Research On The Structure Design Of Commercial Vehicle Passive Safety

In the development of countries'economy,commercial vehicles play a more and more important part.As the rise of the speed, commercial vehicles with big structure size and heavy weight have a high rate of damage to people and vehicle itself. So research and improvement on the structure of commercial vehicles passive safety is an urgent social issue. Combined with"technology of safety development for commercial vehicle cab"as a sub-project of 863 national project"high quality heavy commercial vehicle advanced technology", foucusing on the key issue of commercial vehicle passive safety that the design of the cab must meet ECE R29, this article makes an exploratory evaculation method for passengers'survival space , making up for deficiency of ECE R29. Taking advantage of simplified parameterized model, to choose and determine design scheme in the concept design phase, the article takes a study on the method of building simplified parameterized model in the concept design phase,and mainly studied how to make a top-down design of the section structure of main absorbing energy component. According to another key problem of commercial vehicle passive safety, the article studies the structure design f the underrun protection preventing damage of cars running into the car-bottom.ECE R29 ordains to check survival space at the end of the front pendulum impact test. However, in the course of the entire pendulum impact, the final deformation of the cab is not equal to the maximum deformation because of the material unloading springback resulting in the inability to predict the dummy's injury. In order to observe the changes in survival space more accurately and vividly, this CAE technology is used. The virtual human body model specified in ECE R29 regulations was established, and was placed on the seat according to the actual H-point location in the cab, and then the occupant survival space limits and measurement points was determined. According to the front pendulum collision process, knee and abdominal injuries are the main parts of the occupant characteristics, setting up six evaluation parameters for the dynamic evaluation of occupant survival space. It makes up for the limitation of checking survival space test at the end of pendulum front impact in ECE R29 regulations , realizes virtual living space evaluation in the digital design phase and achieves control of the living space more accurately at the design stage.Regarding the structure design of commercial vehicle cab of pendulum impact passive safety, traditional body structure design method is based on experience or in reference to the reference model to determine structure and cross section form, a detailed re-use of structure-based finite element analysis model to verify , then changes structure with the results of the analysis, until meeting scheduled performance requirements. This proforma approach requires extensive design and development experience, otherwise it is hard to meet the requirements of modern automotive development cycle. In this paper, the dynamic simulation model of the commercial vehicle cab was eestablished based on ECE R29 by LS-DYNA software and was verified by cab deformation and suspension fracture. The finite element model makes a base model. Then it elaborated on the concept design phase of commercial simplified parameterized model of ways and build the principles of simplified parameterized model on the conditions of positive pendulum impact: (1) simplified parameterized model should effectively reflect the characteristics of research questions, and be able to effectively simulate the cab front pendulum collision characteristics, and other properties need not be considered. It should reduce the size of the model solution, thereby reduce the computing time of the model. (2) The parameterized model describing the parameters should be correct and clear, so as to facilitate changing and adjustment of parameters in the concept design stage and achieve rapid assessment of the multi-sheme in concept design phase, and propose the specific mechanical performance requirements of the detailed design of sub-structure. For the stiffness and inertial characteristics of these two aspects affecting the crashworthiness characteristics, the parameterized modeling of key technologies was studied. According to the load transmission and energy distribution analysis, the main energy-absorbing parts was determined. Focusing on its main deformation mode, using sub-structure finite element method to extract its crushing stiffness and bending stiffness characteristic curve and, based on principle that the absorbing energy is equaivalent before and after the simplifying of the structure principle, the corresponding procedures was conducted and crushing stiffness and bending stiffness characteristic curve was simplified with the corresponding crushing and bending stiffness parameters extracted. Regarding to the non-essential energy absorption structure, the cross-sectional properties to ensure that its inertial properties was extracted. The simplified parameterized model was compared and verified with the base model according to the deformation of the cab, fracture form and time of suspension, absorption energy and the back-end maximum displacement in the Z direction of floor rail, the pendulum response .The cross-section structure design methods of commercial vehicle components based on positive crashworthiness design goals was studied emphatically utilizing the simplified parameterized model. First, in accordance with the distance constraints of lower rim of steering wheel and the virtual dummy model in ECE R29, it is able to identify design objectives and design process of the pendulum impact crashworthiness of the cab. Based on the total energy of the collision and the front-end crush space permits, absorbing energy of the previous lower energy-absorbing devices was set. It adjusted the stiffness parameters of the floor rail and energy-absorbing devices to achieve design goals and make energy-absorbing devices, floor rails in the collision course to meet the crush order, preventing the stiffness inversion which may occur in the traditional design method, and eliminated bending deformation of the rear floor rail, preventing the rear cabin crew surviving space narrowing and the space disappearance caused by forward of the front passenger seat. According to Abramowicz Classic thin-walled beam crushing theory, the fold-wavelength formula of symmetry and extension deformation was used to get the size parameters of energy-absorbing devices. Through the self-designed standard cross section databases, the cross-section parameters of floor rail structure were set. And the design goals were verified in the detailed finite element model. So that the cross-section of the performance oriented of commercial vehicle structure design was achieved.Another key issue of the commercial vehicle passive safety is the design of the underrun protection. In the rear end collision of passenger car and heavy commercial vehicle, as the height difference between the truck and the car, if the commercial vehicle doesn't equip the rear underrun protection, passenger car is easy to drill into the bottom of the commercial vehicle because lacking of obstruction. Consequently, the underrun protection must be mounted. The protection devices should meet two requirements. The first one is the resist function that stops the cars from going in bottom of the truck. The other is buffer and energy-absorb, which reduce the passenger injure and improve the compatibility. In this paper, to solve the problem of the low blocking ability, a height-adjustable rear underrun protection were designed first, aiming at the match of height of passenger car's rail and energy-absorbing protective beam. The principle is that when the SUV and vehicle with high front impact, promoting the moving the top level sting, through the ropes energy-absorbing protective beam can be raised. When the vehicle with low front impact, energy-absorbing protective beam doesn't rise, the rail impacts the beam directly. Compared with the original rear underrun protection, it can reduce the amount of drilling amount, providing the obstruction. Compared with the rigid net rear underrun protection, it can significantly reduce the deceleration of drilling vehicle, also shows good impact compatibility. To solve the cost problem brought by the complex mechanism of the height-adjustable rear underrun protection, the expansion-tube rear underrun protection is designed. The design goal is to achieve high-performance of rear underrun protection with the expansion deformation of circular tube. The principle is that when vehicle impact the rear underrn protection, it impact the protection beam first, then protection beam promote the connected punch to extend the expansion-tube, absorbing of impact energy, showing good impact compatibility. Also in the expansion phase, the expansion-tube deformation is stable, with a linear superposition of energy absorption characteristics, and is easy to control absorption energy. So it is a protective device for absorbing components. The front underrun protection was redesigned with topology optimization and size optimization, an"inverted A-shaped"bracket front underrun protection was obtained. It also achieves light-weighted. Joining the buffer components box girder, impact energy can be absorbed in the folding deformation. Compared with the original front underrun protection, it shows good impact compatibility, providing the obstruction.The innovation of this paper is that by overcoming the disadvantage of the survival space examine method in ECE R29, a different examine method of commercial vehicle survival space were proposed. It realizes the virtual evaluation of the survival space in digital design phase which can control the survival space exactly in the design phase. The top-down design method of commercial vehicle front crashworthiness and the establishment of the parameterized model were researched in detail and systematically. The cross-section design according to the front worthiness requirements with the parameterized model is the important part of the paper. It can be used in new models or modified models design, effectively shorten the design cycle and improve design quality. A height-adjustable rear underrun protection and an expansion-tube rear underrun protection and an energy-absorbing front underrun protection were designed, realizing the function of obstruction , buffer and energy-absorbing.