KR102322365B1 - Method for controlling wheel slip - Google Patents

Abstract

The present invention relates to a wheel slip control method for rapidly reducing wheel slip by controlling a driving torque and a braking torque of each wheel in advance when wheel slip is increased while driving a vehicle.

Description

Wheel slip control method {Method for controlling wheel slip}

The present invention relates to a wheel slip control method, and more particularly, to a wheel slip control method for improving vehicle behavioral stability by preventing wheel slip by increasing engine torque.

An increase in wheel slip during vehicle driving has a significant impact on vehicle stability. When the front wheel slip is excessively increased, the frictional force potential for the lateral grip is reduced as the grip of the front wheel is used excessively in the longitudinal direction, and thus the steering ability of the tire is deteriorated. On the other hand, when the rear wheel slip is excessively increased, as the lateral force potential of the rear wheel is similarly lowered, vehicle spin occurs even with small road surface noise, which greatly affects the driver's sense of disparity as well as safety. Accordingly, when wheel slip is increased, especially on a low-friction road surface, including a high-friction road surface, the vehicle stability is increased by controlling the wheel braking pressure through ESC and ABS control.

The Engine Drag Torque Control function provides an engine drag torque control function when there is no braking pressure when wheel slip is increased in situations such as 1) quick release of the accelerator pedal, 2) gear shifting, 3) ABS control, etc. on a slippery road surface. It is a control method to quickly reduce wheel slip by increasing torque.

When controlling the drag torque of the engine, when the braking pressure is actually present, the braking pressure may be reduced to reduce wheel slip. On the other hand, when there is no braking pressure to be reduced due to the reduced braking pressure, the engine torque is increased to reduce wheel slip.

In the existing engine drag torque control, for example, in the ABS situation, when the wheel braking torque increases and the wheel slip increases and the ABS enters, the wheel braking torque is decreased by the ABS to reduce the wheel slip. However, if the braking pressure becomes 0 while reducing the wheel slip, it is no longer possible to reduce the wheel slip by reducing the braking pressure. Therefore, by increasing the engine braking torque by the increase in the negative target braking torque to increase wheel slip, the previously designed ABS control target is achieved and vehicle stability is increased.

However, due to the characteristics of the engine drag torque control, it is possible to increase the engine torque only when the wheel slip of the drive shaft increases to reduce the wheel braking slip. Therefore, in the case of the non-drive shaft wheel, the wheel slip cannot be reduced by the existing engine drag torque control, and thus the stability of the non-driven wheel cannot be increased. In addition, there is a limit that a faster slip reduction cannot be achieved in the limit situation of the slip control by using the negative braking torque by the existing slip control.

Korean Patent Publication No. 2007-0106203 (2007. 11. 1)

The present invention has been devised to solve the above problems. In the present invention, when there is no braking force in a situation in which wheel slip increases while driving a vehicle, the driving torque and braking torque of each wheel are controlled to quickly reduce slip. 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 the steps of: (a) initiating wheel slip reduction control; (b) calculating the required driving torque of each wheel; (c) generating an engine driving torque according to the calculated required driving torque of each wheel; (d) comparing the required driving torque of each front wheel; (e) calculating the wheel correction torque, and applying the wheel correction torque as the braking torque; provides a wheel slip control method comprising a.

In addition, there is provided a wheel slip control method further comprising the step of transmitting a necessary driving torque of the rear wheels to the rear wheels among the engine driving torques generated in step (c) by using 4WD (4-wheel drive).

In addition, it provides a wheel slip control method further comprising the step of distributing the driving torque transmitted to the rear wheels by the ELSD (Electronic Limited-Slip Differential) according to the requested torque of each wheel.

In addition, the method provides a wheel slip control method further comprising: calculating a torque excluding the driving torque transmitted to the rear wheel from among the engine driving torque generated in step (b) as a front wheel driving torque.

In addition, in the step (b), the required driving torque of each wheel provides a wheel slip control method, characterized in that calculated by the following equation.

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

Further, in the step (c), the engine driving torque is provided as a wheel slip control method, characterized in that it is determined by the sum of twice the larger value of the required driving torques of the front wheels and the required driving torque of the rear wheels.

In addition, in step (a), wheel pressure, wheel pressure change rate, wheel slip and wheel slip change rate are detected, and the detected values are compared with a preset reference value, and the detected respective wheel pressure, wheel pressure change rate, wheel slip and wheel slip change rate are obtained. Provided is a wheel slip control method characterized in that the wheel slip reduction control is started only when the respective reference values are greater than or equal to each reference value.

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

In addition, in the step (b), the engine driving torque is provided as a wheel slip control method, characterized in that it is determined to be twice the larger value of the required driving torque of the front wheels.

In addition, in the step (a), the required driving torque of each wheel provides a wheel slip control method, characterized in that calculated by the following equation.

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

In addition, in step (a), wheel pressure, wheel pressure change rate, wheel slip and wheel slip change rate are detected, and the detected values are compared with a preset reference value, and the detected respective wheel pressure, wheel pressure change rate, wheel slip and wheel slip change rate are obtained. Provided is a wheel slip control method characterized in that the wheel slip reduction control is started only when the respective reference values are greater than or equal to each reference value.

According to the present invention, by independently controlling the driving torque of each wheel of the vehicle, there is an effect that it is possible to quickly reduce the slip of all wheels regardless of the front and rear wheels, away from the conventional method of controlling only the drive shaft.

In addition, according to the present invention, it is possible to reduce the wheel slip more quickly by detecting in advance that the wheel slip will increase and preferentially controlling the engine driving torque through this, thereby preventing deterioration of vehicle stability.

1 is a flowchart illustrating a wheel slip control method according to a first embodiment of the present invention;
2 is a conceptual diagram illustrating the control torque of the vehicle,
3 is a graph showing (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 illustrating a wheel slip control method according to a second embodiment of the present invention.

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

In particular, the present invention improves the situation in which only the existing drive shaft can be controlled and distributes the rear wheel drive torque using two controllers related to 4WD and ELSD, thereby reducing slip even in the case of an increase in rear wheel slip, thereby increasing vehicle stability. . Also, in the front wheel torque control, by controlling the engine driving torque according to a relatively large value of the torque required for both wheels, it is characterized in that it is possible to increase the stability by reducing the slip of both front wheels. In addition, according to the present invention, since braking torque calculation and torque distribution are performed through the suggested series of processes, there is another feature in that wheel slip can be reduced faster.

In this specification, examples of vehicles equipped with 4WD and ELSD, as well as vehicles without 4WD and ELSD are included.

In addition, in this specification, as a vehicle capable of four-wheel drive, 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. If it is a system configuration capable of distributing wheel drive torque for , it is not limited to this embodiment.

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.

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

In the wheel slip control method according to the present invention, when wheel slip is expected to occur, the engine driving torque is generated in advance by adding up all the driving torques required by each wheel, and the excessive driving torque is corrected by correcting the braking torque. In addition, the control is performed to distribute the braking force to accurately apply the driving torque required to the rear wheels using the 4WD and eLSD.

Specifically, referring to FIG. 1 , it is preferentially predicted that wheel slip will increase during vehicle driving, and subsequent control is performed only when excessive wheel slip is expected according to the expected result. Step S101 is a step of determining an excessive wheel slip expected condition. In the present embodiment, a wheel pressure change rate, wheel pressure, wheel slip change rate, and wheel slip are used as the excessive wheel slip expected condition. That is, as shown in FIG. 1, under the condition that wheel slip is expected to increase, the reference values of the above suggested values are preset, and the current wheel pressure change rate, wheel pressure, wheel slip change rate, and wheel slip value are compared with preset reference values, respectively. can do. Through this, the wheel pressure change rate, the wheel pressure, the wheel slip change rate, and the wheel slip value are considered to satisfy the excessive wheel slip expectation condition only when all of the reference values exceed the respective reference values, so that the engine drag torque control according to the present embodiment is performed.

The wheel slip control method according to the present invention is divided according to whether the four-wheel drive or the two-wheel drive is performed. That is, in the case of two-wheel driving, since control to the rear wheels is not performed, only the driving torque distribution to the front wheels is performed, and in the case of four-wheel driving, the driving torque is distributed to the front and rear wheels.

First, looking at the case of four-wheel drive, FIG. 1 shows a wheel slip control method for a four-wheel drive vehicle, and excessive wheel slip is expected through step S101. That is, in step S101, the wheel pressure, the wheel slip and each change rate are detected, and by comparing them with a reference value, it is predicted whether the wheel slip will increase excessively.

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

As a result of the determination, if all values exceed the reference value, excessive wheel slip is expected, and thus wheel slip reduction control for reducing wheel slip in advance is started. However, in the present embodiment, it has been described that excessive wheel slip is expected based on wheel pressure, wheel pressure change rate, wheel slip and wheel slip change rate, but predicting that wheel slip will increase excessively is not limited to this example, and wheel slip It can be applied without limitation as long as an overdose can be expected. Also, in the present embodiment, only the case where the wheel pressure, the wheel pressure change rate, the wheel slip, and the wheel slip change rate are all greater than or equal to the reference values are limited, but the above values may be selected and applied.

Meanwhile, a specific control process for reducing wheel slip is described in detail in steps S102 to S108.

First, if wheel slip reduction control is started, a necessary driving torque required for wheel slip reduction is calculated for each wheel ( S102 ). The required driving torque may be determined according to the wheel slip dynamics derived from the moment equilibrium acting on the wheel, and this required driving torque may be calculated according to Equation 1 below.

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

If the required driving torque required for each wheel is calculated, the required engine driving torque is generated according to the calculated required driving torque (S103).

Here, the required engine driving torque is basically calculated by adding up the required driving torque values of each wheel. In particular, in the case of the front wheel, the larger value of the required driving torque of the left wheel and the right wheel is set to be the same. That is, as shown in Equation 2 below, the engine driving torque is determined by the sum of twice the larger value of the required driving torques of the front wheels and the required driving torque of the rear wheels.

(Where, T _D is the engine required driving torque, T _{D , wy} is the required driving torque for the xy wheel, T _{D , FL} is the required driving torque of the front left _{wheel, T D , FR} are the required driving torque of the front right wheel, T _{D , RL} is the required driving torque of the rear left _{wheel, T D , RR} is the required driving torque of the rear right wheel)

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

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

(Here, T _{D , Rear} is the required torque of the entire rear wheel, T _{D , RL} is the required driving torque of the rear left _{wheel, T D , RR} is the required driving torque of the right rear wheel)

Here, the driving torque transmitted to the rear wheels may be distributed according to the requested torque of each wheel by ELSD (Electronic Limited-Slip Differential). That is, when the required torque of the entire rear wheel is transmitted to the rear wheels, the torque difference between the rear wheels is controlled by the ELSD as shown in Equation 4 below, and accordingly, the driving torque transmitted to the rear wheels is distributed according to the required torque of each wheel ( S105).

(Where ΔT _{D , Rear} is the torque difference between the left and right rear wheels, T _{D , RL} are the required driving torques of the rear left _{wheel, and T D,RR} are the required driving torques of the rear right wheels)

Meanwhile, as shown in Equation 5 below, the torque excluding the driving torque transmitted to the rear wheel among the generated engine driving torque becomes the front wheel driving torque and is transmitted to the front wheel (S106).

(Here, T _{D , Front} is the driving torque of the entire front wheel, T _D is the engine required driving torque, T _{D , RL} is the required driving torque of the rear left _{wheel, and T D , RR} is the required driving torque of the right rear wheel)

When the engine driving torque is transmitted to the front wheel through the above steps, a driving torque having a relatively greater value than the required driving torque of the front wheel calculated in the first step S102 is applied to the front wheel. This is because, in step S103, the required driving torque of the engine is calculated based on the required driving torque of a large value in the case of the front wheel side, rather than the value obtained by adding up the required driving torque of each wheel. am.

Accordingly, in the present embodiment, by correcting the excessively applied necessary driving torque by the braking torque, it is possible to suppress wheel slip early.

Specifically, according to this embodiment, through step S107, the required driving torque of each front wheel is compared. In this step, the wheel corresponding to a relatively small required driving torque is identified. In the case of a wheel requiring a relatively small required driving torque, the difference between the required driving torque is determined as the wheel correction torque. Accordingly, the wheel correction torque calculated in step S108 is an absolute value for the difference between the required driving torques of the respective front wheels, and the wheel correction torques for each case are as shown in Equations 6 and 7 below.

(i) T _{D , FL} ≥ T _{D , FR}

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

(Here, T _{b , FR} are the wheel correction torque of the front right wheel, T _{b , FL} are the wheel correction torque of the front left wheel, P _{comp , FR} are the corrected braking pressure of the front right wheel, C _{p , FR} are the torque conversion factors of the front right wheel , P _{comp , FL} are the corrected braking pressure of the front left wheel, C _{p , FL} are the torque conversion factors of the front left wheel)

Meanwhile, as shown in step S108 and Equations 6 and 7 above, the calculated wheel correction torque is converted into braking torque, and a braking torque equal to the wheel correction torque is applied to offset excessive engine torque.

3 illustrates changes in (a) time-vehicle speed, (b) time-driving torque, and (c) time-braking torque according to the application of the wheel slip control method according to the present embodiment.

That is, as shown in the time-driving torque graph of (b) of FIG. 3 , the engine driving torque is applied in advance at a time when excessive slip is expected, and the braking torque is compensated (Fig. In the example of 3, the braking torque compensation for the front right wheel (FR) wheel is implemented, so that, as shown in (a) time-vehicle speed graph, the wheel speed quickly follows the vehicle speed before wheel slip becomes excessive as in the graph indicated by the dotted line. It can be seen that the control (the part indicated by the solid line in (a)) is controlled so that

After the engine driving torque and braking torque for slip control are applied to each wheel through the processes of steps S102 to S108, slip control and other controls are performed according to a general control logic (S109). That is, after the driving torque required for slip and the braking torque to correct it are applied to each wheel and control to quickly reduce wheel slip, basic control is performed for 4WD and ELSD according to the previously set control logic. , slip control is also performed in a preset manner, for example, control such as basic slip control in an ABS situation.

Meanwhile, in the case of the two-wheel drive vehicle, compared to the case of the four-wheel drive vehicle, it is substantially the same as the example of FIG. 1 , except that a portion of the engine driving torque is distributed to the rear wheels.

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

That is, in step S202, the required driving torque of each of the front wheels is calculated according to Equation 1 above induced by the wheel moment equilibrium, and accordingly, the braking torque corresponding to the engine driving torque and the wheel correction torque is applied to each of the front wheels.

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

Thereafter, in step S203, the required driving torques of the front wheels are compared, and the wheel correction torque is calculated according to the comparison result and applied as the braking torque (S204).

After that, the general basic slip control is performed in the same way as in the conventional method (S205).

Although the present invention has been described with reference to preferred embodiments, it will be understood by those skilled in the art that modifications and changes can be made to elements of the present invention without departing from the scope of the present invention. In addition, many changes may be made to materials or specific circumstances without departing from the essential scope of the present invention. Therefore, the present invention is not limited to the detailed description of the preferred embodiments of the present invention, but it is intended to cover all embodiments within the scope of the appended claims.

Claims (11)

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

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

(Where T _{D , wy} is the required driving torque for the xy wheel, J is the wheel moment of inertia, ω _{des , wy} is the angular acceleration of the xy wheel, T _{b , xy} is the braking torque _{of the xy wheel, and R xy} is the radius of the xy wheel , F _{z , xy} is the normal force of the xy wheel, μ _xy is the friction coefficient of the xy wheel)
Wheel slip control method characterized in that.
9. The method of claim 8,
In step (a), wheel pressure, wheel pressure change rate, wheel slip, and wheel slip change rate are detected, the detected values are compared with a preset reference value, and each detected wheel pressure, wheel pressure change rate, wheel slip and wheel slip change rate are respectively A wheel slip control method, characterized in that the wheel slip reduction control is started only when it is equal to or greater than a reference value.

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