Abstract:
A multiple clutch module for an automatic transmission integrates at least two multi-plate wet clutches into a single module. Each of the clutches includes a set of separator plates interleaved with at least one friction plate and a piston configured to compress the separators plates and friction plates. The separator plates of the first clutch are splined to a housing along their inner diameter whereas the separator plates of the second clutch are splined to the housing along their outer diameter. Each piston is associated with an apply chamber and a balance chamber radially inside the respective separator plates and friction plates. The housing rotates about a central shaft. Pressurized fluid is supplied to the clutches from the shaft. The first and second balance chambers are connected by a passageway within the housing such that they can be supplied with fluid from a common orifice in the housing.

Description:
TECHNICAL FIELD 
     This disclosure relates to the field of automatic transmissions for motor vehicles. More particularly, the disclosure pertains to a configuration of clutches for use in a 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 common type of automatic transmission utilizes a collection of clutches and brakes. Various subsets of the clutches and brakes are engaged to establish the various speed ratios. A common type of clutch utilizes a clutch pack having separator plates splined to a housing and interleaved with friction plates splined to a rotating shell. When the separator plates and the friction plates are forced together, torque may be transmitted between the housing and the shell. Typically, a separator plate on one end of the clutch pack, called a reaction plate, is axially held to the housing. A piston applies axial force to a separator plate on the opposite end of the clutch pack, called a pressure plate, compressing the clutch pack. The piston force is generated by supplying pressurized fluid to a chamber between the housing and the piston. For a brake, the housing may be integrated into the transmission case. For a clutch, the housing rotates. As the pressurized fluid flows from the stationary transmission case to the rotating housing, it may need to cross one or more interfaces between components rotating at different speeds. At each interface, seals direct the flow from an opening in one component into an opening in the interfacing component. 
     SUMMARY OF THE DISCLOSURE 
     A transmission includes a clutch housing, three clutch packs, and three pistons. The first and second of the three clutch packs include separator plates splined to the housing and friction plates splined to first and second shells, respectively. An input shaft extends through the housing. The third of the three clutch packs includes separator plates splined to the input shaft and friction plates splined to the second shell. The three pistons are configured to apply force to the respective clutch packs. A sun gear of a first planetary gear set may be fixedly coupled to the second shell. The transmission may also include a second planetary gear set with a sun gear fixedly coupled to the first shell and a ring gear fixedly coupled to the housing. 
     In one embodiment, a clutch module includes a housing configured to rotate about a shaft, a first set of separator plates splined to the housing along their outer edges, and a second set of separator plates splined to the housing along their inner edges. The inner diameter of the second separator plates is less than the outer diameter of the first separator plates. The clutch module may also include a first piston configured to apply force to the first separator plates and, in conjunction with the housing, defining a first apply chamber with an outer diameter less than the inner diameter of the first separator plates. The clutch module may also include a second piston configured to apply force to the second separator plates and, in conjunction with the housing, defining a second apply chamber with an outer diameter less than the inner diameter of the second separator plates. The housing, first piston, and second piston, may also define first and second balance chambers connected to one another by a passageway. 
     In another embodiment, a clutch module includes a housing configured to rotate about a shaft, two clutch packs, and two pistons. The clutch packs each includes separator plates splined to the housing and interleaved with friction plates. The first and second pistons are configured to compress the first and second clutch packs, respectively. The pistons and the housing define first and second apply chambers. The outer diameter of the first apply chamber is less than the inner diameter of the first separator plates. Similarly, the outer diameter of the second apply chamber is less than the inner diameter of the second separator plates. The housing may be fixedly coupled to a ring gear. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a transmission gearing arrangement. 
         FIG. 2  is a cross section of one of the clutches and one of the planetary gear sets of a transmission according to the gearing arrangement of  FIG. 1 . 
         FIG. 3  is a cross section of three of the clutches and one of the planetary gear sets of a transmission according to the gearing arrangement of  FIG. 1 . 
         FIG. 4  is a cross section of three of the clutches and one of the planetary gear sets of a transmission according to the gearing arrangement of  FIG. 1 . 
     
    
    
     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 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. 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 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 . Ring gear  48  is selectively coupled to sun gear  56  by clutch  72  and selectively coupled to ring gear  38  and sun gear  46  by clutch  76 . Carrier  42  is selectively coupled to carrier  22  and ring gear  58  by clutch  74 . 
     As shown in Table 2, engaging the shift elements 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 shift element is required to establish the speed ratio. An (X) indicates the shift element 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 
               
               
                   
               
             
          
         
       
     
       FIG. 2  shows a cross sectional view of the center section of a transmission according to the gearing arrangement of  FIG. 1 . The cross section of  FIG. 2  is taken between the planetary gears  44  of gear set  40 . Housing  80  of clutch  74  is integrated with the carrier  42  of gear set  40 . A collection of separator plates  82  is splined at their inner edges to housing  80 . A collection of friction plates  84  is interleaved with separator plates  82  and splined at their outer edges to shell  86 . Shell  86  is fixedly coupled to carrier  22  and ring gear  58 . Piston  88  is supported to slide axially within housing  80 . The contact points between housing  80  and piston  88  have seals such that housing  80  and piston  88  define two chambers  90  and  92 . The chambers have inner and outer diameters defined by the contact points between the housing and the piston. Clutch  74  is engaged by pressurizing fluid in clutch apply chamber  90  such that piston  88  slides toward gear set  40  and compresses friction plates  84  between separator plates  82 . When housing  80  rotates, centrifugal forces may pressurize fluid within clutch apply chamber  90  which could potentially result in unintended engagement of clutch  74 . However, fluid in balance chamber  92  is subject to the same centrifugal forces, exerting a compensating force on piston  88  to preclude this failure mode. Fluid reaches chambers  90  and  92  via axial passageways in input shaft  60  then through holes in hollow shaft  94 . Hollow shaft  94  is fixedly coupled to ring gear  38  and sun gear  46 . Return spring  96 , which extends into the space between planet gears, forces piston  88  to slide away from gear set  40  when pressure in chamber  90  is relieved. 
       FIG. 3  shows a cross sectional view of a transmission according to the gearing arrangement of  FIG. 1  slightly rearward from the view of  FIG. 2 . The cross section of  FIG. 3  is taken through the center of one of the planetary gears  44  of gear set  40 . Housing  98  of clutches  72  and  74  is fixedly coupled to ring gear  48  of gear set  40 . A collection of separator plates  100  is splined at their outer edges to housing  98 . A collection of friction plates  102  is interleaved with separator plates  100  and splined at their inner edges to shell  104 . Shell  104  is fixedly coupled to hollow shaft  94 . Piston  106  is supported to slide axially within housing  98 . Housing  98  and piston  106  define two chambers  108  and  110 . Clutch  76  is engaged by pressurizing fluid in clutch apply chamber  108  such that piston  106  slides toward gear set  40  and compresses friction plates  102  between separator plates  100 . Centrifugal force acting on the fluid in balance chamber  110  compensates for centrifugal force acting on the fluid in clutch apply chamber  108 . Return spring  112  forces piston  106  to slide away from gear set  40  when pressure in chamber  108  is relieved. 
     A collection of separator plates  114  is splined at their inner edges to housing  98 . A collection of friction plates  116  is interleaved with separator plates  114  and splined at their outer edges to shell  118 . Shell  118  is fixedly coupled to sun gear  56 . Piston  120  is supported to slide axially within housing  98 . Housing  98  and piston  120  define two chambers  122  and  124 . Clutch  72  is engaged by pressurizing fluid in clutch apply chamber  122  such that piston  120  slides toward gear set  40  and compresses friction plates  116  between separator plates  114 . Centrifugal force acting on the fluid in balance chamber  124  compensates for centrifugal force acting on the fluid in clutch apply chamber  120 . Return spring  126  forces piston  120  to slide away from gear set  40  when pressure in chamber  122  is relieved. Fluid reaches chambers  108 ,  110 ,  122 , and  124  via axial passageways in input shaft  60 . A passageway within housing  98  connects balance chambers  110  and  124 . 
     Housings  80  and  98  are described as single components. However, they likely would be manufactured in several pieces which are fastened together during assembly. Clutch  74  may be assembled before installation into the transmission. Similarly, clutches  76  and  72  may be assembled into a two clutch module before installation into the transmission. 
       FIG. 4  shows a cross sectional view of a transmission according to the gearing arrangement of  FIG. 1  slightly rearward from the view of  FIG. 3 . Housing  128  of clutch  70  is fixedly coupled to input shaft  60 . A collection of separator plates  130  is splined at their inner edges to housing  128 . A collection of friction plates  132  is interleaved with separator plates  130  and splined at their outer edges to shell  118 . Piston  134  is supported to slide axially within housing  128 . Housing  128 , piston  134 , and input shaft  60  define two chambers  136  and  138 . Clutch  70  is engaged by pressurizing fluid in clutch apply chamber  136  such that piston  134  slides toward gear set  40  and compresses friction plates  132  between separator plates  130 . Centrifugal force acting on the fluid in balance chamber  138  compensates for centrifugal force acting on the fluid in clutch apply chamber  136 . Return spring  140  forces piston  134  to slide away from gear set  40  when pressure in chamber  136  is relieved. 
     A single passageway in input shaft  60  supplies unpressurized fluid to balance chambers  92 ,  110 ,  124 , and  138 . The same passageway may supply fluid to other parts of the transmission for lubrication. Separate passageways supply clutch apply chambers  90 ,  108 ,  122 , and  136  such that each clutch may be engaged and disengaged independently of the other clutches. Fluid may flow into these five passageways in input shaft  60  either from a front support, through the output shaft, or a combination of these. 
     The configuration of clutches in  FIGS. 2-4  places the apply chamber and balance chamber at the same axial position and radially inside the respective clutch pack. This reduces the axial length of the transmission relative to placing the clutch packs axially in line with the apply chamber and balance chamber. Since fluid pressure is supplied to the clutches from central shaft, locating the chambers near the centerline reduces the need for radial passageways. Furthermore, since the torque capacity of each clutch is directly proportional to the mean diameter of the clutch pack, locating the clutch packs radially outside of the apply chambers reduces the number of friction plates required or the required area of the apply chamber. 
     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.