Title of Invention

"A KICKDOWN CONTROL SYSTEM AND A METHOD THEREOF"

Abstract

A kickdown control system for a continuously variable transmission for a vehicle, in which an acceleration response can be increased, comprises: a vehicle speed sensor detecting a vehicle speed; a gear ratio sensor detecting a gear ratio of a primary pulley to a secondary pulley; a throttle position sensor detecting a throttle opening angle; a primary pressure solenoid regulating a primary pressure acting on the primary pulley; and a TCU performing a kickdown control, on the basis of data inputted from the vehicle speed sensor, the gear ratio sensor and the throttle position sensor, by regulating a primary pressure solenoid duty ratio, wherein the TCU performs the steps of: determining if conditions for kickdown are satisfied; rapidly discharging a primary pressure from a primary pulley if it is determined that the conditions for the kickdown are satisfied; regulating a primary pressure solenoid duty ratio to a null position to prevent an engine speed from suddenly increasing; and controlling a gear ratio by performing a feedback control.

Full Text

KICKDOWN CONTROL SYSTEM FOR A CVT OF A VEHICLE BACKGROUND OF THE INVENTION (a) Field of the Invention The present invention relates to a control system for a continuously variable transmission of a vehicle, and more particularly, to a kickdown control system in which an acceleration response can be increased by rapidly discharging a primary pressure that acts on a primary pulley if conditions for kickdown are satisfied. (b) Description of the Related Art Generally, a continuously variable transmission (CVT) system performs a gear shift by continuously changing a gear ratio of a primary pulley and a secondary pulley. FIG. 1 shows a control system for the CVT. As shown in FIG. 1, in CVT system, power provided from an engine 10 is transmitted to a primary pulley 11 and is then transmitted to a secondary pulley 12 via a belt extended between the primary pulley and the secondary pulley. A transmission control unit (TCU) 20 detects a clutch pressure, a cluster gear RPM, a secondary pulley RPM, a primary pulley RPM and a transmission oil temperature. The TCU 20 controls the clutch pressure, the line pressure and the primary pressure by controlling a clutch pressure solenoid duty ratio, a line pressure solenoid duty ratio and a primary pressure solenoid duty ratio on the basis of an idle switch signal and a throttle position signal that are provided from an electric control unit (ECU) 30 that controls the engine. Generally, a primary pressure solenoid is arranged such that the higher the primary pressure solenoid duty ratio is, the smaller the primary pressure is. If the primary pressure duty ratio becomes higher, the primary pressure becomes smaller and a gear ratio becomes larger and therefore output torque becomes larger. Also, the TCU 20 detects a shift range signal and transmits the same to the ECU 30. If a driver depresses an accelerator pedal to rapidly accelerate a vehicle, a kickdown shift occurs. The kickdown shift means that a down-shift occurs such that torque sufficient to accelerate the vehicle can be acquired. In a belt-pulley type CVT, if the accelerator pedal is depressed to rapidly accelerate the vehicle, the primary pressure solenoid duty ratio is controlled to increase so that the down shift occurs. However, the aforementioned kickdown control system according to the prior art cannot rapidly accelerate the vehicle. SUMMARY OF THE INVENTION The present invention has been made in an effort to solve the above problems. It is an object of the present invention to provide a kickdown control system, in which a primary hydraulic pressure is rapidly discharged if conditions for the kickdown for increasing an acceleration response. To achieve the above object, the present invention provides a kickdown control system for a CVT of a vehicle comprising: a vehicle speed sensor detecting a vehicle speed; a gear ratio sensor detecting a gear ratio of a primary pulley to a secondary pulley; a throttle position sensor detecting a throttle opening angle; a primary pressure solenoid regulating a primary pressure acting on the primary pulley; and a TCU performing a kickdown control, on the basis of data inputted from the vehicle speed sensor, the gear ratio sensor and the throttle position sensor, by regulating a primary pressure solenoid duty ratio, wherein the TCU performs the steps of (a) determining if conditions for kickdown are satisfied; (b) rapidly discharging a primary pressure from a primary pulley if it is determined that the conditions for the kickdown are satisfied; and (c) regulating a primary pressure solenoid duty ratio to a null position to prevent an engine speed from suddenly increasing and performing a feedback control. The step (a) comprises: (d) determining if a vehicle speed is higher than a predetermined critical speed; (e) determining if a gear ratio is smaller than a predetermined critical ratio; (f) determining if a throttle opening angle is greater than a predetermined critical angle; and (g) determining if a throttle opening angle change ratio is grater than a predetermined critical ratio. BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the invention, and, together with the description, serve to explain the principles of the invention, where: FIG. 1 is a schematic block diagram of a conventional control system for a continuously variable transmission; FIG. 2 is a kickdown control system according to the preferred embodiment of the present invention. FIG. 3 is a flow chart of a kickdown control method that can be applied to the preferred embodiment of the present invention for the continuously variable transmission according to the present invention. FIG. 4 illustrates graphs showing a change of a primary pressure solenoid duty ratio with reference to a change of a throttle position according to the prior art and the present invention respectively. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. As shown in FIG. 2, a kickdown control system according to the preferred embodiment of the present invention comprises: a vehicle speed sensor 50 detecting a vehicle speed; a gear ratio sensor 60 detecting a gear ratio of a primary pulley to a secondary pulley; a throttle position sensor 70 detecting a throttle opening angle; a primary pressure solenoid 80 regulating a primary pressure acting on the primary pulley; and a TCU 20 performing a kickdown control, on the basis of data inputted from the vehicle speed sensor, the gear ratio sensor and the throttle position sensor, by regulating a primary pressure solenoid duty ratio. Hereinafter, the kickdown control method applied to the above kickdown control system will be precisely explained with reference to FIG. 3. FIG. 3 is a flow chart of a kickdown control method that can be applied to the preferred embodiment of the continuously variable transmission according to the present invention, and FIG. 3 illustrates graphs showing a change of a primary pressure solenoid duty ratio with reference to a change of a throttle position according to the prior art and the present invention respectively. Preferably, a transmission control means is realized by the TCU 20. The TCU 20 detects a vehicle speed sensed by a vehicle speed sensor and a gear ratio sensed by a gear ratio sensor, then the TCU 20 determines if the vehicle speed is higher than a predetermined critical vehicle speed (ST21). It is preferable that the predetermined critical vehicle speed is determined as a value above which the kickdown control doesn't have adverse bad effects on the vehicle and one at which it is needed to perform the kickdown control according to the present invention. If it is determined that the vehicle speed is higher than the predetermined critical vehicle speed in step ST21, the TCU 20 determines if the gear ratio is smaller than a predetermined critical gear ratio (ST22). If the gear ratio is so high that enough torque to accelerate the vehicle is generated, there is little necessity for performing the kickdown control according to the present invention. Therefore, it is preferable that the predetermined critical gear ratio is determined as a value below which it is needed to perform the kickdown control according to the present invention. If it is determined that the gear ratio is smaller than the predetermined critical gear ratio in step ST22, the TCU 20 detects a throttle opening angle sensed by a throttle position sensor and calculates a throttle opening angle change rate according to time, and the TCU 20 then determines if the throttle opening angle is greater than a predetermined critical angle (ST23). If it is determined that the throttle opening angle is greater than the predetermined critical angle in step ST23, the TCU 20 determines if the throttle opening angle change rate is greater than a predetermined critical rate (ST24). It is preferable that the predetermined critical throttle opening angle and the predetermined critical throttle opening angle change rate are determined as values above which it is needed to increase the acceleration response. If it is determined that the throttle opening angle change rate is greater than the predetermined critical rate in step ST24, the TCU 20 controls the kickdown to be performed (ST25). That is, in steps ST21 through ST24, it is determined if conditions for kickdown are satisfied. FIG. 4 (a) and (b) are graphs respectively showing the changes of the primary pressure solenoid duty ratio according to the prior art and the preferred embodiment of the present invention. If the primary pressure solenoid duty ratio is controlled as shown in FIG. 4 (a), the primary pressure is slowly discharged from the primary pulley so that the acceleration response decreases. As shown in FIG. 4 (b), when the throttle opening angle increase rapidly, the TCU 20 controls the primary pressure to be rapidly discharged from the primary pulley by rapidly increasing the primary pressure solenoid duty ratio. Therefore, the acceleration response can be increased. After the primary pressure is rapidly discharged in the beginning of the kickdown control as shown in FIG. 4 (b), the TCU 20 regulates the primary pressure solenoid duty ratio to a null position such that an overshoot phenomenon whereby in that an engine speed suddenly increases doesn't occur. Then, the TCU 20 controls the gear ratio by performing a feedback control, based on a deviation between a target gear ratio and a present gear ratio, in order that the present gear ratio may approach the target gear ratio. On the other hand, if any one condition for the kickdown is not satisfied in step ST21 to ST24, the TCU 20 stops the kickdown control, and a control logic returns to a main routine. Also, after the kickdown control is performed in step ST25, the control logic returns to the main routine. As stated above, the kickdown control system according to the present invention makes it possible to increase the acceleration response when the driver wants to accelerate the vehicle. Although preferred embodiment of the present invention have been described in detail hereinabove, it should be clearly understood that many variations and/or modifications of the basic inventive concepts herein taught which may appear to those skilled in the present art will still fall within the sprit and scope of the present invention, as defined in the appended claims. We claim: 1. A kickdown control system for a CVT of a vehicle comprising: a vehicle speed sensor detecting a vehicle speed: a gear ratio sensor detecting a gear ratio of a primary pulley to a secondary pulley; a throttle position sensor detecting a throttle opening angle; a primary pressure solenoid regulating a primary pressure acting on the primary pulley; and a TCU performing a kickdown control, on the basis of data inputted from the vehicle speed sensor, the gear ratio sensor and the throttle position sensor, by regulating a primary pressure solenoid duly ratio; wherein the TCU performs the steps of a) determining if conditions for kickdown are satisfied; b) rapidly discharging a primary pressure from a primary pulley if it is determined that the conditions for the kickdown are satisfied; and c) regulating a primary pressure solenoid duty ratio to a null position to prevent an engine speed from suddenly increasing, and controlling a gear ratio by performing a feedback control. 2. The kickdown control system as claimed in claim 1 wherein step (a) comprises: determining if a vehicle speed is higher than a predetermined critical speed. 3. The kickdown control system as claimed in claim 2 wherein step (a) comprises determining if the gear ratio is smaller than a predetermined critical ratio. 4. The kickdown control system as claimed in claim 3 wherein step (a) comprises: determining if a throttle opening angle is greater than a predetermined critical angle. 5. The kickdown control system as claimed in claim 4 wherein step (1) comprises: determining if a throttle opening angle change rate is greater than a predetermined critical rate. 6. A kickdown control method for a CVT of a vehicle comprising: a vehicle speed sensor detecting a vehicle speed: a gear ratio sensor detecting a gear ratio of a primary pulley to a secondary pulley; a throttle position sensor detecting a throttle opening angle; a primary pressure solenoid regulating a primary pressure acting on the primary pulley; and a TCU performing a kickdown control, on the basis of data inputted from the vehicle speed sensor, the gear ratio sensor and the throttle position sensor, by regulating a primary pressure solenoid duly ratio; wherein the TCU performs the steps of d) determining if conditions for kickdown are satisfied; e) rapidly discharging a primary pressure from a primary pulley if it is determined that the conditions for the kickdown are satisfied; and f) regulating a primary pressure solenoid duty ratio to a null position to prevent an engine speed from suddenly increasing, and controlling a gear ratio by performing a feedback control. 7) A kickdown control method for a CVT of a vehicle as claimed in claim 1 comprising: - means for determining if a vehicle speed is higher than a predetermined critical speed. - means for determining if the gear ratio is smaller than a predetermined critical ratio. - means for determining if a throttle opening angle is greater than a predetermined critical angle. - means for determining if a throttle opening angle change rate is greater than a predetermined critical rate

Documents:

1216-del-2001-abstract.pdf

1216-DEL-2001-Claims-19-05-2008.pdf

1216-del-2001-claims.pdf

1216-DEL-2001-Correspondence-Others-19-05-2008.pdf

1216-DEL-2001-Correspondence-Others.pdf

1216-del-2001-correspondence-po.pdf

1216-del-2001-description(complete)-19-05-2008.pdf

1216-del-2001-description(complete).pdf

1216-DEL-2001-Drawings.pdf

1216-DEL-2001-Form-1-19-05-2008.pdf

1216-del-2001-form-1.pdf

1216-del-2001-form-18.pdf

1216-DEL-2001-Form-2-19-05-2008.pdf

1216-del-2001-form-2.pdf

1216-DEL-2001-Form-3.pdf

1216-del-2001-form-5.pdf