The invention relates to a roller bearing, such as a ball bearing or a roller bearing, according to the preamble of claim 1.
The functional surfaces of roller bearings are generally ground, and where necessary honed, with great precision, it being necessary for the surfaces thus formed to be provided with specific roughness and waviness. When the raceways are honed, the main aim is to create lubricant reservoirs using cross-grinding in order to ensure the necessary lubricating film is existing between the ball and the raceway.
Due to centrifugal forces and external influences, for example differences in pressure, the lubricant in roller bearings is transported to undefined areas and is then lacking at the required lubrication points such as ball/roller to the cage or raceway and cage to the inner or outer rings. This could result in a shortening of the operating life of the roller bearing or/and in greater variability in the operating life of the individual bearing within a production series.
In practice, this problem particularly arises for extremely fast rotating roller bearings, as used, for example, to support a compressed air turbine drive of a dental drill or to support the blade wheels in turbochargers. Specifically, the problem for dental turbines, for example, lies in the fact that the lubricant can be forced out of the bearing by the compressed air, or that the lubricant collects within the bearing in areas unfavorable for the bearing due to centrifugal forces. Moreover, dental turbines are regularly disinfected in a disinfectant solution, thus also causing lubricant to be rinsed out of the roller bearing. After disinfection, the roller bearing is re-lubricated in an undefined manner. Although this action does supply the bearing with fresh lubricant, the lubricant does not necessarily reach the areas in the roller bearing needing lubrication.
It is the object of the invention to improve a roller bearing with regard to the distribution of lubricant.
This object has been achieved according to the invention by a roller bearing having an inner bearing ring having a raceway and an outer bearing ring having a raceway and a plurality of rolling elements disposed between the raceways that are lubricated by a lubricant, wherein the surface of the inner bearing ring and/or of the outer bearing ring facing the rolling elements and/or the surface of a cage holding the rolling elements has a surface structure.
Further, a method for lubricating a roller bearing is described, wherein a lubricant for maintaining a lubricating film between a raceway of an inner bearing ring, a raceway of an outer bearing ring and a plurality of rolling elements is introduced, wherein, when the bearing is in operation, the lubricant is actively transported into the region of at least one raceway by using surface structures that are disposed on the surfaces of the inner bearing ring and/or of the outer bearing ring facing the rolling elements and/or a surface of a cage holding the rolling elements.
Preferred embodiments of the invention and further advantageous characteristics are outlined in the dependent claims.
Through appropriate, intended and controlled structuring of the surfaces of the bore of the outer ring or of the outside diameter of the inner ring, as well as potentially parts of the raceways or of the cage, the direction in which the lubricant is transported between the ring and the cage, as well as the ball and raceway, can be influenced to the desired extent. The surfaces can be structured by means of laser ablation, an electrochemical erosion process, forming or a cutting process. The shape and depth of the surface structure can be varied according to the future rotational speed of the roller bearing in order to influence the amount of lubricant that is to be transported.
According to the invention, surfaces of the inner and/or outer ring facing the cage or surfaces of the cage are provided with surface structures that, during operation of the roller bearing, generate a kind of pumping effect on the lubricant. These surface structures preferably consist of contradirectional grooves shaped like screw threads or spiral-shaped grooves. The thread-like or spiral grooves extend inwards from the axial end of the respective bearing ring in the direction of the raceway for the rolling elements. The thread-like or spiral grooves may end directly in the raceway up to or in the area of contact of the ball, or in a groove acting as a reservoir in a region beside the raceways. The balls then take up lubricant from this area and transport it to the ball cage and even to the other bearing ring. It is understood that in this arrangement, the roller bearing can only be operated in one specific rotational direction, otherwise the lubricant would be transported outwards away from the raceways to the edge of the bearing rings.
The respective grooves may also be designed as grooves with a herringbone structure or suchlike, where the number of grooves, their angle, depth and width all act as variables so as to generate a desired pumping effect, depending on the rotational speed and the size of the roller bearing and of course the properties of the lubricant. The grooves may be formed, for example, by laser ablation, a cutting process, forming or ECM and have a preferred depth of about 3 micrometers to about 50 micrometers and a preferred width of 10 to 400 micrometers.
The invention is described in more detail below on the basis of a preferred embodiment with reference to the drawings. Further characteristics and advantages of the invention can be derived from the drawings and the following description.
In
The ball bearing from
The contact surfaces between the raceways 12, 18 and the balls 22 or between the balls 22 and the ball cage respectively are lubricated with a lubricant, such as oil or grease having an appropriate viscosity so as to reduce friction resistance and material wear and to increase the operating life of the ball bearing. When the ball bearing is in operation, the lubricant is distributed in an undefined manner due to differences in pressure and centrifugal forces and a part does not reach the areas needing lubrication.
According to the invention, provision is made for the circumferential surfaces facing each other of the inner bearing ring 10 and/or of the outer bearing ring 16 and/or of the raceways 12, 18 of one or both rings of the bearing to be provided with a surface structure 14, 20. In
In the illustrated embodiment, the surface structures 14, 20 take the form of helical grooves that extend thread-like from the outer ends of the bearing rings 10, 16 in the direction of the balls 22 up to the raceways 12, 18.
The grooves 14, 20, 26, 28 may be formed in the surface of the bearing rings 10, 16 or of the cage 24 either by a cutting process, laser ablation, deformation or an electrochemical erosion process. The depth of the grooves 14, 20, 26, 28 is, for example, 3 to 50 micrometers and depends substantially on the rotational speed of the roller bearing as well as its size and the viscosity of the lubricant. The width of the grooves 14, 20, 26, 28 as well, and the distance and the gradient of the spiral grooves 14, 20, 28 are dependent on the above-mentioned parameters of the roller bearing.
Separate grooves (
Using a known method, the bearing rings may have appropriate sealing means (not illustrated) at their outer edges to seal the bearing and to prevent any lubricant from leaking out of the bearing.
Number | Date | Country | Kind |
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10 2010 034 216.5 | Aug 2010 | DE | national |