Patent Publication Number: US-2019195324-A1

Title: Transmission device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This Nonprovisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No. 2017-248238 filed in Japan on Dec. 25, 2017, the entire contents of which are hereby incorporated by reference. 
     FIELD 
     The present invention relates to a transmission device that transmits power. 
     BACKGROUND AND SUMMARY 
     In related art, there has been proposed a jack equipped with a screw shaft, a nut mounted to the screw shaft, a worm shaft, and a worm wheel which transmits the power from the worm shaft to the nut. The nut is fixed in an axial direction, and the screw shaft moves in the axial direction by the rotation of the worm shaft. A mounting portion is provided on the screw shaft, and by attaching an object to the mounting portion, it is possible to move the object in a linear direction. 
     In the jack, there was a problem that the nut and the worm wheel are arranged in the axial direction of the screw shaft, and are increased in size in the axial direction of the screw shaft. 
     The present disclosure has been made in view of such circumstances, and an object thereof is to provide a transmission device that can prevent an increase in size in the axial direction of the screw shaft. 
     According to an aspect of disclosure, there is provided a transmission device comprising: an input shaft; a screw shaft extending in a direction orthogonal to the input shaft; a transmission member which forms an annular shape surrounding the screw shaft and rotates around the screw shaft by a power which is input from the input shaft; and a nut which is mounted to the screw shaft and rotates by the power transmitted from the transmission member, wherein the nut is disposed on an axis orthogonal to the screw shaft and the input shaft. 
     The above and further objects and features will more fully be apparent from the following detailed description with accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view schematically illustrating a transmission device. 
         FIG. 2  is a plan view schematically illustrating the transmission device. 
         FIG. 3  is a vertical cross-sectional view schematically illustrating the transmission device. 
         FIG. 4  is an explanatory cross-sectional view describing a mounting method of the transmission device when the transmission device is suspended and used. 
         FIG. 5  is an example of a graph showing a relation between a rotational speed of a ball screw shaft of the transmission device having different inter-core distances and an allowable load to the ball screw shaft. 
         FIG. 6  is a perspective view schematically illustrating an example of a transmission device with a partially modified configuration. 
         FIG. 7  is an explanatory cross-sectional view describing a mounting method of the transmission device when the transmission device is suspended and used. 
         FIG. 8  is a perspective view schematically illustrating another example of a transmission device with a partially modified configuration. 
     
    
    
     DETAILED DESCRIPTION OF NON-LIMITING EXAMPLE EMBODIMENTS 
     Hereinafter, the present invention will be described with reference to the drawings illustrating a transmission device according to an embodiment.  FIG. 1  is a perspective view schematically illustrating the transmission device, and  FIG. 2  is a plan view schematically illustrating the transmission device. The transmission device includes a case  1  that accommodates a worm  45   a , a worm wheel  46  (a transmission member), a nut  38 , and a ball screw shaft  37 , which will be described later. The case  1  has a rectangular parallelepiped first case  10 , and a second case  20  protruding from one surface of the first case  10 . The worm wheel  46  corresponds to the transmission member. 
     The second case  20  has an elongated rectangular parallelepiped shape and extends parallel to the one surface of the first case  10 . A longitudinal dimension of the second case  20  is substantially the same as a width of the first case  10 , and both end portions of the second case  20  do not protrude outward beyond the first case  10 . 
       FIG. 3  is a vertical cross-sectional view schematically illustrating the transmission device. In a connecting portion between the first case  10  and the second case  20 , openings  15  and  20   a  are formed in the first case  10  and the second case  20 , respectively. A portion of the second case  20  having the opening  20   a  is disposed inside the opening  15  of the first case  10 , and internal spaces of the first case  10  and the second case  20  are continued. The first case  10  and the second case  20  are integrally formed. 
     The first case  10  includes a first bearing holder  11  and a second bearing holder  12  that face each other. The first bearing holder  11  includes an annular portion  11   a , a first cylindrical portion  11   b  protruding in the axial direction from an inner circumferential portion of the annular portion  11   a , and a second cylindrical portion  11   c  protruding from an outer circumferential portion of the annular portion  11   a  in a direction opposite to the first cylindrical portion  11   b . The protruding end portion of the second cylindrical portion  11   e  protrudes outward in the radial direction into a flange shape, and a groove  11   d  having an L-shaped cross section is annularly formed on the outer circumferential surface of the second cylindrical portion  11   c.    
     The second bearing holder  12  includes an annular portion  12   a , a first cylindrical portion  12   b  protruding in the axial direction from the inner circumferential portion of the annular portion  12   a , and a second cylindrical portion  12   c  protruding from the outer circumferential portion of the annular portion  12   a  in the direction opposite to the first cylindrical portion  12   b . The protruding end portion of the second cylindrical portion  12   c  protrudes outward in the radial direction into a flange shape, and a groove  12   d  having an L-shaped cross section is annularly formed on the outer circumferential surface of the second cylindrical portion  12   c . The first bearing holder  11  and the second bearing holder  12  are arranged coaxially with the second cylindrical portions  11   c  and  12   c  facing each other, respectively. A bottomed cylindrical screw cover  50  is fitted to the first cylindrical portion  12   b  of the second bearing holder  12 . An end portion of the screw cover  50  on the side opposite to the bottom surface is inserted into the first cylindrical portion  12   b.    
     In the first bearing holder  11 , a cylindrical first wheel hub  31  is disposed coaxially inside the protruding end portion of the second cylindrical portion  11   c . The first wheel hub  31  extends toward the second bearing holder  12 , and an extending end portion thereof is disposed to be closer to the second bearing holder  12  than the second cylindrical portion  11   c . An annular oil seal  33  and a bearing  34  are juxtaposed in the axial direction between the second cylindrical portion  11   c  and the first wheel hub  31 . The bearing  34  is disposed to be closer to the second bearing holder  12  than the oil seal  33 . 
     In the second bearing holder  12 , a cylindrical second wheel hub  32  is disposed coaxially inside the protruding end portion of the second cylindrical portion  12   c . The second wheel hub  32  extends toward the first bearing holder  11 , and an extending end portion thereof is disposed to be closer to the first bearing holder  11  than the second cylindrical portion  12   c . An annular oil seal  35  and a bearing  36  are juxtaposed in the axial direction between the second cylindrical portion  12   c  and the second wheel hub  32 . The bearing  36  is disposed to be closer to the first bearing holder  11  than the oil seal  35 . An axial distance between the two bearings  34  and  36  is smaller than outer diameters of the bearings  34  and  36 . The outer diameters of the two bearings  34  and  36  are substantially the same, and the inner diameters of the two bearings  34  and  36  are also substantially the same. 
     Extending end portions of each of the first wheel hub  31  and the second wheel hub  32  are butted against each other. A seal bond  42   a  is applied to a portion in which the first wheel hub  31  and the second wheel hub  32  are butted against each other. Instead of the seal bond  42   a , a seal member such as an O ring may be interposed in the butted portion. The oil seals  33  and  35  and the seal bond  42   a  correspond to a sealant. A groove  31   a  having an L-shaped cross section extending in a circumferential direction is formed on the outer circumferential surface of the extending end portion of the first wheel hub  31 . The groove  31   a  opens toward outer side of the first wheel hub  31  in a radial direction and toward the second wheel hub  32 . An annular protruding portion  32   b  protruding outward in the radial direction is formed at the extending end portion of the second wheel hub  32 . A second groove  42  having a U-shaped cross section, which opens toward outer side in the radial direction and extends in the circumferential direction, is formed by the groove  31   a  and the protruding portion  32   b . The worm wheel  46  is fitted to the second groove  42  having the U-shaped cross section. The second groove  42  having the U-shaped cross section and the worm wheel  46  are fitted to each other. The first wheel hub  31  and the second wheel hub  32  are connected to each other by a connecting member, for example, a bolt  55 . 
     A groove  32   a  having an L-shaped cross section extending in the circumferential direction is formed on the inner circumferential surface of the extending end portion of the second wheel hub  32 . The groove  32   a  opens toward inner side of the second wheel hub  32  in the radial direction and toward the first wheel hub  31 . The outer circumferential surface of the groove  32   a  in the radial direction is disposed outside the inner circumferential surface of the first wheel hub  31  in the radial direction. Therefore, the first wheel hub  31  side of the groove  32   a  is blocked by the end surface of the first wheel hub  31 . A first groove  41  having a U-shaped cross section, which opens toward inner side in the radial direction and extends in the circumferential direction, is formed by the groove  32   a  and the end surface of the first wheel hub  31 . 
     A ball screw shaft  37  is disposed inside the first wheel hub  31  and the second wheel hub  32 . One end portion of the ball screw shaft  37  protrudes from the first cylindrical portion  11   b  of the first bearing holder  11 . A mounting portion  37   a  for mounting an object is provided at the one end portion of the ball screw shaft  37 . The mounting portion  37   a  has fine screws. The other end portion of the ball screw shaft  37  protrudes from the second wheel hub  32  and is accommodated in the screw cover  50 . 
     A nut  38  is mounted to the ball screw shaft  37 . A rolling elements, for example, a ball, is provided between the ball screw shaft  37  and the nut  38 . A ball screw mechanism is constituted by the ball screw shaft  37 , the nut  38 , the ball, and the circulation component, and the ball circulates, for example, by a return tube type. The circulation type of the ball in the ball screw mechanism is not limited to the return tube type, and it may be, for example, a frame type, an end cap type, an end deflector type or a middle deflector type. Although it is also conceivable to use a trapezoidal screw instead of the ball screw mechanism, the ball screw mechanism has higher transmission efficiency and higher positional accuracy than the trapezoidal screw. 
     A flange  38   a  is formed at one end portion of the nut  38 . The flange  38   a  is fitted to the first groove  41  having a U-shaped cross section, and is axially interposed by the first wheel hub  31  and the second wheel hub  32 . A key  31   b  is formed on the inner circumferential surface of the first wheel hub  31 . A key groove  38   b  is formed on the outer circumferential surface of the nut  38 , and the key  31   b  of the first wheel hub  31  is fitted to the key groove  38   b . The nut  38 , the first wheel hub  31 , the second wheel hub  32 , and the worm wheel  46  are separate components. 
     A first mounting board  13  having an annular shape is detachably mounted to the groove  11   d  of the first bearing holder  11 . The first mounting board  13  has an inner ring part and an outer ring part, the inner ring part is provided in the groove  11   d  of the first bearing holder  11 , and the outer ring part slightly protrudes in the axial direction and is provided along the outer circumferential surface of the first bearing holder  11 . In the outer ring part, a plurality of screw holes  13   a  is arranged at equal intervals in the circumferential direction. 
     A second mounting board  14  having an annular shape is detachably mounted to the groove  12   d  of the second bearing holder  12 . The outer circumferential portion of the second mounting board  14  slightly protrudes in the axial direction and is provided along the outer circumferential surface of the second bearing holder  12 . A plurality of screw holes (not illustrated) is disposed on the outer circumferential portion of the second mounting board  14  at equal intervals in the circumferential direction. A side surface portion  16  is provided between the outer ring part of the first mounting board  13  and the outer circumferential portion of the second mounting board  14  to surround the worm wheel  46 . The opening  15  is provided on the side surface portion  16 , and the second case  20  is integrally mounted to the opening  15 . 
     An input shaft  45  is accommodated in the second case  20 . The input shaft  45  extends in a direction orthogonal to the ball screw shaft  37 . Both end portions of the input shaft  45  protrude from the second case  20 , and keys  45   b  are formed at both end portions of the input shaft  45 . A worm  45   a  is formed at the central part of the input shaft  45  in the axial direction. The worm  45   a  is engaged with the worm wheel  46 . As illustrated in  FIG. 3 , the nut  38  is disposed on an axis  60  orthogonal to the ball screw shaft  37  and the input shaft  45 . 
     A key  45   b  of the input shaft  45  is inserted into a key groove of a drive source (not illustrated), and the drive source is driven. The input shaft  45  rotates and the worm  45   a  rotates. The worm wheel  46  engaged with the worm  45   a  rotates, the first wheel hub  31  and the second wheel hub  32  rotate around the axis of themselves, and the nut  38  rotates around the axis of itself. Since the flange  38   a  of the nut  38  is fitted into the first groove  41  having a U-shaped cross section, it does not move in the axial direction. By the rotation of the nut  38 , the ball screw shaft  37  moves in the axial direction. By movement of the ball screw shaft  37  in the axial direction, the object mounted to the mounting portion  37   a  can be moved. 
     Lubricating oil is injected into the second case  20  in order to smoothly rotate the worm  45   a  and the worm wheel  46 . Grease is applied to the ball screw shaft  37  in order to smoothly rotate the nut  38  and the ball screw shaft  37 . As described above, since the oil seals  33  and  35  and the seal bond  42   a  are provided, the lubricating oil is prevented from entering the inside of the first wheel hub  31  or the second wheel hub  32 , that is, the nut  38  and the ball screw shaft  37 . 
     A pressure regulating valve  21  is provided in the second case  20 . A shielding ring  47  into which the input shaft  45  is inserted is provided inside the second case  20 . The shielding ring  47  is disposed to face the pressure regulating valve  21 . Even when the pressure regulating valve  21  is opened, the shielding ring  47  prevents the lubricating oil from flowing out from the pressure regulating valve  21 . The shielding ring  47  is an example of a shielding portion that prevents the outflow of the lubricating oil, and a shielding plate facing the pressure regulating valve  21  may be provided instead of the shielding ring  47 . Radiating fins  22  are provided on the outer circumferential surface of the second case  20 . 
       FIG. 4  is an explanatory cross-sectional view describing a mounting method of the transmission device when the transmission device is suspended and used. The transmission device is mounted, for example, as follows. A mounting hole  71  is formed in an object  70 , and a diameter of the mounting hole  71  is smaller than an inner diameter of the first mounting board  13 . First, a penetration hole  72  corresponding to the screw hole  13   a  of the first mounting board  13  is formed in the object  70 . Further, the mounting portion  37   a  is inserted into the mounting hole  71  from above, the first mounting board  13  is put around the mounting hole  71 , and the screw  56  is inserted into the penetration hole  72  from the lower side, and is fastened to the screw hole  13   a  of the first mounting board  13 . 
     In the case where the transmission device is installed on the object  70  with the mounting portion  37   a  facing upward, the screw cover  50  may be inserted into the mounting hole  71 , the second mounting board  14  may be put around the mounting hole  71 , and the screw  56  may be inserted into the penetration hole  72  from the lower side and fastened to a screw hole of the second mounting board  14 . 
     In the transmission device according to the embodiment, the ball screw shaft  37  and the input shaft  45  are disposed so as to be orthogonal to each other, and the nut  38  is disposed on the axis  60  orthogonal to the ball screw shaft  37  and the input shaft  45 . Accordingly, the nut  38  and the input shaft  45  are disposed at the same position in the axial direction of the ball screw shaft  37 . Therefore, it is possible to prevent the transmission device from becoming large in the axial direction of the ball screw shaft  37 . 
     Since the nut  38  is provided between the ball screw shaft  37  and the worm wheel  46 , a distance (hereinafter, referred to as an inter-core distance) between the center of the worm wheel  46  and the center of the worm  45   a  increases. Therefore, even when the transmission capacity increases and the input rotational speed increases, it is easy to ensure the necessary transmission capacity. 
       FIG. 5  is an example of a graph showing a relation between the rotational speed of the ball screw shaft  37  of the transmission device having different inter-core distances and an allowable load to the ball screw shaft  37 . In  FIG. 5 , the scale of the load is expressed in logarithm conversion. P illustrates a graph of a transmission device having a predetermined inter-core distance, and Q illustrates a graph of a transmission device having an inter-core distance greater than the predetermined inter-core distance of P. As shown in  FIG. 5 , the magnitude of the allowable load with respect to the rotational speed at Q is larger than the magnitude of the allowable load with respect to the rotational speed at P. 
     Further, by sandwiching the flange  38   a  formed on the nut  38  in the axial direction, even when the transmission device is suspended and used, that is, when the transmission device is used with the mounting portion  37   a  facing downward, a force in the same direction acts on the nut  38  and the ball screw shaft  37 . That is, when a downward pulling force is applied to the ball screw shaft  37 , since the flange  38   a  of the nut  38  is sandwiched between the first wheel hub  31  and the second wheel hub  32 , the downward pulling force also acts on the nut  38 . 
     In a case where the nut  38  does not have the flange  38   a  and the nut  38  comes into contact with, for example, the first bearing holder  11 , when the transmission device is suspended and used, compression force is applied to the nut  38 . In this case, the directions of the forces acting on the nut  38  and the ball screw shaft  37  are different from each other, and a difference in stress acting on the nut  38  and the ball screw shaft  37  easily increases. 
     In the embodiment, even if the transmission device is suspended and used, since the force in the same direction acts on the ball screw shaft  37  and the nut  38 , the difference in stress acting on the nut  38  and the ball screw shaft  37  becomes smaller, as compared to a case where the force acts on the ball screw shaft  37  and the nut  38  in the different directions. 
     Also, by inserting the flange  38   a  into the first groove  41  having the U-shaped cross section, fitting by spigot joint is achieved, and the accuracy of centering can be improved. Further, by inserting the worm wheel  46  into the second groove  42  having the U-shaped cross section, fitting by spigot joint is achieved, and the accuracy of centering can be improved. 
     Further, by mounting the first mounting board  13  and the second mounting board  14  to the object  70 , the transmission member can be mounted to the desired object  70 . 
     Further, after the penetration hole  72  corresponding to the screw hole  13   a  is formed in the object  70 , a screw is inserted into the penetration hole  72  and coupled with the screw hole  13   a , and the transmission device is fixed to the object  70 . Since the plurality of screw holes  13   a  is arranged around the axis of the ball screw shaft  37 , it is easy to set the mounting position of the transmission device around the axis of the ball screw shaft  37  at a desired position. By providing the shielding portion, the lubricating liquid is suppressed from leaking from the pressure regulating valve  21 . 
     Further, by providing the oil seals  33  and  35  and the seal bond  42   a , the ball screw shaft  37  and the nut  38  using the grease can be separated from the worm  45   a  and the worm wheel  46  using the lubricating oil. 
     An axial distance between the bearings  34  and  36  is smaller than the diameters of the bearings  34  and  36 . For this reason, large bearings  34  and  36  are used to extend the life of the bearings  34  and  36  and achieve miniaturization in the axial direction. 
       FIG. 6  is a perspective view schematically illustrating an example of a transmission device with a partially modified configuration. As illustrated in  FIG. 6 , a first mounting board  13   c  having a protruding portion  13   d  protruding outward from the side surface portion  16  or the second case  20  in the radial direction may be used. Since the first mounting board  13   c  having no protruding portion  13   d  is detachably mounted, it can be easily replaced with the first mounting board  13   c  having the protruding portion  13   d . In the protruding portion  13   d , a plurality of insertion holes  13   e  into which the screws  56  are inserted is aligned in the circumferential direction of the ball screw shaft  37 . 
       FIG. 7  is an explanatory cross-sectional view describing a mounting method of the transmission device when the transmission device is suspended and used. The transmission device is mounted, for example, as follows. First, a screw hole  73  corresponding to the insertion hole  13   e  of the first mounting board  13   c  is formed in the object  70 . Further, the mounting portion  37   a  is inserted into the mounting hole  71  from above, the first mounting board  13   c  is put around the mounting hole  71 , and the screw  56  is inserted into the insertion hole  13   e  from the upper side, and fastened to the screw hole  73  of the object  70 . In the transmission device having no protruding portion  13   d , the screw  56  is inserted from the lower side. However, by providing the protruding portion  13   d , the screw  56  can be inserted from the upper side, and the transmission device can be easily mounted. 
       FIG. 8  is a perspective view schematically illustrating another example of the transmission device with a partially modified configuration. As illustrated in  FIG. 8 , a second mounting board  14   c  having a protruding portion  14   d  protruding outward from the side surface portion  16  or the second case  20  in the radial direction may be used. In the protruding portion  14   d  of the second mounting board  14   c , a plurality of insertion holes  14   e  into which the screws  56  are inserted is aligned in the circumferential direction of the ball screw shaft  37 . When mounting the transmission device, the screw  56  can be inserted into the insertion hole  14   e  of the protruding portion  14   d  of the second mounting board  14   c  from the upper side, and can be fastened to the screw hole  73  of the object  70 . 
     It is to be noted that, as used herein and in the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise. It should be understood that the embodiments disclosed herein are illustrative and non-restrictive in every respect. The technical features described in the examples may be combined with one another, while all changes that fall within metes and bounds of the claims, or equivalence of such metes and bounds thereof are intended to be embraced by the scope of the present invention.