Patent Application
20230070044
The present invention relates to a method for estimating a degree of wear of a tire and a method for determining whether a wear shape of the tire during travelling is center wear or not.
Conventionally, as a method for estimating a degree of wear of a tire, there has been proposed a method which includes disposing an acceleration sensor inside the tire; calculating an index of deformation velocity at a contact edge of the tire, the index being magnitude of one of or both of positive and negative peaks detected by the acceleration sensor and appearing in a differential waveform of acceleration in a radial direction around the contact edge; calculating a contact time ratio of contact time to rotation time of the tire, the contact time being a time interval between the positive peak and the negative peak, and the rotation time of the tire being a time interval between either of the positive peaks or the negative peaks; and estimating the degree of wear of the tire from the calculated index of deformation velocity and the contact time ratio and maps which have been obtained in advance and which represent relationships among a residual groove amount which is the degree of wear of the tire, the index of deformation velocity and the contact time ratio (See, for example, Patent Document 1).
However, there has been a problem that, as in the above-mentioned Patent Document 1, when the residual groove amount of the tire is estimated from the index of the deformation velocity and the contact time ratio, with a tire whose wear shape is the center wear, an actual residual groove amount is detected to be shifted toward a new tire side (the estimated wear amount becomes smaller than the actual wear amount).
As noted from the figure, the relationship between the index of deformation velocity and the contact time ratio of the tire whose wear shape is the center wear, is shifted toward the new tire side.
The present invention has been made in view of the conventional problem and aims at providing a method for determining whether the wear shape of a tire is the center wear or not, and a method for accurately estimating the degree of wear of the tire during travelling regardless of the wear shape of the tire.
An aspect of the present invention relates to a method for estimating a degree of wear (a residual groove amount or a wear amount) of a tire during travelling, in which the degree of wear is estimated by using: an index of deformation velocity at a tire contact edge or in the vicinity of the tire contact edge, the index of the deformation velocity having been calculated from magnitude (a derivative peak value at a contact edge) of one of or both of positive and negative peaks appearing in a radial acceleration waveform obtained by differentiating a time-series waveform of tire radial acceleration detected by an acceleration sensor mounted on the tire; a contact time ratio of contact time to tire rotation time, the contact time being a time interval between the positive peak and the negative peak, the tire rotation time being a time interval between either of positive peaks or negative peaks; and a deflection amount which is a difference between a tire radius and an effective radius (a distance between the center of the axle and the road surface), the tire radius being a radius of the tire under a non-loaded state and the effective radius being a radius of the tire during travelling.
In this way, since the degree of wear of the tire was estimated by using the deflection amount of the tire as a measure of wear in addition to the index of the deformation velocity and the contact time ratio of the tire during travelling, the degree of wear of the tire can be estimated with high accuracy regardless of whether the wear shape of the tire is the center wear or not.
Incidentally, the degree of wear of the tire may be obtained from a regression formula, which has been obtained in advance, using as variables, the index of deformation velocity, the contact time ratio and the deflection amount, or after determining whether the wear shape is the center wear or not, if it is the center wear, the degree of wear estimated from the index of deformation velocity and the contact time ratio may be corrected.
Alternatively, two master curves, which are a master curve of the even wear and a master curve of the center wear, may be prepared, and the master curve may be selected according to the wear shape.
It should be noted that the above-described summary of the invention does not enumerate all the necessary features of the present invention, and subcombinations of these feature groups can also be the invention.
Each of the means from the acceleration differential waveform arithmetic means 12 to the residual groove amount estimating means 18 is configured by, for example, computer software and memories such as a RAM and the like. Hereinafter, each of the means from the acceleration differential waveform arithmetic means 12 to the residual groove amount estimating means 18 is referred to as an arithmetic unit 10B. In this embodiment, the arithmetic unit 10B was installed on the vehicle body side, but it may be installed inside the tire.
As illustrated in
The first acceleration sensor 11A is so disposed that a detection direction becomes the tire radial direction, and detects tire radial acceleration aR (t) input from the road surface, and the second acceleration sensor 11B is so disposed that a detection direction becomes the tire circumferential direction and detects tire circumferential acceleration aT (t). Incidentally, in each figure, the x direction is a vehicle travel direction, the y direction is a vehicle width direction (tire width direction), and the z direction is a vertical direction.
Although a figure is omitted, amplifiers that amplify outputs of the first and second acceleration sensors 11A and 11B, respectively, A/D converters, a transmitter that transmits the A/D-converted signals to the arithmetic unit 10B, and other components are housed in the sensor case 11. In a case where the arithmetic unit 10B was disposed inside the tire 1, namely, in the sensor case 11 or the like, estimation results obtained by the arithmetic unit 10B may be transmitted to a vehicle control unit (not shown) installed on the vehicle body side.
Since sizes of the first and second acceleration sensors 11A and 11B are quite small compared to the size of the tire 1, it can be assumed that these sensors are in approximately the same position. Hereinafter, the position of the first and second acceleration sensors 11A and 11B, shown at a point A in
The acceleration differential waveform arithmetic means 12 extracts a radial acceleration waveform, which is a time-series waveform of tire radial acceleration detected by the first acceleration sensor 11A, and calculates an acceleration differential waveform, which is a waveform obtained by time-differentiating the extracted radial acceleration waveform.
As illustrated in
The derivative peak value calculating means 13 calculates a derivative peak value VRf on the leading-edge side, which is the magnitude of the peak Pf on the leading-edge side, uses this value as a deformation velocity index VR, and sends this deformation velocity index VR to the residual groove amount estimating means 18. Incidentally, as the deformation velocity index VR, a derivative peak value VRk on the trailing-edge side, which is the acceleration differential value on the trailing-edge side, may be used, or an average value of the derivative peak value VRf on the leading-edge side and the derivative peak value VRk on the trailing-edge side may be used.
The contact time ratio calculating means 14 calculates the rotation time Tr, which is a time difference between time T1 when the trailing-edge side peak Pk has appeared and time T2 when this trailing-edge side peak appears again after one rotation of the tire 1, and the contact time Tt, which is the time between the leading-edge side peal Pf and the trailing-edge side peak Pk, and calculates the contact time ratio Rc obtained by dividing the calculated contact time Tt by the rotation time Tr. The calculated contact time ratio Rc is sent to the residual groove amount estimating means 18.
Incidentally, Tf=T2−T1, and Rc=(Tt/Tr).
The angular velocity estimating means 15 estimates a rotation angular velocity ω(t) of the tire 1 from the tire radial acceleration aR(t) and the tire circumferential acceleration aT(t) respectively detected by the first and second acceleration sensors 11A and 11B.
The deflection amount calculating means 16 calculates the locus of the measurement point A from the tire radial acceleration aR(t) and the tire circumferential acceleration aT(t) respectively detected by the first and second acceleration sensors 11A and 11B, and from the rotation angular velocity ω(t) estimated by the angular velocity estimating means 15, obtains an outer shape of the tire 1, which is a vertical sectional shape of the tire 1 during travelling, and estimates a deformation amount d from this outer shape of the tire 1. The deflection amount d can be expressed as d=R−Reff, where R is a tire radius which is the radius of the tire 1 under a non-loaded state, and Reff is an effective radius which is the radius of the tire during travelling.
The method for estimating the rotation angular velocity ω(t) and the method for calculating the deflection amount d will be described later.
The memory means 17 stores a plurality of Rc-VR maps 17M1 to 17Mn which have been obtained in advance. The Rc-VR maps 17M1 to 17Mn are maps for estimating the degree of wear of the tire 1 and are created for each deflection amount dk (k=1 to n). In this embodiment, the residual groove amount H is used as the degree of wear, however, a wear amount M may be used as the degree of wear. The wear amount M is expressed as M=H0−H, where H0 is the groove depth of the tire 1 when the tire 1 is new and H is the residual groove amount.
As illustrated in
The Rc-VR maps 17M1 to 17Mn can be obtained by using data of the contact time ratio Rc data of the deformation velocity index VR, and data of the deflection amount d, which are the data of the time when a vehicle equipped with multiple test tires including a new tire (New) and a tire worn close to the slip sign (Full-worm), which are different in the residual groove amount HM and the wear shape, was run under various load states.
In the case of shoulder wear, if the residual groove amount of the center part is almost the same with a residual groove amount of even wear, the contact time ratio Rc the deformation velocity index VR, and the deflection amount d become almost the same as in the case of the even wear, hence in this embodiment, as the wear shape, two types of wear shapes were used, which were the center wear and the even wear.
The residual groove amount estimating means 18 estimates the residual groove amount H, which is the degree of wear of the tire 1, by using the deformation velocity index VR calculated by the derivative peak value calculating means 13, the contact time ratio Rc calculated by the contact time ratio calculating means 14, the deflection amount d calculated by the deflection amount calculating means 16, and the Rc-VR maps 17M1 to 17Mn which have been stored in the memory means 17.
As described above, the Rc-VR maps 17M1 to 17Mn were obtained by using the tire radial acceleration aR (t) and the tire circumferential acceleration aT (t), which were detected by running the vehicle equipped with the test tires which are different in the residual groove amount H and the wear shape. Thus, by using the Rc-VR maps 17M1 to 17Mn, it is possible to accurately estimate the residual groove amount H regardless of whether the wear shape is the center wear or not.
Incidentally, as illustrated in
Next, the method for estimating the tire wear according to the first embodiment of the present invention will be described with reference to the flowchart in
First, the first and second acceleration sensors 11A and 11B disposed in the inner liner part 2 of the tire 1 respectively detect the tire radial acceleration aR(t) and the tire circumferential acceleration aT(t), which are input from the road surface to the tire 1 (Step S10).
Next, the acceleration differential waveform, which is the waveform obtained by time-differentiating the tire radial acceleration aR(t), is obtained (Step S11), and the derivative peak value VRf on the leading-edge side, which is the magnitude of the peak Pf on the leading-edge side of this acceleration differential waveform, is calculated, and this is used as the deformation velocity index VR (Step S12). Furthermore, after calculating the contact time Tt which is the interval between the peak Pf on the leading-edge side and the peak pk on the trailing-edge side and the rotation time Tr which is the interval between two peaks Pk1 and Pk2 on the trailing-edge side, in the acceleration differential waveform (Step S13), the contact time ratio Rc, which is the ratio of the contact time Tt to the rotation time Tr, is calculated (Step S14). The contact time ratio Rc can be expressed as Tt/Tr.
Next, from the tire radial acceleration aR (t) and the tire circumferential acceleration aT(t) detected in Step S10 above, the rotation angular velocity ω(t) of the tire 1 is calculated (Step S15). Then, from the tire radial acceleration aR(t), the tire circumferential acceleration aT (t) and the rotation angular velocity ω(t), the deflection amount d of the tire 1 is calculated (Step S16).
Incidentally, the calculation of the deformation velocity index VR, the calculation of the contact time ratio Rc and the calculation of the deflection amount d are not necessarily be performed in this order, and the sequential order may be changed, or may be processed in parallel.
Finally, by using the deformation velocity index VR calculated in Step S13, the contact time ratio Rc calculated in Step S15, the deflection amount d calculated in Steps S16-S17, and the Rc-VR maps 17M1 to 17Mn which have been obtained in advance, the residual groove amount H, which is the degree of wear of the tire 1, is estimated (Step S17).
The method for estimating the rotation angular velocity ω(t) in Step S15 is as follows.
First, as illustrated in
Next, from the tire circumferential acceleration aT(t), the tire circumferential velocity v(t) is calculated by using the following equation (1).
v(t)=∫0taT(s)ds+V0 (1)
where, V0 is the vehicle velocity, which can be calculated from the tire rotation period, the tire radius, GPS data, and so on. For v(t), preprocessing such as centering may be performed.
As illustrated in
Next, from the tire radial acceleration aR(t) and the tire circumferential velocity v(t), the rotation angular velocity ω(t) of the tire 1 is estimated by the following equation (2).
ω(t)=aR(t)/v(t) (2)
The equation (2) above was derived on the assumption that the sensor (measurement point A) is in a uniform circular motion at a given time t. The acceleration aR(t) and the velocity v(t) when the measurement point A is in the uniform circular motion can be expressed by the following equation.
a
R(t)=v2(t)/R(t)
v(t)=R(t)ω(t)
where R (t) is the radius of curvature at the time t.
The above equation (2) can be obtained by eliminating R(t) from the above two equations and solving for ω(t).
Next, an explanation is given as to the method for calculating the deflection amount d in Step S16.
In this embodiment, the deflection amount d is calculated from the locus of the measurement point A.
First, an estimated value of the rotation angular velocity ω(t) is integrated by using the following equation (3) to obtain a temporally-varying waveform of a rotational angle θ. The rotation angle θ of the measurement point is, as illustrated in
θ(t)=∫0tωT(s)ds+θ0 (3)
Next, as shown in the equations (4) and (5) below, by using the above-mentioned rotation angle θ(t), the tire radial acceleration aR(t) and the tire circumferential acceleration aT(t) are coordinate-transformed to acceleration in the front-back direction ax(t) and acceleration in the vertical direction az (t), which are the accelerations of a global coordinate system (x, z). The global coordinate system (x, z) is the coordinate system with the x direction being the vehicle travel direction, the y direction being the vehicle width direction (tire width direction) and the z direction being the vertical direction, which are illustrated in
a
x(t)=aT(t)cos θ(t)−aR(t)sin θ(t) (4)
a
z(t)=aT(t)sin θ(t)+aR(t)cos θ(t) (5)
Temporally-varying waveforms of the acceleration ax(t) in the front-back direction and the acceleration az(t) in the vertical direction are illustrated in
Next, the accelerations transformed to the global coordinate system are integrated and the front-back direction velocity vx(t) and the vertical direction velocity vz(t) of the measurement point A are calculated by using the following equations (6) and (7).
v
x(t)=∫0tax(s)ds+vx0 (6)
v
x(t)=∫0taz(s)ds+vz0 (6)
However, ax(t) and az(t) may involve a preprocessing such as centering. Furthermore, initial values vx0 and vz0 may be set to any values.
The temporally-varying waveforms of the front-back direction velocity vx(t) and the vertical direction velocity vz(t) are illustrated in
Furthermore, the velocities are integrated and displacement ux(t) in the front-back direction and displacement uz(t) in the vertical direction are calculated by using the following equations (8) and (9).
u
x(t)=∫0tvx(s)ds+ux0 (8)
u
x(t)=∫0tvz(s)ds+uz0 (9)
However, vx(t) and vz(t) may involve the preprocessing such as the centering. Furthermore, the initial values ux0 and uz0 may be set to any values.
The temporally-varying waveforms of the displacement ux(t) in the front-back direction and the displacement uz(t) in the vertical direction are illustrated in
Then, by excluding the time component and drawing the displacement ux(t) and uz(t) in a two-dimensional plane, the locus of the measurement point A is obtained as illustrated in
A regression circle Cfit is obtained by fitting the circle with respect to the locus of the measurement point A, and a regression radius Rfit, which is the radius of the regression circle Cfit, is obtained, and also an effective radius Reff, which is the radius of the tire 1 in the deflected state, is obtained. In this embodiment, as illustrated in the schematic diagram of
Finally, the deflection amount d is calculated by using the following equation.
d=R
fit
−R
eff
Incidentally, as the deflection amount d for estimating the degree of wear, or a feature amount to be used in the center wear determination described later, either the deflection amount d or a deflection ratio kd=d/Rfit may be appropriate.
Since from the first and second acceleration sensors 11A and 11B to the deflection amount calculating means 16, each of which is denoted by the same reference sign as that in the first embodiment, have the same configurations as that in the first embodiment, explanations thereof are omitted.
The identification model memory means 21 stores a wear shape identification model 21M which has been obtained in advance.
As illustrated in
After obtaining feature vectors YZ=(RcZ, VRZ, dZ) composed of data of the contact time ratio Rc, data of the deformation velocity index Va and data of the deflection amount d, which were obtained when a vehicle equipped with multiple test tires of different residual groove amounts H and different wear shapes was run under various loading states, the reference feature vector YZSV and the Lagrange multiplier λZ are obtained by a support vector machine (SVM) using these feature vectors Yz as learning data.
The wear shape determining means 22, after calculating the Kernel functions KN (X, YNSV) and KM (X, YMSVV) by using the feature vector X (Rc, VR, d) composed of the deformation velocity index VR calculated by the derivative peak value calculating means 13, the contact time ratio Rc calculated by the contact time ratio calculating means 14 and the deflection amount d calculated by the deflection amount calculating means 16, and the support vectors YNSV and YMCVV and the Lagrange multipliers λN and λM stored in the identification model memory means 21, obtains the value of the identification function fNM (x) for identifying the wear shape of the tire by using these Kernel functions KN (X, YNSV) and KM (X, YMSVV), and determines, from the value of the identification function fNM (x), whether the wear shape of the tire 1 is the N state (even wear) or the M state (center wear). A result of the determination by the wear shape determining means 22 is sent to the residual groove amount estimating means 24.
Incidentally, as the Kernel functions KN and KM, a Gaussian kernel or the like is suitably used, for example.
The R-V map memory means 23 stores a first Rc-VR map 23N (Even-Map) and a second Rc-VR map 23M (Center-Map), which have been obtained in advance, in which a first master line LNj and a second master line LMj are respectively drawn on a plane whose horizontal axis being the contact time ratio Rc and whose vertical axis being the deformation velocity index VR. The first master line LNj represents the relationship between the contact time ratio Rc and the deformation velocity index VR of a worn tire whose residual groove amount is Hj and whose wear shape is the even wear, and the second master line LMj represents the relationship between the contact time ratio Rc and the deformation velocity index VR of a worn tire whose residual groove amount is Hj and whose wear shape is the center wear.
Each of the first and second Rc-VR maps 23N and 23M is a map for estimating the degree of wear from the contact time ratio Rc and the deformation velocity index VR. The first Rc-VR map 23M is obtained by using the data of the contact time ratio Rc and the data of the deformation velocity index VR obtained when the vehicle, which was equipped with plural test tires whose wear shape is the even wear and whose residual groove amount H is different from each other, was run under various load conditions.
On the other hand, the second Rc-VR map 23M is obtained by using the data of the contact time ratio 1 and the data of the deformation velocity index VR obtained when the vehicle, which was equipped with plural test tires whose wear shape is the center wear and whose residual groove amount H is different from each other, was run under the various load conditions.
The residual groove amount estimating means 24 estimates the residual groove amount H, which is the degree of wear of the tire 1, by using the deformation velocity index VR calculated by the derivative peak value calculating means 13, the contact time ratio Rc calculated by the contact time ratio calculating means 14, and the first Rc-VR map 23N or the second Rc-VR map 23M having been stored in the R-V map memory means 23.
More specifically, in a case where the wear shape of the tire 1 was determined to be the even wear by the wear shape determining means 22, the residual groove amount estimating means 24 estimates the residual groove amount H, which is the degree of wear of the tire 1, by using the above-mentioned calculated deformation velocity index VR, the contact time ratio Rc and the first Rc-VR map 23N. In a case where the wear shape was determined to be the center wear, the residual groove amount estimating means 24 estimates the residual groove amount H, which is the degree of wear of the tire 1, by using the above-mentioned calculated deformation velocity index VR, the contact time ratio Rc and the second Rc-VR map 23M.
As described above, after calculating the deformation velocity index VR by the derivative peak value calculating means 13, the contact time ratio Rc by the contact time ratio calculating means 14 and the deflection amount d by the deflection amount calculating means 16, the determination was made as to whether the wear shape of the tire is the even wear or the center wear by using a machine learning algorithm, on the basis of the feature amount vector X (Rc, VR, d) composed of the above-mentioned calculated deformation velocity index VR, the contact time ratio Rc and the deflection amount d, and the determination model (wear shape identification model 21M), which has been obtained in advance for each wear shape and which is structured with, as learning data, the support vector YZ=(RcZ, VRZ, dZ) which is the feature amount vector. Hence, the wear shape of the tire 1 can be determined accurately.
In addition, since the degree of wear of the tire 1 in question was estimated taking the wear shape into consideration, the degree of wear of the tire during travelling can be accurately estimated regardless of the wear shape of the tire.
The present invention has been described using the embodiments, however, the technical scope of the invention is not limited to the scope described in the embodiments. It is clear to those skilled in the art that various modifications or improvements can be made to the above-described embodiments. It is clear from the claims that such modifications or improvements can also be included in the technical scope of the present invention.
For example, in the above-described first and second embodiments, the rotation angular velocity ω(t) was estimated from the tire radial acceleration aR(t) and the tire circumferential acceleration aT(t), however, the rotation angular velocity ω(t) may be directly measured by using an angular velocity sensor such as an oscillation gyroscope. It is preferable to install the angular velocity sensor at the measurement point A.
Also, with respect to the deflection amount d, by disposing a distance sensor on the vehicle equipped with the tire 1 and measuring a distance between the vehicle and the road surface, the deflection amount d may be calculated from the distance between the vehicle and the road surface. Specifically, by converting the distance between the disposed position of the distance sensor and the road surface into a distance between the axle and the road surface and using the converted distance as the effective radius Reff, a difference between this effective radius and the tire radius R may be used as the deflection amount d.
In the above-described second embodiment, the wear shape determining means 22 was configured of the support vector machine (SVM), however, other machine learning algorithm such as a logistic regression, a random forest, a neural network, or the like may be used.
In addition, in the above-described second embodiment, it was configured to select the map for estimating the degree of wear by the wear shape. However, it may be configured to prepare only the first Rc-VR map 23N and obtain a correction amount ΔH in advance, which is a difference between the residual groove amount HN of the case where the wear shape is the even wear and the residual groove amount HM of the case where the wear shape is the center wear, in both cases, the contact time ratio Rc and the deformation velocity index VR are the same, and in the case where the wear shape is the center wear, a residual groove amount H′ obtained by the first Rc-VR map 23N may be corrected to H=H′+ΔH and output. Incidentally, in the case where the wear shape is not the center wear, no correction is required and H′ may be output as it is.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2020-054835 | Mar 2020 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2020/048867 | 12/25/2020 | WO |
