Electrical Conductivity of typical Automotive Engine Compartment Fluids and A Method for determining their Effects when Inadvertently Present in Electrical Connectors of Powertrain Control Modules

摘要

The engine compartment of a typical automobile may be exposed to a variety of fluids including engine oil, brake fluid, ethyJene glycol (antifreeze), windshield washer fluid, car wash solutions, rainwater and salt water. Depending on the chemical constituent of the fluid, the fluid may be electrically conductive or non-conductive. It has been alleged that such fluids may be present in electrical connectors of the Powertrain control modules of automobiles, resulting in mis-operation of the vehicle. As a first step in the analysis, digital conductivity meters were used to determine the electrical conductivity of engine compartment fluids. Measurements indicated that the range of resistivity (reciprocal of conductivity) is very large and spans more than six orders of magnitude, ranging from greater than 10,000 Ω m to 0.01 Ω m. This paper presents the electrical conductivity of eleven engine compartment fluids, and also graphically presents the conductivity of engine coolant for a range of concentrations. These conductivity measurements provide parameter information that is a necessary first step in developing a method to determine their effect on external loads, if present in the connectors of Powertrain control modules. Further investigation indicates that a large variety of variables are involved, including engine temperature, battery voltage, status of injector pins and air conditioner compressor, status of switches, and type, temperature, concentration and thickness of the contaminant. Due to the large number of variables, it is necessary to conduct a series of tests on an exemplar vehicle, to evaluate their effects, which would be cost prohibitive. Prudence dictates that a computer simulation be performed to take all the variables into account This paper presents a technical procedure and system analysis using PSpice computer simulation program to determine the leakage currents in a contaminated hypothetical connector of a Powertrain control module. The paper presents the voltage and current waveforms and further presents the magnitude of the leakage currents as a function of a wide range of concentrations of an IEEE standardized contaminant (salt solution salinity 2.5 g/L to 224 g/L). Results show that for the hypothetical connector, the maximum solenoid current occurs at a salinity of 40-g/L. Further increase in salinity (to 224 g/L) results in a reduction in current, since as the concentration increases, remote pins that are at ground potential start to interact. A comparison is made of the solenoid current due to the conductive contaminant to the 140 mA minimum pull-in current indicting that for this connector configuration, there is no salinity level that will result in the inadvertent pull-in of the solenoid. Since the computer simulation uses the very wide range of salinities (0.1 g/L to 224 g/L), which cover the resistivity range of typical under hood contaminants, it is summarized that there is no under-hood contaminant that will result in the pull-in of the solenoid, irrespective of the nature of the contaminant.