Abstract:
A tire pressure monitoring system ( 12 ) for a vehicle ( 10 ) has a plurality of tires ( 14 A-D) in respective rolling locations having a respective plurality of tire transmitters ( 16 A-D) that generate a respective plurality of transmitter identification signals. A respective plurality of initiators ( 20 A-D) are fixedly attached to the vehicle at a respective plurality of locations. The initiators may include orthogonal coils ( 112, 114 ). A controller ( 22 ) activates the plurality of initiators using the coils ( 112, 114 ) and receives a plurality of respective sensor signals having respective tire identifications. The activations may occur with a duty cycle of less than about fifty percent.

Description:
TECHNICAL FIELD 
     The present invention relates generally to a tire pressure monitoring system for an automotive vehicle, and more particularly, to a method and system for automatically determining the pressure sensor locations relative to the vehicle. 
     BACKGROUND OF THE INVENTION  
     Various types of pressure sensing systems for monitoring the pressure within the tires of an automotive vehicle have been proposed. Such systems generate a pressure signal using an electromagnetic (EM) signal which is transmitted to a receiver. The pressure signal corresponds to the pressure within the tire. When the tire pressure drops below a predetermined pressure, an indicator is used to signal the vehicle operator of the low pressure. Many vehicles require different tire pressures in the front of the vehicle and the rear of the vehicle. Therefore, it is important to know the relative position of the pressure sensor and thus the tires relative to the vehicle. Known systems provide manual means for programming the relative positions. For example, a magnet is positioned manually near the tire to allow the system to recognize the position of the tire. Such systems rely on the vehicle operator performing the recognition in a particular order. Such systems, however, are prone to errors. 
     Other systems use a device attached to the wheel well that forces the sensor contained in the tire to transmit immediately. A central receiver is used to “hear” the sensor&#39;s response to the forcing operation. An initiator is the device used to force the response. The receiver finalizes the auto location by associating the sensor identification with the specific wheel location for which the response is forced. 
     Known initiators use a low frequency magnetic field as the forcing operation. An electric coil within the sensor senses the magnetic field. Due to the nature of the magnetic fields and regulations set forth by the United States Federal Communications Commission the coil in the sensor does not have sufficient sensitivity to the magnetic field to ensure robust operation. 
     Current design trends in automotive vehicles provide increased tire size. One solution to the lack of sensitivity is placing the initiator closer to the wheels or tires. However, as the wheel size increases, less space is available for decreasing the distance to the tire. Also, in truck applications the initiator is typically placed far from the sensor. Placing the coil closer to the tire still has not provided adequate performance gain. 
     The pressure sensors are powered by batteries which are size limited to minimize cost and weight. However, the size limitation also reduces the amount of energy available to power all of the functions, including responding to the sensing of a magnetic field. In order to preserve battery energy, sensors typically do not sense the presence of a magnetic field continuously. Every so often the sensors sample voltage on an electric coil for a very short period of time. Typical time periods are that the sensor samples every four seconds for 250 microseconds. To ensure that the sensor receives the signal, the magnetic field is transmitted for extended periods of time. The problem associated with such a solution is that the United States Federal Communications Commission limits the strength of the field (currently 5.77 nT average field strength at a distance of one meter from the initiator). However, the FCC allows peak field strength to increase by up to 20dB for a device that transmits a field for less than 10ms. Another source of degradation in current solutions is the orientation of the coil in the sensor relative to the electric coil in the initiator. Ideally, the axes of these coils are parallel to ensure maximum coupling. However, the coil in the sensor may be rotated relative to the coil in the initiator as the wheel is turned to turn the vehicle. Misalignments in a locked turn can decrease the amount of power by a factor of 2 (3dB). One solution to this is adding a coil in the sensor orthogonal to the existing coil. As the wheel is turned, the second coil increases its ability to sense the magnetic field. One problem with such a solution is that the package size increases for the addition of the new coil. Because of the design restriction to provide common parts for several vehicles, vehicles that do not require such systems may incur the additional cost and mass increase. 
     It would therefore be desirable to provide a tire pressure monitoring system that automatically and reliably identifies the position of each tire relative to the vehicle. 
     SUMMARY OF THE INVENTION  
     The present invention provides a system and method for automatically identifying the position of the tires relative to the vehicle. 
     In one aspect of the invention, a tire pressure monitoring system for a vehicle has a plurality of tires in respective rolling locations having a respective plurality of tire transmitters that generate a respective plurality of transmitter identification signals. A respective plurality of initiators are fixedly attached to the vehicle at a respective plurality of locations. A controller activates the plurality of initiators to generate an initiator signal, receives a plurality of respective sensor signals having respective tire identifications and stores the tire identifications in the memory. The initiator signal may be generated from a first coil having a first longitudinal axis and a second coil having a second longitudinal axis substantially orthogonal to the first axis. The initiator signal may also have a duty cycle of less than about 50 percent. 
     In a further aspect of the invention, a method of operating a tire pressure monitoring system having a plurality of tire locations comprises activating and transmitting a first initiator signal from a first initiator positioned at a first tire location of the plurality of tire locations, said initiator signal being generated from both a first coil having a first longitudinal axis and a second coil having a second longitudinal axis that is substantially orthogonal to the first axis, and said initiator signal having a duty cycle of less than about 50 percent; receiving the first initiator signal with a sensor coil; periodically detecting the presence of an induced electric field on the sensor coil; when an electric field is detected and determined to exist, generating a first sensor signal having a first tire identification in response to the first initiator signal; receiving the first sensor signal; storing the first tire identification as received in a memory associated with the first of the plurality of tire locations when the first tire identification is not in the memory; and similarly repeating the steps of activating, detecting, generating, receiving, and storing for each of the plurality of tire locations. 
     One advantage of the invention is that no operator intervention is required for the identification, which in one embodiment, may be performed every time the vehicle is running. Also, the orthogonal coils improve energy coupling to the sensor coil. 
     Other advantages and features of the present invention will become apparent when viewed in light of the detailed description of the preferred embodiment when taken in conjunction with the attached drawings and appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagrammatic view of a pressure monitoring system according to the present invention. 
         FIG. 2  is a functional flowchart of the monitoring system according to the present invention. 
         FIG. 3  is a block diagrammatic view of a pressure transmitter according to the present invention. 
         FIG. 4  is a diagrammatic view of a digital word from a pressure transmitter. 
         FIG. 5  is a block diagrammatic view of an initiator according to the present invention. 
         FIG. 6  is time diagram of an operation of an initiator. 
         FIG. 7  is a flow chart illustrating a method of operating an initiation method according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In the following figures, the same reference numerals will be used to illustrate the same components. Those skilled in the art will recognize that the various components set forth herein could be changed without varying from the scope of the invention. 
     Referring now to  FIG. 1 , an automotive vehicle  10  has a pressure monitoring system  12  for monitoring the air pressure within a left front tire  14   a , a right front tire  14   b , a right rear tire  14   c , and a left rear tire  14   d . Each tire  14   a - 14   d  has a respective tire pressure sensor circuit  16   a ,  16   b ,  16   c , and  16   d , each of which has a respective antenna  18   a ,  18   b ,  18   c , and  18   d . Each tire is positioned upon a corresponding wheel. 
     A fifth tire or spare tire  14   e  is also illustrated having a tire pressure sensor circuit  16   e  and a respective antenna  18   e . Although five wheels are illustrated, the pressure of various numbers of wheels may be increased. For example, the present invention applies equally to vehicles such as pickup trucks that have dual wheels for each rear wheel. Also, various numbers of wheels may be used in a heavy duty truck application having dual wheels at a number of locations. Further, the present invention is also applicable to trailers and extra spares. 
     Each tire  14  may have a respective initiator  20   a - 20   e positioned within the wheel welts adjacent to the tire  14 . Initiator  20  generates a low frequency RF initiator signal and is used to initiate a response from each wheel so that the position of each wheel may be recognized automatically by the pressure monitoring system  12 . Initiators  20   a - 20   e  are preferably coupled directly to a controller  22 . In commercial embodiments where the position programming is done manually, the initiators may be eliminated. 
     Controller  22  is preferably a microprocessor based controller having a programmable CPU that may be programmed to perform various functions and processes including those set forth herein. 
     Controller  22  has a memory  26  associated therewith. Memory  26  may be various types of memory including ROM or RAM. Memory  26  is illustrated as a separate component. However, those skilled in the art will recognize controller  22  may have memory  26  therein. Memory  26  is used to store various thresholds, calibrations, tire characteristics, wheel characteristics, serial numbers, conversion factors, temperature probes, spare tire operating parameters, and other values needed in the calculation, calibration and operation of the pressure monitoring system  12 . For example, memory may contain a table that includes the sensor identification thereof. Also, the warning statuses of each of the tires may also be stored within the table. 
     Controller  22  is also coupled to a receiver  28 . Although receiver  28  is illustrated as a separate component, receiver  28  may also be included within controller  22 . Receiver  28  has an antenna  30  associated therewith. Receiver  30  is used to receive pressure and various information from tire pressure circuits  16   a - 16   e . Controller  22  is also coupled to a plurality of sensors. Such sensors may include a barometric pressure sensor  32 , an ambient temperature sensor  34 , a distance sensor  36 , a speed sensor  38 , a brake pedal sensor  41 , and an ignition sensor  42 . Of course, various other types of sensors may be used. Barometric pressure sensor  32  generates a barometric pressure signal corresponding to the ambient barometric pressure. The barometric pressure may be measured directly, calculated, or inferred from various sensor outputs. The barometric pressure compensation is preferably used but is not required in calculation for determining the pressure within each tire  14 . Temperature sensor  34  generates an ambient temperature signal corresponding to the ambient temperature and may be used to generate a temperature profile. 
     Distance sensor  36  may be one of a variety of sensors or combinations of sensors to determine the distance traveled for the automotive vehicle  10 . The distance traveled may merely be obtained from another vehicle system either directly or by monitoring the velocity together with a timer  44  to obtain a rough idea of distance traveled. Speed sensor  38  may be a variety of speed sensing sources commonly used in automotive vehicles such as a two wheel sensor used in anti-lock braking systems, or a transmission sensor. 
     Timer  44  may also be used to measure various times associated with the process set forth herein. The timer  44 , for example, may measure the time the spare tire is stowed, measure a time after an initiator signal or measure the time and duration for transmitting an initiator signal. 
     Brake pedal sensor  41  may generate a brake-on or brake-off signal indicating that the brake pedal is being depressed or not depressed, respectively. Brake pedal sensor  41  may be useful in various applications such as the programming or calibrating of the pressure monitoring system  12 . 
     Ignition sensor  42  may be one of a variety of types of sensors to determine if the ignition is powered on. When the ignition is on, a run signal may be generated. When the ignition is off, an off signal is generated. A simple ignition switch may act as an ignition sensor  42 . Of course, sensing the voltage on a particular control line may also provide an indication of whether the ignition is activated. Preferably, pressure monitoring system  12  may not be powered when the ignition is off. However, in one constructed embodiment, the system receives information about once an hour after the ignition has been turned off. 
     A telemetric system  46  may be used to communicate various information to and from a central location from a vehicle. For example, the control location may keep track of service intervals and use and inform the vehicle operator service is required. 
     A counter  48  may also be included in control system  12 . Counter  48  may count, for example, the number of times a particular action is performed. For example, counter  48  may be used to count the number of key-off to key-on transitions. Of course, the counting function may be inherent in controller  22 . 
     Controller  22  may also be coupled to a button  50  or plurality of buttons  50  for inputting various information, resetting the controller  22 , or various other functions as will be evident to those skilled in the art through the following description. 
     Controller  22  may also be coupled to an indicator  52 . Indicator  52  may include an indicator light or display panel  54 , which generates a visual signal, or an audible device  56  such as a speaker or buzzer that generates an audible signal. Indicator  52  may provide some indication as to the operability of the system such as confirming receipt of a signal such as a calibration signal or other commands, warnings, and controls as will be further described below. Indicator may be an LED or LCD panel used to provide commands to the vehicle operator when manual calibrations are performed. 
     Referring now to  FIG. 2 , a pressure monitoring system  12  having various functional blocks is illustrated. These functional blocks may take place within receiver  28 , controller  22 , or a combination thereof. Also, memory  26  is used to store the various ranges. An end-of-line (EOL) tester  58  may also be coupled to pressure monitoring system. EOL tester  58  provides test functions to EOL diagnostic block  60 . EOL tester  58  in conjunction with EOL diagnostic block  60  may be used to provide acceptable pressure ranges  62  and other diagnostic functions to determine fault within the system. The EOL tester  58  may be used in the manufacturing process to store various information in the memory such as various thresholds, tire characteristics, and to initially program the locations corresponding to the vehicle tires. 
     Vehicle speed sensor  38 , ignition switch  42 , and brake on/off switch  40  may be coupled to a manual learn mode activation input process block  64 . Together, block  64  and sensors  38 ,  40  or  41 , and  42  allow an association block  66  to associate the various tire pressure sensors to the locations of the vehicle(s). Block  66  associates the various tire pressure sensors in the memory at block  68 . The transmissions from the various sensors are decoded in block  70 , which may be performed in receiver  28  above. The decoded information is provided to block  66  and to a block  72 , which processes the various information such as the various sensor locations, and the current transmission process. In the processing frame, the sensor status pressure and transmission ID may be linked to a tire pressure monitor (TPM)  74 , which may be used to provide a warning status to an output block  76 , which in turn may provide information to an external controller  78  and to indicator  52 . 
     An auto learn block  80  may also be used to associate the various tire pressure sensor monitors with the locations of the tires in the vehicle. This process may replace or be in addition to the manual learn block  64 . The auto learn function, however, uses initiators such as the initiator  20   b  as shown. The various features of  FIG. 2  will be described further in more detail. 
     Referring now to  FIG. 3 , a typical tire pressure sensor circuit  16   a  is illustrated. Although only one tire pressure sensor circuit  16   a  is shown, each of the tire pressure sensor circuits  16   a - 16   e  may be commonly configured. Pressure monitoring system  12  has a transmitter/receiver or transceiver  90 . Transmitter/receiver  90  is coupled to antenna  18   a  for transmitting various information to receiver  28 . The antenna  18   a  may, for example, be a coil and thus a sensor coil  91 . An energy monitor circuit  93  may be a separate circuit or included in transmitter/receiver  90 . The circuit  93  is used to determine an amount of energy in the coil  91 . The energy is energy induced from the initiator  20   a . The receiver portion of the transmitter/receiver  90  may be used to receive an activation signal from an initiator located at a wheel. The pressure sensor circuit  16   a  may have various information such as a serial number memory  92 , a pressure sensor  94  for determining the pressure within the tire  14   a , a temperature sensor  96  for determining the temperature within the tire  14   a , and a motion detector  98  which may be used to activate the system pressure sensing system. The initial message is referred to as a “wake” message, meaning the pressure sensing circuit  16   a  is now activated to send its pressure transmissions and the other data. 
     Each of the transceiver  90 , serial number memory  92 , pressure sensor  94 , temperature sensor  96 , and motion sensor  98  are coupled to battery  100 . Battery  100  is preferably a long-life battery capable of lasting through the life of the tire. 
     A sensor function monitor  101  may also be incorporated into tire pressure sensor circuit  16 . Sensor function monitor  101  generates an error signal when various portions of the tire pressure circuit are not operating or are operating incorrectly. Also, sensor function monitor may generate a signal indicating that the circuit  16  is operating normally. 
     Referring now also to  FIG. 4 , a word  102  generated by the tire pressure sensor circuit  16  of  FIG. 3  is illustrated. Word  102  may comprise a transmitter identification serial number portion  104  followed by a data portion  106  in a predetermined format. For example, data section  106  may include a wake or initial status pressure information followed by temperature information. Motion detector  98  may initiate the transmission of the word  102  to the transmitter/receiver  90 . The word  102  is preferably such that the decode RF transmission block  70  is able to decode the information and validate the word while providing the identification number or serial number, the pressure, the temperature, and a sensor function. 
     Referring now to  FIG. 5 , a detailed block diagrammatic view of one of the initiators  20 A is illustrated. It should be noted that any one or several of the initiators  20 A- 20 E may be configured in this manner. The initiator  20 A is coupled to controller  22  as described above. The initiator  20 A may be directly coupled to controller  22  or may include an additional control circuit  110 . The control circuit  110  may be a microprocessor-based circuit or simple transistors. The control circuit  110  is coupled to antenna  218 A. The antenna  218 A may be formed of a first coil  112  and a second coil  114 . First coil  112  includes a first axis  116 . The second coil  114  has a second axis  118 . The axes  116  and  118  of the first coil  112  and the second coil  114  are separated by an angle α. The angle αis preferably greater than about 45 degrees and less than 135degrees. More specifically, the angle αis preferably about 90degrees, which thus makes the coils  112  and  114  orthogonal. By providing orthogonal (perpendicular) coils, when the wheels are turned, a sufficient amount of energy may be coupled to the sensor  16  associated therewith. It should be noted that control circuit  110  and/or controller  22  may control the coils  112  and  114  simultaneously or sequentially. 
     Referring now to  FIG. 6 , the operation of the initiator system will be described. One example of a signal for controlling the initiator coils  112  and  114  is illustrated. In this example, the signal has a duty cycle of 10 percent. That is, the “on” portion of the cycle is on for 10 percent of the total time (T). In this example, the total time T is 100ms, the on time is  10 ms, and the off time is 90ms. The signals generated are provided by the controller  22  and/or the control circuit  110 . The field strength corresponding to the illustrated signal corresponds to 57.7 nT at 1 meter and thus meets the current FCC guidance for peak strength. It should be noted that the coils  112  and  114  may be activated with the signal simultaneously or may be provided with such signals sequentially. 
     At the same time to reduce the power consumed by the tire pressure transmitter/receiver circuit  16   a , the energy monitor circuit  93  may be periodically used to monitor the presence of an energy field such as a magnetic field in the coil  91 . The energy monitoring circuit  93  may use various techniques to determine an amount of energy in the coil  91 . For example, the amount of current induced in the coil  91  is indicative of the amount of magnetic energy. Other types of energy sensors would be known to those skilled in the art. 
     Referring now to  FIG. 7 , one method for operating the present invention is illustrated. In step  130 , a first initiator coil  112  is activated. In step  132 , a second initiator coil  114  is activated. As mentioned above, the first coil  112  and the second coil  114  may be simultaneously or sequentially activated. In step  134 , the sensor  16   a  determines whether an electric field is present in the sensor coil  91 . To determine the electric field in step  134 , the voltage may be sampled on the electric coil  91  for a very short period of time. For example, 250ms every 4 seconds. This may be performed continuously or preferably periodically to reduce the amount of energy consumed by the sensor circuit  16   a . In step  136 , it is determined whether or not an electric field exists. If no electric field exists, step  134  is again executed. In step  136 , if an electric field does exist, the tire identification for the sensor  16   a is generated (step  138 ). Of course, other information from the tire pressure sensor  16   a  may be generated as mentioned above. In step  140 , the tire identification is received by the receiver  28  of the tire pressure monitoring system  12 . In step  142 , the tire identification is stored along with its location so that the tire identification is associated with a particular location of the tire  14   a  within the vehicle  10 . The process continues back to step  130  to repeat the steps so that the plurality of tire identifications are associated with their tire locations. It should be noted that the system  12  may take into account a spare tire  14   e  which may also include an initiator  20   e . It is predicted that the location of the tire  14   e  may be determined within one minute of operation and certainly within 10 minutes of operation of the vehicle  10 . 
     While particular embodiments of the invention have been shown and described, numerous variations and alternate embodiments will occur to those skilled in the art. Accordingly, it is intended that the invention be limited only in terms of the appended claims.