Abstract:
Nine or more forward speeds and at least one reverse speed are achieved by a planetary gear train of an automatic transmission for a vehicle including an input shaft, an output shaft, four planetary gear sets respectively having three rotation elements, and six control elements for selectively interconnecting the rotation elements and a transmission housing.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority to and the benefit of Korean Patent Application No. 10-2015-0144304 filed on Oct. 15, 2015, 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. 
     Description of Related Art 
     Recent increases in oil prices are triggering a hard competition in enhancing fuel consumption of a vehicle. 
     In this sense, research on an engine has been undertaken to achieve weight reduction and to enhance fuel consumption by so-called downsizing and research on an automatic transmission has been performed to simultaneously provide better drivability and fuel consumption by achieving more shift stages. 
     In order to achieve more shift stages for an automatic transmission, the number of parts is typically increased, which may deteriorate installability, production cost, weight and/or power flow efficiency. 
     Therefore, in order to maximally enhance fuel consumption of an automatic transmission having more shift stages, it is important for better efficiency to be derived by a smaller number of parts. 
     In this respect, an eight-speed automatic transmission has been recently introduced, and a planetary gear train for an automatic transmission enabling more shift stages is under investigation. 
     Considering that gear ratio spans of recently developed eight-speed automatic transmissions are typically between 6.5 and 7.5, fuel consumption enhancement is not very large. 
     In the case of a gear ratio span of an eight-speed automatic transmission having a level above 9.0, it is difficult to maintain step ratios between adjacent shift stages to be linear, by which driving efficiency of an engine and drivability of a vehicle deteriorated. 
     Thus, research studies are underway for developing a high efficiency automatic transmission having nine or more speeds. 
     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, by minimal complexity, realizing at least nine forward speeds and at least one reverse speed, increasing a gear ratio span so as to improve power delivery performance and fuel consumption, and achieving linearity of shift stage step ratios. 
     An exemplary embodiment of the present invention includes an input shaft for receiving an engine torque, an output shaft for outputting a shifted torque, a first planetary gear set having first, second, and third rotational elements, a second planetary gear set having fourth, fifth, and sixth rotational elements, a third planetary gear set having seventh, eighth, and ninth rotational elements, a fourth planetary gear set having tenth, eleventh, and twelfth rotational elements, and six control elements for selectively interconnecting the rotational elements and a transmission housing. 
     An exemplary embodiment of the present invention may further include a first connecting member connected with the first rotational element and directly connected with the input shaft, a second connecting member connected with the second rotational element, selectively connectable with the input shaft, and selectively connectable with transmission housing, a third connecting member connected with the third rotational element, a fourth connecting member connected with the fourth rotational element and directly connected with the transmission housing, a fifth connecting member connected with the fifth rotational element and selectively connectable with the third connecting member, a sixth connecting member connected with the sixth rotational element, the seventh rotational element, and the tenth rotational element and selectively connectable with the second connecting member, a seventh connecting member connected with the eighth rotational element and the twelfth rotational element and directly connected with the output shaft, an eighth connecting member connected with the ninth rotational element and selectively connectable with the transmission housing, and a ninth connecting member connected with the eleventh rotational element and selectively connectable with the input shaft. 
     The first planetary gear set may be a single pinion planetary gear set having a first sun gear, a first planet carrier, and a first ring gear, where the first rotational element is the first sun gear, the second rotational element is the first planet carrier, and the third rotational element is the first ring gear. The second planetary gear set may be a single pinion planetary gear set having a second sun gear, a second planet carrier, and a second ring gear, where the fourth rotational element is the second sun gear, the fifth rotational element is the second planet carrier, and the sixth rotational element is the second ring gear. The third planetary gear set may be a single pinion planetary gear set having a third sun gear, a third planet carrier, and a third ring gear, where the seventh rotational element is the third sun gear, the eighth rotational element is the third planet carrier, and the ninth rotational element is the third ring gear. The fourth planetary gear set may be a single pinion planetary gear set having a fourth sun gear, a fourth planet carrier, and a fourth ring gear, where the tenth rotational element is the fourth sun gear, the eleventh rotational element is the fourth planet carrier, and the twelfth rotational element is the fourth ring gear. 
     The six control elements may include a first clutch selectively connecting the input shaft and the second connecting member, a second clutch selectively connecting the input shaft and the ninth connecting member, a third clutch selectively connecting the second connecting member and the sixth connecting member, a fourth clutch selectively connecting the third connecting member and the fifth connecting member, a first brake selectively connecting the second connecting member and the transmission housing, and a second brake selectively connecting the eighth connecting member and the transmission housing. 
     Shift stages realized by selective operation of the six control elements may include a forward first speed formed by simultaneous operation of the third and fourth clutches and the second brake, a forward second speed formed by simultaneous operation of the first and third clutches and the second brake, a forward third speed formed by simultaneous operation of the first and fourth clutches and the second brake, a forward fourth speed formed by simultaneous operation of the first and second clutches and the second brake, a forward fifth speed formed by simultaneous operation of the first, second, and fourth clutches, a forward sixth speed formed by simultaneous operation of the first, second, and third clutches, a forward seventh speed formed by simultaneous operation of the second, third, and fourth clutches, a forward eighth speed formed by simultaneous operation of the second and third clutches and the first brake, a forward ninth speed formed by simultaneous operation of the second and fourth clutches and the first brake, and a reverse speed formed by simultaneous operation of the fourth clutch and the first and second brakes. 
     A planetary gear train according to an exemplary embodiment of the present invention may realize at least nine forward speeds and at least one reverse speed formed by operating the four planetary gear sets as simple planetary gear sets by controlling six control elements. 
     In addition, a planetary gear train according to an exemplary embodiment of the present invention may realize a gear ratio span of more than 9.0, thereby maximizing efficiency of driving an engine. 
     In addition, the linearity of step ratios of shift stages is secured while multi-staging the shift stage with high efficiency, thereby making it possible to improve drivability such as acceleration before and after a shift, an engine speed rhythmic sense, and the like. 
     Further, effects that can be obtained or expected from exemplary embodiments of the present invention are directly or suggestively described in the following detailed description. That is, various effects expected from exemplary embodiments of the present invention will be described in the following detailed description. 
     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 an exemplary embodiment of the present invention. 
         FIG. 2  is an operational chart for respective control elements at respective shift stages in a planetary gear train according to an exemplary embodiment 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. 
     In the figures, reference numbers refer to the same or equivalent parts of the present invention throughout the several figures of the drawing. 
     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. 
     The present invention will be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. 
     The drawings and description are to be regarded as illustrative in nature and not restrictive, and like reference numerals designate like elements throughout the specification. 
     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 diagram of a planetary gear train according to an exemplary embodiment of the present invention. 
     An Referring to  FIG. 1 , a planetary gear train according to an exemplary embodiment of the present invention includes first, second, third, and fourth planetary gear sets PG 1 , PG 2 , PG 3 , and PG 4  arranged on a same axis, input shaft IS, an output shaft OS, nine connecting members TM 1  to TM 9  for interconnecting rotational elements of the first, second, third, and fourth planetary gear sets PG 1 , PG 2 , PG 3 , and PG 4 , six control elements C 1  to C 4  and B 1  to B 2 , and a transmission housing H. 
     Torque input from the input shaft IS is shifted by cooperative operation of the first, second, third, and fourth planetary gear sets PG 1 , PG 2 , PG 3 , and PG 4 , and then output through the output shaft OS. 
     The simple planetary gear sets PG 1 , PG 2 , PG 3 , and PG 4  are arranged 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, and being arranged on a same axis with the input shaft IS, delivers a shifted torque to a drive shaft through a differential apparatus. 
     The first planetary gear set PG 1  is a single pinion planetary gear set, and includes a first sun gear S 1 , a first planet carrier PC 1  that supports a first pinion P 1  externally engaged with the first sun gear S 1 , and a first ring gear R 1  internally engaged with the first pinions P 1 . The first sun gear S 1  acts as a first rotational element N 1 , the first planet carrier PC 1  acts as a second rotational element N 2 , and the first ring gear R 1  acts as a third rotational element 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  that supports a second pinion P 2  externally engaged with the second sun gear S 2 , and a second ring gear R 2  internally engaged with the second pinions P 2 . The second sun gear S 2  acts as a fourth rotational element N 4 , the second planet carrier PC 2  acts as a fifth rotational element N 5 , and the second ring gear R 2  acts as a sixth rotational element 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  that supports a third pinion P 3  externally engaged with the third sun gear S 3 , and a third ring gear R 3  internally engaged with the third pinions P 3 . The third sun gear S 3  acts as a seventh rotational element N 7 , the third planet carrier PC 3  acts as an eighth rotational element N 8 , and the third ring gear R 3  acts as a ninth rotational element 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  that supports a fourth pinion P 4  externally engaged with the fourth sun gear S 4 , and a fourth ring gear R 4  internally engaged with the fourth pinions P 4 . 
     The fourth sun gear S 4  acts as a tenth rotational element N 10 , the fourth planet carrier PC 4  acts as an eleventh rotational element N 11 , and the fourth ring gear R 4  acts as a twelfth rotational element N 12 . 
     In the arrangement of the first, second, third, and fourth planetary gear sets PG 1 , PG 2 , PG 3 , and PG 4 , the sixth rotational element N 6  is directly connected with the seventh rotational element N 7  and the tenth rotational element N 10 , and the eighth rotational element N 8  is directly connected with the twelfth rotational element N 12 , by nine connecting members TM 1  to TM 9 . 
     The nine connecting members TM 1  to TM 9  are arranged as follows. 
     The first connecting member TM 1  is connected with the first rotational element N 1  (first sun gear S 1 ), and directly connected with the input shaft IS, thereby continuously acting as an input element. 
     The second connecting member TM 2  is connected with the second rotational element N 2  (first planet carrier PC 1 ), selectively connectable with the input shaft IS, and selectively connectable with the transmission housing H. 
     The third connecting member TM 3  is connected with the third rotational element N 3  (first ring gear R 1 ). 
     The fourth connecting member TM 4  is connected with the fourth rotational element N 4  (second sun gear S 2 ), and directly connected with the transmission housing H, thereby continuously acting as a fixed element. 
     The fifth connecting member TM 5  is connected with the fifth rotational element N 5  (second planet carrier PC 2 ), and selectively connectable with the third connecting member TM 3 . 
     The sixth connecting member TM 6  is connected with the sixth rotational element N 6  (second ring gear R 2 ), the seventh rotational element N 7  (third sun gear S 3 ), and the tenth rotational element N 10  (fourth sun gear S 4 ), and selectively connectable with the second connecting member TM 2 . 
     The seventh connecting member TM 7  is connected with the eighth rotational element N 8  (third planet carrier PC 3 ) and the twelfth rotational element N 12  (fourth ring gear R 4 ), and directly connected with the output shaft OS, thereby continuously acting as an output element. 
     The eighth connecting member TM 8  is connected with the ninth rotational element N 9  (third ring gear R 3 ), and selectively connectable with the transmission housing H. 
     The ninth connecting member TM 9  is connected with the eleventh rotational element N 11  (fourth planet carrier PC 4 ), and selectively connectable with the input shaft IS. 
     The connecting members TM 1  to TM 9  may be selectively interconnected with one another by control elements of four clutches C 1 , C 2 , C 3 , and C 4 . 
     The connecting members TM 1  to TM 9  may be selectively connectable with the transmission housing H, by control elements of two brakes B 1  and B 2 . 
     The six control elements C 1  to C 4  and B 1  to B 2  are arranged as follows. 
     The first clutch C 1  is arranged between the input shaft IS and the second connecting member TM 2 , such that the input shaft IS and the second connecting member TM 2  may selectively become integral. 
     The second clutch C 2  is arranged between the input shaft IS and the ninth connecting member TM 9 , such that the input shaft IS and the ninth connecting member TM 9  may selectively become integral. 
     The third clutch C 3  is arranged between the second connecting member TM 2  and the sixth connecting member TM 6 , such that the second connecting member TM 2  and the sixth connecting member TM 6  may selectively become integral. 
     The fourth clutch C 4  is arranged between the third connecting member TM 3  and the fifth connecting member TM 5 , such that the third connecting member TM 3  and the seventh connecting member TM 7  may selectively become integral. 
     The first brake B 1  is arranged between the second connecting member TM 2  and the transmission housing H, such that the second connecting member TM 2  may selectively act as a fixed element. 
     The second brake B 2  is arranged between the eighth connecting member TM 8  and the transmission housing H, such that the eighth connecting member TM 8  may selectively act as a fixed element. 
     The control elements of 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 realized as multi-plate hydraulic pressure friction devices that are frictionally engaged by hydraulic pressure. 
       FIG. 2  is an operational chart for respective control elements at respective shift stages in a planetary gear train according to an exemplary embodiment of the present invention. 
     As shown in  FIG. 2 , a planetary gear train according to an exemplary embodiment of the present invention performs shifting by operating three control elements at respective shift stages. 
     In the forward first speed D 1 , the third and fourth clutches C 3  and C 4  and the second brake B 2  are simultaneously operated. As a result, the second connecting member TM 2  is interconnected with the sixth connecting member TM 6  by the operation of the third clutch C 3 , and the third connecting member TM 3  is interconnected with the fifth connecting member TM 5  by the operation of the fourth clutch C 4 . In this state, torque is input to the first connecting member TM 1 . In addition, while the fourth connecting member TM 4  is acting as a fixed element, the eighth connecting member TM 8  simultaneously acts as a fixed element by the operation of the second brake B 2 , thereby realizing the forward first speed and outputting a shifted torque through the output shaft OS connected with the seventh connecting member TM 7 . 
     In the forward second speed D 2 , the first and third clutches C 1  and C 3  and the second brake B 2  are simultaneously operated. As a result, the input shaft IS is interconnected with the second connecting member TM 2  by the operation of the first clutch C 1 , and the second connecting member TM 2  is interconnected with the fifth connecting member TM 5  by the operation of the third clutch C 3 . In this state, torque is simultaneously input to the first, second, and sixth connecting members TM 1 , TM 2 , and TM 6 . In addition, while the fourth connecting member TM 4  is acting as a fixed element, the eighth connecting member TM 8  simultaneously acts as a fixed element by the operation of the second brake B 2 , thereby realizing the forward second speed and outputting a shifted torque through the output shaft OS connected with the seventh connecting member TM 7 . 
     In the forward third speed D 3 , the first and third clutches C 1  and C 4  and the second brake B 2  are simultaneously operated. As a result, the input shaft IS is interconnected with the second connecting member TM 2  by the operation of the first clutch C 1 , and the third connecting member TM 3  is interconnected with the fifth connecting member TM 5  by the operation of the fourth clutch C 4 . In this state, torque is simultaneously input to the first and second connecting members TM 1  and TM 2 . In addition, while the fourth connecting member TM 4  is acting as a fixed element, the eighth connecting member TM 8  simultaneously acts as a fixed element by the operation of the second brake B 2 , thereby realizing the forward third speed and outputting a shifted torque through the output shaft OS connected with the seventh connecting member TM 7 . 
     In the forward fourth speed D 4 , the first and second clutches C 1  and C 2  and the second brake B 2  are simultaneously operated. As a result, the input shaft IS is interconnected with the second connecting member TM 2  by the operation of the first clutch C 1 , and the input shaft IS is interconnected with the ninth connecting member TM 9  by the operation of the second clutch C 2 . In this state, torque is simultaneously input to the first, second, and ninth connecting members TM 1 , TM 2 , and TM 9 . In addition, while the fourth connecting member TM 4  is acting as a fixed element, the eighth connecting member TM 8  simultaneously acts as a fixed element by the operation of the second brake B 2 , thereby realizing the forward fourth speed and outputting a shifted torque through the output shaft OS connected with the seventh connecting member TM 7 . 
     In the forward fifth speed D 5 , the first, second, and fourth clutches C 1 , C 2 , and C 4  are simultaneously operated. As a result, the input shaft IS is interconnected with the second connecting member TM 2  by the operation of the first clutch C 1 , the input shaft IS is interconnected with the ninth connecting member TM 9  by the operation of the second clutch C 2 , and the third connecting member TM 3  is interconnected with the fifth connecting member TM 5  by the operation of the fourth clutch C 4 . In this state, torque is simultaneously input to the first, second, and ninth connecting members TM 1 , TM 2 , and TM 9 . In addition, the fourth connecting member TM 4  acts as a fixed element, thereby realizing the forward fifth speed and outputting a shifted torque through the output shaft OS connected with the seventh connecting member TM 7 . 
     In the forward sixth speed D 6 , the first, second, and third clutches C 1 , C 2 , and C 3  are simultaneously operated. As a result, the input shaft IS is interconnected with the second connecting member TM 2  by the operation of the first clutch C 1 , the input shaft IS is interconnected with the ninth connecting member TM 9  by the operation of the second clutch C 2 , and the second connecting member TM 2  is interconnected with the sixth connecting member TM 6  by the operation of the third clutch C 3 . In this state, torque is simultaneously input to the first, second, sixth, and ninth connecting members TM 1 , TM 2 , TM 6 , and TM 9 . In addition, the fourth connecting member TM 4  acts as a fixed element, thereby realizing the forward sixth speed and outputting a shifted torque through the output shaft OS connected with the seventh connecting member TM 7 . 
     In the forward seventh speed D 7 , the second, third, and fourth clutches C 2 , C 3 , and C 4  are simultaneously operated. As a result, the input shaft IS is interconnected with the ninth connecting member TM 9  by the operation of the second clutch C 2 , second connecting member TM 2  is interconnected with the sixth connecting member TM 6  by the operation of the third clutch C 3 , and the third connecting member TM 3  is interconnected with the fifth connecting member TM 5  by the operation of the fourth clutch C 4 . In this state, torque is simultaneously input to the first, ninth connecting member TM 1  and TM 9 . In addition, the fourth connecting member TM 4  acts as a fixed element, thereby realizing the forward seventh speed and outputting a shifted torque through the output shaft OS connected with the seventh connecting member TM 7 . 
     In the forward eighth speed D 8 , the second and third clutches C 2  and C 3  and the first brake B 1  are simultaneously operated. As a result, the input shaft IS is interconnected with the ninth connecting member TM 9  by the operation of the second clutch C 2 , and the second connecting member TM 2  is interconnected with the sixth connecting member TM 6  by the operation of the third clutch C 3 . In this state, torque is simultaneously input to the first and ninth connecting members TM 1  and TM 9 . In addition, while the fourth connecting member TM 4  is acting as a fixed element, the second connecting member TM 2  simultaneously acts as a fixed element by the operation of the first brake B 1 , thereby realizing the forward eighth speed and outputting a shifted torque through the output shaft OS connected with the seventh connecting member TM 7 . 
     In the forward ninth speed D 9 , the second and fourth clutches C 2  and C 4  and the first brake B 1  are simultaneously operated. As a result, the input shaft IS is interconnected with the ninth connecting member TM 9  by the operation of the second clutch C 2 , and the third connecting member TM 3  is interconnected with the fifth connecting member TM 5  by the operation of the fourth clutch C 4 . In this state, torque is simultaneously input to first and ninth connecting members TM 1  and TM 9 . In addition, while the fourth connecting member TM 4  is acting as a fixed element, the second connecting member TM 2  simultaneously acts as a fixed element by the operation of the first brake B 1 , thereby realizing the forward ninth speed and outputting a shifted torque through the output shaft OS connected with the seventh connecting member TM 7 . 
     In the reverse speed REV, the fourth clutch C 4  and the first and second brakes B 1  and B 2  are simultaneously operated. As a result, third connecting member TM 3  is interconnected with the fifth connecting member TM 5  by the operation of the fourth clutch C 4 . In this state, torque is input to the first connecting member TM 1 . In addition, while the fourth connecting member TM 4  is acting as a fixed element, the second and eighth connecting members TM 2  and TM 8  simultaneously act as fixed element by the operation of the first and second brakes B 1  and B 2 , thereby realizing the reverse speed and outputting a shifted torque through the output shaft OS connected with the seventh connecting member TM 7 . 
     As described above, a planetary gear train according to an exemplary embodiment of the present invention may realize at least nine forward speeds and at least one reverse speed formed by operating the four planetary gear sets PG 1 , PG 2 , PG 3 , and PG 4  by controlling the four clutches C 1 , C 2 , C 3 , and C 4  and the two brakes B 1  and B 2 . 
     In addition, a planetary gear train according to an exemplary embodiment of the present invention may realize a gear ratio span of more than 9.0, thereby maximizing efficiency of driving an engine. 
     Furthermore, a planetary gear train according to an exemplary embodiment of the present invention may achieve step ratios of more than 1.2 for all shifting except for forward 6/7 shifting and realize linearity of step ratios, thereby improving drivability, e.g., acceleration quality before after a shifting and engine speed rhythm. 
     For convenience in explanation and accurate definition in the appended claims, the terms “upper”, “lower”, “inner” and “outer” are used to describe features of the exemplary embodiments with reference to the positions of such features as displayed in the figures. 
     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.