For holistic optimization of the hybrid powertrain, it is desirable to develop operating strategies which take more target variables, e.g. fuel consumption and pollutant emissions, into consideration simultaneously, enabling optimum use of existing components. This permits individual elements to be adjusted at an early stage in development – or even allows entire components to be removed from the combustion engine powertrain altogether. This becomes even more important when considering optimization of the overall cost, with regard to the high additional costs arising from the electric path.
A prerequisite for developing these kinds of strategies is the availability of control unit-compliant, prediction-capable emissions models. To develop these models requires detailed knowledge – both of the raw emissions behavior of the combustion engine, and of the conversion characteristics of all the exhaust aftertreatment system components, even under transitory conditions. It makes sense to run a real combustion engine both for creating these models, and for optimizing and validating them in the overall system. The combustion engine is the powertrain component which is most difficult to simulate. The required boundary conditions for simulating the driving cycles are provided by a real-time-capable simulation of the vehicle environment and driver behavior. In this case, the combustion engine is operated on a test bench as "Hardware-in-the-Loop".
For this purpose, FKFS has built a hybrid engine test bench (HMP) which particularly fulfills the stated requirements. This test bench features powerful electric loading device(470 kW, 990 Nm, 9,000 rpm), a facility for legally-certified exhaust analysis (CVS system: constant volume sampling) – as used on roller dynamometers for vehicle certification, diverse analyzers for online analysis of limited pollutant components (fast FID/CLD/NDIR, particle spectrometer, quantum cascade laser, etc.), as well as equipment for delivering an airflow over the hybrid powertrain which is proportional to the vehicle's speed. In addition, the test stand has flexible facilities for supplying electrical components, such as those installed in hybrid topologies. The focus here is on a battery simulation with which electric motors in the drive train can be supplied with outputs of up to 300kW - at voltages of up to 1000 volts and currents of up to 1200 amperes. Furthermore, on this test bench it is possible to physically represent the components of the electric path (electric machine, battery, power electronics) in coupled operation, as well as depicting the operation of individual subsystems via replacement systems (e.g. HV battery simulation: 1000 V, 1200 A, 300 kW), or to incorporate these entirely as simulations.