JP2024062125A - Tire uniformity measuring method and measuring device, and method for managing said measuring device - Google Patents

Abstract

[Problem] To provide a measurement method and device that can easily and accurately grasp tire uniformity, and a management method for maintaining the measurement accuracy of the measurement device. [Solution] Using data on radial runout d1, d2 over the entire circumference of each bead fitting bottom surface 5a, 5b of a pair of rim portions 4a, 4b, a calculation unit 10 calculates data on the radial runout D of the rim 4, calculates a radial spring constant k of the tire T from the load Fr that presses the tire T mounted on the rim 4 against the outer circumferential surface 2b of a rotating drum 2 and the radial displacement r of the tire T due to this load Fr, and calculates the magnitude of fluctuation of the corrected reaction force Fx by subtracting a reaction force F2 over the entire circumference of the tire in the radial direction caused by the runout D calculated based on the spring constant k and the runout D data from the measurement result F1 of the reaction force F generated in the radial direction during one rotation of the tire T obtained by a uniformity test. [Selected Figure] Figure 10

Description

The present invention relates to a tire uniformity measurement method and device, and a method for managing this measurement device. More specifically, the present invention relates to a tire uniformity measurement method and device that can easily and accurately grasp tire uniformity, and a management method for maintaining the measurement accuracy of this measurement device.

JIS D4233 specifies the uniformity test method for automobile tires. In this test method, the tire tread is pressed against the outer peripheral surface of a rotating drum, and the maximum value of radial reaction force fluctuation (RFV) that occurs during one rotation of a tire under load can be determined. This RFV is one of the indicators of tire quality.

In this test method, the accuracy of the uniformity measurement decreases due to eccentricity and distortion of the rotating parts such as the rim on which the tire is mounted, so various methods have been proposed to eliminate these effects (see, for example, Patent Document 1). In the method proposed in Patent Document 1, correction data is obtained to be used to eliminate the effects of eccentricity and distortion of the rotating parts. To obtain this correction data, it is necessary to take multiple measurements while changing the mounting angle in the rotational direction relative to the rotating part of the tire. To obtain highly accurate correction data, the above mounting angle must be further subdivided and multiple measurements must be taken, making the work process even more complicated. Therefore, there is room for improvement in understanding tire uniformity in a simple yet accurate manner.

JP 2000-234980 A

The object of the present invention is to provide a tire uniformity measurement method and measurement device that can easily and accurately grasp tire uniformity, as well as a management method for maintaining the measurement accuracy of this measurement device.

In order to achieve the above object, the tire uniformity measurement method of the present invention is a tire uniformity measurement method in which a tire to be measured, which is mounted on a rim that rotates around a central axis and set to a specified air pressure, is pressed with a specified load against the outer circumferential surface of a rotating drum that rotates around a drum axis, the central axis and the drum axis are maintained at a constant distance, and the magnitude of fluctuation in the reaction force F generated in the tire radial direction during one rotation of the tire is calculated. In the tire uniformity measurement method, the radial runout data about the central axis of each of the bead fitting bottom surfaces of a pair of rim parts of the rim into which a pair of beads of the tire are fitted is measured over the entire circumferential direction, and the radius of the rim is calculated by performing a predetermined calculation process using each of the runout data. The data on the axial deflection is calculated and stored over the entire circumference, the tire radial spring constant of the tire is calculated based on the load Fr when the tire, which is mounted on the rim and set to the specified air pressure, is pressed against the outer peripheral surface, and the tire radial displacement r of the tire due to this load Fr. The tire radial reaction force F2 caused by the deflection of the rim is calculated over the entire circumference of the tire based on the calculated spring constant and the deflection data of the rim, and the reaction force F2 is subtracted from the measurement result F1 of the reaction force F measured when the tire is mounted on the rim, and the magnitude of the fluctuation of the reaction force F during one rotation of the tire is corrected and calculated.

The tire uniformity measuring device of the present invention comprises a rim that rotates around a central axis, a rotating drum that rotates around a drum axis, a drive unit that drives the rotation of either the central axis or the drum axis, a load application unit that maintains a constant distance between the central axis and the drum axis, a measurement unit that measures force, and a calculation unit to which measurement data by the measurement unit is input. In the tire uniformity measuring device, the central axis and the drum axis are maintained at a constant distance by the load application unit, and a tire to be measured that is mounted on the rim and set to a specified air pressure is pressed with a specified load against the outer circumferential surface of the rotating drum that rotates around the drum axis, a reaction force F generated in the tire radial direction is measured by the measurement unit, and the magnitude of the fluctuation of the reaction force F during one rotation of the tire is calculated by the calculation unit. In the tire uniformity measuring device, data on the radial runout about the central axis of each of the bead fitting bottom surfaces of a pair of rim parts of the rim into which a pair of beads of the tire are fitted is measured circumferentially. The tire has a rim runout measurement unit that measures the rim runout over the entire circumference, and the calculation unit performs a predetermined calculation process using the data on the runout measured by the rim runout measurement unit to calculate and store data on the radial runout of the rim over the entire circumference. The calculation unit calculates the tire's radial spring constant based on the load Fr when the tire, which is mounted on the rim and set to the specified air pressure, is pressed against the outer circumferential surface, and the tire's radial displacement r due to this load Fr is calculated by the calculation unit. The tire's radial reaction force F2 caused by the runout of the rim is calculated over the entire circumference based on the spring constant and the runout data of the rim. The tire is mounted on the rim and a calculation process is performed over the entire circumference in the tire circumferential direction to subtract the reaction force F2 from the measurement result F1 of the reaction force F measured, thereby correcting and calculating the magnitude of the fluctuation of the reaction force F during one rotation of the tire.

The method for managing the tire uniformity measuring device of the present invention is a method for managing the tire uniformity measuring device described above, characterized in that the calculation unit compares the runout data of each of the bead fitting bottom surfaces measured by the rim runout measurement unit with a preset allowable range of the runout of each of the bead fitting bottom surfaces, and issues a warning if the runout data of at least one of the bead fitting bottom surfaces exceeds the allowable range.

According to the tire uniformity measurement method and measurement device of the present invention, the effect of the runout of the rim can be eliminated from the measurement result F1 by performing a calculation process to subtract the reaction force F2 from the measurement result F1 of the reaction force F measured when the tire is mounted on the rim. The reaction force F2 can be calculated by using the radial runout data of the rim calculated by performing a predetermined calculation process using the radial runout data about the central axis over the entire circumferential direction of the bead fitting bottom surface of each of the pair of rim parts of the rim, and the spring constant that can be obtained using a device that measures the reaction force. This makes it possible to grasp the uniformity of the tire simply and accurately.

According to the method for managing a tire uniformity measuring device of the present invention, the issuance of the warning indicates that the radial runout of at least one of the bead fitting bottom surfaces exceeds the allowable range. This warning can be used as an opportunity to inspect the rim, and if an abnormality is found, appropriate measures can be taken quickly, which is advantageous for maintaining the measurement accuracy of the measuring device.

1 is an explanatory diagram illustrating an embodiment of a tire uniformity measuring device as seen from a side with a tire in cross section; FIG. 2 is an explanatory diagram illustrating the measuring device of FIG. 1 in a plan view. 2 is an explanatory diagram illustrating the movement of the pair of rim portions in FIG. 1 . 4 is an explanatory diagram illustrating a process for measuring runout data of each of the bead fitting bottom surfaces of the pair of rim portions in FIG. 1 . FIG. 5 is an explanatory diagram illustrating the process of FIG. 4 in a plan view. FIG. 5 is a graph diagram illustrating the runout data of each bead fitting bottom surface measured by the process of FIG. 4 and the calculated runout data of the rim. 1A to 1C are explanatory diagrams illustrating the process of mounting a tire on a rim, showing a cross section of the tire. 1 is an explanatory diagram illustrating a process of measuring a reaction force F generated in the radial direction of a tire mounted on a rim, the tire being cross-sectionally viewed from the side. FIG. 9 is an explanatory diagram illustrating the process of FIG. 8 in a plan view. 9 is a graph illustrating a measurement result F1 of a reaction force F measured by the process of FIG. 8, a reaction force Fx corrected by subtracting a reaction force F2 from the measurement result F1, and the magnitude of the fluctuation of the reaction force Fx.

The tire uniformity measurement method and measurement device of the present invention, as well as the method for managing this measurement device, are described below based on the embodiment shown in the figures.

The embodiment of tire uniformity measuring device 1 (hereinafter referred to as measuring device 1) illustrated in Figures 1 and 2 is used to grasp RFV (Radial Force Variation) as the uniformity of a vulcanized tire T. This measuring device 1 has a rotating drum 2, a rim 4, a driving unit 3, a load applying unit 8, a measuring unit 9 that measures force, a calculation unit 10 to which measurement data from the measuring unit 9 is input, a rim runout measuring unit 11, and a warning means 12. The warning means 12 can be provided as an option.

The rotating drum 2 is a cylindrical body that rotates around the drum shaft 2a. The tread Tr of the tire T is pressed against the outer peripheral surface 2b of the rotating drum 2. The drum shaft 2a is driven to rotate by a drive unit 3. A motor or the like is used for the drive unit 3.

A tire T is mounted on the rim 4, which rotates around a central axis 7. As shown in FIG. 3, the rim 4 is configured by connecting a pair of opposing rim sections 4a, 4b, which can be connected and disconnected by a connecting section 4c. In this embodiment, a rim drive section 6 is provided to drive the central axis 7 to rotate. A motor or the like is used as the rim drive section 6.

In more detail, the central shaft 7 connected to each of the rim parts 4a and 4b is arranged concentrically, and one rim part 4a moves toward and away from the other rim part 4b. The central shaft 7 connected to the other rim part 4b is driven to rotate by the rim drive part 6. In addition, a connecting part 4c is fixed to the other rim part 4b. The adjacent rim parts 4a and 4b are connected to each other by the connecting part 4c and integrated to form one rim 4. In other words, the rim parts 4a and 4b are integrated by fitting the connecting part 4c into a connecting fitting part formed on one rim part 4a. It is sufficient that at least one of the rim parts 4a and 4b can move in the axial direction of the central shaft 7 to move toward and away from each other, and that a structure in which the integrated rims 4 can be formed can be formed.

Each of the rim portions 4a, 4b corresponds to a pair of beads Tb, Tb of the tire T. Each of the rim portions 4a, 4b has an annular bead fitting bottom surface 5a, 5b. The bottom surface (innermost peripheral surface) of one bead Tb of the tire T abuts and fits onto one of the bead fitting bottom surfaces 5a, and the bottom surface (innermost peripheral surface) of the other bead Tb of the tire T abuts and fits onto the other bead fitting bottom surface 5b.

In this embodiment, the drive unit 3 is designed to rotate the drum shaft 2a, but the drive unit 3 can also be designed to rotate the central shaft 7. In other words, it is sufficient that either the drum shaft 2a or the central shaft 7 is rotated by the drive unit 3.

The load applying unit 8 makes it possible to maintain a constant distance between the central axis 7 and the drum shaft 2a. The load applying unit 8 has a frame 8a that rotatably supports the drum shaft 2a, and a moving mechanism 8b that moves the frame 8a. As the moving mechanism 8b, various known mechanisms such as a hydraulic cylinder can be used. The moving mechanism 8b moves the drum shaft 2a (rotating drum 2) supported by the frame 8a toward and away from the central axis 7 (rim 4) and fixes it at a predetermined position.

In more detail, the central axis 7 and the drum shaft 2a are arranged in parallel and opposed to each other, and the drum shaft 2a can move in a direction perpendicular to the axial direction of the two to move toward and away from each other. In this embodiment, the frame 8a is placed on a base, and a guide groove is formed on the base as shown by the dashed line in FIG. 1. This guide groove extends in a direction perpendicular to the central axis 7 and the drum shaft 2a, and the frame 8a moves along this guide groove to move the central axis 7 and the drum shaft 2a toward and away from each other. This allows the distance between the central axis 7 and the drum shaft 2a to change. When measuring the reaction force F described later, the central axis 7 and the drum shaft 2a are maintained at a constant distance.

The load applying unit 8 may have a structure capable of maintaining a constant distance between the central shaft 7 and the drum shaft 2a in a direction perpendicular to their axial directions when measuring the reaction force F. Therefore, the central shaft 7 and the drum shaft 2a, which are arranged in parallel and opposed to each other, may be arranged such that at least one of them can move in a direction perpendicular to the axial direction so that they can approach and move away from each other.

The measuring unit 9 detects and measures the force (the reaction force F and the load Fr described below). As the measuring unit 9, various known measuring devices such as a load cell can be used.

The calculation unit 10 receives measurement data from the measurement unit 9 and the rim runout measurement unit 11. The calculation unit 10 performs various calculation processes using the input data and stored data. A well-known computer or the like is used as the calculation unit 10. The results calculated by the calculation processes of the calculation unit 10 are output and displayed by well-known display means such as a monitor or printer.

The rim runout measuring unit 11 is disposed at a distance from the outer periphery of the rim 4. The rim runout measuring unit 11 measures the radial runout around the central axis 7 of each of the bead fitting bottom surfaces 5a, 5b when the rim 4 rotates around the central axis 7. The rim runout measuring unit 11 can be a known non-contact type displacement sensor, such as a profile sensor that uses laser light.

The warning means 12 issues a warning in response to an instruction signal from the calculation unit 10. Examples of warnings include an alarm, a warning display, and a warning vibration. Therefore, the warning means 12 can be one or a combination of various well-known devices such as an alarm (speaker), a warning display, and a warning vibrator.

Next, an example of the procedure for measuring uniformity according to the present invention will be described.

As shown in Figures 4 and 5, the rim runout measuring unit 11 is used to measure data on radial runout d1, d2 around the central axis 7 of the bead fitting bottom surfaces 5a, 5b of the pair of rim parts 4a, 4b of the rim 4 over the entire circumferential direction. First, the rim parts 4a, 4b are connected to each other by the connecting part 4c to form an integrated rim 4.

Next, the rim drive unit 6 rotates the central axis 7, thereby rotating the rim 4 around the central axis 7. The rim runout measurement unit 11 detects the distance between the rim runout measurement unit 11 and each of the bead fitting bottom surfaces 5a, 5b. When the rim 4 rotates once, the distance between the rim runout measurement unit 11 and the entire circumferential direction of each of the bead fitting bottom surfaces 5a, 5b is detected.

The arrangement of the central axis 7 and the rim runout measuring unit 11 is known, and the radius (prescribed value d) of each rim portion 4a, 4b can be obtained using this measuring device 1. This prescribed value d is the distance between each rim portion 4a, 4b (bead fitting bottom surface 5a, 5b) and the axis of the central axis 7 at the circumferential position when the tread Tr of the tire T is brought into contact with the outer circumferential surface 2b of the rotating drum 2 and pressed from zero to a prescribed load when measuring the reaction force F described later. Therefore, after obtaining the prescribed value d, the data of the radial runout d1, d2 around the central axis 7 over the entire circumferential circumference of each bead fitting bottom surface 5a, 5b is measured using the detection data by this rim runout measuring unit 11, as illustrated in FIG. 6. In FIG. 6, the data of the runout d1 of one bead fitting bottom surface 5a is shown by a solid thick line, and the data of the runout d2 of the other bead fitting bottom surface 5b is shown by a dashed thick line.

The vertical axis in FIG. 6 shows the difference between the radial distance from the central axis 7 to each bead fitting bottom surface 5a, 5b and the specified value d. The horizontal axis shows the circumferential position with the set starting point of each bead fitting bottom surface 5a, 5b at 0°. When the data values of the runout d1, d2 are in a region smaller than the specified value d shown on the vertical axis, the radius of the rim parts 4a, 4b is run out so as to be smaller than the specified value d, and when they are in a region larger than the specified value d, the radius of the rim parts 4a, 4b is run out so as to be larger than the specified value d. Due to distortion of the rim parts 4a, 4b and the central axis 7, the data of the runout d1, d2 varies with respect to the specified value d as illustrated in FIG. 6, and the data of each runout d1, d2 varies differently depending on the circumferential position. That is, in an actual rim 4, the runouts d1, d2 of the bead fitting bottom surfaces 5a, 5b of a pair of rim parts 4a, 4b rarely match, and there is a difference to some extent. The data for the runouts d1 and d2 are stored in the calculation unit 10 along with information on the starting points (the circumferential positions that serve as the reference for each of the bead fitting bottom surfaces 5a and 5b) mentioned above.

In the present invention, data on runout D of the rim 4, in which the rim portions 4a, 4b are integrated, is calculated. Then, the calculation unit 10 performs a predetermined calculation process using the data on the runouts d1, d2 to calculate data on the radial runout D over the entire circumference of the rim 4. As an example of the predetermined calculation process, the data on runouts d1, d2 is calculated by simply averaging the data on runouts d1, d2. In FIG. 6, the data on runout D calculated by simply averaging the data on runouts d1, d2 is shown by a thin solid line. The calculated data on runout D is stored in the calculation unit 10.

Next, the test device 1 is used to measure the reaction force F generated in the tire radial direction of the tire T to be measured. This measurement is performed in accordance with the uniformity test method for automobile tires specified in JIS D4233. Therefore, the air pressure of the tire T, the load applied to the tire T, and the rotational speed of the tire T are set according to the test conditions specified in JIS D4233. When measuring the reaction force F, the spring constant k and the specified value d of the tire T in the tire radial direction are also obtained.

As shown in FIG. 7, the tire T to be measured is mounted on the rim 4 for which the data of the runout D is known (has been known). The tire T is then placed between the disconnected rim portions 4a and 4b, and the rim portions 4a, which are in the standby position, are moved apart to approach the other rim portion 4b, and the rim portions 4a and 4b are connected to each other by the connecting portion 4c to form an integrated rim 4. The rim 4 on which the tire T is mounted is in the same state as the rim 4 when the data of the runouts d1 and d2 were measured. In other words, the rim portions 4a and 4b are connected at the same circumferential positions as when the data of the runouts d1 and d2 were measured, and the data of the runouts d1 and d2 are as shown in FIG. 6.

Next, the tire T is inflated to a specified air pressure, and the load applying unit 8 is used to press the tread Tr of the tire T against the outer peripheral surface 2b of the rotating drum 2 with a specified load, so that the center axis 7 and the drum shaft 2a are maintained at a constant distance. At this time, the load Fr when the tire T is pressed against the outer peripheral surface 2b and the tire radial displacement r of the tire T due to this load Fr are obtained by the test device 1. For example, the specified load is set to load Fr, and the displacement r when the tire T is pressed with this load Fr is obtained as the tire radial movement amount of the drum shaft 2a. As a result, the spring constant k = load Fr / displacement r is calculated by the calculation unit 10. In this way, when the spring constant k is calculated using the load Fr and displacement r obtained when the tire T is not rotating, a spring constant k in which the influence of the runout D of the rim 4 is eliminated is obtained. Next, based on the calculated spring constant k and the data on the runout D of the rim 4, the calculation unit 10 calculates and stores the tire radial reaction force F2 (= spring constant k x runout D) caused by the runout D of the rim 4 over the entire circumference of the tire. In order to obtain the specified value d at this time, the tread Tr of the tire T is brought into contact with the outer circumferential surface 2b of the rotating drum 2 and pressed from zero to a specified load, and the distance between each of the rim parts 4a, 4b (bead fitting bottom surfaces 5a, 5b) and the axis of the central shaft 7 at the circumferential position is obtained by a known distance sensor or the like.

Next, as shown in Figs. 8 and 9, the tire T is pressed from zero load to a specified load by contacting the tread Tr with the outer peripheral surface 2b of the rotating drum 2, and the drum shaft 2a is rotated by the driving unit 3 to rotate the rotating drum 2 around the drum shaft 2a. As a result, the tire T rolls on the outer peripheral surface 2b. The measuring unit 9 sequentially detects the reaction force F generated in the tire radial direction while the tire T rotates once around the central axis 7, and measures the reaction force F for one rotation, and the measurement result F1 is input to the calculation unit 10. This measurement result F1 is also stored in the calculation unit 10 together with the information on the above-mentioned starting point (the circumferential position that is the reference for each bead fitting bottom surface 5a, 5b) as well as the data on the runouts d1 and d2.

The spring constant k can be calculated based on the load Fr when the tire T, which is mounted on the rim 4 and set to a specified air pressure, is pressed against the outer peripheral surface 2b, and the displacement r of the tire T due to this load Fr, so it can also be calculated by a method different from the above-mentioned method. For example, as shown in Figures 8 and 9, the data of the reaction force F (measurement result F1) obtained by rotating the tire T can be used. When measuring this reaction force F, the central axis 7 and the drum shaft 2a are spaced at a constant distance, so the displacement r of the tire T during this measurement is known. The load Fr that causes this displacement r is equal to the measurement result F1. Therefore, for example, the simple average value of the measurement result F1 during one rotation of the tire T, or the maximum or minimum value of the measurement result F1 during one rotation of the tire T can be used as the load Fr to calculate the spring constant k (= load Fr/displacement r).

Here, when a tire T mounted on a rim 4 and set to a specified air pressure is pressed against the outer peripheral surface 2b of the rotating drum 2 with a specified load, and a constant gap is maintained between the central axis 7 and the drum shaft 2a, the actual reaction force F (i.e., the measurement result F1) generated in the radial direction of the tire while the tire T rotates once is calculated by the following formula (1).
Measurement result F1=(k+Δk)(δt+ΔRt+D)=kδt+kΔRt+kD+Δkδt+Δk(ΔRt+D) (1)
k is the radial spring constant of the tire T. Δk is the change in spring constant, which is caused by the unevenness of the tire T and the internal pressure fluctuation. δt is the radial deflection of the tire T. ΔRt is the radial runout (center runout) of the tire T, which is caused by the unevenness of the tire T. D is the runout of the rim 4 described above.

In equation (1), kδt is a steady term, and Δk(ΔRt+D) is small enough that it can be ignored. Therefore, RFV can be calculated by the following equation (2).
RFV = kΔRt + kD + Δkδt (2)
In formula (2), kΔRt+Δkδt is due to the tire T, and kD is due to the rim 4. That is, the RFV calculated from the measurement result F1 includes kD due to the rim 4.

The calculation unit 10 then performs a calculation process to subtract the reaction force F2 (= kD) from the measurement result F1 around the entire circumference of the tire to calculate the corrected reaction force Fx (= F1 - F2). Then, the magnitude of the fluctuation in the reaction force Fx while the tire T rotates once around the central axis 7 is calculated.

Figure 10 illustrates the measurement result F1 (thick dashed line), the calculated reaction force F2 (thin solid line), the corrected reaction force Fx (thick solid line), and the magnitude of the fluctuation of the reaction force Fx. The vertical axis of Figure 10 indicates the magnitude of the reaction forces (F1, F2, Fx). The horizontal axis indicates the circumferential position of each of the bead fitting bottom surfaces 5a, 5b, with the above-mentioned starting points at the 0° position. The magnitude of the fluctuation of the reaction force Fx is the difference between the maximum and minimum values of the reaction force Fx, which is RFV.

According to this embodiment, the influence of the runout D of the rim 4 can be eliminated from the measurement result F1 by performing a calculation process to subtract the reaction force F2 from the measurement result F1. Therefore, the magnitude of the fluctuation of the corrected reaction force Fx becomes a value that is close to the pure RFV caused by the tire T itself. The reaction force F2 can be calculated using the data of the runout D of the rim 4 calculated using the data of the runouts d1 and d2 of the bead fitting bottom surfaces 5a and 5b of the pair of rim parts 4a and 4b of the rim, and the spring constant k that can be obtained using a device that measures the reaction force F. In addition to the conventional process of measuring the reaction force F, the measurement process only requires a simple process of measuring the data of the runouts d1 and d2, and the time required for this additional process is short. Therefore, according to this embodiment, it is possible to grasp the uniformity (RFV) of the tire T in a simple yet accurate manner.

Every time the rim 4 is replaced with respect to the central axis 7, or every time the reaction force F of each tire T is measured, the data of the runout d1, d2 of each bead fitting bottom surface 5a, 5b is measured and the data of the runout D of the rim 4 is calculated. If it is necessary to grasp the RFV with higher accuracy, it is advisable to measure the data of the runout d1, d2 and calculate the data of the runout D of the rim 4 every time the magnitude of the fluctuation in the reaction force F of each tire T is measured.

The data of the runout D of the rim 4 is not limited to being calculated by a simple average of the data of the runouts d1 and d2 as described above through a predetermined calculation process. It is reasonable to calculate the data of the runout D so that it is within the range of values between the data of the runouts d1 and d2, but it does not necessarily become the simple average of the data of the runouts d1 and d2. For example, the data of the runout D may be more strongly influenced by the data of the runouts d1 and d2 that has a larger difference from the specified value d at each circumferential position, or may be more strongly influenced by the data of the runouts d1 and d2 that has a smaller difference. Therefore, for example, the data of the runout D may be calculated as the average value of the numerical values obtained by multiplying the data of the runouts d1 and d2 by the weighting coefficients a1 and a2 at each circumferential position.

For example, at each circumferential position, the runout D is calculated as (runout d1 x a1 + runout d2 x a2) / 2. Here, the coefficients a1 and a2 are set to 0 or more and 2 or less, and the coefficient a1 + coefficient a2 = 2. When the data of the runouts d1 and d2 are simply averaged, the coefficients a1 and a2 are set to 1 over the entire circumference. The degree of influence of the data of the runouts d1 and d2 on the data of the runout D is grasped based on experimental data or simulation data, and the coefficients a1 and a2 are set based on the grasping result. The degree of influence of the data of the runouts d1 and d2 on the data of the runout D tends to differ slightly depending on the specifications of the tire T (especially the aspect ratio and rim diameter), so it is advisable to grasp the degree of influence of the data of the runouts d1 and d2 on the data of the runout D for at least one of the specifications of the aspect ratio and rim diameter of the tire T, and set the coefficients a1 and a2.

Empirically, it is believed that the data of the runout D is often more strongly influenced by the data of the runouts d1 and d2 that is more different from the specified value d. Therefore, at each circumferential position, the coefficient for the data of the runouts d1 and d2 that is more different from the specified value d can be set to 1.2 to 1.5, and the data of the runouts D can be calculated simply. That is, for the data of the runouts d1 and d2 shown in FIG. 6, the difference between the specified value d and the data of the runouts d1 and d2 is calculated at each circumferential position, and the data with the larger difference is multiplied by a coefficient a between 1.2 and 1.5, and the data with the smaller difference is multiplied by a coefficient (2-a). If the difference is the same, the data of the runouts d1 and d2 is multiplied by a coefficient 1. This calculation process is performed over the entire circumference to calculate the data of the runout D.

Next, an example of the procedure for managing the measuring device 1 according to the present invention will be described.

The calculation unit 10 stores the allowable range AR for each of the runouts d1 and d2. For example, the allowable range AR is set so that the difference between the specified value d and the runouts d1 and d2 is 0.05 mm or less, more preferably 0.03 mm or less.

Then, when the rim runout measuring unit 11 measures the runouts d1 and d2, the calculation unit 10 compares the measured runout data d1 and d2 with a preset allowable range AR. If the result of this comparison indicates that at least one of the runout data d1 and d2 exceeds the allowable range AR, the calculation unit 10 issues an instruction signal to the warning means 12 to issue a warning.

By issuing this warning, it becomes clear that the runout d1, d2 of at least one of the bead fitting bottom surfaces 5a, 5b exceeds the allowable range AR. This warning prompts the worker to inspect the rim 4 and, if there is an abnormality, to take appropriate action quickly, which is advantageous for maintaining the measurement accuracy of the RFV by the measurement device 1.

Reference Signs List 1 Measuring device 2 Rotating drum 2a Drum shaft 2b Outer circumferential surface 3 Driving section 4 Rim 4a, 4b Rim section 4c Connecting section 5a, 5b Bead fitting bottom surface 6 Rim driving section 7 Central shaft 8 Load applying section 8a Frame 8b Moving mechanism 9 Measuring section 10 Calculating section 11 Rim runout measuring section 12 Warning means T Tire Tr Tread Tb Bead

Claims (6)

A tire uniformity measurement method for measuring tire uniformity, comprising the steps of: pressing a test tire, which is mounted on a rim that rotates around a central axis and set to a specified air pressure, against an outer peripheral surface of a rotating drum that rotates around a drum shaft with a specified load; maintaining a constant distance between the central axis and the drum shaft; and calculating a magnitude of fluctuation in reaction force F generated in the tire radial direction during one rotation of the tire,
data on radial runout about the central axis of each of the bead fitting bottom surfaces of a pair of rim portions of the rim into which a pair of beads of the tire are fitted is measured over the entire circumferential direction, and data on radial runout of the rim is calculated and stored over the entire circumferential direction by performing a predetermined arithmetic process using each of the runout data;
calculating a radial spring constant of the tire based on a load Fr when the tire, which is mounted on the rim and set to the specified air pressure, is pressed against the outer peripheral surface and a radial displacement r of the tire due to the load Fr;
Calculating a reaction force F2 in the radial direction of the tire caused by the runout of the rim over the entire circumference of the tire based on the calculated spring constant and the runout data of the rim;
A tire uniformity measurement method in which the reaction force F is calculated by subtracting the reaction force F2 from the measurement result F1 of the reaction force F measured with the tire mounted on the rim, over the entire circumference of the tire, thereby correcting the magnitude of fluctuation in the reaction force F during one rotation of the tire. The tire uniformity measurement method according to claim 1, wherein the data on the radial runout of each of the bead fitting bottom surfaces is measured over the entire circumference each time the rim is replaced with respect to the central axis, or each time the tire is mounted on the rim and the reaction force F is measured, and the data on the radial runout of the rim is calculated over the entire circumference. The tire uniformity measurement method according to claim 1 or 2, wherein the data on the runout of the rim is calculated by simply averaging the data on the runout of each of the bead fitting bottom surfaces using the predetermined calculation process. The tire uniformity measurement method according to claim 1 or 2, wherein the predetermined calculation process calculates the runout data of the rim within a range of values between the runout data of each of the bead fitting bottom surfaces. The device comprises a rim that rotates around a central axis, a rotating drum that rotates around a drum axis, a drive unit that drives and rotates either the central axis or the drum axis, a load applying unit that maintains a constant distance between the central axis and the drum axis, a measurement unit that measures force, and a calculation unit to which measurement data from the measurement unit is input,
a tire uniformity measuring device in which the load application unit maintains a constant gap between the central axis and the drum axis, a tire to be measured is mounted on the rim and set to a specified air pressure, and is pressed with a specified load against an outer circumferential surface of a rotating drum rotating around the drum axis, a reaction force F generated in the radial direction of the tire is measured by the measurement unit, and a magnitude of fluctuation in the reaction force F during one rotation of the tire is calculated by the calculation unit,
a rim runout measuring unit that measures data on radial runout about the central axis of each of the bead fitting bottom surfaces of a pair of rim portions of the rim into which a pair of beads of the tire are fitted, over the entire circumferential direction;
The rim runout data measured by the rim runout measuring unit is used to perform a predetermined calculation process by the calculation unit, and the radial runout data of the rim is calculated and stored over the entire circumference in the circumferential direction,
the calculation unit calculates a radial spring constant of the tire based on a load Fr when the tire, which is mounted on the rim and set to the specified air pressure, is pressed against the outer peripheral surface and a radial displacement r of the tire due to this load Fr, and calculates a radial reaction force F2 of the tire caused by the runout of the rim over the entire circumferential direction of the tire based on the spring constant and the runout data of the rim,
The tire uniformity measuring device is configured such that a calculation process of subtracting the reaction force F2 from the measurement result F1 of the reaction force F measured when the tire is mounted on the rim is performed around the entire circumference of the tire, thereby correcting and calculating the magnitude of fluctuation in the reaction force F during one rotation of the tire. A method for managing the tire uniformity measuring device according to claim 5, comprising the steps of:
A management method for a tire uniformity measuring device, comprising: comparing, by the calculation unit, the runout data of each of the bead fitting bottom surfaces measured by the rim runout measuring unit with a preset allowable range of the runout of each of the bead fitting bottom surfaces; and issuing a warning if the runout data of at least one of the bead fitting bottom surfaces exceeds the allowable range.

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