JP2002234318A - Tire air pressure detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect a tire air pressure drop accurately even under an influence of a tread lift. SOLUTION: An air pressure drop rate is computed from a variation in a corrected wheel speed deviation value D'AVE per unit time, and from the air pressure drop rate, a warning prediction time when the wheel speed deviation value D'AVE will be across a warning threshold level is computed. When the warning prediction time is reached, a tire air pressure drop is detected irrespective of an actual wheel speed deviation value D'AVE. In the course of the drop in air pressure, even if a vehicle speed is increased and a tread lift influences the corrected wheel speed deviation value D'AVE to change to a side causing no tire air pressure drop, the tire air pressure drop can be detected accurately when it is the warning prediction time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tire pressure detecting device for detecting a tire pressure condition in a vehicle.

[0002]

2. Description of the Related Art As a conventional tire air pressure detecting device, there is one disclosed in Japanese Patent Application Laid-Open No. Hei 10-100624. The tire pressure detecting device disclosed in this conventional publication will be described.

The tire pressure detecting device disclosed in the prior art detects a decrease in tire pressure based on the relationship between the wheel speed deviation value D and the front and rear wheel speed ratio β shown as follows.

[0004]

(Equation 1)

[0005]

(Equation 2)

Here, V _FR is the right front wheel speed, V _FL is the left front wheel speed, V _RR is the right rear wheel speed, and V _RL is the left rear wheel speed.

The wheel speed deviation value D is a rotation state value obtained from the wheel speeds of the four wheels, and is a variable given as a difference between the wheel speed ratios of the front and rear wheels in a diagonal relationship, for example. When the air pressure of such a tire decreases, it increases or decreases accordingly. The front and rear wheel speed ratio β is 4
This is a slip state value obtained from the wheel speed of the wheel, and represents a degree of a slip state generated in the drive wheel by the action of the driving force transmitted to the drive wheel. A smaller value indicates that the drive wheel is slipping.

When the tire air pressure of each wheel is a specified value, the wheel speed deviation value D becomes 0. However, when the tire air pressure of any of the four wheels falls below the specified value, the wheel speed deviation value D becomes zero. Since D increases or decreases, it is possible to detect a decrease in tire air pressure based on this.

However, for example, in a rear-wheel drive vehicle, when the tire pressure of the right rear wheel, which is the driving wheel, drops below a specified value, the turning radius of the right rear wheel becomes small due to the decrease of the air pressure. Since the contact area becomes larger than the wheels and the force for suppressing the slip is increased, the other drive wheels are more likely to slip, and the wheel speed deviation value D varies depending on the degree of the slip state.

Therefore, as shown in FIG. 7, the regression line is obtained by regressing the relationship between the front and rear wheel speed ratio β representing the degree of the slip state and the wheel speed deviation value D to a linear function using the least squares method. Then, the wheel speed deviation value D is corrected to a value in an ideal running state in which no slip occurs (that is, the front-rear wheel speed ratio β = 1), thereby eliminating the influence of the slip of the driving wheel and accurately calculating the tire pressure. To be able to detect a decrease in

[0011]

However, the wheel speed deviation value D is a tread lift (a phenomenon in which the dynamic load radius of the tire increases due to centrifugal force) in addition to the slip of the driving wheel.
Therefore, if the vehicle speed increases in the process of decreasing the air pressure, an accurate wheel speed deviation value D cannot be obtained, and it may not be possible to accurately determine a decrease in the tire air pressure.

For example, a difference between a wheel speed deviation value D in an ideal running state obtained from the above-described regression line and a predetermined reference value is used as a judgment value, and when the judgment value exceeds a warning threshold level, When it is determined that the air pressure is low, as shown in FIG. 8, the determination value decreases as the vehicle speed increases, that is, to a side where the tire air pressure does not decrease. It cannot be judged.

In view of the above, it is an object of the present invention to be able to accurately detect a decrease in tire air pressure even if there is an influence of a tread lift.

[0014]

In order to achieve the above object, according to the first aspect of the present invention, based on the rotation state value corrected by the rotation state value correction means, the air pressure reduction determining means determines that the tire air pressure has decreased. Warning time calculating means (3g) for calculating an expected warning time to be performed, and the air pressure drop determining means determines that the tire pressure has dropped when the warning expected time calculated by the warning expected time calculating means has come. It is characterized by.

According to such a configuration, when the estimated warning time comes, it is determined that the tire air pressure has dropped regardless of the rotation state value. For this reason, even if the vehicle speed increases in the process of decreasing the air pressure and the rotation state value changes to the side where the tire pressure does not decrease due to the effect of the tread lift, the tire pressure decreases exactly at the scheduled warning time. Can be detected.

Specifically, as set forth in claim 2, the expected warning time calculating means calculates a time at which the rotation state value corrected by the rotation state value correcting means exceeds a predetermined threshold level as an expected warning time. For example, an expected warning time can be calculated from a change amount per unit time of the rotation state value corrected by the rotation state value correction means. As the rotation state value, a wheel speed deviation value (D) given as a difference between the wheel speed ratios of the front and rear wheels having a diagonal relationship can be adopted as the rotation state value.

According to a fourth aspect of the present invention, there is provided a storage means (3g) for storing data of the predicted warning time calculated by the predicted warning time calculation means, and the storage means stores the data of the previous time stored as data. When the predicted warning time calculated this time is earlier than the predicted warning time, the data of the previous predicted warning time stored in the storage unit is updated to the data of the predicted warning time calculated this time. It is characterized by becoming.

As described above, the data of the estimated warning time is not updated sequentially, but updated only when the timing of detecting the decrease in tire air pressure is advanced. Can be detected.

According to the fifth aspect of the present invention, the ideal running state value calculating means (3e) calculates an ideal state value (βid = F (A)) corresponding to a slip state value in an ideal running state without slip. The rotation state value correction means calculates the rotation state value in the ideal running state from the regression line calculated by the regression calculation means and the ideal state value calculated by the ideal running state calculation means. It is characterized by having.

As described above, the rotation state value in the ideal running state can be obtained from the regression line and the ideal state value, and based on the rotation state value in the ideal running state,
It is possible to accurately determine a decrease in tire air pressure.

Note that the reference numerals in parentheses of the above means indicate the correspondence with specific means described in the embodiments described later.

[0022]

(First Embodiment) FIG. 1 shows a schematic configuration of a tire pressure detecting device according to an embodiment of the present invention. The tire pressure detecting device will be described with reference to FIG.

The tire air pressure detecting device detects that the air pressure of one of the tires of each wheel has decreased, and when the decrease of the tire air pressure is detected, the driver is warned to that effect. . The tire pressure detection device is mounted on a front-wheel drive or rear-wheel drive vehicle. In the present embodiment, a case where the tire pressure detection device is mounted on a rear-wheel drive vehicle will be described as an example.

The tire pressure detecting device is provided for each wheel 1 of the vehicle.
Wheel speed sensors 2a, 2b, 2c, 2d as wheel speed detecting means provided corresponding to a, 1b, 1c, 1d
And an arithmetic processing unit 3 to which detection signals from the wheel speed sensors 2a to 2d are input, and an alarm unit 4 for warning a driver of a decrease in tire air pressure based on a warning signal from the arithmetic processing unit 3. It is configured.

Of the wheel speed sensors 2a to 2d, two wheel speed sensors 2a and 2b are driven wheels (front right wheel and front left wheel).
1a and 1b are detected, and the remaining 2
The two wheel speed sensors 2c and 2d detect wheel speed signals in driving wheels (right rear wheel and left rear wheel) 1c and 1d.

The arithmetic processing unit 3 is constituted by a microcomputer or the like, and performs various arithmetic operations based on detection signals input from the wheel speed sensors 2a to 2d. This arithmetic processing device 3 is configured as follows.

The arithmetic processing unit 3 includes a wheel speed calculating unit 3a as wheel speed calculating means, a wheel speed deviation value processing unit 3b
Is provided. The wheel speed calculator 3a calculates the wheel speed of each of the wheels 1a to 1d based on detection signals (for example, pulse signals) from the wheel speed sensors 2a to 2d. The wheel speed deviation value processing unit 3b includes a wheel speed deviation value calculation unit as a rotation state value calculation unit, a first wheel speed deviation value storage unit, and a wheel speed deviation value average processing unit. Various processes relating to the wheel speed deviation value D are performed based on the calculation result in the wheel speed calculation unit 3a. .

In these configurations, first, the wheel speeds of the wheels 1a to 1d are calculated by the wheel speed calculator 3a based on the detection signals from the wheel speed sensors 2a to 2d. For example, the wheel speeds V _FL , V _FR , V _RL , and V _{RR of} each wheel are calculated from the number of detection signals from the wheel speed sensors 2a to 2d input within a few ms. Next, when the wheel speed is calculated, the wheel speed deviation value D shown in Equation 1 is calculated by the wheel speed deviation value calculation unit based on the data on the wheel speed. Then, data relating to the calculation result is stored in a memory provided in the first wheel speed deviation value storage unit, and the average value D of the wheel speed deviation values D is processed by the wheel speed deviation value averaging unit based on the stored contents. _AVE is required. The average value D _AVE of the wheel speed deviation values D is represented by the following equation, and corresponds to an average of n ₀ wheel speed deviation values D.

[0029]

(Equation 3)

The processing unit 3 is provided with a front and rear wheel speed ratio processing unit 3c. The front and rear wheel speed ratio processing unit 3c includes a front and rear wheel speed ratio calculation unit as a slip state value calculation unit, a front and rear wheel speed ratio storage unit, and a front and rear wheel speed ratio average processing unit. In the front / rear wheel speed ratio processing unit 3c, after the front / rear wheel speed ratio β shown in Expression 2 is calculated by the front / rear wheel speed ratio calculation unit based on the data on the wheel speed sent from the wheel speed calculation unit 3a, Data relating to this calculation result is stored in a memory provided in the front-rear wheel speed ratio storage unit, and the front-rear wheel speed ratio average processing unit calculates an average value β _AVE of the front-rear wheel speed ratio β based on the stored contents. ing. The average value β _AVE of the front-rear wheel speed ratio β is expressed by the following equation: n ₀
This is equivalent to averaging the front-rear wheel speed ratio β.

[0031]

(Equation 4)

The arithmetic processing unit 3 is provided with a slip deviation value calculator 3d, an ideal running state value calculator 3e, and a wheel speed deviation correction processor 3f.

The slip deviation value calculating section 3d calculates the wheel speed deviation value D calculated by the wheel speed deviation value calculating section in the wheel speed deviation value processing section 3b and the front and rear wheel speed ratio processing section 3d.
The slip deviation value A is calculated based on the front-rear wheel speed ratio β calculated by the front-rear wheel speed ratio calculation unit in c. The slip deviation value A corresponds to a change amount (ΔD / Δβ) of the wheel speed deviation value D with respect to the front and rear wheel speed ratio β, and is based on n ₀ wheel speed deviation values D and the front and rear wheel speed ratio β. Is calculated using the least squares method. Note that the slip deviation value calculator 3d corresponds to a regression calculator.

The ideal running state value calculator 3e calculates the ideal running state value βid based on the calculation result in the slip deviation value calculator 3d. The ideal running state value βid is
This is equivalent to the front-rear wheel speed ratio β in an ideal running state without slip as a correction reference, and is calculated as a function of the first order or higher of the slip deviation value A. That is, the ideal running state value βid is represented by βid = F (A). For example, when the ideal running state value βid is a linear function of the slip deviation value A, βid = F (A)
1−Coef × | A | Here, Coef is a constant.

The wheel speed deviation correction unit 3f includes a wheel speed deviation correction unit and a second wheel speed deviation storage unit. The wheel speed deviation value correction unit corresponds to a rotation state value correction unit. In this wheel speed deviation value correction unit, the wheel speed deviation average value D _AVE calculated by the wheel speed deviation value average processing unit in the wheel speed deviation value processing unit 3b and the front and rear wheels in the front and rear wheel speed ratio processing unit 3c. The front-rear wheel speed ratio average value β _AVE calculated by the speed ratio averaging section, the slip deviation value A calculated by the slip deviation value calculation section 3d, and the ideal running state calculated by the ideal running state value calculation section 3e. Based on the value βid, a corrected wheel speed deviation value D ′ _AVE is calculated. The corrected wheel speed deviation value D' _AVE corresponds to the wheel speed deviation value D in an ideal running state. Specifically, the corrected wheel speed deviation value D' _AVE is obtained as in the following equation.

[0036]

(Equation 5)

Then, in the second wheel speed deviation value storage unit,
The reference value D ' _AVE std of the corrected wheel speed deviation value D' _AVE calculated by the wheel speed deviation value correction unit is stored in the memory. The reference value D ′ _AVE std is a corrected wheel speed deviation value D ′ _AVE at the time of equal pressure of the four wheels, which is a reference for determining the air pressure. The wheel speed deviation calculated first after the operation of the arithmetic processing unit 3. value D and the front and rear wheel speed ratio beta from the obtained wheel speed deviation mean D _{AV E,} longitudinal wheel speed ratio average value beta _AVE,
This corresponds to a value calculated from the slip deviation value A and the ideal running state value βid.

Further, the arithmetic processing unit 3 is provided with a predicted warning time calculating section 3g and a pneumatic pressure drop determining section 3h. In the warning expected time calculation unit 3g, the reference value D ′ _AVE std stored in the second wheel speed deviation value storage unit in the wheel speed deviation value correction processing unit 3f and the corrected value obtained by the wheel speed deviation value correction unit A predicted warning time is calculated based on the wheel speed deviation value D' _AVE, and data of the calculated predicted warning time is stored. Here, a threshold level (hereinafter referred to as a warning threshold level) for warning that the tire air pressure has decreased based on the reference value D ' _AVE std is set, and the corrected wheel speed deviation value D' is set.
_The air pressure drop rate is calculated from the change in _AVE , and the time at which the corrected wheel speed deviation value D ′ _AVE exceeds the warning threshold level is predicted from the calculated air pressure drop rate, and is set as a warning predicted time.

The air pressure drop determining unit 3h determines whether the tire pressure has decreased by determining whether the expected time calculated by the expected warning time calculating unit 3g has come. Specifically, when the estimated time comes, a warning signal indicating that the tire air pressure is decreasing is sent to the warning device 4.

When a warning signal indicating that the tire air pressure is low is input, the warning device 4 turns on a warning lamp provided in the vehicle interior, for example. It warns that the air pressure has dropped.

Next, FIGS. 2 and 3 show a flowchart of the tire pressure determination processing by the tire pressure detection device having the above-described configuration, and FIG. 4 shows a flowchart showing details of the warning determination processing in FIG. The details of the tire pressure determination process will be described based on these drawings.

First, in step S100, the operation count N is reset to N = 0. And step S
In 101, as a wheel speed calculation process based on detection signals from the wheel speed sensors 2a to 2d, a wheel speed calculation unit 3a
After calculating the wheel speeds V _FL , V _FR , V _RL , and V _RR of each wheel, the number N of wheel speed calculations is incremented. This processing is performed, for example, by calculating an average value of the wheel speed every several seconds for each wheel based on a wheel speed pulse of several seconds.

In step S102, as a wheel speed deviation value calculation process, a wheel speed deviation value D is calculated by a wheel speed deviation value calculation unit in the wheel speed deviation value processing unit 3b. The wheel speed deviation value D is obtained by substituting each wheel speed obtained in step S101 into the above equation (1).
Then, in step S103, the wheel speed deviation value D stored so far in the memory of the first wheel speed deviation value storage unit.
(N) is one of the wheel speed deviation values D calculated this time.
Is stored. Incidentally, D (N) is an array of the wheel speed deviation value D n ₀ pieces of, so that the wheel speed deviation value D n ₀ or stored, stores the wheel speed deviation D in locations that match the number of calculations N It has become. And n ₀ wheel speed deviation values D
Is stored, for example, when the number of calculations N is reset to 0 in the counter reset process (step S100), the wheel speed deviation value D stored at a location corresponding to the number of calculations N is calculated for the newly calculated wheel. The speed deviation value D is appropriately updated.

In the following step S104, the front and rear wheel speed ratio β is calculated by the front and rear wheel speed ratio calculation section in the front and rear wheel speed ratio processing section 3c as front and rear wheel speed ratio calculation processing. The front and rear wheel speed ratio β is also obtained by substituting each wheel speed obtained in step S101 into the above equation (2).
Then, in step S105, the front-rear wheel speed ratio β stored so far in the memory of the front-rear wheel speed ratio storage unit is used.
As one of (N), the front-rear wheel speed ratio β calculated this time
Is stored. Incidentally, beta (N) is an array of longitudinal wheel speed ratio beta of the n ₀ pieces of the front and rear wheel speed ratio beta n ₀ or stored, to store the longitudinal wheel speed ratio beta in locations that match the number of calculations N It has become. And n ₀ front-rear wheel speed ratios β
Is stored, as in the case of D (N) described above, the data is updated to the newly calculated front and rear wheel speed ratio β as appropriate.

Thereafter, in step S106, the number of operations N
Is greater than or equal to n ₀ . If an affirmative determination is made, the process proceeds to step S107 assuming that the n ₀ wheel speed deviation values D and the front and rear wheel speed ratios β are stored, and if a negative determination is made, the process returns to step S101.

In the following step S107, a slip deviation value A is obtained by a slip deviation value calculation section 3d as a slip deviation value calculation process. That is, using the least squares method, a regression line is derived by regressing the relationship between the n ₀ front-rear wheel speed ratio β and the wheel speed deviation value D to a linear function, and the slip deviation value A is calculated from the slope of the regression line. Ask. The slip deviation value A indicates the dependence of the wheel speed deviation value D on the front-rear wheel speed ratio β.

[0047] Subsequently, in step S108, the wheel speed deviation averaging process, calculates the average value D _{AV E} of the wheel speed deviation D in the wheel speed deviation averaging processor of the wheel speed deviation value processing unit 3b. This average value D _AVE is calculated in step S10.
The wheel speed deviation value D for n ₀ stored in the above equation (3) is calculated by the above equation (3).
Is obtained by substituting into

In step S109, the average value β of the front-rear wheel speed ratio β is calculated by the front-rear wheel speed ratio averaging processor in the front-rear wheel speed ratio processor 3c as the front-rear wheel speed ratio averaging process.
Calculate _AVE . This average value β _AVE is calculated in step S105.
Is obtained by substituting the front and rear wheel speed ratios β for n ₀ stored in the above _equation into the above _equation (4).

In step S110, as an ideal traveling state value calculation process, the ideal traveling state value βid is computed by the ideal traveling state value computing section 3e. This ideal running state value βid is obtained from a first-order or higher-order function relating to the slip deviation value A calculated in step S110.

Subsequently, in step S111, the wheel speed deviation value correction section in the wheel speed deviation value correction processing section 3f performs the wheel speed deviation value correction processing in steps S107 to S11.
The corrected wheel speed deviation value is obtained by substituting the slip deviation value A, the wheel speed deviation average value D _AVE , the front-rear wheel speed ratio average value β _AVE , and the ideal running state value βid obtained at 0 into Equation (5). _Find D ' _AVE .

FIG. 5 shows the corrected wheel speed deviation value D '.
_AVE , the slip deviation value A used to derive the corrected wheel speed deviation value D' _AVE , the ideal running state value βid, the wheel speed deviation average value D _AVE , and the front-rear wheel speed ratio average value β
The correlation of _AVE is shown, and these relationships will be specifically described.

FIG. 5 shows the correlation between the wheel speed deviation value D and the front / rear wheel speed ratio β when the tire pressure of one of the drive wheels 1c and 1d, here the left rear wheel, decreases. In this figure, white circles indicate the relationship between the calculated wheel speed deviation values D for n ₀ and the front and rear wheel speed ratio β,
A black circle indicates the relationship between the wheel speed deviation average value D _AVE and the front-rear wheel speed ratio average value β _AVE .

When the tire pressure of the left rear wheel, one of the driving wheels 1c and 1d, decreases, the wheel speed V _RL of the left rear wheel is reduced.
Increases, the front-rear wheel speed ratio β drops below 1 with a decrease in tire air pressure. Then, in the ideal running state, the ideal running state value βid is βid = F
(A). Therefore, as shown in step S113 of the present embodiment, based on the slip deviation value A,
An ideal running state value βid is obtained from the relationship βid = F (A).

On the other hand, as shown in step S107,
Using the least squares method, it is possible to derive a regression line obtained by regressing the relationship between the front and rear wheel speed ratios β for n ₀ and the wheel speed deviation value D into a linear function.

Therefore, as shown in step S111, the derived regression line and the ideal running state value βid = F
By determining the intersection with (A), the driving wheels 1c, 1d
The wheel speed deviation value D in an ideal running state when the air pressure drops, that is, the corrected wheel speed deviation value D' _AVE , can be obtained.

In this manner, the corrected wheel speed deviation value D' _AVE , which is the wheel speed deviation value D in an ideal running state when the air pressure of the drive wheels 1c and 1d is reduced, can be accurately obtained.

Subsequently, at step S112, the reference value D '
It is determined whether _AVE std has already been detected.
This is determined based on whether or not the reference value D ′ _AVE std is stored in the memory of the second wheel speed deviation value storage unit in the wheel speed deviation value correction processing unit 3f. If the corrected wheel speed deviation value D ' _AVE calculated this time is the first value obtained after the operation of the arithmetic processing unit 3, the reference value D' _AVE std is not stored.
13 to calculate the D ' _AVE calculated this time as the reference value D' _{A VE} s
It is stored in the memory as td, and the process returns to step S100.
At this time, a warning threshold level is set based on the stored reference value D ' _AVE std. In the case of the present embodiment, a value separated from the reference value D' _AVE std by a predetermined value D'sh is set to the warning threshold level. Is set as On the other hand, the corrected wheel speed deviation value D ′ calculated this time is
_{If AVE} is not the one obtained first, step S1
Proceed to 14.

Then, in step S114, a warning determination process is performed. This is performed by the warning expected time calculation unit 3g and the air pressure drop determination unit 3h. Details of the warning determination process will be described based on the flowchart shown in FIG.

First, in step S201, the corrected wheel speed deviation value D ' _AVE is compared with a reference value D' _AVE std.
It is determined whether or not the corrected wheel speed deviation value D ' _AVE has fallen below the reference value D' _AVE std. If a negative determination is made here, since the tire pressure has not decreased, the processing is terminated as it is. Conversely, when an affirmative determination is made, the process proceeds to step S202.

In the following step S202, it is determined whether or not a decrease in tire air pressure is currently being monitored. Whether or not this monitoring is being performed is determined based on the count value of a counter (not shown) provided in the expected warning time calculation unit 3h. When the count value is 0, it is determined that monitoring is not being performed yet.

If a negative determination is made in this step, the process proceeds to step S203, where counting by the counter is started, and the previously stored data is reset as the predicted time to warn. Specifically, the predicted warning time is set to infinity. Thereafter, the process proceeds to step S204. On the other hand, if an affirmative determination is made, the counting by the counter has already been started, and the expected warning time has been set, so the flow directly proceeds to step S204.

Next, after calculating the time T from the start of monitoring in step S204, the amount of decrease in the corrected wheel speed deviation value D' _AVE from the start of monitoring is calculated in step S205. Then, the process proceeds to step S206, and the air pressure reduction rate per unit time (ΔD ′ _AVE / ΔT) is calculated from the time T from the start of monitoring calculated in step S204 and the reduction amount of the corrected wheel speed deviation value D ′ _AVE. Calculate. Thereafter, the process proceeds to step S207, and a predicted warning time at which the corrected wheel speed deviation value D ' _AVE is expected to cross the warning threshold level is calculated based on the air pressure reduction rate per unit time.

Subsequently, in step S208, step S
It is determined whether the predicted warning time calculated in 207 is earlier than the predicted warning time (previous value) currently stored as data in the predicted warning time calculation unit 3h. If the determination is affirmative, the process proceeds to step S209,
After updating the previous value data stored in the predicted warning time calculation unit 3h to the data of the predicted warning time calculated this time, the process proceeds to step S210. On the other hand, if a negative determination is made, the process proceeds directly to step S210. In addition, the data of the expected warning time may be sequentially updated,
Since it is preferable that the timing of warning the driver of a decrease in tire air pressure is as early as possible, the data is updated only when the warning timing is advanced.

Then, in a step S210, it is determined whether or not the predicted warning time has come. Accordingly, if an affirmative determination is made, the process proceeds to step S211 and, assuming that the tire air pressure has decreased, a warning signal to that effect is sent to the alarm device 4, and if a negative determination is made, the process ends as it is. Through the above processing, it can be determined whether or not the tire air pressure at each of the wheels 1a to 1d has decreased.

FIG. 6 is a timing chart when the above-described processing is executed. In the above-described warning determination process, it calculates the warning predicted time at which the _AVE exceeds a warning threshold level 'corrected wheel speed deviation D based on the change of _AVE' corrected wheel speed deviation D. When the predicted warning time comes, the driver is warned of a decrease in tire air pressure regardless of whether or not the corrected wheel speed deviation value D' _AVE actually exceeds the warning threshold level.

Therefore, in the process of decreasing the air pressure, the vehicle speed increases as shown in FIG. 6 (b), and the tire pressure decreases as shown by the solid line in FIG. 6 (a) due to the influence of the tread lift. Even if the corrected wheel speed deviation value D' _AVE changes to the non-corrected side, it is possible to accurately detect a decrease in tire air pressure at the scheduled warning time indicated by the dotted line in the figure.

Further, since the data of the estimated warning time is not updated successively, but updated only when the timing of warning the driver of the decrease in tire pressure is advanced, the decrease in tire pressure is assumed at the earliest possible timing. Can be warned.

In the prior art, the wheel speed deviation value D is corrected with the front and rear wheel speed ratio β = 1 as a reference value for determining an ideal running state. Since the front and rear wheel speed ratio β does not become 1, overcorrection occurs. In such a case, the amount of change in the wheel speed deviation value D with respect to the decrease in tire air pressure differs depending on the driving wheel and the rolling wheel (follower wheel), and the pressure alerted when the tire air pressure decreases varies.

However, in the tire pressure detecting device according to the present embodiment, the slip deviation value A is obtained based on the wheel speed deviation value D and the front and rear wheel speed ratio β, and from this slip deviation value A, the ideal running state value βid = F The wheel speed deviation value D is corrected based on (A). For this reason, the corrected wheel speed deviation value D 'which is the wheel speed deviation value D in an ideal running state when the air pressure of the drive wheels 1c and 1d is reduced.
_AVE can be determined accurately without overcorrection.

Therefore, the variation in the corrected wheel speed deviation value D' _{AVE is} the same for both the driving wheel and the driven wheel, and it is possible to prevent variations in the alarmed pressure when the tire air pressure drops.

(Other Embodiments) In the above embodiment, the correction
Rear wheel speed deviation value D '_AVEIs the warning threshold level
Tire pressure drop is evaluated based on whether
But the reference value D ' _AVEstd and wheel speed deviation value D '
_AVE(ΔD ′_AVE= D '_AVEstd-D ' _AVE)
Differential pressure judgment value ΔD '_AVEAnd the differential pressure determination value ΔD ′_AVEBut
Reference value D '_AVESet to a predetermined width (D'sh) from std
Warning threshold level is exceeded or not.
The tire pressure may be evaluated.

Further, in each of the above-described embodiments, an example in which one embodiment of the present invention is applied to a rear-wheel drive vehicle has been described. However, the present invention may be applied to a front-wheel drive vehicle. In this case, the relationship is such that the ideal running state value βid becomes greater than 1 as the tire pressure of the drive wheel decreases.

In the above description, the wheel speed deviation value D shown in Expression 1 is used as the rotation state value.
Others may be used. That is, the rotation state value is
Any value may be used as long as the wheel speed of each of the wheels 1a to 1d is related so that the deviation of the wheel speed between the left and right wheels that may occur due to the vehicle turning is canceled out. For example, there are the following.

[0074]

(Equation 6)

[0075]

(Equation 7)

[0076]

(Equation 8)

All of these relational expressions are generated due to the turning of the vehicle by taking the respective differences between the left and right front wheels and between the right and left front wheels, where similar wheel speed deviations may occur during turning of the vehicle. The wheel speeds of the wheels 1a to 1d are associated with each other so that the deviation of the wheel speed between the left and right front wheels and between the left and right rear wheels is canceled.

As described in the above embodiment, when the system warns of a decrease in tire air pressure when the wheel speed deviation value D exceeds a predetermined threshold value, the slip deviation value (slope) A Is small, the wheel speed deviation value D due to slip need not be corrected. This is a problem even if there is some error since the wheel speed deviation value D may not exceed the threshold value when the slip deviation value A is small when the rear wheels (drive wheels) are depressurized. This is because the inclination A becomes almost zero in any case when the front wheel (rolling wheel) is depressurized, so that it is not necessary to correct the wheel speed deviation value D due to slip. Therefore, by excluding the case where the slip deviation value A is small from the correction target, it is possible to exclude the case where the necessity of the correction during the rear wheel depressurization and the case where the front wheel depressurization is low from the correction target.

[0079] In the above embodiments, after the average value D _AVE of the wheel speed deviation D, Betaid the average value D _AVE
= F (A) to obtain the corrected wheel speed deviation value D ′ _AVE by projecting the curve on the curve represented by F = (A). Each of the wheel speed deviation values D is represented by βid = F (A). After projecting on a curved line, an average value thereof may be taken.

In each of the above embodiments, each time the number of operations N reaches n ₀ , the wheel speed deviation values D and the front-rear wheel speed ratio β for n ₀ data stored up to that point are used.
The average value D _AVE and the average value β _AVE are obtained, and the absolute value | ΔD ′ _{A VE} | of the differential pressure determination value ΔD ′ _AVE is obtained. However, in such a case, the tire air pressure determination cannot be performed while n ₀ data is accumulated. For this reason, in the wheel speed deviation value storage unit and the front and rear wheel speed ratio storage unit, the oldest stored wheel speed deviation value D and front and rear wheel speed ratio β are newly calculated wheel speed deviation value D and front and rear wheel speed ratio. β is updated as appropriate, and the average value D _AVE and the average value β _AVE are calculated every time the value is updated, so that the tire air pressure can be determined every short time.

In the above embodiment, the case where the rotation state value (wheel speed deviation value D) is corrected based on the ideal traveling state value βid = F (A) has been described as an example. In the one that adopts the rotation state value correction method,
It is also possible to give a warning to be given at the predicted warning time shown in the above embodiment.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of a tire pressure detecting device according to a first embodiment of the present invention.

FIG. 2 is a flowchart of control executed by the tire pressure detecting device shown in FIG.

FIG. 3 is a flowchart of control executed by the tire pressure detecting device following FIG. 2;

FIG. 4 is a flowchart of a warning determination process shown in FIG.

5 is a graph showing a relationship between a wheel speed deviation mean D _{AV E} before correction in the tire air pressure detecting device and the corrected wheel speed deviation D _'AVE shown in FIG.

FIG. 6 is a timing chart for explaining a relationship between a vehicle speed, a corrected wheel speed deviation value D ′ _AVE , and an estimated warning time.

FIG. 7 is a diagram showing a relationship between a wheel speed deviation value D before correction and a wheel speed deviation value D 'after correction in a conventional tire pressure detection device.

FIG. 8 is a timing chart for explaining a relationship between a vehicle speed and a corrected wheel speed deviation value D ′.

[Explanation of symbols]

1a to 1d: wheels, 2a to 2d: wheel speed sensors, 3 ...
Arithmetic processing unit, 3a: wheel speed calculating unit, 3b: wheel speed deviation value processing unit, 3c: front and rear wheel speed ratio processing unit, 3d: slip deviation value calculating unit, 3e: ideal running state value calculating unit,
3f: Wheel speed deviation value correction processing unit, 3g: Warning expected time calculation unit, 3h: Air pressure drop determination unit, 4: Alarm device.

 ────────────────────────────────────────────────── ─── Continuing from the front page (71) Applicant 000000011 Aisin Seiki Co., Ltd. 2-1-1 Asahi-cho, Kariya-shi, Aichi (72) Inventor Motonori Tominaga 14 Iwatani, Shimoba-Kakucho, Nishio-shi, Aichi Japan Automotive Parts Co., Ltd. Within the Research Institute (72) Inventor Shunji Naito 1-1-1, Showa-cho, Kariya-shi, Aichi Prefecture Inside Denso Corporation (72) Inventor Hideki Ohashi 1-Toyota-cho, Toyota-shi, Aichi Prefecture Toyota Motor Corporation (72) Invention Mori Yukio 2-1-1 Asahicho, Kariya City, Aichi Prefecture Inside Aisin Seiki Co., Ltd.

Claims (6)

[Claims] 1. Wheel speed detecting means (2a-2) for detecting the wheel speed of each wheel of a front-wheel drive or rear-wheel drive vehicle.
d, 3a) and the rotational state obtained by relating the wheel speeds detected by the wheel speed detecting means so as to cancel the deviation of the wheel speed between the left and right wheels caused by the turning of the vehicle. Rotation state value calculation means (3) for calculating the value (D)
b) a slip state value calculation means (β) that calculates a slip state value (β) depending on the degree of slip state between the drive wheel and the driven wheel based on the wheel speed detected by the wheel speed detection means. 3c) regressing the rotation state value calculated by the rotation state value calculation means and the slip state value calculated by the slip state value calculation means into a linear function to derive a regression line (3d) ), A rotation state value correction unit (3f) that corrects the rotation state value obtained by the rotation state value calculation unit based on the regression line obtained by the regression operation unit; Tire pressure detection means (3h) for determining a decrease in tire pressure of each wheel based on the corrected rotation state value. It, based on the rotational state value the rotational state value correcting means is corrected, warning estimated time calculation means for the pneumatic pressure drop judging means for calculating a warning predicted time determines the tire air pressure reduction (3
g), wherein the air pressure drop determining means determines that the tire air pressure has dropped when the expected warning time calculated by the expected warning time calculating means has come. 2. The warning expected time calculating means calculates a time at which the rotation state value corrected by the rotation state value correcting means is expected to exceed a predetermined threshold level as the warning predicted time. The tire pressure detecting device according to claim 1, wherein 3. The predicted warning time calculating means calculates the predicted warning time from a change amount per unit time of the rotation state value corrected by the rotation state value correcting means. 3. The tire pressure detecting device according to 2. 4. A storage unit (3g) for storing data of a predicted warning time calculated by the predicted warning time calculating unit, wherein the storing unit stores the data of the previous predicted warning time stored as data. If the currently calculated expected warning time is earlier, the data of the previous predicted warning time stored in the storage unit is updated to the data of the currently calculated expected warning time. The tire pressure detecting device according to any one of claims 1 to 3, wherein: 5. An ideal state value (βid = Fid) corresponding to the slip state value in an ideal running state without slip.
(A)), and an ideal running state value calculating means (3e), wherein the rotation state value correcting means includes a regression line calculated by the regression calculating means and an ideal running state calculated by the ideal running state calculating means. The tire pressure detection device according to any one of claims 1 to 4, wherein a rotation state value in an ideal running state is determined from the state value. 6. A wheel speed deviation value (D) which is given as a difference between wheel speed ratios of front and rear wheels in a diagonal relationship as the rotation state value. The tire pressure detecting device according to any one of claims 1 to 5, wherein