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Custom super precision bearings manufactured by The Barden Corporation, part of the multinational Schaeffler Group, are playing vital roles in the thrust reversing actuator system (TRAS) on the Airbus A350 XWB And Electro-Hydraulic Actuator (EHA) systems on the Airbus A380.

UTC Aerospace Systems (UTAS) supplies thrust reversing actuator systems for the Airbus A350 XWB and primary flight control actuation systems for the Airbus A380. Both systems rely on super precision bearings from The Barden Corporation (UK) Limited, part of the Schaeffler Group’s aerospace division.

The bearings for the primary flight control actuators incorporate sealing technology that helps save space and are designed to withstand the very high axial loads from the hydraulic pumps. The bearings for the electric motor on the A350 thrust reversing actuator system are provided with ceramic balls to minimise friction/adhesive wear, spring preloaded to minimise tolerance stack-up and lubricated-for-life with a special grease that provides high mechanical stability.

Driven by the demand to optimise aircraft performance, decrease operating and maintenance costs and reduce gas emissions, the aircraft industry is pushing towards the concept of more electric aircraft (MEA) and, ultimately, an all-electric aircraft. The MEA concept provides for the utilisation of electric power for all non-propulsive systems. Traditionally, these non-propulsive systems are driven by a combination of different secondary power sources such as hydraulic, pneumatic, mechanical and electrical. However, recent technological advances in the field of power electronics, fault-tolerant architecture, electro-hydrostatic actuators, flight-control systems, high-density electric motors, power generation and conversion systems, have ushered in the era of MEA. This trend is accelerating, as aircraft OEMs collaborate with their suppliers to design new systems and implement new electrical-intensive architectures.

The primary flight control actuators on the Airbus A380 are an example of the push towards More Electric Aircraft (MEA). Custom super precision bearings from Barden play a key role in these actuation systems. Not only do the bearings incorporate sealing technology, which helps save space, they are also designed to withstand very high axial loads generated by the system’s hydraulic pumps.

EHA reduces the need for central hydraulic power generation and distribution systems on the aircraft. The system uses aircraft electrical power to produce the required hydraulic pressure and flow within the actuator at the point of use. EHAs generate hydraulic pressure that flows locally within the actuator, using the aircraft electrical bus as the power source.

The Airbus A380 is the first civil aircraft to use 5,000psi Fly-by-Wire actuators and modern Power-by-Wire EHAs. Typically, a civil aircraft uses a 3,000psi system or 4,000psi, but most modern military aircraft use 5,000psi systems. Increasing the system pressure to 5,000psi for the rudder, elevator and aileron controls enables a reduction in the diameter of the hydraulic pipes and couplings while delivering the same force. This provides additional benefits such as aircraft weight reduction.

For the EHAs to function correctly and withstand such high system pressures, bearings and seals are vital. Barden supplies bearings to UTAS for the EHAs on the rudder, elevator and aileron flight control systems. The bearings are local to the point of actuation, on the wing for example, and so high vibration levels can be expected.

As Robin Kyte of Barden explains: “The design of the bearings was quite a challenge as we had such a small design envelope to work in. UTAS also required wide-ranging duty cycles to be considered. Because of the restricted design envelope we sat down with their engineers at an early stage in the design process to discuss alternative design solutions.”

Ultimately, sealing technology was incorporated into the bearings to save design space and increase the capacity of the bearings. The internal geometry, curvature, ball complement and shoulder height of the bearings were optimised. Super precision geometric tolerances were also applied to track roundness and weave. The raceways are super finished to improve lubrication film generation.

Barden also supplies bearings to UTAS for the electric motor on the Airbus A350’s thrust reversing actuator system (TRAS). During landing of the aircraft, this high-speed electric motor provides reverse thrust during landing.

The motor and therefore the bearings are non-operational for 99.99% of their life. The bearings are therefore provided with ceramic balls to minimise friction and adhesive wear between the balls and raceways due to false brinelling, i.e. wear caused by the slight axial sliding movement (due to vibrations) of the rolling elements while the bearing is stationary.

Loads on the motor bearings are relatively small but vibrations are high and so the bearings are spring preloaded to minimise tolerance stack-up, which again helps to prevent false brinelling.

The bearings are lubricated-for-life with a special grease that provides high mechanical stability. The viscosity of the grease also ensures that friction is minimised in the cold aircraft operating temperatures.

Barden

The Barden Corporation specialises in the design and manufacture of super precision ball bearings used in high performance applications across a broad range of market sectors. The company’s extensive product line includes key components for the aerospace and defence sectors, vacuum pumps, food processing, robotics and medical equipment.

The Barden Corporation specialises in the design and manufacture of super precision ball bearings used in high performance applications across a broad range of market sectors. The company’s extensive product line includes key components for the aerospace and defence sectors, vacuum pumps, food processing, robotics and medical equipment.

These products are predominantly radial, single and double row, angular contact or deep groove super precision ball bearings, which are offered in thousands of standard variations, although a significant proportion of production is devoted to special bearings. Bearings come in inch or metric dimensions with diameters ranging from 4mm (0.16″) outer diameter (OD) up to 180mm (approx 7″) OD and can operate comfortably at speeds of two million dN (bore in mm x RPM) or above. A variety of bearing seals, shields and metallic/non-metallic cage designs are available for all products.

Barden’s engineering team is able to offer unique solutions to bearing-related challenges by developing bearings and complex assemblies to assist customers in reducing parts count, assembly time and operating costs. Products across all ranges can meet and usually exceed ISO P2 (ABEC 9) standards whilst also offering full traceability back to raw materials where required.

The Barden Corporation is a key strategic member of the multinational Schaeffler Group, which specialises in bearing technologies and precision products for aerospace, industrial plant and automotive industries and has over 82,000 employees at approximately 170 locations in 50 countries. Schaeffler is headquartered in Germany and oversees three main brands: FAG, INA and LuK. Barden’s activities are supported by sister sites, The Barden Corporation (US) based in Danbury, USA, and the Winsted Precision Ball Company in Connecticut, USA.

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