JP2002002471A - Traction control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent malfunction of traction control. SOLUTION: This traction control method finds a measured wheel speed by a signal from a wheel speed sensor for each wheel, finds a correction wheel speed by multiplying each measured wheel speed by a correction coefficient, and calculates a slip ratio from the correction wheel speed to control the traction. The correction coefficient starts from an initial value smaller than 1 and is periodically calculated so that the correction wheel speed approaches the lowest measured wheel speed, the correction wheel speed is found by multiplying the measured wheel speed by the calculated correction coefficient. When the slip ratio found by the correction wheel speed is a slip threshold or more, the traction is controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to prevention of malfunction in traction control of a vehicle.

[0002]

2. Description of the Related Art Conventionally, when a mini-spare tire is mounted on a vehicle that performs traction control, the required wheel speed is apparently higher than it actually is, even if the wheel is rotating normally without slipping. As a result, since the slip ratio is calculated as increased, a malfunction may occur in the traction control. Further, the tire may be punctured, the diameter of the wheel may be reduced, and the traction control may malfunction as in the case of mounting the mini spare tire.
In addition, although the estimated vehicle speed is obtained using the signals of the wheel speed sensor and the G sensor, the slip ratio may also increase due to a decrease in the estimated vehicle speed due to factors such as a decrease in the output of the G sensor or a failure of the wheel speed sensor. , The traction control may malfunction.

[0003]

It is an object of the present invention to prevent a malfunction of traction control caused by an increase in a slip ratio. <B> Another object of the present invention is to prevent a malfunction of traction control due to replacement of a mini spare tire. <C> Another object of the present invention is to prevent traction control malfunction due to tire puncture. <D> Another object of the present invention is to prevent a malfunction of the traction control due to a decrease in the estimated vehicle speed.

[0004]

According to the present invention, a measured wheel speed is obtained from a signal from a wheel speed sensor of each wheel, a corrected wheel speed is obtained by multiplying each measured wheel speed by a correction coefficient, and a slip is calculated from the corrected wheel speed. In the traction control method of performing traction control by calculating the rate, the correction coefficient is calculated periodically starting from an initial value smaller than 1 so that the corrected wheel speed approaches the minimum measured wheel speed. Multiplying the measured wheel speed to obtain the corrected wheel speed, and when the slip ratio obtained from the corrected wheel speed is equal to or greater than the slip threshold, performing traction control, a traction control method, or
In the traction control method, when the correction coefficient is smaller than a control prohibition threshold, the traction control is characterized by prohibiting traction control, or, in the traction control method, during traction control, pressure increase or In the holding mode, when the state where the absolute value of the acceleration of the wheel is smaller than the predetermined value has continued for a predetermined time,
A traction control method, or a traction control method, wherein an initial value of the correction coefficient reduces a slip ratio based on a diameter of a mini spare tire provided in the vehicle. A traction control method characterized by setting the direction.

[0005]

Embodiments of the present invention will be described below with reference to the drawings.

<A> Vehicle control system A vehicle control system calculates a wheel speed, a wheel acceleration / deceleration, an estimated vehicle speed, etc. in a brake control as shown in FIG. An electronic control unit for issuing a control instruction; and a hydraulic unit that operates based on the control instruction from the electronic control unit. The hydraulic passage generated by the brake pedal 11, the master cylinder 12, and the main reservoir 13 is provided. Are connected to the wheel cylinders 14 of the respective wheels (left front wheel 1, right front wheel 2, left rear wheel 3, right rear wheel 4) via a hydraulic unit 20.

The rotation speed of each of the wheels 1 to 4 is measured by a wheel speed sensor 31 and input to an electronic control unit 30 to be used for calculating a wheel speed, a wheel acceleration / deceleration, a slip ratio and the like. Further, a signal from the G sensor 32 is also input to the electronic control unit 30 to calculate the acceleration / deceleration of the vehicle. The electronic control unit 30 has a configuration of a dedicated hardware device or a general computer device such as a microcomputer.

<B> Outline of Hydraulic Unit An example of the hydraulic unit 20 is shown in FIG. 2 and includes anti-lock brake control (ABS) and traction control (T).
CS) and other hydraulic circuits for brake control. FIG. 2 shows an example of the X pipe, and one of the first hydraulic circuits 21
Is connected to the right front wheel 2 and the left rear wheel 3, and the other independent second hydraulic circuit 22 is connected to the left front wheel 1 and the right rear wheel 4. The hydraulic unit 20 includes main hydraulic paths I and II connecting the wheel cylinders 14 of the respective wheels via the master cylinder 12 and the inlet valve 23, and an outlet valve 24, an auxiliary reservoir 27, and a pump 25 from the wheel cylinders 14 of the respective wheels. A return flow path 29 is provided to return to the main hydraulic pressure flow path I through the opening and closing of the inlet valve 23 and the outlet valve 24 and the pump 25 to perform predetermined brake control on each wheel. The main reservoir 13
Accumulates brake fluid, check valve 28 prevents backflow,
The motor 26 controls the driving of the pump 25.

<C> Measured wheel speed, corrected wheel speed and estimated vehicle speed The measured wheel speed of each wheel is obtained by processing a signal from a wheel speed sensor 31 attached to the wheel by the electronic control unit 30 and rotating the wheel. Obtained from speed. Therefore, when the normal tires are replaced with mini-spare tires having a small diameter, the measured wheel speeds calculated by the electronic control unit 30 are calculated to be relatively large even when the vehicle runs at the same speed because the rotation of the wheels becomes faster. You. In addition, even if the tire is punctured and the tire diameter is reduced, the measured wheel speed is similarly calculated to be relatively large. Therefore, the corrected wheel speed is calculated by multiplying the measured wheel speed by the correction coefficient. The estimated vehicle speed Vv is calculated using the wheel speed and the G sensor. For example, in the case of a two-wheel drive vehicle, it is estimated from the measured wheel speed Vk and the corrected wheel speed Vh of the non-driven wheels, and in the case of four-wheel drive, it is estimated in consideration of the minimum measured wheel speed and the output value of the G sensor. . The wheel acceleration / deceleration α is calculated from the amount of change in the measured wheel speed Vk and the corrected wheel speed Vh per unit time.

<D> Calculation of Slip Ratio The slip ratio is a ratio at which wheels are slipping with respect to the road surface. For example, the slip ratio S = (wheel speed−vehicle speed) /
(Vehicle speed). Here, the measured wheel speed Vk or the corrected wheel speed Vh can be used as the wheel speed, and the estimated vehicle speed Vv can be used as the vehicle speed.

<E> Traction control Traction control is for optimally controlling the braking force on the road surface when the wheels accelerate, and controls the brake fluid pressure of the wheels according to the degree of slip. For example, when the slip ratio indicating the degree of slip is equal to or greater than a predetermined threshold value, the traction control is started, and the wheel is controlled in a control mode such as a pressure increasing mode for increasing the brake fluid, a holding mode for holding, or a pressure reducing mode for reducing the pressure. Controls brake fluid pressure.

Hereinafter, a method for correcting the measured wheel speed will be described.

<A> Outline of Wheel Speed Correction Rather than determining whether each of the four wheels is a mini spare tire or whether the wheels are punctured, the measured wheel speeds of the four wheels are obtained. The corrected wheel speed is determined by correcting the measured wheel speed from the difference between the measured wheel speeds of the four wheels so that there is no difference in the wheel speed due to the difference in the diameter of the four wheels.

<B> Determination of Reference Measured Wheel Speed The measured wheel speed Vk is obtained by processing the signal of the wheel speed sensor for each wheel. Next, among the four measured wheel speeds Vk, the lowest measured wheel speed V estimated to be closest to the normal tire
min is selected as a reference measured wheel speed (Vref).

<C> Method of correcting the measured wheel speed The measured wheel speed Vk (Vk1, Vk2, Vk3,
Vk4) is calculated, and the minimum measured wheel speed Vmin is calculated from the calculated values.
Ask for. Assuming that the minimum measured wheel speed Vmin is the measured wheel speed V1, the measured wheel speed Vk (Vk1, Vk2, Vk3, Vk
k4) is multiplied by a correction coefficient K (1, K2, K3, K4), and the corrected wheel speed Vh (Vh
1, Vh2, Vh3, Vh4).

[0016]

(Equation 1)

[0017]

(Equation 2)

[0018]

(Equation 3)

[0019]

(Equation 4)

<D> Adjustment of the correction coefficient K The correction coefficient K takes an initial value for each wheel when the ignition of the vehicle is turned on. The initial value is set to a value smaller than 1, and is determined in a direction in which the traction control does not malfunction, for example, in consideration of a mini spare tire. That is, the slip amount calculated by the system is determined to be reduced. For example, the initial value of the correction coefficient is determined to be the wheel speed of a tire having a normal diameter, assuming that a mini spare tire is attached. In traction control,
Since the wheels having relatively high speeds enter control, if the diameter of the mini spare tire is small by about 12.5%, the initial value of the correction coefficient is set to approximately 0.875, so that the mini spare tire is mounted. However, there is no variation between the reference wheel speed and the corrected wheel speed immediately after the ignition is turned on.
Malfunction can be prevented.

The correction coefficient is periodically changed and adjusted so that the corrected wheel speed approaches the reference measured wheel speed (Vref). When the reference measured wheel speed (Vref) is the first wheel at the lowest measured wheel speed (Vmin), the correction coefficient (K1) of the lowest measured wheel speed (Vmin) is corrected so as to approach 1, and for example, Equation 5 The corrected wheel speed (Vh1) is determined as the measured wheel speed, and is calculated by the formula after the formula 5. The corrected wheel speeds of the other three wheels are obtained by Expressions 6 and 7. Here, when the corrected wheel speed exceeds the minimum measured wheel speed (Vmin), the corrected wheel speed is set to the minimum measured wheel speed (Vmin). As described above, by performing correction using the adjusted correction coefficient, the corrected wheel speed is adjusted to match the actual wheel speed. The cycle of this adjustment is determined as appropriate, and is performed, for example, every 0.9 sec.

[0022]

(Equation 5)

[0023]

(Equation 6)

[0024]

(Equation 7)

<E> Early wheel speed correction immediately after startup For a wheel whose measured wheel speed is closest to the minimum wheel speed and the minimum wheel speed, if the correction coefficient a is set to be larger than the other measured wheel speeds b, The minimum wheel speed and the correction coefficient of the wheel closest to the minimum wheel speed can be brought closer to 1 earlier than the initial value immediately after the start, which is set to prevent malfunction due to the installation of a mini spare tire or the like. In the normal case, since the four measured wheel speeds are almost the same, the wheel speed is almost equally selected as the minimum wheel speed and the wheel speed closest thereto due to fluctuations in the wheel speed and left and right turns. All four wheels can return from the initial value immediately after starting to the normal value 1 at a high speed. On the other hand, if a mini spare tire has been installed, the wheel does not reach the minimum wheel speed or the wheel speed closest to it at all after running, or the frequency is extremely low. Even in this case, the correction coefficient of the mini spare tire wheel converges to an appropriate value without causing control malfunction due to erroneous correction or the like.
At the same time, the wheels having the normal tire diameter are uniformly set to the minimum wheel speed or the wheel speed closest to the minimum wheel speed. Therefore, it is possible to quickly return to the normal value 1 and perform optimal control.

That is, normally, it is the correction amount of a that determines the time for completing the correction (from the initial value to the appropriate value).
The correction amount of c functions as a fine adjustment after the correction is completed. Therefore, by setting a to be large and c to be small, it is possible to quickly converge to an appropriate value after startup, and to make it less susceptible to fluctuations thereafter. In particular, since the correction amount for the outer wheel during turning is small, it is hardly affected by turning. Further, since the correction amount of the inner wheel and the outer wheel during turning is the same, even during turning, the diagonal difference ((front wheel left wheel speed-rear wheel right wheel speed)-(front wheel right wheel speed-rear wheel left) The balance of wheel speed)) = 0 is not lost, and the diagonal difference can be used for control as one index of wheel slip.

A method for preventing a malfunction of the traction control will be described below.

<A> Malfunction of Traction Control Malfunction of the traction control occurs when a mini-spare tire having a smaller diameter than usual and a mini-spare tire is mounted or a puncture occurs. For example, even if the mini spare tire grips the road surface, the output signal of the wheel speed sensor that measures the rotation of the wheel has a wheel speed higher than that of a normal tire.

When the slip ratio S exceeds the slip threshold due to the apparent wheel speed, the traction control is started even though the wheel is gripping the road surface,
The system enters the pressure increase mode in which the brake fluid pressure is increased, and the traction control malfunctions. As a result, undesired brake control is performed, such as increasing the brake fluid pressure without the need to increase the brake fluid pressure and conversely causing a slip.

In addition to the mounting of the mini spare tire and the puncturing of the tire, the estimated vehicle speed Vv is reduced, for example, the estimated vehicle speed is obtained using the signals of the wheel speed sensor and the G sensor. Even if the estimated vehicle speed decreases due to factors such as a decrease or a failure of the wheel speed sensor, the slip ratio is calculated as if it were increased, which may cause a malfunction in the traction control.

<B> Prevention of malfunction of traction control The malfunction of the traction control is corrected so that the output signal from the wheel speed sensor has a value similar to that of a normal wheel (wheel having a normal diameter). This can be prevented.

In the correction method, the measured wheel speed Vk obtained from the output value of the wheel speed sensor is multiplied by a correction coefficient K to obtain a value similar to that of a normal wheel. For example, taking a mini spare tire as an example, the diameter of the mini spare tire is 12.5 of the diameter of the normal tire.
%, The correction coefficient K is 0.875
It will be about.

In the case of a malfunction due to the installation of the mini spare tire, the wheel speed becomes an appropriate value or slightly smaller by this correction, and it is possible to escape from the malfunction.

<C> In the case of a tire having a smaller diameter than the mini spare tire, a tire puncture or a tire smaller than an assumed diameter,
For example, when a tire smaller by about 20% is mounted, the limit of the predetermined correction value is exceeded, so that control for multiplying the correction coefficient cannot be performed. In such a case, the off lamp is turned on to prohibit the traction control.

<D> Flow for preventing malfunction of traction control Traction control is performed for each wheel.
First, a measured wheel speed Vk is obtained from a signal from a wheel speed sensor of a certain wheel (S1). Next, the estimated vehicle speed Vv is calculated (S2). Note that the estimated vehicle speed Vv can be obtained by a conventionally performed method. Next, the corrected wheel speed Vh is calculated by multiplying the measured wheel speed Vk by the correction coefficient K (S3). Next, the wheel slip ratio S is calculated.
The slip ratio S is calculated by, for example, subtracting the estimated vehicle speed Vv from the corrected wheel speed Vh and dividing by the estimated vehicle speed Vv (S
4). Here, it is determined whether the traction control is being prohibited (S5). If the traction control is not prohibited, it is determined whether the slip ratio S is greater than a predetermined value (slip threshold) (S6).

If the slip ratio S is larger than the predetermined value (slip threshold value) at step S6, traction control is performed (S7). Next, if the pressure increasing or holding mode has not been continued for a predetermined time (duration, for example, 0.8 seconds) or more (S8), the procedure goes to step S14. When the pressure increasing or holding mode continues for 0.8 seconds or more (S8), a predetermined value (correction value, for example, 0.1) is subtracted from the correction coefficient K (S9). This correction value approximates the diameter of the mini spare tire,
The numerical value is determined by the speed of approach (how many loops to approach). Next, the procedure goes to step S14.

If the slip ratio S is smaller than the predetermined value (slip threshold value) in step S6, the traction control is not performed (S10), and the correction coefficient K is adjusted (S1).
1). Next, when the traction control is prohibited and the correction coefficient K is equal to or more than a predetermined value (controllable threshold, for example, 0.875) (S12), the traction control is enabled,
Then, the off lamp is turned off (S13), and step S14 is performed.
go to. When the traction control is prohibited and the correction coefficient K is not equal to or more than a predetermined value (controllable threshold value, for example, 0.875) (S12), the process proceeds to step S14. Note that the controllable threshold value 0.875 is set to be larger than the control prohibition threshold value 0.85 in consideration of hysteresis.

If the correction coefficient K is not equal to or smaller than the predetermined value (control prohibition threshold, for example, 0.85) in step S14 (S14), the processing of one loop is immediately terminated, and the correction coefficient K is set to the predetermined value (control prohibition threshold, In the case where the traction control is not more than 0.85) (S14), the traction control is prohibited and the off lamp indicating that the traction control is not performed is turned on (S15), and the processing of one loop is ended.

With the above processing, erroneous operation of traction control caused by an increase in the slip ratio can be prevented. As for the increase of the slip rate, besides installing mini spare tires,
There is a reduction in tire diameter due to a puncture of the tire, and a decrease in estimated vehicle speed due to a decrease in output of the G sensor or a failure in the wheel speed sensor. Due to these effects, a predetermined value (for example, 0.1) is subtracted from the correction coefficient K (S8), and the correction coefficient K is set to 0.
If it becomes less than 85 (S14), the traction control is prohibited, and it is possible to escape from the malfunction. Here, the decrease in the output of the G sensor includes, for example, a decrease in the measured value due to a deviation in the mounting angle of the G sensor and a decrease in the measured value due to the gradient of the road surface, and thereby the estimated vehicle speed decreases. As a result, the slip ratio S increases from the formula of the slip ratio S = (wheel speed−estimated vehicle speed) / estimated vehicle speed.

As described above, the correction coefficient K not only indicates the outer shape of the tire, but is also used as a coefficient for escape from malfunction due to an increase in the slip ratio.

[0041]

According to the present invention, the following effects can be obtained. <A> The present invention can easily escape from the malfunction of the traction control caused by the increase in the slip ratio. <B> Further, the present invention can easily escape from a malfunction of the traction control due to the replacement of the mini spare tire. <C> Further, the present invention can easily escape from the malfunction of the traction control malfunction due to the tire puncture. <D> Further, the present invention can easily escape from the malfunction of the traction control malfunction due to the decrease in the estimated vehicle body speed.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a vehicle brake system.

FIG. 2 is an explanatory view of a hydraulic unit.

FIG. 3 is a flowchart for preventing malfunction of traction control.

[Explanation of symbols]

 12, master cylinder 14, wheel cylinder 20, hydraulic unit 30, electronic control unit 31, wheel speed sensor 32, G sensor

Claims (4)

[Claims] The traction control is performed by obtaining a measured wheel speed from a signal from a wheel speed sensor of each wheel, obtaining a corrected wheel speed by multiplying each measured wheel speed by a correction coefficient, and calculating a slip ratio from the corrected wheel speed. In the traction control method to be performed, the correction coefficient is calculated periodically starting from an initial value smaller than 1 so that the corrected wheel speed approaches the minimum measured wheel speed, and the calculated correction coefficient is multiplied by the measured wheel speed to correct the corrected wheel speed. A traction control method comprising: determining a speed; and performing a traction control when a slip ratio calculated from the corrected wheel speed is equal to or greater than a slip threshold. 2. The traction control method according to claim 1, wherein the traction control is prohibited when the correction coefficient is smaller than a control prohibition threshold. 3. The traction control method according to claim 1, wherein during the traction control, in the pressure increasing or holding mode,
A traction control method characterized in that when a state in which the absolute value of the wheel acceleration is smaller than a predetermined value continues for a predetermined time, a predetermined value is subtracted from the correction coefficient. 4. The traction control method according to claim 1, wherein the initial value of the correction coefficient is set in a direction in which the slip ratio is reduced based on the diameter of a mini spare tire provided on the vehicle. , Traction control method.