In today’s scenario, internal combustion engines have conflicting requirements of high power density and best in class weight. High power density leads to higher loads on engine components and calls for a material addition to meet the durability targets. Lightweight design not only helps to improve fuel economy but also reduces the overall cost of the engine. Material change from cast iron to aluminium has a huge potential for weight reduction as aluminium has 62% lesser mass density. But this light-weighting impacts the stiffness of the parts as elastic modulus drops by around 50%. Hence, this calls for revisiting the design and usage of optimization tools for load-bearing members on the engine to arrive at optimized sections and ribbing profiles.
This paper discusses the optimization approach for one of the engine components i.e., the FEAD (front end accessory drive) bracket. FEAD brackets are used to mount one or more auxiliary components and are subjected to vibrational loads due to engine base excitations and the typical mode of failure is vibrational fatigue failure. Hence the bracket ribbing direction, sections and dimensions need to be designed to meet the safe frequency target and desired life through the vibration fatigue duty cycle. Furthermore, the stresses should be within a safe target due to belt load and peak gravity loads.
The objective of this paper is to redesign the existing cast iron bracket and redistribute the material through topology optimization with an alternate material. Aluminium was selected as desired material. The functional requirement is to maximize frequency to the targeted frequency and maximize the stiffness of the bracket. Frequency-based optimization to improve the modal frequency and weighted compliance-based optimization to improve the static stiffness of the bracket has been deployed. Optimization in concept design provided the appropriate ribbing based on load path and faster convergence to a workable solution. The optimized design has been verified and is meeting the acceptance criteria in strength and fatigue simulation. Furthermore, an actual part based on the concept design was developed and has been validated successfully in the critical durability cycle. A comparative vibration measurement was performed for both cast iron and aluminium bracket to understand the NVH capability of the aluminium concept bracket.