Power train of automatic transmission

A power train of an automatic transmission adapted to realize a shift stage comprising five forward speeds and one reverse speed by two simple planetary gear sets and seven friction elements to thereby enable compactness and lightness of the automatic transmission, the power train comprising: a combined planetary gear set provided by fixedly connecting a planetary carrier of a first signal pinion planetary gear set to a ring gear of a second single pinion planetary gear set, and by fixedly connecting a ring gear of a first single pinion planetary gear set to a planetary carrier of a second single pinion planetary gear set; three input units for causing an input to be variably initiated to any of three actuating elements out of various actuating elements at the combined planetary gear set; two output units for causing an output to be variably initiated from any of two actuating elements out of various actuating elements at the first single pinion planetary gear set; and two brakes actuating reaction forces between the respective gear sets and transmission housing.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to a power train of automatic transmission,
 and more particularly to a power train of automatic transmission adapted
 to initiate a shift stage of five forward speeds and one reverse speed
 with two planetary gear sets and seven friction elements for compactness,
 lightness and decreased power loss at three forward speeds.
 2. Description of the Prior Art
 Generally, an automatic transmission is mounted with a transmission control
 unit for automatically controlling a transmission ratio according to
 running speed of a vehicle and load change. The transmission control unit
 controls a plurality of friction elements mounted at a power train in
 operation or inoperation state to adjust revolution at an output terminal
 by selecting any one of three elements at the planetary gear sets (sun
 gear, ring gear and planetary carrier) as an input element and the others
 as reaction force element.
 Actually, in order to design a power train for outputting a transmission
 ratio on four forward speeds and one reverse speed, a combined planetary
 gear set combining two simple planetary gear sets and at least five
 friction elements should be used.
 Furthermore, the combined planetary gear set has planetary carriers
 directly connected for at least two different elements to be commonly
 used, or for a sun gear to be commonly used, or for planetary carrier and
 ring gear to be directly connected, or for the planetary carrier and the
 ring gear to be directly and commonly connected in direct structure,
 possessing four dependent actuating elements.
 However, there is a problem in the power train thus described in that its
 engine performance cannot be fully utilized in a recent trend of high
 powered engine although a shift stage of four forward speeds and one
 reverse speed can be obtained. In other words, the automatic transmission
 cannot achieve good fuel consumption rate, power and driving performances.
 Lately, as a means for fully utilizing an engine performance at a
 high-powered engine, a power train having a shift stage of five forward
 speeds and one speed has been disclosed for multi-staging the transmission
 ratio. A power train according to the prior art proposed for a shift stage
 of five forward speeds and one reverse speed needs three simple planetary
 gear sets and six friction elements, or a power train that requires three
 simple planetary gear sets and seven friction elements has been provided.
 SUMMARY OF THE INVENTION
 However, there is a problem in the power train for providing a shift stage
 of five forward speeds and one reverse speed according to the prior art
 thus described in that the power train needs three simple planetary gear
 set and six friction elements, or three simple planetary gear sets and
 seven friction elements, thereby complication its structure and making it
 difficult to control.
 Furthermore, there is another problem in that manufacturing cost thereof is
 increased to put a heavy financial burden to a vehicle purchaser and
 decrease sales competitive ness.
 The present invention is disclosed to solve the aforementioned problems and
 it is an object of the present invention to provide a power train of
 automatic transmission adapted to initiate a shift stage of five forward
 speeds and one reverse speed with two simple planetary gear sets and seven
 friction elements. There is another object of the present invention to
 provide a power train of automatic transmission adapted to realize
 compactness and lightness and to decrease a power loss at three forward
 speeds.
 In accordance with the objects of the present invention, there is provided
 a power train of automatic transmission, the power training comprising:
 a combined planetary gear set provided by fixedly connecting a planetary
 carrier of a first signal pinion planetary gear set to a ring gear of a
 second single pinion planetary gear set, and by fixedly connecting a ring
 gear of a first single pinion planetary gear set to a planetary carrier of
 a second single pinion planetary gear set;
 three input means for causing an input to be variably initiated to any of
 three actuating elements out of various actuating elements at the combined
 planetary gear set;
 two output means for causing an output to be variably initiated from any of
 two actuating elements out of various actuating elements at the first
 single pinion planetary gear set; and
 two brakes actuating as reaction force.
 According to the preferable embodiment, the input means comprises:
 a first clutch for being mounted between a sun gear of first single pinion
 planetary gear set and an input axle to variably connect same;
 a second clutch for being mounted between a planetary carrier of second
 single pinion planetary gear set and an input axle to variably connect
 same; and
 a third clutch for being mounted between a sun gear of second single pinion
 planetary gear set and an input axle to variably connect same.
 Also, the output means comprises:
 a fourth clutch for being mounted between a planetary carrier of first
 single pinion planetary gear set and a transfer drive gear to variably
 connect same; and
 a fifth clutch for being mounted between a sun gear of first single pinion
 planetary gear set and a transfer drive gear to variably connect same.
 The brake comprises:
 a first brake for selecting a ring gear as reaction force element between
 the ring gear of first single pinion planetary gear set and a transmission
 housing; and
 a second brake for selecting a sun gear as reaction force element between
 the sun gear of second single pinion planetary gear set and a transmission
 housing.

DETAILED DESCRIPTION OF THE INVENTION
 FIG. 1 is a structural drawing of a power train according to the present
 invention, where rotating power of an engine (E) is converted to a torque
 at a torque converter (T) to be transferred to an input axle 1 of the
 transmission.
 In the present embodiment, the input axle 1 transfers a torque from a
 turbin of the torque converter (T) to a first single pinion planetary gear
 set 3 and second single pinion planetary gear set 5, where power may be
 output through a transfer drive gear 25 variably connected to a sun gear 7
 of the first single pinion planetary gear set 3 and a planetary carrier 9
 according to mutually-complementing action of the first and second single
 pinion planetary gear sets 3 and 5, thereby realizing a clutch hook-up.
 Furthermore, the planetary carrier 9 at the first single pinion planetary
 gear set 3 is directly connected through a ring gear 17 of the second
 single pinion planetary gear set 5 and a power transmission member 19, and
 a ring gear 11 at the first single pinion planetary gear set 3 is directly
 connected via a planetary carrier 15 of the second single pinion planetary
 gear set 5 and a power transmission member 21 to thereby transfer a
 mutually rotating power.
 Input means for inputting a rotating power of the input axle 1 to the
 combined planetary gear set thus constructed comprises a first clutch (C1)
 mounted between the input axle 1 and the sun gear 7 of the first single
 pinion planetary gear set 3 to variably connect same, such that the sun
 gear 7 is actuated as an input element at first, second, and third forward
 speeds (D1, D2 and D3).
 Between the input axle 1 and the planetary carrier 15 of the second single
 planetary gear set 5, there is arranged a second clutch (C2) to allow the
 planetary carrier 15 to act as an input element at third, fourth and fifth
 forward speeds (D3, D4 and D5), and between the input axle 1 and a sun
 gear 13 of the second single pinion planetary gear set 5, there is
 provided a third clutch (C3) to allow the sun gear 13 to act as an input
 element at a reverse shift stage (R).
 Furthermore, a fourth clutch (C4) is mounted between the planetary carrier
 9 of the first single pinion planetary gear set 3 and the transfer drive
 gear 25 to cause the planetary carrier 9 to act as an output element at
 the first, second, third and fourth forward speeds and the reverse shift
 stage (R), such that the rotating power input from the input axle 1 can be
 shifted to thereby be output through the planetary carrier 9 of the first
 single pinion planetary gear set 3 and the sun gear 7, and between the sun
 gear 7 and the transfer drive gear 25, there is provided a fifth clutch
 (C5) to make the sun gear 7 act as an output element at the fifth forward
 speed. The first, second, third, fourth and fifth clutches may use a
 clutch with multiple laminated disc generally utilized in the conventional
 automatic transmission. Furthermore, brakes are provided to adjust
 revolution of an output relative to an input.
 A first brake (B1) formed at the brake is so arranged between a ring gear
 11 of the first single pinion planetary gear set 3 and transmission
 housing 23 as to simultaneously select as a reaction force element the
 ring gear 11 and the planetary carrier 15 of the second single pinion
 planetary gear set 5 at the first forward speed and reverse shift stage
 (R).
 A second brake (B2) is equipped between a sun gear 13 of the second single
 pinion planetary gear set 5 and the transmission housing 23 to select the
 sun gear 13 as a reaction force element at the second, fourth and fifth
 forward speeds.
 It should be noted that a construction is omitted in FIG. 1, where the
 transfer drive gear 25 at the power train is meshed with a transfer driven
 gear (not shown) to transfer power to a differential gear via a final
 decelerating gear, and well-known construction may be used, together with
 other constructions to accomplish objects of the present invention, such
 that description thereto is omitted herefrom.
 The power train of automatic transmission according to the present
 invention thus described selects as an input element any one of the three
 elements (sun gear, planetary carrier and ring gear) at the planetary gear
 set according to actuation and deactivation of friction elements (input
 and output means, and brake means) where actuation and deactivation are
 selected by a transmission control unit (not shown), and selects as a
 reaction force element the other elements, thereby outputting a
 transmission ratio of five forward speeds and one reverse speed described
 below.
 FIG. 2 shows an actuation table of friction elements where actuation and
 deactuation are selected by the transmission control unit.
 When a selector lever (not shown) selects a forward drive (D) range to
 start increasing an openness of a throttle valve, the transmission control
 unit supplies hydraulic pressure to the first, fourth clutches (C1 and C4)
 and first brake (B1) via a hydraulic control system (not shown) in order
 for the power train to output a transmission ratio of a first speed.
 The meaning below saying that a clutch or a brake is actuated defines that
 hydraulic pressure is supplied from a hydraulic control system.
 At this time, an input is initiated by the first clutch (C1) via the sun
 gear 7 at the first single pinion planetary gear set 3, the ring gear 11
 at the first single pinion planetary gear set 3, along with planetary
 carrier 15 at the second single pinion planetary gear set 5 integrally
 connected thereto, is acted as a reaction force element by actuation of
 the first brake (B1), and under this state, an outputer is initiated by
 the fourth clutch (C4) at the first single pinion planetary gear set 3 and
 ring gear 17 at the second single pinion planetary gear set integrally
 connected thereto.
 The planetary carrier 9 at the first single pinion planetary gear set 3 as
 an output element is rotated in the same direction as the input axle 1 by
 this action, to thereby output the largest deceleration ratio provideable
 by the power train according to the present invention, such that a shift
 stage of the first speed is initiated.
 When a vehicle speed is increased in the first speed control state, the
 transmission control unit releases the actuation of the first brake (B1)
 under the first speed state and simultaneously actuates the second brake
 24.
 Successively, an input is realized by the first clutch (C1) via the sun
 gear 7 at the first single pinion planetary gear set 3 while the sun gear
 13 at the second single pinion planetary gear set 5 is acted as reaction
 force by the operation of the second brake (B2).
 Under this state, an output is realized by the fourth clutch (C4) along
 with the planetary carrier 9 at the first single pinion planetary gear set
 3 integratally connected to the ring gear 17 of the second single pinion
 planetary gear set 5.
 Successively, the planetary carrier 9 of the first single pinion planetary
 gear set 3 is rotated as an output element in the same direction as that
 of the input axle 2 to output a faster transmission ratio of second speed
 than that of the first speed.
 When the vehicle speed is increased under this control state of second
 speed, the transmission control unit releases the actuation of the second
 brake (B2) to newly actuate the second clutch (C2), such that an input
 from the input axle 1 is simultaneously transmitted to the sun gear 7 of
 the first single pinion planetary gear set 3 and to the planetary carrier
 15 of the second single pinion planetary gear set 5.
 Successively, same input is transmitted to the ring gear 11 of the first
 single pinion planetary gear set fixedly connected to the planetary
 carrier 15 of the second single pinion planetary gear set 5, and by this
 operation, the first single pinion planetary gear set 3 maintains rotation
 in directly-connected state and again transmits the same input to the ring
 gear 17 of the second single pinion planetary gear set 5 fixedly connected
 to the planetary carrier 9 of the first single pinion planetary gear set
 3, where the combined planetary gear set outputs a third speed
 transmission ratio having the same input and output.
 When a vehicle speed is further increased in a third speed state thus
 described, the transmission control unit releases actuation of the first
 clutch (C1) in the third speed state to thereby actuate the second brake
 (B2).
 Successively, the input via the sun gear 7 of the first single pinion
 planetary gear set 3 is blocked by the first clutch (C1) while an input is
 initiated only through the planetary carrier 15 of the second single
 pinion planetary gear set 5 by the second clutch (C2).
 The sun gear 13 at the second single pinion planetary gear set 5 is
 actuated as reaction force element by actuation of the second brake (B2),
 and the planetary carrier 9 of the first single pinion planetary gear set
 3 outputs power of the engine along with the ring gear 17 of the second
 single pinion planetary gear set 5 integrally connected thereto by way of
 the fourth clutch (C4).
 Successively, the planetary carrier 9 of the first single pinion planetary
 gear set 3 is rotated in the same direction as the input axle 1 as output
 element to increase speed, such that a fourth speed transmission ratio
 faster than that of the third speed is output.
 When a vehicle speed in the fourth speed state is increased, the
 transmission control unit releases the actuation of the fourth clutch (C4)
 in the fourth speed state to newly actuate the fifth clutch (C5).
 By this operation, an input is realized by the second clutch (C2) via the
 planetary carrier 15 of the second single pinion planetary gear set 5 and
 the sun gear 13 at the second single pinion planetary gear set 5 is
 actuated as reaction force element by the actuation of the second brake
 (B2), such that output is realized by the fifth clutch (C5) under this
 state to the sun gear 7 of the first single pinion planetary gear set 3.
 Successively, the sun gear 7 of the first single pinion planetary gear set
 3 as output element is rotated in the same direction as that of the input
 axle 1, such that a faster fifth speed transmission ratio than that of the
 fourth speed is output. In other words, the fourth and fifth speeds
 maintain over drive state.
 Furthermore, when the selector lever selects the reverse (R) range, the
 transmission control unit actuates the third and fourth clutches (C4 and
 C4) and the first brake (B1). By this operation, an input is realized by
 the third clutch (C3) through the sun gear 13 of the second single pinion
 planetary gear set 5, and the ring gear 11 of the first single pinion
 planetary gear set 3 is actuated as reaction force element along with the
 planetary carrier 15 of the second single pinion planetary gear set 5
 fixedly connected thereto, whereby, an output is realized by the fourth
 clutch (C4) in this state to the planetary carrier 9 of the first single
 pinion planetary gear set 3.
 Successively, the planetary carrier 9 of the first single pinion planetary
 gear set 3 as output element is reversely rotated relative to the input
 axle 1 and an output is realized thereby, whereby a reverse transmission
 ratio is output.
 As apparent from the foregoing, there is an advantage in the power train of
 automatic transmission according to the present invention thus described
 in that a shift stage comprising forward five speeds and one reverse speed
 can be realized by two simple planetary gear sets and seven friction
 elements to thereby enable compactness and lightness of the automatic
 transmission. Furthermore, there is another advantage in that unnecessary
 power loss can be minimized at the third forward speed stage according to
 idle racing.