A best practice in gear design is to limit the amount of backlash to a minimum value needed to accommodate
manufacturing tolerances, misalignments, and deflections, in order to prevent the non-driving side of the teeth to make contact and rattle. Industry standards, such as ANSI/AGMA 2002 and DIN3967, provide reference values of minimum backlash to be used in the gear design. However, increased customers' expectations in vehicle noise eduction have pushed backlash and allowable manufacturing tolerances to even lower limits. This is especially true in the truck market, where engines are quieter because they run at lower speeds to improve fuel economy, but they quite often run
at high torsional vibration levels. Furthermore, gear and shaft arrangements in truck transmissions have become more complex due to increased number of speeds and to improve efficiency. Determining the minimum amount of backlash is quite a challenge. This paper presents an investigation of minimum backlash values of helical gear teeth applied to a light-duty pickup truck transmission. An analytical model was developed to calculate backlash limits of each gear pair when not transmitting load, and thus susceptible to generate rattle noise, through different transmission power paths.
A statistical approach (Monte Carlo) was used since a significant number of factors affect backlash, such as tooth
thickness variation; center distance variation; lead; runout and pitch variations; bearing clearances; spline clearances; and shaft deflections and misalignments. Analytical results identified the critical gear pair, and power path, which was confirmed experimentally on a transmission. The approach presented in this paper can be useful to design gear pairs
with a minimum amount of backlash, to prevent double flank contact and to help reduce rattle noise to lowest levels.
I'd like to apologize to the dedicated people working on revisions to the AGMA 925 standard and the Technical Report ISO 15144-1, both of which deal with the issue of micropitting. In the
March/April issue of Gear Technology, we published an opinion piece in our Voices column that harshly criticized the methods for predicting micropitting outlined in ISO 15144-1.
According to the U.K.-based WITT Energy website (witt-energy.com), "The WITT is the only device in the world that can capture energy from all movement and turn it into electricity. No other energy system can exploit the full spectrum of movement, enabling it to harvest power from water (sea, river or tidal),
wind and human or animal motion."
This is a very exciting year for AGMA as the organization celebrates its 100-year anniversary. In addition to the anniversary, AGMA President Joe Franklin, jr., who has done an outstanding job at the
helm of AGMA for the last 25 years,
will retire, and we welcome in our new
AGMA President, Matt Croson, who will
lead us into the next 100 years. The centennial kicked off in October with a dinner at the AGMA Gear Expo in Detroit and will continue throughout 2016 with a number of exciting events scheduled to celebrate this milestone anniversary.
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.