Title of Invention

"HYDRAULIC CONTROL SYSTEM FOR AUTOMATIC TRANSMISSION"

Abstract

Disclosed is a hydraulic control system for an automatic transmission that controls a powertrain, which includes a first friction element for use as an engine brake for discontinuing operation of a one-way clutch in the transmission and a second friction element operating only when the first frinction element is disengaged. The hydraulic control system comprises a manual valve including a forward range port for exhausting hydraulic pressure when driving in a forward range, and an L range port for exhausting hydraulic pressure for low speed control; and a switch valve controlled by engine brake signal pressure, solenoid pressure, and forward range pressure supplied from the forward range port, the switch valve selectively supplying control pressure to the first friction element and the second friction element.

Full Text

HYDRAULIC CONTROL SYSTEM FOR AUTOMATIC TRANSMISSION This application claims priorities of Korea patent Application No. 10-2000-0087012, filed on December 30, 2000. BACKGROUND OF THE INVENTION (a) Field of the Invention The present invention relates to a hydraulic control system for an automatic transmission, and more particularly, to a hydraulic control system for an automatic transmission in which the supply of hydraulic pressure to two friction elements operating in different shift ranges is controlled by a single switch valve such that damage to the powertrain, which may result if two friction elements operate simultaneously, is prevented.' (b) Description of the Related Art Conventional automatic transmissions used in vehicles typically include a torque converter, a powertrain realized through a multi-stage gearshift mechanism that is connected to the torque, converter, and a hydraulic control system that selectively operates one of a plurality of operational elements of the powertrain according to a driving state of the vehicle. In such an automatic transmission, although all the advantages of an automatic transmission over a manual transmission are provided (e.g., ease of driving), the generation of significant shift shock nevertheless remains a problem. To minimize shift shock, it is necessary to smoothly control clutches and brakes of the powertrain. In this regard, more effective than the most precise electronic control is the mounting of a one-way clutch. In the case where shifting is performed during an already ongoing shift process, good responsiveness can be expected with the use of a one-way clutch. Because of such advantages, much research is being performed to improve shift feel with the use of two one-way clutches. FIG. 4 shows a schematic view of a hydraulic control system for controlling a four-speed automatic transmission powertrain, which is capable of utilizing the advantages of one-way clutches during 12, 3*->4, and 4«-»2 shifting. With reference to the drawing, lines are formed to enable the supply of a D range pressure provided from a manual valve 200 to a first clutch C1 and to first, second, and third pressure control valves 202, 204, and 206; the supply of L range pressure provided from the, manual valve 200 to the first pressure control valve 202; and the direct supply of R range pressure provided from the manual valve 200 to a third clutch C3 arid to a first brake B1. The D range pressure supplied to the first pressure control valve 202 is selectively supplied, according to control by a first solenoid valve 208, to an operational side of a second brake B2, and the L range pressure is supplied to the first brake B1 in a low L range. The first brake B1 is connected to the first pressure control valve 202 and an R range port of the manual valve 200 via a shuttle valve 210 such that hydraulic pressure is supplied to the first brake B1 no matter which direction hydraulic pressure is supplied from. The D range pressure supplied to the second pressure control valve 204 is supplied to a second clutch C2 and the third pressure control valve 206 according to control by a second solenoid valve 212. Also, the D range pressure supplied to the third pressure control valve 206 is selectively supplied to a fourth clutch C4 according to control by a third solenoid valve 214. In such an instance where the D range pressure is supplied to the fourth clutch C4, the third pressure control valve 206 supplies hydraulic pressure from the second pressure control valve 204 to a non-operational side of the second brake B2. Hence, the first clutch C1 operates in first, second, and third speeds; the second clutch C2 operates in third and fourth speeds; the third clutch C3 operates in a reverse R range; the fourth, clutch C4 operates in a park P range, the reverse R range, a neutral N range, and the low L range, and in the first, second, and third speeds according to driving conditions; the first brake B1 operates in the park P, reverse R, neutral N, and low L ranges; and the second brake B2 operates in the second and fourth speeds. However, in the conventional hydraulic control system as described above, since the system simply acts to control line pressure and the solenoid valves merely operate as switch valves to control timing, precise shift control is not possible. In particular, since control of non-operational sides of the second clutch C2 and the second brake B2 is linked, precise control is not possible during 2 3 shifting. Also, with the operation of the first brake B1 and the fourth clutch C4, which enable operation of the engine brake, since a method is used in which line pressure is directly supplied, significant shift shock is generated. Further, during manual shifting from the low 2 range to the low L range, occurring simultaneously with the exhaust of operational-side pressure of the second brake B2 is the supply of line pressure to the first brake B1, resulting in the generation of substantial shift shock. Also, manual shifting into the reverse R range from the drive D range when travelling at a high speed results in shifting being forcedly performed by line pressure, thereby eausing shift shock as well as possible damage to friction material. In addition, if manual control into the low L range is performed when driving in the third speed or higher, the second clutch C2 is disengaged such that engine fuel cut-off is performed at high speeds. As a result, an abrupt control into neutral occurs so that normal operation of the vehicle is not possible. 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 hydraulic control system for an automatic transmission, in which a powertrain is effectively and stably controlled by hydraulic pressure, the powertrain including a first friction element, which is used as an engine brake for discontinuing the operation of a one-way clutch, and a second friction element, which operates only when the first friction element is not engaged. Accordingly, to achieve the above object, the present invention provides a hydraulic control system for an automatic transmission that controls a powertrain, which includes a first friction element for use as an engine brake for discontinuing operation of a one-way clutch in the transmission and a second friction element operating only when the first friction element is disengaged, the hydraulic control system comprising a manual valve including a forward range port for exhausting hydraulic pressure when driving in a forward range, and an L range port for exhausting hydraulic pressure for low speed control; and a switch valve controlled by engine brake signal pressure, solenoid pressure, and forward range pressure supplied from the forward range port, the switch valve selectively supplying control pressure to the first friction element and the second friction element. According to a feature of the present invention, the engine brake signal pressure is L range pressure supplied from the L range port of the manual valve. According to another feature of the present invention, in the selective supply of control pressure to the first and second friction elements by the switch valve, when the forward range pressure is supplied, the control pressure is supplied to the second friction element only when either or both the engine brake signal pressure and the solenoid pressure is not being supplied. According to yet another feature of the present invention, the switch valve includes a spool, and the forward range pressure acts on one side of the spool and the engine brake signal pressure and the solenoid pressure act on an opposite side of the spool, wherein the spool includes a first land on which the forward range pressure acts, a second land on which the engine brake signal pressure acts, and a third land on which the solenoid pressure acts, and wherein one of either the second land or the third land has a surface area larger than a surface area of the first land and the other of either the second land or the third land has a surface area smaller than the surface area of the first land, and a difference between surface areas of the second land and the third land is smaller than the surface area of the first land. According to still yet another feature of the present invention, a valve body of the switch valve includes an input port for receiving control pressure, a first supply port formed in a direction toward the first land from the input port and connected to the first friction element, and a second supply port formed in a direction toward the second land from the input port and connected to the second friction element, and wherein fourth and fifth lands, which selectively communicate the input port with the first supply port and the second supply port, are formed on either side of the input port. According to still yet another feature of the present invention, the valve body of the switch valve further includes a first exhaust port for exhausting hydraulic pressure from the first supply port, and. a^ second exhaust port for exhausting pressure from the second supply port. 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, wherein: FIG. 1 is a schematic view of a hydraulic control system for an automatic transmission according to a preferred embodiment of the present invention; FIG. 2 is a sectional view of a switch valve of FIG. 1 in D, 3, 2, and L states; FIG. 3 is a sectional view of a switch valve of FIG. 1 in P, R, and N states; and FIG. 4 is a schematic view of a conventional hydraulic control system for an automatic transmission. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings. FIG. 1 shows a schematic view of a hydraulic control system for an automatic transmission according to a preferred embodiment of the present invention. Since line pressure control and damper clutch control are performed identically as in the prior art, a detailed description of these operations will not be provided. In FIG. 1, elements from a manual valve 2, which is directly involved in the control of shifting into the different ranges, to friction elements, are shown in block form. Friction elements C1, C2, C3, C4, B1, and B2 are engaged for different speeds and ranges identically as in the conventional hydraulic control system. That is, the first clutch C1 operates in first, second, and third speeds; the second clutch C2 operates in the third speed as well as a fourth speed; the third clutch C3 operates in a reverse R range; the fourth clutch C4 operates in a park P range, the reverse R range, a neutral N range, and a low L range, and as needed in the first, second, and third speeds; the first brake B1 operates in the park P, reverse R, neutral N and low L ranges; and the second brake B2 operates in the second and fourth speeds. However, in the present invention, structure is realized such that the first clutch C1 and the fourth clutch C4 jointly use a hydraulic pressure, and the second clutch C2 and the first brake B1 jointly use a hydraulic pressure. The third clutch C3 and the second brake B2, on the other hand, are supplied with different control pressures. In more detail, the first and fourth clutches C1 and C4 jointly use an output pressure of a first pressure control valve 4, which is controlled by a first solenoid valve S1, with the output pressure of the first pressure control valve 4 being directed by operation of a first switch valve 6 for the selective supply to the first and fourth clutches C1 and C4. Such joint utilization of pressure is possible since control of the first clutch C1 need only be performed during N—>• D shifting, while the fourth clutch C4 requires operation only in a second speed and higher. Also, the second clutch C2 and the first brake B1 jointly use an output pressure of a second pressure control valve 8 by operation of a second solenoid valve S2. That is, the output pressure of the second pressure control valve 8 is directed by a second switch valve 10 to be selectively supplied to the second clutch C2 and the first brake B1. The first and second switch valve 6 and 10 are both controlled by a fourth solenoid valve S4. Such joint utilization of the output pressure of the second pressure control valve 8 by the second clutch C2 and the first brake B1 is possible since control of the second clutch C2 need only be performed in the third and fourth speeds. To supply hydraulic pressure to the first brake B1 in the park P and neutral N ranges, N range pressure of the manual valve 2 is supplied to the second pressure control valve 8. The second brake B2 receives an output pressure of a third pressure control valve 12, which is controlled by a third solenoid valve S3. A fail-safe valve 14 is mounted between the second brake B2 and the third pressure control valve 12. Also, the third clutch C3 receives an output pressure of a fourth pressure control valve 16, with the fourth pressure control valve 16 also being controlled by the third solenoid valve S3. In the reverse R range, hydraulic pressure supplied to the fourth pressure control valve 16 is supplied to the first brake B1 via a shuttle valve 18 provided between the first brake B1 and the second switch valve 10. Among the various valves comprising the hydraulic circuit as described above, the second switch valve 10 will be described in more detail. For the conversion of port communication, the second switch valve 10 is controlled by D range pressure, and by control pressure of the fourth solenoid valve S4 as well as L range pressure supplied to an opposite side of the second switch valve 10. Lines are connected to the second switch valve 10 to enable the supply of hydraulic pressure supplied from the second pressure control valve 8 to the second clutch C2 and the exhaust of hydraulic pressure supplied to the first brake B1, or to enable the supply of hydraulic pressure supplied from the second pressure control valve 8 to the first brake B1 and the exhaust of hydraulic pressure supplied to the second clutch C2. Since it is possible to operate the second clutch C2 only during typical driving of the vehicle and the first brake in the reverse R range or first speed of the low L range, L range pressure is used as control pressure. However, if at the instant when the manual valve 2 is controlled to the low L range the supply of hydraulic pressure to the second clutch C2 is discontinued while that to the first brake B1 is started, shift shock or the momentary inability to transmit power may result. That is, shift shock results from the sudden supply of hydraulic pressure to the first brake B1, and in the' case where shifting into the low L range is performed when driving at high speeds (e.g., in third or fourth speeds of the drive D range), the sudden disengagement of the second clutch C2 and engagement of the first brake B1 results in the equally sudden increase in engine rpm. If engine rpm increases to a level at or higher than fuel cut-out rpm, normal operation of the vehicle is not possible. . ' /.,- Tosolve this problem, therefore, both L range pressure and pressure of the fourth solenoid valve S4 operate as control pressure on an opposite side of the second switch valve 108 to which D range pressure operates. That is, the conversion of port communication can be accomplished by the operation of both the L range pressure and the pressure of the fourth solenoid valve S4. In more detail, with reference to FIG. 2 and FIG. 3, the second switch valve 10 includes a first port 20 to which the output pressure of the second pressure control valve 8 is supplied, second and third ports 24 and 22 through which the hydraulic pressure supplied to the first port 20 is supplied respectively to the first brake B1 and the second clutch C2, a fourth port 26 to which D range pressure is supplied as control pressure, a fifth port 28 formed in a side of the second switch valve 10 opposite the fourth port 26 and which receives control pressure of the fourth solenoid valve S4, a sixth port 30 formed adjacent to the fifth port 28 and which receives line pressure as control pressure, and exhaust ports EX1 and EX2 for exhausting the hydraulic pressure supplied to the second and third ports 24 and 22, respectively. A valve spool mounted within a valve body of the second switch valve 10 includes a first land 32 on which the control pressure supplied through the fourth port 26 acts, a second land 34 operating together with the first land 32 to selectively communicate the second port.24 with the first port 20 and the first exhaust port EX1, a third land 36 operating together with the second land 34 to selectively communicate the first port 20 with the third port 22 and the second port 24 , a fourth land 38 on which the control pressure supplied through the sixth port 30 acts and which operates together with the third land 36 to •selectively communicate the third port 22 with the second exhaust port EX2, and a fifth land 40 on which the control pressure supplied through the fifth port 28 acts. One of either the fourth land 38 or the fifth land 40 has a surface area greater than that of the first land 32 (i.e., the fourth land 38), and one of either the fourth land 38 or the fifth land 40 has a surface area less than that of the first land 32 (i.e., the fifth land 40). Further, a difference in surface areas between the fourth and fifth lands 38 and 40 is less than the surface area of the first land 32. Accordingly, if hydraulic pressure is supplied either to the fifth port 28 or the sixth port 30 in the case where D range pressure is not supplied to the fourth port 26, the valve spool is displaced to the right (in the drawing) such that the hydraulic pressure supplied through the first port 20 is provided to the first brake Bl.via the second port 24. That is, in ranges and speeds other than a forward driving range or speed, the fourth solenoid valve S4 is operated to control the control pressure supplied through the fifth port 28 such that one-way control of the first brake B1 is possible when in the reverse R range. On the other hand, in the case where D range pressure is supplied to the fourth port 26, hydraulic pressure must be supplied to both the fifth and sixth ports 28 and 30 to move the valve spool to the right for the supply of hydraulic pressure to the first brake B1. As a result, if the driver, while driving at a high speed such as when in the third or fourth speeds, operates the shift lever into the low L range so that the manual valve 2 is also positioned in this range, although L range pressure is supplied to the second switch valve 10 through the sixth port 30, the pressure of the fourth solenoid valve S4 is controlled, thereby enabling suitable control of the timing and force of the hydraulic pressure supplied to the first brake B1. In the hydraulic control system for automatic transmissions according to a preferred embodiment of the present invention described above, a switch valve, which enables the supply of a single supply pressure by line conversion to the second clutch in the third and fourth speeds and to the first brake in the park P, reverse R, neutral N, and low L ranges, is controlled by solenoid control pressure and L range pressure, and by D range pressure supplied to an opposite side of the switch valve. As a result, damage to the powertrain caused by the simultaneous operation of the second clutch and the first brake is effectively prevented. That is, the present invention provides a hydraulic control system that effectively and stably controls the first brake, which operates as an engine brake, and the second clutch, which operates only when the first brake is disengaged. 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. I/WE Claim: 1. A hydraulic control system for an automatic transmission that controls a powertrain, which includes a fist friction element (C1) for use as an engine brake for discontinuing operation of a one-way clutch in the transmission and a second friction element (C2) operating only when the first friction element (C11) is disengaged, the hydraulic control system comprising: a manual valve (2) including a forward range port for exhausting hydraulic pressure when driving in a forward range, and an L range port for exhausting hydraulic pressure for low speed control; and a switch valve (10) controlled by engine brake signal pressure, solenoid pressure, and forward range pressure supplied from the forward range port, the switch valve selectively supplying control pressure to the first friction element (C1) and the second friction element (C2). 2. The hydraulic control system as claimed in claim 1 wherein the engine brake signal pressure is L range pressure supplied from the L range port of the manual valve (2). 3. The hydraulic control system as claimed in claim 1 wherein in the selective supply of control pressure to the first and second friction elements (C1, C2) by the switch valve (10), the control pressure is supplied to the second friction element (C2) only when the forward range pressure is supplied, and either or both the engine brake signal pressure and the solenoid pressure is not being supplied. 4. The hydraulic control system as claimed in claim 1 wherein the switch valve (10) comprises a spool, and the forward range pressure acts on one side of the spool and the engine brake signal pressure and the solenoid pressure act on an opposite side of the spool. wherein the spool includes a first land (32) on which the forward range pressure acts, a second land (34) on which the engine brake signal pressure acts, and a third land (36) on which the solenoid pressure acts, and wherein one of either the second land (34) or the third land (36) has a surface area larger than a surface area of the first land (32), and the other of either the second land (34) or the third land (36) has a surface area smaller than the surface area of the first land (32), and a difference between surface areas of the second land (34) and the third land (36) is smaller than the surface area of the first land (32). 5. The hydraulic control system as claimed in claim 4 wherein a valve body of the switch valve (10) comprises an input port for receiving control pressure, a first supply port formed in a direction toward the first land (32) from the input port and connected to the first friction element (C1), and a second supply port formed in a direction toward the second land (34) from the input port and connected to the second friction element (C2), and wherein fourth and fifth lands (38, 40), which selectively communicate the input port with the first supply port and the second supply port, are formed on either side of the input port. 6. The hydraulic control system as claimed in claim 5 wherein the valve body of the switch valve (10) further comprises a first exhaust port (EX1) for exhausting hydraulic pressure from the first supply port, and a second exhaust port (EX2) for exhausting pressure from the second supply port. 7. The hydraulic control system as claimed in claim 1 for an automatic transmission that controls a powertrain, which compresses a first brake (C1) for discontinuing operation of a one-way clutch operating in a low L range and a reverse R range and comprises a second clutch for transmitting power in third and fourth speeds, the hydraulic control system comprising: a manual valve (2) including a forward range port for exhausting hydraulic pressure when driving in a forward range, and an L range port for exhausting hydraulic pressure for low speed control; and a switch valve (10) controlled by L range pressure of the manual valve (2), forward range pressure, and first solenoid pressure, the switch valve being controlled by a second solenoid valve (S2) to selectively supply pressure to the second clutch (C2) and the fist brake (Bl), wherein the switch valve (10), in the case where the forward range pressure is supplied, supplies pressure controlled by the second solenoid valve (S2) to the second clutch (C2) in the case where L range pressure is not input and supplies the pressure controlled by the second solenoid valve (S2) to the first brake (Bl) by control of the first solenoid pressure in the case where the L range pressure is input, and wherein the switch valve (10) supplies pressure controlled by the second solenoid valve (S2) to the first brake (Bl) when the forward range pressure is not input. 8. The hydraulic control system as claimed in claim 7 wherein the forward range pressure is supplied as control pressure to a side of the switch (10) opposite that to which the L range pressure and the first solenoid pressure are supplied.

Documents:

1167-DEL-2001-Abstract.pdf

1167-DEL-2001-Claims-(08-03-2011).pdf

1167-DEL-2001-Claims.pdf

1167-DEL-2001-Correspondence-Others-(08-03-2011).pdf

1167-DEL-2001-Correspondence-Others-(28-12-2010).pdf

1167-DEL-2001-Correspondence-Others.pdf

1167-DEL-2001-Description (Complete)-(08-03-2011).pdf

1167-DEL-2001-Description (Complete).pdf

1167-DEL-2001-Drawings.pdf

1167-DEL-2001-Form-1.pdf

1167-DEL-2001-Form-18.pdf

1167-DEL-2001-Form-2.pdf

1167-DEL-2001-Form-3-(28-12-2010).pdf

1167-DEL-2001-Form-3.pdf

1167-DEL-2001-Form-5.pdf

1167-DEL-2001-PA.pdf

1167-DEL-2011-Abstract-(04-04-2012).pdf

1167-DEL-2011-Claims-(04-04-2012).pdf

1167-DEL-2011-Correspondence Others-(04-04-2012).pdf

1167-DEL-2011-GPA-(04-04-2012).pdf