Title of Invention

"A LINE PRESSURE VARIABLE CONTROL METHOD AND A SYSTEM THEREOF FOR AN AUTOMATIC TRANSMISSION."

Abstract

A line pressure variable control method for an automatic transmission using a solenoid valve to control a line pressure according to a duty ratio thereof is provided which comprises: determining whether a current shift range is one of forward driving shift ranges; calculating a minimum line pressure based on at least one automatic transmission operating condition, if the current shift range is one of the forward driving shift ranges, and calculating a solenoid duty ratio corresponding to the calculated minimum line pressure; determining whether there is a clutch slip; calculating a solenoid correction duty ratio based on an amount of the clutch slip, if it is determined that there is the clutch slip; modifying the solenoid duty ratio with the solenoid correction duty ratio; and controlling the solenoid valve using the modified solenoid duty ratio.

Full Text

A LINE PRESSURE VARIABLE CONTROL METHOD AND A SYSTEM THEREOF FOR AN AUTOMATIC TRANSMISSION FIELD OF THE INVENTION The present invention relates to a line pressure variable control method and a system thereof for an automatic transmission BACKGROUND OF THE INVENTION As is generally known, an automatic transmission includes a torque converter, a power train that is connected to the torque converter and is a gear shift mechanism, a hydraulic system for selectively driving operating elements of ihe power train, and a transmission control unit controlling the hydraulic system The hydraulic system includes various valves for driving the operating elements of the power train using hydraulic oil exhausted from an oil pump Such hydraulic system generally includes a regulator valve for regulating a pressure of hydraulic oil discharged from the oil pump to a predetermined level of pressure (i e , line pressure) The regulator valve includes a valve housing that is provided with a plurality of ports, a valve spool that is disposed within the valve housing and is provided with a plurality of valve lands, and a coil spring thai elastically supports the valve spool A position of the valve spool of the regulator is changed by an inflow ui control pressure, and thereby a specific line pressure is formed The line pressure that is formed by the regulator valve is supplied to various valves Recently, a line pressure variable control technology that variably controls the line pressure using a variable force solenoid (VFS) that supplies hydraulic oil to the regulator valve has been introduced That is, by controlling a dutv ratio of the solenoid valve through an transmission control unit the line pressure can be variably controlled The object of the line pressure variable control is to improve efficiency of the transmission and fuel economy by minimizing the line pressure in a state in which a specific gear is engaged Therefore, in the line pressure variable control it is preferable that a minimum line pressure exists at which there is no clutch slip Generally, the minimum line pressure is determined in consideration of a turbine input torque and a safety ratio. However, it can occur that a desired line pressure is not formed at a predetermined duty ratio of a solenoid valve due to a piessure deviation or aging of the hydraulic system For example though the solenoid valve is controlled at a specific duty ratio at which a desired minimum line pressure can be formed under normal conditions, the real line pressure can become less than the desired minimum line pressure If the line pressure is too low, slips in friction elements of the automatic transmission or a damper clutch may occur The information disclosed in this Background of the Invention section is only for enhancement of understanding of the background of the invention, and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art that is already known to a person skilled in the art SUMMARY OF THE INVENTION An embodiment of the present invention provides a line pressure control method for an automatic transmission and a system thereof that are capable of preventing clutch slip due to too low a line pressure In a preferred embodiment of the present invention, a line pressure variable control method for an automatic transmission using a solenoid valve to control a line pressure according to a duty ratio thereof comprises: determining whether a current shift range is one of forward driving shift ranges; calculating a minimum line pressure based on at least one automatic transmission operating condition if the current shift range is one of the forward driving shift ranges and calculating a solenoid duty ratio corresponding to the calculated minimum line pressure, determining whether there is a clutch slip, calculating a solenoid connection duty ratio based on an amount of the clutch slip, if it is determined that there is a clutch slip, modifying the solenoid duty ratio with the solenoid connection duty ratio; and controlling the solenoid valve using the modified solenoid duty ratio. It is preferable that the at least one automatic transmission operating condition comprises an input torque and a torque ratio It is further preferable that the minimum line pressure is calculated as a value obtained by a multiplication of the input torque, the torque ratio, and a predetermined safety factor It is still further preferable that the predetermined safety factor is 1 3 It is preferable that the determining whether there is a clutch slip is perormed based on one of a difference between a turbine speed and a calculated turbine speed that is calculated based on a transmission output shaft speed, and a difference between an engine speed and the turbine speed. It is further preferable that the determining whether there is a clutch slip is performed based on the difference between the turbine speed and the calculated turbine speed and the difference between the engine speed and the turbine speed if a damper clutch is in an on state Preferably, in the .calculating a solenoid correction duty ratio the solenoid correction duty ratio is calculated based on the difference between the turbine speed and the calculated turbine speed when the turbine speed is different from the calculated turbine speed. Further preferably, the solenoid correction duty ratio is calculated to be in proportion to the difference between the turbine speed and the calculated turbine speed It is preferable that the solenoid correction duty ratio is calculated based on the difference between the engine speed and the turbine speed when the turbine speed is equal to the calculated turbine speed It is further preferable that the solenoid correction duty ratio is calculated to be in proportion to the difference between the engine speed and the turbine speed Preferably, the determining whether there is a slip is performed based on ihe difference between the turbine speed and the calculated turbine speed if a damper clutch is in an off state. It is preferable that the solenoid correction duty ratio is calculated to be in proportion to a difference between the turbine speed and the calculated turbine speed Preferably the solenoid correction duty ratio is calculated to be m proportion to an amount of the slip. It is also preferable that the modifying the solenoid duty ratio is performed by adding the solenoid correction duty ratio to the solenoid duty ratio In a preferred embodiment of the present invention, a line pressure variable control system for an automatic transmission comprises a shift range sensor detecting a current shift range a turbine speed sensor detecting a turbine speed and outputting a corresponding signal, an engine speed sensor detecting an engine speed and outputting a corresponding signal an output shaft speed sensor detecting an automatic transmission output shaft speed and outputting a corresponding signal, a solenoid valve configured such that a line pressure of the automatic transmission is controlled according to a duty ratio thereof, and a transmission control unit controlling a duty of the solenoid valve based on signals received from an engine control unit and the sensors It is preierable that the transmission control unit is programmed to perform one of the above-stated methods 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 ana together with the description, serve to explain the principles of the invention where FIG 1 is a schematic diagram of a line pressure variable control system for an automatic transmission according to an embodiment of the present invention, and FIG 2 is a flow chart showing a line pressure variable control method according to an embodiment of the present invention 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 1, a line pressure variable control system according to the embodiment of the present invention comprises a solenoid valve 11 and a transmission control unit (TCU) 13. Hydraulic pressure is supplied to the solenoid valve 11 from an oil pump 15, and the solenoid valve 11 regulates the supplied hydraulic pressure to a control pressure and then supplies the control pressure to a regulator valve 7 If the solenoid valve 11 is controlled at a specific duty ratio by the TCU 13, a corresponding control pressure is formed and the control pressure is supplied to the regulator valve 7 If the control pressure is supplied to the regulator valve 7 a conesponding line pressure is formed The line pressure that is formed by the regulator valve 7 is supplied to a damper clutch 21 of a torque converter 19. In addition, the line pressure is supplied to friction elements 25 such as a clutch and a brake through various control valves 23. Such hydraulic system is well known in the art and various hydraulic systems are disclosed, so further detail explanation will be omitted The line pressure variable control system according to the embodiment of ihe present invention includes an engine speed sensor 27 detecting an engine speed and outputting a corresponding signal, a turbine speed sensor 29 detecting a turbine speed and outputting a corresponding signal, an output shaft speed sensor 31 detecting a transmission output shaft speed and outputting a corresponding signal, and a shift range sensor 33 detecting a current shift range and outputting a corresponding signal The shift range sensor 33 can preferably be an inhibitor switch that is configured to detect a shift range The TCU 13 receives signals from the sensors 27, 29, 31, and 33, and is connected to an engine control unit 35 that controls an engine (not shown) The TCU 13 receives information on input torque from the engine control unit 35. The input torque is a torque that is inputted into the transmission from the engine. The TCU 13 may includes a microprocessor, a memory, and related hardware and software, and is preferably programmed to perform a control method according to the embodiment of the present invention that will be explained hereinafter Hereinafter, referring to FIG 2, a line pressure variable control method according to the embodiment of the present invention will be explained At first, the TCU 13 determines whether a current shift range is one of forward driving shift ranges at step S205 The forward driving shift ranges include an arbitrary shift range in which a forward shift speed can be selected For example, the forward driving shift ranges may include a driving D range, a third 3 range, a second 2 range, and a low L range In addition, in a vehicle being provided with a sport mode (i e., manual mode) in which an upshift or a downshift can be manually performed, the forward driving shift ranges include a driving D range and a sport mode range If the current shift range is not one of the forward driving shift ranges, a control process ends. If the current shift range is one of the forward driving shift ranges the TCU 13 calculates a minimum line pressure based on at least one automatic transmission operating condition and a solenoid duty ratio corresponding to the calculated minimum line pressure, at step S210. Preferably, the minimum line pressure is calculated through a multiplication of an input torque, a torque ratio, and a predetermined safety factor The torque ratio indicates a torque transmission ratio in the torque converter 19 The torque ratio can be calculated using a table of torque ratios thai are predetermined according to a speed ratio (turbine speed over engine speed) Preferably, the torque is in inverse proportion to the speed ratio The predetermined safety factor is a value for preventing a slip in a friction element 25 of the transmission or in the damper clutch 21. As an example, the safety factor can preferably be 1.3. If the minimum line pressure is calculated, the TCU 13 calculates a solenoid duty ratio for forming the calculated minimum line pressure The solenoid duty ratio can be calculated from a predetermined table Preferably the line pressure is in proportion to the solenoid duty ratio Then, at step S215, the TCU 13 determines whether a clutch slip has occurred The clutch slip includes a slip of the damper clutch and slips of clutches thai are friction elements of the transmission Preferably, the determination on whether the clutch slip has occurred can be performed based on at least one of a difference between a turbine speed and a calculated turbine speed that is calculated on the basis of a transmission output shaft speed and a difference a turbine speed and an engine speed. The turbine speed is detected by the turbine speed sensor 29 and the engine speed is detected by the engine speed sensor 27 The calculated turbine speed can be calculated based on a transmission output shaft speed that is detected by the output shaft speed sensor 31 That is, because the turbine speed changes based on a current shift speed and the changed turbine speed is output as the output shaft speed the turbine speed can be calculated from the output shaft speed and the current shift speed If there is a slip in the transmission, the calculated turbine speed is not equal to the turbine speed that is detected by the turbine speed sensor 29 Therefore, if the difference between the turbine speed and the calculated turbine speed is not equal to 0, it can be determined that there is a slip In both cases in which the damper clutch 21 is on or off, it can be determined whether there is a slip based on a difference between the turbine speed and the calculated turbine speed In addition, when the damper clutch 21 is on, whether there is a slip can be determined based on a difference between the turbine speed and the engine speed When the damper clutch 21 is on a difference between the turbine speed and the engine speed is substantially small Therefore, for example, if the difference between the turbine speed and the engine speed is greater than 10 rprr, it can be determined that there is a slip in the damper clutch 21 At step S215, if it is determined that the slip has not occurred, the control logic ends On the other hand, if it is determined that the slip has occurred at step S215, the TCU 13 calculates a solenoid correction duty ratio based on an amount of the slip at step S220. When the damper clutch 21 is in an on state, the solenoid correction dutv ratio can be calculated as follows When the turbine speed and the calculated turbine speed are different fron each other, the solenoid correction duty ratio can be calculated based on the difference between the turbine speed and the calculated turbine speed Preferably, the solenoid correction duty ratio is in proportion to the difference between the turbine speed and the calculated turbine speed The solenoid correction duty ratio can be calculated according to a difference Nt-Nt_cal between a turbine speed Nt and a calculated turbine speed Nt_cal For example, the solenoid correction duty ratio is determined as 3% when the difference Nt-Nt_cal is less than 5 rpm, as 10% when the difference is between 5 rpm and 10 rpm, and as 20% when the difference is greater than 10 rprr On the other hand, if the turbine speed and the calculated turbine speed are equal, the solenoid correction duty ratio is calculated based on the difference between the engine speed and the turbine speed. Preferably, the solenoid correction duty ratio is determined to be in proportion to the difference between the engine speed and the turbine speed The solenoid correction duty ratio can be calculated according to a difference Ne-Nt between an engine speed Ne and a turbine speed Nt For example, the solenoid correction duty ratio is determined as 3% when the difference Ne-Nt is between 10 rpm and 20 rpm, as 10% when the difference is between 20 rpm and 30 rpm, and as 20% when the difference is greater than 30 rpm In addition, when the damper clutch 21 is in an off state, the solenoid coriection duty ratio can be calculated based on a difference between the turbine speed and the calculated turbine speed Preferably, the solenoid correction duty ratio is determined to be in proportion to the difference between the turbine speed and the calculated turbine speed The solenoid correction duty ratio can be calculated according to a difference Nt-Nt_cal between a turbine speed Nt and a calculated turbine speed Nt_cal For example, the solenoid correction duty ratio is determined as 3% when the difference Nt-Nt_cal is less than 5 rpm, as 10% when the difference is between 5 rpm and 10 rpm, and as 20% when the difference is greater than 10 rpir Then, at step S225, the TCU 13 modifies the solenoid duty ratio calculated at step S210 with the solenoid correction duty ratio calculated at step S2^'0 Preferably, the solenoid duty is modified by adding the solenoid conection duty ratio to the solenoid duty ratio calculated at step S210 That is, the TCU 13 performs a learning control according to the amount of the slip, thereby suitably modifying the minimum line pressure such that the slip can be prevented The TCU 13 controls the solenoid valve 11 with the modified solenoid dutv ratio at step S230 Although preferred embodiments 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 spirit and scope of the present invention, as defined in the appended claims According to the embodiment of the present invention, the minimum line pressure is modified according to the amount of the slip, so that it is possible to cope with a clutch slip or a damper clutch slip due to a deterioration of a hydraulic system. We claim: 1. A line pressure variable control method for an automatic transmission using a solenoid valve 11 to control a line pressure according to a duty ratio thereof, comprising: determining whether a current shift range is one of forward driving shift ranges; calculating a minimum line pressure based on at least one automatic transmission operating condition if the current shift range is one of the forward driving shift ranges and calculating a solenoid duty ratio corresponding to the calculated minimum line pressure; determining whether there is a clutch slip is performed based on one of a difference between a turbine speed and a calculated turbine speed that is calculated based on a transmission output shaft speed, and a difference between an engine speed and the turbine speed; calculating a solenoid correction duty ratio based on an amount of the clutch slip, if it is determined that there is a clutch slip; modifying the solenoid duty ratio with the solenoid correction duty ratio; and controlling the solenoid valve 11 using the modified solenoid duty ratio. 2. The line pressure variable control method as claimed in claim 1, wherein the at least one automatic transmission operating condition comprises an input torque and a torque ratio. 3. The line pressure variable control method as claimed in claim 2, wherein the minimum line pressure is calculated as a value obtained by a multiplication of the input torque, the torque ratio and a predetermined safety factor. 4. The line pressure variable control method as claimed in claim 3, wherein the predetermined safety factor is 1.3. 5. The line pressure variable control method as claimed in claim 1, wherein the determining whether there is a clutch slip is performed based on the difference between the turbine speed and the calculated turbine speed and the difference between the engine speed and the turbine speed if a damper clutch is in an on state. 6. The line pressure variable control method as claimed in claim 5, wherein in the calculating a solenoid correction duty ratio, the solenoid correction duty ratio is calculated based on the difference between the turbine speed and the calculated turbine speed when the turbine speed is different from the calculated turbine speed. 7. The line pressure variable control method as claimed in claim 6, wherein the solenoid correction duty ratio is calculated to be in proportion to the difference between the turbine speed and the calculated turbine speed. 8. The line pressure variable control method as claimed in claim 6, wherein the solenoid correction duty ratio is calculated based on the difference between the engine speed and the turbine speed when the turbine speed is equal to the calculated turbine speed. 9. The line pressure variable control method as claimed in claim 8, wherein the solenoid correction duty ratio is calculated to be in proportion to the difference between the engine speed and the turbine speed. 10. The line pressure variable control method as claimed in claim 1, wherein the determining whether there is a slip is performed based on the difference between the turbine speed and the calculated turbine speed if a damper clutch is in an off state. 11. The line pressure variable control method as claimed in claim 10, wherein the solenoid correction duty ratio is calculated to be in proportion to a difference between the turbine speed and the calculated turbine speed. 12. The line pressure variable control method as claimed in claim 1, wherein the solenoid correction duty ratio is calculated to be in proportion to an amount of the slip. 13. The line pressure variable control method as claimed in claim 1, wherein the modifying the solenoid duty ratio is performed by adding the solenoid correction duty ratio to the solenoid duty ratio. 14. A line pressure variable control system for an automatic transmission, comprising: a shift range sensor 33 detecting a current shift range; a solenoid valve 11 configured such that a line pressure of the automatic transmission is controlled according to a duty ratio thereof; and a transmission control unit 13 controlling a duty of the solenoid valve 11 based on signals received from an engine control unit 35 and the shift range sensor 33, wherein the transmission control unit is programmed to perform a control logic comprising determining whether the current shift range is one of forward driving shift ranges; calculating a minimum line pressure based on at least one automatic transmission operating condition, if the current shift range is one of the forward driving shift ranges and calculating a solenoid duty ratio corresponding to the calculated minimum line pressure; determining whether there is a clutch slip; calculating a solenoid correction duty ratio based on an amount of the clutch slip, if it is determined that there is a clutch slip; modifying the solenoid duty ratio with the solenoid correction duty ratio; and controlling the solenoid valve 11 using the modified solenoid duty ratio. 15. The line pressure variable control system as claimed in claim 14, further comprising: a turbine speed sensor detecting a turbine speed and outputting a corresponding signal to the transmission control unit; and an engine speed sensor detecting an engine speed and outputting a corresponding signal to the transmission control unit, wherein the engine control unit provides input torque information to the transmission control unit, and wherein the at least one automatic transmission operating condition comprises the input torque and a torque ratio that is calculated based on the engine speed and turbine speed. 16. The line pressure variable control system as claimed in claim 15, wherein the minimum line pressure is calculated as a value obtained by a multiplication of the input torque, the torque ratio and a predetermined safety factor. 17. The line pressure variable control system as claimed in claim 16, wherein the safety factor is 1.3. 18. The line pressure variable control system as claimed in claim 14, further comprising an output shaft speed sensor detecting an automatic transmission output shaft speed and outputting a corresponding signal, and wherein the determining whether there is a clutch slip is performed based on one of a difference between a turbine speed and a calculated turbine speed that is calculated based on a transmission output shaft speed, and a difference between an engine speed and the turbine speed. 19. The line pressure variable control system as claimed in claim 18, wherein the determining whether there is a clutch slip is performed based on the difference between the turbine speed and the calculated turbine speed and the difference between the engine speed and the turbine speed if a damper clutch is in an on state. 20. The line pressure variable control system as claimed in claim 19, wherein in the calculating a solenoid correction duty ratio, the solenoid correction duty ratio is calculated based on the difference between the turbine speed and the calculated turbine speed when the turbine speed is different from the calculated turbine speed. 21. The line pressure variable control system as claimed in claim 20, wherein the solenoid correction duty ratio is calculated to be in proportion to the difference between the turbine speed and the calculated turbine speed. 22. The line pressure variable control system as claimed in claim 20, wherein the solenoid correction duty ratio is calculated based on the difference between the engine speed and the turbine speed when the turbine speed is equal to the calculated turbine speed. 23. The line pressure variable control system as claimed in claim 22, wherein the solenoid correction duty ratio is calculated to be in proportion to the difference between the engine speed and the turbine speed. 24. The line pressure variable control system as claimed in claim 18, wherein the determining whether there is a slip is performed based on the difference between the turbine speed and the calculated turbine speed if a damper clutch is in an off state. 25. The line pressure variable control system as claimed in claim 24, wherein the solenoid correction duty ratio is calculated to be in proportion to a difference between the turbine speed and the calculated turbine speed. 26. The line pressure variable control system as claimed in claim 14, wherein the solenoid correction duty ratio is calculated to be in proportion to an amount of the slip. 27. The line pressure variable control system as claimed in claim 14, wherein the modifying the solenoid duty ratio is performed by adding the solenoid correction duty ratio to the solenoid duty ratio. 28. A line pressure variable control method for an automatic transmission substantially as herein described with reference to the accompanying drawings. 29. A line pressure variable control system for an automatic transmission substantially as herein described with reference to the accompanying drawings.

Documents:

1257-del-2004-abstract.pdf

1257-DEL-2004-Claims-(04-06-2010).pdf

1257-del-2004-claims.pdf

1257-DEL-2004-Correspondence-Others-(04-06-2010).pdf

1257-DEL-2004-Correspondence-Others-(17-12-2009).pdf

1257-del-2004-correspondence-others.pdf

1257-del-2004-description (complete).pdf

1257-del-2004-drawings.pdf

1257-del-2004-form-1.pdf

1257-del-2004-form-19.pdf

1257-del-2004-form-2.pdf

1257-DEL-2004-Form-3-(17-12-2009).pdf

1257-del-2004-form-3.pdf

1257-del-2004-form-5.pdf

1257-del-2004-gpa.pdf