Abstract:
A noise enhancement system for an automobile utilizes a single input of engine speed to derive a control signal used to drive a speaker. The speaker generates sounds that enhance or replicate the desired sounds from the engine. The output from the speaker is crafted dependent on the vehicle operating conditions. Instead of multiple transducers and inputs the noise enhancement system of this invention utilizes the single input of engine RPM engine speed. By utilizing only engine speed, the noise enhancement system is cost effective and significantly less complex.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The application claims priority to U.S. Provisional Application No. 60/573,673 which was filed on May 21, 2004. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to a noise control system for an automobile. More particularly, this invention relates to a noise control system requiring only limited input for generating a noise control signal to enhance sounds produced by an automobile. 
     Active noise control systems for automotive applications are known for reducing or enhancing noise generated by a vehicle engine. An occupant within a passenger compartment of an automobile often can hear engine noises propagated through an air intake manifold. Typical active noise control systems include a speaker for generating a noise canceling or enhancing signal to provide an overall desirable engine sound. The speaker produces a sound determined with respect to current operating conditions of the engine to cancel or enhance engine noise as desired. 
     Typical active noise control systems require several different inputs from the vehicle engine for determining the necessary speaker output. Such information is acquired in some circumstances from a vehicle controller or by sensing directly from analog signals from various transducers. Each source of information requires a separate physical connection along with the accompanying control system support required to gather and use the information. 
     Some of the vehicle parameters that may be required to be read or predicted accurately include engine crank position, rotational speed, throttle opening, temperature, etc. The phase of the induction sound is sensitive to such parameters. Conventional systems rely upon many sensors to obtain information utilized in determining and generating a cancellation or enhancement sound. 
     Disadvantageously, multiple inputs from analog sensors or devices to the active noise control system add cost and use of information from the vehicle controller increases complexity. Either option requires relatively significant interfacing with existing vehicle electronics. Further, the required multiple interfaces with existing vehicle electronics and vehicle controllers have made an after-market noise control impractical. 
     Accordingly, is it desirable to develop a robust, durable and efficient noise enhancement system that can enhance sound quality within a passenger compartment while being simple to install and practical for after-market installation. 
     SUMMARY OF THE INVENTION 
     This invention is a noise control system for enhancing vehicle sounds that generates a sound corresponding with engine operating conditions utilizing a single input from the vehicle. 
     An example noise enhancement system according to this invention generates an audio output to enhance the noise emitted from the engine. The combined engine noise and audio output from the noise control system produces a more desirable overall noise pleasing to passengers within a passenger compartment of the vehicle. The example noise enhancement system utilizes a single input from the engine to generate a sound output from a speaker that combines with sound from the engine to produce desirable acoustic qualities. 
     The one input provides information to a controller of the system indicative of engine speed. Engine speed is a characteristic of engine performance that is available from many different sources, for example a tachometer. The one connection is the only input that is provided to the controller and all that is required by the example system to generate a desired signal from the speaker. 
     Accordingly, the noise enhancement system of this invention provides for a robust sound enhancement system through the use of a single input indicative of engine speed. No other signals or information is required to provide the desired sound enhancement output. Utilizing only a single input value indicative of engine speed reduces the overall complexity of this system while maintaining desired performance. Further, because only a single input is required, this system is favorable for installation as an after-market system. 
     These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of an example noise enhancement system according to this invention installed within a motor vehicle. 
         FIG. 2  is a process flow diagram of an example noise enhancement system according to this invention. 
         FIG. 3  is a graph representing an acoustic gain relative to engine speed and engine angular acceleration. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to  FIG. 1 , a vehicle  10  includes an engine  12  having an intake manifold  14 . In some instances sounds generated from the engine  12  are emitted through the intake manifold  14 . An example noise enhancement system  16  according to this invention is shown that generates an audio output  15  to enhance the noise emitted from the engine  12 . The combined engine noise and audio output  15  from the noise enhancement system  16  produces a more desirable overall noise pleasing to passengers within a passenger compartment  18  of the vehicle  10 . 
     The example noise enhancement system  16  utilizes a single input from the engine  12  to generate a sound output from speaker  24  that combines with sound from the engine  12  to produce desirable acoustic qualities. The single input provides information to a controller  26  of the system  16  indicative of engine speed. Engine speed is a characteristic of engine performance that is available from many different sources. In this example a tachometer  20  provides information to the controller  26  via a single connection  22 . The one connection  22  is the only input that is provided to the controller  26  and all that is required by the example system  16  to generate a desired signal from the speaker  24 . 
     Referring to  FIG. 2 , operation of the noise enhancement system  16  is schematically shown and includes the initial step of reading a tachometer signal  30 . The tachometer signal  30  provides information indicative of engine speed as indicated at  32 . The engine speed is then derived to determine engine angular acceleration as shown at  34 . With knowledge of the engine speed  32  and engine angular acceleration  34 , a signal is derived for output by speaker  24 . The control signal that is utilized to drive the final noise output from the speaker  24  is arrived at by first using the tachometer signal  30  in concert with a desired setting provided by a lookup table as indicated at  36 . The tachometer signal  30  is indicative of engine speed and provides the initial sound character value indicated at  38 . This initial sound character value is combined with an acoustic gain value as indicated at  42 . 
     The acoustic gain value  42  is determined by using both engine speed  32  and engine angular acceleration along with an inventive algorithm  40 . The inventive algorithm  40  utilizes engine speed and engine acceleration to predict various driving conditions. Different driving conditions have different engine sound qualities that are generally expected by a passenger of the vehicle  10 . The specific driving characteristics result in specific and known engine behavior. This known engine behavior is utilized to predict the proper acoustic gain value  38  that is required to provide and enhance the noise signal emitted from the speaker  24 . 
     The noise enhancement system  16  utilizes information derived from the engine speed signal  30  to determine and predict the current driving conditions. The sound emitted from the speaker  24  is therefore modified in view of the predicted driving conditions. As is appreciated, certain driving conditions will result in a certain quality of noise or sound emitted from the engine  112 . This quality of noise emitted from the engine  12  is based on typical driving experiences of an operator. The noise enhancement system  16  of this invention adjusts predicts and crafts the audio signal  15  from the speaker  24  to replicate and enhance engine noise as is expected for the different driving conditions. 
     Some examples of the types of driving conditions that are correlated to the engine speed signal  30  include driving uphill or downhill, driving with a high or low load, up shifting or downshifting of a vehicle transmission along with accelerating and decelerating. The engine speed  32  and the engine angular acceleration  34  are analyzed to determine the current condition and predict how these conditions are changing during use so that the sound emitted by the speaker  24  can be crafted to match and produce an overall desirable sound quality. 
     Certain engine behavior for passenger vehicles is indicative of certain vehicle operating conditions. For instance it is understood that high throttle conditions generally mean that a vehicle is accelerating. Under braking conditions, a throttle is always closed and the vehicle will be decelerating. A gearshift either upwards or downwards is characterized by rapid change in engine speed. Such conditions can be determined with the engine speed  32  and engine angular acceleration  34 . 
     Engine angular acceleration  34  is generally faster at lower engine speeds for the same throttle opening. In other words, at lower engine speeds, acceleration of the vehicle would be much greater for the same throttle opening as compared to the same throttle opening at higher engine speeds. When a vehicle is in a neutral gear the engine acceleration will be much faster as there is no load on the vehicle. 
     This invention includes an algorithm utilizing engine speed  30  and engine angular acceleration  34  to predict the current driving conditions such that the sound emitted form the speaker  24  may be properly adapted to provide the desired overall sound quality. The algorithm predicts future engine sound and uses this prediction to determine the proper input for the speaker  24 . 
     These formulations or conditions provide the input required to predict and apply a proper value for the acoustic gain  42  for an engine speed  32  and angular acceleration  34 . Each range of engine speed  32  and engine acceleration  34  provides a different value for acoustic gain  42 , symbolically represented as β1. What follows is an example set of ranges and accompanying values for the acoustic gain  42  that are utilized to drive the speaker  24 . Ω denotes engine speed, {dot over (Ω)} denotes derived engine angular acceleration and β1 is the acoustic gain. The various examples of engine angular acceleration and engine speed represent or provide an indication of the specific acoustic gain that is required. 
     Range 1 below represents acceleration at a low engine speed as is indicated by the low engine speed and the relatively high angular acceleration. Acoustic gain during operation in this range is 1.0 indicating that full scale output is produced to get the acoustic quality value.
         Range 1: {dot over (Ω)}≧400 rpm/s and {dot over (Ω)}&lt;3000 rpm,
           β1=1.0 (acceleration at low speed).   
               

     Range 2 represents acceleration at a high engine speed. The angular acceleration in this range is less than that of Range 1. As appreciated this is so because at higher engine speeds, common throttle openings would represent different accelerations. In this example the lower range of angular acceleration indicates the acceleration at the higher engine speeds.
         Range 2: {dot over (Ω)}≧100 rpm/s and Ω&gt;3000 rpm,
           β1=1.0 (acceleration at high speed).   
               

     Range 3 indicates deceleration as the engine speed is low and angular acceleration is negative. The acoustic gain can be 0.1 if driving or 0 if this is a neutral condition. Range 4 indicates a deceleration from a high engine speed and modifies the acoustic gain to a value of 0.25, thereby modifying the overall sound character.
         Range 3: {dot over (Ω)}&lt;−100 rpm/s and Ω&lt;3000 rpm,
           β1=0.1 (or 0) (deceleration)   
           Range 4: {dot over (Ω)}&lt;0 rpm/s and Ω&gt;4000 rpm,
           β1=0.25   
               

     Range 5 indicates that the vehicle is under a low acceleration condition where the engine speed is low and the acceleration is low. The acoustic gain value is therefore low to accommodate and craft the sound output to provide the desired overall engine noise.
         Range 5: 0≦{dot over (Ω)}&lt;400 rpm/s and Ω&lt;3000 rpm,   β1=0.5 (low acceleration, low speed)       

     Range 6 indicates that the vehicle is at high speed and undergoing slow acceleration. The ranges of engine angular acceleration and engine speed indicated in example range 6 illustrate the characteristic of accelerating slower at higher engine speeds. The acoustic gain is thereby provided at a value that will so modify the overall sound emitted from the speaker.
         Range 6: {dot over (Ω)}&lt;100 rpm/s and Ω&gt;3000 rpm,   β1=0.5 (slow acceleration, high speed)       

     Range 7 is indicative of the vehicle moving in reverse and therefore the acoustic gain is set to a 0 value.
         Range 7: Ω&lt;0 rpm   β1=0 (reverse)       

     Range 8 includes a negative engine angular acceleration value and a low engine speed that indicates a gearshift in progress. The acoustic gain does not change during this time as this only a temporary condition. The controller  26  recognizes the combined engine angular acceleration values and engine speed values as a gear shift and does not modify the signal to the speaker  24 .
         Range 8: {dot over (Ω)}&lt;−1000 rpm/s or {dot over (Ω)}&gt;1000 rpm/s,   β1=unchanged (gearshift)       

     Each range of engine angular acceleration and engine speed corresponds with a specific desired acoustic gain value. These acoustic gain values are combined with the overall sound character  38 . The sound character  38  is a desired value determined by a passenger to adjust the overall sound emitted from the vehicle. The sound character  38  can include adjustments to make the vehicle sound more powerful or sportier as well as adjustments to minimize sound. 
     The specific ranges are examples of values and are only one set of possible example ranges that may be utilized to predict a desired acoustic gain value. These relationships between engine angular acceleration and engine speed are utilized to provide and formulate a general equation that is in turn utilized to determine the specific acoustic gain. Equation 1 provides the general relationship between engine angular acceleration  34  and engine speed  32  that is utilized to adjust acoustic gain in view of engine operation. 
     
       
         
           
             
               
                 
                   
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     Once the acoustic gain value  42  has been determined, it is combined with the acoustic sound character  38  to provide an initial signal that is utilized to drive the speaker  24 . This signal is then combined with a compensation transfer function  44 . This compensation transfer function  44  is applied to compensate for non-uniform values within the frequency response. This signal is then converted to a discreet control signal  46 , then through summation step  48  that combines each of the variables that have been derived from the tachometer signal to drive the speaker  24 . 
     The controller  24  sends the signal through a power amplifier  28 . The power amplifier  28  converts the control signals that have been determined by the various predictions and derivations originating from the original tachometer signal  30  to an electrical signal that is used to drive the speaker  24 . The speaker  24  then emits audio output  15  that enhances and combines with the sound emitted from the engine  12  through the intake manifold  14  to provide the desired enhanced sounds. 
     Referring to  FIG. 3 , the relationship between acoustic gain value, engine speed and engine angular acceleration is illustrated by graph  45  and includes engine speed values  44 , engine angular acceleration values  46 . The engine speed values  44  and an engine angular acceleration  46  are combined according to the relationship described by Equation 1 to provide a desired acoustic gain value  42 . This acoustic gain value  42  provides for the prediction of a desired sound character that is emitted from the speaker  24 . 
     Accordingly, the noise enhancement system  16  of this invention provides for robust sound enhancement through the use of a single input indicative of engine speed. No additional signals or information are required to provide the desired sound enhancement. The simplicity of this system by utilizing only a single input value that is indicative of engine speed reduces the overall complexity of this system while maintaining acceptable performance. Further, because only the single input of engine speed is required, this inventive noise enhancement system  16  is favorable for installation as an after-market system. 
     Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.