JP2008057629A - Rotation-linear motion converting mechanism and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rotation-linear motion converting mechanism having sufficiently reduced manufacturing cost while suppressing a reduction in the strength and shaping accuracy of a gear. <P>SOLUTION: The rotation-linear motion converting mechanism 10 comprises a sun shaft 31, a nut 51, a planetary shaft 41, and a planetary gear 45. The sun shaft 31 has linear motion in the axial direction of a center axis 201, and the nut 51 has rotating motion around the center axis 201. The planetary shaft 41 is threaded to the sun shaft 31 and the nut 51. The planetary gear 45 is provided on the planetary shaft 41 for revolving around the center axis 201 while self-rotating together with the planetary shaft 41. The planetary gear 45 includes gear components 145x, 145y, 145z arranged in the axial direction of the center axis 201 and connected to one another. The gear components 145 are sintered products, metal powder injection-molded products, resin molded products or cold forged products. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention generally relates to a rotation-linear motion conversion mechanism and a manufacturing method thereof, and more specifically, a planetary differential screw type rotation-linear motion that converts an input rotational motion into a linear motion and outputs the linear motion. The present invention relates to a dynamic conversion mechanism and a manufacturing method thereof.

Regarding a conventional rotation-linear motion conversion mechanism, for example, Japanese Patent Laid-Open No. 10-196757 discloses a rotation-linear motion conversion mechanism for the purpose of improving efficiency and reducing the amount of linear motion per rotation. (Patent Document 1). The rotation-linear motion conversion mechanism disclosed in Patent Document 1 is composed of a roller screw mechanism including a shaft, a roller, and a nut. The shaft, roller and nut are threaded. The rotational movement of the nut is sequentially transmitted to the roller and the shaft through screwing between the screws, and the shaft moves linearly. The roller and nut are provided with gears. The roller revolves around the shaft while rotating while the gear provided on the roller meshes with the gear provided on the nut.
JP-A-10-196757

  In the rotation-linear motion conversion mechanism disclosed in Patent Document 1 described above, a roller is provided with a gear in order to maintain the posture of the roller that revolves around the shaft while rotating. When this gear is formed from sintering, metal injection molding (MIM), resin molding or cold forging, it reduces the manufacturing cost of gear compared to bobbing and other machining. Can be made.

  However, when the total length of the gear is long, when the gear is manufactured by sintering or MIM, a difference in density occurs between the axial end portion and the central portion of the gear. That is, when the metal powder is pressed, the pressure is easily transmitted at the end portion, and the pressure is attenuated and transmitted at the center portion, so that the density tends to decrease from the end portion toward the center portion. As a result, distortion occurs during the sintering or heat treatment of the gear, which may reduce the strength and shape accuracy of the gear. Further, when the gear is manufactured by resin molding, the density is similarly uneven, and a nest due to bubbles is easily generated. In this case as well, the strength and shape accuracy of the gear cannot be ensured sufficiently.

  On the other hand, if the gear is manufactured by cold forging when the total length of the gear is long, an excessive load is applied to the punch used for punching or forming the gear, and the life of the punch may be extremely shortened. For this reason, the manufacturing cost of a gear cannot be reduced sufficiently.

  Accordingly, an object of the present invention is to solve the above-described problems, and provide a rotation-linear motion conversion mechanism and a method for manufacturing the same that can sufficiently reduce the manufacturing cost while suppressing a decrease in the strength and shape accuracy of the gear. It is to be.

  The rotation-linear motion conversion mechanism according to the present invention is a rotation-linear motion conversion mechanism that mutually converts rotational motion and linear motion. The rotation-linear motion conversion mechanism includes a screw shaft, a nut, a planetary screw roller, and a planetary gear. The screw shaft extends along the axis and linearly moves in the axial direction. The nut rotates around the axis. The planetary screw roller is screwed onto the screw shaft and the nut. The planetary gear is provided on the planetary screw roller and revolves around the axis while rotating together with the planetary screw roller. The planetary gear includes a plurality of divided bodies arranged in the axial direction and connected to each other. The divided body is any one of a sintered product, a metal powder injection molded product, a resin molded product, and a cold forged product.

  According to the rotation / linear motion converting mechanism configured as described above, the divided body has a shape obtained by dividing the planetary gear in the axial direction, and therefore, even when the total length of the planetary gear is long, the axial direction of each divided body is The length of can be kept small. Thereby, even when the divided body is a sintered product, a metal powder injection molded product, or a resin molded product, density unevenness is prevented during molding, and a planetary gear excellent in strength and shape accuracy is obtained. Can do. Further, even when the divided body is a cold forged product, it is possible to prevent an excessive load from being applied to the punch and to extend the life of the punch. As a result, it is possible to achieve a sufficient reduction in manufacturing cost while suppressing a reduction in gear strength and shape accuracy.

  Further preferably, the screw shaft includes a gear meshing with the planetary gear. The screw shaft linearly moves in the axial direction while sliding the gear relative to the planetary gear. According to the rotation / linear motion conversion mechanism configured as described above, the total length of the planetary gear in the axial direction becomes longer due to the configuration in which the screw shaft linearly moves while the gear and the planetary gear mesh with each other. For this reason, by applying the present invention, the above-described effects can be obtained more effectively.

  Preferably, a hole extending in the axial direction is formed in the divided body. A plurality of divided bodies are connected to each other by pins press-fitted into the holes. Preferably, the plurality of divided bodies are connected to each other by an adhesive or brazing. Preferably, the divided body includes a convex portion and a concave portion. The convex portion and the concave portion are fitted between the divided bodies adjacent in the axial direction. According to the rotation / linear motion converting mechanism configured as described above, a plurality of divided bodies can be coupled to each other with a simple configuration.

  Preferably, the plurality of divided bodies have the same shape. According to the rotation / linear motion converting mechanism configured as described above, it is possible to simplify the manufacturing and management of the divided body and reduce the manufacturing cost of the planetary gear.

  Preferably, the divided body is any one of a sintered product, a metal powder injection molded product, and a resin molded product. The plurality of divided bodies include a first divided body and a second divided body disposed at both ends in the axial direction, and a third divided body disposed between the first divided body and the second divided body in the axial direction. Including. The lengths of the first divided body and the second divided body in the axial direction are each smaller than the length of the third divided body in the axial direction.

  According to the rotation / linear motion conversion mechanism configured as described above, the planetary gear plays a role of maintaining the posture of the planetary screw roller that revolves around the axis while rotating. For this reason, a larger load is applied to the first divided body and the second divided body arranged at both ends than the third divided body arranged in the central portion in the axial direction. On the other hand, by making the lengths of the first divided body and the second divided body smaller than the length of the third divided body, respectively, the density of the first divided body and the second divided body can be reduced during molding of the divided body. It can be easily set larger than the density of the third divided body. Thereby, the wear resistance of the first divided body and the second divided body can be improved, and consequently the durability of the planetary gear can be improved.

  The manufacturing method of the rotation-linear motion conversion mechanism according to the present invention is a method of manufacturing a rotation-linear motion conversion mechanism that mutually converts rotational motion and linear motion. The rotation-linear motion conversion mechanism includes a screw shaft that extends along an axis and moves linearly in the axial direction, a nut that rotates about the axis, a planetary screw roller that is screwed to the screw shaft and the nut, and a planetary screw roller And a planetary gear having a plurality of divided bodies that revolves around an axis while rotating together with the planetary screw roller. The manufacturing method of the rotation-linear motion conversion mechanism includes a step of manufacturing a plurality of divided bodies by any one of sintering, metal powder injection molding, resin molding, and cold forging, and the plurality of divided bodies in the axial direction. Arranging and connecting to each other.

  According to the manufacturing method of the rotation / linear motion converting mechanism configured as described above, it is possible to sufficiently reduce the manufacturing cost while suppressing a decrease in the strength and shape accuracy of the gear.

  As described above, according to the present invention, it is possible to provide a rotation-linear motion conversion mechanism and a method for manufacturing the same, in which a reduction in manufacturing cost can be sufficiently achieved while suppressing a reduction in gear strength and shape accuracy.

  Embodiments of the present invention will be described with reference to the drawings. In the drawings referred to below, the same or corresponding members are denoted by the same reference numerals.

(Embodiment 1)
FIG. 1 is a front view showing a variable valve lift mechanism to which a rotation / linear motion conversion mechanism according to Embodiment 1 of the present invention is connected. FIG. 2 is a perspective view partially showing the variable valve lift mechanism in FIG. In FIG. 2, a part is broken and shown so that the internal structure can be clearly understood.

  Referring to FIGS. 1 and 2, variable valve lift mechanism 100 is a mechanism that varies the valve lift amount of a valve of the internal combustion engine (in this embodiment, an intake valve). The internal combustion engine may be a gasoline engine or a diesel engine. Although not shown in the drawing to be referred to, a rotation-linear motion conversion mechanism in the present embodiment for linearly moving the drive shaft 20 is connected to the tip of the drive shaft 20 in the drawing.

  The variable valve lift mechanism 100 is provided in the cylinder head of the internal combustion engine. In the cylinder head, a cam shaft 102 on which a cam 103 is formed, a rocker arm 106 pivotally supported, and an intake valve 101 that is driven to open and close according to the rocking of the rocker arm 106 are disposed. The variable valve lift mechanism 100 includes a drive shaft 20 extending in one direction, a support pipe 108 covering the outer peripheral surface of the drive shaft 20, and an input arranged side by side in the axial direction of the drive shaft 20 on the outer peripheral surface of the support pipe 108. An arm 104 and a swing cam 105 are provided.

  In this internal combustion engine, a pair of intake valves 101 and a rocker arm 106 are provided for each cylinder, and the pair of intake valves 101 are driven to open and close by a single cam 103. The variable valve lift mechanism 100 is provided with one input arm 104 corresponding to one cam 103 provided in each cylinder. Two swing cams 105 are provided on both sides of the input arm 104 corresponding to each of the pair of intake valves 101 provided in each cylinder.

  The support pipe 108 is formed in a hollow cylindrical shape and is disposed in parallel to the camshaft 102. The support pipe 108 is fixed to the cylinder head so as not to move or rotate in the axial direction. The drive shaft 20 is inserted into the support pipe 108 so as to be slidable in the axial direction. An input arm 104 and two swing cams 105 are provided on the outer peripheral surface of the support pipe 108 so as to be swingable about the axis of the drive shaft 20 and not to move in the axial direction. Yes.

  The input arm 104 includes an arm portion 104a that protrudes in a direction away from the outer peripheral surface of the support pipe 108, and a roller portion 104b that is rotatably connected to the tip of the arm portion 104a. The input arm 104 is provided at a position where the roller portion 104 b can come into contact with the cam 103.

  The swing cam 105 has a substantially triangular nose portion 105 a that protrudes away from the outer peripheral surface of the support pipe 108. A cam surface 105b that is curved in a concave shape is formed on one side (the lower side in FIG. 1) of the nose portion 105a. The intake valve 101 is provided with a valve spring. Due to the urging force, the roller 106a rotatably attached to the rocker arm 106 is pressed against the cam surface 105b.

  The input arm 104 and the swing cam 105 swing integrally around the axis of the drive shaft 20. For this reason, when the camshaft 102 rotates, the input arm 104 in contact with the cam 103 swings, and the swing cam 105 swings in conjunction with the movement of the input arm 104. The movement of the swing cam 105 is transmitted to the intake valve 101 via the rocker arm 106, and thereby the intake valve 101 is driven to open and close.

  The variable valve lift mechanism 100 is further provided with a mechanism for changing the relative phase difference between the input arm 104 and the swing cam 105 around the axis of the support pipe 108, and by this mechanism, the valve lift of the intake valve 101 is changed. Change the amount accordingly. That is, if the relative phase difference between the two is increased, the swing angle of the rocker arm 106 with respect to the swing angle of the input arm 104 and the swing cam 105 is increased, and the valve lift amount of the intake valve 101 is increased. If the relative phase difference between the two is reduced, the swing angle of the rocker arm 106 with respect to the swing angle of the input arm 104 and the swing cam 105 is reduced, and the valve lift amount of the intake valve 101 is reduced.

  Next, the mechanism for changing the relative phase difference will be described in more detail. As shown in FIG. 2, the space defined between the input arm 104 and the two swing cams 105 and the outer peripheral surface of the support pipe 108 is rotatable with respect to the support pipe 108 and has a shaft. A slider gear 107 is slidably supported in the direction.

The slider gear 107 is provided with a helical gear 107b in which a right-hand spiral helical spline is formed at the center in the axial direction. Further, the slider gear 107 is provided with helical gears 107c that are located on both sides of the helical gear 107b and in which a helical spline having a left-handed spiral shape is formed opposite to the helical gear 107b.

  On the other hand, helical splines corresponding to the helical gears 107b and 107c are formed on the surfaces of the input arm 104 and the two swing cams 105 that define a space for accommodating the slider gear 107, respectively. That is, the input arm 104 is formed with a right-hand spiral helical spline, and the helical spline meshes with the helical gear 107b. Further, the swing cam 105 is formed with a helical spline having a left-hand thread, and the helical spline meshes with the helical gear 107c.

  The slider gear 107 is formed with a long hole 107a extending between the one helical gear 107c and the helical gear 107b and extending in the circumferential direction. The support pipe 108 is formed with a long hole 108a extending in the axial direction so as to overlap a part of the long hole 107a. The drive shaft 20 inserted into the support pipe 108 is integrally provided with a locking pin 20a that protrudes through the overlapping portion of the two long holes 107a and 108a.

  When the drive shaft 20 moves in the axial direction, the slider gear 107 is pushed by the locking pin 20a, so that the helical gears 107b and 107c move in the axial direction of the drive shaft 20 at the same time. In response to the movement of the helical gears 107b and 107c, the input arm 104 and the swing cam 105 that are spline-engaged with the helical gears 107b and 107c do not move in the axial direction. To turn. At this time, since the input arm 104 and the swing cam 105 have the opposite directions of the formed helical splines, the rotation directions are opposite to each other. As a result, the relative phase difference between the input arm 104 and the swing cam 105 changes, and the valve lift amount of the intake valve 101 is changed as described above.

  FIG. 3 is a cross-sectional view showing a rotation / linear motion conversion mechanism connected to the variable valve lift mechanism in FIG. 1. Next, the structure of the rotation / linear motion conversion mechanism in the present embodiment will be described.

  Referring to FIG. 3, the rotation-linear motion conversion mechanism 10 is disposed on a sun shaft 31 extending on a central axis 201 that is a virtual axis, and on the outer periphery of the sun shaft 31, and its circumferential direction is centered on the central axis 201. A plurality of planetary shafts 41, planetary gears 45 provided on the planetary shafts 41, and nuts 51 provided so as to surround the plurality of planetary shafts 41. The rotation / linear motion conversion mechanism 10 is accommodated in a housing 66.

  The sun shaft 31 is arranged on the central axis 201 so as to be aligned with the drive shaft 20 in FIG. The sun shaft 31 is connected to the drive shaft 20 by a coupling mechanism such as a coupling mechanism (not shown). The sun shaft 31 pushes and pulls the drive shaft 20 in the axial direction of the central shaft 201.

  Sunshaft 31 includes a threaded portion 33 and a gear portion 34. The threaded portion 33 is constituted by a male screw formed on the outer peripheral surface of the sun shaft 31. The gear part 34 is formed on the outer peripheral surface of the sun shaft 31 and is constituted by a spur gear with teeth centered around the central axis 201 in the circumferential direction. The screw portion 33 and the gear portion 34 are arranged in the axial direction of the central shaft 201. The sun shaft 31 includes a shaft portion 31p. A screw portion 33 is formed between the shaft portion 31 p and the gear portion 34 in the axial direction of the central shaft 201.

  Sunshaft 31 includes a spline portion 32. The spline portion 32 is configured by a spline formed on the outer peripheral surface of the sun shaft 31. The housing 66 is provided with a detent collar 58. Splines are formed on the inner peripheral surface of the rotation stop collar 58. The rotation of the sun shaft 31 around the central axis 201 is restricted by the spline formed on the rotation stop collar 58 and the spline portion 32 engaging with each other.

  Sun shaft 31 includes a sun gear 35. In the present embodiment, the sun gear 35 is fitted to the shaft portion 31p. On the outer peripheral surface of the sun gear 35, a spur gear having teeth arranged in the circumferential direction around the central axis 201 is formed. The gear portion 34 and the sun gear 35 have substantially the same pitch circle diameter. The sun gear 35 may be formed integrally with the sun shaft 31. The sun gear 35 may be fixed to a member other than the sun shaft 31, for example, a lid 67 that closes the opening of the housing 66.

  The nut 51 has a cylindrical shape centered on the central axis 201. The nut 51 is supported by a bearing 59 so as to be rotatable about the central shaft 201. The nut 51 is disposed with a gap between it and the sun shaft 31. The nut 51 includes a threaded portion 52. The threaded portion 52 is configured by an internal thread formed on the inner peripheral surface of the nut 51. The screw part 52 is provided on the outer periphery of the screw part 33 of the sun shaft 31. The female screw constituting the screw part 52 is opposite to the male screw constituting the screw part 33.

  A ring gear 50 is fixed to the nut 51. The ring gear 50 is provided on each side of the threaded portion 52 along the axial direction of the central shaft 201. Ring gear 50 is provided on the outer periphery of gear portion 34 and sun gear 35. On the inner peripheral surface of the ring gear 50, a spur gear is formed with teeth arranged in the circumferential direction around the central axis 201.

  The rotation-linear motion conversion mechanism 10 includes a motor 61 that inputs a rotational motion to the nut 51. The motor 61 includes a rotor 62 fixed to the nut 51, and a stator 63 disposed on the outer periphery of the rotor 62 and wound with a coil 65. By energizing the coil 65, the nut 51 rotates about the central axis 201 together with the rotor 62.

  FIG. 4 is a cross-sectional view of the rotation-linear motion conversion mechanism along the line IV-IV in FIG. FIG. 5 is a cross-sectional view of the rotation / linear motion conversion mechanism along the line VV in FIG. 3. Referring to FIGS. 3 to 5, planetary shaft 41 extends on central axis 211 that is a virtual axis. The central axis 211 is an axis parallel to the central axis 201.

  The planetary shaft 41 is disposed in the gap between the sun shaft 31 and the nut 51. Planetary shaft 41 includes a screw portion 42 and a gear portion 43. The screw part 42 and the gear part 43 are arranged in the axial direction of the central axis 211. The screw portion 42 is constituted by a male screw formed on the outer peripheral surface of the planetary shaft 41. The screw portion 42 is screwed into the screw portion 33 of the sun shaft 31 and the screw portion 52 of the nut 51. The male screw constituting the screw portion 42 is in the same direction as the male screw constituting the screw portion 33 and is opposite to the female screw constituting the screw portion 52.

  The male screw constituting the screw portion 33 of the sun shaft 31, the male screw constituting the screw portion 42 of the planetary shaft 41, and the female screw constituting the screw portion 52 of the nut 51 are all multi-threaded screws having the same pitch. The pitch circle diameters of these screws are Ds, Dp and Dn, respectively, and the number of threads of each screw is Ns, Np and Nn, respectively. In this embodiment, since the sun shaft 31 is stroked in the axial direction of the central axis 201, for example, the number of threads of each screw is determined so as to satisfy the relationship of Ns: Np: Nn = (Ds + 1): Dp: Dn. ing. It should be noted that the pitch circle diameter and the number of threads of each screw may take other relationships.

  The gear portion 43 is constituted by a spur gear formed on the outer peripheral surface of the planetary shaft 41. The gear portion 43 meshes with the gear portion 34 of the sun shaft 31 and the ring gear 50.

  Planetary shaft 41 includes a shaft portion 41p. A screw portion 42 is formed between the shaft portion 41 p and the gear portion 43 in the axial direction of the central shaft 211. A planetary gear 45 is inserted into the shaft portion 41p. The planetary gear 45 is fitted into the shaft portion 41p with a gap. On the outer peripheral surface of the planetary gear 45, a spur gear having teeth arranged in the circumferential direction around the central shaft 211 is formed. The planetary gear 45 and the gear part 43 have substantially the same pitch circle diameter. The planetary gear 45 meshes with the sun gear 35 and the ring gear 50. The length of the planetary gear 45 in the axial direction of the central shaft 201 is larger than the length of the sun gear 35 in the axial direction of the central shaft 201.

  When the planetary gear 45 is formed integrally with the planetary shaft 41, an excessive load may be applied to the planetary shaft 41 if a phase shift occurs between the rotation of the planetary gear 45 and the gear portion 43. In the present embodiment, since the planetary gear 45 is provided on the planetary shaft 41 with a backlash, such a shift can be absorbed.

  When the nut 51 rotates, the rotational motion is transmitted to the planetary shaft 41 by the meshing of the threaded portion between the nut 51 and the planetary shaft 41. At this time, the gear portion 43 of the planetary shaft 41, the ring gear 50, and the gear portion 34 of the sun shaft 31 are engaged with each other, and the planetary gear 45, the ring gear 50, and the sun gear 35 are engaged with each other. The planetary shaft 41 revolves around the central axis 201 while rotating while remaining stationary in the axial direction of the central axis 201. At this time, the planetary shaft 41 is held in a constant posture parallel to the axial direction of the central shaft 201 by the meshing of the spur gear.

  The rotational movement of the planetary shaft 41 is transmitted to the sun shaft 31 by the engagement of the threaded portion between the planetary shaft 41 and the sun shaft 31. As a result, the sun shaft 31 linearly moves in the axial direction of the central axis 201.

  FIG. 6 is a diagram showing the planetary gear in FIG. FIG. 6 shows a front view of the planetary gear 45 and a cross-sectional view of the planetary gear 45 along the line AA in the front view. FIG. 7 is an exploded view of the planetary gear in FIG.

  6 and 7, planetary gear 45 is a sintered product obtained by sintering metal powder. The planetary gear 45 is formed with a hole 148 into which the shaft portion 41p is inserted. The hole 148 is a through hole extending on the central axis 211.

  The planetary gear 45 includes a gear component 145x, a gear component 145y, and a gear component 145z (referred to as a gear component 145 unless they are particularly distinguished). The gear component 145x, the gear component 145y, and the gear component 145z are arranged in the axial direction of the central shaft 211, that is, the axial direction of the central shaft 201 in FIG. In the axial direction of the central shaft 211, the gear component 145 x and the gear component 145 z are disposed at both ends of the planetary gear 45. The gear part 145y is provided between the gear part 145x and the gear part 145z. The planetary gear 45 may be divided into a plurality of gear parts 145 other than three.

  Gear component 145 includes end faces 145a and 145b. Between the adjacent gear parts 145, the end surface 145a and the end surface 145b face each other. A pin hole 149 is formed in the gear component 145. The pin hole 149 extends in the axial direction of the central axis 211. The pin hole 149 extends from the end surface 145 a to the end surface 145 b and penetrates the gear part 145. The gear component 145 includes a tooth portion 46 having a relatively large diameter and a trough portion 47 having a relatively small diameter. The pin hole 149 is formed on the inner peripheral side of the tooth portion 46. Thereby, compared with the case where the pin hole 149 is formed in the inner peripheral side of the trough part 47, the intensity | strength of the gear component 145 can be ensured more reliably. A pin 81 is press-fitted into a pin hole 149 formed in the gear parts 145x, 145y and 145z. With such a configuration, the gear component 145x, the gear component 145y, and the gear component 145z are integrally connected.

  Instead of the pins 81, the gear components 145x, 145y, and 145z may be connected to each other using an adhesive member such as an adhesive or brazing. In these cases, the gear parts can be connected with a simpler configuration. On the other hand, when the pin 81 is used, there is no possibility that the adhesive member protrudes from the mating surface of the end surface 145a and the end surface 145b, so that the tooth surface shape can be accurately maintained. In addition, a keyway may be formed in the gear part 145, and the gear parts 145x, 145y, and 145z may be connected to each other by a key inserted into the keyway.

  Then, the manufacturing method of the rotation-linear motion conversion mechanism 10 is demonstrated. FIG. 8 is a flowchart showing a process of manufacturing the planetary gear in FIG. Referring to FIG. 8, first, metal powder is put into a mold and press-molded. The pressure acts in a direction along the gear shaft (center axis 211 in FIG. 6). At this time, the mold surface may be coated with a lubricant. Thereby, the surface roughness of the mold is improved, and the frictional resistance between the mold and the powder is reduced. Thereby, the density distribution of a molded object can be made uniform.

  Next, the molded body obtained in the previous step is sintered. Next, sizing is performed on the compact, and the inner diameter of the gear and the shape accuracy of the tooth surface are secured. Next, in order to improve the corrosion resistance and wear resistance of the gear, the molded body is held in water vapor. At this time, since the triiron tetroxide film is formed on the surface of the molded body, the mechanical strength of the gear is improved.

  Next, carburizing and quenching is performed as a heat treatment. At this time, in order to suppress distortion during the heat treatment, the heat treatment may be performed while restraining the outer peripheral portion of the molded body. Next, barrel polishing is performed to remove burrs formed on the molded body. Next, a cleaning process is performed. The gear parts 145x, 145y, and 145z are completed through the steps so far. Next, the gear parts 145x, 145y and 145z are connected by press-fitting the pin 81 into the pin hole 149. Through the above steps, the planetary gear 45 is completed.

  In the rotation-linear motion conversion mechanism 10 in the present embodiment, the sun shaft 31 linearly moves in the axial direction of the central axis 201 while the planetary gear 45 and the sun gear 35 slide. At this time, since the planetary gear 45 and the sun gear 35 are kept in mesh with each other at the stroke end of the sun shaft 31 in the axial direction of the central shaft 201, the total length of the planetary gear 45 in the axial direction of the central shaft 201 is increased. . That is, in FIG. 3, the length of the planetary gear 45 in the axial direction of the central shaft 201 is larger than the stroke length of the sun shaft 31. The length of the planetary gear 45 in the axial direction of the central shaft 201 is at least larger than the total length of the stroke length of the sun shaft 31 and the length of the sun gear 35 in the axial direction of the central shaft 201.

  When the long planetary gear 45 is manufactured by sintering, the pressure acting on the metal powder is increased at the end along the axial direction of the central shaft 201 during the pressure forming process in FIG. The tendency to become small occurs remarkably. For this reason, variation occurs in the density of the molded body. In contrast, in the present embodiment, the length of each gear component 145 can be kept small by dividing the planetary gear 45 into gear components 145x, 145y, and 145z. Thereby, the gear component 145 can be finished into a sintered body having a more uniform density distribution.

  In addition, bubbles exist inside the planetary gear 45 manufactured by sintering. For this reason, it is possible to improve the wear resistance and seizure resistance of the planetary gear 45 by containing oil in the bubbles.

  The rotation-linear motion converting mechanism 10 according to Embodiment 1 of the present invention includes a sun shaft 31 as a screw shaft, a nut 51, a planetary shaft 41 as a planetary screw roller, and a planetary gear 45. The sun shaft 31 extends along the central axis 201 as an axis, and linearly moves in the axial direction of the central axis 201. The nut 51 rotates around the central axis 201. The planetary shaft 41 is screwed into the sun shaft 31 and the nut 51. The planetary gear 45 is provided on the planetary shaft 41 and revolves around the central axis 201 while rotating together with the planetary shaft 41. The planetary gear 45 includes gear parts 145x, 145y, and 145z as a plurality of divided bodies that are arranged in the axial direction of the central shaft 201 and connected to each other. The gear part 145 is a sintered product as one of a sintered product, a metal powder injection molded product, a resin molded product, and a cold forged product. Sintering and metal powder injection molding are manufacturing methods that include a step of pressure molding metal powder. Sintering and metal powder injection molding are manufacturing methods further comprising a step of heat-treating a molded body obtained by pressure molding.

  According to the rotation / linear motion converting mechanism 10 according to Embodiment 1 of the present invention configured as described above, the planetary gear 45 is manufactured as a sintered product, compared with the case where it is manufactured by machining. Cost can be reduced. Even when the planetary gear 45 having a long overall length is a sintered product, the planetary gear 45 can be divided into a plurality of gear parts 145 to suppress variation in density inside the gear part 145. Thereby, distortion can be suppressed during the sintering process or the heat treatment process in FIG. 8, and the planetary gear 45 having excellent strength and shape accuracy can be finished. Thereby, durability of the rotation-linear motion conversion mechanism 10 can be improved. Moreover, the conversion efficiency of the motion between rotation and linear motion can be improved.

  In the present embodiment, the rotation-linear motion conversion mechanism according to the present invention is connected to the variable valve lift mechanism of the internal combustion engine. However, the present invention is not limited to this and can be connected to various mechanisms that require linear drive. . The present invention can also be applied to a rotation-linear motion conversion mechanism that converts an input linear motion into a rotational motion and outputs the rotational motion.

  Next, an embodiment in which the density of the planetary gear 45 in FIG. 6 is evaluated will be described. FIG. 9 is a graph showing the density of the planetary gear in FIG.

  Referring to FIG. 9, planetary gear 45 manufactured according to the process in FIG. 8 was prepared, and the density of gear component 145x, gear component 145y and gear component 145z constituting planetary gear 45 was measured. The gear part 145x, the gear part 145y, and the gear part 145z are set to the measurement positions “front”, “middle”, and “rear”, respectively, and the results are shown in FIG. For comparison, a planetary gear 45 integrally manufactured from metal powder was prepared, and the density at positions corresponding to the gear components 145x, 145y, and 145z was measured.

  As can be seen with reference to FIG. 9, in the comparative example in which the planetary gear 45 is integrally formed, a high density distribution occurred at the measurement positions “front” and “rear” and a low density distribution at the measurement position “medium”. On the other hand, in the example in which the planetary gear 45 was divided and formed, it was confirmed that a substantially uniform density distribution was obtained regardless of the measurement position.

(Embodiment 2)
In the present embodiment, various modifications of the planetary gear 45 in FIG. 6 will be described.

  FIG. 10 is a cross-sectional view showing a first modification of the planetary gear in FIG. Referring to FIG. 10, in this modification, gear components 145x, 145y, and 145z have the same shape. The gear component 145 includes a chamfered portion 82. The chamfered portion 82 is formed at a corner where the end surface 145a and the tooth surface intersect, and at a corner where the end surface 145b and the tooth surface intersect. The chamfered portion 82 is formed at a position where the tooth surfaces are adjacent between the gear parts 145 adjacent to each other.

  By making the gear components 145x, 145y, and 145z have the same shape, manufacturing and management of the gear component 145 can be simplified. Thereby, the manufacturing cost of the planetary gear 45 can be reduced. Further, by forming the chamfered portion 82, the sun gear 35 can be slid more smoothly with respect to the planetary gear 45 during the linear motion of the sun shaft 31.

  FIG. 11 is a cross-sectional view showing a second modification of the planetary gear in FIG. Referring to FIG. 11, in this modification, pin hole 149 in FIG. 6 is not formed in gear component 145. The gear component 145 includes a concave portion 85 and a convex portion 86. The recess 85 is recessed from the end surface 145a. The convex part 86 protrudes from the end surface 145b. The concave portion 85 and the convex portion 86 are fitted between the adjacent gear parts 145. With such a configuration, in this modification, the gear parts 145x, 145y, and 145z are connected to each other by the fitting of the concave portion 85 and the convex portion 86. A plurality of concave portions 85 and convex portions 86 may be formed in the gear component 145.

  FIG. 12 is a cross-sectional view showing a third modification of the planetary gear in FIG. Referring to FIG. 12, in this modification, pin hole 149 in FIG. 6 is not formed in gear component 145. A snap ring groove 91 is formed in the shaft portion 41p. A snap ring 92 is fitted in the snap ring groove 91. With such a configuration, the gear components 145x, 145y, and 145z are coupled to each other by the snap ring 92.

  FIG. 13 is a cross-sectional view showing a fourth modification of the planetary gear in FIG. Referring to FIG. 13, in this modification, gear component 145 x and gear component 145 z have a length L <b> 1 and a length L <b> 2 in the axial direction of central shaft 211, respectively, and gear component 145 y is a component of central shaft 211. It has a length L3 in the axial direction. L1 and L2 are each smaller than L3.

  The planetary gear 45 plays a role of holding the planetary shaft 41 in a constant posture parallel to the central axis 201. When the planetary shaft 41 is inclined with respect to the central axis 201, the planetary shaft 41 is larger than the gear components 145 x and 145 z disposed at both ends than the gear components 145 y disposed at the center in the axial direction of the central shaft 201. Load acts.

  On the other hand, in this modification, the length of the gear components 145x and 145z is smaller than the length of the gear component 145y. For this reason, the density of the gear parts 145x and 145z can be easily set larger than the density of the gear part 145y during the pressure forming step in FIG. 8, and as a result, the strength of the gear parts 145x and 145z is improved. Can be made. Thereby, durability of the planetary gear 45 can be improved more effectively.

  According to the rotation / linear motion converting mechanism according to the second embodiment of the present invention configured as described above, the same effects as those described in the first embodiment can be obtained.

(Embodiment 3)
FIG. 14 is a flowchart showing a process for manufacturing a planetary gear in the rotation-linear motion converting mechanism according to Embodiment 3 of the present invention. The rotation-linear motion conversion mechanism in the present embodiment has basically the same structure as the rotation-linear motion conversion mechanism 10 in the first embodiment. Hereinafter, the description of the overlapping structure will not be repeated.

  Referring to FIG. 14, in the present embodiment, planetary gear 45 is formed by metal powder injection molding (MIM). The manufacturing process of the planetary gear 45 will be described. First, metal powder and a binder are kneaded. Next, a pellet is produced from the kneaded material obtained. Next, a gear is formed from the pellets with an injection molding machine. Next, the binder is removed from the gear by sintering.

  Next, the gears are quenched and tempered as heat treatment. At this time, a jig provided with a recess for positioning the gears at predetermined intervals may be used so that the parts do not overlap each other. Further, the heat treatment may be performed while restraining the outer diameter of the gear so that no distortion occurs during the heat treatment. Next, barrel polishing is performed to remove burrs formed on the molded body. Next, the gear is cleaned. The gear parts 145x, 145y, and 145z are completed through the steps so far. Next, the gear parts 145x, 145y and 145z are connected by press-fitting the pin 81 into the pin hole 149. Through the above steps, the planetary gear 45 is completed.

  In the present embodiment, by dividing the planetary gear 45 into a plurality of gear parts 145, it is possible to suppress the occurrence of a density difference in the gear part 145 during injection molding in FIG. Thereby, the planetary gear 45 excellent in strength and shape accuracy can be produced. Moreover, high density can be ensured by using the planetary gear 45 as an MIM product. Thereby, the intensity | strength of the planetary gear 45 can be improved.

  According to the rotation / linear motion converting mechanism according to the third embodiment of the present invention configured as described above, the same effects as those described in the first embodiment can be obtained.

(Embodiment 4)
FIG. 15 is a flowchart showing a process for manufacturing a planetary gear in the rotation-linear motion converting mechanism according to Embodiment 4 of the present invention. The rotation-linear motion conversion mechanism in the present embodiment has basically the same structure as the rotation-linear motion conversion mechanism 10 in the first embodiment. Hereinafter, the description of the overlapping structure will not be repeated.

  Referring to FIG. 15, in the present embodiment, planetary gear 45 is formed by resin molding. The manufacturing process of the planetary gear 45 will be described. First, pellets made of a resin material are prepared. The pellets are filled into a cylinder of an injection molding machine, and injection, pressure holding, and cooling steps are sequentially performed. Next, the resin molded gear is taken out from the injection molding machine. The gear parts 145x, 145y, and 145z are completed through the steps so far. Next, the gear parts 145x, 145y and 145z are connected by press-fitting the pin 81 into the pin hole 149. Through the above steps, the planetary gear 45 is completed.

  In the present embodiment, by dividing the planetary gear 45 into a plurality of gear parts 145, it is possible to suppress the occurrence of a density difference in the gear part 145 during injection molding in FIG. Thereby, the planetary gear 45 excellent in strength and shape accuracy can be produced. Moreover, the planetary gear 45 can be reduced in weight by using the planetary gear 45 as a resin molded product.

  According to the rotation / linear motion converting mechanism according to the fourth embodiment of the present invention configured as described above, the same effect as that described in the first embodiment can be obtained.

(Embodiment 5)
FIG. 16 is a flowchart showing steps for manufacturing a planetary gear in the rotation-linear motion converting mechanism according to Embodiment 5 of the present invention. The rotation-linear motion conversion mechanism in the present embodiment has basically the same structure as the rotation-linear motion conversion mechanism 10 in the first embodiment. Hereinafter, the description of the overlapping structure will not be repeated.

  Referring to FIG. 16, in the present embodiment, planetary gear 45 is formed by cold forging. The manufacturing process of the planetary gear 45 will be described. First, the coil material is cut into a blank shape. Next, a flat surface is given to the end face of the coil material by a forging process. Next, punching is performed to form a hole 148 in the coil material. Next, a tooth surface shape is provided to the outer peripheral surface of the coil material by a forging process, and a gear is formed. Next, sizing is performed on the hole 148 to ensure the accuracy of the inner diameter.

  Next, the gear is cleaned. Next, a carbonitriding process as a heat treatment is performed on the gear. Next, finishing pressing and barrel polishing are sequentially performed on the inner diameter of the gear. Next, the gear is washed again, and then the gear is subjected to rust prevention treatment. The gear parts 145x, 145y, and 145z are completed through the steps so far. Next, the gear parts 145x, 145y and 145z are connected by press-fitting the pin 81 into the pin hole 149. Through the above steps, the planetary gear 45 is completed.

  When the planetary gear 45 having a long overall length is manufactured by cold forging, it is necessary to repeat the press work in a plurality of times during the punching process or the tooth surface forging process in FIG. In this case, an excessive load is applied to the punch used for the press work, and the punch life may be extremely shortened. On the other hand, in the present embodiment, the planetary gear 45 is divided into a plurality of gear parts 145, whereby the load on the punch can be reduced. As a result, the life of the punch can be increased, and the manufacturing cost of the rotation / linear motion conversion mechanism can be reduced.

  According to the rotation / linear motion converting mechanism in the fifth embodiment of the present invention configured as described above, the same effects as those described in the first embodiment can be obtained.

  In addition, you may comprise a new rotation-linear motion conversion mechanism by combining the structure of the planetary gear demonstrated above suitably.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

It is a front view which shows the valve lift variable mechanism to which the rotation-linear motion conversion mechanism in Embodiment 1 of this invention is connected. It is a perspective view which shows partially the valve lift variable mechanism in FIG. It is sectional drawing which shows the rotation-linear motion conversion mechanism connected to the valve lift variable mechanism in FIG. It is sectional drawing of the rotation-linear motion conversion mechanism along the IV-IV line in FIG. It is sectional drawing of the rotation-linear motion conversion mechanism along the VV line in FIG. It is a figure which shows the planetary gear in FIG. FIG. 4 is an exploded view of the planetary gear in FIG. 3. It is a flowchart figure which shows the process of manufacturing the planetary gear in FIG. It is a graph which shows the density of the planetary gear in FIG. It is sectional drawing which shows the 1st modification of the planetary gear in FIG. It is sectional drawing which shows the 2nd modification of the planetary gear in FIG. It is sectional drawing which shows the 3rd modification of the planetary gear in FIG. It is sectional drawing which shows the 4th modification of the planetary gear in FIG. It is a flowchart figure which shows the process of manufacturing a planetary gear in the rotation-linear motion conversion mechanism in Embodiment 3 of this invention. It is a flowchart figure which shows the process of manufacturing a planetary gear in the rotation-linear motion conversion mechanism in Embodiment 4 of this invention. It is a flowchart figure which shows the process of manufacturing a planetary gear in the rotation-linear motion conversion mechanism in Embodiment 5 of this invention.

Explanation of symbols

  10 rotation-linear motion conversion mechanism, 31 sun shaft, 41 planetary shaft, 45 planetary gear, 51 nut, 81 pin, 85 concave portion, 86 convex portion, 145, 145x, 145y, 145z gear parts, 149 pin hole, 201 central axis .

Claims (8)

A rotation-linear motion conversion mechanism that converts rotational motion and linear motion to each other,
A screw shaft extending along an axis and linearly moving in the axial direction;
A nut that rotates about the axis;
A planetary screw roller threadably engaged with the screw shaft and the nut;
A planetary gear provided on the planetary screw roller and revolving around the axis while rotating together with the planetary screw roller;
The planetary gear includes a plurality of divided bodies arranged in the axial direction and connected to each other, and the divided bodies are any of sintered products, metal powder injection molded products, resin molded products, and cold forged products. There is a rotation-linear motion conversion mechanism. The screw shaft includes a gear meshing with the planetary gear,
The rotation-linear motion converting mechanism according to claim 1, wherein the screw shaft linearly moves in the axial direction while sliding the gear with respect to the planetary gear. A hole extending in the axial direction is formed in the divided body,
The rotation-linear motion conversion mechanism according to claim 1 or 2, wherein the plurality of divided bodies are connected to each other by a pin press-fitted into the hole.   The rotation-linear motion conversion mechanism according to any one of claims 1 to 3, wherein the plurality of divided bodies are connected to each other by an adhesive or brazing. The divided body includes a convex portion and a concave portion,
The rotation-linear motion conversion mechanism according to any one of claims 1 to 4, wherein the convex portion and the concave portion are fitted between the divided bodies adjacent in the axial direction.   The rotation-linear motion conversion mechanism according to any one of claims 1 to 5, wherein the plurality of divided bodies have the same shape. The divided body is one of a sintered product, a metal powder injection molded product, and a resin molded product,
The plurality of divided bodies include a first divided body and a second divided body disposed at both ends in the axial direction, and a third divided body disposed between the first divided body and the second divided body, Including
The length of the said 1st division body in the said axial direction and the said 2nd division body is respectively smaller than the length of the said 3rd division body in the said axial direction, The any one of Claim 1 to 6 Rotation-linear motion conversion mechanism. A method of manufacturing a rotation-linear motion conversion mechanism that converts rotational motion and linear motion to each other,
The rotation-linear motion conversion mechanism is
A screw shaft extending along an axis and linearly moving in the axial direction;
A nut that rotates about the axis;
A planetary screw roller threadably engaged with the screw shaft and the nut;
A planetary gear provided on the planetary screw roller, revolving around the axis while rotating together with the planetary screw roller, and having a plurality of divided bodies;
A step of producing a plurality of the divided bodies by any one of sintering, metal powder injection molding, resin molding and cold forging;
A plurality of divided bodies arranged in the axial direction and connected to each other.

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