Title: Reliability and durability of automotive prime movers

Authors: R. Bertodo

Addresses: Director, Power Train Engineering, Rover Group, Longbridge, Birmingham B31 2TB, UK

Abstract: A new product saddled with a poor reliability reputation at its introduction has little chance of altering its image, whatever improvements are introduced later. There is a need, therefore, for any manufacturer of commercial goods to understand its market|s perception of reliability. There is a further requirement for a methodology capable of ensuring that the market expectations are met from the start. This is particularly relevant in the highly competitive automotive field. The paper reviews past attempts to relate market reaction to statistically meaningful mathematical expressions of |reliability| and |durability|. This experience is extrapolated to define the relevant parameters for automotive engines in the 1.4-2.0 litre capacity range. For a specific definition of |reliability|, a minimum level of 0.82 is derived. A method of maximising market acceptance with optimum initial and repair costs is presented. Given that no comprehensive analytical method exists to demonstrate that a particular power unit will attain a predetermined reliability level, demonstration through testing is required. It is shown theoretically and experimentally that statistically sound validation test programmes require prohibitive times and financial commitment. This is the case even if steps are taken to abbreviate the test schedules with consequent loss of precision. In the circumstances, a reliability growth model is shown as the only viable alternative. Further considerations suggest that the longevity of the power unit is governed mainly by a log-normally distributed wear-out process affecting lub. oil control. In these circumstances, the B50-life appears to relate closely to the market|s perception of |durability|.

Keywords: downtime; durability; failure rates; lubricants; marketing; quality control; reliability; testing; automotive engines; market acceptance; automotive prime movers; vehicle design.

DOI: 10.1504/IJVD.1987.061348

International Journal of Vehicle Design, 1987 Vol.8 No.2, pp.145 - 160

Published online: 25 May 2014 *

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