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06/07/2009
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The Schaeffler Group has launched a family of ball roller bearings which it says offers reduced friction and allows bearing mass and width to be decreased by 20%.
 Schaeffler's 'ball roller' is an energy efficient range of bearings that utilises spherical bearing elements, but with their sides cut off. The research and development programme spanned several years and the ball roller is also based on new assembly methods.
The result is a range of ball roller elements designed to offer the axial load handling capabilities of fully spherical balls, but allows overall bearing width and mass to be decreased by around 20% as well as reducing friction. According to Schaeffler, this means that in the same design space, it is now possible to carry greater loads and provide a larger grease reservoir or more space for improved sealing.
In the new design, Schaeffler has removed all areas of a conventional rolling element 'ball' that are not under load. This means that 15% of the ball's diameter is cut off on both sides. The result is a flattened ball on both sides, which Schaeffler says is 30% narrower than a conventional ball. This saves design space and enables the number of rolling elements to be increased. This in turn enables the filling capacity of the bearing to be increased by up to 90%..
Heinrich Hofmann, development engineer, special projects at the Schaeffler Group, said: "The idea for the ball roller came from our development engineers, who were testing ball bearings and discovered that the spherical balls tended to roll about a single axis and made no use of those areas adjacent to this axis."
In a typical ball bearing, only 70% of the ball width is utilised, so the outer 15% to the left and right of the ball diameter can be considered redundant. This discovery led the company to the idea of cutting off this 'redundant' material from the sides of the balls.
The development team realised that cage design would be critical to the new bearing. Hofmann added: "Because the balls cannot be allowed to greatly change their rotation axes, cage design was crucial. The critical conditions occur during initial rotation. Once the bearings are moving under conditions of speed and load, they become self locating, like a bicycle wheel."
In addition, having moved away from a fully spherical shape, it is possible to give the roller a logarithmic profile, since the rotational axis is always perpendicular to the variable contact angle. The osculation conditions – the 'kiss' between the roller and the bearing groove – therefore do not change. If the load ratio changes from axial to radial and the contact angle changes as a result, the osculation 'creeps' in an optimum manner with the change in load.
The BXRO range of ball roller bearings are double row bearings with the rolling elements in an 'O' arrangement, enabling the bearings to support both radial and axial forces. The optimised raceway geometry of the single piece inner ring has been designed to increase bearing accuracy. Applications include automotive manual transmissions and textile machinery.
The BXRT ball roller series is a double row design with the rows of ball rollers in a tandem arrangement. The rolling elements can be guided using one or two cages. The two cage design enables the optimal adjustment of the two raceways independently of each other to match applications such as manual transmissions, differentials, hydraulic motors and pumps.
Schaeffler has also launched a special ball roller bearing for use as a wheel bearing, reducing friction and weight in passenger cars and commercial vehicles. The four-row, BXR4 wheel bearings offer higher load carrying capacity and therefore enable more compact designs than conventional wheel bearings. The new bearings are suitable for driven axles. Reduced friction and reduced weight of the bearing and wheel carrier are said to contribute to reduced fuel consumption and exhaust emissions.
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Author
Chris Shaw
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