Transmission device for transmitting tire information and tire information monitoring system

A tire information monitoring system includes a transmission device, a receiving device, and a monitoring section. The transmission device includes a sensor which detects tire information, a transmitter which wirelessly transmits the detected tire information and a housing. The housing includes a wall surrounding the sensor and the transmitter, an inner space divided from the tire cavity area by the wall, and an air vent passing through the housing and connecting the inner space and the tire cavity area. An outer opening portion of the air vent formed on a surface of the housing facing the tire cavity area has an opening area of 0.4 mm2 or smaller. An inner opening portion of the air vent formed on a surface of the housing facing the inner space has an opening area larger than that of the outer opening portion.

TECHNICAL FIELD

The present invention relates to a transmission device provided in a tire cavity area to transmit tire information about a tire condition and a tire information monitoring system for determining whether a tire anomaly is caused.

BACKGROUND ART

Conventionally, a check and control of air pressure of a tire mounted to a vehicle are desired for improvement of tire durability, improvement of wear resistance, improvement of fuel economy, or improvement of ride quality, and improvement of handling performance. For these purposes, various systems for monitoring tire pressure have been proposed. In such a system, in general, information about the air pressure of the tire mounted to a wheel is detected, a transmission device for transmitting the information is provided in a tire cavity area of each wheel, and the information of the air pressure of each tire is obtained from the transmission device to monitor the air pressure of the tire.

On the other hand, when a tire goes flat, a puncture repair agent to be injected into a tire cavity area located between the tire and a rim is often used. Because the puncture repair agent is a liquid, the agent adheres to the transmission device provided in the tire cavity area as well as a tire inner surface facing the tire cavity area when the agent is injected into the tire cavity area. In some cases, the agent becomes solidified to close an opening portion formed in the transmission device to affect measurement of the air pressure.

To cope with this problem, a wheel condition detection device capable of maintaining a normal detection condition by preventing entry of foreign matter through a communication portion for detection has been proposed (Japanese Patent Application Laid-Open No. 2008-62730).

To put it concretely, a TPMS (Tire Pressure Monitoring System) valve of the wheel condition detection device is provided with a communication portion opening and closing mechanism for opening and closing a communication hole formed in a housing. At the time of puncture repair, entry of the puncture repair agent into a detection space through the communication hole is prevented. This communication portion opening and closing mechanism is made up of mechanical bodies including a lid body and a torsion coil spring and automatically opens and closes the communication hole by centrifugal force acting on a wheel.

Moreover, there are proposed a tire pressure monitoring system and a tire pressure sensor unit for informing an occupant that tire pressure may drop after a punctured tire is fixed by using a tire puncture repair agent (Japanese Patent Application Laid-Open No. 2007-196834).

To put it concretely, the tire pressure monitoring system is provided to each tire of a vehicle and is provided with a sensor unit having a tire pressure sensor and a transmitter, a receiving device for receiving a radio wave from the sensor unit, and a control ECU for giving an alarm when the air pressure of each tire becomes lower than or equal to a threshold value. The system is provided with a puncture determination means for determining puncture of each tire and a puncture repair agent use determination means for determining whether or not the punctured tire was repaired by using the puncture repair agent after it was determined that the tire went flat. When it was determined that the punctured tire was repaired by using the puncture repair agent, the control ECU continues the alarm even if the tire pressure value from the air pressure sensor is a normal value.

Because the communication portion opening and closing mechanism of the device described in Japanese Patent Application Laid-Open No. 2008-62730 is made up of the mechanical bodies including the lid body and the torsion coil spring, the device itself is complicated and expensive.

In the system and the unit described in Japanese Patent Application Laid-Open No. 2007-196834, it is not certain whether or not the information about the tire pressure measured after the repair of the tire by using the puncture repair agent is correct. Therefore, it is impossible to determine whether a tire anomaly after the puncture repair is caused.

SUMMARY OF INVENTION

Technical Problem

Therefore, an object of the present invention is to provide a transmission device capable of appropriately detecting and transmitting tire information such as tire pressure information even after tire puncture repair by using a puncture repair agent and a tire information monitoring system for determining whether a tire anomaly is caused.

According to an aspect of the invention, there is provided a transmission device provided in a tire cavity area to transmit tire information about a condition of a tire.

The device includes:

a sensor which detects, as the tire information, a condition of gas filled in the tire cavity area surrounded with the tire and a rim to which the tire is mounted;

a transmitter which wirelessly transmits the detected tire information; and

a housing which includes a wall surrounding the sensor and the transmitter, an inner space divided from the tire cavity area by the wall, and an air vent passing through the housing and connecting the inner space and the tire cavity area.

An outer opening portion of the air vent formed on a surface of the housing facing the tire cavity area has an opening area of 0.4 mm2or smaller.

An inner opening portion of the air vent formed on a surface of the housing facing the inner space has an opening area larger than that of the outer opening portion.

The opening area of the inner opening portion is four times the opening area of the outer opening portion or larger.

A hole cross-sectional area of the air vent increases in a stepwise fashion or continuously from the outer opening portion toward the inner opening portion.

A protruding portion protruding by 1 mm or longer from the surface of the housing toward the tire cavity area is provided to a surface of the housing, and

the outer opening portion is formed on a top portion of the protruding portion.

When the protruding portion is cut along a plane including a central axis of the air vent, an inclined face of the protruding portion and facing the tire cavity area protrudes, for example, toward the tire cavity area in a bulge shape.

An edge of the inner opening portion of the air vent is chamfered or rounded.

The inner space includes a sensor space which is provided at least between the air vent and the sensor and which a sensor face of the sensor faces and

the sensor space is formed by an inner wall of an inner member provided in the housing and by the wall of the housing, is narrower than an inner area surrounded with the wall of the housing, and has a cross-section widening from the inner opening portion of the air vent.

A guide groove extending from the inner opening portion of the air vent is provided to the wall of the housing and the inner wall of the inner member facing the inner space.

Each of grooves extending in different directions from the inner opening portion is provided as the guide groove to a face of the wall of the housing facing the inner space.

The inner space includes, for example, a reservoir space for storing a liquid that has entered through the air vent and the guide groove is provided to extend toward the reservoir space.

Or, the inner space includes a reservoir space for storing a liquid that has entered through the air vent, the inner opening portion of the air vent is provided to a wall face of the reservoir space, and the inner space includes, besides the reservoir space, the sensor space which branches off from the wall face of the reservoir space and which the sensor face of the sensor faces.

The guide groove forms a flow path of a liquid that has entered the inner space through the air vent.

According to the other aspect of the invention, there is provided a tire information monitoring system.

The system includes: a transmission device; a receiving device; and a monitoring section.

The transmission device includes

a sensor which detects, as tire information, a condition of gas filled in a tire cavity area surrounded with a tire and a rim to which the tire is mounted,

a transmitter which wirelessly transmits the detected tire information, and

a housing which includes a wall surrounding the sensor and the transmitter, an inner space divided from the tire cavity area by the wall, and an air vent passing through the housing and connecting the inner space and the tire cavity area.

An outer opening portion of the air vent formed on a surface of the housing facing the tire cavity area has an opening area of 0.4 mm2or smaller,

an inner opening portion of the air vent formed on a surface of the housing facing the inner space has an opening area larger than that of the outer opening portion

On the other hand, the receiving device receives the tire information transmitted from the transmitter.

The monitoring section determines whether a tire anomaly is caused based on the tire information and informs a determination result.

The transmission device and the tire information monitoring system are capable of appropriately measuring and obtaining tire information such as tire pressure information even after tire puncture repair by using a puncture repair agent.

DESCRIPTION OF EMBODIMENTS

A transmission device and a tire information monitoring system of the present invention will be described below in detail.

(Overview of Tire Pressure Monitoring System)

FIG. 1is a general overview diagram of a tire pressure monitoring system10which is an embodiment of the tire information monitoring system.

The tire pressure monitoring system (hereafter referred to as system)10is mounted on a vehicle12. The system10includes air pressure information transmission devices (hereafter referred to as transmission devices)16a,16b,16c, and16dprovided in respective tire cavity areas in tires14a,14b,14c, and14dof respective wheels of the vehicle12and a monitoring device18.

All of the transmission devices16a,16b,16c, and16ddetect information about pressure of air filled into the tire cavity areas surrounded with the tires and rims as tire information and wirelessly transmit the tire information to the monitoring device18. Hereafter, to explain all of the transmission devices16a,16b,16c, and16dat a time, the transmission devices16a,16b,16c, and16dwill be collectively referred to as transmission devices16.

(Structure of Transmission device)

FIG. 2is a drawing for explaining an example of a method for fixing the transmission device16in the tire cavity area.FIG. 3is a perspective view of an entire device in which the transmission device16illustrated inFIG. 2is integrated with a tire valve20.

The transmission device16is provided to an end portion of the tire valve20extending on a side of the tire cavity area. As illustrated inFIG. 2, the transmission device16is fixed and disposed in the tire cavity area by mechanically fixing the tire valve20to the rim19.

FIG. 4is a cross-sectional view of the transmission device16taken along a line of A-A illustrated inFIG. 3. As illustrated inFIG. 4, the transmission device16includes a housing22and a circuit24provided in the housing22. The circuit24includes a substrate26and a sensor unit28, a transmitter30, a processing unit32, a power supply section34, and an antenna40(seeFIG. 5) provided to the substrate26. In the housing22, an inner space38is formed and the inner space38has a sensor space38aand a reservoir space38bfor collecting and storing the liquid such as the puncture repair agent that has entered the inner space38.

The housing22is provided with an air vent36connecting the inner space38in the housing22and a tire cavity area and passing through the housing22. A protruding portion37protruding toward the tire cavity area is provided to a surface of the housing22. An outer opening portion37aof the air vent36is formed on a top portion of the protruding portion37. On the other hand, an inner opening portion37bof the air vent36is formed in an inner surface of the housing22where the air vent36faces the inner space38(the sensor space38a).

The sensor space38ais formed between the air vent36and a sensor unit28and a sensor face of the sensor unit28faces the sensor space38a.

An opening area of the outer opening portion37aof the air vent36is 0.4 mm2or smaller. Because the opening area of the outer opening portion37ais 0.4 mm2or smaller, the liquid such as the puncture repair agent becomes less likely to enter the air vent36. The inner opening portion37bof the air vent36has a larger opening area than the outer opening portion37a. The air vent36, the outer opening portion37aand the inner opening portion37bare described below.

In an inner area surrounded with a wall of the housing22, sealing resin39is filled as an inner member while remaining the inner space38. In other words, the inner space38is formed by inner wall faces of the housing22and inner walls of the inner member provided to the housing22. Therefore, the inner space38is smaller than the inner area surrounded with the wall of the housing22. Moreover, as illustrated inFIG. 4, a cross-section of the sensor space38aincreases from a cross-section of the inner opening portion37bof the air vent36.

In the housing22, the air vent36is provided as only one passage connecting the tire cavity area and the inner space38. This is because, it is extremely easy for the liquid such as the puncture repair agent to enter the air vents36if there are a plurality of air vents36. By providing the air vent36as the only one passage connecting the tire cavity area and the inner space38, the liquid such as the puncture repair agent becomes less likely to enter the inner space38against pressure in the closed inner space38when the liquid such as the puncture repair agent closes the outer opening portion37a.

Although at least one of the wall faces of the inner space38is formed by the sealing resin39, the inner member is not limited to the sealing resin39. As the inner member, a resin material formed into a predetermined shape may be disposed.

FIG. 5is a circuit block diagram of the transmission device16.

The sensor unit28includes an air pressure sensor28aand an AM converter28b. The air pressure sensor28asenses the air pressure in an inner space38in the housing22and outputs a pressure signal. The inner space38in the housing22communicates with the space in the tire cavity area through an air vent36(seeFIG. 4) provided in the housing22.

The A/D converter28bcarries out digital conversion of the pressure signal output from the air pressure sensor28aand outputs pressure data.

The processing unit32includes a central processing section32aand a memory section32b. The central processing section32aoperates based on a program stored in a semiconductor memory of the memory section32b. When the central processing section32ais powered and driven, it carries out control so that the pressure data, which is information about the air pressure and sent from the sensor unit28, is transmitted to the monitoring device18via the transmitter30at predetermined time intervals, e.g., every five minutes. Identification information unique to the transmission device16is stored in advance in the memory section32band the central processing section32acarries out control so that the identification information is transmitted to the monitoring device18together with the pressure data.

The memory section32bincludes a ROM for storing the program for operation of the central processing section32aand rewritable nonvolatile memory such as an EEPROM. The identification information unique to the transmission device16is stored in an unwritable area in the memory section32b.

The transmitter30includes an oscillation circuit30a, a modulation circuit30b, and an amplifier circuit30c.

The oscillation circuit30agenerates a carrier signal, e.g., an RF signal belonging to a 315 MHz frequency band.

The modulation circuit30bmodulates the carrier signal by using the pressure data sent from the central processing section32aand the identification information unique to the transmission device16to generate a transmitting signal. As a modulation method, a method such as amplitude shift keying (ASK), frequency modulation (FM), frequency shift keying (FSK), phase modulation (PM), and phase shift keying (PSK) can be used.

The amplifier circuit30camplifies the transmitting signal generated by the modulation circuit30b. The amplified transmitting signal is wirelessly transmitted to the monitoring device18via the antenna40.

A secondary battery, for example, is used as the power supply section34to supply electric power to the sensor unit28, the transmitter30, and the processing unit32.

(Structure of Monitoring Device)

FIG. 6is a circuit block diagram of the monitoring device18.

The monitoring device18is installed in front of a position of a driver's seat of the vehicle10, for example, and informs a driver of the information about the air pressure. The monitoring device18includes an antenna52, a receiving section54, a receive buffer56, a central processing section58, a memory section60, an operation section62, a switch64, a display control section66, a display section68, and a power supply section70.

Frequency of the antenna52is matched to transmit frequency of the transmission device16and the antenna52is connected to the receiving section54.

The receiving section54receives the transmitting signal of a predetermined frequency and sent from the transmission device16and demodulates the signal to take out the pressure data and the data of the identification information. These pieces of data are output to the receive buffer56.

The receive buffer56temporarily stores the pressure data and the data of the identification information output from the receiving section54. The stored pressure data and the data of the identification information are output to the central processing section58according to a direction of the central processing section58.

The central processing section58is mainly made up of a CPU and operates based on a program stored in the memory section60. The central processing section58monitors the air pressure of each of the tires14ato14dfor each piece of identification information based on the received pressure data and data of the identification information. To put it concretely, the central processing section58determines whether a tire anomaly is caused based on the pressure data and informs a determination result to a driver. Determination of whether the tire anomaly is caused is to determine whether or not the air pressure dropped to an abnormally low level or dropped sharply in a short period of time to show that the tire blew out, for example.

The central processing section58outputs a determination result to the display control section66and causes the display section68to output the determination result through the display control section66.

Furthermore, the central processing section58initializes a communication method and the like with the transmission device16according to information from the operation section62and information from the switch64. Moreover, the central processing section58can set determination conditions for determining whether the tire anomaly is caused according to the information from the operation section62.

The memory section60includes a ROM for storing the program for operation of the CPU of the central processing section58and a nonvolatile memory such as an EEPROM. A table of the communication method with the transmission device16is stored in the memory section60during manufacture. The transmission device16and the monitoring device18communicate with each other by the preset communication method at an early stage. The communication method table includes information such as a communication protocol, a transmission bit rate, and a data format corresponding to the identification information unique to the transmission device16. Settings of these pieces of information can be more freely changed by means of input from the operation section62.

The operation section62includes an input device such as a keyboard and is used to input various kinds of information and conditions. The switch64is used to direct the central processing section58to start initialization.

The display control section66controls the display section68to display the tire pressure corresponding to the mounted position of each of the tires14ato14daccording to the determination result from the central processing section58. At the same time, the display control section66carries out control to cause the display section68to display also the determination result that the tire has blown out, for example.

The power supply section70controls electric power supplied from a battery mounted to the vehicle12to suitable voltages and supplies them to respective portions of the monitoring device18via a power-supply line (not shown in the figure).

The transmission device16and the monitoring device18are formed as described above.

As described above, a cross-sectional area of the air vent36connecting the inner space38of the housing22of the transmission device16and the tire cavity area continuously increases as it goes from the outer opening portion37atoward the inner opening portion37b.

The outer opening portion37aof the air vent36is formed on the top portion of the protruding portion37protruding by 1 mm or longer from the surface of the housing22toward the tire cavity area. By forming the outer opening portion37aon the top portion of the protruding portion37, it is possible to prevent the puncture repair agent from adhering to the outer opening portion37aeven if the puncture repair agent is introduced into the tire cavity area for puncture repair. Especially because the protruding portion37is provided to the housing22to protrude outward in a radial direction of a tire, it is possible to cast off the puncture repair agent, that has adhered to the protruding portion37, outward in the radial direction of the tire due to centrifugal force caused by rolling of the tire. As a result, it is possible to effectively prevent adhesion of the puncture repair agent to the outer opening portion37a.

Moreover, by changing the cross-section of the air vent36instead of making it uniform, surface tension in a vicinity of the inner opening portion37bis smaller than that in a vicinity of the outer opening portion37aand a capillary phenomenon becomes less likely to occur, which makes it difficult for the puncture repair agent to enter the air vent36. If the puncture repair agent enters the air vent36, the opening area of the inner opening portion37bis larger than that of the outer opening portion37aand therefore, the puncture repair agent does not stay in the air vent36but swiftly moves into the inner space38.

The opening area of the inner opening portion37bis preferably four times the opening area of the outer opening portion37aor larger in order to prevent the puncture repair agent from entering the air vent36and from closing the air vent36.

The inner opening portion37bof the air vent36is provided with a chamfer36ato prevent the puncture repair agent from staying and it is allowed to swiftly flow out of the air vent36. Instead of the chamfer36a, the edge of the inner opening portion37bmay be rounded with a curvature.

FIG. 7is a drawing for explaining the inner space38in the transmission device16illustrated inFIG. 4.

In the inner space38, the sensor space38awhich the sensor face of the sensor unit28faces is formed between the air vent36and the sensor unit28and is formed by inner walls of the sealing resin39provided in the housing22as well as the inner walls of the housing22. The sensor space38ais smaller than the inner area surrounded with the inner walls of the housing22and a cross-sectional area of the sensor space38aincreases from that of the inner opening portion37bof the air vent36.

The reservoir space38bis provided separately from the sensor space38aand connected to the sensor space38athrough a connecting pipe38c.

The sensor space38ais in a cylindrical shape and grooves38dextending from the inner opening portion37bare formed in a wall face (ceiling face) of the sensor space38aprovided with the inner opening portion37b. The inner opening portion37billustrated inFIG. 7is formed substantially at a center of the circular wall face (ceiling face) and two grooves38dextend in different directions from the inner opening portion37b. In a side face of the cylindrical sensor space38ain the drawing, the two grooves38dextend to a wall face which is a bottom face in the drawing. The grooves38dextending from the side face extend to an edge of the circular wall face which is the bottom face in the drawing and the two grooves38dextend along the edge of the bottom face and are connected to the connecting pipe38c. Therefore, the liquid such as the puncture repair agent that has entered the sensor space38afrom the inner opening portion37bis guided by the grooves38d, flows into the connecting pipe38c, and is stored in the reservoir space38b. In other words, the grooves38dserve as guide grooves for the puncture repair agent.

Because the cross-sectional area of the air vent36increases from the outer opening portion37atoward the inner opening portion37bas described above, the capillary phenomenon is less likely to occur and the liquid such as the puncture repair agent is less likely to enter the air vent36from the outer opening portion37aas compared with a prior-art case in which the cross-sectional area of the air vent is uniform. Even if the liquid such as the puncture repair agent enters the inner space38, it does not stay in the air vent36but flows into the inner space38(sensor space38a) and eventually flows into the reservoir space38balong the grooves38d. As a result, it is possible to prevent the liquid such as the puncture repair agent from adhering to the sensor face and inhibiting operation of the sensor in the sensor space38a.

Although the two grooves38dextend from the inner opening portion37bin the example illustrated inFIG. 7, the number of the grooves38dmay be one, three, or more. However, it is preferable to provide three or more grooves38din order to efficiently allow the liquid such as the puncture repair agent to flow into the reservoir space38b.

FIGS. 8A and 8Bare drawings for explaining an example (first modification) of a reservoir space38edifferent from the reservoir space38billustrated inFIG. 7.FIG. 8Ais a top view andFIG. 8Bis a side view.

The inner space38includes the sensor space38aand the reservoir space38e. The reservoir space38eis provided closer to the substrate26than the sensor space38a.

The sensor space38ais provided between the air vent36and the sensor unit28. The reservoir space38eis provided to surround the sensor unit28. In a wall face of the sensor space38aprovided with the inner opening portion37b, the grooves38dextending from the inner opening portion37btoward the reservoir space38eare formed.

Therefore, in the first modification illustrated inFIGS. 8A and 8B, similarly to the example illustrated inFIG. 7, even if the liquid such as the puncture repair agent adheres to the outer opening portion37a, the cross-sectional area of the air vent36increases from the outer opening portion37atoward the inner opening portion37band therefore the liquid such as the puncture repair agent is less likely to enter as compared with the prior art in which the cross-sectional area of the air vent is uniform. Even if the liquid such as the puncture repair agent enters the inner space38, it does not stay in the air vent36but flows into the inner space38and eventually flows into the reservoir space38ealong the grooves38d. As a result, it is possible to prevent the liquid such as the puncture repair agent from wetting the sensor face and inhibiting operation of the sensor in the sensor space38a.

FIG. 9Ais a drawing for explaining a modification of the air vent36of the transmission device16illustrated inFIG. 4. Although the cross-sectional area of the air vent36increases from the outer opening portion37atoward the inner opening portion37b, the air vent36is different from the air vent36illustrated inFIG. 4. In the modification illustrated inFIG. 9A, the protruding portion37is not provided to the housing22, the outer opening portion37aof the air vent36is provided to an outer wall surface of the housing22. The edge of the inner opening portion37bof the air vent36is chamfered.

In such an air vent36, even if the liquid such as the puncture repair agent adheres to the outer opening portion37a, the cross-sectional area of the air vent36increases from the outer opening portion37atoward the inner opening portion37band therefore the capillary phenomenon is less likely to occur and the liquid such as the puncture repair agent is less likely to enter the air vent36and the inner space38as compared with the prior-art case in which the cross-sectional area of the air vent is uniform.

FIG. 9Bis a drawing for explaining yet another modification of the air vent36of the transmission device16illustrated inFIG. 4. The air vent36illustrated inFIG. 9Bis different from the air vent36illustrated inFIG. 4in that its cross-sectional area increases in a stepwise fashion from the outer opening portion37atoward the inner opening portion37b. The edge of the inner opening portion37bof the air vent36is chamfered.

In such an air vent36, even if the liquid such as the puncture repair agent adheres to the outer opening portion37a, the cross-sectional area of the air vent36increases in the stepwise fashion from the outer opening portion37atoward the inner opening portion37band therefore the capillary phenomenon is less likely to occur and the liquid such as the puncture repair agent is less likely to enter the air vent36and the inner space38as compared with the prior-art case in which the cross-sectional area of the air vent is uniform.

FIG. 10is a drawing for explaining another modification of the protruding portion37of the transmission device16illustrated inFIG. 4. In the case of the protruding portion37illustrated inFIG. 4, when the protruding portion37is cut along a plane including a central axis of the air vent36, the inclined face of the protruding portion37facing the tire cavity area is provided with a bent portion, where the inclination angle reduces from one to another, on its way to the top portion of the protruding portion37. As a result, the inclined face has the bulged shape toward the tire cavity area.

On the other hand, in the modification illustrated inFIG. 10, the inclined face of the protruding portion37is formed in a curved shape to form a bulge portion toward the tire cavity area.

By forming the inclined face of the protruding portion37in the bulge shape toward the tire cavity area in this manner, it is possible to efficiently provide the air vent36having the cross-sectional shape increasing from the outer opening portion37atoward the inner opening portion37b. If the inclined face of the protruding portion37is in a recessed shape toward the tire cavity area, the wall can be thin in a thickness between the inclined face and an inner surface of the air vent having the cross-sectional area increasing from the outer opening portion toward the inner opening portion. Then the protruding portion37may be deformed under small external force (e.g., force received at the time of attachment or detachment of the tire to or from the rim). Therefore, it is preferable to form the inclined face of the protruding portion37into the bulge shape toward the tire cavity area.

FIGS. 11A and 11Bare drawings for explaining modifications of the inner space different from the inner space38illustrated inFIG. 7.

The housing22is provided with the reservoir space38bfor storing the liquid such as the puncture repair agent that has entered the inner space38through the air vent36.

The reservoir space38bis provided to be adjacent to the air vent36and the inner opening portion37bof the air vent36is formed in a wall face of the reservoir space38b. Furthermore, a sensor space38fbranches off from the wall face of the reservoir space37b. A sensor face28c(e.g., a diaphragm) of the sensor unit28faces the sensor space38f. The sensor space38fmay be a narrow branch space corresponding to a width of the sensor face28cas illustrated inFIG. 11Aor may be a branch space wide enough to surround the sensor face28cas illustrated inFIG. 11B.

By disposing such a reservoir space38b, the liquid such as the puncture repair agent does not reach the sensor space38fbut is stored in the reservoir space38band therefore it is possible to prevent the liquid such as the puncture repair agent from wetting the sensor face and inhibiting operation of the sensor.

Although the transmission device and the tire information monitoring system according to the invention have been described above in detail, the transmission device and the tire information monitoring system according to the invention are not limited to the embodiments described above but may be improved or modified in various ways without departing from the gist of the invention.

DESCRIPTION OF REFERENCE NUMERALS

10tire pressure monitoring system

16,16a,16b,16c,16dair pressure information transmission device

28aair pressure sensor

34power supply section

37aouter opening portion

37binner opening portion

58central processing section

66display control section

70power supply section