Abstract:
A multi-speed automatic transmission includes a housing, a transmission input shaft, and a plurality of clutches. Different combinations of clutches of the plurality of clutches are engaged to generate different gear ratios corresponding to respective forward speeds of the automatic transmission. The plurality of clutches are positioned within the housing and include a first friction clutch coupled the input shaft and having a first hub, and a second friction clutch having a second clutch hub. The second friction clutch is disposed about the input shaft and radially nested within the first clutch hub such that the second friction clutch is positioned radially between the first clutch hub and the input shaft. The first friction clutch is engaged to generate at least two forward speeds of the transmission and the second friction clutch is engaged to generate seven forward speeds of the transmission including the two forward speeds.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. Provisional Application Ser. No. 62/290,181, filed Feb. 2, 2016, the contents of which are incorporated herein by reference thereto. 
     
    
     FIELD 
       [0002]    The present application relates generally to an automatic transmission and, more particularly, to a clutch arrangement for improved shifting performance of a motor vehicle automatic transmission. 
       BACKGROUND 
       [0003]    Some automatic transmissions may include clutches that must be rotationally synchronized before they can be engaged, such as a dog clutch. However, use of such a clutch with the required time for synchronization may require a longer duration of time for clutch engagement to occur, for example, when shifting from Reverse (R) to Drive (D) or when downshifting multiple gears. Thus, while such transmissions and associated clutch systems work for their intended purpose, it is desirable to provide improved shifting performance in an automatic transmission. 
       SUMMARY 
       [0004]    In accordance with one example aspect of the invention, a multi-speed automatic transmission is provided. In one exemplary implementation, the transmission includes a housing, a transmission input shaft, and a plurality of clutches. Different combinations of clutches of the plurality of clutches are engaged to generate respective different gear ratios corresponding to respective forward speeds of the automatic transmission. The plurality of clutches includes a first friction clutch coupled the input shaft and having a hub, and a second friction clutch having a second hub and disposed about the input shaft and radially nested within the first clutch hub such that the second clutch is positioned radially between the first clutch hub and the input shaft. The first friction clutch is engaged to generate at least two forward speeds of the transmission and the second friction clutch is engaged to generate seven forward speeds of the transmission including the two forward speeds. 
         [0005]    In addition to the foregoing, in one exemplary implementation, the second friction clutch includes a clutch pack associated with the second friction clutch hub, and the clutch pack includes alternating first and second friction discs. The first friction discs are directly coupled to the second friction clutch hub and the second friction discs are directly coupled to the first friction clutch hub. 
         [0006]    In an exemplary implementation, the first and second friction clutch hubs each include an axially extending base leg portion coupled to input shaft, a radially extending first arm portion, and an axially extending second arm portion extending from the first arm portion. In this exemplary implementation, the second friction clutch is nested within the hub of the first friction clutch such that the axially extending second arm portion of the second clutch is disposed radially between the input shaft and the axially extending second arm portion of the first clutch. In addition, the radially extending first arm portion of the second clutch may be positioned beneath the axially extending second arm portion of the first clutch and radially between the input shaft and the axially extending second arm portion of the first clutch. 
         [0007]    In an exemplary implementation, the transmission a third clutch, a fourth clutch, a fifth clutch, and a sixth clutch; wherein the third clutch, the fourth clutch and the fifth clutch are each brake clutches and the sixth clutch is a dog clutch. In one exemplary implementation, the automatic transmission only includes a single dog clutch. 
         [0008]    In one exemplary implementation, the transmission includes nine forward speeds, and different combinations of three clutches of the plurality of clutches are engaged to generate the respective different gear ratios corresponding to the respective nine forward speeds of the transmission. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0009]      FIG. 1  is a partial schematic view of an exemplary motor vehicle nine-speed automatic transmission in accordance with the principles of the present application; 
           [0010]      FIG. 2  is a partial schematic illustration of the exemplary automatic transmission of  FIG. 1  in accordance with the principles of the present application; 
           [0011]      FIG. 3  is a view of a table illustrating engagement of various transmission clutches in connection with shifting of various transmission gears in accordance with the principles of the present application; and 
           [0012]      FIG. 4  is perspective sectional composite illustration comparing the exemplary nine-speed automatic transmission of  FIG. 1  (shown above line ‘X’) with a typical nine-speed automatic transmission (shown below line ‘X’) in accordance with the principles of the present application. 
       
    
    
       [0013]    Further areas of applicability of the teachings of the present application will become apparent from the detailed description, claims and the drawings. It should be understood that the detailed description, including disclosed embodiments and drawings referenced therein, are merely exemplary in nature intended for purposes of illustration only and are not intended to limit the scope of the present application, its application or uses. Thus, variations that do not depart from the gist of the present application are intended to be within the scope of the present application. 
       DESCRIPTION 
       [0014]    As briefly mentioned above, the present application is directed to a system and method for improving shifting in an automatic transmission. In one exemplary implementation, the present application relates to an improved system and method for engaging a clutch element without rotational synchronization requirements and subsequent time delays in transmission shifting function. In one exemplary implementation, a friction disc clutch, nested within an envelope of another friction disc clutch, is utilized to provide the improved transmission shifting attributes. 
         [0015]    Referring to  FIGS. 1-3 , a nine-speed automatic transmission for use in a motor vehicle is generally shown and indicated at reference numeral  10 . However, the systems and methods described herein are not limited to nine-speed automatic transmissions and may be utilized in other transmissions such as, for example, an eight-speed automatic transmission. As shown in  FIG. 2 , the nine-speed automatic transmission  10  is linked to an engine (not shown) through an engine output shaft  12 . Rotational output from the engine output shaft  12  is received by the automatic transmission  10  through a torque converter assembly  14 . The torque converter assembly  14  then transfers the rotational output through a gear set  16  to a transmission output shaft  32 , and then on to the drivetrain of the motor vehicle. 
         [0016]    The gear set  16  of the automatic transmission  10  includes a first planetary gear set  20 , a second planetary gear set  22 , a third planetary gear set  24 , a fourth planetary gear set  26 , and a housing  28 . In one exemplary implementation, the first and second planetary gear sets  20 ,  22  form a shiftable front-mounted gear set, and the third and fourth planetary gear sets  24 ,  26  form a main gear set. 
         [0017]    With particular reference to  FIG. 2 , in the exemplary implementation, the automatic transmission  10  comprises six shift elements including three clutches and three brakes. In particular, automatic transmission  10  includes a first clutch A, a second clutch B, a third clutch E, and a fourth clutch F, as well as a first brake/clutch C and a second brake/clutch D. Clutches A, B and E are, in the exemplary implementation illustrated, friction clutches. In the example nine-speed automatic transmission  10 , selective shifting of nine forward gears and one reverse gear are accomplished with the six shift elements. As will be described herein in more detail, in one exemplary implementation, first clutch A is a friction disc clutch, and fourth clutch F is a dog clutch. 
         [0018]    In one exemplary implementation, the automatic transmission  10  includes eight rotatable shafts  30 ,  32 ,  34 ,  36 ,  38 ,  40 ,  42 , and  44 , as illustrated in  FIG. 2 . The clutches A, B, and E are each selectively engageable to receive torque input from the torque converter assembly  14  via transmission input shaft  30 . The carriers of the first and second planetary gear sets  20 ,  22  are coupled together by shaft  36 , which is connected to the ring gear of the third planetary gear set  24 . The ring gear of the first planetary gear set  20  is coupled to the sun gear of the second planetary gear set  22  through shaft  44 , which is selectively coupled to the input shaft  30  by disc clutch A. 
         [0019]    The sun gear of the first planetary gear set  20  is coupled to housing  28  through shaft  34  and the brake clutch C. The first planetary gear set  20  is selectively coupled to the transmission input shaft  30  through disc clutch A. The ring gear of the second planetary gear set  22  is coupled to the housing  28  through shaft  38  and brake clutch D. 
         [0020]    In the exemplary implementation, shaft  40  is coupled to the ring gear of the fourth planetary gear set  26  and to the carrier of the third planetary gear set  24 . The shaft  40  is selectively coupled to the transmission input shaft  30  and clutch E, while shaft  42  is coupled to the sun gears of the third and fourth planetary gear sets  24 ,  26 . The shaft  42  is coupled to transmission housing  28  through dog clutch F. The output shaft  32 , which produces output drive for the vehicle, is coupled to the carrier of the fourth planetary gear set  26 . 
         [0021]      FIG. 3  illustrates an exemplary shift pattern of the nine-speed automatic transmission  10 . The table illustrates the combination of clutches and brakes engageable to achieve specific torque input-to-output ratios. In the example table, each clutch and brake combination corresponds to one of nine forward gear speeds and a reverse speed. The shift pattern illustrates example transmission ratios of the individual gear steps, as well as the gear increments and step changes. In this particular transmission, three shift elements are engaged for every gear, as represented by the circles in the table cells. 
         [0022]    As discussed above, clutch F may be designed as a locking shift element or dog clutch element. In one exemplary implementation, the dog clutch F and associated components include a male externally splined clutch member, a female internally splined clutch member configured to receive the male clutch member for engagement of the dog clutch F, a piston, a sensing sleeve and associated sensor(s) and fluid passages. 
         [0023]    Clutch element A is designed as a friction disc clutch. Unlike a dog clutch, which requires rotational speed synchronization prior to and during engagement, disc clutch A enables immediate or substantially immediate engagement without the aforementioned time delays because no speed synchronization and tooth engagement is required with friction or disc clutch A. 
         [0024]      FIG. 4  is a composite illustration comparing the nine-speed automatic transmission  10  of the present application (shown above line ‘X’) compared with a typical nine-speed automatic transmission  900  (shown below line ‘X’). As illustrated, the typical nine-speed automatic transmission includes a clutch element A formed as a dog clutch  950 . The dog clutch  950  arrangement is desirable for its reduced packaging size and reduced drag, which improves transmission efficiency. 
         [0025]    However, due to its splined structure, dog clutch  950  requires rotational synchronization(s) when moving to an engaged position due to the metal-to-metal meshing engagement between spline teeth of dog clutch  950  and spline teeth of the receiving member. The spline teeth of each component will not mesh well if they are not spinning the same speed, thereby requiring rotational synchronization, which may subsequently cause time delays in transmission shifting function. For example, transmission  900  may experience a delay or hesitation during shifting, particularly when shifting from reverse (R) to drive (D), or downshifting from 8 th  gear to 4 th  gear. Further, a typical requirement of full or substantially full engagement of the dog clutch male and female toothed members may cause an additional time delay in shifting associated transmission gears. 
         [0026]    In contrast to the typical nine-speed automatic transmission  900 , the nine-speed automatic transmission  10  of the present application includes a friction disc clutch as clutch element A. Unlike a dog clutch, disc clutch A provides a smoother and more immediate engagement during shifting, thereby eliminating the rotational synchronization requirements before and during engagement that can cause subsequent potentially objectionable time delays when shifting. As such, disc clutch A provides improvement in shift time and shift quality. Moreover, disc clutch A can be packaged within transmission  10  without extending the length of the typical nine-speed transmission  900 , thereby enabling automatic transmission  10  to be used in vehicles designed to accept transmission  900   
         [0027]    With reference to  FIGS. 1 and 4 , transmission  10  includes a friction disc clutch element A instead of a dog clutch element. In the illustrated implementation, disc clutch A is radially nested within a hub  48  of clutch B such that clutch A is positioned radially between hub  48  and input shaft  30 . Moreover, in some examples, clutch A is located radially below clutches B, C, D, and E, radially above clutch F, and axially relative to clutches C, D, E, and F. In this exemplary implementation, the dog clutch F is the only dog clutch in the transmission  10 . 
         [0028]    Disc clutch A includes a hub  50  and a multi-plate clutch pack  52 . In the example implementation, hub  50  is disposed about input shaft  30  and includes an axially extending base leg portion  54  coupled to shaft  30 , a radially extending first arm portion  56 , and an axially extending second arm portion  58 . Similarly, clutch B hub  48  includes an axially extending base leg portion  60  coupled (e.g., splined) to shaft  30 , a radially extending first arm portion  62 , and an axially extending second arm portion  64 . 
         [0029]    Multi-plate clutch pack  52  is formed of intermeshed, alternating first and second friction discs  76 ,  78 . The first friction discs  76  are externally coupled (e.g., splined) to hub  50 , and the second friction discs  78  are internally coupled (e.g., splined) to the clutch B hub  48 . When disc clutch A is disengaged, the first friction discs  76  rotate freely between the second friction discs  78 . When disc clutch A is engaged, for example through pressure applied by a hydraulic piston  80 , first friction discs  76  frictionally engage the second friction discs  78 , and disc clutch A is subsequently rotated by clutch B hub  48 , which is coupled to input shaft  30  for rotation therewith. When engaged, disc clutch A transfers rotary motion through a toothed or splined connection  92  ( FIG. 1 ) to drive a ring gear that goes into the carrier. A return spring  82  causes first friction discs  76  to disengage the second friction discs  78  when the hydraulic pressure is released from hydraulic piston  80 . 
         [0030]    In one exemplary implementation, a second hydraulic piston  84  is coupled to input shaft  30  and configured to engage a clutch pack  86  of clutch B with a hub  94  of clutch C (see  FIG. 1 ). A return spring  88  causes clutch pack  86  (shown only in  FIG. 1 ) to disengage when hydraulic pressure is released from the hydraulic piston  84 . A retainer  90  is coupled between input shaft  30  and second hydraulic piston  84  and is configured to retain the second hydraulic piston  84  on the shaft  30 . 
         [0031]    With continued reference to  FIG. 4 , automatic transmission  10  includes various additional modifications that distinguish it from the typical nine-speed automatic transmission  900 . In particular, clutch B hub  48  has been modified to include an internal spline  100  for clutch A (i.e., discs  78  are splined to hub  48 ), seal grooves  102  are provided for pistons  80  and  84 , and feed holes (not shown) are provided to clutch A circuit  106  and clutch B circuit  108 . Additionally, input shaft  30  is provided with a spline for connecting and driving clutch B hub  48 . Moreover, because packaging space is limited for automatic transmission  10 , a case rear wall  110  was reshaped, internal ribs (not shown) were removed, and rear lube-feed worm trails and cover plate (not shown) were replaced with cross drills and plugs (not shown) to create additional space. 
         [0032]    The systems and methods described herein provide an automatic transmission with improved shifting. The transmission replaces a typical dog clutch arrangement of clutch element A with a disc clutch arrangement. The replacement is such that no change in length or size is required for the transmission. Moreover, the disc clutch A is radially nested within the envelope of the B clutch, which improves packaging. The disc clutch A arrangement eliminates the need for rotational synchronization and subsequent time delays in the transmission function associated with dog clutch A arrangements. Accordingly, the disc clutch A arrangement improves vehicle function when shifting to drive (D) from park (P), reverse (R), or neutral (N), and improves shift time coming out of 8 th  gear. 
         [0033]    It will be understood that the mixing and matching of features, elements, methodologies, systems and/or functions between various examples are expressly contemplated herein so that one skilled in the art will appreciate from the present teachings that features, elements, systems and/or functions of one example may be incorporated into another example as appropriate, unless described otherwise above. It will also be understood that the description, including disclosed examples and drawings, is merely exemplary in nature intended for purposes of illustration only and is not intended to limit the scope of the present disclosure, its application or uses. Thus, variations that do not depart from the gist of the present disclosure are intended to be within the scope of the present disclosure.