METHOD FOR IDENTIFYING A CHANGE IN THE OPERATING BEHAVIOR OF A CRANKSHAFT DRIVE OF A MOTOR VEHICLE

Abstract

The disclosure relates to a method for identifying a change in the operating behavior of a crankshaft drive of a motor vehicle. In particular, the disclosure relates to a method for identifying error states of a torsional-vibration damper in the crankshaft drive, such as a jamming or slipping of a secondary mass of the torsional-vibration damper. The crankshaft drive comprises a crankshaft, a pulse generator that rotates when the crankshaft is in operation and a fixed sensor device, which generates a rotational speed signal N as a function of the rotational speed of the pulse generator. The method comprises the following steps: detecting a current rotational speed signal N.sub.akt of the sensor device during operation of the crankshaft drive; filtering the current rotational speed signal N.sub.akt using a bandpass filter that has at least one first passband range D1 comprising a first center frequency f1; comparing the filtered current rotational speed signal N.sub.akt with a reference signal N.sub.ref stored in a memory; and identifying a change in the operating behavior of the crankshaft drive on the basis of the comparison of the filtered current rotational speed signal N.sub.akt with the reference signal N.sub.ref. The disclosure further relates to a vehicle, such as a commercial vehicle, having a control device which is configured to perform a method of this kind.

Claims

1. A method for detecting a change in an operating behavior of a crankshaft drive of a motor vehicle, wherein the crankshaft drive includes a crankshaft, a pulse generator rotating during operation of the crankshaft, and a fixed sensor unit, which generates a rotational speed signal N dependent on a rotational speed of the pulse generator, the method comprising: detecting a current rotational speed signal N.sub.akt of the fixed sensor unit during the operation of the crankshaft drive; filtering the current rotational speed signal N.sub.akt with a bandpass filter, which has a first passband range D.sub.1 comprising a first center frequency f.sub.1; comparing the filtered current rotational speed signal N.sub.akt with a reference signal N.sub.ref stored in a memory; and detecting the change in the operating behavior of the crankshaft drive based on the comparison of the filtered current rotational speed signal N.sub.akt with the reference signal N.sub.ref.

2. The method as claimed in claim 1, wherein detecting the change in the operating behavior of the crankshaft drive includes detecting a fault condition of a torsional vibration damper located in the crankshaft drive.

3. The method as claimed in claim 1, wherein the first center frequency f.sub.1 is a frequency at which resonance effects occur in the crankshaft if a fault condition of the crankshaft drive is present.

4. The method as claimed in claim 1, wherein, in order to establish the first center frequency f.sub.1 of the bandpass filter, the method further comprises: simulating or measuring resonance behavior of an intact crankshaft drive for multiple excitation frequencies; for at least one fault condition of the crankshaft drive, simulating or measuring the resonance behavior of the crankshaft drive with an appropriate fault condition for multiple excitation frequencies; ascertaining an excitation frequency at which the resonance behavior of the intact crankshaft drive and of the crankshaft drive with a fault condition differ; and establishing the first passband range D.sub.1 of the bandpass filter comprising the first center frequency f.sub.1 based on the ascertained excitation frequency.

5. The method as claimed in claim 1, wherein the current rotational speed signal N.sub.akt is detected as a function of the torque and/or the rotational speed of the crankshaft, wherein the reference signal N.sub.ref of the fixed sensor unit stored in the memory is stored as a function of the torque and/or the rotational speed of the crankshaft, and wherein a rotational speed signal value of the filtered current rotational speed signal N.sub.akt, which is detected at a certain torque and/or a certain rotational speed of the crankshaft, is compared to a reference signal value of the corresponding torque and/or of the corresponding rotational speed of the crankshaft.

6. The method as claimed in claim 1, wherein, before the comparing, the filtered current rotational speed signal N.sub.akt is differentiated or integrated, and wherein the comparing and detecting are performed based on the differentiated or integrated filtered current rotational speed signal N.sub.akt.

7. The method as claimed in claim 1, wherein the bandpass filter comprises the first passband range D.sub.1 and a second passband range D.sub.2 which include different first and second center frequencies f.sub.1 and f.sub.2, respectively.

8. The method as claimed in claim 7, further comprising identifying a fault condition of the crankshaft drive based on the comparison of the filtered current rotational speed signal N.sub.akt with the reference signal N.sub.ref on the basis of signal values at the different first and second center frequencies f.sub.1 and f.sub.2.

9. The method as claimed in claim 8, wherein the second center frequency f.sub.2 is greater than the first center frequency f.sub.1, wherein the fault condition of the crankshaft drive is a jamming or a slipping of a secondary mass of a torsional vibration damper located in the crankshaft drive, and wherein the jamming of the secondary mass of the torsional vibration damper located in the crankshaft drive is identified based on an increased signal value at the first center frequency f.sub.1, or the slipping of the secondary mass of the torsional vibration damper located in the crankshaft drive is identified based on an increased signal value at the second center frequency f.sub.2.

10. The method as claimed in claim 1, wherein the first center frequency f.sub.1 of the bandpass filter is within a range between 0 Hz and 400 Hz and/or the bandpass filter has a bandwidth between 1 Hz and 20 Hz.

11. The method as claimed in claim 1, wherein the reference signal N.sub.ref is a signal that is determined in a reference state of the crankshaft drive, and wherein the reference state is: (a) a new state of the crankshaft drive shortly after installation of the crankshaft drive, in the motor vehicle, or a state of the crankshaft drive shortly after maintenance or repair of the crankshaft drive, or (b) a fault condition of the crankshaft drive.

12. The method as claimed in claim 1, wherein comparing the filtered current rotational speed signal N.sub.akt of the fixed sensor unit with the reference signal N.sub.ref stored in the memory includes forming an absolute difference of the two signals ΔN=|N.sub.akt−N.sub.ref| and outputting a message if the absolute difference of the two signals ΔN exceeds and/or falls below a threshold value SW.

13. The method as claimed in claim 1, wherein the method is carried out at regular time intervals and/or at certain kilometer readings of the motor vehicle, and the current rotational speed signal N.sub.akt of the fixed sensor unit are stored, as trend data, in the memory and are output to a user.

14. A method for detecting a change in operating behavior of a crankshaft drive of a motor vehicle, wherein the crankshaft drive includes a crankshaft, a pulse generator rotating during operation of the crankshaft, and a fixed sensor unit, which generates a rotational speed signal N dependent on a rotational speed of the pulse generator, the method comprising: detecting a current rotational speed signal N.sub.akt of the fixed sensor unit during the operation of the crankshaft drive; differentiating or integrating the current rotational speed signal N.sub.akt; filtering the differentiated or integrated current rotational speed signal N.sub.akt with a bandpass filter, which has a first passband range D.sub.1 comprising a first center frequency f.sub.1; comparing the filtered differentiated or integrated current rotational speed signal N.sub.akt with a reference signal N.sub.ref stored in a memory; and detecting the change in an operating behavior of the crankshaft drive based on the comparison of the filtered differentiated or integrated current rotational speed signal N.sub.akt with the reference signal N.sub.ref.

15. A motor vehicle comprising a crankshaft drive, the crankshaft drive including: a crankshaft; a pulse generator rotating during operation of the crankshaft; a fixed sensor unit, which generates a rotational speed signal N depending on a rotational speed of the pulse generator; and a control unit, which is configured to: receive the rotational speed signal N of the fixed sensor unit; filter the rotational speed signal N with a bandpass filter, which has a first passband range D.sub.1 comprising a first center frequency f.sub.1; compare the filtered rotational speed signal N with a reference signal stored in a memory; and detect a change in operating behavior of the crankshaft drive based on the comparison of the filtered rotational speed signal N with the reference signal.

16. The method as claimed in claim 1, wherein the motor vehicle is a commercial vehicle.

17. The method as claimed in claim 2, wherein the fault condition of the torsional vibration damper is a jamming or a slipping of a secondary mass of the torsional vibration damper.

18. The method as claimed in claim 7, wherein the second passband range D.sub.2 is disjoint from the first passband range D.sub.1.

19. The method as claimed in claim 11, wherein the reference state is the new state of the crankshaft drive after installation of the fixed sensor unit and the pulse generator, or wherein the fault condition of the crankshaft drive is a jamming and/or a slipping of a secondary mass in a torsional vibration damper in the crankshaft drive.

20. The method as claimed in claim 13, wherein the current rotational speed signal N.sub.akt of the fixed sensor unit are output to the user upon request.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Further details and advantages of the disclosure are described in the following with reference to the attached drawing, wherein:

[0033] FIG. 1 shows a schematic representation of a crankshaft drive comprising a pulse generator and a sensor unit;

[0034] FIG. 2 shows a method for detecting a change in the operating behavior of a crankshaft drive of a motor vehicle according to an embodiment of the disclosure;

[0035] FIG. 3 shows a method for detecting a change in the operating behavior of a crankshaft drive of a motor vehicle according to a further embodiment of the disclosure;

[0036] FIG. 4 shows an angular velocity signal (=angular acceleration signal), which has been bandpass-filtered around the center frequency f.sub.1=147.5 Hz and differentiated, as a function of the rotational speed for different operating states of the crankshaft drive; and

[0037] FIG. 5 shows an angular velocity signal (=angular acceleration signal), which has been bandpass-filtered around the center frequency f.sub.2=175 Hz and differentiated, as a function of the rotational speed for the same operating states of the crankshaft drive as in FIG. 4.

DETAILED DESCRIPTION

[0038] FIG. 1 schematically shows a crankshaft drive 1, which is known per se, of a motor vehicle, in particular of a commercial vehicle. The crankshaft drive 1 comprises a crankshaft 2, which is part of an internal combustion engine 8 schematically represented only as an engine block 7, and multiple connecting rods 9 and pistons 10 coupled to the crankshaft 2. Moreover, the crankshaft drive 1 as well as the internal combustion engine 8 comprise further components, which are utilized according to the usual practical application, in particular counterweights, crankshaft bearings, seals, cylinders, injection systems, etc., without these being explicitly represented in FIG. 1. The crankshaft 2 is arranged within the engine block 7 and is guided out of both sides. A torsional vibration damper 11 is provided at an end of the crankshaft 2 guided out of the engine block 7. At an end of the crankshaft 2 positioned opposite this end, the crankshaft drive 1 comprises a flywheel 12, for example, a dual-mass flywheel, comprising a pulse generator 3 designed as a transmitter wheel. The transmitter wheel comprises equidistant angle markings on the circumferential side, which can be designed as holes or projections. A sensor unit 4, for example, an inductive sensor unit, which is suitable for generating a rotational speed signal N or an angular velocity signal ω dependent on the rotational speed or the angular velocity of the pulse generator 3 is provided adjacent to the transmitter wheel—radially in the present embodiment, wherein an axial installation position would also be possible. For this purpose, there is a fixed relationship between the spacing of the angle markings on the transmitter wheel and the corresponding revolution of the crankshaft, whereby the rotational speed or the angular velocity of the crankshaft 2 can be ascertained from the detection of the angle markings per unit of time. In the embodiment represented in FIG. 1, the rotational speed signal N or the angular velocity signal ω detected by the sensor unit 4 is made available to a control unit 6. Moreover, the control unit 6 is connected to a memory 5, on which at least one reference signal N.sub.ref or ω.sub.ref of the sensor unit 4 is stored.

[0039] FIG. 2 shows a flowchart of a method for detecting a change in the operating behavior of a crankshaft drive 1 of a motor vehicle according to an embodiment of the disclosure. In step 61, a current rotational speed signal N.sub.akt of the sensor unit 4 is detected during an, in particular stationary, operation of the crankshaft drive 1. The current rotational speed signal N.sub.akt essentially indicates the revolutions of the pulse generator 3 per unit of time, although further oscillations of the rotational speed (harmonics) are usually always also superimposed on this actual rotational speed signal. Since the frequencies of these further oscillation modes are dependent, among other things, on the present state of the crankshaft drive 1, the presence of possible fault conditions in the crankshaft drive 1 can be inferred from the presence of certain oscillation modes in the current rotational speed signal N.sub.akt. For this reason, in step 62, the current rotational speed signal N.sub.akt of the sensor unit 4 is filtered with the aid of a bandpass filter, which has at least one first passband range D.sub.1 comprising a first center frequency f.sub.1. The first passband range may be a narrow-band passband range, in particular with a bandwidth of approximately 15 Hz. In step 63, the filtered current rotational speed signal N.sub.akt of the sensor unit 4 is then compared to a reference signal N.sub.ref of the sensor unit 4 stored in a memory 5. In order to compare the signals, the filtered current rotational speed signal N.sub.akt can additionally be time-averaged. In step 64, a detection of changes in the operating behavior of the crankshaft drive 1 then takes place based on the comparison of the filtered current rotational speed signal N.sub.akt with the reference signal N.sub.ref. If a change was detected, this can be communicated to a user of the motor vehicle via visual and/or acoustic signals and/or a message in the fault memory of the vehicle.

[0040] FIG. 3 shows a flowchart of a method for detecting a change in the operating behavior of a crankshaft drive 1 of a motor vehicle according to a further embodiment of the disclosure. The starting point is the high-frequency detection of a current angular velocity signal ω.sub.akt of the sensor unit 4 in step 71. This can take place in a stationary mode of the crankshaft drive 1 at a fixed rotational speed or in a manner dependent on rotational speed and/or torque. In order to detect not only the basic presence of a fault condition of the crankshaft drive 1, but also, for example, to detect its precise type of the fault condition, in step 72, the current angular velocity signal ω.sub.akt is filtered with the aid of a bandpass filter, which includes a first passband range D.sub.slippen comprising a first center frequency f.sub.slippen, and a second passband range D.sub.klemmen comprising a second center frequency f.sub.klemmen. The two center frequencies were selected in such a way that, in the case of a slipping of a secondary mass of a torsional vibration damper 11 located in the crankshaft drive 1, an increased signal value occurs at the first center frequency f.sub.slippen and, in the case of a jamming of the secondary mass of the torsional vibration damper 11 located in the crankshaft drive 1, an increased signal value occurs at the second center frequency f.sub.klemmen. In step 73, the filtered current angular velocity signal ω.sub.akt is subsequently differentiated, in order to detect dynamic changes of the crankshaft drive 1 in a more sensitive manner. The resultant differentiated filtered current angular velocity signal ω.sub.akt is referred to in the following as the current angular acceleration signal ω′.sub.akt. In step 74, subsequently, the absolute difference is formed from the current angular acceleration signal ω′.sub.akt and the corresponding reference signal ω′.sub.ref stored in the memory 5, wherein the signal components of the two passband ranges D.sub.slippen and D.sub.klemmen are considered separately. Specifically, for this purpose, on the one hand, the absolute difference Δω′.sub.slippen for the signal component is calculated in the range of the first center frequency f.sub.slippen, i.e., Δω′.sub.slippen=|ω′.sub.akt (f.sub.slippen)−ω′.sub.ref (f.sub.slippen)|, on the other hand, the absolute difference Δω′.sub.klemmen for the signal component is calculated in the range of the second center frequency f.sub.klemmen, i.e., Δω′.sub.klemmen=|ω′.sub.akt (f.sub.klemmen)−ω′.sub.ref (f.sub.klemmen)|. Depending on the value of these two variables Δω′.sub.slippen and Δω′.sub.klemmen, different operations are subsequently carried out:

[0041] If it is established in step 751 that Δω′.sub.klemmen is below a first threshold value SW.sub.klemmen, there is no jamming of the secondary mass of the torsional vibration damper 11 located in the crankshaft drive 1, and/or possible changes in the operating behavior of the crankshaft drive 1 with respect to a reference state—in this case, the new state of the crankshaft drive 1—are situated within the tolerance range (SW.sub.klemmen). The current angular acceleration signal value in the range of the second center frequency ω′.sub.akt (f.sub.klemmen) is subsequently stored in the memory 5 as a data point for a trend data analysis (step 761) and can be output to a user upon request. If it is established in step 751, on the other hand, that Δω′.sub.klemmen exceeds the first threshold value SW.sub.klemmen, there is a jamming of the secondary mass of the torsional vibration damper 11 located in the crankshaft drive 1. Whereupon, in step 771, a message is output to the user that “the torsional vibration damper is jammed”.

[0042] In parallel, it is established in step 752 whether Δω′.sub.slippen is below or above a second threshold value SW.sub.slippen. In this case as well, a certain tolerance range is defined via the threshold value SW.sub.slippen, in which the behavior of the secondary mass of the torsional vibration damper 11 is permitted to deviate from its setpoint behavior. Therefore, if Δω′.sub.slippen<SW.sub.slippen, there is no slipping of the secondary mass of the torsional vibration damper 11. Subsequently, the current angular acceleration signal value in the range of the first center frequency ω′.sub.akt (f.sub.slippen) is stored in the memory 5 as a data point for a trend data analysis (step 762) and can be output to a user upon request. If it is established in step 752, on the other hand, that Δω′.sub.slippen exceeds the second threshold value SW.sub.slippen, there is a slipping of the secondary mass of the torsional vibration damper 11 located in the crankshaft drive 1. Whereupon, in step 772, a message is output to the user that “the torsional vibration damper is slipping”. Due to the utilization of a bandpass filter including two passband ranges and the aforementioned decision rules, it is therefore possible not only to detect the basic presence of a fault condition of the crankshaft drive 1, but also to identify the precise type of the fault condition. Due to the utilization of further passband ranges or more complex decision rules, the aforementioned embodiment can also be expanded with further types of fault conditions.

[0043] FIG. 4 shows, by way of example, a bandpass-filtered (first passband range D.sub.1=140-155Hz, center frequency f.sub.1=147 Hz) and differentiated angular velocity signal (=angular acceleration signal), which was measured as a function of the rotational speed for different operating states of the torsional vibration damper (TDS) 11 in the crankshaft drive 1. In the diagram at the top, the angular accelerations occurring for an intact torsional vibration damper 11 are represented. Hardly increased angular acceleration signal amplitudes occur in this case; slightly increased signal amplitudes due to resonance effects are apparent only in the rotational speed range around 1450 rpm and 1950 rpm. In the course of the claimed method, such a measurement could be stored in the memory 5, for example, as a reference signal α.sub.ref. The diagram in the center shows the rotational speed-dependent angular acceleration signal in the case of a crankshaft drive 1 including a torsional vibration damper 11, the secondary mass of which is jammed. In comparison with the intact torsional vibration damper 11, the signal amplitudes are now increased across the entire rotational speed range, wherein considerable resonance effects occur, for example, in the rotational speed range around 1000 rpm, 1500 rpm, and 2000 rpm. Regardless of whether a rotational speed-dependent comparison takes place or not, a fault condition of the crankshaft drive 1 can be reliably detected with the claimed method due to the signal amplitudes, which are increased overall as compared to the intact torsional vibration damper 11. The same also applies for the case of a torsional vibration damper 11 including a slipping secondary mass, which is represented in the lower diagram. In this case as well, increased angular acceleration signal amplitudes are present across the entire rotational speed range as compared to the intact case. Due to the different resonance behavior as compared to the case of the jammed secondary mass, a distinction can also be made between the two fault conditions (jamming, slipping), however, for example, on the basis of the signal amplitude at 1000 rpm. The possibility for making a distinction becomes even more apparent if another frequency range, represented in FIG. 5, is considered.

[0044] FIG. 5 also shows a bandpass-filtered and differentiated angular velocity signal (=angular acceleration signal) as a function of the rotational speed for different operating states of the torsional vibration damper 11. However, in this case, the signals were filtered with the aid of the bandpass filter in a frequency range of D.sub.2=160 Hz to 190 Hz (center frequency f.sub.2=174 Hz). The uppermost diagram shows the angular accelerations occurring for an intact torsional vibration damper 11, wherein, similarly to the case in FIG. 4, hardly any increased signal amplitudes are apparent across the entire rotational speed range. The same also applies for the case of a torsional vibration damper 11, the secondary mass of which is jammed, represented in the diagram in the center. With respect to the passband range D.sub.2=160 Hz to 190 Hz selected here, therefore, no greatly changed behavior of the angular acceleration signal is detectable, despite the presence of a fault condition, which is a jammed secondary mass in this case. Consequently, this frequency range alone, i.e., within the meaning of a first passband range, would be unsuitable for monitoring the state of the crankshaft drive 1, in order to detect the fault condition of the jamming of the secondary mass. In this frequency range, however, a jamming of the secondary mass can be clearly distinguished from a slipping of the secondary mass. As represented in the lower diagram in FIG. 5, in the presence of a slipping secondary mass, considerable resonances and, therefore, increased signal amplitudes occur, primarily in the rotational speed range around 1800 rpm. Due to these considerably different signal characteristics, the two fault conditions (jamming, slipping) in this frequency range of D.sub.2=160 Hz to 190 Hz can be unambiguously distinguished, which is why this frequency range would be suitable, for example, as a second passband range of the bandpass filter.

[0045] Although exemplary embodiments have been described, it is apparent to a person skilled in the art that various changes can be carried out and equivalents can be utilized as a substitute, without departing from the scope of the disclosure. Consequently, the disclosure is not to be limited to the described exemplary embodiments, but rather is to encompass all exemplary embodiments that fall within the scope of protection.

LIST OF REFERENCE NUMBERS

[0046] 1 crankshaft drive [0047] 2 crankshaft [0048] 3 pulse generator [0049] 4 sensor unit [0050] 5 memory [0051] 6 control unit [0052] 7 engine block [0053] 8 internal combustion engine [0054] 9 connecting rod [0055] 10 piston [0056] 11 torsional vibration damper [0057] 12 flywheel