Looseness detection system and looseness detection method

Abstract

To provide a fastening looseness detection system and a fastening looseness detection method capable of accurately and inexpensively detecting looseness of a fastening screw for fastening a driving body and a driven body.SOLUTION: A fastening looseness detection system detects fastening looseness of a fastening screw part 27 where a driving body 25 and a driven body 13 are fastened by a plurality of fastening screw parts 27. The driven body 13 has a center hole 30 into which the spigot portion 28 can be inserted with a radial gap δ h, and a plurality of fastening holes 26 into which the screw shafts of the fastening screw portions 27 can be inserted. In any one of the fastening holes, a radial dimension δ s of a space formed between an outer peripheral surface of the fastening screw part inserted into the fastening hole and an inner peripheral surface of the fastening hole is narrower than a radial dimension of a space in the other fastening hole 26. Further, a speed sensor for detecting the rotational speed of the driving body and a looseness determination part for determining the looseness of the fastening screw part from the fluctuation of the detected rotational speed of the driving body are further provided.SELECTED DRAWING: Figure 15

Description

[Technical Field]

[0001] The present invention relates to a fastening looseness detection system and a fastening looseness detection method. [Background technology]

[0002] Coupling devices that connect a rotationally driven drive shaft and a driven shaft are known. Coupling devices are widely used for power transmission in various electric motors, reducers, etc., and examples thereof include hub unit bearings in automobiles that connect a drive shaft that is rotated by driving force from the engine to a wheel on which a tire is mounted. In coupling devices such as hub unit bearings, the drive shaft and the driven shaft each have annular flange portions extending radially, and the flange portions are fastened together with fastening screws such as bolts and nuts to transmit power.

[0003] In the above-mentioned coupling device, loosening of the fastening screws may cause abnormal noise and vibration, or separation of the drive shaft and driven shaft. For example, in the case of automobile wheels, the wheel on which the tire is mounted is fixed to the hub, which serves as the rotary drive shaft, by fastening screws. If the fastening screws become loose, accidents such as the tire and wheel falling off may occur.

[0004] To prevent wheel detachment accidents involving large vehicles, the Ministry of Land, Infrastructure, Transport and Tourism and the Japan Automobile Manufacturers Association, Inc. recommend attaching an indicator (see, for example, Patent Document 1) that can detect loose wheel nuts on the left rear wheel, which has a particularly high accident rate. As shown in FIG. 29, the wheel nut cap described in Patent Document 1 has a dome-shaped cap body 111 made entirely of resin and a substantially triangular indicator 115 attached to each wheel nut 113. The indicators 115 are attached to the wheel nuts 113 so that the indicators 115 attached to circumferentially adjacent wheel nuts 113 face opposite each other, or so that all of the indicators 115 face in the same direction. This allows an operator to visually check the change in the orientation of the indicators 115 to detect loose wheel nuts 113. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2022-7274 Summary of the Invention [Problem to be solved by the invention]

[0006] However, while the wheel nut cap described in Patent Document 1 is inexpensive, it has the following problems. The possible mounting phase of the indicator 115 is limited, making it difficult to perfectly align the indicators 115 of adjacent wheel nuts 113, which reduces the accuracy of nut loosening detection. Furthermore, the indicators 115 must be mounted in many locations, making the installation process time-consuming. Considering the amount of work required, it is difficult to mount them on all wheels. Furthermore, there is a risk that the indicators 115 may become dislodged due to airflow while driving, making their application to front wheels particularly difficult. For these reasons, further improvements were desired.

[0007] The above is an example of a coupling device applied to a vehicle, but even in applications other than vehicles, in coupling devices in which a driver and a driven body are connected by a fastening screw, there is a strong demand for a method of accurately and inexpensively detecting loosening of the fastening screw.

[0008] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a system and method for detecting loosening of a fastening screw that connects a driver and a driven body, which can detect loosening of the fastening screw with high accuracy and at low cost. [Means for solving the problem]

[0009] The present invention comprises the following configurations. (1) A coupling device in which a driver that is rotationally driven about a rotation axis and a driven body that rotates following the driver are fastened together by a plurality of fastening screw portions, the coupling device detecting loosening of the fastening screw portions, the driver has a spigot portion that is concentric with the rotation shaft and protrudes toward the driven body, and an annular flange portion that extends radially outward, and the flange portion has fixing portions to which one end of the fastening screw portion is fixed, provided at a plurality of locations along the circumferential direction of the flange portion; the driven body has a central hole formed so that the spigot portion can be inserted with a radial gap therebetween, and a plurality of fastening holes formed at locations corresponding to the plurality of fixing portions and into which the screw shafts of the fastening screw portions can be inserted, In any one of the plurality of fastening holes, a radial dimension of a space formed between an outer peripheral surface of the fastening thread portion inserted into the fastening hole and an inner peripheral surface of the fastening hole is narrower than the radial dimension of the space in the other fastening holes, a speed sensor for detecting the rotation speed of the driving body; further comprising a loosening determination unit that determines loosening of the fastening thread portion based on the detected fluctuation in the rotation speed of the driver; Fastener looseness detection system. (2) A method for detecting loosening of a coupling device in which a driver that is rotationally driven about a rotation axis and a driven body that rotates following the driver are fastened together by a plurality of fastening screw portions, the method comprising: the driver has a spigot portion that is concentric with the rotation shaft and protrudes toward the driven body, and an annular flange portion that extends radially outward, and the flange portion has fixing portions to which one end of the fastening screw portion is fixed, provided at a plurality of locations along the circumferential direction of the flange portion; the driven body has a central hole formed so that the spigot portion can be inserted with a radial gap therebetween, and a plurality of fastening holes formed at locations corresponding to the plurality of fixing portions and into which the screw shafts of the fastening screw portions can be inserted, In any one of the plurality of fastening holes, a radial dimension of a space formed between an outer peripheral surface of a screw shaft of the fastening threaded portion inserted into the fastening hole and an inner peripheral surface of the fastening hole is narrower than the radial dimension of the other fastening holes, when the fastening screw portion is loosened, a speed sensor detects a fluctuation in the rotational speed of the driver caused by the driver being rotationally driven by the fastening screw portion inserted into any one of the fastening holes in a state in which the spigot portion of the driver is abutted against an inner circumferential surface of the central hole of the driven body, determining whether the fastening screw portion is loosened based on the detected fluctuation in the rotation speed of the driver; A method for detecting loose fasteners. [Effects of the Invention]

[0010] According to the present invention, loosening of a fastening screw that connects a driver and a driven body can be detected accurately and inexpensively. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram showing the essential configuration of a wheel supported by a knuckle on the vehicle body side via a hub unit bearing. [Figure 2] FIG. 2 is an enlarged view of part A shown in FIG. [Figure 3]FIG. 3 is a schematic diagram of a rotating hub and wheel as viewed from the axial direction. [Figure 4] FIG. 4 is a schematic diagram showing how a wheel is fastened to a hub with a stud and a nut. [Figure 5] FIG. 5 is an explanatory diagram showing the rotational speed for each rotation angle when the wheel and hub are properly fastened together. [Figure 6] FIG. 6 is an explanatory diagram showing the relative rotation and displacement between the wheel and the hub when the nut loosens during constant speed rotation, according to the degree of looseness. [Figure 7] FIG. 7 is an explanatory diagram showing the state of rotation of the wheel and hub when the stud shaft gap is narrower at one of the multiple fastening holes formed in the wheel than at the other locations. [Figure 8] FIG. 8 is an explanatory diagram showing the rotational speeds of the wheel and the hub for each rotation angle when the wheel and the hub are rotated in the configuration shown in FIG. [Figure 9] FIG. 9 is an explanatory diagram showing the rotation of the wheel and hub when the wheel pushes and turns the stud due to a loose nut. [Figure 10] FIG. 10 is an explanatory diagram showing the rotational speeds of the wheel and the hub for each rotation angle when the wheel and the hub are rotated in the configuration shown in FIG. [Figure 11] FIG. 11 is an explanatory diagram showing the rotation speed for each rotation angle when no rotation speed fluctuation occurs in the hub but a rotation speed fluctuation occurs in the wheel. [Figure 12] FIG. 12 is an explanatory diagram showing the fluctuation of the rotation speed when the axial diameter of the stud is changed to increase or decrease the axial clearance of the stud. [Figure 13] FIG. 13 is an explanatory diagram showing the fluctuation in rotation speed when the diameter of the fastening hole is changed to increase or decrease the stud axial clearance. [Figure 14] FIG. 14 is an explanatory diagram showing the fluctuation in rotation speed when the gap between the hub spigot portion and the center hole of the wheel is changed. [Figure 15] FIG. 15 is an explanatory diagram showing the dimensions of the hub, wheel, and studs when an even number of studs are provided. [Figure 16] FIG. 16 is an explanatory diagram showing the dimensions of the hub, wheel, and studs when an odd number of studs are provided. [Figure 17] FIG. 17 is a schematic diagram showing an example of a waveform of a period ratio from which high frequencies have been removed. [Figure 18] FIG. 18 is a schematic diagram showing an example of a waveform in which the first-order vibration of rotation is extracted from the waveform shown in FIG. [Figure 19] FIG. 19 is a schematic diagram showing an example of a waveform in which the second order vibration of rotation is extracted from the waveform shown in FIG. [Figure 20] FIG. 20 is a schematic block diagram of a fastening loosening detection system. [Figure 21] FIG. 21 is an explanatory diagram showing an example of narrowing the stud axial clearance corresponding to method M1. [Figure 22] FIG. 22 is an explanatory diagram showing an example of a configuration in which the stud shaft gap is narrowed relative to a normal stud and fastening hole corresponding to the M2 method. [Figure 23] FIG. 23 is a schematic diagram showing how a wheel is fastened to a hub using a nut with a spherical seat. [Figure 24] FIG. 24 is a schematic diagram showing how a stud is fastened to a female threaded hole formed in a hub with a wheel sandwiched therebetween. [Figure 25] FIG. 25 is a schematic cross-sectional view of a main part showing a support structure for wheels of a dual tire. [Figure 26] FIG. 26 is a schematic diagram showing a state in which the wheels of a dual tire are fastened to a hub with studs and nuts. [Figure 27] FIG. 27 is an explanatory diagram showing an example of narrowing the inlay gap of the inlay portion corresponding to the method M3. [Figure 28] FIG. 28 is an explanatory diagram showing the test results of Test Examples 1 to 3. [Figure 29] FIG. 29 is an explanatory diagram showing a conventional method for detecting looseness of a nut. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In the following description, a coupling device that fastens a driver that is driven to rotate about a rotation axis and a driven member that rotates following the driver with a plurality of fastening threads and transmits the rotation of the driver to the driven member will be used as an example to describe a fastening loosening detection system that detects loosening of fastening threads. Here, a wheel support bearing unit having a hub unit bearing will be exemplified as the coupling device, but the coupling device is not limited to this.

[0013] First Embodiment FIG. 1 is a diagram showing the configuration of the main parts of a wheel support bearing unit 100, showing how a wheel 13 is supported on a knuckle 15 on the vehicle body side via a hub unit bearing 11. Here, in this specification, the "outside" in the axial direction ("out" indicated by an arrow in FIG. 1) refers to the part that is on the outside in the width direction when assembled to the vehicle, and refers to the left side in FIG. 1. Conversely, the right side in FIG. 1, which is the center in the width direction when assembled to the vehicle, is referred to as the "inside" ("in" indicated by an arrow in FIG. 1).

[0014] Wheel 13, which constitutes the wheel of the automobile, and rotor 17, which constitutes a disc brake, which is a braking device, are rotatably supported by knuckle 15, which constitutes the suspension device. Hub outer ring 21, which constitutes hub unit bearing 11, is fixed by multiple bolts 23 to support hole 19, which is circular in plan view and formed in knuckle 15.

[0015] Meanwhile, the hub 25 constituting the hub unit bearing 11 couples and fixes the above-mentioned wheel 13 and rotor 17 with a plurality of fastening threads, that is, studs 27, and nuts 29. A plurality of fastening holes 26 are formed in each of the wheel 13 and the rotor 17, and the studs 27 are inserted into the fastening holes 26 and nuts 29 are tightened from the outside of the wheel 13 and the rotor 17. The stud 27 has a head and a shaft, and the head is fixed to a fixing portion 38 formed on a mounting flange (flange portion) 37 of the hub 25, and the tip of the shaft, which is inserted into the fastening hole 26, is threadedly engaged with the nut 29.

[0016] Hub outer ring 21 has double-row outer ring raceways 21a, 21b formed on its inner peripheral surface, and an annular connecting flange 31 formed to protrude radially outward from its outer peripheral surface. Hub outer ring 21 is fixed to knuckle 15 by fastening connecting flange 31 to knuckle 15 with multiple bolts 23.

[0017] The hub 25 is formed by combining a hub body 33 and a hub inner ring 35. A mounting flange 37 extending radially outward is formed on part of the outer peripheral surface of the hub body 33. The wheel 13 and rotor 17 are fastened to the flange surface of this mounting flange 37 with the above-mentioned multiple studs 27 and nuts 29. The outside of the hub 25 has a cylindrical spigot portion 28 that extends axially outward from the axially outer side of the mounting flange 37. The outer peripheral surface of the spigot portion 28 faces the inner peripheral surface of the center hole 30 of the wheel 13 and rotor 17.

[0018] An inner ring raceway 35a is formed on the outer peripheral surface of the middle section of the hub body 33 in a portion facing the outer ring raceway 21a, which is the outer of the double-row outer ring raceways 21a, 21b formed on the inner peripheral surface of the hub outer ring 21. A hub inner ring 35, which constitutes the hub 25 together with the hub body 33, is fitted and fixed onto a small-diameter step 39 formed on the axially inner end of the hub body 33. An inner ring raceway 35b formed on the outer peripheral surface of the hub inner ring 35 faces the axially inner outer ring raceway 21b of the double-row outer ring raceways 21a, 21b. A plurality of balls 41, 41 serving as rolling elements are provided between the outer ring raceways 21a, 21b and the inner ring raceways 35a, 35b, respectively, and are held by cages 43, 43 so as to be able to roll freely.

[0019] In this configuration example, a crimped portion 45 is formed by plastically deforming radially outward a portion of the axially inner end of the hub body 33 that protrudes axially inward beyond the axially inner end face of the hub inner ring 35 at the axially inner end of the hub body 33. This crimped portion 45 presses down on the inner end face of the hub inner ring 35, preventing separation of the hub inner ring 35 and the hub body 33. With this configuration, a back-to-back combination double-row angular ball bearing is formed, and the hub 25 is supported on the inner diameter side of the hub outer ring 21 so that it can rotate freely and can bear radial and thrust loads.

[0020] Seal rings 47a, 47b are provided between the inner peripheral surfaces of both axial ends of hub outer ring 21 and the outer peripheral surfaces of the axially middle and inner end portions of hub 25, respectively, to isolate the inner space containing balls 41 from the outer space. Furthermore, a spline hole 49 is formed in the center of hub body 33 to rotate a wheel fastened and fixed to hub 25. A spline shaft 53 of a constant velocity joint 51 is inserted into spline hole 49.

[0021] In other words, the wheel support bearing unit 100 described above is a coupling device that fastens the hub unit bearing 11, which includes the hub 25 that is a driver that is driven to rotate about a rotation axis, to the wheel 13 that is a main driven body that rotates following the driver 25, with studs 27 that form a plurality of stud fastening threaded portions and nuts 29, thereby transmitting the rotation of the hub 25 to the wheel 13. This coupling device is equipped with a speed sensor that detects the rotational speed of the hub 25, the details of which will be described later.

[0022] When using the hub unit bearing 11 of this configuration, the hub outer ring 21 is fixed to the knuckle 15, and the wheel 13 and rotor 17, which are combined with a tire (not shown), are fixed to the mounting flange 37 of the hub 25.

[0023] That is, hub unit bearing 11 comprises hub 25 equipped with hub inner ring 35 which has inner ring raceways 35a, 35b on its outer peripheral surface and is connected to the vehicle drive shaft, hub outer ring 21 which has outer ring raceways 21a, 21b on its inner peripheral surface and is fixed to the vehicle, and balls 41 which are a plurality of rolling elements provided so as to be able to roll between inner ring raceways 35a, 35b and outer ring raceways 21a, 21b. In this way, hub unit bearing 11 rotatably supports wheel 13 with respect to knuckle 15 on the vehicle side.

[0024] The rotor 17 is combined with a support (not shown) and a caliper fixed to the knuckle 15 to form a disc brake for braking. During braking, the linings of a pair of pads sandwiching the rotor 17 are pressed against both sides of the rotor 17 by the action of a hydraulic piston fitted in a hydraulic cylinder inside the caliper.

[0025] Conventionally, vehicle stability control systems, such as antilock brake systems (ABS), traction control systems (TCS), and vehicle stability control systems (VSC), have been used to ensure vehicle stability during braking, acceleration, and cornering. These systems detect wheel rotational speed, vehicle speed, and acceleration (deceleration), compare these values, and adjust the hydraulic pressure introduced into the hydraulic cylinder and engine output accordingly. This ensures vehicle stability by maintaining the wheel slip ratio (= (wheel speed - vehicle speed) / wheel speed) near the peak friction coefficient acting on the contact point between the wheel and the road surface. To configure these vehicle stability control systems, an encoder has traditionally been installed on the rotating wheel of a hub unit bearing, and a speed sensor has been installed on the stationary wheel or knuckle, or other suspension system, to detect the wheel rotational speed.

[0026] Fig. 2 is an enlarged view of portion A shown in Fig. 1. In the case of a hub unit bearing 11 of this configuration, an encoder 55 used to detect the rotational speed of the wheel is attached to a slinger 57 that constitutes the axially inner seal ring 47b of a pair of seal rings 47a, 47b, as shown in Fig. 2. The axially inner seal ring 47b includes a core metal 59, a slinger 57, and a seal member 61. The core metal 59 has an L-shaped cross section and is configured as a ring-shaped member overall. The seal member 61 is configured as a ring-shaped member overall using an elastic material such as an elastomer, and has a base end connected and fixed to the core metal 59, with the tip edges of multiple seal lips 61a, 61b, 61c each in sliding contact with the inner surface of the slinger 57.

[0027] The encoder 55 is configured in a circular ring shape and is attached by adhesive, baking, or the like to the inner surface (right side surface in FIG. 2) of the circular ring portion 57a ​​that constitutes the slinger 57, concentrically with the hub 25 shown in FIG. 1. At the same time, a speed sensor 56 is disposed opposite the inner surface of the encoder 55 to detect the rotational speed of the wheel coupled and fixed to the hub 25. The speed sensor 56 is an axial type sensor that is disposed, for example, at the axial inner end of the hub unit bearing 11, such as near the inner end of the hub outer ring 21, and detects the rotational speed of the hub 25. As a specific location for the speed sensor 56, it may be fixed, for example, to a side cover (not shown) that covers the inner opening of the hub outer ring 21.

[0028] Encoder 55 periodically changes the characteristics (magnetic characteristics, optical characteristics, electrical characteristics, etc.) of the part facing speed sensor 56 in the circumferential direction. Speed ​​sensor 56 is configured to generate a signal therein at a frequency corresponding to the rotational speed of the wheel as encoder 55 rotates together with the wheel. The rotational speed of the wheel is detected based on the frequency of the signal generated inside speed sensor 56.

[0029] The encoder 55 may be, for example, an annular permanent magnet whose magnetization direction in the axial direction is changed alternately and at equal intervals in the circumferential direction, i.e., an encoder in which south and north poles are arranged alternately and at equal intervals in the circumferential direction on the side surface.Other encoders that can be used include an annular magnetic metal plate with through holes or notches formed at equal intervals in the circumferential direction, in which the magnetic properties in the circumferential direction are changed alternately and at equal intervals, and an encoder in which the light reflectance is changed alternately and at equal intervals in the circumferential direction.

[0030] For example, if the encoder 55 is made of a permanent magnet as described above, the speed sensor 56 is made of a magnetic detection element such as a Hall element that can detect changes in the magnitude and direction of magnetic flux. Alternatively, if the encoder 55 has the above-described through-hole or notch formed therein (and does not have a permanent magnet that is the source of magnetic flux), a combination of a magnetic detection element such as a Hall element that can detect changes in the magnitude of magnetic flux and a permanent magnet can be used. If the encoder 55 is one that changes the reflectivity of light as described above, an optical sensor that can detect changes in the intensity of reflected light can be used.

[0031] The above-mentioned speed sensor 56, a so-called active wheel speed sensor, for example, if it is a type that uses magnetism, faces a magnetic encoder and outputs a high voltage when the magnetic flux density is below a threshold, and outputs a low voltage when the poles of the encoder approach and the magnetic flux density exceeds the threshold. This causes the speed sensor 56 to generate a pulse wave corresponding to the rotational speed of the tire. The generation of the pulse wave is similar for other types of sensors that are not magnetic. Generally, this pulse wave is sent to an on-board controller and used for the ABS, TCS, etc. mentioned above, but using this pulse wave to detect loosening of the fastening joint eliminates the need to add a new speed sensor, thereby reducing cost and size.

[0032] There are various known combinations of encoder 55 and speed sensor 56 other than those described above, but in any structure, it is sufficient if the rotation speed of the wheel can be detected based on the frequency of the signal generated.

[0033] FIG. 3 is a schematic diagram of the rotating hub 25 and wheel 13 as viewed from the axial direction. FIG. 4 is a schematic diagram showing how the wheel 13 is fastened to the hub 25 by the studs 27 and nuts 29. As shown in FIGS. 3 and 4, the wheel 13 is fixed to the mounting flange 37 (see FIG. 1) of the hub 25, and the rotation of the hub 25 is transmitted to the wheel 13. When the wheel 13 and hub 25 are fastened together without looseness by the studs 27 and nuts 29, the wheel 13 and hub 25 rotate together, and no rotational phase difference occurs between them. Here, the outer diameter of the spigot portion 28 shown in FIG. 3 is d h , the inner diameter of the center hole 30 of the wheel 13 is D h , outer diameter d h and inner diameter D h The gap δ between h (hereinafter referred to as the inlay clearance δ h (=D h -d h )), and the shaft diameter of the stud 27 shown in FIG. s , the inner diameter of the fastening hole 26 of the wheel 13 is D s The stud 27 shown in FIG. 4 is fixed to the hub 25 side as shown in FIG.

[0034] 5 is an explanatory diagram showing the rotational speed for each rotation angle when the wheel 13 and hub 25 are properly fastened together. In this case, the wheel 13 is centered with respect to the hub 25, and the wheel 13 and hub 25 rotate together at the same speed.

[0035] 6 is an explanatory diagram showing the relative rotation and displacement between the wheel 13 and the hub 25 when the nut 29 loosens during constant speed rotation, depending on the degree of looseness. For example, when changing a tire, the nut 29 can become loose if the nut 29 is tightened when there is rust on the hub 25, if the nut 29 is tightened with less than the specified tightening torque, or if a different type of nut 29 is used. This loosening of the nut 29 can cause a phenomenon that is different from the general rotational loosening that occurs when the nut 29 is properly tightened.

[0036] 6 is a schematic side view of the wheel 13 and hub 25 as viewed from the axial direction, and the lower part is a schematic vertical cross-sectional view of the wheel 13 and hub 25. Note that the schematic cross-sectional view in the lower part does not necessarily match the rotational phase of the wheel 13 and hub 25 in the upper part. Under normal conditions, when the nut 29 is tightening the wheel 13 without loosening, the wheel 13 and hub 25 are arranged concentrically, and the studs 27 are arranged in the center of each fastening hole 26.

[0037] On the other hand, when all the nuts 29 are loosened ("small"), the vertical load of the vehicle weight applied to the hub 25 causes the spigot portion 28 of the hub 25 to abut against the inner peripheral surface of the center hole 30 of the wheel 13, i.e., the gap δ h 6. As the hub 25 is displaced downward by 1 / 2 (arrow D1), the stud 27 is pressed downward against the inner circumferential surface of the fastening hole 26 in a portion (position P1) of the fastening hole 26 of the wheel 13. The wheel 13 then uses the pressing force from the stud 27 at position P1 as a rotational force, causing a slip between the inner circumferential surface of the center hole 30 of the wheel 13 and the spigot portion 28, causing the wheel 13 to rotate slightly (counterclockwise in FIG. 6).

[0038] As the nut 29 loosens further ("middle" in Figure 6), the rotational force of the hub 25 is transmitted to the wheel 13 side by the fastening hole 26 and the stud 27 near the area PD of the wheel 13. At the same time, the wheel 13 tilts from the vertical direction relative to the hub 25 (arrow D2). At this time, the entire wheel weight is placed on the spigot section 28 of the hub 25. Generally, in the case of passenger cars, there is a camber angle, so while the wheel 13 moves in the direction to make the camber angle 0°, it vibrates in the roll direction of the vehicle (arrow V) due to vibrations such as primary rotation. For example, in the case of trucks, the camber angle is smaller than that of passenger cars, so vibrations such as primary rotation cause the roll of the vehicle to increase. Vibrates in the direction.

[0039] If the nut 29 becomes looser further ("extra large" in Figure 6), the wheel 13 will come off the spigot portion 28 of the hub 25 (arrow D3), and the entire wheel load will be applied to the stud 27. In this state, there is a risk that the stud 27 will break.

[0040] If all nuts are slightly loose ("Small" in FIG. 6), the wheel 13 does not tip relative to the hub 25. In this case, the loose nuts 29 cause the wheel 13 to push against the spigot portion 28 of the hub 25, and all of the wheel weight is applied to the spigot portion 28 of the hub 25. In this state, the stud 27 located near the 9 o'clock position (position P1) in FIG. 6 pushes against the wheel 13, regardless of whether the driving force of the drive shaft is smaller than the inertial force of the wheel 13 and lightly pushes the wheel 13 to rotate, or whether the driving force of the drive shaft is greater than the inertial force of the wheel 13 and forcefully pushes the wheel 13 to rotate. As a result, the studs 27 pushing against the wheel 13 alternate smoothly and sequentially. In this case, the hub 25 and the wheel 13 rotate at the same rotational speed. In this state, similar to the rotational speed fluctuations shown in FIG. 5, the rotational fluctuations in the rotational speed of the hub 25 due to the loose nuts 29 are very small, and the speed sensor 56 cannot detect any abnormalities.

[0041] Therefore, in this wheel fastening loosening detection system, in order to detect an abnormality with the speed sensor 56, a rotational fluctuation is actively generated in the rotational speed of the hub 25 when the nut 29 loosens. Specifically, one of the multiple fastening holes 26 formed in the wheel 13 is positioned so that the radial dimension (hereinafter referred to as stud axial clearance δ) of the space (area where no object exists) formed between the outer peripheral surface of the stud 27 and the inner peripheral surface of the fastening hole 26 is measured. s (=D s -d s ) (see Figure 4) was made narrower than the other locations.

[0042] FIG. 7 shows the stud shaft clearance δ at one of the multiple fastening holes 26 formed in the wheel 13. s 1 is an explanatory diagram showing the state of rotation of the wheel 13 and the hub 25 when the outer diameter of the stud 27A inserted into one of the fastening holes 26 is larger than the other studs 27, and the stud axial clearance δ s is narrower than the other fastening holes 26.

[0043] When the driving force of the drive shaft is greater than the inertial force of the wheel 13 and the wheel 13 is being strongly pushed and rotated, the stud 27 located at the position near 9 o'clock (position P1) in the case shown in FIG. 6 pushes and rotates the wheel 13. On the other hand, in the case of this method, the stud shaft clearance δ s Only the studs 27A at the narrowed portion push the wheel 13 around.

[0044] In this method, the positional relationship between the hub 25 and the wheel 13 is also shifted in the load direction (vertical direction) by the amount of the gap between the inner circumferential surface of the center hole 30 of the wheel 13 and the spigot portion 28 of the hub 25. Therefore, speed fluctuations occur due to primary rotational vibrations proportional to the size of the gap between the center hole 30 of the wheel 13 and the spigot portion 28.

[0045] Figure 8 is an explanatory diagram showing the rotational speed of the wheel 13 and hub 25 for each rotation angle when the wheel 13 and hub 25 are rotated in the configuration shown in Figure 7. As shown in Figure 8, the rotational speed of the wheel 13 varies according to an acceleration / deceleration pattern in which the wheel 13 accelerates in the range from about 90° to about 180°, then decelerates to about 270°, and then accelerates again toward 0°.

[0046] In addition, the stud axial clearance δ between the stud 27 and the fastening hole 26 is only at one location. s In this method of narrowing the gap, when the wheel 13 does not tilt relative to the hub 25 due to loosening of the nut 29, the primary rotational vibration is dominant, but as the nut 29 loosens further and the wheel 13 starts to tilt relative to the hub 25, the vibration changes to a rotational component. For example, in the case of a passenger car, the wheel 13 starts to tilt relative to the hub 25 due to the camber angle, so the primary rotational vibration decreases and the secondary rotational vibration becomes dominant.

[0047] Fig. 9 is an explanatory diagram showing the rotation of the wheel 13 and hub 25 when the wheel 13 pushes and rotates the stud 27A due to loosening of the nut 29. Fig. 10 is an explanatory diagram showing the rotational speed of the wheel 13 and hub 25 for each rotation angle when the wheel 13 and hub 25 are rotated in the configuration shown in Fig. 9. In this case, the wheel 13 rotates in an elliptical shape when viewed in the axial direction. Therefore, Figs. 9 and 10 show that this mainly appears as secondary rotational vibration.

[0048] Therefore, by monitoring wheel speed fluctuations with an existing speed sensor such as an ABS sensor, it is possible to extract characteristic quantities of periodic rotational speed fluctuations such as the primary and secondary rotational vibrations described above. Based on these characteristic quantities of rotational speed fluctuations, it is possible to detect looseness of nut 29. With this method of detecting looseness of a wheel, a simple modification is made by replacing only one stud with a larger diameter stud 27A, and by using an existing speed sensor, a looseness detection system can be constructed at low cost by simply adding software to the engine control unit (ECU) and improving the performance of the hardware.

[0049] In other words, when the driving force of the drive shaft is smaller than the inertia force of the wheel 13 and the wheel 13 is lightly pushed and turned, periodic fluctuations in the rotational speed of the drive shaft, such as primary and secondary rotational vibrations, occur, and by detecting these rotational speed fluctuations with a speed sensor, it is possible to detect loosening of the nut 29.

[0050] Incidentally, a two-wheel drive vehicle has a drive shaft and a driven shaft, and the driven shaft is not connected to the drive shaft. Therefore, the rotational torque of the hub unit bearing 11 itself is almost constant, and the hub 25 rotates in accordance with the rotation of the wheel 13. In this case, it is possible to constantly detect looseness of the nut 29.

[0051] On the other hand, for the drive shaft, loosening of the nut 29 can be detected when the inertial force of the wheel is greater than the driving force (or braking force) of the drive shaft. When the inertial force of the wheel 13 is small and the driving force (or braking force) of the drive shaft is large, the driving force rotates the wheel 13 forcefully, so that rotational speed fluctuations do not occur in the hub 25 but do occur in the wheel 13. The braking force here refers to the force exerted by various brakes, such as engine brakes, disc brakes, drum brakes, retarder brakes, and regenerative brakes (for electric vehicles).

[0052] Fig. 11 is an explanatory diagram showing the rotational speed for each rotation angle when rotational speed fluctuations do not occur in the hub but do occur in the wheel 13. Fig. 11 shows the rotational speed fluctuations obtained by reversing the rotational speed fluctuations shown in Fig. 8 between the wheel 13 and the hub 25. Conversely, when the inertial force of the wheel is greater than the driving force (or braking force) of the drive shaft, the rotation of the hub 25 follows in accordance with the rotation of the wheel 13, so that rotational speed fluctuations do not occur in the wheel 13 but occur in the hub 25 (see Fig. 8).

[0053] As described above, because the rotation of the drive shaft and the wheel 13 interact with each other, the rotation speed changes depending on the driving force of the drive shaft and the inertial force of the wheel 13. For this reason, it is preferable to classify cases based on multiple parameters such as speed and engine output and detect looseness of the nut 29. Specifically, it is sufficient to detect looseness in each case, such as when accelerating with high engine output, when at a constant speed with low engine output, when falling, when braking force is applied, etc.

[0054] <Gap between stud and fastening hole> FIG. 12 shows the relationship between the axial diameter of the stud 27A and the axial clearance δ s 10 is an explanatory diagram showing the fluctuation of the rotation speed when the diameter (inner diameter) of each fastening hole 26 is constant. The axial diameter d of all the studs 27 is sIf all nuts have the same shaft diameter d0, the studs 27 will push and rotate the wheel 14 at a position near 9 o'clock (position P1) in Figure 12. As the hub 25 rotates, the studs 27 that reach the position near 9 o'clock (position P1) will sequentially push and rotate the wheel 13, so even when all nuts are loosened, there will be no fluctuation in the rotational speed of the hub 25.

[0055] On the other hand, the stud shaft clearance δ between one stud 27A and the fastening hole 26 s When the diameter of the screw shaft of stud 27A is narrowed, s When the stud 27A is expanded, the shaft diameter d s However, in this state, the rotation speed fluctuation increases depending on the shaft diameter d s When the enlarged stud 27A is positioned near the 1 o'clock position (position P2) or the 5 o'clock position (position P3) in FIG. 12, the normal stud 27 with a shaft diameter d0 pushes and rotates the wheel 13 near the 9 o'clock position (position P1). s As the diameter of the wheel increases, the ratio of the enlarged stud 27A pushing and rotating the wheel 14 increases. s When the shaft diameter d of the stud 27A exceeds a certain value, the stud 27A, which is constantly enlarged, begins to push and rotate the wheel 14. s If the distance exceeds d2, the wheel load is applied to the stud 27A, which may cause breakage of the stud 27A.

[0056] FIG. 13 shows the relationship between the diameter of the fastening hole 26 and the stud shaft clearance δ s 10 is an explanatory diagram showing the fluctuation of the rotation speed when the diameter D of the fastening hole 26 is increased or decreased. s If the diameter D of the fastening hole 26 is small and the entire wheel load is applied to the large-diameter stud 27A when the hub 25 is displaced downward, the stud 27A may break. s exceeds a certain pore diameter, the pore diameter D s has almost no effect on the fluctuation of the wheel rotation speed.

[0057] 14 is an explanatory diagram showing the rotational speed fluctuation when the gap between the spigot portion 28 of the hub 25 and the center hole 30 of the wheel 13 is changed. As shown in FIG. 3, the spigot gap δ, which is the radial gap of the space (area where no object exists) formed between the outer peripheral surface of the spigot portion 28 and the inner peripheral surface of the center hole 30, h (=D h -d h ) is 0, the hub 25 and the wheel 13 are in the same centered state, so no fluctuations in the rotational speed of the hub 25 occur. h The larger the gap between the hub 25 and the wheel 13, the larger the center offset between the hub 25 and the wheel 13. When this center offset and the stud shaft gap δ at one location in the circumferential direction of the wheel 13 are considered, s The presence of the narrowed portion causes fluctuations in the rotation speed of the hub 25. h is a predetermined constant value, the spigot clearance δ h The rotational speed fluctuation increases in proportion to the size of , and the S / N ratio also improves. h If the wheel load exceeds a certain value, the wheel load is applied to the stud 27A, which may cause the stud 27A to break.

[0058] <Dimension settings for each part> Here, the stud shaft clearance δ is set at only one location in the circumferential direction of the wheel 13. s This section explains the recommended dimensions for each part to narrow the gap. Fig. 15 is an explanatory diagram showing the dimensions of the hub 25, wheel 13, and studs 27, 27A when an even number of studs 27 are provided. Fig. 16 is an explanatory diagram showing the dimensions of the hub 25, wheel 13, and studs 27, 27A when an odd number of studs 27 are provided. First, in order to ensure the S / N ratio of rotational speed fluctuations, the spigot clearance δ h (=D h -d h ) is enlarged so that the wheel 13 is pushed and rotated only by the enlarged stud 27A. h It is preferable to set the dimension so as to satisfy the formula (1). δ h =D h -d h <(Ds -d0) / 2 (1)

[0059] Formula (1) is the spigot clearance δ in the rotation direction at the position where the expanded stud 27A is arranged, which is shown in formula (2). a is the spigot clearance δ in the rotation direction at the position where the normal stud 27 is arranged, as shown in formula (3). b It can be derived from the smaller δ a =(D s -d s ) / 2-{(D h -d h ) / 2}cosθ (2) δ b =(D s -d0) / 2-{(D h -d h ) / 2}cosθ (3) Here, θ is the angle between the tangent along the direction of rotation and the vertical direction.

[0060] Furthermore, especially from a safety standpoint, the wheel load is prevented from being applied to the enlarged stud 27A. That is, if a wheel load is applied to the stud 27A, there is a risk that the stud 27A may break. Therefore, when the wheel 13 is on the hub 25 at the spigot portion 28, the wheel load is prevented from being applied to the stud 27A. For this reason, the spigot clearance δ h It is preferable to set the dimension so as to satisfy the formula (4). δ h =D h -d h <(D s -d s ) ···(4)

[0061] <Detecting the amplitude of rotation speed fluctuations> This section describes a method for extracting primary and secondary rotational vibrations from wheel rotational speed fluctuations. A square wave detection signal (square wave pulse) is output from the speed sensor. For this square wave pulse, the period Tp of each pulse and the period T for one rotation of the wheel 13 are obtained. And the period ratio R of N pulses (N is an integer) NBy calculating (=T / Tp), the time taken for the square wave pulse is converted into the ratio of the time taken for the square wave pulse to one rotation of the wheel 13. In other words, error factors such as rotational irregularities during one rotation period and magnetization errors of the encoder are removed, and the detection signal is converted into a dimensionless value.

[0062] Calculated period ratio R N By applying a band pass filter (BPF) to this, the first and second rotational vibrations are extracted, and looseness of the nut 29 is judged based on the increase in the amplitude of these first and second rotational vibrations. Since looseness is judged based on amplitude regardless of phase lag, the BPF can be either an infinite impulse response (IIR) filter or a finite impulse response (FIR) filter. Also, to reduce the calculation load, a BPF using a moving average can be used. Here, the BPF is created by combining and adding / subtracting the period ratio, the moving average of the period ratio over a specific number of pulses (average number X), and the moving average of the period ratio over a specific number of pulses (average number Y) according to the frequency band to be extracted.

[0063] FIG. 17 is a schematic diagram showing an example of a waveform of the period ratio with high-frequency noise removed. FIG. 18 is a schematic diagram showing an example of a waveform in which first-order vibrations of rotation are extracted from the waveform shown in FIG. 17. FIG. 19 is a schematic diagram showing an example of a waveform in which second-order vibrations of rotation are extracted from the waveform shown in FIG. 17. FIGS. 17 to 19 were created using output data from a magnetic encoder with 48 pulses per rotation during running of an actual vehicle, and the horizontal axis shows the number of rotations of the spatial frequency (denoted as "spatial"). As shown in FIGS. 18 and 19, when first-order and second-order vibrations of rotation are extracted using a moving average, the waveform is easily affected by noise if the high-frequency noise is large. Therefore, it is preferable to remove high-frequency noise from the waveform of the period ratio shown in FIG. 17 before extracting the first-order and second-order vibrations of rotation.

[0064] Based on the waveforms described above, as will be described in detail below, it is possible to distinguish between a normal state in which the nuts 29 or studs 27, 27A are not loose and an abnormal state in which they are loose, and it is also possible to determine the degree of looseness, based on the amplitude of the waveform. Therefore, by processing the detection signal output from the speed sensor 56 while the vehicle is running, it is possible to detect looseness of the nuts 29 or studs 27, 27A in real time with high accuracy. This makes it possible to determine the abnormality from the stage when a minor abnormality occurs in a vehicle in which the nuts 29 or studs 27, 27A have loosened, before it develops into a driving abnormality such as a wheel or tire falling off, and to quickly notify the driver or manager of the vehicle of the occurrence of the abnormality.

[0065] Figure 20 is a schematic block diagram of a fastening looseness detection system 200. In the fastening looseness detection system 200, a speed sensor 56 detects the rotation of an encoder 55 (Figures 1 and 2) provided on the hub 25 of a wheel support bearing unit 100 serving as a coupling device, and a looseness determination unit 87 determines loosening of the fastening thread portion from fluctuations in this rotation speed. The looseness determination unit 87 generates a rotation fluctuation signal that extracts fluctuations in the rotation speed of the hub 25 from the output signal of the rotation speed of the hub 25 detected by the speed sensor 56. The looseness determination unit 87 then compares a feature value corresponding to the rotation speed fluctuation of the rotation fluctuation signal with a preset reference, and determines that loosening has occurred in the fastening thread portion if the feature value is greater than the reference.

[0066] The loosening determination unit 87 is included in a control unit 89 that controls loosening detection in an integrated manner. The control unit 89 performs the above-mentioned signal processing based on the pulse signal input from the speed sensor 56. The control unit 89 is configured as a computer equipped with a processor such as a CPU, and storage devices such as a read-only memory (ROM), a random access memory (RAM), a hard disk drive (HDD), and a solid state drive (SSD). The function of the loosening determination unit 87 can be realized by the processor executing a predetermined program stored in the storage device. Furthermore, the control unit 89 is not limited to being directly connected to the wheel support bearing unit 100, and may be connected via communication such as wirelessly or through a network.

[0067] <Stud shaft clearance δ s and spigot clearance δ h Setting example> Next, the stud axial clearance δs of any one of the studs 27A and the spigot clearance δ h Here, we will explain other ways of setting the stud shaft clearance δ using the following methods M1 and M2. s Narrow the gap and use the following M3 method to make the inlay clearance δ h These methods M1 to M3 can be combined appropriately depending on the situation to narrow the stud shaft clearance δ s and spigot clearance δ h It is advisable to form a

[0068] (M1) Stud axial clearance δ between the stud 27A and the fastening hole 26 at one location in the circumferential direction of the wheel s How to narrow (M2) Stud shaft clearance δ at one location in the circumferential direction using the method of M1 s While narrowing the stud shaft clearance δ at other positions s How to adjust (M3) How to change the inlay structure

[0069] Figure 21 shows the stud shaft clearance δ corresponding to the M1 method. s 1 is an explanatory diagram showing an example of narrowing the stud clearance δ, which is the radial dimension of the space formed between the outer peripheral surface of the stud 27 inserted into the fastening hole 26 and the inner peripheral surface of the fastening hole 26. s To narrow the stud axial clearance δ, there are two methods: either increasing the axial diameter (outer diameter) of one of the multiple studs, or decreasing the hole diameter (inner diameter) of one of the multiple fastening holes 26. To increase the axial diameter of the stud, a spacer 71 is attached to the shank of the stud 27 to reduce the stud axial clearance δ. sExamples of methods for reducing the diameter of the fastening hole 26 include narrowing the diameter of the stud 27 (Structural Example 1), widening the outer diameter of a portion of the stud 27 that comes into contact with the wheel 13 (Structural Example 2), and increasing the standard size of the stud 27 (Structural Example 3). In addition to reducing the diameter of the fastening hole 26 (Structural Example 4), other methods for reducing the diameter of the fastening hole 26 include attaching a diameter-reducing spacer 73 to the inner periphery of the fastening hole 26 (Structural Example 5). The configurations of each structural example can be combined as appropriate. For example, the stud 27 of Structural Example 1 may be a stud with a larger diameter at the portion where the spacer 71 is attached, as shown in Structural Example 2.

[0070] FIG. 22 shows a normal stud 27 corresponding to the M2 method, and a stud shaft clearance δ s 1 is an explanatory diagram showing an example of a configuration in which the stud axial clearance δ of the stud 27 at one location in the circumferential direction of the wheel 13 is narrowed. s In order to narrow the stud shaft clearance δ, a spacer 71 is attached to the stud 27 (see structural example 1 in Fig. 21). Normally, in existing vehicles, the stud shaft clearance δ varies depending on the vehicle manufacturer, model, structure, etc. s The gaps may be narrow or wide overall. When the gap is wide, the stud shaft gap δ at all other locations in the circumferential direction is increased to improve the ease of attachment and detachment of the wheel 13 from the hub 25 and the accuracy of positioning the wheel 13 relative to the hub 25. s In such cases, it is preferable to attach low-strength spacers 75 to each of the studs 27 except for one in the circumferential direction. Similarly, low-strength spacers (not shown) may be provided to reduce the diameter of the fastening holes 26 except for one in the circumferential direction.

[0071] This low-strength spacer 75 should be strong enough to withstand the load in the direction of wheel rotation caused by the nut loosening during vehicle operation, without breaking when the wheel is attached or detached. In other words, even if the weight of the wheel 13 or tire (the weight of the driven body) is applied to the spacer 75 when the wheel is attached or detached, the spacer 75 should not be crushed or shattered, but should be strong enough to break or begin plastic deformation when the load in the direction of wheel rotation caused by the nut loosening during vehicle operation. Specific examples of the spacer 75 include resin spacers, sheet metal that has been three-dimensionally processed into a corrugated shape by a press, and a Tolerance Ring (registered trademark). When a resin spacer 75 breaks, it shatters and the gap widens, but a three-dimensionally processed sheet metal part crushes and the gap widens, so no foreign matter is generated.

[0072] The above-described configuration of the stud 27 and the fastening hole 26 is an example, and other configurations are also possible. 23 is a schematic diagram showing how a wheel 13A is fastened to a hub 25 using a nut 29A with a spherical seat. The nut 29A is threaded onto a stud 27 with the spherical seat facing the wheel 13A. A tapered inner circumferential surface 26a is formed in the fastening hole 26 of the wheel 13 on the side facing the nut 29A. A spacer 71 is attached to the stud 27, and when the nut 29A is tightened, the tip of the spherical seat is pressed against the end face of the spacer 71. At this time, the inner circumferential surface 26a of the fastening hole 26 does not come into contact with the spherical seat, and when the nut 29A is loosened, the wheel 13 and the stud 27 can move relative to each other in a plane perpendicular to the axis of the stud 27.

[0073] FIG. 24 is a schematic diagram showing how a stud 27B is fastened to an internally threaded hole 25a formed in a hub 25, sandwiching the wheel 13. The stud 27B has a head 77 and a shaft 79. An external thread is formed on the shaft 79, and the internally threaded hole 25a formed in the hub 25 serves as a fixing portion, to which the tip of the shaft 79 is fastened. A spacer 71 is attached to the shaft 79. The head 77 has a spherical seat, and the fastening hole 26 of the wheel 13 has a tapered inner circumferential surface 26a. In this case, too, when the stud 27B is fastened, the tip of the spherical seat is pressed against the end face of the spacer 71. At this time, the inner circumferential surface 26a of the fastening hole 26 does not come into contact with the spherical seat, and when the stud 27B is loosened, the wheel 13 and the stud 27B can move relative to each other in a plane perpendicular to the axis of the stud 27B.

[0074] In the case of nut 29A or stud 27B having a spherical seat, the spherical seat allows for centering of wheel 13 relative to hub 25, so spacer 71 is not required for stud 27 at any location other than one in the circumferential direction, and there is no need to provide a spacer at spigot portion 28 of hub 25. Furthermore, studs 27 and 27B shown in Figures 23 and 24 may be studs with a larger diameter at the location where spacer 71 is attached, as shown in structural example 2 in Figure 21.

[0075] The wheel attached to the hub 25 is not limited to a single tire type, but may be a double tire type used for the rear wheels of trucks, etc. 25 is a schematic cross-sectional view of the main part showing the support structure for wheels 13A, 13B of a double tire. Although a detailed explanation will be omitted, in the double tire configuration, studs 27 are fixed to mounting flanges 37 formed on hub 25, and a pair of wheels 13A, 13B are fastened to the studs 27 with nuts 29. A tire 81 is mounted on each of the wheels 13A, 13B. FIG. 26 is a schematic diagram showing dual tire wheels 13A, 13B fastened to a hub 25 with studs 27 and nuts 29. In this case, the pair of wheels 13A, 13B are fastened to the hub 25 by inserting the studs 27, to which spacers 71 are attached, into the fastening holes 26 and tightening them with nuts 29. The spacer 71 is attached to one stud 27 in the circumferential direction of the wheels 13A, 13B, but not to the other studs 27. Although not shown, since the wheels 13A, 13B are centered at the spigot portion of the hub 25, it is preferable to attach the low-strength spacer described above to the spigot portion of the hub 25. The studs 27 shown in FIG. 26 may also be studs with a larger diameter at the portion where the spacer 71 is attached, as shown in structural example 2 in FIG. 21.

[0076] FIG. 27 shows the inlay gap δ of the inlay portion 28 corresponding to the M3 method. h In an existing vehicle, when the wheel 13 is centered by the spigot portion 28, the spigot gap δ between the spigot portion 28 and the inner peripheral surface of the center hole 30 of the wheel 13 is narrowed. h Even in the case of a configuration in which centering is performed using the spherical seat of the stud 27 or the nut 29A, the spigot clearance δ h In this way, regardless of the centering method, the inlay clearance δ h is set relatively narrowly.

[0077] On the other hand, the stud shaft clearance δ s In the structure in which the gap δ of the inlay portion 28 is narrowed, h The wider the stud clearance δh, the greater the fluctuation in the rotational speed of the hub 25 when all nuts 29 are loosened, and the better the S / N ratio. However, if the spigot clearance δh is too wide, it can be difficult to center the wheel 13 when removing and attaching the wheel during vehicle maintenance, except when centering using the spherical seat described above. Therefore, it is recommended to set the stud shaft clearance δh at one point in the circumferential direction. s In the structure in which the gap δ of the inlay portion 28 is narrowed, hIt is preferable to provide a predetermined constant amount (for example, about 0.5 mm to 1 mm for a passenger car, and about 1 mm to 3 mm for a truck, although this depends on the type of car).

[0078] The above-mentioned appropriate spigot clearance δ h When a low-strength spacer 85 is installed on the hub 25 side of the spigot portion 28 to provide this, it is preferable to use a low-strength spacer 85 that, like the spacer 75 described above, is strong enough to withstand breaking when the wheel is attached or detached, but crushing under the load in the direction of wheel rotation caused by loosening of the nut during driving. Specific examples include a resin spacer, a metal sheet that has been pressed into a three-dimensional corrugated shape, a Tolerance Ring (registered trademark), and the like. In this case, even if the weight of the wheel 13 or tire (the weight of the driven body) is applied to the spacer 85 when the wheel is attached or detached, the wheel 13 can be positioned on the hub 25 without the spacer 85 being crushed or scattered.

[0079] Furthermore, when the nut loosens, the wheel load is applied to the spacer 85, causing the spacer 85 to collapse, resulting in misalignment between the wheel 13 and the hub 25. This misalignment and the stud axial clearance δ at one location in the circumferential direction s Since the gap between the wheel 13 and the hub 25 is narrower than the other gaps, fluctuations in the rotational speed between the wheel 13 and the hub 25 are more likely to occur.

[0080] <Test example> In the second structural example shown in Fig. 21, the nut 29 is provided with the spherical seat (see nut 29A in Fig. 23) described above, the fastening hole 26 of the wheel 13 is formed with a tapered inner peripheral surface (see inner peripheral surface 26a in Fig. 23), and a running test was carried out using a vehicle having a right rear wheel in which the wheel 13 is fastened to the hub 25. The conditions of the running test are as follows.

[0081] Vehicle: 4-wheeled standard car (FR vehicle) Wheel mounting structure: Structure example 1 in Figure 21 Speed ​​sensor: Installed at four locations above, below, left and right of the rotation axis of the right rear wheel Stud shaft clearance δ at one location in the circumferential direction s : Approx. 0.4 mm (approx. 0.2 mm on each side) Stud shaft clearance δ at other locations s: Approx. 2mm (approx. 1mm on each side) Spigot clearance δ h : Approx. 0.2 mm (approx. 0.1 mm on each side) Traveling speed: 35km / h

[0082] The running tests were conducted by moving back and forth on the same roadway, with Test Example 1 being without nut loosening, and Test Examples 2 and 3 being with nut loosening simulated in two stages. The amount of nut loosening in Test Example 2 was 0.5 mm in the axial direction, and in Test Example 3 it was 2.3 mm. Note that the nuts in Test Examples 2 and 3 had a double nut structure to prevent further loosening and to prevent the wheel from falling off.

[0083] FIG. 28 is an explanatory diagram showing the test results of Test Examples 1 to 3. For each test example, the results of 50-m sections SC1 and SC2, where the vehicle speed is stable, were extracted and evaluated on both the outbound and inbound vehicle travel. The first graph from the top of FIG. 28 shows the output from the speed sensor, and the second graph shows the results of converting the output pulses from the speed sensor into the period ratios described above. The third graph shows the results of extracting first-order rotational vibrations from the period ratios in the second graph. The fourth graph shows the results of extracting second-order rotational vibrations from the period ratios in the second graph. The results were obtained by performing moving average processing (twice) on the above, and mainly show second-order rotational vibrations.

[0084] According to Figure 28, when comparing Test Example 1 and Test Example 2, an increase in the first-order vibration of rotation is observed when focusing on sections SC1 and SC2 in the waveform of the period ratio moving average (1 time). Furthermore, when comparing Test Example 2 and Test Example 3, an increase in the second-order vibration of rotation is observed when focusing on sections SC1 and SC2 in the waveform of the period ratio moving average (2 times). This makes it possible to distinguish between a normal state (Test Example 1) where the nut is not loose and an abnormal state (Test Examples 2 and 3) where the nut has loosened, and the degree of loosening can also be determined by comparing with Test Examples 2 and 3. For example, a criterion can be set in advance that can detect the increase in the first-order and second-order vibration of rotation described above by comparison, and an abnormal state can be determined based on whether the obtained waveform exceeds this criterion.

[0085] As such, the present invention is not limited to the above-described embodiments, and the present invention also contemplates the mutual combination of the various components of the embodiments, as well as modifications and applications by those skilled in the art based on the description in the specification and well-known techniques, and these modifications and applications are included in the scope of protection sought. For example, depending on the type of sensor, the output signal may have waveform distortion or additional information superimposed thereon. Even in such cases, the desired pulse waveform described above can be generated by adding appropriate signal processing, processing circuits, etc. In other words, the required processing may be added as appropriate depending on the waveform of the signal obtained from the sensor, and each of the damage detection steps described above may be performed.

[0086] As described above, the present specification discloses the following: (1) A coupling device in which a driver that is rotationally driven about a rotation axis and a driven body that rotates following the driver are fastened together by a plurality of fastening screw portions, the coupling device detecting loosening of the fastening screw portions, the driver has a spigot portion that is concentric with the rotation shaft and protrudes toward the driven body, and an annular flange portion that extends radially outward, and the flange portion has fixing portions to which one end of the fastening screw portion is fixed, provided at a plurality of locations along the circumferential direction of the flange portion; the driven body has a central hole formed so that the spigot portion can be inserted with a radial gap therebetween, and a plurality of fastening holes formed at locations corresponding to the plurality of fixing portions and into which the screw shafts of the fastening screw portions can be inserted, In any one of the plurality of fastening holes, a radial dimension of a space formed between an outer peripheral surface of the fastening thread portion inserted into the fastening hole and an inner peripheral surface of the fastening hole is narrower than the radial dimension of the space in the other fastening holes, a speed sensor for detecting the rotation speed of the driving body; further comprising a loosening determination unit that determines loosening of the fastening thread portion based on the detected fluctuation in the rotation speed of the driver; Fastener looseness detection system. According to this fastening loosening detection system, if loosening occurs in the fastening thread that fastens the driver and driven body, the spigot portion of the driver abuts against the inner circumferential surface of the center hole of the driven body, and in this state the driver is rotated by the screw shaft of the fastening thread inserted into one of the fastening holes. In this case, fluctuations in the rotational speed of the driver occur, and by detecting these rotational fluctuations with a speed sensor, loosening of the fastening can be detected.

[0087] (2) The fastening loosening detection system according to (1), wherein the loosening determination unit generates a rotation fluctuation signal by extracting fluctuations in the rotation speed of the driver from an output signal of the rotation speed of the driver detected by the speed sensor, compares a feature value corresponding to the rotation speed fluctuation of the rotation fluctuation signal with a preset reference value, and determines that loosening has occurred in the fastening thread portion if the feature value is greater than the reference value. This system for detecting loosening of a fastening screw can determine whether loosening of the fastening screw portion has occurred by comparing a feature value corresponding to the rotational fluctuation with a preset standard.

[0088] (3) The fastening loosening detection system according to (2), wherein the loosening determination unit extracts, as the feature quantity, first-order and second-order vibrations of the rotational speed fluctuation from the waveform of the rotation fluctuation signal. This fastening loosening detection system can accurately determine whether a fastening screw has loosened from the primary and secondary rotational vibrations that significantly indicate loosening of the fastening screw portion.

[0089] (4) A fastening loosening detection system according to any one of (1) to (3), wherein the difference between the diameter of any one of the fastening holes and the diameter of the screw shaft of the fastening screw portion inserted into the fastening hole is larger than the difference between the diameter of the central hole of the driven body and the diameter of the spigot portion of the driver body. With this fastening loosening detection system, when an even number of studs are used for fastening and loosening occurs in the fastening threads, it is possible to prevent the weight from the driver from being concentrated on the fastening threads inserted into any one of the fastening holes with the smallest radial gap.

[0090] (5) A fastening loosening detection system according to any one of (1) to (3), wherein the difference between the radius of the fastening screw portion inserted into any one of the fastening holes and the radius of the fastening screw portion inserted into an insertion hole other than the fastening hole is larger than the difference between the diameter of the central hole of the driven body and the diameter of the spigot portion of the driver body. With this fastening loosening detection system, when an odd number of studs are used for fastening and loosening occurs in the fastening thread portion, it is possible to prevent the weight from the driver from being concentrated on the fastening thread portion inserted into any one of the fastening holes with the smallest radial gap.

[0091] (6) The inner diameters of the plurality of fastening holes are uniform; The fastening loosening detection system according to any one of (1) to (3), wherein a diameter-expanding spacer is attached to any one of the plurality of fastening screw portions, the spacer narrowing the radial gap between the screw shaft of the fastening screw portion and the inner peripheral surface of the fastening hole into which the screw shaft of the fastening screw portion is inserted. According to this fastening loosening detection system, by attaching a spacer to any one of the fastening threaded portions, all of the fastening threaded portions and fastening holes can have a common configuration.

[0092] (7) A low-strength spacer that narrows a radial gap between the inner circumferential surface of the fastening hole and the fastening thread portion other than the one fastening thread portion among the plurality of fastening thread portions is attached, The fastening loosening detection system according to (6), wherein the low-strength spacer starts to break or plastically deform when a load greater than the weight of the driven body is applied thereto. According to this fastening loosening detection system, even if the weight of the driven body acts on the spacer, the spacer maintains its original shape, and if a power greater than this acts on the spacer, the spacer begins to break or undergo plastic deformation, causing fluctuations in the rotational speed of the driver.

[0093] (8) The outer diameters of the plurality of fastening thread portions within the fastening hole are constant, A fastening loosening detection system according to any one of (1) to (3), wherein a diameter-reducing spacer is attached to any one of the plurality of fastening holes, which narrows the radial gap between the fastening hole and the outer circumferential surface of the fastening thread portion within the fastening hole. According to this fastening loosening detection system, by attaching a spacer to any one of the fastening holes, all of the fastening threaded portions and fastening holes can have a common configuration.

[0094] (9) A low-strength spacer that narrows a radial gap between the outer circumferential surface of the fastening thread portion and the fastening holes other than the one fastening hole among the plurality of fastening holes is attached, The fastening loosening detection system according to (8), wherein the low-strength spacer starts to break or plastically deform when a load greater than the weight of the driven body is applied thereto. According to this fastening loosening detection system, even if the weight of the driven body acts on the spacer, the spacer maintains its original shape, and if a power greater than this acts on the spacer, the spacer begins to break or undergo plastic deformation, causing fluctuations in the rotational speed of the driver.

[0095] (10) The inner diameters of the plurality of fastening holes are uniform, The fastening loosening detection system according to any one of (1) to (3), wherein the outer diameter of any one of the plurality of fastening screw portions within the fastening hole is larger than the outer diameters of the other fastening screw portions within the fastening hole. According to this fastening loosening detection system, by increasing the outer diameter of any one of the fastening threaded portions, all other fastening threaded portions and all fastening holes can have a common configuration.

[0096] (11) A low-strength spacer is attached to the outer periphery of the spigot portion of the driver to narrow the radial gap between the spigot portion and the inner periphery of the center hole, The fastening loosening detection system according to any one of (1) to (10), wherein the low-strength spacer starts to break or plastically deform when a load greater than the weight of the driven body is applied. According to this fastening loosening detection system, even if the weight of the driven body acts on the spacer, the spacer maintains its original shape, and if a power greater than this acts on the spacer, the spacer begins to break or undergo plastic deformation, causing fluctuations in the rotational speed of the driver.

[0097] (12) The driving body includes a hub inner ring having an inner ring raceway on its outer circumferential surface and connected to a drive shaft of a vehicle, the follower includes a wheel having the central hole and a plurality of the fastening holes formed therein; A fastening loosening detection system according to any one of (1) to (11), comprising a hub unit bearing having the hub inner ring, a hub outer ring having an outer ring raceway on its inner circumferential surface and fixed to the vehicle, and a plurality of rolling elements provided so as to be able to roll between the outer ring raceway and the inner ring raceway. This fastening loosening detection system can detect loosening of the fastening threads from fluctuations in the rotational speed of the wheel fastened to the inner ring of the hub.

[0098] (13) The fastening loosening detection system according to (12), wherein the speed sensor is a sensor used in at least one of an antilock brake system, a traction control system, and a vehicle stability control system. According to this fastening loosening detection system, speed detection is performed using the sensors that are already installed, without the need for any additional sensors, making it possible to detect loosening of fastening screw portions at low cost and without increasing the complexity of the device.

[0099] (14) The fastening screw portion includes a stud having a head and a shaft portion including the screw shaft, and a nut that is screwed onto the screw shaft, The stud has a head portion fixed to the fixing portion of the hub and a shaft portion inserted into the fastening hole of the wheel, The wheel is fastened to the hub by the nut that is screwed onto the shaft portion. The fastening loosening detection system according to (12) or (13). According to this fastening loosening detection system, the wheel can be fastened to the hub by tightening the nut onto the threaded shaft of the stud.

[0100] (15) The fastening screw portion includes a bolt having a head and a shaft portion including the screw shaft, and a fixing portion formed in the hub and screwed onto the screw shaft, The fastening loosening detection system according to (12) or (13), wherein the shaft portion is inserted into the fastening hole of the wheel, and the tip end of the screw shaft is threadedly engaged with the fixing portion, so that the wheel is fastened between the head and the hub. According to this fastening loosening detection system, the wheel can be fastened to the hub by tightening the threaded shaft of the bolt to the fixing portion.

[0101] (16) A method for detecting loosening of a coupling device in which a driver that is rotationally driven about a rotation axis and a driven body that rotates following the driver are fastened together by a plurality of fastening screw portions, the method comprising: the driver has a spigot portion that is concentric with the rotation shaft and protrudes toward the driven body, and an annular flange portion that extends radially outward, and the flange portion has fixing portions to which one end of the fastening screw portion is fixed, provided at a plurality of locations along the circumferential direction of the flange portion; the driven body has a central hole formed so that the spigot portion can be inserted with a radial gap therebetween, and a plurality of fastening holes formed at locations corresponding to the plurality of fixing portions and into which the screw shafts of the fastening screw portions can be inserted, In any one of the plurality of fastening holes, a radial dimension of a space formed between an outer peripheral surface of a screw shaft of the fastening threaded portion inserted into the fastening hole and an inner peripheral surface of the fastening hole is narrower than the radial dimension of the other fastening holes, when the fastening screw portion is loosened, a speed sensor detects a fluctuation in the rotational speed of the driver caused by the driver being rotationally driven by the fastening screw portion inserted into any one of the fastening holes in a state in which the spigot portion of the driver is abutted against an inner circumferential surface of the central hole of the driven body, determining whether the fastening screw portion is loosened based on the detected fluctuation in the rotation speed of the driver; A method for detecting loose fasteners. According to this method for detecting loosening, if loosening occurs in the fastening thread that fastens the driver and driven body, the spigot portion of the driver abuts against the inner circumferential surface of the center hole of the driven body, and in this state, the driver is rotated by the screw shaft of the fastening thread inserted into one of the fastening holes. In this case, fluctuations in the rotational speed of the driver occur, and loosening of the fastening can be detected by detecting these rotational speed fluctuations with a speed sensor.

[0102] (17) A method for detecting loosening of fastening according to (16), comprising: generating a rotation fluctuation signal by extracting fluctuations in the rotation speed of the driver from an output signal of the rotation speed of the driver detected by the speed sensor; comparing a feature value corresponding to the rotation speed fluctuation of the rotation fluctuation signal with a preset reference value; and determining that loosening has occurred in the fastening thread portion if the feature value is greater than the reference value. According to this method for detecting loosening of a fastening thread, the occurrence of loosening of the fastening thread portion can be determined by comparing a feature quantity corresponding to the rotational fluctuation with a preset reference.

[0103] (18) The driving body includes a hub inner ring having an inner ring raceway on its outer circumferential surface and connected to a drive shaft of a vehicle, the follower includes a wheel having the central hole and a plurality of the fastening holes formed therein; The method for detecting loosening of a fastening member according to (16) or (17), wherein a hub unit bearing is configured having the hub inner ring, a hub outer ring having an outer ring raceway on its inner peripheral surface and fixed to the vehicle side, and a plurality of rolling elements provided so as to be able to roll between the outer ring raceway and the inner ring raceway. According to this method for detecting loosening, loosening of the fastening threads can be detected from fluctuations in the rotational speed of the wheel fastened to the inner ring of the hub. [Explanation of symbols]

[0104] 11 Hub unit bearing 13 Wheel (follower) 13A, 13B Wheel (follower) 15 Knuckles 17 rotor 19 Support hole 21 Hub outer ring 21a, 21b Outer ring raceway 23 volts 25 Hub (driver) 25a female thread hole 26 Fastening hole 26a Inner surface 27 Stud (fastening screw part) 27A stud (fastening thread) 27B Stud 28 Inlay part 29 Nut (fastening screw part) 29A Nut (fastening screw part) 30 center hole 31 Connecting flange 33 Hub body (driver) 35 Hub inner ring (driver) 35a, 35b Inner raceway 37 Mounting flange (flange part) 39 Small diameter stepped section 41 Ball (rolling element) 43 Cage 45 Crimping part 47a, 47b Seal ring 49 spline hole 51 Constant velocity joint 53 Spline shaft 55 Encoder 56 Speed ​​sensor 57 Slinger 57a Circular part 59 Core 61 Sealing material 63 Outer diameter cylindrical part 71 Maza 73 Maza 75 Maza 77 Head 79 Shaft 81 Tires 85 Maza 87 Looseness detection unit 89 Control Unit 100 Wheel support bearing unit 200 Fastener Loosening Detection System

Claims

1. A fastening loosening detection system for detecting loosening of a plurality of fastening screw portions in a coupling device in which a driver that is rotationally driven about a rotation axis and a driven body that rotates following the driver are fastened together by a plurality of fastening screw portions, the driver has a spigot portion that is concentric with the rotation shaft and protrudes toward the driven body, and an annular flange portion that extends radially outward, and the flange portion has fixing portions to which one end of the fastening screw portion is fixed, provided at a plurality of locations along the circumferential direction of the flange portion; the driven body has a central hole formed so that the spigot portion can be inserted with a radial gap therebetween, and a plurality of fastening holes formed at locations corresponding to the plurality of fixing portions and into which the screw shafts of the fastening screw portions can be inserted, In any one of the plurality of fastening holes, a radial dimension of a space formed between an outer peripheral surface of the fastening thread portion inserted into the fastening hole and an inner peripheral surface of the fastening hole is narrower than the radial dimension of the space in the other fastening holes, a speed sensor for detecting the rotation speed of the driving body; further comprising a loosening determination unit that determines loosening of the fastening thread portion based on the detected fluctuation in the rotation speed of the driver; Fastener looseness detection system.

2. the loosening determination unit generates a rotation fluctuation signal by extracting a rotation speed fluctuation of the driver from an output signal of the rotation speed of the driver detected by the speed sensor, compares a feature amount corresponding to the rotation speed fluctuation of the rotation fluctuation signal with a preset reference, and determines that loosening of the fastening thread portion has occurred when the feature amount is greater than the reference. The fastener loosening detection system according to claim 1 .

3. the looseness determination unit extracts, as the feature quantity, first-order and second-order vibrations of the rotation speed fluctuation from the waveform of the rotation fluctuation signal; The fastening loosening detection system according to claim 2 .

4. a difference between the diameter of any one of the fastening holes and the diameter of the screw shaft of the fastening screw portion inserted into the fastening hole is larger than a difference between the diameter of the central hole of the driven body and the diameter of the spigot portion of the driver body; The fastener loosening detection system according to claim 1 .

5. a difference between a radius of the fastening screw portion inserted into any one of the fastening holes and a radius of the fastening screw portion inserted into an insertion hole other than the fastening hole is larger than a difference between a diameter of the central hole of the driven body and a diameter of the spigot portion of the driver body; The fastener loosening detection system according to claim 1 .

6. The inner diameters of the plurality of fastening holes are uniform, A diameter-expanding spacer is attached to any one of the fastening thread portions, which narrows a radial gap between the fastening thread portion and an inner peripheral surface of the fastening hole into which a screw shaft of the fastening thread portion is inserted. The fastener loosening detection system according to claim 1 .

7. a low-strength spacer that narrows a radial gap between the inner circumferential surface of the fastening hole and a fastening thread portion other than the one fastening thread portion among the plurality of fastening thread portions is attached to the fastening thread portion, The low-strength spacer begins to break or plastically deform when a load greater than the weight of the driven body is applied thereto. The fastening loosening detection system according to claim 6 .

8. The outer diameters of the plurality of fastening thread portions within the fastening hole are constant, A diameter-reducing spacer is attached to any one of the fastening holes to narrow a radial gap between the fastening hole and an outer circumferential surface of the fastening thread portion. The fastener loosening detection system according to claim 1 .

9. A low-strength spacer that narrows a radial gap between the fastening thread portion and an outer circumferential surface of the fastening thread portion is attached to a fastening hole other than the one fastening hole among the plurality of fastening holes, The low-strength spacer begins to break or plastically deform when a load greater than the weight of the driven body is applied thereto. The fastener loosening detection system according to claim 8 .

10. The inner diameters of the plurality of fastening holes are uniform, Any one of the plurality of fastening thread portions has an outer diameter in the fastening hole larger than the outer diameters of the other fastening thread portions in the fastening hole. The fastener loosening detection system according to claim 1 .

11. a low-strength spacer that narrows a radial gap between the inner circumferential surface of the center hole and an outer periphery of the spigot portion of the driver is attached; The low-strength spacer begins to break or plastically deform when a load greater than the weight of the driven body is applied thereto. The fastener loosening detection system according to claim 1 .

12. the driving body includes a hub inner ring having an inner ring raceway on its outer circumferential surface and connected to a drive shaft of a vehicle; the follower includes a wheel having the central hole and a plurality of the fastening holes formed therein; a hub unit bearing including the hub inner ring, a hub outer ring having an outer ring raceway on its inner circumferential surface and fixed to the vehicle side, and a plurality of rolling elements provided so as to be able to roll between the outer ring raceway and the inner ring raceway, The fastening loosening detection system according to any one of claims 1 to 11.

13. The speed sensor is a sensor used in at least one of an antilock brake system, a traction control system, and a vehicle stability control system. The fastener loosening detection system according to claim 12.

14. The fastening screw portion includes a stud having a head and a shaft portion including the screw shaft, and a nut that is threaded onto the screw shaft, The stud has a head portion fixed to the fixing portion of the hub and a shaft portion inserted into the fastening hole of the wheel, The wheel is fastened to the hub by the nut that is screwed onto the shaft portion. The fastener loosening detection system according to claim 12.

15. The fastening screw portion includes a bolt having a head and a shaft portion including the screw shaft, and a fixing portion formed in the hub and threadedly engaged with the screw shaft, The shaft portion is inserted into the fastening hole of the wheel, and the tip portion of the screw shaft is screwed into the fixing portion, so that the wheel is fastened between the head and the hub. The fastener loosening detection system according to claim 12.

16. A method for detecting loosening of a fastening screw portion in a coupling device in which a driver that is rotationally driven about a rotation axis and a driven body that rotates following the driver are fastened together by a plurality of fastening screw portions, the method comprising: the driver has a spigot portion that is concentric with the rotation shaft and protrudes toward the driven body, and an annular flange portion that extends radially outward, and the flange portion has fixing portions to which one end of the fastening screw portion is fixed, provided at a plurality of locations along the circumferential direction of the flange portion; the driven body has a central hole formed so that the spigot portion can be inserted with a radial gap therebetween, and a plurality of fastening holes formed at locations corresponding to the plurality of fixing portions and into which the screw shafts of the fastening screw portions can be inserted, In any one of the plurality of fastening holes, a radial dimension of a space formed between an outer peripheral surface of a screw shaft of the fastening threaded portion inserted into the fastening hole and an inner peripheral surface of the fastening hole is narrower than the radial dimension of the other fastening holes, when the fastening screw portion is loosened, a speed sensor detects a fluctuation in the rotational speed of the driver caused by the driver being rotationally driven by the fastening screw portion inserted into any one of the fastening holes in a state in which the spigot portion of the driver is abutted against an inner circumferential surface of the central hole of the driven body, determining whether the fastening screw portion is loosened based on the detected fluctuation in the rotation speed of the driver; A method for detecting loose fasteners.

17. generating a rotation fluctuation signal by extracting a rotation speed fluctuation of the driver from an output signal of the rotation speed of the driver detected by the speed sensor; comparing a feature value corresponding to the rotation speed fluctuation of the rotation fluctuation signal with a preset reference value; and determining that loosening of the fastening thread portion has occurred when the feature value is greater than the reference value. The method for detecting loosening according to claim 16.

18. the driving body includes a hub inner ring having an inner ring raceway on its outer circumferential surface and connected to a drive shaft of a vehicle; the follower includes a wheel having the central hole and a plurality of the fastening holes formed therein; A hub unit bearing is configured having the hub inner ring, a hub outer ring having an outer ring raceway on its inner circumferential surface and fixed to the vehicle side, and a plurality of rolling elements provided so as to be able to roll between the outer ring raceway and the inner ring raceway. The method for detecting loosening according to claim 16.

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