JPH06328920A - Tire pneumatic pressure detector - Google Patents

Abstract

PURPOSE:To detect indirectly a state of pneumatic pressure of a tire and improve accuracy by detecting the state of the tire pneumatic pressure based on resonance frequency of a tire single body extracted from signals including resonance frequency components of the tire. CONSTITUTION:Alternating current signals from pick-up coils 3a-3d of speed sensors corresponding to respective tires 1a-1d are input in ECU4 composed of a waveform arrangement circuit, ROM, RAM, etc., prescribed signal processing including waveform arrangement is performed, and resonance frequency of a tire single body is extracted. The resonance frequency changes according to spring constant of a tire and substantially the tire spring constant changes depending solely on tire pneumatic pressure so that the results of the signal processing based on the resonance frequency are input on a display part 5 and pneumatic states are informed to a driver. Therefore detection accuracy can be improved while indirectly detecting the pneumatic pressure of the tire.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tire air pressure detecting device for detecting a tire air pressure condition of a vehicle.

[0002]

2. Description of the Related Art Conventionally, as a device for detecting the air pressure of a tire, there has been proposed a device in which a pressure responsive member which responds to the tire air pressure is provided inside the tire to directly detect the air pressure of the tire. However, in a device that directly detects the tire air pressure, there is a problem that the structure becomes complicated and the price becomes expensive because it is necessary to provide a pressure responsive member inside the tire.

Therefore, the fact that the tire radius changes (becomes shorter) when the tire air pressure decreases,
It has been proposed to indirectly detect the tire air pressure of a vehicle based on a detection signal of a wheel speed sensor that detects the wheel speed of each wheel.

[0004]

However, the tire radius to be detected is subject to individual differences due to wear and the like, and is easily influenced by running conditions such as turning, braking and starting. Further, radial tires, which have been widely used in recent years, have a small amount of deformation of a tire radius due to a change in tire air pressure (for example, when the tire air pressure decreases by 1 kg / cm ² ,
The amount of deformation of the tire radius is about 1 mm. ). For this reason, the method of indirectly detecting the change in the tire air pressure from the deformation amount of the tire radius has a problem that the detection accuracy cannot be sufficiently secured.

The present invention has been made in view of the above points, and an object of the present invention is to provide a tire air pressure detecting device capable of indirectly detecting the tire air pressure and improving the detection accuracy. Is.

[0006]

In order to achieve the above object, the invention according to claim 1 is an output means for outputting a signal including a vibration frequency component of a tire when the vehicle is running, and a vibration frequency of the tire. A tire air pressure detection device is provided, which includes an extraction unit that extracts a resonance frequency of a tire alone from a signal including a component, and a detection unit that detects a state of air pressure of the tire based on the resonance frequency of the tire unit. .

According to a second aspect of the present invention, output means for outputting a signal including a vibration frequency component of the tire when the vehicle is running, and estimation for estimating a spring constant of the tire from the signal including the vibration frequency component of the tire are provided. The gist is a tire air pressure detection device including a means and a detection means for detecting the state of the air pressure of the tire based on the spring constant.

[0008]

With the above structure, the tire pressure detecting device according to claim 1 extracts the resonance frequency of the tire alone from the signal including the vibration frequency component of the tire, and based on the extracted resonance frequency of the tire alone, the tire The air pressure condition of is detected. Here, when the air pressure of the tire changes, the spring constant of the tire also changes accordingly. Since the resonance frequency of the tire alone in the vibration frequency component of the tire changes due to the change of the spring constant of the tire, it is possible to detect the tire air pressure state based on the extracted resonance frequency.

Further, the tire air pressure detection device according to the second aspect estimates the tire spring constant from a signal including the vibration frequency component of the tire, and based on the estimated spring constant of the tire, the tire air pressure state is determined. Detected. here,
When the tire air pressure changes, the tire spring constant also changes, so that the tire air pressure state can be detected based on the estimated spring constant.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a configuration diagram showing the overall configuration of the first embodiment. As shown in FIG. 1, each tire 1 of the vehicle
Wheel speed sensors are provided corresponding to a to 1d.
Each wheel speed sensor includes gears 2a to 2d and pickup coils 3a to 3d. Gear 2a ~
2d is coaxially attached to the rotating shaft (not shown) of each of the tires 1a to 1d, and is made of a disk-shaped magnetic body.
The pickup coils 3a to 3d have the gears 2a to 3d.
The gear 2 is attached at a predetermined distance in the vicinity of 2d.
a to 2d, that is, an AC signal having a cycle corresponding to the rotation speeds of the tires 1a to 1d is output. The AC signal output from the pickup coils 3a to 3d is a known electronic control unit (E) including a waveform shaping circuit, ROM, RAM and the like.
It is input to the CU) 4 and predetermined signal processing including waveform shaping is performed. The result of this signal processing is input to the display unit 5,
The display unit 5 notifies the driver of the state of air pressure of each tire 1a to 1d. This display unit 5 is for each tire 1a-1
The air pressure status of d may be displayed independently, or one warning lamp may be provided to turn on the light when the air pressure of any one of the tires becomes lower than the reference air pressure to warn it. Is also good.

First, the principle of tire pressure detection in this embodiment will be described. When a vehicle runs on a paved asphalt road surface, for example, the tire is vibrated by the force due to the excitation force due to the minute irregularities on the road surface. The vibration characteristics at this time will be described. Figure 2
As shown in (a), when a load corresponding to an actual usage state is applied to the tire unit and the tire passes through a protrusion installed on the rotating drum, six forces acting on the tire rotation shaft (see FIG. b), the force (F) in the x, y, and z directions and the moment (M) about the x, y, and z axes in FIG. As shown in 3 and 4. However, the moment of inertia in this case is set to the actual vehicle state.

As shown in FIGS. 3 and 4, when the tire receives an input from the road surface, the tire axle has a torsion moment (My) about the axle (y axis) and a longitudinal force (F) of the axle.
x) acts, and both have a resonance point near about 40 Hz. Here, considering the fact that the tire outer circumference has a high rigidity because it is a steel belt and the load is applied in the ground contact state, the resonance point of the torsion moment (My) shown in FIG.
It can be considered as a torsional resonance phenomenon around the axle (y-axis) of the tire sidewall portion. As a result, a longitudinal force is generated in the tire traveling direction (x-axis direction) centering on the road surface and the contact portion of the tire, and as a reaction force of this force, a longitudinal force (Fx) appears on the axle as shown in FIG. It will be.

On the other hand, when the tire air pressure changes, the spring constant of the sidewall portion of the tire also changes, so the resonance points in FIGS. 3 and 4 also change. For example, as shown in FIG. 5, when the tire air pressure changes, the spring constant of the sidewall portion of the tire changes, so the torsional resonance point also decreases. Therefore, if the vibration frequency of the tire is extracted, it is possible to detect the tire air pressure state based on the resonance frequency.

Therefore, in this embodiment, the torsion (rotational direction) resonance frequency of the tire is extracted from the detection signal of the wheel speed sensor (hereinafter referred to as "torsion resonance frequency"). As shown in FIG. 6, as a result of detailed study by the inventors, it was found that the torsional resonance frequencies of FIGS. 3 and 4 can be detected by frequency analysis of the detection signal of the wheel speed sensor. Further, as shown in FIG. 6, it was revealed that the torsional resonance frequency also decreased when the tire air pressure decreased, as in FIG.

As a result, according to this embodiment, the anti-skid control device (ABS), which has been increasing in the number of vehicles equipped with it in recent years,
In a vehicle or the like equipped with the above, since each wheel is already equipped with a wheel speed sensor, the tire air pressure can be detected without adding any new sensor. Further, in the practical range of the vehicle, since the amount of change in the resonance frequency is almost based on the change in the tire spring constant caused by the change in the tire pressure, it is not affected by other factors such as wear of the tire. Stable air pressure detection is possible.

FIG. 7 shows a flowchart showing the contents of processing executed by the ECU 4. It should be noted that the ECU 4 uses each wheel 1
Since the same processing is performed for a to 1d, the flowchart in FIG. 7 shows only the processing flow for one wheel. Further, in the following description, the subscripts of the respective reference numerals are omitted. Further, in the flowchart shown in FIG. 7, it is detected that the tire air pressure has dropped below the reference value,
An example of issuing a warning to the driver is shown.

In FIG. 7, in step 100, after the waveform of the AC signal (FIG. 8) output from the pickup coil 3 is shaped into a pulse signal, the pulse interval is divided by the time interval between the wheel speeds v. Is calculated. As shown in FIG. 9, the wheel speed v usually includes many high frequency components including the torsional resonance frequency. In step 110, the fluctuation width Δv of the calculated wheel speed v
Is greater than the reference value v ₀ . At this time, if it is determined that the variation width Δv of the wheel speed v exceeds the reference value v ₀ , the process proceeds to step 120. In step 120, it is determined whether or not the time period ΔT in which the fluctuation width Δv of the wheel speed v exceeds the reference value v ₀ exceeds the predetermined time t ₀ .
The processing in steps 110 and 120 is performed to determine whether or not the road surface on which the vehicle is traveling is a road surface on which the tire pressure can be detected by the detection method of this embodiment. That is, in the present embodiment, the tire air pressure is detected based on the change in the resonance frequency included in the tire vibration frequency component. Therefore, if the wheel speed v fluctuates to some extent and is not continued, sufficient data for calculating the resonance frequency cannot be obtained. In the determination in step 120, the predetermined time Δt is set when the fluctuation width Δv of the wheel speed v exceeds the reference value v _0, and the fluctuation width Δv of the wheel speed v is again set within the predetermined time Δt. _When it exceeds ₀ , the measurement of the time ΔT is continued.

If both Step 110 and Step 120 are affirmatively determined, the operation proceeds to Step 130, and if either of them is negatively determined, the Step 100 is performed.
Return to. In step 130, frequency analysis (for example, fast Fourier transform (FFT)) is performed on the calculated wheel speed.
The calculation is performed and the number of times N of the calculation is counted.
FIG. 10 shows an example of the result of this FFT calculation.

As shown in FIG. 10, when the FFT calculation is performed on the wheel speed actually obtained by the vehicle traveling on a general road, it is usual that the frequency characteristic becomes extremely random. This is because the shape (size and height) of the minute unevenness existing on the road surface is completely irregular, and therefore the frequency characteristic varies for each wheel speed data. Therefore, in the present embodiment, in order to reduce the variation of the frequency characteristic as much as possible, the average value of the FFT calculation results of a plurality of times is calculated. Therefore, in step 140, step 13
It is determined whether the number of FFT operations N at ₀ has reached a predetermined number n ₀ . Then, when the number of calculations N has not reached the predetermined number n ₀ , the processing from step 100 to step 130 is repeated. On the other hand, when the number of calculations N has reached the predetermined number n ₀ , the routine proceeds to step 150, where averaging processing is performed. This averaging process is
As shown in FIG. 11, the average value of each FFT calculation result is obtained, and the average value of the gain of each frequency component is calculated. By such an averaging process, FF depending on the road surface
It is possible to reduce the fluctuation of the T calculation result.

However, there is a problem that the gain of the torsional resonance frequency does not always reach the maximum peak value as compared with the gains of the frequencies in the vicinity thereof due to noise or the like only by the above averaging processing. Therefore, in the present embodiment, following the averaging process described above, the following moving average process is performed in step 160. This moving average process is performed by obtaining the gain Y _n of the _nth frequency by the following arithmetic expression.

[0021]

## EQU1 ## Y _n = (y _{n + 1} + Y _n-1 ) / 2 That is, in the moving average processing, the gain Y of the nth frequency is obtained.
_n is the (n + 1) th gain y in the previous calculation result
_{n + 1} and the gain Y of the n-1th frequency already calculated
_It is an average value with _n-1 . As a result, the FFT calculation result shows a waveform that changes smoothly. FIG. 12 shows the calculation result obtained by this moving average processing.

The waveform processing here is not limited to the moving average processing described above, but low-pass filter processing may be performed on the FFT calculation result after the averaging processing, or the FFT calculation of step 130 is performed. Before this, the wheel speed v may be differentially calculated, and the FFT calculation may be performed on the differential calculation result. Next, in step 170, the torsional resonance frequency f is calculated based on the FFT operation result smoothed by the moving average process. Then, in step 180, a decrease deviation (f ₀ − from the initial frequency f ₀ set in advance corresponding to normal tire air pressure).
f) is obtained, and the decrease deviation (f ₀ −f) and the predetermined deviation Δf
Compare with. The predetermined deviation Δf is set corresponding to the allowable lower limit value of tire pressure (for example, 1.4 kg / m ² ) with reference to the initial frequency f ₀ corresponding to normal tire pressure. Therefore, if it is determined in step 180 that the decrease deviation (f ₀ −f) exceeds the predetermined deviation Δf, it is considered that the tire air pressure has decreased below the allowable lower limit value, the process proceeds to step 190, and the display unit 5 operates Warning is displayed to persons.

Next, a second embodiment will be described. In the first embodiment, the tire air pressure is detected based on the torsion resonance frequency fk shown in FIG. 12, but there are other resonance frequencies of the tire alone that can be detected by frequency analysis of the wheel speed signal. There are frequencies f1 in FIG.
This is the primary (eccentric) resonance frequency of the tire unit (about 7
0 to 90 HZ), and that the resonance frequency changes depending on the tire air pressure is exactly the same as the resonance frequency in the rotation direction described above. Therefore, from the relationship between the primary resonance frequency f1 and the tire air pressure, it is possible to detect the tire air pressure from the wheel speed signal.

Further, although not shown in the figure, there is a resonance frequency which is an integral multiple of the tire alone at 100 Hz or higher.
Wheel speed calculation and frequency analysis calculation (for example, FFT)
The tire pressure can be estimated by making the calculation) more accurate. Next, a third embodiment will be described. When a vehicle runs on a paved asphalt road surface, for example, the tire is vibrated by the force due to the excitation force due to the minute irregularities on the road surface. The vibration at this time is, as described above, based on the result of the test for passing over the protrusion of the rotating drum,
It has already been explained that this is a torsional resonance phenomenon in the tire axle rotation direction. The detection principle of the present embodiment is characterized in that the spring constant of the tire at this torsion resonance point is estimated and calculated to detect the tire air pressure.

The outline of the method for estimating and calculating the tire spring constant will be described below. The tire model is shown in FIG.
In FIG. 13, the equation of motion of tire / torsional vibration is
It is expressed by the following formula.

[0026]

[Equation 2]

[0027]

[Equation 3] Here, ω1 is the wheel speed (angular speed) detected and calculated by the pickup coils 3a to 3d in FIG. 1, and θ1 is the angle. J1 is the moment of inertia of the unsprung rotating weight part (wheel, axle shaft, etc.). k is the torsion spring constant of the tire, and θ2 is the twist angle of the steel belt portion around the tire and the tread portion.

As already described with reference to FIGS. 2 to 4, the torsional vibration mode has a torsional moment (M
Since this is a mode in which both y) and axle longitudinal force (Fx) are related, it is considered that torsional displacement of the tire outer circumference (steel belt or tread portion) hardly occurs. The reason is that if a torsional displacement occurs on the outer circumference of the tire, the longitudinal force (Fx) of the axle, which is a reaction force of the torsional moment (My), does not occur.

For these reasons, θ 2 in the equation 2 can be approximated to θ 2 ≈0. Therefore, the torsion spring constant k of the tire can be calculated by the following equation.

[0030]

[Equation 4] Here, ω1 can be detected by the pickup coil, and J1 is a value determined by the specifications of the vehicle. Therefore, the torsion spring constant k is calculated by the equation 4.

Next, a method of detecting ω1 will be described with reference to the flowchart of FIG. Steps 220-2
Description up to 20 is omitted because it is the same as in the first embodiment. In step 230, a narrow band filter (B.
P. F. ) Processing is applied to the wheel speed signal calculated in step 200. In steps 240 and 250, the above B. P. F. The differential value and the integral value of the wheel speed (angular speed ω1) extracted in step (4) are calculated, and in step 260, the calculated values are substituted into equation (4) to calculate the torsion spring constant k. Then, in step 270, when the torsion spring constant k fluctuates in the time axis region, an average value K within a predetermined time is obtained.

Then, in step 280, the deviation between the calculated average value K of the torsion spring constants and the reference spring constant K0 (the spring constant corresponding to an appropriate tire air pressure) becomes larger than a preset value ΔK. If so, the routine proceeds to step 290, where an air pressure drop warning is given. As described above, the tire air pressure can be detected by estimating the torsion spring constant k as in the first and second embodiments.

In this embodiment, it is not always necessary to obtain the average value K as in step 270, but instead of this, a representative value of the torsion spring constant k within a predetermined time (for example, an integrated area may be used). May be used. Also,
As another method for obtaining the torsion spring constant, an unsprung up-and-down resonance frequency, which is a method for estimating tire air pressure, which has been previously filed by the applicant of the present application in Japanese Patent Application No. 4-294622, It may be indirectly obtained from the directional resonance frequency or the resonance frequency of the tire alone of the first embodiment. This is because the resonance frequency f is

[0034]

[Expression 5] f∝√ (k / m), and m is a constant that is determined when the vehicle specifications are determined, and can be obtained from the above relationship. Further, as shown in FIG. 15, the relationship between the average value K of the torsion spring constants and the relationship between the tire pressures is stored as a map, the average value K of the torsion spring constants is calculated, and then the tire pressure is directly calculated using the map. It may be estimated. Similarly, as shown in FIG. 16, the relationship between the resonance frequency of the tire alone and the tire pressure is stored as a map, the resonance frequency of the tire alone is calculated, and then the tire pressure is estimated directly using the map. Good. In the method using the map of FIG. 15 or 16, the display form of the display unit 5 may be changed and the tire pressure estimated using the map may be directly displayed for each wheel.

[0035]

As described above, the tire pressure detecting device according to the first aspect of the invention extracts the resonance frequency of the tire alone from the signal including the vibration frequency component of the tire, and based on the extracted resonance frequency of the tire alone. Then, the tire air pressure state is detected. Here, the resonance frequency changes according to the spring constant of the tire, and the spring constant of the tire changes substantially only depending on the air pressure of the tire. Therefore, it is possible to improve the detection accuracy while indirectly detecting the tire air pressure.

Further, the tire pressure detecting device according to the second aspect of the invention extracts the spring constant of the tire from the signal containing the vibration frequency component of the tire and detects the state of the tire pressure based on the extracted spring constant. . Since the tire spring constant changes substantially only depending on the tire pressure,
It is possible to improve the detection accuracy while indirectly detecting the tire air pressure.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a configuration of a first exemplary embodiment of the present invention.

FIG. 2 is an explanatory diagram showing the principle of tire pressure detection according to the first embodiment.

FIG. 3 is a characteristic diagram showing a relationship between a torsion moment power spectrum and frequency.

FIG. 4 is a characteristic diagram showing a relationship between a front-back force power spectrum and a frequency.

FIG. 5 is a characteristic diagram showing how the resonance frequency of the power spectrum changes with changes in tire air pressure.

FIG. 6 is a characteristic diagram showing how the resonance frequency of the wheel speed power spectrum changes due to changes in tire air pressure.

FIG. 7 is a characteristic diagram showing processing contents of the electronic control unit of the first embodiment.

FIG. 8 is a waveform diagram showing an output voltage waveform of a wheel speed sensor.

FIG. 9 is a waveform diagram showing a variation state of a wheel speed v calculated based on a detection signal of a wheel speed sensor.

10 is a characteristic diagram showing a result of performing a frequency analysis calculation on the wheel speed v having the waveform shown in FIG.

FIG. 11 is an explanatory diagram illustrating an averaging process according to the first embodiment.

FIG. 12 is a characteristic diagram showing a frequency analysis result after performing a moving average process in the first example.

FIG. 13 is a tire model diagram for explaining the third embodiment.

FIG. 14 is a characteristic diagram showing processing contents of the electronic control unit of the third embodiment.

FIG. 15 is a characteristic diagram showing the relationship between tire air pressure and torsion spring constant.

FIG. 16 is a characteristic diagram showing a relationship between tire pressure and a resonance frequency of a tire alone.

[Explanation of symbols]

 1 Tire 2 Gear 3 Pickup Coil 4 Electronic Control Unit (ECU) 5 Display

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shunji Naito, 1-1, Showa-cho, Kariya city, Aichi Nihon Denso Co., Ltd.

Claims (3)

[Claims] 1. An output unit that outputs a signal including a vibration frequency component of a tire when a vehicle is running, an extraction unit that extracts a resonance frequency of a tire unit from a signal including a vibration frequency component of the tire, and the tire unit A tire air pressure detecting device for detecting the state of air pressure of the tire based on the resonance frequency of the tire. 2. Output means for outputting a signal including a vibration frequency component of a tire when the vehicle is running, estimating means for estimating a spring constant of the tire from a signal including the vibration frequency component of the tire, and the spring constant A tire air pressure detection device comprising: a detection unit configured to detect the state of air pressure of the tire based on the above. 3. The tire air pressure detection device according to claim 1, wherein the output means is a wheel speed sensor that outputs a signal corresponding to the rotation speed of the wheel.