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The car buying public’s enthusiasm for electric vehicles continues to accelerate rapidly, driven by a desire to fulfil global climate change objectives, and supported by tax incentives. However, range anxiety persists as one of the main barriers to take-up, because larger battery packs remain heavy and expensive (cell price reductions are slowing). One way to mitigate these disadvantages is to fit a range extender system, powered by an efficient internal combustion engine, but such systems can cause noise concerns. Ricardo has developed a simulation-based approach, pragmatically applicable at concept stage, to define the range extender operating conditions that minimize the impact on noise heard by the driver and passengers inside the vehicle. Transfer path analysis considered both air-borne and structure-borne noise contributions from the range extender, in context with noise contributions from electric drive unit, road and wind, under various typical vehicle operating conditions.

A system for realistic augmentation of power unit sound has been applied to an electric car. Augmented interior sound has been shown to be a powerful enabler for the acceptance and appeal of electric cars. In some territories augmented exterior sound is a legal requirement, to provide a safe urban environment particularly for vision-impaired pedestrians. An accelerometer located on the electric motor casing provides a live-streamed signal from the power unit that conveys authentic and genuine information. The sound’s level and frequency content are modulated by acceleration demand and vehicle speed signals respectively, thus tapping into the existing ‘language’ of car sound. Inside the car, this enriches the dynamic driving experience during spirited driving, while retaining acoustic comfort under cruising.

Excitement, image and emotion are key attributes for cars, particularly those with higher power ratings. Engine sound has traditionally acted as the car’s voice, conveying these attributes to the driver and passengers along with the brand image. Engine sound also underpins the dynamic driving experience by giving instant feedback about how a car is operating, enhancing the connection between driver and vehicle. For decades, the automotive industry has engineered engine sound to achieve these benefits, thereby defining the ‘language’ of car sound. Electric vehicles deliver strong and responsive performance but naturally lack the acoustic feedback that internal combustion engines provide. While this gives advantages in terms of comfort and environmental noise, the benefits of engine sound are lost. Carefully controlled acoustic feedback inside the car’s cabin brings tangible and valuable benefits both for the dynamic driving experience and to convey the brand image.

The transfer characteristics, location of the mounting points, where the exhaust system is attached to the vehicle structure, and the level of excitation forces have a significant contribution to the overall interior noise. The aim of this study is to define targets for the excitation forces of the exhaust line in order to identify its contribution to the overall vehicle interior cabin noise in the early vehicle concept phase when the hardware is not yet available. Furthermore, psychoacoustic parameters are calculated, e.g. the articulation index which provide a representation of the human hearing perception. Therefore a software tool was developed in MATLAB to cascade the interior noise contributions of the exhaust system using the corresponding transfer paths. This tool enables a quick prediction of different combinations (different hanger stiffness and other parameters) to evaluate the potential for improvements.

Engine sound quality is a key attribute for sporty cars - it powerfully conveys the brand image to the driver/passengers and onlookers, and provides driver involvement by giving instant feedback about how a car is operating. Providing this has become more difficult with tighter pass-by noise regulations and the near-universal adoption of turbocharging. In the last two decades, sporty sound inside the cabin has been regained using intake sound generator systems that transfer sound more directly to the vehicle interior. The high cost of these systems is more recently driving a move towards electronic Active Sound Design with systems delivering synthetic sound through loudspeakers. However, the purist sports car market perceives this approach to be fake or artificial. An alternative approach is provided by a system for Realistic Augmented Sound by Ricardo (RAS-R) that offers a choice of two realistic engine sound sources.

A new pass-by noise test method has been introduced, in which engine speeds and loads are reduced (compared to the old test method) to better reflect real world driving behavior. New noise limits apply from 1 July 2016, and tighten by up to 4dB by 2026. The new test method is recognized internationally, and it is anticipated that the limits will also be adopted in most territories around the world. To achieve these tough new pass-by noise requirements, vehicle manufacturers need to address several important aspects of their products. Vehicle performance is critical to the test method, and is controlled by the full load engine torque curve, speed of response to accelerator pedal input, transmission type, overall gear ratios, tire rolling radius, and resistance due to friction and aerodynamic drag. Noise sources (exhaust, intake, powertrain, driveline, tires) and vehicle noise insulation are critical to the noise level radiated to the far-field.

Intake and exhaust system development is an important step in automotive design. The intake system must allow sufficient air to flow into the engine, and the exhaust system must allow exhaust gases to depart at the rear of the vehicle, without excessive pressure loss. These systems must also attenuate the acoustic pressure pulsations generated by the engine, such that the noise emitted from the intake and exhaust orifices is constrained within reasonable limits, and exhibits a sound quality in keeping with the brand and vehicle image. Pressure loss and orifice noise tend to be in conflict, so an appropriate trade-off must be sought. Simulation of both parameters allows intake and exhaust systems to be designed effectively, quickly, cheaply and promptly. Linear simulation approaches have been widely used for intake and exhaust acoustic prediction for many decades.

Continued developments in control and integration applied to automatic and twin clutch powershift transmissions have provided smooth, comfortable gearshifts. However, whilst suitable for most vehicles and markets for everyday driving, such characteristics may not suit the character of a sportscar or a vehicle sports mode for elective shifts. The paper reports upon a project[1], extending from [2,3,4], undertaken to determine the main effects and interaction of shift feel and cabin sound that influence the driver's perception of a “sporty” gear shift. Good correlation has been found for models which include data from three very different transmission types, meeting the requirement for a predictor for shift sportiness, independent of transmission type. This has yielded predictive equations and measures of their accuracy based upon longitudinal acceleration and engine speed.

This paper describes a process to achieve a pre-defined vehicle level interior sound quality target, by a sound engineering cascade to targeted noise and vibration development at the system level. Air-borne and structure-borne contributors to interior sound are identified at the system level using a comprehensive Transfer Path Analysis (TPA) in both the frequency and time domains. For significant contributors, the relative importance of the source system (powertrain) and path system (vehicle) are determined. System level changes are simulated, and their effect on interior sound evaluated using TPA. A set of feasible changes is identified that, when combined, achieves the vehicle level interior sound quality target. This set of changes defines system level targets for noise and vibration development, cascaded from the vehicle level target.

Crank rumble is an amplitude-modulation of engine noise perceived inside a car. It is common under full load acceleration but not under part load acceleration, so could cause concern. Honda and Ricardo carried out a program of work to research methods to reduce the perceived (subjective) level of crank rumble inside a vehicle under part load acceleration. Transfer Path Analysis (TPA) is a method of predicting vehicle interior noise by separating sources (the engine) and transfer paths (the vehicle body). TPA was applied in the time domain to allow subjective assessment of the different contributors to the interior sound quality. Subjective assessment was performed by a panel of listeners, to avoid bias caused by individual opinions. This approach identified key contributors to the perceived crank rumble, and allowed targets to be set. Computer Aided Engineering (CAE) was used to study a range of modifications to the engine.