JP4086763B2 - Tire pressure drop detection method and apparatus, and tire decompression determination program - Google Patents

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, when the tire pressure is reduced, the tire pressure drop detecting device has a smaller outer diameter (dynamic load radius of the tire) than a normal inner pressure tire. This principle is used. For example, in the method of detecting a decrease in internal pressure from the relative difference in tire wheel speed,
DEL = {(V1 + V4) / 2- (V2 + V3) / 2} /
{(V1 + V2 + V3 + V4) / 4} × 100 (%)
(See, for example, Patent Document 1). Here, V1 to V4 are wheel speeds 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 the above method, since the wheel speeds on a pair of diagonal lines are relatively compared, simultaneous decompression of all left wheels or right wheels (two-wheel tires on the same side), simultaneous decompression of front two-wheel tires or It is impossible to determine the simultaneous decompression of the rear two-wheel tires and the decompression in the case where the air of all the wheel tires is similarly lowered. For this reason, there is a problem that if the vehicle is kept running 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.

  SUMMARY OF THE INVENTION In view of the above circumstances, the present invention provides a tire pressure drop detection method and apparatus, and a tire pressure reduction determination program capable of expanding a region for determining a tire pressure drop and improving the accuracy of pressure reduction judgment. For the purpose.

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 detects wheel rotation information of each tire. A step of obtaining a vehicle body speed, a wheel speed information comprising the wheel rotation information of the wheel position with respect to the two wheels on the right side, and a wheel rotation of the wheel position with respect to the two wheels on the left side from the wheel rotation information. calculating wheel speed information consisting of information or wheel speed information consisting of a wheel rotational information of the wheel position relative to the wheel of the wheel speed information and the two rear wheels consisting of a wheel rotational information of the wheel position relative to the wheel of the two front wheels calculating a distribution, a step of storing the wheel speed information of the wheel position and wheel rotation information of the respective tires, speed information of a wheel of the wheel position and the vehicle body The wheel position reference value obtained by comparing the wheel speed information of the wheel position and the vehicle body speed at the time of a prescribed internal pressure in advance The method includes a step of comparing the determination value of the position, and a step of determining a decrease in tire air pressure based on a relationship between the reference value and the comparison value of the determination value and a predetermined threshold value.

Also, the tire pressure drop detecting device of the present invention is a tire air pressure reduction detection DeSo location for detecting a decrease in tire air pressure based on wheel rotation information obtained from tires attached to a vehicle, a wheel rotation of the respective tires Wheel speed detecting means for detecting information, vehicle speed calculating means for obtaining the vehicle speed, wheel speed information consisting of wheel rotation information of wheel positions relative to the two wheels on the right side, and left side speed information calculating wheel speed information consisting of wheel rotational information of the wheel position relative to the wheel of the two wheels, or wheel position relative to the wheel of the wheel speed information and the two rear wheels consisting of a wheel rotational information of the wheel position relative to the wheel of the two front wheels stores the velocity information calculation means for calculating the wheel speed information of consisting of wheel rotation information, the wheel speed information of the wheel position and wheel rotation information regarding the respective tires of A memory means, a judgment value calculating means for calculating a judgment value of the wheel position by comparing the speed information of the wheel at the wheel position and the vehicle body speed, and a speed information of the wheel at the wheel position at a predetermined internal pressure in advance. Comparing means for comparing the reference value of the wheel position obtained by comparing the vehicle body speed and the determination value of the wheel position, and based on the relationship between the reference value and the comparison value of the determination value and a predetermined threshold value And a pressure reducing means for determining a decrease in tire air pressure.

Furthermore, the tire decompression determination program of the present invention uses a computer to determine a decrease in tire air pressure based on wheel rotation information obtained from a tire mounted on a vehicle, and from the wheel rotation information, calculating wheel speed information consisting of wheel rotational information of the wheel position relative to the wheel of the two wheels of the wheel speed information and the left side consisting of wheel rotational information of the wheel position relative to the wheel or wheel of the wheel position relative to the wheel of the two front wheels velocity information calculation means for calculating the wheel speed information of consisting of wheel rotational information of the wheel position relative to the wheel speed information of the wheels comprising a rotation information and the two rear wheels, the wheels of the wheel position and wheel rotation information of the respective tires Storage means for storing speed information, comparing the speed information of the wheel at the wheel position with the determined vehicle body speed, and calculating a determination value for the wheel position Constant value calculating means, comparing means for comparing the reference value of the wheel position obtained by comparing the wheel speed information of the wheel position and the vehicle body speed in advance at the specified internal pressure with the determination value of the wheel position, and the reference value Based on the relationship between the comparison value of the determination value and a predetermined threshold value, it functions as a decompression determination means for determining a decrease in tire air pressure.

  According to the present invention, simultaneous (same rate) decompression of a plurality of wheels including a four-wheel tire (left wheel tire, right wheel tire, diagonal wheel tire, etc.) can be detected from decompression of a single wheel tire. Therefore, it is possible to widen the region for determining the decrease in tire air pressure and improve the accuracy of pressure reduction determination.

  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, the vehicle is provided with normal wheel speed detection means 1 provided in association with each tire.

  Examples wheel speed detection means 1, the power generation by utilizing the rotation as the wheel speed sensor or dynamo for by generating rotational pulses by measuring the rotational angular velocity and wheel velocity from the number of pulses by using an electromagnetic pickup For example, an angular velocity sensor including that for measuring the rotational angular velocity and the wheel speed from this voltage can be used. The output of the wheel speed 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 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 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 wheel speed 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 based on the wheel speed pulse output from the wheel speed detecting means 1 at a predetermined sampling period ΔT (sec), for example, ΔT = 1 second.

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) / (F 3 + 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 is calculated.

  In the present embodiment, the wheel speed detecting means 1, the vehicle speed calculating means for obtaining the vehicle speed, the speed information calculating means for calculating the speed information of a predetermined wheel from the wheel speed, the wheel speed of each tire and the wheel speed Storage means for storing speed information; determination value calculating means for calculating a determination value of the wheel position by comparing the speed information of the wheel and the vehicle speed; and the speed information of the wheel and the vehicle body at a predetermined internal pressure in advance. Based on the relationship between the reference value of the wheel position obtained by comparing the speed and the determination value of the wheel position, and the relationship between the reference value and the comparison value of the determination value and a predetermined threshold value, It comprises pressure reduction determination means for determining a decrease in air pressure.

  In the present embodiment, the calculation of the reference value at the specified internal pressure is started by pressing an initialization button operated in advance for initialization.

  The vehicle body speed includes a vehicle body speed that can be obtained from a signal and time received from a GPS (Global Positioning System) radio wave, a vehicle body speed that can be obtained from a road surface embedded sensor, and a passing time. In the case of using the GPS, a GPS device such as a car navigation device using a transceiver, for example, a GPS antenna is provided. This device receives a radio wave from a GPS satellite, measures its own position, and then measures the vehicle speed. The vehicle body speed calculating means for calculating is incorporated.

  As the car navigation device, for example, a GPS (Global Positioning System) antenna or the like is used to detect a travel point, and map data around it is input to a car navigator body from a CD-ROM or the like, and a map display routine In this process, the geographical information is displayed on a display panel, etc., and road information is received from an external transmitter such as a beacon or FM transmitter installed on the road via a beacon antenna. It is possible to use a display panel that adds road information to a display panel or the like by display routine processing.

The comparison between the wheel speed information and the vehicle body speed V and the determination value I of the wheel position include, for example, the following. In addition, as a comparison, it can be set as a ratio or a difference between each other.
(1) When the wheel speed information is the average wheel speed of all left wheels or all right wheels (two-wheel tires on the same side) (i) I = {(front wheel left or right wheel speed + rear axle left or Right wheel speed) / 2} / V
(Ii) I = {(front axle left or right wheel speed + rear axle left or right wheel speed) / 2} −V
(2) When the wheel speed information is the average wheel speed of the front two-wheel tire or the rear two-wheel tire (i) I = {(the wheel speed on the left side of the front or rear axle + the wheel on the right side of the front or rear axle) Speed) / 2} / V
(Ii) I = {(the wheel speed on the left side of the front or rear axle + the wheel speed on the right side of the front or rear axle) / 2} −V
(3) When the wheel speed information is an average wheel speed of a wheel tire on a diagonal line and an average wheel speed of a wheel tire on another diagonal line (i) I = [{(V2 + V3) / 2} / V] / [ {(V1 + V4) / 2} / V]
(Ii) I = [{(V2 + V3) / 2} / V] − [{(V1 + V4) / 2} / V]
(4) When the wheel speed information is the average wheel speed of a four-wheel tire (i) I = {(V1 + V2 + V3 + V4) / 4} / V
(Ii) I = {(V1 + V2 + V3 + V4) / 4} −V
(5) When the wheel speed information is the wheel speed Vi (i = 1 to 4) of each wheel tire (i) I = Vi / V
(Ii) I = Vi−V

  In the present embodiment, if the difference (comparison value) between the wheel position determination value I and the wheel position reference value measured at the specified internal pressure is greater than a predetermined threshold value, it is determined that the air pressure has decreased. To do. Thereby, if the said (1) term is used, the pressure reduction of the two-wheel tire of the right-and-left same side (same side) and the simultaneous pressure reduction of a four-wheel tire can be judged. In addition, when the item (2) is used, it is possible to determine the pressure reduction of the coaxial two-wheel tire or the simultaneous pressure reduction of the four-wheel tire. Moreover, if the said (3)-(5) term is used, the pressure reduction of a several wheel tire, for example, simultaneous pressure reduction of a four-wheel tire can be judged from the pressure reduction of a 1-wheel tire.

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

[Example 1]
A front shaft drive vehicle was prepared as a vehicle. Then, after pressing the initialization button in advance under the tire with the prescribed internal pressure, the road surface was run straight at a constant speed of 40 km / h, and the calculation of the reference value was started. In the present embodiment, the wheel speed reference information is obtained by using the average wheel speed of the left and right two-wheel tires as the wheel speed information, and the wheel position reference value measured in advance with the specified internal pressure (the average of the left and right two-wheel tires) (Wheel speed / body speed) was calculated as shown in Table 1.

  Subsequently, the running test was performed with the air pressure of the four-wheel tires reduced by 20%. The determination value of the wheel position at this time was 0.02004 as shown in Table 2.

  Subsequently, the running test was performed with the air pressure of the four-wheel tires reduced by 40%. The determination value of the wheel position at this time was 0.02008 as shown in Table 3.

  In this example, if the threshold value for detecting a pressure reduction of 30% or more from the specified internal pressure is 0.3%, the reference value at the specified internal pressure is 0.02 as shown in Table 1, As shown in Table 4, the rate of change from the reference value at 20% pressure reduction is 0.2% for both the left and right two-wheel tires. Therefore, when the change of 0.2% is compared with the threshold value of 0.3%, the threshold value is larger, and it was not determined that the pressure is reduced.

  On the other hand, at 40% decompression, the rate of change from the reference value is 0.4% for the two-wheel tires on the left and right sides as shown in Table 5. Therefore, when the change of 0.4% is compared with the threshold value of 0.3%, it is determined that the pressure is reduced on both the left and right sides because the threshold value is smaller. Was issued.

  In this example, a running test was performed in which the left and right two-wheel tires were depressurized at the same time. However, the left side two-wheel tire or the right side two-wheel tire was depressurized simultaneously. By performing the running test, it can be determined that the two-wheel tire on the same side (left side or right side) is simultaneously depressurized.

[Example 2]
A front shaft drive vehicle was prepared as a vehicle. Then, after pressing the initialization button in advance under the tire with the prescribed internal pressure, the road surface was run straight at a constant speed of 40 km / h, and the calculation of the reference value was started. In this embodiment, the average wheel speed of the front two-wheel tire or the rear two-wheel tire is used as the wheel speed information, and the reference values of the front and rear axle wheel positions measured in advance with the prescribed internal pressure (front wheel 2 The average wheel speed of the wheel tire / body speed) and the average wheel speed / body speed of the rear two-wheel tire were calculated as shown in Table 6.

  Subsequently, the running test was performed with the air pressure of the four-wheel tires reduced by 20%. As shown in Table 7, the judgment values of the front and rear wheel positions at this time were 0.02004 and 0.01504, respectively.

  Subsequently, the running test was performed with the air pressure of the four-wheel tires reduced by 40%. As shown in Table 8, the judgment values of the front and rear wheel positions at this time were 0.02008 and 0.01508, respectively.

  In this embodiment, assuming that the threshold value for detecting a pressure reduction of 30% or more from the specified internal pressure is 0.3%, the reference values of the front and rear axes at the specified internal pressure are as shown in Table 1. As shown in Table 9, the change rate from the front and rear axle reference values at 20% pressure reduction is 0.2% for the front axle two-wheel tire, and the rear It is 0.27% for the two-wheel tire on the shaft. Therefore, when these changes are compared with the threshold value of 0.3%, the threshold value is larger, and it was not determined that the pressure was reduced.

  On the other hand, at 40% decompression, the rate of change from the reference values for the front and rear axles is 0.4% for the front axle two-wheel tires as shown in Table 10, and for the rear axle two-wheel tires. 0.54%. Therefore, when these changes are compared with the threshold value of 0.3%, the threshold value is smaller, so it is determined that the pressure is reduced in the front wheel and rear wheel two wheel tires. The depressurization warning was issued.

  In this example, a running test was performed in the case where the front and rear two-wheel tires were depressurized at the same time. However, the front two-wheel tire or the rear two-wheel tire was depressurized simultaneously. By performing the running test in this case, it can also be determined that the two-wheel tires on the front axle or the rear axle are simultaneously depressurized.

[Comparative Example 1]
A front shaft drive vehicle was prepared as a vehicle. Then, after pressing the initialization button in advance under the tire with the prescribed internal pressure, the road surface was run straight at a constant speed of 40 km / h, and the calculation of the reference value was started. In this comparative example, using the average wheel speed of the four-wheel tire as the wheel speed information, the reference value of the wheel position (average wheel speed of the four-wheel tire / body speed) measured in advance with the specified internal pressure is 0.02. Met.

  Subsequently, the running test was performed with the air pressure of the four-wheel tires reduced by 20%. The wheel position determination value at this time was 0.02004.

  Subsequently, the running test was performed with the air pressure of the four-wheel tires reduced by 40%. The wheel position determination value at this time was 0.02008.

In this comparative example, if the threshold value for detecting a pressure reduction of 30% or more from the specified internal pressure is 0.3%, the reference value at the specified internal pressure is 0.02, so The rate of change is 0.2%. Therefore, when the change of 0.2% is compared with the threshold value of 0.3%, the threshold value is larger, and it was not determined that the pressure is reduced.

  On the other hand, at 40% decompression, the rate of change from the reference value is 0.4%. Therefore, when the change of 0.4% is compared with the threshold value of 0.3%, the threshold value is smaller, so that a four-wheel tire pressure reduction warning is issued.

In this comparative example, a running test was performed when the four-wheel tires were depressurized at the same time. However, a one-wheel tire (for example, the left front wheel tire) and a two-wheel tire (for example, the front two-wheel tire and the left side tire) It was also found that the reduced pressure can be determined in the same manner for the two-wheel tire.

[Example 3]
A front shaft drive vehicle was prepared as a vehicle. Then, after pressing the initialization button in advance under a tire having a prescribed internal pressure, the road surface was traveled straight at a constant speed of 40 km / h, and calculation of a reference value was started. In this embodiment, as wheel speed information, the wheel position reference value (each wheel speed / vehicle speed) of each wheel tire measured in advance with a specified internal pressure using the wheel speed of each wheel tire is shown in Table 11. Calculated as follows.

  Subsequently, the running test was performed with the air pressure of the four-wheel tires reduced by 20%. The judgment values of the wheel positions of the respective wheel tires at this time were calculated as shown in Table 12.

  Then, the running test was performed with the air pressure of the four-wheel tires reduced by 40%. The judgment values of the front and rear wheel positions at this time were calculated as shown in Table 13.

  In this embodiment, when the threshold value for detecting a pressure reduction of 30% or more from the specified internal pressure is 0.3%, the reference value of each wheel tire at the specified internal pressure is as shown in Table 1, as shown in Table 1. Since it is 0.020 and 0.015 on the rear axle, the change rate from the reference value of the front axle and the rear axle at 20% decompression is 0 for the two-wheel tire on the front axle as shown in Table 14. .2% and 0.27% for the rear-wheel two-wheel tire. Therefore, when these changes are compared with the threshold value of 0.3%, the threshold value is larger, and it was not determined that the pressure was reduced.

  On the other hand, at 40% decompression, the rate of change from the reference values of the front and rear axles of each wheel tire is 0.4% for the front axle two-wheel tires as shown in Table 15, and the rear axle For a two-wheel tire, it is 0.54%. Therefore, when these changes are compared with the threshold value of 0.3%, the threshold value is smaller, so it is determined that the pressure is reduced in each wheel tire. It was.

  In the present embodiment, a running test was performed in the case where the wheel tires were depressurized at the same time, but the depressurization of a single wheel tire or a plurality of tires can also be determined.

  For example, as shown in Table 16, the determination values of the front and rear axle wheel positions when only the left front tire (one-wheel tire) was depressurized by 40% were calculated.

  As shown in Table 17, the rate of change from the reference value of the front and rear axles of each wheel tire is 0.40% for the left front wheel tire and 0.00% for the remaining tires. Therefore, when these changes are compared with the threshold value of 0.3%, the threshold value is smaller. Therefore, it is determined that the pressure is reduced in the left front wheel tire, so that a one wheel tire pressure reduction alarm is issued. It was.

  Further, the determination values of the front and rear wheel positions when only the front two-wheel tire was depressurized by 40% were calculated as shown in Table 18.

  As shown in Table 19, the rate of change from the reference value of the front and rear axles of each wheel tire is 0.40% for the two-wheel tire for the front axle and 0.00% for the two-wheel tire for the rear axle. It is. Therefore, when these changes are compared with the threshold value of 0.3%, the threshold value is smaller, so it is determined that the pressure is reduced in the front wheel two-wheel tire. Was issued.

  Further, as shown in Table 20, the judgment values of the front and rear wheel positions when only the two-wheel tire on the left side was decompressed by 40% were calculated.

  As shown in Table 21, the rate of change from the reference values for the front and rear axles of each wheel tire is 0.40% for the left-side front wheel tire, 0.53% for the rear wheel tire, It is 0.00% in the two-wheel tire on the same side. Therefore, when these changes are compared with the threshold value of 0.3%, it is determined that the pressure is reduced in the two-wheel tire on the left side because the threshold value is smaller. An alarm was issued.

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.

Explanation of symbols

1 Wheel speed detection means 2 Control unit 3 Display 4 Initialization button 5 Alarm

Claims (5)

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 detecting wheel rotation information of each tire, and the step of obtaining a vehicle body speed; from wheel rotational information, it calculates the wheel speed information consisting of wheel rotational information of the wheel position relative to the wheel of the two wheels of the wheel speed information and the left side consisting of wheel rotational information of the wheel position relative to the wheel of the two wheels on the right side, or, calculating a wheel speed information consisting of a wheel rotational information of the wheel position relative to the wheel of the wheel speed information and the two rear wheels consisting of a wheel rotational information of the wheel position relative to the wheel of the two front wheels, each tire The step of storing wheel rotation information and the wheel speed information at the wheel position, and the wheel speed information and the vehicle body speed at the wheel position are compared to determine the wheel position. Comparing the wheel position reference value obtained by comparing the wheel speed information of the wheel position and the vehicle body speed at the specified internal pressure in advance with the determination value of the wheel position, and the reference A method for detecting a decrease in tire air pressure including a step of determining a decrease in tire air pressure based on a relationship between a comparison value between a value and a determination value and a predetermined threshold value. The tire pressure drop detection method according to claim 1, wherein the vehicle body speed is obtained from a signal and time received from a GPS radio wave. A tire pressure drop detection DeSo location for detecting a decrease in tire air pressure based on wheel rotation information obtained from tires attached to a vehicle, a wheel speed detecting means for detecting a wheel rotational information of the respective tires, the vehicle speed From the wheel rotation information, the wheel speed information of the wheel position with respect to the two wheels on the right side, and the wheel rotation information of the wheel position with respect to the two wheels on the left side. calculating the speed information of the wheels comprising, or the wheel speed information of consisting of wheel rotational information of the wheel position relative to the wheel of the wheel speed information and the two rear wheels consisting of a wheel rotational information of the wheel position relative to the wheel of the two front wheels Speed information calculating means for calculating, storage means for storing wheel rotation information of each tire and wheel speed information at the wheel position, wheel speed information at the wheel position, A reference value for the wheel position obtained by comparing a body speed with a determination value calculating means for calculating a determination value for the wheel position by comparing the body speed with a vehicle speed and a wheel speed information at the wheel position at a specified internal pressure in advance. A comparison means for comparing the value with the determination value of the wheel position, and a decompression determination means for determining a decrease in tire air pressure based on a relationship between the reference value and the comparison value of the determination value and a predetermined threshold value. A tire pressure drop detecting device provided. The tire pressure drop detecting device according to claim 3, wherein the vehicle body speed is obtained from a signal and time received from a GPS radio wave. In order to determine a decrease in tire air pressure based on wheel rotation information obtained from tires mounted on the vehicle, a computer is used to determine the wheel rotation information from the wheel rotation information and the wheel rotation information of the wheel position relative to the two wheels on the right side. calculating wheel speed information consisting of wheel rotational information of the wheel position relative to the wheel of the two wheels of the speed information and the left side, or, wheel speed information and the rear wheel 2 consisting of wheel rotational information of the wheel position relative to the wheel of the two front wheels velocity information calculation means for calculating the wheel speed information of consisting of wheel rotational information of the wheel position relative to the wheel of the wheels, storage means for storing the wheel speed information of the wheel position and wheel rotation information of each tire, the wheel position A judgment value calculation means for calculating a judgment value of the wheel position by comparing the speed information of the wheel with the obtained vehicle body speed, the wheel at a predetermined internal pressure in advance A comparison means for comparing the reference value of the wheel position obtained by comparing the speed information of the set wheel and the vehicle body speed and the determination value of the wheel position, a comparison value of the reference value and the determination value, and a predetermined threshold value A tire decompression determination program for functioning as decompression determination means for determining a decrease in tire air pressure based on the relationship between

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