JPH07156621A - Initial correction method for tire inflation pressure lowering detection device - Google Patents

Abstract

PURPOSE:To provide the initial correction method for the tire inflator pressure lowering detection device, which accurately and quickly corrects the initial difference of a tire, and thereby accurately detects lowering in pressure. CONSTITUTION:Each speed V1 of a tire is detected (step S4), when the speed V1 is found to have been larger than a threshold value Vth, longitudinal acceleration A1 is computed based on the speed V1 (step S7). Furthermore when the computed longitudinal acceleration A1 is found to have been smaller than a threshold value Ath, it is judged whether or not a vehicle is running straight ahead (step S9). As a result, the vehicle is found to have been running straight ahead, the angular velocity F1 of rotation is stored in the angular velocity of rotation area of a RAM to be used for initial correction (step S10), and the aforesaid process is repeated until the running distance of the vehicle arrives at a definite distance. When the running distance of the vehicle has arrived at the definite distance, a correction factor is determined using only the angular velocity of rotation stored in the angular velocity of rotation area (step S14).

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, a tire capable of correcting the initial difference of tires with higher accuracy. The present invention relates to an air pressure drop detecting device.

[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, when the air pressure of a tire W _i decreases, the dynamic load radius of the tire W _i becomes smaller than the dynamic load radius at the normal internal pressure, so that the rotational angular velocity F _i becomes faster than 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 . Tire W in the formula (1) below
A discriminant for detecting a decrease in the air pressure of _i is shown (see Japanese Patent Laid-Open No. 63-305011, Japanese Patent Laid-Open No. 4-212609, etc.).

[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 DEL = 0. Therefore, when DEL = 0, it can be determined that the air pressures of the tires W _i are all the same. On the other hand, for example, when the air pressure of the tire W ₁ is low, F ₁ becomes large, so that DEL> 0. Since DEL> 0 even if the air pressure of the tire W ₄ is low, if DEL> 0, it can be determined that the air pressure of _{one of} the tires W ₁ and W ₄ is low. On the other hand, when DEL <0, it can be determined that the air pressure of one of the tires W ₂ and W ₃ has dropped.

By the way, the respective tires W ₁ , W ₂ , W ₃ , W
No. ₄ does not always have the same dynamic load radius even with normal internal pressure. This is because the tire W _i is always manufactured with a variation (hereinafter referred to as “initial difference”) within the standard at the time of manufacturing. It is known that the degree of variation is about 0.1% in terms of standard deviation. On the other hand, for example, when the air pressure of the tire W _i drops by 0.6 kg / cm ² (normal internal pressure is 2.0 K
The variation of the dynamic load radius of 30% in the case of g / cm ² is about 0.2% at the normal internal pressure. That is,
Because the initial difference and the variation of the dynamic load radius due to a reduction in the dynamic load radius variations and air pressure by the same extent roughly, the difference in rotational angular velocities F _i by the initial difference, a difference in both the rotational angular velocity F _i due to a decrease in air pressure, about the same Is. Therefore, even in the case of DEL ≠ 0, the normal internal pressure may be present. Therefore, the above method using DEL = 0 as a reference cannot accurately detect the decrease in the air pressure.

Further, when the tire is replaced or the tire is replenished with air, an error corresponding to the above initial difference is often included. Therefore, even in such a case, the decrease in air pressure can be accurately detected. Can not do it. In order to solve this, a process for correcting the initial difference (hereinafter referred to as “initial correction process”) must be performed before the detection of the decrease in air pressure. The initial correction processing, for example when the tires _{W 1, W 2, W 3} , W 4 are all at a normal internal pressure, obtain a correction coefficient C _i based on a certain tire W _i, the correction coefficient C _i Can be done by multiplying the other tire W _i .

By the way, in the air pressure drop detection process during actual traveling, although not in the initial correction process described above, there is a possibility that the tire will slip when the longitudinal acceleration of the vehicle is large. If the rotational angular velocity F _i is used, an erroneous determination is made in the tire pressure reduction determination. Therefore, a technique for removing the data corresponding to the rotational angular velocity F _i is disclosed in, for example, Japanese Patent Laid-Open No. 63-
It is disclosed in Japanese Patent No. 305011 and Japanese Utility Model Publication No. 4-11844.

In the technique disclosed in Japanese Patent Laid-Open No. 63-305011, the vehicle is provided with a longitudinal acceleration detecting unit, and the longitudinal acceleration signal output from the longitudinal acceleration detecting unit is for a predetermined time (for example, 6 seconds). If the specified acceleration (for example, 0.03G) is continuously exceeded for
The data of the detected rotational angular velocity F _i is removed. When the longitudinal acceleration is large, for example, when the load moves forward and backward of the vehicle at the time of sudden acceleration, the drive tire may idle. Since idling does not always occur evenly on the left and right of the driving tire, the rotational speed of each driving tire differs even when the internal pressure is normal during straight running. As a result, DEL ≠ 0, and an erroneous determination of pressure reduction is made. Therefore, in this technique, since the data of the rotational angular velocity F _i at this time is removed, the decrease in the air pressure can be detected with a high degree of accuracy.

On the other hand, in the prior art disclosed in Japanese Utility Model Publication No. 4-11844, the ratio between the rotational angular velocity F ₁ of the left front wheel and the rotational angular velocity F ₂ of the right front wheel, and the rotational angular velocity F _{3 of the} left rear wheel. And the rotational angular velocity F ₄ of the right rear wheel are calculated, and it is determined whether or not the rotational angular velocity ratios F ₁ / F ₂ and F ₃ / F ₄ are within a predetermined range. As a result, when the rotational angular velocity ratios F ₁ / F ₂ and F ₃ / F ₄ are out of the predetermined range, it is considered that the tire W _i is idling or locked, and the rotational angular velocity F _i The data is removed.

When the tire W _i is idling or locked, the output of the wheel speed sensor varies, so that the data of the rotational angular velocity F _i includes an error. Therefore, in this technique, the data of the rotational angular velocity F _i that may include this error is removed.
The decrease in air pressure can be detected with high accuracy.

[0014]

However, the prior art disclosed in Japanese Patent Laid-Open No. 63-305011 does not exclude the data of the rotational angular velocities F _i detected when the vehicle is low speed. At low vehicle speeds,
Since the wheel speed sensor cannot provide accurate output,
The data of the rotational angular velocity F _i detected at that time becomes inaccurate. Therefore, even if the decrease in the air pressure is detected based on the rotational angular velocity F _i including such an error, it is not possible to accurately detect the decrease.

On the other hand, in the prior art disclosed in Japanese Utility Model Publication No. 4-11844, a steering angle sensor for detecting the steering angle of the steering wheel in order to prevent erroneous detection of a decrease in air pressure when the vehicle is cornering. Is mandatory. Therefore, there is a drawback that the structure of the device becomes complicated and the device becomes expensive. As described above, although there is a drawback in the above-mentioned prior art, even in the initial correction process that should be performed before the air pressure drop detection process that the above-mentioned prior art was targeted, the drawback in the above-mentioned prior art (the driving tire due to a large longitudinal acceleration is The same drawbacks (including fluctuations in rotation speed) may occur. Therefore, in the initial correction processing performed before the air pressure drop detection processing, the rotational angular velocity F _i
Since the data of (1) includes an error, it is impossible to detect the decrease of the air pressure with high accuracy. Therefore, first, the initial correction process must be performed with high accuracy.

Therefore, an object of the present invention is to solve the above-mentioned technical problem, to correct the initial difference with high accuracy and speed, and thus to detect the decrease in air pressure accurately. Is to provide an initial correction method in.

[0017]

In order to achieve the above object, an initial correction method in a tire pressure drop detecting device according to claim 1 calculates a vehicle speed, and the calculated speed is less than a predetermined threshold value. Is also large, and only when it is determined that the speed is larger than the threshold value, the rotational angular velocity is set to the initial difference in the dynamic load radius of the tire based on the variation in the performance of individual tires and the variation in the air pressure. The correction coefficient is determined based on the rotational angular velocity determined to be used for the correction of the initial difference as a result of the determination, and the initial difference is corrected based on the calculated correction coefficient. It is characterized by doing.

The initial correction method according to claim 2 detects the longitudinal acceleration based on each rotational angular velocity, determines whether the detected longitudinal acceleration is smaller than a predetermined threshold value, and determines the longitudinal acceleration. Only when it is determined that the acceleration is less than the threshold value, the rotational angular velocity is determined to be adopted for the correction of the initial difference in the dynamic load radius of the tire based on the variation in the performance of the individual tires and the variation in the air pressure,
As a result of the determination, a correction coefficient is calculated based on the rotational angular velocity determined to be used for the correction of the initial difference, and the initial difference is corrected based on the calculated correction coefficient.

Further, in the initial correction method according to the third aspect of the present invention, the traveling distance of the vehicle is calculated based on each of the rotational angular velocities, and is collected while the calculated traveling distance reaches a predetermined straight line constant distance. The initial difference according to claim 1 or 2 is corrected based on the rotational angular velocity. The initial correction method according to claim 4 calculates an average value of the correction coefficients obtained based on the rotational angular velocities collected while reaching the straight line constant distance, and based on the calculated average value, The initial difference according to claim 1 or 2 is corrected.

[0020]

According to the structure described in claim 1 or 2, based on the rotational angular velocity determined to be adopted for the correction of the initial difference as a result of the determination of whether or not the detected rotational angular velocity is adopted for the correction of the initial difference. The correction coefficient is calculated, and the initial difference is corrected based on the calculated correction coefficient. In other words, the initial angular difference is corrected by removing the rotational angular speed detected when the vehicle is in low speed including inaccurate rotational angular speed data or when the longitudinal acceleration due to frequent occurrence of tire slip and the like is large. It can be performed.

Further, according to the third aspect of the present invention, the initial difference is calculated based on the rotational angular velocity collected while the traveling distance of the vehicle is calculated and the calculated traveling distance reaches a predetermined straight line constant distance. Is corrected. In other words, in order to correct the initial difference of the tires, it is sufficient to travel a fixed straight line distance. Therefore, if the fixed straight line distance is relatively short, the initial difference can be corrected in a short time.

[0022]

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 3 is a block diagram showing the configuration of the tire pressure drop detecting device. The tire pressure drop detecting device is used for each tire W ₁ , W ₂ , W ₃ , W of a four-wheel vehicle.
A wheel speed sensor 1 having a conventionally known structure provided in association with each of the _four wheels 4 is provided, and the output of the wheel speed sensor 1 is given to the control unit 2. The control unit 2 includes an initialization switch 3 and a CR operated by a driver.
An indicator 4 which is composed of T etc. and which displays a tire whose air pressure has dropped is connected as will be described later.

FIG. 4 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. In the RAM 2d, as will be described later, the rotational angular velocities F _i effective for the initial correction processing (where i is each of the numbers W ₁ , W ₂ , W ₃ , W ₄ "1, 2, 3,
4 ”, and so on. ) For storing the rotational angular velocity, a speed area for storing the speed of the vehicle one cycle before, a distance area for storing the traveling distance of the vehicle, and the like.

From the wheel speed sensor 1, the tire W_iRotation of
Pulse signal corresponding to the number (hereinafter referred to as "wheel speed pulse")
Is output. Specifically, the wheel speed sensor 1 is
Ear W _iMultiple inside wheel (eg 49 or 98
Sensor rotor with a number of teeth.
Generated according to the number of teeth as the rotor rotates
To output the signal. CPU2b is the output vehicle
Every predetermined sampling period ΔT based on the wheel speed pulse
Each tire W₁, W₂, W₃, W_FourAngular velocity of
F₁, F₂, F₃, F_FourTo calculate.

Various detecting operations in the CPU 2b will be described below. The CPU 2b detects the speed V _i of the tire W _i based on the rotational angular speed F _i . That is, if the radius of each tire _{W 1, W 2, W 3} , W 4 and all the R, velocity V _i can be determined as _{V i = R × F i ‥‥} (2).

The CPU 2b also receives the detected speed V
The longitudinal acceleration A _{i of the} vehicle is detected based on _i . The detection method will be described in detail. The CPU 2b uses the detected tires W
_i the speed V _i of storing the speed for the area of RAM2d as VB _i. And the VB stored in this speed area
_i and each tire W detected after the elapse of the sampling period ΔT
Based on the difference between the speed V _i of _i, each tire W by the following equation (4)
_i for detecting a longitudinal acceleration A _i of.

A _i = (V _i −VB _i ) / ΔT (3) The CPU 2b further determines whether the vehicle is traveling straight. That is, whether the vehicle is traveling straight is determined by the front left and right tires W ₁ , W ₂ and the rear left and right tires W ₃ ,
The determination is made based on whether or not the difference or ratio of the rotational angular velocities F _i of W ₄ exceeds a certain specified value with the same sign. If both do not exceed the certain specified value with the same sign, the vehicle is It is determined that the vehicle is traveling straight.

The CPU 2b also calculates the traveling distance L of the vehicle. That is, the traveling distance L is calculated based on the rotational angular velocity F _i , and the calculation formula is L = L + ML × R (4) Here, ML represents the distance traveled by the vehicle during the sampling period ΔT. In other words, this ML is
It is calculated by the equation (6). Note that Σ means the total sum of i = 1 to 4.

ML = (ΣV_i/ 4) × ΔT (5) Next, the tire pressure drop detection device detects the tire pressure drop.
The output processing and the initial correction processing will be described. First of all
The initial correction process will be described below. 1 and 2 show
In the tire pressure drop detecting device, a drop in air pressure
A flow chart showing the initial correction process that is performed before the detection process.
It is This initial correction process is described in the "Conventional Technology" section.
But as I explained, tire W_iError such as initial difference of
It is done to correct it, and is initially set by the driver.
Based on the operation of the switch 3 (see FIG. 3)
It is started (step S1). The driver is initialized
Operating switch 3 is, for example, the first time the vehicle is driven.
When to let the tire W_iWhen replenishing the air pressure of
Ya W_iIt was time to replace. In other words, drive the vehicle for the first time
When making it go and tire W_iWhen replenishing the air pressure of
Ear W _iWhen replacing the old and new tires W_iMovement of
This is because the radius of gyration has variations within the standard.

Now, when the initialization switch 3 is turned on,
VB _i of the speed area of the RAM 2d by the CPU 2b
And L of the distance area is reset (initialized) (step S2). Next, the wheel speed pulse output from the wheel speed sensor 1 is read (step S3), and the rotational angular speed F _i is obtained based on this wheel speed pulse. Then, based on the above equation (5), the speed V _i of each tire W _i is calculated (step S4), and the respective speeds V _i The calculated and the threshold V _TH is compared (step S5).

Here, the threshold value V _TH can be set to 10 Km / h if the number of teeth of the sensor rotor is 49, and the threshold value V _TH can be set lower as the number of teeth increases. Further, the speed V _i is compared with the threshold value V _TH in order to determine whether or not the vehicle is traveling at a certain speed or higher. That is, as described in the section of "Prior Art", when the vehicle is at a low speed, the output of the wheel speed sensor 1 has a large variation, and therefore the rotational angular speed F detected in that case.
_This is because _i is excluded. The comparison may be, for example, a comparison between the average value ΣV _i / 4 of the speed V _i of each tire W _i calculated in step S4 and the threshold value V _TH . It is also possible to obtain a speed signal from a speedometer provided in advance in the vehicle and compare the speed obtained from the speed signal with the threshold value V _TH .

[0032] The results of the comparison, the speed V _i of each tire W _i
If at least one of them is smaller than the threshold value V _TH , each tire W
_i velocity V _i of are stored in the speed for the area of RAM2d as VB _i (step S11). On the other hand, greater than the speed V _i is the threshold value V _TH of all of the tires W _i, whether already VB _i the speed for the area then is stored is determined (step S6). As a result, if VB _i is not stored, that is, if VB _i is still in the initialized state, the speed V _i of each tire W _i is stored as VB _i in the speed area. On the other hand, already when VB _i is stored, based on the above (6), longitudinal acceleration A _i of each tire W _i is calculated (step S7).

Longitudinal acceleration A_iBefore and after
Acceleration A_iThe absolute value of is the predetermined threshold A _THLess than
Is determined (step S8). That is,

[0034]

[Equation 2]

It is determined whether or not Where A _TH
Can be set to 0.1, for example. The reason that 9.8 is included in the denominator is to convert the longitudinal acceleration A _i into G. As a result of this determination, if at least one of the calculated longitudinal accelerations A _i is larger than the threshold value A _TH , it is considered that the tire has slipped, and the velocity V of each tire W _i .
_i is stored in the speed area as VB _i (step S11). On the other hand, if all the calculated longitudinal accelerations A _i are smaller than the threshold value A _TH , then it is 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, when it is determined that the vehicle is not traveling straight, the speed V _i of each tire W _i is stored in the speed area as VB _i . On the other hand, if it is judged to be traveling straight, rotational angular velocity F _i is stored in the area for the rotation angular velocity of the RAM 2d (step S10), and the speed V _i of each tire W _i are stored in the speed for the area (step S11).

When the processing of step S11 is completed, the traveling distance L stored in the distance area is updated (step S12). That is, only the distance traveled during the sampling period ΔT (that is, ML) is updated. Next, the updated traveling distance L is set to a predetermined threshold L.
_It is determined whether or not it is larger than _TH (for example, 200 m) (step S13). As a result, if the updated traveling distance L is shorter than the threshold value L _TH , the above processing is repeated from the processing of step S3. On the other hand, when the traveling distance L reaches the threshold value L _TH , the correction coefficient C is calculated based on the rotational angular velocities F _i stored in the rotational angular velocity area until then.
_i (j) is calculated (step S14). In addition, distance 2
When 00m is set as the threshold value L _TH , if this 200m is traveled at 50 to 60 km / h, the time is 12 to 1
It is about 5 seconds.

The correction coefficient C_i(j) is a tire W_i
Is obtained on the basis of, for example, tire W₁To
Tire W_iCorrection coefficient C for correcting
₁(j), C₂(j), C₃(j), C_Four(j) is C₁(j) = F₁(j) / F₁(j) ‥‥ (7) C₂(j) = F₁(j) / F₂(j) ‥‥ (8) C₃(j) = F₁(j) / F₃(j) ‥‥ (9) C_Four(j) = F₁(j) / F_Four(j) It is calculated as (10). Where j = 1 to N, where N is the rotation angle
Rotational angular velocity F stored in the velocity area_iIs the number of
It That is, each correction coefficient C₁(j), C₂(j), C ₃(j)
 , C_Four(j) will be calculated N times each.
It

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 ... (11) C₂= ΣC₂(j) / N ... (12) C₃= ΣC₃(j) / N ... (13) C_Four= ΣC_FourCalculate (j) / N (14). 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.

Note that the correction coefficients CF and CR different from the above-described correction coefficient C _i may be calculated. That is, first, obtains a _{CF (j) = F 2 (} j) / F 1 (j) ‥‥ (15) CR (j) = F 4 (j) / F 3 (j) ‥‥ (16), then , CF = ΣCF (j) / N ... (17) CR = ΣCR (j) / N ... (18), and the average values CF and CR may be used as the final correction coefficients.

When the calculation of the correction coefficient is completed, the initial correction process is completed. In the tire pressure drop detecting device, after the initial correction processing is finished, pressure drop detection processing of the tire W _i in normal running is performed. This air pressure drop detection processing will be described in more detail. When the initial correction processing is completed and the correction coefficient is calculated, the CPU 2b multiplies the rotation angular velocity F _i detected for each sampling cycle ΔT to rotate the rotation. A correction value F _i0 for the angular velocity F _i is _calculated . That, CPU 2b _{is, F 10 = C 1 × F} 1 ‥‥ (19) F 20 = C 2 × F 2 ‥‥ (20) F 30 = C 3 × F 3 ‥‥ (21) F 40 = C 4 × Find F ₄ (22). When the correction coefficient is CF or CR, F ₁₀ = CF × F ₁ (23) F ₂₀ = F ₂ (24) F ₃₀ = CF × F ₃ (25) F ₄₀ = F ₄ Ask for (26).

Then, thereafter, this correction value F _i0 is used for the processing for detecting the decrease in the air pressure of the tire W _i . The process for detecting the decrease in the air pressure of the tire W _i is performed based on the following equation (27).

[0044]

[Equation 3]

In the present embodiment, if the calculated DEL value satisfies the following equation (28), it is judged that the air pressure has dropped. That is, DEL <DEL _TH1 or DEL> DEL _TH2 (28) where DEL _TH1 and DEL _TH2 are predetermined constants. In this way, the air pressure drop detection process is performed. As a result of this processing, when it is detected that the air pressure is low, the detection result is output to the display 4 and displayed. As the display mode on the display 4, for example, as shown in FIG. 4, four tires W ₁ , W ₂ , W ₃ , W ₄
The indicator lamps corresponding to are turned on at the same time.

As described above, according to the initial correction method of this embodiment, the rotational angular velocity F _i suitable for the initial correction is selected at the time of initial correction, and the correction coefficient C is selected using only the selected rotational angular velocity F _{i. Since i} is obtained, the initial correction process can be performed with higher accuracy. Therefore, the decrease in the air pressure of the tire W _i can be detected with higher accuracy, and thus the traffic safety can be further improved.

Further, since the initial correction processing is performed only by the vehicle traveling straight on a predetermined distance, the time required for the initial correction processing can be greatly shortened. Although the embodiments have been described above, the present invention is not limited to the above embodiments, and various design changes can be made without departing from the scope of the present invention.

[0048]

As described above, according to the initial correction method of the present invention, since the rotational angular velocity that is not suitable for the correction of the initial difference is removed, the initial difference can be corrected accurately. Therefore, a decrease in tire air pressure can be detected with high accuracy. As a result, it can contribute to traffic safety.

According to the third aspect of the invention, in particular, the initial difference is corrected only by the vehicle traveling a predetermined straight distance, so that the time required to correct the initial difference can be greatly reduced. . Further, according to the configuration of claim 4, since the initial difference is corrected based on the average value of the correction coefficients, the initial difference can be corrected with higher accuracy than in the conventional case.

[Brief description of drawings]

FIG. 1 is a flowchart showing an initial correction process in a tire pressure drop detecting device according to an embodiment of the present invention.

FIG. 2 is a flowchart similarly showing an initial correction process.

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

FIG. 4 is a block diagram showing an electrical configuration of the tire pressure drop detecting device.

[Explanation of symbols]

1 Wheel Speed Sensor 2 Control Unit 2b CPU 2d RAM C _i , C ₁ , C ₂ , C ₃ , C ₄ Correction Factors F _i , F ₁ , F ₂ , F ₃ , F ₄ Rotational Angular Velocity W, W ₁ , W ₂ , W ₃ and W ₄ tires

Claims (4)

[Claims] 1. A tire air pressure drop detecting device for detecting the respective rotational angular velocities of four tires provided in a four-wheel vehicle and detecting a decrease in the air pressure of the tire based on the detected respective rotational angular velocities. In the initial correction method, the speed of the vehicle is calculated, it is determined whether the calculated speed is greater than a predetermined threshold value, and only when the speed is determined to be greater than the threshold value,
It was decided to adopt the above rotational angular velocity for the correction of the initial difference in the dynamic load radius of the tire based on the variation in the performance of individual tires and the variation in the air pressure. An initial correction method, wherein a correction coefficient is calculated based on the calculated rotational angular velocity, and the initial difference is corrected based on the calculated correction coefficient. 2. A tire air pressure drop detecting device for detecting the rotational angular velocities of four tires provided in a four-wheeled vehicle and detecting the decrease in the air pressure of the tires based on the detected rotational angular velocities. In the initial correction method, the longitudinal acceleration is calculated based on each of the rotational angular velocities, it is determined whether the calculated longitudinal acceleration is smaller than a predetermined threshold value, and it is determined that the longitudinal acceleration is smaller than the threshold value. It is decided that the above rotational angular velocity should be used to correct the initial difference in the dynamic load radius of the tires based on the variation in the performance of individual tires and the variation in the air pressure only when A feature is that a correction coefficient is calculated based on the rotational angular velocity determined to be adopted for correction, and the initial difference is corrected based on the calculated correction coefficient. The initial correction how. 3. A traveling distance of a vehicle is calculated based on each of the rotational angular velocities, and based on the rotational angular velocities collected while the calculated traveling distance reaches a predetermined straight line constant distance. An initial correction method, characterized in that the initial difference described in 1 or 2 is corrected. 4. The method according to claim 1 or 2, wherein an average value of the correction coefficients calculated based on the rotational angular velocities collected while reaching the straight line constant distance is calculated, and based on the calculated average value. The initial correction method according to claim 3, wherein the initial difference is corrected.