Pascal drichel, a doctoral student at RWTH Aachen University of technology, is committed to developing methods and models for the analysis, optimization and evaluation of vehicle vibration and noise (i.e. NVH) performance. SIMULIA solution is the key tool for FEA and multi-body simulation. They also conduct field tests for parameter setting and verification of component, assembly and system level models.
Drichel is the head of the NVH team in the drive technology department of the Institute of mechanical components and systems engineering (MSE) of the school of mechanical engineering of the University. When he came to the institute about six years ago, he had mastered the professional knowledge of simulation. “More than ten years ago, I started and used ABAQUS and SIMPACK software,” he recalled. “When I started studying in 2007, I used these two software for dynamic simulation as a student of the Institute, and I also interned in a large German automobile OEMs to carry out vehicle simulation for electric drive vehicles.”
The OEM internship is suitable for active students in RWTH Aachen. The university has the concept of close cooperation with various mainstream industries. As far as MSE is concerned, it maintains close contact with wind power manufacturers (who are also interested in drivetrain Technology) and automobile manufacturers. The benefits are two-way: in the current research of drichel team, in cooperation with Germany’s leading drive technology company and under the coordination of the German power transmission Engineering Research Association (FVA), provide real-world data for comparison with the engineer’s model.
This is an ongoing work, drichel pointed out. “Increasing vehicle electrification, such as simultaneous interpreting of e.Go, Volkswagen E-Golf and Tesla Model 3, brings new challenges to NVH performance.” he said, “virtual product development methods are becoming very helpful in solving these problems. We are working to further improve the tools for evaluating and optimizing different transmission products.”
Why is the transmission system (a series of components that provide power to the drive wheels) the main focus of Aachen’s team’s work? Because it is very important for sound control: no matter how quiet the motor itself is, the sound excitation from it is transmitted to the interior of the vehicle through components such as transmission, differential, transmission shaft and axle, which will lead to the generation conditions of vibration and other noise. Electric vehicles need to reduce this problem.
“Dealing with NVH problems related to the power train is a challenging engineering task.” drichel said, “it is required to work in a highly complex system, usually involving different multi physical fields.” in order to understand the overall situation of potential noise generators in the power train, drichel team used multi domain hybrid methods, including simulation and measurement components, to study electricity The core part is the multi-body dynamics model of the transmission system.
Electromagnetism: the team is developing a model to describe the excitation force of inverter fed motors. This includes analytical and numerical modeling methods for efficient force calculation. The analytical modeling method uses the data obtained from the excitation table and conformal mapping, while the numerical modeling uses the finite element method. The force excitation spectrum is analyzed to determine the most important influencing factors that should be dealt with in the next step.
Structural dynamics: the team has created their own user subroutines to apply previously determined electromagnetic forces to the driveline. The ABAQUS FEA model of the driveline assembly includes all flexible boxes and drive shafts. These sub models are combined with SIMPACK multi-body simulation model to significantly reduce the number of degrees of freedom. In this way, an efficient model is established, and many different working conditions can be simulated quickly. The research objects include the transverse isotropic performance of the stator, the fluid structure coupling between the stator box and the coolant, and the nonlinear bearing stiffness.
Acoustics: the complete acoustic performance of electric vehicles must include both air and structural noise. Once the drivetrain simulation is established, the radiated airborne sound from the entire drivetrain can be calculated using internal acoustic tools. In this way, the interior noise can be extrapolated using the transfer path synthesis method. The resonance effect of the system is studied under different motor speed and device adjustment (to avoid excitation and excessive noise). Objective and subjective evaluation of the generated “ear signal” can be carried out to evaluate how the change of powertrain geometry affects the overall noise level in the design of electric vehicle.
“SIMPACK and ABAQUS are our common tools in a lot of work,” drichel said, “From a research point of view, we like to combine the most advanced nonlinear solver, continuously improved and expanded proven modeling component library and user subroutine functions. User subroutine is a very powerful feature because it allows us to integrate our own sub analysis ideas into the software.”
Recently, the team also began to use insight for process automation and optimization. “In the first phase of this three-year project, we didn’t use iSIGHT, and it was really painful to manually integrate everything together,” drichel said. “In the second stage, we decided to use sight to make everything more automated. Now we can combine different software workflows, which is particularly important in our environment because we have too many areas to analyze.”
Drichel pointed out that multi-body and multi-scale simulation and process automation enable product developers to quickly obtain a deep understanding of the system in the process of designing the system. “Modern methods allow a holistic approach to the system simulation of electric vehicle driveline, which requires the understanding, understanding and development of solutions for specific engineering problems characterized by the interaction between components and subsystems.”
“It is an interesting challenge to provide tools and models to realize the research on the essence of electric vehicle driveline noise,” he said. “This ability is very important for the automotive industry. They can spend more time developing cars without studying the process!”
OEM partners are certainly interested in these results. “With our ‘hybrid multidisciplinary tool chain’, the automotive industry will be able to conduct ‘hot spot’ analysis, enabling them to identify resonance effects at specific speeds,” drichel said. “At the same time, it also helps them optimize the internal noise of the vehicle caused by the electric transmission system, making the electric vehicle more comfortable and more attractive to potential buyers.”
The next research objectives of the Institute team are two: first, increase the model fidelity in all fields in order to achieve better correlation between measurement and simulation data; Secondly, in order to balance the result accuracy and calculation time, the “psychoacoustic” measure is used to analyze the fidelity of different models to adapt to the perception of human users. The subjective evaluation of sound is a complex challenge because it depends on loudness, clarity and tone, especially all of which vary according to where the sound comes from in the vehicle.
Obviously, drichel likes the complexity of his team’s project, but does he have his own electric car? “I want to buy an electric car, but it’s too expensive for me now,” he said. At the same time, as a self proclaimed “passionate driver”, he drives BMW M3 series E46 to work. “It’s a beautiful car,” he said proudly. It sounds that the research conducted by drichel and his colleagues in RWTH Aachen will help make future electric vehicles quieter and more affordable.