Fundamental Issues in Suspension Design for Heavy Road Vehicles

Heavy road vehicles play an important role in the economy of many countries by providing an efficient means of transporting freight. Such vehicles can also have a significant impact on safety, the infrastructure and the environment. The design of the suspension affects the performance of the vehicle in terms of ride, infrastructure damage, suspension working space, energy consumption, rollover stability, yaw stability, braking and traction. The published literature on suspension design for heavy road vehicles is reviewed. It is found that extensive knowledge exists, but that there are areas where improved understanding is needed. Areas identified as fundamental issues requiring attention include ride discomfort criteria, secondary suspensions, and controllable suspensions. Two issues in particular are examined in detail: suspension tuning and suspension configuration. In the tuning of suspension parameter values for vibration performance, numerical optimisation techniques have been used extensively, but generic tuning strategies have not been widely developed. Modal analysis is proposed as a technique for gaining the insight into vehicle vibration behaviour necessary to enable tuning strategies to be devised. As an example, the technique is applied to the pitch-plane vibration of a tractor-semitrailer. In analyses of new suspension configurations or concepts, comparison with alternative concepts is not always made. Lack of such comparisons makes the selection of an optimum concept difficult. Analysis of alternative concepts using simple mathematical models, and comparison of their performance using common criteria, is advocated for enabling informed selection of an optimum. An example involving two alternative roll control systems is used to demonstrate the issue.     

Time-series model for vehicle speeds

This paper presents a time-series model for the spot speeds of vehicles on a road section. Based on time-series analysis techniques, the model incorporates information on the extent of existing dependency between the speeds of successive vehicles. The model for the data is chosen while relying heavily on the data, and thus emphasis is given to their special characteristics. The advantages of using the model are examined with regard to the relative speed of two successive vehicles along a road section. The results are compared with those obtained by using a model of independent observations; fewer errors are obtained with the time-series model. Therefore, it is concluded that the sequence of speed observations contains valuable information which should be incorporated into speed models.     

RMS Values of Force, Stroke and Tyre Deflection in a Half-Car Model with Preview Controlled Active Suspension

Summary Matrix expressions are developed for the direct computation of rms values for the optimal control forces, front and rear suspension strokes and dynamic tyre deflections in a half-car model on a random road of given roughness. A quadratic performance index is employed with assumed weighting factors and evaluated in the same computation.     

Towards a simplified performance-linked value for money model as a reference point for bus contract payments

The burgeoning commitment to contracting the delivery of bus services through competitive tendering or negotiated performance-based contracts has been accompanied by as many contract payments schemes as there are contracts. We are now well placed to design a simplified performance-linked payment (SPLP) model that can be used as a reference point to ensure value for money, given the accumulation of experiences throughout the world which have revealed substantive common elements in contracts. Whether the payment to the operator is framed as a payment per passenger or as a payment per service kilometre, the SPLP identifies efficient subsidy outcomes that are linked to a proxy indicator of net social benefit per dollar of subsidy. We illustrate how the SPLP model can be applied to obtain the gross (subsidy) cost per passenger (or per passenger km) from measures of gross cost efficiency and network effectiveness. This model can then be used as part of a benchmarking activity to identify reference value of money prospects in respect of passengers per $ subsidy outlay by adjusting for influences not under the control of the service provider. A single framework to identify contract payments to operators, and to assess (i.e., benchmark) operator performance on critical KPIs, is provided by internalising critical key performance indicators (KPIs) in the design of the SPLP. The proposed SPLP model is sufficiently general to be independent of the procurement method (competitive tendered or negotiated, for example) and of the treatment of revenue allocation (net or gross based contracts), with the additional advantage of being able to assess value for money for government.     

Role of the Railways in the Future of Air Transport

Abstract

The role of the railways in the air transport industry is usually limited to provision of access to airports. However, the development of high-speed rail networks and the congestion and environmental problems faced by the air transport industry suggest the railways could have a greater role in working with the airlines to provide an integrated transport service for medium-distance journeys (up to 800 km). Many air journeys involve two flights and a transfer at a hub airport. The alternative being investigated here would replace air journeys by a rail journey and a flight, and a transfer between them at the hub airport. Such integration could offer a positive alternative to aircraft on some routes and lead to railway journeys to airports becoming part of air transport services, and not only to provide access to them. Integration could therefore provide a better use of available air capacity rather than duplicating some high-speed rail routes and services.     

Witkar: Amsterdam's self-drive hire city car

A small electrically powered city car has been developed for self-drive hire in the centre of Amsterdam; 35 of these cars are now available to hire from 5 stations in the city centre. The. system has been designed for fully automatic control, including direct debit of hirers' accounts at the Amsterdam Savings Bank. The system, which was conceived in 1969 by an industrial designer and former city councillor to reduce traffic in central Amsterdam, failed to win the support of the City Council and has since been developed by a specially formed co-operative society. The co-operative managed to raise loans of US$ 250,000 for the first phase which has now been completed. This included the design and construction of the vehicles, the purchase of a mini-computer for the central control system, development of the control software and construction of the first five stations. A further 10 stations are scheduled for operation by the end of 1976, by which time the fleet should be extended to 100 vehicles. The ultimate target is 150 stations and 1000 vehicles.