JP2009052670A - Planetary roller screw device, rotation-linear motion converting device and its operation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a planetary roller screw device having excellent operation efficiency for converting rotation motion into linear motion in an axial direction. <P>SOLUTION: The planetary roller screw device is provided with a screw shaft 1 in which a screw groove 1a is formed in its outer circumferential surface, a nut 2 in which a screw groove 2a confronting the screw groove 1a of the screw shaft 1 is formed in its inner circumferential surface, and a roller array consisting of a plurality of rollers 3 rollably interposed between both the screw grooves 1a, 2a. By relative rotation motion of the screw shaft 1 and the nut 2, the screw shaft 1 and the nut 2 move relatively and linearly in the axial direction through rolling of the rollers 3. A lubricant for lubricating between both the screw grooves 1a, 2a and the rollers 3 is provided in the planetary roller screw device and an extreme-pressure agent is added to the lubricant. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a planetary roller screw device. The present invention also relates to a rotation / linear motion conversion device and an operation method thereof.

Conventional planetary roller screw devices include a screw shaft having a helical thread groove formed on the outer peripheral surface, a nut having a screw groove facing the screw groove of the screw shaft formed on the inner peripheral surface, and a gap between both screw grooves. And a roller array composed of a plurality of rollers interposed in a freely rolling manner, and a cage that rotatably supports the rollers at both ends of the roller array is interposed between the screw shaft and the nut. It has been known.
In this planetary roller screw device, a gear that meshes with teeth formed on rollers at both ends of a roller row is fixed to a screw shaft or nut, thereby guiding revolving around the screw shaft of the roller (for example, (See Patent Document 1).
US Pat. No. 2,683,379 JP 2003-232373 A Jiro Otsuka et al., “Fundamental Study of Planetary Screws—Structure and Apparent Friction Coefficients”, Journal of Precision Engineering, 1986, Vol. 52, No. 1, p. 176-180

FIG. 7 is a view for explaining the motion of the rolling elements in the planetary roller screw device and the ball screw. In a planetary roller screw device, a roller as a rolling element rolls (rotates) and revolves around a screw shaft in a spiral shape, but the roller and the screw shaft are arranged in parallel and move with the rotation shaft of the roller. Since the locus does not form a right angle, the roller rolls around the screw shaft in the circumferential direction and slides in the axial direction (see FIG. 7A).
On the other hand, in the case of a ball screw, the rotation axis of the ball, which is a rolling element, and the motion trajectory are substantially perpendicular to each other, and the ball rolling direction and the motion trajectory direction substantially coincide. Therefore, although there is differential slip and slip due to skew, the ball is in a rolling motion and does not generate as much slip as the planetary roller screw device (see FIG. 7B).

Generally, since the value of sliding friction is larger than that of rolling friction, the planetary roller screw device has an apparent coefficient of friction larger than that of the ball screw, and the friction loss increases. Therefore, the planetary roller screw device has low operation efficiency when converting rotational motion into axial linear motion (the ball screw is approximately 90% or more, whereas the planetary roller screw device is approximately 80%) There was a problem that heat generation was large. And this heat generation may cause poor lubrication and reduced life. Note that the apparent friction coefficient of the planetary roller screw device is also described in Non-Patent Document 1, for example.
Therefore, the present invention solves the problems of the conventional planetary roller screw device as described above, and provides a planetary roller screw device excellent in operating efficiency for converting rotational motion into linear linear motion. And It is another object of the present invention to provide a rotation / linear motion conversion device that excels in operating efficiency for converting rotational motion into axial linear motion and an operation method thereof.

  In order to solve the above problems, the present invention has the following configuration. That is, in the planetary roller screw device according to the first aspect of the present invention, a screw shaft in which a spirally continuous screw groove is formed on the outer peripheral surface, and a screw groove facing the screw groove of the screw shaft on the inner peripheral surface. A nut that is formed, a plurality of rollers interposed between the screw grooves so as to be freely rollable, and a lubricant that lubricates between the screw grooves and the rollers, and the screw shaft. In the planetary roller screw device in which the screw shaft and the nut are relatively linearly moved in the axial direction through the rolling of the roller by the relative rotational motion with the nut, the lubricant is an extreme pressure. It contains an agent.

The planetary roller screw device according to claim 2 of the present invention is the planetary roller screw device according to claim 1, wherein the lubricant has a kinematic viscosity at 40 ° C. of 50 mm ² / s to 500 mm ² / s. A base oil, a thickener, and an extreme pressure agent composed of at least one of an organic nickel compound, an organic molybdenum compound, and an organic tellurium compound, and has a miscibility of 220 or more as defined in JIS 2220 The grease composition is 395 or less, and the content of the extreme pressure agent in the lubricant is from 0.1% by mass to 15% by mass.

Furthermore, the planetary roller screw device according to claim 3 of the present invention is the planetary roller screw device according to claim 2, wherein the content of the thickener in the lubricant is 3% by mass or more and 40% by mass or less. It is characterized by being.
Furthermore, the planetary roller screw device according to claim 4 of the present invention is the planetary roller screw device according to any one of claims 1 to 3, wherein the surface pressure is 1 GPa or more and 4.5 GPa or less when a dynamic load rating is applied. It is used under the condition that the rotational speed exceeds 100 min ⁻¹ .

Furthermore, the rotation / linear motion conversion device according to claim 5 of the present invention is a rotation / linear motion conversion device that converts an input rotation driving force into a linear driving force and outputs the linear rotation driving force. The planetary roller screw device according to claim 1, a first member attached to one of a screw shaft and a nut constituting the planetary roller screw device, and a screw shaft and a nut constituting the planetary roller screw device. And a second member, wherein the rotational driving force input through the first member is converted into an axial linear driving force by the planetary roller screw device and output through the second member. The planetary roller screw device is used under the conditions that the surface pressure is 1 GPa or more and 4.5 GPa or less and the rotational speed exceeds 100 min ⁻¹ at least at the time of operation.

Furthermore, the driving | running method of the rotation / linear motion conversion apparatus of Claim 6 which concerns on this invention is a planetary roller screw apparatus as described in any one of Claims 1-3, the screw shaft which comprises the said planetary roller screw apparatus, A first member attached to one of the nuts, and a second shaft attached to the other of the screw shaft and the nut constituting the planetary roller screw device, and the rotational drive input via the first member When operating the rotation / linear motion conversion device adapted to convert a force into an axial linear driving force by the planetary roller screw device and output the force via the second member, the operation of the rotation / linear motion conversion device is performed. At least at one time of the operation, the planetary roller screw device is operated such that the usage conditions of the planetary roller screw device are a surface pressure of 1 GPa or more and 4.5 GPa or less and a rotational speed exceeding 100 min ⁻¹ .

  The planetary roller screw device and the rotation / linear motion conversion device of the present invention are excellent in operating efficiency for converting the rotational motion into the linear motion in the axial direction. Moreover, according to the operation method of the rotation / linear motion conversion device of the present invention, the rotation / linear motion conversion device can be operated with excellent operation efficiency.

Embodiments of a planetary roller screw device and a rotation / linear motion conversion device according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a sectional view of a planetary roller screw device according to an embodiment of the present invention, taken along a plane parallel to the axial direction. In the drawings used for the following description, the same or corresponding parts are denoted by the same reference numerals.
As shown in FIG. 1, the planetary roller screw device of the present embodiment includes a screw shaft 1 having a substantially V-shaped screw groove 1 a formed in a spiral shape on the outer peripheral surface, and a screw groove 1 a of the screw shaft 1. A roller array comprising a nut 2 having a substantially V-shaped thread groove 2a opposed to the inner peripheral surface thereof, and a plurality of rollers 3 interposed between the thread grooves 1a and 2a so as to be able to roll. And two gears 4 and 4 fitted to the inner peripheral surface of the nut 2.

The outer peripheral surface of the roller row is formed in a screw shape so as to mesh with both screw grooves 1a, 2a, and the screw threads 1a, 2a and the roller 3 are all twisted in the same direction. The material of the screw shaft 1, nut 2, and roller 3 is not particularly limited, but steel such as SCM415H is preferable.
The gears 4 and 4 are disposed apart from each other in the axial direction, and mesh with the teeth 6 formed on the rollers 3 ′ and 3 ′ at both ends of the roller train. The screw shaft 1 and the nut 2 are moved relative to each other in the axial direction through the rolling of the roller 3 by the relative rotational movement between the screw shaft 1 and the nut 2.

  This planetary roller screw device is provided with two annular cages 5 and 5 and is interposed between the screw shaft 1 and the nut 2 and outside the rollers 3 ′ and 3 ′ at both ends in the axial direction. . The annular cages 5 and 5 are provided with a plurality of roller support holes 5a along the circumferential direction, and the protrusions 7 projecting outward in the axial direction provided in the rollers 3 ′ and 3 ′ at both ends are provided in the roller support holes 5a. The annular cages 5 and 5 support the rollers 3 ′ and 3 ′ so as to be rotatable. The roller support hole 5a may be a through hole or a bottomed hole.

  Further, a retaining ring 9 is attached to the nut 2 on the outer side in the axial direction of the annular cages 5 and 5 so as to contact the annular cages 5 and 5, and the protrusion 7 of the roller 3 ′ is connected to the annular cage 5. Is prevented from coming out of the roller support hole 5a. The retaining ring 9 also has a function of preventing the annular retainer 5 from being displaced in the axial direction relative to the nut 2 and preventing the annular retainer 5 from falling off the planetary roller screw device. The retaining ring 9 may be integral with the nut 2 or may be a separate member.

  Further, inside this planetary roller screw device, a lubricant (not shown) that lubricates between the screw grooves 1a, 2a and the roller 3 is disposed. Since the extreme pressure agent is added to this lubricant, the apparent friction coefficient of the planetary roller screw device is lowered. As a result, the operation efficiency for converting the rotational motion into the linear motion in the axial direction becomes excellent, and heat generation is suppressed. This is considered to be because the extreme pressure agent is drawn into the contact portion between the roller 3 and both screw grooves 1a and 2a, and the formation of the oil film is strengthened. When the formation of the oil film is strengthened, the tangential force due to friction at the sliding portion is reduced, and the operating efficiency is improved.

  In the ball screw, the effect that the operating efficiency is improved by the extreme pressure agent cannot be obtained, but the reason is estimated as follows. In the ball screw, no slip occurs at the contact center where the surface pressure is maximum, and slip occurs at the periphery of the contact ellipse having a lower surface pressure. On the other hand, in the planetary roller screw device, as described with reference to FIG. 7 in the section of the problem to be solved by the invention, slip occurs uniformly regardless of the surface pressure. Therefore, the planetary roller screw device, which has a higher surface pressure and higher sliding speed than the ball screw, is more likely to exhibit a friction reduction effect due to the extreme pressure agent, and as a result, an effect of improving the operation efficiency is likely to appear greatly. It is.

  This lubricant is preferably a grease composition containing a base oil, a thickener, and an extreme pressure agent, and having a penetration degree specified in JIS 2220 of 220 or more and 395 or less. If the penetration is less than 220, the grease composition is too hard and the fluidity of the grease composition is poor, and the lubricity may be insufficient. On the other hand, if the blending degree exceeds 395, the amount of grease composition leaking from the planetary roller screw device may increase because it is too soft. In order to make such problems less likely to occur, the penetration of the grease composition is more preferably from 265 to 350.

The base oil preferably has a kinematic viscosity at 40 ° C. of 50 mm ² / s or more and 500 mm ² / s or less, and the extreme pressure agent is at least one of an organic nickel compound, an organic molybdenum compound, and an organic tellurium compound. It is preferable that Further, the content of the extreme pressure agent in the grease composition is preferably 0.1% by mass or more and 15% by mass or less. When the base oil has a kinematic viscosity at 40 ° C. of less than 50 mm ² / s, it is difficult to secure an oil film having a sufficient thickness, which may cause direct contact between metals and reduce the durability of the planetary roller screw device. There is. On the other hand, if it exceeds 500 mm ² / s, the operation efficiency of the planetary roller screw device may be lowered and heat generation may be increased.

  Further, if the content of the extreme pressure agent is less than 0.1% by mass, the action of the extreme pressure agent may not be sufficiently exhibited, and the operation efficiency may not be sufficiently improved. On the other hand, even if it exceeds 15% by mass, not only the improvement effect of the operating efficiency can be obtained, but also the durability of the planetary roller screw device may be lowered by the chemical action of the extreme pressure agent. In order to make such problems more difficult to occur, the content of the extreme pressure agent in the grease composition is more preferably 0.5% by mass or more and 5% by mass or less.

  Further, the content of the thickener in the grease composition is preferably 3% by mass or more and 40% by mass or less. If it is less than 3% by mass, it may be difficult to form a semi-solid grease composition, and the grease composition may leak from the planetary roller screw device. On the other hand, if it exceeds 40% by mass, the grease composition becomes too hard, the lubricity becomes insufficient, and the operation efficiency may be lowered. In order to make such problems more difficult to occur, the content of the thickener in the grease composition is more preferably 5% by mass or more and 25% by mass or less.

If such a grease composition is used as a lubricant, the apparent friction coefficient can be lowered even when the planetary roller screw device is used under high temperature, high speed and high pressure conditions, and as a result, the operating efficiency is improved. In particular, when it is used under the condition that the surface pressure at the time of dynamic load rating is 1 GPa or more and 4.5 GPa or less and the rotation speed exceeds 100 min ⁻¹ , the effect of improving the operation efficiency is great. In addition, when the rotational speed is 200 min ⁻¹ or more, the effect of improving the operation efficiency is larger, and when it is 300 min ⁻¹ or more, the effect of improving the operation efficiency is further increased.

Such a planetary roller screw device is suitable as a component constituting a rotation / linear motion conversion device that converts an input rotation driving force into a linear driving force and outputs the linear driving force. The rotation / linear motion conversion device includes a planetary roller screw device, a first member attached to one of a screw shaft and a nut of the planetary roller screw device, and a second member attached to the other of the screw shaft and the nut. I have. Then, the rotational driving force input via the first member from the power source (for example, motor) of the rotational driving force is converted into the linear linear driving force by the planetary roller screw device, and output via the second member. It is supposed to be. In this rotation / linear motion conversion device, the planetary roller screw device is preferably used under the conditions that the surface pressure is 1 GPa or more and 4.5 GPa or less and the rotational speed exceeds 100 min ⁻¹ at least at the time of operation.

  Such a rotation / linear motion conversion device can be suitably used for a feed mechanism of a mechanical device such as an electric injection molding machine or an electric press machine or an actuator for an electric brake of an automobile. For example, in an electric injection molding machine, a rotational driving force input from an electric motor through a first member is converted into an axial linear driving force by a planetary roller screw device and output to a screw through a second member. Is done.

  In addition, this embodiment shows an example of this invention and this invention is not limited to this embodiment. For example, in the planetary roller screw device of the present embodiment, the axial position of the roller 3 is restrained by the nut 2 (the two gears 4 and 4 fitted to the nut 2 and the rollers 3 at both ends of the roller train). Since the teeth 6 formed on ', 3' are engaged with each other, the axial position of the roller 3 is restrained by the nut 2). As in the planetary roller screw device shown in FIG. The position may be constrained by the screw shaft 1 (the two gears 4 and 4 fitted to the screw shaft 1 and the teeth formed on the rollers 3 ′ and 3 ′ at both ends of the roller train mesh with each other. Therefore, the axial position of the roller 3 is restrained by the screw shaft 1).

Hereinafter, the structure of the planetary roller screw device of FIG. 2 will be described in detail. The configuration and operation of the planetary roller screw device of FIG. 2 are substantially the same as those of the planetary roller screw device of FIG. 1, and therefore only the different parts will be described and the description of the same parts will be omitted.
The planetary roller screw device of FIG. 2 has a screw shaft 1 having a substantially V-shaped thread groove 1a that is spirally continuous in the outer peripheral surface, and a substantially V-shaped cross-section facing the screw groove 1a of the screw shaft 1. The screw shaft 2 is fitted to a screw shaft 1 and a nut 2 having a screw groove 2a formed on the inner peripheral surface, a roller train composed of a plurality of rollers 3 interposed between the screw grooves 1a and 2a so as to be able to roll. Two gears 4 and 4 are provided. The outer peripheral surface of the roller row is formed in a screw shape so as to mesh with both screw grooves 1a and 2a, and the twist directions of both screw grooves 1a and 2a are the same, but the twist direction of the roller 3 is the both screws. The direction of twisting of the grooves 1a and 2a is opposite.

  The gears 4 and 4 are arranged apart from each other in the axial direction, and mesh with the teeth formed on the rollers 3 'and 3' at both ends of the roller train. Further, a retaining ring 9 is attached to the outer side in the axial direction of the annular cages 5 and 5 on the screw shaft 1 so as to come into contact with the annular cages 5 and 5, and the protrusion 7 of the roller 3 ′ is connected to the annular cage. 5 is prevented from coming out of the roller support hole 5a. Further, the retaining ring 9 has a function of preventing the annular retainer 5 from being displaced in the axial direction with respect to the screw shaft 1 and preventing the annular retainer 5 from dropping from the planetary roller screw device. The retaining ring 9 may be integral with the screw shaft 1 or may be a separate member.

The present invention will be described more specifically with reference to the following examples.
[Evaluation A of planetary roller screw device A]
A planetary roller screw device having substantially the same configuration as that of the planetary roller screw device of FIG. 1 was prepared, a grease composition was disposed therein, and the operation efficiency was measured. The specifications of the planetary roller screw device used are as follows. The composition of the grease composition is as shown in Table 1.

Effective thread groove diameter: 29.840 mm screw shaft, 50 mm nut, 10 mm roller
Lead: Screw shaft 10mm, nut 10mm, roller 2mm
Lead angle: 6 ° 05 '
Number of threads: 5 screw shafts, 5 nuts, 1 roller Effective meshing length: 25 mm
Number of rollers: 6 Basic dynamic load rating: 3530N

First, the grease composition of Comparative Example 1 was arranged inside the planetary roller screw device, and a running ^- in operation was performed at a rotational speed of 500 min ⁻¹ while applying a load of 35% of the basic dynamic load rating. Since it generated heat in the running-in operation, it was cooled to room temperature. Then, the outer diameter part of the nut is covered with a heater and heated, and it is operated at a rotational speed of 500 min ^-1 while applying a load of 35% of the basic dynamic load rating while maintaining a constant temperature. Was measured.

When the measurement was completed, the grease composition of Comparative Example 1 was washed away and the grease composition of Comparative Example 2 was placed inside. The operating efficiency at each temperature was measured in exactly the same manner as in Comparative Example 1.
Further, the grease composition of Comparative Example 2 was removed by washing, and the grease composition of Example 1 was disposed inside. The operating efficiency at each temperature was measured in exactly the same manner as in Comparative Examples 1 and 2. The results are shown in the graph of FIG.

  The grease compositions of Comparative Examples 1 and 2 are in a good lubrication state with respect to the penetration and the kinematic viscosity of the base oil, and are generally used for lubrication of ball screws and the like. When such a grease composition was used for the planetary roller screw device, the operating efficiency was about 81 to 83% as shown in the graph of FIG. On the other hand, since the organic molybdenum compound was added as an extreme pressure agent, the grease composition of Example 1 had excellent operating efficiency of 85% or more as shown in the graph of FIG.

In this test, the running ^- in operation was performed at a rotational speed of 500 min ⁻¹ before measuring the operating efficiency. However, when the operating efficiency was measured without performing the running-in operation, even when the grease composition of Example 1 was used. The operating efficiency was about the same as when the grease compositions of Comparative Examples 1 and 2 were used (about 82%). From this, the operating efficiency of the subsequent operation can be obtained by performing the running-in operation at high temperature, high speed, and high pressure conditions (in the running-in operation of this test, the temperature is about 60 ° C., the rotation speed is 500 min ⁻¹ , and the contact surface pressure is 1.8 GPa) Was found to improve.

  As can be seen from the graph of FIG. 3, the higher the temperature is, the higher the operating efficiency is. Therefore, heat generation due to friction is suppressed, and the operating temperature can be lower than that of the conventional planetary roller screw device. It is. Therefore, it is possible to suppress poor lubrication and life reduction due to temperature rise. The higher the temperature is, the better the operating efficiency is because the low temperature test is acting as a break-in operation. Therefore, for the grease composition of Example 1, the temperature is increased from 30 ° C. to 70 ° C. After measuring the operating efficiency, the operating efficiency was measured while the temperature was lowered from 70 ° C to 30 ° C. As a result, as shown in the graph of FIG. 3, there was almost no difference in operating efficiency when the temperature was rising and when the temperature was falling. From this result, it was confirmed that the test at low temperature did not act as a break-in operation, and the operating efficiency was improved by the break-in operation before the test.

  In this test, the planetary roller screw device having the structure as shown in FIG. 1 was used. However, the same result is obtained with the planetary roller screw device having the structure as shown in FIG. Further, the grease composition used for the planetary roller screw device is not limited to the one shown in Table 1. For example, the type of the base oil is not particularly limited, and any base oil that is generally used as a base oil for a grease composition can be used without any problem. However, mineral oil-based lubricants and synthetic lubricants are preferred.

Further, the thickener is not limited to lithium soap, and metal soap-type thickeners such as calcium soap, sodium soap and aluminum soap, and inorganic thickeners such as bentonite and clay can be used. . Furthermore, organic thickeners such as monourea compounds, diurea compounds, triurea compounds, tetraurea compounds and urethane compounds can also be used.
Furthermore, you may add the various additive generally used as an additive of a grease composition to a grease composition. For example, antioxidants, rust inhibitors, oil agents, metal deactivators and the like. These may be used individually by 1 type and may use 2 or more types together.

[Evaluation B of planetary roller screw device]
The specifications of the planetary roller screw device were changed, and a test almost similar to the evaluation A described above was performed. The specifications of the planetary roller screw device used are as follows. As the grease composition, those of Example 1 and Comparative Example 2 in Table 1 were used.
Effective thread groove diameter: Screw shaft 59.831 mm, nut 100 mm, roller 20 mm
Lead: Screw shaft 15mm, nut 15mm, roller 3mm
Lead angle: 4 ° 34 '
Number of threads: 5 screw shafts, 5 nuts, 1 roller Effective meshing length: 120 mm
Number of rollers: 11

The measuring method of the operating efficiency is almost the same as in the case of the evaluation A, but the conditions of the running-in operation are a surface pressure (surface pressure between the roller and the screw shaft) of 1.6 GPa and a rotational speed of 300 min ⁻¹ , The running-in operation was performed for 500 cycles (500 reciprocations) until the operation efficiency was stabilized. Then, after the break-in operation, the operation efficiency was measured by operating at various rotational speeds while maintaining the outer diameter portion of the nut at 60 ° C. with a heater. The results are shown in the graph of FIG.
When the grease composition of Example 1 was used, the operating efficiency was improved by performing a break-in operation as in the case of Evaluation A. On the other hand, when the grease composition of Comparative Example 2 was used, there was almost no change in the operating efficiency even after running-in.

[Evaluation C of planetary roller screw device]
Next, the grease composition of Example 1 described above is placed inside a planetary roller screw device similar to that used in Evaluation A above, and the outer diameter portion of the nut is covered with a heater and heated to 60 ° C. However, operating efficiency was measured by operating at various rotational speeds while applying a load of 35% of the basic dynamic load rating.

When operating efficiency is measured without running-in (black triangle mark in the graph of FIG. 5), the operating efficiency is the same as when the grease compositions of Comparative Examples 1 and 2 are used, which is about 82%. there were. In contrast, when operating efficiency was measured after running-in at high speed (rotation speed 500 min ^-1 ) while applying a high pressure (35% of the basic dynamic load rating) while maintaining 30 ° C (Fig. The plot of black square mark 5) was about 86 to 88% with improved work efficiency. In addition, when operating efficiency is measured after running-in at high speed (rotation speed 500 min ⁻¹ ) while applying a high pressure (35% of the basic dynamic load rating) while maintaining 70 ° C. (graph in FIG. 5) The plot of white circles) also improved the work efficiency.
However, after maintaining the temperature at 30 ° C and applying a high pressure (load of 35% of the basic dynamic load rating) and running in at a high speed (rotation speed 500 min ^-1 ), then operating at a low speed (in this experiment, the rotation speed 10min ^-1 at 50 cycles), as shown in the plot of the black diamonds in the graph of FIG. 5, the work efficiency was the case was not performed a test operation the same level.

These results are presumed to have occurred for the following reasons. That is, the extreme pressure agent formed a solid lubricating film by running-in operation at high speed and high pressure, and the operating efficiency was improved because the friction coefficient was lowered. Is considered to have peeled off and the coefficient of friction increased.
The rotational speed of the running ^- in operation is not limited to 500 min ⁻¹ , but the specification of the planetary roller screw device, the surface roughness of the thread groove, the load during the running-in operation, the kinematic viscosity of the base oil of the grease composition used , The preferred rotational speed varies depending on the ambient temperature during the running-in operation.

[Evaluation D of planetary roller screw device]
The grease composition of Example 1 described above was placed inside a planetary roller screw device similar to that used in the evaluation A described above, and after running-in under various conditions, the outer diameter portion of the nut was heated with a heater. While covering and heating and maintaining at 60 ° C., operating efficiency was measured by operating at a rotational speed of 500 min ⁻¹ while applying a load of 35% of the basic dynamic load rating.

The surface pressure of the running-in operation (surface pressure between the roller and the screw shaft) is fixed at 1.6 GPa, and the rotational speed is variously changed. Even when the running ^- in operation is performed for 1000 cycles at the rotational speed of 100 min ⁻¹ , The improvement effect was not seen. In contrast, when the break-in speed 150 min ^-1, the effect of improving the working efficiency in a part of the plurality of planetary roller screw device is observed, when the break-in speed 200 min ^-1, 20 A clear effect of improving the operating efficiency was seen even at -50 cycles.
From this result, the rotational speed of the running-in is preferably 100 min ^-1 exceeded, more preferably 150 min ^-1 or more, 200 min ^-1 or more has been found to be more preferable. Moreover, it was found that the break-in operation requires 20 cycles or more.

Furthermore, even when the rotational speed during operation is a low speed condition such as 10 min ⁻¹ or the like, if the running-in operation of the surface pressure of 1 GPa to 4.5 GPa, the rotational speed of 100 min ⁻¹ excess, or 20 to 50 cycles is performed at any time, The planetary roller screw device can be operated with excellent operating efficiency. For example, the planetary roller screw device can be operated with excellent operation efficiency even if the operation is performed under a low speed condition by periodically performing a break-in operation every time the operation is performed under a low speed condition. Since how long the above-mentioned certain period is depends on the operating conditions (load, speed, etc.), it is preferable to obtain it by experiments or the like. For example, in the case of operation at a rotational speed of 10 min ⁻¹ , It is preferable to perform a break-in operation before reaching 50 cycles.
The surface pressure of the running-in operation is preferably 1 GPa or more and 4.5 GPa or less in order to improve the operation efficiency. If it is less than 1 GPa, it is difficult to obtain an effect of improving the operation efficiency. On the other hand, if it exceeds 4.5 GPa, permanent deformation may occur in contact.

[Evaluation of Ball Screw]
As a reference, the results of measuring the operating efficiency of the ball screw are shown. The specifications of the used ball screw are as follows. As the grease composition, those of Example 1 and Comparative Example 2 in Table 1 were used.
Screw shaft diameter: 63mm
Lead: 16mm
Ball diameter: 12.7mm
Number of circuits: 3.7 windings x 2 rows Basic dynamic load rating: 317 kN

  The operation efficiency was measured by operating at various rotational speeds while applying a load of 150 kN. The surface pressure (surface pressure between the roller and the screw shaft) is 2.1 GPa. The results are shown in the graph of FIG. As can be seen from the graph of FIG. 6, there was almost no difference in operating efficiency depending on the presence or absence of the extreme pressure agent in the grease composition. In addition, a running-in operation was performed with the grease compositions of Example 1 and Comparative Example 2, but no improvement in operating efficiency was observed. In the ball screw, the friction is almost rolling friction and the operation efficiency is excellent. Therefore, it is considered that the effect of improving the operation efficiency was not seen. Thus, conventionally, no effective means for improving the operation efficiency has been known.

It is sectional drawing which fractured | ruptured the planetary roller screw apparatus which is one Embodiment of this invention by the plane parallel to an axial direction. It is sectional drawing which fractured | ruptured the planetary roller screw apparatus of the modification of this embodiment by the plane parallel to an axial direction. It is a graph which shows the measurement result of the operation efficiency of a planetary roller screw device. It is a graph which shows the difference in work efficiency by the presence or absence of running-in operation. It is a graph which shows the working efficiency at the time of the driving | running | working after running-in of various conditions. It is a graph which shows the measurement result of the operating efficiency of a ball screw. It is a figure explaining the motion of the rolling element in a planetary roller screw device and a ball screw.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Screw shaft 1a Thread groove 2 Nut 2a Thread groove 3 Roller 3 'End roller 3a Rolling surface 4 Gear

Claims (6)

  A screw shaft in which a spiral groove is formed on the outer peripheral surface, a nut formed on the inner peripheral surface of the screw shaft opposite to the screw groove of the screw shaft, and a roll between the screw grooves. A plurality of intervening rollers, and a lubricant that lubricates between the screw grooves and the rollers, and the rolling of the rollers through the relative rotational movement of the screw shaft and the nut. In the planetary roller screw device in which the screw shaft and the nut are relatively linearly moved in the axial direction, the lubricant contains an extreme pressure agent. The lubricant is at least one of a base oil having a kinematic viscosity at 40 ° C. of 50 mm ² / s to 500 mm ² / s, a thickener, an organic nickel compound, an organic molybdenum compound, and an organic tellurium compound. And a grease composition having a penetration degree specified in JIS 2220 of 220 or more and 395 or less, and the content of the extreme pressure agent in the lubricant is 0.1 mass. The planetary roller screw device according to claim 1, wherein the planetary roller screw device is at least 15% and at most 15% by mass.   The planetary roller screw device according to claim 2, wherein the content of the thickener in the lubricant is 3 mass% or more and 40 mass% or less. The planetary roller screw device according to any one of claims 1 to 3, wherein the planetary roller screw device is used under the conditions of a surface pressure of 1 GPa or more and 4.5 GPa or less when a dynamic rated load is applied, and a rotation speed exceeding 100 min- ¹ . 4. A rotation / linear motion conversion device that converts an input rotational driving force into a linear driving force and outputs the linear driving force, and constitutes the planetary roller screw device according to any one of claims 1 to 3 and the planetary roller screw device. A first member attached to one of the screw shaft and the nut, and a second member attached to the other of the screw shaft and the nut constituting the planetary roller screw device, and input via the first member. The rotational driving force is converted into an axial linear driving force by the planetary roller screw device and output via the second member, and the planetary roller screw device is in contact with at least one time during operation. A rotary-linear motion converter characterized by being used under the conditions of a pressure of 1 GPa or more and 4.5 GPa or less and a rotational speed exceeding 100 min ⁻¹ . The planetary roller screw device according to any one of claims 1 to 3, the first member attached to one of a screw shaft and a nut constituting the planetary roller screw device, and the planetary roller screw device. A second member attached to the other of the screw shaft and the nut, and the rotational driving force input via the first member is converted into an axial linear driving force by the planetary roller screw device, and the first member When operating the rotation / linear motion conversion device designed to output through two members,
The operation is performed such that the use condition of the planetary roller screw device is a surface pressure of 1 GPa or more and 4.5 GPa or less and a rotational speed exceeding 100 min ⁻¹ at least at the time of operation of the rotary / linear motion conversion device. Operation method of the rotation / linear motion conversion device.

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