ON THE SUPERCHARGE!01 May 2012
Torotrak's toroidal continuously variable transmission (CVT) has been on the fringes of the motor industry in one guise or another for more than half a century. But, even when it was being developed by Perbury Engineering all those years ago, it wasn't new technology: a patent had been filed for a toroidal CVT as far back as 1899 and Austin tested complete transmissions in the 1930s.
Despite their best efforts and the technology's advantages over conventional torque convertor automatic transmissions, it always seemed a forlorn hope that Torotrak's toroidal continuously variable transmission would break the stranglehold that big suppliers like ZF, Aisin and others have over the automotive industry.
This is a state of affairs that is acknowledged by Torotrak's CEO Dick Elsy, who joined in 2003, and has been instrumental in developing a new business strategy and model for the business: "Mainstream cars are in the long grass for the time being, but new developments like the supercharger and kinetic energy recovery systems (KERS) etc could reawaken interest in the mainstream in the longer term.
"Our main interest is commercial vehicles, because we're the only variable drive that can handle big torque with the right mechanical efficiency. In small cars, from our experience with ride-on lawnmowers, using a very small device, it's not such a big walk from that technology to the small cars being developed and launched in the newly industrialised nations of the Far East. A lot of those customers come from scooters and mopeds with centrifugal clutches, so changing gear manually is alien to them. Cost wise, it's about on a par with planetary automatics."
But it's the rising cost of fuel, as well as increasingly stringent emissions legislation, that could provide the impetus Torotrak's toroidal variator technology needs to make its commercial breakthrough into the automotive sector.
There are a number of applications, says Elsy, for the technology, but two principal ones are trucks and superchargers. Torotrak already has a deal with Allison in the USA, and an unnamed European bus and truck manufacturer, to develop its CVT. "With fuel costs in a truck accounting for more than a third of operating costs, there's a big incentive to bring that down. We're seeing 10-20% fuel economy savings during normal road use, increasing to over 20% for urban stop-start deliveries.
"It saves fuel, because it enables the truck engine to run at its most efficient, using the Torotrak to vary the vehicle's speed through torque, rather than ratio control."
And while this is an impressive development, with Allison about to move into the prototyping stage, what is really exciting Elsy these days is the 50:50 joint venture with Rotrex to develop a fully variable supercharger under the V-Charge banner.
"Complying with EU6 in 2014 is requiring a lot of expensive after-treatment, especially for diesels. For petrol engines complying with EU6,
it means downsizing, direct injection, variable valve timing and turbocharging to achieve very similar fuel consumption to a diesel, but it's easier and cleaner. That represents a spend, in hardware terms, of about €30 to get a gram per kilometre reduction.
"If you look at hybrids, the conventional ones we know today, it's on a similar trajectory, so it saves fuel, but at a cost by, basically, putting a tariff on a gram per kilometre of about €95. The industry doesn't want that."
Downsized engines in the 1,000cc to 1,200cc category can, says Elsy, be efficient, but at the expense of performance, especially at low engine speeds. Even the addition of a turbocharger doesn't eliminate that shortcoming and might, in fact, exasperate it, as he explains. "It's relatively straightforward to downsize the engine and boost it at steady state for specific outputs, but extremely difficult to get the transient response. The problem is compounded as the engines get smaller, as there's less exhaust energy to put into the turbine. We firmly believe that positively charged supercharging is the way to go for small engines and to bring the fun back into them.
"As small engines will end up in bigger cars, it makes the issue of the lack of bottom end performance and torque even more pertinent. This will result in more turbocharging with variable geometry, twin turbocharger systems or compound charging, which all clearly work and have their place, but have cost and packaging issues."
Another concern with more complex turbochargers on petrol engines, claims Elsy, is that, as the exhaust temperature is higher than diesel, you start moving into more exotic materials, which ups the price, making complex variable turbochargers less attractive.
While conventional, fixed rate superchargers have their limitations as well, he makes the following point: "If you choose to optimise the top end performance, then you have a very limited ability to boost the engine at lower speeds with a fixed ratio device; if you target boost at the bottom end, you clearly have an embarrassment of air at the top end. Which do you do?"
Elsy believes V-Charge offers a "unique" solution, with a variable speed drive that, by varying the ratio, can satisfy the engine throughout its operating envelope. "It's an easy technology to package and, as it's a supercharger, it's packaged on the cold side of the engine, so all the issues of heat go away. It also frees up the exhaust flow, so the catalyst heats up more quickly and, potentially, it can be an enabler for different combustion cycles, like Miller or Atkins where the valve timing is different and you're expanding or increasing the length of time on the expansion stroke.
"By positively forcing the air into the engine, you can start achieving a lot of benefits of variable valve type emissions and efficiencies, but with fixed valve timing and forced induction."
Elsy and his colleagues even talk about the possibility of eliminating the throttle altogether, using the variable nature of the boost instead.
Already working with one, unnamed, tier one, he believes that "for the enlightened OEM or tier one, we're offering a whole new set of tuneables they haven't been able to access before. It's not just about what it does, but how it offers the chance to work with new engine cycles and the ability to have the air much more controllable, where and when you want it."
Fallbrook and supercharging
V-Charge is not the only company pursuing a variable speed supercharger, as Tony Lewin discovers…
The ideal supercharger would be one that could produce boost on demand; one where boost pressure could be made independent of engine speed.
A significant step in that direction comes from Fallbrook Technologies, whose NuVinci variable speed drive is now ready for adoption by automakers, following extensive testing in conjunction with an unnamed tier one supplier. The drive, which sits on the crankshaft pulley, is able to offer a ratio change of around 3.8 to 1, says Fallbrook chief technical officer Rob Smithson.
"This gives a substantial benefit," he says. "Straight off, we got a 30% increase in mid-range torque, using an aftermarket supercharger on a Ford Mustang engine."
The Mustang was chosen because of the easy availability of aftermarket kits, but Smithson insists the variable speed drive will work just as well on engines as small as one litre. "It's actually easier than a turbo installation, as you don't have to deal with high heat levels under the bonnet – and the bypass noise problem often associated with superchargers is eliminated, as the drive can vary its speed on the fly."
While Smithson is reluctant to reveal the likely cost or weight of the new drive, which is still being finalised for production, he does assert that it will be "very competitive" in the market. "We will beat a variable geometry turbo on total system cost, and probably also on fuel efficiency and driving response," he promises.
Torotrak (Development) Ltd
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