Patent ID: 12222031

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

The following describes one or more example embodiments of the disclosed hitch assembly, as shown in the accompanying figures of the drawings described briefly above. Various modifications to the example embodiments may be contemplated by one of skill in the art.

As used herein, unless otherwise limited or modified, lists with elements that are separated by conjunctive terms (e.g., “and”) and that are also preceded by the phrase “one or more of” or “at least one of” indicate configurations or arrangements that potentially include individual elements of the list, or any combination thereof. For example, “at least one of A, B, and C” or “one or more of A, B, and C” indicates the possibilities of only A, only B, only C, or any combination of two or more of A, B, and C (e.g., A and B; B and C; A and C; or A, B, and C).

Furthermore, in detailing the disclosure, terms of direction and orientation, such as “forward,” “front,” “aft,” “rear,” “lateral,” “horizontal,” and “vertical” may be used. Such terms are defined, at least in part, with respect to the direction in which the work vehicle travels during use. For example, the terms “forward” and “front” (including “fore” and any further derivatives or variations) refer to a direction corresponding to the primary direction of travel, while the term “aft” and “rear” (and derivatives and variations) refer to an opposing direction. The term “longitudinal axis” may also reference an axis extending in fore and aft directions. By comparison, the term “lateral axis” may refer to an axis that is perpendicular to the longitudinal axis and extends in a horizontal plane; that is, a plane containing both the longitudinal and lateral axes. The term “vertical,” as appearing herein, refers to an axis or a direction orthogonal to the horizontal plane containing the fore-aft and lateral axes.

This disclosure provides a transmission unit having a clutch piston which is engageable with a clutch pack, a balance piston, and a lubrication mechanism provided in the clutch piston for cooling the clutch pack. The balance piston provides equal and opposite balancing forces to the clutch piston, preventing the clutch piston from self-engaging due to a centrifugal lubricant pressure head. The lubrication mechanism has cooling fluid shutoff pistons which seat within passageways of the clutch piston. The passageways are in fluid communication with a balance piston cavity and a passageway in which the clutch pack is seated. The cooling fluid shutoff pistons of the lubrication mechanism are configured to seat within lubrication supply openings of the clutch piston passageways, and are configured to be unseated from within the lubrication supply openings of the clutch piston passageways. When the cooling fluid shutoff pistons are positioned within the lubrication supply openings, the supply of lubrication which is used to cool the clutch pack is blocked. When the cooling fluid shutoff pistons are not positioned within the lubrication supply openings, the supply of lubrication which is used to cool the clutch pack is allowed. In both positions of the cooling fluid shutoff pistons, the supply of lubrication to the balance piston cavity is always provided. The lubrication supply openings are only unblocked when the clutch is engaged so that the clutch pack is cooled. Since the cooling fluid is prevented from flowing to the clutch pack when the clutch assembly is disengaged, this saves pump energy needs.

The following describes one or more example implementations of the disclosed lubricant mechanism for a transmission unit for a work vehicle, as shown in the accompanying figures of the drawings described briefly above.

FIG.2shows an example transmission unit10having a high speed clutch assembly12that may be included in a work vehicle14, seeFIG.1. The transmission unit10includes lubricant flow paths16a,16b,16cthat provide fluid flow to a clutch pack18of the clutch assembly12. As will be understood, the transmission unit10may be part of the drivetrain20of the work vehicle14and be operably coupled to a hydraulic and electronic control system22. The fluid provided to the lubricant flow paths16a,16b,16cis pumped by a pump (not shown) with hydraulic fluid from a tank (not shown) on the work vehicle14. The components provide a lubricant management system which promotes efficient cooling of the clutch pack18.

Generally, as shown inFIG.3, the transmission unit10includes a housing28which houses the clutch assembly12, a balance piston30, a lubrication mechanism32, and a retainer34. The clutch assembly12includes the clutch pack18, a clutch piston36and its return spring38. The transmission unit10is driven by a drive shaft40. An output gear42is rotatably mounted on the drive shaft40and is coupled to the clutch assembly12. The balance piston30provides equal and opposite balancing forces to the clutch piston36, preventing the clutch piston36from self-engaging due to a centrifugal lubricant pressure head.

The housing28includes a cylindrical drum44and a hub46which are fixed together, such as by welding. The drum44has an annular wall48which defines a central passageway50and which has a plurality of axially extending splines extending into the central passageway50. The hub46has an outer annular wall portion52and an annular end wall portion54. A central passageway56is defined through the hub46with the portion of the central passageway56which is through the end wall portion54defining a reduced diameter opening58. The central passageway50is open at outer axial ends. The housing28may be integrally formed of a single piece.

The output gear42, which may be any suitable type of internal or external gear (e.g., spur, bevel, rack and pinion, etc.), is mounted to the drive shaft40at the open end of the housing28by one or more rolling element bearings, such as ball bearings60, which permit the gear42to mount and rotate relative to the drive shaft40. The gear42has a hub62which extends axially into the passageway50of the housing28. The hub62is outwardly axially splined at or near its axially inner ends, and has a plurality of openings64therethrough.

The drive shaft40has an elongated first cylindrical shaft portion66, a second cylindrical shaft portion68extending from the first shaft portion66, and a third cylindrical shaft portion70extending from the second shaft portion68. The second shaft portion68has a diameter which is less than the diameter of the first shaft portion66thereby forming a first shoulder72, and is greater than the third shaft portion70thereby forming a second shoulder74. A longitudinal axis76is defined between the ends of the drive shaft40. A hydraulic fluid pressure supply passage78extends along the first shaft portion66and extends radially through the second shaft portion68. A separate hydraulic fluid supply passage80extends along the first shaft portion66, extends along a portion of the second shaft portion68, and extends radially through the second shaft portion68. The passages78,80are spaced apart from each other. Hydraulic fluid, such as lubricant, is introduced into the passages78,80, as described herein, from a hydraulic supply (not shown). A control valve82is provided along the passage78for controlling fluid flow through the passage78under control of the hydraulic and electronic control system22. The first shaft portion66seats within the opening58of the hub46and is fixed thereto, such as by welding, the second and third shaft portions68,70extend through the drum44, and the third shaft portion70extends outwardly from the drum44. The hub46, the shoulder72and the second shaft portion68form a pocket84.

The clutch piston36seats within the central passageway50of the housing28proximate to the end wall portion54of the hub46. As shown inFIGS.5and6, the clutch piston36of the clutch assembly12has a cylindrical first body portion86which surrounds the drive shaft40, an annular second body portion88extending radially outward from the first body portion86, and a cylindrical third body portion90extending from the outer end of the second body portion88. The first and third body portions86,90extend in the same direction. The first body portion86defines a central passageway92through which the second shaft portion68of the drive shaft40extends. The first body portion86has a length which is greater than the length of the third body portion90. The clutch piston36seats within the pocket84with the first body portion86engaged with the second shaft portion68of the drive shaft40, the third body portion90engaged with the outer annular wall portion52of the hub46, and the second body portion88proximate to the first shoulder72of the drive shaft40and proximate to the end wall portion54of the hub46. A seal94ais provided between the first body portion86and the second shaft portion68, and a seal94bis provided between the third body portion90and the outer wall portion52of the hub46. The second body portion88has an inner section96extending radially outward from the end of the first body portion86and an outer section98extending radially outward from the end of the inner section96. The inner section96is recessed relative to the outer section98. The area between the end wall portion54of the hub46, the second body portion88, and a first end100of the first body portion86defines a clutch piston cavity102. The clutch piston cavity102always aligns with, and is always in fluid communication with, the passage78. A seal104is mounted on the outer section98and is configured to seal with the end wall portion54. An annular pocket106is formed by the body portions86,88,90. The clutch piston36is slidable axially along the second shaft portion68of the drive shaft40which causes the clutch piston cavity102to enlarge in size or decrease in size as described herein.

A plurality of spaced apart axially extending passageways108extend from the first end100of the first body portion86to an axially extending lubrication supply opening110extending from a second end of the first body portion86. Each passageway108has a first section112extending in the axial direction from the first end100and a second section114extending in the axial direction from the second end of the first section112to the lubrication supply opening110. The second section114has a diameter which is less than the diameter of the first section112and greater than the diameter of the lubrication supply opening110. A first shoulder116is formed between the first and second sections112,114, and a second shoulder118is formed between the second section114and the lubrication supply opening110.

The first body portion86has an elongated internal groove120which extends circumferentially around the interior wall forming the central passageway92, and an external groove122which extends circumferentially around the outer perimeter of the first body portion86. A plurality of spaced apart inner openings124are provided through the first body portion86, and each extends from the internal groove120to the second section114of the respective passageway108. A plurality of spaced apart outer openings126are provided through the first body portion86, and each extends from the external groove122to the second section114of the respective passageway108. Each inner opening124is spaced from the first end100of the first body portion86at a distance which is greater than the distance that each outer opening126is spaced from the first end100. The passage80is always aligned with the elongated internal groove120. As a result, fluid communication is always provided between the passage80, the internal groove120, the inner openings124, the second section114of the respective passageways108, the outer openings126and the external groove122.

The clutch pack18seats in the central passageway50in the housing28proximate to the clutch piston36. The clutch pack18is annular and is engaged with the splines of the drum44and engaged with the splines of the gear42. The clutch pack18seats within a clutch pack cavity128of the central passageway50defined between the balance piston30, the outer annular wall portion52of the drum44, and the hub62of the gear42. The clutch pack cavity128is always in fluid communication with the openings64in the gear42. In a partially engaged position or in an engaged position of the clutch assembly12, an end130of the third body portion90of the clutch piston36is engaged against the clutch pack18. The clutch pack18has interleaved disks, such as separator plates132, which are splined to the drum44at their outer peripheries, and friction disks134, which are interleaved with the separator plates132and splined to the hub62of the gear42at their inner peripheries. The friction disks134may be monolithic or composite structures having friction-enhancing features that are attached to (e.g., adhered, embedded, coated, fixed with mechanical fasteners, etc.) or formed into (e.g., etched, machined, molded, cast, etc.) into a structural backing component thereof. The outer peripheries of the separator plates132may be notched to match, and thereby interfit and engage with, the drum44such that the separator plates132rotate with the drum44. The inner peripheries of the friction disks134may be notched to match, and thereby interfit and engage with, the splined hub such that the friction disks134rotate with the hub62of the gear42. The separator plates132and friction disks134are configured to slide axially along the drum44and the hub62of the gear42. The retainer34is at the outer end of the clutch pack18and affixed to the drum44to retain the clutch pack18in the passageway50in the housing28. Axially compressing or squeezing the clutch pack18between the clutch piston36and the retainer34engages the clutch assembly12and is provided by hydraulic actuation of the clutch piston36as described herein. The clutch pack18may also include springs (not shown) arranged to bias the separator plates132and the friction disks134toward a non-contacting position in a “force-separated” arrangement. For example, one or more large-diameter springs (e.g., wave or Belleville type springs) may be set within the annular gaps or channels extending about the radially outer periphery of the friction disks134. The clutch pack18may be joined in a stacked configuration by a number of fasteners (not shown) (e.g., pins, rods, dowels, bolts, etc.), as needed. The clutch pack18may generate a considerable amount of heat when utilized to clutch the transmission unit10, particularly during periods of relative contacting rotation between the separator plates132and the rapidly rotating friction disks134as a result of friction.

The balance piston30seats within the central passageway50of the housing28proximate to the clutch piston36and the clutch pack18. As shown inFIGS.7and8, the balance piston30has an annular first body portion136, an annular second body portion138extending radially outward from a first end of the first body portion136, and an annular third body portion140extending radially inward from a second end of the first body portion136. The first and third body portions136,140define a central passageway142having a reduced size opening144through the third body portion140at the second end of the balance piston30. The second shaft portion68of the drive shaft40passes through the reduced size opening144. The first body portion136has a first section146extending from the second body portion138, and a second section148extending therefrom to the third body portion140. The first section146is radially offset outwardly from the second section148. A plurality of spaced apart openings150are provided through the second section148of the first body portion136, and each extends from the outer perimeter of the second section148and intersects the passageway142. The first body portion136surrounds the first body portion86of the clutch piston36and the second body portion138seats within the pocket106of the clutch piston36. The second section148extends outwardly from the pocket106. The openings150in the balance piston30are at least partially longitudinally outward of the ends of the lubrication supply openings110of the clutch piston36. The openings150are aligned with and always in fluid communication with the clutch pack cavity128via the openings64in the gear42. A seal152is provided between the first body portion86of the clutch piston36and the first body portion136of the balance piston30, and a seal154is provided between the end of the third body portion90of the clutch piston36and the second body portion138of the balance piston30. A balance piston cavity156is formed between the first section146of the first body portion136of the balance piston30, the second body portion138of the balance piston30, and the clutch piston36. The balance piston30is fixed into position relative to the drive shaft40by suitable means, such as a retaining clip158, which allows the drive shaft40to rotate relative to the balance piston30while preventing the axial outward movement of the balance piston30relative to the drive shaft40. The outer openings126and the external groove122of the clutch piston36open into the balance piston cavity156such that the balance piston cavity156is always aligns with, and is always in fluid communication with, the passage80.

The return spring38of the clutch assembly12surrounds the third shaft portion70of the drive shaft40and sits within an annular pocket160formed by the third shaft portion70of the drive shaft40, the shoulder74, the first body portion86of the clutch piston36, and the first and third body portions136,140of the balance piston30. A first end of the return spring38is engaged with the end of the first body portion86of the clutch piston36and a second end of the return spring38is engaged with the third body portion140of the balance piston30. The return spring38may be a coil spring, a lubricant spring, a plurality of Belleville disc springs, etc. The pocket160is always in fluid communication with the lubrication supply openings110in the clutch piston36and with the openings150in the balance piston30.

The lubrication mechanism32is within the passageways108of the clutch piston36and extends into the clutch piston cavity102, and is configured to seat within the lubrication supply opening110of the clutch piston36. The lubrication mechanism32includes a plurality of cooling fluid shutoff pistons164, a plurality of return springs166, a plurality of retainers168, and a plurality of seals170, with one of each being seated within the respective passageway108of the clutch piston36. In certain situations, the cooling fluid shutoff pistons164are seated within the lubrication supply openings110in a closed position, and when so positioned, the supply of lubrication which is used to cool the clutch pack18is prevented. In certain situations, the cooling fluid shutoff pistons164are not positioned within the lubrication supply openings110in an open position, and when so positioned, the supply of lubrication which is used to cool the clutch pack18is provided. The supply of lubrication to the balance piston cavity156is always provided when the cooling fluid shutoff pistons164are in each position.

Each cooling fluid shutoff piston164has an elongated shaft172having a first enlarged head section174extending therefrom and a second head section176extending from the first head section174. The second head section176forms a first end178, and the shaft172forms a second end180. The first and second head sections174,176seat within the first section112of the respective passageway108and the shaft172seats within the second section114of the respective passageway108. The first head section174is configured to engage with the first shoulder116of the passageway108. The return spring166surrounds the shaft172and engages the first head section174and the second shoulder118of the passageway108. The retainer168, which may be a clip, is seated within an annular groove182in the wall forming the first section112and is configured to engage the first head section174to prevent the cooling fluid shutoff piston164from exiting the passageway108. The seal170is provided between the first head section174in the wall forming the first section112. In the closed position, as described herein, the end180of the shaft172extends into the lubrication supply opening110of the clutch piston36and blocks fluid flow through the lubrication supply opening110.

The lubricant flow paths16a,16cpromote efficient cooling of the clutch pack18. By virtue of this design, the clutch pack18is cooled during the period of time when the clutch assembly12is engaged and during which the most heat is being generated. At one or more other times or states, the clutch pack18will be cut off from the cooling fluid flow. Cooling the clutch pack18at the critical times/states aids in prolonging the serviceable lifespan of the clutch pack18, and thus of the transmission unit10. Efficiently managing the fluid flow avoids using system resources to flow fluid to the clutch pack18unnecessarily that could otherwise be used to cool other components and reduces drag and other friction or pressure losses resulting from the clutch pack18being rotated and/or moved through viscous fluids. Moreover, the efficiency the lubricant flow path16cmay be further enhanced by, as is the case in the illustrated example, delivering the fluid flow to the inner peripheries of the clutch pack18such that the fluid may be carried through the clutch pack18in a radially outward direction by centrifugal force.

A first lubricant flow path16ais provided by the passage78and the clutch piston cavity102. This first lubricant flow path16aurges the clutch piston36away from the end wall portion54of the hub46to engage the clutch pack18. A second lubricant flow path16bis provided by the passage80, the internal groove120, the inner openings124, the second sections114of the passageways108, the outer openings126, the external groove122, and the balance piston cavity156. This second lubricant flow path16bsupplies fluid to the clutch piston cavity102to provide a centrifugal balance to the clutch piston36. A third lubricant flow path16cis provided by the lubrication supply openings110when the ends180of the cooling fluid shutoff pistons164are not positioned therein, the pocket160in which the return spring38seats, the openings150of the balance piston30, the openings64in the gear42, and the clutch pack cavity128in which the clutch pack18seats. Fluid pressure in the first lubricant flow path16amay vary between 0 PSI and 300 PSI depending upon the condition. Fluid pressure in the second lubricant flow path16bis always between 20 PSI and 30 PSI.

When a clutch cycle is not called for, the control valve82is closed, and the clutch piston36is biased toward the end wall portion54by the return spring38to disengage the clutch piston36from the clutch pack18as shown inFIGS.9and9A. The end130of the third body portion90of the clutch piston36is spaced from the clutch pack18. Fluid flow is provided along the second lubricant flow path16binto the balance piston cavity156and provides a centrifugal balance to the clutch piston36. The ends178of the cooling fluid shutoff pistons164engage against the end wall portion54which slightly compresses the return springs166of the cooling fluid shutoff pistons164, thereby causing the ends180of the cooling fluid shutoff pistons164to seat within the lubrication supply openings110in the closed position, and preventing fluid flow along the third lubricant flow path16c. In this disengaged position, the clutch pack18is not compressed and no significant heat is being generated by the clutch pack18so cooling is not needed. The drive shaft70is turning at a first speed and the gear42is turning at a second different speed.

During a clutch cycle, the clutch piston36is moved into a “kiss” condition with the clutch pack18which allows for slipping of the clutch pack18as shown inFIG.10, while providing for cooling of the clutch pack18during the time since heat is being generated by the clutch pack18as a result of the slipping. The control valve82is operated to allow fluid to flow along the first lubricant flow path16aat a first fluid pressure which is greater than the pressure at which the balance piston cavity156is being filled, but not great enough to maintain the cooling fluid shutoff pistons164in their closed positions. This engages the clutch piston36with the clutch pack18but still allows for the slip of the clutch pack18. The first fluid pressure is high enough to move the clutch piston36to engage the clutch pack18and to compress the return spring38, but not high enough to counteract the return springs166to keep the cooling fluid shutoff pistons164engaged within the lubrication supply openings110. Since the first fluid pressure is below what keeps the cooling fluid shutoff pistons164seated in the lubrication supply opening110, the return springs166expand which causes the cooling fluid shutoff pistons164to move toward the end wall portion54of the hub46, into the clutch piston cavity102, and out of the lubrication supply openings110and into the open positions. Since the ends180of the cooling fluid shutoff pistons164are out of the lubrication supply openings110, fluid flows along the third lubricant flow path16cand into the clutch pack cavity128. The third lubricant flow path16csupplies cooling fluid to the clutch pack18, while fluid is simultaneously being supplied along the second lubricant flow path16bto the balance piston cavity156to provide centrifugal balance to the clutch piston36.

Once parameters based upon a desired clutch temperature on the clutch pack18are reduced to a level which indicates that the heat dissipation on the clutch pack18is no longer necessary, the control valve82is operated to increase the pressure of the fluid flowing along the first lubricant flow path16ato a second greater pressure to attain the position shown inFIG.11. The parameters are calculated with an algorithm which actively predicts clutch temperature before, during and after gear shifts. In the position as shown inFIG.11, the clutch piston36is fully pressed against the clutch pack18away from the end wall portion54of the hub46, and the return spring38is compressed. The pressure on the second head sections176of the cooling fluid shutoff pistons164cause the cooling fluid shutoff pistons164to be biased into engagement with the shoulders116to compress the return springs166and seat the ends180of the cooling fluid shutoff pistons164in the lubrication supply openings110, thereby preventing fluid flow through the third lubricant flow path16c. In this condition, the drive shaft70and the gear42turn at the same speed.

As a result, the lubrication to the clutch pack18can be controlled to cool when the clutch assembly12is engaged in the “kiss” position. Since the clutch pack18is only cooled when necessary, pump energy costs are reduced.

As shown inFIG.12, the hydraulic and electronic control system22includes a controller190operably coupled to the control valve82and operably coupled to a clutch demand192which indicates to the controller190that a clutch cycle is to commence. The clutch demand192may commence by an operator depressing a pedal of the work vehicle14or the controller programming indicating that a clutch cycle is necessary. Some components of the controller190are usefully (although non-essentially) remotely located from the transmission unit10; e.g., integrated into the operator station of the work vehicle14. Such remote positioning helps protect such components from the harsh operating environment of the transmission unit10. The example control system22may further include a display device194for providing information to the operator.

The controller190can assume any form suitable for performing the functions described throughout this document. Further, the term “controller,” as appearing herein, is utilized in a non-limiting sense to generally refer to the processing architecture of the transmission unit10, shown as processor196. The controller190can encompass or may be associated with any practical number of processors, control computers, computer-readable memories, power supplies, storage devices, interface cards, and other standardized components. The controller190may also include or cooperate with any number of firmware and software programs or computer-readable instructions designed to carry-out the various process tasks, calculations, and control/display functions described herein. Such computer-readable instructions may be stored within a non-volatile sector of a memory198accessible to the controller190. While generically illustrated inFIG.12as a single block, the memory198can encompass any number and type of storage media suitable for storing computer-readable code or instructions, as well as other data utilized to support the operation of the transmission unit10. The memory198may be integrated into the controller190in embodiments as, for example, a system-in-package, a system-on-a-chip, or another type of microelectronic package or module.

When included in the example control system22, the display device194may be located within the operator station or cabin of the work vehicle14. An operator may refer to imagery generated on the display device194when entering commands or inputting data into the control system22. Additionally or alternatively, visual alerts may be generated on the display device194. The display device194may be affixed to the static structure of the operator cabin or can be a portable electronic display device, such as a tablet computer or laptop, which is carried into the operator station by an operator and which communicates with the various other components of the example control system22over a physical connection or wireless connection to perform the desired display functionalities.

Referring now to the flow chart shown inFIG.13, a clutch cycle process200for the control of the heat dissipation of the clutch pack18is presented in accordance with a non-limiting example embodiment. The clutch cycle process200includes a number of process steps, each of which is described below. Depending upon the particular manner in which the clutch cycle process200is implemented, each step generically illustrated inFIG.13may entail a single process or multiple sub-processes. Further, the steps illustrated inFIG.13and described below are provided by way of non-limiting example only. In alternative embodiments of the clutch cycle process200, additional process steps may be performed, certain steps may be omitted, and/or the illustrated process steps may be performed in alternative sequences.

The clutch cycle process200commences at STEP202in response to a clutch demand192. At STEP204, the valve82is opened to provide a fluid flow at a first fluid pressure, for example the fluid is fed into the first lubricant flow path16aat a pressure of 220 PSI. This engages the clutch piston36with the clutch pack18in the “kiss” condition and allows the cooling fluid shutoff pistons164to move to the open position and allow cooling of the clutch pack18. At STEP206, the controller190determines if the parameters are at a desired level which indicates that cooling of the clutch pack18is no longer necessary. If the controller190determines that the parameters are not at the desired level, STEP208, then the pressure is maintained to keep the cooling fluid shutoff pistons164in the open positions at STEP210, and the clutch cycle process200returns to STEP206. If the controller190determines that the parameters are at the desired level, STEP212, then the valve82is operated at STEP214to increase the pressure of the fluid flowing along the first lubricant flow path16ato a second fluid pressure which is above the first fluid pressure that closes the cooling fluid shutoff pistons164to prevent the fluid flow along the third lubricant flow path16c, and to provide a full clutching action. When the clutch cycle completes, the clutch cycle process200progress to STEP216and the controller190closes the valve82to disengage the clutch pack18.

When the lubrication of the clutch pack18is necessary, the pressure along the lubricant flow path16ais controlled to a setpoint above the 1:1 clutch torque reserve needed for the present gear selection, but below the setpoint needed to move the cooling fluid shutoff pistons164to the closed position. Once the desired temperature of the clutch pack18is achieved, the pressure along the lubricant flow path16acan be raised to the maximum achievable, which will move the cooling fluid shutoff pistons164to the closed position and terminate lubrication of the clutch pack18. Since the lubrication is managed, this allows for optimized use of transmission lubrication. This allows a designer to provide needed lubrication to other components as soon as the clutch pack18is cool. This also avoids having to oversize a transmission lubrication pump, and avoids the addition of separate devices such as priority valving that is more costly.

A graphical example of a clutch cycle is shown inFIG.14. At the start of the graph, the transmission unit10is in the disengaged position as shown inFIG.9. Once a clutch demand192is received, the fluid pressure along the lubricant flow path16ainto the clutch piston cavity102, which is represented by the line showing the clutch valve current command in the chart ofFIG.14, is dramatically increased to fast fill the clutch piston cavity102and move the clutch piston36toward the clutch pack18, and then reduced to a certain level to start the shift. During this time period, the clutch relative speed is high and generally constant, and the clutch torque capacity, the clutch temperature and the clutch lubrication flow rate along lubricant flow path16care low and are generally constant. This reduction of the fluid pressure along the lubricant flow path16ato the first fluid pressure moves the cooling fluid shutoff pistons164to the open position, as shown inFIG.10, thereby dramatically increasing the lubrication flow along lubricant flow path16cand dramatically increasing the lubrication flow rate to the clutch pack18. Just prior to the start of the shift, the clutch valve current command, the clutch torque capacity and the clutch temperature are low. At the start of the shift, the clutch valve current command dramatically rises to increase the pressure along the lubricant flow path16ato move the clutch piston36into the “kiss’ position with the clutch pack18, and the clutch torque capacity generally follows the clutch valve current command for the remainder of the clutch cycle. As a result, during the shift, heat is generated and the clutch temperature begins to rise rapidly. The flow along lubricant flow path16cremains generally constant which provides cooling fluid to the clutch pack18. The clutch valve current command and the clutch torque capacity gradually rise during the shift, and the clutch relative speed gradually decreases during the shift. At the end of the shift when the clutch temperature is at its maximum, the pressure to the lubricant flow path16ashown by the clutch valve current command is again dramatically increased, but does not rise to the level which moves the cooling fluid shutoff pistons164to the closed position. During this time period, the cooling fluid is supplied along lubricant flow path16cto the clutch pack18and the clutch temperature gradually decreases, and the clutch relative speed remains low. When the desired parameter is reached, the clutch valve current command is again dramatically increased, along with clutch torque capacity, which increases the fluid pressure along the lubricant flow path16ato the second fluid pressure, thereby causing the cooling fluid shutoff pistons164to move to the closed position as shown inFIG.11. This causes the clutch piston36to fully engage with the clutch pack18to provide a full clutching action, while shutting off the cooling flow to the clutch pack.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

The description of the present disclosure has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the disclosure in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the disclosure. Explicitly referenced embodiments herein were chosen and described in order to best explain the principles of the disclosure and their practical application, and to enable others of ordinary skill in the art to understand the disclosure and recognize many alternatives, modifications, and variations on the described example(s). Accordingly, various embodiments and implementations other than those explicitly described are within the scope of the following claims.