A Hundred Innovations for Renault’s Eolab Concept

November 1, 2014

Stuart Birch

The Renault Eolab prototype’s active aerodynamics include a front spoiler that deploys to restrict underfloor airflow.

When Renault prepares a motor show concept, it invariably does so comprehensively. But for Paris this year it has excelled itself, claiming that its ultra-lightweight Eolab environmental hybrid (actually, two versions: a pure concept to emphasize visual aspects and an engineering working prototype) contains almost 100 “realistic” production-destined technological innovations including “active wheels.” It has been designed and engineered to achieve a fuel consumption of 1.0 L/100 km. On the official NEDC (New European Driving Cycle) cycle, that would equate to 22 g/ km of CO₂.

It also claims that Eolab conforms to established B-segment levels of performance, practicality, and affordability, providing a vision of what a Renault in this class could be like in 10 years’ time.

The Eolab prototype hybrid has been designed to ultimately be capable of achieving 1.0 L/100 km fuel consumption.

By taking an aggressive and imaginative approach to weight saving, not only via an aluminum architecture but by radical solutions including the use of a magnesium roof, Renault estimates a saving in six specific areas of some 400 kg (900 lb) against a similar-size conventional production car. Renault explains that Eolab forms part of the French government’s “New Industrial Plan,” which includes a fuel consumption target of 2.0 L/100 km by 2020; but Eolab apparently has the ability to eventually halve even that aggressive figure.

Often, OEMs claim all the glory for concepts or prototypes like Eolab, but Renault has been open about many of its weight-saving collaborators. They include Saint Gobain (glass), Faurecia (seats), Michelin (tires), Continental (brake systems) and Posco (magnesium components).

An unlikely aerodynamic aid: the active wheel of the Eolab has moving vanes to smooth airflow. The prototype uses special, narrow Michelin tires.

Aerodynamic efficiency of the Eolab has been honed to a Cd of 0.235 with a CdA of 0.470 m², some 30% less than the figures for a Renault Clio hatchback that compares as a B-segment design. To help achieve this in a small car, aerodynamicists took possible solutions to an extreme.

Totally flush wheel covers were tempting but rejected as both practically and aesthetically unacceptable. Instead, engineers opted for active vane-like covered wheels that would be in a closed position when brakes are unlikely to be in continual use. They are controlled via a rim-mounted sensor. Specially designed 145/70 R17 “tall and narrow” Michelin tires are fitted to the Eolab for improved aerodynamics and low rolling resistance. Active spoilers are common when rear-mounted, but Eolab has one fitted to the front bumper that lowers by 10 cm (3.9 in) beyond 70 km/h (43 mph) to restrict underfloor airflow.

Renault’s determination to achieve meaningful weight reduction for a hybrid is wide ranging.

While weight saving applications reached 400 kg, 145 kg (320 lb) had to be added for the car’s powertrain, including a lithium-ion battery, to achieve the “total” vehicle weight of 955 kg (2105 lb), but it is still around 20% less than a similar-size conventional-powered car.

Bird’s eye view of the Eolab shows rear-hinged door.

Specific savings were for the body, 130 kg (290 lb); equipment and trim, 90 kg (200 lb); suspension, 70 kg (150 lb); engine “peripherals”, 30 kg (70 lb); powertrain, 60 kg (130 lb); and electrical equipment, 20 kg (40 lb).

Eolab Project Leader, Laurent Taupin, explained that various material solutions were used: “But the only way to lighten steel components is to use thinner metal. However, since detracting from a given part’s functional properties was out of the question, it was necessary to upgrade the mechanical properties of steels employed.”

That’s where Very Very High Elastic Limit (VVHEL) steels entered the equation, with yield strength of between 1200 and 1500 MPa (174 and 218 ksi), an improvement of between 200 and 500 MPa (29 and 73 ksi) over the VHEL used for current Renault models. With a tensile strength of up to 150 kg/mm², hot-stamped VVHEL was used “wherever it served a real purpose, notably for the front part of the cabin,” stated the company.

The use of magnesium for the roof outer of the Eolab is a very interesting choice, as the material is usually confined to areas unlikely to experience conditions susceptible to corrosion such as dashboard cross-beams. Renault opted to use magnesium sheeting supplied by Posco of South Korea. The material is also used for the lower part of the dashboard.

A roof section in steel would have weighed about 10 kg (20 lb), stated Renault. The company also explained that as well as producing wide magnesium alloy sheets for the car, Posco also carried out process assessment including warm stamping formability evaluation and development of customized surface treatment.

Weighing in to the mass reduction race is Renault’s multimaterial Eolab.

Other alternative materials R&D work has seen Renault working with university research departments and specialist suppliers on a new family of thermoplastic resins more suitable for recycling than thermoset resins.

Eolab’s front and rear floorpans, B-pillars, and lower crossmember use hot-stamped composite thermoplastic, with the skins of the one-piece hood and front fender assembly plus the concept’s doors using injection-molded thermoplastic.

Running gear has also been subject to very close scrutiny by Renault’s weight saving teams, replacing steel for aluminum in areas including the subframe’s 5.3 kg (12 lb) saved compared to the production Renault Clio IV’s 14 kg (31 lb); suspension arms, 1.8 kg (4.0 lb) lighter; hub carriers 5 kg (11 lb) lighter; and rear suspension arms,9 kg (20 lb) lighter.

Further, more complex weight saving solutions were also examined, including the structure required to meet head-on crashworthiness legislation, particularly regarding the upper part of the chassis, side members, and lower part of the chassis. For Eolab, design changes included relocation and strengthening of the side members to achieve a weight saving of more than 7 kg (15 lb).

Taupin added: “We also looked at making the springs from a glass fiber/thermoset plastic composite, which would have produced a saving of 3 kg.”

Some 4.7 kg (10.4 lb) was also saved via changes to the braking system. This work, with Continental, includes combining steel with aluminum parts for the front brake components and, because the Ecolab has a low curb weight, disc diameter was reduced.

Glass is heavy, so together with Saint Gobain Sekurit, Renault reduced its thickness for the Eolab to 3mm (0.1 in), which it describes as being 1.5 mm (0.06 in) less than the industry norm; it believes the prototype’s thin glass windshield is an industry first. Side windows are of laminated glass and fixed windows utilize polymers. The rear window uses “polymères vernis” (literally: polymer glazing) in place of tempered glass; it incorporates the taillights.

Laurent Taupin, Project Leader for the Eolab, says its innovative technology points the way to future Renault production models.

The result of the work with Saint Gobain has seen vehicle glass weight cut to 21 kg (46 lb) against the Clio IV’s 28 kg (62 lb).

Thickness and weight reduction were also part of the Eolab’s seat design, carried out in conjunction with Faurecia. Frames use steel, aluminum, magnesium, and carbon-fiber composites, combining to save about a third of the weight compared to a typical B-segment car. The cushion structure was optimized via a semi-rigid shaped trim and compliant seatback.

The seat is said to be 30% more compact than a regular production type for no comfort loss with kneeroom gain. Faurecia’s technology was applied to enable the cover to closely match the seatback’s form. Seat shell weight is reduced by about 40%.

As for the hybrid powertrain, it combines a 57-kW (76-hp) three-cylinder 999cm³ ICE and a 50-kW, 200-N·m (148-lb·ft) electric motor, which is housed within the clutch casing. A three-speed gearbox is used, the first two ratios mated to the electric motor, the third to the ICE. A 6.7-kW·h battery is installed—relatively small in keeping with the car’s lighter weight.

Eolab range in pure electric mode is 60 km (40 mi) and top speed 120 km/h (75 mph). Renault was not only working to save weight and reduce packaging with its hybrid system but also to cut costs. It sees the technology as apposite for a small production car by 2020. Jean-Pierre Fouquet, ZE Hybrid Innovation Project Leader, says the aim is to produce a car with two power sources for the price of one.

The Z.E. hybrid powertrain configuration of the Eolab prototype.

This would be a major contribution to Renault’s stated aim of manufacturing a car with ultra-low fuel consumption that offers performance and ownership costs similar to those of a Clio.

The Eolab was designed in close collaboration with Renault’s production-car development and manufacturing teams as a lead towards volume production.

“This project’s process of innovation is therefore already in place for future vehicles in the Renault range,” said Project Leader Taupin.