Research On Safety Design Method For Front Collision Of Monocoque Bus Body

Buses are one of the main means of trafficway transit,and their safety has always been concerned by the society and the government.At present,the passive safety regulations and standards for bus implemented in various countries are mainly aimed at the requirement of rollover safety assess the living space of passengers,while the development of the front collision regulations is lagging behind,therefore there is no written regulations and standards.China has already been one of the world’s largest countries in bus production,sales and ownership.The casualty rate of bus accidents is relatively high,and the safety of front collision is becoming more and more prominent.In recent years,under the promotion of the Bus Association,the joint industry association,mainstream bus OEMs,testing organization and universities have formed a research group.After nearly 10 years’ standard development,related subjects have been studied.The research has completed the 30 km/h front crash test and evaluation of 15 vehicles from 6m light bus to 13.7m super-large bus,and initially formed a complete set of bus front crash safety test and evaluation standard system.In this paper,using the above test and evaluation methods,taking the 12 m monocoque highway bus as the research object,the frontal crash safety design method of the load-carrying highway bus body is studied.The standard adopts 30 km/h full frontal rigid wall collision mode,mainly taking occupant protection as assessment criteria,while the driver and passenger assessment criteria are different.The driver adopts ECER29 regulation of commercial vehicle,which mainly examines the living space.In addition to passenger seat assessment,head,chest and leg injury indicators are added to passenger car neck injury indicators in passenger area.The bus body structure,especially the monocoque bus body,is an integral space truss structure with welded small cross-section beams.The characteristics of the rear engine and staggered structure with the floor of the passenger area higher than the driving area determine that its safety design can not directly copy the experience of cars or commercial vehicles.Therefore,based on this standard and the characteristics of bus structure,and using the mature theory and method of car collision for reference,this paper conducts research on CAE simulation model validation,force transfer path design,deformation control,restraint system optimization,energy absorption optimization and stiffness matching of front sub-structure and acceleration waveform equivalence method,and explores a set of body structure suitable for front-impact of monocoque bus body.This safety design method can be used to guide the improvement of crashworthiness design of body frame structure.Firstly,taking the 12 m monocoque bus as an object,the crashworthiness test and passenger safety evaluation of the full front rigid wall collision are carried out,as well as the CAE simulation analysis.By comparing the main skeleton deformation mode of the front body,the intrusion of the driver’s living space and the main characteristic parameters of acceleration,the validity of the simulation model is verified,and the outstanding problem of the prototype vehicle is summarized.According to the characteristics of bus structure,layout and occupant protection,the general research route of Crashworthiness overall spatial planning and safety design of bus body structure are put forward.Improving the failure problem of restraint system,using seat dynamic test trolley to simulate and reproduce the failure points of seat,by developing structural optimization method,can improve the strength and fixed strength of seat,guardrail and occupant injury to compound the standard of seat trolley first,and then substitute the impact waveform of prototype real vehicle for the assessment of occupant injury.The stability of restraint system will be achieved,while the occupant under the prototype vehicle test waveform will be assessed.Damage indicators can meet the requirements of laws and regulations,but the deformation of the front driving area is serious,which invades the driver’s living space.Then,starting from the deformation control of the front structure,the improved design method of the structure crashworthiness based on the driver’s living space is studied.The topology optimization,optimization design and crashworthiness test of the sub-structure are carried out by means of the sub-structure method.The anti-deformation ability of the front structure is effectively improved,and a structural scheme of the fixed support for the tube string of the reversible steering machine is put forward,which can be effectively used in the crash.By controlling the steering wheel intruding into the living space;in order to prevent the driver’s rear frame intruding into the living space,improve the transition structure between the driving area and the passenger area skeleton partially;by substituting the above optimization scheme into the vehicle collision model,then the deformation of the improved driving area is controlled,and the living space is not intruded.But the acceleration waveform of the passenger area is obviously improved,and the passenger area is substituted for the seat trolley to evaluate the occupant damage.At the same time,the effect of three different seat spacing on occupant injury is discussed.The results show that under the restraint of seat spacing two-point seat belt,the three common seat spacing can not be satisfied.The head HIC and neck MY of occupant injury exceed the standard under each seat spacing,especially the head HIC which is more than 1000,while the three-point seat belt has a better restraint on upper limb trunk,only chest acceleration a little exceed.With the increase of seat spacing and the decrease of damage,the three-point seat belt is beneficial to occupant protection.Without changing the seat restraint system,the acceleration of the car body needs to be further optimized.In order to improve the acceleration waveform of bus body,by studying the crashworthiness of main bus body materials,stainless steel material is selected as the crashworthiness absorber material,and the crashworthiness evaluation and experimental study of conventional cross-sections are carried out.The circular shape is determined as the cross-section form of bus buffer absorber,and the optimization method is applied to optimize the size of the relevant absorber.The vehicle crash analysis of two groups of feasible substructure skeleton matching schemes is discussed.The acceleration waveform of the optimum scheme in passenger area of bus has been better improved.The simulation of seated trolley can pass the regulations.Based on the improved scheme,the vehicle validation test is carried out,and the occupant damage meets the requirements of the standard.The stiffness characterization of the front body of the improved scheme is further studied.The stiffness matching reference values of 12 m correlated vehicle models are proposed.Finally,according to the characteristics of bus structure and crash waveform,ESW and TESW equivalent method are used to analyze waveform equivalence.By comparing the velocity and displacement curves of equivalent waveform,the cusp equivalent waveform TESW has higher accuracy than ESW,which meets the engineering requirements.The multiplication of three different wave equivalent methods,i.e.ascending,horizontal and descending,are further studied.The analysis and comparison of occupant damage shows that the descending wave is the most favorable for occupant protection,and the descending wave should be obtained as far as possible in subsequent body development,which is beneficial to occupant protection.