KR20180060734A - Method for controlling wheel slip - Google Patents

Abstract

The present invention relates to a method for controlling a wheel slip, which can quickly reduce a wheel slip by controlling driving torque and braking torque of each wheel in advance when the wheel slip is increased while driving a vehicle. According to the present invention, the method for controlling a wheel slip comprises a control start step, a wheel drive torque calculation step, an engine drive torque generation step, a drive torque comparison step, and a wheel correction torque approval step.

Description

Method for controlling wheel slip < RTI ID = 0.0 >

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a wheel slip control method, and more particularly, to a wheel slip control method for preventing wheel slip by increasing engine torque to improve vehicle stability.

The increase in wheel slip during vehicle driving greatly affects the stability of the vehicle. When the front wheel slip excessively increases, the excessive use of the grip of the front wheel in the longitudinal direction decreases the frictional potential for the lateral grip, thereby deteriorating the steering ability of the tire. On the other hand, when the rear wheel slip is excessively increased, the lateral force potential of the rear wheel is similarly lowered, so that the vehicle spins also occur on a small road surface noise and the like. Therefore, when the wheel slip is increased on the low friction road including the high friction road surface, the stability of the vehicle is increased by controlling the wheel braking pressure through the ESC and ABS control.

The Engine Drag Torque Control function is used to control the engine drag torque when there is no braking pressure in the slippery road surface due to 1) quick release of the accelerator pedal, 2) gear shift, 3) ABS control, This is a control method for rapidly reducing the wheel slip by increasing the torque.

In this engine drag torque control, when the braking pressure actually exists, the braking pressure can be reduced to reduce the wheel slip. On the other hand, if there is no braking pressure to reduce the braking pressure, the engine torque is increased to reduce the wheel slip.

In the conventional engine drag torque control, for example, when the ABS braking torque increases and the wheel slip increases due to the increase of the wheel braking torque, the wheel braking torque is decreased by the ABS to reduce the wheel slip. However, when the braking pressure becomes zero during the reduction of the wheel slip, the wheel slip can not be reduced through the reduction of the braking pressure. Thus, by increasing the engine braking torque by increasing the negative target braking torque to increase the wheel slip, the vehicle stability is improved while achieving the previously designed ABS control target.

However, due to the characteristics of engine drag torque control, it is possible to reduce the wheel braking slip by increasing the engine torque only when the wheel slip of the drive shaft increases. Therefore, in the case of the non-driving wheel, the wheel slip can not be reduced by the conventional engine drag torque control, so that the stability of the non-driving wheel can not be increased. Also, by using the negative braking torque based on the existing slip control, there is a limit that the slip reduction can not be performed faster in the limit state of the slip control.

Korean Published Patent Application No. 2007-0106203 (November 1, 2007)

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above problems, and it is an object of the present invention to provide a braking force control apparatus and a braking control method thereof, The purpose is to increase stability.

In order to achieve the above object, in a preferred embodiment of the present invention, there is provided a wheel slip control method for a four-wheel drive vehicle, comprising: (a) initiating a wheel slip reduction control; (b) calculating a required drive torque of each wheel; (c) generating an engine drive torque according to the calculated required drive torque of each wheel; (d) comparing the required drive torque of the front wheel; (e) calculating a wheel correction torque, and applying a wheel correction torque as a braking torque.

Further, the present invention provides a wheel slip control method further comprising the step of transmitting a required drive torque of a rear wheel of the engine drive torque generated in the step (c) to a rear wheel by a 4WD (4-wheel drive).

Further, there is provided a wheel slip control method further comprising the step of distributing the drive torque transmitted to the rear wheels according to the required torque of each wheel by ELSD (Electronic Limited-Slip Differential).

The method further includes the step of calculating, as a front wheel driving torque, a torque excluding the driving torque transmitted to the rear wheel among the engine driving torque generated in the step (b).

Further, in the step (b), the necessary drive torque of each wheel is calculated by the following equation.

(Where, T _D, the driving _wy need for xy wheel torque, J is the wheel moment of inertia, ω _{des, wy} is xy angular acceleration of the wheel, T _{b, xy} is the braking torque, R _xy is the radius of the xy wheel of xy wheel , F _{z, xy} is the friction coefficient of the normal force, μ is _xy xy xy wheel of the wheel)

Further, in the step (c), the engine drive torque is determined by a sum of a larger value of the necessary driving torque of the front wheels and a required driving torque of the rear wheels.

In the step (a), the wheel pressure, the wheel pressure change rate, the wheel slip and the wheel slip change rate are detected, and the detected values are compared with a preset reference value to determine the wheel pressure, wheel pressure change rate, wheel slip, And the wheel slip reduction control is started only when the wheel slip control value is equal to or greater than the respective reference value.

According to the present invention, there is provided a wheel slip control method for a two-wheel drive vehicle, comprising: (a) calculating a required drive torque of each wheel; (b) generating an engine drive torque according to the calculated required drive torque of each wheel; (c) comparing the required drive torque of the front wheel; (d) calculating a wheel correction torque and applying the wheel correction torque to the braking torque.

Further, in the step (b), the engine drive torque is determined to be twice the larger of the required drive torque of the front wheels.

Further, in the step (a), the necessary drive torque of each wheel is calculated by the following equation.

(Where, T _D, the driving _wy need for xy wheel torque, J is the wheel moment of inertia, ω _{des, wy} is xy angular acceleration of the wheel, T _{b, xy} is the braking torque, R _xy is the radius of the xy wheel of xy wheel , F _{z, xy} is the friction coefficient of the normal force, μ is _xy xy xy wheel of the wheel)

In the step (a), the wheel pressure, the wheel pressure change rate, the wheel slip and the wheel slip change rate are detected, and the detected values are compared with a preset reference value to determine the wheel pressure, wheel pressure change rate, wheel slip, And the wheel slip reduction control is started only when the wheel slip control value is equal to or greater than the respective reference value.

According to the present invention, the wheel driving torque of the vehicle is independently controlled, thereby making it possible to rapidly reduce the slip of all the wheels irrespective of the front and rear wheels, out of the conventional method of controlling only the driving shaft.

Further, according to the present invention, the wheel slip is detected to be large in advance, and the wheel slip can be reduced more quickly by preferentially performing the engine drive torque control, thereby preventing the vehicle stability from deteriorating.

1 is a flowchart showing a wheel slip control method according to a first embodiment of the present invention,
Fig. 2 conceptually shows the control torque of the vehicle,
FIG. 3 is a graph showing a graph of a time-vehicle speed, (b) time-driving torque, and (c) time-braking torque in a wheel slip control method according to a preferred embodiment of the present invention,
4 is a flowchart showing a wheel slip control method according to a second embodiment of the present invention.

The present invention provides a method capable of rapidly reducing the slip of all wheels by independently controlling each wheel drive torque when the wheel slip is increased during vehicle driving. The present invention can be applied to a vehicle equipped with a 4WD (4-wheel drive) and an ELSD (Electronic Limited-Slip Differential), or even when a 4WD and an eLSD are not mounted.

Particularly, the present invention improves the situation in which only the existing driving axes can be controlled, and distributes the rear wheel driving torque using the two controllers related to 4WD and ELSD, thereby reducing the slip and increasing the vehicle stability even in the case of increase in rear wheel slip . In addition, in the front wheel torque control, the stability of the engine can be improved by controlling the engine drive torque according to a relatively large value of both wheel required torque, thereby reducing the slip of both front wheel wheels. Further, according to the present invention, since the braking torque calculation and the torque distribution are performed through a series of processes, a faster wheel slip reduction can be performed.

The present specification includes examples of vehicles not equipped with 4WD and ELSD as well as vehicles equipped with 4WD and ELSD.

In the present specification, the case where the engine is mounted on the front wheel side and the driving force is distributed through the ELSD in the case of the rear wheel side is described as a vehicle capable of four-wheel drive, but the 4WD and eLSD as well as the 4WD control The present invention is not limited to this embodiment as long as it is a system configuration capable of wheel drive torque distribution for the vehicle.

Hereinafter, a wheel slip control method according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

Fig. 1 is a flowchart showing a wheel slip control method for a four-wheel drive vehicle as a first embodiment of the present invention, and Fig. 2 conceptually shows a control torque of the vehicle.

In the wheel slip control method according to the present invention, when wheel slip is expected to occur, all the necessary driving torques of the wheels are combined to generate the engine driving torque in advance, and the excessive driving torque is corrected by correcting the braking torque. In addition, control is performed to perform braking force distribution to accurately apply the required driving torque to the rear wheels using 4WD and eLSD.

Specifically, referring to Fig. 1, it is firstly expected that the wheel slip will increase during driving of the vehicle, and the subsequent control is performed only when the wheel slip overload is expected according to the expected result. Step S101 is a step of determining a wheel slip excessive presumption condition. In this embodiment, the wheel pressure change rate, the wheel pressure, the wheel slip change rate, and the wheel slip are used as the wheel slip excessive condition. That is, as shown in FIG. 1, the reference value of the above-mentioned values is set in advance under the condition that the wheel slip is expected to increase, and the current wheel pressure change rate, the wheel pressure, the wheel slip rate, and the wheel slip value are compared with preset reference values can do. As a result, the engine drag torque control according to the present embodiment is implemented because the wheel slip excess expected condition is satisfied only when both the wheel pressure change rate, the wheel pressure, the wheel slip change rate, and the wheel slip value exceed the respective reference values.

The wheel slip control method according to the present invention is divided into four wheel drive or two wheel drive. That is, since the rear wheels are not controlled at the time of the two-wheel drive, only the drive torque distribution to the front wheels proceeds, and at the time of four-wheel drive, the drive torque distribution to the front and rear wheels is made.

First, referring to the time of four-wheel drive, FIG. 1 shows a method of controlling a wheel slip for a four-wheel drive vehicle, and a wheel slip overload is predicted through step S101. That is, in step S101, the wheel pressure, the wheel slip, and the respective change rates are detected and compared with the reference value to predict whether the wheel slip will be excessively increased.

1, in this step, the wheel pressure, the wheel pressure change rate, the wheel slip and the wheel slip change rate are detected, and the detected values are compared with preset reference values, It is determined whether the wheel slip change rate is equal to or greater than each reference value.

As a result of the determination, if all the values exceed the reference value, it is expected that the wheel slip is excessive, so that the wheel slip reduction control for reducing the wheel slip in advance is started. However, in this embodiment, it has been described that the wheel slip overload is predicted on the basis of the wheel pressure, the wheel pressure change rate, the wheel slip and the wheel slip change rate, but it is not limited to this example, Anything that can be expected to be excessive can be applied without limit. In this embodiment, only the case where the wheel pressure, the wheel pressure change rate, the wheel slip, and the wheel slip change rate are all above the reference value is limited, but the above values may be selected and applied.

On the other hand, the detailed control procedure for the wheel slip reduction is described in detail in steps S102 to S108.

First, if the wheel slip reduction control is started, the necessary drive torque necessary for wheel slip reduction for each wheel is calculated (S102). The required drive torque can be determined according to the wheel slip dynamics derived from the moment balance acting on the wheel, and such required drive torque can be calculated according to Equation 1 below.

(Where, T _D, the driving _wy need for xy wheel torque, J is the wheel moment of inertia, ω _{des, wy} is xy angular acceleration of the wheel, T _{b, xy} is the braking torque, R _xy is the radius of the xy wheel of xy wheel , F _{z, xy} is the friction coefficient of the normal force, μ is _xy xy xy wheel of the wheel)

If necessary driving torque necessary for each wheel is calculated, the required engine driving torque is generated in accordance with the calculated necessary driving torque (S103).

Here, the required engine drive torque is basically calculated by summing up the necessary drive torque values of the respective wheels. In particular, in the case of the front wheels, the required drive torque of the left wheel and the right wheel is set to a larger value. That is, the engine drive torque is determined by the sum of the larger of the required drive torque of the front wheels and the required drive torque of the rear wheels, as shown in Equation 2 below.

(Where, T _D is the engine-demanded drive torque, T _{D, wy} is required drive torque, T _D for the xy _{wheel, FL} is a front side jwaryun required drive torque, T _{D, FR} is necessary drive torque of the front right wheel, T _{D , RL} is the required drive torque of the rear left wheel, T _{D and RR} are the required drive torque of the rear right wheel)

If the required drive torque of the engine is generated, the drive torque of the engine thus generated is distributed to the front wheels and the rear wheels (S104 and S105), and the wheel correction torque for correcting the drive torque excessively applied to the front wheels is applied as the braking torque (S107, 108).

Specifically, as shown in step S104, the 4WD (4-wheel drive) transmits the necessary drive torque to the rear wheels. That is, as shown in Equation 3 below, the required drive torque of the rear wheel among the generated engine drive torques is transmitted to the rear wheels.

(Where, T _D, is _Rear Wheel full required demand torque, T _{D, RL} is the rear jwaryun required drive torque, T _D, the drive torque of the rear right wheel _RR is required)

Here, the driving torque transmitted to the rear wheels can be distributed according to the required torque of each wheel by ELSD (Electronic Limited-Slip Differential). That is, when the rear wheel is transmitted to the rear wheels by the required total torque of the rear wheels, the ELSD controls the rear wheel left and right torque difference as shown in Equation (4) below, whereby the driving torque transmitted to the rear wheels is distributed according to the required torque of each wheel S105).

(Where, ΔT _{D, Rear} left and right rear wheel torque difference is, T _{D, RL} is the rear jwaryun required drive torque, T _D, the drive torque of the rear right wheel _RR is required)

On the other hand, as shown in Equation 5 below, the torque excluding the drive torque transmitted to the rear wheel among the generated engine drive torque becomes the front wheel drive torque and is transmitted to the front wheel side (S106).

(Where, T _D, the total drive torque of the front wheels _Front, T _D is the engine-demanded drive torque, T _{D, RL} is the rear jwaryun required drive torque, T _D, the drive torque of the rear right wheel _RR is required)

When the engine drive torque is transmitted to the front wheels through the above steps, a relatively large value of the drive torque is applied to the front wheels as compared with the required drive torque of the front wheels calculated in the first step S102. This is because the required drive torque of the engine is calculated on the basis of the required drive torque of a large value in the case of the front wheels, not in the case where the required drive torque of the engine is calculated as the sum of the required drive torques of the wheels in step S103 to be.

Therefore, in the present embodiment, it is possible to suppress the wheel slip prematurely by correcting the excessively applied necessary drive torque by the braking torque.

Specifically, according to this embodiment, through step S107, the required drive torque of the front wheel is compared. In this step, a wheel corresponding to a relatively small required driving torque is to be identified. In the case of a wheel requiring a relatively small required driving torque, the wheel correcting torque is determined by the difference in the required driving torque. Therefore, the wheel correction torque calculated in step S108 is an absolute value with respect to the difference between the required drive torques of the respective front wheel wheels, and the wheel correction torque for each case is expressed by the following equations (6) and (7).

(i) T _{D , FL} ≥ T _{D , FR}

(ii) T _{D , FR} > T _{D , FL}

(Where, T _{b, FR} is a front right wheel of the wheel torque correction, T _{b, FL} is a front jwaryun of wheel torque correction, P _{comp, FR} are corrected braking pressure, C _{p, FR} is the torque conversion factor of the front right wheel of the front right wheel , P _{comp , FL} is the correction braking pressure of the front left wheel, C _{p , FL} is the torque conversion coefficient of the front left wheel)

On the other hand, as shown in the step S108 and the above equations 6 and 7, the calculated wheel correction torque is converted into the braking torque, and the braking torque corresponding to the wheel correction torque is applied to cancel the excessive engine torque.

FIG. 3 shows changes in time-to-vehicle speed, (b) time-drive torque, and (c) time-braking torque according to the wheel slip control method according to the present embodiment.

That is, as shown in the time-drive torque graph of FIG. 3 (b), the engine drive torque is applied in advance at the time when the excessive slip is expected, so that a part of the drive torque added is the braking torque is compensated In the example of (3), braking torque compensation is applied to the front right wheel (FR) wheel so that (a) as shown in the time-vehicle speed graph, the wheel speed follows the vehicle speed quickly before the wheel slip becomes excessive (A portion indicated by a solid line in (a)).

After the engine drive torque and the braking torque for the slip control are applied to the respective wheels through the process of steps S102 to S108, the slip control and other controls are performed according to the general control logic (S109). That is, after the drive torque necessary for the slip and the braking torque for correcting the slip are applied to each wheel to control the wheel slip to be rapidly reduced, the 4WD, the ELSD, etc. perform basic control according to the control logic , The slip control is also performed in a predetermined manner, for example, a basic slip control in the ABS situation.

On the other hand, the case of the two-wheel drive vehicle is substantially the same as that of the example of Fig. 1, except that a portion of the engine drive torque is distributed to the rear wheels as compared with the case of the four-wheel drive vehicle.

That is, as shown in FIG. 4, it is determined in step S201 whether the wheel slip is excessive, and when the wheel slip over is expected, the wheel slip reduction control is started.

That is, in step S202, the necessary drive torque of the front wheel is calculated according to the above-described equation 1 derived from the wheel moment balance, and the braking torque corresponding to the engine drive torque and the wheel correction torque is applied to the front wheel.

Specifically, the required torque of the engine is determined to be twice the larger value of the required driving torque of the front wheels, and this torque is generated as the engine driving torque.

Then, in step S203, the necessary drive torque of the front wheel is compared, the wheel correction torque is calculated according to the comparison result, and the calculated torque is applied as the braking torque (S204).

Thereafter, a general basic slip control is performed in the same manner as in the conventional method (S205).

While the present invention has been described with reference to the preferred embodiments, those skilled in the art will appreciate that modifications and variations are possible in the elements of the invention without departing from the scope of the invention. In addition, many modifications may be made to the particular situation or material within the scope of the invention, without departing from the essential scope thereof. Therefore, the present invention is not limited to the detailed description of the preferred embodiments of the present invention, but includes all embodiments within the scope of the appended claims.

Claims (11)

A wheel slip control method for a four-wheel drive vehicle,
(a) initiating wheel slip reduction control;
(b) calculating a required drive torque of each wheel;
(c) generating an engine drive torque according to the calculated required drive torque of each wheel;
(d) comparing the required drive torque of the front wheel; And
(e) calculating a wheel correction torque, and applying a wheel correction torque as a braking torque;
/ RTI >
The method according to claim 1,
Further comprising the step of transmitting the required drive torque of the rear wheel among the engine drive torque generated in the step (c) to the rear wheels by a 4WD (4-wheel drive).
The method of claim 2,
Further comprising the step of distributing the drive torque transmitted to the rear wheels according to the required torque of each wheel by ELSD (Electronic Limited-Slip Differential).
The method according to claim 2 or 3,
And calculating a torque, excluding a drive torque transmitted to the rear wheel, of the engine drive torque generated in the step (b) to a front wheel drive torque.
The method according to claim 1,
In the step (b), the required drive torque of each wheel is calculated by the following equation

(Where, T _D, the driving _wy need for xy wheel torque, J is the wheel moment of inertia, ω _{des, wy} is xy angular acceleration of the wheel, T _{b, xy} is the braking torque, R _xy is the radius of the xy wheel of xy wheel , F _{z, xy} is the friction coefficient of the normal force, μ is _xy xy xy wheel of the wheel)
The wheel slip control method comprising:
The method according to claim 1,
Wherein in the step (c), the engine drive torque is determined by a sum of two times larger of the required drive torque of the front wheels and the required rear wheel drive torque.
The method according to claim 1,
In the step (a), the wheel pressure, the wheel pressure change rate, the wheel slip and the wheel slip change rate are detected, and the detected values are compared with a predetermined reference value to determine the detected wheel pressure, wheel pressure change rate, wheel slip, And the wheel slip reduction control is started only when it is equal to or greater than the reference value.
A method of controlling a wheel slip of a two-wheel drive vehicle,
(a) calculating a required drive torque of each wheel;
(b) generating an engine drive torque according to the calculated required drive torque of each wheel;
(c) comparing the required drive torque of the front wheel; And
(d) calculating a wheel correction torque, and applying a wheel correction torque as a braking torque;
/ RTI >
The method of claim 8,
Wherein in the step (b), the engine drive torque is determined to be twice the larger of the required drive torque of the front wheels.
The method of claim 8,
In the step (a), the required drive torque of each wheel is calculated by the following equation

(Where, T _D, the driving _wy need for xy wheel torque, J is the wheel moment of inertia, ω _{des, wy} is xy angular acceleration of the wheel, T _{b, xy} is the braking torque, R _xy is the radius of the xy wheel of xy wheel , F _{z, xy} is the friction coefficient of the normal force, μ is _xy xy xy wheel of the wheel)
The wheel slip control method comprising:
The method of claim 8,
In the step (a), the wheel pressure, the wheel pressure change rate, the wheel slip and the wheel slip change rate are detected, and the detected values are compared with a predetermined reference value to determine the detected wheel pressure, wheel pressure change rate, wheel slip, And the wheel slip reduction control is started only when it is equal to or greater than the reference value.

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