Abstract:
The active noise attenuation system comprises a speaker, a control unit in communication with the speaker, and a memory unit in communication with the control unit storing cancellation waveform data. The system uses the stored cancellation waveform data to create a cancellation waveform through a speaker in proximity to an air induction system to thereby attenuate engine noise. Sensors serve to trigger the release of the cancellation waveform as well as to affect the form of the cancellation waveform to ensure noise attenuation.

Description:
[0001]    This application claims priority to Provisional Patent Application Ser. No.  
         [0002]    [0002] 60 / 198 , 077  filed Apr. 17, 2000. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0003]    This invention relates to an active control for automotive induction noise.  
           [0004]    Manufacturers have employed active and passive methods to reduce engine noise within the passenger compartment. Such noise may travel from the engine and through the air induction system.  
           [0005]    Efforts have been made to reduce the amount of engine noise traveling through the air induction system. These efforts include the use of passive devices such as expansion chambers and Helmholtz resonators. Active devices involving anti-noise generators have also been proposed. These systems use a speaker that generates a sound that is out of phase with the engine noise to cancel the noise. This cancellation signal is generated in proximity to the air induction system.  
           [0006]    In one such system, the cancellation signal is generated in real time by a digital signal processor based on detected noise levels. Such a system requires a microphone to detect the current engine noise level and a reference signal such as an engine tachometer signal. Based on the signal from the microphone as well as the reference signal, a cancellation signal is created and passed through an audio amplifier to the speaker located in proximity to the air induction system.  
           [0007]    Several drawbacks exist to the real time measurement of engine noise and creation of its corresponding cancellation signal. First, a digital signal processor controller is more expensive than a microprocessor based controller. Second, a digital model of the acoustical-mechanical-electrical transmission path of the cancellation signal is required for the stable operation of the digital signal processor based controller. Any change in the physical configuration of the elements included in the signal transmission path will result in the speaker generating loud and annoying noise due to the instabilities arising from the poor modeling of the transmission path. Third, the degree of noise cancellation using real time control is limited during engine acceleration since the required cancellation signal must be generated fast enough to track the change in engine noise generated as the engine speed changes. Finally, real time control requires an error microphone, which must be located such that the ambient vehicle noise does not overwhelm the noise radiating from the annular intake/speaker.  
           [0008]    A need therefore exists for a means of creating a cancellation signal using an inexpensive microprocessor based controller to eliminates these problems.  
         SUMMARY OF THE INVENTION  
         [0009]    In a disclosed embodiment of this invention, the active noise attenuation system comprises a speaker, a control unit in communication with the speaker, and a memory unit in communication with the control unit that stores data relating to the cancellation signal. The cancellation signal is preferably related to engine data such as a particular engine speed. Generally, there is a proportional relationship between such data and engine noise. Because the cancellation signal is stored in memory, the system need not calculate the cancellation signal in real time.  
           [0010]    In operation in a vehicle, the speaker is disposed about the air induction system. A sensor communicates with the control unit to trigger the recall from memory of the appropriate cancellation signal necessary to attenuate engine noise at the particular engine speed. In such a configuration, a sensor detects the engine speed and then communicates this speed to the control unit. The control unit then retrieves from the memory unit the appropriate cancellation waveform and then projects this waveform through the speaker to attenuate engine noise. An environmental sensor, such as an air temperature, pressure, or humidity sensor, may serve as input to the control unit to affect the particular form of the cancellation signal.  
           [0011]    An important element of this system is the creation and storage of the cancellation signal in the memory unit. While the system normally operates offline, the cancellation signal data for the system is generated in real time. First, engine noise associated with a particular speed is sensed. The cancellation signal needed to attenuate this noise is then determined and then recorded with the particular engine speed. Finally, the cancellation signal data is stored in the memory unit for later recall by the control unit.  
           [0012]    By storing the cancellation signal data in the memory unit, the cancellation signal is not determined in real time but instead recalled from the memory unit by the control unit. The response time for such a system is faster than systems currently available. Moreover, only a microprocessor rather than a digital signal processor is required for this system. While a microphone is used to sense and aid in the collection of the cancellation signals, in operation in the vehicle, the system requires no microphone. The information may be determined experimentally for a model of a particular vehicle style, and then utilized and programmed into the control for each vehicle made according to that model. Alternatively, the control could be somewhat more complex, and would be stored on the actual individual vehicle. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows:  
         [0014]    [0014]FIG. 1 shows an embodiment of the invention including speaker, control unit, and memory unit.  
         [0015]    [0015]FIG. 2 shows the embodiment of the invention of FIG. 1 in its environment represented schematically.  
         [0016]    [0016]FIG. 3 shows the means by which the cancellation waveform data is generated and stored.  
         [0017]    [0017]FIG. 4 is a graph of the scaling factor used to modify the cancellation waveform of the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0018]    [0018]FIG. 1 shows a cross-sectional representation of the invention. Shown are speaker  10 , control unit  14 , and memory unit  18  within air duct body  22  of an air induction system of a vehicle. As known, the air induction system supplies air to an engine in a manner well-known and not illustrated here. Speaker is an axially symmetric speaker supported to minimize airflow restriction through air induction system. Control unit  14  includes a microprocessor and may include analog to digital converter as well as a digital to analog converter. Control unit  14  is in communication with memory unit  18  as well as speaker  10 . Amplifier  26  serves to amplify any signal from control unit  14  to speaker  10 .  
         [0019]    Memory unit  18  in communication with control unit  14  stores cancellation waveform data. This cancellation waveform data comprises the data necessary to attenuate noise that is preloaded into memory unit  18 . Such data may include the actual attenuating waveforms themselves, scaled versions of these waveforms, or their characteristics all organized in a manner for retrieval by control unit  14 . Preferably, the cancellation waveform data comprises at least one cancellation waveform related with engine data such as engine speed.  
         [0020]    Also shown are two sensors  30  and  34  in communication with control unit  14 . One sensor  30  may detect the engine speed while the other sensor may be a throttle position sensor  34 . As will be explained in detail, the sensor that detects engine speed  30  provides the timing for the release of the cancellation waveform while the throttle position sensor  34  determines the scaling factor for the amplitude of the cancellation waveform. One of ordinary skill in the art could employ other sensors to inform control unit  14  to optimize noise attenuation. Indeed, such sensors may be environmental sensors that sense air temperature, humidity, and pressure. These environmental conditions, especially air temperature, may impact noise attenuation by the cancellation waveform and may therefore be considered.  
         [0021]    As illustrated by FIG. 1 and FIG. 2, speaker  10  is supported within air duct body  22  at mouth  38  as known in the art. In operation, engine noise  42  from engine  40  (shown schematically) has traveled from engine  40  though air duct body  22 . Since speaker  10  is co-axially mounted and in the same plane as mouth  38 , both the radiated engine noise and the cancellation waveform  46  radiating from speaker  10  share a common location thereby minimizing engine noise  42 .  
         [0022]    Sensor  30  detects engine speed and communicates with control unit  14 . The speed of engine  40  may be computed by control unit  14  from sensor  30 . As an example, sensor  30  may emit one pulse every two engine revolutions. Generally, control unit  14  preferably receives a signal from sensor  30  at about half the engine speed. Of course, other ways of identifying engine speed may be used. Based on engine speed, control unit  14  selects the appropriate cancellation waveform  46  from memory unit  18  and determines the amplification necessary to attenuate engine noise based on the size of the throttle opening according to the throttle position sensor  34 . Cancellation waveform  46  has a period corresponding to two engine revolutions to match period of engine noise  42  Sensor  34 , a throttle position sensor, determines the size of the throttle opening and communicates the throttle position to control unit  14 . The amplitude of cancellation waveform  46  is scaled appropriately (a scaling factor of 1 representing a completely open throttle opening while  0  represents a completely closed throttle opening) by control unit  14  through amplifier  26  and then propagated out by speaker  10 . Cancellation waveform  46  is out of phase with engine noise  42 , preferably 180 degrees out of phase. A ring buffer may be employed in the control to continue the cancellation waveform  46  until engine speed, throttle position, or any other sensed condition changes in the system. In this way, cancellation waveform will continuously serve to attenuate engine noise until conditions change.  
         [0023]    It is important to note that the retrieval of cancellation waveform  46  from memory unit  18  take little time to ensure instantaneous response of the system. Even so, the short delay is preferably compensated for the phase of cancellation waveform  46  to accommodate for the delay and ensure optimal wave cancellation. The compensation occurs by delaying cancellation waveform a small time T which is slightly longer than the time required by control unit  14  to retrieve and scale cancellation waveform  46 . The time required by the control unit to retrieve and scale the waveform may be determined experimentally based upon the system and then the time could be programmed into the control.  
         [0024]    For each vehicle, cancellation waveforms stored in memory unit  18  are generated and stored using a real time system as shown in FIG. 3. Speaker  10  is disposed in mouth  38  of air duct body  22  of air induction system with microphone  54  in close proximity. As known in the prior art, amplifier  26  is connected to real-time digital signal processor controller  58  with analog-to-digital inputs  64  and  68  from microphone  54  and engine speed sensor  30 , respectively. Real-time digital signal processor controller  58  also has digital to analog output  72  to computer  76 . The embodiment of FIG. 3 generates the cancellation waveform data for every engine speed of engine  40  in real time by a real-time digital signal processor controller  58  as already known in the art. The cancellation waveform data is collected during a slow acceleration of the engine from idle to redline at wide-open throttle. A high-resolution engine speed sensor  30  such as a high-resolution tachometer is employed. The signal from sensor  30  is at least 60 pulses per engine revolution. Also, the signal from microphone  54  is sampled by the real-time digital signal processor controller  58  through analog-to-digital input  64 . As known in the art, the real-time cancellation waveform data—the cancellation waveform for each engine speed—is created by this arrangement and communicated to computer  72 , which stores this information in memory unit  18  such as an EPROM. Memory unit  18  is subsequently inserted into the system of FIGS. 1 and 2 to permit reference by control unit  14  of data during vehicle operation.  
         [0025]    The system of FIG. 3 also determines the scaling factor used to modify the amplitude of the generated cancellation waveform. This scaling factor is determined by operating the real-time digital signal processor controller  58  and configuration of FIG. 3 for each degree of throttle opening and determining the cancellation waveform for each degree of opening. The degree of change of the amplitude of the cancellation waveform needed to attenuate engine noise over the degrees of throttle opening reflects the scaling factor. The scaling factor will vary from engine to engine and vehicle to vehicle. The scaling factor is stored in memory unit  18  for use by control unit  14  to determine the amplitude of cancellation waveform depending on the size of the throttle opening.  
         [0026]    The scaling factor for a particular engine and vehicle is shown in FIG. 4. The waveform scaling factor is plotted against throttle position in degrees from wide open (WOT). From 0 degrees to about 16 degrees (open throttle) from throttle wide open, the cancellation waveform need not be scaled down for this particular engine and vehicle. Also, from about 72 to about 90 degrees (closed throttle) from throttle wide open, the cancellation waveform is scaled down significantly. Between about 16 degrees to about 72 degrees, the scaling factor is linear. The scaling factor will vary for each engine and vehicle.  
         [0027]    The system of FIG. 3 may be utilized per model type of vehicle to generate information such as that shown in FIG. 4 for a particular vehicle style carrying a particular engine. Then, this information can be stored into each vehicle made according to that model. While more complex, the system could be incorporated into each actual vehicle which would generate the information for the particular vehicle. Further, as mentioned above, sensors sensing environmental factors may also be incorporated into the information such as shown in FIG. 4. Again, while this information would be more complex to generate, store and utilize, it would also provide more effective cancellation of noise. The information tied to particular environmental conditions can be gathered in a similar fashion to that explained above with regard to FIG. 3. Varying environmental conditions can be changed under a control setting, and the resulting information stored. Further, the structure and processes for positioning mounting and operating this speaker may be as known. This invention relates to the generation of a preferred waveform for cancellation of condition.  
         [0028]    The aforementioned description is exemplary rather then limiting. Many modifications and variations of the present invention are possible in light of the above teachings. The preferred embodiments of this invention have been disclosed. However, one of ordinary skill in the art would recognize that certain modifications would come within the scope of this invention. Hence, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. For this reason the following claims should be studied to determine the true scope and content of this invention.