Detection device, state detection device, and detection method

Abstract

A sensor device (100) (detection device) comprises: an acceleration sensor (1) (acceleration detection unit) that rotates in conjunction with the rotation of a nut (240) (fastening member) that fastens a wheel hub (250a) (fastened member) to a wheel (220) (rotating body), and detects acceleration along a detection axis (X) (Y) that intersects with a rotation shaft (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

Detection device, state detection device, and detection method

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

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

[0003] Japanese Patent Application Laid-Open No. 2005-329907

[0004] In a device for detecting the mounting state of a tire (a fastening member that fastens a wheel), there is a demand for a technique that can more easily detect the mounting state of the tire (a fastening member that fastens a wheel).

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

[0006] A detection device according to a first aspect of the present disclosure includes an acceleration detection unit that rotates in conjunction with the rotation of a fastening member that fastens a fastened member to a rotating body and detects acceleration along at least one detection axis that intersects with 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 according to the first aspect of the present disclosure, as described above, the fastening state of the fastening member is detected based on the acceleration detected by the acceleration detection unit. This makes it possible to detect the fastening state of the fastening member based on the acceleration of the fastening member. Here, the acceleration of the fastening member is determined based on the centrifugal acceleration of the rotating body and the rotation angle of the fastening member, but does not change depending on the type, size, etc. of the rotating body. Therefore, the fastening state of the fastening member can be detected regardless of the type, size, etc. of the rotating body. This makes it possible to easily detect the fastening state of the fastening member.

[0008] A state detection device according to a second aspect of the present disclosure is a state detection device that detects the fastening state of a fastening member based on acceleration detected by an acceleration detection unit that rotates in conjunction with the rotation of the fastening member that fastens a fastened member to a rotating body, and includes an acquisition unit that acquires information based on the acceleration along a detection axis that intersects with the rotation axis of the rotating body, and a fastening state detection unit that detects the fastening state of the fastening member based on the 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 fastening state of the fastening member is detected based on the acceleration detected by the acceleration detection unit, thereby providing a state detection device that can easily detect the fastening state of the fastening member.

[0010] A detection method according to a third aspect of the present disclosure is a detection method for a detection device having an acceleration detection unit that rotates in conjunction with the rotation of a fastening member that fastens a fastened member to a rotating body, and includes a step of detecting acceleration along a detection axis that intersects with the rotation axis of the rotating body using the acceleration detection unit, and a step of 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 fastening state of the fastening member is detected based on the acceleration detected by the acceleration detection unit, thereby providing a detection method that can easily detect the fastening state of the fastening member.

[0012] According to the present disclosure, the fastening state of a fastening member that fastens a rotating body such as a wheel can be easily detected.

[0013] 5 is a diagram showing a vehicle provided with a sensor device according to the first to fifth embodiments. FIG. 6 is a cross-sectional view of a nut according to the first embodiment. FIG. 7 is a diagram showing the configuration of the sensor device according to the first embodiment. FIG. 8 is a functional block diagram of a signal processing unit according to the first embodiment. FIG. 9 is a front view showing the configuration of a vehicle tire (initial state). FIG. 10 is a diagram showing the relationship between X-axis acceleration and Y-axis acceleration and centrifugal acceleration. FIG. 11 is a diagram showing the relationship between acceleration and wheel angle when centrifugal force is 0. FIG. 12 is a diagram showing the relationship between acceleration and wheel angle when centrifugal force is 3 G. FIG. 13 is a diagram showing the relationship between the average value of acceleration and sensor angle when centrifugal force is 3 G. FIG. 14 is a diagram showing the relationship between the average value of acceleration and sensor angle when centrifugal force is 10 G. FIG. 15 is a flowchart showing the control flow of the sensor device according to the first embodiment. FIG. 16 is a diagram showing the configuration of a sensor device according to the second embodiment. FIG. 17 is a front view showing the configuration of a tire when the sensor device has rotated from the state of FIG. 5. FIG. 18 is a diagram showing a first example of waveforms of X-axis normalized values, Y-axis normalized values, and centrifugal acceleration. FIG. 19 is a flowchart showing the processing flow of the sensor device according to the second embodiment. FIG. 19 is a diagram for explaining that the direction of centrifugal acceleration is detected as being shifted due to the influence of gravitational acceleration. FIG. 19 is a diagram showing the configuration of a sensor device according to the third embodiment. 1 is a flow chart showing the processing flow of a sensor device according to a third embodiment. FIG. 2 is a diagram showing the configuration of a sensor device according to a fourth embodiment. FIG. 3 is a diagram showing the relationship between acceleration and wheel rotation angle when a centrifugal force is 6 G. FIG. 4 is a diagram showing the relationship between acceleration and wheel angle when a centrifugal force is 6 G with the nut loosened. FIG. 5 is a diagram showing the relationship between the average value of acceleration and sensor angle when a centrifugal force is 6 G. FIG. 6 is a diagram showing the relationship between the average value of acceleration and sensor angle when a centrifugal force is 10 G. FIG. 7 is a diagram showing a second example of waveforms of X-axis normalized values, Y-axis normalized values, and centrifugal acceleration. FIG. 8 is a diagram showing waveforms of X-axis normalized values, Y-axis normalized values, and arctangent functions. FIG. 9 is a flow chart showing processing of a sensor device according to a fourth embodiment. FIG. 10 is a diagram showing the configuration of a sensor device according to a fifth embodiment. FIG. 11 is a front view showing the configuration of a tire of a vehicle according to the fifth embodiment. FIG. 12 is a first diagram showing the relationship between centrifugal acceleration and acceleration detected by an acceleration sensor. FIG. 13 is a second diagram showing the relationship between centrifugal acceleration and acceleration detected by an acceleration sensor.34 is a diagram showing an example of functional blocks configured in a signal processing unit according to a fifth embodiment. FIG. 35 is a flowchart showing an example of processing executed by the signal processing unit according to the fifth embodiment. FIG. 36 is a flowchart showing processing of an initial value setting routine executed by the signal processing unit in Modification 1 of the fifth embodiment. FIG. 37 is a flowchart showing an example of processing executed by the signal processing unit in Modification 1 of the fifth embodiment. FIG. 38 is a side view showing a state in which a wheel is fastened to a wheel hub in Modification 3. FIG. 39 is a cross-sectional view of a fastening portion of a wheel according to Modification 4. FIG. 39 is a diagram showing a modification of FIG. 34. FIG. 39 is a cross-sectional view of a fastening portion using a loosening detection device in a comparative example. FIG. 39 is a diagram showing a state in which a night cap is attached to a wheel nut in a comparative example. FIG. 39 is a diagram explaining individual differences in bolt axial length. FIG. 40 is a diagram showing the relationship between the sensor angle and the average value of the difference between X-axis acceleration and Y-axis acceleration for each different centrifugal force according to Modification 5 of the first embodiment.

[0014] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals, and description thereof will not be repeated.

[0015] [First embodiment] Fig. 1 is a diagram showing a vehicle 200 equipped with a sensor device 100 (see Fig. 2) according to a first embodiment. The vehicle 200 includes a plurality of wheels 210. The vehicle 200 also includes a communication terminal 201 (multi-information display) that can communicate with a communication unit 3 (described below) and that includes a display unit (not shown). The sensor device 100 is an example of a "detection device" in the present disclosure.

[0016] The wheel 210 includes a wheel 220 and a tire 230 attached to the wheel 220. The wheel 220 is fastened to a wheel hub 250a (see FIG. 2) by a plurality of nuts 240 (five in FIG. 1). The number of nuts 240 is not limited to the above example. The wheel hub 250a is an example of a "fastened member" and a "vehicle body" in the present disclosure. The wheel 220 and the nuts 240 are an example of a "rotating body" and a "fastening member" in the present disclosure, respectively.

[0017] 2, nuts 240 fasten bolts 250 to wheel 220. Specifically, wheel 220 is provided with a plurality of (five) wheel holes 221 into which bolts 250 are inserted (pass through). Nuts 240 fasten bolts 250 inserted into wheel holes 221 to wheel 220. Bolts 250 are fixed to wheel hub 250a.

[0018] FIG. 2 shows an example of a double tire, where a wheel 220 consists of an inner wheel 222 and an outer wheel 223 .

[0019] One side of the nut 240 is open. A nut cap 241 is attached to the nut 240. The sensor device 100 is indirectly provided to the nut 240 by being attached to the nut cap 241. Therefore, the sensor device 100 rotates in conjunction with the rotation of the nut 240 (nut cap 241).

[0020] Specifically, the nut cap 241 includes a ceiling portion 241a and a side portion 241b. The side portion 241b is provided so as to circumferentially surround the portion of the bolt 250 that passes through the wheel hole 221. The ceiling portion 241a is provided so as to face the tip portion 251 of the bolt 250 (in the insertion direction of the bolt 250). The ceiling portion 241a is provided continuously with the side portion 241b. A washer 243 may be provided between the nut 240 and the wheel 220.

[0021] The sensor device 100 is attached (adhered) to the inner surface 241c of the ceiling portion 241a of the nut cap 241. Therefore, the sensor device 100 is disposed in the space S of the nut cap 241 in which the bolt 250 is housed.

[0022] The sensor device 100 is provided on some of the nuts 240 provided on each wheel 210. The sensor device 100 may be provided on all of the nuts 240 provided on each wheel 210.

[0023] 3, the sensor device 100 includes an acceleration sensor 1, a signal processing unit 2, a communication unit 3, and a power supply unit 4. The acceleration sensor 1 is an example of an "acceleration detection unit" in the present disclosure. The signal processing unit 2 is an example of a "state detection unit" and a "state detection device" in the present disclosure.

[0024] As shown in FIG. 5 , the acceleration sensor 1 detects accelerations along the X-axis and Y-axis, which are orthogonal to each other, in a plane perpendicular to the rotation axis O of the wheel 220 (the axis extending in a direction perpendicular to the paper surface of FIG. 5 / the rotation axis of the wheel hub 250a). The acceleration detected by the acceleration sensor 1 has a positive or negative magnitude (direction). The arrows indicating the X-axis and Y-axis in FIG. 5 indicate the positive directions of the X-axis and Y-axis, respectively. Note that, when viewed from the paper surface of FIG. 5 , the positive direction of the Y-axis is the direction rotated 90 degrees counterclockwise with respect to the X-axis. The X-axis and Y-axis are examples of the "first axis" and "second axis" of the present disclosure, respectively.

[0025] The Z direction in FIG. 5 indicates the vertical direction (up-down direction). In this embodiment, the nut 240 (nut 240A) is fixed so that the positive direction of the X axis of the acceleration sensor 1 faces upward (Z1 direction) in the initial state (when the nut 240A is not loose). The positive direction of the X axis of the acceleration sensor 1 may face a direction other than the Z1 direction in the initial state. In FIG. 5 , the nut 240 located closest to the Z1 side among the five nuts 240 is referred to as nut 240A. In the following description, when the orientation of the sensor device 100 is as shown in FIG. 5 , the angle (rotation angle) of the sensor device 100 is set to 0 degrees, and the clockwise rotation direction of the sensor device 100 is set to positive.

[0026] 6, the centrifugal acceleration acting on the nut 240A is divided into X-axis acceleration and Y-axis acceleration. In other words, the vector sum of the X-axis acceleration and the Y-axis acceleration becomes the centrifugal acceleration.

[0027] The signal processing unit 2 detects the state (fastened state) of the nut 240 based on the detection signal from the acceleration sensor 1. The signal processing unit 2 includes a centrifugal acceleration calculation unit 2a (see FIG. 4), a rotation angle calculation unit 2b (see FIG. 4), a fastened state detection unit 2c (see FIG. 4), and an acquisition unit 2d (see FIG. 4). Note that the centrifugal acceleration calculation unit 2a, the rotation angle calculation unit 2b, and the fastened state detection unit 2c shown in FIG. 4 each represent software in which the functional features of the signal processing unit 2 are divided into blocks. The acquisition unit 2d may be, for example, a terminal that receives a signal including information about the detection value detected by the acceleration sensor 1. Details of each function will be described later.

[0028] The signal processing unit 2 also acquires speed information of the vehicle 200 (rotation speed of the wheels 220 ) from a processing device (not shown) provided in the vehicle 200 .

[0029] The communication unit 3 transmits the processing result of the signal processing unit 2 or information based on the processing result to the communication terminal 201 (see FIG. 1) of the vehicle 200 by wireless communication.

[0030] The power supply unit 4 supplies power to the acceleration sensor 1, the signal processing unit 2, and the communication unit 3. The acceleration sensor 1 detects X-axis acceleration and Y-axis acceleration every 100 to 200 ms (for example, every 150 ms). The power supply unit 4 is, for example, a lithium-ion battery, and has a limited amount of power storage capacity. In order to reduce the power consumption of the signal processing unit 2, the acceleration sensor 1 does not constantly detect acceleration, but instead repeatedly at predetermined intervals.

[0031] The acceleration sensor 1 detects X-axis acceleration (Xg), which is an acceleration (vector) along the X axis, and Y-axis acceleration (Yg), which is an acceleration (vector) along the Y axis. Each of the X-axis acceleration and the Y-axis acceleration is expressed by a G value (a value where the acceleration of gravity is 1 G).

[0032] FIG. 7 is a graph 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 fluctuate sinusoidally within a range of ±1 G. This is because the X-axis and the Y-axis each contain only an acceleration component based on the gravitational acceleration acting in the Z2 direction. FIG. 7 also shows the results of the sensor device 100 provided on the nut 240A shown in FIG. 5. The horizontal axis of FIG. 7 and FIG. 8 represents the tire rotation angle, and the clockwise rotation direction of the tire 230 shown in FIG. 5 is taken as positive.

[0033] FIG. 8 is a graph showing the relationship between the rotation angle of the tire 230 (wheel 220) and the X-axis acceleration and Y-axis acceleration when a centrifugal force of 3G acts on the nut 240 at a predetermined vehicle speed. Note that in this disclosure, the magnitude of the centrifugal force may be indicated by a G value. In the Y-axis orientation shown in FIG. 5 , no centrifugal force component is applied to the Y-axis, so the Y-axis acceleration remains unchanged from that shown in FIG. 7 . Meanwhile, a centrifugal force component is applied to the X-axis, so the X-axis acceleration is the X-axis acceleration in FIG. 7 plus 3G. The waveform of the difference between the X-axis acceleration and the Y-axis acceleration (see the dashed dotted line in FIG. 7 ) is a sine wave fluctuating ±1.41G around 3G. FIG. 8 also shows the results of the sensor device 100 provided on the nut 240A shown in FIG. 5 .

[0034] FIG. 9A is a graph showing the average value of acceleration versus the angle (rotation angle) of the sensor device 100 when the centrifugal force is 3 G. FIG. 9B is a graph showing the average value of acceleration versus the angle (rotation angle) of the sensor device 100 when the centrifugal force is 10 G. For example, the values ​​of each waveform at the point where the sensor angle is 0 in FIG. 9A represent the average values ​​of each waveform shown in FIG. 8. Note that the average values ​​in FIGS. 9A and 9B correspond to one cycle of one rotation of the tire 230. However, as mentioned above, in reality, it is desirable to repeatedly perform sensing at predetermined intervals to reduce the power consumption of the signal processing unit 2. When the vehicle speed is constant, the average value of the results of a significant number of repetitions (e.g., 50 or more) is likely to approach the average value for one cycle of one rotation of the tire 230.

[0035] 9A and 9B, 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 centrifugal force (although the vertical scales are different), but have the same shape. Therefore, it is possible to obtain information about 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 given time. Specific examples are shown below.

[0036] For example, assume that the X-axis acceleration (average X-axis acceleration, described below), the Y-axis acceleration (average Y-axis acceleration, described below), and the difference between the X-axis acceleration and the Y-axis acceleration (average X-axis acceleration and average Y-axis acceleration, described below) are 0 G, 3 G, and -3 G, respectively. Furthermore, assume that the signal processing unit 2 detects that the centrifugal force (centrifugal acceleration) acting on the sensor device 100 is 3 G based on the acquired vehicle speed information. In this case, the signal processing unit 2 detects that the angle (rotation angle) of the sensor device 100 is near 90 degrees based on the graph of FIG. 9A , which corresponds to the case where the centrifugal force is 3 G. Note that the term "nearby" is used because each waveform in FIG. 9A indicates the average value of each acceleration. Specifically, each of the X-axis acceleration and the Y-axis acceleration may fluctuate within a range of ±1 G from the average value. Furthermore, the difference between the X-axis acceleration and the Y-axis acceleration may fluctuate within a range of ±1.41 G from the average value.

[0037] In other words, when information on the rotation angle of the nut 240 (sensor device 100) is obtained based on at least two of the X-axis acceleration, Y-axis acceleration, and the difference between the X-axis acceleration and the Y-axis acceleration at any timing, the fluctuation range is included.

[0038] As mentioned above, it is desirable to repeatedly execute sensing at predetermined intervals to reduce the power consumption of the signal processing unit 2. By appropriately setting the repetition interval, the aforementioned fluctuations (specifically, ±1 G for each of the X-axis acceleration and Y-axis acceleration, and ±1.41 G for the difference between the X-axis acceleration and the Y-axis acceleration) can be ignored or significantly reduced. As a result, the angle (rotation angle) of the sensor device 100 can be accurately determined.

[0039] Therefore, the signal processing unit 2 acquires information on the X-axis acceleration and the Y-axis acceleration at a sensing period (for example, 150 ms as described above) corresponding to one rotation of the wheel 220. Note that the above period is a period in which the acceleration information detected by the acceleration sensor 1 is acquired twice while the wheel 220 rotates once (one rotation in 300 ms in this case). In other words, the acceleration information is acquired every time the wheel 220 rotates half a rotation.

[0040] In the above example, the X-axis acceleration, Y-axis acceleration, and the difference between the X-axis acceleration and the Y-axis acceleration were 0 G, 3 G, and -3 G, respectively. If acceleration information is acquired at any timing, it can be 0±1 G, 3±1 G, and -3±1.41 G, respectively. However, if acceleration information is acquired every half rotation of the wheel 220, the fluctuation will be zero. For example, if acceleration information is acquired at each of 90 degrees and 270 degrees in FIG. 8, the fluctuation will be zero (the fluctuation can be ignored). Note that 90 degrees and 270 degrees are one of the conditions for every half rotation of the wheel 220. The angular difference between the two points needs to be 180 degrees. In other words, accelerations at two points, 45 degrees and 225 degrees, or accelerations at two points, 60 degrees and 240 degrees, may also be acquired.

[0041] The example in Fig. 8 is the point in Fig. 9A where the sensor angle is 0 degrees (when the orientation of the sensor device 100 is in the state shown in Fig. 5). Therefore, the case where the sensor angle is 0 degrees will be explained again with reference to Fig. 8. It is clear from Fig. 8 that the X-axis acceleration, Y-axis acceleration, and the difference between the X-axis acceleration and the Y-axis acceleration can be 3±1 G, 0±1 G, and 3±1.41 G, respectively.

[0042] If acceleration information is acquired at the 90-degree point in Figure 8, 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. Averaging the results at these two points, the X-axis acceleration, Y-axis acceleration, and the difference are 3G, 0G, and 3G, respectively. This value is equal to the result at the 0-degree sensor angle in Figure 9A. In other words, the average value for one cycle in Figure 8 is equal to the average value of two accelerations detected by the acceleration sensor 1 every half rotation of the wheel 220.

[0043] The interval of each half rotation of the wheel 220 is an appropriate interval set to reduce the power consumption of the signal processing unit 2. Specifically, the interval is the shortest detection timing by the acceleration sensor 1 for determining the sensor angle. Using this detection timing, the sensor angle (the rotation angle of the nut 240) can be accurately determined.

[0044] The waveform data as shown in FIGS. 9A and 9B may be stored in a storage device (not shown) for each different centrifugal force (for each vehicle speed).

[0045] In the above example, the signal processing unit 2 detects that the centrifugal force (centrifugal acceleration) acting on the sensor device 100 is 3 G based on the acquired vehicle speed information, and calculates the angle (rotation angle) of the sensor device 100 based on the graph (see FIG. 9A) corresponding to the case where the centrifugal force is 3 G. However, without vehicle speed information, it is not possible to calculate the angle based on the graph.

[0046] For example, an example will be given using only the X-axis acceleration sensor. When a centrifugal force (centrifugal acceleration) of 3 G occurs, the sensor angle is estimated to be 0 degrees from FIG. 9A. On the other hand, when a centrifugal force (centrifugal acceleration) of 10 G occurs, the sensor angle is estimated to be around 70 degrees or 290 degrees based on FIG. 9A. In other words, if the centrifugal force (centrifugal acceleration, in this case synonymous with vehicle speed) that can occur is not known, the calculated angle will be different, and it will be impossible to determine whether the nut is loose. When vehicle speed cannot be obtained, the sensor angle can be calculated even without vehicle speed information by using the ratio of acceleration information (including calculation results such as differences) of multiple axes, as described below.

[0047] 9A and 9B, the waveforms have the same shape, although the scales of the vertical axes are different. When there is no change in the mounting method of the sensor device 100 (i.e., when there is no loosening), even if the centrifugal force acting on the sensor due to a difference in vehicle speed differs, the relationship between the average acceleration and the sensor angle as shown in FIGS. 9A and 9B will be similar.

[0048] A specific explanation will be given with reference to Figures 9A and 9B. In Figure 9A, when the sensor angle is 20 degrees (near the intersection of the dashed line and the dashed-dotted line), the X-axis acceleration, Y-axis acceleration, and the difference between the X-axis acceleration and the Y-axis acceleration are 2.6 G, 1.3 G, and 1.3 G, respectively. In Figure 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 8.6 G, 4.3 G, and 4.3 G, respectively. Each value in Figure 9B is approximately 3.3 times the value in Figure 9A, and it can be seen that the ratio is similar, with a 2:1:1 ratio. As such, even if the generated centrifugal force (i.e., vehicle speed) is different, the acceleration ratio obtained by the sensor remains the same. Using this ratio, the sensor angle (rotation angle of nut 240) can be calculated even without vehicle speed information.

[0049] Furthermore, the signal processing unit 2 (fastened state detection unit 2c) detects the fastened state of the nut 240 based on the difference between the currently calculated rotation angle of the nut 240 and the previous rotation angle of the nut 240. If the difference is outside a predetermined tolerance, the signal processing unit 2 (fastened state detection unit 2c) determines that the nut 240 is loose. In this case, the signal processing unit 2 notifies the communication terminal 201 (see FIG. 1) via the communication unit 3 (see FIG. 3) that the nut 240 is loose. As a result, a warning may be displayed on a display unit (not shown) of the communication terminal 201, or the communication terminal 201 may emit a warning sound. On the other hand, if the difference is within a predetermined tolerance, the signal processing unit 2 (fastened 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. Furthermore, the previously calculated rotation angle may be the previous rotation angle or the average value of the past several rotation angles including the previous rotation angle.

[0050] Furthermore, the signal processing unit 2 (fastening state detection unit 2c) determines that the rotation of the wheel 220 (tire 230) has stopped if the current detection value and the previous detection value of the calculated average X-axis acceleration and average Y-axis acceleration, whichever has the larger absolute value, are each within a range of ±1 G. The previous detection value may be the previous detection value or an average of the previous several detection values ​​including the previous detection value. The stop of rotation of the wheel 220 (tire 230) may also be determined based on either the X-axis acceleration or the Y-axis acceleration. The stop of rotation of the wheel 220 (tire 230) may also be determined if the current detection value and the previous detection value of both the X-axis acceleration and the Y-axis acceleration are each within a range of ±1 G.

[0051] The nut 240 often loosens when vibrations or external forces are applied to the wheel 220 or the nut 240, and is expected to do so when the wheel hub 250a (wheel 220) is rotating while the vehicle 200 is traveling. When the vehicle 200 is stopped and the wheel hub 250a (wheel 220) is not rotating, it is extremely rare for the nut 240 to loosen. Therefore, when the signal processing unit 2 determines that the wheel 220 (tire 230) is not rotating, it performs processing to lengthen the sensing cycle (the above-mentioned predetermined time) by the sensor device 100 (to a 30-minute cycle, for example).

[0052] Furthermore, the signal processing unit 2 acquires information about the initial value of the rotation angle of the nut 240. The signal processing unit 2 acquires the initial value, for example, based on pressing a predetermined button 201a (see FIG. 1 ) on the communication terminal 201. Specifically, the signal processing unit 2 sets the initial value to the rotation angle of the nut 240 when the vehicle 200 starts traveling after the button is pressed (or a predetermined time after the vehicle starts traveling). Note that the button 201a is preferably pressed, for example, when the tire 230 (wheel 220) is attached to the wheel hub 250a and the nut 240 is fastened with a predetermined tightening torque. A button having the function of the button 201a may be provided in the sensor device 100. The communication unit 3 of the sensor device 100 may be capable of bidirectional communication with the ECU of the vehicle 200. In this case, the information about the initial value may be stored in the signal processing unit 2.

[0053] Furthermore, the signal processing unit 2 (fastened state detection unit 2c) detects the fastened state of the nut 240 based on the difference between the current rotation angle of the nut 240 and the initial value. Specifically, the signal processing unit 2 (fastened state detection unit 2c) determines that the nut 240 is loose (not fastened) when the difference falls outside a predetermined tolerance range. In this case, the signal processing unit 2 notifies the communication terminal 201 (see FIG. 1) via the communication unit 3 (see FIG. 3) that the nut 240 is loose. As a result, a warning may be displayed on a display unit (not shown) of the communication terminal 201, or a warning sound may be emitted from the communication terminal 201.

[0054] Note that the signal processing unit 2 does not have to acquire the initial value based on pressing the predetermined button 201a. For example, when the signal processing unit 2 detects that the vehicle 200 has stopped using the above method, it may detect that the rotation angle of the nut 240 (for at least one wheel 210) has changed before and after the vehicle has stopped. 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 angles detected in multiple sensing operations after the change) as the initial value. This is because a change in the rotation angle before and after the vehicle has stopped means that the tire 230 has been replaced or the nut 240 has been retightened.

[0055] Furthermore, when the signal processing unit 2 (fastened state detection unit 2c) acquires information A indicating that the nut 240 has rotated in the fastening direction, it detects the fastened state of the nut 240, ignoring (removing) the information A. Specifically, the information A includes information indicating that the nut 240 has rotated in the fastening direction by a predetermined angle or more (for example, 30 degrees or more).

[0056] In detail, when information indicating that the nut 240 has rotated in the tightening direction by a predetermined angle or more is acquired as described above, and when the information A is acquired while the nut 240 has not loosened for a certain period of time or more (for example, 10 minutes or more), the signal processing unit 2 (fastened state detection unit 2c) ignores the information A and detects the fastened state of the nut 240. Note that the fact that the nut 240 is not loosened 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.

[0057] More specifically, if the signal processing unit 2 (fastened state detection unit 2c) receives 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 immediately after receiving information indicating that the nut 240 has rotated in the tightening direction by more than a predetermined angle while the nut 240 has not been loosened for a certain period of time, the signal processing unit 2 (fastened state detection unit 2c) will ignore information A and detect the fastened state of the nut 240. Here, the angle equal to the rotation angle in the tightening direction may be within a range of ±X degrees (e.g., 5 degrees) centered on the rotation angle in the tightening direction. Therefore, if the signal processing unit 2 (fastened state detection unit 2c) receives information indicating that the nut 240 has rotated in the loosening direction by an angle different from the rotation angle in the tightening direction (outside the range), the signal processing unit 2 (fastened state detection unit 2c) will detect the fastened state of the nut 240 without ignoring information A (taking information A into consideration). This makes it possible to ignore changes in the detection value due to acceleration or vibration of the vehicle 200.

[0058] (Control Flow of Sensor Device) Next, a control flow of the sensor device 100 will be described with reference to Fig. 10. First, in step S1, the X-axis acceleration and the Y-axis acceleration are each detected by the acceleration sensor 1 at a predetermined cycle (for example, every 150 ms).

[0059] Next, in step S2, the signal processing unit 2 acquires information on the X-axis acceleration and the Y-axis acceleration from the acceleration sensor 1. Specifically, the signal processing unit 2 acquires information on the X-axis acceleration and the Y-axis acceleration at each predetermined cycle in step S1.

[0060] In step S3, the signal processing unit 2 calculates the average values ​​(average X-axis acceleration and average Y-axis acceleration) of every two X-axis accelerations and Y-axis accelerations acquired at predetermined intervals in step S2.

[0061] In step S4, the signal processing unit 2 (centrifugal acceleration calculation unit 2a) calculates the centrifugal acceleration (centrifugal force) of the wheel 220 from the rotational speed of the wheel 220 (the speed of the vehicle 200). Note that the processing of step S4 may be performed before or simultaneously with the processing of step S2 (S3).

[0062] In step S5, the signal processing unit 2 (rotation angle calculation unit 2b) 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.

[0063] In step S6, the signal processing unit 2 determines whether or not the data acquired in step S5 should be rejected (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 rejected (ignored) (Yes in S6), the process returns to step S1. If it is determined that the data should not be rejected (ignored) (No in S6), the process proceeds to step S7.

[0064] In step S6, as described above, if information indicating that nut 240 has rotated in the tightening direction by a predetermined angle or more without loosening for a certain period of time is acquired, and immediately thereafter information B indicating that nut 240 has rotated in the loosening direction by an angle equal to the angle of rotation in the tightening direction is acquired, it is determined that the above data should be excluded (ignored).

[0065] In step S7, the signal processing unit 2 (fastened state detection unit 2c) detects the fastened state of the nut 240 based on the angle (rotation angle) of the sensor device 100 (nut 240) calculated in step S5. If it is detected that the nut 240 is loose (Yes in S7), the process proceeds to step S8. If it is detected that the nut 240 is not loose (No in S7), the process returns to step S1. Note that in step S7, the signal processing unit 2 (fastened state detection unit 2c) determines whether the nut 240 is loose based on the change (difference) in the angle of the sensor device 100 from the previous detection value or the initial value, as described above.

[0066] In step S8, the signal processing unit 2 notifies the communication terminal 201 via the communication unit 3 that the nut 240 is loose.

[0067] As described above, in this embodiment, the rotation angle of nut 240 is detected based on the X-axis acceleration, the Y-axis acceleration, and the rotation speed of wheel 220 (the speed of vehicle 200). As a result, even if the X-axis acceleration and the Y-axis acceleration vary depending on the rotation speed of wheel 220, the rotation angle of nut 240 can be easily detected based on the magnitude of the centrifugal force that can be calculated from the rotation speed of wheel 220.

[0068] Second Embodiment In a second embodiment, the fastening state of the nut 240 is detected based on the ratio of the X-axis acceleration to the Y-axis acceleration. The same components as those in the first embodiment are denoted by the same reference numerals and will not be described again.

[0069] 11 is a diagram showing the configuration of a sensor device 300 according to the second embodiment. The sensor device 300 is an example of the "detection device" of the present disclosure.

[0070] 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.

[0071] The signal processing unit 12 detects the state (fastened state) of the nut 240 (see FIG. 12 ) based on the detection signal of the acceleration sensor 1. The signal processing unit 12 includes a ratio calculation unit 12a, a fastened state detection unit 12b, and an acquisition unit 2d. Note that the ratio calculation unit 12a and the fastened state detection unit 12b each represent software that blocks the functional features of the signal processing unit 12. Details of each function will be described later.

[0072] Furthermore, similar to the signal processing unit 2 of the first embodiment, the signal processing unit 12 calculates the average values ​​(average X-axis acceleration and average Y-axis acceleration) of the X-axis acceleration and the Y-axis acceleration detected twice while the wheel 220 rotates once.

[0073] The signal processing unit 12 (ratio calculation unit 12a) calculates the ratio between the calculated average X-axis acceleration (hereinafter sometimes simply referred to as X-axis acceleration) and the average Y-axis acceleration (hereinafter sometimes simply referred to as Y-axis acceleration). That is, the signal processing unit 12 (ratio calculation unit 12a) calculates the ratio every time it acquires each of the X-axis acceleration and Y-axis acceleration values ​​from the acceleration sensor 1 twice. Specifically, the signal processing unit 12 (ratio calculation unit 12a) calculates a 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). Note that the above ratio is an example of an "acceleration index" in the present disclosure.

[0074] The ratio may be calculated by dividing the absolute value of the Y-axis acceleration by the absolute value of the X-axis acceleration (|Y| / |X|), or by dividing the X-axis acceleration (Y-axis acceleration) by the square root of the sum of the squares of the X-axis acceleration and the Y-axis acceleration.

[0075] In the second embodiment, the signal processing unit 12 (fastened state detection unit 12b) detects the fastened state of the nut 240A based on the calculated ratio. Specifically, the signal processing unit 12 (fastened state detection unit 12b) detects the fastened state of the nut 240A based on the difference between the current ratio and the previous ratio. This will be described in detail below.

[0076] For example, if the previously calculated (average) X-axis acceleration and (average) Y-axis acceleration are −4 G and 10 G, respectively, the signal processing unit 12 (ratio calculation unit 12 a) calculates the ratio to be approximately 0.4 (hereinafter abbreviated as 0.4).

[0077] Next, suppose that a change in the rotation angle of nut 240A causes the (average) X-axis acceleration and (average) Y-axis acceleration calculated this time to become −4 G and 7 G, respectively. In this case, signal processing unit 12 (ratio calculation unit 12a) calculates the ratio to be approximately 0.57 (hereinafter abbreviated as 0.57).

[0078] The signal processing unit 12 (fastened state detection unit 12b) determines that the fastened state of the nut 240A has changed when the amount of change (absolute value) of the ratio is equal to or greater than a predetermined threshold. If the predetermined threshold is, for example, 0.1, then when the ratio changes from 0.4 to 0.57, it is determined that the fastened state of the nut 240A has changed.

[0079] As another example, suppose that the X-axis acceleration and Y-axis acceleration change from -4 G and 10 G, respectively, to -8 G and 20 G, respectively, due to an increase in centrifugal acceleration while the rotation angle of nut 240A remains unchanged. In this case, the ratio is 0.4 before and after the change in centrifugal acceleration. Therefore, the amount of change in the ratio is less than the predetermined threshold, and the signal processing unit 12 (fastened state detection unit 12b) determines that the fastened state of nut 240A has not changed.

[0080] Furthermore, if the X-axis acceleration and Y-axis acceleration change from 1 G and 11 G, respectively, to, for example, 1 G and 1000 G, respectively, the change in the ratio (|X| / |Y|) will be less than 0.1. On the other hand, if the X-axis acceleration and Y-axis acceleration change from 11 G and 1 G, respectively, to, for example, 1000 G and 1 G, respectively, the change in the ratio will be 0.1 or greater. Thus, even if the change in the rotation angle of nut 240A in the two patterns described above is approximately equal, there may be a difference in the determination result of the fastening state of nut 240A.

[0081] Therefore, the signal processing unit 12 (fastened state detection unit 12b) may change the magnitude of the predetermined threshold based on the magnitude of the ratio. For example, if the ratio before the change in the rotation angle of the nut 240A is 0.1 or less, the predetermined threshold may be set to half the ratio before the change, or to a predetermined fixed value less than 0.1 (e.g., 0.05). Note that the above example of changing the predetermined threshold is merely an example and is not limited to the above example.

[0082] Furthermore, when the Y-axis acceleration is 0, the signal processing unit 12 (ratio calculation unit 12a) calculates the ratio by replacing the Y-axis acceleration with a value that approximates 0 (for example, 0.01). Note that 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) calculates the ratio by replacing the X-axis acceleration with a value that approximates 0. Note that 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 square root of the sum of the squares of the X-axis acceleration and the Y-axis acceleration, the square root of the sum of the squares will never be 0, and therefore the approximation process is not necessary.

[0083] Although the above example shows processing based on the difference between the previous ratio and the current ratio, processing may also be performed based on the difference between the average value of the past several ratios, including the previous one, and the current ratio.

[0084] 13 is a graph showing the time variations of the X-axis normalized value (the value obtained by dividing the X-axis acceleration by the square root of the sum of squares; solid line), the Y-axis normalized value (the value obtained by dividing the Y-axis acceleration by the square root of the sum of squares; dashed line), and the centrifugal acceleration (dashed line). The X-axis normalized value and the Y-axis normalized value correspond to the left vertical axis. The centrifugal acceleration corresponds to the right vertical axis.

[0085] 13 , the X-axis normalized value and the Y-axis normalized value each fluctuate relatively greatly up to a centrifugal acceleration of about 5 G (up to approximately time t1 second), but after time t1, the X-axis normalized value and the Y-axis normalized value each remain relatively stable. Therefore, when the centrifugal acceleration is small, the X-axis normalized value (X-axis acceleration) and the Y-axis normalized value (Y-axis acceleration) fluctuate significantly. Therefore, as described above, it is effective to detect the fastening state of the nut 240 based on the average values ​​of the X-axis acceleration and the Y-axis acceleration.

[0086] Furthermore, the signal processing unit 12 detects the fastening state of the nut 240 while ignoring the X-axis acceleration and Y-axis acceleration obtained when the centrifugal acceleration of the wheel 220 suddenly changes (for example, around time t2). Here, a sudden change in centrifugal acceleration is often caused by sudden braking of the vehicle 200, etc. Therefore, it is possible to ignore changes in centrifugal acceleration due to factors other than loosening of the nut 240. Note that a sudden change in centrifugal acceleration means that the absolute value of the rate of change of centrifugal acceleration is equal to or greater than a predetermined value (for example, 2 G / sec).

[0087] (Processing Flow of Sensor Device) Next, the processing flow of the sensor device 300 will be described with reference to Fig. 14. Steps S11 to S13 are the same as steps S1 to S3 (see Fig. 10) of the first embodiment, respectively, and therefore will not be described again.

[0088] In step S14, the signal processing unit 12 (ratio calculation unit 12a) calculates the ratio (|X| / |Y|) of the X-axis acceleration (average X-axis acceleration) to the Y-axis acceleration (average Y-axis acceleration).

[0089] In step S15, the signal processing unit 12 (fastened state detection unit 12b) detects a change in the fastened state of the nut 240 based on the ratio calculated in step S14. If a change in the fastened state of the nut 240 is detected (Yes in S15), the process proceeds to step S16. If no change in the fastened state of the nut 240 is detected (No in S15), the process returns to step S11. Note that in step S15, the signal processing unit 12 (fastened state detection unit 12b) detects a change in the fastened state of the nut 240 based on the ratio up to the previous time or the amount of change (difference) from the initial value, as in the first embodiment.

[0090] Then, in step S16, the signal processing unit 12 notifies the communication terminal 201 via the communication unit 3 that the nut 240 is loose.

[0091] As described above, in the second embodiment, the fastening state of the nut 240 is detected based on the ratio of the X-axis acceleration to the Y-axis acceleration, which makes it possible to detect the fastening state of the nut 240 without taking into account fluctuations in vehicle speed (centrifugal force).

[0092] The other configurations are the same as those of the first embodiment, and therefore will not be described repeatedly.

[0093] [Third Embodiment] Next, a third embodiment will be described. Unlike the second embodiment, in which the fastening 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 third embodiment detects the fastening state of the nut 240 based on the difference in inverse trigonometric function values ​​calculated based on the ratio. In the third embodiment, the same components as those in the first and second embodiments are denoted by the same reference numerals as those in the first and second embodiments, and a repeated description will not be provided.

[0094] 15, the meaning of detecting the fastening state of the nut 240 based on the value of an inverse trigonometric function calculated based on the ratio of the X-axis acceleration and the Y-axis acceleration will be described. As shown in Fig. 15, a case will be described in which acceleration information is acquired when the sensor device 100 is located at the 3 o'clock position and the 9 o'clock position. The description will be made assuming that the direction of centrifugal acceleration is centered between the X-axis direction and the Y-axis direction.

[0095] Since the magnitude of each of the X-axis acceleration and Y-axis acceleration is based on the centrifugal acceleration and the acceleration of gravity, if the centrifugal acceleration is sufficiently greater than the acceleration of gravity, the influence of the acceleration of gravity will be small. If we assume that there is no influence of the acceleration of gravity when the centrifugal acceleration is 1 G, each of the X-axis acceleration and Y-axis acceleration will be 0.707 G. In this case, the angle θ1 between the direction of the centrifugal acceleration relative to the X-axis and the X-axis will be 45 degrees. Any inverse trigonometric function can be used (details of the inverse trigonometric function will be described later), but for ease of explanation, the value of the inverse trigonometric function calculated based on the ratio of the X-axis acceleration and the Y-axis acceleration will be θ1.

[0096] However, in reality, when the centrifugal acceleration is 1 G (i.e., when it is equal to the gravitational acceleration), gravity affects the acceleration detection. When the centrifugal acceleration is 1 G, the magnitude of the X-axis acceleration and the Y-axis acceleration deviates from the above value (0.707 G) due to the gravitational acceleration component.

[0097] Specifically, the X-axis acceleration and Y-axis acceleration detected by acceleration sensor 1 of sensor device 100 located at the 3 o'clock position are 1.414 G and 0 G, respectively. As a result, the angle θ1 is found to be 0 degrees, which is a difference of 45 degrees from the angle θ1 (45 degrees) when gravity is ignored, resulting in an angle error.

[0098] On the other hand, the X-axis acceleration and Y-axis acceleration detected by acceleration sensor 1 of sensor device 100 located at the 9 o'clock position are 0 G and 1.414 G, respectively. As a result, the angle θ1 is found to be -90 degrees, which is a difference of 45 degrees from the angle θ1 (-45 degrees) when gravity is ignored, resulting in an angle error.

[0099] This embodiment is characterized in that the fastening state of the nut 240 is detected based on the difference between the values ​​of the inverse trigonometric function calculated based on the ratio. As described above, if the angle between the direction of centrifugal acceleration relative 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 and the Y-axis acceleration, the difference (angle difference) contributes to detecting the fastening state of the nut 240.

[0100] As explained above, at the 3 o'clock position, there is a difference of 45 degrees from the angle θ1 (45 degrees) when gravity is ignored, and at the 9 o'clock position there is a difference of 45 degrees from the angle θ1 (-45 degrees) when gravity is ignored. However, by taking the average of the two angles, the effect of gravity is canceled out.

[0101] In the above example, the effect of gravity is cancelled out by averaging the angles θ1 calculated at the 3 o'clock position and the 9 o'clock position. Similar effects can be achieved by averaging the detection values ​​of the acceleration sensor 1 at the 3 o'clock position and the 9 o'clock position, as in the first embodiment. This will be explained in more detail below.

[0102] Here, when the influence of gravity is taken into account, the average X-axis acceleration (average X-axis acceleration) and the average Y-axis acceleration (average Y-axis acceleration) calculated at the 3 o'clock and 9 o'clock positions are 0.707 G and 0.707 G, respectively. That is, the average X-axis acceleration and the average Y-axis acceleration are equal to the acceleration values ​​obtained without the influence of gravity. In other words, the detection deviation at each position due to gravitational acceleration is canceled out. As a result, even if the difference between centrifugal acceleration and gravitational acceleration is not large, the rotation angle (fastened state) of the nut 240 can be accurately detected by averaging the two accelerations as described above. Alternatively, the rotation angle of the nut 240 corresponding to the 3 o'clock position and the rotation angle of the nut 240 corresponding to the 9 o'clock position may be averaged.

[0103] There may be differences between a method of calculating an angle using an inverse trigonometric function from acceleration sensor values ​​at two points symmetrical about the center (rotation axis O), such as the 3 o'clock and 9 o'clock positions, and then averaging the results. This is in contrast to a method of calculating an angle using an inverse trigonometric function from the average of the acceleration sensor values ​​at two points. If the centrifugal force (i.e., vehicle speed) occurring when acquiring the acceleration sensor values ​​at the two points is the same, the results obtained by the two methods are identical. On the other hand, if the centrifugal force (vehicle speed) occurring when acquiring the acceleration sensor values ​​at the two points is different, the method of calculating an angle using an inverse trigonometric function from the accelerations at the two points and then averaging the results can reduce the effects of gravity. In the first embodiment, if the vehicle speed differs at two points per half circumference of the tire 230, the centrifugal force generated at the two points differs. This causes problems when calculating the angle based on Figures 9A and 9B, etc. In particular, angle calculation is impossible when the vehicle speed difference is large. On the other hand, the method of calculating an angle and then averaging it, as in this embodiment, does not cause the above-mentioned problems.

[0104] The signal processing unit 2 performs processing to detect the fastening state of the nut 240 when the centrifugal acceleration of the wheel 220 is equal to or greater than a predetermined value (e.g., 1 G). The acceleration sensor 1 detects the X-axis acceleration and the Y-axis acceleration at a period based on the rotational speed (vehicle speed) of the wheel 220 corresponding to the predetermined value (i.e., the minimum value). Specifically, when the centrifugal acceleration is the predetermined value, the wheel 220 rotates once every 300 ms. In this case, the acceleration sensor 1 detects the X-axis acceleration and the Y-axis acceleration at a period of 150 ms, which is half of 300 ms. Information regarding the period is stored in a memory (not shown) or the like of the sensor device 100.

[0105] The cycle of 150 ms is determined in advance through experiments or simulations during the manufacturing stage. For example, it may be calculated based on the pitch circle diameter (PCD) of the bolt 250 on which the nut cap 241 is intended to be used, the tire diameter, etc.

[0106] Alternatively, the period may be 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. Since the direction of gravity and the direction of centrifugal force are the same at both the 6 o'clock position and the 12 o'clock position, the angular error described above does not occur. This makes it possible to accurately calculate the period of one half rotation of the wheel 220. The signal processing unit 2 may calculate the rotation period of the wheel 220 in real time based on the centrifugal acceleration (vehicle speed), etc., and change the period for acquiring acceleration (the period for detecting acceleration by the acceleration sensor 1) in accordance with changes in the rotation period.

[0107] As described above, the acceleration detection period is set based on the minimum value of the centrifugal acceleration (the rotational speed of the wheel 220). As a result, compared to when the rotational speed of the wheel 220 is higher, it is possible to prevent the wheel 220 from rotating nearly one full rotation during the acceleration detection period. This allows the signal processing unit 2 to easily obtain acceleration information at two points: one on the 3 o'clock side of the rotation axis O of the wheel 220 and one on the 9 o'clock side of the rotation axis O (i.e., positions point-symmetrical with respect to the rotation axis O). In other words, it is possible to prevent both acceleration detection points from being on the 3 o'clock side (or the 9 o'clock side). While acceleration information may be obtained at the two points, the 6 o'clock and 12 o'clock positions, the direction of gravity and the direction of centrifugal force are the same at these two points, so no angular error as described above occurs, and this does not pose a problem. The reason for using the minimum value of centrifugal acceleration as the reference is that the influence of gravity is greatest when the centrifugal acceleration is minimum. Even if the acceleration acquisition period is fixed, if the vehicle speed is sufficiently high and the centrifugal acceleration is sufficiently large, the effect of gravity will be relatively small even if both points at which acceleration is detected are on the 3 o'clock side (or 9 o'clock side) (the effect on the sensor angle is small to begin with).

[0108] 16 is a diagram showing the configuration of a sensor device 400 according to the third embodiment. The sensor device 400 is an example of the "detection device" of the present disclosure.

[0109] 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.

[0110] 16, the signal processing unit 22 of the sensor device 400 includes a ratio calculation unit 22a, an angle calculation unit 22b, a fastening state detection unit 22c, and an acquisition unit 2d. Each of the ratio calculation unit 22a, the angle calculation unit 22b, and the fastening state detection unit 22c represents software in which the functional features of the signal processing unit 22 are divided into blocks.

[0111] The signal processing unit 22 (ratio calculation unit 22a) calculates the ratio (X / Y) between the X-axis acceleration and the Y-axis acceleration. Note that this ratio may be calculated as a value (Y / X) obtained by dividing the Y-axis acceleration by the X-axis acceleration. Alternatively, this ratio may be calculated as a value obtained by dividing the X-axis acceleration (Y-axis acceleration) by the square root of the sum of squares.

[0112] The signal processing unit 22 (angle calculation unit 22b) calculates the inverse trigonometric function value (arctangent function value) (arctan(X / Y)) of the calculated ratio. Note that the arctangent function value is an example of the "acceleration index" of the present disclosure. In the previous explanation, the angle θ1 between the direction of centrifugal acceleration relative to the X axis and the X axis was defined as the inverse trigonometric function value calculated based on the ratio of the X-axis acceleration and the Y-axis acceleration. However, the angle θ1 can be calculated using the arctangent as described above.

[0113] Here, the arctangent function value is a value expressed in the range of -90 degrees to 90 degrees. On the other hand, the rotation angle of the nut 240 is expressed in the range of 0 degrees to 360 degrees in a Cartesian coordinate system (see FIG. 17). Therefore, in the third embodiment, a process is performed to convert the arctangent function value into an angle in the Cartesian coordinate system.

[0114] Specifically, the signal processing unit 22 (angle calculation unit 22b) calculates the angle θ2 (see FIG. 15 ) by adding a predetermined value (angle) to the arctangent function value. At this time, the signal processing unit 22 (angle calculation unit 22b) changes the predetermined value based on the positive or negative 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 predetermined value depending on whether the combination of the X-axis acceleration and the Y-axis acceleration is positive / positive, positive / negative, negative / positive, or negative / negative.

[0115] For example, when the X-axis acceleration and the Y-axis acceleration are 4 G and 10 G, respectively (in the first quadrant of FIG. 17 ), the signal processing unit 22 (angle calculation unit 22 b) adds 0 to the arctangent function value (arctan(4 / 10)≈21.8) (in other words, does not add any value). In this case, the angle θ2 becomes approximately 21.8 degrees.

[0116] Furthermore, when the X-axis acceleration and Y-axis acceleration are −4 G and 10 G, respectively (the second quadrant in FIG. 17 ), the signal processing unit 22 (angle calculation unit 22 b) adds 360 to the arctangent function value (arctan(−4 / 10)≈−21.8). In this case, the angle θ2 is approximately 338.2 degrees.

[0117] Furthermore, when the X-axis acceleration and the Y-axis acceleration are −4 G and −10 G, respectively (the third quadrant in FIG. 17 ), 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 is approximately 201.8 degrees.

[0118] Furthermore, when the X-axis acceleration and Y-axis acceleration are 4 G and −10 G, respectively (the fourth quadrant in FIG. 17 ), 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 is approximately 158.2 degrees.

[0119] As described above, by adding 0, 180, or 360 to each positive and negative (quadrant) of the X-axis acceleration and the Y-axis acceleration, it is possible to detect the fastening state of nut 240A based on a Cartesian coordinate system in which the angle increases clockwise from the positive Y-axis (θ2 = 0).

[0120] Here, when the X-axis acceleration and Y-axis acceleration are -4 G and 10 G, respectively, the angle θ is approximately 338.2 degrees, as described above. Furthermore, when the X-axis acceleration and Y-axis acceleration become -4 G and 7 G, respectively, due to the rotation of nut 240A, the angle θ becomes approximately 330.3 degrees. Therefore, the angle θ becomes smaller by approximately 7.9 degrees due to the rotation of nut 240A.

[0121] Here, angle θ2 is the angle between the Y-axis (positive) and the direction of centrifugal acceleration (see the dashed arrow in FIG. 12). Because the direction of centrifugal acceleration is constant in the radial direction (outer diameter direction), the decrease in angle θ2 is due to the Y-axis and X-axis (i.e., sensor device 300) rotating clockwise by approximately 7.9 degrees. In this way, it is possible to detect the rotation direction and rotation angle of sensor device 300 (nut 240A) based on the change in angle θ2.

[0122] Furthermore, similarly to the second embodiment, the fastening state of the nut 240A may be detected based on the previous value or the initial value of the angle θ2.

[0123] Furthermore, as in the first embodiment described above, when the signal processing unit 22 (fastening state detection unit 22c) acquires information A indicating that the nut 240 has rotated in the tightening direction, it ignores (excludes) the information A and detects the fastening state of the nut 240.

[0124] (Processing Flow of Sensor Device) Next, the processing flow of the sensor device 400 will be described with reference to Fig. 18. Steps S21 and S22 are the same as steps S11 and S12 (see Fig. 14) in the second embodiment, and therefore will not be described again.

[0125] In step S23, the signal processing unit 22 (ratio calculation unit 22a) calculates the ratio (X / Y) of the X-axis acceleration (average X-axis acceleration) to the Y-axis acceleration (average Y-axis acceleration).

[0126] In step S24, the signal processing unit 22 (angle calculation unit 22b) calculates the angle θ2 by adding 0, 180, or 360 to the arctangent function value of the ratio calculated in step S23. Specifically, the signal processing unit 22 (angle calculation unit 22b) changes the value to be added (0, 180, or 360) based on the positive or negative of the X-axis acceleration (average X-axis acceleration) and the Y-axis acceleration (average Y-axis acceleration). In more detail, the signal processing unit 22 (angle calculation unit 22b) changes the value to be added (0, 180, or 360) depending on whether the combination of the X-axis acceleration and the Y-axis acceleration is positive / positive, positive / negative, negative / positive, or negative / negative.

[0127] In step S25, the average value of every two times of the angle θ2 acquired at each predetermined cycle in step S24 is calculated.

[0128] Next, in step S26, the signal processing unit 22 determines whether or not the data acquired in step S25 should be rejected (ignored) based on the angle θ2 acquired in step S25. If it is determined that the data should be rejected (ignored) (Yes in S26), the process returns to step S21. If it is determined that the data should not be rejected (ignored) (No in S26), the process proceeds to step S27.

[0129] In step S26, as described above, 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 acquired immediately after information indicating that the nut 240 has rotated in the tightening direction by an angle equal to the angle of rotation in the tightening direction is acquired, it is determined that the data should be rejected (ignored). Also, in step S26, as in the second embodiment, it may be determined that the data should be rejected (ignored) if the centrifugal acceleration of the wheel 220 is less than a predetermined value or if the data was obtained during a sudden change in centrifugal acceleration.

[0130] In step S27, the signal processing unit 22 (fastened state detection unit 22c) detects the fastened state of the nut 240 based on the angle θ2 (average value) calculated in step S25. If it is detected that the nut 240 is loose (Yes in S27), the process proceeds to step S28. If it is detected that the nut 240 is not loose (No in S27), the process returns to step S21. In step S27, the signal processing unit 22 (fastened state detection unit 22c) determines whether the nut 240 is loose based on the change (difference) in the angle θ2 from the previous value or the initial value, as described above. In addition, step S28 is similar to step S16 in the second embodiment.

[0131] As described above, in the third embodiment, the fastening state of the nut 240 is detected based on the arctangent function value of the ratio between the X-axis acceleration and the Y-axis acceleration. This makes it possible to detect the rotation direction and rotation angle of the nut 240, unlike the second embodiment.

[0132] [Fourth Embodiment] Next, a fourth embodiment will be described. In the fourth embodiment, unlike the third embodiment in which the fastening state of the nut 240 is detected based on an inverse trigonometric function value of the ratio between the X-axis acceleration and the Y-axis acceleration, the fastening state of the nut 240 is detected based on an X-axis normalized value obtained by normalizing the X-axis acceleration and a Y-axis normalized value obtained by normalizing the Y-axis acceleration. In the fourth embodiment, the same components as those in the first to third embodiments are assigned the same reference numerals as those in the first to third embodiments, and repeated description will not be provided.

[0133] 19 , 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 the “state detection unit” and the “state detection device” of the present disclosure.

[0134] The signal processing unit 32 includes a square-root-sum-of-squares calculation unit 32a, a normalization unit 32b, a rotation angle calculation unit 32c, a fastening state detection unit 32d, and an acquisition unit 32d. Note that the square-root-sum-of-squares calculation unit 32a, the normalization unit 32b, the rotation angle calculation unit 32c, and the fastening state detection unit 32d shown in Fig. 19 each represent software in which the functional features of the signal processing unit 32 are grouped into blocks. The details of each function will be described later.

[0135] In the fourth embodiment, the nut 240 (nut 240A) is fixed so that the positive direction of the X axis of the acceleration sensor 1 faces upward (Z1 direction) in the initial state (when the nut 240A is not loose) (see FIG. 5). Note that in the initial state, the positive direction of the X axis of the acceleration sensor 1 may face a direction other than the Z1 direction. Note that in the following description, when the orientation of the sensor device 500 is as shown in FIG. 5, the angle (rotation angle) of the sensor device 500 is set to 0 degrees.

[0136] FIG. 20 is a graph showing the relationship between the rotation angle of the tire 230 (wheel 220) and the X-axis acceleration and Y-axis acceleration when a centrifugal force of 6G acts on the nut 240 at a predetermined vehicle speed. In the Y-axis orientation shown in FIG. 19 , no centrifugal force component is applied to the Y-axis, so the Y-axis acceleration remains unchanged from that shown in FIG. 7 . Meanwhile, a centrifugal force component is applied to the X-axis, so the X-axis acceleration is the X-axis acceleration in FIG. 7 plus 6G. In this case, the waveforms of the square root of the sum of the squares of the X-axis acceleration and the Y-axis acceleration are identical to the waveform of the X-axis acceleration. Note that in FIG. 20 , the waveform of the X-axis acceleration and the square root of the sum of the squares are slightly offset from each other for ease of understanding. FIG. 20 also shows the results of the sensor device 500 provided on the nut 240A shown in FIG. 5 .

[0137] FIG. 21 is a graph showing the relationship between the angle of the tire 230 (wheel 220) and the X-axis and Y-axis accelerations when a centrifugal force of 6 G acts on the nut 240 after the nut 240A has been rotated 135 degrees clockwise (loosened and rotated 225 degrees counterclockwise) from the state shown in FIG. 5 (see FIG. 12 ). In this case, the amplitudes of the X-axis and Y-axis acceleration waveforms are the same as those shown in FIG. 20 , while the average values ​​of the X-axis and Y-axis accelerations are different from those shown in FIG. 20 . The average values ​​of the X-axis and Y-axis accelerations reflect the rotation angle of the nut 240 (sensor device 500). Meanwhile, the waveforms of the square root of the sum of the X-axis and Y-axis accelerations are the same as those shown in FIG. 20 and do not change depending on the rotation angle of the nut 240 (sensor device 400). Note that FIG. 21 shows the results of the sensor device 500 attached to the nut 240A shown in FIG. 20 .

[0138] FIG. 22A is a graph showing the average value of acceleration versus the angle (rotation angle) of the sensor device 500 when the centrifugal force is 6 G. FIG. 22B is a graph showing the average value of acceleration versus the angle (rotation angle) of the sensor device 500 when the centrifugal force is 10 G. As shown in FIGS. 22A and 22B , the waveforms of the average values ​​of the X-axis acceleration and the Y-axis acceleration have amplitudes corresponding to the centrifugal force (the vertical axis scales are different), but have the same shape. Also, in each of FIGS. 22A and 22B , the square root of the sum of the squares 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 value of the X-axis acceleration and the Y-axis acceleration by the square root of the sum of the squares is the same regardless of the magnitude of the centrifugal force.

[0139] The signal processing unit 32 (square root sum calculation unit 32a) of the fourth embodiment calculates the square root of the sum of squares of the X-axis acceleration (Xg) (average X-axis acceleration) and the Y-axis acceleration (Yg) (average Y-axis acceleration). The signal processing unit 32 (normalization unit 32b) calculates an X-axis normalized value by dividing the X-axis acceleration (average X-axis acceleration) by the square root of the sum of squares. The signal processing unit 32 (normalization unit 32b) calculates a Y-axis normalized value by dividing the Y-axis acceleration (average Y-axis acceleration) by the square root of the sum of squares. The X-axis normalized value and the Y-axis normalized value are examples of the "first axis normalized value" and the "second axis normalized value" of the present disclosure, respectively. The X-axis normalized value and the Y-axis normalized value are examples of the "acceleration index" of the present disclosure.

[0140] The signal processing unit 32 (rotation angle calculation unit 32c) then 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. As described above with reference to Figures 22A and 22B, when the vehicle speed is equal to or greater than a certain value, the X-axis normalized value and the Y-axis normalized value are values ​​based on the sensor angle regardless of the centrifugal force (vehicle speed). Therefore, by using the X-axis normalized value and the Y-axis normalized value, it is possible to detect the rotation angle of the nut 240 regardless of the vehicle speed.

[0141] 23 is a graph showing the time-dependent changes in the X-axis normalized value (solid line), the Y-axis normalized value (dashed line), and the centrifugal acceleration (dashed line). The X-axis normalized value and the Y-axis normalized value correspond to the vertical axis on the left. The centrifugal acceleration corresponds to the vertical axis on the right. Note that FIG. 23 is a graph showing the case where the nut 240A is rotated 45 degrees counterclockwise from the state shown in FIG. 5.

[0142] Here, at time t11, vehicle 200 starts traveling, and as a result, the centrifugal force acceleration increases to approximately 15 G, as shown in Figure 23. Furthermore, after time t11, the X-axis normalized value is approximately -1 G, and the Y-axis normalized value is approximately 0 G. As shown in Figure 23, the amount of fluctuation (amplitude) of the X-axis normalized value, which is approximately -1 G, is smaller than the amount of fluctuation (amplitude) of the Y-axis normalized value, which is approximately 0 G.

[0143] Therefore, when the fastening state of the nut 240 is detected by directly comparing the X-axis normalized value or the Y-axis normalized value with a predetermined tolerance range, rather than by the rotation angle of the sensor device 500, the tolerance range when the X-axis normalized value or the Y-axis normalized value is near 0 G is set larger than the tolerance range when the X-axis normalized value or the Y-axis normalized value is near -1 G (or 1 G). This makes it possible to more accurately detect the fastening state of the nut 240 even if the X-axis normalized value or the Y-axis normalized value is near 0 G. This control may also be applied to the second and third embodiments described above.

[0144] The tightening state of the nut 240 may also be detected based on the arctangent function value of the X-axis normalized value and the Y-axis normalized value. Figure 24 illustrates the waveform of the inverse trigonometric function value instead of the centrifugal acceleration waveform of Figure 20. In this case, it is possible to narrow the tolerance range more than in the case of Figure 23. As described in the third embodiment, the arctangent function value can only be in the range of -90 degrees to 90 degrees. However, by adding or subtracting 180 degrees or 360 degrees in consideration of the signs of the X-axis acceleration and the Y-axis acceleration, the arctangent function value may be in the range of 0 degrees to 360 degrees.

[0145] (Processing Flow of Sensor Device) Next, the processing flow of the sensor device 500 will be described with reference to Fig. 25. Steps S31 to S33 are the same as steps S11 to S13 in the second embodiment.

[0146] In step S34, the signal processing unit 32 (square root sum calculation unit 32a) calculates the square root sum of the X-axis acceleration (average X-axis acceleration) and the Y-axis acceleration (average Y-axis acceleration).

[0147] In step S35, the signal processing unit 32 (normalization unit 32b) calculates an X-axis normalized value and a Y-axis normalized value based on the square root of the sum of squares calculated in step S34.

[0148] In step S36, the signal processing unit 32 (rotation angle calculation unit 32c) 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.

[0149] In step S37, the signal processing unit 32 determines whether or not the data acquired in step S36 should be rejected (ignored) based on the angle (rotation angle) of the sensor device 500 acquired in step S36. If it is determined that the data should be rejected (ignored) (Yes in S37), the process returns to step S31. If it is determined that the data should not be rejected (ignored) (No in S37), the process proceeds to step S38. Note that the data (measured values) to be rejected (ignored) are not limited to the X-axis normalized value and the Y-axis normalized value, and may also be the X-axis acceleration and the Y-axis acceleration.

[0150] In step S37, similar to the third embodiment, 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 acquired immediately after information indicating that the nut 240 has rotated in the tightening direction by an angle equal to the angle of rotation in the tightening direction is acquired, it is determined that the data should be rejected (ignored), similar to the second embodiment. Also, in step S37, if the centrifugal acceleration of the wheel 220 is less than a predetermined value or if the data was obtained during a sudden change in centrifugal acceleration, it may be determined that the data should be rejected (ignored), similar to the second embodiment.

[0151] Next, in step S38, the signal processing unit 32 (fastened state detection unit 32d) detects the fastened state of the nut 240 based on the angle (rotation angle) of the sensor device 500 (nut 240) calculated in step S36. If it is detected that the nut 240 is loose (Yes in S38), the process proceeds to step S39. If it is detected that the nut 240 is not loose (No in S38), the process returns to step S31. Note that in step S38, the signal processing unit 32 (fastened state detection unit 32d) determines whether the nut 240 is loose based on the change (difference) in the angle of the sensor device 500 from the previous detection value or the initial value, as described above. Note that step S39 is similar to step S16 in the second embodiment.

[0152] 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, which makes it possible to detect the rotation angle of the nut 240 without taking into account fluctuations in vehicle speed (centrifugal force).

[0153] Fifth Embodiment Next, a fifth embodiment will be described. In the fifth embodiment, the fastening state of the nut 240 is detected based on the positive and negative X-axis acceleration and Y-axis acceleration. In the fifth embodiment, the same components as those in the first to fourth embodiments are denoted by the same reference numerals as those in the first to fourth embodiments, and a repeated description will not be provided.

[0154] 26, 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 the "state detection unit" and "state detection device" of the present disclosure.

[0155] FIG. 27 is a side view showing the wheel 220 (wheel 210) fastened to the wheel hub 250a. In FIG. 27, the sensor device 600 is attached to the uppermost nut 240. The detection axis of the acceleration sensor 1a is the X-axis. The acceleration sensor 1a detects acceleration applied along this detection axis (X-axis). The acceleration detected along this detection axis (X-axis) is also referred to as Gx. The arrow on the X-axis indicates the positive direction of Gx. If the acceleration applied to the acceleration sensor 1a has a component (vector) in the direction of the X-axis arrow (the direction of the two-dot chain arrow), Gx will be a positive value (+Gx (positive acceleration)). If the acceleration applied to the acceleration sensor 1a has a component in the opposite direction to the X-axis arrow, Gx will be a negative value (-Gx (negative acceleration)).

[0156] The wheel 220 (wheel 210) is fastened to the wheel hub 250a by a nut 240 on a predetermined pitch circle (see the dashed line in FIG. 27 ). The pitch circle diameter (PCD) may be any size, such as 114.3 mm or 275 mm. FIG. 27 shows the state in which the nut 240 has been tightened with a predetermined tightening torque, fastening the wheel 220 (wheel 210) to the wheel hub 250a. The nut 240 is a right-hand thread, and is tightened by rotating it clockwise in FIG. 27 .

[0157] 28A and 28B are diagrams showing the relationship between centrifugal acceleration and acceleration Gx detected by acceleration sensor 1a. FIG. 28A shows the state in which nut 240 is tightened with a predetermined tightening torque (the state shown in FIG. 27). FIG. 28B shows the state in which nut 240 is rotated in the loosening direction (counterclockwise). As shown in FIG. 27, gravitational acceleration is applied to nut 240 (acceleration sensor 1a). However, in the explanation using FIGS. 28A and 28B, we will ignore gravitational acceleration. In other words, we will explain the relationship between centrifugal acceleration and acceleration Gx detected by acceleration sensor 1a assuming that the rotation axis O of wheel hub 250a (wheel 220) is oriented vertically and the wheel 220 rotates on a horizontal plane. In this case, gravitational acceleration is not applied in the direction of the detection axis (X-axis) of acceleration sensor 1a.

[0158] 28A and 28B, the dashed arrows indicate the direction of centrifugal acceleration (centrifugal force) generated by the rotation of the wheel hub 250a (wheel 220). Because centrifugal acceleration acts in the radial direction around the rotation axis O, it acts in the direction shown in FIGS. 28A and 28B no matter where the nut 240 (acceleration sensor 1a) is located on the pitch circle. Note that in FIGS. 28A and 28B, arrow Gc indicates the centrifugal acceleration vector, and vector Gc always points in the radial direction around the rotation axis O.

[0159] In Fig. 28A, which shows a state in which the nut 240 is tightened with a predetermined tightening torque, the X-axis component (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)." When the nut 240 rotates in the loosening direction (counterclockwise) and the tightening state of the nut 240 loosens, reaching the state shown in Fig. 28B, the X-axis component (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 (negative acceleration)."

[0160] As is clear from FIGS. 28A and 28B , when the detection axis (X-axis) of acceleration sensor 1a rotates across an axis (indicated by a dashed line in FIGS. 28A and 28B ) perpendicular to the centrifugal acceleration vector Gc, the direction of acceleration detected by acceleration sensor 1a changes, and the acceleration Gx detected by 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 sign of the acceleration detected by acceleration sensor 1a is reversed. When centrifugal acceleration is applied to acceleration sensor 1a, the detection axis (X-axis) of acceleration sensor 1a rotates, and the direction in which the positive direction of Gx is detected (the arrow on the X-axis) changes from region A shown in FIG. 28A to region B shown in FIG. 28B. This causes acceleration Gx to change from +Gx to -Gx. As a result, the sign of the acceleration detected by acceleration sensor 1a is reversed. When centrifugal acceleration is applied to the acceleration sensor 1a, the detection axis (X-axis) of the acceleration sensor 1a rotates, and the direction in which the positive direction of Gx is detected (the arrow on the X-axis) changes from region B shown in Fig. 28B to region A shown in Fig. 28A, causing the acceleration Gx to change from -Gx to +Gx. As a result, the sign of the acceleration detected by the acceleration sensor 1a is reversed.

[0161] The acceleration sensor 1a rotates in conjunction with the rotation of the nut 240. Therefore, when centrifugal acceleration due to the rotation of the wheel 220 is applied, the rotation of the nut 240 can be detected based on the inversion of the positive and negative signs of the acceleration Gx detected by the acceleration sensor 1a. Using this, the fifth embodiment detects changes in the fastening state of the nut 240.

[0162] FIG. 29 is a diagram showing an example of functional blocks configured in the signal processing unit 42. The acceleration determination unit 42a determines whether the gravitational acceleration acting on the acceleration sensor 1a is greater than the centrifugal acceleration. As shown in FIG. 27, the rotation axis O of the wheel 220 (the rotation axis O of the wheel hub 250a) is a horizontal axis, and the acceleration sensor 1a is subjected to both centrifugal acceleration and gravitational acceleration. The acceleration Gx detected by the acceleration sensor 1a is a composite acceleration of the centrifugal acceleration and the gravitational acceleration. Therefore, if the gravitational acceleration acting on the detection axis of the acceleration sensor 1a is greater than the centrifugal acceleration acting on the detection axis, the direction (positive or negative) of the acceleration Gx may change depending on the position on the pitch circle of the nut 240, even if the nut 240 is not rotating.

[0163] If the magnitude of the gravitational acceleration is 1 G, the magnitude of the gravitational acceleration (gravitational acceleration acting in the X-axis direction) detected by the acceleration sensor 1a will be a maximum of 1 G. When the absolute value of the acceleration Gx detected by the acceleration sensor 1a is greater than 2 G, a centrifugal acceleration greater than the gravitational acceleration is acting on the acceleration sensor 1a. Therefore, when the absolute value of the acceleration Gx detected by the acceleration sensor 1a is greater than 2 G, 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 2 G, there is a possibility that it will be influenced by the gravitational acceleration.

[0164] 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 5 G or greater, and determines that the gravitational acceleration is greater than the centrifugal acceleration when the absolute value of the acceleration Gx is less than 5 G.

[0165] The stop determination unit 42b determines whether the vehicle 200 is stopped and the wheel hub 250a (wheel 220) has stopped rotating.

[0166] The stop determination unit 42b determines that the rotation of the wheel 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 every predetermined period are the same. In the fifth embodiment, when the magnitude of the previous value of the acceleration Gx is Gx(n-1) and the magnitude of the current value of the acceleration Gx is Gx(n), if the condition "|Gx(n-1) - Gx(n)| < α" continues for a certain period of time, for example, when it is established three times in a row, it is determined that the wheel 220 has stopped. Note that α is a predetermined value that takes into account the influence of noise and disturbances when detecting the acceleration Gx, and is set in advance through experiments, etc.

[0167] The state determination unit 42c determines that the fastening state of the nut 240 is loose when the acceleration Gx (average X-axis acceleration) detected by the acceleration sensor 1a reverses (changes) in sign. The state determination unit 42c determines that the fastening state of the nut 240 is loose when the acceleration Gx reverses in sign in the positive direction (+Gx) or when the acceleration Gx changes from a positive acceleration (+Gx) to a negative acceleration (-Gx) or from a negative acceleration (-Gx) to a positive acceleration (+Gx). The state determination unit 42c is an example of a "fastening state detection unit" in the present disclosure.

[0168] 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 differs 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 determines that the sign of the acceleration Gx has reversed and that a change has occurred in the fastening state of the nut 240. Note that the state determination unit 42c of the fifth embodiment cannot detect the rotation direction of the nut 240. When the wheel hub 250a (wheel 220) is rotating, it is extremely rare for the nut 240 to rotate in the tightening direction (retightening direction). Therefore, when the direction (positive / negative) of the acceleration Gx detected by the acceleration sensor 1a, which rotates in conjunction with the rotation of the nut 240, changes, it can be safely assumed that the nut 240 has rotated in the loosening direction.

[0169] When state determination unit 42c determines that a change has occurred in the fastening state of nut 240, it transmits the information to communication terminal 201 (see FIG. 1 ) of vehicle 200 via communication unit 3. Communication terminal 201 receives the transmitted information and, for example, issues (displays) an alarm that nut 240 is loose.

[0170] 30 is a flowchart showing an example of processing executed by the signal processing unit 42. This flowchart is repeatedly processed at predetermined intervals. The initial predetermined interval is, for example, 300 ms.

[0171] In step S40, the signal processing unit 42 acquires the acceleration Gx detected by the acceleration sensor 1a. The signal processing unit 42 acquires information about the acceleration Gx detected by the acceleration sensor 1a at predetermined intervals (e.g., every 150 ms). When the acceleration sensor 1a receives an acceleration detection request from the signal processing unit 42, it detects the acceleration Gx and transmits a detection signal to the signal processing unit 42. Therefore, the signal processing unit 42 acquires information about the acceleration Gx from the acceleration sensor 1a at the predetermined intervals.

[0172] 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 5 G or greater. Specifically, it determines whether the absolute value |Gx| (average) of the average value (average X-axis acceleration) of two acceleration Gx measurements acquired in step S40 is 5 G or greater. If the absolute value |Gx| (average) is 5 G or greater and a positive determination is made, the process proceeds to step S42. If the absolute value |Gx| (average) is less than 5 G and a negative determination is made, the process proceeds to step S47.

[0173] In step S42, the signal processing unit 42 sets the processing interval (predetermined period) of this flowchart to, for example, 300 ms. Then, the process proceeds to step S43. Note that the processing interval (predetermined period) is, for example, twice the cycle (150 ms in the above example) at which the acceleration Gx is detected by the acceleration sensor 1a. Note that if the predetermined period is already 300 ms in step S42, the predetermined period is maintained at 300 ms.

[0174] In step S43, the signal processing unit 42 determines whether the absolute value |Gx| (average) of the acceleration Gx (previous value Gx(n-1)) acquired in step S40 of the previous process was 5 G or greater. If the absolute value |Gx| (average) of the previous acceleration Gx (previous value Gx(n-1)) is 5 G or greater, a positive determination is made and the process proceeds to step S44. If the absolute value |Gx| (average) of the previous acceleration Gx (previous value Gx(n-1)) is less than 5 G, a negative determination is made and the process proceeds to step S46.

[0175] 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 in the processing of step S40 whether the direction of the acceleration Gx currently detected by the acceleration sensor 1a has changed from the direction of the acceleration Gx at the time of the previous processing (previous value Gx(n-1)). When the sign of the acceleration Gx currently detected by the acceleration sensor 1a is different from the sign of the acceleration Gx at the time of the previous processing (previous value Gx(n-1)), the signal processing unit 42 determines that the direction of the acceleration Gx has changed and the sign of the acceleration Gx has reversed.

[0176] If it is determined in step S44 that the direction of the acceleration Gx (average X-axis acceleration) has changed (positive determination), the process proceeds to step S45. If it is not determined in step S44 that the direction of the acceleration Gx (average X-axis acceleration) has changed (negative determination), the process proceeds to step S46.

[0177] In step S45 , the signal processing unit 42 determines that a change has occurred in the fastening state of the nut 240 , and transmits information about the loosening of the nut 240 to the communication terminal 201 via the communication unit 3 .

[0178] In step S46, the signal processing unit 42 stores the acceleration Gx (average X-axis acceleration) acquired in step S40 in memory as the previous value Gx(n-1) of the acceleration Gx, and then ends the current routine.

[0179] In step S47, the signal processing unit 42 determines whether the difference between the magnitude of the acceleration Gx at the previous processing time (previous value Gx(n-1)) and the magnitude of the acceleration Gx acquired in step S40 during the current processing time (current value Gx(n)) is smaller than a predetermined value α. If the result is "|Gx(n-1)-Gx(n)|<α" and a positive determination is made, the process proceeds to step S48. If the result is "|Gx(n-1)-Gx(n)|≧α" and a negative determination is made, the process proceeds to step S51.

[0180] 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 equal to or greater than 3. In step S49, if the counter Ct is equal to or greater than 3 (Ct≧3), an affirmative determination is made and the process proceeds to step S50, whereas if the counter Ct is less than 3 (Ct<3), a negative determination is made and the process proceeds to step S52.

[0181] In step S50, the signal processing unit 42 sets the processing interval (predetermined period) of this flowchart to 30 minutes, and then goes through the processing of step S46 to end this routine. In step S51, the counter Ct is set to 0.

[0182] In step S52, the signal processing unit 42 sets the processing interval (predetermined period) of this flowchart to 300 ms, and then goes through the processing of step S46 to end this routine.

[0183] According to the fifth embodiment, the acceleration sensor 1a rotates in conjunction with the rotation of the nut 240, rotating integrally with the rotation of the nut 240 in the tightening and loosening directions. The acceleration sensor 1a detects acceleration Gx in one direction along a detection axis (X-axis) perpendicular to the rotation axis O of the wheel hub 250a (axle) as a positive acceleration (+Gx), and detects acceleration Gx in the other direction along the detection axis (X-axis) as a negative acceleration (-Gx). When the detection axis (X-axis) of the acceleration sensor 1a rotates across an axis perpendicular to the centrifugal acceleration vector Gc, 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), reversing the sign of the acceleration Gx. The state determination unit 42c of the signal processing unit 42 determines that a change has occurred in the fastening state of the nut 240 when the sign of the acceleration Gx detected by the acceleration sensor 1a is reversed.

[0184] The state determination unit 42c cannot detect the rotation direction of the nut 240. However, when the wheel hub 250a (wheel 220) is rotating, it is extremely rare for the nut 240 to rotate in the tightening direction (retightening direction). Therefore, when the direction (positive or negative) of the acceleration Gx detected by the acceleration sensor 1a, which rotates integrally with the nut 240, changes, it can be assumed that the nut 240 has rotated in the loosening direction. Therefore, in the fifth embodiment, when the nut 240 rotates in the loosening direction, it can be assumed that the fastened state of the nut 240 has loosened, so that loosening of the nut 240 can be detected even if the loosening is relatively slight.

[0185] In the fifth embodiment, a change in the fastening 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 is only required 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 an acceleration of at least 5 G can be used.

[0186] In the fifth embodiment, when the absolute value |Gx| of the acceleration Gx detected by the acceleration sensor 1a is greater than 5 G, it is determined that a centrifugal acceleration greater than the acceleration of gravity is acting on the acceleration sensor 1a (S41). However, it may also be determined that a centrifugal acceleration greater than the acceleration of gravity is acting on the acceleration sensor 1a when the absolute value |Gx| exceeds a predetermined value greater than 2 G. Furthermore, if the rotational speed of the wheel hub 250a (wheel 220) can be calculated from the vehicle speed of the vehicle 200, a change in the direction (positive or negative) of the acceleration Gx may be detected when the centrifugal acceleration calculated based on the rotational speed of the wheel hub 250a (wheel 220) and the PCD is greater than the acceleration of gravity.

[0187] In the fifth embodiment, the stop determination unit 42b determines whether the wheel hub 250a (wheel 220) has stopped rotating based on the acceleration Gx detected by the acceleration sensor 1a. However, the stop determination unit 42b may obtain vehicle speed information of the vehicle 200 via the communication unit 3, and determine that the wheel hub 250a (wheel 220) has stopped rotating when the vehicle 200 is stopped.

[0188] In the fifth embodiment, the positive / negative reversal 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 1 a. In the first modification, an initial value Gxs of the acceleration Gx (average X-axis acceleration) is set, and the positive / negative reversal of the acceleration Gx is detected based on the sign of this initial value Gxs and the sign of the acceleration Gx (average X-axis acceleration) detected by the acceleration sensor 1 a.

[0189] 31 is a flowchart showing the processing of the initial value setting routine executed by the signal processing unit 42 in the modified example 1. When the button 201 a (see FIG. 1 ) provided on the communication terminal 201 of the vehicle 200 is pressed, the signal processing unit 42 receives the pressing of the button 201 a via the communication unit 3 and starts processing.

[0190] When button 201a is pressed, acceleration Gx is detected by acceleration sensor 1a in step S60. In the following step S61, it is determined whether the absolute value |Gx| (average) of acceleration Gx is equal to or greater than 5 G. If the absolute value |Gx| is less than 5 G, the process returns to step S60, and acceleration Gx is detected again by acceleration sensor 1a.

[0191] When the vehicle 200 starts traveling and the absolute value |Gx| (average) of the acceleration Gx detected by the acceleration sensor 1a exceeds 5 G, 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 to an initial value Gxs, and the current routine ends. Note that the initial value Gxs includes the direction (sign (+ / -)) of the acceleration Gx detected by the acceleration sensor 1a.

[0192] Fig. 32 is a flowchart showing an example of processing executed by the signal processing unit 42 in Modification 1. Similar to the flowchart of Fig. 30, this flowchart is repeatedly processed at predetermined intervals, with the initial predetermined interval being 300 ms. This flowchart eliminates the processing of step S43 in the flowchart of Fig. 30 and executes the processing of step S53 instead of step S43. Therefore, a description of the processing of steps S40 to S42 and S44 to S52 will be omitted.

[0193] In step S53, the signal processing unit 42 determines whether the direction of the acceleration Gx (average X-axis acceleration) detected in the processing of step S40 is different from the direction of the initial value Gxs. If 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 has been reversed, and the processing proceeds to step S45. If the sign of the acceleration Gx is the same as the sign of the initial value Gxs, a negative determination is made, and the processing proceeds to step S46.

[0194] According to this first modification, the initial value Gxs is the acceleration Gx that indicates the rotational position of the nut 240 when the nut 240 is completely tightened, and therefore it is possible to detect a change in the tightening state of the nut 240 from when the nut 240 is tightened with a predetermined tightening torque. As a result, the tightening state of the nut 240 can be detected more appropriately.

[0195] If vehicle 200 (communication terminal 201) does not have button 201a, the initial value setting routine of FIG. 31 may be executed when vehicle 200 returns from a stopped state to a running state. For example, after a positive determination is made in step S47, the initial value setting routine of FIG. 31 may be executed when a positive determination is made in step S41 or a negative determination is made in step S47. Furthermore, when it is determined from the vehicle speed information of vehicle 200 that vehicle 200 has returned from a stopped state to a running state, the initial value setting routine of FIG. 31 may be executed. Furthermore, button 201a may be provided on nut 240.

[0196] (Variation 2) In the fifth embodiment, the acceleration sensor 1a had only one detection axis, the X-axis. If the acceleration sensor 1a had only one detection axis, the X-axis, the direction (positive or negative) of the acceleration Gx might not change unless the nut 240 (acceleration sensor 1) rotates by 180 degrees or more. Furthermore, depending on the rotational position of the nut 240 at the completion of tightening, even a slight rotation might reverse the positive or negative sign of the acceleration Gx. Therefore, in Variation 2, the acceleration sensor 1 may detect both the X-axis acceleration and the Y-axis acceleration, as in the first to fourth embodiments.

[0197] In the second modification, the signal processing unit 42 executes the process of the flowchart in Fig. 30 based on the acceleration Gx detected by the X-axis of the acceleration sensor 1. The signal processing unit 42 also executes the process of the flowchart in Fig. 30 based on the acceleration Gy detected by the Y-axis of the acceleration sensor 1. Note that Gx is replaced with Gy.

[0198] According to this second modification, if the nut 240 rotates at least 90°, the sign of either the acceleration Gx or the acceleration Gy is reversed, so that a change in the fastening state of the nut 240 can be detected.

[0199] According to this second modification, if the fastening state of the nut 240 is determined to have changed when the sign of either the acceleration Gx or the acceleration Gy is reversed after the sign of the other acceleration Gx or the acceleration Gy is reversed, a change in the fastening state of the nut 240 can be detected when the nut 240 rotates by 90 degrees or more. While the acceleration sensor 1 of the second modification and the first to fourth embodiments has two orthogonal detection axes, the X-axis (first detection axis) and the Y-axis (second detection axis), the X-axis (first detection axis) and the Y-axis (second detection axis) do not have to be orthogonal. Furthermore, the detection axes of the acceleration sensor may be three or more axes that intersect at any angle, as long as they are on a plane perpendicular to the rotation axis of the wheel 220 (the rotation axis O of the wheel hub 250a). In this case, it is preferable that the multiple detection axes of the acceleration sensor intersect at equal angles (for example, 120° in the case of three axes).

[0200] (Variation 3) In the first to fifth embodiments described above, an example was shown in which the nut cap 241 was attached to the nut 240, but the present disclosure is not limited to this. As shown in Fig. 33 , the sensor device may be attached to a nut 340, which is a cap nut. The nut 340 is an example of a "fastening member" in the present disclosure. Note that Fig. 33 illustrates the sensor device 100 as a representative sensor device.

[0201] (Modification 4) In Modification 4 shown in FIG. 34 , nut 440 is open on one side but does not include a nut cap. In this example, the sensor device may be provided on side surface 441 of nut 440 (the surface perpendicular to wheel 220). In FIG. 34 , sensor device 100 is illustrated as a representative sensor device. Note that each configuration of Modification 4 may be applied to the second to fifth embodiments. Also, the sensor device may be fitted into recess 541 a (see FIG. 35 ) provided on side surface 541 of nut 540. Note that each of nuts 440 and 540 is an example of a "fastening member" in the present disclosure.

[0202] (Comparative Example) Figure 36 is a cross-sectional view of a fastening portion using a looseness detection device in a comparative example. In Figure 36, wheel hub 250a and bolt 250 are the same as those in the above embodiment. In Figure 36, a single tire is fastened to wheel hub 250a. There is one wheel 220. Also, in Figure 35, nut 640, which is a through nut, is shown in a side view (not a cross-sectional view).

[0203] 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 cap NC. One end of the leaf spring L is fixed to the ceiling surface of the nut cap NC. One end of the coil spring C is attached to 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 ceiling surface of the nut cap NC opposite contact S1. The nut cap NC is attached to the nut 640 as shown by the arrow. For example, the side of the nut 640 is press-fitted into the inner surface of the nut cap NC, thereby fixing the nut cap NC to the nut 640.

[0204] 37 shows a comparative example in which the nut cap NC is attached to the nut 640 (top diagram) and in which the nut 640 is loosened and fastened (bottom diagram). The top diagram shows the state in which the nut 640 is fastened with a predetermined tightening torque. When the nut 640 is fastened with a predetermined tightening torque, the distance between the ceiling surface of the nut cap NC attached to the nut 640 and the upper surface (tip) of the bolt 250 is short. In this case, as shown in the top diagram, the leaf spring L and the coil spring C compress, causing contacts S1 and S2 to come into contact and close.

[0205] As shown in the diagram below, when the nut 640 loosens, a gap occurs between the nut 640 and the fastening surface of the wheel 220. When this gap occurs, the distance between the ceiling surface of the nut cap NC attached to the nut 640 and the upper surface of the bolt 250 increases. In this case, the contact points S1 and S2 move away from each other and open.

[0206] In this comparative example, the loosening detection device electrically detects the opening and closing of contacts S1 and S2, thereby making it possible to detect loosening of nut 640. For example, when contacts S1 and S2 are closed, it is determined that the fastening state of nut 640 is normal, and when contacts S1 and S2 are open, it is determined that loosening of nut 640 has occurred.

[0207] FIG. 38 is a diagram illustrating individual differences in the axial length of bolt 250. The axial length of bolt 250 varies depending on the vehicle model and car manufacturer (vehicle manufacturer). The left diagram of FIG. 38 shows an example of a bolt 250 with a short axial length. The right diagram of FIG. 38 shows an example of a bolt 250 with a long axial length. Due to bolts 250 with different axial lengths, a difference (Δd) occurs in the distance from the fastening surface between wheel 220 and nut 640 to the top surface of bolt 250, as shown in FIG. 38. For this reason, the loosening detection device of the comparative example using nut cap NC may not be able to properly detect loosening of nut 640.

[0208] In contrast, in the detection device according to the above embodiment, the fastening state of the fastening member is detected using the acceleration detected by the acceleration sensor 1 (1a), and therefore the fastening state can be detected without being affected by differences in the axial length of the bolt 250.

[0209] In the above description of the first embodiment, an example was shown in which the acceleration sensor 1 detects accelerations along the X-axis and Y-axis and calculates the accelerations along the X-axis and Y-axis and the difference between the X-axis acceleration and the Y-axis acceleration. However, the present disclosure is not limited to this. For example, in the example of FIG. 12, only the accelerations along the X-axis and Y-axis are used. Alternatively, the acceleration sensor may be configured to detect only one of the accelerations along the X-axis and Y-axis. Furthermore, an example was shown in which the interval for repeatedly performing sensing was appropriately set to reduce the power consumption of the signal processing unit 2. However, the present disclosure is not limited to this. Even if the interval is set arbitrarily, only fluctuations will occur.

[0210] As mentioned above, any arbitrary sensing interval will result in fluctuations. Taking the X-axis as an example, fluctuations of approximately ±1 G will occur in the average value. The effect of fluctuations is illustrated in the example of Figure 9A. If there is no fluctuation and the average acceleration result is 3 G, the sensor angle is 0 degrees. However, if the fluctuation is -1 G, the average acceleration result could be 2 G. If the average acceleration result is 2 G, the sensor angle will be around 40 degrees. Thus, the difference between 0 degrees and 40 degrees is the sensor angle error. In other words, it becomes difficult to reliably determine whether the nut is loose until the sensor angle has loosened beyond 40 degrees to some extent. This reduces the robustness of the system.

[0211] 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, and therefore the rotation angle cannot be specified, but the amount of change in the rotation angle between each sensing can be detected. As a result, it is possible to detect that the nut 240 is not loosened based on the fact that the amount of change is small.

[0212] Specifically, assume that the rotation angle of nut 240 is detected to be near 90 degrees or near 270 degrees based on an X-axis acceleration of 0 G (or a Y-axis acceleration of 3 G), and that the rotation angle is also detected to be near 90 degrees or near 270 degrees in the next sensing. In this case, it can be determined that the amount of change in the rotation angle is 0 (very small), so it is detected that the nut 240 is not loose. Note that looseness of nut 240 may also be detected based on the difference in the rotation angle detected in multiple consecutive sensings.

[0213] (Variation 5) As a variation of the first embodiment, the degree of looseness of the nut 240 may be detected based on the difference between the X-axis acceleration and the Y-axis acceleration. Figure 39 is a graph showing the average value of the difference between the X-axis acceleration and the Y-axis acceleration when the centrifugal force is 3 G, 6 G, and 10 G. For example, if the centrifugal force is 10 G based on the speed of the vehicle 200 and the difference is detected to be 0 G, the rotation angle of the nut 240 is detected to be near 50 degrees or near 225 degrees. Furthermore, if the centrifugal force is 10 G and the difference is detected to be -10 G, the rotation angle of the nut 240 is detected to be near 90 degrees or near 175 degrees.

[0214] Furthermore, in the above first to fifth embodiments, examples have been shown in which the fastening state of nuts 240 provided on wheels 220 of vehicle 200 is detected, but the present disclosure is not limited thereto. For example, the fastening state of fastening members such as nuts attached to elevator pulleys, belt conveyor pulleys, coffee cups and merry-go-rounds provided in amusement parks, and rotating play equipment provided in parks may also be detected. Among the above examples, in the case of rotating bodies that rotate along a plane perpendicular to gravity, centrifugal force is not affected by gravity, so it is possible to easily detect the fastening state of fastening members even when the centrifugal acceleration is small.

[0215] In the first embodiment, the fastening state (looseness) of the nut 240 is detected based on a change in the rotation angle of the nut 240. However, the present disclosure is not limited to this. The fastening state (looseness) of the nut 240 may be detected based on a comparison of the amount of change in the X-axis acceleration (average X-axis acceleration) and the Y-axis acceleration (average Y-axis acceleration) with a predetermined threshold value.

[0216] In the above embodiment, an example has been shown in which, when information A indicating that the nut 240 has rotated in the tightening direction by a predetermined angle or more is acquired, the tightening state of the nut 240 is detected while ignoring the information A. However, the present disclosure is not limited to this. Even when information indicating that the nut 240 has rotated in the tightening direction by less than the predetermined angle is acquired, the tightening state of the nut 240 may be detected while ignoring the information.

[0217] In the above embodiment, an example has been shown in which the fastening state of the nut 240 is detected while ignoring the information A when the information A is acquired in a state in which the nut 240 has not been loosened for a certain period of time, but the present disclosure is not limited to this. Even if the information A is acquired in a state in which loosening of the nut 240 has been detected within a certain period of time, the fastening state of the nut 240 may be detected while ignoring the information A.

[0218] In the above embodiment, an example has been shown in which, 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 acquired immediately after the information A is acquired, the fastening state of the nut 240 is detected while ignoring the information A. However, the present disclosure is not limited to this. If information indicating that the nut 240 has rotated in the loosening direction by an angle different from the angle of rotation in the tightening direction is acquired immediately after the information A is acquired, the fastening state of the nut 240 may be detected while ignoring the information.

[0219] In the above embodiment, an example has been described in which the process for detecting the fastening state of the nut 240 is performed when the centrifugal acceleration of the wheel 220 is equal to or greater than a predetermined value, but the present disclosure is not limited to this. The process for detecting the fastening state of the nut 240 may also be performed even if the centrifugal acceleration of the wheel 220 is less than the predetermined value.

[0220] In addition, in the above embodiment, an example was shown in which the plane on which the X-axis and Y-axis are provided is perpendicular to the rotation axis O of the wheel 220, but the present disclosure is not limited to this. The above plane may not be perpendicular to the rotation axis O but may intersect with it.

[0221] In the third and fourth embodiments, the fastening state of the nut 240 is detected using an arctangent function, but the present disclosure is not limited to this. The fastening state of the nut 240 may be detected using an arcsine function (arcsin), an arccosine function (arccos), an arccotangent function (arccot), an arccosecant function (arccsc), and an arcsecant function (arcsec).

[0222] In the above embodiment, the number of sensor devices for one wheel 220 may be changed as appropriate as long as it is one or more.

[0223] In the fourth embodiment, the fastening state (looseness) of the nut 240 is detected based on a change in the rotation angle of the nut 240. However, the present disclosure is not limited to this. The fastening state (looseness) of the nut 240 may be detected based on a comparison between the amount of change in at least one of the X-axis normalized value and the Y-axis normalized value and a predetermined threshold value.

[0224] In the fourth embodiment, 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 fastening state of the nut 240 (the amount of change in the rotation angle) may be detected based on only one of the X-axis normalized value and the Y-axis normalized value.

[0225] Furthermore, in the first to fifth embodiments, examples have been shown in which the sensor device is provided on the nut 240, but the present disclosure is not limited to this. The sensor device may be provided on a bolt (a bolt separate from the wheel hub). In this case, unlike the above-described embodiments in which the wheel is fastened to the wheel hub with a wheel nut, the wheel is fastened to the wheel hub with a bolt. The bolt in this case is an example of a "fastening member" in the present disclosure.

[0226] Furthermore, in the first to fifth embodiments, examples have been shown in which the fastening state of the nut 240 is detected by a signal processing unit provided in the sensor device, but the present disclosure is not limited to this. For example, the detected value of the acceleration sensor 1 may be transmitted to an ECU (Electronic Control Unit) provided in the vehicle 200 via the communication unit 3, and the ECU may detect the fastening state of the nut 240 based on the detected value. In this case, the ECU corresponds to one form of the "detection device" of the present disclosure.

[0227] Furthermore, in the first to fifth embodiments, an example was described in which the fastening state of the nut 240 was detected based on the average value of two acceleration measurements acquired during one rotation of the wheel 220. However, the present disclosure is not limited to this. The fastening state of the nut 240 may also be detected based on the average value of an even number of acceleration measurements (four, six, eight, etc.) other than two acquired during one rotation of the wheel 220. Note that a smaller number of measurements can reduce the possibility of deviation in the measurement position due to rotation (reduce the influence of deviation), thereby enabling more accurate detection of the fastening state of the nut 240. Furthermore, the fastening state of the nut 240 does not have to be detected using the average value of two (even) acceleration measurements, as in the first to fifth embodiments. In other words, the fastening state may be detected based on the acceleration (single measurement) acquired in each sensing operation.

[0228] The above-described embodiments and modifications can be combined as appropriate within the scope of no technical contradiction.

[0229] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present disclosure is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims.

[0230] 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) (vehicle body), O Rotation axis, X axis (first axis), Y axis (second axis).

Claims

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

2. The sensing apparatus of claim 1 , wherein the sensing axis includes a plurality of sensing axes, each of which intersects with the rotation axis.

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

4. The detection device according to any one of claims 1 to 3, wherein the state detection unit detects the fastening state of the fastening member based on the acceleration detected by the acceleration detection unit and the centrifugal acceleration applied to the rotating body.

5. The state detection unit is The detection device according to claim 3, further comprising: a detection unit for detecting a fastening state of the fastening member based on an acceleration index indicating a ratio between a first axis acceleration, which is the acceleration of the first axis detected by the acceleration detection unit, and a second axis acceleration, which is the acceleration of the second axis detected by the acceleration detection unit.

6. The detection device according to claim 5 , wherein 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, wherein the state detection unit determines that a change has occurred in the fastening state of the fastening member when the positive and negative acceleration detected by the acceleration detection unit is reversed.

8. The acceleration detection unit detects acceleration at predetermined intervals, The state detection unit is Determining whether the rotation of the rotating body has stopped; 4. The detection device according to claim 1, wherein, when it is determined that the rotating body has stopped rotating, the predetermined period is made longer than when the rotating body is rotating.

9. 4. The detection device according to claim 1, wherein the acceleration detection portion is provided on a nut that fixes a wheel to a vehicle body.

10. The state detection unit is acquiring information on the acceleration detected by the acceleration detection unit at every predetermined period so as to acquire the information on the acceleration detected by the acceleration detection unit an even number of times while the rotating body rotates once; A detection device according to any one of claims 1 to 3, which detects the fastening state of the fastening member based on an average value of the acceleration acquired an even number of times, or an average value of the angle of the fastening member calculated from each of the accelerations acquired an even number of times.

11. The state detection unit is When the centrifugal acceleration of the rotating body is equal to or greater than a predetermined value, a process of detecting a fastening state of the fastening member is performed; The detection device according to claim 10 , wherein the acceleration information is obtained for each of the predetermined periods based on a rotation speed of the rotating body corresponding to the predetermined value.

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

13. A detection method for a detection device having an acceleration detection unit that rotates in conjunction with the rotation of a fastening member that fastens a fastened member to a rotating body, comprising: detecting, by the acceleration detector, an acceleration along a detection axis intersecting a rotation axis of the rotating body; detecting a fastening state of the fastening member based on the acceleration detected by the acceleration detection unit.