JP6088908B2 - Deformation state detection method of tire sensor, tire contact state estimation method, and tire contact state estimation device - Google Patents

Description

  The present invention relates to a method for detecting a deformation state of a sensor disposed in a tire when the vehicle travels, a method for estimating a ground contact state of a tire from a deformation state of a sensor that is deformed according to the ground contact state of the tire, and an apparatus therefor. .

Conventionally, as an apparatus for estimating the road surface condition, an acceleration sensor is attached to the inner surface of the tire to detect the tire vibration generated when the tire contacts the ground, and the detected tire vibration data (acceleration data) There is a wide variety of configurations that transmit to the vehicle body side from the transmitter provided in the vehicle, and provide road surface state estimation means on the vehicle body side to estimate the road surface state on the vehicle body side using the transmitted acceleration data. Used (see, for example, Patent Document 1).
Although a road surface state estimating device having a configuration in which road surface state estimating means is provided on the tire side to estimate the road surface state has been proposed, even with such a configuration, the road surface state estimation result is obtained by wireless communication on the vehicle body side. Sent to.

準静電界は磁界成分を含まず、また、電波のように伝搬する性質がないので、人や車両、物質の周りに静電気帯電電界のように分布し、その極性またはレベルが変化する。
したがって、車体の帯電電位を検出すれば、タイヤと路面との間に生じた帯電電位に対応する電位を検出することができるので、路面状態などのタイヤの状態を精度よく推定することができる。 In addition, a method for estimating the road surface state by detecting the charging potential of the vehicle body has been proposed (for example, Japanese Patent Application No. 2011-282858).
In general, the fact that a charging potential due to static electricity is generated between a tire and a road surface due to contact, separation and friction between the tire and the road surface itself is described in, for example, the background art of Japanese Patent Application Laid-Open No. 2011-225023. As you can see, it is a well-known matter.
On the other hand, since the vehicle body and the tire are capacitively coupled, a potential corresponding to the charged potential generated between the tire and the road surface is generated on the outer surface of the vehicle body.
The electric field distributed on the tire surface and the outer surface of the vehicle body is composed of three elements (radiated electromagnetic field proportional to 1 / r, induction electromagnetic field proportional to 1 / r ² ) constituting the electromagnetic field shown in the following formula (1), Quasi-electrostatic field proportional to 1 / r ³ ), and changes with time due to rolling of the tire as the vehicle travels.

Since the quasi-electrostatic field does not include a magnetic field component and does not have the property of propagating like radio waves, the quasi-electrostatic field is distributed around a person, vehicle, or substance like an electrostatic charging electric field, and its polarity or level changes.
Therefore, if the charging potential of the vehicle body is detected, the potential corresponding to the charging potential generated between the tire and the road surface can be detected, so that the state of the tire such as the road surface state can be accurately estimated.

JP 2011-203017 A

However, in order to transmit acceleration data or the like to the vehicle body wirelessly, a large amount of electric energy is required, and thus it is necessary to install a power generation device and a battery on the tire.
In addition, the method of estimating the road surface condition by detecting the charging potential of the vehicle body does not require a power generator or a battery, but since the S / N ratio is not sufficient, it is necessary to acquire data of multiple rotations and average it. There is.

  The present invention has been made in view of conventional problems, and a method for stably detecting the deformation state of a sensor disposed in a tire on the vehicle body side without using wireless communication, and the detection It is an object of the present invention to provide a method and apparatus for estimating the ground contact state of a tire from the deformation state of a sensor.

As a result of intensive studies, the inventors of the present invention have directly connected one electrode of the charge generation type passive sensor and the wheel to float the other electrode, or capacitively coupled one electrode and the wheel to the other electrode. And detecting the charging potential distributed in the vehicle body, the deformation state of the charge generation type passive sensor appearing in the time-varying waveform of the charging potential of the vehicle body can be accurately detected on the vehicle body side. It has come.
That is, the present invention is a method for detecting the deformation state of a charge generation type passive sensor disposed in a tire on the vehicle body side, on the vehicle body side, a detection electrode disposed on the surface of a metal part in the vehicle body, A reference electrode disposed at a distance from an outer surface of the vehicle body, and electrically connecting one electrode of the charge generation type passive sensor with a wheel and floating the other electrode, A time-varying waveform of a charging potential distributed in the vehicle body, which is a potential between the detection electrode and the reference electrode, is detected, and a deformation state of the charge generation type passive sensor is detected from the time-changing waveform of the detected charging potential. It is characterized by that.
Thereby, the deformation | transformation state of the electric charge generation type passive sensor arrange | positioned in a tire can be detected with a sufficient precision by the vehicle body side, without using wireless communication.
Also, since the ground contact state of the tire is estimated based on the change in the charged potential generated by the detected deformation of the charge generation type passive sensor, the road surface state or The ground contact state of the tire such as lateral force can be stably estimated.
Here, the charge generation type passive sensor is a sensor that expands and contracts when an external force such as stress acts on the sensor, and generates a charge such as a piezoelectric sensor such as PZT.
The charge generation type passive sensor is deformed as the tire tread is deformed to generate electric charges. The deformation state of the tire tread changes depending on the ground contact state of the tire during running (the frictional state between the tire and the road surface, the lateral force acting on the tire, etc.). Therefore, the ground contact state of the tire can be estimated by detecting a change in the charging potential caused by deformation of the charge generation type passive sensor as a change in the charging potential distributed in the vehicle body.
Note that “electrically coupling” one electrode of a charge generation type passive sensor to a wheel is not only a case where the electrode and the wheel are directly connected by a conductive wire and coupled, but also the electrode and the wheel are capacitively coupled. Including the case of combining.
In addition, the “floating state” of the electrode means that the electrode is not connected to any of the voltage source, the ground, and the ground reference signal source.

In addition, the present invention provides a tire ground contact state estimation in which a sensor for detecting a deformation state of a tire during traveling of the vehicle is disposed in the tire, and a ground contact state of the tire is estimated from the deformation state of the tire detected by the sensor. The apparatus uses a charge generation type passive sensor as the sensor, a detection electrode disposed on a surface of a metal part in a vehicle body, a reference electrode disposed at a space from an outer surface of the vehicle body, and the detection A charging potential detecting means for detecting a time-varying waveform of a charging potential distributed in a vehicle body that is a potential between an electrode and the reference electrode; and a ground contact state of the tire is estimated from the time-changing waveform of the detected charging potential. Tire ground contact state estimating means, and one electrode of the charge generation type passive sensor is electrically coupled to the wheel, and the other Electrode, characterized in that floated to.
By adopting such a configuration, it is possible to realize a tire ground contact state estimation device that can reliably estimate the tire ground contact state without providing a power supply means such as a battery, a power storage circuit, and a power generation element in the tire. it can.

In addition, the present invention provides the charge generation type passive sensor as a piezoelectric sensor including a piezoelectric element disposed on a tire inner surface corresponding to a tire contact surface, and an element electrode connected to the piezoelectric element, One of the element electrodes is extended to the vicinity of the bead portion of the tire, and the other electrode is floated.
In addition, the bead part vicinity shall refer to the range which opposes the bead part in a tire inside an inner liner. As a result, the wheel and the piezoelectric element can be capacitively coupled with each other, and the charged potential of the wheel can be set to a potential corresponding to the deformation state of the piezoelectric element, so that it is superimposed on the time-varying waveform of the charged potential distributed in the vehicle body. The output waveform of the piezoelectric element can be detected with high accuracy.
In addition, the present invention provides the charge generation type passive sensor as a piezoelectric sensor including a piezoelectric element disposed on a tire inner surface corresponding to a tire contact surface, and an element electrode connected to the piezoelectric element, One of the element electrodes is connected to the wheel of the tire, and the other electrode is floated.
Thus, if one electrode is directly connected to the wheel, the output waveform of the piezoelectric element superimposed on the time-varying waveform of the charging potential distributed in the vehicle body can be detected with high accuracy.
In addition, since the charge generation type passive sensor is disposed on the tire equator surface where the tire is greatly deformed, the deformation state of the tire can be detected with higher accuracy.

It is a block diagram which shows the structure of the road surface state estimation apparatus which concerns on this embodiment. It is a figure which shows arrangement | positioning of a piezoelectric sensor, a detection electrode, and a reference electrode. It is a figure which shows the example of arrangement | positioning of a piezoelectric element. It is a figure which shows an example of the charging potential of a vehicle body. FIG. 2 is a schematic diagram illustrating a tire deformation state and a force acting on a piezoelectric element, and a diagram illustrating an example of a time-varying waveform of a charging potential generated at both ends of the piezoelectric element. It is a figure which shows the other example of arrangement | positioning of a piezoelectric element. It is a figure which shows the electrification waveform when not making it make the other electrode of a piezoelectric sensor float. It is a figure which shows the electrical equivalent model used for the electrostatic field simulation. It is a figure which shows the simulation result of the voltage distribution when not having made the tire side electrode of a piezoelectric sensor float. It is a figure which shows the relationship between the area of a tire side electrode, and a measurement voltage.

FIG. 1 is a block diagram illustrating a configuration of a road surface state estimation device 10 according to the present embodiment.
The road surface state estimation device 10 includes a piezoelectric sensor 11 as a charge generation type passive sensor, a charged potential detection unit 12, a charging waveform extraction unit 13, a storage unit 14, and a road surface state estimation unit 15. The charged potential detection means 12 includes a detection electrode 12a, a reference electrode 12b, and an amplifier 12c.
As shown in FIG. 2, the piezoelectric sensor 11 is installed on the inner surface of the tire 3, and the charged potential detection means 12 is installed on the vehicle body 2. Each means from the charging waveform extracting means 13 to the road surface condition estimating means 15 is composed of a storage device such as a ROM and a RAM and a microcomputer program, and a vehicle control device (not shown) for controlling the running state of the vehicle 1. 2) and incorporated in the electronic unit and disposed on the vehicle body side (for example, on the frame of the vehicle body 2).

The piezoelectric sensor 11 is a charge generation type passive sensor provided with a piezoelectric element 11a and element electrodes 11b and 11c, as shown in FIG. 3A. As shown in FIG. It is attached to the inner surface of the inner liner 3c which is the inner surface.
As a material constituting the piezoelectric element 11a, for example, piezoelectric ceramics such as lead zirconate titanate (PZT; trade name) and piezoelectric polymers such as polyvinylidene fluoride (PVDF) are preferably used. In this example, a piezoelectric film made of PVDF is used as the piezoelectric element 11a, and the piezoelectric sensor 11 having a structure in which element electrodes 11b and 11c are formed on both surfaces of the piezoelectric film is used.
Further, in this example, as shown in FIG. 3C, the piezoelectric sensor 11 is disposed on the inner side in the tire radial direction of the inner liner 3c so that the longitudinal direction of the piezoelectric film faces the tire circumferential direction. This is because when the piezoelectric film expands and contracts in the longitudinal direction, the polarization becomes large, and when the film is used, it is easier to stick to the annular tire inner surface. In the case where the length of the piezoelectric element 11a is shorter than the ground contact length of the tire 3 as in this example, there is no particular problem even if piezoelectric ceramic is used as the piezoelectric element 11a.
In addition, as the mounting position of the piezoelectric sensor 11, there is an amount of electric charge generated to be a position corresponding to the center in the width direction of the ground contact surface of the tread 3 a (tire equatorial plane), which is the position where the deformation during tire traveling is the largest. Since it becomes large, it is preferable.

  In this example, the piezoelectric sensor 11 is attached to the inner surface side of the inner liner 3c using an insulating adhesive such as an epoxy resin. At this time, it is preferable to affix the piezoelectric sensor 11 after buffing the inner surface side of the inner liner 3c in advance to make small irregularities on the bonding surface. Thereby, since the piezoelectric sensor 11 can be firmly adhered to the tire inner surface, the piezoelectric element 11a can be deformed according to the deformation state of the tread 3a. Moreover, since the thickness of the adhesive layer can be made uniform by providing small irregularities on the adhesive surface, it is possible to prevent the generation of unnecessary noise due to the variation in the adhesive state.

In this example, in order to accurately detect the deformation state of the piezoelectric element 11a, one element electrode (here, the element electrode of the tire chamber 3s) 11b of the piezoelectric sensor 11 is connected to the tire via the lead wire 11d. 3 is directly connected to the wheel 3b, and the other element electrode (element electrode on the tire inner surface side) 11c is floated. On the other hand, when the element electrodes 11b and 11c are respectively connected to the wheel 3b and the tire inner surface, the piezoelectric element 11a itself acts as an electrode quasi-electrostatically, so that the piezoelectric element 11a passes through the tire 3. Thus, it is electrically coupled to the road surface 4. As a result, since the wheel 3b and the road surface 4 are short-circuited, not only the charging potential detected by the detection electrode 12a is lowered, but also unnecessary noise is generated, and sufficient and stable sensor output (deformation of the piezoelectric element 11a) It becomes difficult to detect the charging potential due to the state.
In this example, the wiring of the piezoelectric element 11a is only on the wheel 3b side, so that the element electrode 11b electrically connected to the wheel 3b is a ground side electrode and the element electrode 11c which is the other electrode is not wired. I am doing so. Therefore, the electric charge according to the expansion-contraction of the circumferential direction of the tire 3 of the piezoelectric element 11a can be effectively charged to the wheel 3b.

In order to electrically connect the wheel 3b of the tire 3, it is not always necessary to directly couple the element electrode 11b and the wheel 3b with the lead wire 11d. It is good also as the structure extended. Accordingly, the element electrode 11c and the wheel 3b can be reliably capacitively coupled, so that the wheel 3b can be charged with a charge corresponding to the expansion and contraction of the piezoelectric element 11a in the circumferential direction of the tire.
In order to float the element electrode 11c, for example, a high-resistance insulator may be disposed between the element electrode 11c as the other electrode and the inner surface side of the inner liner 3c. Further, the element electrode 11c may be omitted.
In this example, as described above, when the piezoelectric sensor 11 is attached to the tire inner surface, an insulating adhesive such as an epoxy resin is used as an adhesive, so that the element electrode 11c is in a floating state. As in this example, when the length of the piezoelectric element 11a is shorter than the grounding length of the tire 3 and the area of the element electrodes 11b and 11c is small, the element electrode 11c and the tire 3 are directly connected. Even if there is a portion, the element electrode 11c can be regarded as being in a substantially floating state.

The detection electrode 12 a of the charging potential detection means 12 is a flat electrode, is disposed with a predetermined gap from the outer surface of the vehicle body 2, and is capacitively coupled to the vehicle body 2. In this example, by inserting a plate-like dielectric material having a constant thickness in the gap between the outer surface of the vehicle body 2 and the detection electrode 12a, the capacitance between the vehicle body 2 and the vehicle body 2 is increased. The gap is ensured.
On the other hand, the reference electrode 12 b is also composed of a plate-like electrode, and is attached to the outer surface of the vehicle body 2 in a state of being electrically insulated from the vehicle body 2 by the support member 5. As shown in FIG. 2, the support member 5 includes a vibration isolation table 5 a provided on the outer surface of the vehicle body 2, a cylindrical support table 5 b provided on the vibration isolation table 5 a, and an upper end of the support table 5 b. And a bar-like support bar 5c made of a resin such as acrylic or urethane, which is attached so as to protrude, and the reference electrode 12b is attached to the tip of the support bar 5c. Accordingly, the reference electrode 12b can be separated from the charged vehicle body 2 (for example, 100 [mm] or more), and the reference electrode 12b and the vehicle body 2 can be electrically insulated. It can be stably kept at zero potential.
The amplifier 12c includes a detection element such as an FET (Field Effect Transistor) and an amplifier, and detects and amplifies a charged potential that is a potential between the detection electrode 12a and the reference electrode 12b.

Since the vehicle body 2 and the tire 3 are capacitively coupled, the outer surface of the vehicle body 2 has a charging potential (hereinafter referred to as a base potential) due to a change in electrostatic capacitance between the tire 3 and the road surface 4. A charging potential is generated in which a charging potential (hereinafter referred to as a piezoelectric potential) due to the deformation of the tire that appears every rotation of the tire is superimposed. Therefore, between the detection electrode 12a and the reference electrode 12b, the base potential distributed over the entire vehicle body 2 using the electric charge charged to the tread 3a due to the contact between the tire 3 and the road surface 4 as a generation source, and the expansion and contraction of the piezoelectric element 11a. In response, a charge potential signal including a piezoelectric potential generated using the charge generated on the wheel 3b as a generation source is continuously output.
The piezoelectric potential is larger than the base potential regardless of the road surface condition, and the frequency of the base potential is higher than the frequency of the piezoelectric potential, so that the time-varying waveform of the charging voltage is as shown in FIG. The piezoelectric potential is superimposed on the potential. This means that the detection electrode 12a provided on the vehicle body side detects the output of the piezoelectric element 11a provided on the tire side. That is, a signal corresponding to the deformation state of the piezoelectric element 11a generated on the tire side is sent to the vehicle body 2 side without using communication means such as a transmitter.

The charging waveform extracting means 13 performs A / D conversion on the signal of the charging potential that is amplified and continuously output by the amplifier 12c, and also changes the time-dependent waveform of the charging potential for one rotation of the tire (hereinafter referred to as charging waveform). Extract). Note that the charging waveform to be extracted may have a length of two rotations of the tire or three or more rotations. Thereby, since the average in multiple rotation can be taken, the estimation accuracy of a road surface state improves.
At this time, if the high frequency component is removed using a filter and low frequency noise caused by the adhesion state of the piezoelectric element 11a is removed, the base potential is also reduced. A charging waveform close to a time change waveform (sensor output waveform) can be extracted.

The storage means 14 associates the reference peak value V _k (R), which is the peak value at the kicking point E _k that appears in the charging waveform created by running various road surface conditions in advance, with the road surface state R at that time. The R-V table 14T and the threshold value K used for determination of the road surface state are stored.
The road surface state estimation means 15 includes a peak value calculation unit 15 a and a determination unit 15 b, and estimates the state of the road surface 4 on which the tire 3 is traveling from the charging waveform extracted by the charging waveform extraction unit 13. Specifically, the peak value calculation unit 15a calculates the peak value V _k at the kicking point E _k that appears in the charging waveform, and the determination unit 15b calculates the calculated peak value V _k and R−V. The road surface condition is estimated by comparing with the reference peak value V _k (R) stored in the table 14T.
For example, if the road surface condition to determine whether the WET road or a dry road surface, the storage unit 14, the reference peak value V _k of a dry road surface (R _D) and the reference peak value V _k in WET road (R _W ) is stored in the RV table 14T corresponding to the dry road surface and the WET road surface, respectively, and the peak value V _k at the kicking point E _k calculated from the charging waveform and the reference on the dry road surface are stored. The road surface condition is estimated by comparing the peak value V _k (R _D ) with the reference peak value V _k (R _W ) on the WET road surface. Since the reference peak value V _k (R _D ) on the dry road surface is larger than the reference peak value V _k (R _W ) on the WET road surface, the magnitude of the calculated peak value V _k and the reference peak value V _k (R _D ), V _k (R _W ), the road surface condition can be easily estimated by examining the magnitude relationship.

Next, operation | movement of the road surface state estimation apparatus 10 is demonstrated.
A vehicle equipped with a tire 3 with a piezoelectric sensor 11 attached to the inner liner 3c is run, and the capacitance between the tire 3 and the road surface 4 is changed by a detection electrode 12a provided on the vehicle body 2 side. A charging potential in which a piezoelectric potential that changes in accordance with the deformation state of the piezoelectric element 11a is superimposed on the resulting base potential is detected.
The base potential is a charging potential distributed over the entire vehicle body 2 using the electric charge charged on the tread 3a by the contact between the tire 3 and the road surface 4 as a generation source, and the amplitude thereof changes depending on the road surface state. The average value of the base potential amplitude on the WET road surface is about 1/5 of the average value of the base potential amplitude on the dry road surface.
On the other hand, the piezoelectric potential also changes depending on the ground contact state of the tire 3 (here, the frictional force from the road surface 4 acting on the tire 3). Further, as shown in FIG. 4, the base potential changes positively and negatively with time, whereas the piezoelectric potential has a waveform having a large peak at the stepping-on point and the kicking-out point every time the tire rotates. These two peaks have a much larger amplitude than the base potential on both WET and dry road surfaces.

FIG. 5A is a schematic diagram showing the deformation state of the tire 3 during traveling and the force acting on the piezoelectric element 11a. The left-right direction in the figure is the front-rear direction of the vehicle 1, and the direction perpendicular to the paper surface is the axle direction. is there. As shown in the figure, the shape of the tire 3 that was arcuate at the place where the tire 3 is in contact with the ground is stretched by a load. That is, in the region where the tire 3 is grounded (grounding region), the tire 3 is subjected to tensile stress in the vehicle longitudinal direction. In contrast, the region prior to the grounding (the region before the depression point E _f; depression front region); area after kicking area after than the region (trailing point E _k after leaving from the ground plane and ), Compressive stress acts. If the piezoelectric element 11a is polarized so that the tire chamber 3s side is charged to (+) when it receives a compressive stress in the circumferential direction and is charged to (-) when it receives a tensile stress, the piezoelectric element 11a At both ends, a charging potential having a (+) peak at the depression point E _f and a (−) peak at the kicking point E _k as shown in FIG. 5B is generated.

In this example, the element electrode 11b on the tire chamber 3s side of the piezoelectric sensor 11 is electrically connected to the wheel 3b of the tire 3 via the lead wire 11d, and the element electrode 11c on the tire inner surface side is floating. As a result, charges flow from the wheel 3b into the element electrode 11b and are accumulated, and the wheel 3b is charged. At this time, the charging potential of the wheel 3b is a charging potential corresponding to the charging potential of the piezoelectric element 11a, that is, the expansion and contraction of the piezoelectric element 11a in the circumferential direction of the tire 3.
Therefore, if the detection electrode 12a and the reference electrode 12b are provided as the charging potential detection means 12 on the vehicle body 2 side, and the charging potential of the vehicle body 2 is detected, the change in capacitance between the tire 3 and the road surface 4 is caused. The base potential to be detected and the piezoelectric potential that changes in accordance with the deformation state of the piezoelectric element 11a can be detected simultaneously. The charged potential is amplified by the amplifier 12c and sent to the charging waveform extracting means 13.

Next, the charging waveform extraction means 13 extracts a charging waveform that is a time-varying waveform of the length of one rotation of the tire at the charging potential.
Next, the peak value V _k at the kicking point E _k is calculated from the extracted charging waveform, and the calculated peak value V _k , the reference peak value V _k (R _D ) on the dry road surface, and the WET road surface are calculated. Is compared with the reference peak value V _k (R _W ), and if | V _k (R _D ) −V _k | <K _D , the road surface is estimated to be a dry road surface, and | V _k (R _W ) − If V _k | <K _W , the road surface is estimated to be a WET road surface. If none of them is found, the peak value V _k is calculated again and compared with the reference peak value V _k (R).
The road surface condition may be estimated from the magnitude relationship between the magnitude of the calculated peak value V _k and the reference peak values V _k (R _D ), V _k (R _W ).

  As described above, in the embodiment, the element electrode 11b on the tire chamber 3s side of the piezoelectric sensor 11 disposed in the tire 3 is electrically coupled to the wheel 3b, and the element electrode 11c on the tire inner surface side is floated. In addition, the detection electrode 12a and the reference electrode 12b are provided on the vehicle body 2 side to detect the charging potential distributed in the vehicle body 2, thereby generating the charge charged in the tread 3a by the contact between the tire 3 and the road surface 4. As described above, the vehicle body 2 side detects the charging potential distributed throughout the vehicle body 2 and the deformation state of the piezoelectric sensor 11 superimposed on the charging potential, so that the piezoelectric sensor 11 can be used without using wireless communication. It becomes possible to detect the deformation state. In addition, since the ground contact state of the tire is estimated from the charging waveform that is a time-varying waveform of the detected charging potential, the tire is not provided with power supply means such as a battery, a power storage circuit, and a power generation element. The grounding state can be reliably estimated.

In the above-described embodiment, the road surface state is estimated by arranging the piezoelectric film so that the longitudinal direction of the piezoelectric film faces the tire circumferential direction. However, as shown in FIG. 6A, the longitudinal direction of the piezoelectric film is the tire width direction. It is possible to obtain multi-directional forces acting on the tire contact surface such as lateral force and longitudinal force by arranging the tires so as to face each other or crossing the tire circumferential direction and the tire width direction. As shown in FIG. 6B, when road frictional force acts on the tread on the ground contact surface of the tire 3, the peak value of the piezoelectric sensor 11A in which the longitudinal direction of the piezoelectric film faces the tire circumferential direction is the largest. The peak value of the piezoelectric sensor 11B in which the longitudinal direction faces the tire width direction is the smallest, and the peak value of the piezoelectric sensors 11C and 11D in which the longitudinal direction is inclined by 45 ° with respect to the tire circumferential direction is an intermediate size. become. On the other hand, when a lateral force acts on the tire 3, the peak value of the piezoelectric sensor 11A does not change, but the peak values of the piezoelectric sensors 11B to 11D increase. Therefore, the magnitude of the lateral force acting on the tire 3 can be estimated by comparing the peak values of the piezoelectric sensors 11A to 11D.
In addition, when a plurality of piezoelectric films having different longitudinal directions are attached along the circumferential direction of the tire 3, the longitudinal direction has a period T corresponding to one round of the tire, as shown in FIG. 6C. Since the charging potentials of the plurality of piezoelectric sensors 11A to 11D having different values appear at predetermined time intervals, the multi-directional force acting on the tire contact surface is separated by time and the components of the force acting on the tire 3 are separated and extracted. be able to.
Further, by separating multidirectional forces acting on the tire contact surface, it is possible to estimate the tire posture angle such as the slip angle and the camber angle.

In the above embodiment, the road surface state is estimated from the peak value V _{k at} the kicking point E _k that appears in the charging waveform. However, the storage means 14 shows the relationship between the peak value at the depression point E _f and the road surface state. And a table showing the relationship between the peak value at the kicking point E _k and the road surface state are stored, and the road surface state estimating means 15 stores the peak value at the stepping point E _{f and} the peak at the kicking point E _k . The road surface condition may be estimated using both of the values. Alternatively, the storage unit 14 stores the charging waveform itself for each road surface state, and compares the detected charging waveform with the charging waveform stored for each road surface state stored in the storage unit 14 to estimate the road surface state. May be.
In this example, one piezoelectric sensor 11 is provided, but a plurality of piezoelectric sensors 11 are attached at a predetermined distance in the tire circumferential direction, and the peak value V _{k at} the kicking point E _k appearing in the charging waveform is shown. The road surface condition may be estimated by comparing the average value with the reference peak values V _k (R _D ) and V _k (R _W ).

In the above embodiment, the charging waveform extraction unit 13 extracts the charging waveform for one rotation of the tire. However, a charging waveform having a length of two or three or more rotations may be extracted. Thereby, since the average of the piezoelectric potential in a plurality of rotations can be taken, the estimation accuracy of the road surface state can be improved.
Further, if a charging waveform including at least two or more time-varying piezoelectric waveforms is obtained, it is possible to obtain a rotation time that is a time required for the tire 3 to make one rotation. Specifically, the rotation time is the time between the peak of the depression point E _f or the peak of the kicking point E _k of the piezoelectric waveform superimposed on the diameter of the tire 3 and two time-varying waveforms.

<Experimental example>
FIG. 7A shows a charging waveform when one electrode (element electrode 11b) of the piezoelectric sensor 11 is electrically connected to the wheel and the other electrode (element electrode 11c) is in a floating state. ) Is a charging waveform when the element electrode 11c is electrically connected to a copper foil (tire side reference electrode) provided on the inner surface side of the inner liner 3c of the tire 3. Thus, it has been experimentally confirmed that a larger signal voltage can be obtained by floating the element electrode 11c of the piezoelectric sensor.
Further, an electrical equivalent model as shown in FIGS. 8A and 8B was created for such a tendency, and was supported by an electrostatic field simulation (EEM-STF).
Specifically, the piezoelectric element 11a is a point charge 21, the element electrode 11b is a surface electrode (wheel side electrode 22), and the element electrode 11c and the tire side reference electrode are surface electrodes (tire side electrode 23). . Further, the wheel 3b and the lead wire 11d were used as the conductor 24, and the tire 3 was formed as a rectangular parallelepiped dielectric 25 having a dielectric constant ε = 2.4. Reference numeral 26 denotes a road surface.
Here, the length direction of the piezoelectric element 11a is the X direction, the width direction is the Y direction, the thickness direction is the Z direction, and the length of the wheel side electrode 22 is 30 mm and the width is 10 mm. Moreover, the electrode area of the tire side electrode 23 was made variable by setting the width of the tire side electrode 23 to 10 mm and making the length variable. In addition, when the thickness of the dielectric 25 was 10 mm and the element electrode 11c was floated, the area of the tire side electrode 23 was calculated as zero.

FIGS. 9A and 9B are diagrams showing voltage distributions obtained by electrostatic field simulation. FIG. 9A shows a case where the device electrode 11c is in a floating state, and FIG. This is the voltage distribution when the area is 1000 mm ² . The potential of the road surface 26 was set to 0V.
The potential around the wheel-side electrode 22 and the conductor 24 is higher when the element electrode 11c is in a floating state. That is, it can be seen that the amount of charge charged on the wheel 3b is larger when the element electrode 11c is floated.
FIG. 10 is a diagram showing the relationship between the area of the tire-side electrode 23 and the voltage value at the measurement point (conductor 24 tip). As shown in the figure, it can be seen that the measured voltage value decreases as the area of the tire-side electrode 23 increases. Accordingly, it was confirmed by electrostatic field simulation that a larger signal voltage can be obtained by floating the element electrode 11c of the piezoelectric sensor.

  As mentioned above, although this invention was demonstrated using embodiment, the technical scope of this invention is not limited to the range as described in the said embodiment. It will be apparent to those skilled in the art that various modifications or improvements can be added to the embodiment. It is apparent from the claims that the embodiments added with such changes or improvements can be included in the technical scope of the present invention.

1 vehicle, 2 body, 3 tires, 3a tread, 3b wheel,
3c inner liner, 3d bead, 3s tire chamber, 4 road surface,
5 support member, 10 road surface state estimation device, 11 piezoelectric sensor, 11a piezoelectric element,
11b, 11c element electrodes, 11d lead wires, 12 charged potential detection means,
12a sensing electrode, 12b reference electrode, 12c amplifier,
13 charging waveform extraction means, 14 storage means, 14TRV table,
15 road surface state estimation means, 15a peak value calculation unit, 15b determination unit.

Claims (6)

A method for detecting a deformation state of a charge generation type passive sensor disposed in a tire on a vehicle body side,
On the vehicle body side, a detection electrode disposed on the surface of the metal part in the vehicle body and a reference electrode disposed with a space from the outer surface of the vehicle body are provided.
In the state where one electrode of the charge generation type passive sensor is electrically coupled to the wheel and the other electrode is floated, the charged potential distributed in the vehicle body is the potential between the detection electrode and the reference electrode. Detect time-varying waveforms
A method for detecting a deformation state of a sensor in a tire, wherein the deformation state of the charge generation type passive sensor is detected from the time-varying waveform of the detected charging potential. A method for estimating a ground contact state of a running tire based on a deformation state of a charge generation type passive sensor disposed in the tire,
On the vehicle body side, a detection electrode disposed on the surface of the metal part in the vehicle body and a reference electrode disposed with a space from the outer surface of the vehicle body are provided.
In the state where one electrode of the charge generation type passive sensor is electrically coupled to the wheel and the other electrode is floated, the charged potential distributed in the vehicle body is the potential between the detection electrode and the reference electrode. Detect time-varying waveforms
Detecting a change in charging potential generated by deformation of the charge generating passive sensor from the time-varying waveform of the detected charging potential,
A tire ground contact state estimation method, wherein the tire ground contact state is estimated based on a change in the charged potential generated by the detected deformation of the charge generation type passive sensor. A tire ground contact state estimation device for disposing a sensor that detects a deformation state of a tire during vehicle travel in the tire and estimating a ground contact state of the tire from a deformation state of the tire detected by the sensor,
While using a charge generation type passive sensor as the sensor,
A detection electrode disposed on the surface of a metal part in the vehicle body;
A reference electrode disposed at a distance from the outer surface of the vehicle body;
A charging potential detecting means for detecting a time-varying waveform of a charging potential distributed in a vehicle body that is a potential between the detection electrode and the reference electrode;
A tire ground contact state estimating means for estimating the ground contact state of the tire from the time-change waveform of the detected charging potential;
A tire ground contact state estimating device, wherein one electrode of the charge generation type passive sensor is electrically coupled to a wheel and the other electrode is floated. The charge generation type passive sensor is a piezoelectric sensor including a piezoelectric element disposed on a tire inner surface corresponding to a tire contact surface, and an element electrode connected to the piezoelectric element,
4. The tire ground contact state estimating device according to claim 3, wherein one of the element electrodes extends to the vicinity of a bead portion of the tire and the other electrode is floated. 5. The charge generation type passive sensor is a piezoelectric sensor including a piezoelectric element disposed on a tire inner surface corresponding to a tire contact surface, and an element electrode connected to the piezoelectric element,
4. The tire ground contact state estimating device according to claim 3, wherein one of the element electrodes is connected to a wheel of the tire and the other electrode is floated. The tire contact state estimation device according to any one of claims 3 to 5, wherein the charge generation type passive sensor is disposed on a tire equator plane.

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