JPH0692115A - Method and device for detecting air pressure drop of tire - Google Patents

Abstract

PURPOSE:To detect a tire, whose pressure of air is dropped, inexpensively, sensitively, accurately and further quickly by detecting a rotational speed changed of a tire, eliminating a primary factor of fluctuation except a pressure of air influencing upon a dynamic load radius of the tire, abstracting a relation between the pressure of tire air and the dynamic load radius, and detecting the pressure of tire air changed. CONSTITUTION:An analog signal given from a wheel speed sensor 1 is binary code processed in an ABS control unit 6, and a control unit 11 for a tire air pressure drop detector (DWS) receives supply of wheel speed pulses from the ABS control unit 6, to detect a pressure drop of air in tires W1 to W4. Now when assumed F1 to F4 for rotary angular speeds of the four tires, ratio dF =(F1+F4)/(F2+F3) of the sum F1+F4 of rotary angular speeds of a pair of the tires on a diagonal line to the sum F2+F3 of rotary angular speeds of another pair of the tires is obtained, and except at the time of a relation where (1-a)<dF<(1-a), decreased pressure of air in any tire is detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tire pressure drop detection for a four-wheel vehicle, and more particularly to a method and apparatus for detecting a tire pressure drop based on the rotational speeds of four tires. It is about.

[0002]

2. Description of the Related Art As one of safety devices for four-wheeled vehicles such as passenger cars and trucks, a device for detecting a decrease in tire air pressure has been invented, and some of them have been put into practical use. The demand for vehicle tire low pressure detection is particularly high in Europe. This is because in European countries with developed highways, low tire air pressure during high speed driving can lead to serious accidents.

As a conventional tire pressure drop detecting device which has been put into practical use, there is a device which directly measures the tire pressure. In this conventional device, a pressure sensor is provided in the tire, and the tire pressure is directly measured by the pressure sensor. Then, the measured tire pressure is applied to the processing device provided on the vehicle body side. The pressure sensor and the processing device are electromagnetically coupled, for example, and signals can be mechanically transmitted and received in a non-contact state. The tire pressure processed by the processing device is displayed on a display or the like.

Further, as another conventional technique, the rotational angular velocities of four tires are detected, and based on the rotational angular velocities of the respective tires,
A tire air pressure drop detection method for detecting a tire whose air pressure is relatively low has been proposed (see, for example, JP-A-63-305011). In this conventional detection method, the sum of the rotational angular velocities of one pair of tires on the diagonal is subtracted from the sum of the rotational angular velocities of another pair of tires on the other diagonal, and the result is the average of the two totals. Than 0.0
If it is between 5% and 0.6%, and preferably between 0.1% and 0.3%, a decompressed tire is detected.

[0005]

Of the above-mentioned conventional techniques,
In the former configuration with a pressure sensor in the tire,
It has the drawback of being very expensive. Further, although a signal is electromagnetically transmitted from the pressure sensor provided in the tire to the processing device provided on the vehicle body side, there is a drawback that an error is likely to occur during signal transmission. In particular, the vehicle may drive under adverse conditions, for example, on a road with a lot of geomagnetism,
There are also many obstacles to electromagnetic signal transmission.

On the other hand, the latter method of detecting a decompressed tire based on the rotational angular velocity of the tire has the following drawbacks. That is, in order to extract the change in the rotational angular velocity of the depressurized tire, the average value of the rotational angular velocities of the four tires is used as a reference amount, and the variation in the depressurized tire is detected based on the reference amount. Therefore, the reference amount also includes the rotational angular velocity of the pressure-reduced tire, so that the reference amount is not accurate and the detection accuracy is not good.

The present invention has been made against the background of such a conventional technique, and a method for constructing a device at a relatively low cost and for detecting a tire whose air pressure has dropped with high sensitivity, accuracy, and speed is provided. The purpose is to provide a device. The more basic object of the present invention is as follows. First, it is related to the development of runflat tires. Run flat tires are
For example, it is a tire that is designed to be able to run for about 300 km at 80 km / h or less. In a vehicle equipped with such a run-flat tire, the driver often does not notice even if the tire is flat and the air pressure is reduced. In a punctured state, if you are traveling at a speed that exceeds the speed limit, or if you are traveling beyond the mileage limit,
Tires may burst, leading to an accident.
Therefore, initially, one purpose was to detect such a drop in air pressure for a runflat tire.

Another object of the present invention is to prevent the occurrence of an accident in advance by promptly detecting the fact that the air in the tire has been deflated, for example, when 0.5 atm has been deflated, and promptly notifying the driver. It was that. Usually, even if the air in the tire escapes by about 0.5 atm, the driver often does not notice it, so a device that can detect it has been desired.

Further, as another basic purpose, a nail or the like pierces the tire and slowly moves, for example, to 2 degrees.
This is made in order to meet the demand for prompt detection of a decrease in the air pressure when it takes 0 to 30 seconds or more. As described above, the present invention is based on the basic standpoint of detecting a decrease in tire air pressure and preventing an accident, and an accurate method and apparatus for realizing the same. Is to provide.

[0010]

[Means for Solving the Problems]

Principle of the Invention: In a vehicle having four tires, the distance from the center of the tread to the center of rotation of the tire, where each tire is actually in contact with the ground, is called the dynamic load radius of that tire. This dynamic load radius is: tire pressure change (see FIG. 15), tire load change (see FIG. 16), tire rotation speed, that is, vehicle running speed change (see FIG. 17), tire slip Change in angle (see Fig. 18), change in tire camber angle (see Fig. 18), vehicle accelerating or braking (see Fig. 19), vehicle cornering, tire wear (see Fig. 20), etc. Change. When the dynamic load radius of a certain tire changes, the rotational speed of the tire in which the change has occurred changes with respect to the rotational speeds of other tires at any vehicle speed.

Therefore, in the present invention, a. Detecting changes in tire rotation speed, b. Variable factors other than the air pressure that affect the dynamic load radius of the tire (from the above-mentioned) are eliminated by appropriately processing the dynamic load radius information of each tire, c. As a result, the tire with a reduced air pressure is detected based on the procedure of extracting the relationship between the tire air pressure and the dynamic load radius and detecting the change in the tire air pressure. Utilization of ABS: In the present invention, preferably, an ABS (Antilock-Braking-System) already installed in the vehicle is effectively utilized.

ABS currently accounts for about 35% of all vehicles in Europe and about 15-16 of all vehicles in Japan.
Installed with a penetration rate of%. This ABS is a system that has a wheel speed sensor for detecting the rotation states of four tires, detects whether the tire is in a slip state in which the tire is idling, and controls the hydraulic pressure of the brake. A
Since the signal system of the BS controls the hydraulic pressure of the brake as described above to control in the direction in which the brake is not applied, if it malfunctions, the vehicle will be in a very dangerous state.
Therefore, a highly reliable signal system is adopted. In a preferred aspect of the present invention, a highly reliable tire pressure drop detecting device is realized at low cost by utilizing the signal of the wheel speed sensor obtained from this reliable signal system.

According to a first aspect of the present invention, there is provided a tire pressure drop detecting method for a four-wheeled vehicle having four tires, wherein a rotational angular velocity F1 of a front left tire W1 and a rotation of a front right tire W2 of the four-wheeled vehicle. The angular velocity F2, the rotational angular velocity F3 of the rear left tire W3, and the rotational angular velocity F4 of the rear right tire W4 are respectively detected, and from the detected rotational angular velocity of each tire, the sum of the rotational angular velocity of a pair of tires on the diagonal line (F1 + F
4) and the rotational angular velocity of the other pair of tires (F2 + F
The ratio dF with 3) is calculated, and if the calculated ratio dF is between (1 + a ₁ ) and (1-a ₂ ) (where a ₁ and a ₂ are constants determined by the vehicle), a decrease in air pressure occurs. It is characterized in that it is judged that there is no tire present, and if the obtained ratio dF is outside the above range, it is judged that there is a tire having a decrease in air pressure.

According to a second aspect of the present invention, in the tire pressure drop detecting method according to the first aspect, if the obtained ratio dF is dF> 1, the depressurized tire is a front left tire W1 or a rear right tire W4, dF. If <1, the depressurized tire is specified as the front right tire W2 or the rear left tire W3.

According to a third aspect of the present invention, in the tire pressure drop detecting method according to the second aspect, in addition to the specification of the pressure-reduced tire according to the second aspect, if the vehicle is in a straight traveling state and F1> F2, the pressure is reduced. The tire is the front left tire W
If 1, F1 <F2, the decompression tire is the front right tire W2,
If F3> F4, the decompressing tire is the rear left tire W3, F3.
If F4, the depressurized tire is specified as the rear right tire W4.

According to a fourth aspect of the present invention, in the tire pressure drop detecting method according to the first aspect, when it is determined that there is a tire having a reduced air pressure, the vehicle further travels at a substantially constant speed and in a substantially straight line. Under the condition of performing the sum of the rotational angular velocities of the front tires W1 and W2 (F
1 + F2) and the sum (F3 + F4) of the rotational angular velocities of the rear tires W3 and W4 are compared, and if there is a large or small value, the two tires having the larger rotational angular velocities are the tires in which the air pressure decreases. It is characterized by specifying.

The invention according to claim 5 has four tires.
It is a tire pressure drop detection device for four-wheeled vehicles
Rotation to detect each rotational angular velocity of the four tires
Angular velocity detecting means, detected by the rotational angular velocity detecting means
From the rotational angular velocities of the four tires, the four
Angle of a pair of tires on the diagonal
The ratio of the sum of speeds and the sum of the rotational angular velocities of the other pair of tires
The calculation means to be obtained and the ratio calculated by the above calculation means are
(1 + a₁) And (1-a₂) (However, a₁, A ₂Is a car
(Constant determined by both) causes a decrease in air pressure
It is judged that there are no tires that have
If so, there must be a deflated tire that is causing a decrease in air pressure.
Depressurized tire detection means for detecting
It is something.

[0018]

According to the method and apparatus of the present invention, the rotational angular velocity of the decompressed tire among the four tires can be detected as a relative change amount with respect to the other three tires having normal air pressure. Therefore, as described in the related art, since the rotational angular velocity of the pressure-reduced tire is not included in the comparison reference amount, the detection accuracy does not fluctuate or deteriorate, and accurate detection is possible.

Further, according to the present invention, it effectively works for detecting the decrease in the air pressure of one of the four tires or two tires on the diagonal line. Further, according to the invention described in claim 4, it is also possible to detect that both the front tires and the rear tires have a decrease in air pressure under the condition that the vehicle is traveling at a substantially constant speed and in a substantially straight line. You can

[0020]

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a tire pressure drop detecting device (hereinafter referred to as “DWS”) according to an embodiment of the present invention.
Say. ) And a conventionally known ABS are installed in a vehicle.

The ABS mounted on this vehicle electronically determines the brake pressure of the brake 2 of each wheel based on the output of the wheel speed sensor 1 provided in association with each of the four tires W1, W2, W3 and W4. It is a device that avoids the locked state of the wheels at the time of sudden braking operation, etc. That is, when the brake pedal 3 is strongly depressed, the hydraulic pressure from the master cylinder 4 is changed to the hydraulic unit 5
And is transmitted to the brake 2 of each wheel. An ABS control unit 6 that monitors the outputs of the four wheel speed sensors 1 is connected to the hydraulic unit 5. A
In the BS control unit 6, when the so-called locked state of any wheel is determined based on the output of each wheel speed sensor 1, the hydraulic pressure unit 5 is controlled to brake the brake 2 of the locked wheel. Reduce pressure.

By the way, in the ABS, the analog signal given from each wheel speed sensor 1 is first binarized in the ABS control unit 6 and binarized. "Fast pulse") is used for processing. On the other hand, the DWS according to this embodiment
Includes a DWS control unit 11, a display 12 connected to the DWS control unit 11, and an initialization switch 15 connected to the DWS control unit 11 and operated by a driver. And DWS
The control unit 11 receives the wheel speed pulse from the ABS control unit 6 and detects a decrease in the air pressure of any of the tires W1 to W4 based on the wheel speed pulse. Then, when a decrease in the air pressure of any of the tires W1 to W4 is detected, the result is displayed on the display unit 12. The display unit 12 displays tires with reduced air pressure, as will be described later.

FIG. 2 is a perspective view showing an example of a mounting structure of the wheel speed sensor 1 described in FIG. A wheel mounting member 8 and a brake disc 9 are fixed to the end of the axle 7. Inside the brake disc 9 is the axle 7
A sensor rotor 10 that rotates together with the sensor rotor 10 is attached. A plurality of protruding teeth are formed at a constant pitch on the entire circumferential surface of the sensor rotor 10. This sensor rotor 1
The wheel speed sensor 1 is attached so as to face the peripheral surface of 0 at a predetermined interval and in a fixed state in which it does not rotate.

FIG. 3 is an illustrative view for explaining the principle of rotation detection by the wheel speed sensor 1. Wheel speed sensor 1
Guides the magnetic flux φ created by the permanent magnet 11 to the sensor rotor 10 by the pole piece 12, and
The electromotive force e _i generated at both ends of the coil 13 wound around 2 is taken out. A gap g is formed between the tip 12 a of the pole piece 12 and the sensor rotor 10. The sensor rotor 10 is fixed to the axle 7 as described above, and rotates with the rotation of the axle 7, in other words, the rotation of the tire. Further, as described above, a large number of teeth 10a are provided on the peripheral surface of the sensor rotor 10 at a constant pitch. Therefore, the tip 1 of the pole piece 12
The gap g between 2a and the peripheral surface of the sensor rotor 10 changes as the sensor rotor 10 rotates. Due to the change in the gap g, the magnetic flux φ penetrating the pole piece 12 changes,
The electromotive force e _i corresponding to the change of the magnetic flux φ is generated at both ends of the coil 13. Since the electromotive force e _i changes at a frequency corresponding to the rotation of the sensor rotor 10, a voltage signal e _i having a frequency corresponding to the tire rotation speed is finally obtained.

In this embodiment, about 45 teeth 10a are provided on the peripheral surface of the sensor rotor 10, for example. Therefore, when the sensor rotor 10 makes one revolution,
Forty-five teeth 10a face the tip 12a of the pole piece 12. Therefore, when the sensor rotor 10 makes one rotation, that is, when the tire makes one rotation, the coil 13 has 45
AC signals are generated.

FIG. 4 shows a DW according to an embodiment of the present invention.
It is a block diagram which shows the electric constitution of S. As described in FIG. 1, the detection signals of the four wheel speed sensors 1 are given to the ABS control unit 6. The ABS control unit 6 includes a binarization circuit 14 and an ABS microcomputer 16. The detection signal of the wheel speed sensor 1 given to the ABS control unit 6 is first binarized in the binarizing circuit 14 and then supplied to the ABS microcomputer 16.

As described above, the DWS according to this embodiment is adapted to be supplied with the detection signal of the ABS wheel speed sensor 1. In this case, the detection signal of each wheel speed sensor 1 is not directly applied to the DWS control unit 21, but after being binarized by the binarization circuit 14 in the ABS control unit 6. The wheel speed pulse of 1 is applied to the DWS control unit 21.

With such a connection structure, there are two major advantages. One advantage is that even if a failure occurs in the wheel speed signal input portion of the DWS control unit 21, the failure can be prevented from having a fatal effect on the ABS control unit 6. If DW
When the S control unit 21 is configured to directly take in the output of the wheel speed sensor 1, that is, when the signal line of each wheel speed sensor 1 is branched and connected to the DWS control unit 21, this branching is performed. If any of the signal lines that have been set is at the ground level, for example, an incorrect wheel speed detection signal will be given to the binarization circuit 14 of the ABS control unit 6. As a result, the ABS microcomputer 16 may malfunction. Therefore, as in this embodiment, the wheel speed pulse after being binarized by the binarizing circuit 14 in the ABS control unit 6 is DW.
If it is given to the S control unit 21, even if D
Even if a failure occurs in the wheel speed detection signal input portion of the WS control unit 21, the failure does not have a fatal effect on the ABS control unit 6.

Another advantage is that since the binarized wheel speed pulse is given to the DWS control unit 21,
This means that the wheel speed signal input portion of the DWS control unit 21 can be simplified. Now, in the DWS according to this embodiment, the wheel speed pulse is given to the DWS control unit 21, the display 22, and the initialization switch 1.
5 is included. The DWS control unit 21 is composed of a microcomputer, and its hardware configuration includes, as shown in the figure, an input / output interface 23 required for exchanging signals with an external device, a CPU 24 as a center of arithmetic processing, A ROM 25 in which a control operation program of the CPU 24 is stored, a RAM 26 from which data and the like are temporarily written when the CPU 24 performs a control operation, and the written data is read out, and a power supply is turned off.
Included is a non-volatile memory 27 that can retain stored data at any time. The RAM 26 is provided with a time memory area, a measurement timer area, a pulse counter area, a work register area, etc., as will be described later. In addition, in the non-volatile memory 27,
Data rejection conditions, data correction coefficients, etc., which will be described later, are stored.

When the DWS control unit 21 detects a tire with reduced air pressure based on the wheel speed pulse supplied from the binarization circuit 14, the detection result is displayed on the display 22.
Is output to and displayed. As shown in the figure, the display mode on the display 22 includes four tires W1, W2, W.
When a tire whose air pressure has dropped is detected by the display lamp or display element corresponding to 3, W4, the display element corresponding to the tire is turned on.

Further, display lamps or display elements W1 to W
In order to inform the driver that the vehicle itself has not failed, it is preferable to keep all lights on for a certain period of time after the ignition switch of the vehicle is turned on. The operation of the initialization switch 15 in FIG. 4 will be described later. FIG. 5 is a circuit block diagram showing an electrical configuration of a DWS according to another embodiment of the present invention. The configuration shown in FIG. 5 differs from the configuration shown in FIG. 4 in that the DWS microcomputer 28 is added inside the ABS control unit 6. In this way, by adding the DWS-dedicated microcomputer to the other unit, that is, the ABS control unit 6 in this embodiment, the existing control unit can be effectively utilized and the control unit does not increase. There are advantages that the circuit configuration can be reduced and the cost can be reduced.

In addition, the DWS is installed in the ABS control unit 6.
As shown in FIG. 6, instead of the configuration of FIG. 5 in which a microcomputer 28 for an air conditioner is added, if a program for detecting a decrease in air pressure is added to the microcomputer 16 for an ABS in addition to the program for the ABS, the microcomputer With respect to the hardware configuration, the DWS can be configured by simply adding a new program while using the existing ABS microcomputer 16 as it is.

Next, how the applied wheel speed pulse is read by the CPU 24 in the DWS control unit 21 described with reference to FIG. 4 will be described.
The wheel speed pulse input to the CPU 24 in FIG.
Each is a pulse signal as shown in FIG. CPU
In 24, each of the applied wheel speed pulses is counted for each predetermined measurement cycle Δt, and each of the tires W1 to W4 is counted.
The rotation angular velocity (see FIG. 1) is calculated.

By the way, since the cycle of the wheel speed pulse input to the CPU 24 and the measurement cycle Δt in the CPU 24 are asynchronous, the cycle of the wheel speed pulse and the measurement cycle Δt are as shown in FIG. 7 (a). Sometimes have a relationship,
There may be a relationship as shown in FIG. That is, in the case shown in FIG. 7A, the number N of rising edges of the wheel speed pulse within the measurement cycle Δt is N = x, but in the case shown in FIG. 7B, the wheel within the measurement cycle Δt. The number N of rising edges of the fast pulse becomes N = x-1. As described above, when the relationship between the start timing and the end timing of the measurement cycle Δt and the rising edge of the wheel speed pulse is different, the number of wheel speed pulses counted within the same measurement cycle Δt has an error of ± 1. May occur. In particular, when the vehicle is traveling at a low speed, the number of wheel speed pulses is small, and the error rate becomes large.

Therefore, in this embodiment, FIG.
As shown in (c), the time of occurrence of the last detected rising edge in each measurement period Δt, for example, t _x-1, t _X.
I tried to remember. Then, the rotational angular velocity ω of the tire
Is x, where x is the number of rising edges of the wheel speed pulse counted within a certain measurement cycle Δt, then ω = (k1 · x) / (t _x −t _x−1 ) (1) where k1: constant I was asked by. As a result, no error occurs due to the fact that the cycle of the wheel speed pulse and the measurement cycle Δt are asynchronous, the wheel speed pulse can be accurately counted, and the rotational angular speed of each tire can be calculated without error. .

FIG. 8 is a flowchart showing the procedure of the above-described tire rotational angular velocity calculation processing in the CPU 24 (see FIG. 4). Next, with reference to FIG. 8, a method for calculating the rotational angular velocity of the tire will be described more specifically.
The CPU 24 performs a counting process of the applied wheel speed pulse. This process is performed according to the flowchart of FIG. That is, when the input of the rising edge of the wheel speed pulse is determined (step S1), the time when the rising edge is input is stored in a time memory (this time memory uses the storage area of the RAM 26 in FIG. 4). It is stored (step S2). And a pulse counter (this pulse counter is also RAM2
6 storage areas are used. ) Is incremented by one.

The above processing is repeated. On the other hand, the tire rotation angular velocity calculation processing is performed according to the flowchart shown in FIG. That is, a measurement timer for measuring the measurement cycle Δt (this measurement timer also has, for example, the RAM 26).
Storage area is used. It is determined whether or not the time measured in () has reached Δt (step S1).
1) If it is determined that the measurement timer has reached the measurement cycle Δt (Δt can be set to, for example, a comma several seconds to several seconds), the measurement timer is reset (step S12). As a result, the measurement timer starts counting from 0 again. Further, the time t at which the last rising pulse in the previous measurement cycle stored in the work register W1 formed in the storage area of the RAM 26 is detected.
_tx is moved to another work register W2 (step S13). Then, the time t _x (the time stored in step S2) stored in the time memory is stored in the work register W1 (step S14).

As a result, the work register W2 stores the time t _x-1 at which the last rising edge in the immediately preceding measurement cycle was detected, and the work register W1 stores the last rising edge in the current measurement cycle. The detected time t _x is stored. Then
The value of the pulse counter is stored in another work register W3. Then, the pulse counter is cleared.

The three work registers W1 and W
2, the data stored in W3 are read out, and the rotational angular velocity ω of the tire is calculated (step S16). This calculation is performed based on the above-mentioned formula (1). As described above, the rotational angular velocity of the wheel is accurately calculated without error for each measurement cycle Δt.

In the above case, the falling edge may be detected instead of the rising edge of the wheel speed pulse. The wheel speed pulse number counting process and the tire rotation angular velocity calculating process described above are performed for each wheel speed sensor because four wheel speed sensors 1 are provided.

Instead of the tire rotational angular velocity calculation processing as described above, the following calculation processing may be performed. That is, referring to FIG. 9, the time t1 at which the first rising edge (or falling edge) of the wheel speed pulse is detected after the start of measurement is stored, and the rising (or rising) of the wheel speed pulse per tire rotation is stored. (Decreasing) An integer n (n = 1, 2, 3, ...) times the number N0 of edges, and the detection time t2 of the rising edge (or falling edge) of the first wheel speed pulse is stored, and the rotational angular velocity ω of the tire is stored.
Can be calculated by the following equation (2) ω = (k2 · n) / (t2-t1) (2) where k2 is a constant. When such a method of calculating the rotational angular velocity is used, even if the protruding pitch of the teeth 10a in the sensor rotor 10 (see FIG. 3) varies, the variation does not cause an error in the rotational angular velocity ω. Therefore, more accurate calculation of the rotational angular velocity can be performed.

In the calculation of the rotational angular velocity, the wheel speed pulses from the four wheel speed sensors 1 are detected,
The rotational angular velocity is calculated for each of the tires W1 to W4. FIG. 10 is a flowchart showing a processing procedure in the CPU 24 when calculating the rotational angular velocity described with reference to FIG.

Next, the method of calculating the rotational angular velocity will be described more specifically with reference to FIG. When the measurement of the wheel speed pulse is started, for example, a rising edge of the wheel speed pulse is detected (step S21). When the first rising edge is detected, the detection time t1 is stored in the time memory 1 (step S22). Further, the count value of the pulse counter is set to "1" (step S23).

Then, it is judged whether or not the rising edge of the next wheel speed pulse is detected (step S2).
4) Every time a rising edge is detected, the pulse counter is incremented by 1 (step S25). Then, it is determined whether or not the count value of the pulse counter has become a predetermined integer n times the number N0 of rises of the wheel speed pulse per one rotation of the tire (step S26), and the value of the pulse counter becomes N0 × n. The processes of steps S24 and S25 are repeated until the time is reached.

The count number of the pulse counter is N0.
When it is determined that xn has occurred, and the next rising edge of the wheel speed pulse is detected (steps S26, S
If YES in step 27, the time t2 at which the rising edge of the last wheel speed pulse detected in step S24 is detected is stored in the time memory 2 (step S2).
8).

Then, the pulse counter is cleared in preparation for the start of the next measurement (step S29), and the rotational angular velocity ω of the tire is calculated by the above equation (2) using the times stored in the time memory 1 and the time memory 2. It is calculated (step S30). The time memory 1 described in FIG.
The time memory 2 is also formed using the storage area of the RAM 26 in FIG.

The detection processing of the rotational angular velocity ω described above with reference to FIG. 8 or FIG. 10 is performed in parallel on the basis of the wheel speed pulses from the four wheel speed sensors 1 for four tires. It is preferable that the rotational angular velocity is calculated at the same time. This is because, as will be described later, in the detection of a decrease in tire air pressure, a tire whose air pressure is relatively low is detected based on the rotational angular velocities of the four tires, so the rotational angular velocities of the tires are the same at the same time. This is because the detected rotational angular velocity leads to more accurate detection.

Next, a method of detecting a decrease in tire air pressure will be described. In the tire arrangement diagram of the four-wheel vehicle shown in FIG. 11, the rotational angular velocity of the front left tire W1 is F1, the rotational angular velocity of the front right tire W2 is F2, the rotational angular velocity of the rear left tire W3 is F3, and the rear right tire W4. The rotation angular velocity of is set to F4. At this time, a pair of diagonal tires W
Determination for detecting the next decrease in tire air pressure by obtaining the ratio dF between the sum F1 + F4 of the rotational angular velocities of 1 and W4 and the sum F2 + F3 of the rotational angular velocities of another pair of tires W2 and W3 on another diagonal line Equation (3) can be obtained.

DF = (F1 + F4) / (F2 + F3) (3) Now, if the air pressures of the four tires W1 to W4 are all normal, all of F1 to F4 are equal, and therefore dF =
It becomes 1. On the other hand, when the air pressure of any one of the tires drops, dF ≠ 1. _{Thus, dF> (1 + a 1} ), _{or, dF <(1-a 2} ) where, a _1, a _2: When the constant air pressure of any tire can be detected that the decrease.

By using the above determination formula (3), the rotational angular velocity of the decompressed tire among the four tires can be detected as a relative change amount with respect to the other three tires having normal air pressure. Therefore, as described in the prior art, since the rotational angular velocity of the pressure-reduced tire is not included in the comparison reference amount,
The detection accuracy does not fluctuate or deteriorate, and accurate detection is possible.

If the judgment formula (3) according to this embodiment is used, any one of the four tires W1 to W4 or two tires W1 and W4 on the diagonal line.
Alternatively, the decrease in the air pressure of W2 and W3 can be correctly detected. Next, a method of specifying which of the four tires W1 to W4 has the lowered air pressure when the tire pressure drop is detected will be described.

In the above judgment formula (3), if dF> 1, it can be specified that the depressurizing tire is W1 or W4, and if dF <1, the depressurizing tire can be specified as W2 or W3. Further, in the above-mentioned case, when the vehicle is in a straight traveling state, if F1> F2, the pressure reducing tire is W1 F1 <F2, if the pressure reducing tire is W2 F3> F4, if the pressure reducing tire is W3 F3 <F4, the pressure reducing tire is The tire can be identified as W4.

By using the above-mentioned judgment formula (3), two tires which are not on a diagonal line, for example, two front tires W1 and W2 or two rear tires W3 and W4, simultaneously decrease in air pressure. If it occurs, the decrease in tire air pressure may not be detected. Therefore,
After performing the detection determination of the tire pressure drop by the determination formula (3) described above, under the condition that the vehicle is traveling at a substantially constant speed and in a substantially straight line, the sum F1 + F2 of the rotational angular velocities of the front tires W1 and W2, It is preferable to compare with the sum F3 + F4 of the rotational angular velocities of the rear tires W3 and W4, and if there is a large or small value, it is preferable to specify that the larger one is the tire in which the air pressure is decreasing. That is, if (F1 + F2) / (F3 + F4)> C ₀ (C ₀ : a constant determined by the vehicle), the air pressures of W1 and W2 have decreased, and (F1 + F2) / (F3 + F4) <C ₀ (C ₀ : vehicle It is preferable to determine that W3 and W4 have a decrease in air pressure.

Whether or not the vehicle is traveling at a constant speed in the above case may be determined as follows. That is, when the rate of change of the average value of the rotational angular velocities of the four tires obtained from the four wheel speed sensors is within a certain prescribed value, it can be determined that the vehicle is traveling constantly. on the other hand,
When it goes out of the certain specified value, for example, when the rate of change increases from the specified value in the increasing direction, it can be determined that the vehicle is in an accelerating state. When the vehicle exceeds the decreasing direction, it can be determined that the vehicle is in the decelerating state. As described above, by determining whether or not the vehicle is traveling at a constant speed based on the output of the wheel speed sensor as described above, it is not necessary to provide a G sensor or the like in this DWS, and a simple configuration can be achieved. There are advantages.

By the way, in the detection of the decrease in tire air pressure using the above-mentioned judgment formula (3), as described above, when the dynamic load radius of the tire changes, the rotational angular velocity of the tire in which the change occurs changes to that of other tires. It is based on the basis that it changes with the angular velocity of rotation. However, as mentioned above,
The dynamic load radius of the tire is not only the change in tire pressure but also the load on the tire, the rotation speed of the tire, the slip angle of the tire, the camber angle of the tire, whether the vehicle is accelerating or braking, and the vehicle is cornering. It also varies depending on whether or not the tire is worn.

Therefore, in order to accurately detect the decrease in the tire air pressure, in order to eliminate the fluctuations in the dynamic load radius due to the above items, the detection of the decrease in the tire air pressure is prohibited under certain specific conditions, or It is necessary to correct the calculated rotational angular velocity of the tire. Hereinafter, the case where the detection is prohibited and the case where the calculated rotational angular velocity is corrected will be sequentially described. When prohibiting the detection of low air pressure : (1) ~
There are cases of (6).

(1) When the vehicle is in an extremely low speed state, the wheel speed sensor 1 shown in FIG. 3 cannot obtain an AC voltage signal e _i sufficient for binarization. Therefore, the output of the wheel speed sensor 1 may not be properly binarized. Therefore, when the vehicle speed is equal to or lower than a predetermined constant speed, detection of the wheel speed pulse is prohibited.

As a specific method for prohibiting the detection of the wheel speed pulse, for example, if the number of counted pulses is less than a predetermined specified value in the measurement period Δt described with reference to FIG. . Furthermore, preferably, when there is a sudden increase or decrease between the number of pulses in a certain measurement cycle Δt and the number of pulses in the next measurement cycle Δt, detection of a decrease in tire air pressure is prohibited. This is because the rapid increase or decrease in the number of pulses within a certain measurement cycle Δt may be due to, for example, tire slip, and in such a case, using the data may result in an erroneous determination. Is higher.

Furthermore, in the above-mentioned case, more preferably, the generation cycle of the given wheel speed pulse is monitored, and when the generation cycle of the wheel speed pulse exceeds a specified value, a pulse within the measurement cycle Δt including the pulse is included. The number-based tire pressure drop detection is prohibited. This is because if the generation cycle of the wheel speed pulse exceeds the specified value, it is possible that the tire slips, for example.

(2) When the vehicle is suddenly accelerated, the tires may slip, which causes erroneous detection. Therefore, the ratio of the rotational angular velocities of the driving wheels and the non-driving wheels of the vehicle, for example, the front wheels and the rear wheels is calculated, and if the value exceeds a specified value, detection is prohibited. In this case, the ratio between the rotational angular velocity of the driving wheel and the rotational angular velocity of the non-driving wheel is respectively the average value of the rotational angular velocity of the two front tires which are the driving wheels and the rotation angular velocity of the two rear tires which are the non-driving wheels. The average value of the angular velocities may be used.

(3) When the vehicle is cornering abruptly, skid or the like occurs on the tire, which may cause erroneous detection. Therefore,
The radius of curvature R of the road on which the vehicle is traveling is calculated by the following equation (4).
If the value R is below the specified value, the detection is prohibited.

[0062]

[Equation 1]

However, F1, F2, F3, F4: front left tire, front right tire, rear left tire, rear right tire rotational angular velocity, A: constant determined by the vehicle, that is, the road on which the vehicle is traveling is the hairpin In the case of a curve having a relatively small radius of curvature such as a curve or a spoon curve, detection of a decrease in tire air pressure is prohibited.

(4) While the vehicle is cornering, if the vehicle speed is fast, or if the cornering radius is small, a large lateral G is applied, and erroneous detection may occur due to tire skid. Therefore, the lateral G that occurs in the vehicle is estimated by the following equation (5), and when this value exceeds the specified value, detection is prohibited. G = B | {(F1 + F3)-(F2 + F4)} (F1 + F2 + F3 + F4) | (5) However, F1, F2, F3, F4: front left tire, front right tire, rear left tire, rear right tire rotational angular velocity, B: Constant determined by vehicle Note that instead of estimating the lateral G that occurs in the vehicle based on the above equation (5), a G sensor is attached to the vehicle and the lateral G that occurs in the vehicle is detected by the G sensor. May be.

(5) When the vehicle changes from straight running to cornering, or from cornering to straight running, that is, at the beginning or end of cornering, the behavior of the vehicle is in a transient state, and load movement in the vehicle It is indefinite and may cause erroneous detection of tire pressure drop detection. Therefore, detection is prohibited at the beginning and the end of cornering when the behavior of the vehicle is in a transient state.
The determination as to whether or not to prohibit the detection may be the value of the lateral G generated in the vehicle (this value may be the value estimated by the above-described equation (5) or may be the value measured by the G sensor). Detection is prohibited when the rate of change of (.) Exceeds the specified value.

(6) While the ABS, parking brake, traction control device, etc. provided in the vehicle are in operation, the wheel rotation is not in a normal rotation state, and tire slip may occur, which is erroneous for the DWS. It becomes a factor of detection. Therefore, the ABS, the parking brake, and the traction control device are connected to the DWS by signal lines, respectively, and when the ABS, the parking brake, or the traction control device is operating, a signal indicating that the DWS is operating is given. To Then, in the DWS, if any signal indicating that the operation is in progress is given, the detection process is not performed.

Each of the specified values serving as a criterion for determining whether or not to prohibit the detection of each of the above (1) to (5) is predetermined and stored in the non-volatile memory 27 (see FIG. 4). Therefore, the CPU 24 reads the specified value stored in the non-volatile memory 27 and compares it with the specified value to determine whether to perform the tire air pressure drop detection process or to prohibit the tire pressure decrease. When correcting the angular velocity of rotation : (1) and (2) below
In some cases.

(1) As described above, the dynamic load radius of the tire changes not only with the change of the tire air pressure but also with the traveling speed of the vehicle. Therefore, in order to accurately extract the relationship between the dynamic load radius of the tire and the air pressure, for each traveling speed of the vehicle, the variation to be given to the dynamic load radius of the tire is obtained in advance, and when the tire pressure drop detection processing is performed. However, it is necessary to correct this variation, and eventually the rotational angular velocity of the tire.

If the variation of the dynamic load radius of the tire with respect to the traveling speed of the vehicle is Δr, then Δr = f (v), where f is a function determined by the vehicle, v is the traveling speed of the vehicle, and this is four wheels. average rotation angular velocity substitutable now, if the radius at the time of stop of the normal tire pressure and r _0, the dynamic load radius change of the tire _{(r 0 + Δr) / r} 0 = 1 + Δr / r 0 = 1 + f (V) / r ₀ = 1 + Cf (v) where C: constant Therefore, the rotational angular velocity of the tire is Fx (Fx = F1, F
2, F3 or F4), there is a relationship of Fx∝ (1 / r ₀ ),

[0070]

[Equation 2]

Is the actual rotational angular velocity of the tire. Therefore, the rotational angular velocity Fx is corrected to Fx = {1 + Cf (v)} Fx ′. Alternatively, the change rate of the rotational angular velocity of the tire is calculated for each representative velocity of the vehicle, for example, 50 Km /
h, 100 km / h, 150 km / h may be measured in advance, and these may be stored in the non-volatile memory 27 or the ROM as the correction amount of the detected rotational angular velocity. Then, one of the change rates may be read from the non-volatile memory 27 in accordance with the traveling speed of the vehicle, and the rotational angular speed detected thereby may be corrected.

(2) While the vehicle is cornering,
The dynamic load radius of the tire varies depending on the lateral G generated in the vehicle. Therefore, while the vehicle is cornering, the rotational angular velocity also changes due to the change in the dynamic load radius of the tire, which needs to be corrected. By the way, whether the vehicle is in a straight running state or during cornering can be determined as follows based on the output of the wheel speed sensor. That is, the front left and right tires W1, W2 and the rear left and right tires W3,
When both the difference or the ratio of the rotational angular velocities of W4 exceed a certain specified value with the same sign, it can be determined that the vehicle is cornering. And otherwise,
It can be determined that the vehicle is traveling straight. Then, when it is determined that the vehicle is cornering, the following correction is performed. In this way, if it is determined whether the vehicle is in a straight running state or during cornering based on the output of the wheel speed sensor, it is not necessary to provide a steering wheel deviation sensor in this DWS, and the configuration is cheaper and simpler. be able to.

In FIG. 12, when a lateral G is applied to the vehicle, a rotational moment is generated in the vehicle about the roll center, and a force proportional to this is applied to each tire W1, W3, W2.
Acts on W4. The dynamic load radius of the tire is affected by the load as described above, and changes in proportion to the load. Therefore, when the vehicle is cornering, the variation can be expressed as a function of the lateral G. If this variation is Δr and the initial tire radius is r ₀ , the change in the dynamic load radius of the tire is (r ₀ + Δr) / r ₀ = 1 + Δr / r ₀ = 1 + f (G) where f: vehicle It is a function determined by each tire and is determined for each tire.

Therefore, when the vehicle is cornering, if the rotational angular velocity Fx (Fx = F1, F2, F3 or F4) is applied to each tire, then Fx '= Fx * (1 + f (G)).
Thus, the rotational angular velocity can be corrected. The correction coefficient f (G) described above may be expressed as a continuous function, or may be measured for each representative value of G and stored in the non-volatile memory 27 as a correction coefficient. Good.

When the rotational angular velocity of the tire calculated as described above is corrected, the rotational angular velocity of the tire detected during acceleration or deceleration of the vehicle or the rotational angular velocity detected during cornering of the vehicle is corrected. Even if it is the angular velocity,
It is possible to detect the decrease in tire air pressure by using those in which the rotational angular velocities of the tires have been corrected. Therefore, it is possible to reduce the state in which the tire pressure drop detection cannot be performed, and it is possible to avoid the state in which the tire air pressure drop detection cannot be performed for a long period of time due to road conditions or the like.

Next, the depressurized tire discrimination control performed by the CPU 24 shown in FIG. 4 will be described with reference to the flowchart. FIG. 13 is a flow chart showing an initialization processing routine necessary before the processing for discriminating the deflated tire. The initialization process is necessary for the following reasons. Even if the air pressures of the four tires W1, W2, W3, W4 of the vehicle are all normal, the four tires are different due to the difference in the load applied to each tire due to the weight distribution of the vehicle, the wear of the tire, the variation in the manufacturing of the tire, and the like. The dynamic load radii of are not all the same. Therefore, it is indispensable to correct the initial variations in the dynamic load radii of the four tires by initialization in the subsequent accurate detection of the decrease in tire air pressure.

Referring to FIG. 13, the initialization process is started based on the operation of the initialization switch 15 (see FIGS. 1 and 4) (step S41). When it is determined that the initialization switch 15 is turned on, the CPU 24 writes the initialization flag in the nonvolatile memory 27 (step S4).
2). This initialization flag is written in the nonvolatile memory 27 when the power of the DWS is turned off during the initialization process.
The correction coefficient may not be obtained correctly. And if this incorrect correction factor is used, the DWS may make a false detection. Therefore, by writing the initialization flag in the non-volatile memory 27,
Is intended to guarantee the contents of.

Next, the display elements W1 to W4 (see FIG. 4) of the four tires on the display 22 are blinked to notify the driver that the initialization process is being performed (step S4).
3). After the initialization switch 15 is pressed, the vehicle is driven straight by the driver and at a substantially constant speed. The CPU 24 determines whether or not the vehicle is traveling straight and at a constant speed based on the wheel speed pulse from the wheel speed sensor (step S44). As described above, whether the vehicle is traveling straight is determined by the front left and right tires W1, W.
2. If the difference or the ratio of the rotational angular velocities of the rear left and right tires W3, W4 does not exceed a certain specified value with the same sign, it is determined that the vehicle is traveling straight.

Whether or not the vehicle is traveling at a constant speed is determined if the rate of change of the average value of the wheel speed pulses given by the four wheel speed sensors is within a specified value. Is determined. In this case, the rotational angular velocities F1, F2, F3, F4 of the four tires are detected. Further, the rotational angular velocity of any one tire, for example, F1 is used as a reference value, and the ratios of the rotational angular velocity of the other tires to this reference value F1 are respectively obtained and used as the correction coefficient for each tire. That is, the correction coefficient C2 = F2 / F1 for the tire W2, the correction coefficient C3 = F3 / F1 for the tire W3, and the correction coefficient C4 = F4 / F1 for the tire W4 (step S45).

Then, the obtained correction coefficients C2 and C
3, C4 are stored in the non-volatile memory 27 (step S46). On the other hand, the initialization flag written in the non-volatile memory 27 is erased (step S47), and the display 22
The tire display lamp of is turned off (step S48), and this process ends. After the initialization process is completed, when the DWS is operated, that is, when the vehicle ignition key is turned on, the CPU 24 determines whether or not the initialization flag is written in the nonvolatile memory 27, and if When the initialization flag is written, the request is displayed on the display 22 so as to request the initialization again. Alternatively, it may be notified by a buzzer or the like.

Next, with reference to the flow chart shown in FIG. 14, the depressurized tire determination processing will be described. First, the wheel speed pulse given from the binarization circuit 14 of the ABS control unit described in FIG. 4 is read (step S51). Then, the read wheel speed pulse is
Whether or not it is the pulse reading prohibition condition (whether or not it is (1) when prohibiting the detection of the decrease in the air pressure described above) is determined (step S52), and if the pulse reading prohibition condition is satisfied, the subsequent processing is performed. I don't know.

If the pulse reading prohibition condition is not satisfied, the rotational angular velocities F1, F2, F3, F4 of the tires are calculated (step S53). Then, the calculated rotational angular velocity F1
Based on F4, the vehicle prohibits the above-described detection prohibition conditions ((2) in the case of prohibiting the above-described detection of decrease in air pressure)
It is determined whether or not (6)) is satisfied (step S54). If the vehicle is in the detection prohibition condition, the subsequent processing is not performed.

If the vehicle is not in the detection prohibition condition, it is further determined whether or not the correction of the rotational angular velocities F1 to F4 is necessary (step S55). As described above, the correction depends on the traveling speed of the vehicle and whether or not the vehicle is cornering. If correction is necessary, the calculated rotational angular velocities F1 to F4 of the tires are corrected (step S5).
6).

Then, based on the corrected rotational angular velocities F1 to F4, the sum of the rotational angular velocities of the pair of tires on the diagonal line described above, for example, the rotation of F1 + F4 and the other pair of tires on the other diagonal line. The presence or absence of the tire with reduced air pressure as described above is determined based on the determination formula (3) obtained by taking the ratio dF with the sum F2 + F3 of the angular velocities, and the tire with reduced air pressure is specified (step S5).
7).

In the above-mentioned embodiment, the rotation angular velocity of the tires W1 to W4 is calculated by using the output pulse of the wheel speed sensor 1 provided in the ABS.
For vehicles not equipped with S, a wheel speed sensor dedicated to DWS may be attached.

[0086]

As described above, according to the present invention, it is possible to accurately detect whether or not any one of the tires has a decrease in air pressure based on the rotational angular velocities of the four tires. It is possible to provide a useful tire pressure drop detecting device. Further, since the detection is performed using the rotational angular velocity of the tire, the device of the present invention can be constructed at low cost.

[Brief description of drawings]

FIG. 1 is a diagram showing an outline of a vehicle equipped with a tire pressure drop detecting device (DWS) and a conventionally known ABS according to an embodiment of the present invention.

FIG. 2 is a perspective view showing an example of a mounting structure of a wheel speed sensor.

FIG. 3 is an illustrative view for explaining a principle of rotation detection by a wheel speed sensor.

FIG. 4 is a block diagram showing an electrical configuration of a DWS according to an embodiment of the present invention.

FIG. 5 is a circuit block diagram showing an electrical configuration of a DWS according to another embodiment of the present invention.

FIG. 6 is a block diagram showing a circuit configuration example of a DWS according to still another embodiment of the present invention.

FIG. 7 is a diagram illustrating a relationship between a wheel speed pulse input to a CPU 24 and a measurement cycle.

FIG. 8 is a flowchart showing a procedure of tire rotational angular velocity calculation processing.

FIG. 9 is a timing chart for explaining another processing method of tire rotational angular velocity calculation processing.

10 is a flowchart showing a processing procedure when calculating the rotational angular velocity described in FIG.

FIG. 11 is an array diagram of tires of a four-wheel vehicle.

FIG. 12 is an illustrative view for explaining a force acting on each tire when a lateral G is applied to the vehicle.

FIG. 13 is a flowchart showing an initialization processing routine necessary before the processing for determining a depressurized tire.

FIG. 14 is a flowchart showing a determination process for a depressurized tire.

FIG. 15 is a graph showing the influence of air pressure on the dynamic load radius of a tire.

FIG. 16 is a graph showing the effect of load on the dynamic load radius of the tire.

FIG. 17 is a graph showing the effect of speed on the dynamic load radius of a tire.

FIG. 18 is a diagram showing an influence of a slip angle and a camber angle on a dynamic load radius of a tire.

FIG. 19 is a graph showing the influence of vehicle driving or braking on the dynamic load radius of a tire.

FIG. 20 is a graph showing the relationship between tire dynamic load radius and tire wear.

[Explanation of symbols]

 1 Wheel Speed Sensor 10 Sensor Rotor 15 Initialization Switch 21 DWS Control Unit 22 Display 24 CPU 27 Nonvolatile Memory W1, W2, W3, W4 Tire F1, F2, F3, F4, ω Tire Rotational Angular Speed

Claims (5)

[Claims] 1. A tire pressure drop detecting method for a four-wheel vehicle having four tires, comprising: a rotational angular velocity F1 of a front left tire W1 of a four-wheel vehicle; a rotational angular velocity F2 of a front right tire W2; and a rear left tire. The rotational angular velocity F3 of W3 and the rotational angular velocity F4 of the rear right tire W4 are respectively detected, and from the detected rotational angular velocities of the respective tires, the sum (F1 + F4) of the rotational angular velocities of the pair of tires on the diagonal line and the other pair of tires determine the specific dF of the sum of the rotational angular velocity (F2 + F3), determined ratio dF is ₍₁ + a 1) and (1-a ₂₎ (where
a ₁ and a ₂ are constants determined by the vehicle), it is determined that there is no tire whose air pressure is decreasing, and when the obtained ratio dF is outside the above range, the tire whose air pressure is decreasing is determined. A method for detecting a decrease in tire air-pressure, characterized by determining that there is. 2. The tire pressure drop detecting method according to claim 1, wherein when the obtained ratio dF is dF> 1, the depressurized tire is a front left tire W1 or a rear right tire W4, and dF <1. A method for detecting a decrease in tire air pressure, characterized in that the depressurized tire is specified as the front right tire W2 or the rear left tire W3. 3. The tire pressure drop detecting method according to claim 2, further comprising the step of specifying the depressurized tire according to claim 2.
When the vehicle is in a straight running state, if F1> F2, the decompression tire is the front left tire W1, if F1 <F2, the decompression tire is the front right tire W2, and if F3> F4, the decompression tire is the rear left tire W3, F3 < If it is F4, the depressurized tire is identified as the rear right tire W4. 4. The method for detecting a decrease in tire air pressure according to claim 1, when it is determined that there is a tire having a decrease in air pressure, the vehicle is traveling at a substantially constant speed and in a substantially straight line. In, the sum of the rotational angular velocities of the front tires W1 and W2 (F1 + F2) and the sum of the rotational angular velocities of the rear tires W3 and W4 (F3 + F4) are compared. A method for detecting a decrease in tire air-pressure, characterized in that the tires are both specified to have a decrease in air-pressure. 5. A vehicle for a four-wheel vehicle having four tires.
A device for detecting a decrease in air pressure, comprising: a rotational angular velocity for detecting each rotational angular velocity of four tires
Degree detection means, the four tire rotations detected by the rotation angular velocity detection means
Of the four tires in a four-wheeled vehicle,
The sum of the rotational angular velocities of a pair of tires on the diagonal and the other
Calculating means for obtaining the ratio with the sum of the rotational angular velocities of the pair of tires,
And the ratio calculated by the calculating means is (1 + a₁) And (1
-A₂) (However, a₁, A ₂Is determined by the vehicle
Number), there is no tire whose air pressure has dropped.
If the above ratio is not within the above range, the air pressure is low.
A decompression tag that detects the presence of a decompressing tire
Low tire pressure characterized by including an ear detecting means
Lower detection device.