A study of the influence of lubricant viscosity on the operation and efficiency of a Continuously Variable Valve Lift hydraulic valvetrain system

With the ever-increasing demands of reducing carbon emissions as mandated by Euro 5 and 6 emission legislation, vehicle manufacturers are exploring new techniques and technologies. The valvetrain has the most influencing parameters in reducing wasted energy in propelling an internal combustion engine. Schaeffler, a large Tier 1 automotive components supplier, have designed and manufactured an electro-hydraulic system called UniAir, that can fully control of intake valves in an internal combustion engine. Jaguar Land Rover (JLR), a medium-sized luxury vehicle manufacturer, are implementing the UniAir to their AJ200 engine family in order to comply with the emission standards while benefitting from the performance enhancing effects.

This thesis details the design, development and validation of a motored valvetrain test rig that enables the characterisation of the performance of the UniAir system as utilised by JLR. The rig forms part of a test methodology also developed during this work, that can determine the influence of the viscosity of different lubricants to understand the performance, frictional operation and efficiency of a continuously variable valvetrain (CVVT). A testing programme was carried out, measuring the valve lift profiles and torque required to operate the continuously variable valve lift (CVVL) system, while varying oil formulation and temperatures from 0°C to 120°C, and environmental temperatures varying from 0°C to 120°C using climate chambers. The results were then analysed and used to inform recommendations and future research direction for JLR.