Abstract:
A multi-speed automatic transmission includes an input, an output, a first gear unit drivable connected to the input and including a component rotating at the speed of the input and a first gear unit output, the first gear unit producing a gear ratio of a speed of the input and a speed of the first gear unit output, a planetary gear unit including a modified Simpson gearset, the gear unit being secured to first, second, third, fourth and fifth rotating members, the fifth member being secured to the output for rotation therewith, a first clutch being operable to connect the first rotating member and the first gear unit output, a second clutch being operable to connect the second rotating member and the first gear unit output, a third clutch being operable to connect the third rotating member and an element rotating at a speed of the input, a fourth clutch being operable to connect the fourth rotating member and said element rotating at the speed of the input, a first brake being operable to hold the fourth rotating member against rotation, and a second brake being operable to hold the third rotating member against rotation.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to the field of automatic transmissions for motor vehicles. More particularly, the invention pertains to a kinematic arrangement of gearing, clutches, brakes, and the interconnections among them in a power transmission. 
   2. Description of the Prior Art 
   A truck customer may desire improved launch capability, particularly when the vehicle is loaded and/or starting on a grade. The vehicle manufacturer offers customers options to allow improved launch capability. One option is to choose steeper (higher numerical) axle ratios. For those who have chosen a 4×4 truck, the transfer case generally is 2 speeds, one speed of which is a low-range which can also improve launch capability. 
   The steeper axle ratios improve vehicle launch capability when loaded, but reduce fuel economy even when the vehicle is unloaded. Offering multiple axle ratios adds complexity to the vehicle assembly plant. Operators of light trucks having 4×4 drivelines rarely use the low-range capability of a two-speed transfer case. The clutch mechanism for selecting low and high-ranges of the transfer case cannot be shifted unless the vehicle is stopped. 
   Most operators of such vehicle are accustomed to and prefer a small first-second gear step size of the transmission, which is 1.414 in a current production transmission. Eight-speed transmissions that have been proposed have gear mesh losses that exceeded those of highly efficient six-speed transmissions. 
   There is a need for a power transmission that can produce eight forward speeds and two reverse speeds, has high theoretical gear mesh efficiency and a wide speed ratio span. 
   SUMMARY OF THE INVENTION 
   A multiple-speed automatic transmission includes (a) an input, (b) an output, (c) a first gear unit drivable connected to the input and including a component rotating at the speed of the input and a first gear unit output, the first gear unit producing a gear ratio of a speed of the input and a speed of the first gear unit output, the gear ratio being greater than unity, and (d) a modified Simpson gear unit for producing multiple ratios of the speed of the input and a speed of the output, the modified Simpson gear unit being driveably connected to first, second, third, fourth, and fifth rotating members, the fifth member being secured to the output for rotation therewith. The modification to the Simpson gear unit involves extending one of the sets of the planetary pinions to allow engagement to an additional sun gear. A first clutch connects the first rotating member and first gear unit output; a second clutch connects the second rotating member and first gear unit output; a third clutch connects the third rotating member and an element rotating at transmission input speed; a fourth clutch connects the fourth rotating member and an element rotating at transmission input speed; a first brake holds the fourth rotating member against rotation, and a second brake holds the third rotating member against rotation. 
   The transmission can produce eight forward speeds and two reverse speeds, has high theoretical gear mesh efficiency and a wide speed ratio span. The eight-speed transmission provides two drive modes. Mode 1 could replace the conventional offering of optional axle ratios and the two speed transfer case. The transmission has a low-range first gear, which can either be used for launching the vehicle, such as when the operator is hauling a trailer, or as the low-range launch gear for 4×4 operations. 
   The transmission provides the ability to shift from low-range to high-range under full torque. When normal launch mode is required, the transmission provides a second gear with a conventional first-gear launch ratio. The seven speeds from second gear through eighth gear provide a close ratio gearbox with a span greater than five. 
   The transmission provides excellent fuel economy in normal drive mode. A manually operated selector switch for 4×4 vehicles can incorporate 4×2, 4×4 high and 4×4 low selectable positions, and can have added functions, such as 4×4 auto, trailer tow, and snow modes. These modes are achieved by starting the transmission in first, second or third gear and by using a 4×4 on demand clutch in off, stand-by or applied mode. 
   The scope of applicability of the preferred embodiment will become apparent from the following detailed description, claims and drawings. It should be understood, that the description and specific examples, although indicating preferred embodiments of the invention, are given by way of illustration only. Various changes and modifications to the described embodiments and examples will become apparent to those skilled in the art. 

   
     DESCRIPTION OF THE DRAWINGS 
     These and other advantages of the present invention will become readily apparent to those skilled in the art from the following detailed description of a preferred embodiment when considered in the light of the accompanying drawings in which: 
       FIG. 1  is a schematic diagram illustrating the kinematic arrangement of a transmission, which incorporates a modified Simpson gearset; 
       FIG. 2  is chart showing for each forward and reverse speed ratio the operating state of the clutches and brakes that control the transmission of  FIG. 1 , and a preferred speed ratio for each gear; 
       FIG. 3  is a chart showing a preferred number of gear teeth for each gear and pinion of the transmission of  FIG. 1  and the beta ratios of the modified Simpson and speed reduction gearsets; 
       FIG. 4  is a schematic diagram illustrating a second embodiment of a transmission, which incorporates a modified Simpson gearset; 
       FIG. 5  is chart showing for each forward and reverse gear the operating state of the clutches and brakes that control the transmission of  FIG. 4 , and a preferred speed ratio for each gear; and 
       FIG. 6  is a chart showing a preferred number of gear teeth for each gear and pinion of the transmission of  FIG. 4  and the beta ratios of the modified Simpson and speed reduction gearsets. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring now to the drawings, there is illustrated in  FIG. 1  the kinematic arrangement of an automatic transmission  10  A torque converter  11  includes a bladed impeller wheel  12  connected to the crankshaft  14  of an internal combustion engine, a bladed turbine wheel  16 , and a bladed stator wheel  18 . The impeller, stator and turbine wheels define a toroidal fluid flow circuit, whereby the impeller is hydrokinetically connected to the turbine. The stator  18  is supported rotatably on a stationary stator sleeve shaft  20 , and an overrunning brake  22  anchors the stator to the shaft  20  to prevent rotation of the stator in a direction opposite the direction of rotation of the impeller, although free-wheeling motion in the direction of rotation of the impeller is permitted. 
   The torque converter  11  includes a lockup clutch  24  located within the torque converter impeller housing  26 . When clutch  24  is engaged, the turbine and impeller are mechanically connected to a transmission input shaft  28 ; when clutch  24  is disengaged, the turbine and impeller are hydrokinetically connected and mechanically disconnected. Fluid contained in the torque converter is supplied to the torque converter from the output of an oil pump assembly (not shown) and is returned to an oil sump, to which an inlet of the pump is connected hydraulically. 
   A planetary gear system includes first, second, and third gear units  30 ,  32 ,  34 . The first gear unit  30  is a speed reduction gear unit which includes two ring gears  37  and  38 , a carrier  40 , stepped pinions  35  and  36  which are rotatably supported on carrier  40 , and no sun gears. The carrier  40  is secured to the input  28  and the ring gear  37  is grounded on the transmission case  39 . The stepped pinions  35  and  36  are joined to rotate together. The pinion  35  is in mesh with the ring gear  37  and the pinion  36  is in mesh with the ring gear  38 . The second ring gear  38  is the output of gear unit  30  and is underdriven relative to the speed of input  28 . For the specific example set forth in  FIG. 3 , which lists the number of gear teeth, the output speed ratio produced by the front planetary gear unit  30  is 0.444. 
   The second gear unit  32  includes axially spaced sun gears  42 ,  44 , a ring gear  46 , carrier  50 , and long planetary pinions  48 , rotatably supported on carrier  50  and in meshing engagement with sun gears  42 ,  44  and ring gear  46 . A bridging member  51 , secured to carrier  50  and extending radially between the first sun gear  42  and second sun gear  44 , is driveably connected to a clutch  52 . In this way, carrier  50  is accessible to clutch  52  and to a brake  53 . 
   The third gear unit  34  includes a sun gear  54 , ring gear  56 , carrier  58 , and planetary pinions  60 , rotatably supported on carrier  58  in meshing engagement with sun gear  54  and ring gear  56 . 
   The ring gear  37  of the first gear unit  30  is fixed against rotation. The carrier  40  of the first gear unit  30  is driveably connected to the input  28 . The ring gear  46  of the second gear unit  32  is driveably connected to the carrier  58  of the third gear unit  34 , which is driveably connected to output  60 . The second sun gear  44  of the second gear unit  32  is driveably connected to the sun gear  54  of the third gear unit  34 . 
   Ring gear  56  of the third gear unit is alternately connected to and disconnected from ring gear  38  of the first gear unit by clutch  62 . Sun gear  44  of the second gear unit and sun gear  54  of the third gear unit are alternately connected to and disconnected from ring gear  38  of the first gear unit by clutch  64 . Carrier  50  of the second gear unit is alternately connected to and disconnected from carrier  40  of the first gear unit by clutch  52 . Sun gear  42  of the second gear unit is alternately connected to and disconnected from carrier  40  of the first gear unit by clutch  66 . 
   Sun gear  42  is alternately held against rotation, preferably on the transmission case  39 , upon engagement of a brake  68  and are released for free rotation upon disengagement of brake  68 . Carrier  50  is alternately held against rotation, preferably on the transmission case  39 , upon engagement of a brake  53  and is released for free rotation upon disengagement of brake  53 . 
   Clutches  52 ,  66 ,  62 ,  64  and brakes  53 ,  68 , are preferably hydraulically-actuated friction devices having sets of interleaved friction discs and spacer plates, the discs being secured to one element of the clutch or brake, the spacer plates secured to another element of the clutch or brake. When hydraulic pressure increases in the cylinder of a servo that actuates a respective friction element, the discs and plates of the respective friction element are forced by displacement of the servo piston into mutual frictional contact, thereby producing a drive connection between the components of the gear units to which the elements of the clutch or brake are secured. When the pressure is vented from the servo cylinder, the clutch or brake is disengaged and the components are free to rotate independently. U.S. Pat. No. 4,943,921 describes and illustrates examples of hydraulically actuated friction clutches and brakes, which can be used in the transmission of this invention. 
   The front planetary gear unit  30  is a stepped pinion design with two ring gears  37 ,  38  and no sun gears. Input  28  is fixed to carrier  40 . Ring gear  37  is fixed to ground  39 . Ring gear  38  is the fixed a low speed output of the front planetary gear unit  30 , to which is attached one side of a clutch A  62  and one side of clutch B  64 . 
   The rear planetary units  32 ,  34  comprise a modified Simpson design having five elements, one of which provides the output  60 . Sun gears  44  and  54 , ring gears  46  and  56 , and carriers  50  and  58  constitute the Simpson gearset. The modification to the Simpson design comes from extending carrier  50  and pinion  48  so that an additional sun gear  42  can mesh with the pinion  48 . Since sun gears  42  and  44  both have the same number of teeth, and pinion  48  has a constant number of teeth across its width, sun gear  42  is forced to always rotate at the same speed as sun gears  44  and  54 . Sun gear  42  effectively becomes an extension of sun gears  44  and  54 . This is done so that the sun gears  44  and  54  have access to brake C  68  and clutch F  66  via sun gear  42 , while allowing a web from carrier  50  to fit between sun gears  42  and  44  and have access to clutch E  52 . 
   The gear ratio of a power path or a transmission is the ratio of the speed of its input to the speed of its output. A speed reduction power path, whose gear ratio is greater than unity, driveably connects input  28  and carrier  40  of the gear unit  30  through ring gear  38  to clutches  62 ,  64 . A second power path, whose speed ratio is equal to unity, driveably connects input  28  and carrier  40  to clutches  52 ,  66 . Preferably, the first power path underdrives ring gear  38  and the input of clutches  62 ,  64  at 0.444 times the speed of the input  28 , provided the number of gear teeth of the pinions and gears is as set forth in  FIG. 3 . 
   Operation of the transmission  10  is described next with reference to the engaged and disengaged state of the friction elements, which states in combination produce each of the gear ratios. Preferably, the states of the clutches and brakes are changed automatically in accordance with execution of a control algorithm by an electronic transmission controller.  FIG. 2  is a chart indicating the state of engagement and disengagement of the clutches and brakes corresponding to each of the gear ratios. In the chart, symbol “X” identifies an engaged friction clutch and friction brake. A blank indicates that the corresponding clutch and brake is disengaged or released.  FIG. 2  shows for each forward and reverse gear the operating state of the clutches and brakes that control the transmission of  FIG. 1  and the gear ratio for the respective gear. 
   The transmission  10  operates in the first forward gear when clutch  62  and brake  53  are engaged, and the other friction elements are disengaged. With ring gear  37  of the first gear unit  30  held against rotation and its carrier  40  directly connected to input  28 , the speed of ring gear  38  is underdriven relative to the speed of input  28 . Ring gear  56  is driveably connected to ring gear  38  through clutch  62 . Brake  53  holds carrier  50  against rotation and produces a torque reaction on the transmission case  39 . With carrier  50  held against rotation, sun gears  44 ,  54  mutually secured to rotate at the same speed, and carrier  58  and ring gear  46  secured mutually for rotation at the same speed, ring gear  46  and output  60  are underdriven due to an additional speed reduction. With the transmission operating in first gear, the ratio of the speed of input  28  and the speed of output  60  is 6.387, provided the number of gear teeth of the pinions and gears is as set forth in  FIG. 3 . 
   As  FIG. 2  shows, the transmission operates in each of the five lowest forward gears when clutch  62  is engaged; therefore, when the transmission  10  operates in each of the five lowest forward gears, ring gear  56  is underdriven relative to the speed of input  28 . 
   An upshift to the second speed ratio results by maintaining clutch  62  engaged, engaging brake  68 , and disengaging brake  53 . Ring gear  56  is underdriven relative to the speed of input  28  due to the speed reduction produced in gear unit  30 . Sun gear  42 , fixed against rotation due to the engagement of brake  68 , provides a torque reaction. Sun gears  44 ,  54  are secured mutually to rotate at the same speed. Therefore, the ring gear  46  and output  60  are underdriven relative to the ring gear  56  due to a second speed reduction produced in gear units  32 ,  34 . With the transmission operating in second gear, the ratio of the speed of input  28  and the speed of output  60  is 3.498, provided the number of gear teeth of the pinions and gears is as set forth in  FIG. 3 . 
   An upshift to third gear from second gear results upon disengaging brake  68 , engaging clutch  64 , and maintaining clutch  62  engaged. Ring gear  38  is underdriven relative to the speed of the input due to the speed reduction produced in the first gear unit  30 . Clutch  64  driveably connects ring gear  38  to sun gears  44 ,  54 . Clutch  62  driveably connects ring gear  38  to ring gear  56 . Because the speeds of sun gears  46 ,  54  and ring gear  56  are equal and underdriven relative to the speed of input  28 , carrier  58 , ring gear  46  and output  60  are underdriven at that same speed. With the transmission operating in third gear, the ratio of the speed of input  28  and the speed of output  60  is 2.250. 
   An upshift to fourth gear from third gear results upon engaging clutch  66 , disengaging clutch  64 , and maintaining clutch  62  engaged. Clutch  66  driveably connects sun gear  42  and input  28 . Clutch  62  driveably connects ring gear  38  to ring gear  56 . Due to the speed reduction produced in the first gear unit  30 , ring gear  40  is underdriven relative to the speed of the input  28 . With the transmission operating in fourth gear, the ratio of the speed of input  28  and the speed of output  60  is 1.556, provided the number of gear teeth of the pinions and gears is as set forth in  FIG. 3 . 
   An upshift to fifth gear from fourth gear results by maintaining clutch  62  engaged, engaging clutch  52 , and disengaging clutch  66 . Ring gear  56  of the third gear unit  34  is underdriven through clutch  62  relative to the speed of input  28  due to the speed reduction that occurs in gear unit  30 . Carrier  50  is driven at the speed of input  28  through clutch  52 . Sun gears  44 ,  54  are secured mutually; therefore, they rotate at the same speed. Similarly carrier  58  and ring gear  46  are secured mutually; therefore, they rotate at the same speed. With the transmission operating in fifth gear, the ratio of the speed of input  28  and the speed of output  60  is 1.252, provided the number of gear teeth of the pinions and gears is as set forth in  FIG. 3 . 
   An upshift to sixth gear from fifth gear results upon engaging clutch  66 , disengaging clutch  62 , and maintaining clutch  52  engaged. With the friction elements so disposed, clutch  52  driveably connects carrier  40  and input  28  to carrier  50  of the second gear unit  32 , and clutch  66  driveably connects carrier  40  and input  28  to sun gear  42  of the second gear unit  32 . The second gear unit  32  is locked-up; therefore, its ring gear  46  and output  60  rotate at the speed of the input  28 . With the transmission operating in sixth gear, the ratio of the speed of input  28  and the speed of output  60  is 1.000. 
   An upshift to seventh gear from sixth gear results upon engaging clutch  64 , disengaging clutch  66 , and maintaining clutch  52  engaged. Clutch  64  driveably connects the ring gear  38  of the first gear unit  30  to the sun gears  44 ,  54 , and clutch  52  driveably connects input  28  to carrier  50  of the second gear unit  32 . A torque reduction and speed increase produced in the second gear unit  32  causes ring gear  46  and output  60  to rotate faster than the speed of input  28 . With the transmission operating in seventh gear, the ratio of the speed of input  28  and the speed of output  60  is 0.807, provided the number of gear teeth of the pinions and gears is as set forth in  FIG. 3 . 
   An upshift to eighth gear from seventh gear results upon engaging brake  68 , disengaging clutch  64 , and maintaining clutch  52  engaged. With the friction control elements so disposed, clutch  52  driveably connects input  28  to carrier  50  of the second gear unit  32 , and brake  68  holds sun gear  42  of the second gear unit  32  against rotation, thereby providing a torque reaction. The second gear unit  34  produces a torque reduction and speed increase, which overdrives its ring gear  46  and output  60  relative to the speed of input  28 . With the transmission operating in eighth gear, the ratio of the speed of input  28  and the speed of output  60  is 0.698, provided the number of gear teeth of the pinions and gears is as set forth in  FIG. 3 . 
   A low-speed reverse gear is produced upon engaging clutch  64  and brake  53  concurrently, and releasing the other friction elements. Ring gear  38 , the underdriven output of gear unit  30 , underdrives sun gears  44 ,  54  through clutch  64  in a forward direction. With carrier  50  held against rotation by brake  53  and producing a torque reaction, the second gear unit  34  produces a second torque amplification and speed reduction, which further underdrives ring gear  46  and output  60  and reverses the direction of their rotation relative to those of input  28 . With the transmission operating in low-reverse gear, the ratio of the speed of input  28  and the speed of output  60  is −5.211, provided the number of gear teeth of the pinions and gears is as set forth in  FIG. 3 . 
   A higher-speed reverse gear is produced upon engaging clutch  66  and brake  53 , and releasing the other friction elements. Clutch  66  driveably connects carrier  40  of gear unit  30  and the input  28  to sun gear  42 . With carrier  50  held against rotation by brake  53  and producing a torque reaction, the second gear unit  32  produces a torque amplification and speed reduction, which underdrives ring gear  46  and output  60  and reverses the direction of their rotation relative to those at input  28 . With the transmission operating in high-reverse gear, the ratio of the speed of input  28  and the speed of output  60  is −2.316, provided the number of gear teeth of the pinions and gears is as set forth in  FIG. 3 . 
   The planetary gear unit formed by gear units  32 ,  34  includes five rotating members. A first member  70  connects clutch  62  and the ring gear  56  of gear unit  34 . The second member  72  connects clutch  64  and sun gears  44 ,  54 , which rotate as a unit. The third member  51  connects clutch  52  and brake  53  to second carrier  50 . The fourth member  74  connects clutch  66  and brake  68  to sun gear  42 . The fifth member  76  connects carrier  58 , ring gear  46  and output  60  for rotation as a unit. 
     FIG. 4  illustrates the kinematic arrangement of an automatic transmission  90 . In  FIG. 4 , each component that is identical to a component shown in  FIG. 1  is referenced with the identical numeral as that used in  FIG. 1  for the respective component. A speed reduction gear unit  92  includes a first sun gear  94  secured to input  28 , a ring gear  98  grounded on the housing  39 , a carrier  100 , and planet pinions  102  supported on carrier  100  and meshing with sun gear  94  and ring gear  98 . With ring gear  98  held against rotation, sun gear  94  driven by the input  28 , and the gears and pinions having the number of gear teeth shown in  FIG. 6 , carrier  100  is underdriven at 0.400 times the speed of the input, and the gear ratio produced by gearset  32  is 2.500. 
   The second and third gear units  130  and  101  comprise the modified Simpson gearset. The second gear unit  130  includes axially spaced sun gears  132 ,  134 , a ring gear  136 , carrier  138 , and long planetary pinions  140  rotatably supported on carrier  138  and in meshing engagement with sun gears  132 ,  134 , and ring gear  136 . 
   The third gear unit  101  includes a sun gear  104 , axially spaced ring gears  106 ,  108 , a carrier  110 , and long planetary pinions  112 , rotatably supported on carrier  110  in meshing engagement with sun gear  104  and ring gears  106 ,  108 . 
   Clutch  114  alternately driveably connects and disconnects carrier  100  of the speed reduction gear set  92  and ring gear  136  of gear unit  130 . Clutch  116  alternately connects and disconnects the carrier  100  of the speed reduction gear set  92  and sun gears  134 ,  104 . Brake  118  alternately releases and holds sun gears  134 ,  104  against rotation. Brake  120  alternately releases and holds carrier  110  against rotation. Clutch  122  alternately driveably connects and disconnects the input  28  and carrier  110 . Clutch  124  alternately driveably connects and disconnects the input  28  and sun gear  94  of the speed reduction gear set  30  to sun gear  132 . The engaged and disengaged states of the clutches  114 ,  116 ,  122 ,  124  and the brakes  118 ,  120  for each of the eight forward gears and the two reverse gears of transmission  90  are shown in  FIG. 5 . The speed ratios produced by transmission  90  are shown in  FIG. 5 , provided the number of gear teeth of the pinions and gears is as set forth in  FIG. 6 . 
   The front planetary gear unit  92  is a simple planetary design, which includes input  28 , fixed to sun gear  92 ; ring gear  98  fixed to ground  39 ; and carrier  100 , a low speed output of the gear unit  92  that is secured to one side of clutch A  114  and one side of clutch B  116 . 
   The gear unit  32 ,  101  comprise a modified Simpson design of six elements, one of which provides the output  60 . Sun gears  134  and  104 , ring gears  136  and  108 , and carriers  138  and  110  constitute the Simpson gearset. There are two modifications to the Simpson gearset. In the first modification, carrier  138  and pinion  140  are extended so that an additional sun gear  132  can be in mesh with the pinion gear  140 . Since sun gears  132  and  134  both have the same number of teeth, and pinion gear  140  has a constant number of teeth across its width, sun gear  132  is forced to always rotate at the same speed as sun gears  134  and  104 . Sun gear  132  effectively becomes an extension of sun gears  134  and  104 . This is done so that the sun gears  134  and  104  effectively have access to clutch F  124  via sun gear  132 , while allowing a web from carrier  138  to fit between sun gears  132  and  134  and to have access to ring gear  108 . 
   In the second modification, carrier  110  and pinion gear  112  are extended so that an additional ring gear  106  can be in mesh with the pinion gear  112 . Since ring gears  106  and  108  both have the same number of teeth, and pinion gear  112  has a constant number of teeth across its width, ring gear  106  is forced to always rotate at the same speed as ring gear  108 . Ring gear  106  effectively becomes an extension of ring gear  108  and carrier  138 . This is done so that carrier  138  and ring gear  108  effectively have access to output  60  via ring gear  106 , while allowing a web from carrier  110  to fit between ring gears  106  and  108  and to have access to Clutch E. 
   Operation of the transmission  90  is described next with reference to the engaged and disengaged state of the friction elements, which states in combination produce each of the gear ratios. Preferably, the states of the clutches and brakes are changed automatically in accordance with execution of a control algorithm by an electronic transmission controller.  FIG. 5  is a chart indicating the state of engagement and disengagement of the clutches and brakes corresponding to each the gear ratios. In the chart, symbol “X” identifies an engaged friction clutch and friction brake. A blank indicates that the corresponding clutch and brake is disengaged or released.  FIG. 5  shows for each forward and reverse gear the operating state of the clutches and brakes that control the transmission of  FIG. 4  and the speed ratio for the respective gear. 
   The transmission operates in the first forward gear when clutch  114  and brake  120  are engaged, and the other friction elements are disengaged. With ring gear  98  of the first gear unit  92  held against rotation and sun gear  94  of the first gear unit  92  directly connected to input  28 , carrier  100  is underdriven, and ring gear  136  is underdriven relative to the speed of input  28  through clutch  114 . Brake  120  holds carrier  110  against rotation and produces a torque reaction on the transmission case  39 . With carrier  110  held against rotation, sun gears  134 ,  104  mutually secured to rotate at the same speed, and carrier  138  and ring gear  108  secured mutually for rotation at the same speed, ring gear  106  and output  60  are underdriven due to an additional speed reduction. With the transmission operating in first gear, the ratio of the speed of input  28  and the speed of output  60  is 7.097, provided the number of gear teeth of the pinions and gears is as set forth in  FIG. 6 . 
   As  FIG. 5  shows, the transmission operates in each of the five lowest forward gears when clutch  114  is engaged; therefore, when transmission  90  operates in each of the five lowest forward gears, ring gear  136  is underdriven relative to the speed of input  28 . 
   An upshift to the second speed ratio results by maintaining clutch  114  engaged, engaging brake  118 , and disengaging brake  120 . Ring gear  136  is underdriven relative to the speed of input  28  due to the speed reduction produced in gear unit  92 . Sun gears  134 ,  104 , fixed against rotation due to the engagement of brake  118 , provide a torque reaction. Ring gear  106  and output  60  are underdriven relative to the ring gear  136  due to a second speed reduction produced in gear units  130 ,  101 . With the transmission operating in second gear, the ratio of the speed of input  28  and the speed of output  60  is 3.886, provided the number of gear teeth of the pinions and gears is as set forth in  FIG. 6 . 
   An upshift to third gear from second gear results upon disengaging brake  118 , engaging clutch  116 , and maintaining clutch  114  engaged. Ring gear  136  is underdriven through clutch  114  relative to the speed of the input due to the speed reduction produced in the first gear unit  92 . Clutch  116  driveably connects carrier  100  to sun gears  134 ,  104 . Because the speeds of sun gears  134 ,  104  and ring gear  136  are equal and underdriven relative to the speed of input  28 , carrier  110 , ring gear  106  and output  60  are underdriven at that same speed. With the transmission operating in third gear, the ratio of the speed of input  28  and the speed of output  60  is 2.500. 
   An upshift to fourth gear from third gear results upon engaging clutch  124 , disengaging clutch  116 , and maintaining clutch  114  engaged. Clutch  124  driveably connects sun gear  132  and input  28 . Clutch  114  driveably connects carrier  100  to ring gear  136 . Due to the speed reduction produced in the first gear unit  32 , ring gear  106  is underdriven relative to the speed of the input  28 . With the transmission operating in fourth gear, the ratio of the speed of input  28  and the speed of output  60  is 1.629, provided the number of gear teeth of the pinions and gears is as set forth in  FIG. 6 . 
   An upshift to fifth gear from fourth gear results by maintaining clutch  114  engaged, engaging clutch  122 , and disengaging clutch  124 . Ring gear  136  is underdriven through clutch  114  relative to the speed of input  28  due to the speed reduction that occurs in gear unit  92 . Carrier  110  is driven at the speed of input  28  through clutch  122 . Sun gears  134 ,  104  are secured mutually; therefore, they rotate at the same speed. With transmission  90  operating in fifth gear, the ratio of the speed of input  28  and the speed of output  60  is 1.268, provided the number of gear teeth of the pinions and gears is as set forth in  FIG. 6 . 
   An upshift to sixth gear from fifth gear results upon engaging clutch  124 , disengaging clutch  114 , and maintaining clutch  122  engaged. With the friction elements so disposed, clutch  122  driveably connects input  28  to carrier  110 , and clutch  124  driveably connects input  28  to sun gear  132 . The second gear units  130 ,  101  are locked-up; therefore, ring gear  106  and output  60  rotate at the speed of the input  28 . With the transmission operating in sixth gear, the ratio of the speed of input  28  and the speed of output  60  is 1.000. 
   An upshift to seventh gear from sixth gear results upon engaging clutch  116 , disengaging clutch  124 , and maintaining clutch  122  engaged. Clutch  116  driveably connects carrier  100  of the first gear unit  92  to the sun gears  134 ,  104 , and clutch  122  driveably connects input  28  to carrier  110  of gear unit  101 . A torque reduction and speed increase produced in the second gear unit  130  causes ring gear  106  and output  60  to rotate faster than the speed of input  28 . With the transmission operating in seventh gear, the ratio of the speed of input  28  and the speed of output  60  is 0.794, provided the number of gear teeth of the pinions and gears is as set forth in  FIG. 6 . 
   An upshift to eighth gear from seventh gear results upon engaging brake  118 , disengaging clutch  116 , and maintaining clutch  122  engaged. With the friction control elements so disposed, clutch  122  driveably connected input  28  to carrier  110  of the gear unit  101 , and brake  118  holds sun gears  134 ,  104  against rotation, thereby providing a torque reaction. Gear unit  101  produces a torque reduction and speed increase, which overdrives its ring gear  106  and output  60  relative to the speed of input  28 . With the transmission operating in eighth gear, the ratio of the speed of input  28  and the speed of output  60  is 0.698, provided the number of gear teeth of the pinions and gears is as set forth in  FIG. 6 . 
   A low-speed reverse gear is produced upon engaging clutch  116  and brake  120  concurrently, and releasing the other control elements. Carrier  100 , the underdriven output of gear unit  92 , underdrives sun gears  134 ,  104  in a forward direction through clutch  116 . With carrier  110  held against rotation by brake  120  and producing a torque reaction, the gear unit  101  produces a second torque amplification and speed reduction, which further underdrives ring gear  106  and output  60  and reverses the direction of their rotation relative to those of input  28 . With the transmission operating in low-reverse gear, the ratio of the speed of input  28  and the speed of output  60  is −5.790, provided the number of gear teeth of the pinions and gears is as set forth in  FIG. 6 . 
   A higher-speed reverse gear is produced upon engaging clutch  124  and brake  120 , and releasing the other control elements. Clutch  124  driveably connects the input  28  and sun gear  94  to sun gear  132 . With carrier  110  held against rotation by brake  120  and producing a torque reaction, the gear unit  101  produces a torque amplification and speed reduction, which underdrives ring gear  106  and output  60  and reverses the direction of their rotation relative to those at input  28 . With the transmission operating in high-reverse gear, the ratio of the speed of input  28  and the speed of output  60  is −2.316, provided the number of gear teeth of the pinions and gears is as set forth in  FIG. 6 . 
   The modified Simpson gearset formed by gear units  130 ,  101  includes six rotating members. The first rotating member  142  connects clutch  114  and the ring gear  136  of gear unit  130 . The second rotating member  144  connects clutch  116  and brake  118  to sun gear  134  of gear unit  130  and to sun gear  104  of gear unit  101 . The third rotating member  146  connects brake  120  and clutch  122  to carrier  110  of gear unit  101 . The fourth rotating member connects clutch  124  to sun gear  132  of gear unit  130 . The fifth rotating member connects carrier  138  of gear unit  130  to ring gear  108  of gear unit  101 . The sixth rotating member connects ring gear  106  of gear unit  101  to output  60 . 
   From  FIGS. 2 and 5  it can be seen that the same clutch and brake engagement pattern is used for the embodiments of  FIGS. 1 and 4 . For example, clutch A  62 ,  114  and brake D  53 ,  120  are engaged for first gear for both embodiments, clutch A  62 ,  114  and brake C  68 ,  118  are engaged for second gear second for both embodiments, etc. 
   In accordance with the provisions of the patent statutes, the preferred embodiment has been described. However, it should be noted that the alternate embodiments can be practiced otherwise than as specifically illustrated and described.