Turbocharger Structural Integrity

Since the introduction of Euro VI in January 2014, all new diesel powered commercial vehicles have been equipped with turbocharged engines. It is virtually impossible to meet these emission regulations without using a turbocharger. Similarly, in the passenger car sector both on diesel and petrol (gasoline) powered vehicles, legislative pressure to reduce emissions of carbon dioxide are seeing the introduction of turbochargers across almost all new power units. Future legislation will continue this trend with engine manufacturers becoming increasingly reliant on turbocharging. As well as increasing the requirement for turbochargers, these external factors are also demanding that turbochargers become more responsive with reduced rotor inertia and lower thermal inertias. This in turn makes the task of ensuring that turbocharger components remain fit for purpose for the life of the turbocharger that much more difficult. In this paper some of the recent developments in turbocharger technology will be identified and the demands that these place on the structural components will be explored. The limitations of current methods of structural integrity assessment for some of these components will be discussed. Future developments of these methods will then be proposed

Contact Pressure Distribution in Joints Formed by V-Band Clamps

V-band clamps offer an efficient clamping solution in diverse applications including process equipment, exhaust systems and air handling. This paper studies the distribution of interface contact pressure between the V-band and flange when the coupling is established. The determination of the contact area and pressure distribution in a joint is essential information, as it determines the integrity of the coupling. A three dimensional finite element model has been developed for this purpose. Contrary to the previous assumption in developing axisymmetric models, the 3D results showed that the contact pressure is non-uniform around the circumference of V-band with maximum contact pressure near the T-bolt area. This is in agreement with the theory in the literature. The presence and magnitude of friction has a noticeable influence on the form of the interface pressure distribution curve. It is also shown that the diameter of the band interacts with the effect of friction

Analysis of the Torsional Load Capacity of V-Section Band Clamps

This paper investigates the torsional load capacity of three sizes of V-section band clamps when assembled onto rigid flanges by comparing experimental data with a developed theoretical model. This mode of failure is of particular interest for turbocharger applications where, in use, they are subjected to torsional loading via thermal and vibrational effects. The theoretical model developed allows the impact on torsional load capacity of a number of joint parameters to be investigated and good correlation of the results, incorporating variations in coefficients of friction and dimensions, has been shown for the two larger band sizes. For smaller diameter bands, the experimental data suggests that as the band is tightened, contact with the flange is localised rather than being over the full circumference of the band. The coefficients of friction, in particular that between the flanges, and the position of the contact point between band and flange have been shown to have a significant impact on the theoretical torsional load capacity of V-section band clamps

Classical and numerical approaches to determining V-section band clamp axial stiffness

V-band clamp joints are used in a wide range of applications to connect circular flanges, for ducts, pipes and the turbocharger housing. Previous studies and research on V-bands are either purely empirical or analytical with limited applicability on the variety of V-band design and working conditions. In this paper models of the V-band are developed based on the classical theory of solid mechanics and the finite element method to study the behaviour of the V-bands under axial loading conditions. The good agreement between results from the developed FEA and the classical model support the suitability of the latter to model V-band joints with diameters greater than 110 mm under axial loading. The results from both models suggest that the axial stiffness for this V-band cross section reaches a peak value for V-bands with radius of approximately 150 mm across a wide range of coefficients of friction. Also, it is shown that the coefficient of friction and the wedge angle have a significant effect on the axial stiffness of V-bands

Determining a Robust, Pareto Optimal Geometry for a Welded Joint

Multi-criteria optimization problems are known to give rise to a set of Pareto optimal solutions where one solution cannot be regarded as being superior to another. It is often stated that the selection of a particular solution from this set should be based on additional criteria. In this paper a methodology has been proposed that allows a robust design to be selected from the Pareto optimal set. This methodology has been used to determine a robust geometry for a welded joint. It has been shown that the robust geometry is dependent on the variability of the geometric parameters

The development of finite element software for creep deformation and damage analysis of weldment

This paper presents the development of finite element software for creep deformation and damage analysis of weldment. The development and benchmark test of the software under plane stress, plane strain, axisymmetric, and 3 dimensional cases were reported in previous work [1]. This paper primarily consists of two parts: 1) the structure of the new FE software and the existing FE library applied in obtaining such computational tool via an approach for stress and field variable updating; 2) the development and validation of stress update; and 3) the development of validation of multi-material zones version. This paper contributes to the computational creep damage mechanics in general and particular to the design and the development of finite element software for creep damage analysis of multi-material zone

Stress in V-section band clamps

This paper presents an analysis of the stresses in V-section band clamps by examining the correlation between experimental work and theoretical models. Theoretical models incorporating traditional beam-bending theories and allowing for friction were developed to calculate the stress distribution and displacements within the clamps. The theoretical models demonstrated that the normal manufacturing tolerances associated with this type of component, combined with the uncontrolled operating parameters, will produce a wide variation in working stresses. These theoretical models were validated using strain and displacement measurements from a test with a V-section band clamp positioned around rigid flanges. The experimental results all fell within the range of stresses predicted by the theoretical models. The paper provides a knowledge base for the rational design of V-section band clamp

The development of computational FE system for creep damage analysis of weldment

A Finite Element Analysis (FEA) system was designed for the analysis of creep deformation and damage evolution in weldment. This project essentially consists of three parts which involves 1) transfer programme development, 2) numerical integration subroutine development, and 3) validation of complete FEA system. Firstly, the development of a user-friendly pre- and post- processing transfer programme and its assembly with the numerical solver was reported; its primary development was published before. This part includes file format understanding, specific parameter adding, and transfer algorithm design. Secondly, a numerical integration subroutine which developed for specific creep constitutive equations was introduced. This part includes the numerical method selection, accuracy control in finite element method, and its validation. Thirdly, because this project has not finished yet, a demonstration how this system works was assumed in future work. For this part, a circumferentially notched bar with low Cr alloy material case was purposed to prove the capability of transfer programme and integration subroutine

Effect of cusp size, depth and direction on stress concentration

Recently multi-axial machining technology has improved significantly. It has become a widely accepted method of manufacturing components with complex, free form surfaces. Solid billet materials with negligible internal defects are used in this process. This provides increased durability and fatigue life over equivalent cast components. However, multi-axial machining leaves cusps as machining marks. The combination of tool size and step-over generates cusps with different depths and widths. Even though the cusps add extra material on top of the nominal surface, the Finite Element Analysis simulations presented in this paper show that the maximum stress generated within the cusps can be greater than that predicted from the cusp-free geometry. These stress concentrations generated by cusps can reduce the fatigue life and durability of a machined component. In this paper a full factorial analysis of the effect of tool size, cusp width/step-over and cusp direction has been conducted. The analysis uses five different levels of tool size and cusps width and four levels of cusp direction. The results can be used to determine a tool size, cusp width and cusp direction combination with minimum spurious stress raising effect

Electromagnetic and Mechanical Analysis of High Speed SPM Rotor with Copper Shield

For high-speed applications, the surface-mounted permanent magnet (SPM) machine is preferred due to its high torque density and efficiency. However, induced eddy currents in the rotor conductive parts result in a loss of efficiency and rotor heating. Therefore, several methods to reduce such losses have been proposed in the literature including copper shielding. In this paper, a high-speed SPM machine rotor with a copper shield is designed and investigated both electromagnetically and mechanically. Several quantitative investigations including placing the copper sheet around the retaining sleeve or magnets, different copper sheet and airgap thicknesses, different retaining sleeve materials, different harmonic contents in the current waveform, i.e. pulse amplitude modulation (PAM) and pulse width modulation (PWM) generated waveforms, and different frequencies and current levels are reported. Additionally, a mechanical analysis investigating possible failure modes of the rotor with the copper sheet is reported