JP5429211B2 - Tire pressure detector - Google Patents

Description

  The present invention relates to a tire air pressure detecting device that detects a decrease in tire air pressure of a wheel attached to a vehicle.

  Conventionally, various direct-type tire pressure detection devices have been proposed (see, for example, Patent Document 1). In the direct tire pressure detecting device, a transmitter equipped with a sensor such as a pressure sensor is directly attached to a wheel side to which a tire is attached. In addition, an antenna and a receiver are provided on the vehicle body side. When a data signal indicating the detection result of the sensor is transmitted from the transmitter, the data signal is received by the receiver via the antenna and received. The tire pressure is detected from the obtained data.

  In this type of tire pressure detection device, when a data signal is sent from the transmitter at the transmission timing of every fixed transmission cycle, the tire pressure is obtained on the receiver side, and the obtained tire pressure falls below a certain alarm threshold value. And the form of warning the fall of tire air pressure is taken.

JP 2007-015491 A

  However, in the conventional tire air pressure detection device, the alarm threshold value used when detecting the decrease in the tire air pressure is a constant value, and the alarm threshold value that varies with time is not applied.

  In recent years, the United Nations Economic Commission for Europe (UNECE) has been examining the regulation of wearing tire pressure detectors from both safety and environmental perspectives. As a specific legal requirement, it is required to set an alarm threshold value corresponding to the pressure value after the increase when the tire air pressure increases due to traveling of the vehicle or the like. As a technique for realizing this, it is conceivable to obtain an ideal pressure value corresponding to a temperature change using a gas state equation, that is, Boyle's law, and to compare this ideal pressure value with an alarm threshold value. However, when temperature data in the tire is used, it is difficult to realize this method because of a large temperature error.

  The present invention has been made in view of the above points, and it is an object of the present invention to provide a tire air pressure detection device that can more reliably warn of a decrease in tire air pressure based on an alarm threshold value that follows a change in air pressure in the tire as the vehicle travels. .

  In order to achieve the above object, in the invention according to claim 1, the transmitter (2) acquires tire pressure at least every transmission cycle, and transmits the acquired tire pressure data to the receiver (3). The receiver (3) uses the currently received tire pressure as the current received pressure, and sets the first alarm threshold as a value obtained by reducing the pressure by a predetermined rate from the previously received tire pressure. If the lower limit value is equal to or less than the alarm threshold value, which is the second alarm threshold value, it is determined that the tire air pressure has decreased, and an alarm signal is output.

  In this way, the first alarm threshold value that is reduced from the received pressure obtained in the past by the alarm detection pressure reduction rate is set, and when the current received pressure is equal to or lower than the alarm threshold value, it is determined that the tire pressure is reduced. . Further, the lower limit value of the alarm threshold set based on the recommended vehicle pressure or the user setting is set as the second alarm threshold value, and it is determined that the tire pressure is decreased even if the current received pressure is less than or equal to the lower limit value of the alarm threshold value. ing. Accordingly, it is possible to more reliably warn of a decrease in tire air pressure based on an alarm threshold value that follows a change in air pressure in the tire as the vehicle travels.

Furthermore, in the invention according to claim 1 , when the difference between the tire pressure received in the past and the current received pressure is a predetermined value or more, the receiver (3) stores the tire pressure received in the past, and The tire pressure received in the past is used for setting the first alarm threshold when the data indicating the tire pressure is received next, or a value obtained by reducing the pressure by a predetermined rate from the tire pressure received in the past is stored. Then, it is characterized in that it is used as the first alarm threshold when data indicating the tire pressure is received next.

  In this way, it can be determined that the tire pressure has suddenly decreased when the difference between the tire pressure received in the past and the current received pressure is greater than or equal to a certain value. In this case, the tire pressure received in the past is stored, and the tire pressure received in the past is used for setting the first alarm threshold when the data indicating the tire pressure is received next, or received in the past. By storing a value obtained by reducing the pressure by a predetermined ratio from the measured tire pressure and using it as the first alarm threshold when the data indicating the tire pressure is received next time, the tire air pressure becomes less than the lower limit value of the alarm threshold. Even if not, it can be determined that the tire air pressure is reduced.

In the invention described in claim 2 , when the difference between the tire pressure received in the past and the current received pressure is a predetermined value or more, the receiver (3) holds the memory of the tire pressure received in the past for a predetermined period. Then, the tire pressure received in the past is used for setting the first alarm threshold when the data indicating the tire pressure is received next, or the pressure is decreased by a predetermined ratio from the tire pressure received in the past. Is stored as a first alarm threshold value when data indicating tire pressure is received next.

  As described above, whether or not the tire pressure received in the past is stored for a predetermined period, and the tire pressure received in the past is used for setting the first alarm threshold when the data indicating the tire pressure is received next. Alternatively, it is possible to store a value obtained by reducing the pressure by a predetermined ratio from the tire pressure received in the past and use it as the first alarm threshold value when the data indicating the tire pressure is received next.

In this case, as described in claim 3 , the receiver (3) determines that the elapsed time after the ignition switch is turned off exceeds a predetermined time, and the temperature change amount after the ignition switch is turned off is a predetermined amount. When the temperature threshold of the vehicle is exceeded and at least one of the difference between the tire air pressure and the temperature in the tire after the ignition switch is turned off exceeds a certain range. It is sufficient to clear the stored contents of the data.

For example, as described in claim 4 , the receiver (3) can use, as the tire pressure received in the past, the previous received pressure which is the tire pressure received at the previous time before this time. Further, as described in claim 5 , the receiver (3) uses the maximum value of the tire pressure received during the predetermined number of receptions or during the predetermined period as the tire pressure received in the past. You can also. As described above, by using the maximum value of the tire pressure received during the past predetermined number of receptions, it is possible to set a more accurate alarm threshold in consideration of the sensing value error.

In the invention according to claim 6 , the receiver (3) stores the pressure value of the tire air pressure when it is determined that the tire air pressure is reduced, and the tire air pressure sent from the transmitter (2) after the alarm is generated. When the tire pressure indicated by the data exceeds the value obtained by adding the hysteresis value for alarm release to the pressure value at the time of alarm occurrence, a release signal instructing release of the alarm is output to the display (4). It is said.

  In this way, when the receiver (3) determines that the tire air pressure exceeds the value obtained by adding the hysteresis value for alarm release to the pressure value at the time of alarm generation, the alarm display by the display (4) is displayed. Can be released.

  In addition, the code | symbol in the bracket | parenthesis of each said means shows the correspondence with the specific means as described in embodiment mentioned later.

1 is a block diagram showing an overall configuration of a tire air pressure detection device according to a first embodiment of the present invention. (A), (b) is the figure which showed the block configuration of the transmitter 2 and the receiver 3 with which a tire pressure detection apparatus is equipped, respectively. It is the flowchart which showed the detail of the process which the control part 22a of the transmitter 2 performs among tire pressure detection apparatuses. It is the flowchart which showed the detail of the alarm determination which the control part 32b of the receiver 3 performs among tire pressure detection apparatuses. It is the flowchart which showed the detail of the alarm cancellation | release determination process which the control part 32b of the receiver 3 performs among tire pressure detection apparatuses. It is a timing chart showing operation at the time of performing alarm judgment processing and warning cancellation judgment processing. It is a timing chart showing operation at the time of performing alarm judgment processing and warning cancellation judgment processing. It is the flowchart which showed the detail of the alarm determination which the control part 32b of the receiver 3 performs among the tire air-pressure detection apparatuses concerning 2nd Embodiment of this invention. It is a timing chart showing the operation | movement at the time of performing the alarm determination process and the alarm cancellation determination process similar to 1st Embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, the same or equivalent parts are denoted by the same reference numerals in the drawings.

(First embodiment)
A first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing an overall configuration of a tire air pressure detecting device according to an embodiment of the present invention. The upper direction in the drawing of FIG. 1 corresponds to the front of the vehicle 1, and the lower direction of the drawing corresponds to the rear of the vehicle 1. With reference to this figure, the tire pressure detecting device in the present embodiment will be described.

  As shown in FIG. 1, the tire air pressure detection device is attached to a vehicle 1 and includes a transmitter 2, a receiver 3, and a display 4.

  As shown in FIG. 1, the transmitter 2 is attached to each wheel 5 a to 5 d in the vehicle 1, and detects the air pressure of the tire attached to the wheels 5 a to 5 d and the temperature in the tire. The detection signal data indicating the detection result is stored in the transmission frame and transmitted. The receiver 3 is attached to the vehicle body 6 side of the vehicle 1 and receives a frame transmitted from the transmitter 2 and performs various processes and computations based on data stored therein. The tire pressure is to be calculated. 2A and 2B show block configurations of the transmitter 2 and the receiver 3.

  As shown in FIG. 2A, the transmitter 2 includes a sensing unit 21, a microcomputer 22, a battery 23, and a transmission antenna 24.

  The sensing unit 21 is configured to include, for example, a diaphragm type pressure sensor and a temperature sensor, and outputs a detection signal (hereinafter referred to as a detection signal related to the tire pressure) indicating the tire pressure and the temperature in the tire. . The sensing unit 21 detects the tire air pressure and the temperature in the tire for each predetermined detection cycle based on a command from the microcomputer 22.

  The microcomputer 22 is a well-known computer having a control unit 22a, a transmission unit 22b, and the like, and executes predetermined processing according to a program stored in a memory (not shown) in the control unit 22a.

  The control unit 22a receives a detection signal related to the tire air pressure from the sensing unit 21 every predetermined detection period, processes the signal, and processes it as necessary. And the control part 22a is stored in the transmission frame with the ID information of each transmitter 2 as data which shows the detection result (henceforth data regarding tire pressure), and sends a transmission frame to the transmission part 22b after that. The process of sending a signal to the transmitter 22b is executed at predetermined intervals according to the program.

  The transmission unit 22 b functions as an output unit that transmits a frame transmitted from the control unit 22 a to the receiver 3 through the transmission antenna 24.

  The battery 23 supplies power to the control unit 22a and the like, and receives power supply from the battery 23, collects data related to tire pressure in the sensing unit 21, and performs various calculations in the control unit 22a. Is executed.

  The transmitter 2 configured in this way is attached to an air injection valve in each of the wheels 5a to 5d, for example, and is arranged so that the sensing unit 21 is exposed inside the tire. Thereby, the tire air pressure of the corresponding wheel is detected, and the frame is transmitted every predetermined transmission cycle (for example, every minute) through the transmission antenna 24 provided in each transmitter 2.

  As shown in FIG. 2B, the receiver 3 includes an antenna 31 and a microcomputer 32.

  The antenna 31 is one or a plurality of antennas that collectively receive frames transmitted from the transmitters 2, and is fixed to the vehicle body 6.

  The microcomputer 32 is a well-known computer having a receiving unit 32a, a control unit 32b, and the like, and executes predetermined processing according to a program stored in a memory (not shown) in the control unit 32b.

  The receiving unit 32a functions as an input unit that receives a frame from each transmitter 2 received by each antenna 31 and sends the frame to the control unit 32b.

  The control unit 32b obtains tire air pressure (hereinafter referred to as reception pressure) by performing various signal processing and calculation based on the data relating to tire air pressure stored in the received frame, and based on the received pressure, the tire air pressure is calculated. Judge the decline. Specifically, the control unit 32b compares the received pressure with an alarm threshold value, and determines that the tire air pressure decreases when the received pressure falls below the alarm threshold value. And if the fall of a tire air pressure is detected, the control part 32b will output the signal to that effect to the indicator 4. Thereby, the indicator 4 is informed that the tire pressure of any of the wheels 5a to 5d has decreased.

  The alarm threshold value used at this time is set based on the reception pressure and vehicle recommended pressure obtained in the past. The reception pressure obtained in the past is the reception pressure obtained before the current computation cycle, and in the present embodiment, the reception pressure that has been stored in the current computation cycle is obtained in the past. Used as pressure. In the case of the present embodiment, the reception pressure obtained in the past is basically the reception pressure at the previous calculation cycle. However, when the reception pressure is suddenly reduced, the reception pressure before the decrease is stored. The contents are stored and used as the received pressure determined in the past. The vehicle recommended pressure is a recommended pressure of tire pressure determined for each vehicle type.

  A value obtained by reducing the pressure by a predetermined rate (hereinafter, this rate is referred to as an alarm detection pressure reduction rate) with respect to the received pressure and vehicle recommended pressure obtained in the past is set as the alarm threshold value. For example, the alarm detection decompression rate is set to 20%. That is, a value obtained by reducing the alarm detection pressure reduction rate with respect to the reception pressure obtained in the past becomes a variable alarm threshold value (corresponding to the first alarm threshold value) according to the reception pressure, and the alarm detection pressure reduction rate is reduced with respect to the vehicle recommended pressure. This value becomes an alarm threshold value (corresponding to the second alarm threshold value) corresponding to the lower limit value, and it is determined that the tire air pressure has decreased when the reception pressure decreases below the alarm threshold value determined by these values.

  In addition, although the case where the alarm threshold value is set based on the vehicle recommended pressure by the receiver 3 has been described here, the user set pressure that the user sets himself / herself can be used as the alarm threshold value. However, even in this case, the lower limit value of the alarm threshold that can be set as the user set pressure is set to a value that is set based on the vehicle recommended pressure, so that it is at least equal to or lower than the alarm threshold set based on the vehicle recommended pressure. An alarm can be issued when the tire air pressure drops.

  On the other hand, the receiving unit 32a is configured to release the alarm when a predetermined release condition is satisfied after sending a warning signal instructing a warning of a decrease in tire air pressure to the display 4. For example, in the receiving unit 32a, the tire air pressure when the alarm is given (hereinafter referred to as a pressure value when the alarm is generated) is stored in a memory (not shown) in the microcomputer 32 and transmitted from the transmitter 2 after the alarm. When the tire air pressure stored in the frame exceeds the value obtained by adding a predetermined alarm release hysteresis value ΔP to the pressure value at the time of alarm occurrence, the alarm release is performed. The alarm cancellation hysteresis value ΔP at this time may be a constant value or a value that differs for each vehicle.

  As shown in FIG. 1, the display 4 is arranged at a place where the driver can visually recognize, and is configured by an alarm lamp installed in an instrument panel in the vehicle 1, for example. For example, when an alarm signal instructing an alarm for a decrease in tire air pressure is sent from the control unit 32b in the receiver 3, the display device 4 displays an indication to that effect so that the driver is informed of a decrease in tire air pressure. Do.

  As described above, the tire air pressure detection device in the present embodiment is configured.

  Subsequently, an operation example of the tire pressure detection device configured as described above will be described. FIG. 3 is a flowchart showing details of processing executed by the control unit 22a of the transmitter 2 in the tire pressure detecting device. 4 and 5 are flowcharts showing details of the alarm determination and alarm release determination processing executed by the control unit 32b of the receiver 3 in the tire air pressure detection device. With reference to these drawings, an operation example of the tire pressure detecting device will be described.

  First, the control unit 22a of the transmitter 2 executes various processes shown in the flowchart of FIG. 3 for each predetermined control cycle. The timing at which this process is performed is the measurement timing at which the transmitter 2 senses tire pressure.

  In step 100, the tire pressure and the temperature in the tire are sensed by the sensing unit 21. Specifically, when a signal instructing the sensing unit 21 to perform sensing is output, the sensing unit 21 senses the tire air pressure and the temperature in the tire in accordance with the command, and the detection signal is detected by sensing. Since it is sent from the unit 21, it is received as a detection signal related to the tire pressure. Then, the acquired tire pressure data is stored in the frame.

  In the next step 110, it is determined whether or not it is a transmission timing. The transmission timing is set for each transmission cycle defined at regular intervals, and is set, for example, every minute. If the transmission timing is not determined here, only a simple measurement is performed. If it is determined that the transmission timing is determined, the process proceeds to step 120. Then, in step 120, a frame storing data related to tire pressure including tire pressure and temperature in the tire is transmitted, and the process ends. In this way, a frame storing data related to tire air pressure is transmitted from the transmitter 2 to the receiver 3.

  On the other hand, for the receiver 3, when an ignition switch (not shown) is switched from OFF to ON, the control unit 32b of the receiver 3 is turned on, and a frame transmitted from the transmitter 2 is received to make an alarm determination. After the process is performed and the alarm determination is performed, an alarm release determination process is also performed.

  First, as shown in FIG. 4, it is determined whether or not data reception is performed in step 200 as an alarm determination process. If a frame transmitted from the transmitter 2 is received, an affirmative determination is made and the process proceeds to step 205. If not received, the process waits until it is received.

  Subsequently, in Step 205 and Step 210, the received pressure of the tire pressure is acquired based on the data stored in the received frame, and it is determined whether or not the received pressure is equal to or lower than the alarm threshold value.

  Specifically, in step 205, the reception pressure is first acquired. Then, it is determined whether or not the acquired reception pressure is equal to or less than an alarm threshold value (first alarm threshold value) that has been reduced from the reception pressure obtained in the past by the alarm detection pressure reduction rate. Here, the value stored as the previous reception pressure is used as the reception pressure obtained in the past, and the value of 80% of the previous reception pressure is obtained, so that the alarm detection pressure reduction rate is 20% from the previous reception pressure. The alarm threshold value that has decreased is calculated.

  In step 210, it is determined whether or not the received pressure is equal to or lower than the lower limit value of the alarm threshold set based on the recommended vehicle pressure. Here, the lower limit value of the alarm threshold value obtained by reducing the recommended vehicle pressure by 80% from the recommended vehicle pressure is reduced by 20%, which is the alarm detection decompression rate.

  If either step 205 or step 210 is affirmatively determined, the process proceeds to step 215, where alarm determination is performed, and a warning signal instructing a warning of a decrease in tire air pressure is output from the receiver 3 to the display 4. . As a result, the indicator 4 indicates that the tire air pressure has decreased, and the driver is warned of the tire air pressure decrease.

  On the other hand, if a negative determination is made in both step 205 and step 210, the routine proceeds to step 220. In step 220, it is determined whether the flag is being set. The flag here is set when it is determined that the tire air pressure has suddenly decreased as described later (see steps 225 and 230). For this reason, before it is determined that the tire pressure suddenly decreases, a negative determination is made in step 220 and the process proceeds to subsequent step 225.

  In step 225, it is determined whether or not the difference between the currently received previous received pressure and the current received pressure (hereinafter referred to as current received pressure) is greater than or equal to a certain value. The constant value referred to here is a sudden decrease threshold value that allows a difference between the previous reception pressure and the current reception pressure to be large and to be considered that the tire air pressure has suddenly decreased.

  That is, when the reception pressure suddenly decreases, it is highly possible that the tire air pressure will decrease. Therefore, it is preferable to issue a warning by determining that the tire air pressure has decreased as soon as possible. However, as in step 205 described above, the alarm threshold value is basically set to a value obtained by reducing the alarm detection pressure reduction rate with respect to the reception pressure obtained in the past. Following this, the alarm threshold value also fluctuates. For this reason, even if the reception pressure is suddenly lowered, if the alarm threshold is made to completely follow the fluctuation of the reception pressure, the reception pressure does not become lower than the alarm threshold and an alarm cannot be performed. Even in this case, an alarm can be issued if the received pressure is less than or equal to the lower limit value of the alarm threshold, but the received pressure is not necessarily less than or equal to the lower limit value of the alarm threshold. Therefore, when the reception pressure suddenly decreases, it is determined in step 225 that the reception pressure suddenly decreases so that it can be determined that the tire air pressure has decreased even if the reception pressure does not fall below the lower limit of the alarm threshold. .

  If an affirmative determination is made in step 225, the process proceeds to step 230, and the value stored as the previous reception pressure is held as it is as the previous reception pressure. As a result, the previous received pressure is not updated to the current received pressure, the previous received pressure is maintained, and the alarm threshold calculated by multiplying the previous received pressure calculated in step 205 by 80% is the value of The value is set based on the large previous received pressure. In step 230, a flag indicating that the tire pressure has suddenly decreased is set. Thereafter, the alarm determination process is terminated, and the process from step 200 is repeated again every time data is received.

  If a negative determination is made in step 225, the process proceeds to step 235 and the current reception pressure is stored as the previous reception pressure. As a result, the current reception pressure is updated as a new previous reception pressure, and the alarm threshold calculated by multiplying the previous reception pressure calculated in step 205 described above by 80% is the previously received data. Based on the most recent previous received pressure based on this value. Thereafter, the alarm determination process is terminated.

  On the other hand, if it is determined in step 225 that the tire air pressure has suddenly decreased, and a flag is set in step 230, then an affirmative determination is made in step 220 thereafter. For this reason, it progresses to step 240 and it is determined whether the fixed period passed since the flag set. This determination is performed by measuring a certain period with a clock (not shown) provided in the microcomputer 32. If a negative determination is made here, the process proceeds to step 245, and the previous received pressure is held without being updated. As a result, the previous received pressure is maintained without being updated for a certain period from the flag set. If an affirmative determination is made here, the process proceeds to step 250 where the current received pressure is stored as the previous received pressure, and the flag that is set when it is determined that the tire air pressure has suddenly decreased is reset. Exit.

  Note that the alarm determination process shown in FIG. 4 is performed every time a frame transmitted from the transmitter 2 is received. Therefore, even if the tire pressure is lowered and the alarm determination is made, the alarm determination process is transmitted from the transmitter 2. When a frame to be received is received, it is continuously executed again.

  The alarm release determination process is executed, for example, when the pressure value at the time of alarm generation is stored in the alarm determination process. As shown in FIG. 5, in the alarm cancellation determination process, it is determined whether or not data reception is performed in step 300. If a frame transmitted from the transmitter 2 is received, an affirmative determination is made and the process proceeds to step 310. If not received, the process waits until it is received.

  Subsequently, in step 310, it is determined whether or not an alarm cancellation condition is satisfied. For example, here, the alarm release hysteresis value ΔP is added to the alarm pressure value stored in the receiver 3 as the received pressure value indicated in the tire pressure data stored in the received frame. It is determined whether the value is exceeded. If an affirmative determination is made here, the routine proceeds to step 320 where an alarm cancellation determination is made, and a release signal instructing the receiver 3 to release the alarm is output to the display 4. Thereby, the indication that the tire air pressure has decreased on the display 4 is released. At the same time, the stored pressure value at the time of alarm occurrence is cleared, and the process ends.

  6 and 7 are timing charts showing operations when the above-described alarm determination process and alarm release determination process are performed. FIG. 6 is a timing chart when the tire pressure gradually changes, and FIG. 7 is a timing chart when the tire pressure suddenly decreases. In the drawing, a circle represents a control cycle in which sensing by the transmitter 2 is performed.

  First, as shown in FIG. 6, the tire air pressure changes as the vehicle travels between time points T <b> 1 and T <b> 2 from the state where the tire air pressure at the time of sensing coincides with the vehicle recommended pressure at time point T <b> 0. Then, the alarm threshold also varies according to the variation. For this reason, it is possible to change the alarm threshold following the change in the tire air pressure accompanying the temperature change or the like.

  At time T2, an alarm that defines a lower limit value at which an alarm threshold (first alarm threshold) that follows a change in tire air pressure calculated based on a received pressure obtained in the past is calculated based on a vehicle recommended pressure Even if it becomes smaller than the threshold value (second warning threshold value), the warning threshold value is set to a lower limit value calculated based on the vehicle recommended pressure. For this reason, the alarm threshold value can basically be defined by a value calculated based on the recommended vehicle pressure while the lower limit value follows the fluctuation of the reception pressure obtained in the past. .

  In this way, by making the alarm threshold follow the fluctuation of the received pressure obtained in the past, it is possible to set the alarm threshold corresponding to the change in the air pressure in the tire as the vehicle travels.

  On the other hand, as shown in FIG. 7, after the tire pressure fluctuates as the vehicle travels between time points T <b> 1 and T <b> 2 from the state where the tire pressure at the time of sensing coincides with the vehicle recommended pressure at time T <b> 0, It is assumed that the tire air pressure suddenly decreases between time points T2 and T3. In this case, the value of the previous received pressure is constantly updated until time T2, but the difference between the previous received pressure stored at time T2 and the received pressure at time T3 at time T3 becomes a certain value or more. Therefore, the value of the previous reception pressure is not updated at time T3, and the previous reception pressure at time T2 is held as it is. For this reason, the reception pressure at the time T2 is maintained as the previous reception pressure for a certain period, and a decrease in tire air pressure is determined based on the alarm threshold calculated based on the reception pressure at the time T2. Will be.

  In the example of FIG. 7, even if the reception pressure at time T4 is not less than or equal to the lower limit value of the alarm threshold set based on the vehicle recommended pressure, it is set based on the reception pressure obtained in the past. Since it is below the alarm threshold value, it is determined that the tire air pressure is reduced. As described above, when the tire pressure suddenly decreases, the tire pressure decrease is determined using the alarm threshold value set based on the received pressure obtained in the past, so that the tire pressure can be more quickly responded to the sudden decrease in tire pressure. In addition, it is possible to determine a decrease in tire air pressure.

  As described above, in the present embodiment, an alarm threshold (first alarm threshold) is set by reducing the received pressure obtained in the past by the alarm detection pressure reduction rate, and when the received pressure falls below this alarm threshold, the tire is set. It is determined that the air pressure has dropped. In addition, a lower limit value (second alarm threshold value) of an alarm threshold set based on the recommended vehicle pressure is set, and it is determined that the tire air pressure is decreased even if the received pressure falls below the lower limit value of the alarm threshold. Yes. Accordingly, it is possible to more reliably warn of a decrease in tire air pressure based on an alarm threshold value that follows a change in air pressure in the tire as the vehicle travels.

  If the tire pressure suddenly drops, the previous received pressure, which is larger than the current received pressure, is maintained for a certain period of time, and an alarm threshold is set based on the previous received pressure. It is used to determine the decrease. For this reason, it is possible to reliably detect a decrease in tire air pressure even when the tire air pressure suddenly decreases, such as when the tire is punctured.

  Therefore, it is possible to detect a gradual decrease in tire air pressure based on the alarm threshold that is reduced by the alarm detection pressure reduction rate from the previously obtained received pressure and the lower limit of the alarm threshold that is set based on the recommended vehicle pressure. Can do. When a sudden decrease in tire pressure is detected, an alarm threshold is set based on the previous reception pressure that is the reception pressure before the decrease, so that a sudden decrease in tire pressure such as tire puncture is reliably detected. It becomes possible.

(Second Embodiment)
A second embodiment of the present invention will be described. This embodiment is different from the first embodiment because the alarm determination executed by the microcomputer 32 of the receiver 3 is changed with respect to the first embodiment, and the other aspects are the same as the first embodiment. Only the part will be described.

  FIG. 8 is a flowchart showing details of the alarm determination executed by the control unit 32b of the receiver 3 in the tire pressure detection device according to the present embodiment. The alarm release determination is the same as in the first embodiment.

  In this embodiment, in steps 400 to 445 shown in FIG. 8, basically the same processing as that in steps 200 to 245 in FIG. 4 described in the first embodiment is performed. As the received pressure obtained in the past, the maximum value in the tire pressure data for a predetermined number of reception times is used instead of the previous received pressure. Here, the predetermined number of receptions is set to three, and the latest three data, that is, the maximum value of the tire pressure acquired from the current control cycle up to the control cycle three times before is used for setting the alarm threshold. Yes. Then, a value obtained by reducing the pressure by the alarm detection decompression rate with respect to the maximum value is set as the alarm threshold, and it is determined whether or not the tire air pressure in the current control cycle acquired in step 400 is equal to or less than the alarm threshold. Judgment. Here, for example, the alarm detection pressure reduction rate is set to 20%, and the pressure value of 80% of the maximum value of the tire pressure of the latest three data is used as the alarm threshold value.

  For this reason, in step 425, it is determined whether or not the difference between the maximum value of the latest three data and the current reception pressure is equal to or greater than a certain value, and if an affirmative determination is made, the process proceeds to step 430 and the most recently stored three Keep the maximum value of the data as it is and set the flag. If a negative determination is made in step 425, the oldest data is deleted from the three most recently stored data, the current reception pressure is included in the three most recent data, and the maximum value among them is the maximum of the three most recent data. Hold as value. After the flag is set, if a positive determination is made in step 440 and a negative determination is made in step 440, the maximum values of the three most recent data currently stored in step 445 are held as they are, and a positive determination is made in step 440. Then, in step 450, the oldest data is deleted from the three most recently stored data, the current reception pressure is included in the three most recent data, and the maximum value among them is held as the maximum value of the three most recent data.

  FIG. 9 is a timing chart showing the operation when the alarm determination process as described above or the alarm release determination process similar to that of the first embodiment is performed.

  As shown in this figure, when the tire air pressure changes as the vehicle travels between time points T1 and T2 from the state in which the tire pressure at the time of sensing coincides with the vehicle recommended pressure at time point T0. The alarm threshold value also varies according to the variation. At this time, since the alarm threshold value is set based on the maximum value of the tire pressure of the three most recent data, the alarm threshold value is changed following the change of the tire air pressure accompanying the temperature change etc. Since the maximum value of tire pressure is used, it is possible to set a more accurate alarm threshold in consideration of sensing value errors.

  Thereafter, at time T2, an alarm threshold value (first alarm threshold value) that follows a change in tire air pressure calculated based on the received pressure obtained in the past defines a lower limit value calculated based on the vehicle recommended pressure. If it becomes smaller than the warning threshold (second warning threshold), the warning threshold is set to a lower limit value calculated based on the recommended vehicle pressure.

  Thus, in addition to obtaining the effect of the first embodiment by using the maximum value of the tire pressure for a predetermined number of reception times, in addition to the sensing value error, a more accurate alarm threshold value can be obtained. The effect that it becomes possible to set is obtained.

(Other embodiments)
In each of the above embodiments, a value obtained by reducing the pressure by the alarm detection pressure reduction rate with respect to the previous received pressure or the maximum value of the tire pressure of the three most recent data is set as the alarm threshold, and the previous received pressure or The maximum value of the tire pressure of the latest three data is stored. However, the alarm threshold value calculated based on these is stored, and if the difference between the previous received pressure or the maximum value of the tire pressure of the latest three data and the current received pressure is a certain value or more, it is stored at that time. The alarm threshold value may be used to determine a decrease in tire air pressure when the next received pressure is acquired.

  Further, management may be performed not only with the latest number data but also with the current reception timing, that is, the time from the present time. For example, the maximum value of the data received during a predetermined period from the current reception timing is stored so that the “maximum value of the most recent three data” is set to “the maximum value of the data received during the most recent three minutes”. It can also be used for setting. Or, when the value obtained by reducing the pressure by the alarm detection pressure reduction rate from the maximum value of the data received during the predetermined period from the current reception timing is stored, and when the next received pressure is obtained You may make it use for the determination of the fall of the tire air pressure.

  In addition, it is preferable that the previously received pressure and the maximum tire pressure value of the three most recent data used in the alarm thresholds described in the above embodiments and the stored contents of the alarm threshold are cleared when a predetermined condition is satisfied. . For example, the predetermined condition may include time, temperature, or a relationship between pressure and temperature.

  Specifically, as a time condition, the stored content may be cleared when a predetermined time elapses after the ignition switch is turned off.

  For example, since the vehicle handles time information in a meter ECU or the like, by measuring the time information by communication, the time from when the ignition switch is turned off to when it is turned on is measured, and the time is a predetermined time or more If the time has elapsed, the stored content may be cleared. Thus, highly accurate time information can be used by using the time information handled by the vehicle.

  Further, during the period in which the ignition switch is turned off, the receiver 3 is intermittently activated, and a counter (not shown) provided in the microcomputer 32 is operated to measure the period in which the ignition switch is turned off. Anyway. In this way, since time measurement can be performed only by the receiver 3, time measurement can be performed regardless of other vehicle systems.

  Similarly, the transmitter 2 can perform time measurement, and by including time information (for example, a constant time count value) in a frame transmitted from the transmitter 2, a period during which the ignition switch is turned off can be obtained. You may make it measure. In this way, it is not necessary to operate the receiver 3 during the period when the ignition switch is off, so that it is not necessary to generate dark current.

  Further, as a temperature condition, the stored content may be cleared when there is a certain temperature change or more.

  That is, it is considered that the temperature in the tire does not decrease unless a long time has passed since the ignition switch was turned off. Therefore, using the data indicating the temperature included in the received data, the difference between the temperature in the tire just before the ignition switch is turned off and the temperature in the tire when the ignition switch is turned on is calculated. If is equal to or higher than the temperature threshold, the stored content may be cleared.

  Similarly, regarding the outside air temperature, it is considered that the temperature cannot be lowered unless a long time has passed since the ignition switch was turned off. For this reason, when the vehicle handles temperature information, the temperature change amount from when the ignition switch is turned on to when it is turned on is measured by acquiring the temperature information through communication, and the temperature change amount If the temperature is equal to or higher than the temperature threshold value, the stored content may be cleared. In this way, by using the temperature information handled by the vehicle, a temperature threshold corresponding to that is set for each vehicle and each tire, and whether or not the temperature change amount for each wheel is equal to or higher than the temperature threshold is verified. You don't have to. For the outside air temperature, an outside air temperature sensor may be installed in the receiver 3, and data indicating the temperature may be acquired from the outside air temperature sensor. By providing the receiver 3 in this way, temperature measurement can be performed only by the receiver 3, and therefore temperature measurement can be performed regardless of other vehicle systems.

  Further, as the relationship between the pressure and the temperature, the stored content may be cleared when the ratio of the pressure and the temperature when the ignition switch is turned on and when the ignition switch is turned on satisfies a predetermined condition.

  In a state where there is no air leak from the tire, a state equation of PV = nRT is basically established based on the above-described Boyle Charles' law. For this reason, for example, when a difference in P / T value, which is a ratio of pressure and temperature, is obtained immediately before the ignition switch is turned off and when the ignition switch is turned on, and this difference exceeds a certain range. The stored contents may be cleared. For example, tire pressure and temperature data included in the received data may be used to calculate the difference between the straight line where the ignition switch is turned off and the P / T obtained from the data when the ignition switch is turned on. In this way, the relationship between the tire air pressure and the temperature can be obtained only by the receiver 3, so that the relationship can be obtained without depending on other vehicle systems.

DESCRIPTION OF SYMBOLS 1 Vehicle 2 Transmitter 3 Receiver 4 Indicator 5a-5d Wheel 6 Car body

Claims (6)

It is attached to each of a plurality of wheels (5a to 5d) equipped with tires, acquires the tire air pressure at the attached wheels (5a to 5d), and sets the tire air pressure at the transmission timing for each predetermined transmission cycle. A transmitter (2) for transmitting the indicated data;
A receiver (3) that is provided on the vehicle body (6) side, receives data indicating the tire pressure, and outputs a warning signal instructing a warning of a decrease in tire pressure when detecting a decrease in tire pressure;
In a tire pressure detecting device comprising: a display (4) that issues a warning of a decrease in tire pressure based on the warning signal from the receiver (3),
The transmitter (2) acquires the tire pressure at least for each transmission cycle, and transmits the acquired tire pressure data to the receiver (3),
The receiver (3) uses the tire pressure received this time as the current reception pressure, and a value obtained by reducing the pressure by a predetermined rate from the tire pressure received in the past is set as the first alarm threshold value. In addition, if the lower limit value of the tire pressure is equal to or lower than a warning threshold value which is a second warning threshold value, it is determined that the tire pressure is lowered, the warning signal is output , and the tire pressure received in the past is output. And when the difference between the received pressure and the current received pressure is equal to or greater than a predetermined value, the tire pressure data received in the past is stored, and the tire pressure received in the past is then received as data indicating the tire pressure. Is used for setting the first alarm threshold at the time, or data of a value obtained by reducing the pressure by the predetermined ratio from the tire pressure received in the past is stored, and Tire air pressure detecting device is characterized by using as said first alarm threshold upon reception of the data indicating the tire pressure. When the difference between the tire pressure received in the past and the current received pressure is greater than or equal to a predetermined value, the receiver (3) holds a memory of the tire pressure data received in the past for a predetermined period. Then, the tire pressure received in the past is used for setting the first alarm threshold when data indicating the tire pressure is received next, or the tire pressure received in the past is the predetermined ratio. 2. The tire pressure detection device according to claim 1 , wherein the tire pressure detection device according to claim 1 , wherein the tire pressure detection device stores the data of the value obtained by reducing the pressure and uses it as the first alarm threshold when the data indicating the tire pressure is received next time. . The receiver (3) is configured such that an elapsed time after the ignition switch is turned off exceeds a predetermined time, a temperature change amount after the ignition switch is turned off exceeds a predetermined temperature threshold, and an ignition When the difference between the tire air pressure and the temperature in the tire since the switch is turned off satisfies at least one of exceeding a certain range, the stored content of the stored data is cleared. The tire air pressure detecting device according to claim 2 . The receiver (3), said as the tire air pressure received in the past, any of claims 1 to 3, characterized by using a previous reception pressure is a tire air pressure received when the previous is the previous time The tire pressure detecting device according to claim 1. The said receiver (3) uses the maximum value of the tire pressure received during the predetermined number of receptions or the predetermined period before this time as the tire pressure received in the past. 4. The tire air pressure detection device according to any one of 3 above. The receiver (3) stores the pressure value of the tire pressure when it is determined that the tire pressure is reduced, and the tire pressure data sent from the transmitter (2) after the alarm is generated is indicated. When the tire air pressure exceeds a value obtained by adding an alarm cancellation hysteresis value to the pressure value at the time of the alarm occurrence, a release signal for instructing the alarm release is output to the display (4). The tire pressure detection device according to any one of claims 1 to 5 .

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