When a turbocharger exhaust-driven turbine wheel spins fast enough to produce the desired level of boost, a wastegate is typically used to allow the excess exhaust pressure to divert around the turbine wheel. By opening the wastegate (typically boost-pressure referenced), exhaust pressure bypasses the turbo’s turbine wheel to prevent the turbo from reaching an unsafe speed. To actuate wastegate, different actuating mechanisms like pneumatic, vacuum or electric are available, which regulates poppet valve positions e.g. full close, open or partially open.
In electronic wastegate valve, exhaust pressure pass through the bypass hole collides with the face of valve causing vibration. Such vibration is transmitted to the wastegate components causing rattle noise. It is challenging to design a wastegate mechanism which can sustain wastegate loads at high temperature and give quiet and robust performance within the full operating range of the engine. In order to improve the rattle noise, the mass damper for frequency generation for canceling the vibration is additionally applied used to reduce the clearance between parts. Valve spring is one of the critical components of the wastegate system, which absorbs impactive energy coming from wastegate loads exerts on the valve and reduces the vibrations of wastegate linkages transmitting towards the actuator side.
This paper describes methodology to design a functionally optimized wastegate linkage system and valve spring at an early stage. Multi-body dynamic (MBD) along with nonlinear transient dynamic FEA approach was developed for analyzing wastegate washer/cup spring system. The nonlinear FEA tools was used to assess component(s) design robustness due to the MBD generated dynamic loading in balance to geometry, thermal loading and material capabilities. Advanced valve spring and creep modeling are used to quantitatively study the spring relaxation after long time exposure to high temperature and stress. The simulation methodology outlined in this paper is used to investigate turbo wastegate linkage undergoing dynamically varying forces from the pulsation of the exhaust gas in transient engine operation, which results in identifying NVH issues and durability-relevant weak spots in the early-design phase and providing the development tool of robust design.
Testing is done to better understand wear and NVH of all components within the wastegate subsystem caused by engine induced mechanical vibrations. Data from this testing is used early in the turbocharger design and development process to validate analysis models and to size wastegate components