Rolling element bearing

The invention relates to a rolling element bearing having at least one inner bearing inner and at least one outer bearing ring. Rolling elements are arranged between the inner ring and the outer ring, and the rolling elements are guided by a cage. To improve the lubrication of the bearing the invention proposes that the cage includes at least one opening, preferably a bore. The opening penetrates the cage from a radial inner surface to a radial outer surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Great Britain patent application no. 1506449.6 filed on Apr. 16, 2015, the contents of which are fully incorporated herein by reference. Applicant respectfully notes, the one year anniversary of the earliest priority document falls on a non-business day, and therefore, Applicant is afforded through the next business day (Monday, Apr. 18, 2016) to maintain copendency.

TECHNICAL FIELD

The invention relates to a rolling element bearing, comprising at least one inner bearing ring and at least one outer bearing ring, wherein rolling elements are arranged between the inner ring and the outer ring, wherein the rolling elements are guided by a cage, wherein the cage comprises at least one opening, especially a bore, wherein the opening penetrates the cage from a radially inner surface to a radially outer surface.

BACKGROUND

Bearings according to the generic kind are well known in the art. As examples reference is made to JP 2004 340 268 A, to EP 2 562 437 A2 and to U.S. Pat. No. 3,743,369 A. Especially in the case of a high-speed rolling element bearing, a significant amount of heat can be generated in the bearing. Here, cage overheating is mostly the major cause of bearing failure at high speed operations. The cage overheating is often initiated at the cage guiding zone because there exists a small clearance between the cage outer surface and the outer ring guiding surface. Heat is generated at the guiding zone due to sliding friction between the fast rotating cage and the stationary outer ring.

Thus, it is an object of the present invention to further develop a rolling element bearing of the generic kind in such a manner that the lubrication is improved and even at high speed operation the heat generation is reduced in the bearing. Thus, the lifetime of the rolling element bearing should be increased.

SUMMARY OF THE INVENTION

The solution according to the invention is characterized in that the radially outer end of the at least one opening terminates in a groove in the radially outer surface of the cage.

Preferably, a plurality of openings is arranged in the cage. The openings can be arranged equidistantly along the circumference of the cage.

The at least one opening can be arranged in at least an axial end region of the cage. Due to balance reasons it can also be provided that openings are arranged in both axial end regions of the cage.

The at least one opening is preferably a bore and has an axis which extends in radial direction through the cage.

As an alternative it can be provided that the at least one opening is a bore and has an axis which extends under an angle to the radial direction through the cage; the angle is preferably between 5° and 30°. If the holes (bores) are arranged under an angle the lubrication for greased bearings can be further improved (see explanations below).

The at least one opening can be manufactured by means of a drilling process.

The groove can be a ring groove in the radial outer surface of the cage. Furthermore, it can be provided that the groove has an arcuate shape in a radial cross section of the cage; the arcuate shape is preferably an arc of a circle or an arc of an ellipse.

The cage has preferably a sliding surface at the radial outer surface which is designed for a sliding contact with a radial inner sliding surface of the outer bearing ring of the rolling element bearing.

The rolling element bearing can be a ball bearing. Specifically preferred, the ball bearing is an angular contact ball bearing (ACBB).

The cage can be made of plastic material.

Preferably, the bearing is at least partially filled with a lubricant, especially with oil or grease.

Thus, the invention provides a design of the cage with self pumping holes and a damping groove. The radial holes in the cage allow that a fluid pumping flow is introduced by the cage rotation itself. The pumping flow throughout the holes to the guiding surface reduces friction and removes heat generated by the sliding surfaces. So, higher bearing speed is possible due to a high fluid pumping rate.

Mostly, the application is a high speed bearing with an outer ring guided cage. The invention works for both oil and grease lubrication.

Beneficially, the groove on the top of the cage pumping holes allow to hold some oil for better lubrication and cage damping when the cage impacts onto the outer ring guiding shoulder. I.e. the invention thus provides a high speed cage with pumping holes and damping grooves.

Specifically, in addition to the cooling effect to the cage guide surface, the proposed idea with the openings on the other side of the cage, built with an angle to the radial direction, provides an improved lubrication particularly for high speed angular contact ball bearings with grease lubrication.

DETAILED DESCRIPTION OF THE INVENTION

InFIG. 1, a rolling element bearing1is shown which is a ball bearing in the present case. The bearing1has an inner bearing ring2and an outer bearing ring3. Rolling elements4are arranged between the inner ring2and the outer ring3in a common manner. The rolling elements4are guided by a cage5.

The cage5has receiving pockets for the rolling elements4. In the depicted case, the cage5has a radially inner surface7and a radially outer surface8. The radially outer surface8is partially designed to be a sliding surface10of the cage5. This sliding surface10can slide on a sliding surface11of the outer bearing ring3to guide the cage5relatively to the bearing outer ring3. That is, the cage5is guided on a shoulder of the outer bearing ring3with the left axial end region of the cage5.

To provide low friction at the mentioned sliding contact between the sliding surface10of the cage5and the sliding surface11of the outer ring3, the cage5comprises a number of openings6a, which are bores in the present case. At the opposite axial side of the cage, a further set of openings6bmay be provided in the cage5. The openings6a,6bpenetrate the cage5from the radially inner surface7to the radially outer surface8. The openings may have an axis which is directed in the radial direction r. In the present embodiment according to the FIGURE, a solution is provided in which the axis of the openings6a,6bis arranged under an angle □ to the radial direction r, so as to extend axially inward in radially outward direction. The angle is preferably between 5° and 30°.

In the present case, the radial bores6a,6bare drilled into the cage5. In the depicted embodiment, the bores6bon the non-guided (right) side are for the purpose of cage balance; but as explained below, this embodiment has also other advantages.

The fast rotation of the cage5generates the centrifugal force that pumps air/oil through the cage holes into the cage guiding zone. This is depicted by the arrows denoted with F (direction of flow).

The fluid pumped by the cage5brings heat generated by cage shearing and cage sliding friction away from the guiding zone.

For facilitating this effect, the bores6aend into a groove9which is a ring groove which runs around the whole circumference of the cage5. Here, lubricant can be collected and forms a certain lubricant cushion between the two sliding surfaces10and11. The bores6bmay also end into a ring grove.

With respect to the effect of the proposed concept the following explanations are given:

The speed of a grease lubricated bearing is limited by the bearing temperature rise, often due to poor lubrication. At high speed operation, for example speed higher than 10E6 for the product (n×dm) (n is the bearing rotational speed in rpm and dm is the bearing pitch diameter in mm), the speed of the bearing is high so that the grease on the inner raceway and the cage5is thrown off quickly by the centrifugal force. Even on the outer raceway where some grease may be available for some time, the time interval for contact replenishment is too short at high speed operation. To improve grease lubrication for high speed bearing, it is desired to enhance the lubricant replenishment on the raceways.

The openings6bon the cage5improve bearing lubrication at high speed condition. Some of the grease after initial churning-in and thrown-off by the centrifugal force is located on the outer ring shoulder, forming a grease reservoir12.

The openings6bof the cage5, built under the angle α, generate a flow by the centrifugal force when the cage5rotates at high speed. The generated flow pushes part of the grease on the reservoir12closer to the rolling elements and raceway. So the bled oil from the grease reservoir12takes a shorter time to reflow to the contacts.

In addition, when the flow passes through the surface of the grease reservoir12, the bled oil from the reservoir and even a layer of grease on the reservoir surface will be sheared off and brought back to the rolling element and the outer raceway by the flow.

So, the lubrication can be improved significantly.

REFERENCE NUMERALS

1Rolling element bearing2Inner bearing ring3Outer bearing ring4Rolling elements5Cage6a,6bRadial opening (bore)7Radially inner surface of cage8Radially outer surface of cage9Groove10Sliding surface of the cage11Sliding surface of the outer bearing ring12Grease reservoirr Radial directionF Direction of flowα Angle