions as the membrane of the first downstream
high-pressure compressor of the membrane type. It is another
advantage of the present invention that the dimensions of the
membrane or the membrane chambers are independent of the pressure
ratio, the volumetric flow rate and the desired output pressure of
the booster compressor. According to the invention, a booster
compressor further allows to first increase the delivery volume of
a high-pressure compressor of the membrane type by two to nine
times with respect to an operation without a booster
compressor.
[0052] The following is a detailed description of embodiments of
the invention with reference to the accompanying drawings.
[0053] In the Figures:
[0054] FIG. 1 is a schematic longitudinal section through a
multi-chamber membrane pump with membrane chambers arranged in a
star shape around a camshaft,
[0055] FIG. 2 illustrates an embodiment of a compressor formed by a
booster compressor and a single- or multistage high-pressure
compressor of the membrane type,
[0056] FIG. 3 is a schematic general view on the structure and the
division of the membrane chambers in a compressor with a
single-stage booster compressor and a single-stage high-pressure
compressor,
[0057] FIG. 4 is an embodiment with a two-stage booster compressor
and a single-stage high-pressure compressor,
[0058] FIG. 5 is an embodiment with a three-stage booster
compressor and a single stage high-pressure compressor,
[0059] FIG. 6 is a schematic illustration of the camshaft in a
single-stage booster compressor,
[0060] FIG. 7 is an illustration of the camshaft in a two-stage
booster compressor, and
[0061] FIG. 8 is an illustration of the camshaft in a three-stage
compressor.
[0062] FIG. 1 is a schematic illustration of a membrane chamber
pump 50. A camshaft 52 is supported in a housing 51, the camshaft
controlling a plurality of membrane pump chambers 53 arranged in
star shape around the camshaft. Each membrane pump chamber 53 is
delimited by a flexible membrane 54 that is movable between two end
positions. The membrane pump chamber 53 has an inlet line 54 with a
check valve 55 and an outlet line 66 with a check valve 57. gas is
drawn in through the inlet line 64 and the compressed gas is
expelled through the outlet line 66.
[0063] The membrane 54 is moved by a liquid buffer 58 contained in
a cylinder 59 in which a piston can be moved. A spring 61 presses
the piston 60 against a ball bearing 62 sitting on the camshaft 52
and forming an eccentric for driving the piston. The piston 60
performs a linear movement in the cylinder 59 whereby the membrane
54 is moved between its end positions through the liquid buffer
58.
[0064] Besides the ball bearing 62, FIG. 1 illustrates further ball
bearings on the camshaft 52. These serve to actuate the other
membrane chambers arranged in star shape around the camshaft.
[0065] The liquid buffer 58 is supplied or maintained filled with
liquid by a pumping device (not illustrated) that is also driven by
the camshaft.
[0066] FIG. 2 illustrates a compressor formed by a booster
compressor VV and a high-pressure compressor HD. The booster
compressor is formed by the multiple membrane compressor. It
comprises four membrane pump chambers 11, 12, 13, 14 controlled by
the same camshaft. The outlet lines of the membrane pump chambers
are illustrated in FIG. 2. They are connected with a manifold 70
leading to a membrane pump chamber FD1 of the high-pressure
compressor HD. In the present case, the high-pressure compressor is
also designed as a camshaft controlled membrane pump, the other
membrane pump chambers being adapted for use as further stages of
the high-pressure compressor or for other purposes.
[0067] In the booster compressor VV, all membrane pump chambers
11-14 are controlled synchronously and in phase. This means that
all chambers take in simultaneously and expel the compressed gas in
phase. Likewise, the booster compressor VV and the high-pressure HD
are synchronized with each other, the chamber HD1 that receives the
compressed gas from the booster compressor VV being operated in
opposite phase relative to the booster compressor. In other words:
when the booster compressor expels gas, the chamber HD1 has to be
in a position for receiving gas.
[0068] In the present embodiment, it is assumed that the booster
compressor has a compression ratio of .pi.=4. This means that the
entire gas received by the booster compressor is compressed in the
booster compressor to one fourth of its volume. Since, on the other
hand, the volumes of four chambers are combined, a gas volume is
obtained that, in the compressed state, approximately corresponds
to the volume of one of the chambers of the booster compressor.
Thus, the chamber HD1 of the high-pressure compressor has
approximately the same volume as one of the chambers of the booster
compressor.
[0069] FIG. 3 illustrates the structure of a single-stage booster
compressor with four membrane chambers, each having a pressure
ratio of .pi.=4 and an output pressure p.sub.A=4 bar. The first
figure in the schematically illustrated membrane chambers refers to
the compressor stage, the second figure sequentially numbers the
membrane chambers in the associated stage. HD1 refers to the first
stage of the downstream high-pressure compressor, whose dimensions
are identical with the individual membrane chambers of the booster
compressor.
[0070] FIG. 4 illustrates a corresponding structure for a two-stage
booster pressure with a pressure ratio .pi.=3 and an output
pressure p.sub.A=9 bar, wherein a total of twelve membrane chambers
are implemented in the booster compressor. Finally, FIG. 5
illustrates the structure of a three-stage booster compressor of
the membrane type. Here, a pressure ratio of .pi.=2 was chosen,
whereby an output pressure p.sub.A=8 bar is obtained in the third
stage with a total of fourteen membrane chambers.
[0071] In the embodiment of FIG. 3, the booster compressor VV is
formed by a single stage S.sub.1 with n=4 chambers, the pressure
ratio being .pi.=4. In the embodiment of FIG. 4, the booster
compressor VV is formed by two stages S.sub.1, S.sub.2, each stage
having n=3 chambers combined into a group G.sub.1-G.sub.3. In the
embodiment of FIG. 5, the booster compressor VV is formed by three
stages S.sub.1, S.sub.2, S.sub.3, where four groups of chambers are
formed in the first stage S.sub.1 and each group is formed by n=2
chambers. The compression ratio .pi. is also 2. In the second stage
as well, two respective chambers are combined into a group, and the
same is true for the third stage S.sub.3.
[0072] FIG. 6 is a cross section through and a view of the camshaft
for a single-stage booster pressure. By the eccentric shape of the
camshaft that extends over a range from 0.degree. to 180.degree.,
as is evident from the cross section, the individual membranes in
the membrane chambers of the booster compressor are operated during
one half of a rotation of the camshaft. The membrane chambers
operated in a two-stroke mode take in the gas in the first quarter
up to the upper dead centre at 90.degree. and compress the same in
order to subsequently begin the expulsion process in the second
quarter, which is completed at an cam angle of 180.degree.. As is
evident from the illustration, in a single-stage booster compressor
with four membrane chambers, the entire gas volume flows into the
first stage of the downstream high-pressure compressor. In the
illustration, the first figure in the schematically shown eccentric
of the camshaft refers to the compressor stage in the booster
compressor, whereas the second figure indicates the sequential
number of the membrane chambers present in the respective
compressor stage.
[0073] FIG. 7 is a cross section through and a view of the camshaft
using the example of a two-stage booster compressor. However, in
the first stage, the intake and the compression of the gas starts
at an angular position of the cam of 180.degree., the upper dead
centre being at a cam angle of 270.degree. and the expulsion into
the second stage of the booster compressor is completed a cam angle
of 0.degree.. The timing of the intake, the compression and the
expulsion of the gas into the first stage of the downstream
high-pressure compressor in the second stage will then be the same
as in a single-stage booster compressor.
[0074] FIG. 8 is a cross section and a view, illustrating the
course of the control of the membranes in the membrane chambers by
a camshaft for a three-stage booster compressor with a low stage
pressure ratio of .pi.=2. The compression process in the first
stage starts at an angular position of the cam of 0.degree., is
completed at the upper dead centre at a cam angle of 90.degree.,
followed by the process of expulsion into the second compressor
stage that is completed at a cam angle of 180.degree.. The second
compressor stage has its upper dead centre at a cam angle of
270.degree., followed by the process of expulsion into the third
compressor stage up to a cam angle of 0.degree.. The latter has its
upper dead centre at a cam angle of 90.degree. and ends with the
subsequent expulsion of the gas flow from the two membrane chambers
of the first stage of the booster compressor into the first stage
of a downstream high-pressure compressor. This process is completed
at a cam angle of 180.degree..
[0075] The gas forces to be controlled by the camshaft in the form
of an eccentric have a balanced mass moment of inertia only in the
two-stage embodiment of the booster compressor (FIG. 7). This means
the mass moment of inertia caused by the gas forces has to be
balanced only for even numbers of compressor stages. For odd
numbers of stages (FIGS. 6 and 8), the gas forces of a stage that
cause the mass moment of inertia that does not have to be balanced
must be balanced by a circumferential counter-weight at the
camshaft.
* * * * *