Effective Use of Composite Materials in Gearbox Design for an Electric Vehicle

Carbon fiber reinforced polymers (CFRP) have an enormous potential in mass reduction of vehicles and therefore also CO2 emissions. Also, their contribution to noise reduction is considerable. There are, however, challenges during designing as CFRP are not isotropic materials so each application has to be viewed individually according to the current function. The goal of presented project was in using the advantages of CFRP materials for application in gearbox design for an electric vehicle and a research of potential for mass and noise reduction. There was a reference conventional gearbox provided by project partners KIMM (Korea Institute of Machinery and Materials) and Samyang company. The gearbox in electric vehicle is a significant source of noise because of high RPM and absence of combustion engine, so using CFRP can help in noise reduction. The high RPM also lead to higher frequencies that are uncomfortable for people. The first goal was to design and manufacture a CFRP gearbox casing and embedded differential case. That includes specification of material, layout and shape with use of FEM analysis in order to achieve sufficient mechanical properties comparable with those of the reference gearbox. These properties include for example stiffness of casing in bearings in order to achieve small deflection of shafts and thus better contact of gears. Another part of this project was done in order to explore a potential use of filament-wound shafts in gearboxes. There were several versions of hybrid shafts (CFRP/steel) manufactured and then steel gear rings were bonded on the surface of the shafts. There was also a reference steel shaft manufactured. The shafts were later tested on closed-loop test stand and the results of noise, vibration and transmission error of CFRP shafts were compared with the reference steel shaft. Another comparison was focused on evaluation of mass and moment of inertia reduction.