U.S. patent application number 13/199301 was filed with the patent office on 2012-03-01 for charging device for an energy conversion device.
Invention is credited to Reiner Kimmich, Andreas Knoop, Thomas Steidten.
Application Number | 20120051952 13/199301 |
Document ID | / |
Family ID | 45565949 |
Filed Date | 2012-03-01 |
United States Patent
Application |
20120051952 |
Kind Code |
A1 |
Knoop; Andreas ; et
al. |
March 1, 2012 |
Charging device for an energy conversion device
Abstract
A charging device for an energy conversion device, e.g., a fuel
cell, of a motor vehicle, has a rotor rotatably mounted on a
housing of the charging device, the rotor having a shaft and at
least two compressor wheels which are connected in rotationally
fixed fashion to the shaft. The compressor wheels have wheel rear
parts facing away from respective compressor wheel inlets, by which
a medium that is to be supplied to the energy conversion device,
e.g., air, is compressible. The wheel rear parts of the compressor
wheels are matched to one another such that respective forces which
are opposed to one another and which result from respective
compressor wheel outlet forces impressed on the wheel rear parts
substantially balance one another.
Inventors: |
Knoop; Andreas; (Esslingen,
DE) ; Steidten; Thomas; (Ludwigsburg, DE) ;
Kimmich; Reiner; (Bietigheim-Bissingen, DE) |
Family ID: |
45565949 |
Appl. No.: |
13/199301 |
Filed: |
August 24, 2011 |
Current U.S.
Class: |
417/365 ;
415/104; 417/423.12 |
Current CPC
Class: |
F04D 29/057 20130101;
F04D 29/0516 20130101; F04D 17/12 20130101; Y02E 60/50 20130101;
H01M 8/04111 20130101; Y02T 90/40 20130101; B60L 58/30 20190201;
F04D 25/06 20130101 |
Class at
Publication: |
417/365 ;
415/104; 417/423.12 |
International
Class: |
F04D 29/041 20060101
F04D029/041; F04D 29/047 20060101 F04D029/047; F04D 29/32 20060101
F04D029/32; F04D 25/06 20060101 F04D025/06 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 28, 2010 |
DE |
10 2010 035 725.1 |
Claims
1. A charging device for a fuel cell of a motor vehicle,
comprising: a housing; and a rotor rotatably mounted on the
housing, wherein the rotor includes a shaft and at least two
compressor wheels connected to the shaft in rotationally fixed
fashion, wherein each compressor wheel has a wheel rear part facing
away from a respective compressor wheel inlet, wherein the at least
two compressor wheels compress air which is to be supplied to the
fuel cell, and wherein the wheel rear parts of the two compressor
wheels are matched to one another such that opposing forces
resulting from respective compressor wheel outlet pressures
impressed on the wheel rear parts substantially balance one
another.
2. The charging device as recited in claim 1, wherein the wheel
rear parts are matched to one another with regard to their
diameter.
3. The charging device as recited in claim 2, wherein the rotor is
mounted by at least one air bearing in the axial direction.
4. The charging device as recited in claim 2, wherein the at least
two compressor wheels for compressing air are connected in
series.
5. The charging device as recited in claim 2, wherein the at least
two compressor wheels for compressing air are connected in
parallel.
6. The charging device as recited in claim 2, further comprising: a
drive motor configured to drive the rotor.
7. The charging device as recited in claim 2, wherein the rotor has
a turbine wheel connected in rotationally fixed fashion to the
shaft, and wherein the rotor is driven by the turbine wheel.
8. The charging device as recited in claim 7, wherein the turbine
wheel is driven by an exhaust gas of the fuel cell.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a charging device for an
energy conversion device, e.g., a fuel cell.
[0003] 2. Description of the Related Art
[0004] Published Japanese patent application JP 2001/263291
discloses a supporting structure for a high-speed compressor having
an electric motor that includes a rotor shaft mounted by magnetic
bearings.
[0005] U.S. Pat. No. 6,196,809 B1 discloses a two-stage compressor
having two compressor wheels that are attached to opposite end
regions of a shaft. For the axial mounting, magnetic axial bearings
are provided that absorb forces in the axial direction of the
shaft.
[0006] U.S. Pat. No. 6,155,802 discloses a turbo compressor having
a first and a second compression chamber, and having a shaft that
is connected to two compressor wheels.
[0007] U.S. Pat. No. 6,450,780 B1 discloses a method for producing
a gas under pressure using a compressor that is coupled to an
electrical machine. The compressor includes a rotor having a shaft
that is mounted by magnetic bearings. In addition, the rotor
includes two compressor wheels that are connected to the shaft in
rotationally fixed fashion.
[0008] Published international patent application document WO
03/040567 A1 discloses a two-stage compressor having a shaft. The
compressor also includes two compressor wheels by which a fluid is
to be compressed. The compressor wheels are connected to the shaft
in rotationally fixed fashion.
[0009] The known compressors have further potential for making
their operation more efficient.
[0010] Therefore, an object of the present invention is to provide
a charging device for an energy conversion device that has
particularly efficient operation.
BRIEF SUMMARY OF THE INVENTION
[0011] According to the present invention, a charging device for an
energy conversion device, in particular for a fuel cell, of a motor
vehicle includes a rotor that is rotatably mounted on a housing of
the charging device, said rotor having a shaft and having at least
two compressor wheels that are connected to the shaft in
rotationally fixed fashion and that each have wheel rear parts
facing away from respective compressor wheel inlets, by which
wheels a medium that is to be supplied to the energy conversion
device, in particular air, can be compressed.
[0012] According to the present invention, it is provided that the
wheel rear parts of the compressor wheels are matched to one
another, so that respective oppositely oriented forces resulting
from compressor wheel outlet pressures impressed on the rear parts
of the wheels balance one another, at least substantially. Due to
this balancing of the forces acting in particular and at least
substantially in the axial direction of the shaft, no forces, or
only very small forces, have to be absorbed and supported in this
direction. In this way, no, or only very small, frictional losses
occur that would occur as a result of forces to be supported, so
that a very efficient operation of the charging device results.
This is also beneficial for a very efficient operation of the
energy conversion device associated with the charging device, so
that said energy conversion device can thus be operated in a
particularly energy-efficient manner, so that the energy converted
by the energy conversion device can for example be used in very
large part to drive the motor vehicle, and does not for example
remain unused as a result of frictional losses resulting from the
described forces.
[0013] This is advantageous in particular if the shaft or the rotor
is mounted by at least one air bearing, in particular a dynamic air
bearing, having at least one foil for the mounting. As a result of
their design, such air bearings produce higher frictional losses
than do other kinds of bearings such as ball bearings; the
predominant part of these frictional losses, for example two-thirds
of the overall frictional losses, occur in particular in the
absorption of bearing forces in the axial direction of the
shaft.
[0014] Through the use of the compressor wheels having the wheel
rear parts matched to one another, it is possible at least largely
to cancel the opposed forces, in particular the axial forces, in
that the forces counterbalance one another. A result of this is
that a corresponding bearing, in particular an axial bearing, for
the absorption of these forces can be made correspondingly smaller
in its dimensions and therefore less susceptible to losses, or can
even be completely omitted. This also results in very low weight as
well as, in some cases, a very low part count of the charging
device according to the present invention, which on the one hand is
beneficial for the efficient operation of the charging device and
on the other hand keeps the costs of the charging device, and
therefore of the motor vehicle as a whole, low.
[0015] In an advantageous specific embodiment of the present
invention, the wheel rear parts are matched to one another with
regard to their respective diameter. In this way, the balancing of
the oppositely acting forces is realized in a particularly simple
and economical manner, reducing the complexity of the charging
device as well as its part count, and also keeping low the costs of
the charging device. If pressures differing from one another act on
the wheel rear parts, then the respective surfaces of the wheel
rear parts on which the pressures act are correspondingly to be
matched to one another with regard to their surface content, so
that from this matching there result opposed forces that balance
one another. Here, a design parameter suitable for the matching of
the surface contents is the diameter of the wheel rear parts; for
example, a larger diameter results in a larger surface, and a
comparatively smaller diameter results in a smaller surface. If,
for example, a first pressure acts on one of the wheel rear parts
that is greater than a second pressure acting on the other wheel
rear part, then the surface on which the first pressure acts is
correspondingly to be made smaller in its surface content than the
surface of the wheel rear part on which the second pressure acts,
so that forces result whose magnitudes are equal but that are
opposed to one another and therefore counterbalance one another, in
particular in the axial direction of the shaft.
[0016] During operation of the charging device for compressing the
air, in particular axial forces arise that act in the direction of
the respective compressor wheel inlets in the axial direction of
the shaft. These axial forces at least substantially counterbalance
one another in the charging device according to the present
invention, so that a corresponding axial bearing can be omitted, or
at least can be made with smaller dimensions.
[0017] If the charging device according to the present invention is
used in a motor vehicle during whose operation there may occur
non-steady operating states of the energy conversion device and
thus of the charging device, in particular accelerations of the
charging device, then a corresponding axial bearing of the rotor
may be indispensable in order to prevent contact between the rotor
and, in particular, the compressor wheels and the housing of the
charging device, and thus to ensure reliable, long-lived operation
of the charging device.
[0018] Alternatively or in addition, it can be provided that the
rotor is mounted in the radial direction of the shaft by a magnetic
bearing, bringing the advantages already described in connection
with such a magnetic bearing.
[0019] In an advantageous specific embodiment of the present
invention, the rotor is mounted by at least one air bearing, in
particular in the axial direction. Such an air bearing, which has
for example a foil for bearing the rotor, enables an efficient and
reliable bearing of the rotor even, and in particular, at very high
rotational speeds of the rotor which occur for the efficient
compression of the air.
[0020] In order to enable the air to be compressed particularly
efficiently and so as to meet demand, the charging device has for
example a motor, in particular an electric motor, by which the
rotor can be driven. This enables an operation of the charging
device that is efficient and meets the demand for the supply,
proportionate to demand, of compressed air to the energy conversion
device, resulting in efficient operation of the energy conversion
device and thus of the motor vehicle as a whole.
[0021] In a particularly advantageous specific embodiment of the
present invention, the compressor wheels for compressing the medium
are connected in series to one another, resulting in a two-stage
and particularly efficient compression of the medium, in particular
air. Here, one of the compressor wheels acts as a first compressor
stage and the other compressor wheel acts as the second compressor
stage, the diameter of the wheel rear parts, or the diameter of the
compressor wheels, being for example correspondingly matched to one
another so that forces that occur during compression, in particular
axial forces, cancel each other out at least almost completely,
advantageously completely.
[0022] It is also possible for the compressor wheels for
compressing the medium, in particular air, to be connected parallel
to one another. This also enables a particularly advantageous and
efficient compression of the air; here, compressor wheels can be
used that are at least substantially equal with regard to their
diameter, or with regard to the diameter of the wheel rear parts,
and that differ only in their direction of rotation. A stream of
the medium, in particular air, that is to be compressed is then
applied simultaneously and in parallel to these two compressor
wheels. In this specific embodiment, a complete compensation is
possible of the forces resulting from the compression, in
particular the axial forces.
[0023] If the rotor has a turbine wheel that is connected in
rotationally fixed fashion to the shaft, by which the rotor can be
driven, then in this way the operation of the charging device and
in particular of the energy conversion device can be made
particularly efficient. Here, for example the exhaust gas of the
energy conversion device, in particular the fuel cell, can be used
to drive the turbine and, via the turbine, the compressor
wheels.
[0024] In the charging device according to the present invention,
it can be provided that the compressor wheels are situated in
opposite end regions of the shaft. If the turbine wheel is
provided, it is possible for the turbine wheel to be situated
between the compressor wheels in the axial direction of the shaft.
It can also be provided that, in the axial direction of the shaft,
first the first compressor wheel is situated on the shaft and is
connected in rotationally fixed fashion thereto, and is followed by
the second compressor wheel, situated on the shaft and connected in
rotationally fixed fashion thereto, the turbine wheel only then
being situated on the shaft in the axial direction and connected in
rotationally fixed fashion thereto. These specific embodiments are
advantageous and are correspondingly to be selected depending on
conditions of space, demands, boundary conditions, and/or the
like.
[0025] Here it is to be noted that the compressor wheels and the
turbine wheel that may be provided are fashioned as radial
compressor wheels or a radial turbine wheel, so that the medium can
be compressed particularly efficiently and the charging device
requires only very little space. This solves or avoids packaging
problems, in particular in space-critical areas of the motor
vehicle in which the charging device is situated.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 shows a schematic longitudinal sectional view of a
charging device that has a first compressor and a second compressor
by which air that is to be supplied to a fuel cell can be
compressed in two stages, the compressor having respective
compressor wheels having wheel rear parts that are matched to one
another, through which respective, opposed axial forces resulting
from respective compressor outlet pressures impressed on the wheel
rear parts balance one another, at least substantially.
[0027] FIG. 2 shows a schematic longitudinal sectional view of
another specific embodiment of a charging device as shown in FIG.
1, whose compressors are connected to one another in parallel, the
air being compressible by the compressors in one stage.
[0028] FIG. 3 shows a schematic longitudinal sectional view of a
further specific embodiment of the charging device in FIG. 2, the
charging device having a turbine capable of driving the compressor
for compressing the air.
DETAILED DESCRIPTION OF THE INVENTION
[0029] FIG. 1 shows a charging device 10 that is allocated to a
fuel cell and by which air that is to be supplied to the fuel cell
can be compressed. The fuel cell uses this compressed air supplied
to it to convert the oxygen in the air, and the hydrogen supplied
to it, into electrical energy.
[0030] Charging device 10 has a first compressor 12, fashioned as a
radial compressor, having a housing 14 in which a first compressor
wheel 18, having a first wheel rear part 16, is accommodated. In
addition, charging device 10 has a second compressor 20 fashioned
as a radial compressor, having a housing 22 in which a second
compressor wheel 26 having a second wheel rear part 24 is
accommodated.
[0031] Compressor wheels 18 and 26 are situated in respective end
regions 28 and 30 of a shaft 32, on said shaft, and are connected
in rotationally fixed fashion thereto, charging device 10 having a
rotor 34 to which compressor wheels 16 and 26 and shaft 32 are
allocated.
[0032] In addition, charging device 10 has an electric motor 36 by
which compressor wheels 18 and 26 for compressing the air can be
driven via shaft 32. For this purpose, shaft 32, as well as
compressor wheels 18 and 26, rotate about an axis of rotation 51 at
very high rotational speeds.
[0033] The air that is to be compressed is supplied to compressor
12, acting as the first compressor stage, in the direction shown by
arrow 40, the air flowing to the corresponding compressor wheel 18
via a compressor wheel inlet 42, being compressed by compressor
wheel 18, and flowing out of compressor wheel 18 via a compressor
wheel outlet 44, into a channel 46. Via channel 46, the air
pre-compressed by compressor wheel 18 is guided, in the direction
shown by arrow 48, to compressor 20, acting as the second
compressor stage. The pre-compressed air flows to compressor wheel
26 via a corresponding compressor wheel inlet 50, is compressed by
compressor wheel 26, and flows out of compressor wheel 26 via a
corresponding compressor wheel outlet 52 and into a corresponding
channel 54, via which the further compressed air is finally
supplied to the fuel cell in the direction shown by arrow 56.
[0034] In order to keep frictional losses of charging device 10
low, and thus to realize a particularly efficient operation
thereof, wheel rear parts 16 and 24, and thus compression wheels 18
and 26, are matched to one another with regard to their diameter,
whereby opposed forces resulting from compressor wheel outlet
pressures impressed on each of wheel rear parts 16 and 26 balance
one another at least substantially. These forces are axial forces
and act in the axial direction of rotor 34 or of shaft 32, in the
direction shown by arrow 58, and are indicated in FIG. 1 by arrows
60 and 62. Due to their direction of action in the axial direction,
these forces are indicated as axial forces in the direction of
arrow 58.
[0035] As can be seen in FIG. 1, the axial forces indicated by
arrows 60 and 62 are oriented in opposite directions and act in the
direction of the respective compressor wheel inlets 42 and 50 via
which air flows to compressor wheels 18 and 26.
[0036] On the basis of the at least substantial balancing of the
axial forces, a bearing of rotor 34 for the absorption of these
axial forces can be omitted, or can be made particularly small in
its dimensions, so that no, or only very small, frictional losses
occur as a result of an absorption of the axial forces.
[0037] Due to the two-stage compression of charging device 10 shown
in FIG. 1, the compressor wheel outlet pressures prevailing at
corresponding compressor wheel outlets 44 and 52 and impressed on
wheel rear parts 16 and 24 differ from one another, so that
surfaces differing from one another on which the compressor wheel
outlet pressures act are fashioned differently from one another as
a result of a different realization of the corresponding
diameters.
[0038] In contrast to charging device 10 shown in FIG. 1, the
charging device shown in FIG. 2 realizes a two-stage compression of
the air that is to be supplied to the fuel cell. Compressors 12 and
20, or compressor wheels 18 and 26, are here not connected in
series to one another as in FIG. 1, but rather are connected
parallel to one another. This means that air that is to be
compressed is supplied in the direction of an arrow 64 to
compressors 12 and 20, or compressor wheels 18 and 26, in parallel
fashion via the respective compressor wheel inlets 42 and 50.
[0039] Compressors 12 and 20 thus compress the supplied air in
parallel fashion. Correspondingly, the air compressed in parallel
is also led out via channels 46 and 54 in the direction of an arrow
66 and is supplied to the fuel cell. In the one-stage and parallel
compression of the air using charging device 10 shown in. FIG. 2,
as a result of the compressor wheel outlet pressures impressed on
wheel rear parts 16 and 24, axial forces (arrows 60 and 62) result
that balance one another due to the matching of wheel rear parts 16
and 24 to one another. In the one-stage compression shown in FIG.
2, it is possible to use compressor wheels 18 and 26 that are at
least substantially identical and that differ from one another only
with regard to their direction of rotation for compressing the air.
The two compressor wheels 18 and 26 of charging device 10 shown in
FIG. 2 thus share an air mass flow that is to be compressed and
that is to be supplied in the direction of arrow 64, enabling an at
least nearly complete compensation of the axial forces.
[0040] Compressors 12 and 20 compress the air to an at least almost
identical pressure level, so that the compressor wheel outlet
pressures acting on wheel rear parts 16 and 24 are at least
substantially equal. Correspondingly, identical surface contents of
wheel rear parts 16 and 24 on which the compressor outlet pressures
act are sufficient for the at least substantial balancing of the
axial forces.
[0041] If charging devices 10 shown in FIGS. 1 and 2 are used for
example in a motor vehicle, in particular a passenger vehicle, then
during operation of the motor vehicle non-steady operation of
charging devices 10 may occur, in which rotor 34 has to be
alternately accelerated, braked, accelerated again, etc. As a
result of this non-steady operation, despite the corresponding
matching of wheel rear parts 16 and 24 to one another (for the
balancing of the axial forces in at least approximately steady
operation), in some circumstances axial forces may occur that do
not balance one another. In some circumstances, this then requires
an axial bearing of rotor 34 for, if warranted, a very
short-duration absorption and supporting of forces acting in the
axial direction along arrow 58. Because, however, these forces may
occur only for a very short time due to the matching of wheel rear
parts 16 and 24, and their magnitude is small, such an axial
bearing can be made small with regard to its dimension and its
weight, so that only small frictional losses result from the
absorption of these forces, and in addition a particularly
efficient operation of charging device 10 is ensured.
[0042] FIG. 3 shows another specific embodiment of charging device
10 shown in FIG. 2, rotor 34 of charging device 10 having a turbine
wheel 68 that is connected in rotationally fixed fashion to shaft
32 and is accommodated in a housing 70 of a turbine 72 of charging
device 10.
[0043] Turbine 72 with turbine wheel 68 is used to supply exhaust
gas from fuel cell 10, via a channel 74 provided through housing
70, to compressor wheel 68, and to drive compressors 12 and 20, or
corresponding compressor wheels 18 and 26, in order to compress the
air.
[0044] According to charging device 10 shown in FIG. 2, compressors
12 and 20 compress the air in parallel and in one stage, the air
being supplied to compressors 12 and 20 in the direction of arrows
76 via a corresponding channel 78. Via channel 78, the air to be
compressed flows to compressor wheels 12 and 20 via corresponding
compressor wheel inlets 42 and 50.
[0045] When the air is compressed, the air in compressor wheels 12
and 20 flows out as shown via compressor wheel outlets 44 and 52
and is conducted to the fuel cell via channels 46 and 54, in the
direction of an arrow 80.
[0046] As can be seen in FIG. 3, compressor wheel 18 is also
situated in end region 28 of shaft 32. In end region 30 of shaft
32, however, there is situated not compressor wheel 26 but rather
turbine wheel 68, which is connected in rotationally fixed fashion
to shaft 32. Compressor wheel 26 is situated, in the axial
direction of rotor 34 or of shaft 32, between compressor wheel 18
and turbine wheel 68, in an intermediate region 83 of shaft 32, and
is connected in rotationally fixed fashion thereto.
[0047] In order to absorb the axial forces that are shown and that
occur in particular during non-steady operation, and that do not
balance and compensate one another, in FIG. 3 an axial bearing 82
is shown that is capable of absorbing and supporting the axial
forces, thus preventing undesired contact of rotor 34, and in
particular compressor wheels 18 and 26, as well as turbine wheel
68, with housings 14, 22, and 70.
[0048] Axial bearing 82 shown in FIG. 3, which can absorb both
axial forces in the direction of arrow 60 and those in the
direction of arrow 62, is fashioned for example as an air
bearing.
* * * * *