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In powertrain systems, combined deflection of loaded gear tooth as well as that of the shafts on which the gears are mounted is responsible for non-ideal meshing conditions. Uneven load distribution along the teeth between mating gears is one such non-ideal condition that can cause significant NVH issues. Lead mismatch, defined as the amount of mismatch along a pair of gear tooth faces, is a critical parameter to maintain uniform load distribution at the gear contact regions. If each of the adjacent shafts is a balance shaft where a counterweight is mounted at an eccentric location, shaft deflection and the resultant lead mismatch is even more. Also, typically, balance shafts are required to rotate at twice the crankshaft speed. At a high engine speed, Coriolis and centrifugal accelerations acting on the balance shafts can be significant resulting in higher shaft deflection and greater lead mismatch.

Loss of lubrication within an axle assembly due to the formation of through-thickness cracks in structural components can result in severe durability issues for the internal parts (gears, splines, bearings, etc.). One such example of a structural crack resulting in lubrication leakage can be observed in the cover pan of a Salisbury axle that has been subjected to cyclic fore-aft loading conditions (which are intended to replicate the loads acting on the axle during vehicle acceleration or deceleration). Investigation of the cover pan crack locations was performed using Magnetic Particle Inspection (MPI) and indicated the formation and propagation of multiple cracks adjacent to the cover pan bolt holes.

It has been well-documented in academic literature that, when subjected to compressive cyclic loading (R = -∞), weldments can experience fatigue failure. However, unlike non-welded components, it has been shown that mean stress has a negligible impact on the fatigue life of welds (Gurney, 1979). Currently, most analytical weld prediction methods neglect the influence of mean stress and instead focus only on the relationship between the stress (or strain) amplitude and the respective number of cycles to failure.

Weld failure of a brake flange can put a driver’s life at risk. Two critical loading situations-torsional loading and vertical beaming loading-can result in brake flange failure. Two corresponding laboratory tests have been performed to ensure that the brake flanges pass the minimum standard requirement. The first is a brake reaction test, which is conducted in a situation that replicates the sudden braking operation of a vehicle. For this test, length, size, and penetration depth of the weld are critical parameters for determining the ability to prevent braking load failure. Among these factors, the length is the most crucial. The second test is a vertical beaming test, which is done in a condition that mimics the situation where a vehicle encounters a pot hole. Contrary to the previous test, an increased weld length can be detrimental in this case when the weld is moved to a higher stress location.

This paper discusses approaches to properly design aluminum axles for optimized NVH characteristics. By effectively using well established and validated FEA and other CAE tools, key factors that are particularly associated with aluminum axles are analyzed and discussed. These key factors include carrier geometry optimization, bearing optimization, gear design and development, and driveline system dynamics design and integration. Examples are provided to illustrate the level of contribution from each main factor as well as their design space and limitations. Results show that an aluminum axle can be properly engineered to achieve robust NVH performances in terms of operating temperature and axle loads.

Many analytical approaches have been proposed in the literatures to evaluate the brake squeal dynamics, the complex eigenvalue approach probably being the most popular. Although this method is generally accepted, it suffers from several drawbacks. One is that the analysis does not provide a clear indication of the squeal mechanism. Another is that the predictions are sensitive to slight changes to the system model. For this reason, a variation of the complex eigenvalue approach has been developed that is more robust and provides insight into the squeal mechanism. In this paper, the new method is used to identify the types of modal coupling mechanisms that lead to squeal. Based on this investigation, the authors present three different types of mode coupling conditions that cause squeal.

The complex eigenvalue method is commonly used to evaluate brake squeal. This method however does not provide a way to account for variations in modeling, operation and manufacturing. Nor does it provide a clear strategy to fix brake squeal problems. In this study, we present a new modeling approach, which addresses the modal uncertainty issues and provides a strategy to fix squeal problems. The major contribution of this paper is transferring the stability analysis from the physical domain to modal domain. By this transformation, we are able to examine the coupling strength between modes and locate the unstable modes that cause squeal problems. We develop a new stability metric based on the modal coupling strength, which can be used to evaluate design modifications for improvement and takes into account modal variation.

Gear whine can be reduced through a combination of gear parameter selection and manufacturing process design directed at reducing the effective transmission error. The process of gear selection and profile modification design is greatly facilitated through the use of simulation tools to evaluate the details of the tooth contact analysis through the roll angle, including the effect of gear tooth, gear blank and shaft deflections under load. The simulation of transmission error for a range of gear designs under consideration was shown to provide a 3-5 dB range in transmission error. Use of these tools enables the designer to achieve these lower noise limits. An equally important concern is the dynamic mesh stiffness and transmissibility of force from the mesh to the bearings. Design parameters which affect these issues will determine the sensitivity of a transmission to a given level of transmission error.