Abstract
The safety requirements in vehicles continuously increase due to more automated functions using electronic components. Besides the reliability of the components themselves, a reliable power supply is crucial for a safe overall system. Different architectures for a safe power supply consider the lead battery as a backup solution for safety-critical applications. Various ageing mechanisms influence the performance of the battery and have an impact on its reliability. In order to qualify the battery with its specific failure modes for use in safety-critical applications, it is necessary to prove this reliability by failure rates. Previous investigations determine the fixed failure rates of lead batteries using data from teardown analyses to identify the battery failure modes but did not include the lifetime of these batteries examined. Alternatively, lifetime values of battery replacements in workshops without knowing the reason for failure were used to determine the overall time-dependent failure rate. This study presents a method for determining reliability models of lead batteries by investigating individual failure modes. Since batteries are subject to ageing, the analysis of lifetime values of different failure modes results in time-dependent failure rates of different magnitudes. The failure rates of the individual failure modes develop with different shapes over time, which allows their ageing behaviour to be evaluated.
Highlights
Since this work is about the methodology for determining time-dependent failure rates for individual failure modes and no field data from batteries are available that represent future load scenarios and failure criteria, the results are presented in normalised form
The failure rates λ FailureMode (t) of the individual failure modes from Section 3 are normalised to the failure rate λS (t) of the still functional batteries of the failure mode Serviceable after τvehicle,0.6 = 0.6 · τvehicle vehicle lifetimes according to the following Equation (8): λ FailureMode,normalised (t) =
It has been shown that the statistical reliability analysis can be applied to electrochemical components to derive appropriate failure rates
Summary
In addition to automation functions, this leads to higher safety requirements especially for electric braking and steering power assistance. Apart from these essential safety-relevant consumers steering (e.g., steer-by-wire) and braking (e.g., brake-by-wire), automated driving functions require sensors and actuators for position and environment detection as well as for control [1]. These components are supplied via the 12 V on-board power supply system ( known as powernet) of the vehicle and need a safe power supply to ensure a safe operation
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