Method for starting a turbocompressor with a bearing arrangement for an axle shaft of the turbocompressor

Description

[0001] The invention relates to a method for starting a turbocompressor with a bearing arrangement for an axle shaft of the turbocompressor. State of the art

[0002] Hydrogen-based fuel cells are considered the basis for a future mobility concept because they emit only water and enable fast refueling times. For example, PEM (proton-exchange membrane) fuel cells can be operated in an electrocatalytic electrode process using air supplied to the fuel cell cathode with oxygen as the oxidant and hydrogen supplied to the fuel cell anode as the fuel, providing electrical energy with high efficiency.

[0003] Such fuel cells are typically stacked and operated in a fuel cell system. The air supplied to the cathode of the fuel cell stack is compressed by a turbocompressor.

[0004] EP 1 321 680 A2, DE 10 2012 221445 A1, FR 1 280 891 A and EP 2 600 015 A1 each disclose a turbo compressor with a bearing for an axle shaft according to the prior art. revelation

[0005] The drive shaft of such a turbocompressor is mounted either with rolling bearings, which have the disadvantage of high friction and a correspondingly short service life, or with hydrodynamic air bearings, which are complex to manufacture due to the high precision required. Both variants also have the disadvantage that heat generated in the bearings and / or the electrical motor is difficult to dissipate.

[0006] According to one aspect of the invention, a method for starting a turbocompressor with a bearing arrangement according to the features of independent claim 1 is proposed, which at least partially achieves the described objects. Advantageous embodiments are the subject of the dependent claims and the following description.

[0007] Before a water-hydraulic bearing can be put into operation, it must be ensured that a sufficient operating temperature has been reached.

[0008] According to one aspect, a bearing assembly for an axle shaft of a turbocompressor is proposed, comprising at least one water-hydraulic bearing configured to rotatably support the axle shaft of the turbocompressor. The water-hydraulic bearing surrounds the axle shaft at a periphery of the axle shaft, forming a bearing gap. The water-hydraulic bearing is configured to allow water to flow through the bearing gap to hydraulically support the axle shaft and has a cold-start element configured to conduct heat from a stator winding of an electric drive unit of the turbocompressor to the bearing of the bearing assembly.

[0009] Such a turbocompressor typically has two turbomachines that are mechanically connected to a common axle shaft and can have two such bearing arrangements.

[0010] Due to the higher viscosity of water compared to air, the bearing accuracy of such a water-hydraulic bearing in such a bearing arrangement can be significantly reduced and the load-bearing capacity of the bearing increases significantly with similar dimensions.

[0011] This design allows the heat generated in the bearings to be dissipated with the water, and the water can also be used to dissipate the heat from the electric motor. A particularly advantageous feature is that a turbocompressor located in a fuel cell stack system can easily provide the water required for the water-hydraulic bearing, for example, by condensing the air flow exiting the fuel cell stack.

[0012] By exposing both edges of the bearing gap to gas from the turbocompressor, the bearing arrangement can be sealed to prevent water from escaping at the edges of the bearing gap. This results in particularly good sealing of the bearing arrangement. This sealing is particularly important to prevent water from the water-hydraulic bearing from entering the turbine and preventing droplet impact on the turbine blades. Thus, with such a bearing arrangement, reliable sealing and, if necessary, cooling of the hydrodynamic bearings can be achieved by exposing the edge of the bearing gap to compressed air from the turbocompressor to prevent the liquid medium, such as water, from escaping at the edge of the bearing gap. If this water is fed into a cooling circuit of the turbocompressor, it can also be used to cool the stator winding of the turbocompressor's electric drive.

[0013] This gas is advantageously inherently available in such a system with a turbocompressor and can be supplied from both the compressor side and the turbine side of the turbocompressor. The water-hydraulic bearing is a plain bearing and can be designed as a hydrostatic or hydrodynamic bearing.

[0014] The higher pressure of the gas (air), for example from the compressor of the turbo compressor, which acts on the two outer edges of the bearing gap, is used to prevent the escape of the bearing medium, such as water.

[0015] This means that a low-viscosity medium, such as water, allows the turbo compressor to operate at high speeds without excessive heat buildup. The risk of rust formation in water can be prevented by coating the axle shaft in the area of ​​the bearing gap.

[0016] This water in the bearing gap allows the bearing to be rotatably supported with the water-hydraulic bearing arrangement. The number and arrangement of water supply openings for the bearing gap can achieve a uniform distribution of water in the bearing gap, optimizing the sliding properties and load-bearing capacity of the bearing.

[0017] By arranging and numbering the drainage holes for the water in the bearing gap, the flow of water through the bearing gap can be optimized to adapt the sliding properties and load-bearing capacity of the bearing to the requirements.

[0018] The cold start element can advantageously conduct heat from the stator winding of the turbocompressor's electric drive unit to the bearing of the bearing assembly, provided the bearing assembly has not yet reached a sufficient operating temperature. This can be the case, for example, if the water-operated water-hydraulic bearing is frozen. The electric drive unit can be controlled with electrical signals to conduct current within the windings of the drive unit's stator and convert it into heat without causing the axle shaft to rotate.

[0019] In addition, during normal operation, this cold start element transfers heat from the stator winding to the water-cooled bearing to cool the stator.

[0020] To generate heat, the stator can be supplied with direct current or with alternating current that has a phase shift that does not cause the axle shaft of the turbo compressor to rotate.

[0021] The heat flow dQ / dt can be adjusted as required during a cold start by varying the current dQ / dt = PLoss = R*I 2< .

[0022] According to one aspect, it is proposed that a first part of the cold start element is arranged adjacent to the stator winding in order to absorb heat from the stator winding and a second part of the cold start element is arranged adjacent to at least a part of the bearing arrangement in order to release the absorbed heat to the bearing of the bearing arrangement.

[0023] Because a first part of the cold start element is arranged near the stator winding, heat from the stator winding can be effectively transferred to the cold start element in order to warm up the bearing assembly for cold starting of the turbo compressor by conducting the heat.

[0024] According to one aspect, it is proposed that the cold start element is arranged on a body edge of a bearing plate of the turbocompressor, and the body edge of the bearing plate faces the stator winding.

[0025] In this way, the turbocompressor can accommodate the cold start element with minimal modifications, ensuring better cold-start performance through improved heat conduction to the bearing assembly. The cold start element can be shaped to fit snugly against an existing edge of the bearing shield, requiring minimal modification to the turbocompressor's design.

[0026] According to one aspect, it is proposed that the cold start element comprises a material that has better thermal conduction than steel.

[0027] Any material with better thermal conductivity than steel, such as copper or aluminum, can be used. The improved thermal conductivity provided by the cold start element allows more heat to be transferred from the stator winding to the bearing assembly.

[0028] According to one aspect, it is proposed that the cold start element comprise copper or aluminum, or an alloy of copper and aluminum. As already explained above, these are examples of materials that exhibit better thermal conductivity than steel.

[0029] According to one aspect, it is proposed that the cold start element is formed as a stamped and bent part from a sheet metal.

[0030] If the cold start element is formed from sheet metal, it can be manufactured particularly easily and inexpensively. For example, the cold start device can be produced cost-effectively by punching and bending a copper sheet strip. The geometry is punched out of a strip, and the central part is then bent into an open ring.

[0031] From this ring, straight webs point outward toward the stator winding, and straight webs point toward the axis of the bearing assembly. The width and spacing of these webs can be adjusted to meet requirements. The straight webs of the first and second parts of the cold start element are held together by a central part. The cold start element can be inserted into a recess on the machine housing and / or a bearing plate during turbocompressor production.

[0032] According to one aspect, it is proposed that the cold start element forms the part of the bearing shield facing the stator winding.

[0033] This arrangement allows heat to be absorbed particularly effectively by the adjacent stator winding. Alternatively, a portion of the bearing shield located on the stator winding side can be made of a material with better heat conductivity, or a ring-shaped material can be applied to a modified bearing shield.

[0034] According to one aspect, it is proposed that the bearing arrangement comprises a sensor which is thermally coupled to the water-hydraulic bearing for determining the bearing temperature.

[0035] Such a sensor can be used to check whether the operating temperature for the bearing assembly has been reached for starting the turbo compressor.

[0036] According to one aspect, it is proposed that the bearing is designed as a hydrodynamic bearing.

[0037] The hydrodynamic plain bearing is a plain bearing in which the lubricant pressure builds up automatically during operation at the point where force is transferred between the two bearing parts. The lubrication gap is wedge-shaped at this point (lubrication wedge), so that higher pressure is created in the lubricant carried from the surface of the moving bearing part into the constriction, or the force is transferred via an interposed lubricant film. For this purpose, the axle shaft can be arranged so that it can assume an eccentric position with respect to the bearing. Advantageously, a hydrodynamic bearing does not require externally applied water pressure, as it can draw water independently from the reservoir.

[0038] In hydrostatic plain bearings, lubricant is supplied to the force-transmitting point by an external pump at the required pressure. Since the pump can operate continuously, lubricant friction also exists at the beginning and end of bearing operation (during start-up and run-down). However, the pressure required for highly loaded bearings and generated in hydrodynamic plain bearings would not be easily generated with a pump. Highly loaded hydrodynamic plain bearings are occasionally equipped with an additional pump for start-up and run-down.

[0039] If the water-hydraulic bearing is designed as a hydrostatic bearing, such a pump builds up the necessary pressure in the bearing gap. For a hydrodynamic bearing, such a pump can be used, for example, for low-wear start-up of the turbo compressor, because the pump can provide an initial pressure.

[0040] According to the invention, a method for starting a turbocompressor with a bearing arrangement according to claim 1 is proposed, comprising the steps.

[0041] In a first step, a stator winding of an electric drive unit of the turbocompressor is electrically controlled to heat the stator winding without causing an axle shaft of the turbocompressor to rotate. In a further step, the stator winding of the electric drive unit is controlled to cause the axle shaft of the turbocompressor to rotate, provided that sufficient heating of the bearing is ensured.

[0042] The stator winding of the turbocompressor can be designed as a three-phase motor, and the motor can be heated using a pulsed current with a phase position that rotates the turbocompressor's axle shaft and converts only the electrical energy of the pulsed current or even a direct current into heat to heat the stator. This heat can then be transferred to the bearing assembly via the cold start element.

[0043] With this method, the bearing arrangement can be heated in a simple manner with a water-hydraulic bearing in order to reach the necessary operating temperature.

[0044] The control of the heat flow: dQ / dt at cold start, can be adjusted as required by varying the current: dQ / dt = PLoss = R*I 2< .

[0045] According to one aspect, in the method for starting a turbocompressor, the stator winding is electrically controlled primarily for heating for a predefined time in order to ensure sufficient heating of the bearing.

[0046] The heating present here means that additional secondary effects can be caused by the control of the stator winding.

[0047] Such a predefined time can be determined based on an external temperature, or generally be long enough to reach the operating temperature of the bearing assembly under normal operating conditions. This advantageously eliminates the need for an additional sensor near the bearing assembly to determine the temperature of the bearing assembly.

[0048] According to one aspect, in the method for starting a turbo compressor, the stator winding is primarily electrically controlled for heating, and it is ensured by means of a temperature sensor measurement that the bearing is sufficiently heated.

[0049] In this case, the temperature measured by the sensor can advantageously be compared with a target value and the time required to reach the operating temperature of the bearing arrangement can be minimized.

[0050] The use of a bearing arrangement as described above for a cold start of a turbocompressor is proposed.

[0051] The use of one of the bearing arrangements described above for supporting an axle shaft of a turbocompressor is proposed, wherein the turbocompressor is a component of a fuel cell system.

[0052] Since in a fuel cell system such as the one described above, the water is generated during operation, a turbo compressor mounted in this way can be used particularly advantageously here.

[0053] A turbocompressor with a bearing arrangement as described above is proposed, wherein the turbocompressor has a liquid cooling circuit, and the water flowing into and / or out of the bearing gap is passed through the liquid cooling circuit in order to dissipate heat from the electrical machine of the turbocompressor.

[0054] The water required for the hydraulic bearings can be routed through the thermally highly stressed components of the electric motor on its way to the bearing location, cooling them. The drive motor, whose components require cooling, is located between the bearing locations. The water required for the hydraulic bearings can be routed through the thermally highly stressed components of the electric motor on its way to the bearing location.

[0055] A cathode circuit of a fuel cell stack with a turbocompressor as described above and a humidifier for humidifying the cathode gas is proposed, wherein the cathode circuit is configured to supply the water flowing out of the bearing arrangement to the humidifier.

[0056] The air mass flow delivered by the turbocompressor's compressor must be humidified and cooled. The water escaping from the water-hydraulic bearing can also perform this task.

[0057] According to one aspect, it is proposed that a mobile platform comprises a turbocompressor with a bearing arrangement as described above.

[0058] A mobile platform can be an at least partially automated system that is mobile and / or a driver assistance system. An example can be an at least partially automated vehicle or a vehicle with a driver assistance system. That is, in this context, an at least partially automated system includes a mobile platform with respect to at least partially automated functionality, but a mobile platform also includes vehicles and other mobile machines, including driver assistance systems.

[0059] Each of these systems can be a fully or partially autonomous system.

[0060] In the following, embodiments of the invention are described with reference to Figures 1 to 3 explained in more detail. Here, the Figure 1 shows a bearing arrangement for an axle shaft of a turbocompressor; Figure 2 shows an unformed stamped and bent part for a cold start element; and Figure 3 shows a formed stamped and bent part for a cold start element.

[0061] The Figure 1 outlines a bearing arrangement 100 for an axle shaft 120 of a turbocompressor. The common axle shaft 120 of the turbocompressor is supported by two such bearing assemblies 100 with water-hydraulic bearings 110. An electric drive motor of the turbocompressor is arranged between the water-hydraulic bearings 110. The components of the electric drive motor generate heat during operation, which must be dissipated.

[0062] In the Figure 1 the turbo compressor is only indicated with its copper winding 140 in a potting compound, an iron sheet 144 of the motor, a stator holder 146, ie a cooling sleeve, a motor housing 150 with cooling openings and a bearing plate 130.

[0063] The water-hydraulic bearing 110 of the bearing arrangement 100 is configured to rotatably support the axle shaft 120 of the turbocompressor, wherein the water-hydraulic bearing 110 surrounds the axle shaft 120 at a circumference of the axle shaft 120 to form a bearing gap 114 therebetween.

[0064] The water-hydraulic bearing 110 is configured to allow water 116, which is supplied to the bearing 110 through a channel 115, to flow through the bearing gap 114 in order to water-hydraulically support the axle shaft 120.

[0065] For this purpose, the channel 115 can be connected to a water tank via a fluid-permeable connecting line. In a hydrostatic bearing of the bearing assembly 100, a pump can be provided in the connecting line to the tank to pump the water into the bearing gap 114. In a hydrodynamic bearing 100, such a pump can also be provided in the connecting line to the tank to build up water pressure in the bearing gap 114 for starting the turbocompressor.

[0066] Furthermore, the bearing assembly 100 has at least one gas supply 142, 163, which supplies gas at increased pressure from the turbocompressor to both outer edges of the bearing gap 114 to seal the water-hydraulic bearing 110. The gas from the turbocompressor can also be used for air cooling of the electric drive of the turbocompressor.

[0067] The water-hydraulic bearing 110 is equipped with two drainage openings 112 in the region of the bearing gap 114 to allow the water 116 to flow out of the bearing gap 114, and the water 116 can be drained out of the turbocompressor via a drainage channel (not shown here) which can be formed in the bearing shell 130.

[0068] This water, which is passed through the bearing gap 114, can be supplied either to a cathode air flow of a fuel cell system and / or to a liquid cooling circuit of the turbocompressor.

[0069] For this purpose, this water can be fed to a humidifier of a system for operating a fuel cell stack, which is arranged in the air supply for the cathode side of the fuel cell stack.

[0070] The water used for the water-hydraulic bearings, which is taken from a water tank, can comprise condensed water from an air mass flow of an outlet connection on a cathode side of the fuel cell stack. For this purpose, a condenser can be arranged in this air mass flow, and this condensed water can be fed into the water tank via a fluid-permeable line.

[0071] The water-hydraulic bearing 110 can be configured as a hydrodynamic bearing 110 to draw in water through the channel 115 in the bearing plate 130 itself. To seal the bearing gap 114, the axle shaft 120 has structures 122 on its circumference, which, together with the bearing arrangement, form a centrifugal seal for the bearing gap 114. The water-hydraulic bearing 110 is formed in a bearing shell that is positively received by the bearing plate 130.

[0072] In addition, the bearing assembly 100 includes a cold start element 200 configured to conduct heat from the stator winding 140 of an electric drive unit of the turbocompressor to the bearing 110 of the bearing assembly 100. For this purpose, a first portion 230 of the cold start element 200 is disposed adjacent to the stator winding 140 to absorb heat from the stator winding 140, and a second portion 220 of the cold start element 200 is disposed adjacent to at least a portion of the bearing assembly 100 to transfer the absorbed heat to the bearing 110 of the bearing assembly 100. The middle part 210 of the cold start element 200 conducts the heat from the first part 230 of the cold start element 200 to the second part 220 of the cold start element 200. The cold start element 200 is arranged on a body edge of a bearing plate 130 of the turbo compressor, which edge faces the stator winding 140.The cold start element 200 can also form the entire body part of the bearing plate 130 facing the stator winding 140, for example in the form of a ring applied to a part of the bearing plate 130. This is shown in FIG. Figure 1 Not shown. The material of the cold start element 200 comprises a material that has better thermal conductivity than steel, such as aluminum or copper, or an alloy of aluminum and copper. The cold start element 200 can be formed as a stamped and bent part and mounted on the body edge of the turbocompressor's bearing shield facing the stator winding.

[0073] The Figure 2outlines a cut-out sheet metal part for forming a stamped and bent part for manufacturing a cold start element 200. This sheet metal part has a central part 210 which can be bent into a ring and in which webs are provided for both the first part 230 of the cold start element 200 and the second part 220 of the cold start element 200, which webs can be stamped out of the sheet metal part, for example.

[0074] The Figure 3 outlines the formed stamped and bent part for a cold start element 200 in which the webs 220 which form the second part of the cold start element 200 are inserted into the depth of the illustration of the Figure 3 were deformed and the middle part 210 was formed into a ring which can be applied to the body edge of the bearing plate 130 and in which the webs of the first part 230 of the cold start element 280 extend radially from the middle part 210 of the cold start element 200.

Claims

1. Method for starting a turbocompressor having a bearing arrangement (100) for an axle shaft (120) of the turbocompressor, wherein the bearing arrangement (100) has at least one water-hydraulic bearing (110), which is designed to rotatably mount the axle shaft (120) of the turbocompressor, wherein the water-hydraulic bearing (110) surrounds the axle shaft (120) over a circumference of the axle shaft (120), so that a bearing gap (114) is formed, and wherein the water-hydraulic bearing (110) is designed to allow water to flow through the bearing gap (114) in order to water-hydraulically mount the axle shaft (120), and wherein the bearing arrangement has a cold-starting element (200), which is designed to conduct heat from a stator winding (140) of an electric drive assembly of the turbocompressor to the bearing (110) of the bearing arrangement (100), the method comprising the steps of: electrically actuating the stator winding (140) of the electric drive assembly of the turbocompressor, for heating the stator winding (140) without causing the axle shaft (120) of the turbocompressor to rotate; electrically actuating the stator winding (140) of the electric drive assembly in order to cause the axle shaft (120) of the turbocompressor to rotate, provided that sufficient heating of the bearing (110) is ensured.

2. Method according to Claim 1, wherein the stator winding (140) is electrically actuated predominantly for heating for a predefined time in order to ensure sufficient heating of the bearing (110).

3. Method according to Claim 1, wherein the stator winding (140) is electrically actuated predominantly for heating, and a temperature sensor measurement is used to ensure that the bearing (110) is sufficiently heated.

4. Method according to any of the preceding claims, wherein a first part (230) of the cold-starting element (200) is arranged adjacent to the stator winding (140) in order to absorb heat from the stator winding (140) and a second part (220) of the cold-starting element (200) is arranged adjacent to at least one part of the bearing arrangement (100) in order to give off the absorbed heat to the bearing (110) of the bearing arrangement (100).

5. Method according to any of the preceding claims, wherein the cold-starting element (200) is arranged on a body edge of a bearing plate (130) of the turbocompressor, and the body edge of the bearing plate (130) faces the stator winding (140).

6. Method according to any of the preceding claims, wherein the cold-starting element (200) comprises a material which exhibits better heat conduction than steel.

7. Method according to any of the preceding claims, wherein the cold-starting element (200) comprises copper or aluminium or an alloy of copper and aluminium.

8. Method according to any of the preceding claims, wherein the cold-starting element (200) was formed as a punched and bent part from a metal sheet.

9. Method according to any of the preceding claims, wherein the cold-starting element (200) forms the part of the bearing plate (130) that faces the stator winding (140).

10. Method according to any of the preceding claims, wherein the bearing arrangement (100) has a sensor, which is thermally coupled to the water-hydraulic bearing (110) for determining the bearing temperature.

11. Method according to any of the preceding claims, wherein the bearing (110) is in the form of a hydrodynamic bearing (110).