JP2010076702A - Method and device for detecting tire internal pressure drop, and program for detecting tire internal pressure drop - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tire internal pressure drop detecting method can eliminate an erroneous report or a failed alarm by exactly calculating wheel load and internal pressure of each wheel in a four-wheel vehicle. <P>SOLUTION: This tire internal pressure drop detecting method includes a process for detecting wheel rotation information on each tire, a process for calculating wheel speed, a process for determining vehicle speed, a process for determining a dynamic load radius of each tire from the wheel speed and the vehicle speed, a process for determining a slip ratio of each tire, a process for determining the mass of the vehicle, a process for determining a dynamic load radius of each wheel when longitudinal force is zero using driving stiffness determined from driving force of each wheel and the slip ratio, vehicle speed and wheel speed and calculating internal sensitivity and/or load sensitivity of each tire by a relation between the dynamic load radius, the wheel load of the tire, and initial internal pressure of the tire, a process for calculating wheel load of each tire, and a process for calculating the internal pressure of each tire from the obtained wheel load of each tire by utilizing a relation between the dynamic load radius, the wheel load of the tire and internal pressure of the tire. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method and apparatus for detecting a decrease in internal pressure of a tire based on a change in the dynamic load radius of the tire, and a tire internal pressure decrease 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.

  The dynamic load radius varies depending on reasons other than decompression, for example, acceleration / deceleration or turning of the vehicle, or the load on the person or the object mounted on the vehicle. Various devices have been devised to eliminate the effects of radius reduction and prevent false alarms and unalarmed alarms. In the method described in Patent Document 1, in order to prevent an alarm from being issued due to a cause other than a decrease in tire internal pressure, 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). The dynamic load radius obtained in such a state is used as an effective value to detect a decrease in tire internal pressure.

JP 2007-45295 A

  In addition, in order to eliminate the influence of the load, a technique for estimating the total mass of the vehicle has also been proposed, and when the internal pressure is the same for all four wheels, the load of each wheel is calculated based on the estimated total mass. However, if the internal pressures of the four wheels are different from each other, the load of each wheel cannot be obtained accurately, and therefore, false alarms or unwarned may occur.

  The present invention has been made in view of such circumstances, and a tire internal pressure drop detection method and apparatus capable of accurately calculating the wheel load of each wheel of a four-wheel vehicle to eliminate false alarms and unalarms, and The object is to provide a tire internal pressure drop detection program.

A tire internal pressure drop detection method according to a first aspect of the present invention is a method for detecting a drop in internal pressure of a tire mounted on a vehicle based on a rotation speed of a wheel mounted on the vehicle,
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 step of obtaining the slip ratio of each tire using this dynamic load radius,
Determining the mass of the vehicle;
At the time of initialization, using the driving stiffness and the vehicle speed and the wheel speed obtained from the driving force and slip ratio of each wheel, the dynamic load radius of each wheel when the longitudinal force is zero is obtained, and this dynamic load radius, Calculating the internal pressure sensitivity and / or load sensitivity of each tire based on the relationship between the wheel load of the tire and the initial internal pressure of the tire;
Calculating the wheel load of each tire from the relationship between the driving force of each wheel, the slip ratio and the driving stiffness, and the vehicle mass obtained in the step of obtaining the vehicle mass;
The internal pressure of each tire is calculated from the obtained wheel load of each tire by utilizing the relationship between the dynamic load radius, the tire wheel load and the tire internal pressure, with the internal pressure sensitivity and / or load sensitivity as factors. It is characterized by including processes.

  In the tire internal pressure drop detection method according to the first aspect of the present invention, the tire driving stiffness is proportional to (wheel load / internal pressure), the tire dynamic load radius when the tire longitudinal force is zero, and the wheel Even if the relationship between the load and the internal pressure is used, and the internal pressure of each wheel is different, the load distribution ratio of the vehicle mass to each tire can be accurately calculated. Can be calculated accurately. As a result, the influence of the decrease in the tire dynamic load radius due to the load can be eliminated, and false alarms and non-alarms can be reliably prevented.

In the step of calculating the internal pressure sensitivity and / or load sensitivity at the time of initialization, the dynamic load radius of the tire when the longitudinal force is zero is DLR, the wheel load is FZ, the internal pressure is IP, the load sensitivity is b, and the internal pressure sensitivity Is c and the constant is d,
DLR = bFZ + cIP + d
The internal pressure sensitivity and / or load sensitivity can be calculated based on the formula represented by

In the step of determining the vehicle mass, it is assumed that the vehicle is traveling on a road surface having an inclination angle θ, the mass of the vehicle is m, the vehicle speed is V, the vehicle acceleration is α, the axle shaft of the vehicle is T, and the tire load radius. M (α + gsin (θ)) + AV ² = T / R where R is R, road inclination angle is θ, aerodynamic resistance is A, and gravitational acceleration is g.
Thus, the vehicle mass can be obtained.

In the step of obtaining the dynamic load radius of each wheel when the longitudinal force is zero, the dynamic load radius is DLR, the driving force is FX, the driving stiffness obtained from the slip ratio is D, the vehicle speed is V, and the wheel speed is ω. And when
FX = D × {1-V / (ωDLR)}
Thus, the dynamic load radius can be obtained.

Further, the tire internal pressure drop detection device of the present invention is a device that detects a drop in the internal pressure of a tire attached to the vehicle based on the rotational speed of a wheel attached to the vehicle,
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;
Slip rate calculating means for determining the slip rate of each tire using the dynamic load radius;
Vehicle mass calculating means for determining the mass of the vehicle;
At the time of initialization, using the driving stiffness and the vehicle speed and the wheel speed obtained from the driving force and slip ratio of each wheel, the dynamic load radius of each wheel when the longitudinal force is zero is obtained, and this dynamic load radius, Tire sensitivity calculation means for calculating the internal pressure sensitivity and / or load sensitivity of each tire based on the relationship between the wheel load of the tire and the initial internal pressure of the tire;
Tire wheel load calculating means for calculating the wheel load of each tire from the relationship between the driving force of each wheel, the slip ratio and the driving stiffness, and the vehicle mass obtained in the step of obtaining the vehicle mass;
The internal pressure of each tire is calculated from the obtained wheel load of each tire by utilizing the relationship between the dynamic load radius, the tire wheel load and the tire internal pressure, with the internal pressure sensitivity and / or load sensitivity as factors. And a tire internal pressure calculating means.

  Further, the tire internal pressure drop detection program of the present invention uses a computer to detect a drop in the internal pressure of a tire attached to the vehicle based on the rotational speed of the wheel attached to the vehicle, and wheel rotation information of each tire of the vehicle. Wheel speed calculating means for calculating the wheel speed from the wheel, dynamic load radius calculating means for determining the dynamic load radius of each tire from the wheel speed and the vehicle speed, and a slip ratio calculating means for determining the slip ratio of each tire using the dynamic load radius Vehicle mass calculating means for determining the mass of the vehicle, and at the time of initialization, using the driving stiffness and the vehicle speed and the wheel speed obtained from the driving force and slip ratio of each wheel, The dynamic load radius is obtained, and based on the relationship between the dynamic load radius, the tire wheel load, and the initial internal pressure of the tire, the internal pressure sensitivity and / or Tire sensitivity calculation means for calculating load sensitivity, relational expression of driving force, slip ratio and driving stiffness of each wheel, and tire wheel load for calculating the wheel load of each tire from the vehicle mass obtained in the step of obtaining the vehicle mass Using the relationship between the dynamic load radius, the tire wheel load, and the tire internal pressure using the calculation means, the internal pressure sensitivity and / or the load sensitivity as a coefficient, the internal pressure of each tire is obtained from the obtained wheel load of each tire. It is characterized by functioning as a tire internal pressure calculating means for calculating.

  In the tire internal pressure drop detection device and the tire internal pressure drop detection program of the present invention, the tire driving stiffness is proportional to (wheel load / internal pressure) and the tire longitudinal force is zero, as in the tire internal pressure drop detection method. The relationship between the tire dynamic load radius and the wheel load and internal pressure is used to accurately determine the load distribution ratio of the vehicle mass to each tire even when the internal pressure of each wheel is different. The internal pressure for each wheel can be calculated accurately. As a result, the influence of the decrease in the tire dynamic load radius due to the load can be eliminated, and false alarms and non-alarms can be reliably prevented.

Further, the tire internal pressure drop detection method according to the second aspect of the present invention is a method for detecting the internal pressure drop of the tire mounted on the vehicle based on the rotational speed of the wheel mounted on the vehicle,
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 step of obtaining the slip ratio of each tire using this dynamic load radius,
Determining the mass of the vehicle;
At the time of initialization, using the driving stiffness, vehicle speed and wheel speed obtained from the braking force and slip ratio of each wheel, the dynamic load radius of each wheel when the longitudinal force is zero is obtained, and this dynamic load radius, Calculating the internal pressure sensitivity and / or load sensitivity of each tire based on the relationship between the wheel load of the tire and the initial internal pressure of the tire;
Calculating the wheel load of each tire from the relationship between the braking force of each wheel, the slip ratio and the driving stiffness, and the vehicle mass obtained in the step of determining the vehicle mass;
The internal pressure of each tire is calculated from the obtained wheel load of each tire by utilizing the relationship between the dynamic load radius, the tire wheel load and the tire internal pressure, with the internal pressure sensitivity and / or load sensitivity as factors. It is characterized by including processes.

  Also in the tire internal pressure drop detection method according to the second aspect of the present invention, the tire driving stiffness is proportional to (wheel load / internal pressure), and the tire dynamic load radius when the tire longitudinal force is zero, The relationship between wheel load and internal pressure is used, and even if the internal pressure of each wheel is different, the load distribution ratio of vehicle mass to each tire can be accurately calculated. The internal pressure can be accurately calculated. As a result, the influence of the decrease in the tire dynamic load radius due to the load can be eliminated, and false alarms and non-alarms can be reliably prevented.

  According to the tire internal pressure drop detection method and apparatus and the tire internal pressure drop detection program of the present invention, the wheel load and internal pressure of each wheel of a four-wheel vehicle can be accurately calculated even when the internal pressure of each tire is different. False alarms and unwarned alarms can be eliminated.

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 device according to an embodiment of the present invention is equipped with a drive control device 4 that controls the ratio at which the drive torque of the engine of the vehicle is distributed to the front shaft and the rear shaft, respectively. Whether the internal pressures of the four tires FL (left front wheel), FR (right front wheel), RL (left rear wheel), and RR (right rear wheel) provided in the wheeled vehicle (four-wheel drive vehicle) are reduced. In order to detect the wheel rotation information of the tire, a normal wheel speed detection means (wheel rotation information detection means) 1 provided in association with each tire is provided. The drive control device improves the travelability (motion characteristics) of the vehicle, and the front and rear torque distribution rate can be known by communication such as CAN (Control Area Network) if it is of an electronic control type. . Moreover, even if it is a mechanical type, if its characteristics are understood, it can be predicted to some extent from the running state of the vehicle. For example, if the front and rear torque distribution is almost determined by the engine torque, the torque distribution can be estimated by obtaining the engine torque.

  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. In addition, the absolute speed of the vehicle obtained by different methods, such as ground speed, can be used other than the absolute speed of the vehicle obtained by the GPS device.

  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. A GPS speedometer to be obtained; a dynamic load radius calculating means for obtaining a dynamic load radius of each tire from the wheel speed and the vehicle speed; a slip ratio calculating means for obtaining a slip ratio of each tire using the dynamic load radius; Tire load ratio calculating means for calculating the total driving force obtained from the axle shaft, the distribution before and after the driving force, and the load ratio of other tires with respect to a reference tire using the slip ratio, and vehicle mass calculating means for determining the mass of the vehicle And at the time of initialization, the longitudinal force is zero using the driving stiffness, vehicle speed and wheel speed obtained from the driving force and slip ratio of each wheel. Tire sensitivity calculation that calculates the dynamic load radius of each wheel and calculates the internal pressure sensitivity and / or load sensitivity of each tire based on the relationship between the dynamic load radius, the wheel load of the tire, and the initial internal pressure of the tire Tire wheel load calculating means for calculating the wheel load of each tire from the vehicle, the relational expression of the driving force, slip ratio and driving stiffness of each wheel, and the vehicle mass obtained in the step of obtaining the vehicle mass, and the internal pressure sensitivity And / or tire internal pressure calculation that calculates the internal pressure of each tire from the obtained wheel load of each tire using the relationship between the dynamic load radius, the tire wheel load, and the tire internal pressure using the load sensitivity as a coefficient. Means. Then, the tire internal pressure drop detection program causes the control unit 2 to perform wheel speed calculation means, dynamic load radius calculation means, slip ratio calculation means, vehicle mass calculation means, tire sensitivity calculation means, tire wheel load calculation means, and tire internal pressure calculation. It functions as a means.

  The tire dynamic load radius (DLR) of the traveling vehicle can be calculated by V = DLR × 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 (DLR) 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 (DLR). Can do.

  In the present embodiment, the slip ratio (slp) is calculated from the tire dynamic load radius (DLR) of each wheel obtained from the vehicle speed (V) calculated from the GPS and the rotation speed (ω) of the tire. The driving stiffness (driving force at the unit slip ratio) (D) is calculated from the slip ratio (slp) and the driving force (FX) of each wheel, and from these, the wheel load of each wheel and the internal pressure of each tire are calculated. Yes.

More specifically, (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 (1).
Rotational angular velocity (ω) = 2π × Freq (Hz) / N (pieces) (1)
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.

(3) From the obtained rotational angular velocity (ω) and vehicle speed (V), the tire dynamic load radius (DLR) is calculated by DLR = V / ω.
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.

(4) Next, from the obtained dynamic load radius (DLR) of each tire and the dynamic load radius (DLR ₀ ) when the total driving force (FX) of the vehicle is zero, slip according to the following equation (2) The rate (slp) is calculated.
slp = (DLR ₀ −DLR) / DLR ₀ (2)

(5) Moreover, if the vehicle axle torque (Tq) can be obtained, the total driving force can be calculated from the tire load radius (R) by the following equation (3).
FX = Tq / R (3)

(6) On the other hand, the driving stiffness (D) is a proportional constant of the driving force with respect to the slip ratio, and can be expressed as FX = D × slp.
Here, the driving stiffness is related to the ground contact shape of the tire. If the ground contact area of the tire is S and the longitudinal rigidity per unit area is G, it can be approximated by D = G × S.
Furthermore, since the contact area S is proportional to the tire load (FZ) and the tire internal pressure (IP), if the proportionality constant is p, it can be expressed as S = p × FZ / IP.

From the above, the driving force of each wheel is 4 when subscripts 1, 2, 3, and 4 are FL (left front wheel), FR (right front wheel), RL (left rear wheel), and RR (right rear wheel), respectively. In the case of a wheel drive vehicle, if the driving force front / rear distribution (AWDP) = front shaft driving force / total driving force is known,
FX1 = AWDP × FX / 2 = pG (FZ1 / IP1) slp1 (4)
FX2 = AWDP × FX / 2 = pG (FZ2 / IP2) slp2 (5)
FX3 = (1-AWDP) × FX / 2 = pG (FZ3 / IP3) slp3 (6)
FX4 = (1-AWDP) × FX / 2 = pG (FZ4 / IP4) slp4 (7)
It can be expressed as.
As described above, the driving force front-rear distribution (AWDP) can be known by communication such as CAN if an electronically controlled drive control device is provided.

When FL (left front wheel) is a reference wheel, the load ratio of FR (right front wheel), RL (left rear wheel) and RR (right rear wheel) with respect to the FL (left front wheel) is calculated based on equations (4) to (7). Can be expressed by the following formulas (8) to (10).
FZ2 / FZ1 = (IP2 / IP1) (slp1 / slp2) (8)
FZ3 / FZ1 = {(1-AWDP) / AWDP} (IP3 / IP1) (slp1 / slp
3) ... (9)
FZ4 / FZ1 = {(1-AWDP) / AWDP} (IP4 / IP1) (slp1 / slp
4) ... (10)
Therefore, by performing initialization at the normal internal pressure where the tire internal pressure is known, each wheel load ratio at the time of initialization can be obtained by the equations (8) to (10).

(7) Further, the total mass (estimated mass) of the vehicle is calculated using the acceleration, speed, and tilt angle of the vehicle. That is, the vehicle mass m is calculated from the following equation (11) using the vehicle axle shaft torque that is CAN information, the speed calculated from the GPS, the acceleration calculated therefrom, and the inclination angle of the slope. Can do.
m (α + gsin (θ)) + AV ² = T / R (11)
Here, T is the axle shaft torque, R is the tire load radius, FX is the longitudinal force, g is the gravitational acceleration, V is the vehicle speed, A is the aerodynamic resistance, and α is the vehicle acceleration.
θ is the inclination angle of the slope on which the vehicle is traveling, and θ is expressed by θ = arctan (Vxy / Vz) where Vxy (= V) is the plane speed of the vehicle and Vz is the vertical speed. The vehicle acceleration α is expressed by α = dVxy / dt / sin θ.
From the above, the vehicle mass m and the aerodynamic resistance A can be calculated by regression.

(8) On the other hand, the dynamic load radius (DLR) of each wheel is such that the tire load sensitivity is b, the internal pressure sensitivity is c, and the constant is d.
DLR1 = bFZ1 + cIP1 + d
DLR2 = bFZ2 + cIP2 + d
DLR3 = bFZ3 + cIP3 + d
DLR4 = bFZ4 + cIP4 + d
It can be expressed as. “Load sensitivity” refers to the amount of change in the dynamic load radius relative to the load, and “internal pressure sensitivity” refers to the amount of change in the dynamic load radius relative to the internal pressure.

(9) Since the internal pressure sensitivity c and the load sensitivity b are in a proportional relationship (c = eb), at least one tire, preferably about three tires with different sizes are measured, and the proportionality constant (e ), The dynamic load radius of each wheel can be expressed by the following equations (12) to (15).
DLR1 = b (FZ1 + eIP1) + d (12)
DLR2 = b (FZ2 + eIP2) + d (13)
DLR3 = b (FZ3 + eIP3) + d (14)
DLR4 = b (FZ4 + eIP4) + d (15)

(10) Here, the dynamic load radius (DLR) expressed using the load sensitivity and the internal pressure sensitivity in the formulas (12) to (15) is when the longitudinal force is not generated in the tire (between the road surface and the tire). The dynamic load radius value when no slip occurs), and the dynamic load radius value is expressed by the following equation (16) among the slip ratio (slp), the vehicle speed (V), and the wheel speed (ω). Satisfied.
slp = 1-V / (ωDLR) (16)
Also, since FX = D × slp,
FX = D × {1-V / (ωDLR)} (17)
Is established. The DLR when the longitudinal force is zero can be calculated by regressing FX with V / ω.

  At the time of initialization of the detection device, the relational expressions (12) to (15) of the dynamic load radius (DLR), the wheel load (FZ) and the internal pressure (IP) were obtained by the expressions (8) to (11). By substituting each wheel load and each wheel internal pressure (initial time = normal internal pressure), load sensitivity (b), constant (d), and proportionality constant (e) can be calculated. Further, from c = eb The internal pressure sensitivity (c) can be calculated.

(11) At the time of normal pressure reduction determination, since the internal pressure of each wheel is not known, IP = (DLR−d−bFZ) / c is expressed from the equations (12) to (15), and this is expressed by the equations (8) to (10 ) To obtain equations (18) to (20), respectively.
FZ2 / FZ1 = {(DLR2-d-bFZ2) / (DLR1-d-bFZ1)} × (sl
p1 / slp2) (18)
FZ3 / FZ1 = {(1-AWDP) / AWDP} × {(DLR3-d-bFZ3) / (D
LR1-d-bFZ1)} × (slp1 / slp3) (19)
FZ4 / FZ1 = {(1-AWDP) / AWDP} × {(DLR4-d-bFZ4) / (D
LR1-d-bFZ1)} × (slp1 / slp4) (20)
(12) Moreover, vehicle mass (m) is calculated | required from Formula (11). This vehicle mass (m) is
mg = FZ1 + FZ2 + FZ3 + FZ4 (21)
Therefore, FZ1, FZ3, and FZ4 are expressed by FZ1 in equations (18) to (20), respectively, and are substituted into equation (21) and solved by FZ1 to obtain FZ1. . Next, FZ2, FZ3, and FZ4 can be obtained from the equations (18) to (20), respectively.

  (13) Further, if the wheel load (FZ) can be calculated, the internal pressure (IP) of each wheel can be calculated from the equations (12) to (15). Then, when the difference or ratio between the calculated internal pressure and the normal internal pressure exceeds a predetermined threshold value, it is determined that the tire internal pressure has decreased, and the reduced pressure tire is displayed on the display 3 and the alarm device 5 To alert the driver.

Next, examples of the detection method of the present invention will be described. However, the present invention is not limited to such examples.
[Example]
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 to a personal computer (PC) as serial data. The vehicle speed information, the rotational speed information, the front / rear driving force distribution information, and the vehicle axle shaft torque information are synchronized as digital data every 50 msec. I was able to import to PC. And the tire dynamic load radius was calculated every 50 msec from vehicle speed information and rotational speed information, and it calculated as an average value for every second.

[Pre-test]
We measured the dynamic load radius on the table using a flat belt, measured the load on the tire and the decrease in the dynamic load radius due to reduced pressure, and investigated the relationship between the load sensitivity of the tire and the internal pressure sensitivity.

For the three types of tires shown in Table 1, load sensitivity (change in dynamic load radius per 1 kN change in load (mm)) and internal pressure sensitivity (change in dynamic load radius per 1 kPa change in internal pressure (mm)) Examined. The load applied to the tire was set at three levels of 2.5 kN, 3.5 kN, and 4.5 kN, and the tire load was changed at four levels (150 kPa, 180 kPa, 210 kPa, and 240 kPa), and the dynamic load radius was measured.
The load sensitivity and the internal pressure sensitivity of the three types of tires are as shown in Table 1 and FIG. 3. From this, it was found that the relationship between the two sensitivities is internal pressure sensitivity = −0.0369 × load sensitivity. Therefore, e = −0.0369 is preset in the detection device as a proportionality constant (e) between the internal pressure sensitivity and the load sensitivity.

[Real car test]
Tires (215 / 45R17 SP9000) were mounted on a 4WD vehicle, and the following four cases were tested in actual vehicles at the Okayama test course of Sumitomo Rubber Industries, Ltd.
The conditions for initialization and evaluation were as follows. The front-rear distribution of driving force was 45 (front): 55 (rear).
Initialization One person was boarded at the standard internal pressure (front wheel: 230 kPa, rear wheel: 210 kPa).
At the time of evaluation: Evaluation was performed for the case of one person riding and a case where a load was loaded (vehicle loading). The load was 290 kg in total including the front seat (90 kg), the rear seat (100 kg), and the trunk (100 kg). Then, the internal pressures of the front wheels and the rear wheels were changed as shown in Table 3 for evaluation.

[When initializing]
From the dynamic load radius of each tire and the dynamic load radius (R ₀ ) when the total driving force (Fx) of the vehicle is zero, the slip ratio (slp) was calculated according to the equation (2).
Then, at the time of initialization, since the tire internal pressure is a reference value (front wheel: 230 kPa, rear wheel: 210 kPa), FL (left front wheel) is obtained using the obtained slip ratio according to the above formulas (8) to (10). ) (FR front right wheel), RL (left rear wheel) and RR (right rear wheel) load ratio (wheel load ratio) is calculated, and the vehicle mass (estimated mass) obtained from the equation (11) is used. Thus, the wheel load (estimated wheel load) of each wheel was calculated.

Further, the dynamic load radius (DLR) when the longitudinal force is zero is obtained from the equation (17), and the dynamic load radius, the wheel load and the internal pressure are substituted into the equations (12) to (15). The load sensitivity (b) and the constant (d) were obtained, and the internal pressure sensitivity (c) was calculated from the preset internal pressure sensitivity and the proportional constant (e) of the load sensitivity.
The results are shown in Table 2.

[At the time of evaluation]
The dynamic load radius when the slip ratio and the longitudinal force were zero was calculated in the same manner as at the time of initialization. Moreover, the wheel load (estimated wheel load) of each wheel was calculated using the wheel load ratio obtained by the equations (18) to (20) and the vehicle mass obtained by the equation (11). Subsequently, the internal pressure (estimated internal pressure) of each wheel was calculated according to the above equations (12) to (15). The results are shown in Table 3. Table 3 shows the difference between the actual internal pressure and the estimated internal pressure, and the difference between the actual wheel load and the estimated wheel load.

  As can be seen from Table 3, the error ((estimated internal pressure−actual internal pressure) × 100 / actual internal pressure) of the internal pressure of each wheel estimated (calculated) by the detection method of the present invention is within ± 5%, which is practical. The accuracy was satisfactory.

  In the above embodiment, a four-wheel drive vehicle has been described as an example. However, the present invention is not limited to this and can be applied to a two-wheel drive vehicle. That is, in the case of a two-wheel drive vehicle, the driving force acts on only two wheels, but the braking force (when the brake is depressed) acts on the four wheels. Therefore, if the braking force can be known from, for example, the braking force of each wheel, the above-described calculation can be performed by using “braking force” instead of “driving force” in the above-described calculation.

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 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 (7)

A method for detecting a decrease in internal pressure of a tire mounted on a vehicle based on a rotation speed of a wheel mounted on the vehicle,
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 step of obtaining the slip ratio of each tire using this dynamic load radius,
Determining the mass of the vehicle;
At the time of initialization, using the driving stiffness and the vehicle speed and the wheel speed obtained from the driving force and slip ratio of each wheel, the dynamic load radius of each wheel when the longitudinal force is zero is obtained, and this dynamic load radius, Calculating the internal pressure sensitivity and / or load sensitivity of each tire based on the relationship between the wheel load of the tire and the initial internal pressure of the tire;
Calculating the wheel load of each tire from the relationship between the driving force of each wheel, the slip ratio and the driving stiffness, and the vehicle mass obtained in the step of obtaining the vehicle mass;
The internal pressure of each tire is calculated from the obtained wheel load of each tire by utilizing the relationship between the dynamic load radius, the tire wheel load and the tire internal pressure, with the internal pressure sensitivity and / or load sensitivity as factors. A method for detecting a decrease in tire internal pressure, comprising: a step. In the step of calculating the internal pressure sensitivity and / or load sensitivity at the time of initialization, when the internal pressure sensitivity and / or load sensitivity is zero, the dynamic load radius of the tire when the longitudinal force is zero is DLR, the wheel load is FZ, the internal pressure Is IP, load sensitivity is b, internal pressure sensitivity is c, and constant is d,
DLR = bFZ + cIP + d
The method for detecting a decrease in tire internal pressure according to claim 1, wherein the method is calculated based on an expression represented by: In the step of determining the vehicle mass, it is assumed that the vehicle is traveling on a road surface having an inclination angle θ, the mass of the vehicle is m, the vehicle speed is V, the vehicle acceleration is α, the axle shaft of the vehicle is T, and the tire load radius. M (α + gsin (θ)) + AV ² = T / R where R is R, road inclination angle is θ, aerodynamic resistance is A, and gravitational acceleration is g.
The method for detecting a decrease in tire internal pressure according to any one of claims 1 to 2, wherein the vehicle mass is obtained by the following. In the step of obtaining the dynamic load radius of each wheel when the longitudinal force is zero, the dynamic load radius is DLR, the driving force is FX, the driving stiffness obtained from the slip ratio is D, the vehicle speed is V, and the wheel speed is ω. And when
FX = D × {1-V / (ωDLR)}
The method for detecting a decrease in tire internal pressure according to any one of claims 1 to 3, wherein a dynamic load radius is obtained by the following. A device for detecting a decrease in internal pressure of a tire mounted on a vehicle based on a rotational speed of a wheel mounted on the vehicle,
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;
Slip rate calculating means for determining the slip rate of each tire using the dynamic load radius;
Vehicle mass calculating means for determining the mass of the vehicle;
At the time of initialization, using the driving stiffness and the vehicle speed and the wheel speed obtained from the driving force and slip ratio of each wheel, the dynamic load radius of each wheel when the longitudinal force is zero is obtained, and this dynamic load radius, Tire sensitivity calculation means for calculating the internal pressure sensitivity and / or load sensitivity of each tire based on the relationship between the wheel load of the tire and the initial internal pressure of the tire;
Tire wheel load calculating means for calculating the wheel load of each tire from the relationship between the driving force of each wheel, the slip ratio and the driving stiffness, and the vehicle mass obtained in the step of obtaining the vehicle mass;
The internal pressure of each tire is calculated from the obtained wheel load of each tire by utilizing the relationship between the dynamic load radius, the tire wheel load and the tire internal pressure, with the internal pressure sensitivity and / or load sensitivity as factors. A tire internal pressure drop detecting device comprising: tire internal pressure calculating means.   A wheel speed calculation means for calculating a wheel speed from wheel rotation information of each tire of the vehicle, a computer for detecting a decrease in internal pressure of a tire mounted on the vehicle based on a rotation speed of a wheel mounted on the vehicle, Dynamic load radius calculating means for determining the dynamic load radius of each tire from the wheel speed and vehicle speed, slip ratio calculating means for determining the slip ratio of each tire using this dynamic load radius, vehicle mass calculating means for determining the mass of the vehicle, At the time of initialization, using the driving stiffness and the vehicle speed and the wheel speed obtained from the driving force and slip ratio of each wheel, the dynamic load radius of each wheel when the longitudinal force is zero is obtained, and this dynamic load radius, Tire sensitivity calculating means for calculating the internal pressure sensitivity and / or load sensitivity of each tire based on the relationship between the wheel load of the tire and the initial internal pressure of the tire; Tire wheel load calculation means for calculating the wheel load of each tire from the relational expression of force, slip ratio and driving stiffness, and the vehicle mass obtained in the step of obtaining the vehicle mass, the internal pressure sensitivity and / or the load sensitivity as a coefficient Using the relationship between the dynamic load radius, the tire wheel load and the tire internal pressure, and functioning as tire internal pressure calculating means for calculating the internal pressure of each tire from the obtained wheel load of each tire, To detect tire pressure drop. A method for detecting a decrease in internal pressure of a tire mounted on a vehicle based on a rotation speed of a wheel mounted on the vehicle,
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 step of obtaining the slip ratio of each tire using this dynamic load radius,
Determining the mass of the vehicle;
At the time of initialization, using the driving stiffness, vehicle speed and wheel speed obtained from the braking force and slip ratio of each wheel, the dynamic load radius of each wheel when the longitudinal force is zero is obtained, and this dynamic load radius, Calculating the internal pressure sensitivity and / or load sensitivity of each tire based on the relationship between the wheel load of the tire and the initial internal pressure of the tire;
Calculating the wheel load of each tire from the relationship between the braking force of each wheel, the slip ratio and the driving stiffness, and the vehicle mass obtained in the step of determining the vehicle mass;
The internal pressure of each tire is calculated from the obtained wheel load of each tire by utilizing the relationship between the dynamic load radius, the tire wheel load and the tire internal pressure, with the internal pressure sensitivity and / or load sensitivity as factors. A method for detecting a decrease in tire internal pressure, comprising: a step.

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