Lotus proposes hybrid sporty

British sportscar maker, Lotus, has claimed a raft of patents with its high-tech Evora 414E concept car. But arguably patents' most impressive feat collectively is to generate 306kW of power from just 1.2 litres!

The concept version of the critically acclaimed Evora is not only faster than it's conventionally powered stablemate, but cleaner as well. It debuts a host of Lotus Engineering breakthroughs on its way to a sub-four second zero-to-100km/h time. That's about a second faster than the standard 3.5-litre, V6 petrol-powered 2+2.

Debuting at the Geneva Motor Show this week, the Evora 414E (it has 414 horsepower), uses a lightweight, Lotus-developed three-cylinder petrol engine to power a revolutionary new battery. The rear-drive hybrid Evora then uses two electric motors to independently drive each of the rear wheels via two single-speed gearsets.

Though both gearsets share the same housing (which looks much like a conventional differential), the system lets the full flow of Lotus Engineering's electronics creativity loose on a host of new driver-aid systems. These include more accurate Torque Vectoring, simulated gearsets and even advanced engine braking in a package that can reach out to 483km before it needs either electrical or conventional refilling.

Given how quiet the car will be on the road, Lotus worked with audio supplier, Harmon, to simulate engine noise from speakers in the front and rear bumpers to let pedestrians know the 414E is coming.

MORE DETAIL

The Drive System: It's hard to identify any one component as being the "heart" of the 414E's system, so we'll start where most potential buyers will. When you get it home, you just lift the rear number plate and plug it in to the garage wall. That will charge the new 17kW/hr Lithium Polymer battery, which is about enough for 50km of pure-electric driving and zero local tailpipe emissions.

While the first Lithium-Ion batteries first appeared in production cars only last year, Lithium Polymer is a step forward again, holding the battery's electrolyte in a solid polymer composite.

The 414E runs what is called a 'series' hybrid system -- as opposed to the more-familiar 'parallel' system on cars like the Prius. The closest the combustion engine ever comes to driving the wheels is providing the energy to the Lithium Polymer battery. That's just as well, because unlike the engine, the battery has been designed for high-performance work, capable of discharging 100kW. The 1.2-litre petrol engine can muster only 35kW at 3500rpm.

While the semi-omnivorous, three-cylinder petrol engine (it can work equally well on ethanol or methanol) lacks for muscle, it is light (85kg) and cheap to build.
Dubbed the Lotus Range Extender engine, it made its debut at the Frankfurt Motor Show last October. While it has only two-valves per cylinder, its block, cylinder-head and exhaust manifold are all cast in one piece in aluminium. This reduces weight and cost, adds stiffness and, according to Lotus, prolongs engine life.

The engine is linked to the battery by a generator, which converts mechanical energy into electrical energy for the battery. The generator also acts as the starter motor for the engine when it's needed.

The Electric Motors: The real performance for the 414E comes from its pair of electric motors, one for each rear wheel, making the hybrid rear-wheel drive, just like the standard Evora.

Each motor has been limited to 153kW of power, but each gives an instant 400Nm of torque, creating a 306kW, 800Nm powerhouse capable of outsprinting its petrol-powered sibling. The clever part comes from Lotus choosing to send all this power and torque independently, though a single gearset per wheel, then sitting each of the gearsets together in one housing in the middle of the car. Think of it as two one-speed gearboxes sharing a diff housing and you'll be close to the money.

The Rationale: Whole-of-life emissions is a concept most production hybrid makers don't like to bring up, but Lotus claims the 414E's lifetime CO2 emissions will be far less than a comparable full-electric car, while being higher than a petrol-powered Evora. But it's also describing the 414E's driveline as a modular, flexible system, much as it describes the Evora's bonded-and-riveted aluminium chassis as a modular, flexible chassis. There is something in that, because the Lotus Range Extender engine will also be seen in the as-yet-unnamed Giugiaro-Proton hybrid concept car in Geneva as well.

The New Driver Aids: Porsche introduced Torque Vectoring in the 911 Turbo (and Audi and BMW each have systems in production cars), but the 414E claims to be far more accurate, more flexible and more versatile in what it can do. Capable of providing maximum torque to one wheel and zero to the other, the 414E's system extends Torque Vectoring from its original concept as a handling and stability aid and even turns it into an urban assistance tool as well.

Because its electric motors drive the wheels independently, the Lotus-developed central computer system can talk to its G-sensors to replicate everything a modern ESP can do, but without ESP. Not only can it drive each rear wheel forward at different speeds, but it can help with parking. It can automatically correct understeer or oversteer and it can sharpen steering response as well.

It has one other significant boost as well. Most cars add rear toe-in (where the engineers point the rear tyres slightly toward the middle of the car) for high-speed stability, but this is not necessary with the 414E. Instead, it can manage this job electronically, saving in rolling resistance, tyre wear and fuel consumption.

The Fake Gearbox: Drivers of conventional fast cars don't much like the idea of a one-speed car, which is why the Evora 414E has a simulated seven-speed unit on board. Even though it is always a single-speed car, there is a steering column-mounted paddle shift system to drive through the 'gears', complete with a change in the noise and a slight gearshift torque-jolt, just to make people feel they're driving a normal car.

It does have a practical application as well, because instead of engine braking, the 414E has energy regeneration. When you come off the throttle, it simulates engine braking by adding resistance to the electric motors, which also recharges the battery. Lotus claims it feels like standard engine braking, so it lets the driver control the rate of "engine braking" by choosing to come down one, two, three or four gears.

The HALOsonic system: One common complaint about electric cars is their lack of noise, which is unrewarding for their drivers and just-plain dangerous for unobservant pedestrians. Which is most of them.

The 414E counters this with a synthetic sound system, developed with Harmon. Inside the car, the driver has a choice between four different engine sounds (a V6, a V12, a "futuristic" sound and a combination of the futuristic and the V12), which vary with the throttle inputs and the gear changes. Lotus claims it's an intuitive sound, which remains to be seen, but they help pedestrians know the 414E is coming by replicating the chosen engine note through speakers mounted in the front and rear bumpers.

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