Decompression detector of tire, decompression detection method and decompression detection program

Abstract

To provide a decompression detector of a tire which can appropriately distinguish coaxial two-wheel decompression with four-wheel decompression.SOLUTION: A decompression detector of a tire comprises: an acquisition part; an index calculation part; a decompression determination part; a resonance frequency specification part; and a lead-out part. The decompression determination part determines, when both of decompression equivalent amount of a first right tire and decompression equivalent amount of a first left tire are a prescribed first threshold value or more and the difference between the decompression equivalent amount of the first right tire and the decompression equivalent amount of the first left tire are less than a prescribed second threshold value, whether decompression occurs in a second right tire and a second left tire based on rotary speed of the second right tire and the second left tire mounted to a second axle of the vehicle that is one of relative decompression indexes and a relative decompression index comparing rotary speed of the first right tire with that of the first left tire.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a device, a method, and a program for detecting reduced pressure in a tire mounted on a wheel. [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] However, because the deflation indicators DEL1 to DEL3 are indices that relatively compare the rotational speeds of the tires, for example, if one or more tires are slightly depressurized, the amount of depressurization indicated by DEL1 to DEL3 may deviate from the actual amount of depressurization. For this reason, when estimating the absolute amount of depressurization for each tire using both the DLR method and the RFM method, as in the technology of Patent Document 1, the deviations between DEL1 to DEL3 accumulate. As a result, in four-wheel vehicles, there is a possibility that the system may erroneously determine whether two coaxial wheels have depressurized or all four wheels have depressurized, resulting in an erroneous warning for the wheels that have depressurized.

[0008] An object of the present invention is to provide a tire deflation detection device, a deflation detection method, and a deflation detection program that can appropriately distinguish between deflation on two coaxial wheels and deflation on four wheels. [Means for solving the problem]

[0009] A tire deflation detection device according to a first aspect of the present invention includes an acquisition unit, an index calculation unit, a deflation determination unit, a resonance frequency identification unit, and a derivation unit. The acquisition unit acquires rotational speed information of multiple tires mounted on a vehicle. The index calculation unit calculates a relative deflation index for comparing the rotational speeds of the multiple tires based on the acquired rotational speed information. The deflation determination unit determines whether or not a deflation has occurred in at least one tire of the multiple tires based on the calculated relative deflation index. The resonance frequency identification unit identifies the resonance frequencies of a first right tire and a first left tire mounted on a first axle of the vehicle based on the acquired rotational speed information. The derivation unit derives the deflation equivalent amounts of the first right tire and the first left tire based on the identified resonance frequencies. When the amount of decompression equivalent of the first right tire and the amount of decompression equivalent of the first left tire are both equal to or greater than a predetermined first threshold, and the difference between the amount of decompression equivalent of the first right tire and the amount of decompression equivalent of the first left tire is less than a predetermined second threshold, the decompression determination unit determines whether decompression has occurred in the second right tire and the second left tire based on a relative decompression index, among the relative decompression indexes, which compares the rotational speeds of the second right tire and second left tire mounted on a second axle of the vehicle with the rotational speeds of the first right tire and the first left tire.

[0010] A tire decompression detection device according to a second aspect is the decompression detection device according to the first aspect, wherein the decompression determination unit determines that all of the first right tire, the first left tire, the second right tire, and the second left tire have decompressed when the decompression equivalent amount of the first right tire and the decompression equivalent amount of the first left tire are both equal to or greater than a predetermined first threshold, and when the difference between the decompression equivalent amount of the first right tire and the decompression equivalent amount of the first left tire, and the difference between the decompression equivalent amount of the second right tire and the decompression equivalent amount of the second left tire are both less than a predetermined second threshold, and when the decompression equivalent amount of the second right tire and the decompression equivalent amount of the second left tire is converted from a relative decompression index that compares the rotational speeds of the second right tire and the second left tire with the rotational speeds of the first right tire and the first left tire, and is calculated based on the decompression equivalent amounts of the first right tire and the first left tire, is equal to or greater than a predetermined threshold.

[0011] A tire deflation detection device according to a third aspect is the deflation detection device according to the first or second aspect, further comprising an alarm issuing unit that issues a deflation alarm when it is determined that at least one tire among the plurality of tires has deflation. The deflation determination unit identifies the tire among the plurality of tires that has been determined to have deflation, and the deflation alarm includes information identifying the tire that has been determined to have deflation.

[0012] A tire deflation detection method according to a fourth aspect is a tire deflation detection method executed by one or more computers, and includes the following: A tire deflation detection program according to a fifth aspect causes one or more computers to execute the following: (1) Obtaining rotational speed information for multiple tires mounted on a vehicle (2) calculating a relative decompression index for comparing the rotational speeds of the plurality of tires based on the acquired rotational speed information; (3) determining whether or not a decompression has occurred in at least one tire among the plurality of tires based on the calculated relative decompression index; (4) Identifying the resonance frequencies of a first right tire and a first left tire mounted on a first axle of the vehicle based on the acquired rotational speed information. (5) deriving the amount of reduced pressure of each of the first right tire and the first left tire based on the identified resonance frequency. (3) Determining whether or not decompression has occurred in at least one tire among the plurality of tires includes, when the decompression equivalent amount of the first right tire and the decompression equivalent amount of the first left tire are both equal to or greater than a predetermined first threshold, and the difference between the decompression equivalent amount of the first right tire and the decompression equivalent amount of the first left tire is less than a predetermined second threshold, determining whether or not decompression has occurred in the second right tire and the second left tire based on a relative decompression indicator, among the relative decompression indicators, which compares the rotational speeds of the second right tire and the second left tire mounted on a second axle of the vehicle with the rotational speeds of the first right tire and the first left tire. [Effects of the Invention]

[0013] According to the present invention, it is possible to appropriately distinguish between coaxial two-wheel pressure reduction and four-wheel pressure reduction. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a schematic diagram showing a state in which a reduced pressure detection device according to an embodiment of the present invention is mounted on a vehicle; [Figure 2] FIG. 2 is a block diagram showing the electrical configuration of the reduced pressure detection device. [Figure 3] 10 is a flowchart showing the flow of a reduced pressure detection process. DETAILED DESCRIPTION OF THE INVENTION

[0015] 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.

[0016] <1. Configuration of the reduced pressure detection device> FIG. 1 is a schematic diagram showing a state in which a low-pressure detection device 2 according to this embodiment is 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 drivenly. The low-pressure detection device 2 detects the tires T attached to these wheels. FL (1st left tire), T FR (First right tire), T RL (2nd left tire), T RR (second right tire) and has a function to detect decompression of at least one of the tires T FL ,T FR ,T RL ,T RR When a reduced pressure is detected, a warning to that effect is issued via the warning indicator 3 mounted on the vehicle 1. The flow of such a reduced pressure detection process will be described in detail later.

[0017] Tire T FL ,T FR ,T RL ,T RR The decompression state of the tire is detected based on the rotation speeds 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 outputs a rotation speed signal (in other words, a signal representing the rotation speed of the tire T FL ,T FR ,T RL ,T RR The wheel speed sensor 6 is connected to the decompression detection device 2 via a communication line 5. The rotation speed signal detected by the wheel speed sensor 6 is transmitted to the decompression detection device 2 via the communication line 5 in real time.

[0018] 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.

[0019] FIG. 2 is a block diagram showing the electrical configuration of the low-pressure detection device 2. The low-pressure detection device 2 is a control unit (on-board computer) mounted on the vehicle 1 as hardware. As shown in FIG. 2, the low-pressure detection device 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, a derivation unit 23, a low-pressure determination unit 24, and a warning generation unit 25. The operation of each unit 20 to 25 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.

[0020] 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 tire has deflated. The mounting position of the warning indicator 3 can also be selected appropriately, 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 control unit (deflation 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.

[0021] <2. Decompression detection process> Referring to Figure 3, tire T FL ,T FR ,T RL ,T RR The following describes a deflation detection process for detecting deflation in at least one of the above. The deflation detection process shown in Fig. 3 is a combination of the dynamic load radius (DLR) method and the resonance frequency (RFM) method, and cancels the influence of deviation from the actual state of the relative deflation index used in the DLR method, thereby appropriately distinguishing between coaxial two-wheel deflation and four-wheel deflation. Note that coaxial two-wheel deflation is a state in which two tires mounted on the left and right of an axle to which the RFM method is applied have deflation equal to or greater than a predetermined warning threshold, and four-wheel deflation is a state in which all four tires mounted on four wheels have deflation equal to or greater than a predetermined warning threshold. The deflation 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.

[0022] First, the acquisition unit 20 acquires a time-series rotation speed signal 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.

[0023] 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 driving conditions of the vehicle 1 are steady. Since the dynamic load radius of a tire varies depending not only on the tire air pressure state but also on the driving conditions of the vehicle 1, it is preferable that data acquired during, for example, extreme acceleration / deceleration or cornering is rejected and not used in subsequent processing. 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.

[0024] Next, the index calculation unit 21 calculates a relative decompression index based on the rotational speeds V1 to V4 (step S3). The relative decompression index in this embodiment is indexes DEL1 to DEL3 that compare the rotational speeds of the respective tires, as 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)

[0025] As shown in the above formula, the relative decompression index DEL1 of this embodiment is calculated by FL and Tire T RR Pair with Tire T FR and Tire T RL DEL2 is an index that compares the average rotation speed of a pair of tires. FL and Tire T FR Pair with Tire T RL and Tire T RR It is an index that compares the average rotation speed of a pair of tires, and DEL3 is FL and Tire T RL Pair with Tire T FR and Tire T RRIn other words, DEL1 is an index that compares the average rotational speed between pairs of tires located diagonally on vehicle 1, DEL2 is an index that compares the average rotational speed between pairs of tires mounted on the same axle of vehicle 1, and DEL3 is an index that compares the average rotational speed between pairs of tires located on the left and right sides of vehicle 1.

[0026] For each of the relative decompression indicators DEL1 to DEL3, a numerical range that distinguishes between a normal state and a decompression state is predetermined according to the amount of decompression (for example, a 20% decompression from the normal internal pressure) that serves as an alarm threshold, and is stored in the storage device 15. The threshold that defines this numerical range is determined based on the tire T FL ,T FR ,T RL ,T RR One of the tire pressure patterns is one tire pressure T FL ,T FR ,T RL ,T RR Two-wheel deflation pattern with deflation of any two of the tires, tire T FL ,T FR ,T RL ,T RR Theoretically, the above-mentioned deflation pattern can be specified according to the combination of the numerical ranges to which the current values ​​of the relative deflation indicators DEL1 to DEL3 belong. However, as described in Patent Document 1, for example, a deflation of 20% is the threshold for an alarm, and the tire T FL ,T FR Each tire is decompressed by 10%. RL ,T RR If each of DEL1 and DEL3 is reduced by 20%, the amount of pressure reduction estimated from DEL1 and DEL3 will be approximately 0%, and the amount of pressure reduction estimated from DEL2 will be approximately 10%, so no warning will be issued.

[0027] The RFM method is used in combination to avoid such a situation. However, since applying the RFM method to all wheels puts a strain on the calculation resources, the RFM method is often applied to either the front wheels or the rear wheels. Furthermore, from the viewpoint of the accuracy of the resonance frequency estimation, it is preferable that the RFM method be applied to the axle with the heavier load, that is, the axle closer to the driving source such as the engine or motor. For these reasons, in this embodiment, the tire T FL and T FR The RFM method is applied to

[0028] In the next step S4, the resonance frequency identifying unit 22 determines the rotational speed V1 of the tire T from the rotational speeds V1 and V2 of the wheels FL and FR. FL and T FR The resonant frequency R FL and R FR More specifically, the resonance frequency identifying unit 22 differentiates the rotational speeds V1 and V2 of the wheels FL and FR to extract frequency components, and then derives the power spectrum of the rotational acceleration of the wheels FL and FR using a fast Fourier transform (FFT) or the like. However, since this power spectrum contains various noises, it is preferable to average the results of a predetermined number of calculations. Based on the power spectrum thus derived, the resonance frequency identifying unit 22 determines the resonance frequency R FL and R FR In this embodiment, the resonant frequency R FL and R FR The resonance frequency in the torsional direction is determined as

[0029] Next, the derivation section 23 detects the resonant frequency R FL and R FR Based on the tire T FL and T FR The amount of pressure reduction P FL and P FR and are calculated (step S5). FL and P FR is Tire T FL and T FRThe pressure reduction sensitivity is calculated based on a predetermined pressure reduction sensitivity for each of the above. The pressure reduction sensitivity is the amount of change in the resonant frequency from the reference resonant frequency at normal internal pressure per 1% pressure reduction, and is determined by conducting experimental driving of the vehicle 1 under conditions where the tires are reduced to various pressure reduction amounts, and is stored in advance in the storage device 15.

[0030] Next, the derivation unit 23 calculates the relative pressure reduction indices DEL1 to DEL3 and the pressure reduction amount P FL , P FR Based on the tire T RL and T RR The amount of pressure reduction P RL and P RR (Step S6). RL and P RR The method for deriving is not particularly limited, but the method described in Patent Document 1, for example, can be used.

[0031] Next, the pressure reduction determination unit 24 calculates the pressure reduction amount P FL and P FR Based on at least tire T FL and T FR The pressure reduction determination unit 24 determines whether the pressure reduction amount P FL and P FR are compared with a predetermined threshold value Th1 (>0), and the pressure reduction amount P FL and P FR If both exceed a predetermined threshold value Th1, at least tire T FL and T FR In this embodiment, the predetermined threshold value Th1 is set to 20(%), which is the warning threshold value. FL and T FR When it is determined that the pressures of the two tires are reduced (YES), the next step S8 is executed. FL and T FR When it is determined that the two-wheel pressure is not reduced (NO), step S11 is executed next.

[0032] In step S8, the pressure reduction determination unit 24 determines the pressure reduction amount P FL and P FRThe difference and the pressure reduction amount P RL and P RR It is determined whether the differences of are each less than a predetermined threshold Th2 (>0). This determination is a determination as to whether a prerequisite condition is satisfied prior to determining whether it is front axle two-wheel pressure reduction or four-wheel pressure reduction in step S9 described later. The pressure reduction determination unit 24 compares the absolute value of the difference in the pressure reduction amount (P FL -P FR ) with a predetermined threshold Th2. In addition, the pressure reduction determination unit 24 compares the absolute value of the difference in the pressure reduction amount (P RL -P RR ) with a predetermined threshold Th2. If the difference between the pressure reduction amounts P FL and P FR is less than a predetermined threshold Th2 (|P FL -P FR |<Th2), and also the difference between the pressure reduction amounts P RL and P RR is less than a predetermined threshold Th2 (|P RL -P RR [[ID=2⑧]]|<Th2) (YES) is determined, then step S9 is executed next. On the other hand, if the difference between the pressure reduction amounts P FL and P FR is greater than or equal to a predetermined threshold Th2 (|P FL [[ID=④]]-P FR |≧Th2), or the difference between the pressure reduction amounts P RL and P RR is greater than or equal to a predetermined threshold Th2 (|P RL -P RR |≧Th2), and it is determined that the above condition is not satisfied (NO), then step S11 is executed next.

[0033] The predetermined threshold Th2 can be appropriately determined as long as it is a value exceeding and less than the alarm threshold. For example, when the alarm threshold is 20%, the predetermined threshold Th2 can be set to 5 or more and 15 or less. Note that the closer the predetermined threshold Th2 is to 0, the lower the probability that step S9 is executed, and the closer the predetermined threshold Th2 is to the alarm threshold, the higher the probability that step S9 is executed. If the predetermined threshold Th② is greater than or equal to the pressure reduction threshold, in the next step S9, there is a possibility that front axle two-wheel pressure reduction is misjudged as four-wheel pressure reduction. Therefore, the predetermined threshold Th2 is set to be less than the alarm threshold.

[0034] In step S9, the decompression determination unit 24 compares the value of P, which is the decompression equivalent amount of the rear axle two wheels with respect to the decompression equivalent amount of the front axle two wheels, converted based on DEL2 calculated in step S2, with a predetermined threshold value Th3. The decompression equivalent amount P R can be calculated as (DEL2 / decompression sensitivity D of the rear axle two wheels R ). The decompression sensitivity D of the rear axle two wheels R is the change rate of DEL2 when both tires T R and T RL and T RR are assumed to have the same internal pressure, and are both decompressed by 1% with tire T FL and T FR as the reference. The decompression sensitivity D R is specified by conducting experimental running of the vehicle 1 under the condition that the tires are decompressed to various decompression amounts, and is stored in advance in the storage device 15. As described above, DEL2 is an index for comparing the average of the rotational speeds between pairs of tires mounted on the same axle of the vehicle 1. Therefore, after passing through the determinations in steps S7 and S8, step S9 is reached. When the value of the decompression equivalent amount P R is determined to be greater than or equal to the predetermined threshold value Th3 (P R ≥ Th3), it can be determined that not only the tires of the front axle two wheels but also the tires of the rear axle two wheels are decompressed to about the warning threshold value. Therefore, when P R ≥ Th3 in step S9, it is determined that four-wheel decompression has occurred, and then step S10 is executed. On the other hand, when P R < Th3 in step S9, it is determined that front axle two-wheel decompression has occurred, and then step S11 is executed.

[0035] The predetermined threshold value Th3 is a threshold value for distinguishing between the case where the decompression of the front axle two wheels is greater than or equal to the warning threshold value and the decompression of the rear axle two wheels is less than the warning threshold value, and the case where the decompression of the four wheels is greater than or equal to the warning threshold value, and can be determined in advance. For example, when the warning threshold value is 20%, the predetermined threshold value Th3 can be set to 10 (%).

[0036] In step S10, the warning generation unit 25 generates a deflation warning. More specifically, the warning generation unit 25 generates warning data notifying of deflation in a tire and causes the warning display 3 to display this. The warning data includes information identifying the tire determined to have deflation. In other words, the warning data generated in step S10 includes different information based on the determination result in step S9 or step S11 described below. The warning display 3 may, for example, display a graphic that resembles the vehicle 1 and highlight a portion of the graphic that corresponds to the wheel position of the tire that has deflation.

[0037] On the other hand, in step S11, the pressure reduction determination unit 24 calculates the relative pressure reduction indices DEL1 to DEL3 and the pressure reduction amount P FL ,P FR ,P RL ,P RR Based on the above, other than the pressure reduction pattern already determined in steps S7 to S9, tire T FL ,T FR ,T RL ,T RR In other words, the pressure reduction determination unit 24 determines whether or not at least one of the pressure reduction amounts P FL ,P FR ,P RL ,P RR It is determined whether each of these exceeds a predetermined threshold value Th1, and if any of these exceeds the predetermined threshold value Th1, it is further determined whether a decrease in pressure on one wheel, two diagonal wheels, two wheels on the same side (left or right), two rear wheels, or three wheels has occurred, depending on the combination. FL ,T FR ,T RL ,T RR If it is determined that at least one of the tires T is decompressed (YES), step S10 is executed. FL ,T FR ,T RL ,T RR If it is determined that none of the above has been reduced in pressure (NO), step S1 is executed again.

[0038] <3. Features> According to the deflation detection device 2 and deflation detection method of the above embodiment, in a deflation detection system that combines the DLR method and the RFM method, the determination of two-wheel or four-wheel deflation, which is prone to misjudgment, is not made based on the estimated deflation amount of each tire, but is made based on the determination based on the RFM method, which has a higher accuracy in deflation estimation (steps S7 to S9).This eliminates the influence of errors in the relative deflation index used in the DLR method, and makes it possible to properly distinguish between two-wheel deflation and four-wheel deflation on an axle to which the RFM method for deflation amount of each tire is applied.

[0039] <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.

[0040] (1) The relative decompression index is not limited to the one defined by the formula in the above embodiment, as long as it is an index for comparing the rotational speeds of the tires. 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(%)

[0041] (2) The low pressure detection device 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. When the drive source is located near the rear axle, the RFM system may be applied to the two rear axles. In this case, the rear axle is the first axle, the front axle is the second axle, and the tire T RL ,T RR are the first left tire, the first right tire, and tire T FL ,T FR These are the second left tire and second right tire, respectively.

[0042] (3) The order in which the steps of the low-pressure detection process according to the above embodiment are performed can be changed as appropriate. For example, steps S4 and S5 may be performed before step S3.

[0043] (4) The steps of the reduced pressure detection method according to the above embodiment may be executed by multiple computers. That is, at least some of steps S1 to S11 may be executed by another external computer connected to the reduced pressure detection device 2.

[0044] (5) Pressure reduction amount P FL ,P FR ,P RL ,P RR does not have to be a value that indicates the amount of pressure reduction (%) from the normal internal pressure of the tire itself, but may be an amount equivalent to pressure reduction that can be converted into the amount of air pressure reduction from the normal internal pressure, like the amount of pressure reduction (%). Furthermore, the thresholds Th1 and Th2 do not have to be values ​​that correspond to the amount of pressure reduction (%) itself, but may be an amount equivalent to pressure reduction that can be converted into the amount of pressure reduction (%).

[0045] (6) In step S11, the pressure reduction amount P FL ,P FR ,P RL ,P RR The pressure reduction pattern may be determined based on a known DLR method, which determines the pressure reduction pattern based on a combination of the relative pressure reduction indices DEL1 to DEL3, rather than based on the pressure reduction amount PFL ,P FR As long as the pressure drop on all four wheels or the pressure drop on two wheels of the first axle is determined based on DEL2 or DEL3, or their equivalent values, the method of determining whether other pressure drop patterns are occurring is not particularly limited, and the pressure drop amount P RL ,P RR The calculation of may be omitted. [Explanation of symbols]

[0046] 1 vehicle 2. Decompression detection device 20 Acquisition Department 21 Indicator calculation section 22 Resonant frequency identification section 23 Derivation part 24 Decompression determination unit 25 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 Th1 Predetermined threshold (first threshold) Th2 Predetermined threshold (second threshold)

Claims

1. an acquisition unit that acquires rotational speed information of a plurality of tires mounted on a vehicle; an index calculation unit that calculates a relative decompression index for comparing the rotational speeds of the plurality of tires based on the acquired rotational speed information; a decompression determination unit that determines whether or not decompression has occurred in at least one tire among the plurality of tires based on the calculated relative decompression index; a resonance frequency identifying unit that identifies resonance frequencies of a first right tire and a first left tire mounted on a first axle of the vehicle based on the acquired rotational speed information; a derivation unit that derives a pressure reduction equivalent amount of each of the first right tire and the first left tire based on the identified resonance frequency; Equipped with When the amount of reduced pressure equivalent of the first right tire and the amount of reduced pressure equivalent of the first left tire are both equal to or greater than a predetermined first threshold value and the difference between the amount of reduced pressure equivalent of the first right tire and the amount of reduced pressure equivalent of the first left tire is less than a predetermined second threshold value, the reduced pressure determination unit determines whether reduced pressure has occurred in the second right tire and the second left tire based on a relative reduced pressure index, among the relative reduced pressure indexes, which compares the rotational speeds of the second right tire and the second left tire mounted on a second axle of the vehicle with the rotational speeds of the first right tire and the first left tire. Decompression detection device.

2. When the amount of reduced pressure equivalent of the first right tire and the amount of reduced pressure equivalent of the first left tire are both equal to or greater than a predetermined first threshold, and when the difference between the amount of reduced pressure equivalent of the first right tire and the amount of reduced pressure equivalent of the first left tire and the difference between the amount of reduced pressure equivalent of the second right tire and the amount of reduced pressure equivalent of the second left tire are both less than a predetermined second threshold, the reduced pressure determination unit determines that all of the first right tire, the first left tire, the second right tire, and the second left tire have reduced pressure if the amount of reduced pressure equivalent of the second right tire and the second left tire based on the amount of reduced pressure equivalent of the first right tire and the first left tire, which is converted from a relative reduced pressure index that compares the rotational speeds of the second right tire and the second left tire with the rotational speeds of the first right tire and the first left tire, is equal to or greater than a predetermined threshold. The reduced pressure detection device according to claim 1 .

3. an alarm issuing unit that issues a low-pressure alarm when it is determined that low pressure has occurred in at least one tire among the plurality of tires; Furthermore, the deflation determination unit identifies a tire among the plurality of tires that is determined to have a deflation, and the deflation warning includes information identifying the tire that is determined to have a deflation. The reduced pressure detection device according to claim 1 or 2.

4. 1. A tire deflation detection method implemented by one or more computers, comprising: Acquiring rotational speed information of a plurality of tires mounted on a vehicle; calculating a relative decompression index for comparing the rotational speeds of the plurality of tires based on the acquired rotational speed information; determining whether or not a decompression has occurred in at least one tire among the plurality of tires based on the calculated relative decompression index; Identifying resonance frequencies of a first right tire and a first left tire mounted on a first axle of the vehicle based on the acquired rotational speed information; deriving a pressure reduction equivalent amount for each of the first right tire and the first left tire based on the identified resonance frequency; Including, Determining whether or not decompression has occurred in at least one tire among the plurality of tires includes, when both the decompression equivalent amount of the first right tire and the decompression equivalent amount of the first left tire are equal to or greater than a predetermined first threshold value and the difference between the decompression equivalent amount of the first right tire and the decompression equivalent amount of the first left tire is less than a predetermined second threshold value, determining whether or not decompression has occurred in the second right tire and the second left tire based on a relative decompression indicator, among the relative decompression indicators, which compares the rotational speeds of the second right tire and the second left tire mounted on a second axle of the vehicle with the rotational speeds of the first right tire and the first left tire. A method for detecting tire deflation.

5. Acquiring rotational speed information of a plurality of tires mounted on a vehicle; calculating a relative decompression index for comparing the rotational speeds of the plurality of tires based on the acquired rotational speed information; determining whether or not a decompression has occurred in at least one tire among the plurality of tires based on the calculated relative decompression index; Identifying resonance frequencies of a first right tire and a first left tire mounted on a first axle of the vehicle based on the acquired rotational speed information; deriving a pressure reduction equivalent amount for each of the first right tire and the first left tire based on the identified resonance frequency; on one or more computers, Determining whether or not decompression has occurred in at least one tire among the plurality of tires includes, when both the decompression equivalent amount of the first right tire and the decompression equivalent amount of the first left tire are equal to or greater than a predetermined first threshold value and the difference between the decompression equivalent amount of the first right tire and the decompression equivalent amount of the first left tire is less than a predetermined second threshold value, determining whether or not decompression has occurred in the second right tire and the second left tire based on a relative decompression indicator, among the relative decompression indicators, which compares the rotational speeds of the second right tire and the second left tire mounted on a second axle of the vehicle with the rotational speeds of the first right tire and the first left tire. Tire deflation detection program.

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