A wet friction disc includes a lubrication groove and a plurality of lands defined by the lubrication groove. The lubrication groove has a plurality of circumferential groove portions that extends in a circumferential direction and has a predetermined groove width in a radial direction, and a plurality of intersecting groove portions that extends in directions intersecting the circumferential direction. At least some of the circumferential groove portions have an arc shape such that an end in the circumferential direction is located adjacent to one of the lands in the circumferential direction and that the groove width is entirely contained within a range in the radial direction spanned by that land.

A wet friction disc includes a lubrication groove and a plurality of lands defined by the lubrication groove. The lubrication groove has a plurality of circumferential groove portions that extends in a circumferential direction and has a predetermined groove width in a radial direction, and a plurality of intersecting groove portions that extends in directions intersecting the circumferential direction. At least some of the circumferential groove portions have an arc shape such that an end in the circumferential direction is located adjacent to one of the lands in the circumferential direction and that the groove width is entirely contained within a range in the radial direction spanned by that land.

An oil feed structure includes: a hydraulic clutch; a power transmitting shaft coupled to the hydraulic clutch; a valve element inserted into the power transmitting shaft, and a spring configured to bias the valve element. The valve element includes: a pressure receiving surface facing in an axial direction of the power transmitting shaft and configured to receive hydraulic pressure of a hydraulic pressure oil passage; and a port communicable with a clutch lubrication hole of the power transmitting shaft. The spring biases the valve element toward the hydraulic pressure oil passage against the hydraulic pressure received by the pressure receiving surface. When clutch operating hydraulic pressure changes, the valve element moves in the axial direction to change an opening degree of communication between the port and the clutch lubrication hole.

An oil feed structure includes: a hydraulic clutch; a power transmitting shaft coupled to the hydraulic clutch; a valve element inserted into the power transmitting shaft, and a spring configured to bias the valve element. The valve element includes: a pressure receiving surface facing in an axial direction of the power transmitting shaft and configured to receive hydraulic pressure of a hydraulic pressure oil passage; and a port communicable with a clutch lubrication hole of the power transmitting shaft. The spring biases the valve element toward the hydraulic pressure oil passage against the hydraulic pressure received by the pressure receiving surface. When clutch operating hydraulic pressure changes, the valve element moves in the axial direction to change an opening degree of communication between the port and the clutch lubrication hole.

A transfer case comprises a primary output shaft, a secondary output shaft, a clutch, and a plurality of valves. The primary output shaft includes a hub rotationally coupled thereto. The clutch is selectively couples the primary output shaft to the secondary output shaft to transfer torque therebetween. The clutch includes a housing, interleaved plates, and an apply plate. The housing is rotationally coupled to the secondary output shaft. The interleaved plates alternate between a first subset of the interleaved plates rotationally coupled to the hub, and a second subset of the interleaved plates rotationally coupled to the housing. The apply plate compresses the interleaved plates for transferring torque between the hub and the housing. The valves selectively release oil supplied through the primary output shaft into the housing. Each valve includes a bore formed in the hub and a valve rod movable by the apply plate to open the valve.

A transfer case includes a primary output shaft, a secondary output shaft, a clutch, and a hub. The clutch includes a plurality of interleaved plates for selectively rotationally coupling the primary output shaft to the secondary output shaft. The hub rotationally couples the primary output shaft and the clutch. The hub includes an outer annular member and an inner annular member. The inner annular member is rotatable within the outer annular member for the hub to selectively release oil into the clutch.

A transfer case includes a primary output shaft, a secondary output shaft, a clutch, and a hub. The clutch includes a plurality of interleaved plates for selectively rotationally coupling the primary output shaft to the secondary output shaft. The hub rotationally couples the primary output shaft and the clutch. The hub includes an outer annular member and an inner annular member. The inner annular member is rotatable within the outer annular member for the hub to selectively release oil into the clutch.

A lubrication system (400) for a transfer case (200) includes a pump (228) selectively supplying a working fluid to a fluid reservoir of an actuator (226) configured to apply force to a clutch assembly (214) to cause the clutch assembly (214) to move between a disengaged position and an engaged position. The lubrication system also includes a relief valve (302) having a relief valve inlet fluidly coupled to the fluid reservoir of the actuator (226) which opens to receive the working fluid based on a threshold pressure level of the working fluid in the fluid reservoir. The lubrication system also includes a trough (306) fluidly coupled to a relief valve outlet of the relief valve (302). The trough (306) carries the working fluid from the relief valve outlet to a bearing assembly (227) associated with at least one of an input shaft (204) and a primary output shaft (206) of the transfer case (200) when the clutch assembly (214) is in the disengaged position.

A lubrication system (400) for a transfer case (200) includes a pump (228) selectively supplying a working fluid to a fluid reservoir of an actuator (226) configured to apply force to a clutch assembly (214) to cause the clutch assembly (214) to move between a disengaged position and an engaged position. The lubrication system also includes a relief valve (302) having a relief valve inlet fluidly coupled to the fluid reservoir of the actuator (226) which opens to receive the working fluid based on a threshold pressure level of the working fluid in the fluid reservoir. The lubrication system also includes a trough (306) fluidly coupled to a relief valve outlet of the relief valve (302). The trough (306) carries the working fluid from the relief valve outlet to a bearing assembly (227) associated with at least one of an input shaft (204) and a primary output shaft (206) of the transfer case (200) when the clutch assembly (214) is in the disengaged position.

A clutch assembly for a motor vehicle drivetrain includes a rigid support and a wet friction material fixed to a surface of the rigid support. The wet friction material includes a base material including a matrix of fibers and filler particles embedded in the matrix of fibers; and a binder embedded in the base material. The base material includes, by weight percent, 30-55% cellulose fibers and 10-50% calcined kaolin clay. The base material also includes at least one of 1-20% graphite having a mean particle size of 35 to 85 microns, 20-40% diatomaceous earth in combination with the binder being tung modified phenolic resin, 5-20% chopped aramid fibers, or 5-20% of novoloid fibers.