JP5265145B2 - Tire internal pressure drop detection method and apparatus, and tire internal pressure drop detection program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for detecting reduction of the tire internal air pressure, which easily sets a standard for determining reduction of the internal air pressure according to the kind of a fitted tire, and enhancing the detection accuracy for reduction of the internal air pressure of the tire. <P>SOLUTION: The method calculates the dynamic loaded radius of a traveling vehicle, and detects reduction of the internal air pressure of the tire based on the magnitude of the change of the obtained dynamic loaded radius from the reference value of the dynamic loaded radius under the normal internal air pressure. The method includes steps of: detecting information on the wheel rotation of each tire of the vehicle; calculating the wheel speed from the detected information on the wheel rotation; finding the vehicle speed; finding the dynamic loaded radius of each tire from the wheel speed and the vehicle speed; determining reduction of the internal air pressure of the tire when the magnitude of the change of the found dynamic loaded radius from the reference value exceeds the predetermined threshold; and changing the threshold to the tire fitted to the vehicle by finding the threshold, based on the difference between the dynamic loaded radius of the front wheel of the vehicle and the dynamic loaded radius of the rear wheel. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

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

  Conventionally, various methods have been proposed as a method for detecting a decrease in the internal pressure of a tire of a vehicle. For example, Patent Document 1 discloses a tire of a running vehicle based on the relationship between the absolute speed of the vehicle and the rotational angular velocity of the tire. The dynamic load radius is calculated, and when the calculated dynamic load radius becomes smaller by a predetermined degree than the initial value (reference value) stored in advance as the dynamic load radius at the normal internal pressure, the internal pressure of the tire is reduced. A method for alarming is disclosed. In the method described in Patent Document 1, in order to improve the detection accuracy, the running state of the vehicle is limited (limited to a running state in which a flat road is traveling straight at a constant speed), and the dynamic load obtained in such a state The radius is used as an effective value to detect a decrease in tire internal pressure.

In addition, since the dynamic load radius of the tire depends on the vehicle speed, the applicant of the present invention can detect the decrease in the dynamic load radius in any speed region before the dynamic load radius and the vehicle in a plurality of speed regions. A method of initializing the dynamic load radius using an approximate expression from the relationship with speed has been proposed (Japanese Patent Application No. 2006-105927).
When it is determined that the dynamic load radius of the running tire is smaller than the determination standard with respect to the reference value of the dynamic load radius obtained by these initialization methods, the internal pressure of the tire decreases. It is the tire internal pressure drop detection method that focuses on the dynamic load radius.

JP 2007-45295 A

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

  The decrease in the dynamic load radius can be obtained by experimentation, but it is not practical to measure all tires, so that it is determined that the tire internal pressure has decreased. Regarding the determination criteria, in the conventional method including the method described in Patent Document 1, the difference or ratio between the dynamic load radius of a typical tire mounted on a vehicle at a normal internal pressure and the dynamic load radius at a time of 30% pressure reduction, for example. Is used.

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

  The present invention has been made in view of such circumstances, and a tire that can easily set an internal pressure decrease determination criterion according to the type of the tire mounted, and can improve detection accuracy of the tire internal pressure decrease. It is an object of the present invention to provide an internal pressure drop detection method and apparatus, and a tire internal pressure drop detection program.

The tire internal pressure drop detection method of the present invention calculates the tire dynamic load radius of a running vehicle, and based on the magnitude of change of the obtained dynamic load radius from the reference value of the dynamic load radius at normal internal pressure. A method for detecting a decrease in tire internal pressure,
Detecting wheel rotation information of each tire of the vehicle;
Calculating the wheel speed from the detected wheel rotation information;
Determining vehicle speed;
Obtaining a dynamic load radius of each tire from the wheel speed and vehicle speed;
The resulting tire dynamic load radius, wherein the change from baseline magnitude predetermined contains Mutotomoni and determining decrease in internal pressure of a tire when the threshold is exceeded, and after the dynamic load radius of the front wheel of the vehicle by determining the threshold value based on the difference between the dynamic load radius of the wheel, and Nde further contains a threshold setting step vary for a tire to be mounted to the threshold value of the vehicle,
This threshold value setting step is based on an internal pressure sensitivity estimated value obtained as a product of a tire load sensitivity represented by the following formula obtained by running the vehicle at normal internal pressure and a proportionality constant A obtained in advance by an experiment. It is characterized by setting a threshold .
Load sensitivity = (front wheel dynamic load radius-rear wheel dynamic load radius) / front wheel dynamic load radius / (front wheel load-rear wheel load)

  In the tire internal pressure drop detection method according to the present invention, the threshold value, which is a criterion used when detecting that the tire internal pressure has fallen beyond a predetermined range, is set by using the dynamic load radius of the front wheel and the dynamic load of the rear wheel. Based on the difference from the radius, it is changed according to the tire mounted on the vehicle. Therefore, a threshold value corresponding to the tire size can be set easily, and a decrease in tire internal pressure can be accurately detected.

In the step of determining the threshold, Ru Tei using load difference between the front wheels and the rear wheels of the vehicle. Load weight differences This can be easily obtained as a vehicle specification, also, since the difference between the dynamic load radii of the dynamic load radius front and rear wheels of the vehicle can be easily determined, the required threshold readily Can be sought.

In addition, the tire internal pressure drop detecting device of the present invention calculates the tire dynamic load radius of the running vehicle, and changes the magnitude of the obtained dynamic load radius from the reference value of the dynamic load radius at normal internal pressure. A device for detecting a decrease in tire internal pressure based on
Wheel rotation information detecting means for detecting wheel rotation information of each tire of the vehicle;
Wheel speed calculation means for calculating wheel speed from the detected wheel rotation information;
Vehicle speed calculation means for determining the vehicle speed;
A dynamic load radius calculating means for determining a dynamic load radius of each tire from the wheel speed and the vehicle speed;
A determination means for determining a decrease in the internal pressure of the tire when a magnitude of a change from the reference value of the obtained tire dynamic load radius exceeds a predetermined threshold;
By determining the threshold value based on the difference between the dynamic load radii of the front wheels of the dynamic load radius and the rear wheels of the vehicle, and Nde contains a threshold setting means for changing in accordance with the tire to be mounted to the threshold value of the vehicle,
This threshold value setting means is based on an estimated internal pressure sensitivity value obtained as a product of a tire load sensitivity expressed by the following formula obtained by running the vehicle at normal internal pressure and a proportionality constant A obtained in advance by an experiment. It is characterized by setting a threshold .
Load sensitivity = (front wheel dynamic load radius-rear wheel dynamic load radius) / front wheel dynamic load radius / (front wheel load-rear wheel load)

  In the tire internal pressure drop detecting device according to the present invention, the thresholds, which are determination criteria used when detecting that the tire internal pressure has fallen beyond a predetermined range, are set based on the dynamic load radius of the front wheel and the dynamic load of the rear wheel. Based on the difference from the radius, it is changed according to the tire mounted on the vehicle. Therefore, a threshold value corresponding to the tire size can be set easily, and a decrease in tire internal pressure can be accurately detected.

Further, the tire internal pressure drop detection program according to the present invention calculates the tire dynamic load radius of the running vehicle, and changes the obtained dynamic load radius to the magnitude of change from the reference value of the dynamic load radius at normal internal pressure. Based on the wheel speed calculation means for calculating the wheel speed from the wheel rotation information of each tire of the vehicle, and the dynamic load for determining the dynamic load radius of each tire from the wheel speed and the vehicle speed. Radius calculation means, determination means for determining a decrease in tire internal pressure when the magnitude of change of the obtained tire dynamic load radius from the reference value exceeds a predetermined threshold, and dynamic load on the front wheels of the vehicle By obtaining the threshold value based on the difference between the radius and the dynamic load radius of the rear wheel, the threshold value functioning means for changing the threshold value according to the tire mounted on the vehicle ,
This threshold value setting means is based on an estimated internal pressure sensitivity value obtained as a product of a tire load sensitivity expressed by the following formula obtained by running the vehicle at normal internal pressure and a proportionality constant A obtained in advance by an experiment. setting a threshold value Te to is characterized in Rukoto.
Load sensitivity = (front wheel dynamic load radius-rear wheel dynamic load radius) / front wheel dynamic load radius / (front wheel load-rear wheel load)

  In the tire internal pressure drop detection program according to the present invention, the thresholds, which are determination criteria used when detecting that the tire internal pressure has fallen beyond a predetermined range, are set as the dynamic load radius of the front wheel and the dynamic load of the rear wheel. Based on the difference from the radius, it is changed according to the tire mounted on the vehicle. Therefore, a threshold value corresponding to the tire size can be set easily, and a decrease in tire internal pressure can be accurately detected.

  According to the tire internal pressure drop detection method and apparatus, and the tire internal pressure drop detection program of the present invention, it is possible to easily set the internal pressure drop determination standard according to the type of the mounted tire, and to improve the detection accuracy of the tire internal pressure drop. be able to.

Hereinafter, with reference to the accompanying drawings, a tire internal pressure drop detection method (hereinafter also simply referred to as “detection method”) and device (hereinafter also simply referred to as “detection device”), and a tire internal pressure drop detection program according to the present invention will be described. Will be described in detail.
As shown in FIG. 1, the detection apparatus according to an embodiment of the present invention includes four tires FL (left front wheel), FR (right front wheel), RL (left rear wheel), and In order to detect wheel rotation information of the RR (right rear wheel), normal wheel speed detection means (wheel rotation information detection 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 for generating rotation pulses using an electromagnetic pickup or the like and measuring the rotation angular speed and wheel speed from the number of pulses. It is possible to use an angular velocity sensor including that for measuring the rotational angular velocity and the wheel speed from this voltage. The output of the wheel speed detecting means 1 is given to a control unit 2 which is a computer such as ABS. The control unit 2 includes a liquid crystal display element for informing a tire whose internal pressure has decreased, a display 3 composed of a plasma display element or a CRT, an initialization button 4 that can be operated by a driver, and a decrease in tire internal pressure. Are connected to a GPS device 6 that constitutes a vehicle speed calculation means.

As shown in FIG. 2, the control unit 2 stores an I / O interface 2a necessary for passing signals to and from an external device, a CPU 2b that functions as a center of arithmetic processing, and a control operation program for the CPU 2b. The ROM 2c and the RAM 2d from which data is temporarily written or the written data is read when the CPU 2b performs a control operation. In FIG. 2, 6a is a GPS antenna.
The wheel speed detection means 1 outputs a pulse signal corresponding to the number of rotations of the tire (hereinafter also referred to as “wheel speed pulse”). Further, the CPU 2b calculates the rotation angular velocity of each tire at a predetermined sampling period ΔT (sec), for example, ΔT = 0.05 seconds, based on the wheel speed pulse output from the wheel speed detecting means 1.

  The vehicle speed can be obtained using, for example, a GPS speedometer. With the widespread use of car navigation systems, GPS devices are attached to many vehicles. As a result, positioning technology using a GPS device has also been improved, and a device specialized in calculating speed (GPS speedometer VBOX (trade name) manufactured by Race Logic, UK) is now on the market. The speed calculated by the speedometer using such GPS information can be used as the vehicle speed.

  The detection device according to the present embodiment includes wheel speed detection means (wheel rotation information detection means) 1, wheel speed calculation means for calculating wheel speed from the detected wheel rotation information of each tire of the vehicle, and vehicle speed. GPS speedometer to be calculated, dynamic load radius calculating means for determining the dynamic load radius of each tire from the wheel speed and vehicle speed, and the change of the dynamic load radius of the obtained tire from the reference value of the dynamic load radius at normal internal pressure By determining the threshold based on the difference between the dynamic load radius of the front wheel and the dynamic load radius of the rear wheel of the vehicle, the determination means for determining the decrease in the internal pressure of the tire when the size exceeds a predetermined threshold, Threshold setting means for changing the threshold according to the tire mounted on the vehicle. And a tire internal pressure fall detection program makes the said control unit 2 function as a wheel speed calculation means, a dynamic load radius calculation means, a determination means, and a threshold value setting means.

  The tire dynamic load radius (R) of the traveling vehicle can be calculated by V = R × ω from the relationship between the absolute speed (V) of the vehicle and the rotational angular velocity (ω) of the tire. 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.

  The reference of the amount of change (decrease) in the dynamic load radius for determining the decrease in internal pressure, that is, the threshold value is determined by how much the dynamic load radius of the tire decreases when the tire is depressurized by 25% or 30%, for example. can do. It is known that the change in the dynamic load radius due to the change in the internal pressure (hereinafter also referred to as “internal pressure sensitivity”) is almost constant depending on the tire and is almost determined by the tire size. Therefore, if information on the internal pressure sensitivity is obtained in advance through experiments or the like, the threshold value for each tire can be determined.

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

  The present inventor has conducted various studies so as to be able to accurately determine a decrease in the internal pressure of the tire without knowing the internal pressure sensitivity in advance for all tires, and as a result, considering the influence of the internal pressure sensitivity due to the difference in size. A method for setting the threshold was devised. That is, the internal pressure sensitivity was found to be proportional to the amount of change in the dynamic load radius with respect to the load (hereinafter also referred to as “load sensitivity”), and the present invention was completed based on such knowledge.

  Specifically, since the internal pressure sensitivity and load sensitivity are in a proportional relationship, if only the proportional constant between the internal pressure sensitivity and load sensitivity is known in advance through experiments, the internal pressure sensitivity is automatically calculated from the load sensitivity. It is possible to calculate a threshold value corresponding to a tire that is actually mounted. As described later, the load sensitivity can be obtained by calculating the dynamic load radii of the front wheels and the rear wheels of the vehicle when the vehicle axial load is known.

  It is not necessary to perform the experiment in advance for obtaining the relationship between the internal pressure sensitivity and the load sensitivity in all sizes and patterns that are planned to be mounted, and the internal pressure sensitivity and the load sensitivity are in a certain proportional relationship. It is only necessary to measure at least one, preferably about three, tires of different sizes and determine the proportionality constant.

The internal pressure sensitivity and load sensitivity are considered to be proportional for the following reasons.
The dynamic load radius of a tire is mainly determined by the circumference of the tire breaker, but changes when the tire breaker bends due to a decrease in the load acting on the tire or the tire internal pressure. The amount of deflection is proportional to the contact area of the tire, and the amount of deflection when the contact area is large is large. Here, the ground contact area S is
There is a relationship of ground contact area S∝load / internal pressure. That means
Change in dynamic load radius = Change in deflection amount ∝ Contact area S ∝ Load / Internal pressure (1)
Are in a relationship.
From the relationship shown in (1), an increase in the load with respect to the change in the dynamic load radius is equivalent to a decrease in the internal pressure. Therefore, the influence of the internal pressure on the dynamic load radius can be replaced with the influence of the load.

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

  (2) On the other hand, the vehicle speed (V) is obtained from the GPS speedometer. The vehicle speed (V) is directly output to the control unit 2 as serial data. For either one of the calculation time of the rotational angular velocity (ω) and the calculation time of the vehicle speed (V), the numerical value at the same time as the other is interpolated and the numerical values at the same time are calculated and synchronized with each other. For example, can be taken into the control unit 2 as digital data every 50 msec. The dynamic load radius is calculated every 50 msec from the digital data every 50 msec, and can be calculated, for example, as an average value per second.

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

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

(3) Next, the dynamic load radius (R) of each tire is calculated from the rotational angular velocity (ω) and the vehicle speed (V) of each tire, and the dynamic load at normal internal pressure that is set in advance by actual vehicle running or the like. The difference between the radius and the calculated dynamic load radius (R) is calculated.
A predetermined number of the differences can be accumulated, and the tire pressure drop can be determined based on the average value. In this case, the accuracy of the determination can be increased by adopting the average value. Alternatively, the variance of the difference accumulated by a predetermined number may be determined as the mother variance, and the average value of the differences may be calculated when the variance (σ ² ) is smaller than the reference value.

  (4) Next, the calculated difference is compared with a predetermined threshold value, and if the difference is larger than the threshold value, it is determined that the tire internal pressure has decreased, and the reduced pressure tire is displayed on the display 3 and an alarm is issued. A warning is issued to the driver by the device 5.

[Threshold setting]
In order to set the threshold, first, a relational expression between the load sensitivity and the internal pressure sensitivity is obtained, and a constant for obtaining the internal pressure sensitivity from the load sensitivity is determined.
The relational expression between the load sensitivity and the internal pressure sensitivity can be obtained, for example, by measuring a table dynamic load radius using a flat belt. Measurement is performed on at least one tire, preferably about three tires, and a plurality of levels are set for each of the load and the internal pressure, and all combinations of levels are measured. As load levels, for example, three levels of 2.5 kN, 3.5 kN, and 4.5 kN can be used, and as internal pressure levels, for example, four levels of 150 kPa, 180 kPa, 210 kPa, and 240 kPa can be used. it can.

  Then, using the value of the dynamic load radius at a certain load value (for example, 3.5 kN) and an internal pressure value (for example, 210 kPa) as a reference value, the load sensitivity (the amount of change in the dynamic load radius per 1 kN change of load / reference Value) and internal pressure sensitivity (change in dynamic load radius per 1% change in internal pressure / reference value), and a proportional constant A satisfying internal pressure sensitivity = A × load sensitivity is obtained by, for example, the least square method. This proportionality constant A is stored in the ROM 2c of the control unit 2.

Next, the vehicle is driven at the reference internal pressure (normal internal pressure), and the load sensitivity of the tire mounted on the vehicle is obtained by the following equation (3), for example.
Load sensitivity = (front wheel dynamic load radius-rear wheel dynamic load radius) / front wheel dynamic load radius / (front wheel load-rear wheel load) (3)
The vehicle wheel load can be obtained by dividing the axle load described in the vehicle verification by 2 to obtain the wheel load.

  The load sensitivity (% / kN) thus obtained is multiplied by the proportionality constant A to obtain the estimated internal pressure sensitivity (% /%). For example, when it is desired to detect a decrease in internal pressure when the internal pressure decreases by 25%, a dynamic load radius change amount (%) that is a value obtained by multiplying the estimated internal pressure sensitivity value (% /%) by 25% is set as a threshold value. To do.

Next, examples of the detection method of the present invention will be described. However, the present invention is not limited to such examples.
[Examples and Comparative Examples]
In order to obtain the rotational angular velocity of each tire mounted on the vehicle, the rotational angular velocity used for ABS control was converted into the rotational angular velocity. Further, in order to obtain the absolute speed of the vehicle, a VBOX (trade name, a GPS speedometer manufactured by Race Logic, UK) was attached to the vehicle. The vehicle speed is directly output as serial data to a PC (personal computer), and the vehicle speed information and the rotational speed information are synchronized with each other as digital data every 50 msec and can be taken into the PC. And the tire dynamic load radius was calculated every 50 msec from these two pieces of information, and calculated as an average value per second.

[Pre-test]
The dynamic load radius on the table was measured using a flat belt, and the relationship between load sensitivity and internal pressure sensitivity was investigated. The tires examined were of the following three types, each with three load levels (2.5 kN, 3.5 kN, 4.5 kN) and four internal pressure levels (150 kPa, 180 kPa, 210 kPa, 240 kPa). Measurements were made.
Tire I: 185 / 70R14 SP10
Tire II: 195 / 60R15 LM703
Tire III: 205 / 50R15 LM703
Load sensitivity (change in dynamic load radius per 1 kN change of load / reference value) and internal pressure sensitivity (per 1% change in internal pressure) when the value of dynamic load radius when load is 3.5 kPa and internal pressure is 210 kPa The amount of change in the dynamic load radius / reference value). The results are shown in Table 1 and FIG.

From the above, load sensitivity and internal pressure sensitivity are
Internal pressure sensitivity = (-0.0599) x load sensitivity (4)
It was a relationship.

[Real car test]
The tires I to III were sequentially mounted on the FF vehicle, and an actual vehicle test was performed at the Okayama test course of Sumitomo Rubber Industries, Ltd.
First, traveling was performed at a reference internal pressure (210 kPa), and load sensitivity was determined according to the above-described equation (3). The vehicle wheel load was 3.7 kN for the front wheels and 2.2 kN for the rear wheels, and these values were obtained by dividing the axle load described in the vehicle verification of the FF vehicle by 2.

In the case of the tire I, the load sensitivity is −0.14 (% / kN), and the internal pressure sensitivity estimation value from the previously obtained equation (4) is
−0.14 × (−0.0599) = 0.0084 (% /%)
It became.
Similarly, in the case of tire II, the load sensitivity is -0.24 (% / kN), and the internal pressure sensitivity estimate is
−0.24 × (−0.0599) = 0.144 (% /%)
In the case of tire III, the load sensitivity is -0.30 (% / kN), and the internal pressure sensitivity estimate is
−0.30 × (−0.0599) = 0.180 (% /%)
It became.

From the above, the dynamic load radius change amount (threshold value) of tires I to III when 25% decompression was taken as the threshold value was as follows.
Tire I: 0.0084 × 25 = 0.21 (%)
Tire II: 0.0144 × 25 = 0.36 (%)
Tire III: 0.0180 × 25 = 0.45 (%)

  Next, a running test was performed for each tire with the internal pressure reduced by 30%. When the internal pressure sensitivity was obtained from the load sensitivity and a threshold value was set from this internal pressure sensitivity (Example), as shown in Table 2, an internal pressure drop was detected and an alarm was issued for each tire. In the case of a fixed value based on III (when the dynamic load radius becomes 0.45% smaller, an alarm is issued based on a decrease in internal pressure) (comparative example), no warning is given for tire I and tire II. It was.

  In this way, if the threshold value is set to a fixed value, there may be no alarm depending on the size of the tire, but the load sensitivity of the installed tire is calculated from the load difference between the front and rear wheels of the vehicle, and further to the internal pressure sensitivity. When the value obtained by multiplying the proportional constant is used as a threshold value, it is possible to accurately detect a decrease in the internal pressure of the tire.

  In the above-described embodiment, the load sensitivity is obtained by Expression (3), but the load sensitivity can be obtained by other methods. That is, for example, it can be obtained by using fluctuations in the longitudinal axis load during driving. Specifically, when the vehicle wheelbase L and the center-of-gravity height H are known from a prior experiment or a vehicle catalog value and the information on the axle shaft torque T of the vehicle can be acquired from the vehicle, the following is performed. Thus, the load sensitivity can be calculated.

From the balance of moments around the center of gravity, if the wheel load change is ΔFz,
2 × ΔFz × L = Fx × H = (T / R) × H
Is established. Here, R is a tire load radius (distance between the tire shaft and the ground), and Fx (T / R) is a driving force.
From this equation, the wheel load fluctuation amount at the time of driving can be calculated from the axle shaft torque T as follows.
ΔFz = (1/2) × (H / L) × (T / R)
At this time, regression coefficients a and b are obtained by regressing the dynamic load radius DLRr and the wheel load change ΔFz of the driven wheel sampled in time series by the following equation.
DLRr = a × ΔFz (kN) + b
In this equation, the regression coefficient a is the dynamic load radius change amount with respect to the unit load change, and the regression coefficient b is the dynamic load radius when the load change is zero, so the load sensitivity can be expressed by a / b. .

  Moreover, although the absolute speed of the vehicle obtained by the GPS device is used, the present invention is not limited to this, and the absolute speed of the vehicle obtained by a different method such as the ground speed can be used.

It is a block diagram which shows one Embodiment of the detection apparatus of this invention. It is a block diagram which shows the electrical structure of the detection apparatus shown by FIG. It is a figure which shows an example of the relationship between load sensitivity and internal pressure sensitivity.

Explanation of symbols

1 Wheel speed detection means 2 Control unit 2a Interface 2b CPU
2c ROM
2d RAM
3 Display 4 Initialization Button 5 Alarm 6 GPS Device 6a GPS Antenna

Claims (3)

This is a method of calculating the tire dynamic load radius of a running vehicle and detecting the decrease in tire internal pressure based on the magnitude of change of the obtained dynamic load radius from the standard value of the dynamic load radius at normal internal pressure. And
Detecting wheel rotation information of each tire of the vehicle;
Calculating the wheel speed from the detected wheel rotation information;
Determining vehicle speed;
Obtaining a dynamic load radius of each tire from the wheel speed and vehicle speed;
The resulting tire dynamic load radius, wherein the change from baseline magnitude predetermined contains Mutotomoni and determining decrease in internal pressure of a tire when the threshold is exceeded, and after the dynamic load radius of the front wheel of the vehicle by determining the threshold value based on the difference between the dynamic load radius of the wheel, and Nde further contains a threshold setting step vary for a tire to be mounted to the threshold value of the vehicle,
This threshold value setting step is based on an internal pressure sensitivity estimated value obtained as a product of a tire load sensitivity represented by the following formula obtained by running the vehicle at normal internal pressure and a proportionality constant A obtained in advance by an experiment. And a threshold value is set .
Load sensitivity = (front wheel dynamic load radius-rear wheel dynamic load radius) / front wheel dynamic load radius / (front wheel load-rear wheel load) This is a device that calculates the tire dynamic load radius of a running vehicle and detects the decrease in tire internal pressure based on the magnitude of the change of the obtained dynamic load radius from the reference value of the dynamic load radius at normal internal pressure. And
Wheel rotation information detecting means for detecting wheel rotation information of each tire of the vehicle;
Wheel speed calculation means for calculating wheel speed from the detected wheel rotation information;
Vehicle speed calculation means for determining the vehicle speed;
A dynamic load radius calculating means for determining a dynamic load radius of each tire from the wheel speed and the vehicle speed;
A determination means for determining a decrease in the internal pressure of the tire when a magnitude of a change from the reference value of the obtained tire dynamic load radius exceeds a predetermined threshold;
By determining the threshold value based on the difference between the dynamic load radii of the front wheels of the dynamic load radius and the rear wheels of the vehicle, and Nde contains a threshold setting means for changing in accordance with the tire to be mounted to the threshold value of the vehicle,
This threshold value setting means is based on an estimated internal pressure sensitivity value obtained as a product of a tire load sensitivity expressed by the following formula obtained by running the vehicle at normal internal pressure and a proportionality constant A obtained in advance by an experiment. A tire internal pressure drop detecting device, wherein a threshold value is set .
Load sensitivity = (front wheel dynamic load radius-rear wheel dynamic load radius) / front wheel dynamic load radius / (front wheel load-rear wheel load) A computer for calculating a tire dynamic load radius of a running vehicle and detecting a decrease in the internal pressure of the tire based on a magnitude of a change of the obtained dynamic load radius from a reference value of the dynamic load radius at a normal internal pressure. A wheel speed calculating means for calculating a wheel speed from wheel rotation information of each tire of the vehicle, a dynamic load radius calculating means for calculating a dynamic load radius of each tire from the wheel speed and the vehicle speed, and a tire dynamic load radius of the obtained tire Determining means for determining a decrease in tire internal pressure when the magnitude of the change from the reference value exceeds a predetermined threshold, and a difference between the dynamic load radius of the front wheel and the dynamic load radius of the rear wheel of the vehicle. By calculating the threshold value based on the threshold value functioning means for changing the threshold value according to the tire mounted on the vehicle ,
This threshold value setting means is based on an estimated internal pressure sensitivity value obtained as a product of a tire load sensitivity expressed by the following formula obtained by running the vehicle at normal internal pressure and a proportionality constant A obtained in advance by an experiment. tire pressure drop detecting program characterized that you set the threshold Te.
Load sensitivity = (front wheel dynamic load radius-rear wheel dynamic load radius) / front wheel dynamic load radius / (front wheel load-rear wheel load)

Images