Wheel state determination device, wheel state determination method and wheel state determination program

Abstract

To appropriately determine the state of a wheel by cancelling influences of a road surface on which a vehicle travels.SOLUTION: A wheel state determination device comprises an acceleration acquisition section, a variance derivation section, an index calculation section, and a determination section. Regarding each of wheels which are mounted at both ends of an axle of a vehicle, the acceleration acquisition section successively acquires an acceleration in an axle direction. On the basis of the successively acquired acceleration, regarding each of the wheels, the variance derivation section derives a variance of the acceleration in a time direction. The index calculation section calculates an index for comparing the variances between the wheels. The determination section determines whether or not a fixing mechanism which fixes the wheel to the axle is loosened on the basis of the index.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a technique for determining the state of a wheel. [Background technology]

[0002] Patent Document 1 discloses a wheel condition determination device that determines whether there are signs of a wheel falling off a vehicle. This wheel condition determination device sequentially acquires the axial acceleration of the wheel in the axle direction, and determines that there are signs of a wheel falling off if the acquired axial acceleration is greater than a predetermined determination threshold. In addition, the wheel condition determination device determines the vehicle's running condition to prevent erroneous wheel condition determination, and if it determines that the vehicle is running on a rough road, for example, it stops determining the wheel condition. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2023 / 145195 Summary of the Invention [Problem to be solved by the invention]

[0004] According to Patent Document 1, whether a vehicle is traveling on a rough road is determined based on an image of the area ahead of the vehicle captured by an imaging unit installed in the vehicle. However, there are various types of rough roads that affect the determination of the wheel condition, and it is considered difficult to appropriately determine whether the vehicle is traveling on a rough road based on an image. Furthermore, it is even more difficult to make a determination based on an image at night. For these reasons, it is considered that the wheel condition determination process disclosed in Patent Document 1 is affected to a certain extent by the road surface.

[0005] An object of the present invention is to provide a technology that can appropriately determine the state of wheels by canceling the influence of the road surface on which the vehicle is traveling. [Means for solving the problem]

[0006] A wheel state determination device according to a first aspect of the present invention includes an acceleration acquisition unit, a variation deriving unit, an index calculation unit, and a determination unit. The acceleration acquisition unit sequentially acquires acceleration in the axle direction for each of the wheels attached to both ends of an axle of a vehicle. The variation deriving unit derives a variation in the acceleration over time for each of the wheels based on the sequentially acquired acceleration. The index calculation unit derives an index for comparing the variation between the wheels. The determination unit determines whether or not a fixing mechanism that fixes the wheel to the axle is loose based on the index.

[0007] A wheel state determination device according to a second aspect of the present invention is the wheel state determination device according to the first aspect, wherein the index calculation unit derives an index for comparing the variability smoothed for each wheel between the wheels.

[0008] A wheel state determination device according to a third aspect of the present invention is the wheel state determination device according to the first or second aspect, further comprising an alert generation unit that generates and outputs an alert when the determination unit determines that the fixing mechanism is loose.

[0009] A wheel state determination method according to a fourth aspect of the present invention is a wheel state determination method executed by one or more computers, and includes the following steps. (1) Sequentially obtain the acceleration in the axle direction for each wheel attached to both ends of the vehicle axle. (2) deriving a time-dependent variation in the acceleration for each of the wheels based on the sequentially acquired accelerations; (3) Deriving an index for comparing the variations between the wheels. (4) determining whether or not a fixing mechanism that fixes the wheel to the axle is loose based on the index;

[0010] A wheel state determination program according to a fifth aspect of the present invention is a wheel state determination program that causes one or more computers to execute the following: (1) Sequentially obtain the acceleration in the axle direction for each wheel attached to both ends of the vehicle axle. (2) deriving a time-dependent variation in the acceleration for each of the wheels based on the sequentially acquired accelerations; (3) Deriving an index for comparing the variations between the wheels. (4) determining whether or not a fixing mechanism that fixes the wheel to the axle is loose based on the index; [Effects of the Invention]

[0011] According to the present invention, the influence of the road surface on which the vehicle is traveling can be canceled, and the presence or absence of looseness in the fixing mechanism that fixes the wheel to the axle can be appropriately determined as the state of the wheel. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic diagram showing a wheel state determination 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 wheel state determination device; [Figure 3] 4 is a flowchart showing the process of a wheel state determination method. [Figure 4] FIG. 10 is a diagram illustrating an example of the degree of variation in acceleration. [Figure 5] 4A and 4B are diagrams illustrating the principle of a wheel state determination method. DETAILED DESCRIPTION OF THE INVENTION

[0013] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A wheel state determination device, a wheel state determination method, and a wheel state determination program according to embodiments of the present invention will be described below with reference to the accompanying drawings.

[0014] <1. Overall structure> FIG. 1 is a schematic diagram showing a wheel condition determination device 2 (hereinafter simply referred to as the "determination device 2") according to this embodiment mounted on a vehicle 1. The determination device 2 is configured, for example, as a control unit of the vehicle 1. The vehicle 1 according to this embodiment has a front axle 4a and a rear axle 4b. A left front wheel FL, a right front wheel FR, a left rear wheel RL, and a right rear wheel RR are fixed to both ends of each axle via fixing mechanisms. Each of the wheels FL, FR, RL, and RR includes a wheel disc and a tire mounted to the wheel disc. The fixing mechanism for fixing each of the wheels FL, FR, RL, and RR to the axle is, for example, a hub bolt and a wheel nut tightened to the hub bolt. If the wheel nut loosens from the hub bolt, the wheel will rattle, eventually leading to the wheel coming off the axle. The determination device 2 determines whether the wheel nuts are loose as a wheel condition, and if it determines that the wheel nuts are loose, it issues an alert to the driver of the vehicle 1 to prevent the wheel from coming off the axle.

[0015] An acceleration sensor 6 is attached to each of the wheels FL, FR, RL, and RR to detect acceleration in the axle direction or the vehicle width direction. The acceleration sensor 6 is not particularly limited as long as it can detect the acceleration in the axle direction of each of the wheels FL, FR, RL, and RR, and the location of attachment is also not particularly limited. The acceleration sensor 6 in this embodiment is a triaxial acceleration sensor integrated with an air pressure sensor attached to the air valve of each wheel. The acceleration sensor 6 is connected to the determination device 2 via a communication line 5, and sequentially transmits the acceleration detected for each of the wheels FL, FR, RL, and RR to the determination device 2.

[0016] The vehicle 1 further includes an alarm display 3. The alarm display 3 is not particularly limited as long as it can display an alert warning of loose wheel nuts, and can be realized in any form, such as a liquid crystal display element, a liquid crystal monitor, a plasma display, or an organic EL display. The location where the alarm display 3 is attached can also be selected appropriately, but it is preferable to attach it in a location that is easy for the driver to see, such as on the instrument panel. If the determination device 2 is connected to a car navigation system, it is also possible to use the monitor for the car navigation system as the alarm display 3. The alert displayed on the alarm display 3 can be an icon, graphics, or text information.

[0017] <2. Configuration of the determination device> FIG. 2 is a block diagram showing the electrical configuration of the determination device 2. The determination device 2 is configured as a control unit computer for the vehicle 1 in terms of hardware, and 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 storage device 15. The I / O interface 11 is a communication device for communicating with external devices such as the acceleration 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 or USB memory. The CPU 12 reads and executes the program 9 from the ROM 13, thereby virtually operating as an acceleration acquisition unit 120, a variation derivation unit 121, an index calculation unit 122, a determination unit 123, and an alert generation unit 124. The operation of each unit 120 to 124 will be described later. 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 as appropriate for the calculations of the CPU 12.

[0018] <3. Wheel condition determination method> Hereinafter, a determination process (wheel state determination method) for determining whether or not the fixing mechanisms that fix the wheels FL and FR to the front axle 4a are loose, and whether or not the fixing mechanisms that fix the wheels RL and RR to the rear axle 4b are loose, will be described with reference to Fig. 3. The determination process shown in Fig. 3 is repeatedly executed at predetermined intervals (for example, once every 10 minutes) while the electrical system of the vehicle 1 is in an ON state. In the determination process according to this embodiment, whether or not the fixing mechanisms are loose is determined for the front axle 4a and the rear axle 4b.

[0019] In step S1, the acceleration acquisition unit 120 sequentially acquires the acceleration α in the axle direction of each of the wheels FL, FR, RL, and RR from each acceleration sensor 6. The acceleration acquisition unit 120 associates the acquired acceleration α in chronological order with the wheel and temporarily stores it in the RAM 14 or in the storage device 15. In this embodiment, when the number of acceleration α data stored in step S1 reaches or exceeds a predetermined number, step S2 is executed.

[0020] In step S2, the variation derivation unit 121 derives the variation in the time direction of the acquired time-series acceleration α for each wheel. Specifically, the variation derivation unit 121 extracts N pieces of data that fit into a time window of a predetermined length from t1 to t2 from the time-series acceleration data of each wheel. The length of the time window can be set to, for example, 3 seconds. Then, the variation derivation unit 121 derives the standard deviation σ of the extracted N pieces of data as the variation in the time direction of the acceleration α according to the following formula. In the formula, "α t " represents the acceleration α at time t from t1 to t2, and "α ave " represents the average value of N acceleration α data.

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[0021] When a fixing mechanism is loose, such as when a wheel nut is loose, large vibrations are likely to occur in the axle direction. As a result, as shown in FIG. 4, the absolute value of the acquired acceleration α tends to be larger than in normal conditions, and its variation over time also tends to be larger. However, the acceleration α can also change significantly when the vehicle 1 is turning or traveling on a rough road. In step S2 according to this embodiment, multiple time-series standard deviations σ are derived for each wheel. When the derived standard deviations σ reach a predetermined number (for example, a number corresponding to α for 30 seconds), the next step S3 is executed.

[0022] In step S3, the index calculation unit 122 performs a smoothing process on the time-series standard deviation σ derived for each wheel. Specifically, the index calculation unit 122 calculates a moving average value of the time-series standard deviation σ for each wheel.

[0023] In step S4, the index calculation unit 122 derives an index for comparing the variation in acceleration α between wheels on the same axis. More specifically, the index calculation unit 122 calculates left and right wheel differences Δσ1 and Δσ2 (at the same time) of the moving average value of the standard deviation σ calculated in step S3 as the index. In this embodiment, the left and right wheel difference Δσ1 is the absolute value of the difference between the moving average value of the standard deviation σ calculated for wheel FL and the moving average value of the standard deviation σ calculated for wheel FR. Furthermore, the left and right wheel difference Δσ2 is the absolute value of the difference between the moving average value of the standard deviation σ calculated for wheel RL and the moving average value of the standard deviation σ calculated for wheel RR. Vibrations that the wheels receive from the road surface are generally synchronized at both ends of the axle. Therefore, by comparing the variation in acceleration α at the same time for each wheel attached to both ends of the axle, the influence of the road surface on the acceleration α is canceled, and the left and right wheel differences Δσ1 and Δσ2 mainly reflect the influence of loosening of the fixing mechanism.

[0024] 5, if there is no looseness in the fixing mechanism of either the left front wheel FL or the right front wheel FR, the left-right wheel difference Δσ1 will be a value close to 0, and if there is no looseness in the fixing mechanism of either the left rear wheel RL or the right rear wheel RR, the left-right wheel difference Δσ2 will be a value close to 0. On the other hand, if there is looseness in the fixing mechanism of the left front wheel FL or the right front wheel FR, the left-right wheel difference Δσ1 will be a value significantly larger than 0, and if there is looseness in the fixing mechanism of the left rear wheel RL or the right rear wheel RR, the left-right wheel difference Δσ2 will be a value significantly larger than 0.

[0025] In step S5, the determination unit 123 determines whether or not there is looseness in the fixing mechanism based on the left and right wheel differences Δσ1 and Δσ2. Specifically, the determination unit 123 compares the left and right wheel difference Δσ1 with a predetermined threshold value Th1. If the left and right wheel difference Δσ1 exceeds the threshold value Th1 (>0), the determination unit 123 determines that there is looseness in the fixing mechanism of the left front wheel FL or the right front wheel FR. If the left and right wheel difference Δσ1 is equal to or less than the threshold value Th1, the determination unit 123 determines that there is no looseness in the fixing mechanism of the left front wheel FL or the right front wheel FR. Similarly, the determination unit 123 compares the left and right wheel difference Δσ2 with a predetermined threshold value Th2 (>0). If the left and right wheel difference Δσ2 exceeds the threshold value Th2, the determination unit 123 determines that there is looseness in the fixing mechanism of the left rear wheel RL or the right rear wheel RR. If the left and right wheel difference Δσ2 is equal to or less than the threshold value Th2, the determination unit 123 determines that there is no looseness in the fixing mechanism of the left rear wheel RL or the right rear wheel RR. The threshold values ​​Th1 and Th2 can be determined in advance based on experimental data obtained under conditions where there is no loosening in any of the fixing mechanisms of the vehicle 1 and under conditions where loosening is intentionally caused in the fixing mechanisms. The threshold values ​​Th1 and Th2 may be the same value or different values.

[0026] If it is determined in step S5 that there is looseness in the fixing mechanism of the left front wheel FL or the right front wheel FR, or if it is determined that there is looseness in the fixing mechanism of the left rear wheel RL or the right rear wheel RR (YES), step S6 is executed. On the other hand, if it is determined in step S5 that there is no looseness in any of the fixing mechanisms (NO), step S1 is executed again.

[0027] In step S6, the alert generation unit 124 generates an alert that warns of a possible wheel runoff and outputs the alert to the warning display 3. The alert can be text information, an icon, or graphics that notify the driver that the securing mechanism is loose. Furthermore, the alert may include text information, an icon, or graphics that indicate the axle whose securing mechanism is estimated to be loose, or text information, an icon, or graphics that urges the driver to inspect the securing mechanism.

[0028] <4. Features> (1) According to the determination device 2 of the above embodiment, the influence of the road surface on which the vehicle 1 is traveling on the acceleration α is canceled out between wheels attached to the same axle. Therefore, it is possible to appropriately determine whether there is a sign of wheel derailment without separately determining the road surface on which the vehicle 1 is traveling. Furthermore, by deriving the standard deviation σ of the acceleration α extracted within a fixed time window rather than the wheel acceleration α itself, the influence of accidental data is reduced. This reduces the possibility of misjudging the wheel state and issuing an erroneous alert.

[0029] (2) According to the determination device 2 of the above embodiment, a smoothing process is performed before comparing the standard deviations σ between wheels mounted on the same axle. This makes it possible to cancel the influence of the road surface even if the changes in the acceleration α between the wheels are not synchronized at exactly the same timing.

[0030] <5. Variations> 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.

[0031] (1) The vehicle 1 is not limited to a four-wheel vehicle. The vehicle 1 may have more axles or more wheels. The wheel state determination method described above may be applied to only one of the front axle 4a or the rear axle 4b.

[0032] (2) Step S3 may be omitted. In other words, the moving average of the standard deviation σ may not be calculated, and the standard deviations σ calculated at the same time may be compared for wheels attached to the same axle. Furthermore, the determination in step S5 may be performed, for example, for a plurality of chronologically consecutive left-right wheel differences Δσ1 and left-right wheel differences Δσ2, and a "YES" determination may be made if a predetermined number or more of left-right wheel differences Δσ1 exceeding the threshold value Th1 exist, or if a predetermined number or more of left-right wheel differences Δσ2 exceeding the threshold value Th2 exist.

[0033] (3) The acceleration sensor 6 may be attached to the front axle 4a or the rear axle 4b instead of to the wheels. The acceleration sensor 6 may also communicate data with the determination device 2 wirelessly.

[0034] (4) The variation in acceleration α over time is not limited to standard deviation σ, but may be other statistical indicators that represent data variation, such as variance. Furthermore, the indicator for comparing the variation in acceleration α between wheels is not limited to left-right wheel difference Δσ1 and left-right wheel difference Δσ2, but may be, for example, the ratio of the variation between the left and right wheels. [Explanation of symbols]

[0035] 1 vehicle 2 Judgment device 3 Alarm indicator 4a front axle 4b rear axle

Claims

1. an acceleration acquisition unit that sequentially acquires acceleration in the axle direction for each of the wheels attached to both ends of the axle of the vehicle; a variation deriving unit that derives a variation in the acceleration of each of the wheels in a time direction based on the sequentially acquired acceleration; an index calculation unit that derives an index for comparing the variations between the wheels; a determination unit that determines whether or not a fixing mechanism that fixes the wheel to the axle is loose based on the index; Equipped with Wheel condition determination device.

2. the index calculation unit derives an index for comparing the variations smoothed for each wheel between the wheels; The wheel state determination device according to claim 1 .

3. an alert generation unit that generates and outputs an alert when the determination unit determines that the fixing mechanism is loose; Further provided with The wheel state determination device according to claim 1 or 2.

4. 1. A wheel state determination method executed by one or more computers, comprising: Sequentially acquiring acceleration in the axle direction for each of the wheels attached to both ends of the axle of the vehicle; deriving a time-direction variation of the acceleration for each of the wheels based on the sequentially acquired accelerations; deriving an index for comparing the variability between the wheels; determining whether or not a fixing mechanism that fixes the wheel to the axle is loose based on the index; Including, Wheel condition determination method.

5. Sequentially acquiring acceleration in the axle direction for each of the wheels attached to both ends of the axle of the vehicle; deriving a time-direction variation of the acceleration for each of the wheels based on the sequentially acquired accelerations; deriving an index for comparing the variability between the wheels; determining whether or not a fixing mechanism that fixes the wheel to the axle is loose based on the index; on one or more computers, Wheel condition determination program.

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