Abstract:
A family of transmission gearing arrangements produces up to ten forward and one reverse speed ratios by selective engagement of various combinations of three or four shift elements. Each disclosed transmission includes four planetary gear sets and six shift elements. Two of the shift elements can be brakes.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. application Ser. No. 13/480,960 filed May 25, 2012, now U.S. Pat. No. 8,545,362, the disclosure of which is incorporated in its entirety by reference herein. This application claims the benefit of U.S. Provisional Application No. 61/715,706, filed Oct. 18, 2012, the disclosure of which is incorporated in its entirety by reference herein. 
    
    
     TECHNICAL FIELD 
     This disclosure relates to the field of automatic transmissions for motor vehicles. More particularly, the disclosure pertains to an arrangement of gears, clutches, and the interconnections among them in a power transmission. 
     BACKGROUND 
     Many vehicles are used over a wide range of vehicle speeds, including both forward and reverse movement. Some types of engines, however, are capable of operating efficiently only within a narrow range of speeds. Consequently, transmissions capable of efficiently transmitting power at a variety of speed ratios are frequently employed. When the vehicle is at low speed, the transmission is usually operated at a high speed ratio such that it multiplies the engine torque for improved acceleration. At high vehicle speed, operating the transmission at a low speed ratio permits an engine speed associated with quiet, fuel efficient cruising. Typically, a transmission has a housing mounted to the vehicle structure, an input shaft driven by an engine crankshaft, and an output shaft driving the vehicle wheels, often via a differential assembly which permits the left and right wheel to rotate at slightly different speeds as the vehicle turns. 
     SUMMARY OF THE DISCLOSURE 
     In a first embodiment, a transmission includes input, output, and intermediate shafts, four simple planetary gear sets, at least four clutches, and at least one brake. The input shaft is fixedly coupled to the carrier of the first planetary gear set. The output shaft is fixedly coupled to the carrier of the second planetary gear set. The third sun gear is fixedly coupled to the first ring gear. When the first clutch is engaged, the intermediate shaft is coupled to the third ring gear and the second ring gear is coupled to the third carrier. In some embodiments, the intermediate shaft may be fixedly coupled to the third ring gear while a first clutch selectively couples the second ring gear to the third carrier. In other embodiments, the second ring gear may be fixedly coupled to the third carrier while a first clutch selectively couples the intermediate shaft to the third ring gear. A second clutch selectively couples the third sun gear to the intermediate shaft. A third clutch selectively couples the input shaft to the second sun gear. A fourth clutch selectively couples the second sun gear to the intermediate shaft. A first brake selectively holds the first sun gear against rotation. When a sixth shift element is engaged, the fourth sun gear is coupled to the first sun gear, the fourth carrier is coupled to the second ring gear, and the fourth ring gear is held against rotation. The sixth shift element may be a second brake selectively holding the fourth ring gear against rotation. 
     In a second embodiment, a transmission includes input, output, and intermediate shafts, four gearing arrangements, at least four clutches, and at least one brake. The first gearing arrangement imposes a linear speed relationship among a first element, the input shaft, and a second element. The second gearing arrangement imposes a linear speed relationship among a third element, the output shaft, and a fourth element. The third gearing arrangement imposes a linear speed relationship among the second element, a fifth element, and a sixth element. The fourth gearing arrangement selectively constrains the speed of the fourth element to be between zero and the speed of the first element. When the first clutch is engaged, the intermediate shaft is coupled to the sixth element and the fourth element is coupled to the fifth. In some embodiments, the intermediate shaft may be fixedly coupled to the fourth element while a first clutch selectively couples the fifth element to the sixth element. In other embodiments, the fifth element may be fixedly coupled to the sixth element while a first clutch selectively couples the intermediate shaft to the sixth element. A second clutch selectively couples the second element to the intermediate shaft. A third clutch selectively couples the input shaft to the third element. A fourth clutch selectively couples the third element to the intermediate shaft. A first brake selectively holds the first element against rotation. 
     In a third embodiment, a transmission includes input and output shafts, four gearing arrangements, a clutches, a brake, and a clutch module. The first gearing arrangement imposes a linear speed relationship among a first element, the input shaft, and a second element. The second gearing arrangement imposes a linear speed relationship among a third element, the output shaft, and a fourth element. The third gearing arrangement imposes a linear speed relationship among the second element, a fourth element, and a fifth element. The fourth gearing arrangement selectively constrains the speed of the fourth element to be between zero and the speed of the first element. A first clutch selectively couples the third element to the input shaft. A first brake selectively holds the first element against rotation. The clutch module is configured to selectively couple any two of the second element, the third element, and the fifth element. In some embodiments, the clutch module may include an intermediate shaft and three clutches each selectively coupling the intermediate shaft to a respective one of the second, third, and fifth elements. In other embodiments, the clutch module may include three clutches each selectively directly coupling two of the second, third, and fifth elements. 
     In a fourth embodiment, a transmission includes input and output shafts, seven intermediate shafts, four clutches, and two brakes. The brakes selectively hold the first and third intermediate shafts, respectively, against rotation. Three of the clutches selectively couple the seventh shaft to the fourth, fifth, and sixth intermediate shafts, respectively. The remaining clutch selectively couples the input shaft to the sixth shaft. The transmission may also include four gearing arrangements. The first gearing arrangement imposes a linear speed relationship among a first intermediate shaft, the second intermediate shaft, and the third intermediate shaft. The second gearing arrangement imposes a linear speed relationship among a first intermediate shaft, the input shaft, and the fourth intermediate shaft. The third gearing arrangement imposes a linear speed relationship among a fourth intermediate shaft, the second intermediate shaft, and the fifth intermediate shaft. The fourth gearing arrangement imposes a linear speed relationship among a sixth intermediate shaft, the output shaft, and the second intermediate shaft. Each of the gearing arrangements may be a simple planetary gear set. 
     In a fifth embodiment, a transmission includes input and output shafts, seven intermediate shafts, four clutches, and two brakes. The brakes selectively hold the first and third intermediate shafts, respectively, against rotation. Two of the clutches selectively couple the seventh intermediate shaft to the sixth intermediate shaft and input shaft, respectively. The other two clutches selectively couple the fifth intermediate shaft to the second and sixth intermediate shafts, respectively. The transmission may also include four gearing arrangements. The first gearing arrangement imposes a linear speed relationship among a first intermediate shaft, the second intermediate shaft, and the third intermediate shaft. The second gearing arrangement imposes a linear speed relationship among a first intermediate shaft, the input shaft, and the fourth intermediate shaft. The third gearing arrangement imposes a linear speed relationship among a fourth intermediate shaft, the fifth intermediate shaft, and the sixth intermediate shaft. The fourth gearing arrangement imposes a linear speed relationship among a seventh intermediate shaft, the output shaft, and the second intermediate shaft. Each of the gearing arrangements may be a simple planetary gear set. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a first transmission gearing arrangement. 
         FIG. 2  is a schematic diagram of a second transmission gearing arrangement. 
         FIG. 3  is a schematic diagram of a third transmission gearing arrangement. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present disclosure are described herein. It is to be understood, however, that the disclosed embodiments are merely examples and other embodiments can take various and alternative forms. The figures are not necessarily to scale; some features could be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. As those of ordinary skill in the art will understand, various features illustrated and described with reference to any one of the figures can be combined with features illustrated in one or more other figures to produce embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. Various combinations and modifications of the features consistent with the teachings of this disclosure, however, could be desired for particular applications or implementations. 
     A gearing arrangement is a collection of rotating elements and shift elements configured to impose specified speed relationships among the rotating elements. Some speed relationships, called fixed speed relationships, are imposed regardless of the state of any shift elements. Other speed relationships, called selective speed relationships, are imposed only when particular shift elements are fully engaged. A linear speed relationship exists among an ordered list of rotating elements when i) the first and last rotating element in the group are constrained to have the most extreme speeds, ii) the speeds of the remaining rotating elements are each constrained to be a weighted average of the first and last rotating element, and iii) when the speeds of the rotating elements differ, they are constrained to be in the listed order, either increasing or decreasing. A discrete ratio transmission has a gearing arrangement that selectively imposes a variety of speed ratios between an input shaft and an output shaft. 
     A group of rotating elements are fixedly coupled to one another if they are constrained to rotate as a unit in all operating conditions. Rotating elements can be fixedly coupled by spline connections, welding, press fitting, machining from a common solid, or other means. Slight variations in rotational displacement between fixedly coupled elements can occur such as displacement due to lash or shaft compliance. One or more rotating elements that are all fixedly coupled to one another may be called a shaft. In contrast, two rotating elements are selectively coupled by a shift element when the shift element constrains them to rotate as a unit whenever it is fully engaged and they are free to rotate at distinct speeds in at least some other operating condition. A shift element that holds a rotating element against rotation by selectively connecting it to the housing is called a brake. A shift element that selectively couples two or more rotating elements to one another is called a clutch. Shift elements may be actively controlled devices such as hydraulically or electrically actuated clutches or brakes or may be passive devices such as one way clutches or brakes. 
     An example transmission is schematically illustrated in  FIG. 1 . The transmission utilizes four simple planetary gear sets  20 ,  30 ,  40 , and  50 . A planet carrier  22  rotates about a central axis and supports a set of planet gears  24  such that the planet gears rotate with respect to the planet carrier. External gear teeth on the planet gears mesh with external gear teeth on a sun gear  26  and with internal gear teeth on a ring gear  28 . The sun gear and ring gear are supported to rotate about the same axis as the carrier. Gear sets  30 ,  40 , and  50  are similarly structured. 
     A simple planetary gear set is a type of gearing arrangement that imposes a fixed linear speed relationship among the sun gear, the planet carrier, and the ring gear. Other known types of gearing arrangements also impose a fixed linear speed relationship among three rotating elements. For example, a double pinion planetary gear set imposes a fixed linear speed relationship between the sun gear, the ring gear, and the planet carrier. 
     A suggested ratio of gear teeth for each planetary gear set is listed in Table 1. 
     
       
         
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
             
             
               
                   
                 Ring 28/Sun 26 
                 2.20 
               
               
                   
                 Ring 38/Sun 36 
                 1.75 
               
               
                   
                 Ring 48/Sun 46 
                 1.60 
               
               
                   
                 Ring 58/Sun 56 
                 3.70 
               
               
                   
                   
               
             
          
         
       
     
     In the transmission of  FIG. 1 , sun gear  26  is fixedly coupled to sun gear  36 , carrier  22  is fixedly coupled to ring gear  58 , ring gear  38  is fixedly coupled to sun gear  46 , input shaft  60  is fixedly coupled to carrier  32 , and output shaft  62  is fixedly coupled to carrier  52 . Ring gear  28  is selectively held against rotation by brake  66  and sun gears  26  and  36  are selectively held against rotation by brake  68 . Input shaft  60  is selectively coupled to sun gear  56  by clutch  70 . Intermediate shaft  64  is fixedly coupled to ring gear  48 , selectively coupled to sun gear  56  by clutch  72 , and selectively coupled to ring gear  38  and sun gear  46  by clutch  76 . Note that engaging clutch  76  constrains gear set  40  to rotate as a single unit. This effect can alternatively be achieved by a clutch selectively coupling carrier  42  to either sun gear  46  or to ring gear  48 . Carrier  42  is selectively coupled to carrier  22  and ring gear  58  by clutch  74 . 
     As shown in Table 2, engaging the clutches and brakes in combinations of four establishes ten forward speed ratios and one reverse speed ratio between input shaft  60  and output shaft  62 . An X indicates that the clutch is required to establish the speed ratio. An (X) indicates the clutch can be applied but is not required. In 1 st  gear, either clutch  74  or clutch  76  can be applied instead of applying clutch  72  without changing the speed ratio. When the gear sets have tooth numbers as indicated in Table 1, the speed ratios have the values indicated in Table 2. 
     
       
         
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 66 
                 68 
                 70 
                 72 
                 74 
                 76 
                 Ratio 
                 Step 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Rev 
                 X 
                 X 
                   
                 X 
                 X 
                   
                 −4.79 
                 102% 
               
               
                 1 st   
                 X 
                 X 
                 X 
                 (X) 
                   
                   
                 4.70 
               
               
                 2 nd   
                 X 
                 X 
                   
                 X 
                   
                 X 
                 2.99 
                 1.57 
               
               
                 3 rd   
                 X 
                   
                 X 
                 X 
                   
                 X 
                 2.18 
                 1.37 
               
               
                 4 th   
                 X 
                   
                   
                 X 
                 X 
                 X 
                 1.80 
                 1.21 
               
               
                 5 th   
                 X 
                   
                 X 
                   
                 X 
                 X 
                 1.54 
                 1.17 
               
               
                 6 th   
                 X 
                   
                 X 
                 X 
                 X 
                   
                 1.29 
                 1.19 
               
               
                 7 th   
                   
                   
                 X 
                 X 
                 X 
                 X 
                 1.00 
                 1.29 
               
               
                 8 th   
                   
                 X 
                 X 
                 X 
                 X 
                   
                 0.85 
                 1.17 
               
               
                 9 th   
                   
                 X 
                 X 
                   
                 X 
                 X 
                 0.69 
                 1.24 
               
               
                 10 th    
                   
                 X 
                   
                 X 
                 X 
                 X 
                 0.64 
                 1.08 
               
               
                   
               
             
          
         
       
     
     Another example transmission is illustrated in  FIG. 2 . In this transmission, intermediate shaft  64  is selectively coupled to ring gear  48  by clutch  74 ′ while carrier  42  is fixedly coupled to carrier  22  and ring gear  58 . The remaining features are as described with regard to the transmission of  FIG. 1 . Clutch  74 ′ is applied in the same ratios as clutch  74  of  FIG. 1 . 
     A third example transmission is illustrated in  FIG. 3 . In this transmission, clutch  78  selectively couples ring gear  48  to sun gear  56 , clutch  80  selectively couples ring gear  48  to ring gear  38  and sun gear  46 , and clutch  82  selectively couples ring gear  38  and sun gear  46  to sun gear  56 . This module of three clutches, like the module of clutches  72 ,  74 , and  76  in  FIG. 2 , permits the selective coupling of any two of the three rotating elements. In the transmission of  FIG. 2 , selectively coupling two elements is accomplished by engaging two clutches, thereby coupling each element to intermediate shaft  64 . In the transmission of  FIG. 3 , a single clutch is engaged to selectively couple two elements. As shown in Table 3, engaging the clutches and brakes of  FIG. 3  in combinations of three establishes ten forward speed ratios and one reverse speed ratio between input shaft  60  and output shaft  62 . When the gears have the same number of teeth as the corresponding gears in  FIGS. 1 and 2 , the resulting speed ratios are identical. 
     
       
         
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                 66 
                 68 
                 70 
                 78 
                 80 
                 82 
                 Ratio 
                 Step 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Rev 
                 X 
                 X 
                   
                 X 
                   
                   
                 −4.79 
                 102% 
               
               
                 1 st   
                 X 
                 X 
                 X 
                   
                   
                   
                 4.70 
               
               
                 2 nd   
                 X 
                 X 
                   
                   
                   
                 X 
                 2.99 
                 1.57 
               
               
                 3 rd   
                 X 
                   
                 X 
                   
                   
                 X 
                 2.18 
                 1.37 
               
               
                 4 th   
                 X 
                   
                   
                 (X) 
                 X 
                 X 
                 1.80 
                 1.21 
               
               
                 5 th   
                 X 
                   
                 X 
                   
                 X 
                   
                 1.54 
                 1.17 
               
               
                 6 th   
                 X 
                   
                 X 
                 X 
                   
                   
                 1.29 
                 1.19 
               
               
                 7 th   
                   
                   
                 X 
                 X 
                 X 
                 (X) 
                 1.00 
                 1.29 
               
               
                 8 th   
                   
                 X 
                 X 
                 X 
                   
                   
                 0.85 
                 1.17 
               
               
                 9 th   
                   
                 X 
                 X 
                   
                 X 
                   
                 0.69 
                 1.24 
               
               
                 10 th    
                   
                 X 
                   
                 X 
                 X 
                 (X) 
                 0.64 
                 1.08 
               
               
                   
               
             
          
         
       
     
     While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms encompassed by the claims. The words used in the specification are words of description rather than limitation, and it is understood that various changes can be made without departing from the spirit and scope of the disclosure. As previously described, the features of various embodiments can be combined to form further embodiments of the invention that may not be explicitly described or illustrated. While various embodiments could have been described as providing advantages or being preferred over other embodiments or prior art implementations with respect to one or more desired characteristics, those of ordinary skill in the art recognize that one or more features or characteristics can be compromised to achieve desired overall system attributes, which depend on the specific application and implementation. These attributes can include, but are not limited to cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. As such, embodiments described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and can be desirable for particular applications.