Two Promising Boosters For Our Ever-Shrinking Engines – Technologue


Every fortune-teller in the car biz knows that the engine downsizing, down-speeding, and boosting efforts expended to date are but the tip of a metaphorical iceberg that’s expanding even as the literal ones melt. Simple turbocharging, with trick exhaust plumbing, twin-scroll snails, or variable-geometry turbine inlets sufficed for the initial round of modern engine downsizing, but today’s engineers are resorting to smaller, faster-spooling sequential turbos, electric turbos, supercharger/turbo combos, and mild hybridization. Two fresh ideas recently caught my attention.

The Torotrak V-Charge variable-drive blower can work with a standard turbocharger as a lag filler or stand alone. Its centrifugal blower looks like a turbo’s compressor snail and is belt-driven via an interesting toroidal CVT like the car transmission I covered in my March 2008 column. Picture two halves of a donut mold—one connected to the pulley, the other to the blower. Two discs roll between these halves. Changing their angle changes the ratio. When contacting straight across the donut mold, the ratio is 1:1. When contacting high and outside on the input and the low and inside on the output, you get 0.28:1. Low on the input to high on the output equals 2.82:1. Shifts across this broad ratio spread take far less than 400 milliseconds. A second fixed planetary “gear set” provides a further 12.5:1 step up in ratio, but like the donut rollers, these “gears” have no teeth. They transmit torque very quietly via the same special traction fluid.

V-Charge The donut “variator” is housed on the left side of this explosion. The planetary non-gears are just inboard at the right.

With the engine spinning at 1,000 rpm, the blower speed can vary between 8,750 and 88,125 rpm, contributing torque-filling boost more quickly than a two-stage turbo or a clutched supercharger could. A 1.0-liter (125-hp/125-lb-ft) Ford Focus inline-three was fitted with a V-Charge unit and larger main turbocharger sized to peak at 150 hp and 181 lb-ft. Fuel consumption increased by 3 to 4 percent, but acceleration performance matched that of a 1.5-liter EcoBoost I-4, at a 12 percent fuel savings. Torotrak says the unit is 97 percent quieter than a Roots type blower, weighs just 13 pounds, and should cost the same as an electric supercharger (without the power electronics, battery, etc.).

Simple turbocharging sufficed for early downsizing, but two new ideas have caught my attention.

The second idea comes from Hansen Engine Corporation out of Plymouth, Minnesota. Instead of instantly varying the blower’s speed, Hansen’s better mousetrap varies the displacement of a twin-screw Lysholm-type supercharger to deliver the low-rpm responsiveness of a supercharger with the torque and efficiency of a turbo. The secret is never making the engine work to compress air that would only end up getting vented to a wastegate.

Here’s the brief: When idling or cruising, a sliding window on the side of the blower stays open so no air gets compressed and the crankshaft only senses less than 1 hp of friction and oil-seal drag. Drop the hammer, and this window closes enough to generate the maximum pressure the cylinders can tolerate, gradually opening as revs rise to maintain said pressure while reducing crankshaft load.

Ford analysis of a 2.0-liter EcoBoost engine converted to run a Hansen VDS blower showed the engine’s performance surpassed the gain of upsizing to a 2.3-liter EcoBoost engine while maintaining the 2.0-liter’s fuel economy. And that was on an engine using turbo-optimized exhaust plumbing and compression (9.3:1). Free up the exhaust, increase compression, and sacrifice some of the added performance to down-speed the engine with a taller axle ratio, and Hansen VP of engineering Paul Cross is convinced that this could become the first supercharger to outperform a turbo for fuel economy and responsiveness.

Cross is also optimistic the cost can eventually reach parity with turbos, taking into account lower-temperature materials required for “cool side” supercharging and reduced emissions challenges relative to the turbo’s thermal inertia at startup. He notes it will require some acoustic countermeasures in the intake tract. Then again, maybe we can all learn to revere supercharger whine the way some love noisy turbo wastegates.

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