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Methodology for the geometric layout of a mechanically fully variable valve train with two synchronously rotating cam disks
ISSN: 0148-7191, e-ISSN: 2688-3627
To be published on April 06, 2021 by SAE International in United States
Event: SAE WCX Digital Summit
New engine concepts such as Miller, HCCI or highly diluted combustion offer great potential for further optimization of ICEs in terms of fuel economy and pollutant emissions. However, the development of such concepts requires a high degree of variability in the control of gas exchange, characterized by variability in valve spread, maximum valve lift and – ideally independent of these two variables – in valve opening time. In current series variable valvetrains, valve lift and opening duration are usually directly dependent one from the other. In the ideal case, however, engine concepts such as Miller require a fully flexible variation of the closing time of the intake valve while still maintaining the same intake opening time. Here, a methodology for the geometric layout of fully variable valve trains with significantly extended functionalities is presented. In this concept, the control of the valve opening and closing events is distributed to two synchronously rotating cam disks. This geometric separation allows to vary the valve opening duration at constant maximum valve lift by varying the phase offset between the two disks. On the other hand, the geometric properties of the system can be used to vary the maximum valve lift at the constant valve opening and/or valve closing (depending on the layout), as well as for switching additional valve events on or off. The methodology presented here includes the computer-aided and partially automated generation of the characteristic geometric features of the system and the kinematic simulation and evaluation of the concept. By kinematic simulation, various possible resulting valve lift curves can be evaluated and optimized by adapting the geometry and the motion rules. The subsequent investigations on a component test bench serve to assess the newly developed concept with respect to functionality, required drive torque, stiffness and speed capability, thus proving its technical feasibility.