Reducing scrapping of gears by assessment of tip contact threshold torque

While striving for more competitive products as well as reaching the Global Sustainable Development Goals, automotive powertrain manufacturers increase the demands on gears, which translates to decreased manufacturing error tolerances. Too tight tolerances may, however, counteract the goal if it leads to increased material and energy consumption due to unjustified scrapping. This paper presents a method to prevent unjustified scrapping by comparing the severity of different manufacturing error tolerances by means of the tip contact threshold torque. Curve fits are shown to be accurate and helpful to assess the outcome of a produced batch of gears. A case study is made where the method is used with measured data from the industry. It can be concluded from the investigation that considerable amounts of scrapping can be avoided by consideration of the threshold torque.

Impact of Ultra-Low Viscosity Fluids on Drivetrain Functionality and Durability

Increasing automotive powertrain electrification is impacting drivetrain complexity and the profiles of the fluids needed. Since the millennium, drivetrain fluid viscosities have been reduced for better efficiency, but this new challenge is driving them to unprecedented low levels. This paper assesses some of the potential implications of ultra-low viscosity fluids on drivetrain functionality and durability. Model formulations have been prepared from a variety of base fluids combined with additive packages. These have been evaluated in typical automotive drivetrain rig tests, as well as with some selected functional tests. In addition, the thermo-oxidative stability and electrical and thermal properties of the fluids were compared. Based on the results, the impact of low viscosity fluids on drivetrain functionality and durability varies depending on the performance parameter evaluated. For example, gear scuffing and bearing wear is highly dependent on additives, whilst gear and bearing fatigue is mainly affected by fluid viscosity. However, by carefully balancing base fluids and additives, acceptable component and fluid durability can be achieved. With respect to new electric drivetrain performance needs, the thermal properties of the finished fluid are essentially dependent on the base fluid composition, whilst its electrical properties are more influenced by additive chemistry, with some secondary impact from base fluid composition.

The Effects of Gravity on the Response of Centrifugal Pendulum Vibration Absorbers

This paper describes the effects of gravity on the response of systems of identical, cyclically arranged, centrifugal pendulum vibration absorbers (CPVAs). CPVAs are passive devices composed of movable masses suspended on a rotor, suspended such that they reduce torsional vibrations at a given engine order. These absorbers are becoming prevalent in automotive powertrain components in order to expand fuel-efficient engine operating conditions. Gravitational effects acting on the absorbers can be important for a horizontal rotor/CPVA system spinning at relatively low rotation speeds, for example, during engine idle conditions. The main goal of this investigation is to predict the response of a CPVA/rotor system in the presence of gravity. A linearized model which includes the effects of gravity and an order n torque acting on the rotor is analyzed by exploiting the cyclic symmetry of the system. The results show that the N absorbers respond in one or more groups, where the absorbers in each group respond with identical waveforms but shifted phases. The number of groups depends on the engine order n and the ratio Nn. It is shown that there are special resonant effects if the engine order is n = 1 or n = 2, the latter of which is particularly important in applications. In addition, it is shown that for N > 1 the rotor response is not affected by gravity, due to the symmetry of the gravity effects. The analytical predictions are verified by direct simulations of the equations of motion.