ACCELERATE POWERTRAIN STRENGTH & DURABILITY WITH SIMULATION

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EXECUTIVE SUMMARYAs the connection between the engine and the wheels, the performance of the powertrain is crucial to the performance of the vehicle as a whole. Optimizing the powertrain maximises engine performance while enhancing fuel economy and reducing emissions.

The powertrain is a complex, heavy system with numerous components, and the demands of delivering power from the engine to the wheels of the car mean those components experience significant stress and wear. Engineers want to minimize weight and friction, while also ensuring the components can withstand the forces acting on it. Smaller and lighter designs are raising new structural challenges, while new technologies place new demands on the powertrain.

This whitepaper shows how structural simulation with SIMULIA software can be used to design, analyze and optimize powertrain components, both in isolation and as in integrated part of the vehicle system.

CHALLENGES IN POWERTRAIN STRENGTH & DURABILITY

Powertrain development can be a time consuming and expensive process. As a result, a lot of emphasis is placed on time-to-market and cost reduction, which in turn can limit how much of the design space the engineer can explore. New materials and manufacturing processes expand the design space further, potentially offering a competitive edge but also requiring new design paradigms.

The continual trend of engine downsizing and component mass reduction improves the performance of the vehicle as a whole, but it also means powertrain engineers are working within ever-tightening limits.

Changing driving styles, such as increased engine speed and start-stop city driving, put more strain on the powertrain components. The use of lower viscosity oils reduces friction and improves fuel economy and winter performance, but requires higher mechanical, structural design in order to maintain the film strength and oil pressure in the high temperature. Direct fuel injection which increases cylinder pressure, also require fundamental changes to powertrain design.

A good design of vehicle’s powertrain will ensure reliability, durability, efficiency, performance, and safety. Structural simulations are key enablers in achieving this objective in a shorter and more cost-effective time than with physical tests. However, the size and complexity of powertrains require software capable of handling such large models. With so many components, powertrain design also requires input from many different teams and departments.

BENEFITS OF POWERTRAIN STRENGTH & DURABILITY SIMULATIONThe 3DEXPERIENCE® Platform connects teams, disciplines and data into one unified collaborative environment to imagine, design and experience innovations. Thus, it connects design and simulation (CAD-CAE) which open the door for modeling and meshing automation, and even

Figure 1: Meshed model of an engine block, showing the complexity of powertrain components.

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for the entire engineering process automation in order to perform design of experiments and simulation-based design optimization.

SIMULIA software can reduce powertrain design time and cost reduced by as much as 1/3. Simulation activities are tightly integrated with design (CAD), and modeling and meshing tasks can be automated. The ease of use enables democratization of engineering activities across designers and domain experts, breaking down the traditional design silos.

Simulation provides accurate predictions of multidisciplinary KPIs such as bore distortion, bending stiffness, load distributions, stress fields, fatigue safety factors. It also offers the opportunity for multidisciplinary and multi-scale design optimization using best-in-class mechanical simulation technologies (static, dynamic, thermal-stress analysis, contact and others).

By analyzing design performance in realistic use cases, the risk of warranty costs and recalls is reduced. Accurate system behavior prediction with high fidelity models increases confidence in product performance. Fatigue strength can be accurately simulated with advanced plasticity, damage, failure and fatigue models

Improving or reducing physical tests with virtual tests also allows smarter testing. Critical strain locations known by simulations, optimization of the mounting point locations of the real experimental gauge. Prototype design improvements can reduce physical test failures or even eliminate them.

APPLICATIONSThe objective of the Powertrain Strength & Durability process is to ensure that the combustion chamber pressure, the temperature and the motion of the components do not cause reliability or durability problems. Another important objective is to design the powertrain to improve vehicle efficiency and performance. This must be done with minimal impact, or even a positive impact, on vehicle mass and cost.

The Powertrain Strength & Durability process addresses a wide range of simulation workflows to fulfill those objectives:

Cylinder head gasket sealing analysis

The gasket forms a seal between the engine block and cylinder head. It should be able to maintain that sealing and prevent leakage between the two crucial engine parts, when being subjected to the compression process, with the bolt tightening force being an important factor. The simulation can predict possible damage to the gasket and the risk of interfacial leakage.

Figure 2: Sealing analysis on the 3DEXPERIENCE platform.

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Piston, exhaust manifold, cylinder block and head thermal-stress analysis

After calculating combustion chamber pressure and temperature evolutions with SIMULIA’s thermal simulation tools, engineers can predict the temperature field in the parts, the material expansion and the stress field. This allows a durability assessment of powertrain components, using thermal and stress fields prediction to get fatigue safety factors.

Vibration analysisSub-systems are submitted to structural vibration, mainly from the engine, which over time can lead to damage and impair performance. Harmonic excitations can be obtained through multi-body simulation with SIMPACK. First the eigenfrequencies of the parts and the sub-systems are calculated. Those eigenfrequencies should stay inside safe ranges.

Then, modal steady state dynamic analysis can be performed to analyze the vibration of the components. Non-linear preloading conditions are likely to affect the frequencies values and the modal responses. This can be taken into account

Connecting rod strength and wear resistanceThe internal combustion engine relies on fluid-film plain journal bearings, which are an essential component present within the cranktrain. The hydrodynamic oil film should be at sufficient pressure to transmit and support the firing and inertia loads without excessive asperity contact and friction.

The properties required for strength (fatigue) and wear resistance are in opposition to the properties required for conformability (misalignments accommodation), compatibility (no friction welding) and embedability (particle debris circulation). Trade-offs must be done, and simulation results such as bearing fit deformation and the resulting clearance profile can inform decision making here.

Crankshaft or crankcase strength and stiffnessThe dynamics of the crankshaft, connecting rod and piston, as well as the combustion chamber pressure can lead to deformation. The durability assessment of the components can be calculated in simulation, using the deformation and stress field prediction to get fatigue safety factors.

The effect of bending on clearances within the powertrain require loads distribution to be accurately predicted as well. The stiffness matrix of the parts can be extracted and used to inform dynamic simulations of the powertrain.

Crank & Cylinder Bore DistortionDistortion is likely to occur under dynamic stress when heat and pressure are applied, and bore distortion directly affects oil consumption and emission. The challenge is to understand and predict how these changes take place. The aim here is to simulation bore deformation – deviation from the ideal circular shape, usually with a multi-step analysis varying the combustion pressures and temperatures to find the optimal operating point.

Figure 3: Von Mises Stress on Engine Block from Thermal Loading.

CONCLUSIONSimulation can overcome the challenges of designing a powertrain system that is fuel efficient, reliable, and cost-effective while delivering high performance. By implementing simulation into the design process, engineers can analyze factors such as stress, wear, vibration and sealing on a virtual prototype, allowing potential problems to be identified and fixed before beginning physical testing. This can save both time and money, and allow engineers to explore more of the design space than was otherwise possible. The software offering from SIMULIA on the 3DEXPERIENCE platform brings these powerful simulation tools to the designers themselves, democratizing simulation and allowing collaboration between teams all working to produce the best possible powertrain.

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Our 3DEXPERIENCE® Platform powers our brand applications, serving 11 industries, and provides a rich portfolio of industry solution experiences. Dassault Systèmes, the 3DEXPERIENCE® Company, provides business and people with virtual universes to imagine sustainable innovations. Its world-leading solutions transform the way products are designed, produced, and supported. Dassault Systèmes’ collaborative solutions foster social innovation, expanding possibilities for the virtual world to improve the real world. The group brings value to over 250,000 customers of all sizes in all industries in more than 140 countries. For more information, visit www.3ds.com.