This paper investigates the deploying time (or response time) of an active hood lift system (AHLS) of a passenger vehicle activated bygunpowder actuator. In this work, this is accomplished by changing principal design parameters of the latch part mechanism of thehood system. After briefly introducing the working principle of the AHLS operated by the gunpowder actuator, the governingequations of the AHLS are formulated for each different deploying motion. Subsequently, using the governing equations, theresponse time for deploying the hold lift system is determined by changing several geometric distances such as the distance fromthe rotational center of the pop-up guide to the point of the latch in the axial and vertical directions. Then, a comparison is madeof the total response time to completely deploy the hood lift system with the existing conventional AHLS and proposed AHLS. Inaddition, the workable driving speed of the proposed AHLS is compared with the conventional one by changing the powder volumeof the actuator.
1. Introduction
Because of the increasing awareness of pedestrian safetyand strengthening the related regulations, certain systems toreduce pedestrian injuries and prevent accidents have beengreatly developing in vehicle systems [1–4]. One of advancedsystems to achieve this goal is to use an active hood liftsystem (AHLS) which lifts the hood of an automobile whenthe vehicle collides with the pedestrian [5–9]. The main roleof the AHLS is to absorb the shock that would normally betransmitted to the pedestrian, like an airbag for the driver.In other words, this system makes the available deformationspace of the hood at internal room by raising the hood forprotecting pedestrian from colliding with hard structures likethe engine. In particular, this system greatly reduces an injuryof the pedestrian’s head, which causes themajority of fatalities[10, 11]. It has been reported that when the AHLS is appliedin a head impact test, the head impact performance criterion(HPC), which represents the injury value of the head, canbe reduced by a maximum of 90% [5, 12]. Furthermore, ithas been mathematically assessed that the pedestrian lives ofmaximal 80% could be saved by the AHLS [13]. In the past,the conventional AHLS only raised the hinge part located
at the rear of the hood. However, recently, the latch partlocated at the front of the hood has also been considered tobe important to achieve better performance, especially for thechild pedestrian that collides with front area of hood. In theoperation of the AHLS, the most important factor to save thepedestrian is the developing time (response time) after thefirst collision. Because a sufficient operational speed has notyet been achieved, the operation cannot be completed beforecolliding with the pedestrian’s head. Thus, a slow responsetime may cause a terrible impulse to the pedestrian due tothe kinetic energy of the hood.
Recently, a new AHLS activated by gunpowder wasintroduced, and it was verified that it could be operated at avehicle speed of 60 km/h. In contrast, the conventional AHLSnormally operates at less than 40 km/h. When the drivingspeed is 40 km/h, the time from the first collision to contactwith the hood is about 60ms [14]. It is generally knownthat the sensing time and processing time of an electroniccontrol unit (ECU) are 30ms, and the response time of thehood system is 30ms [15]. But, when the driving speed is60 km/h, the time to contact with the hood is 40ms, and thusthe necessary response time of the AHLS should be sharplydecreased to 10ms. However, in this system, the extremely
Hindawi Publishing CorporationShock and VibrationVolume 2016, Article ID 7589598, 17 pageshttp://dx.doi.org/10.1155/2016/7589598
2 Shock and Vibration
Legform
(a)
Hinge
Latch
(b)
Figure 1: Operation photographs of vehicle equipped with AHLS: (a) before and (b) after actuation.
careful treatment should be given to the increase of workabledriving velocity of the system when the increase of criticaldamage is considered. In the worst case, the collision couldoccur before the operation because of the potential variationin the explosive of the gunpowder actuator, and hence thepedestrian may take damage that surpasses the impact ofvehicle in 60 km/h. This is caused by the kinematic energy ofthe hood system. Therefore, the relationship between severalworkable driving velocities and the deploying time of theactive hood system needs to be investigated. In particular,careful treatment should be given to the design of the latchpart of the AHLS which is crucial for the safety of a childpedestrian. This is because the latch part located in the frontpart of the hood directly affects the response time of theAHLS which is a significant factor in mitigating seriousinjury to a child from the collision. Also, as mentionedearlier, it is very important to study the design parametersof the latch part to reduce the response time in relationto fatal pedestrian accidents because the AHLS can protectpedestrians at a broader range of vehicle speeds by reducingthe response time. Today, there is a sharp increase in thenumber of fatal accidents when the driving speed increases[16, 17]. In addition, it should be noted that lifting the hoodhigher through a shorter time can provide some benefitsby absorbing the impact energy of the pedestrian. In otherwords, a pedestrian is protected more safely from the hardstructure beneath the hood when the hood is lifted higherthrough the response time reduction. Despite the significanceof reducing the response time of the AHLS, the researchreported on this issue is considerably rare.
Consequently, the main technical contributions of thiswork are summarized as follows: (1) the investigation ofgeometrical effects of the latch part mechanism in theAHLS on the deploying time in a collision with a childpedestrian, (2) the investigation of the relationship betweenseveral workable velocities which includeworse circumstancethan conventional regulation in which the child pedestrianshould be saved under the vehicle speed of 40 km/h, (3)the determination of principal geometrical parameters tosignificantly reduce the deploying time, and (4) the demon-stration of the faster deploying time of the proposed methodwith the determined principal geometrical parameters thanthe conventional method. In order to achieve these goals,a mathematical model of the AHLS is firstly formulated
for each deploying motion. In this formulation, the dom-inant design factors of the latch that are sensitive to theperformance index are defined in the governing equationsof motion. In the design process, the structural constraintconditions of the system, such as the limited space, aredefined in detail. Because the response time of the systemis an important factor for reducing a pedestrian’s injuries,the kinematic structure of the AHLS is newly designed todecrease the response time under the imposed constraintconditions. A comparison between the proposed AHLS andthe conventional one is performed in terms of the responsetime. It is shown that the newly designed AHLS gives muchbetter performance than the conventional one showing fasterresponse time at several gunpowder volumes.
2. Working Principle of AHLS
Figure 1 presents photographs showing the real operation ofa passenger vehicle equipped with an AHLS. The vehicle’shood is raised immediately based on the sensor signal whenit collides with an adult legform, as shown in Figure 1(b).The system raises both the front and rear of the hood toreduce the pedestrian impact using the AHLS installed atthe latch and hinge of the hood. The latch part of theAHLS deployed by the gunpowder actuator consists of manyelements named as bracket release, pop-up guide, emergencypawl, and pin striker as shown in Figure 2. It is seen that thevehicle hood can be raised by actuating the vertical motionof the latch part. When the pedestrian’s leg collides with thebumper of the automobile, the actuator is exploded basedon the sensor signal. The emergency pawl has a role ofholding the system and preventing an unexpected release andthe spring affects each element involved in maintaining theordinary position. Figure 3 shows the operation sequence ofthe latch part, which is divided into four steps. The systemoperates sequentially from (A) to (E). These five points serveas the boundaries for the four steps, which are governedby different dynamic equations for the changed structure.Point (A) represents the initial structure that has the firstcontact between actuator and bracket release. At point (B),the pop-up guide meets the latch for the first time. At point(C), the pin striker which rotates with the pop-up guidemeets the emergency pawl. At point (D), the resistanceof the emergency pawl is released. Finally, the operation
Shock and Vibration 3
Table 1: Material properties of AHLS.
Symbol Value Specification𝐼1
4.4 × 10−5m4 Inertia moment of bracket release𝐼2
8.3 × 10−5m4 Inertia moment of pop-up guide𝐼3
5.1 × 10−5m4 Inertia moment of emergency pawl𝐼𝑎
9.8 × 10−4m4 Inertia moment of pop-up guide and pin striker, which rotate together after point (B)𝐾1
1 Nm/rad Spring coefficient of spring installed at bracket release𝐾2
1 Nm/rad Spring coefficient of spring installed at pop-up guide𝐾3
3Nm/rad Spring coefficient of spring installed at emergency pawl𝜇𝑎
0.16 Coefficient of rolling friction𝜇𝑏
0.3 Friction coefficient𝑚 6.67 kg Mass of hood that is lifted at latch part
Bracket release
Pop-up guide
Emergency pawl
Latch part
Pin striker
Actuator
Figure 2: Schematic configuration of AHLS.
is completed at point (E). In order to make it easier tounderstand the working principle, the operation sequenceof a performance evaluation test of a conventional AHLS isshown in Figure 4. It is clearly seen from the photographthat the height of the hood increases as time goes on. Thewhite triangle indicates lifted height of the latch part while theblack triangle indicates the original location. As shown in thefigure, the latch part that is directly connected to the hood islifted over the time. In this test, the system has a final heightof 30mm, and the operation is completed about 10ms afterthe actuator operates. The actuator is operated by a microgas generator (MGG) that quickly generates a large quantityof gas from the gunpowder. This system uses an MGG thatproduces a pressure of 35MPa in a 10 cc volume when timepasses 10ms after the gunpowder is exploded.
3. Dynamic Equations
The governing equations of motion for the deployment of theAHLS are derived in order to determine the operating speed
and response time. The geometric structure of the AHLSchanges over time. Hence, the dynamic equation also changesover time. Therefore, the whole operation is divided intofour steps with the boundary points shown in Figure 3. Theoperation that occurs from point (A) to point (B) in Figure 3is step 1. The operation from point (B) to point (C) is step2. The operation from point (C) to point (D) is step 3. Theoperation from point (D) to point (E) is the last step, step4. The material properties used in this work are presented inTable 1. The mass of the hood that is lifted at the total systemis about 16 kg. However, the system raises both the front andrear of the hood installed at the latch and hinges of the hood.Because of the distance from the center ofmass of the hood toeach place installed, the mass of the hood applied to the latchsystem is about 6.67 kg.
The actuator force that is transmitted to the bracketrelease is set at 𝐹
1in this work. The value of 𝐹
1depends on
the deployed distance of the actuator and an internal volumechange due to this deployed distance. As previously men-tioned, the actuator force comes from an internal pressurechange by the MGG. Figure 5(a) shows the pressure changeof 35 MPaMGG in a 10 cc volume, and Figure 5(b) shows theinternal pressure change of the actuator, in which the initialinternal volume of the actuator (660mm3) is applied. On theother hand, Figure 6 shows the actuator force with no volumechange, which is represented by multiplying a cross-sectionalarea of the actuator (38.5mm2) by its internal pressure changewith a fixed initial volume. Consequently, the real actuatorforce𝐹
1can be solved using the actuator forcewith no volume
change and the volume change of the actuator over time.Thevolume change of the actuator is presented by multiplying itscross-sectional area and the deployed distance by the timethat is represented by the entire distance 𝑅
1and 𝜃
1which is
the rotated angle of the bracket release as shown in Figure 7.Thus, the real transmitted force and changed internal volumeof the actuator are, respectively, defined as follows:
Real Transmitted Force
=Actuator Force × Initial Internal Volume of Actuator
Changed Internal Volume of Actuator,
Changed Internal Volume of Actuator
= Initial Volume + 𝑅1× sin (𝜃
1(𝑡)) × 𝐴.
(1)
4 Shock and Vibration
Table 2: Variables for equation distances.
Symbol Specification𝑟11
Distance for moment transmitted to bracket release by actuator force𝑟12
Distance for moment transmitted to bracket release by reaction of pop-up guide𝑟21
Distance for moment transmitted to pop-up guide by force of bracket release𝑟22
Distance for moment transmitted to pop-up guide by reacted force of latch part𝑟23
Distance for moment transmitted to pop-up guide by reaction of emergency pawl𝑟24
Distance for moment transmitted to pop-up guide by reacted force of pin striker𝑟31
Distance for moment transmitted to emergency pawl by force of pop-up guide𝑟32
Distance for moment transmitted to emergency pawl by force of pin striker𝑟𝑓1
Distance for moment transmitted to bracket release by friction force between bracket release and pop-up guide𝑟𝑓2
Distance for moment transmitted to pop-up guide by friction force between bracket release and pop-up guide𝑟𝑓3
Distance for moment transmitted to pop-up guide by friction force between pop-up guide and emergency paw𝑟𝑓4
Distance for moment transmitted to pop-up guide by friction force between pop-up guide and pin striker𝑟𝑓5
Distance for moment transmitted to emergency pawl by friction force between pop-up guide and emergency pawl𝑟𝑓6
Distance for moment transmitted to emergency pawl by friction force between pin striker and emergency pawl
(D) (E)
(A) (B) (C)
Figure 3: Operation sequence of AHLS for latch part.
In the above, 𝐴 is the cross-sectional area of the actuator(38.5mm2) and 𝑅
1is 42mm. It is clearly seen that the real
actuator force 𝐹1is a function of 𝜃
1.
The distances of the elements denoted to formulate thedynamic equations using the variables 𝑟
11, 𝑟12, 𝑟21, 𝑟22, 𝑟23,
𝑟24, 𝑟31, 𝑟32, 𝑟𝑓1, 𝑟𝑓2, 𝑟𝑓3, 𝑟𝑓4, 𝑟𝑓5, and 𝑟
𝑓6are presented in
Table 2. It should be noted here that all the distances used toset up the dynamic equations are called “equation distances.”Here, 𝑟
23, 𝑟𝑓3, 𝑟𝑓4, and 𝑟
𝑓6are a fixed value and each value
has 22mm, 74mm, 18mm, and 18mm, respectively. And the
Shock and Vibration 5
0ms 2ms
4ms 6ms
8ms 10ms
Figure 4: Sequence photographs of performance evaluation test at 35MPa MGG.
0
10
20
30
40
Pres
sure
(MPa
)
0.005 0.010 0.015 0.0200.000Time (s)
(a)
0
200
400
600
Pres
sure
(MPa
)
0.005 0.010 0.015 0.0200.000Time (s)
(b)
Figure 5: Pressure change byMGGs with different volumes: (a) pressure change of 35 MPaMGGwith 10 cc volume and (b) internal pressurechange of actuator with initial volume of 600mm3.
6 Shock and Vibration
0.005 0.010 0.015 0.0200.000Time (s)
0
5
10
15
25
20
Forc
e (N
)
×103
Figure 6: Actuator force without volume change.
values of distances to calculate the moment of components,which change over time, are given as follows:
𝑟11(𝑡) = 𝑙
11sin (45∘ + 0.44𝜃
1(𝑡)) ,
𝑟12𝐴(𝑡) = 𝑙
12cos (28∘ − 𝜃
1(𝑡) − 𝜃
2(𝑡)) ,
𝑟12𝐵(𝑡) = 𝑙
12cos (𝜃
1(𝑡)) ,
𝑟21𝐴(𝑡) = 32 − 7(
𝑥virtual (𝑡)
8) ,
𝑟21𝐵(𝑡) = 25 − 3 (
𝑥 (𝑡)
6) ,
𝑟21𝐶(𝑡) = 𝑙
21cos (28∘ − 𝜃
2(𝑡)) ,
𝑟22(𝑡) =
𝑙22cos (3∘)
cos (17∘ − 𝜃2(𝑡)),
𝑟24(𝑡) = 𝑙
24sin (55∘ + 𝜃
2(𝑡) − 𝜃
3(𝑡)) ,
𝑟31(𝑡) = 19 − 11 (
𝑥virtual (𝑡)
8)mm,
𝑟32(𝑡) = 16 − 8 (
𝑥 (𝑡)
4)mm,
𝑟𝑓1𝐴(𝑡) = 𝑠
𝑎− 𝑙12sin (28∘ − 𝜃
1(𝑡) − 𝜃
2(𝑡)) ,
𝑟𝑓1𝐵(𝑡) = 𝑠
𝑎+ 𝑙12sin (𝜃1(𝑡)) ,
𝑟𝑓2𝐵(𝑡) = 𝑠
𝑏− 𝑙21cos (29∘ − 𝜃
2(𝑡)) ,
𝑟𝑓5(𝑡) = 𝑙
24cos (55∘ + 𝜃
2(𝑡) − 𝜃
3(𝑡)) .
(2)
Because bracket release and pop-up guide make a contactthrough the circle to circle after step 2, several distances arepresented differently after step 2. 𝑟
12is presented by 𝑟
12𝐴until
step 2 and 𝑟12𝐵
after step 2. And 𝑟21is presented by 𝑟
21𝐴and
𝑟21𝐵
in step 1 and step 2, respectively, and 𝑟21𝐶
after step 2. 𝑟𝑓1
and 𝑟𝑓2
are presented by 𝑟𝑓1𝐴
and 𝑟𝑓2𝐴
until step 2 and 𝑟𝑓1𝐵
and 𝑟𝑓2𝐵
after step 2. 𝑟𝑓2𝐴
has a fixed value, 24mm. 𝑟11
canbe presented through the sine value of the rotational angle ofthe vertical line on the contact surface of actuator and bracketrelease to express the change over time. And 𝑙
11is the distance
from the center of arc to the rotational center of bracketrelease, and the value of 𝑙
11is 47mm. Similarly, the distance
of 𝑟12𝐴
can be presented through the cosine value of therotational angle of the vertical line on the contact surface ofbracket release and pop-up guide. And 𝑙
12is the distance from
the center of arc that indicates contact line of bracket releaseand pop-up guide to rotational center of bracket release, andthe value of 𝑙
12is 23mm. As mentioned, because bracket
release and pop-up guide make a different contact, 𝑟12𝐵
canbe presented through the cosine value of the rotational angleof bracket release. The distance of 𝑟
21𝐴is decreased by 7mm
from the 32mm, while 𝑥virtual is increased by 8mm. Here,𝑥virtual is the reduced distance from the surface of pop-upguide to latch in vertical direction by the rotation of pop-up guide in step 1. In the same way, the distance of 𝑟
21𝐵is
decreased by 3 from 25, while 𝑥 that is the lifted distance oflatch is increased by 6mm. 𝑟
21𝐶can be presented by 𝑙
21that is
the distance from the center of arc that indicates contact lineof pop-up guide to rotational center of pop-up guide. Andthe value of 𝑙
21is 25mm. 𝑟
22can be presented by 𝑙
22that is
the distance from the rotational center of pop-up guide tothe latch in horizontal direction, and 𝑟
24can be presented
by 𝑙24
that is the distance from the rotational center of pop-up guide to the end point of the pop-up guide. And thevalues of 𝑙
22and 𝑙24
are 53 and 81mm. The distance of 𝑟31
isdecreased by 11 from 19, while 𝑥virtual is increased by 8mm,and 𝑟32
is decreased by 16 from 18, while 𝑥 is increased by6mm. And 𝑟
𝑓1𝐴and 𝑟𝑓1𝐵
can be presented by 𝑙12. 𝑟𝑓2𝐵
and𝑟𝑓5
can be presented by 𝑙21and 𝑙24, respectively. Here, 𝑠
𝑎is the
radius of arc which is the contact surface of bracket releasebetween bracket release and pop-up guide, and the value of𝑠𝑎is 21mm. 𝑠
𝑏is the radius of arc that is contact surface of
pop-up guide between bracket release and pop-up guide, andthe value of 𝑠
𝑏is 10mm.
All the variables used for dynamic equations derived todetermine the response time and velocity at each step arepresented in Table 3. Figure 8 shows a free body diagram forsolving the moment using the force and friction force at step1. Figure 8(a) presents a free body diagram showing the forcesof the bracket release and Figure 8(b) presents a free bodydiagram showing the friction force of the bracket release.Based on these free body diagrams, the dynamic equation ofthe bracket release at step 1 is derived using the sum of themoments, as given in (3).
Because the actuator is not initially in contact with thebracket release, the short deployed time of the actuator fromthe initial state to point (A) exists. So that is consideredto apply 𝐹
1to derive the dynamic equation accurately and
that time is 0.2ms. And the initial spring torque of thebracket release is 1 Nm. Figure 8(c) presents a free bodydiagram showing the forces of the pop-up guide at step 1, andFigure 8(d) presents a free body diagram showing the frictionforce of the pop-up guide at step 1. Similarly, the dynamicequation for the pop-up guide at step 1 is derived as given in(4). And the initial spring torque of the pop-up guide is 1 Nm.
Shock and Vibration 7
Table 3: Variables used in dynamic equation.
Symbol Specification𝜃1
Rotated angle of bracket release𝜃2
Rotated angle of pop-up guide𝜃3
Rotated angle of emergency pawl𝐹1
Force transmitted by actuator to bracket release𝐹2
Force transmitted by bracket release to pop-up guide𝐹3
Force transmitted by pop-up guide to latch𝐹5
Force transmitted by pop-up guide to emergency pawl𝐹6
Force transmitted by pin striker to emergency pawl
𝐹𝑓1
Friction force between bracket release and pop-up guide, which is represented by multiplying rolling frictioncoefficient 𝜇
𝑎and the normal force 𝐹
2
𝐹𝑓2
Friction force between pop-up guide and emergency pawl, which is represented by multiplying the slidingfriction coefficient 𝜇
𝑏and normal force 𝐹
5
𝐹𝑓3
Friction force between pin striker and emergency pawl, which is represented by multiplying the sliding frictioncoefficient 𝜇
𝑏and normal force 𝐹
6
Deployed distance
𝜃1
R1
R1
Figure 7: Schematic diagram of deployed distance of actuator.
Figure 8(e) presents a free body diagram showing the forcesof the emergency pawl and Figure 8(f) presents a free bodydiagram showing the friction force of the emergency pawl atstep 1.Then, the dynamic equation for the emergency pawl atstep 1 is derived as given in (5). And its initial spring torqueis 3Nm. On the other hand, (6) is the geometrical relationbetween 𝜃
1and 𝜃2and (7) is the geometric relation between 𝜃
2
and 𝜃3. Asmentioned before, the distances 𝑟
11, 𝑟12, 𝑟21, 𝑟22, 𝑟23,
𝑟24, 𝑟31, 𝑟32, 𝑟𝑓1, 𝑟𝑓2, 𝑟𝑓3, 𝑟𝑓4, 𝑟𝑓5, and 𝑟
𝑓6are the distances used
to calculate the moments transmitted by each force. Now, theunknown quantities of 𝜃
1, 𝜃2, 𝜃3, 𝐹2, and 𝐹
5can be solved
using the following five dynamic equations at step 1:
𝐼1𝜃1(𝑡) = 𝑟
11𝐹1(𝑡 + 0.0002) − 𝑟
12𝐹2(𝑡) − 𝑟
𝑓1𝐹𝑓1(𝑡)
− 𝐾1𝜃1(𝑡) − 1,
(3)
𝐼2𝜃2(𝑡) = 𝑟
21𝐹2(𝑡) − 𝑟
23𝐹5(𝑡) + 𝑟
𝑓2𝐹𝑓1(𝑡) − 𝑟
𝑓3𝐹𝑓2(𝑡)
− 𝐾2𝜃2(𝑡) − 1,
(4)
𝐼3𝜃3(𝑡) = 𝑟
31𝐹5(𝑡) − 𝑟
𝑓4𝐹𝑓2(𝑡) − 𝐾
3𝜃3(𝑡) − 3, (5)
𝜃2(𝑡) =𝑟12
𝑟21
𝜃1(𝑡) , (6)
𝜃3(𝑡) =𝑟23
𝑟31
𝜃2(𝑡) . (7)
In the above, 𝜇𝑎is the coefficient of rolling friction and 𝜇
𝑏is
the sliding friction coefficient. The solutions obtained at thisstage indicate the finish time and final angle velocity of step1, and hence they become the initial conditions of step 2.
Figure 9 shows a free body diagram for solving themoment at step 2. Figure 9(a) presents a free body diagramshowing the forces of the bracket release and Figure 10(b)presents a free body diagram showing the friction forceof the bracket release at step 2. Figure 10(c) presents afree body diagram showing the forces of the pop-up guideand Figure 10(d) presents a free body diagram showing thefriction force of the pop-up guide at step 2. Similar to step1, the dynamic equations at step 2 are derived from the freebody diagrams as follows:
𝐼1𝜃1(𝑡) = 𝑟
11𝐹1(𝑡 + 0.0002 + 𝜏
1) − 𝑟12𝐹2(𝑡)
− 𝑟𝑓1𝐹𝑓1(𝑡) − 𝐾
1(𝜃1(𝑡) + 𝜔
11) − 1,
(8)
𝐼𝑎𝜃2(𝑡) = 𝑟
21𝐹2(𝑡) − 𝑟
22𝐹3(𝑡) + 𝑟
𝑓2𝐹𝑓1(𝑡)
− 𝐾2(𝜃2(𝑡) + 𝜔
12) − 1,
(9)
𝑚�� (𝑡) = cos (20∘ − 𝜃2(𝑡)) 𝐹3(𝑡) , (10)
𝜃2(𝑡) =𝑟12
𝑟21
𝜃1(𝑡) , (11)
8 Shock and Vibration
r12
r11
F2
F1
(a)
Ff1
rf1
(b)
r21 r23
F2F5
(c)
rf3
rf2
Ff1
Ff2
(d)
r31
F5
(e)
Ff2
rf4
(f)
Figure 8: Free body diagram for solving moment at step 1: (a) free body diagram showing forces of bracket release, (b) free body diagramshowing friction force of bracket release, (c) free body diagram showing forces of pop-up guide, (d) free body diagram showing friction forcesof pop-up guide, (e) free body diagram showing force of emergency pawl, and (f) free body diagram showing friction force of emergencypawl.
Shock and Vibration 9
r12
r11
F2
F1
(a)
Ff1
rf1
(b)
r12
r22
F2
F3
(c)
Ff1
rf2
(d)
Figure 9: Free body diagram for solving moment at step 2: (a) free body diagram showing forces of bracket release, (b) free body diagramshowing friction force of bracket release, (c) free body diagram showing forces of pop-up guide by force, and (d) free body diagram showingfriction force of pop-up guide showing force of emergency pawl.
�� (𝑡) = cos (20∘ − 𝜃2(𝑡)) 𝑟22𝜃2(𝑡) . (12)
In the above, 𝜏1is the finish time of step 1. 𝜔
11and 𝜔
12are
final angles of bracket release and pop-up guide in step 1.It should be noted that (8) is the dynamic equation of thebracket release. Equation (9) is the dynamic equation of thepop-up guide, and (10) is the dynamic equation of the latch.Equation (11) is the geometric relation between 𝜃
1and 𝜃
2at
this step, and (12) is the geometric relation between 𝜃2and 𝑥
at step 2.Similar to steps 1 and 2, the dynamic equations for steps
3 and 4 are derived from the free body diagrams shown inFigures 10 and 11. The derived equations are given as follows.
Step 3. Consider
𝐼1𝜃1(𝑡) = 𝑟
11𝐹1(𝑡 + 0.0002 + 𝜏
1+ 𝜏2) − 𝑟12𝐹2(𝑡)
− 𝑟𝑓1𝐹𝑓1(𝑡) − 𝐾
1(𝜃1(𝑡) + 𝜔
11+ 𝜔21)
− 1,
(13)
𝐼𝑎𝜃2(𝑡) = 𝑟
21𝐹2(𝑡) − 𝑟
22𝐹3(𝑡) − 𝑟
24𝐹6(𝑡) + 𝑟
𝑓2𝐹𝑓1(𝑡)
− 𝑟𝑓5𝐹𝑓3(𝑡) − 𝐾
2(𝜃2(𝑡) + 𝜔
12+ 𝜔22)
− 1,
(14)
𝐼3𝜃3(𝑡) = 𝑟
32𝐹6(𝑡) − 𝑟
𝑓6𝐹𝑓3(𝑡) − 𝐾
3(𝜃3(𝑡) + 𝜔
13)
− 3,
(15)
𝑚�� (𝑡) = cos (20∘ − 𝜃2(𝑡) − 𝜔
22) 𝐹3(𝑡) , (16)
𝜃2(𝑡) =𝑟12
𝑟21
𝜃1(𝑡) , (17)
𝜃3(𝑡) =𝑟23
𝑟31
𝜃2(𝑡) , (18)
�� (𝑡) = cos (20∘ − 𝜃2(𝑡) − 𝜔
22) 𝑟22𝜃2(𝑡) . (19)
10 Shock and Vibration
r12
r11
F2
F1
(a)
Ff1
rf1
(b)
r21
r22
r24
F2F3
F6
(c)
rf5
rf2
Ff1
Ff3
(d)
r32
F6
(e)
Ff3
rf6
(f)
Figure 10: Free body diagram for solving moment at step 3: (a) free body diagram showing forces of bracket release, (b) free body diagramshowing friction force of bracket release, (c) free body diagram showing forces of pop-up guide, (d) free body diagram showing friction forcesof pop-up guide, (e) free body diagram showing force of emergency pawl, and (f) free body diagram showing friction force of emergencypawl.
Shock and Vibration 11
r12
r11F2
F1
(a)
Ff1
rf1
(b)
r21
r22
F2
F3
(c)
rf2
Ff1
(d)
Figure 11: Free body diagram for solving moment at step 4: (a) free body diagram showing force of bracket release, (b) free body diagramshowing friction force of bracket release, (c) free body diagram showing force of pop-up guide by force, and (d) free body diagram showingfriction force of pop-up guide.
Step 4. Consider
𝐼1𝜃1(𝑡) = 𝑟
11𝐹1(𝑡 + 0.0002 + 𝜏
1+ 𝜏2+ 𝜏3) − 𝑟12𝐹2(𝑡)
− 𝑟𝑓1𝐹𝑓1(𝑡)
− 𝐾1(𝜃1(𝑡) + 𝜔
11+ 𝜔21+ 𝜔31) − 1,
(20)
𝐼𝑎𝜃2(𝑡) = 𝑟
21𝐹2(𝑡) − 𝑟
22𝐹3(𝑡) + 𝑟
𝑓2𝐹𝑓1(𝑡)
− 𝐾2(𝜃2(𝑡) + 𝜔
12+ 𝜔22+ 𝜔32) − 1,
(21)
𝑚�� (𝑡) = cos (20∘ − 𝜃2(𝑡) − 𝜔
22− 𝜔32) 𝐹3(𝑡) , (22)
𝜃2(𝑡) =𝑟12
𝑟21
𝜃1(𝑡) , (23)
�� (𝑡) = cos (20∘ − 𝜃2(𝑡) − 𝜔
22− 𝜔32) 𝑟22𝜃2(𝑡) . (24)
In the above, 𝜏2is the finish time of step 2 and 𝜏
3is the finish
time of step 3. 𝜔13
is final angles of emergency pawl in step1. 𝜔21
and 𝜔22
are final angles of bracket release and pop-up
guide in step 2. And 𝜔31
and 𝜔32
are final angles of bracketrelease and pop-up guide in step 3. It should be noted that(17) is the geometric relation between 𝜃
1and 𝜃
2, and (18) is
the geometric relation between 𝜃2and 𝜃3at step 3. And (19)
is the geometric relation between 𝜃2and 𝑥 at step 3. Similarly,
(23) is the geometric relation between 𝜃1and 𝜃
2, and (24) is
the geometric relation between 𝜃2and 𝑥 at step 4.
Figure 12 shows a flowchart that presents a specificmethod for solving the response time of the system usingthe derived dynamic equations. The final force, final anglevelocity, and final position of the previous step become theinitial conditions of the next step. The finish time of eachstep is defined as the time that the dynamic motion satisfiesa particular condition of the step. The condition is set up asa function of 𝑥virtual or the lifted height of the hood, 𝑥. Step 1is completed when 𝑥virtual increases by 8mm from point (A),and the operation reaches point (B) in Figure 3. That time isdefined as the finish time of step 1, 𝜏
1. Step 2 is completed
when 𝑥 increases by 6mm from point (B) and the operationreaches point (C). That time is defined as the finish time of
12 Shock and Vibration
Point (A): start point
Division 1: (3), (4), (5), (6), and (7)
Division 2: (8), (9), (10), (11), and (12)
Division 3: (13), (14), (15), (16), (17), (18), and (19)
Division 4: (20), (21), (22), (23), and (24)
𝜏1
𝜏2
𝜏3
𝜏4
xvirtual is increased by 6mm to point (B)Point (B):
x is increased by 6mm to point (C)Point (C):
x is increased by 4mm to point (D)Point (D):
x is increased by 20mm to point (E)Point (E):
Figure 12: Flowchart for solving response time.
step 2, 𝜏2. Step 3 is completedwhen 𝑥 increases by 4mm from
point (C) and the operation reaches point (D). That time isdefined as the finish time of step 3, 𝜏
3. Step 4 is completed
when 𝑥 increases by 20mm from point (D) and the operationreaches point (E). That time is defined as the finish time ofstep 4, 𝜏
4. In addition, as mentioned earlier the deployed
time of the actuator from the initial state to point (A) shouldbe considered. That time is defined as 𝜏
0. Consequently, the
sum of the finish times of the steps and initial deployedtime of actuator becomes the total response time of thesystem.
4. Parametric Investigation
The main elements adjusted to reduce the response timedenoted as 𝑅
1, 𝑅2, 𝑅3, 𝑅4, 𝑅5, and 𝑅
6are shown in Figure 13
and presented in Table 4. All of the distances to be adjustedfor the new design are called “entire distances,” and those dis-tances are directly related to “equation distances.” Therefore,the new distance can be found by changing the percentageof the entire distance and comparing the response time. Theresponse time can be found using the flowchart shown inFigure 12, which is associated with the dynamic equations. Inthis work, the influence on the response time is investigatedby changing the entire distance by −20%, −10%, +10%, and
R1
R2
R3
R4
R5
R6
Figure 13: Distances of elements to be adjusted to reduce responsetime.
+20%, as given in Table 5. 𝑅1, 𝑅2, and 𝑅
4have dominant
influences, whereas the other distances have only slightinfluences on the response time.The response time decreaseswith increasing 𝑅
1and 𝑅
4and with decreasing 𝑅
2and 𝑅
4.
Therefore, suitable 𝑅1, 𝑅2, and 𝑅
4values should be suggested
to reduce the response time.In the practical application of the AHLS, several geomet-
ric constraint conditions exist. First, because of the internaldistance limitation of the car, the maximum distances in𝑥 and 𝑦 directions should be constrained. In this work,the maximum 𝑥-direction distance of the internal spaceis considered to be 125mm and that in the 𝑦 directionis 120mm. The entire distance should satisfy this space-constraint condition. In this case, 𝑅
1, which is the distance in
the vertical direction, can be increased by 48%maximally andshould not exceed 62mm. 𝑅
2and 𝑅
4are distances in the hor-
izontal direction, and their sum should not exceed 115.1mmbecause of the space-constraint condition. 𝑅
3should not
exceed 82.6mm to satisfy the constraint. Specifically, theconstraint conditions of 𝑅
2, 𝑅3, and 𝑅
4are caused by the
existence of the emergency pawl and pin striker. It shouldbe noted here that none of the numerical values used inthis work are directly related to a certain car. Second, theheight to be reached by the AHLS should be constrainedusing the geometric conditions of 𝑅
2, 𝑅3, and 𝑅
4. When the
pop-up guide rotates until the operation is completed, thefinal height to be raised and distance 𝑅
3can have a geometric
relation, as shown in Figure 14(a), which is expressed inmathematical terms by (25). When 𝑅
3is decreased to achieve
better performance, the rotated angle 𝜃𝑓2
should be increasedto maintain the fixed height. However, an increase in 𝜃
𝑓2
may cause a delay in the response time.Thus, suitable 𝑅3and
𝜃𝑓2
values should be found to satisfy the imposed geometricconditions.
In this work, the original height value is set at 30mm, andthe value of angle 𝑘 is 0.35 rad, which is the initial angle ofthe pop-up guide between the 𝑥-axis at point (B). 𝑅
2, 𝑅4, and
Shock and Vibration 13
Table 4: Variables for entire distances.
Symbol Specification𝑅1
Distance from rotational center of bracket release to bottom of bracket release in vertical direction𝑅2
Distance from rotational center of bracket release to end point at lift side of bracket release in horizontal direction𝑅3
Distance from rotational center of pop-up guide to a point on latch part in the horizontal direction𝑅4
Distance from rotational center of pop-up guide to contact point with bracket release in the horizontal direction𝑅5
Distance from rotational center of pop-up guide to end point of pop-up guide𝑅6
Distance from rotational center of emergency pawl to contact point with pop-up guide
𝜃f2
R3
Heightk
(a) Geometric relation of height, 𝑅3, and 𝜃𝑓2
d
1.21R4
𝜃f20.8R2
(b) Geometric relation of 𝑅2, 𝑅4, and 𝜃𝑓2
Figure 14: Geometric relation of height and dominant distance.
Table 5: Response time due to change in entire distance.
−20% −10% 0% +10% +20%𝑅1
10.7ms 10.4ms 10.2ms 10.0ms 9.8ms𝑅2
9.8ms 10.0ms 10.2ms 10.3ms 10.5ms𝑅3
10.1ms 10.1ms 10.2ms 10.2ms 10.3ms𝑅4
10.6ms 10.4ms 10.2ms 10.0ms 9.8ms𝑅5
10.1ms 10.2ms 10.2ms 10.2ms 10.2ms𝑅6
10.1ms 10.2ms 10.2ms 10.2ms 10.2ms
𝜃𝑓2
also have a geometric relation, as shown in Figure 14(b),which simplifies the bracket release and pop-up guide at point(E), as shown in Figure 3. When the operation is finished,the final angle of the pop-up guide is represented by 𝑅
2
value that is 20% smaller and 𝑅4value that is 21% larger.
Because of the thickness of the bracket release, its rotationalcenter is located at a position that is lower than the initialposition of the pop-up guide.When𝑅
4is increased to achieve
a suitable design, 𝑅2also increases, because the changing rate
of 𝑅4is proportional to that of 𝑅
2to maintain a fixed value.
However, increasing𝑅2may cause a delay in the operation. To
reduce the response time, suitable 𝑅2and 𝑅
4values should
be found that satisfy the geometric conditions. The relationof 𝑅2, 𝑅4, and 𝜃
𝑓2is mathematically expressed by (26), and
the geometric condition of 𝑅2, 𝑅3, and 𝑅
4is given by (27). It
should be noted that the distance value of 13mm is chosen for𝑑 in this work
𝑅3=
heighttan (𝑘) + tan (𝜃
𝑓2− 𝑘), (25)
𝜃𝑓2= tan−1 (
(0.8𝑅2− 𝑑)
1.21𝑅4
) , (26)
𝑅3
=30mm
tan (0.35) + tan (tan−1 ((0.8𝑅2− 13mm) /1.21𝑅
4) − 0.35)
.(27)
5. Results and Discussions
A preferable structure for the AHLS to reduce the responsetime can be achieved by adjusting the dominant designfactors. First, the suitable distances of 𝑅
2, 𝑅3, and 𝑅
4are
obtained based on the imposed geometric constraints. Thechanging rate of 𝑅
3can be found by changing 𝑅
2and 𝑅
4
using (27), and this variation can be applied to the dynamicequation. 𝑅
2and 𝑅
4are changed by −20%, −10%, +10%, and
+20% to investigate the influences on distance 𝑅3and the
response time, and the results are presented in Table 6. Theresults show that the response time decreases by decreasing𝑅2and increasing 𝑅
4. It is also shown that 𝑅
3increases
by decreasing 𝑅2and increasing 𝑅
4. Consequently, in order
to achieve a better performance in terms of the responsetime, 𝑅
3should be increased maximally. When 𝑅
3increases
maximally while satisfying the geometric condition, 𝑅3can
be increased by 57.6%. When 𝑅3increases by 57.6%, 𝜃
𝑓2
becomes 0.351 rad from (25).Then, themathematical relationbetween 𝑅
2and 𝑅
4can be expressed by (26). Therefore, the
changing rate of 𝑅2and the response time can be obtained
by changing 𝑅4. The influences on the response time and
𝑅2of changing 𝑅
4by −10%, +10%, +20%, +30%, +40%,
and +50% are presented in Table 7. It can be seen that the
14 Shock and Vibration
Table 6: Changing rate of 𝑅3and response time due to changes in 𝑅
response time is decreased by increasing 𝑅4, regardless of 𝑅
2.
Consequently, 𝑅4should be increased maximally to reduce
the response time while satisfying the geometric condition. Itcan be increased by 85.9%, and 𝑅
2can be increased by 5.1%,
based on the geometric relation. As𝑅1increases, the response
time decreases according to Table 5. Thus, in order to obtaina better performance, 𝑅
1should be increased maximally.
𝑅1can be increased by 18% and still satisfy the geometric
condition.The dominant factors for reducing the response time can
be checked based on the results of the previously discussedparameter studies. 𝑅
1increases by 48%, 𝑅
2increases by
39.5%, 𝑅3increases by 58.8%, and 𝑅
4increases by 190.2%.
In other words, 𝑅1increases from 42 to 62mm, 𝑅
2increases
from 37 to 51.6mm, 𝑅3increases from 52 to 82.6mm, and 𝑅
4
increases from 22 to 63.8mm. So it has been demonstratednumerically through computer simulations that the proposedAHLS with the new design parameters provides a betterperformance than the conventional one in terms of the totalresponse time, and the comparison results are presented inTable 8. The response time of the existing AHLS structureis 10.2ms at 35 MPa MGG, which is very similar to theperformance evaluation test result (10ms) shown in Figure 4.It is seen from the table that the response time of the newlydesigned AHLS structure is 8.6ms which is faster than theexisting one. In addition, it is seen that when a 30 MPaMGG is used, the response time is reduced from 10.8 to9.1ms by the new design. In addition, when a 25MPa MGGis used, the response time is reduced from 11.7 to 9.8ms.As previously stated, the response time reduction is directlyrelated to being able to operate at a high vehicle driving speed.Table 9 presents the workable driving speeds of vehicles whenthe response time of the AHLS is reduced based on thiswork. The workable driving speed is increased from 59.2 to61.6 km/h when the new design is applied to the AHLS withan actuator that uses a 35 MPa MGG. It is also noticed from
the table that the workable driving speed is increased from58.3 to 60.8 km/h and from 57.2 to 59.8 km/h, with actuatorsthat use a 25 MPa MGG and 15 MPa MGG, respectively. Thisincrement of workable driving speed directly indicates theeffectiveness of the proposed AHLS which can significantlyreduce the collision injuries due to the fast deployment ofthe hood at higher vehicle speed. It is here remarked that theresponse time evaluated in this work indicates mechanicalresponse time only after electronic processing.
6. Conclusion
In this work, a new geometrical design of an AHLS activatedby a gunpowder actuator has been achieved to reduce theresponse time, which is directly related to the impact forceto pedestrians during a collision. In order to accomplish thisgoal, the governing equations of motion at different deploy-ment steps were derived from a free body diagram. Subse-quently, a flowchart to calculate the total response time forthe full deployment was made. After carefully investigatingthe influences of the design parameters on the response time,new values for the principal design parameters that couldprovide a faster response time were chosen with satisfyingthe geometric constraints. It has been demonstrated througha computer simulation that the proposed AHLS with thenew design parameters provides a better performance thanthe conventional one in terms of the total response time. Inaddition, it has been observed that the response time canbe shortened by changing the volume of gunpowder. Thisdirectly indicates that the response time of the AHLS canbe shortened through both the actuator capacity (gunpowdervolume) and geometric values. It is finally remarked that asolid analytical model integrated with optimization methodsuch as a genetic algorithm will be developed as a secondphase of this work in order to further reduce the responsetime of the AHLS to be deployed by the gunpowder actuator.
Shock and Vibration 15
Table 8: Comparison of response times of existing AHLS and newly designed AHLS with different actuator specifications.
Existing system (ms) Newly designed system (ms)
35 MPa MGG
𝜏0
0.2 0.2𝜏1
0.7 0.6𝜏2
3.9 2.8𝜏3
1.3 1.2𝜏4
4.1 3.8Total response time 10.2 8.6
30 MPa MGG
𝜏0
0.2 0.2𝜏1
0.8 0.6𝜏2
4.1 3.0𝜏3
1.4 1.3𝜏4
4.3 4.0Total response time 10.8 9.1
25 MPa MGG
𝜏0
0.3 0.3𝜏1
0.9 0.6𝜏2
4.4 3.2𝜏3
1.5 1.4𝜏4
4.6 4.3Total response time 11.7 9.8
Table 9: Workable driving speeds of existing AHLS and newlydesigned AHLS with different actuator specifications.
𝑑: Distance for boundary condition due tothickness of bracket release (mm)
𝑘: Initial angle of the pop-up guide between𝑥-axis at point (B) (rad)
𝑙11: Distance from the center of arc thatindicates the contact surface of bracketrelease between actuator and bracketrelease to the rotational center of bracketrelease (mm)
𝑙12: Distance from the center of arc thatindicates contact surface of bracket releasebetween bracket release and pop-up guideto rotational center of bracket release(mm)
𝑙21: Distance from the center of arc thatindicates contact surface of pop-up guidebetween bracket release and pop-up guideto rotational center of pop-up guide (mm)
𝑙22: Distance from the rotational center ofpop-up guide to the latch in horizontaldirection (mm)
𝑙24: Distance from the rotational center ofpop-up guide to the end point of thepop-up guide (mm)
𝑚: Mass of hood applied to a latch system(kg)
𝑟𝑓1: Distance for moment transmitted tobracket release by friction force betweenbracket release and pop-up guide (mm)
𝑟𝑓2: Distance for moment transmitted topop-up guide by friction force betweenbracket release and pop-up guide (mm)
𝑟𝑓3: Distance for moment transmitted topop-up guide by friction force betweenpop-up guide and emergency pawl (mm)
𝑟𝑓4: Distance for moment transmitted topop-up guide by friction force betweenpop-up guide and pin striker (mm)
𝑟𝑓5: Distance for moment transmitted toemergency pawl by friction force betweenpop-up guide and emergency pawl (mm)
𝑟𝑓6: Distance for moment transmitted toemergency pawl by friction force betweenpin striker and emergency pawl (mm)
𝑟11: Distance for moment transmitted tobracket release by actuator force (mm)
𝑟12: Distance for moment transmitted tobracket release by reaction of pop-upguide (mm)
𝑟21: Distance for moment transmitted topop-up guide by force of bracket release(mm)
𝑟22: Distance for moment transmitted topop-up guide by reacted force of latch part(mm)
16 Shock and Vibration
𝑟23: Distance for moment transmitted topop-up guide by reaction of emergencypawl (mm)
𝑟24: Distance for moment transmitted topop-up guide by reacted force of pinstriker (mm)
𝑟31: Distance for moment transmitted toemergency pawl by force of pop-up guide(mm)
𝑟32: Distance for moment transmitted toemergency pawl by force of pin striker(mm)
𝑠𝑎: Radius of arc that is contact surface of
bracket release between bracket releaseand pop-up guide (mm)
𝑠𝑏: Radius of arc that is contact surface of
pop-up guide between bracket release andpop-up guide after step 2 (mm)
𝑥: Lifted height of hood (mm)𝐹1: Force transmitted by actuator to bracket
release (N)𝐹2: Force transmitted by bracket release to
pop-up guide (N)𝐹3: Force transmitted by pop-up guide to
latch (N)𝐹5: Force transmitted by pop-up guide to
emergency pawl (N)𝐹6: Force transmitted by pin striker to
emergency pawl (N)𝐹𝑓1: Friction force between bracket release andpop-up guide (N)
𝐹𝑓2: Friction force between pop-up guide andemergency pawl (N)
𝐹𝑓3: Friction force between pin striker andemergency pawl (N)
𝐼1: Inertia moment of bracket release (m4)𝐼2: Inertia moment of pop-up guide (m4)𝐼3: Inertia moment of emergency pawl (m4)𝐼4: Inertia moment of pin striker (m4)𝐼𝑎: Inertia moment of pop-up guide and pin
striker (m4)𝐾1: Spring coefficient of spring installed atbracket release (N/m)
𝐾2: Spring coefficient of spring installed atpop-up guide (N/m)
𝐾3: Spring coefficient of spring installed atemergency pawl (N/m)
𝑅1: Distance from rotational center of bracketrelease to bottom of bracket release invertical direction (mm)
𝑅2: Distance from rotational center of bracketrelease to end point at lift side of bracketrelease in horizontal direction (mm)
𝑅3: Distance from rotational center of pop-upguide to a point on latch part in thehorizontal direction (mm)
𝑅4: Distance from rotational center of pop-upguide to contact point with bracket releasein the horizontal direction (mm)
𝑅5: Distance from rotational center of pop-upguide to end point of pop-up guide (mm)
𝑅6: Distance from rotational center ofemergency pawl to contact point withpop-up guide (mm)
𝜃1: Rotated angle of bracket release (rad)𝜃2: Rotated angle of pop-up guide (rad)𝜃3: Rotated angle of emergency pawl (rad)𝜃𝑓2: Rotated angle of pop-up guide untiloperation is completed from start (rad)
𝜇𝑎: Rolling friction coefficient𝜇𝑏: Friction coefficient𝜏0: The deployed time of actuator from the
initial state to point (A) (ms)𝜏1: Finish time of step 1 (ms)𝜏2: Finish time of step 2 (ms)𝜏3: Finish time of step 3 (ms)𝜏4: Finish time of step 4 (ms)𝜔11: Final angle of bracket release in step 1 (rad)𝜔12: Final angle of pop-up guide in step 1 (rad)
𝜔13: Final angle of emergency pawl in step 1(rad)
𝜔21: Final angle of bracket release in step 2(rad)
𝜔22: Final angle of pop-up guide in step 2 (rad)𝜔31: Final angle of bracket release in step 3(rad)
𝜔32: Final angle of pop-up guide in step 3 (rad).
Conflict of Interests
The authors declare that there is no conflict of interests.
Acknowledgment
This work was fully supported by Inha University ResearchGrant.
References
[1] J. Mackerle, “Finite element crash simulations and impact-induced injuries,” Shock and Vibration, vol. 6, no. 5-6, pp. 321–334, 1999.
[2] J. R. Crandall, K. S. Bhalla, and N. J. Madeley, “Designing roadvehicles for pedestrian protection,” British Medical Journal, vol.324, no. 7346, pp. 1145–1148, 2002.
[3] UNECE/TRANS/WP.29/AC.3/7, “Proposal to develop a globaltechnical regulation concerning the protection of pedestrianand other vulnerable roads users in collision with vehicles,”2004, http://www.unece.org/trans/main/welcwp29.html.
[4] S. Huang, A Study of an Integrated Safety System for theProtection of Adult Pedestrians from Car Collisions, ChalmersUniversity of Technology, Gothenburg, Sweden, 2010.
[5] R. Fredriksson, Y. Haland, and J. Yang, “Evaluation of a newpedestrian head injury protection system with a sensor in the
Shock and Vibration 17
bumper and lifting of the bonnet’s rear part,” in Proceedingsof the 17th International Technical conference on the EnhancedSafety of Vehicles, p. 131, Amsterdam, The Netherlands, June2001.
[6] M.-K. Shin, K.-T. Park, and G.-J. Park, “Design of the activehood lift system using orthogonal arrays,” Proceedings of theInstitution of Mechanical Engineers, Part D: Journal of Automo-bile Engineering, vol. 222, no. 5, pp. 705–717, 2008.
[7] Y. Inomata, N. Iwai, Y. Maeda, S. Kobayashi, H. Okuyama, andN. Takahashi, “Development of the pop-up engine hood forpedestrian head protection,” in Proceedings of the 1st Interna-tional Technical Conference on the Enhanced Safety of Vehicles(ESV ’09), Stuttgart, Germany, June 2009.
[8] D. Xu, X. Zhu, Q. Miao, Z. Ma, and B. Wu, “The researchof reversible pop-up Hood for pedestrian protection,” in Pro-ceedings of the IEEE International Conference on VehicularElectronics and Safety (ICVES ’10), pp. 42–47, QingDao, China,July 2010.
[9] D. Wu and J. Chen, “Development and evaluation of a newactive engine hood lifting system,” in Recent Advances inComputer Science and Information Engineering, vol. 126 ofLecture Notes in Electrical Engineering, pp. 239–244, Springer,Berlin, Germany, 2012.
[10] T. Kramlich, K. Langwieder, D. Lang, and W. Hell, “Accidentcharacteristics in car-to-pedestrian impacts,” in Proceedings ofthe International IRCOBI Conference on the Biomechanics ofImpact, pp. 119–130, Munich, Germany, September 2002.
[11] S. Yoshida, N. Igarashi, A. Takahashi, and I. Imaizumi, “Devel-opment of a vehicle structure with protective features forpedestrians,” SAE International Congress and Exposition Paper1999-01-0075, Detroit, Misch, USA, 1999.
[12] K. B. Lee, H. J. Jung, and H. I. Bae, “The study on developingactive hood lift system for decreasing pedestrian head injure,”in Proceedings of the 20th International Technical Conference onthe Enhanced Safety of Vehicles (ESV ’07), 07-0198, Lyon, France,June 2007.
[13] C. Oh, Y.-S. Kang, andW. Kim, “Assessing the safety benefits ofan advanced vehicular technology for protecting pedestrians,”Accident Analysis and Prevention, vol. 40, no. 3, pp. 935–942,2008.
[14] X. J. Liu and J. K. Yang, “Development of child pedestrianmath-ematical models and evaluation with accident reconstruction,”Traffic Injury Prevention, vol. 3, no. 4, pp. 321–329, 2002.
[15] K. Nagatomi, K. Hanayama, T. Ishizaki, S. Sasaki, and K.Matsuda, “Development and full-scale dummy tests of a pop-up hood system for pedestrian protection,” in Proceeding of the19th International Technical Conference on the Enhanced Safetyof Vehicles, Washington, DC, USA, June 2005.
[16] E. Rosen and U. Sander, “Pedestrian fatality risk as a function ofcar impact speed,”Accident Analysis & Prevention, vol. 41, no. 3,pp. 536–542, 2009.
[17] G. V. Mariotti and S. Golfo, “Determination and analysis of thehead and chest parameters by simulation of a vehicle-teenagerimpact,” Proceedings of the Institution of Mechanical Engineers,Part D: Journal of Automobile Engineering, vol. 228, no. 1, pp.3–20, 2015.
