Patent Publication Number: US-9850988-B2

Title: Planetary gear train of automatic transmission for vehicle

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority to Korean Patent Application No. 10-2016-0032328, filed Mar. 17, 2016, the entire contents of which is incorporated herein for all purposes by this reference. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to an automatic transmission for a vehicle. More particularly, the present invention relates to a planetary gear train of an automatic transmission for a vehicle that improves power delivery performance and fuel economy by achieving nine forward speed stages with a minimum number of constituent elements being used and improves silent driving of the vehicle by using an operation point positioned at a low engine speed. 
     Description of Related Art 
     Generally, an automatic transmission achieving more speed stages has been developed to enhance fuel economy and optimize drivability. Recent increases in oil prices are triggering stiff competition in enhancing fuel consumption of a vehicle. 
     Therefore, much research for reducing weight and enhancing fuel economy through downsizing of an engine and for securing drivability and fuel economy through multiple speed stages of automatic transmissions has been developed. 
     However, in the automatic transmission, as the number of speed stages increase, the number of internal components (particularly, planetary gear sets) increase, and as a result, a length of the transmission increases. This may deteriorate installability and/or power flow efficiency and may increase production cost, and weight. 
     Accordingly, development of a planetary gear train which may achieve maximum efficiency with a small number of components may be important in order to increase a fuel economy enhancement effect through the multiple speed-stages. 
     In this aspect, in recent years, 8-speed automatic transmissions tend to be implemented and the research and development of a planetary gear train capable of implementing more speed stages has also been actively conducted. 
     However, a conventional 8-speed automatic transmission typically includes three to four planetary gear sets and five to six control elements (frictional elements). In this case, since the length of the automatic transmission increases, mountability may be deteriorated. 
     In recent planetary gear trains, one planetary gear set is disposed above another planetary gear set, but structures of automatic transmissions to which parallel planetary gear sets is applied are very limited. 
     In other planetary gear trains, dog clutches instead of control elements of wet-type are used. However, shift feel may be deteriorated. 
     The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art. 
     BRIEF SUMMARY 
     Various aspects of the present invention are directed to providing a planetary gear train of an automatic transmission for a vehicle having advantages of improving power delivery performance and fuel economy by achieving at least nine forward speed stages and one reverse speed stage. 
     In addition, various aspects of the present invention are directed to providing a planetary gear train of an automatic transmission for a vehicle having further advantages of improving silent driving of the vehicle by using operation point positioned at a low rotation speed region of an engine. 
     According to various aspects of the present invention, a planetary gear train of an automatic transmission for a vehicle may include an input shaft receiving torque of an engine, an output shaft outputting torque of the engine, a first planetary gear set including first, second, and third rotation elements, a second planetary gear set including fourth, fifth, and sixth rotation elements, a third planetary gear set including seventh, eighth, and ninth rotation elements, a fourth planetary gear set including tenth, eleventh, and twelfth rotation elements, a first shaft connecting the first rotation element to the fifth rotation element and the ninth rotation element, a second shaft connected to the second rotation element and directly connected to the input shaft, a third shaft connecting the third rotation element to the seventh rotation element, a fourth shaft connected to the fourth rotation element, a fifth shaft connected to the sixth rotation element and selectively connectable to the third shaft, a sixth shaft connecting the eighth rotation element to the twelfth rotation element and selectively connectable to the third shaft, a seventh shaft connected to the tenth rotation element and selectively connectable to the fourth shaft, and an eighth shaft connected to the eleventh rotation element, selectively connectable to the third shaft, and directly connected to the output shaft. 
     The first shaft and the fourth shaft may each be selectively connectable to a transmission housing. 
     The first, second, and third rotation elements may be a first sun gear, a first planet carrier, and a first ring gear, the fourth, fifth, and sixth rotation elements may be a second sun gear, a second planet carrier, and a second ring gear, the seventh, eighth, and ninth rotation elements may be a third sun gear, a third planet carrier, and a third ring gear, and the tenth, eleventh, and twelfth rotation elements may be a fourth sun gear, a fourth planet carrier, and a fourth ring gear. 
     The planetary gear train may further include a first clutch selectively connecting the third shaft to the eighth shaft, a second clutch selectively connecting the third shaft to the fifth shaft, a third clutch selectively connecting the third shaft to the sixth shaft, a fourth clutch selectively connecting the fourth shaft to the seventh shaft, a first brake selectively connecting the first shaft to the transmission housing, and a second brake selectively connecting the fourth shaft to the transmission housing. 
     A planetary gear train of an automatic transmission for a vehicle may include an input shaft receiving torque of an engine, an output shaft outputting torque, a first planetary gear set including first, second, and third rotation elements, a second planetary gear set including fourth, fifth, and sixth rotation elements, a third planetary gear set including seventh, eighth, and ninth rotation elements, and a fourth planetary gear set including tenth, eleventh, and twelfth rotation elements, in which the input shaft may be directly connected to the second rotation element, the output shaft may be directly connected to the eleventh rotation element, the first rotation element may be directly connected to the fifth rotation element and the ninth rotation element, the third rotation element may be directly connected to the seventh rotation element, the sixth rotation element may be selectively connectable to the third rotation element, the eighth rotation element may be directly connected to the twelfth rotation element and selectively connectable to the seventh rotation element, the tenth rotation element may be selectively connectable to the fourth rotation element, and the eleventh rotation element may be selectively connectable to the third rotation element. 
     The first rotation element and the fourth rotation element may each be selectively connectable to a transmission housing. 
     The planetary gear train may further include a first clutch selectively connecting the seventh rotation element to the eleventh rotation element, a second clutch selectively connecting the third rotation element to the sixth rotation element, a third clutch selectively connecting the seventh rotation element to the eighth rotation element, a fourth clutch selectively connecting the fourth rotation element to the tenth rotation element, a first brake selectively connecting the first rotation element to the transmission housing, and a second brake selectively connecting the fourth rotation element to the transmission housing. 
     Speed stages implemented by selectively operating the first, second, third and fourth clutches and the first and second brakes include a forward first speed stage, implemented by operating the first brake and the third and fourth clutches, a forward second speed stage, implemented by operating the first and second brakes, and the fourth clutch, a forward third speed stage, implemented by operating the second brake and the third and fourth clutches, a forward fourth speed stage, implemented by operating the second brake and the second and fourth clutches, a forward fifth speed stage, implemented by operating the second brake and the first and fourth clutches, a forward sixth speed stage, implemented by operating the first, second, and fourth clutches, a forward seventh speed stage, implemented by operating the second brake and the first and second clutches, a forward eighth speed stage, implemented by operating the second brake and the first and third clutches, a forward ninth speed stage, implemented by operating the first brake and the first and third clutches, and a reverse-speed stage, implemented by operating the first brake and the second and fourth clutches. 
     The planetary gear train according to the various embodiments of the present invention achieves nine forward speed stages and one reverse speed stage by combining four planetary gear sets with six control elements. 
     In addition, the planetary gear train according to various embodiments of the present invention achieves speed stages suitable to a rotational speed of the engine due to multiple-speed stages of the automatic transmission. Particularly, silent driving of the vehicle is improved by using an operation point positioned at a low rotational speed region of an engine. 
     In addition, the planetary gear train according to various embodiments of the present invention maximizes driving efficiency of the engine and improves power delivery performance and fuel consumption. 
     It is understood that the term “vehicle” or “vehicular” or other similar terms as used herein is inclusive of motor vehicles in general such as passenger automobiles including sports utility vehicles (SUV), buses, trucks, various commercial vehicles, watercraft including a variety of boats and ships, aircraft, and the like, and includes hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen-powered vehicles and other alternative fuel vehicles (e.g., fuel derived from resources other than petroleum). As referred to herein, a hybrid vehicle is a vehicle that has two or more sources of power, for example, both gasoline-powered and electric-powered vehicles. 
     The methods and apparatuses of the present invention have other features and advantages which will be apparent from or are set forth in more detail in the accompanying drawings, which are incorporated herein, and the following Detailed Description, which together serve to explain certain principles of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a planetary gear train according to various embodiments of the present invention. 
         FIG. 2  is an operation chart of control elements at each speed stage in the planetary gear train according to various embodiments of the present invention. 
     
    
    
     It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various features illustrative of the basic principles of the invention. The specific design features of the present invention as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes will be determined in part by the particular intended application and use environment. 
     DETAILED DESCRIPTION 
     Reference will now be made in detail to various embodiments of the present invention(s), examples of which are illustrated in the accompanying drawings and described below. While the invention(s) will be described in conjunction with exemplary embodiments, it will be understood that the present description is not intended to limit the invention(s) to those exemplary embodiments. On the contrary, the invention(s) is/are intended to cover not only the exemplary embodiments, but also various alternatives, modifications, equivalents and other embodiments, which may be included within the spirit and scope of the invention as defined by the appended claims. 
       FIG. 1  is a schematic diagram of a planetary gear train according to various embodiments of the present invention. 
     Referring to  FIG. 1 , a planetary gear train according to various embodiments of the present invention includes first, second, third, and fourth planetary gear sets PG 1 , PG 2 , PG 3 , and PG 4  disposed on the same axis, an input shaft IS, an output shaft OS, eight shafts TM 1  to TM 8  connected to at least one of rotation elements of the first, second, third, and fourth planetary gear sets PG 1 , PG 2 , PG 3 , and PG 4 , four clutches C 1  to C 4  and two brakes B 1  and B 2  that are control elements, and a transmission housing H. 
     Torque input from the input shaft IS is changed by cooperation of the first, second, third, and fourth planetary gear sets PG 1 , PG 2 , PG 3 , and PG 4 , and the changed torque is output through the output shaft OS. 
     The planetary gear sets are disposed in the order of first, second, third and fourth planetary gear sets PG 1 , PG 2 , PG 3  and PG 4  from an engine side. 
     The input shaft IS is an input member and the torque from a crankshaft of an engine, after being torque-converted through a torque converter, is input into the input shaft IS. 
     The output shaft OS is an output member, is disposed in parallel with the input shaft IS, and transmits driving torque to a driving wheel through a differential apparatus. 
     The first planetary gear set PG 1  is a single pinion planetary gear set and includes a first sun gear  51 , a first planet carrier PC 1  rotatably supporting a first pinion P 1  that is externally meshed with the first sun gear S 1 , and a first ring gear R 1  that is internally meshed with the first pinion P 1  respectively as first, second, and third rotation elements N 1 , N 2 , and N 3 . 
     The second planetary gear set PG 2  is a single pinion planetary gear set and includes a second sun gear S 2 , a second planet carrier PC 2  rotatably supporting a second pinion P 2  that is externally meshed with the second sun gear S 2 , and a second ring gear R 2  that is internally meshed with the second pinion P 2  respectively as fourth, fifth, and sixth rotation elements N 4 , N 5 , and N 6 . 
     The third planetary gear set PG 3  is a single pinion planetary gear set and includes a third sun gear S 3 , a third planet carrier PC 3  rotatably supporting a third pinion P 3  that is externally meshed with the third sun gear S 3 , and a third ring gear R 3  that is internally meshed with the third pinion P 3  respectively as seventh, eighth, and ninth rotation elements N 7 , N 8 , and N 9 . 
     The fourth planetary gear set PG 4  is a single pinion planetary gear set and includes a fourth sun gear S 4 , a fourth planet carrier PC 4  rotatably supporting a fourth pinion P 4  that is externally meshed with the fourth sun gear S 4 , and a fourth ring gear R 4  that is internally meshed with the fourth pinion P 4  respectively as tenth, eleventh, and twelfth rotation elements N 10 , N 11 , and N 12 . 
     The first rotation element N 1  is directly connected to the fifth rotation element N 5  and the ninth rotation element N 9 , the third rotation element N 3  is directly connected to the seventh rotation element N 7 , and the eighth rotation element N 8  is directly connected to the twelfth rotation element N 12  such that the first, second, third, and fourth planetary gear sets PG 1 , PG 2 , PG 3 , and PG 4  include eight shafts TM 1  to TM 8 . 
     The eight shafts TM 1  to TM 8  will be described in further detail. 
     The eight shafts TM 1  to TM 8  directly connect a plurality of rotation elements among the rotation elements of the planetary gear sets PG 1 , PG 2 , PG 3 , and PG 4 , are rotation members that are each directly connected to at least one rotation element of the planetary gear sets PG 1 , PG 2 , PG 3 , and PG 4  and rotate with the at least one rotation element to transmit torque, or are fixed members that directly connect at least one rotation element of the planetary gear sets PG 1 , PG 2 , PG 3 , and PG 4  to the transmission housing H to fix the at least one rotation element. 
     The first shaft TM 1  directly connects the first rotation element N 1  (first sun gear S 1 ) to the fifth rotation element N 5  (second planet carrier PC 2 ) and the ninth rotation element N 9  (third ring gear R 3 ), and is selectively connectable to the transmission housing H so as to be operated as a selective fixed element. 
     The second shaft TM 2  is connected to the second rotation element N 2  (first planet carrier PC 1 ) and is directly connected to the input shaft IS so as to be continuously operated as an input element. 
     The third shaft TM 3  directly connects the third rotation element N 3  (first ring gear R 1 ) to the seventh rotation element N 7  (third sun gear S 3 ). 
     The fourth shaft TM 4  is directly connected to the fourth rotation element N 4  (second sun gear N 4 ) and is selectively connectable to the transmission housing H so as to be operated as a selective fixed element. 
     The fifth shaft TM 5  is connected to the sixth rotation element N 6  (second ring gear R 3 ) and is selectively connectable to the third shaft TM 3 . 
     The sixth shaft TM 6  directly connects the eighth rotation element N 8  (third planet carrier PC 3 ) to the twelfth rotation element N 12  (fourth ring gear R 4 ) and is selectively connectable to the third shaft TM 3 . 
     The seventh shaft TM 7  is connected to the tenth rotation element N 10  (fourth sun gear S 4 ) and is selectively connectable to the fourth shaft TM 4 . 
     The eighth shaft TM 8  is connected to the eleventh rotation element N 11  (fourth planet carrier PC 4 ), is selectively connectable to the third shaft TM 3 , and is directly connected to the output shaft OS so as to be continuously operated as an output element. 
     In addition, four clutches C 1 , C 2 , C 3 , and C 4  are disposed at portions at which any two shafts among the eight shafts TM 1  to TM 8  including the input shaft IS and the output shaft OS are selectively connectable to each other. 
     In addition, two brakes B 1  and B 2  are disposed at portions at which at least one shaft among the eight shafts TM 1  to TM 8  is selectively connectable to the transmission housing H. 
     Arrangements of the four clutches C 1  to C 4  and two brakes B 1  and B 2  are described in detail. 
     The first clutch C 1  is disposed between the third shaft TM 3  and the eighth shaft TM 8  and selectively connects the third shaft TM 3  to the eighth shaft TM 8 . 
     The second clutch C 2  is disposed between the third shaft TM 3  and the fifth shaft TM 5  and selectively connects the third shaft TM 3  to the fifth shaft TM 5 . 
     The third clutch C 3  is disposed between the third shaft TM 3  and the sixth shaft TM 6  and selectively connects the third shaft TM 3  to the sixth shaft TM 6 . 
     The fourth clutch C 4  is disposed between the fourth shaft TM 4  and the seventh shaft TM 7  and selectively connects the fourth shaft TM 4  to the seventh shaft TM 7 . 
     The first brake B 1  is disposed between the first shaft TM 1  and the transmission housing H and selectively connects the first shaft TM 1  to the transmission housing H. 
     The second brake B 2  is disposed between the fourth shaft TM 4  and the transmission housing H and selectively connects the fourth shaft TM 4  to the transmission housing H. 
     The control elements including the first, second, third, and fourth clutches C 1 , C 2 , C 3 , and C 4  and the first and second brakes B 1  and B 2  may be multi-plates friction elements of wet type that are operated by hydraulic pressure. 
       FIG. 2  is an operation chart of control elements at each speed stage in the planetary gear train according to various embodiments of the present invention. 
     As shown in  FIG. 2 , three control elements among the first, second, third, and fourth clutches C 1 , C 2 , C 3 , and C 4  and the first and second brakes B 1  and B 2  that are control elements are operated at each speed stage in the planetary gear train according to various embodiments of the present invention. 
     The first brake B 1  and the third and fourth clutches C 3  and C 4  are operated at a first forward speed stage D 1 . 
     In a state that the third shaft TM 3  is connected to the sixth shaft TM 6  by operation of the third clutch C 3  and the fourth shaft TM 4  is connected to the seventh shaft TM 7  by operation of the fourth clutch C 4 , rotation speed of the input shaft IS is input to the second shaft TM 2 . In addition, the first shaft TM 1  is operated as the fixed element by operation of the first brake B 1 . Therefore, the rotation speed of the input shaft IS is shifted into the first forward speed stage, and the first forward speed stage is output through the output shaft OS connected to the eighth shaft TM 8 . 
     The first and second brakes B 1  and B 2  and the fourth clutch C 4  are operated at a second forward speed stage D 2 . 
     In a state that the fourth shaft TM 4  is connected to the seventh shaft TM 7  by operation of the fourth clutch C 4 , the rotation speed of the input shaft IS is input to the second shaft TM 2 . In addition, the first shaft TM 1  and the fourth shaft TM 4  are operated as the fixed elements by operation of the first and second brakes B 1  and B 2 . Therefore, the rotation speed of the input shaft IS is shifted into the second forward speed stage, and the second forward speed stage is output through the output shaft OS connected to the eighth shaft TM 8 . 
     The second brake B 2  and the third and fourth clutches C 3  and C 4  are operated at a third forward speed stage D 3 . 
     In a state that the third shaft TM 3  is connected to the sixth shaft TM 6  by operation of the third clutch C 3  and the fourth shaft TM 4  is connected to the seventh shaft TM 7  by operation of the fourth clutch C 4 , the rotation speed of the input shaft IS is input to the second shaft TM 2 . In addition, the fourth shaft TM 4  is operated as the fixed element by operation of the second brake B 2 . Therefore, the rotation speed of the input shaft IS is shifted into the third forward speed stage, and the third forward speed stage is output through the output shaft OS connected to the eighth shaft TM 8 . 
     The second brake B 2  and the second and fourth clutches C 2  and C 4  are operated at a fourth forward speed stage D 4 . 
     In a state that the third shaft TM 3  is connected to the fifth shaft TM 5  by operation of the second clutch C 2  and the fourth shaft TM 4  is connected to the seventh shaft TM 7  by operation of the fourth clutch C 4 , the rotation speed of the input shaft IS is input to the second shaft TM 2 . In addition, the fourth shaft TM 4  is operated as the fixed element by operation of the second brake B 2 . Therefore, the rotation speed of the input shaft IS is shifted into the fourth forward speed stage, and the fourth forward speed stage is output through the output shaft OS connected to the eighth shaft TM 8 . 
     The second brake B 2  and the first and fourth clutches C 1  and C 4  are operated at a fifth forward speed stage D 5 . 
     In a state that the third shaft TM 3  is connected to the eighth shaft TM 8  by operation of the first clutch C 1  and the fourth shaft TM 4  is connected to the seventh shaft TM 7  by operation of the fourth clutch C 4 , the rotation speed of the input shaft IS is input to the second shaft TM 2 . In addition, the fourth shaft TM 4  is operated as the fixed element by operation of the second brake B 2 . Therefore, the rotation speed of the input shaft IS is shifted into the fifth forward speed stage, and the fifth forward speed stage is output through the output shaft OS connected to the eighth shaft TM 8 . 
     The first, second, and fourth clutches C 1 , C 2 , and C 4  are operated at a sixth forward speed stage D 6 . 
     The third shaft TM 3  is connected to the eighth shaft TM 8  by operation of the first clutch C 1 , the third shaft TM 3  is connected to the fifth shaft TM 5  by operation of the second clutch C 2 , and the fourth shaft TM 4  is connected to the seventh shaft TM 7  by operation of the fourth clutch C 4  such that the first, second, third, and fourth planetary gear sets PG 1 , PG 2 , PG 3 , and PG 4  become lock-up states. At this state, the rotation speed of the input shaft IS is input to the second shaft TM 2  and the sixth forward speed stage is output through the output shaft OS connected to the eighth shaft TM 8 . At the sixth forward speed stage, the same rotation speed as the input shaft IS is output. 
     The second brake B 2  and the first and second clutches C 1  and C 2  are operated at a seventh forward speed stage D 7 . 
     In a state that the third shaft TM 3  is connected to the eighth shaft TM 8  by operation of the first clutch C 1  and the third shaft TM 3  is connected to the fifth shaft TM 5  by operation of the second clutch C 2 , the rotation speed of the input shaft IS is input to the second shaft TM 2 . In addition, the fourth shaft TM 4  is operated as the fixed element by operation of the second brake B 2 . Therefore, the rotation speed of the input shaft IS is shifted into the seventh forward speed stage, and the seventh forward speed stage is output through the output shaft OS connected to the eighth shaft TM 8 . 
     The second brake B 2  and the first and third clutches C 1  and C 3  are operated at an eighth forward speed stage D 8 . 
     In a state that the third shaft TM 3  is connected to the eighth shaft TM 8  by operation of the first clutch C 1  and the third shaft TM 3  is connected to the sixth shaft TM 6  by operation of the third clutch C 3 , the rotation speed of the input shaft IS is input to the second shaft TM 2 . In addition, the fourth shaft TM 4  is operated as the fixed element by operation of the second brake B 2 . Therefore, the rotation speed of the input shaft IS is shifted into the eighth forward speed stage, and the eighth forward speed stage is output through the output shaft OS connected to the eighth shaft TM 8 . 
     The first brake B 1  and the first and third clutches C 1  and C 3  are operated at a ninth forward speed stage D 9 . 
     In a state that the third shaft TM 3  is connected to the eighth shaft TM 8  by operation of the first clutch C 1  and the third shaft TM 3  is connected to the sixth shaft TM 6  by operation of the third clutch C 3 , the rotation speed of the input shaft IS is input to the second shaft TM 2 . In addition, the first shaft TM 1  is operated as the fixed element by operation of the first brake B 1 . Therefore, the rotation speed of the input shaft IS is shifted into the ninth forward speed stage, and the ninth forward speed stage is output through the output shaft OS connected to the eighth shaft TM 8 . 
     The first brake B 1  and the second and fourth clutches C 2  and C 4  are operated at a reverse speed stage REV. 
     In a state that the third shaft TM 3  is connected to the fifth shaft TM 5  by operation of the second clutch C 2  and the fourth shaft TM 4  is connected to the seventh shaft TM 7  by operation of the fourth clutch C 4 , the rotation speed of the input shaft IS is input to the second shaft TM 2 . In addition, the first shaft TM 1  is operated as the fixed element by operation of the first brake B 1 . Therefore, the rotation speed of the input shaft IS is shifted into the reverse speed stage, and the reverse speed stage is output as an inverse rotation speed through the output shaft OS connected to the eighth shaft TM 8 . 
     The planetary gear trains according to various embodiments of the present invention achieves at least nine forward speed stages and one reverse speed stage by combining four planetary gear sets PG 1 , PG 2 , PG 3 , and PG 4  with the four clutches C 1 , C 2 , C 3 , and C 4  and the two brakes B 1  and B 2 . 
     In addition, the planetary gear train according various embodiments of the present invention achieves suitable speed stages according to rotation speed of the engine. Particularly, silent driving of the vehicle may be improved by using operation point positioned at a low rotational speed region of the engine. 
     Furthermore, the planetary gear train according to various embodiments of the present invention maximizes driving efficiency of the engine and improves power delivery performance and fuel consumption. 
     The foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teachings. The exemplary embodiments were chosen and described in order to explain certain principles of the invention and their practical application, to thereby enable others skilled in the art to make and utilize various exemplary embodiments of the present invention, as well as various alternatives and modifications thereof. It is intended that the scope of the invention be defined by the Claims appended hereto and their equivalents.