JP2001027300A - Ball screw - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ball screw excellent in productivity and lubricating performance allowing oil to be easily retained at a land part and retained oil to easily flow into a thread groove. SOLUTION: An oil retaining spiral groove 8 is formed at least at one of a land part 6 between thread grooves 3 of a screw shaft 1 and a land part 7 between thread grooves 4 of a nut 2. The spiral groove 8 is communicated with the thread grooves 3, 4. The spiral groove 8 is formed by eliminating grinding of the screw shaft 1 and nut 2 or reducing the quantity of grinding, and the ridge part of the spiral groove 8 is formed into a flat face. A lead angle θ2 of the spiral groove 8 is formed to be larger than a lead angle θ1 of the thread grooves 3, 4 or formed in a reverse direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ball screw which can be applied to ball screws for various uses and improves lubricity.

[0002]

2. Description of the Related Art In a ball screw, lands 55 and 56 are formed between screw grooves 53 and 54 of a screw shaft 51 and a nut 52 as shown in an enlarged cross section in FIG. These land portions 55 and 56 are formed by turning, and are subjected to grinding after heat treatment or after this heat treatment and further after hardened steel cutting.

[0003]

In the conventional ball screw, a gap between the land 55 of the screw shaft 51 and the land 56 of the nut 52 and a gap between the screw grooves 53, 54 and a ball (not shown) are provided. Oil such as grease is held in the gap. However, since the surfaces of the lands 55 and 56 are flat, it is difficult to always retain the oil. In particular, in the conventional thread groove processing, the outer diameter portion of the screw shaft 51 is rested so that the screw shaft 51 is not bent by the grinding process, but the land portion 55 is used because the rest is used.
In addition, more grinding than necessary is performed. Therefore, the processing time is long, and the surface is too flat, so that it is difficult to hold oil. Further, since the oil between the land portions 55 and 56 has no flow path, the flow between the screw grooves 53 and 54 is only agitated by the centrifugal force due to the rotation of the screw shaft 51, and is difficult to flow. It is difficult to use it effectively for lubrication.

An object of the present invention is to provide a ball screw which is easy to hold oil on a land portion, has excellent lubricity and is excellent in productivity. Another object of the present invention is to make it easy for the oil held in the land to flow into the thread groove and to effectively use it for lubrication.

[0005]

In the ball screw of the present invention, spiral screw grooves are provided on an outer peripheral surface of a screw shaft and an inner peripheral surface of a nut loosely fitted on the outer periphery of the screw shaft, respectively.
In a ball screw in which a plurality of balls are interposed between these screw grooves, a spiral groove for holding oil is formed on at least one of the lands between the screw shaft and the screw groove of the nut. As used herein, "oil" generally includes a fluid lubricant and includes grease. According to this configuration, when the screw shaft is used for rotation, the spiral groove in the land portion of the screw shaft becomes an oil reservoir, and when the screw shaft rotates, the oil in the spiral groove flows along this groove, and to go into.
Thus, oil is supplied between the ball and the thread groove from the land portion. Further, the oil is removed from the thread groove by the circulation of the ball, and the removed oil collects in the spiral groove of the land and is supplied to the thread groove again. for that reason,
The oil is circulated and prevented from leaking out,
Lubricity is maintained for a long time. When the nut is used for rotation, the spiral groove in the land portion of the nut becomes an oil reservoir, and when the nut rotates, the oil in the spiral groove flows along this groove and is supplied to the screw groove portion. Further, the oil removed from the thread groove portion by the ball circulation accumulates in the spiral groove of the land portion, is again supplied to the thread groove, and is used repeatedly. As described above, by forming the spiral groove in the land portion, the oil is easily held in the spiral groove, and the spiral groove serves as a lubrication path, so that the oil is easily supplied to the screw groove, and the lubricating property is excellent. It becomes a low torque ball screw. Further, since the oil retaining groove is a spiral groove, it can be easily formed by turning or the like, and can be formed by ordinary turning or grinding steps without increasing the number of steps, thereby increasing productivity. good.

In the present invention, the peak of the spiral groove of the land may be formed on a flat surface. Such a helical groove with a flat ridge eliminates grinding after turning in machining the outer diameter surface of the screw shaft or the inner diameter surface of the nut, or makes the grinding allowance thinner than the depth of the turning groove. Obtained by: Therefore, the spiral groove can be obtained by simplifying the usual processing of the land portion without adding a groove forming process to the formation of the spiral groove, thereby improving the productivity. In addition, by forming the ridges of the spiral grooves of the lands on the flat surface as described above, it is possible to grind the screw grooves using the rests on the lands while providing the spiral grooves.

[0007] In the present invention, the spiral groove of the land portion may communicate with the screw groove. In this way, by making the spiral groove communicate with the screw groove, the oil of the spiral groove easily enters the screw groove.

In the present invention, the lead angle of the spiral groove in the land may be formed larger than the lead angle of the screw groove. As described above, by increasing the lead angle of the spiral groove, the effect that the oil in the spiral groove flows into the screw groove with rotation becomes more likely to occur.

In the present invention, the lead angle of the spiral groove in the land may be formed in a direction opposite to the lead angle of the screw groove. As described above, even when the lead angle of the spiral groove is set in the opposite direction to the lead angle of the screw groove, the effect that the oil in the spiral groove flows into the screw groove with rotation easily occurs.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to FIGS. The ball screw is provided with helical thread grooves 3 and 4 on the outer peripheral surface of a screw shaft 1 and the inner peripheral surface of a nut 2 loosely fitted on the outer periphery of the screw shaft 1, respectively. In a ball screw in which a plurality of balls 5 are interposed, between the screw grooves 3 of the screw shaft 1 and the nut 2
Spiral grooves 8 and 9 (FIG. 2) for retaining oil are formed in land portions 6 and 7 between the screw grooves 4.

A nut 2 shown in FIG.
A circulation path 10 is provided for circulating the ball 5 interposed between the screw grooves 3 and 4 from the screw grooves 3 and 4. Although the type of the circulation path 10 is not particularly limited, in this example, guide grooves 10b and 10c that follow the space between the screw grooves 3 and 4 are formed on both sides of the through hole 10a that extends in the axial direction.

Spiral grooves 8 for retaining oil in each of the lands 6 and 7
9 has both ends communicating with the screw grooves 3 and 4, and the spiral grooves 8 and 9 have ridges formed on a flat surface. The flat surface is a surface having a flatness similar to a finish turning surface or a grinding surface. The lead angle θ2 of the spiral grooves 8, 9 is formed larger than the lead angle θ1 of the screw grooves 3, 4.
The lead angle θ2 of the spiral grooves 8, 9 may be formed in a direction opposite to the lead angle θ1 of the screw grooves 3, 4.

The spiral grooves 8, 9 are formed by, for example, any of the following methods. In any case, as the basic processing, the screw shaft 1 is formed by forming a thread groove 3 by turning from a round bar-shaped material and then grinding. The nut 2 is ground after forming a thread groove 4 by turning on the inner diameter surface of a cylindrical material such as a cast product or a plastic processed product. On the premise of such basic processing, any of the following methods (1) to (4) is adopted. These methods can be performed in any combination. For example,
,, May be performed. In the above-mentioned turning process of the screw shaft 1 and the nut 2, a larger amount of cut is taken than in the ordinary turning, and the spiral grooves 8, 9 are formed in the lands 6, 7. When turning the outer diameter of the screw shaft 1 and the inner diameter of the nut 2,
Speed up feeding. The grinding of the outer diameter of the screw shaft 1 is eliminated, or the grinding allowance is made thinner than the depth of the groove generated by turning. In this case, the peak between the spiral grooves 8 is formed flat, and the turning remains as the spiral groove 8.

According to the ball screw having this configuration, when the screw is used for rotating the shaft, the spiral groove 8 of the land portion 6 of the screw shaft 1 becomes an oil reservoir, and the oil in the spiral groove 8 is rotated by the rotation of the screw shaft 1. It flows along the groove 8 and enters the thread groove 3. In this way, oil is supplied from the land portion 6 between the ball 5 and the thread grooves 3 and 4. The oil is removed from between the screw grooves 3 and 4 by the circulation of the ball 5, and the removed oil collects in the spiral groove 8 of the land 6 and is supplied again between the screw grooves 3 and 4. You. Therefore, the oil is circulated and prevented from flowing out, and excellent lubricity is maintained for a long time. When the nut 2 is used for rotation, the spiral groove 9 of the land portion 7 of the nut 2 becomes an oil reservoir, and when the nut 2 rotates, the oil of the spiral groove 9 flows along the groove 9 and the screw groove 3 , 4. The oil removed from between the screw grooves 3 and 4 by the ball circulation accumulates in the spiral groove 9 of the land 7 and is again supplied between the screw grooves 3 and 4 so that the oil is circulated and used many times. By forming the spiral grooves 8 and 9 in the lands 6 and 7 in this manner, a low-torque ball screw that easily holds oil and has excellent lubricity can be obtained.

Further, since the oil retaining grooves are the spiral grooves 8 and 9, the outer peripheral surface and the inner peripheral surface which are usually performed without adding a groove processing step as in each of the above examples. It can be easily formed in the turning process, etc., and has good productivity. Moreover, by forming the spiral grooves 8 and 9 in this manner, the grinding allowance of the lands 6 and 7 can be reduced, and the processing time of the ball screw can be shortened. If the thread groove 3 of the screw shaft 1 can be ground without using a rest, it is not necessary to perform the grinding process, and the processing time of the ball screw can be similarly reduced. The rest used when machining the thread groove 3 of the screw shaft 1 generally has a width of at least one pitch of a ball screw, and can be rested if the land 6 is flat. It is sufficient to perform only the processing, and it is not necessary to perform the grinding processing more deeply than necessary as conventionally performed in general. When the length of the screw shaft 1 is short, the screw groove can be ground without using a rest.

[0016]

According to the ball screw of the present invention, since a spiral groove for holding oil is formed in at least one of the land portions between the screw grooves in the screw shaft and the nut, oil is easily held in the land portion. In addition, the retained oil easily flows into the thread groove, and has excellent lubricity and excellent productivity. When the peak of the spiral groove of the land is formed on a flat surface, the spiral groove is formed by simplifying the processing of the normal land without any additional processing of the spiral groove. Yes, good productivity. When the spiral groove of the land portion is communicated with the screw groove, the oil held in the spiral groove flows more easily into the screw groove. When the lead angle of the spiral groove of the land portion is formed larger than the lead angle of the screw groove, and when the lead angle of the spiral groove of the land portion is formed in the opposite direction to the lead angle of the screw groove. In any case, the action of oil flowing in the spiral groove with rotation easily occurs,
The supply of oil to the screw groove is further improved.

[Brief description of the drawings]

FIG. 1 is a sectional view of a ball screw according to an embodiment of the present invention.

FIG. 2 is an enlarged sectional view showing a screw groove and a land portion of the screw shaft and the nut.

FIG. 3 is a sectional view of a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Screw shaft 2 ... Nut 3, 4 ... Screw groove 5 ... Ball 6, 7 ... Land part 8, 9 ... Spiral groove

Claims (5)

[Claims] A helical screw groove is provided on each of an outer peripheral surface of a screw shaft and an inner peripheral surface of a nut loosely fitted on the outer periphery of the screw shaft, and a plurality of balls are interposed between the screw grooves. In a ball screw, a helical groove for retaining oil is formed in at least one of lands between the screw shaft and the screw groove of the nut. 2. The ball screw according to claim 1, wherein a ridge of the spiral groove of the land is formed on a flat surface. 3. The ball screw according to claim 1, wherein the spiral groove of the land portion communicates with the screw groove. 4. The ball screw according to claim 1, wherein a lead angle of the spiral groove of the land portion is larger than a lead angle of the screw groove. 5. The ball screw according to claim 1, wherein a lead angle of the spiral groove of the land is formed in a direction opposite to a lead angle of the screw groove.