Structural transmission acoustic resonance detection using electric dynamic structural transmission acoustic

Abstract

The invention relates to a method for detecting the connection state of metal laminations (P) pressed together on a rotor (R) of an electric machine (EM). According to the invention, structural transmission sound is introduced into the shaft (W) or the rotor (R) by generating a magnetic field acting on the rotor (R). The sound propagating within the rotor EM (R) is detected during the introduction of structure-transmitted sound and / or during a time period immediately after the introduction of structure-transmitted sound. It is determined whether the detected sound exhibits a resonance behavior (RV) within a frequency band (FB) characterized for the vibration of the single metal lamination (P). If a resonance behavior is detected in the frequency band (FB), a signal indicating insufficient compression of the metal laminations (P) is output, otherwise a signal indicating sufficient compression of the metal laminations (P) is output.

Description

Background Technology

[0001] An electric motor has a rotor that rotates relative to a stator. For example, the stator can generate a rotating magnetic field, and the rotor follows or is driven by this magnetic field to rotate. For this purpose, the rotor must also be magnetic (at least in synchronous and DC motors), for example, permanent magnets are fixed within the rotor. To guide the magnetic flux within the rotor, soft iron material is also used, typically in the form of rotor laminations. These laminations are stacked in layers. By using individual, electrically insulated soft iron laminations, eddy current losses in the rotor's soft iron material can be significantly reduced.

[0002] These metal sheets can be arranged as metal laminations (P), which are pressed together. Axial compression provides reinforcement, particularly to prevent axial torsion and bending of the rotor. This is especially important in high-performance motors, where the excitation induces vibrations that, in addition to bearing damage, contribute to noise and interference signals in the electrical controls. In fully compressed metal laminations, the laminations are firmly connected by compression, so the high rigidity resulting from the compression only leads to resonance effects at very high frequencies and small amplitudes, with minimal impact. This weak resonance effect is related to sufficient compression, i.e., high rigidity in the connection between the metal laminations.

[0003] It has been recognized that insufficient compaction can lead to undesirable strong resonance effects, which also occur at unfavorable lower frequencies. The objective of this invention is to provide a simple method for detecting insufficient compaction between metal laminations.

[0004] Therefore, a vibration test is proposed to detect insufficient compaction between rotor laminations. In this test, a vibration exciter (shaker) causes the shaft or rotor to vibrate at different frequencies, thereby detecting resonance effects. In insufficiently compacted laminations, the laminations vibrate individually and relative to each other, while in fully compacted laminations, the laminations vibrate as a single unit, or vibrate as a whole due to the reinforcement caused by compaction.

[0005] If the metal laminations are not properly compressed, a resonance effect will occur within a frequency range that characterizes the resonant frequencies of the mutually vibrating metal laminations (different from the resonance frequencies of properly reinforced or compressed metal laminations). This invention identifies the relevant resonance effect by detecting the frequency and its corresponding amplitude (or the frequency dependence of the amplitude), thereby enabling the rotor to be flagged as under-compressed. The term "resonance effect" is synonymous with "resonance behavior (RV)".

[0006] The frequency range of resonance effects associated with under-compacted metal laminations is significantly lower than that of rotors reinforced by compaction. Therefore, defective (under-compacted) metal laminations can be identified through simple spectral analysis of vibration test results.

[0007] It has been recognized that under-compressed metal laminations can be reliably detected even when the rotor is installed in the motor, or even when gears or pulleys are mounted on the rotor shaft, or even when the rotor is mechanically coupled to other (external) components. Therefore, the method described in this specification allows for the detection of under-compressed metal laminations inside the rotor without disassembling the motor. This particularly allows for testing the compactness of the metal laminations after motor manufacturing or during maintenance. Specifically, under-compressed metal laminations can be detected even when the motor is already installed in a vehicle, for example, as a starter-generator or traction motor.

[0008] Therefore, a method for detecting the connection state of mutually pressed metal laminations is proposed. The metal laminations are metal laminations of a motor rotor, particularly composed of a soft magnetic material into which permanent magnets can be embedded. The rotor can be a permanent magnet excitation motor rotor or a separately excited motor rotor. The connection state specifically refers to the pressing (axial connection) between different metal laminations arranged sequentially in the axial direction. The metal laminations are mounted on the motor shaft and pressed against each other there. The connection state reflects whether the pressing between the metal laminations is rigid, or whether there is potential movement between the metal laminations, resulting in vibration (reciprocal movement) between them. The connection state reflects the mechanical rigidity of the connection between the metal laminations (adjacent end faces). The metal laminations are stamped, aligned sheets of soft magnetic material, preferably stacked by an insulating layer (e.g., varnish). The metal laminations are rotatably fixed to the rotor shaft. The shaft extends through the center of the iron sheets. Summary of the Invention

[0009] To detect the connection between metal laminations (not just indirect connections via shafts, but direct connections), the rotor or shaft is excited to vibrate. To simplify operation, structurally transmitted sound is introduced into the rotor (and therefore also into the shaft) via a stator excitation signal. In other words, structurally transmitted sound is generated and introduced into the rotor electrically. At least one existing winding in the motor (stator winding, field winding) is used here, which is also used to generate force during motor rotation (generating torque when the speed is greater than zero). At least one stator winding is excited (electrically) by a stator signal. The stator signal, in particular alternating current or voltage, is applied to or injected into at least one stator winding. The stator signal is an alternating signal. The electric stator signal generates an alternating magnetic field in the stator. The magnetic field generates force or motion in the rotor. The magnetic field generated by exciting the stator acts on the rotor. The magnetic flux generated by exciting the stator is transmitted to the rotor. The magnetic field generates force through magnetostriction, magnetic reluctance, and / or magnetostatics, causing the rotor to move or deform (bending, torsion, etc.). The magnetic field generates structurally transmitted sound in the rotor (and also in the shaft due to structurally transmitted sound transmission from the rotor to the shaft) through magnetostriction, magnetic reluctance, and / or magnetostatics. The stator, or its excitation via stator signals, thus acts as a vibration exciter, causing the rotor to vibrate. The introduction of structurally transmitted sound involves either generating structurally transmitted sound in the rotor or generating structurally transmitted sound in the stator and transmitting it to the rotor.

[0010] The rotor is excited to vibrate by a magnetic field generated by a stator signal acting on it, thus exciting the entire rotor to vibrate. Exciting the stator via a stator signal specifically causes the rotor or shaft to vibrate. Due to the physical connection between the metal laminations and the rotor shaft, typically when one component is excited, every component of the rotor will be excited to vibrate. Therefore, by exciting the stator (especially at least one stator winding) via a stator signal, structurally transmitted sound or vibration is introduced into or generated within the shaft or rotor. Operating the stator in this way—that is, exciting the stator via a stator signal—excites the rotor to vibrate, especially the shaft or metal laminations.

[0011] A magnetic field is generated in the rotor, producing an acoustic signal. This acoustic signal contains different frequencies, which can occur simultaneously (e.g., as noise, especially white noise or spectral adjustment noise) or sequentially (e.g., in a swept-frequency signal). Therefore, the structural transmission sound generated in the rotor contains different frequencies. Furthermore, structural transmission sound is also generated in the stator by exciting it. This structural transmission sound propagates particularly into the rotor, so generating a magnetic field also introduces structural transmission sound (originating in the stator) into the rotor.

[0012] In addition, sound, especially structural transmission sound propagating within the rotor, is detected. This is performed during the introduction of structural transmission sound, during the period when the rotor is excited to vibrate, or immediately after the introduction of structural transmission sound. In the latter period, reverberation can be detected, and its spectrum is also characteristic of the connection state between the metal laminations.

[0013] Sound detection typically involves determining the vibrations generated by introducing structure-transmitted sound into the rotor. This allows determination of the rotor's acoustic response to the introduced structure-transmitted sound, thus enabling inference of the connection status. Sound can be detected directly using structure-transmitted sound sensors (contact microphones), laser microphones, or air microphones, or by detecting induced signals in the rotor and / or stator windings generated by structure-transmitted sound and associated magnetic field changes within the relevant windings. To some extent, the motor windings themselves can be used as (magnetodynamic) structure-transmitted sound microphones.

[0014] Structure-transmitted sound (STMS) sensors sensitive to all three spatial directions can be used. Individual signals from each spatial direction can be analyzed separately or combined for post-processing. Typically, at least one STMS sensor can be used. This sensor can be positioned on the cylindrical surface (or end face) of the shaft; STMS on the cylindrical surface (or end face) can typically be detected by the sensor positioned there. The same applies to the end face or cylindrical surface of the rotor. Multiple STMS sensors can be arranged circumferentially (especially at uniform intervals) on the cylindrical surface of the shaft (or rotor). Multiple groups of STMS sensors can be arranged, each group positioned at the same longitudinal position on the shaft (or rotor) and circumferentially (especially at uniform intervals) apart from each other. The groups can be positioned at different longitudinal positions (=axial positions) on the shaft (or rotor), i.e., staggered axially. STMS can typically be detected at locations where STMS sensors can be placed, especially by using laser microphones instead of STMS sensors.

[0015] Sound can be obtained by detecting structurally transmitted sound within a rotor or shaft, by detecting vibrations on the rotor or shaft surface, or by detecting airborne sound generated by rotor or shaft vibrations. When detecting sound, different frequencies are also detected, especially those corresponding to the introduced frequency. Sound detection also includes determining the frequency dependence of the sound amplitude. Sound detection may include measuring sound power, sound velocity, or sound pressure, or detecting signals induced in the rotor and / or stator (e.g., in the rotor's excitation windings and / or the stator's stator windings) by structurally transmitted sound. In particular, characteristic quantities of the rotor or shaft vibration amplitude can be determined to detect sound.

[0016] The detected sound undergoes spectral analysis to determine whether it exhibits resonant behavior within a specific frequency band. This band is characteristic of the vibration of individual metal laminations. In particular, this band contains components that occur when individual metal laminations (but not fully compressed ones) are excited to vibrate. This band covers the resonant frequency range of individual metal laminations that are not mechanically rigidly connected to other metal laminations at their end faces (e.g., connected only by a shaft). This band particularly covers the range of resonant behavior or resonant effects of rotors whose metal laminations are not fully or only partially compressed. Therefore, this band covers frequencies corresponding to the mechanical resonant frequencies of individual metal laminations (mounted on a shaft).

[0017] Resonance behavior can be represented by a specific amplitude curve (which varies with frequency), a specific amplitude height, or sound signal intensity (when it is exceeded), or by a strong rise or fall in sound intensity with frequency. The latter is a typical characteristic of the signal when the system frequency is close to the resonant frequency.

[0018] Output a signal characterizing the connection status, depending on whether significant resonant behavior is detected in the frequency band. This signal can be a fault signal, particularly specific to the current motor or a particular rotor. This signal can lead to the relevant rotor or motor being scrapped or discarded, re-compacted, or at least marked as defective. If resonant behavior is detected in the frequency band, output a signal indicating insufficient compaction of the metal laminations. Otherwise, output a signal indicating adequate compaction of the metal laminations. A adequately compacted metal lamination is one that cannot vibrate independently due to its mutual compaction. An inadequately compacted metal lamination is one that can at least partially vibrate independently due to insufficient compaction. "Adequate" and "inadequate" indicate the degree of reinforcement of the detected connection. When resonant behavior reaches a certain intensity, the rotor (or its metal laminations) is classified as insufficiently compacted.

[0019] Sound detection can be achieved by detecting structurally transmitted sound propagating inside the rotor. A structurally transmitted sound sensor can be used for this purpose. This sensor is preferably acoustically coupled and mounted on the rotor. In particular, it can be mounted on the rotor (or shaft) at a different location from the vibration exciter. Both can be mounted at the same end of the rotor, especially the same end or end face of the shaft, but are preferably offset from each other radially and / or axially.

[0020] Structurally transmitted sound (STI) sensors convert the vibration of a rotor or shaft into electrical signals. The device used to detect sound can be part of a vibration testing system, similar to a vibration exciter. STI sensors can be connected to the rotor or shaft directly or via an acoustic connection. Furthermore, sound can also be detected by detecting vibrations on the surface of the rotor or shaft. This can be achieved non-contactly using a laser microphone. The laser microphone scans the surface, detecting vibrations on the rotor or shaft surface based on the change in brightness (over time) caused by the interference changes between emitted and reflected laser light. Additionally, sound can also be detected by detecting (airborne) sound emitted by the rotor or shaft or the entire motor. For this purpose, a microphone positioned near the motor and pointed towards it can be used.

[0021] Furthermore, structurally transmitted sound can also be detected by detecting the signal induced in at least one stator winding and / or excitation winding by the structurally transmitted sound. The induced signal reflects the structurally transmitted sound, so structurally transmitted sound propagating in the rotor can be detected by detecting the induced signal. If the stator winding used to generate the magnetic field is the same as the winding used to detect the induced signal, or if different windings are used, the induced signal can be detected after the stator is excited, thereby detecting residual vibration.

[0022] Different windings can also be used to generate the magnetic field and detect the induced signal, for example, by exciting the stator and detecting the induced signal at the rotor, by exciting the rotor and detecting the induced signal at the stator, or by exciting the first stator winding and detecting the induced signal at the second stator winding. Here, the excitation signal (or related signal components) can be removed from the detected (induced) signal, specifically by subtracting the (amplitude-adjusted) excitation signal from the detected signal, or by subtracting the signal component related to the excitation signal in the detected signal (i.e., exceeding a predetermined correlation threshold), or by high-pass filtering (in which the excitation signal is strongly attenuated while the signal used for sound detection is attenuated relatively less), or a combination thereof. By detecting the induced signal, sound propagating inside the rotor can be detected (among other things).

[0023] Structurally transmitted sound can be introduced into the rotor (or shaft) as a longitudinal wave. Its (primary) propagation direction can be aligned with the axial extension of the rotor or shaft. The propagation direction of structurally transmitted sound or longitudinal waves can also be tangential to the rotor or shaft. Furthermore, the propagation direction of the longitudinal wave representing sound can be oriented radially to the rotor or shaft. The direction of the force generated by the magnetic field can therefore be radial, tangential, or axial relative to the rotor or shaft. The terms radial, axial, and tangential refer to the cylindrical structure of the shaft or rotor. The magnetic field can also generate axial forces in the rotor or shaft. The magnetic field can also generate torsional loads acting circumferentially on the rotor. Opposite stator windings of the stator can be excited with the same excitation signal or with complementary signals, especially signals with a phase difference of 90° or 180°. At least one stator winding of the stator and the excitation winding of the rotor can also be excited with the same or complementary signals (especially signals with a phase difference of 90° or 180°). Furthermore, different stator windings arranged at different angles (<180°) within the stator can be excited using an electrical excitation signal to specifically generate torsional vibration. Here, the different stator windings can be excited with the same excitation signal, or with excitation signals that are phase- or time-staggered. The time stagger can be selected to produce rotational motion of the rotor in alternating directions. The offset of the rotational motion can be very small (<10 μm <10 nm circumferential motion) and can specifically correspond to the desired structural transmission sound velocity. In particular, the excitation signal causes the rotor's rotational motion to be less than 0.1°, 0.01°, or 0.001°. This can be referred to as "virtually no" rotational motion. The angular velocity of the rotational motion is preferably greater than 500 or 1000 ω. Pi / s, where 2 Pi represents the full angle of the shaft / rotor cross-section. The electrical excitation signal is, in particular, an alternating signal with periodically changing polarity. The frequency component of the excitation signal is preferably at least 100Hz, 1000Hz, or 2000Hz. The excitation signal is specifically configured to prevent the excited stator from generating a magnetic rotational field, preferably not a rotational field that the rotor (e.g., due to an excessively large angular velocity difference between the rotor and stator) can follow. The excitation signal is preferably not a multiphase alternating current, especially not a multiphase alternating current used to generate significant rotational motion in the rotor (e.g., greater than 0.01°, 0.001°, 0.1°, or 1°). The excitation signal is configured not to generate impulsive motion in the rotor, but rather to generate continuous rotational motion in alternating directions, and preferably the rotor deflection is insignificant, i.e., the deflection does not exceed 0.01°, 0.001°, 0.1°, or 1°.

[0024] The frequency of the alternating signal can vary. The excitation signal is particularly a swept-frequency signal, i.e., an (preferably continuously) alternating signal with a variable frequency, preferably based on a variable-frequency sine wave. The excitation signal can also be a noise signal, such as a signal containing multiple different frequency components at any given time. The excitation signal is particularly white noise or spectral-adjusted noise. Therefore, the excitation signal has components with different frequencies, which appear simultaneously (in the case of noise) or sequentially (in the case of a swept-frequency signal). The excitation signal is especially not a signal that produces significant rotational motion of the rotor, and is preferably not used for starting or braking. This improves the safety of the method execution.

[0025] Furthermore, structurally transmitted sound can be introduced at different relative positions of the rotor and the motor stator. In this case, the rotor's pole shoe surface can be directly opposite the center of the stator's armature surface or the center of the stator slot. It can be configured to place the stator relative to the rotor at different positions during the introduction of structurally transmitted sound. Preferably, a frequency range is scanned at each position (i.e., sound is introduced and detected at each frequency within the frequency range).

[0026] In the step of introducing structurally transmitted sound, the stator is excited to generate sound waves whose main propagation direction is perpendicular or parallel to the rotor's longitudinal axis. In particular, the vibration exciter may have multiple sound emitting surfaces, one of which has a normal to the main propagation direction, and another sound emitting surface is perpendicular to or at least inclined to that direction.

[0027] To determine whether a detected sound exhibits resonant behavior within a frequency band, it can be determined whether the detected sound exceeds a predetermined threshold within that band. Alternatively, it can be determined whether the detected sound intensity exceeds that of a sound detected in an adjacent frequency band. A frequency band or adjacent frequency band can be directly or indirectly adjacent to the aforementioned frequency band. Therefore, a predetermined threshold can be used as a comparison standard, or the sound intensity within an adjacent frequency band can be used as a comparison standard. The interval between an adjacent frequency band and the aforementioned frequency band does not exceed 2, 5, or 10 times (if the adjacent frequency band is higher than the aforementioned frequency band). If the adjacent frequency band is lower than the aforementioned frequency band, the interval between the aforementioned frequency band and the adjacent frequency band also does not exceed 2, 5, or 10 times. Furthermore, resonant behavior can also be detected through the intensity-frequency dependence corresponding to resonant behavior.

[0028] Significant resonant behavior can be detected as follows: if the intensity decreases significantly with frequency, or increases significantly with frequency, or exhibits frequency-selective decreases or increases in intensity within a frequency band, this indicates the presence of resonant behavior within that band. Therefore, it can be determined whether the absolute value of the derivative of sound intensity with respect to frequency exceeds a threshold within a frequency band characterizing the vibration of a single metal lamination. Sound intensity can be its amplitude, power, sound velocity, or sound pressure level, or the electrical quantity derived therefrom, generated by a device used to detect the sound transmitted through a rotor (or shaft) structure.

[0029] In addition to detecting whether the connection between the metal laminations to be pressed is insufficient, it can also detect the presence of bearing damage. Therefore, it can also be determined whether the detected sound is located within the frequency band characterizing bearing damage. Here, the same detection sound as that used to detect resonance behavior can be used. Only the frequency band is different; therefore, in addition to the aforementioned frequency band, another frequency band characterizing bearing damage is considered so that bearing damage can be detected in addition to insufficient connection. The frequency band characterizing bearing damage preferably does not overlap with adjacent frequency bands.

[0030] The introduction and / or detection of structure-transmitted sound can be performed on motors that are already installed, mechanically coupled to other components driving or outputting the vehicle, with the housing still in place, or with gears or transmission gears mounted on the shaft. In other words, the method can also be performed on fully assembled, especially installed, motors or rotors. There is no need to remove the housing or wheels (gears, pulleys, general output pulleys) mounted on the shaft, because the housing and wheels have minimal impact on vibrational behavior when the metal laminations are not adequately reinforced (except that they are collectively fixed to the shaft).

[0031] The frequency band used to characterize the vibration of a single metal lamination extends from the lower cutoff frequency to the upper cutoff frequency. This frequency band is defined by its upper and lower cutoff frequencies. The lower cutoff frequency is no greater than 3000 Hz or 2500 Hz. The upper cutoff frequency is preferably no less than 4000 Hz or 4500 Hz. For example, the lower cutoff frequency is 3100 Hz, 2750 Hz, or 2600 Hz. The upper cutoff frequency can be 3750 Hz or 4000 Hz. The excitation signal, in particular, does not contain significant components below 2500 Hz, 2000 Hz, 1500 Hz, 1000 Hz, 500 Hz, or 100 Hz (i.e., power components < 5% of the total signal power).

[0032] The motor can be, in particular, a separately excited or self-excited synchronous motor. The excitation winding (EW) is used to excite the rotor to achieve the rotational operation of the motor (electric motor, generator), and is therefore connected to or can be connected to an excitation signal generator (DC, possibly adjustable), and can be connected to or can be connected to a detection circuit for detecting structurally transmitted sound. A signal processing circuit can be connected after the detection circuit (e.g., an amplifier) ​​to remove the excitation signal (or related signal components) from the detected (induced) signal as described above. An evaluation circuit can be connected after the detection circuit and (if any) the signal processing circuit to determine the resonant behavior or frequency behavior related to bearing damage. The circuits described herein can be analog circuits, partially analog and partially digital circuits, or digital circuits. In particular, these circuits, or their functions, can be implemented by at least one software module that implements the relevant functions. Attached Figure Description

[0033] Figure 1This is used to further illustrate the working principle of the method of the present invention, especially the motor based on symbolic representation.

[0034] Figure 2 Used to illustrate the vibration process or resonance effect that may occur in a poorly connected metal stack.

[0035] Figure 3 This is used as an example to demonstrate the resonance effect in the detected sound. Detailed Implementation

[0036] Figure 1 A symbolic representation of an electric motor EM is shown, featuring a rotor R (located inside the machine) surrounded by a stator. The stator has a stator yoke SJ and multiple pole cores PK, each surrounded by a stator winding SW. The pole cores point radially toward the rotor R, with the longitudinal axis of the stator windings aligned with this radial direction. When the SW windings are energized, a magnetic field is generated, which acts on the motor EM from the pole cores.

[0037] The rotor R has magnetic polarization (magnetization), and its direction RP is from Figure 1 The arrows in the diagram indicate polarization. The rotor may have at least one permanent magnet to indicate polarization. One embodiment is shown, in which the rotor is magnetized by an excitation winding EW. To achieve rotational operation of the motor, the excitation winding EW is supplied with direct current to obtain constant (controllable) magnetization; to perform the method of the invention, the excitation winding may be supplied with an excitation signal to introduce or generate structurally transmitted sound in the rotor. Alternatively, the excitation signal may be applied to stator windings SW or multiple stator windings SW to introduce or generate structurally transmitted sound in the rotor.

[0038] The stator yoke is used to guide the magnetic flux between the pole cores PK or stator teeth. In the rotor, the excitation winding EW is wound around the symbolically represented armature (shaded with diagonal lines).

[0039] Figure 1 A top view of the motor end face is shown. Figure 2 A rotor R is shown, with a shaft W (or a portion of that shaft) protruding from it. For clarity, Figure 1 The rotor shaft is not shown. The excitation signal generates an alternating magnetic field in the rotor and / or stator, thereby producing structurally transmitted sound, and thus introducing it into the rotor (directly or indirectly). Figure 2 This is used to further illustrate the vibrations caused by the transmission of sound through the structure, which vary depending on the connection between the metal laminations.

[0040] Figure 2A rotor R with three metal laminations P mounted on a shaft W is symbolically shown. For ease of understanding, the spacing between the metal laminations P is clearly shown in the figure to illustrate vibrations between the laminations P under both insufficient and sufficient connection conditions. The double arrow SA above symbolically represents vibration in the fully connected state, where the metal laminations P are firmly connected to each other (specifically through the end faces, not just through the common shaft W). In this case, the metal laminations P collectively form a single unit, as shown, and can vibrate radially along the entire length of all the metal laminations P.

[0041] and Figure 2 Conversely, as shown by the double arrow SA above, when there is insufficient connection between the metal laminations P, the laminations P can vibrate independently. This is represented by the double arrow SU below. In this case, rigidity is not achieved through direct connection between the metal laminations, but simply by fixing the laminations P to a common axis W.

[0042] It is easy to see that with sufficient reinforcement, i.e., when the metal laminations P are directly and fully connected (i.e., through rigid connections on the end faces or cylindrical surfaces of the metal laminations), these laminations together form a whole. However, with insufficient reinforcement, i.e., when the connections between the metal laminations P are inadequate, these laminations can vibrate independently. In the latter case, unlike the former, there is no strong reinforcement; they are only connected by the shaft W. Therefore, the metal laminations P can vibrate independently, and their resonant frequency is determined by the rigidity of the shaft (rather than by the rigidity of the connections between the laminations P).

[0043] Individual vibrations between metal laminations P can be obtained from Figure 3 As can be seen, the horizontal axis in the figure represents the intensity ST of the acquired / detected sound, and the vertical axis represents the frequency. As mentioned earlier, structurally transmitted sound can be detected by a structurally transmitted sound sensor (end face, rotor, or circumferential surface) mounted on the rotor, or by detecting the signal induced by structurally transmitted sound in the rotor and / or stator (especially in the rotor winding such as the excitation winding EW or at least one stator winding SW).

[0044] Figure 3The graphs show the spectral characteristics of the intensity ST of the acquired sound. The first curve, A, shows the frequency response of the fully connected metal lamination P. It is clear that, especially within the frequency band FB, the intensity ST continuously decreases with frequency f. In contrast, curve U shows the behavior of the same rotor but with insufficient connection of the metal lamination P. Within the frequency band FB, it can be seen that individual metal laminations can vibrate independently, with RV representing resonant behavior. Therefore, curve U exhibits a strong intensity decrease (varying with frequency) caused by resonance within the frequency band FB, followed by a strong increase caused by resonance. There are both negative and positive peaks, which characterize the resonant behavior of the insufficiently connected metal lamination P. This behavior is not visible in curve A. Therefore, the connection status can be directly inferred from the spectral characteristics within the frequency band FB.

[0045] On one hand, resonance behavior RV can be detected by checking whether the sound intensity ST exceeds a certain threshold, while curve A does not exceed this threshold. For example, if the threshold is -10 dB, resonance behavior RV can be clearly detected by a high amplitude, distinguishing it from the (insignificant) resonance behavior in curve A. Furthermore, it can be seen that, compared to curve A, the intensity ST of curve U varies significantly with frequency within the frequency band FB, whether decreasing or increasing dramatically. This strong frequency dependence (the magnitude of the intensity change with frequency) provides another possibility for detecting resonance effects RV. Additionally, for example, an intensity can be determined within an adjacent frequency band X, such as the average intensity within band X, and then this (average) intensity can be compared with the maximum sound intensity within frequency band FB. Here, the adjacent frequency band X constitutes a standard or threshold for comparison with the intensity within frequency band FB. For example, frequency band X is located between 2600 Hz and 2800 Hz. The design of frequency band X ensures that resonance effects caused by insufficiently connected metal laminations have minimal impact within this frequency band X.

[0046] The slight frequency shift of curves U and A below approximately 2750 Hz may be due to insufficient connection of the metal laminations P, since the connection status between the metal laminations obviously also affects the overall frequency characteristics of the rotor.

[0047] In addition, a frequency band LS was shown, in which frequency dependence of sound intensity was found, which is characteristic of bearing damage. This frequency band can also be considered when analyzing or acquiring sound to enable additional detection of bearing damage.

Claims

1. A method for detecting the connection state of pressed metal laminations (P) of a motor (EM) rotor (R), comprising the following steps: By generating a magnetic field acting on the rotor (R), and by exciting the stator (SW, PK, SJ) and / or the rotor with the aid of an electrical excitation signal, structural transmission sound is introduced into the shaft (W) or rotor (R). Sound propagating within the rotor (R) is detected during and / or immediately following the introduction of structurally transmitted sound. Determine whether the detected sound exhibits resonant behavior (RV) within the frequency band (FB) characterized by the vibration of a single metal lamination (P); If resonant behavior is detected in the frequency band (FB), a signal indicating insufficient compaction of the metal lamination (P) is output; otherwise, a signal indicating sufficient compaction of the metal lamination (P) is output.

2. The method according to claim 1, wherein Structurally transmitted sound propagating within the rotor is detected by means of a structurally transmitted sound sensor (A) acoustically coupled to the rotor (R). Sound detection is performed by detecting vibrations on the surface (O) of the rotor (R) or shaft (W) using a laser microphone, or by detecting sounds emitted from the rotor (R) or shaft (W) using a microphone, or by detecting signals induced in the rotor and / or stator by sound transmitted through the structure.

3. The method according to claim 1 or 2, wherein The structurally transmitted sound is introduced into the rotor (R) in the form of a longitudinal wave, the propagation direction of which corresponds to the axial extension direction (a) of the rotor (R) or shaft (W), the propagation direction of which corresponds to the tangential direction (t) of the rotor (R) or shaft (W), or the propagation direction of which corresponds to the radial direction (r) of the rotor or shaft.

4. The method according to claim 1, 2 or 3, wherein The stator (SW, PK, SJ) includes the stator winding (SW), where - The stator (SW, PK, SJ) is excited by an excitation signal by injecting alternating current into at least one stator winding (SW) of the stator or by applying alternating voltage to at least one stator winding (SW) of the stator, or wherein... - The rotor includes an excitation winding (EW), in which the rotor is excited by an excitation signal by injecting an alternating current into the excitation winding (EW) or by applying an alternating voltage to the excitation winding (EW).

5. The method according to any of the preceding claims, wherein The stator (SW, PK, SJ) is excited by an electrical excitation signal, which is supplied to at least one stator winding of the stator through at least one ohmic load resistor, or by connecting the secondary winding of the transformer to at least one stator winding of the stator and applying an alternating signal to the primary winding of the transformer. Alternatively, the rotor may be excited by an electrical excitation signal supplied to the rotor's excitation winding (EW) through an ohmic load resistor, or by connecting the secondary winding of a transformer to the rotor's excitation winding (EW) and applying an alternating signal to the primary winding of the transformer.

6. The method according to any of the preceding claims, wherein Determining whether the detected sound exhibits resonant behavior (RV) within its frequency band (FB), including frequency dependence characteristic of bearing damage, This is achieved by determining whether the intensity (ST) of the detected sound in the frequency band (FB) is higher than a predetermined threshold, or higher than the intensity (ST) of the detected sound in the adjacent frequency band (X), or whether the amplitude of the derivative of the sound intensity (ST) as a function of frequency in the frequency band (FB) that is characteristic of the vibration of a single metal lamination is higher than a threshold.

7. The method according to any of the preceding claims, wherein It also determines whether the detected sound is located in a frequency band (LS) characteristic of bearing damage, or whether the detected sound exhibits a frequency dependence characteristic of bearing damage.

8. The method according to any of the preceding claims, wherein The steps of introducing structural sound transmission and detecting sound are performed on motors installed in the vehicle or mechanically coupled to other components of the vehicle drive or vehicle output, or when their housings are not removed, or when gears or transmission gears are mounted on their shafts.

9. The method according to any of the preceding claims, wherein The characteristic frequency band (FB) for the vibration of a single metal lamination (P) extends from the lower cutoff frequency to the upper cutoff frequency, with the lower cutoff frequency not greater than 3000 Hz or 2500 Hz and the upper cutoff frequency not less than 4000 Hz or 4500 Hz.

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