Abstract:
A power takeoff unit is comprised of: a casing dividable into a first part and a second part; an inner shaft receiving torque from an engine; an outer shaft independently rotatable and coaxial with the inner shaft; a clutch for connecting the inner shaft with the outer shaft; an actuator configured to connect the clutch; an output shaft for outputting torque; and a gear set drivingly coupling the outer shaft with the output shaft, wherein the outer shaft and the output shaft are rotatably supported by the first part, the clutch is rotatably supported by the second part, and the actuator is fixed to the second part, whereby the clutch and the actuator along with the second part are separable from the first part.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation Application of PCT International Application No. PCT/JP2013/006734 (filed Nov. 15, 2013), the entire contents of which are incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    In an automobile of front-wheel drive for example, an engine set at the front of the vehicle&#39;s body generates torque, and a differential receives and distributes this torque to right and left front wheels. In a case of a four-wheel drive vehicle, a power takeoff unit (PTU) is, in general, in combination with a transmission with a differential, used to take off torque in part and transmit it to rear wheels. 
         [0003]    A construction that time-limitedly switches its drive mode into a two-wheel drive mode is often applied even to a four-wheel drive vehicle loaded with a PTU. In this case, one or more clutches for temporarily cutting off power transmission are inserted into any part of a powertrain system from the PTU through the rear-differential. When one of the clutches gets disengaged, the engine does not bear rotation of part of the transmission downstream relative to the concerned clutch and therefore this construction is advantageous in improvement of energy consumption. 
         [0004]    Japanese Patent Unexamined Application Laid-open No. 2012-193779 discloses a related art. To maximize energy consumption improvement, it is advantageous to provide at least one of the clutches to an upstream section in the transmission path of the torque, and therefore, in the example of Japanese Patent Unexamined Application Laid-open No. 2012-193779, a clutch is incorporated in a PTU. The PTU is inevitably designed to have a complex structure, which causes some problems. For example, its assembly inherently becomes troublesome and accordingly its disassembly also becomes troublesome, thereby causing problems in maintenance. Further, modification of the construction of the PTU is difficult to realize by partially changing the construction and instead it is necessary to replace the PTU as a whole with a PTU structured in a desired construction. The device described below has been devised in light of these problems. 
       SUMMARY 
       [0005]    The disclosure herein includes a power transmission device of an automobile and in particular relates to a power takeoff unit for an automobile for distributing torque from axles to the other axles of a four-wheel drive vehicle. 
         [0006]    According to an aspect, a power takeoff unit for taking off torque from a transmission of an automobile is comprised of: a casing dividable into a first part and a second part combined together; an inner shaft formed to be hollow to allow insertion of a shaft of the transmission and coupled with the transmission to rotate about an axis; an outer shaft independently rotatable and coaxial with the inner shaft; a clutch interposed between the inner shaft and the outer shaft and configured to drivingly connect the inner shaft with the outer shaft when the clutch is connected; an actuator configured to connect the clutch; an output shaft being so disposed as to be rotatable and intersect with, or be not parallel and not intersect with, the outer shaft; and a gear set drivingly coupling the outer shaft with the output shaft, wherein the outer shaft and the output shaft are rotatably supported by the first part, the clutch is rotatably supported by the second part, and the actuator is fixed to the second part, whereby the clutch and the actuator along with the second part are separable from the first part. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a drawing schematically showing a powertrain system of an automobile. 
           [0008]      FIG. 2  is a cross sectional view of an example power takeoff unit, which shows planes passing through both central axes of an input shaft and an output shaft. 
           [0009]      FIG. 3  is a partial sectional view magnifying a clutch and an actuator for driving the clutch in the example power takeoff unit. 
           [0010]      FIG. 4  is a plan view schematically showing peripheries of clutch members in a state before connecting the clutch. 
           [0011]      FIG. 5  is a plan view schematically showing the peripheries of the clutch members in a state of connecting the clutch. 
       
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0012]    Exemplary embodiments will be described hereinafter with reference to the appended drawings. 
         [0013]    Throughout the following description and appended claims, the term “axial direction” means a direction of axes of an inner shaft  5  and an outer shaft  7  unless otherwise stated. 
         [0014]    Referring to  FIG. 1 , a powertrain system of an automobile  100  is for example comprised of an engine and/or electric motor  201  and a transmission  203  at the front of the vehicle&#39;s body. The transmission  203  is comprised of a front differential  205 , a casing  207  that receives torque from the engine and/or electric motor  201  to rotate. 
         [0015]    The front differential  205  is equipped with a differential gear set to transmit torque, which is input into the casing  207 , to right and left axles  213 ,  215  via each of its side gears  209 ,  211 , allowing differential motion therebetween. A bevel gear type is an example of the differential gear but any other type may be applied thereto. 
         [0016]    In the example four-wheel drive vehicle shown in the drawings, its rear part is further comprised of a rear differential  219  coupled with rear axles  221 ,  223 , thereby allowing differential motion between rear wheels. Further, to cut off torque transmission to the left rear axle  223  a clutch  225  is provided, for example. The clutch  225  is, along with the rear differential  219 , housed in a carrier casing. The clutch  225  may be provided on, instead of the left rear axle  223 , a right rear axle  221  or a propeller shaft  217 . 
         [0017]    For the purpose of transmitting torque in part from the transmission  203  via the propeller shaft  217  to the rear differential  219 , a power takeoff unit (PTU)  1  is used. 
         [0018]    The PTU  1  takes off part of the torque transmitted to the differential casing  207  and transmits it to the output shaft  15 . The output shaft  15  is coupled with the rear differential  219  via a constant-velocity joint and the propeller shaft  217 . To cut off the torque transmission, the PTU  1  is comprised of a clutch  9 . When the clutch  9  gets disconnected in concert with the clutch  225 , the propeller shaft  217  is separated from the system. 
         [0019]    Referring to  FIG. 2 , the PTU  1  is comprised of an inner shaft  5 , an outer shaft  7  independently rotatable and coaxial therewith, a clutch  9  for, when connected, drivingly connecting the inner shaft  5  with the outer shaft  7 , an actuator  11  for operating the clutch  9 , and an output shaft  15  drivingly coupled with the outer shaft  7  by a gear set  13 , all of which is housed in a casing  3 . Although further descriptions will be given below, the inner shaft  5  is coupled with the differential casing  207  to receive its torque, and thus the torque is, when the clutch  9  is connected, transmitted to the outer shaft  7  and output via the gear set  13  to the output shaft  15 . 
         [0020]    The casing  3  is separable into a first part  31  and a second part  33 . The casing  3  is structured so as to seal its interior when the second part  33  is combined with the first part  31  with its internal members housed therein. 
         [0021]    The casing  3  coaxially supports the inner shaft  5 , the outer shaft  7 , the clutch  9 , and the actuator  11 . The first part  31  of the casing  3  is comprised of a portion  37  directed in a direction distinct from the direction of this common axis, and this portion  37  supports the output shaft  15  directed to intersect with, or be not parallel and not intersect with, (namely, be in a skew relation with) the outer shaft  7 . 
         [0022]    The first part  31  is, at its end  31   c,  combinable with the transmission  203 . The first part  31  houses and rotatably supports the outer shaft  7 , the gear set  13  and the output shaft  15 . The second part  33  houses the clutch  9  and the actuator  11 , rotatably supports the clutch  9  and anti-rotatably supports the actuator  11 . Although further descriptions will be given below, when the second part  33  is separated from the first part  31 , the clutch  9  and the actuator  11  are in association therewith separated from the other elements. 
         [0023]    The first part  31  may further include a third part  35  separable therefrom. The outer shaft  7  is, in a state where the third part  35  is separated, housed into the first part  31  and, by combining the third part  35  with the first part  31 , supported by them. To allow rotation thereof, bearings  61 ,  63  such as ball bearings are interposed between the outer shaft  7  and the casing  3 . One bearing  61  may be supported by the first part  31  and another bearing  63  may be supported by the third part  35 . 
         [0024]    To precisely hold the third part  35  in place relative to the first part  31 , the third part  35  may be comprised of a structure  35   c  fitting in the internal surface of the first part  31 . Alternatively, in reverse, the first part  31  may fit in the internal surface of the third part  35 . To prevent leakage of internal oil, an O-ring or a gasket may be interposed therebetween. 
         [0025]    Likewise, to precisely hold the second part  33  in place relative to the first part  31 , the third part  35  may be comprised of a structure  35   e  fitting in the internal surface of the second part  33 . Alternatively, in reverse, the second part  33  may fit in the internal surface of the third part  35 . To likewise prevent leakage of internal oil, an O-ring or a gasket may be interposed therebetween. 
         [0026]    The second part  33  is fixed to the first part  31  by means of fastener elements such as bolts inserted therein in the axial direction from its end  33   c.  The fastener elements may penetrate the third part  35  and may be tightened to the first part  31 , thereby fixing these three parts together. Alternatively, individual fastener elements may be used for fixation between the first part  31  and the third part  35  and for fixation between the second part  33  and the third part  35 . 
         [0027]    The outer shaft  7  is hollow and the inner shaft  5  coaxially extends to penetrate it. Around an end  71  close to the front differential  205 , e.g., overlapping with the bearing  61 , a plain bearing member  67  is interposed between the outer shaft  5  and the inner shaft  7 , thereby rotatably supporting the inner shaft  5 . 
         [0028]    The inner shaft  5  is also hollow and the axle  213  extends rightward through its internal cavity  51 . On an end portion of the inner shaft  5  closer to the front differential  205 , splines  53  are cut in the axial direction, thereby being drivingly coupled with the differential casing  207 . The end portion may be made slightly smaller in diameter than a portion in contact with the plain bearing member  67  so as not to impede press-fitting the plain bearing member  67 . 
         [0029]    Around an end portion at its opposite side of the inner shaft  5 , splines  55  are cut in the axial direction and are used to drivingly couple the inner shaft  5  with a first clutch member  91  described later. The inner shaft  5  is, around the splines  55 , and along with the first clutch member  91 , rotatably supported by a bearing  65  such as a ball bearing. 
         [0030]    An end  73  of the outer shaft  7  opposed to the end  71  toward the front differential  205  is exposed through an opening of the third part  35  toward the second part  33  and thus approaches the clutch  9 . Although further descriptions will be given below, the end  73  of the outer shaft  7  and a second clutch member  93  of the clutch  9 , as shown in  FIGS. 4 and 5 , engage with each other by means of first teeth  101 , thereby transmitting the torque. 
         [0031]    Referring back to  FIG. 2 , the outer shaft  7  can, at the midway part between both the ends  71 , 73 , be made greater in diameter, and a bevel gear  77  fixed here. For the purpose of fixation and to receive thrust force, a flange portion  75  may integrally project out therefrom. The fixation of the bevel gear  77  may be made by press-fitting, bolt fixation using the flange portion  75 , or welding. 
         [0032]    In the example shown in  FIG. 2 , teeth of the bevel gear  77  are directed toward the front differential  205  and the flange portion  75  abuts on the back of the bevel gear  77 . This arrangement is advantageous in bringing the output shaft  15  that engages with the bevel gear  77  closer to the front differential  205  and accordingly embodying an arrangement in which the propeller shaft  217  is brought closer to the center of the automobile  100 . Of course, this arrangement can be arbitrarily modified. 
         [0033]    The output shaft  15  is disposed so as to intersect with, or be not parallel and not intersect with, the outer shaft  7 . The output shaft  15  is, at one end thereof, and preferably as a unitary body, comprised of a gear  151 . The combination of the gear  151  and the bevel gear  77  constitutes the bevel or hypoid gear set  13 . The torque transmitted to the outer shaft  7  is thereby output to a direction distinct from its axial direction through the output shaft  15 . 
         [0034]    For the purpose of rotatably supporting the output shaft  15 , a bearing set  69  is available. The output shaft  15  and the bearing set  69  may be assembled in advance and then unitarily incorporated into the portion  37  of the casing  3 . 
         [0035]    Referring to  FIG. 3  in combination with  FIG. 2 , the clutch  9  is in general constituted of the first clutch member  91  and the second clutch member  93 . 
         [0036]    The first clutch member  91  is generally cylindrical, its outer face being rotatably supported by the bearing  65 , and, on its outer face, splines  95  are cut in the axial direction. As described above, the splines  95  mesh with the splines  55  of the inner shaft  5  so that the inner shaft  5  and the first clutch member  91  rotate together. Further, the inner shaft  5  is rotatably supported by the bearing  65  with having the first clutch member  91  interposed therebetween. 
         [0037]    The second clutch member  93  is also generally cylindrical, fits in the actuator  11 , thereby being supported, and is movable in the axial direction. Alternatively, instead of intervening between the actuator  11  and the inner shaft  5 , the second clutch member  93  may be supported directly, or by a bearing interposed therebetween, by the second part  33 . Referring to  FIGS. 4 and 5 , the first clutch member  91  and the second clutch member  93  comprise second teeth  103  engageable with each other, thereby forming the clutch  9 . 
         [0038]    Referring back to  FIG. 3 , the actuator  11  drives the second clutch member  93  in the axial direction to operate the clutch  9 . The actuator  11  can use a solenoid, for example. Alternatively, instead of the solenoid, another device such as a pneumatic or hydraulic device may be used. The solenoid is comprised of a coil  11  wound in the circumferential direction to generate magnetic flux, and a core  113  for conducting the generated magnetic flux. 
         [0039]    The coil  11  is made of a conductor such as copper and is molded in resin. The core  113  is made of a magnetic material and surrounds the coil  111 , leaving a gap  115  at its inner periphery. The core  113  fits in a corner of the second part  33 , and a tab  41  fits in an inner periphery of the second part  33  so as to prevent its displacement. 
         [0040]    To bridge the gap  115 , a cylindrical or ring-like plunger  117  fits in the core  113  and is also of a magnetic material. More specifically, the combination of the core  113  and the plunger  117  forms a closed magnetic circuit enclosing the coil  111 . The magnetic flux does not leap over the gap  115  but generally flows through the plunger  117 , thereby driving the plunger  117  in the axial direction. 
         [0041]    A by-plunger  119  can further fit in the plunger  117 . The by-plunger  119  is also cylindrical or ring-like but is of a nonmagnetic material and fixed to the plunger  117  so as to move together. One end of the by-plunger  119  abuts on the second clutch member  93  and drives it in the axial direction. Intervention of the by-plunger  119  of the nonmagnetic material is advantageous to suppression of leakage of the magnetic flux. 
         [0042]    Between the plunger  117  or the by-plunger  119  and the second clutch member  93 , a sleeve portion  121  may be interposed. This is advantageous as this stabilizes support of the second clutch member  93  and limits contact points between the plunger  117  or the by-plunger  119  and the second clutch member  93 . The sleeve portion  121  may be radially extended from the solenoid or any other stationary member. The plunger  117  and the by-plunger  119  are movable in the space between the core  113  and the sleeve portion  121 . 
         [0043]    A repulsive body  97  such as a spring can intervene between the first clutch member  91  and the second clutch member  93 . The repulsive body  97  biases the second clutch member  93  toward the direction where the clutch  9  gets disconnected. To reduce friction of the repulsive body  97 , a thrust bearing  99  is used. 
         [0044]    As described already, the end  73  of the outer shaft  7  and the second clutch member  93  engage with each other by means of the first teeth  101 , and the first clutch member  91  and the second clutch member  93  are engageable with each other by means of the second teeth  103 . Referring to  FIG. 4 , to retain the engagement of the first teeth  101  even when the second teeth  103  engage, the first teeth  101  have a teeth length longer than the second teeth  103 . To facilitate engagement, any of the first teeth  101  and the second teeth  103  may form a relatively small angle with the axial direction. An angle a 1  that the first angle forms may be made relatively large so as to give a cam function to the first teeth  101 . In this case, an angle a 2  that the second teeth  103  forms can be made smaller than the angle a 1  that the first teeth  101  form. 
         [0045]    The first clutch member  91  follows the rotation of the inner shaft  5  to be in rotational motion R. Before the clutch  9  is connected, the outer shaft  7  and the second clutch member  93  do not necessarily rotate in accordance with the rotational motion R but can be at rest, for example. Referring to  FIG. 5 , the solenoid, when excited, drives the second clutch member  93  in the axial direction so that the clutch  9  is connected. Then the second clutch member  93  follows the first clutch member  91  to produce a relative rotation R′ between the second clutch member  93  and the outer shaft  7 . This relative rotation R′, by the cam function of the first teeth  101 , produces an axial force F, which acts on the second teeth  103  to enhance its connection. More specifically, the cam function of the first teeth  101  assists the actuator  11  to retain the connection of the clutch  9 . Although the second teeth  103  produce a counter cam function in forming the angle a 2 , if a 2  is smaller than the angle a 1  that the first teeth  101  form, the cam function of the first teeth  101  is superior to the cam function of the second teeth  103 , thereby ensuring the function of assistance by the first teeth  101 . When suspending the excitation, the clutch  9  is disconnected by the repulsive body  97 . 
         [0046]    Meanwhile, while in the aforementioned example the combination of the first clutch member  91  and the second clutch member  93  forms a clutch and the combination of the second clutch member  93  and the outer shaft  7  steadily forms a coupling, this relation may be reversed. In this case, the second clutch member may be directly coupled with the inner shaft  5  and, for this coupling, an axially movable spline-coupling is used. 
         [0047]    In the present example, a part that belongs to the first part  31  and another part that belongs to the second part  33  can be respectively independently assembled. More specifically, a process for incorporating the outer shaft  7  into the first part  31  can be pursued independent of assembly of the second part  33 . A process for incorporating the clutch  9 , the actuator  11  and the inner shaft  5  into the second part  33  can be likewise pursued independent of assembly of the first part  31 . After these processes, by assembling the second part  33  with the first part  31  with inserting the inner shaft  5  into the outer shaft  7 , assembly of the PTU  1  is generally completed. As connection between the second clutch member  93  and the outer shaft  7  is simple engagement of the first teeth  101 , this process does not cause any difficulty. More specifically, although the PTU  1  according to the present embodiment has a complex structure, it is easy to assemble. 
         [0048]    The structure described above further enables easy maintenance. When the solenoid becomes to require maintenance, nothing is necessary other than separating the second part  33  from the first part  31  to expose the solenoid. As it is not required to disassemble the PTU  1  totally, maintenance is made easy. 
         [0049]    The structure described above furthermore enables easy modifications to the structure. For example, when the clutch  9  and the actuator  11  are omitted from the second part  33  and instead any member connecting the splines  55  of the inner shaft  5  and the first teeth  101  of the outer shaft  7  are applied thereto, the torque is steadily transmitted to the output shaft  15 . More specifically, without replacing the PTU  1  as a whole, a construction of a part-time 4WD can be changed into a construction of a full-time 4WD. 
         [0050]    More specifically, the present example solves many problems coming from structural complexity of PTUs. 
         [0051]    Although certain embodiments have been described above, modifications and variations of the embodiments described above will occur to those skilled in the art, in light of the above teachings.