DE102022116933A1 - Compressor for a fuel cell system, and fuel cell system with the same - Google Patents

Abstract

The invention relates to a compressor (1) for a fuel cell system (100), in particular a commercial vehicle (300), with a compressor housing (3), a compressor wheel (11), a rotationally driven compressor shaft (5), which is connected to the compressor wheel (11). is operatively connected, and a bearing arrangement (6), which supports the compressor shaft (5) in the compressor housing (3) rotatably about an axis of rotation (A), the bearing arrangement (6) having an axial air bearing (7c) for absorbing axial forces (Faxial ) between the compressor housing (3) and the compressor shaft (5). It is proposed that the compressor shaft is operatively connected to a one-way magnetic force compensation unit (23), the force compensation unit (23) being set up to apply a magnetic force (Fmag) opposite the axial forces (Faxial) to the compressor shaft in the direction of the rotation axis (A). (5), and wherein the force compensation unit (23) is set up to vary the strength of the magnetic force (Fmag).

Description

Compressor for a fuel station system, as well as fuel cell system and method for its operation

The present invention relates to a compressor for a fuel cell system, in particular for a fuel cell system of a commercial vehicle, with a compressor housing, a compressor wheel, a rotationally driven compressor shaft which is operatively connected to the compressor wheel, and a bearing arrangement which rotates the compressor shaft in the compressor housing about an axis of rotation is stored, 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 axis of rotation (hereinafter also: axial forces).

For correct operation, fuel cell systems generally require a controlled cathode-side air supply in order to be able 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 and thus supply the fuel cell with a controlled mass or volume flow of air.

The higher the power to be generated by the fuel cell, the higher the necessary mass or volume flow that must be conveyed by the compressor or compressors. When the compressor is in operation, the suction process of air creates an axial force which acts on the compressor shaft. As the speed of the compressor shaft and the compressor wheel increases - with a constant cross section - the amount of air sucked in and thus the pressure built up and thus also the axial force increases. This effect is more pronounced in single-stage compressors than in two-stage compressors, in which the axial forces are at least partially balanced.

If the axial force is too high for the bearing used, increased wear occurs, especially at the prevailing speeds. The axial forces that occur must therefore be absorbed by the bearing arrangement in all compressor systems so that unintentionally high wear does not occur between the rotating elements and the stationary elements in the compressor. Due to the high speeds of operation of the compressors mentioned above, it has already proven useful in the past to use an axial air bearing in the bearing arrangement, which is intended to absorb the axial forces that occur between the compressor shaft and the compressor housing.

Two-stage compressors can usually sufficiently compensate for the axial forces that occur using an axial air bearing. However, the installation space that two-stage compressors take up due to their design principle is seen as a challenge, especially given the increasingly limited space available in vehicles. Two-stage compressors are therefore usually unsuitable for applications in passenger cars, and installation space is also becoming increasingly scarce in commercial vehicles due to technological developments.

It is known to support rotating shafts using axial magnetic bearings. Such magnetic bearings are, for example EP 1811183 A1 , DE 102008050314 A1 , DE 102010035727 A1 , DE 102019215391 A1 , DE 102011051885 A1 , or EP 3579390 A1 known.

However, when using conventional magnetic bearings, complex control is necessary to ensure that the stationary parts (coils) and rotating parts (running disks) are at the correct distance from one another. As a rule, the electrical parameters of current and voltage must be constantly monitored in order to be able to correctly energize the coils of the magnetic bearing, so that the running disk is prevented from striking the stationary parts of the magnetic bearing. For this purpose, sensors are usually also necessary, such as position sensors, in order to determine the position of the rotor disk relative to the magnetic bearing. This effort is perceived as disadvantageous, especially against the background of the operation of a compressor of the type mentioned at the beginning, in which the axial forces change during operation as explained above.

Against this background, the invention was based on the object of specifying a compressor in which the disadvantages described above are mitigated as much as possible. In particular, the invention was based on the object of improving a compressor of the type described at the outset in such a way that axial forces acting on the compressor shaft can be better absorbed and at the same time the compressor requires as little space as possible. In particular, the invention was based on the object of implementing the above as cost-effectively as possible.

The invention solves the underlying problem by proposing a compressor according to claim 1. In particular, the invention proposes a compressor at the beginning designated type that the compressor shaft is operatively connected to a unidirectional magnetic force compensation unit, the force compensation unit being set up to apply a magnetic force opposite to the axial forces to the compressor shaft in the direction of the axis of rotation, and the force compensation unit being set up to control the strength of the magnetic force to vary.

The invention makes use of the knowledge that the axial force, which is transmitted from the compressor wheel to the compressor shaft, always acts in the same direction due to the design. The force compensation unit only needs to be set up to apply a magnetic force that is opposite to this direction of force, and can therefore be designed to act on one side. The comparatively more complex construction of a magnetic bearing can be dispensed with. This also eliminates the need to implement a complex control system, as would be necessary for magnetic bearings given the narrow bearing gaps used there. The variation of the strength of the magnetic force of the force compensation unit can be done more roughly and implemented with much simpler control concepts. At the same time, the invention uses the advantage of magnetic force and the efficient development of force, which can be achieved using electromagnetism.

In an advantageous development, the compressor has a control unit, or can be connected to it in a signal-conducting manner, which is set up to control the force compensation unit to vary the magnetic force. In preferred embodiments, the control unit is part of the compressor control and is integrated there in hardware or software. In preferred embodiments, the control unit can also be part of the fuel cell system, for example in that the fuel cell system has a fuel cell control and the control unit is integrated into the fuel cell control in software or hardware. In further preferred embodiments, the control unit can also be designed as a dedicated control unit.

In a preferred embodiment, the control unit is set up to vary the magnetic force in several stages, preferably in 10 or fewer stages, more preferably in 5 or fewer stages, particularly preferably in 3 or fewer stages. The efficiency of staged control lies in its simplicity. A predetermined number of load ranges can be roughly identified and magnetic forces or force ranges can be determined for these load ranges through calibration in preliminary tests, which can then be controlled by the control unit without the need for regulation.

In a preferred embodiment, the control unit is set up to control the force compensation unit as a function of one or more operating parameters that are representative of the axial forces. The operating parameters can be determined empirically in preliminary tests, and pairs of values and/or characteristic maps can be easily determined that simply relate the axial forces that occur from the compressor wheel to the compressor shaft to the various operating variables of the compressor. It should also be noted here that the force compensation unit does not have to fulfill a (main) bearing function, but is only intended to provide an additional magnetic supporting force that is opposite to the axial forces and which is intended to prevent the axial air bearing from hitting after its load capacity has been exceeded and can be damaged. No exact regulation is necessary for this. Rather, it is sufficient if operating parameters are assigned comparatively roughly to specific expected ranges for the axial forces that can be expected at those operating parameters and the force compensation unit then changes the magnetic force in comparatively coarse steps in order to reduce the forces acting on the compressor in total to a level that can be tolerated by the axial air bearing to be able to, for example in the gradations outlined above.

The operating parameter(s) is/are preferably selected from the following: a speed of the compressor shaft; a speed specification of the fuel cell system; an air mass flow promoted by the compressor; a compressor output pressure; an ambient air pressure; a load capacity of the axial air bearing; or a combination of several or all of the above parameters.

Speeds or speed bands can be determined, for example, by reading out the power electronics of the electrical machine of the compressor, in particular based on the frequency of a converter. The speed specification can, for example, be taken from a fuel cell control of the fuel cell system, or from a compressor control, provided that the speed specification is managed there. The load capacity of the axial air bearing depends on the type and design of the bearing. For example, spiral groove bearings will be able to develop a higher load capacity than foil bearings. However, due to the powerful support option provided by the force compensation unit, the use of foil bearings is sufficient in the present case and advantageous for cost-effectiveness reasons.

The magnetic force generated by the force compensation unit is preferably below the load capacity of the axial air bearing. The magnetic force is particularly preferably in a range of 10% - 35% below the load-bearing capacity of the axial air bearing, in particular 15% to 25% below the load-bearing capacity of the axial air bearing. This can reliably prevent the force compensation unit from deflecting the compressor shaft “in the wrong direction” against the effective direction of the axial force.

Air mass flow, output pressure at the compressor and ambient air pressure can be determined in a generally known manner with conventional sensors or received as (if necessary derived) characteristic values from other control systems of the commercial vehicle.

• - Die Verdichterwelle erreicht oder überschreitet eine vorbestimmte Mindestdrehzahl;
• - der Ausgangsdruck erreicht oder überschreitet einen vorbestimmten Mindestdruck;
• - der Luftmassenstrom des Verdichters erreicht oder überschreitet einen vorbestimmten Mindestmassenstrom;
• - der Umgebungsluftdruck erreicht oder unterschreitet einen vorbestimmten Mindestluftdruck.

In a further preferred embodiment, the control unit is set up to only activate the force compensation unit when one, several or all of the following criteria are met:

• - The compressor shaft reaches or exceeds a predetermined minimum speed;
• - the output pressure reaches or exceeds a predetermined minimum pressure;
• - the air mass flow of the compressor reaches or exceeds a predetermined minimum mass flow;
• - The ambient air pressure reaches or falls below a predetermined minimum air pressure.

In this regard, the invention makes use of the knowledge that the force compensation unit does not have to be in permanent operation. At less challenging operating points of the fuel cell system, i.e. usually at low speeds of the compressor shaft, the axial air bearing is usually able to absorb the axial forces alone, without support from the force compensation unit. Only when it is expected that the axial air bearing alone will no longer be able to absorb the expected axial forces is the force compensation unit switched on according to the preferred embodiments by means of control by the control unit and makes its magnetic force available for additional support and compensation of the axial forces.

In a further preferred embodiment, the force compensation unit has an energized coil arrangement which is stationary relative to the compressor housing for generating the magnetic force, and a force transducer which is stationary relative to the compressor shaft and which is arranged in the magnetic field of the coil arrangement and is set up to transmit the magnetic force to the compressor shaft.

The force transducer is preferably designed as a running disk which is arranged on one side and axially adjacent to the coil arrangement in such a way that the magnetic force counteracts the axial forces. In an alternative embodiment, the force transducer is arranged in the area of the coil core of the coil arrangement, but also in this case advantageously acts in such a way that the magnetic force counteracts the axial forces.

The control unit is preferably set up to control the current supply to the coil arrangement as a function of the operating parameter(s). The voltage of the coil arrangement is preferably at the same voltage level as that of the electrical machine of the compressor, for example in the range from 400 V to 820 V.

In a preferred embodiment, the force transducer, for example in the form of a running disk, has a permanently magnetic material or at least magnetized with sufficient remanence, such as a ferromagnetic, in particular hard magnetic material. Preferably, the force transducer is at least partially formed from one of the following metals: iron, iron alloy, nickel, nickel alloy, cobalt, cobalt alloy; or a combination of several of the above materials. These materials can be magnetized in such a way that they can be used as permanent magnets and thus enable an arrangement of the coil arrangement for pushing - i.e. magnetic repulsion - of the force transducer as well as for pulling - i.e. magnetic attraction - of the force transducer. The magnetic field generated by the coil arrangement preferably has a low field strength compared to the magnetic field of the force transducer, so that any remagnetization of the force transducer in embodiments in which the force transducer is to be repelled can be carried out within the scope of usual maintenance intervals of the compressor.

In preferred embodiments, in which the force transducer is designed as a running disk, the surface of the running disk is preferably hardened, for example surface hardened, and/or additionally coated with a material cover to protect against wear. This means that the force transducer can survive direct frictional contact with the compressor housing or the coil arrangement without damage, even in an emergency.

In a further preferred embodiment, the axial air bearing has a first movement play in the direction of the rotation axis, the compressor wheel has a second movement play in the direction of the rotation axis, and the force transducer has a third movement play in the direction the axis of rotation, the third movement play being greater than the second and/or the first movement play. In the case of the compressor wheel and the force transducer, the movement play is defined by a clear width in the axial direction between the moving components and the stationary components, especially the compressor housing.

With the axial air bearing, the movement play results from the difference between the width of the air gap and the thickness of a running disk of the axial air bearing, which rotates in the air gap. The fact that the third movement range is the largest of the three different movement ranges ensures that the force compensation unit works without wear. The force transducer hitting the compressor housing can be avoided. The movement play of the compressor wheel is preferably less than the movement play of the axial air bearing and the force transducer.

In a further preferred embodiment, the compressor is a single-stage compressor, wherein the compressor wheel is arranged on a first end section of the compressor shaft, and wherein the magnetic force compensation unit is arranged on a second end section of the compressor shaft opposite the first end section.

By arranging the compressor wheel on the one hand and the force compensation unit on the other side opposite each other, the balance of the rotating masses is improved. In single-stage compressors in particular, this is a major design advantage, particularly for the bearing arrangement, which benefits a longer service life.

In a preferred embodiment, the bearing arrangement has a radial bearing arrangement. The radial bearing arrangement preferably has a number of radial bearings arranged between the axial air bearing and the force compensation unit. According to the invention, a number is understood to mean a number of 1 or more units.

The bearing arrangement particularly preferably has two radial bearings, which can be designed, for example, as radial air bearings. By weighting and spacing the axial air bearing and the force compensation unit from the closest radial bearings, a favorable weight distribution can be achieved, and the accessibility of the force compensation unit for maintenance purposes is also ensured to a good extent.

In a further preferred embodiment, the number of radial bearings therefore has a first radial bearing, which is arranged at a first axial distance from the axial air bearing, and a second radial bearing, which is at a distance from the first radial bearing and at a second axial distance from the Force compensation unit is arranged, wherein the second axial distance and the first axial distance are different. Preferably, the second axial distance is greater than the first axial distance.

The compressor wheel is usually also arranged on the side of the compressor shaft on which the axial air bearing is located, so that the rotating masses and tilting moments on that side of the compressor shaft are, as expected, greater than on the left side. By increasing the distance between the force compensation unit and the next radial bearing adjacent to it, the second radial bearing, at least partial compensation of the tilting moments can be achieved.

In particular, a first radial force acts on the radial bearing arrangement from the axial air bearing, and a second radial force acts on the radial bearing arrangement from the force compensation unit. A third radial force acts on the radial bearing arrangement from the compressor wheel, which is arranged at a third axial distance from the first or second radial bearing. The radial forces and distances result in tilting moments that act on the radial bearing arrangement via the compressor shaft.

Preferably, the first, second and third distances are dimensioned such that the resulting tilting moments at least partially, and preferably completely, eliminate each other.

Alternatively or additionally, the first, second and/or third distances are preferably dimensioned such that the same radial forces act on the radial bearings of the bearing arrangement.

In a further preferred embodiment, the axial air bearing is designed as a foil bearing. Preferably, a running disk of the axial air bearing is arranged between two standing film disks spaced apart from one another by the air gap. The axial air bearing is preferably designed as a bump type or another foil bearing type. These cost-efficient bearing types, in conjunction with the design principle according to the invention, have sufficient load capacity to compensate for the axial forces even in single-stage compressors. However, the invention does not exclude the use of spiral groove bearings and other types of bearings.

The invention has been described above using a first aspect with reference to the compressor.

• - rotatorisches Antreiben einer Verdichterwelle zur kathodenseitigen Luftversorgung einer Brennstoffzelle, wobei die Verdichterwelle in einem Verdichtergehäuse drehbar um eine Rotationsachse gelagert wird, und wobei Axialkräfte zwischen dem Verdichtergehäuse und der Verdichterwelle wirken,
• - Aufbringen einer den Axialkräften entgegengesetzten Magnetkraft auf die Verdichterwelle mittels einer einseitig wirkenden magnetischen Kraftkompensationseinheit, und
• - Variieren der Magnetkraft mittels der Kraftkompensationseinheit.

In a second aspect, the invention further relates to a method for operating a fuel cell system, in particular a commercial vehicle, which preferably has a compressor according to one of the preferred embodiments described above. The method solves the task described at the beginning by comprising the following steps:

• - rotationally driving a compressor shaft for supplying air to a fuel cell on the cathode side, the compressor shaft being rotatably mounted in a compressor housing about an axis of rotation, and axial forces acting between the compressor housing and the compressor shaft,
• - Applying a magnetic force opposite the axial forces to the compressor shaft by means of a unidirectional magnetic force compensation unit, and
• - Varying the magnetic force using the force compensation unit.

The method makes use of the same advantages as the compressor of the type described above. Preferred embodiments of the compressor are at the same time preferred embodiments of the method and vice versa, which is why reference is also made to the above statements in order to avoid repetition and the following.

• - Ansteuern der Kraftkompensationseinheit zur Variation der Magnetkraft., vorzugsweise in mehreren Stufen, insbesondere in 10 oder weniger Stufen, weiter vorzugsweise in 5 oder weniger Stufen, besonders bevorzugt in 3 oder weniger Stufen.

The method is advantageously further developed in that varying the magnetic force includes:

• - Controlling the force compensation unit to vary the magnetic force, preferably in several stages, in particular in 10 or fewer stages, more preferably in 5 or fewer stages, particularly preferably in 3 or fewer stages.

• - eine Drehzahl der Verdichterwelle,
• - eine Drehzahlvorgabe des Brennstoffzellensystems,
• - ein von dem Verdichter geförderter Luftmassenstrom,
• - ein Ausgangsdruck des Verdichters,
• - ein Umgebungsluftdruck,
• - Tragkraft des Axial-Luftlagers; oder

eine Kombination mehrerer oder sämtlicher der vorstehenden Parameter.The control preferably takes place as a function of one or more operating parameters that are representative of the axial forces; wherein further preferably the operating parameters are selected from the following:

• - a speed of the compressor shaft,
• - a speed specification of the fuel cell system,
• - an air mass flow conveyed by the compressor,
• - an output pressure of the compressor,
• - an ambient air pressure,
• - Load capacity of the axial air bearing; or

a combination of several or all of the above parameters.

• - die Verdichterwelle erreicht oder überschreitet eine vorbestimmte Mindestdrehzahl;
• - der Ausgangsdruck des Verdichters erreicht oder überschreitet einen vorbestimmten Mindestdruck;
• - der Luftmassenstrom des Verdichters erreicht oder überschreitet einen vorbestimmten Mindestmassenstrom;
• - der Umgebungsluftdruck erreicht oder unterschreitet einen vorbestimmten Mindestluftdruck.

The force compensation unit is preferably only activated when one, several or all of the following criteria are met:

• - the compressor shaft reaches or exceeds a predetermined minimum speed;
• - the output pressure of the compressor reaches or exceeds a predetermined minimum pressure;
• - the air mass flow of the compressor reaches or exceeds a predetermined minimum mass flow;
• - The ambient air pressure reaches or falls below a predetermined minimum air pressure.

In a further aspect, the invention relates to a fuel cell system for driving a vehicle, in particular a commercial vehicle, with a compressor for supplying air to a fuel cell on the cathode side. The invention solves the underlying problem with regard to such a fuel cell system by designing the compressor according to one of the preferred embodiments described above, and / or by the fuel cell system having a control unit which is set up in a method according to one of the ones described above Embodiments to control the force compensation unit of the compressor.

With regard to the fuel cell system, the invention also makes use of the same advantages as described above with reference to the compressor and the method. Preferred embodiments of the compressor and the method are therefore also preferred embodiments of the fuel cell system and vice versa, which is why reference is made to the above statements to avoid repetition.

The invention is described in more detail below with reference to the attached figures using a preferred exemplary embodiment.

• 1 eine schematische Darstellung eines Brennstoffzellensystems gemäß einem bevorzugten Ausführungsbeispiel, und
• 2 eine schematische Detailansicht einer Verdichterwelle des Brennstoffzellensystems gemäß 1.

Show here:

• 1 a schematic representation of a fuel cell system according to a preferred embodiment, and
• 2 a schematic detailed view of a compressor shaft of the fuel cell system according to 1 .

In 1 a fuel cell system 100 for a commercial vehicle 300 is shown schematically. The fuel cell system 100 has a fuel cell 101, which is designed to provide electrical energy. To supply air, the fuel cell 101 is operatively connected to a compressor 1, which is set up to suck in an air flow L, compress it, and supply it to the fuel cell 101 on the cathode side.

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 arrangement 6 comprising an axial air bearing 7 and a radial bearing arrangement 8. The radial bearing arrangement 8 includes a first radial bearing 8a and a second radial bearing 8b. The axial air bearing 7 and/or the two radial bearings 8a, 8b are preferably designed as foil bearings

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 rotationally rigid manner.

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 with an air mass flow m, compresses it and releases it in the direction of the fuel cell 101 at an output pressure pv .

The compressor 1 in the exemplary embodiment shown is designed as a single-stage compressor. In a second end section 15, which lies opposite the first end section 9, a force compensation unit 23 is arranged on the compressor shaft 5. The force compensation unit 23 thereby performs several relevant functions for the compressor 1: On the one hand, the force compensation unit 23 provides a magnetic compensation force F _mag , which acts _axially in the opposite direction to the axial forces F and thus reduces the axial load on the axial air bearing 7. Furthermore, the force compensation unit 23 contributes to reducing the radial forces acting on the radial bearing arrangement 8 (cf. 2 ) and/or to balance tilting moments at least partially, because the mass emanating from the force compensation unit 23 acts on the compressor shaft 5 on a side of the radial bearing arrangement 8 facing away from the compressor wheel 11 and thus in particular also the radial forces and tilting moments of the axial air bearing 7 and the compressor wheel 11 at least can partially compensate.

The axial air bearing 7 has a running disk 17 which is connected in a rotationally rigid manner to the compressor shaft 5 and which is positioned between two stationary film disks 19. An air gap 21 is formed between the two film disks 19.

The force compensation unit 23 has a force transducer 25, which can be designed as a permanent magnetic rotor disk and is connected to the compressor shaft 5 in a rotationally rigid manner, the force transducer being arranged axially adjacent in the magnetic field H of a coil arrangement 26. The coil arrangement 26 has a number of coils 27 which are distributed, preferably evenly, over the circumference of the force transducer.

In the 2 The configuration of the force compensation unit 23 shown provides that the coil arrangement 26 is arranged between the force transducer 25 and the compressor wheel 11. In order to be able to _axially compensate for the axial forces F, the coil arrangement 26 repels the force transducer 25 when the current is supplied accordingly, indicated by the arrow of the magnetic force F _mag in 1 .

It is also conceivable to have the coil arrangement 26 on the other side of the force transducer 25, which is in 1 to the left of the force transducer 25 would have to be arranged and energized in such a way that the force transducer 25 is attracted by the coil arrangement 26. A possible advantage is seen in the fact that the magnetic field H of the coil arrangement 26 can then have a weakening effect on the remanent magnetization of a force transducer 25, which is not permanent magnetic, but merely ferromagnetic.

The fuel cell system 100 according to 1 also has a control unit 103. The control unit 103 is shown as a dedicated control unit, but can also be, for example, part of a fuel cell control (not shown) of the fuel cell 101 or part of a compressor control (not shown) of the compressor 1. The control unit 103 has, in a generally known manner, one or more processors and a data memory as well as corresponding data interfaces and is set up to control the coil arrangement 26 in order to vary the magnetic force F _mag generated by the coils 27.

For this purpose, the control unit 103 is connected to the force compensation unit 23 in a signal-conducting manner and is set up to transmit control commands B to the force compensation unit. In a simple, preferred case, the control commands B are directly in the form of different current intensities for the coils 27 of the coil arrangement 26.

The control unit 103 is preferably set up to receive the control commands B as a function of a to transmit several or all of the operating parameters P _B generally described above, whereby the operating parameters P _B can be, for example, the following: a speed n of the compressor shaft 5, a speed specification nv of the fuel cell 101, the air pressure pv at the output of the compressor 1, an ambient pressure pu , the air mass flow ṁ, or a load capacity T of the axial air bearing 7.

The control unit 103 is preferably set up to continuously monitor the operating parameters and, if necessary, to adjust the magnetic force F _mag . For this purpose, the force compensation unit 23 does not have to be actively controlled during the entire operating period of the compressor 1. Particularly at low speeds n, it is usually sufficient for the axial air bearing 7 to _axially absorb the axial forces F that occur within the scope of its load capacity T alone.

The control unit 103 is set up to detect, for example, whether a predetermined minimum speed n _min has been reached or exceeded, and/or whether the output pressure p _V of the compressor reaches or exceeds a predetermined minimum pressure p _V,min , and/or whether the air mass flow m of the compressor 1 reaches or exceeds a predetermined minimum mass point ṁ _min , and / or whether the ambient air pressure pu reaches or exceeds a predetermined minimum air pressure p _{U, min} . Only when one, several or all of these criteria are reached does the control unit 103 then control the force compensation unit 23 to adjust the magnetic force F _mag in such a way that the resulting remaining force in the axial direction can be absorbed by the axial air bearing 7 without risk of wear.

In 2 is shown roughly and under simplifying assumptions, such as the assumption of a massless compressor shaft 5, a force balance for the compressor shaft 5 and the radial bearing arrangement 8. The first radial bearing 8a is loaded with a radial force F _R1 , while the second radial bearing 8b is loaded with a radial force F _R2 . A radial force F _L emanates from the running disk 17 of the axial air bearing 7, and a radial force F _K emanates from the force transducer 25 of the force compensation unit 23, each of which acts on the compressor shaft 5. A radial force Fv emanates from the compressor wheel 11 and also acts on the compressor shaft 5.

The centers of the two radial bearings 8a, 8b are apart from each other by the distance L _R in the direction of the rotation axis A, i.e. in the axial direction. The first running disk 17 is located at an axial distance L ₁ from the radial bearing closest to it, namely the first radial bearing 8a. The force transducer 25 is located at a distance L ₂ from the radial bearing closest to it, namely the second radial bearing 8b. The compressor wheel 11 is located with its center of mass in the axial direction at a distance L ₃ from the radial bearing closest to it, namely the first radial bearing 8a as above.

Based on the force and moment balances for this constellation, the distances L ₁ , L ₂ , and L ₃ as well as L _R in the design can be coordinated with one another in such a way that the radial loads F _R1 , F _R2 on the radial bearing arrangement 8 are the same, or at least essentially the same. In preferred embodiments, the distance L ₂ will be greater than L ₃ and L ₃ will be greater than L ₁ . L _R is preferably greater than L ₂ .

Through a structurally favorable design, ie, for example, by minimizing the distance L ₁ and L ₃ as far as possible, an overall quite compact bearing concept can be set up, which offers good use of installation space and at the same time makes possible a purely air-bearing compressor shaft 5 that is advantageously balanced compared to the prior art. Due to the balancing effect that comes from the force compensation unit, long service lives can be achieved even when using single-stage compressors, as in the preferred exemplary embodiment. At the same time, the bearing concept allows the use of simple bearing types for the axial air bearing, such as bump type or other foil bearing types.

The rotor disk 17 has a first axial movement play s ₁ relative to the compressor housing 3. The compressor wheel 11 has a second axial movement play s ₂ , which is preferably less than the first movement play s ₁ . The force transducer 25 has a third axial movement play s ₃ , which is preferably greater than s ₂ and than s ₁ . This protects the force compensation unit 23 from wear and ensures that it can maintain its support function for the axial air bearing 7 for a long time, which in turn benefits the service life of the axial air bearing 7.

Reference symbols (part of the description)

1

compressor

3

Compressor housing

5

Compressor shaft

6

Bearing arrangement:

7

Axial air bearing

8th

Radial bearing arrangement

8a

first radial bearing

8b

second radial bearing

9

first end section

11

Compressor wheel

13

electric machine

15

second end section

17

running disc

19

Foil disc

21

air gap

23

Force compensation unit

25

force transducer

26

Coil arrangement

27

Wash

100

Fuel cell system

101

Fuel cell

103

Control unit

300

Commercial vehicle

A

Axis of rotation

b

Control commands

Fmag

magnetic force

Fax

Axial forces

FL

Radial force, axial air bearing

FK

Radial force, force compensation unit

Fv

Radial force, compressor

FR1, FR2

radial loads

H

Magnetic field

L

Air, compressor

LR L1, L2, L3

distances

ṁ

Air mass flow

ṁ min

Minimum mass flow

n

number of revolutions

n/a

Speed specification

nmin

Minimum speed

PB

Operating parameters

pv

Air pressure

pu,

Ambient pressure

pv,min

Minimum pressure

s1, s2, s3

movement game

T

Load capacity

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 1811183 A1 [0007]
• DE 102008050314 A1 [0007]
• DE 102010035727 A1 [0007]
• DE 102019215391 A1 [0007]
• DE 102011051885 A1 [0007]
• EP 3579390 A1 [0007]

Claims (16)

Compressor (1) for a fuel cell system (100), in particular a fuel cell system (100) of a commercial vehicle (300), with a compressor housing (3), a compressor wheel (11), a rotationally driven compressor shaft (5) which is connected to the compressor wheel (11 ) is operatively connected, and a bearing arrangement (6), which supports the compressor shaft (5) in the compressor housing (3) so that it can rotate about an axis of rotation (A), the bearing arrangement (6) having an axial air bearing (7c) for absorbing axial forces ( F _axial ) between the compressor housing (3) and the compressor shaft (5), characterized in that the compressor shaft is operatively connected to a one-way magnetic force compensation unit (23), the force compensation unit (23) being set up to move in the direction of the rotation axis ( A) to apply a magnetic force (F _mag ) which is opposite to the axial forces (F _axial ) to the compressor shaft (5), and wherein the force compensation unit (23) is set up to vary the magnetic force (F _mag ). Compressor (1) after Claim 1 , characterized in that the compressor (1) has, or can be connected to, a control unit (103), which is set up to control the force compensation unit (23) to vary the magnetic force (F _mag ). Compressor after Claim 2 , characterized in that the control unit (103) is set up to vary the magnetic force (F _mag ) in several stages, preferably in 10 or fewer stages, more preferably in 5 or fewer stages, particularly preferably in 3 or fewer stages. Compressor (1) after Claim 2 or 3 , characterized in that the control unit (103) is set up to control the force compensation unit (23) as a function of one or more operating parameters (P _B ) which are representative of the axial forces (F _axial ). Compressor (1) after Claim 4 , whereby the operating parameters (P _B ) are selected from the following: - a speed (n) of the compressor shaft (5), - a speed specification (nv) of the fuel cell system (100), - an air mass flow (ṁ.) conveyed by the compressor (1). ), - an output pressure (pv) of the compressor (1), - an ambient air pressure (pu), - load capacity (T) of the axial air bearing (7), or a combination of several or all of the above parameters. Compressor (1) according to one of the Claims 2 until 5 , characterized in that the control unit (103) is set up to control the force compensation unit (23) only when one, several or all of the following criteria are met: - the compressor shaft (5) reaches or exceeds a predetermined minimum speed (n _min ); - the output pressure (pv) of the compressor (1) reaches or exceeds a predetermined minimum pressure (p _V,min ); - the air mass flow (m) of the compressor (1) reaches or exceeds a predetermined minimum mass flow (ṁ _min ); - The ambient air pressure (pu) reaches or falls below a predetermined minimum air pressure (p _U,min ). Compressor (1) according to one of the preceding claims, characterized in that the force compensation unit (23) has an energized coil arrangement (26) which is stationary relative to the compressor housing (3) for generating the magnetic force (F _mag ), and one relative to the compressor shaft (5 ) stationary force transducer (25), which is arranged in a magnetic field (H) of the coil arrangement (26) and is designed to transmit the magnetic force (F _mag ) to the compressor shaft (5). Compressor (1) according to one of the preceding claims, wherein the axial air bearing (7) has a first movement play (s ₁ ) in the direction of the rotation axis (A), the compressor wheel (11) has a second movement play (s ₂ ) in the direction of the rotation axis (A), and the force transducer (25) has a third movement play (s ₃ ) in the direction of the axis of rotation (A), the third movement play (s ₃ ) being greater than the second movement play (s ₂ ) and/or the first movement play (s ₁ ) is. Compressor (1) according to one of the preceding claims, 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 magnetic force compensation unit (23) is arranged on a second end section (15) of the compressor shaft (5) opposite the first end section (9). Compressor (1) according to one of the preceding claims, characterized in that the compressor has a radial bearing arrangement (8), the radial bearing arrangement (8) being arranged between the axial air bearing and the magnetic force compensation unit (23). Compressor (1) after Claim 10 , wherein the radial bearing arrangement (8) has a first radial bearing (8a) which is arranged at a first axial distance (L ₁ ) from the axial air bearing (7c), and a second radial bearing (8b) which is at a distance (L _R ) is arranged to the first radial bearing (8a) and at a second axial distance (L ₂ ) to the force compensation unit (23), the second axial distance (L ₂ ) and the first axial distance (L ₁ ) being different. Compressor (1) after Claim 11 , wherein the first, second and third distances (L ₁ , L ₂ , L ₃ ) are dimensioned such that radial forces (F _R1 , F _R2 ). Method for operating a fuel cell system, in particular a commercial vehicle, which preferably has a compressor (1) according to one of the preceding claims, wherein the method comprises the steps: - rotationally driving a compressor shaft (5) for supplying air to a fuel cell (101) on the cathode side, - wherein the compressor shaft (5) is rotatably mounted in a compressor housing (3) about an axis of rotation (A), with axial forces (F _axial ) acting between the compressor housing (3) and the compressor shaft (5), - applying one of the axial forces (F _axial ) opposing magnetic force (F _mag ) on the compressor shaft (5) by means of a unidirectional magnetic force compensation unit (23), and - varying the magnetic force (F _mag ) by means of the magnetic force compensation unit (23). Procedure according to Claim 13 , comprising the step: - controlling the force compensation unit (23) to vary the magnetic force (F _mag ), preferably in several stages, in particular in 10 or fewer stages, more preferably in 5 or fewer stages, particularly preferably in 3 or fewer stages. Procedure according to Claim 14 , wherein the control preferably takes place as a function of one or more operating parameters that are representative of the axial forces (F _axial ); wherein further preferably the operating parameters (P _B ) are selected from the following: - a speed (n) of the compressor shaft (5), - a speed specification (nv) of the fuel cell system (100), - an air mass flow conveyed by the compressor (1) ( m), - an output pressure (pv) of the compressor (1), - an ambient air pressure (pu), - load capacity (T) of the axial air bearing (7), or a combination of several or all of the above parameters; and/or wherein further preferably the force compensation unit (23) is only activated when one, several or all of the following criteria are met: - the compressor shaft (5) reaches or exceeds a predetermined minimum speed (n _min ); - the output pressure (pv) of the compressor (1) reaches or exceeds a predetermined minimum pressure (p _V,min ); - the air mass flow (ṁ) of the compressor (1) reaches or exceeds a predetermined minimum mass flow (ṁ _min ); - The ambient air pressure (pu) reaches or falls below a predetermined minimum air pressure (p _U,min ). Fuel cell system (100) for driving a vehicle (300), in particular a commercial vehicle, with a compressor (1) for supplying air to the cathode side of a fuel cell (101), characterized in that the compressor (1) according to one of Claims 1 until 12 is designed, and / or that the fuel cell system has a control unit (103) which is set up in a method according to one of Claims 13 until 15 to control the force compensation unit (23) of the compressor.

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