JP2999978B2 - Tire rotation detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tire rotation detecting device for detecting the rotation of a tire in order to measure the speed or moving distance of a vehicle such as an automobile, and more particularly to a tire for detecting the rotation of a tire magnetically. The present invention relates to a rotation detection device.

[0002]

2. Description of the Related Art A car navigation system (hereinafter abbreviated as a car navigation system) used for confirming the current position of a vehicle, guiding roads, and the like.
Appeared around 1990 and has become quite popular.

[0003] Car navigation systems have a function of detecting an absolute position by radio waves from artificial satellites by GPS navigation. Recently, however, a car navigation system has a self-sustained status indicating a vehicle movement condition based on angular displacement by a gyro sensor and vehicle speed data from a vehicle body. The number of hybrid systems incorporating navigation has increased and has become mainstream. With this hybrid method, the accuracy of map matching can be improved.

However, in order to obtain the function of the self-contained navigation, it is necessary to obtain vehicle speed data from the vehicle main body, and for this purpose, it is necessary to have a specialized dealer having a wiring diagram of the vehicle main body connect the apparatus. . It is difficult for general users to perform this connection work in terms of safety, and it is becoming an obstacle for the further spread of car navigation systems in the future due to the high cost and the fact that connection cannot be performed without a specialized dealer.

[0005]

The above problem can be solved by providing a sensor which can detect the rotation of the tire for measuring the vehicle speed or the moving distance and can be easily mounted, but the ideal method is to use the tire. It is best if the rotation can be detected without contact.

Therefore, the present inventor has paid attention to the fact that steel radial tires have become the mainstream in recent tires, and this tire includes a steel belt inside the outer periphery. We predicted that the steel belt itself had a weak but remanent magnetization and emitted a magnetic field outside the tire. Actually, when the magnetic field was measured with one rotation of the tire, a magnetic field distribution as shown in FIG. 10 appeared. The measurement was performed along the outer circumference at a position about 15 cm away from the tire, but it was found that there was a clear peak corresponding to one rotation of the tire, and the possibility of magnetic detection of tire rotation was known. Was.

However, the magnetic field from this tire has a peak-to-peak value of 0.38 gauss, is smaller than the geomagnetism (about 0.5 gauss), and may be 0.1 gauss depending on the type of tire and the installation location of the sensor. A lower case is expected. Therefore, it is necessary to detect a weak magnetic field from such a tire with high sensitivity.

In the detection of tire rotation during actual running of a vehicle, a magnetic field generated from remanent magnetization of a reinforcing bar or a steel frame of a bridge or a tunnel becomes a disturbance. Therefore, it is necessary to eliminate the influence of the magnetic field as a disturbance.

It is an object of the present invention to provide a tire rotation detecting device which satisfies the above conditions and is capable of satisfactorily magnetically detecting the rotation of the tire for a tire including a steel belt.

[0010]

According to the present invention, a magnetic field caused by residual magnetization of a steel belt of a tire is externally provided by a pair of magnetic sensing elements arranged at a predetermined interval. In a tire rotation detection device that performs differential detection and detects rotation of the tire based on the detection result, a magnetic member that guides a magnetic flux from the tire is disposed near the pair of magnetic detection elements. Preferably, the magnetic field detection directions of the pair of magnetic detection elements are the same. Further, the magnetic member is, for example, permalloy,
It is formed in a flat plate shape from an amorphous magnetic material or ferrite, and is disposed so as to be parallel to a line connecting the pair of magnetic detection elements and perpendicular to a magnetic field detection direction of the magnetic detection elements.

According to such a configuration, it is possible to eliminate the influence of the magnetic field which becomes a disturbance by the differential detection. In addition, the magnetic field from the tire is guided by the magnetic member, thereby increasing the detection magnetic field at the position of the magnetic detection element,
A phase difference occurs between the detection magnetic fields of the pair of magnetic detection elements, and the difference between the magnetic fields increases. Therefore, differential detection can be performed with high sensitivity, and the S / N of the differential output is significantly improved.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Before describing the embodiments of the present invention, an embodiment of a configuration which is a premise of the present invention will be described.

First, an embodiment of a tire rotation detection method and apparatus and a tire rotation number detection method as a basic embodiment of a configuration which is a premise of the present invention will be described with reference to FIGS. explain.

First, the configuration and installation of a magnetic sensor used for rotation detection will be described.

In this embodiment, in the vehicle 10 shown in FIG. 1A, first, a steel radial tire having a steel belt inside the outer peripheral portion is used as the tire 12,
The magnetic sensor 14 is installed near the rear side of the rear tire 12 in the trunk room or cabin of the vehicle 10. The magnetic sensor 14 may be installed on either the right or left back side of the rear tire 12. Although it is possible to install the sensor on the front wheel side, it is not suitable because the distance between the tire and the sensor is not constant due to the change in the angle of the tire by operating the steering wheel, and the output waveform of the sensor fluctuates. .

The details of the installation position will be described with reference to FIG. 1B which is an enlarged perspective view taken along the arrow in FIG. As shown here, the sensor 14 is located on the trunk side wall or the trunk bottom,
2 is set at a position about 15 cm from the outer circumference. FIG. 1 shows an example of an ordinary passenger car, but other mini cars, vans,
Even in a recreational vehicle (RV) vehicle, there is an installation space in the cabin or trunk behind the rear tire.

The connection to the car navigation body is made by a cable 16, but unlike the case where a sensor is provided outside the vehicle body,
It is easy to route to the car navigation body via the cabin.

Next, the configuration of the magnetic sensor 14 will be described. The magnetic sensor 14 includes a pair of magnetic detecting elements 18A,
18B. These magnetic detecting elements 18A, 18B
For this purpose, a magneto-impedance element utilizing the magneto-impedance effect (hereinafter abbreviated as MI element) disclosed in JP-A-7-181239 is suitable. The magneto-impedance effect is a phenomenon in which, when a high-frequency current in the MHz band is applied to an amorphous wire or a magnetic thin film, the impedance at both ends of the magnetic material changes by several tens of percent due to an external magnetic field, and the MI element has a practical sensitivity of several milligauss or more. ing.

The advantage of the MI element is that the sensitivity is equal to or higher than that of the flux gate sensor and that the sensor can be easily miniaturized because of its length of about several mm. Furthermore, it is suitable for the present sensor because it is strong against magnetism and can perform stable operation in a situation where the external magnetic field changes drastically.

In the present sensor, the two MI elements 18A and 18B are operated differentially in order to reduce the influence of the external magnetic field and detect only the magnetic field from the tire as much as possible.
In order to make the operation effective, two elements 18A and 18B
Are arranged so that the magnetic detection directions are parallel or coaxial. Regarding the setting of the magnetic field detection direction, in FIG. 1B, the magnetic field detection direction is a direction perpendicular to the trunk bottom as shown by an arrow, but there is no particular advantage in other directions. Is also good.

Next, the magnetic detection circuit of the magnetic sensor 14 for detecting a magnetic field from the tire by the MI elements 18A and 18B has a configuration as shown in FIG. In this magnetic detection circuit, buffers 22A, 22B
A high-frequency current is applied to each of the MI elements 18A and 18B via the corresponding element, and the MI elements 18A and 18B are driven. M
The other ends of the I elements 18A and 18B are grounded. The change in the external magnetic field changes the impedance of each of the MI elements 18A and 18B, and the voltage between both ends of each of the MI elements 18A and 18B changes. The signals are detected by the two detection circuits 24A and 24B, respectively,
Extracted as magnetic detection signals of the elements 18A and 18B,
Further, the signal is input to the differential amplifier circuit 26 and differentially amplified.
The MI elements 18A and 18B have D
The C bias magnetic field Hb is applied by about 1 to 2 gauss by a fixed magnet or a coil.

The MI elements 18A and 18B shown in FIG.
If the distance d is too small, the output decreases if the distance is too small. Therefore, it is necessary to select an appropriate dimension. Therefore, the magnetic field detection output due to the rotation of the tire was measured while changing the distance d. As a result, as shown in FIG. 3, the output sharply drops below d = 2 cm as seen from the output of the peak-to-peak value, but d = 2
cm or more, a practical output can be obtained.

The high frequency current is supplied to the MI elements 18A and 18A.
Unnecessary impedance such as stray capacitance increases when the length of the lead wire connecting the MI element to the magnetic detection circuit increases to apply the voltage to B, and as shown in FIG. 4, the impedance change efficiency decreases with the length of the lead wire. So 80%
If the reduction to the extent is allowed, 10 cm on one side is a standard, and it is desired to keep the distance d between the elements to 20 cm or less. Therefore, it is preferable that the distance d be 2 cm or more and 20 cm or less.

Next, the configuration of the sensor described so far,
The measurement result of the differential output of the sensor when the tire is actually rotated in the installation will be described.

For the measurement, two elements patterned on a glass substrate with an Fe—Ta—C magnetic thin film (2 μm in thickness) are used for the MI elements 18A and 18B, and the distance d between the elements is set.
Was set to 3 cm. The magnetic detection circuit used was the circuit described in FIG. 2 and was built in the sensor. Then, as shown in FIG.
The magnetic sensors 1 are provided at six points (a) to (f)
4 was installed and its differential output was measured. The measurement condition is M
A DC bias magnetic field of 1 Gauss is applied to the I-elements 18A and 18B, a high-frequency current of 20 MHz is applied, and the differential amplifier circuit 2
The gain of No. 6 was set to 100 times. FIG. 6 shows the result.

First, the waveform at the point (a) will be described. The range of the arrow corresponds to one rotation, and it can be seen that four positive and negative peaks are present therein, of which two positive peaks are large peaks. It has become. S / N is good.

At point (b), the magnetic field detection direction is (a)
However, although the upper and lower polarities are inverted due to the polarity of the bias magnetic field, the waveforms are similar.

Since the points (c), (d) and (f) are close to the outer periphery of the tire, the output is more than twice that of the point (a).

Conversely, the output at the point (e) is about half of that at the point (a) because the distance is long.

Although the low output can be covered by the amplifier gain, the low output is originally due to the small magnetic field from the tire, and the difference from the external disturbance magnetic field cannot be obtained. Fluctuations increase.

Therefore, it is necessary to select a place where the sensor is installed as close as possible to the outer peripheral portion of the tire in which the steel belt is embedded, and to secure the output.

From the above description, the configuration of a sensor capable of detecting a magnetic field from a tire with high sensitivity and a suitable installation location have been clarified. Next, a method for detecting the number of rotations of the tire will be described.

FIG. 6 shows the measurement results of the magnetic field from the tire in a stable condition without any disturbance magnetic field. In this condition, the number of zero crosses or crosses of a certain threshold value is counted, and one rotation is performed. It is easy to determine the number of rotations from the number of pulses per hit.

However, in the actual running of the vehicle, the output waveform is affected by the influence of residual magnetization of steel frames and reinforcing bars of bridges and tunnels, the position fluctuation between tires and sensors due to vehicle vibration, the influence of residual magnetization of oncoming vehicles, and the like. A undulating level fluctuation occurs. It is not easy how to determine the number of revolutions from the output waveform of the sensor that has received this fluctuation.

As an example, FIG. 7 shows that about 5
The continuous data which measured the magnetic field change by rotation of a tire in 0km / h vehicle driving | running is shown. According to this data, the waveform has one large peak as shown at point C for one rotation of the tire. If this peak can be reliably detected, the number of rotations is accurately detected, and the speed and the moving distance are obtained. Can be requested.

However, it can be seen from the entire waveform that a swell has occurred, and it is difficult to handle this swell. The undulation is due to the effect of a reinforcing bar or a steel frame existing in the bridge, and undulation is generated on the output waveform due to magnetic disturbance due to the residual magnetization. The configuration of the sensor is differential operation,
Although the effect of disturbance is reduced, the effect of disturbance cannot be reduced to zero.

Since this swell is a frequency component lower than the frequency component of the output waveform of tire rotation, swell was removed by a high-pass filter, and a study was made to count a zero cross or a cross at a certain threshold. Considering that the speed is lower than the walking speed of humans and that the high-speed performance requires performance up to an operation of about 200 km / h, the band is almost DC to 200 Hz.
It is necessary to consider the degree, and a plurality of filters must be prepared, and problems such as a decrease in S / N due to a decrease in output after passing through the filters at a low speed occur.

Therefore, the output waveform is sequentially digitized by the microcomputer, and the peak of the output waveform is detected based on whether the change (increase or decrease) of the data is inverted, and the potential difference between the peak and the immediately preceding peak has a predetermined value. It is determined whether the peak is a valid peak suitable for detecting the rotation of the tire by determining whether the peak exceeds the threshold, and the number of rotations of the tire is obtained by counting the number of the valid peaks. A method of determining the moving distance or speed of the vehicle from the rate was adopted.

According to this method, the influence of a disturbance having a relatively low frequency in the output waveform can be almost eliminated, and the tire rotation can be detected independently of the speed.

Next, FIG. 8 shows a configuration of a tire rotation detecting device for detecting the rotation of the tire by this method. In the configuration shown here, the configuration of the MI elements 18A and 18B to the differential amplifier circuit 26, that is, the configuration of the magnetic detection circuit in FIG. 2 may be used as the magnetic sensor 14, or the configuration of the entire device in FIG. .

In the configuration shown in FIG. 8, as described above, the high-frequency current output from the high-frequency oscillation circuit 20 is supplied to the MI elements 18A and 18B.
, And a signal of a change in the voltage between both ends of the MI elements 18A and 18B is passed through detection circuits 24A and 24B to remove high-frequency components and taken out as a magnetic detection signal. After amplification, the differential output is
The A / D conversion is performed by the converter 28, and the digital signal is input to a microcomputer (hereinafter abbreviated as a microcomputer) 30. The microcomputer 30 performs the above-described peak detection and valid peak determination from the digital signal.

Here, the details of the processing after the AD conversion will be described with reference to the flowchart of FIG. 9 and the signal waveform diagram of the differential output of FIG.

In the processing shown in the flowchart of FIG.
First, in step S1, the differential output voltage of the sensor is AD-converted by the AD converter 28, and is taken into the microcomputer 30.

Next, in step S2, it is determined whether the data taken in step S1 is a peak. The discrimination is based on the fact that the change of the data acquired this time with respect to the data acquired last time is inverted from the change (positive) to the negative (decrease) or the change from negative to positive with respect to the change of the previously acquired data with respect to the data acquired twice before. It is done whether or not. If it is determined that it is not the peak, step S1
Returning to step S3, if it is determined that the peak is reached, the process proceeds to step S3.

For example, in the case of the point B of the differential output waveform shown in FIG. 7, it is determined that the change remains negative (decreasing) and not a peak, and the process returns to step S1 to AD-convert the next data. Thereafter, when the data at the point C is digitized, the inversion of the change from negative to positive is recognized, the data at the point C is determined as a peak, and the process proceeds to step S3.

In step S3, the data of the point C determined as the peak, for example, is stored as the peak value Sp in the RAM or the like in the microcomputer 30.

Next, in step S4, whether the absolute value of the difference between the current peak value Sp and the previous peak value Sp-1 exceeds a predetermined threshold value L, the data of the peak value Sp It is determined whether or not the peak is valid for rotation detection. The relationship between the peak values Sp and Sp-1 is, for example, in FIG.
When Sp is point C, Sp-1 is point A, and when Sp is point D, point C is Sp-1.

The intention of setting the threshold value L is to secure a reliability by targeting only a relatively large peak because only a small peak is not treated because the S / N is low and weak against disturbance. is there. Naturally, if the threshold value L is set to a small value, fine peaks can be picked up. Conversely, if the threshold value L is set to a large value, only large peaks can be targeted, and the output waveform varies depending on the magnetization state of the steel belt of the tire and the installation position of the sensor. Respectively.
The threshold value L is preferably set in the range of 10% to 90% of the maximum peak-to-peak potential difference since the output waveform itself has a variation of about 10% with reference to the previously measured maximum peak-to-peak potential difference. .

In the example of FIG. 7, when the entire waveform is viewed, the maximum peak-to-peak potential difference is about 0.5 V, and the threshold value L is 60%.
When the effective peak is determined by setting to 0.3 V, the difference from the immediately preceding peak A is about 0.55 V in the case of the peak C, and exceeds the threshold L of 0.3 V. Is done. However, in the case of the peak E, the difference from the immediately preceding peak D is about 0.02 V, and is ignored because it does not exceed the threshold L. Therefore, in the range corresponding to one rotation of the tire indicated by the range of the arrow in the figure, two peaks C and D are determined as effective peaks.

Referring again to FIG. 9, if it is determined in step S4 that the peak is an effective peak, the microcomputer 30 proceeds to step S5.
A pulse signal narrower than the output pin is output. The purpose of this is to transmit the recognition of the effective peak to the car navigation body, and another form of output may be a pulse signal that is inverted each time it is determined to be a valid peak.

After step S5, the process moves to step S6. Also, when it is determined in step S4 that the peak is not a valid peak, the process proceeds to step S6. Step S6
Then, the current peak value Sp is set as the previous peak value Sp-1, the peak value Sp-1 is updated and stored in the RAM, and thereafter, the process returns to the AD conversion in step S1, and the above-described processing is repeated.

Since the peak detection and the effective peak determination in the above-described processing do not include a time parameter, tire rotation detection independent of the tire rotation speed can be performed. Therefore, a constant detection performance can be maintained even when the speed of the vehicle is running from extremely low speed to high speed.

In the above processing, step S5
The number of pulses output in the step, that is, the number of detected effective peaks may be counted, and a process of calculating the number of rotations of the tire from the number may be performed. Alternatively, a process for determining the moving distance of the vehicle may be performed. However, in this case, since the present apparatus does not output one pulse corresponding to one rotation of the tire, it is necessary to check in advance how many pulses correspond to one rotation. In addition, since the number of pulses for one rotation is an integral multiple, it is also effective to perform a correction of 1 / integer in comparison with car navigation GPS distance measurement data.

According to the embodiment described above, the magnetic sensor 14 has extremely high sensitivity using the MI element, and does not have a state change due to magnetization as seen in the flux gate sensor. Further, by installing the magnetic sensor 14 in the vicinity of the rear tire in the cabin or the trunk room of the vehicle, the magnetic sensor 14 can be easily installed and the magnetic field from the tire can be detected well. In addition, by performing the above-described differential detection, and by performing the peak detection and the effective peak determination processing of the microcomputer 30, the influence of the disturbance magnetic field can be eliminated, and the rotation or the rotation speed of the tire can be accurately detected.

In this embodiment, the MI element is used as the magnetic detection element. However, it is needless to say that another magnetic detection element may be used as long as the sensitivity is good.

Lastly, a description will be given of the result of measuring a moving distance by traveling a distance of 10 km in an urban area with a 2000 cc ordinary passenger car equipped with the rotation detecting device of the present embodiment.

In the test running, the vehicle stops and starts repeatedly because of running in an urban area, and the speed changes considerably. Note that the tire diameter of the test vehicle is 60 cm, and the tire moves 1.88 m per rotation. As a result of the measurement, the number of output pulses obtained by the above-described configuration of FIG. 8 is 21982, and two pulses are output in one rotation. Therefore, the moving distance is measured as 9.782 km. The measurement error was as good as 2.2%, and it was proved that the car navigation system had the required accuracy for self-contained navigation even in an urban area where the speed of the vehicle was variable and there were many disturbance magnetic fields.

[Embodiment of Presupposed Tire Magnetization Method and Tire Magnetic Field Detection Method] In the basic embodiment described above, the steel belt of the tire whose rotation or rotation number is to be detected is naturally magnetized. It is assumed that the state has been controlled, that is, the magnetization has not been artificially controlled.

In this case, as described above with reference to FIG. 10, there are a plurality of peaks corresponding to one rotation of the tire in a pattern of a magnetic field change accompanying the rotation of the tire.

However, in the above magnetic field pattern, the tire 1
When there are a plurality of peaks during rotation, it is necessary to perform a correction of a fraction of an integer when counting the peaks and calculating the tire rotation speed, as in the case of calculating the tire rotation speed in the basic embodiment described above. Since the number of peaks differs for each tire, it is necessary to set a correction value for each tire.

Therefore, if a signal corresponding to one pulse per rotation is obtained by controlling the magnetization of the tire, magnetic detection of the rotation of the tire becomes easy. Therefore, as a premise of the present invention, an embodiment of a tire magnetization method suitable for magnetic rotation detection of a tire in consideration of this point and a method of detecting a magnetic field of a tire magnetized by the magnetization method are stable. FIGS. 11 to 1 show an embodiment of a magnetic field detecting method capable of obtaining an output waveform.
9 will be described below.

Embodiment of Tire Magnetization Method First, an embodiment of a tire magnetization method will be described. In the magnetizing method of the present embodiment, first, as a first magnetizing step, one direction along the circumferential direction continuously over the entire outer circumference of the tire 12 including the steel belt inside the outer circumference shown in FIG. Magnetized.

For this purpose, as shown in FIG.
2. The magnetizing magnet 11 is brought into contact with or close to the outer peripheral surface of the tire 2, and the magnet 11 is rotated by one rotation along the circumferential direction of the tire 12.
Relatively move at least 60 °. That is, the magnet 11 itself is moved one or more turns along the outer peripheral surface of the tire 12, or the tire 12 is rotated one or more turns without moving the magnet 11. Here, as shown in the enlarged view of FIG. 12, the magnet 11 is disposed such that the NS pole is arranged in the circumferential direction of the tire 12, that is, in the relative movement direction, and the generated magnetic field Hw of the magnet 11 is arranged in the circumferential direction of the tire 12. Along the outer circumference of the tire.

It is preferable that the magnet is magnetized over the entire width of the outer peripheral surface of the tire 12. Therefore, when the width of the magnet 11 arranged as shown in FIGS. 11 and 12 is smaller than the width of the outer peripheral surface of the tire 12, as shown by the arrow in FIG.
1 is relatively moved along the width direction of the outer peripheral surface of the tire 12 (the axial direction of the tire 12), and the magnet 11 is relatively moved at least two rotations along the circumferential direction of the tire 12, whereby the outer peripheral surface of the tire 12 is Magnetized over the entire width.
However, it is not always necessary to magnetize over the entire width of the tire outer peripheral surface, and it is also possible to magnetize a portion of the tire outer peripheral surface, for example, about 2/3 of the full width near the magnetic sensor described later.

Further, the relative movement direction of the magnet 11 and the tire 12 may be one direction along the circumferential direction of the tire 12 or may be reciprocated in both directions as two directions along the circumferential direction.

When magnetizing the tire with the tire mounted on the vehicle, the tire to be magnetized is lifted by a jack and a magnet for magnetizing is applied to the outer peripheral surface of the tire to rotate the tire by hand. The magnet can be easily magnetized by first rubbing the magnet on the outer peripheral surface of the tire other than the ground contact portion with a magnet without jacking up, and then moving the vehicle a little and rubbing the remaining portion to magnetize. .

As described above, by the first magnetizing step,
The tire is continuously magnetized in one direction along the circumferential direction over the entire circumference of the outer peripheral portion of the tire, and the residual magnetization originally held by the tire is re-magnetized in one direction and reset.

Here, there is a method of completely demagnetizing the initial remanent magnetization by applying an AC attenuating magnetic field to the tire. However, the completely demagnetized steel belt portion is easily magnetized, and a random magnetization by an external magnetic field is performed. It is not suitable because noise caused by the generation is a problem.

Next, as a second magnetizing step, as shown in FIG. 13, the polarity of the magnetizing magnet 11 is reversed with respect to the circumferential direction of the tire 12 so that the magnet 11 abuts on the outer peripheral surface of the tire 12 or By causing the tire 12 to move closer along the circumferential direction of the tire 12, a range of a predetermined angle θ smaller than 360 ° of the outer peripheral portion of the tire 12 is continuously changed in a direction opposite to the magnetization direction of the first magnetization step. Re-magnetize. As a result, the tire 12
Can be magnetized for magnetically detecting the rotation of the magnetic field, and a magnetic field that can be easily detected by a magnetic sensor can be generated.

Here, the angle θ of the second magnetization influences the pattern and magnitude of the generated magnetic field, and there is an optimum angle. The result of studying the optimum value will be described below.

First, in the study, the angle θ of the second magnetization was set to 2
The magnetic field along the circumferential direction at a distance of 20 cm from the outer periphery of the tire was measured by changing the angle by 2.5 ° and rotating the tire magnetized at each angle, and the pattern was examined. The magnets used had an NS pole spacing of 2 mm and a magnetizing magnetic field Hw of about 200 Gauss at a location 10 mm from the magnetized facing surface. The result is shown in FIG. The horizontal axis of the data is the time axis, and the rotation of the tire at the time of measurement varies because it is not constant speed.
Rotation can be recognized.

Looking at the magnetic field pattern, when the angle θ is 90 ° or less, it has a sharp peak below, and when θ = 90 °, the change in the magnetic field is largest. As a matter of course, if the polarity of the magnetization is reversed, the peak will be sharpened upward. 9 more
When the angle exceeds 0 °, a sharp peak is dented, and the concavity becomes deeper as the angle increases.

In order to detect the magnetic field generated from the tire and to detect the rotation of the tire, a predetermined threshold value is set. However, considering that a level variation occurs in the magnetic field pattern from the tire due to the external magnetic field, It is necessary that the setting range of the threshold can be set widely. The discrimination width, which is a range suitable for setting the threshold, is such that when the magnetization angle θ is about 90 ° or less, the distance between the lower peak and the bottom of the upper dent is L.
(See the figure of 67.5 °), and when the magnetization angle exceeds 90 ° and a dent occurs in the peak that is pointed downward, L ′ (see the figure of 157.5 °) between the upper and lower dents It becomes the discrimination width.

FIG. 15 is a graph of the discrimination widths L and L '. From this graph, it can be seen that 90 ° is the optimum magnetization angle. Further, considering the practical range, the magnetic field generated from the tire is small in the region where the angle of magnetization θ is small, and the influence of the disturbance magnetic field becomes relatively large. The magnetization angle θ is suitably from 30 ° to 180 °. Further, if the optimum range is set to 80% of the maximum discrimination width, the range from 55 ° to 105
° range, and a more stable magnetic field can be obtained.

Although the angle range has been described up to 180 °, the second magnetization angle θ is 180 °.
Is exceeded, it is symmetrical only by reversing the polarity.
The angle 360 ° -θ of the remanent magnetization of the first magnetization in which the second magnetization was not performed can be considered in the same manner as described above. That is, the range of the optimum magnetization angle described above is the first range.
And the smaller of the angles of the remanent magnetization in the direction opposite to the one direction and the direction of the residual magnetization in the outer peripheral portion of the tire magnetized in the second magnetizing step.

In the tire magnetizing method described so far, the description has been made on the assumption that the tire is magnetized by a magnetic field along the circumferential direction of the tire. There is a concern that optimal conditions for magnetization by the circumferential magnetic field may be maintained due to the fact that the magnetization is not necessarily in the circumferential direction and the magnetic field direction changes depending on the detection position due to the arc shape of the magnetization. However, according to the results of the actual study, the optimal conditions observed in the magnetization by the circumferential magnetic field were
It has been found that it can be applied even under the conditions actually used. The details of the study will be described below.

When a magnetic field from a tire is detected by a magnetic sensor, it is considered that a suitable place for installing the sensor is a trunk room on the back side of the tire in the case of a normal passenger car. It is conceivable to arrange the sensor on the XY plane as shown in b).

In the study, a tire having a diameter of 60 cm was used, and X
Height H from the Y plane to the tire top is 10 cm, XZ
The distance S between the plane and the tire side was set to 15 cm. Also,
In the magnetization of the tire, the angle range θ of the smaller one of the two residual magnetizations at the outer periphery of the tire in the first and second magnetization steps was set to 90 ° by the method described above. The magnetic field detection direction is the Z-axis direction, and is indicated by A, B, C, D, and E on the X-axis in the figure.
The state of the magnetic field change due to the rotation of the tire was measured at each point at 0 cm intervals.

The results are shown in FIG. 17, and when compared with the data at the angle θ = 90 ° described in FIG. 14, the waveform at point A is such that the phase is differentiated by 90 °. As the point approaches the outer point D, the magnetic field and the waveform in the outer peripheral direction become similar. Thus, it is understood that the phase change is influenced by the angle between the magnetization direction of the tire outer peripheral portion closest to the measurement point and the Z-axis direction which is the magnetic field detection direction.

At points A to E, there is a phase change in the waveform. However, the peak at the lower end is stably output once per rotation, and the discrimination width L between the peak and the upper peak is small. Obtained stably. This indicates that the optimum condition of the magnetization viewed from the circumferential magnetic field is maintained.

Therefore, the method of magnetizing with the magnetic field along the circumferential direction of the tire is effective for any position where the actual sensor is installed and the magnetic field detecting direction.

As described above, a method of magnetizing a tire that generates an optimal magnetic field for rotation detection of a tire having a steel belt in the outer peripheral portion is established, and an optimal magnetization angle range is set. Was completed.

In the magnetizing method according to the above-described embodiment, the tire is magnetized continuously in one direction along the circumferential direction over the entire circumference of the outer peripheral portion of the tire in the first magnetizing step. Thus, a range of a predetermined angle smaller than 360 ° at the tire outer peripheral portion is continuously re-magnetized in the direction opposite to the one direction. On the other hand, as a second magnetizing method, the arrangement of magnetizing magnets,
The direction of the generated magnetic field, the relative movement, the method of reversing the polarity of the magnet, and the like are the same as described above, and in the first magnetization step, a range of a predetermined angle smaller than 360 ° of the outer peripheral portion of the tire is continuously circumferentially set. In the second magnetizing step, the non-magnetized portion which has not been magnetized in the first magnetizing step is continuously formed in the outer peripheral portion of the tire in the direction opposite to the one direction. It may be magnetized. However, since it is not easy to accurately magnetize only the unmagnetized portion, the magnetized portion may be magnetized including the portion adjacent to the unmagnetized portion. Also in the second magnetization method, the setting of the optimum angle range of 30 ° to 180 °, particularly 55 ° to 105 ° for the smaller angle of the residual magnetization in the two directions described above applies.

According to the second magnetizing method, magnetizing can be performed without jacking up the tire.

Embodiment of Tire Magnetic Field Detecting Method Next, an embodiment of a tire magnetic field detecting method for detecting a magnetic field of a tire magnetized by the above-described magnetizing method will be described. In particular, the optimum arrangement of the magnetic detection elements when detecting the magnetic field of the tire with the magnetic sensor will be described.

As a device for detecting a magnetic field from a tire, any of a flux gate sensor, an MI device, a Hall device and the like may be used as long as it has a practical sensitivity of about several milligauss. Magnetic field effects,
For example, it is affected by a magnetic field from an adjacent passing vehicle and a magnetic field from a residual magnetization of a reinforcing bar, a steel frame, and the like around a road, so that only a magnetic field from a tire can be detected as much as possible by a differential operation of two magnetic detecting elements. I do. However, in this differential detection, if the two magnetic detection elements are not properly arranged, the phase will greatly change due to the detection of the magnetic field from the tire, making it difficult to set the threshold value and making it difficult to handle.

Therefore, in the present embodiment, it is intended to define the positional relationship when detecting the magnetic field of the tire with respect to the two magnetic detection elements for differential detection.

The conditions regarding the arrangement of the elements are as follows: (1) One large positive or negative sharp peak is obtained for one rotation of the tire in the detection output.

(2) The judgment width L for setting the above-mentioned threshold value in the detection output can be widened.

(3) The conditions (1) and (2) do not greatly change depending on the installation position of the magnetic sensor composed of two magnetic detecting elements.

(1) and (2) are intended to maintain the optimum conditions for the magnetization of the tire, and (3) is to simplify the installation of the magnetic sensor without requiring precision in its installation position. is there.

The optimization regarding the arrangement of the two magnetic sensing elements was obtained by the following study.

In the study of the arrangement of the two magnetic detecting elements for differential detection, the magnetic sensors were placed at the measurement points A, B, C, and D based on the positional relationship of the coordinates described with reference to FIGS. put,
The two magnetic detecting elements used in the sensor are arranged in parallel along the X-axis direction with an interval of 3 cm.
The comparison of the arrangement arranged in parallel along the axial direction was performed. An MI element was used as the magnetic detection element used in the study, and was configured to have a magnetic field detection sensitivity in the Z direction, that is, a direction parallel to the side surface of the tire 12.

The results are shown in FIG. 18. In the case of parallel arrangement along the X-axis direction, the phase of the detected output waveform changes drastically at each of the points A to D, the waveform changes, and the threshold value is changed. The determination width L to be set is not constant and needs to be adjusted according to the installation location of the magnetic sensor, which is not practical.

Compared to this, when arranged in parallel along the Y-axis direction, that is, along the direction perpendicular to the side surface of the tire, the peak at the lower end of the detected output waveform is stable at each measurement point, and the influence of the phase change is the same. Only the magnitude of the peak appearing in the threshold value changes, the determination width L for setting the threshold value is stable.
This indicates that the optimum condition of magnetization by the magnetic field along the circumferential direction is maintained, and it is not necessary to finely adjust the threshold value depending on the installation location of the magnetic sensor, and it is extremely easy to handle.

Therefore, as shown in the perspective view of FIG. 19, using the tire 12 magnetized by the aforementioned magnetizing method, the magnetic field emitted from the tire 12 to the outside is
When the differential detection is performed by the two magnetic detecting elements 18, 2
The magnetic field detection directions of the two magnetic detection elements 18 are both the tire 12
And two magnetic sensing elements 18
Are arranged in parallel along the direction perpendicular to the side surface of the tire 12, the installation of the magnetic sensor 14 is easy, and the determination width for setting the threshold value in the detection output waveform is wide and stable. It became clear that it could be obtained.

[Embodiment of Improved Tire Rotation Detection Apparatus and Tire Rotation Detection Signal Processing Method as Premise]
In the magnetizing method described above, for example, by setting the magnetizing angle θ in FIG. 13 to 90 ° as the optimum condition, the magnetic field changes greatly when viewed in a magnetic field along the tire circumferential direction as shown in FIG. A magnetic field pattern having two large peaks is obtained. However, this magnetic field is detected from the trunk room or the cabin side of the vehicle by the above-described magnetic sensor to obtain a tire rotation detection output, but in order to perform highly reliable detection,
The following points are issues.

(1) The level fluctuation due to disturbance can be absorbed.

The magnetic field from the tire is as small as 1 gauss or less at the detection position, and the influence of the external magnetic field during running of the vehicle, for example, the residual magnetization of a reinforcing bar, an iron plate, a steel frame, etc. becomes a disturbance, and the level of the sensor output fluctuates. I will. FIG. 21 shows the sensor output of the tire rotation when traveling at 65 km / h on the bridge. It can be seen that the level is changed due to the influence of the steel frame in some places. This data shows that although the MI element is used as the magnetic detection element and differential operation is performed at 3 cm intervals, disturbance cannot be sufficiently removed.

(2) Variation in sensor output can be absorbed.

Next, the magnitude of the output of the sensor is influenced by the fact that the distance between the tire and the sensor varies depending on the type of vehicle, and the magnitude of magnetization differs depending on the type and size of the tire.
A variation of about several times occurs. As a result, the setting of the threshold value of the rotation detection becomes difficult when the fixed value is set.

(3) The sensor output is resistant to waveform distortion.

Further, the relative positional relationship between the sensor and the tires is not constant depending on the type of vehicle, and the placement varies.
When the magnetic field from the tire is differentially detected, the phase of the magnetic field pattern from the tire shown in FIG. 20 is likely to change, and in some cases, waveform distortion such as a pseudo peak as shown in FIGS. Occurs.

In the basic embodiment described above, the problem (1) is considered, but the problems (2) and (3) are not considered. Therefore, an embodiment of a tire rotation detection device and a tire rotation detection signal processing method which are premised on the present invention and are improved taking these factors into consideration will be described below with reference to FIGS.

FIG. 23 shows a circuit configuration for obtaining a tire rotation detection output from the magnetic sensor of the tire rotation detecting device according to the present embodiment. In the figure, MI elements 18A, 18
B, high frequency oscillation circuit 20, buffers 22A and 22B,
The part including the detection circuits 24A and 24B and the differential amplifier circuit 26 is the same as the circuit of FIG. 2 in the basic embodiment described above, and is a circuit constituting the magnetic sensor 14 described above. In this circuit, a high-frequency current is applied from the high-frequency oscillation circuit 20 to the MI elements 18A and 18B via the buffers 22A and 22B, as described above. The impedance of the MI elements 18A and 18B changes according to the change in the magnetic field from the tire, and the voltage across each end changes. The signals are detected by the detection circuits 24A and 24B, respectively, extracted as magnetic detection signals of the MI elements 18A and 18B, and further input to the differential amplifier circuit 26 where they are differentially amplified to obtain sensor outputs. For this sensor output, for example, a signal having the waveform shown in FIGS. 21 and 22 is obtained.

As a modification of the magnetic sensor circuit, as shown in FIG. 24, MI elements 18A and 18B
Are connected in series, a high-frequency current is applied thereto from a high-frequency oscillation circuit 20 via a buffer 22, and a signal at a connection point between the MI elements 18A and 18B is detected and extracted by a detection circuit 24, which is inverted. The sensor output may be obtained by amplifying with the amplifier 27. Further, the magnetic detection element is not limited to the MI element, and other elements such as a flux gate sensor, a Hall element, and an MR element may be used. In this case, the configuration of the drive circuit that drives the magnetic detection element in the stage preceding the differential amplifier circuit 26 in FIG. 23 to the inverting amplifier 27 in FIG. 24 differs depending on the type of the magnetic detection element.

Referring again to FIG. 23, the configuration subsequent to the differential amplifier circuit 26 is different from the configuration of FIG. 8 in the basic embodiment described above, and is as follows.

The differential amplification output of the differential amplification circuit 26, that is, the signal of the sensor output is supplied to the maximum hold circuit 32.
And the minimum hold circuit 34. Each of the circuits 32 and 34 includes two operational amplifiers, a diode, a resistor, and a capacitor C1 or C2, and holds a positive peak (maximum value) and a negative peak (minimum value) voltage level of the sensor output waveform, respectively. This is a peak hold circuit. The maximum hold and the minimum hold are used as means for automatically and variably setting a threshold value described below according to the output level even when the output level of the magnetic sensor varies. In addition, although the continuity of the hold voltage is determined by the capacitance of the capacitors C1 and C2 for holding, considering that the level of the sensor output fluctuates,
It is easier to handle if you do not increase the hold unnecessarily and recognize some attenuation.

Next, the outputs of the maximum hold circuit 32 and the minimum hold circuit 34 are applied to voltage dividers 38A and 38B, each having two resistors connected in series, and a voltage between the respective hold voltage and zero potential is obtained. Voltages D1 (plus side) and D2 (minus side) divided at a predetermined ratio are set as threshold values, respectively, and comparators 36A and 36 each composed of an operational amplifier and a resistor.
B is input as a comparison voltage. The reason for setting the threshold values on the plus side and the minus side is to extract the plus side peak and the minus side peak, and the voltage dividers 38A, 3
By appropriately setting the resistance division ratio at 8B, fluctuations in the waveform level can be absorbed. The details will be described later.

Next, the sensor outputs from the differential amplifier circuit 26 are input to the comparators 36A and 36B, respectively, and the sensor outputs in each of the comparators 36A and 36B are pulsed by comparison with threshold values D1 and D2. The pulse is input to the set input and the reset input of the RS flip-flop circuit 40, respectively.
In the S flip-flop circuit 40, one pulse of the final tire rotation detection output is obtained for one rotation of the tire. The reason for using the RS flip-flop circuit 40 is that the peaks exceeding the two thresholds D1 and D2 are recognized and the peaks on the plus side and the minus side are alternately recognized, so that one per rotation is used. In order to generate the pulse of As a result, signal processing for tire rotation detection that is resistant to output level fluctuation and waveform distortion can be performed.

Next, details of the operation of the circuit of the tire rotation detecting device will be described with reference to FIG. FIG. 25 shows a waveform of an actual sensor output (output of the differential amplifier circuit 26) in the above-described circuit and signal waveforms of respective units that process the output.

The upper part of FIG. 25 shows a periodic waveform of the sensor output. This waveform is a waveform having a level fluctuation due to a magnetic disturbance on the way. When the above-described maximum hold and minimum hold are performed on this waveform, a waveform of an envelope H1 connecting a positive peak and a waveform of an envelope H2 connecting a negative peak is obtained as shown by a broken line in FIG.
In the waveforms of the envelopes H1 and H2, there is an attenuation after each peak of the sensor output waveform, but this is attenuated so as to cope with the level fluctuation of the sensor output waveform.

Using the waveforms of the envelopes H1 and H2, the comparator 36A, 36B obtains a pulse for which a positive peak has been recognized and a pulse for which a negative peak has been recognized from the sensor output. For this purpose, the envelopes H1 and H2 are divided by the voltage dividers 38A and 38B.
The potentials of the thresholds D1 and D2 are set between the respective hold voltages and the zero potential, and the comparators 36A and 36B compare the potentials with the potentials and generate pulses from the sensor outputs.

In FIG. 25, the voltage between the hold voltage and the zero potential is changed by the resistance values R2 / (R1 + R2) and R4 / (R3 +) of the respective resistors of the voltage dividers 38A and 38B shown in FIG.
The waveforms of the threshold values D1 and D2 when the voltage is divided at a ratio of 50% determined by R4) are shown by dotted lines. The partial pressure ratio is 5
About 0% is good, and positive and negative peaks can be reliably captured. If the partial pressure ratio is too small, such as 10%, it becomes easy to pick up a pseudo peak near the zero potential as indicated by the sign P1, and if it is too large, the sign P2
Because you may miss the actual peak like
It is good to choose between 10% and 90%.

In the above description, the threshold voltages D1 and D2 are set by dividing the hold voltage with respect to the zero potential. However, when the output of the sensor is constituted by AC coupling, Since the voltage becomes zero in the stationary state, a dead zone is provided near zero potential so that noise is not picked up, so that the voltage is divided between the voltage slightly shifted from the zero potential to the hold voltage side and the hold voltage. .

Next, the comparators 36A and 36B compare the voltage of the sensor output with the threshold values D1 and D2, and obtain the outputs like the pulses A and B shown in the second and third stages in FIG. Pulse A corresponds to the positive peak of the sensor output, and pulse B corresponds to the negative peak of the sensor output. Note that the polarity of the pulses A and B is set so that the RS flip-flop circuit 40 operates at a low level input, so that the pulses A and B become low level when a peak is recognized.

The pulses A and B are input to the RS flip-flop circuit 40, and the output of the circuit 40 becomes a pulse that falls in response to the falling edge of the pulse A and rises in response to the falling edge of the pulse B (falling edge). , The rising relationship may be reversed). That is, the output of the circuit 40 becomes a pulse that falls in response to recognition of a positive peak in the output waveform of the sensor and rises in response to recognition of a negative peak. In this manner, one pulse rotation detection output is finally obtained for one rotation of the tire.

By the way, in the pulse B of FIG. 25, an erroneous detection pulse corresponding to the pseudo peak P3 of the sensor output shown in the upper part is generated, but the pulse is generated in a period between the erroneous detection pulse and the immediately preceding pulse. Because there is no fall of A,
The erroneously detected pulse B is ignored by the flip-flop circuit 40.

In other words, the adoption of the flip-flop circuit 40 allows the pseudo-peak to produce the tire rotation detection output unless the pseudo peak due to the waveform distortion of the sensor output continuously exceeds the plus and minus thresholds D1 and D2. The pulse is not generated erroneously, and the influence of the pseudo peak due to the waveform distortion of the sensor output can be avoided. In addition, the above-mentioned case hardly appears in an installation environment of a magnetic sensor in a normal vehicle. That is, according to the signal processing method of the present embodiment, waveform distortion of the sensor output becomes very strong. Further, according to the present embodiment, by performing the maximum hold, the minimum hold, and the division of the hold voltage of the sensor output as described above, the peak of the sensor output waveform is recognized according to the level fluctuation and variation of the sensor output. Threshold values D1 and D2 can be automatically variably set.
Level fluctuations and variations in sensor output can be absorbed.
As described above, the method for processing a tire rotation detection signal according to the present embodiment is very effective, and a highly reliable tire rotation detection device can be realized.

[Embodiment of the Present Invention] The embodiment of the configuration which is the premise of the present invention has been described above. However, the following problem is further encountered in tire rotation detection.

It is necessary to set the magnetic sensor of the tire rotating device so that it can be mounted on an unspecified vehicle as easily as possible. However, in the case where the tire and the sensor installation position are separated depending on the vehicle, the magnetic field from the tire is reduced. As the size becomes smaller, the sensitivity of the sensor decreases, and it may be difficult to find the installation location or the worst case.

For example, in the case of installation on an RV vehicle or a 4WD vehicle, the tire and the sensor installation position are often farther apart than a general passenger vehicle. Even in the case where there is a seat, there is a case where the sensor installation position cannot be secured close to the tire.

As the distance from the magnetic field from the tire increases, the magnitude of the magnetic field decreases, and the difference between the magnetic fields of the two magnetic detection elements for performing differential detection decreases. Being unable to do so is a problem.

The present invention is an improvement of the above-mentioned premise in order to solve this problem. The embodiment will be described below with reference to FIGS.

First, FIG. 26 shows the structure of the magnetic sensor 100 constituting the tire rotation detecting device. This figure 2
As shown in FIG. 6, a pair of magnetic detecting elements 112A and 112B are mounted on a sensor circuit board 116 provided in a case 118 of the magnetic sensor 100 at predetermined intervals. These magnetic detecting elements 112A, 112
The magnetic field detection directions of B are the same, that is, parallel to each other, and perpendicular to the sensor circuit board 116 as indicated by the arrow.

The magnetic detecting elements 112A and 112B are preferably the above-described MI elements. In this case, the circuits shown in FIGS. 2, 8, 23, and 24 are mounted on a sensor circuit board, and the operation of the above-described circuits is performed. Performs differential detection and rotation detection of the tire magnetic field. At this time, as in the tire magnetic field detecting method described above, the magnetic detecting element 112 is used.
The magnetic sensors 100 are arranged such that the magnetic field detection directions of A and 112B are parallel to the side surface of the tire, and the magnetic detection elements 112A and 112B are arranged in parallel in a direction perpendicular to the side surface of the tire.

On the other hand, as a constituent element according to the present invention, the lead plate 114 includes the magnetic detecting elements 112A and 112B.
Is fixed on the bottom surface of the case 118 immediately below the case 118. The lead plate 114 guides a magnetic flux from the tire 12, and is made of a magnetic material having a high magnetic permeability (especially in a band of an alternating magnetic field from DC to several hundred Hz), for example, a permalloy, an amorphous magnetic material, or a ferrite. Here, it is formed in a rectangular flat plate shape. The lead plate 114 is parallel to a line connecting the magnetic detection elements 112A and 112B and perpendicular to the magnetic field detection direction of the magnetic detection elements 112A and 112B, that is, in this case, parallel to the sensor circuit board 116. It is arranged to become.

The reason why the lead plate 114 is arranged in parallel to the line connecting the magnetic sensing elements 112A and 112B is as follows.
The reason why the influence on the disturbance magnetic field is made equal and the differential magnetic field is efficiently canceled by the differential, and the arrangement perpendicular to the magnetic field detecting direction is to increase the difference between the magnetic fields required for the differential detection. The reason will be described later.

Next, the effect of the lead plate 114 will be described.

First, the result of examining how the lead plate 114 affects the magnetic field from the tire will be described. In the study, a line 80 mm apart from the side of the tire 12 150 mm parallel as shown in FIG. 27 and a line 30 2 away from the side of the tire 12 in a direction perpendicular to the side of the tire 12, as shown in FIG. And 5 pairs of measurement points A
To E, a magnetic detection element 112A is arranged on the (1) side and a magnetic detection element 112B is arranged on the (2) side of each pair of measurement points,
The magnetic field when the tire was rotated was measured simultaneously at each pair of measurement points, and a comparison was made with and without a lead plate.

As the magnetic detecting elements 112A and 112B, highly sensitive MI elements were used, and the magnetic field detection direction was the vertical direction in the figure parallel to the side surface of the tire 12 as indicated by the arrow.

The lead plate 114 is a flat plate having a width of 25 mm × 47 mm and a thickness of 0.2 mm made of 78% Ni permalloy, and is arranged in two magnetic sensing elements 112 A and 112.
It was arranged 8.5 mm below B so as to be parallel to the line connecting the magnetic detection elements and perpendicular to the magnetic field detection direction.

The tire 12 had an outer diameter Φ of 50 cm, and a steel belt was included in the outer peripheral portion. The tire 12 was magnetized in one direction all around, and was then magnetized in the opposite direction by 90 °.

The measurement results of the magnetic field at the measurement points (1) and (2) and the magnetic field difference between the measurement points (1) and (2) are shown in FIGS. 28 and 29. When there is no lead plate, as shown in FIG. 28, at the measurement point (1) close to the tire and the measurement point (2) far from the tire, (1) naturally has a larger magnetic field. The waveforms are almost the same and the phase relationship is not deviated. However, when there is a lead plate, as shown in FIG. 29, the magnetic field in the direction (2) farther from the tire becomes larger on the contrary, and the waveforms are clearly shifted in phase between (1) and (2). It has become. In particular, it can be seen that the phases are shifted by approximately 90 ° at the measurement points A and E near the tire outer peripheral side.

As a result, as shown in FIG. 30, the magnetic field difference between (1) and (2) relating to the differential detection indicates the peak-to-peak value at the measurement points A to E when the lead plate is placed. It turns out that it is several times larger than the case without. In particular, it can be seen that it becomes larger near the tire outer periphery (measurement points A and E).

The two magnetic sensing elements arranged on the lines (1) and (2) change the magnitude and phase of the magnetic field due to the installation of the lead plate because the magnetic flux from the tire is drawn by the lead plate and the magnetic flux is reduced. Because the magnetic field increases due to concentration and the distance between the end of the lead plate on the tire side and the magnetic detection element differs between the two magnetic detection elements, the effect of the lead plate differs. This is probably due to the occurrence of

To summarize, the effect of using the lead plate is as follows.
-The detection magnetic field itself can be increased by drawing magnetic flux from the tire into the lead plate.

The difference between the magnetic fields required for differential amplification can be increased by causing a phase difference between the magnetic fields at the two magnetic sensing elements.

Is as follows.

Next, the arrangement of the lead plate is as follows.
The lead plate has an optimal position for the magnetic sensing element,
A direction perpendicular to the magnetic field detection direction of the magnetic detection element is desirable.

In order to confirm this, the lead plate 114 is temporarily removed from the configuration of the magnetic sensor 100 shown in FIG.
As shown in FIG. 31, the lead plate 114 was arranged on the lower surface, the side surface, the upper surface, and the upper and lower surfaces on the outside of the case 18, and the tires magnetized nearby were rotated to compare the outputs of the sensors. The results are shown in Table 1 below.

[0142]

[Table 1]

From these results, it is understood that it is important to dispose the lead plate so as to be perpendicular to the magnetic field detection direction of the magnetic detection element. The difference between the lower surface and the upper surface is that the effect is more pronounced when placed on the lower surface side because the distance to the magnetic sensing element is slightly shorter. If the distance is the same, the difference between the upper and lower sides does not appear.

Further, if the lead plates are arranged on both the upper and lower sides, a magnetic shielding effect will be produced on the contrary, and the magnetic field applied to the magnetic detecting element will decrease. It is good to arrange the lead plate.

Finally, data on an actual vehicle will be shown.

FIG. 32 shows the difference depending on the presence or absence of the lead plate of the magnetic sensor installed in the trunk room in a certain RV vehicle. Without the lead plate, the magnetic field in the magnetic detection element of H1 closer to the tire has a peak-to-peak value. When a lead plate is adopted, the detection magnetic field itself is larger than that of 0.14 gauss, which is 0.25 gauss. The detection magnetic field itself is large. It can be seen that the difference of can be taken one digit larger.

As a result, the sensor output actually increased the sensitivity by almost 10 times, and the differential amplification gain of the circuit was 35 times.
As shown in the figure, while the output without the lead plate was 0.15 Vpp, the output with the lead plate was 1.4 Vpp.

In the above embodiment, the lead plate 114 has a rectangular flat plate shape. However, the lead plate 114 may have another shape such as an elliptical shape, or may have a curved or bent shape instead of being flat. Other shapes such as a block shape instead of a plate shape are also conceivable.

[0149]

As is apparent from the above description, according to the present invention, the magnetic field due to the residual magnetization of the steel belt of the tire is differentially externally detected by the pair of magnetic detecting elements arranged at predetermined intervals. In the tire rotation detection device that detects and detects the rotation of the tire based on the detection result, a configuration is adopted in which a magnetic member that guides a magnetic flux from the tire is disposed near the pair of magnetic detection elements. The differential detection of the magnetic field from the tire can be performed with extremely high sensitivity, and the S / N of the differential output is significantly improved. Therefore, even if the distance from the tire to the installation position of the tire rotation detecting device is slightly away, an excellent tire rotation detecting device that can perform magnetic detection of the rotation of the tire satisfactorily and can be easily installed regardless of the vehicle type. Can be provided.

[Brief description of the drawings]

FIG. 1 is a plan view of a vehicle and a perspective view of a trunk room showing an installation position of a magnetic sensor in a vehicle and an arrangement of a magnetic detection element (MI element) in a basic embodiment of a configuration which is a premise of the present invention.

FIG. 2 is a circuit diagram showing a configuration of a magnetic detection circuit of the magnetic sensor of the embodiment.

FIG. 3 is a graph showing a relationship between an interval d between MI elements of the magnetic sensor and a magnetic detection output.

FIG. 4 is a graph showing a relationship between a lead wire length of the MI element of the magnetic sensor and impedance change efficiency.

FIG. 5 is a perspective view in a trunk room showing different installation positions (measurement points) of a magnetic sensor in a magnetic field change measurement test due to tire rotation.

FIG. 6 is a photograph of an oscilloscope waveform showing measurement results at each measurement point in the same test.

FIG. 7 is a waveform diagram of a differential output showing a measurement result of a magnetic field change due to tire rotation during vehicle running on a bridge.

FIG. 8 is a block diagram showing an overall configuration of an embodiment of the tire rotation detecting device.

FIG. 9 is a flowchart illustrating a procedure of signal processing by a microcomputer 30 in FIG. 8;

FIG. 10 is a waveform chart showing a measurement result of a magnetic field change due to tire rotation.

FIG. 11 is a perspective view illustrating a first magnetizing step in an embodiment of a tire magnetizing method having a configuration as a premise of the present invention.

FIG. 12 is an enlarged view in which main parts of FIG. 11 are enlarged.

FIG. 13 is a perspective view illustrating a second magnetizing step in the embodiment.

FIG. 14 is a waveform diagram showing each of the generated magnetic field patterns of the tire according to the difference in the magnetization angle θ in the second magnetization step.

FIG. 15 is a graph showing discrimination widths L and L ′ for setting a rotation detection threshold value of a magnetic field detection output according to the magnetization angle θ.

FIG. 16 is a top view and a side view showing respective positions of magnetic field measurement points with respect to a tire in a study of the effectiveness of the magnetizing method of the embodiment with respect to the actual arrangement of the magnetic sensors.

17 is a waveform chart showing a magnetic field change due to tire rotation at each measurement point in FIG.

FIG. 18 is a view for explaining an embodiment of a tire magnetic field detection method having a configuration which is a premise of the present invention, and shows a relationship between element arrangement and a detection output waveform when differential detection is performed by two magnetic detection elements. It is a wave form diagram of a table.

FIG. 19 is a perspective view showing an arrangement of two magnetic sensing elements determined in the same embodiment.

FIG. 20 is a waveform diagram showing a magnetic field pattern accompanying rotation of a tire which is magnetized at a magnetization angle of 90 ° by a magnetization method having a configuration premised on the present invention.

FIG. 21 is a graph showing actual measurement data of a sensor output for tire rotation detection when the vehicle is running on a bridge.

FIG. 22 is a waveform chart showing waveform distortion accompanied by a pseudo peak of a sensor output for tire rotation detection.

FIG. 23 is a circuit diagram showing a circuit configuration of another embodiment of a tire rotation detecting device having a configuration premised on the present invention.

FIG. 24 is a circuit diagram showing a partially modified example of the circuit configuration.

FIG. 25 is a waveform chart showing signal waveforms at various parts for explaining the operation of the circuit of FIG. 23;

FIG. 26 is a perspective view illustrating a configuration of a magnetic sensor included in the tire rotation detecting device according to the embodiment of the present invention.

FIG. 27 is an explanatory diagram illustrating measurement of a magnetic field of a tire in which the effect of a lead plate of the magnetic sensor has been examined.

FIG. 28 is a waveform chart showing a magnetic field at each measurement point and a change in the difference between the magnetic fields at each measurement point in the case where there is no lead plate in the measurement results.

FIG. 29 is a waveform diagram showing a waveform of a change in a magnetic field at each measurement point and a difference between the magnetic fields at a measurement point when there is a lead plate in the measurement result.

FIG. 30 is a graph showing the peak-to-peak value of the magnetic field difference at each measurement point when there is a lead plate and when there is no lead plate in the measurement results.

FIG. 31 is an explanatory diagram showing how to arrange lead plates.

FIG. 32 is a waveform diagram showing a result of measuring a magnetic field of a tire with and without a lead plate in an actual vehicle.

FIG. 33 is a waveform diagram showing a waveform of a sensor output by the same measurement.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Vehicle 11 Magnet for magnetization 12 Tire 14 Magnetic sensor 18, 18A, 18B Magnetic detection element (MI element) 20 High frequency oscillation circuit 22, 22A, 22B Buffer 24A, 24B Detection circuit 26 Differential amplifier circuit 27 Inverting amplifier 28 AD conversion Device 30 Microcomputer 32 Maximum hold circuit 34 Minimum hold circuit 36A, 36B Comparator 38A, 38B Voltage divider 40 RS flip-flop circuit 100 Magnetic sensor 112A, 112B Magnetic detection element 114 Lead plate 116 Sensor circuit board 118 Case

Continuation of the front page (58) Fields investigated (Int. Cl. ⁷ , DB name) G01P 3/487 B60C 19/00 G01D 5/245 G01R 33/02 G01C 21/00 G09B 29/10

Claims (3)

(57) [Claims] 1. A differential detection of a magnetic field due to a residual magnetization of a steel belt of a tire from outside by a pair of magnetic detection elements arranged so as to be arranged at a predetermined interval, and a rotation of the tire based on the detection result. The tire rotation detecting device according to claim 1, wherein a magnetic member that guides a magnetic flux from the tire is disposed near the pair of magnetic detecting elements. 2. The magnetic field detecting direction of the pair of magnetic detecting elements is the same, and the magnetic member is formed in a flat plate shape, is parallel to a line connecting the pair of magnetic detecting elements, and The tire rotation detecting device according to claim 1, wherein the tire rotation detecting device is arranged to be perpendicular to a magnetic field detection direction of the detecting element. 3. The tire rotation detecting device according to claim 1, wherein the magnetic member is made of permalloy, amorphous magnetic material, or ferrite.