Patent Abstract:
A family of transmissions has four planetary gear sets, five controllable clutches and brake, and a passive one way brake. Selective engagement of the brakes and clutches in combinations of three produces eight forward speed ratios and one reverse speed ratio. The passive one way brake is engaged in the first forward speed ratio and overruns in the second through fifth forward speed ratios.

Full Description:
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. 
     A gearing arrangement is a collection of rotating elements and clutches configured to impose specified speed relationships among elements. Some speed relationships, called fixed speed relationships, are imposed regardless of the state of any clutches. A gearing arrangement imposing only fixed relationships is called a fixed gearing arrangement. Other speed relationships are imposed only when particular clutches are fully engaged. A gearing arrangement that selectively imposes speed relationships is called a shiftable gearing arrangement. A discrete ratio transmission has a shiftable gearing arrangement that selectively imposes a variety of speed ratios between an input shaft and an output shaft. 
     A group of elements are fixedly coupled to one another if they are constrained to rotate as a unit in all operating conditions. Elements may 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. In contrast, two elements are selectively coupled by a clutch when the clutch constrains them to rotate as a unit whenever the clutch is fully engaged and they are free to rotate at distinct speeds in at least some other operating condition. Clutches include actively controlled devices such as hydraulically or electrically actuated clutches and passive devices such as one way clutches. A clutch that holds an element against rotation by selectively connecting the element to the housing may be called a brake. A group of elements are coupled if they are fixedly coupled or selectively coupled. 
     The speed ratio of a shiftable gearing arrangement may be changed by altering which clutches are engaged. An upshift occurs when the speed ratio is decreased and a downshift occurs when the speed ratio is increased. During a shift, a controller typically manipulates the torque capacity of at least one controllable clutch. When the state of more than one controllable clutch must change during a shift event, the relative torque capacity of these clutches must be carefully synchronized to avoid torque disturbances that annoy vehicle occupants. Vehicle occupants are most likely to be annoyed by torque disturbances associated with shifts between high speed ratios because the torque disturbances are multiplied by the gearing. The challenge of coordinating the clutch torque capacities during a shift is avoided if either the on-coming or off-going clutch is a passive device. 
     SUMMARY OF THE DISCLOSURE 
     A family of transmissions is disclosed. Each transmission includes an input shaft, an output shaft, a number of rotating elements, and gearing arrangements and clutches that impose specified fixed and selectable speed relationships. Additionally, a method of operating a transmission of the disclosed family is described. 
     In one embodiment, a transmission includes at least first, second, third, fourth, and fifth elements in addition to the input shaft and output shaft. A first gearing arrangement fixedly constrains the relative speeds of the input shaft, first element, second element, and third element. The first gearing arrangement may be, for example, two simple planetary gear sets with the two sun gears fixedly coupled and forming the third element, the first carrier fixedly coupled to the input shaft, the first ring gear and second carrier fixedly coupled and forming the second element, and the second ring gear forming the first element. A second gearing arrangement fixedly constrains the relative speeds of the second, fourth, and fifth elements. The second gearing arrangement may be, for example, a simple planetary gear set having a sun gear as the second element, a planet carrier as the fourth element, and a ring gear as the fifth element. Alternatively, the second gearing arrangement may be, as another example, a double pinion planetary gear set having a sun gear as the second element, a planet carrier as the fifth element, and a ring gear as the fourth element. A third gearing arrangement selectively constrains the relative speeds of output shaft, third element, and fourth element. The third gearing arrangement may be, for example, a simple planetary gear set having a sun gear fixedly coupled to the third element, a planet carrier selectively coupled to the fourth element by a clutch, and a ring gear fixedly coupled to the output shaft. Alternatively, the third gearing arrangement may be, as another example, a simple planetary gear set having a sun gear fixedly coupled to the third element, a planet carrier fixedly coupled to the fourth element, and a ring gear selectively coupled to the output shaft by a clutch. Alternatively, the third gearing arrangement may be, as yet another example, a simple planetary gear set having a sun gear selectively coupled to the third element by a clutch, a planet carrier fixedly coupled to the fourth element, and a ring gear fixedly coupled to the output shaft. Clutches and brakes may selectively hold the fifth element against rotation, selectively hold the first element against rotation, selectively operatively couple the fourth element to the output shaft, and selectively couple the third element to the fifth element. 
     In another embodiment, a transmission includes at least second, third, fourth, and fifth elements in addition to the input shaft and output shaft. A first gearing arrangement selectively constrains the relative speeds of the second and third elements. The first gearing arrangement may be, for example, a simple planetary gear set having a sun gear as the third element, a planet carrier as the second element, and a ring gear selectively held against rotation by a brake. A second gearing arrangement fixedly constrains the relative speeds of the input shaft, the second element, and the third element. The second gearing arrangement may be, for example, a simple planetary gear set having a sun gear as the third element, a planet carrier fixedly couple to the input shaft, and a ring gear as the second element. A third gearing arrangement fixedly constrains the relative speeds of the second, fourth, and fifth elements. A fourth gearing arrangement selectively constrains the relative speeds of output shaft, third element, and fourth element. Clutches and brakes may selectively hold the fifth element against rotation, selectively operatively couple the fourth element to the output shaft, and selectively couple the third element to the fifth element. 
     In another embodiment, a transmission includes five controllable clutches, a passive clutch, and gearing configured to establish eight forward speed ratios and one reverse speed ratio between the input shaft and the output shaft. The passive clutch is engaged in the first forward speed ratio and overruns in the second forward speed ratio. A first forward ratio is established by engaging the first and second controllable clutch while the third, fourth, and fifth controllable clutches remain disengaged. An upshift to a second ratio is accomplished by engaging the third clutch while the first and second clutches remain engaged and the fourth and fifth clutches remain disengaged. Additional upshifts to third through eighth forward ratios are accomplished by engaging one of the five controllable clutches and disengaging another of the five controllable clutches. A reverse ratio is established by engaging the first, third, and fourth controllable clutches while the second and fifth controllable clutches remain disengaged. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a first transmission gearing arrangement; 
         FIG. 2  is a clutch application chart for the first and fourth transmission gearing arrangements; 
         FIG. 3  is a schematic diagram of a second transmission gearing arrangement; 
         FIG. 4  is a clutch application chart for the second transmission gearing arrangement; 
         FIG. 5  is a schematic diagram of a third transmission gearing arrangement; 
         FIG. 6  is a clutch application chart for the third transmission gearing arrangement; 
         FIG. 7  is a schematic diagram of a fourth transmission gearing arrangement; and 
         FIG. 8  is a lever diagram corresponding to the first and fourth transmission gearing arrangements. 
     
    
    
     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 may 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 may 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. 
     An example transmission is schematically illustrated in  FIG. 1 . The transmission utilizes four planetary gear sets  20 ,  30 ,  40 , and  50 . Gear sets  20 ,  30 , and  50  are simple planetary gear sets. A simple planetary gear set is a type of fixed gearing arrangement. 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. A simple planetary gear set imposes the fixed speed relationship that the speed of the carrier is between the speed of the sun gear and the speed of the ring gear. (This relationship is defined to include the condition in which all three rotate at the same speed.) More specifically, the speed of the carrier is a weighted average of the speed of the sun gear and the speed of the ring gear with weighting factors determined by the number of teeth on each gear. 
     Gear set  40  is a double pinion planetary gear set, which is another type of fixed gearing arrangement. A planet carrier  42  rotates about a central axis and supports an inner set of planet gears  44  and an outer set of planet gears  45 . External gear teeth on each of the inner planet gears  44  mesh with external gear teeth on a sun gear  46  and with internal gear teeth on one of the outer planet gears  45 . External gear teeth on each of the outer planet gears  45  mesh with internal gear teeth on a ring gear  48 . The sun gear and ring gear are supported to rotate about the same axis as the carrier. A double pinion planetary gear set imposes the fixed speed relationship that the speed of the ring gear is between the speed of the sun gear and the speed of the carrier. (This relationship is defined to include the condition in which all three rotate at the same speed.) More specifically, the speed of the ring gear is a weighted average of the speed of the sun gear and the speed of the carrier with weighting factors determined by the number of teeth on each gear. Similar speed relationships are imposed by other known types of fixed gearing arrangements. 
     A suggested ratio of gear teeth for each planetary gear set in  FIG. 1  is listed in Table 1. 
     
       
         
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
             
             
               
                   
                 Ring 28/Sun 26 
                 2.73 
               
               
                   
                 Ring 38/Sun 36 
                 1.50 
               
               
                   
                 Ring 48/Sun 46 
                 2.80 
               
               
                   
                 Ring 58/Sun 56 
                 2.29 
               
               
                   
                   
               
             
          
         
       
     
     Input shaft  10  is fixedly coupled to carrier  22 . Output shaft  12  is fixedly coupled to ring gear  58 . Sun gear  26 , sun gear  36 , and sun gear  56  are fixedly coupled to one another. Ring gear  28 , carrier  32 , and sun gear  46  are fixedly coupled to one another. Ring gear  38  is selectively held against rotation by controllable brake  62  and passively held against rotation in one direction by one way brake  60 . Carrier  42  is selectively coupled to sun gear  26 , sun gear  36 , and sun gear  56  by clutch  70  and selectively held against rotation by brake  64 . Ring gear  48  is selectively coupled to carrier  52  by clutch  66  and selectively coupled to ring gear  58  and output shaft  12  by clutch  68 . 
     As shown in  FIG. 2 , engaging the clutches and brakes in combinations of three establishes eight forward speed ratios and one reverse speed ratio between input shaft  10  and output shaft  12 . An X indicates that the clutch is engaged to establish the speed ratio. When the gear sets of  FIG. 1  have tooth numbers as indicated in Table 1, the speed ratios have the values indicated in  FIG. 2 . The highest forward speed ratio, which can be used to accelerate from rest, is established by engaging controllable brake  64  and controllable clutch  68 . One way brake  60  engages passively to transmit power in the positive direction. To upshift into the second highest speed ratio, clutch  66  is engaged. As the torque capacity of clutch  66  increases, the torque carried by one way brake  60  decreases. When the torque capacity of one way brake  60  reaches zero, it overruns. An overrunning condition for a passive clutch is characterized by relative speed between the corresponding elements. For one way brake  60 , the corresponding elements are the transmission case  14  and ring gear  38 . The remaining shifts are accomplished by the coordinated engagement of a controllable clutch or brake and release of a different clutch or brake as indicated in  FIG. 2 . 
     Another example transmission is illustrated in  FIG. 3 . The transmission utilizes three simple planetary gear sets  20 ,  30 , and  50  and one double pinion planetary gear set  40 . A suggested ratio of gear teeth for each planetary gear set is listed in Table 1 above. Input shaft  10  is fixedly coupled to carrier  22 . Sun gear  26 , sun gear  36 , and sun gear  56  are fixedly coupled to one another. Ring gear  28 , carrier  32 , and sun gear  46  are fixedly coupled to one another. Ring gear  48  is fixedly coupled to carrier  52 . Ring gear  38  is selectively held against rotation by controllable brake  62  and passively held against rotation in one direction by one way brake  60 . Carrier  42  is selectively coupled to sun gear  26 , sun gear  36 , and sun gear  56  by clutch  70  and selectively held against rotation by brake  64 . Output shaft  12  is selectively coupled to ring gear  58  by clutch  72  and selectively coupled to ring gear  48  and carrier  52  by clutch  68 . As shown in  FIG. 4 , engaging the clutches and brakes in combinations of three establishes eight forward speed ratios and one reverse speed ratio between input shaft  10  and output shaft  12 . 
     A third example transmission is illustrated in  FIG. 5 . The transmission utilizes three simple planetary gear sets  20 ,  30 , and  50  and one double pinion planetary gear set  40 . A suggested ratio of gear teeth for each planetary gear set is listed in Table 1 above. Input shaft  10  is fixedly coupled to carrier  22 . Output shaft  12  is fixedly coupled to ring gear  58 . Sun gear  26  is fixedly coupled to sun gear  36 . Ring gear  28 , carrier  32 , and sun gear  46  are fixedly coupled to one another. Ring gear  48  is fixedly coupled to carrier  52 . Ring gear  38  is selectively held against rotation by controllable brake  62  and passively held against rotation in one direction by one way brake  60 . Carrier  42  is selectively held against rotation by brake  64 . Sun gear  26  and sun gear  36  are selectively coupled to carrier  42  by clutch  70  and selectively coupled to sun gear  56  by clutch  74 . Output shaft  12  and ring gear  58  are selectively coupled to ring gear  48  and carrier  52  by clutch  68 . Note that engaging clutch  68  forces gear set  50  to rotate as a unit. Clutch  68  could alternatively accomplish this function by selectively coupling any two of the elements of gear set  50 . As shown in  FIG. 6 , engaging the clutches and brakes in combinations of three establishes eight forward speed ratios and one reverse speed ratio between input shaft  10  and output shaft  12 . 
     A fourth example transmission is illustrated in  FIG. 7 . The transmission utilizes four simple planetary gear sets  20 ,  30 ,  80 , and  50 . The planet gears  84  of gear set  80  are wide enough to mesh with two ring gears  88  and  90 . Although ring gear  88  and ring gear  90  are not directly connected, they are forced to rotate at the same speed by the interaction with planet gear  84 . The carrier  82  of gear set  80  extends outwardly between ring gears  88  and  90  in the circumferential space between the planet gears  84 . A suggested ratio of gear teeth for each planetary gear set is listed in Table 2. 
     
       
         
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
             
             
               
                   
                 Ring 28/Sun 26 
                 2.73 
               
               
                   
                 Ring 38/Sun 36 
                 1.50 
               
               
                   
                 Ring 48/Sun 46 
                 1.80 
               
               
                   
                 Ring 58/Sun 56 
                 2.29 
               
               
                   
                   
               
             
          
         
       
     
     Input shaft  10  is fixedly coupled to carrier  22 . Output shaft  12  is fixedly coupled to ring gear  58 . Sun gear  26 , sun gear  36 , and sun gear  56  are fixedly coupled to one another. Ring gear  28 , carrier  32 , and sun gear  86  are fixedly coupled to one another. Ring gear  38  is selectively held against rotation by controllable brake  62  and passively held against rotation in one direction by one way brake  60 . Ring gear  90  is selectively coupled to sun gear  26 , sun gear  36 , and sun gear  56  by clutch  70 . Ring gear  88  is selectively held against rotation by brake  64 . Carrier  82  is selectively coupled to carrier  52  by clutch  66  and selectively coupled to ring gear  58  and output shaft  12  by clutch  68 . As shown in  FIG. 2 , engaging the clutches and brakes in combinations of three establishes eight forward speed ratios and one reverse speed ratio between input shaft  10  and output shaft  12 . 
       FIG. 8  describes the transmissions of  FIGS. 1 and 7  in the form of a lever diagram. Gear elements which rotate about a common axis and have speeds with a fixed linear relationship are shown along a lever according to their relative speeds. The two elements that have the most extreme speeds are shown at the endpoints of the lever. The remaining elements are shown at intermediate points according to the weighting factors. Four node lever  92  corresponds to gear sets  20  and  30  with ring gear  38  as the 1st element, ring gear  28  and carrier  32  as the 2nd element, and sun gears  26  and  36  as the 3rd element. The 1st and 3rd elements will have the most extreme speeds among the four elements in all operating conditions. The input and 2nd element will have intermediate speeds with the speed of the 2nd element closer to that of the 1st element and the speed of the input closer to that of the 3rd element. Many known fixed gearing arrangements impose the speed relationship represented by a four node lever. Specifically, any two simple or double pinion planetary gear sets with two fixed connections can be represented by a four node lever. Also, the speed relationship may be implemented by arrangements with shared planet gears or stepped planet gears. Gear sets  20  and  30  may be replaced with another fixed gearing arrangement that imposes the same speed relationships without impacting the operation or resulting speed ratios. Some of these gearing arrangements will be preferable to others in terms of packaging, efficiency, and planet gear speeds. Similarly, lever  94  corresponds to either gear set  40  of  FIG. 1  or gear set  80  of  FIG. 7 . In  FIG. 1 , sun gear  46  is the 2nd element, ring gear  48  is the 4th element, and carrier  42  is the 5th element. In  FIG. 7 , sun gear  86  is the 2nd element, carrier  82  is the 4th element, and ring gears  88  and  90  are the 5th element. Finally, lever  96  corresponds to gear set  50 , with the 3rd element corresponding to sun gear  56 , the 6th element corresponding to carrier  52 . 
     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 may be made without departing from the spirit and scope of the disclosure. As previously described, the features of various embodiments may 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 may 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.

Technology Classification (CPC): 5