Tire physical quantity calculation device

Abstract

To provide a tire physical quantity calculation device which can improve calculation accuracy of a ground load of a tire and calculate tire lateral force at an actual vehicle level.SOLUTION: There is provided a tire physical quantity calculation device 10 which calculates a physical quantity acting on a tire 3 on the basis of the shape of the tire 3 during travel. The tire physical quantity calculation device comprises: a marker group 11 which is set on an internal surface 3b of the tire 3; a camera 30 which can image the entire region of the marker group 11 every time a portion corresponding to the marker group 11 on an outer surface 3a of the tire 3 touches the ground; and a control board 33 which analyzes the internal surface grounding shape of the tire 3 on the basis of the image captured by the camera 30 and extracts a prescribed feature quantity in the internal surface grounding shape. The device is configured to calculate the tire lateral force Fy and ground load Fz acting on the tire 3 on the basis of the prescribed feature quantity by using a prescribed conversion formula.SELECTED DRAWING: Figure 1

Description

[[Technical Field]]

[0001] The present invention relates to a tire physical quantity calculation device that calculates physical quantities acting on a running tire. [[Background Art]]

[0002] Conventionally, various techniques have been proposed for detecting the state of a tire during running and calculating physical quantities acting on the tire based on the detected tire state.

[0003] For example, Patent Document 1 discloses a tire motion parameter sensing system that estimates five motion parameters including load, contact patch area, ground contact normal vector, rotation speed, and lateral inclination angle by detecting, with a detection wave sensor mounted on a wheel, a detection wave that is emitted from an emission source mounted on the wheel toward the inner wall of the tire and reflected therefrom. [[Prior Art Literature]] [[Patent Literature]]

[0004] [[Patent Document 1]] Japanese Unexamined Patent Application Publication No. 2017-075944 [[Summary of the Invention]] [[Problem to be Solved by the Invention]]

[0005] However, in the arrangement of Patent Document 1 mentioned above, the ground contact load is estimated from the product of the vertical deformation amount of the tire and the longitudinal elastic modulus. However, the detection range of the detection wave sensor, which has one-to-one correspondence between emission and reflection, is originally narrow, and when the vehicle turns, deformation in the width direction of the tire increases the range that cannot be detected by the detection wave sensor. As a result, there is a problem that the measurement accuracy of the vertical deformation amount decreases, which in turn reduces the calculation accuracy of the tire ground contact load.

[0006] Furthermore, although tire lateral force is an important physical quantity during vehicle turning, it is difficult to estimate tire lateral force from the five motion parameters estimated by Patent Document 1, and existing six-component force meters capable of measuring tire lateral force cannot be applied to actual vehicles.

[0007] This invention has been made in view of the above, and its objective is to provide a tire physical quantity calculation device that can improve the accuracy of calculating the tire contact load and calculate the tire lateral force at the level of an actual vehicle. [Means for solving the problem]

[0008] To achieve the above objective, the tire physical quantity calculation device according to the present invention calculates the tire lateral force and contact load acting on the tire using a predetermined conversion formula based on predetermined characteristic quantities in the inner contact shape of the tire.

[0009] Specifically, the present invention relates to a tire physical quantity calculation device that calculates the physical quantities acting on a tire based on the shape of the tire while it is in motion.

[0010] The tire physical quantity calculation device comprises a marker set on the inner surface of the tire, a camera capable of capturing the entire area of ​​the marker each time the corresponding part of the outer surface of the tire makes contact with the road surface, and a feature quantity extraction unit that analyzes the inner contact shape of the tire based on the image captured by the camera and extracts predetermined feature quantities from the inner contact shape. The marker is set on the inner surface of the tire as a black and white grid pattern, corresponding to the contact shape of the outer surface of the tire when it makes contact with the road surface. The feature quantity extraction unit extracts the contact length on the inner side in the vehicle width direction, the contact length at the center in the vehicle width direction, the contact length on the outer side in the vehicle width direction, and the contact area with respect to the inner contact shape. Based on the three contact lengths, it calculates the tire lateral force acting on the tire using a predetermined conversion formula, and based on the contact length at the center in the vehicle width direction and the contact area, it calculates the ground load acting on the tire using a predetermined conversion formula. Furthermore, in calculating the inner contact shape of the tire based on the image captured by the camera, a point cloud representing the coordinates of a minute portion of the tire in three-dimensional space is estimated based on the known position and orientation of the camera and a two-dimensional image of the black and white grid pattern of the marker captured by the camera. A longitudinal section of the tire is then created based on these estimated point clouds, and the boundary between the contact portion and the non-contact portion of the tire is determined based on this longitudinal section. It is characterized by the following:

[0011] Furthermore, "internal contact shape" refers to the shape of the inner surface of the tire that corresponds to the contact shape of the outer surface of the tire when the tire actually makes contact with the road surface.

[0012] With this configuration, a camera with a relatively wide field of view is used to image the entire area of ​​the marker set on the inner surface of the tire, and the inner surface contact shape of the tire is analyzed based on the captured image, thereby enabling the accurate extraction of predetermined feature quantities in the inner surface contact shape.

[0013] By using a predetermined conversion formula based on these precisely extracted features, the accuracy of calculating the tire's contact load can be improved, and the lateral tire force, which was previously difficult to calculate at the actual vehicle level, can now be calculated. [Effects of the Invention]

[0014] As described above, the tire physical quantity calculation device according to the present invention improves the accuracy of calculating the tire's contact load and enables the calculation of tire lateral force at the level of an actual vehicle. [Brief explanation of the drawing]

[0015] [Figure 1] This figure schematically shows a tire physical quantity calculation device according to an embodiment of the present invention. [Figure 2] Figure (a) schematically shows the analyzed inner contact shape of the tire and the contact shape (the distribution of contact pressure where the tire and road surface actually make contact). Figure (b) is a graph showing regression line 1 related to tire lateral force, and Figure (c) is a graph showing regression line 2 related to contact load. [Figure 3] This flowchart shows an example of the process performed by the tire physical quantity calculation device. [Modes for carrying out the invention]

[0016] Hereinafter, embodiments for carrying out the present invention will be described based on the drawings.

[0017] -Device configuration- Figure 1 is a schematic diagram of the tire physical quantity calculation device 10 according to this embodiment, where Figure (a) is a side view of the wheel 1 to which the tire physical quantity calculation device 10 is attached, Figure (b) is a cross-sectional view taken along the line bb in Figure a, and Figure (c) is a diagram showing an example of a marker. The tire physical quantity calculation device 10 calculates the physical quantities acting on the tire 3 based on the shape of the tire 3 while it is running.

[0018] The wheel 1 to which the tire physical quantity calculation device 10 is attached, as shown in Figure 1(a), has a pneumatic rubber tire 3 attached around a wheel 5, and is the same as a normal wheel except that a battery 40 and the like are attached to the wheel 5.

[0019] A tire physical quantity calculation apparatus 10, as shown in FIG. 1(b), includes a marker group 11, a magnetic sensor 20, a magnet 21, a bracket 23, a camera 30, a control board 33, a lighting 35, a battery 40, a bracket 41, and a wiring 50 that electrically connects the magnetic sensor 20, the control board 33 and the battery 40.

[0020] As shown in FIG. 1(c), the marker group 11 is provided on the inner surface 3b of a tire 3 as a black-and-white grid pattern formed of a plurality of white markers 13 and a plurality of black markers 15. Each white marker 13 is formed in a rectangular shape, and its shape is grasped by the three-dimensional coordinates (x, y, z) of four vertices 13a, 13b, 13c, 13d and midpoints 13e, 13f, 13g, 13h of four sides. The same applies to each black marker 15.

[0021] The magnetic sensor 20 is attached to a wheel 5 on the side opposite to the marker group 11 by 180 degrees in the wheel 1. The magnet 21 is connected to a vehicle fixing part 7 such as a brake caliper via the bracket 23 so that the magnet 21 comes closest to the magnetic sensor 20 when the portion corresponding to the marker group 11 on the outer surface 3a of the tire 3 touches the ground, in other words, when the magnetic sensor 20 attached to the wheel 5 reaches the highest position. Therefore, when the magnetic sensor 20 detects the magnetism of the magnet 21, the ground contact timing of the portion corresponding to the marker group 11 on the outer surface 3a of the tire 3 can be grasped. The detection result obtained by the magnetic sensor 20 is transmitted to the control board 33 via the wiring 50.

[0022] The camera 30 and the control board 33 are attached to a portion of the wheel 5 that faces the marker group 11. In the vicinity of the camera 30 on the wheel 5, a lighting 35 for illuminating the inner surface 3b of the tire 3 is attached. The imaging timing of the camera 30 and the lighting timing of the lighting 35 are controlled by the control board 33. The image data captured by the camera 30 is transmitted to the control board 33. A lens 31 adjusted to enable capturing an image of the entire area of the marker group 11 is attached to the camera 30.

[0023] With this configuration, when the magnetic sensor 20 detects the magnetism of the magnet 21, the control board 33 triggers the illumination 35 and causes the camera 30 to image the inner surface 3b of the tire 3. As a result, each time a part of the outer surface 3a of the tire 3 corresponding to the marker group 11 touches the ground, the entire area of ​​the marker group 11 is imaged by the camera 30. The analysis of the inner surface contact shape 103 (see Figure 2) of the tire 3 by the control board 33, the extraction of predetermined feature quantities in the inner surface contact shape 103, and the calculation of physical quantities acting on the tire 3 will be described later.

[0024] The battery 40 is attached to the wheel 5 via a bracket 41 which is attached to the center of the wheel 5 with bolts 43. The battery 40 supplies power to the magnetic sensor 20, camera 30, control board 33, and lighting 35 via wiring 50.

[0025] -Calculation of physical quantities- Figure 2(a) schematically shows the analyzed inner contact shape 103 of the tire 3 and the contact shape (contact pressure distribution where the tire actually contacts the road surface) 101. More specifically, Figure 2(a) overlays the inner contact shape 103 estimated by the tire physical quantity calculation device 10 and the contact pressure distribution (contact shape 101) obtained by the tire stand testing machine described later, in order to make this embodiment easier to understand. In Figure 2(a), the contact shape 101 is hatched so that the hatching interval becomes narrower in areas with higher contact pressure. The white areas in the contact shape 101 represent the parts where the tire 3 does not make contact with the road surface, i.e., the grooves in the tread pattern.

[0026] The control board (feature extraction unit) 33 includes a microcomputer consisting of a CPU (Central Processing Unit), ROM (Read Only Memory) for storing processing programs, and RAM (Random Access Memory) for temporarily storing data. It is configured to perform the following analyses and calculations by coordinating the CPU, ROM, RAM, etc.

[0027] First, the control board 33 is configured to analyze the inner contact shape 103 of the tire 3 based on the images of the marker group 11 captured by the camera 30. Specifically, the control board 33 is configured to analyze the inner contact shape 103 of the tire 3 by applying a method for solving the PnP problem (Perspective-n-Point Problem). The "inner contact shape 103" refers to the shape of the inner surface 3b of the tire 3, which corresponds to the contact shape 101 of the outer surface 3a of the tire 3 when the tire 3 actually makes contact with the road surface.

[0028] The method for solving the PnP problem is a well-known method, so a detailed explanation will be omitted, but in short, it estimates the camera's position and orientation from the relationship between a known point cloud in 3D space and a point cloud on a 2D image. The control board 33 then applies this to estimate a point cloud in 3D space (coordinates of a small part of the tire 3) based on the known position and orientation of the camera 30 and the 2D image of a black and white grid pattern captured by the camera 30, and uses these point clouds to estimate the inner contact shape 103.

[0029] This makes it possible to obtain the inner contact shape 103 of the tire 3 as shown in Figure 2(a). Furthermore, if the boundary between the contact portion and the non-contact portion of the tire 3 (inner contact shape 103) needs to be calculated in more detail, a method may be used in which a longitudinal section of the tire 3 is created based on the estimated point cloud, and the boundary is determined based on this longitudinal section.

[0030] Next, the control board 33 is configured to extract predetermined feature quantities from the analyzed (estimated) inner ground shape 103. Specifically, based on the inner ground shape 103, the control board 33 extracts the amount of movement of the grounding center (X, Y, Z), the grounding length Li on the inside in the vehicle width direction, the grounding length Lc at the center in the vehicle width direction, the grounding length Lo on the outside in the vehicle width direction, the grounding width W, and the grounding area A, as shown in Figure 2(a). If the center coordinates of the marker group 11 in the non-grounded state are set to (0, 0, 0), the amount of movement of the grounding center (X, Y, Z) can be easily calculated by calculating the center coordinates of the marker group 11 in the grounded state.

[0031] The control board 33 is configured to calculate the tire lateral force Fy acting on the tire 3 based on predetermined feature quantities (X, X, Y, Lc, Lc, Lc and Lc), using the following conversion formula 1 (Equation 1).

[0032] Fy=Cy1×X+Cy2×Y+Cy3×Lc+Cy4×Lo+Cy5×Li +CTy (Formula 1) Furthermore, the control board 33 is configured to calculate the ground contact load (up and down force of the tire) Fz acting on the tire 3 based on predetermined characteristic quantities (vertical movement amount Z of the center of contact, contact length Lc, and contact area A) using the following conversion formula 2 (Equation 2).

[0033] Fz=Cz1×Z+Cz2×Lc+Cz3×A+CTz (Formula 2) These conversion formulas 1 and 2 are tire-specific conversion formulas created by multiple regression analysis to convert the predetermined feature quantities into tire contact force, obtained as linked data (simultaneously measured data) from the tire contact force (tire lateral force Fy and contact load Fz) obtained under test conditions selected from slip angle, camber angle, contact load, vehicle speed, and tire pressure on a tire stand testing machine (not shown). In other words, the coefficients Cy1, Cy2, Cy3, Cy4, Cy5, Cz1, Cz2, Cz3, and the constant terms CTa and CTz are tire-specific values ​​that differ for each tire 3.

[0034] Incidentally, the test tires used in the following explanation yielded the following values: Cy1=14.889, Cy2=137.275, Cy3=33.606, Cy4=33.281, Cy5=-61.546, CTa=-1046.801, CZ1=-781.1634, CZ2=108.295, CZ3=886.567, and CTz=6206.3.

[0035] Figure 2(b) is a graph showing regression line 1 for tire lateral force Fy, and Figure 2(c) is a graph showing regression line 2 for ground contact load Fz. These graphs plot physical quantities calculated based on images of the marker group 11 when the measured values ​​were acquired, with the horizontal axis representing the measured values ​​from the six force components on the tire stand testing machine (more precisely, the tire mounting axis of the tire stand testing machine), and the vertical axis representing the calculated values ​​from the tire physical quantity calculation device 10. They also show the regression lines obtained from multiple regression analysis.

[0036] If the measured values ​​from the six force components on the tire stand testing machine and the calculated values ​​from the tire physical quantity calculation device 10 perfectly match, then the regression line will be y=x. Also, the coefficient of determination R 2 The closer this value is to 1, the better the estimated regression line fits the actual data.

[0037] As shown in Figure 2(b), the regression line 1 for the tire lateral force Fy in the test tire was y = 0.9832x. Furthermore, all plots fell within a range of ±1000N from regression line 1, and the coefficient of determination R 2 The result was 0.9854.

[0038] Furthermore, the regression line 2 for the ground contact load Fz on the test tire, shown in Figure 2(c), was y = 0.9996x. Also, all plots fell within a range of ±300N from regression line 2, and the coefficient of determination R 2 The result was 0.9949.

[0039] These findings confirm that the values ​​calculated by the tire physical quantity calculation device 10 have a high correlation with the measured values, and that predetermined feature quantities obtained from the analyzed inner surface contact shape 103 have a high correlation with the tire lateral force Fy and the contact load Fz.

[0040] As described above, the tire physical quantity calculation device 10 according to this embodiment improves the accuracy of calculating the contact load Fz of the tire 3, and makes it possible to calculate the tire lateral force Fy, which was previously difficult to calculate, at the actual vehicle level. The calculated tire lateral force Fy and contact load Fz are stored in ROM and, after retrieval, are used to evaluate the handling stability at the actual vehicle level.

[0041] -Control Flow- Figure 3 is a flowchart showing an example of the process performed by the tire physical quantity calculation device 10. This flowchart is executed repeatedly at predetermined intervals, for example, when ignition ON or brake OFF is detected. The tire-specific coefficients Cy1, Cy2, Cy3, Cy4, Cy5, Cz1, Cz2, Cz3, and constant terms CTa, CTz are acquired in advance before installation on the vehicle and stored in the ROM of the control board 33.

[0042] First, in step S1, the control board 33 determines whether or not the magnetic sensor 20 has detected a magnetic field. If the result is NO, the process ends and returns to START. On the other hand, if the result is YES, the process proceeds to step S2.

[0043] In the next step S2, the control board 33 acquires images of the marker group 11 captured by the camera 30 and then proceeds to step S3. In the next step S3, the control board 33 analyzes the inner contact shape 103 of the tire 3 by applying a method for solving the PnP problem and then proceeds to step S4. In the next step S4, the control board 33 extracts predetermined feature quantities from the analyzed inner contact shape 103 and then proceeds to step S5.

[0044] In the next step S5, the control board 33 calculates the tire lateral force Fy and the ground contact load Fz using conversion formulas 1 and 2, and then proceeds to step S6. In the next step S6, the control board 33 stores the tire lateral force Fy and the ground contact load Fz, and then ends the process.

[0045] (Other embodiments) The present invention is not limited to its embodiments and can be implemented in various other ways without departing from its spirit or main features.

[0047] Furthermore, in the above embodiment, markers 13 and 15 set on a part of the inner surface 3b of the tire 3 are imaged with one camera 30, but the invention is not limited to this, and markers set around the entire circumference of the inner surface 3b of the tire 3 may be imaged with multiple cameras 30.

[0048] Furthermore, in the above embodiment, the magnetic sensor 20 was attached to the wheel 5 at a position on the wheel 1 that corresponds to the 180-degree opposite side of the marker group 11. However, as long as the timing at which the magnetic sensor 20 approaches the magnet 21 is the same as the timing at which it touches the ground, the magnetic sensor 20 may be attached anywhere on the wheel 5.

[0049] Furthermore, in the above embodiment, the control board 33 is responsible for all of the following: analysis of the internal grounding shape 103, extraction of feature quantities, and calculation and storage of physical quantities. However, the invention is not limited to this, and all or part of these processes may be performed, for example, by an in-vehicle ECU (Electronic Control Unit).

[0050] Thus, the embodiments described above are merely illustrative in all respects and should not be interpreted restrictively. Furthermore, any modifications or changes that fall within the equivalent scope of the claims are all within the scope of the present invention. [Industrial applicability]

[0051] According to the present invention, the accuracy of calculating the tire contact load is improved, and the lateral force of the tire can be calculated at the level of a real vehicle. Therefore, it is extremely useful when applied to a tire physical quantity calculation device that calculates the physical quantities acting on a tire while it is in motion. [Explanation of symbols]

[0052] 3 Tire, 3a Outer surface, 3b Inner surface, 10 Tire physical quantity calculation device, 13 White marker, 15 Black marker, 30 Camera, 33 Control board (feature extraction unit), 103 Inner surface contact shape

Claims

[Claim 1] A tire physical quantity calculation device that calculates the physical quantities acting on a tire based on the shape of the tire while it is in motion, The marker set on the inner surface of the above tire, Each time the portion of the tire's outer surface corresponding to the marker touches the ground, a camera capable of imaging the entire area of ​​the marker is used. The system includes a feature extraction unit that analyzes the inner contact shape of the tire based on the image captured by the camera and extracts predetermined feature quantities from the inner contact shape, The above marker is set on the inner surface of the tire as a black and white grid pattern, with a shape corresponding to the contact shape of the outer surface of the tire when it makes contact with the road surface. The feature extraction unit extracts, with respect to the inner surface contact shape, the contact length on the inside in the vehicle width direction, the contact length at the center in the vehicle width direction, the contact length on the outside in the vehicle width direction, and the contact area. Based on the three contact lengths described above, the system is configured to calculate the lateral force acting on the tire using a predetermined conversion formula, and also to calculate the contact load acting on the tire using a predetermined conversion formula based on the contact length at the center in the vehicle width direction and the contact area. Furthermore, in calculating the inner contact shape of the tire based on the image captured by the camera, the tire physical quantity calculation device is characterized by estimating a point cloud, which is the coordinate of a minute portion of the tire in three-dimensional space, based on the known position and orientation of the camera and a two-dimensional image of the black and white grid pattern of the marker captured by the camera; creating a longitudinal section of the tire based on these estimated point clouds; and determining the boundary between the contact portion and the non-contact portion of the tire based on this longitudinal section.

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