Improved torque tracking on internal combustion engine test benches equipped with EURO 6-engines

Test benches for internal combustion engines are used for many purposes in the automotive industry with strong advantages in terms of reproducibility and costs. The torque and the speed at the crankshaft of the engine must be tracked simultaneously to simulate the operation of an internal combustion engine in a vehicle. Single-input single-output proportional-integral-controllers are usually used to this end. Additional limitations have been introduced in the Engine Control Unit to meet the continuously strengthened emission levels. Especially, for new engines these limitations lead to significant overshoots in the torque tracking which have to be prevented in any case. The limitations are studied and the impacts to the tracking are analyzed in this paper. The existing proportional-integral-controller is extended based on this analysis. In particular, the controller parameters are scheduled with respect to the change of the torque reference and the tracking error. No model of the plant is required for controller design, the controller parameters can be tuned quickly and easily during the set-up of a test bench. Measurements on a test bench equipped with a passenger car Diesel engine confirm the improvements compared to the industrial standard.