Abstract:
A parallel axes type automatic transmission including a first input shaft having m or more (m is an integer not less than 2) wet multiplate clutches and drive gears rotatably mounted, a second input shaft having n or more (n is an integer greater than m and not less than 3) wet multiplate clutches and drive gears rotatably mounted, and a third input shaft having m or less wet multiplate clutches and drive gears rotatably mounted. The automatic transmission further includes an output shaft having a fixed final drive gear and a plurality of fixed driven gears. The first, second, and third input shafts are arranged at different levels so that the second input shaft is arranged at the highest level, the first input shaft is arranged at the middle level, and the third input shaft is arranged at the lowest level.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a parallel axes type automatic transmission, and more particularly to a shaft arrangement structure in a parallel axes type automatic transmission. 
     2. Description of the Related Art 
     A parallel axes type automatic transmission is configured so that a plurality of input shafts are arranged in parallel to an output shaft and that shift gears (drive gears) rotatably mounted on the input shafts are selectively coupled by wet multiplate clutches to transmit the rotation of the input shafts to the output shaft. The number of wet multiplate clutches is the same as that of shift gears. For example, a parallel axes type automatic transmission having three input shafts and one output shaft is known. This automatic transmission has such a configuration that two wet multiplate clutches for fourth-speed and fifth-speed gears are provided on the first input shaft, two wet multiplate clutches for first-speed and second-speed gears are provided on the second input shaft, one wet multiplate clutch for a third-speed gear is provided on the third input shaft, and the output shaft has no wet multiplate clutch. In this parallel axes type automatic transmission, the second input shaft is arranged at the highest level, and the third input shaft is arranged at the lowest level. 
     However, the conventional parallel axes type automatic transmission mentioned above has a problem such that the automatic transmission cannot be sufficiently reduced in size because of limiting conditions including the feasibility of mating surfaces of the automatic transmission and an engine and a mounting space for the automatic transmission on a vehicle. Further, splashes of a lubricating oil from the wet multiplate clutches mounted on the input shafts are scattered onto the inner wall of a transmission case, causing the occurrence of aeration and an increase in friction. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a compact parallel axes type automatic transmission which can reduce the amount of oil scattering in a transmission case. 
     In accordance with an aspect of the present invention, there is provided a parallel axes type automatic transmission including a first input shaft having m or more (m is an integer not less than 2) wet multiplate clutches and drive gears rotatably mounted; a second input shaft having n or more (n is an integer greater than m and not less than 3) wet multiplate clutches and drive gears rotatably mounted; a third input shaft having m or less wet multiplate clutches and drive gears rotatably mounted; and an output shaft having a fixed final drive gear and a plurality of fixed driven gears; said first, second, and third input shafts being arranged at different levels so that said second input shaft is arranged at the highest level, said first input shaft is arranged at the middle level, and said third input shaft is arranged at the lowest level. 
     In the parallel axes type automatic transmission of the present invention, said second input shaft having a largest lubrication flow coefficient is arranged at the highest level, said first input shaft having a middle lubrication flow coefficient is arranged at the middle level, and said third input shaft having a smallest lubrication flow coefficient is arranged at the lowest level. 
     The lubrication flow coefficient mentioned above is defined as the product of a speed reducing ratio of a certain shaft with respect to a transmission input shaft and the number of wet multiplate clutches provided on said certain shaft. In the present invention, said first input shaft corresponds to the transmission input shaft. The speed reducing ratio of a certain shaft with respect to a transmission input shaft indicates the magnitude of torque to be transmitted by this certain shaft. Therefore, the lubrication flow coefficient defined above indicates the amount of cooling and lubricating oil required by the wet multiplate clutch or clutches provided on this certain shaft. 
     According to the present invention, the input shaft having a larger torque load and a larger number of wet multiplate clutches is arranged at a higher level. For example, m is 2, n is 3, and one wet multiplate clutch is provided on the third input shaft. 
     According to the present invention, the second input shaft having a largest value for the lubrication flow coefficient is arranged at the highest level, so that the oil discharged from the wet multiplate clutches mounted on the second input shaft can be effectively used as a lubricating oil to be splashed onto the first and third input shafts lower in level than the second input shaft. 
     As a result, the amount of oil to be supplied into the first and third input shafts can be reduced, so that the load on an oil pump can be reduced. Further, the amount of oil scattering in a transmission case can also be reduced, so that the prevention of aeration can be expected. 
     The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description and appended claims with reference to the attached drawings showing some preferred embodiments of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an elevational view of a parallel axes type automatic transmission according to a preferred embodiment of the present invention; 
         FIG. 2  is a side view of the automatic transmission shown in  FIG. 1 ; 
         FIG. 3  is a cross section taken along the line III-III in  FIG. 1 ; 
         FIG. 4  is a cross section taken along the line IV-IV in  FIG. 2 ; 
         FIG. 5A  is a perspective view of a baffle plate as viewed from the bottom side thereof; and 
         FIG. 5B  is a side view of the baffle plate shown in  FIG. 5A . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIG. 1 , there is shown an elevational view of a parallel axes type automatic transmission  2  according to a preferred embodiment of the present invention.  FIG. 2  is a side view of the automatic transmission  2  shown in  FIG. 1 . Reference numeral  4  denotes a transmission case of the automatic transmission  2 . As best shown in  FIG. 2 , the automatic transmission  2  has a first input shaft (main shaft)  6 , a second input shaft  8 , a third input shaft  10 , an output shaft (counter shaft)  12 , and an idle shaft  14 . These shafts  6 ,  8 ,  10 ,  12 , and  14  are arranged in parallel to each other. Reference numeral  16  denotes a final driven gear. 
     As shown in  FIG. 1 , a third-speed drive gear  18  and a top (or highest-speed) drive gear  22  are rotatably mounted on the first input shaft  6 , and a gear  26  is fixedly mounted on the first input shaft  6 . When a wet multiplate clutch  20  is engaged, the third-speed drive gear  18  is fixed to the first input shaft  6 , and when a wet multiplate clutch  24  is engaged, the top drive gear  22  is fixed to the first input shaft  6 . 
     A first-speed drive gear  28 , a second-speed drive gear  32 , and a fifth-speed drive gear  36  are rotatably mounted on the second input shaft  8 , and a gear  39  is fixedly mounted on the second input shaft  8 . When a wet multiplate clutch  30  is engaged, the first-speed drive gear  28  is fixed to the second input shaft  8 . When a wet multiplate clutch  34  is engaged, the second-speed drive gear  32  is fixed to the second input shaft  8 . When a wet multiplate clutch  38  is engaged, the fifth-speed drive gear  36  is fixed to the second input shaft  8 . 
     A fourth-speed drive gear  40  is rotatably mounted on the third input shaft  10 , and a gear  44  is fixedly mounted on the third input shaft  10 . When a wet multiplate clutch  42  is engaged, the fourth-speed drive gear  40  is fixed to the third input shaft  10 . 
     Three driven gears  46 ,  48 , and  50  and a gear  52  are fixedly mounted on the output shaft  12 . The driven gear  46  is in mesh with the second-speed drive gear  32  and the third-speed drive gear  18 . The driven gear  48  is in mesh with the fifth-speed drive gear  36  and the top drive gear  22 . The driven gear  50  is in mesh with the first-speed drive gear  28 . The gear  52  is a final drive gear, which is in mesh with the final driven gear  16 . The idle shaft  14  shown in  FIG. 2  is not shown in  FIG. 1  for the purpose of clarification. 
     Referring to  FIG. 2 , an integral baffle plate  54  is provided so as to cover the lower side of the first, second, and third input shafts  6 ,  8 , and  10 , the output shaft  12 , and the idle shaft  14 . The baffle plate  54  has such a shape as shown in  FIGS. 5A and 5B , and it is integrally molded of resin.  FIG. 5A  is a perspective view of the baffle plate  54  as viewed from the bottom side thereof, and  FIG. 5B  is a side view of the baffle plate  54 . As shown in  FIG. 5A , the baffle plate  54  has a cutout  55  for insertion of a shift fork  68 . 
     As shown in  FIG. 2 , an oil strainer  56  is provided at a bottom portion of the transmission case  4 . As shown in  FIG. 4 , the oil strainer  56  has a communication hole  58  connected to an oil pump  66 . The oil pump  66  is connected through a case  64  of a torque converter  62  to a crankshaft  60  of an engine (not shown), so that the oil pump  66  is always driven by the engine. 
     As mentioned above, the gear  26  is nonrotatably fixed to the first input shaft  6 , and the third-speed drive gear  18  and the top drive gear  22  are rotatably mounted on the first input shaft  6 . When the wet multiplate clutch  20  is engaged, the third-speed drive gear  18  is fixed to the first input shaft  6 , and when the wet multiplate clutch  24  is engaged, the top drive gear  22  is fixed to the first input shaft  6 . 
     As apparent from  FIG. 2 , the relation in level among the first, second, and third input shafts  6 ,  8 , and  10  is such that the second input shaft  8  is arranged at the highest level, the first input shaft  6  is arranged at the middle level, and the third input shaft  10  is arranged at the lowest level. Further, the second input shaft  8  has a speed reducing ratio of 1.2 to 1.3 with respect to the first input shaft  6  as a transmission input shaft, and the third input shaft  10  has a speed reducing ratio of 1.1 to 1.2 with respect to the first input shaft  6 . 
     In the case that a lubrication flow coefficient is defined as the product of the speed reducing ratio of a certain shaft with respect to a transmission input shaft and the number of wet multiplate clutches provided on this certain shaft, the second input shaft  8  having a largest value for the lubrication flow coefficient is arranged at the highest level, the first input shaft  6  having a middle value for the lubrication flow coefficient is arranged at the middle level, and the third input shaft  10  having a smallest value for the lubrication flow coefficient is arranged at the lowest level. The speed reducing ratio of a certain shaft with respect to a transmission input shaft indicates the magnitude of torque to be transmitted by this certain shaft. Therefore, the lubrication flow coefficient defined above indicates the amount of cooling and lubricating oil required by the wet multiplate clutch or clutches provided on this certain shaft. 
     According to this preferred embodiment, the oil stored at the bottom portion of the transmission case  4  is raised through the oil strainer  56  by the oil pump  66 , and is supplied to a hydraulic control valve and various portions to be lubricated. Further, the oil stored at the bottom portion of the transmission case  4  is also taken up by the rotation of the final driven gear  16 . The oil scattered by the rotation of each shaft is guided by the inner wall of the transmission case  4  as shown by arrows  70 . Further, an oil passage as shown by arrows  72  is also formed by the baffle plate  54  integrally molded. 
     Accordingly, the oil discharged from the wet multiplate clutch or clutches mounted on each shaft and the oil scattered from a mesh point between the shift gears can be gathered through these two oil passages  70  and  72  and returned to a position near an oil level at the bottom portion of the transmission case  4 . As a result, the scattering of oil in the transmission case  4  and the agitation resistance to the final driven gear  16  can be reduced, so that the occurrence of aeration can be suppressed. 
     Since the second input shaft  8  having a largest value for the lubrication flow coefficient is arranged at the highest level, the oil discharged from the wet multiplate clutches mounted on the second input shaft  8  can be effectively used as a lubricating oil to be splashed onto the first and third input shafts  6  and  10  lower in level than the first input shaft  8 . Accordingly, the amount of oil to be supplied into the first and third input shafts  6  and  10  can be reduced, so that the load on the oil pump  66  can be reduced. Further, the oil can be splashed through the cutout  55  of the baffle plate  54  to any machine elements including the shift fork  68  difficult in oil supplying into the relevant shaft, so that the wear, seizure, etc. of these machine elements can be prevented.