JP5555486B2 - Tire internal pressure drop detection method and apparatus, and tire internal pressure drop detection program - Google Patents

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 tire movement of a vehicle during traveling from the relationship between the absolute speed of the vehicle and the rotational angular velocity of the tire. The load radius is calculated, and when the calculated dynamic load radius is smaller than the initial value (reference value) stored in advance as the dynamic load radius at normal internal pressure, a warning is given of a decrease in tire internal pressure. A method 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 tire dynamic load radius depends on the vehicle speed, an approximate expression is derived from the relationship between the dynamic load radius and the vehicle speed in a plurality of speed regions so that a decrease in the dynamic load radius can be detected in any speed region. There is also known a method for initializing the dynamic load radius using the method (see Patent Document 2).

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.
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. In the conventional method including the method described in Patent Document 1 as the determination criterion, a difference between a dynamic load radius of a typical tire mounted on a vehicle at a normal internal pressure and a dynamic load radius at a time of 30% decompression, for example, The ratio is used.

However, in general passenger cars, there are generally multiple sizes of tires that can or will be installed in the passenger car, and which of the multiple set sizes is installed in the vehicle. I don't know if it will be done 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.

In view of this, the present applicant has proposed a tire internal pressure decrease determination method that can easily set an internal pressure decrease determination standard according to the type of the mounted tire (see Patent Document 3).
In the method described in Patent Document 3, the threshold value that is a criterion for reducing the internal pressure is changed in accordance with the tire mounted on the vehicle based on the difference between the dynamic load radius of the front wheel and the dynamic load radius of the rear wheel. ing. Thereby, the threshold value according to a tire size can be set easily, and the internal pressure fall of a tire can be detected correctly.

JP 2007-45295 A JP 2007-276646 A JP 2009-6793 A

  However, in the method described in Patent Document 3, the tire load sensitivity is estimated by using the dynamic load radius difference between the front and rear wheels and the front and rear load difference (front wheel load-rear wheel load). It is effective for vehicles such as FF vehicles with large front-rear load differences, but the accuracy of estimation may be reduced for vehicles where the front-rear load distribution is almost unchanged, leaving the problem that applicable vehicle types are limited. It was.

  The present invention has been made in view of such circumstances, and a tire internal pressure drop detection method and apparatus, and a tire internal pressure drop detection program capable of easily setting an alarm threshold according to the tire size for all vehicle types. The purpose is to provide.

The tire internal pressure drop detection method of the present invention (hereinafter also simply referred to as “detection method”) calculates the tire dynamic load radius of a running vehicle, and the obtained dynamic load radius of the dynamic load radius at normal internal pressure is calculated. A method of detecting a decrease in tire internal pressure based on the magnitude of change from a reference value,
Detecting wheel rotation information of each tire of the vehicle;
Calculating the wheel speed from the detected wheel rotation information;
Calculating vehicle speed based on speed information from a GPS device mounted on the vehicle;
Obtaining a dynamic load radius of each tire from the calculated vehicle speed and the wheel speed;
Determining the decrease in the internal pressure of the tire when the magnitude of the change from the reference value of the obtained tire dynamic load radius exceeds a predetermined threshold,
The predetermined threshold is a pressure reduction obtained from the relationship between the load sensitivity and the pressure reduction sensitivity when turning the vehicle related to the tire to be mounted on the vehicle, and the load sensitivity obtained by turning during initialization. and Nde further contains a threshold setting step that is set based on the sensitivity,
The load sensitivity is calculated from the relationship between the lateral acceleration and the dynamic load radius change due to load movement at the time of turning, calculated from the speed information and the wheel speeds of the left and right wheels of the vehicle,
The vehicle is a front wheel drive vehicle or a rear wheel drive vehicle;
The relational expression, the center of gravity height of the vehicle, the tread width of the vehicle, and the vehicle mass, and the load shift share of according to the driven wheel axis to all axes characterized by the free Mukoto the formula.

  In the detection method of the present invention, the change in dynamic load radius during turning, that is, the change in dynamic load radius due to load movement, that is, the load sensitivity, is obtained by utilizing the fact that load movement occurs on the left and right wheels during vehicle turning. Then, the pressure reduction sensitivity is obtained from the relationship between the load sensitivity and the pressure reduction sensitivity at the time of turning of the vehicle related to the tire to be mounted on the vehicle and the load sensitivity obtained by turning at the time of initialization. A threshold is set based on the sensitivity. Since the load movement during turning occurs in any vehicle, the threshold value can be easily set regardless of the vehicle type.

Change in tire dynamic load radius is ΔDLR, tire load sensitivity is b, vehicle center of gravity height is H, vehicle tread width is W, vehicle mass is m, vehicle speed is V, yaw rate is θ ', driven for all axes When the load movement share ratio applied to the wheel shaft is α, the relational expression is
ΔDLR = b × α × (H / W) × m × Vθ ′
The load sensitivity at the time of turning of the vehicle and the load sensitivity obtained by turning at the time of initialization related to the tire to be mounted is a load sensitivity representative characteristic represented by b × α × (H / W) × m. It can be a value.

The relationship between the load sensitivity and reduced pressure sensitivity during a vehicle turning of the tire will be attached may be assumed to be represented by a linear function of the decreased pressure sensitivity and the load sensitivity typical characteristic values.

The tire internal pressure drop detection device (hereinafter, also simply referred to as “detection device”) of the present invention calculates the tire dynamic load radius of a running vehicle, and the obtained dynamic load radius of the dynamic load radius at normal internal pressure is calculated. A device for detecting a decrease in internal pressure of a tire based on the magnitude of change from a reference value,
Wheel rotation information detecting means for detecting wheel rotation information of each tire of the vehicle;
Wheel speed calculating means for calculating the wheel speed from the wheel rotation information detected by the wheel rotation information detecting means;
Vehicle speed calculation means for calculating a vehicle speed based on speed information from a GPS device mounted on the vehicle;
Dynamic load radius calculating means for determining the dynamic load radius of each tire from the vehicle speed calculated by the vehicle speed calculating means and the wheel 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,
The predetermined threshold value is determined in advance from the relationship between the load sensitivity and the depressurization sensitivity when turning the vehicle related to the tire to be mounted on the vehicle, and the load sensitivity obtained by turning during initialization. and Nde further contains a threshold setting means for setting, based on the sensitivity,
The load sensitivity is calculated from the relationship between the lateral acceleration and the dynamic load radius change due to load movement at the time of turning, calculated from the speed information and the wheel speeds of the left and right wheels of the vehicle,
The vehicle is a front wheel drive vehicle or a rear wheel drive vehicle;
The relational expression, the center of gravity height of the vehicle, the tread width of the vehicle, and the vehicle mass, and the load shift share of according to the driven wheel axis to all axes characterized by the free Mukoto the formula.

  In the detection device of the present invention, the change in the dynamic load radius during turning, that is, the change in the dynamic load radius due to the load movement, that is, the load sensitivity is obtained by utilizing the fact that the load movement occurs in the left and right wheels when the vehicle is turning. Then, the pressure reduction sensitivity is obtained from the relationship between the load sensitivity and the pressure reduction sensitivity at the time of turning of the vehicle related to the tire to be mounted on the vehicle and the load sensitivity obtained by turning at the time of initialization. A threshold is set based on the sensitivity. Since the load movement during turning occurs in any vehicle, the threshold value can be easily set regardless of the vehicle type.

Change in tire dynamic load radius is ΔDLR, tire load sensitivity is b, vehicle center of gravity height is H, vehicle tread width is W, vehicle mass is m, vehicle speed is V, yaw rate is θ ', driven for all axes When the load movement share ratio applied to the wheel shaft is α, the relational expression is
ΔDLR = b × α × (H / W) × m × Vθ ′
The load sensitivity at the time of turning of the vehicle and the load sensitivity obtained by turning at the time of initialization related to the tire to be mounted is a load sensitivity representative characteristic represented by b × α × (H / W) × m. It can be a value.

The relationship between the load sensitivity and reduced pressure sensitivity during a vehicle turning of the tire will be attached may be assumed to be represented by a linear function of the decreased pressure sensitivity and the load sensitivity typical characteristic values.

The tire internal pressure drop detection program (hereinafter also simply referred to as “program”) of the present invention calculates the tire dynamic load radius of a running vehicle, and uses the obtained dynamic load radius as a reference for the dynamic load radius at normal internal pressure. Computer to detect a decrease in tire internal pressure, based on the magnitude of the change from the value
Wheel speed calculating means for calculating wheel speed from wheel rotation information of each tire of the vehicle,
Vehicle speed calculation means for calculating a vehicle speed based on speed information from a GPS device mounted on the vehicle;
Dynamic load radius calculating means for determining the dynamic load radius of each tire from the vehicle speed calculated by the vehicle speed calculating means and the wheel speed;
Determination means for determining a decrease in tire internal pressure when the magnitude of change from the reference value of the obtained tire dynamic load radius exceeds a predetermined threshold, and the predetermined threshold is determined in advance. It functions as a threshold setting means that is set based on the pressure reduction sensitivity obtained from the relationship between the load sensitivity and the pressure reduction sensitivity when turning the vehicle related to the tire to be mounted on the vehicle, and the load sensitivity obtained by turning at the time of initialization. ,
The load sensitivity is calculated from the relationship between the lateral acceleration and the dynamic load radius change due to load movement at the time of turning, calculated from the speed information and the wheel speeds of the left and right wheels of the vehicle,
The vehicle is a front wheel drive vehicle or a rear wheel drive vehicle;
The relational expression includes the height of the center of gravity of the vehicle, the tread width of the vehicle, the vehicle mass, and the load transfer share ratio applied to the driven wheel shaft with respect to all the axes .

  According to the tire pressure drop detection method and apparatus and the tire pressure drop detection program of the present invention, it is possible to easily set an alarm threshold corresponding to the tire size for all vehicle types.

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 the relationship between the ground speed of the inner and outer wheel at the time of left turn, and vehicle speed. It is a figure explaining various parameters of vehicles. It is the figure which plotted dynamic load radius variation | change_quantity (DELTA) DLR and lateral acceleration (theta) 'V about tire size 185 / 70R14. It is a figure which shows the relationship between pressure reduction sensitivity and a load sensitivity representative characteristic value. It is the figure which plotted dynamic load radius variation | change_quantity (DELTA) DLR and lateral acceleration (theta) 'V about a certain tire.

Hereinafter, embodiments of a tire internal pressure drop detection method and apparatus, and a program according to the present invention will be described in detail with reference to the accompanying drawings.
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 an alarm device 5 that informs the driver of the vehicle and a GPS device 6 that provides vehicle speed information.

  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 speed information obtained from a GPS device mounted on the vehicle. 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 detected wheel rotation information, and a GPS device mounted on the vehicle. Vehicle speed calculation means for calculating a vehicle speed based on speed information from the vehicle, dynamic load radius calculation means for obtaining a dynamic load radius of each tire from the vehicle speed and the wheel speed calculated by the vehicle speed calculation means, and Determination means for determining a decrease in tire internal pressure when the magnitude of a change in the tire dynamic load radius from the reference value exceeds a predetermined threshold, and the vehicle for which the predetermined threshold has been determined in advance Threshold setting to be set based on the relationship between the load sensitivity when turning the vehicle and the pressure reduction sensitivity of the tire scheduled to be mounted on the tire and the load sensitivity obtained by turning during initialization It is composed of a stage. Then, the tire internal pressure drop detection program causes the control unit 2 to function as wheel speed calculation means, vehicle speed calculation means, dynamic load radius calculation means, determination means, and threshold 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 this change in internal pressure (hereinafter also referred to as “decompression sensitivity”) is substantially constant depending on the tire and is substantially determined by the tire size. Therefore, if the information about the pressure reduction 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 you know the pressure reduction sensitivity 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 ratio of the tire having grasped the decompression sensitivity is 70, whereas the flatness ratio of the tire actually mounted is 50, the decompression sensitivity depending on the size is large. Therefore, if the threshold value is determined based on the pressure reduction sensitivity of a tire with a flatness ratio of 70, a decrease in the internal pressure of a tire with 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 pressure reduction sensitivity is known).

  The present inventor has various methods so that it is possible to accurately determine a decrease in the internal pressure of the tire without having to know the pressure reduction sensitivity in advance for all tires, and to accurately determine without limitation on applicable vehicle types. As a result of repeated studies, we have devised a method for setting the threshold in consideration of the effect of reduced pressure sensitivity due to the difference in size. That is, the pressure reduction sensitivity is based on the knowledge that there is a proportional relationship with the amount of change in the dynamic load radius with respect to the load (hereinafter also referred to as “load sensitivity”). The present invention has been completed by utilizing the phenomenon that occurs.

  Specifically, since the decompression sensitivity and load sensitivity are in a proportional relationship, if only the proportional constant between the decompression sensitivity and load sensitivity is known in advance by experiment, the decompression 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 will be described later, the load sensitivity can be obtained from the relational expression between the lateral acceleration and the dynamic load radius change due to the load movement at the time of turning calculated from the speed information and the wheel speeds of the left and right wheels of the vehicle.

  The preliminary experiment for determining the relationship between the reduced pressure sensitivity and the load sensitivity does not need to be performed for all sizes and patterns that are planned to be mounted, and the reduced pressure sensitivity and the load sensitivity are in a fixed proportional relationship. It is only necessary to measure at least one, preferably about three, tires of different sizes and determine the proportionality constant.

The pressure reduction 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 speed information obtained from the GPS device. For example, the vehicle speed (V) can be obtained from the following equation (3) from the north-south direction speed (Vn) and the east-west direction speed (Ve) obtained from the GPS device.

  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 method]
In order to set the threshold, first, as a first step, an actual vehicle experiment (calibration) is performed to obtain a relational expression between the load sensitivity and the decompression sensitivity, and a constant for obtaining the decompression sensitivity from the load sensitivity is determined. Store in the storage means. Then, as the second stage, the load sensitivity is estimated when the vehicle is turning at the time of initialization of the actual driving, and the pressure is automatically reduced at the initialization stage by multiplying the estimated load sensitivity by the stored proportionality constant. Set the threshold.
Hereinafter, the threshold setting method will be described in detail.

[Calibration]
In the first stage, an actual vehicle experiment (calibration) is performed in advance on the relationship between the pressure reduction sensitivity and the load sensitivity. In the preliminary experiment, turning with various sizes of tires is performed, and load sensitivity is calculated. Further, the pressure is reduced to an internal pressure at which a pressure reduction alarm is issued (for example, 25% pressure reduction. This value can be changed), and the dynamic load radius change amount (pressure reduction sensitivity) at that time is calculated. Then, a proportional constant between the pressure reduction sensitivity and the load sensitivity is obtained, and the value is stored in the storage means in advance.

  As described above, the pressure reduction sensitivity and the load sensitivity are proportional to each other, so it is not necessary to perform this preliminary experiment on the relationship between the pressure reduction sensitivity and the load sensitivity. It is only necessary to measure at least one tire, preferably about three tires of different sizes, and obtain a proportionality constant.

A feature of the present invention is that the load sensitivity is obtained from the amount of change in the dynamic load radius caused by the load movement by utilizing the fact that the load movement occurs between the left and right wheels when the vehicle is turning. When turning, load movement occurs in the left and right wheels regardless of the type of vehicle, so load sensitivity can be obtained regardless of the type of vehicle.
Next, the relationship between the change in the dynamic load radius of the left and right driven wheels and the load movement amount when the front wheel drive vehicle is turning will be described.

First, as shown in FIG. 3, it is assumed that the vehicle is turning left on the circumference of the radius R.
It is assumed that information on the north-south direction velocity (Vn) and the east-west direction velocity (Ve) is obtained from the GPS device every 50 ms. In this case, the traveling direction speed (V) of the vehicle can be obtained by the above equation (3).

Using this V and θ ′, the ground speed (V _L ) of the inner ring and the ground speed (V _R ) of the outer ring are expressed with the tread width of the vehicle as W.
V _L = V−θ ′ × W / 2
V _R = V + θ ′ × W / 2
It becomes.

Also, assuming that the dynamic load radius is DLR and the change in dynamic load radius due to load movement is ΔDLR, the DLR of the inner and outer wheels depends on the vehicle speed obtained from the GPS device and the wheel speeds of the left and right wheels (ω _L , ω _R ) It can represent with Formula (4) and (5).

  Furthermore, from equations (4) and (5), ΔDLR can be calculated from the vehicle speed obtained from GPS information and the wheel speeds of the left and right wheels, as shown in equation (6) below.

  Further, the load movement amount (ΔFz, see FIG. 4) at this time is calculated from the GPS speed when the load movement sharing ratio applied to the driven wheel shafts with respect to all the axes is α (0 <α <1).

Since the load transfer share α, the height of the center of gravity (H), the tread width (W), and the mass (m) are basically determined uniquely for the same vehicle, the left side with respect to Vθ ′ (that is, the lateral acceleration of the vehicle) The value of increases as the tire has a higher load sensitivity b.

[Initialize]
The detection device is initialized by operating the initialization button 4 after the tire is replaced with a new one and adjusted to a predetermined internal pressure. However, when the vehicle is turned during this initialization, it is the same as the calibration described above. To estimate the load sensitivity. Then, by multiplying the estimated load sensitivity by a proportional constant with the decompression sensitivity stored in advance in the storage means, a decompression threshold value is automatically set at the initialization stage, and is also stored in the storage means.

〔Example〕
Next, examples of the detection method of the present invention will be described. However, the present invention is not limited to such examples.
In order to obtain the rotation angular velocity of each tire mounted on the vehicle, the rotation angular velocity was converted into the rotation angular velocity using the rotation velocity information used for the ABS control. 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.

  The experiment was performed with an FF vehicle, and the reference internal pressure was 200 kPa. In addition, calibration was performed with three types of tires (see Table 1).

Calibration Three types of tires shown in Table 1 were sequentially attached to the FF vehicle, and calibration was performed at the Okayama test course of Sumitomo Rubber Industries, Ltd. to calculate load sensitivity and reduced pressure sensitivity.
For load sensitivity, the slope of the approximate line (coefficient = b × α × m × H / W) was determined as shown in FIG. 5 according to the following equation (8). The slope can be calculated online by using a sequential least square method or the like. The factor because changes only by the load sensitivity b, which was used as a load sense Dodai table characteristic value. In this specification, “load sensitivity” is not only mere load sensitivity, but also a value that varies only with load sensitivity , such as the load sensitivity representative characteristic value (from load sensitivity and a value uniquely determined in the vehicle). May also be included).

FIG. 5 is a graph plotting the dynamic load radius change ΔDLR and the lateral acceleration θ′V for the tire size 185 / 70R14. The coefficient indicating the slope of a straight line approximating the relationship between the two was −0.44. Similarly, the coefficient was obtained for tire sizes 195 / 60R15 and 205 / 50R16.
On the other hand, with respect to the pressure reduction sensitivity, the pressure was actually reduced by a predetermined amount (for example, 25%), and ΔDLR at that time was calculated. The results are shown in Table 1.

  From the result of the calibration, as shown in FIG. 6, a proportional constant between the load sensitivity representative characteristic value and the pressure reduction sensitivity was obtained, and the value (−0.0726) was preset in the storage means.

Threshold setting When a certain tire T was mounted on the FF vehicle and the vehicle was turning at the time of initialization, the lateral acceleration and ΔDLR were calculated in the same manner as described above, and the inclination of the approximate straight line indicating the relationship between the two was calculated.
The coefficient (−0.540637) obtained here is multiplied by a proportional constant (−0.0726) with the decompression sensitivity obtained in advance in calibration to obtain a decompression sensitivity, and this is the decompression amount (for example, the decompression alarm desired) 25%), the depressurization threshold can be calculated as follows.
Depressurization threshold = −0.540637 × (−0.0726) × 25 = 0.98 (mm)
That is, in the case of the tire T, the threshold value is automatically set to 0.98 mm after the initialization is completed.

  Next, each tire shown in Table 1 was decompressed 30% after initialization, and the presence or absence of false alarms or no alarms was compared with a conventional method (adopting a fixed threshold obtained with a typical tire as a decompression threshold). The results are shown in Table 2.

  As shown in Table 2, when the threshold value is set to a fixed value, depending on the setting of the threshold value, there may be an unalarmed (or false alarm). However, according to the method of the present invention, the decompression can be accurately determined. Can do.

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 (7)

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;
Calculating vehicle speed based on speed information from a GPS device mounted on the vehicle;
Obtaining a dynamic load radius of each tire from the calculated vehicle speed and the wheel speed;
Determining the decrease in the internal pressure of the tire when the magnitude of the change from the reference value of the obtained tire dynamic load radius exceeds a predetermined threshold,
The predetermined threshold is a pressure reduction obtained from the relationship between the load sensitivity and the pressure reduction sensitivity when turning the vehicle related to the tire to be mounted on the vehicle, and the load sensitivity obtained by turning during initialization. A threshold setting step set based on the sensitivity;
The load sensitivity is calculated from the relationship between the lateral acceleration and the dynamic load radius change due to load movement at the time of turning, calculated from the speed information and the wheel speeds of the left and right wheels of the vehicle,
The vehicle is a front wheel drive vehicle or a rear wheel drive vehicle;
The tire internal pressure drop detection method, wherein the relational expression includes a vehicle center-of-gravity height, a vehicle tread width, a vehicle mass, and a share of load movement applied to the driven wheel shaft with respect to all axes. Change in tire dynamic load radius is ΔDLR, tire load sensitivity is b, vehicle center of gravity height is H, vehicle tread width is W, vehicle mass is m, vehicle speed is V, yaw rate is θ ', driven for all axes When the load movement share ratio applied to the wheel shaft is α, the relational expression is
ΔDLR = b × α × (H / W) × m × Vθ ′
The load sensitivity at the time of turning of the vehicle and the load sensitivity obtained by turning at the time of initialization related to the tire to be mounted is a load sensitivity representative characteristic represented by b × α × (H / W) × m. The method for detecting a decrease in tire internal pressure according to claim 1, which is a value. The relationship between the load sensitivity and reduced pressure sensitivity during a vehicle turning according to tires will be fitted, the tire pressure drop detecting method according to claim 2 represented by a linear function of the decreased pressure sensitivity and the load sensitivity typical characteristic values. 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 calculating means for calculating the wheel speed from the wheel rotation information detected by the wheel rotation information detecting means;
Vehicle speed calculation means for calculating a vehicle speed based on speed information from a GPS device mounted on the vehicle;
Dynamic load radius calculating means for determining the dynamic load radius of each tire from the vehicle speed calculated by the vehicle speed calculating means and the wheel 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,
The predetermined threshold value is determined in advance from the relationship between the load sensitivity and the depressurization sensitivity when turning the vehicle related to the tire to be mounted on the vehicle, and the load sensitivity obtained by turning during initialization. It further includes a threshold setting means for setting based on the sensitivity,
The load sensitivity is calculated from the relationship between the lateral acceleration and the dynamic load radius change due to load movement at the time of turning, calculated from the speed information and the wheel speeds of the left and right wheels of the vehicle,
The vehicle is a front wheel drive vehicle or a rear wheel drive vehicle;
The tire internal pressure drop detecting device, wherein the relational expression includes the height of the center of gravity of the vehicle, the tread width of the vehicle, the vehicle mass, and the share of load movement applied to the driven wheel shaft with respect to all axes. Change in tire dynamic load radius is ΔDLR, tire load sensitivity is b, vehicle center of gravity height is H, vehicle tread width is W, vehicle mass is m, vehicle speed is V, yaw rate is θ ', driven for all axes When the load movement share ratio applied to the wheel shaft is α, the relational expression is
ΔDLR = b × α × (H / W) × m × Vθ ′
The load sensitivity at the time of turning of the vehicle and the load sensitivity obtained by turning at the time of initialization related to the tire to be mounted is a load sensitivity representative characteristic represented by b × α × (H / W) × m. The tire internal pressure drop detecting device according to claim 4, which is a value. Wherein the vehicle turning relation load sensitivity and reduced pressure sensitivity during relating to tires will be fitted, the tire pressure drop detecting device according to claim 5 which is represented by a linear function of the decreased pressure sensitivity and the load sensitivity typical characteristic values. 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. The
Wheel speed calculating means for calculating wheel speed from wheel rotation information of each tire of the vehicle,
Vehicle speed calculation means for calculating a vehicle speed based on speed information from a GPS device mounted on the vehicle;
Dynamic load radius calculating means for determining the dynamic load radius of each tire from the vehicle speed calculated by the vehicle speed calculating means and the wheel speed;
Determination means for determining a decrease in tire internal pressure when the magnitude of change from the reference value of the obtained tire dynamic load radius exceeds a predetermined threshold, and the predetermined threshold is determined in advance. It functions as a threshold setting means that is set based on the pressure reduction sensitivity obtained from the relationship between the load sensitivity and the pressure reduction sensitivity when turning the vehicle related to the tire to be mounted on the vehicle, and the load sensitivity obtained by turning at the time of initialization. ,
The load sensitivity is calculated from the relationship between the lateral acceleration and the dynamic load radius change due to load movement at the time of turning, calculated from the speed information and the wheel speeds of the left and right wheels of the vehicle,
The vehicle is a front wheel drive vehicle or a rear wheel drive vehicle;
The tire internal pressure drop detection program characterized in that the relational expression includes the height of the center of gravity of the vehicle, the tread width of the vehicle, the vehicle mass, and the share of load movement applied to the driven wheel shaft with respect to all the axes.

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