Kiran Govindswamy

Application of Combustion Sound Level (CSL) Analysis for Powertrain

Powertrain noise is a significant factor in determination of the overall vehicle refinement expected by today’s discriminating automotive customer. Development of a powertrain to meet these expectations requires a thorough understanding of the contributing noise sources. Specifically, combustion noise greatly impacts the perception of sound levels and quality. The relevance of combustion noise development has increased with the advent of newer efficiency-driven technologies such as direct injection or homogeneous charge compression ignition. This paper discusses the application of a CSL (Combustion Sound Level) analysis – a method for the identification and optimization of combustion noise. Using CSL, it is possible to separate mechanical and combustion noise sources. Combustion noise is then further classified as direct combustion noise (directly proportional to the combustion gas pressures), indirect combustion noise (proportional to rotational forces as well as combustion-induced piston side forces) and flow noise. During the development stage of new powertrains, benchmarking testing and analysis helps to identify the state-of-the-art. Incorporation of the CSL process into the benchmarking process facilitates a more in-depth comparison of powertrains, providing valuable information to drive potential design improvements. In this investigation, two benchmark four cylinder engines were compared using the CSL process. This provided a comprehensive comparison of the noise shares as well as the combustion excitation levels. In addition, the paper compares engine specific combustion noise share weighting functions to obtain insights into the relative strengths and weaknesses of each benchmarked engine.

Driveline Boom Interior Noise Prediction Based on Multi Body Simulation

It is important to develop powertrain NVH characteristics with the goal of ultimately influencing/improving the in-vehicle NVH behavior since this is what matters to the end customer. One development tool called dB(VINS) based on a process called Vehicle Interior Noise Simulation (VINS) is used for determining interior vehicle noise based on powertrain level measurements (mount vibration and radiated noise) in combination with standardized vehicle transfer functions. Although this method is not intended to replace a complete transfer path analysis and does not take any vehicle specific sensitivity into account, it allows for powertrain-induced interior vehicle noise assessments without having an actual test vehicle available. Such a technique allows for vehicle centric powertrain NVH development right from an early vehicle development stage. While this is a proven tool for powertrain level sound quality evaluations and correlates well for front wheel drive (FWD) vehicles, the interior noise for rear wheel drive (RWD) vehicles is often under-predicted on account of missing contributions from the driveline. RWD vehicles can have significant contributions through the rear axle mounting paths, especially for powertrains with manual transmissions or during lock up of the torque converter clutch with conventional automatic transmissions. Torsional vibrations are transmitted through the driveline, causing reaction forces at the rear axle, resulting in driveline boom. Resonances in the driveline system typically amplify the driveline boom excitation. This publication extends the dB(VINS) approach for interior noise simulation by determining the driveline-induced noise of a RWD vehicle. The influence of the structureborne path and firing order related torsional vibration through the rear axle is demonstrated with a time domain transfer path process. Generic transfer functions for extension of the dB(VINS) process are developed in order to capture driveline noise share of RWD vehicles. In addition to vehicle measurements, a multi body simulation (MBS) model is generated and rear axle vibrations are calculated via MBS simulation of the vehicle driveline. The results are discussed in the context of driveline NVH integration and appropriate conclusions provided.

Aspects of engine start/stop comfort

In this paper, the start/stop process of combustion engines is considered as a functional chain from excitation over amplification mechanisms acting on the vehicle body and finally on the passengers. The functional chain is lined up in three fields to display the causality of the different influencing parameters: “Engine Excitation at Start/Stop”, “P/T Body Oscillation System” and “Vehicle Body”. For each field, exemplarily parameters are chosen to improve the start/stop behaviour. In the thematic field “Engine Excitation at Start/Stop” a comparison between a conventional key start to a re-start of a gasoline engine is shown. The excitation mechanisms are depicted and a countermeasure is derived to reduce the excitation in the shown example. In the field “P/T Oscillation System”, the eigenfrequency shift of the most critical P/T body mode as countermeasure has proved effectivity in vibration reduction. Further on, the advantage of a 24V/48V starter regarding vibration reduction is outlined. The last chain element “Vehicle Body” provides an explanation of vehicle sensitivity in different directions of the vehicles´ coordinate system. Finally, the human perception of vibrations is projected on the engine start/stop event. The relevant weighting functions, which take the frequency depending perception into account are outlined. A comparison of two NVH metrics to objectify the sense of vibration is conducted.

NVH-Aspekte der Integration des Antriebsstrangs in das Fahrzeug

Die Modularisierung im Fahrzeugbau ermoglicht eine Vielfalt an Varianten. Fur die „Hochzeit“ des Antriebsstrangs mit der Karosserie wurde das Aufgebot schon lange vorher in Form von CAE-Aktivitaten und Prototypfahrzeugen bestellt. In dem folgenden Beitrag werden Gerausch- und Schwingungskomfortaspekte dieser Phase im Hinblick auf einsetzbare Berechnungsmethoden, wie sie bei der FEV Motorentechnik GmbH in Aachen eingesetzt werden, beispielhaft diskutiert.