Compound turbocharging will be coming to more of tomorrow’s vehicles thanks tot engineers at Borg Warner. Turbochargers are compressor powered by the energy of hot exhaust gasses as they rush out of the engine after the power stroke — energy is wasted in non-turbocharged cars. They are vital in the quest to make internal combustion engines more efficient.
Conceptually, they work the same as fanning the flames of a camp fire. More oxygen makes a hotter fire. Cram more of it into a cylinder nearing the top of its compression stroke and you get more power with fewer emissions. If that sounds like magic, it is. But there’s a catch. At low engine speeds, exhaust gas flow is low. It usually takes a few seconds after the driver whistles down to the engine room for more power before the turbo is spinning fast enough to make a noticeable difference. The period leads to what is known as “turbo lag.”
Volvo is leading the way in compound turbocharging systems that uses an electric supercharger to provide boost as soon as the throttle pedal is pressed and before the turbo spools up. The result is the best of both worlds — nearly instantaneous power at slow speeds and lots of extra power at higher engine speeds.
Borg Warner has just introduced what it calls its e-booster, an electric supercharger about the size of a cantaloupe. The company says it can improve fuel economy by 10 percent with no loss of performance. The e-booster is little more than a really powerful hair dryer that pushes more air through the intake tract.
The e-booster can spin up to its full 70,000 rpm operating speed in just three fifths of a second. Borg Warner says it improves torque by 85 percent at 1,500 rpm and by 55 percent at 2,000 rpm.Thanks to electronic engine management systems, the supercharger and the turbocharger can be managed so the driver feels nothing but a smooth, continuous flow of power all the way from idle to red line.
The e-booster needs up to 6 kilowatts of power — more than a traditional 12 volt system can supply. But a 48 volt electrical system can supply the needed juice and power other vehicle systems like electric steering, electric brake boosters, heated seats, and electric water pumps.
On Friday, BorgWarner announced that Mercedes Benz will introduce the e-booster on a 3.0-liter six-cylinder engine that will be used in an as yet unnamed model. CEO James Verrier says two more automakers will use the e-booster system soon but won’t name the other companies yet. “It’s going become relatively mainstream over the next five years,” he says.
“There’s very little that’s new under the sun when it comes to most engine technologies,” says Stephen Ciatti, a mechanical engineer at Argonne National Laboratory. “What changes is our ability to either manufacture them cheaply and effectively … or the need for a more expensive approach to solving a problem when market demands or regulatory pressures don’t force it.”