case study

Predicting mechatronic performance with a digital twin

VHIT uses Simcenter Amesim to create virtual sensors and speed simulation time for developing electrical oil pumps

Predicting mechatronic performance with a digital twin

VHIT

VHIT specializes in vacuum braking, lubrication and power train cooling systems for internal combustion engines and electric applications for passenger cars and commercial vehicles. VHIT also has extensive experience in developing hydraulic actuators for off-road braking systems and clutches. VHIT offers solutions for original equipment manufacturers and the aftermarket for the automotive and off-road markets.

https://vhit-weifu.com/?lang=en

Headquarters:
Offanengo, Lombardia, Italy
Products:
Simcenter Amesim
Industry Sector:
Automotive & transportation

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This new Simcenter Amesim model takes just five seconds to simulate 1,000 seconds of real time.
Federico Tramaglia , Simulation Team Leader, VHIT

From mechanical to mechatronic

For over 60 years, VHIT, part of the Weifu Group, has developed mechanical products such as vacuum pumps and oil pumps for the automotive sector. By focusing on innovation, sustainability and the future, it has evolved to also incorporate the development of mechatronic products.

Federico Tramaglia, simulation team leader at VHIT, explains that to meet customer requirements for an electrical oil pump, specific pressure and flow rates need to be produced at a particular oil temperature. So engineers need to calculate the power demand and current consumed by the pump. As part of the design process, they need to assess if the pump can reach the required pressure and flow rates, how much power it uses and if the electronics can withstand the thermal load at the operating temperature.

It would be easy to overengineer the motor and pump to guarantee effectiveness, but this would significantly increase developmental and energy costs of the operation. To make it cost-effective, the pump must be optimized to fulfill all the operating requirements with the lowest energy use and most efficient design.

Comprehensive 1D model and virtual sensor

Tramaglia used Simcenter™ Amesim™ software to create a comprehensive 1D model of the electrical oil pump. This consisted of a printed circuit board (PCB), a permanent magnet synchronous motor (PMSM) and the mechanical element that pumps the fluid.

He designed these three subsystems separately at first, using the Simcenter Amesim electrical, fluid, thermal and mechanical libraries. Simcenter is part of the Siemens Xcelerator business platform of software, hardware and services.

Tramaglia developed a multiscale simulation approach for modeling these subsystems. First, a detailed model was developed to capture the physics starting with extensive component
information. This was run to generate data for a more functional and faster model.

This model accounts for the pump geometry and computes the flow rate for the requested output pressure as well as the torque. “Simcenter Amesim provides a detailed model that is precise with the viscous and dry friction that arises in certain conditions,” says Tramaglia. “It also simulates the pressure dynamics inside the chambers.”

The only problem with this comprehensive model was the time it took to run the simulation.

“Instead of integrating this detailed model in a full electric pump simulation, we used it to create lookup tables of the performance of the pump such as average flow rate and torque request,” says Tramaglia. “We then attached them to the PMSM model and ran a much faster simulation. This new Simcenter Amesim model takes just five seconds to simulate 1,000 seconds of real time.”

They used the same approach for the other subsystems as well.

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Electrical modeling and thermal validation

Once the hydraulic model was delivering similar results to the test bench, Tramaglia moved onto the electrical and thermal modeling and validation, which he highlights as the most critical element of the design. “It’s vital that the electronics can withstand the load requested, and the current that has been absorbed doesn’t cause the temperature of the electronic components to rise too high,” he explains.

The pump takes the direct current (DC) from the vehicle and uses an inverter to transform it into an alternating current (AC). This inverter consists of a metal-oxide-semiconductor field-effect transistor (MOSFET) and other components that combine to power the electronics. So the temperature of each component after current absorption must be evaluated to ensure it is within safe operating boundaries.

For this reason, a detailed model of the DC/AC inverter was developed, considering MOSFET conduction and switching losses as well as the pulse width modulation (PWM) control signal. This model was used to create a fast average inverter model, with losses as a function of the root mean square (RMS) voltage, current and temperature.

“The behavior of a PCB is extremely complex as it’s composed of many layers and copper wires, making it almost impossible to model in 1D,” says Tramaglia. This is why VHIT employed another modeling strategy: a lumped thermal network model with accurate tuning of parameters (conductance and resistances) using real test data. “To do this, we added thermocouples to the pump and ran testing, then fed this test data into the 1D model to tune it,” Tramglia explains.

The drawback of such test-based model is if the thickness of the copper or any other physical element is changed then the model must be retrained from new thermocouple test data. “In the future, we want to work with Siemens to develop a new methodology that enables predictive simulation using Simcenter FLOEFD,” says Tramaglia. “This would mean we wouldn’t have to keep going back to the thermocouple test and only use it for verification.”

This is the final piece to add to the other elements of the model that are already robust. Once the more detailed electronics model is complete, they will be able to carry out much more simulation before validating with physical testing. “This will make the design and development process significantly faster as we won’t have to keep rerunning testing,” Tramaglia says. “It will be mostly proving simulation results that we are already very confident in.”

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Complete performance evaluation with reduced order models

There are multiple benefits of the multiphysics electro-pump model: Traditionally, simulation models are developed to represent a physical product with the objective of improving its performance by virtually modifying the design. Tramaglia’s intention is to make this the
standard approach for future projects. “Our electronic engineers need to understand
the temperature performance of components within a system,” he says. “With accurate simulation they can avoid overengineering and keep the costs of components down, which is vital to developing competitive products.”

The objective of VHIT is also to re-use the detailed multiphysics model to generate a digital twin of the electrical oil pump using reduced order model (ROM) techniques. This brings many advantages: The ability to create virtual sensors, estimate the lifetime in real time of electronic components or continually develop other components for the electrical oil pump using real data to reduce overengineering.

Tramaglia notes that the digital twin enables the evaluation of performance, which was previously impossible. “Imagine the pump is mounted on a customer application with no visibility into pressure and flow rate,” he says. “We can’t physically attach sensors so the data we have is very limited. What we do know is the torque developed by the pump and temperature of the electronics. So with these parameters, we can create a machine-learning
model that builds a virtual sensor to estimate the oil temperature, flow rate or pressure. We can then predict system performance across any operating conditions. We simply input parameters such as oil temperature, delivery pressure and pump speed, and create a performance map from the simulated data.”

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Simcenter Amesim provides a detailed model that is precise with the viscous and dry friction that arises in certain conditions. It also simulates the pressure dynamics inside the chambers.
Federico Tramaglia, Simulation Team Leader, VHIT