by P Sanchez
Last week we talked about next level technologies applied to the internal combustion engine as they make themselves available to the public through luxury brands and the high-end of the high-ends. We went into some detail on how Infiniti’s simple but ingenious rocker-armed piston assembly is giving in-chassis variable compression another shot at commercial reality. We also looked at the latest iterations of camless valve control technologies as they make their first production intro in exotic cars.
Today, we’re discovering more of these engineering marvels that promise better performance, higher operating efficiencies, and safer emissions. For now, these technologies come as part of a car that’ll cost you an arm and a leg (and perhaps a house mortgage) but wait a few years as they’ll come standard on more sensible price models.
Whether it’s a turbo or a supercharger, forced induction works great in cramming more air into the cylinders. More air means more fuel can be burned. More burning, more performing.
But forced induction is a double-edged sword. Among its penalties, straightforward turbocharging or supercharging means throwing fuel economy out the window. Then there is also the increase in car emissions as well as the ever-present risk of blowing-up the engine.
It’s simple physics really. The turbo packs more air mass into a restricted space and though this increases the air’s density as intended, it also raises the temperature. The piston compressing the air (that may have fuel already mixed-in at this point) further raises the temperature to a point of self-ignition (knock) or create the other aforementioned baddies.
BMW is now using a novel way of lowering the temperature of pre-compressed air coming into the intake. The BMW M4 GTS uses a rare water-injection system to dramatically improve boost characteristics. The technology works simple enough. Air first goes through a typical forced induction route. First, the impeller takes-in air, compresses it, and pushes it along and into the intercooler where it gets cooled down a bit. The dense but still very warm air is sent to a chamber right before the cylinder intake where it is further cooled by jets of water mists sprayed by high-pressure water injectors. The resulting air going into the cylinder is denser and cooler than any regular force induction system could achieve. BMW claims an increase from 444 horsepower to 493, increase fuel efficiency by 13%, better knock avoidance, and reduction of overall thermal stress on the engine’s components.
It’s interesting to note that it’s not an entirely new technology. The water (or more specifically fluid) injection was used in the 1962 Oldsmobile Jetfire which was also the first production car to be fitted with a turbocharged V8. The working principle is the same as BMW’s but the tech in the ’60s used a complex hydraulic and mechanical control system that surely made it costly to produce and required maintenance.
The technology took a long leave-of-absence and has only recently resurfaced following advances in material technology, electric actuation, and engine management; advances that make such system reliable and practical enough for the needs of the modern performance car.
Extroid Continuously Variable Transmission
You’ve probably noticed that there’s a “what’s old is new again” theme going with these luxury level engine technologies. And we’re going to explore this further in our last section by diving into Toroidal CVTs.
Now CVTs or continuously variable transmission has been around for decades but only in the past few years that they’ve become a popular transmission option, especially for fuel-sipping cars. Their downside? Their belt-driven nature is their Achilles heel and this gives CVTs their dodgy reputation and long-term unreliability, suitable only for light vehicles with low-torque demands.
Nissan is steering up renewed interest for its “Extroid CVT” which promises the seamless gear changes and transmission efficiencies of CVTs but with higher load applications, faster response and better reliability. Instead of belts going around input and output pulleys of changing diameters, toroidal CVTs use input and output discs that - when facing together - gives the inner shape of a toroid (that’s a donut shape for you and me). Between these discs are power rollers or simply, metal wheels that provide the gearing connection.
Differences in gearing ratio are achieved by how the power rollers are positioned in the “toroid”: If a roller wheel is in contact with the inner diameter of the input disc while simultaneously in contact with the outer diameter of the output disc, then this arrangement creates a low speed/high torque gearing. Conversely, if the roller wheel is angled in a way that it’s in contact with the outer diameter of the input wheel while in contact with the inner diameter of the output wheel, this creates high speed/low torque gearing. However a power roller is angled, it always maintains simultaneous contact between the input and output disc, and it can infinitely vary the gearing ratio by riding the curved space between the two facing toroidal discs.
With no belt to break, the design lends itself suitable for high torque scenarios and the Extroid transmission has last seen application with the Nissan’s defunct large-sized sedan Cedric taht has a 3.0 L engine. The Cedric’s line has been continued to this day by the Nissan Fuga line which also shares a platform with Infiniti’s M or Q70 line but neither carries the Extroid CVT.
In fact, Nissan or Infiniti does not have the Extroid CVT in any of its current line-ups. However the technology is still promoted in its global site and there are talks of releasing an updated version of the technology which we know for sure, we’ll see it first with their high end and luxury models.