Suspensão - artigo - amortecedores como causa de acidentes de veículos

8/3/2019 Suspenso - artigo - amortecedores como causa de acidentes de veculos

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SHOCK ABSORBER AS A CONTRIBUTING CAUSE TO MOTOR VEHICLE

ACCIDENT

1

Osama Youssef Abdel-Fattah2

Samir M. El-Demerdash

1

Lecturer, Automotive Department, Buraydah College of Technology Gotevot KSA.

B.O Box 2663 Buraydah 81999 E mail: [email protected]

2

Prof. of Vehicle Dynamic and Control, Faculty of Engineering Mataria, Helwan University,

Cairo, Egypt. Email: [email protected]

AbstractTraffic accidents appear to play an important role in overall mortality rates worldwide. Many factors combine to

produce circumstances that may lead to a motor vehicle crash- there is rarely a single cause of such an event.

There are three sources of factors contribute vehicle crashes: human factors, roadway environment factors, and

vehicle factors. Human factors involve the actions taken by or the condition of the driver of the automobile,

including speeding and violating traffic laws, as well as being affected by alcohol or drugs, in attention, decision

error, and age. Roadway environment factors include the design of the roadway, roadside hazard, and roadway

conditions. Vehicle factors include any failures that may exist in the automobile or design of the vehicle. The

objectives of this paper are to study how much the vehicle factors (especially shock absorbers) affect traffic

accidents and how much knowledge drivers has about the function and effect of shock absorbers on vehiclesafety and stability. The results showed that, with worn shock absorbers, the stopping distance during braking is

increased from 5% to 25% depending on vehicle speed and weight. Also, using 200 drivers questionnaire

showed that, more than 60% of the drivers did not know the function of shock absorber in cars and the effect of

worn shocks on the vehicle safety and stability and driver's fatigue. The findings are discussed to the necessity of

changing knowledge of drivers and assist decision makers in the development to improve transportation system

in the KSA.

1- IntroductionTraffic accidents appear to play an important

role in overall mortality rates worldwide [1].

Many factors combine to producecircumstances that may lead to a motor vehicle

crash- there is rarely a single cause of such an

event. Three categories of factors contribute to

crashes: human factors, roadway environment

factors, and vehicle factors [2]. Most researches

today agree that it is not appropriate to attempt

to isolate a single main cause of an accident,

early accident studies demonstrated that more

than 70 % of all accidents could be attributed to

road user behaviour characteristics [,3,6,18],

but there are another factors that contribute to

road traffic accidents such as vehicle and

roadway environment, as shown in figures1, 2and 3. A number of studies have reported

differences in traffic accident causes related to

vehicle mechanical components, KHAA[4],

reviewed the major vehicle components which

may affect road safety, the components are:Braking system, tyres, suspension system,

steering system, lighting, and visibility (glass,

windscreen wiper, and rear mirrors). A study

published by the university of Valencia [5]

shows that of the 200,000 accidents that

occurred on Spanish roads, 5000 were caused

by mechanical failure. 40% of these incidents of

mechanical failure could be traced to a problem

with the suspension system, and thus with the

shock absorbers. In Kenya, according to [6],

the main categories of causes of motor vehicle-

related traffic injuries are human factor(85.5%),

vehicle factor (5.1%), environment (2.9%) andother factors (6.4%).


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In Spain, six of the world's leading shock

absorber manufactures [7] surveyed 400

Spanish motorists, when asked which parts of

their car needed to be checked regularly, 67.5%

cited brakes, 62.6% tyres, 58% oil, but just

7.5% mentioned shock absorber. 28.9% of

interviewees (and 47% of female interviewees )didn't know how many shock absorbers their

vehicles had, and 93.4% of drivers questioned

were unaware of the need to check their

absorbers every 12000 miles (20000 km), this

lack of awareness becomes even more alarming

in view of high number of road accidentscaused by warn shock absorbers. More than

165,000 vehicles have been tested by [8] in

Italy, Germany, Belgium, Luxembourg and

Netherlands, initial results showed that 47% of

all vehicles tested with an average 111,000 kms

driven have seriously worn or damage shock

absorber.In Britain [9], the study showed that

mechanical faults are a factor in 5.5% of road

accidents, environmental factor around 18% of

road accidents and human factor more than

80%. In South Africa, 40% of the vehicles onthe suburban road and 29% of the vehicles on

the highway [10] had mechanical defaults that

contravened current road and traffic regulations

and may, therefore, be at risk of causing an

accident due to a mechanical failure.

85.5

5.12.6

6.4

0

10

20

30

40

50

60

70

80

90

HumanVehicleEnvironmentalOthers

Figure 1 : Primary causes of highway

crashes [ 6]

Figure2:Primary causes of highway

crashes [11 ]

2- Dangerous of worn shock absorber

To show how worn shock absorbers can affect a

cars safety, Tenneco Automotive [6,8] has

worked with a number of independent research

bodies. When compared to a car with shock

absorbers that function at 100%, a car with 50%worn shock absorber:

(1)Takes 2.6 meters longer to stop from a speed

of 80 km/h on a straight road with only a driver

in the car.

(2) Takes 11.3 meters longer to stop when fully

loaded (with a driver and three passengers) andtravelling on a straight road with an uneven

surface from a speed of 70km/hr.(3) Begins to aquaplane at 109 km/h. If the

shocks are perfectly efficient, aquaplaning will

start at125 km/hr.

(4) Takes 23% longer to make an emergency

stop in snow or ice, even when equipped with

an ABS system, as the wheels block while

braking because the shocks provoke the

malfunctioning of the ABS control unit.

After 9,000 km a car with 65% worn out shocks

suffers 10% more tyre wear than when

equipped with perfectly efficient shock

absorbers, costing the cars owner more moneyand potentially reducing the vehicles safety.

Also Monroe [13], presents these facts about

the effect of worn shock absorbers on vehicle

safety and driver (in comparison with new

shock absorber) such as :

(1) Braking : At 55km/h on a bend the braking

distance (for worn shock) may be increased by

2.3menough to cause an accident.

(2) Road holding : If shock absorbers are 50%

worn, the maximum safe speed, even on a dry

road, can be reduced by 10%.

(3) Aquaplaning: With a 50 % worn shock

absorber and on 6mm of surface water,skidding and aquaplaning can begin at


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a speed 10% lower than with new shock

absorber.

(4) Driver fatigue: Defective shock absorbers

increase driver fatigue and can extend reaction

time by 26%.

(5) Reduced visibility: Unstable and irregular

illumination of the road makes night drivingdangerous and visually tiring.

(6) Dazzle Exaggerated oscillation dazzles the

drivers of oncoming vehicles. Worn shockabsorbers also increase wear on importantmechanical parts of the vehiclesprings,

steering gear, universal joints, differential, tires,

rubber suspension bushes, the gear box, wheel

bearing, suspension and steering arm ball joints,see figure 4

Figure 3: factors that contribute to road traffic accidents (driver, vehicle and roadway-environment)

[12].

Figure 4 : effect of worn shock absorber on vehicle components [14].


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Discussion :200 of drivers at El-Qassim city are reviewed,

the analysis of questionnaire revealed several

important finding which are summarized asfollow:(1) About 90% of the drivers had finish the

secondary school. Accordingly, it can beassumed that 90% of the drivers were familiarto some extent, with the English language andcould read the instructions from the vehicle

guide about checking up and maintenance of

the vehicles.

(2) More than 60% of the drivers between 21

30 years as shown in figure 5.

(3) The questionnaire revealed that more than

60% of the drivers did not know the function or

types of shock absorbers as shown in figure 6,

also 64% of the drivers did not know the effect

of worn shock absorber on the braking distance,

figure 7.

(4) Figure 8shows that only 1%of the driversknow the bad effect of worn shock absorber on

the driver's fatigue and 64% of the interviewed

drivers said that no relation and 35% did not

know the relation.(5) The majority of drivers did not know the

effect of worn shock absorber on vehicle

stability and safety specially at corners

(6) About 40% of the drivers checking up the

suspension only when braking down and 40%

checking the tyre pressure and condition beforelong trip only.

(7) The questionnaire revealed that about 60%

of the drivers using commercial spare parts and

about 20% using original parts while 19% using

used spare parts

22.2

62.5

12.5

2.70

10

20

30

40

50

60

70

%

under

20

21 - 3031 - 4546 - 60

Driver's age

Figure5: The driver's age

Do worn shock absorbers

increase brake stoping

distance?

63.8

29.1

6.9

No

Yes

dont

know

Figure 7: Knowledge of relation between shock

absorber and stopping distance.

Do you know the function of shock

absorber ?

61.1

38.3

NoYes

Figure 6: Knowledge of shock absorbers&

function

Do worn shock absorber

increase driver fatige

1.38

34.7

63.8

No

Yes

dont

know

Figure 8: Knowledge of effect of worn shockabsorber on the driver's fatigue


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Does the s uspension system

affect on the vehicle stability

and safety specially in

cornering?

23.6

76.3

Dontknow

No

How often do you check the tyre

pressure and condition ?

18

38.8

16.6

26.3

Onec

everywheekOneceverymonthBeforelon tri

Figure 9: Effect of worn shock absorber on the

vehicle safety and stability.

Figure 11: Checking tyre pressure and

condition

How often do you check the

suspension system ?

26.3

33.3

13.88

40.3

Onec every 6

month

Onec every

yearBefor long

trip only

At Brake

down only

Figure 10: Checking the suspension system

components.

What type of spare parts do you

use ?

59.7

21.3818.8

020406080

Comm

ercial

Orig

enal

Used

Figure 12: Types of spare parts

6- Conclusion :

Three categories of factors contribute to

crashes: human factors, roadway environment

factors, and vehicle factors. more than 70 % of

all accidents could be attributed to road user

behaviour characteristics, at least 5% attributed

tovehicle failure and 5% attributed to roadwayenvironment. A number of studies (all over

the world) have reported differences in traffic

accident causes related to vehicle mechanical

components such as tyre, suspension, steering

and brake system. In this study all the results

indicates that drivers need proper education

through media campaigns on how to select,

check and maintain the suspension system

components specially shock absorber. It is

hoped that the finding of this study may assist

decision makers in the formulation of policies

and the development of alternative plans to

decrease road traffic accident in the KSA.

AcknowledgmentThe authors would like to acknowledge Dr. Adel

H. Alzenedy, and Dr. Nabil Gohar. For their

valuable advice and information, which have

improved the presentation of this paper.

APPINDEX

1- Function of shock absorberA shock absorber is a hydraulic mechanism

positioned between the tyre and body to dissipate

energy generated by road surface irregularities,

then reduce the forces transmitted to vehicle body

and passengers as well as that generated between

the tyres and roads. These functions can be

summarized in the following two points : (1)

Limit spring oscillations (compression

extension movements) to smooth the vehicle ride

(Figure 13). (2) Control the contact between tyre

and road surface, good contact between tyre and


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road surface means good traction, braking and

steering (figure 14).

2- Indication of worm shock absorber

2-1 Visual and manual inspectionWe don't need to be a mechanics though to see the

signs of worn shock absorbers. Any of the

following problems may indicate worn shockabsorbers requiring professional inspection [15].

(1)The vehicle nose-dives under braking, the

bonnet dips excessively increasing braking

distance. (2)The steering wheel vibrates,

sometimes wrongly diagnosed as a wheel

alignment or wheel balance problem. (3)Thevehicle shakes, rattles and rolls due to lack of

damping forces and the vehicle does not hug the

road on bends. Worn shocks mean that over

bumps the wheels bounce and tyres loose contact

with the road surface. (4)The vehicle veers

sideways in cross winds or swerves sideways

under heavy braking(5)The shock absorber leakoil. Check the ground after parking your car

overnight. (6)The tyres on the vehicle wear

unevenly, due to wheels bouncing uncontrollably.

Bald patches develop called scalloping.

Any of these observations will leave no doubt asto the condition of the shock absorbers. One final

test that can easily be undertaken is the age old

bounce test. With your car parked safely, push

down firmly on the boot, the vehicle should

bounce back and settle in place after one bounce.

Repeat this test several times at the boot and then

test the front suspension by pushing several times

on the bonnet. If the vehicle continues to rock

several times, like this it is a good sign the shock

absorber have worn

2-2 Suspension testing apparatusThe European Shock Absorber Manufacturer's

Association (EuSAMA) [16] was established a set

of guideline for vehicle suspension evaluation

called " Recommendations for a vehicle

suspension performance evaluation ". Test devicethat conform to the EuSAMA specification have

been developed for the in-service testing of

vehicle suspension system, these devices displace

a wheel and measure the response of the wheel to

the displacement. From the individual responses,

the device determines the condition of the shock

absorbers, figure 15 shows the sample result forthe test.

2-3 Laboratory test of shock absorberTo get the characteristics of chock absorber,

damping coefficient, must be using the special testmachine, the test result is a force-travel diagram

and we convert it to force velocity diagram to get

the damping coefficient [17] , as shown in figure

16

Figure 13 : shock absorber limit spring oscillations


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Figure 14 : Forces acting on the vehicle [12].

Figure 15: Sample EuSAMA result print out

Figure 16 Shock absorber test result


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References1- Jaun S, Akihiro K, Pei S and Junichi M.

"Population characteristics of traffic

accident- related deaths in JAPAN and

IRELAND",1950-2000.The Journal of

Medicine, Vol.27, No.4, pp.333-338, 2004.

2- United States General Accounting Office,

GAO,. "Research Continues on a Varity

of Factors that Contribute to Motor Vehicle

Crashes". 2003.

3- A. Benner and D. Crundall. "Road Traffic

Accidents in the United Arab Emirates

Compared to Western Countries". Dept. of

Medical Statistics Epidemiology, Hamad

General Hospital, Doha, QATAR, 2005

4- Hong Kong Automotive Associations, http://

www.hkaa.com.hk

5- Monoro Safety Triangle Promotion, http://

www.eu.tenneco-automotive.com

6- Wilson Odero. "Road Traffic Injuries inKenya, Magnitude, Causes and Status of

Intervention. Injury Control and Safety

Promotion". Vol. 10,No. 1-2, pp. 53-61.

2003.

7- Tenneco Automotive, http://

www.automechani kagulf.com

8- Worrying Results in European Shock Tests,

Monroe, 2005.

9-The RoSPA Guide to Road Safety Projects inBratain. 2005. http://

www.rospa.com/roadsafty/advice/general/p

roject.

10-Van Schoor O. "Mechanical Failuers as a

Contributing Cause to Motor Vehicle

Accidents South Africa". Accid. Anal.

Prev. 33(6): 713-21. 2001.

11-http://

www.ctre.iastate.edu/educweb/crp445/Safe

ty2.ppt

12- Robert Bosch GmbH. Driving Stability

System. Germany, 2005.

13- Effect of Worn Shock Absorbers.

MONROE. http://

www.taeu.com/monroe/effects-worn-

shock.htm

14-

http://www.midwestautocare.com/shocks2.

html.

15- Ful Crum. http://

www.sdt.com.au/CARSUSPENSION.htm

16- Steven B. and Wayne B. "ExperimentalEvaluation of a Non-Intrusive Automotive

Suspension Testing Apparatus". Society of

Automotive Engineers. 2001-01-1329.

17- O. Y. Abd- Elfattah. "Hydro-Pneumatic

Suspension System for Passenger Cars".

M.Sc. Thesis, Helwan University. Egypt.

2000.

18- Abdulbari B. "Road Traffic Accident

Admissions in the United Arab Emirates".Dept. of Community Medicine, Faculty of

Medicine and Health Sciences, UAE

University

.

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