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

Each year the new Chairman of the Automobile Division is given the opportunity to give a review. This can cover a wide variety of subjects including the history of his company's products, some new technology developed by his organization, but frequently it is a reflection on his own experience in the engineering scene. This is not intended as a narcissistic exercise but one from which other people can benefit, particularly young engineers, in giving an insider's view of life as a professional engineer and some of the reasons and background to decisions and activities that have taken place in the profession.

Rover Group has seen rapid growth in vehicle impact simulation techniques in recent years. This has been brought about partly by the increasing power of computer hardware and software, and partly because of increasing legislative and consumer pressure. This paper describes the development of impact simulation within Rover Group, from simple discrete element mass and spring models to complex component non-linear finite element models. It subsequently describes how all of these approaches were combined to provide an integrated modelling capability which allows the complexity of models to evolve as design and development progresses, and concludes with a description of how these modelling methods are being applied to the design of new vehicles within Rover Group.

This paper is concerned with the steady state combustion performance of a port-injected spark-ignition engine operating at low load and low speed. The main areas of investigation were the effects of mixture quality and trapped combustion residuals on combustion performance. The behaviour of the inlet manifold fuel film was also investigated under various engine running conditions.

The effects of injection timing were quantified, both with warm and hot engine coolant. Each of the six fuel injectors on the engine was equipped with an air-shrouded injector which improved fuel-spray atomization. Tests were carried out both with and without air flowing through the shrouds. A new method is also presented which provides a measure of the size of the inlet-manifold wall film under various engine running conditions. Finally, measurements of the amount of trapped combustion residuals are presented, and their effect on combustion performance is quantified.

A study of engine oil consumption (OC) was conducted both theoretically and experimentally. It was found that oil blowing into the combustion chamber through the top ring gap (termed ‘reversed oil’) and oil returning to the crankcase through the oil ring gap (termed ‘blowby oil’) are important factors affecting OC. It was also observed that depending on the ring gap clearance, enlarged because of ring wear (for example the radial ring wear of 50 μ corresponds to a gap enlargement of roughly 0.31 mm) or non-optimal ring gap clearance and inter-ring volume, the 2nd land pressure can exceed cylinder pressure—leading to increasing reversed oil and consequently higher OC. The deterioration of OC with increasing operation has been traced to lowered oil-scraping capability with ring wear. This is true. However, the above-mentioned phenomenon can be considered as another reason for such OC. This paper describes the relationship between reversed oil/blowby oil ratio and OC, and presents a procedure for optimizing ring gap clearance and interring volume for acceptable OC. This study, however, neglected oil supplied to the ring pack via the valve set.

This paper develops an alternative optimization approach for systematic design of a parametrized engine system and illustrates the procedure through application to a novel conversion device, the patented Stiller-Smith mechanism (1, 2). Using simultaneous interplay between a simulation scheme, presented in detail elsewhere (3), and an optimization scheme, the proposed structural design process integrates the multiple objectives of structural design. Developed here in detail, optimization involves intermediate continuous optimization via a penalty function method, and integer or discrete programming through the branch-and-bound algorithm. The ensuing application illustrates the approach by optimizing a 16-cylinder Stiller-Smith engine for minimum weight-power and dimensions-power ratios under several types of constraints. In the context of a multi-objective constrained non-linear programming problem, the design example proceeds through three stages: (a) preliminary, in which the designer applies the simulation scheme to obtain the system response variables from the design requirements to reflect trade-off relationships among multiple design objectives; (b) secondary, the intermediate continuous optimal design stage, in which a penalty function method is used to specify constraints within a general range to allow variation in the choice of parameters; and (c) final, in which the branch-and-bound algorithm constrains integer variables to take integer values and discrete variables to take discrete values, thereby arriving at an optimal design.

It has been known for some time that, in single-degree-of-freedom differential systems, the sensitivity of the overall transmission ratio to a change in ratio of one of the differentials is proportional to the fraction of the input power flowing in the relevant differential. A complete and general proof of this theorem is presented, using matrix algebra, determinants and a coherent subscript notation.

The theorem provides a direct method for calculating the internal power flows during the synthesis of multi-epicyclic systems, and defines a theoretical limit to the ratio range and efficiency of a split-path continuously variable transmission.

Analysis of the Allison WT is used to illustrate application of the theory to a change-speed transmission.

A simple methodology to estimate static rollover threshold of trucks and tractor-semitrailers, equipped with a partially filled clean-bore cylindrical tank, is presented. Lateral liquid load transfer is determined as a function of fill level, tank geometry, roll angle of the sprung mass and lateral acceleration. The static rollover threshold is then estimated by balancing the total overturning moment against the restoring moment. Results are compared to those obtained from software based on comprehensive kineto-static analysis of tank vehicles.