Not only applicable as original equipment in cars, CPT’s switched-reluctance technology is also being trialled in trucks and buses and off-highway vehicles.
The cooperative study, by one of the UK’s leading 48V specialists and one of the most successful technical universities in Europe, verified a 9% reduction of this troublesome air pollutant in raw engine-out emissions, while retaining the fuel economy and CO2 benefits of diesel engine technology. The cost effectiveness of this approach is further underscored by its impact on lean NOx trap (LNT) and selective catalytic reduction (SCR) aftertreatment systems, which have less raw NOx emissions to process, potentially allowing for a reduction in exhaust system cost and complexity, and a longer service life, reports CPT.
“The result of our research programme, incorporating e-motor characterisation, simulation and engine emission dynamometer testing was a clear benefit in terms of raw NOx reduction of a premium saloon with a 3-litre V6 engine,” says CPT’s manager responsible for applications engineering and strategic projects, Paul Bloore. “The decrease in NOx emissions, moreover, was achieved with a near 5% fuel economy improvement and corresponding CO2 reduction, delivered simultaneously by the SpeedStart starter-generator.”
Belt-integrated starter-generator (BISG) systems have already been successfully applied by the industry to reduce CO2 emissions by the simple expedient of stop-start. In principle, the same low voltage technology can be used to modify the load on the engine and optimise its performance for minimal NOx and particulate emissions. The challenge is having a fast-enough response time for real world driving conditions. CPT’s switched reluctance technology is by its very nature fast acting as well as being highly controllable, and well suited to optimising diesel and petrol engines for minimal NOx and particulate emissions, according to CPT.
Like mild hybrid systems generally, CPT’s SpeedStart technology harvests kinetic energy when the vehicle decelerates, which is then reapplied as torque by the switched reluctance machine during accelerations to offset fuel burn in the combustion engine. The sophisticated electronic control offered by an SRM, however, can further influence the engine operating point by absorbing or supplying electrical energy to move the combustion engine into a more favourable operating region. The benefits are achieved, because an SRM machine can respond swiftly to fast changing and transient road conditions.
The control strategies being developed and refined by CPT are based not only on this latest study, but also numerous other R&D programmes, as well as extensive real world driving and vehicle systems simulation work. This enables interrelated systems, such as battery management, exhaust aftertreatment and complementary thermal energy recovery, to be operated seamlessly, while also providing a valuable computer-aided engineering capability to explore further potential avenues of development through 48V electrification, CPT concludes.