CPT developments support switch to 48 V

  • 26-Jul-2012 04:52 EDT
CPT 7-12 COntrolled Boosting for Rapid reponse Applications COBRA.jpg

CPT's Cobra liquid-cooled electric supercharger has been developed for 12-, 24-, and now 48-V applications.

“Battery modules of 48-V standard configuration could form the building blocks for more electric vehicles, where battery system costs are presently the foremost constraint to full hybrid and electric vehicle affordability,” said Control Power Technologies (CPT) Chief Executive Nick Pascoe.

Mild electrification of a conventional powertrain has much to offer, he stated, because it “side-steps” the complexity of high-voltage pure electric and hybrid vehicle technologies, taking a more conservative approach to facilitate low-voltage micro/mild hybridization in lower cost gasoline engines in the campaign to achieve improved fuel consumption and lower CO2 emissions. Hybridized diesel engines using 48 V would benefit from both lower NOx and particulate emissions.

CPT has a lengthy background in the development of automotive applications of switched reluctance (SR) motor-generators using advanced control software and low-voltage power electronics.

As part of its focus on 48-V architectures for future vehicles, the company has developed its SpeedStart starter-generator for stop/start applications. Pascoe explained that it integrates its control and power electronics into the rear of the machine, which is sealed for life and is designed to provide efficient thermal management by connecting with the engine cooling system. It has a “coast down engine off" strategy that provides longer periods of energy recuperation.

“A key focus of 48-V functionality is low engine speed motoring and regenerative braking,” explained Pascoe. In an SR machine, electrical current is available in the coils within 20 ms, a tenth the time taken by permanent magnet motors—delivering engine idle within one-third of a second. That’s about half the time of a conventional starter motor and sufficiently fast to be perceived as virtually instantaneous by most drivers.”

With 48 V, SpeedStart “harvests” short duration regenerative braking. In total, with its torque-boosting and -shaping capability, it can deliver up to 8 kW of transient power, which is recycled with “minimal” losses.

Pascoe says its performance benefits have already been independently demonstrated at both 12-  and 24-V systems: “At a more optimal 48 V, the benefits increase significantly.”

CPT is also working on a turbo-generator integrated gas-energy recovery system (TIGERS). It comprises a liquid-cooled SR generator coupled to an exhaust-driven turbine. It is being developed for 12-, 24-, and now 48-V applications, as is the company’s Cobra liquid-cooled electric supercharger, which has particular applications for trucks and off-highway vehicles. CPT’s low-voltage automotive electric supercharger business was recently sold to Valeo.

The use of higher voltage systems than the auto industry’s long-established 12 V has been a subject that has ebbed and flowed for many years. In the U.S. in particular during the late 1990s and also considered by Daimler-Benz in Europe, there were signs that 36-V (42-V charging voltage) electrical systems might become established in regular road cars as onboard electronic systems multiplied, but this possible move soon lost momentum as 12-V capability increased and on-demand energy-saving systems were introduced.

However, Pascoe believes the new trend of 48 V (as a multiple of 12 V), this time focused on the powertrain rather than the entire vehicle electrical system, offers considerable, cost-effective benefits for future products.

“The availability of 48 V on the next generation of vehicles already fitted with state-of-the-art stop/start systems will improve their fuel economy and mileage by an additional 4% on the conservative NEDC (New European Driving Cycle) and significantly more under real-world driving cycles, with a corresponding reduction in CO2 emissions,” claimed Pascoe. “The technology offers driving characteristics comparable to the instant torque of electric vehicles and large displacement, naturally aspirated gasoline engines but with none of the downsides.”

He sees European vehicle manufacturers, in particular, together with their Tier 1 suppliers, moving to introduce a 48-V grid in addition to the conventional 12 V.

The timing of the 48-V introduction into series production vehicles is not certain. Pascoe confirms that his company has been responding to inquiries from auto makers for “some while” and that discussions with them had shown him that 48 V is an emerging technology enabler for further development of internal-combustion engines.

Questioned recently by AEI about 48-V architectures for road cars, Dr. Dieter Zetsche, Chairman of the Board of Management of Daimler AG and Head of Mercedes-Benz cars, said it would not be used for the next S-Class, but he did not rule out the possibility for the generation following.

This caution is understandable, not least because of growing public awareness of the crash safety aspects of higher-voltage applications in electric vehicles. Pascoe, though, regards charging voltages between 50 and 60 V as the transition zone from low to high for road vehicles. At 48 V, there would not be the need for occupant protection that would be present for electric-vehicle architecture operating in the 200- to 600-V band.

Pascoe also cited 48-V applications development as giving vehicle, traction motor, and battery manufacturers more time to pursue their major investment in more expensive electric and hybrid vehicles.

“In the 12 to 48 V [range] in which CPT’s modular solutions are primarily focused, modest voltage increases offer significant efficiency improvements. The company is already upgrading development rigs to handle the much greater generating and motoring power range.” He anticipated that CPT will be the first company to build a 48-V vehicle technology demonstrator for direct comparison against a 12-V vehicle, supported by the Advanced Lead-Acid Battery Consortium (ALABC), an international R&D organization.

Such lead-acid battery solutions, already evolving into state-of-the-art lead-carbon batteries, would help keep down costs when compared with NiMH and lithium-ion types.

He concluded: “If adopted as a global industry standard, 48 V available on every car would facilitate high-volume commercialization of battery modules at this voltage. It would also offer a potential mass-market opportunity not only for emerging carbon-enhanced lead-acid valve-regulated batteries but also more expensive NiMH as well as high-end lithium-ion-based energy storage solutions of a similarly standardized modular configuration.”

CPT is also helping to develop range-extended electric vehicles and hybrid vehicle technology.

The company was established in 2007 as a management buy-in funded by venture capital initially to acquire advanced powertrain technologies from Visteon Corp. and is described as being backed by major clean-technology investors.

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