Noise and vibration sensing

A noise and vibration sensing system is provided. The sensing system includes an acceleration sensor arrangement and a summer module. The acceleration sensor arrangement includes at least one acceleration sensor and is configured to generate at least two sense signals representative of acceleration that acts on the acceleration sensor arrangement. The at least two sense signals includes dynamic ranges that are ratios between maximum amplitudes of the at least two sense signals and noise created by the acceleration sensor arrangement. The summer module is configured to sum up the at least two sense signals to provide a sum signal that includes noise and a dynamic range which is a ratio between a maximum amplitude of the sum signal and the noise included in the sum signal. The dynamic range of the sum signal is greater than the arithmetic mean of the dynamic ranges of the at least two sense signals.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to EP application Serial No. 15185236.5 filed Sep. 15, 2015, the disclosure of which is hereby incorporated in its entirety by reference herein.

TECHNICAL FIELD

The disclosure relates to noise and vibration sensing systems, particularly for use in active road noise control systems, active road noise control systems and noise and vibration sensing methods.

BACKGROUND

Land based vehicles, when driven on roads and other surfaces, generate low frequency noise known as road noise. Even in modern vehicles, cabin occupants may be exposed to road noise that is transmitted through the structure, e.g., tires-suspension-body-cabin path, and through airborne paths, e.g., tires-body-cabin path, to the cabin. It is desirable to reduce the road noise experienced by cabin occupants. Active Noise, vibration, and harshness (NVH) control technologies, also known as active road noise control (RNC) systems, can be used to reduce these noise components without modifying the vehicle's structure as in active vibration technologies. However, active sound technologies for road noise cancellation may require very specific noise and vibration (N&V) sensor arrangements throughout the vehicle structure in order to observe road noise related noise and vibration signals.

SUMMARY

An exemplary noise and vibration sensing system includes an acceleration sensor arrangement including at least one acceleration sensor and is configured to generate at least two sense signals representative of the acceleration that acts on the acceleration sensor arrangement, wherein the sense signals have dynamic ranges which are the ratios between maximum amplitudes of the sense signals and noise created by the acceleration sensor arrangement. The noise and vibration sensing system further includes a summer module configured to sum up the at least two sense signals to provide a sum signal. The sum signal includes noise created by the acceleration sensor arrangement and the sum signal has a dynamic range which is the ratio between a maximum amplitude of the sum signal and the noise included in the sum signal. The dynamic range of the sum signal is greater than an arithmetic mean of the dynamic ranges of the sense signals.

An exemplary road noise control system includes a noise and vibration sensing system, a road noise control module and at least one loudspeaker.

An exemplary noise and vibration sensing method includes generating, with an acceleration sensor arrangement, at least two sense signals representative of at least one of accelerations, motions and vibrations that act on the acceleration sensor arrangement. The sense signals have dynamic ranges that are ratios between maximum amplitudes of the sense signals and noise created by the acceleration sensor arrangement. The method further includes summing up the at least two sense signals to provide a sum signal. The sum signal includes noise created by the acceleration sensor arrangement. The sum signal has a dynamic range which is the ratio between a maximum amplitude of the sum signal and the noise included in the sum signal. The dynamic range of the sum signal is greater than an arithmetic mean of the dynamic ranges of the sense signals.

DETAILED DESCRIPTION

Noise and vibration sensors provide reference inputs to active RNC systems, for example, multichannel feedforward active road noise control systems, as a basis for generating the anti-noise that reduces or cancels road noise. Noise and vibration sensors may include acceleration sensors such as accelerometers, force gauges, load cells, etc. For example, an accelerometer is a device that measures proper acceleration. Proper acceleration is not the same as coordinate acceleration, which is the rate of change of velocity. Single- and multi-axis models of accelerometers are available for detecting magnitude and direction of the proper acceleration, and can be used to sense orientation, coordinate acceleration, motion, vibration, and shock.

Airborne and structure-borne noise sources are monitored by the noise and vibration sensors in order to provide the highest possible road noise reduction (cancellation) performance between 0 Hz and 1 kHz. For example, acceleration sensors used as input noise and vibration sensors may be disposed across the vehicle to monitor the structural behavior of the suspension and other axle components for global RNC. Above a frequency range that stretches from 0 Hz to approximately 500 Hz, acoustic sensors that measure the airborne road noise may be used as reference control inputs. Furthermore, two microphones may be placed in the headrest in close proximity of the passenger's ears to provide an error signal or error signals in case of binaural reduction or cancellation. The feedforward filters are tuned or adapted to achieve maximum noise reduction or noise cancellation at both ears.

A simple single-channel feedforward active RNC system may be constructed as shown inFIG. 1. Vibrations that originate from a wheel101moving on a road surface are detected by a suspension acceleration sensor102which is mechanically coupled with a suspension device103of an automotive vehicle104and which outputs a noise and vibration signal x(n) that represents the detected vibrations and, thus, correlates with the road noise audible within the cabin. At the same time, an error signal e(n) representing noise present in the cabin of the vehicle104is detected by a microphone105arranged within the cabin in a headrest106of a seat (e.g., the driver's seat). The road noise originating from the wheel101is mechanically transferred to the microphone105according to a transfer characteristic P(z).

A transfer characteristic W(z) of a controllable filter108is controlled by an adaptive filter controller109which may operate according to a known least mean square (LMS) algorithm based on the error signal e(n) and on the road noise signal x(n) filtered with a transfer characteristic F′(z) by a filter110, wherein W(z)=−P(z)/F(z). F′(z)=F(z) and F(z) represents the transfer function between a loudspeaker and the microphone105. A signal y(n) having a waveform inverse in phase to that of the road noise audible within the cabin is generated by an adaptive filter formed by controllable filter108and filter controller109, based on the thus identified transfer characteristic W(z) and the noise and vibration signal x(n). From signal y(n) a waveform inverse in phase to that of the road noise audible within the cabin is then generated by the loudspeaker111, which may be arranged in the cabin, to thereby reduce the road noise within the cabin. The exemplary system described above employs a straightforward single-channel feedforward filtered-x LMS control structure107for the sake of simplicity, but other control structures, for example, multi-channel structures with a multiplicity of additional channels, a multiplicity of additional noise sensors112, a multiplicity of additional microphones113, and a multiplicity of additional loudspeakers114, may be applied as well.

FIG. 2shows an active road noise control system200which is a multi-channel type active road noise control system capable of suppressing noise from a plurality of noise and vibration sources. The active road noise control system200comprises a multiplicity n of noise and vibration sensors201, a multiplicity1of loudspeakers202, a multiplicity m of microphones203, and an adaptive control circuit204which operates to minimize the error between noise from the noise and vibration sources (primary noise) and cancelling noise (secondary noise). The adaptive control circuit204may include a number of control circuits provided for each of the loudspeakers202, which create cancelling signals for cancelling noise from corresponding noise and vibration sources.

In conventional active RNC systems, the frequency range of noise to be reduced is limited to a low frequency range. That is, the conventional systems are not intended to reduce noise over its entire frequency range. Further, adaptive digital filters used in these systems have such characteristics as to be able to reduce only low frequency noise components, although processing noise over a wide frequency range is desired. In the active RNC systems disclosed herein, careful arrangement of the sensors allows for more sensitivity and a broader operating frequency range.

RNC systems as described above may exhibit a limited noise reduction capability when the acceleration sensors' dynamic ranges, i.e., the ratios between maximum amplitudes of signals output by the sensors and noise that originates from the sensors and that is contained in the signals output by the sensors (i.e., signal-to-noise ratio), are not sufficient, as is the case with conventional acceleration sensors used for suspension set-up and vibration control. However, it is rather costly to provide sensors with better dynamic ranges. In the following, simple ways are described that allow for using acceleration sensors with minor dynamic ranges in active road noise systems.

Referring toFIG. 3, a multiplicity of (i.e., at least two) acceleration sensors, which is in the present example four (identical) acceleration sensors301-304, are connected to a summer module305which sums up sense signals306-309provided by the acceleration sensors301-304and outputs a sum signal310representative of the sum of sense signals306-309. The acceleration sensors301-304may be unidirectional sensors, i.e., sensors that have their maximum sensitivity only in one single direction such as a direction x of a given coordinate system x-y-z (referred to herein as pointing in this direction). In contrast, multi-directional sensors have their maximum sensitivities in at least two directions but not in all directions. For example, a two-directional sensor has two sensitivity maxima in two different (perpendicular) directions. Omni-directional sensors have approximately constant sensitivities independent of the direction. In the example shown inFIG. 3, the acceleration sensors301-304may form a sensor arrangement in which all sensors are unidirectional and point in the same direction x or may, alternatively, point in different directions.

FIG. 4shows a three-directional acceleration sensor401with three sensitivity maxima in three different (perpendicular) directions x, y and z. The acceleration sensor401generates three sense signals402-404which are summed up by a summing module405to provide a sum signal406. Instead of the three-directional acceleration sensor401three unidirectional sensors, each pointing in one of the three directions x, y and z, may be used.

Furthermore, an array with a multiplicity of (e.g., four) acceleration sensors501-504, which are arranged in a specific pattern, for example, evenly distributed over a virtual or real sphere's surface and pointing radial (r) outward from the sphere, may be employed as shown inFIG. 5. A summing module505receives sense signals506-509from the acceleration sensors501-504, sums them up and provides a sum signal510representative of the sum of the sense signals506-509.

FIG. 6illustrates two exemplary sense signals601and602, each of which have a harmonic component603,604such as a (pure) sinus signal, and a noise component605,606. The harmonic components603and604may have a power A and the noise may have a power N. When summing up the sense signals601and602, a sum signal607is obtained in which the harmonic components603and604add to a harmonic component608of sum signal607and noise components605and606are combined to provide a noise component609of sum signal607. The power of the noise component609is almost the same as either noise component605or noise component609since the summation of random signals such as noise does not increase the power of the summed noise significantly due to the random amplitudes of the noise components. However, with harmonic signals such as sinus signals, the power of the sum of two identical sinus signals is twice the power that one signal has, so that when summing up mixed signals with harmonic and random components the dynamic range increases. In general, the increase I in dynamic range (or signal-to-noise ratio) can be described as: I[dB]=10 log10N, wherein N is the number of sensors combined.

The summing modules305,405and505may include, in case of digital signal processing, simple digital hardware adders or signal processors that perform respective adding operations, or may include, in case of analog signal processing, analog summing circuits such as the example circuit shown inFIG. 7. In the summing circuit shown inFIG. 7, an operational amplifier701has an inverse input, a non-inverse input and an output. An ohmic resistor702is connected between output and inverse input of operational amplifier701to provide a feedback path. Sense signals703-706from four acceleration sensors (not shown) are supplied via ohmic resistors707-710to the inverse input of operational amplifier701. The non-inverse input of operational amplifier701is connect to ground711and the output of operational amplifier701forms an output712of the analog summing module. Assuming that an output voltage Uoutis provided at output712and that the sense signals703-706provide identical input voltages, namely input voltage Uin, and further assuming that the resistors707-710have the same resistance Rinand resistor702has a resistance Rout, the output voltage Uoutis as follows:

Referring toFIG. 8, an exemplary noise and vibration sensing method may include (801) generating with an acceleration sensor arrangement at least two sense signals representative of the acceleration that acts on the acceleration sensor arrangement, wherein the sense signals have dynamic ranges which are the ratios between maximum amplitudes of the sense signals and noise created by the acceleration sensor arrangement, and (802) summing up the at least two sense signals to provide a sum signal, wherein the sum signal includes noise created by the acceleration sensor arrangement and wherein the sum signal has a dynamic range which is the ratio between a maximum amplitude of the sum signal and the noise included in the sum signal, the dynamic range of the sum signal being greater than the arithmetic mean of the dynamic ranges of the sense signals.

In RNC applications acceleration sensors are used as noise and vibration sensors, delivering the desired reference signals. If those signals exhibit a considerable noise floor, which is noise generated by the sensors themselves in contrast to noise and vibrations to be measured, and thus exhibit a small dynamic range, the whole RNC system is doomed to fail. However, acceleration sensors and acceleration sensor arrangements often output a multiplicity of sense signals. If sensor signals stem from multi-axis sensors or sensor arrangements mounted at almost the same local area and/or having the same orientation (x, y or z axis), these signals may be combined as described above to increase the system's dynamic. Thus, an underperforming RNC system may be enhanced by combining appropriate sense signals of a multiplicity of under-performing sensors. Furthermore, multiple cheap low-performing acceleration sensors may be used instead of a single expensive high-performing acceleration sensor to reduce overall costs, balancing out sensor costs and differences in their performance.

The description of embodiments has been presented for purposes of illustration and description. Suitable modifications and variations to the embodiments may be performed in light of the above description or may be acquired from practicing the methods. For example, unless otherwise noted, one or more of the described methods may be performed by a suitable device and/or combination of devices. The described methods and associated actions may also be performed in various orders in addition to the order described in this application, in parallel, and/or simultaneously. The described systems are exemplary in nature and may include additional elements and/or omit elements.

As used in this application, an element or step recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural of said elements or steps, unless such exclusion is stated. Furthermore, references to “one embodiment” or “one example” of the present disclosure are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. The terms “first,” “second,” and “third,” etc. are used merely as labels, and are not intended to impose numerical requirements or a particular positional order on their objects.