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Continental Engineering Services (CES) has been a worldwide provider of comprehensive engineering services since 2006. CES focuses on automotive electronics, drive and chassis technology and electrical mobility. The company is also experienced in adapting automobile technologies to a broad spectrum of industrial applications.
One of the major concerns about battery systems used in electric vehicles is that their performance and durability can be diminished by extreme temperatures. In cold temperatures, the need for cabin and battery heating and the increased rolling resistance of winter tires are the most adverse conditions for any electric vehicle. The key is to determine how to allocate battery energy to make the most energy-efficient use of the vehicle.
On cold days, warming a battery gradually brings the system’s temperature to a level that allows it to provide enough discharge power for expected vehicle performance. Like humans, a battery functions best at room temperature, and any deviations in temperature changes the battery performance and/or longevity. Battery heating systems and optimal thermal management are critical for effective operation in all climates. The objective is to deliver a battery pack at an optimum average temperature with even temperature distribution. The question is: how do you determine the best heating architecture?
Since 2006, Continental Engineering Services (CES) has been active worldwide as an independently operating provider of comprehensive engineering services. The extensive know-how and creativity of its engineers, as well as access to the entire technology pool of international automotive suppliers puts the organization in the unique position of being able to combine the flexibility and speed of a small engineering team with the strength of a leading international company. In addition, the adaptability of CES enables the company to provide established mass production technology for small series as well as niche applications at economical costs.
Based on years of experience and the constant exchange of knowledge within the Continental divisions, the CES Department of System Integration and Vehicle Test has achieved a great understanding of the entire hybrid and electric vehicle, including drive trains, transmissions and interior electronics.
The expertise of CES has positioned the company to work on projects such as vehicle architecture and powertrain analysis of electric automobiles. That’s why major original equipment manufacturers (OEMs) have turned to CES, especially for electrified drivetrain performance studies, optimization of heating systems and build-up of electrified prototype vehicles and demonstrators.
In the design phase, the layout of the high-voltage battery and the thermal and energy management strategies have to be specified. Despite space limitations, weight, complexity and cost limits, the requirements of driving range and performance have to be met. Finding the best possible solution takes numerous optimization loops, testing, experience and time, and that’s where Simcenter Amesim™ software from Siemens Digital Industries Software comes in. It enables engineers to optimize complex mechatronic systems in record time at reasonable cost.
The CES Department of System Integration and Vehicle Test started an investigation into cooling systems so it could understand the driving range implications. CES engineers had modeled the complete system of mission profile, virtual driver and vehicle, including the electric drivetrain containing electric motor and inverter with integrated DC/DC, LiOn battery (electrical data open-circuit voltage,resistance, cells, convective heat exchange to coolant) as well as the cooling circuit and the electric vehicle controller.
The objective was to test three different battery-heating approaches in winter conditions to get the best performance in terms of range and power.
The first approach was the internal energy battery-heating scenario: as the internal resistance is high at low temperatures, it dissipates energy that will naturally heat the battery. The second approach uses the wasted heat from the drivetrain to heat the battery through more complex circuits. The third option relies on active electric heating in which additional circuits are designed that will use the energy of the battery for its own heating.
Simulation conditions were the same for all three approaches: they started at minus 30 degrees Celsius (C) and ran two worldwide harmonized light vehicle test cycles (WLTC), and performed a simulation that showed very interesting results that were then confirmed by tests.
The battery cells reached optimal temperature much faster with the third approach, active electric heating. It reached 0 degrees C in 14 minutes and 40 seconds and 6.5 kilometers driven, whereas it took about 28 minutes and 21 kilometers for the other two approaches to reach 0 degrees C and the same final state of charge of the battery (around 55 percent of capacity) at the end of the driving cycle. The active electric heating strategy was selected to be used to optimize the driving range and vehicle performance.
“By using Simcenter Amesim, we were able to model three approaches for the battery heating strategy and get the first results in a matter of hours instead of days,” says Sebastian Brixner, a system engineer in the Department of System Integration and Vehicle Test. “We were able to rapidly select the right architecture with the best performance and focus on the next steps of the project.”
Before using Simcenter Amesim, every test was run mechanically on prototypes with the associated costs and delays to obtain results and make the necessary changes to reach the expected performance.
By using Simcenter Amesim for multi-domain mechatronic system simulation, the electric vehicle’s performance and driving had been accurately predicted in an early phase of the development cycle. As a result, different battery sizes and configurations could be tested in the virtual vehicle environment. The influence of driving strategies and thermal management can be determined in a driving cycle, which allows the manufacturer to immediately choose the best architecture and components available for the application.
With the use of Simcenter Amesim and its application- oriented libraries (cooling system, thermal hydraulics, mechanical, electric motors and drive), CES engineers were able to rapidly build a functional prototype and demonstrate results to management in order to validate selection of system architecture and components early in the design cycle.
The unique Simcenter Amesim user-friendly interface – the drag and drop approach of ready-to-use components, the intuitive operation and the easy parameter setup – have helped CES engineers to rapidly select the best architecture and move forward in the component and subsystems selection to reach expected vehicle performance.
“I can state categorically that I am very enthusiastic about Simcenter Amesim,” says Brixner. “The intuitive operation and environment, the excellent support as well as the easy and stable model building that doesn’t require advanced programming skills really help me in my daily work, and provide first results in record times. Simcenter Amesim really helps us by accelerating the early design phases of prototype development as well as optimizing the process of determining strategies and functions.”