CROSS-REFERENCE TO RELATED APPLICATION

This application is based on and claims the benefit of priorities from earlier Japanese Patent Application No. 2006-253042 filed on Sep. 19, 2006 the description of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention in general relates to a detecting technique and more particular to a wheel position detecting device that detects a wheel position on a vehicle, the wheel position detecting device is preferably applied to a tire air pressure detecting device that detects tire air pressure.

2. Description of the Related Art

Conventionally, a direct-type tire air pressure detecting device is known as a tire air pressure detecting device. In the direct-type tire air pressure detecting device, a transmitter including a sensor, such as a pressure sensor, is directly mounted on a wheel side of a vehicle. A tire is attached to the wheel. An antenna and a receiver are provided on the vehicle-body side. The tire air pressure detecting device operates as follows. After the transmitter transmits a detection signal from the sensor, the receiver receives the detection signal, via the antenna, and the tire air pressure detecting device performs tire air pressure detection.

The tire air pressure detecting device adds identification (ID) information (identifier) to data transmitted from the transmitter so that whether the transmitting data is that of the vehicle on which the tire air pressure detecting device is mounted (own vehicle) and the wheel on which the transmitter is mounted can be determined. The ID information is used to determine whether the vehicle is the own vehicle or another vehicle. The ID information is also used to determine the wheel on which the transmitter is mounted. The ID information is registered to the receiver in advance. When the data transmitted from the transmitter is received, the tire air pressure detecting device determines the wheel to which the data belongs using the received ID information (refer to, for example, Japanese Patent Publication No. 3212311).

When a user himself changes the position of the wheel, such as through tire rotation, the tire air pressure detecting device cannot respond to the change in the wheel position unless the ID information of the wheels of which the tires have been rotated by the user is read and the read ID information is registered to the receiver over current ID information.

SUMMARY OF THE INVENTION

In light of the above-described issues, an object of the present invention is that the tire position detecting apparatus can automatically respond to the change in the wheel position which occurred, for example, when the user have been rotated the tire positions. Further object of the present invention is to prevent erroneous wheel position detection caused by erroneous trigger signal reception strength data sent from a transmitter to a receiver.

To achieve the above-described objects, the invention provides a wheel position detecting device and a tire air pressure detecting device using the wheel position detecting device. The wheel position detecting device includes a receiver and a transmitter, described hereafter.

A transmitter is provided on each of a plurality of wheels. The wheel is provided with a tire. The transmitter Includes a receiving unit, a first controlling unit, and a transmitting unit. The receiving unit receives a trigger signal, via a reception antenna. The first controlling unit determines reception strength of the trigger signal received by the receiving unit and stores reception strength data indicating the reception strength in a frame to be transmitted. The transmitting unit transmits the frame processed by the first controlling unit, via a transmission antenna.

The receiver, provided on the vehicle-body side, includes a triggering device, a receiving unit, and a second controlling unit. The triggering device outputs a trigger signal so that a plurality, of wheels among the plurality of wheels can receive the trigger signal. The receiving, unit receives the frame. The second controlling unit performs the wheel position detection based on the reception strength indicated by the reception strength data stored in the frame. In the wheel position detection, the wheel on which the transmitter is mounted is detected from among the plurality of wheels. The second controlling unit judges whether to use the reception strength data for the wheel position detection, based on whether the reception strength is within a predetermined range.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred form of the present invention is illustrated in the accompanying drawings in which:

FIG. 1 is a diagram of an overall configuration of a tire air pressure detecting device to which a wheel position detecting device is applied, according to a first embodiment of the Invention;

FIG. 2A is a block diagram of a transmitter;

FIG. 2B is a block diagram of a receiver;

FIG. 3 is a diagram of a relationship between a distance from a triggering device to a transmitter and reception strength of a trigger signal received by the transmitter;

FIG. 4A is a graph of a relationship between the distance from the triggering device to the transmitter and the reception strength of the trigger signal of a left-hand side wheel disposed near the triggering device;

FIG. 4B is a graph of a relationship between the distance from the triggering device to the transmitter and the reception strength of the trigger signal of a right-hand side wheel disposed away from the triggering device;

FIG. 5 is a flowchart of a wheel position detection process performed by a controlling unit in the receiver; and

FIG. 6 is a timing chart of when the wheel position detection process and a tire air pressure detection process are performed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Exemplary embodiments of the present invention are below described in detail with reference to the attached drawings.

Embodiments

FIG. 1 is a diagram of an overall configuration of a tire air pressure detecting device to which a wheel position detecting device is applied, according to a first embodiment of the invention. The upper section of FIG. 1 when the diagram is printed on paper indicates the front of a vehicle 1. The lower section of FIG. 1 indicates the rear of the vehicle 1.

As shown in FIG. 1, the tire air pressure detecting device is mounted on the vehicle 1. The tire air pressure detecting device includes transmitters 2, a receiver 3, a display 4, and triggering devices 5. According to the embodiment, the transmitters 2, the receiver 3, and the triggering devices 5 are equivalent to the wheel position detecting device of the invention.

A transmitter 2 is mounted on each of four wheels 6a to 6d (five wheels if a spare tire is included) of the vehicle 1. The transmitter 2 detects the air pressure of a tire attached to each wheel 6a to 6d. The transmitter 2 also stores detection signal data indicating a detection result in a frame to be transmitted and transmits the frame. The receiver 3 is mounted on a vehicle-body 7 side of the vehicle 1. The receiver 3 receives the frame transmitted from the transmitter 2. The receiver 3 also performs various processes, calculations, and the like based on the detection signal stored in the frame, thereby determining the tire air pressure.

FIG. 2A and FIG. 2B are block diagrams of the transmitter 2 and the receiver 3. The transmitter 2 and the receiver 3 are sequentially described, hereafter.

As shown in FIG. 2A, the transmitter 2 includes a sensing unit 21, a microcomputer 22, a battery 23, a transmission antenna 24, and a reception antenna 25.

The sensing unit 21 includes, for example, a diaphragm-type pressure sensor or a temperature sensor. The sensing unit 21 outputs a detection signal depending on the tire air pressure or a detection signal depending on the temperature.

The microcomputer 22 is a known microcomputer including a controlling unit (a first controlling unit) 22a, a transmitting unit 22b, a receiving unit 22c, and the like. The microcomputer 22 performs a predetermined process in adherence to a program stored in a memory (not shown) in the controlling unit 22a.

The controlling unit 22a receives the detection signal related to the tire air pressure from the sensing unit 21 and performs signal processing on the received detection signal. The controlling unit 22a also processes the detection signal as required. The controlling unit 22a stores the processed detection signal, in addition to the ID Information of each transmitter 2, in a frame to be transmitted. The detection signal is stored as data indicating the detection result (referred to, hereinafter, as tire air pressure-related data). Then, the controlling unit 22a transmits the frame to the transmitting unit 22b. The process for transmitting the signal to the transmitting unit 22b is performed at a predetermined cycle in adherence to the program.

In addition, the controlling unit 22a receives a trigger signal from the triggering device 5, via the reception antenna 25 and the receiving unit 22c. The controlling unit 22a performs signal processing on the trigger signal, thereby determining the reception strength of the trigger signal. The controlling unit 22a also processes the trigger signal as required. The controlling unit 22a stores trigger signal reception strength data in the frame storing the tire air pressure-related data or in a separate frame. The controlling unit 22a then transmits the frame to the transmitting unit 22b. The process for transmitting the signal to the transmitting unit 22b is also performed in adherence to the program.

The controlling unit 22a controls the timing at which the frame is transmitted to the transmitting unit 22b to prevent simultaneous transmissions of data from the transmitters 2. For example, a different transmission timing, indicating the number of seconds after the reception of the trigger signal that the frame is transmitted, is set in advance for each transmitter 3. Therefore, the respective transmitters 2 of the wheels 6a to 6d transmit the frames at different timings.

However, if a different transmission timing is merely stored in the controlling unit 22a of each transmitter 2 to enable each transmitter 2 of each wheel 6a to 6d to transmit the frame at a different timing, the content stored in each transmitter 2 differs. A shared program can be stored in the controlling unit 22a of all transmitters 2 can be shared if, for example, a map allowing the transmission timing to be selected depending on the reception strength or a function expression determining the transmission timing using transmission strength as a variable is stored in the controlling unit 22a, allowing the frame transmission timing to be shifted depending on the reception strength, and the respective transmission timings of the transmitters 2 differ by necessity as a result of the differences in the reception strengths.

The program stored in the controlling unit 22a can be set so that the transmission timing is randomly changed every time. When the transmission timing is randomly changed in this way, the probability that all transmission timings of the transmitters 2 differ becomes higher.

The transmitting unit 22b functions as an outputting unit that transmits the frame sent from the controlling unit 22a to the receiver 3, via the transmission antenna 24. The transmitting unit 22b uses radio frequency (RF) bandwidth, such as a 310 MHz radio wave.

The receiving unit 22c functions as an inputting unit that receives the trigger signal and transmits the received trigger signal to the controlling unit 22a, via the reception antenna 25.

The battery 23 supplies power to the controlling unit 22a and the like. Tire air pressure-related data collection performed by the sensing unit 21, various calculations performed by the controlling unit 22a, and the like are achieved through reception of the power supply from the battery 23.

The transmitter 2 configured as described above is, for example, mounted on an air injection valve in each wheel 6a to 6d. The transmitter 2 is disposed so that the sensing unit 21 is exposed on the inner side of the tire. As a result, the tire air pressure of the tire is detected. The frame is transmitted at a predetermined cycle (for example, every minute), via the transmission antenna 24 provided on each transmitter 2.

As shown in FIG. 2B, the receiver 3 includes an antenna 31 and a microcomputer 32.

The antenna 31 is a single, shared antenna that performs an overall reception of the frames each transmitted from a transmitter 2. The antenna 31 is fixed onto the vehicle-body 7.

The microcomputer 32 is a known microcomputer including a receiving unit 32a, a controlling unit (second controlling unit) 32b, and the like. The microcomputer 32 performs a predetermined process in adherence to a program stored in a memory (not shown) within the controlling unit 32b.

The receiving unit 32a functions as an Inputting unit that, when the frame transmitted from the transmitter 2 is received by the antenna 31, inputs the frame and transmits the frame to the controlling unit 32b.

The controlling unit 32b outputs a trigger instruction signal instructing the triggering device 5 to output the trigger signal. The controlling unit 32 receives the frame sent from the receiving unit 32a and performs wheel position detection, based on the trigger signal reception strength data of the transmitter 2 stored in the frame. In the wheel position detection, the controlling unit 32 identifies the wheel on which the transmitter 2, to which the frame belongs, is mounted from among the four wheels 6a to 6b.

Information related to speed is inputted from a speed sensor 8 to the controlling unit 32b and is also used for wheel position detection. A wheel position detection method will be described in detail hereafter.

The controlling unit 32b determines the tire air pressure by performing various kinds of signal processing, calculations, and the like, based on the data indicating the detection result stored in the received frame. The controlling unit 32b also outputs an electrical signal to a display 4, depending on the determined tire air pressure. For example, the controlling unit 32b compares the determined tire air pressure with a predetermined threshold value Th. When a decrease in the tire air pressure is detected, the controlling unit 32b outputs a signal indicating the decrease in the tire air pressure to the display 4. As a result, the display 4 is notified of the decrease in the tire air pressure in a wheel among the four wheels 6a to 6d.

The display 4 will be described (see FIG. 1). The display 4 is disposed in a location visible to a driver. The display 4 is, for example, a warning lamp provided on an instrument panel in the vehicle 1. For example, when a signal indicating the decrease in the tire air pressure is sent from the controlling unit 32b in the receiver 3, the display 4 displays a notification of the decrease, thereby notifying the driver of the decrease in the tire air pressure.

The triggering device 5 outputs the trigger signal when a trigger instruction signal sent from the controlling unit 32b in the receiver 3 is inputted. The trigger signal is a low frequency (LF) signal of, for example, 134 kHz and has a predetermined signal strength.

In this embodiment, the triggering device 5 is another device arranged to communicate the receiver 3 and locate out of the receiver 3. Alternatively, the triggering device 5 can be arranged to be a triggering unit 5 of the receiver 3.

According to the embodiment, two triggering devices 5 are used, a first triggering device 5a disposed on the front-wheel side and a second triggering device 5b disposed on the rear-wheel side. The field strength that can be used has an upper limit regulated by law. Therefore, if only one triggering device 5 is used, the radio wave may not reach all transmitters 2.

Therefore, according to the embodiment, the trigger signal transmitted from the first triggering device 5a reaches the transmitters 2 mounted on the right front wheel 6a and the left front wheel 6b. The trigger signal transmitted from the second triggering device 5b reaches the transmitters 2 mounted on the right rear wheel 6c and left rear wheel 6d.

Each triggering device 5 is disposed to be offset from a center line bilateral-symmetrically dividing the vehicle 1. As a result, each triggering device 5 is a different distance away from the corresponding wheels. According to the embodiment, the first triggering device 5a is disposed near the left front wheel 6b. The second triggering device 5b is disposed near the left rear wheel 6d. Both triggering devices 5 are disposed closer to the left-hand side than to the center line.

Therefore, the distance from the first triggering device 5a to the right front wheel 6a is longer than the distance from the first triggering device 5a to the left front wheel 6b. The distance from the second triggering device 5b to the right rear wheel 6c is longer than the distance from the second triggering device 5b to the left rear wheel 6c.

The triggering device 5 can be mounted anywhere as long as the location is not completely covered by metal. The triggering device 5 is preferably mounted on a location that is not covered by metal and is not hit by stones and the like while moving, such as within a liner or within the interior of the vehicle 1.

The tire air pressure detecting device to which the wheel position detecting device is applied according to the embodiment is configured as described above.

Next, a wheel position detection method used by the tire air pressure detecting device according to the embodiment will be described.

FIG. 3 shows a relationship between the distance from the triggering device 5 to the transmitter 2 and the reception strength of the trigger signal received by the transmitter 2. As shown in FIG. 3, in free space, the trigger signal reception strength (field strength of the radio wave) weakens depending on the distance from the triggering device 5 to the transmitter 2. Therefore, the trigger signal reception strength at the transmitter 2 tends to decrease as the distance from the triggering device 5 to the transmitter 2 increases.

The distance from a single triggering device 5 to each wheel differs. According to the embodiment, the distance from the first triggering device 5a to the right front wheel 6a is longer than the distance to the left front wheel 6b. Therefore, between the reception strengths of the trigger signal received by the transmitter 2 mounted on the wheel 6a and of that received by the transmitter 2 mounted on the wheel 6b, the reception strength of the trigger signal received by the transmitter 2 connected to the right front wheel 6a is weaker.

Whether the transmitter 2 is mounted on the right front wheel 6a or the left front wheel 6b can be determined through a comparison of the trigger signal reception strengths. Similarly, whether the transmitter 2 is mounted on the right rear wheel 6c or the left rear wheel 6d can be determined through the comparison of the trigger signal reception strengths.

According to the embodiment, the reception strength of the trigger signal received by each transmitter 2 is sent to the receiver 3. The receiver 3 determines the wheel on which each transmitter 2 is mounted from among the wheels 6a to 6d, based on the relationship between the trigger signal reception strength and the distances from the triggering device 5 to each transmitter 2.

However, the trigger signal reception strength of which notice is given to the receiver 3 is not necessarily accurate, such as in the following situations. For example, a problem of some sort occurs, such as the reception strength itself of the trigger signal transmitted from the triggering device 5 being an unexpected, abnormal value. Alternatively, the trigger signal reception strength data transmitted from the transmitter 2 differs from the reception strength that has actually been received, as a result of an error occurring during the signal processing performed within the transmitter 2. Therefore, the trigger signal reception strength data is required to be verified, and whether the data can be used for wheel position detection or the trigger signal is to be outputted and the trigger signal reception strength measured by each transmitter 2 again is required to be decided.

The verification of whether the trigger signal reception strength data is correct or incorrect can be performed based on the following idea. FIG. 4A and FIG. 4B are graphs showing the relationship between the distances from the triggering device 5 to each transmitter 2 and the trigger signal reception strength. FIG. 4A shows the relationship involving the left wheels 6b and 6d disposed near the triggering device 5. FIG. 4B shows the relationship involving the right wheels 6a and 6c disposed away from the triggering device 5.

The distance between the triggering device 5 and the transmitter 2 changes with the rotation of the wheels 6a to 6d. When the distance when the transmitters 2 mounted on the left wheels 6b and 6d are closest to the corresponding triggering device 5 is a and the distance when the transmitters 2 are the farthest is b, a maximum value Vmax(L) and a minimum value Vmin(L) of the reception strength are each expressed by the following equations, based on the distances a and b and the strength (referred to, hereafter, as trigger output Itrig[x]) of the trigger signal outputted from the triggering device 5.

The trigger output Itrig(x) indicates a value Itrig(3000) when the triggering device 5 outputs the trigger signal and the signal strength is measured at a location that is a predetermined distance, x millimeters (three meters, herein), away from the triggering device 5. Î² indicates a correction value taking into consideration effects of the setting position of the triggering device 5, external environment, and the like (in other words, effects excluding the effect the vehicle-body has on the trigger signal).

Vmax(L)=trigger output Itrig(3000)+60Ã—log(3000/a)+Î²â€ƒâ€ƒ(Equation 1)

Vmin(L)=trigger output Itrig(3000)+60Ã—log(3000/b)+Î²â€ƒâ€ƒ(Equation 2)

Therefore, the range of the reception strengths of the trigger signals received by the transmitters 2 mounted on the left wheels 6b and 6d is from Vmin(L) to Vmax(L).

As a result, whether the data is correct or incorrect can be verified when whether the reception strength data sent from the receiver 3 is within the range is judged.

Similarly, if the distance when the transmitters 2 mounted on the right wheels 6a and 6c are closest to the corresponding triggering device 5 is c and the distance when the transmitters 2 are the farthest is d, the maximum value V(max)(R) and the minimum value Vmin(R) are each expressed by the following equation, based on the distances c and d and the trigger output. Î± is a correction value taking into consideration an effect the vehicle-body has on the trigger signal. The value is decided based on the vehicle type.

Vmax(R)=trigger output Itrig(3000)+60Ã—log(3000/c)+Î±+Î²â€ƒâ€ƒ(Equation 3)

Vmin(R)=trigger output Itrig(3000)+60Ã—log(3000/d)+Î±+Î²â€ƒâ€ƒ(Equation 4)

Therefore, the range of the reception strengths of the trigger signals received by the transmitters 2 mounted on the right wheels 6a and 6c is from Vmin(R) to Vmax(R).

As a result, whether the data is correct or incorrect can be verified when whether the reception strength data sent from the receiver 3 is within the range is judged. The wheel position detection is performed based on a verification method such as this.

The equations 1 to 4 describes the method of determining the reception strength of the trigger signal at each transmitter 2 mounted on the wheels 6a to 6d, when each triggering device 5a and 5b outputs the trigger signal. However, the correction value Î² and the correction value Î± within the equations described above change depending on the extent to which factors expected to affect the reception strength are taken into consideration in advance. Therefore, the range of the reception strength may vary to a degree depending on the correction method.

Next, an operation performed by the tire air pressure detecting device according to the embodiment will be described. First, the tire air, pressure detecting device performs the wheel position detection when an ignition switch (not shown) is switched from OFF to ON. The wheel position detection is performed as a result of the controlling unit 32b of the receiver 3 performing a wheel position detection process.

FIG. 5 is a flowchart of the wheel position detection process performed by the controlling unit 32b of the receiver 3. The wheel position detection process is performed when the ignition switch (not shown) is switched from OFF to ON and the power of the controlling unit 32b of the receiver 3 is turned ON.

At Step 100, the controlling unit 32b outputs a trigger instruction signal to the first triggering device 5a after a predetermined period has elapsed after the power has been turned ON. When the trigger instruction signal is inputted into the first triggering device 5a, the first triggering device 5a outputs a trigger signal of a predetermined signal strength towards the transmitters 2 mounted on the right front wheel 6a and the left front wheel 6b.

When the trigger signal is inputted into the controlling unit 22a, via the antenna 25 and the receiving unit 22c of each transmitter 2 mounted on the right front wheel 6a and the left front wheel 6b, the controlling unit 22a enters a wake-up state and measures the reception strength of the received trigger signal.

When the trigger signal reception strength is determined, each transmitter 2 stores the trigger signal reception strength in a frame to be transmitted, in addition to ID information (identifier) added to differentiate each transmitter 2. The frame is then transmitted towards the receiver 3.

At this time, the transmission timing of each transmitter 2 differs. Therefore, cross-talk does not occur between the frames sent from the transmitters 2. The receiver 3 can receive the frame with certainty.

Next, at Step 105, whether a predetermined number of transmitters 2 have responded to the trigger signal outputted from the first triggering device 5a is judged.

The predetermined number of transmitters 2 mentioned here is assumed to be, for example, two or three transmitters 2. The predetermined number differs depending on the vehicle 1. In other words, if only the two transmitters 2 mounted on the front wheels 6a and 6b are expected to receive the trigger signal outputted from the first triggering device 5a, the predetermined number is two. If the transmitter 2 mounted on the left rear wheel 6d that is a relatively short distance from the first triggering device 5a is also expected to receive the trigger signal, the predetermined number is three. The number changes depending on the signal strength of the trigger signal, the distances from the first triggering device 5a to the back wheels 6c and 6d, and the like. Therefore, the predetermined number can be four depending on the conditions.

The transmitters 2 may not be able to receive the trigger signal when the trigger signal output strength is affected by the surrounding environment of the vehicle 1, such as when a road surface is formed from iron plates or when the vehicle 1 is parked near a facility or equipment emitting radio interference. When at least one of either of the two transmitters 2 mounted on the front wheels 6a and 6b cannot receive the trigger signal, the frames cannot be sent from the two transmitters 2.

In this case, two or more transmitters 2 may not be able to respond. The judgment result at Step 105 is NO. When the judgment result is NO, the controlling unit 32b proceeds to Step 110 to retry each of the above-described processes. A counter value of a counter (not shown) installed in the controlling unit 32b is incremented by one, and the number of re-tries is stored.

At Step 110, whether the number of re-tries is equal to or less than five times is judged. When the number of re-tries is equal to or less than five times, the controlling unit 32b returns to Step 100 and retries the process. If the number of re-tries exceeds five times, the controlling unit 32b stops the process without retrying the process. In this case, a transmitter 2 failure, a dead battery, and the like are thought to have occurred. Therefore, a notification of the number of re-tries exceeding five times can be given through the display 4.

At the same time, when the judgment result at Step 105 is YES, the controlling unit 32b proceeds to Step 115. The controlling unit 32b judges whether the reception strength data stored in the received frame is within the ranges set in advance. The ranges set in advance refer to the two ranges described above, Vmin(L) to Vmax(L) and Vmin(R) to Vmax(R).

When the reception strength data meets a condition in which a piece of reception strength data is within the range Vmin(L) to Vmax(L) and another piece of reception strength data is within the range Vmin(R) to Vmax(R), the judgment result is YES. When the condition is not met, the judgment result is NO. The reason for performing a judgment such as this will be explained.

The first triggering device 5a basically outputs the trigger signal to the transmitters 2 of the front wheels 6a and 6b. However, the transmitter 2 mounted on the left rear wheel 6d, disposed relatively close to the first triggering device 5a, may also receive the trigger signal.

In this case, the transmitter 2 mounted on the left rear wheel 6d also responds and transmits a frame that is received by the receiver 3. Therefore, for example, if a transmitter 2 among the transmitters 2 mounted on the front wheels 6a and 6b is broken, and the transmitter 2 mounted on the left rear wheel 6d also transmits the frame, the judgment result at Step 105 is YES. However, the reception strength data that are required to be acquired here are of the transmitters 2 mounted on the front wheels 6a and 6b. Therefore, whether the acquired reception data are really those of the transmitters 2 mounted on the front wheels 6a and 6b is required to be verified.

At this time, as explained in the description of the verification method above, the reception strengths of the trigger signals at the transmitters 2 mounted on the front wheels 6a and 6b are each within the range Vmin(L) to Vmax(L) and the range Vmin(R) to Vmax(R). However, the reception strength of the trigger signal at the transmitter 2 mounted on the left rear wheel 6d is not within the range.

Therefore, when the receiver 3 receives the frames Including the reception strength data from the transmitters 2 mounted on the front wheels 6a and 6b, the above-described condition is met. However, even if two or more frames are received, the condition cannot be met unless the received frames are sent from the transmitters 2 mounted on the front wheels 6a and 6b.

In this way, whether the trigger signal reception strength data have been successfully transmitted from the transmitters 2 mounted on the front wheels 6a and 6b, or in other words, whether the reception strength data are correct can be verified.

If the judgment result is NO, the controlling unit 32b proceeds to Step 120. The counter value of the counter (not shown) installed in the controlling unit 32b is incremented by one, and the number of re-tries is stored. Next, as at Step 110, the controlling unit 32b judges whether the number of re-tries is equal to or less than five times. When the number of re-tries is equal to or less than five times, the controlling unit 32b returns to Step 100 and retries the process. If the number of re-tries exceeds five times, the controlling unit 32b stops the process without retrying the process. If the judgment result is YES, the controlling unit 32b proceeds to Step 125.

Subsequently, in the processes at Step 125 to Step 145, the controlling unit 32b performs the same processes as those at Step 100 to Step 120, described above, for the rear wheels 6c and 6d side, as a result of the second triggering device 5b outputting the trigger instruction signal to the triggering device 5b at Step 125.

The processes are exactly the same as those performed for the front wheels 6a and 6b. Therefore, explanations thereof are omitted. As a result of these processes being performed, whether the trigger signal reception strength data have been successfully transmitted from the transmitters 2 mounted on the rear wheels 6c and 6d, or in other words, whether the reception strength data are correct can be confirmed.

In the process at Step 130, as in the process at Step 105 described above, whether the predetermined number of transmitters 2 has responded is judged. A spare tire (not shown) may be disposed near the rear wheels 6c and 6d. A transmitter 2 may be mounted on the spare tire.

In this case, the predetermined number is set taking into consideration the frame sent from the transmitter 2 mounted on the spare tire. In other words, when the spare tire is not taken into consideration, the trigger signal is expected to be received by only the transmitters 2 mounted on the rear wheels 6c and 6d or, in addition to the transmitters 2, the transmitter 2 mounted on the left front wheel 6b. Therefore, the predetermined number of transmitters 2 is two or three.

When the spare tire is taken into consideration, the predetermined number increases by one and becomes three or four. The predetermined number changes depending on the signal strength of the trigger signal, the distances from the first triggering device 5a to the rear wheels 6c and 6d, and the like. Therefore, depending on the conditions, the predetermined number may be further increased by one.

Next, at Step 150, the controlling unit 32b reads the ID information stored in the frame storing the reception strength data judged to be within the range at Step 115 and arranges the ID Information in order, from the ID information with the highest reception strength. The ID information with the higher reception strength is determined to be that of the transmitter 2 mounted on the left front wheel 6b. The ID information with the lower reception strength is determined to be that of the transmitter 2 mounted on the right front wheel 6a.

The controlling unit 32b corresponds the ID information stored in each frame with the right front wheel 6a and the left front wheel 6b on which the transmitters 2 are mounted and stores (registers) the ID information in the memory within the controlling unit 32b.

Similarly, at Step 150, the controlling unit 32b reads the ID information stored in the frame storing the reception strength data that is within the range and arranges the ID information in order, from the ID information with the highest reception strength. The ID Information with the higher reception strength is determined to be that of the transmitter 2 mounted on the left rear wheel 6d. The ID information with the lower reception strength is determined to be that of the transmitter 2 mounted on the right rear wheel 6c.

The ID information stored in each frame is corresponded with the right rear wheel 6c and the left rear wheel 6d on which the transmitters 2 are mounted and stored (registered) in the memory within the controlling unit 32b. The wheel position detection process is completed.

In this way, when the receiver 3 performs the tire air pressure detection, described hereafter, and a frame storing tire air pressure-related data is transmitted, the receiver 3 can determine the wheel on which the transmitter 2 that has transmitted the frame is mounted from among the four wheels 6a to 6d, using the ID information stored in the frame. The receiver 3 can determine the tire air pressure of each wheel 6a to 6d. As a result, the wheel on which each transmitter 2 is mounted can be detected from among the wheels 6a to 6d without the user being required to read the ID information or the like.

Hereafter, the tire air pressure detecting device using the wheel position detecting device, described above, will be described.

The tire air pressure detecting device performs the tire air pressure detection after the wheel position detection is performed as described above.

Specifically, the tire air pressure detecting device enters periodic transmission mode. As described above, in each transmitter 2, the detection signal from the sensing unit 21 indicating the tire air pressure and the temperature within the tire is inputted into the controlling unit 22a. The signal processing is performed as required on the detection signal, and the detection signal becomes tire air pressure-related data. The tire air pressure-related data, in addition to the ID information of the transmitter 2, is stored in the frame to be transmitted. Subsequently, the frame is transmitted to the receiver 3 side, via the transmitting unit 22b, at a predetermined cycle.

At the same time, when the transmitter 2 transmits the frame, the antenna 31 of the receiver 3 receives the frame. The frame is inputted into the controlling unit 32b, via the receiving unit 32a. The controlling unit 32b extracts the data indicating the tire air pressure and the data indicating the temperature within the tire from the received frame. The controlling unit 32b performs temperature correction as required, based on the data indicating the temperature, and determines the tire air pressure.

The ID information is stored in the frame. Therefore, the ID information is collated with the ID information stored during wheel position detection. The wheel on which the transmitter 2 from which the frame has been sent is mounted is determined from among the four wheels 6a to 6d.

When a difference between the determined tire air pressure and a previously determined tire air pressure does not exceed a predetermined threshold value and the change in the tire air pressure is small, the cycle at which the tire air pressure is detected remains as is (such as every minute). When the predetermined threshold value is exceeded and the change in the tire air pressure is large, the cycle is quickened (such as every five seconds).

If the determined tire air pressure is judged to be lower than the predetermined threshold value, the controlling unit 32b outputs a signal notifying the display 4 of the judgment. The notification is displayed by the display 4 so that the wheel having the decreased tire air pressure is identified from among the four wheels 6a to 6d. As a result, the driver can be notified of the wheel among the wheels 6a to 6d having the decreased tire air pressure.

When the ignition switch is switched from ON to OFF, the controlling unit 32b of the receiver 3 again outputs the trigger instruction signal to the triggering device 5. The triggering device 5 outputs the trigger signal. When the trigger signal is inputted into the controlling unit 22a, via the reception antenna 25 and the receiving unit 22c, the transmitter 2 switches to a sleep state. As a result, the tire air pressure detection performed by the tire air pressure detecting device is completed.

For reference, a timing chart of when the wheel position detection process and the tire air pressure detection process, described above, are performed is shown in FIG. 6. As shown in the diagram, the first triggering device 5a and the second triggering device 5b successively output the trigger signals simultaneously with the ignition switch being turned ON. In response, each transmitter 2 mounted on the wheels 6a to 6d transmits the frame storing the reception strength data and the ID information. When the receiver 3 receives the frames, the receiver 3 switches to periodic transmission mode. The tire air pressure detection is performed until the ignition switch is switched to OFF.

Hereafter, advantages achieved by the invention according to the embodiment will be described.

As described above, according to the embodiment, whether the reception strength data is correct or incorrect is judged based on whether the reception strength indicated by the reception strength data transmitted from each transmitter 2 is within the range set in advance. Whether the reception strength data is used is then judged.

Therefore, use of incorrect reception strength data can be prevented. The occurrence of erroneous wheel position detection can also be prevented. If a frame storing data including the reception strength data and the like is received by mistake from a transmitter of another vehicle in which the same system is installed, whether the reception strength is that of the own vehicle or another vehicle can be identified based on whether the reception strength indicated in the reception strength data is within the range set in advance. Therefore, use of erroneous data from another vehicle can be prevented.

When each triggering device 5a and 5b outputs the trigger signals, the number of transmitters 2 that will respond is set in advance. When the actual number of responding transmitters 2 differs from the set number, the reception of the frame is unsuccessful. When the frame cannot be received and when the reception strength data cannot be used, such as in the situations described above, the controlling unit 32b again outputs the trigger signal from the triggering device 5 and requests the reception strength data.

Therefore, the wheel position detection can still be performed even if the frame cannot be received or the reception strength data once transmitted from the transmitter 2 is incorrect. The correct reception strength data can be acquired by repeated tries and the wheel position detection can be performed.

Such re-tries need only be performed on the wheel of which the reception strength data cannot be successfully acquired. Therefore, the trigger signal is only required to be outputted from the triggering device that corresponds with the wheel among the triggering devices 5a and 5b.

The re-tries are preferably performed while the vehicle 1 is moving. For example, when the trigger signal is outputted when the position of the transmitter 2 happens to be in a location where the trigger signal reception is difficult or the like, the transmitter 2 may again be unable to receive the trigger signal if the re-try is performed while the transmitter 2 is in the same location.

If the re-try is performed while the vehicle 1 is moving, the position of the transmitter 2 changes. Therefore, the possibility of the trigger signal being received can be increased. Detection of whether the vehicle 1 is moving can be performed based on the signal from the speed sensor 8 inputted Into the controlling unit 32b. The receiver 3 can transmit a trigger signal outputting instruction to the triggering device 5 when a condition, such as the generation of speed, is met.

The controlling unit 32b can detect whether the vehicle 1 is moving. When the vehicle 1 is moving, the controlling unit 32b can instruct the triggering device 5 to output the trigger signal.

Alternatively, the controlling unit 32b can include means (115 and 140) of judging whether the number of pieces of reception strength data including the reception strength that is within the range set in advance, among the pieces of reception data, is a number decided in advance. When the number of pieces of reception data is not the number decided in advance, the controlling unit 32b can instruct the triggering device to output the trigger signal.

As a result, when the trigger signal is outputted while the position of the transmitter 2 happens to be in a location where the trigger signal reception is difficult or the like, the transmitter 2 may not be able to receive the trigger signal if the re-try is performed while the transmitter 2 is in the same location. If the re-try is performed while the vehicle 1 is moving, the position of the transmitter 2 changes. Therefore, the possibility of the trigger signal being received can be increased.

When the triggering device 5 includes the first triggering device 5a and the second triggering device 5, and the controlling unit 32b cannot successfully receive the reception strength data, the controlling unit 32b preferably instructs only the triggering device that outputs the trigger signal to the wheel that cannot successfully receive the reception strength data, among the first triggering device 5a and the second triggering device 5b, to output the trigger signal. As a result, unnecessary communication is not required to maintain the accuracy of the wheel position detection. The first triggering device 5a outputs the trigger signal to some of the wheels (6a and 6b) among the plurality of wheels. The second triggering device 5b outputs the trigger signal to other wheels (6c and 6d) among the plurality of wheels.

All advantages of the wheel position detecting device described above can be achieved in the tire air pressure detecting device including the wheel position detecting device.

Variation Examples

According to the embodiment, the first triggering device 5a is disposed on the front wheels 6a and 6b side. The second triggering device 5b is disposed on the rear wheels 6c and 6d side. The first triggering device 5a outputs the trigger signal to the right front wheel 6a and the left front wheel 6b as a pair. The second triggering device 5b outputs the trigger signal to the right rear wheel 6c and the left rear wheel 6d as a pair.

On the other hand, the first triggering device 5a can be disposed on the left wheels 6b and 6d side. The second triggering device 5b can be disposed on the right wheels 6a and 6c side. The first triggering device 5a can output the trigger signal to the left wheels 6b and 6d as a pair. The second triggering device 5b can output the trigger signal to the right wheels 6a and 6c as a pair.

In this case, if the first triggering device 5a is disposed closer to one wheel than the other, among the left wheels 6b and 6d, and the second triggering device 5b is disposed closer to one wheel than the other, among the left wheels 6a and 6c, the reception strengths become different values when the first triggering device 5a and the second triggering device 5b output the trigger signals. Therefore, the same advantages as those acquired according to the embodiment can be achieved.

According to the embodiment, when the triggering device 5 is the first triggering device 5a and the second triggering device 5b is explained.

However, if the trigger signal can to reach all transmitters 2, a single triggering device 5 can be provided so that the distances from the triggering device 5 to each wheel 6a to 6d all differ. In this case, four pieces of reception strength data are acquired, each from the transmitters 2 of the wheels 6a to 6d. Whether the reception strength data is to be used can be judged by judgment of whether the four pieces of reception strength data are each within the expected reception strength range using the relationship of the distance between the triggering device 5 and each transmitter 2.

According to the embodiment, when the invention according to the embodiment is applied to a four-wheel vehicle is described. However, the vehicle is not limited to the four-wheel vehicle. The present invention can be applied to a wheel position detecting device and a tire air pressure detecting device provided in a vehicle including more than four wheels, such as a large vehicle.

According to the embodiment, whether the vehicle 1 is moving is detected based on the detection signal from the speed sensor 8. However, the detection can be performed based other known signals and on detection signals from a wheel speed sensor, a longitudinal acceleration sensor, and the like.

The steps shown in the diagrams correspond with means performing the various processes.