JPH05294120A - Tire pressure detecting device - Google Patents

Abstract

PURPOSE:To avoid erroneous judgment by comparing each resonance frequency component extracted from the vibration frequency components of each tire to detect the lowering condition of tire pressure, comparing each rate of change in lowering with a criterion when it is judged that pressure is lowered, and thereby outputting a warning when change in lowering is small but is continued repeatedly as specified. CONSTITUTION:Signals from each wheel speed sensor which is made up of each pluser 2a through 2d composed of each magnetic body corresponding to the tires la through 1d of a vehicle, and of each pick-up coil 3a through 3d, are inputted into an electronic control means 4, and are operated so as to be processed in accordance with a specified program, so that each condition of tire pressure is thereby displayed in a display section 5. Each resonance component is extracted out of signals from the pick-up coils 3a through 3d to be compared with a criterion, and when tire pressure is found to have been lowered, the electronic control means 4 compares a rate of change in lowering with the criterion to judge whether change in lowering is large or small. And when a rate of change in lowering is judged that it is small but has been continued repeatedly as specified, the aforesaid means gives a warning for lowered tire pressure. This constitution thereby can enhance reliability with no chance of erroneous judgment.

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 the air pressure of a tire of a vehicle.

[0002]

2. Description of the Related Art Conventionally, as a device for detecting a tire air pressure, the fact that the tire radius changes in accordance with the tire air pressure is used to detect the wheel speed of each wheel by using a detection signal of a wheel speed sensor. Based on this, a device for indirectly detecting the air pressure of a tire of a vehicle has been proposed.

[0003]

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 transmission. Further, radial tires, which have been widely used in recent years, have a small amount of deformation of the 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.

In view of the above problems, the inventors of the present application have extracted the resonance frequency f _K in the up-down direction or the front-rear direction of the unsprung part, and decrease the deviation (f ₀ −) based on this resonance frequency f _K.
We invented a device for detecting the state of tire air pressure by comparing f _K ) with a predetermined deviation Δf, and filed an application for this (Japanese Patent Application No. 3-294622). However, the above-mentioned device is designed to immediately notify the driver of a tire pressure drop warning when the drop deviation (f ₀ −f _K ) becomes equal to or greater than the predetermined deviation Δf, and therefore there is a risk of misjudgment. .. The present invention has been made in view of the above points, and an object thereof is to provide a highly reliable tire air pressure detection device without the risk of erroneous determination.

[0005]

In order to achieve the above object, a tire air pressure detecting device according to the present invention includes an output means for outputting a signal including a vibration frequency component of a tire when the vehicle is running, and an output means for outputting the signal. Extraction means for extracting the signal of the resonance frequency component, detection means for detecting the decrease state of the tire air pressure by comparing the signal of the resonance frequency component with a determination value, and the decrease of the tire air pressure is detected by the detection means. When the change rate of the decrease in tire air pressure is compared with the determination value, the determining means determines the size of the change in the decrease in tire air pressure, and the determining means determines that the change in the decrease in tire pressure is small, and that And a warning unit that outputs a tire pressure drop warning when the number of tires is continuously detected.

[0006]

With the above structure, when the determination means determines that the decrease in tire air pressure is small and continues for a predetermined number of times, the alarm means outputs a tire air pressure decrease alarm.

[0007]

Embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram of the first embodiment. Wheel speed sensors are installed corresponding to the four tires 1a to 1d on the front, rear, left, and right mounted on the vehicle. Wheel speed sensor
It is composed of gear-shaped pulsars 2a to 2d and pickup coils 3a to 3d made of a magnetic material. Pulsar 2a
2d are rotating axles (not shown) of the tires 1a to 1d.
Fixed to. The pickup coils 3a to 3d are attached to the pulsars 2a to 2d with a predetermined space therebetween, and output pick-up AC signals having a cycle corresponding to the rotation of the pulsars 2a to 2d, that is, the rotation speed of each of the tires 1a to 1d.

AC signals output from the pickup coils 3a to 3d are input to an electronic control unit (hereinafter referred to as ECU) 4. The ECU 4 includes a CPU, a waveform shaping circuit, an RO
It is composed of M, RAM, etc., and processes various signals inputted according to a predetermined program. Then, the signal processing result is input to the display unit 5, and the display unit 5 notifies the driver of the air pressure state of each of the tires 1a to 1d. As the notification mode, the state of the air pressure of each of the tires 1a to 1d may be specially displayed, and one warning lamp
When the air pressure of any one of the tires becomes lower than the reference air pressure, the warning lamp may be turned on to give a warning.

The principle of tire pressure detection in this embodiment will now be described. When a vehicle travels on a paved asphalt road surface, minute irregularities on the surface of the road surface receive forces in the vertical and longitudinal directions, and the forces cause the tire to vibrate in the vertical and longitudinal directions. The frequency characteristics of the unsprung acceleration of the vehicle during tire vibration show peak values at points a and b as shown in FIG. Point a is the vertical resonance frequency of the vehicle under the spring, and point b is the front-rear resonance frequency of the vehicle under the spring.

When the tire air pressure changes, the spring constant of the tire rubber portion also changes, so that the resonance frequencies in the vertical direction and the front-back direction both change. For example, as shown in FIG. 3, when the tire air pressure decreases, the spring constant of the tire rubber portion also decreases, so the resonance frequencies in the up-down direction and the front-rear direction generally shift to the low frequency side, and the peak value a point is The peak value b point at point a ′ shifts to point b ′. Therefore, by extracting at least one of the resonance frequency in the up-down direction and the front-rear direction under the spring of the vehicle from the vibration frequency of the tire, it is possible to detect the tire air pressure state based on the resonance frequency.

On the other hand, as a result of a detailed study by the present inventors, it was clarified that the detection signal of the wheel speed sensor contains the vibration frequency component of the tire. That is, it is clear that 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 that the peak values at those two points also decrease as the tire air pressure decreases. Became. For this reason, in the present embodiment, the tire air pressure is detected by extracting the vertical and longitudinal resonance frequencies of the unsprung portion of the vehicle from the detection signal of the wheel speed sensor.

As described above, according to the present embodiment, the anti-skid control device (ABS), which has been increasing in the number of vehicles equipped with it in recent years,
A vehicle or the like equipped with is equipped with a wheel speed sensor in each tire, so that tire pressure can be detected without adding any new sensor. In the practical range of the vehicle, the amount of change in the resonance frequency is almost based on the change in the spring constant of the tire rubber portion caused by the change in tire air pressure, and is stable without being affected by other factors such as tire friction. Air pressure can be detected.

Referring to the flowchart of FIG. 5 below, E
The signal processing performed by the CU 4 will be described. The ECU 4
Performs the same process for each wheel 1a to 1d, the flowchart of FIG. 5 shows only the process for any one wheel. Therefore, in the following description, the subscript of each code is omitted. In addition, an example will be given, in particular, in which it is detected that the tire air pressure has dropped below a reference value and the driver is warned. Then, the following signal processing is independently performed for each of the four tires.

When the process is started by turning on the ignition switch, in step 101, the AC signal (FIG. 6) output from the pickup coil 3 is shaped into a pulse signal, and the pulse interval is divided by the time interval. Thus, the wheel speed v is calculated. This wheel speed v
As shown in FIG. 7, it usually contains many high frequency components including the vibration frequency component of the tire.

In step 102, a road surface condition determination process is performed to determine whether the calculated fluctuation width Δv of the wheel speed v is equal to or greater than the reference value v ₀ . At this time, the fluctuation range of the wheel speed v Δ
When v is determined to be the reference value v ₀ or more, the process proceeds to step 103. In step 103, a road surface length determination process is performed to determine whether or not the time period ΔT in which the fluctuation range Δv of the wheel speed v is the reference value v ₀ or more is the predetermined time t ₀ or more. Step 10
The road surface condition determination processing of 2 and the road surface length determination processing of step 103 are performed to determine whether or not the road surface on which the vehicle is traveling is a road surface on which the tire air pressure can be detected by the detection method of this embodiment. It is a thing. That is, in the present embodiment, since the tire air pressure is detected based on the change in the resonance frequency included in the vibration frequency component of the tire, if the wheel speed v fluctuates to some extent and is not continued, the resonance frequency It is not possible to obtain sufficient data for calculating In the determination in step 103, the predetermined time Δt is set when the fluctuation width Δv of the wheel speed v becomes equal to or larger than the reference value v ₀ . Further, when the fluctuation width Δv of the wheel speed v again becomes equal to or larger than the reference value v ₀ within the predetermined time Δt, the measurement of the time ΔT is continued.

If both steps 102 and 103 are affirmatively determined, the process proceeds to step 104, and if one or the other is negatively determined, the process returns to step 101. In step 104, frequency analysis is performed on the calculated wheel speed v by frequency analysis (hereinafter referred to as FFT) calculation, and the number of times N of calculation is integrated. When the FFT calculation is actually performed on the wheel speed obtained when the vehicle actually travels on a general road, the frequency characteristics are usually very random as shown in FIG. This is the shape (size and height) of the subtle unevenness that exists on the road surface.
Is completely irregular, and the frequency characteristic fluctuates for each wheel speed data. Therefore, in this 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 obtained.

Therefore, in step 105, it is judged whether or not the number N of FFT operations in step 104 has reached a predetermined number n ₀ . When the number of calculations N has not reached the predetermined number n ₀ , the processing from step 101 to step 104 is repeatedly executed. On the other hand, when the number of calculations N reaches the predetermined number n ₀ , the process proceeds to step 106 to perform the averaging process. As shown in FIG. 9, this averaging process is to obtain an average value of the FFT calculation results,
The average value of the gain of each frequency component is calculated. By this averaging process, it is possible to reduce the fluctuation of the FFT calculation result due to the road surface.

However, with the above averaging process alone, the gain of the resonance frequency in the vertical direction and the front-back direction of the unsprung part of the vehicle does not always reach the maximum peak value as compared with the gain of the frequencies in the vicinity thereof due to noise or the like. There is a problem that it is not limited. Therefore, following the averaging process described above, the moving average process is performed in step 107. This moving average processing is performed by obtaining the gain Y _n of the _nth frequency by the following arithmetic expression.

[0019]

## 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 from slippage. FIG. 10 shows the calculation result obtained by this moving average processing.

The waveform processing here is not limited to the above moving average processing, but low pass filter processing may be applied to the FFT calculation result after the averaging processing, or the FFT calculation of step 105 is performed. Before that, the wheel speed v may be differentially calculated, and the FFT calculation may be performed on the differential calculation result.

In the following step 108, the resonance frequency f _K of the unsprung vehicle in the front-rear direction is calculated based on the FFT calculation result smoothed by the moving average processing. Then, in step 109, it is determined whether or not the calculated resonance frequency f _K becomes equal to or lower than a preset air pressure drop determination value f _L. Next, in step 110, the rate of change df _K of the resonance frequency f _K per unit time is determined.
By comparing with (Δf _K / Δt), the degree (degree) of decrease in tire air pressure is determined. Here, Δf _K is the difference between the present calculation result of the resonance frequency and the previous calculation result, and Δt is the time between them. If the rate of change is equal to or less than the determination value, that is, if the tire air pressure does not drop suddenly, the process proceeds to step 111 and the counter is set. In the following step 112, it is determined whether or not the calculated rate of change of the resonance frequency f _K is equal to or less than the determination value and is continuously less than or equal to m ₀ times and equal to or less than the air pressure decrease determination value f _L. If the result in step 112 is affirmative, the process proceeds to step 113, and a warning that the air pressure of the tire to be detected has decreased is displayed on the display unit 5.

When the result in step 109 is negative, the counter value is initialized to "0" in order to count the number of continuous processes after step 109. Further, when the rate of change of the resonance frequency f _K is equal to or higher than the determination value in step 110, it is determined that the tire air pressure has suddenly leaked and the tire air pressure has dropped, and the process jumps to step 113 and immediately Display a warning of the contents.

In the above embodiment, once the warning is displayed in step 113, the warning is continued until the vehicle is stopped. Then, after the vehicle is restarted or after the ignition switch is turned on and restarted, if the value of the resonance frequency f _K calculated first is larger than the air pressure drop determination value, the tire air pressure drop determination state is released and a warning display is displayed. To cancel. If the value of the resonance frequency f _K calculated first is less than or equal to the air pressure decrease determination value, the warning display is continued until the next vehicle stop, and the above steps are repeated.

In the above embodiment, the rate of change of the resonance frequency f _K per time is obtained, and whether or not this rate of change is not more than the judgment value and continuously not less than m ₀ times and not more than the air pressure drop judgment value f _L. Since the warning indicating that the tire air pressure has dropped is issued based on the two-stage determination result, it is possible to avoid erroneous determination and improve reliability.

[0025]

The present invention has the above-mentioned structure, and when it is determined that the change in the decrease in tire air pressure is small, if this state continues for a predetermined number of times, the alarm means outputs a tire air pressure decrease alarm. There is an excellent effect that it is possible to provide a highly reliable tire air pressure detection device without the risk of misjudgment.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a tire air pressure detection device according to the present invention.

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

FIG. 3 is a characteristic diagram showing how the resonance frequency changes in the up-down direction and the front-rear direction of the unsprung part of the vehicle with changes in tire air pressure.

FIG. 4 is an explanatory diagram showing the principle of tire pressure detection.

FIG. 5 is a flowchart showing the processing contents of the ECU.

FIG. 6 is a waveform diagram showing an output voltage waveform of a wheel speed sensor.

FIG. 7 is a waveform diagram showing a variation state of a wheel speed v calculated based on a detection signal of a wheel speed sensor.

8 is a characteristic diagram showing an FFT calculation result for the wheel speed v of the waveform shown in FIG. 7.

FIG. 9 is an explanatory diagram illustrating an averaging process.

FIG. 10 is a characteristic diagram showing an FFT calculation result after performing a moving average process.

[Explanation of symbols]

 1a to 1d ... tires 2a to 2d ... pulser 3a to 3d ... pickup coil 4 ... ECU (electronic control unit) 5 ... display section

Claims (1)

[Claims] 1. When the vehicle is running, output means for outputting a signal including a vibration frequency component of a tire, extraction means for extracting a signal of a resonance frequency component from the signal, and a signal of the resonance frequency component as a judgment value. When a decrease in tire air pressure is detected by the detection unit that detects the decrease in tire air pressure by comparing, a decrease in tire air pressure is changed by comparing the change rate of decrease in tire air pressure with a determination value. Of the determination means for determining the magnitude of the, and the change in the decrease in tire air pressure is determined to be small by the determination means,
A tire air pressure detection device, further comprising: an alarm unit that outputs a tire air pressure drop alarm when it is detected a predetermined number of times continuously.