JPH09203680A - Tire-air-pressure detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect the pressure of air in a tire by excluding the effect of disturbance from road surfaces and the like. SOLUTION: An electronic control device (ECU) 5 operates the wheel speeds from the detected signals of wheel-speed sensors 2a-2d, performs frequency analysis (FET operation) for the wheel speeds and obtains the signal strength for every frequency. Furthermore, the resonance frequency is obtained within the specified frequency range in order to make the resonance vibration appearing in the vicinity of 40Hz to be the object to be detected. Furthermore, two kinds of weighting processings for the resonance frequency are performed in accordance with whether the speed is located in the wheel-speed band (Vα-Vβ), where the resonance vibration is liable to occur, or not. That is to say, when the wheel speed is located in the wheel speed band of Vα-Vβ, a relatively large weighting amount Jα is used, and the weighting operation is performed. When the wheel speed is not located in the wheel speed band of Vα-Vβ, a relatively small weighting amount Jβ is used, and the weighting operation is performed. Thereafter, the ECU 5 computes the average resonance frequency from the resonance frequency of (n) times and operates the pressures of air of the tires 1a-1d from the above described resonance frequency.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tire air pressure detecting device for detecting a tire air pressure state based on a tire resonance frequency.

[0002]

2. Description of the Related Art As an inexpensive and highly reliable tire air pressure detecting device, there is one disclosed in Japanese Patent Application Laid-Open No. 5-133831. In this disclosed example, the resonance frequency of the tire is extracted from the signal including the vibration frequency component of the tire, and the air pressure is detected from the change in the resonance frequency.

[0003]

The signal containing the vibration frequency component of the tire includes resonance vibration of the tire, vibration due to disturbance from the road surface, and the like. When the vehicle travels, the resonance vibration of the tire appears in the vicinity of about 40 Hz, and the resonance frequency is obtained by frequency analysis (for example, FFT calculation) of this, and as a result, the tire pressure can be detected. However, there are many vibrations due to disturbance from the road surface or the like in the signal, and the vibrations due to the disturbance from the road surface or the like are so large that they cannot be ignored when compared with the intensity of the resonance vibration around 40 Hz. As a result, there is a problem that the detection accuracy is lowered due to the influence of the random signal of the disturbance vibration.

The present invention has been made in view of the above problems, and an object of the present invention is to eliminate the influence of disturbance from a road surface or the like and to accurately detect the tire air pressure. It is to provide a detection device.

[0005]

When the vehicle is traveling, the resonance vibration of the tire generally appears around 40 Hz, but the vibration intensity of the resonance signal has the maximum value at a predetermined wheel speed for each vehicle. It shows a decreasing tendency as it goes away from the wheel speed. More specifically, as shown in FIG. 4, the peak value of the power spectrum (signal intensity) of the resonance vibration of the vibration system including the tire exhibits the maximum value at the wheel speed V0 in the figure, and The smaller the distance, the smaller it gets. In this case, the fact that the peak value of the power spectrum of the resonance vibration becomes smaller as the distance from the wheel speed V0 becomes smaller means that it is easily affected by the disturbance (noise) from the road surface or the like. From this,
In the present invention, it is found that there exists a wheel speed band (for example, Vα to Vβ in FIG. 4) in which the tire resonance vibration is likely to occur, and the weighting amount for the signal of the tire resonance vibration is set according to the wheel speed.

That is, the tire air pressure detecting device of the present invention detects the vibration frequency component of the tire when the vehicle is running, and calculates the resonance frequency of the tire using the detection result of the tire vibration frequency component. Further, the air pressure of the tire is detected based on the calculated resonance frequency of the tire. At this time, a weighting amount is set around the wheel speed V0 at which the peak value of the power spectrum of the resonance vibration of the vibration system including the tire exhibits the maximum value, the weighting amount becoming larger toward the wheel speed (weighting amount setting means). Using the weighting amount set by the weighting amount setting means, weighting calculation is performed on the detection result of the tire vibration frequency component at that time (weighting calculation means). Further, the resonance frequency is calculated by averaging processing according to the weighting amount (resonance frequency calculating means).

According to the above construction, when the influence of the disturbance from the road surface or the like is small (when the wheel speed is in the vicinity of V0 in FIG. 4), the weighting amount is set to a large value, and also due to the disturbance from the road surface or the like. When there is a lot of influence (Wheel speed is
(When moving away from V0), the weighting amount is set to a small value. As a result, the influence of noise such as disturbance can be eliminated, and the tire air pressure can be accurately detected.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) Hereinafter, a first embodiment of the present invention will be described.
Embodiments will be described with reference to the drawings.

FIG. 1 is a schematic diagram showing the overall construction of a tire pressure detecting device according to this embodiment. As shown in the figure, wheel speed sensors 2a, 2b, 2c and 2d corresponding to the tires 1a to 1d are provided on rotating shafts (not shown) of vehicle tires 1a, 1b, 1c and 1d. Therefore, the sensors 2a to 2d output signals including vibration frequency components of the tires 1a to 1d. More specifically, the wheel speed sensors 2a to 2d include gears 3a, 3b, 3c, 3d.
And pickup coils 4a, 4b, 4c and 4d. The gears 3a to 3d are used for the tires 1a to 1d.
It is attached coaxially to the rotation axis of and is made of a disk-shaped magnetic body. The pickup coils 4a to 4d are gears 3a.
.About.3d, that is, an AC signal having a cycle corresponding to the rotation speeds of the tires 1a to 1d is output.

AC signals output from the wheel speed sensors 2a to 2d are well-known electronic control units (hereinafter referred to as ECUs) including a waveform shaping circuit, CPU, ROM, RAM and the like.
5 is input to the signal processing unit 5 and predetermined signal processing including waveform shaping is performed. The result of this signal processing is input to the display unit 6, and the display unit 6 notifies the driver of the air pressure states of the tires 1a to 1d. The display unit 6 may independently display the air pressure states of the tires 1a to 1d, or one warning lamp may be provided to turn on the light when the air pressure of any one of the tires falls below a reference value. , It may be warned. In the present embodiment, the wheel speed sensors 2a-2
d is a means for detecting the vibration frequency component of the tire when the vehicle is running. Further, the ECU 5 constitutes weighting amount setting means, weighting calculation means, resonance frequency calculation means, weighting amount addition means, and resonance frequency average value calculation means.

FIG. 2 is a functional block diagram showing the configuration of the ECU 5 for each action, and its outline will be briefly described. In FIG. 2, the wheel speed calculation unit 11 waveform-shapes the AC signals output from the wheel speed sensors 2a to 2d (pickup coils 3a to 3d) into pulse signals, and determines the wheel speed V from the pulse interval and the tire diameter. [Km / h] is calculated. The wheel speed V is the speed at which the tire travels in the vehicle traveling direction, and matches the vehicle speed (vehicle speed).

The frequency analysis unit 12 also performs a frequency analysis (for example, FFT calculation) on the wheel speed V calculated by the wheel speed calculation unit 11 to calculate a signal strength for each frequency. Also, the resonance frequency of the tire that appears near 40 Hz is calculated. The weighting amount setting unit 13 has a plurality of weighting amounts in advance, and selectively sets the weighting amount according to the wheel speed V. The air pressure detection unit 14 detects the tire air pressure based on the tire resonance frequency (or spring constant) obtained by the frequency analysis unit 12 and the weighting amount set by the weighting amount setting unit 13.

Next, the operation of the tire air pressure detecting device constructed as described above will be described in detail focusing on the processing operation of the ECU 5. FIG. 3 is a flowchart showing a tire pressure determination routine executed by the ECU 5. Since the ECU 5 performs the same processing on each tire 1a to 1d, only the processing on the tire 1a is shown here.

Now, when the routine of FIG. 3 starts,
At step 101, the wheel speed V [km / h] is calculated by dividing the pulse interval (rotation angle) of the pulse signal corresponding to the detection signal of the wheel speed sensor 2a by the required time and multiplying the tire diameter. Calculate Step 1
In 02, frequency analysis (FFT calculation) is performed on the calculated wheel speed V to obtain the signal strength for each frequency. In step 103, the frequency range is f1 to f2 so that the resonance vibration of the tire appearing near 40 Hz is detected.
Then, the resonance frequency Fk is obtained within the range of f1 to f2.

On the other hand, it was confirmed from the experimental results of the present inventor that the resonance vibration of the tire generally has the following characteristics. That is, as shown in FIG. 5, the resonance vibration of the tire mainly appears near about 40 Hz. Further, as shown in FIG. 4, the signal intensity of the wheel speed V has a peak at a predetermined wheel speed V0 (50 km / h in the present embodiment), and tends to decrease at a wheel speed of V0 or lower or V0 or higher. From this, it was found that the resonance vibration of the tire has a correlation with the wheel speed, and that there exists a wheel speed band (Vα to Vβ) in which the resonance vibration is likely to occur.

In other words, the signal including the vibration frequency component of the tire also includes the vibration component (noise) due to the disturbance from the road surface or the like. At this time, if the wheel speed V is in the wheel speed range of Vα to Vβ, the signal strength of the wheel speed V due to the resonance vibration is sufficiently large, so that it is unlikely to be affected by the vibration component due to the disturbance from the road surface or the like. On the other hand, the wheel speed V is V
When the wheel speed deviates from the wheel speed range of α to Vβ, the signal strength of the wheel speed V due to the resonance vibration becomes small, so that the vibration component due to the disturbance from the road surface or the like is greatly affected. At this time, the obtained resonance frequency Fk largely reflects the influence of a random signal due to the disturbance vibration from the road surface or the like, so that it becomes difficult to obtain a stable frequency due to the resonance vibration of the tire.

Therefore, in the present embodiment, two types of weighting processing are performed on the resonance frequency Fk depending on whether the wheel speed V is in the wheel speed range of Vα to Vβ. That is, if the wheel speed V is in the wheel speed range of Vα to Vβ, a relatively large weighting amount Jα is set, and if the wheel speed V is not in the wheel speed range of Vα to Vβ, a relatively small weighting amount Jβ is set. (Ie Jα> J
β).

As shown in the process of FIG. 3, in step 104, it is judged whether or not the wheel speed V is in the wheel speed range of Vα to Vβ, and in the following steps 105 to 108, the judgment result of step 104 is determined. Perform a weighting operation. That is, if the wheel speed V is in the wheel speed range of Vα to Vβ, a positive determination is made in step 104, and the weighting amount is set to “Jα” in step 105. Further, in the following step 106,
Weighting processing Fkn = Fk for the resonance frequency Fk extracted in step 103 based on the weighting amount Jα.
・ Perform Jα.

If the wheel speed V is not within the wheel speed range of Vα to Vβ, a negative decision is made in step 104 and step 107
Then, the weighting amount is set to “Jβ” (Jβ <Jα). Also,
In the following step 108, the resonance frequency F extracted in step 103 is calculated based on the set weighting amount Jβ.
A weighting process Fkn = Fk · Jβ is performed on k. In this way, the weighting amount is changed every time the wheel speed changes.

After the weighting calculation is performed, in step 109, the weighting amount (J1 to J) set for each of the plurality of resonance frequencies (Fk1 to Fkn) extracted so far.
n) are all added and the total weighting amount Jt up to that point is calculated (Jt = J1 + J2 + J3 + ... + Jn). In step 110, it is determined whether or not the total weight amount Jt is larger than the preset determination amount Jref. If the total weight amount Jt is equal to or smaller than the determination amount Jref, the process returns to step 101 and the above-mentioned step is performed. 101-109
And try again.

When the total weighting amount Jt becomes larger than the determination amount Jref, the routine proceeds to step 111, where the resonance frequencies Fk1 to Fkn after the weighting processing are averaged to calculate the average value Fkave of the resonance frequencies at a predetermined number of times. {Fkave = (Fk1 + Fk2 + Fk3 + ・
.. + Fkn) / Jt}.

Thereafter, in step 112, the air pressure P is calculated from the relationship between the resonance frequency and the air pressure shown in FIG. 6 based on the resonance frequency Fkave detected in step 111. Further, in step 113, it is determined whether or not the obtained air pressure P is equal to or lower than a preset allowable lower limit value Pd. If the air pressure P is equal to or lower than the allowable lower limit value Pd, step 1
Proceeding to 14, the display unit 6 causes the driver to display an alarm.

According to this embodiment described in detail above, the following effects can be obtained. (A) When the influence of the disturbance from the road surface or the like is small (when the wheel speed is near V0 in FIG. 4), the weighting amount is set to a relatively large value “Jα”, and the influence of the disturbance from the road surface or the like is also set. Is large (when the wheel speed is moving away from V0 in FIG. 4), the weighting amount is a relatively small value "Jβ".
I set it to. Then, the weighting amount is multiplied by the resonance frequency at that time to perform the weighting calculation. As a result, the influence of noise such as disturbance can be eliminated, and the tire air pressure can be accurately detected.

(B) In the present embodiment, a plurality of wheel speed zones (Vα to Vβ) are provided around the wheel speed V0 at which the peak value of the power spectrum of the resonance vibration of the vibration system including the tire exhibits the maximum value. , Two kinds of weighting amounts are prepared for the same wheel speed zone and the other, and the weighting amount is selected according to the wheel speed at that time. In such a case, by changing the weighting amount depending on whether or not the wheel speed is in the wheel speed range (Vα to Vβ), highly accurate tire pressure detection can be realized by a simpler method.

(C) Further, in the present embodiment, the weighting amounts are successively added, and the average value of the tire resonance frequencies is calculated using the sum. Then, the tire air pressure is calculated from the average value of the resonance frequencies. In this case, as compared with the case where the weighting calculation is not performed, the tire air pressure calculation accuracy is improved.

(Second Embodiment) Next, a second embodiment of the present invention will be described.
An embodiment will be described. However, in the configuration of the present embodiment, the description of the same components as those in the above-described first embodiment will be omitted. Then, the differences from the first embodiment will be mainly described below.

In the first embodiment described above, the weighting process is performed on the extracted resonance frequency.
In the embodiment, the weighting process is performed on the waveform of the frequency characteristic obtained by the frequency analysis. Hereinafter, the tire air pressure determination process according to the present embodiment will be described with reference to the flowchart of FIG. 7.

Now, when the routine of FIG. 7 starts,
In step 201, the wheel speed V [km / h] is calculated,
In the following step 202, frequency analysis (FFT calculation) is performed on the calculated wheel speed V to obtain the signal strength for each frequency. In step 203, the frequency characteristic waveform Wk before the resonance frequency is extracted within the frequency range of f1 to f2 is obtained.

Then, in step 204, the wheel speed V
Is in the wheel speed range of Vα to Vβ, and in the following steps 205 to 208, weighting calculation is performed according to the determination result of step 204. That is, the wheel speed V
Is in the wheel speed range of Vα to Vβ, an affirmative decision is made in step 204, and the weighting amount is set to “Jα” in step 205. Further, in the following step 206, the weighting amount Jα
Based on the above, weighting processing Wkn = Wk · Jα is performed on the frequency characteristic waveform Wk extracted in step 203. If the wheel speed V is not in the wheel speed range of Vα to Vβ,
A negative determination is made in step 204, and the weighting amount is set to "Jβ" in step 207 (where Jβ <Jα). Further, in the following step 208, the weighting process Wkn = Wk · Jβ is performed on the frequency characteristic waveform Wk extracted in step 203 based on the set weighting amount Jβ.

After the weighting calculation, step 209
Then, the plurality of frequency characteristic waveforms (W
Weighting amount (J1 to Jn) set for each k1 to Wkn)
Are all added, and the total weighting amount Jt up to that point is calculated (Jt = J1 + J2 + J3 + ... + Jn). In step 210, it is determined whether or not the total weight amount Jt is larger than the preset determination amount Jref. If the total weight amount Jt is equal to or less than the determination amount Jref, the process returns to step 201 and the above-mentioned step is performed. 201 to 209 are executed again.

When the total weighting amount Jt becomes larger than the determination amount Jref, the routine proceeds to step 211, where the weighted frequency characteristic waveforms Wk1 to Wkn are averaged so that the average frequency characteristic waveform Wkave at a predetermined number of times.
Calculate {Wkave = (Wk1 + Wk2 + Wk3 +
... + Wkn) / Jt}. In addition, the step 20
The processing contents relating to the weighting processings 6, 208 and the calculation processing of the average frequency characteristic waveform in step 211 are as shown in FIG.

After that, in step 212, the average resonance frequency Fkave is extracted from the average frequency characteristic waveform Wkave, and in the following step 213, the air pressure P is calculated based on the average resonance frequency Fkave from the relationship shown in FIG. Further, in step 214, it is determined whether or not the air pressure P is equal to or lower than a preset allowable lower limit value Pd. If the air pressure P is equal to or lower than the allowable lower limit value Pd, the process proceeds to step 215, and the display unit 6 prompts the driver Make an alarm display.

In the second embodiment as described above, the same operation and effect as in the first embodiment can be obtained,
As a result, the influence of disturbance from the road surface or the like can be eliminated, and the tire pressure can be detected accurately.

(Third Embodiment) The third embodiment will be described below, focusing on the differences from the first and second embodiments described above. In the first and second embodiments, when the wheel speed V is in the wheel speed range of Vα to Vβ, the weighting amount is “Jα”, and when the wheel speed V is not in the wheel speed range of Vα to Vβ. Sets the weighting amount to “Jβ”, and 2
Although different types of weighting amounts have been set, in the third embodiment, different weighting amounts are set for each wheel speed at that time. Hereinafter, the air pressure determination processing of the present embodiment will be described using the flowchart shown in FIG.

In summary, the routine of FIG. 9 differs in that steps 104 to 108 of FIG. 3 in the first embodiment are replaced with steps 301 and 302. That is,
In step 301 of FIG. 9, the weighting amount J corresponding to the wheel speed V at that time is set using the relationship between the wheel speed and the weighting amount shown in FIG. 10. Here, in FIG. 10, the wheel speed V0 is centered around the wheel speed V0 at which the power spectrum of the resonance vibration of the vibration system including the tire exhibits the maximum value.
The maximum weighting amount (J = 1) is set in. In addition, the weighting amount is set to decrease as the distance from the wheel speed V0 increases.

Then, in the following step 302, weighting processing Fkn = Fk · J is performed on the resonance frequency Fk extracted in step 103. The other processing is already described and will be omitted.

Also in the third embodiment, similarly to the first and second embodiments, the influence of the disturbance from the road surface or the like can be eliminated and the tire air pressure can be detected accurately. In particular, in the present embodiment, the weighting amount is precisely obtained, and the tire air pressure detection accuracy can be further increased.

The present invention can be embodied in the following modes other than the above embodiment. (1) In the first and second embodiments described above, two types of weighting amounts are set according to the wheel speed, but they may be changed. For example, in the wheel speed range of Vα to Vβ in FIG. 4, V centered on a wheel speed V0 having a narrower width than that.
A wheel speed band of γ1 to Vγ2 is provided (see FIG. 11). Then, three types of weighting amounts are set according to each wheel speed band. That is, when the wheel speed V is in the wheel speed range of Vγ1 to Vγ2, the largest weighting amount Jα ′ is given, and when the wheel speed V is in the wheel speed range of Vα to Vγ1 or Vγ2 to Vβ, the intermediate weighting is performed. Give the quantity Jβ ',
When the wheel speed V is in the wheel speed range of Vα or less or Vβ or more, the smallest weighting amount Jγ ′ is given (that is,
Jα '>Jβ'> Jγ '). In such a case, setting the weighting amount more finely improves the detection accuracy of the resonance frequency. Alternatively, four or more types of wheel speed zones may be provided and different weighting amounts may be set for each.

(2) In each of the above embodiments, the wheel speed (= vehicle speed [km / h]) is obtained from the detection results of the wheel speed sensors 2a to 2d, and the weighting amount is set according to the wheel speed. However, this may be changed. For example, the rotational speed of the tires 1a to 1d [deg / unit time]
And the weighting amount may be set according to the rotation speed. In such a case, the horizontal axis of FIG. 4 represents the rotational speed of the tire, and the weighting amount is set based on the rotational speed at which the peak value of the power spectrum of resonance vibration becomes the maximum value.

(3) In each of the above embodiments, the value of the weighting amount is not specified, but for example, "Jα = 1.0,
If the weighting amount is set as “Jβ = 0”, the average resonance frequency Fkave can be calculated using only the data with few noise components, that is, the resonance frequency data of the wheel speed bands Vα to Vβ.

(4) The power spectrum in the present invention is for indicating the signal strength of the vibration frequency component, and other signal strengths (energy spectrum, intensity spectrum, etc.) used to agree with it are used. Even if it is, the same operation and effect as the above embodiment can be obtained.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an outline of a tire air pressure detection device according to an embodiment of the invention.

FIG. 2 is a functional block diagram showing the configuration of an ECU for each action.

FIG. 3 is a flowchart showing a tire air pressure determination routine according to the first embodiment.

FIG. 4 is a diagram showing a power spectrum peak of resonance vibration in correspondence with a wheel speed.

FIG. 5 is a waveform chart showing the relationship between the power spectrum of wheel speed and frequency.

FIG. 6 is a diagram showing a relationship between resonance frequency and tire pressure.

FIG. 7 is a flowchart showing a tire air pressure determination routine according to the second embodiment.

FIG. 8 is a waveform chart for explaining weighting processing of frequency characteristic waveforms.

FIG. 9 is a flowchart showing a tire air pressure determination routine according to the third embodiment.

FIG. 10 is a diagram showing a relationship between weighting amounts and wheel speeds according to the third embodiment.

FIG. 11 is a diagram showing a power spectrum peak of resonance vibration in correspondence with a wheel speed.

[Explanation of symbols]

1a to 1d ... tires, 2a to 2d ... wheel speed sensors, 5
... An ECU as weighting amount setting means, weighting calculating means, resonance frequency calculating means, weighting amount adding means, resonance frequency average value calculating means.

Claims (3)

[Claims] 1. A vibration frequency component of a tire when a vehicle is traveling is detected, a resonance frequency of the tire is calculated using the detection result of the tire vibration frequency component, and further, based on the calculated resonance frequency of the tire. A tire air pressure detection device for detecting the air pressure of the tire, wherein the peak value of the power spectrum of the resonance vibration of the vibration system including the tire is centered on the wheel speed at which the peak value is reached, and becomes larger as the wheel speed is approached. A weighting amount setting means for setting a weighting amount; a weighting amount calculating means for performing a weighting operation on the detection result of the tire vibration frequency component at that time using the weighting amount set by the weighting amount setting means; And a resonance frequency calculating means for calculating the resonance frequency by averaging processing according to the amount. It hates the air pressure detection device. 2. A plurality of wheel speed zones are provided around a wheel speed at which the peak value of the power spectrum of resonance vibration of a vibration system including a tire exhibits a maximum value, and a weighting amount is preset for each wheel speed zone. The tire air pressure detection device according to claim 1, wherein the weighting amount setting means selects a weighting amount of a wheel speed band according to a wheel speed at that time. 3. A weighting amount adding means for sequentially adding the weighting amounts, and a resonance for calculating an average value of the resonance frequency of the tire when the addition result of the weighting amounts reaches a predetermined value. The tire air pressure detection device according to claim 1 or 2, further comprising frequency average value calculation means.