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Variable Supercharger Blends Fuel Economy, Performance: Video


Contrary to popular belief, not all of us who love speed embrace gas-guzzling V-8s. Many of us can’t wait for the day when affordable performance cars come in electric-powered versions, too.

There’s a lot to be said for maximum torque at zero rpm, something internal combustion engines (ICE) can’t match. That said, one company is working on a variable drive supercharger that could offer significant gains in both ICE power and fuel economy.

Rotrak is a joint venture between Torotrak, a traction drive company, and Rotrex A/S, a centrifugal supercharger manufacturer. Rotrak has produced a prototype centrifugal supercharger that also employs a continuously variable transmission (CVT) drive.

To understand the benefits, it’s first necessary to understand the drawbacks of forced induction, which includes both turbocharging and supercharging.

Small turbocharged engines, unless they employ complex twin-turbo systems, often suffer from turbo lag when tuned to make top-end power. Turbo engines tuned for low-end performance can’t supply the boost needed for high-rpm benefit.

Superchargers are generally better at providing low-end torque, but their fixed drive ratio means that they produce too much boost at higher engine speeds. In other words, they’re wasteful above a certain engine speed.

An ideal supercharger system would have an infinitely variable drive ratio, which would allow it to vary compressor speed based on throttle setting and engine load. Such a system would provide enough boost at low end without creating too much boost at high engine speeds.

As Green Car Congress explains, that’s where the prototype Rotrak system comes into play. The CVT drive allows the supercharger to maximize efficiency across an engine’s entire range, which allows smaller engines to drive like bigger ones.

While no data on real-world performance or fuel economy gains is available yet, the system has a tremendous amount of promise. Ultimately, it would allow further downsizing of engines from today’s small-displacement turbos, like Ford's EcoBoost line.

A drivable prototype is expected in the next few months, which (hopefully) means we’ll be hearing more about the Rotrak system later this year.
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Comments (6)
  1. Oh, just drive the supercharger with an electric motor.
     
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  2. Yes electric is the way with the supercharger and use the conventional exhaust driven turbo.
    IMO the TRK variator will be noisey due to the manifold heat and the failing of the traction fluid.
    The variators imo will never ever make it to volume production due to the heat failings and short working life.
     
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  3. John, simpler said than done. Only the most exotic of motors (like the digital drives in Dyson products) can ramp to 150,000 rpm, so you would still need gears / or variable transmission to hit those speeds, so the benefits usually associated with just using a motor aren't really gained.
     
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  4. electro magnetic clutch [Recardo] will be all that is needed with the drive take up.
    the super charger is only needed for the low revs for low speed engine torque untill the conventional turbo cuts in.
    The supercharger can be belt driven or electric if enough volume of air is obtained.
    Forget the TRK varistor imo it has a fundamental flaw that will not allow volume production with a short working life.
     
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  5. Current exhaust driven variable geometry turbos can vary turbine swallowing capacity to change compressor speed independant of engine speed I believe so transient response
    should be improved over a conventional fixed turbo. This supercharger-CVT setup is doing essentially the same but robbing engine power. Correct me if I'm wrong.
     
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  6. @Ron, even variable geometry turbos can't be optimized for best performance across an engine's speed range. In terms of efficiency, the new tri-turbo systems developed by BMW (and under development by Porsche) are probably best. Their drawback, obviously, is cost and complexity.
     
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