Patent Application
20170330547
The technical field generally relates to active noise cancellation systems, and more particularly relates to active noise cancellation systems for motor vehicles.
The cabin environment is an important aspect for the user of a motor vehicle. Many people spend extended periods of time in a motor vehicle, so comfort is a key consideration. However, there are inherent aspects associated with a motor vehicle that are not comfortable. For example, a motor vehicle has a motor and moves over the terrain of a road. Noise and vibrations are typical in most motor vehicles, and these can prove displeasing over extended periods of time. The motor for many vehicles generates noise and vibration, and the tires rolling over the road can also generate noise and vibration. Other factors can also produce noise or vibration within a vehicle. In some cases, vibrations are produced below the normal human hearing range of humans, which is commonly referred to sub-audible sound for humans. An example of such a phenomenon is the cabin boom effect oftentimes produced when driving with a single window down. This example presents an open cavity specific forced example but can be extended to a closed cavity and other forced response cases. Systems and methods that reduce or cancel noise can be expensive and/or heavy, and price and weight are important aspects of a motor vehicle.
Accordingly, it is desirable to provide systems and methods to reduce noise or other pressure waves in a motor vehicle. In addition, it is desirable to provide systems and methods of noise reduction that utilize existing components in a motor vehicle. Furthermore, other desirable features and characteristics of the present embodiment will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.
Methods and systems for reducing a pressure wave are provided. In an exemplary embodiment, a motor vehicle comprises a cabin and a receiver positioned to detect an input pressure wave within the cabin. The receiver is configured to produce an input signal. A fan with a blade having a variable pitch is positioned within the vehicle where the fan is audible within the cabin. A processor is in communication with the receiver and the fan, where the processor is configured to receive the input signal and determine an input frequency and an input phase. The processor is further configured to instruct the fan to control a pitch of the blade to produce a cancellation pressure wave with a cancellation frequency that is about the same as the input frequency and a cancellation phase that is about 180° out of phase with the input phase.
A method for reducing a pressure wave is provided in another embodiment. The method includes measuring an input pressure wave with a receiver, and determining an input frequency and an input phase of the input pressure wave. A fan operation is adjusted to produce a cancellation pressure wave with a cancellation frequency that is about the same as the input frequency and a cancellation phase that is about 180° out of phase with the input phase. Adjusting the fan operation includes adjusting one or more of a fan speed and a pitch of a blade of a fan.
A system of reducing a pressure wave is provided in yet another embodiment. The system includes a receiver positioned to monitor and measure an input pressure wave and to produce an input signal. A fan in positioned within audible range of the input pressure wave, where the fan has a blade with a variable pitch. A processor is in communication with the receiver and the fan, and the processor is configured to receive the input signal and determine an input frequency and an input phase of the input signal. The processor is further configured to instruct the fan to vary a pitch of the blade to produce a cancellation pressure wave having a cancellation frequency that is about the same as the input frequency and a cancellation phase that is about 180° out of phase with the input phase.
The present embodiments will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and wherein:
The following detailed description is merely exemplary in nature and is not intended to limit the various embodiments or the application and uses thereof. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description.
Active noise cancellation is a newly emerging technology employed on many modern vehicles. While the specific techniques may vary, the underlying goal remains the same: to monitor an existing noise field within a vehicle cabin and mitigate/suppress it. Rather than using traditional speakers and amplifiers to provide a cancellation noise, this method employs an active fan equipped with variable pitch blades to produce a sound equal in magnitude and opposite in phase to the nuisance sound. This effectively “cancels” the nuisance sound. This is the same theory governing existing active noise cancellation systems. Specifically, this variable pitch rotor technique addresses both sub audible (below ˜20 Hz) and Audible (above ˜20 Hz) “cavity boom”. A common example of this phenomenon is most commonly experienced while driving with only a single window open. Vortices shed from the body structure interfere with the vehicle cavity air mass and pressure, producing the sound. This example presents an open cavity specific forced example but can be extended to a closed cavity and other forced response cases.
Reference is made to an exemplary embodiment illustrated in
An active noise control system 14 is configured to limit or reduce pressure waves within the cabin 12, as illustrated in an exemplary embodiment in
The motor vehicle 10 includes a processor 20 that may include a wide variety of hardware and software configurations. The processor 20 can include any type of processor hardware or multiple processors, integrated circuits such as microprocessors, or any suitable number of integrated circuit devices and/or circuitry working in cooperation to accomplish the tasks of the processor 20. The processor 20 executes one or more programs that may be stored within memory. The processor 20 may include, or have access to, any type of memory, including but not limited to random access memory (RAM), read only memory (ROM), erasable programmable read only memory (EPROM), electrically erasable programmable read only memory (EEPROM), and non-volatile random access memory (NVRAM). The memory can store any information needed for the operation of the processor 20, as described herein. The processor 20 may be part of other systems on the motor vehicle 10, or it may be a dedicated device.
The processor 20 is in communication with the receiver 18. A wide variety of communication systems may be employed in various embodiments. For example, a wire may be used for electrical communication, fiber optics may be used for light communication, and various wireless techniques may also be utilized. The processor 20 is configured to receive the input signal and determine its frequency content and an input phase of the input signal, where the input signal is representative of the input pressure wave 16. The input pressure wave 16 has an input frequency and an input phase, where the input frequency is the number of occurrences of a repeating event over time, such as the number of pressure peaks over time. The input phase is a relationship in time between successive states of an oscillating system as compared to a reference point. The phase may represent when the peaks or valleys of a pressure wave occur, and the phase can be relative to another wave or relative to a fixed time. The input pressure wave 16 also has an input amplitude, where the input amplitude is the distance between a neutral pressure and a peak pressure. The neutral pressure is typically about half way between a maximum and a minimum pressure of the input pressure wave 16. The processor may also be configured to determine the input amplitude.
The processor 20 may further be configured to compare the input signal to an expected signal, where the expected signal is a pre-determined signal based on operating conditions. For example, the expected signal may be based on the engine's revolutions per minute (RPM), where the sound or pressure wave produced by the engine at set RPMs is known. Alternatively, the expected signal may be based on vehicle speed, where the expected signal corresponds to an expected noise the tires produce at a given speed. Many other factors may influence the expected signal, and the expected signal may change. For example, at low speeds the expected signal may depend on the engine RPM, and at higher speeds the expected signal may depend on the noise produced by the tires on the road. Many other factors may influence the expected signal as well, such as noise from the transmission or other sources, sound from a radio or other entertainment system, or a combination of various factors. The input signal may be compared to the expected signal by the processor 20, where aspects of the input signal matching the expected signal are referred to as coherent pressure waves, and aspects of the input signal differing from the expected signal are referred to as incoherent pressure waves. The coherent pressure waves may represent the undesired sound, such as engine noise, and the incoherent pressure waves typically represent desired sounds, such as speech or music. The processor 20 may optionally be configured to cancel the coherent pressure waves, and not to cancel the incoherent pressure waves, as described more fully below.
The motor vehicle 10 also includes a fan 30 with one or more blades 32, where the fan 30 includes multiple blades 32 in many embodiments. The fan 30 is positioned such that the fan 30 is audible within the cabin 12, or within audible range of the input pressure wave 16 for embodiments other than a motor vehicle 10. The fan 30 may urge air into the cabin 12 in some embodiments, but it is also possible for the fan 30 to be audible within the cabin 12 without urging air into the cabin 12. The blade 32 of the fan 30 has a variable pitch, as illustrated in
In an exemplary embodiment, all the blades 32 of the fan 30 have a variable pitch, where the pitch of all the blades 32 are controlled in unison such that each blade 32 has the same pitch as every other blade 32. As such, the fan 30 is capable of changing the pitch of each and every one of the plurality of blades 32 simultaneously and to the same degree. However, in other embodiments, one or more of the blades 32 may be controlled differently than one or more other blades 32 such that the fan 30 includes blades 32 with different pitches at a given moment in time. The fan 30 may be one or more of several different types of fans, including a squirrel cage, a propeller fan, and other types of fans, but the fan 30 does include a variable pitch blade 32 in all embodiments. The fan 30 produces an audible noise or pressure wave, and the frequency and phase depends on the speed of the fan 30 and the pitch of the blades 32.
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In some embodiments, the fan 30 and processor 20 are configured to produce a cancellation pressure wave 40 with a cancellation frequency of from about 10 to about 100 hertz. This relatively low frequency range matches much of the unwanted noise or pressure waves from a motor vehicle 10. This also fits within the frequency range of pressure waves most fans 30 produce. The fan 30 serves to produce the cancellation pressure wave 40, as described above, and in some embodiments one or more fans 30 are the only device(s) producing the cancellation pressure wave 40. Thus, the cancellation frequency is limited to what can be achieved by controlling the fan's operation, as described above. The active noise control system 14 with a fan 30 allows for good control of lower frequency pressure waves, as described above. These lower frequency pressure waves are generally consistent throughout the cabin so fan placement and the input pressure wave generation point are not critical. Higher frequencies tend to be more localized within a cabin 12, so effective active noise cancellation systems targeting the higher frequencies may benefit from targeting specific locations within the cabin 12.
In some embodiments, the input pressure wave 16 may not have a constant input frequency, and/or the input pressure wave 16 may not have a single spectral peak. In such cases, the fan 30 may be controlled to produce a variable cancellation pressure frequency that matches the inconsistent and varied input frequency of the input pressure wave 16.
The fan 30 may be positioned in a wide variety of locations where the fan 30 is audible within the cabin 12, and some of those locations are within the cabin 12. For example, the fan 30 may be positioned within a heating, ventilation, and air conditioning (HVAC) unit 42, as illustrated in
The active noise control system 14 described herein uses a fan 30 in place of a speaker to cancel unwanted pressure waves. A fan 30 is generally lighter than the typical active noise cancellation speakers. In addition, a fan 30 also weights less and is less massive than layers of sound adsorbing material used to suppress unwanted noise. The fan 30 may be quite effective at producing a cancellation pressure wave 40 at the lower frequencies described above, so the reduced weight with good pressure wave cancellation provides a benefit to the cabin occupants.
While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the application in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient plan for implementing one or more embodiments, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope, as set forth in the appended claims.
