Effects of residual stresses on the static and fatigue strength of laser-welded lap joints with different welding speeds

This study was conducted to determine whether the different residual stresses caused by different welding speeds affect the static and fatigue strength of laser-welded lap joints. Residual stresses in STS301L laser-welded lap joints of different thicknesses under two laser-welding speed conditions, 4.1 m/min and 5.1 m/min, were evaluated with the incremental hole-drilling strain gage method at the middle of the heat-affected zone (HAZ). Then, static and fatigue tests were performed. The results show that higher static and fatigue strengths were obtained from the specimens welded with a 4.1 m/min welding speed than from the specimens welded at 5.1 m/min. The main difference was due to the compressive principal residual stress magnitude and its orientation near the HAZ. Also, the micro-hardness profile along the failure interface was measured to verify the static and fatigue failure behavior.     

Analytical study on the performance of a high power pretensioner

In this paper, a numerical procedure to estimate the performance of the high power pretensioner used in the seatbelt of a passenger vehicle is presented. The data on the gas explosion pressure in a 10-cc volume and the data on the displacement of the rack according to time were applied to the numerical procedure. The procedure was implemented using MATLAB. The testing device, which met the automobile industry standards, was created. Experiments were carried out seven times under the same conditions, and the mean values of the web retraction and belt load were used as the representative data. By comparing the simulation results to the test results, the numerical procedure presented in this paper was verified.     

Experimental investigation of the valvetrain friction in actual engine operation conditions

Recently, the demands for improved fuel economy have been continually rising because of environmental protection policies, legislative pressures on emissions and increases in the price of oil. Reducing the friction power loss in a production engine may be regarded as one of the most effective technologies for improving fuel economy because the technology is cost effective and applicable to a great number of vehicles. This paper describes attempts to measure the torque needed to drive a camshaft and to examine the sources of the torque fluctuations in order to analyze the friction in valvetrains. The measurements were performed through a cam sprocket-type torquemeter, which was able to measure the torque of the valvetrain under actual engine operating conditions. In the cam torque measured, the fluctuations were mainly dependent on the primary oscillations caused by cam events and the secondary oscillations caused by the valvetrain natural frequency. The range of the fluctuations became greater at high speed because of the inertial mass. The resulting FMEP (friction mean effective pressure) of the valvetrain decreased, and the effective peak tension increased with an increase in the engine speed.     

Decision fusion of a multi-sensing embedded system for occupant safety measures

The need for an embedded system that can fuse incomplete, inconsistent, and imprecise decisions from several sensing systems is a crucial step in achieving an effective decision for occupant safety measures. This paper deals with the decision fusion strategies of a multi-sensing embedded system to achieve significant enhancement in the reliability of occupant safety through the fused decisions. Multi-sensing approaches to determine weight, vision, and crash sensing are developed for occupant detection, classification, position calculation, and crash detection. A rule-based decision fusion algorithm is then developed to fuse the multi-sensing decisions. The developed sensing systems are incorporated into an embedded device. To execute the embedded system, a system interface between the software and hardware is developed using Lab Window/CVI with the C programming language. The experimental results demonstrated that the real time operation of the embedded system validate the effectiveness of the decision fusion algorithm, characterize the safety measures and monitor the decision application. Several events were tested that prove the performance of the embedded system is robust towards occupant safety measures.     

Stress analysis of ventilated brake discs using the finite element method

One of the most common problems related to ventilated brake discs are crack formations, particularly under high brake loads or from the associated stresses during braking. In this study, three different ventilated brake discs, the crossdrilled disc, the cross-slotted disc, and the cross-slotted with a side groove disc, were manufactured, and their braking force performances were investigated experimentally together with a solid disc. Stress analyses were subsequently performed by the finite element method. Analyses results showed that the maximum stress generations were formed on the ventilated discs in comparison to the solid disc. However, these comparisons indicate that the application of varying force distributions along brake pads reduces the stresses on ventilated discs by 8.8% to 19.1%.     

Modeling and control strategy development for fuel cell hybrid vehicles

Using MATLAB/Simulink, we constructed a comprehensive simulation model for the fuel cell hybrid vehicle (FCHV) power train in parallel with a power control strategy that uses a logic threshold approach implemented with a hybrid control unit (HCU). The simulation implements power flow and power distribution under different vehicle operating modes using the accelerator and decelerator pedal positions deduced from the driving schedule as primary inputs. The HCU control strategy also incorporates regenerative braking and recharging for recovery of battery capacity. Using the D-optimality method for selection of the optimal experiment values, three control threshold variables for the HCU are selected to maximize the hydrogen fuel economy under certain driving cycles. The proposed method provides the optimal configuration of the FCHV model, which has the capability of achieving the requested drive power while also meeting the vehicle driving schedule and recovery needs of the state of charge (SOC) battery, with lower fuel consumption levels.     

Development and analysis of an air spring model

The analytical model of an air spring can be effectively used for the design of air spring equipped vehicles to provide better ride and handling characteristics along with various functions for passenger convenience. However, establishing a general model of an air spring poses particular difficulties due to the severe nonlinearities in the stiffness and the hysteresis effects, which are hardly observed in conventional coil springs. The purpose of this study is to develop a general analytic model of an air spring — one which represents the main characteristics of stiffness and hysteresis and which can be connected to a model of pneumatic systems desigined to control air spring height. To this end, the mathematical model was established on the basis of thermodynamics with the assumptions that the thermodynamic parameters do not vary with the position inside the air spring, that the air has the ideal gas property, and that the kinetic and potential energies of the air are negligible. The analysis of the model has revealed that the stiffness is affected by the volume variation, the heat transfer, and the variation of the air mass and the effective area. However, the hysteresis is mainly affected by the heat transfer and the variation of the effective area. In particular, it was revealed that the increase of the volume due to the cross-sectional area increases the stiffness, while the increase of the volume due to the other reason decreases it. In addition, the model was used to develop the sufficient stability condition, and the stability of the model was analyzed. The paper also presents the comparison between the simulation and experimental results to validate the established model and demonstrates the potential of the model to be usefully employed for the development of the air spring and its algorithm for use in a pneumatic system.     

Optimization and Performance Enhancement of Active Suspensions for Automobiles under Preview of the Road

The problem of deriving control laws which minimize specified performance indices for a vehicle moving on a rough surface with preview of the surface elevation is considered. The approach is based on linear optimal tracking theory and consequently the system elements are taken to be linear and the performance index is constrained to be of quadratic form.

The ideas of overtaking optimality are applied to the problem in order to achieve a closed form solution for the control. Then, using the control laws derived, computer simulations of performance are conducted and time histories are shown. In the absence of limitations on either processing or actuator speeds, and for cases in which the preview is sufficient to give good control laws, the value of the preview in enhancing vehicle suspension performance is assessed. Comparisons are made with results in the literature.     

Competition policy and the liberalisation of European aviation

The European aviation industry is undergoing a process of liberalisation. One of the important lessons of American deregulation was that the industry is not perfectly contestable. One implication of this is that actual competition on a route is important in order to be able to secure the benefits of deregulation or liberalisation. Another is that effective competition policy is important in order to prevent anti-competitive mergers or predatory behaviour. This paper reviews the merger investigations in European aviation which have accompanied the search by carriers to secure the benefits of market power, and considers the extent of route competition within the European Community and its relationship to the different route licensing policies of different national governments. The paper considers the extent of present competition on the busiest routes, and stresses the importance of cabotage rights in opening up the European market to effective competition.     

Waterfront redevelopment in Canadian port cities: some viewpoints on issues involved

This paper reports on a component of a research project on Canadian Dimensions of Waterfront Revitalization wherein forty-five interviews were held in Canadian port cities with port authority representatives, urban planners and developers. Respondents were asked to fill in a questionnaire, and the findings from this questionnaire survey are discussed in this paper. Anticipated contrasts between planning philosophies in different professions were largely but not invariably confirmed.