JP2008247243A - Threshold setting method in method for judging lowering of internal pressure of tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a threshold setting method added with dispersion of a measured value of a dynamic load radius of a tire in a method for calculating the dynamic load radius of the tire of a vehicle during actual traveling from speed information by a GPS mounted on the vehicle and rotating speed information on each tire and deciding lowering of internal pressure of each tire by the size of a change from the tire dynamic load radius at a normal internal pressure time from the dynamic load radius calculated value. <P>SOLUTION: In this method, the dynamic load radius of the tire of the vehicle during actual traveling is calculated from the speed information by the GPS mounted on the vehicle and the rotating speed information of each tire and lowering of internal pressure of each tire is decided by the size of the change from the tire dynamic load radius at the normal internal pressure time from the dynamic load radius calculated value. In this threshold value setting method in the method, change amount of the dynamic load radius of the tire at a prescribed pressure reduction time is calculated from the dynamic load radius of the tire at the normal internal pressure time in advance, and the threshold value for the pressure reduction decision of the tire is made as a value that dispersion of the measured value of the dynamic load radius of the tire by the actual traveling is subtracted from the change amount. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a threshold setting method for calculating a dynamic load radius of a tire of a running vehicle and determining a decrease in the internal pressure of the tire based on a change from the dynamic load radius of the tire at a normal internal pressure.

  Conventionally, Patent Documents 1 to 3 disclose a method for detecting a decrease in the internal pressure of a tire from the vehicle speed and distance calculated from GPS information and the rotation speed of the tire. However, in order to detect a decrease in tire internal pressure from the vehicle speed and tire rotation speed calculated from GPS information, it is necessary to detect a change in tire rotation speed due to only a decrease in internal pressure. In other words, it is necessary to eliminate the rotational speed change due to the running state of the vehicle.

  Patent Document 1 discloses a method for detecting a decrease in tire air pressure by comparing a vehicle travel locus calculated from tire rotation information with a vehicle travel locus obtained from vehicle position information by GPS or the like. However, it does not show that the change in the rotational speed due to the running state of the vehicle is excluded. In Patent Document 2 and Patent Document 3, the running state is specified by comparing the rotation states of the tires. However, when a decrease in the internal pressure of the tire occurs, the relationship between the rotational speeds of the four wheels is already out of balance. Therefore, it is impossible to specify the exact driving state. Also known is a method of detecting a decrease in tire air pressure by calculating the tire dynamic load radius from the travel distance calculated from GPS information and the tire rotation speed. Is not accurate enough.

  Therefore, the running condition of the vehicle is limited, the effective value of the measured dynamic load radius at that time is selected, the average value is set as the dynamic load radius during running, and when the dynamic load radius becomes smaller than the reference value, the internal pressure A method for alarming the drop has been proposed. In addition, this method considers the influence of the dynamic load radius measurement value due to the road surface μ and load, and if there is a possibility of such influence, it should be noted that there is an influence of the road surface or the load in parallel with the warning of a decrease in internal pressure. A method of prompting is disclosed.

  In addition, since the dynamic load radius of the tire depends on the speed, there is a method to initialize from the relationship between the dynamic load radius and speed in several speed ranges so that the decrease in the dynamic load radius can be detected at any speed range. Proposed.

  However, in any of these methods, there is no clear criterion for determining the pressure reduction when the measured value of the dynamic load radius decreases, and the pressure reduction is determined when a predetermined threshold value is exceeded. become.

  If you are a tire manufacturer, you can measure the amount of change due to a decrease in the internal pressure of the dynamic load radius of a tire by experiment, so you can set a threshold for each tire, but measure the amount of change for every tire. That requires a great deal of effort.

  In general, the dependency of the tire dynamic load radius on the internal pressure is almost the same depending on the tire size, and the amount of decrease in the dynamic load radius can be determined almost uniquely if the amount of decrease in the internal pressure to be detected is determined.

JP 2003-94920 A JP 2005-186739 A JP 2003-146037 A

  When measuring the dynamic load radius of a tire in the actual running state, there is a possibility of misreporting because the measurement value inevitably varies. In addition, although calculation is performed from information when a certain range of traveling conditions is satisfied, measurement variation varies greatly depending on the type of tire (for example, summer tire or studless tire). For this reason, unless the threshold value for performing the pressure reduction determination is changed, an accurate pressure reduction determination may not be made, resulting in a false alarm.

  In particular, tires with different tread stiffness, such as studless tires and summer tires, have the same internal pressure sensitivity depending on the size, but the range of slip ratios when generating the same range of driving force differs, so the calculated tire The range of the dynamic load radius is different. As a result, the variation in measured values of both tires is greatly different. Therefore, with the same threshold value, the certainty of pressure reduction determination is different.

  In order to solve the above problem, the present invention calculates a dynamic load radius of a tire of a vehicle that is actually running from speed information by a GPS mounted on the vehicle and rotation speed information of each tire, and the dynamic load radius. In a method for determining a decrease in the internal pressure of each tire based on the magnitude of change from the tire dynamic load radius at the normal internal pressure of the calculated value, the tire at a predetermined pressure reduction from the predetermined dynamic load radius of the tire at the normal internal pressure It is an object of the present invention to provide a threshold setting method including a step of setting a threshold value for tire decompression determination with respect to a change amount of the dynamic load radius of the tire in consideration of variations in a measured value of the dynamic load radius of the tire due to actual traveling. To do.

  The threshold setting method of the present invention calculates the dynamic load radius of the tire of the vehicle currently running from the speed information by the GPS mounted on the vehicle and the rotational speed information of each tire, and the calculated dynamic load radius is normal. In the method of determining the decrease in the internal pressure of each tire by the magnitude of the change from the tire dynamic load radius at the internal pressure, the dynamic load radius of the tire at a predetermined pressure reduction from the predetermined dynamic load radius of the tire at the normal internal pressure The method includes a step of setting a threshold value for determining the pressure reduction of the tire with respect to the amount of change in consideration of variations in the measured value of the dynamic load radius of the tire due to actual running.

  Here, the predetermined reduced pressure is not particularly limited, but it is preferably 20% to 40% from the normal internal pressure.

  Further, in the above method, in order to calculate the magnitude of the variation in the dynamic load radius measurement value due to actual running, a predetermined number of data are accumulated for the dynamic load radius measurement value of the tire due to actual running in a predetermined speed range, It is preferable to include a step of calculating a standard deviation σ of the population of the dynamic load radius measurement value.

  The determination of the amount of change in the dynamic load radius of the tire from the normal internal pressure to the reduced pressure is preferably set in advance according to the size and type of the tire.

  In addition, it is preferable that the variation in the measured value of the dynamic load radius of the running tire is calculated in a timely manner, and the threshold for determining the pressure reduction is changed along with the change with time of the tire.

  In addition, the present invention calculates the dynamic load radius of the tire of the vehicle that is actually running from the speed information by the GPS mounted on the vehicle and the rotational speed information of each tire, and the calculated dynamic load radius at the normal internal pressure In the method for determining the decrease in the internal pressure of each tire based on the magnitude of the change from the tire dynamic load radius, the amount of change in the dynamic load radius of the tire at a predetermined pressure reduction from the predetermined dynamic load radius of the tire at the normal internal pressure On the other hand, the present invention relates to a tire internal pressure drop warning device including means for setting a threshold value for determining the pressure reduction of a tire to a value that takes into account the variation in the measured value of the dynamic load radius of the tire due to actual travel.

  Also, in order to calculate the magnitude of the variation in the measured value of the dynamic load radius due to actual driving, a predetermined number of data is accumulated for the dynamic load radius measurement value of the tire due to actual driving in a predetermined speed range, and the dynamic load radius measurement is performed. Preferably, means for calculating a standard deviation σ of the population of values is included.

  The determination of the amount of change in the dynamic load radius of the tire from the normal internal pressure to the reduced pressure is preferably set in advance according to the size and type of the tire.

  In addition, it is preferable that the variation in the measured value of the dynamic load radius of the running tire is calculated in a timely manner, and the threshold for determining the pressure reduction is changed along with the change with time of the tire.

  In addition, the present invention calculates the dynamic load radius of the tire of the vehicle that is actually running from the speed information by the GPS mounted on the vehicle and the rotational speed information of each tire, and the calculated dynamic load radius at the normal internal pressure In the method of determining the decrease in the internal pressure of each tire based on the magnitude of the change from the tire dynamic load radius, the computer determines the dynamic load radius of the tire at a predetermined pressure reduction from the predetermined dynamic load radius of the tire at the normal internal pressure. The present invention relates to a program for setting a threshold value by executing a procedure for setting a threshold value for tire decompression determination with respect to the change amount in consideration of variations in a measured value of a dynamic load radius of the tire due to actual travel.

  Further, the above program accumulates a predetermined number of data of dynamic load radius measurement values of tires by actual running in a predetermined speed range in order to calculate the magnitude of variation of the measured dynamic load radius values by actual running. It is preferable to include a procedure for calculating the standard deviation σ of the population of dynamic load radius measurement values.

  Moreover, it is preferable that the above-mentioned program is set in advance according to the size and type of the tire when determining the amount of change in the dynamic load radius of the tire from the normal internal pressure to the reduced pressure.

  In addition, it is preferable that the program calculates the variation in the measured dynamic load radius of the running tire in a timely manner, and changes the threshold value for determining the pressure reduction with the change with time of the tire.

  According to the present invention, the dynamic load radius of the tire of the vehicle during actual traveling is calculated from the speed information by the GPS mounted on the vehicle and the rotational speed information of each tire, and the calculated dynamic load radius at the normal internal pressure is calculated. In the method for determining the decrease in the internal pressure of each tire based on the magnitude of the change from the tire dynamic load radius, the amount of change in the dynamic load radius of the tire at a predetermined pressure reduction from the predetermined dynamic load radius of the tire at the normal internal pressure For example, the tire depressurization determination threshold is set to a value that takes into account the variation in the measured value of the dynamic load radius of the tire due to actual travel, and the type of tire, such as summer tires and studless tires, can be determined. Even if the measured values vary differently, it is possible to set a threshold value that takes into account each variation. Camphor it can can make an accurate decompression judgment (see Fig. 5).

  Hereinafter, a threshold setting method of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 and FIG. 2 are a block diagram showing an embodiment of an internal pressure drop alarm device for a vehicle of the present invention and a block diagram showing an electrical configuration of the internal pressure fall alarm device.

  As shown in FIG. 1, in a vehicle internal pressure drop alarm device according to an embodiment of the present invention, for detecting wheel speed rotation information of four tires FL, FR, RL and RR provided in a four-wheel vehicle. A normal wheel speed detecting means 1 provided in association with each tire is provided. The wheel speed detection means 1 generates power using rotation like a wheel speed sensor or dynamo that generates rotation pulses using an electromagnetic pickup or the like and measures wheel speed rotation information from the number of pulses. An angular velocity sensor including one that measures tire speed rotation information from voltage can be used.

  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 of each tire at a predetermined sampling period ΔT (sec), for example, ΔT = 0.05 seconds, based on the wheel speed pulse output from the wheel speed detecting means 1.

  The output of the wheel speed detecting means 1 is given to a control unit 2 which is a computer such as ABS. A GPS device 3 is connected to the control unit 2 as a vehicle speed detection device. The GPS device 3 is provided with a conventionally known GPS antenna 3a.

  As shown in FIG. 2, the control unit 2 stores an I / O interface 2a required 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 from which data is temporarily written or the written data is read when the CPU 2b performs a control operation.

  The vehicle speed is obtained by using a GPS speedometer, for example. With the widespread use of car navigation systems, GPS devices can be attached to many vehicles, positioning technology using GPS devices has improved, and now a device specialized for calculating speed (GPS Speedometer VBOX manufactured by Race Logic, UK) ) Is also sold.

  The tire dynamic load radius (R) during traveling of the vehicle can be calculated from the relationship between the absolute speed (V) of the vehicle and the rotational angular velocity (ω) of the tire (V = R · ω). The tire dynamic load radius (R) is known to decrease as the tire internal pressure decreases, and this is used to estimate the decrease in tire internal pressure from the decrease in tire dynamic load radius (R). can do.

  However, the tire dynamic load radius (R) is dependent on speed. That is, the faster the tire rotates, the greater the centrifugal force due to the mass of the tire tread, and the dynamic load radius increases as a function of speed (roughly proportional to the square of the speed). Therefore, the setting of the reference value for the dynamic load radius needs to be determined for each of several speed regions.

  When determining the tire dynamic load radius reference value at normal internal pressure, first divide the speed range into at least two different areas (setting of the speed window), and assign to each window each time the tire dynamic load radius is calculated The dynamic load radius is memorized, and when a certain number (N) of dynamic load radius measurement values of a certain window are collected, the average value of the speed and the dynamic load radius value is obtained.

  When a certain number (for example, 2 or more, preferably 5 or more, more preferably 8 or more) of windows for which the average value has been obtained gathers, it approximates a theoretical formula provided as a function of speed. Thereby, the reference value of the dynamic load radius in all speed ranges can be determined. As described above, the dynamic load radius tends to increase in proportion to the square of the speed. Therefore, by using a quadratic equation as the theoretical formula, it is possible to set the reference value of the dynamic load radius with high accuracy. it can.

  Note that the accuracy of the obtained data may vary in reliability for each speed range. For example, when measurement is performed at regular time intervals, the higher the speed, the longer the moving distance and the higher the data reliability. Therefore, changing the number N of sampling data to be averaged for each speed window (specifically, increasing N as the speed is lower) shortens the initialization time of the reference value of the dynamic load radius and improves the accuracy. Can be set. It is also preferable to change the width of the speed window for each speed window (specifically, the window width is increased as the speed is lower).

Once the above initialization is completed, even if the vehicle is traveling in an arbitrary speed range, if the dynamic load radius of the tire at that time can be measured, it is possible to determine the pressure reduction. Based on the technical matters described here, the dynamic load of the tire One embodiment of a method for initializing a radius reference value will be described based on the flowchart of FIG.

  In steps S1 and S2, the rotational speed of each tire at normal internal pressure is acquired (calculated) based on the output signal of the tire rotational speed detection device.

  In steps S3 and S4, the traveling speed of the vehicle based on GPS information is acquired (calculated).

  In step S5, the dynamic load radius of each tire is calculated from the rotational speed of each tire and the GPS speed of the vehicle.

  In step S6, a combination of the dynamic load radius and the GPS speed is acquired and databased under various driving conditions. As a method for creating a database, the GPS load obtained at each sampling is associated with the calculated dynamic load radius obtained at the sampling interval and temporarily stored.

  In step S7, the obtained dynamic load radius and GPS speed are allocated to each preset speed window.

  In step S8, the number of data N accumulated for each speed window is compared with a predetermined number of necessary data, and if smaller than the necessary number of data, the process returns to the remeasurement routine. When N reaches the required number of data, an average value of the vehicle speed V and the dynamic load radius R is calculated in step S9.

  Next, in step S10, the speed window number W in which the accumulated data number N exceeds the necessary data number is compared with the predetermined necessary window number, and if smaller than the necessary window number, the process returns to the re-measurement routine. When W reaches the required number of windows, an approximate curve is obtained from the average value W of vehicle speed V and dynamic load radius R for each speed window in step S11. Thereby, the dynamic load radius reference value in the entire speed region is determined.

  Next, an embodiment of a threshold setting method for determining a decrease in the internal pressure of a tire using the dynamic load radius reference value initialization method will be described based on the flowchart of FIG.

  First, in step S1, vehicle travel conditions (flat road, straight line constant speed, etc.) are limited.

  Next, in steps S2 and S3, the rotational speed of each tire at normal internal pressure is acquired (calculated) based on the output signal of the tire rotational speed detection device.

  In steps S4 and S5, the traveling speed of the vehicle based on the GPS information is acquired (calculated).

  In step S6, the dynamic load radius of each tire is calculated from the rotational speed of each tire and the GPS speed of the vehicle.

  In step S7, a combination of the dynamic load radius and the GPS speed is acquired and databased under various driving conditions. As a method for creating a database, the GPS load obtained at each sampling is associated with the calculated dynamic load radius obtained at the sampling interval and temporarily stored.

  In step S8, the obtained dynamic load radius and GPS speed are allocated to each preset speed region.

  Here, the method for calculating the dynamic load radius of the tire necessary for determining the pressure reduction is preferably the same as the calculation method and the number of sample data used at the time of initialization in the corresponding speed region.

  In S9, the difference D between the average value of the obtained dynamic load radii and the dynamic load radius reference value obtained by the initialization in the allocated speed region is calculated.

  In S10, the variance σ of the measured tire dynamic load radius for each speed range or each speed range is obtained. In order to set the threshold value for determining the pressure reduction, for example, the threshold value is set to the decrease amount of the dynamic load radius due to the pressure reduction−3σ. Here, the variance σ may be, for example, the average value of the measurement variations σ in each speed region, or the measurement variation σ in a certain speed region may be a representative value. The variance σ is calculated by, for example, moving averages every n measured values for each speed region, and calculating a variation σ of the moving average value every time m moving average values are collected.

  Further, since the dynamic load radius of the tire and the variation thereof vary depending on the travel distance and the wear factor, it is preferable to change the threshold value with time.

  In S11, if D is equal to or greater than a preset threshold value, an internal pressure drop alarm is issued. If D is smaller than the threshold value, the process returns to the re-measurement routine without issuing an internal pressure drop alarm.

  It should be noted that the tire internal pressure drop determination can be performed for each of the four wheels.

  In order to detect the rotational angular velocity of the tire, the rotational angular velocity information used for ABS control was used and converted into the rotational angular velocity. A GPS speedometer (manufactured by Race Logic) was attached to obtain the absolute speed of the vehicle. The vehicle speed was directly output to the PC as serial data.

  These two pieces of information can be taken into the PC synchronously as digital data every 50 msec. From these two pieces of information, the dynamic load radius was calculated every 50 msec and calculated as an average value per second.

<Test conditions>
Vehicle: Four-wheel drive vehicle Tire: 215 / 45R17 SP9000 and DS-X
Road surface: Driving on ordinary roads and expressways in Kobe City Initial driving conditions: 1 person rides at standard internal pressure (230 kPa) Decompression test: 4 people 25% reduced pressure (170 kPa) rides 1 person

<Limitation of driving conditions>
The condition determined to be traveling straight at a constant speed on a flat road is selected, the dynamic load radius is calculated, and data is accumulated. Here, GPS information indicates that GPS reception is good and speed information is normal on condition that | G | <0.05G, azimuth change is 1 degree or less, road surface gradient is 5% or less, and the brake is not depressed. It was decided to adopt only when output. Since the dynamic load radius is dependent on speed, as a speed window,
20 km / h to 50 km / h 10 km / h step 50 km / h to 100 km / h 5 km / h step.

<Calculation of reference value>
When 60 data are collected in each window as the representative value at each speed, the average value of the dynamic load radius of the tire is obtained. When five representative values are accumulated, the average value for the speed in each window and the dynamic load radius are obtained. The relationship between the average values was connected by an approximate curve, and used as a reference value for the entire speed range.

<Setting of dynamic load radius reduction value for pressure reduction detection>
The tire dynamic load radius can be measured by a drum experiment if it is a tire manufacturer. The dynamic load radius is measured at a target speed by applying a load corresponding to the axle load of the target vehicle. The internal pressure is measured at two levels: normal pressure and reduced pressure targeted for detection.

  In this case, 215 / 45R17 SP9000 (summer tire) and DS-X (studless tire) were measured at a load of 2.5 kN, an internal pressure of 230 kPa and 170 kPa, and a speed of 60 km / h, which is the central speed of the above region.

  At this time, the decrease in the dynamic load radius due to the decrease in internal pressure was about 1.5 mm for both tires.

<Calculation of variation in measured values>
The moving average was collected every 60 measured values of the dynamic load radius accumulated in each speed window, and the variance (σ) was obtained when 200 average values were collected, and averaged when five speed windows accumulated.
For summer tires σ = 0.032
For studless tires σ = 0.089

<Threshold setting>
Here, assuming that 3σ of variation in the measured value is a correction amount of the threshold value, the threshold value of the summer tire = 1.4 mm
Studless tire threshold = 1.2 mm

<Running results>
All four wheels were run with a reduced pressure of 25%, and the frequency at which a decrease in internal pressure was detected was measured.

  In other words, without taking into account variations in measured values, the frequency of detection of reduced pressure when using a tire dynamic load radius reduction allowance of 1.5 mm due to a decrease in internal pressure as a threshold, and when correcting for each tire's measured value variations Was as follows.

  As measurement conditions, the tire internal pressure is 158 kPa, the measurement time is about 30 minutes, and the detection is performed by the average value of the dynamic load radius every second, so that it can be performed every second. It was determined that the vehicle was traveling on a straight road at a constant speed on a flat road for 10 minutes, that is, 600 determinations were possible (actually the data was stopped at the 600th time).

  When the threshold value is corrected (summer tire = 1.4 mm / studless tire = 1.2 mm), it can be detected almost 100%, but without correction, the detection rate is about 90% for summer tires and 78% for studless. End up.

  In addition, as shown in the distribution of sampling data of the dynamic load radius of the tire in FIG. 5, when a threshold value is set based on the variation of only the summer tire and the decompression determination is performed, the hatched portion is detected for the studless tire. It is not possible to accurately determine the pressure reduction.

  As described above, it was confirmed that the threshold value setting method considering the variation in the measured dynamic load radius of the tire was effective.

It is a block diagram which shows one Embodiment of the internal pressure fall alarm apparatus of this invention. It is a block diagram which shows the electrical structure of the internal pressure fall alarm apparatus of FIG. It is a flowchart which shows one Embodiment of the calculation program for initializing the reference value of the tire dynamic load radius concerning this invention. It is a flowchart which shows one Embodiment of the threshold value setting program for the tire internal pressure fall determination concerning this invention. It is a figure which shows distribution of the sampling data of the dynamic load radius of a tire.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Wheel speed detection means 2 Control unit 3 GPS apparatus 3a GPS antenna

Claims (12)

Calculate the dynamic load radius of the tire of the vehicle during actual running from the speed information by GPS mounted on the vehicle and the rotational speed information of each tire, and calculate the dynamic load radius from the tire dynamic load radius at normal internal pressure. In the method of determining the decrease in the internal pressure of each tire based on the magnitude of the change in the tire, the pressure reduction of the tire with respect to the amount of change in the dynamic load radius of the tire at a predetermined pressure reduction from the dynamic load radius of the tire at the normal internal pressure determined in advance. A threshold value setting method including a step of setting a threshold value for determination in consideration of variation in a measured value of a dynamic load radius of a tire by actual traveling with respect to the change amount. In order to calculate the magnitude of the variation in the measured value of the dynamic load radius due to actual running, a predetermined number of data is accumulated for the dynamic load radius measured value of the tire due to actual running in a predetermined speed range, and the measured dynamic load radius value The method according to claim 1, further comprising the step of calculating a standard deviation σ of the population. 2. The method according to claim 1, wherein the determination of the amount of change in the dynamic load radius of the tire from the normal internal pressure to the reduced pressure is set in advance according to the size and type of the tire. The method according to claim 1, wherein the variation in the measured value of the dynamic load radius of the running tire is calculated in a timely manner, and the threshold value for determining the pressure reduction is changed along with the change with time of the tire. Calculate the dynamic load radius of the tire of the vehicle during actual running from the speed information by GPS mounted on the vehicle and the rotational speed information of each tire, and calculate the dynamic load radius from the tire dynamic load radius at normal internal pressure. In the method of determining the decrease in the internal pressure of each tire based on the magnitude of the change in the tire, the pressure reduction of the tire with respect to the amount of change in the dynamic load radius of the tire at a predetermined pressure reduction from the dynamic load radius of the tire at the normal internal pressure determined in advance. A tire internal pressure drop warning device including means for setting a threshold value for determination in consideration of variations in a measured value of a dynamic load radius of a tire by actual traveling with respect to the change amount. In order to calculate the magnitude of the variation in the measured value of the dynamic load radius due to actual running, a predetermined number of data is accumulated for the dynamic load radius measured value of the tire due to actual running in a predetermined speed range, and the measured dynamic load radius value 6. The apparatus of claim 5, further comprising means for calculating a standard deviation σ of the population of 6. The apparatus according to claim 5, wherein the determination of the amount of change in the dynamic load radius of the tire from the normal internal pressure to the reduced pressure is set in advance according to the size and type of the tire. 6. The apparatus according to claim 5, wherein the variation of the measured value of the dynamic load radius of the running tire is calculated in a timely manner, and the threshold value for determining the pressure reduction is changed along with the change with time of the tire. Calculate the dynamic load radius of the tire of the vehicle during actual running from the speed information by GPS mounted on the vehicle and the rotational speed information of each tire, and calculate the dynamic load radius from the tire dynamic load radius at normal internal pressure. In the method of determining the decrease in the internal pressure of each tire based on the magnitude of the change in the amount of change in the dynamic load radius of the tire at a predetermined pressure reduction from the predetermined dynamic load radius of the tire at the normal internal pressure A program for setting a threshold value by executing a procedure in which a variation value of a tire dynamic load radius by actual running is taken into consideration for the change amount of the threshold value for determining a tire pressure reduction. In order to calculate the magnitude of the variation in the measured value of the dynamic load radius due to actual running, a predetermined number of data is accumulated for the dynamic load radius measured value of the tire due to actual running in a predetermined speed range, and the measured dynamic load radius value The program of Claim 9 including the procedure of calculating the standard deviation (sigma) of the population of. 10. The program according to claim 9, wherein the determination of the amount of change in the dynamic load radius of the tire from the normal internal pressure to the reduced pressure is set in advance according to the size and type of the tire. The program according to claim 9, wherein the magnitude of variation in the measured value of the dynamic load radius of the running tire is calculated in a timely manner, and the threshold value for determining the pressure reduction is changed along with the change with time of the tire.

Images