Automatic transmission

A first element of a duplex planetary gear set is selectively coupled to an input shaft via a third clutch, or is selectively fixed via a first brake. A second element is selectively coupled, via a second clutch, to an intermediate shaft that is directly coupled to a speed-increasing element of a simplex planetary gear set which increases the rotational speed of the input shaft, or is selectively fixed via a second brake. A third element is directly coupled to an output shaft. A fourth element is selectively coupled to the input shaft via a first clutch. Therefore, by increasing the speed of the rotation of the input shaft by the simplex planetary gear set and transferring it to the duplex planetary gear set, it is possible to reduce the torques on individual components of an automatic transmission and therefore to reduce the sizes of the individual components and the capacities of the individual friction engagement elements.

TECHNICAL FIELD

The present invention relates to an automatic transmission in which elements of a simplex planetary gear set, coupled to an input shaft, are selectively connected to elements of a duplex planetary gear set via clutches and fixed via brakes for shifting, in which the speed of rotation of the input shaft is changed and output at an output shaft.

BACKGROUND ART

Japanese Patent Application Publication No. HEI 4-219553 discloses an automatic transmission that is provided with a simplex planetary gear set including a first ring gear coupled to an input shaft, a first sun gear fixed to the transmission case, and a first carrier that supports pinions that mesh with the first ring gear and the first sun gear, and a duplex planetary gear set having second and third sun gears, long pinions that directly mesh with the second sun gear and mesh with the third sun gear via intermediate pinions, a common carrier that supports the long pinions and the intermediate pinions, and a common ring gear that meshes with the long pinions. The common ring gear of the duplex planetary gear set is directly coupled to the output shaft, and the rotation of the first carrier of the simplex planetary gear set, reduced in rotational speed from that of the input shaft, is selectively transferred to the third and second sun gears of the duplex planetary gear set via first and third clutches, while the rotation of the input shaft is selectively transferred to the carrier of the duplex planetary gear set via a second clutch. The second sun gear and the common carrier of the duplex planetary gear set are selectively fixed via first and second brakes, respectively, thereby establishing six forward shift speeds and a reverse speed.

U.S. Pat. No. 5,542,889 describes, as shown inFIG. 1, an automatic transmission having a simplex planetary gear set52including a carrier74directly coupled to an input shaft44, which is rotationally coupled to a crankshaft14of an engine, a sun gear70fixed to a transmission case80, and a ring gear72that is rotated at a speed higher than that of the input shaft44, and a duplex planetary gear set50,48including a ring gear64and a carrier58which are directly coupled, and a carrier66and a ring gear56which are selectively connected via a clutch CL1. A sun gear62in the duplex planetary gear set50,48is selectively connected to the carrier74of the simplex planetary gear set via a clutch CL3, or is fixed to the transmission case80via a brake B2. Reverse rotation of the carrier66is prevented by a one-way clutch82. Reverse rotation of the ring gear56, coupled to the carrier66via the clutch CL1, is prevented by a one-way clutch82. The carrier66is selectively connected (coupled) to the ring gear72of the simplex planetary gear set52via the clutch CL2, and is selectively fixed to the transmission case80via a brake B1. The directly connected ring gear64and carrier58are directly coupled to an output shaft90, and a sun gear54of the planetary gear set48is directly coupled to the input shaft44.

The automatic transmission described in Japanese Patent Application Publication No. 2000-220704 is similar to that described in Japanese Patent Application Laid-Open Publication No. HEI 4-219553, but includes an input shaft11which is rotationally driven by an engine and which is divided into a forward half portion11A and a rearward half portion11B, which portions are spline-joined as shown inFIGS. 6 and 7. An oil passage11pfor supplying operating oil to a hydraulic servo6, and a lubricating oil passage11rfor supplying lubricating oil to the elements disposed in a transmission case10are formed in parallel in the forward portion11A. A lubricating oil passage11sis formed in the forward portion11B. The carrier C1of simplex planetary gear set G1is not coupled to the input shaft11, but is coupled to the common hub74of first and third clutches C-1, C-3.

In the automatic transmissions described in Japanese Patent Application Publication No. HEI 4-219553 and Japanese Patent Application Publication No. 2000-220704, the output rotation of the engine is reduced in speed by the simplex planetary gear set and then input to the duplex planetary gear set. Therefore, an increased torque is transferred to the duplex planetary gear set. In particular, if the engine outputs high torque at relatively low speeds as in, for example, diesel engines, the transferred torque becomes even larger, and therefore it is necessary to increase the sizes of various components and to increase the capacities of clutches and brakes in order to cope with the high torque.

In order to solve the above-described problem, the automatic transmission described in of U.S. Pat. No. 5,542,889 increases the output speed of rotation of the engine by transfer through a simplex planetary gear set52and then through a duplex planetary gear set48,50. However, in the automatic transmission described in U.S. Pat. No. 5,542,889, the carrier66is prevented from reverse rotation by the one-way clutch82, and the ring gear56is coupled to the carrier66by the clutch CL1and is therefore prevented from rotating, so that the rotation of the input shaft44directly coupled to the sun gear54is reduced in speed, thereby achieving the first speed. Therefore, this automatic transmission is complicated in structure. In addition, in order to prevent rotation of the ring gear56that receives the reaction force for the first speed, where the transfer torque is large, there is a need to increase the capacity of the clutch CL1that couples the ring gear56to the one-way clutch82, resulting in an increased size of the apparatus.

SUMMARY OF THE INVENTION

Accordingly, the objective of the present invention is to provide an automatic transmission in which the rotation of the input shaft is increased in speed and then transferred to a duplex planetary gear set through a simplex planetary gear set, so that the torques assigned to individual portions of the automatic transmission are reduced and therefore the sizes of the individual components and the capacities of the friction engagement elements can be reduced.

In order to solve the aforementioned problem and achieve the above-stated objective, the present invention provides automatic transmission that shifts the rotation of an input shaft among a plurality of speeds and transfers the rotation to an output shaft by coupling or fixing elements of (1) a simplex planetary gear set coupled to the input shaft and (2) a duplex planetary gear set coupled to the output shaft, wherein the simplex planetary gear set comprises an input element directly coupled to the input shaft, a fixed element fixed to the transmission case, and a speed-increasing element that is rotated at a speed greater than that of the input shaft and that is directly coupled to an intermediate shaft. The duplex planetary gear set has first, second, third and fourth elements, which can be represented in a speed diagram arranged with intervals corresponding to gear ratios, wherein the first element is selectively connected to the input shaft via a third clutch and is selectively fixed via a first brake, wherein the second element is selectively connected to the intermediate shaft via a second clutch and is selectively fixed via a second brake, wherein the third element is directly coupled to the output shaft, and wherein the fourth element is selectively connected to the input shaft via a first clutch.

Since the rotation of the input shaft, rotationally coupled to the engine, is increased in speed by the simplex planetary gear set and is then input to the duplex planetary gear set, the torque transferred to the duplex planetary gear set is reduced, so that the sizes of the individual components and the capacities of the clutches and the brakes can be reduced. Therefore, merely by providing commonality of the duplex planetary gear set with a related-art gasoline engine-purpose automatic transmission (a sharing of components), wherein the rotation of the input shaft rotationally coupled to the gasoline engine is reduced in speed and then input to a duplex planetary gear set via a simplex planetary gear set, and by changing the speed reduction of the rotation of the input shaft via the simplex planetary gear set to a speed increase, an automatic transmission suitable for an engine that outputs higher torque at lower rotational speeds than related-art gasoline engines, e.g. a diesel engine, can easily be provided without increasing the sizes of individual components or the capacities of clutches and brakes. Furthermore, in the first speed where the transfer torque is large, rotation of the second element can be prevented without using a clutch. Therefore, the need for a clutch of large capacity is eliminated, and the automatic transmission can be reduced in size, weight and cost.

In the improved automatic transmission of the present invention, the input shaft and the output shaft are supported by the transmission case for rotation on a common axis, and the intermediate shaft is supported at its distal end within a journal hole formed in an end portion of the input shaft, so as to be rotatable coaxially with the input shaft.

Thus, in an automatic transmission in which the rotation of the input shaft rotationally coupled to the engine is increased in speed and is transferred to the intermediate shaft by the simplex planetary gear set, and the rotation of the intermediate shaft is shifted among a plurality of speeds and transferred to the output shaft by the duplex planetary gear set, the speed-increasing intermediate shaft is supported by an end portion of the input shaft for rotation relative thereto. Therefore, the intermediate shaft can be rotatably supported in a small space with a high rigidity.

In a second embodiment of the improved automatic transmission of the present invention, the intermediate shaft extends, from a distal end portion of the intermediate shaft, through an inner peripheral side of the duplex planetary gear set, to an end portion on the transmission case for rotation on the common axis. Accordingly, the speed-increasing intermediate shaft can be supported at both ends thereof on the transmission case in a small space with high rigidity.

In the preferred embodiments of the improved automatic transmission, the duplex planetary gear set is made up of two simplex planetary gear sets, and has four rotary elements including two different elements in one of the two simplex planetary gear sets always connected to two different elements of the other simplex planetary gear set.

Thus, with a simple design, the rotation of the input shaft can be shifted between six forward speeds and a reverse speed that are appropriately separated from one another, and then output at the output shaft.

In the preferred embodiments of the present invention, the simplex planetary gear set includes a first sun gear, a first carrier supporting a pinion that meshes with the first sun gear, and a first ring gear that meshes with the pinion, wherein the first carrier is the input element, the sun gear is the fixed element, and the first ring gear is the speed-increasing element. The duplex planetary gear set includes second and third sun gears, a long pinion that directly meshes with the second sun gear and meshes with the third sun gear via an intermediate pinion, a common carrier that supports the long pinion and the intermediate pinion, and a common ring gear that meshes with the long pinion, wherein the second sun gear is the first element, the common carrier is the second element, the common ring gear is the third element, and the third sun gear is the fourth element.

Accordingly, the second sun gear is selectively coupled to the first carrier via the third clutch, or is selectively fixed via the first brake. The common carrier is selectively coupled to the first ring gear via the second clutch, or is selectively fixed via the second brake. The common ring gear is directly coupled to the output shaft. The third sun gear is selectively coupled to the first carrier via the first clutch.

Accordingly, the present invention provides a compact structure of a reduced length, wherein the rotation of the input shaft can be shifted between six forward speeds and the reverse speed that are appropriately separated from each other.

In the preferred embodiments of the present invention, the first and third clutches are disposed in a vicinity of the simplex planetary gear set.

In a second embodiment of the present invention a carrier is the input element and is coupled via a member radially extending from an end portion of the input shaft. A sun gear is the fixed element and is coupled via an axially extending fixing member coupled to the transmission case, and a ring gear is the speed-increasing element. The ring gear and the intermediate shaft are coupled via a coupling member having a first portion that extends radially inward from the ring gear and a second portion that extends axially from the first portion, wherein the second portion is coupled to the intermediate shaft and has an oil passage that supplies oil pressure to a hydraulic servo of a friction engagement element. The coupling with the intermediate shaft is on the side of the oil passage which is axially opposite the support shaft at the distal end of the intermediate shaft. In this embodiment, the intermediate shaft is supported in a journal hole that is bored in the end portion of the input shaft, the oil passage in the axially extending portion of the coupling member is fit liquid-tight to the intermediate shaft, and the coupling member may be coupled to the intermediate shaft.

In another preferred embodiment, the fixing member coupled to the transmission case and extending in the axial direction is disposed around the outer periphery of the input shaft. The oil passage in the intermediate shaft is connected in communication with oil passages formed in the fixing member and the input shaft, and operating oil for the hydraulic servo is supplied via these oil passages. In this embodiment the length of the oil passage formed in the intermediate shaft can be shortened, as compared with a structure in which the coupling portion is disposed on the same axial side of the oil passage as the distal end of the intermediate shaft.

Further, a lubricating oil passage can be formed in the transmission case and the intermediate shaft without interference with the oil passage for supplying operating oil to the hydraulic servo. Furthermore, the length of the oil passage formed in the intermediate shaft for supplying the operating oil can be shortened in comparison with a structure in which the oil passage is disposed on the same axial side as the distal end of the intermediate shaft. Therefore, the lubricating oil passage length can be correspondingly increased to supply sufficient lubricating oil to the elements.

In the aforementioned first and second embodiments, the simplex planetary gear set includes a carrier that is the input element, a sun gear that is the fixed element, and a ring gear that is the speed-increasing element, and has a hub member that extends axially from the carrier at an outer periphery of the simplex planetary gear set, and the carrier and the hub member are formed as a single integral body. The carrier is formed of a carrier body and a carrier cover, and has a cutout for receiving a pinion formed in the carrier cover. Accordingly, pinions can easily be mounted within the carrier coupled to the input shaft, the number of components is reduced, the structure is simplified, and the operation of the friction engagement element is made smoother.

Preferably, a plurality of cutouts are formed in the carrier cover, point-symmetrically about the common axis, whereby the carrier becomes better rotationally balanced and can rotate without vibration.

In another preferred embodiment, the simplex planetary gear set includes a carrier that is the input element, a sun gear that is the fixed element, and a ring gear that is the speed-increasing element, and has a hub member that extends axially from the carrier at an outer periphery of the simplex planetary gear set, and the carrier and the hub member are separate components and are restricted in movements by a spline and a snap ring, respectively. In this embodiment, pinions can easily be mounted within the carrier coupled to the input shaft, through a window formed in the outer periphery of the carrier body.

In a modification of the foregoing embodiment, the simplex planetary gear set includes a carrier that is the input element, a sun gear that is the fixed element, and a ring gear that is the speed-increasing element, and has a hub member that extends axially from the carrier at the outer periphery of the simplex planetary gear set, and the carrier and the hub member are formed as a single integral body, and a hole for inserting the pinion is formed in the hub member.

Accordingly, pinions can easily be mounted within the carrier coupled to the input shaft, through the holes formed in the hub member and the windows in an outer periphery of the carrier body.

DESCRIPTION OF PREFERRED EMBODIMENTS

Embodiments of the automatic transmission of the present invention will be described hereinafter with reference to the drawings.FIG. 1shows an automatic transmission10in accordance with the present invention, which is used, for example, to shift the output speed of a fluid torque converter11, that is rotationally driven by a diesel engine of a motor vehicle, and to transfer the rotation at the changed speed to drive wheels. The automatic transmission10includes an input shaft14, the fluid torque converter11, a simplex planetary gear set15, a duplex planetary gear set16, an output shaft17, clutches C-1to C-3, and brakes B-1, B-2that are supported sequentially on a common axis13within a transmission case12attached to the body of a vehicle.

The simplex planetary gear set15includes a first sun gear S1fixed to the case12, a first carrier C1, which supports pinions18in mesh with the first sun gear S1and which is directly coupled to the input shaft14, and a ring gear R1in mesh with the pinions18. The first carrier C1serves as an input element and is coupled to the input shaft14. The first sun gear S1(a fixed element) is fixed to the case12. The first ring gear R1serves as a speed-increasing element that increases the speed of the rotation of the input shaft14.

The duplex planetary gear set16includes second and third sun gears S2, S3that are rotatably supported on the common axis13, long pinions23that directly mesh with the second sun gear S2and that mesh with the third sun gear S3via intermediate pinions24, a common carrier C2, C3that supports the long pinions23and the intermediate pinions24, and a common ring gear R2, R3that meshes with the long pinions23.

The second sun gear S2of the duplex planetary gear set16is selectively connected to the first carrier C1of the simplex planetary gear set15via the third clutch C-3, and is selectively fixed to the case12via a first brake B-1. The common carrier C2, C3is selectively to the first ring gear R1via the second clutch C-2, and is selectively fixed to the case12via a second brake B-2. The common carrier C2, C3is selectively coupled to the case12by a one-way clutch F-1that is disposed in parallel with the second brake B-2, and therefore prevented from reverse rotation. The common ring gear R2, R3is directly coupled to the output shaft17. The third sun gear S3is selectively connected to the first carrier C1via the first clutch C-1.

The pump impeller30of the fluid torque converter11is rotationally driven by the engine to generate a flow of oil, and a stator31receives the reaction force of the oil flow and generates a torque on turbine32. The input shaft14is directly coupled to the turbine32. A lockup clutch33, when engaged, directly couples the pump impeller30to the turbine32.

The automatic transmission10described above is able to establish six forward speeds and a reverse speed by selectively coupling or fixing the input shaft14, the output shaft17, and the elements of the simplex planetary gear set15and the duplex planetary gear set16through selective engagement and disengagement of the first to third clutches C-1to C-3and selective actuation of the first and second brakes B-1, B-2. InFIG. 2, the circles provided in the columns for the clutches and the brakes indicate a coupled state for the clutches, and an engaged state for the brakes.

For the simplex planetary gear set15and a single-pinion planetary gear subset21of the duplex planetary gear set16, the relationship between the rotational speed Ns of the sun gear, the rotational speed Nc of the carrier, the rotational speed Nr of the ring gear and the gear ratio λ of the single-pinion planetary gear subset is represented by the following equation (1). For a double-pinion planetary gear subset22of the duplex planetary gear set16, the relationship between the rotational speed Ns of the sun gear, the rotation speed Nc of the carrier, the rotation speed Nr of the ring gear and the gear ratio λ of the double-pinion planetary gear subset is represented by the equation (2). The gear ratios for the individual shift speeds are computed on the basis of the equations (1) and (2). Where the numbers of teeth of the first to third sun gears S1, S2, S3are Zs1, Zs2, Zs3and the numbers of teeth of the first and common ring gears R1, R2and R3are Zr1, Zr, and Zr3the gear ratios of the simplex planetary gear set15, the single-pinion planetary gear subset21and the double-pinion planetary gear subset22may be expressed as λ1=Zs1/Zr1, λ2=Zs2/Zr2and λ3=Zs3/Zr3.
Nr=(1+λ)Nc−λNs(1)
Nr=(1−λ)Nc+λNs(2)

By selective engagement of first to third clutches C-1to C-3and the first and second brakes B-1, B-2, the speed ratios of the elements of the simplex planetary gear set15and the duplex planetary gear set16become as indicated in the speed diagram ofFIG. 3. In the speed diagrams, the elements of a planetary gear set, including the sun gear, the carrier and the ring gear, are arranged in the direction of the horizontal axis at intervals corresponding to the gear ratios, and the speed ratios for the various elements are plotted in the direction of the vertical axis. InFIG. 3, the speed diagrams of the simplex planetary gear set15and the duplex planetary gear set16are arranged side by side. In the duplex planetary gear set16, the carrier C2, C3and the ring gear R2, R3of the single-pinion planetary gear subset21and the double-pinion planetary gear subset22are shared. Therefore, the speed ratios of the common carrier C2, C3are indicated on a single vertical line designated C2, C3, and the speed ratios of the common ring gear R2, R3are on a single vertical line designated R2, R3. As for the simplex planetary gear set15, where the interval between the vertical line of the first carrier C1and the vertical line of the sun gear S1is assigned a value of “1”, the vertical line of the ring gear R1is spaced an interval λ1from the vertical line of the first carrier C1, on the side opposite the vertical line of the sun gear S1. For the single-pinion planetary gear set21, where the interval between the vertical line of the common carrier C2, C3and the vertical line of the sun gear S2is assumed to be “1”, the vertical line of the common ring gear R2, R3is spaced an interval λ2from the vertical line of the common carrier C2, C3, on the side opposite the vertical line of the sun gear S2. As for the double-pinion planetary gear subset22, where the interval between the vertical line of the common carrier C2, C3and the vertical line of the sun gear S3is assigned a value of “1”, the vertical line of the common ring gear R2, R3is disposed at a gear ratio λ3from the vertical line of the common carrier C2, C3, on the same side as the vertical line of the sun gear S3. In the speed diagram, C-1to C-3, and B-1and B-2indicate the points of selective actuation of the first to third clutches C-1to C-3, and the first and second brakes B-1, B-2.

In the speed diagram for the duplex planetary gear set16as described above, the elements corresponding to the four vertical lines are designated the first, second, third and fourth elements, in that order from the extreme left vertical line. In this first embodiment, the second sun gear S2of the duplex planetary gear set16is the first element, the common carrier C2, C3is the second element, the common ring gear R2, R3is the third element, and the third sun gear S2is the fourth element.

A controller35for the automatic transmission10will now be described with reference to the block diagram ofFIG. 4. Detection signals are input to the controller35(which includes a CPU), from an engine rotational speed sensor36that detects the engine-side rotational speed Ne of the torque converter11to which the rotational of the engine is transferred, from an input rotation speed sensor37that detects the rotational speed Ni of the input shaft14of the automatic transmission10, from an output rotational speed sensor38that detects the rotational speed Nv of the output shaft17of the automatic transmission10, from a range position sensor39that sends a signal D, N, or R which indicates the position of the shift lever at the drive range D, the neutral range N or the reverse range R, from a throttle opening sensor40that detects the amount of depression of an accelerator pedal Ss, etc. On the basis of these detection signals, the controller35selects an optimum shift speed, and outputs control currents to hydraulic servos57to61that actuate the clutches and the brakes to selectively engage or disengage the first to third clutches C-1to C-3and the first and second brakes B-1, B-2as shown inFIG. 2, thus achieving six forward speeds and one reverse speed.

The first speed (1st) is achieved by engagement of the first clutch C-1and automatic engagement of the one-way clutch F-1. The rotation of the first carrier C1of the simplex planetary gear set15is input to the third sun gear S3of the duplex planetary gear set16via the first clutch C-1, and the common carrier C2, C3is prevented from reverse rotation by the one-way clutch F-1and therefore receives the reaction force. Hence, the common ring gear R2, R3and therefore the output shaft17rotate forward at the reduced rotational speed of the first speed gear ratio.

When engine braking is applied traveling downhill, the rotational speed of the common ring gear R2, R3, that is driven by the drive wheels, exceeds the rotational speed transferred from the engine side to the second sun gear S2, so that the direction of reaction force acting on the common carrier C2, C3is reversed. Therefore, in engine braking, the common carrier C2, C3is fixed by engagement of the second brake B-2as indicated by ▴ inFIG. 2.

The second speed (2nd) is achieved by engagement of the first clutch C-1and the first brake B-1. The rotation of the first carrier C1of the simplex planetary gear set15which is directly coupled to the input shaft14, is input to the third sun gear S3of the duplex planetary gear set16via the first clutch C-1. The second sun gear S2is fixed by the first brake B-1. Hence, the common ring gear R2, R3and therefore the output shaft17rotate forward at the reduced rotational speed of the second speed gear ratio.

The third speed (3rd) is achieved by engagement of the first and third clutches C-1, C-3. The rotation of the first carrier C1, directly coupled to the input shaft14, is input to the third and second sun gears S3, S2of the duplex planetary gear set16via the first and third clutches C-1, C-3, so that the duplex planetary gear set16integrally rotates. Hence, the common ring gear R2, R3and therefore the output shaft17rotate forward at a rotational speed equal to that of the input shaft14, i.e. at the 1.0 gear ratio of the third speed.

The fourth speed (4th) is achieved by engagement of the first and second clutches C-1, C-2. The rotation of the first carrier C1of the simplex planetary gear set15which is directly coupled to the input shaft14is input to the third sun gear S3of the duplex planetary gear set16via the first clutch C-1. The rotation of the first ring gear R1, at a speed increased from that of the input shaft, is input to the common carrier C2, C3via the second clutch C-2. Hence, the common ring gear R2, R3and therefore the output shaft17rotate forward with the increased rotational speed of the gear ratio of the fourth speed.

The fifth speed (5th) is achieved by engagement of the second and third clutches C-2, C-3. The rotation of the first carrier C1of the simplex planetary gear set15, which is directly coupled to the input shaft14, is input to the second sun gear S2of the duplex planetary gear set16via the third clutch C-3. The rotation of the first ring gear R1, at a speed increased from that of the rotation of the input shaft14, is input to the common carrier C2, C3via the second clutch C-2. Hence, the common ring gear R2, R3and therefore the output shaft17rotate forward at the increased rotational speed of the fifth speed gear ratio.

The sixth speed (6th) is achieved by engagement of the second clutch C-2and the first brake B-1. The rotation of the first ring gear R1, at a speed increased from that of the rotation of the input shaft14of the simplex planetary gear set15, is input to the carrier C2, C3of the duplex planetary gear set16via the second clutch C-2. The second sun gear S2is fixed via the first brake B-1. Hence, the ring gear R2, R3and therefore the output shaft17rotate forward at the increased rotational speed of the sixth speed gear ratio.

The reverse speed (REV) is achieved by engagement of the third clutch C-3and the second brake B-2. The rotation of the first carrier C1of the simplex planetary gear set15, which is directly coupled to the input shaft14, is input to the second sun gear S2of the duplex planetary gear set16via the third clutch C-3. The common carrier C2, C3is fixed by the brake B-2. Hence, the common ring gear R2, R3and therefore the output shaft17rotate in reverse at the reduced rotational speed of the reverse speed gear ratio.

If the gear ratios of the individual shift speeds are computed using equations (1) and (2), when the gear ratios λ1, λ2, λ3(the sun gear's number of teeth/the ring gear's number of teeth) of the simplex planetary gear set15, the single-pinion planetary gear subset21and the double-pinion planetary gear subset22are set at, for example, 0.556, 0.458 and 0.375, the ratio of rotational speeds of the first carrier C1and the common ring gear R2, R3, i.e. the gear ratios, for the individual shift speeds become the values given inFIG. 2, that is, 2.667 for the first speed, 1.524 for the second speed, 1.000 for the third speed, 0.742 for the fourth speed, 0.552 for the fifth speed, 0.441 for the sixth speed, and 2.182 for the reverse speed. The steps between the gear ratios are: 1.75 between the first and second speeds; 1.52 between the second and third speeds; 1.35 between the third and fourth speeds; 1.34 between the fourth and fifth speeds; and 1.25 between the fifth and sixth speeds. Thus, the step between gear ratios becomes appropriately smaller as the shift speed becomes higher. Hence, the automatic transmission of this embodiment provides gear ratios for six forward speeds and one reverse speed which are appropriately spaced.

In this case, the torques assigned to the first to third sun gears S1to S3, the first carrier C1, the first ring gear R1, the common carrier C2, C3and the common ring gear R2, R3as well as the first to third clutches C-1to C-3and the first and second brakes B-1, B-2are as shown inFIGS. 5 and 6.

Next, the first embodiment of the invention, as applied to the automatic transmission10for an FF vehicle in which front wheels are driven by an engine mounted on the front side of the vehicle, will be described with reference toFIG. 7. The transmission case12has a rear case portion12rin the shape of a bottomed cylinder, and a front wall portion12ffixed forward of the rear case portion12r. The front wall portion12fis formed of an oil pump body12athat is fixed to the transmission case11by bolts107and that houses an oil pump gear. An oil pump cover12bfixed to the oil pump body12aby bolts108. The oil pump cover12bhas a boss portion12cthat extends axially from its inner periphery. A stator shaft87coupled to the stator31via a one-way clutch86is press-fitted and fixed to the inner peripheral surface of the boss portion12c. The input shaft14is journaled on the stator shaft87via a needle bearing88and a metal bush89so as to be rotatable about the common axis13. A journal hole65is provided in a rear side end of the input shaft14. A support shaft41a41is inserted and supported within the journal hole65via a needle bearing81for rotation relative to and coaxial with input shaft14. A rear side end portion of the intermediate shaft41is rotatably supported via a needle bearing82in a bottom portion of the rear case12r. The pump impeller30of the torque converter11is rotatably supported via a needle bush91on the oil pump body12a. The stator31is coupled, via a one-way clutch86, to the stator shaft87that is press-fitted into a boss portion of the oil pump cover12b. The turbine32is fitted to the distal end of the input shaft14with relative rotation therebetween restricted. As used herein, the “forward” axial end of the automatic transmission10is the torque converter side, and the axial “rear” end is at the side of the duplex planetary gear set.

The first sun gear S1of the simplex planetary gear set15is arranged on the common axis13and is fixed to the stator shaft87which, in turn, is press-fitted to the oil pump cover12b. A carrier body43aof the first carrier C1is fastened to an input flange that protrudes from the end portion of the input shaft14, and is thus directly coupled to the input shaft14. The first ring gear R1and the intermediate shaft41are coupled via a coupling member42in the form of a radially extended portion42athat is integral with the first ring gear R1and extends radially inward from the first ring gear R1, and an axially extended portion42bthat is integral with and extends axially from the radially extended portion42aand that is spline-fitted to the intermediate shaft41. Pinion shafts45rotatably support the pinions18that mesh with the first sun gear S1and the first ring gear R1. The pinion shafts45are supported at both ends thereof by the carrier body43aof the first carrier and a carrier cover43bfixed to the carrier body43a.

The third sun gear S3of the duplex planetary gear set16is rotatably supported on the intermediate shaft41via two metal bushes92. The second sun gear S2is rotatably supported on an outer periphery of a cylindrical shaft portion of the third sun gear S3via two metal bushes93. The common carrier C2, C3is rotatably supported, at its forward wall portion located on the torque converter side, on a cylindrical shaft portion of the second sun gear S2, via a metal bush94. The long pinions23and the intermediate pinions24are rotatably supported via needle bushes on pinion shafts46,47, respectively, which are each supported at both ends by the common carrier C2, C3. The long pinions23are directly meshed with the second sun gear S2, and are meshed with the third sun gear S3via the intermediate pinions24, and also are meshed with the common ring gear R2, R3. A supported body48with a protruding central cylinder portion is fixed to the rear case12rby a bolt95, between the simplex planetary gear set15and the duplex planetary gear set16. The output shaft17coupled to the common ring gear R2, R3, with relative rotation therebetween restricted, is supported on the central cylinder portion of the supported body48, via a ball bearing96.

The counter shaft49is rotatably supported in the transmission case12, in parallel with the common axis13. A driven gear50is fixed to the counter shaft49and is meshed with a drive gear51mounted on the output shaft17. Differential drive pinions, smaller in diameter than the driven gear50, are fixed to the counter shaft49. The differential drive pinions are meshed with a differential ring gear of a not-shown differential device that transfers rotation of the output shaft17to the left and right front wheels of the vehicle.

In the transmission case12, the first and third clutches C-1, C-3and the first brake B-2are provided adjacent to the simplex planetary gear set15, and the second clutch C-2and the second brake B-2are provided adjacent to the duplex planetary gear set16. The first to third clutches C-1to C-3, and the first and second brakes B-1, B-2function as friction engagement elements wherein a plurality of separator plates are selectively engaged with a plurality of friction discs. The friction engagement elements respectively include friction engagement portions52to56and hydraulic servo portions57to61. Each friction engagement portion52to56includes a plurality of separator plates and a plurality of friction discs which are selectively engaged and which are spline-engaged for relative movement in the axial direction with restricted relative rotation. The separator plates and the friction discs are alternately arranged.

Hydraulic servo portions57to59of the first to third clutches C-1to C-3each include of a cylinder97, a piston98disposed slidably in the cylinder97, a servo chamber99formed oil-tight between the piston and the cylinder, a cancel plate100, a cancel chamber101that is formed between the cancel plate and the piston for canceling the centrifugal force generated in the servo chamber by supply of cancel oil, and a compressed spring102that urges apart the separator plates and the friction discs.

Hydraulic servo portions60,61of the first and second brakes B-1, B-2each include a cylinder103, a piston110disposed slidably in the cylinder103, a servo chamber111formed oil-tight between the piston and the cylinder, and a compressed spring112that urges apart the separator plates and the friction discs.

A cylindrical hub member44is integrally formed on the outer periphery of the carrier cover43bof the first carrier C1of the simplex planetary gear set15. A cylinder portion of a coupling member62, coupled to the second sun gear S2of the duplex planetary gear16, is disposed around the outer periphery of the hub44of the third clutch C-3. The plurality of separator plates and the plurality of friction discs, forming the friction engagement portion54of the third clutch C-3, are spline-engaged with the inner peripheral surface of the cylinder portion and the outer peripheral surface of the hub member44, respectively. The hydraulic servo portion59of the third clutch C-3is provided on the coupling member62, between the front wall portion12fand the simplex planetary gear set15. The separator plates and the friction discs (friction engagement portion55) of the first brake B-1are spline-engaged with the outer peripheral surface of the cylinder portion of the coupling member62and the inner peripheral surface of the rear case12r, respectively. The hydraulic servo portion60of the first brake B-1, has its cylinder103formed by the oil pump body12a. A cylinder portion of a coupling member63, coupled to the third sun gear S3, surrounds the outer periphery of the hub44. The separator plates and the friction discs of the friction engagement portion52of the first clutch C-1are spline-engaged with the inner peripheral surface of the cylinder portion and the outer peripheral surface of the hub44, respectively. The hydraulic servo portion57of the first clutch C-1is formed in the coupling member63.

A cylinder portion of a coupling member64fixed to the rear side end of the intermediate shaft41surrounds the outer periphery of the common carrier C2, C3of the duplex planetary gear set16. The separator plates and the friction discs of the friction engagement portion53of the second clutch C-2are spline-engaged with the inner peripheral surface of the cylinder portion and the outer peripheral surface of the common carrier C2, C3, respectively. The hydraulic servo portion58of the second clutch C-2is provided on the coupling member64. The separator plates and the friction discs of the friction engagement portion56of the second brake B-2are spline-engaged with the outer peripheral surface of the common carrier C2, C3and an inner peripheral surface of the rear case portion12r, respectively. The hydraulic servo portion61of the second brake B-2is formed in a bottom portion of the rear case12r. The one-way clutch F-1is disposed between the outer peripheral surface of the common carrier C2, C3and the inner peripheral surface of the rear case12r.

A rear side end portion of the input shaft14and a front end portion of the intermediate shaft41are provided with an oil passage72that is open to the journal hole65for supply and discharge of operating oil to and from the servo chamber99of the hydraulic servo57of the first clutch C-1. A seal member74provides a seal between the journal hole65and the distal end of the intermediate shaft41, preventing high-pressure operating oil from penetrating to the outer periphery of the intermediate shaft41and mixing with the lubricating oil. An oil passage80, providing communication with the servo of a lockup clutch33, is bored in a front end portion of the input shaft14. An oil passage78that supplies operating oil to and discharges it from the hydraulic servo portion58of the second clutch C-2is formed in a bottom portion of the rear case12r. The intermediate shaft41and a rear end portion of the input shaft14have lubricating oil passages75,77for supplying lubricating oil separately from the oil passage72.

Next, a second embodiment in which the present invention is applied to an automatic transmission for an FF vehicle, in which an engine is mounted on the vehicle front side and the front wheels are driven, will be described with reference toFIGS. 8 to 10. Components which are the same as in the foregoing automatic transmission10of the first embodiment are assigned the same reference numerals, and a detailed description thereof will be omitted.

A stator shaft87is press-fitted and fixed within a boss portion12cextending axially rearward from the inner periphery of an oil pump cover12bthat forms a portion of a front wall12fof a transmission case12. An input shaft14is journaled within the boss portion12C via a needle bearing88and a metal bush89so as to be rotatable about a common axis13. A journal hole65is provided in the rear end portion of the input shaft14. A support shaft portion41a, formed at a distal end of an intermediate shaft41, is mounted in the journal hole65via a needle bearing81so as to be coaxially rotatable therein. The intermediate shaft41extends through duplex planetary gear set16, and extends out on the rear side. A rear end portion of the intermediate shaft41is journaled in a bottom portion of a rear case portion12rof the transmission case12via a needle bearing82so as to be rotatable on the common axis13.

The simplex planetary gear set15includes a first sun gear S1fixed to the transmission case12, a first ring gear R1coupled to the intermediate shaft41, and a first carrier C1that is fixed to the input shaft14and that rotatably supports pinions18which mesh with the first sun gear S1and the first ring gear R1. The first sun gear S1is spline-fitted and fixed to the stator shaft87which, in turn, is press-fitted and fixed in the boss portion12cwhich extends axially rearward from the inner periphery of the oil pump cover12b.

The first ring gear R1and the intermediate shaft41are coupled via a coupling member42that has a radially extended portion42athat extends radially inward from an outer periphery that is spline-fitted to the first ring gear R1, and an axially extended portion42bthat extends axially from the radially extended portion42aand that is spline-fitted to the intermediate shaft41. The axially extended portion42bis provided with a coupling portion42cspline-fitted to the intermediate shaft41, and a supply portion42dfor supply of oil pressure to a hydraulic servo of a friction engagement element, that is, in this embodiment, a servo chamber99of the hydraulic servo57that engages and disengages a friction engagement portion52of a first clutch C-1. The coupling portion42cis disposed on the axially opposite side of the supply portion42drelative to the simplex planetary gear set15. A support shaft41a, a supply shaft41bcovering to the supply portion42d, and a spline shaft portion41cspline-fitted to a coupling portion42cform the intermediate shaft41, are arranged sequentially from the distal end, with the diameter increasing stepwise.

The first carrier C1is provided with a carrier body43athat is fastened by welding or the like to an input flange portion14awhich extends radially from a rear end portion of the input shaft14. The carrier body43aextends in a radial direction, and is bent at an outer edge to extend axially over a length that is slightly greater than the width of the pinions18. An annular carrier cover43bis integrally fixed to a front end of an outer peripheral portion of the carrier body43aby welding or the like. A plurality of (six inFIG. 10) pinion shafts45are supported at both ends by the carrier body43aand the carrier cover43b, in parallel with the input shaft14. Pinions18are rotatably supported on input shaft14. The pinions18mesh with the first sun gear S1, and also mesh with the first ring gear R1via window portions43cthat are formed in the outer periphery of the carrier body43a.

At an outer periphery of the first ring gear R1is a cylindrical hub member44shared by the first and third clutches C-1, C-3. The hub member44is formed integrally with the outer periphery of the carrier cover43b. A plurality of separator plates and a plurality of friction discs, constituting the friction engagement portions52,55of the first and third clutches C-1, C-3, are spline-engaged with an outer peripheral surface of the hub member44and with inner peripheral surfaces of cylinder portions of coupling members63,62, respectively, as in the case of the first embodiment. Through engagement and disengagement of the friction engagement elements by hydraulic servos57,59, the first carrier C1is disengageably coupled to third and second sun gears S3, S2of the duplex planetary gear set16via the coupling members63,62.

Since the first carrier C1is formed integrally with the input shaft14and the hub member44is formed integrally with the carrier cover43b, it is impossible to insert the pinions18into the first carrier C1through the windows43cformed in the outer periphery of the carrier body43aand to fit the pinions18on pinion shafts45. Therefore, in this second embodiment, cutouts83for inserting the pinions18are formed in a small diameter-side inner peripheral surface of the carrier cover43b. The plurality of pinions18are sequentially inserted into the carrier C1through spaces between the cutouts83and the outer peripheral surface of the input shaft14. A pinion shaft45is fitted into the center hole of each of the pinions18via bushes and the pinion shaft45is then inserted into support holes bored in the carrier body43aand the carrier cover43b. The pinion shaft45is then fixed in the support hole of the carrier body43aby caulking or the like. A plural number of cutouts83are formed in the small diameter-side inner peripheral surface of the carrier cover43b, point symmetrically about the common axis13. Thus, the first carrier C1has good rotational balance, and is able to smoothly rotate without vibrating.

While in the above embodiment, the cutouts83are formed on the inner peripheral surface of the carrier cover43bin order to allow mounting of the pinions18, instead of the cutouts83, holes84for inserting the pinions18may be formed in alignment with the window portions43cformed in the outer periphery of the carrier body43aof the hub member44, as shown by imaginary lines inFIG. 9. According to this alternative, the pinions18are inserted into the first carrier C1through the holes84and the window portions43c, and are supported on the pinion shafts45via bushes.

As shown inFIGS. 8 and 9, the stator shaft87is press-fitted and fixed within the boss12cwhich extends axially rearward from the inner peripheral portion of the oil pump cover12band is provided with an oil passage87afor supplying operating oil to and discharging it from the servo chamber99of the hydraulic servo. The oil passage87ais connected in communication with an annular groove14bformed on the outer periphery of the input shaft14. An oil passage72is connected at one end in communication with (open to) the annular groove14band opens at its other end to a bottom surface of the journal hole65bored in the input shaft14. An oil passage72′, open at one end to the distal end surface of the intermediate shaft41and open at its other end to the outer peripheral surface of the supply shaft portion41b, is bored in a distal end portion of the intermediate shaft41. An inner peripheral surface of the supply member42dis provided with an annular groove42ethat is in communication with the oil passage72′ and that is sealed at both sides thereof. The outer peripheral surface of the supply member42dis provided with an annular groove42fin communication with an oil passage113. The oil passage113is formed in a boss portion which extends axially toward the torque converter from the inner periphery of a coupling member63that forms the drum (cylinder) of the first clutch. The oil passage113is in communication with the servo chamber99of the first clutch, via an oil passage114formed in a sleeve press-fitted in a boss portion forming the inner peripheral surface of the drum. The annular groove42fis sealed at both sides thereof. Furthermore, the annular groove42eand the annular groove42fare connected via a radial oil passage42g. Therefore, the annular grooves42e,42fare in communication with the oil passage72,72′ that supplies operating oil to and discharges it from the servo chamber99of the hydraulic servo57of the first clutch C-1. Thus, oil passages for supplying operating oil to hydraulic servos are formed in the transmission case12, the input shaft14and the intermediate shaft41. While not shown in the drawings, the oil passage87aformed in the stator shaft87is connected to a hydraulic control apparatus which controls the oil supplied as operating oil to the servo chambers of the hydraulic servos.

A lubricating oil passage is open to a bush hole in a bottom portion of the rear case portion12rin which is fitted a needle bearing82that supports the rear end of the intermediate shaft41. In the intermediate shaft41, a lubricating oil passage77extends axially from the end surface of intermediate shaft41to the vicinity of the oil passage72′. From a distal end of the lubricating oil passage77, a lubricating oil passage77aof a small diameter is bored at an incline so as not to interfere with the oil passage72′. The lubricating oil passage77aextends through the supply shaft portion41b, and opens at the outer peripheral surface of the support shaft portion41a. The lubricating oil supplied from the lubricating oil passage77alubricates elements, such as a needle bearing65located between the coupling member42and the first carrier C1of the simplex planetary gear set15, and the like. Thus, lubricating oil passages for supplying lubricating oil to elements disposed within the transmission case12are formed in the transmission case12and in the intermediate shaft41.

In a third embodiment shown inFIG. 11, a first carrier C1and a hub44are formed as separate members. Splines formed on the inner periphery of hub44are in mesh with splines on the outer periphery of carrier cover43bto restrict relative rotation therebetween. Two snap rings85are placed in two annular grooves at opposite sides of the carrier cover43bon the inner peripheral surface of the hub member44, so that the hub member44is restricted in axial movement with respect to the first carrier C1.

In the third embodiment, before the hub member44is attached to the first carrier C1, the pinions18are inserted into the first carrier C1through windows43cformed in an outer periphery of the carrier body43a, and are supported by pinion shafts45via bushes. The hub member44is then spline-fitted to the carrier cover43b, and held in place by the snap rings85.

Next, a fourth embodiment, in which the present invention is applied to an automatic transmission for an FR vehicle wherein an engine is mounted in the front of the vehicle and rotation of the engine is transferred to and drives the rear wheels, will be described with reference toFIG. 12. The features which are the same as in the above-described automatic transmission10are assigned the same reference numerals, and detailed description thereof will be omitted.

A stator shaft87is press-fitted and fixed within a boss12cwhich extends axially rearward from an inner peripheral portion of an oil pump cover12bthat constitutes a portion of front wall12fof transmission case12. Input shaft14is journaled within stator shaft87so as to be rotatable on a common axis13via a needle bearing115and a not-shown metal bush. An output shaft17is supported by the rear case via a needle bush104so as to be rotatable on the common axis13. The output shaft17extends rearward from the transmission case12, and is rotationally coupled, via a propeller shaft, to a differential ring gear of a not-shown differential device that transfers rotation to the left and right rear wheels of the vehicle.

A cylinder portion of a coupling member62is coupled to a second sun gear S2of a duplex planetary gear set16and is disposed at the outer periphery of a cylinder portion of an engagement member44that constitutes a first carrier C1of a simplex planetary gear set15. A plurality of friction discs and a plurality of separator plates are alternatively arranged to form a friction engagement portion54of a third clutch C-3and are respectively spline-engaged with an inner peripheral surface and an outer peripheral surface of the two cylinder portions. A cylinder portion of a coupling member63is coupled to a third sun gear S3and is disposed at the inner periphery of a cylinder portion of the engagement member44. A plurality of separator plates and a plurality of friction discs are alternatively arranged to form the friction engagement portion52of first clutch C-1and are respectively spline-engaged with an outer peripheral surface and an inner peripheral surface of the two cylinder portions.

A journal hole65is provided in the rear end of the input shaft14. A shaft portion66aof an intermediate member66is supported within the journal hole65via two metal bushes105for rotation relative to and coaxially with the input shaft14. A distal end of the intermediate shaft41, coaxial with the intermediate member66, is splined within and a coupling hole68formed in a rear end portion of the intermediate member66so as to be incapable of relative rotation. The rear end of the intermediate shaft41is supported within a hole69bored in a distal end of the output shaft17, via a needle bearing106, so as to be rotatable on the common axis13. In this embodiment, the “intermediate shaft” may be considered to be the combination of the intermediate shaft41and the intermediate member66. The first ring gear R1is directly coupled to the intermediate member66through spline-fitting to a speed-increasing flange portion66bthat extends radially from the intermediate member66. On an inner peripheral surface of the rear case portion12r, an annular body70is fixed forward of the friction engagement portion56of the second brake B-2. A one-way clutch F-1is disposed between the annular body70and the outer peripheral surface of the common carrier C2, C3.

Oil passages72,78,80, for supplying operating oil to and discharging it from hydraulic servos57,58of first and second clutches C-1, C-2and a hydraulic servo of a lockup clutch33, are formed in the shaft portion66aof the intermediate member66, a rear end portion of the intermediate shaft41, and the input shaft14. Lubricating oil passages75,77for supplying lubricating oil to various portions are bored separately from oil passages72,78, in the shaft portion66aof the intermediate member66and the intermediate shaft41.

In the automatic transmission10, both that for FF vehicles and that for FR vehicles, the first and third clutches C-1, C-3are disposed in the vicinity of the simplex planetary gear set15. Therefore, merely by achieving commonality, i.e. a sharing of a portion of the duplex planetary gear set16with a related-art gasoline engine automatic transmission, and changing the speed reduction of the input shaft via the simplex planetary gear set to a speed increase, an automatic transmission suitable for an engine that outputs higher torque at lower rotational speeds than related-art gasoline engines, for example a diesel engine, is provided.

A related-art gasoline engine automatic transmission71, as shown inFIG. 13, includes an input shaft14, a torque converter11, a simplex planetary gear set73, a duplex planetary gear set16, an output shaft17, clutches C-1to C-3, and brakes B-1, B-2which are sequentially supported on a common axis13within a transmission case12. A first sun gear S1of the simplex planetary gear set73is fixed, and the input shaft14is directly coupled to a first ring gear R1. A second sun gear S2of the duplex planetary gear set16is selectively connected to a first carrier C1of the simplex planetary gear set73via the third clutch C-3, and is selectively fixed to the case12via the first brake B-1. A common carrier C2, C3is selectively connected to the input shaft14via the second clutch C-2, and is selectively fixed to the case12via the second brake B-2. The common carrier C2, C3is designed to be coupled to the case12via a one-way clutch F-1disposed in parallel with the second brake B-2, so as to be prevented from reverse rotation. A common ring gear R2, R3is directly coupled to an output shaft17. A third sun gear S3is selectively connected to the first carrier C1via the first clutch C-1.

Therefore, by dividing the input shaft14of the related-art gasoline engine automatic transmission71into the input shaft14and the intermediate shaft41so that they are capable of relative rotation, by directly coupling the first carrier C1of the simplex planetary gear set73to the input shaft14, by directly coupling the first ring gear R1to the intermediate shaft41, and by fixing the first sun gear S1, it is possible to make an automatic transmission suitable for an engine that outputs higher torque at lower rotational speeds than a related-art gasoline engine, for example a diesel engine, while sharing a large portion of the related-art gasoline engine automatic transmission71without increasing the sizes of various components or the capacities of clutches or brakes.

The related-art gasoline engine automatic transmission71, as shown inFIG. 13, achieves six forward speeds and one reverse speed by selectively engaging and disengaging the first to third clutches C-1to C-3and the first and second brakes B-1, B-2in substantially the same manner as in the automatic transmission10in accordance with the present invention. If the gear ratios λ1, λ2, λ3of the simplex planetary gear set73, the single pinion planetary gear subset21, and the double pinion planetary gear subset22are 0.556, 0.458, and 0.375, respectively, the gear ratios at the individual shift speeds, and the steps between gear ratios are as shown in the columns with the headings GEAR RATIO and STEP inFIG. 14. In this case, the speed ratios of the individual elements of the simplex planetary gear set73and the duplex planetary gear set16are as indicated in the speed diagram shown inFIG. 15. The torques assigned to the first to third sun gears S1to S3, the first carrier C1, the first ring gear R1, the common carrier C2, C3, and common ring gear R2, R3, as well as the first to third clutches C-1to C-3and the first and second brakes B-1, B-2, are as shown inFIGS. 16 and 17.

The automatic transmission10in accordance with the present invention, as compared with the related-art gasoline engine automatic transmission71, achieves a reduction to, for example, 1/1.556 fold, of all the gear ratios of the first to six speeds and the reverse speed, and is therefore able to convert the output rotational speed of an engine that outputs high torque at low rotational speeds, to a desired rotational speed, and to transfer it to the drive wheels. Because the torque assignments to the first to third sun gears S1to S3, the first carrier C1, the first ring gear R1, the common carrier C2, C3, and the common ring gear R2, R3, and the torque assignments to the first to third clutches C-1to C-3, the first and second brakes B-1, B-2, and the one-way clutch F-1all reduced 1/1.556 fold, the sizes of various components and the capacities of clutches and brakes can be made smaller. In particular, in first speed where the transfer torque is large, rotation of the second element can be prevented without using a clutch. Therefore, the need for a clutch of large capacity is eliminated.