Adaptive Road Noise Control
Vehicle Dynamics without Compromise
Colin Peachey Lotus Engineering
04/22/082
Overview
• Modern vehicle suspensions balance refinement (isolation) and dynamics (control).
• OEM’s frequently compromise dynamics to keep refinement acceptable (and vice versa).
• Active noise control (ANC) was developed by Lotus to reduce low frequency noise inside the vehicle cabin by generating an opposing sound field through the audio system.
• Using ANC the level of compromise can be reduced and the vehicle optimised for dynamics with less regard for roadnoise asthe NVH problems can be resolved using active technology.
04/22/083
How Sound Balance in cars has changed
60
65
70
1994 2004
RoadnoiseEnginenoisewindnoise
• Roadnoise has increased • Engine noise has decreased• Windnoise has marginally
decreased
• Roadnoise is now dominant sound when cruising.
• Engine noise conveys purpose / power & provides driver feedback for gear change etc..
• Roadnoise is just fatiguing and annoying and has zero purpose or benefit.
Lotus Data – C segment model
04/22/084
Why is Roadnoise increasing?
225/45W17Volkswagen Golf V. GTi195/65H15Volkswagen GOLF V195/65V15Volkswagen Golf IV. 1.8 GTi175/80T14Volkswagen GOLF IV185/60H14Volkswagen Golf III. 1.8i GT175/70T13Volkswagen GOLF III185/60V14Volkswagen Golf II. Gti155/80T13Volkswagen GOLF IIStandard Tyre SizeModel
Universal trend for wider low profile tyres
Example of VW Golf
04/22/085
Suspension inputs increasing
Multi link suspensions create multiple noise paths into the vehicle.
Bushes are harder for improved handling capability reducing isolation levels.
04/22/086
Adaptive Road Noise Control (ARNC)
Engine Sound Synthesis
Engine Order Cancellation (EOC)
Lotus ANC technologies
850 44001000 2000 3000 40001200 1400 1600 1800 2200 2400 2600 2800 3200 3400 3600 3800 4200
rpm
30
80
40
50
60
70
35
45
55
65
75
33
38
43
48
53
58
63
68
73
78
dB(A
)Pa
F Overall level Driver_DX (A) Runup_neutral_OFFF Overall level Driver_DX (A) Runup_neutral_ONF Order 2.00 Driver_DX (A)F Order 2.00 Driver_DX (A)
reduction in overall noise
reduction in 2nd
order engine noise
04/22/087
Principle of Noise Cancellation
ANC output
Vehicle noise
Resultant Noise Phase
correct
Cancellation
Phase incorrect
Noise increase
04/22/088
Schematic of Lotus RNC System
Loudspeaker System
(Common with Audio)
Error Microphones
(Feedback adaption)
Adaptive Controller
Accelerometers –(feedforward reference)
04/22/089
Frequency range of Active Control
250 Hz
PASSIVE RANGE
(Sealing and absorption treatments)
Frequency
ACTIVE RANGE
(Conventional treatments are mass and stiffness)
0
System off
System on
04/22/0810
Example of system benefits
• Two European premium sector luxury saloons were tested.• Comfort Car – premium brand high comfort and refinement RWD
– Limited to 250 kph– Tyres: Front 255/45/18 Rear 275/45/18
• Dynamics Car – premium brand sports saloon 4WD– >300 kph maximum speed.– Tyres: 275/40/19
• Both cars were rated subjectively on 1 to 10 scale for all aspects of driving dynamics and comfort and measured for interior noise.
• The Dynamics car was then fitted with the Lotus Active Roadnoisesystem and re-measured.
04/22/0811
Overall Vehicle Dynamics Performance
6
6.5
7
7.5
8
8.5
9Steering Response
Steering Connection
Handling - CorneringIsolation
Road Noise
Dynamics Car
Comfort Car
04/22/0812
Dynamics Car 1 Vs Comfort Car 2
• Base cars no ARNC, Coarse Chip Road 80 km/h
LHF RHF
RHRLHR
04/22/0813
Dynamics car with ARNC Vs Comfort car
• Dynamic car with ARNC , Coarse Chip Road 80 km/h
LHF RHF
RHRLHR
04/22/0814
• ARNC Comparison, Coarse chip Road 80 km/h
Dynamics car ARNC Off ARNC On
LHF RHF
RHRLHR
04/22/0815
Noise influence on “isolation feel”
• The subjective “isolation feel” is created by the combined noise and vibration response experienced by the driver.
• Reduced noise response generally creates a more favourable isolation impression even if vibration is unaffected.
• However to maximise vibration isolation the steering column and seat needs to optimised for vibration transmission.
• This is easier to do if the constraint of roadnoise isolation has been reduced as a development priority.
• In addition stiffer suspensions will have better yaw stability which benefits steering response :- hence very rigid rack mounting stiffness may not be essential.
04/22/0816
Effect of Impact Strip – isolation improvement
Impact response – RHR noiseARNC Off
ARNC On
04/22/0817
Impact strip noise – Effect of ARNC - detail
RHR Seat ARNC Off RHR Seat ARNC OnFr
eque
ncy
30 –
450
Hz
Freq
uenc
y 30
–45
0 H
z
04/22/0818
ARNC- Smooth to rough transition response
ARNC Off ARNC On
04/22/0819
Overall Vehicle Dynamics Performance
6
6.5
7
7.5
8
8.5
9Steering Response
Steering Connection
Handling - CorneringIsolation
Road Noise
Dynamics Car
Comfort Car
04/22/0820
Overall vehicle Dynamics Performance – with ARNC
6
6.5
7
7.5
8
8.5
9Steering Response
Steering Connection
Handling - CorneringIsolation
Road Noise
Dynamics Car
Comfort Car
04/22/0821
• Landstrom and Landstrom (1985) showed low frequency monotonous noise and vibration increased drowsiness levels.
• Loftstedt and Landstrom (1987) showed truckdrivers become more readily fatigued driving trucks that generated high levels of low frequency noise.
• ROSPA (2001) have shown 20% of UK road accidents are fatigue related.
Noise contributes to accidents
04/22/0822
Further Applications of Lotus Active noise technology
• The range of ANC technologies can also be applied to realise other specific benefits.
• CO2 reduction– Vehicle weight reduction– Extended operation of engine cylinder deactivation– Maintain refinement with engine balancer shaft deletion
• Reduced programme costs– High end Halo models from high volume platforms– Reduced development time for derivative models– Increased product differentiation from common platform strategy
• Improved customer feature– Improved dynamics– Improved refinement– Enhanced driver enjoyment (sound synthesis) – Pedestrian safety for electric and hybrid vehicles
04/22/0823
Summary
• Roadnoise is now the dominant NVH problem in a majority of vehicles.• Refinement and vehicle dynamics requirements are often in conflict
requiring compromise (NVH is usually the victim).• ANC is a viable solution to low frequency noise in vehicle interiors
which can negate much of the conflict.• The system can have a dramatic effect on vehicles with high levels of
low frequency structural noise.
• This technology can be exploited to achieve class leading dynamics and refinement on the same vehicle – and achieve vehicle dynamics without compromise.
• The technology is available now and we are already working with a number of potential suppliers of the production solution.
04/22/0824
Further information
For further information on the full range of Lotus active noise technologies please contact:-
Colin Peachey - Chief Engineer NVHLotus EngineeringHethel NorwichNorfolkEnglandNR14 8EZ+44 (0)1953 608926E mail [email protected]
Or go tohttp://www.grouplotus.com/engineering/products_services.html