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Virtual Design and Performance Analysis of Run-Flat Inserts

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Tutor: ZuoJin;S.J.Zhang
School: Jilin University
Course: Agricultural Mechanization Engineering
Keywords: Tire,Run-Flat,Insert,Theoretical Model,Parameter Selection,Self-adaptive Design,
CLC: U463.341
Type: PhD thesis
Year:  2007
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Abstract:
Safety, endurance, economy, and comfort are the basic requirements of the tire, especially, safety is the most important. The traffic accidents will occur and vehicle will stop walking when the tire is punctured. Run-Flat tire technique has been paid more and more attention to as one of the key techniques for improving vehicle safety in recent years. There are three types of main techniques of run-flat, that are, self-sealing, self-supporting, and inserts-supporting. The standard rim and the tire equipped with inserts can protect vehicle safety when vehicle tire blowout occurs and can continue its journey for certain distance at a lower speed than a specified maximum speed after losing pressure. The inserts can be equipped with military vehicles, VIP cars, SUV, ambulances, engineering vehicles, farm trucks and others. The key technologies of inserts include configuration forms, dimensional parameters, and material properties. Because of no systematical design theory, less mathematics modes for parameters selection and the design methods depended on the conventional experience, the insert techniques can not be extend to more vehicles. In order to obtain the optimum performance of inserts, the theory and parameters selection formulas for insert design were established, and digital model of inserts was created through self-adaptive design method by AIP and the 3D structure was optimized through collaborative finite element analysis (FEA) by ANSYS in this work.The zero rolling concept of Run-Flat Tire (RFT) was put forward, including RFT rolling mechanism, inserts design, and RFT application. The research of RFT system is related to terrain-vehicle system mechanics, tire technologies and vehicle dynamics. RTT system is a sub-system of the terrain-vehicle systems at zero air pressure, and a special sub-dynamic of the vehicle dynamics as well. The inserts become a core parts from a spare states after tire blowout. It is important that the inserts must be cooperated with the rim, the tire, and the terrain to keep the vehicle running forward. Effective System Model of the RFT Zero Rolling was established referenced from pneumatic tire modeling ideas and based on the tire deformation disciplinarian with the change of air pressure. Tire crown consists of series-wound spring-damping elements and tire sidewall consists of shunt-wound spring-damping elements. Grounding part of deflated tire is a rectangle elastic gasket which is pressed by inserts and friction against road surface. Inserts coupled rigidly with rim to form a wrapping angle with tire. Spring-damping elements can be stretched or compressed to do work and rectangle elastic gasket can create friction force work, which will be transformed the heat energy into inserts, tire and rim.In order to explain the zero rolling behavior and ability, the Mane Brush Model of deflated tire was established. That were, Length and width of tire print surface are constants; tire belt is flexible strap with bending character and no extending capability; crown rubber is a series of mane connected with strap; shear deformation or the mane can occur due to adhesion between the road-engaging end of mane and the road surface; the number of mane with shear deformation is associated with the inner touched surface of wrapping angle.A integratiag formula of the tangential force of tire were presented during driving and braking conditions according to shear deformation of mane. It was found that the maximum value of tangential force under the zero pressure is smaller than the longitudinal force under the standard pressure; the side force under the zero pressure is increased with the side slip angle enlargement, but the slope is small in the smaller side slip angle, the side force is the same as tire inflated under the bigger side slip angle. The aligning torque under the zero pressure will be increased with the side slip angle and, as a result, the steering performance will become difficulty. The zero rolling resistances include elastic hysteresis resistances, contacting friction force against ground and revolved air flow resistances. The indications of no running ability are the tire slipped along the wheel-flange and the bead unseated on the rim. The height and width of inserts should protect the tire from folding together during running. The bigger inserts is, the better zero running performance is. The vibrations of the RFT system consist of self-excitation vibration and exterior vibration. The sympathetic vibration can lead to destroy due to acute distortion. The friction between the surface of inserts and tire or rim can lead to wear of the inside and the outside of tire. The inner fictions among the surfaces of tire structure materials can lead to rubber body fatigue damage, part interface destruction and polyester cord breakage. The temperature of RFT in zero running should not exceed the highest durable temperature of tire. The high speed standing wave and the zero pressure standing wave can increase the energy loss of RFT system.The pressure distribution of tire on contact footprint tends to concentration and has a distance relative to wheel center line. RFT has rolling and slipping movement in driving and driven conditions. The movement of insert element was analyzed for pure rolling condition and it was demonstrated that there are the most instantaneous velocity and inertia force at the highest position of the wheel. The conneting pars should keep balance between the applied force and the most instantaneous inertia force for a non-integral insert structure. The inserts, as the accessories of the wheel, increase its moment of inertia, thus, the inserts should use the lighter material under the premise condition of the enough height and width parameters and the configuration designs at best to symmetry.The design requirements of the inserts were determined according to the RFT performance. The design factors were analyzed and the mathematics models for preferences were established. The different types of rim should be equipped with different divisions of insert. The basic sizes of the insert are equal to the rim gutter sizes. It is more difficulty to design inserts for the flat tire. Based on the calculated principles of the equilibrium contour of inflated tire and the important parameters, the cross section profiles of inflated tire were found and the constraint formulas of inserts parameters were established. The radial deformation, cornering deformation, camber deformation and the enveloping deformation of pneumatic tire were analyzed. It was indicated that the inner space of tire with inserts must be able to contain the maximum combined deformation of tire. The center trochoids of checking tool ball were ascertained with the ball diameter enlargement. The minimum scales The culmination of the insert being at the outside of the trochoid can avoid the pulling off of the tire. The calculating formulas for minimum and maximum scales of inserts were established according to installation methods of inserts. The calculating formula of pretightening force for bolt was presented adapted to the docking approaches. The insert parameters based on 6J standard rim and 205/60R15 radial tire were calculated through the CAGD method. It was found that the height and the width coefficients calculated are in good agreement with the golden section, which adapted to others similar as 60 series of tires.The inserts were designed for 6J rim and 205/60R15 radial tire through self-adaptive design method by AIP software and the connecting parts and the bolts were also created based on the RFT virtual assembly model. Five materials were selected for inserts and 3D structural strength was analyzed by AIP module in ANSYS. The results showed that the inserts made from glass fiber-reinforced and nano-modified PA6 materials have a better safety performance. The weakness places are at the end of the insert and the material waste place exists in the middle of insert body. In order to reduce the insert mass and enhance the structural strength, the 10¡ãelement of the insert was selected and topological optimization was done by ANSYS collaborative analysis technology. The results showed that the bilateral parts and middle area of cross section on the insert can remove some material. The improvement of 3D structure forms were carried out and the insert mass decrease were close to 30 percent according to the topological optimization results. The effects of main geometry features on the structure strength were investgated and the final configurations of the insert were confirmed. That were, top width was 80mm, middle width was 60mm, bottom width was 86.5mm, loop trough for installing tire was 22mm in width, lock trough was 12mm in width, locking wall was 18mm in thickness, bolt-pin hole diameter was 10mm, and hole diameter for reducing mass 25mm and 3-5 in the number.The intrinsic frequency and natural mode of vibration were predicted using modal analysis. The results showed that the intrinsic frequency of the insert was far higher than the tire and, as a result, the destruction due to the resonance was difficultly.Through controlling the sizes of the whole elements and refining the two terminal elements, the precision structural strength results were obtained. That were, the equivalent stress and max main stress position located in the lock hole and near the front of lower inner surface. It was concluded applying the weak spring element of ANSYS to simulate the insert rotated in the rim gutter that the safety coefficient was depressed when slipping and the destroyed place was in the contact region between the insert bottom and the rim gutter. The safety degree was predicted at varied vehicle speeds, the results showed that the insert was safety when the vehicle speed is less than 140 Km/h and the insert for test can be manufactured using PA6 or PA66 materials.The steady temperature field was analyzed through applying the boundary conditions of the third kind. It was found that the high temperature area was continuation and centralization in outer loop surface; the continuation of the insert temperature was divided to several parts by reducing mass holes. The steady temperature field distributed in the contact area of the insert with the rim was also analyzed. it was demonstrated that the insert temperature would be in higher temperature than 70¡æ. The two types of dispersing thermal structure, loop trough and concave-convex surface, were designed on the outer surface of insert and analysis of the steady temperature field results showed that the dispersing thermal structure designed can reduce the high temperature area and the depressed the temperature inside the insert. Under the assembly contact condition, the high temperature area moved to up a little on the bottom of the insert and the most insert body was in a higher temperature than 70¡æ. Moreover, the thermal-structural coupling analysis was done and then the stress field was found. It was shown that the safety coefficient of the insert was depressed as the insert structure equivalent stress was increased and the deformation area was enlarged.The assembly performance checkout were carried out using the interference checking tool based on the virtual RFT model and the results showed that the assembly have no interference, the insert can be lock up, and the all parts of RFT can be disassemble and assemble smoothly. The engineering drawings and the technical documents were created based on the RFT virtual assembly. The block of the physical insert was made using centrifugal casting method and the product for test was manufactured by machine tools. The connecting parts were manufactured by NC machine tools. The assembly results showed that the inserts can be assembled in reason and locked up into inner room of tire.Finally, some performance tests of RFT have been done using the flat testing bed. The results showed that the contact footprint of the RFT without air pressure was very close to rectangle; the rebounding capability of tire was natural at the pure rolling condition; the maximum value of tangential force under the zero pressure was smaller than the longitudinal force under the standard pressure. The side force under the zero pressure was increased with the side slip angle enlargement, but the slope was smaller in the small side slip angle; the side force was same as tire inflated under the bigger side slip angle; the aligning torque was increased with the side slip angle addition under the zero pressure; the offset with bigger side slip angle was asymmetric but no phenomena of tire slipping and pulling off occur. The tests results have proved that RFT Zero Rolling Equivalent System Model and the Mane Brush Model of deflated tire established were effective; the selected methods and calculating formula for parameters of the insert were reasonabe and effective; the virtual design process were creditable; and the insert product achieved can meet the main performance requirements of RFT.
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