Abstract:
A multiple-speed transmission for use in an automotive vehicle driveline includes a torque converter, three simple planetary gear units, or two simple planetary gear units and a compound planetary gear unit, friction clutches and brakes, and an optional one-way coupling. The engaged and disengaged states of the friction elements permit the transmission to produce several underdrive speed ratios, a direct drive ratio, and several overdrive speed ratios.

Description:
BACKGROUND OF THE INVENTION 
   This invention relates to the field of automatic transmissions for motor vehicles. More particularly, the invention pertains to the kinematic arrangement of planetary gearing, clutches, brakes, and overrunning couplings for such transmissions. 
   Minimizing the package size of a geared automatic transmission for motor vehicles, its lateral dimensions and particularly its axial dimensions, has long been an objective in the automotive industry. Realizing this goal has become more difficult because of the need for transmissions to provide a continually increasing number of forward gear ratios and a need for non-synchronous shifting among the gear ratios. Automatic transmissions having five and six forward gear ratios are replacing current transmissions having four and five forward gear ratios. 
   In order to minimize the axial length of an automotive transmission, the number of friction clutches and brakes is minimized. It has become conventional to provide non-synchronous gear ratio changes, especially among the lower gears, by providing a one-way coupling in parallel with a hydraulically actuated friction clutch or brake. However, a one-way coupling requires additional space along the axis of the transmission. Its presence also adds to assembly time, material cost, and weight. 
   In addition to minimizing the package size of automatic transmissions, it is important also to minimize the rotational speed of the pinion gears, which are supported on a carrier of the planetary gear units within the transmission. 
   Excessive planet pinion gear speed can adversely affect the service life of the bearings on which the planet pinions are supported for rotation on the carrier. It is not uncommon that the rotational speed of planet pinions of certain gear units be five to seven times the engine speed. 
   SUMMARY OF THE INVENTION 
   It is an advantage of this invention that the rotational speed of the planet pinion gears is relatively low in comparison to transmissions in the prior art, and that the transmission is compact and has a minimal axial length. Nearly ideal steps between gear ratios can be obtained with reasonable “betas” in all gearsets. Beta is the ratio of the diameter or number of teeth of a ring gear and a sun gear of the same planetary gear unit. 
   It is another advantage of this invention that six forward speed ratios are produced with only five friction clutches and brakes and without need for an overrunning coupling. However, if non-synchronous gear ratio changes between first gear and second gear are desired, a one-way coupling can be provided in parallel with a friction brake. 
   In realizing these advantages, a multiple-speed ratio automatic transmission according to this invention includes an input and output. A planetary gear system includes first, second and third planetary gear units, each gear unit having a sun gear, a ring gear, planet pinions meshing with the sun gear, planet pinions meshing with the ring gear, and a carrier rotatably supporting the planet pinions. 
   Certain gear unit components are functionally secured continually to other components, but some components are releasably secured to others. For example, the input is driveably connected to the sun gear of the first gear unit, the output is driveably connected to the carrier of the third gear unit, the ring gear of the third gear unit is driveably connected to the carrier of the second gear unit, one of the carrier of the first gear unit and the ring gear of the first gear unit is secured against rotation, and the sun gear of the second gear unit is driveably connected to the sun gear of the third gear unit. 
   A first brake releasably holds the ring gear of the second gear unit against rotation. A second brake releasably holds the carrier of the second gear unit and ring gear of the third gear unit against rotation. A first clutch driveably connects and disconnects the input and the sun gears of the second and third gear units. A second clutch driveably connects and disconnects the input and carrier of the second gear unit. A third clutch releasably connects the other of the carrier of the first gear unit and ring gear of the first gear unit to the ring gear of the second gear unit. 
   Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic diagram of the kinematic arrangement of the gears, clutches, brakes, and couplings for a preferred embodiment of this invention; 
       FIG. 2  is a chart that shows the pattern of engagement and release of the clutches and brakes required to produce the various forward drive ratios and reverse drive ratio of the transmission of  FIGS. 1 and 3 ; 
       FIG. 3  is a schematic diagram of the kinematic arrangement of an alternate embodiment of the automatic transmission of this invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring now to the drawings, there is illustrated in  FIG. 1  the kinematic arrangement of an automatic transmission according to the present invention. The torque converter  10  includes an 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 opposite direction is permitted. 
   The torque converter assembly includes a lockup clutch  24  located within the torque converter impeller housing  25 . The torque output side of lockup clutch  24  includes a damper  26  located between the impeller and the turbine shaft, which is the transmission input shaft  28 . When clutch  24  is engaged, the turbine and impeller are mechanically connected; when clutch  24  is disengaged, they are hydrokinetically connected and mechanically disconnected. The damper absorbs transitory torque fluctuations associated with engagement of a lockup clutch. Fluid contained in the torque converter is supplied to the torque converter from the output of an oil pump assembly  30  and is returned to an oil sump, to which an inlet of the pump is connected hydraulically. 
   Planetary gearing includes first, second, and third planetary gear units  32 ,  34 , and  36 . The first gear unit  32  includes a sun gear  38 , ring gear  40 , carrier  42 , and planetary pinions  44 , supported on carrier  42  in meshing engagement with sun gear  38  and ring gear  40 . The second gear unit  34  includes a sun gear  46 , ring gear  48 , carrier  50 , and planetary pinions  52 , rotatably supported on carrier  50  in meshing engagement with sun gear  46  and ring gear  48 . The third gear unit  36  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 . 
   Clutch  64  releasably connects input shaft  28  and sun gears  46  and  54 . Clutch  66  releasably connects input shaft  28  and carrier  50 . Clutch  68  releasably connects carrier  42  and ring gear  48 . 
   Carrier  50  of the second gear unit  34  is continually driveably connected to ring gear  56  of third gear unit  36  and to a brake  74 . Member  62  continually driveably connects sun gear  38  to input shaft  28 . Ring gear  40  is continually held against rotation on the transmission case  70 . 
   Ring gear  48  is held against rotation on the transmission case  70  by engagement of a first friction brake  72 , and ring gear  48  is released for free rotation by disengagement of brake  72 . Engagement of the second friction brake  74  holds carrier  50  and ring gear  56  against rotation on the transmission case  70 ; carrier  50  and ring gear  56  are released for free, independent rotation upon disengagement of brake  74 . 
   Clutches  64 ,  66 ,  68  and brakes  72 ,  74 , are hydraulically-actuated friction devices having sets of interleaved friction discs and spacer plates, the discs secured to one element of the clutch or brake, the spacer plates secured to another element of the clutch or brake. Hydraulic pressure forces the discs and plates into frictional contact and completes a drive connection between the components to which the elements of the clutch or brake are secured. When the pressure is vented from the device, 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, and a one-way coupling that can be used in the transmission of this invention. 
   If non-synchronous gear ratio changes between first gear and second gear are desired, a one-way coupling can be provided in parallel with brake  74 . Preferably, the coupling provides a one-way drive connection between the case  70  and the mutually connected ring gear  56  and carrier  50 . The coupling produces a drive connection to the case  70  in first gear and it overruns in all other gears. The coupling includes an inner race  80  connected to ring gear  56 , which is secured to carrier  50 , an outer race  84  secured to case  70  against rotation, and a set of rollers or sprags  86  located between the races and adapted to complete a one-way drive connection between the races. 
   A differential mechanism (not shown), driveably connected to output  84 , transmits power to the drive wheels of a vehicle, as described and illustrated in U.S. Pat. No. 5,261,862. A gear selector lever, controlled by the vehicle operator to select the operating range of the transmission, is movable among positions where the various gear ratios are produced automatically and other positions where the gear ratios are produced manually. 
   Operation of the kinematic components of the transmission is described next with reference to the state of the friction elements and the coupling corresponding to 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 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. 
   When the transmission operates in the first gear ratio, forward clutch  64  is engaged and brake  74  is engaged, thereby holding ring gear  56  against rotation on the transmission casing  70 . The first speed ratio, produced in the third gear unit  36 , is taken at carrier  58 , which is underdriven in relation to the speed of input  28 . Carrier  58  drives output shaft  84 . 
   An upshift to the second speed ratio results by maintaining forward clutch  64  engaged, engaging brake  72 , and disengaging brake  74 . Sun gears  46  and  54  are driven at the speed of input shaft  28 . Ring gear  48  provides the torque reaction on case  70 . Carrier  50 , which is underdriven in the second gear unit  34 , drives ring gear  56 . Therefore, carrier  58  is underdriven at a faster speed than in first gear. 
   An upshift to the third speed ratio from the second speed ratio results upon disengaging brake  72  and engaging clutch  68 , while maintaining the forward clutch  64  engaged. The sun gears  38 ,  46  and  54  are driven at the speed of input shaft  28 . Ring gear  40 , held against rotation on case  70 , provides the torque reaction. Carrier  42 , which is underdriven in the first gear unit  32 , drives ring gear  48  through clutch  68 . Carrier  50  and ring gear  56  are under driven in relation to the speed of input  28  but are overdriven in relation to carrier  42 . Carrier  58  and output  84  are underdriven, but at a faster speed than in second gear. 
   A fourth forward speed ratio is produced by maintaining forward clutch  64  engaged, engaging clutch  66 , and disengaging the other friction elements. Sun gears  46  and  54 , and the mutually interconnected carrier  50 -ring gear  56  subassembly are driven at the speed of input shaft  28  through clutches  64  and  66 , respectively. Therefore, the third gear unit  36  is locked-up and output shaft  84  is driven at the speed of shaft  28 , a direct drive speed ratio. 
   The fifth speed ratio is produced upon engaging clutches  66  and  68 , and disengaging clutch  64 . Ring gear  40  provides the torque reaction on the case  70 . Carrier  42 , the underdriven output of the first gear unit  32 , drives ring gear  48  through clutch  68 . Carrier  50  and ring gear  56  are driven at the speed of the input shaft  28  through clutch  66 . Sun gear  46 , the overdriven output of the second gear unit  34 , drives sun gear  54 . Therefore, output carrier  58  and output shaft  84  are overdriven compared to the speed of input shaft  28 . 
   The sixth forward speed ratio results when clutch  66  and brake  72  are engaged, and the other friction elements are disengaged. Carrier  50  and ring gear  56  are driven at the speed of input shaft  28  through clutch  66 . Ring gear  48  is held against rotation, thereby providing a torque reaction on the case  70 . The second gear unit  34  overdrives sun gears  46  and  54 . An additional speed increase occurs in the third gear unit  36 , whereby carrier  58  and shaft  84  are overdriven in comparison to the speed of input shaft  28  faster than they are in the fifth gear ratio. 
   Reverse drive results by engaging clutch  68  and brake  74 , and releasing the other friction elements. Carrier  42 , the underdriven output of gear unit  32 , underdrives ring gear  48  through clutch  68 . The second gear unit  34 , whose carrier  52  is held against rotation due to engagement of brake  74 , further tends to overdrive sun gear  46  and reverses its direction of rotation in comparison to the speed and direction of carrier  42 . The third gear unit  36 , with ring gear  56  held, produces a speed reduction driving carrier at relatively low speed in the reverse directional sense. 
   In  FIG. 3 , the various components on the transmission are marked with the same reference numbers as corresponding components of FIG.  1 . The first gear set  32 ′ is a compound planetary gear unit including a sun gear  38 , ring gear  40 , carrier  42 ′, and two sets of planetary pinions  88 ,  90  of equal size, supported on a carrier  42 ′. The first pinion set  88  is in continuous meshing engagement with sun gear  38 ; the second pinion set  90  is in continuous meshing engagement with ring gear  40  and with the first pinion set  88 . Carrier  42 ′ is secured to the case  70  against rotation. 
   If non-synchronous gear ratio changes between first gear and second gear are desired, a one-way coupling can be provided in parallel with brake  74 . Preferably, the coupling provides a one-way drive connection between the case  70  and the mutually connected ring gear  56  and carrier  50 . The coupling produces a drive connection to the case  70  in first gear and it overruns in all other gears. 
   The description that follows describes operation of the kinematic arrangement of  FIG. 3  for and each of the forward and reverse gear ratios with reference to the schedule of FIG.  2 . 
   When the transmission operates in the first gear ratio, forward clutch  64  is engaged and brake  74  is engaged, thereby holding ring gear  56  against rotation on the transmission casing  70 . The first speed ratio, produced in the third gear unit  36 , is taken at carrier  58 , which is underdriven in relation to the speed of input  28 . Carrier  58  drives output shaft  84 . 
   An upshift to the second speed ratio results by maintaining forward clutch  64  engaged, engaging brake  72 , and disengaging brake  74 . Sun gears  46  and  54  are driven at the speed of input shaft  28 . Ring gear  48  provides the torque reaction on case  70 . Carrier  50 , which is underdriven in the second gear unit  34 , drives ring gear  56 , and carrier  58  is underdriven at a faster speed than in first gear. 
   An upshift to the third speed ratio from the second speed ratio results upon disengaging brake  72  and engaging clutch  68 ′, while maintaining the forward clutch  64  engaged. The sun gears  38 ,  46  and  54  are driven at the speed of input shaft  28 . Carrier  42 ′, held against rotation on case  70 , provides the torque reaction. Ring gear  40 , which is underdriven in the first gear unit  32 , drives ring gear  48  through clutch  68 ′. Carrier  50  and ring gear  56  are under driven in relation to the speed of input  28 , but are overdriven in relation to ring gear  40 . Carrier  58  and output  84  are underdriven, but at a faster speed than in second gear. 
   Maintaining forward clutch  64  engaged, engaging clutch  66 , and disengaging the other friction elements produces the fourth forward speed ratio. Sun gears  46  and  54 , and the mutually interconnected carrier  50 -ring gear  56  subassembly are driven at the speed of input shaft  28  through clutches  64  and  66 , respectively. Therefore, the third gear unit  36  is locked-up and output shaft  84  is driven at the speed of shaft  28 , a direct drive speed ratio. 
   The fifth speed ratio is produced upon engaging clutches  66  and  68 ′, and disengaging clutch  64 . Carrier  42 ′ provides the torque reaction on the case  70 . Ring gear  40 , the underdriven output of the first gear unit  32 , drives ring gear  48  through clutch  68 ′. Carrier  50  and ring gear  56  are driven at the speed of the input shaft  28  through clutch  66 . Sun gear  46 , the overdriven output of the second gear unit  34 , drives sun gear  54 . Therefore, carrier  58  and output shaft  84  are overdriven compared to the speed of input shaft  28 . 
   The sixth forward speed ratio results when clutch  66  and brake  72  are engaged, and the other friction elements are disengaged. Carrier  50  and ring gear  56  are driven at the speed of input shaft  28  through clutch  66 . Ring gear  48  is held against rotation, thereby providing a torque reaction on the case  70 . The second gear unit  34  overdrives sun gears  46  and  54 . An additional speed increase occurs in the third gear unit  36 , whereby carrier  58  and shaft  84  are overdriven in comparison to the speed of input shaft  28  faster than they are in the fifth gear ratio. 
   Reverse drive results by engaging clutch  68 ′ and brake  74 , and disengaging the other friction elements. Ring gear  40 , the underdriven output of gear unit  32 , underdrives ring gear  48  through clutch  68 ′. The second gear unit  34 , whose carrier  52  is held against rotation due to engagement of brake  74 , further overdrives sun gears  46  and  54 , and it reverses their direction of rotation in comparison to the speed and direction of ring gear  40 . The third gear unit  36 , with ring gear  56  held, produces still a speed reduction driving carrier  58  at relatively low speed in the reverse directional sense. 
   In accordance with the provisions of the patent statutes, the principle and mode of operation of this invention have been explained and illustrated in its preferred embodiment. However, it must be understood that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope.