JP5039804B2 - Tire internal pressure drop detection method and apparatus, and tire internal pressure drop detection program - Google Patents

Description

  The present invention relates to a tire internal pressure drop detection method and apparatus, and a tire internal pressure drop detection program.

  There is known a method of indirectly detecting whether or not the air pressure of the tire is decreased by comparing the rotational angular velocities of the tires mounted on the vehicle (see, for example, Patent Documents 1 and 2).

  In these methods, the running state of the vehicle is limited (running at a constant speed on a straight road), the wheel speeds of the four wheels at that time are relatively compared, and when the wheel speed increases by one wheel, the tire is reduced by decompression. It is judged that this is because the dynamic load radius (DLR) has decreased, and an alarm is issued.

In the relative comparison, for example, a pressure reduction determination value (DEL) as shown in the following formula (1) is used, and when the pressure reduction determination value exceeds a predetermined threshold, it is determined that the pressure is reduced. Yes.
DEL = {(F1 + F4) / 2− (F2 + F3) / 2} / {(F1 + F2 + F3 + F4) / 4} × 100 (%) (1)
Here, F1 to F4 are rotational angular velocities of the tires of the left front wheel, the right front wheel, the left rear wheel, and the right rear wheel, respectively.

  In this case, there is no clear standard for how much the dynamic load radius decreases, in other words, how much the rotational speed increases, and it is determined that the pressure is reduced. If it exceeds, it will be determined that the pressure is reduced.

JP 63-305011 A Japanese Patent Laid-Open No. 2005-1419

  By the way, in general, the internal pressure dependence of the dynamic load radius of the tire (the degree of change in the dynamic load radius due to the decrease in the tire internal pressure) is almost the same depending on the tire size, and the amount or amount of decrease in the internal pressure to be detected is large. If determined, the margin of decrease in the dynamic load radius due to such a decrease in internal pressure can be determined almost uniquely for each tire size.

  The decrease in the dynamic load radius can be obtained by experimentation, but it is not practical to measure all tires, so that it is determined that the tire internal pressure has decreased. In the conventional method including the method described in Patent Document 1, the threshold value is calculated in consideration of a reduction margin when, for example, 30% of one tire is depressurized, assuming a case where a representative tire is mounted. The decompression judgment value is used.

However, in general passenger cars, there are generally multiple sizes of tires that can or will be installed in the passenger car, and which of the multiple set sizes is installed in the vehicle. I don't know if it will be done individually.
Therefore, if the determination criterion, which is the threshold value of the tire internal pressure drop warning device, is set to a constant value (fixed value), an alarm may not be issued accurately depending on the size of the mounted tire.

  This invention is made in view of such a situation, and provides the tire internal pressure fall detection method and apparatus which can set the alarm threshold value according to a tire size simply, and a tire internal pressure fall detection program. It is an object.

The tire internal pressure drop detection method of the present invention (hereinafter also simply referred to as “detection method”) is based on relative comparison of the wheel speeds of tires mounted on each wheel of a front-wheel drive vehicle or a rear-wheel drive vehicle that is running. A method for detecting a decrease in tire internal pressure,
Detecting wheel rotation information of each tire of the vehicle;
Calculating the wheel speed from the detected wheel rotation information;
Obtaining a decompression determination value by relative comparison of the calculated wheel speeds;
A step of determining a decrease in the internal pressure of the tire when the magnitude of the obtained decompression judgment value exceeds a predetermined threshold,
It further includes a threshold value setting step set based on the pressure reduction sensitivity obtained from the relationship between the load sensitivity and the pressure reduction sensitivity and the load sensitivity obtained by turning during initialization.
The load sensitivity is estimated by comparing the amount of change in the dynamic radius of the left and right driven wheels when turning the vehicle obtained from the wheel speed and the amount of change in the dynamic radius of the left and right driven wheels when turning the vehicle obtained from the wheel speed. Further, when the wheel speeds of the right wheel and the left wheel of the driven wheel (idler) and the driving wheel (drive) are respectively ω _R and ω _L , the regression coefficients are obtained from the following equations.

  In the detection method of the present invention, the change in the dynamic load radius during turning, that is, the rate of change in the dynamic load radius due to the load movement, that is, the load sensitivity, is obtained by utilizing the fact that load movement occurs on the left and right wheels when the vehicle is turning. Then, the pressure reduction sensitivity is obtained from the relationship between the load sensitivity and the pressure reduction sensitivity at the time of turning of the vehicle related to the tire to be mounted on the vehicle and the load sensitivity obtained by turning at the time of initialization. A threshold is set based on the sensitivity. Since the load movement during turning occurs in any vehicle, an alarm threshold value corresponding to the tire size can be easily set. The load sensitivity can be estimated by comparing the change amount of the dynamic load radius on the left and right of the driven wheel and the change amount of the dynamic load radius on the left and right of the driving wheel when turning the vehicle obtained from the wheel speed. Since no kind is required, the apparatus can be simplified.

The tire internal pressure drop detection device (hereinafter also simply referred to as “detection device”) according to the present invention performs relative comparison by comparing wheel speeds of tires mounted on each wheel of a front-wheel drive vehicle or a rear-wheel drive vehicle that is running. An apparatus for detecting a decrease in tire internal pressure,
Wheel rotation information detecting means for detecting wheel rotation information of each tire of the vehicle;
Wheel speed calculating means for calculating the wheel speed from the wheel rotation information detected by the wheel rotation information detecting means;
Determination value calculation means for obtaining a pressure reduction determination value by relative comparison of wheel speeds calculated by the wheel speed calculation means;
Determining means for determining a decrease in the internal pressure of the tire when the magnitude of the obtained decompression judgment value exceeds a predetermined threshold,
The predetermined threshold value is determined in advance from the relationship between the load sensitivity and the depressurization sensitivity when turning the vehicle related to the tire to be mounted on the vehicle, and the load sensitivity obtained by turning during initialization. It further includes a threshold setting means for setting based on the sensitivity,
This threshold value setting means is based on a comparison between the amount of change in the dynamic load radius on the left and right of the driven wheel at the time of vehicle turning obtained from the wheel speed and the amount of change in the dynamic load radius on the left and right of the drive wheel at the time of vehicle turning obtained from the wheel speed. The load sensitivity is estimated, and assuming that the wheel speeds of the right wheel and the left wheel of the driven wheel (idler) and the driving wheel (drive) are ω _R and ω _L respectively, the regression coefficient is obtained from the following formula: Yes.

  In the detection device of the present invention, the change in the dynamic load radius during turning, that is, the rate of change in the dynamic load radius due to the load movement, that is, the load sensitivity, is obtained by utilizing the fact that load movement occurs on the left and right wheels when the vehicle is turning. Then, the pressure reduction sensitivity is obtained from the relationship between the load sensitivity and the pressure reduction sensitivity at the time of turning of the vehicle related to the tire to be mounted on the vehicle and the load sensitivity obtained by turning at the time of initialization. A threshold is set based on the sensitivity. Since the load movement during turning occurs in any vehicle, an alarm threshold value corresponding to the tire size can be easily set. The load sensitivity can be estimated by comparing the change amount of the dynamic load radius on the left and right of the driven wheel and the change amount of the dynamic load radius on the left and right of the driving wheel when turning the vehicle obtained from the wheel speed. Since no kind is required, the apparatus can be simplified.

The tire internal pressure drop detection program (hereinafter also simply referred to as “program”) according to the present invention compares the wheel speeds of tires mounted on each wheel of a front-wheel drive vehicle or a rear-wheel drive vehicle that is running, thereby comparing the tires. Computer to detect a decrease in internal pressure,
Wheel speed calculating means for calculating wheel speed from wheel rotation information of each tire of the vehicle,
Determination value calculation means for obtaining a pressure reduction determination value by relative comparison of wheel speeds calculated by the wheel speed calculation means;
A determination means for determining a decrease in the internal pressure of a tire when the magnitude of the obtained pressure reduction determination value exceeds a predetermined threshold, and a vehicle related to a tire to be attached to the vehicle for which the predetermined threshold is determined in advance The threshold setting means functions as threshold setting means for setting based on the pressure sensitivity obtained from the relationship between the load sensitivity and the pressure reduction sensitivity during turning and the load sensitivity obtained by turning during initialization. The load sensitivity is estimated by comparing the amount of change in the dynamic load radius on the left and right of the driven wheel when turning the vehicle obtained from the speed and the amount of change in the dynamic load radius on the left and right of the drive wheel when turning the vehicle obtained from the wheel speed. If the wheel speeds of the right wheel and the left wheel of the driving wheel (idler) and the driving wheel (drive) are ω _R and ω _L respectively, the regression coefficient is obtained from the following equation.

  According to the tire internal pressure drop detection method and apparatus and the tire internal pressure drop detection program of the present invention, it is possible to easily set an alarm threshold corresponding to the tire size.

It is a block diagram which shows one Embodiment of the detection apparatus of this invention. It is a block diagram which shows the electrical structure of the detection apparatus shown by FIG. It is a figure which shows the relationship between the ground speed of a driven wheel left-right wheel at the time of left turn, and vehicle speed. It is a figure explaining various parameters of vehicles. It is a figure which shows the relationship between the ground speed of the driving wheel right-and-left wheel at the time of left turn, and vehicle speed. It is a figure which shows the relationship between pressure reduction sensitivity and a load sensitivity representative characteristic value (coefficient of X). It is a figure which shows the relationship between pressure reduction sensitivity and a load sensitivity representative characteristic value (coefficient of Y).

Hereinafter, embodiments of a detection method and apparatus and a program according to the present invention will be described in detail with reference to the accompanying drawings.
As shown in FIG. 1, the detection device according to an embodiment of the present invention includes four tires FL (left front wheel), FR (right front wheel) provided in a four-wheel vehicle that is a front-wheel drive vehicle or a rear-wheel drive vehicle. In order to detect wheel rotation information of front wheels), RL (left rear wheel) and RR (right rear wheel), a normal wheel speed detection means (wheel rotation information detection means) 1 provided in association with each tire is provided. ing.

  The wheel speed detection means 1 generates power using rotation like a wheel speed sensor or dynamo for generating rotation pulses using an electromagnetic pickup or the like and measuring the rotation angular speed and wheel speed from the number of pulses. It is possible to use an angular velocity sensor including that for measuring the rotational angular velocity and the wheel speed from this voltage. The output of the wheel speed detecting means 1 is given to a control unit 2 which is a computer such as ABS. The control unit 2 includes a liquid crystal display element for informing a tire whose internal pressure has decreased, a display 3 composed of a plasma display element or a CRT, an initialization button 4 that can be operated by a driver, and an internal pressure of the tire. An alarm device 5 is connected to notify the driver of the decrease.

  As shown in FIG. 2, the control unit 2 stores an I / O interface 2a necessary for passing signals to and from an external device, a CPU 2b that functions as a center of arithmetic processing, and a control operation program for the CPU 2b. The ROM 2c and the RAM 2d from which data is temporarily written or the written data is read when the CPU 2b performs a control operation.

  The wheel speed detection means 1 outputs a pulse signal corresponding to the number of rotations of the tire (hereinafter also referred to as “wheel speed pulse”). Further, the CPU 2b calculates the rotation angular velocity of each tire at a predetermined sampling period ΔT (sec), for example, ΔT = 0.05 seconds, based on the wheel speed pulse output from the wheel speed detecting means 1.

  The detection device according to the present embodiment includes wheel speed detection means (wheel rotation information detection means) 1, wheel speed calculation means for calculating wheel speed from wheel rotation information detected by the wheel rotation information detection means, Determination value calculation means for obtaining a pressure reduction determination value by relative comparison of wheel speeds calculated by the wheel speed calculation means, and determination of a decrease in tire internal pressure when the magnitude of the obtained pressure reduction determination value exceeds a predetermined threshold value The determination means, the relationship between the load sensitivity at the time of turning of the vehicle and the pressure reduction sensitivity related to the tire to be mounted on the vehicle, and the load sensitivity obtained by turning at the time of initialization And a threshold value setting means for setting based on the pressure reduction sensitivity obtained from the above. The threshold value setting means is based on a comparison between a change amount of dynamic load radii on the left and right of a driven wheel obtained from the wheel speed and a change amount of dynamic load radii on the left and right sides of the drive wheel obtained from the wheel speed. The load sensitivity is estimated. The tire internal pressure drop detection program causes the control unit 2 to function as wheel speed calculation means, determination value calculation means, determination means, and threshold setting means.

The threshold value of DEL for determining the decrease in internal pressure can be determined, for example, by how much the dynamic load radius of the tire decreases when the tire is depressurized 25% or 30%.
That is, assuming that the change amount DEL ′ of DEL when the tire air pressure is reduced by 1% is the pressure reduction sensitivity, this pressure reduction sensitivity is proportional to the rate of change β (= ΔDLR / DLR) of the dynamic load radius at the time of 1% pressure reduction.
For example, when the RR wheel is depressurized by 1%, if the dynamic load radius of the RR wheel becomes smaller by β than the dynamic load radius at normal pressure, the wheel speed of the RR wheel increases by about β. At this time, DEL '
DEL ′ = 2 × {(V + V + βV) − (V + V)} / (V + V + V + V + βV) × 100
It becomes. Here, V is the wheel speed of the four wheels at normal internal pressure.

Since β is a very small value and 4 + β≈4, DEL ′ = (β / 2) × 100. Thus, the pressure reduction sensitivity is proportional to the rate of change (β) in the dynamic load radius during pressure reduction. Further, since the rate of change (β) of the dynamic load radius during decompression is proportional to the load sensitivity as will be described later, the decompression sensitivity is also proportional to the load sensitivity.
It is known that the rate of change of the dynamic load radius due to the change in internal pressure is almost constant depending on the tire and is almost determined by the tire size. Therefore, if the information about the pressure reduction sensitivity is obtained in advance through experiments or the like, the threshold value for each tire can be determined.

  However, even if the specifications of the developed vehicle are actually decided, there are usually multiple tire size settings, so even if you know the pressure reduction sensitivity for only one of the tire sizes, the tire size to be installed is different. In the case of the size, since the threshold value does not match the actual tire, it is impossible to accurately detect a decrease in the internal pressure of the tire. In particular, when the flatness ratio of the tire having grasped the decompression sensitivity is 70, whereas the flatness ratio of the tire actually mounted is 50, the decompression sensitivity depending on the size is large. Therefore, if the threshold value is determined based on the pressure reduction sensitivity of a tire with a flatness ratio of 70, a decrease in the internal pressure of a tire with a flatness ratio of 50 cannot be accurately detected. The same applies to the opposite case (when the flatness of the actually mounted tire is considerably larger than the flatness of the tire whose pressure reduction sensitivity is known).

  The present inventor has various methods so that it is possible to accurately determine a decrease in the internal pressure of the tire without having to know the pressure reduction sensitivity in advance for all tires, and to accurately determine without limitation on applicable vehicle types. As a result of repeated studies, we have devised a method for setting the threshold in consideration of the effect of reduced pressure sensitivity due to the difference in size. That is, the pressure reduction sensitivity is based on the knowledge that there is a proportional relationship with the amount of change in the dynamic load radius with respect to the load (hereinafter also referred to as “load sensitivity”). The present invention has been completed by utilizing the phenomenon that occurs.

  Specifically, since the decompression sensitivity and load sensitivity are in a proportional relationship, if only the proportional constant between the decompression sensitivity and load sensitivity is known in advance by experiment, the decompression sensitivity is automatically calculated from the load sensitivity. It is possible to calculate a threshold value corresponding to a tire that is actually mounted. As described later, the load sensitivity can be obtained by comparing the amount of change in the dynamic load radius of the left and right driven wheels with the amount of change in the dynamic load radius of the left and right wheels of the driving wheel when the vehicle is turning. The amount of change in the dynamic load radius of the left and right wheels of the driven wheel and the amount of change in the dynamic load radius of the left and right wheels of the driven wheel can be obtained only from the wheel speed calculated from the wheel rotation information of the tire mounted on the vehicle. That is, since a GPS device and sensors (a yaw rate sensor and a lateral acceleration sensor) are unnecessary, the detection device can be simplified.

  The preliminary experiment for determining the relationship between the reduced pressure sensitivity and the load sensitivity does not need to be performed for all sizes and patterns that are planned to be mounted, and the reduced pressure sensitivity and the load sensitivity are in a fixed proportional relationship. It is only necessary to measure at least one, preferably about three, tires of different sizes and determine the proportionality constant.

The pressure reduction sensitivity and load sensitivity are considered to be proportional for the following reasons.
The dynamic load radius of a tire is mainly determined by the circumference of the tire breaker, but changes when the tire breaker bends due to a decrease in the load acting on the tire or the tire internal pressure. The amount of deflection is proportional to the contact area of the tire, and the amount of deflection when the contact area is large is large. Here, the ground contact area S is
There is a relationship of ground contact area S∝load / internal pressure. In other words,
Change in dynamic load radius = Change in deflection amount ∝ Contact area S ∝ Load / Internal pressure (2)
Are in a relationship.

  From the relationship shown in (2), since an increase in load with respect to a change in dynamic load radius is equivalent to a decrease in internal pressure, the influence of internal pressure on the dynamic load radius can be replaced with the influence of load.

[Internal pressure drop detection method]
Hereinafter, the detection method of the present invention will be described.
(1) First, based on the output signal (pulse signal) of the wheel speed detection means 1, the rotational angular velocity (ω) of each tire is calculated by the following equation (3).
Rotational angular velocity (ω) = 2π × Freq (Hz) / N (pieces) (3)
Here, N is the number of teeth per one rotation of the axle of the wheel speed detecting means 1, and Freq (Hz) is a numerical value obtained by counting the teeth of the wheel speed detecting means 1 per second.

  The tire dynamic load radius also changes due to factors other than a decrease in tire internal pressure, such as acceleration / deceleration, turning, and running on a slope, so the vehicle's running condition is limited (running on a flat road at a constant speed) It is preferable to adopt the data obtained in such a state as valid data, and in this way, by excluding changes in the tire dynamic load radius due to other factors from the data for determining the internal pressure drop, A decrease in internal pressure can be determined.

  Specifically, whether or not the driving conditions satisfy conditions such as constant speed driving, flat road driving, and straight driving are compared with the respective determination conditions, and the data obtained during actual driving is used for calculating the determination value. It is determined whether the data is suitable for the data. If the data is inappropriate, the data is excluded without being used as data for calculating the determination value. As the determination conditions, for example, the vehicle front-rear direction | G | <0.05G, the direction change is 1 degree or less, the road surface gradient is 5% or less, and the brake is not stepped on.

  (2) Next, for example, DEL for determining the reduced pressure is calculated according to the equation (1).

It should be noted that a predetermined number of the DELs can be accumulated, and the determination of a decrease in tire internal pressure can be made based on the average value. In this case, the accuracy of the determination can be increased by adopting the average value. Alternatively, the dispersion of DEL accumulated in a predetermined number may be determined as mother variance, and the average value of DEL may be calculated when the variance (σ ² ) is smaller than the reference value.

(3) Next, the calculated DEL is compared with a predetermined threshold value, and if the DEL is larger than the threshold value, it is determined that the tire internal pressure has decreased, and the depressurization is displayed by the display unit 3, and the alarm device 5 gives a warning to the driver.
[Threshold setting method]
In order to set the threshold, first, as a first step, an actual vehicle experiment (calibration) is performed to determine the relationship between the load sensitivity and the pressure reduction sensitivity, and a constant for determining the pressure reduction sensitivity from the load sensitivity is determined, and this constant is stored. It is memorized in the means. Then, as the second stage, the load sensitivity is estimated when the vehicle is turning at the time of initialization of the actual driving, and the pressure is automatically reduced at the initialization stage by multiplying the estimated load sensitivity by the stored proportionality constant. Set the threshold.
Hereinafter, the threshold setting method will be described in detail.

[Calibration]
In the first stage, the relationship between the pressure reduction sensitivity and the load sensitivity is obtained by conducting an actual vehicle experiment (calibration) in advance. In the preliminary experiment, turning is performed with tires of various sizes (in each experiment, four wheels are the same type of tire), and load sensitivity is calculated. Further, the pressure is reduced to an internal pressure at which a pressure reduction alarm is issued (for example, 25% pressure reduction. This value can be changed), and the dynamic load radius change ratio (dynamic load radius change amount / dynamic load radius) at that time is calculated. Then, a proportional constant between the pressure reduction sensitivity and the load sensitivity proportional to the dynamic load radius change ratio is obtained, and the value is stored in the storage means in advance.

  As described above, the pressure reduction sensitivity and the load sensitivity are proportional to each other, so it is not necessary to perform this preliminary experiment on the relationship between the pressure reduction sensitivity and the load sensitivity. It is only necessary to measure at least one tire, preferably about three tires of different sizes, and obtain a proportionality constant.

  A feature of the present invention is that the load sensitivity is obtained from the amount of change in the dynamic load radius caused by the load movement by utilizing the fact that the load movement occurs between the left and right wheels when the vehicle is turning. When turning, the load movement occurs between the left and right wheels in any vehicle, so that the load sensitivity can be obtained regardless of the vehicle type. Moreover, since the dynamic load radius change amount can be calculated only from the wheel speed, the threshold value can be easily set even in a vehicle not equipped with a GPS device or a special sensor (yaw rate sensor or lateral acceleration sensor). it can.

  In the present invention, the load sensitivity is estimated by utilizing the fact that the amount of load movement during turning is generally different between the driven wheel and the drive wheel. That is, since the amount of load movement during turning differs between the driven wheel and the driving wheel, the amount of change in the dynamic load radius during turning also differs between the driven wheel and the driving wheel. Since it is possible to relatively compare the dynamic load radius change amount (wheel speed change amount) of the driven wheel left and right wheels and the dynamic load radius change amount (wheel speed change amount) of the drive wheel left and right wheels, this is used. Thus, the load sensitivity can be estimated.

<Driver wheel left and right wheels>
Next, the relationship between the change in the dynamic load radius of the left and right driven wheels and the load movement amount when the front wheel drive vehicle is turning will be described.
First, as shown in FIG. 3, it is assumed that the vehicle is turning left on the circumference of the radius (R) at the yaw rate (θ ′) and the speed (V). At this time, the relationship of the following formula (4) is established among the turning radius (R), the yaw rate (θ ′), and the velocity (V).
θ ′ = V / R (4)

If the ground speed of the outer ring (right wheel) is V _R , the ground speed of the inner ring (left wheel) is V _L , and the tread width is W,
(R + W / 2) × θ ′ = V _R
(R−W / 2) × θ ′ = V _L
Therefore, the yaw rate (θ ′) is expressed by the following equation (5). The vehicle speed (V) is expressed by the following equation (6).

Then, from the equations (5) and (6), the equation (7) can be derived as follows. Here, the ground speeds V _L and V _R are determined by V _L = (DLR + ΔDLR) × ω _L from the wheel speed (ω) and the dynamic load radius (DLR).
V _R = (DLR−ΔDLR) × ω _R
It is expressed.
Here, the sum of ground speeds V _L and V _R (V _R + V _L ) is
V _R + V _L = (DLR + ΔDLR) × ω _L + (DLR−ΔDLR) × ω _R
= DLR (ω _R + ω _L ) −ΔDLR (ω _R −ω _L )
However, since ΔDLR (ω _R −ω _L ) ≈0,
V _R + V _L ≈DLR (ω _R + ω _L ).

  Further, the following formula (8) can be derived from the formula (7).

  (ΔDLR / DLR) in the equation (8) is proportional to the load movement amount (ΔFz, see FIG. 4), the load sensitivity is b, and the load movement share ratio applied to the driven wheel shaft with respect to all the axes is α (0 <α <1). ), It is expressed by the following formula (9).

Since the load movement share α, the height of the center of gravity (H), the tread width (W), and the mass (m) are basically uniquely determined for the same vehicle, the coefficient of a _y (lateral acceleration) is determined by the load sensitivity b. The bigger the tire, the bigger.

<Drive wheel left and right wheels>
Next, the relationship between the change in the dynamic load radius of the left and right wheels of the driving wheel and the load movement amount when the front wheel drive vehicle is turning will be described.
As in the case of the driven wheel (FIG. 3), as shown in FIG. 5, it is assumed that the vehicle is turning left on the circumference of the radius (R). In the case of driving wheels, slip due to driving force is generated, and it is necessary to consider the influence. Furthermore, it is necessary to consider that the slip ratio of the outer ring becomes smaller than the slip ratio of the inner ring due to an increase in the contact area of the outer ring during turning.

The driving force (Fx) and the slip ratios (s + Δs, s−Δs) of the left and right wheels satisfy the relationship represented by the following formula (10), where the driving stiffness at that time is D _L and D _R.
Fx = D _L · (s + Δs) + D _R · (s−Δs) (10)
Further, since the driving force is evenly distributed to the left and right by the differential of the vehicle, D _L · (s + Δs) = D _R · (s−Δs) (11)
It becomes.

Here, since the tires for the left and right wheels are basically the same, D _L and D _R are the driving stiffness per unit area of the mounted tire, G, the ground contact area at the standard load is reduced by load movement due to turning Let ΔA be the amount of change in the ground contact area that increases (increases).
D _L = G (A−ΔA) (11) ′
D _R = G (A + ΔA) (11) ″
It becomes.

Further, the ground contact area (A) and the change amount (ΔA) satisfy the following formula (11) with the reference load (Fz) and the load movement amount (ΔFz).
ΔA / A = ΔFz / Fz (12)
That is, the slip ratio and the load are obtained from the equations (11), (11) ′, (11) ″.

Satisfy the relationship.
As in the case of driven wheels, looking at the relationship between 1 / R and wheel speed,

  Here, since Δs · ΔDLR, ΔDLR (ωR−ωL) and Δs · (ωR−ωL) on the right side can be regarded as almost zero,

<Relationship between driven wheel and drive wheel>
When the vehicle is turning around the radius R, the relationship between the turning radius of each of the driven wheel (idler) and the driving wheel (drive)

[Initialization]
The detection device is initialized by operating the initialization button 4 after the tire is replaced with a new one and adjusted to a predetermined internal pressure. However, when the vehicle is turned during this initialization, it is the same as the calibration described above. To estimate the load sensitivity. Then, by multiplying the estimated load sensitivity by a proportional constant with the decompression sensitivity stored in advance in the storage means, a decompression threshold value is automatically set at the initialization stage, and is also stored in the storage means.

〔Example〕
Next, examples of the detection method of the present invention will be described. However, the present invention is not limited to such examples.
In order to obtain the rotation angular velocity of each tire mounted on the vehicle, the rotation angular velocity was converted into the rotation angular velocity using the rotation velocity information used for the ABS control.

  The experiment was performed with an FF vehicle, and the reference internal pressure was 200 kPa. In addition, calibration was performed with three types of tires (see Table 1).

Calibrate the Okayama test course of sequentially attached to Sumitomo Rubber Industries, Ltd. three types of tires shown in Table 1 in the calibration FF vehicle, the load sense Dodai table characteristic value X ₁ (Formula (15) It was calculated coefficients) and reduced pressure sensitivity of X ₂ (see Table 1). And the proportionality constant between load sensitivity-decompression sensitivity was calculated | required.
For load sensitivity, the slope of the approximate straight line was determined according to equation (15). The slope can be calculated online by using a sequential least square method or the like. The factor because changes only by the load sensitivity b, which was used as a load sense Dodai table characteristic value. In this specification, “load sensitivity” includes not only mere load sensitivity but also values that change only by this load sensitivity (parameters consisting of load sensitivity and a value uniquely determined in the vehicle). There is.
On the other hand, for the pressure reduction sensitivity, the pressure was actually reduced by a predetermined amount (for example, 25%), and the dynamic load radius change amount at that time was calculated. The results are shown in Table 1.

Wherein the results of the calibration, seeking load sensitivity representative characteristic value (coefficient of X _1, the coefficients X ₂₎ proportional constant of the decreased pressure sensitivity, as shown in FIGS. 6 and 7, and preset the value in the storage means. In this embodiment, the proportionality constant relating to a coefficient of _{X 1} is -0.0005, proportionality constant relating to a coefficient of _{X 2} was -0.0015. 6 and 7, the equation shown at the top of the graph is an equation representing an approximate line of the relationship between the load sensitivity representative characteristic value and the pressure reduction sensitivity, and “R ² ” is a phase of the approximate line. Indicates the number of relationships.
Therefore,
1. Decompression sensitivity = −228 × (X ₁ coefficient) −0.0007
2. Decompression sensitivity = −729 × (X ₂ coefficient) −0.00024
It became.

When a tire T having a threshold value set was attached to the FF vehicle and the vehicle made a turn during initialization, the coefficients of X ₁ and X ₂ were calculated in the same manner as described above. The obtained coefficients of X ₁ and X ₂ were −3.27 × 10 ⁻⁵ and −9.12 × 10 ⁻⁶ , respectively.

Assuming that the decompression amount at which the decompression alarm is desired is 25%, the decompression sensitivity is estimated from this. Threshold = 25 (% decompression) × Decompression sensitivity = 25 × {−228 × (−3.27 × 10 ⁻⁵ ) −0.0007} = 0.17
2. Threshold = 25 (% decompression) × Decompression sensitivity = 25 × {−729 × (−9.12 × 10 ⁻⁶ ) −0.00024} = 0.16
It becomes.
The values estimated from the respective coefficients are averaged to obtain a pressure reduction sensitivity estimated value. That is, in the case of the tire T of this embodiment, the threshold value is automatically set to 0.17 (= (0.17 + 0.16) / 2) at the end of initialization.

  Next, each tire shown in Table 1 was decompressed 30% after initialization, and the presence or absence of false alarms or no alarms was compared with a conventional method (adopting a fixed threshold obtained with a typical tire as a decompression threshold). The results are shown in Table 2.

  As shown in Table 2, when the threshold value is set to a fixed value, depending on the setting of the threshold value, there may be an unalarmed (or false alarm). However, according to the method of the present invention, the decompression can be accurately determined. Can do.

1 Wheel speed detection means 2 Control unit 2a Interface 2b CPU
2c ROM
2d RAM
3 Display 4 Initialization button 5 Alarm

Claims (3)

A method of detecting a decrease in internal pressure of a tire by comparing the wheel speeds of tires mounted on each wheel of a front wheel drive vehicle or a rear wheel drive vehicle that is running,
Detecting wheel rotation information of each tire of the vehicle;
Calculating the wheel speed from the detected wheel rotation information;
Obtaining a decompression determination value by relative comparison of the calculated wheel speeds;
A step of determining a decrease in the internal pressure of the tire when the magnitude of the obtained decompression judgment value exceeds a predetermined threshold,
The predetermined threshold value is a pressure reduction sensitivity obtained from a relationship between a load sensitivity and a pressure reduction sensitivity at the time of turning of the vehicle relating to a tire to be mounted on the vehicle, which has been obtained in advance, and a load sensitivity obtained by turning at the time of initialization. Further including a threshold setting step set based on
The load sensitivity is estimated by comparing the amount of change in the dynamic radius of the left and right driven wheels when turning the vehicle obtained from the wheel speed and the amount of change in the dynamic radius of the left and right driven wheels when turning the vehicle obtained from the wheel speed. The tire internal pressure drop detection is characterized by the regression coefficient obtained from the following equations, where the wheel speeds of the right wheel and the left wheel of the driven wheel (idler) and the driving wheel (drive) are ω _R and ω _L respectively. Method.

A device for detecting a decrease in the internal pressure of the tire by comparing the wheel speeds of the tires mounted on each wheel of the front-wheel drive vehicle or the rear-wheel drive vehicle that is running,
Wheel rotation information detecting means for detecting wheel rotation information of each tire of the vehicle;
Wheel speed calculating means for calculating the wheel speed from the wheel rotation information detected by the wheel rotation information detecting means;
Determination value calculation means for obtaining a pressure reduction determination value by relative comparison of wheel speeds calculated by the wheel speed calculation means;
Determining means for determining a decrease in the internal pressure of the tire when the magnitude of the obtained decompression judgment value exceeds a predetermined threshold,
The predetermined threshold value is determined in advance from the relationship between the load sensitivity and the depressurization sensitivity when turning the vehicle related to the tire to be mounted on the vehicle, and the load sensitivity obtained by turning during initialization. It further includes a threshold setting means for setting based on the sensitivity,
This threshold value setting means is based on a comparison between the amount of change in the dynamic load radius on the left and right of the driven wheel at the time of vehicle turning obtained from the wheel speed and the amount of change in the dynamic load radius on the left and right of the drive wheel at the time of vehicle turning obtained from the wheel speed. The load sensitivity is estimated, and when the wheel speeds of the right wheel and the left wheel of the driven wheel (idler) and the driving wheel (drive) are respectively ω _R and ω _L , the regression coefficient is obtained from the following formulas: Tire internal pressure drop detecting device.

A computer for detecting a decrease in the internal pressure of the tire by comparing the wheel speed of the tire mounted on each wheel of the front-wheel drive vehicle or the rear-wheel drive vehicle that is running,
Wheel speed calculating means for calculating wheel speed from wheel rotation information of each tire of the vehicle,
Determination value calculation means for obtaining a pressure reduction determination value by relative comparison of wheel speeds calculated by the wheel speed calculation means;
A determination means for determining a decrease in the internal pressure of a tire when the magnitude of the obtained pressure reduction determination value exceeds a predetermined threshold, and a vehicle related to a tire to be attached to the vehicle for which the predetermined threshold is determined in advance The threshold setting means functions as threshold setting means for setting based on the pressure sensitivity obtained from the relationship between the load sensitivity and the pressure reduction sensitivity during turning and the load sensitivity obtained by turning during initialization. The load sensitivity is estimated by comparing the amount of change in the dynamic load radius on the left and right of the driven wheel when turning the vehicle obtained from the speed and the amount of change in the dynamic load radius on the left and right of the drive wheel when turning the vehicle obtained from the wheel speed. wheel (idler) and the driven wheel (where drive) right wheel and the left wheel, respectively omega _R the wheel speeds _of, when omega _L, the tire pressure drop detection, characterized in that the regression coefficient obtained from the following formula Program.

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