Traditionally vehicle manufacturers run durability tests with each drivetrain or even vehicle variant. Customer duty cycles are represented by several durability test profiles operated at different places on the globe to demonstrate system robustness for all customer types and climates. Vehicle fleet testing as final validation activity is executed after a variety of component and sub-system tests, addressing primarily sub-system interactions, un-known and unexpected failure modes. Uptime Engineering was asked by an OEM in the automotive sector to verify the robustness of this approach for hybrid drive trains.
Validation of a hybrid drivetrain uncovered the limit of this concept. In hybrids there are at least two energy sources to drive a vehicle. Various influence factors define whether the actuation of the vehicle happens through each energy source separately or in combination. Thus, the load of hybrid drivetrain components varies with the drivetrain control strategy, the operation mode, the charging condition, the ambient temperature, the geographic location, etc. A multitude of operating conditions would be required to cover the parameter space.
The following process was initiated and subsequently moderated by Uptime Engineering supported by the implementation of Uptime LOCATE™. As usual the coverage of reliability risks by component and sub-system testing was executed for extreme load situations of components using common parts synergy for proper effort allocation. For the subsequent vehicle operation hardware-in-the-loop and software-in-the-loop testing delivered system behaviour for different controlling strategies. These results were used as input for simulation of vehicle load under various controller strategies and boundaries. With this approach moderated by Uptime Engineering a minimum set of durability vehicle configurations was selected and operated under certain driving conditions, control strategies, start conditions and climates. It was demonstrated analytically that the selected sub-set of test variants delivered the highest reliability demonstration within the given restrictions in time and budget.
Highly innovative concepts are characterised by strongly increasing failure rates. A factor of two is well documented in literature. Unexpected failure modes, appearing under load conditions, which were not well covered during validation, are a severe warranty threat. The described systematic investigation supported by Uptime Engineering of the parameter space and the testing at critical parameter locations reduced this risk. Moreover, this approach was also used by the OEM to identify a risk related vehicle monitoring concept for early warning, protective operation and pre-emptive maintenance concepts.
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