Abstract:
A vehicle has an electric drive mode, a body defining a vehicle interior, a first and second set of audio speakers positioned outside and inside of the interior, respectively, and a controller. The controller generates an acoustic signal, broadcasts the acoustic signal via the first set of speakers during an electric drive mode, and generates and broadcasts a cancelling signal via the second set of speakers. The broadcasts are coordinated to substantially cancel an attenuated portion of the acoustic signal resulting from propagation of the acoustic signal into the interior. A method cancels a synthesized sound within a vehicle interior by collecting vehicle operating values, generating an acoustic signal as the synthesized sound during an electric drive mode, and processing the acoustic signal to generate a modified acoustic signal approximating an attenuated portion of the acoustic signal propagating into the vehicle interior.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates generally to the control of noise or sound within a vehicle, and in particular to the active cancellation of a synthesized noise or sound within a vehicle interior during a predetermined synthesized sound event. 
       BACKGROUND OF THE INVENTION 
       [0002]    Electric vehicles (EV) and hybrid electric vehicles (HEV) obtain optimal fuel economy largely by means of electric propulsion, wherein a high-voltage battery, working in conjunction with one or more onboard electric motor/generators and/or an offboard electrical power supply, provides the required propulsive energy. For example, a typical full HEV can selectively utilize a high-voltage battery module or energy storage system (ESS) as a propulsive energy source during conditions under which an electric motor is relatively efficient, automatically transitioning to propulsion via an internal combustion engine at higher speeds. Likewise, an extended-range EV equipped with a suitable high-voltage ESS can operate exclusively using electric power. 
         [0003]    In addition to the distinct performance advantages of using an electric motor as a vehicular propulsion device, an electric motor can operate almost noiselessly, i.e., without the familiar combustion and fan sounds generated by a conventional gasoline-powered internal combustion engine. As a result, the relatively tranquil environment in an EV or HEV interior can be another desirable feature of such vehicle designs. However, for other drivers the familiar engine sounds can be desirable during all operating modes. Therefore, in order to optimize the driving experience some modern vehicles are adapted to synthesize or broadcast engine sounds in response to throttle and/or speed signals, such as by generating the sound of a sporty or high-performance engine during an electric drive mode. 
         [0004]    Additionally, certain vehicles are configured to transmit or broadcast synthesized engine noises or other warning sounds outside of the vehicle when propelled via electric power in order to alert pedestrians, cyclists, and other persons or animals in the path of or in close proximity to the otherwise nearly silent vehicle. While such synthesized sounds have notable advantages, the perception of synthesized sounds within the vehicle interior may be undesirable to some drivers and passengers, particularly those who highly value the relative tranquility of electric propulsion. 
       SUMMARY OF THE INVENTION 
       [0005]    Accordingly, a vehicle is provided having an active noise cancellation (ANC) system that reduces a passenger-perceptible level of an acoustic signal generated or synthesized aboard the vehicle, and broadcast outside of the vehicle, e.g., for signaling or alerting pedestrians to the approach of the vehicle. The ANC system includes an electronic control unit or controller that is provided or pre-armed with the characteristics of the particular waveform describing the acoustic signal prior to its transmission or broadcast outside of the vehicle interior. The controller is also provided with a model of or means of determining the unique acoustic characteristics of the vehicle body so as to estimate or determine the attenuating and/or damping effects of the vehicle body on the acoustic signal as it propagates into the vehicle interior, as well as accounting for the time required for such a propagation. Any desirable sounds, such as those emitted by an on-board entertainment system, are allowed to be broadcast within the vehicle interior with minimal interference, while the synthesized noises or sounds as well as actual powertrain noises from the engine or electric motor are selectively cancelled within the vehicle interior, thereby optimizing the user-perceived acoustics. 
         [0006]    The vehicle selects, synthesizes, or otherwise generates the acoustic signal during a predetermined vehicle operating state, such as when the vehicle is operating exclusively under electric power in a reverse or a relatively low forward rate of speed. Prior to broadcast of the acoustic signal, the waveform characteristics of the acoustic signal are processed to determine an appropriate cancelling signal, rather than relying on the sensing or detecting of the acoustic signal after its broadcast using a microphone or other detection means in the manner of conventional noise cancellation systems. The broadcast of the cancelling signal is then coordinated with that of the acoustic signal for optimal waveform interference and cancelling effect. 
         [0007]    In particular, a vehicle having an electric drive mode, such as reverse and/or a threshold forward speed mode as noted above, includes a vehicle body defining a vehicle interior, a first set of audio speakers positioned outside of the vehicle interior, and a second set of audio speakers positioned within the vehicle interior. An electronic control unit or controller is also included. During the electric drive mode or modes, the controller automatically generates or synthesizes an acoustic signal that is suitable for warning a pedestrian or other being as to the approach of the vehicle, with the acoustic signal being determined by a plurality of vehicle operating values, e.g., vehicle speed, throttle level, transmission state or mode, etc. A cancelling signal is generated or synthesized by the controller for broadcast within the vehicle interior. 
         [0008]    In determining the appropriate cancelling signal, the controller can consider, for example, the rate of propagation of the acoustic signal from the first set of speakers at the front and/or rear of the vehicle as the waveform travels through the vehicle body and into the vehicle interior, as well as the unique acoustic characteristics of the vehicle body itself. That is, the controller processes or filters the acoustic signal to produce a modified acoustic signal, i.e., a signal representing the attenuated portion of the acoustic signal as it is perceived within the vehicle interior. The cancelling signal is then broadcast into the vehicle interior via the second set of audio speakers in a coordinated manner with the broadcast of the acoustic signal via the first set of audio speakers. In this manner, the acoustic signal is rendered substantially inaudible to any passengers traveling within the vehicle interior. 
         [0009]    A method is also provided for actively cancelling a synthesized sound within the vehicle interior described above. The method includes collecting a set of vehicle operating values, including detecting an electric drive mode, and generating an acoustic signal as the synthesized sound during the electric drive mode. The acoustic signal has a characteristic that is determined at least in part by the set of vehicle operating values. The method also includes processing the acoustic signal to generate a modified acoustic signal, which as noted above approximates the attenuated portion of the acoustic signal ultimately reaching the vehicle interior after propagating from the first set of speakers positioned outside of the vehicle interior, through the vehicle body, and into the vehicle interior. A cancelling signal is automatically generated that is adapted to substantially cancel the modified acoustic signal within the vehicle interior, and the acoustic signal is broadcast via the first set of audio speakers while the cancelling signal is broadcast via the second set of audio speakers. 
         [0010]    The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a schematic illustration of a vehicle having an active noise cancellation (ANC) system in accordance with the invention; 
           [0012]      FIG. 2  is a schematic illustration of an ANC system that can be used with the vehicle of  FIG. 1 ; and 
           [0013]      FIG. 3  is a graphical flow chart describing a method or algorithm for actively cancelling a synthesized noise or sound within the interior of the vehicle shown in  FIG. 1 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0014]    Referring to the drawings, wherein like reference numbers correspond to like or similar components throughout the several figures, and beginning with  FIG. 1 , a vehicle  10  includes a passenger compartment or interior  12  having one or more seats  13  each being suitable for transporting a passenger  11 , with the interior  12  defined by a vehicle body  14 . Within the scope of the invention, the vehicle  10  can be configured as an extended-range electric vehicle (EV), a two-mode or plug-in style hybrid electric vehicle (HEV), a fuel-cell powered vehicle, or any other vehicle design or configuration having at least one electric-only operating state or electric propulsion mode, hereinafter referred to as “electric drive”. 
         [0015]    The vehicle  10  includes a powertrain  16 . As noted above, the powertrain  16  can be of either a hybrid-electric or a purely electric design. Regardless of the particular configuration of the powertrain  16 , the powertrain  16  includes a high-voltage battery or electric storage system (ESS)  17  suitable for storing and supplying electrical energy necessary for propelling the vehicle  10  during the electric drive mode or modes. As will be understood by those of ordinary skill in the art, the ESS  17  can be selectively recharged via one or more onboard motor/generators (not shown), for example during a regenerative braking event or whenever such motor/generators are operating as a generator. 
         [0016]    The vehicle  10  is equipped with an audio and/or entertainment system (AS)  27 , e.g., a radio, a compact disc player, an MP3 player, etc., suitable for providing a sound signal  31 , and an active noise cancellation (ANC) system  32  (see  FIG. 2 ) having an electronic control unit or controller (C)  18 . The controller  18  is specially adapted for selecting, synthesizing, or otherwise generating an acoustic signal  20 , as well as for transmitting, emitting, or otherwise broadcasting the acoustic signal  20  outside of the vehicle  10 , i.e., in a direction away from the interior  12 . Within the scope of the invention, the acoustic signal  20  can be a simulated engine, fan, and/or other desired vehicle noise, a steady or intermittent warning tone or signal, and/or any other tone or signal suitable for alerting a pedestrian, cyclist, animal, etc., positioned in the path of the vehicle  10 . 
         [0017]    As noted above, in an electric drive mode the vehicle  10  can operate very quietly, particularly when traveling at a low rate of speed, and therefore the approach of the vehicle  10  can be relatively difficult to perceive, particularly for a person having obstructed or impaired vision. Because electric drive can be used for both forward and reverse directions of travel, the vehicle  10  can be equipped with a weatherproof front set of audio speakers  19 F and a weatherproof rear set of audio speakers  19 R, with the particular set of speakers  19 F,  19 R being automatically selectable by the controller  18  based on the direction of travel in an exemplary embodiment. 
         [0018]    Referring to  FIG. 2 , the ANC system  32  includes the controller  18 , a set of sensors  23 A,  23 B, and  23 C, and the sets of audio speakers  19 I,  19 F, and  19 R. The controller  18  includes a microprocessor unit or processor (P)  21  adapted to receive and process a set of vehicle operating values  80 . The vehicle operating values  80  can include, without necessarily being limited to, a throttle level (Th %), a vehicle speed (N), a transmission mode or state (T), window, sunroof, or convertible top open or close state, and/or any other vehicle operating values suitable for determining when to generate the acoustic signal  20 , and the particular characteristics such a waveform should take. The controller  18  can be configured as a self-contained system or device, or can be included as an integral part of a distributed or a central control module for the vehicle  10 , thus having additional control modules and capabilities as might be necessary to execute all required system control functionality aboard the vehicle  10  in the desired manner. 
         [0019]    Additionally, the controller  18  can be configured as a general purpose digital computer generally comprising a microprocessor or central processing unit, read only memory (ROM), random access memory (RAM), electrically-programmable read only memory (EPROM), high speed clock, analog to digital (A/D) and digital to analog (D/A) circuitry, and input/output circuitry and devices (I/O), as well as appropriate signal conditioning and buffer circuitry. Any algorithms resident in the controller  18  or accessible thereby, including an algorithm  100  described below with reference to  FIG. 3 , can be stored in ROM and automatically executed to provide the respective functionality. 
         [0020]    The controller  18  is in electrical communication with the sensors  23 A,  23 B, and  23 C, each of which is specially adapted for measuring, detecting, calculating, or otherwise collecting an associated one of the vehicle operating values  80  shown in  FIG. 2 , and for relaying or transmitting the associated information to the controller  18 . In response to the vehicle operating values  80 , the controller  18  generates the acoustic signal  20  for later broadcast via some or all of the audio speakers  19 F,  19 R, e.g., when the vehicle  10  of  FIG. 1  is operating in electric drive mode. However, the scope of the invention is not intended to be limited to sound generation solely during an electric drive mode. For example, if the vehicle  10  is equipped with a modem internal combustion engine that operates quietly at low rates of travel, it may be desirable to generate the acoustic signal  20  while the engine is running. 
         [0021]    Still referring to  FIG. 2 , in order to facilitate generation of the acoustic signal  20 , the controller  18  can include or can have access to a digital sound synthesizer module or DSS  24  and/or a sound file library (SFL)  26  of pre-generated or pre-recorded sound files having a suitable digital or analog format. In particular, the DSS  24  is configured to generate the acoustic signal  20  having an appropriate or suitable amplitude and waveform for the given set of vehicle operating values  80 . For example, at very low rates of travel of the vehicle  10  of  FIG. 1 , the acoustic signal  20  could simulate engine or fan noise with a relatively low amplitude, with the amplitude and/or frequency increasing in conjunction with the throttle level (Th %) and/or vehicle speed (N). 
         [0022]    Likewise, a particular pre-generated or pre-recorded sound file could be extracted or selected from the SFL  26 , with the characteristics of the selected sound file to be broadcast via the audio speakers  19 F and/or  19 R being dependent to some extent on the vehicle operating values  80 . For example, an optional lookup table  28  or other suitable reference file could be provided, e.g., a lookup table that is indexed by each of the throttle level (Th %) and the vehicle speed (N), with the particular sound file extracted from the SFL  26  being determined by the corresponding entry in the lookup table  28 . Such an SFL  26  could include analog waveforms in addition to or instead of digital waveforms without departing from the intended scope of the invention. 
         [0023]    Still referring to  FIG. 2 , the controller  18  can be adapted to include a processing module  34 A suitable for processing, filtering, and/or delaying the broadcast of the acoustic signal  20  via the speaker or speakers  19 F,  19 R in order to a provide sufficient time lag for generating a cancelling signal  30 , described below, which is then later broadcast within the vehicle interior  12  via the set of interior audio speakers  19 I in a coordinated manner with the broadcast of the acoustic signal  20 . That is, the controller  18  can first route the generated or extracted acoustic signal  20  through the processing module  34 A, wherein the acoustic signal  20  is sufficiently processed, filtered, and/or delayed for a calibrated duration before being broadcast via the audio speakers  19 F and/or  19 R. 
         [0024]    Within the first processing module  34 A, the acoustic signal  20  can also be processed using a calibrated attenuation model of the vehicle body or other suitable processing means in order to determine a modified acoustic signal  20 A. The modified acoustic signal  20 A thus approximates the characteristics of the acoustic signal  20  as it would be perceived by a passenger  11  seated within the vehicle interior  12  after broadcast via the audio speakers  19 F and/or  19 R. 
         [0025]    The modified acoustic signal is then transmitted or relayed to a second processing module  34 B, wherein a cancelling signal  30  is generated as a function of the modified acoustic signal  20 A. As will be understood by those of ordinary skill in the art, for proper interference the cancelling signal  30  should have an amplitude that is substantially equal to or directionally proportional to that of the acoustic signal  20 , and a phase that is opposite that of the modified acoustic signal  20 . The cancelling signal  30  is designed to substantially minimize perception by the passenger  11  of the acoustic signal  20  within the vehicle interior  12 , without otherwise interfering with any desirable sounds therein, such as the sound signal  31  shown in  FIG. 1 . 
         [0026]    In order to prevent alternating zones of constructive and destructive interference within the vehicle interior  12 , the number and position of interior audio speakers  19 I can be varied as needed depending on the particular design and/or the particular modal response or sound damping characteristics of the vehicle  10 , with one or more audio speakers  19 I being positioned on a portion of the seat  13  shown in  FIG. 1  in an exemplary embodiment so as to be in close proximity to the passenger  11 . 
         [0027]    Unlike conventional active noise cancellation methods that only sense or detect an incoming audio signal using a microphone or other means after the signal has been produced, the controller  18  is effectively pre-armed with foreknowledge of the incoming dynamic acoustic signal, i.e., the acoustic signal  20 , prior to its broadcast. By accounting for the unique effect of the vehicle  10  on the acoustic signal  20  as it propagates to the interior  12 , such as by providing the processing module  34 A with a pre-calibrated filter or attenuation model, the controller  18  can be pre-tuned and adapted for optimal performance. The broadcast of the acoustic signal  20  outside of the vehicle  10  of  FIG. 1  via the audio speakers  19 F,  19 R and the broadcast of the cancelling signal  30  within the interior  12  via the audio speakers  19 I are closely coordinated or synchronized for optimal interference and resultant cancelling effect. 
         [0028]    Referring to  FIG. 3 , and with reference to the various systems and components shown in  FIGS. 1 and 2  and described above, the algorithm  100  resident within or accessible by the controller  18  begins with step  102 , wherein the algorithm  100  determines whether the present transmission state or mode (T) corresponds to a predetermined transmission mode (X), as determined by the sensor  23 C of  FIG. 1  or by any other suitable means. For example, the predetermined transmission mode (X) can be a presently commanded reverse or a forward electric drive mode as set forth above. If T=X, the algorithm  100  proceeds to step  104 , with the algorithm  100  otherwise exiting. 
         [0029]    At step  104 , the vehicle operating values  80  are collected as described above and relayed to the controller  18 . That is, the sensors  23 A,  23 B, and  23 C each detect, sense, measure, calculate, or otherwise collect a vehicle operating value, such as throttle level (Th %), the vehicle speed (N), and the transmission mode or state (T), respectively. Once collected, the algorithm  100  proceeds to step  106 . 
         [0030]    At step  106 , the acoustic signal  20  to be broadcast via the audio speakers  19 F,  19 R is generated by the controller  18 , such as by synthesizing the acoustic signal  20  using the DSS  24  or by accessing or selecting an appropriate sound file from the SFL  26 . As noted above, the particular sound file generated or selected at step  106  can vary in conjunction with the characteristics of the vehicle operating values  80  determined via the sensors  23 A,  23 B and  23 C. Once the acoustic signal  20  is generated, and prior to broadcasting of the acoustic signal  20 , the algorithm  100  proceeds to step  108 . 
         [0031]    At step  108 , the acoustic signal  20  is filtered and/or processed within the controller  18 , e.g., by the processing module  34 A, in order to temporarily delay the broadcast of the acoustic signal  20 , as well as to compensate for any signal attenuation, damping, and/or other interference provided by the vehicle body  14 . That is, as will be understood by those of ordinary skill in the art, the acoustic signal  20  transmitted or broadcast outside of the vehicle  10  and away from the passenger  11  will not be perceived within the interior  12  in the same manner, i.e., with the same volume, frequency, pitch, etc., of the original or unadulterated waveform describing the acoustic signal  20 , i.e., approximately as perceived by one positioned in the path of the vehicle  10  in close proximity thereto. 
         [0032]    Therefore, by accounting for the unique acoustic characteristics of the vehicle  10 , such as by processing the acoustic signal  20  at step  108  through a calibrated acoustic model or filter representing the known or modeled acoustic characteristics of the vehicle  10 , the modified acoustic signal  20 A to be cancelled represents an attenuated, damped, or otherwise modified portion of the acoustic signal  20  broadcast at step  110  as described below. Also, the length of the required delay can be dependent to at least some extent on the speed of the processor  21  and the processor modules  34 A,  34 B, which can be separate devices as shown in  FIG. 2  or integrated into a common device without departing from the intended scope of the invention. Once the acoustic signal  20  has been sufficiently processed, the modified acoustic signal  20 A is generated, and the algorithm  100  proceeds to step  110 . 
         [0033]    At step  110  of the algorithm  100 , the waveform of the modified acoustic signal  20 A generated or otherwise determined at step  108  is analyzed or processed as needed to generate the cancelling signal  30 . As noted above, the cancelling signal  30  is a noise-cancelling waveform or sound wave having an amplitude that is directionally proportional to that of the modified acoustic signal  20 A, but having opposite phase or polarity. Phase cancellation is thus provided by the combination of the modified acoustic signal  20 A and the cancelling signal  30  within the vehicle interior  12 . That is, destructive interference provided by the cancelling signal  30  reduces the amplitude of the perceived noise, i.e., the acoustic signal  20 , within the interior  12 . The resultant waveform perceived by a passenger  11  within the interior  12  is thus substantially reduced or quieted in relation to the acoustic signal  20  being broadcast via the audio speakers  19 F,  19 R. Once the cancelling signal  30  is generated, the algorithm  100  proceeds to step  112 . 
         [0034]    At step  112 , the modified acoustic signal  20 A and the cancelling signal  30  are broadcast via the audio speakers  19 F,  19 R and the audio speakers  19 I, respectively. The acoustic signal  20  is thus broadcast in its original form, to be perceived by any person in the path of the vehicle  10 , while the cancelling signal  30  is broadcast within the vehicle interior  12  to substantially cancel the attenuated or modified acoustic signal  20 A as described above. In this manner, relative tranquility is preserved within the vehicle interior  12 , without otherwise affecting the operation of the pedestrian warning functionality of the ANC system  32  shown in  FIG. 2 . 
         [0035]    While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.