JPH11235908A - Tire pressure estimation device - Google Patents

Abstract

(57) [Problem] To provide a device capable of accurately detecting tire air pressure according to the characteristics of each wheel of a vehicle or even when the environment of the vehicle changes. SOLUTION: For a driving wheel capable of extracting a resonance frequency or a spring constant from a vibration frequency component of a tire included in a wheel speed signal without being largely influenced by a vehicle environment such as a vehicle speed, a first tire pressure estimating means determines a wheel. The tire pressure is estimated by frequency analysis of the speed signal. Then, the vibration level of the vibration frequency component of the tire is varied according to the vehicle environment such as the vehicle speed, etc., and the frequency analysis of the wheel speed signal is used to estimate the tire pressure. To estimate the tire pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tire pressure estimating apparatus for indirectly estimating air pressure or a change in air pressure of a tire of an automobile or the like.

[0002]

2. Description of the Related Art Conventionally, as an apparatus for estimating a tire pressure state, a signal including a tire vibration frequency component included in a wheel speed signal is frequency-analyzed to extract a tire resonance frequency, and based on the resonance frequency. One that detects the state of tire pressure is known. (Japanese Patent Laid-Open No. 5-1338
As described above, the resonance frequency used when estimating the tire air pressure based on the resonance frequency is about 30 to 50 Hz. However, as described below, the tire air pressure is accurately estimated depending on the environment where the vehicle is placed. There is a problem that can not be.
For example, at a vehicle speed in a low to middle speed range when the vehicle travels in an urban area or the like, the resonance frequency range of about 30 to 50,
Although the tire pressure can be estimated in Hz, when the speed of the vehicle is in a high speed region, the tire vibration phenomenon is less likely to occur, the power spectrum level of resonance is reduced, and the tire pressure estimation accuracy is reduced.

On the other hand, Japanese Patent Application Laid-Open No. 7-217
As described in Japanese Patent No. 23, the vibration frequency component included in the wheel speed signal is approximately 30 to 50 Hz and approximately 60 to 50 Hz.
It is known that the resonance frequency is selected in a plurality of frequency ranges such as 90 Hz to improve the accuracy of tire pressure estimation in a high-speed region. That is, in the high-speed region, the frequency range in which the resonance phenomenon becomes strong changes from the low-speed / medium-speed region, but the frequency range used for estimating the tire pressure is selected following this.

[0004]

However, the applicant of the present application has reported that the higher-order resonance frequency (for example, about 60 to 90 Hz) included in the wheel speed signal is different from the resonance frequency with respect to the change in tire pressure in the driving wheels of the vehicle. Although it was confirmed that the characteristics were large and the characteristics were suitable for estimating the tire pressure, it was found that it was difficult to accurately estimate the air pressure of the rolling wheels even at this higher resonance frequency.

Accordingly, an object of the present invention is to provide a device capable of accurately detecting tire air pressure according to the characteristics of each wheel of a vehicle or even when the environment of the vehicle changes.

[0006]

In order to achieve the above object, a tire pressure estimating apparatus according to the present invention comprises a wheel speed detecting means for sequentially calculating wheel speeds of each wheel during running of a vehicle; Extracting means for extracting a tire resonance frequency or a tire spring constant from a vibration frequency component included in a wheel speed signal which is a detection result of the means; and a driving wheel based on the resonance frequency or the tire spring constant extracted by the extraction means. First tire pressure estimating means for estimating tire pressure, rotation state value calculating means for calculating a tire rotation state value based on the wheel speed detected by the wheel speed detection means, and rotation state value calculation means Second tire pressure estimating means for estimating the tire pressure of the rolling wheel based on the deviation of the obtained rotation state value. .

That is, for a driving wheel capable of extracting a resonance frequency or a spring constant from a tire vibration frequency component included in a wheel speed signal without being greatly influenced by a vehicle environment such as a vehicle speed, the first tire pressure estimating means. The tire pressure is estimated by frequency analysis of the wheel speed signal. Then, the vibration level of the vibration frequency component of the tire is varied according to the vehicle environment such as the vehicle speed, etc., and the frequency analysis of the wheel speed signal is used to estimate the tire pressure. To estimate the tire pressure. This makes it possible to accurately estimate the tire air pressure regardless of the vehicle environment, rolling wheels, and driving wheels.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a tire pressure estimation device according to the present invention will be described below with reference to the drawings. FIG.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory diagram of an entire tire pressure estimation device according to the present invention. As shown in FIGS. 1 and 2, each tire 1a of the vehicle
Wheel speed sensors 2 to 5 are provided corresponding to .about.1d. Each of the wheel speed sensors 2 to 5 has a rotor 2a.
5a and pickup coils 2b to 5b. The rotors 2a to 5a are connected to the respective tires 1a to 1d.
Tires 1a to 1a of the wheels coaxially with the rotation axis (not shown)
It is attached so as to rotate with 1d, and is made of a disk-shaped magnetic material. Pickup coils 2b-5
b denotes the rotors 2a to 5a, that is, the tire 1
An AC signal having a cycle corresponding to the rotation speeds a to 1d is output.

The AC signals output from the pickup coils 2b to 5b are input to a microcomputer including a CPU, a ROM, a RAM, and the like, and a known electronic control unit (hereinafter referred to as an ECU) 6 having a waveform shaping circuit.
Predetermined signal processing including waveform shaping of the pick-up coils 2b to 5b to output AC signals is performed. This signal processing result is output to the display unit 7 to notify the driver of the state of the air pressure of each of the tires 1a to 1d.

The display unit 7 may independently display the state of the air pressure of each of the tires 1a to 1d, or may be provided with one warning lamp so that the air pressure of any one of the tires becomes lower than the reference air pressure. The driver may be notified of the fact. Reference numeral 8 in FIG. 1 denotes an initialization switch for initializing the detection results and the like up to the previous time stored in the memory for estimating the tire air pressure.

Next, the signal processing executed by the ECU 6 will be described in detail. First, the basic principle of the resonance frequency estimation based on the wheel speed signal performed in the resonance frequency calculation unit 61 of the ECU in FIG. 2 will be described.
Reference numeral 62 denotes a rotation state value calculation unit that calculates a wheel speed of each wheel by receiving a signal from each wheel speed sensor. The determination units 160a and 160b are units that determine the tire pressure by comparing the wheel speeds of the wheels, which are rotation state values, or determine the tire pressure based on the resonance frequency.

A physical model for tire pressure estimation is as follows:
It can be represented as shown in FIG. That is, the road surface disturbance m (k), which is white noise, is applied as an input to the tire suspension system, and as a result, the wheel speed signal y
(K) includes a resonance component depending on the tire pressure. In the tire pressure estimating apparatus according to the embodiment, the tire-suspension system is approximated by a linear prediction model, and parameters of the model are identified using the least squares method. In addition, considering that there is one resonance point depending on the air pressure for each tire, the order of this linear prediction model is “second order”. Further, by setting the order of the model to the second order, the amount of calculation and the data memory (RAM) capacity required for the ECU 6 can be minimized.

Now, let k be the number of times of sampling, m (k) be the road surface disturbance and y be the wheel speed signal as described above.
(K), the second-order discrete-time model is given by the following equation 1.
Can be expressed as

[0014]

Y (k) =-c1y (k-1) -c2y (k-1) + m (K) (Equation 1) The purpose of parameter identification is to obtain a finite number of observation data y (k).
Is used to estimate road parameters c1 and c2. Here, the unknown parameters c1 and c2 are identified using the least squares method.

That is, θ is a parameter vector,
Further, a two-dimensional vector of the following Expressions 2 and 3 is defined by using z as a measurement value vector.

[0016]

(Equation 2)

[0017]

(Equation 3)

Thus, the above equation (1) becomes:

[0019]

(Equation 4)

It becomes possible to write in such a form. In Equation 4, m (k) is a road surface disturbance as described above and can be regarded as white noise.
Estimation of an unknown parameter by the least squares method is an evaluation function.

[0021]

(Equation 5)

Is to find the value of the above equation (2) that minimizes The estimated value of Equation 2 that minimizes Equation 5 can be expressed as Equation 6 of the following equation according to the concatenated least squares method. (For example, see "Introduction to Robust Adaptive Control, Kimio Kanai, Ohmsha, or System Control Information Library 9" Introduction to System Identification, "Toru Katayama, Asakura Shoten, see

[0023]

(Equation 6)

Next, the resonance frequency ω is obtained from c1 and c2 thus identified. The relationship between the parameters c1 and c2 of the second-order discrete-time model, the number of resonance types and the damping coefficient 、, and the relationship with the sampling period as T are expressed by Expressions 7 and 8, respectively.

[0025]

(Equation 7)

[0026]

(Equation 8)

Therefore, the resonance frequency ω and the damping coefficient ζ
Can be calculated as in Equations 9 and 10, respectively.

[0028]

(Equation 9)

[0029]

(Equation 10)

Hereinafter, a first embodiment of the tire pressure estimating apparatus according to the present invention will be described based on a flowchart showing the processing contents of the ECU 6. In the first to third embodiments described below, the ECU 6 executes different flows for the rolling wheels and the driving wheels among the tires 1a to 1d. FIG. 4 is a flowchart showing the processing contents of the drive wheels.

First, the ignition switch of the vehicle is turned on.
If the answer is N, the process proceeds to step 10, where it is determined whether or not the initialization switch 8 shown in FIG. 1 has been turned ON. The function of this initialization switch will be briefly described. Since the tire resonance frequency or the tire spring constant used in the tire pressure estimation in the present invention is affected by the tire size and the tire brand, only when the tire is replaced, the determination value for determining the tire pressure drop is initialized. Need to be updated.

In the following description, this initialization switch is turned on.
This is the case where the vehicle is not in the state, that is, the case where the determination value for determining the decrease in tire air pressure has already been determined and the tire air pressure estimating calculation at the normal time is performed. Note that a description of the processing when the initialization switch is turned on in step 10 will be described later. First, in step 100, a pulse signal obtained by shaping the waveform of the AC signal output from the pickup coil 2b is read, the pulse length is divided by the pulse time, and the wheel speed Vx is calculated independently for each wheel.

As shown in the flow chart, the operation for calculating the resonance frequency of the tire or the spring constant of the tire based on the linear prediction method will be described below.
As described in Japanese Patent Publication No. 21723, it has been found that the resonance vibration of the tire has the following characteristics. That is, in a low vehicle speed to a medium vehicle speed region where the vehicle travels in an urban area, the power spectrum of the output signal of the wheel speed for each frequency is approximately 30 to 5 as shown in FIG.
A resonance peak appears in the range of 0 Hz.

However, as the vehicle speed shifts to the high vehicle speed region, the resonance peak gradually decreases as shown in FIG. 6 (b), so that the resonance peak is not detected. On the other hand, the resonance peak (about 30 to 50 Hz)
As shown in FIG. 6D, the relationship between the decrease of
A new resonance peak appears at 0 to 90 Hz.
As shown in FIG. 6C, the resonance peak at about 60 to 90 Hz is not clear in the low to middle vehicle speed region where the resonance peak at about 30 to 50 Hz appears.

This first resonance peak (about 30 to 50 H
z) is the torsional resonance frequency in the tire rotation direction, and the second resonance peak (about 60 to 90 Hz) is considered to be a secondary component of the torsional resonance frequency. And when the air pressure of the tire decreases, the elastic deformation of the tire side wall occurs, so the spring constant in the torsion direction also changes,
Since both resonance peaks have a dependency on tire pressure, they can be applied as detection targets for tire pressure estimation.

FIG. 7 shows the first resonance peak (about 30 to 30).
50 Hz) and a second resonance peak (about 60-90H).
2 shows the relationship between z) and tire pressure. Therefore, from the relationship between the first resonance peak (about 30 to 50 Hz) and the second resonance peak (about 60 to 90 Hz), the tire air pressure is determined by the resonance frequency included in the wheel speed signal regardless of the vehicle speed. In order to make estimation possible, in step 110, it is determined whether or not the vehicle speed V is equal to or less than a preset vehicle speed Vo.

If it is determined that the vehicle speed V is lower than the preset reference vehicle speed Vo1, that is, if the running speed of the vehicle is in the low to medium vehicle speed range, the routine proceeds to step 120, where the first step is performed. Resonance peak (about 30-50Hz)
In order to further increase the signal strength of, the signals in other frequency bands are cut. For this reason, the preset frequency range (f
11 to f12) (hereinafter referred to as a band-pass filter). As shown in FIG. 7, the reference frequencies f11, f12, etc. are f11 <f12 <f2.
1 <f22.

The wheel speed signal that has passed through the band-pass filter becomes the wheel speed signal y (k) of Equation 1 defined in the above description of the principle. Step 130 as a parameter identification unit is based on the wheel speed signal y (k) extracted in step 120 of the band-pass filter unit, based on Equation 6, based on the parameter c of the discrete time model.
1, a part for identifying c2.

Next, in step 140, the resonance frequency converter outputs the parameter c output in step 130.
The resonance frequency ω is obtained from Equation (1) and c2 according to Equation 9 defined in the principle. In addition, the resonance frequency-tire pressure conversion unit in step 150 is a part that converts the resonance frequency ω obtained in these steps into tire pressure.
As described above, the higher the tire air pressure, the higher the resonance frequency, and conversely, the lower the tire air pressure, the lower the resonance frequency. FIG. 8 shows an example of a relationship map between the tire pressure and the resonance frequency used in step 150. That is, the relationship is stored in advance as a table (map), and the corresponding tire pressure p is directly estimated from the value of the resonance frequency ω obtained above. Then, the value of the tire pressure estimated value p obtained from the value of the resonance frequency ω is
It outputs to the determination part 160 corresponding to each wheel.

The judging section 160 compares the tire pressure p value output from step 150 with a predetermined judgment value as a threshold value for judging a tire air pressure abnormality, and determines a tire air pressure abnormality corresponding to each wheel. Is determined independently for each wheel. Then, if the tire air pressure p-value output from step 150 is lower than the predetermined judgment value, the display unit 170 is driven as an air pressure abnormality. In the display unit 170, when the drive signal is given from the determination unit 160, the lamp is turned on to notify the driver of the tire pressure abnormality. In addition, the embodiment of the lamp detects the tire pressure abnormalities of the four wheels independently from each other.
It is also possible to display a light, or a single light that only indicates that one of the tires is abnormal.

According to the tire pressure estimating apparatus of this embodiment, even in a wide range of vehicle speeds where the vehicle is actually used, it is possible to obtain highly reliable four-wheel punctures such as natural leaks and nail punctures almost simultaneously decreasing. Can be detected. FIG. 9 shows the result of calculating the tire resonance frequency by the tire pressure estimation device according to the present embodiment. According to this, it is possible to read that the estimated resonance frequency of the tire changes almost linearly with respect to the tire pressure.

Next, when it is determined that the vehicle speed V is higher than the preset reference vehicle speed Vo1, that is, when the running speed of the vehicle is in the high vehicle speed region, the routine proceeds to step 220, where the second resonance peak is obtained. (Approximately 60 to 90 Hz), and a frequency range (f21 to f21) set in advance for the purpose of cutting signals in other frequency bands.
The bandpass filter of 22) is used.

The following processing (steps 230 to 260)
Is the same as the above-described processing of the first resonance peak (about 30 to 50 Hz) (steps 130 to 160), and thus the description is omitted. Next, an embodiment of a rolling wheel will be described with reference to FIG. First, before starting the description of the flowchart of FIG. 5, FIG. 10 shows the result of a detailed investigation by the present inventors on the characteristics of the second resonance peak (about 60 Hz to 90 Hz) described in the embodiment of the driving wheel. This will be described with reference to FIG.

FIG. 10 is a graph in which the second resonance peaks are arranged for the driving wheel and the rolling wheel using the tire pressure as a parameter. As is clear from the figure, the change in the second resonance frequency with respect to the change in the tire pressure is large in the driving wheel and can be used for estimating the tire pressure, but the change in the second resonance frequency is extremely large in the rolling wheel. The present inventors have found that it is very difficult to use the tire pressure estimation for the tire pressure estimation in consideration of the variation due to running and the like.

The inventors of the present invention confirmed that the ratio of the change in the resonance frequency to the change in the tire air pressure at the second resonance peak was remarkable in the driving wheels, but was slight in the rolling wheels. Investigation was conducted on rear-wheel drive vehicles, front-wheel drive vehicles, and four-wheel drive vehicles. Since this tendency exists in all drive types, the dependence of the second resonance peak (about 60 to 90 Hz) on the change in tire air pressure is observed. Is considered to be general. In addition, as a cause, considering the ground contact state between the tire and the road surface when the vehicle is running at high speed, the driving force is constantly applied between the road surface and the tire in the drive wheels, and this driving force is applied. As a result, the tread portion of the tire outer peripheral portion comes into stable contact with the road surface, so that it can be estimated that the change in the resonance frequency with respect to the change in the air pressure is remarkable.

On the other hand, as described in Japanese Patent Publication No. 5-55332, the rotational state values (wheel speed, wheel angular speed, number of rotation pulses, etc.) of each tire are integrated for a certain period of time based on the detected wheel speed. Values) are determined, and from the relative relationship between the rotational state values of the respective tires of the four wheels, many tire pressure reducing devices for the purpose of warning puncture in which the pressure of one wheel is mainly reduced have been proposed. The basic principle by which the decrease in air pressure such as puncture can be determined based on this rotation state value is that, for wheels with reduced tire pressure, the tire rubber part in contact with the road surface has a normal tire pressure due to the load of the vehicle. Deflection in comparison. As a result,
As the distance between the center of rotation of the tire (wheel center) and the road surface becomes shorter and the effective rolling radius of the tire decreases, the tire rotation state value (a value obtained by integrating the wheel speed, the wheel angular speed, the number of rotation pulses, and the like for a certain period of time). However, since other tire air pressures increase with respect to normal wheels, a decrease in tire air pressure can be detected.

However, the present inventors have clarified the advantages and disadvantages of judging a decrease in tire air pressure based on a tire rotation state value by investigating the above detection mechanism in detail. In FIG. 5, the above-mentioned rolling wheel has a second resonance peak (about 60
(90 Hz), it is difficult to estimate the tire pressure. By applying this advantage, it is possible to determine a decrease in tire pressure in a wide range of vehicle speeds where the vehicle is actually used, even in rolling wheels. The processing is shown.

The advantages and disadvantages of the tire rotation state value will be described with reference to FIG. The two charts (a) and (b) shown in FIG. 11 are the rolling wheels and the driving wheels of the rear wheel drive vehicle, the rotation state values of each tire, that is, the left and right wheels of the wheel speed (FR: front right, FL: front right) Left, RR: rear wheel right, RL: rear wheel left) plotted with normal pressure (2.0 kg / cm2 in the example) for each right wheel
And the case where the air pressure of the left wheel is reduced to 2.0, 1.6, 1.2 kg / cm 2 is shown.

In the chart showing the rolling wheels (FR / FL), the ratio of the left and right wheel speeds (FR / FL) changes with respect to the decrease in the tire pressure of the front left wheel (FL) and decreases with respect to the vehicle speed. Even in such a state, it is possible to determine a decrease in tire air pressure. On the other hand, in the chart showing the driving wheels (RR / RL), the ratio of the right and left wheel speeds (RR / RL) to the tire pressure drop at the rear left wheel (RL) is smaller at a relatively low vehicle speed even in a high vehicle speed region. Although it clearly changes with the decrease in air pressure, it shows a characteristic that it does not change as the tire pressure of one wheel decreases as the speed becomes higher.

The cause is considered as follows. In a high vehicle speed region where the air pressure resistance and the vehicle speed of the vehicle are balanced, the thrust output of the vehicle is maintained at a high state, and it is considered that a large driving force is acting on the driving wheels.
In other words, it is considered that slip occurs even when the tire has a normal pressure of 2.0 kg / cm 2 on both the left and right wheels.

Here, considering the slip state of the left wheel where the tire pressure has been reduced, the tire bends with the decrease in the air pressure, so that the contact area between the tire and the road surface increases, traction recovers, and the tire pressure becomes normal. Than the state
It is a well-known fact that it is more difficult to slip. On the other hand, considering the influence of the slip state of the tire on the rotation state value (integrated value of the wheel speed) of the tire as described above, the effective rolling radius of the wheel with a reduced tire pressure is reduced due to the decrease in the tire pressure. Therefore, although the wheel speed integrated value is in the direction of increasing, the decrease in slip due to the recovery of traction acts in a direction to cancel the increase in the wheel speed integrated value.

In other words, this means that a fixed relationship is no longer established between the tire air pressure drop and the wheel speed integrated value, which means that it is difficult to determine the tire air pressure drop. . Tokuho 5-5533 mentioned earlier
The tire pressure reduction device using the tire rotation state value (integrated value of the wheel speed, etc.) disclosed in Japanese Patent Publication No. 2 and the like is used to determine the decrease in tire air pressure by mutual comparison of the tire rotation state values of the four wheels. The effect of the wheels is inevitable, and the vehicle speed range in which a decrease in tire pressure can be detected has a fundamental problem that the vehicle speed range is limited in principle.

The present invention shown in the flow chart of FIG. 5 is used for judging a decrease in tire air pressure of a rolling wheel for which it is difficult to estimate the tire air pressure based on the second resonance peak (about 60 to 90 Hz).
The advantage of the determination of a decrease in tire air pressure based on the rotation state value of the tire (e.g., the integrated value of the wheel speed), that is, in the case of a rolling wheel on which no driving force is applied, the above-described tire state quantity value has good characteristics with respect to the decrease in tire air pressure Focusing on this, by introducing the tire left / right ratio of the rolling wheel tire rotation state value as a parameter to the tire pressure drop judgment, if the tire pressure drop judgment is possible even in a wide range of vehicle speed where the vehicle is actually used It is an invention aimed at closing.

Hereinafter, the present invention will be described for each step of the flowchart of FIG. First, when the ignition switch of the vehicle is turned on, the routine proceeds to step 90.
As described in the section of the drive wheels, the following description is based on the case where the initialization switch is not in the ON state, that is, the case where the determination value for determining the decrease in tire air pressure has already been determined.
This is a case of a tire pressure estimation calculation in a normal state.
Note that the description of the processing when the initialization switch is turned on in step 10 will be described later, similarly to the case of the driving wheels.

In step 100, a pulse signal obtained by shaping the waveform of the AC signal output from the pickup coil 2b is read, the pulse length is divided by the pulse time, and the wheel speed Vx is calculated independently for each wheel. Next, step 110
In the case where it is determined that the vehicle speed V obtained from the wheel speed Vx is smaller than the preset vehicle speed Vo2,
If the running speed of the vehicle is in the low to medium vehicle speed range, the process proceeds to step 120. It should be noted that a preset vehicle speed Vo2
May be the same as or different from the vehicle speed Vo1.

Here, Steps 100 to 160 shown in FIG. 5 are the same as the processing contents already described in the embodiment of the driving wheels, so that they will be omitted. Vehicle speed V
Is equal to or higher than the preset vehicle speed Vo2, that is, the first vehicle speed
At the resonance peak (approximately 30 to 40 Hz), the processing for the case where the tire pressure estimation is difficult (steps 320 to 3)
30), a description will be given of a process to which the advantage of the determination of a decrease in tire air pressure based on the rotation state value of each tire is applied. The processing content of step 320 will be described by taking a wheel speed integrated value as an example of a tire rotation state value. In this step, for each of the right wheel and the left wheel of the rolling wheel, the detected wheel speed Vx is used, and D, which is the wheel speed deviation of the rolling wheel, is obtained by the following equation (11). The calculation of the wheel speed deviation D is performed every calculation cycle of the wheel speed, for example, every 5 ms.

[0057]

D = Vxfr / Vxfl (Equation 11) Vxfr: Wheel speed on the right of the rolling wheel Vxfl: Wheel speed on the left of the rolling wheel Step 330 calculates the wheel speed deviation D obtained as described above as in the following equation. , Stored in the memory of the ECU 6
This is the averaging process.

[0058]

(Equation 12) The purpose of this process is for the rolling wheels on which no driving force acts,
Although the influence of the driving situation is small, it is to eliminate the influence of turning, climbing downhill, and the like. In step 340, the average wheel speed deviation Do is compared with a predetermined reference value to determine the average wheel speed deviation Do.
Is a process of determining that a decrease in tire air pressure has occurred when the reference value has exceeded the reference value.

Step 170 is a process for lighting a display device such as a lamp based on the drive signal from step 340, as described in the embodiment of the drive wheel. As the display method here, since the decrease in air pressure is determined by comparing the left and right of the rolling wheels, it is possible to determine whether the wheel with the decreased tire pressure is either left or right. Display is also possible, and display of only one light is also possible.

Hereinafter, the case of the initial state or the switch ON state in FIGS. 4 and 5 will be described. The above-described processing content is a case where the initialization switch is not ON in both the driving wheel and the rolling wheel embodiments, but the processing content in the case where the initialization switch is ON is described below. A description will be given based on FIG. First, the initialization of the drive wheels will be described with reference to FIG. In step 100, similarly to the above embodiment, the AC signal output from the pickup coil 2b is waveform-shaped, a pulse signal which is a processed waveform thereof is read, the pulse length is divided by the pulse time, and each wheel is independently controlled. Calculates the wheel speed Vx.

As described above, the purpose of setting the initialization switch is to determine the relationship between the tire-specific resonance frequency and the tire pressure required for tire pressure estimation when the tire is replaced. Therefore, when the initialization switch is turned on, it is premised that the tire air pressure is known. Therefore, when the tire is replaced, it is assumed that the user of the vehicle sets the tire air pressure to the standard air pressure. Therefore, in step 410, the tire resonance frequency (first resonance peak) when the tire is at standard air pressure
Is calculated and stored in the memory of the ECU 6 as ωk1.

Since the first resonance peak is obtained in step 410, the tire resonance frequency ωK2 (second resonance peak) when the tire is at the standard air pressure is obtained in step 420. In this case, the first resonance peak ωK2 is obtained. Resonance peak and second
Since the physical relationship with the resonance peak is known, it is determined from this relationship. In step 430, the resonance frequency (ωL1) corresponding to the warning pressure is obtained from the resonance frequency (first resonance peak) of the standard air pressure obtained in step 410 by the following equation, and the determination of a decrease in tire air when the vehicle speed is equal to or lower than Vo is made. Is performed, the memory in the ECU 6 is rewritten in order to obtain a new air pressure drop determination value.

[0063]

ΩL1 = ωK1−Δω1 (Equation 13) (where Δω1 is a constant) Similarly, in step 440, the tire air pressure drop determination value ωL2 when the vehicle speed is equal to or higher than Vo is determined by the resonance frequency ωK2 ( From the second resonance peak), a new air pressure drop determination value is obtained by the following equation.

[0064]

ΩL2 = ωK2−Δω2 (constant) (Equation 14) The above is the processing content of the drive wheels when the initialization switch is ON. Next, the initialization of the rolling wheels will be described with reference to FIG. In step 100, the wheel speed Vx is calculated in the same manner as described above.

In step 510, it is assumed that the tire pressure is set to the standard pressure when the tire is replaced.
The wheel speed deviation Dk at the standard pressure is obtained by the following equation.

[0066]

Dk = Vxfr / Vxfl (Equation 15) Vxfr: Wheel speed on the right side of the rolling wheel Vxfl: Wheel speed on the left side of the rolling wheel Then, in step 520, the wheel speed deviation Dk obtained by the equation 15 is expressed by (Equation 22). Add n as shown in
The average wheel speed deviation Dko is obtained, and the obtained value is used as the tire air pressure drop determination value DL, and the memory in the ECU 6 is updated. In step 530, the air pressure drop determination value DL is updated.

The second embodiment will be described with reference to FIGS. FIG. 14 shows a first tire pressure estimating means for obtaining a tire resonance frequency from a vibration component of a wheel speed signal and estimating a tire pressure of a driving wheel based on the resonance frequency.
As a selection means for selecting the vibration frequency range of the resonance frequency, the frequency range is divided into two ranges, the signal strength in each frequency range is calculated, and based on this signal strength, the frequency range for which the resonance frequency is to be extracted is determined. This is an embodiment to be selected.

This will be described below with reference to the flowchart of FIG. Note that the flow of FIG. 14 is performed for the drive wheels. Steps up to step 100 have already been described in the embodiments up to this point, and a description thereof will be omitted. Step 10
Reference numerals 1 and 102 denote the first resonance peak (about 30 to 50).
Hz) and the second resonance peak (approximately 60 to 90 Hz), in order to further increase the signal strength, in order to cut signals in other frequency bands, a frequency range (f11 to f12) as shown in FIG. , (F21 to f22) are set.

In step 103, the signal intensities Ga of the first resonance peak (about 30 to 50 Hz) and the second resonance peak (about 60 to 90 Hz) extracted in step 101,
This is a process of performing Gb operation and comparing the magnitudes. A specific method of calculating the signal strength will be described below with reference to FIG.
FIG. 18 is a waveform after the calculation of the wheel speed Vx after passing through the C band-pass filter. The horizontal axis represents the time, and the vertical axis represents the gain indicating the magnitude of the vibration component of the first resonance peak. Here, assuming that the value of Vx for each calculation cycle (for example, 5 ms) of the wheel speed Vx is Vx (i), the signal strength Ga of the first resonance peak can be expressed by the following equation.

[0070]

(Equation 16) That is, it can be expressed as a value obtained by adding n square values of Vx (i) calculated for each wheel speed calculation cycle.

The signal strength Gb is similarly calculated for the second resonance point peak. The calculated Ga and Gb are compared, and if the signal strength Ga is large, the resonance frequency range used for tire pressure estimation is set to the first resonance peak (about 30 to 50 Hz), and the routine proceeds to step 130. In step 130 and subsequent steps, the processing for the drive wheels already described with reference to FIG. 4 is performed.

When the signal strength Gb is large, the resonance frequency range used for the estimation of the tire pressure becomes the second resonance peak, and the processing of step 230 and subsequent steps described above is performed. FIG. 15 shows a tire tire pressure obtained from a vibration component of a wheel speed signal of a rolling wheel, and a tire pressure based on the rotational state value of the tire in a second tire pressure estimating means for estimating a tire pressure of a driving wheel based on the resonance frequency. As determination means for determining whether or not to use the determination means, the frequency obtained from the vibration component of the wheel speed signal is divided into two, and the signal intensities Ga and Gb at the respective vibration frequencies are calculated to obtain the vibration at the first resonance peak. This is an example of a selection unit that determines whether to calculate the resonance frequency from the frequency component and estimate the tire pressure, or determine the rotational state value of the tire and determine whether to determine the decrease in the tire pressure of the rolling wheel.

The details of the processing in each step are exactly the same as those in the above-described example, and therefore will not be described. A third embodiment will be described with reference to FIGS. FIG. 16 shows the tire resonance frequency obtained from the vibration component of the wheel speed signal, and the first tire pressure estimating means for estimating the tire pressure of the driving wheel based on the resonance frequency. In this embodiment, a vibration input intensity is calculated from components, and a frequency range in which a resonance frequency is to be extracted is selected based on the vibration input intensity. Note that the flow in FIG. 16 is applied to the drive wheels.

The following is a description based on the flowchart of FIG. Steps up to step 100 have already been described in the embodiments up to this point, and a description thereof will be omitted. Step 104 is a band-pass filter set to cut signals in other frequency bands in order to further increase the signal strength of vibration input from the road surface caused by the tire vibration phenomenon described above.

In step 105, the vibration input intensity Gc is calculated from the vibration frequency component from the road surface extracted in step 104.
Is calculated, and the magnitude is compared with a preset reference value Gco. FIG. 1 shows a specific method of calculating the signal strength.
This will be described below using No. 9. It is already disclosed in Japanese Patent Application Laid-Open No. 6-27061 that vibration input from the road surface can be extracted from wheel speed fluctuations by using an appropriate band-pass filter.
No. 8, and FIG. 19 illustrates a specific calculation method thereof.

FIG. 19 shows a waveform after passing through the E-band pass filter as a result of the calculation of the wheel speed Vx, and the horizontal axis represents the time and the vertical axis represents the gain indicating the magnitude of the vibration component from the road surface. Here, the calculation cycle of the wheel speed Vx (for example, 5 ms)
When the value of Vx for each is Vx (i), the vibration input intensity Gc
Can be expressed by the following equation.

[0077]

[Equation 17] That is, it can be expressed as a value obtained by adding m square values of Vx (i) calculated for each wheel speed calculation cycle.

FIG. 20 shows another embodiment of the method of calculating the vibration input strength from the road surface. Then, the calculated Gc is compared with a preset reference value Gco. If the vibration input strength Gc is large, the resonance frequency range used for tire pressure estimation is changed to the first resonance peak (about 30).
５０50 Hz) and proceeds to step 130. Step 1
For 30 and below, the processing for the drive wheels already described in FIG. 4 is performed.

If the vibration input strength Gc is smaller than the reference value Gco, the resonance frequency range used for tire pressure estimation becomes the second resonance peak, and the processing of step 230 and subsequent steps described above is performed. FIG. 17 shows the tire resonance frequency obtained from the vibration component of the wheel speed signal of the rolling wheel, and the tire pressure obtained by the second tire pressure estimation means for estimating the tire pressure of the driving wheel based on the resonance frequency. As a determination unit for determining whether to use the determination unit, a vibration input intensity Gc is calculated from a vibration frequency component from a road surface caused by a tire vibration phenomenon, and based on the vibration input intensity Gc, an abnormality in the air pressure of the rolling wheel is determined. This is an example.

The present invention is not limited to the above-described embodiment, but can be variously modified as follows. For example, in the above-described embodiments, the inside of the ECU 6 is configured so that the driving wheel and the rolling wheel advance to different flows in advance (that is, the independent calculating unit capable of performing the parallel arithmetic processing on the driving wheel and the rolling wheel and the determination). Example where a unit is provided)
However, regardless of this, right driving wheel → left driving wheel → right rolling wheel →
Calculation processing is performed in the ECU 6 like the left rolling wheel, and after determining whether or not the initialization switch is ON after the ignition is turned on, it is determined whether the wheel to be controlled is a driving wheel or a rolling wheel,
For the driving wheels, for example, the flow of FIG. 4 may be performed in the first embodiment, and for the rolling wheels, the flow may proceed to the flow of FIG. The same applies to the second and third embodiments.

In the above-described embodiment, the method of estimating the air pressure of the rolling wheels or the method of judging the abnormal air pressure is switched based on the vehicle speed, the signal strength or the signal input strength. That is, based on the vehicle speed, the signal strength or the signal input strength, it is switched between the determination using the resonance frequency or the determination based on the deviation of the rotation state value such as the wheel speed difference. Regardless, all the rolling wheels may make the determination based on the deviation of the rotation state value, and the driving wheels may make the determination based on the resonance frequency. For example, in FIG.
0 to step 160 are omitted, and if the wheel is a rolling wheel, step 1
From 00, steps 320, 330, 340, and 170 may be performed in this order. This is the same for the second and third embodiments.

In the above-described embodiment, the change in the resonance frequency has been used for the estimation of the air pressure of the drive wheels or the determination of the abnormality of the air pressure. However, instead of this, the change of the spring constant is estimated to estimate the air pressure or determine the abnormality of the air pressure. May be performed. The change in the spring constant can be detected, for example, by detecting a change in the resonance frequency.

As the signal analysis processing of the wheel speed signal performed at the time of detecting the resonance frequency in the above-described embodiment, any analysis method such as FFT operation (fast Fourier transform) and linear prediction method can be applied.

[Brief description of the drawings]

FIG. 1 is a model diagram of a main configuration of the present invention.

FIG. 2 is a block diagram of a main configuration of the present invention.

FIG. 3 is a diagram showing a physical model in tire pressure estimation.

FIG. 4 is a flowchart showing a processing flow for driving wheels in the first embodiment.

FIG. 5 is a flowchart showing a processing flow for rolling wheels in the first embodiment.

FIG. 6 is a characteristic diagram illustrating a power spectrum of a wheel speed signal in relation to a vehicle speed.

FIG. 7 is a characteristic diagram showing a relationship between a resonance frequency and an air pressure in relation to a vehicle body speed.

FIG. 8 is a map showing a relationship between a resonance frequency and an air pressure.

FIG. 9 is a waveform diagram showing a waveform of a relationship between a resonance frequency and a tire pressure when a resonance frequency is calculated by performing a frequency analysis on a wheel speed signal.

FIGS. 10A and 10B are characteristic diagrams showing a change depending on air pressure of a second resonance peak in a driving wheel and a rolling wheel, wherein FIG. 10A is a characteristic diagram of a driving wheel, and FIG. 10B is a characteristic diagram of a rolling wheel.

FIG. 11 shows a determination characteristic of tire air pressure based on a rotation state value deviation (rotation state value ratio) between a rolling wheel and a driving wheel,
(A) is a characteristic diagram showing a change in the right and left wheel speed ratios of the driving wheels with respect to the vehicle speed, and (b) of FIG.

FIG. 12 is a flowchart illustrating a flow when an initialization switch is turned on in a driving wheel.

FIG. 13 is a flowchart showing a flow when an initialization switch in a rolling wheel is ON.

FIG. 14 is a flowchart for driving wheels in the second embodiment.

FIG. 15 is a flowchart for a rolling wheel in the second embodiment.

FIG. 16 is a flowchart for driving wheels in the third embodiment.

FIG. 17 is a flowchart for a rolling wheel in the third embodiment.

FIG. 18 is a waveform after a C-band pass filter is obtained as a result of calculating the wheel speed Vx.

FIG. 19 is a reference characteristic diagram when showing a specific calculation method of signal strength.

FIG. 20 is a characteristic diagram showing another embodiment of a method for calculating the vibration input intensity from the road surface.

[Explanation of symbols]

 1a to 1d Wheels 2 to 4 Wheel speed sensor 6 ECU 61 Resonance frequency calculation unit 62 Rotation state value calculation unit 160a, 160b Judgment unit

Claims (8)

[Claims] 1. A wheel speed detecting means for sequentially calculating a wheel speed of each wheel during running of a vehicle, and a tire resonance frequency or a tire based on a vibration frequency component included in a wheel speed signal which is a detection result of the wheel speed detecting means. Extraction means for extracting the spring constant of the first wheel, first tire pressure estimation means for estimating the tire pressure of the drive wheel based on the resonance frequency or the tire spring constant extracted by the extraction means, and the wheel speed detection means Rotation state value calculation means for calculating a rotation state value of the tire based on the wheel speed obtained, and estimating the tire pressure of the rolling wheel based on the deviation of the rotation state value calculated by the rotation state value calculation means. A tire pressure estimation device, comprising: a tire pressure estimation unit. 2. The first tire pressure estimation means selects a vibration frequency range of a vibration frequency component included in the wheel speed signal from which the resonance frequency or the spring constant is extracted by the extraction means. 2. The tire pressure of the drive wheel is estimated by extracting the resonance frequency or the spring constant in a frequency range selected by the selection means.
Tire pressure estimation device described in 3. The tire pressure according to claim 2, wherein the selection unit includes a traveling speed detecting unit that detects a traveling speed of the vehicle, and selects the vibration frequency range based on the traveling speed. Estimation device. 4. The selecting means comprises: a dividing means for dividing the frequency range into a plurality of frequency ranges; and a signal strength calculating means for calculating a signal strength in each frequency range. 4. The frequency range in which the resonance frequency or the spring constant is to be extracted is selected from the plurality of frequency ranges based on the signal strength obtained.
The tire pressure estimation device according to any one of claims 1 to 4. 5. The apparatus according to claim 2, wherein said selecting means calculates a vibration input strength from the road surface to the tire, and selects the frequency range based on a vibration input strength obtained as a result of the calculation. The tire pressure estimating device according to claim 4. 6. The tire pressure estimating means includes condition determining means for determining whether or not a permission condition for estimating a tire pressure is satisfied based on a rotation state value of the tire. Claim 1 to Claim 5
The tire pressure estimation device according to any one of the above. 7. The tire pressure estimating device according to claim 6, wherein the condition determining unit includes a traveling speed detecting unit that detects a traveling speed of the vehicle, and determines the traveling speed as a permission condition. 8. A wheel speed detecting means for sequentially calculating a wheel speed of each wheel during running of the vehicle, and a tire resonance frequency or a tire resonance frequency based on a vibration frequency component included in a wheel speed signal which is a detection result of the wheel speed detecting means. Extracting means for extracting a spring constant; first tire pressure estimating means for estimating tire pressures of driving wheels and rolling wheels based on the resonance frequency or tire spring constant extracted by the extracting means; and the wheel speed detecting means Rotation state value calculation means for calculating the rotation state value of the tire based on the detected wheel speed; running speed detection means for detecting the running speed of the vehicle; when the running speed of the vehicle becomes equal to or higher than a reference value, The tires of the rolling wheels are estimated such that the tire pressure of the rolling wheels is estimated based on the deviation of the rotating state values calculated by the rotating state value calculating means. Only the tire air pressure estimating apparatus, characterized in that it comprises a second tire pressure estimation means for changing the method of determining tire pressure, a.