Model-based control of an electrical compressor to increase low-end torque and its impact to fulfil “real drive emissions” of diesel engines

03. November 2017

Additional electrical compressors have long been considered to enhance response behavior of engines. In combination with appropriate software and motor parametrization, an additional compressor can also reduce pollutant emission. Robert Bosch GmbH works on the development of the required software and components for the use of an electrical turbo compressor for diesel engines. Bosch has successfully tested, combined with the respective control, the Celeroton turbo compressor CT-14-1000 in a diesel motor test rig.

Regulations have become stricter and are forcing automotive manufacturers to look for innovations in engine technology, especially for treatment of the exhaust gas. The publication “Control of an Electric Compressor for a Passenger Car Diesel Engine” by G. Cornetti, A. Henle and W. Knühl, published at the 2016 Supercharging Conference sheds a new light on using electrically driven compressors for passenger cars. The model-based control scheme allows a swift response of the electrical compressor and a fast torque generation, which for example avoids shifting speeds in automatic transmission under many drive conditions. This improved controllability has a positive impact on engine emissions in the acceleration phase and allows for an improved cooperation with the exhaust after-treatment system. It particularly helps to reach the road traffic emission targets, namely the legislative “real driving emissions”.  In order to test the optimized control, Robert-Bosch GmbH positioned a Celeroton turbo compressor CT-14-1000 together with a Celeroton converter CC-230-3500 downstream of the turbo charger as an additional electrical turbo charger or booster in a 1.7 liter, 4-cylinder diesel engine test rig. To withstand an inlet pressure of up to 3 bar, the compressor was placed within a customized, pressure-rated housing. The following picture illustrates the CT-14-1000 compressor and pressure-rated housing.

Figure 1: Pressure rated Celeroton turbo compressor CT-14-1000.

Giovanni Cornetti, team leader air-system engineering at Bosch, says: “Electrically driven turbo compressors have a great, currently unutilized potential: In combination with respective control schemes, an improved cooperation with the exhaust gas after-treatment system of the diesel engine as well as a power increase is possible. The electrically driven turbo compressor from Celeroton is most suitable because of its compact design, high efficiency and sufficient power.” First measurements at Bosch prove the effectiveness of the concept that is enabled by the Celeroton turbo compressor.

Figure 2: Measurements at Bosch.

Further steps towards making the concept viable is the development of a customized turbo compressor for passenger cars.

Carlo Scaffidi et al. recently published the assessment “Electrically assisted internal combustion engines: a comparative analysis” where different hybrid concepts for cars are compared. The potentially most promising concept uses a Celeroton Turbo Compressor CT-14-1000 for assisting a turbo charged internal combustion engine to overcome the so called turbo-lag.

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