The Influence of In-Plane Tyre Dynamics on ABS Braking of a Quarter Vehicle Model

For efficient analysis it is important to choose the proper model that fits the problem that needs to be solved. This paper discusses three pragmatic simulation models for longitudinal behaviour of a passenger car tyre (Steady State, Transient and Rigid Ring) that may be used in e.g. an ABS simulation. The characteristics of the simulation models are evaluated using some simple simulations. Simulations with a quarter vehicle model that includes load transfer effects are carried out to determine the deviation in results between the mentioned tyre models for an ABS application. The results show that the Steady State model may only be used below 10 Hz and that the Transient model is valid up to about 30 Hz. The results from the ABS simulation with the Rigid Ring model are most reliable and are clearly different from the Steady State and Transient model, which indicates that ABS simulations should be carried out with the Rigid Ring model. Additionally it is demonstrated that for tyre behaviour on uneven roads the influence of the tyre belt cannot be neglected.     

Physically Realisable Feedback Controls for a Fully Active Preview Suspension Applied to a Half-Car Model

An optimal preview type active suspension with feedback control based on easily measured relative displacements, velocities and accelerations is proposed. Measurements relative to the road, except by the preview sensor, are not required and the front and rear spring rates are quite arbitrary. Also, state estimators or observers are unnecessary and as a practical alternative the body accelerometers may be replaced by load cells. The effects of preview on the performance, for a theoretical step type road input and an analogous random road input, are described. The definition of the optimum preview function, and its consequent effects on performance, receives attention and an example is given.     

Robust Scalable Vehicle Control via Non-Dimensional Vehicle Dynamics

A temporal and spatial re-parameterization of the linear vehicle Bicycle Model is presented utilizing non-dimensional ratios of vehicle parameters called p-groups. Investigation of the p-groups using compiled data from 44 published sets of Vehicle Dynamics reveals a normal distribution about a line through p-space. The normal distribution suggests numerical-values for an 'average' vehicle and maximum perturbations about the average. A state-feedback controller is designed utilizing the p-space line and the expected p-perturbations to robustly stabilize all vehicles encompassed by the normal distribution of vehicle parameters. Experimental verification is obtained using a scaled vehicle.     

PC-based sketch planning methods for transport and urban applications

Historically, computer models have grown in complexity, and consequently have become more difficult to use. At the same time there is a growing need for quick-response methods and techniques for broad-brush policy formulation and decision making. The personal computer and its attendant software offer new means for quantitative sketch planning. This paper illustrates two PC-based applications for quick-response exercises. These involve interactive mapping and data analysis methods for the appraisal and interpretation of transport data, and the development and use of eclectic models for systems analysis and scenario generation. The LAMM and DIAMONDS packages are described, and their use in data analysis is illustrated. The Trends Integrator Procedure (TIP) is used to formulate a simple but versatile model for investigation of developments in an urban retailing system. These packages all run on PC's and offer powerful and adaptive tools for improved transport planning.Nomenclature a _i a technical coefficient indicating the influence of the unique factor component (U _i ) for factor F _i - c _ij a technical coefficient relating the influence of factor F _i on factor F _j - F _i the relative change in the level of factor F _i - U _i the relative change in the unique factor component for F _i      

Korean liner shipping in the era of global alliances

In the course of the last two decades Korean shipping has emerged as a major player in the liner market. In 1970 there was not a single container ship in the Korean fleet; yet, within the next two decades, shipping companies from Korea have become included among the top 10 liner operators in the world, in the context of a spectacular ascent of Asian companies in international container shipping. During the same period the organization of liner shipping itself underwent major changes. In the 1970s and 1980s, pools and powerful consortia prevailed, maximizing frequency and optimizing fleet deployment under pressure from the high investment entailed by containerization. The era of consortia, however, came to a close in the early 1990s; intermodalism and the expansion of the major liner companies into forward and backward segments of the transport chain rendered them inflexible for pursuing individual strategies of product diversification with a view to larger market shares. Global alliances were finally born as a result of a major reshuffling of co-operation agreements and of the globalization of the production process on the demand side. The aim of this paper is to follow and assess the options available to an aggressive low-cost national fleet in its journey to competitive maturity through a period of changing organization of liner shipping, focusing on the course of the leading Korean container company, and one of the largest in the world today, Hanjin. It highlights at the same time both the deep structural changes which liner shipping has undergone in the last two decades and the effects of current changes, such as the recent wave of mergers in this sector.     

Rail policy in Britain — What next?

The 1974 Railways Act set British Rail (BR) the rather vague objective of providing a passenger service broadly comparable with that then existing within a given level of support. For the first few years under the Act, BR succeeded in operating within the financial constraints imposed, but only by considerable increases in charges and by negotiating wage settlements which implied declining real wages. From 1978 on, rising labour costs and reduction in traffic led to a rapidly developing crisis in BR's financial position.The position of each section of BR's business is discussed briefly. It is shown that the designation of some sectors as being purely commercial is inappropriate, since this means that benefits to users and to the community at large are ignored in decision-making. Similarly, the direction to maintain social passenger services at a given level means that finance and investment are concentrated unduly on preservation of the existing pattern of service, rather than on providing value for money. In both sectors, the likelihood is that in general fares are too high and services too frequent.At an operational level, the criterion of maximising the (weighted) volume of traffic carried is advocated as a practical way of choosing between alternative fare and service-level packages. More broadly based strategic studies would be needed to decide on the weights to be adopted, the level of finance to be made available, and the overall strategy.     

Speed behaviour of car drivers: A statistical analysis of acceptance of changes in speed policies in the Netherlands

Lowering the speed of car drivers will have positive impacts on environmental pollution and the number of road accidents. It is therefore a potentially interesting policy option for governments which want to reduce negative externalities of transport. In this paper, the acceptance of such policies is analysed by means of a survey questionnaire among car drivers and public transport users. First, an analysis is presented on the general speed behaviour, the behaviour on distinct road types, the acceptance of lower limits, and the acceptance and perception of electronic speed limiters. Next, a statistical analysis of subgroups is carried out. It is concluded that the speed of car drivers is, in general, not considered to be a main problematic issue by drivers and non-drivers; therefore, there is little scope for the acceptance of changes in speed policies. When speed policies are changed (lower limits), it seems to be most effective to emphasize safety aspects in order to increase the support of the public. However, psychological factors of speed behaviour may play an important role in this respect.     

Critical Speed and Limit Speed in Phenomena of Lateral Instability on Railway Vehicles

A comparison between theoretical calculations on dynamic lateral behaviour of railway vehicles and experimental results shows quite a sizeable difference between the calculated critical speed and the actual speed at which side impact phenomena will repeatedly occur between wheel flange and rail (running speed limit), such impact speed being remarkably lower than calculated.

Another typical experimental aspect is that the running speed limit will considerably vary for the same vehicle depending on the test track conditions. Such difference is usually attributed to alterations of the wheel-rail contact surfaces, only.

This paper will discuss some concurrent causes which may prove far from negligible, such as the effects of track defects, an amplification of the dynamic lateral displacement between wheel and rail on approaching the critical speed, the track mechanical properties, and in particular the track lateral rigidity.

The influence of some geometrical factors typical of the wheel-rail contact, such as side clearance and linearized conicity, will also be discussed. The approach is based on the application of statistical methods to dynamic linear systems.     

Optimal Control of a Vehicle Suspension Incorporating the Time Delay between Front and Rear Wheel Inputs

An optimal control law for a vehicle suspension is developed using a discrete linear quadratic regulator framework. The time delay between the disturbance due to the road at the front and rear wheels is incorporated into the model, and it is shown that the optimal control law requires information gathered at the front wheels. A comparison is made between the optimal control law and a suboptimal one which does not incorporate front wheel road information.     

An Active Suspension with Optimal Linear State Feedback

In this paper modern optimal control theory is applied to the design of an active suspension system for a motor vehicle. The road profile is assumed to be continuous and random with a power spectral density (P.S.D.) which varies inversely with the square of the frequency. The quadratic integral type performance index employed is a weighted sum of the integral squares of body acceleration, dynamic tyre deflection and relative body-to-axle displacement. A solution is obtained for the infinite time case which is both computationally and physically realizable as an active suspension in which the only continuous measurements required are the body absolute velocity and the body displacement relative to the road. The performance is compared with that of a conventional type passive suspension and found to be significantly better in practically all respects.