Abstract:
A parallel axes type transmission including a first idle drive route and a second idle drive route for transmitting the relation of an input shaft to an intermediate shaft. The first idle drive route includes a one-way clutch capable of transmitting the rotation of the input shaft to the intermediate shaft only. The second idle drive route includes wet multiplate clutches for connecting gears rotatably mounted on the intermediate shaft to the intermediate shaft when engaged. Thus, the intermediate shaft is rotated at a first rotational speed through the first idle drive route and at a second rotational speed faster than the first rotational speed through the second idle drive route when the clutch is engaged.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a parallel axes type automatic transmission having a plurality of shafts extending in parallel to each other and a plurality of gears provided on the shafts and meshing with each other, wherein the connection and disconnection between each shaft and the gears provided thereon are made to thereby switch between power transmitting routes formed between the shafts, thereby obtaining a desired gear ratio. 
         [0003]    2. Description of the Related Art 
         [0004]    Such a parallel axes type transmission is used not only in a vehicle, but also in various power machines. In such a transmission for a vehicle, the number of shift steps tends to be increased to meet the requirements for a vehicle driving performance and effects on the environment, and a transmission having five or more forward speeds has already been put into practical use. Generally in a transmission not limited to a transmission for a vehicle, the number of gears provided on each shaft increases with an increase in number of shift steps, so that the overall size of the transmission, particularly the axial size thereof tends to increase. A transmission is required to be installed in a certain space defined in a machine using this transmission. Accordingly, in the case that the number of shift steps increases to cause an increase in axial size of the transmission, it is necessary to make the transmission compact by adopting any means. Particularly in a vehicle transmission limited in various sizes from the viewpoint of the size of a vehicle body, making the transmission compact is a very important issue. 
         [0005]    Various inventions have conventionally made to reduce the axial size of a parallel axes type transmission. For example, an intermediate shaft is interposed between an input shaft and an output shaft, and the intermediate shaft is driven through gears by the input shaft, whereby the number of gears provided on each shaft is reduced to thereby reduce the axial size of the transmission (see Japanese Patent Laid-open No. 2000-220700, for example). Further, in addition to the above configuration, it is known that the gear provided on the output shaft and meshing with the gear provided on the input shaft is the same as the gear provided on the output shaft and meshing with the gear provided on the intermediate shaft (see Japanese Patent Publication No. Hei 7-94854, for example). 
         [0006]    In this configuration, the gears provided on the output shaft for providing two different gear ratios are provided by a common gear. As a result, the number of gears provided on the output shaft can be reduced, and the gears provided on the input shaft and the intermediate shaft and meshing with the common gear provided on the output shaft can be arranged in substantially the same plane. As a result, the axial size of the transmission can be greatly reduced. Further, as disclosed in Japanese Patent Laid-open No. 2005-54958, it is known in the art that an idle gear train is used to drive the intermediate shaft and that the number of shift steps can be increased and the axial size can be reduced by increasing the number of intermediate shafts with the use of idle gear trains. 
         [0007]    However, in the configuration described in Japanese Patent Publication No. Hei 7-94854 wherein the common gear for two different gear ratios is provided on the output shaft, there is a case that the effect of reducing the axial size is insufficient in a recent transmission having a tendency to increase the number of shift steps, and it is therefore desired to provide a configuration which can reduce the axial size more greatly. Further, the parallel axes type transmission described in Japanese Patent Laid-open No. 2005-54958 has a compact structure with a reduced axial size for the number of shift steps. However, it is necessary to provide a plurality of wet multiplate clutches whose number is equal to the number of shift steps, causing a somewhat complicated configuration. 
       SUMMARY OF THE INVENTION 
       [0008]    It is therefore an object of the present invention to provide a parallel axes type transmission which can be reduced in axial size for the number of shift steps and can provide an increased number of shift, steps greater than the number of clutches. 
         [0009]    In accordance with an aspect of the present invention, there is provided a parallel axes type transmission including an input shaft, an intermediate shaft, an idle shaft, and an output shaft extending in parallel to each other; a common gear fixed to the input shaft; a first intermediate gear idly rotatably provided on the intermediate shaft; a second intermediate gear fixed through a one-way clutch to the intermediate shaft; a third intermediate gear idly rotatably provided on the intermediate shaft; a fourth intermediate gear idly rotatably provided on the intermediate shaft; a first idle gear provided on the idle shaft and meshing with the common gear and the second intermediate gear; a second idle gear idly rotatably provided on the output shaft and meshing with the common gear and the first intermediate gear; a first output gear fixed to the output shaft and meshing with the third intermediate gear; a second output gear fixed to the output shaft and meshing with the fourth intermediate gear; a first clutch for making the connection and disconnection between the first intermediate gear and the intermediate shaft; a second clutch for making the connection and disconnection between the third intermediate gear and the intermediate shaft; and a third clutch for making the connection and disconnection between the fourth intermediate gear and the intermediate shaft, wherein a first idle drive route is formed by the common gear, the first idle gear, the second intermediate gear, and the one-way clutch, a second idle drive route is formed by the common gear, the second idle gear, the first intermediate gear, and the first clutch, and when the first clutch is engaged to connect the first intermediate gear to the intermediate shaft, slippage occurs in the one-way clutch to cut off the drive through the first idle drive route. 
         [0010]    With this arrangement, the output through the intermediate shaft can be made double or more, so that an increase in axial size of the transmission can be suppressed in spite of an increase in number of shift steps. Further, the number of shift steps can be increased without increasing the number of intermediate shafts and/or clutches, so that the complication in structure of the transmission can be prevented. Further, in the case that the number of shift steps is fixed, the number of clutches and gears can be reduced and the axial size of the transmission can accordingly be reduced. Accordingly, the transmission of the present invention is effective particularly when applied to a front-drive vehicle having a transversely mounted transmission. 
         [0011]    Preferably, the parallel axes type transmission further includes a first input gear rotatably provided on the input shaft and meshing with the first output gear; a second input gear rotatably provided on the input shaft and meshing with the second output gear; a fourth clutch for making the connection and disconnection between the first input gear and the input shaft; and a fifth clutch for making the connection and disconnection between the second input gear and the input shaft. 
         [0012]    More preferably, the parallel axes type transmission further includes a second intermediate shaft extending in parallel to the input shaft; a fifth intermediate gear idly rotatably provided on the second intermediate shaft and meshing with the common gear; a sixth intermediate gear idly rotatably provided on the second intermediate shaft and meshing with the first input shaft; a reverse drive gear idly rotatably provided on the second intermediate shaft; and a selective clutch fixed in the rotational direction of the second intermediate shaft and axially slidably provided on the second intermediate shaft for selectively connecting any one of the sixth intermediate gear and the reverse drive gear to the second intermediate shaft. 
         [0013]    More preferably, the parallel axes type transmission further includes a second idle shaft extending in parallel to the input shaft; and an idle driven gear fixed to the second idle shaft and meshing with the reverse drive gear and the second input gear. 
         [0014]    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 
         [0015]      FIG. 1  is a skeleton diagram showing the configuration of a parallel axes type automatic transmission according to a first preferred embodiment of the present invention; and 
           [0016]      FIG. 2  is a skeleton diagram showing the configuration of a parallel axes type automatic transmission according to a second preferred embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0017]    Some preferred embodiments of the present invention will now be described with reference to the drawings.  FIG. 1  shows a first preferred embodiment of the parallel axes type automatic transmission (which will be hereinafter referred to simply as transmission) according to the present invention. The transmission according to the first preferred embodiment has an input shaft  2 , an intermediate shaft  4 , and an output shaft  6  extending in parallel to each other. The input shaft  2  is connected to the crankshaft of an engine (not shown), so that the input shaft  2  is rotationally driven by the engine. A common gear  8  is fixed to the input shaft  2 . There are provided on the intermediate shaft  4  a first clutch  10 , a first intermediate gear  12 , a second intermediate gear  14 , a third intermediate gear  18 , a second clutch  20 , a third clutch  22 , and a fourth intermediate gear  24 . These elements  10 ,  12 ,  14 ,  18 ,  20 ,  22 , and  24  are arranged in this order in the axial direction of the intermediate shaft  4  from the right end thereof as viewed in  FIG. 1 . 
         [0018]    The first intermediate gear  12 , the third intermediate gear  18 , and the fourth intermediate gear  24  are idly rotatable relative to the intermediate shaft  4 , and the second intermediate gear  14  is mounted through a one-way clutch  16  to the intermediate shaft  4 . More specifically, the second intermediate gear  14  is mounted on the outer race of the one-way clutch  16 , and the inner race of the one-way clutch  16  is fixed to the intermediate shaft  4 . Accordingly, torque is allowed to be transmitted from the second intermediate gear  14  through the one-way clutch  16  to the intermediate shaft  4 , but disallowed to be transmitted from the intermediate shaft  4  to the second intermediate gear  14  because of the slippage in the one-way clutch  16 . Each of the first, second, and third clutches  10 ,  20 , and  22  is a hydraulic piston type wet multiplate clutch generally known in the art, and the description thereof will therefore be omitted herein. 
         [0019]    There are provided on the output shaft  6  a final drive gear  34 , a second idle gear  30 , a first output gear  36 , and a second output gear  38 . These elements  34 ,  30 ,  36 , and  38  are arranged in this order in the axial direction of the output shaft  6  from the right end thereof as viewed in  FIG. 1 . The final drive gear  34 , the first output gear  36 , and the second output gear  38  are fixed to the output shaft  6 , and the second idle gear  30  is idly rotatable relative to the output shaft  6 . The second idle gear  30  is in mesh with the common gear  8  and the first intermediate gear  12 . The first output gear  36  is in mesh with the third intermediate gear  18 , and the second output gear  38  is in mesh with the fourth intermediate gear  24 . Further, the final drive gear  34  is in mesh with a final driven gear (not shown). 
         [0020]    Reference numeral  26  denotes a first idle gear, which is fixed to an idle shaft  27  rotatably provided. Alternatively, the idle shaft  27  may be fixed and the first idle gear  26  may be idly rotatable relative to the idle shaft  27 . The first idle gear  26  is in mesh with the common gear  8  and the second intermediate gear  14 . A first idle drive route  28  for providing lower gear ratios is formed by the common gear  8 , the first idle gear  26 , the second intermediate gear  14 , and the one-way clutch  16 , and a second idle drive route  32  for providing higher gear ratios is formed by the common gear  8 , the second idle gear  30 , the first intermediate gear  12 , and the first clutch  10 . 
         [0021]    The operation of the first preferred embodiment will now be described. When the first clutch  10  is in a disengaged condition, the first intermediate gear  12  idly rotates relative to the intermediate shaft  4 , so that the rotation of the input shaft  2  is not transmitted through the second idle drive route  32  to the intermediate shaft  4 . In this case, the rotation of the input shaft  2  is transmitted through the first idle drive route  28  composed of the common gear  8 , the first idle gear  26 , the second intermediate gear  14 , and the one-way clutch  16  to the intermediate shaft  4 , and the intermediate shaft  4  is rotated at a first rotational speed. 
         [0022]    Accordingly, when the third clutch  22  is engaged, the fourth intermediate gear  24  is fixed to the intermediate shaft  4 , and the output shaft  6  is rotated at a rotational speed corresponding to a first forward speed through the second output gear  38 . On the other hand, when the third clutch  22  is disengaged and the second clutch  20  is engaged, the third intermediate gear  18  is fixed to the intermediate shaft  4 . As a result, the output shaft  6  is rotated at a rotational speed corresponding to a second forward speed through the first output gear  36 . 
         [0023]    On the other hand, when the first clutch  10  is engaged, the first intermediate gear  12  is fixed to the intermediate shaft  4 . Accordingly, the rotation of the input shaft  2  is transmitted not only through the first idle drive route  28 , but also through the second idle drive route  32  composed of the common gear  8 , the second idle gear  30 , the first intermediate gear  12 , and the first clutch  10  to the intermediate shaft  4 , so that the intermediate shaft  4  is rotated at a second rotational speed higher than the first rotational speed. At this time, the rotation of the intermediate shaft  4  at the second rotational speed is not transmitted to the first idle gear  26  because of the slippage in the one-way clutch  16  interposed between the second intermediate gear  14  and the intermediate shaft  4 . 
         [0024]    Accordingly, when the third clutch  22  is engaged, the fourth intermediate gear  24  is fixed to the intermediate shaft  4 , and the output shaft  6  is rotated at a rotational speed corresponding to a third forward speed. Further, when the third clutch  22  is disengaged and the second clutch  20  is engaged, the third intermediate gear  18  is fixed to the intermediate shaft  4 , and the output shaft  6  is rotated at a rotational speed corresponding to a fourth forward speed. In this preferred embodiment, the first forward speed and the second forward speed are provided through the first idle drive route  28 , and the third forward speed and the fourth forward speed are provided through the second idle drive route  32 . However, depending upon the gear ratios of the first and second idle drive routes  28  and  32 , there is a case that the second forward speed may be provided through the second idle drive route  32  and the third forward speed may be provided through the first idle drive route  28 . 
         [0025]    There will now be described a second preferred embodiment of the parallel axes type automatic transmission according to the present invention with reference to  FIG. 2 . The transmission according to the second preferred embodiment is an automatic transmission having seven forward speeds and one reverse speed as constructed by applying the principle of the present invention. The transmission according to the second preferred embodiment has an input shaft  42 , a first intermediate shaft  44 , a second intermediate shaft  46 , and an output shaft  48  extending in parallel to each other. These elements  42 ,  44 ,  46 , and  48  are rotatably supported by bearings. 
         [0026]    The input shaft  42  is connected to the crankshaft of an engine (not shown), so that the input shaft  42  is rotationally driven by the engine. There are provided on the input shaft  42  a common gear  50 , a first input gear  52 , a first clutch  54 , a second clutch  56 , and a second input gear  58 . These elements  50 ,  52 ,  54 ,  56 , and  58  are arranged in this order in the axial direction of the input shaft  42  from the right end thereof as viewed in  FIG. 2 . The common gear  50  is fixed to the input shaft  42 . The first input gear  52  and the second input gear  58  are idly rotatable relative to the input shaft  42 . Each of the first and second clutches  54  and  56  is a hydraulic piston type wet multiplate clutch generally known in the art, and the description thereof will therefore be omitted herein. 
         [0027]    There are provided on the first intermediate shaft  44  a third clutch  60 , a first intermediate gear  62 , a second intermediate gear  64 , a third intermediate gear  68 , a fourth clutch  70 , a fifth clutch  72 , and a fourth intermediate gear  74 . These elements  60 ,  62 ,  64 ,  68 ,  70 ,  72 , and  74  are arranged in this order in the axial direction of the first intermediate shaft  44  from the right end thereof as viewed in  FIG. 2 . The second intermediate gear  64  is mounted through a one-way clutch  66  to the first intermediate shaft  44 . More specifically, the second intermediate gear  64  is fixed to the outer race of the one-way clutch  66 , and the inner race of the one-way clutch  66  is fixed to the first intermediate shaft  44 . Accordingly, torque is allowed to be transmitted from the second intermediate gear  64  through the one-way clutch  66  to the first intermediate shaft  44 , but disallowed to be transmitted from the first intermediate shaft  44  to the second intermediate gear  64  because of the slippage in the one-way clutch  66 . 
         [0028]    The first intermediate gear  62 , the third intermediate gear  68 , and the fourth intermediate gear  74  are idly rotatable relative to the first intermediate shaft  44 . Each of the third, fourth, and fifth clutches  60 ,  70 , and  72  is a hydraulic piston type wet multiplate clutch generally known in the art, and the description thereof will therefore be omitted herein. 
         [0029]    There are provided on the second intermediate shaft  46  a sixth clutch  84 , a fifth intermediate gear  86 , a sixth intermediate gear  88 , a selective clutch  90 , and a reverse drive gear  92 . These elements  84 ,  86 ,  88 ,  90 , and  92  are arranged in this order in the axial direction of the second intermediate shaft  46  from the right end thereof as viewed in  FIG. 2 . The fifth intermediate gear  86  and the sixth intermediate gear  88  are idly rotatable relative to the second intermediate shaft  46 . The fifth intermediate gear  86  is in mesh with the common gear  50 , and the sixth intermediate gear  88  is in mesh with the first input gear  52 . The reverse drive gear  92  is in mesh with an idle driven gear  102  fixed to an idle shaft  100  rotatably provided. The idle driven gear  102  is in mesh with the second input gear  58 . 
         [0030]    The selective clutch  90  is axially slidably provided on the second intermediate shaft  46 . When the selective clutch  90  is moved rightward as viewed in  FIG. 2 , the second intermediate gear  88  is connected through the selective clutch  90  to the second intermediate shaft  46 , whereas when the selective clutch  90  is moved leftward as viewed in  FIG. 2 , the reverse drive gear  92  is connected through the selective clutch  90  to the second intermediate shaft  46 . The sixth clutch  84  is a hydraulic piston type wet multiplate clutch generally known in the art, and the description thereof will therefore be omitted herein. 
         [0031]    There are provided on the output shaft  48  a final drive gear  94 , a second idle gear  80 , a first output gear  96 , and a second output gear  98 . These elements  94 ,  80 ,  96 , and  98  are arranged in this order in the axial direction of the output shaft  48  from the right end thereof as viewed in  FIG. 2 . The final drive gear  94 , the first output gear  96 , and the second output gear  98  are fixed to the output shaft  48 , and the second idle gear  80  is idly rotatable relative to the output shaft  48 . The second idle gear  80  is in mesh with the common gear  50  and the first intermediate gear  62 . The first output gear  96  is in mesh with the first input gear  52  and the third intermediate gear  68 . The second output gear  98  is in mesh with the second input gear  58  and the fourth intermediate gear  74 . The final drive gear  94  is in mesh with a final driven gear (not shown). 
         [0032]    Reference numeral  76  denotes a first idle gear, which is fixed to an idle shaft  77  rotatably provided. Alternatively, the idle shaft  77  may be fixed and the first idle gear  76  may be idly rotatable relative to the idle shaft  77 . The first idle gear  76  is in mesh with the common gear  50  and the second intermediate gear  64 . A first idle drive route  78  for providing lower gear ratios is formed by the common gear  50 , the first idle gear  76 , the second intermediate gear  64 , and the one-way clutch  66 , and a second idle drive route  82  for providing higher gear ratios is formed by the common gear  50 , the second idle gear  80 , the first intermediate gear  62 , and the first clutch  60 . 
         [0033]    The operation of the second preferred embodiment will now be described. When the third clutch  60  is in a disengaged condition, the rotation of the input shaft  42  is transmitted through the first idle drive route  78  composed of the common gear  50 , the first idle gear  76 , the second intermediate gear  64 , and the one-way clutch  66  to the first intermediate shaft  44 . Accordingly, when the fifth clutch  72  is engaged, the rotation of the first intermediate shaft  44  is transmitted through the fourth intermediate gear  74  and the second output gear  98  to the output shaft  48 , and the output shaft  48  is rotated at a rotational speed corresponding to a first forward speed. 
         [0034]    When the fifth clutch  72  is disengaged and the fourth clutch  70  is engaged, the rotation of the first intermediate shaft  44  is transmitted through the third intermediate gear  68  and the first output gear  96  to the output shaft  48 , and the output shaft  48  is rotated at a rotational speed corresponding to a second forward speed. When the third clutch  60  is engaged, the rotation of the input shaft  42  is transmitted through the second idle drive route  82  composed of the common gear  50 , the second idle gear  80 , the first intermediate gear  62 , and the third clutch  60  to the first intermediate shaft  44 . 
         [0035]    In this case, the first intermediate shaft  44  is rotated at a speed higher than that of rotation through the first idle drive route  78 . Accordingly, the slippage in the one-way clutch  66  occurs and the high-speed rotation of the first intermediate shaft  44  through the second idle drive route  82  does not have an effect on the first idle drive route  78 . Accordingly, when the fifth clutch  72  is engaged simultaneously with engagement of the third clutch  60 , the rotation of the first intermediate shaft  44  is transmitted through the fourth intermediate gear  74  and the second output gear  98  to the output shaft  48 , and the output shaft  48  is rotated at a rotational speed corresponding to a third forward speed. 
         [0036]    On the other hand, when the fourth clutch  70  is engaged simultaneously with engagement of the third clutch  60 , the rotation of the first intermediate shaft  44  is transmitted through the third intermediate gear  68  and the first output gear  96  to the output shaft  48 , and the output shaft  48  is rotated at a rotational speed corresponding to a fourth forward speed. When the sixth clutch  84  is engaged and the selective clutch  90  is moved rightward as viewed in  FIG. 2  to connect the sixth intermediate gear  88  to the second intermediate shaft  46 , the rotation of the input shaft  42  is transmitted through the common gear  50  and the fifth intermediate gear  86  to the second intermediate shaft  46 , and the rotation of the second intermediate shaft  46  is transmitted through the selective clutch  90 , the sixth intermediate gear  88 , the first input gear  52 , and the first output gear  96  to the output shaft  48 . Thus, the output shaft  48  is rotated at a rotational speed corresponding to a fifth forward speed. 
         [0037]    When the second clutch  56  is engaged, the rotation of the input shaft  42  is transmitted through the second input gear  58  and the second output gear  98  to the output shaft  48 , and the output shaft  48  is rotated at a rotational speed corresponding to a sixth forward speed. Finally, when the first clutch  54  is engaged, the rotation of the input shaft  42  is transmitted through the first input gear  52  and the first output gear  96  to the output shaft  48 , and the output shaft  48  is rotated at a rotational speed corresponding to a seventh forward speed. 
         [0038]    In the case of reverse running, the sixth clutch  84  is engaged and the selective clutch  90  is moved leftward as viewed in  FIG. 2 . As a result, the rotation of the input shaft  42  is transmitted through the common gear  50  and the fifth intermediate gear  86  to the second intermediate shaft  46 , and the rotation of the second intermediate shaft  46  is transmitted through the selective clutch  90 , the reverse drive gear  92 , the reverse driven gear  102 , the second input gear  58 , and the second output gear  98  to the output shaft  48 , and the output shaft  48  is rotated in a reverse direction. 
         [0039]    According to the second preferred embodiment, it is possible to provide a parallel axes type automatic transmission having seven forward speeds by using six wet multiplate clutches. Thus, the number of wet multiplate clutches can be reduced to thereby achieve the simplification of a transmission structure and the reduction in axial size of the transmission. Further, since the one-way clutch  66  is less expensive than a wet multiplate clutch, the transmission according to this preferred embodiment can be reduced in cost as compared with a transmission using a plurality of wet multiplate clutches whose number corresponds to the number of shift steps (forward speeds). 
         [0040]    It should be noted that the description on the first to seventh forward speeds mentioned above in the second preferred embodiment is merely illustrative and the first to seventh forward speeds may be provided through any other transmission routes depending upon the gear ratios of the first idle drive route  78  and the second idle drive route  82 . 
         [0041]    The present invention is not limited to the details of the above described preferred embodiments. The scope of the invention is defined by the appended claims and all changes and modifications as fall within the equivalence of the scope of the claims are therefore to be embraced by the invention.