Weigh to go

Lotus develops a lightweight composite family hatchback that could be mass produced.

Lotus Engineering is developing a composite family hatchback that will weigh around a third less than conventional cars, and could be mass produced.

The automotive consultant is working with German firm Jacob Composite to produce the car, which will have a chassis structure and body panels produced predominantly from composites.

Composites are tough but lightweight, improving fuel efficiency and performance. But the materials are costly and difficult to manufacture, limiting their use to expensive, low-volume vehicles such as sports cars.

Cost-effective

Lotus claims the car, being developed under the Ecolite (Efficient composites, lightweight and thermoformed) programme, will be cost-effective enough for production volumes of between 30,000 and 50,000.

The team ultimately hopes to achieve at least a 30 per cent weight reduction compared to a typical 1,200kg steel-bodied hatchback, said Jason Rowe, Lotus chief materials engineer. This would give the car a weight of around 840kg.

‘When we started the project we based it around an Elise derivative, and we were looking to get around a 30 per cent saving in weight against that. I would expect at least 30 per cent against a steelbodied car, bearing in mind that the Elise already has an aluminium structure and a composite shell,’ he said.

For the first nine months of the programme, due to be completed in October, the Ecolite team are focusing on the crash performance of a composite front end, with the panels fitted to a five-star NCAP rated family hatchback.

The team is producing a prototype front-end, which will be unveiled at next month’s JEC show in Paris.

In tests so far, the material has shown very good specific energy absorption, according to Rowe. ‘We are seeing real-life energy absorption numbers in the order of 7–10 Joules/gram. If you look at component testing, we are seeing numbers of around 45+ J/g for some of the components we’ve tested.’

This compares well with conventional thermoset composites, and is much better than components built from steel or aluminium, he said.

The material should, therefore, help car makers meet increasingly stringent pedestrian safety legislation, particularly as the composite crash structure also completely disintegrates after impact. This will limit forces acting on a pedestrian.

‘Unlike a metallic solution where you still end up with a lump of metal at the end of the impact, which obviously has to be managed within the packaging space during the initial design of the car, you haven’t got that problem with a composite material,’ said Rowe.

As space does not have to be found to accommodate this crumpled metal, it also offers car designers more scope for installing pedestrian protection measures.

The crash structure (inset) could be used on volume cars such as the Ford Focus.

In the second phase of the programme the team will expand its work to cover the remainder of the vehicle structure and body. The companies hope to attract the interest of a major car maker to take part in the project, which could use the technology to produce a mass-market vehicle.

The cost of the material is being brought down to volume production levels by the use of thermoforming, rather than the conventional resin transfer moulding process. Thermoforming allows the parts to be produced much more quickly, increasing the volume of components that can be made.

This is because unlike the manual process of resin transfer moulding, where the fibre is placed in the tool and the resin injected into it and then cured, in the thermoforming process the fibre and resin are already together in sheet form. Heat is applied to the sheet, which is then stamped into shape.

The material’s good specific energy absorption will also help to cut the cost of the composite car by allowing engineers to use the materials conservatively and only fit glass fibre reinforcing where necessary, said Rowe.