JP2000001111A - Tire pressure detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve detection frequency and improve detection accuracy by sampling a predetermined frequency component from an oscillation frequency of a wheel speed and sampling a frequency component of a frequency range used for inflation pressure detection, and selecting a wheel revolution speed based on gain ratio such as deflection. SOLUTION: Pickup coils 14a through 14d fixed to rotation axles of tires 10a through 10d are connected to an ECU 16 The ECU 16 calculates a wheel speed from outputted alternating current signals, sampling oscillation frequency component thereof, performs frequency analysis (FFT), and calculates an overall gain. Next, calculation of gain in a frequency range used for inflation pressure detection is performed based on a result of FFT calculation, a gain ratio between the overall gain and the frequency range used for the inflation pressure detection is calculated, and it is determined whether the gain ratio is in an appropriate range. Even if the overall gain is small, as long as gain of the sampled frequency component is suitable for detection, this value is used for detection, increasing a detection frequency thereby.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tire pressure detecting device for detecting the pressure of a tire of an automobile or the like.
More specifically, the present invention relates to a tire pressure detecting device that determines a tire spring constant based on a wheel speed signal and detects tire pressure.

[0002]

2. Description of the Related Art The fact that there is a fixed relationship between the tire air pressure and the tire spring constant and that there is a fixed relationship between the tire spring constant and the tire resonance frequency makes use of the wheel. Conventionally, there has been proposed a tire pressure detecting device which obtains a resonance frequency in a vertical direction or a front-rear direction of a tire based on a vibration frequency component of a speed signal, and detects a tire pressure based on the resonance frequency.

[0003] In a tire pressure detecting device disclosed in Japanese Patent Application Laid-Open No. 8-156536, the magnitude of a vibration component input to a tire from a road surface is detected, and the detected vibration component is selected according to the vehicle speed. Vibration components within a set predetermined range are selected, and the tire pressure is detected based on the selected vibration components.

[0004]

However, in this tire pressure detecting device, whether or not this vibration component is used for detecting the tire pressure is selected based on the absolute value of the vibration component. . Therefore, even when the vibration component is in a vibration state suitable for detecting the tire air pressure, if the absolute value of the vibration component is small, the vibration component is not used for detecting the tire air pressure, and the tire air pressure is not detected. There is a problem that the frequency of detection of the image is low.

[0005] It is an object of the present invention to provide a tire pressure detecting device that increases the frequency of detecting the tire pressure and improves the detection accuracy.

[0006]

According to a first aspect of the present invention, there is provided a tire pressure detecting device for detecting a tire pressure from a vibration frequency component of a wheel speed based on a wheel rotational speed detected by a wheel rotational speed detecting means. A first extracting means for extracting a predetermined frequency component from the vibration frequency component of the wheel speed; and a second extracting means for extracting a frequency component in a frequency region to be used when detecting tire air pressure from the vibration frequency component of the wheel speed. 2 extracting means, and based on a ratio of a gain of the frequency component extracted by the first extracting means to a gain of the frequency component extracted by the second extracting means, calculates wheel rotation speed data used for detecting the tire air pressure. Selecting means for selecting.

According to the tire pressure detecting device of the present invention, the gain of the frequency component extracted by the first extracting means, for example, the gain of the entire frequency component and the gain of the frequency component extracted by the second extracting means, is obtained. Based on the ratio,
Since the selecting means selects the wheel rotation speed data used for detecting the tire air pressure, even if the gain of the frequency component extracted by the first extracting means is small, the gain of the frequency component extracted by the second extracting means is reduced. When the state is suitable for detecting the tire pressure, this frequency component is used for detecting the tire pressure. Therefore, the frequency of detecting the tire air pressure can be increased, and the detection accuracy can be improved.

According to a second aspect of the present invention, the predetermined frequency component of the tire air pressure detecting device does not include a sprung vibration frequency component and is extracted by the second extracting means. It is characterized by including a frequency component.

According to the tire pressure detecting device of the present invention, the frequency component used for detecting the tire pressure is selected based on the frequency component excluding a relatively large gain such as the sprung vibration frequency component. The accuracy of air pressure detection can be further improved.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A tire pressure alarm system to which a tire pressure detecting device according to an embodiment of the present invention is applied will be described below with reference to the drawings.

FIG. 1 is a schematic configuration diagram of a tire air pressure warning system 2. Wheel speed sensors are provided for each of the four front, rear, left and right tires 10a to 10d mounted on the vehicle. The wheel speed sensor includes gear-shaped pulsars 12a to 12d made of a magnetic material and pickup coils 14a to 14d. The pulsars 12a to 12d are fixed to a rotating axle (not shown) of each of the tires 10a to 10d.
Reference numerals 4a to 14d are attached at predetermined intervals to the pulsars 12a to 12d and output an AC signal having a cycle corresponding to the rotation of the pulsars 12a to 12d, that is, the rotation speed of each of the tires 10a to 10d.

The pickup coils 14a to 14d are E
An AC signal that is connected to a CU (electronic control unit) 16 and output from the pickup coils 14a to 14d
It is input to the ECU 16. The ECU 16 includes a CPU, a waveform shaping circuit, a ROM, a RAM, and the like, and performs processing such as detection of tire air pressure and warning based on various input signals.

Here, the tire pressure warning system 2
The principle of detecting the tire pressure in the above will be described. When a vehicle travels on a paved asphalt road surface, the tire receives vertical and longitudinal forces due to minute irregularities on the road surface, and the tire vibrates in the vertical and longitudinal directions. The frequency characteristics of the unsprung acceleration of the vehicle at the time of the tire vibration show peak values at points a and b as shown in FIG. Point a is the vertical resonance frequency under the spring of the vehicle, and point b is the longitudinal resonance frequency under the spring of the vehicle.

When the air pressure of the tire changes, the spring constant of the tire rubber portion also changes, so that both the above-mentioned vertical and vertical resonance frequencies change. For example, as shown in FIG. 3, when the air pressure of the tire decreases, the spring constant of the tire rubber part also decreases, so that the resonance frequency in the vertical direction and the front-rear direction generally shifts to the low frequency side, and the peak value point a becomes a
The point b peak value shifts to the point b '. Therefore, if at least one of the resonance frequencies in the vertical and longitudinal directions under the spring of the vehicle is extracted from the vibration frequency of the tire, it is possible to detect the state of the tire pressure based on the resonance frequency.

On the other hand, it is known that the detection signal of the wheel speed sensor includes a tire vibration frequency component. That is, the result of frequency analysis of the detection signal of the wheel speed sensor shows peak values at two points as shown in FIG. 4, and the frequency of the peak values at the two points also decreases as the tire air pressure decreases. For this reason, in this embodiment, the tire pressure is detected by extracting the resonance frequency in the vertical direction and the front-back direction under the spring of the vehicle from the detection signal of the wheel speed sensor.

Next, referring to the flowchart of FIG.
The detection and warning processing of the tire pressure will be described. Since the ECU 16 performs the same processing for each wheel, this flowchart shows only signal processing for one wheel 10a.

[0017] When the ignition switch is turned on, EC is started.
The signal processing by U16 starts. First, a wheel speed signal is acquired (step 10). That is, the AC signal output from the pickup coil 14 is captured. After the waveform of this AC signal is shaped into a pulse signal, the wheel interval V is calculated by dividing the pulse interval by a predetermined time.

Next, a vibration frequency component of the wheel speed is extracted from the wheel speed V (step 11), and the vibration frequency component is subjected to frequency analysis (hereinafter, referred to as FFT).
An operation is performed (step 12). FIG. 6 is a graph showing the result of the FFT operation performed in step 12 with the vertical axis representing gain and the horizontal axis representing frequency (Hz). In addition,
In this graph, data A, which are the results of performing FFT calculations on the wheel speeds V at different times,
Three data, data B and data C, are shown.

Next, the FFT performed in step 12
The overall gain is calculated based on the result of the calculation (step 13). That is, since the gain for the data A appears as an area below the data A in FIG. 6, the area of this part is calculated. The gain of the data B and the data C can be calculated in the same manner.

Next, the FFT performed in step 12
Based on the result of the calculation, the gain of the frequency band used in the tire pressure detection is calculated (step 14). The frequency band used in this tire air pressure detection includes a vertical vibration frequency component below the spring, and does not include a vibration frequency component above the spring and a vibration frequency component below the spring in the front-rear direction. Therefore, the gain of data A is as shown in FIG.
Since the area appears as an area below the data A in the range indicated by the arrow in FIG. The gain of the data B and the data C can be calculated in the same manner.

Next, the ratio between the total gain calculated in step 13 and the gain of the frequency band used for tire pressure detection calculated in step 14 is calculated (step 1).
5). Then, it is determined whether or not the gain ratio is within a proper range (step 16). If the gain ratio is too large or too small, it is not appropriate as data used for tire pressure detection, that is, When the data is used for detecting the tire pressure, the accuracy of the tire pressure detection is reduced.
The process of step 15 is performed again. On the other hand, if it is determined that the gain ratio calculated in step 15 is a value within an appropriate range (step 16), the number of times of FFT calculation is incremented by 1 and stored as data used in tire pressure detection.

For example, in the data A, since the gain of the frequency band used for tire pressure detection is too small as compared with the entire gain, it is determined in step 16 that the gain ratio is not a value within an appropriate range, and Return to the processing of. On the other hand, in the data B and the data C, since the gain of the frequency band used for the tire pressure detection is more appropriate than the entire gain, the gain ratio in the step 16 is set to a value within an appropriate range. In step 17, the number of FFT operations is incremented by 1 and stored as data used in tire pressure detection.

Next, FFT calculation number N is the reference value N _O of whether or not (positive constant integer) equal to or higher than the determination is performed, the flow returns to step 10 when the negative determination has been performed, an affirmative determination is Line If so, go to step 19. Here, the N _o data is stored as the data used in the tire pressure detection because the shape (size and height) of the fine irregularities existing on the road surface is irregular, so that the frequency of each wheel speed data is different. Since the characteristics fluctuate, the fluctuation of the frequency characteristics is to be reduced as much as possible.

Next, sorted data in step 16, that is, by the average value of the results of the FFT operation on the N _O pieces of data is calculated, the average value of the gain of each frequency component is calculated (step 19). In this averaging process, the average value of each FFT operation result is calculated. By calculating the average value of the gain of each frequency component, it is possible to reduce the variation of the FFT operation result due to the road surface.

Next, a moving average process is performed on the average value of the gain of each frequency component. That is, the gain Yn of the n-th frequency is the gain Yn of the (n + 1) -th and (n-1) -th frequencies.
The average value of n + 1 and Yn-1 is calculated according to the following equation 1 (step 20).

(Equation 1) Yn = (Yn + 1 + Yn-1) / 2 Next, the tire resonance frequency fx is calculated based on the gain Yn after the moving average processing (step 21), and the tire air pressure P is calculated based on the resonance frequency fx. Is calculated (step 22).

Next, it is determined whether or not the tire pressure P is an appropriate value (step 23). If the tire pressure P is an appropriate value, the process returns to step 10 and the processes of steps 10 to 22 are performed again. On the other hand, if it is determined that the tire pressure P is not an appropriate value, a warning is issued to the driver by display or the like (step 24).

According to the tire pressure alarm system of this embodiment, even when the overall gain is small, the vibration frequency component of the band used for tire pressure detection clearly appears, that is, the tire pressure detection. When the state is suitable for the tire pressure, since this data is used for the tire pressure detection, the data used for the tire pressure detection can be increased, and the detection frequency of the tire pressure can be increased. Therefore, even when the vehicle is traveling on a flat road surface, the number of times of detecting the tire air pressure can be increased (the detection time can be shortened), and the detection accuracy can be improved.

In the above embodiment, whether or not data is used for tire pressure detection is determined based on the ratio between the overall gain and the gain of the frequency band used for tire pressure detection. A specific frequency band (specified frequency band) is defined, and whether to use data for tire pressure detection is determined based on a ratio of a gain in this frequency band to a gain of a frequency band used for tire pressure detection. May be. In this case, as shown in FIG. 7, the specified frequency band should be set within a range that includes the unsprung vibration frequency components in the front-rear direction and does not include the sprung vibration frequency components (frequency components with extremely large gain). Is preferred. By thus defining the specified frequency band, the detection accuracy of the tire pressure can be further improved.

In the above-described embodiment, the data used for tire pressure detection is selected based on the ratio between the overall gain and the gain of the frequency band including the vibration frequency component in the unsprung longitudinal direction. However, the sprung or unsprung vibration is detected by a separately provided sensor, and the tire pressure is detected based on a comparison between the gain of the detected vibration and the gain of a frequency band including a vibration frequency component in the unsprung longitudinal direction. Selection of data to be used may be performed.

Further, the tire pressure warning system of the above embodiment may be provided with an initial value learning function. That is, at the time of tire replacement, at the time when the tire pressure is initially appropriate, a plurality of data samples in which the ratio between the overall gain and the gain of the frequency band used for tire pressure detection is appropriate are sampled, and the tire A reference value for selecting data used for air pressure detection is determined. In this case, it is preferable that the criterion for judging that the ratio between the overall gain and the gain of the frequency band used for tire pressure detection be appropriate is strict.

In the above-described embodiment, the tire pressure may be detected based on the shape of the gain in the frequency band used for estimating the pressure shown in FIG. In this case, the area of a region having a lower frequency than the center line is larger than the area of a region having a higher frequency than the center line with reference to the center line (center frequency) of the air pressure estimation use frequency band. In this case, it is determined that the tire pressure has decreased.

In the above embodiment, the FF
The resonance frequency of the tire is calculated based on the result of the T calculation, and the tire pressure is detected based on the calculated frequency. However, the present invention is not limited to this. Bandpass filtering is performed on the wheel speed signal. A disturbance may be obtained by a disturbance observer from the wheel speed signal, and the tire air pressure may be detected based on the disturbance.

[0034]

According to the first aspect of the present invention, the tire pressure is detected based on the ratio of the gain of the frequency component extracted by the first extracting means to the gain of the frequency component extracted by the second extracting means. In order to select the wheel rotation speed data to be used, the gain of the frequency component extracted by the second extraction unit is suitable for detecting the tire air pressure even when the gain of the frequency component extracted by the first extraction unit is small. When in the state, this frequency component is used for detecting the tire air pressure. Therefore, the frequency of detecting the tire air pressure can be increased, and the detection accuracy can be improved.

According to the second aspect of the present invention, the frequency component used for detecting the tire air pressure is selected based on the frequency component excluding a relatively large gain such as the sprung vibration frequency component. Can be further improved.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a tire pressure warning system according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram illustrating frequency characteristics of unsprung acceleration of a vehicle.

FIG. 3 is a characteristic diagram showing a change in a frequency characteristic of unsprung acceleration of a vehicle with a change in tire air pressure;

FIG. 4 is an explanatory diagram illustrating a principle of detecting tire air pressure.

FIG. 5 is a flowchart illustrating a tire pressure detection process in the tire pressure warning system according to the embodiment of the present invention.

FIG. 6 is a diagram showing a result of an FFT operation performed for detecting a tire air pressure and an air pressure estimation use area according to the embodiment of the present invention;

FIG. 7 is a diagram showing an FFT calculation result, an air pressure estimation use band, and a specified frequency band performed for detecting a tire air pressure according to the embodiment of the present invention.

[Explanation of symbols]

2. Tire pressure warning system, 10a to 10d tires, 12a to 12d pulsers, 14a to 14d pickup coils, 16 ECU.

 ──────────────────────────────────────────────────続 き Continuation of the front page (71) Applicant 000003609 Toyota Central R & D Co., Ltd. 41 No. 41, Chuchu-Yokomichi, Oku-cho, Nagakute-cho, Aichi-gun, Japan Inside the Automobile Co., Ltd. (72) Inventor Shoji Inagaki 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Automobile Co., Ltd. (72) Inventor Koji Umeno 41 shares, Ochi-Cho, Yokomichi, Oku-cho, Nagakute-cho, Aichi-gun, Aichi Prefecture (72) Inventor Shunji Naito 1-1-1, Showa-cho, Kariya-shi, Aichi Pref. Inside DENSO Corporation (72) Inventor Yukio Mori 2-1-1 Asahi-cho, Kariya-shi, Aichi Aisin Seiki Co., Ltd. Inside

Claims (2)

[Claims] 1. A tire pressure detecting device for detecting a tire pressure from a vibration frequency component of a wheel speed based on a wheel rotation speed detected by a wheel rotation speed detecting means, wherein a predetermined frequency component is detected from the vibration frequency component of the wheel speed. First extracting means for extracting; second extracting means for extracting a frequency component in a frequency range to be used when detecting tire air pressure from the vibration frequency component of the wheel speed; and a frequency extracted by the first extracting means. Selecting means for selecting wheel rotation speed data used for detecting the tire air pressure based on a ratio of a gain of the component to a gain of the frequency component extracted by the second extracting means. Detection device. 2. The tire pressure detecting device according to claim 1, wherein the predetermined frequency component does not include a sprung vibration frequency component and includes the frequency component extracted by the second extracting unit.