ACTIVE NOISE REDUCTION APPARATUS AND METHOD FOR A VEHICLE

Abstract

 An active noise reduction apparatus (1) for a vehicle comprises a detecting device (11) configured to detect at least one reference signal which is indicative of at least one component of a noise (50) generated at a contact area (41) between a wheel (3) of the vehicle and a track (4) on which the vehicle is travelling, a sound emitting device (13, 13-1, 13-2) for emitting sound waves (60) towards the at least one contact area (41) between the wheel (3) of the vehicle and the track (4) on which the vehicle is travelling, and a control device (12) which is operatively coupled with the detecting device (11) and the sound emitting device (13, 13-1, 13-2). The control device (12) is configured to control the sound emitting device (13, 13-1, 13-2) for emitting sound waves (60) based on the detected at least one reference signal so as to reduce the at least one component of the noise (50) through active noise cancellation by the emitted sound waves (60).

Description

[0001] The present disclosure relates to an active noise reduction apparatus and active noise reduction method for a vehicle.

[0002] Such apparatuses and methods are known in the art for reduction or cancellation of noise of various forms in a vehicle. For example, JP 2005-234203 A discloses a small-sized silencing device capable of eliminating only a target noise sound without causing a silencing wave to scatter. Employed is the constitution of a silencing device which is equipped with a microphone, an electric circuit performing conversion into an electric signal opposite in phase to and equal in amplitude to an electric signal generated by converting a noise sound picked up by the microphone, and a speaker which outputs the electric signal as a sound signal. The silencing device uses a directional speaker as this speaker. Electronic equipment mounted with the silencing device is configured to silence the noise sound by arranging the silencing device where a noise sound outputted from a noise generating source incorporated in a housing can be silenced.

[0003] US 8 706 351 B2 discloses an active noise cancellation apparatus capable of reliably reducing road noise by a technique other than mounting a vibration generator on a floor panel itself or another plate-like interior part itself, while reducing costs and size of the apparatus. A reference signal detector is mounted on a knuckle and the vibration generator is mounted on a wheel housing or a suspension member. An error signal detector detects vibration of the wheel housing or vibration of the suspension member as an error signal, or detects sound in a vehicle interior as an error signal. A controller controls the vibration generator based on the reference signal and the error signal so as to reduce the error signal.

[0004] JP 2003-216163 A provides a noise controller capable of reducing noise from a plurality of noise sources without increasing microphones for detecting the noise to be generated by the noise sources. A data reading part reads pieces of pseudo noise data corresponding to noise source information acquired via an IF (interface) part from a pseudo noise data base based on the noise source information and successively supplies them to a specified adaptive controller. No microphone for detecting the noise to be generated by the noise sources is required to be installed.

[0005] JP 2011-168151 A provides a vehicle-mounted silencer capable of silencing sound that is uncomfortable to an occupant in an electric vehicle, a hybrid vehicle or the like, although, when such a vehicle is traveling with an electric motor, there is no engine sound of a conventional vehicle and only there is a quiet motor sound, but this motor sound generates the uncomfortable sound because of the quietness of the motor sound. This vehicle-mounted silencer mounted to a vehicle comprises a silencing sound output means for outputting sounds to muffle noises in a car generated during travelling of the vehicle, and the noises are silenced by the silencing sounds outputted by the silencing sound output means.

[0006] A typical source of noise generated by a vehicle, such as a car, is noise generated at the contact surface between a tire of a wheel of the vehicle and the road. Such "road noise" can be heard inside and outside the vehicle, and in particular can include noise frequencies dependent on speed of the vehicle which can be heard far away from a motorway, for example. Such noise can hardly be reduced or avoided at the source of the noise, i.e. at the contact surface between tire and road. According to one known solution for reducing road noise, some newly built or refurbished roads are constructed with a special kind of "quiet tarmac" which produces reduced noise between road surface and wheel as compared to conventional roads. However, such solutions are very cost intensive and often less effective.

[0007] It would therefore be beneficial to provide a noise reduction apparatus and method for a vehicle which is capable of effectively reducing road noise at comparatively low cost.

[0008] The invention relates to an active noise reduction apparatus and active noise reduction method for a vehicle according to the independent claims. Embodiments thereof are disclosed in the dependent claims.

[0009] According to an aspect, there is provided an active noise reduction apparatus for a vehicle, comprising a detecting device configured to detect at least one reference signal which is indicative of at least one component of a noise generated at a contact area between a wheel of the vehicle and a track on which the vehicle is travelling, a sound emitting device for emitting sound waves towards the at least one contact area between the wheel of the vehicle and the track on which the vehicle is travelling, and a control device which is operatively coupled with the detecting device and the sound emitting device. The control device is configured to control the sound emitting device for emitting sound waves based on the detected at least one reference signal so as to reduce the at least one component of the noise through active noise cancellation by the emitted sound waves.

[0010] According to another aspect, there is provided an active noise reduction method for a vehicle, comprising detecting at least one reference signal which is indicative of at least one component of a noise generated at a contact area between a wheel of the vehicle and a track on which the vehicle is travelling, and emitting sound waves towards the at least one contact area between the wheel of the vehicle and the track on which the vehicle is travelling based on the detected at least one reference signal so as to reduce the at least one component of the noise through active noise cancellation by the emitted sound waves.

[0011] According to another aspect, there is provided a vehicle comprising an active noise reduction apparatus according to aspects of the invention as described herein.

[0012] For example, the sound emitting device comprises a directed speaker which outputs cancellation sound waves towards the source of the noise (in particular contact surface of wheel and track). At this point the emitted sound waves overlay the noise, so that any road noise can be reduced in accordance with the principle of active noise cancellation (emitting sound waves opposite in phase and approximately equal in amplitude to respective noise frequencies to be reduced or canceled).

[0013] As such, according to aspects of the invention, cancellation sound waves are generated to reduce the noise generated at a contact area between a wheel of the vehicle and a track on which the vehicle is traveling. Preferably, it shall not create additional audible sound. Therefore, the sound waves are directed towards the source of the noise generated at a contact area between wheel and track, such that in other directions from the sound emitting device the emitted sound waves shall not be audible.

[0014] The invention is preferably applicable in an automobile which typically drives on roads, such as a passenger car or freight vehicle (e.g. motor truck). The invention is, in principle, applicable to any type of vehicles having wheels running on a track. In the following, it is also referred simply to "road noise" when referring to noise generated at a contact area between a wheel of the vehicle and a track on which the vehicle is traveling. This shall, however, not imply any restriction as to the type of vehicle and the underground or track on which the vehicle is traveling.

[0015] According to an embodiment, the control device is configured to determine at least one frequency from the detected at least one reference signal, and to control the sound emitting device to emit sound waves having the determined at least one frequency. For example, the control device determines at least one frequency from the detected at least one reference signal which is caused by track surface contact of the wheel and air displacement.

[0016] According to an embodiment, the control device is configured to adjust a phase delay for the determined at least one frequency and to control the sound emitting device to emit sound waves having the determined at least one frequency at the adjusted phase delay.

[0017] According to an embodiment, the control device is configured to determine at least one regular repeating frequency, which is particularly depending on a rotation speed of the wheel, from the detected at least one reference signal.

[0018] According to an embodiment, the control device is configured to determine at least one frequency in a range between 100 and 1000 Hz from the detected at least one reference signal, and to control the sound emitting device to emit sound waves having the determined at least one frequency.

[0019] In a preferred embodiment, the detecting device, the control device, and the sound emitting device are operatively coupled in a closed loop configuration. Particularly, the closed loop configuration is self-calibrating.

[0020] Particularly, the control device is configured to determine in an iterative process at least one frequency from the detected at least one reference signal while the sound emitting device emits sound waves, to adjust a phase delay for the determined at least one frequency, and to control the sound emitting device to emit sound waves having the determined at least one frequency at the adjusted phase delay.

[0021] According to an embodiment, the detecting device comprises a microphone. With using microphone(s) for real noise measurement, the apparatus and method may react on any changes of the road surface or weather conditions.

[0022] According to a further embodiment, the control device is configured to determine at least one exemption frequency from the detected at least one reference signal which is indicative of a characteristic road marking on the track on which the vehicle is travelling. The control device controls the sound emitting device to not emit sound waves having the determined at least one exemption frequency.

[0023] According to an embodiment, the sound emitting device comprises an array of loudspeakers configured to emit directional sound waves, in particular unidirectional sound waves.

[0024] Any aspects and embodiments described herein with respect to the apparatus can equally be employed in the method or as method steps in such method, and vice versa, with the control device configured (by software and/or hardware) appropriately.

[0025] For example, the control device and/or parts of the detecting device and sound emitting device may be implemented in hardware and/or in software. Each one or some of them, particularly the control device, may be, for example, implemented in, or part of, an ECU of the vehicle, or may be a separate component (in hardware and/or software), or may be a distributed system (in hardware and/or software) using one or more processors and/or integrated circuits.

[0026] Aspects of the invention and embodiments will now be described with reference to the following Figures in which

Fig. 1

depicts a schematic diagram illustrating a wheel of a vehicle generating noise at a contact area between the wheel and a track on which the vehicle is travelling,

Fig. 2

depicts another schematic diagram illustrating a wheel of a vehicle running on a track and a part of an active noise reduction apparatus for a vehicle according to an embodiment of the invention,

Fig. 3

shows an active noise reduction apparatus for a vehicle according to an embodiment of the invention,

Fig. 4

shows a flow diagram of an active noise reduction method according to an embodiment of the invention,

Fig. 5

depicts a schematic diagram illustrating an exemplary road with a road marking, which embodiments of the invention take account of.

[0027] Fig. 1 depicts a schematic diagram illustrating a wheel 3 of a vehicle (not expressly shown) which is running on a track 4 during traveling, such as a road. The wheel comprises a tire 31 having a profile on the outer circumference, as is commonly known. As a result of the rotation 32 of the wheel 3 and tire 31, noise 50 is generated at a contact area 41 between the wheel 3 and the road 4. In particular, the noise 50 is caused by rotation of the wheel 3 with the tire profile, which results in air displacement, deformation of wheel and/or tire and road surface contact.

[0028] Aspects and embodiments of the invention will now be described with reference to Figures 2 to 4 which show exemplary embodiments thereof.

[0029] Fig. 3 shows an active noise reduction apparatus 1 for a vehicle according to an embodiment of the invention. It comprises a detecting device 11, which particularly includes a microphone. The detecting device 11, in particular the microphone, detects at least one reference signal which is indicative of at least one component of the noise 50 as described above (step S1 in Fig. 4). For example, the at least one reference signal is one or more acoustic signals detected by the microphone which are indicative of at least one component of the noise 50. The at least one component may be one or more frequencies of sound waves of the noise 50.

[0030] A control device 12 is operatively coupled with the detecting device 11. According to an embodiment, the control device 12 receives the detected reference signal from the microphone and performs a noise measurement, such as a signal analysis of the components (such as of the frequencies) included in the detected reference signal (step S2 in Fig. 4). Such noise measurement may be performed in a noise measurement unit 21 of the control device 12. The control device 12 may then determine at least one frequency which is included in the noise 50 from the detected at least one reference signal. For example, the control device determines at least one frequency having the highest amplitude and/or power within the sound waves of the noise 50. According to a further embodiment, the control device determines at least one regular repeating frequency within the noise 50, which is, for example, depending on a rotation speed of the wheel 3. That is, the rotation of the wheel causes regular repeating noise frequencies which depend on the rotation speed of the wheel, e.g. by air displacement and deformation of the tire which are varying with rotation speed. According to a further embodiment, the control device 12 determines at least one frequency in a range between 100 and 1000 Hz, which often are typical road noise frequencies. The determination of the one or more frequencies may also be performed by the noise measurement unit 21.

[0031] A phase adjustment unit 22 may then adjust a phase delay for the determined at least one frequency determined by the noise measurement unit 21 (step S3 in Fig. 4). For example, a phase delay may be adjusted for one or more frequencies determined by the noise measurement unit 21 such that noise cancellation sound waves 60 emitted with the one or more frequencies are at least roughly opposite in phase to respective sound waves contained in the noise 50 having these frequencies according to the known principles of active noise cancellation.

[0032] In a DSP (digital signal processor) sound generation unit 23, control signals are generated which cause the sound emitting device 13 to emit sound waves 60 having the determined at least one frequency at the adjusted phase delay (steps S4 and S5 in Fig. 4). For example, the sound emitting device 13 comprises loudspeakers 13-1 and/or 13-2 as shown in Fig. 2 for emitting the sound waves 60 towards the at least one contact area 41 between the wheel 3 of the vehicle and the track 4. The loudspeakers 13-1, 13-2 emit sound waves 60 which - as they are roughly opposite in phase - reduce noise at the respective frequency through active noise cancellation. If a vehicle has four wheel, for example four or eight such loudspeakers may be arranged on the vehicle for emitting cancellation sound waves 60 towards the respective contact area 41 between the respective wheel 3 of the vehicle and the track 4.

[0033] Preferably, the loudspeakers 13-1, 13-2 are located on one or both sides of a rotation axis of the wheel 3, e.g. when viewed in driving direction of the vehicle in front of and/or behind the wheel 3, as shown in Fig. 2. As these are the more dominant noise emitting directions, such arrangement can achieve an effective noise reduction. For example, the sound emitting device 13 comprises an array of loudspeakers which emit directional sound waves 60, in particular unidirectional sound waves 60, towards the contact area 41 between the wheel 3 of the vehicle and the track 4. This reduces additional sound wave emission in other directions than the source of the noise.

[0034] As shown in Figures 3 and 4, the detecting device 11, the control device 12, and the sound emitting device 13 are operatively coupled in a closed loop configuration 14 which is self-calibrating.

[0035] Particularly, in an iterative process, the control device 12 determines one or more frequencies from the detected one or more reference signals while the sound emitting device 13 emits sound waves 60 for noise cancellation towards the contact area 41, adjusts a respective phase delay for the determined frequencies, and controls the sound emitting device 13 to emit sound waves 60 having the determined frequencies at the respective adjusted phase delay. Such adjustment may be performed step by step in each respective iteration until a full flat cancellation is achieved.

[0036] Any of the noise measurement unit 21, phase adjustment unit 22 and DSP sound generation unit 23 may be implemented at least partially in software and/or hardware within one or more processor units, such as a microprocessor of an ECU of the vehicle.

[0037] Fig. 5 depicts a schematic diagram illustrating an exemplary road 4 with road markings 42, which embodiments of the invention take account of. In such case, it may not be desirable to reduce noise which is generated by the road markings 42, as they may have a warning effect on the driver, e.g. warn the driver that the vehicle leaves a dedicated lane. For example, such road markings 42 protrude from the road surface in a particular height (e..g. caused by alternating paint thickness) which causes a characteristic noise which the driver recognizes when the wheel 3 rotates along the road markings 42.

[0038] According to an embodiment, the control device 12 determines at least one exemption frequency from the detected one or more reference signals which is indicative of sound or noise caused by such characteristic road marking 42 on the track 4. It then controls the sound emitting device 13 to not emit sound waves 60 having the determined at least one exemption frequency. In other words, the control device 12 determines at least one frequency in the noise 50 which is indicative of a characteristic road marking 42 on the track 4. Such frequency is determined to be an exemption frequency at which no noise cancellation sound waves 60 shall be emitted to keep the warning effect of the noise 50 caused by the road marking 42. Preferably, the system keeps data of typical structures of noise generating road markings (such as alternating paint thickness) and may adjust the noise cancellation accordingly.

[0039] According to aspects of the invention, cancellation sound waves are created to reduce noise caused by the vehicle running on a track, such as road noise. Preferably, it does not create an additional audible sound. To this end, the cancellation sound waves are directed towards the source of road noise, so that in other directions from the sound emitting device nothing shall be audible.

[0040] In typical cases, road noise generated by the tire profile includes regular repeating frequencies depending on the profile which are variable by the rotation speed of the wheel. When emitting the cancellation sound, the system measures the resulting noise by microphone. Then the phase delay may be adjusted step by step for each frequency until preferably a full flat cancellation is achieved. As a result the system becomes self-calibrating.

[0041] In a typical implementation, it will not be possible to reduce the road noise to zero. In most cases, it may achieve a reduction by approximately 50 - 80% for the main frequencies caused by the tire profile (air displacement and road surface contact). Due to the fact that road noise is a mixture of many frequencies, noise frequencies in total may be reduced in a range of 10 - 20%. However, when considering in particular truck tires and the noise caused by them, a strong reduction of the loud humming noise and may be a minor reduction of the remaining noise would be a great improvement. For example, if such humming noise is reduced to the level of a normal car tire, there is already a considerable positive effect.

Claims

1. An active noise reduction apparatus (1) for a vehicle, comprising:

- a detecting device (11) configured to detect at least one reference signal which is indicative of at least one component of a noise (50) generated at a contact area (41) between a wheel (3) of the vehicle and a track (4) on which the vehicle is travelling,

- a sound emitting device (13, 13-1, 13-2) for emitting sound waves (60) towards the at least one contact area (41) between the wheel (3) of the vehicle and the track (4) on which the vehicle is travelling,

- a control device (12) which is operatively coupled with the detecting device (11) and the sound emitting device (13, 13-1, 13-2), wherein the control device (12) is configured to control the sound emitting device (13, 13-1, 13-2) for emitting sound waves (60) based on the detected at least one reference signal so as to reduce the at least one component of the noise (50) through active noise cancellation by the emitted sound waves (60).

2. The active noise reduction apparatus according to claim 1, wherein the control device (12) is configured to determine at least one frequency from the detected at least one reference signal, and is configured to control the sound emitting device (13, 13-1, 13-2) to emit sound waves (60) having the determined at least one frequency.

3. The active noise reduction apparatus according to claim 2, wherein the control device (12) is configured to adjust a phase delay for the determined at least one frequency and to control the sound emitting device (13, 13-1, 13-2) to emit sound waves (60) having the determined at least one frequency at the adjusted phase delay.

4. The active noise reduction apparatus according to one of claims 1 to 3, wherein the control device (12) is configured to determine at least one regular repeating frequency, which is particularly depending on a rotation speed of the wheel (3), from the detected at least one reference signal, wherein the control device (12) is configured to control the sound emitting device (13, 13-1, 13-2) to emit sound waves (60) having the determined at least one frequency.

5. The active noise reduction apparatus according to one of claims 1 to 4, wherein the control device (12) is configured to determine at least one frequency in a range between 100 and 1000 Hz from the detected at least one reference signal, and to control the sound emitting device (13, 13-1, 13-2) to emit sound waves (60) having the determined at least one frequency.

6. The active noise reduction apparatus according to one of claims 1 to 5, wherein the detecting device (11), the control device (12), and the sound emitting device (13, 13-1, 13-2) are operatively coupled in a closed loop configuration (14).

7. The active noise reduction apparatus according to claim 6, wherein the control device (12) is configured to determine in an iterative process at least one frequency from the detected at least one reference signal while the sound emitting device (13, 13-1, 13-2) emits sound waves (60), to adjust a phase delay for the determined at least one frequency, and to control the sound emitting device (13, 13-1, 13-2) to emit sound waves (60) having the determined at least one frequency at the adjusted phase delay.

8. The active noise reduction apparatus according to claim 6 or 7, wherein the closed loop configuration (14) is self-calibrating.

9. The active noise reduction apparatus according to one of claims 1 to 8, wherein the detecting device (11) comprises a microphone.

10. The active noise reduction apparatus according to one of claims 1 to 9, wherein the control device (12) is configured to determine at least one exemption frequency from the detected at least one reference signal which is indicative of a characteristic road marking (42) on the track (4) on which the vehicle is travelling, and is configured to control the sound emitting device (13, 13-1, 13-2) to not emit sound waves (60) having the determined at least one exemption frequency.

11. The active noise reduction apparatus according to one of claims 1 to 10, wherein the sound emitting device comprises an array of loudspeakers (13-1, 13-2) configured to emit directional sound waves (60), in particular unidirectional sound waves.

12. A vehicle comprising an active noise reduction apparatus according to one of the preceding claims.

13. An active noise reduction method for a vehicle, comprising:

- detecting at least one reference signal which is indicative of at least one component of a noise (50) generated at a contact area (41) between a wheel (3) of the vehicle and a track (4) on which the vehicle is travelling,

- emitting sound waves (60) towards the at least one contact area (41) between the wheel (3) of the vehicle and the track (4) on which the vehicle is travelling based on the detected at least one reference signal so as to reduce the at least one component of the noise (50) through active noise cancellation by the emitted sound waves (60).

14. The method according to claim 13, comprising determining at least one frequency from the detected at least one reference signal, adjusting a phase delay for the determined at least one frequency and emitting sound waves (60) having the determined at least one frequency at the adjusted phase delay.

Drawing