Design and Optimization for the Occupant Restraint System of Vehicle Based on a Single Freedom Model

Throughout the vehicle crash event, the interactions between vehicle, occupant, restraint system (VOR) are complicated and highly non-linear. CAE and physical tests are the most widely used in vehicle passive safety development, but they can only be done with the detailed 3D model or physical samples. Often some design errors and imperfections are difficult to correct at that time, and a large amount of time will be needed. A restraint system concept design approach which based on single-degree-of-freedom occupant-vehicle model (SDOF) is proposed in this paper. The interactions between the restraint system parameters and the occupant responses in a crash are studied from the view of mechanics and energy. The discrete input and the iterative algorithm method are applied to the SDOF model to get the occupant responses quickly for arbitrary excitations (impact pulse) by MATLAB. By studying the relationships between the ridedown efficiency, the restraint stiffness, and the occupant response, the design principle of the restraint stiffness aiming to reduce occupant injury level during conceptual design is represented. Higher ridedown efficiency means more occupant energy absorbed by the vehicle, but the research result shows that higher ridedown efficiency does not mean lower occupant injury level. A proper restraint system design principle depends on two aspects. On one hand,the restraint system should lead to as high ridedown efficiency as possible, and at the same time, the restraint system should maximize use of the survival space to reduce the occupant deceleration level. As an example, an optimization of a passenger vehicle restraint system is designed by the concept design method above, and the final results are validated by MADYMO, which is the most widely used software in restraint system design, and the sled test. Consequently, a guideline and method for the occupant restraint system concept design is established in this paper.

Research on Key Issues of Consistency Analysis of Vehicle Steering Characteristics

Given the global lack of effective analysis methods for the impact of design parameter tolerance on performance deviation in the vehicle proof-of-concept stage,it is difficult to decompose performance tolerance to design parameter tolerance.This study proposes a set of consistency analysis methods for vehicle steering performance.The process of consistency analysis and control of automotive performance in the conceptual design phase is proposed for the first time.A vehicle dynamics model is constructed,and the multi-objective optimization software Isight is used to optimize the steering performance of the car.Sensitivity analysis is used to optimize the design performance value.The tolerance interval of the performance is obtained by comparing the original car performance value with the optimized value.With the help of layer-by-layer decomposition theory and interval mathematics,automotive performance tolerance has been decomposed into design parameter tolerance.Through simulation and real vehicle experiments,the validity of the consistency analysis and control method presented in this paper are verified.The decomposition from parameter tolerance to performance tolerance can be achieved at the conceptual design stage.

Establishment and Validation for the Theoretical Model of the Vehicle Airbag

The current design and optimization of the occupant restraint system（ORS） are based on numerous actual tests and mathematic simulations. These two methods are overly time-consuming and complex for the concept design phase of the ORS, though they＇re quite effective and accurate. Therefore, a fast and directive method of the design and optimization is needed in the concept design phase of the ORS. Since the airbag system is a crucial part of the ORS, in this paper, a theoretical model for the vehicle airbag is established in order to clarify the interaction between occupants and airbags, and further a fast design and optimization method of airbags in the concept design phase is made based on the proposed theoretical model. First, the theoretical expression of the simplified mechanical relationship between the airbag＇s design parameters and the occupant response is developed based on classical mechanics, then the momentum theorem and the ideal gas state equation are adopted to illustrate the relationship between airbag＇s design parameters and occupant response. By using MATLAB software, the iterative algorithm method and discrete variables are applied to the solution of the proposed theoretical model with a random input in a certain scope. And validations by MADYMO software prove the validity and accuracy of this theoretical model in two principal design parameters, the inflated gas mass and vent diameter, within a regular range. This research contributes to a deeper comprehension of the relation between occupants and airbags, further a fast design and optimization method for airbags＇ principal parameters in the concept design phase, and provides the range of the airbag＇s initial design parameters for the subsequent CAE simulations and actual tests.

Simulation Research on Dynamic Characteristics of Hydraulic Mount

At present,research on hydraulic mounts has mainly focused on the prediction of the dynamic stiffness and loss angle.Compared to the traditional finite element analysis method,the programming method can be used to analyze hydraulic mounts for a rapid and accurate understanding of the influence of the different mounting parameters on the dynamic stiffness and loss angle.The aims of this study were to investigate the nonlinear dynamic characteristics of a hydraulic mount,and to identify the parameters that affect the dynamic stiffness and loss angle using MATLAB software programs to obtain the influence curves of the parameters,so as to use suitable parameters as the basis for vibration analysis.A nonlinear mechanical model of a hydraulic mount was established according to the basic principles of fluid dynamics.The dynamic stiffness and loss angle of the dimensionless expression were proposed.A numerical calculation method for the dynamic performance evaluation index of the hydraulic mount was derived.A one-to-one correspondence was established between the structural parameters and peak frequency of the evaluation index.The accuracy and applicability of the mechanical model were verified by the test results.The results demonstrated the accuracy of the nonlinear mechanical model of the hydraulic mount,and the vehicle driving comfort was greatly improved by the optimization of the structural parameters.

Novel Evaluation Method of Vehicle Suspension Performance Based on Concept of Wheel Turn Center

The current research of suspension performance evaluation is mixed in the evaluation of vehicle handling and ride comfort. However, it is lack of a direct and independent evaluation method for suspension performance. In this paper, a novel wheel turn center method is proposed to evaluate the suspension performance. This method is based on the concept and application of wheel turn center （WTC） and sprung mass turn center （SPTC）. The vehicle body and each wheel are regarded to be independent rigid bodies and have their own turn centers which reflect respective steering motions and responses. Since the suspension is the link between vehicle body and wheels, the consistence between the sprung mass turn center and the wheel turn center reflects the effect and performance of the suspension system. Firstly, the concept and appropriate calculation method of WTC and SPTC are developed. Then the degree of inconsistence between WTC and SPTC and the time that they achieve consistence, when the vehicle experiences from transient steering to steady steering state, are proposed to evaluate suspension performance. The suspension evaluation tests are conducted under different vehicle velocities and lateral accelerations by using CarSim software. The simulation results show that the inconsistence of steering motion between vehicle body and wheels are mainly at high speeds and low lateral accelerations. Finally, based on the proposed evaluation indexes, the influences of different suspension characteristic parameters on suspension performance and their matches to improve steering coordination are discussed. The proposed wheel turn center method provides a guidance and potential application for suspension evaluation and optimization.

Numerical simulation of the aerodynamic characteristics of heavy-duty trucks through viaduct in crosswind

In our numerical simulation the hybrid mesh and the SST k-ω turbulence model are adopted to investigate the variations of the aerodynamic loads and the flow field of heavy-duty trucks while crossing a viaduct with 1.1 m high fences in a crosswind at a velocity of 20 m/s. The results show that, with the protection of a fence, the side force is weakened, and the rolling and yaw moments are strengthened while the truck is crossing the viaduct, which relatively reduces the roll-over safety and the driving stability of the truck. Meanwhile, the direction of the side force changes when the truck enters the viaduct, which makes the roll-over safety and the driving stability the lowest during the process.

Experimental and numerical investigations of the aerodynamic noise reduction of automotive side view mirrors

This paper studies the aeroacoustics of the side view mirrors by wind tunnel tests and numerical simulations. The mirror is placed on a table in the wind tunnel test. Based on the experiment results, a numerical analysis model is established to analyze the acoustic field in the wake of the side view mirror by the Large Eddy Simulation（LES）. The flow field and the noise level of two different side view mirrors are compared in the simulation. It is shown that, with the serration structures applied onto the mirror surface, the turbulence zone and the pressure fluctuation in the wake of the bionic model are improved effectively, which helps its flow control and noise reduction. Meanwhile, as is shown in the noise spectra, when the noise frequency is over 500 Hz, for the bionic mode, the noise is reduced to a lower level than with the original one, which further shows its effectiveness in the noise reduction.

Vehicle Positioning Method Based on RFID in Vehicular Ad-Hoc Networks

With the rapid development of vehicular ad hoc network( VANET) technology,VANET applications such as safe driving and emergency rescue demand high position accuracy,but traditional GPS is difficult to meet new accuracy requirements. To overcome this limitation,a new vehicle positioning method based on radio frequency identification( RFID) is proposed. First RFID base stations are divided into three categories using fuzzy technology,and then Chan algorithm is used to calculate three vehicles' positions,which are weighed to acquire vehicles' accurate position. This method can effectively overcome the problem that vehicle positioning accuracy is not high resulting from the factors such as ambient noise and base distribution when Chan algorithm is used. Experimental results show that the performance of the proposed method is superior to Chan algorithm and 2-step algorithm based on averaging method,which can satisfy the requirements of vehicle positioning in VANETs.

Investigation of the combustion deterioration of an automotive diesel engine under transient operation

With increasingly stringent emission regulations and demand for fuel economy by the public,the combustion and emission problems of automotive diesel engines during transient operation have become vital and urgent issues.In this study,combustion deterioration has been experimentally analyzed using a heavy-duty turbocharged diesel engine running under transient conditions(constant speed and increasing torque).Optimization of the transient combustion process was performed by adjusting the fuel injection parameters.The results indicated that the notable combustion deterioration relative to steady state operation while transient was a function of the delay in the air-supply to the turbocharged engine,and took the form of combustion phasing delay,resulting in rapidly increasing smoke emission and fuel consumption.However,the delay in combustion phasing can be controlled by advancing the fuel injection timing,effectively increasing thermal efficiency.Unfortunately,smoke and NO x emissions increased at the same time.The deterioration in combustion phasing can also be improved by increasing injection pressure,resulting in decreased smoke emission while NO x emission increased.It is worth noting that the effective thermal efficiency first increased and then decreased as fuel injection pressure increased during transient operation.

Application of Omega vortex identification method in cavity buffeting noise

The cavity buffeting noise is related to the free shear layer oscillation and the periodic vortex shedding,where weak vortices coexist with strong vortices and the strong shear phenomenon also exists at the opening of the cavity.Therefore,it is of great significance to accurately capture vortices at the opening for the control of the cavity buffeting noise.This paper first compares the Omega vortex identification method with the Q andλ2criteria based on the large eddy simulation(LES)of the backward-facing step flow,and it is found that the Omega method enjoys the following advantages:it is not sensitive to a moderate threshold change andΩ=0.52 can be used as a fixed threshold,it can capture both the strong and weak vortices at the same time;and it will not be contaminated by the shear.Then the Omega(Ω)method is applied to the LES of the cavity buffeting noise:the mechanism of the cavity buffeting noise is studied based on a simple cavity model firstly,and then the effects of the incoming boundary layer thicknesses and the incoming boundary layer shapes on the cavity buffeting noise are analyzed.The results show that:theΩmethod clearly captures the processes of the vortex generation,development,collision and fragmentation,verifying that the generation of the cavity buffeting noise is related to the free shear layer oscillation and the periodic vortex shedding;as the thickness of the incoming boundary layer increases,the free shear layer becomes more stable and the Helmholtz resonance is avoided effectively,thereby the cavity buffeting noise is reduced effectively,adding a convexity upstream of the cavity opening to interfere the shape of the incoming boundary layer to reduce the acoustic feedback effect can reduce the cavity buffeting noise effectively.

Robust control for active suspension system under steering condition

To minimize the auto body's posture change caused by steering and uneven road, and improve the vehicle's riding comfort and handling stability, this paper presents an H∞ robust controller of the active suspension system, which considers the effects of different steering conditions on its dynamic performance. The vehicle's vibration in the yaw, roll, pitch and vertical direction and the suspension's dynamic deflection in the steering process are taken into account for the designed H∞ robust controller, and it introduces the frequency weight function to improve the riding comfort in the specific sensitive frequency bands to human body. The proposed robust controller is testified through simulation and steering wheel angle step test. The results show that the active suspension with the designed robust controller can enhance the anti-roll capability of the vehicle, inhibit the changes of the body, and improve the riding comfort of the vehicle under steering condition. The results of this study can provide certain theoretical basis for the research and application of active suspension system.

Challenges and solutions in automotive powertrain systems

Automotive powertrain mainly consisting of combustion engine,motor and battery(i.e.special for hybrid powertrain)is a very complicated integration system,and the research on the automotive powertrain control techniques remains hot-spot in past decades.This paper proposes some challenging issues and control solutions of automotive powertrain system from the perspective of the dynamic system theory.The typical characteristics of automotive powertrain system are analysed for control development,and the several control applications using model-based and model-free control design are demonstrated with sufficient experimental validation.In addition,some open issues for future powertrain control development are summarised.

Multi-mode energy management strategy for hydraulic hub-motor auxiliary system based on improved global optimization algorithm

Heavy commercial vehicles equipped with a hydraulic hub-motor auxiliary system(HHMAS)often operate under complex road conditions.Selecting appropriate operating mode and realizing reasonable energy management to match unpredictable road conditions are the keys to the driving performance and fuel economy of HHMAS.Therefore,a multi-mode energy management strategy(MM-EMS)based on improved global optimization algorithm is proposed in this study for HHMAS.First,an improved dynamic programming(DP)algorithm for HHMAS is developed.This improved DP algorithm considers the effect of SOC and vehicle speed,thereby preventing the calculation results from falling into local optimization.This algorithm also reduces the dimension of the control variable data grid,and the calculation time is reduced by 35%without affecting the accuracy.Second,a MM-EMS with hierarchical control is proposed.This strategy extracts the optimal control rules from the results of the improved DP algorithm.Then it divides the system’s operating region into two types,namely,single-mode working region and mixedmode working region.In the single-mode working region,mode switching is realized through fixed thresholds.In the mixedmode working region,a linear quadratic regulator(LQR)is adopted to determine a target mode and realize SOC tracking control.Finally,the designed MM-EMS is verified separately in offline simulation and hardware-in-the-loop(HIL)under actual vehicle test cycles.Simulation results show that the results between HIL and offline simulation are largely coincidence.Besides,in comparison with the engine optimal control strategy,the designed MM-EMS can achieve an approximate optimal control,with oil savings of 3.96%.