KR20110081434A - Stability method of vehicle for electric power steering - Google Patents

Abstract

PURPOSE: A stabilization method of a vehicle by electronic power steering is provided to control the posture of a vehicle stably before a vehicle operates unstably by controlling with the verified stability of a vehicle through an alignment torque value. CONSTITUTION: A stabilization method of a vehicle by electronic power steering comprises the steps of: producing vehicle alignment torque according to a current steering angle of a vehicle, the sum of the steering demanded torque of a driver and the steering motor torque(S1); producing a state index which the vehicle alignment torque is divided by the standard alignment torque(S2); verifying whether or not the state index is below the standard index(S3); and, if the state index is below the standard index, performing a vehicle stabilization control and controlling a vehicle in the safe direction(S4,S5).

Description

STABILITY METHOD OF VEHICLE FOR ELECTRIC POWER STEERING}

The present invention relates to a stabilization method of a vehicle using electric power steering, and in more detail, it is determined whether the stability of the vehicle through the alignment torque value and controlled through it, thereby stably controlling the attitude of the vehicle before the vehicle is unstable. The present invention relates to a stabilization method of a vehicle using electric power steering.

In general, a vehicle stability control (Electric stability control) that controls the attitude of the vehicle by the brake system in order to improve the dangerous situation in which the stability of driving is reduced due to the occurrence of slip or spin (spin) It is used.

The vehicle stabilization control is performed such that the yaw rate, which detects the yaw direction movement of the vehicle from the yaw rate sensor, is minimized so that the yaw rate error value, which is a difference from the reference yaw rate value, is minimized. The vehicle's attitude is controlled by adjusting the brake pressure of each wheel.

The control by the yaw rate is that when the lateral force of the tire of the vehicle decreases non-linearly and slip occurs in the vehicle, the yaw direction safety becomes unstable and a yaw rate error value is generated. After the slip or spin has occurred, the attitude control of the vehicle can be executed. That is, the attitude control of the vehicle can be executed after the running of the vehicle becomes unstable.

The present invention is to overcome the above-mentioned conventional problems, the object of the present invention is to determine whether the stability of the vehicle through the alignment torque value and control it through the control of the vehicle stably before the vehicle is unstable operation The present invention provides a method for stabilizing a vehicle using electric power steering.

In order to achieve the above object, a stabilization method for a vehicle using electric power steering according to the present invention includes an alignment torque calculating step of calculating a vehicle alignment torque according to a steering angle of a current vehicle, which is a sum of a steering request torque and a steering motor torque of a driver; A state indicator calculating step of calculating a state indicator obtained by dividing the vehicle alignment torque by a reference alignment torque, a state indicator checking step of checking whether the state indicator is less than a reference indicator, and vehicle stabilization control when the state indicator is less than the reference indicator ESC operation step of controlling the vehicle in a safe direction by executing.

In the ESC operation step, the attitude of the vehicle may be stabilized by adjusting the brake pressure of each wheel of the vehicle such that the state indicator is greater than or equal to the reference indicator.

The vehicle may further include a vehicle stabilization step of determining that the vehicle operates stably when the state indicator is greater than or equal to the reference indicator in the state indicator checking step.

The stabilization method of the vehicle using the electric power steering according to the present invention determines the stability of the vehicle through the alignment torque value and controls it through this, it is possible to stably control the attitude of the vehicle before the vehicle unstable operation.

1 is a flowchart illustrating a stabilization method of a vehicle using electric power steering according to an embodiment of the present invention.
FIG. 2 is an example of alignment torque shown according to the steering angle and road surface friction of FIG. 1.
3 is a reference alignment torque according to the steering angle of FIG. 1.
4 is a graph illustrating a relationship between alignment torque and tire lateral force according to slip angles.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings, so that those skilled in the art can easily carry out the present invention. Here, parts having similar configurations and operations throughout the specification are denoted by the same reference numerals.

Referring to FIG. 1, a flowchart illustrating a stabilization method of a vehicle using electric power steering according to an embodiment of the present invention is shown.

As shown in FIG. 1, a stabilization method of a vehicle using electric power steering includes alignment torque calculation step S1, status indicator calculation step S2, status indicator checking step S3, ESC operation step S4, and vehicle stabilization. Step s5 is included.

First, in the alignment torque calculation step S1, the vehicle alignment torque of the current vehicle is calculated by adding the driver's steering request torque and the torque of the steering motor. The equation for calculating the tire reaction force of the wheel, which is the vehicle alignment torque, is expressed by Equation 1 below.

Here, Ta is vehicle alignment torque, Td is driver torque, which is the torque at which the driver steered the steering wheel, and Tm is steering motor torque, which is the drive torque corresponding to the column axis of the steering motor.

And the steering motor torque (Tm) is as shown in equation (2).

Here, Gg is a column rotation ratio with respect to motor rotation which is an electric power steering gear ratio, Kt is a motor torque constant, Im is a current of a steering motor applied to a steering motor, and (eta) e is an efficiency constant of a motor. In other words, the motor current Im is multiplied by the motor torque constant Kt to convert the motor current Im into a torque value, which is multiplied by the motor efficiency constant ηe to calculate the actual drive torque of the motor. The motor torque is converted into a torque corresponding to the column axis which is the drive torque Tm of the steering motor through the electric power steering gear ratio Gg. At this time, the motor torque constant Kt and the motor efficiency constant ηe are constant values indicating the characteristics of the steering motor, and the electric power steering gear ratio Gg is a fixed value indicating the characteristics of the steering motor.

Therefore, the vehicle alignment torque Ta for the steering angle of the current vehicle is calculated through the steering motor torque Tm calculated through the current Im of the steering motor and the driver torque Td at which the driver steers the steering wheel.

As shown in FIG. 2, the vehicle alignment torque Ta of the current vehicle varies with the alignment torque T according to the steering angle As at which the driver steers the steering wheel, and the steering angle (Aa) is adjusted to the steering angle (Aa). It increases linearly with respect to As) and decreases nonlinearly after a certain steering angle (Aa). The vehicle alignment torque Ta further decreases in torque value when the friction coefficient is small (fh_Tb) compared with when the friction coefficient is large (fh_Ta).

The state indicator Si is calculated by dividing the vehicle alignment torque Ta according to the current steering angle calculated as above by the reference alignment torque Ts for the same steering angle. That is, the equation for calculating the state indicator is as shown in Equation 3.

Here, Si is a state index, Ta is vehicle alignment torque, and Ts is reference alignment torque. The reference alignment torque Ts is an alignment torque for a high friction road surface, and is a reference value for determining the relative stability of the vehicle from the vehicle alignment torque Ta. The reference alignment torque Ts is stored in the electric power steering controller as the alignment torque change for the high friction road surface according to the steering angle As, as shown in FIG. 3.

And the state indicator Si becomes "1" when the vehicle alignment torque Ta is equal to the reference alignment torque Ts which is the alignment torque for a high friction road surface. The state indicator Si calculates a value closer to "1" as the frictional force between the road surface and the vehicle is greater, and calculates a value closer to "0" as the frictional force between the road surface and the vehicle is smaller. Therefore, the vehicle becomes a stable state as the state indicator Si approaches "1", and becomes unstable as it approaches "0". That is, since the state indicator Si is closer to "1" as the vehicle alignment torque Ta is larger, the vehicle is in a stable state.

Then, the calculated state indicator Si is compared with the reference indicator stored in the electric power steering controller, and it is checked whether the state indicator Si is smaller than the reference indicator (S3). At this time, the reference indicator is a reference value for controlling the vehicle to be stabilized and is close to "1", and is set within a range in which no slip or spin occurs in the vehicle.

If the status indicator is smaller than the reference indicator, which is a reference value, the vehicle is determined to be in an unstable state, and the vehicle stabilization controller (Electric Stability Control, hereinafter referred to as "ESC") is executed (S4) to move the vehicle in a stable direction. Control (S5). The ESC adjusts the brake pressure of each wheel of the vehicle to control the attitude of the vehicle to stabilize before the vehicle slips.

When the state indicator is greater than or equal to the reference index, it is determined that the vehicle is in a stable state (S5), and the ESC control of the vehicle is not executed.

As the vehicle alignment torque Ta is shown in FIG. 4, when the slip angle Aslip increases, the vehicle alignment torque Ta increases linearly up to the first slip angle A1, and after the first slip angle A1 is non-linearly. Decreases. That is, when the steering torque steered by the driver increases, the state indicator also decreases when the alignment torque Ta is relatively decreased, so that the electric power steering controller determines that the vehicle is in an unstable state.

Therefore, since the stabilization method of the vehicle using the electric power steering calculates the alignment torque Ta of the current vehicle and controls the vehicle through this, the slip angle Aslip is increased to become the second slip angle A2 and thus the lateral force of the tire ( Since the Fs) decreases non-linearly, the vehicle may be controlled through the ESC to stabilize the posture of the vehicle from the time when the slip is generated in the vehicle and when the first slip angle A1 is generated earlier. That is, the posture of the vehicle may be controlled before the slip is generated in the vehicle by using the electric power steering.

What has been described above is only one embodiment for carrying out the stabilization method of the vehicle using the electric power steering according to the present invention, the present invention is not limited to the above-described embodiment, as claimed in the following claims As described above, any person having ordinary knowledge in the field of the present invention without departing from the gist of the present invention will have the technical spirit of the present invention to the extent that various modifications can be made.

Ta; Alignment torque Td; Driver torque
Tm; Steering motor torque Kt; Motor torque constant
Im; Steering motor current Ts; Reference alignment torque

Claims (3)

An alignment torque calculating step of calculating a vehicle alignment torque according to a steering angle of a current vehicle which is a sum of a driver's steering request torque and a steering motor torque;
Calculating a state indicator obtained by dividing the vehicle alignment torque by a reference alignment torque;
A status indicator checking step of checking whether the status indicator is less than a reference indicator; And
And an ESC operation step of controlling the vehicle in a safe direction by executing vehicle stabilization control when the state indicator is less than the reference indicator. The method according to claim 1,
In the ESC operation step of controlling the vehicle to stabilize the attitude of the vehicle by adjusting the brake pressure of each wheel of the vehicle so that the state indicator is more than the reference indicator. The method according to claim 1,
And stabilizing the vehicle when the state indicator is greater than or equal to the reference indicator in the state indicator checking step, determining that the vehicle operates stably.

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