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INNOVATIVE BODY STRUCTURE FOR THE SELF-PROTECTION OF A SMALL CAR IN AFRONTAL VEHICLE-TO-VEHICLE CRASH

Masuhiro SaitoTetsuya GomiYoshinori TaguchiTakeshi YoshimotoTomiji SugimotoHonda R&D Co., Ltd. Tochigi R&D CenterJapanPaper Number 239

ABSTRACT

Preservation of passenger compartment spaceduring a frontal vehicle-to-vehicle collision isextremely significant for the self-protection ofsmall cars.

It is well known that crash speed, mass, stiffnessand geometric interaction all have an influence on theintrusion of the passenger compartment in a frontalimpact between vehicles. This paper reports on a newenhanced body structure to reduce passengercompartment intrusion in a crash between large andsmall cars. The test discussed in this report set thecrash speed of both cars at 50kph, the mass of thelarge car at almost twice that of the small car, and thesmall car over lap at 50%. The proposed innovativebody structure for the front end of small carsachieved a previously unavailable level of efficiencyof energy absorption and was able to maintain cabinintegrity.

INTRODUCTION

In recent years the use of stationary barrier crashtests as a method of evaluation of crash safetyperformance has increased internationally. This hasbeen very effective in improving vehicle crash safetyperformance and reducing the number of casualties intraffic accidents.

However, in the case of frontal collisions betweensmall cars and large cars in the real world accident�itis said that the risk of injury to the small car’soccupants is higher than that to occupants of the largecar� This is caused by incompatibility between‘mass’ ‘stiffness� and ‘geometry� in vehicle-to-vehicle collisions�A collision in which the mass andstiffness ratios of the vehicles are large is equivalentto an extremely high speed� stationary� barriercrash for a small car�Small cars which receive good evaluations in full lapand offset frontal crash barrier tests are therefore notalways sufficiently safe in a small car to large carcollision in the real world accident. And it begins tobe pointed out the necessity to have an anothermanner to evaluate it in the collisions with relativelydifferent sized vehicles.

In particular in the case of narrow offset collisionsin which overlap distance is relatively small in the

direction of the vehicle�s width and collisions withdiffering bumper height, it is very difficult for�conventional body structures to maintain crash safetyperformance. It is therefore necessary to proposeinnovative body structures based on new designconcepts�Of course it goes without saying that it isextremely significant for compatibility not only toconsider the progress of self-protection but alsopartner-protection (for opposite vehicles). Thisresearch reports on the possibility to improve the selfand partner protection which are discussed in thesociety by modifying the body structure such as oneof the unique technique.

THE SAFETY IMPROVEMENT FOR SMALLCARS

In frontal vehicle-to-vehicle collisions it has beendiscussed that mainly ‘mass’ ‘stiffness’ and‘geometry’ are the factors for incompatibility. In thispart we report on some subjects and solutions in theview of the self-protection for small cars.

The portion of the velocity change before andafter collisions is influenced by mass ratio � asfollows.

Vr = 1/Mr (1.)Vr = �V2/�V1 �Vi: velocity change ofVehicle i Mr = M2/M1 Mi: mass of Vehicle iThe lighter vehicles are forced to a higher

deceleration level than the heavier vehicles. As aresult the risk of injuries in small cars is higher thanin large cars. We will be able to solve such massincompatibility developing superior restraint systemsfor small cars and to reduce mass in large cars.

The portion of energy absorption in vehicledeformation depends on stiffness ratio of twovehicles as follows.

Er = 1/Kr (2.)Er = E2/E1 Ei: energy absorption of Vehicle iKr = K2/K1 Ki: stiffness of vehicle i

The problem is how to balance several vehicles’stiffness. To be realistic we need to improve thestiffness for small cars.

Certainly as stated above the difference betweenmass and stiffness is a problem for the compatibility,however we should first improve geometricalcompatibility.

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In recently years the level of self-protection forsmall cars has advanced greatly because of theadoption of offset deformable barrier testing.However the deformable barrier is very uniform instiffness. But in reality, the front of vehicle invehicle-to-vehicle collisions lack uniform stiffness,which causes severe damage to small cars. After thiswe focus on the improvement of interaction in frontalstructures.

NEW DESIGN CONCEPT

To improve the offset and full lap frontal crashperformance, conventional body structures aregenerally designed� with two main frames located�on each side of the engine compartment to absorbvehicle energy and to� control vehicle deceleration�

However, in the case of vehicle-to-vehicle collisionssuch as narrow offset collisions in which there is lessoverlap distance in the direction of vehicle width andcollisions between a passenger cars and a SportsUtility Vehicle (SUV) in which the bumper beamheights of the vehicles differ (as shown in Figure 1)�this body type allows structural penetration into theengine compartment.

� Plan view frame misalignment

Side view frame misalignmentFigure 1. Misalignment of stiffness betweenvehicles in vehicle-to-vehicle collision.

In particular when there is a significant differencein vehicle weight, the bumper beam and mainframe of the large car passes into the frame of thesmall car without sufficient energy absorption anddeceleration, penetrating the weaker part of the smallcar�As a result, deformation extends to the smallcar’s passenger compartment, increasing injuries tooccupants from secondary collisions in the passengercompartment,� as shown in Figure 2.

It is important for the improvement of the level ofprotection offered by small cars to prevent structuralpenetration of major frontal components, increase thehomogeneity of strength distribution and improveenergy absorption in the engine compartment in theevent of vehicle-to-vehicle collisions betweenvehicles with misalignment of stiffness. The designconcept will be expected not only to achieveprogress for self-protection but also the effect ofpartner-protection for compatibility.

Figure 2. Large deformation of the passengercompartment after narrow offsetvehicle-to-vehicle collision.

STRUCTURAL OUTLINE AND CRASHPERFORMANCE

The proposed structure consists of threecomponents, as shown in Figure 3.

A; Lower memberB; Closed bulk head upper cross memberC; Polygonal main frame

Figure 3. Structural outline.

These components are A; A lower member toprevent penetration. B; A closed bulk head uppercross member to assist energy absorption in theupper part of the engine compartment. and C; A �polygonal main frame enabling high efficiencyenergy absorption. This paper will offer a structuraloutline of the lower member system and discuss thepredicted effectiveness of this system as determinedby computer simulations.

The new ‘lower member’ was positioned in front ofthe tires extending from the wheel house uppermember, and was connected to the main frame andbulk head cross member. This prevents thepenetration of the frames of the respective vehicles innarrow offset collisions and collisions betweenvehicles with differing bumper heights. ( See Figure4 ). On impact, the lower member makes contactwith the front structure of the other vehicle anddeforms, thus achieving a high level of energyabsorption (as shown in Figure 5).

�

�

�

�Frame layout

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Preventing the penetration ofthe frame in narrow offset collision

� Preventing the penetration of the fame in� collision with differing bumper height

Figure 4. Preventing the penetration of the Frame.

Figure 5. Increasing energy absorption in theengine compartment from vehicle-to-vehiclecollision.

This leads to a significant reduction in theproportion of energy absorption in the cabin and ofthe degree of passenger compartment intrusion. Theeffectiveness of the new structure in reducingpassenger compartment intrusion is shown in Figure6.

Figure 6. Reducing passenger compartmentintrusion in vehicle-to-vehicle collision.

The new structure also enables reduction of thestrength and weight of the main frame, allowing amore homogeneous distribution of strength in thefront end structure.

It is predicted that this structure will be effective inreducing passenger compartment intrusion forvarious overlap distances in the direction of vehiclewidth (as shown in Figure 7), for the difference ofbumper height (as shown in Figure 8) and for angleof approach (as shown in Figure 9).

Figure 7. Reducing passenger compartmentintrusion in various offset vehicle-to-vehiclecollisions.

Opposite vehicle’sframe

Oppositevehicle’sframe

Small car withnew Structure

Small car withnew structure

Energy absorption inengine compartment

Energy absorption inpassenger compartment

+50%

Small car with new structure

Small car with conventional structure

Front pillardeformation

Dash paneldeformation

Conventional structure New structure

Overlap ratio (%)

Dash panel deformation – Overlap ratio

0 50 100

Conventional structureNew structure

Das

h

�

pane

l

�

defo

rmat

ion

New structure

Conventionalstructure

�30%

Before

After

Before

After

�85%

�40%

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Figure 8. Reducing passenger compartmentintrusion for vehicle-to-vehicle collisions withdiffering bumper height.

Figure 9. Reducing passenger compartmentintrusion for angle of approach in vehicle-to-vehicle collision.

AGGRESSIVENESS

Secondly we give consideration to aggressiveness.As a result of above-mentioned vehicle-to-vehicle

simulations, energy absorption in the enginecompartment has increased slightly and the energyabsorption in the cabin is decreased in large cars withconventional body structures by means of the effectfrom the new structure. It can therefore be predictedthat the new body structure will not increaseaggressiveness towards the partner vehicle in acollision (as shown in Figure 10)�

Figure 10. Improving of energy absorption.

Further we analyzed aggressiveness towards smallcars as follows. We describe the simulation results ina frontal collision between similar small cars A and Bwith conventional structure (case 1), and between asmall car A with conventional structure and a smallcar C with the new proposed structure (case 2)inFigure 11. Opposite car’s intrusion in the passengercompartment was approximately similar in both cases.We could assess that our proposed new structuregreatly improved self-protection, and doesn’t increasethe aggressiveness towards the small car, and wecould find the possibility for compatibility.

Case 1: Frontal collision between similar smallcars with conventional structure

Case 2: Frontal collision between a small car withnew structure and a small car with conventionalstructure

Figure 11. Not increasing aggressiveness to smallcars.

Small car with new structure

Small car with conventional structure

Front pillardeformation

Dash paneldeformation

Conventional structure New structure

Front pillardeformation

Dash paneldeformation

Front pillardeformation

Dash paneldeformation

Case2; Car A to Car Cwith new structure

Large car’s heightshifted 100mm up

Small car withconventional structure

Small car withnew structure

Energy absorption inengine compartment

Energy absorptionin passengercompartment

+5% �10%

Large car tonew structure

Large car toconventionalstructure

Conventionalstructure

New structure

Conventionalstructure

Conventionalstructure

Case1; Car A to Car Bwith conventional structure

Conventional structure New structure

Large car

Large car

Car A

Car A Car C

Car B

�42%

�40%

�66%

�52%

+6%

+6%

Car A;

Car A;

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ACCIDENT ANALYSIS

This time the condition in a vehicle-to-vehicle crashtest was based on the accident analysis in Japan.Some accident data were provided from the Institutefor Traffic Accident Research and Data Analysis(ITARDA) established in 1992.

Almost half of the number of occupant deaths is inthe case of frontal collisions as shown in Figure 12[1].About 90% of the frontal collision deaths were atspeeds lower than 50kph as shown in Figure 13 [1].And when the opposite vehicles are heavier than thesubject vehicles, the driver deaths in frontal collisionsare about 75% as shown in Figure 14 [1]. Withrelation to overlap in frontal collisions, 30% and 50%overlap cases are the primary overlap conditions foroffset collisions (as shown in Figure 15) [1].

For reduction casualties, we would get effective testresults from test condition based on accidentsanalysis.

Figure 12. The collision direction in the fatalaccidents for vehicle-to-vehicle collisions.

Figure 13. Fatal accident speed and percentage infrontal collisions.

Figure 14. Vehicle mass and the driver fatalitiesof subject vehicle in frontal collisions.; a) The opposite vehicle is heavier than the

subject vehicle.; b) The opposite vehicle is lighter than the

subject vehicle.

� Figure 15. Overlap ratio in frontal collisions.

TEST CONDITIONS

� The target in this test is the verification for a smallcar�s self-protection in the conditions based on realworld accidents, especially the improvement ofgeometrical interaction in the frontal structure.

Small car: Prototype model(This time only the ‘Lower member

system’ was added on.)Large car: Conventional modelSpeed: 50kph per carMass : Small car 985kg Large car 1855kgMass ratio: 1.9 (Large car�Small car)Overlap ratio: 50% of small car

The 50% overlap case is the reason that the risk ofinjury is higher than 30%. ( as shown in figure 7)Impact angle is 0°to the car’s longitudinal axis.Figure 16 shows the two cars before the crash test�The main structural layouts of the cars are shown inFigures 17.

etc

43.3 %

11.8 %11.1 %

16.0 % 13.2 %

0.7 %

1.5 %1.0 %1.2%

The statistics on traffic accidents:Death accidents in the common car

Mass of subject vehicle

ab

~1200 1201~1500 1501~1800 1801�0

200

600

1000

1400

(kg)

(person)

Overlap ratio100 90 80 70 60 50 40 30 20 10

10

0

5

15

20

25(%)

(%)

Fata

lacc

iden

t(%

)

40

0

20

60

80

100

20 40 60 80 100

(%)

( kph )Barrier equivalent speed

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Figure 16. Two cars before the crash test.

Bumper heights are approximately the same.

The main frame of the vehicles did not overlap in thedirection of width.

Figure 17. Main structural layout of two cars.

In this test the main frames of the cars did notoverlap in the direction of the cars’ width, and thebumper heights were approximately the same.Dummy: Hybrid�Restraint system: airbag and seat belt pretensionerwith load limiter.

The restraint specification is similar to a small carwithout suitable modification for the change of thevehicle’s deceleration characteristic.

TEST RESULTS

Speed: Small car 50.0kphLarge car 49.9kph

Overlap ratio: 48% of Small carFigure 18 shows two cars after the crash test.

The structural deformation of the small car and thelarge car is shown in Figures 19 and 20 respectively.

The mode of structural deformation in the enginecompartment of the small car during the crash isshown in Figure 21�Figure 22 shows deformation inthe engine compartment of the small car after thecrash.Each part of deformation in both cars is listed inTable 1. Figure 23 shows the velocity change of bothcars.

Figure 18. Two cars after the crash.

Figure 19. Deformation of small car with the newstructure after the crash.

Small car Large car

Small carLarge car

Small carLarge car

Small carLarge car

Small carLarge car

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Figure 20. Deformation of large car after thecrash.

0msec 10msec 38msec

Figure 21. Deformation mode of small car’s newstructure during the crash.

Before the crash After the crash

Figure 22. Deformation of small car in the enginecompartment after the crash.

Table 1. Deformation

Figure 23. Velocity & Deceleration of both cars.

The vehicle-to-vehicle crash test confirmed theeffectiveness of the new design in increasing the levelof self-protection of small cars. The mode ofdeformation on impact confirmed that the bumperbeam and main frame of the large car collided withthe new lower member fitted in the small car.

The lower member restrained intrusion into thesmall car by making contact with the tire and wheel.Intrusion of the passenger compartment was thereforesignificantly reduced and the integrity of the cabinwas maintained for occupants. The large cardeformations in each part were approximately similarwith the small car deformations.

The risk of injury to the small car’s occupants weregenerally low by the prevention of secondarycollisions in the passenger compartment.

The test results show the small car driver’s injuryrisk is higher than the large car driver’s injury risk.The reason is that the small car’s �V[65kph],(namely the velocity change of before and afterimpact) is higher than the large car’s �V[35kph],due to the influence by mass ratio.

CONCLUSION

A small car to large car crash test confirmed that thenew body structure is one of the ways in increasingthe level of self-protection of small cars.

It is very difficult for small vehicles withconventional body designs to maintain cabin integrityin narrow offset collisions and collisions with SUVbecause of the intrusion of the frame of the othervehicle

Small carwith newstructure

Large car

Deformation

Frontpillar(mm)

Dashpanel(mm)

13

114 162

9

Lower member

[G][kph]

0

-50

20 40 60 80 100

time [ms]

�Small car velocity�Small car deceleration

�Large car velocity�Large car deceleration

Vel

ocity

&D

ecel

erat

ion 50

0

V=65kph

V=35kph

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The innovative body structure proposed in thisresearch reduces passenger compartment intrusionand occupant injury by restraining frame intrusionand enabling a high level of energy absorption in theengine compartment�

The structure improves the level of self-protectionin small cars, it is also expected to improve the levelof partner-protection offered by large car. As a furtherstep we are going to research the aggressiveness forlarge cars based on the proposed new structure in thisreport.

Therefore, new design concept in making vehiclesisn’t an individualistic one and doesn’t aim for onlysuperior self-protection. Rather, the concept isharmony with the society of automobiles.

Finally it is hoped that the proposal of this newstructure will trigger further research on bodystructures enabling reduction of traffic accidentcasualties in the future�

REFERENCES

[1] The Annual Reports of Traffic Accident Researchand Data Analysis.1996.ITARDA.