FIELD OF THE DISCLOSURE

The present disclosure relates to a wet clutch. More particularly, the present disclosure relates to a wet clutch assembly assembled to a transmission and to a method for using the same.

BACKGROUND

A clutch can transfer power from a prime mover, such as an internal combustion engine or an electric motor, to a transmission and an output. In motor vehicle applications, the output may be the wheels or tracks of a drivetrain. In stationary applications, the output may be a pump, wench, auger, or another output.

Wet clutches have clutch fluid which circulates within and/or through the clutch housing and provides for cooling and/or lubrication of the clutch components. However, wet clutches are also prone to losing some energy to the clutch fluid, particularly when the clutch piston is not engaged such that the clutch plates are rotating relative to the piston. In some transmission systems, a wet clutch may operate in such a disengaged state during vehicle operation, such that energy losses arising become significant to overall vehicle efficiency.

SUMMARY

The present disclosure provides a wet clutch system including fluid-flow apertures in the clutch piston which allow for reduction of oil shear forces between rotating clutch plates and a stationary piston. In particular the apertures pass through the piston in the area of the piston's engagement with the clutch plates. When the piston is in its deactivated position and spaced from the clutch plates, the radially-outward position of these apertures allows high-pressure, centrifugally-driven clutch fluid to migrate away from the clutch plates through the piston to a backfill cavity on the opposite side of the piston. An air-inlet aperture may be provided in or near the clutch hub to facilitate this oil migration.

In one form, the present disclosure provides a clutch assembly including a housing, a clutch disposed within the housing rotatable relative thereto, the clutch having a frictional-engagement portion on at least one side thereof, and a piston having a piston hub and a wall extending radially outwardly from the piston hub. The wall of the piston has a first side facing the clutch that is configured to engage the frictional-engagement portion of the clutch, the first side cooperating with the housing to define a first fluid cavity. The wall of the piston has a second side opposite the first side that faces the housing to define a second fluid cavity, the piston having at least one aperture extending through the wall of the piston to selectively establish fluid communication between the first fluid cavity and the second fluid cavity, the at least one aperture disposed at a radial location overlapped by the frictional-engagement portion of the clutch such that the fluid communication is eliminated when the piston and the frictional-engagement portion of the clutch are in contact.

In another form, the present disclosure provides a method of operating a clutch, including delivering a lubricating fluid to a first cavity within a clutch housing, the first cavity containing a clutch plate having a friction area; delivering an actuation fluid to a second cavity with the clutch housing, the second cavity separated from the first cavity by a clutch piston having at least one aperture radially overlapped by the friction area; and delivering makeup air to the first cavity when fluid migrates from the first cavity to the second cavity through the at least one aperture.

