Patent Application
20180119741
The disclosure relates to a method for producing rolling bodies with crowned end surfaces for anti-friction bearings, such as bearing needles for high-speed axial needle bearings. The disclosure furthermore relates to rolling bodies produced by this method, to anti-friction bearings having rolling bodies of this kind and to the use thereof.
Plain bearings are increasingly being replaced by axial needle bearings in transmissions. One advantage is that bearing friction may be reduced, with the result that a fuel savings may be achieved in the case of use in motor vehicles, for example.
In the case of transmission applications, high bearing speeds of up to 10,000 rpm are achieved, as a result of which an acceleration of up to 6000 times that of gravity acts radially on the rolling bodies, and this must be absorbed radially by a rolling body cage surrounding the rolling bodies. The rolling bodies are typically bearing needles subject to enhanced quality requirements on the ends thereof, wherein the bearing needles typically have a diameter of less than 2 mm and a length of less than 4 mm.
Bearing needles are currently mass-produced for the industrial and automotive sector using extremely productive manufacturing methods. The procedure in one conventional production method for bearing needles is that, first of all, a metal blank is produced by stretching a wire to a predetermined pre-grinding diameter. Pieces of suitable length are then cut off from the wire by means of a cutting tool. The wire segments produced in this way are then hardened, abraded, ground and superfinished. Cutting takes place at very high speeds with a high-speed cutting tool. In this process, the cutting contour typically formed on the needle end faces is that resulting from the technical process. The shape of the cutting contour is highly dependent on the guidance conditions for the wire in the cutting zone, on the state of wear of the cutting tools and on the wire diameter per se.
Test bed tests have shown that rolling bodies or bearing needles produced in this way may be unsuitable for very high-speed axial needle bearings. The undefined end face contour of the bearing needles can lead to high mechanical stress on the radial contact points of the rolling body pockets of the cage, resulting in a service life of the axial needle bearing which is only unsatisfactorily short. Further reaching optimization of the needle end faces only leads to a successful outcome if the needle end faces are ground and are smoothed and rounded by expensive finishing processes.
This technical problem is discussed in DE 10 2006 041 586 A1 and is solved by arranging a bearing needle and a bearing ball in series in a radial direction in each pocket of the cage of an axial needle bearing, wherein the bearing needles are arranged radially on the inside and the bearing balls are arranged radially on the outside. This ensures that bearing needles with an undefined end face contour cannot destroy the cage, even at high speeds of rotation. However, the disadvantage with this axial needle bearing is that the additionally required balls increase the production costs thereof.
Given this background situation, one object of the disclosure is to present a method for producing rolling bodies having crowned end surfaces for anti-friction bearings which is suitable for mass production and can be implemented at low cost. It is another object of the disclosure to specify rolling bodies produced by this method. Finally, it is another object of the disclosure to specify an anti-friction bearing having rolling bodies of this kind and the use thereof.
These objects may be achieved by a method for producing cylindrical rolling bodies with crowned end surfaces for anti-friction bearings, in particular bearing needles for high-speed axial needle bearings, having the following steps:
a) providing a spherical blank having a diameter D which corresponds to the rolling body length L of the rolling body;
b) grinding the spherical blank into a cylindrical shape of the rolling bodies, to the predefined diameter d thereof, wherein centerless cylindrical plunge grinding or centerless cylindrical throughfeed grinding may be used.
The use of centerless cylindrical plunge grinding or centerless cylindrical throughfeed grinding to produce cylindrical rolling bodies having crowned end surfaces makes possible inexpensive mass production at particularly low cost.
The grinding methods for centerless cylindrical plunge grinding and centerless cylindrical throughfeed grinding are already known; see, for example, http://www.hermle-schleiftechnik.de/pages/de_spitzenlos_durchlaufschleifen.php
or http://www.hermle-schleiftechnik.de/pages/de_spitzenlos_einstechschleifen.php
According to the disclosure, use is made here of a spherical blank, which is typically available as a mass-produced product, e.g. as a spherical rolling body, and which is then brought to a predefined diameter d by grinding into the cylindrical shape. Here, the ball diameter D corresponds to the rolling body length L. A material and a heat treatment for the blanks that are suitable for rolling bodies need to be selected in this context.
Use of spherical rolling bodies as blanks is advantageous since they typically already have a precise and laboriously smoothed surface. The radius of the ball corresponds to the radius of the crowned end surfaces of the rolling bodies, which is defined with a geometrically defined concentric crown and has very high surface quality without re-machining.
There is no need for precisely grouped balls since the length tolerance of the bearing needles is many times greater than the ball diameter, which is typically grouped within the μm range. It is therefore possible to use less expensive balls than those used in anti-friction bearings.
The object is furthermore achieved for cylindrical rolling bodies having crowned end surfaces by producing them by the method according to the disclosure.
The cylindrical rolling bodies produced in the manner described above having crowned ends for anti-friction bearings can be used wherever the presence of a defined, concentrically crowned end contour is required. This is the case especially with axial bearings, which are exposed to relatively high bearing speeds with correspondingly high centrifugal forces.
Here, the cylindrical rolling body is designed, in particular, as a bearing needle having a diameter d of less than 2 mm and a length L of less than 4 mm. However, barrel-shaped rolling bodies for toroidal bearings can also be produced in the manner described.
For economic reasons, a ratio of the length L to the diameter d may be no more than 3:1.
The object is furthermore achieved for the anti-friction bearing, such as axial needle bearing or toroidal bearing, if said bearing comprises a rolling body ring, which has a cage and furthermore the rolling bodies according to the disclosure. An anti-friction bearing of this kind can be produced at particularly low cost and can be operated at high speeds.
Use of the anti-friction bearing according to the disclosure at bearing speeds of up to 10,000 revolutions per minute has proven to be feasible.
The disclosure is explained by way of example below by means of
All the features mentioned in the preceding description of the figures, in the claims and in the introduction to the description can be used both individually and in any desired combination and also include the use of a profiled control disk (feed screw) of the kind used in the production of taper rollers, for example. Thus, the disclosure is not restricted to the combinations of features described and claimed; on the contrary, all combinations of features should be regarded as disclosed.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2015 207 106.5 | Apr 2015 | DE | national |
This application is the U.S. National Phase of PCT Appln. No. PCT/DE2016/200190 filed Apr. 18, 2016, which claims priority to DE 102015207106.5 filed Apr. 20, 2015, the entire disclosures of which are incorporated by reference herein.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/DE2016/200190 | 4/18/2016 | WO | 00 |
