Multipart balanced piston clutch

A clutch assembly for a transmission of an agricultural work vehicle. The clutch assembly includes a housing, a clutch pack located within the housing, a piston chamber located within the housing, and a multipart piston located within and slidable relative to the piston chamber. The multipart piston is operably connected to the clutch pack for engaging and disengaging the clutch pack. The multipart piston includes a lower piston extension part. The clutch assembly further includes a balance chamber that is located within the housing. The lower boundary wall of the balance chamber and the lower boundary wall of the piston chamber are radially separated from one another by a substantial distance. The lower piston extension part is located within the balance chamber for adding to a collective surface area of the balance chamber.

BACKGROUND OF THE INVENTION

The present invention pertains to a driveline of a vehicle and, more specifically, to a hydraulically operated clutch assembly for the driveline of a work vehicle.

A work vehicle, such as a large truck or tractor, generally includes a chassis, wheels and/or tracks supporting the chassis, an engine, such as a diesel engine, a transmission, and a drivetrain. The transmission may transmit the motive force, in various gear ratios, to the wheels through the drivetrain which may selectively couple the drive axles in order to operate the vehicle in one or more tractive, i.e., drive, configurations. Work vehicles typically run at or near the operational capacity of their engines due to the power demands required for earth moving and/or towing various implements. Hence, it is generally critical to rapidly shift between gears to maintain sufficient power at the wheels.

The transmission may include one or more clutch assemblies operably connected in between respective input and output shafts for switching between gears. A clutch assembly generally includes a housing, a clutch pack, springs or Belleville spring washers, a piston, and a sealed piston chamber. The piston has an annular body and an extension member which is selectively engageable with the clutch pack. The springs act against the piston, returning the piston away from the clutch pack when hydraulic piston pressure is reduced. In operation, the piston chamber, located behind the piston, is selectively pressurized with hydraulic fluid to engage or disengage the clutch. For example, to engage the clutch, the piston chamber may be filled with additional fluid to build pressure therein for overcoming the force of the springs and accordingly pushing the piston toward the clutch pack to compress the clutch pack. To disengage the clutch, the pressure within the piston chamber may be relieved and the springs may return the piston, i.e. push the piston away from the clutch pack, to decompress the clutch pack.

In an effort to decrease the time required to shift gears, the piston chamber may contain a certain amount of hydraulic fluid therein so that little to no fluid flow is required to sufficiently fill the piston chamber for moving the piston. Since the clutch assembly rotates with the shaft, the hydraulic fluid which remains in the piston chamber is subjected to a centrifugal force. This centrifugal force pushes the hydraulic fluid outwardly toward the outer perimeter of the piston chamber, which accordingly creates an axial force, i.e., a centrifugal head force that acts upon the piston. The centrifugal head force pushes the piston towards the clutch pack. Typically, the springs resist the centrifugal head force; however, if the centrifugal head force becomes greater than the return force of the springs then the clutch may undesirably engage or be prevented from disengaging. Thus, the maximum speed of the vehicle may be limited as a result of the centrifugal head force interfering with the operation of the piston clutch. To counteract the undesired effects of the centrifugal head force, the piston clutch may include stronger springs, a mechanical flywheel, or a balance chamber located on an opposite side of the piston. The stronger springs can withstand a greater centrifugal force; however, such springs directly reduce the capacity and efficiency of the clutch.

A piston clutch equipped with a balance chamber helps to reduce the effects of the centrifugal head force at the piston chamber by creating an opposing, albeit lessor, centrifugal force on an opposite side of the piston. The balance chamber is comprised of a shield that is sealed to the underside of the piston extension. The balance chamber may be filled with low pressure oil which, in a similar fashion to the fluid within the piston chamber, creates the opposing centrifugal force. In this regard, the centrifugal head force at the piston chamber may be partially negated such that the piston clutch is not undesirably engaged or prevented from being disengaged. As a result of the shield-to-piston connection, the outer diameter of the piston chamber is always larger than the outer diameter of the balance chamber. Hence, the centrifugal force of the balancing chamber may never be equal to or greater than the piston chamber centrifugal force.

What is needed in the art is a cost-effective and efficient balance chamber for more desirably balancing the centrifugal force in the piston chamber.

SUMMARY OF THE INVENTION

In one exemplary embodiment formed in accordance with the present invention, there is provided a clutch assembly for a transmission of an agricultural work vehicle. The clutch assembly includes a housing, a clutch pack located within the housing, a piston chamber located within the housing, a multipart piston located within and slidable relative to the piston chamber, and a balance chamber. The multipart piston includes a lower piston extension part. The lower boundary wall of the balance chamber and the lower boundary wall of the piston chamber are radially separated from one another by a substantial distance. This distance allows the balance chamber to provide a greater balance force to counteract a centrifugal head force acting on the piston. The lower piston extension part is located within the balance chamber for adding to a collective surface area of the balance chamber. The lower piston extension part may be vented for preventing a build up of fluid in an area behind the lower piston extension part.

In another exemplary embodiment formed in accordance with the present invention, there is provided a clutch assembly for a transmission of an agricultural work vehicle. The clutch assembly includes a housing, a clutch pack located within the housing, a piston chamber located within the housing and including a lower boundary wall and an upper boundary wall, and a multipart piston located within and slidable relative to the piston chamber. The multipart piston is operably connected to the clutch pack for engaging and disengaging the clutch pack. The multipart piston includes a lower piston extension part. The clutch assembly also includes a balance chamber located within the housing and including a lower boundary wall and an upper boundary wall. The lower boundary wall of the balance chamber and the lower boundary wall of the piston chamber are radially separated from one another by a substantial distance. The lower piston extension part is located within the balance chamber for adding to a collective surface area of the balance chamber.

In yet another exemplary embodiment formed in accordance with the present invention, there is provided an agricultural work vehicle that includes a chassis and a transmission supported by the chassis. The transmission includes at least one clutch assembly. The at least one clutch assembly includes a housing, a clutch pack located within the housing, a piston chamber located within the housing and including a lower boundary wall and an upper boundary wall, and a multipart piston located within and slidable relative to the piston chamber. The multipart piston is operably connected to the clutch pack for engaging and disengaging the clutch pack. The multipart piston includes a lower piston extension part. Each clutch assembly also includes a balance chamber located within the housing and including a lower boundary wall and an upper boundary wall. The lower boundary wall of the balance chamber and the lower boundary wall of the piston chamber are radially separated from one another by a substantial distance. The lower piston extension part is located within the balance chamber for adding to a collective surface area of the balance chamber.

One possible advantage of the exemplary embodiment of the agricultural vehicle is that the balance chamber provides for a substantial balance force for counteracting a centrifugal head force acting on the piston as a result of an increased radial distance between the lower boundary walls of the piston chamber and the balance chamber.

Another possible advantage of the exemplary embodiment of the agricultural vehicle is that the piston includes a lower piston extension part which increases the collective surface area of the balance chamber.

Yet another possible advantage of the exemplary embodiment of the agricultural vehicle is that the increased surface area in the balance chamber can create a balance force greater than the centrifugal head force if the radial separation between the piston inner diameter and the balance chamber inner diameter is large enough, which is made possible by the multipart piston.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, and more particularly toFIG. 1, there is shown an agricultural work vehicle10which generally includes a chassis, wheels and/or tracks supporting the chassis, an engine for providing motive power, a transmission12, and a driveline for transferring the motive power to the wheels. The agricultural work vehicle10may be in the form of any desired work vehicle such as a tractor or windrower.

The transmission12is supported by the chassis and generally includes a shaft14, two annular clutch assemblies16, and a hydraulic system for operating the clutch assemblies16in order to cycle through the gears of the agricultural work vehicle10. The transmission12is a continuously variable transmission (CVT). Each clutch assembly16may generally include a housing18, a clutch pack20, multiple Belleville spring washers22, a piston chamber24, and a piston26disposed within the piston chamber24.

As each clutch assembly16spins along with the shaft14, the fluid retained within the piston chamber24causes a centrifugal head force that acts upon the piston26. Since the centrifugal head force is directly correlated to the rotational speed of the shaft14, the centrifugal head force limits the maximum ground speed of the agricultural work vehicle10. If the centrifugal head force becomes greater than the return spring force of the Belleville spring washers22, then the centrifugal head force will cause the piston26to undesirably move or become immobilized, thus interfering with the operation of the clutch pack20and accordingly limiting the ground speed of the agricultural work vehicle10.

Referring now toFIG. 2, there is shown a cross-sectional view of an exemplary embodiment of a transmission30according to the present invention. The transmission30may be incorporated into any desired work vehicle, such as the agricultural work vehicle10as described above. The transmission30is supported by the chassis of the agricultural work vehicle10and generally includes a shaft32, one or more clutch assemblies34, and a hydraulic system for hydraulically operating the clutch assemblies34. The shaft32defines a longitudinal axis and has an outer diameter. The transmission30may be in the form of a hydromechanical CVT transmission.

Each clutch assembly34may generally include a housing36, a clutch pack38, one or more biasing members40, a piston chamber42, a piston44, and a balance chamber46. Also, each clutch assembly34may further include a hydraulic inlet port48that is fluidly connected to the piston chamber42.

The housing36, e.g. clutch carrier, is connected to the shaft32. For instance, the housing36and the shaft32may have corresponding splines which mate with one another such that the housing36rotates with the shaft32. The housing36may comprise any desired shape and material.

The clutch pack38is located within the housing36and includes multiple clutch plates (unnumbered). The clutch plates may be selectively compressed together by the piston44, which in turn causes the sets of plates to rotate together as one unit in order to engage a certain gear. Thus, when the clutch pack38is engaged, the corresponding gear will rotate with the shaft32.

The one or more biasing members40are operably connected in between the clutch pack38and the piston44. The one or more biasing members40may be positioned within a shield50which covers or shields the one or more biasing members40. When the piston chamber42is not pressurized, the biasing member(s)40will push the piston44away from the clutch pack38back into its resting, disengaged position. Each biasing member40may be in the form of a coil spring40. Due to the balance force supplied by the balance chamber46, the coil spring(s)40may have a reduced or weaker coil strength or spring return force which in turn increases the capacity of the clutch pack38at 0 revolutions per minute (rpm). Thereby, the clutch assembly34may not need to include stronger biasing members, such as Belleville spring washers.

The piston chamber42is located within the housing36. The piston chamber42has an annular configuration with an end wall42E, a lower, i.e., inner, boundary wall42L, and an upper, i.e., outer, boundary wall42U. The end wall42E is perpendicular to the longitudinal axis of the shaft32, and the lower and upper boundary walls42L,42U are parallel to the longitudinal axis of the shaft32. The lower boundary wall42L defines an inner diameter of the piston chamber42relative to the longitudinal axis of the shaft32. The upper boundary wall42U defines an outer diameter of the piston chamber42relative to the longitudinal axis of the shaft32.

The multipart piston44is located within and slidable relative to the piston chamber42. The piston44is also centered about the shaft32. The piston44may include a piston head part52, an upper, piston extension part54connected to the head part52, and a lower, piston extension part56connected to the piston head part52. Also, the piston44may include one or more sealing rings which sealably connect the piston44to the piston chamber42. When the piston chamber42is pressurized to a particular level, the piston44slides away from the end wall42E of the piston chamber42, overcomes the spring force of the one or more springs40, and compresses the clutch pack38. When the piston chamber42is depressurized, the piston44is overcome by the spring force, disengages or decompresses the clutch pack38, and slides toward the end wall42E of the piston chamber42. The piston44may be in the form of an annular piston ring.

The piston extension part54operably connects the piston44to the clutch pack38for selectively engaging and disengaging the clutch pack38as the piston44slides back and forth. The upper piston extension part54may be a standalone component fixedly connected to or integrated with an upper end of the piston head part52. The lower piston extension part56may be a standalone component fixedly connected to or integrated with a lower end of the piston head part52. The lower piston extension part56increases the collective surface area of balance chamber46upon which fluid pressure may act. Hence, the collective surface area of the balance chamber46is a collective area of the rear surface areas of the piston head and lower piston extension parts52,56. In this regard, the lower piston extension part56may maximize the balance force of the balance chamber46. The lower piston extension part56may have an “L”-shaped cross-section; however, the lower piston extension part56may comprise any desired shape and size. The lower piston extension part56may at least partially extend underneath the one or more biasing members40inside the balance chamber46. The lower piston extension part56may include at least one fluid passage58or through-hole that is fluidly connected to the transmission fluid tank for venting an area behind the lower piston extension part56. This fluid passage58prevents a vacuum from being created by the lower piston extension part56, which would otherwise reduce the overall piston force. It is also noted that a vacuum would fill with oil, which would thereby create its own centrifugal force, negating the benefit of the lower piston extension part56. As can be appreciated, the fluid passage58eliminates these aforementioned issues since any oil that is collected behind the lower piston extension part56will be evacuated through the fluid passage58by centrifugal force. Thus, oil cannot be trapped behind the lower piston extension part56.

The balance chamber46is located within the housing36, opposite to the piston chamber42. In other words, the piston and balance chambers42,46are located on opposite sides of the piston44. The balance chamber46is bounded by the shaft32and the shield50, which is sealably connected in between the piston44, e.g. piston extension54, and the shaft32. Hence, the outer diameter of the shaft32defines a lower boundary wall46L of the balance chamber46. As can be appreciated, a lower portion of the housing36, which rests against the shaft32, may instead define the lower boundary wall46L of the balance chamber46. Therefore, fluid may be captured within the balance chamber46. The balance chamber46may include the lower, i.e., inner, boundary wall46L, and an upper, i.e., outer, boundary wall46U. The lower boundary wall46L defines an inner diameter of the balance chamber46relative to the longitudinal axis of the shaft32. The upper boundary wall46U defines an outer diameter of the balance chamber46relative to the longitudinal axis of the shaft32.

It is common to leave a sufficient amount of fluid within the piston chamber42in order to more quickly engage the clutch pack38. However, as the housing36rotates with the shaft32, the fluid within the piston chamber42applies a centrifugal head force onto the piston44. The centrifugal head force accordingly pushes the piston44toward the clutch pack38. Generally, under most operating conditions, the spring force is sufficient to counteract and overcome the centrifugal head force. Yet, the centrifugal head force may nevertheless limit the maximum velocity of the agricultural work vehicle10. At the opposite side of the piston44, fluid within the balance chamber46applies an opposing centrifugal force, i.e., balance force, which additionally helps to counteract the centrifugal head force acting within the piston chamber42and onto the piston44. It should be appreciated that a pressure within the piston chamber42initially builds at a minimum pressure-building diameter, which is indicative of a radial distance from the shaft32to a location within the inlet port48at which pressure initially builds. The minimum pressure-building diameter is radially closer to the shaft32than the lower boundary wall42L of the piston chamber42.

The lower boundary wall42L of the piston chamber42is radially separated from the lower boundary wall46L of the balance chamber42by a substantial distance60. As used herein, the term substantial difference may refer to a distance60of at least 20 mm (0.78 in.), plus or minus 10 mm. For example, the distance60may be approximately 21.75 mm (0.86 in.). The distance60causes the balance chamber46to provide a significantly greater balance force. Accordingly, the balance force may be at least 80 percent of the centrifugal force acting within the piston chamber42. For instance, the balance force may be equal to or greater than the centrifugal force acting within the piston chamber42.

Referring now toFIG. 3, there is shown a cross-sectional view of an exemplary embodiment of a transmission70according to the present invention. The transmission70may be substantially similar to the transmission30as described above; and thereby, like elements have been identified with like reference characters. The transmission70includes a dry chamber venting alternative for venting fluid out from behind the lower piston extension part56. More particularly, the hydraulic inlet port48of the transmission30is reconfigured to be a dual-purpose hydraulic inlet port72which fluidly connects to the piston chamber42at a lower location directly behind the lower piston extension part56. Thus, the inlet port72dually allows fluid flow to and from the piston chamber42and vents the area behind the lower piston extension part56. Accordingly, the lower piston extension part56may not require the fluid passage58therein.