It is well established that simulation provides substantial time and cost savings by accurately predicting performance of a proposed design, reducing the need for physical tests. However, a challenge for many design teams is that analyzing multiple non-linear components requires huge computational resources. A typical simulation takes about 30 hours to perform, which limits the degree to which nonlinear analysis can be used in the design process.
The Litens Automotive Group was looking for an approach that would allow them to simulate the performance of their TorqFiltr torque modulators, including material and geometric nonlinearities, in a fraction of the time so that they could integrate advanced nonlinear analysis into the design process. They wanted to combine multibody dynamics (MBD) simulation at the system level with nonlinear finite element analysis at the component level for components with large deformation to achieve a fast solution and accurate results. MBD software has previously been integrated with linear FEA software, but not with nonlinear FEA, which is needed to provide accurate results for components with large deformations and material nonlinearities, such as the right and left side springs used in the torque modulator.
The patented TorqFiltr torque modulator uses an arc spring isolator mechanism to decouple the accessory drive system inertia from the engine torsional vibrations. The Litens torque modulator controls the system resonant frequency by tuning the spring stiffness to the system inertia. Because the spring stiffness is softer than traditional rubber isolators, vibrations from the engine are mostly absorbed before being transmitted to the accessory drive belt. This results in isolation of all components in the accessory drive, and any accessory drive resonance has very small peak amplitudes, since there is very little excitation.
The product is dimensionally rather small, but incorporates a complex mechanism consisting of a series of components that transmit power to each other through complicated frictional contacts rather than fixed connections. The team needed to fully understand the behavior of the design under dynamic loading conditions and the product needed to be customized to deliver optimal performance for many different automotive engines. In the past, this involved a time-consuming and expensive trial and error process.
MSC engineers coupled Marc and Adams so that the interaction between the motion behavior in Adams and the nonlinear behavior in Marc is taken into account in the simulation at both the system and component level and solved at each integration time step. Deflections calculated by Adams are taken into account at each time step in Marc and dynamic loading conditions are transferred from Marc to Adams. Marc determines stress and deformation at the component level with geometric, material, and contact nonlinearities taken into account.
Litens CAE engineers set up the typical simulation so that only the left and right springs are modeled as flexible bodies in Marc and all other components are modeled as rigid bodies. Six contact points are established between the shell of the torque modulator and the springs, and these points are used by Adams to provide displacements to Marc, and by Marc to provide forces back to Adams. Under these conditions, Adams-Marc co-simulation analyzes the torque modulator in only two hours, 1/15 of the time required for Marc simulation
Hence, using Adams-Marc co-simulation in the early stages of the design process to evaluate different design alternatives can significantly speed up the design process. This fast turnaround time, coupled with the results that closely correlate with physical tests, makes it possible to utilize advanced nonlinear FEA as an integral part of the design process.