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The structure-, fluid- and air-borne excitation generated by HVAC compressors can lead to annoying noise and low frequency vibrations in the passenger compartment. These noises and vibrations are of great interest in order to maintain high passenger comfort of EV vehicles. The main objective of this paper is to develop a numerical model of the HVAC system and to simulate the structure-borne sound transmission from the compressor through the HVAC hoses to the vehicle in a frequency range up to 1 kHz. An existing automotive HVAC system was fully replicated in the laboratory. Vibration levels were measured on the compressor and on the car body side of the hoses under different operational conditions. Additional measurements were carried out using external excitation of the compressor in order to distinguish between structure- and fluid-borne transmission. The hoses were experimentally characterised with regard to their structure-borne sound transmission characteristics.

Minimizing rattle noises is becoming increasingly important for hybrid and electrical vehicles as masking from the internal combustion engine is missing and in view of the functional requirements of the office-like interiors of next generation automated vehicles. Rattle shall therefore be considered in the design phase of component systems. One hurdle is the modelling of the excitation mechanisms and its experimental validation. In this work we focus on excitation by loose parts having functional clearances such as gear systems or ball sensors in safety belt retractors. These parts are excited by relatively large low frequency displacements such as road-induced movements of the car body or low order rigid body engine vibrations generating multiple impacts with broad band frequency content. Direct measurement of the impact forces is in many cases not possible.

Nowadays a large proportion of the overall acoustic vehicle development takes place within virtual phases. Increasingly, projects require the auralization of virtually developed acoustics measures, e.g. from the disciplines of electro-acoustic, ride comfort, rolling noise or passive acoustic on dynamic or static driving simulators. In practice, it turns out that in addition to engine noise also a realistic reproduction of rolling and wind noise is important. In this article, approaches to synthetic rolling and wind noise generators are discussed. We developed such real-time capable sound generators that are parametrizable according to arbitrary driving conditions. Furthermore, spatial reproduction of the driving sounds is achieved for binaural headphones, as well as for other arbitrary loudspeaker setups, like often found in driving simulators. Derived models and parametrization are based on measurements and recordings from several real vehicles.

Radiation of sound from an open pipe with a hot mean flow presents one of the classic problems of acoustics in inhomogeneous media. The problem has been especially brought into focus in the last several decades, in the context of noise control of vehicle exhaust systems and jet engines. However, the reports on the measurements of the radiated sound field are still rare and scattered over different values of subsonic and supersonic flow speeds, cold and hot jets, as well as different sound frequency ranges. This paper focuses on low Mach number values of the mean flow speed and low frequencies of the incident (plane) sound waves inside an unflanged cylindrical pipe with a straight cut. It presents the results of the far-field radiation pattern measurements and compares them with an existing analytical model from the literature. The mean flow inside the pipe reached Mach number values up to 0.25 and temperature up to 300°C.

For vibration and acoustics vehicle development, one of the main challenges is the identification and the analysis of the noise sources, which is required in order to increase the driving comfort and to meet the stringent legislative requirements for the vehicle noise emission. Transfer Path Analysis (TPA) is a fairly well established technique for estimating and ranking individual low-frequency noise or vibration contributions via the different transmission paths. This technique is commonly applied on test measurements, based on prototypes, at the end of the design process. In order to apply such methodology already within the design process, a contribution analysis method based on dynamic substructuring of a multibody system is proposed with the aim of improving the quality of the design process for vehicle NVH assessment and to shorten development time and cost.

Automotive industry is becoming more and more interested in assessing the noise of electric motors, since their integration in many types of road vehicles is rapidly growing in a market oriented to hybridization and electrification. The acoustic characterization of an electric motor is often being performed numerically, having as consequence the fact that the investigation is confined to one specific model belonging to one particular type of motor. This paper proposes an experimental airborne sound characterization methodology, suitable for any type of cylindrical source, based on a set of data acquired following a cylindrical Nearfield Acoustical Holography (NAH) scheme. Such an approach allows the evaluation of sound intensity, as well as pressure level and particle velocity.

Due to future directives of the European Union regarding fuel consumption and CO2 emissions the automotive industry is forced to develop new and unconventional technologies. These include for example stop-start-systems, cylinder deactivation or even reduction of the number of cylinders which however lead to unusual acoustical perceptions and customer complaints. Therefore, it is necessary to evaluate the sound character of engines with low numbers of cylinders (2 and 3 cylinders) and also the differences to the character of the more common 4-cylinder engines. Psychoacoustic parameters are used to describe and understand the differences. Based on the gained knowledge possible potentials for improvement can be derived in the future. The used data base consists of artificial head recordings of car interior noise according to defined driving conditions measured on the AVL test track. Naturally, there are more recordings available for 4-cylinder engines than for 2- and 3-cylinder engines.

Today, the number of downsized engines with two or three cylinders is increasing due to an increase in fuel efficiency. However, downsized engines exhibit unbalanced interior sound in the range of their optimal engine speed, largely because of their dominant engine orders. In particular, the sound of two-cylinder engines yields half the perceived engine speed of an equivalent four-cylinder engine at the same engine speed. As a result when driving, the two-cylinder engine would be shifted to higher gears much later, diminishing the expected fuel savings. This contribution presents an active in-car sound generation system that makes a two-cylinder engine sound like the more familiar four-cylinder engine. This is done by active, load-dependent playback of signals extracted from the engine vibration through a shaker mounted on the firewall. A blind test with audio experts indicates a significant reduction of the engine speed when shifting to a higher gear.

In the past the exterior and interior noise level of vehicles has been largely reduced to follow stricter legislation and due to the demand of the customers. As a consequence, the noise quality and no longer the noise level inside the vehicle plays a crucial role. For an economic development of new powertrains it is important to assess noise quality already in early development stages by the use of simulation. Recent progress in NVH simulation methods of powertrain and vehicle in time and frequency domain provides the basis to pre-calculated sound pressure signals at arbitrary positions in the car interior. Advanced simulation tools for elastic multi-body simulation and novel strategies to measure acoustical transfer paths are combined to achieve this goal. In order to evaluate the obtained sound impression a roughness prediction model has been developed. The proposed roughness model is a continuation of the model published by Hoeldrich and Pflueger.