With further emission and environmental legislation impending OEMs are showing an interest in composite systems. Lotus has developed a range of composite based energy absorbing crash systems for use in the highly demanding vehicle front-end environments for both Lotus product and client vehicles.

Project Ecolite is the next phase of Lotus Engineerings research to develop thermoplastic composite crash systems that are economical for higher volume production. With benefits including energy absorption improvements, reduced mass and improved package efficiency, these will be the evolution of the highly successful composite crash systems that Lotus has developed for its own products.
The Lotus Elise, Vauxhall VX220, and AML Vanquish crash structures are based on polyester RTM systems and glass fibre reinforcement. The Vanquish assembly also has a small amount of carbon fibre reinforcement in the crash rails to improve local stability.

The RTM process has been extremely successful in terms of producing crash elements because it allows the design to be tuned. The fibre reinforcement can be tailored to suit the particular static or dynamic properties required both in terms of material type, amount, and orientation. Likewise the manufacturing process can accommodate changes to part thickness and geometry.

A RTM crash structure in a glass reinforced polyester system can have a specific energy absorption (SEA) of up to 50kJ/kg. (Much higher values can be achieved under laboratory conditions but are usually for small samples over a limited crush distance). Real world metallic systems are typically capable of achieving up to 30kJ/kg. The other benefit of composite over metallic is that there is virtually no residual length allowing the full use of the packaging space.

The disadvantage of the RTM crash structures, however, is that they are constrained by the long cycle times restricting them to economic volumes of typically 10,000 units per annum. To address this point Lotus has developed crash elements in thermoplastic materials. These materials offer extremely short cycle times (around 4 - 5 minutes) but are relatively new in high speed impact environments.

Technically, the thermoplastic structures have been shown to perform as well as the thermoset based systems in terms of energy absorption. Economically, the success of these new systems will depend on the ability to form geometries that allow full optimisation of the available space whilst achieving excellent fibre impregnation and matrix consolidation. The next phase of our development work, defined as Project Ecolite, is set to demonstrate these aspects by manufacturing a full thermoplastic crash system based on the design of an existing five star NCAP vehicle.

Benefits of thermoplastic energy absorbing crash structures are:

  • Because of the composite material and manufacturing process we can achieve stable tuneable crush
  • Using specific design features we can manage low and high speed impacts
  • Again using the flexibility of the composite material and manufacturing process we can accommodate Federal as well as European legislative requirements
  • Reinforced thermoplastic material exhibits extremely high, consistent, temperature and humidity resistant energy absorption characteristics
  • The entire length of the composite structure can be used to absorb energy - there is very little crush length remaining which offers significant packaging benefits
  • A 30% weight saving compared to the steel structure is available
  • The use of composite material and manufacturing processes allows a significant reduction in design complexity and the ability to improve functional integration
  • The Ecolite structure offers at least a 50% reduction in tooling investment versus the steel benchmark structure
  • The aim is to achieve a breakeven of at least 30,000 units per annum by optimising the design in the next iteration
  • And being a thermoplastic the recycling opportunities are greater than the current RTM structures