Abstract:
A power transmitting that includes an epicyclic multi-speed transmission that employs friction to torsionally ground one or more elements of the transmission to either inhibit their rotation or to couple the elements together for common rotation. The epicyclic multi-speed transmission avoids clutch configurations that employ stationary clutch packs that are configured to exert force on a rotatable element of the transmission through a thrust bearing, as well as clutch configurations that employ a hydraulically operated piston that rotates with a clutch pack, to reduce drag force and eliminate the need for rotary seals.

Description:
FIELD 
     The present disclosure relates to a two-speed epicyclic gear arrangement. 
     BACKGROUND 
     This section provides background information related to the present disclosure which is not necessarily prior art. 
     In a multi-speed epicyclic transmission, various elements within the transmission are alternately held from rotation relative to a housing or are coupled to another element of the transmission to cause the components to co-rotate to cause the transmission to operate in the several different overall gear ratios. When one or more elements of an epicyclic transmission are coupled together to co-rotate, the coupling that is used to couple the elements together needs to rotate with the rotating elements of the transmission. If a multi-plate friction clutch were to be used to couple the elements together, it would be necessary to apply a normal force to the rotating friction clutch. 
     One way to apply a normal force to the rotating friction clutch is to have a stationary element that is capable of exerting a force on the friction clutch act through a thrust bearing. This solution, however, suffers from the drawback that the bearing imparts a relatively high drag force that reduces the efficiency of the transmission. 
     Another way to apply a normal force to the rotating friction clutch is to use a piston assembly that rotates with the friction clutch and to distribute fluid power to the piston assembly through a rotary seal. This solution, however, suffers from the drawback that the rotating seal creates drag and necessitates a continuous supply of pressurized fluid to maintain a desired pressure due to leakage. 
     Accordingly, there remains a need in the art for an improved multi-speed epicyclic transmission. 
     SUMMARY 
     This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
     In one form, the present disclosure provides a power transmitting that includes a housing, a transmission, a first clutch and a second clutch. The transmission is received in the housing and includes a first sun gear, a first ring gear disposed about the first sun gear, a first planet carrier, a plurality of first planet gears, a second planet carrier coupled to the first ring gear for common rotation, a second sun gear disposed about the first planet carrier, a second ring gear disposed about the second sun gear and non-rotatably coupled to the housing, a plurality of second planet gears, a third sun gear coupled to the second sun gear for common rotation, a third planet carrier coupled to the first planet carrier for common rotation, a third ring gear disposed about the third sun gear and a plurality of third planet gears. Each of the first planet gears is journally supported on the first planet carrier and is meshingly engaged with the first sun gear and the first ring gear. Each of the second planet gears is journally supported on the second planet carrier and is meshingly engaged with the second sun gear and the second ring gear. Each of the third planet gears is journally supported on the third planet carrier and is meshingly engaged to the third sun gear and the third ring gear. The first clutch is operable in a first clutch mode, in which the first ring gear is non-rotatably coupled to the housing, and a second clutch mode in which the first ring gear is rotatable relative to the housing. The second clutch is operable in a third clutch mode, in which the third ring gear is rotatable relative to the housing, and a fourth clutch mode in which the third ring gear is non-rotatable relative to the housing. 
     Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
         FIG. 1  is a longitudinal section view of an exemplary power transmitting device having a multi-speed epicyclic transmission that is constructed in accordance with the teachings of the present disclosure; 
         FIG. 2  is a section view similar to that of  FIG. 1  but depicting a second multi-speed epicyclic transmission constructed in accordance with the teachings of the present disclosure; and 
         FIG. 3  is a section view similar to that of  FIG. 1  but depicting a third multi-speed epicyclic transmission constructed in accordance with the teachings of the present disclosure. 
     
    
    
     Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION 
     With reference to  FIG. 1  of the drawings, an exemplary power transmitting device  10  having a multi-speed epicyclic transmission  12  that is constructed in accordance with the teachings of the present disclosure. The power transmitting device  10  can also include a housing  14 , a first clutch  16  and a second clutch  18 . The housing  14  can define a cavity  20  into which the transmission  12  and the first and second clutches  16  and  18  can be housed. 
     The transmission  12  can be received in the cavity  20  in the housing  14  and can include first, second and third planetary gearsets  30 ,  32  and  34 , respectively. The first planetary gearset  30  can include a first sun gear  40 , a first ring gear  42 , a first planet carrier  44  and a plurality of first planet gears  46  (only one shown). The second planetary gearset  32  can include a second sun gear  50 , a second ring gear  52 , a second planet carrier  54  and a plurality of second planet gears  56  (only one shown). The third planetary gearset  34  can include a third sun gear  60 , a third ring gear  62 , a third planet carrier  64  and a plurality of third planet gears  66 . 
     The first sun gear  40  can be rotatably disposed about a longitudinal axis  70  of the transmission  12  and can be the input of the transmission  12  that receives rotary power from a source of rotary power (not shown). In the particular example provided, the first sun gear  40  is integrally formed with an input shaft  72 . The first ring gear  42  can be disposed about the first sun gear  40  and can include an annular body onto which a plurality of internal teeth are formed. If desired, a bearing or bushing (not shown) can be disposed between the first ring gear  42  and the housing  14 . The first planet carrier  44  can include a first carrier body  76  and a plurality of first carrier pins  78  that can be coupled, e.g., fixedly coupled, to the first carrier body  76 . Each of the first planet gears  46  can be rotatably received on a corresponding one of the first carrier pins  78  such that the first planet gears  46  are journally supported on the first planet carrier  44 . The first planet gears  46  can be meshingly engaged with the first sun gear  40  and the first ring gear  42 . The first planet carrier  44  can be an output of the transmission  10 . In the particular example provided, a fourth sun gear  80  associated with another planetary reduction (not shown) is coupled to the first carrier body  76  for rotation therewith. 
     The second sun gear  50  can be an annular structure that can be disposed about the first carrier body  76 . The second ring gear  52  can be disposed about the second sun gear  50  and can include an annular body onto which a plurality of internal teeth are formed. The second ring gear  52  can be non-rotatably coupled to the housing  14 . The second planet carrier  54  can include a second carrier body  86 , which can be fixedly coupled to the first ring gear  42  for common rotation, and a plurality of second carrier pins  88  that can be coupled, e.g., fixedly coupled, to the second carrier body  86 . If desired, a bearing or bushing (not shown) can be disposed between the second carrier body  86  and the housing  14 . Each of the second planet gears  56  can be rotatably received on a corresponding one of the second carrier pins  88  such that the second planet gears  56  are journally supported on the second planet carrier  54 . The second planet gears  56  can be meshingly engaged with the second sun gear  50  and the second ring gear  52 . 
     The third sun gear  60  can be an annular structure that can be disposed about the first carrier body  76  and can be coupled to the second sun gear  50  for common rotation. In the particular example provided, the second and third sun gears  50  and  60  are unitarily and integrally formed. If desired, a bearing or bushing (not shown) can be disposed between the first carrier body  76  and the second and third sun gears  50  and  60 . The third ring gear  62  can be received about the third sun gear  60  and can include an annular body onto which a plurality of internal teeth are formed. The third planet carrier  64  can include a third carrier body  96 , which can be fixedly coupled to the first carrier body  76  for common rotation, and a plurality of third carrier pins  98  that can be coupled, e.g., fixedly coupled, to the third carrier body  96 . If desired, a bearing or bushing (not shown) can be disposed between the third carrier body  96  and the housing  14 . Each of the third planet gears  66  can be rotatably received on a corresponding one of the third carrier pins  98  such that the third plant gears are journally supported on the third planet carrier  64 . The third planet gears  66  can be meshingly engaged to the third sun gear  60  and the third ring gear  62 . 
     The first clutch  16  can be operable in a first clutch mode, in which the first ring gear  42  is non-rotatably coupled to the housing  14 , and a second clutch mode in which the first ring gear  42  is rotatable relative to the housing  14 . Any desired type of clutch or coupling can be employed, such as a friction clutch. In the particular example provided, the first clutch  16  is a multi-plate friction clutch having a first clutch member  100 , a second clutch member  102 , a plurality of first clutch plates  104 , a plurality of second clutch plates  106  and a first actuator  108 . The first clutch member  100  can be non-rotatably but axially slidably mounted to the first ring gear  42 . A snap ring  110  or other element that is assembled to or formed on the first ring gear  42  can limit movement of the first clutch member  100  on the first ring gear  42  along the axis  70 . The second clutch member  102  can be non-rotatably but axially slidably mounted to the housing  14 . The first clutch plates  104  can be non-rotatably but axially slidably coupled to the first ring gear  42 . The second clutch plates  106  can be interleaved with the first clutch plates  104  and can be non-rotatably but axially slidably coupled to the housing  14 . The first and second clutch plates  104  and  106  can be received between the first and second clutch members  100  and  102 . The first actuator  108  can comprise any well known means for selectively applying force to the second clutch member  102  to move the second clutch member  102  toward the first clutch member  100  and cause engagement of the first and second clutch plates  104  and  106  to transfer torque therebetween. In the particular example provided, the first actuator  108  comprises a hydraulic cylinder assembly having an annular cylinder  114 , which is formed in the housing  14  and an annular piston  116  that is received into the annular cylinder  114 . It will be appreciated that one or more fluid conduits (not shown) can connect the annular cylinder  114  to a source of fluid power, such as a pump (not shown). 
     The second clutch  18  can be operable in a third clutch mode, in which the third ring gear  62  is rotatably coupled to the housing  14 , and a fourth clutch mode in which the third ring gear  62  is non-rotatable relative to the housing  14 . Any desired type of clutch or coupling can be employed, such as a friction clutch. In the particular example provided, the second clutch  18  is a multi-plate friction clutch having a third clutch member  120 , a fourth clutch member  122 , a plurality of third clutch plates  124 , a plurality of fourth clutch plates  126  and a second actuator  128 . The third clutch member  120  can be non-rotatably but axially slidably mounted to the third ring gear  62 . A snap ring  130  or other element that is assembled to or formed on the third ring gear  62  can limit movement of the third clutch member  120  on the third ring gear  62  along the axis  70 . The fourth clutch member  122  can be non-rotatably but axially slidably mounted to the housing  14 . The third clutch plates  124  can be non-rotatably but axially slidably coupled to the third ring gear  62 . The fourth clutch plates  126  can be interleaved with the third clutch plates  124  and can be non-rotatably but axially slidably coupled to the housing  14 . The third and fourth clutch plates  124  and  126  can be received between the third and fourth clutch members  120  and  122 . The second actuator  128  can comprise any well known means for selectively applying force to the fourth clutch member  122  to move the fourth clutch member  122  toward the third clutch member  120  and cause engagement of the third and fourth clutch plates  124  and  126  to transfer torque therebetween. In the particular example provided, the second actuator  128  comprises a hydraulic cylinder assembly having an annular cylinder  134 , which is formed in the housing  14  and an annular piston  136  that is received into the annular cylinder  134 . It will be appreciated that one or more fluid conduits (not shown) can connect the annular cylinder  134  to a source of fluid power, such as a pump (not shown). 
     The first clutch  16  can be operated in the first clutch mode (so that the first ring gear  42  does not rotate relative to the housing  14 ) and the second clutch  18  can be operated in the third clutch mode (to permit rotation of the third ring gear  62  relative to the housing  14 ) so that the transmission  12  provides a first overall reduction ratio. 
     The first clutch  16  can be operated in the second clutch mode (so that the first ring gear  42  is rotatable relative to the housing  14 ) and the second clutch  18  can be operated in the fourth clutch mode (to inhibit rotation of the third ring gear  62  relative to the housing  14 ) so that the transmission  12  provides a second overall reduction ratio. 
     From the foregoing, it will be appreciated that the first overall reduction is dictated by the reduction ratio of the first planetary gearset  30 , and that that the second and third reduction gearsets  32  and  34  are employed solely to selectively lock the first ring gear  42  to the first planet carrier  44  so that the second overall reduction ratio is 1:1. 
     While the first and second clutches  16  and  18  have been described as being multi-plate friction clutches, it will be appreciated that one or both of these clutches can be configured differently. For example, one or both of the first and second clutches  16   a  and  18   a  can be a band clutch having a clutch band  200  that can be coupled to the housing  14   a  and disposed about the first ring gear  42   a  or the third ring gear  62   a  as is shown in  FIG. 2 . The clutch band(s)  200  can be selectively tightened to apply a frictional force to the outer perimeter of the first ring gear  42   a  and/or the third ring gear  62   a  to resist rotation of the first ring gear  42   a  and/or the third ring gear  62   a  relative to the housing  14   a . Operation of the transmission  12   a  is similar to that of the transmission  12  of  FIG. 1 . 
     Another alternative is shown in  FIG. 3  in which the first clutch  16   b  comprises a one-way clutch, such as a sprag clutch  300 , which is configured to permit rotation of the first ring gear  42   b  in a first rotational direction, and to inhibit rotation of the first ring gear  42   b  in a second rotational direction that is opposite the first rotational direction. When rotary power is input to the first sun gear  40  in a predetermined rotational direction and the second clutch  18  operates in the third clutch mode (so that the third ring gear  62  rotates relative to the housing  14 ), a torque reaction acting on the first ring gear  42   b  will be applied in a first rotational direction. The sprag clutch  300  is configured to inhibit rotation of the first ring gear  42   b  in the first rotational direction and consequently, the transmission  12   b  will operate in the first overall reduction ratio. When rotary power is input to the first sun gear  40  in the predetermined rotational direction and the second clutch  18  operates in the fourth clutch mode (so that the third ring gear  62  does not rotate relative to the housing  14 ), a torque reaction acting on the first ring gear  42   b  will be applied in a second rotational direction that is opposite the first rotational direction. The sprag clutch  300  is configured to permit rotation of the first ring gear  42   b  in the second rotational direction and consequently, the transmission  12   b  will operate in the second overall reduction ratio. 
     The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.