ebm-papst developed, tested, and calibrated the auxiliary oil pump using Model-Based Design with MATLAB and Simulink.
Working in Simulink, the engineers developed a controller model for the permanent magnet synchronous motor (PMSM) based on field-oriented control principles. They used Stateflow®to manage pump operating modes, including idle mode and various pressure-level modes.
They incorporated IIR filters from Signal Processing Toolbox™ to remove noise from current measurements and speed measurements coming from Hall sensors.
The engineers refined their controller design based on the results of closed-loop simulations of the controller model and a plant model of the PMSM.
To create a real-time prototype, they generated code from the controller model using Simulink Coder™, and used Simulink Real-Time™ to run the code on Speedgoat target hardware. They used this prototype to validate the control design in a test rig with actual motor and pump hardware.
Tests showed that calculating pressure from a current draw measurement was possible, but due to variations in pump components, the calculations were not accurate across all operating conditions.
Using MATLAB and Stateflow, the team created an automated test suite that systematically varied temperature, pressure, and motor speed while logging current draw and other measurements on the test rig. They ran this test setup 24 hours a day for three months to fully characterize about 100 motor-pump combinations and component variants.
The team developed simple Simulink models of the pumps using lookup tables filled with data from the experiments, and ran simulations to fine-tune the control design and identify the best pump to use in production.
Software engineers developed ANSI-C code for the controller for the target microcontroller based on the Simulink model. They verified the implementation by comparing the code’s output with simulation results.
To maximize the accuracy of the pressure control, the team developed a calibration system for the end-of-line manufacturing process. This system runs tests to characterize the motor and pump, uses Curve Fitting Toolbox™ to populate a lookup table based on the test measurements, and then calibrates a system model inside the controller with the lookup table.
The ebm-papst auxiliary oil pump is in volume production, and is already being used by German automobile manufacturers.