EP3060820A1

EP3060820A1 - Rolling bearing

Info

Publication number: EP3060820A1
Application number: EP14799329.9A
Authority: EP
Inventors: Wolfgang Braun; Vasilios Bakolas
Original assignee: Schaeffler Technologies AG and Co KG
Current assignee: Schaeffler Technologies AG and Co KG
Priority date: 2013-10-25
Filing date: 2014-09-30
Publication date: 2016-08-31
Also published as: WO2015058758A1; DE102013221685A1; US20160273584A1

Abstract

A rolling bearing (1) comprises balls (4) made of a shape memory alloy, in particular Nitinol 60, as rolling elements which roll on at least one bearing ring (2, 3) comprising a groove-shaped raceway (5). The balls (4) contact the raceway (5) with at least 108% osculation.

Description

Name of the invention

roller bearing

description

FIELD OF THE INVENTION The invention relates to a rolling body, namely balls, rolling bearings having a shape memory alloy, in particular a nickel-titanium alloy, according to the preamble of claim 1.

Background of the invention

US Pat. No. 6,886,986 B1 discloses antifriction bearings made of a nickel-titanium alloy, namely Nitinol 60. To produce the rolling elements, a ceramic casting mold is used. After casting, additional processing steps are provided which include polishing the nitinol beads.

Nickel-titanium alloys are distinguished by high corrosion resistance combined with high hardness, which makes them fundamentally suitable for rolling elements in bearings which are operated under unfavorable environmental conditions, in particular lack of lubrication and / or exposure to aggressive media.

Object of the invention

The invention has for its object to extend the applications of rolling bearings, namely ball bearings, with rolling elements of a shape memory alloy over the cited prior art. Description of the invention

This object is achieved by a trained as a ball bearing bearings with the features of claim 1. The rolling bearing has in known per se basic structure rolling elements of a shape memory alloy, which roll between two raceways of bearing rings or between a raceway of a bearing ring and a career located directly on a shaft, wherein at least one raceway is grooved. A raceway of the rolling bearing can also be formed directly by a housing component. According to the invention, the balls contact the groove-shaped raceway with an osculation of at least 108%. By oscillation in this case, the ratio between the radius of the groove forming the track and the radius of the ball understood. As a material for producing the without restriction of the generality as a bearing ring designated, the groove-shaped raceway bearing part of the rolling bearing, for example, a nickel-titanium alloy is suitable. Preferably, the alloy has a weight percent nickel content greater than 55%. In particular, the alloy Nitinol 60 (60% nickel, 40% titanium) is suitable for the production of the bearing ring.

In comparison to the prior art, the osculation has a relatively high value. This means that the raceway on which the ball rolls, is formed relatively flat, so that the contact surface between the ball and the bearing ring tends to be reduced. This basically causes a reduction in the bearing capacity of the rolling bearing. In the present case, thanks to the use of rolling elements of a shape memory alloy, in particular a nickel-titanium alloy, however, this effect is low, since such alloys have a significantly lower modulus of elasticity than steel. Due to the high elastic compliance of shape memory alloys, in particular nickel-titanium alloys, in comparison to steel, the load-reducing effect of a relative to the dimensioning of the balls is reduced. The radius of the groove, in which the balls roll, is overcompensated.

In an advantageous embodiment, the balls of the rolling bearing are made of a material whose modulus of elasticity is less than 60% of the modulus of elasticity of the bearing ring on which the balls roll. Preferably, the modulus of elasticity of the balls is at most 120 GPa. In contrast, the bearing rings preferably have a modulus of elasticity of over 200 GPa. Due to the associated with the increase in the value of the oscillation reduction of the contact surface between the bearing ring and rolling elements, the friction and thus the heat in the bearing is reduced in comparison to conventional bearings with closer osculation, especially when operating with low loads. The bearing with a value of at least 108%, which has a particularly wide osculation, is therefore particularly suitable for operation under unfavorable lubrication conditions and thus in many cases also unfavorable conditions of heat dissipation.

The mentioned minimum amount of osculation of 108% applies in preferred embodiments for the inner ring of a roller bearing designed as a deep groove ball bearing, while the outer ring of such a ball bearing has a osculation of at least 1 10%. Also in embodiments of the rolling bearing which have an osculation of more than 108% on the inner ring, a further greater osculation is preferably given on the outer ring. The value of the osculation on the outer ring is, for example, more than 1.05 times the value of the osculation on the inner ring.

With 108% osculation on the inner ring results in a pressure that corresponds approximately to the pressure in a conventional inner ring made of steel with 103% osculation. On the outer ring corresponds to the pressure in a designed according to the invention roller bearing with 1 17% osculation of the pressure in a conventional bearing with about 105% osculation on the outer ring. Another advantage of the production of the balls of the rolling bearing of a nickel-titanium alloy, preferably Nitinol 60, lies in the much lower compared to steel density of such an alloy. The rolling bearing is therefore particularly suitable for high speeds, even under unfavorable lubrication conditions.

The surface hardness of the rolling elements is in a preferred embodiment more than 58 HRC, with hardness values up to 62 HRC can be achieved. The rolling elements of the rolling bearing can be subjected to a heat treatment. Further advantages of the rolling elements made of a shape memory alloy are their compatibility with lubricants, their corrosion resistance and their wear resistance.

The bearing rings of the rolling bearing are made of steel, for example, from conventional bearing steel or from a corrosion-resistant steel. Steel which is available under the name Cronidur (X 30 CrMoN 15 1, material number 1 .4108) has proven particularly suitable.

A preferred application of the rolling bearing are fast-moving and media-lubricated bearings. Under a media lubrication is generally understood to act on the Wälzkontaktflächen with a medium which is not intended primarily for lubrication. This may be, for example, a fluid which is conveyed in a pump equipped with the roller bearing or a compressor. The use of a roller bearing under water, especially in seawater, which is not or only partially sealed, is also considered to be the medium-lubricated operation of a roller bearing.

An embodiment of the invention will be explained in more detail with reference to a drawing. Herein show:

Short description of the drawing 1 shows a rolling bearing with rolling elements of a shape memory alloy in a sectional view,

Fig. 2 is a diagram of the relationship between osculation and pressure in the rolling bearing according to the invention on the one hand and a

Comparative rolling bearing on the other.

DETAILED DESCRIPTION OF THE DRAWING FIG. 1 shows a roller bearing, designated overall by the reference numeral 1, which has two bearing rings 2, 3, namely an outer ring 2 and an inner ring 3, between which rolling elements 4 roll. The rolling elements 4 are formed as balls of Nitinol 60 (60% Ni, 40% Ti). The groove-shaped raceways of the bearing rings 2, 3, on which the balls 4 roll, are identified by the reference numeral 5. Using the example of the inner ring 3, in addition to the illustrated raceway 5 of the rolling bearing 1, a comparative race 6 is indicated, which snuggles closer to the ball 4 and corresponds to the contour of a bearing ring of an unclaimed conventional rolling bearing, namely a radial deep groove ball bearing.

The radius of the ball 4 is designated in Figure 1 with r _K , the radius of the raceway 5 with r _L. The ratio between the raceway radius r _L and the ball radius r _K is significantly more than 108% and is defined as osculation. In comparison to conventional bearing constructions, which are indicated by the contour of the comparison raceway 6, the osculation of the rolling bearing 1 is exceptionally far. In the mechanically unloaded or slightly loaded state, as shown in FIG. 1, this results in a considerably smaller contact surface between the rolling body 4 and the raceway 5 than bearings with a narrower osculation.

However, this is overcompensated, at least during operation of the rolling bearing 1 under high mechanical load, in that the modulus of elasticity of the rolling element 4 with 1 14 GPa is only slightly more than half that Young's modulus of the bearing rings 2, 3. The bearing rings 2, 3 are made of steel with a modulus of elasticity of 208 GPa. The density of the material having shape memory properties, from which the rolling element 4 is made, is between 6 and 7 g / cm ³ and is thus considerably lower than the density of steel. Accordingly, occurring during operation of the rolling bearing 1 centrifugal forces are significantly reduced compared to conventional bearings with steel rolling elements.

The relationships between osculation S (in%) of the rolling bearing 1, maximum pressure P (in MPa) in the contact between rolling elements 4 and raceway 5, and modulus of elasticity of the rolling elements 4 are illustrated in FIG. Characteristics of a conventional deep groove ball bearing, which balls from common bearing steel, for example, 100Cr6, are outlined in Figure 2 by a dashed line. At higher values of osculation, ie when the raceway becomes flatter, the maximum pressure in the rolling contact increases significantly. This relationship is basically also in the rolling bearing 1 according to the invention of Figure 1, as described in Figure 2 by an increasing solid line, can be seen. Because of the rolling bearing 1 according to the invention compared to the conventional rolling bearing significantly lower modulus of elasticity of the rolling elements 4, the pressure P, which acts in the rolling contact, drastically reduced. The preferred range of osculation of the rolling bearing 1 is highlighted in Figure 2 by a hatched over the solid line hatching. The entire solid line, which shows characteristics of embodiments of the rolling bearing 1 according to the invention (from 108% osculation), lies significantly below the dashed line, which shows properties of a conventional comparative rolling bearing. Even the highest point within the shaded area, which is a bearing with a very wide groove compared to the ball radius, is below the maximum pressure that occurs in a conventional bearing with steel balls and extremely tight lubrication (lowest point of the dashed line) , Another advantage of the very wide osculation of the rolling bearing 1 according to the invention lies in the fact that compared to conventional deep groove ball bearings, a larger axial offset between the bearing rings 2, 3 is possible, and a larger angle error between the rotatable relative to each other, mounted by means of the rolling bearing parts 1 acceptable is.

Due to the material of the rolling elements 4 and the described geometric relationships, the rolling bearing 1 is characterized by a particularly high corrosion resistance and wear resistance, a variety of lubricants are used and even an unlubricated operation within limited speed and load ranges is possible.

LIST OF REFERENCE NUMBERS

1 rolling bearing

2 outer ring

3 inner ring

4 rolling elements, ball

5 career

6 Comparative Runway P Pressing

r _L radius of the raceway

r _K sphere radius

S oscillation

Claims

claims

1 . Rolling bearing (1), with balls (4) made of a shape memory alloy as rolling elements, which roll on at least one bearing groove (2,3) having a groove-shaped track (5), characterized in that the balls (4) form the track (5 ) with an osculation of at least 108%.

2. Rolling bearing (1) according to claim 1, characterized in that the balls (4) are made of a nickel-titanium alloy having a nickel content of more than 55 wt .-%.

3. rolling bearing (1) according to claim 2, characterized in that the balls (4) contain 60 wt .-% nickel and 40 wt .-% titanium.

4. rolling bearing (1) according to one of claims 1 to 3, characterized in that the balls (4) have a surface hardness of more than 58 HRC.

5. rolling bearing (1) according to one of claims 1 to 4, characterized in that the balls (4) have a modulus of elasticity of at most 120 GPa.

6. rolling bearing (1) according to one of claims 1 to 5, marked thereby, that the modulus of elasticity of the balls (4) is less than 60% of the modulus of elasticity of the bearing rings (2,3).

7. rolling bearing (1) according to one of claims 1 to 5, characterized in that the bearing rings (2,3) made of a stainless steel, in particular steel with the material number 1 .4108, are made.

8. Rolling bearing (1) according to one of claims 1 to 3, characterized in that the balls (4) designed as an outer ring (2) bearing ring Contact with a further osculation as a bearing ring designed as an inner ring (3).

9. Rolling bearing (1) according to claim 8, characterized in that the osculation on the outer ring (2) is at least 1 10%.

10. Use of a roller bearing (1) according to claim 1 as a water-lubricated, in particular seawater lubricated, bearing.