Abstract:
A tire pressure management system for a tractor/trailer system uses exterior sidewall mounted tire RFID tags, valve mounted tire pressure sensors and transmitters, radio repeaters, a tire pressure management system receiver with controller area network interface, a body computer for execution of software modules of the system and a controller area network for carrying data between the body computer and tire pressure management system receiver. The system provides varying functionality depending upon which elements are present. To deal with absence of a tractor, variation in the complimentary TPMS components installed on the tractor, or lack of any complimentary TPMS components installed on the tractor a trailer mounted repeater includes sufficient local processing power and display capability to alert users of any tire pressure problem on the trailer.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The invention relates to tire pressure monitoring systems (TPMS) and more particularly to tire pressure monitoring systems which provide tire location identification and are integrated with tire service life management. 
     2. Description of the Problem 
     TPMS provide for monitoring of tire pressure for tires installed on a vehicle and for alerting a driver to variation in measured pressure from desired norms. Maintaining an individual tire at its recommended pressure helps extend tire life and promotes good vehicle fuel economy. Maintaining all of the tires on a vehicle at the recommended pressures promotes vehicle stability and driver control of the vehicle. Extension of TPMS to provide tire temperature data allows more accurate measurement of pressure. 
     Recent developments in radio frequency identification (RFID) have provided a particularly convenient way to identify and track specific tires. RFID tags applied to tires and the use of scanners to locate the tags allows maintaining databases of tire history indexed to specific tires and allows the quick location of a tire if such is needed. RFID tags may provide data storage capability and limited sensing functions, allowing the tags to be repository for data relating to a tire&#39;s service history and to be a source of data as to internal conditions. 
     TPMS have typically provided tire pressure sensors mounted on the wheel rim or positioned inside a tire installed on the wheel. Tire pressure sensors may also be mounted outside of the tire on the valve stem, in place of a valve cap. Radio frequency identification (RFID) systems have been proposed for read/write tire identification. However, when a rim mounted sensor incorporates the identification feature (ID) there has been no way to guarantee that data written thereon will follow the tire to a different rim if the tire is moved. Where an inner sidewall mounted pressure sensor is used, then ID remains with a tire, but new tires must come with compatible sensors or have them installed. 
     Many prior art TPMS have not allowed for both permanent tire radio frequency identification and tire pressure monitoring without the removal of tires for installation or replacement of associated hardware. In TPMS that requires removal of tires since pressure sensors are often mounted to the inner surface of the rim. Since the sensor does not necessarily stay mated to the tire, tire identification information is not provided with the sensor. Systems have been proposed that provide a combination device incorporating a pressure sensor and RFID. This combination device is mounted to the inner surface of the tire itself. A battery can be incorporated for power, allowing for direct transmission of data through the tire wall to a central system controller. In still other systems, a transponder would be mounted in the wheel well which would provide power to the combined sensor/RFID device by coupled radio waves. These solutions still suffer from the necessity of removal of the tires from rims in order to install or replace components of the system. 
     Some prior art TPMS have provided tire ID information located the sensor/RFID package inside the tire. This requires a hand held reader or antennas be located in, or be brought into, close proximity to the wheels in order for information to be retrieved or communicated. A more recent teaching is U.S. Pat. No. 6,724,301 to Ginman et al. Ginman proposed a dual tag tire and wheel RFID system. Ginman utilized a temporary tire tag located a tire and with RF read/write capability and another wheel mounted tag with RF read/write capability. Both tags were provided with the capability of storing data pertinent to tire and wheel condition. An external RFID interrogator is used to effect sharing of data between the two RFID tags. Data is not lost due to discard or rotation of tires. 
     SUMMARY OF THE INVENTION 
     According to the invention a fully featured tire pressure management system for a motor vehicle integrates sidewall mounted tire RFID tags, valve mounted pressure sensors and transmitters, strategically placed radio repeaters, a tire pressure management system receiver with controller area network interface, a body computer for execution of software modules of the system and a controller area network for carrying data between the body computer and tire pressure management system receiver. The system allows for partial operation in the absence of some selected components. For example, the system may be applied to a tractor/trailer vehicle with the trailer mounted components, and provide partial stand alone functionality for the trailer in case of absence of a tractor, variation in the complimentary TPMS components installed on the tractor and trailer, or lack of any complimentary TPMS components installed on the tractor. In one embodiment, a repeater is mounted on the trailer and includes sufficient local processing power and display capability to alert users of any tire pressure problem on the trailer even when no tractor is present. Additional variations in functionality depend upon whether the tire mounted RFID tags are passive or active. 
     Additional effects, features and advantages will be apparent in the written description that follows. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself however, as well as a preferred mode of use, further objects and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a schematic illustration of the major components of the present tire pressure monitoring system. 
         FIG. 2  is a data flow diagram illustrating operation of the invention. 
         FIG. 3  is a block diagram of a tire pressure monitoring system receiver. 
         FIG. 4  includes block diagrams for a valve mounted sensor and a system repeater. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the figures a tractor/trailer combination  10  is illustrated on which a tire pressure monitoring system  30  has been installed. Tractor/trailer combination  10  comprises a tractor  12  and a trailer  14 . Tractor  12  is equipped with tires  18  installed on wheels  15 . The internal pressure of tires  18  is monitored. Trailer  14  is equipped with tires  20  installed on wheels  17 . Tires  20  are similarly monitored for internal pressure. A low pressure warning light is installed on the forward exterior wall of trailer  14  from where it can be seen from the cab of tractor  12 . Antennae  22 ,  26  are strategically located on trailer  14  and tractor  12  for enabling radio frequency data links between the tractor and trailer. 
     A complete tire pressure monitoring system (TPMS)  30  includes components installed on both the trailer  14  as well as on the tractor  12  and is topologically illustrated in  FIG. 1 . The TPMS  30  illustrated is a preferred embodiment suited for an OEM installation where tractor  12  is equipped with an SAE J1939 compliant controller area network (CAN)  56 . Simplified systems for aftermarket installation on vehicles not equipped with a CAN are certainly possible as will be clear to those skilled in the art. Trailer  14  components are the subset of the TPMS  30  and are capable of limited, stand alone operation. A trailer  14  may be attached to a tractor  12  not including components required to provide a complete system. Thus a trailer warning light  16  is installed on the exterior of the forward wall of trailer  14 . Trailer warning light  16  should be installed so as to be readily visible in a rear view mirror from the cab of tractor  12  and the base portion  29  of TPMS  30  should be configured so as to support activation of the warning light  16  even in the absence of additional functionality of tractor based portion  31  when low pressure is detected in any of tires  20 . Trailer base portion  29  is also configured to switch automatically from battery to vehicle power if tractor power is available. The trailer warning light  16  may indicate only that a tire is low on pressure, but not indicate which tire. 
     Even a minimal tractor portion  31  and provision for some RFID functionality can provide for identification of which tire is low. The information is made available in the cab of tractor  12  on a display  60 . A receiver having the service functionality of TPMS receiver  44  less (or not using) its CAN interface could serve as such a receiver. Where a vehicle is equipped with a controller area network  56  TPMS receiver  44  is connected to CAN  56  for transfer of data to drive display  60 . Where a body computer  58  is available additional management functions, such as lifetime service tracking of tires, and data download services, are made readily available. 
     The capabilities of the system become more varied as capabilities of individual components are enhanced. For example, tire RFID tags  32 ,  46  may be either passive or active devices. A passive RFID tag is one which is energized by an impinging interrogation signal while an active RFID tag will have an internal power source, typically a battery. If passive tags are used the interrogation signal, with contemporary technology, must come from quite close by. In the present invention the preferred source for such an interrogation signal is the valve pressure sensor for the associated wheel. Where this it eh case the rotational position of the tire  20  on the wheel  17  may have to be adjusted to bring the RFID tag  32 ,  46  within range of the interrogator. Alternatively, a hand held tool  24  may be used to transfer tire ID from the RFID tags  32 ,  46  to the valve pressure sensor  38 . If though, the RFID tag  32 ,  46  is an active device, it can generate a signal strong enough to reach a trailer repeater  42  or the TPMS receiver  44 . Either a passive or active RFID tag can be implemented to supply tire sidewall temperature readings though this feature may be more readily implemented in an active device. 
     A complete TPMS  30  includes a valve pressure sensor  38  for each tire  18 ,  20  on both tractor  12  and trailer  14 . Preferably the valve pressure sensors  38  are installed on the valve stem for each wheel. The considerations involved in such installations are the usual ones of weight, balance, stem vibration, visual appeal, environmental resistance, ease of installation, clearance from the wheel and theft deterrence. Batteries are used for power and they generally will not be replaceable. Thus efforts are taken to maximize battery life to avoid frequent replacement of valve pressure sensors  38 . This is achieved using a sleep mode when the vehicle is off. Transmission frequency may be varied depending upon circumstances, for example, it may be reduced when pressure levels are acceptable. Transmission frequency can be increased in response to variance of pressure from desired norms and upon request of the host system. Typically the transmission rate is elevated when the vehicle is moving. 
     As is well known, tire pressure and temperature are positively correlated. If a pressure drop occurs due to a leak then temperature will also decrease, provided all other factors remaining unchanged. However, if a vehicle is in motion a pressure drop will result in more sidewall flexing of the tire, resulting in the generation of heat and a rise in the temperature inside the tire (with a consequent increase in pressure and, often, the leak rate). Leaks may be difficult to detect quickly if the only variable to be monitored is pressure. Temperature compensation may be required and thus temperature sensors may be incorporated into TPMS  30  for each tire  18 ,  20 . Such sensors will provide cold fill pressure at the start of a vehicle service cycle. Temperature sensors may be incorporated into tire RFID tags  32 ,  46  and placed in contact with the outside of tire sidewalls to provide operational tire temperature. 
     Tire RFID tags  32 ,  46  are installed on the outside sidewalls of the tires  20 ,  18 , respectively. Tire RFID tags  32 ,  46  always include a unique tire identifier  34 ,  48  unalterably recorded at a read only memory location on the tags. As described above, RFID tags  32 ,  46  may come equipped with a sidewall temperature sensor  36 ,  50 . Tire RFID tags  32 ,  46  are passive devices, energized by valve pressure sensors  38  which are battery powered. RFID tags are well known devices and their design and operation will not be further discussed here. Hand held tool  24  may be used to transfer data from RFID tags  32 ,  46  to valve pressure sensors  38 . 
     Tire RFID tags  32 ,  46  respond to interrogation by valve pressure sensors  38  as represented by radio data link  37 . Alternatively, for active RFID tags, the data may be communicated directly to repeater  42  or receiver  44 . In turn valve pressure sensors  38  provide data to either a trailer repeater  42  or a TPMS receiver  44 , depending upon whether the particular valve pressure sensor is installed on trailer  14  or tractor  12 . Trailer repeater  42 , as described in more detail below, can provide for control of a trailer mounted, external warning light  16 . Trailer repeater  42  communicates over a radio frequency link to an RFID interrogator unit  25  over a radio datalink  41  or to a hand tool  24 . Repeater  42  also communicates with TPMS receiver  44  if installed on tractor  12 . 
     A full TPMS  30  may require two or more antenna per vehicle. Provided here are a tractor antenna  26  and a trailer antenna  22  for establishing a data link  43  between the vehicle sections. Trailer antenna  22  serves for repeater station  42 . Tractor  12  is preferably equipped with a controller area network (CAN)  56  conforming to the SAE J1939 standard for transferring data to computers implementing higher level functions of the TPMS  30 . CAN  56  will include a body computer  58  which executes management programs and which passes data on to a cab display  60  through which warnings and indications of tire condition are imaged. 
       FIG. 2  illustrates data flow in a full TPMS  30 . Tire tags  32 ,  46  automatically provide tire identification (a unique manufacturer&#39;s identifying serial number) and sidewall temperature to the valve sensors  38  with which they have bidirectional information. RFID tire tags  32 ,  46  may be programmed with tire location, which is also passed to the associated valve sensor  38 . RFID tags  32 ,  46  may include additional memory to allow storage of additional information. This information can include tire mileage, average pressure, high and low pressure events, tread depth, retread status, rotation mileages and such other service information as might be needed. This data is updated either by the TPMS management software, or manually by use of a hand tool  24 . As indicated in the figure, vocation, vehicle type, mileage and retread status may be bidirectionally passed from an RFID tag  32 ,  46  to hand tool  24 . Hand tool  24  is also programmable from an upload port with various parameters including vocation, vehicle type, mileage, retread status and tread depth. The data typically can come from TPMS receiver  44  or the body computer  58 , or by hand entry. 
     Valve sensors  38  pass on information supplied locally by the associated tire RFID tag  32 ,  46 . Valve sensors  38  pass the information to the TPMS receiver  44  (either directly or by repeater  42 ) and add pressure measurements and stem temperature (if available). Valve sensors  38  receive wake up calls and calibration signals from TPMS receiver  44  (again either directly or by repeater  42 ). 
     TPMS receiver  44  provides an access point to the motor vehicle CAN  56 . TPMS receiver  44  is the broadcast source of sensor data requests and acknowledgment signals and is connected to the CAN  56 . All relevant data required by body computer  58  for tire pressure management is provided as data packets over CAN  56 . Body computer  58  in turn determines what information to display on display  60 , which is also transmitted over CAN  56 . Body computer  58  provides for execution of up to three software modules used to implement the TPMS  30 . The modules include a monitoring module  66  which handles reported data received over CAN  56  from TPMS receiver  44 . Monitoring module  66  determines occasions of departures from operating norms and issues threshold warnings, leak warnings and tire pressure readings to display  60  over CAN  56 . Determination of which warnings to display occurs after appropriate normalization of the data, adjustment of pressure readings for temperature changes and comparison to predetermined limits. Tire pressure can simply be reported or corrected. A management module  64  may be provided. This module tracks long term data such as mileage on tires and can track operating history to provide service reminders and forecast failures. A pre-trip module  62  retains pressure readings taken upon start up of the vehicle. It is not strictly necessary that leak detection be determined by the body computer  58  and it may, in some instances, be done at the trailer repeater  42  or the TPMS receiver  44 . 
     Referring to  FIG. 3  a block diagram schematic of a TPMS receiver  44  is illustrated. TPMS receiver  44  includes pressure monitoring and fault detection functionality through a programmed microprocessor  76  for use in case of installation on a vehicle not having a CAN. TPMS receiver  44  typically receives wireless reports of data from valve pressure sensors  38 ,  46  over an antenna connected to a radio frequency transceiver  74 , and reports the data to microprocessor  76 . Microprocessor  76  can receive data over other channels as well including CAN  56  through J1939 interface  70  and, optionally, J1587/J1708 interface  86 . A reprogramming interface may be connected to CAN  56 . All interfaces are connected to supply data directly to microprocessor  76 . The network interfaces  70 ,  86  are further connected to exchange data with diagnostics block  78 . Memory  80  is available to microprocessor  76  and diagnostics block  78 . Microprocessor  76  also receives inputs over a digital input/output port  82 . Inputs potentially relate to axle positions specifically identified with tires. Outputs including a drive LED warning light output can be generated over digital I/O  82 . 
     Referring to  FIG. 4 , functional block diagrams for valve pressure sensors  38  and trailer repeater  42  are provided. Valve pressure sensor  38  includes a battery  86 , a low frequency transceiver  88  for communication with TPMS receiver  44  or trailer repeater  42 , a microprocessor  90 , an RFID reader  92 , a sensor package transceiver  94  and a sensor package  96  including a stem pressure sensor  98 , a temperature sensor  100  providing ambient temperature at start up and a motion sensor  102 . Start up ambient temperature readings provide some level of correlation with sidewall temperature taken later during driving and may be used for temperature compensation. Trailer repeater  42  includes a local processor  106  and memory  108  and, in case no tractor TPMS is available, can function as a stand alone system performing the required comparisons to determine if a low pressure condition exists in any tire. Trailer repeater  42  further includes a rechargeable battery  110 , recharge circuit  112  and an LED driver  114 . In order to save power repeater  42  has a power down or sleep mode and a wake up circuit  118  is provided. An RFID interrogator  116  is provided as well as a TPMS transceiver  120  for the exchange of data with transceiver  44 . 
     Valve sensors  38  transmit data to a TPMS receiver  44  either directly or by trailer repeater  42 . Microcontroller  90  is programmed with a pressure threshold. In response to detection of pressure falling below the threshold the pressure reading transmission rate increases. Normally the pressure transmission rate is quite slow to prolong battery life. A motion sensor  102  enables sensor transmission rate increases if the vehicle is moving. This allows TPMS  30  to determine fast leakage rates and other warning conditions. The programmable threshold can be reprogrammed by TPMS  30  if the system determines that operational parameters for the truck have changed. The parameters can include average climate, average load and other factors. Default parameters are selected to be universally applicable, but are preferably optimized for specific vehicles in order to improve fuel economy and prolong battery life. LF receiver  88  allows sensor  38  to be awakened and communicated with by a hand tool  24  or by repeater  42 . 
     Repeater  42  is used as a bridge from tire pressure sensors  38  to TPMS receiver  44  which is mounted on tractor  12 . RF retransmission is provided. In order to extend battery service life, repeater  42  is not always in a listening mode. An embedded RFID transceiver  116  detects when a tractor  12  has backed to the trailer  14  and a handshake signal is transmitted to TPMS receiver  44 . The handshake provides the unique tire ID numbers for tires installed on the trailer  14 , along with axle locations and may be used to activate repeater  42 . 
     Wheel valve sensors  38  transmit at a slow rate when the vehicle is not moving. Repeater  42  includes a rechargeable battery  86 , which provides power allowing the repeater to receive these signals and to store the most recent data. If a leak is detected an LED, which is mounted on trailer  14  where easily seen, is set to flashing. This serves to alert yard mechanics to attend to the tires when a tractor is not present. If a tire pressure problem exists when the tractor comes into position to connect to the trailer  14 , repeater  42  alerts the TPMS  30  upon activation. When a tractor  12  connects to a trailer  14  the repeater&#39;s battery  86  goes into recharge mode and the repeater begins to use the tractor&#39;s power supply. 
     Tractor  12  is also equipped with an RFID interrogator, which maybe UHF or LF based depending upon the required transmission range. RFID interrogator  25  is located in an area where it will activate a trailer mounted RFID tag  116  when the tractor comes within five feet of the trailer which can in turn supply a wake up signal to repeater  42 . Interrogator  25  may be triggered by the driver, automatically or when a particular state is true, for example, if the tractor is in reverse. Tractor RFID interrogator  25  listens for a response identifying the trailer  14  and for trailer conditions requiring attention. 
     While the invention is shown in only one of its forms, it is not thus limited but is susceptible to various changes and modifications without departing from the spirit and scope of the invention.