Hybrid electric vehicles have gained enormous credibility in recent years but the cost-to-benefit ratios of some are questionable. Diesel hybrids are an extreme example, with their impressive fuel consumption/emissions figures offset by the high cost of the diesel-electric powertrain. Sometimes the hybrid technology solution simply does not add up to high-volume commercial viability.
A potential alternative is further development of micro-hybrid systems. At the 22nd International AVL Conference in Graz, Austria, in early September, U.K. consultancy Controlled Power Technologies (CPT) put forward its views on the future of micro-hybrid technology. The conference, titled "Engine & Environment," was organized by AVL List GmbH, which claims to be the world’s largest independent developer of vehicle powertrains.
Amongst those presenting technical papers for discussion was Guy Morris, CPT's Engineering Director and Chief Technical Officer. He believes that in the current spectrum of hybrid development, there is a band of opportunity in the middle ground of so-called "micro-to-mild" technologies that can generate the level of cost:benefits that is essential for commercial success via economies of scale.
“Integrated starter-generators and electric superchargers are good examples of advanced 12-volt micro-hybrid technologies,” states Morris. “When applied simultaneously, these compact machines can help deliver a low-voltage equivalent to a mild hybrid solution that avoids the cost, weight, and packaging penalties of a full hybrid or high-voltage electric vehicle."
According to Morris, the lower cost "micro/mild" solution also reduces the industry’s dependence on government subsidies that are often required to make such vehicles affordable under current market conditions.
Using a new generation of low-voltage micro-hybrid technologies and retaining a gasoline or diesel engine as the main driving force can bring a 25% fuel saving without incurring the expense that higher voltages and massive battery packs bring, he explained.
CPT’s core competencies include low-voltage power electronics, advanced control software, and the application of 12-24 V electrical machines to vehicle powertrains. Morris believes the opportunities for low-voltage solutions in high-volume sectors can, therefore, effectively tackle the critical “mild hybrid” middle ground, with low-voltage solutions generating technology and commercial opportunities. OEM interest is increasing, he noted.
At its Laindon headquarters east of London, CPT has developed two production-ready systems that meet these needs, explained Morris. One is the VTES (Variable Torque Enhancement System) supercharger, and the other is the SpeedStart B-ISG (Belt Integrated Starter Generator).
The recent availability of low-cost, low-voltage power electronic devices has, in particular, given a significant boost to the viability of such technologies, Morris told the Graz conference, where both were demonstrated.
He stated that CPT had engineered compact and highly scalable solutions that were previously unavailable. The company is able to manufacture these using industry standard processes, with minimal capital investment and tooling, he said.
The CPT technical paper presented at Graz concluded that a synergistic approach enables existing technology engine and transmission combinations to be aggressively downsized and down-speeded to support very significant vehicle CO2 reduction of more than 25%. The paper was jointly authored by Morris, Mark Criddle, Mike Dowsett, and Toby Heason from CPT, and by Dr. Paul Kapus and Matthias Neubauer from AVL—both of whom have worked closely with CPT since early 2009.
During that time, CPT has supported AVL in the development of an enhanced version of a low-voltage mild hybrid demonstrator. The vehicle is designed to deliver the best possible value for improving powertrain efficiency at an affordable system cost.
Based on a VW Passat sedan, the demonstrator incorporates a state-of-the-art AVL-developed 2.0-L gasoline engine currently delivering a claimed fuel consumption of 6.6 L/100km and CO2 emissions of 154 g/km. Those figures represent a 20% reduction from the 192 g/km of a series production Passat (MY2006) fitted with a 2.0-L TGDI engine. They are also close to the 146 g/km of the current Passat 2.0-L common rail TDI engine.
A significant feature of the demonstrator is its long gearing to enable down-speeding of the engine. Normally, this would result in unacceptable high-gear vehicle acceleration, but the integration of the VTES is designed to provide a significant dynamic performance boost. The system reacts immediately to transient load conditions by delivering up to 25 kW of additional power to the crankshaft in less than one second, even at very low engine speeds.
Next technology step is to further develop AVL’s efficient low-carbon ELC-hybrid concept by incorporating CPT’s SpeedStart system. In combination with the VTES electric supercharger, this will create what the companies describe as a cost-effective “micro/mild” hybrid system. They claim the system, when applied to a downsized 1.4-L variant of the ELC-hybrid power unit, would meet the European industry’s 2012 fleet-average 130 g/km CO2 emissions target.
The use of a "carbon enhanced" valve-regulated lead-acid (VRLA) battery will help maximize energy recuperation during deceleration.
CPT’s micro-hybrid technologies can be applied to a wide range of engines and are being evaluated by a number of carmakers. A major incentive is that in Europe the auto industry has less than two years in which to ensure that each manufacturer can meet the 130 g/km figure and the subsequent target of 95 g/km by 2020.
A similar deadline has been imposed in the U.S. with its first nationwide carbon emissions target of 250 g/mile (155 g/km) by 2012, with individual states able to impose tighter limits.
“The combination of low-voltage micro-hybrid technologies incorporating stop-start, brake regeneration, and electric boosting—as well as exhaust gas regeneration which we’re also working on for the longer term—can help minimize the additional cost of CO2 compliance to the consumer to between 1500 and 4000 euros within the 2015 to 2020 timeframe,” says Morris. “This compares with 6000 euros to more than 18,000 euros for a full hybrid or electric vehicle.”
To demonstrate the production-ready version of the SpeedStart system, CPT is undertaking a tour of European carmakers with an Audi A4 equipped with its next-generation B-ISG technology. The system includes intelligent torque and current control, plus significantly enhanced stop-start capabilities.