In the news today, two promising prototypes of new style superchargers. The technology employed here is not novel in any way in that it has been around for a while now, but it is new to see this applied to superchargers:
1- Variable Gearing Chargers:
The first is a variable gearing drive system similar to continuous variable transmission designs which utilizes a variable coupling ratio to maximize torque delivery. On the supercharger , this variable gearing can be used to overdrive the charger at lower engine speeds for higher midrange boost pressure, while reducing the drive ratio at higher engine rpms to reduce the compressor wheel speed, maintain boost levels, and reduce heat.
The result is a centrifugal supercharger with a fatter midrange torque output without an astronomically high peak boost pressure in the higher rpm (which would be the typical result of overdriving a standard geared centrifugal).
This hybrid system is being developed as a 50/50 joint venture between rotrak (http://www.torotrak.com/) which is:
“The world leader in full-toroidal traction-drive transmission technology, focused on the development of IVT (Infinitely Variable Transmission) and TCVT (Toroidal Continuously Variable Transmission) systems “
… and rotrex (http://www.rotrex.com) who are
“currently developing a new smaller unit, the C8, which will be ideal for many new applications. Availability expected in the latter part of 2010.”
This speaks directly towards the industry trend of using smaller displacement engines on OEM cars to reduce emissions and fuel consumption, while supporting power and performance levels and maintaining them at current levels of current model cars by using supercharger technology.
In the next years we will continue to see smaller and smaller engines (as small as 1.3 litres in some markets) assisted with supercharger technology to replace existing 1.6 to 2.0 litre compacts.
2- Variable Blade Compressiors
Similar to the concept of the Aerocharger – Variable Area Turbine Nozzles (VATN) technology that is used on the porsche 911 997 to boost midrange power delivery and delivery peak boost as low as 1500 rpms, a UK startup Lontra (http://www.lontra.co.uk/technologies/the_bladesupercharger.htm) is working on a prototype in conjunction with Ford Motor Co. to produce a variable pitch compressor wheel on a centrifugal supercharger unit.
This product also targets ‘downsized engines’ to produce comparable power output from smaller displacement motors. This new technology also incorporates a compound compressor (with two sets of compressor wheels) inside a single housing which has been available on drag diesel applications for some time now.
Prototypes demonstrate a 20% efficiency gain over traditional compressors, and has an innovative variable port design which allows it to meet changing application requirements while maintaining constant speed.
The compressor is designed for high volumetric and thermal efficiency, and the geometry of the compressor allows high efficiency heat recovery. It is oil free, and other features include small size, low vibration and quiet operation. A key feature is the compressor’s ability to vary flow and pressure with minimal efficiency loss, without the use of Variable Speed Drive.
Aerocharger illustration showing the boost response advantage of VATN on their turbos (please note the green line for positive displacement is incorrect, it should be flat at 9psi at all rpms)
So in conclusion, both of these efforts are targeting improved efficiency and better power band performance (rather than just peak performance typically associated to centrifugal chargers). Obviously, this will make the compact centrifugals more competitive as OEM solutions compared to the low end power friendly twin screw or roots blower designs.
What may not be as obvious here, is that these technologies are working on opposite ends of the supercharger, with Lontra working on the compressor side, and Rotrex/Rotrak working on the drive system, and so there is the potential of creating an even more amazing hybrid charger with BOTH a variable drive system AND a variable characteristic compressor.
This kind of hybrid can offer extreme centrifugal performance with really low spool rpms, impressive midrange, and very efficient top end power… and with a promised increase of at least 20% thermal efficiency, these kinds of setups will require reduced octane and intercoolering demands before the knock limit is reached.
Very very exciting overall… so exciting that THIS was the thing that made me come out of hiding to blog again. I’d love to have one of these hybrids on an Ariel atom, I think that would be something to marvel at.
