Abstract:
A method is provided for suppressing interference in a motor vehicle radio that is capable of executing a seek/scan function. Interference may occur from signals generated by a source of time varying signal that operates in the motor vehicle at a predetermined operating frequency. The method comprises the steps of sending a message indicating initiation of a seek/scan function. In response to this message, the operating frequency of the source of time varying signal is cycled between the predetermined operating frequency and an adjusted operating frequency.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS  
       [0001]     This is a continuation-in-part of application Ser. No. 10/665,795, filed Sep. 18, 2003. 
     
    
     TECHNICAL FIELD  
       [0002]     The present invention generally relates to a method for reducing interference in a motor vehicle radio, and more particularly relates to a method for reducing interference in a motor vehicle radio caused by sources of time varying signals such as switching power supplies when the motor vehicle radio utilizes a seek/scan function.  
       BACKGROUND  
       [0003]     There may be many sources in a motor vehicle that generate and broadcast time varying signals. For example, motor vehicles frequently employ switching power supplies that utilize pulse width modulation to convert the voltage from the vehicle power supply (usually twelve volts) to whatever particular voltage levels are required to run the various electronic modules connected to the power supplies. The switching power supplies nominally operate at an operating frequency in the frequency range from about 20 to 500 kilohertz (kHz). The operating frequencies or harmonics of the operating frequencies generated by the power supplies may cause interference with some motor vehicle radios, especially with the amplitude modulation (AM) frequency band of a motor vehicle radio. The AM frequency band extends from 520 kHz to 1710 kHz and especially the low-order harmonics of switching power supply operating frequencies may fall within that AM band frequency range. Because AM radio tuners have a ten kHz resolution, radio interference is experienced whenever a power supply operating frequency or harmonic of that operating frequency is within plus or minus five kHz (the interference range) of the frequency to which the radio is tuned.  
         [0004]     As disclosed in commonly assigned patent application Ser. No. 10/665,795, the entire disclosure of which is incorporated herein by reference, the problem of interference from switching power supplies and other sources of time varying signals in a motor vehicle can be largely overcome by switching the operating frequency of potential sources of such time varying signals to insure that the operating frequencies and all of the harmonics of the operating frequency are outside the interference range of the frequency selected by the tuned radio. The method disclosed in the above identified patent application comprises the steps of communicating to the source of the time varying signal the frequency selected by the tuned radio, comparing the selected frequency to the operating frequency of the source of the time varying signal and to the harmonics of that operating frequency, and adjusting the operating frequency if the operating frequency or any of the harmonics of the operating frequency fall within a predetermined interference range of the selected frequency. A further problem occurs, however, when using such frequency shift interference reduction in a motor vehicle having a motor vehicle radio that is capable of executing a seek/scan function. The message used to communicate the selected frequency must be sent out over a bus that couples the radio and the module that is the source of the time varying signal. Unfortunately, sending such a message can cause a problem because of bus latency. The receiving module must receive the message, decode the message, and then adjust its frequency (if necessary). If these steps are carried out at every tuned frequency encountered during the seek/scan function, including frequencies corresponding, not to a radio station signals, but to the operating frequency or a harmonic of the operating frequency of the module generating the time varying signal, this will result in a significant delay and a correspondingly long seek/scan time.  
         [0005]     Accordingly, it is desirable to provide a method for suppressing motor vehicle radio interference, caused by a module within the motor vehicle that generates a time varying signal, when the motor vehicle radio is capable of executing a seek/scan function. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.  
       BRIEF SUMMARY  
       [0006]     A method is provided for suppressing interference in a motor vehicle radio that is capable of executing a seek/scan function. Interference may occur from signals generated by a source of time varying signal that operates in the motor vehicle at a predetermined operating frequency. The method comprises the steps of sending a message indicating initiation of a seek/scan function. In response to this message, the operating frequency of the source of time varying signal is cycled between the predetermined operating frequency and an adjusted operating frequency. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]     The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and wherein  
         [0008]      FIG. 1  schematically illustrates a series of linked electronic modules in accordance with one embodiment of the invention; and  
         [0009]      FIG. 2  schematically illustrates, in matrix form, results of application of one embodiment of the invention. 
     
    
     DETAILED DESCRIPTION  
       [0010]     The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description.  
         [0011]     Motor vehicles commonly include electronic power supplies or other sources that generate time varying signals. Such sources include, for example, but are not limited to switching power supplies that are used to convert the battery or alternator voltage to whatever voltage level is needed to power a particular electronic module such as a display unit, anti-lock brake controller, and the like. Without loss of generality, but for ease of description and understanding, in the following description of the invention, such sources of time varying signal will hereinafter be referred to simply as power supplies or switching power supplies. The time varying signals generated by such power supplies can cause interference in the reception of signals by a radio in the motor vehicle. As disclosed in the above identified patent application Ser. No. 10/665,795, much of this interference can be suppressed by frequency shifting the operating frequency of any power supply causing the interference. Such frequency shifting to suppress interference, however, is inefficient when using the seek/scan function available in most motor vehicle radios.  
         [0012]     As is well known, enabling the seek function causes the radio to tune to the next higher (or lower) frequency at which a signal is present if the signal is of a magnitude exceeding the threshold discrimination level of the radio receiver. By repeatedly enabling the seek function, the radio will tune to consecutively occurring higher (or lower) frequency signals. Enabling the scan function causes the radio to tune to the next higher (or lower) frequency at which a signal is present if the signal is of a magnitude exceeding the threshold level of the radio receiver, remain tuned at that frequency for a predetermined length of time (the dwell time of the seek/scan function), and then repeat the process over and over with each next higher (or lower) frequency. As used herein, the term “seek/scan function” will be used for either or both the seek function and the scan function. Methods for implementing the seek/scan function in a motor vehicle radio are well known and need not be discussed here.  
         [0013]     A motor vehicle may have a plurality of electronic modules that generate and broadcast time varying signals that interact unfavorably with received radio signals. Although the problem of interference with radio reception is particularly troublesome for AM radio reception, the potential problem also exists for other radio reception.  FIG. 1  schematically illustrates a number of electronic modules  10 ,  12 , and  14  that are coupled together in a manner commonly found in a motor vehicle. One of the electronic modules, module  10  for example, can include a motor vehicle radio. The remaining electronic modules can be related, for example, to display units, anti-lock brake controllers, or other electronic functions now commonly found on motor vehicles. In accordance with an embodiment of the invention, the electronic modules are all coupled to a data bus  16  and to a wiring harness  18 . Although only three electronic modules are illustrated in  FIG. 1 , a motor vehicle electronics system may have any number of such electronic modules. Data bus  16  is preferably a serial data bus and may be implemented as a local area network (LAN) or the like. Wiring harness  18  is provided for the distribution of a DC voltage from motor vehicle power supply  19  which can be, for example, the motor vehicle  12  volt battery or the motor vehicle alternator (not illustrated). Each of electronic modules  10 ,  12 , and  14  comprises an electronic control unit (ECU)  20 ,  22 , and  24 , a switching power supply  26 ,  28 , and  30 , and an electronic unit  32 ,  34 , and  36 , respectively. Those of skill in the art will recognize that motor vehicle electronics typically involve a number of switching power supplies, but that other motor vehicle electronics besides switching power supplies are also potential sources of interfering time varying signals. For illustration purposes only, electronic unit  32  can be, for example, a radio, electronic unit  34  can be an electronic display unit, and electronic unit  36  can be an anti-lock brake controller. Electronic units  34  and  36  could also be other electronic units that perform other function in the operation or enjoyment of the motor vehicle. Switching power supplies  26 ,  28 , and  30  are coupled to and receive the DC voltage distributed by wiring harness  18  and, using pulse width modulation (PWM), convert the standard motor vehicle voltage to the correct voltage needed to run its associated electronic module. In common motor vehicle usage the switching power supplies are each designed to operate with an operating frequency that falls within the range of about 20 kHz to 500 kHz although other frequencies may also be used. The ECUs in each electronic module control, at least in part, the operation of the electronic units in the corresponding module and, as will be explained more fully below, control the operating frequency of the switching power supplies. Data bus  16  is coupled to each of electronic control units  20 ,  22 , and  24  and allows the ECUs to send and receive communication signals over the data bus. The various ECUs and switching power supplies illustrated need not all be the same, but rather can be specified for compatibility with the electronic unit with which they are associated. The ECUs can be microcontrollers or the like programmed in conventional manner as is known to those of skill in the art. Each of the switching power supplies is configured to provide the voltage level needed by its associated ECU and electronic unit. In accordance with an embodiment of the invention, electronic unit  32 , the motor vehicle radio, is coupled to a control  52  that enable the seek/scan function in the radio. When the seek/scan function is enabled by control  52 , for example when the radio operator in the motor vehicle pushes a seek or scan button, the radio tunes to the next available higher (or lower) frequency. When in the scan mode, the radio remains at that next available frequency for a predetermined dwell time (the seek/scan function predetermined dwell time), typically a fraction of a second, before tuning to the next still higher (or lower) frequency.  
         [0014]     In accordance with an embodiment of the invention, electronic unit  32  is a motor vehicle radio capable of tuning and receiving AM frequency signals. The motor vehicle radio preferably has a tuning resolution of 10 kHz and a corresponding interference range of plus or minus 5 kHz. Further in accordance with this embodiment of the invention, when the seek/scan function of the motor vehicle radio is enabled, a message is sent over bus  16  to each of the ECUs in each of the electronic modules indicating to each of the ECUs that a seek/scan function is being initiated. Receipt of the message indicating initiation of the seek/scan function causes each of the sources of time varying signal (the switching power supplies in this illustrative embodiment) in each of the electronic modules to begin cycling the operating frequency of the switching power supply between the nominal operating frequency for that power supply and an adjusted operating frequency. Preferably the adjusted operating frequency differs from the nominal operating frequency by an amount greater than the predetermined interference range of the motor vehicle radio. Preferably the cycle time period for cycling the frequency of the power supply is less than the dwell time of the seek/scan function.  
         [0015]     In accordance with one embodiment of the invention, during the time that the power supplies are cycling the operating frequency, the motor vehicle radio is set to lock onto a selected frequency only if the signal received by the radio is a continuous signal at a given frequency. Thus the motor vehicle radio will lock onto a radio station transmitting at a continuous frequency, but will not lock onto a noise source generated within the motor vehicle because the noise sources generated within the motor vehicle will not be constant, but instead will be cycling between two frequencies at a cycle time period less than the seek/scan function dwell time. This effect of this embodiment of the invention is illustrated by the matrix in  FIG. 2 . In the matrix left hand column  60  illustrates the status of signals from the possible noise sources present in the motor vehicle, center column  62  illustrates the status of possible radio station broadcast signals, and right hand column  64  illustrates the net effect of these signals on a motor vehicle radio operating in accordance with an embodiment of the invention. In the matrix an arrow indicates a signal at a frequency that is within the resolution range of the motor vehicle radio and a circle illustrates the absence of such a signal. As illustrated in box  66  of  FIG. 2 , a potential noise source is cycling between two frequencies: one frequency, either the operating frequency of a power source or one of its harmonics, illustrated by the arrow, is within the resolution range of the motor vehicle radio and a second adjusted frequency, illustrated by the circle, that is outside the resolution range of the motor vehicle radio. As illustrated in box  68  a radio station is broadcasting at a frequency within the resolution range of the motor vehicle radio as indicated by the arrow in that box. As illustrated in box  70 , the effect of the noise source in box  66  and the radio signal in box  68  is that the radio locks onto the radio station signal because that signal is broadcast at a continuous frequency and the noise signal is not at a continuous frequency. Similarly, as illustrated in the second row of the matrix, if a radio broadcast signal occurs within the resolution range of the motor vehicle radio (box  74 ) and no noise signal is present within that resolution range (box  72 ), the radio will lock onto the radio broadcast signal (box  76 ). As illustrated in the third row of the matrix, if a potential noise source is cycling between two frequencies (box  78 ): one frequency, either the operating frequency of a power source or one of its harmonics that is within the resolution range of the motor vehicle radio and a second adjusted frequency that is outside the resolution range of the motor vehicle radio but no radio broadcast signal occurs (box  80 ), the motor vehicle radio will not lock onto the noise signal (box  82 ) because the noise signal is not a continuous signal at a given frequency. And finally, as illustrated by the last line of the matrix, if no noise signal occurs (box  84 ) and no radio broadcast signal occurs (box  86 ), the motor vehicle will not lock onto a frequency in this range (box  88 ) but instead will continue to scan for a higher (or lower) frequency.  
         [0016]     In accordance with another embodiment of the invention, when the seek/scan function is completed a second message is communicated over bus  16  indicating the motor vehicle radio has locked on a selected frequency and has exited from the seek/scan function. In response to receiving this second message, the power sources, each of the sources of time varying signal, terminates the cycling of operating frequency. Either as a part of the message indicating the exit from the seek/scan function or in a separate further message communicated on bus  16 , the selected frequency is communicated to each source of time varying signal. The selected frequency is compared to the operating frequency and to the harmonics of the operating frequency of each source of time varying signal. If any operating frequency or harmonic of that operating frequency is found to fall within a predetermined interference range (typically plus or minus 5 kHz for an AM radio signal), that operating frequency is adjusted by a sufficient amount to avoid interference of the operating frequency or harmonic with the selected frequency.  
         [0017]     The message indicating initiation of the seek/scan function, the message indicating exiting from the seek/scan function, and the message communicating the selected frequency can be sent from ECU  20  associated with motor vehicle radio  32  or they can be sent by a centralized control unit that has control over a plurality of motor vehicle functions. Although in the illustrative embodiment a separate ECU and a separate power supply has been indicated for each of the electronic modules, in some applications electronic control units and/or power supplies may be shared between certain electronic modules.  
         [0018]     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 embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing the exemplary embodiment or exemplary embodiments. It should be understood that various changes can be made in the function and arrangement of elements without departing from the scope of the invention as set forth in the appended claims and the legal equivalents thereof.