Engine downsizing combined with forced induction is one of the hottest trends in the global auto industry, with turbocharging typically the boost method of choice. French supplier Valeo will soon put a new twist on the trend, as it prepares to launch production of its new electric supercharger in the 2015-2016 timeframe.
Valeo engineers see the e-supercharger, using a low-inertia switched-reluctance motor, as a key solution for hybrid vehicles. They believe the technology can address the low-speed turbo lag issues associated with downsized engines.
“The electric supercharger is a product that has a very fast response time—going from idle to 70,000 rpm in less than 350 ms,” said Pierre-Emmanuel Strohl, Valeo's Product Marketing Director of Powertrain Systems, at a media briefing in late July at the company's North American headquarters in Troy, MI.
While Strohl did not reveal Valeo's first customer for the technology, he said various evaluation programs have been under way with various OEMs. Ten automakers have paired the e-supercharger and its fully integrated electronics with turbocharged gasoline engines. Six paired the product with a turbocharged diesel engine, and three OEMs evaluated it with naturally aspirated gasoline engines.
Strohl compared the product's benefits, including additional low-rpm torque, with conventional turbo systems. He noted that a single-stage turbocharger architecture "is well adapted to light downsizing—up to 30% cubic capacity reduction while keeping the same power output. For instance, by doing that you can easily shift from a 3.5-L V6 naturally aspirated engine to a 2.4-L 4-cylinder turbocharged engine,” Strohl, an electrical/electronics engineer, told AEI.
But downsizing by 50%—going from a 3.5-L six-cylinder to a 1.8-L 4-cylinder, for example—radically alters the performance picture, particularly when longer-ratio vehicle gearing is part of the equation.
“That’s the reason why you need another device for low-end torque," he explained. "It could be a two-stage turbo architecture. It could be some kind of hybrid with electric motors having the maximum torque at low revolution. Or it could be a two-stage architecture with one turbo and one supercharger—either mechanical on the belt or electrical,” Strohl said.
Supercharging Ford's 1.0-L triple
Valeo technical specialists have completed advanced engineering work on a range of electric superchargers. Technology demonstrations have addressed various engine types and sizes, including naturally aspirated engines from 1.0-L to 2.4-L and turbocharged gasoline and diesel engines from 1.0-L to 4.0-L.
The most visible demonstrator involving Valeo’s electric supercharger is the HyBoost vehicle electrification project led by Ricardo. When the multipartner project started, the U.K.’s Controlled Power Technologies (CPT) was the electric supercharger supplier. However, with the December 2011 acquisition of CPT’s Variable Torque Enhancement System business, Valeo added the electric supercharger with switched reluctance motor technology to its powertrain portfolio.
For the HyBoost project vehicle, engineers replaced the 2.0-L naturally aspirated, 145-hp 4-cylinder gasoline engine in a 2009 Ford Focus with a 1.0-L, 143-hp 3-cylinder EcoBoost engine. The demonstrator car employs a slew of electrification technologies, including several Valeo products: StARS (trademarked) stop-start system, a floating voltage electric recovery system with ultracapacitors and dc/dc converter, gasoline cooled EGR system, an air intake module with embedded water-cooled charge-air cooler as well as a cooling module.
Strohl said that the HyBoost technology demonstrator improved the combined fuel economy in the standard European driving cycle to between 41% and 52% when compared to the non-electrified base vehicle.
Low-inertia, switched-reluctance motor is key
Valeo’s technology demonstrators include a car fitted with a 2-kW, 12-v electric supercharger on a two-stage architecture. When driven on a real road test cycle that includes a mix of mountain roads, city streets, and highways, the vehicle’s electric supercharger has an average boost duration of 7 s with an average boost frequency of 5 boost/km, according to Strohl.
In addition to 12-v vehicle architectures, Valeo’s electric supercharger is compatible with up to 27-v systems using ultracapacitors, and the electric supercharger also is being developed for use with 48-v architectures.
The key component of Valeo’s 4 kg (8.8 lb) electric supercharger is its switched reluctance motor.
“Switched reluctance motor technology has a rotor with very low inertia. That’s the reason why we are able to go from idle speed to the maximum speed of the compressor wheel (70,000 rpm) in less than 350 ms,” said Strohl.
In the coming years, use of supercharger technology is forecast to grow dramatically.
Using third-party forecasts, Valeo planners expect that the number of twin- and 3-cylinder engines in the European market will jump from 900,000 units in 2011 to 5 million in 2019 with specific power increasing from 47 kW/L to 63 kW/L.
“It also means 60% of the 2- and 3-cylinder engines in 2019 in Europe will be turbocharged or supercharged compared to 20% in 2011,” said Strohl.