JP2010060066A - Planetary differential type motion converting mechanism - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a planetary differential type motion converting mechanism, in which biased abrasions and defects caused due to a tilt state of a planetary shaft can be restrained from occurring in screws and gears formed in the planetary shaft and occurring in screws and tooth faces of the gears engaged with these screws and the gears. <P>SOLUTION: A bearing hole 34, penetrating along an axial direction, is made in a planetary gear 32b on a rear side of the planetary shaft 30 and besides a shaft 33 extending along its axial direction is made in an intermediate portion 35 of the planetary shaft 30. Furthermore, In the shaft 33, a displacement restricting portion 40a for restricting a rear-side planetary gear 32b from being displaced so as to come closer to a sun shaft 20 is formed integrally with a cover 40 and a penetrated part 33a which is penetrated from the hole 34 so as to approach from the side of the sun shaft 20. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  According to the present invention, a plurality of planetary shafts are interposed between a cylindrical rotor and a sun shaft inserted into the rotor, and a rotor is formed by utilizing the action of screws formed on these members and screwed together. This is a planetary differential motion conversion mechanism that converts the rotational motion of the shaft into the linear motion of the sunshaft.

  As such a planetary differential motion conversion mechanism, for example, the one described in Patent Document 1 is known. FIG. 9 is a configuration diagram schematically showing this motion conversion mechanism. As shown in FIG. 9, a sunshaft 20 is inserted in the cylindrical rotor 10, and a plurality of planetary shafts 30 (in FIG. 9, between these rotors 10 and the sunshaft 20). (Only one of them is shown). The planetary shaft 30 includes a pair of planetary gears 32a and 32b provided at both ends thereof, and an intermediate portion 35 that connects the planetary gears 32a and 32b. The pair of planetary gears 32 a and 32 b are respectively engaged with a pair of ring gears 12 a and 12 b fixed to the inner peripheral surface of the rotor 10 and a pair of sun gears 22 a and 22 b provided on the outer peripheral surface of the sun shaft 20. Yes. Further, a screw 31 is provided on the outer peripheral surface of the intermediate portion 35 of the planetary shaft 30, and this screw 31 is provided with a screw 11 provided in a portion between the ring gears 12 a and 12 b on the inner peripheral surface of the rotor 10, It is screwed together with both the screw 21 provided in the portion between the sun gears 22a and 22b on the outer peripheral surface of the sun shaft 20. In this motion conversion mechanism, the lead angle between the screw 11 of the rotor 10 and the screw 31 of the planetary shaft 30 is the same, while the lead of the screw 31 of the planetary shaft 30 and the screw 21 of the sun shaft 20 is the same. The corners are different.

With this structure, when the rotor 10 rotates relative to the sun shaft 20, the planetary shaft 30 rolls along the inner peripheral surface of the rotor 10 and the outer peripheral surface of the sun shaft 20. When the planetary shaft 30 rolls in this way, the planetary shaft 30 is not displaced relative to the rotor 10 in the axial direction, but the sun shaft 20 is a lead between the screw 21 and the screw 31 with respect to the rotor 10. It is displaced in the axial direction by the angle difference. That is, in such a planetary differential motion conversion mechanism, when the rotor 10 rotates relative to the sun shaft 20, the rotational motion of the rotor 10 is converted into a linear motion of the sun shaft 20.
JP 2007-192388 A

  By the way, when the rotational motion of the rotor 10 is converted into the linear motion of the sun shaft 20 as described above, a torque that tilts the planetary shaft 30 in the planetary shaft 30 may be generated. Specifically, for example, when the sun shaft 20 is driven in the direction R of FIG. 9 by the rotation of the rotor 10, the screw 31 of the planetary shaft 30 is engaged with the screw 21 of the sun shaft 20 in the direction F. A resistance load f <b> 1 is generated, and a driving load f <b> 2 in the direction R may be generated at a portion of the screw 31 of the planetary shaft 30 that meshes with the screw 11 of the rotor 10. Due to these loads f1 and f2, torque W for tilting the planetary shaft 30 counterclockwise is generated in the planetary shaft 30. Further, when the sunshaft 20 is driven in the direction F of FIG. 9, a torque for tilting the planetary shaft 30 clockwise is generated. That is, when the rotational motion of the rotor 10 is converted into the linear motion of the sunshaft 20, the planetary shaft 30 is set so that one of the planetary gears 32a and 32b is close to the sunshaft 20 and the other is close to the rotor 10. A tilting torque may be generated.

  On the other hand, in this planetary differential motion conversion mechanism, the rotor 10, the sun shaft 20 and the planetary shaft 30 are engaged with each other by a screw having different lead angles and a pair of gears arranged so as to sandwich the screw. Therefore, in order to move each member smoothly, it is necessary to provide a certain amount of clearance between the members. Here, when the clearance is provided between the members as described above, if the torque for tilting the planetary shaft 30 is generated in the planetary shaft 30 as described above, the rotor 10 and the sun shaft 20 The planetary shaft 30 is inclined so that one of the planetary gears 32 a and 32 b is close to the sun shaft 20 and the other is close to the rotor 10.

  When the planetary shaft 30 is inclined in this way, the planetary gears 32a and 32b, the ring gears 12a and 12b formed on the inner peripheral surface of the rotor 10, and the sun gears 22a and 22b formed on the outer peripheral surface of the sun shaft. At the contact portion, these gears come into contact with each other in an inclined state and come into contact with each other. Similarly, one-side contact also occurs at the meshing portions of the screw 31 of the planetary shaft 30 with the screw 11 of the rotor 10 and the screw 21 of the sun shaft 20, and uneven wear and loss of gears and screws occur at these portions. As a result, the durability of the planetary differential motion conversion mechanism may be reduced.

  The present invention has been made in view of such circumstances, and the object thereof is to provide a screw and a gear formed on the planetary shaft due to the inclination of the planetary shaft, and a screw meshing with these screws and gear. Another object of the present invention is to provide a planetary differential motion conversion mechanism that can suppress the occurrence of uneven wear or loss on the tooth surface of the gear.

Hereinafter, means for solving the above-described problems and the effects thereof will be described.
According to the first aspect of the present invention, a plurality of planetary shafts are interposed between a cylindrical rotor and a sun shaft inserted into the rotor, and a pair of planetary gears respectively provided at both ends of the planetary shaft. Of the planetary shaft for engaging the pair of planetary gears with each of the pair of ring gears provided on the inner peripheral surface of the rotor and the pair of sun gears provided on the outer peripheral surface of the sun shaft. Screws provided on the outer peripheral surface of the intermediate portion are screwed into both the screws provided on the inner peripheral surface of the rotor and the screws provided on the outer peripheral surface of the sun shaft. In the planetary differential motion conversion mechanism that converts the rotational motion of the rotor into the linear motion of the sunshaft using the difference in lead angle between the pair of planetars A bearing hole penetrating along the axial direction is formed in one of the gears, and a shaft portion extending along the axial direction is formed in the intermediate portion, and the shaft portion is connected to the planetary shaft. A planetary gear that is connected to the planetary gear by being inserted into the bearing hole of the gear, and that is in contact with the sunshaft side at a portion of the shaft portion that protrudes from the bearing hole, forms the bearing hole. The gist is that a displacement restricting member that restricts displacement so as to be close to the shaft is disposed in the vicinity of the planetary gear.

  According to a second aspect of the present invention, in the planetary differential motion converting mechanism according to the first aspect, a load directed to one of the sun shafts in the axial direction always acts on the sun shaft, and the pair of planetary The gist is that the bearing hole is formed in a planetary gear located on the opposite side of the gear from the direction of the load.

  According to a third aspect of the present invention, a plurality of planetary shafts are interposed between a cylindrical rotor and a sun shaft inserted into the rotor, and a pair of planetary gears respectively provided at both ends of the planetary shaft. Of the planetary shaft for engaging the pair of planetary gears with each of the pair of ring gears provided on the inner peripheral surface of the rotor and the pair of sun gears provided on the outer peripheral surface of the sun shaft. Screws provided on the outer peripheral surface of the intermediate portion are screwed into both the screws provided on the inner peripheral surface of the rotor and the screws provided on the outer peripheral surface of the sun shaft. In the planetary differential motion conversion mechanism that converts the rotational motion of the rotor into the linear motion of the sunshaft using the difference in lead angle between the pair of planetars A bearing hole penetrating along the axial direction is formed in one of the gears, and a shaft portion extending along the axial direction is formed in the intermediate portion, and the shaft portion is connected to the planetary shaft. A planetary gear that is connected to the planetary gear by being inserted into the bearing hole of the gear, and that is in contact with the shaft portion protruding from the bearing hole from the rotor side to form the bearing hole is connected to the rotor. The gist is that a displacement restricting member that restricts displacement so as to be close to each other is disposed in the vicinity of the planetary gear.

  According to a fourth aspect of the present invention, in the planetary differential motion conversion mechanism according to the third aspect, a load directed to one of the sun shafts in the axial direction always acts on the sun shaft, and the pair of planetary The gist is that the bearing hole is formed in a planetary gear located on the load acting direction side of the gear.

  When a pair of planetary gears are provided at both ends of the planetary shaft, the screws and gears of each member interfere when the sun shaft, planetary shaft, and rotor are assembled together, making it difficult to install the planetary differential. This will cause deterioration of the assembly of the motion conversion mechanism. Therefore, as described in claim 1 and claim 3, a bearing hole is formed in one of the pair of planetary gears, and the planetary gear and the planetary gear are inserted by inserting the shaft portion formed in the intermediate portion into the bearing hole. The structure which connects an intermediate part can be employ | adopted. Thus, by making one of the pair of planetary gears detachable from the intermediate portion, it is possible to suppress the deterioration of the assembling property of the planetary differential motion conversion mechanism.

  According to the first aspect of the present invention, the planetary gear in which the bearing hole is formed by the displacement regulating member that abuts from the sun shaft side at the portion that protrudes from the bearing hole in the shaft portion so as to be close to the sun shaft. The displacement is regulated. Therefore, when the rotational motion of the rotor is converted into the linear motion of the sunshaft, the planetary gear so that one of the pair of planetary gears in which the bearing hole is formed is close to the sunshaft and the other is close to the rotor. Even if the torque to incline the reshaft acts on the planetary shaft, the displacement restricting member restricts the planetary gear having the bearing hole formed from being displaced toward the sunshaft, and the torque. This suppresses the inclination of the planetary shaft. Therefore, according to the above configuration, there is uneven wear or chipping on the screw or gear formed on the planetary shaft due to the inclination of the planetary shaft, and on the tooth surface of the screw or gear meshing with the screw or gear. Generation | occurrence | production can be suppressed now.

  In the configuration according to claim 3, the planetary gear in which the bearing hole is formed by the displacement regulating member that abuts from the rotor side in the portion that protrudes from the bearing hole in the shaft portion is displaced so as to be close to the rotor. To regulate. Therefore, when the rotational motion of the rotor is converted into the linear motion of the sunshaft, the planetary gear so that one of the pair of planetary gears in which the bearing hole is formed is close to the rotor and the other is close to the sunshaft. Even when a torque for tilting the reshaft acts on the planetary shaft, the displacement restricting member restricts the planetary gear having the bearing hole formed therein from being displaced toward the rotor, and the torque Inclination of the planetary shaft is suppressed. Therefore, according to the above configuration, there is uneven wear or chipping on the screw or gear formed on the planetary shaft due to the inclination of the planetary shaft, and on the tooth surface of the screw or gear meshing with the screw or gear. Generation | occurrence | production can be suppressed now.

  Here, when a load directed to one of the sun shafts in the sun shaft always acts on the sun shaft, one of the pair of planetary gears located on the opposite side to the acting direction of the load is close to the sun shaft. At the same time, a torque for tilting the planetary shaft so that the other is close to the rotor always acts on the planetary shaft. Therefore, in this case, the uneven wear and loss of the screws and gears described above due to the inclination of the planetary shaft become more prominent.

  In this regard, according to the configuration of claim 2, the displacement of one of the pair of planetary gears located on the side opposite to the direction of the action of the load acting on the sunshaft so as to be close to the sunshaft is restricted. Since a displacement regulating member is provided, a torque that tilts the planetary shaft so that one of the pair of planetary gears located on the side opposite to the direction of the load action is close to the sun shaft and the other is close to the rotor. Even if it always occurs, the inclination of the planetary shaft due to the torque is suppressed. As a result, it is preferable that uneven wear or chipping occurs on the screw or gear formed on the planetary shaft due to the inclination of the planetary shaft, and on the tooth surface of the screw or gear meshing with the screw or gear. Can be suppressed.

  Moreover, according to the structure of Claim 4, the displacement control member which controls that the one located in the action direction side of the load which acts on a sun shaft among a pair of planetary gears adjoins to a rotor is displaced. Even if a torque that always inclines the planetary shaft is generated so that one of the pair of planetary gears located on the load acting direction side is close to the rotor and the other is close to the sun shaft. The inclination of the planetary shaft due to the torque is suppressed. As a result, it is preferable that uneven wear or chipping occurs on the screw or gear formed on the planetary shaft due to the inclination of the planetary shaft, and on the tooth surface of the screw or gear meshing with the screw or gear. Can be suppressed.

  According to a fifth aspect of the present invention, in the planetary differential motion conversion mechanism according to any one of the first to fourth aspects, the planetary gear fixed to the rotor and having the bearing hole formed therein is an axial direction thereof. An axial displacement restricting member that suppresses displacement is provided, and the displacement restricting member is formed integrally with the axial displacement restricting member.

  When one of the pair of planetary gears is detachable from the intermediate portion as in the configuration described in claims 1 to 4, the planetary gear in which a bearing hole is formed as described in claim 5, that is, a pair By adopting a configuration in which one of the planetary gears that can be detached from the intermediate portion is provided with an axial displacement restricting member that suppresses displacement in the axial direction, the planetary gear is driven when the motion conversion mechanism is driven. Can be prevented from being detached from the intermediate portion.

  Further, according to this configuration, since the displacement restricting member is formed integrally with the axial displacement restricting member, for example, compared to the case where the displacement restricting member is provided as a member different from the axial displacement restricting member, the planetary An increase in the number of members of the differential motion conversion mechanism can be suppressed.

  According to a sixth aspect of the present invention, a plurality of planetary shafts are interposed between a cylindrical rotor and a sun shaft inserted into the rotor, and a pair of planetary gears respectively provided at both ends of the planetary shaft. Of the planetary shaft for engaging the pair of planetary gears with each of the pair of ring gears provided on the inner peripheral surface of the rotor and the pair of sun gears provided on the outer peripheral surface of the sun shaft. Screws provided on the outer peripheral surface of the intermediate portion are screwed into both the screws provided on the inner peripheral surface of the rotor and the screws provided on the outer peripheral surface of the sun shaft. In the planetary differential motion conversion mechanism that converts the rotational motion of the rotor into the linear motion of the sun shaft using the difference in the lead angle of the planetary gear, the planetary gear A magnet that is made of a magnetic material and urges the planetary gear toward the sunshaft side by magnetic force to suppress displacement of the planetary gear so as to be close to the rotor is disposed in the vicinity of the planetary gear. This is the gist.

  According to a seventh aspect of the present invention, in the planetary differential motion conversion mechanism according to the sixth aspect, a load directed in one axial direction of the sun shaft always acts on the sun shaft, and the magnet The gist of the invention is to urge one of the pair of planetary gears located on the load acting direction side toward the sunshaft side to suppress displacement of the planetary gear so as to be close to the rotor. .

  According to an eighth aspect of the present invention, a plurality of planetary shafts are interposed between a cylindrical rotor and a sun shaft inserted into the rotor, and a pair of planetary gears provided respectively at both ends of the planetary shaft. Of the planetary shaft for engaging the pair of planetary gears with each of the pair of ring gears provided on the inner peripheral surface of the rotor and the pair of sun gears provided on the outer peripheral surface of the sun shaft. Screws provided on the outer peripheral surface of the intermediate portion are screwed into both the screws provided on the inner peripheral surface of the rotor and the screws provided on the outer peripheral surface of the sun shaft. In the planetary differential motion conversion mechanism that converts the rotational motion of the rotor into the linear motion of the sun shaft using the difference in the lead angle of the planetary gear, the planetary gear A magnet that is made of a magnetic material and urges the planetary gear toward the rotor side by magnetic force to prevent the planetary gear from being displaced so as to be close to the sun shaft is disposed in the vicinity of the planetary gear. This is the gist.

  A ninth aspect of the present invention is the planetary differential motion conversion mechanism according to the eighth aspect of the present invention, wherein the sun shaft is always subjected to a load directed in one axial direction of the sun shaft, and the magnet is One of the pair of planetary gears, which is located on the opposite side of the direction of the load application, is urged toward the rotor side to suppress displacement of the planetary gear so as to be close to the sun shaft. The gist.

  In the configuration according to claim 6, the planetary gear made of a magnetic material is urged toward the sun shaft by the magnetic force of the magnet disposed in the vicinity of the planetary gear, and the planetary gear is displaced so as to be close to the rotor. I try to suppress it. Therefore, when the rotational motion of the rotor is converted into the linear motion of the sunshaft, the planetary shaft is placed so that one of the pair of planetary gears located near the magnet is close to the rotor and the other is close to the sunshaft. Even when the torque to be tilted acts on the planetary shaft, the planetary gear located near the magnet is prevented from being displaced so as to be close to the rotor by the magnetic force of the magnet. This suppresses the inclination of the planetary shaft. Therefore, according to the above configuration, there is uneven wear or chipping on the screw or gear formed on the planetary shaft due to the inclination of the planetary shaft, and on the tooth surface of the screw or gear meshing with the screw or gear. Generation | occurrence | production can be suppressed now.

  In the configuration according to claim 8, the planetary gear made of a magnetic material is urged toward the rotor side by the magnetic force of the magnet disposed in the vicinity of the planetary gear, and the planetary gear is displaced so as to be close to the sun shaft. I try to suppress it. Therefore, when the rotational motion of the rotor is converted into the linear motion of the sunshaft, the planetary shaft is adjusted so that one of the pair of planetary gears located near the magnet is close to the sunshaft and the other is close to the rotor. Even when the torque to be tilted acts on the planetary shaft, the planetary gear located near the magnet is restrained from being displaced close to the sun shaft by the magnetic force of the magnet. Inclination of the planetary shaft by torque is suppressed. Therefore, according to the above configuration, there is uneven wear or chipping on the screw or gear formed on the planetary shaft due to the inclination of the planetary shaft, and on the tooth surface of the screw or gear meshing with the screw or gear. Generation | occurrence | production can be suppressed now.

  Here, when a load directed toward one of the sunshafts in the sunshaft always acts on the sunshaft, one of the pair of planetary gears located on the acting direction of the load is close to the rotor and the other is the sunshaft. A torque for tilting the planetary shaft so as to be close to the shaft always acts on the planetary shaft. Therefore, in this case, the uneven wear and loss of the screws and gears described above due to the inclination of the planetary shaft become more prominent.

  In this regard, according to the configuration described in claim 7, one of the pair of planetary gears that is located on the load acting direction side is urged toward the sun shaft by a magnetic force so that the planetary gear is close to the rotor. Since a magnet that suppresses displacement is provided, a torque that tilts the planetary shaft so that one of the pair of planetary gears located on the load acting direction side is close to the rotor and the other is close to the sun shaft. Even if it always occurs, the inclination of the planetary shaft due to the torque is suppressed. As a result, it is preferable that uneven wear or chipping occurs on the screw or gear formed on the planetary shaft due to the inclination of the planetary shaft, and on the tooth surface of the screw or gear meshing with the screw or gear. Can be suppressed.

  According to the ninth aspect of the present invention, one of the pair of planetary gears, which is located on the opposite side of the direction of load application, is urged toward the rotor side by magnetic force so that the planetary gear is close to the sun shaft. The planetary shaft is tilted so that one of the pair of planetary gears located on the direction in which the load is applied is close to the rotor and the other is close to the sun shaft. Even when torque is always generated, the inclination of the planetary shaft due to the torque is suppressed. As a result, it is preferable that uneven wear or chipping occurs on the screw or gear formed on the planetary shaft due to the inclination of the planetary shaft, and on the tooth surface of the screw or gear meshing with the screw or gear. Can be suppressed.

(First embodiment)
FIG. 1 is a diagram showing a first embodiment in which the present invention is applied to a planetary differential motion conversion mechanism mounted on an actuator that drives a variable valve mechanism that changes the maximum lift amount and valve opening period of an engine valve of an internal combustion engine. 1 to 5 will be described.

  FIG. 1 is a partial cross-sectional view showing the internal configuration of the planetary differential motion conversion mechanism according to the present embodiment. As shown in FIG. 1, the planetary differential motion conversion mechanism 100 of this embodiment includes a sun shaft 20 inserted into a cylindrical rotor 10 and a plurality of sun shafts 20 between the sun shaft 20 and the rotor 10. It is configured by interposing a planetary shaft 30. In the planetary differential motion conversion mechanism 100, nine planetary shafts 30 are arranged at equal angular intervals so as to surround the sun shaft 20, but only two of them are shown in FIG. Show.

  Hereinafter, the internal structure of the planetary differential motion conversion mechanism 100 will be described in more detail. As shown in FIG. 1, on the inner peripheral surface of the rotor 10, five left-hand screws that advance counterclockwise from the front side (right side in the figure) toward the rear side (left side in the figure) at the center part A screw 11 made of is formed. Further, a front side ring gear 12 a and a rear side ring gear 12 b are fixed to the inner peripheral surface of the rotor 10 so as to sandwich the screw 11. Each of the ring gears 12 a and 12 b is a spur gear that has a tooth line extending along the extending direction of the central axis C of the rotor 10.

  On the other hand, on the outer peripheral surface of the sun shaft 20 inserted in the rotor 10, four right-hand screws that advance clockwise from the front side to the rear side at positions facing the screws 11 formed on the rotor 10. A screw 21 made of is formed. Further, a front-side sun gear 22 a and a rear-side sun gear 22 b are formed on the outer peripheral surface of the sun shaft 20 so as to sandwich the screw 21. Each of the sun gears 22 a and 22 b is a spur gear that has a tooth line extending along the extending direction of the central axis C of the sun shaft 20.

  Each planetary shaft 30 interposed between the rotor 10 and the sun shaft 20 has a front planetary gear 32a at the front end and a rear planetary gear 32b at the rear end. Has been. Each of the planetary gears 32 a and 32 b is a spur gear that has a tooth line extending along the direction of extension of the central axis of the planetary shaft 30. The front planetary gear 32 a meshes with both the front ring gear 12 a formed on the rotor 10 and the front sun gear 22 a formed on the sun shaft 20, and the rear planetary gear 32 b is formed on the rotor 10. The rear side ring gear 12b and the rear side sun gear 22b formed on the sun shaft 20 are meshed with each other.

  Further, on the outer peripheral surface of the intermediate portion 35 of the planetary shaft 30 connecting the planetary gears 32 a and 32 b, there are a screw 11 formed on the inner peripheral surface of the rotor 10 and a screw 21 formed on the outer peripheral surface of the sun shaft 20. A screw 31 is formed to be screwed to both of them. The screw 31 is a single left-hand screw that proceeds counterclockwise from the front side toward the rear side.

  Thus, when a pair of planetary gears 32a and 32b are provided at both ends of the planetary shaft 30, the screws and gears of the respective members interfere when the sun shaft 20, the planetary shaft 30, and the rotor 10 are assembled together. The assembly becomes difficult, and the assemblability of the planetary differential motion conversion mechanism 100 is deteriorated.

  Therefore, in the planetary shaft 30 according to the present embodiment, the rear-side planetary gear 32 b is formed to be detachable from the intermediate portion 35 of the planetary shaft 30. Specifically, the planetary shaft 30 includes a main body part in which an intermediate part 35 and a front planetary gear 32a are integrally formed, and a rear planetary gear 32b. The rear planetary gear 32b is formed with a bearing hole 34 penetrating along the axial direction thereof, while the intermediate portion 35 is formed with a shaft portion 33 extending along the axial direction. . The intermediate portion 35 is connected to the rear planetary gear 32 b by inserting the shaft portion 33 into the bearing hole 34. By adopting such a configuration, it is possible to suppress the deterioration of the assembling property of the planetary differential motion conversion mechanism 100. A method for assembling the planetary differential motion conversion mechanism 100 will be described later with reference to FIGS.

  Further, in the planetary differential motion conversion mechanism 100 of the present embodiment, as shown on the left side of FIG. 1, a lid 40 that closes the rotor 10 is fitted to the rear end of the rotor 10. The lid 40 prevents the rear planetary gear 32b from being displaced in the axial direction on the rear side and falling off from the intermediate portion 35.

  In the planetary differential motion conversion mechanism 100 configured as described above, the rotor 10, the sun shaft 20, and the planetary shaft 30 are meshed with each other via screws and gears formed in the respective members. Therefore, by rotating the rotor 10 relative to the sun shaft 20, the rotational force of the rotor 10 is transmitted to the planetary shaft 30 through these screws and gears, and the planetary shaft 30 is connected to the inner peripheral surface of the rotor 10. It rolls along the outer peripheral surface of the sun shaft 20.

  Here, in the screw 11 of the rotor 10 and the screw 31 of the planetary shaft 30, the ratio of the pitch circle diameter and the ratio of the number of screw threads are both set to “5: 1”. Thus, the lead angles of the screw 11 of the rotor 10 and the screw 31 of the planetary shaft 30 are the same. Therefore, when the planetary shaft 30 rolls along the inner peripheral surface of the rotor 10, no relative axial displacement occurs between the rotor 10 and the planetary shaft 30.

  On the other hand, in the screw 31 of the planetary shaft 30 and the screw 21 of the sun shaft 20, the ratio of the pitch circle diameter and the ratio of the number of screw threads are different. Specifically, while the ratio of pitch circle diameters is set to “1: 3”, as described above, the number of threads 31 of the planetary shaft 30 is 1, and the sunshaft 20 is threaded. Since the number of screw threads 21 is 4, the ratio of the thread threads is set to “1: 4”. Thus, the lead angle is different between the screw 21 of the sun shaft 20 and the screw 31 of the planetary shaft 30. Therefore, when the planetary shaft 30 rolls along the outer peripheral surface of the sunshaft 20, the sunshaft 20 and the planetary shaft 30 are displaced in the axial direction by the difference in the lead angle, and the relative position changes. To come.

  In short, in the planetary differential motion conversion mechanism 100, the planetary shaft 30 moves along the inner peripheral surface of the rotor 10 and the outer peripheral surface of the sun shaft 20 by rotating the rotor 10 relative to the sun shaft 20. The sun shaft 20 is displaced in the axial direction by the difference in the lead angle. Therefore, the rotational motion input to the rotor 10 through the planetary differential motion conversion mechanism 100 can be converted into a linear motion of the sun shaft 20 and output.

  The planetary differential motion conversion mechanism 100 is mounted on an actuator that drives a control shaft of a valve characteristic changing mechanism that changes the maximum lift amount and valve opening period of an intake valve of an internal combustion engine. Specifically, a permanent magnet is attached on the outer peripheral surface of the rotor 10, and the rotor 10 is configured to function as a rotor of the electric motor. And the front-end | tip part 24 of the sun shaft 20 shown by the right side of FIG. 1 is connected with the control axis | shaft of a valve characteristic change mechanism. The valve characteristic changing mechanism changes the maximum lift amount and the valve opening period of the engine valve in accordance with the axial displacement of the control shaft.

  As shown on the right side of FIG. 1, a straight spline 23 is formed on the outer peripheral surface of the sun shaft 20. When the planetary differential motion conversion mechanism 100 is fixed to the internal combustion engine as an actuator of the valve characteristic changing mechanism, the straight spline 23 is meshed with the straight spline formed in the opening portion of the casing of the internal combustion engine. Thus, the sun shaft 20 is allowed to move in the axial direction by the action of the straight spline 23, but the rotation is restricted.

  Thus, by applying the planetary differential motion conversion mechanism 100 of this embodiment to the actuator of the valve characteristic changing mechanism and attaching it to the internal combustion engine, the rotational motion of the motor is controlled through the planetary differential motion conversion mechanism 100. It is possible to adjust the position of the control shaft in the axial direction. That is, by controlling the rotation amount of the motor, the valve characteristic changing mechanism can be controlled to arbitrarily change the maximum lift amount and the valve opening period of the intake valve.

  By the way, the control shaft of the valve characteristic changing mechanism of the internal combustion engine that changes the maximum lift amount and the valve opening period of the engine valve is designed to reduce the maximum lift amount and the valve opening period of the engine valve by the reaction force of the valve spring (this In the embodiment, a load for displacing the control shaft always acts in the direction F) shown in FIG. Therefore, a load G in one direction always acts on the sun shaft 20 connected to the control shaft.

  As a result, a load f1 in the direction F is generated at the site where the screw 31 of the planetary shaft 30 is engaged with the screw 21 of the sun shaft 20, and the site of the screw 31 of the planetary shaft 30 is engaged with the screw 11 of the rotor 10. A load f2 in the direction R may occur. With these loads f1 and f2, the torque for tilting the planetary shaft 30 counterclockwise, that is, the rear planetary gear 32b of the planetary shaft 30 is close to the sun shaft 20 and the front planetary gear 32a is close to the rotor 10. A torque W for inclining the planetary shaft 30 is always generated.

  On the other hand, in the planetary differential motion conversion mechanism 100 as described above, the rotor 10, the sun shaft 20, and the planetary shaft are constituted by the screws having different lead angles and the pair of gears arranged so as to sandwich the screws. Therefore, in order to smoothly move each member, it is necessary to provide a certain amount of clearance between the members. Here, when the clearance is provided between the members as described above, if the torque W for inclining the planetary shaft 30 is generated in the planetary shaft 30 as described above, the rotor 10 and the sun shaft 20 corresponding to the clearance are generated. The planetary shaft 30 is inclined so that the rear planetary gear 32 b of the planetary shaft 30 is close to the sun shaft 20 and the front planetary gear 32 a is close to the rotor 10.

  When the planetary shaft 30 is thus inclined, the planetary gears 32a and 32b of the planetary shaft 30, the ring gears 12a and 12b formed on the inner peripheral surface of the rotor 10, and the sun gears 22a and 22b formed on the outer peripheral surface of the sun shaft, These gears are in contact with each other in an inclined state and come into contact with each other. Similarly, one-side contact also occurs at the meshing portions of the screw 31 of the planetary shaft 30 with the screw 11 of the rotor 10 and the screw 21 of the sun shaft 20, and uneven wear and loss of gears and screws occur at these portions. As a result, the durability of the planetary differential motion conversion mechanism may be reduced.

  Therefore, in the present embodiment, as described above, a configuration that suppresses uneven wear and loss of screws and gears caused by the inclination of the planetary shaft 30 is employed. Hereinafter, this configuration will be described with reference to FIG. 2 is a cross-sectional view showing a cross-sectional structure taken along line 2-2 of FIG.

  As shown in FIGS. 1 and 2, an annular groove 41 is formed on the bottom surface of the lid 40 on the planetary shaft 30 side, and the groove 41 protrudes toward the planetary shaft 30 side at the center. A disc-shaped displacement restricting portion 40 a is formed integrally with the lid 40. In the shaft portion 33 formed in the intermediate portion 35, a protruding portion 33 a that protrudes from the bearing hole 34 formed in the rear planetary gear 32 b is inserted into the groove 41, and the rotor 10 is relative to the sun shaft 20. When rotating, the protruding portion 33 a rolls along the groove 41. Here, the displacement restricting portion 40 a restricts the rear planetary gear 32 b from being displaced so as to be close to the sun shaft 20 by contacting the protruding portion 33 a from the sun shaft 20 side.

Hereinafter, a method for assembling the planetary differential motion conversion mechanism 100 will be described with reference to FIGS.
First, as shown in FIG. 3, the main body of the planetary shaft 30 with the rear planetary gear 32b removed is disposed around the sun shaft 20, and the front sun gear 22a and the front planetary gear 32a are engaged with each other. At the same time, the screw 31 is engaged with the screw 21 of the sun shaft 20. And while maintaining the meshing state of the planetary shaft 30 and the sun shaft 20, the main body part of the sun shaft 20 and the planetary shaft 30 is covered with the rotor 10 from the rear side, and the screw 11 of the planetary shaft 30 is rotated while rotating this. Screwed into the screw 31.

  Thus, after the sunshaft 20 and the main body of the planetary shaft 30 and the rotor 10 are engaged with each other and assembled together, the front ring gear 12a and the rear ring gear 12b are fixed to the inner peripheral surface of the rotor 10, respectively. Then, after the ring gears 12a and 12b are attached, as shown in FIG. 4, the rear side planetary gear 32b is engaged with both the rear side ring gear 12b and the rear side sun gear 22b, while the main body of the planetary shaft 30 is engaged. Assemble.

  Then, after assembling the rear planetary gear 32b in this way and bringing the rotor 10, the sun shaft 20 and the planetary shaft 30 into mesh with each other by the formed gears and screws, as shown in FIG. The lid 40 is attached to the rotor 10. Specifically, with the protruding portion 33a of the shaft portion 33 being inserted into the groove 41 formed in the lid body 40, the lid body 40 is fitted to the rear end portion of the rotor 10, and the planetary differential type is fitted. The assembly of the motion conversion mechanism 100 is completed.

According to the first embodiment described above, the following effects can be obtained.
(1) The rear side planetary gear 32b is displaced so as to be close to the sun shaft 20 by the displacement restricting portion 40a that abuts from the sun shaft 20 side to the protruding portion 33a that protrudes from the bearing hole 34 in the shaft portion 33. I tried to regulate it. Therefore, when the rotational motion of the rotor 10 is converted into the linear motion of the sun shaft 20, the planetary shaft 30 so that the rear planetary gear 32 b is close to the sun shaft 20 and the front planetary gear 32 a is close to the rotor 10. Even when the torque W to incline is always generated, the displacement restricting portion 40a restricts the rear planetary gear 32b from being displaced toward the sun shaft 20, and the torque W causes the planetary shaft 30 to move. Inclination is suppressed. Therefore, according to the configuration of the present embodiment, the screw or gear formed on the planetary shaft 30 due to the inclination of the planetary shaft 30 and the tooth surfaces of the screw or gear meshing with these screws or gears. Occurrence of uneven wear and defects can be suppressed.

(2) The displacement restricting portion 40a is formed integrally with the lid 40. Thereby, for example, the increase in the number of members of the planetary differential motion conversion mechanism 100 can be suppressed as compared with the case where the displacement regulating member that contacts the protruding portion 33a is provided as a member different from the lid 40. it can.
(Second Embodiment)
Hereinafter, the second embodiment according to the present invention will be described focusing on differences from the first embodiment. The planetary differential motion conversion mechanism of the second embodiment is the same in basic structure as the planetary differential motion conversion mechanism 100 of the first embodiment described above, and the planetary shaft 30. Only the configuration for suppressing the inclination is different from that of the first embodiment.

  FIG. 6 is a partial cross-sectional view showing the internal configuration of the planetary differential motion conversion mechanism according to the present embodiment. As shown in FIG. 6, a magnet 25 is provided in a portion of the sun shaft 20 of the present embodiment that is located on the front side of the sun gear 22a adjacent to the front sun gear 22a. Further, the portion other than the magnet 25 in the sun shaft 20 is made of a nonmagnetic material, and the planetary shaft 30 is made of a magnetic material. Thereby, the magnetic force fq which urges | biases the front side planetary gear 32a of the planetary shaft 30 located in the vicinity of the magnet 25 to the sun shaft 20 side generate | occur | produces. The magnet 25 urges the front planetary gear 32 a toward the sun shaft 20 by the magnetic force fq to suppress the displacement of the planetary gear 32 a so as to be close to the rotor 10.

According to the second embodiment described above, the following effects can be obtained.
(3) The front planetary gear 32a made of a magnetic material is urged toward the sun shaft 20 by the magnetic force fq of the magnet 25 disposed in the vicinity of the planetary gear 32a so that the planetary gear 32a comes close to the rotor 10. The displacement is suppressed. Therefore, when the rotational motion of the rotor 10 is converted into the linear motion of the sun shaft 20, the front planetary gear 32 a located near the magnet 25 is close to the rotor 10 and the rear planetary gear 32 b is moved to the sun shaft 20. Even when a torque W is always generated to incline the planetary shaft 30 so as to be close to each other, the front side planetary gear 32a is prevented from being displaced close to the rotor 10 by the magnetic force fq of the magnet 25. Therefore, the inclination of the planetary shaft 30 by the torque W is suppressed. Therefore, according to the above-described configuration, uneven wear occurs on the screw or gear formed on the planetary shaft 30 due to the inclination of the planetary shaft 30 and the tooth surfaces of the screw or gear meshing with the screw or gear. Occurrence of defects can be suppressed.

In addition, the said embodiment can also be implemented with the following forms which changed this suitably.
-The surface of the displacement restricting portion 40a according to the first embodiment, that is, the surface treatment for reducing the frictional force such as plating is adopted on the inner peripheral surface of the groove 41 in contact with the protruding portion 33a. can do. By performing such surface treatment, it is possible to reduce friction generated when the protruding portion 33a rolls along the groove 41.

  In the first embodiment, the displacement restricting portion 40 a that contacts the protruding portion 33 a that protrudes from the bearing hole 34 in the shaft portion 33 is formed integrally with the lid body 40. On the other hand, for example, when it is difficult to integrally form the displacement regulating member that abuts the protruding portion 33a with the lid 40 due to the size of the lid 40, the displacement regulating member is referred to as the lid 40. May be provided as a separate member. FIG. 7 is a partial cross-sectional view showing the internal structure of an example of a planetary differential motion conversion mechanism employing such a structure, and FIG. 8 is a cross-sectional view showing the cross-sectional structure taken along line 8-8 in FIG. It is. As shown in FIGS. 7 and 8, an annular displacement restricting member 50 is provided on the sun shaft 20 side of the protruding portion 33 a, and the displacement restricting member 50 includes two connecting members 51. Via the lid 40. The displacement restricting member 50 restricts the rear-side planetary gear 32b from being displaced so as to come close to the sun shaft 20 by coming into contact with the protruding portions 33a from the sun shaft 20 side. Note that when the rotor 10 rotates relative to the sun shaft 20, the protruding portions 33 a roll along the outer periphery of the displacement regulating member 50. By restricting the displacement of the rear planetary gear 32b in this manner, the inclination of the planetary shaft 30 due to the torque W can be suppressed.

  In the first embodiment, the rear-side planetary gear 32b is formed to be detachable from the intermediate portion 35 of the planetary shaft 30, and the projecting portion 33a that protrudes from the bearing hole 34 formed in the rear-side planetary gear 32b. Is provided with a displacement restricting portion 40a that comes into contact with the sun shaft 20 side. On the other hand, when the front side planetary gear 32a is formed so as to be detachable from the intermediate portion 35 of the planetary shaft 30, the protruding portion protruding from the bearing hole formed in the front side planetary gear 32a is provided on the rotor 10. It is possible to employ a configuration in which a displacement restricting member that abuts from the side and restricts displacement of the front planetary gear 32a so as to approach the rotor 10 can be employed. By restricting the displacement of the front planetary gear 32a in this manner, the inclination of the planetary shaft 30 due to the torque W can be suppressed. In this case, a configuration in which the displacement regulating member is fixed to the rotor 10 can be employed.

  In the second embodiment, the magnet 25 is provided in a portion of the sun shaft 20 located near the front planetary gear 32a, and the front planetary gear 32a is biased toward the sun shaft 20 by the magnetic force fq of the magnet 25. Like to do. On the other hand, for example, a magnet is provided in a portion of the rotor 10 located in the vicinity of the rear planetary gear 32b, and the rear planetary gear 32b is urged toward the rotor 10 by the magnetic force of the magnet. A configuration that suppresses displacement so as to be close to the sun shaft 20 can also be employed. By restricting the displacement of the rear planetary gear 32b in this manner, the inclination of the planetary shaft 30 due to the torque W can be suppressed.

  In each of the above embodiments, the case where the load G in the direction F always acts on the sun shaft 20 has been described. However, the maximum lift amount and the valve opening period may be reduced as the control shaft is displaced in the direction R in FIG. When the present invention is applied to the actuator that drives the variable valve mechanism, the load G1 in the direction R always acts on the sun shaft 20. In this case, since a torque in the direction opposite to the torque W is generated in the planetary shaft 30, that is, a torque that tilts the planetary shaft 30 clockwise, a configuration that restricts the planetary shaft 30 from tilting clockwise is adopted. It is desirable to do. Specifically, for example, when the rear-side planetary gear 32b is formed to be detachable from the intermediate portion 35 of the planetary shaft 30, the projecting portion that protrudes from the bearing hole formed in the rear-side planetary gear 32b is used as the rotor 10. A displacement restricting member that abuts from the side and restricts displacement of the rear planetary gear 32b so as to approach the rotor 10 can be provided. On the other hand, when the front-side planetary gear 32a is formed so as to be detachable from the intermediate portion 35 of the planetary shaft 30, the projecting portion that protrudes from the bearing hole formed in the front-side planetary gear 32a from the sun shaft 20 side. A displacement regulating member that abuts and regulates displacement of the front-side planetary gear 32 a so as to approach the sun shaft 20 can be provided. Further, a magnet that urges the rear planetary gear 32b toward the sun shaft 20 by magnetic force to suppress displacement of the planetary gear 32b so as to be close to the rotor 10, or a front planetary gear 32a that moves to the rotor 10 by magnetic force. It is also possible to arrange a magnet that is biased to the side and suppresses displacement of the planetary gear 32a so as to be close to the sun shaft 20.

  A configuration in which an actuator including the planetary differential motion conversion mechanism 100 according to the present invention is applied as an actuator for driving a valve characteristic changing mechanism that changes the maximum lift amount and valve opening period of the intake valve is illustrated. On the other hand, an actuator including the planetary differential motion conversion mechanism 100 of the present invention can also be applied as an actuator of a valve characteristic changing mechanism that changes the maximum lift amount and valve opening period of the exhaust valve. An actuator including the planetary differential motion conversion mechanism 100 according to the present invention can also be applied as an actuator other than the actuator of the valve characteristic changing mechanism of the engine valve.

  The number of threads and the lead angle of the screws formed on the rotor 10, the sun shaft 20, and the planetary shaft 30 in each of the above embodiments are based on the difference between the lead angle of the screw 21 and the lead angle of the screw 31. This is merely an example of a setting mode of the number of threads and the lead angle that can convert the rotational motion into the linear motion of the sun shaft 20. That is, the present invention is not limited to the planetary differential motion conversion mechanism 100 having the screws 11, 21, 31 formed with the number of threads and the lead angle shown in the above embodiments.

  -Although the permanent magnet was attached to the rotor 10 of the planetary differential type | formula motion conversion mechanism 100 and the actuator which comprises a rotor 10 itself as a rotor of a motor was illustrated, the planetary differential type | mold motion conversion mechanism 100 concerning this invention is such a structure. The present invention is not limited to this actuator. For example, the planetary differential motion conversion mechanism 100 of the present invention can be applied even to an actuator that transmits the driving force of an electric motor to the rotor 10 via a gear, a belt, a chain, or the like.

The fragmentary sectional view which shows the internal structure about the planetary differential type | formula motion conversion mechanism concerning the 1st Embodiment of this invention. Sectional drawing which shows the cross-sectional structure along line 2-2 in FIG. The perspective view which shows the assembly | attachment aspect of the planetary differential type | formula motion conversion mechanism concerning the embodiment. The perspective view which shows the assembly | attachment aspect of the planetary differential type | formula motion conversion mechanism concerning the embodiment. The perspective view which shows the assembly | attachment aspect of the planetary differential type | formula motion conversion mechanism concerning the embodiment. The fragmentary sectional view which shows the internal structure about the planetary differential type | formula motion conversion mechanism concerning the 2nd Embodiment of this invention. The fragmentary sectional view which shows the internal structure about the modification of the planetary differential type | formula motion conversion mechanism concerning 1st Embodiment. FIG. 8 is a cross-sectional view showing a cross-sectional structure taken along line 8-8 in FIG. The block diagram which shows typically the conventional planetary differential type | formula motion conversion mechanism.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Rotor, 11 ... Screw, 12a ... Front side ring gear, 12b ... Rear side ring gear, 20 ... Sun shaft, 21 ... Screw, 22a ... Front side sun gear, 22b ... Rear side sun gear, 23 ... Straight spline, 24 ... Tip portion, 25 ... Magnet, 30 ... Planetary shaft, 31 ... Screw, 32a ... Front side planetary gear, 32b ... Rear side planetary gear, 33 ... Shaft portion, 33a ... Projection portion, 34 ... Bearing hole, 35 ... Intermediate portion , 40: Lid (axial displacement restricting member), 40a: Displacement restricting portion, 41 ... Groove, 50 ... Displacement restricting member, 51 ... Connecting member, 100 ... Planetary differential motion conversion mechanism.

Claims (9)

A plurality of planetary shafts are interposed between a cylindrical rotor and a sun shaft inserted into the rotor, and a pair of planetary gears respectively provided at both ends of the planetary shaft are provided on the inner peripheral surface of the rotor. The pair of ring gears and the pair of sun gears provided on the outer peripheral surface of the sun shaft are respectively meshed with each other and provided on the outer peripheral surface of the intermediate portion of the planetary shaft connecting the pair of planetary gears. A screw is screwed into both a screw provided on the inner peripheral surface of the rotor and a screw provided on the outer peripheral surface of the sun shaft, and a difference in lead angle of the screw provided in each member is utilized. In a planetary differential motion conversion mechanism that converts rotational motion of the rotor into linear motion of the sun shaft,
A bearing hole penetrating along the axial direction is formed in one of the pair of planetary gears, and a shaft portion extending along the axial direction is formed in the intermediate portion. The planetary gear is connected to the planetary gear by being inserted into the bearing hole of the planetary gear, and the planetary gear is formed in contact with the portion protruding from the bearing hole in the shaft portion from the sun shaft side. A planetary differential motion conversion mechanism, wherein a displacement restricting member that restricts the gear from being displaced so as to be close to the sun shaft is disposed in the vicinity of the planetary gear. The planetary differential motion conversion mechanism according to claim 1,
A load directed to one of the sun shafts in the axial direction always acts on the sun shaft, and the bearing hole is formed in the planetary gear located on the opposite side of the pair of planetary gears from the acting direction of the load. A planetary differential motion conversion mechanism characterized by A plurality of planetary shafts are interposed between a cylindrical rotor and a sun shaft inserted into the rotor, and a pair of planetary gears respectively provided at both ends of the planetary shaft are provided on the inner peripheral surface of the rotor. The pair of ring gears and the pair of sun gears provided on the outer peripheral surface of the sun shaft are respectively meshed with each other and provided on the outer peripheral surface of the intermediate portion of the planetary shaft connecting the pair of planetary gears. A screw is screwed into both a screw provided on the inner peripheral surface of the rotor and a screw provided on the outer peripheral surface of the sun shaft, and a difference in lead angle of the screw provided in each member is utilized. In a planetary differential motion conversion mechanism that converts rotational motion of the rotor into linear motion of the sun shaft,
A bearing hole penetrating along the axial direction is formed in one of the pair of planetary gears, and a shaft portion extending along the axial direction is formed in the intermediate portion. A planetary gear in which a portion is connected to the planetary gear by being inserted into a bearing hole of the planetary gear, and a portion that protrudes from the bearing hole in the shaft portion abuts from the rotor side to form the bearing hole A planetary differential motion conversion mechanism, characterized in that a displacement restricting member that restricts displacement so as to be close to the rotor is disposed in the vicinity of the planetary gear. In the planetary differential motion conversion mechanism according to claim 3,
A load directed toward one of the sun shafts in the axial direction always acts on the sun shaft, and the bearing hole is formed in the planetary gear located on the load acting direction side of the pair of planetary gears. Features a planetary differential motion conversion mechanism. In the planetary differential motion conversion mechanism according to any one of claims 1 to 4,
An axial displacement restricting member that suppresses displacement of the planetary gear fixed to the rotor and having the bearing hole in the axial direction is provided, and the displacement restricting member is formed integrally with the axial displacement restricting member. A planetary differential motion conversion mechanism characterized by being made. A plurality of planetary shafts are interposed between a cylindrical rotor and a sun shaft inserted into the rotor, and a pair of planetary gears respectively provided at both ends of the planetary shaft are provided on the inner peripheral surface of the rotor. The pair of ring gears and the pair of sun gears provided on the outer peripheral surface of the sun shaft are respectively meshed with each other and provided on the outer peripheral surface of the intermediate portion of the planetary shaft connecting the pair of planetary gears. A screw is screwed into both a screw provided on the inner peripheral surface of the rotor and a screw provided on the outer peripheral surface of the sun shaft, and a difference in lead angle of the screw provided in each member is utilized. In a planetary differential motion conversion mechanism that converts rotational motion of the rotor into linear motion of the sun shaft,
The planetary gear is formed of a magnetic material, and a magnet that urges the planetary gear toward the sunshaft side by magnetic force to prevent the planetary gear from being displaced so as to be close to the rotor is located near the planetary gear. A planetary differential motion conversion mechanism characterized by being arranged. The planetary differential motion conversion mechanism according to claim 6,
A load directed to one of the sun shafts in the axial direction always acts on the sun shaft, and the magnet attaches one of the pair of planetary gears located on the acting direction side of the load to the sun shaft side. A planetary differential motion conversion mechanism characterized in that the planetary gear is prevented from being displaced so as to be close to the rotor. A plurality of planetary shafts are interposed between a cylindrical rotor and a sun shaft inserted into the rotor, and a pair of planetary gears respectively provided at both ends of the planetary shaft are provided on the inner peripheral surface of the rotor. The pair of ring gears and the pair of sun gears provided on the outer peripheral surface of the sun shaft are respectively meshed with each other and provided on the outer peripheral surface of the intermediate portion of the planetary shaft connecting the pair of planetary gears. A screw is screwed into both a screw provided on the inner peripheral surface of the rotor and a screw provided on the outer peripheral surface of the sun shaft, and a difference in lead angle of the screw provided in each member is utilized. In a planetary differential motion conversion mechanism that converts rotational motion of the rotor into linear motion of the sun shaft,
The planetary gear is formed of a magnetic material, and a magnet that urges the planetary gear toward the rotor side by magnetic force to prevent the planetary gear from being displaced so as to be close to the sun shaft is located in the vicinity of the planetary gear. A planetary differential motion conversion mechanism characterized by being arranged. The planetary differential motion conversion mechanism according to claim 8,
A load directed to one of the sunshafts in the axial direction always acts on the sunshaft, and the magnet has one of the pair of planetary gears located on the side opposite to the direction of the load acting on the rotor side. The planetary differential motion conversion mechanism is characterized in that the planetary gear is prevented from being displaced so as to be close to the sun shaft.

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