BACKGROUND OF THE INVENTION 1. Field of the Invention

[0001 ] This invention relates to a wheel state notification apparatus which includes a wheel sensor fixed to a wheel and a vehicle body side device fixed to a vehicle body and which notifies a driver of a wheel state by transmitting a wheel state amount such as tire pressure from the wheel sensor to the vehicle body side device using a radio signal.

2. Description of Related Art

[0002] A tire pressure monitoring apparatus that notifies tire pressure information to a driver is available as an example of a wheel state notification apparatus. The tire pressure monitoring apparatus includes a tire pressure sensor unit (referred to as a wheel sensor) that detects tire pressure for each wheel and is configured so as to transmit tire pressure information from the wheel sensor via a radio signal and _. to receive the radio signal by a vehicle body side device to acquire the tire pressure information. When it is determined that tire pressure has dropped based on the received tire pressure information, the vehicle body side device displays the drop in tire pressure on a notifying device to noti y a driver of the drop in tire pressure.

[0003] With such a tire pressure monitoring apparatus, in order to discriminate which wheel sensor had transmitted a radio signal received by the vehicle body side device, radio signals include a sensor identification (ID ) that is information of a wheel sensor in addition to tire pressure information. For example, an apparatus disclosed in Japanese Patent Application Publication No. 2006-15955 (JP 2006- 15955 A) notifies a drop in tire pressure for two types of wheels including a traveling wheel and a spare wheel by separately registering sensor IDs for traveling wheels and spare wheels. Sensor IDs are registered to the vehicle body side device in advance at a vehicle factory. [0004] When one of the traveling wheels is replaced with a spare wheel or when tire rotation is performed including a spare wheel, a registration state of the sensor IDs ends up being different from an actual state. In consideration thereof, the apparatus proposed in JP 2006-15955 A is configured so as to automatically discriminate among traveling wheels and spare wheels. In this apparatus, the wheel sensor includes an acceleration sensor in addition to a pressure sensor and transmits a radio signal including acceleration data. Based on acceleration data included in a radio signal received when the vehicle is traveling at or above a prescribed vehicle speed, the vehicle body side device presumes that a wheel sensor corresponding to acceleration below a prescribed value is provided on a spare wheel. Based on this presumption, sensor IDs are separately registered for traveling wheels and spare wheels. Therefore, a drop in tire pressure can be distinguishably notified as to whether the pressure drop had occurred at a traveling wheel or a spare wheel.

[0005] However, the apparatus described above is incapable of discriminating whether a spare wheel is an emergency wheel mounted with an emergency tire (temporary tire) or a wheel mounted with a grand tire that is designed for normal travel (hereinafter, referred to as a regular wheel) instead of emergency use. When one of the traveling wheels blows out or the like and is replaced with a spare wheel, no problems should arise if the replacement wheel is a regular wheel. On the other hand, if the replacement wheel is an emergency wheel, the emergency wheel must be replaced with a regular wheel at the earliest opportunity. However, since the apparatus described above cannot distinguish between an emergency wheel and a regular wheel, the apparatus is incapable of making a driver aware of the fact that an emergency wheel is being used as a traveling wheel. SUMMARY OF THE INVENTION

[0006] An object of the invention is to make a driver aware that an emergency wheel is being used as a traveling wheel.

[0007] An aspect of the invention relates to a wheel state notification apparatus including: a wheel sensor that is fixed to each wheel of a host vehicle and that detects a wheel state amount and transmits wheel state amount data representing the detected wheel state amount together with a sensor ID via a radio signal; and a vehicle body side device that is fixed to a vehicle body and that receives radio signals transmitted by an unspecified large number of wheel sensors including those of the wheels of the host vehicle, acquires a wheel state amount detected by the wheel sensor of the host vehicle as specified by the sensor ID, and performs a notification process corresponding to the wheel state amount, wherein the vehicle body side device includes: a sensor ID storage unit that stores the sensor ID of the wheel sensor provided on the wheel of the host vehicle so as to be capable of distinguishing whether the sensor ID is a first sensor ID of a wheel sensor provided on a traveling wheel or a second sensor ID of the wheel sensor provided on a spare wheel; an emergency wheel specifying data storage unit that stores emergency wheel specifying data that specifies a third sensor ID of the wheel sensor provided on an emergency wheel mounted with an emergency tire; and a notification control unit that determines whether the emergency wheel is mounted as a spare wheel or being used as the traveling wheel based on the sensor ID stored in the sensor ID storage unit and the emergency wheel specifying data stored in the emergency wheel specifying data storage unit, and that notifies wheel states in different modes between a case where the emergency wheel is mounted as the spare wheel and a case where the emergency wheel is used as the traveling wheel.

[0008] The wheel state notification apparatus includes the wheel sensor fixed to each wheel and a vehicle body side device fixed to the vehicle body. The wheel sensor detects a wheel state amount and transmits wheel state amount data representing the detected wheel state amount together with the sensor ID via a radio signal. For example, the wheel sensor includes a tire pressure sensor that detects tire pressure and transmits information representing the detected tire pressure together with the sensor ID via a radio signal. The sensor ID is ID information that specifies the wheel sensor. The vehicle body side device receives radio signals transmitted by an unspecified large number of wheel sensors, acquires a wheel state amount detected by the wheel sensor of the host vehicle as specified by the sensor ID, and performs a notification process corresponding to the wheel state amount. For example, the vehicle body side device performs a notification process of tire pressure information.

[0009] The vehicle body side device includes a sensor ID storage unit, an emergency wheel specifying data storage unit, and a notification control unit. The sensor ID storage unit stores the sensor ID of each wheel sensor provided on the wheel of the host vehicle so as to be capable of distinguishing whether the sensor ID is the first sensor ID of the wheel sensor provided on the traveling wheel or the second sensor ID of the wheel sensor provided on the spare wheel. The emergency wheel specifying data storage unit stores emergency wheel specifying data that specifies the third sensor ID of the wheel sensor provided on the emergency wheel mounted with an emergency tire. Therefore, with respect to the wheel provided with the wheel sensor that is specified by the sensor ID, discrimination may be made as to whether the wheel is the spare wheel or the traveling wheel and whether the wheel is the emergency wheel or a regular wheel.

[0010] For example, when the sensor ID specified by emergency wheel specifying data is the same as the second sensor ID of the wheel sensor provided on the spare wheel, the emergency wheel specifying data indicates that the emergency wheel is being mounted as the spare wheel. On the other hand, when the sensor ID specified by emergency wheel specifying data is the same as the first sensor ID of the wheel sensor provided on the traveling wheel, the emergency wheel specifying data indicates that the emergency wheel is being used as the traveling wheel. In the case of the latter, the driver must be made aware that the emergency wheel is being used as the traveling wheel.

[0011] To this end, the notification control unit determines whether the emergency wheel is being mounted as the spare wheel or being used as the traveling wheel based on the sensor ID that is stored in the sensor ID storage unit and on the emergency wheel specifying data that is stored in the emergency wheel specifying data storage unit, and notifies wheel states in different modes between a case where the emergency wheel is being mounted as the spare wheel and a case where the emergency wheel is being used as the traveling wheel. Accordingly, the driver can be made aware that the emergency wheel is being used as the traveling wheel. [0012] The notification control unit may issue a warning to attract attention of a driver when the emergency wheel is being used as the traveling wheel even if the wheel state detected by the wheel sensor is normal.

[0013] According to the invention, since a warning is issued when the emergency wheel is being used as the traveling wheel even if the wheel state detected by the wheel sensor is normal, the driver can be made aware that the use of the emergency wheel is not favorable. As a result, the driver can be prompted to replace the emergency wheel with the regular wheel.

[0014] The notification control unit may display a symbol representing a wheel position on a wheel state display screen and switches the display of the symbol depending on whether the wheel of the host vehicle is the emergency wheel.

[0015] The display of the symbol is switched depending on whether the wheel provided at the wheel position on the wheel state display screen is the emergency wheel. For example, display is performed so that shapes of the symbol differ between an emergency wheel and the regular wheel. Alternatively, display is performed so that colors of the symbol differ between the emergency wheel and the regular wheel.

Therefore, the driver can understand whether the emergency wheel is being mounted as the spare wheel, at which wheel position the emergency wheel is being used, and the like.

[0016] The vehicle body side device may include: an emergency wheel mounting data storage unit, into which emergency wheel mounting data indicating that the emergency wheel provided with the wheel sensor is mounted as the spare wheel, is written; a spare wheel discriminating unit that discriminates the second sensor ID of the wheel sensor that is provided on the spare wheel of the host vehicle at the present moment by extrapolation among the sensor IDs included in radio signals transmitted by an unspecified large number of wheel sensors; and a writing unit that causes the sensor ID discriminated by the spare wheel discriminating unit to be stored in the sensor ID storage unit as the second sensor ID of the wheel sensor provided on the spare wheel and, when the emergency wheel mounting data is written into the emergency wheel mounting data storage unit, causes emergency wheel specifying data indicating that the discriminated sensor ID is the third sensor ID of the wheel sensor provided on the emergency wheel to be stored in the emergency wheel specifying data storage unit.

[0017] Emergency wheel mounting data indicating that the emergency wheel provided with the wheel sensor is being mounted as the spare wheel can be written into the emergency wheel mounting data storage unit. For example, when the emergency wheel provided with the wheel sensor is mounted as the spare wheel, emergency wheel mounting data can be written into the emergency wheel mounting data storage unit. The emergency wheel mounting data may be data indicating whether the emergency wheel provided with the wheel sensor is being mounted as the spare wheel.

[0018] The spare wheel discriminating unit discriminates the sensor ID of the second wheel sensor that is provided on the spare wheel of the host vehicle at the present moment by extrapolation among the sensor IDs included in radio signals transmitted by an unspecified large number of wheel sensors. In other words, the second sensor ID of the wheel sensor provided on the spare wheel of the host vehicle is discriminated by extrapolation instead of based on the sensor ID stored in the sensor ID storage unit. The discrimination of the sensor ID may be .performed based on a difference in radio signals between a case where the wheel is being mounted as the spare wheel and a case where the wheel is being used as the traveling wheel. For example, the second sensor ID of the wheel sensor provided on the spare wheel of the host vehicle can be extrapolated based on characteristics of a received radio signal, a detected physical amount that is included in the radio signal, and the like. The writing unit causes the sensor ID discriminated by the spare wheel discriminating unit to be stored in the sensor ID storage unit as the second sensor ID of the wheel sensor provided on the spare wheel and, when the emergency wheel mounting data is written into the emergency wheel mounting data storage unit, causes emergency wheel specifying data indicating that the discriminated sensor ID is the third sensor ID of the wheel sensor provided on the emergency wheel to be stored in the emergency wheel specifying data storage unit.

[0019] Therefore, for example, when a user attaches the wheel sensor to the emergency wheel that is being mounted as the spare wheel, by simply writing emergency wheel mounting data into the emergency wheel mounting data storage unit, emergency wheel specifying data that specifies the third sensor ID of the wheel sensor provided on the emergency wheel is automatically stored in the emergency wheel specifying data storage unit. As a result, since the third sensor ID of the wheel sensor provided on the emergency wheel need not be registered by a manual operation, excellent usability is achieved.

[0020] The wheel sensor may include an acceleration sensor that detects acceleration con-esponding to a magnitude of a centrifugal force acting on the wheel sensor and may transmit a radio signal including acceleration data indicating the acceleration detected by the acceleration sensor. The vehicle body side device may include an emergency wheel specifying data writing unit that discriminates the wheel, which is hte emergency wheel being used, from among the traveling wheels based on magnitude of the acceleration during traveling of the vehicle and that causes the emergency wheel specifying data storage unit to store emergency wheel specifying data that adopts the sensor ID of the wheel sensor of the discriminated wheel as the third sensor ID of the wheel sensor provided on the emergency wheel.

[0021] The wheel sensor may include an acceleration sensor that detects acceleration corresponding to a magnitude of a centrifugal force acting on the wheel sensor and may transmit a radio signal including acceleration data indicating the acceleration detected by the acceleration sensor. While a tire outer diameter of the emergency wheel is equal to that of the regular wheel, a wheel diameter of the emergency wheel is smaller than that of the regular wheel. In addition, the wheel sensor is attached to the wheel. Therefore a distance between a center of rotation of a wheel to a wheel sensor (acceleration sensor) is shorter for the emergency wheel than the regular wheel. Consequently, when wheels are rotating at a same rotational speed, acceleration detected by an acceleration sensor of the emergency wheel is smaller than acceleration detected by an acceleration , sensor of a sensor unit of the regular wheel. As a result, the emergency wheel and the regular wheel can be discriminated based on the acceleration detected by an acceleration sensor. [0022] The emergency wheel specifying data writing unit discriminates the wheel at which the emergency wheel is being used among the traveling wheels based on magnitude of the acceleration during traveling of the vehicle, and causes the emergency wheel specifying data storage unit to store emergency wheel specifying data that adopts the sensor ID of the wheel sensor of the discriminated wheel as the third sensor ID of the wheel sensor provided on the emergency wheel. Therefore, when the emergency wheel is used as the traveling wheel, emergency wheel specifying data that specifies the third sensor ID of the wheel sensor provided on the emergency wheel is automatically stored in the emergency wheel specifying data storage unit. As a result, the driver can be made aware that the emergency wheel is being used as the traveling wheel without having to perform a registration operation of the third sensor ID related to the emergency wheel.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Features, advantages, and technical and industrial significance of exemplary embodiments of the invention will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein:

FIG. 1 is a schematic configuration diagram of a wheel state notification apparatus according to an embodiment of the invention;

FIG. 2 is a functional block diagram of a sensor unit and a wheel electronic control unit (ECU);

FIG. 3,is a flow chart representing a spare wheel discriminating routine;

FIG. 4 is a flow chart representing a sensor ID nominating routine;

FIG. 5 is a flow chart representing an emergency wheel discriminating routine;

FIG. 6 is a flow chart representing a modification of an emergency wheel

discriminating routine;

FIG. 7 is a flow chart representing a warning display control routine;

FIG. 8 is a diagram showing a display screen that is displayed by a notifying device;

FIG. 9 is a diagram showing a display screen that is displayed by a notifying device; FIG. 10 is a diagram showing a display screen that is displayed by a notifying device; and

FIG. 1 1 is a diagram showing a display screen that is displayed by a notifying device.

DETAILED DESCRIPTION OF EMBODIMENTS

[0024] Hereinafter, a wheel state notification apparatus of a vehicle according to an embodiment of the invention will be described with reference to the drawings. FIG. 1 shows a schematic configuration of a wheel state notification apparatus that is used in a tire pressure monitoring system (TPMS). The wheel state notification apparatus is an apparatus for notifying pressure information of a tire to a driver and includes a tire pressure sensor unit 10 (hereinafter, referred to as a sensor unit 10) that is fixed to each wheel W, a wheel state information processing unit 50 (hereinafter, referred to as a wheel ECU 50) that is fixed to a vehicle body B, and a notifying device 100. FIG. 2 is a functional block diagram of the sensor unit 10 and the wheel ECU 50. Since all of the sensor units 10 provided on the respective wheels W share the same function, only one sensor unit 10 is shown in FIG. 2.

(0025] The sensor unit 10 is attached to a tire air injection valve of the wheel W. The sensor unit 10 includes a pressure sensor 1 1 , a temperature sensor 12. an acceleration sensor 13, a control unit 20, an antenna 14, and a battery 15. The pressure sensor 1 1 detects pressure of a tire and outputs a detection, signal representing pressure P to the control unit 20. The temperature sensor 12 detects a temperature of a tire and outputs a detection signal representing a tire temperature T to the control unit 20. The acceleration sensor 13 detects acceleration in a direction of centrifugal force of the wheel W and outputs a detection signal representing acceleration G to the control unit 20. The acceleration G represents a value corresponding to a magnitude of a centrifugal force that acts on the sensor unit 10 (a centrifugal force that acts on the acceleration sensor 13).

[0026] The control unit 20 includes a microcomputer and a communication circuit as substantial components. In terms of functions, the control unit 20 includes a timing setting unit 21 that sets a timing at which a radio signal is transmitted, an ID storage unit 22 storing a sensor ID that is ID information of the sensor unit 10, and a transmission processing unit 23 that generates a radio signal and transmits the radio signal via the antenna 14.

[0027] While a radio signal is periodically transmitted at constant time intervals, the intervals are to be set by the timing setting unit 21. When the wheel W is not rotating, the timing setting unit 21 sets the time interval at which a radio signal is transmitted (transmission period) to TO, and when the wheel W is rotating, the timing setting unit 21 sets the time interval at which a radio signal is transmitted (transmission period) to Tl . The transmission period TO is set longer than the transmission period Tl . For example, the transmission period TO is set to 1 minute 30 seconds and the transmission period Tl is set to 1 minute. With respect to an input of an acceleration G detected by the acceleration sensor 13. the timing setting unit 21 determines that the wheel W is rotating when the acceleration G is equal to or higher than a reference acceleration Gref and determines that the wheel W is not rotating when the acceleration G is lower than the reference

acceleration Gref. The timing setting unit 21 includes a time measuring timer and, based on a timer value thereof, outputs a transmission instruction to the transmission processing unit 23 each time the time interval TO or the time interval Tl lapses.

[0028] Every time a transmission instruction is inputted from the timing setting unit 21 , the transmission processing unit 23 reads pressure P outputted by the pressure sensor 1 1. a tire temperature T outputted by the temperature sensor 12, an acceleration G outputted by the acceleration sensor 13, and a sensor ID stored in the ID storage unit 22, generates transmission data representing the sensor ID, the pressure P. the tire temperature T, and the acceleration G, and transmits a radio signal obtained by modulating the transmission data via the antenna 14. The pressure P, the tire temperature T, and the acceleration G are latest information as of the transmission of the radio signal.

[0029] The battery 15 supplies power to respective electric loads in the sensor unit 10. [0030J The sensor unit 10 according to this embodiment is configured so as to be only capable of transmitting to the wheel ECU 50 (bidirectional communication disabled) and unilaterally transmits the radio signal at the period described above.

[0031] The sensor unit 10 may be provided on the spare wheel in addition to the four traveling wheels. As the spare wheel, an emergency wheel in which an emergency tire (temporary tire) is mounted on a wheel may be mounted or a wheel for ordinary travel (a wheel of the same type as the wheels mounted as traveling wheels; hereinafter, referred to as a regular wheel) in which a tire that is designed for normal travel (generally referred to as a grand tire) instead of emergency use is mounted on a wheel may be mounted.

[0032] Some automobiles adopting a TPMS may have the sensor unit 10 attached to the spare wheel while some do not. Presently, the sensor unit 10 is often attached when a regular wheel is mounted as the spare wheel while the sensor unit 10 is often not attached when an emergency wheel is mounted as the spare wheel. Even when an emergency wheel is mounted, the user may attach the sensor unit 10 to the emergency wheel. In this case, at the automobile dealer, data indicating that the sensor unit 10 is attached to the emergency wheel can be written into the wheel ECU 50 when the sensor unit 10 is being attached. Accordingly, the wheel ECU 50 can discriminate whether an emergency wheel exists in the five wheels W including the spare wheel.

[0033] Next, the wheel ECU 50 will be described. The wheel ECU 50 includes a microcomputer and a communication circuit as substantial components. In terms of functions, the wheel ECU 50 includes a reception processing unit 51. a notification control unit 70, a registered ID storage unit 54, an emergency wheel mounting flag storage unit 55, and an ID discriminating unit 60. In addition, the notifying device 100 provided near the driver's seat is connected to the wheel ECU 50.

[0034] The reception processing unit 51 is connected to an antenna 90, and when other vehicles in the vicinity of the host vehicle, the reception processing unit 51 receives radio signals transmitted by the sensor units 10 of the other vehicles via the antenna 90 in addition to radio signals transmitted by the sensor units 10 of the host vehicle. In other words, the reception processing unit 51 receives radio signals transmitted by an unspecified large number of sensor units 10. Every time a radio signal is received, the reception processing unit 51 extracts data representing a sensor ID, the pressure P, the tire temperature T, and the acceleration G from the radio signal.

[0035] The notification control unit 70 is constituted by a notification data generating unit 52 and a display control unit 53. The notification control unit 70 can be regarded as the notification control unit according to the invention.

[0036] Among the data extracted by the reception processing unit 51 , the notification data generating unit 52 accepts input of the sensor ID, the pressure P, and the tire temperature T and based on the inputted data and the sensor ID (hereinafter referred to as a registered ID sensor storage unit) stored in the registered ID storage unit 54, generates notification data of tire pressure related to a sensor ID that matches the registered sensor ID. Data inputted to the notification data generating unit 52 includes data included in radio signals transmitted by other vehicles. Therefore, to enable discrimination regarding whether or not data has been transmitted by a sensor unit 10 attached to the wheel W of the host vehicle, the registered ID storage unit 54 stores a sensor ID of the sensor unit 10 attached to the wheel W of the host vehicle in association with a wheel position. The notification data generating unit 52 refers to the registered sensor ID stored in the registered ID storage unit 54, generates notification data of tire pressure only with respect to the registered sensor ID, and outputs the notification data to the ^' display control unit 53.

[0037] The display control unit 53 generates display control data (image data) for controlling the display of the notifying device 100 according to the notification data outputted by the notification data generating unit 52 and outputs the display control data to the notifying device 100. The notifying device 100 includes, for example, a display provided at a location that is visible from the driver's seat and a display driver that drives the display, and displays a tire pressure monitoring screen on the display according to display control data outputted by the display control unit 53.^

[0038] Tire pressure information to be notified to the driver will be described later. First, other functional units of the wheel ECU 50 will be described. [0039] The registered ID storage unit 54 includes a storage area for storing the sensor ID of the sensor unit 10 attached to the wheel W of the host vehicle and

discriminatingly stores sensor IDs according to wheel position. The storage area is divided into a traveling wheel ID storage area 54a that discriminatingly stores sensor IDs provided on the sensor units 10 of a left front wheel, a right front wheel, a left rear wheel, and a right rear wheel that are traveling wheels according to wheel position, a spare wheel ID storage area 54b that stores a sensor ID provided on the sensor unit 10 on the spare wheel, and an emergency wheel ID storage area 54c that stores a sensor ID provided on the sensor unit 10 on the emergency wheel.

[0040] The traveling wheel ID storage area 54a and the spare wheel ID storage area 54b can be regarded as the sensor ID storage unit according to the invention and the emergency wheel ID storage area 54c can be regarded as the emergency wheel specifying data storage unit according to the invention. In addition, the sensor ID stored in the emergency wheel ID storage area 54c can be regarded as emergency wheel specifying data.

[0041] In a case of a vehicle in which an emergency wheel is mounted as a spare wheel and the sensor unit 10 is attached to the spare wheel, the emergency wheel ID storage area 54c is provided so as to be capable of discriminating between an emergency wheel and a regular wheel. In some cases, the spare wheel mounted to a vehicle delivered from a vehicle factory is a regular wheel. In other cases, the spare wheel mounted to a vehicle delivered from a vehicle factory is an emergency wheel. Usually, in the case of a regular wheel, the sensor unit 10 is attached to the regular wheel, and in the case of an emergency wheel, the sensor unit 10 is not attached to the emergency wheel. Therefore, when an emergency wheel is mounted as the spare wheel, a sensor ID is not registered in the spare wheel ID storage area 54b and the emergency wheel ID storage area 54c.

[0042] While registered sensor IDs stored in the registered ID storage unit 54 are correct as of the shipment of the vehicle, when the wheels are subsequently replaced by other wheels as a result of replacing one of the traveling wheels with a spare wheel or performing tire rotation, a registration state that is stored in the registered ID storage unit 54 ends up being different from an actual state. In addition, in a case of a vehicle to which an emergency wheel is mounted as a spare wheel, the user may subsequently attach a sensor unit 10 to the emergency wheel. Furthermore, the sensor unit 10 may be replaced due to malfunction or the like.

|0043] In order to address such situations, the wheel ECU 50 includes an emergency wheel mounting flag storage unit 55 and an ID discriminating unit 60.

[0044] The emergency wheel mounting flag storage unit 55 is a dedicated storage area for storing a flag (discriminating data) representing the fact that the user has attached the sensor unit 10 to an emergency wheel that is mounted as _. a spare wheel. The flag is written by a prescribe operation. When set to " 1 ", the flag represents that an emergency wheel to which the sensor unit 10 is attached is mounted to the vehicle, and when set to "0", the flag represents that an emergency wheel to which the sensor unit 10 is attached is not mounted to the vehicle. The wheel ECU 50 includes a terminal 56 to which a writing device (not shown) is to be connected. When attaching the sensor unit 10 to the emergency wheel mounted as a spare wheel, car dealership personnel connects the writing device to the terminal 56 and performs a prescribed flag writing operation. Accordingly, a flag of "1 " is written into the emergency wheel mounting flag storage unit 55. A method of writing of a flag is not limited to the above. For example, a flag may be written by inputting the flag from an operating panel (not shown) provided at the driver's seat. The flag can be regarded as emergency wheel mounting data according to the invention.

[0045] The ID discriminating unit 60 includes a 4-wheel discriminating unit 61 , a spare wheel discriminating unit 62, and an emergency wheel discriminating unit 63. The ID discriminating unit 60 receives input of vehicle state information representing a vehicle speed, rotational speeds of the respective wheels, and the like and discriminates a sensor ID of a wheel sensor of the host vehicle by extrapolation for each wheel position based on the vehicle state information. The ID discriminating unit 60 repetitively operates at timings set in advance and discriminates a sensor ID of the host vehicle at the present moment by extrapolation. [0046] The 4-wheel discriminating unit 61 is a functional unit that selects and registers sensor IDs of the sensor units 10 attached to the traveling wheels of the host vehicle in association with wheel positions from a plurality of sensor IDs included in radio signals (radio signals transmitted by an unspecified large number of sensor units 10 including other vehicles) received by the reception processing unit 51 . Since all vehicles adopting a TPMS transmit radio signals from the sensor units 10. the wheel ECU 50 receives radio signals transmitted by the sensor units 10 of other vehicles that are located in the vicinity of the host vehicle. Therefore, discrimination of sensor IDs includes discriminating sensor IDs of the host vehicle from those of other vehicles.

[0047] Various methods are available for selecting sensor IDs of the host vehicle in association with wheel positions from the sensor IDs included in the radio signals transmitted from an unspecified large number of sensor units 10. Therefore, the 4-wheel discriminating unit 61 may adopt any one of such methods. In the embodiment, since a radio signal includes data representing acceleration G. a method of automatically discriminating a sensor ID using the acceleration G is to be adopted.

[0048] For example, the 4-wheel discriminating unit 61 receives input of a rotational speed ω detected by a wheel speed sensor (not shown) that outputs a detection signal in accordance with a rotational speed of each wheel W. The wheel speed sensor is fixed to the vehicle body so as to correspond to each traveling wheel. During a prescribed period while the vehicle is traveling, the 4-wheel discriminating unit 61 stores and accumulates data representing acceleration G for each sensor ID with respect to all received radio signals. At the same time, during the prescribed period, the 4-wheel discriminating unit 61 stores and accumulates a transition of the rotational speed ω detected by the wheel speed sensor for each wheel. The prescribed period is set to a period in which radio signals can be received a plurality of times from one sensor unit.

[0049] The rotational speed ω detected by the wheel speed sensor can be converted into a value corresponding to the acceleration G detected by the acceleration sensor 13 of the sensor unit 10. If a distance between a center of rotation of the wheel W to a position where the acceleration sensor 13 of the sensor unit 10 is provided is denoted by r, then acceleration Gx in a radial direction that is generated when the wheel W rotates at the rotational speed ω may be expressed by the following equation. Gx = r ^χ ω ²

[0050] Therefore, by comparing a transition of the acceleration Gx with respect to the rotational speed ω detected by the wheel speed sensor with the acceleration G for each sensor ID, a sensor ID can be selected for each wheel based on a correlation between the transition of the acceleration Gx and the acceleration G. In other words, for each wheel, a seiisor ID for which acceleration G that is closest to the transition of the acceleration Gx is detected can be extrapolated as belonging to the sensor unit 10 disposed on the wheel W. The 4-wheel discriminating unit 61 stores sensor IDs selected based on such principles in the registered ID storage unit 54 (the traveling wheel ID storage area 54a) for each wheel position. Accordingly, sensor IDs of the sensor units 10 of the traveling wheels can be updated to latest information. While a spare wheel can be selected according to the method described above, in order to favorably discriminate a space wheel from the sensor IDs of other vehicles, discrimination of a spare wheel is to be performed by the spare wheel discriminating unit 62 in the embodiment.

[0051] Next, the spare wheel discriminating unit 62 will be described. The spare wheel discriminating unit 62 is a functional unit that selects and registers sensor IDs of a spare wheel of the host vehicle (a wheel W mounted at a position where the spare wheel is placed) from a plurality of sensor IDs included in radio signals transmitted by an unspecified large number of sensor units 10 including other vehicles.

[0052] Various methods of automatically registering an ID of a spare wheel are conventionally available. For example, one such method involves determining whether a wheel is a rotating wheel (in other words, a traveling wheel) or a non-rotating wheel (in other words, a spare wheel) based on whether or not a magnitude of the acceleration G (corresponding to centrifugal force) receiving while the vehicle is traveling is greater than a prescribed value. Another method involves determining a wheel with minimum amplitude of a radio signal received while the vehicle is traveling as a spare wheel.

However, such methods are for selecting a spare wheel from the five wheels of a host vehicle and do not particularly consider the influence of radio signals transmitted by other vehicles. In other words, there is a problem of inferior accuracy in terms of accuracy of discriminating between a sensor ID of a sensor unit of another vehicle and a sensor ID of a spare wheel of the host vehicle.

[0053] In consideration thereof, a spare wheel discriminating unit 62 with a superior discriminating with sensor IDs of other vehicles is provided. FIG. 3 shows a spare wheel discriminating routine performed by the spare wheel discriminating unit 62. Upon start of the routine, in step S 10, the spare wheel discriminating unit 62 first performs a sensor ID nominating routine. A sensor ID nominati g process is a process of listing candidates of a sensor ID of a spare wheel based on a received radio signal. FIG. 4 shows a sensor ID nominating subroutine which represents the process performed in step S 10 as a subroutine.

[0054] When the sensor ID nominating routine is started, in step S I 1 , the spare wheel discriminating unit 62 first substitutes a count value n into " 1 ". The count value represents the number of times a radio signal has been received during traveling.

Subsequently, in step S I 2, a vehicle speed (vehicle body speed) detected by the vehicle speed sensor is read to determine whether or not the vehicle is traveling. When the vehicle is traveling, reception of a radio signal is awaited in step S I 3. When a radio signal is received while traveling, in step S I 4, a determination is made as to whether the count value n has exceeded a set value N. For example, the set value N is set to 20.

When the count value n does not exceed the set value N, in step S I 5, a sensor ID included in the radio signal is stored as ID (n). In step S I 6, the count value n is incremented by "1 " and the process is returned to step S I 2. As the count value n reaches the set value N by repeating the process described above, the sensor ID nominating routine is finished and the process is advanced to step S21 shown in FIG. 3.

[0055] In a sensor ID nominating routine, a sensor ID (n) obtained by adding a count value n to the sensor ID is stored in an order of receiving the radio signal during a traveling period of the host vehicle. Therefore, when the set value N is 20, sensor IDs (1) to (20) are stored as candidate IDs of a spare wheel of the host vehicle. A sensor ID of the spare wheel of the host vehicle is selected from the sensor IDs (1 ) to (20) by a process to be described later. Moreover, while a nominating period is limited by the number of receptions on the assumption that a sensor ID of a spare wheel can be received by

N-number of receptions, the nominating period may be limited by travel time (for example, around 3 minutes).

[0056] After finishing the sensor ID nominating routine, the spare wheel discriminating unit 62 performs selection of the sensor ID of the spare wheel of the host vehicle from the nominated sensor IDs by the process of step S21 and thereafter. While the subsequent process is performed regardless of whether or not the vehicle is traveling, a final sensor ID of the spare wheel is selected due to an interim occurrence of a stopping period.

[0057] As described above, the sensor unit 10 switches transmission periods of radio signals between when a wheel is rotating (Tl ) and when the wheel is not rotating (TO). Therefore, in the case of a spare wheel, the transmission period of a radio signal is a constant period TO regardless of whether the vehicle is traveling or stopping. However, in the case of a traveling wheel, the transmission period of a radio signal varies depending on whether the vehicle is traveling or stopping. The spare wheel discriminating unit 62 selects a sensor ID of the spare wheel using the presence or absence of the variation in the transmission period.

[0058] In step S21 , the spare wheel discriminating unit 62 sets the count value n to "T ". Next, a reception interval Tx is measured with respect to a sensor ID (n). In this case, after awaiting reception of a radio signal of the sensor ID (n), a time Tx from the reception to a next reception of a radio signal with the same sensor ID (n) is measured by a timer. Subsequently, in step S23, a determination is made as to whether or not the reception interval Tx is equal to the transmission period TO. When comparing the reception interval Tx and the transmission period TO, a determination that the reception interval Tx and the transmission period TO are equal to one another may be made if (TO - a) < Tx < (TO + a) is satisfied, where a denotes a slight margin that is taken into

consideration. [0059] When the reception interval Tx is equal to the transmission period TO, the spare wheel discriminating unit 62 advances the process to step S27, and when the reception interval Tx is not equal to the transmission period TO, the spare wheel discriminating unit 62 advances the process to step S24. In this case, when a radio signal of the sensor ID (n) is not received during a prescribed period (a period corresponding to TO) or when a radio signal of the same sensor ID (n) is not received after the transmission period TO even after receiving a radio signal of the sensor ID (n), a determination of "No" is made at that point.

[0060] When the radio signal has been transmitted from the sensor unit 10 of a traveling wheel, a detennination of "No" is made in step S23 if the vehicle is traveling. When the spare wheel discriminating unit 62 makes a determination of "No" in step S23, the spare wheel discriminating unit 62 erases the sensor ID (n) in step S24. In other words, the spare wheel discriminating unit 62 excludes the sensor ID (n) from candidates ' of sensor IDs of the spare wheel. Subsequently, in step S25, the value of the count value n is incremented by "1 ", and in step S26, a detennination is made as to whether the count value n has exceeded the set value N. When the count value n has not exceeded the set value N, the process is returned to step S22.

[00611 The spare wheel discriminating unit 62 repeats the process described above and when a detennination of "Yes" is made in step S23 or, in other words, when the sensor ID (n) transmitted by the sensor unit 10 of a non-rotating wheel W is received in step S23, in step S27, the spare wheel discriminating unit 62 stores the number of receptions of the sensor ID (n) and a current traveling state of the host vehicle. The number of receptions refers to the number of times step S27 is performed with respect to the sensor ID (n). In addition, a traveling state of the host vehicle represents a result of a determination made as to whether the host vehicle is "traveling" or "stopping" based on a vehicle speed detected by the vehicle speed sensor.

[0062] Subsequently, in step S28, the spare wheel discriminating unit 62 determines whether or not the sensor ID (n) has been respectively received twice or more during stopping of the host vehicle and during traveling of the host vehicle based on a storage history in step S27, and when a determination of "No" is made, the spare wheel discriminating unit 62 returns the process to step S26. The spare wheel discriminating unit 62 repeats the process described above and when a determination of "Yes ^" is made in step S28, the spare wheel discriminating unit 62 advances the process to step S29 to extrapolate that the sensor ID (n) is the sensor ID of the spare wheel of the host vehicle and stores the sensor ID (n). In other words, the sensor ID (n) is stored (registered) in the spare wheel ID storage area 54b of the registered ID storage unit 54.

[0063] For example, with respect to a sensor ID of a traveling wheel, the sensor ID is excluded by the determination made in step S23 since the transmission period is Tl when the vehicle is traveling, the sensor ID (n) is to remain as a candidate in step S27 since the transmission period is TO when the vehicle is stopping. However, in the case of a traveling wheel of the host vehicle, the traveling state stored in step S27 is always

"stopping" and the conditions of step S28 are no longer satisfied.

[0064] A case where sensor IDs of other vehicles are included in nominated sensor IDs will now be considered. In the embodiment, since sensor IDs that become selection objects of a spare wheel only during traveling are nominated, radio signals from other vehicles are less likely to be received during nomination. In other words, when a sensor ID is nominated in a stopped state, radio signals transmitted by vehicles parked around the host vehicle and vehicles traveling around the host vehicle are inadvertently received. Therefore, while the number of sensor ID candidates increases, since nomination is performed during traveling in the embodiment, the number of candidates can be reduced in an initial stage.

[0065] In addition, when a radio signal transmitted by another vehicle that is stopping is received during nomination, the sensor ID (n) of the other vehicle is added to the candidates. However, since the host vehicle is traveling and a distance from the other vehicle increases, it is basically conceivable that the sensor ID (n) will not be subsequently received. Therefore, the sensor ID (n) is excluded by the determination in step S23.

[0066] Furthermore, when a radio signal of another vehicle traveling so as to' approach the host vehicle is received during nomination, if the radio signal is transmitted from the sensor unit 10 of a traveling wheel, the radio signal is excluded by the determination of step S23 due to a transmission period thereof. Moreover, in the case of a radio signal transmitted from the sensor unit 10 of a spare wheel, while the radio signal cannot be excluded solely based on the transmission period thereof, the conditions of step S28 are not satisfied unless traveling and stopping are performed twice while maintaining a state where the other vehicle is near the host vehicle. In other words, in case of normal traveling, a state where the other vehicle moves away from the host vehicle and a radio signal cannot be received occurs at least once before satisfying the conditions and the radio signal is excluded in step S23 upon such an occurrence. Therefore, substantially, the conditions of step S28 are not satisfied if not a spare wheel of the host vehicle. Moreover, while two or more receptions respectively made during traveling and during stopping are adopted as conditions in the embodiment, the number of receptions need not necessarily be set to 2 and may instead be set to 1 or 3 or more.

[0067] In step S29, the spare wheel discriminating unit 62 stores the sensor ID (n) as the sensor ID of the spare wheel. Subsequently, in step S30, the spare wheel discriminating unit 62 reads the flag stored in the emergency wheel mounting flag storage unit 55 and determines whether or not the flag is set to "1 ". The flag is data representing whether or not the sensor unit 10 is attached to an emergency wheel mounted as a spare wheel and is written into the emergency wheel mounting flag storage unit 55 when the user (including car dealership personnel ) attaches.the sensor unit 10 after delivery of the vehicle. When the flag is set to ' '. in step S31 , the spare wheel discriminating unit 62 stores (writes) the same sensor ID as the sensor ID (n) of the spare wheel stored in step S29 to the emergency wheel ID storage area 54c and finishes the routine. Accordingly, the sensor ID of the emergency wheel is automatically registered. On the other hand, when the flag is not set to " 1 " (S30: No), the process of step S31 is skipped and the routine is finished.

[0068] In addition, when the spare wheel discriminating unit 62 repeats the process of steps S22 to S26 and the count value n exceeds the set value N (S26: Yes), in step S32, the spare wheel discriminating unit 62 assumes that a spare wheel having the sensor unit 10 is not mounted to the host vehicle, writes data representing "absent" in the spare wheel ID storage area 54b and the emergency wheel ID storage area 54c, and finishes the routine.

[0069] According to the spare wheel discriminating unit 62, even when the spare wheel is replaced, the sensor ID of a current spare wheel is readily distinguished and a correct sensor ID can be stored (registered) in the spare wheel ID storage area 54b. In addition, when an emergency wheel is mounted as the spare wheel and the sensor unit 10 is attached to the emergency wheel, the sensor ID of the sensor unit 10 of the emergency wheel is not only stored (registered) in the spare wheel ID storage area 54b but also stored (registered) in the emergency wheel ID storage area 54c. Accordingly, notification modes to the driver to be described later can be switched between a regular wheel and an emergency wheel.

[0070] Furthermore, since the sensor ID of the spare wheel is distinguished based on a traveling state of the host vehicle and the transmission period of the radio signal of the sensor unit 10 using the fact that the transmission period differs between when the wheel W is rotating and when the wheel W is stopping, distinguishing of the sensor ID of the spare wheel from particularly a sensor ID of another vehicle can be performed with high accuracy and in a simple manner.

[0071] If a flag is written into the emergency wheel mounting flag storage unit 55 when the sensor unit 10 is attached to an emergency wheel, the sensor ID of the emergency wheel can be automatically registered in the emergency wheel ID storage area 54c by the spare wheel discriminating unit 62. However, if the user has not performed writing to the emergency wheel mounting flag storage unit 55, the sensor ID of the emergency wheel is registered in the spare wheel ID storage area 54b (S29) but not in the emergency wheel ID storage area 54c. In this case, while mounting the emergency wheel as-is as a spare wheel does not pose a problem, when the emergency wheel replaces one of the traveling wheels and is subsequently used, a warning is favorably issued to the driver to prevent the emergency wheel from being continuously used. In order to do so, the wheel ECU 50 must keep track of whether a traveling wheel is a regular wheel or an emergency wheel. [0072] To handle such situations, the ID discriminating unit 60 includes the emergency wheel discriminating unit 63. The emergency wheel discriminating unit 63 automatically discriminates the use of an emergency wheel as a traveling wheel and registers the sensor ID of the emergency wheel in the emergency wheel ID storage area 54c.

[0073] While a tire outer diameter of an emergency wheel is equal to that of a regular wheel, a wheel diameter of an emergency wheel is smaller than that of a regular wheel. The sensor unit 10 is attached to a wheel. Therefore a distance between a center of rotation of the wheel W to the sensor unit 10 (the acceleration sensor 13) is shorter for an emergency wheel than a regular wheel. Consequently, when wheels W are rotating at a same rotational speed, acceleration G detected by the acceleration sensor 13 of the sensor unit 10 of an emergency wheel is smaller than acceleration G detected by the acceleration sensor 13 of the sensor unit 10 of a regular wheel. Using this fact, the emergency wheel discriminating unit 63 discriminates an emergency wheel from traveling wheels.

[0074] FIG. 5 shows an emergency wheel discriminating routine that is an example of a process performed by the emergency wheel discriminating unit 63. The emergency wheel discriminating routine is performed when the vehicle is traveling straight. Straight traveling can be determined by. for example, inputting detection values of a steering angle sensor that detects a steering angle of a wheel, a yaw rate sensor that detects a yaw rate of the vehicle body, and the like.

[0075] When the emergency wheel discriminating routine is started, in step S41 , the emergency wheel discriminating unit 63 samples acceleration G included in the radio signals transmitted by the sensor units 10 for each sensor ID of a traveling wheel that is stored in the traveling wheel ID storage area 54a. The sampled acceleration G is updated to latest acceleration G every time new data is received. The acceleration G that is sampled for each sensor ID will be denoted by Gl , G2, G3, and G4.

[0076] In step S42, the emergency wheel discriminating unit 63 reads a vehicle speed V detected by the vehicle speed sensor at a prescribed short period and determines whether or not the vehicle speed V is constant during a prescribed period Tl . The prescribed period Tl is a period corresponding to a period at which the sensor unit 10 transmits a radio signal when the wheel is rotating and may include a slight margin a. Alternatively, the time required to sample one set of the accelerations Gl to G4 of the four wheels may be adopted as the prescribed period. In other words, any prescribed period may be adopted as long as a determination can be made on whether or not all vehicle speeds V upon detection of the accelerations of the four wheels share the same value.

[0077] The emergency wheel discriminating unit 63 continues sampling the accelerations Gl to G4 until a constant vehicle speed condition of step S42 is satisfied. Once the constant vehicle speed condition is satisfied (step S42: Yes), in step S43, differences between the respective accelerations are calculated in order to determine a dispersion of the four sampled accelerations Gl to G4. For example, when one emergency wheel is included in the traveling wheels, dispersion occurs such that only the acceleration of the emergency wheel differs from the accelerations of the other wheels. Therefore, by calculating the differences between the respective accelerations G to G4, a determination can be made as to whether or not an emergency wheel is included in the traveling wheels.

[0078] Subsequently, in step S44, the emergency wheel discriminating unit 63 determines whether or not a difference in acceleration G is large only for one wheel, and when a determination of "Yes" is made, in step S45, the emergency wheel discriminating unit 63 determines (extrapolates) that the one wheel is an emergency wheel and registers the sensor ID of the sensor unit 10 of the determined emergency wheel in the emergency wheel ID storage area 54c. Therefore, while the registration state of the traveling wheel ID storage area 54a remains the same, the sensor ID of the wheel determined to be an emergency wheel is registered in the emergency wheel ID storage area 54c. Once the ID of the emergency wheel is registered, the emergency wheel discriminating unit 63 finishes the routine.

[0079] On the other hand, when a "No" determination is made in step S44, a determination is made that the emergency wheel is not being used as a traveling wheel and the routine is finished. In this case, writing into the registered ID storage unit 54 is not performed.

[0080] According to this process performed by the emergency wheel

discriminating unit 63, even if the user does not perform writing to the emergency wheel mounting flag storage unit 55, a sensor ID of a traveling wheel determined to be an emergency wheel can be registered to the emergency wheel ID storage area 54c.

[0081] The ID discriminating unit 60 automatically performs the discriminating process described above every time a preset timing arrives (for example, upon start of traveling after the ignition switch is turned on). Alternatively, for example, an operating switch (not shown) may be provided and the discriminating process described above may be started when the user inputs an operation input using the operating switch.

[0082] Next, modes of notification of tire pressure information to the driver will be described. Notification of tire pressure information is performed by the notification control unit 70 (the notification data generating unit 52 and the display control unit 53). As described earlier, the notification data generating unit 52 refers to the registered sensor ID that is stored in the registered ID storage unit 54 and generates notification data of tire pressure only with respect to the registered sensor ID.

[0083] For each registered sensor ID stored in the registered ID storage unit 54, the notification data generating unit 52 outputs pressure numerical value data representing tire pressure P to the display control unit 53 in association with wheel position data representing a wheel position thereof. In addition, the notification data generating unit 52 ^• compares the pressure P with a proper determination value Pref for each registered sensor ID and outputs insufficient pressure wheel position data that specifies a position of an insufficient pressure wheel to the display control unit 53 when the pressure P is lower than the proper determination value Pref.

[0084] Furthermore, when a sensor ID is registered in the emergency wheel ID storage area 54c of the registered ID storage unit 54, the notification data generating unit 52 refers to the traveling wheel ID storage area 54a and the spare wheel ID storage area 54b to determine at which position (the left front wheel, the right front wheel, the left rear wheel, the right rear wheel, and the spare wheel) of the vehicle the emergency wheel is provided based on a storage area storing a same sensor ID as the sensor ID of the emergency wheel. Subsequently, the notification data generating unit 52 outputs emergency wheel position data representing a position at which an emergency wheel is attached to the display control unit 53.

[0085] Moreover, the notification data generating unit 52 also determines whether or not the tire temperature T has reached an abnormally high temperature based on inputted tire temperature T. and when an overheated state of the tire is detected, the notification data generating unit 52 outputs tire overheating information to another vehicle control device (not shown). In addition, a warning display instruction may be outputted to the display control unit 53. Furthermore, the proper determination value Pref for determining whether or not tire pressure is proper may be corrected based on the tire temperature T.

[0086] The display control unit 53 controls display on the notifying device 100 based on notification data inputted by the notification data generating unit 52. FIG. 8 shows a monitor screen A displayed on the display of the notifying device 100. The monitor screen A displays a vehicle body symbol Ml representing a two-dimensional picture of the vehicle body, a wheel symbol M2 individually representing a wheel position, a pressure numerical value displaying unit M3 which is provided next to each wheel symbol M2 and which displays tire pressure as a numerical value, and a warning symbol M4 for attracting the driver's attention. The display control unit 53 causes the pressure numerical value displaying unit M3 to display pressure as a numerical value based on pressure numerical value data of each wheel position that is inputted by the notification data generating unit 52. The warning symbol M4 is configured so as to be visible to the driver only when lit and is not visible to the drive when turned off. In addition, when a spare wheel is mounted, the wheel symbol M2 is also displayed at a mounting position thereof. In the example shown in FIG. 8, the wheel symbol M2 is also displayed in the trunk in addition to positions of the left/right and front/rear wheels.

[0087] The display control unit 53 displays the wheel symbols M2 to be displayed on the monitor screen A in shapes that differ between a regular wheel and an emergency wheel. In other words, when emergency wheel position data is inputted from the notification data generating unit 52, the wheel symbol M2 at the wheel position thereof is displayed as a symbol with a shape that differs from the wheel symbol of a regular wheel. For example, while the display screen shown in FIG. 8 shows that all five wheels are regular wheels, when an emergency wheel is mounted as a spare wheel, the wheel symbol M2 of the spare wheel is displayed as a symbol with a shape that differs from the wheel symbol M2 of the regular wheel as shown in FIG. 9.

[0088] In this example, the wheel symbols M2 are displayed with a circular shape for regular wheels and a triangular shape for an emergency wheel. Therefore, the user can recognize the type of the spare wheel by looking at the display. Moreover, even when an emergency wheel is mounted as the spare wheel, if the sensor ID is not registered in the emergency wheel ID storage area 54c. the wheel symbol M2 of the spare wheel is displayed using a wheel symbol of a regular wheel as shown in FIG. 8. While the embodiment is configured so as to differentiate the shapes of the wheel symbols M2 between regular wheels and an emergency wheel, for example, a text for ID or the like may also be added. In addition, the shapes of the wheel symbols M2 are not limited to circular and triangular shapes and an arbitrary shape can be adopted.

[0089] Furthermore, when insufficient pressure wheel position data is inputted by the notification data generating unit 52, the display control unit 53 highlights the pressure numerical value displaying unit M3 of the wheel with insufficient pressure as shown in FIG. 10. Therefore, the driver is able to recognize which wheel is experiencing insufficient pressure together with a pressure value of the wheel.

[0090] Next, lighting control of the warning symbol M4 will be described. FIG. 7 shows a warning display control routine that is perfonned by the display control unit 53. The warning display control routine is repetitively performed at a prescribed period.

When the warning display control routine is started, in step S61 , the display control unit 53 determines whether or not there is a wheel with insufficient pressure. When insufficient pressure wheel position data is inputted by the notification data generating unit 52, a determination of "Yes" is made. In this case, in step S62, the display control unit 53 lights a warning symbol. For example, when the pressure of the right front wheel is insufficient, the pressure numerical value displaying unit M3 of the right front wheel is highlighted and the warning symbol M4 is lighted as shown in FIG. 10.

[00911 On the other hand, when there is no wheels with insufficient pressure (S61 : No), in step S63, a determination is made as to whether or not an emergency wheel is being used as a traveling wheel. In this case, the display control unit 53 determines whether or not the emergency wheel position data inputted by the notification data generating unit 52 represents a traveling wheel position. When the emergency wheel is being used as a traveling wheel, the process is advanced to step S62 to light the warning symbol M4. For example, when the emergency wheel position data represents the left rear wheel, the wheel symbol M2 representing an emergency wheel is displayed at the left rear wheel position and the warning symbol M4 is lighted as shown in FIG. 1 1. In this case, the display control unit 53 may display the wheel symbol M2 of the emergency wheel so as to be more prominent than when the emergency wheel had been mounted as a spare wheel. For example, the brightness of the wheel symbol M2 may be set higher than the brightness when the emergency wheel had been mounted as a spare wheel. Alternatively, the color of the wheel symbol M2 may be changed to a color that draws more attention.

[0092] When the emergency wheel is not being used as a traveling wheel or, in other words, when the emergency wheel is mounted as a spare wheel, in step S64, the display control unit 53 turns off the warning symbol M4.

[0093] The display control unit 53 repetitively performs this process. Therefore, the driver's attention may be attracted not only when insufficient tire pressure is detected but also when the emergency wheel is being used as a traveling wheel.

[0094] With the wheel state notification apparatus according to the embodiment described above, since sensor IDs of the sensor units 10 of a spare wheel and an

emergency wheel are stored in the registered ID storage unit 54 in addition to those of traveling wheels, the wheel ECU 50 can determine that the emergency wheel is being used as a traveling wheel. Accordingly, notifications may be performed in different modes (lighting of the warning symbol M4, changing shapes of the wheel symbol M2 of a traveling wheel that is being used as an emergency wheel, changing brightness of the wheel symbols M2, and the like) between a case where the emergency wheel is mounted as a spare wheel and a case where the emergency wheel is being used as a traveling wheel. As a result, the driver can be informed that the use of the emergency wheel is not favorable and can be prompted to replace the emergency wheel with a regular wheel.

[0095] In addition, since the wheel symbols M2 are displayed in shapes that differ between an emergency wheel and a regular wheel, the driver can learn from the monitor screen A whether or not the emergency wheel is mounted as a spare wheel, which wheel position the emergency wheel is being used, and the like.

[0096] Furthermore, when an emergency wheel is attached with the sensor unit 10, by simply writing a flag indicating the attachment of the sensor unit 10 in the emergency wheel mounting flag storage unit 55, the spare wheel discriminating unit 62 discriminates the sensor ID of the sensor unit 10 of the host vehicle and stores the sensor ID in the spare wheel ID storage area 54b and the emergency wheel ID storage area 54c. Therefore, since a sensor ID of the sensor unit 10 attached to the emergency wheel need not be registered by a manual operation, excellent usability is achieved.

[0097] In addition, it is conceivable that a flat may not be written into the emergency wheel mounting flag storage unit 55 when the sensor unit 10 is attached to the emergency wheel by the user. However, even in such a case, when the emergency wheel is being used as a traveling wheel, the emergency wheel discriminating unit 63

discriminates a wheel for which the emergency wheel is being used among the traveling wheels. Subsequently, the sensor ID of the sensor unit 10 provided on the discriminated wheel is stored in the emergency wheel ID storage area 54c. Therefore, the driver can be made aware that the emergency wheel is being used as a traveling wheel without having to perform a registration operation of a sensor ID related to the emergency wheel.

[0098] Furthermore, since the spare wheel discriminating unit 62 discriminates a sensor ID of the sensor unit 10 provided on the spare wheel of the host vehicle among an unspecified large number of sensor IDs based on a relationship between a traveling state of the host vehicle and a transmission period of a received radio signal, high discrimination accuracy is achieved.

[0099] While the wheel state notification apparatus according to the embodiment has been described above, the invention is not limited to the embodiment described above and various modifications can be made without departing from the object of the invention.

[0100] <Modification of emergency wheel discriminating routine>

A modification of the process performed by the emergency wheel discriminating unit 63 will now be described. While the emergency wheel discriminating routine according to the embodiment requires traveling at a constant speed for a prescribed period Tl , this modification disregards such conditions. FIG. 6 shows an emergency wheel

discriminating routine as a modification that is performed by the emergency wheel discriminating unit 63. This emergency wheel discriminating routine is also performed when the vehicle is traveling straight in a similar manner to the embodiment.

[0101] When the emergency wheel discriminating routine is started, in step S51. the emergency wheel discriminating unit 63 awaits for a radio signal that is transmitted by the sensor unit 10 of a traveling wheel. In step S52, upon receiving the radio signal, a vehicle speed V detected by a vehicle speed sensor is read. In step S53, reference acceleration Gref that corresponds to the vehicle speed V is set. Since the acceleration sensor 13 included in the sensor unit 10 outputs a detection value of acceleration in a direction of centrifugal force, acceleration G that is a detection value thereof is a value corresponding to a rotational speed of the wheel W. In addition, the rotational speed of the wheel W corresponds to the vehicle speed V during straight travel.

[0102] The emergency wheel discriminating unit 63 stores a map representing a relationship between the vehicle speed V and the acceleration G when a regular wheel is rotating, and by referring to the map, the emergency wheel discriminating unit 63 sets reference acceleration Gref that corresponds to the vehicle speed V read in step S52.

[0103] In step S54, the emergency wheel discriminating unit 63 calculates a deviation (|G - Gref|) between the received acceleration G and the reference acceleration Gref and determines whether or not the deviation is greater than a reference value a. The reference value a is set to a value that is greater than a deviation with respect to the acceleration G received from the sensor unit 10 of a regular wheel.

[0104] When a determination of "No" is made in step S54, the emergency wheel discriminating unit 63 determines that the received radio signal has been transmitted by a sensor unit 10 of a regular wheel and, in subsequent step S55, determines whether or not a determination has been made for the four traveling wheels. When there is a traveling wheel for which a determination has not been made (S55: No), the emergency wheel discriminating unit 63 returns the process to step S51 . The emergency wheel

discriminating unit 63 repeats this process, and when a determination of "Yes" is made in step S54, the emergency wheel discriminating unit 63 determines in step S56 that the sensor unit 10 having sent the radio signal is attached to an emergency wheel and registers the sensor ID in the emergency wheel ID storage area 54c of the registered ID storage unit 54. On the other hand, when the deviations of all four wheels are equal to or smaller than the reference value a (S55: Yes), in step S57, the emergency wheel discriminating unit 63 determines that the emergency wheel is not being used as a traveling wheel and finishes the routine. In this case, writing into the registered ID storage unit 54 is not performed.

[0105] According to this emergency wheel discriminating routine, in a similar manner to the emergency wheel discriminating routine according to the embodiment, even if the user does not perform writing to the emergency wheel mounting flag storage unit 55, a sensor ID of a traveling wheel determined to be an emergency wheel can be registered to the emergency wheel ID storage area 54c.

[0106] <Other modifications>

For example, while the embodiment adopts a configuration in which tire pressure information of the four traveling wheels is displayed according to wheel position, a simple configuration may be adopted in which the four traveling wheels are not respectively distinguished. In this case, the appropriateness of tire pressure may be notified discriminatingly for traveling wheels and a spare wheel, and when an emergency wheel is being used as a traveling wheel, a warning symbol may be lighted regardless of whether the pressure of the emergency wheel is insufficient or not. In addition, the traveling wheel ID storage area 54a of the registered ID storage unit 54 need not discriminatingly store the sensor IDs of the four wheels.

[0107] Furthermore, while the embodiment is configured so as to light the warning symbol M4, change shapes of the wheel symbol M2 of a traveling wheel, change brightness of the wheel symbols M2, and the like when an emergency wheel is being used as a traveling wheel, a configuration may be adopted in which a change is made to a display mode that displays a message reading, for example, "An emergency wheel is being used".

[0108] In addition, while he embodiment is configured so as to discriminate a sensor ID of the sensor unit 10 provided on a spare wheel of the host vehicle from an unspecified large number of sensor IDs based on a relationship between a traveling state of the host vehicle and a transmission period of a received radio signal, various

conventionally used methods may be adopted to discriminate the sensor ID of the spare wheel. Examples of methods that may be adopted include a method of discriminating between a rotating wheel (in other words, a traveling wheel) and a non-rotating wheel (in other words, a spare wheel) based on whether or not a magnitude of acceleration G

(corresponding to centrifugal force) that is received during traveling of a vehicle is greater than a prescribed value and a method of determining a wheel with a minimum amplitude of reception strength of a corresponding radio signal received during traveling of the vehicle as a spare wheel.

[0109] In addition, while the embodiment is configured so that both tire pressure and tire temperature are acquired as wheel state information, a configuration may be adopted in which only one of tire pressure and tire temperature is acquired. Alternatively, other wheel state information may be notified to the driver.

[0110] Furthermore, while the embodiment is configured so that a wheel state

(tire pressure information) is notified by a display screen, a configuration that does not use a display screen such as a configuration in which a wheel state is notified using an audio announcement device may be adopted. In this configuration, audio announcements are performed in different modes between a case where an emergency wheel is mounted as a spare wheel and a case where the emergency wheel is being used as a traveling wheel. For example, a message such as "An emergency wheel is being used" may be audibly notified when it is determined that the emergency wheel is being used as a traveling wheel.

[0111 ] In addition, while the sensor unit 10 according to the embodiment is configured so as to be only capable of transmitting to the wheel ECU 50, for example, a configuration may be adopted in which the sensor unit 10 is capable of bidirectional transmission and reception with the wheel ECU 50.