Patent Application
20120070012
I. Field of the Invention
The present invention relates generally to noise reduction systems and, more particularly, to a noise reduction system for an automotive vehicle powered at least in part by an electric motor.
Ii. Description of Related Art
In a conventional automotive vehicle of the type powered by a fuel engine, the sound from the combustion of the fuel in the engine forms the dominant noise source for the vehicle whenever the engine is running. Such combustion engines contain various frequency components and usually mask other noises from the engine compartment originating from auxiliary systems.
Conversely, in an automotive vehicle at least partially powered by an electric motor, such as an electric vehicle or a hybrid electric vehicle, the vehicle can operate when the combustion engine is not running or there is no engine at all. Consequently, the noise from the electric motor, which is unique to both electric vehicles and hybrid electric vehicles, is not masked by the sound of the combustion engine.
The noise from an electric motor in an electric vehicle or hybrid electric vehicle is usually a mix of pure tone sound together with its harmonics. Additionally, the frequency of the sound is typically much higher than the engine noise of a conventional internal combustion engine powered vehicle.
Humans, however, are more sensitive to higher frequency noise, i.e. noise in the range of 500 hertz-10 kilohertz, than to the lower frequency noise from a conventional internal combustion engine. Attempts to dampen or absorb such high frequency noise from an electric vehicle or hybrid electric vehicle by the inclusion of sound-absorbing material not only consumes engine volume and space, but is also expensive both in material and labor costs thus increasing the overall cost of the vehicle.
There have, however, been previously known active noise control systems for automotive vehicles which utilize the speakers within the vehicle passenger compartment to cancel engine noise. In the well-known fashion, these active noise control systems ideally generate sound of the same frequency and amplitude, but inverted phase, of the engine noise resulting in cancellation of the overall noise within the passenger compartment of the vehicle.
Unfortunately, these active noise control systems for automotive vehicles, while proving effective at lower noise frequencies common to internal combustion engines, are ineffective at higher audible frequencies of the type common to the motors of the type used in electric vehicles and hybrid electric vehicles. Instead, due to the relatively shorter wavelength of the high frequency audible signal, noise cancellation within the passenger compartment by using the passenger compartment speakers is achieved only in small spots and, worse, in other spots the noise is amplified rather than canceled.
The present invention provides a noise reduction system for an automotive vehicle powered at least in part by an electric motor. Such vehicles are known as electric vehicles or hybrid electric vehicles, i.e. vehicles with both an internal combustion engine as well as an electric motor which power the vehicle.
In brief, in the present invention at least one sensor is provided which produces an output signal having a frequency, amplitude and phase representative of the noise generated by the electric motor. Although a wide variety of different sensors may be utilized, one or more piezoelectric elements may be mounted between the stator of the motor and the motor casing, or on the surface of the motor casing, or between the motor casing and the transmission case, or on the transmission case, which generate an output signal in response to vibration of the electric motor. This vibration causes the electric motor to generate noise at the same frequency as the vibration.
At least one speaker is positioned closely adjacent the electric motor and thus closely adjacent the source of the noise from the electric motor. A speaker output controller receives the output signal from the sensor and generates an output signal to the speaker or speakers having substantially the same frequency and amplitude, but inverted in phase, as the estimated motor noise. Such a speaker output effectively cancels the noise from the electric motor. Furthermore, since the speaker is positioned at or at least closely adjacent the source of the noise, the noise cancellation is effective throughout the passenger compartment. Moreover, the piezoelectric elements may absorb the vibration energy of the electric motor and convert it to electrical power. This energy harvesting feature not only reduces the motor vibration and noise, but also supplies power to the speakers and speaker controller, eliminating the necessity of additional power supply to them.
A better understanding of the present invention will be had upon reference to the following detailed description when read in conjunction with the accompanying drawing, wherein like reference characters refer to like parts throughout the several views, and in which:
With reference first to
The vehicle 10 is powered at least in part by an electric motor 16 which may be contained within the engine compartment 12. Thus, the vehicle 10 may be either an all-electric vehicle in which the electric motor 16 provides all of the power to propel the vehicle 10, or a hybrid electric vehicle which contains an internal combustion engine in addition to the electric motor 16 to power the vehicle 10. In either case, in at least some circumstances, the electric motor 16 provides the sole propulsion for the vehicle 10. It is during those periods of operation of the automotive vehicle 10 where noise cancellation for the relatively high frequency noises generated by the electric motor 16 is desirable.
With reference now to
One or more vibration sensors 26, such as piezoelectric elements, are positioned at spaced apart locations around the source of the noise, motor 16, at such position that vibration energy is efficiently absorbed, e.g. between the motor casing 24 and the stator 22. The compressive and tensile deformation of the piezoelectric elements would have an effect of absorbing the vibration energy, thus reducing the noise from the motor. However, the vibration sensors may alternatively be positioned at other locations around the motor 16 without deviation from the spirit or scope of the instant invention, such as on the surface of the motor casing 24. If the motor 16 is stored in a transmission case, the piezoelectric elements may be positioned between the motor casing 24 and the transmission case, or on the surface of the transmission case.
With reference now to
With reference now to
Unlike the previously known systems, however, the speaker 34 is mounted closely adjacent the source of the noise, e.g. the motor 16, the transmission, etc. As such, the cancellation of the noise by the phase inverted audible signal from the speaker 34 effectively cancels out the electric motor noise throughout the passenger compartment 14. This can be explained by the formulas followed. If d1−d2=(n+φ/2/pi−1/2)λ (λ: wavelength of sound, φ: phase difference of noise source and speaker sound, d1: distance between the noise source and target point, d2: distance between the target point and the speaker), the noise will be cancelled. However, in the target vicinity point if d1′−d2′=(n+φ/2pi)λ (λ: wavelength of sound, φ: phase difference of noise source and speaker sound, d1': distance between the noise source and target vicinity point, d2′: distance between the target vicinity point and the speaker), the noise would rather be amplified. When the frequency is relatively low, the wavelength is long, thus the equation d1′−d2′=(n+φ/2pi)λ would not easily be met. However, as the frequency goes up, the wavelength gets shorter, and the equation could be easily met at target vicinity area if the noise source and the speaker are not located close to each other. If driver moves his head a little bit, the noise changes a lot and the noise level is even worth, thus having the speaker close to the noise source is effective for cancelling the noise at high frequencies common to motors used in electric vehicles or hybrid electric vehicles.
It will, of course, be appreciated that one or more speakers 34 may be utilized adjacent to the motor 16 to cancel the noise from the electric motor 16. An example of actual implementation on an electric vehicle or hybrid electric vehicle is illustrated in
It will be understood, of course, that other types of sensors 26 may be used in lieu of a piezoelectric element. For example, a simple microphone could form the sensor 26. In that case, the microphone would provide an output signal to the speaker output controller 30 which varies in both frequency and amplitude in a manner well known to microphones.
With reference now to
In this case, the speaker output controller is programmed to use the data inputs from both the resolver 40 (which may be either analog or digital in nature) as well as the current sensor 42 to determine the appropriate output signal on its output 32 to the speaker 34 to cancel the motor noise. The speaker 34 creates a noise at a frequency and amplitude substantially the same as the motor noise, but inverted in phase. Such inversion cancels the motor noise throughout substantially the entire passenger compartment.
With reference now to
Once the rotational speed 50 is determined from either the resolver 40 or sensors 26, or both, a frequency of the noise is determined or at least estimated at block 54. That estimate is then coupled as an input signal to a frequency controller 56 in the speaker output controller 30.
Similarly, once the rotational timing 52 is determined, either from the resolver, sensor 26, or both, the phase estimate of the noise from the motor 16 may be determined at block 60. The signal from block 60 is then coupled as an input signal to a phase controller 62 in the speaker output controller 30 which ensures that the phase generated by the controller 30 is inverted in phase from the motor noise.
Still referring to
However, if the resolver 40 is utilized without the sensor 26, additional circuitry must be used to estimate the amplitude of the motor noise at block 64. Consequently, the current sensor 42, if present, provides an output signal to an electric magnetic force estimation block 66. The block 66 in turn provides a signal to the block 64 which estimates the amplitude of the noise signal from the motor 16. A higher current is indicative of a higher motor torque and, in turn, indicative of a higher amplitude of noise from the motor 16.
In lieu of the current sensor, the electric magnetic force estimation block 66 may receive a signal from the engine control unit 70 which provides an output signal 72 indicative of the torque demand on the motor 16. From that motor torque demand, a motor current estimation may be made at block 74 and coupled as an input signal to the electric magnetic force estimation block 66.
Regardless of how the amplitude is estimated at block 64, block 64 is coupled to an amplitude controller 76 in the speaker output controller 30. Consequently, the speaker output controller determines the frequency, phase, and amplitude of the output signal from the controller 30 to the speaker 34 to cancel, or at least greatly reduce, the noise from the motor 16.
From the foregoing, it can be seen that the present invention provides an effective system for canceling noise generated by the electric motor in either an electric vehicle or hybrid electric vehicle. Since the speakers are placed closely adjacent the motor, and thus closely adjacent the noise source, noise cancellation within the passenger compartment 14 even at high frequencies is achieved.
As an additional feature of the present invention, the noise generated by the speaker 34 may also be used as a pedestrian warning noise since both electric vehicles and hybrid electric vehicles are very quiet as contrasted to internal combustion engines of the type used in automotive vehicles. For example, as shown in
Having described our invention, many modifications thereto will become apparent to those skilled in the art to which it pertains without deviation from the spirit of the invention as defined by the scope of the appended claims.
