JP2006138668A - Warning method and device for drop in pneumatic pressure of tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a warning method and device for drop in pneumatic pressure of a tire and a program for determining the pressure drop, capable of simultaneously detecting the four-wheel pressure drop. <P>SOLUTION: The process of the warning device is composed of a process of detecting the rotational speed of each wheel mounted on a vehicle; a process of finding the turning radii of the front wheels from the wheel rotational speed of the front wheels of the vehicle; a process of finding the turning radii of the rear wheels from the rotational speed of the rear wheels of the vehicle; a process of finding the difference between the turning radii of the front wheels found and the rear wheels, a process of finding the acceleration in the lateral direction of the vehicle; a process of finding the relation of the difference of the turning radii and the lateral directional acceleration; and a process of finding the drop of the pneumatic pressure from the relation between the difference of turning radii. Furthermore, the primary coefficient of the regression of the relation between the difference in the turning radii of the front and rear wheels and the acceleration of lateral direction are obtained, and the primary coefficient of regression obtained is compared with that obtained previously in normal state, then the drop in the pneumatic pressure of the mounted tire can be detected. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a tire pressure drop warning method and apparatus, and a tire decompression determination program. More specifically, the present invention relates to a tire pressure drop warning method and apparatus capable of detecting coaxial two-wheel pressure reduction, four-wheel simultaneous pressure reduction or tire wear, and a tire pressure reduction determination program.

Conventionally, the indirect tire pressure drop detection device reduces the outer diameter (tire dynamic load radius) of a tire with normal pressure (normal internal pressure) when the tire is depressurized. Therefore, the rotational angular velocity is different from that of other normal tires. The principle that (wheel speed) increases is used. For example, in the method of detecting a decrease in air pressure from the relative difference in tire rotation angular velocity,
DEL = {(F1 + F4) / 2− (F2 + F3) / 2} /
{(F1 + F2 + F3 + F4) / 4} × 100 (%)
(See, for example, 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.

  However, since this method determines the pressure reduction from the difference between the sum of the rotational angular velocities at the diagonals of the four wheels, it is possible to determine the simultaneous pressure reduction of the coaxial two-wheel tire or the case where the four-wheel tire is simultaneously naturally decompressed. could not.

  Therefore, the present applicant has previously proposed a method and an apparatus for reducing tire air pressure that can detect at least the pressure reduction of the drive wheel tire in the indirect method using tire rotation information (see Patent Document 2).

  The method disclosed in Patent Document 2 calculates a wheel speed, a vehicle acceleration, a front / rear wheel slip ratio, a travel distance, and a turning radius from the tire rotation information, and stores the rotation information of each tire. A step of moving and averaging the vehicle acceleration and the slip ratio of the front and rear wheels, and a step of accumulating the travel distance, the moving average of the vehicle acceleration and the slip ratio of the front and rear wheels when the turning radius is equal to or greater than a predetermined value; When the accumulated travel distance is equal to or greater than a predetermined distance, a step of obtaining a first-order regression coefficient and a correlation coefficient between the vehicle acceleration and the slip ratio of the front and rear wheels, and the correlation coefficient is predetermined The primary regression coefficient in the case where the value is equal to or greater than the value is used as a determination value, and the determination value of the primary regression coefficient is compared with the internal pressure reference value of the primary regression coefficient calculated in advance by the above process at the time of the tire reference internal pressure. By It is intended to include a step of determining whether at least a driving wheel tire is being reduced pressure, based on the result of the judging decompression, and a step for issuing an alarm of decrease in tire air-pressure. In this method, the vehicle acceleration and the slip ratio are obtained based on the wheel speed of the four-wheel tire by utilizing the fact that the relationship between the vehicle acceleration and the slip ratio is changed when the internal pressure of the tire of the drive wheel is reduced. From the temporal change of the next regression coefficient, the simultaneous decompression of one drive wheel tire or the left and right drive wheel tires is determined.

  Patent Document 3 is a method of detecting simultaneous depressurization of four wheels by comparing the turning radius of a vehicle obtained from the rotational speed of a wheel and the steering angle. Patent Document 4 determines a decrease in air pressure in a vehicle equipped with a differential limiting device by correcting the turning radius using a difference in turning radius obtained from the rotational speeds of the driving wheel and the driven wheel as a shift amount.

  Further, although not a method of detecting simultaneous depressurization of four wheels, Patent Documents 5, 6 and 7 are methods of using the turning radius of a vehicle for depressurization determination. Patent Document 5 is a method for determining a decrease in air pressure for each region of the turning radius from the relationship between the reciprocal of the turning radius obtained from the rotational speed of the drive wheel and the tire air pressure determination value. Patent Document 6 obtains a turning radius from the rotational speed of the driven wheel, compares the turning radius obtained from the corrected rotational speed of the driving wheel with the turning radius obtained from the driven wheel, and determines the pressure reduction of the driven wheel. It is. Patent Document 7 is a method of accurately detecting a decrease in tire air pressure by calculating a turning radius of a vehicle that eliminates variations caused by load movement of the vehicle.

JP 63-305011 A Japanese Patent Laid-Open No. 2003-211925 JP 2003-205717 A JP 2000-190718 A Japanese Patent Laid-Open No. 11-123911 JP-A-9-66714 JP-A-8-145654

  However, since the method described in Patent Document 2 basically detects a decrease in the internal pressure of the driving wheel, it cannot detect the pressure reduction of only the driven wheel. Even if the drive wheels are depressurized, the relationship between the vehicle acceleration and slip ratio used as the depressurization criterion shows the same tendency as when the tires are worn. It must be determined whether the tire's internal pressure is decreasing or the tire is worn. For this reason, in the method described in Patent Document 2, when the initialization switch is not operated for a predetermined period or after the initialization switch is operated, the total travel distance until the initialization switch is operated again is the predetermined distance. In such a case, a warning can be issued to check the tire pressure.

  In the conventional method of detecting four-wheel pressure reduction, the steering angle is detected (Patent Document 3) or limited to a vehicle equipped with a differential limiting device (Patent Document 4).

  In view of the above circumstances, an object of the present invention is to provide a tire pressure drop alarm method and apparatus capable of detecting simultaneous reduction of four wheels, and a tire decompression determination program.

  When the tire air pressure decreases, the longitudinal spring constant and torsional rigidity of the tire change, so that the tire turning performance changes, and the vehicle posture at the time of turning appears when the internal pressure is normal and when the air pressure decreases. As a result, a difference appears in the tire rotation behavior of the front and rear wheels during turning. Generally, when turning, the tire rotation center plane rotates at a certain angle with respect to the traveling direction of the vehicle. This is a so-called slip angle, and even if a curve having the same curvature is turned at the same speed, the slip angle differs if the tire internal pressure is different. As a result, when organized by lateral acceleration, there is a difference in the difference in turning radius calculated for each of the front and rear wheels when normal internal pressure and when air pressure drops. From this difference, the basic idea of this patent is to detect that the air pressure has dropped.

  The turning performance of the tire also changes depending on the slipperiness of the road surface, but in the low μ road, the slip area in the tire contact surface is large, and it is accompanied by a large slip ratio compared to the high μ road. There is no clear correlation between the difference between acceleration and front and rear wheel turning radius.

  A tire pressure drop warning method according to the present invention is a tire pressure drop warning method for detecting a tire pressure drop of a tire mounted on a vehicle based on a rotation speed of a wheel mounted on the vehicle and issuing an alarm. A step of detecting the rotational speed of each mounted wheel, a step of obtaining a turning radius of the front wheel from the wheel rotational speed of the front wheel of the vehicle, and a step of obtaining a turning radius of the rear wheel from the wheel rotational speed of the rear wheel of the vehicle Determining the difference between the determined turning radius of the front wheel and the turning radius of the rear wheel, determining the lateral acceleration of the vehicle, and determining the relationship between the difference in the turning radius and the lateral acceleration; And a step of detecting a decrease in tire air pressure from the relationship between the difference in turning radius and lateral acceleration.

  Further, in the tire pressure drop warning method of the present invention, a primary regression coefficient is obtained from the relationship between the turning radius difference and lateral acceleration, and the difference between the turning radii of the front and rear wheels of the vehicle previously obtained at normal internal pressure is obtained. It is characterized by detecting a decrease in the air pressure of the mounted tire by comparing with a linear regression coefficient in relation to the lateral acceleration.

  Further, the tire pressure drop alarm device according to the present invention is a tire pressure drop warning device that detects a pressure drop of a tire mounted on a vehicle based on a rotation speed of a wheel mounted on the vehicle and issues an alarm. Rotational speed detecting means for detecting the rotational speed of each wheel of the vehicle, front wheel turning radius calculating means for obtaining a turning radius of the front wheel from the rotational speed of the front wheel of the vehicle, and rear wheel speed from the rotational speed of the rear wheel of the vehicle. Rear wheel turning radius calculating means for obtaining a turning radius, turning radius difference calculating means for obtaining a difference between the obtained turning radius of the front wheel and the turning radius of the rear wheel, means for obtaining a lateral acceleration of the vehicle, Correlation calculation means for obtaining a relationship between a difference in turning radius and lateral acceleration, a decompression determination means for detecting a decrease in tire air pressure from the relationship between the difference in turning radius and lateral acceleration, and a result of the decompression judgment. There are, made and a warning means for issuing an alarm of decrease in tire air-pressure.

  Further, the tire decompression determination program according to the present invention is based on the rotational speed of the wheel mounted on the vehicle, and determines the decrease in the air pressure of the tire mounted on the vehicle, and the wheel rotational speed of the front wheel of the vehicle. Front wheel turning radius calculating means for determining the turning radius of the front wheel from the rear wheel turning radius calculating means for determining the turning radius of the rear wheel from the wheel rotational speed of the rear wheel of the vehicle, the obtained turning radius of the front wheel and the turning of the rear wheel Turning radius difference calculating means for obtaining a difference from the radius, means for obtaining the lateral acceleration of the vehicle, correlation calculating means for obtaining a relationship between the turning radius difference and the lateral acceleration, relation between the turning radius difference and the lateral acceleration It is made to function as a pressure reduction determination means for detecting a decrease in tire air pressure.

  According to the tire pressure drop alarm method of the present invention, simultaneous depressurization of four wheels can be detected based on the rotational speed of wheels mounted on a vehicle. In the example to be described later, when the four wheels are depressurized at the same depressurization rate of 30% in the front-wheel drive vehicle, the primary regression coefficient related to the lateral acceleration of the turning radius difference between the front and rear wheels is normal tire pressure. It was possible to determine that the pressure was reduced when the pressure was smaller than 0.8 times that in the above case, and the driver could be warned of the pressure reduction. As a result, the vehicle can run while simultaneously reducing the pressure of the four wheels, thereby deteriorating fuel consumption and avoiding the risk of tire burst.

  Even when the four wheels simultaneously depressurize, such as when the internal pressure of the tire naturally leaks, a decrease in tire air pressure can be detected.

  The tire pressure drop alarm method and apparatus and tire decompression determination program of the present invention will be described below in detail with reference to the accompanying drawings.

  As shown in FIG. 1, a tire pressure drop alarm device according to an embodiment of the present invention includes four tires FL, FR, RL and RR (hereinafter collectively referred to as Wi) provided in a four-wheel vehicle. Here, i = 1 to 4, 1: front left tire, 2: front right tire, 3: rear left tire, 4: rear right tire) is detected whether or not the air pressure is decreased. A normal rotation speed detecting means 1 provided in association with each Wi is provided.

  As the rotational speed detection means 1, a wheel speed sensor that generates a rotational pulse using an electromagnetic pickup or the like and measures the rotational speed from the number of pulses can be used. The output of the rotational 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 air pressure has dropped, an internal pressure drop alarm 3 composed of a plasma display element or a CRT, and a reference internal pressure (normal air pressure) when the tire is replaced. An initialization switch 4 that is operated by the driver when adjusted to is connected. The initialization switch 4 is operated when the tire is changed or adjusted to the normal internal pressure, thereby resetting the reference value held so far and resetting a new reference value.

  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.

  In the present embodiment, the front wheel turning radius and the rear wheel turning radius are obtained from the rotational speeds of the front wheels and the rear wheels and the respective distances between the treads. Here, the rotational speed of the wheel is a value obtained by multiplying the rotational angular speed of the wheel by a given tire radius.

  The present embodiment includes a rotational speed detecting means 1 for detecting the rotational speed of each tire Wi, and a front wheel turning radius calculating means for obtaining a turning radius of the front wheel from the rotational speed of the front wheel out of the rotational speeds of the tires Wi. Rear wheel turning radius calculating means for obtaining a turning radius of the rear wheel from the rotational speed of the rear wheel of the vehicle, and a turning radius difference calculating means for obtaining a difference between the obtained turning radius of the front wheel and the turning radius of the rear wheel; A means for obtaining a lateral acceleration of the vehicle, a correlation calculating means for obtaining a relationship between the difference in turning radius and the lateral acceleration, and a decompression for detecting a decrease in tire air pressure from the relationship between the difference in turning radius and the lateral acceleration. It is comprised from the determination means and the internal pressure fall alarm 3 which issues the warning of the tire air pressure fall based on the result of the said pressure reduction judgment.

  Further, the correlation calculating means obtains a primary regression coefficient from the relationship between the turning radius difference and the lateral acceleration, and the decompression determining means is a primary regression coefficient relating to the relationship between the turning radius difference and the lateral acceleration. And the first-order regression coefficient of the relationship between the turning radius difference of the vehicle and the lateral acceleration obtained in advance at the normal internal pressure.

  In the tire decompression determination program according to the present embodiment, the control unit 2 causes the front wheel turning radius calculation means to obtain the turning radius of the front wheel from the rotational speed of the front wheel of the vehicle, and the rear wheel from the rotational speed of the rear wheel of the vehicle. A rear-wheel turning radius calculating means for obtaining a turning radius of the vehicle, a turning-radius difference calculating means for obtaining a difference between the obtained turning radius of the front wheel and a turning radius of the rear wheel, a means for obtaining a lateral acceleration of the vehicle, the turning radius Correlation calculation means for obtaining the relationship between the difference between the two and the lateral acceleration, and a decompression determination means for detecting a decrease in tire air pressure from the relationship between the turning radius difference and the lateral acceleration.

  Next, a procedure for detecting simultaneous depressurization of the four wheels from the rotational speed of the wheels will be described. First, as shown in FIG. 3, in the present embodiment, the tire decompression determination program is activated (reset) when the initialization switch 4 is turned on. After taking in the rotational speed of the wheel (step S1), the turning radius of the front wheel is calculated from the rotational speed of the front wheel, and the turning radius of the rear wheel is calculated from the rotational speed of the rear wheel (step S2).

If the rotational speeds of the four wheels of the vehicle (right front wheel, left front wheel, right rear wheel, left rear wheel) are V1, V2, V3, and V4, respectively, the reciprocal RecF of the front wheel turning radius is
RecF = ((V2−V1) / (V2 + V1)) × (2 / TwF) (1)
The reciprocal RecR of the rear wheel turning radius is
RecR = ((V4−V3) / (V4 + V3)) × (2 / TwR) (2)
It is. Here, TwF is the distance between the treads of the front wheels, and TwR is the distance between the treads of the rear wheels.

Multiply the difference between the reciprocal of the front wheel turning radius and the rear wheel turning radius by an integer,
RemRec = (RecF−RecR) × α (3)
As such, the relationship (regression coefficient) with the lateral acceleration may be obtained. Here, α is a constant for multiplying ReR by an integer.

  Next, the lateral acceleration of the vehicle is detected from the rotational speed of the four wheels or the rotational speed of the driven wheel (step S3). In order to detect the lateral acceleration of the vehicle, for example, a method of obtaining from an acceleration sensor mounted on the vehicle may be used. Moreover, it can obtain | require with the following arithmetic expression from the rotational speed of a wheel.

When the lateral acceleration with the gravitational acceleration g as a unit is expressed by LatG,
LatG = V ² · Rec / g (4)
Here, V is the vehicle speed (m / s), Rec is the reciprocal of the turning radius (1 / m), and g is the gravitational acceleration 9.8 (m / s ² ). It is desirable to calculate the turning radius used for the calculation of the lateral acceleration from the driven wheel. For example, it is calculated from the rear wheel in the case of a front wheel drive vehicle and from the front wheel in the case of a rear wheel drive vehicle. Further, the vehicle speed can be obtained as an average speed of the driven wheel.

  Next, for example, the RemRec and LatG for each predetermined distance (for example, every 1000 m) are accumulated (steps S4 and S5), and the primary regression coefficient and correlation coefficient are obtained for each predetermined distance (step S6).

  When the travel distance reaches a predetermined value, it is cleared to zero (step S6). The predetermined distance interval for obtaining the regression coefficient is not particularly limited, but if it is too short, the data is insufficient and the decompression cannot be detected accurately. On the other hand, if it is too long, data cannot be detected with high accuracy due to variations in data due to factors other than decompression, for example, disturbance factors such as road gradient. Therefore, it is appropriate that the predetermined distance interval for obtaining the regression coefficient is about 1000 to 5000 m.

  In the tire pressure drop alarm device according to the present invention, since the continuous relationship between the lateral acceleration and the turning radius difference is obtained, the sampling period of the wheel rotation speed is preferably 2 seconds or less. The travel distance can be obtained by calculating and accumulating the travel distance for each sampling period. For example, if the sampling period is T (sec) and the vehicle speed in the meantime is V (m / s), the travel distance L within the sampling period time can be expressed by L = T × V.

  It is desirable that the obtained regression coefficients are averaged by a plurality of (for example, five) or more and compared as average regression coefficients. The average regression coefficient may be a moving average. Similarly, it is desirable to average the regression coefficient Lo as a reference and the regression coefficient Ln for determination.

  In the present embodiment, a plurality of (for example, five) or more regression coefficients obtained are averaged and compared as an average regression coefficient. The reference regression coefficient is set to the average of 5 times (step S12), and the regression coefficient to be compared is also set to the average of 5 times (step S16).

  If the correlation coefficient is less than or equal to a predetermined value (for example, 0.8), the accuracy of tire pressure drop determination can be improved by rejecting and not using it for averaging (step S7).

  Then, the regression coefficient (reference regression coefficient) of the relationship between the lateral acceleration and the front and rear wheel turning radius previously obtained at the normal internal pressure is held (step S12), and the held reference regression coefficient and the predetermined regression coefficient are stored. The regression coefficient (step S16) obtained every distance or every predetermined time is compared (step S17).

Assuming that the standard regression coefficient obtained at normal internal pressure is Lo and the regression coefficient obtained at every predetermined distance is Ln,
| Ln | <0.8 × | Lo | (5)
When it becomes, it judges that the air pressure of 4 wheels has fallen, and issues a warning (step S18). The comparison with the absolute value of the regression coefficient is because the sign changes depending on the difference between RecF and RecR. The threshold value (Lo coefficient) in equation (5) needs to be set for each vehicle in advance. In order to prevent false alarms, an alarm may be issued in consideration of changes over time. For example, in the case of four-wheel simultaneous decompression, the tire air naturally leaks in most cases, so the judgment value Ln gradually decreases, so if it suddenly decreases, it only falls below the threshold value once. A method may be considered in which an alarm is issued with reference to the amount of change with time up to that time and, for example, two times of Ln thereafter.

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

  The test vehicle was an Audi A4 manufactured by Audi, which is a front-wheel drive vehicle, and the tire used SP9000 manufactured by Sumitomo Rubber Industries, Ltd., and traveled 1000 m on an asphalt road including slalom driving.

  In this example, in order to examine the determination of simultaneous decompression of a four-wheel tire, three types of tire pressure conditions were set: normal internal pressure, four-wheel 30% decompression, and four-wheel 50% decompression.

  The rotational speed of the wheel was calculated from the output value of the ABS sensor.

  The sampling period of the rotational speed of the wheel was 0.4 seconds.

  The average wheel speed of the rear wheel, which is a driven wheel, was taken as the vehicle speed.

  The mileage was calculated from the vehicle speed and sampling period.

  The reciprocal of the turning radius was determined from the rotational speed of the front and rear wheels and the distance between the treads, and the difference was determined.

  The lateral acceleration was obtained from the reciprocal of the vehicle speed and the rear wheel turning radius.

  FIG. 3 shows the relationship between the lateral acceleration measured by actually running under each tire pressure condition and the difference between the front and rear wheel turning radii. The values of the regression coefficient at that time are shown in Table 1.

As can be seen from Table 1, when the tire air pressure changes, the primary regression coefficient between the lateral acceleration and the difference in turning radius determined from the front and rear wheel speeds changes. According to Table 1, | −0.053 | <0.8 × | −0.071 |
Therefore, if the alarm should be given when the four wheels are 30% depressurized, the depressurization determination can be made with the same coefficient 0.8 as the coefficient of the equation (5). By setting a coefficient in accordance with the tire pressure to be depressurized, an alarm can be issued at an arbitrary depressurization rate.

  As a result, a first-order regression coefficient between the lateral acceleration at normal internal pressure and the difference in turning radius determined from the front and rear wheel speeds is stored, and the lateral acceleration and the front and rear wheel speeds during the subsequent travel are stored. By comparing the first-order regression coefficient with the obtained difference in turning radius with the value at the normal internal pressure, it was possible to detect that the tire air pressure decreased.

  In actual use, when the tire pressure is set to normal pressure, the driver presses a predetermined switch (initialization switch), and the difference between the turning radius obtained from the lateral acceleration at normal internal pressure and the front and rear wheel speeds And a first order regression coefficient can be set. At this time, for example, the regression coefficient is obtained every 1000 m. However, if the correlation coefficient is less than 0.8, the data is rejected. When five regression coefficients with a correlation coefficient of 0.8 or more are accumulated, the average value is stored as the reference value Lo at the normal internal pressure.

  After that, similarly, the regression coefficient is obtained every 1000 m and the average of the five is compared with the reference value Lo to determine whether or not the internal pressure has decreased. The average value of the regression coefficient may be obtained by a moving average.

It is a block diagram which shows one Embodiment of the tire pressure fall warning apparatus of this invention. FIG. 2 is a block diagram showing an electrical configuration of the tire pressure drop alarm device shown in FIG. 1. It is an example of the flowchart in connection with the tire pressure drop warning method of the present invention. It is a graph showing the relationship of the difference of the lateral direction acceleration in the three types of tire air pressure of the Example of this invention, and a front-and-back wheel turning radius.

Explanation of symbols

1 Rotational speed detection means 2 Control unit 3 Internal pressure drop alarm 4 Initialization switch

Claims (4)

A tire pressure drop alarm method for detecting a decrease in air pressure of a tire mounted on the vehicle based on a rotation speed of a wheel mounted on the vehicle and issuing an alarm, the method detecting the rotation speed of each wheel; A step of obtaining a turning radius of the front wheel from the rotational speed of the front wheel of the vehicle, a step of obtaining a turning radius of the rear wheel from the rotational speed of the rear wheel of the vehicle, and the obtained turning radius of the front wheel and the turning of the rear wheel A step of obtaining a difference between the radius, a step of obtaining a lateral acceleration of the vehicle, a step of obtaining a relationship between the difference in turning radius and the lateral acceleration, and a relationship between the difference in turning radius and the lateral acceleration. And a method for alarming a decrease in tire air pressure. A primary regression coefficient is obtained from the relationship between the turning radius difference and the lateral acceleration, and compared with the primary regression coefficient of the relationship between the turning radius difference of the vehicle and the lateral acceleration obtained in advance at the normal internal pressure. The tire pressure drop warning method according to claim 1, wherein a drop in the air pressure of the mounted tire is detected. A tire pressure drop alarm device for detecting a decrease in air pressure of a tire mounted on the vehicle based on a rotation speed of a wheel mounted on the vehicle and issuing an alarm, and detecting a rotation speed of each wheel of the vehicle. A rotational speed detecting means; a front wheel turning radius calculating means for obtaining a turning radius of the front wheel from the rotational speed of the front wheel of the vehicle; and a rear wheel turning radius calculating means for obtaining a turning radius of the rear wheel from the rotational speed of the rear wheel of the vehicle; A turning radius difference calculating means for obtaining a difference between the obtained turning radius of the front wheel and a turning radius of the rear wheel, means for obtaining a lateral acceleration of the vehicle, and a relationship between the difference in turning radius and the lateral acceleration. Correlation calculating means to be obtained; pressure reduction determination means for detecting a decrease in tire air pressure from the relationship between the difference in turning radius and lateral acceleration; and a warning of a decrease in tire air pressure based on the result of the pressure reduction determination Tire deflation warning device comprising a warning means. Front wheel turning radius calculation means for determining a turning radius of a front wheel from a rotation speed of a front wheel of the vehicle, in order to determine a decrease in air pressure of a tire attached to the vehicle based on a rotation speed of a wheel attached to the vehicle. Rear wheel turning radius calculating means for obtaining a turning radius of the rear wheel from the rotational speed of the rear wheel of the vehicle, turning radius difference calculating means for obtaining a difference between the obtained turning radius of the front wheel and the turning radius of the rear wheel, Functions as a means for obtaining a lateral acceleration of the vehicle, a relation calculating means for obtaining a relationship between the difference in turning radius and the lateral acceleration, and a pressure reducing judgment means for detecting a decrease in tire air pressure from the relationship between the difference in turning radius and the lateral acceleration. A program for tire pressure reduction judgment.

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