|The VTES unit (inset) and installed in the AVL VW Passat demonstrator. in Click to enlarge.|
Controlled Power Technologies’ VTES (Variable Torque Enhancement System) electric supercharger (earlier post) is being incorporated in a project by engine developer AVL (earlier post) and will also feature in the Ricardo-led £3 million (US$5-million) HyBoost program announced by the Technology Strategy Board on 9 September (earlier post). Both projects are seeking to maximize powertrain efficiency at the lowest possible cost.
VTES is an air-cooled Switched Reluctance machine, coupled to power electronics and an optimized radial compressor, that delivers high airflow, pressure and efficiency. The electric supercharger operates independently of engine speed, making it suitable to maintaining vehicle transient performance and driveability. The product is designed for integration into both Otto and Diesel engines to deliver enhanced torque, emissions control and CO2 reduction. VTES is optimized to use the standard 12V vehicle architecture.
When applied to a radically downsized 1.2-liter turbocharged engine, VTES delivers in excess of a 50% increase in torque at engine speeds below 3,000rpm, more than compensating for insufficient power from the exhaust turbine. More than 90% of the available torque is delivered in less than a second. Compared with a 1.6-liter naturally aspirated engine, the downsized engine with electric supercharger reduces the 70-100 km/h (44-63 mph) top gear acceleration time from 18 to 11 seconds.
CPT’s electric supercharger significantly increases an engine’s air charge density over the critical first 10 combustion cycles of a low speed transient. Fitted with a low inertia compressor, the supercharger accelerates from idle to its maximum speed of 70,000 rpm in less than a third of a second enabling even a turbocharged engine to achieve full load torque within one second at very low engine speeds. This fast dynamic response and rapid air boosting enables the system to react instantly to high transient load conditions, delivering up to 25 kW (33 bhp) of additional power at the crankshaft. This is more than enough to compensate for any turbo lag and more cost effective than integrating a 25 kW electric motor into the powertrain since only a 12-volt alternator and battery system is required, according to CPT.
CPT recommends a combination of the highly dynamic electric supercharger in series with a conventional exhaust-driven turbocharger to optimize the overall response of the system, compared to other air charging methods. The VTES technology can also help reduce soot and particulate emissions from diesel engines, particularly when the driver accelerates at low engine revs, which, in turn, creates an opportunity to reduce the size and cost of the diesel particulate filter (DPF).
Our electric supercharger is an ideal enabling technology for the extreme engine downsizing being advocated by European carmakers. The system has been designed to be sufficiently flexible to enable use of a common solution across a wide range of gasoline and diesel engine platforms. It delivers the required economies of scale and complements the micro-hybrid strategy of using the existing 12-volt vehicle architecture as an economic alternative to higher voltage ISG based torque assistance.—Mark Criddle, CPT senior engineering manager
CPT will showcase VTES at the international supercharging conference held in Dresden 24-25 September 2009. The company says it’s progressing a number of confidential development contracts that will lead to commercial applications, initially for small- and medium-volume production, and will continue to work with the industry’s powertrain developers to verify and validate the benefits of electric superchargers.
Controlled Power Technologies was set up in 2007 as a management buy-in funded by venture capital initially to acquire advanced powertrain technologies from Visteon Corporation and its technology development partner Emerson Corporation.