Compressor for a fuel-cell system, and fuel-cell system having same
Patent Information
- Application Number
- EP2023728273
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-06-09
- Filing Date
- 2023-05-16
- Publication Date
- 2025-04-16
AI Technical Summary
Fuel cell systems face high axial forces during air compression, leading to increased wear on bearings, especially at high speeds, and two-stage compressors are unsuitable due to space constraints, making them impractical for vehicles.
A compressor design featuring two axial air bearings arranged along the axis of rotation, with a radial bearing arrangement between them, to enhance axial load capacity and balance, allowing for efficient absorption of axial forces while minimizing space requirements.
This design significantly increases axial load capacity, reduces wear, and optimizes space usage, enabling longer service life and cost-effective production, even in single-stage compressors, while maintaining a compact footprint.
Smart Images
Figure 1.1
Abstract
Description
[0001] Compressor for a fuel cell system, and fuel cell system with the same
[0002] The present invention relates to a compressor for a fuel cell system, in particular for a fuel cell system of a commercial vehicle, having a compressor housing, a compressor wheel, a rotationally driven compressor shaft which is operatively connected to the compressor wheel, and a bearing arrangement which supports the compressor shaft in the compressor housing so as to be rotatable about a rotational axis, wherein the bearing arrangement has an axial air bearing for absorbing forces between the compressor housing and the compressor shaft in the direction of the rotational axis (hereinafter also: axial forces).
[0003] Fuel cell systems generally require a controlled air supply on the cathode side for proper operation in order to maintain the optimal reactant balance within the fuel cell, the so-called stack, for the operation of the fuel cell system. It is known to compress the air using one or more compressors, thus supplying the fuel cell with a controlled mass or volume flow of air.
[0004] The higher the power to be generated by the fuel cell, the higher the required mass or volume flow that must be delivered by the compressor(s). During operation of the compressor, the intake of air creates an axial force that acts on the compressor shaft. As the speed of the compressor shaft and compressor wheel increases - at a constant cross-section - the amount of air drawn in also increases, and with it the built-up pressure, and thus also the axial force. This effect is more pronounced in single-stage compressors than in two-stage compressors, where the axial forces at least partially balance each other out. If the axial force becomes too high for the bearings used, increased wear occurs, particularly at the speeds prevailing at that time.The axial forces occurring in all compressor systems must therefore be absorbed by the bearing arrangement to prevent undesirable wear between the rotating and stationary elements in the compressor. Due to the high speeds of the compressors mentioned above during operation, it has already proven successful in the past to use an axial air bearing in the bearing arrangement, which is intended to absorb the axial forces occurring between the compressor shaft and the compressor housing.
[0005] Two-stage compressors can usually adequately compensate for the resulting axial forces by using an axial air bearing. However, the installation space required by two-stage compressors due to their design principle is considered a challenge, particularly given the increasingly limited space available in vehicles. Two-stage compressors are therefore generally unsuitable for applications in passenger cars, and installation space in commercial vehicles is also becoming increasingly limited due to technological advances.
[0006] Against this background, the invention was based on the object of providing a compressor in which the disadvantages described above are mitigated as far as possible. In particular, the invention was based on the object of improving a compressor of the type described above so that axial forces acting on the compressor shaft can be better absorbed while simultaneously requiring the smallest possible installation space. Furthermore, the invention was based on the object of implementing the above as cost-effectively as possible.
[0007] The invention solves the underlying problem by proposing a compressor according to claim 1. In particular, the invention proposes that in a compressor of the type initially described, the axial air bearing is a first axial air bearing, and the bearing arrangement additionally has a second axial air bearing, which is arranged at a distance from the first axial air bearing in the direction of the rotation axis (hereinafter also: axial direction) and is configured (in addition to the first axial air bearing) to absorb forces between the compressor housing and the compressor shaft in the direction of the rotation axis, i.e., axial forces. In other words, according to the invention, both the first axial air bearing and a second axial air bearing are provided to provide an axial bearing function, so that the axial forces introduced by the compressor wheel via the compressor shaft can be absorbed by both axial air bearings.
[0008] The invention is based on the finding that the use of a second axial air bearing represents a surprisingly good compromise between increasing the axial load capacity, i.e., the ability to absorb axial forces, on the one hand, and the required installation space for the extension, on the other. Even if it actually seems counterintuitive to install an additional bearing, which would inevitably require additional installation space, it has been shown that the additional axial installation space required for the second axial air bearing can lead to a significantly more suitable enclosed volume of the entire compressor than, for example, a traditional approach, such as replacing the existing axial air bearing of the known compressor with a radially larger axial air bearing.At the same time, the use of multiple bearings can significantly increase the axial load capacity of the overall bearing arrangement, even when using bearing types that are simply constructed on their own, eliminating the need to use expensive special bearings such as spiral groove bearings. Nevertheless, the invention also demonstrates its advantages when using spiral groove bearings, improving load capacity with a moderate increase in installation space.
[0009] Further advantages also arise from the preferred embodiments and developments of the invention, which are described below. In an advantageous development, the compressor is a single-stage compressor, wherein the compressor wheel is arranged at a first end section of the compressor shaft, and wherein the second axial air bearing is arranged at a second end section of the compressor shaft opposite the first end section. By arranging the compressor wheel on the one hand and the second axial air bearing on the other hand opposite each other, the balance of the rotating masses is improved. Especially in single-stage compressors, this is a major design advantage, particularly for the bearing arrangement, which has the effect of increasing the service life.
[0010] In a preferred embodiment, the bearing assembly comprises a radial bearing assembly. The radial bearing assembly preferably comprises a number of radial bearings arranged between the first axial air bearing and the second axial air bearing. According to the invention, a number is understood to be one or more units.
[0011] The radial bearing arrangement is preferably arranged between the first axial air bearing and the second axial air bearing.
[0012] Particularly preferably, the bearing arrangement comprises two radial bearings, which can be designed, for example, as radial air bearings. By weighting and spacing the axial air bearings from the radial bearings, a favorable weight distribution can be achieved, and the axial air bearings are also easily accessible for maintenance purposes.
[0013] In a further preferred embodiment, the first axial air bearing has a first rotor disk configured to rotate in a first air gap, and the second axial air bearing has a second rotor disk configured to rotate in a second air gap. To achieve the highest possible number of identical parts, it may be preferable to construct the two axial air bearings identically, particularly with regard to their essential elements (film, film carrier, rotor disk). This can increase cost efficiency, for example, in terms of production and assembly costs.
[0014] In an alternative preferred embodiment, one of the running disks, for example the first running disk, is dimensioned larger in the radial direction than the other running disk, for example the second running disk. Depending on the extent of the difference, this leads to a different load capacity in the axial direction for the two axial air bearings, which can support the clear definition of the effective direction of the axial bearing.
[0015] In a further preferred embodiment, the number of radial bearings thus comprises a first radial bearing arranged at a first axial distance from the first axial air bearing, and a second radial bearing arranged at a distance from the first radial bearing and at a second axial distance from the second axial air bearing, wherein the second axial distance and the first axial distance are different.
[0016] Preferably, the second axial distance is greater than the first axial distance.
[0017] The compressor wheel is usually located on the side of the compressor shaft where the first axial air bearing is located, so the rotating masses and tilting moments on that side of the compressor shaft are, as expected, greater than on the left side. However, by increasing the distance between the second axial air bearing and the adjacent radial bearing, the second radial bearing, at least partial compensation of the tilting moments can be achieved.
[0018] In particular, a first radial force acts on the radial bearing assembly from the first rotor disk, and a second radial force acts on the radial bearing assembly from the second rotor disk. A third radial force acts on the radial bearing assembly from the compressor wheel, which is arranged at a third axial distance from the first or second radial bearing. The radial forces and distances each result in tilting moments that act on the radial bearing assembly via the compressor shaft.
[0019] Preferably, the first, second and third distances are dimensioned such that the resulting tilting moments at least partially, and preferably completely, eliminate each other.
[0020] Alternatively or additionally, the first, second and / or third distances are preferably dimensioned such that equal radial forces act on the radial bearings of the bearing arrangement.
[0021] In a further preferred embodiment, the first air gap and the second air gap are dimensioned differently in the direction of the rotation axis. The reason for this is that at low speeds, the running disks of the axial air bearings can sometimes still rest on the corresponding bearing part or rub during movement, and only when a predetermined lift-off speed is reached do they move apart on both sides of the running disk and rotate freely in the air gap. By dimensioning one of the two air gaps somewhat narrower than the other, for example by means of narrower dimensions or tighter tolerances of the air gap, it is possible to predict which of the two axial air bearings will experience wear when operating at lower speeds. This results in advantages in maintenance planning and service life prediction of the bearing arrangement.In addition, the larger air gap of one axial air bearing has a positive effect on the friction losses.
[0022] In a further preferred embodiment, the first axial air bearing and / or the second axial air bearing are designed as foil bearings. Preferably, the running disks of each axial air bearing are arranged between two stationary foil disks spaced from each other by the air gap. The axial air bearings are preferably designed as bump types or another foil bearing type. These cost-effective bearing types, in conjunction with the design principle according to the invention, have sufficient load-bearing capacity to compensate for the axial forces, even in single-stage compressors. However, the invention does not preclude the use of spiral groove bearings and other bearing types. In a preferred embodiment, one of the axial air bearings, for example the first axial air bearing, is designed as a spiral groove bearing, and the other axial air bearing, for example the second axial air bearing, is designed as a foil bearing.
[0023] Particularly preferably, one of the axial air bearings is designed as a spiral groove bearing, and the air gap to which it is assigned, for example the first air gap, is dimensioned larger than the air gap to which the other axial air bearing is assigned, for example the second air gap.
[0024] The invention was described above in a first aspect with reference to the compressor itself. In a further aspect, the invention also relates to a fuel cell system for driving a vehicle, in particular a commercial vehicle, with a compressor for supplying air to the cathode side of a fuel cell.
[0025] The invention achieves the underlying problem in such a fuel cell system by designing the compressor according to one of the preferred embodiments described above. The fuel cell system thus utilizes the same advantages as the compressor according to the first aspect. Preferred embodiments of the compressor are simultaneously preferred embodiments of the fuel cell system, and vice versa. To avoid repetition, reference is therefore made to the above explanations.
[0026] The invention is described in more detail below with reference to a preferred embodiment and the accompanying figures.
[0027] Fig. 1 is a schematic representation of a fuel cell system according to a preferred embodiment, and
[0028] Fig. 2 is a schematic detailed view of a compressor shaft of the fuel cell system according to Fig. 1 .
[0029] Fig. 1 schematically depicts a fuel cell system 100 for a commercial vehicle 300. The fuel cell system 100 includes a fuel cell 101 configured to provide electrical energy. For air supply, the fuel cell 101 is operatively connected to a compressor 1 configured to draw in an air stream L, compress it, and supply it to the fuel cell 101 on the cathode side.
[0030] The compressor 1 has a compressor housing 3 in which a compressor shaft 5 is rotatably mounted. The compressor shaft 5 is mounted in the compressor housing 3 by means of a bearing assembly 7, wherein the bearing assembly 7 includes, among other things, a radial bearing assembly 8. The radial bearing assembly 8 comprises a first radial bearing 7a and a second radial bearing 7b. The two radial bearings 7a, 7b are preferably designed as radial air bearings, for example as foil bearings.
[0031] The bearing arrangement 7 further comprises a first axial air bearing 7c and a second axial air bearing 7d.
[0032] A compressor wheel 11 is arranged in a first end section 9 of the compressor shaft 5 and is connected to the compressor shaft 5 in a torsionally rigid manner.
[0033] The compressor 1 has an electric machine 13 which can be operated as an electric motor and in this case drives the compressor shaft 5 in rotation, whereby the compressor wheel 11 sucks in the air flow L, compresses it and discharges it in the direction of the fuel cell 101.
[0034] The compressor 1 in the illustrated embodiment is designed as a single-stage compressor. The second axial air bearing 7d is arranged on the compressor shaft 5 in a second end section 15, which is opposite the first end section 9. The second axial air bearing 7d thus performs several relevant functions for the compressor 1: Firstly, the second axial air bearing 7d provides additional load-bearing capacity, which significantly increases the axial load-bearing capacity of the bearing arrangement 7, i.e., the ability to absorb axial forces Faxiai in the direction of a rotational axis A of the compressor shaft 5.
[0035] Furthermore, the second axial air bearing 7b contributes to at least partially balancing the radial forces (cf. Fig. 2) and tilting moments acting on the radial bearing arrangement 8, because the mass emanating from the second axial air bearing 7d acts on the compressor shaft 5 on a side of the radial bearing arrangement 8 facing away from the compressor wheel 11 and can thus also partially balance the radial forces and tilting moments of the first axial air bearing 7c and the compressor wheel 11.
[0036] The first axial air bearing 7c has a rotor disk 17, which is rigidly connected to the compressor shaft 5 and positioned between two stationary foil disks 19. An air gap 21 is formed between the two foil disks 19.
[0037] The second axial air bearing 7d also has a running disk 23 which is torsionally rigidly connected to the compressor shaft 5, wherein the second running disk 23 is arranged between two stationary foil disks 25 which define an air gap 27 between them.
[0038] The diameters, i.e., radial dimensions, of the running disks 17, 23 can be configured differently according to preferred embodiments, to better define an effective direction along the axis A, or to support a common-parts philosophy, they can be configured identically. The same applies conversely to the respective foil disks 19, 25.
[0039] The air gaps 21, 27 can be of equal size in the axial direction; however, in preferred embodiments, as described above, one of the two gaps 21, 27 can also be narrower than the other in order to clearly define a wear point and to be able to make the maintenance forecast more precise. This could be the air gap 27, for example. If the bearing arrangement 7 requires maintenance, it would then be reliably ensured, at least with regard to the axial air bearings 7c, 7d, that it is the second axial air bearing 7d where wear will have occurred. And in order to service or replace this, the compressor wheel 11 would not have to be dismantled.
[0040] Fig. 2 shows an approximate force balance for the compressor shaft 5 and the radial bearing arrangement 8, based on simplifying assumptions, such as the assumption of a massless compressor shaft 5. The first radial bearing 7a is loaded with a radial force FRI, while the second radial bearing 7b is loaded with a radial force FR2. A radial force FLI emanates from the first rotor disk 17 of the first axial air bearing 7c, and a radial force FL2 emanates from the second rotor disk 23 of the second axial air bearing 7d, each acting on the compressor shaft 5. A radial force Fv emanates from the compressor wheel 11 and also acts on the compressor shaft 5.
[0041] The centers of the two radial bearings 7a, 7b are spaced apart from each other by a distance L in the direction of the rotation axis A, i.e., in the axial direction. The first rotor disk 17 is located at an axial distance Li from the radial bearing closest to it, namely the first radial bearing 7a. The second rotor disk 23 is located at a distance L2 from the radial bearing closest to it, namely the second radial bearing 7b. The compressor wheel 11, with its center of mass, is located at a distance L3 in the axial direction from the radial bearing closest to it, namely, the first radial bearing 7a, as above.
[0042] Based on the force and moment balances for this configuration, the distances Li, L2, and L3, as well as LR, can be coordinated in the design such that the radial loads FR1, FR2 on the radial bearing assembly 8 are equal, or at least substantially equal. In preferred embodiments, the distance L2 will be greater than L3, and L3 will be greater than Li. LR is preferably greater than L2.
[0043] A favorable design, for example, by minimizing the distance Li and L3 as much as possible, allows for a very compact bearing concept overall, which offers good use of installation space and, at the same time, enables a compressor shaft 5 with purely air bearings that is advantageously balanced compared to the prior art. Due to the balancing effect exerted by the second axial air bearing 7d, long service lives can be achieved even when using single-stage compressors, as in the preferred embodiment here. At the same time, the bearing concept allows the use of simple bearing types for the axial air bearings, such as bump-type or other foil bearing types.
[0044] Reference symbol (part of the description):
[0045] 1 compressor
[0046] 3 Compressor housing
[0047] 5 Compressor shaft
[0048] 7 Bearing arrangement:
[0049] 7a first radial bearing
[0050] 7b second radial bearing
[0051] 7c first axial air bearing
[0052] 7d second axial air bearing
[0053] 8 Radial bearing arrangement
[0054] 1 1 Compressor wheel
[0055] 13 Machine
[0056] 15 Final section
[0057] 17 Running disc
[0058] 19 foil discs
[0059] 21 Air gap
[0060] 23 Running disc
[0061] 25 foil discs
[0062] 27 Air gap
[0063] 100 fuel cell system
[0064] 101 Fuel Cell
[0065] 300 commercial vehicles
[0066] A rotation axis, compressor shaft
[0067] R Radial direction, relative to A
[0068] FRI, FR2 radial force, radial bearing
[0069] FLI, FL2 radial force, axial air bearing
[0070] Fv radial force, compressor
[0071] F axial axial force
[0072] L Airflow
[0073] Li, L2, L3, LR axial distance
Claims
Patent claims:
1. Compressor (1) for a fuel cell system (100), in particular a fuel cell system (100) of a commercial vehicle (300), comprising a compressor housing (3), a compressor wheel (11), a rotaryally driven compressor shaft (5) which is operatively connected to the compressor wheel (11), and a bearing arrangement (7) which rotatably supports the compressor shaft (5) in the compressor housing (3) about an axis of rotation (A), wherein the bearing arrangement (7) comprises an axial air bearing (7c) for absorbing axial forces (faxiai) between the compressor housing (3) and the compressor shaft (5), characterized in that the axial air bearing (7c) is a first axial air bearing, and the bearing arrangement (7) further comprises a second axial air bearing (7d) which is arranged axially spaced from the first axial air bearing (7c) and is configured to absorb axial forces (faxiai) between the to accommodate the compressor housing (3) and the compressor shaft (5).
2. Compressor (1 ) according to claim 1 , characterized in that the compressor (1 ) is a single-stage compressor (1 ) wherein the compressor wheel (11 ) is arranged on a first end section (9) of the compressor shaft (5) and wherein the second axial air bearing (7d) is arranged on a second end section (15) of the compressor shaft (5) opposite the first end section (9).
3. Compressor (1 ) according to claim 1 or 2, characterized in that the bearing arrangement (7) has a radial bearing arrangement (8).
4. Compressor (1 ) according to claim 3, wherein the radial bearing arrangement (8) is arranged between the first axial air bearing and the second axial air bearing (7d).
5. Compressor (1 ) according to one of the preceding claims, characterized in that the first axial air bearing (7c) has a first running disk (17) which is arranged to rotate in a first air gap (21 ) and the second axial air bearing (7d) has a second running disk (23) which is arranged to rotate in a second air gap (27).
6. Compressor (1 ) according to claim 5, wherein the first impeller (17) is dimensioned larger in radial direction (R) than the second impeller (23).
7. Compressor (1) according to one of the preceding claims, wherein the radial bearing arrangement (8) comprises a first radial bearing (7a) arranged at a first axial distance (Li) to the first axial air bearing (7c), and a second radial bearing (7b) arranged at a distance (LR) TO the first radial bearing (7a) and at a second axial distance (L2) to the second axial air bearing (7d), wherein the second axial distance (L2) and the first axial distance (Li) are different.
8. Compressor (1 ) according to claim 7, wherein a first radial force (FLI) acts on the radial bearing arrangement (8) from the first running disk (17), a second radial force (F1.2) acts on the radial bearing arrangement (8) from the second running disk (23), and a third radial force (Fv) acts on the bearing arrangement (7) from the compressor wheel (1 1 ), which is arranged at a third axial distance (L3) to the first or second radial bearing (7a, 7b).
9. Compressor (1 ) according to claim 8, wherein tilting moments result from the radial forces (FLI, FL2, FV) and distances (Li, L2, L3, LR) which act on the bearing arrangement (7) via the compressor shaft (5), wherein the first, second and third distance (Li, L2, L3) are dimensioned such that the resulting tilting moments partially or completely eliminate each other.
10. Compressor (1 ) according to claim 8 or 9, wherein the first, second and third distance (Li, l_2, L3) are dimensioned such that the radial forces (FRI, FR2) of the radial bearing arrangement (7) are of equal or at least substantially equal magnitude.
11. Compressor (1) according to one of claims 5 to 10, wherein the first air gap (21) and the second air gap (27) are dimensioned differently in the direction of the axis of rotation (A).
12. Compressor (1 ) according to one of the preceding claims, wherein the first axial air bearing (7c) and / or the second axial air bearing (7d) are designed as foil bearings.
13. Compressor according to one of the preceding claims, wherein one of the axial air bearings (7c, 7d), preferably the first axial air bearing (7c), is designed as a spiral groove bearing, and the other of the axial air bearings (7c, 7d), preferably the second axial air bearing (7d), is designed as a foil bearing.
14. Fuel cell system (100) for propelling a vehicle (300), in particular a commercial vehicle, with a compressor (1 ) for the cathode-side air supply of a fuel cell (101 ), characterized in that the compressor (1 ) is designed according to one of the preceding claims.