AGMA 13FTM13-2013 Gear Failure Analysis and Lessons Learned in Aircraft High-Lift Actuation.pdf
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1、13FTM13 AGMA Technical Paper Gear Failure Analysis and Lessons Learned in Aircraft High-Lift Actuation By A. Wang, S. Gitnes, L. El-Bayoumy and J. Davies, MOOG Inc. Aircraft Group2 13FTM13 Gear Failure Analysis and Lessons Learned in Aircraft High-Lift Actuation Anngwo Wang, Seth Gitnes, Lotfi El-Ba
2、youmy and Jonathan Davies, MOOG Inc. Aircraft Group The statements and opinions contained herein are those of the author and should not be construed as an official action or opinion of the American Gear Manufacturers Association. Abstract Several gear failure cases and lessons learned in the develop
3、ment phase of aircraft high lift actuation systems are presented, including leading edge geared rotary actuators, and trailing edge geared rotary actuators, sector gears and pinions, and offset gearboxes. The high lift system of an aircraft, which contains trailing edge flaps and/or leading edge sla
4、ts, increases lift for takeoff, controls flight during cruise, and reduces speed while increasing lift for shorter landing distance. Many of these components contain highly loaded gears to increase the power to weight ratio. Because of requirements on weight or envelope and consideration of cost, th
5、e gears are always designed to the limit with reasonable margins of safety in a high lift system. The structure which supports the gears is limited in size and simplified, and the gear material and heat treatment are selected for easy manufacturing. Therefore, when misalignment and/or deflection of
6、the gears are large enough to cause reduction in tooth contact area, the stress on gears becomes large enough to cause damage. The failure modes can be classified as spalling or pitting at the location of concentrated loads. Most of the problems can be resolved by providing correct lead modification
7、 to alleviate the concentrated loading, while some need increase of the gear diameters, design modifications, or introduction of materials with higher allowable. Copyright 2013 American Gear Manufacturers Association 1001 N. Fairfax Street, Suite 500 Alexandria, Virginia 22314 September 2013 ISBN: 9
8、78-1-61481-070-4 3 13FTM13 Gear Failure Analysis and Lessons Learned in Aircraft High-Lift Actuation Anngwo Wang, Seth Gitnes, Lotfi El-Bayoumy and Jonathan Davies, MOOG Inc. Aircraft Group Introduction The high lift system of an aircraft, including trailing and/or leading edge slats/flaps, increase
9、s lift for take-off, controls flight during cruise, and reduces landing distance for touch-down. This flight control system is usually composed of power drive units (PDUs), torque tubes, bevel gear boxes, offset gearboxes, leading edge (LE) geared rotary actuators (GRAs), trailing edge (TE) GRAs, an
10、d leading edge sector gears and pinions (Figure 1). The system also includes other components, such as torque limiters, slip clutches, no-back drive devices, and wing tip brakes to provide system protection from overloading. Many of these components contain different types of gears that are usually
11、highly loaded to increase the power to weight ratio. Because of the requirements on weight or envelope and consideration of cost, the gears in a high lift system are always designed with minimal margins. The structure which supports the gears is limited in size or simplified, and the gear material a
12、nd heat treatment are selected for easy manufacturing. Deflections and misalignments between meshing gears cause edge loading which generates noise and high bending and contact stresses. The deflection emanates from the high loading and the misalignment comes from wing bending or the deflection of g
13、ear shafts and housings. Irrespective of the load, once the misalignment and/or deflection cause the contact area to shift and diminish, the stress becomes large enough to cause problems. AGMA publishes an atlas of failure modes 1 that identify some common types of wear. Bajpai et. al. 2 combines a
14、contact analysis model and a wear prediction model to describe the evaluation of tooth surface wear of spur and helical gear pairs. In these previous papers, the focus is on the outcome of failures, and not the reasons and sources of gear wear. Drago 3 discussed spalling caused by tip interference a
15、nd showed that a contact failure can lead to a more severe tooth fracture. Drago et. al. 4also discussed the relation between micropitting to specific lubrication additive package combinations, gear quality and surface finish, which can be resolved by profile modifications. Errichello et. al. 5 inve
16、stigated that the root cause of macropitting is the geometric stress concentration caused by tip-to-root interference. All these previous three papers deal with failures caused by tooth geometries and quality of gears. Errichello 6 investigated a gear set which failed due to lubrication breakdown. T
17、he main objective of this presentation is to find out how to solve these problems if the cause is due to edge loading from the misalignment of gear mounting and/or deflection of supporting structure. In this paper, several different gear failure cases in the development phase of high lift systems ar
18、e presented, including leading edge geared rotary actuators, and trailing edge geared rotary actuators, sector gears and pinions, and offset gearboxes. The failure modes can be classified as spalling or pitting at the location of concentrated loads. Most of the problems can be resolved by providing
19、correct lead modifications to alleviate the concentrated loading, while some can only be corrected by increasing the gear diameters, design modifications, or introduction of materials with higher allowable. Detailed analyses to predict deflections and misalignments on system and component levels is
20、the key to the amount of lead modification, from which increased local contact stresses can be calculated. Figure 1. Schematic of the high lift system of an aircraft (left LE shown, TE similar) 4 13FTM13 The cases presented in this paper are from the pre-production risk mitigation units (RMUs). Norm
21、ally the RMUs were designed with little margin to achieve minimum weight. Most system or component deflections can be predicted by analyses during the design phase. If there are any unanticipated misalignments or deflections, then failures will show up and the situation can be improved with correcti
22、ons in the production units. In this way designs are optimized for minimum weight. Leading edge rotary geared actuators The cross section of a typical leading edge geared rotary actuator is shown in Figure 2. There are three gear meshes on each one of the planet gears. The output is on the left side
23、 of the actuator. The output planet gears are overhung and balanced by the planet gears on the right. The center planet gears act as a pivot point. Because the output planet gears are overhung, it is called a cantilever GRA. Trailing edge geared rotary actuators The cross section of a typical traili
24、ng edge geared rotary actuator is shown in Figure 3, and the gear schematic is shown in Figure 4. The output consists of two load paths from two end ring gears. The sun gear drives the right end planet gears. The stiffness difference between the right and left load paths causes the compound planet g
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