Patent Description:
In recent years, a tire pressure monitoring system (TPMS) that monitors a tire pressure (inner pressure) of a tire mounted to a vehicle, is widely adopted. The tire pressure monitoring system warns that the pressure has dropped, when the pressure monitored continuously is below a predetermined threshold. Further, a tire pressure monitoring system that warns that a tire is punctured apart from a warning that the pressure has dropped, is also proposed (see Patent Literature <NUM>).

Specifically, the tire pressure monitoring system disclosed in Patent Literature <NUM> determines whether the tire is punctured, based on a difference of tire pressures of the tires mounted to the vehicle, and a drop quantity of the pressure from a reference pressure. Attention is also drawn to the disclosures of <CIT>, <CIT> and <CIT>.

A main object for warning the puncture by the tire pressure monitoring system is to inform a driver as soon as possible that the tire pressure gradually drops due to the air leak caused by a sharp object such as a nail stuck into the tire (so-called slow puncture) while distinguishing a natural drop of the tire pressure (natural air leak) due to a change of the outer air or the like from the slow puncture.

However, in such a case, since the tire pressure gradually drops, it is difficult to inform the puncture as soon as possible by the determination using the difference of the tire pressures and the drop quantity of the pressure from the reference pressure described above.

Accordingly, an object of the present invention is, in consideration of the problem described above, to provide a tire pressure monitoring system, a tire pressure monitoring method, a tire pressure monitoring program and a vehicle capable of precisely detecting a puncture, which is caused by leak of air filled in a tire, as soon as possible while distinguishing a natural drop of a tire pressure, which is caused by a change of an outer air temperature or the like, from the puncture.

One aspect of the present invention is a tire pressure monitoring system as claimed in claim <NUM>.

Another aspect of the present invention is a tire pressure monitoring system as claimed in claim <NUM>.

Another aspect of the present invention is a tire pressure monitoring method as claimed in claim <NUM>.

Another aspect of the present invention is a tire pressure monitoring program as claimed in claim <NUM>.

Another aspect of the present invention is a vehicle having the tire pressure monitoring system described above.

The same reference signs or similar reference signs are assigned to the same functions or the same components and the description thereof is omitted as needed.

<FIG> is a schematic plane view of a vehicle <NUM> including a tire pressure monitoring system <NUM>. As shown in <FIG>, the vehicle <NUM> is a car having a four wheel. A type of the vehicle <NUM> is not especially limited, and therefore the vehicle <NUM> may be formed as a passenger vehicle, a truck, a bus or a mine vehicle. As described below, a rear wheel may be formed as a double tire.

A tire 20FL, a tire 20FR, a tire 20RL, and a tire 20RR are mounted to respective wheel positions in the vehicle <NUM>. Each of the tire 20FL, the tire 20FR, the tire 20RL, and the tire 20RR is formed as a tire mounted to a wheel rim (it may be called a tire wheel assembly).

The tire 20FL, the tire 20FR, the tire 20RL, and the tire 20RR are mounted to a left front wheel, a right front wheel, a left rear wheel, and a right rear wheel, respectively.

The tire pressure monitoring system <NUM> monitors a tire pressure of the tire mounted to the vehicle <NUM>. The tire pressure monitoring system <NUM> is also called a TPMS. The tire pressure monitoring system <NUM> is formed by a sensor mounted to each tire, and a TPMS main unit <NUM>. The TPMS main unit <NUM> may be installed as a part of an electronic control unit (ECU) mounted to the vehicle <NUM>.

A sensor 50FL that measures the pressure (inner pressure) and the temperature of the tire 20FL is mounted to the tire 20FL. Similarly, a sensor 50FR, a sensor 50RL, and a sensor 50RR are mounted to the tire 20FR, the tire 20RL, and the tire 20RR, respectively. Specifically, each of the sensors is mounted to a rim wheel to which the tire is mounted, a valve, or an inner surface of the tire.

The TPMS main unit <NUM> is arranged in the vehicle <NUM> so as to receive a radio signal (radio wave) transmitted by the sensor 50FL, the sensor 50FR, the sensor 50RL, and the sensor 50RR.

Next, a functional block configuration of the tire pressure monitoring system <NUM> will be described. <FIG> is the functional block diagram of the tire pressure monitoring system <NUM>. As shown in <FIG>, the tire pressure monitoring system <NUM> is provided with the sensors (sensor 50FL, sensor 50FR, sensor 50RL, and sensor 50RR) mounted to respective wheel positions, and the TPMS main unit <NUM>.

The sensor 50FL (sensor 50FR, sensor 50RL, and sensor 50RR are the same) has a temperature sensor <NUM>, a pressure sensor <NUM>, a sensor ID setting portion <NUM>, and a transmitter <NUM>. Hereinafter, the sensor 50FL is exemplarily described.

The temperature sensor <NUM> measures a temperature (tire temperature) in an air chamber of the tire 20FL mounted to the rim wheel. For example, a semiconductor type sensor is adopted as the temperature sensor <NUM>.

The pressure sensor <NUM> measures a pressure (inner pressure: hereinafter, tire pressure) in the air chamber of the tire 20FL. For example, an electrostatic type sensor is adopted as the pressure sensor <NUM>.

Measurement accuracy of each of the temperature sensor <NUM> and the pressure sensor <NUM> may be changed depending on the temperature in the air chamber of the tire 20FL. Further, the sensor 50FL may include a sensor that measures acceleration.

The sensor ID setting portion <NUM> sets a sensor ID that identifies the sensor 50FL. Specifically, the sensor ID setting portion <NUM> stores identifier information of the sensor 50FL and provides the stored identifier information to the transmitter <NUM>. As the identifier information, data of <NUM> bits may be adopted. In a case in which much more information (tire type or the like) is included, data of much more bits may be adopted. The identifier information is multiplexed into the radio signal transmitted by the transmitter <NUM>.

The transmitter <NUM> transmits the radio signal (radio wave) in which the data indicating the measured temperature output from the temperature sensor <NUM> and the data indicating the measured pressure (tire pressure) output from the pressure sensor <NUM> are multiplexed, to the TPMS main unit <NUM>.

The TPMS main unit <NUM> is provided with a receiver <NUM>, a data acquisition portion <NUM>, a puncture determination portion <NUM>, a warning processing portion <NUM>, a volume setting portion <NUM>, a threshold setting portion <NUM>, and a display portion <NUM>.

The receiver <NUM> receives the radio signal transmitted by the transmitter <NUM>. The intensity (transmission power) and a use frequency band of the radio signal may be changed depending on a use area of the tire pressure monitoring system <NUM> or a type of the vehicle <NUM>. Further, the receiver <NUM> may be arranged separately from the TPMS main unit <NUM>.

The data acquisition portion <NUM> acquires data indicating the tire pressure and the tire temperature from the sensor 50FL, the sensor 50FR, the sensor 50RL, and the sensor 50RR. Specifically, the data acquisition portion <NUM> acquires the data indicating the tire pressure and the tire temperature output by the receiver <NUM>, for each sensor.

The puncture determination portion <NUM> determines whether each of the tire 20FL, the tire 20FR, the tire 20RL, and the tire 20RR is punctured. Specifically, the puncture determination portion <NUM> determines whether each of the tire 20FL, the tire 20FR, the tire 20RL, and the tire 20RR is punctured, based on a puncture determination threshold PTH.

Hereinafter, a cause of a change of the tire pressure is described. The cause of the change of the pressure in the tire (tire 20FL, tire 20FR, tire 20RL, and tire 20RR) is (i) a change of an outer air temperature, (ii) a change of the temperature due to heat generation of the tire or the like in association with travelling, (iii) natural air leak, and (iv) air leak due to a puncture caused by a nail, failure of an air valve, or a crack of the rim wheel (namely, an external factor).

That is, the drop (air leak) of the tire pressure (tire inner pressure) is caused by the natural air leak or the external factor. In the present embodiment, the change of the tire inner volume is focused on in order to determine the puncture (especially, slow puncture).

The tire inner volume is represented as below based on the Boyle-Charles' law.

Here, when the tire inner volume determined in advance as a reference is set as a reference volume Vs, the tire inner volume V is largely changed due to generation of the leak of the air in the tire.

In the present embodiment, the generation of the puncture is determined as soon as possible by using the change of the tire inner volume V described above.

The puncture determination portion <NUM> determines whether the tire is punctured, based on the puncture determination threshold PTH defined by a relationship between the tire pressure P and the tire temperature T measured by the sensor 50FL, the sensor 50FR, the sensor 50RL and the sensor 50RR.

Specifically, the puncture determination portion <NUM> determines whether the tire is punctured, based on the puncture determination threshold PTH defined by the reference volume Vs calculated by using the reference tire pressure Ps and the reference tire temperature Ts.

The reference tire pressure Ps denotes the tire pressure defined in advance as a reference and generally corresponds to a standard tire pressure of the vehicle <NUM>. The reference tire temperature Ts denotes the tire temperature defined in advance as a reference and generally corresponds to an outer air temperature when the tire pressure is adjusted (before travelling).

The reference tire pressure Ps and the tire pressure P may be corrected by using a correction coefficient kP corresponding to at least one of the measurement accuracy of the sensor and the type (including a size) of the tire. That is, the reference tire pressure Ps and the tire pressure P are defined by using the correction coefficient kP.

Similarly, the reference tire temperature Ts and the tire temperature T may be also corrected by using a correction coefficient kT corresponding to at least one of the measurement accuracy of the sensor and the type (including a size) of the tire. That is, the reference tire temperature Ts and the tire temperature T are defined by using the correction coefficient kT.

A variation range of the reference volume Vs is defined by using these values, and thereby the drop of the tire pressure P due to an influence of the temperature change and the air leak due to the puncture can be determined with higher accuracy.

By using the reference tire pressure Ps, the reference tire temperature Ts, the tire pressure P, the tire temperature T, the correction coefficient kT for the tire temperature T, and the correction coefficient kP for the tire pressure P, based on the Boyle-Charles' law,
Formula <NUM> <MAT>
the reference volume Vs is calculated.

The tire pressure P and the tire temperature T are an actual tire pressure and an actual tire temperature measured by the sensor 50FL, the sensor 50FR, the sensor 50RL, and the sensor 50RR.

Further, the calculated tire pressure Pr, which is the tire pressure at the set tire temperature Tr and is calculated by using the reference volume Vs, is represented as below. Formula <NUM> <MAT>.

The set tire temperature Tr is a tire temperature (for example, - <NUM> to <NUM>) in a temperature range of the tire 20FL, the tire 20FR, the tire 20RL and the tire 20RR in a normal use environment and corresponds to the calculated tire pressure Pr.

Specifically, the calculated tire pressure Pr at the set tire temperature Tr is calculated by inputting a temperature change condition, namely the set tire temperature Tr, into the equation <NUM>. For example, in a case in which the reference tire temperature Ts is <NUM> and the set tire temperature Tr is <NUM>, the calculated tire pressure Pr (P<NUM>) is calculated as below.

Here, the reference volume Vs (<NUM>) is calculated by the equation <NUM> as the reference tire temperature Ts is <NUM> and the reference tire pressure Ps is <NUM> kPa (the correction coefficient kT and the correction coefficient kP are not applied). In the present embodiment, as shown in <FIG>, an equation for determining the puncture is defined based on the calculated tire pressures Pr (Pt°C) corresponding to the set tire temperatures Tr.

<FIG> is a table illustrating one example of a relationship between the set tire temperature Tr and the calculated tire pressure Pr (Pt°C) (the reference tire temperature Ts is <NUM> and the reference tire pressure Ps is <NUM> kPa).

According to the set tire temperature Tr and the calculated tire pressure Pr shown in <FIG>, the relationship between Tr and Pr is represented by a linear equation. However, a predetermined coefficient (α, β or the like described below) may be applied to Tr and Pr. Further, as described below, in a case in which the measurement error of the sensor is corrected, the equation may be not the linear equation but an nth-degree equation.

That is, the puncture determination portion <NUM> may determines whether the tire is punctured, by using at least one of the tire pressure in which the measurement error of the sensor is corrected (the tire pressure P or the calculated tire pressure Pr (specifically, Prx)), and the tire temperature in which the measurement error of the sensor is corrected (the tire temperature T or the set tire temperature Tr). Specifically, the puncture determination portion <NUM> may determine whether the tire pressure in which the measurement error is corrected is less than the puncture determination threshold PTH linked to the tire temperature.

As described above, the tire pressure P and the tire temperature T to be measured are changed due to the travelling or in accordance with the change of the outer air temperature. Accordingly, the puncture determination portion <NUM> determines that the tire is punctured, when the tire pressure P measured by the sensor 50FL, the sensor 50FR, the sensor 50RL and the sensor 50RR is less than the puncture determination threshold PTH linked to the tire temperature T at the measurement timing.

Specifically, the puncture determination portion <NUM> determines whether the tire is punctured, based on the equation <NUM>. Formula <NUM> <MAT>.

Here, Prx is the calculated tire pressure Pr corresponding to the set tire temperature Tr, and the relationship between Tr and Pr may be not a linear equation but an nth-degree equation. α is a temperature coefficient of the equation, and β is a pressure coefficient of the equation. α and β are coefficients that correct the set reference tire pressure Ps, the set reference tire temperature Ts, and measurement error (instrumental error) of each sensor.

Further, the puncture determination portion <NUM> may determine whether the air leak of the tire is not generated, based on the change of the tire pressure P of each of the tire 20FL, the tire 20FR, the tire 20RL, and the tire 20RR after filling air.

For example, in a case in which although the puncture of the tire is repaired by using a tire puncture emergency repair kit that fills the puncture repair liquid in the tire, the puncture is not completely repaired, the tire inner volume V gradually drops, and thereby the tire pressure P to be measured is changed. The drop of the tire pressure P in such a case is very small as described below, however the puncture determination portion <NUM> can determine the presence of the puncture based on the change of the tire inner volume V.

The warning processing portion <NUM> generates a warning indicating that the tire is punctured apart from the drop of the tire pressure P, when the puncture determination portion <NUM> determines that one or more of the tire 20FL, the tire 20FR, the tire 20RL, and the tire 20RR are punctured.

In particular, the warning processing portion <NUM> generates the warning indicating that the tire is punctured apart from the warning due to the drop of the tire pressure P (the warning based on a tire pressure drop threshold), when the puncture determination portion <NUM> determines that one or more of the tire 20FL, the tire 20FR, the tire 20RL, and the tire 20RR are punctured. Specifically, the warning processing portion <NUM> generates the warning indicating that the tire is punctured at an earlier stage than the warning that is based on the tire pressure drop threshold.

Further, the warning processing portion <NUM> generates a warning indicating that the temperature is increased, when the tire temperature T reaches a tire temperature warning threshold.

Specifically, the warning processing portion <NUM> generates the warnings (or shows no warning generated) shown in <FIG>.

<FIG> show image examples of a state of the tire displayed by the TPMS main unit <NUM>. As shown in <FIG>, the warning processing portion <NUM> displays either of "Normal" (in a case in which the drop of the tire pressure and the puncture are not generated), "Low tire pressure", and "Puncture (air leak)" on the display portion <NUM>. Further, the warning processing portion <NUM> may display "High temperature" on the display portion <NUM>.

Here, in a case in which "Low tire pressure", "Puncture (air leak)", or "High temperature" is displayed on the display portion <NUM>, a warning sound may be output at the same time. Further, an operation flow for displaying is further described below.

The volume setting portion <NUM> sets the reference volume Vs. Specifically, the volume setting portion <NUM> sets the reference volume Vs based on the tire pressure P and the tire temperature T of the normal tire without air leak.

That is, the volume setting portion <NUM> calculates the reference volume Vs corresponding to the tire pressure P at the tire temperature T, based on the tire pressure P and the tire temperature T measured by the sensor 50FL, the sensor 50FR, the sensor 50RL, and the sensor 50RR. The reference volume Vs is calculated by using the equation <NUM> described above. In this case, the measured tire pressure P and the measured tire temperature T are applied to the reference tire pressure Ps and the reference tire temperature Ts of the equation <NUM>.

Here, <FIG> shows one example of a relationship between the set tire temperature Tr and the reference volume Vs (the reference tire pressure Ps is <NUM> kPa). As shown in <FIG>, when the set tire temperature Tr is increased, the reference volume Vs is increased, and when the set tire temperature Tr is decreased, the reference volume Vs is decreased.

<FIG> shows a relationship between the tire temperature T and the tire pressure P measured by the sensor, and a relationship between the set tire temperature Tr and the calculated tire pressure Pr.

In <FIG>, a horizontal direction (row direction) denotes the measured tire temperature T (corresponding to the outer air temperature) or the set tire temperature Tr, and a vertical direction (column direction) denotes a tire temperature Ti when air is filled to be the standard set tire pressure (<NUM> kPa). <FIG> includes one example of the relationship between the set tire temperature Tr and the calculated tire pressure Pr (Pt°C) shown in <FIG> (the reference tire temperature Ts is <NUM> and the reference tire pressure Ps is <NUM> kPa).

As shown in <FIG>, in a case in which the tire temperature T (or the set tire temperature Tr) is changed from the tire temperature Ti when air is filled, the tire pressure P based on the reference volume Vs (or the calculated tire pressure Pr) is changed as shown by cells in <FIG>. In the actual environment, the tire pressure shown in each cell is used as the calculated tire pressure Pr, which is a basis of the puncture determination threshold PTH.

For example, when the tire temperature T is decreased to <NUM>, the calculated tire pressure Pr to be the basis is <NUM> kPa as described above. While, for example, when the tire temperature T is increased to <NUM>, the calculated tire pressure Pr to be the basis is <NUM> kPa (= (<NUM> + <NUM>) / <NUM>).

That is, when the measured tire temperature T is decreased to be less than the set tire temperature Tr, the tire pressure P is decreased, and when the measured tire temperature T is increased to be more than the set tire temperature Tr, the tire pressure P is increased.

The volume setting portion <NUM> sets the reference volume Vs based on the tables as shown in <FIG> and <FIG> and determines a relationship between the set reference volume Vs and the tire temperature T (the set tire temperature Tr).

Here, the volume setting portion <NUM> may store the table as shown in <FIG> or <FIG>, or alternatively the volume setting portion <NUM> may calculate the reference volume Vs or the like by using the equation <NUM> and the equation <NUM> described above. Further, the change of the tire pressure P corresponding to the change of the tire temperature T may be calculated by using an equation (a linear equation) as described above.

The threshold setting portion <NUM> sets the puncture determination threshold PTH. Specifically, the threshold setting portion <NUM> sets the puncture determination threshold PTH linked to the reference volume Vs set by the volume setting portion <NUM>.

More specifically, the threshold setting portion <NUM> sets the puncture determination threshold PTH based on the equation <NUM> described above. It is preferable that the puncture determination threshold PTH is set to be <NUM> or more of the calculated tire pressure Pr (the reference tire pressure) linked to the set tire temperature Tr (the reference tire temperature), and <NUM> or less of the calculated tire pressure Pr. Further, it is preferable that the puncture determination threshold PTH is set to be more than the tire pressure drop threshold (for example, <NUM> or less of the standard set tire pressure) used for determining the drop of the tire pressure P.

With this, the puncture can be determined at an earlier stage than the drop of the tire pressure P due to the natural air leak.

Further, the threshold setting portion <NUM> may set the warning threshold (tire temperature warning threshold) against the tire temperature T. The threshold setting portion <NUM> informs the set tire temperature warning threshold to the warning processing portion <NUM>.

The display portion <NUM> displays the image shown in <FIG> in accordance with the instruction of the warning processing portion <NUM>. Specifically, the display portion <NUM> includes a display such as a liquid crystal panel so as to display the image shown in <FIG> on the display. Here, the display portion <NUM> may be formed by an independent display or may be formed to use a display of other device mounted to the vehicle <NUM>.

Next, operation of the tire pressure monitoring system <NUM> described above will be described. Specifically, an initial setting operation, and a puncture and tire pressure drop detection operation of the tire pressure monitoring system <NUM> will be described.

<FIG> is a flow chart illustrating a flow of the initial setting operation of the tire pressure monitoring system <NUM>. As shown in <FIG>, at first, an operator (user) of the tire pressure monitoring system <NUM> checks the presence of the air leak of the tire 20FL, the tire 20FR, the tire 20RL, and the tire 20RR (S10). In case in which the air leak is found, the operator aborts a registration process and takes a countermeasure to the air leak (S20). This is because the reference volume Vs might fail to be calculated precisely in a case in which the air leak is generated.

Next, the operator registers the sensor 50FL, the sensor 50FR, the sensor 50RL, and the sensor 50RR mounted to the wheel positions (FL, FR, RL, and RR) (S30). Specifically, the operator registers the sensor ID of each sensor to be linked with the wheel position, in the tire pressure monitoring system <NUM>. With this, the tire pressure monitoring system <NUM> (TPMS main unit <NUM>) can determine that each sensor is located at which wheel position by the signal (data) output from each sensor.

Further, the operator sets the tire pressure drop threshold (S40). The tire pressure drop threshold is generally set based on the standard set tire pressure (for example, <NUM> kPa) of the vehicle <NUM> (for example, less than the standard set tire pressure).

Further, the operator sets the reference volume Vs (S50). Specifically, as the calculated tire pressure Pr is defined by the standard set tire pressure of the vehicle <NUM>, the tire pressure monitoring system <NUM> calculates the reference volume Vs based on the calculated tire pressure Pr and the tire temperature T measured by the tire pressure monitoring system <NUM>.

In a case in which the failure such as the air leak is not found, the reference volume Vs may be calculated by using the measured tire pressure P and the measured tire temperature T.

Further, the tire pressure monitoring system <NUM> sets the puncture determination equation (puncture determination threshold PTH) in accordance with the equation <NUM> described above, based on the calculated tire pressure Pr corresponding to the set reference volume Vs (S60). For example, the calculated tire pressure Pr is set to <NUM> kPa, and the puncture determination threshold PTH is set to <NUM> or more of the calculated tire pressure Pr and <NUM> or less of the calculated tire pressure Pr.

After the initial setting operation of the tire pressure monitoring system <NUM> is finished, the puncture and the tire pressure drop can be detected.

<FIG> is a flow chart illustrating a flow of the detection operation of the puncture and the tire pressure drop by the tire pressure monitoring system <NUM>. As shown in <FIG>, the tire pressure monitoring system <NUM> acquires data indicating the tire pressure P and the tire temperature T from the sensor 50FL, the sensor 50FR, the sensor 50RL, and the sensor 50RR mounted to the wheel positions, respectively (S105).

The tire pressure monitoring system <NUM> determines whether the tire temperature T reaches the tire temperature warning threshold (S110). In a case in which the tire temperature T reaches the tire temperature warning threshold, the tire pressure monitoring system <NUM> displays the warning of "High temperature" as the temperature of the tire is increased (S170). For example, the tire pressure monitoring system <NUM> displays the image shown in <FIG>, on the display portion <NUM>.

The tire pressure monitoring system <NUM> determines whether the tire pressure P fulfills the puncture determination threshold PTH (S120).

In a case in which the tire pressure P fulfills the puncture determination threshold PTH, the tire pressure monitoring system <NUM> displays the warning of "Puncture/Failure" as the failure is generated (S160). For example, the tire pressure monitoring system <NUM> displays the image shown in <FIG>, on the display portion <NUM>.

In a case in which the tire pressure P does not fulfill the puncture determination threshold PTH, the tire pressure monitoring system <NUM> determines whether the tire pressure reaches the tire pressure drop threshold (S130). In a case in which the tire pressure P does not reach the tire pressure drop threshold, the tire pressure monitoring system <NUM> displays "OK" as a normal (S140). For example, the tire pressure monitoring system <NUM> displays the image shown in <FIG>, on the display portion <NUM>.

In a case in which the tire pressure P reaches the tire pressure drop threshold, specifically, the tire pressure monitoring system <NUM> determines whether the tire pressure P is less than the puncture determination threshold PTH at the measured tire temperature T, namely the measured tire pressure P reaches the puncture determination threshold PTH (for example, <NUM> or more of the calculated tire pressure Pr and <NUM> or less of the calculated tire pressure Pr), which is set based on the calculate tire pressure Pr as shown in <FIG>.

In a case in which the tire pressure P does not fulfill the puncture determination threshold PTH, the tire pressure monitoring system <NUM> displays the warning of "Inflate" as the air should be filled (S150). For example, the tire pressure monitoring system <NUM> displays the image shown in <FIG>, on the display portion <NUM>.

Next, correction of the measurement error of the sensor will be described. Each of the sensor 50FL, the sensor 50FR, the sensor 50RL, and the sensor 50RR has its individual measurement error (instrumental error). It is preferable that the error of the temperature and the pressure (inner pressure) measured by the sensor is corrected to improve the accuracy of the puncture determination.

<FIG> show examples of the measurement error of the sensor. Specifically, <FIG> is a graph illustrating an example of the measurement error of the pressure measured by the sensor (pressure sensor <NUM>). <FIG> is a graph illustrating an example of the measurement error of the temperature measured by the sensor (pressure sensor <NUM>).

As shown in <FIG>, the measurement value (pressure and temperature) of the sensor includes an error having a certain tendency against an ideal line (true value). That is, there is the reproducibility of such an error for each sensor. Thus, in the present embodiment, the tire pressure monitoring system <NUM> (puncture determination portion <NUM>) corrects the error by using an nth-degree equation approximated to an actual measurement value of the sensor or by using a table that links the true value with the measurement value of the sensor, for each of the sensor 50FL, the sensor 50FR, the sensor 50RL, and the sensor 50RR.

According to the embodiment described above, the following functions and effects are obtained. Specifically, the tire pressure monitoring system <NUM> determines whether the tire is punctured, based on the puncture determination threshold PTH defined by the relationship between the tire pressure P and the tire temperature T measured by the sensor 50FL, the sensor 50FR, the sensor 50RL, and the sensor 50RR. Further, in a case in which it is determined that the tire is punctured, the tire pressure monitoring system <NUM> generates the warning indicating that the tire is punctured at an earlier stage than the warning indicating the drop of the tire pressure P.

Further, in the present embodiment, the tire pressure monitoring system <NUM> determines whether the tire is punctured, based on the puncture determination threshold PTH defined by the reference volume Vs calculated by using the reference tire pressure Ps and the reference tire temperature Ts. More specifically, the tire pressure monitoring system <NUM> determines that the tire is punctured, when the tire pressure P measured by the sensor 50FL, the sensor 50FR, the sensor 50RL, and the sensor 50RR fulfills the puncture determination threshold PTH linked to the tire temperature T at the measurement timing, namely when tire pressure P is less than the puncture determination threshold PTH.

That is, since the puncture is not determined by the mere drop of the tire pressure P but determined based on the puncture determination threshold PTH defined by the reference volume Vs, the puncture, which is caused by the leak of the air filled in the tire 20FL, the tire 20FR, the tire 20RL, and the tire 20RR, can be detected precisely as soon as possible, while distinguishing the natural drop (natural leak of the air) of the tire pressure P, which is caused by the change of the outer air temperature or the like, from the puncture.

Such an early and precise detection of the puncture is based on the fact that, in a case in which the tire inner volume determined in advance as a reference is set as the reference volume Vs, the tire inner volume V is largely changed due to generation of the leak of the air in the tire. That is, even if the drop amount of the tire pressure P is very small, the generation of the puncture can be determined by linking the change amount of the tire inner volume V due to the air leak with the change amount (drop amount) of the tire pressure P at the measured tire temperature T.

On the other hand, the drop of the tire pressure P due to the natural air leak proceeds more slowly than that due to the puncture, and therefore the puncture can be distinguished from the drop of the tire pressure P due to the natural air leak.

In the present embodiment, when the tire pressure monitoring system <NUM> determined that either of the tire 20FL, the tire 20FR, the tire 20RL, and the tire 20RR (hereinafter, merely referred to as tire as needed) is punctured, the tire pressure monitoring system <NUM> generates the warning indicating that the tire is punctured apart from the drop of the tire pressure (tire pressure drop threshold).

With this, a driver of the vehicle <NUM> or the like is promoted to repair the puncture as soon as possible. In particular, in a case of the slow puncture in which the pressure gradually drops due to the air leak caused by a sharp object such as a nail stuck into the tire, the driver is apt to determine it as the natural air leak and to neglect the inspection of the tire. However, such an action of the driver can be avoided. Accordingly, it can be prevented that the tire is damaged severely by leaving the slow puncture.

In the present embodiment, the puncture determination threshold PTH is set to <NUM> or more of the calculated tire pressure Pr (reference tire pressure) linked to the set tire temperature Tr (reference tire temperature) and <NUM> or less of the calculated tire pressure Pr, and therefore the puncture determination threshold PTH is more than the tire pressure drop threshold (for example, less than <NUM> of the standard set tire pressure) used for determining the drop of the tire pressure P. Thus, it can be detected that the tire is punctured as soon as possible while distinguishing the drop of the tire pressure (tire pressure drop threshold).

In the present embodiment, the correction coefficient kT for the tire temperature (specifically, the reference tire temperature Ts and the set tire temperature Tr) and the correction coefficient kP for the tire pressure (specifically, the reference tire pressure Ps and the calculated tire pressure Pr) are adopted. Specifically, the reference volume Vs or the like can be calculated by using the equations <NUM> to <NUM> described above.

With this, the reference volume Vs having high accuracy used for determining the puncture can be set while considering the measurement accuracy of the sensor and the type of the tire.

In the present embodiment, the tire pressure monitoring system <NUM> sets the reference volume Vs based on the tire pressure P and the tire temperature T of the tire without the air leak and sets the puncture determination threshold PTH linked to the set reference volume Vs. Thus, when the reference volume Vs is calculated by using the measured tire pressure P and the measured tire temperature T, the reference volume Vs can be precisely calculated.

In the present embodiment, the tire pressure monitoring system <NUM> determines whether the air leak of the tire is not generated, based on the change of the tire pressure P of the tire with the air filled after the puncture is repaired. That is, in a case in which the tire pressure P of the tire with the air filled is more than the puncture determination threshold PTH according to the detection operation flow of the puncture and tire pressure drop shown in <FIG>, it is determined that the puncture is repaired.

In particular, in a case in which a tire puncture emergency repair kit that fills the puncture repair liquid in the tire is used, it can be determined immediately whether a puncture hole is sealed by the puncture repair liquid. Accordingly, it is not necessary to check the tire pressure by using a compressor or an air gauge after the puncture repair liquid is filled.

In the present embodiment, the tire pressure monitoring system <NUM> determines whether the tire is punctured, by using either of the tire pressure (the tire pressure P or the calculated tire pressure Pr (specifically, Prx)) in which the measurement error of the sensor 50FL, the sensor 50FR, the sensor 50RL, and the sensor 50RR is corrected, and the tire temperature (the tire temperature T or the set tire temperature Tr) in which the measurement error (instrumental error) of the sensors is corrected.

With this, even in a case in which the sensor has a certain tolerance (instrumental error), the determination accuracy of the puncture can be further improved.

As described above, the contents of the present invention are described with reference to the examples, however the present invention is not limited to those descriptions. It is obvious for a person skilled in the art to adopt various modifications and improvement.

For example, in the embodiment described above, the TPMS main unit <NUM> is mounted to the vehicle <NUM>, however, the functions achieved by the TPMS main unit <NUM> may be provided at an outside of the vehicle <NUM>.

<FIG> is a schematic network configuration view including a schematic plane view of a vehicle 10A according to other embodiment. As shown in <FIG>, the vehicle 10A is provided with a communication device <NUM> instead of the TPMS main unit <NUM>. The vehicle 10A is formed as a so-called connected car that can be connected to a server computer <NUM> via the communication network. The communication device <NUM> may be formed as a part of a so-called telematics unit.

The communication device <NUM> can execute radio communication with a radio base station <NUM>. The communication device <NUM> is formed by, for example, a radio communication terminal connectable to a mobile communication network (LTE or the like).

The server computer <NUM> (database site) is arranged on the communication network so as to achieve a whole or a part of the functions (the data acquisition portion <NUM>, the puncture determination portion <NUM>, the warning processing portion <NUM>, the volume setting portion <NUM>, and the threshold setting portion <NUM>), which are achieved by the TPMS main unit <NUM>.

Further, a program (software) that achieves the functions may be stored on the communication network in a downloadable state, or may be provided by a storage medium in which the program is stored.

Further, in the embodiments described above, the vehicle <NUM> having four wheels is described as an example, however the present invention may be applied to other types of vehicle.

<FIG> is a schematic plane view of a vehicle 10B according to another embodiment. As shown in <FIG>, the vehicle 10B has a rear axle different from that of the vehicle <NUM>. Specifically, a so-called double tire is mounted to the rear axle of the vehicle 10B, namely the vehicle 10B is formed as a large vehicle such as a truck and a mine vehicle.

The vehicle 10B includes a tire 20RLo (left rear outer wheel), a tire 20RL<NUM> (left rear inner wheel), a tire 20RRo (right rear outer wheel), and a tire 20RR<NUM> (right rear inner wheel) as rear tires. Further, a sensor 50RLo, a sensor 50RL<NUM>, a sensor 50RRo, and a sensor 50RR<NUM> are mounted to the tire 20RLo, the tire 20RL<NUM>, the tire 20RRo, and the tire 20RR<NUM>, respectively.

The TPMS main unit <NUM> receives a radio signal from each sensor of two front wheels and four rear wheels. The number of the axles of the vehicle and the number of the wheels of the vehicle are not limited to those of the vehicle <NUM> and the vehicle 10B. For example, a tractor or a trailer having much more axles and wheels may be adopted.

Claim 1:
A tire pressure monitoring system (<NUM>) that monitors a tire pressure of a tire (20FL, 20FR, 20RL, 20RR) mounted to a vehicle (<NUM>), the tire pressure monitoring system (<NUM>) comprising:
a data acquisition portion (<NUM>) that acquires data indicating the tire pressure and a tire temperature of the tire (20FL, 20FR, 20RL, 20RR), from a sensor (50FL, 50FR, 50RL, 50RR) mounted to the tire (20FL, 20FR, 20RL, 20RR);
a puncture determination portion (<NUM>) that determines whether the tire (20FL, 20FR, 20RL, 20RR) is punctured, based on a puncture determination threshold defined by a relationship between the tire pressure and the tire temperature; and
a warning processing portion (<NUM>) that generates a warning indicating that the tire (20FL, 20FR, 20RL, 20RR) is punctured apart from a warning of a drop of the tire pressure, when the puncture determination portion (<NUM>) determines that the tire (20FL, 20FR, 20RL, 20RR) is punctured, characterized in that
the puncture determination portion (<NUM>) determines whether the tire pressure is less than the puncture determination threshold linked to the tire temperature, by using at least one of the tire pressure and the tire temperature in which measurement error of the sensor (50FL, 50FR, 50RL, 50RR) is corrected.