JP2005127975A - Method and system for tire air failure sensing, and program of tire pressure reduction determining - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for tire air failure sensing which can extend detectable area of tire air failure to enhance accuracy of pressure reduction determining by detecting simultaneous pressure reduction in all wheels. <P>SOLUTION: This is the tire air failure sensing method to detect reduction of tire air pressure based on wheeling information obtained from tires loaded on a car. It comprises a process for seeking wheeling information obtained from each of the above tires, a process for memorizing the wheeling information, a process for computing load sensitivity of energy load radius of the tire depending on load traveling in revolution, a process for comparing the load sensitivity of energy load radius of the tire depending on load traveling in revolution with the previously-memorized load sensitivity of an energy load radius of the tire in initialization, and aprocess for determining air failure of the tire based on the result of such comparison. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a tire pressure drop detection method and apparatus, and a tire decompression determination program. More specifically, the present invention relates to a tire air pressure drop detection method and apparatus, and a tire decompression judgment program that can expand a region for judging a decrease in tire air pressure and improve the accuracy of pressure reduction judgment.

Conventionally, the tire pressure drop detection device uses the principle that when the tire is depressurized, the outer diameter (dynamic load radius of the tire) is smaller than that of a tire with normal internal pressure, so the rotational angular velocity is increased compared to other normal tires. ing. For example, in the method of detecting a decrease in internal pressure from the relative difference in the rotational angular velocity of the tire,
DEL = {(F1 + F4) / 2- (F2 + F3) / 2} / {(F1 + F2
+ F3 + F4) / 4} × 100 (%)
(Patent Document 1). Here, F1 to F4 are rotational angular velocities of the front left tire, the front right tire, the rear left tire, and the rear right tire, respectively.

JP 63-305011 A

  However, in order to detect tire decompression using so-called decompression sensitivity, the conventional device reduces the dynamic load radius of the tire by reducing the pressure from the difference between the rotational angular velocities at the diagonals of the four wheels. Judging. Therefore, simultaneous decompression of the two front wheels, simultaneous decompression of the two rear wheels, and simultaneous decompression of all the wheels cannot be detected. For this reason, there is a problem that if the vehicle is running under reduced pressure without knowing that the pressure has been reduced, fuel consumption deteriorates due to an increase in rolling resistance of the tire, leading to a burst.

  In view of the above circumstances, the present invention expands an area for determining a decrease in tire air pressure by detecting simultaneous depressurization of all wheels, and a tire pressure decrease detection method and apparatus capable of improving the accuracy of the depressurization determination. An object of the present invention is to provide a tire decompression determination program.

  A tire pressure drop detection method according to the present invention is a tire pressure drop detection method for detecting a drop in tire pressure based on wheel rotation information obtained from a tire mounted on a vehicle, wherein the wheel rotation information obtained from each tire is detected. A step of determining, a step of storing the wheel rotation information, a step of determining a load sensitivity of a dynamic load radius of the tire by the load movement at the time of turning, a load sensitivity of the dynamic load radius of the tire by the load movement at the time of turning The method includes a step of comparing the stored load sensitivity of the dynamic load radius of the tire at the time of initialization, and a step of determining a decrease in tire air pressure based on a result of the comparison.

  The tire pressure drop detection method of the present invention is a tire pressure drop detection method for detecting a tire pressure drop based on wheel rotation information obtained from a tire mounted on a vehicle, and the wheel rotation obtained from each tire. A step of obtaining information, a step of storing the wheel rotation information, a step of obtaining a relational expression between a lateral acceleration and a determination value that is a relative comparison of wheel rotation information on a pair of diagonal lines, and storing the relational expression in advance And a step of comparing a lateral acceleration at initialization and a relational expression of a determination value, and a step of determining a decrease in tire air pressure based on a result of the comparison.

  Furthermore, the tire pressure drop detection device of the present invention is a tire pressure drop detection device that detects a drop in tire pressure based on wheel rotation information obtained from a tire mounted on a vehicle, and the wheel rotation information obtained from each tire. Rotation information detecting means for determining the wheel rotation information, storage means for storing the wheel rotation information, sensitivity calculating means for determining the load sensitivity of the dynamic load radius of the tire due to load movement during turning, and movement of the tire due to load movement during turning Sensitivity comparison means for comparing the load sensitivity of the load radius with the load sensitivity of the dynamic load radius of the tire at the time of initialization stored in advance, and a determination means for determining a decrease in tire air pressure based on the result of the comparison It is characterized by.

  The tire pressure drop detecting device of the present invention is a tire pressure drop detecting device that detects a drop in tire air pressure based on wheel rotation information obtained from a tire mounted on a vehicle, and the wheel rotation obtained from each tire. Rotation information detecting means for obtaining information, storage means for storing the wheel rotation information, relational expression calculating means for obtaining a relational expression between a lateral acceleration and a determination value that is a relative comparison of wheel rotation information on a pair of diagonal lines; A comparison means for comparing the relational expression with a relational expression of a lateral acceleration at initialization stored in advance and a judgment value; and a judgment means for judging a decrease in tire air pressure based on the comparison result. It is characterized by that.

  Furthermore, the tire decompression determination program of the present invention includes a computer for determining a decrease in tire air pressure based on wheel rotation information obtained from a tire mounted on a vehicle, storage means for storing the wheel rotation information, Sensitivity calculation means for obtaining the load sensitivity of the dynamic load radius of the tire by load movement, load sensitivity of the dynamic load radius of the tire by load movement at the time of turning, and load sensitivity of the dynamic load radius of the tire at the time of initialization stored in advance It is characterized by functioning as a sensitivity comparison means for comparing the tire pressure and a judgment means for judging a decrease in tire air pressure based on the result of the comparison.

  Further, the tire decompression determination program according to the present invention includes a computer for determining a decrease in tire air pressure based on wheel rotation information obtained from a tire mounted on a vehicle, storage means for storing the wheel rotation information, and lateral direction. Relational expression calculating means for obtaining a relational expression between the acceleration and a judgment value that is a relative comparison of wheel rotation information on a pair of diagonal lines, the relational expression and a relational expression between the lateral acceleration at initialization and the judgment value stored in advance It is characterized by functioning as a comparison means for comparing the tire pressure and a determination means for judging a decrease in tire air pressure based on the result of the comparison.

  According to the present invention, since all-wheel depressurization can be detected, the accuracy of depressurization determination can be improved.

  Hereinafter, a tire pressure drop detecting method and apparatus and a tire decompression determination program according to the present invention will be described with reference to the accompanying drawings.

  As shown in FIG. 1, the tire pressure drop detecting device according to one embodiment of the present invention detects whether or not the pressures of the four tires FL, FR, RL and RR provided in the vehicle are lowered. Therefore, it is provided with normal rotation information detecting means 1 provided in association with each tire.

  The rotation information detecting means 1 uses rotation like a wheel speed sensor or dynamo for generating rotation pulses by using an electromagnetic pickup or the like and measuring wheel speed information of rotation angular speed and wheel speed from the number of pulses. Then, it is possible to use an angular velocity sensor including one for generating power and measuring the rotational angular velocity and wheel speed from this voltage. The output of the rotation information detecting means 1 is given to a control unit 2 which is a computer such as ABS. Connected to the control unit 2 are a liquid crystal display element for informing a tire whose air pressure has dropped, a display 3 composed of a plasma display element or a CRT, an initialization switch 4 that can be operated by a driver, and an alarm 5. Has been.

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

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

By the way, since tires are manufactured with variations (initial differences) within the standard, the effective rolling radius of each tire (the value obtained by dividing the distance advanced by one rotation by 2π) is normal even for all tires. Even air pressure is not necessarily the same. Therefore, the rotational angular velocity Fi of each tire varies. Therefore, for example, there is a method of eliminating the influence of the initial difference from the rotational angular velocity Fi. In this method, first, initial correction coefficients K1, K2, and K3 shown below are calculated.
K1 = F1 / F2 (1)
K2 = F3 / F4 (2)
K3 = (F1 + K1 × F2) / (F2 + K2 × F4) (3)

Next, a new rotational angular velocity F1 _i is obtained using the calculated initial correction coefficients K1, K2, and K3 as shown in equations (4) to (7).
F1 ₁ = F1 (4)
F1 ₂ = K1 × F2 (5)
F1 ₃ = K3 × F3 (6)
F1 ₄ = K2 × K3 × F4 (7)
Here, the initial correction coefficient K1 is a coefficient for correcting the difference in effective rolling radius due to the initial difference between the front left and right tires. The initial correction coefficient K2 is a coefficient for correcting the difference in effective rolling radius due to the initial difference between the rear left and right tires. The initial correction coefficient K3 is a coefficient for correcting a difference in effective rolling radius due to an initial difference between the front left tire and the rear left tire.

And based on said F1 _i , the wheel speed Vi of the tire of each wheel, the vehicle speed V, a lateral acceleration, etc. are calculated. For example, for the lateral acceleration of the vehicle, in the case of an FR vehicle, the speeds V1 and V2 of the driven wheel tires FL and FR are calculated, and then the turning radius R is calculated.
R = {(V2 + V1) / (V2-V1)} × T _W / 2 (8)
Here, T _W is the distance between kingpins (tread width) (m).

Based on the turning radius R of the vehicle, the lateral acceleration of the vehicle can be calculated by the following equation (9).
Lateral acceleration = V ² / R (9)
The lateral acceleration can also be obtained by a lateral acceleration sensor.

Further, in the present embodiment, as a determination value DEL for detecting a decrease in air pressure, as shown in the following equation (10), the pressure reduction sensitivity of the tire dynamic load radius is used on a pair of diagonal lines. A judgment value that is a relative comparison of wheel speeds is used. That is, the average value of the wheel speed from the other pair of wheels on the diagonal line is subtracted from the average value of the wheel speed from the pair of wheels on the diagonal line, and the ratio between the result and the average value of the two totals is calculated. Use.
DEL = {(V1 + V4) / 2- (V2 + V3) / 2} /
{(V1 + V2 + V3 + V4) / 4} × 100 (%) (10)
Here, V1 to V4 are wheel speeds of the front left tire FL, the front right tire FR, the rear left tire RL, and the rear right tire RR, respectively.

  Since the judgment value DEL uses the pressure reduction sensitivity and compares the diagonal sum of the wheel speeds on a pair of diagonal lines, the difference between the wheel speeds on the outside and inside of the turn is canceled during the turn, There should be no shift in the determination value DEL. However, in actuality, the judgment value DEL during turning shifts due to the influence of load movement during turning and the influence of slipping of the drive wheels.

(1) That is, first, in a vehicle that is turning, because the load is moved by lateral acceleration toward the outside of the turn, the load applied to the tire on the outside of the turn becomes heavy, and the load applied to the tire on the inside of the turn becomes light. The tire dynamic load radius (wheel speed) changes.

For example, if the increase amount (deceleration amount) of the front wheel tire and the rear wheel tire due to the load movement at the time of left turn is dVf and dVr, the determination value DEL of the equation (10) is
DEL '= {(V1-dVf + V4 + dVr) / 2- (V2 + dVf + V3-dVr) / 2} / {(V1 + V2 + V3 + V4) / 4} × 100 (%)
= {(V1 + V4)-(V2 + V3) -2 * (dVf-dVr)} /
{(2 × V)} × 100 (%) (11)
It is.

Taking the difference between Equation (10) and Equation (11),
ΔDEL = {(dVf−dVr) / V} × 100 (%) (12)
It becomes.

  This ΔDEL is the difference between the wheel speed change (dVf / V) due to the load movement of the front tire and the wheel speed change (dVr / V) due to the load movement of the rear tire, and the shift of the judgment value DEL during turning. It corresponds to the amount. This shift amount does not include the effect of slipping.

  The wheel speed changes (dVf / V) and (dVr / V) indicate how much the dynamic load radius of the tire changes depending on the load by normalizing with a proportional load movement amount, respectively. It is proportional to the load sensitivity of the rear wheel tire and the load sensitivity of the rear wheel tire.

That is, the wheel speed change (dVf / V) is proportional to the load movement amount and load sensitivity of the front wheel tire, and the wheel speed change (dVr / V) is proportional to the load movement amount and load sensitivity of the rear wheel tire. Since the load movement amount of the rear wheel is proportional to the lateral acceleration, the formula (12) is eventually expressed as follows. That is, when the lateral acceleration LG is taken on the X axis and ΔDEL is taken on the Y axis, ΔDEL is proportional to the lateral acceleration LG, and the inclination thereof is proportional to the tire load sensitivity. Note that the% display is omitted.
ΔDEL = α × LG × LSf−β × LG × LSr = (α × LSf−β × LSr) × LG
... (13)
Here, LG: lateral acceleration LSf: front wheel tire load sensitivity LSr: rear wheel tire load sensitivity α, β: coefficient.

Further, if the slope of the relationship between the lateral acceleration LG and ΔDEL (the shift amount of the DEL value) is F1,
F1 = α × LSf−β × LSr (14)
It is.

Further, the load sensitivity LSf, LSr decreases due to a decrease in the pressure reduction sensitivity of the front and rear wheel tires, and assuming that the load sensitivity is proportional to the pressure reduction rate, if the pressure is reduced at the same ratio for all four wheels, the slope F1 ′ after pressure reduction is
F1 ′ = γ × (α × LSf−β × LSr) (15)
It can be expressed as However, | γ | ≦ 1.

(2) Further, the determination value DEL is shifted because the slip caused by driving the lighter turning inner drive wheel is larger than the slip caused by driving the heavier turning outer drive wheel.

  When the load movement amount of the front wheel and the rear wheel is the same (equal), the influence of the load movement amount is canceled by the calculation of the determination value of the above formula (8), and therefore the determination value DEL after the slip correction even during turning. Does not shift. However, since the front-to-back ratio of the load movement amount of the vehicle during turning is not 1 and is substantially constant regardless of the magnitude of the lateral acceleration, the corrected determination value DEL shifts.

  However, since the load movement amount is proportional to the lateral acceleration generated by the turn, the shift amount ΔDEL of the determination value DEL after correcting the influence of the slip is also proportional to the lateral acceleration.

(3) Since the judgment value (DEL) during turning is shifted under the influence of the load movement and the slip due to driving, it is usually corrected as follows.
Correction DEL = DEL−F (f1, f2) (16)
Here, F (f1, f2) is a function of the correction factor, f1 corresponds to the slope F1, and f2 is obtained from the relationship between the judgment value DEL and lateral acceleration × (front and rear wheel ratio−1). Factor. Accordingly, F1 is obtained by calculating f1 by correcting only the influence of slip from the DEL value during turning.

  In addition, the load sensitivity of the dynamic load radius of the tire varies depending on the type of tire (size, flatness, etc.). The aspect ratio of the tire is a ratio (H / W) × 100 (%) of the tire cross-sectional height H to the tire maximum width W.

  Next, the present invention will be described based on the first embodiment, but the present invention is not limited to the first embodiment.

Example 1
Tires having substantially the same outer diameter and different flatness ratios (for example, 185 / 70R14 88S (tire T1), 205 / 60R16 92H (tire T2) or 225 / 50R17 94V (tire T3)), so-called compatible sizes For tires, the relationship between load sensitivity and pressure reduction sensitivity associated with air pressure and vehicle speed was investigated.

  In this example, for the tires T1, T2 and T3, a drum test is performed by setting the case where the pressure of all the tires is 200 kPa of normal pressure and 140 kPa of reduced pressure, and the case where the vehicle speed is 50 km / h and 100 km / h. Was done.

  The load sensitivity in this example is the dynamic load radius change when the wheel load is changed by 50% in the case of the air pressure (200 kPa, 140 kPa) and the vehicle speed (50 km / h, 100 km / h). It was obtained by dividing by the dynamic load radius at the time. The load at 200 kPa (the LI value specified load) is specified by the tire LI (load index) according to JATMA, 4.95 kN for tire T1, 5.54 kN for tire T2, and 5.88 kN for tire T3. It is. For example, with respect to the tire T2, the dynamic load radius at the time of 100% wheel load is 314.9 mm. Then, when the air pressure is 200 kPa and the vehicle speed is 100 km / h, the dynamic load radius when the wheel load is changed by 2.77 kN of 50%, depending on the rotation speed ratio between the drum and the tire whose circumference is known. Therefore, this change was expressed as a ratio to 314.9 mm, and 0.66% was obtained as load sensitivity.

  Similarly, load sensitivity was determined for an air pressure of 200 kPa, a vehicle speed of 50 km / h, an air pressure of 140 kPa, a vehicle speed of 100 km / h, and 50 km / h.

  For tires T1 and T3, the dynamic load radii when the load is changed by 2.77 kN are obtained from the 100% wheel load as in the tire T1, and then the dynamic load radii at the time of 100% load are 297.4 mm and 317.4 mm. To obtain the load sensitivity.

  On the other hand, the pressure reduction sensitivity is a value obtained by subtracting a dynamic load radius at a pressure of 140 kPa from a dynamic load radius at a pressure of 200 kPa under a load of 75% of a load load (LI value specified load) at 200 kPa (dynamic load). (Radius change) was divided by the dynamic load radius at an air pressure of 200 kPa. For example, for the tire T2, a dynamic load radius of 314.2 mm at an air pressure of 140 kPa is subtracted from a dynamic load radius of 315.7 mm at an air pressure of 200 kPa in a state of 75% load (4.155 kN). Then, the subtracted value was divided by 315.7 mm to obtain 0.48% as the reduced pressure sensitivity.

  Therefore, as shown in FIG. 3, there is a high correlation between the pressure reduction sensitivity and the load sensitivity, and the following relationship. In FIG. 3, x is a pressure reduction sensitivity, y is a load sensitivity, and R is a correlation coefficient.

Load sensitivity at high internal pressure (200 kPa)> Load sensitivity at low internal pressure (140 kPa) That is, as described above, the pressure reduction sensitivity correlates with the load sensitivity, and the load sensitivity at low internal pressure is at normal air pressure (at high internal pressure). It was found to be smaller than the load sensitivity.

  Therefore, in the present embodiment, the storage means, the sensitivity calculation means for obtaining the load sensitivity during turning, the sensitivity comparison means for comparing the load sensitivity during turning with the load sensitivity during initialization stored in advance, and the comparison First determination means for determining a decrease in tire air pressure based on the result is provided. The tire decompression determination program according to the present embodiment causes the control unit 2 to function as a storage unit, a sensitivity calculation unit, a sensitivity comparison unit, and a first determination unit.

  As a result, the load sensitivity at the time of initialization performed at the time of a new car or tire replacement (at normal air pressure) is memorized, and the load sensitivity of the tire dynamic load radius due to load movement at the time of turning is measured periodically. Simultaneous pressure reduction (all-wheel pressure reduction) can be detected by comparing with the stored initial load sensitivity.

  By using the conventional apparatus together with the apparatus according to the present embodiment, a region for determining a decrease in tire air pressure is widened, and the accuracy of pressure reduction determination can be improved. As the comparison, for example, a method of comparing a difference or a ratio with a predetermined threshold value can be used. It should be noted that the relationship between the pressure reduction sensitivity and the load sensitivity immediately after initialization is obtained by running at the time of initialization, and is stored in the ROM 2c of the control unit 2.

Example 2
1800cc FF vehicle (tire size tire 185 / 70R14) is prepared, and slip correction is performed for traveling with the tires in normal pressure (200 kPa) and 50% decompression of all wheels (round trip between Okayama Test Course and Tsuyama City). Later determination value DEL and lateral acceleration were obtained. As a result, as shown in FIGS. 4 to 5, the slope at normal air pressure is 0.3125, whereas the slope at the time of all-wheel decompression is as small as 0.1434. Thus, it was found that the all-wheel depressurization can be detected from the inclination of the judgment value DEL during turning with respect to the lateral acceleration.

  Also, for example, when the decompression judgment for a four-wheel tire is set to 30% decompression, 0.3125 × 30 ÷ 50 = 0.1875 is set as an alarm threshold value, and the inclination becomes smaller than this threshold value. If a warning is sometimes issued, it can be determined that the four-wheel tire has been decompressed by 30%.

  Therefore, the inclination of the judgment value DEL during turning with respect to the lateral acceleration (during non-driving) is measured periodically after initialization, and the initial inclination is compared with the inclination during actual running to reduce the pressure, for example, Wheel decompression can be estimated. In addition, the pressure reduction sensitivity of the attached tire can be estimated by comparing the inclination at the time of initialization with the inclination at the time of the previous initialization.

  In the present embodiment, a relational expression calculating means for obtaining a relational expression between the lateral acceleration and the judgment value, and a comparison means for comparing the relational expression with a relational expression between the lateral acceleration at initialization stored in advance and the judgment value. And determination means for determining a decrease in tire air pressure based on the result of the comparison. The tire decompression determination program according to the present embodiment causes the control unit 2 to function as storage means, relational expression calculation means, comparison means, and determination means.

  In addition to the device according to this embodiment, a conventional device, for example, a device that detects coaxial two-wheel pressure reduction or same-side two-wheel pressure reduction is used because load sensitivity is reduced even if the pressure of two coaxial wheels or two wheels on the same side is reduced. As a result, a region for determining a decrease in tire air pressure is widened, and the accuracy of pressure reduction determination can be improved.

  For example, in the coaxial two-wheel depressurization, after obtaining the slip rate when the acceleration / deceleration of the vehicle is within a predetermined range near zero, the slip rate is compared with the slip rate obtained at the normal air pressure obtained in advance. Then, the determination can be made based on the relationship between the comparison value of the two slip ratios and a predetermined threshold value. Further, as the same-side two-wheel depressurization, after comparing the wheel speeds of all the left wheels of the vehicle and the wheel speeds of all the right wheels when running in a straight line, the relationship between the comparison value and a predetermined threshold value. Can be determined based on

1 is a block diagram showing a tire pressure drop detecting device according to an embodiment of the present invention. FIG. 2 is a block diagram showing an electrical configuration of the tire pressure drop detecting device of FIG. 1. It is the figure which compared the load sensitivity of the dynamic load radius of a tire, and the correlation of the pressure sensitivity, and the load sensitivity at the time of normal pressure (200 kPa) and pressure reduction (140 kPa). It is a figure which shows the relationship between the determination value DEL and lateral acceleration in the state of normal air pressure. It is a figure which shows the relationship between the determination value DEL and the lateral acceleration in the state of all-wheel 50% pressure reduction.

Explanation of symbols

1 Rotation information detection means 2 Control unit 3 Display 4 Initialization switch 5 Alarm

Claims (6)

A method for detecting a decrease in tire air pressure based on wheel rotation information obtained from a tire mounted on a vehicle, the step of obtaining wheel rotation information obtained from each tire, and storing the wheel rotation information The step of determining the load sensitivity of the dynamic load radius of the tire due to the load movement during turning, the load sensitivity of the tire dynamic load radius due to the load movement during turning and the movement of the tire during initialization stored in advance. A tire pressure drop detection method including a step of comparing load sensitivity of a load radius and a step of determining a tire pressure drop based on a result of the comparison. A method for detecting a decrease in tire air pressure based on wheel rotation information obtained from a tire mounted on a vehicle, the step of obtaining wheel rotation information obtained from each tire, and storing the wheel rotation information A step of obtaining a relational expression between a lateral acceleration and a judgment value that is a relative comparison of wheel rotation information on a pair of diagonal lines; a lateral acceleration and judgment value at initialization stored in advance A method for detecting a decrease in tire air pressure, including a step of comparing the relational expression and a step of determining a decrease in tire air pressure based on the comparison result. A tire pressure drop detecting device for detecting a drop in tire pressure based on wheel rotation information obtained from a tire mounted on a vehicle, the rotation information detecting means for obtaining wheel rotation information obtained from each tire, and the wheel rotation Storage means for storing information; sensitivity calculation means for obtaining the load sensitivity of the dynamic load radius of the tire due to load movement during turning; and load sensitivity of the dynamic load radius of the tire due to load movement during turning and the initial stored in advance A tire pressure drop detection device comprising sensitivity comparison means for comparing the load sensitivity of a dynamic load radius of a tire at the time of conversion, and determination means for determining a tire pressure drop based on a result of the comparison. A tire pressure drop detecting device for detecting a drop in tire pressure based on wheel rotation information obtained from a tire mounted on a vehicle, the rotation information detecting means for obtaining wheel rotation information obtained from each tire, and the wheel rotation A storage means for storing information; a relational expression calculating means for obtaining a relational expression between a lateral acceleration and a judgment value that is a relative comparison of wheel rotation information on a pair of diagonal lines; A tire pressure drop detecting device comprising: comparing means for comparing the lateral acceleration of the tire and a relational expression of the judgment value; and judging means for judging a decrease in tire air pressure based on the result of the comparison. A computer for determining a decrease in tire air pressure based on wheel rotation information obtained from a tire mounted on a vehicle, storage means for storing the wheel rotation information, load sensitivity of a dynamic load radius of a tire due to load movement during turning Sensitivity calculating means for obtaining the sensitivity, means for comparing the load sensitivity of the dynamic load radius of the tire due to load movement at the time of turning and the load sensitivity of the dynamic load radius of the tire at the time of initialization stored in advance, the result of the comparison A tire decompression determination program for functioning as a determination means for determining a decrease in tire air pressure based on the above. A computer for determining a decrease in tire air pressure based on wheel rotation information obtained from a tire mounted on a vehicle, storage means for storing the wheel rotation information, a relative acceleration between lateral acceleration and a pair of diagonal wheel rotation information Relational expression calculating means for obtaining a relational expression with a judgment value as a comparison, comparison means for comparing the relational expression with a relational expression between a lateral acceleration at initialization stored in advance and a judgment value, based on the result of the comparison A tire decompression determination program for functioning as a determination means for determining a decrease in tire air pressure.

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