JP2002248914A - Transmitter and transmission method for tire condition monitoring equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a transmitter for tire condition monitoring equipment that can alarm a change of a tire condition firmly and keep its battery life longer. SOLUTION: The transmitter for tire condition alarming equipment is driven by a battery force. The transmitter is equipped with a sensor to measure data showing a tire condition, a transmission circuit to transmit data showing a measured tire condition by wireless, and a controller to control the sensor and the transmission circuit. The controller makes the sensor measure the tire condition at a predetermined measuring time interval, and only when Pt showing the latest measured tire condition changes more than a predetermined value α1, it controls the transmission circuit so as to transmit data showing the latest tire condition.

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for monitoring the condition of a tire of a vehicle, and more particularly to a transmitter and a transmitter for transmitting data indicating the condition of a tire to a receiver provided on a vehicle body of the vehicle. About the method.

2. Description of the Related Art Conventionally, a wireless tire condition monitoring device has been used to check the condition of tires mounted on a vehicle in a vehicle cabin. A transmitter for measuring the state of the corresponding tire, such as air pressure and temperature, and wirelessly transmitting data indicating the measured tire state is attached to the wheel of each tire. The vehicle body is provided with a receiver for receiving transmission data from the transmitter. Because the transmitter is powered by a battery, the transmitter becomes inoperable when the battery reaches its end of life. However, the transmitter is mounted on the wheel such that it is located inside the tire. Therefore,
If you want to change the battery, you have to remove the tire from the wheel, which is very troublesome. Moreover, the transmitter is carefully designed to withstand the harsh environment inside the tire. Therefore, the operation of opening the transmitter case to replace the battery may reduce the reliability of the operation of the transmitter. For the above reasons, it is not practical to replace the battery. In order to be able to use the transmitter for a long time without replacing the battery, it is conceivable to increase the capacity of the battery. However, this increases the size and weight of the battery, deteriorating the balance of the tire, and thus has a limit in increasing the capacity of the battery. For this reason, data transmission from a transmitter is not performed continuously, but is performed intermittently at regular intervals. In this way, the cumulative operation time of the transmitter can be reduced as much as possible, and a battery with a limited capacity can be used for a long period of time.

The rate of change of the tire pressure varies. For example, if air naturally leaks from the tire, the air pressure will drop relatively slowly.
When a tire punctures, the air pressure drops sharply. Moreover, the rate of decrease in air pressure in the case of a natural leak or puncture varies depending on the situation. Whatever the speed of the air pressure changes, there is a need for a monitoring device that can immediately detect an air pressure abnormality and extend the battery life. However, simply performing transmission from the transmitter at regular intervals does not sufficiently meet the above-mentioned requirements. For example, when the time interval between transmissions from the transmitter is relatively long, if the decrease in air pressure is slow, no problem occurs in reporting an abnormality in air pressure. However, if the air pressure drops rapidly, it is not possible to immediately notify the air pressure abnormality. Conversely, when the time interval between transmissions from the transmitter is relatively short, even if the air pressure drops sharply, an abnormality in the air pressure can be immediately reported. However, since the accumulated operation time of the transmitter increases, the life of the battery is shortened. An object of the present invention is to be able to reliably notify a change in tire condition,
Moreover, it is an object of the present invention to provide a transmitter and a transmission method of a tire condition monitoring device capable of extending battery life.

SUMMARY OF THE INVENTION To achieve the above object, the present invention provides a transmitter which is driven by a battery and wirelessly transmits data indicating the condition of a vehicle tire. The transmitter includes a sensor for measuring the condition of the tire,
It includes a transmission circuit for wirelessly transmitting data indicating the measured tire state, and a controller for controlling the sensor and the transmission circuit. The controller causes the sensor to measure the tire state at predetermined time intervals, and when the value indicating the latest measured tire state changes by a predetermined value or more from the value indicating the tire state transmitted last time, the measured value is measured. The transmitting circuit is controlled so as to transmit data indicating the latest tire state. In another transmitter provided by the present invention, the controller causes the sensor to measure the tire condition at predetermined time intervals, and when the latest measured tire condition changes from the previously measured tire condition. Only the transmission circuit is controlled to transmit data indicating the latest measured tire condition. Preferably, the controller controls the transmission circuit to transmit the data indicating the latest measured tire state only when the latest measured tire state changes from the last measured tire state. The tire condition includes at least one of pressure and temperature in the tire. The transmitter of the present invention constitutes a tire condition monitoring device for a vehicle together with a receiver that receives data wirelessly transmitted from the transmitter. The present invention also provides a method for wirelessly transmitting data indicative of a condition of a vehicle tire. The method includes the steps of measuring a tire state at a predetermined time interval, and a difference between a value indicating the latest measured tire state and a value indicating the previously transmitted tire state is equal to or greater than a predetermined value. And transmitting data indicating the latest measured tire condition. Another transmission method provided by the present invention is a step of measuring a tire state at a predetermined time interval, and only when the latest measured tire state changes from a tire state measured in the past, Transmitting data indicating the latest measured tire condition. Preferably, data indicating the latest measured tire state is transmitted only when the latest measured tire state changes from the previously measured tire state.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a first embodiment of the present invention will be described.
This will be described with reference to FIGS. As shown in FIG. 1, the tire condition monitoring device includes four transmitters 3 mounted on four tires 2 of the vehicle 1 and one receiver 4 provided on the vehicle body of the vehicle 1. Each transmitter 3, for example,
Tire 2 to be placed inside the corresponding tire 2
Fixed to the wheel. Each transmitter 3 measures the state of the corresponding tire 2, that is, the internal air pressure and the internal temperature, and transmits data indicating the measured state to the receiver 4.
Send to As shown in FIG. 2, the transmitter 3 includes a controller 10 including a microcomputer or the like. The controller 10 is, for example, a central processing unit (CP
U), a random access memory (RAM) and a read only memory (ROM). The controller 10 includes
A unique ID code is registered in advance. The ID code is used to identify the four transmitters 3 provided in the vehicle 1. The pressure sensor 11 measures the internal air pressure of the tire 2 and outputs pressure data obtained by the measurement to the controller 10. The temperature sensor 14 measures the internal temperature of the tire 2 and outputs temperature data obtained by the measurement to the controller 10. The controller 10 outputs the input pressure / temperature data and the ID code registered therein to the transmission circuit 12. The transmission circuit 12 wirelessly transmits the transmission data including the pressure / temperature data and the ID code to the receiver 4 via the transmission antenna 13. Battery 15 is a driving source of transmitter 3. The transmitter 3 operates with the power from the battery 15. The plurality of components 10 to 15 described above are housed in a case (not shown). As shown in FIG. 5, the controller 10 includes:
The pressure sensor 11 and the temperature sensor 14 perform a measuring operation at every predetermined time interval t1. Time t2 shown in FIG. 5 is a time from when the pressure sensor 11 and the temperature sensor 14 start measurement to when data obtained by the measurement is processed by the controller 10, that is, a measurement operation time. The controller 10 also controls the pressure sensor 1
Only when it is determined that a predetermined transmission condition has been established based on the pressure data from 1 and the temperature data from the temperature sensor 14, the data is transmitted to the transmission circuit 12 as exemplified by a two-dot chain line in FIG. Perform the operation. Time t3 shown in FIG. 5 is a time during which the transmission circuit 12 is performing a transmission operation, that is, a transmission operation time. The transmission conditions will be described later in detail with reference to the flowchart of FIG. The transmitter 3 performs the measurement operation time t2 and the transmission operation time t described above.
Other than 3, the sleep state is set in which the power of the battery 15 is hardly consumed. Note that the measurement time interval t1 is, for example,
, The power consumption of the transmitter 3 and the operation time t of the transmitter 3
2, t3. In the present embodiment, the measurement time interval t1 is a 15-second interval. As shown in FIG.
The receiver 4 includes a controller 20 including a microcomputer or the like. The controller 20 is, for example, a CP
U, including RAM and ROM. The RF circuit 21 receives the transmission data from each transmitter 3 via the reception antenna 22 and sends it to the controller 20. Controller 2
“0” identifies the internal air pressure and internal temperature of the tire 2 corresponding to the transmitter 3 of the transmission source based on the ID data and the pressure / temperature data included in the received data. The controller 20 also causes the display 23 to display information on the air pressure / temperature and other necessary information. Display 23
Are arranged in the visible range of the driver of the vehicle 1. The controller 20 further notifies the alarm 24 of the air pressure / temperature abnormality. As the alarm 24, for example, a device for notifying an abnormality by sound or a device for notifying an abnormality by light is applied. Of course, the display 23
May be displayed. The receiver 4 is activated, for example, when a key switch (not shown) of the vehicle 1 is turned on. Next, the operation of the transmitter 3 will be described with reference to the flowcharts of FIGS. 4A and 4B. FIG. 4A and FIG.
The routine shown in (b) is repeatedly executed by the controller 10 of the transmitter 3 at intervals of 15 seconds, which is the measurement time interval t1. When a battery 15 is attached to the transmitter 3 when assembling the transmitter 3, the controller 10 causes the pressure sensor 11 and the temperature sensor 14 to perform an initial measurement operation. Then, the controller 10
The obtained initial pressure measurement value Pn and temperature measurement value Tn are stored in its own memory as an initial pressure transmission value Pt and an initial temperature transmission value Tt, respectively.
And the transmission circuit 12 transmits the initial temperature transmission value Tt.
The routine shown in FIG. 4A relates to detection and transmission of the air pressure of the tire 2. First, in step S1, the controller 10 causes the pressure sensor 11 to measure the air pressure of the tire 2. In the following step S2, the controller 10 determines whether or not the absolute value of the difference between the pressure transmission value Pt and the pressure measurement value Pn is equal to or greater than a predetermined pressure determination value α1. The pressure transmission value Pt is the value of the air pressure transmitted last time, that is, the pressure transmission value Pt currently stored in the memory of the controller 10. The pressure measurement value Pn is the value of the air pressure measured in step S1, that is, the latest pressure measurement value Pn obtained in this routine. The pressure determination value α1 is a relatively small value. Even if the air pressure of the tire 2 changes within the range of the pressure determination value α1, the running state of the vehicle 1 has almost no effect. If the absolute value of the difference between the pressure transmission value Pt and the measured pressure value Pn is smaller than the pressure determination value α1, the controller 10 determines that the change in the air pressure of the tire 2 is small, and terminates the process once. On the other hand, if the absolute value of the difference between the pressure transmission value Pt and the measured pressure value Pn is equal to or greater than the pressure determination value α1, the controller 10 determines that the change in the air pressure of the tire 2 is relatively large, and proceeds to step S
Proceed to 3. In step S3, the controller 10 sets the latest pressure measurement value Pn obtained in this routine as a new pressure transmission value Pt and stores it in its own memory. In step S4, the controller 10 causes the transmission circuit 12 to transmit data including the newly set pressure transmission value Pt, and ends the process once. The routine shown in FIG. 4B relates to the detection and transmission of the temperature of the tire 2. The routine of FIG. 4B is executed, for example, in parallel with the routine of FIG. First, in step S11, the controller 10 causes the temperature sensor 14 to measure the temperature of the tire 2. In the following step S12, the controller 10 determines whether or not the absolute value of the difference between the temperature transmission value Tt and the measured temperature value Tn is equal to or greater than a predetermined temperature determination value α2. The temperature transmission value Tt is the previously transmitted temperature value, that is, the temperature transmission value Tt currently stored in the memory of the controller 10. The temperature measurement value Tn is
This is the temperature value measured in step S11, that is, the latest temperature measurement value Tn obtained in this routine. The temperature determination value α2 is a relatively small value. Even if the temperature of the tire 2 changes within the range of the temperature determination value α2, the running state of the vehicle 1 has almost no effect. When the absolute value of the difference between the temperature transmission value Tt and the measured temperature value Tn is smaller than the temperature determination value α2, the controller 10 determines that the change in the temperature of the tire 2 is small, and ends the process once. On the other hand, if the absolute value of the difference between the temperature transmission value Tt and the measured temperature value Tn is equal to or greater than the temperature determination value α2, the controller 10 determines that the change in the temperature of the tire 2 is relatively large, and proceeds to step S
Proceed to 13. In step S13, the controller 10
Sets the latest temperature measurement value Tn obtained in this routine as a new temperature transmission value Tt and stores it in its own memory. In step S14, the controller 10 causes the transmission circuit 12 to transmit data including the newly set temperature transmission value Tt, and terminates the process once. FIG. 6 is a graph for explaining the relationship between the change over time in tire pressure and the operation of the transmitter 3. During the time Ta during which the vehicle 1 is stopped, the air pressure of the tire 2 only slightly changes due to the influence of the outside air temperature. Therefore, the pressure measurement value Pn obtained at each measurement time interval t1 hardly changes, and only slightly differs from the value of the air pressure transmitted last time, that is, the current pressure transmission value Pt within the range of the pressure determination value α1. It is. Therefore, even if the air pressure data is not transmitted during the time Ta, it can be determined that the current air pressure is maintained near the value of the air pressure transmitted last time. Vehicle 1
During the running time Tb, the temperature and the air pressure of the tire 2 rise due to the friction generated between the tire 2 and the running surface. Therefore, the pressure measurement value Pn obtained at each measurement time interval t1 gradually increases. When the pressure measurement value Pn becomes higher than the current pressure transmission value Pt by the pressure determination value α1 or more, the data of the pressure measurement value Pn is transmitted, and the transmitted pressure measurement value Pn is set as a new pressure transmission value Pt. In a stable running state of the vehicle 1, the temperature and the air pressure of the tire 2 are maintained substantially constant. Therefore, the measured pressure value Pn hardly changes, and the air pressure data is not transmitted. In this case, even if the air pressure data is not transmitted,
It can be determined that the current air pressure is maintained near the value of the air pressure transmitted last time. When the vehicle 1 is stopped again and the stopped state continues for the time Tc, the temperature of the tire 2 decreases so as to approach the outside air temperature, and accordingly, the air pressure of the tire 2 also decreases. Also in this case, when the difference between the pressure measurement value Pn and the current pressure transmission value Pt becomes equal to or greater than the pressure determination value α1, the data of the pressure measurement value Pn is transmitted, and the transmitted pressure measurement value Pn is used as a new pressure transmission value. It is set as the value Pt. When the tire 2 is punctured during the time Td during which the vehicle 1 is running, the air pressure of the tire 3 rapidly decreases. Therefore, the difference between the pressure measurement value Pn and the current pressure transmission value Pt becomes equal to or greater than the pressure determination value α1, and the data of the pressure measurement value Pn is transmitted immediately. Therefore, the driver of the vehicle 1 can use the display 23 or the alarm 24 of the receiver 4
An abnormality in the air pressure of the tire 2 can be immediately recognized. When the vehicle 1 is stopped (time Te) and the air pressure of the tire 2 becomes equal to the atmospheric pressure, the decrease of the air pressure of the tire 2 stops. Therefore, the air pressure data is not transmitted.
However, it can be determined that the current air pressure is maintained near the value of the air pressure transmitted last time, that is, substantially equal to the atmospheric pressure. Therefore, even if the data of the air pressure is not transmitted, the abnormality of the air pressure of the tire 2 can be accurately and reliably grasped. As described above, the transmitter 3 of the present embodiment measures the tire state at predetermined measurement time intervals,
Only when the measured value indicating the latest tire condition changes from the value indicating the previously transmitted tire condition by a predetermined judgment value or more, data indicating the measured latest tire condition is transmitted. In other words, transmission is not performed when the tire state is maintained substantially constant, and transmission is performed only when the tire state changes relatively significantly. The power required for transmission is extremely large compared to the power required for measurement.
However, in the present embodiment, transmission is hardly performed when the vehicle 1 is stopped or when the vehicle 1 is running stably. Therefore, the power consumption of the transmitter 3 can be reduced as much as possible, and the battery 15 having a limited capacity can be used for a long time. This eliminates the need to use a large and heavy battery 15 having a large capacity. When it is necessary to immediately notify the abnormality of the tire state, for example, when the tire state changes greatly, the transmission is always performed. Therefore, the driver can immediately know the abnormality of the tire condition. Further, even if the transmission is not performed for a long time, the driver can determine the current tire state almost accurately based on the tire state previously received by the receiver 4. Next, a second embodiment of the present invention will be described with reference to the flowcharts of FIGS. 7A and 7B. The routine shown in FIGS. 7A and 7B is repeatedly executed by the controller 10 of the transmitter 3 at intervals of 15 seconds, which is the measurement time interval t1. When the battery 15 is attached to the transmitter 3 when assembling the transmitter 3, the controller 10
Causes the pressure sensor 11 and the temperature sensor 14 to perform an initial measurement operation. Then, the controller 10 stores the obtained initial pressure measurement value Pn and temperature measurement value Tn in its own memory as initial values. These initial pressure measurement values Pn and temperature measurement values Tn may or may not be transmitted from the transmission circuit 12. The routine shown in FIG. 7A relates to detection and transmission of the air pressure of the tire 2. First, in step S21, the controller 10
Causes the pressure sensor 11 to measure the air pressure of the tire 2.
In the following step S22, the controller 10 determines whether the absolute value of the difference between the latest pressure measurement value Pn obtained in the current routine and the past pressure measurement value Pn-1 obtained in the previous routine is zero. Determine whether or not. The previous pressure measurement value Pn-1 is stored in the memory of the controller 10. If the absolute value of the difference between the latest pressure measurement value Pn and the previous pressure measurement value Pn-1 is zero, the controller 10 determines that there is no change in the air pressure of the tire 2 and proceeds to step S
Proceed to 24. On the other hand, if the absolute value of the difference between the latest pressure measurement value Pn and the previous pressure measurement value Pn-1 is not zero, the controller 10 determines that the air pressure of the tire 2 has changed, and proceeds to step S23. . In determining whether or not the absolute value of the difference is zero, a measurement error within an allowable range, such as a measurement error due to the characteristics and performance of the pressure sensor 11, is considered. In step S23, the controller 10
Transmits data including the latest pressure measurement value Pn to the transmission circuit 12.
To be sent. In step S24, the controller 10
Stores the latest pressure measurement value Pn as the previous pressure measurement value Pn-1 in its own memory, and terminates the process once. FIG.
The routine shown in (b) relates to the detection and transmission of the temperature of the tire 2. The routine of FIG. 7B is executed, for example, in parallel with the routine of FIG. 7A. First, in step S31, the controller 10
4 causes the temperature of the tire 2 to be measured. Subsequent step S32
In, the controller 10 determines whether or not the absolute value of the difference between the latest temperature measurement value Tn obtained in the current routine and the past temperature measurement value Tn-1 obtained in the previous routine is zero. judge. The previous temperature measurement value Tn-1 is stored in the memory of the controller 10. When the absolute value of the difference between the latest temperature measurement value Tn and the previous temperature measurement value Tn-1 is zero, the controller 10 determines that there is no change in the temperature of the tire 2, and proceeds to step S34. On the other hand, if the absolute value of the difference between the latest temperature measurement value Tn and the previous temperature measurement value Tn-1 is not zero, the controller 10 determines that the temperature of the tire 2 has changed, and proceeds to step S33. . In determining whether or not the absolute value of the difference is zero, a measurement error within an allowable range, such as a measurement error due to the characteristics and performance of the temperature sensor 14, is considered. Step S
At 33, the controller 10 sets the latest temperature measurement value Tn.
Is transmitted to the transmission circuit 12. Step S
At 34, the controller 10 sets the latest temperature measurement value Tn.
Is stored in its own memory as the previous temperature measurement value Tn-1, and the process is temporarily terminated. In the above-described embodiment, the same advantages as those in the embodiment of FIGS. 1 to 6 can be obtained. In addition to the above-described embodiment, the following modifications are possible. The measurement time interval t1 is not limited to 15 seconds, and may be appropriately changed according to, for example, the type of the tire 2 on which the transmitter 3 is to be mounted. 1 to 6, the pressure determination value α1 and the temperature determination value α2 may be appropriately changed according to, for example, the type of the tire 2 on which the transmitter 3 is to be mounted. In the embodiment of FIG. 7, data indicating the latest measured tire state is transmitted only when the latest measured tire state changes from the last measured tire state. However, instead of this, the data indicating the measured latest tire state may be transmitted only when the measured latest tire state changes a plurality of times from the previously measured tire state. At least the measurement and transmission of the air pressure need only be performed, and the measurement and transmission of the temperature may be omitted. By doing so, it is possible to provide the transmitter 3 having the minimum necessary functions at low cost.

As described in detail above, according to the present invention,
A change in the state of the tire can be reliably notified, and the battery life can be prolonged.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a tire condition monitoring device according to a first embodiment of the present invention.

FIG. 2 is a block circuit diagram showing a transmitter in the monitoring device of FIG. 1;

FIG. 3 is a block circuit diagram showing a receiver in the monitoring device of FIG. 1;

FIG. 4 is a flowchart for explaining the operation of the transmitter of FIG. 2;

FIG. 5 is a timing chart for explaining the operation of the transmitter of FIG. 2;

FIG. 6 is a graph for explaining the relationship between the change over time in tire pressure and the operation of the transmitter in FIG. 2;

FIG. 7 is a flowchart for explaining the operation of the transmitter according to the second embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... vehicle, 2 ... tire, 3 ... transmitter, 4 ... receiver, 10
... Controller, 11 ... Pressure sensor, 12 ... Transmission circuit,
14: temperature sensor, 15: battery.

Claims (8)

[Claims] 1. A transmitter which is driven by a battery and wirelessly transmits data indicating a tire condition of a vehicle, the sensor for measuring the tire condition and wirelessly transmits data indicating the measured tire condition. And a controller for controlling the sensor and the transmission circuit, the controller causes the sensor to measure the tire state at a predetermined time interval, a value indicating the latest measured tire state The transmitter controls the transmission circuit to transmit data indicating the latest measured tire condition when the value of the tire condition changes by a predetermined value or more from the value indicating the tire condition transmitted last time. 2. A transmitter which is driven by a battery and wirelessly transmits data indicating a tire condition of a vehicle, the sensor for measuring the tire condition and wirelessly transmits data indicating the measured tire condition. And a controller for controlling the sensor and the transmission circuit, the controller causes the sensor to measure the tire state at predetermined time intervals, and the latest measured tire state is A transmitter that controls the transmission circuit to transmit data indicating the latest measured tire state only when the tire state has changed from the measured tire state. 3. The controller controls the transmission circuit to transmit data indicating the latest measured tire state only when the latest measured tire state changes from the last measured tire state. 3. The transmitter according to claim 2, wherein: 4. The tire condition according to claim 1, wherein the tire condition includes at least one of a pressure and a temperature in the tire.
4. The transmitter according to claim 3. 5. A tire condition monitoring device comprising: the transmitter according to claim 1; and a receiver for receiving data wirelessly transmitted from the transmitter. 6. A method for wirelessly transmitting data indicating a tire condition of a vehicle, comprising: measuring a tire condition at a predetermined time interval; and a value indicating the latest measured tire condition. Transmitting a data indicating the latest measured tire condition when the difference between the value and the value indicating the tire condition transmitted last time is equal to or greater than a predetermined value. 7. A method for wirelessly transmitting data indicating the condition of a tire of a vehicle, comprising the steps of: measuring the condition of a tire at a predetermined time interval; Transmitting a data indicating the latest measured tire condition only when the tire condition has changed from the measured tire condition. 8. The data according to claim 7, wherein the data indicating the latest measured tire state is transmitted only when the latest measured tire state changes from the last measured tire state. Transmission method.