Abstract
Despite the increasing trend towards the hybridization and electrification of automotive power trains the internal combustion engine will continue to play a decisive role in the next few decades. The increasingly strict limits for CO2 emissions and thus fuel consumption define the optimization of the internal combustion engine as the automotive industry’s main task. Along with electrification, hybridization and the development of low cost vehicles, the optimization of fuel consumption has become a megatrend (Figure 1). One possible method of meeting ambitious fuel consumption and emissions targets is the use of variable valve trains.
The Schaeffler Group has been working on the different types of variable valve trains for a long time. A distinction is made between valve train systems with variable phases and valve trains systems with variable lift. Variable camshaft phasing units that adjust the phases can influence exhaust gas recirculation and the effective compression ratio. Systems with variable lift can have a discrete two- or three-step lift actuation or be fully-variable. This article focuses on fully-variable valve train systems (Figure 2). The Schaeffler Group soon recognized that, cam shaft phasing and the switchable components cannot optimally meet all challenges in terms of flexibility, and secured the license rights to “UniAir”, potentially today’s most flexible valve train system, as early as in 2001.
Keywords: Variable Valve Train, UniAir, Electro-hydraulic, Mass production, Control system