Patent Publication Number: US-10766352-B2

Title: Power transmission apparatus for a vehicle

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2018-0091541, filed on Aug. 7, 2018, the entire contents of which are incorporated herein by reference. 
     FIELD 
     The present disclosure relates to a power transmission apparatus for a vehicle. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     An environmentally-friendly technology of a vehicle is a core technology which controls survival of a future automobile industry, and advanced car makers have focused on the development of an environmentally-friendly vehicle to comply with regulations for environment and fuel efficiency. 
     An electric vehicle (EV) or a hybrid electric vehicle (HEV) that utilizes electrical energy, or a double clutch transmission (DCT) improving efficiency and convenience of a transmission may be examples of such future vehicle technology. 
     The double clutch transmission (DCT) includes two clutches devices and a gear train of a basically manual transmission, selectively transmits a torque input from an engine to two input shafts by using the two clutches devices, and outputs a torque shifted by the gear train. 
     Such a double clutch transmission (DCT) attempts to compactly realize a multi-stage transmission of more than five speeds. The DCT achieves an automated manual transmission (AMT) that removes the inconvenience of a manual shifting of a driver, by controlling two clutches and synchronizing devices by a controller. 
     In comparison with an automatic transmission using planetary gears, such a DCT shows merits, such as higher efficiency in power delivery, easier modification in revising or adding parts in order to achieve more shift-stages, etc., and thus gathers more spotlight since it can more comfortably conform to fuel consumption regulations and efficiency in achieving more shift-stages. 
     The above information disclosed in this Background section is only for enhancement of understanding of the background of the present disclosure and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art. 
     SUMMARY 
     The present disclosure provides a power transmission apparatus for a vehicle having an advantage of achieving shift-stages in an electric vehicle mode and in a parallel hybrid mode by employing a simple arrangement of a planetary gear set and a motor/generator to a double clutch scheme, thereby improving fuel consumption and better applicability to a hybrid vehicle. 
     An exemplary power transmission apparatus is for a vehicle having an engine and a motor/generator. The power transmission apparatus may include: a first input, a second input shaft, a third input shaft, a torque mediating shaft, a first intermediate shaft, a second intermediate shaft, a first shifting section, a second shifting section, and an output shaft. The first input shaft may be selectively connected with the motor/generator. The second input shaft may be formed as a hollow shaft, disposed coaxial with and external to the first input shaft without rotational interference, and selectively connected with the motor/generator. The third input shaft may be formed as a hollow shaft, disposed coaxial with and external to the second input shaft without rotational interference, and selectively connected with the motor/generator. The torque mediating shaft may be formed as a hollow shaft disposed coaxial with and external to the first input shaft without rotational interference. The first intermediate shaft may be disposed in parallel with the first input shaft. The second intermediate shaft may be disposed in parallel with the first input shaft, and selectively connected with a transmission housing. The first shifting section may include five gear sets (i.e., a first gear set, a second gear set, a third gear set, a fourth gear set, and a fifth gear set) disposed on the first and third input shafts, the first and second intermediate shafts, and the torque mediating shaft. The first shifting section may selectively receive torque through the first and third input shafts and provide a plurality of intermediate shift-stages shifted from the received torque. The second shifting section may include a planetary gear set having a sun gear fixedly connected with the torque mediating shaft, form an output torque by combination of a torque selectively transmitted from the first shifting section and a torque selectively input through the second input shaft, and output the output torque to the output shaft through the one gear set selected among the first, second, third, fourth and fifth gear sets of the first shifting section. The output shaft may be disposed coaxially with and selectively connected with the second intermediate shaft and output a torque received from the first and second shifting sections. 
     The first gear set may include a first drive gear fixedly connected with the third input shaft and a first driven gear fixedly connected with the first intermediate shaft and externally gear-meshed with the first drive gear. The second gear set may include a second drive gear disposed coaxial with and external to the first intermediate shaft without rotational interference, an intermediate gear fixedly connected with the torque mediating shaft and externally gear-meshed with the second drive gear, and a second driven gear fixedly connected with the second intermediate shaft and externally gear-meshed with the intermediate gear. The third gear set may include a third drive gear fixedly connected with the first input shaft, and a third driven gear rotatably disposed on an external circumference of the second intermediate shaft without rotational interference and externally gear-meshed with the third drive gear. The fourth gear set may include a fourth drive gear fixedly connected with the first input shaft, and a fourth driven gear rotatably disposed on an external circumference of the second intermediate shaft without rotational interference and externally gear-meshed with the fourth drive gear. The fifth gear set may include a fifth drive gear disposed coaxial with and external to the first intermediate shaft without rotational interference, and a fifth driven gear fixedly connected with the second intermediate shaft and externally gear-meshed with the fifth drive gear. 
     The third driven gear and the fourth driven gear are selectively connected with the second intermediate shaft through a first synchronizer; and 
     The second drive gear and the fifth drive gear are selectively connected with the first intermediate shaft through a second synchronizer. 
     Gear ratios of the first gear set and the second gear set may be used for realizing the forward second speed and the forward sixth speed. A gear ratio of the third gear set may be used for realizing the forward first speed and the forward seventh speed. A gear ratio of the fourth gear set may be used for realizing the forward third speed and the forward fifth speed. A gear ratio of the fifth gear set may be used for realizing the forward ninth speed and the reverse speed in cooperation with the gear ratio of the first gear set. 
     A sun gear of the planetary gear set may be fixedly connected with the torque mediating shaft. A planet carrier of the planetary gear set may be fixedly connected with the second input shaft. A ring gear of the planetary gear set may be externally gear-meshed with the output shaft through the sixth gear set. 
     The sixth gear set may include a sixth drive gear fixedly connected with the ring gear of the planetary gear set, and a sixth driven gear fixedly connected with the output shaft and externally gear-meshed with the sixth drive gear. 
     The planetary gear set may be a single pinion planetary gear set. 
     The power transmission apparatus may further include five clutches each selectively connecting a corresponding pair among the first, second and third input shafts, the torque mediating shaft, and the first and second intermediate shafts, and a brake selectively connecting a corresponding shaft selected among the first, second and third input shafts, the torque mediating shaft, and the first and second intermediate shafts to the transmission housing. 
     The five clutches may include an engine clutch arranged between an engine output shaft of the engine and a motor shaft of the motor/generator, a first clutch arranged between the motor shaft and the first input shaft, a second clutch arranged between the motor shaft and the second input shaft, a third clutch arranged between the motor shaft and the third input shaft, and a fourth clutch arranged between the second intermediate shaft and the output shaft. The brake may be arranged between the second intermediate shaft and the transmission housing. 
     The first and second shifting sections may be disposed in the order of the second shifting section and the first shifting section from the engine. 
     A power transmission apparatus for a vehicle according to an exemplary form of the present disclosure realizes shift-stages of nine forward speeds and one reverse speed by employing a planetary gear set and two synchronizers to a multiple clutch transmission, thereby enabling multiple shift-stages by a simplified arrangement, improving installability, and reducing an overall weight. 
     In addition, an exemplary form of the present disclosure may receive torque from a motor/generator as well as an engine, such that a vehicle may be driving in an electric vehicle mode and parallel hybrid mode, thereby improving fuel consumption. 
     Further, effects that can be obtained or expected from exemplary forms of the present disclosure are directly or suggestively described in the following detailed description. That is, various effects expected from exemplary forms of the present disclosure will be described in the following detailed description. 
     Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       In order that the disclosure may be well understood, there will now be described various forms thereof, given by way of example, reference being made to the accompanying drawings, in which: 
         FIG. 1  is a schematic view of a power transmission apparatus for a vehicle according to an exemplary form of the present disclosure; and 
         FIG. 2  is a shifting operational chart of a power transmission apparatus for a vehicle according to an exemplary form of the present disclosure. 
     
    
    
     The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. 
     As those skilled in the art would realize, the described forms may be modified in various different ways, all without departing from the spirit or scope of the present disclosure. 
     In the following description, dividing names of components into first, second and the like is to divide the names because the names of the components are the same as each other and an order thereof is not particularly limited. 
       FIG. 1  is a schematic view of a power transmission apparatus for a vehicle according to an exemplary form of the present disclosure. 
     Referring to  FIG. 1 , a power transmission apparatus shifts torques of an engine ENG as a primary power source and a motor/generator MG as an auxiliary power source, and includes first, second, and third input shafts IS 1 , IS 2 , and IS 3 , a torque mediating shaft TMS, first and second intermediate shafts CS 1  and CS 2 , first and second shifting sections TM 1  and TM 2 , and an output shaft OS. 
     The engine ENG is a primary power source and a variety of typical engines such as a gasoline engine or a diesel engine that uses fossil fuel may be used as the engine ENG. 
     The motor/generator MG as an auxiliary power source may act as a motor and also as a generator, and includes a stator ST and a rotor RT, where the stator ST is fixed to the transmission housing H and the rotor RT is rotatably supported within the stator ST. 
     Torques from the engine ENG and/or the motor/generator MG are supplied to the first shifting section TM 1 , and a plurality of intermediate shift-stages are formed at the first shifting section TM 1  by the supplied torques. Receiving a torque from the first shifting section TM 1  and selectively receiving a torque from the engine ENG through the second input shaft IS 2 , the second shifting section TM 2  performs shifting operation and outputs a shifted torque through the output shaft OS. 
     The first, second, and third input shafts IS 1 , IS 2 , and IS 3  and the torque mediating shaft TMS are disposed on a same axis. The first and second intermediate shafts CS 1  and CS 2  and the output shaft OS are disposed in parallel with the first input shaft IS 1 . The second intermediate shaft CS 2  and the output shaft OS are disposed on a same axis and selectively interconnected with each other. 
     The motor/generator MG is disposed to be rear of the engine ENG. A motor shaft MDS fixedly connected with the rotor RT of the motor/generator MG is selectively connected with an output shaft EOS of the engine ENG interposing an engine clutch ECL. 
     The first input shaft IS 1  is selectively connected with the motor shaft MDS. The first input shaft IS 1  delivers torques from the engine ENG and the motor/generator MG to the first shifting section TM 1   
     The second input shaft IS 2  is formed as a hollow shaft and disposed coaxial with and external to the first input shaft IS 1  without rotational interference, and selectively connected with the motor shaft MDS thereby selectively transmitting torques of the engine ENG and the motor/generator MG to the second shifting section TM 2 . 
     The third input shaft IS 3  is formed as a hollow shaft and disposed coaxial with and external to the second input shaft IS 2  without rotational interference, and selectively connected with the motor shaft MDS thereby transmitting the torques of the engine ENG and the motor/generator MG to the first shifting section TM 1 . 
     The torque mediating shaft TMS is formed as a hollow shaft and disposed coaxial with and external to the first input shaft IS 1 . 
     The second intermediate shaft CS 2  is selectively connected with the transmission housing H through a first brake B 1 , and may be selectively fixed in a rotating direction. 
     The first shifting section TM 1  includes the first and third input shafts IS 1  and IS 3 , the first and second intermediate shafts CS 1  and CS 2 , and first, second, third, fourth, and fifth gear sets GL 1 , GL 2 , GL 3 , GL 4 , and GL 5  disposed on the torque mediating shaft TMS. 
     The second shifting section TM 2  includes a planetary gear set PG. The planetary gear set PG is a single pinion planetary gear set, and includes a sun gear S, a planet carrier PC rotatably supporting a plurality of pinion gears P externally gear-meshed with the sun gear S, and a ring gear R internally gear-meshed with the plurality of pinion gears P. 
     The planetary gear set PG is arranged between the second input shaft IS 2  and the torque mediating shaft TMS. The sun gear S is fixedly connected with the torque mediating shaft TMS. The planet carrier PC is fixedly connected with the second input shaft IS 2 . The ring gear R is externally gear-meshed with the output shaft OS through sixth gear set GL 6 . 
     The first gear set GL 1  includes a first drive gear IDG 1  fixedly connected with the third input shaft IS 3 , and a first driven gear IPG 1  fixedly connected with the first intermediate shaft CS 1  and externally gear-meshed with the first drive gear IDG 1 . 
     The second gear set GL 2  includes a second drive gear IDG 2  rotatably disposed on an external circumference of the first intermediate shaft CS without rotational interference, an intermediate gear ICDG fixedly connected with the torque mediating shaft TMS and externally gear-meshed with the second drive gear IDG 2 , and a second driven gear IPG 2  fixedly connected with the second intermediate shaft CS 2  and externally gear-meshed with the intermediate gear ICDG. 
     The third gear set GL 3  includes a third drive gear IDG 3  fixedly connected with the first input shaft IS 1 , a third driven gear IPG 3  rotatably disposed on an external circumference of the second intermediate shaft CS 2  without rotational interference and externally gear-meshed with the third drive gear IDG 3 . 
     The fourth gear set GL 4  includes a fourth drive gear IDG 4  fixedly connected with the first input shaft IS 1 , a fourth driven gear IPG 4  rotatably disposed on an external circumference of the second intermediate shaft CS 2  without rotational interference and externally gear-meshed with the fourth drive gear IDG 4 . 
     The fifth gear set GL 5  includes a fifth drive gear IDG 5  rotatably disposed on an external circumference of the first intermediate shaft CS 1  without rotational interference, and a fifth driven gear IPG 5  fixedly connected with the second intermediate shaft CS 2  and externally gear-meshed with the fifth drive gear IDG 5 . 
     The sixth gear set GL 6  includes a sixth drive gear IDG 6  fixedly connected with the ring gear R of the planetary gear set PG, and a sixth driven gear IPG 6  fixedly connected with the output shaft OS and externally gear-meshed with the sixth drive gear IDG 6 . 
     The third driven gear IPG 3  and the fourth driven gear IPG 4  selectively connected to the second intermediate shaft CS 2  by a first synchronizer SN 1 . 
     The second drive gear IDG 2  and the fifth drive gear IDG 5  selectively connected to the first intermediate shaft CS 1  by a second synchronizer SN 2 . 
     Gear ratios between drive and driven gears of the first, second, third, fourth, and fifth gear sets GL 1 , GL 2 , GL 3 , GL 4 , GL 5 , and GL 6  may be appropriately set in consideration of transmission requirements. The gear ratios of the first gear set GL 1  and the second gear set GL 2  are used for realizing the forward second speed and the forward sixth speed. The gear ratio of the third gear set GL 3  is used for realizing the forward first speed and the forward seventh speed. The gear ratio of the fourth gear set GL 4  is used for realizing the forward third speed and the forward fifth speed. The gear ratio of the fifth gear set GL 5  is used for realizing the forward ninth speed and the reverse speed in cooperation with the gear ratio of the first gear set GL 1 . 
     The output shaft OS is an output member, and by receiving torques input from the second intermediate shaft CS 2  and from the sixth gear set GL 6 , transmits the received torque to a differential DIFF through the output gear OG and the final reduction gear FDG. 
     In addition, five engagement elements of an engine clutch ECL and first to fourth clutches CL 1 , CL 2 , CL 3 , and CL 4  are disposed between rotating members such as various shafts, and one engagement element of a brake B 1  is disposed between a rotating member and the transmission housing H. 
     The engine clutch ECL is arranged between the engine output shaft EOS (e.g., engine crankshaft) and the motor shaft MDS, and selectively interconnects the engine output shaft EOS and the motor shaft MDS. 
     The first clutch CL 1  is arranged between the motor shaft MDS and the first input shaft IS 1 , and selectively connects the motor shaft MDS and the first input shaft IS 1 . 
     The second clutch CL 2  is arranged between the motor shaft MDS and the second input shaft IS 2 , and selectively connects the motor shaft MDS and the second input shaft IS 2 . 
     The third clutch CL 3  is arranged between the motor shaft MDS and the third input shaft IS 3 , and selectively connects the motor shaft MDS and the third input shaft IS 3 . 
     The fourth clutch CL 4  is arranged between the second intermediate shaft CS 2  and the output shaft OS, and selectively connects the second intermediate shaft CS 2  and the output shaft OS. 
     The first brake B 1  is arranged between the second intermediate shaft CS 2  and the transmission housing H, and therefore, the second intermediate shaft CS 2  and the idle shaft IDS selectively act as fixed elements. 
     The engagement elements of the engine clutch ECL, the first to fourth clutches CL 1  to CL 4 , and the first brake B 1  may be realized as multi-plate hydraulic pressure friction devices that are frictionally engaged by hydraulic pressure, however, it should not be understood to be limited thereto, since various other configuration that are electrically controllable may be available. 
     The first and second synchronizers SN 1  and SN 2  may be formed as a known scheme, and the first and second sleeves SLE 1  and SLE 2  applied to the first and second synchronizers SN 1  and SN 2  may be operated by respective actuators (not shown) that may be controlled by a transmission control unit. 
     According to one form, the second shifting section TM 2  is disposed at a rear side of the engine ENG, and the first shifting section TM 1  is disposed at a rear side of the second shifting section TM 2 . 
       FIG. 2  is a shifting operational chart for a power transmission apparatus for a vehicle according to an exemplary form of the present disclosure, and the power transmission apparatus for a vehicle according to an exemplary form performs shifting operation as follows. 
     [Engine and Parallel Mode Reverse Speed] 
     In the engine and parallel mode reverse speed REV, as shown in  FIG. 2 , the fifth drive gear IDG 5  is synchronously connected to the first intermediate shaft CS 1  by the operation of the sleeve SLE 2  of the second synchronizer SN 2 , and the engine clutch ECL and the third and fourth clutches CL 3  and CL 4  are operated. 
     As a result, by the operation of the engine clutch ECL, the third clutch CL 3  and the second synchronizer SN 2 , the torque of the engine ENG is input to the second intermediate shaft CS 2  through the motor shaft MDS, the third input shaft IS 3 , the first gear set GL 1 , the second synchronizer SN 2 , the first intermediate shaft CS 1 , and the fifth gear set GL 5 . 
     Then, the torque received at the second intermediate shaft CS 2  is transmitted to the differential DIFF through the output shaft OS by the operation of the fourth clutch CL 4 , thereby realizing the reverse speed. 
     [The Engine and Parallel Mode Forward First Speed] 
     In the engine and parallel mode forward first speed FD 1 , as shown in  FIG. 2 , the third driven gear IPG 3  is synchronously connected to the second intermediate shaft CS 2  by the operation of the sleeve SLE 1  of the first synchronizer SN 1 , and the engine clutch ECL and the first, fourth clutch CL 1  and CL 4  are operated. 
     As a result, by the operation of the engine clutch ECL, the first clutch CL 1 , and the first synchronizer SN 1 , the torque of the engine ENG is transmitted to the second intermediate shaft CS 2  through the motor shaft MDS, the first input shaft IS 1 , the third gear set GL 3 , and the first synchronizer SN 1 . 
     Then, the torque received at the second intermediate shaft CS 2  is transmitted to the differential DIFF through the output shaft OS by the operation of the fourth clutch CL 4 , thereby realizing the forward first speed. 
     [The Engine and Parallel Mode Forward Second Speed] 
     In the engine and parallel mode forward second speed FD 2 , as shown in  FIG. 2 , the second drive gear IDG 2  is synchronously connected to the first intermediate shaft CS 1  by the operation of the sleeve SLE 2  of the second synchronizer SN 2 , and the engine clutch ECL and the third and fourth clutches CL 3  and CL 4  are operated. 
     As a result, by the operation of the engine clutch ECL, the third clutch CL 3  and the second synchronizer SN 2 , the torque of the engine ENG is input to the second intermediate shaft CS 2  through the motor shaft MDS, the third input shaft IS 3 , the first gear set GL 1 , the second synchronizer SN 2 , the first intermediate shaft CS 1 , and the second gear set GL 2 . 
     Then, the torque received at the second intermediate shaft CS 2  is transmitted to the differential DIFF through the output shaft OS by the operation of the fourth clutch CL 4 , thereby realizing the forward second speed. 
     [The Engine and Parallel Mode Forward Third Speed] 
     In the engine and parallel mode forward third speed FD 3 , as shown in  FIG. 2 , the fourth driven gear IPG 4  is synchronously connected to the second intermediate shaft CS 2  by the operation of the sleeve SLE 1  of the first synchronizer SN 1 , and the engine clutch ECL and the first, fourth clutch CL 1  and CL 4  are operated. 
     As a result, by the operation of the engine clutch ECL, the first clutch CL 1 , and the first synchronizer SN 1 , the torque of the engine ENG is transmitted to the second intermediate shaft CS 2  through the motor shaft MDS, the first input shaft IS 1 , the fourth gear set GL 4 , and the first synchronizer SN 1 . 
     Then, the torque received at the second intermediate shaft CS 2  is transmitted to the differential DIFF through the output shaft OS by the operation of the fourth clutch CL 4 , thereby realizing the forward third speed. 
     [The Engine and Parallel Mode Forward Fourth Speed] 
     In the engine and parallel mode forward fourth speed FD 4 , as shown in  FIG. 2 , the first and second synchronizers SN 1  and SN 2  are maintained neutral, and the engine clutch ECL and the second, fourth clutch CL 2  and CL 4  are operated. 
     As a result, by the operation of the engine clutch ECL and the second clutch CL 2 , the torque of the engine ENG is input to the planet carrier PC of the planetary gear set PG through the motor shaft MDS and the second input shaft IS 2 . 
     By the operation of the fourth clutch CL 4 , the sixth gear set GL 6 , the output shaft OS, the second intermediate shaft CS 2 , the second gear set GL 2 , and the torque mediating shaft TMS are interconnected, and thereby the ring gear R connected to the sixth gear set GL 6  is connected with the sun gear S connected to the torque mediating shaft TMS. The speed relation between the ring gear R and the sun gear S is formed by the gear ratios of the second and sixth gear sets GL 2  and GL 6 , while the planet carrier PC of the planetary gear set PG receives an input torque through the second input shaft IS 2 . Therefore, the sun gear S and the ring gear R of the planetary gear set PG rotate at respective speeds satisfying the speed relation while the planet carrier PC rotates at the speed of the second input shaft IS 2 . 
     By such a cooperative operation of rotation members of the planetary gear PG, the speed and torque of the output shaft OS connected to the sixth gear set GL 6  is determined and transmitted to the differential DIFF through the output shaft OS, thereby realizing the forward fourth speed. 
     [The Engine and Parallel Mode Forward Fifth Speed] 
     In the engine and parallel mode forward fifth speed FD 5 , as shown in  FIG. 2 , the fourth driven gear IPG 4  is synchronously connected to the second intermediate shaft CS 2  by the operation of the sleeve SLE 1  of the first synchronizer SN 1 , and the engine clutch ECL and the first and second clutches CL 1  and CL 2  are operated. 
     As a result, by the operation of the engine clutch ECL, the first clutch CL 1 , and the first synchronizer SN 1 , the torque of the engine ENG is partially input to the sun gear S of the planetary gear set PG through the motor shaft MDS, the first input shaft IS 1 , the fourth gear set GL 4 , the first synchronizer SN 1 , the second intermediate shaft CS 2 , and the second gear set GL 2 . 
     In addition, by the operation of the second clutch CL 2 , the torque of the engine ENG is partially input to the planet carrier PC of the planetary gear set PG through the motor shaft MDS and the second input shaft IS 2 . 
     Then, the planetary gear set PG realizes shifting based on speed difference between the sun gear S and the planet carrier PC, and outputs the shifted torque to the differential DIFF through the output shaft OS, thereby realizing the forward fifth speed. 
     [The Engine and Parallel Mode Forward Sixth Speed] 
     In the engine and parallel mode forward sixth speed FD 6 , as shown in  FIG. 2 , the second drive gear IDG 2  is synchronously connected to the first intermediate shaft CS 1  by the operation of the sleeve SLE 2  of the second synchronizer SN 2 , and the engine clutch ECL and the second and third clutches CL 2  and CL 3  are operated. 
     As a result, by the operation of the engine clutch ECL and the second clutch CL 2 , the torque of the engine ENG is partially input to the planet carrier PC of the planetary gear set PG through the motor shaft MDS and the second input shaft IS 2 . 
     In addition, by the operation of the third clutch CL 3  and the second synchronizer SN 2 , the torque of the engine ENG is partially input to the sun gear S of the planetary gear set PG through the motor shaft MDS, the third input shaft IS 3 , the first gear set GL 1 , the second synchronizer SN 2 , the first intermediate shaft CS 1 , and the second gear set GL 2 . 
     Then, the planetary gear set PG realizes shifting based on speed difference between the sun gear S and the planet carrier PC, and outputs the shifted torque to the differential DIFF through the output shaft OS, thereby realizing the forward sixth speed. 
     [The Engine and Parallel Mode Forward Seventh Speed] 
     In the engine and parallel mode forward seventh speed FD 7 , as shown in  FIG. 2 , the third driven gear IPG 3  is synchronously connected to the second intermediate shaft CS 2  by the operation of the sleeve SLE 1  of the first synchronizer SN 1 , and the engine clutch ECL and the first and second clutches CL 1  and CL 2  are operated. 
     As a result, by the operation of the engine clutch ECL, the first clutch CL 1 , and the first synchronizer SN 1 , the torque of the engine ENG is partially input to the sun gear S of the planetary gear set PG through the motor shaft MDS, the first input shaft IS 1 , the third gear set GL 3 , the and the first synchronizer SN 1 , the second intermediate shaft OS 2 , and the second gear set GL 2 , torque mediating shaft TMS. 
     In addition, by the operation of the second clutch CL 2 , the torque of the engine ENG is partially input to the planet carrier PC of the planetary gear set PG through the motor shaft MDS and the second input shaft IS 2 . 
     Then, the planetary gear set PG realizes shifting based on speed difference between the sun gear S and the planet carrier PC, and outputs the shifted torque to the differential DIFF through the output shaft OS, thereby realizing the forward seventh speed. 
     [The Engine and Parallel Mode Forward Eighth Speed] 
     In the engine and parallel mode forward eighth speed FD 8 , as shown in  FIG. 2 , the first and second synchronizers SN 1  and SN 2  are maintained neutral, and the engine clutch ECL, the second clutch CL 2 , and the first brake B 1  are operated. 
     As a result, by the operation of the engine clutch ECL and second clutch CL 2 , the torque of the engine ENG is input to the planet carrier PC of the planetary gear set PG through the motor shaft MDS and the second input shaft IS 2 , and by the operation of the first brake B 1 , the sun gear S of the planetary gear set PG acts as a fixed element. 
     Then, since the planet carrier PC of the planetary gear set planetary gear set PG receives input torque while the sun gear S acts as a fixed element, the planetary gear set planetary gear set PG outputs an increased speed through the ring gear R, and the torque output through the ring gear R is transmitted to the differential DIFF through the sixth gear set GL 6  and the output shaft OS, thereby realizing the forward eighth speed. 
     In such a forward eighth speed, the planetary gear set PG outputs a further increased speed than in the forward seventh speed. 
     [The Engine and Parallel Mode Forward Ninth Speed] 
     In the engine and parallel mode forward ninth speed FD 9 , as shown in  FIG. 2 , the fifth drive gear IDG 5  is synchronously connected to the first intermediate shaft CS 1  by the operation of the sleeve SLE 2  of the second synchronizer SN 2 , and the engine clutch ECL and the second and third clutches CL 2  and CL 3  are operated. 
     As a result, by the operation of the engine clutch ECL and the second clutch CL 2 , the torque of the engine ENG is partially input to the planet carrier PC of the planetary gear set PG through the motor shaft MDS and the second input shaft IS 2 . 
     In addition, by the operation of the third clutch CL 3 , the torque of the engine ENG is partially input to the sun gear S of the planetary gear set PG through the motor shaft MDS, the third input shaft IS 3 , the first gear set GL 1 , the first intermediate shaft CS 1 , the second synchronizer SN 2 , the fourth gear set GL 5 , the second intermediate shaft CS 2 , and the second gear set GL 2 . 
     Then, the planetary gear set PG outputs a further increased speed than in the forward eighth speed through the ring gear R, and the torque output through the ring gear R is transmitted to the differential DIFF through the sixth gear set GL 6  and the output shaft OS, thereby realizing the forward ninth speed. 
     In such a forward ninth speed, the planetary gear set PG outputs a further increased speed than in the forward eighth speed. 
     In the above description of the “engine and parallel mode”, only the engine ENG is exampled as a power source. However, it may be obviously understood that such shifting operation may be maintained even if the motor/generator MG is activated to form a parallel mode and assist the engine ENG. 
     An electric vehicle mode EV mode differs from the engine and parallel mode, only in that the engine ENG is stopped while releasing the engine clutch ECL and only the motor/generator MG is used as sole power source. It may be understood that such a difference will not affect the above-described shifting operation, and thus, in such an electric vehicle mode EV mode the same shift-stages of one reverse speed REV and nine forward speeds of the forward first speed FD 1  to the forward ninth speed FD 9  may be obtained by the same operational chart. 
     A power transmission apparatus for a vehicle according to an exemplary form of the present disclosure realizes shift-stages of nine forward speeds and one reverse speed by employing a planetary gear set and two synchronizers to a multiple clutch transmission, thereby enabling multiple shift-stages by a simplified arrangement, improving installability, and reducing an overall weight. 
     In addition, an exemplary form of the present disclosure may receive torque from a motor/generator as well as an engine, such that a vehicle may be driving in an electric vehicle mode and parallel hybrid mode, thereby improving fuel consumption. 
     While this present disclosure has been described in connection with what is presently considered to be practical exemplary forms, it is to be understood that the present disclosure is not limited to the disclosed forms, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the present disclosure. 
     DESCRIPTION OF SYMBOLS 
     
         
         
           
             B 1 : first brake 
             CL 1 , CL 2 , CL 3 , CL 4 : first, second, third, and fourth clutches 
             CS 1 , CS 2 : first and second intermediate shafts 
             ECL: engine clutch 
             EOS: engine output shaft (crankshaft) 
             GL 1 , GL 2 , GL 3 , GL 4 , GL 5 , GL 6 : first, second, third, fourth, fifth, and sixth gear sets 
             ICDG: intermediate gear 
             IDG 1 , IDG 2 , IDG 3 , IDG 4 , IDG 5 , IDG 6 : first, second, third, fourth, fifth, and sixth drive gears 
             IPG 1 , IPG 2 , IPG 3 , IPG 4 , IPG 5 , IPG 6 : first, second, third, fourth, fifth, and sixth driven gears 
             IS 1 , IS 2 , IS 3 : first, second, and third input shafts 
             MDS: motor shaft 
             OG: output gear 
             OS: output shaft 
             PG: planetary gear set 
             SN 1 , SN 2 : first and second synchronizers 
             TMS: torque mediating shaft 
             TM 1 , TM 2 : first and second shifting sections