WO2007054487A1

WO2007054487A1 - Ball screw

Info

Publication number: WO2007054487A1
Application number: PCT/EP2006/068163
Authority: WO
Inventors: Jürgen OSTERLAENGER; Manfred Kraus
Original assignee: Schaeffler Kg
Priority date: 2005-11-10
Filing date: 2006-11-07
Publication date: 2007-05-18
Also published as: DE102005053621A1; DE102005053621B4

Abstract

The ball screw comprises a threaded spindle and a nut having an internal thread, which is guided on the threaded spindle over balls engaging on both sides of the thread, said balls being diverted via a nut-side ball diversion, whereby the ball diameter (D) of the balls (6) guided in at least two ball rows (I, II, III) surrounding once is equal or greater than the thread pitch (S), whereby at least one turn (7) does not contain a ball between two ball rows (I, II, III).

Description

Description of the invention

Ball Screw

Field of the invention

The invention relates to a ball screw drive comprising a threaded spindle having an external thread and a nut having an internal thread, which is guided on the threaded spindle via balls engaging in the two-sided threads, which balls are deflected via a nut-side ball deflection.

Background of the invention

Such ball screws are used for actuating tasks in a variety of applications in the field of mechanical engineering or automotive technology. Often there is the desire for the smallest possible pitch of the screw drive in order to save an otherwise often required additional actuating gear. However, with decreasing slope, a number of difficulties arise. On the one hand, the balls, whose diameter is always smaller than the thread pitch in known ball screws, can not be made arbitrarily small, without the tolerance sensitivity increasing. The smaller the balls are, the smaller their spring deflection under load. As a result, inaccuracies such as pitch differences between the nut thread and the spindle thread have a greater effect on smaller and stiffer balls than on larger ones. As a result, the load distribution is more uneven and may not even support individual balls. Also, the production of such ball screws with pitches ≤ 4 mm, in particular ≤ 3 mm, very expensive, since due to the very small diameter balls a precision engineering production is required. For example, with a pitch of 2 mm balls with a diameter of 1, 5 mm are common, which leads to mounting problems. Another disadvantage is that for small gradients of the distance between two adjacent balls relative is small, so that there is often not enough space to position the ball deflection, especially when individual deflections are selected. If, as a result, the ball diameter is further reduced, the above difficulties increase.

Summary of the invention

The invention is therefore based on the problem to provide a ball screw, with the small and smallest gradients can be realized, and beyond its production compared to previously known ball screws with low pitch cheaper and robust against lateral forces and bending moments.

To solve this problem is provided according to the invention in a ball screw of the type mentioned above that the ball diameter of the guided in at least two once circumferential rows of balls balls is equal to or greater than the thread pitch, wherein between two rows of balls at least one thread is free of balls.

In the ball drive according to the invention is in departure from all previously known designs, the ball diameter at least equal to, but preferably greater than the thread pitch, so it will be compared with ball screws with a corresponding pitch, larger balls used. The balls are inventively guided in two or more separate rows of balls, each circulating once, so therefore single ball deflections are provided. Due to the larger ball diameter, at least one thread is ball-free between two rows of balls, in order to avoid ball collisions.

Consequently, very small pitches can be realized with the ball screw drive according to the invention, with sufficiently large balls being used which, on the one hand, enable good handling, and consequently the production is also relatively simple and also cost-effective. In addition, compared to comparable solutions with small balls, significantly higher lateral forces and Bending moments can be absorbed, therefore, the screw drive itself is much more robust, the load capacity is great. As a result of the inevitably provided spacing of the rows of balls, there are also no difficulties with regard to the ball deflection, which according to the invention are realized here as individual deflections and can be integrated without further ado.

With the ball screw according to the invention consequently smallest pitches, ie gradients less than 4 mm, in particular in the range of 3 mm or 2 mm, due to the application and therefore even smaller, can be realized. Relative to the ball diameter, this means that with the ball screw according to the invention with a ball diameter of z. B. 3 mm the slope - instead of z. B. about 4 mm in a conventional ball screw and already "minimal" executed slope - according to the invention, for example, 2.5 mm or less.

The ratio between ball diameter to thread pitch is according to the invention> 1 and <1, 8. At a ratio> 1, 8, the possible pressure angles between the nut or spindle and the ball are so small that the axial load bearing capacity becomes insignificant. The design of the ball screw drive with regard to pitch and ball diameter should be such that the pressure angle between nut and ball or spindle and ball is> 15 ° and ≤35 ° and the osculation is> 110% and <130%. At values below 1 10%, the pressure ellipse becomes too large for which there is insufficient space, while values above 130% give poor load ratings. Depending on the application or field of application, the design should be selected such that the respectively most appropriate pressure angle or the respectively most appropriate osculation is achieved.

As already described, the ball deflection is formed in the ball screw according to the invention as a single deflection, each separate Einzelumlenkungen are provided for each separate rows of balls. Brief description of the drawings

Further advantages, features and details of the invention will become apparent from the following description of the embodiments. Showing:

1 is a sectional view through a ball screw according to the invention in the form of a schematic diagram,

2 is an enlarged partial view of FIG. 1,

3 is a schematic diagram of a ball deflection,

Fig. 4 is a partial view of a possible single ball deflection, and

Fig. 5 is a perspective view of the individual deflection.

Detailed description of the drawings

Fig. 1 shows in the form of a schematic representation of a ball screw 1 according to the invention consisting of a threaded spindle 2 with an external thread 3 and a nut 4 with an internal thread 5, wherein between external thread 3 and internal thread 5 balls 6 are guided, which are in separate rows of balls I, II and III, each ball row I - III is associated with a Einzelkugelumlenk- kung, which will be discussed below. In the example shown, three rows of balls are provided, of course, only two or more rows of balls can be realized.

In the case of the ball screw drive 1 according to the invention, the ball diameter D is now at least equal, but in the embodiment shown larger than the pitch S of the external thread 3 or the internal thread 5, as can be seen in FIG. In order to avoid ball collisions between balls of adjacent rows of balls, the respectively intermediate thread or thread is Deabschnitt 7 each ball-free. In addition, the pressure angle α between internal thread 5 and external thread 3 and the respective ball 6 compared to that in conventional ball screws with balls whose diameter is smaller than the thread pitch, reduced from usually 45 ° to values between 15 ° and 35 °. In the exemplary embodiment, the pressure angle α is 28 °. Although the lower pressure angle causes formally a lower load rating, which is defined axially in ball screws. By the larger balls, which are used in the invention, however, this effect is compensated by far.

Fig. 3 shows an enlarged view of a section of the ball screw 1 of FIG. 1 in the ball deflection 8. In a corresponding nut-side recess 9, a single deflection 10 is used, which is a plastic part. Fig. 3 shows the section along the center of the single ball deflection. The deflecting ball 6 is located in an area above the two threads 7 separating web 1 1, it is transferred from one thread 7 in the other, as indicated by the arc line, which represents the two centers Z of the respective Kugelendlagen. As a result of the ball clearance of the two adjacent threads 7 (ie, the left and right threads shown in FIG. 3), there is sufficient space to provide a sufficiently large recess 9, thus also sufficiently dimensioning the single ball deflection 10, so that wall thicknesses in the region of the lower , inner end of 0.5 mm or depending on the selected slope also more readily can be used. This means that a safe ball deflection can be realized without the risk of any damage during threading and unthreading on the plastic part.

Finally, FIGS. 4 and 5 show in detail a possible embodiment of the ball deflection. 4 shows a sectional view corresponding to the illustration from FIG. 3, while FIG. 5 shows a detailed perspective view of the individual deflector 10, as shown in section in FIG. 4. Overall, a very small pitch can be realized with the ball screw according to the invention, while still sufficiently manageable balls can be used and consequently the production can still be realized sufficiently simple and inexpensive. For example, with a pitch of 2 mm, balls with a diameter of 2.4 mm or 3 mm may be used, depending on how the respective threads are to be designed in terms of pressure angle and osculation, based on the particular application. Even lower gradients can be realized, whereby the ratio between ball diameter and thread pitch should be in the range given at the outset, correspondingly also the respective contact angle as well as the osculation.

As a result, such a ball screw according to the invention is suitable for many applications, in particular those in which the requirement of a separate reduction gear would be required in order to realize a desired gear ratio. Such is unnecessary when using the ball screw according to the invention, which sometimes considerable cost and space can be saved, but the motor can then directly drive the mother. Finally, the production of sufficiently robust, force and torque stable drives is possible.

reference numerals

1 ball screw

2 threaded spindle

3 external threads

4 mother

5 internal thread

6 balls

7 threaded section

8 ball deflection

9 recess

10 individual diversion

1 1 bridge

I ball row

Il ball row

III ball row

D ball diameter

S slope

Z center point

Claims

claims

1. ball screw comprising an externally threaded threaded spindle and an internal thread nut, which is guided on the threaded spindle via engaging in the double-sided thread balls, which balls are deflected via a nut side ball deflection, characterized in that the ball diameter (D) the balls (6) guided in at least two once circumferential rows of balls (I, II, III) are equal to or larger than those

Thread pitch (S) is, wherein between two rows of balls (I, II, III) at least one thread (7) is ball-free.

2. Ball screw according to claim 1, characterized in that the ratio of ball diameter to thread pitch (D / S)> 1 and <1, 8.

3. Ball screw according to claim 1 or 2, characterized in that the pressure angle (α) between the nut (4) or spindle (2) and ball (6)> 15 ° and <35 °.

4. Ball screw according to one of the preceding claims, characterized in that the osculation is> 110% and <130%.

5. Ball screw according to one of the preceding claims, characterized in that the ball deflection (8) is a Einzelum- steering (10), preferably separate Einzelumlenkungen (10) for each separate rows of balls (I, II, III) are provided.