Thermal Expansion Measurements on Operating Automobile Engine - MTI Instruments - #1

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MTI Instruments, Inc. 325 Washington Avenue Extension Albany, NY 12205 PH: +1-518-218-2550 OR USA TOLL FREE: 1-800-342-2203 FX: +1-518-218-2506 sales@mtiinstruments.com www.mtiinstruments.com APPLICATION NOTE Thermal Expansion Measurements on Operating Automobile Engine Introduction As today’s automobile engine become more sophisticated the need to perform additional testing becomes essential. Many components now serve several purposes in order to produce higher horsepower in a smaller overall package. This requires each component to be manufactured to tighter tolerances. An example would be the oil pan. For years the sole purpose of the oil pan was to act as a reservoir for the engine lubricant. Some modern engines now utilize the pan as a structural component. It is machined from a rigid steel or aluminum casting and designed to support the lower portion of the crankshaft bearings and rear main seal. This development has introduced a potential problem area that must be analyzed. The Problem As engines go through heating and cooling cycles it is essential that the engine block and oil pan expand and contract at nearly the same rate. If not, stresses can be introduced to the pan gasket, main seal and bearing races. This can cause oil leaks, premature bearing failures and unwanted noise and vibration. The Solution GM engineers approached MTII looking for a way to monitor the relative motion between the block and the pan to determine if excessive stresses were occurring. The Accumeasure 1500 capacitance system was selected, because of its high accuracy and multi-channel capabilities. A test was performed using 16 capacitance probes strategically mounted to an engine. Each probe had an operating range of 0.04” (1mm) with a resolution of better than 10 micro-inches (0.25 microns). Before starting the test, all outputs were set to zero volts. As the engine was started, and brought up to operating temperature, the output of each sensor was recorded. This data was used to determine the relative displacement between the two components. MTII appnote: thermalexpansion.pdf - Page 1 of 2