JP3428524B2 - Tire pressure detector and wheel speed signal frequency detector - 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 air pressure detecting device, and more particularly to a tire air pressure detecting device for determining a frequency of a rotation speed signal from a wheel rotation speed signal and determining a tire air pressure state from the frequency.

[0002]

2. Description of the Related Art A tire air pressure detection device notifies a driver or the like of an abnormality in a tire such as a deflation of a vehicle. The tire air pressure detection device is adapted to directly detect the air pressure of the tire, and is disclosed in JP-A-5-133831. Some of the tire pressure detection devices described above utilize the resonance frequency of the tire by paying attention to the correlation between the tire pressure and the resonance frequency of the tire.
This tire air pressure detection device obtains a spectrum of a vibration component of a wheel speed by performing a fast Fourier transform (FFT) operation of the wheel speed, detects a resonance frequency of the tire, and when the resonance frequency falls below a predetermined value, air pressure such as puncture on the tire is detected. A warning is issued when it is determined that the omission has occurred.

Further, based on the response output vector of the dynamic system, a total disturbance vector is estimated as a sum of an external disturbance vector acting from the outside of the dynamic system and an internal disturbance vector generated by a failure in the dynamic system. In addition, the internal state vector of the dynamic system is estimated, and the component related to the internal disturbance is separated from the total disturbance vector by calculating the cross-correlation between the estimated total disturbance vector and the internal state vector. , A dynamic system diagnostic device for diagnosing the system from the separated components related to the internal disturbance using the corresponding location of the dynamic system as a failure location (Japanese Patent Laid-Open No. 7-98268 and Japanese Patent Application No. 8-34).
6380 gazette) is proposed. For example, it is conceivable to determine a decrease in air pressure using this diagnostic device.

In this case, when a wheel including a tire is used as a dynamic system, a disturbance vector acting from the outside of the wheel becomes a vibration input input to a wheel resonance system, and a failure in the wheel causes an internal disturbance caused by a decrease in air pressure. If it is a vector, it is possible to determine a decrease in air pressure.

[0005]

However, the tire air pressure detecting device disclosed in Japanese Patent Laid-Open No. 5-133831 has a complicated method of calculating the resonance frequency.

Further, the above-mentioned diagnostic device (Japanese Patent Laid-Open No. 7-982)
No. 68, Japanese Patent Application No. 8-346380), when the air pressure is determined, a response output in which the magnitude of the response output vector is suddenly large or a response output in which a periodic change does not significantly appear May include. If the decrease in air pressure is judged based on the response output that includes a suddenly large response output, the suddenly large response output will have too much influence, and the original periodic response output will be sudden. It is hidden in the large response output. Therefore, the estimated value of the physical quantity for determining the decrease in air pressure varies, and the accuracy deteriorates,
There is a problem that the accuracy of the air pressure drop determination becomes poor.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a tire air pressure detecting device capable of easily performing a highly accurate determination of a tire air pressure state from a detected wheel speed signal. And

[0008]

In order to achieve the above object, the invention according to claim 1 is a wheel speed detecting means for detecting a wheel speed of a wheel including a tire, and at least the wheel speed signal.
Signal passing in the frequency range including the resonance frequency of the signal.
A filter, a reference value setting means as the reference value the amplitude center of the wheel speed signal passed through the filter, of the tire on the basis of the number of crossings of the wheel speed signal for the set reference value by the reference value setting means Tire air pressure state determination means for determining an air pressure state.

According to the first aspect of the present invention, the wheel speed detecting means detects the wheel speed such as the rotation speed of the wheel including the tire and outputs the wheel speed signal. As the wheel speed detecting means, it is possible to use a so-called vehicle speed sensor or the like that detects a gear-shaped rotor provided on a brake rotor or a hub with a sensor such as an optical sensor or a magnetic sensor.
The filter has at least the resonance frequency of the wheel speed signal.
Passes signals in the included frequency domain.

The reference value setting means sets the amplitude center of the vehicle wheel speed signal passing through the filter as a reference value. For example, the amplitude center of the wheel speed signal can be corrected with reference to zero by subtracting the value serving as the amplitude center of the wheel speed signal from the wheel speed signal output from the wheel speed detecting means. The reference value is not limited to the zero reference, and may be any value that allows relative determination of the amplitude of the wheel speed signal.

Further, since the wheel speed signal output from the wheel speed detecting means detects the wheel speed of the wheel including the tire, it has a correlation with the tire air pressure state. Further, since the amplitude center of the wheel speed signal output from the wheel speed detecting means is used as the reference value, even if the amplitude center of the wheel speed signal output from the wheel speed detecting means fluctuates significantly, the intersection with the reference value will occur. The number of times is not affected by the fluctuation. Therefore, according to the invention described in claim 1, the number of times (the number of times of intersections) at which the wheel speed signal intersects with the reference value set by the reference value setting means by the tire air pressure state determining means is obtained and obtained. It is possible to easily make a highly accurate determination of the tire air pressure state based on the number of intersections.

That is, it is possible to easily make a highly accurate determination of the tire air pressure state from the detected wheel speed signal without performing complicated calculations such as fast Fourier transform calculations.

According to a second aspect of the present invention, in the first aspect of the present invention, the reference value setting means sets the reference value based on a change amount of the wheel speed signal in a predetermined time. I am trying.

According to the invention of claim 2, claim 1
In the invention described in (1), the reference value can be appropriately set by the reference value setting means setting the reference value based on the amount of change of the wheel speed signal in the predetermined time. Therefore, it is possible to determine the tire air pressure state with high accuracy.

According to a third aspect of the present invention, in the first aspect of the present invention, the reference value setting means includes signal conversion means for converting the amplitude center of the wheel speed signal into a signal with a zero reference. Is characterized by.

According to the invention of claim 3, claim 1
In the invention described in (1), the reference value setting means includes signal conversion means for converting the amplitude center of the wheel speed signal into a reference signal, and converting the amplitude center of the wheel speed signal into a zero reference signal. The number of times the wheel speed signal intersects with the reference value can be calculated by counting the number of times the sign has been inverted, and the calculation process can be simplified. Therefore, it is possible to easily and highly accurately determine the tire air pressure state.

The invention according to claim 4 is the invention according to claims 1 to 3.
In the invention of any one of claim 3, the reference value setting means further includes an amplifying means for amplifying the wheel speed signal.

According to the invention of claim 4, claim 1
In the invention according to any one of claims 3 to 3 , the reference value setting means includes an amplifying means for converting the amplitude center of the wheel speed signal into a reference signal and amplifying the wheel speed signal. It is possible to suppress digit loss when calculating the number of times of intersection between the wheel speed signal and the reference value, and improve the calculation accuracy of the number of times of intersection between the wheel speed signal and the reference value.

[0019] The invention described in claim 5 is the invention according to any one of claims 1 to 4, wherein the fill
Data is from the passing means for passing a signal of only a predetermined frequency band of the wheel speed signal, based on the detected frequency by the frequency detection means for detecting a frequency of the wheel speed signal, the predetermined frequency band of said passing means correction means to correct
It is characterized by further comprising a.

According to the invention of claim 5, claim 1
To the invention described in any one of claims 4, Fi
The filter comprises a passage means, and further comprises a correction means, so that the passage means removes frequencies other than the frequency of the predetermined frequency band. That is, it becomes possible to remove a component (noise) that is not necessary for detecting the tire air pressure state included in the wheel speed signal. Further, since the predetermined frequency band passing through the passing means is corrected based on the frequency of the wheel speed signal detected by the correcting means, it is possible to efficiently remove the noise included in the wheel speed signal.

The frequency of the wheel speed signal detected by the frequency detecting means can be detected by a general Fourier transform operation or the like.

According to a sixth aspect of the invention, in the fifth aspect of the invention, the correcting means corrects the center of the predetermined frequency band of the passing means to be the frequency detected by the frequency detecting means. It is characterized by doing.

According to the invention of claim 6, claim 5
In the invention described in (1), the correction means causes the center of the predetermined frequency band of the passage means to be the frequency detected by the frequency detection means, so that the wheel speed signal passing through the passage means is detected by the frequency detection means. Therefore, the frequency components other than the frequency components necessary for the above are removed. Therefore, it is possible to determine the air pressure state with high accuracy.

[0024]

[0025]

The invention according to claim 7 is the invention according to claim 5 or the contract.
In the invention of claim 6 , the frequency detecting means is
The frequency of the wheel speed signal is detected based on the number of crosses.

According to the invention described in claim 7, claim 5
Alternatively, in the invention according to claim 6 , the frequency detecting means can detect the resonance frequency of the wheel speed signal based on the number of times the wheel speed signal intersects with the reference value.

Since the wheel speed signal output by the wheel speed detecting means detects the wheel speed of the wheel including the tire as described above, it has a correlation with the resonance frequency of the tire. That is, the frequency of the detected wheel speed signal also has a correlation with the tire resonance frequency. Therefore, the passage means can be set in the predetermined frequency band including the tire resonance frequency based on the detected frequency of the wheel speed signal.

According to an eighth aspect of the invention, in the seventh aspect of the invention, the frequency detecting means is the wheel speed signal.
T for a predetermined time of issue, the number of measurements of the wheel speed signal N, the
If the number of times the wheel speed signals intersect is C, the frequency f = C / (2
It is characterized by being calculated by TN).

According to the invention described in claim 8 , claim 7
In the invention according to a frequency detection means, a constant time T at the wheel speed signal, the number of measurements of the wheel speed signal N, and the number of intersections between the wheel speed signal and the reference value at this time as a C, a frequency f = C / (2TN), the frequency of the wheel speed signal can be calculated. The invention according to claim 9 is
The invention according to any one of claims 1 to 8
A calculator for calculating the judgment value for selecting the wheel speed signal.
And a selector for selecting a necessary signal based on the judgment value
It is characterized in that it further comprises a step. Note in claim 9
According to the invention described in any one of claims 1 to 8,
In the invention described in, the wheel speed signal is calculated by the calculating means.
Calculate a judgment value for selection, based on the judgment value,
The necessary wheel speed signal is selected by the selecting means. Therefore,
The calculation means does not include too much noise in the wheel speed signal.
The judgment value for selecting a signal with a good S / N ratio
By calculating, a wheel with a good S / N ratio in the sorting means
High speed signals can be sorted. That is, selected
It is possible to judge the tire pressure condition from the wheel speed signal.
It is possible to judge the tire pressure condition with high accuracy.
You can

According to a tenth aspect of the present invention, in the invention according to the ninth aspect , the calculating means converts the judgment value so as to change in accordance with the number of intersections and the change in the wheel speed signal. It is characterized in that a comparison value with the number of crossings of the signal thus obtained with respect to the reference value is calculated.

According to the invention described in claim 10,
In the invention described in 9 , the signal converted by the calculating means so as to change in response to the change in the wheel speed signal and the number of times the wheel speed signal intersects with the reference value as the determination value for selecting the wheel speed signal. A comparison value with the number of intersections with respect to the reference value of is calculated.

Here, for example, even if the wheel speed signal in which the noise suddenly has a large noise is converted as described above, the converted value contains many components other than the periodic component. That is, the signal that is generated by suddenly converting a large amount of noise as described above does not change in response to the change in the wheel speed signal, so that the resonance is weak (the cycle is long), and the number of times the wheel speed signal intersects with the reference value, A comparison value, for example, a difference between the reference value of the signal converted so as to change corresponding to the change of the wheel speed signal and the number of times of intersection becomes large. Therefore, the wheel speed signal is calculated based on the comparison value of the number of crossings between the wheel speed signal and the reference value and the number of crossings with respect to the reference value of the signal converted to change corresponding to the change in the wheel speed signal, for example, based on the difference. By selecting, it is possible to select a wheel speed signal having a good S / N ratio.

According to a tenth aspect of the present invention, in the invention according to the tenth aspect, the conversion performed so as to change corresponding to the change of the wheel speed signal is n times difference or n times differentiation (n is Is a natural number).

According to the eleventh aspect of the invention, in the invention of the tenth aspect, the conversion performed so as to change in response to the change of the wheel speed signal is n times difference or n times differentiation (n is It is performed by a natural number), and the conversion removes extremely prominent noise included in the wheel speed signal. Further, by setting n = 2, the calculation load of conversion can be reduced and noise can be effectively removed.

The invention according to claim 12 is characterized in that, in the invention according to any one of claims 1 to 11, the air pressure state is a tire air pressure reduction state.

According to a twelfth aspect of the invention, in the invention according to any one of the first to eleventh aspects,
If the number of intersections of the wheel speed signal and the reference value at normal air pressure or the frequency of the wheel speed signal is measured in advance, the tire pressure state is determined from the number of intersections of the wheel speed signal and the reference value or the frequency of the wheel speed signal. It is possible to determine whether or not it is decreasing.

[0038]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of a tire air pressure detecting device 10 according to an embodiment of the present invention.

As shown in FIG. 1, the tire air pressure detection device 10 is mainly composed of a wheel speed detection means 12, a reference value setting means 14, a selection means 16, a frequency detection means 18, and an air pressure state determination means 20. There is.

The wheel speed detecting means 12 detects a wheel speed of a wheel including a tire of an automobile, for example, a wheel speed sensor which outputs a sensor output signal corresponding to the wheel speed, and the sensor output signal. And a calculation means for calculating the actual rotation speed of each wheel.
Further, as shown in FIG. 2, a gear-shaped rotor 22 is provided on a rotating member (hub, rotor, etc.) of the wheel, and the teeth of the rotor 22 rotating with the rotation of the wheel are detected by a detector 24 such as an optical sensor or a magnetic sensor. It is possible to configure by means for generating an AC signal having a frequency proportional to the rotation speed of the wheel, and calculating the wheel speed based on the cycle of the AC signal.

The reference value setting means 14 is composed of a signal converting means for converting the wheel speed signal detected by the wheel speed detecting means 12 so that the center of amplitude of the wheel speed signal becomes zero reference, and an amplifying means for amplifying the wheel speed signal. It is possible to configure, and it is possible to enhance the amplitude of the wheel speed signal by converting the reference value of the wheel speed signal and amplifying the wheel speed signal. The signal converting means can set the amplitude center of the wheel speed signal as the zero reference by calculating the difference between the change amount of the wheel speed signal in the predetermined time and the change amount in the subsequent predetermined time. By passing the wheel speed signal through a high-pass filter or a band-pass filter, the center of the amplitude of the wheel speed signal can be converted to the zero reference.

In the present embodiment, the above-mentioned signal converting means and amplifying means use a filter for converting the amplitude center of the wheel speed signal into a zero reference by passing the wheel speed signal through a high pass filter or a band pass filter. The secondary case will be described. The transfer function H (z) of this filter is

[0044]

[Equation 1]

Let's say. Here, a ₁ , a ₂ , b ₁ and b ₂ are filter coefficients, and Z ⁻¹ is one sample delay.

To realize the filter, it is necessary to normalize the real number coefficient of the filter into an integer expression. So the real number 2
^{-If BBP} is normalized so as to correspond to 1 bit in the integer representation of the real number coefficient of the filter, equation (1) can be expressed by the following equation.

[0047]

[Equation 2]

Here, LBP = 2 ^BBP .

The BBP is set so that the coefficient at the time of normalization has a sufficient number of digits in calculation, and the amplitude center of the wheel speed signal can be converted to the zero reference by performing calculation based on the transfer function. it can.

The frequency detecting means 18 detects the frequency by counting the number of times the reference value (zero reference) converted as described above and the wheel speed signal intersect at a predetermined time interval,
The air pressure state determination means 20 determines a tire air pressure state, for example, a decrease in air pressure, based on the frequency detected by the frequency detection means 18.

Further, when some noise is mixed in the resonance vibration component of the wheel speed signal and the S / N ratio of the wheel speed signal is bad, the selecting means 16 makes the wheel speed signal zero as shown in FIG. If a section that does not intersect occurs, the frequency detected by the frequency detection unit 18 becomes smaller than the original frequency, the frequency detection accuracy of the frequency detection unit 18 decreases, and the main component of the spectrum relatively decreases. This will cause an increase in variation. Therefore, it is possible to prevent a decrease in frequency detection accuracy by selecting a signal having a poor S / N ratio of the wheel speed signal, and
It is possible to suppress an increase in estimated variation. The selecting means 16 may not be provided, but it is preferable to provide the selecting means 16 as described above because the frequency detecting accuracy can be improved.

Next, the operation of the tire air pressure detecting device 10 constructed as described above will be described.

The wheel speed signal detected by the wheel speed detecting means 12 is output to the reference value setting means 14. As described above, the reference value setting means 14 converts the amplitude center of the wheel speed signal into the zero reference by the filter converted by the transfer function of the expression (2).

In order to calculate this transfer function so that there is little cancellation of digits when the microcomputer performs the calculation process, the calculation as shown in FIG. 3 is performed. The data length of the microcomputer used for the calculation has the following specifications. When adding or subtracting, 16-bit length ± 16-bit length → 16-bit length, 32-bit length ± 32
Bit length → 32 bits length, and when performing multiplication,
16-bit length × 16-bit length → 32-bit length.

N-bit right shift means to multiply by 2 ^−N (N natural number), and N-bit left shift is 2
Means to multiply by ^N. Further, in FIG. 3, the bit right shift is indicated by ">>", and the bit left shift is "<<".
Indicate.

In the figure, the input u, the internal output y and the constants A ₁ , A ₂ , B ₀ , B ₁ and B ₂ are 16 bits long. First, X ₀ is calculated by adding the output of the 2-stage delay operator to the product of the input u and B ₀ .

[0057] X ₀ is has a 32-bit length, because in the feedback loop of the filter must be performed multiplication of A _1, A ₂ it is necessary to drop the X ₀ to 16 bits long. To be precise, it shifts right by B _BP bits.

Therefore, in FIG. 3, X ₀ , which is 32 bits long, is right-shifted until it fits in 16 bits long. If the amount of right shift at that time is B _D1 , then a value obtained by right-shifting X ₀ by B _D1 bits becomes y. Further, the remaining bit shift amount B _D2 =
B _BP -B _D1 must be right-shifted, but this operation is performed after the multiplication of y by A ₁ and A ₂ .

[0059] because it is only right shift the B _D1 bit when it should be B _BP bit right shift the X ₀ if the original here, and as a result, this operation, B _BP -B _D1 bit left shift the y That is, it means that the amount of 2 to the power of B _BP −B _D1 is amplified.

By doing so, it is possible to reduce the precision loss during the calculation within the range of the restriction on the data length in the multiplication. Further, the filter output is obtained by shifting the internal output y of the filter by B _D2 bits to the right, but with this alone, a digit loss occurs due to the bit shift. Therefore, 16-bit left shift (2 ¹⁶ times amplification) is performed in advance. Then, shift B _D2 bits to the right. That is, as a result (16-
B _D2 ) Shift left by bits. Since the output y ₀ obtained here is amplifying the output, the detection accuracy for detecting the intersection with the reference value can be improved.

FIG. 4B shows the vibration component waveform of the wheel speed signal when only the center of amplitude of the wheel speed signal is converted to the zero reference, and the portion indicated by arrow A in FIG. 4B. Indicates a portion that does not cross the zero reference due to cancellation of digits during calculation, and it can be seen that the detection accuracy for detecting the intersection of the wheel speed signal and the zero reference deteriorates.

On the other hand, FIG. 4A shows the reference value setting means 1
As the signal converting means and amplifying means of No. 4, as described above, the amplitude center of the wheel speed signal is corrected to the zero reference by passing through the high pass filter or the band pass filter.
The vibration component waveform in which the output (wheel speed signal) at that time is amplified is shown. As shown in FIG.
It can be seen that the portion indicated by arrow A in (B) is corrected, and the detection accuracy of the intersection between the wheel speed signal and the zero reference is improved.

In this operation, even if the internal output y of the filter is shifted to the left by B _D2 bits and then shifted to the left by 16 bits (amplification by 2 ¹⁶ times), the information lost by the bit shift does not return. It is necessary to shift (amplify 2 ¹⁶ times) and then shift B _D2 bits to the right.

Further, although the amplification is set to 2 ¹⁶ times, the value is not limited to this value and may be any value as long as the accuracy sufficient for detecting the zero crossing of the wheel speed signal is secured.

Next, the frequency detection process will be described with reference to FIG.
This will be described with reference to the flowchart shown in FIG.

First, in step 100, the reference value is corrected (converted) by the reference value setting means 14 as described above.
The wheel speed signal that has been subjected to is input and the process proceeds to step 102. In step 102, 1 is added to the number k of times of frequency detection processing performed in a predetermined time, and the process proceeds to step 104. In step 104, it is determined whether the wheel speed signal has a sign reversal, that is, whether the observed sample crosses the zero reference.

If it is determined in step 104 that the sign is not inverted, the process returns to step 100 and the above-mentioned step 10 is performed.
0 to step 104 are repeated. Step 104
When it is determined that the sign has been inverted, the process proceeds to step 106, where 1 is added to the code inversion number c (the number of code determinations is integrated) in step 106, and the process proceeds to step 108.

In step 108, k = n, that is,
It is determined whether or not the number k of times of frequency detection processing performed in a predetermined time has reached a specified number n of times that defines the specified time. If it is determined in step 108 that k = n is not satisfied, step 1
00, the above steps 100 to 108 are repeated until k = n is determined in step 108.

When it is determined in step 108 that k = n, the process proceeds to step 110, and the sorting means 16 performs sorting (details will be described later) and determines whether or not to sort. If the determination is positive, the process proceeds to step 112.

In step 112, K = K + n, C = C
+ N, move to step 114, step 114
Then, it is determined whether or not K = N, that is, whether or not the number of samples N reaches a predetermined value N.

When the determination at step 114 is affirmative, the routine proceeds to step 116, where the total number C of times when the wheel speed signal crosses the zero reference is output, and based on the total number C, the frequency detecting means 18 determines the frequency. Is detected. It should be noted that in the frequency detection, the total number C of the code inversion times and the time T required until the predetermined value N is reached are f = C / (2T
It can be detected by substituting it into N).

On the other hand, step 110 and step 114
If the determination is negative, the process proceeds to step 118, the frequency detection process count k and the sign inversion count integrated value c are set to 0, and the process returns to step 100. The process is repeated until the determinations at steps 110 and 114 are positive.

As described above, in the tire air pressure detection device 10 of the present embodiment, the wheel speed signal (FIG. 6A) detected by the wheel speed detection means 12 is converted into the wheel speed signal by the reference value setting means 14. The amplitude center is corrected to zero reference (FIG. 6 (B)), and the wheel speed signal is amplified (FIG. 6).
(C)). Then, since the frequency of the wheel speed signal can be detected by counting the number of times (the number of sign reversals) of the wheel speed signal and the zero reference for a predetermined time, it is possible to perform a complicated operation such as a fast Fourier transform operation. Therefore, the frequency of the wheel speed signal can be easily detected.

In the present embodiment, the total number C of the code inversion times of the plurality of selected periods (time) is output when the number of samples K is determined to be the predetermined value N, and the frequency is detected. However, for example, when the total number of times C exceeds a predetermined value or when the number of times the signal used for frequency detection is selected by the selecting means 16 reaches a predetermined value (the selecting means 16 determines a predetermined value Y). The frequency may be detected according to the number of times.

Further, in the present embodiment, the frequency is detected by using the total number of times of intersection of the wheel speed signal and the reference value in the plurality of selected periods (time), but the plurality of selected A value obtained by statistically processing the total number of intersections of the wheel speed signal and the reference value during the period (1) (median (median value), most frequent value, etc.) may be used.

By the way, the selecting means 16 selects the wheel speed signal as follows by taking advantage of the feature that the resonance frequency of the wheel speed signal can be easily detected.

The number of times the wheel speed signal crosses the zero reference in a predetermined section of the signal after passing through the band pass filter is C1, and the signal obtained by differentiating (or differentiating) this signal n (n is a natural number) times is in the same section. The number of crossings with the zero reference is C2, and the difference αα = C2-C1 (3) is obtained from the equation (3). When α exceeds a predetermined value, the wheel speed signal and the zero reference in that section are calculated. Do not adopt the count value of the number of intersections with.

By making such a determination, for example, in the case shown in FIG. 7, α increases as the number of missing points at the intersection of the wheel speed signal and the zero reference increases.
It is possible to suppress the drop of the estimated frequency (the frequency detected by the frequency detecting means 18).

A signal having a poor S / N ratio is sensitive to the above-described differential operation, and thus it can be similarly omitted. For example, as shown in FIG.
When the S / N ratio is good, the difference between the peaks of the signal a and the differential signal is small ( FIG. 10 (A)), but when the S / N ratio is bad, the peak of the differential signal with the signal a is high. The difference becomes large (FIG. 10 (B)). Theoretically, it can be explained as follows.

Now, when the resonance characteristic of the wheel speed signal is approximated by the secondary characteristic, the wheel speed signal follows the characteristic of the following equation.

[0081]

[Equation 3]

Here, d is the input from the road surface, and ζ is the damping coefficient of the resonance system. Resonance is attenuated as ζ increases,
At ζ = 1 / √2, critical vibration (resonance point disappearance) occurs.

The peak angular frequency in equation (3) is

[0084]

[Equation 4]

The peak angular frequency of the signal obtained by first-order differentiating the equation (3) is

[0086]

[Equation 5]

The peak angular frequency of the second-order differentiated signal is

[0088]

[Equation 6]

It becomes

Here, when the peak angular frequency is used for the second-order differentiated signal and a judgment value similar to that of the equation (3) is derived,

[0091]

[Equation 7]

It becomes This value β becomes 0 when ζ = 0, increases monotonically with an increase in ζ, and becomes ∞ when ζ → 1 / √2.

Therefore, it can be seen that the determination value β can also take a large value for a signal with a poor S / N ratio (a signal with a large ζ). However, since it actually passes through a bandpass filter, it saturates at a value determined by this passband.

When extremely prominent noise (engine noise or the like) is included, ζ approaches 0 on the contrary.
By providing a predetermined threshold value also on the lower side of α, it is possible to remove extremely protruding noise.

The difference from the peak angular frequency of the first-order differential signal is ω _p1 −ω _p = ω _p {1-√ (1-ζ ^ 2)}. From this, it can be seen that for the same ζ, the difference from the peak angular frequency of the second-order differential signal is larger than the difference from the peak angular frequency of the first-order differential signal, that is, the sensitivity is higher. This means that the sensitivity of the third-order differential signal becomes higher than that of the second-order differential signal, and in general, the difference between the third-order differential signal and the peak angular frequency of the n-th order differential signal (n is a natural number) The S / N can be determined, and the sensitivity of selection can be increased by increasing n.

The same thing exists in the difference in the number of zero crossings correlated with the resonance frequency of the signal, and generally, it can be selected based on the difference between the number of zero crossings in the n-th order differential signal (or differential signal).

However, considering the calculation load and the calculation error generated at the time of the difference calculation, n is not so large and n = 2.
The degree is the desired value.

Next, the air pressure state determination by the air pressure state determination means 20 based on the number of crossings detected as described above will be described.

By detecting the number of times of intersection as described above from the wheel speed signal detected by the wheel speed detecting means 12 at normal air pressure, it is possible to detect the change in tire air pressure from the change in the number of times of intersection.

As shown in FIG. 8, when the tire air pressure at a certain speed is reduced stepwise, for example, the integrated value of the number of crossings of the wheel speed signal and the zero reference changes every one minute,
As the tire air pressure decreases, the number of intersections also decreases, and the integrated value of the number of intersections of the tire air pressure, the wheel speed signal, and the zero reference has a correlation. That is, it is possible to determine the decrease in tire air pressure from the number of times the wheel speed signal crosses the zero reference. Further, since the frequency can be calculated from the integrated value of the number of intersections per minute, the frequency calculated by the frequency detecting means 18 and the tire air pressure have a correlation. Therefore, by measuring the tire pressure frequency in a steady state in advance, when the tire pressure decreases with time, the decrease in tire pressure can be detected by detecting the frequency from the wheel speed signal at that time. You can also

Further, by pre-storing the frequency of the wheel speed signal corresponding to the tire pressure for each speed, it is possible to detect the tire pressure from the frequency detected by the frequency detecting means 18.

Next, a modified example of the tire air pressure detecting device of the present embodiment will be described.

As shown in FIG. 9, the tire air pressure detection device has a passage means 30 which allows the tire air pressure detection device 10 to pass only a predetermined frequency band in the wheel speed signal detected by the wheel speed detection means 12. The frequency detecting means 18 is provided with a correcting means 32 for correcting a predetermined frequency band passing through the passing means 30 based on the frequency detected as described above.

The passing means 30 is the wheel speed detecting means 1
Only the predetermined frequency component of the wheel speed signal of each wheel detected by 2 is passed. For example, a bandpass filter that passes only frequency components in a certain band centered on the frequency expected to be the resonance frequency of the wheel speed signal, a high-pass filter that passes only frequency components in the high frequency band that includes the resonance frequency component, etc. Can be configured.

By thus providing the passage means 30, only the frequency component of the component related to the tire pressure can be extracted, and the correction means 32 further causes the passage means 3 to be extracted.
Since the predetermined frequency passing 0 is corrected, unnecessary noise is largely excluded, and the tire air pressure detection accuracy can be improved.

[0106]

As described above, according to the present invention, it is possible to provide a tire air pressure detecting device capable of easily performing highly accurate determination of the tire air pressure state from the detected wheel speed signal. There is an effect.

[Brief description of drawings]

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

FIG. 2 is a diagram showing an example of wheel speed detection means.

FIG. 3 is a diagram for explaining a transfer function of a filter.

FIG. 4A is a diagram showing a case where a wheel speed signal is corrected to a zero reference and amplified so as to suppress a cancellation of digits during calculation;
(B) is a diagram when the wheel speed signal is corrected as it is with the zero reference.

FIG. 5 is a flowchart showing a frequency detection process.

FIG. 6A is a diagram showing an example of a wheel speed signal,
It is a figure showing the wheel speed signal which correct | amended the amplitude center of a wheel speed signal on the basis of zero (B), and is a figure showing the wheel speed signal which corrected and amplified the amplitude center of a wheel speed signal on the basis of zero. .

FIG. 7 is a diagram showing a vibration component of a wheel speed signal.

FIG. 8 is a diagram showing a frequency variation when the tire air pressure is gradually reduced.

FIG. 9 is a block diagram showing a modified example of the tire air pressure detection device according to the embodiment of the present invention.

FIG. 10 is a diagram for explaining the relationship between the resonance frequency and the difference in the count value of the number of crossings between the signal a and the zero reference of the difference signal.

[Explanation of symbols]

10 Tire pressure detection device 12 Wheel speed detection means 14 Reference value setting means 16 Sorting means 18 Frequency detection means 20 Air pressure state determination means 30 Passing means 32 correction means

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP 62-149503 (JP, A) JP 5-273265 (JP, A) JP 8-219920 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) G01L 17/00 B60C 23/02

Claims (15)

(57) [Claims] 1. A wheel speed detecting means for detecting a wheel speed of a wheel including a tire, and a frequency range including at least a resonance frequency of the wheel speed signal.
A filter that passes a signal of a range, a reference value setting unit that uses the amplitude center of the wheel speed signal that has passed through the filter as a reference value, and the number of times the wheel speed signal intersects the reference value set by the reference value setting unit. A tire air pressure state determination means for determining an air pressure state of the tire based on the above. 2. The tire air pressure detection device according to claim 1, wherein the reference value setting means sets the reference value based on a change amount of the wheel speed signal in a predetermined time. 3. The tire air pressure detection device according to claim 1, wherein the reference value setting means includes signal conversion means for converting the amplitude center of the wheel speed signal into a signal having a zero reference. 4. The tire air pressure detecting device according to claim 1, wherein the reference value setting means further includes an amplifying means for amplifying the wheel speed signal. 5. A consists passing means wherein said filters passing signals of only a predetermined frequency band of the wheel speed signal, based on the detected frequency by the frequency detection means for detecting a frequency of the wheel speed signal, the passage tire pressure detecting apparatus according to any one of claims 1 to 4, further comprising a correction means to correct the predetermined frequency band of the unit. 6. The correcting means corrects the center of a predetermined frequency band of the passing means to a frequency detected by the frequency detecting means.
The tire pressure detection device according to. 7. The tire air pressure detection device according to claim 5, wherein the frequency detection means detects the frequency of the wheel speed signal based on the number of crosses. 8. The frequency detecting means has a frequency f = C / (2T) where T is a predetermined time of the wheel speed signal, N is the number of measurements of the wheel speed signal, and C is the number of times the wheel speed signal intersects.
The tire air pressure detection device according to claim 7, wherein the tire air pressure detection device is calculated by N). 9. The method according to claim 1, further comprising calculation means for calculating a judgment value for selecting the wheel speed signal, and selection means for selecting a necessary signal based on the judgment value.
The tire pressure detection device according to claim 8. 10. The calculation means, as the judgment value,
The tire air pressure detection device according to claim 9, wherein a comparison value of the number of intersections and the number of intersections of the signal converted so as to change corresponding to the change of the wheel speed signal with the reference value is calculated. . 11. The n-th difference or n-th derivative (n
Is a natural number), The tire pressure detection device according to claim 10. 12. The tire air pressure detection device according to claim 1, wherein the air pressure state is a tire air pressure reduction state. 13. A wheel speed detecting means for detecting a wheel speed of a wheel including a tire, and a frequency range including at least a resonance frequency of the wheel speed signal.
A filter that passes a signal of a range, a reference value setting unit that uses the amplitude center of the wheel speed signal that has passed through the filter as a reference value, and the number of times the wheel speed signal intersects the reference value set by the reference value setting unit. A wheel speed signal frequency detecting device comprising: a frequency detecting means for detecting the frequency of the wheel speed signal based on the above. 14. The method according to claim 13, further comprising calculation means for calculating a judgment value for selecting the wheel speed signal, and selection means for selecting a necessary wheel speed signal based on the judgment value. The wheel speed signal frequency detection device described. 15. The amplifying means outputs a signal at every sample time.
Claim characterized by changing the amplification degree while adapting to the number
Item 4. The tire pressure detection device according to item 4.