Tire condition monitoring system and method

A tire condition monitoring system for a vehicle has a chassis-side transmitter/receiver and a tire-side transmitter/receiver. The tire-side transmitter/receiver measures an interval between two successive request signals of the chassis-side transmitter and controls a time point of transmission of a response signal of the tire-side transmitter/receiver based on the measured interval so that the response signal is transmitted when the tire-side transmitter/receiver is in the communication range of the chassis-side transmitter/receiver. A control unit determines a time interval of one rotation of a tire based on a vehicle speed, and drives the chassis-side transmitter/receiver to transmit the request signal at an interval set to be shorter than an interval in which the tire rotates the communication range of the chassis-side transmitter/receiver.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on and incorporates herein by reference Japanese Patent Applications No. 2004-146094 and No. 2004-146104, both being filed on May 17, 2004.

FIELD OF THE INVENTION

The present invention relates to a tire condition monitoring system and method, which monitor a tire condition such as a pneumatic pressure of a tire of a vehicle.

BACKGROUND OF THE INVENTION

Some tire condition monitoring systems for vehicles have pressure sensors and transmitters mounted on tire wheels, respectively, and receivers mounted on wheel houses, respectively. In this system, the pressure sensors periodically detect air pressures in the tires as tire information and the transmitters transmit the tire information to the receivers, respectively, when a predetermined condition defined by pressure changes, times or the like holds.

Other tire condition monitoring systems further have transmitters on the wheel houses to transmit trigger signals from the chassis side and receivers on the tire wheels, so that the transmitters on the tire side transmit the tire information in response to the trigger signals from the chassis side.

In the latter systems, in which bi-lateral communications are attained between the chassis side and the tire side, a communication range is limited to be less than an entire periphery (360°) due to communication regulations, power consumption or the like. The communication is enabled only when the tire-side transmitter/receiver enters the limited communication range of the chassis-side transmitter/receiver. This results in low rate of reception of the tire information. Since the communication period becomes shorter as the vehicle travels at higher speeds, the communication rate becomes further low. In the case in which the tire-side transmitter/receiver receives electric power from the chassis side, the period for receiving the electric power from the chassis side becomes shorter as the vehicle travels at higher speeds, thus resulting in insufficient power reception from the chassis side.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a tire condition monitoring system and method, which enable a chassis-side transmitter/receiver to receive tire information from a tire-side transmitter/receiver with higher reception rate and enables the tire-side transmitter/receiver to receive more electric power from the chassis side.

A tire condition monitoring system for a vehicle has a chassis-side transmitter/receiver for transmitting a request signal and a tire-side transmitter/receiver for detecting a tire condition and transmitting a response signal including tire condition information in response to the request signal.

According to one aspect of the present invention, the tire-side transmitter/receiver measures a vehicle speed or a rotation speed of the tire, which may be represented with an interval between two successive receptions of a request signal, and controls a time point of transmission of the response signal based on the vehicle speed so that the response signal is transmitted when the tire-side transmitter/receiver is in the communication range of the chassis-side transmitter/receiver. The tire-side transmitter/receiver preferably converts electromagnetic energy of the request signal to electric energy, and transmits the response signal only when the electric energy reaches a predetermined threshold level.

According to another aspect of the present invention, a control unit determines a time interval of one rotation of a tire based on a vehicle speed, and drives the chassis-side transmitter/receiver to transmit the request signal at an interval set to be shorter than an interval in which the tire rotates the communication range of the chassis-side transmitter/receiver. The control unit determines that the tire-side transmitter/receiver is at a position in the communication range when the response signal is received by the chassis-side transmitter/receiver.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

First Embodiment

Referring toFIG. 1, a tire condition monitoring system has tire-side transmitter/receivers11-14mounted on tires1-4, respectively, and chassis-side transmitter/receiver21-24mounted on a vehicle chassis to face the tires1-4in correspondence with the transmitter/receivers11-14, respectively. The system further has an electronic control unit (ECU)30connected to the chassis-side transmitter/receivers21-24, and a display40mounted in a passenger compartment for displaying the tire conditions. The display40may use a display of other electronic devices in a vehicle like a navigation device. The transmitter/receivers11-14and21-24perform bi-lateral (two-way) radio signal communications, respectively.

Each tire-side transmitter/receiver11-14may be constructed in the same way and may be a known-type integrated with an air valve of a disk wheel of a tire. As shown inFIG. 2, the tire-side transmitter/receiver11includes a communication control circuit11a, an antenna capacitor11band an antenna11c. The control section11aincludes a tire condition sensor11d, which detects air pressure in the tire1, and a capacitor11e, which stores energy. The tire condition sensor11dmay detect a temperature in the tire1as a tire condition in addition to or alternative to the air pressure.

The control circuit11agenerates a response signal including the detected tire condition detected by the sensor11dand transmits it from the antenna11cin response to a request signal from the transmitter/receiver21on the chassis side. This response signal also includes an identification code of the transmitter/receiver11as a part of tire condition information. The radio frequency used for transmitting the request signal from the transmitter/receiver21and the radio frequency used for transmitting the detection signal from the transmitter/receiver11are different.

The transmitter/receiver11has no storage battery therein. It receives the request signal from the transmitter/receiver21as an electromagnetic energy wave, converts this signal to electric energy and stores it in the capacitor11e, which is used as an electric power source.

The transmitter/receivers21-24on the chassis-side are connected to the ECU30through respective signal lines28. The transmitter/receivers21-24may alternatively be wireless-connected without signal lines28. Each transmitter/receiver21-24receives the response signal from the corresponding transmitter/receiver11-14and applies a voltage signal corresponding to the received response signal to the ECU30.

The ECU30is constructed with a microcomputer, a ROM, a RAM and the like. The ECU30is supplied with electric power from a storage battery (not shown) mounted on the vehicle, and each transmitter/receiver21-24is supplied with electric power through the ECU30.

The range of communications between each transmitter/receiver11-14on the tire side and a corresponding transmitter/receiver21-24on the chassis side is limited to a certain angle (hatched) as shown inFIG. 3. That is, the communication range between the transmitter/receiver11and21are limited to an area in which the transmitter/receiver11is close to the transmitter/receiver21. The transmitter/receiver11can receive the request signal as the power signal from the transmitter/receiver21only when its rotational position is within the limited area.

As shown inFIG. 4, the transmitter/receiver21continues to transmit the request signal during a predetermined time interval. During the first rotation (time interval T1from time t1) of the tire1, the transmitter/receiver11receives the request signal (ON) during a certain interval T11corresponding to the communication range and converts its electromagnetic energy to the electric power to charge the capacitor11e. If the electric power, that is, charged voltage, does not exceed a threshold level TH, which is required for the transmitter/receiver11to transmit the response signal to the transmitter/receiver21. With this stored power, however, the transmitter/receiver11detects the air pressure in the tire1.

During the subsequent rotation (time interval T2from time t2) of the tire1, the transmitter/receiver11repeats the conversion and charging operation for a time interval T21corresponding to the communication range in the similar manner as in the first rotation. The charged voltage will exceed the threshold level TH. The transmitter/receiver11measures the time interval T1(=t2−t1) between two receptions of the request signal from the transmitter/receiver21. This measured time interval T1corresponds to a rotational speed of the tire1and hence a vehicle travel speed. From this measured time interval T1, the transmitter/receiver11determines or estimates a time point t3when it will enter the communication range next time. Thus, the transmitter/receiver11transmits tire condition information as the response signal to the transmitter/receiver21at the determined time point t3, that is, when the tire1rotates to the position at which communication with the transmitter/receiver21becomes possible, after waiting for a certain interval and on a condition that the request signal is not transmitted from the transmitter/receiver21.

The transmitter/receiver11, specifically the control circuit11a, determines the rotational position of the tire1by executing the processing shown inFIG. 5. The control circuit11achecks at step S10whether the request signal from the transmitter/receiver21is received. If not (NO), it continues step S10until the request signal is received. If received (YES), the control circuit11astarts to measure a time interval (e.g., T1) at step S11. At this time, the tire condition such as tire air pressure is detected.

The control circuit11achecks at step S12a next reception of the request signal in the similar manner as at step S10. When the next reception is made (YES), the control circuit11aobtains the measured time interval (e.g., T1) between the successive receptions of the request signal at step S13.

The control circuit11athen checks at step S14whether the transmitter/receiver11is within the specified range of communication with the transmitter/receiver21and whether the tire condition has been detected. This checking of the position of the transmitter/receiver11may be attained by checking whether the measured time interval (e.g., T1) has passed after the reception of the request signal (S12: YES). When the tire1is within the specified range (YES), that is, the measured time interval (e.g., T1) has passed, the transmitter/receiver11transmits the response signal to the transmitter/receiver21at step S15. For completing the transmission within the communication range, it is preferred to measure also the time interval of the communication range (e.g., T11) and use this measured time interval to limit the transmission interval of S15.

According to the first embodiment, each transmitter/receiver11-14determines a communication range based on the time interval of successive request signals and transmits the tire condition information only when the transmitter/receiver11-14rotates to a position at which the communication with the transmitter/receiver24becomes possible. Therefore, the rate of reception of the tire condition information at the chassis side is increased.

The transmitter/receiver11-14transmits the response signal to the transmitter/receiver21-24only when the converted and stored electric power rises to the threshold level. Therefore, even in the case that the vehicle travels at high speeds and the electric power increase per tire rotation is small, the response signal transmission from the transmitter/receiver11-14can be attained without fail by continuing the conversion and storage for a plurality of request signals and transmitting it only after the stored power rises to the threshold level.

Second Embodiment

The second embodiment is similar to the first embodiment. In the second embodiment, however, a speed sensor31for detecting a vehicle travel speed is provided as a part of the ECU30as shown inFIG. 1. Further, as shown inFIG. 6, the transmitter/receiver21transmits the response signal intermittently and the transmitter/receiver11on the tire1transmits the response signal at a time point of termination of the request signal from the transmitter/receiver21when the stored electric power in the transmitter/receiver11exceeds the threshold level TH.

When the transmitter/receiver11is in the communication range of the transmitter/receiver21, the transmitter/receiver21receives the response signal from the transmitter/receiver11in response to the request signal from the transmitter/receiver21. Therefore, the transmitter/receiver21can determine the position of the transmitter/receiver11by transmitting the request signal from the transmitter/receiver21at a predetermined interval and receiving the response signal from the transmitter/receiver11.

Specifically, the ECU30executes the processing shown inFIG. 7to determine the position of the transmitter/receiver11. The ECU30determines at step S20a sampling period, that is, a time interval of transmitting the request signal from the transmitter/receiver21based on the vehicle speed SPD detected by the speed detector31. If the communication range (hatched inFIG. 8) is 100° relative to one rotation angle 360° of the tire1, the position of the transmitter/receiver11, that is, whether the transmitter/receiver11is in the communication range, can be detected at least once as long as transmitting the request signal, that is, sampling, is made more than 3.6 (360°/100°) times per rotation of the tire1.

The ECU30then checks at step S21whether it is a sampling timing to transmit the request signal. If so (YES), the ECU30drives the transmitter/receiver21to transmit the request signal at step S22. The ECU30checks at step S23whether the transmitter/receiver21received the response signal. If no response signal was received (NO), the processing returns to step S20. If the response signal was received (YES), the ECU30stores at step S24the position of the transmitter/receiver11in its memory. This position is represented with one of the samplings in which the response signal was received.

The ECU30checks at step S25whether the position of the transmitter/receiver11was determined with required resolution. Here, the required resolution is determined based on the vehicle speed. The allowable communication period becomes shorter as the vehicle speed increases. Therefore, the position of the transmitter/receiver11is required to be determined with higher resolution, that is, in unit of a smaller rotation angular interval. Therefore, this unit of rotation angular interval must be determined in consideration of a highest possible vehicle speed or rotation speed of the tire1.

If the position is not determined with the required resolution (NO), the ECU30newly determines the transmission timing at step S26. In this step S26, for instance, the ECU30changes of shifts the sampling interval and checks whether the response signal is received near (preceding to or following from) the position stored at step S24. The ECU30repeats steps S20to S26until the position of the transmitter/receiver11is successfully specified with the required resolution.

The above operation is exemplified inFIG. 8. In this example, it is assumed that the sampling is made four times in each rotation and the response signal from the transmitter/receiver11is received when sampling is made at a position (sampling time) B among four positions (sampling times) A to D. This sampling time B is stored in the memory (step S24).

If the transmitter/receiver11is near the position B, which is close to the limit of the communication range, the communication between the transmitter/receivers11and21may become impossible when the vehicle travel speed increases. This is because the time interval corresponding to the communication range is narrowed when the vehicle travel speed increases. Therefore, after the position of the transmitter/receiver11is stored, similar samplings are made at two different sampling times B1and B2before and after the sampling time B by changing the sampling interval (step S26). One of the two sampling times (position B1) is stored in the memory in place of the previous position B. By repeating this operation until the position of the transmitter/receiver11changes less than a predetermined angular interval (required resolution), the position of the transmitter/receiver11is finally defined.

According to the second embodiment, the ECU30determines the position of each transmitter/receiver11-14on the tire1-4by execution of the above processing for other transmitter/receivers. After the position determination, the ECU30calculates the position of the transmitter/receiver11-14in accordance with the vehicle speed and drives the transmitter/receiver21-24to transmit the request signal only when the transmitter/receiver11-14is within the communication range. As a result, the rate of reception of the response signal from the tire side can be increased. The ECU30preferably stops transmission of the request signal when the transmitter/receiver11-14is not in the communication range, that is, not close to the transmitter/receiver21-24, thereby reducing power consumption.

In the second embodiment, the processing of determination of the transmitter/receiver11-14may be executed at the time of installing the system on the vehicle for the first time. Alternatively, it may be executed when the transmitter/receiver11-14and the transmitter/receiver21-24cannot communicate each other, respectively, for more than a predetermined number of times. The position data about the transmitter/receiver11-14which the transmitter/receiver21-24holds is considered to include an error. Therefore, the position determination processing may be executed after a certain time elapse in which the error will increase.

The sampling interval need not be set shorter than a time interval of one rotation of the tire when the tire rotates at high speeds, but may be set longer than the one rotation time interval. That is, assuming that the tire rotation time interval is Tr and the sampling interval is Ts, the request signal may be transmitted from the transmitter/receiver21-24at an interval of Tr+Ts.

The position determination may be attained based on the signal level of the response signal received by the transmitter/receiver21-24.

In the case of communication in the LF band, for instance, the level of reception of the response signal at the transmitter/receiver21-24is proportional to 1/D3(an inverse of a distance D to the third power, the distance D being between the transmitter/receiver11-14and the corresponding transmitter/receivers21-24). Therefore, the response signal reception level becomes higher as the transmitter/receiver11-14is closer to the transmitter/receiver21-24. If a maximum value of the response signal reception level is known, the transmitter/receiver11-14can be determined to be at the position closest to the transmitter/receiver21-24when the response signal reception level reaches the maximum value by comparing the actual response signal level with the maximum value.

The position of the transmitter/receiver11-14may be determined based on changes of the response signal reception level without using the maximum value. Specifically, when the signal reception level increases, the transmitter/receiver11-14may be determined to be at a position which is rear side from the position of communication. On the other hand, when the signal reception level decreases, the transmitter/receiver11-14may be determined to be at a position which is front side from the position of communication.

Both of the embodiments may be modified in other ways. For instance, as shown inFIG. 9, the transmitter/receivers21-24, the ECU30and the display40may be connected with an in-vehicle LAN29in place of signal lines28. The transmitter/receiver11-14may be operated with a built-in battery without getting electric energy from the request signal.