Detection device, state detection device, and detection method

Abstract

The invention provides a detection device, a state detection device and a detection method. A sensor device (100) (detection device) is provided with: an acceleration sensor (1) (acceleration detection unit) that rotates in conjunction with the rotation of a nut (240) (fastening member) that fastens a hub (250a) (fastened member) to a wheel (220) (rotating body), and that detects acceleration along a detection axis (X) (Y) that intersects the rotation axis (O) of the wheel (220); and a signal processing unit (2) (state detection unit) that detects the fastening state of the nut (240) on the basis of the acceleration detected by the acceleration sensor (1).

Description

Technical Field

[0001] The present disclosure relates to a detection device, a state detection device and a detection method. Background Art

[0002] Japanese Patent Application Laid-Open No. 2005-329907 (Patent Document 1) discloses a detection device that detects the mounting state of a tire (a nut fastening a wheel) based on a detection value of a detector (G sensor) mounted on the tire or wheel.

[0003] Patent Document 1: Japanese Patent Application Publication No. 2005-329907

[0004] However, in an apparatus for detecting the mounting state of a tire (a fastening member for fastening a wheel), a technique for more simply detecting the mounting state of the tire (a fastening member for fastening a wheel) is desired. Summary of the invention

[0005] The present disclosure has been made to solve such a problem, and an object of the present disclosure is to provide a detection device, a state detection device, and a detection method that can easily detect the mounting state of a fastening member that fastens a rotating body such as a wheel.

[0006] The detection device of the first aspect of the present disclosure comprises: an acceleration detection unit that rotates in conjunction with the rotation of a fastening member that fastens the fastened member to a rotating body and detects acceleration along at least one detection axis that intersects the rotation axis of the rotating body; and a state detection unit that detects the fastening state of the fastening member based on the acceleration detected by the acceleration detection unit.

[0007] In the detection device of the first aspect of the present disclosure, as described above, the tightening state of the tightening member is detected based on the acceleration detected by the acceleration detection unit. Thus, the tightening state of the tightening member can be detected based on the acceleration of the tightening member. Here, the acceleration of the tightening member is determined based on the centrifugal acceleration of the rotating body and the rotation angle of the tightening member, but does not change according to the type, size, etc. of the rotating body. Therefore, the tightening state of the tightening member can be detected regardless of the type, size, etc. of the rotating body. Thus, the tightening state of the tightening member can be easily detected.

[0008] The state detection device of the second aspect of the present disclosure detects the tightening state of the tightening member based on the acceleration detected by the acceleration detection unit that rotates in conjunction with the rotation of the tightening member that tightens the tightened member to the rotating body. The above-mentioned state detection device includes: an acquisition unit that acquires information obtained based on the above-mentioned acceleration along the detection axis that intersects the rotation axis of the rotating body; and a tightening state detection unit that detects the tightening state of the tightening member based on the above-mentioned information acquired by the acquisition unit.

[0009] In the state detection device according to the second aspect of the present disclosure, as described above, the fastened state of the fastening member is detected based on the acceleration detected by the acceleration detection unit. Thus, it is possible to provide a state detection device that can easily detect the fastened state of the fastening member.

[0010] The detection method according to the third aspect of the present disclosure is a detection method of a detection device having an acceleration detection unit that rotates in conjunction with the rotation of a fastening member that fastens the fastened member to a rotating body, and comprises the following steps: detecting the acceleration along a detection axis that intersects the rotation axis of the rotating body by the acceleration detection unit; and detecting the fastening state of the fastening member based on the acceleration detected by the acceleration detection unit.

[0011] In the detection method according to the third aspect of the present disclosure, as described above, the fastened state of the fastening member is detected based on the acceleration detected by the acceleration detection unit. This provides a detection method that can easily detect the fastened state of the fastening member.

[0012] According to the present disclosure, it is possible to easily detect the fastening state of a fastening member that fastens a rotating body such as a wheel. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a diagram showing a vehicle provided with the sensor device according to the first to fifth embodiments.

[0014] Figure 2 It is a cross-sectional view of the nut according to the first embodiment.

[0015] Figure 3 It is a diagram showing the structure of the sensor device according to the first embodiment.

[0016] Figure 4 This is a functional block diagram of the signal processing unit according to the first embodiment.

[0017] Figure 5 This is a front view showing the structure of a tire of a vehicle (initial state).

[0018] Figure 6 It is a diagram showing the relationship between the X-axis acceleration, the Y-axis acceleration, and the centrifugal acceleration.

[0019] Figure 7 This is a diagram showing the relationship between acceleration and wheel angle when the centrifugal force is zero.

[0020] Figure 8 This is a diagram showing the relationship between acceleration and wheel angle when the centrifugal force is 3G.

[0021] Fig.9AThis is a diagram showing the relationship between the average value of acceleration and the sensor angle when the centrifugal force is 3 G.

[0022] Fig. 9B This is a diagram showing the relationship between the average value of acceleration and the sensor angle when the centrifugal force is 10G.

[0023] Fig.10 This is a flowchart showing a control flow of the sensor device according to the first embodiment.

[0024] Fig.11 It is a diagram showing the structure of a sensor device according to a second embodiment.

[0025] Fig.12 It means that the sensor device Figure 5 A front view of the structure of a tire when it is rotating is formed in a state.

[0026] Fig.13 It is a diagram showing a first example of waveforms of the X-axis normalized value, the Y-axis normalized value, and the centrifugal acceleration.

[0027] Fig.14 This is a flowchart showing the flow of processing by the sensor device according to the second embodiment.

[0028] Fig.15 This is a diagram for explaining a situation in which the direction of centrifugal acceleration is deviated due to the influence of gravitational acceleration and is detected.

[0029] Fig.16 It is a diagram showing the structure of a sensor device according to a third embodiment.

[0030] Fig.17 It is a diagram showing the angle θ2 in the orthogonal coordinate system.

[0031] Fig.18 This is a flowchart showing the processing flow of the sensor device according to the third embodiment.

[0032] Fig.19 It is a diagram showing the structure of a sensor device according to a fourth embodiment.

[0033] Fig. 20 This is a diagram showing the relationship between the acceleration and the rotation angle of the wheel when the centrifugal force is 6G.

[0034] Fig.21 This is a diagram showing the relationship between the acceleration and the wheel angle when the centrifugal force is 6 G in a state where the nut is loose.

[0035] Fig.22A This is a diagram showing the relationship between the average value of acceleration and the sensor angle when the centrifugal force is 6G.

[0036] Fig. 22B This is a diagram showing the relationship between the average value of acceleration and the sensor angle when the centrifugal force is 10G.

[0037] Fig.23 It is a diagram showing a second example of the waveforms of the X-axis normalized value, the Y-axis normalized value, and the centrifugal acceleration.

[0038] Fig.24 It is a graph showing the waveforms of the X-axis normalized value, the Y-axis normalized value, and the arctangent function.

[0039] Fig.25 This is a flowchart showing the processing of the sensor device according to the fourth embodiment.

[0040] Fig.26 It is a diagram showing the structure of a sensor device according to a fifth embodiment.

[0041] Fig. 27 It is a front view showing the structure of a tire of a vehicle according to a fifth embodiment.

[0042] Fig.28A FIG. 1 is a first diagram showing the relationship between the centrifugal acceleration and the acceleration detected by the acceleration sensor.

[0043] Fig.28B FIG. 2 is a second diagram showing the relationship between the centrifugal acceleration and the acceleration detected by the acceleration sensor.

[0044] Fig.29 This is a diagram showing an example of functional blocks configured in a signal processing unit according to the fifth embodiment.

[0045] Fig.30 This is a flowchart showing an example of processing executed by the signal processing unit of the fifth embodiment.

[0046] Fig.31 This is a flowchart showing the processing of the initial value setting program executed by the signal processing unit in the first modification of the fifth embodiment.

[0047] Fig.32 This is a flowchart showing an example of processing executed by the signal processing unit in the first modification of the fifth embodiment.

[0048] Fig.33 It is a side view showing a state in which a wheel according to Modification 3 is fastened to a hub.

[0049] Fig.34 It is a cross-sectional view of a fastening portion of a wheel according to Modification 4.

[0050] Fig.35 Yes means Fig.34 FIG. 1 is a diagram of a modified example of .

[0051] Fig.36 4 is a cross-sectional view of a fastening portion using a looseness detection device according to a comparative example.

[0052] Fig.37 It is a figure which shows the state which attached the nut cover to the wheel nut in a comparative example.

[0053] Fig.38 This is a diagram for explaining individual differences in the length of the screw shaft of a bolt.

[0054] Fig.39 This is a diagram showing the relationship between the average value of the difference between the X-axis acceleration and the Y-axis acceleration for each different centrifugal force and the sensor angle in Modification 5 of the first embodiment. DETAILED DESCRIPTION

[0055] Hereinafter, the embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In addition, the same reference numerals are given to the same or corresponding parts in the drawings, and their description will not be repeated.

[0056] [First embodiment]

[0057] Figure 1 The sensor device 100 according to the first embodiment (see Figure 2 ) is a diagram of a vehicle 200. The vehicle 200 includes a plurality of wheels 210. In addition, the vehicle 200 includes a communication terminal 201 (multi-information display) that can communicate with a communication unit 3 described later and includes a display unit not shown. In addition, the sensor device 100 is an example of a "detection device" of the present disclosure.

[0058] The wheel 210 includes a wheel 220 and a tire 230 mounted on the wheel 220. The wheel 220 is provided with a plurality of ( Figure 1 5) nuts 240 are fastened to the hub 250a (refer to Figure 2 ). In addition, the number of nuts 240 is not limited to the above example. In addition, the hub 250a is an example of the "fastened member" and the "vehicle body" of the present disclosure. In addition, the wheel 220 and the nut 240 are examples of the "rotating body" and the "fastening member" of the present disclosure, respectively.

[0059] like Figure 2 As shown, the nut 240 fastens the bolt 250 to the wheel 220. Specifically, the wheel 220 is provided with a plurality of (five) wheel holes 221 into which the bolt 250 is inserted (penetrated). The nut 240 fastens the bolt 250 inserted into the wheel hole 221 to the wheel 220. In addition, the bolt 250 is fixed to the wheel hub 250a.

[0060] Figure 2 In the example of a dual tire, the wheel 220 is composed of an inner wheel 222 and an outer wheel 223 .

[0061] One side of the nut 240 is open. In addition, a nut cover 241 is attached to the nut 240. The sensor device 100 may be indirectly provided on the nut 240 by being attached to the nut cover 241. Therefore, the sensor device 100 rotates in conjunction with the rotation of the nut 240 (nut cover 241).

[0062] Specifically, the nut cover 241 includes a top portion 241a and a side portion 241b. The side portion 241b is provided to surround the portion of the bolt 250 that passes through the wheel hole 221 in a circumferential shape. The top portion 241a is provided to face the end portion 251 of the bolt 250 (the insertion direction of the bolt 250). The top portion 241a and the side portion 241b are provided continuously. In addition, a washer 243 may be provided between the nut 240 and the wheel 220.

[0063] The sensor device 100 is attached (bonded) to the inner surface 241 c of the top portion 241 a of the nut cover 241 . Therefore, the sensor device 100 is disposed in the space S of the nut cover 241 that accommodates the bolt 250 .

[0064] The sensor device 100 is provided on a part of the nuts 240 of the plurality of nuts 240 provided on each wheel 210. Alternatively, the sensor device 100 may be provided on all of the nuts 240 of the plurality of nuts 240 provided on each wheel 210.

[0065] like Figure 3 As shown, the sensor device 100 includes an acceleration sensor 1, a signal processing unit 2, a communication unit 3, and a power supply unit 4. In addition, the acceleration sensor 1 is an example of the "acceleration detection unit" of the present disclosure. In addition, the signal processing unit 2 is an example of the "state detection unit" and "state detection device" of the present disclosure.

[0066] like Figure 5 As shown, the acceleration sensor 1 is located relative to the rotation axis O of the wheel 220 (along the same axis as the rotation axis O of the wheel 220). Figure 5 The acceleration of each of the X-axis and Y-axis perpendicular to each other in a plane perpendicular to the plane of the paper (the axis extending in a direction perpendicular to the paper plane; the rotation axis of the hub 250a) is detected. The acceleration detected by the acceleration sensor 1 has a positive or negative magnitude (direction). Figure 5 The arrows indicating the X-axis and Y-axis respectively indicate the positive directions of the X-axis and Y-axis respectively. Figure 5 In the paper shown, the Y axis is rotated 90 degrees counterclockwise relative to the X axis as the positive direction. In addition, the X axis and the Y axis are examples of the "first axis" and the "second axis" of the present disclosure, respectively.

[0067] also, Figure 5 The Z direction shown in the figure represents the vertical direction (up and down direction). Here, in the present embodiment, the nut 240 (nut 240A) is fixed in the initial state (the state where the nut 240A is not loose) so that the positive direction of the X axis of the acceleration sensor 1 faces upward (Z1 direction). Alternatively, in the initial state, the positive direction of the X axis of the acceleration sensor 1 faces a direction other than the Z1 direction. Figure 5 The nut 240 located closest to the Z1 side among the five nuts 240 is referred to as nut 240A. Figure 5 When in the state of, the angle (rotation angle) of the sensor device 100 is set to 0 degrees, and the direction of the sensor device 100 rotating in the clockwise direction is set to positive.

[0068] like Figure 6 As shown, the centrifugal acceleration applied to the nut 240A is divided into the X-axis acceleration and the Y-axis acceleration. In other words, the vector sum of the X-axis acceleration and the Y-axis acceleration becomes the centrifugal acceleration.

[0069] The signal processing unit 2 detects the state (tightening state) of the nut 240 based on the detection signal of the acceleration sensor 1. The signal processing unit 2 includes a centrifugal acceleration calculation unit 2a (see Figure 4 )、Rotation angle calculation unit 2b (refer to Figure 4 )、Tightening state detection unit 2c (refer to Figure 4 )、Acquisition unit 2d (refer to Figure 4 ).in addition, Figure 4 The centrifugal acceleration calculation unit 2a, the rotation angle calculation unit 2b, and the tightening state detection unit 2c shown in the figure respectively represent software that modularizes the functional features of the signal processing unit 2. The acquisition unit 2d may also be a terminal for receiving a signal including information on the detection value detected by the acceleration sensor 1. The details of each function will be described later.

[0070] Furthermore, the signal processing unit 2 acquires speed information of the vehicle 200 (rotation speed of the wheel 220 ) from a processing device (not shown) provided in the vehicle 200 .

[0071] The communication unit 3 transmits the processing result of the signal processing unit 2 or information obtained based on the processing result to the communication terminal 201 of the vehicle 200 (see Figure 1 ).

[0072] The power supply unit 4 supplies power to the acceleration sensor 1, the signal processing unit 2, and the communication unit 3, respectively. The acceleration sensor 1 detects acceleration such as the X-axis acceleration and the Y-axis acceleration every 100 to 200 ms (for example, 150 ms). The power supply unit 4 is, for example, a lithium-ion battery, and its storage capacity is limited. In order to reduce the power consumption of the signal processing unit 2, the acceleration detection performed by the acceleration sensor 1 is not always performed, but is repeated every predetermined period.

[0073] The acceleration sensor 1 detects X-axis acceleration (Xg) as X-axis acceleration (vector) and Y-axis acceleration (Yg) as Y-axis acceleration (vector). The X-axis acceleration and the Y-axis acceleration are each expressed by a G value (a value in which the gravitational acceleration is expressed as 1G).

[0074] Figure 7 It is a coordinate diagram showing the relationship between the angle of the tire 230 (wheel 220) and the X-axis acceleration and the Y-axis acceleration when the vehicle speed of the vehicle 200 is 0 (the centrifugal force acting on the nut 240 is 0). In this case, the X-axis acceleration and the Y-axis acceleration each change in a sine wave shape within the range of ±1G. This is because the X-axis and the Y-axis each contain only the acceleration component obtained based on the gravitational acceleration applied to the Z2 direction. In addition, Figure 7 It means setting Figure 5 The results of the sensor device 100 for the nut 240A are shown in FIG. Figure 7 , Figure 8 The horizontal axis, that is, the rotation angle of the tire is Figure 5 The direction of rotation of the tire 230 is shown as positive in a clockwise direction.

[0075] Figure 8 The coordinate diagram shows the relationship between the rotation angle of the tire 230 (wheel 220) and the X-axis acceleration and the Y-axis acceleration when the centrifugal force with a centrifugal acceleration of 3G acts on the nut 240 at a predetermined vehicle speed. In addition, in the present disclosure, the magnitude of the centrifugal force is sometimes expressed by the G value. On the one hand, Figure 5 In the direction of the Y axis shown, there is no centrifugal force applied to the Y axis, so the Y axis acceleration is relative to Figure 7 On the other hand, the centrifugal force is applied to the X-axis, so the X-axis acceleration becomes Figure 7 The value is obtained by adding 3G to the X-axis acceleration. In addition, the difference between the X-axis acceleration and the Y-axis acceleration (see Figure 7 The waveform of the single-dot dash line is a sine wave with a fluctuation of ±1.41G around 3G. Figure 8 It means setting Figure 5 A graph of the results of the sensor device 100 for the nut 240A is shown.

[0076] Fig.9A : is a graph showing the average value of acceleration with respect to the angle (rotation angle) of the sensor device 100 when the centrifugal force is 3G. Fig. 9B : is a graph showing the average value of acceleration relative to the angle (rotation angle) of the sensor device 100 when the centrifugal force is 10G. For example, Fig.9A The value of each waveform at the point where the sensor angle is 0 represents Figure 8 The average value of each waveform shown. Fig.9A and Fig. 9B The respective average values ​​become the amount of one cycle of one rotation of the tire 230. In reality, as mentioned above, in order to reduce the power consumption of the signal processing unit 2, it is desirable to repeat the sensing detection at each predetermined period. When the vehicle speed is constant, it is highly likely that the average value of the results of multiple (for example, 50 times or more) repetitions is close to the average value of one cycle of one rotation of the tire 230.

[0077] like Fig.9A and Fig. 9B As shown in FIG. 1 , the waveforms of the average values ​​of the X-axis acceleration, the Y-axis acceleration, and the difference between the X-axis acceleration and the Y-axis acceleration have amplitudes corresponding to the centrifugal force (different on the scales on the vertical axis), but have the same shape. Therefore, it is possible to obtain information on the rotation angle of the nut 240 (sensor device 100) based on at least two of the X-axis acceleration, the Y-axis acceleration, and the difference between the X-axis acceleration and the Y-axis acceleration at any time. A specific example is shown below.

[0078] For example, the X-axis acceleration (the average X-axis acceleration described later), the Y-axis acceleration (the average Y-axis acceleration described later), and the difference between the X-axis acceleration and the Y-axis acceleration (the average X-axis acceleration and the average Y-axis acceleration described later) are 0G, 3G, and -3G, respectively. In addition, based on the acquired vehicle speed information, the signal processing unit 2 detects that the centrifugal force (centrifugal acceleration) applied to the sensor device 100 is 3G. In this case, the signal processing unit 2 detects that the centrifugal force (centrifugal acceleration) applied to the sensor device 100 is 3G. Fig.9A The coordinate diagram of the sensor device 100 detects that the angle (rotation angle) is close to 90 degrees. In addition, the fact that it is recorded as close to 90 degrees is because Fig.9A Each waveform represents the average value of each acceleration. Specifically, each X-axis acceleration and Y-axis acceleration may vary within the range of ±1G relative to the average value. In addition, the difference between the X-axis acceleration and the Y-axis acceleration may vary within the range of ±1.41G relative to the average value.

[0079] In other words, if the information of the rotation angle of the nut 240 (sensor device 100 ) is acquired based on at least two of the X-axis acceleration, the Y-axis acceleration, and the difference between the X-axis acceleration and the Y-axis acceleration at any time, the fluctuation range is included.

[0080] As mentioned above, in order to reduce the power consumption of the signal processing unit 2, it is desirable to repeat the sensing detection at each predetermined period. By appropriately setting the repetition interval, the above-mentioned variation (specifically, the X-axis acceleration and the Y-axis acceleration are ±1G respectively, and the difference between the X-axis acceleration and the Y-axis acceleration is ±1.41G) can be ignored or greatly reduced. As a result, the angle (rotation angle) of the sensor device 100 can be accurately identified.

[0081] Therefore, the signal processing unit 2 acquires the information of the X-axis acceleration and the Y-axis acceleration at each sensing detection cycle (e.g., 150 ms as described above) corresponding to one rotation of the wheel 220. In addition, the above cycle is a cycle in which the information of the acceleration detected by the acceleration sensor 1 is acquired twice during one rotation of the wheel 220 (one rotation in 300 ms in this case). In other words, the acceleration information is acquired every time the wheel 220 rotates half a circle.

[0082] In the above example, the X-axis acceleration, the Y-axis acceleration, and the difference between the X-axis acceleration and the Y-axis acceleration are 0G, 3G, and -3G, respectively. Although if the acceleration information is acquired at any time, it can be 0±1G, 3±1G, and -3±1.41G, respectively, if the acceleration information is acquired every time the wheel 220 rotates half a circle, the variation becomes zero. For example, if Figure 8 If the acceleration information is obtained at 90 degrees and 270 degrees respectively, the variation becomes zero (the variation can be ignored). In addition, 90 degrees and 270 degrees are one of the conditions every time the wheel 220 rotates half a circle. As long as the angle difference between the two points is 180 degrees, it is sufficient. In other words, it is also possible to obtain the acceleration of the two points of 45 degrees and 225 degrees, and the acceleration of the two points of 60 degrees and 240 degrees.

[0083] Figure 8 An example is Fig.9A The sensor angle is 0 degrees (the orientation of the sensor device 100 is Figure 5 Therefore, refer to Figure 8 , the case where the sensor angle is 0 degrees is used as an example to explain again. Figure 8 , it can be seen that the X-axis acceleration, Y-axis acceleration and the difference between the X-axis acceleration and the Y-axis acceleration can be 3±1G, 0±1G and 3±1.41G respectively.

[0084] If you want to Figure 8If we take the acceleration information at the 90-degree point, the X-axis acceleration, Y-axis acceleration, and the difference between the X-axis acceleration and the Y-axis acceleration are 3G, -1G, and 4G, respectively. At the 270-degree point, the X-axis acceleration, Y-axis acceleration, and the difference are 3G, 1G, and 2G, respectively. If we take the average of the results of the above two points, the X-axis acceleration, Y-axis acceleration, and the difference are 3G, 0G, and 3G, respectively. This value is consistent with Fig.9A The sensor angle is 0 degrees. In other words, Figure 8 The average value of the amount of one cycle of is equal to the average value of the amount of acceleration detected by the acceleration sensor 1 twice every time the wheel 220 rotates half a circle.

[0085] The interval every time the wheel 220 rotates half a circle is an appropriate interval set to reduce the power consumption of the signal processing unit 2. Specifically, the above interval is based on the minimum detection time point of the acceleration sensor 1 for solving the sensor angle. If this detection time point is used, the sensor angle (rotation angle of the nut 240) can be accurately solved.

[0086] Alternatively, it can be, Fig.9A and Fig. 9B The waveform data shown is stored in a storage device (not shown) for each different centrifugal force (for each vehicle speed).

[0087] In the above example, the signal processing unit 2 detects that the centrifugal force (centrifugal acceleration) applied to the sensor device 100 is 3G based on the acquired vehicle speed information, and generates a coordinate map corresponding to the centrifugal force of 3G (see Fig.9A ) is used to determine the angle (rotation angle) of the sensor device 100. However, without vehicle speed information, it is impossible to determine the angle based on the above-mentioned coordinate graph.

[0088] For example, only the acceleration sensor of the X axis is used as an example. On the one hand, when a 3G centrifugal force (centrifugal acceleration) is generated, according to Fig.9A , the sensor angle is estimated to be 0 degrees. On the other hand, if a centrifugal force (centrifugal acceleration) of 10G is generated, based on Fig.9A If the sensor angle is estimated to be around 70 degrees or around 290 degrees, the sensor angle is estimated to be around 70 degrees or around 290 degrees. In other words, if the centrifugal force (centrifugal acceleration, which is synonymous with the vehicle speed in this case) that can be generated is not determined, the calculated angle will be different, and it will be impossible to determine whether the nut is loose. In the case where the vehicle speed is not obtained, by using the ratio of the acceleration information (including the calculation results such as the difference) of multiple axes described below, the sensor angle can be calculated even without the vehicle speed information.

[0089] If you will Fig.9A and Fig. 9BBy comparison, although the scales of the vertical axis are different, the waveforms have the same shape. If the installation method of the sensor device 100 does not change (in other words, if there is no looseness), even if the centrifugal force generated on the sensor is different due to different vehicle speeds, Fig.9A and Fig. 9B The relationship between the average value of acceleration and the sensor angle is similar.

[0090] Reference Fig.9A and Fig. 9B The following will be described in detail. Fig.9A When the sensor angle is 20 degrees (near the intersection of the dotted line and the single-point chain line among the three lines), the X-axis acceleration, Y-axis acceleration, and the difference between the X-axis acceleration and the Y-axis acceleration are 2.6G, 1.3G, and 1.3G, respectively. Fig. 9B When the sensor angle is around 20 degrees, the X-axis acceleration, Y-axis acceleration, and the difference between the X-axis acceleration and the Y-axis acceleration are 8.6G, 4.3G, and 4.3G, respectively. Fig. 9B The values ​​in become Fig.9A The value in is approximately 3.3 times the value in , and the ratio is known to be a similar value of 2:1:1. Even if the centrifugal force (i.e., vehicle speed) generated is different, the ratio of acceleration obtained by the sensor is the same. If this ratio is used, the sensor angle (rotation angle of nut 240) can be calculated even without vehicle speed information.

[0091] Furthermore, the signal processing unit 2 (tightening state detection unit 2c) detects the tightening state of the nut 240 based on the difference between the rotation angle of the nut 240 calculated this time and the rotation angle of the nut 240 until the last time. On the other hand, if the difference is outside the predetermined allowable range, the signal processing unit 2 (tightening state detection unit 2c) determines that the nut 240 is loose. In this case, the signal processing unit 2 sends a signal to the communication unit 3 (see Figure 3 ) to the communication terminal 201 (refer to Figure 1 ) notifies that the nut 240 has loosened. Thus, a warning may be displayed on a display unit (not shown) of the communication terminal 201, or the communication terminal 201 may generate a warning sound. On the other hand, if the above-mentioned difference is within a predetermined allowable range, the signal processing unit 2 (tightening state detection unit 2c) determines that the nut 240 is fixed. In this case, the signal processing unit 2 does not notify the communication terminal 201. In addition, the above-mentioned rotation angle up to the last time may also be the last rotation angle, or may be the average value of the rotation angles of several past times including the last time.

[0092] In addition, the signal processing unit 2 (fastening state detection unit 2c) determines that the rotation of the wheel 220 (tire 230) has stopped when the current detection value and the detection value until the last time, whichever of the calculated average X-axis acceleration and average Y-axis acceleration has a larger absolute value, are within the range of ±1G. In addition, the detection value until the last time may be the last detection value, or may be the average value of those detection values ​​in the past several times including the last time. In addition, it is also possible to determine that the rotation of the wheel 220 (tire 230) has stopped based on either the X-axis acceleration or the Y-axis acceleration. In addition, it is also possible to determine that the rotation of the wheel 220 (tire 230) has stopped when the current detection value and the detection value until the last time of both the X-axis acceleration and the Y-axis acceleration are within the range of ±1G.

[0093] The nut 240 is often loosened when vibration or external force is applied to the wheel 220 or the nut 240, and it is assumed that the hub 250a (wheel 220) is rotating while the vehicle 200 is running. When the vehicle 200 stops and the rotation of the hub 250a (wheel 220) stops, the nut 240 rarely becomes loose. Therefore, when the signal processing unit 2 determines that the rotation of the wheel 220 (tire 230) stops, it performs processing such as lengthening the cycle (the above-mentioned predetermined time) of the sensing detection by the sensor device 100 (for example, to a 30-minute cycle).

[0094] In addition, the signal processing unit 2 acquires information on the initial value of the rotation angle of the nut 240. The signal processing unit 2 acquires information on the initial value of the rotation angle of the nut 240 based on, for example, a predetermined button 201a (see Figure 1 ) is pressed to obtain the above-mentioned initial value. Specifically, the signal processing unit 2 sets the rotation angle of the nut 240 when the vehicle 200 starts to travel (or after a predetermined time from the start of travel) after the above-mentioned button is pressed as the initial value. In addition, the button 201a is preferably pressed, for example, when the tire 230 (wheel 220) is installed on the wheel hub 250a and the nut 240 is tightened with a predetermined tightening torque. In addition, it is also possible that a button having the function of the above-mentioned button 201a is provided in the sensor device 100. In addition, it is also possible that the communication unit 3 of the sensor device 100 is capable of bidirectional communication between itself and the ECU of the vehicle 200. It is also possible that, in this case, the information of the above-mentioned initial value is stored in the signal processing unit 2.

[0095] Furthermore, the signal processing unit 2 (tightening state detection unit 2c) detects the tightening state of the nut 240 based on the difference between the current rotation angle of the nut 240 and the initial value. Specifically, when the difference is outside the predetermined allowable range, the signal processing unit 2 (tightening state detection unit 2c) determines that the nut 240 is loose (not fixed). In this case, the signal processing unit 2 communicates with the communication unit 3 (refer to Figure 3 ) to the communication terminal 201 (refer to Figure 1 ) notifies that the nut 240 has been loosened. Thus, a warning may be displayed on a display unit (not shown) of the communication terminal 201, or the communication terminal 201 may generate a warning sound.

[0096] In addition, the signal processing unit 2 may not obtain the above-mentioned initial value based on the pressing of the above-mentioned predetermined button 201a. For example, it is assumed that the signal processing unit 2 detects that the rotation angle of the nut 240 (of at least one wheel 210) has changed before and after parking when the signal processing unit 2 detects that the vehicle 200 has stopped by the above-mentioned method. In this case, the signal processing unit 2 sets the rotation angle of the nut 240 after the change (or the average value of the rotation angle detected in multiple sensing detections after the change) as the initial value. This is because the change in the rotation angle before and after parking means that the tire 230 needs to be replaced or the nut 240 needs to be retightened.

[0097] Furthermore, when the signal processing unit 2 (tightening state detection unit 2c) acquires the information A indicating that the nut 240 has rotated in the tightening direction, it ignores (excludes) the information A and detects the tightening state of the nut 240. Specifically, the information A includes information indicating that the nut 240 has rotated in the tightening direction by a predetermined angle or more (for example, 30 degrees or more).

[0098] Specifically, when the information indicating that the nut 240 has rotated in the tightening direction by more than a predetermined angle is obtained as described above, and the information A is obtained in a state where the nut 240 has not been loosened for a constant time or more (for example, more than 10 minutes), the signal processing unit 2 (tightening state detection unit 2c) ignores the information A and detects the tightening state of the nut 240. In addition, the fact that the nut 240 has not been loose means that the difference between the calculated rotation angle and the previous rotation angle (or the initial value of the rotation angle) is within the predetermined allowable range.

[0099] More specifically, in the state where the nut 240 has not loosened for a constant time or more as described above, the signal processing unit 2 (tightening state detection unit 2c) detects the tightening state of the nut 240 by ignoring the above information A when it obtains information B indicating that the nut 240 has rotated in the loosening direction by a rotation angle equal to the rotation angle in the tightening direction immediately after obtaining information indicating that the nut 240 has rotated in the tightening direction by a predetermined angle or more. Here, the angle equal to the rotation angle in the tightening direction may also be a range of ±X degrees (e.g., 5 degrees) in the tightening direction with the rotation angle as the center. Therefore, when the signal processing unit 2 (tightening state detection unit 2c) obtains information indicating that the nut 240 has rotated in the loosening direction by a rotation angle different from the rotation angle in the tightening direction (outside the above range), it detects the tightening state of the nut 240 without ignoring the above information A (under the premise of considering the above information A). Thus, changes in the detection value caused by acceleration and vibration of the vehicle 200 can be ignored.

[0100] (Control flow of sensor device)

[0101] Next, refer to Fig.10 The control flow of the sensor device 100 will be described. First, in step S1, the acceleration sensor 1 detects the X-axis acceleration and the Y-axis acceleration at every predetermined period (for example, every 150 ms).

[0102] Next, in step S2, the signal processing unit 2 obtains information on the X-axis acceleration and the Y-axis acceleration from the acceleration sensor 1. Specifically, the signal processing unit 2 obtains information on the X-axis acceleration and the Y-axis acceleration at each predetermined cycle of step S1.

[0103] In step S3 , the signal processing unit 2 calculates average values ​​of each of the X-axis acceleration and the Y-axis acceleration acquired at each predetermined period in step S2 (average X-axis acceleration and average Y-axis acceleration) every two times.

[0104] In step S4, the signal processing unit 2 (centrifugal acceleration calculation unit 2a) calculates the centrifugal acceleration (centrifugal force) of the wheel 220 based on the rotation speed (speed of the vehicle 200) of the wheel 220. In addition, the processing of step S4 may be performed before the processing of step S2 (S3) or simultaneously with the processing of step S2 (S3).

[0105] In step S5 , the signal processing unit 2 (rotation angle calculation unit 2 b ) calculates the sensor angle of the sensor device 100 (nut 240 ) based on the average X-axis acceleration and average Y-axis acceleration calculated in step S3 and the centrifugal acceleration (centrifugal force) of the wheel 220 .

[0106] In step S6, the signal processing unit 2 determines whether the data acquired in step S5 should be excluded (ignored) based on the angle (rotation angle) of the sensor device 100 acquired in step S5. If it is determined that the data should be excluded (ignored) (if it is YES in S6), the process returns to step S1. If it is determined that the data should not be excluded (ignored) (if it is NO in S6), the process proceeds to step S7.

[0107] In addition, in step S6, as described above, after information indicating that the nut 240 has rotated in the tightening direction by an angle greater than a predetermined angle has just been obtained in a state where the nut 240 has not loosened for a period of time greater than a constant time, if information B indicating that the nut 240 has rotated in the loosening direction by an angle equal to the rotation angle in the tightening direction is obtained, it is determined that the above data should be excluded (ignored).

[0108] In step S7, the signal processing unit 2 (tightening state detection unit 2c) detects the tightening state of the nut 240 based on the angle (rotation angle) of the sensor device 100 (nut 240) calculated in step S5. When it is detected that the nut 240 is loose (in S7: Yes), the process proceeds to step S8. In addition, when it is detected that the nut 240 is not loose (in S7: No), the process returns to step S1. In addition, in step S7, the signal processing unit 2 (tightening state detection unit 2c) determines whether the nut 240 is loose based on the detection value of the angle of the sensor device 100 up to the last time or based on the change (difference) from the initial value as described above.

[0109] In step S8 , the signal processing unit 2 notifies the communication terminal 201 through the communication unit 3 that the nut 240 is loose.

[0110] As described above, in the present embodiment, the rotation angle of the nut 240 is detected based on the X-axis acceleration and the Y-axis acceleration and the rotation speed of the wheel 220 (the speed of the vehicle 200). Thus, even when the X-axis acceleration and the Y-axis acceleration vary due to the rotation speed of the wheel 220, the rotation angle of the nut 240 can be easily detected based on the magnitude of the centrifugal force that can be calculated from the rotation speed of the wheel 220.

[0111] [Second embodiment]

[0112] In the second embodiment, the tightening state of the nut 240 is detected based on the ratio of the X-axis acceleration to the Y-axis acceleration. The same reference numerals are used for the same structures as those in the first embodiment, and the description thereof will not be repeated.

[0113] Fig.112 is a diagram showing a configuration of a sensor device 300 according to the second embodiment. The sensor device 300 is an example of a “detection device” in the present disclosure.

[0114] The sensor device 300 includes an acceleration sensor 1, a signal processing unit 12, a communication unit 3, and a power supply unit 4. The signal processing unit 12 is an example of a “state detection unit” and a “state detection device” in the present disclosure.

[0115] The signal processing unit 12 detects the nut 240 based on the detection signal of the acceleration sensor 1 (see Fig.12 ) state (tightening state). The signal processing unit 12 includes a ratio calculation unit 12a, a tightening state detection unit 12b, and an acquisition unit 2d. In addition, the ratio calculation unit 12a and the tightening state detection unit 12b are each a part of software that modularizes the features of the functions of the signal processing unit 12. The details of each function will be described later.

[0116] Further, similarly to the signal processing unit 2 of the first embodiment, the signal processing unit 12 calculates the average values ​​of the X-axis acceleration and the Y-axis acceleration detected twice during one rotation of the wheel 220 (average X-axis acceleration and average Y-axis acceleration).

[0117] The signal processing unit 12 (ratio calculation unit 12a) calculates the ratio of the calculated average X-axis acceleration (hereinafter, sometimes only recorded as X-axis acceleration) to the average Y-axis acceleration (hereinafter, sometimes only recorded as Y-axis acceleration). That is, the signal processing unit 12 (ratio calculation unit 12a) calculates the above ratio each time it obtains the values ​​of the X-axis acceleration and the Y-axis acceleration twice from the acceleration sensor 1. Specifically, the signal processing unit 12 (ratio calculation unit 12a) calculates the value (|X| / |Y|) obtained by dividing the absolute value of the X-axis acceleration (average X-axis acceleration) by the absolute value of the Y-axis acceleration (average Y-axis acceleration). In addition, the above ratio is an example of an "acceleration index" disclosed in the present invention.

[0118] Alternatively, the ratio may be a value obtained by dividing the absolute value of the Y-axis acceleration by the absolute value of the X-axis acceleration (|Y| / |X|). Alternatively, the ratio may be a value obtained by dividing the X-axis acceleration (Y-axis acceleration) by the root mean square of the X-axis acceleration and the Y-axis acceleration.

[0119] Here, in the second embodiment, the signal processing unit 12 (tightening state detection unit 12b) detects the tightening state of the nut 240A based on the calculated ratio. Specifically, the signal processing unit 12 (tightening state detection unit 12b) detects the tightening state of the nut 240A based on the difference between the current ratio and the previous ratio. The following is a detailed description.

[0120] For example, assume that the (average) X-axis acceleration and (average) Y-axis acceleration calculated last time are respectively -4 G and 10 G. At this time, the signal processing unit 12 (ratio calculation unit 12a) calculates the ratio as approximately 0.4 (hereinafter abbreviated as 0.4).

[0121] Next, by changing the rotation angle of the nut 240A, the (average) X-axis acceleration and (average) Y-axis acceleration calculated this time become -4 G and 7 G, respectively. In this case, the signal processing unit 12 (ratio calculation unit 12a) calculates the above ratio to be approximately 0.57 (hereinafter abbreviated as 0.57).

[0122] The signal processing unit 12 (tightening state detection unit 12b) determines that the tightening state of the nut 240A has changed when the change amount (absolute value) of the above ratio is greater than a predetermined threshold value. If the above predetermined threshold value is set to 0.1, for example, when the above ratio changes from 0.4 to 0.57, it is determined that the tightening state of the nut 240A has changed.

[0123] As another example, from the state where the X-axis acceleration and the Y-axis acceleration are -4G and 10G, respectively, the centrifugal acceleration increases but the rotation angle of the nut 240A does not change, and thus the X-axis acceleration and the Y-axis acceleration change to the state where they are -8G and 20G, respectively. In this case, before and after the change in the centrifugal acceleration, the above ratio is 0.4 and is equal to each other. Therefore, the change in the above ratio is less than the above predetermined threshold value, and therefore, the signal processing unit 12 (tightening state detection unit 12b) determines that the tightening state of the nut 240A has not changed.

[0124] In addition, on the one hand, when the X-axis acceleration and the Y-axis acceleration are changed from the state of 1G and 11G, for example, to the state of 1G and 1000G, respectively, the change amount of the above ratio (|X| / |Y|) is less than 0.1. On the other hand, when the X-axis acceleration and the Y-axis acceleration are changed from the state of 11G and 1G, for example, to the state of 1000G and 1G, respectively, the change amount of the above ratio becomes greater than 0.1. In this way, even when the change amount of the rotation angle of the nut 240A in the above two modes is approximately equal, there is a case where a difference occurs in the determination result of the tightening state of the nut 240A.

[0125] Therefore, the signal processing unit 12 (fastening state detection unit 12b) may change the size of the predetermined threshold value based on the size of the ratio. For example, when the ratio before the rotation angle of the nut 240A changes is less than 0.1, the predetermined threshold value may be 1 / 2 of the ratio before the change, or the predetermined threshold value may be a predetermined fixed value less than 0.1 (for example, 0.05). In addition, the above example of changing the predetermined threshold value is only an example and is not limited to the above example.

[0126] Furthermore, when the Y-axis acceleration is 0, the signal processing unit 12 (ratio calculation unit 12a) replaces the Y-axis acceleration with a value close to 0 (e.g., 0.01) and calculates the above ratio. Furthermore, when the signal processing unit 12 (ratio calculation unit 12a) calculates the ratio by dividing the Y-axis acceleration by the X-axis acceleration, if the X-axis acceleration is 0, the signal processing unit 12 (ratio calculation unit 12a) replaces the X-axis acceleration with a value close to 0 to calculate the ratio. Furthermore, when the signal processing unit 12 (ratio calculation unit 12a) calculates the ratio by dividing the X-axis acceleration or the Y-axis acceleration by the root mean square of the X-axis acceleration and the Y-axis acceleration, the root mean square does not become 0, and therefore the above approximation processing is not required.

[0127] In the above, an example is shown in which processing is performed based on the difference between the previous ratio and the current ratio, but processing may be performed based on the difference between the average value of the ratios of several past times including the previous time and the current ratio.

[0128] Fig.13 This is a graph showing the time changes of the X-axis normalized value (the value obtained by dividing the X-axis acceleration by the above-mentioned root mean square, solid line), the Y-axis normalized value (the value obtained by dividing the Y-axis acceleration by the above-mentioned root mean square, dotted line), and the centrifugal acceleration (dash-dotted line). The X-axis normalized value and the Y-axis normalized value correspond to the vertical axis on the left, respectively. The centrifugal acceleration corresponds to the vertical axis on the right.

[0129] like Fig.13 As shown, until the centrifugal acceleration reaches about 5G (until around time t1 seconds), the changes in the X-axis normalized value and the Y-axis normalized value are relatively large, and after time t1, the X-axis normalized value and the Y-axis normalized value are relatively stable. Therefore, if the centrifugal acceleration is small, the changes in the X-axis normalized value (X-axis acceleration) and the Y-axis normalized value (Y-axis acceleration) are large. Therefore, as described above, when detecting the tightening state of the nut 240, it is more effective to detect based on the average values ​​of the X-axis acceleration and the Y-axis acceleration.

[0130] In addition, the signal processing unit 12 detects the tightening state of the nut 240 by ignoring the X-axis acceleration and the Y-axis acceleration obtained when the centrifugal acceleration of the wheel 220 changes suddenly (for example, near time t2). Here, the sudden change of centrifugal acceleration is often caused by emergency braking of the vehicle 200. Therefore, the change of centrifugal acceleration caused by reasons other than the loosening of the nut 240 can be ignored. In addition, the sudden change of centrifugal acceleration means that the absolute value of the rate of change of centrifugal acceleration is greater than a predetermined value (for example, 2G / sec).

[0131] (Processing flow of sensor device)

[0132] Next, refer to Fig.14 The processing flow of the sensor device 300 is described. Steps S11 to S13 are respectively the same as steps S1 to S3 of the first embodiment (see Fig.10 ) are the same, therefore, no repeated description is given.

[0133] In step S14 , the signal processing unit 12 (ratio calculation unit 12 a ) calculates the ratio (|X| / |Y|) of the X-axis acceleration (average X-axis acceleration) and the Y-axis acceleration (average Y-axis acceleration).

[0134] In step S15, the signal processing unit 12 (tightening state detection unit 12b) detects a change in the tightening state of the nut 240 based on the ratio calculated in step S14. When it is detected that the tightening state of the nut 240 has changed (in S15: Yes), the process proceeds to step S16. In addition, when it is detected that the tightening state of the nut 240 has not changed (in S15: No), the process returns to step S11. In addition, similar to the above-mentioned first embodiment, in step S15, the signal processing unit 12 (tightening state detection unit 12b) detects a change in the tightening state of the nut 240 based on the above-mentioned ratio up to the last time or the change (difference) relative to the above-mentioned initial value.

[0135] Then, in step S16 , the signal processing unit 12 notifies the communication terminal 201 through the communication unit 3 that the nut 240 is loose.

[0136] As described above, in the second embodiment, the tightening state of the nut 240 is detected based on the ratio of the X-axis acceleration to the Y-axis acceleration. This makes it possible to detect the tightening state of the nut 240 without considering the change in vehicle speed (centrifugal force).

[0137] In addition, other structures are the same as those of the first embodiment, and therefore, the description thereof will not be repeated.

[0138] [Third Embodiment]

[0139] Next, the third embodiment will be described. In the third embodiment, unlike the second embodiment described above, in which the tightening state of the nut 240 is detected based on the difference in the ratio between the X-axis acceleration and the Y-axis acceleration, the tightening state of the nut 240 is detected based on the difference in the inverse trigonometric function values ​​calculated based on the ratio. In the third embodiment, the same reference numerals as those of the first and second embodiments are given to the same structures as those of the first and second embodiments described above, and repeated descriptions are not given.

[0140] Reference Fig.15 , the meaning of detecting the tightening state of the nut 240 based on the value of the inverse trigonometric function calculated based on the ratio of the X-axis acceleration and the Y-axis acceleration is described. Fig.15 As shown, the case where acceleration information is acquired when the sensor device 100 is located at the 3 o'clock position and the 9 o'clock position is described. Furthermore, the case where the direction of the centrifugal acceleration is located at the center of the X-axis direction and the Y-axis direction is described.

[0141] The X-axis acceleration and the Y-axis acceleration are respectively obtained based on the centrifugal acceleration and the gravitational acceleration, so when the centrifugal acceleration is sufficiently larger than the gravitational acceleration, the influence of the gravitational acceleration is small. On the one hand, here, assuming that the centrifugal acceleration is 1G, under the assumption that there is no influence of the gravitational acceleration, the X-axis acceleration and the Y-axis acceleration are each 0.707G. In this case, the angle θ1 formed by the direction of the centrifugal acceleration with the X-axis as the reference and the X-axis becomes 45 degrees. The inverse trigonometric function used is arbitrary (the details of the inverse trigonometric function will be described later), but for easy understanding of the description, the value of the inverse trigonometric function calculated based on the ratio of the X-axis acceleration and the Y-axis acceleration is set to θ1.

[0142] On the other hand, in reality, when the centrifugal acceleration is 1G (i.e., equal to the gravitational acceleration), gravity affects the acceleration detection. When the centrifugal acceleration is 1G, the magnitude of the X-axis acceleration and the Y-axis acceleration deviate from the above value (0.707G) due to the gravitational acceleration component.

[0143] Specifically, on the one hand, the acceleration sensor 1 of the sensor device 100 at the 3 o'clock position detects an X-axis acceleration of 1.414 G and a Y-axis acceleration of 0 G, respectively. As a result, the angle θ1 is 0 degrees, which is 45 degrees different from the angle θ1 (45 degrees) when gravity is ignored, resulting in an angle error.

[0144] On the other hand, the acceleration sensor 1 of the sensor device 100 at the 9 o'clock position detects X-axis acceleration and Y-axis acceleration of 0 G and 1.414 G, respectively. As a result, the angle θ1 is -90 degrees, which is 45 degrees different from the angle θ1 (-45 degrees) when gravity is ignored, resulting in an angle error.

[0145] In this embodiment, the tightening state of the nut 240 is detected based on the difference of the inverse trigonometric function value calculated based on the ratio. As described above, when the angle between the direction of the centrifugal acceleration with respect to the X-axis and the X-axis is the value (θ1) of the inverse trigonometric function calculated based on the ratio of the X-axis acceleration to the Y-axis acceleration, the difference (angle difference) helps to detect the tightening state of the nut 240.

[0146] As described above, at the 3 o'clock position, there is a 45 degree difference from the angle θ1 (45 degrees) when gravity is ignored, and at the 9 o'clock position, there is a 45 degree difference from the angle θ1 (-45 degrees) when gravity is ignored. However, by taking the average of the above two angles, the influence of gravity is offset.

[0147] In the above example, the gravity effect is canceled by taking the average of the angles θ1 calculated at the 3 o'clock position and the 9 o'clock position. As in the first embodiment described above, the same effect can be obtained by taking the average of the detection values ​​of the acceleration sensor 1 at the 3 o'clock position and the 9 o'clock position. This will be described in more detail below.

[0148] Here, the average value of the X-axis acceleration (average X-axis acceleration) and the average value of the Y-axis acceleration (average Y-axis acceleration) calculated at the above-mentioned 3 o'clock position and 9 o'clock position respectively in consideration of the influence of gravity are 0.707G and 0.707G, respectively. That is, the average X-axis acceleration and the average Y-axis acceleration are respectively equal to the acceleration in the absence of the influence of gravity. That is, the detection deviation at each position caused by the gravitational acceleration is offset. As a result, even when the difference between the centrifugal acceleration and the gravitational acceleration is not large, the rotation angle (tightening state) of the nut 240 can be accurately detected by obtaining the average value of the two accelerations as described above. In addition, the average value of the rotation angle of the nut 240 corresponding to the 3 o'clock position and the average value of the rotation angle of the nut 240 corresponding to the 9 o'clock position may be calculated.

[0149] There is sometimes a difference between a method of calculating the angle by using an inverse trigonometric function from the values ​​of the acceleration sensors at two points that are point-symmetrical with respect to the center (rotation axis O), such as the 3 o'clock position and the 9 o'clock position, and then taking the average value, and a method of calculating the angle by using an inverse trigonometric function from the average value of the acceleration sensors at the two points. On the one hand, if the centrifugal force (in other words, the vehicle speed) generated when the values ​​of the acceleration sensors at the two points are obtained is the same, the results based on the above two methods are equal. On the other hand, if the centrifugal force (vehicle speed) generated when the values ​​of the acceleration sensors at the two points are different, the method of calculating the angle by using an inverse trigonometric function from the accelerations of the two points and then taking the average value can further reduce the influence of gravity. On the one hand, in the first embodiment, if the vehicle speed is different at two points every half a circle of the tire 230, the centrifugal force generated is different at the above two points. Therefore, in the method based on Fig.9A and Fig. 9B Problems arise when calculating angles. In particular, when the vehicle speed difference is large, the angle calculation itself cannot be performed. On the other hand, the method of calculating the angle and then taking the average value as in the present embodiment does not cause the above-mentioned disadvantages.

[0150] The signal processing unit 2 detects the tightening state of the nut 240 when the centrifugal acceleration of the wheel 220 is greater than a predetermined value (e.g., 1G). The acceleration sensor 1 detects the X-axis acceleration and the Y-axis acceleration in each cycle obtained based on the rotation speed of the wheel 220 (the speed of the vehicle) corresponding to the above-mentioned predetermined value (i.e., the minimum value). Specifically, when the centrifugal acceleration is the above-mentioned predetermined value, the wheel 220 rotates once in 300 ms. In this case, the acceleration sensor 1 detects the X-axis acceleration and the Y-axis acceleration in a cycle of 150 ms, which is 1 / 2 of 300 ms. Information related to the above-mentioned cycle is stored in a memory (not shown) of the sensor device 100, etc.

[0151] The cycle of 150 ms is obtained in advance by experiments or simulations in the manufacturing stage, and may be calculated based on, for example, the pitch circle diameter (PCD) of the bolt 250 to which the nut cover 241 is to be applied and the tire diameter.

[0152] In addition, the difference between the time when the sensor device 100 passes the 6 o'clock position and the time when it passes the 12 o'clock position can also be used as the above-mentioned period. At each of the 6 o'clock position and the 12 o'clock position, the direction of gravity is the same as the direction of the centrifugal force, so no angular error such as the above-mentioned is generated. In this way, the period of half a circle of the wheel 220 can be accurately calculated. In addition, the signal processing unit 2 can calculate the rotation period of the wheel 220 in real time based on parameters such as centrifugal acceleration (vehicle speed), and according to the change of the above-mentioned rotation period, the period of obtaining acceleration (the period of acceleration detection by the acceleration sensor 1) changes.

[0153] As described above, the acceleration detection cycle is set based on the minimum value of the centrifugal acceleration (rotation speed of the wheel 220). As a result, the situation where the wheel 220 rotates nearly one circle during the acceleration detection cycle can be suppressed compared with the case where the rotation speed of the wheel 220 is greater. As a result, the signal processing unit 2 can easily obtain the acceleration information of the two points, namely, the position at the 3 o'clock side relative to the rotation axis O of the wheel 220 and the position at the 9 o'clock side relative to the rotation axis O (i.e., the position symmetrical with respect to the rotation axis O). That is, it is possible to suppress the situation where both of the two points where the acceleration is detected are the points on the 3 o'clock side (or the 9 o'clock side). In addition, there is also the possibility of obtaining the acceleration information at the two points, namely, the 6 o'clock position and the 12 o'clock position, but at the above two points, the direction of gravity is the same as the direction of centrifugal force, and the above-mentioned angle error does not occur, so there is no problem. In addition, the minimum value of the centrifugal acceleration is used as a reference because the influence of gravity is the largest when the centrifugal acceleration is the minimum. Even if the acceleration acquisition cycle is a fixed cycle, when the vehicle speed is large enough and the centrifugal acceleration is large enough, the two points where the acceleration is detected are both at the 3 o'clock side (or the 9 o'clock side), and the influence of gravity becomes relatively small (the original influence on the sensor angle is small).

[0154] Fig.16 3 is a diagram showing a configuration of a sensor device 400 according to a third embodiment. The sensor device 400 is an example of a “detection device” in the present disclosure.

[0155] The sensor device 400 includes an acceleration sensor 1, a signal processing unit 22, a communication unit 3, and a power supply unit 4. The signal processing unit 22 is an example of a “state detection unit” and a “state detection device” in the present disclosure.

[0156] like Fig.16As shown, the signal processing unit 22 of the sensor device 400 includes a ratio calculation unit 22a, an angle calculation unit 22b, a tightening state detection unit 22c, and an acquisition unit 2d. The ratio calculation unit 22a, the angle calculation unit 22b, and the tightening state detection unit 22c each represent software that modularizes the functional features of the signal processing unit 22.

[0157] The signal processing unit 22 (ratio calculation unit 22a) calculates the ratio (X / Y) of the X-axis acceleration and the Y-axis acceleration. Alternatively, the ratio may be a value obtained by dividing the Y-axis acceleration by the X-axis acceleration (Y / X). Alternatively, the ratio may be a value obtained by dividing the X-axis acceleration (Y-axis acceleration) by the root mean square.

[0158] The signal processing unit 22 (angle calculation unit 22b) calculates the inverse trigonometric function value (inverse tangent function value) (arctan (X / Y)) of the calculated ratio. In addition, the inverse tangent function value is an example of the "acceleration index" of the present disclosure. In the previous description, the angle θ1 formed by the direction of the centrifugal acceleration with respect to the X-axis and the X-axis is the value of the inverse trigonometric function calculated based on the ratio of the X-axis acceleration to the Y-axis acceleration, but the angle θ1 can be calculated by using the inverse tangent as described above.

[0159] Here, on the one hand, the inverse tangent function value is a value represented by -90 degrees to 90 degrees. On the other hand, the rotation angle of the nut 240 is in the orthogonal coordinate system (refer to Fig.17 ) is represented by 0 to 360 degrees. Therefore, in the third embodiment, a process of converting the arctangent function value into an angle in an orthogonal coordinate system is performed.

[0160] Specifically, the signal processing unit 22 (angle calculation unit 22b) calculates the angle θ2 by adding a predetermined value (angle) to the arc tangent function value (see Fig.15 ). At this time, the signal processing unit 22 (angle calculation unit 22b) changes the above-mentioned predetermined value based on the positive and negative signs of the X-axis acceleration (average X-axis acceleration) and the Y-axis acceleration (average Y-axis acceleration). Specifically, the signal processing unit 22 (angle calculation unit 22b) determines the above-mentioned predetermined value based on whether the combination of the X-axis acceleration and the Y-axis acceleration is positive-positive, positive-negative, negative-positive, or negative-negative.

[0161] For example, when the X-axis acceleration and the Y-axis acceleration are 4G and 10G respectively ( Fig.17 In the case of the first quadrant of ), the signal processing unit 22 (angle calculation unit 22b) adds 0 to the arctangent function value (arctan(4 / 10)≈21.8) (in other words, does not add the numerical value). In this case, the angle θ2 becomes approximately 21.8 degrees.

[0162] In addition, when the X-axis acceleration and Y-axis acceleration are -4G and 10G respectively ( Fig.17 In the case of the second quadrant of FIG. 1 , the signal processing unit 22 (angle calculation unit 22 b ) adds 360 degrees to the arctangent function value (arctan (-4 / 10) ≈ -21.8). In this case, the angle θ2 becomes approximately 338.2 degrees.

[0163] In addition, when the X-axis acceleration and Y-axis acceleration are -4G and -10G respectively ( Fig.17 In the case of the third quadrant of FIG. 1 , the signal processing unit 22 (angle calculation unit 22 b ) adds 180 to the arctangent function value (arctan (-4 / -10) ≈ 21.8). In this case, the angle θ2 becomes approximately 201.8 degrees.

[0164] In addition, when the X-axis acceleration and Y-axis acceleration are 4G and -10G respectively ( Fig.17 In the case of the fourth quadrant of FIG. 1 , the signal processing unit 22 (angle calculation unit 22 b ) adds 180 to the arctangent function value (arctan (4 / -10) ≈ -21.8). In this case, the angle θ2 becomes approximately 158.2 degrees.

[0165] As described above, by adding the signs (quadrants) of the X-axis acceleration and the Y-axis acceleration to either 0, 180 or 360, the tightening state of the nut 240A can be detected based on an orthogonal coordinate system in which the angle increases in the clockwise direction with the positive Y-axis as the starting point (θ2=0).

[0166] Here, when the X-axis acceleration and the Y-axis acceleration are -4G and 10G, respectively, the angle θ is about 338.2 degrees as described above. In addition, when the X-axis acceleration and the Y-axis acceleration are -4G and 7G, respectively, due to the rotation of the nut 240A, the angle θ is about 330.3 degrees. Therefore, the rotation of the nut 240A reduces the angle θ by about 7.9 degrees.

[0167] Here, angle θ2 is the angle between the Y axis (positive) and the direction of centrifugal acceleration (see Fig.12 The direction of centrifugal acceleration is constant in the radial direction (outer diameter direction), so the decrease in angle θ2 is caused by the Y-axis and X-axis (i.e., sensor device 300) rotating about 7.9 degrees in the clockwise direction. In this way, the rotation direction and rotation angle of sensor device 300 (nut 240A) can be detected based on the change in angle θ2.

[0168] Moreover, similarly to the above-described second embodiment, the tightening state of the nut 240A may be detected based on the previous value or initial value of the angle θ2.

[0169] Further, similar to the first embodiment, when the signal processing unit 22 (tightening state detecting unit 22 c ) acquires the information A indicating that the nut 240 has rotated in the tightening direction, it ignores (excludes) the information A and detects the tightening state of the nut 240 .

[0170] (Processing flow of sensor device)

[0171] Next, refer to Fig.18 , the processing flow of the sensor device 400 is described. Steps S21 and S22 are similar to steps S11 and S12 of the second embodiment described above (see Fig.14 ) are the same, therefore, no repeated description is given.

[0172] In step S23 , the signal processing unit 22 (ratio calculation unit 22 a ) calculates the ratio (X / Y) of the X-axis acceleration (average X-axis acceleration) and the Y-axis acceleration (average Y-axis acceleration).

[0173] In step S24, the signal processing unit 22 (angle calculation unit 22b) calculates the angle θ2 by adding 0, 180, or 360 to the inverse tangent function value of the above ratio calculated in step S23. Specifically, the signal processing unit 22 (angle calculation unit 22b) changes the value of the sum (0, 180, or 360) based on the positive and negative signs of the X-axis acceleration (average X-axis acceleration) and the Y-axis acceleration (average Y-axis acceleration). In detail, the signal processing unit 22 (angle calculation unit 22b) changes the value of the sum (0, 180, or 360) according to whether the combination of the X-axis acceleration and the Y-axis acceleration is positive-positive, positive-negative, negative-positive, or negative-negative.

[0174] In step S25 , the average value of the angles θ2 acquired twice at every predetermined period in step S24 is calculated.

[0175] Next, in step S26, the signal processing unit 22 determines whether the data acquired in step S25 should be excluded (ignored) based on the angle θ2 acquired in step S25. If it is determined that the data acquired in step S25 should be excluded (ignored) (in S26: Yes), the process returns to step S21. If it is determined that the data acquired in step S25 should not be excluded (ignored) (in S26: No), the process proceeds to step S27.

[0176] In addition, in step S26, as described above, after obtaining information indicating that the nut 240 has rotated in the tightening direction by an angle greater than a predetermined angle in a state where the nut 240 has not loosened for a constant time or longer, if information B indicating that the nut 240 has rotated in the loosening direction by an angle equal to the rotation angle in the tightening direction is obtained, it is determined that the above data should be excluded (ignored). In addition, in step S26, similar to the above second embodiment, when the centrifugal acceleration of the wheel 220 is less than a predetermined value and when the above data is obtained when the centrifugal acceleration changes suddenly, it is determined that the above data should be excluded (ignored).

[0177] In step S27, the signal processing unit 22 (tightening state detection unit 22c) detects the tightening state of the nut 240 based on the angle θ2 (average value) calculated in step S25. When it is detected that the nut 240 is loose (in S27: Yes), the process proceeds to step S28. In addition, when it is detected that the nut 240 is not loose (in S27: No), the process returns to step S21. In addition, in step S27, the signal processing unit 22 (tightening state detection unit 22c) determines whether the nut 240 is loose based on the value of the angle θ2 up to the last time or the change (difference) relative to the initial value as described above. In addition, step S28 is the same as step S16 of the above-mentioned second embodiment.

[0178] As described above, in the third embodiment, the tightening state of the nut 240 is detected based on the arctangent function value of the ratio of the X-axis acceleration to the Y-axis acceleration. Thus, unlike the second embodiment, the rotation direction and rotation angle of the nut 240 can be detected.

[0179] [Fourth embodiment]

[0180] Next, the fourth embodiment will be described. In the fourth embodiment, unlike the third embodiment described above, in which the tightening state of the nut 240 is detected based on the inverse trigonometric function value of the ratio of the X-axis acceleration to the Y-axis acceleration, the tightening state of the nut 240 is detected based on the X-axis normalized value obtained by normalizing the X-axis acceleration and the Y-axis normalized value obtained by normalizing the Y-axis acceleration. In the fourth embodiment, the same reference numerals as those in the first to third embodiments are given to the same structures as those in the first to third embodiments described above, and repeated descriptions are not given.

[0181] like Fig.19 As shown, the sensor device 500 includes an acceleration sensor 1, a signal processing unit 32, a communication unit 3, and a power supply unit 4. The signal processing unit 32 is an example of a "state detection unit" and a "state detection device" in the present disclosure.

[0182] The signal processing unit 32 includes a root mean square calculation unit 32a, a normalization unit 32b, a rotation angle calculation unit 32c, a tightening state detection unit 32d, and an acquisition unit 2d. Fig.19 The RMS calculation unit 32a, the normalization unit 32b, the rotation angle calculation unit 32c, and the tightening state detection unit 32d shown are each a software part that modularizes the functional features of the signal processing unit 32. The details of each function will be described later.

[0183] In the fourth embodiment, the nut 240 (nut 240A) is fixed in an initial state (a state where the nut 240A is not loose) so that the positive direction of the X axis of the acceleration sensor 1 faces upward (Z1 direction) (see Figure 5 ). In addition, in the initial state, the positive direction of the X axis of the acceleration sensor 1 may be oriented in a direction other than the Z1 direction. In the following description, the sensor device 500 is oriented in a direction other than the Z1 direction. Figure 5 When in the state of, the angle (rotation angle) of the sensor device 500 is set to 0 degrees.

[0184] Fig. 20 The coordinate diagram shows the relationship between the rotation angle of the tire 230 (wheel 220) and the X-axis acceleration and the Y-axis acceleration when a centrifugal force of 6G acts on the nut 240 at a predetermined vehicle speed. Fig.19 In the direction of the Y axis shown, on the one hand, there is no centrifugal force applied to the Y axis, so the Y axis acceleration is relative to Figure 7 On the other hand, the centrifugal force is applied to the X-axis, so the X-axis acceleration becomes Figure 7 The value is obtained by adding 6G to the X-axis acceleration. In this case, the waveform of the root mean square of the X-axis acceleration and the Y-axis acceleration is the same as the waveform of the X-axis acceleration. Fig. 20 In order to facilitate understanding, the waveform of the X-axis acceleration and the waveform of the root mean square are slightly offset and illustrated. Fig. 20 It means setting Figure 5 A graph of the results of sensor device 500 for nut 240A is shown.

[0185] Fig.21 It means that the nut 240A is Figure 5 135 degrees clockwise (loose and 225 degrees counterclockwise) (refer to Fig.12) is a coordinate diagram showing the relationship between the angle of the tire 230 (wheel 220) and the X-axis acceleration and the Y-axis acceleration when a centrifugal force of 6G acts on the nut 240. In this case, on the one hand, the amplitude of the waveform of the X-axis acceleration and the Y-axis acceleration is Fig. 20 On the other hand, the average values ​​of the X-axis acceleration and the Y-axis acceleration are equal to Fig. 20 On the one hand, the average values ​​of the X-axis acceleration and the Y-axis acceleration reflect the rotation angle of the nut 240 (sensor device 500). On the other hand, the waveform of the root mean square of the X-axis acceleration and the Y-axis acceleration is different from Fig. 20 The same is true for the case where the rotation angle of the nut 240 (sensor device 400) does not change. Fig.21 It means setting Fig. 20 A graph of the results of sensor device 500 for nut 240A is shown.

[0186] Fig.22A This is a graph showing the average value of acceleration with respect to the angle (rotation angle) of the sensor device 500 when the centrifugal force is 6G. Fig. 22B : is a graph showing the average value of acceleration relative to the angle (rotation angle) of the sensor device 500 when the centrifugal force is 10G. Fig.22A and Fig. 22B As shown in FIG. 1 , the waveforms of the average values ​​of the X-axis acceleration and the Y-axis acceleration have amplitudes corresponding to the centrifugal force (the scales of the vertical axes are different from each other), but have the same shape. Fig.22A and Fig. 22B The root mean square of the average values ​​of the X-axis acceleration and the Y-axis acceleration is a constant value corresponding to the centrifugal force. Therefore, the value obtained by dividing the average values ​​of the X-axis acceleration and the Y-axis acceleration by the root mean square is equal regardless of the magnitude of the centrifugal force.

[0187] The signal processing unit 32 (root mean square calculation unit 32a) of the fourth embodiment calculates the root mean square of the X-axis acceleration (Xg) (average X-axis acceleration) and the Y-axis acceleration (Yg) (average Y-axis acceleration). In addition, the signal processing unit 32 (standardization unit 32b) calculates the X-axis normalization value by dividing the X-axis acceleration (average X-axis acceleration) by the above-mentioned root mean square. In addition, the signal processing unit 32 (standardization unit 32b) calculates the Y-axis normalization value by dividing the Y-axis acceleration (average Y-axis acceleration) by the above-mentioned root mean square. In addition, the X-axis normalization value and the Y-axis normalization value are examples of the "first axis normalization value" and the "second axis normalization value" of the present disclosure, respectively. In addition, the X-axis normalization value and the Y-axis normalization value are examples of the "acceleration index" of the present disclosure, respectively.

[0188] Then, the signal processing unit 32 (rotation angle calculation unit 32c) detects the rotation angle of the nut 240 (sensor device 500) based on both the X-axis normalized value and the Y-axis normalized value. Fig.22A and Fig. 22B As described above, when the vehicle speed is above a constant value, regardless of the centrifugal force (vehicle speed), the X-axis normalized value and the Y-axis normalized value are values ​​obtained based on the sensor angle. Therefore, by using the X-axis normalized value and the Y-axis normalized value, the rotation angle of the nut 240 can be detected regardless of the vehicle speed.

[0189] Fig.23 This is a coordinate diagram showing the time changes of the X-axis normalized value (solid line), the Y-axis normalized value (dashed line), and the centrifugal acceleration (single-point dashed line). The X-axis normalized value and the Y-axis normalized value each correspond to the vertical axis on the left. The centrifugal acceleration corresponds to the vertical axis on the right. In addition, Fig.23 Is the nut 240A from Figure 5 The coordinate diagram is a diagram of a state where the image is rotated 45 degrees counterclockwise.

[0190] Here, at time t11, the vehicle 200 starts to travel, and thus, Fig.23 As shown in FIG. 1 , the centrifugal acceleration increases to 15G. In addition, after time t11, the X-axis normalized value is about -1G, and the Y-axis normalized value is about 0G. Fig.23 As shown, the variation (amplitude) of the X-axis normalized value around -1G is smaller than the variation (amplitude) of the Y-axis normalized value around 0G.

[0191] Therefore, when the tightening state of the nut 240 is detected by directly comparing the X-axis normalized value or the Y-axis normalized value with the predetermined allowable range instead of directly comparing the rotation angle of the sensor device 500 with the predetermined allowable range, the allowable range when the X-axis normalized value or the Y-axis normalized value is near 0G is larger than the allowable range when the X-axis normalized value or the Y-axis normalized value is near -1G (or 1G). Thus, even if the X-axis normalized value or the Y-axis normalized value is near 0G, the tightening state of the nut 240 can be detected more accurately. In addition, this control can also be applied to the second embodiment and the third embodiment described above.

[0192] Furthermore, the tightening state of the nut 240 may also be detected based on the inverse tangent function value of the X-axis normalized value and the Y-axis normalized value. Fig.24 replace Fig. 20 The waveform of the inverse trigonometric function value is shown in FIG. Fig.23In addition, as described in the third embodiment, the inverse tangent function value can only be in the range of -90 degrees to 90 degrees, but the inverse tangent function value can also be in the range of 0 degrees to 360 degrees by adding or subtracting 180 degrees or 360 degrees in consideration of the signs of the X-axis acceleration and the Y-axis acceleration.

[0193] (Processing flow of sensor device)

[0194] Next, refer to Fig.25 , the processing flow of the sensor device 500 will be described. Steps S31 to S33 are the same as S11 to S13 of the second embodiment described above.

[0195] In step S34 , the signal processing unit 32 (RMS calculation unit 32 a ) calculates the RMS of the X-axis acceleration (average X-axis acceleration) and the Y-axis acceleration (average Y-axis acceleration).

[0196] In step S35 , the signal processing unit 32 (normalization unit 32 b ) calculates an X-axis normalization value and a Y-axis normalization value based on the root mean square calculated in step S34 .

[0197] In step S36 , the signal processing unit 32 (rotation angle calculation unit 32 c ) calculates the angle (rotation angle) of the sensor device 500 (nut 240 ) based on the X-axis normalized value and the Y-axis normalized value calculated in step S35 .

[0198] In step S37, the signal processing unit 32 determines whether the data acquired in step S36 should be excluded (ignored) based on the angle (rotation angle) of the sensor device 500 acquired in step S36. When it is determined that the above data should be excluded (ignored) (in S37: Yes), the process returns to step S31. When it is determined that the above data should not be excluded (ignored) (in S37: No), the process proceeds to step S38. In addition, the object of the data (measurement value) to be excluded (ignored) is not limited to the X-axis normalized value and the Y-axis normalized value, but may also be the X-axis acceleration and the Y-axis acceleration.

[0199] In addition, in step S37, similarly to the third embodiment, after obtaining information indicating that the nut 240 has rotated in the tightening direction by more than a predetermined angle in a state where the nut 240 has not loosened for more than a constant time, if information B indicating that the nut 240 has rotated in the loosening direction by an angle equal to the angle of rotation in the tightening direction is obtained, it is determined that the above data should be excluded (ignored). In addition, in step S37, similarly to the second embodiment, if the centrifugal acceleration of the wheel 220 is less than a predetermined value and if the above data is obtained when the centrifugal acceleration suddenly changes, it is determined that the above data should be excluded (ignored).

[0200] Next, in step S38, the signal processing unit 32 (tightening state detection unit 32d) detects the tightening state of the nut 240 based on the angle (rotation angle) of the sensor device 500 (nut 240) calculated in step S36. When it is detected that the nut 240 is loose (in S38: Yes), the process proceeds to step S39. In addition, when it is detected that the nut 240 is not loose (in S38: No), the process returns to step S31. In addition, in step S38, the signal processing unit 32 (tightening state detection unit 32d) determines whether the nut 240 is loose based on the detection value of the angle of the sensor device 500 up to the last time or based on the change (difference) formed relative to the initial value as described above. In addition, step S39 is the same as step S16 of the above-mentioned second embodiment.

[0201] As described above, in the fourth embodiment, the rotation angle of the nut 240 is detected based on each of the X-axis normalized value and the Y-axis normalized value. This makes it possible to detect the rotation angle of the nut 240 without considering changes in the vehicle speed (centrifugal force).

[0202] [Fifth embodiment]

[0203] Next, the fifth embodiment is described. In the fifth embodiment, the tightening state of the nut 240 is detected based on the positive and negative signs of the X-axis acceleration and the Y-axis acceleration. In the fifth embodiment, the same reference numerals as those in the first to fourth embodiments are given to the same structures as those in the first to fourth embodiments, and no repeated description is given.

[0204] like Fig.26 As shown, the sensor device 600 includes an acceleration sensor 1a, a signal processing unit 42, a communication unit 3, and a power supply unit 4. The signal processing unit 42 is an example of a "state detection unit" and a "state detection device" in the present disclosure.

[0205] Fig. 27It is a side view showing a state where the wheel 220 (wheel 210) is fastened to the hub 250a. Fig. 27 In the figure, a sensor device 600 is provided on the nut 240 located at the top. The detection axis of the acceleration sensor 1a is set to the X-axis. The acceleration sensor 1a detects the acceleration applied along the detection axis (X-axis). The acceleration detected on the detection axis (X-axis) is also referred to as Gx. The arrow of the X-axis indicates the positive direction of Gx. In the case where the acceleration applied to the acceleration sensor 1a has a component (vector) in the direction of the arrow of the X-axis (the direction of the arrow of the double-dotted line), Gx is a positive value (+Gx (positive acceleration)). In addition, in the case where the acceleration applied to the acceleration sensor 1a has a component in the opposite direction to the arrow of the X-axis, Gx becomes a negative value (-Gx (negative acceleration)).

[0206] The wheel 220 (wheel 210) is on a predetermined pitch circle (refer to Fig. 27 The wheel hub 250a is fastened to the wheel hub 250a by the nut 240 on the single-dot chain line. In addition, the size of the pitch circle diameter (PCD: Pitch Circle Diameter) can also be arbitrary, for example, it can be 114.3 mm or 275 mm. Fig. 27 The nut 240 is tightened with a predetermined tightening torque and the wheel 220 (wheel 210) is tightened to the wheel hub 250a. The nut 240 is a right-hand thread. Fig. 27 Tighten by turning in a clockwise direction.

[0207] Fig.28A and Fig.28B : is a diagram showing the relationship between the centrifugal acceleration and the acceleration Gx detected by the acceleration sensor 1a. Fig.28A The state where the nut 240 is tightened by a predetermined tightening torque is shown ( Fig. 27 status shown). Fig.28B The nut 240 is shown to be rotated in the loosening direction (counterclockwise). Fig. 27 As shown, gravity acceleration is applied to the nut 240 (acceleration sensor 1a), but when using Fig.28A and Fig.28B In the description of , the method of ignoring the gravitational acceleration is described. In other words, the relationship between the centrifugal acceleration and the acceleration Gx detected by the acceleration sensor 1a is described, assuming that the rotation axis O of the hub 250a (wheel 220) is oriented in the vertical direction and the wheel 220 rotates on the horizontal plane. In this case, the gravitational acceleration is not applied in the detection axis (X-axis) direction of the acceleration sensor 1a.

[0208] Fig.28A and Fig.28BIn FIG. 1 , the dotted arrow indicates the direction of the centrifugal acceleration (centrifugal force) generated by the rotation of the hub 250a (wheel 220). The centrifugal acceleration acts in the radial direction centered on the rotation axis O. Therefore, the nut 240 (acceleration sensor 1a) is in the same position as the nut 240 at any position on the pitch circle. Fig.28A and Fig.28B In addition, Fig.28A and Fig.28B In FIG. 1 , an arrow Gc represents a vector of centrifugal acceleration, and the vector Gc always points to a radial direction with the rotation axis O as the center.

[0209] In the state indicating that the nut 240 is tightened with a predetermined tightening torque, Fig.28A In the X-axis direction component (the component in the detection axis direction of the acceleration sensor 1a) of the vector Gc (centrifugal acceleration) is detected by the acceleration sensor 1a as "+Gx (positive acceleration)". If the nut 240 rotates in the loosening direction (counterclockwise), the tightening state of the nut 240 becomes loose, and becomes Fig.28B In this state, the X-axis direction component of the vector Gc (centrifugal acceleration) (the component in the detection axis direction of the acceleration sensor 1a) is detected by the acceleration sensor 1a as "-Gx (negative acceleration)".

[0210] As from Fig.28A and Fig.28B As can be seen, if the detection axis (X axis) of the acceleration sensor 1a crosses the axis ( Fig.28A and Fig.28B If the acceleration sensor 1a is rotated about the axis (the axis indicated by the single-dot dash line in the figure), the direction of the acceleration detected by the acceleration sensor 1a changes, and the acceleration Gx detected by the acceleration sensor 1a changes from positive acceleration (+Gx) to negative acceleration (-Gx), or from negative acceleration (-Gx) to positive acceleration (+Gx). In other words, the positive and negative directions of the acceleration detected by the acceleration sensor 1a are reversed. If the detection axis (X-axis) of the acceleration sensor 1a rotates while centrifugal acceleration is applied to the acceleration sensor 1a, the direction of detecting the positive direction of Gx (the arrow of the X-axis) changes from +Gx to +Gx. Fig.28A The area A shown changes to Fig.28B If the acceleration sensor 1a is in the region B shown in FIG. 1 , the acceleration Gx changes from +Gx to -Gx. As a result, the acceleration detected by the acceleration sensor 1a is reversed in sign. If the detection axis (X axis) of the acceleration sensor 1a rotates while centrifugal acceleration is applied to the acceleration sensor 1a, the direction for detecting the positive direction of Gx (the arrow of the X axis) changes from +Gx to -Gx. Fig.28B The area B shown changes to Fig.28AIn the region A shown in FIG. 1 , the acceleration Gx changes from −Gx to +Gx. As a result, the acceleration detected by the acceleration sensor 1 a reverses in sign.

[0211] The acceleration sensor 1a rotates in conjunction with the rotation of the nut 240. Therefore, based on the reversal of the positive and negative of the acceleration Gx detected by the acceleration sensor 1a when the centrifugal acceleration generated by the rotation of the wheel 220 is applied, the rotation of the nut 240 can be detected. Using this fact, in the fifth embodiment, the change in the tightening state of the nut 240 is detected.

[0212] Fig.29 4 is a diagram showing an example of a functional block constituting the signal processing unit 42. The acceleration determination unit 42a determines whether the gravitational acceleration applied to the acceleration sensor 1a is greater than the centrifugal acceleration. Fig. 27 As shown, the rotation axis O of the wheel 220 (the rotation axis O of the hub 250a) is a horizontal axis, and in addition to the centrifugal acceleration, the gravity acceleration is also applied to the acceleration sensor 1a. The acceleration Gx detected by the acceleration sensor 1a is the composite acceleration of the centrifugal acceleration and the gravity acceleration. Therefore, when the gravity acceleration applied to the detection axis of the acceleration sensor 1a is greater than the centrifugal acceleration applied to the detection axis, even if the nut 240 does not rotate, there is a possibility that the direction (positive or negative sign) of the acceleration Gx will change due to the different positions of the nut 240 on the pitch circle.

[0213] If the magnitude of the gravitational acceleration is set to 1G, the magnitude of the gravitational acceleration (the gravitational acceleration acting in the X-axis direction) detected by the acceleration sensor 1a becomes 1G at maximum. When the absolute value of the acceleration Gx detected by the acceleration sensor 1a is greater than 2G, a centrifugal acceleration greater than the gravitational acceleration acts on the acceleration sensor 1a. Therefore, when the absolute value of the acceleration Gx detected by the acceleration sensor 1a is greater than 2G, the influence of the gravitational acceleration can be eliminated and the rotation of the nut 240 can be detected based on the acceleration Gx. In other words, when the absolute value of the acceleration Gx detected by the acceleration sensor 1a is less than 2G, there is a possibility that the nut 240 is affected by the gravitational acceleration.

[0214] In the fifth embodiment, the acceleration determination unit 42a determines that the centrifugal acceleration is greater than the gravitational acceleration when the absolute value of the acceleration Gx detected by the acceleration sensor 1a is 5G or more, and determines that the gravitational acceleration is greater than the centrifugal acceleration when the absolute value of the acceleration Gx is less than 5G.

[0215] The stop determination unit 42b determines whether the vehicle 200 is stopped and the rotation of the hub 250a (wheel 220) has stopped.

[0216] The stop determination unit 42b determines that the rotation of the hub 250a (wheel 220) has stopped when the magnitude of the previous value and the current value of the acceleration Gx (average X-axis acceleration) detected by the acceleration sensor 1a at each predetermined period is the same. In the fifth embodiment, when the magnitude of the previous value of the acceleration Gx is set to Gx(n-1) and the magnitude of the current value of the acceleration Gx is set to Gx(n), and when "|Gx(n-1)-Gx(n)|<α" continues for a constant period, for example, when it is established three times in succession, it is determined that the wheel 220 has stopped. In addition, α is a predetermined value, which is a value that takes into account the influence of noise and interference when detecting the acceleration Gx, and is set in advance through experiments, etc.

[0217] The state determination unit 42c determines that the tightening state of the nut 240 is loose when the sign of the acceleration Gx (average X-axis acceleration) detected by the acceleration sensor 1a is reversed (changed). When the sign of the acceleration Gx is reversed, it is when the acceleration Gx changes from positive acceleration (+Gx) to negative acceleration (-Gx), or when it changes from negative acceleration (-Gx) to positive acceleration (+Gx). In addition, the state determination unit 42c is an example of the "tightening state detection unit" of the present disclosure.

[0218] In the fifth embodiment, when the sign of the previous value of the acceleration Gx (average X-axis acceleration) detected by the acceleration sensor 1a is different from the sign of the current value of the acceleration Gx (average X-axis acceleration) detected by the acceleration sensor 1a, the state determination unit 42c regards that the sign of the acceleration Gx has reversed and determines that the tightening state of the nut 240 has changed. In addition, in the state determination unit 42c of the fifth embodiment, the rotation direction of the nut 240 cannot be detected. It is very rare that the nut 240 rotates in the tightening direction (increasing the tightening direction) when the wheel hub 250a (wheel 220) rotates. Therefore, when the direction (sign) of the acceleration Gx detected by the acceleration sensor 1a that rotates in conjunction with the rotation of the nut 240 changes, it can also be inferred that the nut 240 has rotated in the loosening direction.

[0219] When the state determination unit 42c determines that the tightening state of the nut 240 has changed, the state determination unit 42c transmits the information to the communication terminal 201 of the vehicle 200 via the communication unit 3 (see Figure 1 ). The communication terminal 201 receives the transmitted information, such as warning (displaying) that the nut 240 is loose.

[0220] Fig.30 4 is a flowchart showing an example of processing executed by the signal processing unit 42. This flowchart repeats the processing every predetermined period. The first predetermined period is, for example, 300 ms.

[0221] In step S40, the signal processing unit 42 obtains the acceleration Gx detected by the acceleration sensor 1a. The signal processing unit 42 obtains the information of the acceleration Gx detected by the acceleration sensor 1a at each predetermined period (for example, 150ms). In addition, if the acceleration sensor 1a receives an acceleration detection request from the signal processing unit 42, it detects the acceleration Gx and sends a detection signal to the signal processing unit 42. Therefore, the signal processing unit 42 obtains the information of the acceleration Gx from the acceleration sensor 1a at each of the above-mentioned predetermined periods.

[0222] In step S41, the signal processing unit 42 determines whether the absolute value |Gx| of the acceleration Gx (detected by the acceleration sensor 1a) acquired in step S40 is greater than 5G. Specifically, it is determined whether the absolute value |Gx| (average value) of the average value of the two amounts of acceleration Gx acquired in step S40 (average X-axis acceleration) is greater than 5G. If the absolute value |Gx| (average value) is greater than 5G, a positive determination is made, and the process enters S42. If the absolute value |Gx| (average value) is less than 5G, a negative determination is made, and the process enters step S47.

[0223] In step S42, the signal processing unit 42 sets the processing interval (predetermined period) of this flowchart to, for example, 300 ms. And, the processing proceeds to step S43. In addition, the above-mentioned processing interval (predetermined period) is, for example, twice the period (150 ms in the above-mentioned case) of detecting the acceleration Gx by the acceleration sensor 1a. In addition, in the case where the predetermined period is already 300 ms in step S42, the predetermined period is maintained at 300 ms.

[0224] In step S43, the signal processing unit 42 determines whether the absolute value |Gx| (average value) of the acceleration Gx (last value Gx (n-1)) acquired in step S40 of the previous process is greater than 5G. If the absolute value |Gx| (average value) of the last acceleration Gx (last value Gx (n-1)) is greater than 5G, a positive determination is made, and the process proceeds to step S44. If the absolute value |Gx| (average value) of the last acceleration Gx (last value Gx (n-1)) is less than 5G, a negative determination is made, and the process proceeds to step S46.

[0225] In step S44, the signal processing unit 42 determines whether the direction of the acceleration Gx (average X-axis acceleration) has changed. The signal processing unit 42 determines whether there has been a change between the direction of the acceleration Gx detected by the acceleration sensor 1a this time and the direction of the acceleration Gx (last value Gx(n-1)) at the time of the previous processing in the processing of step S40. When the sign of the acceleration Gx detected by the acceleration sensor 1a this time is different from the sign of the acceleration Gx (last value Gx(n-1)) at the time of the previous processing, the signal processing unit 42 determines that the direction of the acceleration Gx has changed and the sign of the acceleration Gx has reversed.

[0226] If it is determined in step S44 that the direction of acceleration Gx (average X-axis acceleration) has changed (affirmative determination), the process proceeds to step S45. If it is not determined in step S44 that the direction of acceleration Gx (average X-axis acceleration) has changed (negative determination), the process proceeds to step S46.

[0227] In step S45 , the signal processing unit 42 determines that the tightening state of the nut 240 has changed, and transmits loosening information of the nut 240 to the communication terminal 201 via the communication unit 3 .

[0228] In step S46 , the signal processing unit 42 stores the acceleration Gx (average X-axis acceleration) acquired in step S40 in the memory as the previous value Gx(n−1) of the acceleration Gx, and then ends the current routine.

[0229] In step S47, the signal processing unit 42 determines whether the difference between the magnitude of the acceleration Gx during the last processing (the last value Gx(n-1)) and the magnitude of the acceleration Gx acquired in step S40 during the current processing (the current value Gx(n)) is less than a predetermined value α. If "|Gx(n-1)-Gx(n)|<α", a positive determination is made, and the process proceeds to step S48. If "|Gx(n-1)-Gx(n)|≥α", a negative determination is made, and the process proceeds to step S51.

[0230] In step S48, the signal processing unit 42 increments the counter Ct and then proceeds to step S49. In step S49, the signal processing unit 42 determines whether the counter Ct is greater than 3. In step S49, if the counter Ct is greater than 3 (Ct≥3), a positive determination is made and the process proceeds to step S50. If the counter Ct is less than 3 (Ct<3), a negative determination is made and the process proceeds to step S52.

[0231] In step S50, the signal processing unit 42 sets the processing interval (predetermined period) of this flowchart to 30 minutes, and then ends the current routine through the processing of step S46. In step S51, the counter Ct is set to zero.

[0232] In step S52 , the signal processing unit 42 sets the processing interval (predetermined period) of this flowchart to 300 ms, and then ends the current routine through the processing of step S46 .

[0233] According to the fifth embodiment, the acceleration sensor 1a rotates in conjunction with the rotation of the nut 240, and rotates integrally with the rotation of the nut 240 in the tightening direction and the loosening direction. The acceleration sensor 1a detects the acceleration Gx in one direction on the detection axis (X axis) orthogonal to the rotation axis O of the hub 250a (axle) as a positive acceleration (+Gx), and detects the acceleration Gx in another direction on the detection axis (X axis) as a negative acceleration (-Gx). If the detection axis (X axis) of the acceleration sensor 1a rotates while crossing the axis orthogonal to the vector Gc of the centrifugal acceleration, the direction of the acceleration detected by the acceleration sensor 1a changes, and the acceleration Gx detected by the acceleration sensor 1a changes from the positive acceleration (+Gx) to the negative acceleration (-Gx), or from the negative acceleration (-Gx) to the positive acceleration (+Gx), and the sign of the acceleration Gx is reversed. The state determination unit 42 c of the signal processing unit 42 determines that the tightening state of the nut 240 has changed when the sign of the acceleration Gx detected by the acceleration sensor 1 a is reversed.

[0234] In the state determination unit 42c, the rotation direction of the nut 240 cannot be detected. However, when the hub 250a (wheel 220) rotates, it is very rare that the nut 240 rotates in the tightening direction (increasing the tightening direction). Therefore, when the direction (positive or negative) of the acceleration Gx detected by the acceleration sensor 1a that rotates integrally with the nut 240 changes, it can be inferred that the nut 240 has rotated in the loosening direction. Therefore, in the fifth embodiment, when the nut 240 has rotated in the loosening direction, it can be inferred that the tightening state of the nut 240 is loose, and therefore, even if the loosening is relatively light, the loosening of the nut 240 can be detected.

[0235] In the fifth embodiment, the change in the tightening state of the nut 240 (rotation of the nut 240) is detected based on the direction (positive or negative) of the acceleration Gx detected by the acceleration sensor 1a. Therefore, the acceleration sensor 1a only needs to be able to detect the direction (positive or negative) of the acceleration Gx, and a low-G acceleration type acceleration sensor with a relatively small acceleration detection range can be used. For example, in the fifth embodiment, an acceleration sensor that can detect at least 5G acceleration can be used.

[0236] In the fifth embodiment described above, when the absolute value |Gx| of the acceleration Gx detected by the acceleration sensor 1a is greater than 5G, a centrifugal acceleration greater than the acceleration due to gravity acts on the acceleration sensor 1a (S41). However, it is also possible that when the absolute value |Gx| exceeds a predetermined value greater than 2G, a centrifugal acceleration greater than the acceleration due to gravity acts on the acceleration sensor 1a. In addition, it is also possible that, in a case where the rotation speed of the hub 250a (wheel 220) can be calculated based on the speed of the vehicle 200, etc., when the centrifugal acceleration calculated based on the rotation speed of the hub 250a (wheel 220) and the PCD is greater than the acceleration due to gravity, a change in the direction (positive or negative) of the acceleration Gx is detected.

[0237] In the fifth embodiment, the stop determination unit 42b determines whether the rotation of the hub 250a (wheel 220) has stopped based on the acceleration Gx detected by the acceleration sensor 1a. However, the vehicle speed information of the vehicle 200 may be acquired via the communication unit 3, and when the vehicle 200 stops, it may be determined that the rotation of the hub 250a (wheel 220) has stopped.

[0238] (Variant 1)

[0239] In the fifth embodiment, the reversal of the sign of the acceleration Gx is detected based on the sign of the previous value and the sign of the current value of the acceleration Gx detected by the acceleration sensor 1a. In the first modification, the initial value Gxs of the acceleration Gx (average X-axis acceleration) is set, and the reversal of the sign of the acceleration Gx is detected based on the sign of the initial value Gxs and the sign of the acceleration Gx (average X-axis acceleration) detected by the acceleration sensor 1a.

[0240] Fig.31 This is a flowchart showing the processing of the initial value setting program executed by the signal processing unit 42 in the modification example 1. Figure 1 ) is pressed, the signal processing unit 42 receives the pressing of the button 201a via the communication unit 3 and starts processing.

[0241] If the button 201a is pressed, the acceleration Gx is detected by the acceleration sensor 1a in step S60. In the next step S61, it is determined whether the absolute value |Gx| (average value) of the acceleration Gx is greater than 5G. If the absolute value |Gx| is less than 5G, a negative determination is made, and the process returns to step S60, and the acceleration Gx is detected again by the acceleration sensor 1a.

[0242] The vehicle 200 starts to travel. If the absolute value |Gx| (average value) of the acceleration Gx detected by the acceleration sensor 1a exceeds 5G, a positive determination is made in step S61, and the process proceeds to step S62. In step S62, the acceleration Gx detected by the acceleration sensor 1a is set as the initial value Gxs, and the program ends. In addition, the initial value Gxs includes the direction (sign (+ / -)) of the acceleration Gx detected by the acceleration sensor 1a.

[0243] Fig.32 FIG. 4 is a flowchart showing an example of processing executed in the signal processing unit 42 in the modification example 1. Fig.30 The flowchart is the same as that of , which is repeated for each scheduled period, with the initial scheduled period being 300ms. Fig.30 The process of step S43 of the flowchart of FIG. 4 is replaced with the process of step S53. Therefore, the description of the processes of S40 to S42 and S44 to S52 is omitted.

[0244] In step S53, the signal processing unit 42 determines whether the direction of the acceleration Gx (average X-axis acceleration) detected in the process of step S40 is different from the direction of the initial value Gxs. When the sign of the acceleration Gx is different from the sign of the initial value Gxs (yes in S53), it is determined that the sign of the acceleration Gx is reversed, and the process proceeds to step S45. When the sign of the acceleration Gx is the same as the sign of the initial value Gxs, a negative determination is made, and the process proceeds to step S46.

[0245] According to this modification 1, the initial value Gxs is the acceleration Gx indicating the rotational position when the nut 240 is tightened. Therefore, the change in the tightening state from when the nut 240 is tightened with a predetermined tightening torque can be detected. As a result, the tightening state of the nut 240 can be detected more appropriately.

[0246] In addition, when the vehicle 200 (communication terminal 201) does not have the button 201a, the vehicle 200 may be executed when returning from the parking state to the driving state. Fig.31 For example, after a positive determination is made in step S47, when a positive determination is made in step S41 or a negative determination is made in step S47, the execution Fig.31 In addition, when it is determined based on the vehicle speed information of the vehicle 200 that the vehicle 200 is restored from the parking state to the driving state, the execution Fig.31 In addition, the button 201a may be set on the nut 240.

[0247] (Variant 2)

[0248] In the fifth embodiment described above, the detection axis of the acceleration sensor 1a is the X-axis. There is a situation where, if the detection axis of the acceleration sensor 1a is the X-axis, sometimes when the nut 240 (acceleration sensor 1) is not rotated more than 180°, the direction (sign) of the acceleration Gx does not change. In addition, there is also a situation where, depending on the rotational position of the nut 240 when the tightening is completed, the sign of the acceleration Gx is reversed only by a slight rotation. Therefore, in the second modification, as in the first to fourth embodiments described above, the acceleration of the X-axis and the acceleration of the Y-axis are detected by the acceleration sensor 1.

[0249] In the second modification, the signal processing unit 42 performs the following operation based on the acceleration Gx detected by the X-axis of the acceleration sensor 1. Fig.30 In addition, the signal processing unit 42 performs the processing of the flowchart based on the acceleration Gy detected by the Y axis of the acceleration sensor 1. Fig.30 In addition, Gx is replaced by Gy.

[0250] According to the second modification, when the nut 240 is rotated by at least 90°, the sign of one of the acceleration Gx or the acceleration Gy is reversed, so that a change in the tightening state of the nut 240 can be detected.

[0251] According to the second modification, if it is determined that the tightening state of the nut 240 has changed when the sign of the other of the acceleration Gx or the acceleration Gy is reversed after the sign of either the acceleration Gx or the acceleration Gy is reversed, then when the nut 240 rotates more than 90°, the change in the tightening state of the nut 240 can be detected. In addition, the acceleration sensor 1 of the second modification and the first to fourth embodiments described above has two axes, the X-axis (first detection axis) and the Y-axis (second detection axis), which are orthogonal to each other, as detection axes, but the X-axis (first detection axis) and the Y-axis (second detection axis) may not be orthogonal. In addition, as long as it is a plane orthogonal to the rotation axis of the wheel 220 (the rotation axis O of the hub 250a), the detection axes of the acceleration sensor may be three or more axes intersecting at any angle. In this case, it is preferred that the multiple detection axes of the acceleration sensor intersect at equal angles (for example, 120° in the case of three axes).

[0252] (Variant 3)

[0253] In the first to fifth embodiments described above, an example in which the nut cover 241 is mounted on the nut 240 is shown, but the present disclosure is not limited thereto. Fig.33As shown, the sensor device may be mounted on a nut 340 which is a bag-shaped nut. The nut 340 is an example of a "fastening member" of the present disclosure. Fig.33 In FIG. 1 , a sensor device 100 is shown as a representative sensor device.

[0254] (Variant 4)

[0255] In addition, Fig.34 In the modification 4 shown, one side of the nut 440 is open but does not include a nut cover. In this example, the sensor device may be provided on a side surface 441 of the nut 440 (provided as a surface perpendicular to the wheel 220). Fig.34 , the sensor device 100 is shown as a representative of the sensor device. In addition, the structure of each of the above-mentioned modification example 4 may be applied to the above-mentioned second to fifth embodiments. In addition, the sensor device may be embedded in the recess 541a (see Fig.35 ). In addition, the nut 440 and the nut 540 are each an example of a “fastening member” of the present disclosure.

[0256] (Comparative Example)

[0257] Fig.36 4 is a cross-sectional view of a fastening portion using a looseness detection device according to a comparative example. Fig.36 In the embodiment, the hub 250a and the bolt 250 are respectively the same as those in the above-mentioned embodiment. Fig.36 In the embodiment, a single tire is fastened to the wheel hub 250a. The wheel 220 is one. In addition, Fig.35 , the nut 640 is illustrated as a through nut by a side view (not a cross-sectional view).

[0258] In the comparative example, a leaf spring L, a coil spring C, and contacts S1 and S2 are provided in the space inside the nut cover NC. One end of the leaf spring L is fixed to the top surface of the nut cover NC. One end of the coil spring C is mounted on the other end of the leaf spring L. Contact S1 is fixed to the other end of the coil spring C. Contact S2 is provided on the top surface of the nut cover NC facing the contact S1. The nut cover NC is mounted on the nut 640 as indicated by the arrow. For example, the nut cover NC is fixed to the nut 640 by pressing the side surface of the nut 640 against the inner surface of the nut cover NC.

[0259] Fig.37: is a diagram showing a state where the nut cover NC is mounted on the nut 640 in a comparative example (upper figure) and a tightening state where the nut 640 is loose (lower figure). The upper figure shows a state where the nut 640 is tightened by a predetermined tightening torque. When the nut 640 is tightened by a predetermined tightening torque, the distance between the top surface of the nut cover NC mounted on the nut 640 and the upper surface (end portion) of the bolt 250 is short. In this case, as shown in the upper figure, the leaf spring L and the coil spring C are compressed, the contact S1 contacts the contact S2, and the contact S1 and the contact S2 are closed.

[0260] As shown in the following figure, if the tightening state of the nut 640 is loosened, a gap is generated between the nut 640 and the tightening surface of the wheel 220. If this gap is generated, the distance between the top surface of the nut cover NC mounted on the nut 640 and the upper surface of the bolt 250 becomes longer. In this case, the contact point S1 is separated from the contact point S2 and the contact point S1 and the contact point S2 are opened.

[0261] In the looseness detection device of this comparative example, by electrically detecting the opening and closing of the contact S1 and the contact S2, it is possible to detect the looseness of the nut 640. For example, when the contact S1 and the contact S2 are closed, it is determined that the tightening state of the nut 640 is normal, and when the contact S1 and the contact S2 are opened, it is determined that the nut 640 is loose.

[0262] Fig.38 This is a diagram for explaining individual differences in the length of the screw shaft of the bolt 250. The length of the screw shaft of the bolt 250 varies depending on the model of the car and the car manufacturer (vehicle manufacturer). Fig.38 The left figure shows an example in which the screw rod length of the bolt 250 is shorter. Fig.38 The right figure shows an example in which the screw rod length of the bolt 250 is longer. Fig.38 As shown, the bolts 250 with different screw lengths cause a difference (Δd) in the distance from the fastening surface between the wheel 220 and the nut 640 to the upper surface of the bolt 250. Therefore, in the looseness detection device of the comparative example using the nut cover NC, the looseness of the nut 640 may not be properly detected.

[0263] In contrast, in the detection device according to the above embodiment, the tightening state of the tightening member is detected using the acceleration detected by the acceleration sensor 1 ( 1 a ), and therefore the tightening state can be detected without being affected by the difference in the screw length of the bolt 250 .

[0264] In the description of the first embodiment, the acceleration sensor 1 detects the acceleration of each of the X-axis and the Y-axis, and detects the acceleration of each of the X-axis and the Y-axis and the difference between the acceleration of the X-axis and the acceleration of the Y-axis, but the present disclosure is not limited to this. Fig.12In the example, only the acceleration of the X-axis and the Y-axis is used. In addition, the acceleration sensor can be configured to detect only one of the acceleration of the X-axis and the Y-axis. In addition, an example is shown in which the interval of repeated sensing detection is appropriately set in order to reduce the power consumption of the signal processing unit 2, but the present disclosure is not limited to this. Even if the interval is arbitrary, only the change amount is generated.

[0265] As described above, if the sensing interval is arbitrary, a fluctuation occurs. Taking the X-axis as an example, the average value fluctuates by about ±1G. Fig.9A In the example, the influence of the variation is illustrated. Assume that the sensor angle is 0 degrees when there is no variation and the average value of the acceleration is 3G. However, if the variation is to become -1G, the average value of the acceleration may become 2G. The sensor angle at which the average value of the acceleration is 2G becomes around 40 degrees. In this way, the difference between 0 degrees and 40 degrees becomes the error of the sensor angle. In other words, it is difficult to reliably judge the looseness of the nut before the looseness of the sensor angle exceeds 40 degrees to a certain extent. Therefore, the robustness of the system is reduced.

[0266] When the acceleration sensor 1 detects only one of the X-axis and the Y-axis, two candidates for the rotation angle of the nut 240 are detected, so the rotation angle is not determined, but the change in the rotation angle during each sensing period can be detected. Therefore, based on the fact that the change is small, it can be detected that the nut 240 is not loose.

[0267] Specifically, based on the situation that the X-axis acceleration is 0G (or the Y-axis acceleration is 3G), the rotation angle of the nut 240 is detected to be around 90 degrees or around 270 degrees, and the rotation angle is also detected to be around 90 degrees or around 270 degrees in the subsequent sensing detection. In this case, it can be determined that the change in the rotation angle is 0 (small), and therefore, it is detected that the nut 240 is not loose. Alternatively, the looseness of the nut 240 can be detected based on the difference in the rotation angle detected in multiple consecutive sensing detections.

[0268] (Variant 5)

[0269] Furthermore, as a modification of the first embodiment, the looseness of the nut 240 may be detected based on the difference between the X-axis acceleration and the Y-axis acceleration. Fig.39It is a coordinate graph showing the average value of the difference between the X-axis acceleration and the Y-axis acceleration when the centrifugal force is 3G, 6G, and 10G, respectively. For example, when the centrifugal force is detected to be 10G based on the speed of the vehicle 200 and the difference is 0G, the rotation angle of the nut 240 is detected to be around 50 degrees or around 225 degrees. In addition, when the centrifugal force is detected to be 10G and the difference is -10G, the rotation angle of the nut 240 is detected to be around 90 degrees or around 175 degrees.

[0270] In addition, in the above-mentioned first to fifth embodiments, an example of detecting the tightening state of the nut 240 provided on the wheel 220 of the vehicle 200 is shown, but the present disclosure is not limited to this. For example, it is also possible to detect the tightening state of a tightening member such as a nut installed on a pulley of an elevator, a pulley of a conveyor belt, a coffee cup and a carousel equipped in an amusement park, and a rotating amusement equipment equipped in a park. In addition, in the above-mentioned example, in the case of a rotating body rotating along a plane perpendicular to gravity, the centrifugal force is not affected by gravity, so the tightening state of the tightening member can be easily detected even when the centrifugal acceleration is small.

[0271] In addition, in the first embodiment described above, an example of detecting the tightening state (looseness) of the nut 240 based on the change in the rotation angle of the nut 240 is shown, but the present disclosure is not limited thereto. The tightening state (looseness) of the nut 240 may also be detected based on the comparison between the change in the X-axis acceleration (average X-axis acceleration) and the Y-axis acceleration (average Y-axis acceleration) and a predetermined threshold value.

[0272] In addition, in the above embodiment, when information A indicating that the nut 240 has rotated in the tightening direction by more than a predetermined angle is obtained, the above information A is ignored and the tightening state of the nut 240 is detected, but the present disclosure is not limited to this. Alternatively, when information indicating that the nut 240 has rotated in the tightening direction by less than the predetermined angle is obtained, the above information is also ignored and the tightening state of the nut 240 is detected.

[0273] In addition, in the above embodiment, when the information A is obtained in a state where the nut 240 is not loosened for a constant time or more, the example of ignoring the information A and detecting the tightening state of the nut 240 is shown, but the present disclosure is not limited to this. Alternatively, when the information A is obtained in a state where the looseness of the nut 240 is detected within a constant time, the information A is also ignored and the tightening state of the nut 240 is detected.

[0274] In addition, in the above embodiment, the following example is shown: when information B indicating that the nut 240 has rotated in the loosening direction by a rotation angle equal to the rotation angle in the tightening direction is obtained just after the above information A is obtained, the above information A is ignored and the tightening state of the nut 240 is detected, but the present disclosure is not limited to this. Alternatively, when information indicating that the nut 240 has rotated in the loosening direction by a rotation angle different from the rotation angle in the tightening direction is obtained just after the above information A is obtained, the above information is ignored and the tightening state of the nut 240 is detected.

[0275] In addition, in the above embodiment, the following example is shown: when the centrifugal acceleration of the wheel 220 is greater than a predetermined value, the process of detecting the tightening state of the nut 240 is performed, but the present disclosure is not limited to this. It is also possible that the process of detecting the tightening state of the nut 240 is performed even if the centrifugal acceleration of the wheel 220 is less than the predetermined value.

[0276] In the above embodiment, an example is shown in which the plane provided with the X-axis and the Y-axis is orthogonal to the rotation axis O of the wheel 220, but the present disclosure is not limited thereto. The plane may intersect the rotation axis O instead of being orthogonal.

[0277] In addition, in the third and fourth embodiments described above, an example of using the arctangent function to detect the tightening state of the nut 240 is shown, but the present disclosure is not limited thereto. The tightening state of the nut 240 may also be detected using an arcsine function (arcsin), an arccosine function (arccos), an arccotangent function (arccot), an arccosecant function (arccsc), and an arcsecant function (arcsec).

[0278] Furthermore, in the above-described embodiment, the number of sensor devices for one wheel 220 may be appropriately changed as long as it is one or more.

[0279] In the fourth embodiment described above, an example of detecting the tightening state (looseness) of the nut 240 based on the change in the rotation angle of the nut 240 is shown, but the present disclosure is not limited thereto. Alternatively, the tightening state (looseness) of the nut 240 may be detected based on a comparison between the change in at least one of the X-axis normalized value and the Y-axis normalized value and a predetermined threshold value.

[0280] In addition, in the fourth embodiment, an example is shown in which the rotation angle of the nut 240 is detected based on both the X-axis normalized value and the Y-axis normalized value, but the present disclosure is not limited to this. The tightening state (the amount of change in the rotation angle) of the nut 240 may also be detected based on only one of the X-axis normalized value and the Y-axis normalized value.

[0281] In addition, in the above-mentioned first to fifth embodiments, an example in which the sensor device is provided on the nut 240 is shown, but the present disclosure is not limited to this. Alternatively, the sensor device may be provided on a bolt (a bolt separated from the wheel hub). In this case, unlike the above-mentioned embodiment in which the wheel is fastened to the wheel hub by a wheel nut, the wheel is fastened to the wheel hub by a bolt. The bolt in this case is an example of a "fastening member" of the present disclosure.

[0282] In addition, in the above-mentioned first to fifth embodiments, an example is shown in which the tightening state of the nut 240 is detected by the signal processing unit provided in the sensor device, but the present disclosure is not limited to this. For example, the detection value of the acceleration sensor 1 may be sent to the ECU (Electronic Control Unit) provided in the vehicle 200 through the communication unit 3, and the ECU may detect the tightening state of the nut 240 based on the detection value. In this case, the ECU is equivalent to one form of the "detection device" of the present disclosure.

[0283] In addition, in the above-mentioned first to fifth embodiments, an example is shown in which the tightening state of the nut 240 is detected based on the average value of the acceleration of two times acquired during one rotation of the wheel 220, but the present disclosure is not limited to this. It is also possible to detect the tightening state of the nut 240 based on the average value of the acceleration of an even number of times (4 times, 6 times, 8 times, ...) other than twice acquired during one rotation of the wheel 220. In addition, the fewer the number of times, the lower the possibility of deviation of the measurement position caused by rotation (reducing the influence of deviation), and the tightening state of the nut 240 can be detected more accurately. In addition, it is also possible not to use the average value of the acceleration of two times (even times) to detect the tightening state of the nut 240 as in the above-mentioned first to fifth embodiments. That is, it is also possible to detect the tightening state based on the acceleration (one time) acquired in each sensor detection.

[0284] The above-described embodiment and the above-described modified examples can be appropriately combined within a range where no technical contradiction occurs.

[0285] The embodiments disclosed this time should be considered to be illustrative in all aspects and not restrictive. The scope of the present disclosure is indicated by the claims rather than the above description, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0286] Description of Reference Numerals

[0287] 1, 1a...acceleration sensor (acceleration detection unit); 2, 12, 22, 32, 42...signal processing unit (state detection unit); 2c, 12c, 22c, 32c...fastening state detection unit; 2d...acquisition unit; 42c...state determination unit (fastening state detection unit); 100, 300, 400, 500, 600...sensor device (detection device); 220...wheel (rotating body); 240, 340, 440, 540...nut (fastening member); 250a...wheel hub (fastened member) (body); O...rotation axis; X...axis line (first axis line); Y...axis line (second axis line).

Claims

1. A detection device, characterized in that: have: an acceleration detection unit that rotates in conjunction with the rotation of a fastening member that fastens the fastened member to the rotating body and detects acceleration along at least one detection axis that intersects the rotation axis of the rotating body; as well as A state detection section detects a fastened state of the fastening member based on the acceleration detected by the acceleration detection section.

2. The detection device according to claim 1, characterized in that: The detection axis includes a plurality of detection axes respectively intersecting the rotation axis.

3. The detection device according to claim 2, characterized in that: The plurality of detection axes include the first axis and a second axis intersecting the first axis on a plane intersecting the rotation axis.

4. The detection device according to any one of claims 1 to 3, characterized in that: The state detection section detects a fastened state of the fastening member based on the acceleration detected by the acceleration detection section and the centrifugal acceleration applied to the rotating body.

5. The detection device according to claim 3, characterized in that: The state detection unit detects the fastening state of the fastening member based on an acceleration index indicating a ratio between the first axis acceleration detected by the acceleration detection unit and the second axis acceleration detected by the acceleration detection unit.

6. The detection device according to claim 5, characterized in that: The acceleration index includes at least one of a first-axis normalized value obtained by normalizing the first-axis acceleration and a second-axis normalized value obtained by normalizing the second-axis acceleration.

7. The detection device according to any one of claims 1 to 3, characterized in that: The state detection unit determines that the fastening state of the fastening member has changed when the sign of the acceleration detected by the acceleration detection unit is reversed.

8. The detection device according to any one of claims 1 to 3, characterized in that: The acceleration detection unit detects acceleration at each predetermined period. The state detection unit determines whether the rotation of the rotating body has stopped, and, if it is determined that the rotation of the rotating body has stopped, extends the predetermined period longer than the rotation time of the rotating body.

9. The detection device according to any one of claims 1 to 3, characterized in that: The acceleration detection unit is provided on a nut that fixes the wheel to the vehicle body.

10. The detection device according to any one of claims 1 to 3, characterized in that: The state detection unit acquires the acceleration information at each predetermined period in a manner such that the acceleration information detected by the acceleration detection unit is acquired an even number of times during one rotation of the rotating body, and detects the fastening state of the fastening member based on an average value of the acceleration acquired the even number of times or based on an average value of the angles of the fastening member calculated based on each of the accelerations acquired the even number of times.

11. The detection device according to claim 10, characterized in that: The state detection unit detects the fastened state of the fastening member when the centrifugal acceleration of the rotating body is equal to or greater than a predetermined value, and acquires the acceleration information at each predetermined period obtained based on the rotation speed of the rotating body corresponding to the predetermined value.

12. A state detection device for detecting a fastening state of a fastening member based on acceleration detected by an acceleration detection unit that rotates in conjunction with the rotation of a fastening member fastening the fastened member to a rotating body, The state detection device is characterized by comprising: an acquisition unit that acquires information based on the acceleration along a detection axis that intersects the rotation axis of the rotating body; and A fastening state detection unit detects a fastening state of the fastening member based on the information acquired by the acquisition unit.

13. A detection method, comprising a detection device including an acceleration detection unit that rotates in conjunction with the rotation of a fastening member that fastens the fastened member to a rotating body, characterized in that: The following processes are available: detecting, by the acceleration detection unit, an acceleration along a detection axis intersecting the rotation axis of the rotating body; and Based on the acceleration detected by the acceleration detection portion, a fastened state of the fastening member is detected.

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