What is Engine Lightweighting?
Engine lightweighting involves reducing overall engine weight by optimizing components so that only the minimum material necessary to handle mechanical and thermal loads remains in the design. This improves efficiency without compromising structural integrity.
Engine downsizing is a specific form of lightweighting where engine displacement and cylinder count are reduced while maintaining the power output of a larger engine. This is typically achieved through technologies like turbocharging and direct injection.
While downsized engines experience higher structural loads compared to their larger counterparts, they are usually more optimized. As a result, they offer a higher power-to-weight ratio, improving performance and efficiency.
Interaction, Balance and Trade Offs
Component mass and durability are closely linked, with changes in one often affecting the other. Understanding these interactions is essential for effective design.
Lightweighting requires careful trade-offs. Reducing weight can sometimes compromise durability, so achieving optimal performance demands a balanced approach.
All lightweighting decisions must align with durability targets to ensure the components meet long-term reliability and performance requirements.
Benchmarking and Target Setting
Benchmarking existing engines allows the client to gain an understanding of the absolute and relative performance of competitive Engines
Following could be the components of the benchmarking:
- Design Review
- Manufacturing process review
- Assembly review
- Integration and packaging approach
- Virtual Teardown
- Virtual durability and performance analysis
- BOM Analysis
- Component Weight Analysis
- Durability and Performance Test Benchmarking
- Costing analysis
Armed with the data from benchmarking of the clients’ existing (where available) and competitive Engines, targets for how the project Engine will perform can be made:
- Define market/ territory
- Calculate customer usage profile
- Agree and define durability and reliability targets (e.g. life, usage target etc.)
- Review specific market aspirations/ trends or requirements
- Loading patterns
Design
Design for lightweighting involves development of engine by identifying failure modes by Design Failure Mode and Effects Analysis (DFMEA) and mitigating them for components and systems throughout the design process.
The general rules for keeping the engine mass minimum by design is to:
- Use geometries that maximizes the second moment of area for bending loads and polar moment of area for twisting loads.
- Use high strength and high fatigue limit materials.
- Use lighter materials
- Use bolted joints effectively for application of relatively low weight bolts.
- Use belt or chain drives rather than gear drives.
- Use plastic/composites for intake plenums and manifolds, and wherever possible.
- Combine an assembly into a single part where possible.
- Avoid brackets and clamps, and incorporate these into the engine structure.
The crankshaft is heavily loaded in twisting and bending. It is designed with low stiffness to avoid excitation and torsional vibration, using a shaft diameter and crank-webs sized just enough (second moment of area and polar moment of area) to withstand loads.
The camshaft experiences similar loading and is designed with the same principles as the crankshaft.
The piston endures direct, bending, and high thermal loads but is made as light as possible to improve engine responsiveness, along with the connecting rod and crankshaft.
The cylinder block and cylinder head are critically loaded and, bolted together, withstand combustion and cranktrain reactive loads.
The cylinder block offers significant weight-saving opportunities by minimizing thickness in low-load areas, while maintaining strength with ribbing and bolt bosses for through-bolting.
The cylinder head is designed similarly, balancing weight reduction with structural integrity.
Extreme weight saving designs and use of expensive high strength materials such as Titanium can be seen in high performance engines.
Simulation
Preliminary design calculations determine critical dimensions and masses of major dynamic and static components.
Time-domain response of the 3-dimensional vibration of the coupled crank train and cylinder block system with non-linear oil films at each of the main journal bearings will be predicted
Similarly, secondary motions in piston assemblies, i.e. departures from the nominal motions as predicted by analysis of the slider-crank mechanism are analyzed
The objective of the thermal analysis is to predict the temperature distribution in the components to assist with material selection and provide inputs to distortion, stress and fatigue analysis
Thermo-structural analysis is performed to generate the stress history of the component considering assembly loads, thermal loads and operating loads
Stress history generated from the thermo-structural analysis is further postprocessed for the high cycle fatigue and low cycle fatigue for the applicable components
Prototype and Testing
Build test rigs to assess mechanical performance and confirm structural integrity under load.
Use test results to validate CAE tools and address simulation gaps.
Refine design through simulations and test updated components.
Iteratively simulate and test components until performance targets are met.
Conduct endurance tests to verify component and system robustness.
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