Abstract:
A multiple speed automatic transmission includes an input member, an output member, a plurality of planetary gear sets, a plurality of interconnecting members and a plurality of torque transmitting devices. Each of the plurality of planetary gear sets has a sun gear, a planet carrier with a plurality of planet gears and a ring gear. The torque transmitting devices include three clutches, a conventional first brake and a second brake comprising a parallel combination of an overrunning clutch and a light duty or coast clutch. Eight forward speeds and one reverse speed are achieved by selective engagement of the five torque transmitting devices.

Description:
TECHNICAL FIELD 
       [0001]    The invention relates to a multiple speed automatic transmission having both a plurality of planetary gear sets and torque transmitting devices that are selectively engageable to achieve multiple gear ratios. 
       BACKGROUND 
       [0002]    A typical modern multiple speed automatic transmission includes a combination of planetary gear assemblies and selectively engaged friction clutches and to achieve a plurality of gear ratios. 
         [0003]    Increasingly demanding economic and performance goals continue to encourage automatic transmission research and development. A result of this effort has been an increase in the number of available forward gears or speed ratios provided by the transmission. 
         [0004]    Whereas three and four speed automatic transmissions were once commonplace, considered both suitable and to provide sufficient flexibility and performance, the industry and consumer preference is moving to six, seven and eight speed automatic transmissions. 
         [0005]    In such transmissions, the various elements of a plurality of planetary gear assemblies are connected by permanent couplings, selectively connected by clutches and selectively grounded by brakes. Specific combinations of the clutches and brakes are engaged or activated to provide a sequence of numerically related gear ratios and thus speed and torque ratios. 
         [0006]    Because they so closely match the power and torque curves of the engine to the vehicle speed and load, such six, seven and eight speed transmissions provide significant performance enhancements and fuel consumption reduction. 
         [0007]    Careful study of these transmission configurations, however, reveals that improvements are both possible and desirable. For example, each of the torque transmitting devices, i.e., the clutches and brakes, contribute to frictional losses, referred to as spin losses, when they are not engaged. Two primary factors influence spin losses: the size or torque capacity of the clutch and the instantaneous speed difference across the clutch. A particularly disadvantageous condition arises if the device is a high torque capacity, multiple plate clutch functioning as a brake with a high speed difference across it. Since a brake typically has one half of its friction members connected to ground which are therefore always stationary, the spin losses in such a situation may be relatively significant. 
         [0008]    The present invention is directed to reducing frictional or spin losses created by the clutches and brakes of a multiple speed automatic transmission. 
       SUMMARY 
       [0009]    A multiple speed automatic transmission is provided having an input member, an output member, a plurality of planetary gear sets, a plurality of interconnecting members and a plurality of torque transmitting devices. The input member is connected to and drives a planet gear carrier of a first planetary gear set. The output member is connected to and is driven by a planet gear carrier of the third planetary gear set. A first interconnecting member connects a sun gear of the first planetary gear set with a sun gear of the fourth planetary gear set. A second interconnecting member connects a planet gear carrier of the fourth planetary gear set with a ring gear of the second planetary gear set. A third interconnecting member connects a ring gear of the first planetary gear set with a sun gear of the second planetary gear set. A fourth interconnecting member connects a planet gear carrier of the third planetary gear set with a planet gear carrier of the second planetary gear set. 
         [0010]    The plurality of torque transmitting devices including two brakes and three clutches are selectively engageable in various combinations of three to establish eight forward gear ratios and one reverse gear ratio between the input member and the output member. A first brake selectively connects the sun gear of the fourth planetary gear set with a stationary member. A second compound brake selectively connects a ring gear of the fourth planetary gear set with the stationary member. The second compound brake includes a selectable one way clutch and a light duty or coast clutch disposed in mechanical parallel. Preferably, the light duty clutch includes a single rotating disc or plate. A first clutch selectively connects the planet gear carrier of the first planetary gear set with a sun gear of the third planetary gear set. A second clutch selectively connects the sun gear of the second planetary gear set with the sun gear of the third planetary gear set. A third clutch selectively connects a ring gear of the second planetary gear set with the sun gear of the third planetary gear set. 
         [0011]    A multiple speed automatic transmission incorporating the present invention exhibits significantly reduced frictional, i.e., spin losses. 
         [0012]    Thus it is an object of the present invention to provide a multiple speed automatic transmission having four planetary gear sets and five selectable torque transmitting devices. 
         [0013]    It is a further object of the present invention to provide a multiple speed automatic transmission having a compound brake including a selectable one way clutch. 
         [0014]    It is a further object of the present invention to provide a multiple speed automatic transmission having a compound brake including a selectable one way clutch and a light duty or coast clutch in parallel. 
         [0015]    It is a still further object of the present invention to provide a multiple speed automatic transmission exhibiting reduced spin losses. 
         [0016]    The above features and advantages and other features and advantages of the present invention will be readily apparent from the following detailed description of the preferred embodiment for carrying out the invention when taken in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is a schematic representation of an embodiment of an automatic transmission in accordance with the present invention; 
           [0018]      FIG. 2  is a truth table listing the engaged torque transmitting devices for selected torque or gear ratios achieved by the automatic transmission of  FIG. 1 ; and 
           [0019]      FIG. 3  is a lever diagram of the automatic transmission of  FIG. 1  illustrating the power flow from the input through the planetary gear sets to the output, in accordance with the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0020]    Referring to the drawings, wherein like reference numbers refer to the same component, element or feature, in  FIG. 1  a multiple speed automatic transmission  10  is depicted. The automatic transmission  10  includes an input member  12  and an output member  14 . In the present embodiment, the input member  12  and the output member  14  are shafts, and will be referred to as such. Those skilled in the art will appreciate that the input member  12  and the output member  14  may be components other than shafts such as quills. The input shaft  12  is continuously connected to an engine (not shown) or to a turbine of a torque converter (not shown). The output shaft  14  is continuously connected with the final drive unit such as a differential or transfer case (both not shown). 
         [0021]    The automatic transmission  10  includes four planetary gear sets  16 ,  18 ,  20  and  22 . The planetary gear sets  16 ,  18 ,  20  and  22  are operably disposed between the input shaft  12  and the output shaft  14 . In the preferred embodiment of the present invention, the first planetary gear set  16  is a simple planetary gear set that includes a first sun gear member  24 , a first ring gear member  26  and a first planet carrier member  28  that rotatably supports a first plurality of pinion gears  30  (only one of which is shown). The first plurality of pinion gears  30  are configured to intermesh with the first sun gear member  24  and the first ring gear member  26 . The first sun gear member  24  is connected for common rotation with a first intermediate shaft or quill  32 . The first ring gear member  26  is connected for common rotation with a second intermediate shaft or quill  34 . The first planet carrier member  28  is connected for common rotation with the input shaft  12 . 
         [0022]    In the preferred embodiment of the present invention, the second planetary gear set  18  is a simple planetary gear set that includes a second sun gear member  42 , a second ring gear member  44  and a second planet carrier member  46  that rotatably supports a second plurality of pinion gears  48  (only one of which is shown). The second plurality of pinion gears  48  are configured to intermesh with both the second sun gear member  42  and the second ring gear member  44 . The second sun gear member  42  is connected for common rotation with the second intermediate shaft or quill  34 . The second ring gear member  44  is connected for common rotation with a third intermediate shaft or quill  36 . The second carrier member  46  is connected for common rotation with a fourth intermediate shaft or quill  38 . 
         [0023]    In the preferred embodiment of the present invention, the third planetary gear set  20  is a simple planetary gear set that includes a third sun gear member  52 , a third ring gear member  54  and a third planet carrier member  56  that rotatably supports a third plurality of pinion gears  58  (only one of which is shown). The third plurality of pinion gears  58  are configured to intermesh with both the third sun gear member  52  and the third ring gear member  54 . The third sun gear member  52  is connected for common rotation with a fifth intermediate shaft or quill  62  and a sixth intermediate shaft or quill  64 . The third ring gear member  54  is connected for common rotation with a seventh intermediate shaft or quill  66 . The third carrier member  56  is connected for common rotation with the output shaft  14 . 
         [0024]    In the preferred embodiment of the present invention, the fourth planetary gear set  22  is a simple planetary gear set that includes a fourth sun gear member  72 , a fourth ring gear member  74  and a fourth planet carrier member  76  that rotatably supports a fourth plurality of pinion gears  78  (only one of which is shown). The fourth plurality of pinion gears  78  are configured to intermesh with both the fourth sun gear member  72  and the fourth ring gear member  74 . The fourth sun gear member  72  is connected for common rotation with a first outer shaft or quill  68  and the first intermediate shaft or quill  32 . The fourth ring gear member  74  is connected for common rotation with a second outer shaft or quill  70 . The fourth carrier member  76  is connected for common rotation with the seventh intermediate shaft or quill  66 . 
         [0025]    The automatic transmission  10  includes a variety of torque transmitting mechanisms or devices including a first intermediate clutch  80 , a second intermediate clutch  82 , a third intermediate clutch  84 , a first brake  90  and a second, compound brake  92 . The first intermediate clutch  80  is selectively engageable to connect the sixth intermediate shaft or quill  64  to the first planet carrier member  28  and the input shaft  12 . The second intermediate clutch  82  is selectively engagable to connect the fifth intermediate shaft or quill  62  to the second sun gear member  42 . The third intermediate clutch  84  is selectively engagable to connect the third intermediate shaft or quill  36  to the fifth intermediate shaft or quill  62 . The first brake  90  is selectively engageable to connect the first outer shaft or quill  68  to a housing  110  of the automatic transmission  10  to restrict or inhibit rotation of the first outer shaft or quill  68  and the fourth sun gear member  72  relative to the housing  100 . 
         [0026]    The second, compound brake  92  is operably disposed between the second outer shaft or quill  70  which is connected to the fourth ring gear member  74  and the housing  110  of the transmission  10  and selectively restricts or inhibits rotation of the second outer shaft or quill  70  and the fourth ring gear member  74  relative to the housing  110 . The second, compound brake  92  comprises a selectable one way or overrunning clutch assembly  94  having a plurality of sprags, struts or rollers  96  disposed between inner and outer members  98 A and  98 B. The inner member  98 A is connected to the second outer shaft or quill  70  and rotates therewith. The outer member  98 B is connected to the housing  110  and is therefore stationary. The selectable one way or overrunning clutch  94  reacts, i.e., carries to ground, namely, the housing  110  of the automatic transmission  10 , the large torque developed within the automatic transmission  10  in reverse gear. The one way clutch assembly  94  also carries the lower torques associated with operation in first through fifth gears. 
         [0027]    The selectable one way clutch assembly  94  also includes a first two state or two position actuator  100 . In a first state or position of the first actuator  100 , the one way clutch assembly  94  operates conventionally, allowing relative rotation between the inner and outer members  98 A and  98 B in one direction while inhibiting such rotation in the opposite direction. In the second state or position of the first actuator  100 , the one way clutch assembly  94  is fully locked and relative rotation between the members  98 A and  98 B in either direction is prohibited. The first actuator  100  is energized or engaged, i.e., placed in the second state or position, which locks up the one way or overrunning clutch assembly  94  in accordance with the truth table presented in  FIG. 2 , described below. The first actuator  100  may be any suitable device such as, for example, an electrically driven motor and gear reduction assembly, a solenoid or a hydraulically or pneumatically powered piston and cylinder assembly. 
         [0028]    It should be appreciated that the inventor is familiar with the convention of characterizing a torque controlling or transferring device disposed between two rotatable members as a clutch whereas such a device disposed between one rotatable member and one fixed or stationary member is characterized as a brake. Nonetheless, the one way or overrunning device described above is characterized as a clutch rather than a brake as the inventor is unaware of any instance in which such a device utilized as a brake is referred to or characterized as a one way or overrunning brake rather than a one way or overrunning clutch. 
         [0029]    The second, compound brake  92  also includes an auxiliary or coast plate clutch or brake  104  disposed in mechanical parallel with the one way or overrunning clutch assembly  94 . The coast plate clutch or brake  104  is a brake having a torque capacity lower than what would be required in this location and application in the automatic transmission  10  if the one way or overrunning clutch assembly  94  were not present. This limited or low torque capability is sufficient because the one way or overrunning clutch assembly  94  carries the reaction torque between the first ring gear  26  and the transmission housing  110  during most operating modes. As such, the auxiliary or coast plate clutch or brake  104  may include a single clutch plate or disc  106 A adjacent a single stationary plate or disc  106 B, one of which includes friction material or facing. While such a single plate or disc configuration will typically provide the lowest frictional or spin losses when the auxiliary or coast plate brake  104  is disengaged and is therefore preferred, it should be appreciated that other clutch or brake configurations having multiple plates or discs are within the scope of the present invention. The auxiliary or coast plate brake  104  also includes a second two state or position actuator  108  which engages the auxiliary or coast plate brake  104  and transfers limited torque from the fourth ring gear member  74  and the second outer shaft or quill  70  to the transmission housing  110 . This operating state is utilized to react coast torque in first through fifth gears when needed. 
         [0030]    It should be appreciated that while the second, compound brake  92  has been described in a particular location within the automatic transmission  10 , i.e., operably disposed between the fourth ring gear member  74  of the fourth planetary gear set  22  and the housing  110  of the automatic transmission  10 , the compound brake  92  according to the present invention may replace or be substituted for other clutches or brakes in other locations in this automatic transmission  10  or other multiple speed, planetary gear set automatic transmissions in order to provide the benefit of reduced frictional or spin losses. 
         [0031]    For example, in an alternate embodiment eight speed transmission, four simple planetary gear sets may be arranged with the input connected to the planet carrier of a second planetary gear set, the output may be connected to a planet carrier of a fourth planetary gear set and permanent couplings may be established between a ring gear of a first planetary gear set and a sun gear of a fourth planetary gear set, a sun gear of the first planetary gear set and a ring gear of the second planetary gear set, a sun gear of the second planetary gear set and a sun gear of a third planetary gear set and a planet carrier of the third planetary gear set and a ring gear of the fourth planetary gear set. Three selectively engageable clutches may be operably disposed between a planet carrier of the first planetary gear set and the planet carrier of the fourth planetary gear set, the ring gear of the first planetary gear set and the sun gear of the first planetary gear set and the ring gear of the first planetary gear set and the input shaft. A first brake may selectively ground the sun gear of the second planetary gear set and the sun gear of the third planetary gear set. A second, compound brake according to the present invention may be utilized in this transmission configuration between a ring gear of the third planetary gear set and ground to provide overrunning action in one direction of relative rotation and inhibited rotation in the opposite direction when not activated or energized, lockup in both directions when energized, for example, when selecting reverse gear. The auxiliary or coast clutch may be activated to provide engine braking in accordance with desired performance criteria. 
         [0032]    The transmission  10  is capable of transmitting torque from the input shaft  12  to the output shaft  14  in at least eight forward torque, gear or speed ratios and one reverse torque, gear or speed ratio as indicated in the truth table of  FIG. 2 . Each of the forward and reverse torque, gear or speed ratios is attained by engagement of various combinations of the torque transmitting devices, i.e. the first intermediate clutch  80 , the second intermediate clutch  82 , the third intermediate clutch  84 , the first brake  90  and the second, compound brake  92 . Thus, at least eight forward gear or speed ratios and at least one reverse gear or speed ratio may be attained by the automatic transmission  10 . An example of the gear ratios that may be obtained using the present invention are also shown in  FIG. 2 . Of course, other gear ratios are achievable depending on the gear diameter, gear tooth count and gear configuration selected. 
         [0033]    A lever diagram  10 A is shown in  FIG. 3  that is representative of the automatic transmission  10  of  FIG. 1 , as well as the connections for the clutches  80 ,  82 ,  84  and the brakes  90 ,  92 . The nodes  24 A,  26 A,  28 A,  42 A,  44 A,  46 A,  52 A,  54 A,  56 A,  72 A,  74 A and  76 A of the lever diagram  10 A represent the gear members  24 ,  26 ,  28 ,  42 ,  44 ,  46 ,  52 ,  54 ,  56 ,  72 ,  74  and  76  of  FIG. 1  such that the same numerical designation with the addition of an A suffix is used to identify the corresponding node. For example, the nodes  24 A and  42 A shown in  FIG. 3  represent the first and second sun gear members  24  and  42 , respectively, shown in  FIG. 1 . Other components of  FIG. 3  have the same numbering convention for the corresponding components in  FIG. 1 . 
         [0034]    The operation or engagement of the clutches  80 ,  82  and  84  and the brakes  90  and  92  to establish the various forward and reverse speed or gear ratios will now be described with continuing reference to  FIGS. 1 and 2 . 
         [0035]    To establish the reverse gear ratio (Rev), the torque transmitting clutches and brakes are engaged or activated as set forth in the truth table of  FIG. 2 . As shown in  FIG. 2 , the first brake  90 , the actuator  100  of the one way or overrunning clutch assembly  94  of the second compound brake  92  and the third intermediate clutch  84  are engaged to achieve the reverse gear ratio (Rev). As noted previously when the second, compound brake  92  is engaged or activated, the actuator  100  is in its second state which locks the one way or overrunning clutch assembly  94  and locks or inhibits rotation of the second outer shaft or quill  70  and the fourth ring gear member  74  in both directions. 
         [0036]    In neutral, none of the clutches or brakes are carrying torque. As indicated by the O in  FIG. 2 , in this gear state, the first brake  90  and the second, compound brake  92  are engaged but not carrying torque. 
         [0037]    A first forward gear ratio, indicated as 1st (first gear) in the truth table of  FIG. 2 , is achieved by engaging the first brake  90 , the second, compound brake  92  and the first intermediate clutch  80 . It should be understood that although the truth table of  FIG. 2  indicates that the second, compound brake  92  is engaged or activated, such activation is optional in first through fifth gears as the overrunning feature of the one way or overrunning clutch assembly  94  will provide the appropriate and necessary mechanical connection and operation. 
         [0038]    The next forward gear ratio, indicated as 2 nd  (second gear) in  FIG. 2 , is established by engagement of the first brake  90 , the second intermediate clutch  82  and optional engagement of the second, compound brake  92 . The shift from first gear to second gear occurs as follows: releasing the first intermediate clutch  80  and engaging the second intermediate clutch  82  while maintaining engagement of the brakes  90  and  92 . 
         [0039]    The next gear ratio, indicated as 3 rd  (third gear) in the truth table of  FIG. 2 , is established by optional engagement of the second, compound brake  92  and engagement of the first and second intermediate clutches  80  and  82 . The shift from second gear to third gear occurs as follows: the second clutch  82  and the second, compound brake  92  remain engaged, the first brake  90  is released and the first clutch  80  is engaged. 
         [0040]    The next forward gear ratio, indicated as 4 th  (fourth gear) in the truth table of  FIG. 2 , is established by optional engagement of the second, compound brake  92  and engagement of the second and third intermediate clutches  82  and  84 . The shift from third gear to fourth gear is achieved as follows: engagement of the second clutch  82  and the second brake  92  are maintained, the first clutch  80  is released and the third clutch  84  is engaged. 
         [0041]    The next forward gear ratio indicated as 5 th  (fifth gear) in  FIG. 2 , is established by optional engagement of the second, compound brake  92  and engagement of the first and third intermediate clutches  80  and  84 . The shift from fourth gear to fifth gear occurs as follows: engagement of the third clutch  84  and the second brake  92  are maintained, the second clutch  82  is released and the first clutch  80  is engaged. 
         [0042]    The next forward gear ratio indicated as 6 th  (sixth gear), in the truth table of  FIG. 2 , is established with the engagement of the first, second and third intermediate clutches  80 ,  82  and  84 . The shift from fifth gear to sixth gear occurs as follows: engagement of the clutches  80  and  84  is maintained, the second, compound brake  92 , if engaged, is released and the third clutch  82  is engaged. 
         [0043]    The next gear ratio, indicated as 7 th  (seventh gear) in the truth table of  FIG. 2 , is established by engagement of the first brake  90  and the first and third intermediate clutches  80 ,  84 . The shift from sixth gear to seventh gear occurs as follows: engagement of the clutches  80  and  84  is maintained, the second clutch  82  is released and the first brake  90  is engaged. 
         [0044]    The final forward gear ratio, indicated as 8 th  (eight gear) in the truth table of  FIG. 2 , is established by engagement of the first brake  90  and the second and third intermediate clutches  82 ,  84 . The shift from seventh gear to eighth gear occurs as follows: engagement of the third clutch  84  and the first brake  90  are maintained, the first clutch  80  is released and the second clutch  82  is engaged. 
         [0045]    The present invention contemplates that downshifts follow the reverse sequence of the corresponding upshifts (as described above), and several power-on skip-shifts that are single-transition shifts are possible, e.g. from 1st to 3rd. 
         [0046]    While the best mode for carrying out the invention has been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.