Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
  • G01M7/00—Vibration-testing of structures; Shock-testing of structures
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
  • G01M7/00—Vibration-testing of structures; Shock-testing of structures
  • G01M7/02—Vibration-testing by means of a shake table
  • G01M7/025—Measuring arrangements

Definitions

• the invention relates to a method for evaluating a vibration behavior of an electric motor, in particular an electric motor of a fan, and/or its operating environment, as well as an electric motor, a fan and a system, which are preferably each designed to carry out the method.
• vibrations When an electric motor is operated - regardless of whether it is operated properly or improperly - vibrations are excited. These vibrations may originate from the electric motor itself and/or be excited by a load driven by the electric motor (e.g. a fan impeller) and/or by an operating environment of the electric motor.
• harmonic excitations e.g. due to unbalance
• stochastic excitations e.g. due to noise
• impulse-like excitations e.g. due to impacts or sequences of impacts
• Electric motors are therefore known in which sensors for detecting vibrations are installed. Such an electric motor is described, for example, in DE 10 2018 211 838 A1 and in DE 10 2018 211 846 A1.
• the detection of resonance points requires the scanning of vibrations of the electric motor over at least parts of the possible operating speeds of the electric motor.
• this sampling usually takes place during a run-up or a run-down.
• the fan is accelerated from a minimum speed (usually when the fan is at a standstill) to a maximum speed within a specified time, ideally with a linear speed ramp.
• the speed is reduced from a non-zero starting speed (usually maximum speed) to a minimum speed.
• the vibrations of the electric motor are recorded and evaluated as a function of the speed. Reference is made to DE 20 2019 101 262 U1 and DE 102018211 850 A1 for such a detection of a vibration behavior.
• a detected vibration value exceeds a predefined limit value, for example 7 millimeters/second (RMS - Root Mean Square) or 9 millimeters/second (RMS), it is concluded that a resonance point is present.
• a predefined limit value for example 7 millimeters/second (RMS - Root Mean Square) or 9 millimeters/second (RMS)
• limit values are often defined in standards or other regulations, for example IS014694. All speeds at which this limit value is exceeded are recorded as "forbidden" speeds and, if possible, skipped or quickly exceeded during subsequent operation.
• the disadvantage of such an evaluation of the vibration behavior of the electric motor is that it has to be run up or run down. In application scenarios in which resonances are unchangeable, such a test run is sufficient when the electric motor is started up.
• resonance points change, for example as a result of deposits or wear/aging or changes in the operating environment of the fan, for example due to adjustments or expansion of the system or maintenance.
• the present invention is therefore based on the object of designing and developing a method, an electric motor, a fan and a system of the type mentioned at the outset in such a way that the vibration behavior of an electric motor can be evaluated flexibly and reliably, if possible with a load and/or operating environment. an assessment during ongoing operation of the electric motor is desirable.
• the second evaluation measure is representative of the strength of the vibrations of the at least one part of the electric motor at the evaluation frequency, and Assessing the vibration behavior by comparing the first assessment criterion with the second assessment criterion.
• the electric motor in question comprises: a vibration sensor, which is designed to detect vibrations of at least part of the electric motor and to generate detected vibration values, a first evaluation unit, which is used to determine a first
• evaluation measure is designed, the first evaluation measure being representative of the strength of the vibrations of the at least one part of the electric motor, an analysis unit designed to determine a spectral component of the detected vibration values for an evaluation frequency, a second evaluation unit designed to determine a second
• the second evaluation measure being representative of the strength of the vibrations of the at least one part of the electric motor at the evaluation frequency
• an evaluation unit for evaluating the vibration behavior by comparing the first evaluation measure with the second evaluation measure is trained.
• the fan in question comprises an impeller and an electric motor according to the invention, the impeller being coupled to a rotor of the electric motor.
• the system in question comprises an operating environment and a drive, the drive comprising an electric motor and/or a fan according to the invention, the operating environment interacting with the drive and wherein the drive is designed to detect and evaluate both vibrations of the drive and vibrations of the operating environment.
• first detected vibration values are generated by detecting vibrations of at least a part of the electric motor using a vibration sensor. This detection usually takes place over a detection time window.
• a first assessment measure which is representative of the strength of the vibrations of the at least one part of the electric motor, is determined for the detected vibration values.
• a spectral component for an evaluation frequency is determined from the recorded vibration values. This means that it is determined how large the proportion of the detected vibrations is at the evaluation frequency.
• a second evaluation parameter is determined for the spectral component, which is representative of the strength of the vibrations of the at least one part of the electric motor at the evaluation frequency.
• the comparison can be carried out using the relationship between the second evaluation measure and the first evaluation measure. When this ratio exceeds a threshold, the presence of a resonance site can be decided.
• the method according to the present disclosure does not necessarily require a ramp-up or a ramp-down. Rather, a current operating state can be evaluated directly. This enables the condition of the electric motor to be checked during operation. Nevertheless, the method can also be used during acceleration or deceleration, in order to be able to obtain a comprehensive picture of the vibration behavior of the electric motor, for example.
• the vibration behavior can be evaluated repeatedly, preferably periodically. For example, a new evaluation can be initiated after 15 minutes, an hour or a day. Changes in the electric motor, the load driven by the electric motor and/or its operating environment can be recognized and—if necessary—appropriate measures can be taken, particularly in the case of a repeated evaluation.
• the acquisition time window can be chosen arbitrarily. However, it makes sense not to select the acquisition time window that is too narrow, so that the time window has a sufficiently small effect on the specific spectral component and the vibration signals are acquired sufficiently well.
• the recording time window should not be too long, since changes, for example in the speed of the electric motor or in the operating environment, could falsify the recorded vibration values.
• a dimensioning of the detection time window will depend on the respective application situation of the electric motor and its operating environment.
• the detection time window is at least one period long of a harmonic oscillation signal wide.
• the acquisition time window is several period lengths of a harmonic Oscillation signal wide, where it makes sense to choose the detection time window a maximum of 10 period lengths wide.
• the evaluation frequency can also be selected relatively arbitrarily. It should be important here that resonances are also to be expected with a selected evaluation frequency. Very low evaluation frequencies, for example below 2 hertz, are likely to be just as unhelpful in many cases as very high evaluation frequencies, for example in the range of several kilohertz.
• the evaluation frequency can be chosen relatively freely, or evaluation frequencies can be used in a quantization, for example with a spacing of 5 or 10 Hertz. Frequencies can also be selected for the selection of the evaluation frequencies, which lie at a resonance point recognized from earlier measurements. If a change in the resonance frequency is to be expected, the evaluation frequency can also be selected around the previously measured resonance frequency. This short list shows how flexibly the evaluation frequency can be selected.
• the evaluation frequency can also be selected in a particularly advantageous manner as a function of the speed of the electric motor.
• the evaluated vibration behavior can be triggered by a wide variety of excitations.
• the vibrations can originate from the electric motor itself, from the driven load, for example an impeller, and/or from an operating environment of the electric motor. As long as the vibrations can be detected by the vibration sensor, they can be evaluated using the method disclosed here.
• the operating environment is understood here as the area around the electric motor, which has a retroactive effect on the electric motor. This means in particular mechanical repercussions.
• the operating environment can be formed by a part of the system to which the electric motor is connected.
• the operating environment may additionally include a plenum to direct the air moved by the fan.
• the operating environment may include additional other vibrators. An impeller that through the Electric motor is driven can be considered part of the operating environment.
• the detected vibration values can be represented in different ways.
• the detected vibration values can be described by simple scalars that specify an amplitude of the vibrations independently of the direction of the vibration.
• the detected vibration values can also be vectors which, for example, indicate vibrations in three different spatial directions. All that is important for the present disclosure is that an evaluation measure can be determined from the recorded vibration values, which can practically always be implemented. How concretely the vibration values are represented, in which directions vibrations are detected and whether the vibrations are detected along one or more axes can depend on the respective application scenario.
• the vibration sensor that detects the vibrations can be designed in various ways and can be based on a wide variety of technologies.
• An example is a MEMS sensor (micro-electro-mechanical system).
• the sensor can measure in one or more directions.
• the vibration sensor itself can be arranged at different locations.
• the vibration sensor is arranged on the outside of the electric motor.
• the vibration sensor can be located in a housing that is arranged on the outside of the electric motor.
• the vibration sensor is integrated into the electric motor and is therefore part of the electric motor.
• Such an electric motor is disclosed, for example, in DE 10 2018 211 838 A1, which was already mentioned in the introduction.
• the results of an assessment can be used in many different ways.
• the evaluation results can thus be used when forecasting the life expectancy of the electric motor or components of the electric motor. For example, it can be stated how the current present load case affects the service life of the electric motor.
• the evaluation results can also be sent to a cloud to be used there, for example, to monitor the condition or improve the electric motor.
• the sensor signals and/or evaluation results can also be entered into a digital twin of the electric motor, for example for a more extensive evaluation of the operating state of the electric motor. This brief and non-exhaustive list shows how extensively the present disclosure can be used.
• the evaluation frequency is formed by an order of a base frequency, with the base frequency preferably being dependent on a speed of the electric motor.
• a dependency between base frequency and speed can be achieved, for example, in that the base frequency is formed by the rotational frequency, ie the revolutions of the electric motor per second.
• An order of a base frequency is a multiple of this base frequency, i.e. the nth order corresponds to n times the base frequency.
• the current speed can be determined in a variety of ways. For example, a speed sensor can be used. However, since information about the rotational speed is available in any case, particularly in the case of electronically commutated electric motors, this information can also be transferred from a motor controller.
• a first order is used as the evaluation frequency to determine a resonance caused by an imbalance.
• the vibration behavior is evaluated for multiple evaluation frequencies. This approach is particularly useful when several different resonance effects are to be examined. Since different resonance effects are expressed in different resonance frequencies (when using orders of a base frequency in different orders), different resonance effects can be evaluated by using several evaluation frequencies. When choosing the multiple Evaluation frequencies, knowledge about the likely occurrence of resonance effects can be used. This knowledge can come from detailed measurements of identical or similar electric motors and/or from simulations, for example.
• a detected resonance point is additionally evaluated by comparing an amplitude of the detected vibration values with a predefined amplitude limit value and/or determining a vibration shape and/or a vibration mode and/or carrying out other evaluations.
• the evaluation of the amplitude enables a distinction between critical and non-critical resonance points and the effects of the resonance points on the electric motor and its operating environment.
• the amplitude limit can be determined from empirical values or from calculations. They can also come from standards or other regulations, such as IS014694. For example, amplitude limit values of 7 millimeters/second (RMS) or 9 millimeters/second (RMS) would be conceivable.
• Determining the deflection shape enables a statement to be made about how the excited structure vibrates. Determining the vibration mode enables a summary description of the vibrations in terms of frequency, vibration shape and damping.
• the vibration behavior is evaluated when the electric motor is started up and/or during ongoing operation of the electric motor and/or after a predefined period of time has elapsed and/or when an operating parameter of the electric motor changes.
• An evaluation during commissioning can determine how a specific electric motor behaves in terms of vibration in a specific operating environment. A run-up or a run-down can be carried out. An evaluation during operation is particularly helpful in those application situations in which the electric motor is used in continuous operation.
• such an assessment also makes it possible to identify a vibration behavior that changes during operation. A rating after After a predefined period of time has elapsed, the vibration behavior can be monitored in a defined and comprehensive manner. In this way, changes in the vibration behavior can also be reliably detected.
• the predefined period of time can be selected depending on the respective operating environment.
• a shorter period of time can be appropriate in operating environments with highly variable parameters, for example due to buildup on an impeller driven by the electric motor, than in an operating environment in which the parameters are largely stable. Accordingly, the period of time can be in the range of minutes, hours, days, weeks or even months.
• a suggestion for mitigating negative effects of a resonance point is generated and/or output, the suggestion preferably including a location and/or extent of a balancing mass and/or a blanking corridor.
• the presence of a resonance point is decided if the ratio between the second assessment criterion and the first assessment criterion exceeds a specified limit value, the specified limit value being greater than or equal to 50%, preferably greater than or equal to 60%, particularly preferably greater than or equal to 70% .
• the specification of the limit value should depend on the spectrum of the recorded vibration values. Furthermore, how closely the detected vibrations of the electric motor to be evaluated or the operating environment approach a sinusoidal vibration can be included. With a limit value greater than or equal to 50%, resonance points can be reliably detected. A threshold greater than or equal to 60% further improves detection. With a limit value greater than or equal to 70%, a point of resonance can be detected particularly reliably.
• the first and/or the second assessment measure is determined by forming an effective value.
• an effective value can be formed, for example, by a square mean (RMS—Root Mean Square).
• RMS Root Mean Square
• An effective value is an easy-to-calculate and yet meaningful evaluation measure.
• the vibration sensor is designed to detect vibrations along a number of axes, with the number of axes preferably being in pairs perpendicular to one another and with one of the number of axes being arranged parallel to a motor axis/motor shaft of the electric motor. In this way, further information about the vibration behavior can be obtained and the evaluation of the vibration behavior and/or a point of resonance can be further improved
• the vibration sensor is designed to detect a vibration speed and/or a vibration acceleration.
• the electric motor includes a control system that is designed to adapt a regulation and/or control of the electric motor based on an evaluation of the vibration behavior. This enables the evaluated vibration behavior to be used immediately.
• the control system and the units used for the evaluation for example the evaluation units, the analysis unit and/or the evaluation unit, can be implemented in common electronics. Motor electronics arranged in an electronics housing of the electric motor would be conceivable for this purpose, for example.
• the electric motor includes an output device that is designed to output information about an evaluation of the vibration behavior. This allows the evaluation results to be used flexibly.
• the output unit can be wired, optical and/or wireless. an optical one
• the output unit can be formed, for example, by a simple lamp, for example an LED (Light Emitting Diode), which signals a critical vibration state.
• the output unit can thus provide visual information.
• the output unit can provide “outside” communication. This can include, for example, the output unit enabling information to be output to a higher-level control unit or for information to be uploaded to a cloud system. In this way, the electric motor can be part of an Industry 4.0 environment.
• the analysis unit is designed to carry out a Fourier transformation, an FFT—Fast Fourier Transform—and/or a Görtzel algorithm and/or more or less wide frequency band filtering.
• a spectral component can be determined in various ways, as long as the vibrations can be evaluated at an evaluation frequency.
• Using an FFT provides a comprehensive picture of the spectral components.
• Görtzel algorithm which was published by Gerald Görtzel in 1958, individual spectral components of a signal can be determined very efficiently. A spectral component can thus also be determined with low computing resources.
• Frequency band filtering makes it possible to restrict an oscillation signal to frequencies that are specifically of interest. In this case, frequency band filtering can take place before the determination of the spectral components.
• FIG. 2 shows a block diagram with functional units of an embodiment of an electric motor according to the present disclosure
• FIG. 3 shows a flow chart with steps of an embodiment of a method according to the present disclosure
• FIG. 5 shows a diagram with associated spectral components over the speed of the electric motor.
• FIG. 1 shows a section through a stator 2 of an exemplary embodiment of an electric motor 1 according to the present disclosure.
• a bearing tube 4 is formed, on each of whose longitudinal ends a bearing receiving area 5 is formed. Bearings, not shown, are accommodated in the bearing receiving areas 5, via which a shaft of the electric motor, also not shown, is rotatably mounted.
• a stator bushing 6 is formed by an aluminum component, at one end of which the bearing tube 4 is formed and at the other end an electronics housing 7 for accommodating motor electronics.
• the motor electronics generates feed signals and outputs them to the stator and/or rotor windings. For the sake of clarity, only one printed circuit board 8 of the motor electronics is shown.
• a vibration sensor 9 is arranged on the printed circuit board 8 .
• the circuit board 8 is embedded in a casting compound 10, 11, with the casting compound 10, 11 being connected to the edge region of the circuit board 8.
• the casting compound 10 acts as a coupling element and transmits vibrations from the stator bushing 6 to the printed circuit board 10 and thus to the vibration sensor 9 .
• the vibration sensor 9 in an electric motor be arranged and detect vibrations of at least part of the electric motor.
• FIG. 2 shows a block diagram of functional units of the electric motor 1 that can be implemented on the printed circuit board 8 .
• the vibration sensor 9 detects vibrations from at least a part of the electric motor.
• the vibration values recorded in this way are transferred to a first evaluation unit 14 and to an analysis unit 15 and an evaluation unit 17 .
• the first evaluation unit 14 determines a first evaluation measure from the recorded vibration values. This first evaluation measure indicates how strongly one part of the electric motor oscillates.
• the analysis unit 15 determines a spectral component of the detected vibration values for an evaluation frequency. This evaluation frequency can be an order of the rotational frequency, i.e. a multiple of the number of revolutions of the electric motor per second.
• the spectral component is supplied to a second evaluation unit 16, which uses it to determine a second evaluation measure.
• the second evaluation parameter indicates how strongly the electric motor oscillates at the evaluation frequency.
• the first and second assessment measure is formed by a square mean.
• the first evaluation unit 14 and the second evaluation unit 16 enter the respectively determined first and second evaluation measure into an evaluation unit 17 which compares the evaluation measures with one another. For this purpose, a quotient is formed from the second evaluation parameter and the first evaluation parameter, which thus reflects the proportion of vibrations with the evaluation frequency in the overall vibration of the electric motor. The result of this quotient formation is compared with a predetermined limit value, which is loaded from a limit value memory 18 . If the specified limit value is exceeded, a decision is made as to the presence of a resonance point. In addition, the evaluation unit 17 assesses the recorded vibration values in order to evaluate the criticality of the point of resonance.
• the evaluation unit 17 further evaluations Make resonance point, for example with regard to the vibration shape or the vibration mode.
• the information obtained in this way can be transferred to an output unit 19, which can output this information to a user, a higher-level control unit, the engine electronics, a cloud or other systems.
• step S1 the method starts with the detection of vibration values using a vibration sensor 9.
• step S2 the general vibration state of the electric motor 1 is determined. This is done by determining a first evaluation measure for the recorded vibration values. This first assessment measure thus indicates how strongly the detected part of the electric motor oscillates across all detected frequencies.
• step S3 a spectral component (or also several spectral components) of the detected vibration values is determined for one (or also several) evaluation frequencies, the evaluation frequency(s) being formed in the present case by an order of the rotational frequency.
• step S4 the vibration values of individual orders are evaluated by determining a second evaluation measure for the spectral component/the spectral components.
• step S5 the evaluation parameters are compared and the vibration behavior is thereby evaluated.
• a quotient is formed from the second evaluation measure and the first evaluation measure and is compared with a limit value. If the quotient does not exceed the limit value ("no"), the process continues with step S6, in which the current evaluation frequency is not recognized as a resonance point. Thereafter, it returns to step S1. If the quotient exceeds the limit value ("yes"), a decision is made as to the presence of a resonance point and the criticality of the resonance point is evaluated in step S7. For this purpose, the effective value of the recorded vibration values is compared with an amplitude limit value in step S8.
• step S9 If the rms value does not exceed the amplitude limit ("no"), the resonance point is assessed as non-critical in step S9 and therefore does not have to be treated in a special way. The process returns to step S1. If the effective value exceeds the amplitude limit ("yes"), the resonance point is classified as critical in step S10. In step S11 one or more actions are triggered. This can include issuing an error message, correcting operating parameters, etc. Thereafter, it returns to step S1.
• the fourth shows a diagram with a quotient of the second evaluation parameter and the first evaluation parameter over the speed.
• the first order is selected as the evaluation frequency, i.e. a frequency that corresponds to the rotational frequency of the electric motor.
• the electric motor is part of a fan, more precisely a radial fan.
• the diagram shows how strongly the vibrations of the electric motor or the fan are characterized by the first order. Two speed ranges can be seen where there is a resonance point: around 480 rpm (first peak) and between 680 and 870 rpm (two broad speed ranges with high values).
• This example shows that the current operating status of a fan can be evaluated in this way.
• the condition monitoring disclosed herein does not require the fan to be ramped up or down. Vibrations can be measured continuously or at regular time intervals.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Measurement Of Mechanical Vibrations Or Ultrasonic Waves (AREA)
• Control Of Electric Motors In General (AREA)

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• 2021
  • 2021-04-20 DE DE102021203932.4A patent/DE102021203932B3/de active Active
• 2022
  • 2022-03-22 US US18/555,957 patent/US20240210271A1/en active Pending
  • 2022-03-22 CN CN202280029206.XA patent/CN117178177A/zh active Pending
  • 2022-03-22 EP EP22718060.1A patent/EP4275028A1/de active Pending
  • 2022-03-22 BR BR112023021056A patent/BR112023021056A2/pt unknown
  • 2022-03-22 WO PCT/DE2022/200051 patent/WO2022223082A1/de active Application Filing
  • 2022-03-22 JP JP2023563939A patent/JP2024514669A/ja active Pending

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