OEM&Lieferant Ausgabe 1/2019

99 tronics directly attached to the core assembly. The more compact eBooster can be attached to the engine or to the vehicle, whereas BorgWarner’s eTurbo is ideal for applications that provide ample installation space for a larger turbocharger. The permanent output of 3 kW and the peak output of 6 kW for the eBooster and of 7 kW for the eTurbo were selected to achieve considerable improvements in the response behavior of conventional engines with dis- placements of up to 3 l. Comparison At the same drive power of the electric motor in each case, the eBooster achieves a larger air supply for the internal combustion engine in the partial load range as a result of the higher efficiencies of the compressor. In the range of higher loads, however, the eTurbo is operated at better efficiencies, thus supplying more air. At higher loads, the eBooster system is usually in bypass mode, with the turbocharger carry- ing out all of the compression work. However, the response behavior benefits from the ad- ditional exhaust gas mass flow at low speeds, and this increases the speed level of the tur- bocharger at an early stage. BorgWarner’s concepts also have different effects on the acceleration behavior (Fig. 3). One simulation compares a supercharged 2.0-l four-cylinder engine with a 1.5-l four-cylinder engine with electrically assisted supercharg- ing while starting up at traffic lights. The vehicle with the eBooster initially accelerates better due to the higher efficiency of the tech- nology used. At an acceleration from 0 to 100 km/h under full load, the partial load area plays only a mi- nor role, so the better pumping power of the eTurbo has a stronger effect at higher speeds. The vehicles with electrically assisted super- charging outperform the conventionally su- percharged vehicle both times in spite of the downsizing of the engine. The effects on fuel consumption were ex- amined too. A simulated comparison showed a conventionally supercharged vehicle with a 2.0-l four-cylinder gasoline engine and a 48-V hybrid vehicle with a 1.5-l gasoline engine and a 15-kW electric motor – one of them equipped with an eBooster and one with an eTurbo. The study also included a 48-V hybrid with a 15-kW electric motor and no electrically assisted supercharging system and a naturally aspirated 2.7-l en- gine. Gear ratios and switching points were BorgWarner www.borgwarner.com Website Dr. Hermann Breitbach Vice President Global Engineering and Innovation BorgWarner Turbo Systems Kirchheimbolanden www.borgwarner.com adjusted to give both vehicles an identical driving performance, and hybrid strategies were designed on a case-to-case basis. The study was based on a WLTP cycle with a ve- hicle weighing 1600 kg. Downsizing with a 48-V hybrid and a power- train with a smaller gear ratio allows fuels sav- ings of more than 15 g CO 2 /km to be achieved. Using the eBooster technologywith additional downsizing allows fuel savings amounting to a further 4 g CO 2 /km. In the case of the eTurbo, this equals 2 g CO 2 /km. Conclusion The spread of the 48-V vehicle electrical sys- tem and the progress made in power elec- tronics and electric motor technology allow electrically assisted supercharging to be im- plemented in an effective way – technically as well as commercially. BorgWarner’s eBooster has been in series production since 2017, and the eTurbo is currently in the development phase. The eBooster system is a two-stage concept, whereas the eTurbo is a one-stage concept. The operating principles of the two con- cepts differ with regard to the compressor wheels used. The eBooster concept requires additional effort due to the separate com- ponents. In contrast, the higher speeds of the eTurbo require faster power electronics, a motor running at higher speeds and more complex bearings, so overall complexity and cost are similar. The installation space required by the concepts differ widely. Only the eTurbo allows the regeneration of elec- trical energy, which is effective at high loads and speeds. The eBooster technology sup- ports downsizing and the reduction of fuel consumption by optimizing the response behavior of the engine at low speeds. In contrast, the eTurbo provides a more fun- to-drive experience throughout the entire operating range and works better at high engine loads while making a certain amount of downsizing possible. Fig. 2: In the eTurbo, the power electronics is directly attached to the core assembly. Fig.3: Comparison of the eBooster and eTurbo concepts in terms of starting behavior.