The Swedish company Scania has struck a unique balance between mass production and customization. The manufacturer of trucks, buses, coaches, and industrial and marine engines uses a modular vehicle configuration system to provide customers with vehicles tailored specifically to their needs.
Scania assembles vehicles from pre-engineered components connected to standard interfaces and then optimizes them for each customer’s requirements. This system enables the company to create individual configurations for a large number of customers.
The modular customization approach has contributed to Scania’s success but has also been a significant cost management challenge. Before delivering vehicles to customers, Scania had to determine whether they met customers’ requirements for handling, comfort, and promised fatigue life under a variety of conditions. Traditionally, the only way to do that was to build a vehicle complete with custom hardware, equip it with sensors, and run it around a test track. This approach was expensive and inefficient for two reasons.
The first and most obvious is the cost of building a vehicle, paying highly skilled employees to configure it for testing, and then interpreting the data that comes from the test. The second and more onerous cost is making modifications if testing reveals a problem. At this point in the production cycle, Scania had hundreds of thousands of dollars invested in the vehicle’s design. Every issue that required a modification or a redesign increased expenses geometrically because the company lost time against production goals as well as labor, material, and tooling costs.
Scania has improved its testing processes by integrating simulation software into the process prior to prototyping and track testing. Simulation has enabled the company to test more vehicle configurations at a lower cost and with less disruption than it took to test just one configuration using its previous process. The new approach makes it possible to provide each customer with an optimized product, while keeping costs throughout the value chain at a competitive level.
“Simulation gives us the ability to explore design alternatives in the early stages of the design process,” said Anders Ahlström, Ph.D., Structural and Vehicle Dynamics Engineer for Scania. “The result is that we have been able to significantly improve the handling, comfort, and fatigue life of our vehicles.”
Scania used MSC Software’s Adams/Car multibody dynamics analysis software to create models of its vehicles, its 10-channel test rig, and its test track. In most cases, engineers can create a simulation model of a new vehicle simply by selecting and connecting Adams modules. They can then model the components as flexible bodies composed of either shell or solid elements using MSC Nastran finite-element analysis (FEA) software.
The simulations enable engineering teams to quickly evaluate functional virtual prototypes of complete vehicles and vehicle subsystems. Working in the simulation environment, engineering teams can exercise their vehicle designs under various road conditions, performing the same tests they normally run in a test lab or on a test track but in a fraction of the time.
The models enable Scania’s engineers to evaluate vehicle designs using the virtual simulator and test track—without, of course, building an actual test vehicle. They first test the model by exciting selected points using the simulated test rig. If the model performs well on the test rig, they add wheels and simulate the model running over a 3-D road.
Scania engineers have been able to achieve simulated results within 5% of physical measurements on the test rig and within 20% of physical measurements on the virtual track. The 20% is a reasonable margin of accuracy because of the difficulty of accurately modeling tires and interconnecting parts.
Once engineers have validated the vehicle model, they can use it to evaluate handling and driver comfort. They apply loads to various components and use the results to estimate their fatigue life.
“On a new vehicle configuration, we typically simulate the vehicle performing steering maneuvers on a flat surface to evaluate steering and handling,” Ahlström said. “We drive the vehicle over a number of different road obstacles and study the vehicle behavior and driver experience.”
Simulation enables Scania to evaluate vehicle performance under very demanding conditions that would be difficult to duplicate with physical testing. Simulations also generate loads on the components that can then be used for stress analysis or fatigue life analysis. Finally, engineers perform failure mode analysis, simulating failure of major systems and their effects on driveability.
Modifications can be done easily in the virtual world, which saves a significant amount of time and money in the design process. Modifications that could cost tens of thousands of dollars using Scania’s previous testing regime are essentially free in simulated environments.
“Adams/Car helps us understand how the multiple moving parts of the chassis interact with each other and their environment,” Ahlström said. “This knowledge helps us to identify potential problems early in the design process and make corrections on the virtual model at a much lower cost and in less time than would be required to correct the physical truck. Simulation helps encourage innovative design methods because engineers can easily explore alternative design concepts in very little time or expense. As a result, we have made significant improvements in handling and comfort of many of our designs. We have also reduced stress levels in many parts, resulting in improvements in component life.”
Chris Baker, Product Manager for Adams and Easy5 at MSC Software, wrote this article for SAE Magazines.