Four point contact bearings are particularly suitable where:
- Predominantly axial loads must be supported ➤ section
- The axial design envelope is not sufficient for double row radial angular contact ball bearings
- Radial forces must be supported by a separate radial bearing ➤ Figure
- Axial forces occur in both directions and a close axial clearance is required in conjunction with a small bearing width, e. g. in gearbox engineering.
Four point contact bearing and double row angular contact ball bearing – comparison of design envelope
Four point contact bearings are available as:
- bearings of basic design ➤ Figure
- bearings with retaining slots in the outer ring ➤ Figure
- X-life bearings ➤ link.
Bearings of basic design
Comparable, in terms of product design, with single row radial angular contact ball bearings
Four point contact bearings are single row, non self-retaining radial ball bearings. They are similar in their structure to single row radial angular contact ball bearings; the raceways on the inner rings are, however, designed such that they can support axial loads in both directions ➤ Figure and ➤ section. The centre points of curvature of the arc-shaped raceways on the inner and outer ring are offset relative to each other in such a way that the balls are in contact with the bearings at four points under radial load ➤ Figure and ➤ section.
Smaller axial section height than double row angular contact ball bearings
These bearings have solid outer rings, split inner rings and ball and cage assemblies with brass or polyamide cages ➤ section. The two-piece inner ring allows a large complement of balls to be accommodated in the bearing. The inner ring halves are matched to the particular bearing and must not be interchanged with those of other bearings of the same size. In an axial direction, four point contact bearings are considerably narrower than, for example, double row angular contact ball bearings.
Four point contact bearing of basic design
α = nominal contact angle
M1, M2 = centres of curvature of outer ring raceway
Fr = radial load
Fa = axial load
Four point contact bearing, split inner ring, without retaining slots in the outer ring
Bearings with retaining slots in the outer ring
The retaining slots allow simple location of the bearing in the housing
Four point contact bearings are often combined with a radial bearing and used as an axial bearing with radial clearance in a housing ➤ Figure, ➤ section. For quick and secure location of the bearings in the housing, larger bearings therefore have two retaining slots in one end face of the outer ring offset by 180° ➤ Figure. Locking pins engage in these retaining slots and locate the outer ring in the housing.
Four point contact bearing used as an axial bearing, radial clearance on outer ring, axial force flow
Cylindrical roller bearing (radial bearing)
Four point contact bearing with retaining slots in outer ring (axial bearing, outer ring not radially retained)
Locking pin for location of outer ring
X-life premium quality
Four point contact bearings are available in certain sizes as X-life bearings. These bearings exhibit considerably higher performance than standard four point contact bearings ➤ Figure. This is achieved, for example, through the modified internal construction, higher surface quality of the contact surfaces and optimised cage design, as well as through the improved quality of the steel and rolling elements.
Increased customer benefits due to X-life
The technical enhancements offer a range of advantages, such as:
- a more favourable load distribution in the bearing and thus a higher dynamic load carrying capacity of the bearings ➤ Figure
- quieter running
- running with reduced friction and greater energy efficiency
- lower heat generation in the bearing
- higher possible speeds
- lower lubricant consumption and, consequently, longer maintenance intervals
- a measurably longer operating life
- high operational security
- compact, environmentally-friendly bearing arrangements.
Lower operating costs, higher machine availability
In conclusion, these advantages improve the overall cost-efficiency of the bearing position significantly and thus bring about a sustainable increase in the efficiency of the machine and equipment.
Comparison of basic dynamic load rating Cr – bearing series QJ3..-XL, bore code 5 to 14, with a bearing which is not of X-life quality
Cr = basic dynamic load rating
Areas of application
Wide application range
Due to their special technical features, X-life four point contact bearings are highly suitable for bearing arrangements in:
- fluid and hydraulic pumps
- automotive chassis and gearboxes
- gearboxes for industrial, rail and wind turbine applications
- agricultural vehicles and equipment.
X-life indicates a high product performance density and thus a particularly significant benefit to the customer. Further information on X-life ➤ link.
Load carrying capacity
Capable of supporting high axial loads in both directions
Due to the design of the raceways with their high shoulders, the large nominal contact angle of α0 = 35° and the large number of rolling elements, four point contact bearings have a very high axial load carrying capacity. They are suitable for alternating, purely axial loads or predominantly axial load. The balls are in contact with the inner ring and outer ring each at one point only, as is the case with a single row angular contact ball bearing under axial load➤ Figure.
The radial load carrying capacity of the bearings is low. If predominantly radial load is present, four point contact bearings should not be used due to the higher friction in the four point contact.
Compensation of angular misalignments
Four point contact bearings cannot compensate misalignments
Four point contact bearings are not suitable for the compensation of angular misalignments due to housing deformations or shaft deflections. The possible skewing of the inner ring in relation to the outer ring depends, for example, on the bearing load, the operating clearance and the bearing size, and is very small.
Skewing of the bearing rings increases the running noise, places increased strain on the cages and has a harmful influence on the operating life of the bearings.
Oil or grease lubrication
The bearings are not greased. They must be lubricated with oil or grease.
Compatibility with plastic cages
When using bearings with plastic cages, compatibility between the lubricant and the cage material must be ensured if synthetic oils, lubricating greases with a synthetic oil base or lubricants containing a high proportion of EP additives are used.
Observe oil change intervals
Aged oil and additives in the oil can impair the operating life of plastics at high temperatures. As a result, stipulated oil change intervals must be strictly observed.
The bearings are of an open design
Four point contact bearings are supplied without seals. As a result, sealing of the bearing position must be carried out in the adjacent construction. The sealing system should reliably prevent:
- moisture and contaminants from entering the bearing
- the egress of lubricant from the bearing.
Higher speeds are only possible under purely axial load
Due to the four point contact and resulting higher level of friction, the speed suitability of the bearings is heavily restricted under radial load. High speeds can only be achieved if four point contact ball bearings are subjected to purely axial load.
Limiting speeds and reference speeds in the product tables
Two speeds are generally indicated in the product tables ➤ dimension table:
- the kinematic limiting speed nG
- the thermal speed rating nϑr.
The limiting speed nG is the kinematically permissible speed of a bearing. Even under favourable mounting and operating conditions, this value should not be exceeded without prior consultation with Schaeffler ➤ link. The values in the product tables are valid for oil lubrication.
Values for grease lubrication
For grease lubrication, 75% of the value stated in the product tables is permissible in each case.
nϑr is used to calculate nϑ
The thermal speed rating nϑr is not an application-oriented speed limit, but is a calculated ancillary value for determining the thermally safe operating speed nϑ ➤ link.
The Schaeffler Noise Index (SGI) has been developed as a new feature for comparing the noise level of different bearing types and series. As a result, a noise evaluation of rolling bearings can now be carried out for the first time.
Schaeffler Noise Index
The SGI value is based on the maximum permissible noise level of a bearing in accordance with internal standards, which is calculated on the basis of ISO 15242. In order that different bearing types and series can be compared, the SGI value is plotted against the basic static load rating C0.
This permits direct comparisons between bearings with the same load carrying capacity. The upper limit value is given in each of the diagrams. This means that the average noise level of the bearings is lower than illustrated in the diagram.
The Schaeffler Noise Index is an additional performance characteristic in the selection of bearings for noise-sensitive applications. The specific suitability of a bearing for an application in terms of installation space, load carrying capacity or speed limit for example, must be checked independently of this.
Schaeffler Noise Index for four point contact bearings
SGI = Schaeffler Noise Index
C0 = basic static load rating
The operating temperature of the bearings is limited by:
- the dimensional stability of the bearing rings and rolling elements
- the cage
- the lubricant.
Possible operating temperatures for four point contact bearings ➤ Table .
Permissible temperature ranges