Clutch cooling system

A transmission clutch cooling system includes a clutch housing defined between a drive hub of a drive member and a clutch hub of a driven member and a clutch assembly housed in the clutch housing. The clutch hub includes a hub deck having a plurality of bores therethrough, an inner annulus extending axially from the hub deck, and an outer annulus extending axially from the hub deck, the outer annulus including a plurality of radial orifices therethrough and a lip flange extending from a distal end towards the inner annulus. The clutch assembly includes a plurality of clutch plates secured to the drive hub and a plurality of friction plates secured to the driven member. A piston assembly is provided for engaging or disengaging the plurality of friction plates against the plurality of clutch plates to cause or release integrated rotation of the drive member and the driven member.

TECHNICAL FIELD

The disclosure relates to transmission clutches and, more particularly, to a passive clutch cooling system to reduce drag loss between the interleaved friction discs and the clutch plates of a rotating clutch.

BACKGROUND

Rotational clutches are frequently used as one of the mechanisms for engaging or disengaging the various gear components of a transmission in order to establish different gear ratios between an input member and an output member. A conventional rotational clutch assembly typically includes a set of clutch plates and a set of friction discs, sometimes referred to as a clutch pack, interleaved between one another in a clutch housing. When the clutch assembly is disengaged, the clutch plates and friction discs normally turn past one another without contact. However, when the corresponding components of a particular clutch, i.e., a drive member and a driven member, are to be engaged during a particular gear range, for example, a hydraulically actuated or spring-loaded piston forces the clutch plates and friction discs together. Friction surfaces on the clutch plates and the friction discs interact until the drive member and the driven member of the clutch assembly rotate in unison without slip.

In operation, a great deal of thermal energy is generated during the engagement and disengagement of the clutch plates and the friction discs, as well as during the period of full engagement, when the kinetic energy generated by the engaged clutch pack is also translated into a large amount of thermal energy. This thermal energy must be dissipated to prevent damage to the various components of the clutch assembly, particularly the frictional surfaces of the clutch plates and the friction discs. A continuous supply of a coolant, such as transmission fluid, is typically supplied to the clutch housing to serve this purpose. In a rotational clutch assembly, the transmission fluid may be supplied to an inside diameter portion of the engaged clutch plates and the friction discs and allowed to flow by centrifugal force across the plate surfaces to an outside diameter portion. The hot transmission fluid is then directed away from the clutch assembly to pass through a heat exchange process for transfer and release of the thermal energy absorbed into the transmission fluid.

When the rotational clutch assembly is not engaged, the clutch plates and the friction discs simply rotate past one another without contact. During this period of disengagement, the amount of thermal energy that must be dissipated is minimal. Furthermore, simply maintaining a continuous flow of transmission fluid to the clutch pack during disengagement may also result in significant inefficiencies. For example, depending on the relative speed of the rotating drive member with respect to the disengaged, driven member, drag losses may be generated as a result of shear experienced by the transmission fluid between the clutch plates and the friction discs. The shear increases proportionally with the amount of transmission fluid provided to the clutch pack during disengagement. Thus, particularly in gears where the relative rotational speed differential between the clutch plates and the friction discs is highest, it is desirable to limit the flow of coolant to the clutch pack.

Various clutch cooling systems have been proposed to address controlling the flow of coolant to the clutch pack during engagement and disengagement. For example, U.S. Pat. No. 5,988,335 describes actively controlling the flow to the clutch with a diverter valve and a sensor arrangement to sense the gear ratio of the transmission and divert flow from the clutch assembly in response to the transmission being in a selected gear ratio. U.S. Pat. No. 6,244,407 proposes a more passive system that does not rely on a sensor actuated valve. Rather, an outer ring is mounted onto the piston used to actuate engagement of the clutch pack. The outer ring has an orifice provided therein for allowing a flow of coolant therethrough. The outer ring is movable between a first position wherein the orifice is closed and the drive and driven members are disconnected and a second position where the orifice is open to allow the flow of pressurized fluid through the orifice to the clutch pack when dictated by movement of the piston to engage the clutch plates and the friction discs. Other types of “slider valve” arrangements are common in the industry, wherein the piston moves the slider valve in a direction to uncover an orifice for increasing coolant flow to the clutch pack during engagement. Typically, a spring, for example, may be employed to close the slider valve over the orifice when the clutch disengages.

As described above, conventional clutch cooling systems can often be complex and/or require the addition of various components to provide a variable flow of coolant to the clutch pack. The increased complexity of these designs may add to the cost of manufacture, assembly, and maintenance of the transmission and creates additional opportunities for failure during operation. As such, a clutch cooling system is needed that eliminates the requirement for additional components while taking advantage of the natural operational characteristics of rotational clutch assemblies.

SUMMARY

The foregoing needs are met, to a great extent, by aspects of the present disclosure, wherein a transmission clutch cooling system includes a drive member including a drive hub situated about an axis of rotation, a driven member including a clutch hub concentrically situated about the axis of rotation, wherein the clutch hub includes a hub deck having a plurality of bores therethrough, an inner annulus extending axially from the hub deck, and an outer annulus extending axially from the hub deck, the outer annulus including a plurality of radial orifices therethrough and a lip flange extending from a distal end towards the inner annulus. A clutch housing is defined between the drive hub and the clutch hub, and a clutch assembly is housed in the clutch housing that includes a plurality of clutch plates secured to the drive hub to rotate with the drive member, a plurality of friction plates secured to the driven member to rotate with the clutch hub, and a piston assembly for engaging or disengaging the plurality of friction plates against the plurality of clutch plates to cause or release integrated rotation of the drive member and the driven member.

In accordance with other aspects of the present disclosure, a clutch hub includes a hub deck having a plurality of bores therethrough, an inner annulus extending axially from the hub deck, and an outer annulus extending axially from the hub deck, the outer annulus including a plurality of orifices therethrough and a lip flange extending from a distal end towards the inner annulus.

In accordance with yet other aspects of the present disclosure, a method of cooling a rotational clutch includes supplying a flow of coolant to an annular clutch hub having axial bores and radial holes, the radial holes being in fluid communication with a clutch pack, increasing the flow of coolant to the clutch pack through the radial holes during engagement of the clutch pack, and diverting a portion of the flow away from the clutch pack through the axial bores when the clutch pack is disengaged.

DETAILED DESCRIPTION

The disclosure will now be described with reference to the drawing figures, in which like reference numerals refer to like parts throughout.

Referring toFIG. 1, a multi-speed transmission10may be included in a machine12. An input member14may connect the transmission10to a prime mover16by a torque converter18, and an output member20may connect the transmission10to one or more traction devices22. Although the machine12is shown as a truck, it may be any type of machine that may benefit from the use of a multi speed transmission. The prime mover16may be of any type that outputs power in a form usable by the multi-speed transmission10. For example, the prime mover16may be an internal combustion engine (such as a diesel engine, a gasoline engine, a turbine engine or a natural gas engine), an electric motor, or other device capable of generating a power output. The traction devices22may be any type of traction devices, such as, for example, wheels as shown inFIG. 1, tracks, belts, or any combinations thereof.

As shown in the schematic illustration ofFIG. 2, the multi-speed transmission10may be a planetary transmission having a series of annular components rotatably supported and aligned about a rotational axis24, the schematic illustrating aspects of the transmission on one side of the axis24only. Torque may be supplied to the input member14by the prime mover16through the torque converter18, for example. At least one, and often a plurality of gear sets, may be interconnected between the input member14and the output member20. As shown inFIG. 2, the multi-speed transmission10may have four interconnected planetary gear sets,30,32,34and36rotatably supported concentrically along the rotational axis24in a transmission casing28. Each planetary gear set30,32,34and36includes at least one sun gear, at least one planetary carrier, and at least one ring gear.

The transmission10may also include a number of control elements operatively coupled to the planetary gear sets30,32,34and36. As used herein, the term “control element” includes clutches (which are alternatively referred to in the industry as rotational clutches), brakes (which are alternatively referred to in the industry as stationary clutches), synchronizers (including dog and other types of synchronizing clutches) or other torque control components that may conventionally be used in a transmission. As shown inFIG. 2, the transmission10may include three rotational clutch assemblies40,42, and44and three brake assemblies50,52, and54. The rotational clutch assemblies40,42, and44and brake assemblies50,52, and54cooperate with and may selectively couple particular elements of the planetary gear sets to establish, for example, a set of ten forward gear ratios and one reverse gear ratio between the input member14and the output member20.

FIG. 3illustrates a rotational clutch assembly100in accordance with aspects of the present disclosure. The rotational clutch assembly100may be used in the transmission10, for example, as one or more of the rotational clutch assemblies40,42, and44. The clutch assembly100may include a drive member, generally indicated at102, and a driven member104, generally indicated at104, which rotate about a common axis. A clutch housing106is generally defined between the drive member102and the driven member104and is formed to house a clutch pack, generally indicated at110, that is engaged or disengaged through actuation of a piston112, such as through hydraulic actuation or spring force actuation. A balance piston assembly114may be included and housed in the clutch housing106along with the piston112in order to introduce reverse pressure on the low pressure side of the piston112to counteract the large thrust generated by the hydraulic pressure fluid on the high pressure side of the piston and prevent the piston from engaging the clutch at high rotational speeds.

The annular clutch pack110may be composed of annular clutch plates116that are splined to and extend inward from a drive hub portion118of the drive member102and annular friction discs120that are splined to and extend outward from a clutch hub122of the driven member104. The clutch plates116and friction discs120are interleaved as shown inFIG. 3. In accordance with aspects of the present disclosure, when the clutch assembly100is in a disengaged position, the drive member102maintains a certain rotational speed based on an input speed of the input member14of the transmission10and the driven member104is disengaged and not rotating or rotating at a different relative speed. When the clutch assembly100is in the disengaged position, the clutch plates116rotate freely past the friction discs120in a non-contacting manner. However, when the clutch pack110is to be placed into an engaged position during a particular gear change, for example, when moving from the fifth gear to the sixth gear in the transmission10described previously, pressurized hydraulic fluid is introduced into a pressure chamber124to produce axial movement of the piston112. In turn, actuation of the piston112forces a frictional engagement of the clutch plates116with the friction discs120to reduce or eliminate relative rotation between the clutch plates116and the friction discs120.

As discussed above, during engagement of the clutch pack110, the relative rotational speed of the drive member102and the driven member104may be synchronized. The frictional energy and kinetic energy generated by the engaged clutch pack110translates into a large amount of thermal energy that must be dissipated to reduce or eliminate wear or damage that may occur to the clutch plates116and the friction discs120. To facilitate cooling during this time, a continuous flow of coolant, such as automatic transmission fluid, may be provided to the clutch hub122.

In accordance with aspect of the present disclosure, the clutch hub122may be formed with an inner annulus126connected to an outer annulus128by a hub deck130. The inner annulus126and the outer annulus128extend from the hub deck130in a direction toward the piston112and cooperate with the shape of the hub deck130to form an interior space132. The outer annulus128may be provided with a series of radial bores134. The radial bores134provide fluid communication from the interior space132to the clutch pack110for a fluid to flow through the outer annulus128toward the clutch pack110. Thus, when the clutch pack110is engaged to cause rotation of the clutch hub122at the same speed as the drive member102, by way of centrifugal action, the transmission fluid is forced through the radial bores134and into the clutch pack110at an accelerated rate versus when the clutch pack is disengaged and motion of the transmission fluid into the clutch pack110is primarily by force of gravity. The radial bores134are sized to provide a maximum flow of coolant during a particular period of clutch engagement, for example, to provide sufficient cooling during engagement and disengagement between particular gears when thermal energy generation is greatest. Yet the radial bores134are also sized to restrict a majority of the coolant flow to the clutch pack110during a period of disengagement when centrifugal force is reduced or nonexistent.

As explained above, the issue of providing sufficient cooling during engagement of the clutch assembly100can also lead to inefficiencies due to transmission fluid sheer during disengagement.FIG. 4is a chart illustrating the relative speed difference between the constantly rotating drive member102, including the clutch plates116, and the driven member104, including the friction discs120, for a typical range of gears in a multi-speed transmission10. The relative speed line indicates that the relative rotational speed between the driven member and the drive member is greatest in forward gears one (1F) and two (2F). In forward gears three (3F) through five (5F), the driven member104is controlled to increase speed relative to the drive member102until the clutch assembly100is engaged during a shift from gear5F to forward gear six (6F) where it remains engaged through forward gear ten (10F). As illustrated by the chart, because the rotational speeds of the clutch plates116and the friction discs120are synchronized in gears6F-10F, the difference in relative speed is zero. When the transmission is controlled to provide the reverse gear (R), the relative speed difference between the clutch plates116and the friction discs is again at its highest.

FIG. 5is provided to illustrate the estimated power loss experienced as a result of the shearing of lubrication fluid in the clutch pack110if lubrication fluid is not diverted in accordance with aspects of the present disclosure. As shown by the chart, if the input speed of the transmission is maintained at a steady speed of, for example, 1500 rpm, the power losses are clearly highest in gears1F,2F and Reverse when the relative speed difference between the drive member102and the driven member104are highest, as illustrated inFIG. 4. Conversely, the power loss decreases successively in gears3F-5F as the relative speed difference decreases until the power losses due to shearing are essentially zero in gears6F-10F because of the concurrent rotation of the clutch plates116and the friction discs120with the clutch assembly100engaged. It should be noted that the particular power numbers shown inFIG. 5may vary significantly for different transmissions depending on a number of factors, including the number and diameter of the clutch plates116and/or the friction discs120, for example. However, the relative amounts of power loss experienced across the gear range, e.g., power loss being highest in gears1F,2F, and1R, remains substantially as shown inFIG. 5.

As shown inFIGS. 6 and 7, a cooling system in accordance with aspects of the present invention may include a series of axial facing bores136provided in the hub deck130of the clutch hub122. The axial facing bores136may be spaced peripherally toward an outside diameter of the hub deck130and sized to permit a substantial quantity of the flowing coolant to escape the interior space132, primarily during a period of disengagement of the clutch assembly. Placement of the axial facing bores136near the outside diameter of the hub deck130also allows the clutch hub122to retain and direct a significant quantity of the flowing coolant toward and through the radial bores134during the period of engagement to lubricate and cool the clutch pack110. Lengthening the run of fluid flow allows development of a significant amount of centrifugal force to act on the fluid as it flows toward the radial bores134.

Referring back toFIG. 3, a lip flange140may be provided toward a distal end of the outer annulus128to extend a predetermined distance toward the inner annulus126. The axial bores136may be displaced radially inward from an inner diameter of the outer annulus128to create a step138. The lip flange140may be formed to extend toward the inner annulus126a distance greater than the radial dimension of the step138. Accordingly, a trough area142is formed in the outer annulus128between the step138and the lip flange140to maintain a small amount of coolant in the trough area142when the clutch hub122is not rotating or is rotating slowly. Thus, even during a period of clutch disengagement, although a majority of the coolant fluid flow is able to drain out of the interior space132through the axial bores136, the radial bores134may be appropriately dimensioned to allow an appropriate amount of coolant to drain by force of gravity from the trough area142into the clutch pack110. Thus, a minimal amount of fluid flow may be established during disengagement of the clutch assembly100, enough of a fluid flow from the interior space132to the clutch pack110to maintain viability and efficiency of the moving components without introducing the inefficiencies of shear caused by excessive fluid flow during the period of disengagement. As shown inFIG. 3, through-holes139, for example, may be provided in a housing component of the drive member for further routing of the fluid flow away from the clutch assembly.

FIGS. 6 and 7illustrate that the axial bores136may be arcuately spaced at equal angles θ around the perimeter of the hub deck130such that at least a portion of one or more of the axial bores136will always be below the fluid level in the trough area142formed in the outer annulus128of the clutch hub122when the clutch hub122is not rotating, i.e., when the clutch pack110is disengaged. Accordingly, when the clutch hub122is stopped and the relative speed between the clutch plates116and the friction discs120is highest, such as in gears1F,2F and R, for example, the larger axial bores136are configured to drain away a majority of the transmission fluid and the smaller radial bores134are configured to allow only a select quantity of transmission fluid into the clutch pack110. Similarly, when the clutch hub122of the driven member104begins to rotate faster relative to the drive hub portion118of the drive member102, such as in gears3F-5F, or when the the clutch assembly100is engaged in gears6F-10F, centrifugal force will once again operate to pump the transmission fluid through the outer annulus128and into the clutch pack110.

In accordance with yet other aspects of the present disclosure, a seal (not shown) may be provided to close a gap146that may exist between the lip flange140and components of the driven member104, such as the balance piston114(seeFIG. 3), if it is determined that excess amounts of transmission fluid are spilling over the lip flange140into the clutch pack110during the disengagement period of the clutch assembly100.

FIG. 8illustrates a rotational clutch assembly200in accordance with yet other aspects of the present disclosure. The rotational clutch assembly200may be used in the transmission10, for example, as one or more of the rotational clutch assemblies40,42, and44. The clutch assembly200may include a drive member, generally indicated at202, and a driven member, generally indicated at204, which rotate about a common axis. A clutch housing206is generally defined between the drive member202and the driven member204and is formed to house a clutch pack, generally indicated at210, that is engaged or disengaged through actuation of a piston212, such as through hydraulic actuation or spring force actuation. A balance piston assembly214may be included and housed in the clutch housing206along with the piston212in order to introduce reverse pressure on the low pressure side of the piston212to counteract the large thrust generated by the hydraulic pressure fluid on the high pressure side of the piston and prevent the piston from engaging the clutch at high rotational speeds.

The annular clutch pack210may be composed of annular clutch plates216that are splined to and extend inward from a drive hub portion218of the drive member202and annular friction discs220that are splined to and extend outward from a clutch hub222of the driven member204. The clutch plates216and friction discs220are interleaved as shown inFIG. 8. In accordance with aspects of the present disclosure, when the clutch assembly200is in a disengaged position, the drive member202maintains a certain rotational speed based on an input speed of an input member of the transmission10and the driven member204is disengaged and not rotating or rotating at a slower relative speed. When the clutch assembly200is in the disengaged position, the clutch plates216rotate freely past the friction discs220in a non-contacting manner. However, when the clutch pack210is to be placed into an engaged position during a particular gear change, for example, when moving from the fifth gear to the sixth gear in the transmission10described previously, pressurized hydraulic fluid is introduced into a pressure chamber224to produce axial movement of the piston212. In turn, actuation of the piston212forces a frictional engagement of the clutch plates216with the friction discs220to reduce or eliminate relative rotation between the clutch plates216and the friction discs220.

As discussed above, during engagement of the clutch pack210, the relative rotational speed of the drive member202and the driven member204may be synchronized. To facilitate cooling during transition to and from an engaged state, and to reduce the transferred kinetic energy while the members are engaged, a continuous flow of coolant, such as automatic transmission fluid, may be provided to the clutch hub222. In accordance with aspects of the present disclosure, the clutch hub222may be formed with an inner annulus226connected to an outer annulus228by a hub deck230. The inner annulus226and the outer annulus228extend from the deck230in a direction toward the piston212and cooperate to form an interior space232. The outer annulus228may be provided with a series of radial bores234that provide fluid communication from the interior space232to the clutch pack210for a fluid to flow through the outer annulus228toward the clutch pack210.

A slinger plate250may be mounted to the hub deck230and configured to divide the interior space232into an upper space233and a lower space235while providing a trough242for collecting transmission fluid pumped into the interior space232. A series of axial facing bores236may be provided in the hub deck230of the clutch hub222. The axial facing bores236are spaced peripherally a radial distance from the center of the hub deck230and just above where the slinger plate250divides the interior space232. The axial bores236are sized to permit a substantial quantity of the flowing coolant to escape the upper space233, primarily during a period of disengagement of the clutch assembly200.

The slinger plate250is also provided with a series of radially situated slinger bores244at the bottom of the trough242. The slinger bores244provide fluid communication from the upper space233to the lower space235for the transmission fluid to flow therethrough. Thus, when the clutch pack210is engaged to cause rotation of the clutch hub222at the same speed as the drive member202, or during a period when rotation of the driven member204is increased relative to the rotation of the drive member202, such as in gears3F-10F, by way of centrifugal action transmission fluid is forced through the slinger bores244and into the lower space235. Once in the lower space235, the transmission fluid may continue under centrifugal force to flow through the radial bores234into the clutch pack210. The size of the slinger bores244and the radial bores234are determined in order to restrict a majority of the coolant flow to the lower space235and thus the clutch pack210during a period of disengagement, when most of the transmission fluid is intended to drain from the trough242by way of the axial bores236.

The axial bores236may be arcuately spaced at equal angles θ around the perimeter of the hub deck230such that at least a portion of one or more of the axial bores236will always be below the fluid level in the trough area242when the clutch hub222is not rotating, i.e., when the clutch pack210is disengaged. Accordingly, when the clutch hub222is stopped and the relative speed between the clutch plates216and the friction discs220is highest, such as in gears1F,2F, or R, the larger axial bores236may drain away a majority of the coolant before the coolant drains through the slinger bores244and the radial bores234into the clutch pack210. Once the clutch assembly200is engaged and/or the clutch hub222starts to rotate, the slinger bores244and the radial bores234will work again to pump the transmission fluid into the clutch pack210to provide adequate removal of the thermal heat generated therein.

Various aspects of systems and methods for cooling a clutch assembly may be illustrated by describing components that are connected, attached, and/or joined together. As used herein, the terms “connected”, “attached”, and/or “joined” are used to indicate either a direct connection between two components or, where appropriate, an indirect connection to one another through intervening or intermediate components. In contrast, if a component is referred to as being “directly coupled”, “directly attached”, and/or “directly joined” to another component, there are no intervening elements present.

Industrial Applicability

The disclosure includes a clutch cooling system and methods for cooling a clutch that include passively controlling the flow of coolant to a clutch pack in the clutch. The cooling system efficiently transfers thermal energy generated by the engagement and disengagement of the clutch pack while reducing drag losses of the clutch assembly when the clutch is disengaged. The clutch cooling system is disclosed for use in transmissions on vehicles, including heavy haul trucks or ground moving equipment, for example, but may be used in any machine that uses clutches for the engagement and disengagement of component members.

In a rotational clutch having a drive member and a driven member, the clutch cooling system employs a unitary clutch hub attached to the driven member that has axial bores and radial holes, the radial holes being in fluid communication with a clutch pack and the axial bores providing an outlet from the clutch assembly. Through placement and sizing of the axial bores and the radial holes, passive cooling control depends simply on the rotational speed of the clutch hub by increasing a flow of coolant to the clutch pack through the radial holes during engagement of the clutch pack, when the clutch hub is rotating, while diverting a larger portion of the flow away from the clutch pack via the axial bores when the clutch pack is disengaged, when the clutch hub is not rotating or rotating at a much slower speed.