WO2019057446A1

WO2019057446A1 - Detection of compressor instability on the basis of the axial position of the compressor shaft and a temperature

Info

Publication number: WO2019057446A1
Application number: PCT/EP2018/073034
Authority: WO
Inventors: Fabian BRANDL; Simon Grilc
Original assignee: Bayerische Motoren Werke Aktiengesellschaft
Priority date: 2017-09-21
Filing date: 2018-08-27
Publication date: 2019-03-28
Also published as: DE102017216763A1

Abstract

The invention relates to a method for operating a turbomachine and to a turbomachine. The method comprises the following steps: i) capturing at least one value indicative of an axial position change of a shaft (540) of the turbomachine (500), which shaft is coupled to at least one compressor wheel (512) of the turbomachine (500); and ii) changing at least one operating parameter of the turbomachine (500) if, on the basis of the at least one value, it was detected that the turbomachine (500) is operated in an unstable operating state.

Description

DETECTION OF COMPRESSOR STABILITY BY MEANS OF THE AXIAL POSITION OF THE COMPRESSOR SHAFT AND TEMPERATURE

The technology disclosed herein relates to a method of operating a turbomachine. Further, the technology disclosed herein relates to a turbomachine, such as a compressor. Compressors are used to increase performance in internal combustion engines and in

Fuel cell systems used. Depending on the load requirement, the amount of air and / or boost pressure should be able to be varied. Will the

Turbomachine operated at unfavorable operating points, this can lead to compressor pumps (English: surge). This results in a stall on the compressor blades, resulting in backflow of air through the compressor. As a result, the pressure ratio decreases and the compressor promotes again until it comes to pumping again. These processes are repeated several times per second and cause unwanted vibrations and pulsations. Therefore, the boost pressure is monitored and regulated consuming, whereby a safety area is defined, which must not be exceeded or fallen below. in the

Pump characteristic field, this safety range is represented by an operation with a certain distance to the surge line (English: surge line). The detection of the sizes brings a certain inaccuracy with it. Consequently, the safety margin to the surge line must be relatively large. This limits the possible operating range of the turbomachine. In addition, operation near the surge line is also desired depending on the application. So there is a desire to operate the compressor near the surge limit or to design the safety distance to the surge limit as small as possible.

It is a preferred object of the technology disclosed herein to reduce or eliminate at least one disadvantage of a previously known solution or to suggest an alternative solution. In particular, it is a preferred object of the technology disclosed herein to improve the detection of compressor pumps or a compressor

to propose, which is closer to the surge limit operable. Other preferred objects may result from the beneficial effects of the technology disclosed herein. The object (s) is / are solved by the subject matter of patent claim 1 of the independent

Claims. The dependent claims are preferred

Embodiments

The technology disclosed herein relates to a turbomachine to

Air supply of an energy converter. The turbomachine is in particular designed to convey air to an energy converter, in particular to at least one fuel cell. The turbomachine may in particular be an air-bearing turbocompressor, turbocompressor or centrifugal compressor. Preferably, the compressor has a working speed range from about 15,000 rpm to about 170,000 rpm, and more preferably from about 20,000 rpm to about 130,000 rpm. The

Turbomachine can be set up in particular via a

Energy converter inflow path to supply air to at least one energy converter of a motor vehicle. The turbomachine preferably comprises a compressor unit with at least one compressor wheel and / or a turbine unit with at least one turbine wheel. The compressor wheel is set up to convey the air to be compressed.

The turbine wheel is set up, the falling of the internal energy from the incoming gas into mechanical power (here torque times

Speed), which it delivers to the shaft. Preferably, the turbine wheel is designed as a Abgasturbinenrad. The turbine wheel is particularly adapted to expand incoming gas. The turbomachine preferably comprises a compressor wheel and a turbine wheel.

The compressor wheel and the turbine wheel are also referred to as impeller. If the term "impeller" is mentioned below, then the im

As related to the impeller technology described as applicable to the at least one compressor and the at least one turbine wheel.

The at least one impeller is useful with a wave of

Turbomachine rotatably coupled, for example via a shaft-hub connection, gluing or any other suitable connection. The at least one impeller is i.d.R. circular and concentric with the central axis of the shaft. The impeller and the shaft are arranged coaxially with each other.

The impeller may be used on its impeller front or impeller outer side or front side of the impeller (hereinafter for the purposes of convenience of description: "front of the impeller" or in general)

"Front") have air guide elements, in particular rotating

Guide vanes, which are also referred to as blades below. The rear of the wheel or the inner side of the wheel or rear side (for the sake of simplification, the following is used for all terms: "rear of the wheel" or generally "rear") is the rear of the wheel. The front may be configured to suck air axially and convey it into the compressor housing, thereby compressing the intake air. The front side can be configured to allow gas to flow out axially into the turbine housing, in particular radially, wherein in the turbine unit the gas expands and the shaft is driven.

The turbomachine disclosed here may comprise at least one electric drive, the rotor of which is rotatably connected to the shaft. The drive is set up to supply the energy converter with sufficient air. Any suitable motor may be used, e.g.

permanent-magnet synchronous motors.

The at least one energy converter is set up to convert the chemical energy of the fuel into other forms of energy, for example electrical energy and / or kinetic energy. The energy converter, for example, an internal combustion engine or a

Fuel cell system / fuel cell stack with at least one

Be fuel cell.

The turbomachine disclosed herein may further include at least one distance sensor. Distance sensors as such are known. For example, the distance sensor may be an optical distance sensor.

The distance sensor may be configured to be an actual axial one

To detect position changes of the shaft directly or indirectly. The

Distance sensor may be arranged in particular, the distance to the Front side of the impeller (= indirect detection) and / or to determine the end face of the shaft (= direct detection). In particular, the distance sensor is capable of generating a signal or value that is indicative of the axial position change of the shaft. The at least one value can be, for example, a signal of a distance sensor which represents the detected / measured distance between the distance sensor and the end face of the impeller or of the shaft. The distance sensor is particularly adapted to detect dynamic change in position of the shaft, such as vibrations or ornaments.

The at least one distance sensor is preferably arranged in the compressor intake duct and / or in the turbine outlet of the turbomachine. Preferably, the at least one distance sensor is in

Essentially arranged coaxially with the shaft of the turbomachine. The term "essentially coaxial" in this context means that the distance sensor can also be arranged slightly offset axially, without any noticeable influence on the flow distribution in and / or turbine outlet Such a configuration is particularly space-saving and enables a precise detection of the axial displacements the wave.

The system disclosed here expediently also comprises at least one control unit. The control unit is u.a. set up to perform the process steps disclosed herein. For this purpose, the controller based on provided signals, the actuators of the system at least partially and preferably fully regulate (engl, closed loop control) or control (engl, open loop control). The control unit can influence at least the fuel cell system, in particular the

Cathode subsystem, anode subsystem and / or the cooling system of the fuel cell system. Alternatively or additionally, the control unit may also be integrated in another control unit, for example in one higher-level control unit. The controller can with more

Control units of the motor vehicle interact.

The controller may be configured to detect the at least one value that is indicative of the axial position change of the shaft of the turbomachine, which is coupled to the at least one compressor wheel of the turbomachine. Furthermore, the control unit can be set up to change the at least one operating parameter of the turbomachine, if, based on the at least one value, it has been detected that the turbomachine is operated in the unstable operating state.

Likewise, the technology disclosed herein includes a method for operating the turbomachine. The method comprises the steps:

- detecting at least one value indicative of the actual axial position change of a shaft of the turbomachine coupled to at least one compressor wheel of the turbomachine; and

Changing at least one operating parameter of the

Turbomachine, if based on the at least one value has been detected that the turbomachine due to

Compressor pump is operated in unstable operating condition.

The at least one operating parameter is in particular one of the following operating parameters: pressure ratio of the turbomachine, air flow rate through the compressor wheel and / or rotational speed of the shaft.

An unstable operating condition in the technology disclosed herein is an operating condition in which compressor pumps occur; i.e. it will occur

mechanical vibrations of the shaft arising from return flows in the Compressors result). Such an unstable operating state occurs

For example, if the turbomachine beyond the for the

Turbomachine characteristic pumping limit is operated.

According to the method disclosed here, the at least one

Operating parameters in particular changed so that the

Turbomachine is transferred from the unstable operating condition in the stable operating condition, for example by

- Reduction of the speed of the turbomachine; and or

- Increase of the compressor-side throughput by reducing the pressure ratio of the turbomachine

How a turbomachine on the basis of the characteristic curve of the turbomachine can be converted into the stable operating state, the skilled person is familiar.

The method disclosed herein may further comprise the step of detecting at least one speed value indicative of the speed of the shaft of the turbomachine.

In the detection of the unstable operating state, the speed value is preferably taken into account. Particularly preferably, at least a plurality of rotational speed values are in each case in the stable operating state

Oscillation value recorded and stored, which is indicative of the dynamic position changes of the shaft (especially in the axial direction), resulting from the imbalance of the shaft including rotating parts. The method disclosed herein may further comprise the step of comparing the stored vibration values with currently detected values, and assuming an unstable operating condition if the Difference between currently recorded values and stored values

Vibration values is greater than a threshold value.

The method disclosed herein may further include the steps of:

- (proximal) detecting the temperature of the energy converter

air to be provided, wherein the temperature so adjacent to the compressor wheel of the turbomachine detected upstream or in

Compressor is measured that a return flow due to compressor pumps of already (more) compressed and heated air in the compressor housing of the turbomachine using a

Temperature increase of the air is detectable;

Comparing the temperature sensed proximal to the compressor wheel with a reference temperature sensed distally of the compressor wheel (e.g., spaced upstream of the compressor wheel such that there can be no backflow from the compressor wheel, such as sensed by a temperature sensor on the air filter); and

- Changing the actually used for controlling the turbomachine pumping limit as a function of from the

Comparison resulting deviation (for example, the temperature difference).

The method may further include the step of selecting the maximum allowable limit deviation (limit temperature difference) such that there will be backflow in the compressor housing, but this

Reverse flow causes essentially no mechanical vibrations of the shaft. The term "substantially none" in this context means that no vibration or optionally

negligible low mechanical vibrations occur. Advantageously, therefore, an actual surge limit specific to each

Turbomachine in the installed state of the turbomachine before the Operation or during operation of the turbomachine. Any manufacturing tolerances or component tolerances can thus be taken into account.

In other words, the technology disclosed herein relates, inter alia. a method for the detection of compressor pumps and a correspondingly formed turbomachine, in which / a temperature sensor / thermocouple may be arranged in the compressor intake region, preferably in the

Intake air flow, and particularly preferably arranged close to the compressor wheel, in particular max. 10 cm or max. 5 cm from the compressor wheel. Preferably, the air temperature in the intake silencer (= AGD) may be measured (e.g., via a hot film air mass meter). The temperature in the compressor intake area during normal operation (i.e., steady state) may be about the same as the air temperature in the AGD or as a reference value depending on the measurement accuracy, with small deviations permitted. Is it now?

Compressor pumps, so heated by the compression air flows backwards through the compressor wheel, resulting in a significant

Increase in temperature (depending on load point +10 ° C, +20 ° C) before

Compressor wheel leads. The measured temperature in the intake area increases. Suitably, a difference is formed between the temperature in the AGD and the intake temperature. If it comes to compressor pumping, the calculated difference value changes significantly.

Alternatively or in addition to the temperature sensor, an optical sensor may be provided, which may preferably be mounted centrally in the intake area of the compressor at the level of the shaft end side. This sensor may preferably optically detect the distance to the shaft. Optical measuring methods for distance measurements are familiar to the person skilled in the art. Is it now? Compressor pumps cause vibrations, which cause the shaft to pulsate axially. About the distance measurement, this pulsation can be reliably detected. It should be noted that under normal dynamic operating conditions, the shaft also "works" axially.

Advantageously, it can therefore be provided that in the pump detection

Behavior pattern of the wave (especially depending on frequency,

Pulsation) to distinguish effects from the dynamic operation of the turbomachinery from effects caused by compressor pumps. For this purpose, a speed detection can be provided quite generally. The turbomachine may comprise an electric drive. If the turbomachine

electrically driven, the speed can also be determined based on the engine speed. An indicative of the speed of the shaft or the motor signal / value can also be used as input for a detection of the dynamic operation.

Alternatively or additionally, according to the technology disclosed herein, a spread in the surge margin can be corrected. Due to tolerances in the manufacturing and the components (in particular with regard to the compressor column), the actual compressor pumping may occur at operating points that are not on the characteristic surge line. This scattering is taken into account in previously known solutions by a greater safety distance.

According to the technology disclosed herein, a method can be provided in which the turbomachine is taught, in particular by one of the methods disclosed herein for detecting compressor pumps, in particular by the temperature adjacent to the compressor downstream of the compressor is determined and this example with a

Reference air temperature (eg the air temperature at the air filter) is compared. An advantage of this method is that already the temperature in

Suction range increases before the limit of the surge limit is reached. Advantageously, by teaching the distance to the surge limit can be reduced, which allows a better operation of the turbomachine.

The compressor can be operated at different operating points during learning, until a return flow in the compressor housing or in the intake of the compressor is detected. Preferably, the compressor is operated during training under normalized conditions. Preferably, the method comprises the step of determining the operating range (s)

Operating parameters (e.g., speed, pressure, pressure ratio, backpressure or wastegate setting, etc.). Advantageously, an exact, permissible operating range can thus be determined individually for each compressor. By normalizing the quantities, the stored values can be applied to any other operating condition (e.g., summer / winter;

Altitude operation, etc.), or a kind of recalibration can be carried out again at certain intervals. also a comparison with a previously determined normalized value is carried out, e.g. to detect possible compressor damage / compressor characteristics changes.

Experiments by the inventors have shown that an operation close to the pumping limit already a temperature increase due to backflow can be determined, although substantially no mechanical or acoustic signs for a compressor pumps (ie, no vibrations, pulsations) are still recognizable. This backflow can already be detected via the "temperature sensor / differential temperature" method, which can bring about further advantages: A learning process can be carried out very precisely according to the method disclosed here but also be avoided when learning. Advantageously, with the method disclosed herein, the operating range can be accurately determined without putting the compressor directly into heavy pumping and possibly damaging it. About a comparison of

Anlernwerte can also be a possible damage or wear / tear

Property change can be detected.

The methods disclosed herein for detecting an unstable

Operating state can alternatively be used as a redundant system.

The technology disclosed herein will now be explained with reference to the figures. Show it:

Fig. 1 is a schematic representation of a fuel cell system;

and

Fig. 2 is a schematic cross-sectional view of a

Turbomachine 500.

Fig. 1 shows an energy converter 300, here as

Fuel cell stack 300 is formed with a plurality of fuel cells. The fuel cell stack 300 is schematically divided into a cathode K and an anode A. The structure of such a fuel cell stack 300 is familiar to the person skilled in the art. The anode subsystem includes a

Fuel source H2, which provides fuel, eg hydrogen. By the pressure reducer 21 1, the pressure in the anode inflow path 215 is reduced before the fuel enters the anode A from the fuel cell stack 300. After the electrochemical reaction in the fuel cell stack 300, the anode exhaust gas leaves the fuel cell stack 300 and is at least partially recirculated via the recirculation conveyor 236. in the Water separator 232, water is separated from the anode exhaust gas. Through the anode purge valve 238, water and purge gas from the

Anodensubsystem drained into the Anodenspülleitung 239.

The turbomachine 500 sucks in air 02 and compresses it. The compressed air is cooled in the intercooler 420 and optionally humidified further downstream in the cathode inflow path 415 (= energy converter inflow path) by means 430 for humidifying the air. Subsequently, the humidified air passes into the cathode K of the fuel cell stack 300, where the electrochemical reaction takes place with the fuel of the anode A.

Further shown are cathode-side stack shut-off valves 470,480, which may be provided as well as the bypass 460. However, this need not be so. After the electrochemical reaction in the fuel cell stack 300, the cathode exhaust gas passes through the cathode exhaust path 416 into the environment.

The turbomachine 500 shown here comprises a compressor unit 510, which forms the cathode inflow path 415. Furthermore, the turbomachine 500 shown here comprises a turbine unit 520, which forms the (cathode) exhaust path 416 with. The compressor unit 510, the turbine unit 520 and the electric drive 530 are here rigidly connected to one another via a shaft 540.

Upstream of the turbomachine, an air filter 402 is provided here. In the air filter 402, the reference temperature of the air is detected here. Fig. 2 shows schematically a cross section through a

Turbomachine 500. At one end of the turbomachine, the compressor unit 510 is provided. The compressor unit 510 includes the spiral compressor housing 516 with the volute V510. The

Compressor unit 510 further includes compressor wheel 512. The

Compressor wheel 512 has rotating blades on its front side 514. Likewise, the turbomachine 500 includes a turbine unit 520 having a spiral turbine housing 526 that forms the volute V520. The turbine wheel 522 is arranged here in the turbine housing 526. The turbine wheel 522 has rotor blades 522 on its front side. An axial air bearing of the turbomachine has been omitted here for simplicity.

Between the compressor unit 510 and the turbine unit 520, the electric drive machine 530 is arranged in the drive housing 436. The electric drive machine 530 here comprises a stator with

Stator plates 532 and a stator winding 534. On the shaft 540, a rotor 535 of the electric drive 530 is further provided here. The

Coolant channel 537 in drive housing 536 serves to cool the stator. Similarly, the at least one cooling liquid channel 537 can also serve to cool the at least one air bearing. But there are also other cooling concepts conceivable. In the compressor intake passage 518, a distance sensor 550 and a temperature sensor 560 are provided here.

Alternatively, only one of the two sensors can be provided.

The temperature sensor 560 is provided here in the wall of the compressor intake passage 518. Similarly, the temperature sensor 560 could also be located slightly further upstream or downstream. Preferably, however, no further than max. 10 cm or preferably max. 5 cm from the front side of the compressor wheel 512. Thus, the temperature sensor can be sufficient precise temperature changes in the compressor housing 510

capture backflowing air.

The distance sensor 550 is here coaxial with the longitudinal axis A-A

arranged. Thus, the distance of the shaft can be detected very precisely. This area of the compressor intake passage 518 is a dead center of the flow. Thus, the distance sensor 550 is not large

Flow obstruction. The distance sensor 550 can thus be provided in a particularly space-saving. Alternatively, the distance sensor could also be provided at the other end of the shaft or on the front side of the turbine or generally in the turbine outlet 528. The distance sensor 550 is held here by webs 552, which form a centering suspension here.

For the sake of legibility has been simplified the term

In some instances, a feature of the technology disclosed herein is singularly described (eg, the turbomachine, the shaft, the operating parameter, the compressor wheel) Energy converter, the / a distance sensor, the / a temperature sensor, etc.) should be at the same time with their plurality disclosed (eg, the at least one turbomachine, the at least one shaft, the at least one operating parameter, the at least one compressor, the at least one energy converter , the at least one distance sensor, the at least one temperature sensor, etc.).

The foregoing description of the present invention is for illustrative purposes only and not for the purpose of limiting the invention

Invention. In the context of the invention, various changes and modifications are possible without the scope of the invention and their

To leave equivalents.

Claims

claims

1 . Method for operating a turbomachine (500), comprising the step:

Detecting at least one value which is indicative of an axial change in position of a shaft (540) of the turbomachine (500) connected to at least one compressor wheel (512) of the

Turbomachine (500) is coupled; and

Changing at least one operating parameter of the

Turbomachine (500), if it has been detected based on the at least one value, that the turbomachine (500) is operated in the unstable operating state.

2. The method of claim 1, further comprising the step of:

- detecting at least one speed value indicative of the rotational speed of the shaft (540) of the turbomachine (500);

wherein in the detection of the unstable operating state of

Speed value is taken into account.

3. A method for operating a turbomachine (500), in particular according to claim 1 or 2, comprising the steps:

- Detecting the temperature of the air, the temperature being such

is detected adjacent to the compressor wheel (514) of the turbomachine (500) that a return flow of already compressed and heated air in the compressor housing (510) of the turbomachine (500) is detectable;

- comparing the detected temperature with a reference temperature; and - Changing the underlying for controlling the turbomachine pumping limit as a function of the deviation resulting from the comparison.

4. The method of claim 3, wherein the maximum allowable

Limit deviation is chosen so that, although it comes to the backflow, but this backflow substantially no mechanical

Caused vibrations of the shaft.

5. turbomachine (500) for supplying air to an energy converter (300),

full:

at least one compressor wheel (512) that is set to

to promote compressed air,

at least one shaft (540) coupled to the compressor wheel (512); and

at least one distance sensor (550);

wherein the distance sensor (550) is arranged axial

To detect changes in position of the shaft (540) directly or indirectly.

6. Turbomachine (500) according to claim 5, wherein the distance sensor (550) is arranged substantially coaxially with the shaft (540).

7. Turbomachine (500) according to claim 5 or 6, wherein the

Distance sensor (550) in a compressor intake passage (518) and / or in a turbine outlet (528) of the turbomachine (500) is arranged.

8. Turbomachine (500) according to one of the preceding claims 5 to 7, wherein the distance sensor (550) is an optical distance sensor.

9. Turbomachine (500) according to one of the preceding claims 5 to 8, further comprising at least one control device, wherein the control device is set up,

- to detect at least one value which is indicative of an axial change in position of a shaft of the turbomachine, which is coupled to at least one compressor wheel of the turbomachine; and

- To change at least one operating parameter of the turbomachine, if it was detected based on the at least one value that the turbomachine is operated in the unstable operating condition.

10. Turbomachine (500) according to one of the preceding claims 5 to 9, further comprising means for detecting the rotational speed of the shaft.

1 1. Turbomachine (500) according to one of the preceding claims 5-10, further comprising at least one temperature sensor (560), which is arranged immediately adjacent to the compressor wheel (514), in particular in the compressor intake passage (518).