Automatic transmission

An automatic transmission is configured to achieve at least ten forward speeds and one reverse speeds. This is achieved through the use of two planetary gear sets with a plurality of clutches and brakes configured to operably couple different components of the two planetary gears to achieve different speeds. For example, operation of a first clutch inputs decelerated rotation of a reduction planetary gear to a third sun gear. Operation of a second clutch transmits from an input shaft to a third ring gear, a third clutch inputs decelerated rotation of the reduction planetary gear to the second sun gear, a fourth clutch transmits from the input shaft to the second carrier, a first brake prevents a second sun gear from rotating, a second brake prevents a carrier from rotating, a third brake capable prevents a third ring gear from rotating.

INCORPORATION BY REFERENCE

The disclosure of Japanese Patent Application No. 2012-074915 filed on Mar. 28, 2012 including the specification, drawings and abstract is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

The present invention relates to automatic transmissions that are mounted on, for example, vehicles etc., and more particularly to automatic transmissions that include a reduction planetary gear capable of outputting decelerated rotation and a planetary gear set achieving multi-speed shifting based on decelerated rotation and input rotation.

DESCRIPTION OF THE RELATED ART

In recent years, the number of shift speeds of stepped automatic transmissions that are mounted on vehicles has been increased in order to improve fuel economy of the vehicles. Stepped automatic transmissions that include a reduction planetary gear capable of outputting decelerated rotation and a planetary gear set achieving multi-speed shifting based on decelerated rotation and input rotation have been proposed as such stepped automatic transmissions (see Japanese Patent Application Publication No. 2000-220704 (JP 2000-220704 A) and Japanese Patent Application Publication No. 2006-161927 (JP 2006-161927 A)).

In the automatic transmission of JP 2000-220704 A, decelerated rotation decelerated by a reduction planetary gear can be input by two clutches (C-1, C-3) to two rotating elements (S2, S3) of a Ravigneaux type planetary gear formed by four rotating elements, and input rotation of an input shaft can be input by one clutch (C-2) to one rotating element (C2). Moreover, two rotating elements (S2, C2) can be locked by two brakes (B-1, B-2). This automatic transmission achieves six forward speeds and one reverse speed in this manner.

On the other hand, in the automatic transmission shown by, for example, FIG. 7 of JP 2006-161927 A, a planetary gear set is not formed by a Ravigneaux type planetary gear, but instead is formed by a planetary gear set in which a long pinion is formed by a stepped pinion having a stepped portion and which is formed by five rotating elements additionally including a ring gear (R2). Decelerated rotation decelerated by a reduction planetary gear can be input by one clutch (C-3) to one rotating element (CR2) of the Ravigneaux type planetary gear set formed by the five rotating elements, and input rotation of an input shaft can be input by two clutches (C-1, C-2) to two rotating elements (S2, R2). Moreover, three rotating elements (CR2, S3, R2) can be locked by three brakes (B-1, B-2, B-3). This automatic transmission achieves eight forward speeds and one reverse speed in this manner.

SUMMARY OF THE INVENTION

One method to further increase the number of shift speeds from that of the automatic transmission of JP 2000-220704 A or JP 2006-161927 A is to merely add a planetary gear, but this may hinder downsizing and weight reduction. It is therefore possible to increase the number of shift speeds by changing the Ravigneaux type planetary gear of JP 2000-220704 A to such a planetary gear set formed by the five rotating elements as in JP 2006-161927 A.

However, in the case where the planetary gear set is used in the manner described in JP 2006-161927 A, it is difficult to increase the gear spread (the gear ratio coverage=minimum shift speed/maximum shift speed) (in FIG. 8 of JP 2006-161927 A, the spread is 5.856=3.359/0.613). Thus, merely increasing the number of shift speeds does not improve fuel economy unless the gear spread (the speed ratio coverage) is increased, because it is difficult to optimize the engine speed usage region with respect to the vehicle speed. Moreover, gear meshing loss at the maximum shift speed that is used for a relatively long time during, for example, high-speed traveling etc. need also be considered in order to improve the fuel economy.

It is an object of the present invention to provide an automatic transmission that achieves at least ten forward speeds and one reverse speed and achieves downsizing and weight reduction, and that is capable of increasing the gear spread and reducing gear meshing loss at the maximum shift speed.

An automatic transmission according to an aspect of the present invention includes: an input shaft that is drivingly coupled to a drive source; a reduction planetary gear that has a first sun gear, a first carrier, and a first ring gear, and that can output decelerated rotation decelerated from input rotation of the input shaft; a planetary gear set that has a second sun gear, a third sun gear, a second carrier supporting a short pinion meshing with the third sun gear and a stepped pinion having a small diameter portion meshing with the short pinion and a large diameter portion meshing with the second sun gear such that the short pinion and the stepped pinion are rotatable, a second ring gear meshing with the large diameter portion, and a third ring gear meshing with the small diameter portion; a first clutch capable of inputting the decelerated rotation of the reduction planetary gear to the third sun gear; a second clutch capable of inputting the input rotation of the input shaft to the third ring gear; a third clutch capable of inputting the decelerated rotation of the reduction planetary gear to the second sun gear; a fourth clutch capable of inputting the input rotation of the input shaft to the second carrier; a first brake capable of preventing the second sun gear from rotating; a second brake capable of preventing the second carrier from rotating; a third brake capable of preventing the third ring gear from rotating; and an output member drivingly coupled to the second ring gear. The automatic transmission is configured to achieve at least ten forward speeds and one reverse speed.

Thus, the automatic transmission can be provided which achieves ten forward speeds and one reverse speeds and which is capable of obtaining a relatively satisfactory step ratio between the shift speeds. The gear spread from the minimum shift speed to the maximum shift speed can be increased. This makes it easier to optimize the engine speed usage region with respect to the vehicle speed in a vehicle having the automatic transmission mounted thereon, and can improve fuel economy. Moreover, since the maximum shift speed is achieved by engagement of the fourth clutch and the first brake, the maximum shift speed can be obtained by meshing at only two locations, namely, meshing between the second sun gear and the large diameter portion of the stepped pinion and meshing between the second ring gear and the large diameter portion of the stepped pinion. This can minimize gear meshing loss at the maximum shift speed that is used for a relatively long time, and can improve fuel economy.

In the automatic transmission according to the aspect of the present invention, the reduction planetary gear (DP) is formed by a double pinion planetary gear in which the first carrier (CR1) has a first pinion (P1) meshing with the first sun gear (S1) and a second pinion (P2) meshing with the first pinion (P1) and the first ring gear (R1), and rotatably supports the first pinion (P1) and the second pinion (P2), and the first sun gear may be held stationary, the input shaft may be drivingly coupled to the first carrier, and the decelerated rotation may be output from the first ring gear.

Thus, since the reduction planetary gear may be formed by the double pinion planetary gear, the speed reduction ratio in the reduction planetary gear can be increased, and a satisfactory step interval of the gear ratio can be obtained particularly at a low shift speed.

In the automatic transmission according to the aspect of the present invention, the output member may be formed by a counter gear placed between the reduction planetary gear and the planetary gear set in an axial direction.

Thus, since the output member may be formed by the counter gear placed between the reduction planetary gear and the planetary gear set in the axial direction, this automatic transmission can be used in a preferable manner in vehicles in which an output shaft (crankshaft) of an engine is placed transversely with respect to a travel direction of the vehicle.

In the automatic transmission according to the aspect of the present invention, a friction plate of the second brake and a friction plate of the third brake may be placed on an outer peripheral side of the planetary gear set so as to overlap in the axial direction as viewed in a radial direction.

Thus, since the friction plate of the second brake and the friction plate of the third brake may be placed on the outer peripheral side of the planetary gear set so as to overlap in the axial direction as viewed in the radial direction, the second brake and the third brake can be arranged without causing interference between the members, and the automatic transmission can be configured in a compact manner in the axial direction.

In the automatic transmission according to the aspect of the present invention, a hydraulic servo of the second clutch and a hydraulic servo of the fourth clutch may be placed on an axially opposite side of the planetary gear set from the output member, and the hydraulic servo of the second clutch may be placed on an outer peripheral side of the hydraulic servo of the fourth clutch so as to overlap in the axial direction as viewed in the radial direction.

Thus, since the hydraulic servo of the second clutch and the hydraulic servo of the fourth clutch may be placed on the axially opposite side of the planetary gear set from the output member, and the hydraulic servo of the second clutch may be placed on the outer peripheral side of the hydraulic servo of the fourth clutch so as to overlap in the axial direction as viewed in the radial direction, the second clutch and the fourth clutch can be arranged without causing interference between the members, and the automatic transmission can be configured in a compact manner in the axial direction as compared to the case where the second clutch and the fourth clutch are arranged next to each other in the axial direction.

In the automatic transmission according to the aspect of the present invention, the first clutch, the third clutch, and the first brake may be placed on an axially opposite side of the output member from the planetary gear set.

Thus, since the first clutch, the third clutch, and the first brake may be placed on the axially opposite side of the output member from the planetary gear set, the first clutch, the third clutch, and the first brake can be arranged in a compact manner without causing interference between the members. Moreover, the structure on the axially opposite side of the output member from the planetary gear set can be made similar to the structure of the existing automatic transmission. Thus, the automatic transmission of the present invention and the existing automatic transmission can be produced on a common production line, whereby the automatic transmission capable of achieving ten forward speeds and one reverse speed can be provided at low cost.

DETAILED DESCRIPTION OF THE EMBODIMENTS

First Embodiment

A first embodiment of the present invention will be described below with reference toFIGS. 1 to 4. First, the general configuration of an automatic transmission11to which the present invention can be applied will be described with reference toFIG. 1. As shown inFIG. 1, the automatic transmission11that is preferably used for, for example, front-engine, front-drive (FF) type vehicles has an input shaft11of the automatic transmission11which can be connected to an engine (drive source)2, and includes a torque converter4and a speed change mechanism51which are disposed about the axial direction of the input shaft11.

In the automatic transmission11that is described below and is preferably mounted on an FF type vehicle, the lateral direction in the figures actually corresponds to the lateral direction of the vehicle, and as used herein, the “front side” refers to the engine2side of a power transmission path in the axial direction, and the “rear side” refers to the opposite side of the power transmission path from the engine2in the axial direction.

The torque converter4has a pump impeller4aconnected to the input shaft11of the automatic transmission11, and a turbine runner4bto which rotation of the pump impeller4ais transmitted via working fluid. The turbine runner4bis connected to an input shaft12of the speed change mechanism51which is disposed coaxially with the input shaft11. The torque converter4is provided with a lockup clutch7. When the lockup clutch7is engaged by hydraulic control of a hydraulic control device, not shown, the input shaft11of the automatic transmission11is directly drivingly coupled to the input shaft12of the speed change mechanism51.

The speed change mechanism51is provided with a planetary gear (reduction planetary gear) SP and a planetary gear unit (planetary gear set) PU on the axis of the input shaft12and an intermediate shaft14(seeFIG. 4) coupled to the input shaft12. The planetary gear SP is a so-called single-pinion planetary gear which includes a first sun gear S1, a first carrier CR1, and a first ring gear R1, and in which the first carrier CR1has a single pinion P1meshing with the first sun gear S1and the first ring gear R1and rotatably supports the pinion P1.

The planetary gear unit PU has a second sun gear S2, a third sun gear S3, a second carrier CR2, a second ring gear R2, and a third ring gear R3as five rotating elements. In the planetary gear unit PU, The second carrier CR2has a short pinion PS meshing with the third sun gear S3, and a stepped pinion PST having a small diameter portion PSTa meshing with the short pinion PS and a large diameter portion PSTb meshing with the second sun gear S2, and rotatably supports the short pinion PS and the stepped pinion PST.

The first sun gear S1of the planetary gear SP is connected to a boss portion3bintegrally fixed to a case3described in detail below, and is held stationary. The first ring gear R1is connected to the input shaft12, and makes the same rotation (hereinafter referred to as the “input rotation”) as that of the input shaft12. Moreover, the first carrier CR1makes decelerated rotation that is decelerated from the input rotation by the first sun gear S1held stationary and the first ring gear R1making the input rotation, and is connected to a first clutch C-1and a third clutch C-3.

The second sun gear S2of the planetary gear unit PU is connected to a first brake B-1formed by a band brake, and can be locked (fixed) with respect to the case3. The second sun gear S2of the planetary gear unit PU is also connected to the third clutch C-3, so that the second sun gear S2can receive the decelerated rotation of the first carrier CR1via the third clutch C-3. The third sun gear S3is connected to the first clutch C-1, so that the third sun gear S3can receive the decelerated rotation of the first carrier CR1.

Moreover, the second carrier CR2is connected to a fourth clutch C-4that receives the rotation of the input shaft12via the intermediate shaft14, so that the second carrier CR2can receive the input rotation via the fourth clutch C-4. The second carrier CR2is also connected to a second brake B-2, so that the second brake B-2can prevent the second carrier CR2from rotating. In addition, the third ring gear R3is connected to a second clutch C-2that receives the rotation of the input shaft12via the intermediate shaft14, so that the third ring gear R3can receive the input rotation via the second clutch C-2. The third ring gear R3is also connected to a third brake B-3, so that the third brake B-3can prevent the third ring gear R3from rotating. The second ring gear R2is connected to a counter gear (output member)13that outputs rotation to wheels via a countershaft and a differential unit, both not shown.

Functions of the speed change mechanism51will be described based on the above configuration with reference toFIGS. 1,2, and3. In the velocity diagram ofFIG. 3, the ordinate represents the rotational speed of each rotating element (each gear), and the abscissa corresponds to the gear ratio of the rotating elements. In the portion corresponding to the planetary gear SP in the velocity diagram, the ordinate in the endmost portion in the lateral direction (on the right side inFIG. 3) corresponds to the first sun gear S1, and the ordinate sequentially corresponds to the first carrier CR1and the first ring gear R1leftward in the figure. The gear ratio of the first sun gear S1and the first carrier CR1is “1,” and the gear ratio of the first carrier CR1and the first ring gear R1is “λ1.” “λ1” is the ratio of the number of teeth in the planetary gear SP.

Moreover, in the portion corresponding to the planetary gear unit PU in the velocity diagram, the ordinate in the endmost portion in the lateral direction (on the right side inFIG. 3) corresponds to the third sun gear S3, and the ordinate sequentially corresponds to the second ring gear R2, the third ring gear R3, the second carrier CR2, and the second sun gear S2leftward in the figure. The gear ratio of the second sun gear S2and the second carrier CR2is “1/λ2,” the gear ratio of the third sun gear S3and the second carrier CR2is “0.5789/λ3,” the gear ratio of the second carrier CR2and the second ring gear R2is “1,” and the gear ratio of the second carrier CR2and the third ring gear R3is “0.5789.” “λ2” is the ratio of the number of teeth in a planetary gear portion on the front side (the engine side) meshing with the large diameter portion PSTb of the stepped pinion PST in the planetary gear unit PU, and “λ3” is the ratio of the number of teeth in a planetary gear portion on the rear side (the opposite side from the engine) meshing with the small diameter portion PSTa of the stepped pinion PST in the planetary gear unit PU.

The ratios of the number of teeth λ1, λ2, and λ3are obtained from an optimal number of teeth by determining the sun gear diameter and the ring gear diameter from the outer diameter of a transmission case of an existing automatic transmission (for example, an automatic transmission achieving eight forward speeds and one reverse speed), the outer diameter of an input shaft based on known input torque to the input shaft (due to, for example, engine performance), etc., and determining the pinion diameter and the carrier diameter. The gear ratio of each shift speed described below is the gear ratio obtained by optimizing setting of the ratios of the number of teeth λ1, λ2, and λ3.

For example, at a first forward speed (1st) in the drive (D) range, as shown inFIG. 2, the first clutch C-1and the third brake B-3are engaged. Thus, as shown inFIGS. 1 and 3, rotation of the first carrier CR1that makes decelerated rotation by the first sun gear S1held stationary and the first ring gear R1making the input rotation is input to the third sun gear S3via the first clutch C-1. Since the third brake B-3is locked, the third ring gear R3is prevented from rotating. Thus, the second carrier CR2makes slight reverse rotation, and the decelerated rotation that has been input to the third sun gear S3is output to the second ring gear R2via the second carrier CR2making the slight reverse rotation, and forward rotation at the gear ratio of 5.067 as the first forward speed is output from the counter gear13.

At a second forward speed (2nd), as shown inFIG. 2, the first clutch C-1is engaged, and the second brake B-2is locked. Thus, as shown inFIGS. 1 and 3, rotation of the first carrier CR1that makes decelerated rotation by the first sun gear S1held stationary and the first ring gear R1making the input rotation is input to the third sun gear S3via the first clutch C-1. Since the second brake B-2is locked, the second carrier CR2is prevented from rotating. Thus, the decelerated rotation that has been input to the third sun gear S3is output to the second ring gear R2via the second carrier CR2held stationary, and forward rotation at the gear ratio of 2.621 as the second forward speed is output from the counter gear13.

At a third forward speed (3rd), as shown inFIG. 2, the first clutch C-1is engaged, and the first brake B-1is locked. Thus, as shown inFIGS. 1 and 3, rotation of the first carrier CR1that makes decelerated rotation by the first sun gear S1held stationary and the first ring gear R1making the input rotation is input to the third sun gear S3via the first clutch C-1. Since the first brake B-1is locked, the second sun gear S2is prevented from rotating. Thus, the decelerated rotation that has been input to the third sun gear S3is output to the second ring gear R2via the second carrier CR2making slight forward rotation, and forward rotation at the gear ratio of 1.832 as the third forward speed is output from the counter gear13.

At a fourth forward speed (4th), as shown inFIG. 2, the first clutch C-1and the third clutch C-3are engaged. Thus, as shown inFIGS. 1 and 3, rotation of the first carrier CR1that makes decelerated rotation by the first sun gear S1held stationary and the first ring gear R1making the input rotation is input to the third sun gear S3via the first clutch C-1and is input to the second sun gear S2via the third clutch C-3. The entire planetary gear unit PU is thus brought into a directly coupled state by the decelerated rotation from the planetary gear SP, and forward rotation at the gear ratio of 1.520 as the fourth forward speed is output from the counter gear13.

At a fifth forward speed (5th), as shown inFIG. 2, the first clutch C-1and the fourth clutch C-4are engaged. Thus, as shown inFIGS. 1 and 3, rotation of the first carrier CR1that makes decelerated rotation by the first sun gear S1held stationary and the first ring gear R1making the input rotation is input to the third sun gear S3via the first clutch C-1, and the input rotation is input to the second carrier CR2via the fourth clutch C-4. Accordingly, rotation slightly accelerated with respect to the decelerated rotation by the input rotation due to the decelerated rotation that has been input to the third sun gear83and the second carrier CR2making the input rotation is output to the second ring gear R2, and forward rotation at the gear ratio of 1.248 as the fifth forward speed is output from the counter gear13.

At a sixth forward speed (6th), as shown inFIG. 2, the first clutch C-1and the second clutch C-2are engaged. Thus, as shown inFIGS. 1 and 3, rotation of the first carrier CR1that makes decelerated rotation by the first sun gear S1held stationary and the first ring gear R1making the input rotation is input to the third sun gear S3via the first clutch C-1, and the input rotation is input to the third ring gear R3via the second clutch C-2. Accordingly, the second carrier CR2makes rotation slightly accelerated with respect to the input rotation due to the decelerated rotation that has been input to the third sun gear S3and the third ring gear R3making the input rotation, and the rotation slightly decelerated with respect to the input rotation is output to the second ring gear R2. Thus, forward rotation at the gear ratio of 1.114 as the sixth forward speed is output from the counter gear13.

At a seventh forward speed (7th), as shown inFIG. 2, the second clutch C-2and the fourth clutch C-4are engaged. Thus, as shown inFIGS. 1 and 3, since the second clutch C-2is engaged, the input rotation is input to the third ring gear R3. Moreover, since the fourth clutch C-4is engaged, the input rotation is input to the second carrier CR2. The entire planetary gear unit PU is thus brought into a directly coupled state by the input rotation, and forward rotation at the gear ratio of 1.000 as the seventh forward speed is output from the counter gear13.

At an eighth forward speed (8th), as shown inFIG. 2, the second clutch C-2and the third clutch C-3are engaged. Thus, as shown inFIGS. 1 and 3, rotation of the first carrier CR1that makes decelerated rotation by the first sun gear S1held stationary and the first ring gear R1making the input rotation is input to the second sun gear S2via the third clutch C-3, and the input rotation is input to the third ring gear R3via the second clutch C-2. Accordingly, rotation slightly accelerated with respect to the input rotation due to the decelerated rotation that has been input to the second sun gear S2and the third ring gear R3making the input rotation is output to the second ring gear R2, and forward rotation at the gear ratio of 0.968 as the eighth forward speed is output from the counter gear13.

At a ninth forward speed (9th), as shown inFIG. 2, the second clutch C-2is engaged and the first brake B-1is locked. Thus, as shown inFIGS. 1 and 3, since the first brake B-1is locked, the second sun gear S2is prevented from rotating. Moreover, the input rotation is input to the third ring gear R3via the second clutch C-2. Accordingly, rotation slightly accelerated with respect to the eighth forward speed by the second sun gear S2held stationary and the third ring gear R3making the input rotation is output to the second ring gear R2, and forward rotation at the gear ratio of 0.912 as the ninth forward speed is output from the counter gear13.

At a tenth forward speed (10th), as shown inFIG. 2, the fourth clutch C-4and the first brake B-1are engaged. Thus, as shown inFIGS. 1 and 3, since the first brake B-1is locked, the second sun gear S2is prevented from rotating. Moreover, the input rotation is input to the second carrier CR2via the fourth clutch C-4. Accordingly, rotation slightly accelerated with respect to the ninth forward speed by the second sun gear S2held stationary and the second carrier CR2making the input rotation is output to the second ring gear R2, and forward rotation at the gear ratio of 0.717 as the tenth forward speed is output from the counter gear13.

At this tenth forward speed (10th), the tenth forward speed is achieved by meshing only in the planetary gear portion on the front side (the engine side) in the planetary gear unit PU. That is, the tenth forward speed is achieved by meshing at two locations, namely, meshing between the second sun gear S2and the large diameter portion PSTb of the stepped pinion PST, and meshing between the large diameter portion PSTb of the stepped pinion PST and the second ring gear R2. This minimizes gear meshing loss at the maximum shift speed at which the number of meshing locations in the planetary gear unit PU is the smallest, and which is likely to be used for a relatively long time on highways or the like.

At a reverse speed (Rev), as shown inFIG. 2, the third clutch C-3is engaged, and the second brake B-2is locked. Thus, as shown inFIGS. 1 and 3, rotation of the first carrier CR1that makes decelerated rotation by the first sun gear S1held stationary and the first ring gear R1making the input rotation is input to the second sun gear S2via the third clutch C-3. Since the second brake B-2is locked, the second carrier CR2is prevented from rotating. Thus, the decelerated rotation that has been input to the second sun gear S2is output as reverse rotation to the second ring gear R2via the second carrier CR2held stationary, and reverse rotation at the gear ratio of 3.848 as the reverse speed is output from the counter gear13.

This automatic transmission11can also achieve a reverse speed ((Rev)) having a large gear ratio as shown inFIG. 3. In this case, the third clutch C-3is engaged, and the third brake B-3is latched. Thus, as shown inFIGS. 1 and 3, rotation of the first carrier CR1that makes decelerated rotation by the first sun gear S1held stationary and the first ring gear R1making the input rotation is input to the second sun gear S2via the third clutch C-3. Since the third brake B-3is locked, the third ring gear R3is held stationary. Thus, the decelerated rotation that has been input to the second sun gear S2is output as reverse rotation to the second ring gear R2via the second carrier CR2making slight forward rotation by the third ring gear R3is prevented from rotating, and the reverse rotation as the reverse speed having the large gear ratio is output from the counter gear13.

This automatic transmission11can also achieve an eleventh forward speed by engaging the second clutch C-2and engaging the second brake B-2(see, for example,FIG. 3). However, this automatic transmission11does not achieve this eleventh forward speed because it requires disengagement of the fourth clutch C-4and the first brake B-1from the tenth forward speed and engagement of the second clutch C-2and locking of the second brake B-2, namely, it requires engagement/disengagement of the four friction engagement elements. In the case where the automatic transmission11does not achieve the tenth forward speed and achieves the eleventh forward speed described above, it requires disengagement of the first brake B-1and engagement of the second brake B-2with the second clutch C-2being held engaged, namely, it requires engagement/disengagement of only two friction engagement elements. However, this is not preferable because the gear ratio step becomes too large.

In a parking (P) range and a neutral (N) range, for example, the first clutch C-1, the second clutch C-2, the third clutch C-3, and the fourth clutch C-4are disengaged. Thus, the first carrier CR1is disconnected from the third sun gear S3, and the first carrier CR1is disconnected from the second sun gear S2. Namely, the planetary gear DP is disconnected from the planetary gear unit PU. Moreover, the input shaft12(the intermediate shaft14) is disconnected from the second carrier CR2, and the input shaft12(the intermediate shaft14) is disconnected from the third ring gear R3. Thus, power transmission between the input shaft12and the planetary gear unit PU is cut off. Namely, power transmission between the input shaft12and the counter gear13is cut off.

The general configuration of the speed change mechanism51, especially the relative positional relation between the components, will be briefly described with reference toFIG. 4.

In the following description, each of the terms “clutch” (the first to fourth clutches C-1to C-4) and “brake” (the first to third brakes B-1to B-3) is used as including friction plates (outer and inner friction plates) and a hydraulic servo that engages and disengages the clutch or brake.

As shown inFIG. 1, the speed change mechanism51is accommodated in the case3, and an oil pump unit6serves as a partition wall on the front side of the case3, and closes the front side of the case3. A sleeve-like boss portion6aextended toward the rear side is formed on the inner peripheral side of the oil pump unit6, and a hollow stator shaft8that supports a stator of the torque converter4, not shown, is fixedly attached to the inner peripheral side of the boss portion6a. The boss portion6aof the oil pump unit6and the stator shaft8form the boss portion3bof the case3in a broad sense. A boss portion3aextended toward the front side is formed in an inner peripheral portion on the rear side of the case3.

The input shaft12and the intermediate shaft14, which are spline coupled together approximately in the center to form a single shaft, are placed in the central portions of the boss portions3a,3b. The input shaft12and the intermediate shaft14are rotatably supported with both ends thereof being supported by the boss portions3a,3b.

An axially front portion of the speed change mechanism51will be described. The planetary gear SP, the first clutch C-1, the third clutch C-3, and the first brake B-1are placed on the outer peripheral side of the input shaft12, specifically on the axially opposite side of the counter gear13described in detail below from the planetary gear unit PU.

More specifically, in the planetary gear SP, the first sun gear S1is spline coupled and fixed to the tip end of the boss portion3b, and the first carrier CR1that rotatably supports the pinion P1is placed on the outer peripheral side of the first sun gear S1. Moreover, the first ring gear R1is placed on the outer peripheral side of the pinion P1. The first ring gear R1extends on the rear side of the first carrier CR1, and is coupled to the input shaft12.

A side plate on the front side of the first carrier CR1is coupled to a hub member29placed so as to cover the outer peripheral side of the first ring gear R1. Friction plates41of the third clutch C-3are placed on the outer peripheral side of the front side of the hub member29. A hydraulic servo40of the third clutch C-3is placed on the front side of the planetary gear SP, and is contained, together with the friction plates41, in a clutch drum42. The clutch drum42is rotatably supported on the boss portion3b.

A brake band61of the first brake B-1formed by a band brake is placed around the outer peripheral side of the clutch drum42. The end on the rear side of the clutch drum42is coupled to a coupling member48by spline coupling, and the coupling member48is coupled by spline coupling to the outer peripheral side of an extended portion47extending from the second sun gear S2and on the inner peripheral side of a center support90. A hydraulic servo (not shown) that tightens the brake band61of the first brake B-1so that the clutch drum42can be locked is placed so as to be adjacent to the outer peripheral side of the clutch drum42.

The friction plates41of the first clutch C-1are placed on the outer peripheral side of the rear side of the hub member29. A hydraulic servo20of the first clutch C-1is placed on the rear side of the planetary gear SP, and is contained, together with friction plates21, in a clutch drum22. The clutch drum42is rotatably supported on the input shaft12. The end on the rear side of the clutch drum22is coupled by spline coupling to the outer peripheral side of an extended portion27extending from the third sun gear S3and on the inner peripheral side of the center support90.

The above arrangement structure of the planetary gear SP, the first clutch C-1, the third clutch C-3, and the first brake B-1is the arrangement structure similar to that of, for example, the existing automatic transmission that achieves six forward speeds and one reverse speed (see JP 2000-220704 A). The number of teeth of each gear of the planetary gear SP need only be changed, and substantially the same parts can be used as they are. Accordingly, like the existing automatic transmission that achieves six forward speeds and one reverse speed, for example, the first clutch C-1, the third clutch C-3, and the first brake B-1can be arranged in a compact manner without causing interference between the members, and the above automatic transmission and the existing automatic transmission can be produced on a common production line.

Moreover, since the above arrangement structure of the planetary gear SP, the first clutch C-1, the third clutch C-3, and the first brake B-1is similar to that of, for example, the existing automatic transmission that achieves six forward speeds and one reverse speed, the center support90and the counter gear13which are adjacent to these elements can be placed in a manner similar to that of the exiting automatic transmission that achieves six forward speeds and one reverse speed. Thus, the countershaft and the differential unit, both not shown, can be arranged in a similar arrangement structure, and the above automatic transmission and the existing automatic transmission can be produced on a common production line.

That is, the front half portion with respect to the planetary gear unit PU in the speed change mechanism51can be configured in a manner similar to that of the existing automatic transmission that achieves six forward speeds and one reverse speed. Thus, the rear half portion of the automatic transmission11where the planetary gear unit PU etc. is placed may be slightly extended rearward in the axial direction, but the rear half portion is configured not to have a large diameter so as not to interfere with the countershaft and the differential unit. This more easily allows this automatic transmission11and the existing automatic transmission to be produced on a common production line.

The structure of the rear half portion of the speed change mechanism51will be described below. The planetary gear unit PU, the second clutch C-2, the fourth clutch C-4, the second brake B-2, and the third brake B-3are arranged on the outer peripheral side of the intermediate shaft14on the axially opposite side of the counter gear13from the planetary gear SP.

More specifically, in the planetary gear unit PU, the third sun gear S3together with its extended portion27is rotatably supported and placed on the outer peripheral side of the intermediate shaft14, and a plurality of short pinions PS (seeFIG. 1) are arranged so as to be evenly distributed in the circumferential direction on the outer peripheral side of the tooth surface of the third sun gear S3.

The second sun gear S2together with its extended portion47is rotatably supported and placed on the outer peripheral side of the extended portion27of the third sun gear S3. A plurality of stepped pinions PST are arranged so as to be evenly distributed in the circumferential direction on the outer peripheral side of the plurality of short pinions PS and the outer peripheral side of the tooth surface of the third sun gear S3so as to extend between the short pinions PS and the third sun gear S3. As described above, the small diameter portion PSTa of each stepped pinion PST meshes with a corresponding one of the short pinions PS, and the large diameter portion PSTb of each stepped pinion PST meshes with the second sun gear S2. The plurality of short pinions PS and the plurality of stepped pinions PST are rotatably supported by the second carrier CR2as a frame member having both side plates coupled by a bridge (not shown).

The third ring gear R3is placed on the outer peripheral side of the small diameter portion PSTa of each stepped pinion PST so as to mesh therewith, and the second ring gear R2is placed on the outer peripheral side of the large diameter portion PSTb of each stepped pinion PST so as to mesh therewith. The front side of the second ring gear R2is coupled to the counter gear13rotatably supported by the center support90.

The bridge (not shown) of the second carrier CR2extends between the stepped pinions PST in the circumferential direction, and a hub member79extending on the outer peripheral side of the second ring gear R2is fixedly attached to the bridge. Friction plates71of the second brake B-2are arranged between the outer peripheral side of the hub member79and the case3, and a hydraulic servo70of the second brake B-2is placed on the front side of the friction plates71so as to overlap the outer peripheral side of the second ring gear R2.

On the other hand, a hub member89covering the rear side of the planetary gear unit PU and extending on the outer peripheral side of the third ring gear R3is fixedly attached to the rear side of the third ring gear R3. Friction plates81of the third brake B-3are arranged between the outer peripheral side of the hub member89and the case3, and a hydraulic servo80of the third brake B-3is placed on the rear side of the friction plates81so as to overlap the outer peripheral sides of the second clutch C-2and the fourth clutch C-4described below.

Thus, the friction plates71of the second brake B-2and the friction plates81of the third brake B-3are placed on the outer peripheral side of the planetary gear unit PU so as to overlap in the axial direction as viewed in the radial direction, whereby the second brake B-2and the third brake B-3can be placed without causing interference between the members. Since the friction plates71of the second brake B-2and the friction plates81of the third brake B-3are arranged within the range of the axial position of the planetary gear unit PU, the speed change mechanism51can be configured in a compact manner in the axial direction.

A hub member39extending rearward is fixedly attached to the rear side of the hub member89. Friction plates31of the second clutch C-2are arranged between the outer peripheral side of the hub member39and the hydraulic servos80of the third brake B-3. On the rear side of the friction plates31, a hydraulic servo30of the second clutch C-2is placed on the outer peripheral side of a hydraulic servo50of the fourth clutch C-4described below. The hydraulic servo30of the second clutch C-2together with the friction plates31and the fourth clutch C-4is contained in a clutch drum32configured integrally with the intermediate shaft14. That is, the hydraulic servo30of the second clutch C-2forms the outer one of the two hydraulic servos, that is, the inner and outer hydraulic servos formed like a two-story structure. The clutch drum32is rotatably supported on the boss portion3a.

On the rear side of the hub member89, a hub member59extending rearward is placed on the inner peripheral side of the second clutch C-2so as to be spline coupled to the rear side plate of the second carrier CR2at a position on the inner peripheral side of the hub member89. Friction plates51of the fourth clutch C-4are arranged between the outer peripheral side of the hub member59and the hydraulic servo30of the second clutch C-2.

The hydraulic servo50of the fourth clutch C-4is placed on the inner peripheral side of the hydraulic servo30of the second clutch C-2at a position located on the rear side and the inner peripheral side of the friction plates51. The hydraulic servo50of the fourth clutch C-4together with the second clutch C-2is contained in the clutch drum32. The hydraulic servo50of the fourth clutch C-4is placed on the inner peripheral side of a clutch drum52fixedly attached to the front side of the clutch drum32and containing the friction plates51. As described above, the hydraulic servo50of the fourth clutch C-4forms the inner one of the two hydraulic servos formed like a two-story structure.

As described above, the hydraulic servo30of the second clutch C-2and the hydraulic servo50of the fourth clutch C-4are placed on the axially opposite side of the planetary gear unit PU from the counter gear13, and the hydraulic servo30of the second clutch C-2is placed on the outer peripheral side of the hydraulic servo50of the fourth clutch C-4so as to overlap the hydraulic servo50in the axial direction as viewed in the radial direction. Thus, the second clutch C-2and the fourth clutch C-4can be arranged without causing interference between the members, and the speed change mechanism51can be configured in a compact manner in the axial direction as compared to the case where the second clutch C-2and the fourth clutch C-4are arranged side by side in the axial direction.

According to the automatic transmission1described above, as shown inFIG. 2, the step between the first forward speed and the second forward speed is 1.933, the step between the second forward speed and the third forward speed is 1.431, the step between the third forward speed and the fourth forward speed is 1.205, the step between the fourth forward speed and the fifth forward speed is 1.218, the step between the fifth forward speed and the sixth forward speed is 1.120, the step between the sixth forward speed and the seventh forward speed is 1.114, the step between the seventh forward speed and the eighth forward speed is 1.033, the step between the eighth forward speed and the ninth forward speed is 1.061, and the step between the ninth forward speed and the tenth forward speed is 1.272. Thus, the automatic transmission11capable of obtaining a relatively satisfactory step ratio between the shift speeds can be provided.

The gear spread from the minimum shift speed to the maximum shift speed (the gear ratio of the first forward speed 5.067/the gear ratio of the tenth forward speed 0.717) can be made as large as 7.067. This makes it easier to optimize the engine speed usage region with respect to the vehicle speed in a vehicle having the automatic transmission11mounted thereon, and can improve fuel economy.

Moreover, since the tenth forward speed as the maximum shift speed is achieved by engagement of the fourth clutch C-4and the first brake B-1, the maximum shift speed can be obtained by meshing at only two locations, namely, meshing between the second sun gear S2and the large diameter portion PSTb of the stepped pinion PST and meshing between the second ring gear R2and the large diameter portion PSTb of the stepped pinion PST. This can minimize gear meshing loss at the maximum shift speed that is used for a relatively long time, and can improve fuel economy.

With the configuration of the automatic transmission11, the automatic transmission can be configured by replacing a long pinion of a Ravigneaux type planetary gear set with a stepped pinion and adding the third ring gear R3, the second clutch C-2, and the third brake B-3to, for example, the existing automatic transmission (see JP 2000-220704 A). Moreover, the automatic transmission having a relatively satisfactory step ratio and an increased gear spread as described above can be configured substantially without changing the size of the existing automatic transmission.

In other words, the automatic transmission having a satisfactory step ratio and a satisfactory gear spread with respect to the existing automatic transmission can be configured under significant restrictions such as size restriction and restriction of the production line of automatic transmissions. Thus, this automatic transmission can be manufactured by using a large part of the production line of the existing automatic transmission, which eliminates the need for cost to newly construct a production line. Therefore, the automatic transmission capable of achieving ten forward speeds and one reverse speed can be provided at low cost.

It should be understood that since the output member is formed by the counter gear13placed between the planetary gear SP and the planetary gear unit PU in the axial direction, the automatic transmission11can be used in a preferable manner in vehicles in which an output shaft (crankshaft) of the engine2is placed transversely with respect to the travel direction of the vehicle.

Second Embodiment

A second embodiment in which the first embodiment is partially modified will be described with reference toFIGS. 5 to 8. In the second embodiment, portions similar to those of the automatic transmission11according to the first embodiment will be denoted by the same reference characters, and description thereof will be omitted.

An automatic transmission12according to the second embodiment is different from the first embodiment in that the planetary gear SP outputting the decelerated rotation shown inFIGS. 1 and 4is replaced with a double pinion planetary gear shown inFIGS. 5 and 8. Specifically, in a planetary gear DP, a first carrier CR1has a first pinion P1meshing with a first sun gear S1, and a second pinion P2meshing with the first pinion P1and a first ring gear R1, and rotatably supports the first pinion P1and the second pinion P2.

As shown inFIGS. 5 and 8, this planetary gear SP is configured so that the first sun gear S1is fixed to a boss portion3b, the first carrier CR1is coupled to an input shaft12, and the first ring gear R1is formed integrally with a hub member29that is drivingly coupled to friction plates21of a first clutch C-1and friction plates41of a third clutch C-3, namely, decelerated rotation is output from the first ring gear R1.

In the case where the planetary gear DP that outputs the decelerated rotation is formed by the double pinion planetary gear as described above, a large speed reduction ratio can be achieved even if the double pinion planetary gear has substantially the same diameter as that of the single pinion planetary gear of the first embodiment, as shown inFIG. 7.

Thus, as shown inFIG. 6, by optimizing setting of the ratios of the number of teeth λ1, λ2, and λ3, the gear ratio of the first forward speed can be set to 6.198, the gear ratio of the second forward speed can be set to 3.444, the gear ratio of the third forward speed can be set to 2.447, the gear ratio of the fourth forward speed can be set to 2.083, the gear ratio of the fifth forward speed can be set to 1.459, the gear ratio of the sixth forward speed can be set to 1.212, the gear ratio of the seventh forward speed can be set to 1.000, the gear ratio of the eighth forward speed can be set to 0.952, the gear ratio of the ninth forward speed can be set to 0.912, and the gear ratio of the tenth forward speed can be set to 0.733.

Thus, according to the automatic transmission12, as shown inFIG. 6, the step between the first forward speed and the second forward speed is 1.800, the step between the second forward speed and the third forward speed is 1.407, the step between the third forward speed and the fourth forward speed is 1.175, the step between the fourth forward speed and the fifth forward speed is 1.428, the step between the fifth forward speed and the sixth forward speed is 1.204, the step between the sixth forward speed and the seventh forward speed is 1.212, the step between the seventh forward speed and the eighth forward speed is 1.050, the step between the eighth forward speed and the ninth forward speed is 1.044, and the step between the ninth forward speed and the tenth forward speed is 1.244. Thus, the automatic transmission12capable of obtaining a relatively satisfactory step ratio between the shift speeds can be provided.

The gear spread from the minimum shift speed to the maximum shift speed (the gear ratio of the first forward speed 6.198/the gear ratio of the tenth forward speed 0.733) can further be increased to 8.460. This makes it easier to optimize the engine speed usage region with respect to the vehicle speed in a vehicle having the automatic transmission12mounted thereon, and can improve fuel economy.

The planetary gear DP in the second embodiment can use a double pinion planetary gear for use in, for example, the existing automatic transmission that achieves eight forward speeds and one reverse speed, and the production line of the double pinion planetary gear can be used as it is. This eliminates the need for cost to newly construct a production line, and the automatic transmission capable of achieving ten forward speeds and one reverse speed can be provided at low cost.

Since the configuration, functions, and effects of the second embodiment are otherwise similar to those of the first embodiment, description thereof will be omitted.

The first and second embodiments are described above with respect to an example in which the automatic transmission of the present invention is used for FF type vehicles. However, it is to be understood that this automatic transmission can be applied to any vehicles in which an output shaft of an engine is placed transversely, such as rear-engine, rear-drive (RR) type vehicles and mid-engine, rear-drive (MR) type vehicles.

The first and second embodiments are described with respect to an example in which the automatic transmission changes the speed of rotation output from the engine2. However, the present invention is not limited to this, and the present invention is also applicable to automatic transmissions that changes the speed of rotation output from a motor generator. That is, the automatic transmission of the present invention can be used for hybrid vehicles and electric cars.

The arrangement of the friction plates of the clutches and brakes and the hydraulic servos of the automatic transmission, the arrangement of the reduction planetary gear, the arrangement of the planetary gear set, the arrangement of the output member, etc. described in the first and second embodiments are shown by way of example, design of the arrangement structure can be changed particularly if a similar coupling relation between the gears and the clutches and brakes is maintained, and such a changed arrangement structure is within the scope of the present invention.

The automatic transmission according to the present invention can be used for vehicles such as passenger cars and trucks, and is preferably used particularly for vehicles that achieve at least ten forward speeds and one reverse speed, achieve downsizing and weight reduction, and are desired to increase the gear spread and to reduce gear meshing loss at the maximum shift speed.