With the ongoing push towards electric vehicles (EVs), there is likely to be increasing focus on the noise impact of the gearing required for the transmission of power from the (high-speed) electric motor to the road. Understanding automotive noise,
vibration and harshness (NVH) and methodologies for total in-vehicle noise presupposes relatively large, internal combustion (IC) contributions, compared to gear noise. Further, it may be advantageous to run the electric motors at significantly higher rotational speed than conventional automotive IC engines, sending geartrains into yet higher speed ranges. Thus the move to EV or hybrid electric vehicles (HEVs) places greater or different demands on geartrain noise. This work combines both a traditional NVH approach (in-vehicle and rig noise, waterfall plots, Campbell diagrams and Fourier analysis) - with highly detailed transmission error measurement and simulation of the complete drivetrain - to fully understand noise sources
within an EV hub drive. A detailed methodology is presented, combining both a full series of tests and advanced simulation to troubleshoot and optimize an EV hub drive for noise reduction.
The cutting process consists of either
a roll only (only generating motion), a plunge only or a combination of plunging and rolling. The material removal and flank forming due to a pure generating motion is demonstrated in the simplified sketch in Figure 1 in four steps. In the start roll position (step 1), the cutter
profile has not yet contacted the work. A rotation of the work around its axis (indicated by the rotation arrow) is coupled with a rotation of the cutter around the axis of the generating gear (indicated by
the vertical arrow) and initiates a generating motion between the not-yet-existing tooth slot of the work and the cutter head (which symbolizes one tooth of the generating gear).
Effective case depth is an important factor and goal in gas carburizing, involving complicated procedures in the furnace and requiring precise control of many thermal parameters. Based upon diffusion theory and years of carburizing experience, this
paper calculates the effective case depth governed by carburizing temperature, time, carbon content of steel, and carbon potential of atmosphere. In light of this analysis,
carburizing factors at various temperatures and carbon potentials for steels with different
carbon content were calculated to determine the necessary carburizing cycle time.
This methodology provides simple (without computer simulation) and practical guidance
of optimized gas carburizing and has been applied to plant production. It shows that measured, effective case depth of gear parts covering most of the industrial application range (0.020 inch to over 0.250 inch) was in good agreement with the calculation.
Chapter 2, Continued
In the previous sections, development of conjugate, face milled as well as face hobbed bevel gearsets - including the application of profile and length crowning - was demonstrated. It was mentioned during that demonstration that in order to optimize the common surface area, where pinion and gear flanks have meshing contact (common flank working area), a profile shift must be introduced. This concluding section of chapter 2 explains the principle of profile shift; i.e. - how it is applied to bevel and hypoid
gears and then expands on profile side shift, and the frequently used root angle correction which - from its gear theoretical
understanding - is a variable profile shift that changes the shift factor along the face width. The end of this section elaborates on
five different possibilities to tilt the face cutter head relative to the generating gear, in order to achieve interesting effects on the
bevel gear flank form. This installment concludes chapter 2 of the Bevel Gear Technology book that lays the foundation of the following
chapters, some of which also will be covered in this series.
In order to properly select a grease for a particular application, a sound knowledge of the influence of different grease components and operating conditions on the lubrication supply mechanism and on different failure modes is of great benefit.
Detection of impending gear tooth failure is of interest to every entity that utilizes geared transmissions. However, it is of particular significance at the Gear Research Institute (GRI), where sponsored
efforts are conducted to establish
gear material endurance limits, utilizing gear fatigue tests. Consequently, knowing when a gear is about to fail in each and every test, in a consistent manner, is essential for producing reliable and useful
data for the gear industry.
Hard finishing technology, e.g. — honing — is used to manufacture high-performance gears. Gear honing is primarily used to hard finish small- and medium-sized automotive gears. And yet trials have shown that gears with a module larger than mn = 4 mm can also be honed efficiently, but problems often occur due to unstable process design. In this paper a model to improve the process design is described.
In the previous sections, the development of conjugate bevel gearsets via hand calculations was
demonstrated. The goal of this exercise was to encourage the reader to gain a basic understanding of
the theory of bevel gears. This knowledge will help gear engineers to better judge bevel gear design
and their manufacturing methods.
In order to make the basis of this learning experience even more realistic, this chapter will convert
a conjugate bevel gearset into a gearset that is suitable in a real-world application. Length and profile
crowning will be applied to the conjugate flank surfaces. Just as in the previous chapter, all computations
are demonstrated as manual hand calculations. This also shows that bevel gear theory is not as
complicated as commonly assumed.