Proceedings of the Institution of Mechanical Engineers,Part D: Journal of Automobile Engineering

In a previous paper [see reference (4)], it was shown that the restoring force surface (RFS) procedure provides a direct and clear method for characterizing the dynamic properties of automotive shock absorbers or dampers. The procedure was based on repetitive harmonic testing of the absorbers at fixed frequency but with varying amplitude. The current paper describes how the surfaces can be obtained from tests using random excitation. The merits and demerits are discussed relative to the harmonic test procedure. It is shown that the random excitation approach offers a useful alternative but produces force surfaces which are corrupted by small stochastic components; an explanation of the distortion is given in terms of the mathematical model proposed in the previous paper. The implications for identification of shock absorbers are discussed

Within the context of vehicle suspension component characterization, that of shock absorbers is one of the more difficult to achieve, yet it is a very critical factor in the prediction of vehicle dynamic behaviour. Strongly non-linear output force functions are always linked to a frequency-dependent behaviour. Using the internal fluid-dynamic phenomenon with respect to a motorcycle shock absorber, different physical models of increasing complexity are presented: using these models it is possible to evaluate the importance of different factors, for example oil compressibility or oil inertia. Comparisons with experimental data confirm the validity of these models

An articulated lorry was instrumented in order to measure its performance in straight-line braking. The trailer was fitted with two interchangeable tandem axle sub-chassis, one with an air suspension and the other with a steel monoleaf four-spring suspension. The brakes were only applied to the trailer axles, which were fitted with anti-lock braking systems (ABS), with the brake torque controlled in response to anticipated locking of the leading axle of the tandem. The vehicle with the air suspension was observed to have significantly better braking performance than the steel suspension, and to generate smaller inter-axle load transfer and smaller vertical dynamic tyre forces.

Computer models of the two suspensions were developed, including their brakes and anti-lock systems. The models were found to reproduce most of the important features of the experimental results. It was concluded that the poor braking performance of the steel four-spring suspension was mainly due to interaction between the ABS and inter-axle load transfer effects. The effect of road roughness was investigated and it was found that vehicle stopping distances can increase significantly with increasing road roughness

Two alternative anti-lock braking control strategies were simulated. It was found that independent sensing and actuation of the ABS system on each wheel greatly reduced the difference in stopping distances between the air and steel suspensions. A control strategy based on limiting wheel slip was least susceptible to the effects of road roughness

During any synchromesh development programme, reliable methods for evaluating and assessing the gear-shift quality are necessary. In order to overcome the reliance on a trained driver and associated subjective judgement, methods have been investigated to describe the gear-shift characteristics using objective, rather than subjective measures

This paper describes the measurement and calculation of objective measures that relate to perceived shift quality. Examples are given on the use of these measures to evaluate the effect of production variability on shift quality, and to allow comparisons of shift quality to be made between competitive vehicles

The paper describes the design of a single cylinder base engine which provides optical access to the combustion chamber via glass cylinders and a piston with a glass crown. The application of this engine to the visual analysis of gasoline mixture formation and combustion is demonstrated with examples given for two- and four-valve cylinder heads.

The optical methods used in this study comprise laser-induced fluorescence (LIF) to image the unburned mixture within the laser light sheet illuminating a plane of the combustion chamber and flame photography to visualize flame propagation. Simultaneous recording of engine thermodynamic data allows the comparison of conventional engine diagnostics with the results gained from the optical techniques.

Flow details through an axisymmetric exhaust valve-port assembly have been investigated numerically. Computations were performed for steady compressible subsonic air flow at different valve lifts. The numerical procedure used for this purpose solves the governing equations using the SIMPLE algorithm. The governing equations are expressed in a general curvilinear coordinate system and are discretized in a finite volume fashion. The time-averaged governing equations are closed using the k–e. turbulence model. The predictions are assessed by comparing with the available experimental flow field data. Good agreement is observed between the predictions and the experiment.

Mapping the performance of an internal combustion engine over a wide range of operating conditions is a common procedure during development. The generation and post-processing of the data are high-cost activities. Two approaches which offer advantages over parametric test plans have been investigated. A statistically designed matrix of tests has been employed to map engine stability and combustion performance parameters. This approach minimizes the number of tests required and post-processing techniques provide valuable insight to relationships which exist between variables. This is particularly useful and efficient when qualitative trends are of prime interest. When large data sets are necessarily acquired and quantitative relationships between variables are of particular concern, then data processing using neural networks is shown to be an effective approach. The use of this technique is illustrated by application to evaluate relationships between engine-out emissions and engine state variables.

Mass spectrometry provides a powerful and versatile method for the characterization of the unburnt and also the pyrolysed and partially oxidized gaseous hydrocarbon species present in exhaust gases. Flame ionization detection, the usual analysis method for measuring exhaust hydrocarbons, can give only a total hydrocarbon figure when used on-line. A mass spectrometer can perform the on-line characterization of the individual gaseous hydrocarbon species in the exhaust and can detect any trends in their concentrations. This permits the rapid assessment of experimental approaches for reducing these pollutants.

In the present work exhaust gases have been sampled from the exhaust of a Ricardo E6 research engine fuelled with gasoline and they pass to the analysis equipment via heated sample lines. The gases can be analysed as discrete samples by gas chromatography mass spectrometry (GC–MS) in order to identify the components, or can be continuously monitored by mass spectrometry alone (MS) in order to measure any trends in the component concentrations.

These mass spectrometric analysis techniques have been compared with other gas analysis and general data acquisition methods, and have permitted the collection of much information about engine exhaust emissions. This information has been related to engine operating parameters with special reference to the fuel–air ratio.

The results from this work show that not only does the combustion result in an increase in the relative amounts of NO and CO₂, but also suggest that the substituted aromatic hydrocarbons may be products of combustion. Continuous monitoring of specified exhaust components has been performed mass spectrometrically and related to the air–fuel ratio used for the engine. With lean fuels, the hydrocarbons are not totally combusted, but those that are burnt are combusted with reasonable efficiency. On the other hand, rich mixtures are associated with not only inefficient combustion, but also incomplete oxidation (that is CO–CO₂ ratio is increased), and an increase in the substituted aromatic hydrocarbons. Stoichiometric mixtures have been found to be associated with most efficient combustion (highest CO₂–CO ratio) and minimal hydrocarbon emissions.