Abstract:
A multispeed automatic transmission is provided having four planetary gear sets, a plurality of friction and synchronizer clutches and two chain drive assemblies. The transmission is arranged along two parallel axes of rotation: a first axis defined by the input shaft and a second axis defined by the output shaft. The chain drive assemblies transfer power between sprockets disposed on the two axes. Various combinations of clutches may be engaged to provide nine forward speed ratios and five reverse speed ratios.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. Pat. Ser. No. 12/105,819, now U.S. Pat. No. 8,113,978 filed on Apr. 18, 2008 and as such, claims priority thereto under 35 U.S.C. §120. 
    
    
     FIELD 
     The present disclosure relates to an automatic transmission for a motor vehicle and more particularly to a nine speed automatic transmission for a motor vehicle having four planetary gear sets and a plurality of friction and synchronizer clutches. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art. 
     Many current passenger car multiple speed automatic transmissions include a combination of planetary gear sets and selectively engaged clutches and brakes which provide a plurality of forward torque or gear ratios. 
     Whereas three and four speed automatic transmissions were once commonplace and considered suitable to provide the requisite flexibility and performance, increasingly demanding economic and performance goals as well as consumer preference continue to encourage automatic transmission research and development. One result of this effort has been an increase in the number of available forward gears or speed ratios provided by the transmission. Six, seven and eight speed automatic transmissions are increasingly available. 
     Because they so closely match the power and torque curves of an engine to the vehicle speed and load, such six, seven and eight speed transmissions provide significant performance enhancements and fuel economies. 
     Study of these transmissions configurations, however, reveals that improvements are possible. For example, each of the selectively engaged frictional couplings, i.e., the clutches and the brakes, contribute to frictional losses, referred to as spin losses, when they are not engaged. Such spin losses are the result of relative rotation between the multiple, interleaved plates or discs of such devices. Two primary factors influence spin losses: the size or torque capacity of the clutch or brake and the speed difference across the clutch or brake. Reducing such spin losses therefore provides improved transmission efficiency which is highly desirable. 
     SUMMARY 
     The present invention provides a nine forward speed automatic transmission for a motor vehicle which includes four planetary gear sets, a plurality of friction and synchronizing clutches and two chain drive assemblies. The transmission is arranged along two parallel axes of rotation: a first axis defined by the input shaft and a second axis defined by the output shaft. The chain drive assemblies transfer power between sprockets disposed on the two axes. 
     Input torque is selectively provided to either a sun gear, a planet carrier or a ring gear of a first, double pinion planetary gear set by engagement of one of three input clutches. The sun gear and the planet gear carrier are coupled to a respective pair of chain sprockets disposed on the input axis. A pair of chains transfer torque to a respective pair of chain sprockets disposed on the output axis. The chain driven by the sun gear of the first, double pinion planetary gear set directly drives a sun gear of a second, simple planetary gear set that, with a third, simple planetary gear set, acts as a first sub-transmission. The chain driven by the planet gear carrier of the first, compound planetary gear set directly drives a sun gear of a fourth, simple planetary gear set that acts as a second sub-transmission. The transmission output is commonly connected to and driven by a ring gear of the third, simple planetary gear set and a planet gear carrier of the fourth, simple planetary gear set. Engagement of various combinations of the input clutches and a plurality of synchronizer clutches provides nine forward speeds and five reverse speeds. 
     It is thus an object of the present invention to provide an automatic transmission for motor vehicles which provides nine forward speeds. 
     It is a further object of the present invention to provide an automatic transmission for motor vehicles having an input shaft on a first axis and an output shaft and a second, offset, parallel axis. 
     It is a still further object of the present invention to provide an automatic transmission for motor vehicles having four planetary gear sets and a plurality of friction and synchronizer clutches. 
     It is a still further object of the present invention to provide an automatic transmission for motor vehicles having a pair of chain drives connecting components disposed on a pair of parallel, spaced apart axes. 
     Further objects, advantages and areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples 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 illustration purposes only and are not intended to limit the scope of the present disclosure in any way. Like reference numbers in the various Figures consistently refer to the same element, component or feature. 
         FIG. 1  is a diagrammatic view of a first embodiment of a nine speed automatic transmission according to the present invention; 
         FIG. 2  is a diagrammatic view of a second embodiment of a nine speed automatic transmission according to the present invention; 
         FIG. 3  is a truth table presenting the various combinations of engaged clutches which achieve a given forward or reverse gear or speed ratio; and 
         FIG. 4  is a diagram illustrating the relationship between the physical gears and the virtual or blended gears of a nine speed automatic transmission according to the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application or uses. 
     With reference to  FIG. 1 , a first embodiment of a nine speed automatic transmission according to the present invention is illustrated and designated by the reference number  10 . The automatic transmission  10  includes an input member or shaft  12  which is coupled to and driven by, for example, the output of an engine (not illustrated) or the turbine of a torque converter (not illustrated). The transmission  10  also includes an output shaft  14  having first and second ends  16 A and  16 B. If the transmission  10  is longitudinally mounted in a vehicle, one of the ends  16 A or  16 B may be utilized to drive a final drive unit in the front or rear of a vehicle or both may be utilized to drive final drive units in the front and rear of a vehicle. Alternatively, if the transmission  10  is mounted transversely in a vehicle, either or both of the ends  16 A and  16 B may be utilized to provide drive torque to either or both sides of the vehicle. 
     The automatic transmission  10  also includes a first, double pinion planetary gear set or assembly  20  disposed about the axis of the input shaft  12 , a second, simple planetary gear set or assembly  30  disposed about the axis of the output shaft  14 , a third, simple planetary gear set or assembly  40  disposed about the axis of the output shaft  14  and a fourth, simple planetary gear set or assembly  50  also disposed about the axis of the output shaft  14 . 
     The first, double pinion planetary gear assembly  20  includes a first sun gear  22 , a first planet gear carrier  24  and a first ring gear  26 . Rotatably disposed in the first planet gear carrier  24  are a plurality of pairs of inner and outer intermeshing first planet gears  28 A and  28 B, one pair of which is illustrated in  FIG. 1 . Each of the inner first planet gears  28 A is in constant mesh with the first sun gear  22  and its associated outer first planet gear  28 B and each of the outer first planet gears  28 B is in constant mesh with the first ring gear  26 . The second, simple planetary gear assembly  30  includes a second sun gear  32 , a second planet gear carrier  34  and a second ring gear  36 . Rotatably disposed in the second planet gear carrier  34  are a plurality of second planet gears  38 , one of which is illustrated in  FIG. 1 . Each of the plurality of second planet gears  38  is in constant mesh with the second sun gear  32  and the second ring gear  36 . 
     The third, simple planetary gear assembly  40  includes a third sun gear  42 , a third planet gear carrier  44  and a third ring gear  46 . Rotatably disposed in the third planet gear carrier  44  are a plurality of third planet gears  48 , one of which is illustrated in  FIG. 1 . Each of the plurality of third planet gears  48  is in constant mesh with the third sun gear  42  and the third ring gear  46 . The fourth, simple planetary gear assembly  50  includes a fourth sun gear  52 , a fourth planet gear carrier  54  and a fourth ring gear  56 . Rotatably disposed in the fourth planet gear carrier  54  are a plurality of fourth planet gears  58 , one of which is illustrated in  FIG. 1 . Each of the plurality of fourth planet gears  58  is in constant mesh with the fourth sun gear  52  and the fourth ring gear  56 . It should be noted that depending upon the desired gear ratios to be provided by the fourth, simple planetary gear assembly  50 , the plurality of fourth, single planet gears  58  may be replaced by pairs of meshing planet gears (not illustrated) creating a double pinion planetary gear assembly. 
     The automatic transmission  10  also includes a first chain drive assembly  60  having a first drive chain sprocket  62  disposed on the axis of the input shaft  12 , a first multiple link chain  64  and a first driven chain sprocket  66  disposed on the axis of the output shaft  14 . Adjacent the first chain drive assembly  60  is a second chain drive assembly  70  having a second drive chain sprocket  72  disposed on the axis of the input shaft  12 , a second multiple link chain  74  and a second driven chain sprocket  76  disposed on the axis of the output shaft  14 . 
     The automatic transmission  10  further includes a plurality of torque transmitting devices such as friction clutches and synchronizer clutches. As utilized herein, the term “friction clutch” refers to a torque transmitting device having first and second pluralities of interleaved friction plates or discs which are compressed by an associated operator or actuator and which is capable of carrying high levels of torque, i.e., the actual torque carried by the automatic transmission  10 . On the other hand, a “synchronizer clutch,” as utilized herein, refers to a torque transmitting device having a limited torque capacity synchronizer which is capable of carrying sufficient torque to overcome the inertia of an associated gear in order to synchronize it with a shaft and a positive clutch such as a dog clutch which engages to positively couple the gear and shaft and which is capable of carrying high levels of torque. Furthermore, it should be understood that while these devices are referred to as synchronizer clutches which suggests that they synchronize and connect two rotating members, several of the synchronizer clutches are, in fact, utilized as brakes, i.e., they slow and connect a rotatable member to a fixed or stationary member, thereby inhibiting rotation of the rotatable member. In the following description, those synchronizer clutches functioning as brakes will be noted by the parenthetical addition of the word “brake.” 
     A first high torque capacity friction clutch  82  having, as noted, interleaved pluralities of friction clutch plates or discs is operably disposed between and selectively connects the input shaft  12  and a first shaft, quill or concentric member  102  which is coupled to and drives the first sun gear  22  of the first, double pinion planetary gear assembly  20  and the second drive chain sprocket  72  of the second chain drive assembly  70 . A second high torque capacity friction clutch  84  is operably disposed between and selectively connects the input shaft  12  and a second shaft, quill or concentric member  104  which is coupled to and drives the first planet gear carrier  24  of the first, double pinion planetary gear assembly  20 . The first planet gear carrier  24  of the first, double pinion planetary gear assembly  20  is, in turn coupled to a third shaft, quill or concentric member  106  which is coupled to and drives the first drive chain sprocket  62  of the first chain drive assembly  60 . A third high torque capacity friction clutch  86  is operably disposed between and selectively connects the input shaft  12  to the first ring gear  26  of the first, double pinion planetary gear assembly  20 . 
     A first synchronizer clutch (brake)  88  having, as noted above, a synchronizer and positive clutch is operably disposed between and selectively connects or grounds the first ring gear  26  of the first, double pinion planetary gear assembly  20  to a stationary housing  108  of the automatic transmission  10 . A second synchronizer clutch (brake)  90  is operably disposed between and selectively connects or grounds to the stationary housing  108  a fourth shaft, quill or concentric member  110  which is coupled to the second planet gear carrier  34  of the second, simple planetary gear assembly  30 . A third synchronizer clutch (brake)  92  is operably disposed between and selectively connects or grounds a fifth shaft, quill or concentric member  112  which is coupled to both the second ring gear  36  of the second, simple planetary gear assembly  30  and the third sun gear  42  of the third, simple planetary gear assembly  40 . 
     A fourth synchronizer clutch  94  is operably disposed between and selectively connects a sixth shaft, quill or concentric member  114  to the fourth shaft, quill or concentric member  110 . The sixth shaft, quill or concentric member  114  couples the second sun gear  32  of the second, simple planetary gear set  30  and the second driven chain sprocket  72  of the second chain drive assembly  70 . A fifth synchronizer clutch (brake)  96  is operably disposed between and selectively connects or grounds the fourth ring gear  56  of the fourth, simple planetary gear assembly  50  to the stationary housing  108 . A sixth synchronizer clutch  98  is operably disposed between and selectively connects the fourth ring gear  56  of the fourth, simple planetary gear assembly  50  to a seventh shaft, quill or intermediate member  116 . The seventh shaft, quill or intermediate member  116  interconnects the fourth sun gear  52  of the fourth, simple planetary gear assembly  50  and the first driven chain sprocket  66  of the first chain drive assembly  60 . 
     An eighth shaft, quill or concentric member  118  couples the second planet gear carrier  34  of the second, simple planetary gear assembly  30  to the third planet gear carrier  44  of the third, simple planetary gear assembly  40 . Alternatively, the eighth shaft, quill or concentric member may be an extension of the fourth shaft, quill or concentric member  110 . Similarly, extensions or portions of the output shaft  14  are coupled to the third ring gear  46  of the third, simple planetary gear assembly  40  and the fourth planet gear carrier  54  of the fourth, simple planetary gear assembly  50 . 
     Inspection of the nine speed automatic transmission  10  just described and illustrated in  FIG. 1  reveals that the second and third planetary gear assemblies  30  and  40  and the second, third and fourth synchronizer clutches  90 ,  92  and  94  constitute a first sub-transmission A having an input which is coupled to and driven by the second driven chain sprocket  76  and an output which is coupled to and drives the output shaft  14 . The first sub-transmission A provides three speeds or gear ratios. Similarly, the fourth planetary gear assembly  50  and the fifth and sixth synchronizer clutches  96  and  98  constitute a second sub-transmission B having an input which is coupled to and driven by the first driven chain sprocket  66  and an output which is coupled to and drives the output shaft  14 . The second sub-transmission B provides two speeds or gear ratios. 
     Referring now to  FIG. 2 , a second embodiment of the nine speed automatic transmission  10  according to the present invention is illustrated and designated by the reference number  10 ′. Upon examination, it will be appreciated that the second embodiment of the automatic transmission  10 ′ includes all of the same active components, i.e., planetary gear assemblies and friction and synchronizer clutches and that the differences between the two embodiments relate to the arrangement of the active components and shafts or concentric members associated with the second, third and fourth planetary gear sets or assemblies  30 ,  40  and  50 . In this regard, it should be noted that the arrangement of the active components and shafts associated with the first, double pinion planetary gear assembly  20  is the same in both embodiments. 
     Thus, the second embodiment nine speed automatic transmission  10 ′ includes an input shaft  12 ′ and an output shaft  14 ′ having first and second ends  16 A′ and  16 B′. 
     A first, double pinion planetary gear assembly  20 ′ includes a first sun gear  22 ′, a first planet gear carrier  24 ′, a first ring gear  26 ′ and a plurality of pairs of intermeshing first planet gears  28 A′ and  28 B′. A second, simple planetary gear assembly  30 ′ includes a second sun gear  32 ′, a second planet gear carrier  34 ′, a second ring gear  36 ′ and a plurality of second planet gears  38 ′. A third, simple planetary gear assembly  40 ′ includes a third sun gear  42 ′, a third planet gear carrier  44 ′, a third ring gear  46 ′ and a plurality of third planet gears  48 ′. A fourth, simple planetary gear assembly  50 ′ includes a fourth sun gear  52 ′, a fourth planet gear carrier  54 ′, a fourth ring gear  56 ′ and a plurality of fourth planet gears  58 ′. Again, depending upon the desired gear ratios to be provided by the fourth, simple planetary gear assembly  50 ′, the plurality of fourth, single planet gears  58 ′ may be replaced by pairs of meshing planet gears (not illustrated) creating a double pinion planetary gear assembly. 
     Arranged on the side of the first, double pinion planetary gear assembly  20 ′ opposite the input shaft  12 ′ and between the second, simple planetary gear assembly  30 ′ and the fourth, simple planetary gear assembly  50 ′ are a first chain drive assembly  60 ′ and a second chain drive assembly  70 ′. The first chain drive assembly  60 ′ includes a first chain drive sprocket  62 ′, a first multiple link drive chain  64 ′ and a first driven chain sprocket  66 ′. The second chain drive assembly  70 ′ includes a second chain drive sprocket  72 ′, a second multiple link drive chain  74 ′ and a second driven chain sprocket  76 ′. 
     The second embodiment nine speed automatic transmission  10 ′ also includes a first friction clutch  82 ′, a second friction clutch  84 ′ and a third friction clutch  86 ′ all of which are coupled to and driven by the input shaft  12 ′. A first shaft or concentric member  102 ′ couples the output of the first friction clutch  82 ′ to the first sun gear  22 ′ of the first, double pinion planetary gear assembly  20 ′ and to the second chain drive sprocket  72 ′. A second shaft or concentric member  104 ′ couples the output of the second friction clutch  84 ′ to the first planet gear carrier  24 ′ of the first, double pinion planetary gear assembly  20 ′. A third shaft or concentric member  106 ′ couples the first planet gear carrier  24 ′ of the first, double pinion planetary gear assembly  20 ′ to the first chain drive sprocket  62 ′. The output of the third friction clutch  86 ′ is coupled to the first ring gear  26 ′ of the first, double pinion planetary gear assembly  20 ′. 
     A first synchronizer clutch (brake)  88 ′ selectively connects or grounds the first ring gear  26 ′ of the first, double pinion planetary gear assembly  20 ′ to a stationary housing  108 ′ of the automatic transmission  10 ′. A second synchronizer clutch (brake)  90 ′ is coupled to a fourth shaft or concentric member  110 ′ and selectively grounds the second planet gear carrier  34 ′ of the second, simple planetary gear assembly  30  to the stationary housing  108 ′. A third synchronizer clutch (brake)  92 ′ selectively grounds a fifth shaft or concentric member  112 ′ which is coupled to both the second ring gear  36 ′ of the second, simple planetary gear assembly  30 ′ and the third sun gear  42 ′ of the third, simple planetary gear assembly  40 ′. A fourth synchronizer clutch  94 ′ selectively connects the fourth shaft or concentric member  110 ′ to a sixth shaft or concentric member  114 ′ which is coupled to the second sun gear  32 ′ of the second, simple planetary gear assembly  30 ′ and the second driven chain sprocket  76 ′. A fifth synchronizer clutch (brake)  96 ′ selectively grounds the fourth ring gear  56 ′ of the fourth, simple planetary gear assembly  50 ′ to the stationary housing  108 ′. A sixth synchronizer clutch  98 ′ selectively connects the fourth ring gear  56 ′ of the fourth, simple planetary gear assembly  50 ′ to a seventh shaft or concentric member  116 ′ which is coupled to the fourth sun gear  52 ′ of the fourth, simple planetary gear assembly  50 ′ and the first driven chain sprocket  66 ′. 
     The second embodiment of the nine speed automatic transmission  10 ′ illustrated in  FIG. 2  includes a first sub-transmission A′ encompassing the second and third planetary gear assemblies  30 ′ and  40 ′ and the second, third and fourth synchronizer clutches  90 ′,  92 ′ and  94 ′ which is coupled to and driven by the second driven chain sprocket  76 ′ and is coupled to and drives the output shaft  14 ′. The first sub-transmission A′ provides three speeds or gears ratios. Similarly, a second sub-transmission B′ encompasses the fourth planetary gear assembly  50 ′ and the fifth and sixth synchronizer clutches  96 ′ and  98 ′ which is coupled to and driven by the first driven chain sprocket  66 ′ and is coupled to and drives the output shaft  14 ′. The second sub-transmission B′ provides two speeds or gear ratios. 
     Referring now to  FIGS. 3 and 4 , the operation of both embodiments  10  and  10 ′ of the nine speed automatic transmission will be described. It will be appreciated that the transmissions  10  and  10 ′ are capable of transmitting torque from their input shafts  12  and  12 ′ to their output shafts  14  and  14 ′ in nine forward speed, torque or gear ratios and five reverse speed, torque or gear ratios. Each forward or reverse gear ratio is attained by activation or engagement of various combinations of two or three of the clutches as will be explained below.  FIG. 3  is a truth table which presents the various combinations of friction and synchronizer clutches that are activated or engaged to achieve the various forward and reverse gear ratios. Gear ratios and ratios steps are also provided although it should be understood that these numerical values are presented for purposes of example and illustration only and that such values may be adjusted over significant ranges to accommodate various applications and operational criteria of the automatic transmissions  10  and  10 ′. 
     In neutral, none of the clutch elements are activated or engaged. 
     In the lowest speed (highest gear ratio) reverse gear, denominated R 1 , the second friction clutch  84 , the first synchronizer clutch (brake)  88  and the second synchronizer clutch (brake)  90  are activated or engaged. 
     Moving to the next, higher speed (lower gear ratio) reverse gear, denominated R 2 , the second friction clutch  84  and the second synchronizer clutch (brake)  90  are deactivated or disengaged and the first friction clutch  82  and the fifth synchronizer clutch (brake)  96  are activated or engaged while the first synchronizer clutch (brake)  88  remains activated or engaged. 
     As higher speed reverse gears, e.g., R 3 , R 4 , etc., are selected and engaged, this process of friction and synchronizer clutch disengagement and engagement continues according to the truth table of  FIG. 3 . Note that the first synchronizer clutch (brake)  88  remains activated or engaged in all five reverse gear ratios. It should be appreciated that the five reverse gear ratios are, in fact, those three pure gear ratios provided by the sub-transmission A and the two pure gear ratios provided by the sub-transmission B. 
     From neutral, first gear is achieved by activating or engaging the first friction clutch  82  and the second synchronizer clutch (brake)  90 . First gear is an actual or pure gear ratio achieved by utilizing the lowest speed gear (highest gear ratio) provided by the sub-transmission A. 
     Second gear is achieved by deactivating or disengaging the first friction clutch  82  and activating or engaging the third friction clutch  86  and the fifth synchronizer clutch (brake)  96 . As the truth table of  FIG. 3  presents, the second synchronizer clutch (brake)  90  remains activated or engaged. As illustrated in  FIG. 4 , second gear is a virtual or blended gear ratio achieved by mixing or blending the lowest speed gear (highest gear ratio) provided by the sub-transmission A and the lower speed gear (higher gear ratio) provided by the sub-transmission B. 
     Third gear is achieved by deactivating or disengaging the third friction clutch  86  and the second synchronizer clutch (brake)  90  and maintaining activation or engagement of the fifth synchronizer clutch (brake)  96 . The second friction clutch  84  is activated or engaged. Third gear is an actual or pure gear ratio achieved by utilizing the lower speed gear (higher gear ratio) provided by the sub-transmission B. 
     Fourth gear is achieved by deactivating or disengaging the second friction clutch  84  and activating or engaging the third friction clutch  86  and the third synchronizer clutch  92 . Engagement or activation of the fifth synchronizer clutch (brake)  96  is maintained during the third gear to fourth gear shift and in fourth gear. Once again and as illustrated in  FIG. 4 , fourth gear is a virtual or blended gear ratio which is achieved by mixing or blending the lower speed gear (higher gear ratio) provided by the sub-transmission B with the middle speed gear (middle gear ratio) provided by the sub-transmission A. 
     Fifth gear is achieved by deactivating or disengaging the third friction clutch  86  and the fifth synchronizer clutch (brake)  96  and activating or engaging the first friction clutch  82  while maintaining activation or engagement of the third synchronizer clutch (brake)  92 . Fifth gear is an actual or pure gear ratio achieved by utilizing the middle speed gear (middle gear ratio) provided by the sub-transmission A. 
     Sixth gear is achieved by deactivating or disengaging the first friction clutch  82  and activating or engaging the third friction clutch  86  and the sixth synchronizer clutch  98  while maintaining activation or engagement of the third synchronizer clutch (brake)  92 . As illustrated in  FIG. 4 , sixth gear is also a virtual or blended gear ratio which is achieved by mixing or blending the middle speed gear (middle gear ratio) of the sub-transmission A and the higher speed gear (lower gear ratio) of the sub-transmission B. 
     Seventh gear is achieved by deactivating or disengaging the third friction clutch  86  and the third synchronizer clutch (brake)  92  and activating or engaging the second friction clutch  84  while maintaining activation or engagement of the sixth synchronizer clutch  98 . Seventh gear is an actual or pure gear ratio achieved by utilizing the higher speed gear (lower gear ratio) of the sub-transmission B. 
     Eighth gear is achieved by deactivating or disengaging the second friction clutch  84  and activating or engaging the third friction clutch  86  and the fourth synchronizer clutch  94  while maintaining activation or engagement of the sixth synchronizer clutch  98 . Eighth gear is also a virtual or blended gear ratio which is achieved by mixing or blending the highest speed gear (lowest gear ratio) of the sub-transmission A and the higher speed gear (lower gear ratio) of the sub-transmission B. 
     Ninth gear is achieved by deactivating or disengaging the third friction clutch  86  and the sixth synchronizer clutch  98  and activating or engaging the first friction clutch  82  while maintaining activation or engagement of the fourth synchronizer clutch  94 . Ninth gear is an actual or pure gear ratio achieved by utilizing the highest speed gear (lowest gear ratio) of the sub-transmission A. 
     It will be appreciated that the foregoing explanation of operation and gear states of the first embodiment of the nine speed automatic transmission  10  is wholly and accurately applicable to operation of the second embodiment of the nine speed transmission  10 ′. Furthermore, the explanation assumes that all clutches not specifically referenced in a given gear ratio are inactive or disengaged. The explanation also assumes that during gear shifts between at least adjacent gear ratios, a clutch that is activated or engaged in both gear ratios will remain activated or engaged during the shift. Finally, the foregoing explanation assumes that downshifts follow essentially the opposite sequence of the corresponding up shifts and that several power on skip shifts, e.g., from first to third, are possible. 
     Referring now to  FIG. 4 , a diagrammatic representation of the relationship between the actual, physical gears and the virtual or blended gears of the nine speed automatic transmissions  10  and  10 ′ is provided. As described above, second gear, fourth gear, sixth gear and eighth gear are virtual or blended gear ratios achieved by a utilizing various combinations of the gear ratios provided by the sub-transmission A and the sub-transmission B whereas first gear, third gear, fifth gear, seventh gear and ninth gear are actual physical or pure gear ratios provided individually by either the sub-transmission A or the sub-transmission B. In  FIG. 4 , the horizontal axis represents neutral and greater distances above the neutral axis represent larger forward numerical gear ratios whereas greater distances below the neutral axis represent larger reverse numerical gear ratios. The left vertical axis relates to pure gear ratios provided by the sub-transmission A and the right vertical axis relates to pure gear ratios provided by the sub-transmission B. Solid black circles represent physical or pure gear ratios, open or white circles represent virtual or blended gear ratios and cross-hatched circles represent reverse gear ratios. Note that there are no reverse virtual or blended gear ratios. 
     The oblique line joining first gear and third gear is exemplary and illustrative of the fact that second gear is a virtual gear which is a mixture or blend of the first gear ratio provided by the sub-transmission A and the third gear ratio provided by the sub-transmission B. The intersection of this oblique line with the center vertical line labeled A-B represents the blended second gear ratio achieved by the sub-transmissions A and B which is between the first gear ratio and the third gear ratio. 
     The description of the invention is merely exemplary in nature and variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.