JP2005132304A - Tire air pressure alarm device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tire air pressure alarm device controlling so as to suppress the variation of an alarm threshold by a vehicle. <P>SOLUTION: A signal detection part 102 detects a signal including vibration component of a tire by a wheel speed sensor 30. A resonance frequency extraction part 108 detects a resonance frequency related to the air pressure of the tire from this signal. An alarm threshold processing part 118 sets the alarm threshold based on the detected resonance frequency. The resonance frequency extraction part 108 detects the resonance frequency a plurality of times and the alarm threshold processing part 118 appropriately renews the alarm threshold based on it. An alarm informing part 116 warns a driver of the effect that the air pressure of the tire is reduced when the resonance frequency detected by the resonance frequency extraction part 108 is less than the alarm threshold in the traveling of the vehicle. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a tire pressure alarm device, and more particularly to a technique for determining a threshold value for determining whether or not to notify a tire pressure alarm.

  In order for the vehicle to travel safely, it is important that the tire air pressure is kept above a certain value. Since the tire air pressure gradually decreases as the vehicle travels, it is necessary to appropriately monitor the tire air pressure when the vehicle travels.

  As a method for estimating the tire air pressure, there is a method of extracting a vibration component of the tire during traveling of the vehicle. In this method, a vibration component caused by tire vibration is extracted from a wheel speed signal, and a resonance frequency is obtained from the vibration component. A relationship is established between the tire pressure and the resonance frequency of the tire that the resonance frequency is lower as the tire pressure is lower. Therefore, the tire pressure can be estimated by measuring the resonance frequency. This method has an advantage that the tire pressure can be indirectly estimated by measuring the resonance frequency without providing a means for directly measuring the tire pressure such as a pressure sensor (for example, patent) Reference 1).

  The tire pressure warning device based on this method warns the driver that the tire pressure has dropped if the resonance frequency of the tire monitored during the running of the vehicle falls below a predetermined threshold (hereinafter referred to as “pneumatic pressure drop warning”). Notification). Thereby, it is possible to avoid a state in which the vehicle travels in a state where the tire air pressure is too low.

In this apparatus, it is necessary to set a frequency threshold value (hereinafter referred to as “alarm threshold value”) that determines the timing at which the tire resonance frequency decreases and the driver should be warned. Usually, when a tire is attached to a vehicle, a process for determining an alarm threshold according to the characteristics of the vehicle and the tire is started. When the vehicle is running, the resonance frequency of the tire is detected, and for example, a frequency lower than the detected resonance frequency by a predetermined value is set as the alarm threshold value. In the conventional tire air pressure alarm device, the alarm threshold value corresponding to the characteristics of the vehicle and the tire has been determined in this way.
JP 11-235907 A

  The environment at the time of various measurements such as outside air temperature, wheel speed, and road surface condition affects the resonance frequency of the tire. For example, due to the properties of the tire as rubber, the resonance frequency increases when the tire temperature is low, and decreases at a high temperature. As a result, there is a possibility that the alarm threshold value varies depending on the same tire pressure due to a difference in measurement conditions.

  The present invention has been made in view of these problems, and an object of the present invention is to provide a tire air pressure alarm device that performs control so as to suppress variations in alarm thresholds caused by vehicles.

  In order to solve the above-described problems, a tire pressure alarm device according to the present invention relates to tire pressure from signal detection means for detecting a signal including a vibration component of a tire when the vehicle travels, and from the signal including the detected vibration component. Resonance frequency detection means for detecting a resonance frequency, threshold setting means for setting a predetermined threshold based on the resonance frequency detected a plurality of times by the resonance frequency detection means, and the detected resonance frequency for the set threshold value An alarm notifying means for notifying an alarm when triggered by being below is provided.

  Since a plurality of resonance frequencies are detected and an alarm threshold value is set based on these, it is effective in suppressing variation of the alarm threshold value due to measurement conditions. As an example, the resonance frequency may be detected a plurality of times, and the alarm threshold may be set based on the average value of the detected resonance frequencies.

  The threshold setting means may set the threshold based on the largest resonance frequency among the plurality of resonance frequencies detected by the resonance frequency detection means.

  For example, when the outside air temperature is high, the resonance frequency of the tire is low, so that the alarm threshold may be set low under such measurement conditions. According to the aspect of the present invention, since the alarm threshold is set based on the highest resonance frequency among the resonance frequencies measured a plurality of times, the alarm threshold can be set higher by absorbing the difference in measurement conditions. By setting the alarm threshold value higher, an air pressure decrease alarm is likely to occur, which is effective for the vehicle to travel safely.

  The threshold setting means may update the threshold based on the resonance frequency detected by the resonance frequency detection means even after setting the threshold.

  The threshold setting means is further based on the resonance frequency detected by the resonance frequency detection means even after the alarm notification means has started a determination process as to whether or not to notify an alarm based on the set threshold. The threshold value may be updated.

  The tire pressure warning device further includes band setting means for setting a predetermined frequency band, and the threshold setting means is configured to select the threshold based on a resonance frequency within the set frequency band among the detected resonance frequencies. May be set.

  When the detected resonance frequency is too high or low, it may be caused by various abnormal factors such as the measurement conditions being far from the external environment during normal driving, or the detection device being malfunctioning. is there. According to the aspect of the present invention, it is possible to avoid setting an alarm threshold based on a resonance frequency detected in an abnormal state by setting a frequency range in which the resonance frequency is to be detected. It is effective.

  The tire pressure warning device further includes wheel speed detecting means for detecting the wheel speed of the vehicle, and the threshold value setting means sets the resonance speed at which the detected wheel speed is equal to or higher than a predetermined value when the resonance frequency is detected. Based on this, the threshold value may be set.

  The resonance frequency is also affected by the road running state of the vehicle. According to the aspect of the present invention, the alarm threshold is set based on the detected resonance frequency when the detected wheel speed is equal to or higher than a certain value. Therefore, for example, it is effective in avoiding setting the alarm threshold based on the resonance frequency detected in an abnormal state such as when driving slowly, idling, or traveling on a rough road.

  Filtering means for passing only a signal within a predetermined frequency band among signals including vibration components of the tire, and band control means for controlling a position of a frequency band through which the signal is allowed to pass, the resonance frequency detection The means detects a resonance frequency from the signal passed by the filtering means, and the band control means is based on a difference value between the detected resonance frequency and a center value of a frequency band through which the signal should pass. The position of the frequency band may be changed.

  According to the tire air pressure alarm device having the above-described configuration, it is possible to suppress variations in the threshold value for notifying the air pressure lowering alarm, which is effective even when the driver performs safe driving.

  According to the tire pressure alarm device of the present invention, it is possible to suppress variations in the alarm threshold value for notifying the alarm to be notified when the tire air pressure decreases.

  FIG. 1 is a diagram illustrating a hardware configuration of a tire pressure alarm device. The left front wheel 32a, the right front wheel 32b, the left rear wheel 32c, and the right rear wheel 32d of the vehicle 10 are respectively provided with a left front wheel speed sensor 30a, a right front wheel speed sensor 30b, and a left rear wheel. A wheel speed sensor 30c for wheels and a wheel speed sensor 30d for the right rear wheel are provided. Hereinafter, the left front wheel speed sensor 30a, the right front wheel speed sensor 30b, the left rear wheel speed sensor 30c, and the right rear wheel speed sensor 30d are collectively referred to as a "wheel speed sensor 30". Further, the left front wheel 32a, the right front wheel 32b, the left rear wheel 32c, and the right rear wheel 32d are collectively referred to as “wheels 32”. The wheel speed sensor 30 includes a rotor that rotates together with the wheel 32, a plurality of teeth provided at a constant pitch on the outer periphery of the rotor, and an electromagnetic pickup that electromagnetically detects passage of these teeth as the rotor rotates. . Then, an AC signal generated in the electromagnetic pickup is taken into the tire pressure alarm device 100 as a wheel speed signal that is an output of the wheel speed sensor 30.

  The tire pressure warning device 100 extracts a signal including a tire vibration component (hereinafter referred to as a “vibration component signal”) from the wheel speed signal acquired from each wheel speed sensor 30 by frequency analysis. A resonance frequency related to tire air pressure is detected from the extracted vibration component signal, and based on the resonance frequency, it is determined whether or not the actual tire air pressure is below the alarm threshold. Hereinafter, the process of determining whether or not the detected resonance frequency is below the alarm threshold is referred to as “alarm determination process”, and the process for setting the alarm threshold is referred to as “initial setting process”. The stop lamp signal sensor 20 generates a stop lamp signal when the driver depresses the brake. The tire pressure alarm device 100 also acquires this stop lamp signal as an input signal.

  FIG. 2 is a functional block diagram showing the configuration of the tire pressure alarm device. Each block shown here can be realized in hardware by an element such as a CPU of a computer or a mechanical device, and in software it is realized by a computer program or the like. Draw functional blocks. Therefore, those skilled in the art will understand that these functional blocks can be realized in various forms by a combination of hardware and software.

  The signal detection unit 102 appropriately acquires the wheel speed signal of each wheel 32 from the wheel speed sensor 30 and the stop lamp signal from the stop lamp signal sensor 20. The vibration component signal when the vehicle 10 is traveling also includes a frequency component that is a noise component that is not related to a change in tire air pressure. The frequency filter unit 104 filters the vibration component signal with a frequency filter having a frequency bandwidth of 23 Hz, for example, in order to filter only the vibration component signal near the resonance frequency related to the tire pressure. Hereinafter, this frequency filter is particularly referred to as a “signal extraction filter”. The filter control unit 106 moves the frequency position of the signal extraction filter and performs control so that the center value of the signal extraction filter matches the resonance frequency. The resonance frequency extraction unit 108 extracts the tire resonance frequency from the vibration component signal that has passed through the signal extraction filter set by the frequency filter unit 104. For example, when the frequency band of the signal extraction filter is 34.0 Hz to 57.0 Hz, its center value is 45.5 Hz. When the resonance frequency detected through this signal extraction filter is 48.0 Hz, the resonance frequency is 2.5 Hz higher than the center value. At this time, the filter control unit 106 controls to raise the position of the signal extraction filter by 2.5 Hz. That is, the filter control unit 106 performs control so that the frequency band of the signal extraction filter is changed from 36.5 Hz to 59.5 Hz. The signal detection unit 102 periodically acquires a vibration component signal, and accordingly, the frequency filter unit 104, the filter control unit 106, and the resonance frequency extraction unit 108 repeat the above processing, and finally the filter control unit 106 Sets the signal extraction filter at the proper position. When the position of the signal extraction filter is determined in the initial setting process described in detail later, the position may be fixed as it is until the tire is replaced. The position of may be updated.

  The resonance frequency selection unit 110 performs a selection process of the resonance frequency extracted by the resonance frequency extraction unit 108. Even if the resonance frequency is extracted, depending on the measurement conditions at the time of extraction, it may not be appropriate to perform processing based on the resonance frequency. For example, the resonance frequency selection unit 110 does not select the resonance frequency detected when the signal detection unit 102 acquires a stop lamp signal from the stop lamp signal sensor 20. The resonance frequency selection unit 110 includes a wheel speed determination unit 112 and a frequency range determination unit 114. The wheel speed determination unit 112 determines whether or not the wheel speed when the resonance frequency is detected is equal to or higher than a predetermined value. The resonance frequency selection unit 110 does not select the resonance frequency detected when the wheel speed detected by the wheel speed sensor 30 is equal to or lower than a predetermined value. The frequency range determination unit 114 determines whether or not the value of the resonance frequency is included in a predetermined frequency range. The resonance frequency selection unit 110 does not select when the detected resonance frequency is outside this frequency range.

  The resonance frequency selection unit 110 stores the selected resonance frequency in the resonance frequency storage unit 120. The alarm threshold value processing unit 118 determines an alarm threshold value based on the resonance frequency stored in the resonance frequency storage unit 120 and stores it in the alarm threshold value storage unit 122. For example, the alarm threshold value processing unit 118 sets a frequency 3 Hz lower than the resonance frequency stored in the resonance frequency storage unit 120 as the alarm threshold value. For example, when the resonance frequency is detected three times and the maximum value is 47.0 Hz, 44.0 Hz which is a value lower by 3 Hz is set as the alarm threshold. Alternatively, the alarm threshold processing unit 118 may set the alarm threshold based on an average value of a plurality of resonance frequencies stored in the resonance frequency storage unit 120. For example, when the resonance frequency is detected three times and the average value is 46.5 Hz, the alarm threshold value processing unit 118 may set 43.5 Hz, which is a value lower by 3 Hz, as the alarm threshold value. In the alarm determination process, the alarm notification unit 116 compares the resonance frequency selected by the resonance frequency selection unit 110 with the alarm threshold stored in the alarm threshold storage unit 122. If the resonance frequency is below the alarm threshold, the alarm notification unit 116 notifies the driver. Notify low air pressure warning. The alarm notification unit 116 may acquire the resonance frequency from the resonance frequency extraction unit 108. The air pressure lowering alarm may be notified by an in-vehicle display device (not shown), or may be notified by a voice device such as a voice or a buzzer.

FIG. 3 is a diagram showing the relationship between the frequency and the signal intensity in the vibration signal component depending on the tire air pressure. The horizontal axis indicates the frequency of the tire vibration component signal detected by the wheel speed sensor 30, and the vertical axis indicates the intensity. Generally, if the resonance frequency is different by 1 Hz, the tire air pressure is different by about 20 kilopascals. Since the normal tire pressure is about 200 kilopascals, a difference of 1 Hz in the resonance frequency corresponds to a difference of about 10% of the tire pressure. F _H from f _L of FIG. 3 shows the frequency band of the signal extraction filter. f _S represents the resonance frequency extracted by the resonance frequency extraction unit 108. The filter control unit 106 moves the frequency position of the signal extraction filter so that the center value of the signal extraction filter matches the detected resonance frequency by the method described above.

  When a new tire is attached to the vehicle 10, an initial setting process is executed. In the initial setting process, the alarm threshold processing unit 118 sets an alarm threshold based on the resonance frequency extracted by the resonance frequency extraction unit 108. The resonance frequency extraction unit 108 detects the resonance frequency multiple times at regular time intervals. When the detected resonance frequency is higher than the center value of the signal extraction filter, the filter control unit 106 moves the position of the signal extraction filter in the direction of high frequency, and controls so that the center value of the signal extraction filter matches the resonance frequency. To do. On the other hand, when the center value of the signal extraction filter is lower than the detected resonance frequency, the filter control unit 106 does not move the signal extraction filter. The alarm threshold value processing unit 118 is controlled so that the alarm threshold value is not set low by controlling the signal extraction filter not to move to the low frequency side in the initial setting process. Since the alarm threshold value is not updated low, there is a merit that it is not easily affected by natural leakage of air in the tire.

FIG. 4 is a schematic diagram illustrating a state in which a difference occurs in the alarm determination processing result due to variation in the alarm threshold. f _I1 is a resonance frequency detected in the initial setting process, and f _T1 indicates an alarm threshold obtained based on f _I1 . _{Here, f T1} is set from _{f I1} to 3Hz partial low value. f _I2 is a resonance frequency detected in the initial setting process under another measurement condition, and f _T2 indicates an alarm threshold obtained based on f _I2 . _{Similarly, f T2} is set from _{f I2} to 3Hz partial low value. f _SR indicates the resonance frequency detected when the alarm determination process is performed. If _{the f T1} is set as the alarm _{threshold, f SR} because below _{f T1,} alarm notification section 116 notifies the deflation warning. On the other hand, when the f _T2 is set as an alarm threshold value, f _SR is is greater than f _T2, the alarm notification section 116 does not notify the deflation warning. The tire air pressure alarm device 100 according to the present embodiment is effective in suppressing variation in alarm threshold value due to such a difference in measurement conditions during the initial setting process.

  FIG. 5 is a flowchart showing an initial setting process for setting a tire air pressure alarm threshold. In the initial setting process, the resonance frequency is detected a plurality of times. The detection of the resonance frequency is periodically performed at regular time intervals. The number of times that the resonance frequency is detected for the initial setting process is hereinafter referred to as “setting update number”. Prior to the initial setting process, the setting update count and the resonance frequency are first set to zero as an initial value. When the initial setting process is started, first, the alarm threshold value processing unit 118 increments the number of setting updates (S10). The resonance frequency extraction unit 108 extracts the resonance frequency via the signal extraction filter (S12). If the number of setting updates is within 3 (N of S14), the resonance frequency detected in S12 is compared with the resonance frequency detected in the previous step of S12 (S16). Note that immediately after the start of the initial setting process, zero is used as the resonance frequency detected last time, and therefore the process automatically proceeds to S18. When the number of setting updates exceeds 3 (Y in S14), the initial setting process is terminated.

  If the resonance frequency detected in S12 is larger than the resonance frequency detected last time (Y in S16), the filter control unit 106 moves the signal extraction filter to the high frequency side, and the resonance frequency and the center value of the signal extraction filter To match. Then, the position of the signal extraction filter after movement is set as a new position (S18). In the subsequent initial setting process, the process is performed based on the signal extraction filter after the movement. When the position of the signal extraction filter is updated, an alarm threshold is set by calculation based on the position of the resonance frequency extracted in S12 (S20). If the detected resonance frequency is equal to or lower than the previously detected resonance frequency (N in S16), the process returns to S10 without updating the alarm threshold.

  FIG. 6 is a flowchart showing an alarm determination process for notifying an air pressure reduction alarm. After the initial setting process described with reference to FIG. 5 is completed and the alarm threshold value is set, the alarm determination process is performed. When the vehicle 10 starts running, the resonance frequency extraction unit 108 detects the resonance frequency (S30). When the detected resonance frequency falls below the alarm threshold (Y in S32), the alarm notification unit 116 notifies an alarm (S34). The above processing is performed every time the resonance frequency is detected at a constant time interval while the vehicle 10 is traveling.

  The initial setting process described with reference to FIG. 5 and the alarm determination process described with reference to FIG. 6 may be performed in parallel. For example, once the alarm threshold is determined by the initial setting process, the alarm notification determination may be performed based on the alarm threshold. On the other hand, an initial setting process is performed based on the resonance frequency detected in the alarm determination process to determine whether the alarm threshold should be updated. With this control, the alarm determination process can be performed while performing the initial setting process.

  Hereinafter, the correspondence relationship between the tire pressure alarm device of the present embodiment and the members in the claims will be exemplified. Mainly, the signal detection unit 102 in FIG. 2 is the “signal detection unit” in claim 1 and the “wheel speed detection unit” in claim 6, and the resonance frequency extraction unit 108 is in the resonance frequency detection unit in claim 1. The processing unit 118 is a “threshold setting unit”, the alarm notification unit 116 is a “warning notification unit”, and the frequency range determination unit 114 is a “band setting unit”. The section 104 corresponds to the “filtering means” in claim 7, and the filter control section 106 corresponds to the “band control means” in claim 7.

  The present invention has been described above based on the embodiment. The present invention is not limited to this embodiment, and various modifications thereof are also effective as aspects of the present invention.

It is a figure which shows the hardware constitutions of a tire pressure alarm device. It is a functional block diagram which shows the structure of a tire pressure alarm device. It is a figure which shows the relationship between the frequency and signal strength in the vibration signal component depending on tire pressure. It is a schematic diagram which shows a mode that a difference arises in the alarm determination processing result by the dispersion | variation in an alarm threshold value. It is a flowchart which shows the initial setting process process which sets the warning threshold value of a tire pressure. It is a flowchart which shows the alarm determination process process for notifying an air pressure fall alarm.

Explanation of symbols

  30 wheel speed sensor, 100 tire pressure alarm device, 102 signal detection unit, 104 frequency filter unit, 106 filter control unit, 108 resonance frequency extraction unit, 110 resonance frequency selection unit, 112 wheel speed determination unit, 114 frequency range determination unit, 116 alarm notification unit, 118 alarm threshold processing unit, 120 resonance frequency storage unit, 122 alarm threshold storage unit.

Claims (7)

Signal detection means for detecting a signal including a vibration component of a tire when the vehicle is running;
Resonance frequency detection means for detecting a resonance frequency related to tire air pressure from a signal including the detected vibration component;
Threshold setting means for setting a predetermined threshold based on the resonance frequency detected a plurality of times by the resonance frequency detection means;
A tire pressure warning device comprising: a warning notification means for notifying a warning when the detected resonance frequency falls below the set threshold value.   2. The tire pressure alarm device according to claim 1, wherein the threshold value setting unit sets the threshold value based on a highest resonance frequency among a plurality of resonance frequencies detected by the resonance frequency detection unit.   3. The tire pressure alarm device according to claim 1, wherein the threshold value setting unit updates the threshold value based on the resonance frequency detected by the resonance frequency detection unit even after the threshold value is set. 4. .   The threshold setting means is further based on the resonance frequency detected by the resonance frequency detection means even after the alarm notification means has started a determination process as to whether or not to notify an alarm based on the set threshold. The tire pressure alarm device according to claim 3, wherein the threshold value is updated. A band setting means for setting a predetermined frequency band;
The tire pressure according to any one of claims 1 to 4, wherein the threshold value setting means sets the threshold value based on a resonance frequency within the set frequency band among the detected resonance frequencies. Alarm device. A wheel speed detecting means for detecting a wheel speed of the vehicle;
6. The threshold value setting unit according to claim 1, wherein the threshold value setting means sets the threshold value based on a resonance frequency at which a wheel speed detected at the time of detection of the resonance frequency is a predetermined value or more. Tire pressure alarm device. Filtering means for allowing only signals within a predetermined frequency band to pass among signals including vibration components of the tire,
Band control means for controlling the position of the frequency band through which the signal is to pass, and
The resonance frequency detecting means detects a resonance frequency from the signal passed by the filtering means, and the band control means is a difference value between the detected resonance frequency and a center value of a frequency band to pass the signal. The tire pressure alarm device according to any one of claims 1 to 6, wherein the position of the frequency band is changed based on

Images