JP2003285728A - Method of measuring force on tire and method of measuring friction coefficient - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of easily and highly accurately measuring vertical force on a tire, required for highly accurately measuring a road surface friction coefficient. <P>SOLUTION: With the rotation of the tire having a magnetized pattern along the peripheral direction, a characteristic value to be changed depending on the vertical force for a magnetic flux density pattern corresponding to the rotation of the tire, detected by using a magnetic sensor fixed to the side of a vehicle body, is measured to find the vertical force on the tire. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention works on a tire for accurately measuring a road surface friction coefficient required for control of a vehicle anti-skid brake system (hereinafter referred to as "ABS") or a traction control system. It relates to a method for measuring vertical forces.

[0002]

2. Description of the Related Art In order to improve the performance of an ABS used in a vehicle, it is effective to perform lock / unlock control with a road friction coefficient as large as possible. This road friction coefficient is constant. Since the state depends on the slip ratio of the wheel, the ABS is designed to control locking and unlocking in the vicinity of the slip ratio that gives the maximum road surface friction coefficient.

Therefore, in conventional ABS, the slip ratio is generally calculated from the measured vehicle speed and the wheel rotation speed, and the braking is automatically controlled so that the slip ratio falls within a predetermined range. Target.

However, this method of controlling the slip ratio to obtain the optimum road surface friction coefficient is effective on a constant road surface, but in actual running, the slip ratio and the road surface friction are dependent on the road surface material, weather and the like. There is a problem that the relationship with the coefficient is greatly influenced and the optimum road surface friction coefficient cannot be obtained even if the slip ratio is controlled within a predetermined range. Therefore, the road surface acts on the tire in the circumferential and vertical directions, and the coefficient of friction is determined directly from the measured force.
It is desirable to control the braking so that the obtained coefficient of friction becomes optimum, and as a method for obtaining the force acting on this tire, the method described in Japanese Patent Publication No. 10-506346 is known.

In this conventional force measuring method, four pairs of magnets having magnets arranged at two reference points on one side wall portion of the tire on the same radius and at different radial positions are used. They are arranged 90 degrees apart around the central axis, and magnetic sensors are fixedly provided on the vehicle at radial positions corresponding to the respective reference points. The timing at which the point and the magnetic sensor corresponding to these points are positioned so as to face each other is regarded as the timing at which the peak of the magnetic flux density detected by the magnetic sensor appears, and from the mutual time lag with respect to each reference point of this timing, the magnet The relative displacement of the reference points within the pair and the relative displacement of the reference points between the magnet pairs are calculated, and based on these relative displacements, the tire circumferential direction and Calculate the distortion of straight direction and from the calculated strain and the known tire stiffness and requests the force acting in the circumferential direction and the vertical direction.

However, according to this method, when calculating the relative deviation between the reference points from the time deviation, it is necessary to take in the data of the rotational speed of the wheel which constantly changes, and the control becomes complicated. There is a problem that the accuracy of calculation deteriorates due to the influence of the accuracy of the wheel rotation speed.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and it is possible to easily and easily generate a vertical force acting on a tire, which is necessary for highly accurate measurement of a road surface friction coefficient. It is intended to provide a method for measuring with high accuracy.

[0008]

SUMMARY OF THE INVENTION The present invention has been accomplished in order to achieve the above-mentioned object, and its gist structure and operation will be described below.

According to a first aspect of the present invention, there is provided a method for measuring a force acting on a tire, wherein a tire having a predetermined magnetization pattern is rotated in a circumferential direction to generate a rotating magnetic field, and a magnetic flux density of the generated rotating magnetic field. Is continuously detected by a magnetic sensor fixed to the vehicle body, and from the detected magnetic flux density, a magnetic flux density pattern representing the magnetic flux density for each rotation angle position of the tire is specified for each rotation of the tire, and specified. The force in the vertical direction acting on the tire is obtained in real time from the predetermined characteristic value of each magnetic flux density pattern.

The method of measuring the force acting on the tire according to the present invention will be described in more detail below. At least a part of the tire is magnetized, or a magnet is embedded in this part to form a magnetization pattern that changes along the circumferential direction on the tire, and the tire is mounted on a wheel. On the other hand, the magnetic sensor is fixedly provided in a non-rotating portion of the vehicle body on the side opposite to the tire with the suspension in between, for example, inside the fender immediately above the tire. At this time, the magnetic sensor can detect the magnetic flux density of the magnetic field generated by the magnetization pattern of the tire at the position of the magnetic sensor.

When the tire is rotated, the magnetic field generated by the magnetization pattern formed on the tire also rotates,
When the tire is rotated exactly once, the time change of the magnetic flux density corresponding to this one rotation is obtained.If this time change is replaced by the change of the tire rotation angle position, each tire rotation angle for one rotation of the tire is obtained. A magnetic flux density pattern that represents a pattern of magnetic flux density that changes depending on the position can be specified.

The shape of the magnetic flux density pattern specified in this way changes depending on the vertical force applied to the tire. This is because when a vertical force is applied to the tire, the same force also acts on the axle that supports the tire, and this force deforms the suspension. The relative position of the sensor with the tire changes. This is because the change in the relative position appears as a change in the magnetic flux density pattern.

From this, the vertical load applied to the tire is changed to create a magnetic flux density pattern for each level of the vertical load, and the vertical load and the predetermined characteristics of the magnetic flux density pattern, for example, the size of the magnetic flux density peak are compared. The relational expression can be prepared in advance, and if the peak size of the magnetic flux density pattern specified in real time when the tire is run on the actual road surface is substituted into this relational expression, the vertical force is calculated backwards. You can ask.

According to the method for measuring the force acting on the tire according to the present invention, as described above, a predetermined characteristic of the magnetic flux density pattern, which is specified from the time change of the magnetic flux density detected by the magnetic sensor, for example, Since the peak size can be determined independently of the tire rotation speed, the measurement system can be simplified and highly accurate.

In the above description, the magnitude of the peak is taken as an example of the predetermined characteristic of the magnetic flux density pattern, but in addition to this, the vertical force acting on the tire, such as the phase of the peak or the phase difference between the two peaks, is also used. Any characteristic may be used as long as it changes according to. The term "magnetization pattern" as used herein refers to the magnetic flux density of a magnetic field emitted from the surface of a magnetized object, the component being perpendicular to this surface, as a change along a predetermined direction on this surface. Yes, specifically, a magnetic sensor such as a Gauss meter, which is brought close to the surface of this object, is moved by controlling its posture so that the magnetic field lines whose detection direction is perpendicular to the surface of the object are captured. The magnitude of the magnetic flux density appearing on the vertical axis and the position along the predetermined direction on the horizontal axis are the magnetization patterns of this object.

According to a second aspect of the present invention, there is provided a method for measuring a force acting on a tire, according to the first aspect, wherein the belt is magnetized to form a predetermined magnetization pattern on the tire.

The belt of the tire is usually made of steel. By applying a predetermined magnetic field to the tire having the steel belt, a tire having a desired magnetization pattern can be easily obtained, which is advantageous. Is.

According to a third aspect of the present invention, there is provided a method for measuring a force acting on a tire, according to any one of the first and second aspects, wherein the peak size of the magnetic flux density pattern is set as a predetermined characteristic, and the tire rotates once. The force in the vertical direction acting on the tire is obtained in real time from the size of the peak specified for each.

For example, in the case where a tire magnetization pattern is formed so that the magnetic flux density pattern has one peak and the magnitude of the peak value is measured, the peaks appearing with the rotation are measured in the order in which they appear. Since the peak size can be measured regardless of the rotation speed of the tire regardless of whether the rotation speed of the tire is fast or slow, the method of measuring the force acting on this tire is as described above. As described above, the measurement system can be simplified and highly accurate.

According to a fourth aspect of the present invention, there is provided a method for measuring a force acting on a tire according to any one of the first and second aspects, wherein the peak phase of the magnetic flux density pattern is set to a predetermined characteristic and the tire is rotated once per revolution. The force in the vertical direction acting on the tire is calculated in real time from the phase of the peak specified in.

The phase of the peak of the magnetic flux density pattern can be measured from the time change of the magnetic flux density detected by the magnetic sensor as follows. When the rotational position of the tire reaches a predetermined position with respect to the non-rotating part of the axle,
A rotary position sensor that generates a pulse with this position as the zero degree position is provided, the interval between successive pulses from the rotary position sensor is T, and the time from the first pulse to the peak is Tp.
Then, assuming that α = (Tp / T) × 360 ° is the peak phase α, the phase α has a value that is not related to the rotation speed.

As described above, the method of measuring the force acting on the tire can measure the peak phase regardless of the rotational speed of the tire. Therefore, the method of measuring the force acting on the tire is As described above, the measurement system can be simplified and highly accurate.

According to a fifth aspect of the present invention, there is provided a method for measuring a tire friction coefficient, wherein the force in the vertical direction obtained by the method for measuring a force acting on a tire according to any one of the first to fourth aspects is separately measured. The friction coefficient of the tire is obtained in real time from the obtained circumferential force acting on the tire.

In this tire friction coefficient measuring method, the friction coefficient of the tire is directly measured from the frictional force acting on the tire and the vertical force. Therefore, the tire friction coefficient can be measured according to its definition. The coefficient of friction can be obtained.

According to a sixth aspect of the present invention, in the method of measuring a tire friction coefficient according to the fifth aspect, at the time of determining the force acting in the circumferential direction, at least one location in the circumferential direction of the sidewall portion of the tire. A magnetic body extending substantially in the radial direction crosses an annular magnetic path that is fixedly formed on the vehicle body side as the tire rotates and crosses the sidewall portion at two points on the tire radius. Then, the change in the amount that correlates with the magnetic flux density of the annular magnetic path is measured, the change in the tilt angle of the magnetic body is calculated based on this measurement value, and the force acting in the circumferential direction is calculated from this tilt angle. It is a thing.

This tire friction coefficient measuring method is as follows:
When the magnetic substance arranged in the tire enters the annular magnetic path and the magnetic flux density of the magnetic path is maximized, the change in the physical quantity correlated with this magnetic flux density is measured, and from the size of this physical quantity,
The inclination of the magnetic body in the radial direction is calculated, and the circumferential force is calculated from the calculated inclination of the magnetic body.

That is, the annular magnetic path is divided into an inner tire portion and an outer tire portion with the outer surface of the sidewall as a boundary. However, when there is no magnetic material in the inner tire portion, the magnetic path is substantially open. Since the magnetic flux density is extremely low, the magnetic flux density rises sharply when a magnetic material enters this magnetic path. The peak magnetic flux density becomes maximum when the projection line of the magnetic material onto the tire equatorial plane completely coincides with the radial direction, and the larger the inclination angle with respect to the radial direction, the smaller the peak magnetic flux density. Therefore, it is possible to know the tilt angle by measuring the peak value of the physical quantity by preparing in advance the relational expression between the peak value of the physical quantity that correlates with the magnetic flux density and the tilt angle of the magnetic body by experiments or the like. it can.

Since the inclination angle of the magnetic body is substantially proportional to the force in the circumferential direction of the tire, the relational expression between the inclination angle and the force in the circumferential direction is also obtained in advance by experiments and the like. If the inclination angle of is known, the force in the circumferential direction can be calculated and measured by checking this relational expression.

According to a seventh aspect of the present invention, in the tire friction coefficient measuring method according to the sixth aspect, an amount correlating with the magnetic flux density of the annular magnetic path is spirally wound around the magnetic path. It is the integral value of the electromotive force induced in the coil.

In this tire friction coefficient measuring method, when the force acting in the circumferential direction is obtained, an amount correlating with the magnetic flux density of the annular magnetic path is induced in a coil spirally wound around this magnetic path. Since the integrated value of the electromotive force is calculated, the inclination angle of the magnetic body can be easily calculated by preparing a relational expression that represents the relationship between the integrated value of the electromotive force at the peak position and the inclination angle of the magnetic body. Therefore, the circumferential force acting on the tire can be measured.

Moreover, since the electromotive force is represented by the time derivative of the magnetic flux density, even if the circumferential magnetic flux density distribution of the annular magnetic path is the same, the electromotive force itself has a larger peak value as the tire rotates faster. However, the time-integrated electromotive force represents the original circumferential magnetic flux density distribution, and its peak value does not depend on the rotation speed. This allows the electromotive force integral value at the peak position and the tilt angle of the magnetic material to be uniquely related.

According to this tire friction coefficient measuring method,
When determining forces acting in either the vertical direction or the circumferential direction, it is possible to measure these forces without using data relating to the rotational speed of the tire, so that the measurement system can be simplified and the accuracy can be improved. It can be expensive.

The tire friction coefficient measuring method according to claim 8 is the method according to claim 6, wherein an amount correlating with the magnetic flux density of the annular magnetic path is spirally wound around the magnetic path. It is an inductance for a predetermined alternating current applied to the coil.

In this tire friction coefficient measuring method, when determining the force acting in the circumferential direction, an amount correlating with the magnetic flux density of the annular magnetic path is applied to the coil spirally wound around this magnetic path. Since the inductance for a predetermined alternating current, by preparing in advance a relational expression representing the relationship between the inductance at the peak position and the inclination angle of the magnetic body, the inclination angle of the magnetic body can be easily calculated, thus, The circumferential force acting on the tire can be measured.

Moreover, the inductance measured here does not depend on the rotation speed, and therefore the inductance at the peak position and the inclination angle of the magnetic material can be uniquely related.

According to this tire friction coefficient measuring method,
When determining forces acting in either the vertical direction or the circumferential direction, it is possible to measure these forces without using data relating to the rotational speed of the tire, so that the measurement system can be simplified and the accuracy can be improved. It can be expensive.

[0037]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of a method for measuring a force acting on a tire according to the present invention will be described below with reference to FIGS. 1 to 5. FIG. 1 shows a state of being mounted on a vehicle,
It is sectional drawing of the tire 1 used for this embodiment, and FIG. 2 is the side view. Steel belt 4 of this tire 1
Is magnetized only on a part 4A in the circumferential direction thereof, and on the other hand, on the lower surface of the fender portion 5 on the opposite side of the tire 1, which sandwiches a suspension that supports the tire 1 swingably around a point O. A magnetic sensor 6 for measuring the magnetic flux density of the magnetic field generated from the magnetized portion of the steel belt 4 is attached to the.

When the vertical force applied to the tire 1 is increased, the vertical force increases the deformation of the suspension, and as a result, the tire 1 causes the magnetic sensor 6 to
Relative swing displacement of Θa around point O causes tire 1A
Move to position. Then, the relative position between the magnetic field generated from the tire 1 and the magnetic sensor 6 changes, and the magnetic flux density detected by the magnetic sensor 6 changes with this change.

FIG. 3 is a graph showing a magnetization pattern formed along the circumferential direction of the tire 1 by magnetizing a part 4A of the steel belt 4, with the horizontal axis representing the rotational angle position of the tire 1 and the vertical direction. The axis represents the magnitude of magnetization. This magnetization pattern has a peak P0 magnetized to the N pole.

FIG. 4 is a graph showing a magnetic flux density pattern that appears in the magnetic sensor 6 when the tire 1 having the magnetization pattern shown in FIG. 3 is rotated, in which the vertical axis represents the magnetic flux density and the horizontal axis represents time. is there. FIG. 4 shows an example in which only four tire rotations are taken out from the continuously continuous magnetic flux density pattern, and PA1 to PA4 sequentially show the peaks for each rotation of the tire 1, and the magnitudes of these peaks are φp1. ~ Φ
Each is represented by p4.

A method of measuring the magnitude of the vertical load Fr acting on the tire 1 from the magnetic flux density pattern shown in FIG. 4 will be described below. The peaks PA1 to PA4 appear at the tire rotation position where the position on the tire corresponding to the peak P0 of the magnetization pattern of the tire 1 is closest to the magnetic sensor 6, and the magnetic flux density φp of each of the peaks PA1 to PA4.
The size of 1 to φp4 is uniquely determined depending on the distance between the magnetic sensor 6 and the position on the tire corresponding to the peak P0 of the magnetization pattern of the tire 1 at the tire rotation position. In addition, the vertical load Fr acting on the tire 1,
Since the distance from the tire 1 of the magnetic sensor 6 is uniquely related via the spring constant of the suspension, the peak magnetic flux density φp and the vertical load Fr can be related in a one-to-one relationship. Fr and peak magnetic flux density φ
By preparing a relational expression with p and substituting the peak magnetic flux density φp into this relational expression, the vertical load Fr can be calculated backward.

For example, in FIG. 4, since the peak magnetic flux density φp3 of the peak PA3 is larger than the peak magnetic flux density φp1 of the peak PA1, the vertical load acting on the tire 1 corresponding to the peak PA3 corresponds to the peak PA1. It can be said that it is larger than the vertical load acting on the tire 1 in the state, and the magnitude of each vertical load Fr is obtained from the above-mentioned relational expression.

In the method of determining the magnitude of the vertical load Fr acting on the tire 1 in this manner, the magnitude of the peak can be specified regardless of the rotation speed of the tire. As shown in FIG. 4, even if the time intervals between consecutive peaks differ depending on the rotation speed of the tire, it is possible to specify the peak position that appears for each rotation regardless of this, and therefore the peak position of each peak can be specified. The sizes φp1 to φp4 can also be specified regardless of the rotation speed.

In the above description, the tire magnetization pattern shown in FIG. 3 has one peak for one rotation of the tire, but it may be a magnetization pattern having a plurality of peaks. In this case, the magnetic flux density pattern detected by the magnetic sensor 6 also has peaks corresponding to the number of peaks of the tire magnetization pattern for one rotation of the tire. Then, for each peak of one rotation of the magnetic flux density pattern, the relation between the peak size and the vertical load is prepared in advance, so that the measured value of the peak size of the magnetic flux density corresponds to each peak. The vertical load can be obtained by substituting it into the relational expression.

When a magnetization pattern having a plurality of peaks is formed for one rotation of the tire, the magnitudes of the respective peaks of the magnetization pattern may be different from each other, or the phase difference between the peaks may be different from each other. It is also possible to individually identify multiple peaks that appear during one rotation of the tire by using the relational expression for the peak of interest among the peaks of the specified magnetic flux density pattern. Therefore, it is possible to clearly distinguish whether to convert the vertical force.

The above method in which the tire magnetization pattern has a plurality of peaks makes it possible to obtain the vertical load data corresponding to the number of peaks per one rotation of the tire, and thus the sampling time can be shortened. Since it is possible to obtain the friction coefficient data with, it is possible to control the braking with high responsiveness, and as described above, it is not necessary to add a special device or labor for this, so that it is an extremely advantageous method. is there.

The method of obtaining the force acting in the vertical direction from the magnitude of the magnetic flux density of the peaks PA1 to PA4 has been described above, but this force can also be obtained from the phase of the peak.
In this case, the magnetic sensor 7 is preferably mounted near a line extending in the front-rear direction of the vehicle body from the center of the tire 1 as shown by the chain double-dashed line in FIG. 2. In FIG. 6 is a graph showing a magnetic flux density pattern appearing in the magnetic sensor 7, with the magnetic flux density on the vertical axis and the time on the horizontal axis. In this case, when the tire reaches a predetermined rotational position with respect to the non-rotating portion of the axle, a timing signal S indicating that the tire has come to this position is generated to measure the phase of the peak appearing at each one revolution of the tire. However, the timing signal S is also shown in FIG.

FIG. 5 shows an example in which only four tire revolutions are taken out from the magnetic flux density pattern which continues continuously.
PB1 to PB4 represent the peaks for each rotation of the tire 1 in order, and T1 to T4 represent the time required for each rotation of the tire, which is divided by the timing signal S. Then, assuming that the time from the generation of the timing signal S to the appearance of the peak is Tp1 to Tp4, the peak phase αi for each one rotation is calculated from these values by the equation (1). αi = (Tpi / Ti) × 360 (°) (1) where i = 1 to 4

As is apparent from FIG. 2, when the vertical load Fr changes, the peak position P of the magnetizing pattern of the tire with respect to the magnetic sensor 7 located almost right beside the tire.
The rotation position of the tire where 0 is closest is different. As a result, the peak phase αi of the magnetic flux density pattern detected by the magnetic sensor 7 also changes depending on the vertical load Fr.
Since the peak phase αi and the vertical load Fr have a one-to-one relationship, a relational expression between the vertical load Fr and the peak phase αi is prepared in advance, and the measured peak phase is substituted into this relational expression. The vertical load Fr can be calculated by back calculation.

The magnetic flux density pattern shown in FIG. 5 is for the tire magnetization pattern having one peak for one rotation of the tire shown in FIG. 3, but it should be a magnetization pattern having a plurality of peaks. In this case, the magnetic flux density pattern detected by the magnetic sensor 7 also has the same number of peaks as the tire magnetization pattern for one rotation of the tire. Then, by preparing in advance a correlation between the peak phase and the vertical load for each peak of one rotation of the magnetic flux density pattern, the value of the peak phase of the magnetic flux density is related to each peak. The vertical load can be obtained by substituting it into the formula. In addition,
Even if a plurality of peaks appear during one rotation of the tire, the respective peaks can be individually distinguished by the order from the timing signal S as a reference.

In this way, when the tire magnetization pattern has a plurality of peaks, as described above, the friction coefficient data can be obtained in a shorter sampling time, and a highly responsive braking control is possible. Therefore, it is a very advantageous method.

As the magnetic sensor 6 or 7 used in the embodiment of the method of measuring the force acting on the tire 1 described above, an MI sensor capable of accurately measuring the magnetic flux density even at a position slightly away from the tire is selected. Is preferred. Further, as a method of forming a magnetization pattern along the circumferential direction of the tire 1, a method of magnetizing a part 4A of the steel belt 4 constituting the tire 1 has been shown. The magnetization pattern can also be formed by embedding or sticking the body.

Next, an embodiment of the tire friction coefficient measuring method according to the present invention will be described with reference to FIGS. The friction coefficient μ of a tire is the tangential force from the road surface that acts on the tire, that is, the circumferential force F that acts on the outer circumference of the tire.
It is clear from the definition of the friction coefficient that t and the vertical force Fr are obtained based on the equation (2), and the tire friction coefficient measuring method of the present invention is perpendicular to the circumferential force Ft. Direction force Fr and each are measured in real time,
The friction coefficient is measured from these measured values based on the equation (2). μ = Ft / Fr (2)

Then, the vertical force Fr in equation (2) is
The force Ft in the tangential direction is obtained by the method described above in the embodiment of the method for measuring the force acting on the tire. FIG. 6 shows the tangential force Ft.
FIG. 3 is a partial line cross-sectional view showing a force measuring device 10 for measuring the vehicle, in which IN indicates the vehicle width direction center side of the tire 1 mounted on the vehicle, and OUT indicates the vehicle width direction outer side.
FIG. 7 is a front view showing the tire 1 as seen from the arrow VII-VII in FIG. 6 in a state where no force is applied in the circumferential direction. The magnetic body 3 extending in the radial direction of the tire 1 at one position in the circumferential direction of the sidewall portion 2 of the tire 1 on the vehicle width direction center side.
Is provided.

The force measuring device 10 comprises two electromotive force measuring units 19A and 19B. One electromotive force measuring unit 19A includes an iron core and an exciting coil 12A spirally wound around the iron core to form an electromagnet. A yoke portion 11A composed of
Induced electromotive force measurement coil 13A, excitation coil 1
It has a battery 14A for supplying a direct current to 2A and a voltmeter 15A for measuring the induced electromotive force, and the other electromotive force measuring unit 19B has the same structure. The yoke portion 11A of the one electromotive force measurement unit 19A and the yoke portion 11B of the other electromotive force unit 19B are arranged in opposite directions to the tire radial direction. Note that, for convenience of illustration, the illustration of the electromotive force measurement unit 19B is omitted in FIG.

The yoke portion 11A of one electromotive force measuring unit 19A forms an annular magnetic path F, and the yoke portion 11A and the electromotive force measuring coil 13A are close to the vehicle center side sidewall portion 2 of the tire. Then, the battery 14A and the voltmeter 15A may be provided anywhere on the vehicle body side, although they are attached to a non-rotating portion of the vehicle body such as an axle or a suspension. The other electromotive force measurement unit 19
The same applies to B.

FIG. 8 is a schematic partial cross-sectional view of the electromotive force measuring unit 19A, in which the magnetic body 3 provided on the sidewall portion 2 of the tire is not in proximity to one electromotive force measuring unit 19A. . In this state, the annular magnetic path F is configured to include a large amount in a portion other than the magnetic body, such as air and rubber, so that the magnetic flux density is small. When the tire rotates and the magnetic body 3 coincides with the circumferential position where the yoke portion 11A is arranged, the state shown in FIG. 1 is obtained. At this time, since the annular magnetic path F is almost composed of a magnetic body, its magnetic flux The density becomes higher. The same applies to the other electromotive force measurement unit 19B.

FIG. 9A shows, on the vertical axis, the change in the magnetic flux density generated in the magnetic path F of one electromotive force measuring unit 19A when the tire 1 on which the circumferential force Ft acts is rotated. 4B is a graph showing magnetic flux density φA and time t on the horizontal axis, and FIG. 4B similarly shows magnetic flux density φB on the vertical axis and time t on the horizontal axis for the other electromotive force measurement unit 19B. It has been shown. With the rotation of the tire 1, the magnetic body 3 has the yoke portions 11A and 11B of the electromotive force measurement units 19A and 19B at times tA and tB, respectively.
The magnetic flux densities φA and φB respectively exhibit their peak values φAmax and φBmax.

This graph shows the voltmeters 15A and 15B.
The magnetic flux density is obtained by time-integrating each of the electromotive forces measured in (1). A method for obtaining the circumferential force and the radial force acting on the tire from these two graphs will be described below.

FIG. 10 is a front view corresponding to FIG. 7, showing the tire 1 in a state when a circumferential force Ft is applied. As shown in FIG. 7, when the circumferential force Ft is not applied to the tire 1, no twist occurs between the inner diameter side and the outer diameter side of the sidewall portion 2, so the magnetic body 3 is Facing in the radial direction. When the circumferential force T acts on the tire 1, the sidewall portion of the tire is twisted in proportion to the circumferential force. Therefore, as shown in FIG. 10, the magnetic body 3 has a large circumferential force. It is inclined with respect to the radial direction by an angle .theta.

When the magnetic body 3 passes through the circumferential position corresponding to the yoke portion 11A, the magnetic flux density generated in the magnetic path F becomes maximum as described above, but the maximum generated in magnetic path F. The magnetic flux density φAmax changes according to the inclination angle θ of the magnetic body 3 with respect to the radial direction. That is, when the magnetic body 3 crosses the yoke portion 11A, the magnetic body 3 and the yoke portion 1
When the magnetic substance 3 is inclined at an angle such that the direction with 1A is the same and the gap amount between them is minimized,
The maximum magnetic flux density φAmax becomes maximum, and the maximum magnetic flux density φAmax decreases as the amount of these gaps increases, and the degree of decrease is uniquely determined by the tilt angle θ. This allows maximum identification and hence circumferential force measurement.

However, the above is the case where the sectional shape of the tire does not change, and if the tire 1 swells and the gap between the magnetic body 3 and the yoke portion 11A becomes narrower, the magnetic flux density of the magnetic path F becomes smaller. To rise. 11 (a) and 11 (b) are sectional views of the tire showing this state, and FIG. 11 (a) shows a case where the gap is large.
(B) shows the case where the gap is small. Thus, when the cross-sectional shape of the tire is changed, the maximum magnetic flux density φAmax of the yoke portion 11A is not limited to the inclination angle θ of the magnetic body 3 and also the bulge in the width direction of the tire 1 and the size of the gap. Since it is affected, it becomes impossible to uniquely calculate the tilt angle θ from the maximum magnetic flux density φAmax.

By the way, the yoke portion 11A and the yoke portion 11B
Are arranged so as to be inclined in the opposite direction to the tire radial direction, so that the magnetic substance 3 is applied by the force Ft in the tire circumferential direction.
Is inclined in a direction parallel to the yoke portion 11A, but is inclined in a direction in which the yoke portion B is increased in inclination. Therefore, if the difference between the maximum value .phi.Amax of the magnetic flux density appearing in the yoke portion 11A and the maximum value .phi.Bmax of the magnetic flux density appearing in the yoke portion 11B is obtained, this difference changes in proportion to the tilt angle and at the same time. Therefore, the cross-sectional shape of the tire is not affected by the change. Because
The change in the cross-sectional shape of the tire changes the respective gaps of the yoke portion 11A and the yoke portion 11B with the magnetic body 3 by the same amount, so that the maximum magnetic flux densities φAmax, φ
This is because Bmax is also changed by the same amount.

From the above, the maximum magnetic flux densities .phi.Amax and .phi.Bm generated in the yoke 11A and the yoke 11B.
When the increase / decrease of ax with respect to the maximum value of the magnetic flux density when the tire 1 is not deformed in the circumferential direction or the cross-sectional direction is ΔφAmax and ΔφBmax, respectively, the magnetic substance 3
The angle θ of inclination with respect to the tire radial direction can be obtained by the equation (3), and the θ obtained by this is not affected by the deformation of the tire 1 in the width direction. θ = K · (ΔφAmax−ΔφBmax) / 2 (3) where K is a proportional constant.

In the above description, it is assumed that ΔφAmax and ΔφBmax change linearly with respect to θ in order to make the explanation easy to understand. However, even when not linear, θ is uniquely determined by the same simultaneous equations. You can decide.

Further, in the above-described embodiment, the paired yoke portions 11A and 11B are arranged so as to be oppositely inclined with respect to the tire radial direction, so that the maximum magnetic flux density generated in each of them is maximized. Although θ was uniquely determined from the value, in addition to this, for example, the yoke parts forming pairs with different lengths are arranged on a plane passing through the center axis of the tire, and the magnetic flux density generated in these yoke parts is arranged. Can be uniquely determined from the change of. FIG. 12 is a schematic cross-sectional view showing the arrangement of the yoke portions 11A and 11B with respect to the tire 1 in this case. In FIG. 12, the electromagnet is omitted.

Here, in order to provide the magnetic body 3 on the side wall portion 2, the magnetic body is formed into a film and attached to the surface of the side wall portion 2, or the side wall rubber itself is powdered on the side wall rubber. Alternatively, the magnetic material may be kneaded and dispersed. Further, it is easy to use a soft magnetic material having a high magnetic permeability such as iron for the magnetic body provided in the sidewall portion 2 of the tire, but a hard magnetic material typified by a permanent magnet can be used instead. In this case, since the hard magnetic material itself forms the magnetic path, it is not necessary to provide the exciting coil 12A forming the yoke portion and forming the electromagnet.

FIG. 13 is a schematic cross-sectional view of the force measuring device 10 showing an example in which a yoke portion having a structure different from that of the yoke portion shown in FIG. 6 is used. An exciting coil 12A is wound around an iron core of the yoke portion. Instead of forming electromagnets, permanent magnets 21 may be attached to both ends of the iron core. Here, the permanent magnets 21 do not need to be provided at both ends of the yoke portion, and may be provided at any position of the yoke portion, such as the center of the yoke portion. As described above, when the magnetic body provided on the sidewall portion 2 of the tire is made of a hard magnetic material, it is not necessary to provide the permanent magnet on the yoke portion.

Further, as the magnetic material provided in the sidewall portion 2, instead of iron, a carcass cord arranged in the radial direction of the radial tire can be used. When the cord is made of steel, this can be used. As it is magnetic body 3
However, even if the cord is an organic fiber, sacrifice the adhesion between the fiber and rubber by applying cobalt plating to at least one of the cords arranged in the circumferential direction. However, this can be the magnetic material.

FIG. 14 is a schematic sectional view showing a force measuring device 20 used in another method for measuring the circumferential force Ft acting on the tire 1. In the figure, IN indicates the vehicle width direction center side of the tire 1 mounted on the vehicle, OUT indicates the vehicle width direction outside, and the side wall portion 2 of the tire 1 on the vehicle center side. The magnetic body 3 extending in the radial direction of the tire is provided at one location in the circumferential direction,
This is similar to that described with reference to FIG.

The force measuring device 20 comprises two exciting units, and one exciting unit 29A includes a yoke portion 21A made of an iron core, an inductance coil 22A spirally wound around the yoke portion 21A, and an exciting coil. It has a constant current power supply 24A for supplying an alternating current to 22A and a voltmeter 25A for measuring the inductance of the inductance coil 22A.
The other excitation unit has the same structure, but the two ends of the yoke portion 21A of the one excitation unit 29A are arranged at positions substantially corresponding to the radial positions of both ends of the magnetic body 3. The gap between both ends of the yoke portion of the other unit is extremely small, and both ends are in contact with each other. In addition, in FIG. 14, only one excitation unit 29A is shown.

The yoke portion 21 of one excitation unit 29A
A and the inductance coil 22A form an annular magnetic path F, and the yoke portion 21A and the inductance coil 22A are arranged close to the side wall portion 2 on the center side of the vehicle, and the constant current power supply 24A and the voltmeter are provided. 25A is arranged on the vehicle body side. The same applies to the excitation unit 29B.

In this force measuring device 20, when the magnetic body 3 approaches the position corresponding to the yoke portion 21A of the one excitation unit 29A, the magnetic flux density of the magnetic path F including the yoke portion 21A increases. Therefore, this inductance increases, and the change can be read by the voltmeter 25A. The other excitation unit 29B operates similarly. That is, in the method for measuring the magnetic flux density using the force measuring device 10 shown in FIG. 6, the magnetic flux density was obtained by measuring the electromotive force generated by the time change of the magnetic flux density, whereas in FIG. The method for measuring the magnetic flux density using the force measuring device 20 is to measure the magnetic flux density by measuring the magnitude of the inductance with respect to the inductance coil 22A. Although it is different from the measurement method, the other points are exactly the same, and the description of other points will be omitted.

[0074]

As is apparent from the above description,
According to the present invention, by rotating the tire having the magnetization pattern along the circumferential direction, the magnetic sensor fixed to the side of the vehicle body,
Since the vertical force acting on the tire is obtained by measuring the characteristic value of the magnetic flux density pattern corresponding to one rotation of the tire that is detected and changing depending on the vertical force, it is possible to obtain a highly accurate road friction coefficient. The vertical force acting on the tire, which is necessary for the measurement, can be easily measured with high accuracy.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a tire used in an embodiment of a force measuring device acting on a tire according to the present invention.

FIG. 2 is a side view of the tire shown in FIG.

FIG. 3 is a graph showing a magnetization pattern formed in the tire circumferential direction.

FIG. 4 is a graph showing a magnetic flux density pattern detected by a magnetic sensor.

FIG. 5 is a graph showing a magnetic flux density pattern detected by a magnetic sensor.

FIG. 6 is a schematic partial cross-sectional view of a force measuring device used in the embodiment of the method for measuring the friction coefficient of the tire according to the present invention.

FIG. 7 is a front view showing the arrow VII-VII in FIG.

FIG. 8 is a schematic partial cross-sectional view showing another state of the force measuring device of FIG.

FIG. 9 is a graph showing changes with time of magnetic flux density.

FIG. 10 is a front view showing the arrow VII-VII in FIG.

FIG. 11 is an explanatory diagram showing a difference depending on the degree of inflation of the tire.

FIG. 12 is a schematic partial cross-sectional view showing another form of the force measuring device.

FIG. 13 is a schematic line partial cross-sectional view showing another form of the force measuring device.

FIG. 14 is a schematic partial cross-sectional view showing another form of the force measuring device.

[Explanation of symbols]

1, 1A tire 2 Side wall part 3 magnetic material 4 steel belt 4A Steel belt magnetized part 5 Fender part 6, 7 Magnetic sensor 10, 20 force measuring device 11A, 11B, 21A Yoke part 12A excitation coil 13A electromotive force measurement coil 14A, 24A battery 15A, 25A voltmeter 19A electromotive force measurement unit 21 Permanent magnet 22A inductance coil 29A excitation unit F ring magnetic path

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hiroshi Shima             3-1-1 Ogawa Higashi-cho, Kodaira-shi, Tokyo Stock market             Bridgestone Technology Center (72) Inventor Hideyuki Susa             3-1-1 Ogawa Higashi-cho, Kodaira-shi, Tokyo Stock market             Bridgestone Technology Center (72) Inventor Masami Kikuchi             3-1-1 Ogawa Higashi-cho, Kodaira-shi, Tokyo Stock market             Bridgestone Technology Center (72) Inventor Yukio Aoike             3-1-1 Ogawa Higashi-cho, Kodaira-shi, Tokyo Stock market             Bridgestone Technology Center (72) Inventor Takahisa Shizuku             3-1-1 Ogawa Higashi-cho, Kodaira-shi, Tokyo Stock market             Bridgestone Technology Center F term (reference) 2F051 AA01 AB05 BA07                 3D046 BB23 BB28 BB29 HH35 HH46

Claims (8)

[Claims] 1. A tire having a predetermined magnetization pattern is rotated in the circumferential direction to generate a rotating magnetic field from the tire,
The magnetic flux density of the generated rotating magnetic field is continuously detected by a magnetic sensor fixed to the vehicle body, and from the detected magnetic flux density, the magnetic flux density representing the magnetic flux density for each rotation angle position of the tire for each rotation of the tire. A method for measuring a force acting on a tire, in which a density pattern is specified, and a vertical force acting on the tire is obtained in real time from predetermined characteristic values of the specified magnetic flux density patterns. 2. The method for measuring a force acting on a tire according to claim 1, wherein the belt is magnetized to form a predetermined magnetization pattern on the tire. 3. The vertical force acting on the tire is obtained in real time from the magnitude of the peak specified for each revolution of the tire, with the magnitude of the peak of the magnetic flux density pattern as a predetermined characteristic. The method for measuring the force acting on the tire according to any one of claims. 4. The vertical force acting on the tire is obtained in real time from the peak phase specified for each rotation of the tire, with the peak phase of the magnetic flux density pattern as a predetermined characteristic. The method for measuring the force acting on the tire according to 1. 5. A force in the vertical direction obtained by the method for measuring the force acting on the tire according to claim 1, and a force in the circumferential direction acting on the tire obtained by a separate measurement. The method for measuring the tire friction coefficient is to obtain the tire friction coefficient in real time. 6. When the force acting in the circumferential direction is obtained, a magnetic body provided in at least one position in the circumferential direction of the sidewall portion of the tire and extending substantially in the radial direction is accompanied by rotation of the tire. , A change in the amount that correlates with the magnetic flux density of the annular magnetic path is measured when the annular magnetic path that is fixed to the vehicle body and intersects the sidewall portion at two points on the tire radius is crossed. The tire friction coefficient measuring method according to claim 5, wherein a change in the inclination angle of the magnetic material is calculated based on the measured value, and the force acting in the circumferential direction is obtained from the inclination angle. 7. The tire friction coefficient according to claim 6, wherein an amount correlating with a magnetic flux density of the annular magnetic path is an integrated value of electromotive force induced in a coil spirally wound around the magnetic path. Measuring method. 8. The inductance correlating with the magnetic flux density of the annular magnetic path is an inductance for a predetermined alternating current applied to a coil spirally wound around the magnetic path.
The method for measuring the tire friction coefficient according to.