Hybrid vehicle sales in the USA are forecast to exceed 1 million per year by 2012 according to JD Power and Associates. With this potential market in mind, the Automotive Composites Alliance (ACA) (an industry alliance of the American Composites Manufacturers Association) carried out a benchmarking study of a prototype hybrid sedan to demonstrate how composites can play a major role in hybrid development programmes. The results of the study generally show that in numerous hybrid vehicle components composites can provide significant savings in mass and tooling investment, as well as advantages in parts consolidation, corrosion resistance, opportunities for model differentiation and improvements in noise, vibration and harshness (NVH).
The parts used on hybrid vehicles are typically production parts from the production vehicles that have received powertrain changes to make it a hybrid.
Seven components were studied:
- hoods (bonnets);
- fenders (wings);
- deck lids;
- battery modules;
- floor pans;
- trunk (boot) compartments; and
- front and rear bumper beam supports.
In the hybrid car studied all the parts compared were steel.
“We disassembled the hybrid car, weighed and measured the components and discovered a lot of opportunities for improvements,” explains David Dyke, Advanced Engineering Manager at Meridian Automotive Systems. “We are excited about the opportunities composites provide as hybrids continue to grow in acceptance.”
Hybrids
A hybrid vehicle combines two or more sources of power. The term is often used to refer to hybrid electric vehicles which are cars that run off an electric motor (powered by a rechargeable battery) and petrol or diesel engines. The electric motor handles normal stop-and-go travel and initial highway acceleration. The petrol- or diesel-powered internal combustion engine kicks in whenever the vehicle gets to higher speeds. A computer control system decides when to switch from one power source to the other. This process of switching power between the two types of engines saves fuel and reduces pollution.
Several car makers are developing ‘plug-in’ hybrid electric vehicles in which the battery can be recharged by connecting it to an electric power source.
Hybrid cars are often lighter and more aerodynamic, and tyres are often stiffer and inflated higher to reduce drag. The combustion engine is smaller than that used in conventional cars.
Hoods
In the study, ACA compared a composite hood with a steel hood from the benchmarked vehicle. It found that a 30-40% saving in mass and a 60-70% reduction in tooling investment could be achieved with composites.
Fenders
The results show a 25-35% reduction in mass and a 55-65% reduction in tooling investment. The fenders could be consolidated into a single composite piece from four separate metal parts.
Unique styling is also possible, as is the integration of wheel lip mouldings.
Deck lids
ACA's benchmarking indicates mass savings of 25-35% by consolidating four metal parts into a two-piece composite deck lid assembly. This lowers weight, which helps to increase fuel economy, and reduces tooling investment by 50-60%. Using sheet moulding compound (SMC) on deck lids also allows the transmission of radio frequency (RF) waves so that antennas for communication, navigation and audio systems can be seamlessly integrated.
Battery modules
These modules contain the vehicle's battery pack, electronic controller, wiring harness and other components and often are comprised of several metal stampings. Using composites it is to reduce the module to a two-piece moulding, resulting in major mass and tooling investment savings.
Another advantage of composites is that they do not conduct electricity, so they provide an extra measure of safety compared to metal battery modules. They also enhance battery life because they do not corrode and allow integrated airflow cooling in the module's tunnel.
Floor pans
These are typically large structures made up of numerous steel stampings welded together. ACA results indicate a mass reduction of 30-40% with tooling investment savings of up to 60% by using a lightweight core in a single-sandwich mould.
Improvements in stiffness and sound reduction are also possible.
Trunk compartments
Using structural low-density composites in a one-piece moulding can reduce mass up to 50% in trunk compartments. Composites can replace six to eight metal stampings in the complex geometry of the trunk at a saving of up to 70% in tooling investment.
Bumper beams
Composite front and rear bumper reinforcements can offer mass savings in the 30-40% range. The ACA study also concluded that vehicle crash-worthiness can be improved if carbon fibre composites are used in crush cans.
Valuable
“We think this was a valuable and worthwhile study,” says Dyke. “It validated our contention that composites technologies are right for hybrid vehicles. As fuel prices rise, so will the demand for hybrid cars, trucks and SUVs [sport utility vehicles], and the ACA and its member companies are committed to providing composites solutions that will add the greatest value in hybrid vehicle applications.”
