Pressure sensor, transmitter, and tire condition monitoring apparatus

A tire condition monitoring apparatus has a pressure sensor that measures air pressure in a tire of a vehicle. The apparatus also has a transmitter that transmits pressure data measured by the pressure sensor, and a receiver that receives and processes data transmitted by the transmitter. The pressure sensor has a diaphragm exposed to air of the tire, and metallic material covering the diaphragm. The transmitter has a power supply circuit and a connecting member. The power supply circuit supplies electricity for activating the transmitter. The connecting member connects the power supply circuit with the metallic material such that the potential of the metallic material is the same as the potential of the power supply circuit.

BACKGROUND OF THE INVENTION

The present invention relates to a pressure sensor, a transmitter that has the pressure sensor, and a tire condition monitoring apparatus that has the transmitter.

For example, Japanese Laid-Open Patent Publication No. 8-94468 discloses a structure of a pressure sensor unit, in which a pressure sensor is adhered to a lead terminal that also functions as a shielding member. The pressure sensor is three-dimensionally covered by the lead terminal. This structure prevents the pressure sensor from being affected by outside electromagnetic fields and thus allows the pressure sensor to accurately measure a pressure.

However, the pressure sensor is three-dimensionally covered with the lead terminal, which also functions as a shielding member. This increases the size of the pressure sensor unit. In other words, the structure of the publication cannot reduce a size of a pressure sensor unit that includes a shielding member.

SUMMARY OF THE INVENTION

Accordingly, it is an objective of the present invention to provide a compact pressure sensor that accurately measures a pressure. The present invention also relates to a transmitter having such a pressure sensor and a tire condition monitoring apparatus having such a transmitter.

To achieve the foregoing and other objectives and in accordance with the purpose of the present invention, a pressure sensor having a diaphragm and metallic material is provided. The diaphragm is exposed to gas. The metallic material covers the diaphragm. A predetermined voltage can be applied to the metallic material.

The present invention also provides a transmitter having a pressure sensor that has a diaphragm exposed to gas. The transmitter transmits pressure data detected by the pressure sensor. The transmitter includes a power supply circuit, metallic material, and a connecting member. The power supply circuit supplies electricity to the transmitter. The metallic material covers the diaphragm. The connecting member connects the power supply circuit with the metallic material such that the potential of the metallic material is the same as the potential of the power supply circuit.

Further, the present invention provides a tire condition monitoring apparatus having a pressure sensor that measures air pressure in a tire of a vehicle, a transmitter that transmits pressure data measured by the pressure sensor, and a receiver that receives and processes data transmitted by the transmitter. The pressure sensor includes a diaphragm and metallic material. The diaphragm is exposed to air in the tire. The metallic material covers the diaphragm. The transmitter includes a power supply circuit and a connecting member. The power supply circuit supplies electricity for activating the transmitter. The connecting member connects the power supply circuit with the metallic material such that the potential of the metallic material is the same as the potential of the power supply circuit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A pressure sensor, transmitters, and a tire condition monitoring apparatus according to the present invention will now be described with reference to the drawings.

As shown inFIG. 1, the tire condition monitoring apparatus1includes four transmitters30and a receiver40. Each transmitter30is located in one of the tires20of a vehicle10. The receiver40is located on a body frame11of the vehicle10.

Each transmitter30is located in the corresponding tire20and is fixed, for example, to a wheel21of the tire20. Each transmitter30measures the condition of the corresponding tire20, that is, the pressure of the tire20. The transmitter30then wirelessly transmits data containing air pressure data.

The receiver40is located at a predetermined position on the body frame11and is activated by electricity of a battery (not shown) of the vehicle10. The receiver40includes a single reception antenna41. The reception antenna41is connected to the receiver40with a cable42. The receiver40receives data transmitted by the transmitters30through the reception antenna41.

A display50is located in the view of the driver of the vehicle10, for example, in the passenger compartment. The display50is connected to the receiver40with a cable43.

As shown inFIG. 2, each transmitter30is accommodated in a casing70, that is located below a valve stem60. Air is injected into the tire20through the valve stem60. The casing70is substantially formed into a rectangular box. The casing70accommodates a substantially rectangular substrate80. Electronic elements such as transmission controller31, a pressure sensor32, a transmission circuit33, a transmission antenna34, and a battery35are mounted on the substrate80. The substrate80is fixed to bosses71that are integrally formed with the casing70. The casing70has a through hole (not shown) to permit the pressure sensor32to measure the air pressure in the tire20. The casing70has an opening72, which is closed with a lid (not shown) for protecting the electronic elements.

As shown inFIG. 3, each transmitter30includes a transmission controller31, which is a microcomputer. The transmission controller31includes, for example, a central processing unit (CPU), a read only memory (ROM), and a random access memory (RAM). A unique ID code is registered in an internal memory, for example, the ROM, of the transmission controller31. The ID code is used to distinguish the associated transmitter30from the other three transmitters30.

The pressure sensor32measures the air pressure in the interior of the associated tire20and provides the transmission controller31with pressure data, which is obtained from the measurement. The transmission controller31sends data containing the air pressure data and the registered ID code to a transmission circuit33. The transmission circuit33encodes and modulates the data sent from the transmission controller31. The transmission circuit33then wirelessly sends the data through a transmission antenna34. The transmitter30is provided with a battery35. The transmitter30is driven by electricity of the battery35.

As shown inFIG. 4, the pressure senor32is made of ceramic, and has an upper base100and a lower base200. A metallic material film101is formed on the outer surface of the upper base100. A frustoconical recess102is formed in a central portion of the upper base100. As a result, a diaphragm103is formed in an central upper portion of the upper base100. A first inner electrode104is formed on the lower surface of the diaphragm103.

A second inner electrode201is formed in a center of the upper surface of the lower base200. The metallic material film101, the first inner electrode104, and the second inner electrode201are formed by aluminum deposition. The upper base100and the lower base200are hermetically attached to each other such that the first inner electrode104and the second inner electrode201face each other. As a result, a hermetic space105is defined between the first inner electrode104and the second inner electrode201. The hermetic space105is filled with gas having a predetermined pressure.

The metallic material film101, which covers the diaphragm103, is exposed to the air inside the tire20through the through hole (not shown) formed in the casing70. In other words, the metallic material film101is exposed to air, which is a measured gas. Therefore, when the air pressure in the tire20changes, the difference between the air pressure in the tire20and the pressure of the gas filling the hermetic space105is changed. Accordingly, the diaphragm103is flexed. Then, the distance between the first inner electrode104and the second inner electrode201, which changes a capacitance between the first inner electrode104and the second inner electrode201, accordingly. Therefore, the air pressure in the tire20is measured based on the capacitance between the first inner electrode104and the second inner electrode201. That is, the pressure sensor32is a capacitance type pressure sensor.

As shown inFIG. 5, the metallic material film101on the upper base100is connected to the battery35with a lead wire300and traces of the wiring pattern on the substrate80. The lead wire300and the traces function as connecting means. Specifically, the metallic material film101is connected to a power supply potential Vdd (+3V) or a ground potential GND (0V) of the battery35. As a result, the metallic material film101on the upper base100is maintained to the same potential as the power supply potential Vdd (+3V) or the ground potential GND (0V) of the battery35. The ground potential GND (0V) of the battery35is connected to a ground potential GND of the transmission circuit33. The battery35and the transmission circuit33function as a power supply circuit that supplies electricity to the transmitter30.

This embodiment has the following advantages.

(1) The metallic material film101is formed on the outer surface of the upper base100to cover the diaphragm103. The metallic material film101on the upper base100is connected to the power supply potential Vdd (+3V) or the ground potential GND (0V) of the battery35with the lead wire300and the traces on the substrate80. Accordingly, the metallic material film101on the upper base100is maintained to the same potential as the potential of the battery35. As a result, the first inner electrode104and the second inner electrode201of the pressure sensor32are shielded by the metallic material film101. This structure prevents the pressure sensor32from being affected by outside electromagnetic fields and thus allows the pressure sensor32to accurately measure the air pressure in the tire20. Unlike the structure disclosed in Japanese Laid-Open Patent Publication No. 8-94468, where the pressure sensor is three-dimensionally covered with a lead terminal that also functions as a shielding member, the metallic material film101on the upper base100is connected to the ground potential GND on the substrate80with the lead wire300. Therefore, the size of the pressure sensor32is reduced.

(2) Since the size of the pressure sensor32is reduced, the size of the transmitter30is reduced. Therefore, when attaching the tire20to the wheel21, the bead of the tire20is prevented from contacting the casing70, which accommodates the transmitter30. Therefore, when attaching the tire20, the casing70and the transmitter30are not damaged.

(3) The pressure sensor32is scarcely affected by outside electromagnetic fields. This permits the pressure sensor32to accurately measure even small changes in the air pressure in the tire20. Therefore, the transmitter30wirelessly transmits accurate air pressure data to the receiver40.

(4) The receiver40receives data through the reception antenna41and, based on the received data, causes the display50to display air pressure data. This informs a driver of the vehicle10of the accurate air pressure data. In other words, the present invention provides the tire condition monitoring apparatus1, which accurately measures the air pressure in the tire20.

The metallic material film101on the upper base100may be directly connected to the power supply potential Vdd (+3V) or the ground potential GND (0V) of the battery35with the lead wire300, without using the traces on the substrate80.

As shown inFIG. 6, the metallic material film101on the upper base100may be connected to the power supply potential Vdd (+3V) or the ground potential GND (0V) of the battery35with the traces on the substrate80and a tungsten plated through hole400.

As shown inFIG. 7, a conductor500having bent ends may be provided on a lid73of the casing70. The metallic material film101on the upper base100may be connected to the battery35(for example, a positive terminal) with the conductor500when the opening72is closed with the lid73. In this case, the shielding effect is obtained only by closing the opening72of the casing70with the lid73with the conductor500. Compared to conventional assembly procedure, only a step for attaching the conductor500to the lid73is added. In other words, no complicated step is added to the procedure for obtaining the shielding effect. Thus, with the structure of the lid73having the conductor500, the transmitter30is easily assembled with the casing70.

In the illustrated embodiment, the metallic material film101is formed on the entire upper surface of the upper base100. However, the metallic material film101may be formed on a part of the upper surface of the upper base100to cover the diaphragm103. That is, the metallic material film101may be formed only on a center portion of the upper surface of the upper base100.