Effect of bearing thermally induced preload on the efficiency of automotive manual transmission under RDE

Abstract

In order to calculate the efficiency of an automotive manual transmission, taking into consideration the effect of its most power consuming components – gears and bearings – as well as the interactions between them is of high importance. In this paper, a dynamic model has been developed which can predict the frictional losses of a complete gearbox as a system and, thus, its efficiency. The effect of temperature on bearing preload is also considered and taken into account from a system perspective identifying its effect on the bearings frictional losses (as well as the overall efficiency). The operating conditions used are snapshots of the Real Driving Emissions driving cycle, which is a standard metric for automotive manufacturers. Results show that doubling the temperature can lead to 120% increase of the bearing losses and up to 140% increase of the total transmission losses. The effect of the variation of operating conditions (velocity and torque) is also taken into account. The novelty of this paper lays in the development of a dynamic model which takes into account the performance of a complete gearbox under transient operating conditions, as well as the interaction among its main components and the ability to make changes on the influencing factors of transmission efficiency so that their effect on the complete gearbox efficiency can be tracked. This has not been yet reported in the relevant literature which mainly focuses on the influencing factors of transmission power loss and efficiency experimental measurements under various operating conditions for gear pairs instead of complete gearboxes.

On the Effect of DLC and WCC Coatings on the Efficiency of Manual Transmission Gear Pairs

“…Figure 10 presents the results of the simulations for the operating conditions of scenario 1, when all gears are considered uncoated. It has to be noted that the uncoated gear model has been validated experimentally at system level, as presented in [29]. For each gear, as described in Table 7, different operating conditions apply.…”

Investigation of the Influences of Thrust Loads Resulted by Helix Angle Directions of Planetary Gear Sets on Bearing Power Losses in Automotive Planetary Gear Trains

“…Studies on power loss subjects related to gear pairs, bearings, and gear systems have been extensively performed and presented by many researchers [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. For rolling element bearings, empirical models of power losses and friction moments involving mechanical loads and fluid viscous frictions are found in the literature [1][2][3], while the SKF Group [4] developed a model composed of individual contributions of rolling, sliding, sealing and drag.…”

“…As a system level consisting of gears, bearings and shafts, such as a gearbox or transmission, Talbot et al [9] proposed a power loss model for an axle, which includes contributions of rolling and sliding of hypoid gears, loads and spins of radial rolling bearings, as well as drags, while splash power losses in a gearbox were analyzed by simulations of computational fluid dynamics and the influences of design parameters on the losses were presented by Gorla et al [10]. Laderou et al [11] developed a tapered bearing model and dynamic model of parallel shaft gear systems in order to predict the transmission power efficiency considering the effects of temperature on bearing preload. Michaelis et al [12] proposed that the influential factors affect power loss of a gearbox by investigating bearings, gearings, oil temperatures, and gear churning under load and no-load conditions.…”