Test tailoring approach for reliability assessment of automotive heat exchangers

The drastic reduction in pollutants emission that has followed recent international regulations imposes that engine fuel consumption be optimized as ever. Efficient engine cooling components together with an improved thermal management strategy play an important role in increasing engine performance, resulting in reduced fuel consumption and decreased pollution emissions. At the same time, new market trends are imposing longer warranty commitments, therefore challenging the capability of automotive suppliers to design products capable of high performance and extended reliability. In this framework, the reliability of engine cooling modules is a real economical and technical topic which has to be validated according to a rigorous methodology. By avoiding the over-use of standard and generic specifications (which cause over or under testing of the component during development phase), this paper proposes the so-called “test tailoring approach.” The goal is to validate the mechanical endurance of our products according to accelerated durability tests that are the most representative as possible to the environmental stresses that the components expect to see during their in-service life. This method permits the generation of customized accelerated bench tests, based on real measurements taken on the vehicle during field tests. The use of safety coefficients and Weibull analysis of destructive tests allows ensuring that the reliability targets are reached. These tailored specifications are employed to validate the mechanical endurance of the engine cooling module undergoing vibration, pressure pulsation and thermal shock stress loadings. This paper presents how this holistic philosophy has been used to validate the design of a new generation of heat exchangers (CO₂ gas cooler and evaporator).