Inner pressure change detection device, inner pressure change detection method, and inner pressure change detection program for tire

Abstract

To provide an inner pressure change detection device for a tire, which can detect an inner pressure change of the tire including decreased pressure and increased pressure.SOLUTION: This inner pressure change detection device for a tire comprises: an acquisition unit; an index calculation unit; a resonance frequency calculation unit; and an inner pressure change determination unit. The acquisition unit acquires rotation speed information of a plurality of tires included in a vehicle. The index calculation unit calculates a relative index for comparing the rotation speeds of the tires on the basis of the acquired rotation speed information. The resonance frequency calculation unit identifies a resonance frequency of at least one of the tires on the basis of the acquired rotation speed information. The inner pressure change determination unit determines an inner pressure change including increased pressure of the tires on the basis of the calculated relative index and the identified resonance frequency.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a technique for detecting changes in the internal pressure of a tire included in a vehicle. [Background technology]

[0002] To ensure a vehicle runs smoothly, it is important to keep tire pressure properly adjusted. If tire pressure falls below the proper value, problems such as poor ride comfort and poor fuel economy can occur. For this reason, research has been conducted on systems that automatically detect tire deflation (Tire Pressure Monitoring Systems; TPMS). Information that a tire is deflated can be used, for example, to warn the driver.

[0003] Methods for detecting tire deflation include direct measurement of tire air pressure using a pressure sensor attached to the tire, as well as indirect evaluation of tire deflation using other indicators. Known methods include the Dynamic Loaded Radius (DLR) method and the Resonance Frequency Method (RFM). The DLR method utilizes the phenomenon that a deflated tire compresses during driving, reducing its dynamic loaded radius and causing it to rotate faster, and estimates tire deflation from the tire's rotational speed. Meanwhile, the RFM method utilizes the fact that when a tire deflates, the spring constant in the tire's sidewall changes, resulting in a change in resonance frequency.

[0004] Patent Document 1 discloses a low-pressure detection device that uses both the DLR method and the RFM method. In Patent Document 1, the absolute amount of low-pressure in the front tires is calculated from the resonance frequencies RF1 and RF2 of the front tires. In addition, low-pressure indicators DEL1 to DEL3 are calculated for evaluating low-pressure in the DLR method. In Patent Document 1, DEL1 to DEL3 are defined as follows: where V1 to V4 are the rotational speeds of the left front wheel, right front wheel, left rear wheel, and right rear wheel tires, respectively. DEL1=[(V1+V4) / 2-(V2+V3) / 2] / [(V1+V2+V3+V4) / 4]×100(%) DEL2=[(V1+V2) / 2-(V3+V4) / 2] / [(V1+V2+V3+V4) / 4]×100(%) DEL3=[(V1+V3) / 2-(V2+V4) / 2] / [(V1+V2+V3+V4) / 4]×100(%)

[0005] In Patent Document 1, the absolute amount of pressure reduction of the left front wheel, right front wheel, left rear wheel, and right rear wheel tires is estimated by appropriately combining the absolute amount of pressure reduction of the front wheel tires and the pressure reduction indicators DEL1 to DEL3. This makes it possible to accurately detect the absolute amount of pressure reduction of each tire even if the tires have various pressure reduction patterns. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2019-111896 Summary of the Invention [Problem to be solved by the invention]

[0007] Patent Document 1 only anticipates detecting a depressurized tire state, where the air pressure has decreased from the normal internal pressure. However, in reality, it is not desirable to leave an inflated tire state, where the air pressure has increased from the normal internal pressure, unattended. An inflated tire state can occur due to factors such as the driver adjusting the tire pressure to a level higher than the normal internal pressure, or an increase in tire pressure due to rising temperatures.

[0008] An object of the present invention is to provide a tire internal pressure change detection device, an internal pressure change detection method, and an internal pressure change detection program that can detect changes in tire internal pressure, including pressure increases. [Means for solving the problem]

[0009] A tire internal pressure change detection device according to a first aspect of the present invention includes an acquisition unit, an index calculation unit, a resonance frequency identification unit, and an internal pressure change determination unit. The acquisition unit acquires rotational speed information of multiple tires included in a vehicle. The index calculation unit calculates a relative index for comparing the rotational speeds of the multiple tires based on the acquired rotational speed information. The resonance frequency identification unit identifies the resonance frequency of at least one tire of the multiple tires based on the acquired rotational speed information. The internal pressure change determination unit determines internal pressure changes, including pressure increases, of the multiple tires based on a combination of the calculated relative index and the identified resonance frequency.

[0010] A tire internal pressure change detection device according to a second aspect is the tire internal pressure change detection device according to the first aspect, wherein the resonance frequency identification unit identifies the resonance frequencies of at least two tires that are mounted coaxially among the plurality of tires.

[0011] A tire internal pressure change detection device according to a third aspect is an internal pressure change detection device according to the first or second aspect, wherein the plurality of tires include a first tire mounted on a first axle, a second tire mounted on the first axle, a third tire mounted on the same side of the second axle as the first tire, and a fourth tire mounted on the same side of the second axle as the second tire.

[0012] A tire internal pressure change detection device according to a fourth aspect is the tire internal pressure change detection device according to any one of the first aspect to the third aspect, wherein the relative indicators include an indicator that compares the rotational speed of the first tire and the rotational speed of the fourth tire with the rotational speed of the second tire and the rotational speed of the third tire, an indicator that compares the rotational speed of the first tire and the rotational speed of the second tire with the rotational speed of the third tire and the rotational speed of the fourth tire, and an indicator that compares the rotational speed of the first tire and the rotational speed of the third tire with the rotational speed of the second tire and the rotational speed of the fourth tire.

[0013] A tire internal pressure change detection method according to a fifth aspect is a tire internal pressure change detection method executed by one or more computers, and includes the following. Acquiring rotational speed information of multiple tires included in a vehicle Calculating a relative index for comparing the rotational speeds of the plurality of tires based on the acquired rotational speed information. Identifying a resonance frequency of at least one tire among the plurality of tires based on the acquired rotational speed information. Determining internal pressure changes, including pressure increases, of the plurality of tires based on a combination of the calculated relative index and the identified resonance frequency.

[0014] A tire internal pressure change detection program according to a sixth aspect causes one or more computers to perform the following: Acquiring rotational speed information of multiple tires included in a vehicle Calculating a relative index for comparing the rotational speeds of the plurality of tires based on the acquired rotational speed information. Identifying a resonance frequency of at least one tire among the plurality of tires based on the acquired rotational speed information. Determining internal pressure changes, including pressure increases, of the plurality of tires based on a combination of the calculated relative index and the identified resonance frequency. [Effects of the Invention]

[0015] According to the present invention, it is possible to detect changes in tire internal pressure, including pressure increases and decreases. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a schematic diagram showing an internal pressure change detection device according to an embodiment of the present invention mounted on a vehicle; [Figure 2] FIG. 2 is a block diagram showing the electrical configuration of the internal pressure change detection device. [Figure 3] 10 is a flowchart showing the flow of an internal pressure change detection process. DETAILED DESCRIPTION OF THE INVENTION

[0017] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a reduced pressure detection device, a reduced pressure detection method, and a reduced pressure detection program according to embodiments of the present invention will be described with reference to the accompanying drawings.

[0018] <1. Configuration of the reduced pressure detection device> FIG. 1 is a schematic diagram showing an internal pressure change detection device 2 (hereinafter also simply referred to as "detection device 2") according to this embodiment mounted on a vehicle 1. The vehicle 1 is a four-wheel vehicle, and is equipped with a left front wheel FL, a right front wheel FR, a left rear wheel RL, and a right rear wheel RR. In this embodiment, the vehicle 1 is a FF (front drive, front engine) vehicle, and two wheels on the front axle (first axle) drive and rotate, while two wheels on the rear axle (second axle) rotate driven. The detection device 2 detects the internal pressure change of tires T mounted on these wheels. FL (First tire), T FR (2nd tire), T RL (Third tire) and T RR When a pressure increase or decrease equal to or greater than a predetermined threshold is detected, a warning to that effect is issued via a warning indicator 3 mounted on the vehicle 1. The flow of such internal pressure change detection processing will be described in detail later.

[0019] Tire T FL ,T FR ,T RL ,T RR The change in internal pressure of the tire is detected based on the rotation speed of the left front wheel FL, the right front wheel FR, the left rear wheel RL, and the right rear wheel RR. The left front wheel FL, the right front wheel FR, the left rear wheel RL, and the right rear wheel RR are each equipped with a wheel speed sensor 6, and each wheel speed sensor 6 detects rotation speed information (in other words, tire T FL ,T FR ,T RL ,T RRThe wheel speed sensor 6 is connected to the detection device 2 via a communication line 5. The rotation speed information detected by the wheel speed sensor 6 is transmitted to the detection device 2 via the communication line 5 in real time.

[0020] Any type of wheel speed sensor 6 can be used as long as it can detect the wheel speeds of the wheels FL, FR, RL, and RR while the vehicle is moving. For example, a sensor of the type that measures wheel speed from the output signal of an electromagnetic pickup can be used, or a sensor of the type that generates electricity using rotation, like a dynamo, and measures wheel speed from the resulting voltage can be used. The installation position of the wheel speed sensor 6 is not particularly limited, and can be selected appropriately depending on the type of sensor, as long as it is capable of detecting wheel speed.

[0021] FIG. 2 is a block diagram showing the electrical configuration of the detection device 2. The detection device 2 is an on-board computer installed in the vehicle 1, and as shown in FIG. 2, includes an I / O interface 11, a CPU (Central Processing Unit) 12, a ROM (Read Only Memory) 13, a RAM (Random Access Memory) 14, and a non-volatile rewritable storage device 15. The I / O interface 11 is a communication device that realizes communication with external devices such as the wheel speed sensor 6 and the warning indicator 3. The ROM 13 stores a program 9 for controlling the operation of each part of the vehicle 1. The program 9 is written to the ROM 13 from a storage medium 8 such as a CD-ROM. The CPU 12 reads and executes the program 9 from the ROM 13, thereby virtually operating as an acquisition unit 20, an index calculation unit 21, a resonance frequency identification unit 22, an internal pressure change determination unit 23, and an alarm generation unit 24. The operation of each unit 20 to 24 will be described in detail below. The storage device 15 is configured with a hard disk, a flash memory, or the like. The program 9 may be stored in the storage device 15 instead of the ROM 13. The RAM 14 and the storage device 15 are used for the calculations of the CPU 12 as appropriate.

[0022] The warning indicator 3 can be realized in any form, such as a liquid crystal display element or a liquid crystal monitor, as long as it can notify the user that a change in tire internal pressure has occurred. The mounting position of the warning indicator 3 is not particularly limited and can be selected as appropriate, but it is preferable to mount it in a location that is easy for the driver to see, such as on the instrument panel. If the detection device 2 is connected to a car navigation system, the monitor for the car navigation system can also be used as the warning indicator 3. If a monitor is used as the warning indicator 3, the warning can be displayed as an icon or text information on the monitor.

[0023] <2. Internal pressure change detection process> Referring to Figure 3, tire T FL ,T FR ,T RL ,T RR An internal pressure change detection process for detecting an internal pressure change in at least one of the above will be described. The internal pressure change detection process shown in Fig. 3 is a combination of the dynamic load radius (DLR) method and the resonance frequency (RFM) method, which are known methods for detecting low pressure, and in this embodiment, the low pressure index described in Patent Document 1 and the resonance frequencies of the first tire and the second tire are derived. The internal pressure change detection process shown in Fig. 3 is executed repeatedly at a predetermined cycle, for example, while the electrical system of the vehicle 1 is in an ON state.

[0024] First, the acquisition unit 20 acquires time-series rotation speed information from each wheel speed sensor 6 attached to the wheels FL, FR, RL, and RR (step S1). FL ,T FR ,T RL ,T RR These are converted into rotational speeds V1 to V4 and stored in the RAM 14 or the storage device 15.

[0025] Next, the index calculation unit 21 determines whether the data saved in step S1 is valid (step S2). Valid data is data acquired when the vehicle 1 is in a steady driving condition. The dynamic load radius of a tire varies depending not only on the tire internal pressure state but also on the driving conditions of the vehicle 1, so it is preferable that data acquired during extreme acceleration / deceleration or cornering, for example, is not used in subsequent processing and is rejected. If it is determined in step S2 that the data is valid (YES), step S3 is then executed. If it is determined in step S2 that the data is not valid (NO), step S1 is executed again.

[0026] Next, the index calculation unit 21 calculates relative indexes for comparing the rotational speeds of the tires based on the rotational speeds V1 to V4 (step S3). The relative indexes in this embodiment include three indexes DEL1 to DEL3 defined by the following equations (1) to (3). DEL1=[(V1+V4) / 2-(V2+V3) / 2] / [(V1+V2+V3+V4) / 4]×100(%) (1) DEL2=[(V1+V2) / 2-(V3+V4) / 2] / [(V1+V2+V3+V4) / 4]×100(%) (2) DEL3=[(V1+V3) / 2-(V2+V4) / 2] / [(V1+V2+V3+V4) / 4]×100(%) (3)

[0027] As shown in the above formula, the indicator DEL1 of this embodiment is FL and tire T RR and tire T FR and tire T RL The indicator DEL2 is an index for comparing the rotation speed of the tire T FL and tire T FR and tire T RL and tire T RR The indicator DEL3 is an index for comparing the rotation speed of the tire T FL and tire T RL and tire T FR and tire T RRIn other words, DEL1 is an index for comparing the average rotational speed of pairs of tires located diagonally on the vehicle 1, DEL2 is an index for comparing the average rotational speed of pairs of tires mounted on the same axle of the vehicle 1, and DEL3 is an index for comparing the average rotational speed of pairs of tires located on the same left and right sides of the vehicle 1.

[0028] The relative indicators DEL1 to DEL3 are tire T FL ,T FR ,T RL ,T RR Depending on the pattern of the internal pressure change of tire T FL ,T FR ,T RL ,T RR These values ​​may change to the positive side, change to the negative side, or barely change from the reference value (0 or a value close to 0) when the tire is under normal internal pressure. FL ,T FR ,T RL ,T RR If positive and negative thresholds of the relative indicators DEL1 to DEL3 are determined when the amount of change in internal pressure reaches a warning threshold (for example, a 20% decrease or increase in pressure relative to the normal internal pressure), if any of the relative indicators DEL1 to DEL3 is above or below these warning thresholds, it can be inferred that a change in internal pressure that reaches the warning threshold has occurred in one of the tires. These warning thresholds are specified in advance and stored in the storage device 15 or ROM 13.

[0029] However, by comparing the relative indicators DEL1 to DEL3 with the predetermined thresholds, it is not possible to distinguish between a case where the pressure in one or two specific tires has dropped to the warning threshold and a case where the pressure in three or two tires other than the specific tire has risen to the warning threshold.Furthermore, the relative indicators DEL1 to DEL3 show almost no change even when the pressure in all tires has dropped to the warning threshold or when the pressure in all tires has risen to the warning threshold, so these cases cannot be detected.

[0030] Therefore, the resonance frequency identifying unit 22 determines the tire T FL The resonance frequency R1 and the tire T FRThe resonance frequency identifying unit 22 further identifies the resonance frequency R2 of the tire T from the rotational speeds V1 and V2 of the wheels FL and FR (step S4). FL and T FR More specifically, the resonance frequency identification unit 22 receives an input u from the road surface and calculates the resonance frequencies R1 and R2 of the tire T FL Assume a transfer function G(s) whose output is the rotational speed θ of the tire T. The resonance frequency identifying unit 22 assigns white noise to the input u and the rotational speed V1 to the rotational speed θ, and identifies the transfer function G(s) by sequential updating. Next, the resonance frequency identifying unit 22 converts the transfer function G(s) into a function G(f) in the frequency domain by substituting s=jω(ω=2πf) into the transfer function G(s). Furthermore, the resonance frequency identifying unit 22 calculates the power spectrum of G(f), and identifies f at which the power spectrum of G(f) is maximized as the frequency of the tire T. FL The resonance frequency identifying unit 22 identifies the resonance frequency R1 of the tire T FR The same procedure is used to identify the resonant frequency R2.

[0031] Since the power spectrum contains various noises, it is preferable to average the results of a predetermined number of calculations. Therefore, the resonance frequency identifying unit 22 may identify the resonance frequencies R1 and R2 based on the power spectrum thus averaged. In this embodiment, the resonance frequencies R1 and R2 are identified as the resonance frequencies in the torsional direction. However, the method for identifying the resonance frequencies R1 and R2 is not limited to the above method.

[0032] The resonance frequency of the tire is set to the reference resonance frequency when the tire is under normal internal pressure, and changes to the lower frequency side when the tire is depressurized and changes to the higher frequency side when the tire is pressurized. FL and T FR For each of the tires T, the resonance frequency when the pressure is reduced to a predetermined rate that does not reach the warning threshold is specified in advance, and this is set as the lower threshold for determining the resonance frequency. FL and T FRFor each of the resonant frequencies R1 and R2, the resonant frequencies when they are boosted to a predetermined rate that does not reach the warning threshold are specified in advance, and these are set as the upper thresholds for judging the resonant frequencies. The lower and upper thresholds for judging the resonant frequencies R1 and R2 are stored in advance in the storage device 15 or the ROM 13. In this embodiment, the lower and upper thresholds for judging are common to the resonant frequencies R1 and R2, but different lower and upper thresholds for judging the resonant frequencies R1 and R2 may be set.

[0033] Next, the internal pressure change determination unit 23 determines whether or not any tire has experienced a change in internal pressure, and which tire has experienced a change in internal pressure, based on a combination of changes in the relative indicators DEL1 to DEL3 and changes in the resonance frequencies R1 and R2 (step S5). More specifically, the internal pressure change determination unit 23 identifies the pattern of changes in the internal pressure of the tire by referring to the data shown in Table 1 below. In Table 1, each of the relative indicators DEL1 to DEL3 is indicated as "-" when it is a negative value, "+" when it is a positive value, and "0" when it is 0 or almost 0. Also in Table 1, each of the resonance frequencies R1 and R2 is indicated as "-" when it is below the lower threshold for determination, "+" when it is above the upper threshold for determination, and "0" when it is equal to or greater than the lower threshold for determination and equal to or less than the upper threshold for determination. [Table 1]

[0034] If the changes in the relative indices DEL1 to DEL3 and the changes in the resonance frequencies R1 and R2 do not correspond to any of the patterns in Table 1 (that is, if the changes in DEL1 to DEL3 and the changes in the resonance frequencies R1 and R2 are all "0"), the internal pressure change determination unit 23 determines that no tire has experienced a change in internal pressure (NO). In this case, steps S1 to S5 are executed again. On the other hand, if the changes in the relative indices DEL1 to DEL3 and the changes in the resonance frequencies R1 and R2 correspond to any of the patterns in Table 1, the internal pressure change determination unit 23 determines that there is a tire whose internal pressure has changed (YES). Furthermore, it determines which tire has experienced a change in internal pressure and whether the pressure has increased or decreased according to Table 1.

[0035] Next, the internal pressure change determination unit 23 compares each of the relative indicators DEL1 to DEL3 with the warning threshold value described above, and determines whether the internal pressure change determined in step S5 is of a level that warrants a warning (step S6). Specifically, the internal pressure change determination unit 23 determines whether any of the relative indicators DEL1 to DEL3 is above or below the warning threshold value in the pattern identified in step S5. If the internal pressure change determination unit 23 determines that a warning should be issued for the internal pressure change (YES), step S7 is then executed. On the other hand, if the internal pressure change determination unit 23 determines that a warning should not be issued for the internal pressure change (NO), steps S1 to S5 are executed again.

[0036] In step S7, the alarm generating unit 24 generates an alarm notifying the user of the internal pressure change and displays it on the alarm display 3. The alarm includes information about the tire whose internal pressure is changing and whether the change in internal pressure is an increase or decrease. The alarm display 3 may, for example, display a graphic that resembles the vehicle 1 and highlight the area on the graphic that corresponds to the wheel position of the tire whose internal pressure is changing. Furthermore, the display mode may be changed depending on whether the change in internal pressure is an increase or decrease, for example by painting the area corresponding to the wheel position in a different color.

[0037] <3. Features> According to the detection device 2 and the internal pressure change detection method of the above embodiment, the tire T FL ,T FR ,T RL ,T RR This allows the tire T to detect pressure increases and decreases without introducing any new equipment. FL ,T FR ,T RL ,T RR This allows for better management of the internal pressure.

[0038] <4. Modifications> Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications are possible without departing from the spirit of the present invention. For example, the following modifications are possible. Furthermore, the gist of the following modifications can be combined as appropriate.

[0039] (1) The relative indexes may be any indexes for comparing the rotational speeds of the tires, and are not limited to those defined by the formulas in the above embodiment. For example, DEL1 to DEL3 may be defined by the following formulas: DEL1=[(V2+V3) / 2-(V1+V4) / 2] / [(V1+V2+V3+V4) / 4]×100(%) DEL2=[(V3+V4) / 2-(V1+V2) / 2] / [(V1+V2+V3+V4) / 4]×100(%) DEL3=[(V2+V4) / 2-(V1+V3) / 2] / [(V1+V2+V3+V4) / 4]×100(%) Furthermore, DEL1 to DEL3 may be defined by the following formulas, respectively. DEL1=[(V2+V3) / (V1+V4)-1]×100(%) DEL2=[(V3+V4) / (V1+V2)-1]×100(%) DEL3=[(V2+V4) / (V1+V3)-1]×100(%) Furthermore, DEL1 to DEL3 may be defined by the following formulas, respectively. DEL1=[(V1+V4) / (V2+V3)-1]×100(%) DEL2=[(V1+V2) / (V3+V4)-1]×100(%) DEL3=[(V1+V3) / (V2+V4)-1]×100(%)

[0040] (2) The detection device 2 according to the above embodiment is not limited to a drive system for a four-wheel vehicle, and can be applied to any of FF vehicles, FR vehicles, MR vehicles, and 4WD vehicles. The drive source may be an engine, a motor, or both. From the viewpoint of improving the accuracy of resonant frequency estimation, it is preferable to identify the change in the resonant frequency of the tire of the axle closer to the power source (the axle subjected to a greater load).

[0041] (3) The order in which the steps of the low-pressure detection process according to the above embodiment are performed may be changed as appropriate. For example, the order in which steps S3 and S4 are performed may be reversed.

[0042] (4) The steps of the internal pressure change detection method according to the above embodiment may be executed by multiple computers. That is, at least some of steps S1 to S7 may be executed by another external computer connected to the detection device 2.

[0043] (5) In the above embodiment, the tire T FL The resonance frequency R1 and the tire T FR The resonance frequency R2 of the tire T FL ,T FR ,T RL ,T RRIt is also possible to identify the resonance frequency of at least one tire among the above, and detect a change in internal pressure based on this and the relative indicators DEL1 to DEL3. Note that for the relative indicators DEL1 to DEL3, for example, the amount of change from the reference value of the relative indicators DEL1 to DEL3 when all tires of the vehicle 1 are under normal internal pressure may be compared with a threshold value, and the determination in step S5 may be performed. The same applies to the determination in step S6. Similarly, the determination thresholds for the resonance frequencies R1 and R2 may be set relative to the amount of change from the reference resonance frequency. Furthermore, in determining whether the relative indicators DEL1 to DEL3 are positive or negative, a determination method that combines two indicators may be used, rather than determining whether the relative indicators DEL1 to DEL3 are positive or negative alone. For example, if the absolute value of (DEL1 / DEL3) is less than a first threshold, DEL1 is considered to be 0, and if the absolute value exceeds a second threshold that is greater than the first threshold, DEL3 is considered to be 0. Furthermore, in the patterns shown in Table 1, when tire T FL In the case where only the pressure of tire T is increased or decreased, the determination in step S6 may be made by comparing the resonance frequency R1 or the amount of change therein with the warning threshold value. FR If the pressure is increased or decreased only in the tire T, the determination in step S6 may be made by comparing the resonance frequency R2 or the amount of change therein with a warning threshold value. FL or Tire T FR can be determined based on the resonant frequency R1 or R2 when the pressure is reduced or increased to the alarm threshold value, or the amount of change therein. [Example]

[0044] Examples of the present invention will be described below, but the present invention is not limited to the following examples.

[0045] <Experiment 1> The tires were mounted on the wheels of a four-wheeled vehicle (FF vehicle), and the vehicle was driven on a flat asphalt road at three different speeds: 90 km / h, 100 km / h, and 120 km / h. The wheel speed sensors were used to obtain rotational speed data for each tire. Only the left front wheel was inflated 20% above the normal internal pressure, while the others were kept at normal internal pressure. Based on the rotational speed data obtained at this time, the relative indices DEL1 to DEL3 were calculated. In addition, the tire T of the two front wheels was FL and T FR The resonance frequencies R1 and R2 were calculated for each tire, and the amount of change from the reference resonance frequency at normal internal pressure was calculated. Whether or not a tire had a change in internal pressure was determined based on the signs of the calculated relative indicators DEL1 to DEL3 and the amount of change in the resonance frequencies R1 and R2. The lower threshold for determining the amount of change in the resonance frequencies R1 and R2 was set to -0.65, and the upper threshold for determining the amount of change in the resonance frequencies R1 and R2 was set to 0.65. The warning thresholds for the relative indicators DEL1, DEL3, and DEL2 were set to ±0.082, ±0.163, and ±0.22, respectively. These warning thresholds were set to issue a warning when the tire had a pressure drop or increase of 16% to 20% from the normal internal pressure, as shown in Table 1. Such vehicle experiments can be affected by tire break-in and tire pressure adjustment errors. However, to ensure reliable warning of changes in tire internal pressure even under such conditions, the target pressure drop or increase range for the warning was set as described above.

[0046] <Result 1> The calculated relative indices DEL1 to DEL3 and the tire T FL and T FR The amount of change in the resonant frequency is shown in Table 2 below. [Table 2]

[0047] According to Table 2, the values ​​of the relative indicators DEL1 to DEL3 are all negative, and furthermore, the relative indicator DEL1 is below the warning threshold value. FL 16% to 20% increase in pressure, or tire T FR ,T RL and TRR However, when the changes in the resonance frequencies R1 and R2 are compared with the lower and upper thresholds for judgment, it is possible to distinguish between the tire T FR The tire pressure is not increased or decreased. FL This confirms that it is possible to detect changes in tire internal pressure, including both pressure increases and decreases, by combining changes in the relative indices DEL1 to DEL3 with changes in the resonance frequency.

[0048] <Experiment 2> A tire was attached to each wheel of a four-wheel vehicle (FF vehicle), and the vehicle was driven on a flat asphalt road while changing the driving speed to three stages: 90 km / h, 100 km / h, and 120 km / h, and rotational speed data of each tire was obtained using a wheel speed sensor. Only the left front wheel was in a state where the tire pressure was reduced by 20% from the normal internal pressure, while the others were in a state where the tire pressure was normal. Based on the rotational speed data obtained at this time, relative indices DEL1 to DEL3 were calculated. In addition, the tire pressure of the two front wheels was FL and T FR The resonance frequencies R1 and R2 were calculated for each tire, and the amount of change from the reference resonance frequency at normal internal pressure was calculated. Whether or not there was a tire whose internal pressure had changed was determined based on the signs of the calculated relative indices DEL1 to DEL3 and the amount of change in the resonance frequencies R1 and R2. The various thresholds were the same as in Experiment 1.

[0049] <Result 2> The calculated relative indices DEL1 to DEL3 and the tire T FL and T FR The change in the resonant frequency is shown in Table 3 below. [Table 3]

[0050] According to Table 3, the values ​​of the relative indicators DEL1 to DEL3 are all positive, and furthermore, the relative indicator DEL1 exceeds the warning threshold value. FL 16% to 20% reduction in pressure or tire TFR ,T RL and T RR However, when the amounts of change in the resonance frequencies R1 and R2 are compared with the lower and upper thresholds for judgment, it is possible to distinguish between the tire T FR The tire pressure is not increased or decreased. FL This confirms that by combining the change in the relative indices DEL1 to DEL3 with the change in the resonance frequency, it is possible to detect changes in the internal pressure, including both pressure increases and decreases in the tire. [Explanation of symbols]

[0051] 1 vehicle 2. Internal pressure change detection device 20 Acquisition Department 21 Indicator calculation section 22 Resonant frequency identification section 23 Internal pressure change determination unit 24 Alarm generation unit V1 Rotational speed of the left front tire V2 Rotational speed of the right front tire V3 Left rear tire rotation speed V4 Right rear tire rotation speed DEL1~DEL3 Relative decompression index

Claims

1. an acquisition unit that acquires rotational speed information of a plurality of tires included in a vehicle; an index calculation unit that calculates a relative index for comparing the rotational speeds of the plurality of tires based on the acquired rotational speed information; a resonance frequency identifying unit that identifies a resonance frequency of at least one tire among the plurality of tires based on the acquired rotational speed information; an internal pressure change determination unit that determines an internal pressure change, including an increase in pressure, of the plurality of tires based on a combination of the calculated relative index and the identified resonance frequency; Equipped with A device for detecting changes in tire internal pressure.

2. the resonance frequency identifying unit identifies resonance frequencies of at least two coaxially mounted tires among the plurality of tires.

2. The tire internal pressure change detection device according to claim 1.

3. the plurality of tires include a first tire mounted on a first axle, a second tire mounted on the first axle, a third tire mounted on the same side of the second axle as the first tire, and a fourth tire mounted on the same side of the second axle as the second tire, 3. The tire internal pressure change detection device according to claim 1 or 2.

4. the relative indicators include an indicator comparing the rotational speed of the first tire and the rotational speed of the fourth tire with the rotational speed of the second tire and the rotational speed of the third tire, an indicator comparing the rotational speed of the first tire and the rotational speed of the second tire with the rotational speed of the third tire and the rotational speed of the fourth tire, and an indicator comparing the rotational speed of the first tire and the rotational speed of the third tire with the rotational speed of the second tire and the rotational speed of the fourth tire.

4. The tire internal pressure change detection device according to claim 3.

5. A method for detecting a change in tire internal pressure executed by one or more computers, comprising: Obtaining rotational speed information of a plurality of tires included in a vehicle; calculating a relative index for comparing the rotational speeds of the plurality of tires based on the acquired rotational speed information; Identifying a resonance frequency of at least one tire among the plurality of tires based on the acquired rotational speed information; determining a change in internal pressure, including an increase in pressure, of the plurality of tires based on a combination of the calculated relative index and the identified resonance frequency; Including, A method for detecting changes in tire pressure.

6. Obtaining rotational speed information of a plurality of tires included in a vehicle; calculating a relative index for comparing the rotational speeds of the plurality of tires based on the acquired rotational speed information; Identifying a resonance frequency of at least one tire among the plurality of tires based on the acquired rotational speed information; determining a change in internal pressure, including an increase in pressure, of the plurality of tires based on a combination of the calculated relative index and the identified resonance frequency; on one or more computers, A program to detect changes in tire pressure.

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