Turbomachinery and how turbomachinery works

Abstract

The present invention relates to a turbo machine (1) for supplying air to a fuel cell system, comprising: one or more compressor wheels (3) connected to rotate integrally with a shaft (2); and an electric motor (4) for driving the shaft (2). The compressor wheel (3) is connected to rotate integrally with a shaft section (6), preferably a hollow cylindrical shaft section (6) of the shaft (2), through a hub section (5). According to the present invention, one or more air channels (7, 8) are formed within the hub section (5), and through these air channels, a compressor inlet (9) is connected to an annular space (10) on the side opposite the compressor inlet (9) of the compressor wheel (3), so that substantially equal air pressure is applied to the two sides of the compressor wheel (3). The present invention also relates to a method of operating the turbo machine (1).

Description

Technology Field

[0001] The present invention relates to a turbo machine having the features of the preamble of claim 1. Such a turbo machine can be used particularly for supplying air to fuel cell systems. Furthermore, the present invention relates to a method of operating such a turbo machine. Background Technology

[0002] Fuel cell systems require oxygen to react with hydrogen within the system's fuel cell to produce water or water vapor. In this way, electricity is generated through electrochemical conversion, and this electricity can be used, for example, as driving energy for driving a vehicle. Typically, ambient air supplied to the fuel cell by an air compression system is used as the oxygen source, as this process requires a specific air mass flow rate and a specific pressure level. Such an air compression system includes a high-speed rotary turbo machine equipped with one or more compressor wheels arranged on a shaft and driven by an electric motor. For energy recovery, a turbine wheel supplied with fuel cell exhaust air may be arranged on the shaft. In this case, the turbo machine is an exhaust gas turbocharger equipped with an additional electric motor.

[0003] The maximum rotational speed of the additional electric motor is limited to a maximum value of, for example, 100,000 to 125,000 rpm for reasons of control technology and strength. Exhaust gas turbochargers without an additional electric motor achieve rotational speeds of 180,000 to 250,000 rpm. The achievable compressor outlet pressure in a turbomachine is proportional to the square of the circumferential velocity at the outer diameter of the compressor wheel. That is, this pressure is determined by the rotational speed and outer diameter of the compressor wheel. Due to the pressure required for fuel cell systems, compressor wheels with relatively large outer diameters appear, along with the aforementioned rotational speed limitations. Since the pressure formed at the compressor outlet during operation is applied to the rear of the compressor wheel, these compressor wheels generate a large axial force in the direction of the compressor inlet. High axial forces again require thrust bearings of a corresponding size. However, output loss increases with the size of the thrust bearing, and the thrust bearing has a much larger proportion (2 / 3 ratio) of the total bearing loss than the radial bearing (1 / 3 ratio).

[0004] Turbomachines used to supply air to fuel cell systems typically include gas-lubricated foil bearings to keep the system oil-free. However, gas-lubricated foil bearings generate air friction losses and are consequently cooled by additional air. To this end, typically about 5 to 10 percent of the compressed air is diverted for cooling. Since this diverted air volume can no longer be used for subsequent processes within the fuel cell, it reduces the efficiency of the turbomachine. To ensure that the diverted air can generally generate cooling power, this air is pre-cooled. Typically, for this purpose, the cooling air is diverted from the rear of the supercharger air cooler of the fuel cell system. Additional cooling requirements must be considered when configuring the supercharger air cooler. Furthermore, an additional line must be provided to allow the cooling air to be supplied to the turbomachine. Prior art literature

[65535] German Patent Publication DE 102015007379 A1 (2016.01.21.) The problem to be solved

[0005] Based on the prior art described above, the objective of the present invention is to improve the efficiency of a turbo machine for air supply to a fuel cell system. means of solving the problem

[0006] To solve these problems, a turbomachine having the features of claim 1 and a method having the features of claim 10 are proposed. Preferred improvements of the present invention are presented in their respective dependent claims.

[0007] A turbomachine proposed for air supply to a fuel cell system comprises one or more compressor wheels connected to rotate integrally with a shaft and an electric motor for driving the shaft, wherein the compressor wheels are connected to rotate integrally with the shaft, preferably a hollow cylindrical shaft section, through a hub section. According to the present invention, one or more air channels are formed within the hub section, and through these air channels, the compressor inlet is connected to an annular space on the side opposite the compressor inlet of the compressor wheel, so that substantially equal air pressure is applied to the two sides of the compressor wheel. Consequently, axial forces that completely or nearly completely cancel each other out act on the compressor wheel; that is, axial force compensation is induced. This, in turn, allows for a reduction in power loss within the thrust bearings. Additionally, the cooling air requirement within the bearings is reduced. Consequently, both lead to an increase in efficiency. Furthermore, when the turbomachine is used in a vehicle, the robustness of the turbomachine against external acceleration, for example during driving on rough roads, is improved.

[0008] Preferably, the hub section includes one or more air channels extending axially. That is, these one or more air channels extend parallel to the longitudinal axis of the shaft. These air channels may be formed, for example, as axial bores. If only one air channel extending axially is provided, this air channel is preferably arranged at the center of the longitudinal axis of the shaft or coaxially with it. Since the one or more axially extending air channels are preferably directly connected to the compressor inlet side, a portion of the air flow supplied to the compressor wheel is branched through these one or more axially extending air channels and guided to the rear of the compressor wheel.

[0009] Additionally, preferably, the hub section includes one or more air channels extending substantially radially. Through these one or more air channels extending substantially radially, a connection can be formed between the annular space at the rear of the compressor wheel and one or more air channels extending axially. These air channels extending substantially radially can be formed, for example, through a radial bore within the hub section. Preferably, the hub section includes a plurality of air channels extending substantially radially, arranged at equal angular distances from one another. Accordingly, the air guided to the rear of the compressor wheel is uniformly distributed within the annular space.

[0010] Preferably, the hub section is inserted, in particular, press-fitted into a hollow cylindrical shaft section at least section by section. The interlocking of these sections increases the strength of the joint and, consequently, its stability.

[0011] Additionally, it is proposed that the hollow cylindrical shaft section comprises one or more air channels extending substantially radially, arranged to overlap with one or more air channels extending radially of the hub section. Thus, these one or more air channels extending substantially radially of the hub section may be arranged within the hollow cylindrical shaft section, particularly within a press-fit area. In this way, a turbomachine having an axially compact structure is provided.

[0012] In an improved embodiment of the present invention, it is proposed that an annular space on the side opposite the compressor inlet of the compressor wheel be connected to one or more bearings of the shaft through one or more additional air channels. In this case, air supplied through one or more additional air channels can be used for cooling one or more bearings. Preferably, one or more bearings are formed as gas-lubricated foil bearings so that an oil-free state of the system is ensured.

[0013] One or more shaft bearings are connected to an annular space, and accordingly, one or more additional air channels for connecting to the compressor inlet side can also be guided through the annular gap between the shaft and the windings of the electric motor surrounding the shaft. In this case, air supplied through the one or more additional air channels can be used for cooling the electric motor.

[0014] Alternatively or additionally, it is proposed that one or more additional air channels be guided through an internally ventilated thrust bearing disc connected to rotate integrally with the shaft for supporting the turbine wheel. Accordingly, a pressure increase can be achieved simultaneously with the cooling of the thrust bearing. Through the internally ventilated thrust bearing disc, the air pressure of the air supplied through the one or more additional air channels can be raised to a level in front of the turbine wheel.

[0015] Air is drawn in from the surroundings through the compressor inlet. Consequently, the drawn-in air has the ambient temperature and thus a very low temperature level. As a result, the rotor and bearing cooling functions can generally already be optimally satisfied.

[0016] If necessary, cooled ambient air, i.e., air that has been pre-cooled itself, may also be supplied to the air channels. Accordingly, according to a preferred embodiment of the present invention, cooled or uncooled ambient air can be supplied to all air channels connecting the compressor inlet to the rear annular space and, if applicable, to one or more shaft bearings.

[0017] As the air pressure of the ambient air, whether cooled or not, passes through the internally ventilated thrust bearing disc, it can rise to the level in front of the turbine wheel, so that at least a portion of the energy required for the transfer of cooling air is recovered by the turbine.

[0018] There exists a variation that omits the pressure rise through an internally ventilated thrust bearing disc and returns ambient air into the system from behind the turbine outlet.

[0019] To solve the problem mentioned in the introduction, a method of operating a turbomachine according to the present invention is also proposed. In this method, at least, ambient air, whether cooled or not, is supplied to air channels connecting the compressor inlet to the rear annular space. Preferably, since the annular space is connected to one or more bearings via one or more additional air channels, ambient air is supplied to these one or more bearings. In this way, one or more bearings can be cooled by ambient air.

[0020] Additionally, when the method of the present invention is executed by an internally ventilated thrust bearing disc guided by one or more air channels, it is proposed that the cooling air pressure be increased. In this way, at least a portion of the energy required for transporting ambient air can be recovered.

[0021] The present invention is explained in more detail below by the attached drawings. Brief explanation of the drawing

[0022] FIG. 1 is a schematic cross-sectional view of a turbo machine according to the present invention. FIG. 2 is a schematic cross-sectional view of the turbo machine of FIG. 1, showing the air guide section. Specific details for implementing the invention

[0023] The turbo machine (1) illustrated in FIG. 1 includes a shaft (2) having a compressor wheel (3) arranged at one end and a turbine wheel (19) arranged at the other end. The shaft (2) is driven by an electric motor (4) to rotate about its longitudinal axis (A). To this end, the electric motor (4) includes a winding (17) arranged around the shaft (2) and a permanent magnet (23) housed within the shaft (2). To enable the shaft (2) to perform rotational motion, the shaft is rotatably supported through two radial bearings (14). Additionally, two thrust bearings (15) are provided in the area of ​​a thrust bearing disk (18) connected to the shaft (2). The bearings (14, 15) are integrated into the motor housing (22) of the electric motor (4). The compressor wheel (3) is surrounded by a compressor housing (21), and the turbine wheel (19) is surrounded by a turbine housing (20).

[0024] When the turbo machine (1) is in operation, air is introduced into the compressor wheel (3) through the compressor inlet (9). In this case, to minimize the axial force acting on the compressor wheel (3), the compressor wheel (3) of the illustrated turbo machine (1) includes a plurality of air channels (7, 8) within a hub section (5) that is inserted into a hollow cylindrical shaft section (6). The air channels (7, 8) connect the compressor inlet (9) to an annular space (10) on the side of the compressor wheel (3) opposite the compressor inlet (9). Accordingly, a partial flow of air from the compressor inlet (9) is supplied to the annular space (10), so that equal air pressure is formed in the two spaces. As a result, the axial forces acting on the compressor wheel (3) cancel each other out. Correspondingly, bearing loss in the area of ​​the thrust bearing (15) is reduced.

[0025] In this case, since the radially extending air channels (8) are arranged in the area of ​​the hub section (5) inserted into the hollow cylindrical shaft section (6), the shaft section (6) includes air channels (11) arranged to overlap with the air channels (8).

[0026] As can be seen in FIG. 2, the illustrated turbo machine (1) includes additional air channels (12, 13). The air channels (12, 13) connect the annular space (10) to one or more bearings (14, 15). In this case, one or more axially extending air channels (12) from the annular space (10) are guided through the radial bearings (14) from the compressor side to the turbine side of the turbo machine (1), so that cooling of the radial bearings (14) is performed through the supplied air. In this case, one or more air channels (12) are guided through the annular gap (16) between the winding (17) and the shaft (2), so that cooling of the electric motor (4) is also achieved. At the turbine-side end of the shaft (2), one or more air channels (12) are connected to one or more radially extending air channels (13) that extend from the radially inside to the radially outside through the thrust bearing disk (18). As a result, not only is cooling of the thrust bearing (15) achieved, but an increase in air pressure to a level in front of the turbine wheel (19) is also achieved. The air flow (24) guided through the air channels (7, 8, 12, 13) is indicated by arrows in FIG. 2.

Claims

Claim 1 A turbo machine (1) for supplying air to a fuel cell system, comprising: one or more compressor wheels (3) connected to rotate integrally with a shaft (2); and an electric motor (4) for driving the shaft (2); wherein the compressor wheel (3) is connected to rotate integrally with a hollow cylindrical shaft section (6) of the shaft (2) through a hub section (5), wherein one or more air channels (7, 8) are formed within the hub section (5), and through these air channels a compressor inlet (9) is connected to an annular space (10) on the side opposite the compressor inlet (9) of the compressor wheel (3), so that the same air pressure is applied to two sides of the compressor wheel (3), and wherein the air channels (7, 8) have an opening on the outer surface of the hollow cylindrical shaft section (6) adjacent to the wall of the compressor wheel (3) on the side opposite the compressor inlet (9). Claim 2 A turbo machine (1) for supplying air to a fuel cell system, wherein, in claim 1, the hub section (5) comprises one or more air channels (7) extending axially. Claim 3 A turbo machine (1) for supplying air to a fuel cell system, wherein, in claim 1 or 2, the hub section (5) comprises one or more air channels (8) extending radially. Claim 4 A turbo machine (1) for supplying air to a fuel cell system, characterized in that, in claim 1 or 2, the hub section (5) is inserted or pressed into a hollow cylindrical shaft section (6) at least section by section. Claim 5 A turbo machine (1) for supplying air to a fuel cell system, wherein, in paragraph 4, the hollow cylindrical shaft section (6) comprises one or more radially extending air channels (11) arranged to overlap with one or more air channels (8) extending radially from the hub section (5). Claim 6 A turbomachine (1) for supplying air to a fuel cell system, characterized in that, in claim 1, the annular space (10) on the side opposite the compressor inlet (9) of the compressor wheel (3) is connected to one or more bearings (14, 15) of the shaft (2) through one or more additional air channels (12, 13), and one or more bearings (14, 15) are formed as gas-lubricated foil bearings. Claim 7 A turbo machine (1) for supplying air to a fuel cell system, characterized in that, in claim 6, one or more additional air channels (12) are guided through an annular gap (16) between a shaft (2) and a winding (17) of an electric motor (3) surrounding the shaft (2). Claim 8 A turbo machine (1) for supplying air to a fuel cell system, characterized in that, in claim 6, one or more additional air channels (13) are guided through an internally ventilated thrust bearing disc (18) connected to rotate integrally with a shaft (2) for supporting a turbine wheel (19). Claim 9 A turbo machine (1) for supplying air to a fuel cell system, wherein, in any one of claims 6 to 8, the air channels (7, 8, 12, 13) for connecting the compressor inlet (9) are capable of supplying cooled or uncooled ambient air. Claim 10 A method of operating a turbo machine (1) according to any one of claims 1, 2, or 6 to 8, wherein the air channels (7, 8, 12, 13) are supplied with cooled or uncooled ambient air. Claim 11 A method of operating a turbo machine according to claim 10, characterized in that the cooling air pressure is increased by an internally ventilated thrust bearing disc (18) through which one or more air channels (13) are guided.

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