Abstract: Disclosed is a method for operating a multi-gear vehicle transmission having a plurality of shifting elements (A, B, C, D, E) for engaging gears of the vehicle transmission. In a neutral gear, in which some of the shifting elements (A, B) are already actuated, a transmission input (1) is decoupled from a transmission output (2) of the vehicle transmission. In a driving gear the transmission input (1) is coupled to the transmission output (2) of the vehicle transmission by closing the shifting elements (A, B, C, D, E) associated with the driving gear, in order to propel the vehicle. With the neutral gear engaged a transmission condition is determined, and if a transmission condition with elevated drag losses exists, then in addition to the shifting elements (A, B) actuated in the neutral gear a shifting element (D) associated with a reversing gear of the vehicle transmission is also closed.

Abstract: Provided are a wet friction plate and a wet multiplate clutch device capable of reduction drag torque while suppressing a decrease in the area of a friction member. The wet friction plate includes multiple friction members through oil grooves on a flat plate annular core metal. The friction member has first fine grooves opening at an inner peripheral edge of the friction member and extending to an outer peripheral edge side and second fine grooves opening at an outer peripheral edge of the friction member and extending to an inner peripheral edge side. The first fine groove and the second fine groove are formed to have a groove width of equal to or greater than 0.1 mm and equal to or less than 0.8 mm, and overlap portions overlapping with each other in a circumferential direction at the same position in a radial direction of the core metal.

Abstract: The present invention relates to a disk (2) for a disk clutch or brake (4) comprising a first friction surface (28) and a second friction surface (34) facing away from the first friction surface (28), in which recesses and/or grooves (40, 42, 44) are provided. A first type of recesses and/or grooves (40), which is generated by a material shaping and/or a material casting and/or a non-material removing first manufacturing method, is provided in the first friction surface (28), and a second type of recesses and/or grooves (42), which is generated by a material removing second manufacturing method, is provided in the second friction surface (34). In addition, the present invention relates to a disk clutch and brake (4) comprising such a disk (2) and a method for producing such a disk (2).

Abstract: The wet friction member 1 of the invention includes a core plate 2 formed in a flat ring shape, a friction part 3 arranged in a ring shape. The friction part 3 has segment pieces including rectangular shaped G1 to G4: G1 in which a lower right corner of rectangular piece is notched; G2 in which an upper left corner of rectangular piece is notched; G3 in which an upper right corner of rectangular piece is notched; G4 in which a lower left corner of rectangular piece is notched. The friction part 3 has arrangements T1 and T2: T1 in which G1 and G2 are arranged in a manner a right side of G1 and a left side of G2 face each other; T2 in which G3 and G4 are arranged in a manner a right side of the G3 and a left side of G4 face each other.

Abstract: The present invention relates to a disk clutch comprising a first disk set (32) which is connected rotationally fixed to a first disk carrier (18) and a second disk set (42) which is connected rotationally fixed to a second disk carrier (24), wherein the disks (34 through 40, 46 through 52) of the two disk sets (32, 42) may be brought into frictional engagement with one another via friction surfaces (54, 56), wherein recesses and/or grooves are provided in at least one or more friction surfaces (54, 56) of the disks (34 through 40; 46 through 52) of the first and/or second disk sets (32; 42). A first type of recesses and/or grooves (68) is thereby provided, which is generated by a material shaping and/or a material casting and/or a non-material removing first manufacturing method, and a second type of recesses and/or grooves (70) is provided, which is generated by a material removing second manufacturing method.

Abstract: A piston, comprising: a shaft side with a first circumferential groove, said first circumferential groove bounded by a continuous circumferential seal plateau, said seal plateau extending axially outward from said first circumferential groove, wherein a planar outboard surface extends radially outboard from said seal plateau; a clutch side having two grooves alternating with two lands; an inner circumferential surface having a seal groove formed therein; and an outer circumferential surface having a seal groove formed therein, wherein the sides and surfaces form a ring shape.

Abstract: Disclosed is a method for optimizing feature parameters of straight grooves of a wet friction element and relates to the technical field of heavy-duty vehicle transmission. By using the method, the feature parameters of the straight grooves of the wet friction element can be improved by optimization, and the thermoelastic stability of the wet friction element can be improved.

Abstract: Provided is a clutch friction plate and a clutch device configured so that stiction torque can be reduced and each of in gear, shift feeling, and neutral find can be smoothly performed. A clutch device (100) includes clutch friction plates (101). In the clutch friction plate (101), multiple small-piece-shaped friction members (103) are radially bonded to surfaces of a core bar (102) formed in a flat-plate annular shape through an oil groove (105). Each friction member (103) includes an outer side (104a) facing an outer edge portion of the core bar (102) and an inner side (104b) facing an inner edge portion of the core bar (102) and extending parallel to the outer side (104a), and is formed in a rectangular shape.

Abstract: A present wet friction body includes a core plate, a plurality of friction parts disposed on a main surface thereof in a ring shape at intervals, a plurality of oil grooves defined by the corresponding friction parts. The friction parts include first to third friction parts in which forms of the pair of sidewalls are different each other. The first friction part includes a left sidewall inclining to the right and a right sidewall inclining to the left, with respect to an imaginary line segment, and an outer peripheral wall having a length less than a length of an inner peripheral wall. The second friction part includes a pair of sidewalls, both inclining to the right with respect to an imaginary line segment. The third friction part includes a pair of sidewalls, both inclining to the left with respect to an imaginary line segment.

Abstract: The lubricating structure includes a rotary shaft, a power transmission apparatus having a power transmission element disposed on an outer circumference of the rotary shaft and formed by alternately stacking frictional members, and a flow channel guides a lubricating liquid to the power transmission element. The power transmission element includes an inner circumferential cylindrical section rotated integrally with the rotary shaft, an outer circumferential cylindrical section rotated integrally with the frictional member, and a disk section configured to connect the inner circumferential cylindrical section and the outer circumferential cylindrical section.

Abstract: Described herein are various embodiments of a clutch assembly and separator plates for a clutch assembly. The clutch assembly may comprise a first separator plate; a second separator plate; and a spring coupled to the first separator plate and contacting the second separator plate, such that when compressed the spring applies a repulsive force separating the first separator plate and the second separator plate.

Abstract: A multi-plate clutch is comprised of: one or more core plates respectively coupled with a first rotary body rotatable about an axis; one or more reaction plates arranged alternately with the core plates and respectively coupled with a second rotary body rotatable about the axis, the reaction plates receiving the pressure force from the driver mechanism to brake the first rotary body relative to the second rotary body; one or more friction members respectively fixed to faces on the respective core plates, the faces to come into contact with the reaction plates, and including a bundle of warp yarns and a bundle of weft yarns mutually weaved perpendicular to each other, the yarns being formed of carbon fibers; and a plurality of bottomed grooves formed on faces on the respective reaction plates, the faces to come into contact with the core plates.

Abstract: A friction plate has a plurality of friction material segments circularly fixed on an annular core plate, wherein each of the friction material segments includes an oil groove having an opening that opens in the direction of an outer circumferential edge of the friction plate and an end portion that ends between an inner circumferential edge and the outer circumferential edge, oil passages in communication in the direction of the inner and the outer circumferential edges of the friction plate are provided among the friction material segments, and at least some of the oil passages have a first shape, the width of which in a circumferential direction decreases from the inner circumferential edge of the friction plate toward the outer circumferential edge thereof.

Abstract: A work vehicle drive assembly has a bimodal clutch module that includes a pressure plate, a module housing containing first and second cavities located on opposing sides of the pressure plate, and an actuator. The actuator is controllable to move the pressure plate along a working axis of the clutch module. A clutch member is installed in a selected one of the first and second cavities. The clutch member is (i) engaged by movement of the pressure plate along the working axis in a first direction when the clutch member is installed in the first cavity and (ii) disengaged by movement of the pressure plate along the working axis in the first direction when the clutch member is installed in the second cavity.

Abstract: A clutch and/or brake module has a heat sink which is attached to a transmission housing for the purpose of discharging heat. The brake module further has a brake disc, which is connected to a rotational member formed by a shaft (schematically indicated by a center line). The brake disc is provided on one side with a lining and faces with this side towards the heat sink. The brake is a dry brake and is not lubricated. The brake module further has an actuation system (cylinder with piston movable therein, schematically indicated by an arrow) which can exert an axial pressing force directly on the brake disc. The brake disc is located axially between the heat sink and the actuation system. The cooling plate is secured to a transmission housing, a part of which is schematically shown.

Abstract: A multi-electric motor driven gearbox assembly includes a main gear coupled to at least two pinion gears. Each pinion gear is connected via an associated secondary shaft to corresponding secondary shaft pulleys that are adapted to be driven by an electric motor. A one-way bearing is coupled to each pinion gear and disposed so as to allow the pinion gear to decouple relative to the secondary shaft pulley when the associated electric motor fails and to do so without creating drag on the main gear during decoupling.

Abstract: A transmission includes a case having a front support that defines a reservoir, and a first passageway in fluid communication with the reservoir. The transmission also includes a torque converter having a bypass clutch having a piston disposed between a balance chamber and an apply chamber. The clutch fixes the turbine to the impeller in response to fluid pressure in the apply chamber exceeding fluid pressure in the balance chamber. The transmission further includes a hollow stator shaft fixed to the front support and a turbine shaft driveably connected to the turbine. The turbine shaft extends through the stator shaft and defines a second passageway in fluid communication with the first passageway and the balance chamber. The reservoir, the first passageway, the second passageway, and the balance chamber are arranged such that fluid travels from the reservoir to the balance chamber when the piston is de-stroked.

Abstract: Power transmission systems including clutch arrangements and systems are adapted to be used in marine and other environments. Such power transmission systems may include clutch arrangements that provide more effective power transmission capabilities as well as greater durability and longer life. Slipping clutch arrangements may effectively vary the output speed of a clutch arrangement from the speed of the engine or other driver as desired for the particular application. Various clutch arrangements also provide for greater flexibility and drive options, lighter weight, and diverse types of capabilities.

Abstract: A friction plate is formed by annularly fixing a plurality of friction material segments to a substantially annular core plate, and a minute groove is formed on a surface of the friction material segment.

Abstract: A thrust washer is provided. The thrust washer includes a wet friction material and a phenolic resin layer coating an outer surface of the wet friction material. A torque converter comprising the thrust washer is also provided. A method of forming a thrust washer is further provided. The method includes providing a layer of phenolic resin on an outer surface of a wet friction material.

Abstract: A fastening friction plate is wedged between the fastening surfaces of two fastening members in order to increase the fastening force between them. The fastening friction plate has a friction plate main body of a fixed thickness, and engaging protuberances having an approximately truncated cone shape formed on the both surfaces of the friction plate main body at a fixed pitch. The friction plate main body and the engaging protuberances are integrally formed by photo-etching into the both surfaces of a steel plate material having a fixed thickness. The hardness of the fastening friction plate is equal to or greater than that of the fastening surfaces of the fastening members.

Abstract: A piston assembly, including: a piston for a clutch in a torque converter including: first and second radial surfaces; and a radially inner-most end connecting the first and second radial surfaces. The piston assembly includes a radially displaceable bushing assembly: arranged to engage an input shaft for a transmission and form a first seal against the input shaft; including a first radial wall disposed parallel to the first radial surface and forming a second seal against the first radial surface; and including a second wall facing the second radial surface. The bushing assembly is radially displaceable with respect to the piston while maintaining the first seal between the first radial wall and the first radial surface and the second seal between the bushing assembly and the input shaft.

Abstract: A gearbox for a motor vehicle including a plurality of forward gear ratios and at least one reverse gear ratio. The gearbox including an electro-hydraulic actuation unit configured for selection and engagement of the gear ratios. The gearbox comprises a first hydraulic pump and a second hydraulic pump. The first hydraulic pump is driven in rotation by an electric motor and is configured for supplying hydraulic fluid taken in from a first intake environment to said electro-hydraulic actuation unit. The second hydraulic pump is driven in rotation by an engine of said motor vehicle and is configured for supplying hydraulic fluid taken in from a second intake environment to said gearbox, for lubrication thereof, and to said first intake environment.

Abstract: A method for braking a vehicle driving forward towards stop. The vehicle has a propulsion system including a combustion engine with an output shaft (2a), a gearbox (3) with an input shaft (3a), an electric machine (9) comprising a stator and a rotor, and a planetary gear comprising a sun gear (10), a ring gear (11) and a planet wheel carrier (12). When braking the vehicle, a reverse gear of the gearbox is engaged and the electric machine is controlled to apply brake torque requested to the input shaft of the gearbox.

Abstract: In a wet friction material, a plurality of segment pieces is disposed at both sides of inter-segment grooves. The segment pieces are composed of first segment pieces and second segment pieces. The first segment piece has at least two inner peripheral recesses formed on an inner periphery thereof and at least two outer peripheral recesses formed on an outer periphery thereof. The outer periphery of the first segment piece has a short dimension. The second segment piece has at least two inner peripheral recesses formed on an inner periphery thereof and at least two outer peripheral recesses formed on an outer periphery thereof. The outer periphery of the second segment piece has a long dimension.

Abstract: When an internal combustion engine that is provided in a work machine and that serves as a power source for the work machine is controlled, the following lines are used: a first equal throttle line which is defined to correspond to a case where an amount of fuel injection for the internal combustion engine is maximum where the rotation speed of the internal combustion engine is the same and so that an output of the internal combustion engine becomes constant, a second equal throttle line which is defined to correspond to a case where the amount of fuel injection for the internal combustion engine is zero where the rotation speed of the internal combustion engine is the same and so that the torque decreases with increase of the rotation speed, and a third equal throttle line which is obtained from the first equal throttle line and the second equal throttle line.

Abstract: To be able to promote discharge of lubricating oil in a disengaged state while maintaining a large lining area to such an extent that it does not affect torque transmission capacity, heat resistance, and peeling resistance thereby to obtain an excellent effect to reduce a drag torque in a wide range of relative rotation speeds. In a segment friction material 1A as a wet friction material, drag torque reducing grooves 5A are provided only on top surfaces of part of segment pieces 3A among thirty pieces of segment pieces 3, 3A. A series of drag torque reducing grooves 5A extend over five segment pieces 3A along a direction almost at right angles to a straight line connecting a center point 5Aa thereof and a center O of a circumference. The series of drag torque reducing grooves 5A are provided at three places on the circumference. Thereby, discharge of ATF is promoted without reducing a lining area and an oil film is formed on the top surface of the segment piece 3A.

Abstract: A clutch assembly with a rotatable clutch hub which is connected rotationally fixedly to several inner plates which may be brought into friction connection with outer plates of an associated clutch basket and form a plate pack. The clutch hub has at least one bore which allows a throughflow of a fluid from the interior of the clutch to the plates, and an oil conduction device attached to the clutch hub at the at least one bore.

Abstract: A segment-type friction material comprises segment pieces each having a supply passage formed thereon to supply lubricating oil to a surface of each of the segment pieces. The segment-type friction material further comprises oil grooves each having an outer peripheral opening portion extended in a curved shape or a linear shape. Thereby, lubricating oil is sufficiently supplied to the surface of each of the segment pieces from an outer peripheral side thereof or an inner peripheral side thereof and a clearance between the segment-type friction material and its associated separator plate is assured. Moreover, a space for the lubricating oil to flow through an outer periphery is sufficiently assured and a drag torque is reduced.

Abstract: A friction plate for a clutch assembly includes a core plate and a plurality of friction segments made of a friction material. A plurality of grooves are disposed between said plurality of friction segments. Each segment has tapered sides so that the grooves have a first width adjacent the outer diameter of the core plate and a smaller second width smaller adjacent the inner diameter of the core plate. This tapered groove structure directs oil from the outside the clutch assembly to the inside to improve cooling efficiency.

Abstract: A braking system includes at least one rotating disc, and at least one brake disc having a front face and a rear face. The brake disc has at least four inner chambers disposed therein. Each of the at least four inner chambers has a liquid inlet and a liquid outlet and defines a liquid pathway. At least one biasing element is configured to move the front face of the at least one brake disc into contact with the at least one rotating disc.

Abstract: The invention relates to a friction lamella (1) comprising a disk-shaped carrier element (2) having a first surface (3) and a second surface (4) opposite thereto, a first friction lining (5) being situated on the first surface (3) and a second friction lining (6) being situated on the second surface (4), which are formed from a composite material, comprising a resin and a fibrous material, and grooves (9, 10) being situated in the first and in the second friction linings (5, 6), which divide the friction linings (5, 6) into segments (7, 8) at least in surface-proximal areas. The segments (7) of the first friction lining (5) are implemented offset by a defined offset angle (11) to the segments (8) of the second friction lining (6). Furthermore, the invention relates to a method and a device for producing the friction lamella and the use of the friction lamella.

Abstract: A segment-type friction material is composed of segment pieces. An outer circumference of the segment piece is away from an outer circumference of a core plate. A setback amount is about 2 mm. Then, a gap between the outer circumference of the segment piece and an inner peripheral part of an automatic transmission case becomes large. Thus, there is generated a part at which a gap between the segment pieces and a separator plate becomes large in a disengaged state.

Abstract: The present invention provides a starting clutch disposed between a transmission and an engine and having a wet type multi-plate clutch for transmitting a power, in which the wet type multi-plate clutch includes a plurality of friction plates housed for an axial sliding movement, a clutch drum for housing the friction plates, and a piston for urging a radial central region or therearound of the friction plate to engage the friction plates, and oil which has lubricated the wet type multi-plate clutch is temporarily trapped within the clutch drum and then is discharged.

Abstract: The present invention provides a friction plate having a friction surface formed by sticking an annular friction material to a substantially annular core plate and wherein the friction surface is provided with a first oil groove having an opening portion opened to an inner peripheral edge of the friction plate and an end terminating at a point between the inner peripheral edge and an outer peripheral edge, and a second oil groove having an opening portion opened to the outer peripheral edge of the friction plate and an end terminating at a point between the inner peripheral edge and the outer peripheral edge.

Abstract: An automotive car and truck transmission clutch module friction plate and a method of manufacture thereof is provided wherein the friction plate is fabricated from a polymeric material, which is less expensive and lighter than comparable steel friction plates.

Abstract: A synchronizing ring for a synchronizing device of a motor vehicle gearing with a ring body. The ring body has a plurality of recesses, and frictional elements are arranged in the recesses.

Abstract: Disclosed is a lock-up clutch operative to uniform temperatures on a multiple number of friction surfaces, thereby improving accuracy of a lock-up control and to prevent shudders of a vehicle from being generated. The lock-up clutch includes a front cover, a lock-up piston, a plurality of torque transmitting plates, and a plurality of friction materials formed on the torque transmitting plates and having three or more friction surfaces. The friction materials are constituted by a first friction material frictionally contactable with the front cover, a second friction material frictionally contactable with the lock-up piston, and third friction materials frictionally contactable with at least one of the plates. Three or more friction surfaces are constituted by outside friction surfaces formed on the first and second friction materials and each having a small area, and inside friction surfaces formed on the third friction materials and each having a large area.

Abstract: A friction plate, including: a ring-shaped piece of friction material with an inner circumference, and first and second surfaces facing in first and second opposite axial directions, respectively; a first core plate with a first ring-shaped body, a first plurality of protrusions extending radially outward from the first ring-shaped body and imbedded in the first surface, and a second plurality of protrusions extending radially inward from the first ring-shaped body; and a second core plate with a second ring-shaped body, a third plurality of protrusions extending radially outward from the second ring-shaped body and embedded in the second surface, and a fourth plurality of protrusions extending radially inward from the second ring-shaped body. The first and second bodies are at least partially disposed radially inward of the inner circumference. The second and fourth pluralities of protrusions are for engagement with a rotatable element.

Abstract: The invention relates to a clutch assembly, particularly for use in force transmission devices for motor vehicle, comprising a housing arrangement that is or can be filled with a fluid, and a frictional arrangement that has a first frictional surface arrangement and a second frictional surface arrangement which can be effectively interconnected by means of an actuator. Each frictional surface arrangement is provided with at least one frictional surface-supporting element. A fluid flow can be generated in the housing arrangement for cooling the frictional surface arrangements. The invention is characterized in that means are provided for creating at least one circuit which repeatedly flows through at least one frictional surface-supporting element of the frictional arrangement and conducts the fluid flow when the rotational speed differs between the effectively interconnectable frictional surface-supporting elements of the different frictional surface arrangements.

Abstract: A vehicle final drive includes a fixed spindle about which a wheel hub is mounted for rotation by wheel bearings, and within which a park and service brake assembly is mounted including a stack of Belleville springs carried by an input quill mounted within an inner end region, and a disc brake pack mounted within an outer end region. Located in the hub outboard of the spindle is a two-stage planetary reduction transmission. A reaction plate is fixed to an outer end face of the spindle cylindrical portion and holds the disc brake pack and a hub of a double ring gear of the transmission in place and preloads the wheel bearings. A fluid distribution manifold is defined by a passage in the spindle for distributing flow for cooling and/or lubricating an input thrust bearing, input drive shaft coupling splines, the brake disc pack, the wheel bearings, and the first stage planet gear bearings.

Abstract: A friction part for a frictionally acting device comprising an annular friction surface which has an inner edge and an outer edge, with the friction surface having provided in it an encircling first groove which extends in zig-zag or undulating form between radially inner and radially outer deflection points, a plurality of second grooves which extend from the inner edge to the outer deflection points and a plurality of third grooves which extend from the outer edge into the encircling first groove and which open into the encircling first groove at opening-in points between the deflection points.

Abstract: The present invention relates to a friction part for a frictionally acting device, having an annular friction face which has an inner edge and an outer edge, wherein at least one set of grooves is provided in the friction face, which set of grooves has a first groove which extends from the inner edge or the outer edge to a branching point between the inner edge and the outer edge, and a second and third groove which extend in each case from the branching point to the other edge. According to the invention, the second groove is inclined in the one peripheral direction and the third groove is inclined in the other peripheral direction of the direction face with respect to a radial line through the branching point. The present invention also describes a frictionally acting device having a frictions part of said type.

Abstract: An embodiment of a multidisk oil-bath clutch having: a housing mounted to rotate about a longitudinal axis of rotation; at least one hub mounted to rotate about the longitudinal axis of rotation and housed inside and coaxially with the housing; a number of drive disks housed inside the housing and angularly integral with the housing or the hub; a number of driven disks housed inside the housing, alternating with the drive disks, and angularly integral with the hub or the housing; at least one oil inlet into the housing; and at least one oil outlet from the housing. Each drive disk has a number of first circulation channels equally spaced about the longitudinal axis of rotation and extending radially from an inner edge of the drive disk to an outer edge of the drive disk; and each driven disk has a number of second circulation channels equally spaced about the longitudinal axis of rotation and extending radially from an inner edge of the driven disk to an outer edge of the driven disk.

Abstract: The present invention provides a friction plate having a friction surface formed by sticking an annular friction material to a substantially annular core plate and wherein the friction surface is provided with a first oil groove having an opening portion opened to an inner peripheral edge of the friction plate and an end terminating at a point between the inner peripheral edge and an outer peripheral edge, and a second oil groove having an opening portion opened to the outer peripheral edge of the friction plate and an end terminating at a point between the inner peripheral edge and the outer peripheral edge.

Abstract: The present invention provides a friction plate having a friction surface formed by sticking an annular friction material to a substantially annular core plate and wherein the friction surface is provided with a first oil groove having an opening portion opened to an inner peripheral edge of the friction plate and an end terminating at a point between the inner peripheral edge and an outer peripheral edge, and a second oil groove having an opening portion opened to the outer peripheral edge of the friction plate and an end terminating at a point between the inner peripheral edge and the outer peripheral edge.

Abstract: In a frictional engagement apparatus that includes a clutch drum, separator plates, a clutch hub, and friction plates, a plurality of concave portions that dip inward in the plate thickness direction and a plurality of convex portions that protrude outward in the plate thickness direction are formed on an edge of the separator plates and/or a an edge of the friction plates, with each convex portion being arranged between two adjacent concave portions. Ridge lines of the concave portions and the convex portions pass through positions away from a center point of the separator plates and/or the friction plates.

Abstract: A friction disk for a wet-running clutch for a motor vehicle includes a lining carrier ring, provided with connecting areas for connecting the friction disk to a drive side or to a takeoff side of a clutch, and a plurality of friction lining elements, carried on at least one side of the lining carrier ring, fluid flow channels are provided between the friction lining elements which are directly adjacent to each other in the circumferential direction, wherein at least some of the fluid flow channels have different channel widths.

Abstract: A wet clutch having friction surfaces, where at least one friction surface consists of a porous friction lining with essentially flat surface placed on a supporting part. In order to achieve better cooling of the friction lining and supporting part and of the opposing friction surface by means of cooling oil pressed through the porous friction lining under pressure, the friction lining is provided with at least one cut-out.

Abstract: The present invention provides a friction plate having a friction surface formed by sticking an annular friction material to a substantially annular core plate and wherein the friction surface is provided with a first oil groove having an opening portion opened to an inner peripheral edge of the friction plate and an end terminating at a point between the inner peripheral edge and an outer peripheral edge, and a second oil groove having an opening portion opened to the outer peripheral edge of the friction plate and an end terminating at a point between the inner peripheral edge and the outer peripheral edge.