Holistic Calibration

Cost benefits by solutions from a sinlge source

20. November 2018 | Engineering Service

As the technical complexity of modern electrified powertrains is increasing significantly, the effort for systems engineering, function development, system calibration, and system validation will increase. For the specification of the system requirement FEV has developed a structured approach of system analysis and controller design that helps to identify system requirement parameters and reduces the time and associated costs for function development and calibration.

The powertrain calibration engineer must have deep systems knowledge to be able to calibrate modern electrified propulsion systems. FEV has qualified resources to develop and calibrate these kinds of modern powertrains with over 1,000 experts possessing “e”-powertrain know-how & the mindset to work in interdisciplinary teams to bring these “e”-powertrain to the streets. All powertrain application activities are integrated within FEV’s vehicle application centers, in which all vehicle-related activities and departments work together.

Effective Transmission Calibration Process, Tools and Methods

The complexity of modern control units, the increasing diversity of powertrain applications and the need for shortened development cycles require novel approaches towards powertrain calibration. A model-based calibration process to transfer major parts of the calibration activities from the vehicle to the calibrator’s desktop is an answer to these contemporary challenges. Against this background FEV has developed tools and processes for efficient powertrain calibration. Typical tools and processes that are used by FEV in the field of transmission calibration are:

  •  For efficient driving mode calibration FEV developed the TOPEXPERT Transmission Calibration Expert toolset (TraCE). This calibration tool is used for calibrating accelerator pedal maps, shift lines, variograms, driving resistance and e-powertrain functions such as load-point shifting, boost, sailing and regeneration operation. This model-based calibration tool reduces the required time for transmission control function calibration significantly and increases the calibration robustness.
  • To increase the vehicle testing and calibration efficiency, FEV has developed the TOPEXPERT Vehicle Test Automator (VTA), a unique solution that’s able to transfer the automation approaches from the test bed environment to vehicle calibration.
  • A requirement-based parameter management system is used for effective handling of calibration datasets in projects with numerous vehicle variants. This tool is based on physical system dependencies. Depending on these physical dependencies the transmission control unit (TCU) parameters are assigned to powertrain components. If a calibration parameter that is assigned to a component needs to be changed the change will be valid for all vehicle variants which are assigned to this particular component. At every calibration release the calibration maturity will be compared to the agreed program targets.
  • FEVcal makes the powerful Design of Experiment (DoE) technique easily applicable for a calibration engineer. The state-of-the-art global modeling techniques based on Gaussian processes have been adapted to also address the specific characteristics of transmission and powertrain modeling.

Transmission Calibration Process

The combination of above mentioned processes and tools allows FEV to deliver a high quality dataset for all possible applications and variants. FEV has the experience from numerous projects with AT, CVT, AMT, DCT, modular hybrid, DHT and EDU transmissions to handle multi-variant production transmission calibration projects. Therefore, FEV has developed an in-house calibration process that allows a secure and reliable project management. Main features of the calibration process are:

  • Clear change management of calibration parameters based on a web server to enable project traceability and risk management that’s completely transparent to our clients.
  • Defined maturity levels for datasets to track the actual status of calibration level of TCU functionality and the overall calibration.
  • Easy adaptation to customers processes to support the needs of different customers.
  • With this level of organization FEV has the capability to take over production calibration projects with turnkey responsibility including project management, supplier handling, homologation support and after production assistance.

Transmission Calibration by Design of Experience

One of the developed methods for efficient shift quality calibration is based on the Design of Experiment approach (DoE). Shift quality calibration means, regulating the clutch torque capacity control and engine control parameters to ensure a comfortable shifting behavior in every driving situation with respect to the customer-defined requirements. The DoE approach is used to predict the shift quality of the system, based on calibration parameters. The shift quality is characterized by various objective physical metrics from FEV’s objectification toolbox (FEVos). Examples of such metrics are the Vibration Dose Value (VDV) and the Low Frequency Percentage (LFP). The clustered calibration parameters, which form the input for the creation of DoE measurement plans and for the DoE model in the TOPEXPERT Tool FEVcal, are restricted within certain boundaries in the operating range of the system. These calibration parameters are then optimized based on the DoE model outputs which describe the shift quality objective ratings.
Finally, the optimized calibration parameters are tested at the vehicle level to validate the results of the shift quality calibration with subjective and objective ratings.
For several production applications FEV has optimized “problem areas” using the DOE method. An example of results from a 6-speed production automatic transmission calibration program is shown below.

In this example the shift quality improvement was also confirmed via subjective evaluation by an experienced calibration engineer. The calibration test runs are performed by the TOPEXPERT VTA tool.

Vehicle Test Automator for Efficient Transmission Calibration

To increase the vehicle testing and calibration efficiency, FEV has developed the TOPEXPERT Vehicle Test Automator (VTA), a unique solution to be able to transfer automation approaches from the test bed environment to vehicle calibration. It allows the calibration engineer to plan experiments at the desk using a comfortable graphical workflow editor. With libraries of calibration-specific blocks and the open environment for custom evaluation algorithms, VTA provides a platform to easily document, transfer and standardize calibration expertise. On this basis the use of model-based calibration approaches can be expanded to vehicle calibration. The generated test descriptions can be executed in the vehicle, either guiding the calibration engineer through the maneuvers or completely taking over vehicle control and to collect appropriate data in a structured way.

For transmission calibration and validation FEV has developed rating sheet workflows which will guide the driver through the maneuvers. After the VTA run is started the calibration engineer will be guided by the tool through graphical interfaces. The calibration engineer can monitor the important signals and will be guided through the defined set of maneuvers. If the maneuver is driven successfully VTA will save the recording. The recording will only be saved when all pre-defined boundary conditions are fulfilled (e.g., vehicle has to be stationary, accelerator pedal position within a bandwidth, air conditioning must be switched off, engine must be running, etc.), otherwise the recording will be rejected and the tool will ask the driver to repeat the maneuver. Accordingly, the tool collects data from only those maneuvers which are performed in a right way which makes offline analysis and dataset improvements highly efficient. At the end of the procedure the tool will request the calibration engineer to provide a subjective rating value to the maneuver. All important data will be stored in the measurement file comment or the measurement file name to make the documentation complete.

Drivability Improvements With Electrified Powertrain

To be able to use the advantages of modern electrified powertrains with increasing technical complexity the engineer will be challenged to find smart solutions. FEV has experienced system engineers to develop electrified powertrain concepts and use the advantages of these systems. For example, a dedicated hybrid transmission in combination with a P4 system can improve the shift quality by providing torque support during the shift by the electric machine in the transmission and by the electric machine at the rear axle. At the inertia phase of the shift the belt starter generator (BSG) can regenerate energy by compensating the internal combustion engine (ICE) inertia torque. To achieve the optimum shift quality all the sub-systems needs to be controlled and calibrated by considering the whole system.
To be able to calibrate these modern electrified powertrains FEV has developed an efficient calibration process in combination with smart tools and methods to achieve optimum energy management, fuel economy, emissions, NVH, and drivability.

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