KR101687561B1 - Power steering system and control method thereof - Google Patents

Abstract

A power steering system and a control method thereof according to the present invention are characterized in that in a counter steer mode of a driver implemented in an over steer or an under steer mode, the degree of oversteer or understeer The assist steering assist is assisted by the total assist torque amount obtained by adding the secondary assist torque amount corresponding to the steering angle of the steering handle to the first assist torque amount according to the steering angle of the steering wheel, .

Description

[0001] POWER STEERING SYSTEM AND CONTROL METHOD THEREOF [0002]

The present invention relates to a power steering system and a control method thereof, and more particularly, to an electronic stability control (ESC) A method of controlling a steering assist system, comprising the steps of: generating a total assist torque by adding a second assist torque amount to a first assist torque amount in a counter steer mode of a driver implemented when the steering wheel is over steer or under steer; Steering torque is controlled by the amount of torque to reduce steering weight so that the driver has a sense of steering resilience and stability, and a control method thereof.

In general, when the driver suddenly rotates the steering wheel at the time of driving the vehicle, or when the vehicle suddenly turns according to the traveling road surface state, the electronic stability control (ESC) System) is provided.

During normal driving, if the vehicle turns or changes lanes, the steering of the steering wheel is rotated according to the driver's will to follow the movement of the vehicle. However, since the coefficient of friction of the road surface is low, When an abrupt change occurs due to a vehicle speed, steering, etc., an understeer or an oversteer phenomenon occurs.

Here, the over-steering phenomenon refers to a state in which a slip phenomenon may occur on the outer-wheel side when the yaw rate of the vehicle under running is larger than the target yaw rate, and the under-steering phenomenon refers to a state in which the yaw rate Is lower than the target yaw rate, there is a possibility that a sliding phenomenon may occur on the inner wheel side.

As described above, the ESC is configured to provide a braking input to the outer ring or the inner ring side in a direction to stabilize the posture of the vehicle in the area where the oversteer or understeer phenomenon occurs, when the vehicle suddenly turns and the steering wheel suddenly steers Or by adjusting the output of the engine, thereby improving the stability of the vehicle.

In recent years, by interlocking the ESC with a power steering system of a motor drive system (MDPS), the amount of steering torque of the MDPS is changed in accordance with the operating state of the ESC in the understeer or oversteer situation, The steering performance of the steering wheel is improved as well as the steering of the driver is stabilized in a direction to stabilize the behavior of the steering wheel.

However, the control method of the power steering system according to the related art has a problem that when the vehicle suddenly turns, such as a lane change, that is, in the understeer or oversteer condition, the steering torque is changed to the counter- In the counter-steer mode as described above, an artificial steering force is applied, which causes a driver to feel a sense of steering disturbance.

In addition, in the oversteer situation, there is a problem that steering stability (flick steer) adversely affects at high speed due to high frictional force because a single impulse type steering force (steering torque) is applied.

The present invention relates to a method of controlling a power steering system in which an ESC (Electronic Stability Control) is used to steer a steering wheel of a vehicle using a motorized driving system (MDPS), wherein the oversteer or understeer In the counter steer mode of the driver, which is implemented at the time of understeering, by controlling the total assist torque amount by adding the second assist torque amount to the first assist torque amount, the driver can reduce the steering weight, And a control method of the power steering system.

A power steering system according to the present invention is a motor-driven (MDPS) power steering system in which the operation of a steering wheel is controlled by an ESC for sensing and stabilizing the behavior of a vehicle, A countersteering mode in which the understeer or the oversteer is determined based on a difference between a rate and a target yaw rate, and a countersteering mode in which the driver steers the steering handle to stabilize the posture of the vehicle at the occurrence of the understeer or the oversteer And a second assist torque corresponding to the steering angle of the steering wheel is added to the first assist torque corresponding to the degree of the understeer or the oversteer in the countersteering mode, The assist torque is inputted to the steering wheel, To assist with the steering of the steering wheel ring.

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A control method of a power steering system according to the present invention is a control method of a motor-driven (MDPS) power steering system in which the operation of a steering wheel is controlled by an ESC for detecting and stabilizing the behavior of the vehicle, Determining an understeer and an oversteer of the vehicle on the basis of a difference between a yaw rate and a target yaw rate of the vehicle; and, when the understeer or the oversteer is generated, Determining whether the vehicle is in a counter steer mode based on the steering angle of the steering wheel when the vehicle is in the counter steer mode; The total assist torque plus the vehicle assist torque And steering the steering wheel by inputting it to the steering wheel.

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The power steering system and the control method thereof according to the present invention can improve the steering disturbance as well as improve the steering feel by inputting and controlling the secondary assist torque value according to the steering angle magnitude before the control by the ESC, Effect.

Further, the power steering system and its control method according to the present invention can prevent incorrect steering by giving a steering weight when the driver steers the steering steering wheel in an abnormal turning direction during the countersteering mode control by the ESC, When the steering wheel is steered in the turning direction, it helps to steer more quickly, thereby giving a feeling of quick operation.

1 is a schematic view showing an abnormal turning phenomenon of a vehicle and a steering weight control in a counter-steer mode control according to the abnormal turning phenomenon,
2 and 3 are graphs comparing the conventional control method of the power steering system and the control method of the power steering system according to the present invention,
4 is a block diagram showing a control method of the power steering system according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a preferred embodiment of a method of controlling a power steering system according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a schematic view showing an abnormal turning phenomenon of a vehicle and a steering weight control in a counter-steer mode control according to the vehicle. FIG. 2 and FIG. 3 are diagrams showing a control method of a conventional power steering system and a control method of a power steering system according to the present invention FIG. 4 is a block diagram showing a control method of the power steering system according to the present invention.

The power steering system according to the present invention includes an electronic stability control system (ESC) that performs control to stabilize the posture of the vehicle when the vehicle is turning or steeply steering the steering wheel.

The control method of the power steering system according to the present invention proposes concrete control of the ESC, and in particular, when the vehicle is suddenly turned when the vehicle is controlled so that the running of the vehicle is stabilized by the ESC, The control logic for preventing the steering wheel from being broken and recognizing the steering wheel and for handling the steering wheel in a stable state can be more easily performed.

More specifically, when it is determined that the vehicle suddenly turns while driving, or when the driver steers the steering wheel suddenly, that is, in an abnormal driving state, the ESC applies the braking input in a direction to stabilize the posture of the vehicle.

1, when the center of gravity of the vehicle is shifted to the rear wheel side when the vehicle suddenly turns, and the front wheel side is moved in the normal turning direction of the vehicle The understeer 10a (under-steer) phenomenon in which the center of gravity moves to the outside of the vehicle 10 and the vehicle finally travels outside the normal turning direction 10, The center of gravity of the vehicle is shifted to the front wheel side and the center of gravity moves to the outside of the normal turning direction 10 of the vehicle on the rear wheel side with the front wheel side as the center of gravity so that the vehicle finally reaches the inside of the normal turning direction 10 And an over-steer phenomenon 10b which is a running state of the vehicle to be driven.

: Yawrate Error)으로 언더스티어(10a) 현상인지 오버스티어(10b) 현상인지를 알 수 있다. Generally, the above-mentioned understeer 10a or oversteer 10b of the vehicle is determined by the ESC. The target yaw-rate of the vehicle is calculated with the vehicle speed and the steering angle, The yaw rate error value obtained by comparing the yaw rate of the vehicle currently running with the value

: Yawrate Error, it is possible to know whether the understeer 10a phenomenon or the oversteer 10b phenomenon.

That is, if the yaw rate of the vehicle currently running is lower than the target yaw rate, the understeer 10a is present, and if the yaw rate is high, the oversteer 10b is present.

In such an abnormal driving state, if the driver steers an additional steering in the steering direction of the steering wheel, the following abnormal driving state may be maintained or a safety accident may occur.

That is, in the case of the vehicle under running of the understeer 10a, if the driver further steers the steering wheel in the direction in which the steering wheel is steered, the front wheel of the vehicle is more slippery and the contact force with the road surface is weakened And the oversteer 10b, the vehicle may be spun by the centrifugal force, which may make the running behavior of the vehicle even more unstable . Therefore, when the understeer 10a or the oversteer 10b develops in the abnormal driving state, the driver must be controlled in a counter-steering mode for steering the steering wheel to stabilize the traveling behavior of the vehicle do.

In the counter steer mode, when an abnormal driving state is encountered as described above while driving the vehicle, an assist torque is forcibly input to the steering handle of the motor drive system (MDPS) controlled by the ESC, Which is a control mode for stabilizing the output voltage.

For example, as shown in Fig. 1, in the case of a vehicle running under the above-described understeer 10a, since the front wheel side moves to the left in the drawing with reference to the rear wheel side, An assist torque value for rotating the steering wheel in the clockwise direction to move in the turning direction 10 should be input. In the case of the vehicle running in the oversteer 10b state, the rear wheel side is to the left The ESC must input an assist torque value that rotates the steering handle counterclockwise so that the vehicle moves in the normal turning direction 10 because there is a tendency to move.

Whether the vehicle is in the under-steering state 10a or the over-steering 10b state is determined based on the yaw rate of the vehicle currently traveling measured by the yaw rate sensor mounted on the vehicle .

However, as described above, the counter-steer control mode can be presumed to be a situation where the ESC controls the road surface while the vehicle is actually traveling, and the situation where the steering is suddenly performed in the middle- There is no meaning in the case of performing additional steering in the direction in which the driver is steering (abnormal turning directions 10a and 10b that caused the vehicle to turn), and the original purpose of stabilizing the behavior of the vehicle is achieved There is a difficult problem.

Therefore, a preferred embodiment of the control method of the power steering system according to the present invention is characterized in that, in accordance with the above-described abnormal running state, that is, the degree of the understeer 10a or the oversteer 10b phenomenon, By inputting the torque amount, when the driver operates the steering handle in abnormal turning directions 10a and 10b, he / she is given steering weight to recognize that the vehicle is in abnormal turning, and at the same time, It has been proposed to reduce the steering weight so as to stabilize the behavior of the vehicle at a high speed in the case of steering of the steering wheel.

The control method of the power steering system according to the present invention for realizing this is characterized in that the ESC for sensing and stabilizing the behavior of the vehicle and the power steering system of a motor drive system (MDPS) in which the operation of the steering handle is controlled by the ESC , The ESC controls as follows.

That is, the ESC inputs a predetermined first-order assist torque to the steering wheel when the vehicle turns abnormally, and further inputs a second-order assist torque according to the steering angle magnitude of the current vehicle. Here, the primary assist torque refers to an input torque value required when the vehicle is controlled in the countersteering mode when it is determined that the vehicle is turning abnormally. Further, in the present invention, even when controlled in the counter-steer mode, since the secondary assist torque corresponding to the steering angle of the vehicle currently traveling is calculated, the degree of development of the understeer 10a or the oversteer 10b Since the second assist torque is additionally inputted, it is possible to reduce the steering weight when the driver rotates the steering wheel in the turning direction of the normal vehicle. On the other hand, in the abnormal turning directions 10a and 10b The steering weight can be increased when the vehicle is rotated, thereby providing an advantage that the driver can sensibly transmit whether the vehicle is traveling abnormally.

In other words, the ESC senses the understeer 10a or the oversteer 10b phenomenon, and in the counter steer mode in which the vehicle travels in the normal turning direction 10 with the first assist torque being input, The second assist torque is further inputted to the steering wheel according to the degree of the understeer 10a or the oversteer 10b phenomenon, whereby the above-described effect can be created.

A difference between a yaw-rate and a target yaw rate of a currently running vehicle is calculated to calculate a first assist torque amount for the countersteer mode control in accordance with the understeer 10a or the oversteer 10b, May be referred to as a first-stage control in the present invention.

In addition, the step of further inputting different secondary assist torque amounts depending on the steering angle magnitudes of the currently running vehicle to the primary assist torque amount after the first step may be referred to as a control of the second step.

In this manner, the ESC controls the operation of the steering wheel of the motor drive system (MDPS) based on the total amount of assist torque calculated and inputted through the first and second steps, .

As described above, according to a preferred embodiment of the control method of the power steering system according to the present invention, the above-described first to third steps are sequentially applied to allow the driver to easily respond to an abnormal turning vehicle when the vehicle turns abnormally .

)은, 상기 ESC에 추가 입력되는 토크량으로써, 상기 현재 주행 중인 차량의 요레이트와 상기 목표 요레이트의 차이인 요레이트 오차값(

)과 현재의 조향각(SWA) 크기를 변수로 둔 함수값(f)에 조향 무게감을 조절하는 요청토크 게인값(

)을 곱하는 다음 수식에 의하여 산출된다. Here, the second assist torque amount inputted in the second step (

) Is a torque amount additionally input to the ESC, and is a yaw rate error value which is a difference between the yaw rate of the current running vehicle and the target yaw rate

) And the required torque gain value (f) for adjusting the steering weight to the function value (f) with the present steering angle (SWA)

) ≪ / RTI >

[Equation]

)은 논리적으로, 아래 수식처럼 1차 어시스트 토크량(

)에 상술한 2차 어시스트 토크량(

)을 더한 값이 될 것이다.Also, for the third step, the total assist torque amount input to the ESC

) Logically expresses the first-order assist torque amount (

) To the above-described second-order assist torque amount (

).

[Equation]

=

+

=

+

In the control method of the power steering system according to the present invention, the first assist torque amount due to the yaw rate error and the second assist torque amount based on the steering angle of the vehicle currently traveling are input continuously, It goes without saying that it is easy to operate the steering handle in the normal turning direction 10 according to the weight. However, it is needless to say that the steering unbalance can be tuned by the requested torque gain value separately controlling it.

The control method of the power steering system according to the present invention, as shown in FIG. 2, is integrated control from before the control point by the ESC, so that it is possible to shorten the active intervention time of the original ESC . That is, the control method of the power steering system according to the present invention is configured to give an additional torque according to the magnitude of the steering angle currently being traveled, so that the driver can feel The steering disturbance is reduced, and the continuous torque is input, thereby improving the steering through the driver's perception by the continuous feedback.

The applicant of the present invention has analyzed the steering angle and the steering torque curve in the case where the control method of the power steering system according to the present invention is applied and the steering angle in the case where the control method is not applied as shown in FIG.

In the graph of FIG. 3, the X-axis represents the steering angle hysteresis and the Y-axis represents the steering torque hysteresis.

Referring to FIG. 3, it can be seen that the control method of the power steering system according to the present invention reduces the steering torque hysteresis and the steering angle hysteresis in comparison with the conventional ESC control indicated by the dotted line. Particularly, when the steering angle hysteresis is reduced When the driver drives the steering wheel in the countersteering control mode, steering assist to the origin (SWA = 0) is accelerated by the secondary assist torque to be additionally input, and the steering resilience is improved.

The control process of the control method of the power steering system according to the present invention will now be described in detail with reference to the accompanying drawings (see FIG. 4 in particular).

First, when the driver steers the steering handle when the vehicle is traveling at a speed higher than a specific speed, the difference between the yaw rate of the current vehicle and the target yaw rate is detected.

Next, when a yaw rate error occurs, it is determined that the steering angle of the steering wheel is reduced after it is determined that the understeer or the oversteer is generated. In the case where the steering angle is decreasing, it can be seen that the steering wheel is operated in the normal steering direction for the driver in the turning direction 10. In this case, the understeer or the oversteer The total assist torque obtained by adding the secondary assist torque calculated by the above-described formula to the first assist torque according to the degree of the second assist torque is input to the steering handle. The input secondary assist torque at this time will be an active torque value according to the current steering angle.

Finally, if the steering of the driver is controlled by the ESC, it is re-detected whether there is a difference between the yaw rate of the current running vehicle and the target yaw rate, and if there is no difference, the control is returned to the first control step , And if the difference still occurs, it returns to the next step in the case where the yaw rate error occurs.

Hereinafter, a preferred embodiment of a power steering system and a control method thereof according to the present invention will be described in detail with reference to the accompanying drawings. However, it should be understood that the embodiments of the present invention are not necessarily limited thereto, and that various modifications and equivalents may be made by those skilled in the art. Therefore, the true scope of the present invention should be determined by the following claims.

10: normal turning direction 10a: understeer phenomenon
10b: oversteer phenomenon

Claims (5)

1. A power steering system of a motorized drive (MDPS) system in which the operation of a steering handle is controlled by an ESC which senses and stabilizes the behavior of the vehicle,
The ESC,
The understeer and the oversteer of the vehicle are determined based on the difference between the yaw rate and the target yaw rate of the vehicle currently being driven,
The steering angle of the steering wheel is determined by the steering angle of the steering wheel when the understeer or the oversteer is generated, the counter steering mode in which the driver steers the steering handle to stabilize the posture of the vehicle,
A total assist torque obtained by adding a second assist torque in accordance with the steering angle of the steering wheel to a first assist torque corresponding to the degree of the understeer or the oversteer is input to the steering wheel, Power steering system to assist steering of steering wheel.
The method according to claim 1,
The secondary assist torque (

),
A yaw rate error value (a difference between the yaw rate of the vehicle currently running and the target yaw rate

) And the required torque gain value (f) for adjusting the steering weight to the function value (f) with the present steering angle (SWA)

), ≪ / RTI >
Equation :

delete A control method of a motor-driven (MDPS) power steering system in which the operation of a steering wheel is controlled by an ESC that senses and stabilizes the behavior of the vehicle,
Determining an understeer and an oversteer of the vehicle on the basis of a difference between a yaw rate and a target yaw rate of a currently running vehicle;
Determining, through the steering angle of the steering wheel, whether the understeer or the oversteer is generated in a countersteering mode in which the driver steers the steering handle to stabilize the posture of the vehicle; And
A total assist torque obtained by adding a second assist torque in accordance with the steering angle of the steering wheel to a first assist torque corresponding to the degree of the understeer or the oversteer is input to the steering wheel, And steering the steering wheel to assist steering of the steering wheel.
The method of claim 4,
The secondary assist torque (

),
A yaw rate error value (a difference between the yaw rate of the vehicle currently running and the target yaw rate

) And the required torque gain value (f) for adjusting the steering weight to the function value (f) with the present steering angle (SWA)

) ≪ / RTI > of the power steering system.
Equation :

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