Comparative Evaluation for Pedestrian Safety Systems

Transcription

1 Comparative Evaluation for Pedestrian Safety Systems Mukesh Chaudhari Mukesh9803@gmail.com Abstract Pedestrian injuries, fatalities, and accessibility continue to be a serious concern in India and also across the world. There are major two systems used to protect the pedestrian from injury or death. Collisions between pedestrians and road vehicles present a major challenge for public health and traffic safety professionals. Pedestrian safety is a complicated problem due to the many variables that comprise the built environment and the complexity of understanding behavioral decisionmaking and outcomes. This literature review explores recent research on the roles of human factors and environmental factors in vehicle-pedestrian crashes, including a brief summary of recent sources that address countermeasures to improve the safety of the physical environment for pedestrians. Adult skull and face injuries in car pedestrian accidents is account for 60 percent of all pedestrian serious injuries, whereas 18 percent of skull injuries were due to the structure of bonnet. The above values show the essential to think more carefully the role of the bonnet in pedestrian skull safety. In 2010, 4,280 pedestrians were killed and an estimated 70,000 were injured in traffic crashes in the United States. On average, a pedestrian was killed every two hours and injured every eight minutes in traffic crashes. Pedestrians are the main fatality of fatal accidents. Nearly 90 percent of the total fatalities in our country occur on rural roads while only 10 percent occur on urban roads. Conventional planning is greatly biased to the motorized modes of transport, even though every road users is a pedestrian at some stage of journey. The problem is realized but efforts are negligent; therefore, authors suggest the need to address it within an integrated system of roads, road users and vehicles. As automobile transportation continues to increase around the world, bicyclists, pedestrians, and motorcyclists, also known as Vulnerable Road Users (VRU), will become more susceptible to traffic crashes, especially in countries where traffic laws are poorly enforced. Keywords bonnet, head injury, optimal design, Pedestrian safety I. INTRODUCTION A large proportion of the vehicular population enlargement in the country has taken place in the towns and cities. As towns and cities expand the outing lengths increase. Provision of public transport services has not matched the demand, culminating in large number of personalized modes on road. The supply of road infrastructure has also fallen short of the requirements. As a result, the congestion on roads has increased beyond capacity leading to delay, fuel loss, accidents and environmental pollution. Safety of operation is an area of concern in all modes of transport including walk mode. Though the accident rate is coming down, the number of fatalities is still high. As automobile transportation continues to boost around the world, bicyclists, pedestrians, and motorcyclists, also known as Vulnerable Road Users (VRUs), will become more at risk to traffic crashes, especially in countries where traffic laws are poorly enforced. In particular, nations such as India and China, which have growing populations as well as a growing middle class, will see a substantial increase in traffic injuries and fatalities if strategies are not found to ensure the safety of Vulnerable Road Users. Many countries, however, are employing innovative strategies to ensure that road users can more safely navigate the urban landscape. While bicyclists and motorcyclists are important road users, this paper will focus on pedestrian crash problems and solutions. Pedestrians are most at risk in urban areas due in part to the large amount of pedestrian and vehicle activity in urban areas. No matter if the primary mode of transportation is the automobile, bicycle, or public transportation; people must walk as a part of the trip, such as from their home to the store or place of employment, and/or to the transportation stop. Fig.1: Distribution of Road Traffic Fatalities by Road User Group [2] 31

2 With this in mind, designing safe, accessible, and comprehensive facilities for pedestrians is vital to reducing pedestrian crashes. Beginning with pedestrian safety statistics at the global, regional, and national levels, this paper will address potential countermeasures and strategies for improving pedestrian safety from an international perspective. As expected, more crowded countries will have higher total numbers of pedestrian deaths with China, India, and the Russian Federation in first, second, and third in that category, respectively. Fig. 2: Number of Pedestrian Deaths by Country [3.0] A Research on adult pedestrian protection currently is focusing mainly on passenger cars and commercial vehicles. However, impacts with heavy goods vehicles and buses are also important, especially in urban areas and in developing countries. Pedestrian safety is the important issues across the world. Transportation network is a heart of a nation and transport services are considered as growth engine of economy. Thousands of pedestrians are killed or badly injured in automotive accidents annually. According to the National Highway Traffic Safety Administration (NHTSA), In 2010, 32,885 people died in motor vehicle traffic crashes in the United States the lowest number of fatalities since 1949 (30,246 fatalities in 1949) This was a 2.9-percent decline in the number of people killed, from 33,883 in 2009, according to NHTSA s 2010 Fatality Analysis Reporting System (FARS). In 2010, an estimated 2.24 million people were injured in motor vehicle traffic crashes, compared to 2.22 million in 2009 according to NHTSA s National Automotive Sampling System (NASS) General Estimates System (GES). This slight increase (1.0% increase) in the estimated number of people injured is not statistically significant from the number of people injured in crashes in 2009 [1]. The above values show the need to consider carefully the bonnet of the passenger car to ensure pedestrian safety. As traffic safety emphasizes pedestrian protection, pedestrian safety systems were designed to protect pedestrians. Two main approaches have been developed to protect pedestrians against the effects of automotive accidents. The first approach is active protection, which involves sensors placed in automobiles to detect oncoming pedestrians and potential accidents, and it subsequently offers solutions to avoid accidents [4]. Although this approach can be solved efficiently and offers an efficient means of responding to safety problems, the sensor system which must be installed in the car is more expensive and required more care. Also the sensor system is activated when the vehicles crashes to any other objects, beams, dividers, etc The second approach is passive protection, in which design measures are implemented either to protect pedestrians from injury or to minimize the severity of potential injury [4]. For instance, passenger cars can be equipped with advanced devices such as external air bags and lifting-bonnet systems [10 12], which reduce pedestrian injuries in the event of accidents. All solutions are continuously developing because each solution highlights the role of automobile owners for protecting pedestrians. There are mainly two systems to protect the pedestrian from collision with vehicle, one is pop-up hood system and second is to optimize the bonnet thickness for pedestrian safety. II. POP-UP ENGINE HOOD SYSTEM This section describes the basic structure and mechanisms of the pop-up engine hood system. As illustrated in Fig. 2, the system consists of the following three basic components. Fig.3 : Pop-up hood system. [5] (1) Sensors: Detect a collision between the vehicle and a pedestrian. Fig. 4 : Sensing system. [6] 32

3 (2) Control unit: Judge the necessity of raising the hood. (3) Actuators: Raise the rear of the hood. The function of each component is explained in detail below. Sensors - Three sensors for detecting a collision with a pedestrian are installed behind the front bumper fascia as shown in Fig. 3. This structure was adopted because the front bumper is usually the first part to come in contact with a pedestrian's body in a collision with a vehicle. The sensors are positioned on the right and left sides and in the center. The sensors function to detect a change in acceleration and have experience of use as the airbag sensors. These devices detect the movement of the bumper fascia caused by contact with a pedestrian's legs. closes by rotating upward or downward centered on the hood hinges (Fig. 6 (a) and (b)). In contrast, when the pop-up system is deployed, the rear of the hood is raised centered on the hood lock at the front of the vehicle (Fig. 6 (c)). The hood hinge adopted is a link type hinge, as shown in Figure 5. The link hinge is composed of an upper bracket, lower bracket, arm A, arm B, three pivots, and a pin. According to an ignition signal from the ECU, gas from the micro gas generator raises the shaft. The shaft shears the hood hinge pin, lifting the rear portion of the hood approximately 100mm, thereby providing a space between the hood and the hard components under the hood, such as the engine. Before operation Fig. 7. Hood hinge of link type. [7] after operation Fig. 5. Sensor for pedestrian detection. [5] Actuators - The actuators that provide the driving force for raising the rear of the hood are constructed with an extendable cylinder operated by pyrotechnics. As shown in Fig. 5, the length of the three-stage cylinder before operation is less than one-half of its extended size. Fig. 6. Actuator. [5] Figure 6 shows the relationship between the operation of the actuators and the hood hinges for opening/closing the hood. Normally, the hood opens or Fig. 8. Operation of hinge and actuator.[8] A detailed diagram of the hood hinge mechanism is shown in Fig. 7. During normal opening or closing of the hood, the lock lever fixes link (a) and link (b), allowing only link (a) to rotate. When the pop-up hood system is deployed, the actuator head presses on the lock lever, allowing link (b) to rotate. The actuator cylinder extends to raise the rear of the hood, with the hood lock serving as the fulcrum of the hood's upward rotation. As a result of these operations, the rear of the hood is raised by approximately 100 mm to secure buffer space between the hood and the high-stiffness parts beneath it. 33

4 deployment time from the moment of the impactor contact with the front bumper. Fig. 9. Pop-up mechanism of hood hinge. [9] Collapsible Mechanism of Actuators:- This section presents an example of numerical simulations [5], [6] that were conducted to validate the effectiveness of the collapsible mechanism of the actuators. These simulations were performed with the PAM-CRASH. Software using a headform impactor. Figure 8 shows acceleration histories of the headform impactor when it struck the hood surface near one of the actuators. The impactor acceleration is indicated along the vertical axis in relation to its displacement along the horizontal axis. The solid line is for a pop-up hood system with collapsible actuators and the dashed line is for a system with rigid actuators. The waveform for the system without the collapsible mechanism indicates that, following the initial peak for the primary impact with the hood surface, the secondary impact with the actuator produced a relatively large acceleration peak. In contrast, the waveform for the system with the collapsible mechanism indicates that the actuators initially supported the rear of the hood until the preset load was reached, after which the collapsible mechanism worked to avoid another increase in impactor acceleration. As a result, the system with the collapsible mechanism kept the subsequent impactor acceleration below that of the level of the primary impact with the hood, thereby verifying the effectiveness of this mechanism. Validation of System Deployment Completion Time In order to validate that the pop-up engine hood system could be deployed before the targeted system deployment completion time explained in the preceding section, tests were conducted with impactors that simulated the mass of pedestrians. Figure 10 shows an example of the displacement history of the pop-up hood, where the amount of hood displacement near the actuators is shown along the vertical axis in relation to elapsed time along the horizontal axis. The results indicate that the hood was raised the specified amount with sufficient time to spare in relation to the targeted Fig. 10. Example of displacement history of pop-up. [8] Method of Evaluating Head Protection Performance The headform impactor was projected against the hood and other areas of the vehicle front-end to investigate head protection performance, which was evaluated using the head injury criterion (HIC) as defined in Eq. (1) below. With the condition Where A is the acceleration of the headform impactor and t1 and t2 are the initial and final times. In order to reduce the HIC, the mean acceleration should be low and there should not be any pronounced acceleration peak. III REDESIGNING THE BONNET FOR PEDESTRIAN SAFETY Redesigning the structure of the bonnet to improve pedestrian protection has recently received considerable attention by automobile manufacturers and industry, institutes. Figure 11 illustrates a method of protecting pedestrians by creating more holes in the ribs of reinforcement to reduce the bonnet stiffness [11]. Previous research on improving pedestrian safety also increased the number of ribs to create a bonnet surface with more uniform stiffness [13]. Figure 12 shows the reinforcement structure developed to protect pedestrians in accidents. Currently, some automobiles use a multicone structure (Fig. 12) instead of a rib structure for bonnet reinforcement. 34

5 It is very important to select the most helpful thicknesses of the bonnet skin and bonnet reinforcement for each bonnet structure. Kalliske and Friesen [14] reduced the bonnet stiffness and mass by reducing the bonnet skin thickness to protect the pedestrian head. However, this research did not expose the basis for selecting the bonnet skin thickness. This research has simply reduced the bonnet skin thickness rather than seeking a basis for optimizing the values. Moreover, the bonnet stiffness must be systematically optimized because some components within the engine compartment can often be very close to the bonnet surface and these components can damage the skull of human head when collision occurs. Fig. 11 Pedestrian protection by the modified original reinforcement structure [11] If the bonnet has poor stiffness, there is a risk that components within the engine compartment may strike the bonnet during collision, increasing the danger to the pedestrian and negating the benefits of the reduced stiffness. Therefore, bonnet redesign not only must simply reduce the bonnet stiffness and mass but also should consider the bonnet deflection during collision. Presently there are two methods for evaluating pedestrian injury. The first method uses pedestrian impactors to evaluate corresponding areas on the vehicle. The second method uses a complete dummy to evaluate the vehicle s frontal structure. Both the complete dummy and the pedestrian impactor methods require complicated physical testing systems. Furthermore, the pedestrian impactors must pass a series of tests to obtain certification. Testing the material properties of pedestrian impactors is time consuming. Numerical simulation offers another reliable method of solving the above problems. One advantage of this method is its ability to solve optimization problems. While mathematical analysis is not an easy method of solving optimization problems, analysis of simulation results is relatively simple and effective. Because of the above advantages, all pedestrian-head-to-bonnet-top tests in this study will be performed using numerical simulation. Fig. 12 The solution of an alternative design for protection of the pedestrian head [13]: (a) traditional design; (b) increased number of ribs; (c) multi-cone design This study analyses the effects of the bonnet skin and bonnet reinforcement thickness on pedestrian head injury by performing number of simulation of head form impactor to bonnet top test as per European Enhanced Vehicle-safety Committee (EEVC) Working Group 17 (WG17) regulations using different thicknesses. Many points on the bonnet surface will be considered to enhance pedestrian friendliness by using this method. A bonnet with the optimal thicknesses not only is pedestrian friendly but also is as stiff as possible. Based on the proposed method, this study presents steps for optimizing the bonnet skin and bonnet reinforcement thicknesses for a particular automobile model. 1 SIMULATION OF PEDESTRIAN-HEAD-TO BONNET TESTS 1.1 Pedestrian-head-to-bonnet tests The European Commission also published a directive to assess the level of pedestrian protection for vehicle fronts in The European Parliament supported the commitment on pedestrian safety proposed by the European Automobile Manufacturers Association, and thus pedestrian protection measures have been required on all passenger cars sold in Europe since 2005 [15]. The EEVC WG17 established a series of component tests based on the three most important areas of injury: head, upper leg, and lower leg. The EEVC WG17 developed this method for assessing the pedestrian friendliness of a vehicle. The EEVC WG17 tests consist of four models of pedestrian impactor models, namely child headform, adult headform, upper-legform and lower-legform impactors. Figure 13 illustrates the pedestrian protection concept proposed by the EEVC WG17 [16]. 35

6 Fig. 13 Pedestrian protection concept proposed by the EEVC WG17 [16] These EEVC WG17 regulations thus will be completed and applied to vehicle manufacturing in Europe. In India there is no such regulation for vehicle manufacturing. The adult headform impactor is used to test the points lying on boundaries described by a WAD of 1500mm and the rear of the bonnet top, or a WAD of 2100mm for a long bonnet. Each section is divided into three parts, as illustrated in Fig.14. Fig. 15. Determination of WAD [16] 1.2 Finite element model and simulation In Finite element the model of vehicle and adult headform is crated. This study analyses the effect of the bonnet skin and bonnet reinforcement thicknesses on pedestrian head injury by performing headform impactor simulations of the EEVC WG17 regulations using different thicknesses. Figure 16(b) shows the finite element models of adult headform impactors. Fig. 14 Description of the impact area for pedestrian headform- impactor-to-bonnet-top tests In each part, a minimum of three tests is carryout at spots with high injury risk. Test points should vary according to the types of structure, which vary throughout the assessment area. The selected test points for the adult headform impactor should be a minimum of 165mm apart, a minimum of 82.5mm inside the defined bonnet side reference lines, and a minimum of 82.5mm forwards of the defined bonnet rear reference line. The impact angle for tests with the adult headform impactors must be 65 0 with respect to the ground reference level. The initial impact velocity is 40 km/h for the adult headform impactors. Distances (WADs) (Fig. 15) of 1000mm and rear reference line. Each selected test point for the child headform impactor should also be a minimum of 130mm rearwards of the bonnet leading-edge reference line. The impact angle for tests with the adult headform impactors must be 65 0 respectively with respect to the ground reference level. The initial impact velocity is 40 km/h for and the adult headform impactors. Fig. 16.The finite element model used in pedestrian head bonnet impact simulations: (a) the passenger car model [18]; (b) the headform impactor model [17] The vinyl skin is modelled using viscoelastic material, and a steel core with elastic material [17]. All headform impactor parts use solid elements. The adult headform impactor model consists of 3713 nodes and solid elements. The adult headform impactors satisfy the EEVC WG17 certification tests [17], demonstrating the feasibility of their use in simulating headform impactor tests. Bonnet-top simulations are performed using the adult headform impactors simulations of the headform-to-bonnet-top test are performed using the finite element models of the headform impactor mentioned above and a Ford Taurus car model [18], as shown in Fig. 16 (a). In the engine compartment, components that are close to the bonnet top include the oil cap and the battery. This study does not consider the effect of the engine compartment arrangement on the head injury criterion (HIC) value. Therefore, all parts in the engine compartment that are close to the bonnet are moved down to ensure that the bonnet does not impact any parts in the engine compartment during simulation. 36

7 IV. CONCLUSIONS Both the methods give the optimal results to protect the pedestrian safety. In both the methods the Hypermesh and Ls-Dyna software are used. To protect the pedestrian these systems must be implemented to all the manufactures of automobile vehicles. This study analyses and proposes a method of identifying the most effective values for the bonnet reinforcement thickness and the bonnet skin thicknesses to protect pedestrians while maximizing the bonnet stiffness. The method presented in this study uses the regression technique to design constraints for the optimization problem. The proposed algorithm identifies numerous critical positions on the bonnet surface with respect to pedestrian safety. The algorithm used to optimize the thicknesses is solved by combining LS-DYNA and LS- OPT to simulate and analyze the simulation results. V. REFERENCES [1] National Center for Statistics and Analysis, Motor vehicle traffic crash fatality counts and estimates of people injured for 2012: 2012 annual assessment. DOT HS National Highway Traffic Safety Administration, 1200 New Jersey Avenue SE. Washington, DC, USA, August [2] Naci, H., Chisholm, D., & Baker, T. D. (2009). Distribution of Road Traffic Deaths by Road User Group: A Global Comparison. Injury Prevention, 15, doi: [3] World Health Organization. Global Status Report on Road Safety: Time for Action. Geneva, Switzerland: WHO Press. (2009). [4] F. Laimbock and Resele, Safety and crash behavior, Da-Yeh Inst. Technol., Taiwan, AE&ICE Ser., 1993, 21, [5] Yusuke Inomata, DEVELOPMENT OF THE POP-UP ENGINE HOOD FOR PEDESTRIAN HEAD PROTECTION NISSAN MOTOR CO., LTD., Japan Paper Number [6] Kaoru Nagatomi, Kaoru Nagatomi DEVELOPMENT AND FULL-SCALE DUMMY TESTS OF A POP-UP HOOD SYSTEM FOR PEDESTRIAN PROTECTION, Paper number [7] S.Yoshida, et al. Simulation of Car-Pedestrian Accident for Evaluate Car Structure 16th ESV Conference 1998 [8] Iwai, N., "Numerical Simulation of Vehicle Body Structures for Pedestrian Head Protection, Lecture Series Abstracts of The Japan Society for Computational Engineering and Science, Vol. 8, No. 1, , 2003 (in Japanese). [9] Ishikawa, H., et al.: Computer Simulation of impact Response of the Human Body in Car Pedestrian Accidents. SAE Paper No , 1993 [10] A. Zanella, F. Butera, E. Gobetto, and C. Ricerche, Smart bumper for pedestrian impact recognition, European Workshop on Smart structures in engineering and technology, Proceedings of the SPIE, vol. 4763, 2003, pp (SPIE, Bellingham, Washington). [11] Y. H. Han, and Y. W. Lee, Development of a vehicle structure with enhanced pedestrian safety, SAE paper , 2003 [12] T. Maki and T. Asai, Development of pedestrian protection technologies for ASV, JSAE Rev., 2002, 23(3), [13] C. K. Simms, Developments in crash safety: a triumph of design in bioengineering, In Perspectives on design and bioengineering: essays in honour of C. G. Lyons (Eds C. K. Simms and P. J. Prendergast), 2008, pp (Trinity Centre for Bioengineering, Dublin). [14] I.Kalliske, and F.Friesen, Improvements to pedestrian protection as exemplified on a standardized car, 17 th International Technical Conference on The enhanced safety of vehicles (ESV), Amsterdam, The Netherlands, 4 7 June 2001, paper 283, 10 pp. (National Highway Traffic Safety Administration, Washington, DC [15] Directive 2003/102/EC of the European Parliament and of the Council of 17 November 2003 Report. Off. J. Eur. Un., 2003, L 321/15 (OJEU, Luxembourg). [16] Improved test methods to evaluate pedestrian protection afforded by passenger cars. Report, Working Group 17, European Enhanced Vehicle safety Committee, [17] T. L. Teng and T. H. Nguyen, Development and validation of FE models of impactor for pedestrian testing, J. Mech. Sci. Technol., 2008, 22(9), [18] FHWA/NHTSA National Crash Analysis Center, The George Washington University, Ashburn, Virginia, USA, Applications, Finite element model archive, , [19] A. R. Payne, and S. Patel, Head injury criteria tolerance levels, Report (Project ), Motor Industry Research Association, Nuneaton, Warwickshire, UK,