Patent Publication Number: US-2003232689-A1

Title: Dual input clutch transmission having synchronizers for establishing speed ratios

Description:
TECHNICAL FIELD  
       [0001] This invention relates to dual input clutch transmissions having synchronizers for establishing speed ratios within the transmission gear portions.  
       BACKGROUND OF THE INVENTION  
       [0002] Dual clutch manual transmissions, as they are often called, have two selectively engageable input clutches and a plurality of meshing gear pairs downstream of the input clutches between the input clutches and the transmission output shaft. In most dual clutch arrangements, the gear section includes a central or main shaft aligned with the input shaft and output shaft and two countershafts disposed parallel with the input shaft. Meshing pairs of gears are mounted on the center shaft and on each of the countershafts. The gear pairs are interconnected between the shafts by synchronizers or a mechanical clutch mechanism. The dual input clutch arrangement permits the oncoming speed ratio to be synchronized prior to the power path being moved from one head gearset to another by way of the selectively engageable input clutches. This permits ratio interchanging without torque interruption, which is normally found in single clutch-type transmissions.  
       [0003] In a dual clutch transmission which will produce six forward speeds and one reverse speed, the system requires two selectively engageable input clutches, seven and one-half pairs of external gears, one single synchronizer, and three two-way synchronizers. The seven and one-half pairs of gears consists of two head gear set pairs and one pair for each forward ratio, other than direct, and one and one-half pairs for reverse. In other words, an idler gear must be installed somewhere within the reverse gear train.  
       SUMMARY OF THE INVENTION  
       [0004] It is an object of the present invention to provide an improved dual clutch manual transmission.  
       [0005] In one aspect of the present invention, the transmission has two selectively engageable input clutches and two planetary gearsets.  
       [0006] In another aspect of the present invention, the transmission incorporates three three-way synchronizers and one two-way synchronizer.  
       [0007] In yet another aspect of the present invention, each of the planetary gearsets is continuously interconnected with the transmission output shaft.  
       [0008] In yet still another aspect of the present invention, one of the planetary gearsets is interconnected with the output shaft through a synchronizer mechanism such that two members of this planetary gearset can be selectively individually connected with the output shaft.  
       [0009] In a yet still another aspect of the present invention, each of the selectively engageable input clutches is connected with a respective one of the planetary gearsets through a three-way synchronizer, thereby permitting the input shaft to be selectively interconnected with three members of each of the planetary gearsets.  
       [0010] In a further aspect of the present invention, one of the planetary gearsets is connected to a transmission ground member, such as a housing, through another three-way synchronizer, thereby permitting three members of this planetary gearset to serve as a reaction member for the planetary gearset.  
       [0011] In yet a further aspect of the present invention, the other of the planetary gearsets includes at least one member continuously interconnected with the transmission ground member and one member continuously interconnected with the transmission output shaft.  
       [0012] In a yet still further aspect of the present invention, one of the planetary gearsets provides a reverse ratio, two underdrive ratios, and an overdrive ratio.  
       [0013] In a still further aspect of the present invention, the other of the planetary gearsets provides an underdrive ratio, a direct drive ratio, and an overdrive ratio. 
     
    
    
     DESCRIPTION OF THE DRAWING  
     [0014] The drawing is a schematic representation of a power transmission incorporating the present invention. 
    
    
     DESCRIPTION OF THE EXEMPLARY EMBODIMENT  
     [0015] Referring to the drawing, there is seen a power transmission generally designated  10  having an input shaft  12 , a planetary gear arrangement  14 , and an output shaft  16 . The planetary gear arrangement  14  includes two selectively engageable input clutches  18  and  20 , two planetary gearsets  22  and  24 , three three-way mechanical clutches or synchronizer clutches  26 ,  28 , and  30 , and one two-way mechanical clutch or synchronizer clutch  32 . The selectively engageable input clutches  18  and  20  are conventional fluid-operated friction clutches, commonly used with power transmissions, and the synchronizers  26 ,  28 ,  30 , and  32  are conventional mechanical synchronizer mechanisms, the construction and operation of which is well known in the art of countershaft transmissions.  
     [0016] The planetary gearset  22  includes a sun gear member  34 , a first ring gear member  36 , a second ring gear member  38 , and planet carrier assembly member  40 . The planet carrier assembly member  40  includes a plurality of pinion members  42  rotatably mounted on a planet carrier member  44  and disposed in meshing relationship between the sun gear member  34  and both of the ring gear members  36  and  38 . By providing two ring gear members  36 ,  38 , the planet carrier member  44  can be connected with three of the synchronizers  26 ,  28 ,  32  as described later.  
     [0017] The planetary gearset  24  includes a first sun gear member  46 , a second sun gear member  48 , a ring gear member  50 , and a planet carrier assembly member  52 . The planet carrier assembly member  52  includes a plurality of long pinion gear members  54  meshing with the sun gear member  48  and a plurality of short pinion gear members  56  each meshing with the sun gear member  46 , the ring gear member  50 , and respective ones of the long pinion gear members  54 . The pinion gear members  54  and  56  are rotatably mounted on a planet carrier member  58 , which is continuously interconnected with the output shaft  16 .  
     [0018] The selectively engageable input clutch  18  is continuously connected with the synchronizer clutch  26 . The selectively engageable input clutch  20  is continuously connected with the synchronizer clutch  30 . Thus, when the clutch  18  is engaged, the synchronizer clutch  26  rotates with the input shaft  12 , and when the clutch  20  is engaged, the synchronizer clutch  30  rotates with the input shaft  12 .  
     [0019] The synchronizer clutch  26  is a three-way synchronizer, which permits selective engagement with the sun gear member  34 , the planet carrier member  44 , and the ring gear member  36 . Thus, each of these planetary members can be selectively interconnected with the input shaft  12  through the synchronizer clutch  26  and the selectively engageable input clutch  18 .  
     [0020] The synchronizer clutch  30  is a conventional three-way synchronizer clutch, which permits selective connection with the sun gear member  46 , the ring gear member  50 , and the planet carrier member  58 , individually. Therefore, each of these planetary members, sun gear member  46 , planet carrier member  58 , and ring gear member  50 , can be selectively connected with the input shaft  12  through the synchronizer clutch  30  and the input clutch  20 .  
     [0021] The synchronizer clutch  28  has one portion thereof continuously connected with a transmission housing or transmission ground member. The synchronizer clutch  28  is a conventional three-way synchronizer assembly, which permits interconnection with the sun gear member  34 , the planet carrier member  44 , and the ring gear member  38 . Thus, each of these planetary members can be selectively interconnected with a transmission ground member or housing and held stationary.  
     [0022] The synchronizer clutch  32  has one portion thereof continuously interconnected with the output shaft  16  and is a conventional two-way synchronizer permitting selective interconnection with the planet carrier member  44  and the ring gear member  36 . Therefore, each of these planetary members can be selectively interconnected with the transmission output shaft  16 .  
     [0023] The selective engagement of the input clutches  18  and  20  and the synchronizer clutches  26 ,  28 ,  30 , and  32  will permit the establishment of six forward speed ratios and one reverse speed ratio between the input shaft  12  and the output shaft  16 .  
     [0024] The reverse speed ratio is established by selectively connecting the synchronizer clutch  26  with the sun gear member  34 , the synchronizer clutch  28  with the planet carrier member  44 , and the synchronizer clutch  32  with the ring gear member  36 . Thus, the ring gear member  36  is connected with the output shaft  16 . By engaging the input clutch  18 , the sun gear member  34  will be driven by the input shaft  12  and the ring gear member  36  will be rotated in a direction opposite to the input shaft  12 , and therefore the transmission will operate in a reverse speed ratio.  
     [0025] The first forward speed ratio is established with the manipulation of the synchronizer clutch  26  to engage the sun gear member  34 , the synchronizer clutch  28  to engage the ring gear member  38 , and the synchronizer clutch  32  to engage the planet carrier member  44 . By engaging the input clutch  18 , the sun gear member  26  is rotated in the same direction as the input shaft  12  and the planet carrier member  44  is rotated in the same direction as the input shaft  12  at a reduced speed ratio. Therefore, the output shaft  16 , which is connected with the planet carrier member  44  in this condition, will rotate forwardly at a reduced speed ratio.  
     [0026] A neutral condition between reverse and first forward ratio is established by disengaging both input clutches  18  and  20 .  
     [0027] The second forward speed ratio can be preselected while the first forward speed ratio is operating. The second forward speed ratio is preselected by manipulating the synchronizer clutch  30  to engage the sun gear member  46 . Then by swapping or interchanging the clutches  18  and  20 , the input shaft  12  will be drivingly connected with the sun gear member  46  and the synchronizer clutch  26  will be disconnected from the input shaft  12 . The sun gear member  46  will cause forward rotation of the planet carrier member  58  and therefore output shaft  16  at a speed reduced from the speed of the input shaft  12 . Therefore, the second forward speed ratio is an underdrive ratio.  
     [0028] The third forward speed ratio can be preselected by manipulating the synchronizer clutch  26  to engage the ring gear member  36 , the synchronizer clutch  28  to engage the sun gear member  34 , and the synchronizer clutch  32  to engage the planet carrier member  44 . These interchanges are accomplished while the clutch  18  is disengaged and the clutch  20  is engaged. To enforce or complete ratio change from second-to-third ratio, the clutches  18  and  20  are again swapped, such that the synchronizer clutch  30  is disengaged from the input shaft  12 , while the synchronizer clutch  26  is engaged with the input shaft  12 . This interchange can, of course, occur without a torque interruption at the output shaft  16 . During the third forward speed ratio, the ring gear member  36  is rotated by the input shaft  12 , the sun gear member  34  is held stationary through the synchronizer clutch  28 , and the planet carrier member  44  is rotated in the same direction as the input shaft  12  at a reduced speed ratio. The planet carrier member  44  is connected with the output shaft  16  through the synchronizer clutch  32 ; therefore, a reduced speed ratio is accomplished between the input shaft  12  and the output shaft  16 .  
     [0029] The fourth forward speed ratio is preselected during the third speed ratio by connecting the synchronizer clutch  30  with the planet carrier member  58 , which is directly connected with the output shaft  16 . An interchange from the third ratio to the fourth ratio is then accomplished by disengaging the clutch  18  while simultaneously engaging the clutch  20  permitting an upshift to fourth ratio without a torque interruption at the output shaft  16 . The fourth forward speed ratio is a direct drive in that the input shaft  12  is connected directly to the output shaft  16  through the clutch  20 , the synchronizer clutch  30 , and the planet carrier member  58 . Direct drive can also be achieved by connecting synchronizer  30  to both ring gear member  50  and sun gear member  46 .  
     [0030] The fifth forward speed ratio is preselected by manipulating the synchronizer clutch  26  to engage the planet carrier member  44 , the synchronizer clutch  28  is manipulated to engage the sun gear member  34 , and the synchronizer clutch  32  is manipulated to engage the ring gear member  36 . Under this condition, the planet carrier member  44  is connected with the input clutch  18 , the sun gear member  34  is connected to the transmission ground member, and the ring gear member  36  is connected with the output shaft  16 . To complete the fifth forward speed ratio engagement, the clutch  18  is engaged while the clutch  20  is disengaged. With the clutch  18  engaged in this condition, the planet carrier member  44  is rotated at the speed of the input shaft  12 , and the ring gear member  36  and therefore the output shaft  16  are rotated at an increased speed or overdrive ratio compared with the input shaft  12 . The fifth forward speed ratio is therefore an overdrive ratio.  
     [0031] The sixth forward speed ratio is preselected by manipulating the synchronizer clutch  30  to engage between the clutch  20  and the ring gear member  50 . Then by interchanging the input clutches  20  and  18 , the sixth forward speed ratio is completed such that the ring gear member  50  is rotated in unison with the input shaft  12 , and the output shaft  16  is rotated at an increased speed ratio through the planet carrier member  58 . The sixth forward speed ratio is an overdrive speed ratio.  
     [0032] Upon reviewing the description of the speed ratios, those skilled in the art will recognize that the reverse speed ratio, the first forward speed ratio, the third forward speed ratio, and the fifth forward speed ratio are all established through the planetary gearset  22 . The second forward speed ratio, the fourth forward speed ratio, and the sixth forward speed ratio are all established through the planetary gearset  24 . The planetary gearset  24  is described above as having a short pinion member  56  engaged between the sun gear member  46  and the ring gear member  50 . The pinion gear  56  also engaged with the long pinion gear  54 .  
     [0033] Alternatives are available with this meshing relationship. A short pinion meshing between the sun gear member  34  and the long pinion member  54 , and another short pinion meshing between the ring gear member  50  and the long pinion member  54  can also be employed. There are other alternative embodiments that those skilled in the art will recognize as viable. What should be noted is that an odd number of pinion meshes occur between the sun gear member  46  and the ring gear member  50 , while an even number of pinion meshes occurs between the sun gear member  48  and the ring gear member  50 .  
     [0034] If ring gears  36  and  38  both have  78  teeth, sun gear  34  had  30  teeth, ring gear  50  has  77  teeth, sun gear  46  has  28  teeth, and sun gear  48  has  32  teeth, the following ratios will be attained:  
                                                      First gear   3.60           Second gear   2.143           Third gear   1.385           Fourth gear   1.00           Fifth gear   0.722           Sixth gear   0.584           Reverse   −2.60                      
 
     [0035] The step ratio between successive forward ratios decreases as the ratios progress from first to sixth.  
     [0036] Obviously, many modifications and variations are possible in light of the above disclosure. Therefore, it should be understood that the invention is only to be limited by the scope of the appended claims.