GDS vs. FEA
(Gear Deflection System vs. Finate Element Analysis)
Two surfaces in contact will develop a reaction force between both members- sometimes known as a force of separation since it tends to separate one member from another.
Considering a (Free-Body-Diagram) FBD of the system, that force, normal to both surfaces in contact, will lead to a number of reaction forces developed between components such as: shafts, bearings, housing, etc.
Due to this deflection, gear and pinion will move relatively to each other. The result of that is a new “mounting” position of the pinion relatively to the gear, which can be always determined by a set of four parameters: E, P, G, Alpha. At nominal “home” unloaded (unstressed) position those four parameters would have zero values.
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So, the effect of shafts, bearings and supporting structure (housing) deflection can be measured and represented by certain changes in 4 DOF vector with component parameters: E, P, G and Alpha. Working surfaces will just find another relative position in space.
What are those numbers and how to get them? It is done on the Gear Deflection System or GDS.
The main goal for GDS is to measure the 3D stiffness of the housing or gear box where this gearset to be mounted for the normal service conditions and present it in form of four functions E,P,G and A a functions of load.
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Gear Deflection System (GDS) is designed to apply loads and measure the deviations in E, P, G and A under different loads. When the process is completed and functions for E, P, G and A are obtained for different loads, those numbers will be used in both TCA and SFT.
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Gleason has developed a procedure how to set the instrumentation and what the critical point should be used on the gear box to sensor locations.
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Reference:
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Coleman, W. "Analysis of Mounting Deflections on Bevel and Hypoid Gears", 1975 SAE Paper 750152
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“Application Testing of Bevel and Hypoid Gears”, Gleason Works (84-MTB 3480), Technical Report No.93032
H. Xu, J. Chakraborty and J.C. Wang:
“Effects of Axle Deflection and Tooth Flank Modification on Hypoid Gear Stress Distribution and Contact Fatigue Life”, The American Gear Manufacturers Association, Aug., 2009
J. H. Yoon, B. J. Choi, I. H. Yang, J.E. Oh: “Deflection test and transmission error measurement to identify hypoid gear whine noise”, National Journal of Automotive Technology, Feb. 2011
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Recently as a result of extended development in FEA area the conventional GDS test has been replaced with a computer model of the differential and supporting components inside the housing.
The same conclusion can be drawn here about the uncertainty of the model versus the real part as it has been noted about “real” smartSFT vs. TCA. But the presence of a good model even with some assumptions reduces the time for the development.
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Once FEA techniques were only used by big companies due to their complexity and price, but with the development of computer technology they have become more and more accessible to small gear companies, which are the majority of participants in the market.
In today’s market even a small gear company usually possesses a modern CAD system, which always includes a basic or advanced FEA package.
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