Abstract:
A power transmission for a motor vehicle In realizing these advantages, a power transmission according to this invention includes an input shaft, an output, and a layshaft disposed parallel to the input shaft. A pair of drive elements includes a first element secured to the input shaft, and a second element journalled on the layshaft and driveably connected to the first element. A first coupler is secured to the layshaft for releasably coupling the second element and the layshaft. A planetary gear unit driveably connecting the layshaft and the output, includies a sun gear secured to the layshaft, a ring gear surrounding the sun gear and fixed against rotation, a carrier driveably connected to the output, and a set of planet pinions meshing with the sun gear and ring gear and rotatably supported on the carrier.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     This invention relates to automatic transmissions having a layshaft kinematic arrangement, particularly to such transmissions having input clutches but no torque converter.  
         [0003]     2. Description of the Prior Art  
         [0004]     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.  
         [0005]     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. 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 because there is no torque converter or producing a hydrokinetic connection between the engine and transmission input.  
         [0006]     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, the couplers can be moved to configure the transmission for the next even numbered gear. Dual clutch transmissions have parasitic losses only slightly higher than ASM transmissions.  
         [0007]     Layshaft ASM transmissions offer significant efficiency improvements over traditional automatic transmissions with torque converters. However, ASMs must produce more torque multiplication in the lower gears than would be required of a transmission having a torque converter in order to compensate for the torque multiplication that a torque converter produces at lower speeds. Layshaft ASM transmissions must produce more torque multiplication in the lower gears also to avoid excessive energy into the clutch during launch of a vehicle from a stop condition.  
         [0008]     A transmission having a large span usually requires many gear ratios to keep the ratio steps small. Consequently, there are many gears and synchronizer or couplers in large span transmissions.  
       SUMMARY OF THE INVENTION  
       [0009]     This invention reduces the magnitude of gear mesh losses to a much lower magnitude than is present in a conventional ASM transmission. A transmission according to this invention uses only one gear mesh for the high gears, thereby keeping gear mesh loss to a minimum. A planetary gear unit is used to produce additional torque multiplication in the low gears. Furthermore, this transmission reuses some of the pinion-gear meshes to produce multiple gears, resulting in a low number of gears for the number of speed ratios produced.  
         [0010]     In one embodiment, the direction of output rotation is opposite that of the input. In a conventional rear wheel drive application, this would require changes to a conventional inter-wheel differential mechanism. However, this requirement is avoided in a second embodiment, in which sprocket wheels and chains replace the pinions and gears.  
         [0011]     Because a layshaft ASM transmission must provide a large torque multiplication in first gear, the distance between the main shaft and layshaft, called “center distance,” is usually large and requires a correspondingly large package size. Here, however, much of the torque multiplication is achieved near the output end of the transmission by a planetary gear unit, the other components carry relatively low torque loads, and the center distance is kept small. Therefore, the package size is compact.  
         [0012]     Gear ratio changes are accomplished through the use of couplers, such as synchronizers or dog clutches, which mutually driveably connect components operative in each speed ratio. The couplers produce very little drag loss when engaged, and do not require a continuous supply of power to stay engaged.  
         [0013]     In realizing these advantages, a power transmission according to this invention includes an input, first input shaft and second input shaft arranged coaxially with a first axis. An output and layshaft are arranged coaxially on a second axis. A first clutch alternately connects and disconnects the input and the first input shaft. A second clutch alternately connects and disconnects the input and the second input shaft. A first torque path driveably connecting the first and second input shafts to the layshaft. A second torque path driveably connects the second input shaft and the output. A third torque path, which includes a planetary gear unit, produces a speed reduction between the layshaft and the output.  
         [0014]     In realizing these advantages, a power transmission according to this invention includes an input shaft, an output, and a layshaft disposed parallel to the input shaft. A pair of drive elements includes a first element secured to the input shaft, and a second element journalled on the layshaft and driveably connected to the first element. A first coupler is secured to the layshaft for releasably coupling the second element and the layshaft. A planetary gear unit driveably connecting the layshaft and the output, includies a sun gear secured to the layshaft, a ring gear surrounding the sun gear and fixed against rotation, a carrier driveably connected to the output, and a set of planet pinions meshing with the sun gear and ring gear and rotatably supported on the carrier.  
         [0015]     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  
       [0016]      FIG. 1  is a schematic diagram showing a gear arrangement of the transmission according to the present invention;  
         [0017]      FIG. 2  is a chart containing an example of the number of teeth for each of the gears and pinions of the transmission shown in  FIG. 1 ;  
         [0018]      FIG. 3  is a chart containing the torque ratios between the input and output and steps between the torque ratios for each of the forward gears and the reverse gear of the transmission of  FIG. 1 , the gears and pinions having the number of teeth shown in  FIG. 2 ;  
         [0019]      FIG. 4  is a schematic diagram showing a kinematic arrangement of the transmission according to the present invention;  
         [0020]      FIG. 5  is a chart containing an example of the number of teeth for each of the sprockets, gears and pinions of the transmission shown in  FIG. 4 ; and  
         [0021]      FIG. 6  is a chart containing the torque ratios between the input and output and steps between the torque ratios for each of the forward gears and the reverse gear of the transmission of  FIG. 4 , the sprockets, gears and pinions having the number of teeth shown in  FIG. 5 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0022]     Referring now to  FIG. 1 , 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.  
         [0023]     A first friction clutch  14  alternately connects and disconnects a first input shaft  16  as the clutch is engaged and disengaged, respectively. A second friction clutch  18  alternately connects and disconnects a second input shaft  20  as the clutch is engaged and disengaged, respectively.  
         [0024]     Pinions  22 ,  24 ,  26  are secured to input shaft  16 , which is supported for rotation on a transmission case. Pinions  28 ,  30 , and  32  are secured to the second input shaft  20 . Pinion  28  is in continuous meshing engagement with gear  34 , which is journalled on output  12 . Pinion  30  is in continuous meshing engagement with gear  36 , which is journalled on layshaft  38 . Pinion  32  is in continuous meshing engagement with gear  40 , which is journalled on layshaft  38 . Pinion  24  is in continuous meshing enga first torque transmitting paths for driveably connecting the layshaft to the first input shaft and second input shaft; 
        gement with gear  44 , which is journalled on layshaft  38 . Pinion  26  is in continuous meshing engagement with gear  46 , which is journalled on a second layshaft  48 . Reverse pinion  22  is continuously driveably connected to an idler gear (not shown), which in turn is in continuous meshing engagement with reverse gear  42 , journalled on layshaft  38 .        
 
         [0026]     A planetary gear unit  50 , preferably located near the output end of output  12 , includes a sun gear  52  secured to the layshaft  38 , a ring gear  54  secured to a transmission case  56  and held there against rotation, a set of planet pinions  58  in continuous meshing engagement with sun gear  52  and ring gear  56 , and a carrier  60  driveably connected to the second layshaft  48  and output  12  and rotatably supported the planet pinion  58 . When the transmission being described here is operating in the first, second and third forward gear ratios, and in reverse drive, the planetary gear unit  50  produces a speed reduction and torque increase at output  12  relative to the speed of, and torque transmitted by layshaft  38 . As described here, the planetary gear unit is not included in the torque delivery path for fourth, fifth, sixth and seventh forward gear ratios.  
         [0027]     Couplers  60 ,  62 ,  64  and  66  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 may also disconnect 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 the output  12  or a layshaft  38 ,  48 . For example, coupler  60  is secured by hub  68  to output  12  for rotation with the output.  
         [0028]     In the case where a coupler is a synchronizer, it is provided with a conical surface, which engages mutually with a corresponding conical surface located on a gear or sprocket adjacent the synchronizer. When coupler  60  is engaging either of its adjacent gears  34 ,  36  or sprockets  82 ,  86 , these conical surfaces are forced together into frictional contact, and that frictional engagement synchronizes the speed of the gear or sprocket to that of the output  12 . Each synchronizer is equipped with a sleeve  70  supported on the hub  68  for sliding movement leftward and rightward into engagement with the conical surfaces and dog teeth carried on the adjacent gear and sprocket. When the dog teeth of the sleeve engage those of the gear or sprocket, the layshaft is driveably connected to the gear or sprocket.  
         [0029]     In the case where a coupler is a dog clutch, displacement of the sleeve  70  in opposite axial directions causes mutual engagement of dog teeth formed on the sleeve with dog teeth carried on the gear and sprocket, such that a drive connection is made between the layshaft and the gear or sprocket, but without first synchronizing the rotational speed of the layshaft with the speed of the gear or sprocket.  
         [0030]     In  FIGS. 1 and 4 , the couplers  60 - 66  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 and sprocket completes the drive connection to the output  12  or layshaft  38 ,  48 . The hubs of couplers  62 ,  64  are rotatably secured to layshaft  38 ; the hub of coupler  66  is rotatably secured to layshaft  48 ; and the hub of coupler  60  is secured to output  12 .  
         [0031]     Coupler  60 , located between gears  34 ,  36  and between sprockets  82 ,  86 , releasably connects alternately those gears and sprockets to output  12 , and coupler  60  may be disengaged from both gears and both sprockets. Coupler  62 , located between gears  36 ,  40  and between sprockets  86 ,  90  releasably connects alternately those gears and sprockets to layshaft  38 , and coupler  60  may be disengaged from both gears and both sprockets. Coupler  64 , located between gears  42 ,  44  and between sprockets  102 ,  94 , releasably connects alternately those gears and sprockets to layshaft  38 , and coupler  64  may be disengaged from both gears and both sprockets. Coupler  66 , located between gears  44 ,  46  and between sprockets  94 ,  98 , releasably connects alternately those gears and sprockets to layshaft  48 , and coupler  66  may be disengaged from both gears and both sprockets.  
         [0032]     Operation of the transmission will be discussed next with reference to the positional state of the coupler sleeves and the applied and released state of clutches  14  and  18 . The first forward gear ratio is produced by first moving the selector sleeve of coupler  62  leftward to connect gear  36  to layshaft  38 , and then engaging friction clutch  18 . The speed of gear  36  is reduced and the torque it transmits is increased relative to those of the input  10 . A second torque multiplication occurs in the planetary gear unit  50 , where sun gear  52  is driven by layshaft  38 , ring gear  54  provides a torque reaction, and the carrier  60  is the output that drives output  12 . The output  12  is driven at a torque ratio of 5.321, and the torque ratio produced by planetary gear unit  50  is about 4.273 using the gear and pinion sizes of  FIG. 2 .  
         [0033]     The transmission is prepared for an upshift to the second ratio from the first forward ratio by moving the sleeve of coupler  64  rightward to connect gear  44  to layshaft  38 . Disengaging clutch  18 , engaging clutch  14  and returning the sleeve of coupler  62  to the neutral position complete the upshift. These actions produce a first speed reduction due to the engagement of pinion  24  and gear  44 , such that layshaft  38  and sun gear  52  are driven at a slower speed and higher torque relative to those of input  10 . An additional speed reduction and torque multiplication occurs at the planetary gear unit  50 . The output  12  is driven at a torque ratio of 3.909.  
         [0034]     The transmission is prepared for an upshift to the third ratio from the second ratio by moving the sleeve of coupler  62  rightward to connect gear  40  to layshaft  38 . Then disengaging clutch  14 , engaging clutch  18  and returning the sleeve of coupler  64  to the neutral position complete the upshift. These actions produce a first speed reduction due to the engagement of pinion  32  and gear  40 , such that layshaft  38  and sun gear  52  are driven at a slower speed and higher torque relative to those of input  10 . An additional speed reduction and torque multiplication occurs at the planetary gear unit  50 . The output  12  is driven at a torque ratio of 2.719.  
         [0035]     The transmission is prepared for an upshift to the fourth speed ratio by moving the selector sleeve of coupler  66  rightward to driveably connect gear  46  to second layshaft  48 . Then disengaging clutch  18 , engaging clutch  14 , and returning the sleeve of coupler  62  to the neutral position complete the upshift. Layshaft  48 , carrier  60 , and output  12  are driven at a lower speed than that of input  10  due to the meshing engagement of pinion  26  and gear  46 . The output  12  is driven at a ratio of 1.813.  
         [0036]     The transmission is prepared for an upshift to the fifth speed ratio by moving the selector sleeve of coupler  60  rightward to driveably connect gear  36  to layshaft  38 . Then engaging clutch  18 , disengaging clutch  14 , and returning the sleeve of coupler  66  to the neutral position complete the upshift. Output  12  is driven at a lower speed than that of input  10  due to the meshing engagement of pinions  30  and gear  36 . The output  12  is driven at a ratio of 1.245.  
         [0037]     The transmission is prepared for an upshift to the sixth speed ratio by moving the selector sleeve of coupler  66  leftward to driveably connect gear  44  to second layshaft  48 . Then disengaging clutch  18 , engaging clutch  14 , and returning the sleeve of coupler  60  to the neutral position complete the upshift. Layshaft  48 , carrier  60 , and output  12  are driven at a higher speed than that of input  10  due to the meshing engagement of pinion  24  and gear  44 . The output  12  is driven at a ratio of 0.915.  
         [0038]     The transmission is prepared for an upshift to seventh speed ratio by moving the selector sleeve of coupler  60  left to driveably connect gear  34  to output  12 . Then engaging clutch  18 , disengaging clutch  14 , and returning the sleeve of coupler  66  to the neutral position complete the upshift. Output  12  is driven at a higher speed than that of input  10  due to the meshing engagement of pinion  28  and gear  34 . The output  12  is driven at a ratio of 0.730.  
         [0039]     The transmission is prepared for a shift from the first forward speed ratio to the reverse drive by disengaging clutch  14  moving the selector sleeve of coupler  62  to the neutral position and moving the selector sleeve of coupler  64  leftward to driveably connect reverse output gear  42  to layshaft  38 . Then clutch  18  is engaged The first speed reduction occurs due to the drive connection between pinion  22  and gear  42 , which is driveably connected through coupler  64  and layshaft  38  to sun gear  52 . A second speed reduction is produced in the planetary gear unit such that output  12  is driven by carrier  60  at a slower speed and higher torque than those of input  10 . The output  12  is driven at a ratio of −5.298.  
         [0040]     Because the direction of rotation of output  12  is opposite to the direction of input  10  in the arrangement of  FIG. 1 , sprocket wheels  70 ,  72  and  74 , secured to input shaft  20 , replace pinions  28 ,  30  and  32 ; and sprocket wheels  76 ,  78 , secured to input shaft  16 , replace pinions  76  and  78 , in the embodiment of  FIG. 4 . A chain  80  driveably connects sprocket  70  to sprocket wheel  82 , which journalled on output  12 . A chain  84  driveably connects sprocket wheel  86 , which is journalled on layshaft  38 , to sprocket  72 . A chain  88  driveably connects a sprocket wheel  90 , which is journalled on layshaft  38 , to sprocket wheel  74 . Chain  92  driveably connects sprocket  76  to sprocket wheel  94 , which is journalled on layshaft  38 . Chain  96  driveably connects sprocket  78  to sprocket wheel  98 , which is journalled on layshaft  48 . A reverse pinion  100  is in continuous meshing engagement with a reverse output gear  102 , journalled on layshaft  38 .  
         [0041]     Each of the forward drive and reverse drive gears of the arrangement of  FIG. 4  is produced by operating the clutches  14 ,  18  and the couplers  60 - 66  in the same way as described with reference to  FIG. 1 .  
         [0042]     The planetary gear unit operates with three concentric shafts on the output  12  axis. The inner and outer shafts  12 ,  48 , respectively, are directly connected to the output. The middle shaft  38  is connected to the planetary sun gear  52 , resulting in torque multiplication at the output. By alternately connecting one of the driven gears to either the middle shaft or the inner shaft, first and fifth gears are produced. Similarly, by alternatively connecting another driven gear to either the middle shaft or the outer shaft, second and sixth gears are produced.  
         [0043]     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.