EP4211358A1

EP4211358A1 - Bearing assembly

Info

Publication number: EP4211358A1
Application number: EP21773315.3A
Authority: EP
Inventors: Ingo Schulz; Lijun CAO; Christoph ZEUG
Original assignee: SKF AB
Current assignee: SKF AB
Priority date: 2020-09-09
Filing date: 2021-09-02
Publication date: 2023-07-19
Also published as: WO2022053382A1; US20230313837A1; DE102020211329A1; KR20230066008A; CN116234991A; JP2023539897A

Abstract

The invention relates to a bearing assembly (1) having a first raceway element (2) and a second raceway element (4), wherein: balls (6) are arranged between the raceway elements (2, 4); the balls (6) roll on raceways (8) which are arranged on the raceway elements (2, 4); the cross-section of the bearing assembly (1) is divided conceptually into four quadrants (I, II, III, IV) by the axis of rotation (AR) of one ball (6) and an axis (As) perpendicular to the axis of rotation (AR) of the ball (6), which quadrants are arranged clockwise; the ball (6) has four contact points (P-I, P-II, P-III, P-IV) with the raceways (8), and each contact point (P-I, P-II, P-III, P-IV) is situated in one of the four quadrants (I, II, III, IV); the raceway (8) of the second raceway element (4) is situated in the first and second quadrants (I, II), and the raceway (8) of the first raceway element (2) is situated in the third and fourth quadrants (III, IV); the midpoint (M-I) of the radius of curvature (R-I) of the raceway (8-1) of the first quadrant (I) is situated in the third quadrant (III); the midpoint (M-II) of the radius of curvature (R-II) of the raceway (8-II) of the second quadrant (II) is situated in the fourth quadrant (IV); the midpoint (M-III) of the radius of curvature (R-III) of the raceway (8-III) of the third quadrant (III) is situated in the first quadrant (I); and the midpoint (M-IV) of the radius of curvature (R-IV) of the raceway (8-IV) of the fourth quadrant (IV) is situated in the second quadrant (II).

Description

bearing arrangement

The present invention relates to a bearing arrangement with a first raceway element and a second raceway element according to patent claim 1.

In high-precision gears, especially in the joints of robots or the bearings of wind turbine blades, the bearings used there often have to perform a rotational movement of less than 360° at a low speed. At the same time, a complex load situation can occur with both radial and axial forces, tilting moment loads and a combination of loads. Crossed roller bearings are often used for this purpose and can be used as a single bearing, whereas two bearings would be required with other types of bearings. Crossed roller bearings have high rigidity, high running accuracy and low backlash. Cylindrical rollers are used for crossed roller bearings, which are inserted in an alternating sequence at an angle of 45° between the bearing rings. Such crossed roller bearings are known for both rotary motion applications and linear motion applications.

However, in the case of cylindrical rollers, sliding, so-called slip, occurs more frequently between the rollers and the raceway surfaces and between the roller side surfaces and the opposite raceway, which leads to increased wear. Sliding also occurs between the rollers themselves, making spacers advantageous, which in turn increases the complexity of the bearing and introduces additional effort in assembling the bearing. Sliding also leads to high energy loss in such bearings. Furthermore, edge stress can occur with crossed roller bearings, This edge stress can be mitigated by special raceway profiles, but these are only intended for a single load case and produce poor load distribution in other load cases. The closer the load direction is to the axis of rotation of the roller, the less load will be carried by the roller. This results in the load being carried by only 50% of the available sheaves under specific load conditions. Furthermore, in some cases, due to the alternating positioning of the rollers, half of the rollers can carry more load than the other half, creating an unequally distributed loaded zone. The alternating positioning of the rollers also causes additional effort when assembling the bearing, since special mechanisms are required to position the rollers.

Other potential solutions to support loads when axial forces are dominant include a thrust ball bearing or a four-point contact ball bearing when a bending moment needs to be supported as well. However, these bearings also have some disadvantages. Thrust ball bearings have minimal radial load stiffness and radial load can cause eccentricity between the bearing rings. The balls in a thrust ball bearing exhibit increased sliding due to centrifugal forces. Since there are only two points of contact between the balls and the raceways, this can result in high contact pressure. The two points of contact between the balls and the raceways change with the direction of the load, causing a dynamic change in the ball's axis of rotation and therefore high and non-constant sliding and therefore high energy losses.

It is therefore an object of the present invention to provide a bearing arrangement which is a stable bearing for radial and axial loads with a low energy loss and which is cheap and easy to manufacture.

This object is achieved by a bearing arrangement according to patent claim 1.

The bearing arrangement has a first raceway element and a second raceway element, with balls being arranged between the raceway elements. The balls each roll on raceways that are arranged on the raceway elements. The bearing arrangement can be a ball bearing, in the form of a radial bearing or an axial bearing, or a linear bearing. In the case of a radial bearing, the first raceway element and the second raceway element correspond to the inner ring and the outer ring. In the case of a thrust bearing, the inner ring and the outer ring (ie, the first raceway member and the second raceway member) are referred to as the housing washer and the shaft washer. In the case of a linear bearing, the first raceway element and the second raceway element correspond to a rail and a carriage.

In order to enable low sliding and friction losses as well as high flexural rigidity and a low maximum contact pressure with the raceways, the balls each have four contact points with the raceways. This means that each ball has a total of four contact points, i.e. two contact points per track element. At the point of contact, the respective raceway and ball have the same tangent and the radius of curvature, i.e. the distance between the center of the circle of curvature of the raceway curvature and the point of contact, is perpendicular to this tangent. These four contact points distribute the contact pressure unlike other bearings, reducing contact stresses and therefore wear, friction and other surface damage.

Conventional four-point contact ball bearings that can be used as thrust bearings also have four contact points, but these are only theoretically available. In operation, only two of the four theoretical contact points are active, thus resulting in high contact pressure at these two active contact points. In contrast, four contact points are always active in the bearing arrangement proposed here, which means that the contact pressure is better distributed. A conventional four-point contact ball bearing also has reduced contact rigidity in both the axial and radial directions because the normal direction of the contact points is not aligned with either the axial or the radial axis. Furthermore, such a bearing requires a high axial preload in order to be able to absorb radial loads.

To achieve this, the bearing assembly is notionally divided in cross section by the axis of rotation of a ball and an axis perpendicular to the axis of rotation of the ball into four quadrants arranged clockwise. The axis of rotation of the sphere is seen here as an imaginary axis of rotation at a standstill. In operation, the axis of rotation of the sphere is not fixed but can move.

The track of the second track element lies in the first and second quadrants and the track of the first track element lies in the third and fourth quadrants. The center of the radius of curvature of the trajectory of the first quadrant lies in the third quadrant, the center of the radius of curvature of the trajectory of the second quadrant lies in the fourth quadrant, the center of the radius of curvature of the trajectory of the third quadrant lies in the first quadrant, and the center of the radius of curvature of the Fourth quadrant career is in the second quadrant. Each of the four contact points of a sphere lies in one of the four quadrants. This special arrangement ensures that each ball always has four contact points with its raceways and these contact points are maintained even under load. With a conventional four-point contact ball bearing, only two or a maximum of three contact points are loaded during operation. A thrust ball bearing works with only two points of contact and crossed roller bearings also work with only two lines of contact. The four contact points thus generate less contact pressure per point of contact with the ball, which can, for example, reduce wear on the bearing assembly, while at the same time radial and axial loads can be absorbed by the arrangement of the contact points.

The use of balls can simplify assembly of the bearing assembly since the balls can be installed without a specific orientation compared to rollers. The use of balls is further advantageous because a ball is a fully symmetrical element that does not require alternating orientation of the rolling elements as is known from crossed roller bearings. This allows all rolling elements to carry the load between all raceways, even when working under special conditions, instead of only half the elements as is the case with crossed roller bearings. Furthermore, spheres are free to rotate about their center and can therefore transfer the load through any point on their surface. This utilizes the surface area of the balls to a maximum, spreading the contact over the full surface of the ball and thus spreading the wear over the full surface of the ball. In contrast, only some areas of the rolling element surface would be worn, for example, with crossed roller bearings. The bearing arrangement described here can be implemented as a full bearing without additional wear always taking place at the same point, as is the case with roller bearings. The punctiform ball-to-ball contact causes wear on the balls. However, since the contact points "wander" on the surface of the balls and therefore not always the same place is loaded, this leads to a lower overall load for the balls. This is because the orientation of the spherical body to the axis of rotation varies, in contrast to a roller bearing. Alternatively, a cage can also be used, it also being possible to use spacers instead of a complete cage. The bearing assembly provides enough space in the area along the ball's axis of rotation to use both spacers and a cage.

According to one embodiment, the intersection of the two radii of curvature of the raceway of the first raceway element lies on an axis perpendicular to the axis of rotation of the ball and the intersection of the two radii of curvature of the raceway of the second raceway element also lies on an axis perpendicular to the axis of rotation of the ball. These axes can also be a common axis, in particular the axis which is perpendicular to the axis of rotation and passes through the center of the sphere. The points of intersection can also lie on the axis of rotation. Each track thus has two radii of curvature whose centers do not coincide, whereby each track consists of two segments between which there is a transition. The transition between the two raceways or the contact line of the two raceways lies on a plane which passes through the center of the sphere and is perpendicular to the imaginary axis of rotation of the sphere. These two radii of curvature and their special arrangement ensure that the ball always has four contact points with the raceways. The two radii of curvature can be different or identical.

According to a further embodiment, the radii of curvature are identical. This leads to a symmetrical distribution of the radii of curvature and their centers to the four quadrants. This symmetrical arrangement distributes the load evenly over the four contact points between the balls and the raceways. According to a further embodiment, the contact points are offset from the axis perpendicular to the axis of rotation of the ball. This means that the contact points are preferably not on the axis of rotation of the sphere and on the axis perpendicular to the axis of rotation of the sphere. In this way, the bearing assembly can be prevented from behaving as a thrust or radial ball bearing that has only two points of contact, which would reduce the radial or axial stiffness. Furthermore, the bearing arrangement can absorb radial or axial loads in a defined manner right from the start of the load, in contrast to a radial or axial ball bearing, which has a contact point on one of the raceway elements. Likewise, axial or radial loads can be absorbed in a defined manner right from the start of the load, unlike a ball bearing which also has a contact point on one of the axles.

According to a further embodiment, the contact points are arranged in a range of ±20°, preferably ±10° around the axis perpendicular to the axis of rotation of the sphere. The contact points between the ball and the raceways can vary within this range depending on the application. With this arrangement, the four contact points create special kinematics for the balls, since the axis of rotation of the balls always remains perpendicular to the axis around which the contact points are arranged, even during loading.

According to one embodiment, the radius of curvature is a variable radius. This means that the respective tracks can be circular arc segments, but also ellipses or ovals in general.

The first raceway element and/or the second raceway element may be formed as a split raceway element with a biasing mechanism provided to control the points of contact between the ball and the raceways. By preloading the respective track element, the preload of the contact points can be adjusted by adjusting the play between the parts of the split track element.

The bearing arrangement can be implemented as an axial bearing, radial bearing or linear bearing.

Depending on the particular design of the bearing assembly, the axis of rotation of the ball can be perpendicular to the axis of rotation of the bearing (in the case of a thrust bearing), parallel to the axis of rotation of the bearing (in the case of a radial bearing), and perpendicular to the direction of motion (in the case of a linear bearing).

Many different bearing configurations are thus possible with the bearing arrangement described here, each showing the advantages of the bearing arrangement as described above. In particular, the bearing arrangement described here provides good radial load rigidity and low wear behavior due to low sliding behavior.

According to a further aspect, a gear, in particular a high-precision gear, is provided with a bearing arrangement as described above. Such a high-precision gear can be used, for example, in robots that require very precise control of the movement sequences and therefore of the joints in which bearings are used. For example, the bearing arrangement can be used as a bearing in a robotic application to connect successive arms or arm parts.

Further advantages and advantageous embodiments are specified in the description, the drawings and the claims. In particular, the combinations of features specified in the description and in the drawings are purely exemplary, so that the features can also be present individually or in a different combination.

The invention is to be described in more detail below with reference to exemplary embodiments illustrated in the drawings. The exemplary embodiments and the combinations shown in the exemplary embodiments are purely exemplary and are not intended to define the scope of protection of the invention. This is defined solely by the appended claims.

Show it:

1 : a schematic cross-sectional view of a bearing arrangement;

FIG. 2 shows a schematic cross-sectional view of the bearing arrangement from FIG. 1 as a single-row axial bearing; FIG. 3 shows a schematic cross-sectional view of the bearing arrangement from FIG. 1 as a single-row radial bearing;

FIG. 4 shows a schematic cross-sectional view of the bearing arrangement from FIG. 1 as a double-row axial bearing;

FIG. 5 shows a schematic cross-sectional view of the bearing arrangement from FIG. 1 as a double-row radial bearing; and

FIG. 6: a schematic cross-sectional view of the bearing arrangement of FIG. 1 as a linear bearing with a split raceway element.

Elements that are identical or have the same functional effect are identified below with the same reference symbols.

1 shows a bearing arrangement 1 with a first raceway element 2 and a second raceway element 4. Between the raceway elements 2, 4, balls 6 are arranged as rolling bodies. The balls 6 roll on raceways 8 which are arranged on the raceway elements 2,4.

The bearing arrangement 1 can be designed as a ball bearing, in particular as a radial or axial bearing, or as a linear bearing. In the case of a radial bearing, the first raceway element 2 and the second raceway element 4 correspond to the inner ring and the outer ring. In the case of a thrust bearing, the first raceway element 2 and the second raceway element 4 correspond to the shaft washer and the housing washer. In the case of a linear bearing, the first raceway element 2 and the second raceway element 4 correspond to the rail and the carriage.

In the case of the bearing arrangement 1 shown in FIG. 1, the raceways 8 can be divided into four quadrants I, II, III, IV. The division into the four quadrants I, II, III, IV takes place through the axis of rotation AR of the sphere and an axis As, which is perpendicular to the axis of rotation AR. The track of the second track element 4 is formed by two segments 8-1, 8-II and lies in the first and second quadrant I, II and the track of the first track element 2 is formed by two track segments 8-III and 8-IV and lies in the third and fourth quadrants III, IV. The ball 6 comes with raceways 8-1, 8-II at two contact points PI, P-II located in two contact zones 10-1 and 10-11, and with raceways 8-III and 8-IV at two Contact points P-III, P-IV located in contact zones 10-III and 10-IV. In order to ensure that the ball 6 touches the raceways 8 at the contact points PI, P-II, P-III, P-IV, the raceways 8 have a special design: the center point MI of the radius of curvature RI of the raceway segment 8-1 is in the third quadrant III, the center M-II of the radius of curvature R-II of the raceway segment 8-II lies in the fourth quadrant IV, the center M-III of the radius of curvature R-III of the raceway segment 8-III lies in the first quadrant I and the Center M-IV of the radius of curvature R-IV of the raceway segment 8-IV is in the second quadrant II.

In the embodiment shown in Fig. 1, the intersection of the radii of curvature RI, R-II of the first and second quadrant I, II lies on the axis As and the intersection of the radii of curvature R-III, R-IV of the third and fourth quadrant III , IV also lies on the As axis. However, the point of intersection cannot lie on the axis As either. The radius of curvature R is understood here as the radius defining the curvature, i.e. the distance between the track 8 and the center point M. In particular, as shown in FIG. 1, the straight line through MI and M-III intersects the straight line through M-II and M-IV at the point of intersection S. In the case shown here, the point of intersection S lies simultaneously on the point of intersection of the axis of rotation AR and the axis As, but this is not absolutely necessary. This specific configuration of the radii of curvature R of the raceways 8 ensures that the ball 6 touches the raceways 8 at the contact points P-I, P-II, P-III, P-IV. The contact points P-I, P-II, P-III, P-IV are in the contact zones 10 in a range of ±20°, in particular ±10° around the axis As.

In order to ensure that the ball bearing 1 cannot only absorb axial or radial loads, the contact points PI, P-II, P-III, P-IV are always offset from the axis As. In this way, the ball 6 always has four points of contact PI, P-II, P-III, P-IV with the raceways 8, located respectively in the contact zones 10-1, 10-11, 10-III and 10-IV located, whereby a good radial load stiffness and a good load and pressure distribution and thus a low wear behavior is achieved. The bearing arrangement 1 can be used in different configurations, as shown in FIGS.

As shown in FIG. 2, the bearing assembly can be used as a single row thrust ball bearing, in which case the axis of rotation AR is perpendicular to the axis of rotation AL of the bearing. The axis As, around which the contact zones 10-1, 10-11, 10-III, 10-IV are arranged, is parallel to the axis of rotation AL of the bearing.

Alternatively, the bearing assembly 1 can be used as a single row radial ball bearing as shown in FIG. In this case, the axis of rotation AR is parallel to the axis of rotation AL of the bearing 1. The axis As, around which the contact zones 10-1, 10-11, 10-III and 10-IV are arranged, is in this case perpendicular to the axis of rotation of the bearing AL.

The bearing arrangement 1 can also be used as a double-row axial ball bearing (Fig. 4) or as a double-row radial ball bearing (Fig. 5). In the case of a double row thrust ball bearing, the axis of rotation AR is perpendicular to the bearing axis of rotation AL and in the case of a double row radial ball bearing, the axis of rotation AR is parallel to the bearing axis AL.

In the case of such a double-row thrust or radial ball bearing, the inner or outer rings 2, 4 can be designed as split rings (not shown). In this case, a preloading mechanism, for example a screw connection, can be used to control the contact points P-I, P-II, P-III, P-IV or contact zones 10 between the ball 6 and the raceways 8. By preloading the respective ring 2, 4, the preload of the contact points P-I, P-II, P-III, P-IV can be adjusted by adjusting the clearance between the parts of the split ring 2,4. Single-row axial or radial ball bearings can also be implemented with split rings 2, 4 and preload mechanisms.

The bearing assembly 1 can also be used as a linear bearing, as shown in FIG. In this case, the first track element 2 is formed by a rail and the second track element by a carriage 12 and a separate element 4'. In this case, too, the second raceway element 4' can be adjusted by a prestressing element 14 in its prestressing or its play in order to correspondingly Adjust contact points PI, P-II, P-III, P-IV or contact zones 10-1, 10-11, 10-III, 10-IV. In the case of the linear bearing 1 of Fig. 6, the ball rotation axis AR is perpendicular to the direction of movement of the bearing 1 in the carriage 12.

With the ball bearing described here, good radial and axial load rigidity and low wear behavior due to lower friction can be achieved.

Reference List

1 bearing arrangement

2 first track element

4 second track element

6 balls

8 careers

10 contact zones

12 sleds

14 biasing mechanism

I, II, III, IV quadrants

AL bearing axis of rotation

AR ball rotation axis

As axis perpendicular to the sphere's axis of rotation

M Center of curvature radius

P contact points

R radius of curvature

5 intersection

Claims

P a t e n t claims

Bearing arrangement Bearing arrangement (1) with a first raceway element (2) and a second raceway element (4), balls (6) being arranged between the raceway elements (2, 4), the balls (6) being on raceways (8) which are on are arranged on the raceway elements (2, 4), characterized in that the bearing arrangement (1) in cross section through the axis of rotation (AR) of a ball (6) and an axis (As) perpendicular to the axis of rotation (AR) of the ball ( 6) conceptually divided into four quadrants (I, II, III, IV) arranged clockwise, with the ball (6) having four points of contact (PI, P-II, P-III, P-IV) with the raceways (8) and wherein each contact point (PI, P-II, P-III, P-IV) is in one of the four quadrants (I, II, III, IV), the raceway (8) of the second raceway element (4 ) in the first and in the second quadrant (I, II) and the raceway (8) of the first raceway element (2) in the third and in the fourth quadrant (III, IV), the center ( MI) of the radius of curvature (RI) of the raceway (8-1) of the first quadrant (I) lies in the third quadrant (III), the center (M-II) of the radius of curvature (R-II) of the raceway (8-II) of the second quadrant (II) lies in the fourth quadrant (IV), the center (M-III) of the radius of curvature (R-III) of the raceway (8-III) of the third quadrant (III) lying in the first quadrant (I), and wherein the center (M-IV) of the radius of curvature (R-IV) of the raceway (8-IV) of the fourth quadrant (IV) lies in the second quadrant (II). Bearing arrangement according to claim 1, wherein the intersection of the two radii of curvature (R-III, R-IV) of the raceway (8-III, 8-IV) of the first raceway element (2) on an axis perpendicular to the axis of rotation (AR) of the ball ( 6) and wherein the intersection of the two radii of curvature (RI, R-II) of the raceway (8-1, 8-II) of the second raceway element (4) lies on an axis perpendicular to the axis of rotation (AR) of the ball (6). . Bearing arrangement according to claim 1 or 2, wherein the radii of curvature (RI, R-II, R-III, R-IV) are identical. Bearing arrangement according to one of the preceding claims, wherein the contact points (PI, P-II, P-III, P-IV) are arranged offset to the axis (As) perpendicular to the axis of rotation (AR) of the ball (6). Bearing arrangement according to claim 4, wherein the contact points (PI, P-II, P-III, P-IV) of the ball (6) with the raceways (8) in a range of ± 20°, preferably ± 10°, around the axis (As) are arranged, which is perpendicular to the axis of rotation (AR) of the ball (6). Bearing arrangement according to one of the preceding claims, wherein the radius of curvature (RI, R-II, R-III, R-IV) of the raceways (8) is a variable radius. Bearing arrangement according to one of the preceding claims, wherein the first raceway element (2) and/or the second raceway element (4) is designed as a split raceway element, with a pretensioning mechanism being provided in order to keep the contact points (PI, P-II, P-III, P -IV) between the ball (6) and the raceways (8). Bearing arrangement according to one of the preceding claims, wherein the bearing arrangement (1) is a ball bearing, wherein the first raceway element (2) is an inner ring or a shaft washer and the second raceway element (4) is an outer ring or a housing washer. Bearing arrangement according to claim 8, wherein the axis of rotation (AR) of the balls (6) is perpendicular or parallel to the axis of rotation (AL) of the ball bearing (1). 15 Bearing arrangement according to one of claims 1 to 7, wherein the bearing arrangement (1) is a linear bearing, wherein the first track element (2) is a rail and wherein the second track element (4 ', 12) is a carriage.