SAE-TPS-402006-01-0779.pdf
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1、400 Commonwealth Drive, Warrendale, PA 15096-0001 U.S.A. Tel: (724) 776-4841 Fax: (724) 776-5760 Web: www.sae.org SAE TECHNICAL PAPER SERIES 2006-01-0779 Fatigue Analysis for Axle Differential Cases S. Sreedhar Ford Motor Co. D. Marla Automotive Components Holdings, LLC D. Guo DaimlerChrysler Corp.
2、Reprinted From: Fatigue Research & Applications, 2006 (SP-2031) 2006 SAE World Congress Detroit, Michigan April 3-6, 2006 The Engineering Meetings Board has approved this paper for publication. It has successfully completed SAEs peer review process under the supervision of the session organizer. Thi
3、s process requires a minimum of three (3) reviews by industry experts. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior writt
4、en permission of SAE. For permission and licensing requests contact: SAE Permissions 400 Commonwealth Drive Warrendale, PA 15096-0001-USA Email:permissionssae.org Tel:724-772-4028 Fax:724-776-3036 For multiple print copies contact: SAE Customer Service Tel:877-606-7323 (inside USA and Canada) Tel:72
5、4-776-4970 (outside USA) Fax:724-776-0790 Email:CustomerServicesae.org ISSN 0148-7191 Copyright 2006 SAE International Positions and opinions advanced in this paper are those of the author(s) and not necessarily those of SAE. The author is solely responsible for the content of the paper. A process i
6、s available by which discussions will be printed with the paper if it is published in SAE Transactions. Persons wishing to submit papers to be considered for presentation or publication by SAE should send the manuscript or a 300 word abstract to Secretary, Engineering Meetings Board, SAE. Printed in
7、 USA 2006-01-0779 Fatigue Analysis for Axle Differential Cases S. Sreedhar Ford Motor Co. D. Marla Automotive Components Holdings, LLC D. Guo DaimlerChrysler Corp. Copyright 2006 SAE International ABSTRACT The recent trends of increasing driveline torque and use of traction control devices call for
8、increasingly higher durability capacity from driveline components. Bench and vehicle durability tests are often used to validate designs, but they are not cost-effective and take months to complete. Traditional finite element analysis (FEA) procedures have been used effectively in the re-design of d
9、riveline components to reduce stress, and occasionally, to predict fatigue life. But in the case of certain rotating components, such as the Axle Differential Case, where the component sees large stress/strain fluctuations within the course of one complete rotation, even under constant input torque,
10、 historical fatigue analysis (when conducted) yields very conservative results. The axle differential case tends to be one of the weakest links in the rear axle assembly. Therefore, there is a crucial need for analytical methods to more accurately predict fatigue life to reduce testing time and cost
11、. In this paper, a new CAE procedure for differential case fatigue life prediction is outlined. This analysis procedure takes into account the variation of stress within each revolution for a given input torque, as well as the variation in the input torque itself. The analytical result has been show
12、n to correlate very closely with bench testing using a torsional Axle Inertia Impact Test. INTRODUCTION Most Front Wheel Drive and Rear Wheel Drive drivetrain configurations use a differential device to transfer torque and simultaneously allow the left and right wheels to rotate at different speeds
13、when turning around a corner. A differential case is used to house various gears and clutches. In a typical 90-degree torque-transfer device, such as in an axle design (Fig. 1), the ring gear is rigidly mounted on a differential case. A drive pinion gear transfers driving torque as it meshes with th
14、e ring gear. This ring gear changes the driving direction by 90 degrees, and passes the torque to the differential case. Through the internal mechanism, differential gears transfer the torque to the wheels to drive the vehicle. At a given point on the differential case, variations in strain/stress a
15、re observed even under constant driving torque. Fig 1. Cutaway view of a typical automotive axle Traditionally, bench and vehicle tests are used to validate the case design, but these take weeks, if not months, to set up and run. Finite Element Analysis (FEA) methods are widely used to design and an
16、alyze automotive components. Currently, when designing and analyzing automotive components using finite element analysis (FEA), it is usual practice to evaluate the stresses and deflections of the part using a worst-case loading condition, then proceed to fatigue analysis, and predict fatigue life a
17、s a Carrier Housing Hypoid Ring Gear Differential case Hypoid Pinion number of repeats of that cycle. In the case of rotating components like a rear axle differential case, this yields a very conservative estimate of the fatigue life. This is due to the cyclical variation of the case stress/strain d
18、uring the course of one complete revolution, and stays well below the maximum value for most of the revolution. Since the case is not completely axisymmetric in shape, impacts at different angular locations on the ring-gear flange produce different stress/strain distributions in the differential cas
19、e. WORST-CASE ANALYSIS The usual current practice is to perform linear static finite element (FE) analysis to determine the stresses in the differential case (Fig. 2). A worst-case stress/strain distribution on the case is then determined by evaluating multiple positions of the hypoid gear mesh-poin
20、t around the case. Fig 2. FE model set-up This stress/strain distribution would then be used in a fatigue analysis where varying loads (from a test or durability route) would be applied to calculate the predicted fatigue life of the case. This life prediction would be in terms of repeats of the test
21、 load or of the durability route. Clearly this is a quick and simple process. However, the main drawback is that it gives highly conservative results, since the worst-case stress/strain distribution is assumed to act on the case throughout the full loading cycle. Also, this procedure does not accoun
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