Method of protecting frictional element of clutch for automatic transmission

1. A method of protecting a frictional element of a clutch for an automatic transmission, comprising:

calculating, by a control unit, an equivalent rotation number X of a frictional element using a trigonometric function equation on the basis of a virtual right triangle;

if a rotation number of an engine exceeds a predetermined boundary value during driving in a constant speed stage over a predetermined shift stage of an automatic transmission, entering a frictional element protection mode, by the control unit;

if the control unit enters the frictional element protection mode, determining whether the calculated equivalent rotation number X of the frictional element exceeds a predetermined critical value, by the control unit; and

if the equivalent rotation number X of the frictional element exceeds the predetermined critical value in a state in which the control unit enters the frictional element protection mode, reducing the rotation number of the engine by applying a target engine torque limiting value, by the control unit,

wherein the virtual right triangle is obtained using a rotation number Z of an output shaft, a rotation number Y of a turbine, and an equivalent rotation number X of the frictional element of the automatic transmission as a height, and using a number of teeth α corresponding to the turbine, a number of teeth β corresponding to the output shaft, and a virtual extension line γ as a base line.

2. The method of claim 1 , further comprising releasing the frictional element protection mode not to apply the target engine torque limiting value, by the control unit, if the automatic transmission is shifted under a predetermined stage, or the rotation number of the engine is below the predetermined critical value.

3. The method of claim 1 , wherein the predetermined shift stage is 4 th -stage.

4. The method of claim 1 , wherein the virtual right triangle is obtained by:

drawing a virtual straight line (a first height) corresponding to the equivalent rotation number of the frictional element X to correspond to the height in a Y-axis direction on the basis of a right point of the virtual right triangle,

drawing a virtual straight line to correspond to the base line in an X-axis direction, wherein the virtual straight line corresponds to a sum of a number of teeth α corresponding to the turbine, a number of teeth β corresponding to the output shaft, and the virtual extension line γ,

drawing a virtual straight line (a second height) corresponding to a rotation number Y of the turbine at an end point of the number of teeth α corresponding to the turbine in a Y-axis direction,

drawing a virtual straight line (a third height) corresponding to the rotation number Z of the output shaft at an end point of the number of teeth β corresponding to the output shaft in the Y-axis direction,

connecting end points of the first, second, and third heights to draw a virtual straight line corresponding to a hypotenuse of the virtual triangle, and

extending the hypotenuse of the virtual triangle to a point meeting the X-axis to correspond to the base line.

5. The method of claim 4 ,

wherein a distance from the end point of the number of teeth β corresponding to the output shaft to a vertex at which the virtual extension line of the hypotenuse meets the base line, becomes a length of the virtual extension line γ.

6. The method of claim 4 ,

wherein the length of the virtual extension line γ is calculated using the following equation 1 by the control unit.

1

)

⁢

⁢

Z

⁢

:

⁢

⁢

Y

=

γ

⁢

:

⁢

⁢

γ

+

β

→

γ

=

Z

×

β

(

Y

-

Z

)

7. The method of claim 4 ,

wherein the equivalent rotation number X of the frictional element is calculated using the following equations 2 and 3 by the control unit.

2

)

⁢

⁢

Y

⁢

:

⁢

⁢

X

=

γ

+

β

⁢

:

⁢

⁢

γ

+

β

+

α

⁢

⁢

3

)

⁢

⁢

X

=

Y

⁡

(

α

+

β

+

Z

×

β

Y

-

Z

)

Z

×

β

Y

-

Z

+

β