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Exterior Noise Perception of BEV
Kathrin Dudenhöffer, Sven Staudt Universität Duisburg Essen
Bonn, 5th December 2011
Agenda
1. Concept of the study
2. Interviews with blind people
3. Acoustic measurements, subjective
perception, and critical distance
4. Possible solutions
5th December 2011 CAR Universität Duisburg-Essen 2
Concept of the study
Three runs of the study in Juli 2010, November 2010, and April 2011
3
Acoustic measurements
At the test location and on the vehicle
measurement site of Ford in Cologne-
Merkenich (according to ISO 362,
7.5 m distance)
Experimental study, written
questionnaires (questionnaires were
developed together with blind people)
Group discussions with blind and visually
impaired persons (October 2010, April 2011)
5th December 2011 CAR Universität Duisburg-Essen
Interviews with blind people
Subjective perception Critical distance
Time to arrival measures via Buzzer-System
Research Problem
Group discussion I with members of an German organization of blinds, October 2010
Focus: Necessity of artificial sounds for quiet cars
Results:
• Fear of being limited in mobility and of being excluded from social life due to the
diffusion of electric cars;
• Demand of organizations to fit quiet electric cars with artificial sounds;
• Necessity of being able to follow the drive of a vehicle via its soundscape;
• A common, traditional engine sound is better predictable than uncommon, new
sounds (like Nissan Leaf or Chevrolet Volt);
• Special problem for blinds at crossings without signals, because standing cars (BEV,
HEV or ICE with automatic start/stop) cannot be heard.
CAR Universität Duisburg-Essen 4 5th December 2011
Research Background
5
Concept HEV (in electric mode) vs. ICE BEV vs. ICE
Subjective perception Field study
JASIC 2009 (only for warning system)
Subjective perception Laboratory study
NHTSA 2010 JASIC 2009 (HEV, CNG) Rosenblum 2008
Acoustic measurements Field study
---
Acoustic measurements Laboratory study
NHTSA 2010 JASIC 2009 (HEV, CNG) Rosenblum 2008 Wiener et al. 2006
Focus of research
5th December 2011 CAR Universität Duisburg-Essen
Test vehicles
6
Ford Transit Peugeot Partner
Smart Fortwo e.d.
Comparisons of BEV with one or two identical ICE (Diesel and Petrol) (only BEV shown)
Mega e-City German-E-Cars Stromos
5th December 2011 CAR Universität Duisburg-Essen
Average sound levels at measurement site
CAR Universität Duisburg-Essen 7
65
65
65
62,5
61,5
60,5
60
59
58
57,5
57
Peugeot Partner Benzin
Ford Transit Diesel
Ford Transit BEV
Smart Fortwo Diesel
Smart Fortwo Benzin
Ford Fiesta Benzin
Peugeot Partner BEV
Opel Agila Benzin
Smart Fortwo BEV
Mega e-City BEV
German-E-Cars Stromos BEV
Sound level in dB(A) Vehicle Test condition: Constant drive
German-E-Cars Stromos BEV 30 km/h
Mega E-City BEV 30 km/h
Smart Fortwo BEV 30 km/h
Opel Agila Petrol 30 km/h (2nd gear)
Peugeot Partner BEV 40 km/h
Ford Fiesta Petrol 30 km/h
Smart Fortwo Petrol 30 km/h (2nd gear)
Smart Fortwo Diesel 30 km/h (2nd gear)
Ford Transit BEV 40 km/h
Ford Transit Diesel 40 km/h (3rd gear)
Peugeot Partner Petrol 40 km/h (2nd gear)
Quiet BEVs
Quiet ICE
Noise Map – CRS Fiesta Petrol/e-City
CAR Universität Duisburg-Essen 8 5th December 2011
7060504030
80
75
70
65
60
55
50
V_PP [km/h]
SPL_
avg
[dBA
]
E-City BEV - CRS - 1Fiesta ICE - CRS - 2Fiesta ICE - CRS - 3
Veh - Test - Gear
CRS - SPL_avg vs V_PP
Standing and Slowly Driving Cars
• While standing Stromos ist not perceivable.
• At a speed of 10 km/h (constant drive, equals to walking speed) Stromos is quieter
than Agila. Stopping distance is 4 m (less dangerous).
• From a speed of 20 km/h on Stromos and Agila converge.
• While accelerating the Stromos is quieter than Agila.
Average sound levels at test location:
*) Difference of one decibel perceivable, difference of three decibel equates to a 1,23-fold loudness, difference
of 10 decibel equates to double loudness.
5th December 2011 CAR Universität Duisburg-Essen 9
Speed, constant drive Stromos (BEV) Agila (ICE) Difference*
10 km/h 49 dB(A) 52,5 dB(A) (1st gear) 3,5 dB
20 km/h 53,5 dB(A) 54,5 dB(A) (2nd gear) 1 dB
Experimental Study
Sample: 240 Participants
• 40% female, 58% male, 2% n.a.
• Middle age: 35 years, range: 5 – 94 years
• Visually impaired or blind: 15% (36 persons)
• Hearing impaired: 14%
• Driver licence: 51%
• Experience with BEV: 6%, Experience with HEV: 8%
Task: Cross street after vehicle has passed!*
*) Help offered for blind persons at crossing and for answering the
questionnaires.
CAR Universität Duisburg-Essen 10 5th December 2011
Extreme Rather Neither nor Rather Extreme
-2 -1 0 1 2
quiet loud
faint powerful
smooth tight
dull metallic²
ordinary unique
damped booming³
soft hard
deep high
Sound Perception Transit
11
Semantic Differential¹
CAR Universität Duisburg-Essen
1) Means, 2) difference significant, 3) difference not significant. Ford Transit Diesel Ford Transit BEV
Extreme Rather Neither nor Rather Extreme
-2 -1 0 1 2
quiet loud²
faint powerful
smooth tight³
dull metallic
ordinary unique
damped booming
soft hard
deep high
Sound Perception Smart
12
Semantic Differential¹
CAR Universität Duisburg-Essen
Smart Fortwo Diesel Smart Fortwo Benzin Smart Fortwo BEV
1) Means, 2) difference significant, 3) difference not significant.
Extreme Rather Neither nor Rather Extreme
-2 -1 0 1 2
quiet loud²
faint powerful
smooth tight
dull metallic³
ordinary unique
damped booming
soft hard
deep high
Sound Perception Fiesta/e-City
13
Semantic Differential¹
CAR Universität Duisburg-Essen
1) Means, 2) difference significant, 3) difference not significant. Ford Fiesta Petrol Mega E-City
Extreme Rather Neither nor Rather Extreme
-2 -1 0 1 2
quiet loud³
faint powerful
smooth tight
dull metallic
ordinary unique
damped booming
soft hard
deep high
Sound Perception Agila/Stromos
14
Semantic Differential¹
CAR Universität Duisburg-Essen
1) Means, 2) difference significant, 3) difference not significant. Opel Agila Petrol German E-Cars Stromos
Subjective Perception: Emergence
15
3%
13% 14%
3% 5%
13%
Smart Fortwo Diesel Smart Fortwo Benzin Smart Fortwo BEV
Fahrzeug tauchte unerwartet auf unsicher/weiß nicht
27%
6%
17%
Difference significant
5th December 2011 CAR Universität Duisburg-Essen
Vehicle appeared unexpectedly Unsure/I don‘t know
Smart Diesel Smart Petrol Smart BEV
Subjective Perception: Emergence
16 5th December 2011 CAR Universität Duisburg-Essen
11%
15%
8%
17%
7%
9%
4% 5%
Agila Stromos Fiesta e-City
Fahrzeug tauchte unerwartet auf unsicher/weiß nicht
Unterschied nicht signifikant
18%
24%
12%
22%
Vehicle appeared unexpectedly Unsure/I don‘t know
Difference not significant Difference not significant
Petrol Agila Petrol Stromos Fiesta Petrol
4% 6%
11%
Smart Fortwo Diesel
Smart Fortwo Benzin
Smart Fortwo BEV
In wie vielen Fällen wird in dieser Situation ein Fußgänger verletzt?
8%
14%
Ford Transit ICE Ford Transit BEV
Subjective Perception: Probability of accident
17
Difference significant Difference significant
5th December 2011 CAR Universität Duisburg-Essen
In how many cases will a pedestian be hurt?
Petrol Smart Diesel Smart Petrol Smart BEV Transit Diesel Transit BEV
Subjective Perception: Probability of accident
5th December 2011 CAR Universität Duisburg-Essen 18
16% 16%
12%
16%
Agila Stromos Fiesta e-City
In wie vielen Fällen wird in dieser Situation ein Fußgänger verletzt?
In how many cases will a pedestian be hurt?
Difference not significant Difference not significant
Agila Petrol Fiesta Petrol
19
Subjective Perception: Fear of accident
0%
7% 7%
Smart Fortwo Diesel Smart Fortwo Benzin Smart Fortwo BEV
5th December 2011 CAR Universität Duisburg-Essen
Have you been feared of an accident? – Yes.
Difference significant
Smart Diesel Smart Petrol Smart BEV
10%
9%
7%
11%
Agila Stromos Fiesta e-City
Subjective Perception: Fear of accident
5th December 2011 CAR Universität Duisburg-Essen 20
Have you been feared of an accident? – Yes.
Difference not significant Difference not significant
Agila Petrol Fiesta Petrol
Objective perception
5th December 2011 CAR Universität Duisburg-Essen 21
At a speed of 30 km/h: breaking distance: 9 m
+ reacting distance: 9 m = total stopping distance: 18 m
8%
20%
Fiesta e-City
Critical Distance
Vehicle perception too late
(vehicle distance < stopping distance)
Difference significant
Fiesta Petrol
Objective perception
5th December 2011 CAR Universität Duisburg-Essen 22
Differences not significant
15% 16%
4% 6%
Agila Stromos
kritische Distanz missed detection Vehicle perception
within stopping distance
Vehicle perception after
passing critical distance
Agila Petrol
Agila/Stromos at lower speeds
Group discussion II with participants of the study subsequent to the 3rd run, April 2011
Focus: Evaluation of Stromos/Agila Petrol in different driving modes at lower speeds
Results:
• Stromos (BEV) is quiet, but perceivable at 20km/h constant drive (no combustion
noise, but tire noise);
• At 10 km/h constant drive Stromos is too quiet and the situation is more dangerous
(no combustion noise, less tire noise);
• The perception of the identical vehicle Agila Petrol is similar to the BEV (less
combustion noise compared to other ICE);
• Parallel parking at the roadside is hardly perceivable and therefore dangerous for
Stromos and Agila Petrol;
• In the situation “stop at cross-walk” decelerating of Stromos is quiet, but
perceivable, while accelerating is too quiet to be heard; Agila is perceivable.
CAR Universität Duisburg-Essen 23 5th December 2011
Discussion of Possible Solutions
Focus: Solution of the problem: Sound or warning system
CAR Universität Duisburg-Essen 24 5th December 2011
Group I (organized and more conventional
thinking people)
Group II (highly technophile and more
open minded people)
Sound as single acceptable solution • Traditional engine sound preferred • Sound should correspond to speed • Acoustical tracking of moving vehicles • Demografic change has to be considered
(increasing number of hearing impaired people)
Problems • Acustic impulse overload • All quiet vehicles are dangerous (also bicycles)
Resistance against technic-based warning system • Not-technophiles excluded
Several soultions conceivable • Additional sounds for quiet cars in general
necessary (especially for lower speeds and while standing)
• Acoustical signal at the car helps, but does not prevent accidents
• Specific haptic warning via white cane, if vehicle approaches
• Additional warning for driver of approaching car via transmitter in the white cane
• Problem also relevant for children or hearing impaired persons
The far side of additional sounds
• Traffic noise can have heavy consequences like risks of sleep disorder, lack of
concentration or damage to hearing;
• People who are constantly exposed to traffic noise of 65 decibel have a higher risk
of infarction;
• Noise results in detachment of stress hormones and in the long run this causes
body overstraining;
• Noise abatement is highly expensive
(silent asphalt, quiet goods trains,
noise barriers);
• The diffusion of electric cars would
implicate noise reduction as a free add-on.
CAR Universität Duisburg-Essen 25 5th December 2011
5th December 2011 CAR Universität Duisburg-Essen 26
In the short run:
Natural engine sound for all quiet vehicles in general.
In the long run:
Electronic assistant system, which is able to warn the affected person
(haptically or acustically) and the driver of the vehicle at the same time.
Possible solution
Electronic Warning System
Backup
5th December 2011 CAR Universität Duisburg-Essen 28
Noise Map – ROL Fiesta Petrol/E-City
CAR Universität Duisburg-Essen 29 5th December 2011
7060504030
80
75
70
65
60
55
50
V_PP [km/h]
SPL_
avg
[dBA
]
E-City BEV - ROL - NFiesta ICE - ROL - N
Veh - Test - Gear
ROL - SPL_avg vs V_PP
Noise Map – DBY Fiesta Petrol/E-City
CAR Universität Duisburg-Essen 30 5th December 2011
7060504030
80
75
70
65
60
55
50
V_PP [km/h]
SPL_
avg
[dBA
]
E-City BEV - DBY - 1Fiesta ICE - DBY - 2Fiesta ICE - DBY - 3
Veh - Test - Gear
DBY - SPL_avg vs V_PP
Acoustic measures Transit - cruise
31
6050403020100
75
70
65
60
55
50
v_avg
spl_
avg
Transit - BEV - crs - 0Transit - ICE - crs - 1Transit - ICE - crs - 2Transit - ICE - crs - 3Transit - ICE - crs - 4
code
TRANSIT - CRS - Rolling with engine noise
code BEV – 0 ICE – 1 ICE – 2 ICE – 3 ICE – 4
5th December 2011 CAR Universität Duisburg-Essen
Acoustic measures Transit - roll
32
605040302010
75
70
65
60
55
50
v_avg
spl_
avg
Partner BEV - cstPartner ICE - cstTransit - BEV - cstTransit - ICE - cst
code
CST - Free rolling w/o engine noise
6 dB
5th December 2011 CAR Universität Duisburg-Essen
Experiment Location
33 5th December 2011 CAR Universität Duisburg-Essen
Subjective Safety of Blinds
34
Extremely safe Rather safe Neither nor Rather
unsafe Extremely
unsafe
In general
Rain and wet conditions
Strong wind
Snow
5th December 2011 CAR Universität Duisburg-Essen
Blind and visually impaired persons
Relevance of Vehicle Exterior Noise
35
Extremly unimportant
Rather unimportant Neither nor Rather
important Extremely important
Sound of a standing vehicle
Sound of a slowly driving vehicle
Sound of a fast driving vehcile
Not visually impaired persons Blind and visually impaired persons
5th December 2011 CAR Universität Duisburg-Essen
Differences significant