DE102011014079A1 - Multipoint radial bearing, has rolling elements constructed such that contact region with cylindrical mold is provided in middle of rolling elements, where elements are guided on ring by line contact and on another ring over point contacts - Google Patents

Abstract

The bearing has rolling elements (4) constructed such that a contact region with cylindrical mold (4'') is provided in middle of the rolling elements and the contact region with convex, spherical geometry (4') is provided at sides of the rolling elements. The rolling elements are guided on a bearing ring (3) by a line contact (7) and on another bearing ring over two point contacts (5, 6). A spacer ring with higher thermal expansion coefficient is mounted between ring halves (1, 2) having a concave groove geometry.

Description

The invention relates to a radial bearing that allows high combination of two point contacts and a line contact a high speed suitability at the same time relative axial displacement between inner and outer ring (floating bearing function) and high radial stiffness.

In many applications, it is necessary for fast-rotating shafts to be radially as stiff and accurate as possible, but axially free to move. H. execute as a floating bearing. This is often required, for example, in machine tool main spindles to allow the compensation of thermal shaft and housing expansion and so to avoid the unwanted distortion of front and rear bearing package.

According to the current state of the art, highly accurate radial bearings with non-locating function are realized in three ways:
Cylindrical roller bearings have by their line contact a high radial stiffness and make by their free axial displacement an ideal floating bearing. The disadvantage, however, that relative thermal changes in size between inner and outer ring, which inevitably by the comparatively high friction of the Lininenkontakt and the unequal heat dissipation set inside and outside, lead to a change in their bias. A compensation of radial expansion is not possible in the warehouse. There is thus the risk that cylindrical roller bearings, especially at high speeds, jam due to the frictional heat generation and thus fail. Furthermore, by tilting the shaft, the edges of the rolling elements are heavily loaded, which can lead to premature material fatigue and thereby damage to the track in this area. The utility model DE 7140218 describes an approach to mitigate this effect by a withdrawal of the Wälzkörperdurchmessers at its ends, associated with a reduction of the rolling element stiffness in this area. The achievable speeds are still significantly lower than those that can be realized by spindle bearings due to the thermal stress of the bearing.

So-called floating displacement bearings (FD bearings) combine, such as in the EP 342 172 and the EP 926 368 A2 executed, the characteristics of cylindrical roller bearings with those of deep groove ball bearings. In this case, a bearing ring with a cylindrical ring geometry and thus free axial displacement relative to the rolling elements, the other with shoulders for axial guidance of the rolling elements, which are designed as balls executed. The disadvantage here are the high pressures in the point contact between the ball and cylindrical bearing ring and the associated wear and tear or to avoid the low tolerable loads. There is the same problem regarding the compensation of radial strains, problem as with the cylindrical roller bearing (see above).

In the high-speed range, combined radial / thrust bearings (spindle bearings) are typically used as floating bearings, which are mounted axially movable relative to the housing. This is realized for example by a sliding fit on the outer ring or by mounting the bearings in an additional, axially movable sliding bushing. A disadvantage is the lower rigidity of the spindle bearings compared to cylindrical roller bearings. In the case of tight fits, there is a risk that displaceability is no longer guaranteed by changes in the operating situation. By using a linear bearing (ball bushing), the floating bearing function can be largely ensured. However, such a solution is costly and associated with losses in rigidity and accuracy.

Radial bearings which enable the compensation of radial deformations, in particular by thermal size changes and play-free operation are known in various embodiments. For example, describes the UK 2 053 380 a three-point bearing, which biases the rolling elements by a radially elastic Wälzoberfläche. However, such a bearing offers only low stiffness and poor running accuracy. The publications DE 10 2004 048 720 A1 and DE 4231 272 A1 describe bearing variants, which are to ensure a backlash-free run by a two-part, axially preloaded outer ring. The compensation of axial displacements within the bearing is not possible. The patent DE 198 07 514 B4 discloses an embodiment which is biased backlash by a two-part, axially biased inner ring and can respond to size changes of the individual components by shifting. Due to a significantly larger radius of the outer race compared to Wälzkörperradius axial and angular compensation movements are possible to a limited extent. A disadvantage of the design, however, is the reduced load capacity by the point contact with further osculation on the outer ring.

The object of the invention is therefore to enable a possibility for radially rigid, axially freely movable and at the same time at high speeds (n × d _m > 10 °) reliable storage of waves and to solve the above-described problems of compensation radial expansions.

The object is achieved by the use of a designed according to claims 1 to 5 rolling bearing.

The new bearing according to the invention has the advantage of being able to compensate radial expansion of the inner ring relative to the outer ring by an axial displacement of the two halves of the split bearing ring. It is therefore suitable for highest speeds, which are usually associated with the uneven heating of inner and outer ring. At the same time a free axial displacement of the inner ring relative to the outer ring is ensured. Due to the double point contact on the one hand and the line contact on the other hand, a high rigidity with acceptable contact pressures and thus good service life is given.

In the following, three embodiments of the invention are described with reference to drawings. Show it

1 an inventive bearing in the sectional view with a sectional plane through the bearing axis.

2 an advantageous embodiment of the bearing after 1 with spacer ring between the ring halves.

3 a further advantageous embodiment of the bearing according to 1 with integrated preload application.

The bearing of the invention combines the advantageous features of a spring-loaded multi-point spindle bearing with those of a cylindrical roller bearing. The rolling elements ( 4 ) are designed in such a way that in the middle of a contact area with a cylindrical shape ( 4 '' ) and at the sides contact areas with convex, spherical geometry ( 4 ' ), which merge tangentially into one another. The first bearing ring ( 3 ) is cylindrical without axial guide board and forms with the central region of the rolling elements a line contact ( 7 ). This allows the free axial relative movement between inner and outer ring at the same time lower pressures than in ball-cylinder contact. The other bearing ring consists of two separate, axially mutually displaceable ring halves ( 1 . 2 ), each having a concave track, for example, a circular track groove on which the rolling elements in their convex areas ( 4 ' ) under certain, production-technically preset pressure angles α ₁ and α ₂ via point contacts ( 5 . 6 ). The individual rolling elements are separated by a cage ( 10 ) separated and guided in their rolling axis.

The Wälzkörper- and bearing ring geometries of the two ring halves are mirror-symmetrical to the axial bearing center, so that in the normal. Operation, the two pressure angles α ₁ and α _{2 are the} same size and depending on the application in the range of 5 ° to 40 °. Small tilting of the shaft can be absorbed by changes in the operating pressure angle α ₁ and α ₂ without local increase in pressure.

One of the two ring halves with concave groove geometry ( 2 ) is mounted axially freely movable relative to the housing and axially resiliently employed with respect to the other ring half, whereby the rolling elements are biased radially defined by the pressure angle α ₁ and α ₂ . The Schmiegungen the contact points are between 70% and 98%. In the case of a relative expansion of the inner ring relative to the outer ring of the bias voltage increase can be largely compensated by a shift of the employed ring half against the biasing spring. Here, however, there is the danger that the displacement of the ring half is hampered by jamming due to the radial load or thermal expansion.

In an advantageous embodiment according to 2 Therefore, a spacer ring is mounted between the two halves of the bearing rings, which has a higher thermal expansion coefficient than the bearing material. The movable half ring is pressed against the fitted spacer with high spring force. This pushes the two halves of the ring when heating the bearing with a high thermal expansion force apart whereby the bias voltage decreases. The risk of jamming one of the two bearing halves is counteracted by the high displacement forces. The thermal expansion coefficients of the spacer ring, the raceway and Wälzkörperwerkstoffe and their geometric dimensions are coordinated with each other to achieve a meaningful compensation of the thermal size changes and thus the biasing force change.

In a further advantageous embodiment, as in 3 shown, the guidance and bias of the second half ring ( 13 ) in the first half of the ring ( 12 ) realized. For this purpose, in the first half of the ring ( 12 ), one, with a suitable guide game made guide surface for axially displaceable mounting of the second ring half ( 13 ) brought in. Furthermore, in the first ring half a lid ( 14 ) is fastened with integrated spring clamping elements via an external thread or a securing ring, which holds the second ring half ( 13 ) axially against the first ring half ( 12 ) braced.

The cylindrical bearing ring can, as in the 1 . 2 and 3 represented as inner ring and the split bearing ring with concave raceways are designed as an outer ring, or vice versa, the cylindrical ring as an outer ring and the split ring as an inner ring.

In order to avoid high pressure peaks in the ends of the cylindrical Wälzkörperbereiche the cylindrical bearing ring can be carried out slightly spherical in a further embodiment on its raceway side in the axial direction. Alternatively, the cylindrical Wälzkörperbereich spherical, that is to be carried out in the axial direction with a slightly convex surface.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 7140218 U [0003]
• EP 342172 [0004]
• EP 926368 A2 [0004]
• GB 2053380 [0006]
• DE 102004048720 A1 [0006]
• DE 4231272 A1 [0006]
• DE 19807514 B4 [0006]

Claims (5)

Radial multi-point bearing with axial floating bearing function for high speeds, characterized in that the rolling elements ( 4 ) are designed such that in the middle of a contact area with a cylindrical shape ( 4 '' ) and at the sides contact areas with convex, spherical geometry ( 4 ' ), whereby they roll on the one bearing ring by a line contact and are guided on the other bearing ring via two point contacts. Rolling bearing according to claim 1, characterized in that the two point contacts via a split bearing ring ( 1 . 2 ), in which the two ring halves are made resiliently against each other realized. Rolling bearing according to claim 2, characterized in that between the ring halves with concave groove geometry an adapted spacer ring ( 11 ) is mounted with a higher thermal expansion coefficient than that of the bearing rings. Rolling bearing according to claim 2, characterized in that the one half of the ring with concave groove geometry ( 13 ) in the other ring half with concave groove geometry ( 12 ) is guided over a cylindrical guide surface. Rolling bearing according to claim 5, characterized in that the axial prestressing by a spring mechanism in a lid ( 14 ) of the ring half with concave groove geometry ( 12 ) is applied, and that the bearing so forms a self-prestressed operational unit.

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