Rotor assembly system of a charging system and charging system for a fuel cell

Abstract

The invention relates to a rotor assembly system (19) of a charging system (1), in particular for a charging system (1) for a fuel cell, the rotor assembly system (19) comprising a rotor assembly (9) and a bearing arrangement (11) which supports the rotor assembly (9), and the rotor assembly (9) having a compression wheel (3), an expansion wheel (4) and a shaft (14) which is connected to the compression wheel (3) and the expansion wheel (4) for conjoint rotation, the compression wheel (3) and the expansion wheel (4) being received on a first shaft end (15) of the shaft (14), and the bearing arrangement (11), which is designed to support the shaft (14), comprising a first bearing (17) and a second bearing (18), the first bearing (17) being close to the wheels and the second bearing (18) being remote from the wheels. According to the invention, to reduce natural frequencies during operation of the rotor assembly system (19), the bearing arrangement (11) has a bearing cage (20), the rotor assembly system (19) having a vibration absorber (30), and the vibration absorber (30) being connected to the bearing cage (20) for conjoint rotation. The invention furthermore relates to a charging system (1) for a fuel cell.

Description

[0001] Rotor system of a charging system and charging system for a fuel cell

[0002] The invention relates to a rotor system of a charging system according to the preamble of patent claim 1. Furthermore, the invention relates to a charging system for a fuel cell according to patent claim 10.

[0003] Drive systems, especially in motor vehicles, increasingly feature fuel cells as power units. Oxygen in the form of atmospheric oxygen must be supplied to the fuel cell during operation. A turbocharging system, a well-known and proven system for supplying air and increasing the performance of internal combustion engines, is suitable for this purpose: an exhaust gas turbocharger.

[0004] However, due to the significantly lower temperatures of an exhaust gas flowing out of the fuel cell, which in this context is referred to as expansion gas because it acts on an expansion wheel of the charging system and does not have a composition corresponding to the usual known exhaust gas, support of the charging system, which has a rotatably arranged compression wheel and the expansion wheel, which is connected in a rotationally fixed manner to the compression wheel and is also rotatably arranged, may be required, which support is preferably designed in the form of an electric motor.

[0005] For example, published patent application DE 10 2009 052 919 A1 discloses a charging system for a fuel cell, wherein a compression wheel and an expansion wheel are arranged on one side of a shaft connecting the two wheels. An electric motor is provided with a permanent magnet, wherein the permanent magnet is arranged within the shaft, which has a hollow space. The shaft is rotatably supported by means of bearings in the form of axial and radial bearings, wherein the bearings are designed as magnetic bearings. A bearing is arranged to support the shaft on the other side of the shaft, facing away from the one side.

[0006] German Patent Application DE 10 2021 127 332 A1 discloses a charging system for a fuel cell, wherein a compression wheel and an expansion wheel are arranged on one side of a shaft connecting the two wheels. An electric motor with a permanent magnet is provided, wherein the permanent magnet is arranged within the shaft, which has a hollow space. The shaft is mounted by means of a bearing arrangement comprising an air bearing and a rolling bearing.

[0007] The one-sided arrangement of the compression wheel and the expansion wheel on the shaft as well as the bearing arrangement, which can also be referred to as hybrid bearing, requires stiffness compensation of the bearing arrangement so that resonances in the operating range with high amplitudes can be prevented.

[0008] The object of the present invention is to provide an improved rotor system of a charging system. A further object of the present invention is to provide an improved charging system for a fuel cell.

[0009] This object is achieved by a rotor system of a charging system having the features of patent claim 1. The further object is achieved by a charging system for a fuel cell having the features of patent claim 10. Advantageous embodiments with expedient and non-trivial further developments of the invention are specified in the remaining claims.

[0010] In a first aspect, the invention relates to a rotor system of a charging system, in particular for a charging system for a fuel cell, wherein the rotor system comprises a rotor and a bearing arrangement supporting the rotor. The rotor has a compression wheel, an expansion wheel, and a shaft that is non-rotatably connected to the compression wheel and the expansion wheel. The compression wheel and the expansion wheel are received at a first shaft end of the shaft. The bearing arrangement, which is designed to support the shaft, comprises a first bearing and a second bearing. The first bearing is arranged close to the wheel, and the second bearing is remote from the wheel. According to the invention, to reduce, or preferably eliminate, natural frequencies during operation of the rotor system, the bearing arrangement has a bearing cage. The rotor system has a vibration damper, and the vibration damper is non-rotatably connected to the bearing cage.Advantageously, with the help of the bearing cage, the bearing arrangement can have different bearing types, as the bearing cage makes it possible to compensate for different stiffnesses of the different bearing types. In other words, this means that, for example, the bearing arrangement can be equipped with an air bearing and a rolling bearing, which have different stiffnesses. The air bearing has a low stiffness, and the rolling bearing has a high stiffness, which together can cause natural vibrations with high vibration amplitudes during operation of the running gear system. Another key advantage of the bearing cage is that an axial movement gap, which is required for the wheels in the form of radial wheels, can be reliably maintained between the wheels and their associated housing sections, since the bearing cage forms an axial positioning lock.To specifically reduce, or preferably eliminate, these vibrations, a vibration damper is designed to operate in a critical resonance frequency range. The vibration damper is non-rotatably connected to the bearing cage and can thus oscillate with the rotor system independently of the housing. However, it is non-rotatably mounted and thus decoupled from the rotating rotor. The bearing cage, i.e., without a vibration damper, typically has no damping properties and is designed only to a target stiffness to provide elastic support for the rolling bearing. Therefore, unavoidable resonances can occur in the operating range due to undamped vibrations, which can lead to high bearing forces. These can be eliminated with the rotor system according to the invention.

[0011] In one embodiment of the rotor system according to the invention, the first bearing is designed as an air bearing and the second bearing as a rolling bearing. A rolling bearing can absorb axial and radial loads. Thus, a radial and an axial air bearing can be replaced by a single rolling bearing. The rolling bearing as a second bearing, and thus installed away from the wheel, has the advantage that the bearing diameter can be reduced, thus increasing the service life of the rolling bearing. If the rolling bearing were installed close to the wheel, the problem would arise that the rolling bearing would have to have a significantly larger diameter to achieve the necessary rotor rigidity due to a larger shaft diameter at this point. Designing the first bearing as an air bearing has the advantage that the air bearing is virtually media-free.

[0012] In a further embodiment of the running gear system according to the invention, the bearing cage is designed to accommodate the second bearing.

[0013] In a further embodiment of the rotor system according to the invention, the compression wheel and the expansion wheel are designed as a one-piece system wheel. The advantage of the rotor system according to the invention is that the one-piece design of the compression wheel and the expansion wheel allows for a charging system with a significantly reduced axial extent than previously known. Furthermore, components of the charging system, such as the shaft or the housing, can be manufactured at reduced cost. A further advantage is that any potential leakage of hydrogen or lubricant can be diverted away from the charging system with the expansion gas. This also prevents lubricant from penetrating the fuel cell.

[0014] The system wheel can be made of two different materials. In other words, the compression wheel is made of the first material and the expansion wheel is made of a second material that differs from the first material. This typically requires a cost-intensive joining process. However, since the temperatures of the gases, the compression gas and the expansion gas, are not temperatures known from combustion engine construction and its exhaust gas temperatures, the expansion wheel is cost-effectively made of a second material that corresponds to the first material. In other words, the system wheel is made of a single material, which can also be a composite material and / or an alloy or similar.

[0015] In a further embodiment of the running gear system according to the invention, the first bearing is advantageously arranged in the region of the first shaft end and the second bearing is advantageously arranged in the region of a second shaft end of the shaft facing away from the first shaft end.

[0016] In a further embodiment of the running gear system according to the invention, the bearing cage has a first cage section for securely receiving the first bearing and a second cage section for absorbing radial and / or axial forces.

[0017] In a further embodiment of the rotor system according to the invention, the bearing cage has a third cage section for axial and radial mounting in a housing of the charging system. The third cage section serves to secure the bearing cage, so that the other two cage sections advantageously do not need to be used for fastening. In particular, the third cage section is designed to at least partially enclose the second cage section. This allows vibrations to be easily absorbed.

[0018] Overall, a bearing system can be provided that is characterized by the ability to specifically adapt radial and axial stiffness to specific requirements. Furthermore, a so-called hybrid bearing arrangement can be designed, comprising a soft and a stiff bearing, in which, in particular, cost-effective rolling bearings can be used.

[0019] The invention further relates, in a second aspect, to a charging system for a fuel cell, comprising a housing comprising a rotor system mounted in the housing, and an electric motor comprising a rotor and a stator. According to the invention, the rotor system is designed according to one of claims 1 to 9.

[0020] Further advantages, features, and details of the invention will become apparent from the following description of preferred embodiments and from the drawings. The features and feature combinations mentioned above in the description, as well as the features and feature combinations mentioned below in the description of the figures and / or shown alone in the figure, can be used not only in the respective combinations specified, but also in other combinations or on their own, without departing from the scope of the invention. They show:

[0021] Fig. 1 shows a longitudinal section of a charging system according to the invention for a fuel cell,

[0022] Fig. 2 shows a section through a rotor system of the charging system according to the invention. Fig. 1 ,

[0023] Fig. 3 shows a perspective view of a bearing cage of the running gear system shown in Fig. 2.

[0024] Fig. 4 shows a partial longitudinal section of the bearing cage. Fig. 3,

[0025] Fig. 5 in a longitudinal section of the bearing cage. Fig.3, and

[0026] Fig. 6 shows a detail of the rotor system of the charging system according to the invention, comprising a vibration damper. A charging system 1 according to the invention, which is designed for use in supplying air to a fuel cell, is designed as shown in Fig. 1, wherein it comprises a vibration damper 30 as shown in Fig. 6. The charging system 1 has a housing 2 for the rotatable accommodation of a compression wheel 3 and an expansion wheel 4, wherein the housing 2 comprises a compression section 5 and an expansion section 6. The compression section 5 is designed to accommodate the compression wheel 3 and the expansion section 6 is designed to accommodate the expansion wheel 4. The compression wheel 3 and the expansion wheel 4 are designed in the form of radial wheels.

[0027] Adjacent to the expansion section 6 is a motor housing 7 of an electric motor 8. The electric motor 8 can be encapsulated or impregnated with resin. This creates a solid, enclosed structure for the electric motor 8, which can be enclosed by a cooling medium.

[0028] The expansion wheel 4 is arranged in the housing 2 to convey the expansion gas flowing through the expansion wheel 4 into the engine housing 7. In other words, the expansion wheel 4 is arranged between the compression wheel 3 and the engine housing 7. Accordingly, the expansion section 6 is formed between the compression section 5 and the engine housing 7. It should be noted at this point that the engine housing can also be assigned to the housing 2, which forms an overall housing of the charging system 1.

[0029] Furthermore, to achieve a compact and cost-effective design, the charging system 1 according to the invention is characterized by a system wheel 13, which comprises the compression wheel 3 and the expansion wheel 4 formed integrally. The compression wheel 3 is made of a first material, which corresponds to a second material from which the expansion wheel 4 is made. Likewise, two different materials could also be used, whereby a cost-effective production of the system wheel 13 can be achieved using a single material composed of different material components. The expansion wheel 4 is supplied with expansion gas from the fuel cell, so that it exerts a rotating movement, which is transferred to the compression wheel 3, which is formed integrally with the expansion wheel 4.The system gear 13 is connected by means of a shaft 14 to a rotor 10 of the electric motor 8, which has a stator 12 enclosing the rotor 10. The shaft 14, which is rotationally fixedly connected to the system gear 13, is designed in the form of a hollow shaft that receives the rotor 10. The shaft 14 has a first shaft end 15 and a second shaft end 16 facing away from the first shaft end 15, with the system gear 13 being arranged at the first shaft end 15.

[0030] The compression wheel 3, the expansion wheel 4, and the shaft 14 form a rotor assembly 9 of the charging system 1. The rotor assembly 9 is rotatably mounted in the housing 2 by means of a bearing assembly 11. Fig. 2 shows a longitudinal section of a rotor assembly system 19 according to the invention. The rotor assembly system 19 consists of the rotor assembly 9 and the bearing assembly 11. The bearing assembly 11 has a first bearing 17 and a second bearing 18, with the first bearing 17 being arranged at the first shaft end 15, thus close to the wheel, and the second bearing 18 being arranged at the second shaft end 16, thus remote from the wheel. The first bearing 17 is in the form of an air bearing, and the second bearing 18 is in the form of a rolling bearing. At this point it should be mentioned that near the wheel and far from the wheel does not necessarily mean an arrangement on or in the area of ​​the shaft ends 15, 16, but that near the wheel means closer to the wheels 3, 4 than far from the wheel, which means further away from the wheels 3, 4.

[0031] The bearing arrangement 11 can also be referred to as a so-called hybrid bearing, as it comprises two different bearing types: an air bearing and a roller bearing. During operation of the charging system 1, the two different bearings 17, 18 require that the bearing arrangement 11 be designed to have a certain rigidity. Constructing a plain bearing in the bearing arrangement 11 would be unsuitable, as lubricant could penetrate the expansion gas escaping from the expansion section 6. Thus, it is suitable to design the first bearing 17 in the form of an air bearing, which is designed for radial bearing support. With the help of the second bearing 18, designed as a roller bearing, it is easily possible to realize a stable and precise axial and radial bearing.

[0032] During operation of the turbocharging system 1, it is necessary for both bearings 17, 18 to have a largely similar bearing stiffness, since otherwise, natural frequencies may occur in the rotor system 19 during operation of the turbocharging system 1. The second bearing 18, in the form of a rolling bearing, has a significantly greater bearing stiffness than the first bearing 17, in the form of an air bearing. This means that a bearing housing accommodating the bearings 17, 18, which in the present embodiment is the engine housing 7, must provide reduced stiffness in the radial direction for the second bearing 18. In other words, this means that the "stiff" rolling bearing must be converted into a "soft" rolling bearing.

[0033] To reduce, or in particular to eliminate, possible natural frequencies, the bearing assembly 11 has a bearing cage 20. Furthermore, a clear and precise positioning of the second bearing 18, which serves as an axial bearing, is designed to ensure a movement gap 21 between the compression wheel 3 and the compression section 5, as well as between the expansion wheel 4 and the expansion section 6.

[0034] The bearing cage 20, which is shown in different views in Figures 3 to 5, is designed to accommodate the second bearing 18 in the form of a rolling bearing. To securely accommodate the second bearing 18, the bearing cage 20 has a first cage section 22. A second cage section 23, which adjoins the first cage section 22 in the axial direction, is designed to resiliently or elastically absorb axial and radial forces. Furthermore, the bearing cage 20 has a third cage section 24 for the axial and radial mounting of the rotor system 19 in the bearing housing, thus in the motor housing 7 in the present embodiment. The third cage section 24 is designed to at least partially encompass the second cage section 23.

[0035] The first cage section 22 is also referred to as the freely oscillating side of the bearing cage 20. The first cage section 22 is connected to the third cage section 24 via the second cage section 23, wherein the second cage section 23 is designed for elastic deformation.

[0036] The second cage section 23 consists of a plurality of ribs 25, preferably evenly spaced from one another, which extend axially along a longitudinal axis 26 of the charging system 1. Under the action of a radial force R, the ribs 25 allow a relative radial displacement between the free first cage section 22 and the third cage section 24 of the bearing cage 20 through elastic deformation.

[0037] The ribs 25 are relatively thin, thus having a thin structure, which results in low radial stiffness of the third cage section 24 relative to the other two cage sections 22, 23. For example, a radial force R of 100 N results in a radial deformation of 0.1 mm, resulting in a stiffness of 1000 N / mm.

[0038] When an axial force A is applied to the first cage section 22, the ribs 25 are either compressed or stretched. Resistance to compression or stretching is significantly higher than to bending. This results in high stiffness in the axial direction. For example, an axial force of 100 N results in an axial deformation of 0.001 mm, resulting in a stiffness of 100,000 N / mm.

[0039] In Fig. 6, the rotor system 1 according to the invention is illustrated, comprising the vibration damper 30 for providing damping properties. The vibration damper 30 is connected to the bearing cage 20 in a rotationally fixed manner and has a spring element 31 and a mass element 32. The rotationally fixed connection to the bearing cage 20 allows the vibration damper 30 to oscillate with the rotor system 19 independently of the motor housing 7 or, in general, the bearing housing. However, since it is mounted in a rotationally fixed manner on the bearing cage 20, which is also rigidly or, in other words, immovably mounted in the motor housing 7 or, in general, in the bearing housing, the vibration damper 30 is decoupled from the rotating rotor 9.

[0040] The vibration absorber 30 can be tuned by a suitable ratio of mass and stiffness so that unwanted resonances are eliminated.

[0041] The stator 12 of the charging system 1 according to the invention is designed as an actively gas-cooled, in particular air-cooled stator. The motor housing 7 is connected to the expansion section 6 in a flow-through manner so that the expansion gas emerging from the expansion section 6 can flow past the stator 12 and cool it. Downstream of the expansion wheel 4, the expansion gas has an expansion gas temperature below the temperature of conventional liquid coolants and can be used to cool the motor housing 7, with a cooling jacket 34 being connected to the expansion section 6 in a flow-through manner. Liquid cooling of the motor housing 7 can thus be completely dispensed with, since in particular the smallest water droplets absorb heat from the motor housing 7 and evaporate. The expansion gas flows out of the charging system 1 via a bearing cap 33 arranged adjacent to the motor housing 7.The bearing cover 33 advantageously serves to simplify the fixing of the bearing cage 20 in the housing 2.

[0042] The bearing cage 20 is preferably made of steel, as this has preferred elastic properties, and has a radial stiffness in a range of 200 to 2000 N / mm. A ratio between the axial stiffness and the radial stiffness is preferably selected with a value greater than 10. The number of ribs 25 should preferably be in a range of 4 to 20, with a value of 19 being preferred. A length 11 of the first cage section 22 relative to a total length 1g of the bearing cage 20 has a value between 0.3 and 0.7. For the effective elasticity of the ribs 25, their thickness D must be adjusted.

[0043] List of reference symbols

[0044] 1 charging system

[0045] 2 housings

[0046] 3 compression wheel

[0047] 4 Expansion wheel

[0048] 5 Compression section

[0049] 6 Expansion section

[0050] 7 Engine housing

[0051] 8 Electric motor

[0052] 9 Running gear

[0053] 10 Rotor

[0054] 11 Bearing arrangement

[0055] 12 Stator

[0056] 13 System rad

[0057] 14 Wave

[0058] 15 First wave end

[0059] 16 Second shaft end

[0060] 17 First Camp

[0061] 18 Second Camp

[0062] 19 Running gear system

[0063] 20 bearing cage

[0064] 21 Movement gap

[0065] 22 First cage section

[0066] 23 Second cage section

[0067] 24 Third cage section

[0068] 25 ribs

[0069] 26 Longitudinal axis

[0070] 27

[0071] 28 -

[0072] 29 -

[0073] 30 vibration dampers

[0074] 31 spring element 32 mass element

[0075] 33 bearing cap

[0076] 34 Cooling jacket

[0077] A axial force

[0078] D Thickness

[0079] R Radial force

[0080] Ig total length

[0081] 11 Length

Claims

Patent claims 1 . Running gear system (19) of a charging system (1 ), in particular for a charging system (I ) for a fuel cell, wherein the rotor system (19) comprises a rotor (9) and a bearing arrangement (11) supporting the rotor (9), and wherein the rotor (9) has a compression wheel (3), an expansion wheel (4) and a shaft (14) which is connected in a rotationally fixed manner to the compression wheel (3) and the expansion wheel (4), and wherein the compression wheel (3) and the expansion wheel (4) are accommodated at a first shaft end (15) of the shaft (14), and wherein the bearing arrangement (II ), which is designed to support the shaft (14), comprises a first bearing (17) and a second bearing (18), wherein the first bearing (17) is arranged close to the wheel and the second bearing (18) is arranged remote from the wheel, characterized in that in order to reduce natural frequencies during operation of the running gear system (19), the bearing arrangement (11 ) has a bearing cage (20), wherein the running gear system (19) has a vibration damper (30), and wherein the vibration damper (30) is connected to the bearing cage (20) in a rotationally fixed manner.

2. Running gear system (19) according to claim 1, characterized in that the first bearing (17) is designed in the form of an air bearing and the second bearing (18) is designed in the form of a rolling bearing.

3. Running gear system (19) according to claim 1 or 2, characterized in that the bearing cage (20) is designed to accommodate second bearings (18).

4. Running gear system (19) according to one of the preceding claims, characterized in that the compression wheel (3) and the expansion wheel (4) are designed in the form of a one-piece system wheel (13).

5. Running gear system (19) according to one of the preceding claims, characterized in that the first bearing (17) is arranged in the region of the first shaft end (15) and the second bearing (18) is arranged in the region of a second shaft end (16) of the shaft (14) facing away from the first shaft end (15).

6. Running gear system (19) according to one of the preceding claims, characterized in that the bearing cage (20) has a first cage section (22) for securely receiving the second bearing (18) and a second cage section (23) for absorbing radial and / or axial forces (R, A).

7. Running gear system (19) according to claim 6, characterized in that the bearing cage (20) has a third cage section (24) for axial and radial mounting in a housing (2) of the charging system (1).

8. Running gear system (19) according to claim 7, characterized in that the third cage section (24) is designed to at least partially encompass the second cage section (23).

9. Running gear system (19) according to one of the preceding claims, characterized in that the vibration damper (30) has a spring element (31) and a mass element (32).

10. Charging system (1) for a fuel cell, with a housing (2) comprising a rotor system (19) which is mounted in the housing (2), and with an electric motor (8) comprising a rotor (10) and a stator (12), characterized in that the rotor system (19) is designed according to one of claims 1 to 9.

11. Charging system (1) according to claim 10, characterized in that the shaft (14) is designed in the form of a hollow shaft, receiving the rotor (10).

12. Charging system (1) according to one of claims 10 or 11, characterized in that the rotor (10) is arranged between the first bearing (17) and the second bearing (18).

13. Charging system (1) according to one of claims 10 to 12, characterized in that the stator (12) is an actively gas-cooled stator.

14. Charging system (1) according to one of claims 10 to 13, characterized in that the bearing cage (20) is fixed in the housing (2) by means of a bearing cover (33).

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