Wet dual clutch transmission control system

Pairs of variable feed solenoid valves provide fluid to a pair of input clutch actuators and a pair of inlet ports of a first or 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 fluid to a first piston which selects two speed ratios. 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.

FIELD

The present disclosure relates to a hydraulic control system for a transmission and more particularly to a hydraulic control system for a wet dual clutch transmission.

BACKGROUND

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 wet dual clutch transmission having an engine driven pump. A first pair of variable force solenoid (VFS) valves independently and mutually exclusively provide hydraulic fluid to a respective pair of main or input clutch actuators. A second pair of variable force 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.

Thus it is an aspect of the present invention to provide a hydraulic control system for a wet dual clutch transmission.

It is a further aspect of the present invention to provide a hydraulic control system for a wet 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 wet dual clutch transmission having an engine driven pump.

It is a still further aspect of the present invention to provide a hydraulic control system for a wet dual clutch transmission having a plurality of three area shift actuators.

DETAILED DESCRIPTION

With reference toFIG. 1, a wet dual clutch transmission incorporating the present invention is illustrated and generally designated by the reference number10. The wet dual clutch transmission10includes a housing12having a plurality of bores, openings, flanges and the like which receive, locate and retain the components of the transmission10. An input shaft14is coupled to and driven by a prime mover (not illustrated) such as a gasoline, Diesel, hybrid or electric power plant. The input shaft14is coupled to an input or housing16of a dual clutch assembly18. The dual clutch assembly18includes a pair of wet input clutches, a first input clutch20and a second input clutch22which are commonly driven by the housing16. The pair of input clutches20and22are controllably engaged or disengaged by a respective pair of hydraulic actuators or operators24and26. The controlled output of the first input clutch20drives a first drive shaft28and the controlled output of the second input clutch22drives a second, concentrically disposed quill, drive tube or hollow shaft30.

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 wet dual clutch transmission10is configured to operate in this manner. On the first drive shaft28are a first drive gear32and a larger, second drive gear34. The first drive gear32and the second drive gear34are coupled to and driven by the first drive shaft28. On the second quill or drive tube30are a third drive gear36and a smaller, fourth drive gear38. The third drive gear36and the fourth drive gear38are coupled to and driven by the second quill or drive tube30.

A first countershaft or driven shaft40A 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 gears32,34,36or38. A first large, driven gear42which provides the largest speed reduction and corresponds to first gear is in constant mesh with the first drive gear32on the first drive shaft28. A second, smallest driven gear44provides the smallest speed reduction and corresponds to the highest gear, in this case, fifth gear. The second driven gear44is in constant mesh with the second drive gear34on the first drive shaft28. A third, intermediate size driven gear46provides an intermediate speed ratio which corresponds to fourth gear. The third driven gear46is in constant mesh with the third drive gear36on the second quill or drive tube30. A fourth intermediate size driven gear48provides another intermediate speed ratio which corresponds to second gear. The fourth driven gear48is in constant mesh with the fourth drive gear38on the second quill or drive tube30. A first output gear50A is coupled to and driven by the first countershaft or driven shaft40A.

A second countershaft or driven shaft40B 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 gear52provides another intermediate speed ratio which corresponds to third gear. The fifth driven gear52is in constant mesh with the second drive gear34on the first drive shaft28. A sixth, larger driven gear54provides reverse. A reverse idler gear (not illustrated) is in constant mesh with both the sixth driven gear54and the fourth drive gear38on the second quill or drive tube30. A second output gear50B is coupled to and driven by the second countershaft or driven shaft40B.

The first output gear50A and the second output gear50B mesh with and commonly drive an output gear (not illustrated) which is coupled to and drives an output shaft62. The output shaft62, in turn, drives a final drive assembly (FDA)64which may include a prop shaft, transfer case, at least one differential, axles and wheels (all not illustrated). The drive shaft28and the drive quill30as well as the countershafts40A and40B are preferably rotatably supported by pairs of ball bearing assemblies66.

It should be appreciated that the actual numerical gear ratios provided by the driven gears42,44,46,48,52and54(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 gears42,44,46,48,52and54on the countershafts40A and40B 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 gear52and the reverse gear54is a first double synchronizer clutch70. The first synchronizer clutch70is slidably coupled to the second countershaft40B by a spline set72and rotates therewith. The first synchronizer clutch70includes synchronizers and face or dog clutches (not illustrated) which selectively synchronize and then positively couple the fifth driven gear52or the reverse gear54to the second countershaft40B when it is translated to the left or right. The first synchronizer clutch70includes a circumferential channel or groove74which is engaged by a second shift fork76.

Disposed intermediate the first driven gear42and the second driven gear44is a second double synchronizer clutch80. The second synchronizer clutch80is slidably coupled to the first countershaft40A by a spline set82and rotates therewith. The second synchronizer clutch80includes synchronizers and face or dog clutches (not illustrated) which selectively synchronize and then positively couple the first driven gear42or the second driven gear44to the first countershaft40A when it is translated to the left or right, as illustrated inFIG. 1. The second synchronizer clutch80includes a circumferential channel or groove84which is engaged by a first shift fork86.

Disposed intermediate the third driven gear46and the fourth driven gear48is a third double synchronizer clutch90. The third synchronizer clutch90is slidably coupled to the first countershaft40A by a spline set92and rotates therewith. The third synchronizer clutch90also includes synchronizers and face or dog clutches (not illustrated) which selectively synchronize and then positively couple the third driven gear46or the fourth driven gear48to the first countershaft40A when it is translated to the left or right. The third synchronizer clutch90includes a circumferential channel or groove94which is engaged by a third shift fork96.

Referring now toFIG. 2, a first embodiment of a hydraulic control system for the wet dual clutch transmission10illustrated inFIG. 1is illustrated and generally designated by the reference number100. The hydraulic control system100includes a sump102which is preferably disposed in a lower portion of the transmission housing12. A first suction line104which preferably includes an inlet filter106communicates between the sump102and an inlet or suction port108of an engine driven mechanical pump110. The engine driven pump110is preferably a vane, gear or gerotor pump and provides pressurized hydraulic fluid in a first supply line112. The first supply line112is in fluid communication with a pressure relief or line blow off valve114and a filter116which is in fluid parallel with a cold oil bypass valve118. The cold oil bypass valve118ensures that, notwithstanding the high viscosity of cold oil or hydraulic fluid and reduced flow through the filter116during cold weather start-ups, oil or hydraulic fluid will be available and supplied to downstream components. The filter116and the cold oil bypass valve118communicate with a main supply line120having a first branch122which includes a flow restricting orifice124and a second branch126. Both of the branches122and126communicate with a cooling priority and line pressure regulator130.

The cooling priority and line pressure regulator130includes a cylindrical housing132having a plurality of ports and which receives a spool134having multiple lands. The line pressure regulator130includes a first inlet port130A in communication with the second branch126of the main supply line120, a second inlet port130B in communication with a line138to a cooler pressure feed limit valve150and a first control port130CA in communication with the orifice124. Adjacent the first control port130CA is an exhaust port130D which communicates with the sump102. A first outlet port130E of the line pressure regulator130communicates with the sump102through a line142, a second outlet port130F communicates through a flow restricting orifice144in a line146to an oil or hydraulic fluid cooler148. The line pressure regulator130also includes a second control port130CB.

The cooler pressure feed limit valve150includes a cylindrical housing152having a plurality of ports and which receives a spool154having two lands. The line138from the second inlet port130B of the line pressure regulator130communicates with a control port150C of the cooler pressure feed limit valve150through an orifice156. An outlet port150B of the cooler pressure feed limit valve150is also connected to the line138. An inlet port150A communicates with a manifold170through a fifth manifold supply line170E. An exhaust port150D is connected to a fluid exhaust manifold190. The line138also communicates with a cooler overpressure check valve158which relieves or limits maximum pressure in the line138.

A line pressure variable force solenoid (VFS) valve160includes an inlet port160A which is connected to a third manifold supply line170C, an outlet port160B which is connected to the second control port130CB of the line pressure regulator130through a line162having a flow restricting orifice164and an exhaust port160D which communicates with the fluid exhaust manifold190through a line166.

The main supply line120communicates with the main manifold170which includes a plurality of ports, outlets or manifold supply lines. A first manifold supply line170A communicates through a filter172with an inlet port174A of a first (even) clutch variable force solenoid (VFS) valve174having an outlet port174B which communicates through a filter176to a first (even) clutch pressure sensor or switch178, a cylinder182of the first (even) clutch actuator or operator24and a logic valve supply line184. An exhaust port174D of the first clutch solenoid valve174is in fluid communication with a fluid exhaust manifold190. A second manifold supply line170B communicates through a filter192with an inlet port200A of a first shift variable force solenoid (VFS) valve200. The first shift variable force solenoid valve200includes an outlet port200B which is in fluid communication with a filter202and a fluid supply line204. An exhaust port200D is in fluid communication with the fluid exhaust manifold190.

As noted above, the third manifold supply line170C communicates with the inlet port160A of the line pressure solenoid valve160. A fourth manifold supply line170D communicates through a filter208with an inlet port210A of a second shift variable force solenoid (VFS) valve210. The second shift variable force solenoid valve210includes an outlet port210B which is in fluid communication with a filter212and a fluid supply line214. An exhaust port210D is in fluid communication with the fluid exhaust manifold190. As noted above, the fifth manifold supply line170E communicates with the inlet port150A of the cooler pressure feed limit valve150. A sixth manifold supply line170F communicates with an inlet port220A of a master logic solenoid valve220. Finally, a seventh manifold supply line170G communicates through a filter228with an inlet port230A of a second (odd) clutch variable force solenoid (VFS) valve230having an outlet port230B which communicates through a filter232to a second (odd) clutch pressure sensor or switch234, a cylinder236of the second clutch actuator or operator26and a logic valve supply line238. An exhaust port230D of the second clutch solenoid valve230is in fluid communication with the fluid exhaust manifold190.

Returning to the master logic solenoid valve220, it includes an outlet port220B which is in fluid communication with a control port240C of a first or master logic spool or control valve240. The first or master logic spool or control valve includes a housing242having or defining a plurality of inlet and outlet ports and which receives a spool244having a plurality of lands which separate and control fluid flows through the housing242. When the master logic solenoid valve220is de-energized or inactive, no pressurized hydraulic fluid is provided to the control port240C and the spool244resides in the position illustrated inFIG. 2. When the master logic solenoid valve220is energized or active, pressurized hydraulic fluid is provided to the control port240C and the spool244translates to the left inFIG. 2.

The first or master logic spool or control valve240includes a first inlet port240A which is fluid communication with the outlet port200B of the first shift variable force solenoid valve200through the line204and a second inlet port240B which is fluid communication with the outlet port210B of the second shift variable force solenoid valve210through the line214. The first or master logic spool or control valve240includes a plurality of exhaust ports240D,240E,240F and240G which communicate through a branch or extension of the fluid exhaust manifold190to the sump102. The first or master logic spool or control valve240also includes a first outlet port240H which communicates through a line248with a port252A in a housing or cylinder252of a first shift actuator assembly250. At the opposite end of the cylinder252, a second port252B communicates through a line254to a third outlet port240J.

The first shift actuator assembly250includes a three area piston256. The three area piston256is 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 piston256(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 three area piston256is connected to a piston rod258which, in turn, is connected to the first shift fork76. The first shift actuator assembly250and specifically the piston rod258preferably includes or is connected to a position switch or position sensor (not illustrated) which provides data regarding its current position. Dependent on failure modes, there are cases in which the switch on two of the rails may be eliminated and replaced with pressure switches on the outlet ports200B and210B of the first and second shift variable force solenoid (VFS) valves,200and210. 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. A first detent assembly262having a spring biased detenting ball264or similar structure cooperates with a detenting recess78on the first shift fork76and assists obtaining and maintaining a selected position of the shift fork76.

When the master logic solenoid220is energized or active, pressurized hydraulic fluid is provided to the control port240C and the spool244translates to the left. So disposed, hydraulic fluid controlled by the first shift variable force solenoid valve200travels through the lines204and248and translates the three area piston256to the right to engage, for example, reverse. Alternatively, hydraulic fluid controlled by the second shift variable force solenoid valve210travels through the lines214and254and translates the three area piston256to 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 cylinder252to the fluid exhaust manifold190. Moreover, the neutral, center position of the piston256is achieved by providing pressurized hydraulic fluid through both shift variable force solenoid valves200and210and both lines248and254, as described above. When the master logic solenoid220is de-energized or inactive, the spool244returns to and resides in the position illustrated inFIG. 2, as noted above.

A second outlet port240I of the first or master logic spool or control valve240communicates with a line266to a first inlet port270A of a second or slave logic spool or control valve270and a fourth outlet port240K of the first or master logic spool or control valve240communicates with a line268to a second inlet port270B of the second or slave logic valve270. The second or slave logic valve270includes a housing272having or defining a plurality of inlet and outlet ports and which receives a spool274having a plurality of lands which separate and control fluid flows through the housing272.

The second or slave logic valve270includes a first control port270CA which is in fluid communication with the hydraulic line184and a second control port270CB which is in fluid communication with the hydraulic line238. It will thus be appreciated that the position of the spool274of the second or slave logic valve270is dictated by whether the first (even) input clutch20is activated and thus that there is hydraulic pressure in the line184or that the second (odd) input clutch22is activated and thus that there is hydraulic pressure in the line238. The second or slave logic valve also includes a plurality of exhaust ports270D,270E and270F which communicate through the fluid exhaust manifold190which flows to the sump102.

The second or slave logic spool or control valve270also includes a second outlet port270I which communicates through a line276with a port282A in a housing or cylinder282of a second shift actuator assembly280. At the opposite end of the cylinder282, a second port282B communicates through a line278to a fourth outlet port270K. The second shift actuator assembly280also includes a three area piston286. The three area piston286is connected to a second piston rod288which, in turn, is connected to the second shift fork86. A second detent assembly292having a spring biased detenting ball294or similar structure cooperates with a detenting recess88on the second shift fork86and assists obtaining and maintaining a selected position of the second shift fork86.

The second or slave logic spool or control valve270further includes a first outlet port270H which communicates through a line296with a port302A in a housing or cylinder302of a third shift actuator assembly300. At the opposite end of the cylinder302, a second port302B communicates through a line298to a third outlet port270J. The third shift actuator assembly300also includes a three area piston306. The three area piston306is connected to a third piston rod308which, in turn, is connected to the third shift fork96. A third detent assembly312having a spring biased detenting ball314or similar structure cooperates with a detenting recess98on the third shift fork96and assists obtaining and maintaining a selected position of the third shift fork96.

Selection and operation of first, second, fourth and fifth gears will now be described with emphasis on the second spool or control valve270. When the second spool or control valve270is in the de-energized or relaxed position illustrated inFIG. 2, and the spool244of the first spool or control valve240is also in its de-energized or relaxed position as also illustrated inFIG. 2, pressurized hydraulic fluid provided through the line266and the first inlet port270A will be routed to the second outlet port270I and through the line276and the port282A to translate the second piston286to the right to engage, for example, fifth gear. Alternatively, pressurized hydraulic fluid provided through the line268and the second inlet port270B will be routed to the fourth outlet port270K and through the line278and the port282B to translate the second piston286to the left to engage, for example, first gear.

When the second spool or control valve270is in the energized or active position, to the left inFIG. 2, and the spool244of the first spool or control valve240is in its de-energized or relaxed position as illustrated inFIG. 2, pressurized hydraulic fluid provided through the line266and the first inlet port270A will be routed to the first outlet port270H and through the line296and the port302A to translate the third piston306to the right to engage, for example, second gear. Alternatively, pressurized hydraulic fluid provided through the line268and the second inlet port270B will be routed to the third outlet port270J and through the line298and the port302B to translate the third piston306to the left to engage, for example, fourth gear.

Last of all, the second or slave logic spool or control valve270includes a clutch cooler inlet port270Y which is in fluid communication with the outlet of the hydraulic fluid cooler148through a hydraulic line320. When the spool274of the second spool or control valve270is in the de-energized or relaxed position illustrated inFIG. 2, hydraulic fluid flows out an outlet port270Z and returns in a line322to provide cooling of the first clutch20associated with the even numbered gears. A flow controlling orifice326is disposed between the hydraulic line320and the line322.

When the spool274of the second spool or control valve270is in the energized or active position, to the left inFIG. 2, hydraulic fluid flows out an outlet port270X and returns in a line324to provide cooling of the second clutch22associated with the odd numbered gears. Another flow controlling orifice328is disposed between the hydraulic line320and the line324. In operation, hydraulic fluid from the cooler pressure regulator150flows in the line138, through the cooling priority and line pressure regulator valve130, through the orifice194and the cooler148. Then the hydraulic fluid flows either through the line320to the inlet port270Y of the second logic or spool valve270which prioritizes fluid flow to either the line322and the first clutch20or the line324and the second clutch22or simply through the orifices326and328to the respective clutches20and22.

Referring now toFIG. 3, a second embodiment of a hydraulic control system for the wet dual clutch transmission10illustrated inFIG. 1is illustrated and generally designated by the reference number400. The second embodiment hydraulic control system400is similar in most respects to the first embodiment control system100, especially with regard to the hydraulic fluid supply components, the clutch actuation components and the fluid logic and shift actuation components. Thus, the second embodiment control system400includes the engine driven pump110, the line pressure regulator130, the line pressure solenoid valve160, the manifold170, the first clutch solenoid valve174, the first shift solenoid valve200, the second shift solenoid valve210, the master logic solenoid valve220, the second clutch solenoid valve230, the first or master logic spool or control valve240, the first shift actuator assembly250, a modified or simplified second or slave logic spool or control valve270′, the second shift actuator assembly280, the third shift actuator assembly300and all the related filters and hydraulic lines. It should thus be apparent and understood that shift logic and actuation, i.e., gear selection, is the same with regard to the second embodiment control system400as the first embodiment shift control system100described in detail above.

The second embodiment400differs in the components and configuration of the cooler pressure feed limit valve150. As will be seen inFIG. 3, there is included an additional variable force solenoid (VFS) valve, namely, a cooler pressure variable force solenoid valve402having an inlet port402A which receives hydraulic fluid from the fifth manifold supply line170E. The cooler pressure solenoid valve402also includes an outlet port402B which communicates through a line404having a flow controlling orifice406with a first control port410CA of a cooler pressure regulator410. The cooler pressure solenoid valve402also includes an exhaust port402D that is connected to the fluid exhaust manifold190. In the second embodiment control system400, the clutch cooling circuit has also been somewhat simplified by omitting the dual, independent clutch cooling circuits.

The cooler pressure regulator410includes an inlet port410A which communicates with the manifold170through an eighth manifold supply line170H. The cooler pressure regulator410also includes an outlet port410B in communication with the hydraulic line138and a second control port410CB, also in communication with the hydraulic line138. In addition to responding to the line pressure in the hydraulic line138, it will be appreciated that the output pressure of the cooler pressure regulator410is also controlled by the output pressure of the cooler pressure solenoid valve402which is applied to the first control port410CA of the cooler pressure regulator410. It should be understood, however, that in certain applications, the cooler pressure solenoid valve402may be omitted and the line pressure in the fifth manifold supply line170E provided or supplied directly to the first control port410CA of the cooler pressure regulator410.

In the second embodiment control system400, the clutch cooling circuit has also been somewhat simplified by omitting the dual, independent clutch cooling circuits. Thus, the second or slave logic spool or control valve270′ has been simplified by omitting the three ports270X,270Y and270Z (and the associated land of the spool274). The associated hydraulic lines320,322and324have also been omitted. Instead, the output from the cooler148is fed directly to the two wet input clutches20and22.

The foregoing embodiments of the invention having the engine driven pump110provide good operational efficiency. The hydraulic control systems100and400have essentially minimum content to control a wet dual clutch transmission such as the transmission10and are thus an efficient control system design.