Patent Publication Number: US-2020292049-A1

Title: Power transmission device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. National stage application of International Application No. PCT/JP2017/035315, filed on Sep. 28, 2017. This U.S. National stage application claims priority under 35 U.S.C. § 119(a) to Japanese Patent Application No. 2016-189235, filed in Japan on Sep. 28, 2016, the entire contents of which are hereby incorporated herein by reference. 
    
    
     BACKGROUND 
     Field of the Invention 
     The present invention relates to a power transmission device. 
     Background Information 
     With a conventional work vehicle such as a wheel loader or a wheeled excavator, a sealing device is provided in the gap between the transmission case and the output shaft, or the gap between the axle case and the propeller shaft, in order to help keep soil, mud, and the like (hereinafter collectively referred to as “foreign matter”) from coming in from the outside. 
     In Japanese Laid-Open Utility Model Application S63-128320 is proposed a sealing device having a labyrinth structure configured such that a plurality of fixed-side annular bodies attached to a bearing case and a plurality of rotation-side annular bodies attached to a rotary shaft attached are alternately incorporated. With this sealing device, even if foreign matter gets in, it is discharged to the outside by the centrifugal force that accompanies the rotation of the rotation-side annular bodies. 
     SUMMARY 
     However, with the sealing device described in Japanese Laid-Open Utility Model Application S63-128320, foreign matter that is flung off by the rotation-side annular bodies tends to build up in the gaps between the fixed-side annular bodies, so there is a need for a way to discharge this foreign matter more effectively. 
     The present invention was conceived in light of the above situation, and it is an object thereof to provide a power transmission device with which foreign matter can be efficiently discharged. 
     The power transmission device pertaining to a first aspect comprises a rotary shaft, a bearing case, an annular inner cover, and an annular outer cover. The bearing case rotatably supports the rotary shaft. The annular inner cover is attached to the rotary shaft and is disposed between the rotary shaft and the bearing case in the radial direction of the rotary shaft. The annular outer cover is attached to the rotary shaft and is disposed on the outside of the inner cover in the axial direction. 
     With the power transmission device pertaining to the first aspect, since the inner cover and outer cover rotate along with the rotary shaft, even if foreign matter should work its way in between the inner cover and the outer cover, this foreign matter can be efficiently discharged to the outside by the rotational force of the inner cover and outer cover. 
     The power transmission device pertaining to a second aspect is the power transmission device pertaining to the first aspect, wherein the bearing case has a case body and an annular projecting portion that projects in the axial direction from the case body. The outer end portion of the inner cover in the radial direction is adjacent to the inner peripheral face of the projecting portion in the radial direction. The outer end portion of the outer cover in the radial direction is adjacent to the outer peripheral face of the projecting portion in the radial direction. 
     With the power transmission device pertaining to the second aspect, foreign matter will be less likely to come in through the gap between the outer cover and the projecting portion, and foreign matter will also be less likely to come in through the gap between the inner cover and the projecting portion. 
     The power transmission device pertaining to a third aspect is the power transmission device pertaining to the second aspect, wherein the outer end portion of the inner cover in the radial direction is inclined toward the outside in the axial direction closer to the inner peripheral surface of the projecting portion. 
     With the power transmission device pertaining to the third aspect, foreign matter is flung away from the gap between the inner cover and the projecting portion by the outer end portion of the rotating inner cover, so it is less likely that foreign matter will get in. 
     The power transmission device pertaining to the fourth aspect is the power transmission device pertaining to the second or third aspect, wherein the width of the gap between the projecting portion and the inner cover in the radial direction is no more than 1/10 the overall width of the inner cover in the radial direction. 
     With the power transmission device pertaining to the fourth aspect, the gap between the inner cover and the projecting portion can be made narrow enough to make it less likely that foreign matter will get in. 
     The power transmission device pertaining to the fifth aspect is the power transmission device pertaining to any of the second to fourth aspects, wherein the inner peripheral face of the projecting portion in the radial direction is parallel to the axial direction. 
     With the power transmission device pertaining to the fifth aspect, even if the entire rotary shaft should oscillate in the axial direction, the inner cover will be inhibited from clashing with the protruding portion. 
     The power transmission device pertaining to the sixth aspect is the power transmission device pertaining to any of the second to fifth aspects, wherein the projecting portion is opposite to and a specific distance away from the outer end portion of the outer cover in the radial direction. The width of the gap between the projecting portion and the outer end portion of the outer cover in the radial direction is no more than 1/20 the overall length of the projecting portion in the axial direction. 
     With the power transmission device pertaining to the sixth aspect, the gap between the outer cover and the projecting portion can be made narrow enough to make it less likely that foreign matter will get in. 
     The power transmission device pertaining to the seventh aspect is the power transmission device pertaining to any of the second to sixth aspects, wherein the outer peripheral face of the projecting portion in the radial direction is parallel to the axial direction. 
     With the power transmission device pertaining to the seventh aspect, even if the entire rotary shaft should oscillate in the axial direction, the outer cover will be inhibited from clashing with the protruding portion. 
     The present invention provides a power transmission device with which foreign matter can be discharged with a simple configuration. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a side view of a wheel loader in an embodiment. 
         FIG. 2  is a cross section of a transmission in this embodiment. 
         FIG. 3  is a detail view of  FIG. 2 . 
         FIG. 4  is a detail view of  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENT(S) 
     Configuration of Wheel Loader  1   
       FIG. 1  is a side view of a wheel loader  1  in an embodiment.  FIG. 1  shows the power transmission system of the wheel loader  1  as a simplified see-through view. In the following description, “front” and “rear” are the same as the “front” and “rear” as seen by the operator seated in the driver&#39;s seat. 
     The wheel loader  1  comprises a body  2 , a bucket  3 , a working implement drive mechanism  4 , and a cab  5 . The body  2  consists of a front body and a rear body. A bucket  3  used for excavation and loading is attached to the front of the body  2  via the hydraulic working implement drive mechanism  4 . The working implement driving mechanism  4  is constituted by a boom, a bell crank, a connecting link, a bucket cylinder, a boom cylinder, and so forth. 
     A box-shaped cab  5  in which an operator sits is disposed on the body  2 . An engine compartment  6  is provided at the rear end portion of the body  2 . The engine compartment  6  houses an engine  7  as a power source. In this embodiment, the crankshaft (not shown) of the engine  7  is laid out longitudinally. 
     Power from the engine  7  is transmitted to the transmission  9  via a propeller shaft  8 . Some of the power outputted from the transmission  9  is transmitted to a rear drive shaft  11  via an output shaft  10 . The power transmitted to the rear drive shaft  11  is transmitted to the rear wheels via a rear axle  12 . Some of the power outputted from the transmission  9  is transmitted to a front drive shaft  14  via the output shaft  10 . The power transmitted to the front drive shaft  14  is transmitted to the front wheels via a front axle  1 S. 
     In this embodiment, the transmission  9 , the output shaft  10 , the rear drive shaft  11 , the rear axle  12 , the front drive shaft  14 , and the front axle  15  constitute the “power transmission device” pertaining to this embodiment. 
     Configuration of Transmission  9   
       FIG. 2  is a cross section of the overall configuration of the transmission  9  in this embodiment.  FIG. 3  is a detail view of  FIG. 2 . 
     The transmission  9  comprises a transmission case  20 , an input shaft  21 , a torque converter  22 , a first intermediate shaft  23 , a second intermediate shaft  24 , a third intermediate shaft  25 , and the output shaft  10 . 
     The transmission case  20  houses the input shaft  21 , the torque converter  22 , the first intermediate shaft  23 , the second intermediate shaft  24 , the third intermediate shaft  25 , and the output shaft  26 . The transmission case  20  is an example of the “bearing case” in this embodiment. The output shaft  10  is an example of the “rotary shaft” in this embodiment. 
     The power from the engine  7  is inputted to the input shaft  21  via the torque converter  22 . The first intermediate shaft  23  is provided with a front clutch  27  and a first clutch  28 . The second intermediate shaft  24  is provided with a rear clutch  29  and a second clutch  30 . The third intermediate shaft  25  is provided with a third clutch  31  and a fourth clutch  32 . A transfer shalt  33  is linked to the front end portion of the third intermediate shaft  25 . The transfer shaft  33  is provided with a transfer gear  33   g.    
     Power is transmitted from the transfer shaft  33  to the output shaft  10 . The output shaft  10  is provided with an output gear  10   g  that meshes with a transfer gear  33   a , and a parking brake  34 . 
     The output shaft  10  is disposed longitudinally. The rear end portion of the output shaft  10  protrudes rearward from the transmission case  20 . The front end portion of the output shaft  10  protrudes forward from the transmission case  20 . As shown in  FIG. 3 , the output shaft  10  is supported by the transmission case  20 . The output shaft  10  is able to rotate around an axis AX. 
     The rear end portion of the output shaft  10  is provided with a rear coupling  10   a  to which the front end portion of the rear drive shaft  11  is linked. The front end portion of the output shaft  10  is provided with a front coupling  10   b  to which the rear end portion of the front drive shaft  14  is linked. 
     As shown in  FIG. 3 , the transmission case  20  has a case main body  20   a , a rear projecting portion  20   b  (an example of a “projecting portion”), and a front projecting portion  20   c . The case main body  20   a  houses the middle portion of the output shaft  10  in the axial direction. The axial direction is a direction parallel to the axis AX of the output shaft  10 . The rear projecting portion  20   b  projects rearward from the case main body  20   a . The rear projecting portion  20   b  is formed in an annular shape with the axis AX at the center. The front protruding portion  20   c  projects forward from the case body  20   a . The front projecting portion  20   c  is formed in an annular shape with the axis AX at the center. 
     A rear oil seal  35  and a rear dust seal  36  are disposed between the output shaft  10  and the rear projecting portion  20   b  of the transmission case  20 . The rear oil seal  35  and the rear dust seal  36  are each formed in an annular shape with the axis AX at the center. An ordinary oil seal and dust seal can be used for the rear oil seal  35  and the rear dust seal  36 , respectively. 
     An annular labyrinth structure  37  that covers the portion of the transmission case  20  on the outside of the rear projecting portion  20   b  in the axial direction is attached to the output shaft  10 . The labyrinth structure  37  makes it less likely that soil, mud, or the like (hereinafter referred to as “foreign matter”) will get into the interior of the transmission case  20  from between the output shaft  10  and the rear projecting portion  20   b  of the transmission case  20 . The configuration of the labyrinth structure  37  will be described below. 
     A front oil seal  38  and a front dust seal  39  are disposed in the gap between the output shaft  10  and the front protruding portion  20   c  of the transmission case  20 . The front oil seal  38  and the front dust seal  39  are each formed in an annular shape with the axis AX at the center. An ordinary oil seal and dust seal can be used for the front oil seal  38  and the front dust seal  39 , respectively. 
     An annular seal cover  40  that covers the portion of the transmission case  20  on the outside of the front projecting portion  20   c  in the axial direction is attached to the output shaft  10 . The seal cover  40  makes it less likely that foreign matter will get into the interior of the transmission case  20  from between the output shaft  10  and the front protruding portion  20   c  of the transmission case  20 . 
     Configuration of Labyrinth Structure  37   
     The labyrinth structure  37  attached to the output shaft  10  will now be described.  FIG. 4  is a detail view of  FIG. 3 . The labyrinth structure  37  is constituted by the inner cover  41  and the outer cover  42 . 
     1. Inner Cover  41   
     The inner cover  41  is formed in an annular shape with the axis AX at the center. The inner cover  41  is attached to the outer peripheral face  10 S of the output shaft  10 . The inner cover  41  rotates around the axis AX along with the output shaft  10 . The inner cover  41  is disposed inside the outer cover  42  in the axial direction. The inner cover  41  is disposed between the output shaft  10  and the rear projecting portion  20   b  of the transmission case  20  in the radial direction of the output shaft  10 . The radial direction is a direction perpendicular to the axis AX of the output shaft  10 . The inner cover  41  covers the outside of the rear oil seal  35  and the rear dust seal  36  in the axial direction. 
     The inner cover  41  has a press-fit portion  43 , an extension  44 , and an outer end portion  45 . In this embodiment, the cross sectional shape of the inner cover  41  is substantially C-shaped. 
     The press-fit portion  43  is formed in a cylindrical shape with the axis AX at the center. The press-fit portion  43  extends along the axial direction. The press-fit portion  43  is press-fitted to the output shaft  10 . 
     The extension  44  is continuous with the inner end of the press-fit portion  43  in the axial direction. The extension  44  is formed in the shape of a perforated disk with the axis AX at the center. The extension  44  extends along the radial direction. The extension  44  is opposite the rear dust seal  36  in the axial direction. 
     The outer end portion  45  is the part of the inner cover  41  located on outermost side in the radial direction. The outer end portion  45  is continuous with the outer end of the extension  44  in the radial direction. The outer end portion  45  is inclined with respect to the extension  44 . The outer end portion  45  tilts outward in the axial direction moving toward the inner peripheral face  20 S of the rear projecting portion  20   b  of the transmission case  20 . The outer end portion  45  extends in a direction that is inclined with respect to both the radial direction and the axial direction. In this embodiment, the outer end portion  45  extends toward the distal end of the rear projecting portion  20   b.    
     The distal end of the outer end portion  45  is adjacent to the inner peripheral face  20 S of the rear projecting portion  20   b . The distal end of the outer end portion  45  is separated from the inner peripheral face  20 S of the rear projecting portion  20   b . An inner gap  46  is formed between the distal end of the outer end portion  45  and the inner peripheral face  20 S of the rear projecting portion  20   b . There are no particular restrictions on the length L 1  of the gap  46  in the radial direction, but it is preferably no more than 1/10 the overall width L 2  of the inner cover  41  in the radial direction, and preferably at least 1/15 the overall width L 2  of the inner cover  41 . 
     Here, the inner peripheral face  20 S of the rear projecting portion  20   b  of the transmission case  20  is parallel to the axial direction. Therefore, even when the entire output shaft  10  oscillates in the axial direction, the outer end portion  45  of the inner cover  41  will be inhibited from clashing with the rear protruding portion  20   b.    
     2. Outer Cover  42   
     The outer cover  42  is formed in an annular shape with the axis AX at the center. The outer cover  42  is attached to the outer peripheral face  10 S of the output shaft  10 . The outer cover  42  rotates around the axis AX along with the output shaft  10 . The outer cover  42  is disposed on the outside of the inner cover  41  in the axial direction. Outer cover  42  is disposed on the outside of the rear oil seal  35  and the rear dust seal  36  in the axial direction. The outer cover  42  covers the outside of the rear projecting portion  20   b  in the radial direction. 
     The outer cover  42  has a press-fit portion  47 , an extension  48 , and an outer end portion  49 . In this embodiment, the cross sectional shape of the outer cover  42  is substantially L-shaped. 
     The press-fit portion  47  is formed in a cylindrical shape with the axis AX at the center. The press-fit portion  47  extends along the axial direction. The press-fit portion  47  is press-fitted to the output shaft  10 . 
     The extension  48  is continuous with the outer end of the press-fit portion  47  in the axial direction. The extension  48  is formed in the shape of a perforated disk with the axis AX at the center. The extension  48  extends along the radial direction. The extension  48  extends more to the outside than the rear projecting portion  20   b  of the transmission case  20  in the radial direction. The extension  48  is opposite the extension  44  and the outer end portion  45  of the inner cover  41  in the axial direction. 
     The outer end portion  49  is the part of the outer cover  42  located on outermost side in the radial direction. The outer end portion  49  is formed in a cylindrical shape with the axis AX at the center. The outer end portion  49  is disposed more to the outside than the rear projecting portion  20   b  of the transmission case  20  in the radial direction. The outer end portion  49  is bent by about 90 degrees with respect to the extension  48 . 
     The outer end portion  49  is adjacent to the outer peripheral face  20 T of the rear projecting portion  20   b . The outer end portion  49  is separated from the outer peripheral face  20 T of the rear projecting portion  20   b . The rear projecting portion  20   b  of the transmission case  20  includes a opposing portion  20   d  that is opposite the outer end portion  49  in the radial direction. The outer end portion  49  extends along the opposing portion  20   d . The outer end portion  49  is parallel to the opposing portion  20   d.    
     An outer gap  50  is formed between the outer end portion  49  and the opposing portion  20   d . There are no particular restrictions on the distance M 1  of the outer gap  50  in the radial direction, but it is preferably no more than 1/20 and preferably at least 1/30 the overall length M 2  of the opposing portion  20   d  in the radial direction. 
     Here, the outer peripheral face  20 T of the rear projecting portion  20   b  of the transmission case  20  is parallel to the axial direction. Therefore, even when the entire output shaft  10  oscillates in the axial direction, the outer end portion  49  of the outer cover  42  will be inhibited from clashing with the rear projecting portion  20   b.    
     Features 
     (1) The transmission  9  comprises the output shaft  10 , the transmission case  20 , the annular inner cover  41 , and the annular outer cover  42 . The transmission case  20  supports the output shaft  10  rotatably around the axis AX. The inner cover  41  is attached to the output shaft  10 . The inner cover  41  is disposed between the output shaft  10  and the transmission case  20  in the radial direction. The outer cover is attached to the output shaft  10 . The outer cover  42  is disposed on the outside of the inner cover  41  in the axial direction. 
     Since the inner cover  41  and outer cover  42  rotate along with the output shaft  10 , even if foreign matter works its way in between the inner cover  41  and outer cover  42  as indicated by the dotted arrow in  FIG. 4 , the foreign matter can be efficiently discharged to the outside by the rotational force of the inner cover  41  and the outer cover  42 . 
     (2) The transmission case  20  has the case main body  20   a  and the annular rear projecting portion  20   b  that projects in the axial direction from the case main body  20   a . The outer end portion  45  of the inner cover  41  in the radial direction is adjacent to the inner peripheral face  20 S of the rear projecting portion  20   b  in the radial direction. The outer end portion  49  of the outer cover  42  in the radial direction is adjacent to the outer peripheral face  20 T of the rear projecting portion  20   b  in the radial direction. 
     Therefore, foreign matter will be less likely to get in from the gap  50  between the rear projecting portion  20   b  and the outer cover  42 , and foreign matter will also be less likely to get in from the inner gap  46  between the rear projecting portion  20   b  and the inner cover  41 . 
     (3) The outer end portion  45  of the inner cover  41  in the radial direction is inclined outward in the axial direction closer to the inner peripheral face  20 S of the rear projecting portion  20   b.    
     Therefore, the outer end portion  45  of the cover  41  to rotate can fling off foreign object away from the inner gap  46 , which further suppresses the entry of foreign matter from the inner gap  46 . 
     (4) In the radial direction, the rear projecting portion  20   b  is separated from the inner cover  41 , and the length L of the inner gap  46  between the rear projecting portion  20   b  and the inner cover  41  in the radial direction is no more than 1/10 the overall length L 2  of the inner cover  41  in the radial direction. 
     Consequently, the inner gap  46  can be made narrow enough to further suppress the entry of foreign matter from the inner gap  46 . 
     (5) The inner peripheral face  20 S of the rear projecting portion  20   b  in the radial direction is parallel to the axial direction. Therefore, even if the entire output shaft  10  oscillates in the axial direction, the inner cover  41  can be inhibiting from clashing with the rear projecting portion  20   b.    
     (6) The rear projecting portion  20   b  is opposite the outer end portion  49  of the outer cover  42  with a specific spacing in between in the radial direction. The length M 1  of the outer gap  50  between the rear projecting portion  20   b  and the outer end portion  49  of the outer cover  42  in the radial direction is no more than 1/20 the overall length M 2  of the rear projecting portion  20   b  in the axial direction. 
     Consequently, it is possible to narrow the outer gap  50  enough to further suppress the entry of foreign matter from the outer gap  50 . 
     (7) The outer peripheral face  20 I of the rear projecting portion  20   b  in the radial direction is parallel to the axial direction. Therefore, even if the entire output shaft  10  oscillates in the axial direction, the outer cover  42  can be inhibited from clashing with the rear projecting portion  20   b.    
     OTHER EMBODIMENTS 
     The present invention is not limited to or by the above embodiment, and various modifications or revisions can be made without departing from the scope of the present invention. 
     The above embodiment describes a case in which the labyrinth structure  37  pertaining to the present invention is applied between the output shaft  10  and the transmission case  20 , but this is not the only option. The labyrinth structure  37  pertaining to the present invention is widely applicable between a rotary shaft and a bearing case in a power transmission device. For example, the labyrinth structure  37  pertaining to the present invention can be applied between the front drive shaft  14  and the front axle  15 , between the rear drive shaft  11  and the rear axle  12 , and so on. 
     The above embodiment describes a case in which the labyrinth structure  37  pertaining to the present invention is applied to the power transmission device of a wheel loader, but this is not the only option. The labyrinth structure  37  pertaining to the present invention is widely applicable, not only to a work vehicle such as a motor grader or a dumper truck, but also to a power transmission device in a passenger car, a motorcycle, or the like. 
     In the above embodiment, the inner cover  41  was press-fitted to the output shaft  10 , but the inner cover  41  may instead be welded to the output shaft  10 . In this case, the inner cover  41  need not have the press-fit portion  43 . 
     In the above embodiment, the outer cover  42  was press-fitted to the output shaft  10 , but the outer cover  42  may instead be welded to the output shaft  10 . In this case, the outer cover  42  need not have the press-fit portion  47 . 
     In the above embodiment, the inner cover  41  has the outer end portion  45  that is inclined with respect to the extension  44 , but it need not have the outer end portion  45 . In this case, the extension  44  is preferably extended to a position in contact with the rear projecting portion  20   b.    
     In the above embodiment, the inner peripheral face  20 S of the rear projecting portion  20   b  of the transmission case  20  is parallel to the axial direction, but may be any shape as long as it is unlikely to clash with the inner cover  41 . For instance, the inner peripheral face  20 S may be wholly or partially recessed. 
     In the above embodiment, the inner peripheral face  20 S of the rear projecting portion  20   b  of the transmission case  20  is parallel to the axial direction, but may be any shape as long as it is unlikely to clash with the outer cover  42 . For instance, the outer peripheral face  20 T may be wholly or partially recessed.