Connection structure for automatic transmission

A connection structure for an automatic transmission includes a drum member that includes a base portion, an outer diameter portion that extends from an outer diameter side of the base portion in an axial direction, and a collar portion that extends from an inner diameter side of the base portion in the axial direction; a base member that includes a raised portion, an outer diameter portion that extends from an outer diameter side of the raised portion in the axial direction, a boss portion that extends from an inner diameter side of the raised portion in the axial direction, and a connection portion that extends from an end of the outer diameter portion; and a ring gear of a planetary gear that includes a spline groove and a circular concave groove on an end portion of an inner peripheral face.

INCORPORATION BY REFERENCE

The disclosure of Japanese Patent Application No. 2005-148745, filed May 20, 2005, and Japanese Patent Application No. 2005-332099, filed Nov. 16, 2005, including the specifications, drawings and abstracts are incorporated herein by reference in their entireties.

BACKGROUND

The invention relates to a connection structure for an automatic transmission.

Automatic transmissions often use many clutch (and brake) drums in which an inner peripheral face of a clutch (and/or brake) drum member formed from a press-molded cylindrical member is outwardly engaged to a base member formed from a cylindrical member. The engaging faces are then welded by an electron beam or the like from the outside (see, for example, Japanese Patent Application Publication No. JP-A-61-48616).

In addition, a planetary gear is disposed adjacent to the clutch drum, and a connection structure is used so as to integrally fix a predetermined element of the planetary gear, such as a ring gear, to the clutch drum (see, for example, published patent application, Japanese translation of PCT international application No. 2005-527744).

The above connection structure is generally a welded structure. As such, precision may be compromised in predetermined rotation elements such as the ring gear due to warping or the like caused by the effects of heat during welding. Furthermore, other problems such as gear noise and less gear durability can occur.

Furthermore, the clutch (or brake) drum member is in spline engagement with a plurality of friction plates and has a predetermined length in the axial direction. A large bending moment (wrenching force) acts on the engaging faces in accordance with the engagement of friction plates and the like. A bending moment thus acts on the welded portion in a concentrated manner. As a result, the structure of the clutch (or brake) drum member has disadvantages in terms of strength with respect to the welded portion and a portion thereof affected by heat.

In addition, formed on an inner peripheral portion of the drum member is a boss-shaped collar portion extending toward the axial direction. The collar portion is often pressed into an outer peripheral face of the base member and an edge portion thereof may be welded. However, this involves a significant amount of surface area for the press fitting and is accompanied by a corresponding increase in the pressing load.

Moreover, the drum member may be integrally fixed to the base member as follows to reduce such a load and simplify assembly. An engaging face of the base member has a stepped structure in which only an edge portion thereof is dimensioned for press fitting, whereas other portions are set to have a slight minor diameter. Only an edge portion of the collar portion is pressed into and positioned in the base member. In such a state, the entire periphery of the edges of the collar portion and the base member are welded.

With the engaging face formed in such a stepped structure, a narrow clearance is created between an outer peripheral face of a minor diameter portion of the base member and an inner peripheral face of the collar portion. Thus, if a foreign substance were to penetrate the clearance during production, it would be impossible to eliminate the foreign substance by a washing process or the like due to the narrowness of the clearance. The contaminated connection member is subsequently assembled to an automatic transmission as a friction engagement device, after which the foreign substance may escape from the clearance during operation of the automatic transmission. The foreign substance could then cause a problem in the automatic transmission.

SUMMARY

The present invention thus provides, among other things, a connection structure for an automatic transmission that solves the problems described above by integrally fixing a drum member and a base member through press fitting, and integrally connecting the drum and a predetermined rotation element of a planetary gear using splines and snap rings.

A connection structure for an automatic transmission, according to an exemplary aspect of the invention, includes a drum member that includes a base portion, an outer diameter portion that extends from an outer diameter side of the base portion in an axial direction, and a collar portion that extends from an inner diameter side of the base portion in the axial direction; a base member that includes a raised portion, an outer diameter portion that extends from an outer diameter side of the raised portion in the axial direction, a boss portion that extends from an inner diameter side of the raised portion in the axial direction, and a connection portion that extends from an end of the outer diameter portion; and a ring gear of a planetary gear that includes a spline groove and a circular concave groove on an end portion of an inner peripheral face. A drum is structured by press fitting an inner peripheral face of the collar portion of the drum member onto an outer peripheral face of the outer diameter portion of the base member. A spline formed on an outer peripheral face of the connection portion of the base member is engaged with the spline groove of the ring gear, and a snap ring is engaged with and held in the circular concave groove.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinafter, an embodiment in which the present invention is applied to an automatic transmission will be explained with reference to the drawings. First, a schematic configuration of an automatic transmission11to which the present invention can be applied will be described with reference toFIG. 1. The automatic transmission11may be one suitable for use in an FR-type (front engine, rear-wheel drive) vehicle. Provided in the automatic transmission11is an input shaft11capable of connecting to an engine (not shown). The automatic transmission11also has a speed change mechanism21and a torque converter7centered on the axial direction of the input shaft11. Note that for this automatic transmission, “front” means toward the front of the vehicle, i.e., an engine side of the automatic transmission, and “rear” means toward the rear of the vehicle, i.e., an output shaft (a propeller shaft) side of the automatic transmission is a side opposite from the engine.

The torque converter7has a pump impeller7athat is connected to the input shaft11of the automatic transmission11, and a turbine runner7bto which the rotation of the pump impeller7ais transmitted via operation fluid. The turbine runner7bis connected to an input shaft12of the speed change mechanism21, with the input shaft12disposed on the same axis as the input shaft11. Also provided in the torque converter7is a lock-up clutch10, and when the lock-up clutch10is engaged through hydraulic control of a hydraulic control device (not shown), the rotation of the input shaft11of the automatic transmission11is directly transmitted to the input shaft12of the speed change mechanism21.

The speed change mechanism21is provided with a planetary gear (a reduction planetary gear) DP, and a planetary gear unit (a planetary gear set) PU on the input shaft12(and an intermediate shaft13). The planetary gear DP is a so-called double pinion planetary gear set, and has a sun gear S1, a carrier CR1, and a ring gear R1. The carrier CR1has a pinion P1that meshes with the sun gear S1, and a pinion P2that meshes with the ring gear R1. The pinions P1and P2also mesh together.

The planetary gear unit PU is a so-called Ravigneaux planetary gear set, and has four rotation elements: a sun gear S2, a sun gear S3, a carrier CR2, and a ring gear R3. The carrier CR2has a long pinion P4that meshes with the sun gear S2and the ring gear R3, and a short pinion P3that meshes with the sun gear S3. The long pinion P4and the short pinion P3also mesh together.

In the planetary gear DP, the sun gear S1is held stationary and connected to a stator shaft3bthat is integrally fixed to a transmission case3. The carrier CR1is connected to the input shaft12and has the same rotation as that of the input shaft12(hereinafter called “input rotation”). Also, the carrier CR1is connected to a fourth clutch C-4(an input transmission clutch). The ring gear R1has a reduced rotation, the input rotation for which has been reduced by the stationary sun gear S1and the carrier CR1, which provides the input rotation, i.e., which rotates together with the input shaft12. Also, the ring gear R1is connected to a first clutch C-1(a reduced transmission clutch) and a third clutch C-3(a reduced transmission clutch).

In the planetary gear unit PU, the sun gear S2is connected to a first brake B-1, and fixable to the transmission case3. Also, the sun gear S2is connected to the fourth clutch C-4and the third clutch C-3. The input rotation of the carrier CR1is inputable to the sun gear S2via the fourth clutch C-4, and the reduced rotation of the ring gear R1is inputable to the sun gear S2via the third clutch C-3. In addition, the sun gear S3is connected to the first clutch C-1, and the reduced rotation of the ring gear R1is inputable to the sun gear S3.

The carrier CR2is connected to a second clutch C-2, to which the rotation of the input shaft12is input via the intermediate shaft13, and the input rotation for the carrier CR2is inputable via the second clutch C-2. Also, the carrier CR2is connected to a one-way clutch F-1and a second brake B-2. One direction of rotation of the carrier CR2with respect to the transmission case3is controlled via the one-way clutch F-1, and the rotation of the carrier CR2is fixable via the second brake B-2. The ring gear R3is connected to an output shaft15that outputs rotation to a drive wheel (not shown).

Based upon the configuration described above, the operation of the speed change mechanism21will be explained next with reference toFIGS. 1 to 3. Note that the vertical axis and horizontal axis of a speed diagram shown inFIG. 3denote the rotational speeds of the rotation elements (gears), and the corresponding gear ratios of the rotation elements, respectively. For the planetary gear DP part of the speed diagram, an outermost vertical axis in the horizontal direction (a left side inFIG. 3) corresponds to the sun gear S1, and the remaining vertical axes toward the right side in the figure correspond to the ring gear R1and the carrier CR1in that order. For the planetary gear unit PU part of the speed diagram, an outermost vertical axis in the horizontal direction (a right side inFIG. 3) corresponds to the sun gear S3, and the remaining vertical axes toward the left side in the figure correspond to the ring gear R3, the carrier CR2, and the sun gear S2in that order.

Regarding a D (drive) range, for instance, at a forward first speed (1st), the first clutch C-1and the one-way clutch F-1are engaged, as shown inFIG. 2. Accordingly, the rotation of the ring gear R1, which is reduced by the stationary sun gear S1and the carrier CR1that provides the input rotation, is input to the sun gear S3via the first clutch C-1as shown inFIGS. 1 and 3. The rotation of the carrier CR2is also controlled in one direction (a direction of normal rotation), i.e., reverse rotation of the carrier CR2is prevented and the carrier CR2is held stationary. Accordingly, the reduced rotation input to the sun gear S3is output to the ring gear R3via the stationary carrier CR2. Normal rotation acting as the forward first speed is thus output from the output shaft15.

Note that during times of engine braking (coasting), the second brake B-2is engaged to hold the carrier CR2, so that the forward first speed is maintained with normal rotation of the carrier CR2prevented. At the forward first speed, reverse rotation of the carrier CR2can also be prevented by the one-way clutch F-1while allowing normal rotation. Therefore, the forward first speed can be smoothly achieved through automatic engagement of the one-way clutch F-1when, for example, changing from a non-traveling range to a traveling range.

At a forward second speed (2nd), the first clutch C-1is engaged and the first brake B-1is held, as shown inFIG. 2. Accordingly, the rotation of the ring gear R1, which is reduced by the stationary sun gear S1and the carrier CR1that provides the input rotation, is input to the sun gear S3via the first clutch C-1as shown inFIGS. 1 and 3. Holding of the first brake B-1also holds the sun gear S2stationary. Accordingly, the carrier CR2has a reduced rotation that is lower than the sun gear S3, and the reduced rotation input to the sun gear S3is output to the ring gear R3via the carrier CR2. Normal rotation acting as the forward second speed is thus output from the output shaft15.

At a forward third speed (3rd), the first clutch C-1and the third clutch C-3are engaged, as shown inFIG. 2. Accordingly, the rotation of the ring gear R1, which is reduced by the stationary sun gear S1and the carrier CR1that provides the input rotation, is input to the sun gear S3via the first clutch C-1as shown inFIGS. 1 and 3. The reduced rotation of the ring gear R1is also input to the sun gear S2through engagement of the third clutch C-3. In other words, the reduced rotation of the ring gear R1is input to both the sun gear S2and the sun gear S3. Therefore, the planetary gear unit PU achieves a directly coupled state of reduced rotation, and the reduced rotation is output unchanged to the ring gear R3. Normal rotation acting as the forward third speed is thus output from the output shaft15.

At a forward fourth speed (4th), the first clutch C-1and the fourth clutch C-4are engaged, as shown inFIG. 2. Accordingly, the rotation of the ring gear R1, which is reduced by the stationary sun gear S1and the carrier CR1that provides the input rotation, is input to the sun gear S3via the first clutch C-1as shown inFIGS. 1 and 3. The input rotation of the carrier CR1is also input to the sun gear S2through engagement of the fourth clutch C-4. Accordingly, the carrier CR2achieves a reduced rotation that is faster than the sun gear S3, and the reduced rotation input to the sun gear S3is output to the ring gear R3via the carrier CR2. Normal rotation acting as the forward fourth speed is thus output from the output shaft15.

At a forward fifth speed (5th), the first clutch C-1and the second clutch C-2are engaged, as shown inFIG. 2. Accordingly, the rotation of the ring gear R1, which is reduced by the stationary sun gear S1and the carrier CR1that provides the input rotation, is input to the sun gear S3via the first clutch C-1as shown inFIGS. 1 and 3. The input rotation is also input to the carrier CR2through engagement of the second clutch C-2. Accordingly, a reduced rotation that is higher than the forward fourth speed is achieved due to the reduced rotation input to the sun gear S3and the input rotation input to the carrier CR2, and is output to the ring gear R3. Normal rotation acting as the forward fifth speed is thus output from the output shaft15.

At a forward sixth speed (6th), the second clutch C-2and the fourth clutch C-4are engaged, as shown inFIG. 2. Accordingly, the input rotation of the carrier CR1is input to the sun gear S2through engagement of the fourth clutch C-4. The input rotation of the carrier CR2is also input via the second clutch C-2. In other words, input rotation is input to the sun gear S2and the carrier CR2. Therefore, the planetary gear unit PU achieves a directly coupled state of input rotation, and the input rotation is output unchanged to the ring gear R3. Normal rotation acting as the forward sixth speed is thus output from the output shaft15.

At a forward seventh speed (7th), the second clutch C-2and the third clutch C-3are engaged, as shown inFIG. 2. Accordingly, the rotation of the ring gear R1, which is reduced by the stationary sun gear S1and the carrier CR1that provides the input rotation, is input to the sun gear S2via the third clutch C-3as shown inFIGS. 1 and 3. The input rotation is also input to the carrier CR2through engagement of the second clutch C-2. Accordingly, an accelerated rotation that is slightly higher than the input rotation is achieved due to the reduced rotation input to the sun gear S2and the input rotation input to the carrier CR2, and is output to the ring gear R3. Normal rotation acting as the forward seventh speed is thus output from the output shaft15.

At a forward eighth speed (8th), the second clutch C-2is engaged and the first brake B-1is held, as shown inFIG. 2. Accordingly, input rotation is input to the carrier CR2through engagement of the second clutch C-2as shown inFIGS. 1 and 3. Holding of the first brake B-1also holds the sun gear S2stationary. Accordingly, the input rotation of the carrier CR2achieves an accelerated rotation that is higher than the forward seventh speed by the stationary sun gear S2, and the accelerated rotation is output to the ring gear R3. Normal rotation acting as the forward eighth speed is thus output from the output shaft15.

At a reverse first speed (Rev1), the third clutch C-3is engaged and the second brake B-2is held, as shown inFIG. 2. Accordingly, the rotation of the ring gear R1, which is reduced by the stationary sun gear S1and the carrier CR1that provides the input rotation, is input to the sun gear S2via the third clutch C-3as shown inFIGS. 1 and 3. Holding of the second brake B-2also holds the carrier CR2stationary. Accordingly, the reduced rotation input to the sun gear S2is output to the ring gear R3via the stationary carrier CR2. Reverse rotation acting as the reverse first speed is thus output from the output shaft15.

At a reverse second speed (Rev2), the fourth clutch C-4is engaged and the second brake B-2is held, as shown inFIG. 2. Accordingly, the input rotation of the carrier CR1is input to the sun gear S2through engagement of the fourth clutch C-4. Holding of the second brake B-2also holds the carrier CR2stationary. Accordingly, the input rotation input to the sun gear S2is output to the ring gear R3via the stationary carrier CR2. Reverse rotation acting as the reverse second speed is thus output from the output shaft15.

Note that in a P (parking) and N (neutral) range, for example, the first clutch C-1, the second clutch C-2, the third clutch C-3, and the fourth clutch C-4are all released. Accordingly, the connection between the carrier CR1and the sun gear S2is severed, as well as between the ring gear R1, the sun gear S2and the sun gear S3. That is, the planetary gear DP and the planetary gear unit PU are disconnected. The connection between the input shaft12(intermediate shaft13) and the carrier CR2is also severed. Thus, the transmission of driving force between the input shaft12and the planetary gear unit PU is severed, i.e., there is no transmission of driving force from the input shaft12to the output shaft15.

Next, the first clutch C-1, which is a friction engagement device according to the present invention, will be described in detail with reference toFIG. 4. The first clutch C-1, as mentioned earlier, is a multi-plate clutch that can connect and disconnect the ring gear R1of the reduction planetary gear DP and the sun gear S3(not shown inFIG. 4) of the planetary gear unit PU. The first clutch C-1has a clutch drum20, a clutch hub21, in addition to clutch plates (outer friction plates)22and clutch discs (inner friction plates)23provided between the drum and the hub.

In the clutch drum20, as shown in detail inFIG. 5, a drum member25and a base member26are fixedly attached. The drum member25is made from an integral part press-formed (i.e., press-forming) so as to have a C-shape (as shown inFIG. 5). Furthermore, the drum member25includes: a base portion25a, an outer diameter portion25bthat extends rearward from an outer diameter side of the base portion in the axial direction, and a collar portion25cthat extends rearward from an inner diameter side of the base portion25ain the axial direction. The base member26includes: a raised portion26athat forms a cylinder bottom face, an outer diameter portion26bthat extends rearward from an outer diameter side of the raised portion26a, and a boss portion26cthat extends rearward from an inner diameter side of the raised portion26a. In addition, the outer diameter portion26bhas an engaging face26dthat engages with the drum member25at an outer peripheral face thereof, and has a connection portion26ethat extends from a front end in the axial direction toward an outer diameter direction.

As described earlier, the reduction planetary gear DP is accommodated in the transmission case3along with the rest of the speed change mechanism21. Included in the reduction planetary gear DP are: the sun gear S1, the ring gear R1, and the carrier CR1. The carrier CR1also supports the first pinion P1that meshes with the sun gear S1, and the second pinion P2that meshes with the ring gear R1and with the first pinion P1. The sun gear S1is in spline engagement with a stator shaft3b, which is pressed into an inner periphery of a pump cover that is integral with the transmission case3. The carrier CR1is fixedly attached to a collar portion11aof the input shaft11, and the input shaft11is rotatably supported on the stator shaft3b, which is a fixed member, via a needle bearing24. Regarding the ring gear R1, teeth h on an inner peripheral face thereof are engaged with the connection portion26eof the base member26, and a snap ring28is fitted into a concave groove formed on the ring gear R1so as to clamp the base member26. Furthermore, splines29are formed on an outer peripheral face of the ring gear R1. Between the splines29and a drum30rotatably supported on an oil pump boss portion3f(not particularly shown), clutch plates (outer friction plates)31and clutch discs (inner friction plates)32are respectively engaged so as to structure the third clutch C-3. The drum30is in spline engagement with a connection drum member33via their respective ends, and both are integrally connected in the direction of rotation. The connection drum member33extends rearward so as to cover the first clutch C-1. The connection drum member33is also joined with a connection boss member35by rivets at a rear portion of the C-1clutch hub21. An end of the connection boss member35is connected to the second sun gear S2(seeFIG. 1). Note that reference numeral38denotes the one-way clutch that prevents rotation in one direction of the carrier CR2(seeFIG. 1) in the planetary gear unit PU (not shown).

Included in the clutch hub21are: a raised portion21a, an outer diameter portion21bthat extends forward from an outer diameter side of the raised portion in the axial direction, and a boss portion21cthat extends rearward from an inner diameter side of the raised portion in the axial direction. A multi-plate wet clutch is structured as follows. The clutch discs23and the clutch plates22are alternately disposed. The clutch discs23are engaged with splines21dformed on the outer diameter portion21b, and the clutch plates22are engaged with splines25dformed on an inner peripheral face of the outer diameter portion25bof the clutch drum20. Moreover, a snap ring36held by the outer diameter portion25bof the drum member25clamps a backup plate34that is disposed at ends of the clutch discs23and the clutch plates22. The clutch hub boss portion21chas a stepped structure, and splines are formed on a minor diameter portion thereof. Also, an end of the boss portion21cis engaged with a hollow intermediate shaft37that is connected with the third sun gear S3(seeFIG. 1).

The base member boss portion26cof the C-1clutch drum20is rotatably supported on the input shaft11via a bushing39or the like. Also, the boss portion26cis positioned in the axial direction such that a thrust bearing40is disposed between an end of the boss portion26cin the axial direction and the collar portion11aof the input shaft11, and a thrust bearing41is disposed between another end of the boss portion26cin the axial direction and a step portion a of the clutch hub boss portion21c. A hydraulic servo A for the clutch C-1is structured on the drum20as follows. The base member raised portion26aacts as a cylinder bottom face. An outer peripheral face of the collar portion25cof the drum member25and an outer peripheral face of the boss portion26cof the base member26act as sliding faces. A fluid-tight piston member43is fitted between O-rings42,42. The piston member43is formed with a piston portion43athat opposes the raised portion26aforming the cylinder bottom face, a cylindrical portion43bthat extends laterally toward the axial direction from an outer diameter portion of the piston portion43a, and a piston rod portion43cthat extends from a front end of the cylindrical portion43btoward an outer diameter side. In addition, the O-rings42,42are respectively fitted in a concave groove formed on an inner peripheral face of the cylindrical portion43band in a concave groove formed on an inner peripheral face of the piston portion43a.

An end of the piston rod portion43cis engaged with the splines25dof the outer diameter portion25bin the clutch C-1drum member, and the piston rod portion43cis engaged such that the clutch drum20and the piston member43integrally rotate. Also, a projection portion43d, which partially projects toward a side face of the piston rod portion43c, opposes a base end side of the respective friction plates22,23of the first clutch C-1via a cushion plate46. A fluid-tight cancel plate49is fitted to the cylindrical portion43bon a back face side of the piston portion43avia an O-ring47. The cancel plate49forms a cancel oil chamber51with a back face of the piston that is clamped using a snap ring50held by the base member boss portion26c. Provided energized between the cancel plate49and the back face of the piston member43are a plurality of circular return springs48.

In the first clutch C-1, the piston rod portion43cis formed rising in the outer diameter direction from the piston portion43a. Furthermore, the cylindrical portion43bis located on the inner diameter side of the outer diameter portion21bof the clutch hub21, and the cylindrical portion43bforms the cancel oil chamber51with the cancel plate49. Therefore, a plurality of the friction plates22,23can be arranged on the outer diameter side of the piston portion43aand the cancel oil chamber51, and it is possible to structure a compact clutch C-1including the hydraulic servo A, which is particularly compact in the axial direction.

The input shaft11is formed with oil passages52,53. Operating oil pressure is supplied to the oil passage52. Additionally, operating oil pressure is supplied to the hydraulic servo A via a lateral oil passage e of the input shaft11and an oil-tight circular groove f defined by an O-ring, and also via an oil gallery55formed on the boss portion26cof the base member26. Lubrication oil pressure is supplied to the oil passage53. The oil passage53is in communication with an oil passage57of the intermediate shaft56that is in spline engagement with the input shaft11. Furthermore, the oil passage53discharges from an oil gallery59formed on the base member boss portion26cto the cancel oil chamber51via a lateral oil passage g and an oil chamber k. A notch49ais formed on an inner diameter portion of the cancel plate49, and overflowing oil from the cancel oil chamber51is guided to the first clutch C-1.

Next, the C-1clutch drum20, as well as a connection structure for the drum20and a ring gear R according to the present invention will be described in detail with reference toFIG. 5. As explained above, the clutch drum20is formed fixedly attached to the drum member25and the base member26. The outer peripheral face of the outer diameter portion26bof the base member26acts as the engaging face26d. A central portion of the engaging face26dis slightly cut in a circular shape so as to form a hollow portion26d2. Both front and rear sides thereof form pressed portions26d1,26d3having a press fit dimension. The inner peripheral face of the collar portion25cof the drum member25is fitted to the engaging face26dof the base member26. Only the pressed portions26d1,26d3are pressed and in contact at this time, and the hollow portion26d2has a slight clearance with the inner peripheral face of the inner diameter portion25c. Thus, when the drum member25is pressed onto the base member26, a relatively wide surface area is involved in such press fitting based on the drum member collar portion25c. However, an axial length of the pressed portions26d1,26d3is relatively short, and press fitting can be achieved with a relatively small pressing load. In other words, both end portions in an axial direction of engaging faces of an inner peripheral face of the collar portion25cof the drum member25and an outer peripheral face of the outer diameter portion26bof the base member26are designated as a press fit dimension, and a clearance is formed by the hollow portion26d2between both end portions.

The drum member25and the base member26are positioned by press fitting with rearward positions of the collar portion25cand the cylindrical portion26baligned. In such a state, the collar portion25cand the cylindrical portion26bare welded at the aligned end faces (w). Accordingly, the drum member25and the base member26are fixedly attached, and there is a clearance between central portions of the engaging faces thereof due to the hollow portion26d2. However, the clearance is obstructed by the pressed portions26d1,26d3on both sides thereof such that no foreign substances or the like penetrate.

The raised portion26aof the base member26is formed into a circular disc shape whose outer diameter side thickness (b1) is less than an inner diameter side thickness (b2), i.e., b1<b2. Note that inFIG. 5, reference numeral25edenotes a circular concave groove for engaging the snap ring36used to hold the backup plate34, and reference numeral26fdenotes a circular concave groove for engaging the snap ring50used to hold the cancel plate49. Moreover, reference numeral60denotes a concave portion for accommodating the thrust bearing40.

The clutch drum20is arranged adjacent to the planetary gear DP, and is integrally connected with the ring gear R1, which is a predetermined rotation element of the planetary gear. Teeth h of the ring gear R1extend in the axial direction, and form spline grooves hs on a clutch drum side. In addition, an end portion of the connection portion26eof the base member26is formed into splines61capable of engaging with the spline grooves hs.

A clutch-drum-side end of the ring gear R1forms a circular portion62that projects in the axial direction. An inner peripheral face of the circular portion62is adjacent to the spline grooves hs to form a circular concave groove63. The circular portion62, as shown inFIG. 6, is notched at two locations so as to form notch portions62a,62balong a periphery thereof that are spaces where the circular portion62does not exist.

The snap ring28fitted in the circular concave groove63is C-shaped when viewed from the front, as shown inFIGS. 7A-7C, and both end portions thereof have tabs28a,28athat extend toward the outer diameter direction. A side face of the tab portions is cut so as to have less thickness than a remaining portion (body portion)28c. Additionally, a concave portion28dis formed adjacent to the tab28aand between the tab28aand the body portion28c.

More specifically with respect to the clutch drum20, the drum member25and the base member26are fixedly attached by pressing the inner peripheral face of the collar portion25conto the engaging face26dof the outer diameter portion26b. Consequently, the effect of heat from welding is small. In addition, the clutch drum20and the ring gear R1are integrally connected such that the rotational direction thereof is controlled by spline engagement of the portions hs,61of the connection portion26e, and the axial direction thereof is controlled by engagement with the circular concave groove63of the snap ring28. Accordingly, heat from welding has little effect on the connection between the clutch drum20and the ring gear R1, thus making it possible to maintain the high precision of the ring gear R1.

Given the need to structure the clutch drum and the ring gear R1compact for mounting in the vehicle, both are arranged so as to minimize clearances as much as possible, and there is no space to manipulate the snap ring28from the axial direction. Accordingly, the circular portion62that projects toward the clutch drum side of the ring gear R1is formed with the notch portions62a,62b. A pair of the tabs28a,28aof the snap ring28projecting in the outer diameter direction is sandwiched in the circular portion62via one of the notch portions62a,62b, and the diameter of the snap ring28is reduced. In such a state, the ring gear R approaches the connection portion26ewith the spline grooves hs of the ring gear R engaged with the splines61of the connection portion26e, such that the snap ring28aligns with the circular concave groove63. The snap ring28then engages with the circular concave groove63following cancellation of the diameter reduction of the snap ring28by manipulating the tab28afrom the outer diameter direction.

At this time, it is possible to visually confirm that the snap ring28is positioned in alignment with the circular concave groove63via another notch portion62bof the circular portion62, thereby enabling easy and reliable engagement of the snap ring28. Also, the concave portion28dadjacent to the tab28aof the snap ring28is used to prevent interference with an end face y of the circular portion62(i.e., portion) facing the notch portion62aof the circular portion62. For instance, the tab28amay come in contact with the end face y while the snap ring28rotates relative to the concave groove63. But even in such cases, the end face y contacts a portion adjacent and diagonal to the tab28aand the body portion28csuch that there is no force acting in a direction reducing the diameter of the snap ring28.

Next, the operation of the first clutch C-1(friction engagement device) portion according to the present invention will be explained. In a state where hydraulic pressure is not supplied to the hydraulic servo A, the piston member43achieves the state shown inFIG. 4due to the return spring48, and the projection portion43dof the piston portion43aseparates from the clutch plates21,22,46, whereby the first clutch C-1is released. If a predetermined hydraulic pressure is supplied to the hydraulic servo A via the oil passages52, e, f,55in this state, then the piston member43moves against the return spring48such that the piston rod projection portion43dclosely contacts and presses against the plurality of clutch plates22and clutch discs23via the cushion plate46. Accordingly, the first clutch C-1is connected, and the rotation of the ring gear R1is transmitted to the third sun gear S3via the clutch drum20, the clutch plates22,23, the clutch hub21, and the hollow intermediate shaft37.

Furthermore, the pressing force on the clutch plate by the piston portion43aacts on an end portion of the outer diameter portion25bof the drum member25via the backup plate34and the snap ring36. Consequently, the drum member25acts as a bending moment (wrenching force) on the engaging face26d, which is a face of the base member26that engages therewith. However, the drum member25has the collar portion25cof a predetermined length in the axial direction, and front and rear portions thereof are pressed to engage with the pressed portions26d1,26d3. Therefore, the bending moment does not become a concentrated load and is instead dispersed and reliably supported.

Meanwhile, the planetary gear DP is formed from helical gears, and the ring gear R1generates a thrust force in a rightward direction (arrow z direction) inFIG. 5based upon the transmission of driving force by the planetary gear DP. The thrust force acts on the raised portion26aof the base member26via the stepped portion of the spline grooves hs and the connection portion26e. However, the raised portion26aof the base member26has a thickness that increase toward the inner diameter side (b1>b2). Therefore, a structure with the strength to withstand the above-mentioned clutch pressing force and the thrust force caused by the helical gear of the ring gear R1can be achieved. As a consequence, problems such as damage caused by a load concentrated on a welded portion w can be prevented. Moreover, the drum member25can be reliably supported by the base member26with high precision. Thus, even if a great force occurs when engaging the clutch, the drum member25can be smoothly moved towards the plurality of clutch plates22,23for highly precise engagement.

Furthermore, the outer diameter side of the piston member43slides toward the outer peripheral face of the collar portion25c. Due to the reliable support of the clutch drum member25as described above, the collar portion25cacting as the sliding face is held in position with high precision so as to maintain the smooth movement of the piston member43. In addition, the piston surface area can be increased by an amount corresponding to the thickness of the drum member collar portion25cand the base member outer diameter portion26b, whereby greater clutch pressing force can be achieved.

To disconnect the clutch through the release of hydraulic pressure in the hydraulic servo A, the piston member43returns due to the return spring48and a centrifugal force that acts on oil in the cancel oil chamber51. At this time, the piston member43smoothly slides against the collar portion25cthat is held in position with high precision and the boss portion26cso as to quickly release the clutch.

Note that the above embodiment has the pressed portions26d1,26d3and the hollow portion26d2formed on the outer peripheral face of the outer diameter portion26bof the base member26. However, the pressed portions26d1,26d3and the hollow portion26d2may also be formed on the inner peripheral face of the collar portion25cof the drum member25. Furthermore, the present invention is applied to the first clutch C-1as a friction engagement device, but it may also be applied to other clutches or brakes, and may further be applied as a friction engagement device for other automatic transmissions. In addition, a ring gear was designated as the predetermined rotation element of the planetary gear to be connected to the clutch (or brake) drum. However, the present invention is not particularly limited by this, and other predetermined rotation elements such as a carrier may be used instead.

According to an exemplary aspect of the present invention, a drum is structured by pressing to integrally fix a drum member and a base member, and the drum and a ring gear of a planetary gear are connected through splines and a snap ring. This can therefore reduce the effect of heat from welding, increase the precision of the ring gear and the drum, and prevent noise, in addition to lengthening the life of the parts.

According to a second exemplary aspect of the present invention, the snap ring can be engaged and disengaged from a circular concave groove by manipulating a tab that extends toward an outer diameter direction of the snap ring through a notch portion of a circular portion. Accordingly, there is no need for a space in the axial direction for manipulating the snap ring, thus making it possible to arrange the planetary gear and the drum close together in the axial direction for a more compact automatic transmission.

According to a third exemplary aspect of the present invention, while the circular portion has the notch portion, a concave portion of the snap ring prevents interference of an end face of the notch portion with a portion adjacent to the tab. Therefore, it is possible to prevent the tab portion from overlapping the end face of the notch portion and producing a force in a direction that reduces the diameter of the snap ring.

According to a fourth exemplary aspect of the present invention, the circular portion has at least two notch portions. Therefore, an operation to reduce the diameter of the snap ring can be performed through one notch, while engagement of the snap ring to the circular concave portion can be confirmed via the other notch portion. Consequently, operations to engage and disengage the snap ring can be easily and reliably performed.

According to a fifth exemplary aspect of the present invention, the drum member is formed with an outer diameter portion having splines engaged with friction plates. A collar portion is formed on the outside of the outer diameter portion and extends toward an inner diameter side in the axial direction. The collar portion engages with an outer peripheral face of an outer diameter portion of the base member. Both end portions in the axial direction of such engaging faces are designated as a press fit dimension, and a clearance is formed at a portion therebetween. Therefore, even if a large bending moment acts on the drum member due to a large pressing force for engaging the friction plates, the base member is supported by the pressing of both end portions of the collar portion. Consequently, the drum member can be supported by the base member in a stable manner and with a high degree of supporting precision, thus making it possible to maintain the smooth movement of the friction plates and the performance of the friction engagement device over a long period of time.

In addition, the press fit dimension when pressing the collar portion of the drum member onto the outer diameter portion of the base member is both end portions separated in the axial direction, which reduces the pressing load and simplifies assembly. Also, the clearance is obstructed by pressed portions on both sides thereof. Consequently, problems related to foreign substances can be eliminated, such as the penetration of foreign substances or the like that are subsequently released after assembly to an automatic transmission.

According to a sixth exemplary aspect of the present invention, the collar portion of the drum member is supported on the base member by the pressed portions separated in the axial direction. Therefore, a load based on a large bending moment from the drum member can be prevented from concentrating on a welded portion of the drum member and the base member, thus preventing any deterioration in the durability of the welded portion and a portion thereof affected by heat.

According to a seventh exemplary aspect of the present invention, the drum member can be easily manufactured at low costs through the press forming of an integral part. In addition, the outer diameter portion of the base member is formed with a pressed portion having the press fit dimension and a hollow portion, which further facilitates manufacturing.

According to an eighth exemplary aspect of the present invention, a clutch hub is provided and the drum is applied to a clutch drum. Therefore, the precision and strength of the clutch drum can be maintained over a long period of time regardless of large bending moments acting on the drum member.

According to a ninth exemplary aspect of the present invention, a hydraulic servo is structured by fitting a drum acting as a cylinder with a piston, where an outer peripheral face of the collar portion of the drum member acts as a sliding face on an outside diameter side of a piston member. Therefore, a large surface area can be secured for bearing the pressure of the piston, and a large engagement force can be applied to the friction plates. Consequently, operation of the friction engagement device can be performed in a stable and reliable manner.

According to a tenth exemplary aspect of the present invention, a piston rod is provided on an outer diameter side of the piston portion, and a cancel plate is provided spanning a cylindrical portion and a boss portion. This in turn provides a cancel oil chamber on a back face side of the piston. Therefore, a plurality of the friction plates operated by the piston rod are disposed on an outer diameter side of the piston portion and the cancel oil chamber. It is thus possible to structure a compact friction engagement device including the hydraulic servo, which is particularly compact in the axial direction.

According to an eleventh exemplary aspect of the present invention, the raised portion of the base member is formed such that a thickness on an inner diameter side is greater than a thickness on an outer diameter side. Therefore, a structure with the strength to withstand a pressing force caused by the drum member and a thrust force caused by a predetermined rotation element such as a ring gear can be achieved.