Evora 414E proves Lotus' range-extender hybrid technology

  • 06-Nov-2012 05:08 EST
Lotus10-12Steve Doyle and elec Evora.jpg

Lotus Chief Engineer Steve Doyle with the one-off, rapid Evora 414E technology demonstrator. "There is a lack of high-voltage safety standards for the practical side of developing hybrid systems for cars at present," he said.

The sound of a Lotus engine rising and falling as speed increases, engine rpm soars, and gears are shifted rapidly has always been an essential part of the marque’s identity. So driving quickly around the company’s F1-standard test track to the accompaniment of just whirring twin electric motors, a 3-cylinder gasoline engine starting and stopping, and no gear changes is, to say the least, odd.

But that is how it is with Lotus’s 414E Evora range-extended (REx) hybrid technology demonstrator now undergoing durability and dynamics testing.

This AEI editor was taking care with the car, under the eye of Steve Doyle, Chief Engineer, Hybrid and Electric Vehicle Integration. “We’ve only built one, so it is very important to us,” Doyle said. Translation: “Please don’t break it — and remember it weighs 377 kg (831 lb) more than the standard car.”

In fact, the 414E Evora is both quick—0-100 km/h in 4.4 s; top speed 214 km/h (133 mph)—and very well balanced through the Hethel, U.K., track’s corners. Here, the effect of 1000 N·m (737.5 lb·ft) of vectored torque in a car with a curb weight of 1759 kg (3878 lb) is interesting. Claimed CO2 emissions are 55 g/km, as tested on the ECE-R101 schedule.

The 414E’s raison d’etre does raise questions. It is, explained Doyle, a demonstration of what Lotus Engineering can provide in its EV consultancy role. It is doing so with various projects, some commercially confidential but others in the public domain such as the hybrid Infiniti EMERG-E using 414E chassis and driveline (two built by Lotus and then shipped to Nissan to be bodied and returned to Lotus for commissioning).

A high-performance, low-emissions demonstrator

But could the 414E itself be an indication of a future Lotus model? This is neither confirmed nor totally denied by the company and Doyle spoke of the development of a faux gearshift action (the car has a single-speed gearbox) being under development. He also mentioned the possibility of installing an in-cabin active noise system to simulate an engine sound to complement the “gear changes,” plus an external pedestrian-warning system.

The 414E was revealed at the 2010 Geneva Motor Show having been conceived and assembled in a matter of weeks. Its ability to mature from show car to technology demonstrator was enabled by a U.K. Government Technology Strategy Board award to develop a supply base in the EV market place in partnership with Nissan, Jaguar Land Rover (JLR, who developed the XJ-e as part of the project), Xtrac, and Evo Electric.

Lotus’ role with the 414E is to demonstrate hybrid technologies and capability including integration of a high-power motor/inverter drive and a high-energy battery pack (14.9 kW·h lithium-ion phosphate cylindrical cell, with 112 cells in series and 16 in parallel) to meet its particular requirements. Also included are range-extender technology and integration, plus modular control systems integration, ISO 26262 functional safety, and torque vectoring capability.

“There is a lack of high-voltage safety standards for the practical side of developing hybrid systems for cars at present,” stated Doyle. “As a result, we have had to develop our own working procedures and safety management systems."

He noted that the ISO 26262 standard is relatively new and intended to help the design of safe systems. It is, however, a bit like a recipe without ingredients—or vice-versa. Lotus Engineering used the 414E project to work out how to apply such standards, which in turn supported what Doyle's team considered to be best practice for issues such as a midpack disconnect, battery-earth leakage monitoring, safety interlocking loop systems, and redundancy in systems such as torque sensors and controller safety.

Doyle added that while safety standards are now being established, these generally lagged behind EV development. He also stated that high-voltage batteries should have a physically removable disconnect plug for servicing.

“It is amazing that some batteries do not have this essential aspect," he observed. "Battery quality and variety demonstrates just how immature is the market place at present and why a lot of OEMs are doing the work in-house.”

Active noise, simulated gearchange, in-house controller

The 414E’s technology configuration includes a two-motor approach: each motor driving one rear wheel and producing 150 kW/500 N·m (201 hp/369 lb·ft). Torque vectoring was a key part of the design. The range extender, positioned just behind the rear cabin bulkhead, is a Lotus design producing 35kW (47 hp). It supports the synchronous axial-flux electric motors when the driver operates in “performance mode”—high power output and/or under load, so on a track it constantly cuts in and out.

Maximum electric-only-mode target range is 48 km (approximately 30 mi). Operating as a series hybrid, target range is 482 km (nearly 300 mi). If battery state-of-charge drops to 35%, the REx operates continuously. The 414E is a plug-in design needing grid-sourced charging for maximum battery charge and minimum vehicle CO2.

Since its Geneva debut, a great deal of work has gone into the 414E, particularly regarding what Doyle terms “electrics and cooling plumbing,” plus EMC (electromagnetic compatibility) issues and adaptive energy management. Packaging was always going to be a challenge and the car now has four inverters.

The vehicle control unit is Lotus’ own rather than a bespoke design. It works with EV or hybrid vehicles and is a development of the type used on Lotus production cars. “Similarly, we use a Lotus controller to look after the overall vehicle: safety to check all messages and data; dynamics for torque split to the two rear wheels, and the range extender,” Doyle said.

The test program initially focused on performance but is now concentrating on achieving maximum required economy, which demonstrates why a small REx was chosen. The modular 3-cylinder unit could produce 50 kW (67 hp) via supercharging.

“We are also looking at developing systems to make the driver feel more a part of the vehicle: Halosonic (active noise) and simulated gearshifting. Drivers want the ‘driving experience’ and some EVs (not ours!) can be rather boring,” stated Simon Corbett, Lotus’ Principal Group Engineer, Vehicle Dynamics as he monitored this AEI editor’s track driving efforts. The one-off, exotic 414E experience was certainly not boring.

As for electric machines, Doyle sees a move away from the use of specialist magnetic materials, such as rare-earth metals, only available in areas of the world where markets are “difficult to deal with.”

The 414E, though, is a research project. It's not a production car and “not a Lotus,” insisted Doyle.

“Much of the technology we have will end up on other people’s cars; we are showing what we can do," he noted. "So as EVs progress to having no gearbox—we do not support the view that two or three speeds are needed—and to wheels driven by hub motors, torque vectoring will be essential. Our work is the foundation for that technology journey.”

The Lotus EV teams take a pragmatic view of the sector. Mark James, Director of Lotus’ Group Engineering, says of the EV and hybrid debate: “All solutions are technically viable but the issues remain cost and infrastructure. For example, a 350-bar carbon-wrapped hydrogen tank for a fuel-cell car can cost close to $50,000.”

Which is why there is huge pressure to downsize combustion engines, which can bring a 35% reduction in fuel burn and CO2 emissions. But even then they will not meet future CO2 fleet requirements so other technologies have to be introduced eventually, believes Doyle.

“Because companies can’t sell many ZEVs, they are moving towards hybrids and range extender solutions," he said. "At present, the automotive industry is in a hiatus; it does not know which products to make, and the buying public—that wants powerplants that can meet full duty cycles of cost, performance, and range—does not know which products to buy.”

So, a production Lotus 414E to help them make up their minds? Doyle gives a classic “neither confirm nor deny” answer. “We have no plans at present—and don’t read too much into ‘at present’!”

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