09/15/2016

Virtual injection needles-in-the-loop

Before now, the fuel injection in modern engines has followed predefined intervals. But a new technology is coming: mechatronic real-time control, which monitors and controls injectors individually. With a new Hardware-in-the-Loop solution, ETAS is making a decisive contribution to this breakthrough.

The ideal engine is agile, clean, and efficient. Modern downsized engines are getting ever closer to this ideal thanks to precise injection technology. Dosed to milligram precision, pre-, main, and post-injections ensure that the fuel combusts optimally and leave almost no residue.

Before now, the injection followed preset intervals. Because of production tolerances and aging effects, however, injectors implement control commands at different speeds. As delayed opening and closing reduces efficiency, developers are now designing ECUs that can monitor each injector individually and correct changes in behavior by means of targeted control interventions. This is important particularly in view of upcoming CO2 regulation and on-board emissions controls.

High-precision development tools pave the way
In order to redesign engine ECUs for the monitoring and exact readjustment of injectors, developers need precise tools. To this end, ETAS has developed a new Hardware-in-the-Loop (HiL) solution, which is based on the ES4452.1 plug-in board for ETAS LABCAR. Using resistance and inductance, it simulates the behavior of individual injection valves much more accurately than has been possible with previous HiL systems.

The system uses the electromagnetic signals of the injection valves: to lift the needle, an electrical current flows into a coil in the injector. Pushing against the pressure of a closing spring, the resulting magnetic field raises the needle and the fuel begins to flow. As soon as no more current is flowing, the spring pushes the needle back down again. The injection finishes. However, the start and end of the supply of electrical current are not the only information needed. The ECU also has to know how quickly the valve responds. This information can be gleaned from specific characteristics of how voltage and current shape over time depending on inductance and ohmic resistances in the injectors, which gives the corresponding charging and discharging curves. These curves provide the basis for the sequential monitoring of the injectors and for any corrective interventions needed.

Theory deftly translated into practice
It is important to test this new function of ECU software in a wide variety of operating states. With modern development tools from ETAS, the tests can be largely virtualized. Using simulation and emulation, developers are able not only to bring software to maturity earlier, but also to precisely simulate the aging and changes in behavior of injectors, something that, at best, would be very costly to do on the test bench.

As a prerequisite for meaningful HiL tests of mechatronic injection control, the ECU must receive realistic, millisecond-precise voltage, current, inductance, and resistance values for the virtual injectors. Only by extrapolating from this data can it determine the opening and closing and the injected fuel volume. Interference signals due to switching the test hardware are to be strictly avoided, because the ECU would wrongly interpret them as signal deflections. Even eddy current effects in the injector coil affect the discharging curves and have to be taken into account in the simulation.

In several months of practical testing, the HiL solution has proven that it precisely models injector behavior even with variable boundary parameters. This means that injector aging can be simulated for the first time. Based on the altered charging and discharging curves, new control strategies can now be tested in a closed-loop control circuit comprising the ECU and the virtual injection system.

Solution for gasoline and diesel engines
With the ES4452.1 plug-in board, the system is tailored to gasoline direct injection, while the solution with ES4457.1 is tailored to diesel systems. Both supply digital output signals with millisecond precision in order to simulate the injection duration and opening and closing times of virtual injectors. The signals are synchronous with each other in the crankshaft angle for up to four injector simulations. Developers can set and change the configurations in advance and during the simulation depending on the rail pressure, shifts in opening times, fuel temperature, and voltage and current thresholds. In addition, the solution offers a dynamic analog output in order to display information such as the current or voltage curves of the virtual injectors via oscilloscope – and to visualize changed configurations without needing an expensive high-precision current clamp.

Conclusion
By comparing the target and actual states of working injectors, it is possible to implement new control strategies that balance out aging-related changes in injector behavior. For the testing of mechatronic injection control, virtualized Hardware-in-the-Loop tests are indispensable. With its LABCAR HiL system in conjunction with the ES4452.1 and ES4457.1 plug-in boards, ETAS offers the first ever solution capable of virtually simulating injector behavior so precisely that ECU software can thereby learn to recognize and correct deviating injector behavior.