Patent Document

CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application is a divisional of the co-pending U.S. patent application Ser. No. 10/853,094, filed May 25, 2004. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     This invention relates to automatic transmissions having a layshaft kinematic arrangement, particularly to automatic transaxles having dual input clutches, but no torque converter.  
         [0003]     Automatic transmissions for transmitting power between an input and an output, either over a continuously variable range of speed ratios or in discrete step changes among speed ratios, have associated with them several sources of parasitic losses, which adversely affect fuel economy. These losses are associated with a torque converter, open hydraulic friction clutches and brakes, hydraulic pump, and gear meshes.  
         [0004]     To improve fuel economy in a motor vehicle having an automatic transmission, an automated shift manual (ASM) transmission can be used to eliminate or substantially reduce all of these parasitic losses except gear mesh losses. An ASM transmission generally performs gear ratio changes by first interrupting torque transmitted from the engine to the transmission input, preparing the transmission components associated with the next speed ratio, and then restoring torque at the input. A primary functional feature of ASM transmissions is the need to interrupt power transmitted from the engine to the transmission input shaft before or during each gear ratio change.  
         [0005]     Dual clutch layshaft transmissions are essentially two ASM transmissions, one providing odd numbered gears and one providing even numbered gears. Shifts between odd numbered gears and even numbered gears can be accomplished without interrupting power flow. While operating in an odd numbered gear, couplers can be actuated to configure the transmission for the next even numbered gear. Dual clutch transmissions have parasitic losses only slightly higher than ASM transmissions.  
         [0006]     Motor vehicles, in which the front wheels are the driven wheels and the engine and transmission are located in a forward engine compartment, generally require the engine and transmission to be arranged in a space whose lateral dimension is limited by the spacing between the front wheels. The engine compartments of such vehicles are both narrow and short. When the engine is also of the type having six in-line cylinders, there is an acute need to minimize the package space occupied by the transaxle, particularly its lateral dimension, in order to conserve space for long engines.  
       SUMMARY OF THE INVENTION  
       [0007]     A transaxle according to this invention is a layshaft transaxle having dual friction clutches and two final drive pinions. The sixth forward drive gear is located on an idler shaft, which transmits torque to an output shaft associated with particular gear ratios, e.g., odd-numbered gear ratios. A driving gear for the fifth gear ratio is also an idler gear for the sixth gear ratio. Producing the sixth gear in this way allows a substantial reduction in length of the transaxle.  
         [0008]     It is an advantage of this invention that the axial dimension of the transaxle, its lateral dimensions when installed in the vehicle, is reduced sufficiently to accommodate an I6 engine in the engine compartment. It is another advantage that its longitudinal dimension, as installed, provides sufficient space for V6 engines in the engine compartment.  
         [0009]     A multiple speed transaxle according to this invention includes first and second input shafts, first and second output shafts, a layshaft, an idler shaft, a first set of selectable torque paths between the first input shaft and first output shaft, a second set of selectable torque paths between the second input shaft and the second output shaft, the second set including the layshaft and idler shaft, and a selectable torque path between the first input shaft and second output shaft, the torque path including the layshaft and the idler shaft.  
         [0010]     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  
       [0011]      FIG. 1  is a schematic diagram showing an end view of a transmission according to the present invention;  
         [0012]      FIG. 2  is a cross section taken at planes  2 - 2  of  FIG. 1  showing the kinematic gear arrangement of a transmission having six forward speeds;  
         [0013]      FIG. 3  is a chart containing a preferred number of teeth for each of the gears and pinions of the transmission of  FIG. 2 ;  
         [0014]      FIG. 4  is a chart containing the torque ratios between the input and output and steps between the torque ratios for each of the forward speeds and reverse drive of the transmission of  FIG. 2 , the gears and pinions having the number of teeth shown in  FIG. 3 .  
         [0015]      FIG. 5  is a cross section taken at planes  2 - 2  of  FIG. 1  showing the kinematic gear arrangement of a transmission having seven forward speeds;  
         [0016]      FIG. 6  is a chart containing a preferred number of teeth for each of the gears and pinions of the transmission of  FIG. 5 ; and  
         [0017]      FIG. 7  is a chart containing the torque ratios between the input and output and steps between the torque ratios for each of the forward speeds and reverse drive of the transmission of  FIG. 5 , the gears and pinions having the number of teeth shown in  FIG. 6 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0018]     Referring to  FIGS. 1 and 2 , a transmission according to the present invention includes an input  10  for driveably connecting a power source, such as an internal combustion engine or electric motor, to the transmission, and an output  12  for driving a load, such as the driven wheels of a motor vehicle, through a powertrain that may include a drive shaft, differential mechanism, and axle shafts. A first friction clutch  14 , consisting of a clutch housing and a clutch disc, alternately connects and disconnects a first input shaft  16  as clutch  14  is engaged and disengaged, respectively. A second friction clutch  18 , consisting of a clutch housing and a clutch disc, connects and disconnects a second input shaft  20  as clutch  18  is engaged and disengaged, respectively.  
         [0019]     A first output shaft  22  supports a first output pinion  24 , which is secured to shaft  22  in continuous meshing engagement with an output gear  25 , secured to output  12 . A second output shaft  26  supports a second output pinion  28 , which is secured to the shaft in continuous meshing engagement with output gear  25 . An idler shaft  30  and layshaft  32  are arranged substantially parallel to the other shafts  16 ,  20   22  and  26 .  
         [0020]     First pairs of mutually engaged pinions and gears include a pinion  34 , secured to input shaft  16  and engaged with gear  36 , which is supported on shaft  22  for rotation relative to shaft  22 . A pinion  38 , secured to input shaft  16 , is engaged with gear  40  and with gear  42 , which is secured to idler shaft  30 . Gear  40  is supported on shaft  22  for rotation relative thereto. A pinion  44 , secured to input shaft  20 , is engaged with idler gear  46 , which is supported on idler shaft  30  for rotation relative to shaft  30  and is engaged with gear  48 , which is secured to layshaft  32 .  
         [0021]     A pinion  50 , which is supported on idler shaft  30  for rotation relative to shaft  30 , is engaged with gear  52 , which is supported on layshaft  32  for rotation relative to shaft  32 .  
         [0022]     Second pairs of mutually engaged pinions and gears include gear  52 , engaged with gear  54 , which is secured to output shaft  26 . A pinion  56 , which is supported on layshaft  32  for rotation relative to shaft  32 , is engaged with gear  58 , which is secured to output shaft  26 . A pinion  60 , secured to layshaft  32 , is engaged with gear  62 , which is supported on output shaft  26  for rotation relative to shaft  26 . A reverse output gear  64  is supported on output shaft  26  for rotation relative to shaft  26 .  
         [0023]     A reverse idler gear (not shown) is continually meshing with pinion  60  and reverse output gear  64 , thereby providing an additional mesh so that the direction of rotation of gear  64  is opposite the direction of rotation of the other output gears  36 ,  40 ,  54 ,  58 ,  62  when reverse drive is selected.  
         [0024]     Couplers  70 ,  72 ,  74  and  76  are preferably synchronizers of the type used in automotive manual transmissions to connect a gear or pinion to a shaft, after synchronizing the speed of the shaft and that of the pinion or gear. Each coupler also disconnects the shaft and the associated pinion or gear. An example of such a synchronizer is disclosed in U.S. Pat. No. 4,222,281. Alternatively, each coupler may be a toothed clutch having dogteeth that are engaged with clutch teeth on a gear or pinion. This invention may use couplers in any combination of synchronizers and dog clutches. Each coupler is secured by a hub to a shaft. For example, coupler  70  is secured by hub  78  to output shaft  22  for rotation with output shaft  22 .  
         [0025]     In the case where a coupler is a synchronizer, it is provided with a conical surface  80  on a blocker ring, located adjacent the hub  78  and supported for axial displacement. The conical surface on each blocker ring engages with a corresponding conical surface  82  located on a gear  36 ,  40  located adjacent the blocker ring. Each synchronizer includes a sleeve  84 , supported on the hub  78  for axial displacement leftward and rightward from the positions shown in  FIG. 2 . When the sleeve  84  is displaced axially causing the synchronizer  70  to engage either of its adjacent gears  36 ,  40 , the conical surface  80  on a blocker ring is forced into frictional contact with a conical surface  82  on the gear. This frictional engagement synchronizes the speed of the gear with that of the shaft  22 . When the rotational speeds of the shaft and gear are synchronized, further axial displacement of the sleeve  84  causes dog teeth on the radially inner surface of the sleeve to engage dog teeth carried on the adjacent gear. When the dog teeth of the sleeve engage those of the gear, the shaft  22  is driveably connected to the gear.  
         [0026]     In the case where a coupler is a dog clutch, displacement of the sleeve  84  in opposite axial directions causes mutual engagement of dog teeth formed on the sleeve with dog teeth carried on the gear, such that a drive connection is made between the shaft and the gear, but without first synchronizing the rotational speed of the shaft with the speed of the gear.  
         [0027]     In  FIG. 2 , the couplers  70 - 76  are shown in a neutral position, between the left-hand and right-hand extremities of travel of the connecting sleeve, whose engagement with dog teeth carried on the gear completes the drive connection to the shaft. The hubs of couplers  70 ,  76  are rotatably secured to output shafts  22  and  26 , respectively; the hub of coupler  72  is rotatably secured to idler shaft  30 ; the hub of coupler  74  is secured to layshaft  32 .  
         [0028]     Coupler  70 , located between gears  36 ,  40 , releasably connects alternately those gears to output shaft  22 , and coupler  70  may be disengaged from both gears  36 ,  40 . Coupler  74 , located between gears  52 ,  56 , releasably connects alternately those gears to layshaft  32 , and coupler  74  disengages those gears from shaft  32 . Coupler  76 , located between gears  62 ,  64 , releasably connects alternately those gears to second output shaft  26 , and coupler  76  disengages those gears from shaft  26 . Coupler  72 , located between gears  50 ,  42 , releasably connects and disconnects only gear  50  and idler shaft  30 .  
         [0029]     To produce the first forward speed, clutch  18  is engaged, and the selector sleeve of coupler  76  is displaced leftward to connect gear  62  and output shaft  26  mutually. Input  10  is driveably connected to shaft  20  through clutch  18 , causing pinion  44  to drive gear  48  and layshaft  32  through idler gear  46 . Pinion  60  drives gear  62 , which is driveably connected to output shaft  26  through coupler  76 . Output pinion  28  drives output  12  due to its engagement with output gear  25 .  
         [0030]     The second forward speed results by disengaging coupler  76 , sliding the selector sleeve of coupler  70  leftward to connect gear  36  to output shaft  22 , disengaging friction clutch  18 , and engaging clutch  14 . Input  10  is driveably connected to input shaft  16  through clutch  14 , causing pinion  34  to drive gear  36 , which drives output shaft  22  through coupler  70 . Output pinion  24  drives output  12  due to its engagement with output gear  25 .  
         [0031]     The third forward speed results by disengaging coupler  70 , sliding the selector sleeve of coupler  74  rightward to connect pinion  56  to layshaft  32 , disengaging friction clutch  14 , and engaging clutch  18 . Input  10  is driveably connected to input shaft  20  through clutch  18 , causing pinion  44  to drive gear  48  and layshaft  32  through idler gear  46 . Gear  48  drives layshaft  32  and pinion  56  through coupler  74 . Pinion  56  drives gear  58  and output shaft  26 . Output pinion  28  drives output  12  due to its engagement with output gear  25 .  
         [0032]     The fourth speed results by disengaging coupler  74 , sliding the selector sleeve of coupler  70  rightward to connect gear  40  to output shaft  22 , disengaging friction clutch  18 , and engaging clutch  14 . Input  10  is driveably connected to input shaft  16  through clutch  14 , causing pinion  38  to drive gear  40 , which drives output shaft  22  through coupler  70 . Output pinion  24  drives output  12  due to its engagement with output gear  25 .  
         [0033]     The fifth speed results by disengaging coupler  70 , sliding the selector sleeve of coupler  74  leftward to connect pinion  52  to layshaft  32 , disengaging friction clutch  14 , and engaging clutch  18 . Input  10  is driveably connected to input shaft  20  through clutch  18 , causing pinion  44  to drive gear  48  and layshaft  32  through idler gear  46 . Gear  48  drives layshaft  32  and pinion  52  through coupler  74 , and pinion  52  drives gear  54  and output shaft  26 . Output pinion  28  drives output  12  due to its engagement with output gear  25 .  
         [0034]     The sixth speed results by disengaging coupler  74 , sliding the selector sleeve of coupler  72  leftward to connect pinion  50  to idler shaft  30 , disengaging friction clutch  18 , and engaging clutch  14 . Input  10  is driveably connected to input shaft  16  through clutch  14 , causing pinion  38  to drive gear  42 , which drives idler shaft  30  and pinion  50  through coupler  72 . Pinion  50  drives gear  54  through gear  52 , which, for sixth gear operation, functions as an idler. Gear  54  drives output shaft  26 . Output pinion  28  drives output  12  due to its engagement with output gear  25 .  
         [0035]     The output  12  is driven in the reverse direction by sliding the selector sleeve of coupler  76  rightward to connect gear  64  to output shaft  26 , and engaging friction clutch  18 . Input  10  is driveably connected to input shaft  20  through clutch  18 , causing pinion  44  to drive gear  48  and layshaft  32  through idler  46 . Pinion  60  is driveably connected to reverse output gear  64 , which drives output shaft  26  through coupler  76 . Output pinion  28  drives output  12  due to its engagement with output gear  25 .  
         [0036]     Refer now to the kinematic arrangement of the seven speed transmission of  FIG. 5 , which adds to the arrangement of  FIG. 2 a  third pinion  90  secured to input shaft  16 , and a second forward drive gear  92 , supported on idler shaft  30  and engaged with the pinion  90 . The first forward drive gear  94  is supported on idler shaft  30 , but it is not secured to shaft  30 .  
         [0037]     The coupler  96 , which replaces coupler  72 , includes a hub that is secured to forward drive pinion  98 , rather than being secured to idler shaft  30 . Moving the selector sleeve of coupler  96  rightward from the neutral position driveably connects pinion  98  and gear  94 ; moving that sleeve leftward driveably connects pinion  98  and idler shaft  30 .  
         [0038]     The first five forward speeds and reverse drive of the transmission of  FIG. 5  are produced identically as described with reference to  FIG. 2 . The sixth speed results by sliding the selector sleeve of coupler  96  rightward to connect pinion  98  and gear  94 , disengaging clutch  18 , and engaging clutch  14 . Input  10  is driveably connected to input shaft  16  through clutch  14 , causing pinion  38  to drive gear  94 , which drives pinion  98  through coupler  96 . Pinion  98  drives gear  54  through gear  52 , which, for sixth and seventh gear operation, functions as an idler. Gear  54  drives output shaft  26 . Output pinion  28  drives output  12  due to its engagement with output gear  25 .  
         [0039]     The seventh speed results by disengaging clutch  14 , sliding the selector sleeve of coupler  96  leftward to connect pinion  98  and idler shaft  30 , and re-engaging clutch  14 . Input  10  is driveably connected to input shaft  16  through clutch  14 , causing pinion  90  to drive gear  92 , which drives idler shaft  30  due to gear  92  being secured to shaft  30 . Coupler  96  driveably connects idler shaft  30  and pinion  98 , which drives gear  54  through idler gear  52 . Gear  54  drives output shaft  26 . Output pinion  28  drives output  12  due to its engagement with output gear  25 .  
         [0040]     An upshift from sixth to seventh gear, unlike all other single step shifts, requires a torque break, i.e., the torsional connection between the input  10  and output  25  is briefly interrupted by disengaging clutch  14  while the state of coupler  96  is changed. This is mitigated because the 6-7 upshift is never made at high throttle; instead, it usually occurs as a result of the driver reducing power demand when reaching cruising speed. Downshifts inherently involve an output torque reduction, even for powershift transmissions, because some of the engine torque must be used to increase the engine speed. Double step shifts, such as those from fifth gear to seventh gear, and from seventh gear to fifth gear can be performed without interrupting torque.  
         [0041]     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.

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