JP3013723B2 - Tire pressure drop detection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting a decrease in tire air pressure, and more particularly to a method for accurately detecting a decrease in tire air pressure in a four-wheeled vehicle from a wheel speed to improve vehicle driving safety and steering stability. The present invention relates to a method for detecting a decrease in tire air pressure.

[0002]

2. Description of the Related Art When the tire air pressure decreases, the tire may be damaged or the steering stability of the vehicle may be impaired.
Therefore, as disclosed in Japanese Patent Application Laid-Open No. 3-135806, it is known to detect a tire air pressure based on an output signal from a pressure sensor incorporated in a wheel.
It is also known to detect tire pressure indirectly from detection results such as fluctuations in wheel speeds and fluctuations in the distance between the vehicle body and the road surface. Furthermore, as disclosed in JP-A-63-305011, the angular velocity of each wheel is detected, and the sum of the angular velocities of a pair of wheels on a diagonal line and the sum of the angular velocities of a pair of wheels on another diagonal line are detected. It is known to determine the deviation between the tires and the average angular velocity, and determine the decrease in tire air pressure based on the comparison result between the deviation and the average angular velocity and the comparison result between the angular velocity of each wheel and the average angular velocity.

[0003]

However, the detection of tire air pressure based on the output of the pressure sensor requires a pressure sensor and requires processing on the wheel side to incorporate the sensor into the wheel, which increases the cost. Further, when the tire pressure is detected based on a change in the wheel speed or the like, the change in the wheel speed or the like with respect to the decrease in the tire pressure is extremely small, and is affected when the vehicle is turning or accelerating or decelerating. It is difficult to accurately detect tire pressure.

As suggested in Japanese Patent Application Laid-Open No. Sho 63-305011, it is conceivable to improve the accuracy of judging a decrease in air pressure by calibrating a wheel speed signal.
In the case where the determination system is configured to perform some manual operation on the driver side during this calibration, if there is an error in the manual operation on the driver side, an accurate determination of the decrease in air pressure will be hindered.

[0005] Therefore, the present invention is intended to prevent tire damage and improve vehicle steering stability by reliably detecting a decrease in tire air pressure based on wheel speed even when calibration relating to wheel speed is not performed. An object of the present invention is to provide a method for detecting a decrease in tire air pressure that can be achieved.

[0006]

According to a first aspect of the present invention, there is provided a method for detecting a decrease in tire air pressure, comprising detecting a wheel speed of at least two of the front, rear, left and right wheels, A wheel acceleration / deceleration state detection process for detecting at least one of the acceleration / deceleration states of the vehicle, a steering state detection process for detecting the steering state of the vehicle, and a vehicle speed of the vehicle from two or more wheel speeds of the front, rear, left and right wheels. and the vehicle speed detection step for detecting a car
One or more wheel speeds detected during the wheel speed detection process and another one
A wheel speed ratio calculation process for calculating a wheel speed ratio represented by a ratio of the difference between the wheel speed and the sum of the two, a brake device operation state detection process for detecting an operation state of a vehicle brake device, and a vehicle body. Based on the speed, the wheel acceleration / deceleration state, the steering state, and the operation state of the braking device, it is determined that the vehicle is in a stable driving state in the vehicle movement state determination step of determining the movement state of the vehicle and the vehicle movement state determination step. If the wheel speed ratio calculated in the wheel speed ratio calculation process repeatedly executed during the period exceeds a first predetermined value for a certain period of time, it is determined that at least one of the front, rear, left, and right wheels is in a reduced air pressure state. A first tire pressure drop determination step, and a vehicle movement state determination step.
The first time that it is determined that both are in a stable operation state,
The wheel speed ratio calculated in the wheel speed ratio calculation step
Thereafter, while the stable driving state of the vehicle is determined,
The multiples calculated in the wheel speed ratio calculation
Difference from at least one of the wheel speed ratios
If it is larger than the fixed value, at least the front, rear, left and right wheels
A second tire, one of which determines that the air pressure is low
And an air pressure drop determining step .

[0007] according to claim 2 method is the method of claim 1, the second tire pressure drop judging stroke, characterized in that it is executed each time the vehicle travels with the engine start is performed.

[0008]

[0009]

[0010]

[0011]

According to the method of claim 1, during traveling of the vehicle, two or more of the front and rear left and right wheels, the acceleration and deceleration of one or more of the front and rear left and right wheels, the steering state of the vehicle, The operating state of the braking device of the vehicle is detected. Further, the vehicle speed is detected from the wheel speed, and a wheel speed ratio is calculated based on the wheel speed. In calculating the wheel speed ratio, one or more wheel speeds and
Difference from one or more other wheel speeds is calculated and this difference
The average of these wheel speeds (more generally, one or more
Wheel speed plus one or more other wheel speeds).
The wheel speed obtained by this calculation is one or more wheel speeds.
And the difference between one and more wheel speeds and the sum of the two.
It is. Further, the driving state of the vehicle is determined based on the vehicle speed, the wheel acceleration / deceleration state, the steering state, and the operation state of the braking device.

If the calculated wheel speed ratio continuously exceeds the first predetermined value for a certain period of time while the vehicle is in a stable driving state, it is determined that at least one of the front, rear, left and right wheels is in a reduced air pressure state. Is determined. When the vehicle is in a stable driving state, a factor other than the tire pressure exerts little influence on the wheel speed ratio, and therefore, a wheel speed ratio that favorably reflects the tire pressure is required. For this reason, during the achievement of the vehicle stable driving state, the error factor for the air pressure drop determination based on the wheel speed ratio is removed. Further, since it is assumed that the wheel speed ratio fluctuation indicating the air pressure drop is continuous for a certain period of time as the air pressure drop determination requirement, the influence of noise added to the determination system is eliminated. Therefore, according to the method of the first aspect, even if the wheel speed ratio is not calibrated, if the tire pressure decreases by a certain degree or more, the decrease in the tire pressure is reliably detected. In other words, it is possible to determine the air pressure drop based on the absolute value of the wheel speed ratio. In the method according to claim 1, the second tire is provided.
An air pressure drop determination step is performed. Preferably, this format
The fixed stroke is performed every time the vehicle travels with the engine started.
Be executed. In this determination process, the vehicle is in a stable operation state for the first time.
The wheel speed ratio calculated at the time of the
Cars that were calculated while both stable driving states were determined
The difference from each of the wheel speed ratios is determined. And either
If the difference is greater than a second predetermined value, a decrease in air pressure is determined.
It is. As a result, a stable vehicle operation state is achieved for the first time.
With the wheel speed ratio at the time of
A change in the wheel speed ratio is detected. Therefore, the method of claim 1
According to the report, some time elapses after the vehicle starts
If the tire pressure drops below a certain level for a reason, this empty
A pressure drop is reliably detected. 2. The method of claim 1, wherein the wheel acceleration / deceleration state detection step includes a step of detecting acceleration of each of the front, rear, left and right wheels, and the steering state detection step includes a step of detecting a steering angle. In the state determination process, the vehicle speed detected in the vehicle speed detection process is greater than a fourth predetermined value, the operation of the braking device is not detected in the brake device operation status detection process, and the steering detected in the steering condition detection process is performed. The angle is smaller than the fifth predetermined value, and the acceleration of each of the front and rear left and right wheels detected in the wheel acceleration / deceleration state detection process is smaller than the sixth predetermined value, and the front and rear detected in the wheel acceleration / deceleration state detection process If the difference between the accelerations of the left and right wheels is smaller than a seventh predetermined value, the process may include a step of determining that the vehicle is operating in a stable state. in this case,
The acceleration of each of the front, rear, left and right wheels is detected, and the steering angle is detected. Then, the vehicle speed is greater than the fourth predetermined value, the braking device is not operating, and the steering angle, the acceleration of each wheel, and the difference between the accelerations of each wheel are respectively equal to the fifth to seventh predetermined values. If less than, the vehicle stable driving state is determined. When the vehicle speed is low, when braking, or when the steering angle, the wheel acceleration or the wheel acceleration difference is large, the wheel speed ratio fluctuates in any case, and the tire pressure cannot be properly represented by the wheel speed ratio. According to the above preferred method, in such a case, the determination of the decrease in the air pressure is prohibited, so that the erroneous determination is prevented. In the above preferred method, the vehicle motion state determination step may include a step of changing the fifth and sixth predetermined values in accordance with the vehicle speed detected in the vehicle speed detection step. In this case, the fifth and sixth predetermined values are changed according to the vehicle speed. For this reason, whether the vehicle is in a stable driving state and, consequently, whether there is a decrease in air pressure is properly determined. The method according to claim 1, wherein the wheel speed detection step includes a step of detecting the wheel speed of each of the front, rear, left and right wheels, and the wheel speed ratio calculation step includes a pair of wheels on one diagonal line of the vehicle. The value obtained by subtracting the sum of the wheel speeds of the pair of wheels on the other diagonal from the sum of the wheel speeds of the other wheel is divided by the average value of the wheel speeds of the front, rear, left, and right wheels to obtain the diagonal sum wheel speed ratio. It may include a step of calculating as a speed ratio. As described above, when the diagonal sum wheel speed ratio is taken, the difference in the wheel running state (for example, the acceleration / deceleration state, the turning state) between the front and rear wheels and between the left and right wheels is offset to some extent, and the vehicle driving state is changed to the wheel speed ratio. The effect on mitigation is reduced. Therefore, the determination of the decrease in the air pressure is appropriately performed.

[0013]

[0014]

[0015]

[0016]

[0017]

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, a vehicle is equipped with a controller 5 for an anti-lock brake system (ABS), and has a front right wheel FR, a front left wheel FL and a rear right wheel RR.
And a rear right wheel speed RL, a front left wheel speed sensor 2, a rear right wheel speed sensor 3, and a rear left wheel speed sensor 4
Are installed respectively. The ABS controller 5 obtains the wheel speed signals FVFR, FVFL, FVRR, and FVRL shown in FIG. 2 from the wheel speed pulse signal output sent from the wheel speed sensors 1 to 4 as the wheels FR to RL rotate, and also outputs the wheel speed signals. , An ABS control for applying an appropriate braking force to each wheel is performed based on the wheel speed signal and the estimated vehicle speed signal. This ABS
During the execution of the control, the ABS controller 5 sends out the ABS control signal ABSOR.

Reference numeral 6 denotes an electronic control unit (ECU) including a computer, a memory, an input / output circuit, and the like. The ECU 6 includes an ABS controller 5, a steering sensor 8 attached to a steering device 7 of the vehicle, An alarm lamp 9 provided on an instrument panel (not shown) or the like of the vehicle is connected to a brake lamp switch 10 that is linked to a brake pedal (not shown) of the vehicle. The ECU 6 constitutes an apparatus for implementing the method for detecting a decrease in tire air pressure according to one embodiment of the present invention in cooperation with the elements 1 to 5 and 8 to 10.

Although not shown in detail, the steering sensor 8 includes, for example, two sets of photo-interrupters and a neutral point detecting unit.
Two steering pulse signals ST1, ST2 having a phase difference used for determining the steering wheel rotation direction and the steering wheel rotation amount.
In addition to transmitting ST2, a neutral position signal STN is transmitted each time the steering wheel reaches the neutral position.

The ECU 6 controls the wheel speed signals FVFR, FVFL, FVRR, FVRL,
Estimated vehicle speed signal VREFB and ABS control signal ABS
OR, the steering pulse signals ST1, ST2, STN from the steering sensor 7, and the brake lamp signal BLS from the brake lamp switch 10 are input (see FIG. 2), and a decrease in tire air pressure is determined based on these signals. Sometimes, the alarm lamp 9 is turned on.

In order to detect the above-mentioned decrease in air pressure, the ECU
Numeral 6 functionally has various functional units shown by blocks in FIG. Reference numeral 61 denotes wheel speed signals FVFR, FVFL, FVRR input from the ABS controller 5,
4 shows a filter unit that performs a filter process for removing high-frequency components (variations in wheel speed signals due to variations in tooth spacing accuracy of wheel speed rotors (not shown) of wheel speed sensors 1 to 4) included in FVRL. Filtered wheel speed signals VFR, VFL, VRR and VR from the filter unit 61
L is a wheel speed ratio calculation unit 62 and a wheel acceleration calculation unit 63
Sent to

Based on the filtered wheel speed signals VFR, VFL, VRR and VRL, the wheel speed ratio calculating section 62 calculates the diagonal sum wheel speed ratio VXPERF from the following equation, for example.
(%) Is calculated. VXPERF = ｛(VFR + VRL)-(VFL + VRR)｝ ÷ ｛(VFR + VFL + VRR + VR
L) / 4} That is, from the sum of the right front wheel speed VFR and the left rear wheel speed VRL, the left front wheel speed VFL and the right rear wheel speed VRR are obtained.
(More generally, when the vehicle is viewed on a plane, the wheel speed of the pair of wheels on the other diagonal is calculated from the sum of the wheel speeds of the pair of wheels on one diagonal of the vehicle. Diagonal sum wheel speed ratio VX
Find the PERF.

The diagonal sum wheel speed ratio VXPERF shows a constant value when the steering wheel angle is substantially neutral and the wheel acceleration is almost zero, and the air pressure of any one of the four wheels decreases and the wheel speed of the wheel becomes lower. As it increases, its value fluctuates. Wheel speed ratio V
XPERF takes a positive value when the air pressure of the right front wheel or the left rear wheel decreases, and takes a negative value when the air pressure of the left front wheel or the right rear wheel decreases. This diagonal sum wheel speed ratio VXPERF
Is transmitted to the reference wheel speed ratio setting unit 66, the speed range-specific wheel speed ratio calculation unit 67, and the air pressure drop determination unit 68.

The wheel acceleration calculator 63 includes a filter 61
, The wheel speed signals VFR and VF of each wheel input one after another
The wheel acceleration (acceleration / deceleration state) of each wheel is calculated based on L, VRR, and VRL. In the figure, symbols DVFR, DVF
L, DVRR, and DVRL represent right front wheel acceleration, left front wheel acceleration, right rear wheel acceleration, and left rear wheel acceleration, respectively. The steering angle calculation unit 64 includes steering pulse signals ST1, ST2, and S transmitted from the steering sensor 8.
Based on the TN, a steering angle (steering state) STR from the steering wheel neutral position is obtained.

The air pressure drop estimating condition determining unit 65 determines whether or not the vehicle is running in a stable state in which the wheel speed ratio does not fluctuate due to factors other than the tire air pressure drop, based on various determination parameters. When it is determined that the vehicle is in a stable traveling state, that is, the condition for estimating the air pressure drop is satisfied, the flag F_
X is set to a value “1”, thereby permitting determination of a decrease in air pressure.

In this embodiment, the steering angle STR and the wheel acceleration DVFRＦＲ
DVRL, ABS control signal ABSOR, estimated vehicle speed VR
The EFB and the brake lamp signal BLS are used. Then, (i) the vehicle speed is high, (ii) the brake operation is off, (iii) the ABS control is off, (iv) the wheel acceleration of the four wheels is almost zero, (v) the wheel acceleration difference of the four wheels is almost zero, and ( vi) The steering angle is almost zero 6
When the two conditions are satisfied at the same time, it is determined that the vehicle is in a stable running state (the air pressure drop estimation condition is satisfied).

At low vehicle speeds, the calculation accuracy of the wheel speed ratio decreases,
When the brake operation is ON or the ABS control is performed, the wheel speed is disturbed. If the wheel acceleration of the four wheels is large, the slip ratio of the four wheels is not the same, and if the wheel acceleration difference of the four wheels is large, the vehicle is traveling on a rough road. If the steering angle is large, the turning radii of the four wheels are not the same. In any case, the wheel speed ratio is affected, and it is difficult to properly determine the air pressure drop based on the wheel speed ratio. On the other hand, when the above six conditions are satisfied at the same time, the influence of such erroneous determination factors is eliminated, and the determination accuracy in the air pressure reduction determination based on the wheel speed ratio is ensured.

More specifically, the air pressure drop estimating condition determining unit 65
ECU 6 executes an estimation condition determination subroutine shown in FIG. Each of this subroutine and various subroutines described later is executed at a predetermined cycle for each subroutine. In the subroutine of FIG. 4, the wheel acceleration DV of the four wheels input from the wheel acceleration calculation unit 63
The maximum value and the minimum value of FR, DVFL, DVRR, and DVRL are respectively obtained and stored in the A register and the B register (both not shown) of the ECU 6 (step S1,
S2). Then, the wheel acceleration initial value and the predetermined acceleration absolute value X preset and stored in the memory of the ECU 6 are stored.
X_DV is read from the memory and added, respectively, and then the A register value TMP_A (the maximum value of the wheel acceleration of the four wheels) is compared with the added value (step S3).

If it is determined in step S3 that the A register value is equal to or smaller than the addition value, a value obtained by subtracting the above-described absolute acceleration value XX_DV from the above-described wheel acceleration initial value and a B register value TMP_B (the wheel acceleration of the four wheels) are obtained. Is compared with the minimum value (step S4). It is determined in step S4 that the value of the B register is equal to or greater than the subtraction value.
If the determination result at step 4 indicates that the wheel acceleration of the four wheels falls within the predetermined range and is almost zero, the estimated vehicle speed data VREF is obtained from a map (illustrated in FIG. 5) stored in advance in the memory. The obtained acceleration band determination value YX_DVB is obtained, and the value obtained by subtracting the B register value from the A register value is compared with the acceleration band determination value (step S5).

The difference between the register values (TMP_A-TMP_
B) is equal to or smaller than the acceleration band determination value YX_DVB, and therefore, when it is determined in step S5 that the wheel acceleration difference between the four wheels falls within the predetermined range and is substantially zero, the value TX_DV of the acceleration timer of the ECU 6 is decremented. (Step S6). This acceleration timer value TX_DV is calculated in step S
If the result of the determination in any one of 3, S4 and S5 is opposite to the case described above, a predetermined acceleration timer value XX_DVT is set in step S7.

Subsequently to step S6 or S7, a steering wheel angle determination value YX_STR corresponding to the estimated vehicle speed data VREF is obtained from the map shown in FIG. 6, and the absolute value of the steering angle STR minus the neutral point angle | STR
-Neutral point angle | is compared with steering wheel angle determination value YX_STR (step S8). If it is determined in step S8 that the absolute value | STR-neutral point angle | is equal to or smaller than the determination value YX_STR, the value TX_STR of the steering wheel timer of the ECU 6 is decremented (step S9). ). This timer value T
X_STR is, when the absolute value exceeds the determination value,
In step S10, a predetermined handle angle timer value XX_ST
Set to RT.

Subsequent to step S9 or S10, the estimated vehicle speed VREFB and a predetermined estimated vehicle speed determination value XX_VRE
FB is compared (step S11). Estimated vehicle speed V
When it is determined in step S11 that REFB is equal to or greater than the determination value XX_VREFB and the vehicle speed is high, the value TX_DV of the acceleration timer is checked (step S12). It is determined in step S12 that the acceleration timer value is “0” and that the state in which the wheel acceleration of the four wheels and the wheel acceleration difference are substantially zero has continued for the predetermined time corresponding to the above-described predetermined acceleration timer value XX_DVT. Then
The value of the handle angle timer TX_STR is determined (step S13). If it is determined in step S13 that the steering angle timer value is “0” and the steering angle is substantially zero for a predetermined time corresponding to the above-described predetermined steering wheel timer value XX_STRT,
The value of the brake lamp signal BLS is checked (step S14). When it is determined in step S14 that the brake lamp signal value is “0” and the brake operation is off (the brake pedal is not depressed),
The value of the ABS control signal ABSOR is further determined (step S15). ABS control signal value is "0" and AB
When it is determined in step S15 that the S control is off (the ABS control by the ABS controller 5 is not executed), the value of the flag F_X is changed to "1" indicating the vehicle stable running state (the condition for estimating the air pressure drop is satisfied). It is set (step S16). That is, when the high vehicle speed, the wheel acceleration of the four wheels, and the wheel acceleration difference are substantially zero, the steering angle is substantially zero, the brake operation is off, and the ABS control is sequentially determined in steps S11 to S15, the air pressure drop estimation condition is satisfied. Is determined.

On the other hand, if the determination result in any one of steps S11 to S15 is opposite to the above case, the value of the flag F_X is reset to "0" (step S1).
7). That is, the low vehicle speed, the wheel acceleration of the four wheels and the wheel acceleration difference are large, the steering angle is large, and any one of the brake operation ON and the ABS control ON is performed in step S1.
When it is determined in 1 to S15, it is determined that the condition for estimating the air pressure drop is not satisfied. The value of the air pressure drop estimation condition satisfaction determination flag F_X is sent to the reference wheel speed ratio setting section 66, the speed range-specific wheel speed ratio calculation section 67, and the air pressure drop determination section 68.

The reference wheel speed ratio setting unit 66 is a wheel speed ratio VXPERF from the wheel speed ratio calculation unit 62, a flag value F_X from the air pressure drop estimation condition determination unit 65, and an ignition interlocking with an ignition key (not shown). A signal IG from a switch (not shown) is input, and the value of the flag F_X is set to “0” after the ignition key is turned on for starting the engine and the ignition switch signal IG becomes, for example, high level “1”. From the wheel speed ratio VXPERF at the time of the first change from "1" to "1"
Set as X_IGON. That is, the reference wheel speed ratio VX_IGON represents a wheel speed ratio when a stable vehicle running state is achieved for the first time after the vehicle starts running with the engine started. A preferred method of setting the reference wheel speed ratio will be described later.

The speed range-specific wheel speed ratio calculation unit 67 calculates the wheel speed ratio VXPERF from the wheel speed ratio calculation unit 62, the flag value F_X from the air pressure drop estimation condition determination unit 65, and the estimated vehicle speed from the ABS controller 5. Enter VREFB and
When the vehicle is in the stable running state (F_X = 1), it is determined based on the estimated vehicle speed VREFB whether the current vehicle speed belongs to any of a plurality of speed ranges that have been divided in advance. The speed range is, for example, a first speed range of 30 to 60 km / h,
70 km / h second speed range, 70-80 km / h third speed range
Speed range, fourth speed range of 80 to 90 km / h, 90 to 10
It is divided into a fifth speed range of 0 km / h, a sixth speed range of 100 to 110 km / h, a seventh speed range of 110 to 120 km / h, and an eighth speed range of 120 km / h or more. Then, the wheel speed ratio VXPERF at the time of the speed range determination is obtained as the wheel speed ratio in the determination speed range.

As described above, by determining the wheel speed ratio for each speed range, it is possible to detect a change in the wheel speed ratio due to the vehicle speed and, consequently, a decrease in air pressure. The reason is that if the air pressure of the four wheels is standard, the wheel speed ratio will be almost constant over the entire speed range, but if the air pressure of any of the wheels decreases, the wheel speed ratio will fluctuate as the vehicle speed changes. By comparing the wheel speed ratios for each region, it is possible to detect a change in the wheel speed ratio due to a change in the vehicle speed, and to determine a decrease in air pressure.

FIG. 18 shows a measurement example in which the tire rolling radius is expressed as a function of the vehicle speed and the tire pressure in relation to this point. In FIG. 18, marks ○, ×, □, and ● are provided to distinguish the tire air pressure, and the tire air pressure takes a smaller value in this order. As is clear from FIG. 18, the lower the air pressure is, the larger the tire rolling radius and, consequently, the wheel speed change with vehicle speed change. The reason for this is that as the tire stiffness decreases due to a decrease in tire air pressure, the degree of increase in the rolling radius increases when the centrifugal force applied to the tire increases as the vehicle speed increases.

The above-mentioned speed range division is set in consideration of the influence of the vehicle speed in the low speed range and the memory capacity, and the range of 30 to 60 km / h is set in the low speed range (the first speed range). 1 speed range) and 10 other speed ranges.
It is divided by km / h. More preferably, the entire vehicle speed range up to the maximum speed is divided at suitable intervals. The speed range-specific wheel speed ratio calculation unit 67 of this embodiment executes a speed range / calculation condition determination subroutine shown in FIGS. 7 and 8 and a speed range-specific wheel speed ratio calculation subroutine shown in FIGS. 9 and 10.

In this subroutine, the estimated vehicle speed V
The value of REFB is checked and the estimated vehicle speed data VR
EF is temporarily stored in the memory (step S2
1). If the value of the estimated vehicle speed VREFB is not zero and therefore the vehicle is running, the value of the flag F_X is checked (step S22). Further, if the value of the flag F_X is "1", the estimated vehicle speed data VREF is checked (step S23). Then, the estimated vehicle speed data VREF is 60 k
If m / h or less, the value “6” is set as the filter status S_X used in the processing described below (step S)
24). The estimated vehicle speed data VREF is 60 km
/ H and less than 70 km / h, 70 km / h and less than 80 km / h, 80 km / h and 90 km / h
Less than 90 km / h and less than 100 km / h, 10
0 km / h or more and less than 110 km / h, 110 km / h
h or more and less than 120 km / h, or 120 km / h
If it is not less than h, one of the values “7” to “13” is set as the filter status S_X (step S
25 to S31), this subroutine ends.

On the other hand, if it is determined in step S22 that the value of the flag F_X is "0", the filter status S
The value “0” is set to _X (step S32), and this subroutine ends. It is determined in step S that the estimated vehicle speed data VREF is "0" and the vehicle is stopped.
When the determination is made at 21, the value "60" is set as the vehicle speed index V used in the following processing (step S33). Next, the value “0” or the initial value is stored in the integration buffer V_vSU.
M, integration counter C_vSUM, filtering status data S_v, and speed range wheel speed ratio VX_vF are set (steps S34 to S37). As described above, the integration buffer, the integration counter, the filtering status data, and the speed range wheel speed ratio for the first speed range are initialized.

The integration counter C_vSUM is used for integrating the speed range wheel speed ratio, and the integrated value is stored in the integration buffer V_vSUM. The filtering status data S_v is used to determine whether the filter constant and the filter value (speed range wheel speed ratio VX_vF) are stable, and is composed of, for example, 7 bits. The lower 4 bits of the stator data constitute a sign determination counter, and the sixth bit is a sign flag. The sign of the value obtained by subtracting the average wheel speed ratio from the current wheel speed ratio is positive as described later. Is reset to the value "0" at the time of, and set to the value "1" when the sign is negative. The seventh bit is a filter value stable flag. If the filter value is stable, the value is set to “1”. If the filter value is not stable, the value is “0”.
Is reset to

Next, the value "10" is added to the vehicle speed index V to update the vehicle speed index V (step S38), and it is determined whether or not the updated value of the vehicle speed index V is "140". (Step S39). If the decision result in the step S39 is negative, the control flow proceeds to a step S34. As a result, the integration buffer, the integration counter, the filtering status data, and the speed range wheel speed ratio for the second to eighth speed ranges are sequentially initialized. When the initialization for the eighth speed range is completed, immediately after that, step S3
At step 8, the value of the vehicle speed index V is updated to "140", and the result of the determination at the next step S39 becomes affirmative, so this subroutine ends.

Next, in the wheel speed ratio calculation subroutine for each speed range shown in FIGS.
The buffer content is updated by adding the wheel speed ratio VXPERF to SUM (step S41), and the value C of the integration counter is updated.
_VSUM is decremented (step S42).
Next, it is determined whether a borrow (negative carry) has occurred, that is, whether the integration has been completed (step S).
43). If the integration has not been completed, this subroutine ends.

Thereafter, when the end of the integration is determined in step S43, an initial value (for example, 128) is set in an integration counter C_vSUM (step S44), and the integration buffer value is set to a value corresponding to the initial value (for example, "128"). ) Is set in the integration buffer (step S45). When the sampling of the wheel speed ratio is performed a predetermined number of times (for example, 128 times),
The following filtering process is started.

That is, the filtering status data S_v is checked (step S46). If the value is "0" and it is determined that the filtering is the first time, the value V_vSUM of the integrating buffer is set to the speed range wheel speed VX.
_VF (step S47) and the value “01”
Is set as the filtering status data S_v (step S48). Next, the control flow is shown in FIG.
Goes to step S60, and the integrated buffer value V_vSUM
Is cleared to "0", and this subroutine ends.

In step S46 of the next subroutine execution cycle, it is determined that the filtering status data S_v is not "0", so that the speed region wheel speed ratio VX
_VF and an integrated buffer value V_vSUM representing the average value (for example, an average value of 128 times) are compared (step S4).
9), thereby performing sign determination. If the wheel speed ratio is greater than the accumulated buffer value, a value “0” representing a positive sign
Is set in the register A (step S50),
If the wheel speed ratio is smaller than the integrated buffer value, a value “1” indicating a negative sign is set in the register A. Following step S50 or S51, or step S49
If it is determined that the wheel speed ratio is equal to the integrated buffer value, the control flow proceeds to step S52 in FIG.

In step S52, the value of the seventh bit of the filtering status data S_v is checked.
If this value is “0” and it is determined that the filtering has not yet been stabilized, the value of the sixth bit of the status data S_v representing the previous sign determination result and A representing the current sign determination result The value of the register is compared (step S53). If it is determined that the sixth bit value is not equal to the A register value, and thus the sign has been inverted, the lower 4 bits of the status data S_v as a sign inversion counter are counted up (step S54). Subsequent to step S54, or if it is determined in step S53 that the sixth bit value is equal to the A register value and the sign is not inverted, the control flow proceeds to step S55.
Then, the lower 4 bits are compared with the value "4".

If it is determined in step S55 that the lower 4 bits of the status data S_v are smaller than the value "4", and thus the sign inversion has not been performed three times, the control flow proceeds to step S58. This step S58
Then, the integrated buffer value V_ is added to the speed range wheel speed ratio VX_vF.
The value obtained by dividing the value obtained by adding vSUM by the value “2” is
It is set as the speed region wheel speed ratio VX_vF. That is, 1/2 filter processing for improving the followability to the target value is performed. Next, the A register value TMP_A is set to the sixth bit of the status data S_v for the next sign determination (step S59), and the integrated buffer value V_vSUM is cleared for the next wheel speed ratio integration ( Step S60), this subroutine ends.

On the other hand, if it is determined in step S55 that the lower 4 bits of the status data S_v are equal to or more than the value "4" and that the sign inversion has been performed three times, the status data S_v of the status data S_v is determined for the next number of sign inversions. After the lower 4 bits are reset to the value "0" (step S56), the value "1" indicating that the filter value (speed range-specific wheel speed ratio) has been stabilized is added to the seventh bit of the status data S_v. It is set (step S58). Next, the above-described step S
58 to S60 are sequentially executed, and this subroutine ends.

When the value "1" is set to the seventh bit of the status data S_v when the filter value is stabilized as described above, the control flow proceeds from step S52 to step S52.
Proceeding to 61, the sixth bit of status data S_v and A
The value is compared with the register value TMP_A. 6th bit and A
If the register value does not match, the lower 4 bits of the status data S_v are reset to the value “0” (step S62), and the above-described steps S59 and S60 are sequentially executed, and this subroutine ends.

Thereafter, in step S61, the sixth bit of the status data S_v and the A register value TMP_
If it is determined that A matches and the same code continues twice,
The value “1” is set in the lower 4 bits of the status data S_v (step S63), and ± 1 filter processing for reducing the influence of noise is started. That is, the wheel speed ratio VX_vF and the integrated buffer value V_ representing the average value thereof
vSUM is compared (step S64). If the wheel speed ratio is larger than the integrated buffer value, a value obtained by subtracting the value "1" from the wheel speed ratio is set as the wheel speed ratio (step S65), while the wheel speed is set. If the ratio is smaller than the accumulation buffer, a value obtained by adding the value "1" to the wheel speed ratio is set as the wheel speed ratio (step S66). Then, step S65
Alternatively, following S66, steps S59 and S6 described above are performed.
0 are sequentially executed, and this subroutine ends.

The graph of FIG. 11 illustrates the change over time of the wheel speed ratio, the sign inversion counter and the filter value stable flag during the above-mentioned filtering process. In FIG. 11, a V mark indicates sign inversion. Referring to FIGS. 2 and 3, the air pressure drop determining unit 68 determines the maximum value of the speed range wheel speed ratio based on the speed range wheel speed ratio VX_vF from the speed range-specific wheel speed ratio calculation unit 67 and the filtering status data S_v. VX_MAX and minimum value VX_MIN
Is calculated. The determination unit 68 determines the estimated vehicle speed VXPERF from the ABS controller 5 and the air pressure drop estimation condition determination unit 6
5, a first air pressure reduction determining unit 682 for determining whether there is a reduction in air pressure based on the flag F_X from the flag F_X, and a maximum and minimum wheel speed ratio VX_MA from a wheel speed ratio variation value calculating unit 681.
A second air pressure drop determining unit 683 that determines whether there is a decrease in air pressure based on X, VX_MIN and the reference wheel speed ratio VX_IGON from the reference wheel speed ratio setting unit 66;
A third air-drop determining unit 684 that determines whether there is a decrease in air pressure based on the maximum / minimum wheel speed ratio from 1;
A total air pressure drop determining unit 685 that makes a final air pressure drop determination based on the air pressure drop flag.

EC as wheel speed ratio fluctuation value calculation section 681
In this embodiment, U6 executes a wheel speed ratio fluctuation value calculation subroutine shown in FIG. 12 to obtain the maximum value and the minimum value of the speed region wheel speed ratio calculated by the speed region-specific wheel speed ratio calculation section 67. In this subroutine, the values of the maximum value register and the minimum value register (both not shown) of the ECU 6 are reset to "0" (steps S71 and S72), and the value "60 (km / km)" representing the first speed range is set in the vehicle speed index V. h) is set (step S73), and then the vehicle speed index V
The seventh bit of the filtering status data S_v corresponding to is checked (step S74). If the value of the seventh bit is “0” and the speed range wheel speed ratio VX_vF corresponding to the vehicle speed index V has not been calculated, the maximum and minimum wheel speed values in the speed range corresponding to the vehicle speed index V are calculated. It is determined that the calculation cannot be performed, and the control flow proceeds to step S
Go to 82.

On the other hand, it is determined in step S that the value of the seventh bit of the status data S_v is "1" and the speed-range wheel speed ratio VX_vF corresponding to the vehicle speed index V has been calculated.
74, the value of the minimum value register TMP_MI
N is checked (step S75). Immediately after the register is reset, the register value TMP_MIN is “0”. In this case, the speed range wheel speed ratio VX_vF (= VX_60F) corresponding to the vehicle speed index V (= 60 km / h) is sequentially stored in the maximum value register and the minimum value register (steps S76 and S77). Speed ratio VX_
vF is compared with the value TMP_MAX of the maximum value register. Here, since both values are equal, the control flow proceeds to step S80, and the speed range wheel speed ratio VX_vF is compared with the value TMP_MIN of the minimum value register. Here, since the two values are equal, the control flow proceeds to step S82.
Then, the value "10" is added to the vehicle speed index V, and in the next step S83, it is determined whether or not the vehicle speed index V is the value "140". Here, the result of the determination in step S83 is negative, and the control flow returns to step S74.

Next, the vehicle speed index V (= 7) representing the second speed range
0 km / h) of the status data S_v corresponding to the seventh
If the bit value is “1” and the speed-range wheel speed ratio VX_70F corresponding to the second speed range has been calculated, the control flow proceeds to step S75. In the last cycle, when the speed range wheel speed ratio VX_60 corresponding to the first speed range is stored in the maximum value register and the minimum value register, it is determined that the value of the value TMP_MIN of the minimum value register is not “0”, and The flow proceeds to step S78, and the speed range wheel speed ratio VX_70F of the second speed range and the value TMP_MAX of the maximum value register (the speed range wheel speed ratio VX_ of the first speed range).
60F). The value VX_70F is equal to the value TMP_
If it is larger than MAX, the value of the maximum value register is the value VX
_70F (step S79). On the other hand, the value V
If X_70F is equal to or less than the value TMP_MAX, the value VX_
70F and the value TMP_MIN of the minimum value register are compared (step S80). If the value VX_70F is smaller than the value TMP_MIN, the value of the minimum value register is updated to the value VX_70F (step S81). Following step S79 or S81, or step S
If it is determined at 80 that the value VX_70F is equal to or greater than the value TMP_MIN, the control flow proceeds to step S82 described above.

The speed range wheel speed ratio VX_70F has already been calculated, and the speed range wheel speed ratio VX
If _60F is not stored in the maximum and minimum registers, the value VX_70F is stored in both registers. After that, the vehicle speed index V is set to the values “80”, “9”.
0 ”,...,“ 130 ”, and the corresponding ones of the above-described steps S74 to S81 are executed, whereby the value of the maximum value register or the minimum value register is added to the comparison result in steps S78 and S80. Updated or maintained accordingly. The vehicle speed index V (= 130 km / h), that is, the eighth
When the corresponding one of steps S74 to S81 is executed for the speed range, the vehicle speed index V is updated to the value “140” in the next step S82, so that the determination result in step S83 becomes positive. In this case, the control flow is step S
Proceeding to 84, the value TMP_MAX of the maximum value register is set as the maximum value VX_MAX of the speed range wheel speed ratio, and in the next step S85, the value TMP_MIN of the minimum value register is set.
Is set as the minimum value VX_MIN of the speed range wheel speed ratio, and this subroutine ends.

The first air pressure drop judging section 682 judges a decrease in air pressure when the wheel speed ratio VXPERF deviates from a predetermined range continuously for a predetermined time. The predetermined range is set to, for example, a range of ± 1% with respect to the standard air pressure. This is because if the four wheels are at standard air pressure, the wheel speed ratio is usually ± 10% even if there is an individual error of the tire due to a difference in the wear rate.
This is because it does not exceed ± 1% at about 0.3%.

In order to determine the air pressure drop, the first air pressure drop determining section 682 of this embodiment executes a first air pressure drop determining subroutine shown in FIG. In this subroutine, the flag F_X from the air pressure drop estimation condition determination unit 65 is
Is checked (step S91). If the value of the flag F_X is "0" and the condition for estimating the air pressure drop is not satisfied, a predetermined time XXPER is set in the air pressure drop determination timer in step S92, and this subroutine ends. I do.
On the other hand, when the value of the flag F_X is “1” and it is determined that the estimation condition is satisfied, it is determined whether the wheel speed ratio VXPERF is equal to or more than a first predetermined value and equal to or less than a second predetermined value (step). S93). The magnitudes of the two predetermined values may be the same, and in this case, it is determined in step S93 whether or not the absolute value of the wheel speed ratio is equal to or less than the predetermined value. Step S93
If the determination result in step is affirmative, the control flow proceeds to step S92 described above. That is, the determination of the decrease in the air pressure is not performed.

On the other hand, if the decision result in the step S93 is negative, the value TXPER of the decision timer is decremented (step S94), and the timer value TXPER is checked (step S95). If the timer value TXPER is not "0", the deviation of the wheel speed ratio from the predetermined range has not continued for the predetermined time, so the determination of the presence or absence of the decrease in air pressure is suspended, and this subroutine ends. On the other hand, the timer value TXPER becomes “0”, and accordingly, the wheel speed ratio V
If it is determined that the XPERF has continued to deviate from the predetermined range for the predetermined time XXPER, it is determined that the air pressure has dropped, and the first air pressure drop flag FAIR_P is set to a value “1” representing the pressure drop (step S9).
6).

The first air pressure drop determination subroutine shown in FIG. 13 determines that the air pressure has dropped when the wheel speed ratio deviates from a predetermined range during running of the vehicle.
Unlike the case of a second air pressure drop determination subroutine described later, the presence or absence of the air pressure drop is determined based on the wheel speed ratio itself without setting the reference level of the wheel speed ratio (calibration of the wheel speed ratio). . That is, the determination of the decrease in air pressure is performed based on the absolute value of the wheel speed ratio. According to the subroutine of FIG. 13, for example, a tire of one of the wheels is in a completely punctured state (more generally, an air pressure drop of about 70% or more), or different size tires such as tempered tires are mounted on the left and right wheels. State can be detected. Then, when this subroutine is completed as described above, the flag value FAIR_P (= 1) is sent to the air pressure drop comprehensive determination unit 685.

The determination of the air pressure reduction by the second air pressure reduction determining unit 683 is based on the maximum and minimum wheel speed ratios VX_MAX and VX_MIN from the wheel speed ratio variation value calculating unit 681 and the reference wheel speed ratio VX_IGON from the reference wheel speed ratio setting unit 66. It is performed based on. Although the setting of the reference wheel speed ratio has been described above, a preferred example thereof will be described below. Reference wheel speed ratio V
In setting X_IGON, the reference wheel speed ratio setting unit 66
ECU 6 preferably executes a reference wheel speed ratio setting subroutine shown in FIG.

In this subroutine, the value of the IG on-edge flag FIGON is checked (step S10).
1) If the flag value FIGON is "0" and the on-edge of the ignition switch signal IG is not detected, this subroutine ends. Thereafter, when the ignition switch is turned on to start the engine, and when the ignition switch signal IG rises and its on-edge is detected, the flag value FIGON is set to "1". As a result, the result of the determination in step S101 is determined. Be affirmative. In this case, the seventh bit of the filtering status data S_60 corresponding to the vehicle speed of 60 km / h or less, that is, the first speed range is checked (step S1).
02). The value of the seventh bit is “0”,
If the calculation of the speed range wheel speed ratio VX_60F corresponding to the speed range has not been completed, this subroutine ends.

On the other hand, if the value of the seventh bit is "1" and it is determined that the wheel speed ratio VX_60F has been calculated, the wheel speed ratio VX_60F is set as the reference wheel speed ratio VX_IGON (step S103). Next step S1
At 04, the flag value FIGON is reset to “0”,
This subroutine ends. Note that the wheel speed ratio VX_60
Since F is calculated when the flag F_X = 1, that is, when the condition for estimating air pressure drop is satisfied, the above-described reference wheel speed ratio VX_IGON is set when the condition F_X = 1 is satisfied.

In this embodiment, the second air pressure drop judging section 68
The ECU 6 as 3 executes a second air pressure drop determination subroutine shown in FIG. In this subroutine, the reference wheel speed ratio VX_
The value of IGON is checked (step S111). If this value is "0" and the setting of the reference wheel speed ratio is not completed,
This subroutine ends. On the other hand, if the value of the reference wheel speed ratio is not “0” and the reference wheel speed ratio has been set, the minimum value VX_MIN of the speed-range wheel speed ratio from the wheel speed ratio variation value calculation unit 681 is checked (step). S112). If the minimum value is “0” and the calculation of the speed range wheel speed ratio has not been completed, this subroutine ends. On the other hand, if the minimum value is not “0” and the speed range wheel speed ratio has been calculated, Reference wheel speed ratio VX_IGON and maximum value VX_MAX of speed range wheel speed ratio
Is compared with the minimum value VX_MIN of the speed range wheel speed ratio, the maximum value and the minimum value of these three values are respectively obtained, and stored in the maximum value register and the minimum value register of the ECU 6 (step S113). , S114).

Next, the value TMP_MAX of the maximum value register
(TMP_MAX-TMP_MIN) obtained by subtracting the value TMP_MIN of the minimum value register from the above and the determination value XAIR
_T (for example, 0.2%) (step S11).
5) If the difference between the maximum value register value and the minimum value register value is smaller than the determination value, it is determined that the air pressure does not decrease because the wheel speed ratio has not changed from the reference wheel speed ratio by the determination value or more, and this subroutine is executed. finish. On the other hand, the difference between the maximum value register value and the minimum value register value (TMP_MAX-TMP
If _MIN) is equal to or greater than the determination value XAIR_T, it is determined that the air pressure has decreased because the wheel speed ratio has changed by the value equal to or greater than the determination value, and the second air pressure reduction flag FAIR_T is set to a value “1” representing the decrease in air pressure (step). S116).

As described above, in the second air pressure drop judging subroutine of FIG. 15, while the vehicle is running with the engine being started and ending with the engine being stopped, the wheel speed ratio is changed from the reference wheel speed ratio as time passes. A predetermined value (for example, 0.
2%) or more is determined, and based on the determination result, the presence or absence of a decrease in air pressure is determined. Therefore, according to this subroutine, a decrease in air pressure can be detected when the vehicle is traveling, for example, when an air pressure decrease of, for example, about 20% or more corresponding to a wheel speed ratio fluctuation of 0.2% occurs. Then, when such a decrease in air pressure is detected, the present subroutine ends. The flag value FAIR_T (= 1) is sent to the air pressure drop comprehensive determination unit 685.

EC as third air pressure drop judging section 684
U6 executes a third air pressure drop determination subroutine shown in FIG. In this subroutine, the minimum value VX_MIN of the speed range wheel speed ratio sent from the wheel speed ratio fluctuation value calculation unit 681 is checked (step S121), and the minimum value is "0" and the calculation of the minimum value has not been completed. If it is determined that the subroutine is completed, the present subroutine ends. On the other hand, the minimum value V
If it is determined that the value of X_MIN is not “0” and the minimum value has been calculated, the control flow proceeds to step S122, where the maximum value VX_MAX of the speed-range wheel speed ratio is changed from the minimum value VX_MAX to the minimum value VX_MAX.
The value obtained by subtracting X_MIN is compared with the determination value XAIR_V. The determination value XAIR_V is, for example, a value VX
_MAX and VX_MIN are set according to the speed range to which each belongs, and are set to, for example, values around 0.15%.

Then, the difference between the maximum value and the minimum value (VX_M
If (AX-VX_MIN) is smaller than the determination value XAIR_V, it is determined that there is no decrease in air pressure because the wheel speed ratio has not changed by the vehicle speed or more than the determination value, and this subroutine ends. On the other hand, if the difference is equal to or greater than the determination value, it is determined that the air pressure has decreased because the wheel speed ratio has changed with the change in vehicle speed, and the third air pressure decrease flag FAIR_V is set to a value “1” representing the decrease in air pressure. (Step S
123).

In the third air pressure drop determination subroutine shown in FIG. 16, the degree of increase in the rolling radius of the tire due to the centrifugal force applied to the tire overcoming the tire rigidity increases as the vehicle speed becomes higher.
In addition, this subroutine is based on the physical phenomenon that the greater the degree of decrease in the tire air pressure, the greater the degree. As described above, this subroutine determines whether or not the wheel speed ratio has fluctuated by more than a predetermined value due to the change in vehicle speed. An air pressure drop is determined based on the determination result. The degree of decrease in the tire air pressure that can be detected by this subroutine changes according to the vehicle speed, for example, 20% or more in a high vehicle speed range and 60% or more in a low vehicle speed range. This subroutine ends when a decrease in air pressure is detected. Flag value FAI
R_V (= 1) is sent to the air pressure drop comprehensive determination unit 685.

EC as air pressure drop comprehensive judgment section 685
U6 executes an air pressure drop comprehensive judgment subroutine shown in FIG. In this subroutine, the first air pressure drop flag F sent from the first air pressure drop determination unit 682
AIR_P is checked (step S131), and if the value of the first air pressure drop flag is “0”, the second air pressure drop flag FAIR_T is checked (step S132).
If the value of the second air pressure drop flag is also "0", the third air pressure drop flag FAIR_V is checked (step S13).
3). If the value of the third air pressure drop flag is also “0”, it is determined that there is no air pressure drop, and the present subroutine ends.

On the other hand, the first air pressure drop flag FAIR_P
Is determined in step S131, or the value of the second air pressure reduction flag FAIR_T is determined to be "1" in step S132, or the value of the third air pressure reduction flag FAIR_V is determined. Is determined to be “1” in step S133, it is determined that the air pressure has decreased, and the control flow proceeds to step S134.
Then, the air pressure reduction flag FAIR is set to a value "1" representing the air pressure reduction, and this subroutine ends. The air pressure drop flag value FAIR (= 1) is sent to the alarm lamp drive unit 69 (FIG. 2).

ECU as Alarm Lamp Drive Unit 69
6 monitors the value of the air pressure drop flag FAIR in an alarm lamp output subroutine (not shown), and if the flag value is "0", the alarm lamp drive flag FAIR
OUT is reset to "0", while if the value of the air pressure drop flag FAIR is "1", the flag FAIROU
Set the value of T to "1". The alarm lamp drive flag FAIROUT is sent to the alarm lamp 9 (FIG. 1), and when the flag is set to "1" and the drive power is supplied, the alarm lamp 9 is turned on to notify the driver or the like of a decrease in air pressure. Inform.

Hereinafter, the operation of the tire pressure drop detecting device having the above-described structure will be described. When the ignition key of the vehicle is turned on, the ignition signal IG rises, the flag FIGON (FIG. 14) is set to "1", the engine is started, and the vehicle starts running. While the vehicle is running, the ABS controller 5 controls the front and rear left and right wheels FR to R
Wheel speed signals FVFR to FVR based on wheel speed pulse signals supplied from the wheel speed sensors 1 to 4 as the L rotates.
L and the estimated vehicle speed signal VREFB are obtained. The wheel speed signal is filtered by the filter unit 61, and the filtered wheel speed signals VFR to VRL are output to the wheel speed ratio calculation unit 62 and the wheel acceleration calculation unit 63. Also,
The steering angle calculation unit 64 calculates the steering angle STR based on the steering pulse signals ST1, ST2, and STN sent from the steering sensor 8 in accordance with the operation of the steering wheel while the vehicle is running.

The wheel speed ratio calculation unit 62 calculates the diagonal sum wheel speed ratio VXPERF based on the wheel speed signal after the filter processing.
Is output to the reference wheel speed ratio setting unit 66, the speed range-specific wheel speed ratio calculation unit 67, and the air pressure drop determination unit 68. The diagonal sum wheel speed ratio is suitable for determining a decrease in air pressure because a difference in wheel running state between the wheels can be offset. Then, in the wheel acceleration calculation unit 63, the wheel speed signals VFR to VR
L, wheel accelerations DVFR to DVRL are calculated,
The wheel accelerations DVFR to DVRL are supplied to the air pressure drop estimation condition determination unit 65.

In the determination section 65, the wheel accelerations DVFR to DVFR-D
VRL, steering angle STR from the steering angle calculator, brake lamp signal BLS from brake lamp switch 10, ABS control signal ABSOR from ABS controller 5, and estimated vehicle speed VREFB
(I) high vehicle speed, (ii) brake operation off,
(Iiii) ABS control is off, (iv) the wheel acceleration is almost zero, (v) the wheel acceleration difference is almost zero, and (vi) the steering angle is almost zero. It is determined whether the drop estimation condition is satisfied or not. Then, when the condition is satisfied, that is, when a vehicle stable running state in which the determination of the air pressure drop based on the wheel speed ratio can be appropriately performed is achieved, the air pressure drop estimation condition satisfaction determination flag F_X is set to a value “1”.
The flag value is output to the reference wheel speed ratio setting unit 66, the speed range-specific wheel speed ratio calculation unit 67, and the air pressure drop determination unit 68.

The first air pressure drop judging section 682 of the air pressure drop judging section 68 monitors the wheel speed ratio VXPERF from the wheel speed ratio calculating section 62 while the air pressure drop estimating condition is satisfied (FIG. 1).
3) If the wheel speed ratio deviates from a predetermined range for a predetermined time XXPER, it is determined that the air pressure has dropped. As described above, the determination unit 682 performs the air pressure reduction determination based on the absolute value of the wheel speed ratio. This makes it possible to detect a considerable decrease in air pressure, such as a completely punctured state, immediately after the vehicle starts running.

In the speed range-specific wheel speed ratio calculation section 67, the estimated vehicle speed VR from the ABS controller 5 is output while the estimation condition is satisfied.
Which of the first to eighth speed ranges the current vehicle speed belongs to is determined based on the EFB, and the wheel speed ratio VXPERF successively input from the wheel speed ratio calculator 62 at the time of the speed range determination.
Is subjected to a filtering process (FIGS. 9 and 10), and the resulting filter value is used as the wheel speed ratio VX_v in the determination speed range.
It is obtained as F. When the filter value becomes stable,
The seventh bit of the filtering status data S_v is set to the value “1”.

In the reference wheel speed ratio setting section 66, the ignition key is turned on and the IG on-edge flag FIG.
When the value of ON becomes “1”, the first speed range (vehicle speed ≦ 60 k)
m / h) is determined, and the calculated wheel speed ratio VX_60F is set as the reference wheel speed ratio VX_IGON (see FIG. 14). The reference wheel speed ratio is output to the second air pressure reduction determining unit 683 of the air pressure reduction determining unit 68.

The wheel speed ratio fluctuation value calculation unit 681 of the air pressure drop determination unit 68 receives the speed range wheel speed ratio VX_vF and the status data S_v from the speed range-specific wheel speed ratio calculation unit 67, and Maximum and minimum values VX_MAX, VX of the speed range wheel speed ratios calculated for the speed range
Determine X_MIN. The maximum value and the minimum value are output to the second and third air pressure drop determination units 683 and 684.

In the second air pressure drop determining section 683, while the air pressure drop estimation condition is satisfied (F_X = 1), the reference wheel speed ratio VX
_IGON, the difference between the maximum value and the minimum value of the maximum wheel speed ratio VX_MAX and the minimum wheel speed ratio VX_MIN are compared with the determination value XAIR_T (FIG. 15). When the speed ratio fluctuates from the reference wheel speed ratio by a certain amount or more, a decrease in air pressure is determined.
As a result, a relatively slight decrease in air pressure can be detected.

In the third air pressure drop judging section 684, the difference between the maximum value VX_MAX and the minimum value VX_MIN of the speed range wheel speed VX_vF is determined while the air pressure drop estimating condition is satisfied.
It is compared with IR_V (FIG. 16). If the difference is equal to or greater than the determination value and the wheel speed ratio fluctuates by a certain value or more with the change in vehicle speed, it is determined that the air pressure has decreased. Thus, when the vehicle travels over a wide vehicle speed range, a decrease in air pressure is reliably detected.

In the air pressure drop comprehensive judgment section 685, the first to
When any of the third air pressure reduction determining units 682 to 684 determines that the air pressure has decreased, the air pressure reduction is determined. As described above, in the present embodiment, the absolute value of the wheel speed ratio, the presence or absence of a change in the wheel speed ratio from the reference wheel speed ratio with the passage of time after the reference wheel speed ratio is set, and the wheel speed Three types of determinations are made based on the presence or absence of a change in the ratio. When any of the determinations indicates a decrease in air pressure, the alarm lamp 9 is turned on to notify the occurrence of a decrease in air pressure.

The method for detecting a decrease in tire air pressure according to the present invention is not limited to the above embodiment, but can be variously modified. In the above embodiment, when the tire air pressure drops in any one of the four wheels, the absolute value of the wheel speed ratio (the wheel speed ratio without calibration) is set so that this air pressure drop can be detected more accurately. ) Is not only detected by the first air pressure reduction determining unit 682 as air pressure reduction, but also a vehicle stable operation state is achieved for the first time after the vehicle starts running with the engine started. When the wheel speed ratio fluctuates as time elapses from the reference wheel speed ratio VX_IGON detected at this time, the wheel speed ratio fluctuation is detected as a decrease in air pressure by the second air pressure drop determination unit 683, and the wheel speed ratio fluctuation is further detected. The third air pressure drop determining unit 684 detects the presence or absence of a change in the wheel speed ratio, and detects the wheel speed ratio change due to the vehicle speed change as the air pressure drop. It was. However, in the method of the present invention, it is not essential to perform the determination of the decrease in the air pressure based on the change in the wheel speed ratio with the passage of time or the change in the vehicle speed.

That is, in the method of the present invention, only the determination of the decrease in the air pressure based on the absolute value of the wheel speed ratio needs to be performed, and this can be performed using the apparatus illustrated in FIG. The apparatus in FIG. 19 includes a wheel speed ratio calculation unit 161 corresponding to the wheel speed ratio calculation unit 62 in FIG. 2, an estimation condition determination unit 162 corresponding to the air pressure drop estimation condition determination unit 65 in FIG. 1
Air pressure drop determining unit 1 corresponding to air pressure drop determining unit 682
63, the ignition signal IG sent out at the time of starting the engine, and the wheel speed ratio calculation unit 1
The wheel speed ratio from 61 and the estimated condition flag from the estimated condition determination unit 162 are supplied.

In the air pressure drop determining section 163, after the ignition signal IG rises, the wheel speed ratio calculated when the estimated condition flag takes a value indicating the vehicle stable driving state (estimated condition satisfied) is a predetermined value. Is determined. If the wheel speed ratio repeatedly calculated during the vehicle stable driving state continuously exceeds the predetermined value for a certain period of time, it is determined that at least one of the front, rear, left and right wheels of the vehicle is in a reduced air pressure state.

In the above embodiment, the diagonal sum wheel speed ratio is calculated as the wheel speed ratio used for determining the air pressure drop, but this is not essential. For example, the front wheel speed ratio instead of the diagonal sum wheel speed ratio may be calculated according to the following equation, and the presence or absence of a decrease in the air pressure of one of the left and right front wheels may be determined based on the calculated value. Front wheel speed ratio = (VFR−VFL) / ｛(VFR + VF
L) / 2} Alternatively, the rear wheel speed ratio may be calculated according to the following equation, and a decrease in the air pressure of one of the left and right rear wheels may be determined based on the calculated value.

Rear wheel speed ratio = (VRR-VRL) /
{(VRR + VRL) / 2} In the above-described embodiment, the high vehicle speed, the wheel acceleration, the acceleration difference and the steering angle are small, and the ABS control and the brake operation off are the conditions for estimating the air pressure drop.
Other requirements may be included in the estimation conditions to improve the determination accuracy. For example, it is possible to include a requirement that the vehicle lateral acceleration is equal to or less than a certain value and / or the vehicle longitudinal acceleration is equal to or less than a certain value.

Furthermore, in the above-described embodiment, the tire pressure drop detecting device is mounted on the vehicle equipped with the ABS so that the elements used for the ABS control are shared. However, this is not essential. It is also applicable to non-equipped vehicles. The configuration of the device used in this case is clear from the above description, and the description is omitted.

[0090]

As described above, the method for detecting a decrease in tire air pressure according to the first aspect of the present invention comprises: a wheel speed detection process for detecting two or more wheel speeds of front, rear, left and right wheels; A vehicle acceleration / deceleration state detection process for detecting one or more acceleration / deceleration states of the vehicle, a steering state detection process for detecting a vehicle steering state, and a vehicle body of the vehicle from two or more wheel speeds of the front, rear, left and right wheels Vehicle speed detection process for detecting vehicle speed and wheel speed
One or more wheel speeds detected during the detection process and another one or more
A wheel speed ratio calculating step for calculating a wheel speed ratio represented by a ratio of a difference between the wheel speed and the sum of the two, a braking device operating state detecting process for detecting an operating state of a vehicle braking device, and a vehicle speed. A vehicle motion state determination step of determining the vehicle motion state based on the wheel acceleration / deceleration state, the steering state, and the braking device operation state; and determining that the vehicle is in a stable driving state in the vehicle motion state determination step. If the wheel speed ratio calculated in the wheel speed ratio calculation process repeatedly executed during the predetermined period continuously exceeds the first predetermined value for a certain period of time, it is determined that at least one of the front, rear, left, and right wheels is in a low air pressure state. A first tire pressure drop determination step. Therefore, an error factor for the determination of the decrease in the air pressure based on the wheel speed ratio is removed, and the influence is also eliminated when the noise is added to the tire pressure decrease detection device as the determination system. Therefore, it is possible to reliably detect a decrease in tire air pressure without performing any special calibration on the wheel speed ratio, that is, based on the absolute value of the wheel speed ratio. Therefore, the logic for determining the decrease in air pressure can be simplified. Also, when the air pressure drops immediately after the vehicle travels, the air pressure reduction can be determined.

The method according to claim 1 is characterized in that the wheel speed ratio calculated in the wheel speed ratio calculation step executed when the vehicle stable operation state is determined for the first time in the vehicle motion state determination step and the vehicle stable operation state thereafter. When the difference from at least one of the plurality of wheel speed ratios calculated in the wheel speed ratio calculation process repeatedly executed during the determination is larger than the second predetermined value, at least one of the front, rear, left, and right wheels is The second tire pressure decrease judgment process for judging that the air pressure is low
Because it contains, as a criterion wheel speed ratio when the vehicle steady state operation is first achieved, variation of the wheel speed ratio with time is detected. Therefore, it is possible to reliably detect a decrease in air pressure that causes the wheel speed ratio to fluctuate by a certain amount or more.

[0092]

[0093]

[0094]

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating an apparatus for implementing a method for detecting a decrease in tire air pressure according to an embodiment of the present invention, together with an ABS controller.

FIG. 2 is a functional block diagram showing the functions of an electronic control unit (ECU) shown in FIG. 1 in detail.

FIG. 3 is a functional block diagram showing in detail an air pressure drop determining unit shown in FIG. 2;

FIG. 4 is a flowchart showing an estimation condition determination subroutine executed by an ECU serving as an air pressure drop estimation condition determination unit shown in FIG. 2;

FIG. 5 is a graph illustrating an estimated vehicle speed / acceleration band determination value map used during execution of a subroutine shown in FIG. 4;

6 is a graph illustrating an estimated vehicle speed / steering wheel angle determination value map used during execution of a subroutine shown in FIG. 4;

7 is a flowchart showing a part of a speed range / calculation condition determination subroutine executed by an ECU as a speed range-specific wheel speed ratio calculation unit shown in FIG. 2;

FIG. 8 is a flowchart showing the rest of the subroutine partially shown in FIG. 7;

FIG. 9 is a flowchart illustrating a part of a speed region-specific wheel speed ratio calculation subroutine executed by an ECU serving as a speed region-specific wheel speed ratio calculation unit.

FIG. 10 is a flowchart showing the rest of the subroutine partially shown in FIG. 9;

FIG. 11 exemplifies changes over time of a wheel speed ratio, a sign inversion counter, and a filter value stable flag during a filtering process executed in a speed region-specific wheel speed ratio calculation subroutine shown in FIGS. 9 and 10; It is a graph to do.

12 is a flowchart illustrating a wheel speed ratio variation value calculation subroutine executed by an ECU serving as a wheel speed ratio variation value calculation unit illustrated in FIG. 3;

FIG. 13 is a flowchart showing a first air pressure drop determination subroutine executed by an ECU serving as a first air pressure drop determination unit shown in FIG. 3;

14 is a diagram showing a reference wheel speed ratio setting unit E shown in FIG.
It is a flowchart which shows the reference wheel speed ratio setting subroutine performed by CU.

FIG. 15 is a flowchart showing a second air pressure drop determination subroutine executed by an ECU serving as a second air pressure drop determination unit shown in FIG. 3;

FIG. 16 is a flowchart showing a third air pressure drop determination subroutine executed by an ECU as a third air pressure drop determination unit shown in FIG. 3;

FIG. 17 is a flowchart showing an air pressure drop comprehensive determination subroutine executed by an ECU serving as an air pressure drop overall determination unit shown in FIG. 3;

FIG. 18 is a graph illustrating tire rolling determination / vehicle speed / tire pressure characteristics;

FIG. 19 is a functional block diagram showing a main part of a tire pressure drop detecting device according to a modification.

[Explanation of symbols]

 1, 2, 3, 4 Wheel speed sensor 5 ABS controller 6 Electronic control unit (ECU) 8 Steering sensor 9 Alarm lamp 10 Brake lamp switch 61 Filter unit 62 Wheel speed ratio calculation unit 63 Wheel acceleration calculation unit 64 Steering angle calculation unit 65 Air pressure drop estimation condition determination unit 66 Reference wheel speed ratio setting unit 67 Speed range-specific wheel speed ratio calculation unit 68 Air pressure reduction determination unit 69 Alarm lamp drive unit 161 Wheel speed ratio calculation unit 162 Estimation condition determination unit 163 Air pressure reduction determination unit 681 Wheel Speed ratio fluctuation value calculating section 682 First air pressure drop determining section 683 Second air pressure drop determining section 684 Third air pressure drop determining section 685 Total air pressure drop determining section

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-8-142615 (JP, A) JP-A-5-213019 (JP, A) JP-A-63-305011 (JP, A) 135806 (JP, A) JP-A-8-142616 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B60C 23/06

Claims (2)

(57) [Claims] 1. A wheel speed detection step for detecting two or more wheel speeds of front, rear, left and right wheels of a vehicle, and a wheel acceleration / deceleration state detection for detecting one or more acceleration / deceleration states of the front, rear, left and right wheels. A steering state detection step of detecting a steering state of the vehicle; a vehicle body speed detection step of detecting a vehicle body speed of the vehicle from two or more wheel speeds of the front, rear, left and right wheels; and a wheel speed detection step. Different from one or more wheel speeds detected in
A wheel speed ratio calculation process for calculating a wheel speed ratio represented by a ratio of a difference between one or more wheel speeds and a sum of the two, and braking for detecting an operation state of a braking device of the vehicle. A device operation state detection step, a vehicle operation state determination step of determining an operation state of the vehicle based on the vehicle speed, the wheel acceleration / deceleration state, the steering state, and the braking apparatus operation state, and the vehicle operation state The wheel speed ratio calculated in the wheel speed ratio calculation process, which is repeatedly executed while it is determined in the determination process that the vehicle is in a stable driving state, continuously exceeds a first predetermined value for a certain period of time. A first tire pressure reduction determining step for determining that at least one of the front, rear, left and right wheels is in a low pressure state; and a stable driving state of the vehicle in the vehicle motion state determining step.
The above wheel speed executed when it is determined for the first time that there is something
The wheel speed ratio calculated in the ratio calculation process and the vehicle stability described above
The above that is repeatedly executed while the driving state is being determined
Of the plurality of wheel speed ratios calculated in the wheel speed ratio calculation process,
Difference from at least one is greater than a second predetermined value
And at least one of the front, rear, left and right wheels has a reduced air pressure
And a second tire pressure drop determining step of determining that the tire is in a state . Wherein said second tire pressure drop judging process, every time the running of the vehicle with the engine start is performed
The method according to claim 1, wherein the method is executed .