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There are a number of numerical and experimental studies of the aerodynamic performance of wheels that have been published. They show that wheels and wheel-housing flows are responsible for a substantial part of the total aerodynamic drag on passenger vehicles. Previous investigations have also shown that aerodynamic resistance moment acting on rotating wheels, sometimes referred to as ventilation resistance or ventilation torque is a significant contributor to the total aerodynamic resistance of the vehicle; therefore it should not be neglected when designing the wheel-housing area. This work presents a numerical study of the wheel ventilation resistance moment and factors that affect it, using computational fluid dynamics (CFD). It is demonstrated how pressure and shear forces acting on different rotating parts of the wheel affect the ventilation torque. It is also shown how a simple change of rim design can lead to a significant decrease in power consumption of the vehicle.

The foremost aim of the work presented in this paper is to improve fuel economy and decrease CO2 emissions by reducing the aerodynamic drag of passenger vehicles. In vehicle development, computer aided engineering (CAE) methods have become a development driver tool rather than a design assessment tool. Exploring and developing the capabilities of current CAE tools is therefore of great importance. An efficient method for vehicle shape optimization has been developed using recent years' advancements in neural networks and evolutionary optimization. The proposed method requires the definition of design variables as the only manual work. The optimization is performed on a solver approximation instead of the real solver, which considerably reduces computation time. A database is generated from simulations of sampled configurations within the pre-defined design space. The database is used to train an artificial neural network which acts as an approximation to the simulations.

Recent cadaver studies have provided data for the development of force and stiffness characteristics of the side of the human head. A Hybrid III Anthropomorphic Test Dummy (ATD) head was modified to allow direct measurement of impact forces on the parietal and temporal regions by recasting the upper left half of the skull and installing triaxial piezoelectric force transducers. Dynamic impact tests of this modified head were conducted and force/stiffness characteristics for the temporal and parietal areas were compared to existing data on cadaver subjects. It was found that the existing Hybrid III vinyl skin satisfactorily represents the force/stiffness characteristics of the human head in these areas. This modified Hybrid III dummy head was also impacted against typical interior components likely to be contacted during a side impact. The force and acceleration test results are presented.

A positive trend to more frequent use of child restraint systems (CRS) in Sweden, during the last 20 years, is shown in this report. During the same period, the overall injury risk, for different age groups of child occupants, has decreased substantially. This indicates the high effectiveness of the child restraint systems. Children need car occupant safety systems specially designed for their size. This paper clearly states the need for child safety systems and discusses benefits and drawbacks with regard to different restraints, ages and injuries. The analysis points out, that when a crash occurs, the maximum effect of a child restraint system is not reached, if the child is not using the correct system for their size. There is even a tendency that the injury risk increases when children switch from one restraint system to another, i.e. are at the youngest ages for which the specific restraint is recommended. The background data used, is based on Volvo's traffic accident research.

Neck injuries resulting from rear end car impacts have attracted increasing attention in recent years. Although usually not life-threatening these injuries can have long-term consequences. The exact mechanism of injury has not yet been established. Several probable mechanisms occurring at different phases during the crash sequence have been suggested by researchers. The accident experience with existing seat and head restraint designs is summarized. The results show that there are many factors influencing the risk of neck injury. A high and fixed-in-position head restraint, positioned close to the head, is beneficial. Also, Individual factors, such as gender and height, and seating position, are shown to have influence on the injury risk.

In the early stages of an aerodynamic development programme of a road vehicle it is common to use wind tunnel scale models. The obvious reasons for using scale models are that they are less costly to build and model scale wind tunnels are relatively inexpensive to operate. It is therefore desirable for model scale testing to be utilized even more than it is today. This however, requires that the scale models are highly detailed and that the results correlate with those of the full size vehicle. This paper presents a correlation study that was carried out in the Chalmers and Volvo Car Aerodynamic Wind Tunnels. The aim of the study was to investigate how successfully a correlation of the cooling air flow between a detailed scale model and a real full size vehicle could be achieved. Results show limited correlation on absolute global aerodynamic loads, but relative good correlation in drag and lift increments.

Automotive wind tunnel testing is a key element in the development of the aerodynamics of road vehicles. Continuous advancements are made in order to decrease the differences between actual on-road conditions and wind tunnel test properties and the importance of ground simulation with relative motion of the ground and rotating wheels has been the topic of several studies. This work presents a study on the effect of active ground simulation, using moving ground and rotating wheels, on the aerodynamic coefficients on a passenger car in yawed conditions. Most of the published studies on the effects of ground simulation cover only zero yaw conditions and only a few earlier investigations covering ground simulation during yaw were found in the existing literature and all considered simplified models. To further investigate this, a study on a full size sedan type vehicle of production status was performed in the Volvo Aerodynamic Wind Tunnel.

This study focus on the aerodynamic influence of the engine bay packaging, with special emphasis on the density of packaging and its effect on cooling and exterior flow. For the study, numerical and experimental methods where combined to exploit the advantages of each method. The geometry used for the study was a model of Volvo S60 sedan type passenger car, carrying a detailed representation of the cooling package, engine bay and underbody area. In the study it was found that there is an influence on the exterior aerodynamics of the vehicle with respect to the packaging of the engine bay. Furthermore, it is shown that by evacuating a large amount of the cooling air through the wheel houses a reduction in drag can be achieved.

This paper reports how numerical simulation can be used as a tool to guide vehicle design with respect to brake cooling demands. Detailed simulations of different brake cooling concepts are compared with experimental results. The paper consists of two parts. The first part places the emphasis on how to model the flow inside and around the brake disc. The boundary layer and the pumping effect is investigated for a ventilated single rotor. The numerical results will be compared to experimental results. In the second part, an engineering approach is applied in order to rank different technical solutions on a Volvo S80 vehicle in terms of brake cooling and aerodynamic drag. The results from the free brake disc simulations indicate that the tangential velocity can be predicted with high accuracy, e.g. standard k-ε model with prism near wall cells typically within 4% of measured data.

Even though child restraint systems (CRS) are very effective there are still serious problems because of non-use or misuse. This is often due to the fact that the installation of the CRS in the cars is difficult, complicated and unstable. A standardised interface between the CRS and the car seat would solve these problems. Within the IS0 Committee ISO/TC22/SC12NVGl this item has been raised and several proposals for an “ISOFIX have been discussed. Apart from the installation aspects, other features e.g. disconnection of passenger airbags can be included in the system. Several concepts called ISOFlX type 1 to 7 with different working names e.g. DELTAFIX, EASY-FIX, MONOFIX and UNlFlX have been evaluated. The handling performance of some of the prototypes have been tested by customer evaluation with very positive results. Crash performance has also been investigated. The paper will give an update on the latest progress of this development, including a preliminary specification.

Frontal collisions account for the majority of car accidents. Regulations have been in effect since the late sixties, aiming at assuring a basic safety performance for cars in this type of crash. From a legislative point of view tests as e.g. FMVSS 208 are about to be complemented by other frontal impact configurations. Two of the reasons behind this is to allow assessment also of asymmetric loads to the vehicle front and the level of passenger compartment intrusion. This paper offers a comparison of different frontal crash tests, including Volvo's Severe Partial Overlap Collision (SPOC) and offset tests against a deformable barrier. The methods are evaluated with respect to their results, both from a dummy performance point of view and based on car deformation characteristics. Also, the practicability and possible effect on vehicle designs are discussed.

Injuries in side impact collisions constitute one fourth of the serious or fatal injuries sustained by occupants in ordinary passenger cars. The Volvo Side Impact Protection System (SIPS) provides a substantially enhanced protection for car occupants in side collisions. The protection level of the SIPS system has been further increased by the addition of the Sipsbag, a quick-deploying side impact airbag system integrated in the seat backrest. The design of the non-electrical Sipsbag system is explained, as well as the advantages with a completely seat-integrated system. The process to industrialise the side airbag concept is summarised. Laboratory test results are discussed. Using methodology to correlate laboratory test data with accident data, an estimate of the injury-reducing effectiveness of the SIPS and Sipsbag system is made.

In air bag tests without a restraining seat belt (FMVSS208) several users of the Hybrid III dummy have reported a pelvic interference problem during the tests. An insufficient range of motion and a hard metal to metal contact between the pelvis and femur has lead to unexpected chest acceleration waveforms. The paper gives a mechanical analysis of this phenomenon, explaining how the forces acting on the dummy lead to a rotation of the pelvis and femur and how forces arise between the pelvis and the chest. Finally two sample tests where the pelvic interference problem has occurred are presented.

The performance of three different six-year old dummies, the new Hybrid III six-year-old from First Technology Safety Systems, the Part 572 Subpart I and the TNO P6, was compared in a series of HYGE sled tests. The dummies were tested on aftermarket booster cushions in a Volvo 850 sled buck. Two different sled pulses were used: a Volvo 850 30 mph frontal crash pulse and an ECE R.44 pulse. The behavior of the dummies was compared for these two sled pulses. Motion analysis from high speed film was performed, showing the trajectories of the dummy heads. All dummies were fitted with triaxial accelerometers in the head, chest and pelvis. The Hybrid III was also equipped with a chest deflection transducer and Denton six-channel upper neck and five-channel lumbar spine load cells. The signals from a number of these sensors were compared.

A rear seat belt system with a submarining-preventing seat design was developed. The seat has a contoured floor pan with a pronounced ridge at the front end and a seat belt with carefully located attachment points. Sled tests simulating 30 mph barrier crashes were run with both a standard Part 572 dummy and a Part 572 dummy with a modified pelvis. Both dummies had pelvis mounted submarining indicators. Comparative tests were run with a rear seat with a flat floor pan. The tests proved the efficacy of the ridge type seat in preventing submarining as well as giving low injury criteria. The modified pelvis was found to have submarining characteristics slightly different from the Part 572 pelvis. Under certain conditions the submarining indicators were capable of detecting when the lap belt loads the abdomen, but failed in some cases where the pelvis rotation was excessive.

The level at which forces are transmitted from the striking vehicle in side impacts may influence the response of the struck car in several different ways. A better contact between the front bumper of the striking and the sill area of the struck car has been considered to be desirable in this respect. In side impacts, the most frequent direction of the impact is from 3 and 9 o'clock, while the direction of the forces is usually from 2 and 10 o'clock due to the velocity of the struck car. A European car and the EEVC moving deformable barrier have, therefore, been used in a crabbed mode to study the problem of load transfer at different levels above the ground. Volvo and Saab cars were used as targets in 55 km/h side impact with an APROD-81 side impact dummy placed on the struck side in the front seat. The results indicate that a difference in the level at which the loads were applied could influence the deformations, the kinematics of the struck cars, and the loading of the occupant.

The airbag simulation program DRACR has been revised to include belt routines. The amended program is used to indicate optimal choice of parameters for a driver supplementary airbag system. As a validation, results from sled tests are given and compared with the computer runs. A good agreement is found for the values of the most essential protection criteria such as chest g's and HIC's. The model has proven to be useful in the engineering process of an airbag restraint system. The interrelationship between important input variables is easily studied. Further validation of the model by other teams is encouraged

This paper describes some of the engineering situations encountered during the development of a three point belt for the rear center seating position in a sedan car. The belt will be sold as an accessory for the after market. The reinforcement of the parcel shelf to achieve a sufficiently strong anchorage for the retractor and the geometrical locations of the belt anchorages are presented. The conflict between the geometrical requirements, the design and the visibility will be focussed. The need for updated requirements for belt installations in the rear center seating position will be pointed out. Data from the performed tests show that all demands from regulations and “in-house” requirements are fulfilled.

The Inflatable Curtain (IC) has shown great potential to reduce head injuries in side impacts. This study explores and presents enhanced performance in two steps of improved activation algorithms. Crash data analysis, 21 full scale crash tests and component tests in a custom built drop tower rig have been performed. The IC performance in wider crash scenarios, including side impacts outside the occupant compartment (L-type impacts), was evaluated. Both statistical crash data and in-depth studies were used. It was found in the analysis of real life crashes that moderate to fatal head injuries can occur without intrusion in the occupant compartment. In L-type side impacts, the motion of the occupant relative to the vehicle interior may cause a head impact of sufficiently high severity to cause moderate to severe head injuries. A combined analysis of real world crash data and crash test results indicates that a substantial reduction in moderate to fatal head injuries can be achieved.

Under a global impulse for less man-made emissions, the automotive manufacturers search for innovative methods to reduce the fuel consumption and hence the CO2-emissions. Aerodynamics has great potential to aid the emission reduction since aerodynamic drag is an important parameter in the overall driving resistance force. As vehicles are considered bluff bodies, the main drag source is pressure drag, caused by the difference between front and rear pressure. Therefore increasing the base pressure is a key parameter to reduce the aerodynamic drag. From previous research on small-scale and full-scale vehicles, rear-end extensions are known to have a positive effect on the base pressure, enhancing pressure recovery and reducing the wake area. This paper investigates the effect of several parameters of these extensions on the forces, on the surface pressures of an SUV in the Volvo Cars Aerodynamic Wind Tunnel and compares them with numerical results.