Abstract:
A tire parameter monitoring system has a plurality of sensor units each mounted with a different vehicle tire. Each sensor unit has a magnetic sensing element for converting magnetic field signals generated by a proximate set of magnets mounted to the vehicle at the tire locations. Each magnet set generates a unique magnetic field which identifies the magnet set location. Each sensor unit has a microcontroller for combining the converted magnetic field signals with fire parameter signals, and a transmitter for transmitting the combined signals to a receiving location. Received tire parameter signals are correlated with the tire location using the location signals, and driver advisory signals are presented to the driver.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to vehicle tire parameter monitoring systems. More particularly, this invention relates to a fire parameter monitoring system having a sensor unit position location feature using permanent magnets. 
     Tire parameter monitoring systems are known and are commonly used to monitor one or more parameters of interest in individual pneumatic tires of a vehicle and to provide an advisory signal to the driver, usually via an on-board computer system, containing information about the fire parameter(s). The portion of the fire parameter monitoring system located at or in the individual fires is termed the sensor unit, and is coupled to one or more sensors capable of measuring the parameter(s) of interest and generating an electrical signal representative of the value of the measurement, a signal generator (typically an r.f. signal generator) capable of generating a wireless signal corresponding to the electrical signal, a microcontroller (such as a microprocessor or a digital signal processor) and a power source. Electrical power to the sensor circuitry is usually provided by a battery, which must be replaced (if possible) when the available battery power drops below a useful level. In some known systems, the battery cannot be replaced so that the entire sensor assembly must be replaced when the battery has reached the end of its useful lifetime. A tire parameter sensor system which monitors internal tire pressure is disclosed in commonly assigned, U.S. Pat. No. 6,959,594 issued Nov. 1, 2005 for “External Mount Tire Pressure Sensor System”, the disclosure of which is hereby incorporated by reference. A tire pressure monitoring system which incorporates a power saving unit providing extended useful battery life is disclosed in commonly assigned, U.S. Pat. No. 7,222,523 issued May 29, 2007 for “Tire Pressure Sensor System With Improved Sensitivity And Power Saving”, the disclosure of which is hereby incorporated by reference. A tire parameter monitoring system which eliminates the usual battery is disclosed in commonly-assigned, co-pending patent application Ser. No. 11/473,278 filed Jun. 22, 2006 for “Tire Parameter Monitoring System With Inductive Power Source” (the &#39;278 application), the disclosure of which is hereby incorporated by reference. 
     The advisory signal produced by the sensor unit may indicate (a) whether a given parameter in the associated vehicle tire has a current value lying within or outside of a predetermined safe range, (b) the measured value of the parameter, or (c) some other fire parameter information of interest. Examples of common tire parameters are internal tire pressure, tire temperature, internal tire air temperature, and lateral tire force. In some cases, the parameter may be related to the condition of the wheel on which the tire is mounted, such as the angular moment of the wheel, concentricity or the like. 
     The advisory signal is typically generated by the r.f. signal generator controlled by the microprocessor connected to the tire parameter sensor, the advisory signal being generated in accordance with the system design characteristics: i.e., whether the system uses the range indicator value (in range/outside range), the measured value, or the other information of interest. This r.f. signal is transmitted to a vehicle-mounted receiver, which uses the advisory signal to alert the driver either visually (by activating a warning lamp or display) or audibly (by activating an audible alarm) or both. Alternatively, or in addition, the receiver may use the advisory signal for some other system purpose, such as to activate a vehicle control system, such as braking control, suspension control, and the like; to store the parameter data for future analysis; or for any other desired purpose. 
     In order to provide an operable system, it is necessary to correlate the advisory signals received by the vehicle-mounted receiver with the physical location on the vehicle of the tire whose parameter condition is specified by a given advisory signal. In the past, various techniques have been devised for this purpose. A common technique is the inclusion of an identification signal along with the parameter condition in a given advisory signal: the identification signal is unique to the sensor unit which generates the parameter condition. This unique identification signal is initially correlated to tire location on the vehicle by a technician having the required skill and training to operate the system in an initial training mode. Once each sensor unit has been initially correlated to its physical location on the vehicle, any advisory signal generated by a given sensor unit and received by the vehicle-mounted receiver can be uniquely identified with the location of the tire whose parameter condition is specified by the advisory signal. 
     A disadvantage with this type of location correlation technique is that any change to the original tire and sensor unit location requires that the system be re-correlated. For example, if the vehicle tires are relocated to different positions in the normal course of vehicle servicing, the physical locations of the sensor units will change if the sensor units are fixed to the tires or the wheels on which the tires are mounted (which is typical), and each individual sensor unit must be re-correlated to the physical location of the associated tire. The same is true (a) when a spare tire is exchanged for a flat tire on the vehicle; (b) when one or more new tires are installed on the vehicle wheels and mounted on the vehicle; and (c) when a new sensor unit is installed in place of a unit which stops functioning property. As noted above, re-correlation requires the efforts of someone having the required skill and training to operate the system in a training mode. While some vehicle owners may be capable of acquiring the necessary skill and training, others may not. The latter will necessarily suffer delay and expense when re-configuring the vehicle tires and wheels; the former will suffer at least the delay attendant upon re-familiarizing oneself with the steps required to re-program an electronic system. 
     A variation of this type of sensor unit correlation system uses a manually actuatable transmitter installed in the valve stem of a tire. The transmitter is actuated by inserting a small object into the valve stem a sufficient axial distance to operate a switch, which causes the transmitter to send an appropriate signal to a vehicle-mounted receiver capable of correlating the signal from the operating transmitter to the tire to which the transmitter is attached. An example of this type of system is disclosed in U.S. Pat. No. 6,998,975 B2 issued Feb. 14, 2006, the disclosure of which is hereby incorporated by reference. This system requires some provision for ensuring that any change to the original sensor unit/tire location configuration will cause a re-correlation of the sensor units with the new configuration. 
     Another common technique used to correlate the advisory signals received by the vehicle-mounted receiver with the physical location on the vehicle of the tire whose parameter condition is specified by a given advisory signal incorporates a special multiple antenna interrogator system connected to a vehicle-mounted controller and a complementary set of sensor units. Each antenna is connected to the controller in such a way that only one antenna is actively coupled to the controller during any given interrogation interval. Each antenna is located adjacent a different associated one of the sensor units in sufficiently close proximity that an interrogation signal generated by a given antenna is operatively coupled essentially only to the associated sensor unit. Each sensor unit has a circuit responsive to an interrogation signal from the associated antenna to initiate a parameter signal transmission sequence during which the value measured by a sensor is transmitted to a receiver located in the vehicle-mounted controller, where it is processed. Since the location of each individual interrogation antenna is fixed, it can be permanently correlated to a wheel location. Therefore, when the controller activates a given interrogation antenna, the subsequently received parameter signal is automatically correlated with the correct tire location. Examples of this type of unit are disclosed in U.S. Patent Application Publication No. US 2003/0145650 A1 published Aug. 7, 2003; and U.S. Pat. No. 6,838,985 B2, the disclosures of which are hereby incorporated by reference. 
     A disadvantage to the interrogator antenna system described above lies in the requirement for the installation of the separate interrogation antennae adjacent the tire parameter sensor units. The necessary electrical cabling must be routed between the controller and the individual antennae. This imposes a requirement of careful routing of the cables to avoid mechanical abrasion, electrical interference, and thermal stresses over time. As a consequence, installation cost and hardware durability are factors of concern when deciding to implement such a system. 
     Efforts to provide a simple, inexpensive, reliable, and accurate sensor unit location feature for a tire parameter sensing system devoid of the above-noted disadvantages have not been successful to date. 
     SUMMARY OF THE INVENTION 
     The invention comprises a method and system for providing sensor unit location information which is simple and inexpensive to implement, highly reliable, and accurate. 
     In a first apparatus aspect, the invention comprises a sensor unit for use with a vehicle mounted tire parameter monitoring system having at least one tire parameter sensor, the sensor unit including a magnetic sensing element for generating location signals from magnetic fields encountered by the magnetic sensing element; a microcontroller coupled to the magnetic sensing element for receiving and processing the location signals and tire parameter signals from an associated tire parameter sensor; and a signal generator controlled by the microcontroller for transmitting the processed location signals and the tire parameter signals to a receiving location. The magnetic sensing element of the sensor unit preferably comprises an inductive coil having an output coupled to an input of the microcontroller. 
     The sensor unit further preferably includes an analog-to-digital converter having an input coupled to the magnetic sensing element and an output coupled to the microcontroller for converting the analog location signals to digital form. 
     The sensor unit further includes one or more tire parameter sensors each having an output coupled to the microcontroller for supplying current values of the monitored tire parameters for processing by the microcontroller. 
     In a second apparatus aspect, the invention comprises a tire parameter monitoring system for monitoring the current values of tire parameters of tires mounted on a vehicle, the system comprising a plurality of sensor units each associated to a different tire on the vehicle, each sensor unit including a magnetic sensing element for generating location signals from magnetic fields encountered by the magnetic sensing element; a microcontroller coupled to the magnetic sensing element for receiving and processing the location signals and tire parameter signals from an associated tire parameter sensor; and a signal generator controlled by the microcontroller for transmitting the processed location signals and the tire parameter signals to a receiving location; and a plurality of sets of magnets for generating a plurality of different magnetic field signals, each set of magnets being located in proximity to a different one of the plurality of sensor units in a location at which the magnetic field generated thereby is encountered by the corresponding sensor unit as the associated tire rotates. Each magnetic sensing element preferably comprises an inductive coil. 
     Each sensor unit preferably includes an analog-to-digital converter having an input coupled to the magnetic sensing element and an output coupled to the microcontroller for converting analog location signals to digital form. 
     Each said sensor unit further preferably includes one or more tire parameter sensors each having an output coupled to the microcontroller for supplying current values of the monitored tire parameters for processing by the microcontroller. 
     The system further includes a receiver processor for receiving and processing the location signals and tire parameter signals from the sensor units. 
     From a process standpoint, the invention comprises a method of correlating tire parameter signals generated by sensor units associated to different ones of a plurality of tires on a vehicle with the location of tires whose parameters are monitored by the sensor units, the method comprising the steps of:
         (a) generating a plurality of different magnetic field signals in proximity to the sensor units, each different magnetic field signal being associated to a different tire location on the vehicle;   (b) converting each different magnetic field signal to an electric sensor unit location signal;   (c) combining each electric sensor unit location signal with the tire parameter signals from the sensor unit at the location specified by the electric sensor unit sensor signal, and   (d) transmitting the signals combined in step (c) to a receiving location.       

     Step (a) of generating preferably includes the step of using a plurality of sets of permanent magnets, each set being located in proximity to a different tire. 
     Step (b) of converting preferably includes the steps of moving a magnetic sensing element located on a given sensor unit through the proximate magnetic field signal. 
     Each electric sensor unit location signal is preferably an analog signal; and step (b) of converting preferably includes the step of converting the analog signal to a digital signal. 
     The method further preferably includes the step (e) of processing the signals transmitted in step (d) at the receiving location, and the step (e) of processing preferably includes the step of generating a driver advisory signal for a given tire parameter. 
     For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic top plan view of a tire parameter sensing system incorporating the sensor unit location feature of the invention; 
         FIG. 2  is a schematic side view showing one magnet pair mounting arrangement according to the invention; 
         FIG. 3  is a schematic front view showing a tire and wheel mounted in operative relation to the magnet mounting arrangement of  FIG. 2 ; 
         FIG. 4  is a schematic perspective view showing another magnet pair mounting arrangement according to the invention; 
         FIG. 5  is a schematic front partial sectional view showing a tire and wheel mounted in operative relation to the magnet mounting arrangement of  FIG. 4 ; 
         FIG. 6  is a schematic block diagram of a preferred embodiment of a sensor unit; 
         FIG. 7  is a compound diagram illustrating four different, unique magnetic polarity orientations and the corresponding associated electric waveforms; 
         FIG. 8  is a compound diagram illustrating a plurality of unique magnetic polarity orientations using three magnets and the corresponding eight associated electric waveforms. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Turning now to the drawings,  FIG. 1  is a schematic top plan view of a tire parameter sensing system incorporating the sensor unit location feature of the invention. As seen in this Fig., which illustrates a vehicle having four tires and wheels, each tire has an associated tire parameter sensor unit SU. Thus, left front tire  11  is provided with SU  12 ; right front tire  13  is provided with SU  14 ; left rear tire  15  is provided with SU  16 ; and right rear tire  17  is provided with SU  18 . As described more fully below in connection with  FIG. 6 , each SU  12 ,  14 ,  16 , and  18  is connected to one or more tire parameter sensors for monitoring the state of individual tire parameters, such as internal tire pressure, tire temperature, internal tire air temperature, and lateral tire force. Such sensors are well known in the art and will not be described further to avoid prolixity. The physical location of the individual SUs  12 ,  14 ,  16 , and  18  is a matter of design choice and may include the outer side wall of the associated tire, the inner side wall of the tire, within the tire carcass at an appropriate location (such as within the inner side wall of the tire as illustrated in  FIG. 3  or within the tread wall of the tire as illustrated in  FIG. 5 ), or on the wheel hub. Each SU  12 ,  14 ,  16 , and  18  further incorporates a magnetic field sensing element for a purpose to be described. Each SU  12 ,  14 ,  16 , and  18  also incorporates a microcontroller unit for processing sensor signals and magnetic field signals, and an r.f. transmitter unit for transmitting tire parameter advisory signals and magnetic field signals to a central receiver/processor  25 . Central receiver/processor  25  uses the magnetic field signals to associate the tire parameter advisory signals with the correct tire, and converts the tire parameter advisory signals into driving signals for a display/alarm unit  26  of conventional design, in which the parameter states can be displayed for the user and in which audible alarm signals can be generated to alert the driver of a dangerous tire condition. 
       FIGS. 2 and 3  illustrate one magnet pair mounting arrangement used in conjunction with SUs  12 ,  14 ,  16 , and  18  to provide sensor unit location signals according to the invention.  FIG. 2  is a schematic side view showing the magnet pair mounting arrangement, while  FIG. 3  is a schematic front view showing a tire and wheel mounted in operative relation to the magnet mounting arrangement of  FIG. 2 . With reference to  FIG. 2 , a pair of permanent magnets  31 ,  32  is secured to a suspension component  34  at a location adjacent a wheel mounting hub  35 . Magnets  31 ,  32  are thus stationary with respect to the wheel and tire when the wheel and tire are rotating. The exact location of magnets  31 ,  32  is a function of the geometry of the wheel and tire and the location of the sensor unit. As seen in  FIG. 3 , which illustrates the left front tire  11  viewed from the rear and looking forward, for a sensor unit  12  mounted within the side wall of tire  11 , magnets  31 ,  32  are mounted on suspension unit  34  in a location at which the combined magnetic fields will encounter the magnetic field sensing element incorporated into sensor unit  12 . Thus, whenever tire  11  is rotating, sensor unit  12  will encounter the combined magnetic field from magnets  31 ,  32  once per tire revolution. 
       FIGS. 4 and 5  illustrate another magnet pair mounting arrangement used in conjunction with SUs  12 ,  14 ,  16 , and  18  to provide sensor unit location signals according to the invention. This arrangement is used in those installations in which the sensor unit is mounted in the tread wall of the tire.  FIG. 4  is a schematic perspective view showing this magnet pair mounting arrangement, while  FIG. 5  is a schematic front view partially in section showing a tire and wheel mounted in operative relation to the magnet mounting arrangement of  FIG. 4 . With reference to  FIG. 4 , a pair of permanent magnets  31 ,  32  is secured to a mechanical component  37  (such as a fender) at a location adjacent the upper surface of the tire tread wall  38 . Magnets  31 ,  32  are thus stationary with respect to the wheel and tire when the wheel and tire are rotating. The exact location of magnets  31 ,  32  is a function of the geometry of the wheel and tire and the location of the sensor unit. As seen in  FIG. 5 , which illustrates the left front tire  11  viewed from the rear and looking forward, for a sensor unit  12  mounted within the tread wall  38  of tire  11 , magnets  31 ,  32  are mounted on mechanical component  37  at a location at which the combined magnetic fields will encounter the magnetic field sensing element incorporated into sensor unit  12 . Thus, whenever tire  11  is rotating, sensor unit  12  will encounter the combined magnetic field from magnets  31 ,  32  once per tire revolution. 
       FIG. 6  is a schematic block diagram of a preferred embodiment of a sensor unit SU. As seen in this Fig., a magnetic field sensing element  41 , illustrated as a multi-turn coil, is ohmically connected to two different circuit paths. The upper path comprises an analog-to-digital converter  42  having a pair of input terminals to which the output of magnetic field sensing element  41  is connected. The output of analog-to-digital converter  42  is connected to an input of a microcomputer unit  43 . The lower path comprises a rectifier circuit  45  having a pair of input terminals to which the output of magnetic field sensing element  41  is connected. The output of rectifier circuit  45  is connected to a D.C. power regulator circuit  46 . Elements  45 ,  46  function to develop D.C. power from the electrical current developed in coil  41  from passing through the magnetic field produced by magnets  31 ,  32  once per revolution of the associated tire. This process is more fully described in the afore-mentioned &#39;278 application. 
     One or more tire parameter sensors  47  supply tire parameter electrical signals representative of the value of the sensor measurement(s) to the microcomputer unit  43 . Microcomputer unit  43  combines these signals with the digital version of the magnetic field sensing element  41  signals and supplies these to an r.f. generator  48 . R.f. generator  48  converts the received signals and transmits the converted signals to central receiver processor  25 , in which the received signals are processed and used to drive display/alarm unit  26 . Since the received signals contain the magnetic field identification signals, the accompanying tire parameter measurement signals are correlated to the magnetic field identification signals. The microcomputer unit  43  and r.f. generator  48  are preferably combined in a commercially available Freescale type MC68HC908RF2 unit or the equivalent, having a transmitter section for generating r.f. information signals containing tire parameter measurement results and magnetic field sensing element signals, and a microcomputer for supervising and controlling the operation of the transmitter section and for sensing the analog-to-digital converter  42  signals and the sensor output signals and converting these sampled signals to measurement data to be supplied to the transmitter section. 
       FIG. 7  is a compound diagram illustrating four different, unique magnetic polarity orientations and the corresponding associated electric waveforms which uniquely identify the location of a given sensor unit  12 ,  14 ,  16 ,  18 . As seen in this Fig., magnets  31 ,  32  can be arranged in four different and unique magnetic polarity orientations: NS, SN, SS, and NN. In this Fig., the legend N signifies that the north pole of the magnetic field generated by a magnet faces the viewer and the south pole is located at the hidden reverse surface of the magnet; while the legend S signifies that the south pole of the magnetic field generated by a magnet faces the viewer and the north pole is located at the hidden reverse surface of the magnet. When magnetic field sensing element  41  passes through the compound magnetic field produced by a given combination of magnets  31 ,  32 , the resulting induced analog electrical signal has a unique shape as illustrated for the four different magnetic orientations. Each unique shape is permanently assigned to a tire location on the vehicle. In the example illustrated in  FIG. 7 , the uppermost signal shape is assigned to the front right tire location; the next signal shape is assigned to the front left tire location; the next signal shape is assigned to the rear right tire location; and the lowermost signal shape is assigned to the rear left tire location. As will be appreciated by those skilled in the art, the signal shape assignments are arbitrary: what is necessary is that the signal shape assignments be unique, invariant and programmed into the central receiver/processor  25 . In this way, any tire parameter measurement signals received by the central receiver/processor  25  can be correlated to the transmitting location by the accompanying magnetic field sensing element signals. 
     When installing a system according to the invention at the vehicle factory, the usual quality control procedures can readily assure that the orientation of magnets  31 ,  32  conforms to the signal shape assignments for the fire locations, which are programmed into the central receiver/processor  25 . Similarly, when installing a system according to the invention as an aftermarket item, care need only be taken that the orientation of magnets  31 ,  32  conforms to the signal shape assignments for the tire locations. Once installed, re-location of tires does not affect the accuracy and reliability of the system since the location of the sensor units is irrelevant to the identification of the location of the transmitting sensor unit. Thus, a spare tire can be exchanged for a tire on the vehicle without affecting the operation of the system. 
     While the preferred embodiment has been described with reference to vehicles having four running tires, the invention is not so limited. For vehicles having more than four running tires, additional magnets can be added at each location and the signal shape assignments can be altered accordingly to accommodate analog signals having three or more components.  FIG. 8  illustrates a three magnet arrangement which can uniquely identify up to 8 individual tires. In general, for N magnets, the number of individual tires which can be uniquely identified is 2 exp N. 
     Further, although the sensor unit has been described above as including an inductive D.C. power generating section comprising rectifier circuit  45  and D.C. power regulation unit  46 , if desired this section may be omitted and some other D.C. power source—such as a battery—may be included. In such a configuration, the location signals and the sensor signals are processed in the same way as in the sensor unit described above. 
     As will now be apparent, the invention provides a tire parameter sensing system incorporating a sensor unit location feature which is simple and inexpensive to implement, highly reliable, and accurate. Installation of systems according to the invention can be readily done at the vehicle factory as an integral part of the manufacturing operation, or by aftermarket installers to retro-fit existing vehicles with the latest tire parameter monitoring technology. Once installed, tires can be re-located to other arbitrary locations without affecting the accuracy and reliability of the location information. 
     While the invention has been described with reference to particular preferred embodiments, various modifications, alternate embodiments, and equivalents may be employed, as desired. For example, other magnetic sensing elements, such as Hall effect sensors or MR sensors, may be employed in place of the simple multi-turn coil element, as desired. Therefore, the above should not be construed as limiting the invention, which is defined by the appended claims.