KR20030028128A - Shaft assembly using cavities for skin-friction torque reduction - Google Patents

Abstract

PURPOSE: A shaft assembly is provided to reduce frictional torque generated when a shaft is relatively rotated with respect to a coupling member by forming a plurality of slots in the shaft or in the coupling member. CONSTITUTION: A shaft assembly includes a coupling member(10) and a shaft(20). The coupling member(10) is hollow-shaped. The shaft(20) is inserted into an inner peripheral portion(11) of the coupling member(10). The shaft(20) is rotatably inserted into the coupling member(10) and has an outer peripheral portion corresponding to the inner peripheral portion of the coupling member(10). Fluid(30) is interposed between the inner peripheral portion(11) of the coupling member(10) and the outer peripheral portion of the shaft(20). Four slots(25) are formed at the outer peripheral portion of the shaft(20).

Description

Shaft assembly using cavities for skin-friction torque reduction

The present invention relates to a shaft coupling including a hollow coupling member having an inner circumferential surface and a shaft fitted to the coupling member and rotated relative to the coupling member, in particular, so that friction torque generated during rotation of the coupling member or shaft can be reduced. It is directed to an axial assembly with improved structure.

A shaft coupling body comprising a hollow coupling member and a shaft that is fitted to the coupling member and that is rotatable relative to the coupling member is widely used in various industrial fields. For example, as schematically shown in FIG. 1, the configuration includes a hollow journal bearing 1 having an inner circumferential surface 1a and a shaft 2 fitted to the journal bearing 1 and rotatably supported therein. Corresponds to the conjugate. In this case, the journal bearing 1 corresponds to the coupling member. Moreover, the structure which consists of a hollow roller which has an inner peripheral surface, and the axis | shaft which is fitted to the roller and is fixed to a predetermined object and supports the roller rotatably with respect to a predetermined object also corresponds to the said shaft coupling body. In this case, the roller corresponds to the coupling member, and the shaft is fixed and the roller rotates, but the shaft rotates relative to the roller corresponding to the coupling member.

On the other hand, during operation of the shaft coupling member, the shaft is rotated relative to the coupling member with the outer circumferential surface of the portion engaged with the coupling member facing the inner circumferential surface of the coupling member, thereby suppressing direct friction between the inner circumferential surface of the coupling member and the shaft. In general, a fluid such as lubricating oil is interposed between the outer circumferential surface of the shaft and the inner circumferential surface of the coupling member.

However, even if the fluid is interposed between the outer circumferential surface of the shaft and the inner circumferential surface of the coupling member as described above, when the shaft assembly is operated, that is, when the shaft is rotated relative to the coupling member, the shaft and the coupling member are actually powered and rotated. Member (in the shaft assembly including the journal bearing and the shaft as described with reference to FIG. 1, the shaft is actually the member to be rotated, and in the shaft assembly including the roller and the shaft as described above is the member in which the roller is actually rotated.) Friction torque is generated between the fluid and the fluid to hinder the rotation of the rotating member, which requires additional power. Therefore, in order to enable the shaft assembly to operate more smoothly, it is necessary to reduce the friction torque due to friction with the fluid at the relative rotation of the shaft relative to the coupling member.

The present invention has been made in view of this point, and an object of the present invention is to provide a shaft assembly having an improved structure so as to reduce friction torque generated during relative rotation of the shaft with respect to the coupling member.

1 is a schematic perspective view of an example of a conventional shaft assembly;

Figure 2 is a schematic perspective view of the shaft assembly according to an embodiment of the present invention,

3A is a schematic cross-sectional view taken along line III-III of the shaft assembly shown in FIG. 2;

3B is an enlarged view of the “K” site of FIG. 3A,

Figure 4 is a view for explaining the friction torque in the shaft assembly shown in Figures 3a and 3b,

5 is a schematic cross-sectional view of the shaft assembly according to another embodiment of the present invention;

6 is a view for explaining the friction torque in the shaft assembly shown in FIG.

Figure 7 is a schematic cross-sectional view of the shaft assembly according to another embodiment of the present invention.

<Description of the reference numerals for the main parts of the drawings>

10, 110 ... coupling member 20, 120 ... shaft

25, 115 ... groove 30, 130 ... fluid

Groove application shaft coupling for reducing the friction torque according to the present invention for achieving the above object, has a hollow coupling member having an inner peripheral surface, and has an outer peripheral surface fitted to the coupling member and facing the inner peripheral surface of the coupling member And a shaft having a fluid interposed between the outer circumferential surface and the inner circumferential surface of the coupling member to allow relative rotation with respect to the member, wherein the friction torque generated between the fluid and the fluid during relative rotation of the shaft with respect to the coupling member. A plurality of grooves disposed along the circumferential direction are formed on the main surface of the member that is actually powered by the inner peripheral surface of the coupling member and the outer peripheral surface of the shaft so as to be reduced.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Figure 2 is a schematic perspective view of the shaft assembly according to an embodiment of the present invention, Figure 3a is a schematic sectional view taken along line III-III of the shaft assembly shown in Figure 2, Figure 3b is an enlarged view of the "K" region in Figure 3a It is also.

2, 3A and 3B, the shaft assembly of the present embodiment includes a coupling member 10 and the shaft 20. The coupling member 10 has a hollow shape having an inner circumferential surface 11 so that the shaft 20 can be fitted, and in this embodiment, performs a so-called journal bearing function. The shaft 20 is rotatably supported by being fitted to the coupling member 10 and has an outer circumferential surface opposite to the inner circumferential surface 11 of the coupling member. A fluid 30 is interposed between the inner circumferential surface 11 of the coupling member 10 and the outer circumferential surface of the shaft 20. In this embodiment as such a fluid 30, a lubricating oil is provided in order to suppress that the inner peripheral surface 11 of the coupling member 10 and the outer peripheral surface of the shaft 20 contact each other directly.

On the other hand, the shaft assembly of this embodiment is a characteristic structure of this invention, and is provided with four groove parts 25 formed concave with respect to the outer peripheral surface of the shaft 20. As shown in FIG. The grooves 25 are spaced apart from each other along the rotational direction of the shaft 20 with respect to the coupling member 10, that is, the circumferential direction of the shaft 20. The intervals between the grooves 25 are preferably equal to each other. In the present embodiment, the grooves 25 are disposed at 90 degree intervals along the circumferential direction of the shaft 20. In addition, it is preferable that each groove part 25 has the shape of the same specification mutually. For example, it is preferable to make the center angles a between the position at which the grooves 25 begin and the position at which the grooves 25 end to be the same, and to make the depths d of each groove 25 equal to each other. Do. And, as shown in Figure 3b, the corner portion of each groove portion 25, it is preferable to form a curved surface (CS) in order to suppress the concentration of stress.

In the shaft assembly having such a configuration, when the coupling member 10 is fixed to a predetermined object (not shown) and the shaft 20 rotates with respect to the coupling member 10 fixed to the object, a conventional shaft As in the assembly, friction torque is generated between the shaft 20 and the fluid 30. However, the magnitude of the friction torque in the shaft assembly of this embodiment is reduced compared to the friction torque in the conventional shaft assembly because of the following.

First, in the conventional shaft assembly as described with reference to FIG. 1, the shear stress of the fluid 30 acts on the entire surface of the shaft 2 facing the inner circumferential surface 1a of the coupling member 1, and thus The entire surface becomes the friction area. On the other hand, in the shaft coupling body of the present embodiment, a plurality of grooves 25 arranged in the circumferential direction are provided on the shaft 20 so that the fluids 30 are accommodated in the grooves 25, and the grooves ( Most of the fluid 30 contained in 25 has a velocity distribution nearly similar to the rotation of the rigid body within the grooves 25 when the shaft 20 is rotated. If the fluid has a velocity distribution such as rigid body rotation, the shear stress is zero, so friction torque acting in a direction that substantially prevents rotation of the shaft 20 between the bottom surface of each groove 25 and the fluid 30. Will not occur. Therefore, the portion of the shaft 20 in contact with the fluid 30 in which the shear stress of the fluid 30 acts is limited to the outer circumferential surface of the portions located between the grooves 25, and eventually the shaft The area generating friction torque that hinders the rotation of 20 is limited only to the outer circumferential surface area of the portions excluding the grooves 25. As a result, in the shaft assembly of this embodiment, the friction torque is reduced as compared with the conventional shaft assembly.

The reduction of the friction torque by the grooves 25 can be easily confirmed by numerical analysis performed by the present inventors. For example, in the shaft assembly as shown in FIG. 3A, the outer diameter of the shaft 20 ( D1) is 9 cm, inner diameter D2 of coupling member 10 is 10 cm, depth d of each groove portion 25 formed in shaft 20 is 5 mm, and center angle α of each groove portion 25 is 60 °. The fluid 30 interposed between the outer circumferential surface of the shaft 20 and the inner circumferential surface 11 of the coupling member 10 is a lubricant having a kinematic viscosity of 0.00033 m ² / sec and a density of 891 kg / m ³ , It is assumed that the shaft 20 is rotated at a rotational speed of 1261 rpm in the direction of the arrow R, so that the shaft 20 is rotated from the predetermined first point SP and the first point SP in the opposite direction to the arrow R. a numerical analysis results for the friction torque generated between the second point 90 ^o portion with fluid 30 which is located between the (EP) in the rotated position in FIG. 4 It is shown as graphs.

In FIG. 4, the angle θ of the horizontal axis indicates that the first point SP and the second point EP of the axis 20 and each measuring point therebetween are respectively indicated by arrows R from the first point SP. This is an angle indicating how much the position is rotated in the opposite direction of. For example, when the angle θ is 30, the position is rotated by 30 ^{° in} the opposite direction of the arrow R from the first point SP. It means the point located in. When the angle θ is 90, it means a point located at a position rotated 90 ° from the first point SP in the opposite direction to the arrow R, that is, the second point EP. The vertical axis represents the friction torque per unit area (unit is N / m) at each measurement point on the outer surface of the shaft 20. And the graph shown by the solid line shows the numerical analysis result in a present Example. On the other hand, shown by the dashed line in the graph of Figure 4 shows the numerical results of the conventional shaft coupling body, except that only the groove portion is not formed, other conditions are different from the measurement conditions in this embodiment The numerical results are shown under the same conditions.

As can be seen in FIG. 4, while the friction torque in the conventional shaft assembly has the same value at all the measurement points, in the shaft assembly of the present embodiment, due to the above-described groove 25, the friction is part by part. The distribution of the magnitude of the torque will be different. That is, the friction torque at the points where the angle θ in the shaft assembly of the present embodiment is in the range of 0 ° to 15 ° is slightly larger than that of the conventional shaft assembly, but the difference is not severe. The friction torque slightly increases in the portion just before θ reaches 15 °, which is the starting point of the groove 25, but the angle range is very small. On the other hand, the angle θ is 15 °, which is the starting point of the groove 25. The friction torque at the points in the 75 ° range at which the groove 25 ends at, i.e., the friction torque at the points on the bottom surface of the groove 25, is received in the groove 25 and the bottom of the groove 25 The shear force between the fluid 30 and the bottom surface of the groove 25 is insignificant because the fluid 30 in contact with the surface has a velocity distribution that is almost similar to the rotation of the rigid body. Significantly reduced. Then, from 75 ° where the groove ends, the shear stress by the fluid 30 is again affected, and the friction torque is greatly increased at points within the range of 75 ° to approximately 76 °. However, this greatly increased portion is limited to a very small angular range as shown, and the friction torque of a size substantially similar to the 0 ° to 15 ° section is generated from the position beyond the angular range to 90 °. . On the other hand, Figure 4 shows the numerical analysis results for the portion between the angle (θ) between 0 ° and 90 °, wherein the angle (θ) is between the portion between 90 ° and 180 °, the angle (θ) It goes without saying that the friction torque distribution is the same between the portion between 180 ° and 270 ° and the angle θ between 270 ° and 360 °.

Thus, in the shaft assembly of the present embodiment, the groove 25 has a different friction torque distribution for each position of the surface of the shaft, the total friction torque in the range of the angle (θ) is 0 ° to 90 ° That is, it can be easily seen that the value of the friction torque integrated in the section from 0 degrees to 90 degrees is smaller than the total friction torque of the conventional shaft assembly.

The friction torque distribution is slightly different depending on the quantity or size of the groove 25, but the overall distribution shape is not significantly changed, and the reduction rate of the overall friction torque, that is, in the conventional shaft assembly without the groove portion described above It was confirmed that the reduction rate of the friction torque in the case of the above-described grooves with respect to the friction torque of does not change significantly.

For example, as shown in FIG. 5, two grooves 25 formed on the outer circumferential surface of the shaft 20 are formed at intervals of 180 degrees along the circumferential direction, and the center angle α of each groove portion 25 is set to 120 °. With respect to the formed shaft assembly, the outer diameter of the shaft 20 is 9 cm, the inner diameter of the coupling member 10 is 10 cm, and the depth d of each groove 25 formed in the shaft 20 is 5 mm, and the shaft 20 A lubricant having a kinematic viscosity of 0.00033 m ² / sec and a density of 891 kg / m ³ as a fluid between the outer circumferential surface of the coupling member and the inner circumferential surface 11 of the coupling member 10 and rotating the shaft 20 at a rotational speed of 1261 rpm. As a result of numerically analyzing the distribution of the friction torque by the same method as described above for the portion located within the range of 180 ° of the central angle of the shaft, as shown in FIG. 6, the friction torque distribution shown in FIG. It was confirmed that the friction torque distribution of similar shape appeared. The friction torque distribution shown in FIG. 6 may be easily understood with reference to FIGS. 4 and 4, and thus detailed description thereof will be omitted.

In addition, as a result of numerical analysis by varying the size of the groove, the number of grooves, and the rotational speed of the shaft, the respective friction torque distributions were not significantly different from the friction torque distributions shown in FIGS. 4 and 6, and the total friction torque was It was confirmed that it is reduced compared to the conventional shaft assembly without addition.

In the above embodiments, four or two grooves are described and illustrated, but three or five or more grooves may be formed.

In the present embodiment, the grooves 25 are arranged at the same angular intervals, but the grooves 25 should not necessarily have the same angular spacing to obtain a friction torque reduction effect. In addition, the specification of each groove portion 25, that is, the depth (d) or the center angle (α) should also be those of the above embodiments does not achieve the object of the present invention, and each groove portion 25 must have the same standard with each other It is not.

In the above embodiments, the fluid interposed between the coupling member 10 and the shaft 20 is lubricating oil. However, when the coupling member supports the shaft by the so-called air bearing effect, the fluid is used. Only air may be interposed.

In addition, in the above-described embodiments, the coupling member 10 is described as being fixed to a predetermined object and the shaft 20 is rotated, but the shaft is fixed and the shaft is rotated relative to the coupling member by rotating the coupling member. Of course, the present invention can also be applied to the shaft assembly of the form. For example, as illustrated in FIG. 7, the coupling member 110 and the shaft 120 are included, and the shaft 120 is fixed to a predetermined object (not shown), and the coupling member 110 is formed on the shaft. In the case of the shaft assembly having a configuration of a roller rotatably supported by the 120, when the groove 115 as described above is formed on the inner peripheral surface 111 of the coupling member 110 that is actually powered and rotated By the same principle as in the above-described embodiment, the friction torque caused by the friction between the coupling member 110 and the fluid 130 is reduced as compared with the friction torque in the conventional shaft assembly.

While the present invention has been described with reference to some examples, various modifications, such as a form in which simple design changes have been made to the above-described elements or a combination of the above-described elements, within the scope not departing from the technical spirit of the present invention. It may be embodied in the form.

As described above, the groove-applied shaft assembly for reducing frictional torque according to the present invention includes a coupling member and a shaft which rotates relative to the coupling member, and actually supplies power among the inner circumferential surface of the coupling member and the outer circumferential surface of the shaft. By having a configuration in which a plurality of grooves are formed in the circumferential direction on the main surface of the receiving and rotating member, friction torque due to friction between the engaging member and the fluid interposed between the shaft and the shaft during relative rotation of the engaging member can be reduced. Can be.

Claims (6)

A hollow coupling member having an inner circumferential surface and a relative rotation with respect to the coupling member can be inserted into the coupling member, and have an outer circumferential surface opposite to the inner circumferential surface of the coupling member, and a fluid is interposed between the outer circumferential surface and the inner circumferential surface of the coupling member. In the shaft assembly comprising an axis to be formed, In accordance with the circumferential direction, the main surface of the member which is actually powered by the inner circumferential surface of the coupling member and the outer circumferential surface of the shaft is rotated so that the friction torque generated between the fluid and the fluid during the relative rotation of the coupling member with the shaft is reduced. A groove application shaft assembly for reducing friction torque, characterized in that a plurality of groove portions arranged are formed. And a hollow coupling member having an inner circumferential surface, the shaft being rotatably fitted to the coupling member and having an outer circumferential surface opposite the inner circumferential surface of the coupling member, the shaft being interposed between the outer circumferential surface and the inner circumferential surface of the coupling member. In Groove application shaft assembly for reducing the friction torque, characterized in that a plurality of grooves disposed along the circumferential direction is formed on the outer circumferential surface of the shaft so that the friction torque generated between the fluid and the fluid during rotation of the shaft is reduced . 3. The grooved shaft assembly as claimed in claim 2, wherein the grooves are formed at equal angular intervals along the circumferential direction of the shaft. 3. The grooved shaft assembly as claimed in claim 2, wherein the grooves have the same size as each other. The shaft assembly of claim 2, wherein the fluid is a lubricant. 3. The grooved shaft assembly as claimed in claim 2, wherein the edges of the grooves are curved.