Method and device for imbalance detection using a sensor cluster

Abstract

The present invention relates to a method for imbalance detection in a motor vehicle, in which a passive, semi-active, or active suspension is arranged in the motor vehicle, in which a sensor signal (311) is continuously transformed into an FT frequency profile (313) by means of a Fourier transform (312) during driving operation, in which the presence of a wheel imbalance is identified by the occurrence of a frequency anomaly in the FT frequency profile beyond a body natural frequency and / or a respective wheel natural frequency and proportional to a current driving speed (321), in which, in the case of identification (342) of the wheel imbalance, an error message is stored in the control unit if an anomaly threshold is exceeded and a critical danger threshold of the frequency anomaly is simultaneously undershot.However, if a critical hazard threshold is exceeded, the driver is prompted to visit a workshop, and in the case of semi-active suspension, the valve current is predictively adjusted according to an expected imbalance, or in the case of active suspension, the valve current is predictively and proactively adjusted according to the expected imbalance. Furthermore, a device is presented.

Description

[0001] The present invention relates to a method for imbalance detection using a sensor cluster, wherein the sensor cluster comprises wheel acceleration sensors, body acceleration sensors and / or a central inertial measurement unit. Furthermore, a device with which the method can be implemented is presented.

[0002] Modern chassis systems utilize active control systems. These systems employ sensor clusters that continuously monitor the movements and accelerations of the wheels and body during driving, such as wheel acceleration sensors, level sensors, body acceleration sensors, and inertial measurement units (IMUs).

[0003] German patent application DE 38 17 809 A1 describes a device for monitoring the vibrations of the wheel systems of motor vehicles while driving. At least one acceleration sensor is arranged as a vibration transducer in the area of ​​the bearing and / or suspension of each vehicle wheel. An evaluation circuit processes the signals from the individual vibration transducers separately. A display unit is connected downstream of the evaluation circuit, providing a display for each wheel system and an error indicator for each monitored function, such as wheel balance, shock absorber, tire pressure, and tire geometry.

[0004] German patent application DE 10 2017 001 119 A1 discloses a noise reduction system for vehicles, consisting of four sensor units. Two sensor units each detect vertical wheel acceleration and / or axle vibrations to identify road conditions or wheel imbalances. Another sensor unit detects the drive speed and the resulting drive vibrations. A fourth sensor unit, equipped with a microphone, detects noise inside the vehicle. This information is sent to an evaluation and control unit, which checks whether the applied force has sufficiently reduced the disturbing vibrations and noise in the vehicle interior.

[0005] The German patent application DE 10 2014 107 765 A1 discusses a method for the automatic or semi-automatic adjustment of a vehicle's suspension. The vehicle assesses the road conditions using its sensors, which include at least one wheel acceleration sensor connected to the suspension for detecting the acceleration of each wheel. This detected road condition is transmitted to a central server. Another vehicle can query the road conditions from this server and recommend a suspension adjustment based on the queried road conditions.

[0006] German patent DE 40 14876 A1 describes a method for determining and / or monitoring the condition of a tire with regard to tire pressure and / or a shock absorber with regard to shock absorber defects. For this purpose, stochastically excited vibrations are introduced into the chassis and measured at components of the wheel suspension relative to the body.

[0007] DE 60 037 097 T2 discloses a monitoring system for vehicle conditions that affect a vehicle tire, such as tread wear. This system scans the radial and / or lateral acceleration of the tire to determine its resonant frequency and compare it to a stored frequency. The tread wear is then inferred from this comparison.

[0008] DE 11 2017 003 063 T5 relates to a wheel vibration control system for a vehicle, whereby, if a vibration value is exceeded, an adaptive suspension damper is prompted to reduce the wheel vibration.

[0009] Against this background, an object of the present invention is to provide a method for detecting wheel imbalance during driving. The extent of the wheel imbalance is to be assessed and a corresponding response is to be taken. Depending on the available chassis control system, the wheel imbalance is to be compensated. Furthermore, a device with which the method can be implemented is to be presented.

[0010] To solve the aforementioned problem, a method for imbalance detection in a motor vehicle is proposed, in which a sensor cluster and a passive, semi-active, or active suspension system are arranged within the vehicle. The sensor cluster comprises several wheel acceleration sensors, each arranged on a wheel carrier, and / or several body acceleration sensors, each arranged at a contact point between the wheel carrier and the vehicle body, and / or a centrally located inertial measurement unit. In the case of a semi-active or active suspension system, each wheel carrier is equipped with at least one damper controlled by a valve current. During operation, a sensor signal from the sensor cluster is continuously transformed into an FT frequency response using Fourier transform (FT).The presence of at least one wheel imbalance is identified by the occurrence of a frequency anomaly in the FT frequency response that exceeds a body natural frequency and / or a respective wheel natural frequency and is proportional to the current driving speed. If at least one wheel imbalance is identified, the following steps are performed: • If a frequency anomaly threshold is exceeded and a critical danger threshold is simultaneously undercut, an error message is stored in the control unit, whereby the error message, which is accompanied by an instruction to balance the affected wheel, is read out during regular maintenance in a workshop. • If the critical danger threshold of the frequency anomaly is exceeded, a message to the driver requesting a workshop is displayed on a vehicle display. • In the case of semi-active suspension, the valve current to the respective wheel where at least one wheel imbalance is identified is predictively adjusted according to an expected imbalance, thereby reducing the influence on the vehicle structure. • In the case of active suspension, the valve current to the respective wheel on which at least one wheel imbalance is identified is predictively and proactively adjusted according to the expected imbalance, thereby weakening or neutralizing any influence on the vehicle structure by means of destructive interference.

[0011] According to the invention, in a semi-active or active suspension system, the valve current is regulated to reduce wheel imbalance. This process can generally be applied to other system designs and is not limited to a wheel carrier with at least one damper.

[0012] The Fourier transform is performed numerically, for example quickly and efficiently using the Fast Fourier Transform.

[0013] The imbalance frequency f, based on the current driving speed v, achse This results in a dynamic wheel radius r. axis=v2πr.

[0014] For example, during operation up to 240 km / h and with a dynamic wheel radius r = 0.3 m, imbalance frequencies between 1 Hz and 35 Hz result, and, for example, at v = 100 km / h approximately f achse = 15 Hz.

[0015] The specified amplitude thresholds, in particular the detection threshold or the critical hazard threshold, can be defined, for example, by a respective proportion of an amplitude or acceleration value at the imbalance frequency, e.g., 10% with respect to the detection threshold or 150% with respect to the critical hazard threshold.

[0016] A typical natural frequency for the assembly is in the range of 1 to 2 Hz, while a typical natural frequency for the wheel is in the range of 10 to 15 Hz.

[0017] Significantly elevated areas are visible in the FT signal at the respective natural frequencies. Such a frequency anomaly is also visible in the case of wheel imbalance and manifests itself in the aforementioned frequency range (1 to 35 Hz) as a region in the FT signal that increases with vehicle speed, although this region can also decrease again with further increases in vehicle speed.

[0018] In one embodiment of the method according to the invention, a spring-damper system is arranged on the respective wheel carrier.

[0019] According to the invention, the occurrence of a frequency anomaly is determined by comparing the current FT frequency profile with a frequency profile stored in a characteristic map for the respective driving speed. The characteristic map was defined during previously conducted test drives in which no imbalance was present.

[0020] In a further embodiment of the method according to the invention, the characteristic map is formed over speed ranges and frequency ranges. Thus, for given tire parameters (wheel radius, tire inflation pressure), the characteristic map can contain, depending on the speed, only those frequency ranges that lie outside the body's natural frequency and / or the wheel's natural frequency, so that an investigation for frequency anomalies can be carried out directly in these ranges.

[0021] In a further embodiment of the method according to the invention, a maximum driving speed is limited when an amplitude limit (or an acceleration value) of the frequency abnormality is exceeded.

[0022] Furthermore, a device is claimed, wherein the device comprises a motor vehicle with a passive, semi-active, or active suspension, a control unit, and a sensor cluster. The sensor cluster is formed by several wheel acceleration sensors, each arranged on a wheel located on a respective wheel carrier, and / or several body acceleration sensors, each arranged at a respective contact point between the wheel carrier and a vehicle body, and / or a centrally arranged inertial measurement unit. In the case of a semi-active or active suspension, the respective wheel carrier has at least one damper, which is designed to be controlled by a valve current. The control unit is configured to • to continuously transform a sensor signal from the sensor cluster into an FT frequency profile using Fourier transformation during driving operation, • to identify the presence of at least one wheel imbalance by detecting a frequency anomaly in the FT frequency profile that is beyond a body natural frequency and / or a respective wheel natural frequency and proportional to a current driving speed, and in the event of the identification of at least one wheel imbalance • If a frequency anomaly threshold is exceeded and a critical hazard threshold is simultaneously not reached, an error message containing instructions for balancing the affected wheel is stored in the control unit, and the error message is read out during regular maintenance in a workshop. • if the specified amplitude threshold of the frequency anomaly is exceeded, a request to visit a workshop is displayed to the driver on a vehicle display, • In the case of semi-active suspension, the valve current to the respective wheel on which at least one wheel imbalance is identified is predictively adjusted according to an expected imbalance, thereby reducing the influence on the vehicle structure, • In the case of active suspension, the valve current to the respective wheel on which at least one wheel imbalance is identified is adjusted predictively and proactively according to the expected imbalance, thereby weakening or neutralizing any influence on the vehicle structure by means of destructive interference.

[0023] In one embodiment of the device according to the invention, a spring-damper system is arranged on the respective wheel carrier.

[0024] According to the invention, the control unit is further configured to detect the occurrence of a frequency anomaly by comparing the current FT frequency profile with a frequency profile stored in a characteristic map for the respective driving speed. The characteristic map is previously defined by test drives carried out without any existing imbalance.

[0025] In a further embodiment of the device according to the invention, the characteristic map is formed over speed ranges and frequency ranges.

[0026] In a further embodiment of the device according to the invention, the control unit is further configured to limit a maximum driving speed when an amplitude limit of the frequency anomaly is exceeded.

[0027] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawing. Fig. Figure 1 schematically shows a system view of a motor vehicle in an embodiment of the method according to the invention. Fig. Figure 2 shows a frequency spectrum for the setup acceleration sensor signal in a further embodiment of the method according to the invention. Fig. Figure 3 shows a flowchart for a control unit in a further embodiment of the method according to the invention.

[0028] In Fig. Figure 1 schematically shows a system view 100 of a motor vehicle 101 in an embodiment of the method according to the invention. The motor vehicle 101 has a semi-active or an active suspension. A wheel acceleration sensor 111, 121, 131, 141 is arranged at each wheel 110, 120, 130, 140. A body acceleration sensor 113, 123, 133, 143 is also arranged at each contact point of a respective spring-damper system s 112, 122, 132, 142 with the vehicle body. During driving, sensor signals from the wheel acceleration sensors 111, 121, 131, 141 and the body acceleration sensors 113, 123, 133, 143 are continuously transmitted to a control unit 102. The control unit 102 uses Fast Fourier Transform to calculate an FT frequency profile assigned to each wheel 110, 120, 130, 140 from the sensor signals, based on which a wheel imbalance is detected.

[0029] In Fig. Figure 2 shows a frequency spectrum 200 for the sensor signal in a further embodiment of the method according to the invention. A frequency value 201 in Hertz is plotted on an x-axis, while an acceleration value 202 in m / s² is plotted on a y-axis. 2 is plotted. During driving operation without imbalance, the FT frequency curve 220 shows a single extremum at a wheel / axle natural frequency 203. If an imbalance is present, the FT frequency curve 210 shows, in addition to the extremum at the wheel / axle natural frequency 203, a frequency anomaly 211, which can be calculated from a driving speed and a tire radius using Eq. (1).

[0030] In Fig. 3 A flowchart 300 for the control unit (reference number 102 in Fig. 1) shown in a further embodiment of the method according to the invention. For example, a wheel acceleration sensor (reference numbers 111, 121, 131, 141 in Fig. 1) or a body acceleration sensor (reference numbers 113, 123, 133, 143 in Fig.1) The transmitted sensor signal 311 is converted into an FT frequency profile 313 using a Fast Fourier Transform 312 and fed to a calibration 330. Simultaneously, a rotational speed is determined from the current vehicle speed 321 and wheel-specific parameters 322, such as tire dimensions and tire inflation pressure, and converted into a current rotational frequency or wheel speed 323, which is also fed to the calibration 330. Areas of the current FT frequency profile are examined for frequency anomalies, such as extrema, when compared to regularly existing natural frequencies 340. If the detected frequency matches a regularly existing natural frequency, no action is taken 341. However, if the frequency maximum is far from regular natural frequencies, an action is taken 342, such as incrementing a trigger counter or directly identifying an imbalance.

Claims

[1] Method for imbalance detection in a motor vehicle, wherein a sensor cluster and a passive, semi-active, or active suspension are arranged in the motor vehicle (101), wherein the sensor cluster is formed by several wheel acceleration sensors (111, 121, 131, 141), each of which is arranged on a wheel (110, 120, 130, 140) located on a respective wheel carrier, and / or several body acceleration sensors (113, 123, 133, 143), each of which is arranged at a respective contact point between a wheel carrier and a vehicle body, and / or a centrally arranged inertial measurement unit, wherein, in the case of a semi-active or active suspension, the respective wheel carrier is formed with at least one damper which is controlled by a valve current,in which, during continuous operation, a sensor signal (311) of the sensor cluster is transformed by means of a Fourier transform (312) into an FT frequency profile (313), in which the presence of at least one wheel imbalance is identified by the occurrence of a frequency anomaly (211) in the FT frequency profile (313) beyond a body natural frequency and / or a respective wheel natural frequency and proportional to a current driving speed (321), in which, in the case of the identification (342) of the at least one wheel imbalance, • If an anomaly threshold is exceeded and a critical hazard threshold of the frequency anomaly (211) is simultaneously undershot, an error message is stored in the control unit (102), whereby the error message, which is accompanied by an instruction to balance the affected wheel (110, 120, 130, 140), is read out during regular maintenance in a workshop, • if the critical danger threshold of the frequency anomaly (211) is exceeded, a vehicle driver is shown a request to visit a workshop on a vehicle display, • In the case of the semi-active suspension, the valve current to the respective wheel (110, 120, 130, 140) on which at least one wheel imbalance is identified is predictively adjusted according to an expected imbalance, thereby reducing the influence on the vehicle structure, • In the case of active suspension, the valve current to the respective wheel (110, 120, 130, 140) on which at least one wheel imbalance is identified is predictively and proactively adjusted according to the expected imbalance, thereby weakening or neutralizing any influence on the vehicle structure by means of destructive interference. characterized by, that the occurrence of a frequency anomaly (211) is determined by comparing the current FT frequency profile (313) with a frequency profile stored in a map for the respective driving speed (321), whereby the map is previously determined during test drives which are carried out without any existing imbalance. [2] Method according to claim 1, wherein a spring-damper system (112, 122, 132, 142) is arranged on the respective wheel carrier. [3] Method according to one of the preceding claims, wherein the characteristic map is formed over speed ranges and frequency ranges. [4] Method according to one of the preceding claims, wherein a maximum driving speed (321) is limited when an amplitude limit of the frequency abnormality (211) is exceeded. [5] Device comprising a motor vehicle (101) with a passive or semi-active or active suspension, a control unit and a sensor cluster, wherein the sensor cluster is formed by several wheel acceleration sensors (111, 121, 131, 141), each of which is arranged on a wheel (110, 120, 130, 140) located on a respective wheel carrier, and / or several body acceleration sensors (113, 123, 133, 143), each of which is arranged at a respective contact point between a wheel carrier and a vehicle body, and / or a centrally arranged inertial measurement unit, wherein in the case of a semi-active or an active suspension the respective wheel carrier has at least one damper and the damper is designed to be controlled by a valve current, wherein the control unit (102) is configured to • to continuously transform a sensor signal (311) of the sensor cluster into an FT frequency profile (313) using Fourier transformation (312) during driving operation, • to identify the presence of at least one wheel imbalance by detecting a frequency anomaly (211) in the FT frequency profile (313) beyond a body natural frequency and / or a respective wheel natural frequency and proportional to a current driving speed (321), and in the case of identification (342) of the at least one wheel imbalance • if an anomaly threshold is exceeded and a critical hazard threshold of the frequency anomaly (211) is simultaneously undershot, an error message, which is provided with an instruction to balance the affected wheel (110, 120, 130, 140), is to be stored in the control unit (102), whereby the error message is read out during regular maintenance in a workshop, • if the specified amplitude threshold of the frequency anomaly (211) is exceeded, a request to visit a workshop is displayed to a driver on a vehicle display, • In the case of the semi-active suspension, the valve current to the respective wheel (110, 120, 130, 140) on which at least one wheel imbalance is identified is predictively adjusted according to an expected imbalance, thereby reducing the influence on the vehicle structure, • In the case of active suspension, to predictively and proactively adjust the valve current to the respective wheel (110, 120, 130, 140) on which at least one wheel imbalance is identified, according to the expected imbalance, thereby weakening or neutralizing any influence on the vehicle structure by means of destructive interference, characterized by, that the control unit is configured to determine the occurrence of a frequency anomaly (211) by comparing the current FT frequency profile (313) with a frequency profile stored in a map for the respective driving speed (321), the map being previously determined by test drives carried out without any existing imbalance. [6] Device according to claim 5, wherein a spring-damper system (112, 122, 132, 142) is arranged on the respective wheel carrier. [7] Device according to one of claims 5 or 6, wherein the characteristic map is formed over speed ranges and frequency ranges. [8] Device according to one of claims 5 to 7, wherein the control unit is configured to limit a maximum driving speed (321) when an amplitude limit of the frequency abnormality (211) is exceeded.

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