JPH07125512A - Tire air pressure drop judging method and tire air pressure drop detecting device using it - Google Patents

Abstract

PURPOSE:To provide a tire air pressure drop judging method and a tire air pressure drop detecting device using this method, capable of reliably detecting tire air pressure drop even in high-speed traveling of a vehicle. CONSTITUTION:The mean values of the judging values at the time that four tires W1 to W4 are previously and individually depressurized are found for every speed, and the reference speed is set out of the speeds. The square value of the ratio of the other speed corresponding to this reference speed is taken in the axis of an abscissa, and the ratio of the judging value of the other speed corresponding to the judging value of the reference speed is taken in the axis of an ordinate, and the relational expression between the speed and the judging value is found, so as to be previously stored in a ROM provided on a control unit 2. In the actual traveling of a vehicle, the speed is calculated on the basis of the rotational angle speeds of the tires W1 to W4, and the value of the relational expression corresponding to this speed is found, and the calculated judging value is divided by this value, thereby the calculated judging value is corrected according to the speed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for detecting a decrease in air pressure of each tire of a four-wheel vehicle, and more specifically, it reliably detects a decrease in air pressure even when the vehicle is traveling at high speed. The present invention relates to a tire air pressure drop determining method and a tire air pressure drop detecting device using this method.

[0002]

2. Description of the Related Art In recent years, a device for detecting a decrease in tire air pressure has been invented as one of safety devices for four-wheeled vehicles such as passenger cars and trucks, and some of them have been put into practical use. The importance of the air pressure drop detecting device has been recognized and developed mainly due to the following reasons. That is, when the air pressure is low, the temperature of the tire rises due to the increased deflection. When the temperature rises, the strength of the polymer material used for the tire decreases, leading to tire burst. In general, even if the air in the tire escapes by about 0.5 atm, the driver often does not notice it. Therefore, a device that can detect it has been desired.

A method for detecting a decrease in air pressure in the above device
Is, for example, four tires W of the vehicle ₁, W₂, W₃, W
_Four(Note that tire W₁, W₂Corresponds to the front left and right wheels respectively
And tire W₃, W_FourRespectively correspond to the rear left and right wheels.
Further, hereinafter, when collectively referred to, "tire W_i". )
Each angular velocity F of₁, F₂, F₃, F_Four(Hereinafter, collectively
If you want to_i". ) Based on the difference
There is a way.

[0004] According to this method, the rotational angular velocity F _i of the tires W _i, for example on the basis of the signal outputted from the wheel speed sensor mounted on the tire W _i, is detected for each predetermined sampling period. This rotational angular velocity F _i is the dynamic load radius of each tire W _i (the apparent rolling radius of the tire is calculated by dividing the distance traveled by the vehicle during one rotation of the tire during one revolution by 2π). All are the same, all are the same if the vehicle is running straight.

On the other hand, the dynamic load radius of the tire W _i is, for example, varies with changes in the pressure of the tire W _i. That is, when the air pressure of the tire W _i decreases, the dynamic load radius becomes smaller than that under normal internal pressure. Therefore, the rotational angular velocity F _i of the tire W _i becomes faster than that at the normal internal pressure. That is, it is possible to detect the decrease in the air pressure of the tire W _{i based on} the difference in each rotational angular velocity F _i . A judgment formula for detecting a decrease in the air pressure of the tire W _i is shown in the following formula (1) (JP-A-63-305011 and JP-A-4-212609).
No.

[0006]

[Equation 1]

For example, if the dynamic load radii of the tires W _i are all the same, the rotational angular velocities F _i are all the same (F ₁ = F ₂ = F ₃ = F ₄ ), and the judgment value D is 0. is there. Therefore, the thresholds D _TH1 , D _TH2 (D _TH1 , D _TH2 >
0) is set, and if the determination formula of D <-D _TH1 or D> D _TH2 (2) is satisfied, it is determined that there is a tire W _i whose air pressure has dropped, and the above determination formula is not satisfied. In this case, it can be determined that the air pressure has not dropped.

[0008]

By the way, the tire W _i
The dynamic load radius of the property increases as the vehicle speed increases (this property is called treadlifting)
(See FIG. 7). This is because the centrifugal force acting on the tire W _i increases as the vehicle speed increases. However, this treadlifting makes it possible to easily detect a decrease in air pressure during low-speed traveling, but it becomes very difficult to detect a decrease in air pressure during high-speed traveling.

More specifically, during low speed running, the centrifugal force acting on the tire W _i whose air pressure is lowered as shown in FIG. 8 (a) is small, so that the dynamic load radius R1 is as shown in FIG. It becomes smaller than the dynamic load radius R2 of the tire W _{i with} normal internal pressure shown in b). Thus, during low-speed running, the difference between the rotational angular velocities F _i of the tires W _i of the rotational angular velocities F _i and a normal internal pressure of the tire W _i whose air pressure has dropped becomes remarkable. Therefore, it is possible to easily detect the decrease in the air pressure with the relatively large determination value D.

On the other hand, during high speed running, the air pressure drops
Tire W_iIs a large centrifugal force acting on the tire itself
For this reason, the tire W whose air pressure shown in FIG.
_iAs shown in FIG. 9 (a), the dynamic load radius R1 of
Normal internal pressure tire W shown in (b) _iDynamic load radius R2
It will grow almost as much as it does. Conversely, FIG.
Normal internal pressure tire W shown in (b)_iThe dynamic load radius R2 of
The tension acting on the ear itself and its centrifugal force cancel each other out.
Yes, almost unchanged. Therefore, while driving at high speed
Is a tire W whose air pressure is low_iRotational angular velocity F_i
And tire with normal internal pressure W _iRotational angular velocity F_iThe difference with
It almost disappears, and the judgment value D becomes very close to zero. That
Therefore, the judgment formula (2) above is sufficiently satisfied to ensure that the air pressure
A drop can be detected. On the other hand, when traveling at high speed, the judgment value
Since D will be far away from 0, the above judgment formula
(2) may not be satisfied. That is, while driving at high speed
At the same time, the air pressure is decreasing as it is when driving at low speed.
However, it is not possible to reliably detect a decrease in air pressure.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve the above-mentioned technical problems and to reliably detect a decrease in tire air pressure even when the vehicle is traveling at a high speed, and a tire air pressure decrease determining method and this method. It is to provide a tire air pressure drop detecting device using the.

[0012]

In order to achieve the above object, a tire pressure drop determining method according to a first aspect of the present invention is such that each tire is individually decompressed in advance and a vehicle in this state is run at a predetermined speed. Then, the determination value at that time is obtained based on the determination formula, and the determination value corresponding to a predetermined reference speed among the obtained determination values is set as the reference determination value, The correspondence relationship between the obtained determination value ratio and the speed is stored in advance, the speed of the vehicle is calculated during actual traveling of the vehicle, and the ratio corresponding to the calculated speed is stored in advance. It is characterized in that the determination value obtained based on the determination formula is corrected on the basis of the obtained correspondence ratio and the obtained ratio.

Further, in the tire pressure drop detecting device according to the second aspect of the invention, the tires are individually decompressed in advance and the vehicle in this state is run at a predetermined speed, and the determination value at that time is determined. Obtained based on the formula, set the determination value corresponding to a predetermined reference speed among the determined determination value as a reference determination value, the ratio of the determined determination value to the reference determination value and the speed And a speed calculation means for calculating a speed when the vehicle is actually traveling, and the determination value calculation means includes the above-mentioned correspondence value corresponding to the speed calculated by the speed calculation means. The ratio is obtained based on the correspondence relationship previously stored in the storage means, and based on the obtained ratio,
It is characterized in that the judgment value obtained based on the above judgment formula is corrected.

In the tire pressure drop determining method according to the third aspect of the present invention, the tires are individually decompressed in advance and the vehicle in this state is run at a predetermined speed, and the determination value at that time is determined. Obtained based on the formula, set the determination value corresponding to a predetermined reference speed among the determined determination value as a reference determination value, the ratio of the determined determination value to the reference determination value and the speed Is stored in advance, the speed of the vehicle is calculated when the vehicle is actually traveling, and the ratio corresponding to the calculated speed is obtained based on the previously stored correspondence, The threshold value is corrected based on the obtained ratio.

Further, in the tire pressure drop detecting device according to claim 4, the tires are individually decompressed in advance, the vehicle in this state is caused to travel at a predetermined speed, and the judgment value at that time is made into a judgment formula. Correspondence between the speed and the ratio of the determined judgment value to the reference judgment value is set as a judgment value corresponding to a predetermined reference speed among the calculated judgment values It includes a storage unit that stores the relationship in advance and a speed calculation unit that calculates the speed of the vehicle when the vehicle is actually traveling, and the determination value calculation unit corresponds to the speed calculated by the speed calculation unit. The above-mentioned ratio is obtained based on the previously stored correspondence, and the threshold value is corrected based on the obtained above-mentioned ratio.

[0016]

According to the above-mentioned structure of the present invention, the tires are individually decompressed, and the vehicle in this state is allowed to test-run at a predetermined speed. Here, the reason why the tire is depressurized is to obtain the ratio used for correcting the determination value, as described later. During the test run or after the test run is finished, a judgment value for judging a decrease in air pressure is obtained based on a judgment formula. Among the obtained determination values, the determination value corresponding to the predetermined reference speed is set as the reference determination value. Then, the correspondence relationship between the ratio of the other determined determination value to the reference determination value and the speed is stored.

As a form of storing the above correspondence in the storage means, for example, it is stored in the form of an approximate expression, or the speed is substituted into this approximate expression to obtain a judgment value, and the obtained judgment value and speed are obtained. And may be stored as a table. During actual traveling of the vehicle, the vehicle speed is calculated, and the determination value is obtained based on the detected rotational angular velocities of the tires. Then, the ratio corresponding to the calculated speed is obtained based on the above correspondence, and the obtained determination value is corrected based on the obtained ratio. That is, since the determination value is corrected according to the speed, it is possible to ignore the influence of so-called treadlifting that occurs during high-speed traveling, for example.

Further, in the configuration according to claim 3 or 4,
Based on the ratio corresponding to the speed of the vehicle, a threshold value that is a reference for determining whether or not the air pressure is reduced is corrected. That is, since the threshold value is corrected based on the ratio according to the speed, it is possible to ignore the influence of so-called treadlifting that occurs during high-speed traveling, for example.

[0019]

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. In the order of description, the configuration of the device will be described first, then the initial correction process and the air pressure drop detection process, and finally the speed correction process according to the present invention.

-Structure- FIG. 2 is a block diagram showing the structure of the tire pressure drop detecting device. The tire pressure drop detecting device is provided with a wheel speed sensor 1 having a conventionally known configuration provided in association with each tire W ₁ , W ₂ , W ₃ , W ₄ of a four-wheel vehicle. The output of 1 is provided to the control unit 2. The control unit 2 includes an initialization switch 3 operated by a driver, and an indicator (CRT or the like) 4 for displaying a tire whose air pressure has dropped, as will be described later.
Are connected.

FIG. 3 is a block diagram showing the electrical construction of the tire pressure drop detecting device. Control unit 2
Is composed of a microcomputer, and the hardware configuration thereof is, as shown in the figure, an I / O interface 2a required for exchanging signals with an external device, a CPU 2b as a center of arithmetic processing, and a control operation of the CPU 2b. When the control operation is performed by the ROM 2c storing the program and the CPU 2b, data and the like are temporarily written,
A RAM 2d for reading the written data is included. The ROM 2c stores in advance a relational expression between the square value of the vehicle speed and the average value of the determination values. In addition,
Details of how to obtain the relational expression will be described later.

From the wheel speed sensor 1, the tire W _i (where i corresponds to each number “1, ₂ , ₃ , 4” of each tire W ₁ , W ₂ , W ₃ , W ₄ ) A pulse signal corresponding to the number of rotations (hereinafter referred to as "wheel speed pulse") is output. The CPU 2b calculates the rotational angular velocity F _i of the tire W _i for each predetermined sampling period ΔT based on the output wheel speed pulse.

-Initial correction processing-In the following, the initial correction processing in the tire pressure drop detecting device will be described. This initial correction process is necessary for the following reason. The four tires W ₁ of the vehicle,
Even if the air pressures of W ₂ , W ₃ , and W ₄ are all normal, the four tires W ₁ , W ₁ , due to the variation (called an initial difference) within the specifications at the time of manufacturing the tire W _i .
The dynamic load radii of W ₂ , W ₃ and W ₄ are not always the same. Therefore, it is indispensable to correct the initial difference by the initial correction process in the subsequent accurate detection of the decrease in tire air pressure.

Referring to FIGS. 4 and 5, this initial correction process is started based on the driver operating the initialization switch 3 (see FIG. 2) (step S1). When the initialization switch 3 is turned on, the CPU 2b
The velocity VB _i and the traveling distance L stored in the RAM 2d are reset (initialized) by the step S
2). Here, the velocity VB _i is the longitudinal acceleration A _i described later.
Is used to calculate Next, the wheel speed pulse output from the wheel speed sensor 1 is read (step S3), and the rotational angular velocity F is determined based on this wheel speed pulse.
_i is required. Then, (the R radius of the tire W _i) V _i = R × F _i based on the speed V _i of each tire W _i is calculated (step S4), and predetermined and each speed V _i of the calculated The threshold value V _TH (for example, 10 Km / h) is compared (step S5).

As a result of the above comparison, each speed V_iOut of 1
Any threshold V_THIf there is something smaller than the speed V_iBut
VB_iIs stored in the RAM 2d as (step S1
1). Meanwhile, all speeds V_iIs the threshold V_THBigger than
If so, next RAM2d already has VB_iIs remembered
It is determined whether or not (step S6). As a result, VB
_iIs not stored, that is, VB_iIs still initialized
If it is in a state, its speed V _iIs VB_iAs RAM2d
Remembered. On the other hand, already VB_iIs stored
Has A_i= (V_i-VB_i) / ΔT (ΔT is the sample
Tire W based on the_iLongitudinal acceleration A_iBut
It is calculated (step S7).

The tires W when the longitudinal acceleration A _i is calculated for _i, the threshold A absolute value of a predetermined Each longitudinal acceleration A _i
It is determined whether it is smaller than _TH (eg, 0.1) (step S8). That is,

[0027]

[Equation 2]

It is determined whether or not As a result of this determination, even one of the calculated longitudinal accelerations A _{i has} a threshold value A _i.
If it is larger than _TH , the tire is considered to have slipped,
The speed V _i is stored in the RAM 2d as VB _i (step S11). On the other hand, the calculated longitudinal acceleration A _i
Are all smaller than the threshold value A _TH, it is next determined whether or not the vehicle is traveling straight (step S9).

In this initial correction process, it is desired to know only the difference in the dynamic load radius due to the initial difference in each tire W _i . However, during cornering, the dynamic load radius of each tire fluctuates due to the influence of lateral G and the like, so the rotational angular velocity F _i when it is determined to be cornering is not suitable for the initial correction process. Therefore, it is necessary to determine whether or not the vehicle is traveling straight.

As a result of the above determination, it is determined that the vehicle is not traveling straight.
Separately, the speed V_iIs VB_iAs RAM2d
Remembered. On the other hand, if it is determined that the vehicle is traveling straight,
Rotational angular velocity F_iIs stored in the RAM 2d (step S1
0), and speed V_iIs VB _iStored in RAM2d as
(Step S11). The process of step S11 ends
After that, the traveling distance L stored in the RAM 2d is updated.
It is renewed (step S12). That is, the sampling frequency
Only the distance traveled during the period ΔT is updated. Then this
Updated mileage L of the predetermined threshold L_TH(Ta
It is determined whether it is larger than 200 m (for example, 200 m).
Step S13). As a result, the updated mileage L is the threshold
Value L_THIf it is shorter than the above, it is the process of step S3 again.
The above processing is repeated. On the other hand, the mileage L
Threshold L _THIf it reaches, it will be stored in RAM2d by then
Rotational angular velocity F_iBased on the correction coefficient C_i(j) is calculated
(Step S14).

The above correction coefficient C _i (j) is calculated for a tire W _i
Is based on the tire W ₁ , for example, the correction coefficients C ₁ (j) and C _{2 of} each tire W _i
(j), C ₃ (j) and C ₄ (j) are C ₁ (j) = F ₁ (j) / F ₁ (j) ... (4) C ₂ (j) = F ₁ (j) / F ₂ (j) ‥‥ (5) C ₃ (j) ＝ F ₁ (j) ／ F ₃ (j) ‥‥ (6) C ₄ (j) ＝ F ₁ (j) ／ F ₄ (j) It is calculated as (7). Where j = 1 to N, where N is a RAM
2d is the number of rotational angular velocities F _i stored in 2d. That is, each correction coefficient C ₁ (j), C ₂ (j), C ₃ (j), C
₄ (j) will be calculated for each N pieces.

Next, the correction coefficient C_iimprove the accuracy of (j)
Therefore, each of the N correction coefficients C₁(j), C₂(j), C
₃(j), C_FourTake the average of (j). That is, C₁= ΣC₁(j) / N ... (8) C₂= ΣC₂(j) / N ... (9) C₃= ΣC₃(j) / N ... (10) C_Four= ΣC_FourCalculate (j) / N (11). Note that Σ means the total sum of j = 1 to N
It This average value C₁, C ₂, C₃, C_FourIs the final correction
It becomes a coefficient.

When the calculation of the correction coefficient C _i is completed, the initial correction process is completed. - air pressure reduction detection processing - When the initial correction processing is finished, the tire W _i in normal running
The air pressure drop detection process is performed. To explain this process in detail, the CPU 2b multiplies the rotation angular velocity F _i detected at each sampling period ΔT by the correction coefficient C _i to obtain the correction value F _i0 of the rotation angular velocity F _i . That is,
The CPU 2b has: F ₁₀ = C ₁ × F ₁ (12) F ₂₀ = C ₂ × F ₂ (13) F ₃₀ = C ₃ × F ₃ (14) F ₄₀ = C ₄ × F ₄ Ask for (15).

After that, the corrected rotational angular velocity F _i0 is used for detecting the decrease in the air pressure of the tire W _i . This decrease in air pressure is detected based on the judgment value D obtained by the following equation (16).

[0035]

[Equation 3]

Here, when the vehicle is traveling at a high speed, this determined judgment value D is an accurate value due to the action of centrifugal force, as described in the section "Problems to be solved by the invention". It doesn't. That is, the determination value D cannot accurately detect the decrease in air pressure. Therefore, in this embodiment, in order to make the determination value D an accurate value, the determination value D is subjected to speed correction processing.

-Velocity Correction Process-This velocity correction process is a process according to the present invention.
Based on the relational expression between the squared value of the speed V ′ of the
It is carried out according to. The speed V'is the corrected rotation angle.
Speed F_i0Tire W calculated based on_iEach speed V_i0
(V_i0= R × F _i0) Average value (V_Ten+ V₂₀+ V₃₀+
V₄₀) / 4. This speed
V'is, for example, a speed meter which is provided in advance in the vehicle.
Can also be obtained by getting a signal from the data,
By various other methods that can obtain the speed of the vehicle
You can also ask.

The above relational expression is obtained in advance before the tire pressure drop detecting device of this embodiment is shipped from the factory, and is stored in the ROM 2c as described above. Therefore, in the following, first, how to obtain this relational expression will be described, and then the details of the speed correction processing will be described. First, four somewhat from normal internal pressure the air pressure of any one of the tires W _i of the tires W ₁ to _W-4 (e.g. 30%, because: a maximum speed of the vehicle which are considered in Japan by the vehicle 180km When driving at / h, if the pressure is reduced by 30%, there is a strong possibility that the tire will burst.) Reduce the pressure and keep the other three tires at normal internal pressure. Here, the reason why the air pressure of the tire W _i is decreased is that the relational expression is obtained by actually measuring how much the determination value D changes according to the speed when the air pressure is actually decreased. Is. The vehicle is caused to travel at a certain speed V'in the above state, and the determination value D is obtained based on the above equation (16) during the traveling. Since the determination value D is obtained for each sampling period ΔT, the determination value D actually obtained for each sampling period ΔT
Is determined as the judgment value D at the speed V '. This is, for example, 20 Km / h, 30 Km / h, 40 Km / h ...
., 180 Km / h .. .., for each speed V ', and the determination value D is obtained for each speed V'. The above operation is performed for all the tires W _i , and the determination value D corresponding to each speed V ′ is obtained for each tire W _i .

When the determination value D corresponding to each speed V'is obtained for the four tires W _i , then the four tires W _i
The average value D _AV of the judgment value D at _i is calculated for each speed V '. On the other hand, an appropriate speed V'from the above speeds V '
(For example, V '= 120 Km / h) is set as the reference speed V ₀ . The horizontal value α (= (V ′ / V ₀ ) ² ) of the ratio of the speed V ′ to the reference speed V ₀ is plotted on the horizontal axis, and the average of each speed V ′ with respect to the average value D _AV0 of the reference speed V _0. A graph is drawn with the vertical axis representing the ratio β of the value D _AV (= D _AV / D _AV0 ). As a result, the graph becomes a straight line descending to the right as shown in FIG. 1, and the value β on the vertical axis of the reference speed V ₀ becomes 1. The reason why the above graph is a straight line descending to the right is that as the speed increases, centrifugal force acts on the tire W _i and the determination value D decreases. Further, the above graph intersects zero of the value β on the vertical axis when the vehicle speed is 2
Since it is about 50 Km / h, normally β is positive.

Based on the obtained graph, the relational expression f (α) between the square value α of the speed ratio and the average value β of the judgment value D
Is calculated using, for example, the least squares method. The relational expression f
Since (α) is a straight line in which the graph descends to the right,
It can be obtained as a linear expression such as (α) = − aα + b. Here, a and b are constants. The relational expression f (α) thus obtained is stored in the ROM 2c.

Next, the speed correction process during actual traveling will be described. This speed correction processing is performed when the vehicle is actually traveling. In this speed correction processing, first, based on the corrected rotational angular speed F _i0 obtained in the air pressure drop detection processing, the vehicle Speed V '
To calculate. When the velocity V'is calculated, the velocity V'is substituted into the relational expression f (α) stored in the ROM 2c. As a result, the ratio f (α) of the determination values corresponding to the calculated speed V ′ on a one-to-one basis is obtained. Based on the obtained ratio f (α) of determination values, the determination value D detected in the air pressure drop detection process is corrected. That is, assuming that the correction value is D ', the judgment value D is corrected as follows: D' = (1 / f (α)) × D (17)

The speed correction process is performed as described above. When this speed correction process is completed, it is determined whether the air pressure is reduced by the following equation (18) using the correction value D ′. D '<-D _TH1 or D'> D _TH2 (18) As a result, the judgment value D'is as shown in a and b of FIG.
If it extends from between -D _TH1 and D _TH2 , that is, if the above equation (18) is satisfied, it is determined that the air pressure has dropped. On the other hand, the judgment value D ′ is −D _TH1 , D
If it is within _TH2 , that is, if the above expression (18) is not satisfied, it is determined that the air pressure has not dropped.

In this way, the air pressure is low while the vehicle is running.
The bottom is detected. Where the air pressure is decreasing
While detecting and notifying the driver only of that
Which tire W_iThe air pressure in
It is easier for the driver to understand if it can be notified
Become. Therefore, next, the tire W whose air pressure is reduced
_iA method of identifying the will be described.

Since the correction coefficient 1 / f (α) is positive, the positive / negative of the corrected judgment value D'obtained by the above equation (14) is the value before the amendment obtained by the above equation (16). It is the same as the positive / negative of the determination value D. Therefore, if D '> 0, the tire under reduced pressure is W ₁ or W
_{If 4} D '<0, then the deflated tire is W ₂ or W
It can be specified as ₃ . Further, in this case, when the vehicle is in a straight traveling state, if F ₁ > F _2, then the decompressed tire is W ₁ F ₁ <F ₂ , and if the decompressed tire is W ₂ F ₃ > F _4. For example, if the depressurized tire is W ₃ F ₃ <F ₄ , the depressurized tire can be specified as W ₄ .

As a result of the above, when the tire W _i whose air pressure is low is specified, the result is output to the display unit 4 and displayed. As the display mode on the display 4, for example, as shown in FIG. 3, four tires W ₁ , W ₂ ,
W _3, W ₄ corresponding display lamp is to be lit at the same time. As described above, according to the speed correction processing in the tire pressure drop detecting device of the present embodiment, the determination value D calculated according to the speed of the vehicle is corrected, so that, for example, treadlifting that occurs during high speed running of the vehicle. The effect of can be ignored. Therefore, it is possible to reliably detect a decrease in air pressure even during high-speed traveling.

The embodiments have been described above, but the present invention is not limited to the above embodiments. For example, in the above-described embodiment, the determination value D is corrected in the speed correction process, but the determination value D is not corrected and the threshold value D is not corrected.
You may make it correct _TH1 and D _TH2 . That is,
First, D _TH1 ′ = f (α) × D _TH1 (19) D _TH2 ′ = f (α) × D _TH2 (20) is calculated. Next, the uncorrected judgment value D is (2
1) It is judged whether the judgment formula of the formula is satisfied.

D <−D_TH1′ Or D> D_TH2′ ‥‥ (21) As a result, if the judgment formula (21) is satisfied, the air pressure has dropped.
If the judgment formula (21) is not satisfied, the air pressure is low.
It is determined that it has not been made. Speed correction according to this modification
According to the processing, the threshold D according to the speed V '_TH1, D _TH2To
Because it is corrected, even if the vehicle is running at high speed tread
Even if the judgment value D is calculated to be low due to the effect of lifting,
It is possible to detect a decrease in air pressure.

[0048] In the above embodiment, any speed V relative to the reference speed V ₀ 'of the square value α ratio, any speed V with respect to the determination value D _AV0 for the reference speed V _0' of the determination value D _AV The configuration example in which the form of the relational expression f (α) with the ratio β is stored in advance in the ROM 2c has been described. However, for example, the value of the relational expression corresponding to the speed V ′ is obtained in advance, and each value thereof is used as a table. It may be configured to be stored in the ROM 2c. With such a configuration, the CPU 2b can save the time for calculating the value of the relational expression corresponding to the speed V '.

In addition, various design changes can be made without changing the gist of the present invention.

[0050]

As described above, according to the first or second aspect of the present invention, since the calculated judgment value is corrected according to the speed, it is possible to ignore the influence of so-called treadlifting that occurs during high speed running. You can Therefore, even during high-speed traveling, it is possible to reliably detect a decrease in air pressure. Therefore, it can contribute to safe driving.

Further, according to the configuration of claim 3 or 4, the threshold value for determining the presence or absence of a decrease in air pressure is corrected according to the speed of the vehicle. Similarly, a decrease in air pressure can be reliably detected even during high-speed traveling.

[Brief description of drawings]

FIG. 1 is a graph showing a change in a judgment value with respect to a change in speed in a tire pressure drop detecting device according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of the tire pressure drop detecting device.

FIG. 3 is a block diagram showing an electrical configuration of the tire pressure drop detecting device.

FIG. 4 is a flowchart showing an initial correction process in the tire pressure drop detecting device.

FIG. 5 is likewise a flowchart showing an initial correction process.

FIG. 6 is a diagram for explaining a threshold value that is a reference for detecting a decrease in air pressure.

FIG. 7 is a graph showing changes in dynamic load radius due to changes in speed.

FIG. 8 is a diagram for explaining a difference in dynamic load radius of a tire during low speed running of a vehicle.

FIG. 9 is a diagram for explaining a difference in dynamic load radius of tires during high-speed running of a vehicle.

[Explanation of symbols]

1 Wheel Speed Sensor 2 Control Unit 2b CPU 2c ROM 2d RAM W, W ₁ , W ₂ , W ₃ , W ₄ Tire

Claims (4)

[Claims] 1. A method for detecting whether or not the air pressure of a tire is lowered by detecting the rotational angular velocities of four tires provided in a four-wheel vehicle and substituting the detected rotational angular velocities into a determination formula. A determination value for determining, a tire pressure drop determination method for determining whether or not the tire air pressure is reduced based on a value corrected as follows of the determined determination value, Each of the tires is individually decompressed, the vehicle in this state is run at a predetermined speed, the determination value at that time is determined based on the determination formula, and the determination value is determined in advance. A judgment value corresponding to a predetermined reference speed is set as a reference judgment value, and the correspondence relationship between the speed and the ratio of the judgment value obtained with respect to the reference judgment value is stored in advance, and when the vehicle actually travels. At Both speeds are calculated, the above-mentioned ratio corresponding to the calculated speed is obtained based on the previously stored correspondence, and based on the obtained above-mentioned ratio, it is obtained based on the above-mentioned judgment formula. A method for judging a decrease in tire air pressure, characterized by correcting a judgment value. 2. A rotation angular velocity detecting means for detecting respective rotation angular velocities of four tires provided in a four-wheel vehicle, and the respective rotation angular velocities detected by the rotation angular velocity detecting means are substituted into a judgment formula, Judgment value calculating means for obtaining a judgment value for judging whether or not the tire air pressure is decreasing, and whether or not the tire air pressure is decreasing based on the judgment value obtained by the judgment value calculating means. A tire pressure drop detecting device including a judging means for judging, wherein each of the tires is individually decompressed, and a vehicle in this state is run at a predetermined speed, and the judgment value at that time is Obtained based on the determination formula, and set the determination value corresponding to the predetermined reference speed among the determined determination values as the reference determination value, and the determined determination for the reference determination value The determination value calculation means includes storage means for storing in advance a correspondence relationship between the value ratio and the speed, and speed calculation means for calculating the speed when the vehicle actually travels. The above-mentioned ratio corresponding to the calculated speed is obtained based on the correspondence relationship previously stored in the storage means, and the determination value obtained based on the above-mentioned determination formula is corrected based on the obtained ratio. A tire pressure drop detecting device characterized by: 3. A determination for detecting respective rotational angular velocities of four tires provided on a four-wheeled vehicle, and determining whether or not the tire air pressure is reduced based on the detected respective rotational angular velocities. The value is obtained based on the determination formula, and the obtained determination value is compared with the threshold value corrected as follows, and based on the result of the comparison, it is determined whether or not the tire air pressure is reduced. A tire pressure drop determination method, in which each of the tires is individually decompressed, the vehicle in this state is run at a predetermined speed, and the determination value at that time is obtained based on the determination formula, Of the obtained determination values, a determination value corresponding to a predetermined reference speed is set as a reference determination value, and a correspondence relationship between the speed and the ratio of the determined determination value to the reference determination value is stored in advance. Well, During actual traveling of the vehicle, the speed of the vehicle is calculated, the ratio corresponding to the calculated speed is calculated based on the previously stored correspondence relationship, and the threshold value is calculated based on the calculated ratio. A method for determining a decrease in tire air pressure, characterized by: 4. A rotational angular velocity detecting means for detecting respective rotational angular velocities of four tires provided on a four-wheel vehicle, and the tire air pressure is reduced based on the respective rotational angular velocities detected by the rotational angular velocity detecting means. Determination value calculating means for determining a determination value for determining whether or not the determination value is determined based on a determination expression, a determination value obtained by the determination value calculating means, and a threshold value corrected by the determination value calculating means as follows. A tire pressure drop detecting device including: a comparing unit that compares the tire pressure and a determining unit that determines whether or not the tire air pressure is lowered based on the result of the comparison by the comparing unit. Are individually decompressed, the vehicle in this state is run at a predetermined speed, and the above judgment value at that time is obtained based on the above judgment formula. A determination value corresponding to the determined reference speed is set as a reference determination value, and a storage unit that stores in advance a correspondence relationship between the speed and the ratio of the determined determination value to the reference determination value and the vehicle And a speed calculation means for calculating the speed of the vehicle during actual traveling, wherein the determination value calculation means calculates the ratio corresponding to the speed calculated by the speed calculation means on the basis of the correspondence relationship stored in advance. The tire pressure drop detecting device is characterized in that the threshold value is corrected based on the calculated ratio.