# Patent

## Title
High efficiency hydraulic transmission control system

## Abstract

Pairs of variable feed solenoid valves provide fluid to a pair of input clutch actuators and a pair of inlet ports of a first logic valve. The position of the first logic valve spool is controlled by a solenoid valve. A first pair of outlet ports of the first logic valve provide hydraulic to a first piston which selects two speed ratio. A second pair of outlet ports of the first logic valve provide fluid to a pair of inlet ports of a second logic valve. The position of the second logic valve spool is controlled by fluid from the input clutch circuits. A first pair of outlet ports of the second logic valve provide fluid to a second piston which selects two other speed ratios and a second pair of outlet ports of the second logic valve provide fluid to a third piston which selects two additional speed ratios.

## Background
FIELD
The present disclosure relates to a hydraulic control system for a transmission and more particularly to a high efficiency hydraulic control system for a dual clutch transmission.
BACKGROUND
The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
In addition to conventional manual transmissions which employ an operator guided shift lever to selectively engage one of a plurality of parallel shift rails having shift forks coupled to synchronizer clutches and conventional automatic transmissions which employ a plurality of planetary gear sets and clutches and brakes that engage and disengage various components thereof, there is now an increasingly popular third option: the dual clutch transmission or DCT. In a typical dual clutch transmission, a plurality of synchronizer clutches and adjacent gears disposed on two parallel countershafts are exclusively engaged, followed by engagement of one of two main or input clutches associated with the respective countershafts.
Such dual clutch transmissions typically have five or six forward gears or speeds and reverse and thus three or four actuators to translate the synchronizer clutches. Such actuators are typically bi-directional hydraulic, electric or pneumatic devices. Electric actuators may be controlled by microprocessors having embedded logic software and hydraulic and pneumatic actuators may be controlled by fluid logic circuits having solenoid valves under microprocessor control.
Because of their excellent fuel economy and sporty performance including rapid shifts, which parallels that of manual transmissions, dual clutch transmissions are gaining recognition and acceptance in the marketplace. Given this trend, activity directed to all aspects of dual clutch design, control and operation is ongoing and the present invention is the result of such activity.
SUMMARY
The present invention provides a high efficiency hydraulic control system for a dual clutch transmission having one or two hydraulic pumps. In a first embodiment, a single hydraulic pump provides pressurized hydraulic fluid to a pressure control valve, filter and accumulator. A first pair of variable feed (VFS) solenoid valves independently and mutually exclusively provide hydraulic fluid to a respective pair of main or input clutch actuators. A second pair of variable feed solenoid valves provide hydraulic fluid to a pair of inlet ports of a first spool or logic valve. The position of the spool of the first logic valve is controlled by an on-off (two position) solenoid valve. A first pair of outlet ports of the first logic valve selectively provide hydraulic fluid to a first three area piston which selects two gear or speed ratios, for example, reverse and third gear. A second pair of outlet ports of the first logic valve selectively provide hydraulic fluid to a pair of inlet ports of a second spool or logic valve. The position of the spool of the second logic valve is controlled by hydraulic fluid from the main or input clutch circuits. A first pair of ports of the second logic valve selectively provide hydraulic fluid to a second three area piston which selects two other gear or speed ratios, for example, first and fifth gears and a second pair of ports of the second logic valve selectively provide hydraulic fluid to a third three area piston which selects two additional gear or speed ratios, for example, second and fourth gears. The hydraulic control system of the present invention is a high efficiency design that has particular utility in engine start-stop applications.
Thus it is an aspect of the present invention to provide a hydraulic control system for a dual clutch transmission.
It is a further aspect of the present invention to provide a high efficiency hydraulic control system for a dual clutch transmission.
It is a still further aspect of the present invention to provide a hydraulic control system for a dual clutch transmission having two main or input clutch actuators and two logic valves.
It is a still further aspect of the present invention to provide a hydraulic control system for a dual clutch transmission having a pump and an accumulator.
It is a still further aspect of the present invention to provide a hydraulic control system for a dual clutch transmission having a plurality of three area shift actuators.
Further aspects, advantages and areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.



DRAWINGS
The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.
FIG. 1 is a diagrammatic top plan view of a five speed dual clutch automatic transmission incorporating a hydraulic control system according to the present invention;
FIGS. 2A, 2B, 2C and 2D are a schematic flow diagram of a first embodiment of a hydraulic control system for a dual clutch transmission according to the present invention; and
FIG. 3 is a schematic flow diagram of a portion of a second embodiment of a hydraulic control system for a dual clutch transmission according to the present invention.



DETAILED DESCRIPTION
The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses.
With reference to FIG. 1, a dual clutch transmission incorporating the present invention is illustrated and generally designated by the reference number 10. The dual clutch transmission 10 includes a housing 12 having a plurality of bores, openings, flanges and the like which receive, locate and retain the components of the transmission 10. An input shaft 14 is coupled to and driven by a prime mover (not illustrated) such as a gasoline, Diesel, hybrid or electric power plant. The input shaft 14 is coupled to an input or housing 16 of a dual clutch assembly 18. The dual clutch assembly 18 includes a pair of input clutches, a first input clutch 20 and a second input clutch 22 which are commonly driven by the housing 16. The pair of input clutches 20 and 22 are controllably engaged or disengaged by a respective pair of hydraulic actuators or operators 24 and 26. The controlled output of the first input clutch 20 drives a first drive shaft 28 and the controlled output of the second input clutch 22 drives a second, concentrically disposed quill, drive tube or hollow shaft 30.
One of the features and benefits of dual clutch transmissions is the speed of an adjacent gear shift, e.g., a second gear to third gear upshift. Exceedingly rapid shifts are possible because the gear that is next to be engaged (third, for example) can be preselected or prestaged by synchronizing and connecting it to its countershaft. Actual engagement then involves only opening the input clutch associated with the currently engaged gear (second, for example) and engaging the input clutch associated with the new, desired gear (third). This feature requires that the gears be arranged so that numerically adjacent gears are not driven by the same input clutch. For example, first, third and fifth gears, the odd numbered gears, are arranged so that they are driven by one clutch and second, fourth and reverse gears, the even numbered gears, are driven by the other clutch—thereby permitting alternation of the active input clutches as a normal upshift progression through the gears occurs.
The dual clutch transmission 10 is configured to operate in this manner. On the first drive shaft 28 is a first drive gear 32 and a larger, second drive gear 34. The first drive gear 32 and the second drive gear 34 are coupled to and driven by the first drive shaft 28. On the second quill or drive tube 30 are a third drive gear 36 and a smaller, fourth drive gear 38. The third drive gear 36 and the fourth drive gear 38 are coupled to and driven by the second quill or drive tube 30.
A first countershaft or driven shaft 40A receives four freely rotating gears which are disposed in two, spaced-apart pairs. Each of the four gears is in constant mesh with one of the drive gears 32, 34, 36 or 38. A first large, driven gear 42 which provides the largest speed reduction and corresponds to first gear is in constant mesh with the first drive gear 32 on the first drive shaft 28. A second, smallest driven gear 44 provides the smallest speed reduction and corresponds to the highest gear, in this case, fifth gear. The ratio provided by the second driven gear 44 may be 1:1 or the second driven gear 44 may provide overdrive. The second driven gear 44 is in constant mesh with the second drive gear 34 on the first drive shaft 28. A third, intermediate size driven gear 46 provides an intermediate speed ratio which corresponds to fourth gear. The third driven gear 46 is in constant mesh with the third drive gear 36 on the second quill or drive tube 30. A fourth intermediate size driven gear 48 provides another intermediate speed ratio which corresponds to second gear. The fourth driven gear 48 is in constant mesh with the fourth drive gear 38 on the second quill or drive tube 30. A first output gear 50A is coupled to and driven by the first countershaft or driven shaft 40A.
A second countershaft or driven shaft 40B receives two freely rotating gears which are disposed in a spaced-apart pair. Each of the gears is in constant mesh with a drive gear. A fifth, smaller driven gear 52 provides another intermediate speed ratio which corresponds to third gear. The fifth driven gear 52 is in constant mesh with the second drive gear 34 on the first drive shaft 28. A sixth, larger driven gear 54 provides reverse. A reverse idler gear (not illustrated) is in constant mesh with both the sixth driven gear 54 and the fourth drive gear 38 on the second quill or drive tube 30. A second output gear 50B is coupled to and driven by the second countershaft or driven shaft 40B.
The first output gear 50A and the second output gear 50B mesh with and commonly drive an output gear (not illustrated) which is coupled to and drives an output shaft 62. The output shaft 62, in turn, drives a final drive assembly (FDA) 64 which may include a prop shaft, transfer case, at least one differential, axles and wheels (all not illustrated). The drive shaft 28 and the drive quill 30 as well as the countershafts 40A and 40B are preferably rotatably supported by pairs of ball bearing assemblies 66.
It should be appreciated that the actual numerical gear ratios provided by the driven gears 42, 44, 46, 48, 52 and 54 (and their associated drive gears) are a matter of design choice based upon the actual specifications and desired characteristics of the vehicle and its powertrain. Moreover, it should be appreciated that the arrangement of the gears 42, 44, 46, 48, 52 and 54 on the countershafts 40A and 40B is illustrative only and that they may be disposed in other arrangements with the proviso, stated above, that the gears of adjacent gear ratios, i.e., first and second, fourth and fifth, must be configured so that one input clutch provides one gear and the other input clutch provides the adjacent gear ratio.
Disposed intermediate the fifth driven gear 52 and the reverse gear 54 is a first double synchronizer clutch 70. The first synchronizer clutch 70 is slidably coupled to the second countershaft 40B by a spline set 72 and rotates therewith. The first synchronizer clutch 70 includes synchronizers and face or dog clutches (not illustrated) which selectively synchronize and then positively couple the fifth driven gear 52 or the reverse gear 54 to the second countershaft 40B when it is translated to the left or right. The first synchronizer clutch 70 includes a circumferential channel or groove 74 which is engaged by a second shift fork 76.
Disposed intermediate the first driven gear 42 and the second driven gear 44 is a second double synchronizer clutch 80. The second synchronizer clutch 80 is slidably coupled to the first countershaft 40A by a spline set 82 and rotates therewith. The second synchronizer clutch 80 includes synchronizers and face or dog clutches (not illustrated) which selectively synchronize and then positively couple the first driven gear 42 or the second driven gear 44 to the first countershaft 40A when it is translated to the left or right, as illustrated in FIG. 1. The second synchronizer clutch 80 includes a circumferential channel or groove 84 which is engaged by a first shift fork 86.
Disposed intermediate the third driven gear 46 and the fourth driven gear 48 is a third double synchronizer clutch 90. The third synchronizer clutch 90 is slidably coupled to the first countershaft 40A by a spline set 92 and rotates therewith. The third synchronizer clutch 90 also includes synchronizers and face or dog clutches (not illustrated) which selectively synchronize and then positively couple the third driven gear 46 or the fourth driven gear 48 to the first countershaft 40A when it is translated to the left or right. The third synchronizer clutch 90 includes a circumferential channel or groove 94 which is engaged by a third shift fork 96.
Referring now to FIGS. 2A, 2B, 2C and 2D, a hydraulic control system for the dual clutch transmission 10 illustrated in FIG. 1 is illustrated and generally designated by the reference number 100. The hydraulic control system 100 includes a common sump 102 which is preferably disposed in the lower portion of the transmission housing 12. A first suction line 104 which preferably includes an inlet fiter (not illustrated) communicates between the sump 102 and an inlet or suction port of a first mechanical pump 106. The first mechanical pump 106 is preferably a vane, gear or gerotor pump and provides pressurized hydraulic fluid in a first supply line 108 to a clutch cooling circuit. The first supply line 108 communicates with an inlet port 112A of a cooler pressure regulator 112. The first supply line also communicates with a first control port 112C through a flow restricting orifice 114 and with a pressure relief valve 115. An outlet port 1128 of the cooler pressure regulator 112 is connected through a line 116 and an orifice 118 with a hydraulic fluid cooler or heat exchanger 120 through which also passes (in isolation) a heat sink medium. The cooler pressure regulator 112 also includes a second control port 112D which is connected through an orifice 124 and a hydraulic line 126 to an outlet port 130B of a variable force solenoid valve (VFS) 130. The variable force solenoid valve 130 also includes an inlet port 130A and an exhaust port 130D.
The hydraulic control system 100 also includes a second suction line 138 which communicates between the common sump 102 and an inlet or suction port of a second mechanical pump 140. The second mechanical pump 140 is also preferably a vane, gear or gerotor pump and provides pressurized hydraulic fluid in a second supply line 142 to shift logic and clutch control components. The second supply line 142 communicates with an inlet port 144A of a pump bypass valve 144. The position of a spool 146 within the bypass valve 144 is controlled by an on-off (two position) pump bypass solenoid valve 148 having an inlet port 148A and an outlet port 148B which is in fluid communication with a control port of the pump bypass valve 144. When the pump bypass solenoid valve 148 is de-energized, the spool 146 of the bypass valve 144 is in the position illustrated in FIG. 2A and hydraulic fluid in the second supply line 142 is routed along a supply line 150. When the pump bypass solenoid valve 148 is energized, the spool 146 of the bypass valve 144 translates to the left in FIG. 2A and hydraulic fluid in the second supply line 142 is routed back to the common sump 102 through a line 152. The supply line 150 is in fluid communication with a pressure relief or line blow off valve 154 and a filter 156 which is in fluid parallel with a cold oil bypass valve 158. Downstream of the filter 156 and the cold oil bypass valve 158 is a pressure retention check valve 160. The pressure retention check valve 160 is configured to maintain hydraulic pressure and fluid in a downstream main supply line 162 while permitting fluid flow from the supply line 150 to the main supply line 162. A gas filled or spring accumulator 166 and a main pressure sensor 168 are also in fluid communication with the main supply line 162.
The main supply line 162 communicates with a main manifold 170 having a plurality of ports, outlets or manifold supply lines. A first manifold supply line 170A communicates through a filter 172 with an inlet port 174A of a first (even) clutch variable force (VFS) solenoid valve 174 having an outlet port 174B which communicates through a filter 176 to a first (even) clutch pressure sensor or switch 178 which detects clutch fill, a cylinder 182 of the first (even) clutch actuator or operator 24 and a logic valve supply line 184. An exhaust port 174D of the first clutch solenoid valve 174 is in fluid communication with a fluid exhaust manifold 190. A second manifold supply line 170B communicates through a filter 186 with the inlet port 130A of the variable force solenoid valve 130. A third manifold supply line 170C communicates through a filter 192 with an inlet port 200A of a first shift variable force solenoid (VFS) valve 200. The first shift variable force solenoid valve 200 includes an outlet port 200B which is in fluid communication with a filter 202 and a fluid supply line 204. An exhaust port 200D is in fluid communication with the fluid exhaust manifold 190. A fourth manifold supply line 170D communicates with the inlet port 148A of the on-off (two position) pump bypass solenoid valve 148. A fifth manifold supply line 170E communicates through a filter 208 with an inlet port 210A of a second shift variable force solenoid (VFS) valve 210. The second shift variable force solenoid valve 210 includes an outlet port 210B which is in fluid communication with a filter 212 and a fluid supply line 214. An exhaust port 210D is in fluid communication with the fluid exhaust manifold 190. A sixth manifold supply line 170F communicates with an inlet port 220A of a master logic solenoid valve 220. Finally, a seventh manifold supply line 170G communicates through a filter 228 with an inlet port 230A of a second (odd) clutch variable force solenoid (VFS) valve 230 having an outlet port 230B which communicates through a filter 232 to a second (odd) clutch pressure sensor or switch 234 which detects clutch fill, a cylinder 236 of the second clutch actuator or operator 26 and a logic valve supply line 238. An exhaust port 230D of the second clutch solenoid valve 230 is in fluid communication with the fluid exhaust manifold 190.
Returning to the master logic solenoid valve 220, it includes an outlet port 220B which is in fluid communication with a control port 240C of a first or master logic spool or control valve 240. The first or master logic valve 240 includes a housing 242 having or defining a plurality of inlet and outlet ports and which receives a spool 244 having a plurality of lands which separate and control fluid flows through the housing 242. When the master logic solenoid valve 220 is de-energized or inactive, no pressurized hydraulic fluid is provided to the control port 240C and the spool 244 resides in the position illustrated in FIG. 2C. When the master logic solenoid 220 is energized or active, pressurized hydraulic fluid is provided to the control port 240C and the spool 244 translates to the left in FIG. 2C.
The first or master logic spool or control valve 240 includes a first inlet port 240A which is fluid communication with the outlet port 200B of the first variable flow shift solenoid valve 200 through the line 204 and a second inlet port 240B which is fluid communication with the outlet port 210B of the second variable flow shift solenoid valve 210 through the line 214. The first or master logic spool or control valve 240 includes a plurality of exhaust ports 240D, 240E, 240F and 240G which communicate through a branch or extension of the fluid exhaust manifold 190 to the sump 102. The first or master logic spool or control valve 240 also includes a first outlet port 240H which communicates through a line 248 with a port 252A in a housing or cylinder 252 of a first shift actuator assembly 250. At the opposite end of the cylinder 252, a second port 252B communicates through a line 254 to a third outlet port 240J.
The first shift actuator assembly 250 includes a three area piston 256. The three area piston 256 is a conventional hydraulic component that, by virtue of its construction, provides three distinct operational positions: a first position at one end or limit of piston travel, a second fixed or defined position generally midway in its travel and a third position at the other end or limit of piston travel. The end positions of the piston 256 (and the other three area pistons) typically engage gears whereas the center position is neutral. The end positions are achieved by appropriate application and release of hydraulic fluid on the faces of the pistons whereas the center position is achieved by pressurizing both faces of the pistons equally. The first shift actuator assembly 250 and specifically the piston rod 258 preferably includes or is connected to a position sensor or position switch (not illustrated) which provides data regarding its current position. The three area piston 256 is connected to the piston rod 258 which, in turn, is connected to the first shift fork 76. A first detent assembly 262 having a spring biased detenting ball 264 or similar structure cooperates with a detenting recess 78 on the first shift fork 76 and assists obtaining and maintaining a selected position of the shift fork 76. Alternatively, shift actuators having two area pistons, which lack the defined center position, may be utilized instead of the three area pistons but will require the addition of linear (proportional) position sensors to provide continuous data regarding the position of the piston, piston rod and shift fork.
When the master logic solenoid 220 is energized or active, pressurized hydraulic fluid is provided to the control port 240C and the spool 244 translates to the left. So disposed, hydraulic fluid controlled by the first variable flow shift solenoid valve 200 travels through the lines 204 and 248 and translates the three area piston 256 to the right to engage, for example, reverse. Alternatively, hydraulic fluid controlled by the second variable flow shift solenoid valve 210 travels through the lines 214 and 254 and translates the three area piston 256 to the left to engage, for example, third gear. It will be appreciated that accompanying such operation, and that described below, is the release of hydraulic fluid from the unpressurized side of the cylinder 252 to the fluid exhaust manifold 190. Moreover, the neutral, center position of the piston 256 is achieved by providing pressurized hydraulic fluid through both variable flow shift solenoid valves 200 and 210 and both lines 248 and 254, as described above. When the master logic solenoid 220 is de-energized or inactive, the spool 244 returns to and resides in the position illustrated in FIG. 2C, as noted above.
A second outlet port 240I of the first or master logic spool or control valve 240 communicates with a line 266 to a first inlet port 270A of a second or slave logic spool or control valve 270 and a fourth outlet port 240K of the first or master logic spool or control valve 240 communicates with a line 268 to a second inlet port 270B of the second or slave logic valve 270. The second or slave logic valve 270 includes a housing 272 having or defining a plurality of inlet and outlet ports and which receives a spool 274 having a plurality of lands which separate and control fluid flows through the housing 272.
The second or slave logic valve 270 includes a first control port 270CA which is in fluid communication with the hydraulic line 184 and a second control port 270CB which is in fluid communication with the hydraulic line 238. It will thus be appreciated that the position of the spool 274 of the second or slave logic valve 270 is dictated by whether the first (even) input clutch 20 is activated and thus that there is hydraulic pressure in the line 184 or that the second (odd) input clutch 22 is activated and thus that there is hydraulic pressure in the line 238. The second or slave logic valve also includes a plurality of exhaust ports 270D, 270E and 270F which communicate through the fluid exhaust manifold 190 which flows to the sump 102.
The second or slave logic spool or control valve 270 also includes a second outlet port 270I which communicates through a line 276 with a port 282A in a housing or cylinder 282 of a second shift actuator assembly 280. At the opposite end of the cylinder 282, a second port 282B communicates through a line 278 to a fourth outlet port 270K. The second shift actuator assembly 280 also includes a three area piston 286. The three area piston 286 is connected to a second piston rod 288 which, in turn, is connected to the second shift fork 86. A second detent assembly 292 having a spring biased detenting ball 294 or similar structure cooperates with a detenting recess 88 on the second shift fork 86 and assists obtaining and maintaining a selected position of the second shift fork 86.
The second or slave logic spool or control valve 270 further includes a first outlet port 270H which communicates through a line 296 with a port 302A in a housing or cylinder 302 of a third shift actuator assembly 300. At the opposite end of the cylinder 302, a second port 302B communicates through a line 298 to a third outlet port 270J. The third shift actuator assembly 300 also includes a three area piston 306. The three area piston 306 is connected to a third piston rod 308 which, in turn, is connected to the third shift fork 96. A third detent assembly 312 having a spring biased detenting ball 314 or similar structure cooperates with a detenting recess 98 on the third shift fork 96 and assists obtaining and maintaining a selected position of the third shift fork 96.
Last of all, the second or slave logic spool or control valve 270 includes a clutch cooler inlet port 270Y which is in fluid communication with the outlet of the hydraulic fluid cooler 120 through a hydraulic line 320. When the spool 274 of the second spool or control valve 270 is in the de-energized or relaxed position illustrated in FIG. 2D, hydraulic fluid flows out an outlet port 270Z and returns in a line 322 to provide cooling of the first clutch 20 associated with the even numbered gears. A flow controlling orifice 326 is disposed between the hydraulic line 320 and the line 322.
When the spool 274 of the second spool or control valve 270 is in the energized or active position, to the left in FIG. 2D, hydraulic fluid flows out an outlet port 270X and returns in a line 324 to provide cooling of the second clutch 22 associated with the odd numbered gears. Another flow controlling orifice 328 is disposed between the hydraulic line 320 and the line 324. In operation, hydraulic fluid from the cooler pressure regulator 112 flows in the line 116, through the orifice 118 and the cooler 120. Then the hydraulic fluid flows either through the line 320 to the inlet port 270Y of the second logic or spool valve 270 which prioritizes fluid flow to either the line 322 and the first clutch 20 or the line 324 and the second clutch 22 or through the orifices 326 and 328 to the respective clutches 20 and 22.
Selection and operation of first, second, fourth and fifth gears will now be described with emphasis on the second spool or control valve 270. When the second spool or control valve 270 is in the de-energized or relaxed position illustrated in FIG. 2D, and the spool 244 of the first spool or control valve 240 is also in its de-energized or relaxed position as illustrated in FIG. 2C, pressurized hydraulic fluid provided through the line 266 and the first inlet port 270A will be routed to the second outlet port 270I and through the line 276 and the port 282A to translate the second piston 286 to the right to engage, for example, fifth gear. Alternatively, pressurized hydraulic fluid provided through the line 268 and the second inlet port 270B will be routed to the fourth outlet port 270K and through the line 278 and the port 282B to translate the second piston 286 to the left to engage, for example, first gear.
When the second spool or control valve 270 is in the energized or active position, to the left in FIG. 2D, and the spool 244 of the first spool or control valve 240 is in its de-energized or relaxed position as illustrated in FIG. 2C, pressurized hydraulic fluid provided through the line 266 and the first inlet port 270A will be routed to the first outlet port 270H and through the line 296 and the port 302A to translate the third piston 306 to the right to engage, for example, second gear. Alternatively, pressurized hydraulic fluid provided through the line 268 and the second inlet port 270B will be routed to the third outlet port 270J and through the line 298 and the port 302B to translate the third piston 306 to the left to engage, for example, fourth gear.
Referring now to FIGS. 2A and 3, FIG. 3 illustrates a second embodiment of the hydraulic control system 100 of FIGS. 2A through 2D which incorporates an alternate fluid supply configuration. As such, the second embodiment hydraulic control system 100′ includes only a single mechanical pump, the pump 106, having the suction line 104 which withdraws hydraulic fluid from the sump 102. The mechanical pump 106 is, once again, preferably a vane, gear or gerotor pump. The outlet or supply line 108 communicates with the inlet port 144A of the pump bypass valve 144. The position of the spool 146 within the bypass valve 144 is controlled by the on-off (two position) pump bypass solenoid valve 148 which includes the inlet port 148A and the outlet port 148B which is in fluid communication with the control port of the pump bypass valve 144.
When the spool 146 is in the position illustrated, to the right in FIG. 3, hydraulic fluid flow from the mechanical pump 106 and the supply line 108 is provided to the main supply line 150 and flow, through an outlet port 144D limited by an orifice 330, occurs in a line 332 which communicates with the inlet port 112A of the cooler pressure regulator 112, the control port 122C of the cooler pressure regulator 112 through the orifice 114 and the pressure relief valve 115. The orifice 330 always provides minimal hydraulic fluid flow and cooling to the clutches 20 and 22. When the pump bypass valve 148 is energized or active and hydraulic pressure translates the spool 146 to the left, pressurized hydraulic fluid is not supplied to the main supply line 150 and unrestricted flow occurs through an outlet port 144E to the inlet port 112A of the cooler pressure regulator 112. The inlet port 148A of the pump bypass solenoid valve 148 is supplied with hydraulic fluid from the second manifold supply line 170B. The cooler pressure variable force solenoid valve 130 regulates pressure or flow to the outlet port 130D The second outlet port 130D communicates through the line 126 and the orifice 124 to the control port 112D of the cooler pressure or flow regulator 112.
The components and operation of the remainder of the second embodiment control system 100′ are the same as the first embodiment and include the cooler 120, the main manifold 170, the first clutch solenoid valve 174, the first shift solenoid valve 200, the second shift solenoid valve 210, the second clutch solenoid valve 230, the master logic solenoid valve 220, the first logic or spool valve 240, the second logic or spool valve 270, the shift actuator assemblies 250, 280 and 300 and the associated hydraulic lines and filters.
The foregoing embodiments of the invention having the accumulator 166, the pump bypass valve 144, and the engine driven pump 106 or pumps 106 and 140 provide operational efficiency much greater than a hydraulic control system without the accumulator. The incorporation of the accumulator 166 allows downsizing of the pump, and improved engine start-stop capability. The hydraulic control systems 100 and 100′ have essentially minimum content to control a wet dual clutch transmission such as the transmission 10 and are thus an efficient control system design.
The description of the invention is merely exemplary in nature and variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.

## Claims

1. A hydraulic control system for a dual clutch transmission comprising, in combination,
a source of hydraulic fluid including a pump, a bypass valve, an accumulator and a cooling pressure regulator valve,
a first variable force solenoid valve in fluid communication with said source of fluid and having a first output provided to a first clutch actuator,
a second variable force solenoid valve in fluid communication with said source of fluid and having a second output,
a third variable force solenoid valve in fluid communication with said source of fluid and having a third output,
a fourth variable force solenoid valve in fluid communication with said source of fluid and having a fourth output provided to a second clutch actuator,
a fifth variable force solenoid valve in fluid communication with said source of fluid and having a fifth output provided to said cooling pressure regulator valve,
an on-off solenoid valve in fluid communication with said source of fluid and having a output provided to said bypass valve,
a first logic valve having a pair of inlets in respective fluid communication with said second output and said third output and four outlets,
a first shift actuator having a pair of ports in fluid communication with a pair of said outlets,
a second logic valve having a pair of inlets in fluid communication with another pair of said outlets, two control ports and four actuator outlets, said control ports in respective fluid communication with said first output and said fourth output,
a second shift actuator having a pair of ports in fluid communication with a pair of said actuator outlets, and
a third shift actuator having pair of ports in fluid communication with another pair of said actuator outlets.

2. The hydraulic control system of claim 1 wherein said shift actuators each include three area pistons.

3. The hydraulic control system of claim 1 wherein said bypass valve is a two position valve.

4. The hydraulic control system of claim 1 further including a first input clutch acted upon by said first clutch actuator and a second input clutch acted upon by said second clutch actuator.

5. The hydraulic control system of claim 4 further including a heat exchanger for cooling hydraulic fluid provided to said first and said second input clutches.

6. The hydraulic control system of claim 1 further including a two position solenoid valve for selectively providing hydraulic fluid to a control port of said first logic valve.

7. A hydraulic control system for a dual clutch transmission comprising, in combination,
a source of hydraulic fluid including two pumps, a pump bypass valve and an accumulator,
a first variable force solenoid valve in fluid communication with said source of fluid and having a first output communicating with a first input clutch actuator,
a second variable force solenoid valve in fluid communication with said source of fluid and having a second output,
a third variable force solenoid valve in fluid communication with said source of fluid and having a third output,
a fourth variable force solenoid valve in fluid communication with said source of fluid and having a fourth output communicating with a second input clutch actuator,
a fifth variable force solenoid valve in fluid communication with said source of fluid,
an on-off solenoid valve in fluid communication with said source of fluid and having a output provided to said pump bypass valve,
a first logic valve having a pair of inlets in respective fluid communication with said second output and said third output and four outlets,
a first shift actuator having a pair of ports in fluid communication with a pair of said outlets,
a second logic valve having a pair of inlets in fluid communication with another pair of said outlets, two control ports and four actuator outlets, said control ports in respective fluid communication with said first output and said fourth output,
a second shift actuator having a pair of ports in fluid communication with a pair of said actuator outlets, and
a third shift actuator having pair of ports in fluid communication with another pair of said actuator outlets.

8. The hydraulic control system of claim 7 wherein said shift actuators each include three area pistons.

9. The hydraulic control system of claim 7 further including a two position solenoid valve for selectively providing hydraulic fluid to a control port of said first logic valve.

10. The hydraulic control system of claim 7 wherein said pump bypass valve is a two position valve.

11. The hydraulic control system of claim 7 further including a first input clutch acted upon by said first clutch actuator and a second input clutch acted upon by said second clutch actuator.

12. The hydraulic control system of claim 11 further including a heat exchanger for cooling hydraulic fluid provided to said first and said second input clutches.

13. The hydraulic control system of claim 7 further including a cooling pressure regulator valve and wherein said fifth variable force solenoid valve includes a fifth output provided to said cooling pressure regulator valve.

14. The hydraulic control system of claim 7 further including a shift fork and a synchronizer clutch associated with each of said shift actuators.