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Reducing Noise, Vibration and Harshness in vehicles
August 09th, 2021
The automotive industry is changing at a rapid pace.
As we progressively move from the internal combustion engine (ICE) to electric vehicles (EVs) via hybrid technologies the priorities for automotive engineers are changing. It is becoming clear that there will be significant changes to the Noise, Vibration and Harshness (NVH) considerations of future vehicles.
What is Noise, Vibration and Harshness?
Noise
Noise emanates from vibration and is the general term for what you hear as a result of acoustic waves travelling through the air or other medium.
Vibration
Vibrations are the oscillating, reciprocating, or other motion of a rigid or elastic body or medium forced from a position or state of equilibrium.
Harshness
Harshness is now more usually defined as psychoacoustics and considers the human perception to sound based on frequency and time structures of the sound rather than just sound level.
As the automotive industry moves forward to hybrid and electric vehicles, NVH will develop (or become more apparent) from both new and existing sources. Whilst powertrain configurations for electric motors are still developing, the interior and exterior components largely remain the same. Noise and vibrations from the vehicle’s electronics, gear boxes, motors, road/tyre interface and aerodynamics will present new challenges to component engineers to manage NVH which was previously partially or totally masked by the combustion engine. Component engineers will need to develop new solutions to overcome these noises and meet the evolving expectations of customers.
Changes affecting NVH
As drivetrains become increasingly electrified, engineers need to pay more attention to the following four categories that create NVH in a vehicle:
- Noises previously concealed by the ICE
- High customer expectation and good NVH management
- Interior adjustment features driven by electric motors
- Increase in the number of electric motors, both driveline and mechatronics
Previously concealed NVH
Replacing the combustion engine with an Electric Vehicle drive train means previously masked noises can now be heard by the vehicle passengers. Noises such as road surface changes, squeaks, rattle and tonal whine will need to be more seriously considered by vehicle and component engineers and designed out.
NVH management
Whilst the general perception is that electric vehicles will be silent inside; this is not the case. With development, they can be very quiet. Yet more development work and testing is needed to reduce squeak, rattle, tonal noise, tyre and aerodynamic noise. ‘The devil is in the detail’, a well-known saying that emphasises the importance of the smallest details having a large impact.
Interior adjustment features
There are a number of factors impacting the interior design of vehicles.
Electrification of the drive train has resulted in the removal of the combustion engine, smaller e-motor drive, almost no transmission and batteries located below the cabin. These changes open up new interior design possibilities that where not possible in traditional, internal combustion engine cars. These changes are becoming common in electric vehicles today.
The other factor is the move to more autonomous driving, more options become attractive in terms of cabin layouts and seat adjustments such as swivel seats and greater recline. Other mechatronics such as powered door systems are likely to become more prevalent.
Any feature that facilitates movement creates noise and vibrations. To meet customer and passenger expectations, the motors driving these interior features will need to be developed with low-friction components that aid smooth operation through-out their lifetime, if they are to reduce NVH.
Increase in electric motors
As more vehicle functions are motorised: window lifter, parking brakes, tailgates, there will be an increase in in-vehicle motor noise. Some noise is welcome as it shows that the parking brake does it’s job, other is just annoying especially when there is no other noise around. The prominence ratio or other psychoacoustic parameters need to be measured to understand the human perception of any tonal whine created by electric motors.
The other trend is greater focus on driver and passenger comfort. On-going development of mechatronic features and adjustable systems will continue to grow as car manufacturers bid to keep pace with luxury cars and provide the features customers demand, increasing electric motor deployment.
Future vehicle NVH concerns
These changes yield NVH challenges in the following areas:
Squeak – Excitation of a surface from sliding friction of two surfaces moving over each other and affected by coefficient of friction, stick-slip and surface roughness.
Rattle – Broadband noise due to shock impact when movement or vibration overcomes clearances in a joint.
OSQ – Operational sound quality is the human perception of noise from a human action in the vehicle such as door closure, window motor noise, switch clicking etc.
Whine – Tonal noise having a narrow frequency band which can be generated by motors, gearboxes, motor switching electronics etc. This can be strongly perceived and disturbing when present.
Tyre Noise – Comes from the interaction between the tyres and the road surface. It will obviously not be removed in future vehicles and its low/mid-speed presence will increase with the reduction/removal of ICE noise. At low frequency, inputs through the chassis can increase rattle noise perception but at mid/high speeds it is airborne and will need greater attention to vehicle sealing and sound pack.
Aerodynamic Noise – This will again be more perceptible at higher speeds as other masking noise reduces. This source generally originates from turbulence and is perceived when flow separation at A-pillars, mirrors, sunroof etc. re-attach to the structure, often near relatively flexible panel locations. This high frequency noise will require careful attention to general vehicles‘ aerodynamic, door sealing, underbody and glazing systems.
Improving NVH with Saint-Gobain
The Saint-Gobain Group, uniquely has products and knowledge which can improve NVH performance in all of these noise categories.
In NORGLIDE® plain bearings, the PTFE layer provides low friction, no stick-slip and noise-free movements.
Both NORGLIDE® Bearings and RENCOL® Tolerance Rings can provide interfaces between shafts and housings which avoid rattle by removing clearance and compensating tolerances. Additionally, there is self-compensation for joints with dissimilar materials when differential expansion is taken in the interface joint rather than changing the clearance. Operational sound quality benefits from low friction and better aligned clearance free joints. The features of these products have been combined in our SPRINGLIDE™ solution.
Tolerance rings act as three dimensional springs between components. As such, there is the opportunity to tune the joint interfaces in electric motors, de-coupling the teeth/stator electromagnetic vibration from the housing.
The airborne noise transfer functions (ANTF) associated with tyre noise can be improved with sound pack treatment and vehicle sealing. Our sound pack supplier, Pritex, has extensive experience in automotive sound pack development.
Our NVH testing capabilities
The NVH development team, undertakes test and development across many of these products.
In our Semi-Anechoic chamber in Bristol we can measure and assess noise, vibration, transmissibility, order analysis of motors under operational conditions and custom requirements to suit specific projects.
In vehicle sealing, we can advise on painted body and full vehicle equivalent body hole size (PBHS and FVBHS) and production conformity.
To find out more about our products and their role in NVH reduction, talk to us at Saint-Gobain, engineer to engineer. We have a wealth of experience to share. You can Contact Us or email: makingabigdifference@saint-gobain.com.