Simulation Methodology for Failure Analysis of Catalytic Converter Mounting on Commercial Vehicles

Abstract

<div class="section abstract"><div class="htmlview paragraph">Catalytic converters have been considered as an integral part of the vehicle powertrain for over a decade now, their application along with the engines increased significantly with the constant evolution of emission standards. Recent regulations keep a strict control on the major four pollutants of engine exhaust gas, i.e., Carbon Monoxide (CO), Nitrogen Oxides (NOx), Hydrocarbons (HC) &amp; Particulate Matter (PM), which demands a highly efficient aftertreatment system. Efforts are continuously being made to downsize the engine for better fuel economy and low emissions, this puts additional requirement of designing a compact aftertreatment system equipped with Diesel Oxidation Catalyst (DOC), Diesel Particulate Filter (DPF) and Selective Catalytic Reduction (SCR).</div><div class="htmlview paragraph">Compact catalytic converters experience larger vibration force transferred from the vehicle and hence the durability of the product is significantly impacted. Vibration sources are a) Engine, b) Road Load, using a long flex pipe can contribute to the dampening of vibrations coming from engine but cannot prevent the vibrations transferred from the chassis. And it is very rare to use rubber-based isolator to decouple chassis vibration in a commercial vehicle because the heaviness of parts, packaging space constraints and cost increase reduce the benefit of having several isolators. Such components are extensively applied in light vehicle systems, where the packaging space is comparatively more, parts are lighter, and the system mass is distributed as compared to concentrated mass in commercial vehicles.</div><div class="htmlview paragraph">Generally, the lead time for basic durability tests of aftertreatment systems for commercial vehicles is around one week, including the test setup and calibration. It is a bottleneck in the development process, so engineers are highly motivated to develop simulation models that are validated with high accuracy to replace the time-consuming testing phase. The authors propose a Finite Element Analysis (FEA) model in this paper to evaluate the failure limit of mounting belts used to fix an aftertreatment device weighing over 100kg on the vehicle frame. The model calculates the contact force for the belts and uses it to predict the failure point of the holding force.</div><div class="htmlview paragraph">This simulation model was validated against the vibration tests conducted on a shaker bench capable of generating acceleration level of 25G at a frequency of 20Hz uniaxially for a system weighing nearly 100kg. It is important to note that the focus of this model is on the mounting bracket clamps and their functionality for holding the catalytic converter. Hence the objective is to check the frictional capability, where in even at high acceleration force the system should not move relative to the clamp. The acceleration force and frequency are the input boundary conditions, which are controlled on the test bench using acceleration sensors, and the output is the frictional capability which is monitored by observing slippage of the system.</div></div>