1 a study on approach warning systems for hybrid vehicle in motor mode jasic, japan informal...

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A Study on Approach Warning Systems for hybrid vehicle in

motor mode

JASIC, JAPAN

Informal document No. GRB-49-10(49th GRB, 16-18 February 2009, agenda item 10(b))

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CONTENTS

1. Background

2. Assessing the Situation

3. Experiments Using Sample Sounds　 (1) Experiment for Evaluating Perception by

Pedestrians　 (2) Experiment for Evaluating Acceptability by

Residents/Pedestrians　 (3) Overall Evaluation

4. Investigations on Public Roads, etc. from the Perspectives of Pedestrians

5. Conclusions

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CONTENTS

1. Background






5. Conclusions

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Sal

es

(000

un

its)

Hybrid vehicles (HV) and Electric vehicles (EV) increasing;

Those vehicles are very quiet and difficult to be noticed by pedestrians

However, no reported accident has been confirmed.

Background to the Study

Sharp increases in annual sales since 2004

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CONTENTS

1. Background






5. Conclusions

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Assessing the Situation

• No reported accident by vehicles to be quiet has been confirmed.

• It is not even known how quiet hybrid vehicles in motor mode are.

• We compared the noise level between hybrid vehicles in motor mode (HV (EV mode)) and the gasoline engine vehicles (GE) to determine how difficult they are to notice.

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Method for Assessing the Situation

(1) Comparison of Equivalent Sound Level (LAeq) Between HV (EV mode) and GETo eliminate the effect of background noise, vehicle noises of HV (EV mode) and GE was recorded in the special environment resembling an anechoic chamber (i.e., at a test course in a mountain with no insect), and LAeq of them were compared.

(2) Perception of Pedestrians EvaluatedUnder a specific environmental condition (indoor), those vehicle noises mixed with background noise were played to subjects, and their perception was evaluated.

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(1) Comparison of Noise Level (LAeq) Between HV (EV mode) and GE

♦ Noise level of HV (EV mode) and GE at 2 m to the side

Measurement schematic

3m1m

D = 2 m

Microphone

Vehicle speed0 ～ 30km/h

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60

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0 5 10 15 20 25 30 35

GE1

GE2

HV (EV mode)

Ground Noise

Maximum noise level difference between HV (EV mode) and GE : 20 dB

Noise level of GE in stationary or running at low speed

•The slower the speed of HV (EV mode), the bigger the noise-level difference from GE.•Noise level difference maximum at about 20dB when stationary.•Noise level difference smaller at speed 20 km/h or above.

(1) Comparison of Equivalent Sound Level (LAeq) Between HV (EV mode) and GE

Vehicle Speed [km/h]

Eq

uiv

alen

t N

ois

e L

evel

[d

B(A

)]

Noise level difference small

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Subwoofer Observer Loudspeaker

Setup of noise hearing experiment

•Evaluation of perception using recorded vehicle noises and 3 ground noises by 20 subjects.

Recording vehicle noise

LAeq=45.2dB(A)

61.7dB(A)Mix

(2) Evaluation of Perception by Pedestrians

A residential area 52.6dB(A)

A bustling street

Recording ground noise (3 level)

Between

11

2 m

In stationary state

2 m

Assumed scene

Noise-perception evaluated at this location

♦ Stationary Vehicle Perception Results

•Perception of HV (EV mode) in stationary lower than GE•Subjects able to perceive the HV (EV mode) : 0%

0

20

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60

80

100

Back ground noise45.2dB(A)

Back ground noise52.6dB(A)

GE1 GE2 GE3 HV(EV mode)

Rat

io o

f te

st s

ub

ject

s ab

le t

o

per

ceiv

e th

e ve

hic

le (

%)

HV(EV mode)

Background noise varied

0 0

HV(EV mode)


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40 45 50 55 60 65

20km/h

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40 45 50 55 60 65

6.5km/h

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40 45 50 55 60 65

10km/h

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15km/h

♦ Approaching Vehicle Perception Results

2 m

Approaching

Assumed scene

GE1

•Perception of HV (EV mode) is lower than GE when the background noise level is low and the speed is 15 km/h or below. •The noise level difference became smaller as the vehicle speed exceeded 20 km/h.

Distance at which vehicle was perceived

GE2 HV (EV mode)

Noise-perception evaluated at this location

Dis

tan

ce a

t ve

hic

le p

erce

pti

on

[m

]

Background noise level [dB(A)]

Small difference


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0

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25

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40 45 50 55dB(A)暗騒音ﾚﾍﾙ゙，

m認

知し

た距

離，

Stopping distance (maximum conditions)Stopping distance (average conditions)

GE1GE2GE3HV (EV mode)

Pedestrian's HV (EV mode) perception distance may measure shorter than the stopping distance of maximum conditions.

10km/h

Ground noise, dB(A)

EV

GE

The stop distance of vehicles was calculated from the following theoretical formulas and test results.1.Calculation of Stop Distance.　　 Stop distance = free running distance + braking distance 　　　　　　　　　　　　 = speed x reaction time + speed^2/(2x9.8x coefficient of friction)2. Free running distance (speed x reaction time).　　 The running-out reaction time test result in a public road .　　 (Japan Safe Driving Center carried out in 2000)　　 Reaction time: Average =0.82 (second), an average of+3sigma=1.966 (second)3. Braking Distance　 Braking distance = speed^2/(2x9, 8x coefficient of friction).　 A coefficient of friction is the following (from Ichiro Emori "automobile accident engineering").　　・ It is 0.6 in case of the worn-out tire on dry asphalt　　・ With the ordinary tire on dry asphalt, it is 0.7.

♦ Approaching Vehicle Perception Distance and Stopping (braking) Distance


However, more study is necessary for this issueby the safety experts.

Dis

tan

ce a

t ve

hic

lep

erc

ep

tion

[m

]

Background noise level [dB(A)]

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(3) Summaries1. Perception of the stationary HV (EV mode) was significantly lower

than GE. Hence, there could be the case where it is useful and

therefore necessary for preventing contact with the pedestrians to

improve the perception, by audible means, of HV vehicles before

they are in forward motion.

2. The distance between HV (EV mode) and pedestrian measured when

the pedestrian perceives the vehicle is shorter than GE when the

vehicle is run at low speed. Hence, there also could be the case

where it is useful and therefore necessary for preventing contact

with pedestrians to improve the perception of HV (EV mode) in the

low-speed range.

3. No major difference in perception between HV (EV mode) and GE

above 20 km/h.

4. As there used to be no concerns related to perception of GE at this

stage, we can focus on HV (EV mode) at low speed.

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CONTENTS

1. Background






5. Conclusions

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Since the noise of HV (EV mode) at low speed is difficult to be perceived because it is too quiet, the vehicle was experimentally driven while playing sample sounds to study its perception and acceptability by pedestrians.

Experiments Using Sample Sounds

Perception by pedestrians evaluated

Acceptability by residents/pedestrians evaluated

Sample sounds selected (11 sounds, including existing sounds, created sound, simulated engine sound)

Test vehicle created

Overall evaluation

Procedures

Purpose and Method

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(1) Selection of Sample Sounds

9 sounds selected out of the pre-selected 20 sample sounds,plus 2 actual engine noises

No. Sound type Remarks(1) Non-steady sound Existing sound(2) Non-steady sound Existing sound(3) Non-steady sound Existing sound(4) Non-steady sound Created sound(5) Non-steady sound Created sound(6) Steady sound Created sound(7) Steady sound Created sound(8) Steady sound Created sound(9) Steady sound Simulated engine sound

(10) Steady sound Actual engine sound (L4, 1496 cc)(11) Steady sound Actual engine sound (V8, 4292 cc)

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(2) Creation of Test Vehicle

AMPPC Volume

Toggle switch

● Speaker and buzzer => Fixed behind bumper

● PC, AMP, volume on/off switch, toggle switch => Fixed in passenger compartment

Veh

icle

ap

pro

ach

w

arn

ing

sys

tem

PCAMP Speaker

Buzzer

Toggle switchSound file

Volume controller with on/off

switch

♪♪

♪

AmplifierComputer

♪♪

● Vehicle horn=> Not modified in this experiment; It functions normally.

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CONTENTS

1. Background






5. Conclusions

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(1) Experiment for Evaluating Perception by Pedestrians

• Purpose　 To evaluate perception of sample sounds by using test

subjects• Procedures　 1. The volume of the selected sample sounds was set at around

the same level as GE (LAeq=50 dB at 2 m in front).　 2. Under specific environmental conditions (indoor experiment),

a vehicle approaching at 10 km/h was simulated; the three background noises mixed with the sample sounds were played for 20 subjects; the following was evaluated:

　　 (1) Distance required to perceive the sound at LAeq=50 dB　　 (2) LAeq of sample sounds when they were perceived at around

the same distance as GE

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0

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40 50 60 70

Background　noise　[dB(A)]

Dis

tanc

e　at

　whi

ch　v

ehic

le　

perc

eive

d　　[

m]

(6)(7)(8)(9)GE1GE2HV

0

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40 50 60 70

Background　noise　[dB(A)]

Dis

tanc

e　at

　whi

ch　v

ehic

le　p

erce

ived

　　[m

]

(1)(2)(3)(4)(5)GE1GE2HV

•Even at the same LAeq, perception largely differs for each sample sound type (frequency).•Perception is higher for non-steady sounds.

(1) Result of Experiment for Evaluating Perception by Pedestrians

Vehicle speed 10 km/h

Non-steady sounds

Dis

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t ve

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erce

pti

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[m

]

Background noise [dB(A)]

Background noise [dB(A)]

Steady sounds

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pti

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[m

]

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•In additional test result, LAeq of the sample sounds for which almost the same perception as GE was listed below.•Some of these sample sounds had lower LAeq than GE noise and yet had almost the same perception.

(1) Result of Experiment for Evaluating Perception by Pedestrians

No. Sound type LAeq (dB(A)) at 2 m

(1) Non-steady sound 50.0(2) Non-steady sound 42.6(3) Non-steady sound 42.9(4) Non-steady sound 41.1(5) Non-steady sound 39.3(6) Steady sound 50.0(7) Steady sound 50.0(8) Steady sound 50.0(9) Simulated engine sound 50.0

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CONTENTS

1. Background






5. Conclusions

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* Test conducted with sample sounds at 3 different volumes* 59 subjects

1 m

15 km/h

(2) Experiment for Evaluating Acceptability by Residents/Pedestrians

Prefabricated building simulatinga Japanese wooden house

Solving crossword puzzles to take their mind off the vehicle

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-3

-2

-1

0

1

2

3

44dB 50dB 56dB

Level of sampled sounds (LAeq, dB(A))

Ac

ce

pta

bil

ity

sc

ore

(1) (2)

(3) (4)

(5) (6)

(7) (8)

(9) (10)

(11) GE4

GE5

•Even at the same LAeq, acceptability differs for each sample sound type.•For any sample sound, acceptability is higher at lower volume.•Acceptability tends to be higher for non-steady sounds.

Results of acceptability test

(2) Experiment for Evaluating Acceptability by Residents/Pedestrians

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CONTENTS

1. Background






5. Conclusions

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(3) Overall Evaluation

• Purpose　 To study, based on the results of evaluating perception

and acceptability, the acceptability of those sample sounds which showed almost the same level of perception as GE.

• Procedures　 1. From the results of perception experiment, sample

sounds that had almost the same perception level as GE vehicle and whose LAeq was particularly low were selected.

　 2. For these selected sample sounds, the acceptability score was calculated. The score was also evaluated for the actual vehicle.

　 3. The results were compared and evaluated.

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-1.0

-0.5

0.0

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(5) (3) (2) (4) (1) (8) (7) (6) (9)

Ac

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ore

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LA

eq

of

sa

mp

le s

ou

nd

eq

uiv

ale

nt

to G

E n

ois

e [

dB

(A)]

•Some sample sounds have higher acceptability than GE noise even at equivalent noise level (LAeq) lower than GE noise by about 10 dB(A) and have almost the same perception level as GE noise.

Comparison of acceptability between engine noise and sample sounds with almost the same perception level as engine noise

(3) Overall Evaluation

■ Acceptability score◆ LAeq of sample sound equivalent to GE noise [dB(A)]

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CONTENTS

1. Background






5. Conclusions

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At various locations on public roads, the engine idling noise and sample sounds were emitted from the test vehicle and the “distance required for perception” was investigated.

(1) Main investigation•Locations: Parking lots, expressway service areas, commercial facilities, parking lots for employees; Straight ways in residential areas, intersections with poor visibility;•Interviews to visually-impaired people.

Visually-impaired person

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(2) Main results:• Many people were unaware of the sample sounds being emitted

from the vehicle and didn’t turn their heads.• At intersections with poor visibility, the “distance required for

perception” of the sample sounds was better than for engine sound.

• Some visually-impaired people didn’t realize the sounds were coming from the vehicle even when they heard them.

• A request from visually-impaired people: either a sound that is obviously coming from vehicles or a uniform warning sound is desirable.

(3) Conclusions• When it was obvious to pedestrians that the sound was coming

from vehicles, the “distance required for perception” of the sample sounds was more favorable more favorable than the engine noise.

• As the warning sound of an approaching vehicle, it is important to use a sound that is obviously coming from vehicles or a uniform sound that is widely known as such sound.

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CONTENTS

1. Background






5. Conclusions

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Conclusions1. This study was conducted because of the concern that the

increasing number of hybrid vehicles could cause accidents due to their excessive quietness, such as hitting pedestrians who are not aware of their approach.

2. To date, no accidents caused by vehicles being too quiet have been found in the database on accidents statistics.

3. Comparisons made to assess the situation also showed that there was no significant difference in the perception between HV (EV mode) and GE when traveling above 20km/h.

4. Although the relationship between quiet vehicles and accidents is not known, indoor experiments and investigations on public roads were conducted to examine the vehicle approach sounds that can be considered at this stage.

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Conclusions

5. Results of experiments and investigations

(1)Even at the same LAeq, the perception largely differs for each sound type (frequency or sound quality).

(2) Some sample sounds have higher acceptability than GE noise even at equivalent noise level (LAeq) lower than GE noise by about 10 dB(A) and have almost the same perception level as GE noise. (LAeq=50dB at 2 m)

(3) When it is obvious to pedestrians that the sound is coming from vehicles, the sample sounds was more perceptible than the GE noise.

(4) As the vehicle approach warning sound, a sound that is obviously coming from vehicles or that is widely promoted as such sound.

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For the future

(1) Since safety is closely involved in this issue; therefore, it is difficult to for the issue to be discussed by GRB alone.

(2) Further discussions are necessary based on reported accidents and complaints.

(3) For this reason, more information from GRB members is expected.

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Thank you very muchfor your attention

1 a study on approach warning systems for hybrid vehicle in motor mode jasic, japan informal...

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