Vehicle wheel alignment detection device

Abstract

The present invention provides a vehicle wheel alignment detection device that can detect wheel alignment with a simple configuration. [Solution] The wheel alignment detection device 30 of the vehicle 1 includes an acceleration sensor 32 attached to the inner circumferential surface of the rim 7 for detecting acceleration aY acting in the outer diameter direction of the rim 7, and an ECU 35. The ECU 35 calculates a first acceleration component aY1 generated in the outer diameter direction by the rotation of the tire wheel 6 based on the rotation radius r and rotation speed v of the acceleration sensor 32, calculates a second acceleration component aY2 which is a component of the gravitational acceleration acting in the outer diameter direction based on the acceleration aY and the first acceleration component aY1, and calculates the camber angle θ of the wheel 3 based on the ratio of the second acceleration component aY2 to the gravitational acceleration g.

Description

Technical Field

[0001] The present invention relates to a vehicle wheel alignment detection device that detects the posture of a wheel.

Background Art

[0002] In general, vehicle wheel alignment affects steering performance, steering stability, vehicle straight-line driving performance, and the like. Therefore, detecting wheel alignment during traveling or the like is important from the viewpoint of ensuring vehicle performance and the like.

[0003] As a technique for detecting such wheel alignment, for example, Patent Document 1 discloses a known technique. In the technique of Patent Document 1, two acceleration sensors provided inside a tire respectively detect the ground contact states at two tire measurement positions on the tire shoulder side that are the same distance away from the tire center position. Then, the ground contact lengths at the two tire measurement positions are respectively obtained based on the detected ground contact states. Then, based on the ratio of the ground contact lengths at the two tire measurement positions, a determination is made as to whether the camber angle is positive camber or negative camber, and the like.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problem to be Solved by the Invention

[0005] However, in the technique disclosed in the above-mentioned Patent Document 1, it is necessary to provide two acceleration sensors inside the tire. Therefore, in the technique of the above-mentioned Patent Document 1, the mounting structure and the like of the acceleration sensors are complicated, and the assemblability and the like are degraded.

[0006] The present invention aims to provide a vehicle wheel alignment detection device that can detect wheel alignment with a simple configuration. [Means for solving the problem]

[0007] A vehicle wheel alignment detection device according to one aspect of the present invention includes: an acceleration detection means attached to the inner circumferential surface of the rim of a tire wheel on which a tire is mounted on the outer circumference, for detecting acceleration acting in the outer diameter direction of the rim; a first acceleration component calculation means for calculating a first acceleration component generated in the outer diameter direction by the rotation of the tire wheel based on the rotation radius and rotation speed of the acceleration calculation means; a second acceleration component calculation means for calculating a second acceleration component, which is a component of the gravitational acceleration acting in the outer diameter direction, based on the acceleration and the first acceleration component; and a camber angle calculation means for calculating the camber angle of the wheel based on the ratio of the second acceleration component and the gravitational acceleration. [Effects of the Invention]

[0008] According to the vehicle wheel alignment detection device of the present invention, wheel alignment can be detected with a simple configuration. [Brief explanation of the drawing]

[0009] [Figure 1] Schematic diagram showing a vehicle wheel alignment detection device. [Figure 2] Diagram showing the wheel alignment detection device for the right front wheel. [Figure 3] An explanatory diagram showing the Cartesian coordinate system of an acceleration sensor calibrated for the wheel. [Figure 4] This diagram illustrates the acceleration in the outer diameter direction of the rim when the acceleration sensor is at its lowest point during driving. [Figure 5] An explanatory diagram showing the acceleration component and gravitational acceleration component generated by the rotational movement of an acceleration sensor. [Figure 6]Characteristic diagram schematically showing a transition of acceleration in an outer radial direction of a rim detected by an acceleration sensor during traveling [Figure 7] Flowchart showing a camber angle detection routine [Figure 8] Configuration diagram showing a wheel alignment detection device for a right wheel according to a modified example [Description of Embodiments for Carrying Out the Invention]

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The respective drawings used in the following description are drawn with different scales for each constituent element so that each constituent element has a size recognizable on the drawing. Therefore, the present invention is not limited only to the number of constituent elements, the shape of the constituent elements, the ratio of the sizes of the constituent elements, and the relative positional relationship of the respective constituent elements described in these drawings.

[0011] First, with reference to FIGS. 1 and 2, an example of a wheel to which a wheel alignment detection device 30 for a vehicle 1 is applied and a support structure for the wheel will be briefly described.

[0012] As shown in FIG. 1, the vehicle 1 has wheels 3 (a left front wheel 3fl, a right front wheel 3fr, a left rear wheel 3rl, and a right rear wheel 3rr) on left and right side portions in front and rear of a vehicle body 2, respectively.

[0013] Hereinafter, the configuration of the right front wheel 3fr which is one wheel will be described with reference to FIG. 2. Regarding the left front wheel 3fl, the left rear wheel 3rl, and the right rear wheel 3rr, descriptions of configurations similar to the right front wheel 3fr and configurations associated with the right front wheel 3fr will be appropriately omitted by adding suffixes "fl", "rl", and "rr" after the same reference numerals.

[0014] As shown in FIG. 2, the right front wheel 3fr has a tire 5fr and a tire wheel 6fr.

[0015] The tire 5fr is formed using, for example, rubber as a main material.

[0016] The tire wheel 6fr is formed using, for example, an aluminum alloy as the main material.

[0017] This tire wheel 6fr has a rim 7fr and a disk 8fr.

[0018] The rim 7fr is formed in a substantially cylindrical shape. A tire 5fr is fitted onto the outer peripheral side of this rim 7fr.

[0019] The disk 8fr has a plurality of spoke portions 9fr and a center portion 10fr.

[0020] Each spoke portion 9fr extends radially from the center portion 10fr. The extending end of each spoke portion 9fr is connected to the end of the rim 7fr on the vehicle width direction outer side.

[0021] The center portion 10fr is provided with a center bore 10a. Further, the center portion 10fr is provided with a plurality of bolt holes 10b around the center bore 10a.

[0022] A center hub 15a protruding from a hub unit 15fr is inserted into the center portion 10fr. Further, a bolt 15b protruding from the hub unit 15fr is inserted through each bolt hole 10b. Then, by fastening a nut 16 to each bolt 15b, the center portion 10fr of the tire wheel 6fr is connected to the hub unit 15fr.

[0023] Further, a brake disk 17fr is fixed to the hub unit 15fr.

[0024] Furthermore, a knuckle 18fr is rotatably connected to the hub unit 15fr via a bearing (not shown).

[0025] The knuckle 18fr includes, for example, a link mounting arm 18a and a strut mounting arm 18b.

[0026] The link mounting arm 18a extends downward from the knuckle 18fr. A transverse link 19fr is connected to this link mounting arm 18a via a ball joint (not shown).

[0027] The strut mounting arm 18b extends above the knuckle 18fr. A shock absorber 20fr, which constitutes a strut-type suspension, is connected to this strut mounting arm 18b, for example.

[0028] Next, the configuration of the wheel alignment detection device 30 of vehicle 1 will be described.

[0029] For example, as shown in Figure 1, the wheel alignment detection device 30 of this embodiment includes, for each wheel 3fl, 3fr, 3rl, and 3rr, a wheel speed sensor 31 (31fl, 31fr, 31rl, 31rr), an acceleration sensor 32 (32fl, 32fr, 32rl, 32rr), a transmitter 33 (33fl, 33fr, 33rl, 33rr), and a receiver 34 (34fl, 34fr, 34rl, 34rr). Furthermore, the wheel alignment detection device 30 includes, for example, one electronic control unit (ECU) 35.

[0030] Referring to Figure 2, an example of the right front wheel 3fr is shown, where the wheel speed sensor 31fr is attached to the knuckle 18fr of the right front wheel 3fr. This wheel speed sensor 31fr detects, for example, a change in the magnetic flux of a rotor (not shown) that rotates integrally with the hub unit 15fr. As a result, the wheel speed sensor 31fr detects the rotational speed of the right front wheel 3fr. The wheel speed sensor 31fr then outputs the detected rotational speed signal to the ECU 35.

[0031] Thus, in this embodiment, the wheel speed sensor 31fr corresponds to one specific example of a wheel speed detection means.

[0032] The acceleration sensor 32fr is mounted on the inner circumferential surface of the rim 7fr of the right front wheel 3fr. In this embodiment, the acceleration sensor 32fr is configured as a three-axis acceleration sensor capable of detecting acceleration in three mutually orthogonal axes (X-axis, Y-axis, and Z-axis).

[0033] As shown in Figure 3, the X-axis of the acceleration sensor 32fr is set in a direction parallel to the rotation axis Ofr of the rim 7fr, for example. The Y-axis of the acceleration sensor 32fr is set in a direction parallel to the outer diameter of the rim 7fr, for example. Furthermore, the Z-axis of the acceleration sensor 32fr is set in a direction perpendicular to the X and Y axes and tangential to the rim 7fr, for example.

[0034] Here, it is desirable that the three axes of the acceleration sensor 32fr be calibrated with the acceleration sensor 32fr fixed to the rim 7fr. For example, as shown in Figure 3, the Y-axis calibration of the acceleration sensor 32fr can be performed with the right front wheel 3fr standing vertically and the rim 7fr positioned at a rotational position where the acceleration sensor 32fr is at its lowest point.

[0035] As a result, the acceleration sensor 32fr is capable of detecting the acceleration aXfr in the direction parallel to the rotation axis Ofr of the rim 7fr, the acceleration aYfr acting in the direction of the outer shape of the rim 7fr, and the acceleration aZfr acting in the tangential direction of the rim 7fr. Thus, in this embodiment, the acceleration sensor 32fr corresponds to one specific example of an acceleration detection means.

[0036] The transmitter 33fr is mounted on the inner circumferential surface of the rim 7fr of the right front wheel 3fr. This transmitter 33fr is electrically connected to the acceleration sensor 32fr. The transmitter 33fr transmits the three-axis acceleration signals aXfr, aYfr, and aZfr detected by the acceleration sensor 32fr to the receiver 34fr. In this embodiment, when the vehicle 1 is in motion, the transmitter 33fr can also be configured to transmit only the Y-axis acceleration signal aYfr to the receiver 34fr.

[0037] The receiver 34fr is mounted on the vehicle body 2 in an area where it can receive signals from the transmitter 33fr. The receiver 34fr transmits the received acceleration signal to the ECU 35.

[0038] The ECU35 consists of a well-known microcomputer equipped with a CPU, RAM, ROM, non-volatile memory, etc., and its peripheral devices. The ROM pre-stores fixed data such as programs executed by the CPU and data tables. In this embodiment, the data table stored in the ROM stores, for example, the distance from the rotation center of each wheel 3fl, 3fr, 3rl, 3rr to each acceleration sensor 32fl, 32fr, 32rl, 32rr as the rotation radius r of each acceleration sensor 32fl, 32fr, 32rl, 32rr. Note that all or part of the processor's functions may be configured with logic circuits or analog circuits, and the processing of various programs may be implemented using electronic circuits such as FPGAs.

[0039] For example, the ECU35 calculates the camber angles θfl, θfr, θrl, and θrr for each wheel 3fl, 3fr, 3rl, and 3rr based on signals from each wheel speed sensor 31fl, 31fr, 31rl, and 31rr, and signals from each acceleration sensor 32fl, 32fr, 32rl, and 32rr.

[0040] The calculation of these camber angles θfl, θfr, θrl, and θrr is performed, for example, when vehicle 1 is traveling at a constant speed on a flat road at a predetermined speed.

[0041] To explain this in detail using the calculation of the camber angle θfr of the right front wheel 3fr as an example, the ECU 35 samples the acceleration signal aYfr input from the acceleration sensor 32fr for a set time.

[0042] Here, for example, as shown in Figure 5, a first acceleration component aYfr1 acts on the Y-axis direction of the acceleration sensor 32fr, which is generated in the radial direction (direction of the rotation radius r) due to the rotational movement (circular movement) of the acceleration sensor 32fr. In addition, a second acceleration component aYfr2 acts on the Y-axis direction of the acceleration sensor 32fr, which is the acceleration component due to gravity.

[0043] As is clear from Figure 5, when the acceleration sensor 32fr is moving at a constant velocity, the first acceleration component aYfr1 acting on the acceleration sensor 32fr in the Y-axis direction is constant. In contrast, the second acceleration component aYfr2 acting on the acceleration sensor 32fr in the Y-axis direction changes according to the rotational position of the acceleration sensor 32fr.

[0044] Therefore, for example, as shown in Figure 6, the acceleration aYfr acting on the acceleration sensor 32fr in the Y-axis direction changes periodically.

[0045] As is clear from Figures 4 and 5, the acceleration aYfr is at its maximum value when the acceleration sensor 32fr is at its lowest point due to rotational movement. This is because the gravitational acceleration (the second acceleration component aYfr2) acts most strongly on the Y-axis direction of the acceleration sensor 32fr. At this time, the second acceleration component aYfr2 is g·cosθ, assuming that the camber angle of the right front wheel 3fr is θ.

[0046] The ECU 35 samples the periodically fluctuating acceleration aYfr for a set time (set period) and then obtains the maximum value of acceleration aYfr. In other words, the ECU 35 obtains the acceleration aYfr when the acceleration sensor 32fr reaches the lowest point on its rotating circular orbit. It is also possible to extract the maximum value of acceleration aYfr for each fluctuation period and use the average of the maximum values ​​of each acceleration aYfr.

[0047] Furthermore, the ECU 35 calculates a first acceleration component aYfr1 that acts on the acceleration sensor 32fr. Prior to calculating this first acceleration component aYfr1, the ECU 35 calculates the velocity v of the acceleration sensor 32fr based on the turning radius r of the acceleration sensor 32fr and the rotational speed of the wheel speed sensor 31fr. Then, the ECU 35 calculates the first acceleration component aYfr1 (=v) based on the turning radius r and velocity v of the acceleration sensor 32fr. 2 Calculate / r).

[0048] Furthermore, the ECU 35 calculates the second acceleration component aYfr2 (=g·cosθ) by subtracting the first acceleration component aYfr1 from the maximum value of the acceleration aYfr detected by the acceleration sensor 32fr.

[0049] Then, the ECU35 calculates the camber angle θfr of the right front wheel 3fr based on the ratio of the gravitational acceleration g and the second acceleration component aYfr2.

[0050] Thus, in this embodiment, the ECU35 corresponds to a specific example of the first acceleration component calculation means, the second acceleration component calculation means, and the camber angle calculation means.

[0051] Next, the process for calculating the camber angle θ will be explained according to the flowchart of the camber angle calculation routine shown in Figure 7.

[0052] When the routine starts, in step S101, the ECU 35 obtains the wheel speeds detected by each wheel speed sensor 31fl, 31fr, 31rl, and 31rr.

[0053] In the following step S102, the ECU 35 checks whether the vehicle (own vehicle) 1 is in motion. This determination is made, for example, based on the wheel speeds of each wheel 3fl, 3fr, 3rl, and 3rr detected by the respective wheel speed sensors 31fl, 31fr, 31rl, and 31rr.

[0054] Then, in step S102, if it is determined that vehicle 1 is stationary and not moving (step S102: NO), ECU 35 exits the routine.

[0055] On the other hand, if it is determined in step S102 that vehicle 1 is in motion (step S102: YES), the ECU 35 proceeds to step S103.

[0056] In step S103, the ECU 35 checks whether the vehicle 1 is traveling at a constant speed. This determination is made, for example, based on the history of the wheel speeds of each wheel 3fl, 3fr, 3rl, and 3rr detected by each wheel speed sensor 31fl, 31fr, 31rl, and 31rr.

[0057] Then, in step S103, if it is determined that vehicle 1 is not traveling at a constant speed (step S103: NO), ECU 35 exits the routine.

[0058] On the other hand, if step S103 determines that vehicle 1 is traveling at a constant speed (step S103: YES), the ECU 35 proceeds to step S104.

[0059] In step S104, the ECU 35 checks whether vehicle 1 is traveling on a slope. Although details are omitted, the determination of the slope relative to the road on which vehicle 1 is traveling is made based on, for example, map information input from a navigation device (not shown), information from cameras that detect the driving environment, or information from acceleration sensors attached to the vehicle body 2.

[0060] Then, in step S104, if it is determined that vehicle 1 is traveling on a slope (step S104: YES), the ECU 35 exits the routine.

[0061] On the other hand, if step S104 determines that vehicle 1 is traveling on a flat road and not on a slope (step S104: NO), the ECU 35 proceeds to step S105.

[0062] In step S105, the ECU 35 acquires the Y-axis accelerations aYfl, aYfr, aYrl, and aYrr detected by each acceleration sensor 32fl, 32fr, 32rl, and 32rr.

[0063] In the following step S106, the ECU 35 first acquires each acceleration Yfl, aYfr, aYrl, and aYrr, and then checks whether the set period has elapsed.

[0064] Then, in step S106, if it is determined that the set cycle has not elapsed (step S106: NO), the ECU35 returns to step S101.

[0065] On the other hand, if it is determined in step S107 that the set cycle has elapsed (step S106: YES), the ECU 35 proceeds to step S107.

[0066] In step S107, the ECU 35 calculates the acceleration components (first acceleration components aYfl1, aYfr1, aYrl1, aYrr1) acting in the Y-axis direction due to the rotation of each acceleration sensor 32fl, 32fr, 32rl, and 32rr. These first acceleration components aYfl1, aYfr1, aYrl1, and aYrr1 are calculated based, for example, on the rotation radius r of each acceleration sensor 32fl, 32fr, 32rl, and 32rr, and the wheel speeds detected by each wheel speed sensor 31fl, 31fr, 31rl, and 31rr.

[0067] In the subsequent step S108, the ECU 35 extracts the maximum values ​​of accelerations aYfl, aYfr, aYrl, and aYrr obtained from each acceleration sensor 32fl, 32fr, 32rl, and 32rr in step S105.

[0068] In the subsequent step S109, the ECU 35 calculates the gravitational acceleration components (second acceleration components aYfl2, aYfr2, aYrl2, aYrr2) acting in the Y-axis direction on each acceleration sensor 32fl, 32fr, 32rl, and 32rr. These second acceleration components aYfl2, aYfr2, aYrl2, and aYrr2 are calculated by subtracting the first acceleration components aYfl1, aYfr1, aYrl1, and aYrr1 from the maximum values ​​of each acceleration aYfl, aYfr, aYrl, and aYrr, respectively.

[0069] Then, in step S110, the ECU35 calculates the camber angles θfl, θfr, θrl, and θrr for each wheel 3fl, 3fr, 3rl, and 3rr based on the ratio of the gravitational acceleration g to each second acceleration component aYfl2, aYfr2, aYrl2, and aYrr2, and then exits the routine.

[0070] Incidentally, the wheel alignment detection device 30 of the vehicle 1 in this embodiment can detect the camber angles θfl, θfr, θrl, and θrr of each wheel 3fl, 3fr, 3rl, and 3rr not only when the vehicle is in motion, but also when it is stopped.

[0071] For the camber angles θfl, θfr, θrl, θrr at the time of stopping, for example, the accelerations in the X-axis direction aXfl, aXfr, aXrl, aXrr and the accelerations in the Y-axis direction aYfl, aYfr, aYrl, aYrr detected by the acceleration sensors 32fl, 32fr, 32rl, 32rr are used.

[0072] For example, when calculating the camber angle θfr of the right front wheel 3fr when it is stopped, the ECU35 calculates the gravitational acceleration component (aXfr) acting on the right front wheel 3fr in the XY plane. 2 +aYfr 2 ) 1 / 2 Calculate.

[0073] Then, the ECU35 uses the gravitational acceleration g and the calculated gravitational acceleration component (aXfr 2 +aYfr 2 ) 1 / 2 Based on the ratio, the camber angle θfr of the right front wheel 3fr when stopped is calculated.

[0074] According to this embodiment, the wheel alignment detection device 30 of the vehicle 1 includes an acceleration sensor 32 attached to the inner circumferential surface of the rim 7 for detecting acceleration aY acting in the outer diameter direction of the rim 7, and an ECU 35. The ECU 35 calculates a first acceleration component aY1 generated in the outer diameter direction by the rotation of the tire wheel 6 based on the rotation radius r and rotation speed v of the acceleration sensor 32, calculates a second acceleration component aY2 which is a component of the gravitational acceleration acting in the outer diameter direction based on the acceleration aY and the first acceleration component aY1, and calculates the camber angle θ of the wheel 3 based on the ratio of the second acceleration component aY2 to the gravitational acceleration g.

[0075] This allows for the detection of camber angle θ, one of the wheel alignment parameters, using a simple configuration.

[0076] In other words, the acceleration sensor 32 of this embodiment is configured to be attached to the inner circumferential surface of the rim 7, and not to be attached inside the tire 5, etc., so the acceleration sensor 32 can be attached to the wheel 3 with a simple configuration. Furthermore, by calculating the camber angle θ based on a comparison between the second acceleration component aY2, which is the gravitational acceleration component included in the radial acceleration aY when the acceleration sensor 32 rotates, and the gravitational acceleration g, the camber angle θ can be detected with a simple configuration.

[0077] In this case, the ECU 35 calculates the second acceleration component aY2 by subtracting the first acceleration component aY1 from the maximum value of the periodically alternating acceleration aY during constant-speed driving of the vehicle 1. This allows for accurate calculation of the second acceleration component aY2 and precise detection of the camber angle θ.

[0078] Furthermore, the acceleration sensor 32 has three axes. By configuring the system with acceleration sensors and mounting the acceleration sensor 32 on the inner circumferential surface of the rim 7, and then calibrating it so that at least the Y-axis direction of the acceleration sensor 32 coincides with the outer diameter direction of the rim 7, the acceleration aY can be detected with high accuracy, and the detection accuracy of the camber angle θ can be improved.

[0079] Here, for example, as shown in Figure 8, the wheel alignment detection device 30 of vehicle 1 can also be applied to vehicle 1 equipped with an in-wheel motor 40 as a drive source.

[0080] Even in this case, the acceleration sensor 32 can be mounted if there is a small space on the inner circumferential surface side of the rim 7. Therefore, there are fewer layout constraints on the mounting of the wheel alignment detection device 30 of the vehicle 1.

[0081] Furthermore, even if noise is generated by the in-wheel motor 40, the acceleration sensor 32 can detect acceleration accurately by providing a shielding material or the like. Alternatively, the influence of noise from the in-wheel motor 40 can be reduced by applying a predetermined filter process to the acceleration signal detected by the acceleration sensor 32.

[0082] The inventions described in the above embodiments are not limited to those forms, and various modifications can be made in the implementation stage without departing from the gist of the invention. Furthermore, the above embodiments include inventions at various stages, and various inventions can be extracted by appropriate combinations of the multiple constituent elements disclosed.

[0083] For example, if the problem described can be solved and the effect described can be obtained even if some of the constituent elements shown in each form are removed, then the configuration with the removed constituent elements can be extracted as an invention. [Explanation of Symbols]

[0084] 1 ... Vehicle (own vehicle) 2… Vehicle body 3 … wheels 5... Tires 6… Tire and wheel 7… Rim 8… Disc 9… Spoke section 10… Center Department 10a ... Centaboa 10b ... Bolt hole 15 … Hub unit 15a ... Center Hub 15b ... Bolt 16… Nut 17… Brake disc 18… Knuckle 18a ... Arm for link mounting 18b ... Strut mounting arm 19… Transverse Link 20… Shock absorber 30… Wheel alignment detection device 31… Wheel speed sensor 32… Accelerometer 33… Transmitter 34 ... Receiver 35… Electronic Control Unit (ECU) 40… In-wheel motor

Claims

1. An acceleration detection means is attached to the inner circumferential surface of the rim of a tire wheel on which a tire is mounted on the outer circumference, and detects acceleration acting in the outer diameter direction of the rim. A first acceleration component calculation means calculates a first acceleration component generated in the outer diameter direction by the rotation of the tire wheel based on the rotation radius and rotation speed of the acceleration calculation means, A second acceleration component calculation means calculates a second acceleration component, which is a component of the gravitational acceleration acting in the outer diameter direction, based on the acceleration and the first acceleration component. A camber angle calculation means for calculating the camber angle of a wheel based on the ratio of the second acceleration component to the gravitational acceleration, A vehicle wheel alignment detection device characterized by comprising the following:

2. The vehicle wheel alignment detection device according to claim 1, characterized in that the second acceleration component calculation means calculates the second acceleration component by subtracting the first acceleration component from the maximum value of the acceleration that changes periodically when the vehicle is traveling at a constant speed.

3. The acceleration detection means is a three-axis acceleration sensor capable of detecting acceleration in three mutually orthogonal axis directions. The wheel alignment detection device for a vehicle according to claim 1 or 2, characterized in that the three-axis acceleration sensor is calibrated so that one of the three axes coincides with the outer diameter direction of the rim when the wheel is in a vertically upright position.

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