Underhood Polymers

Polymers used under the hood have to be able to withstand very high temperatures. In a typical vehicle temperatures can get as high as 125°C under the hood

Figure 17.7. Silverado composite pickup box.

during operation. In a turbo diesel they can get as high as 150°C. Therefore, the choice of available polymers and the extent of their use under the hood is more limited. Rubber materials are typically used for hoses. Polymers are also used for brackets, splash shields, fluid reservoirs, cases, and fans. They all offer mass savings and better corrosion resistance over metal parts as well as afford increased design flexibility.

Hoses There are a variety of rubber hoses found under the hood, made from various types of elastomers. The most common elastomer used is ethylene-propylene-diene (EPDM) with a reinforcement material, mostly rayon yarn and aramid yarn. The rubber hoses are lighter in weight than metal and can better endure the harsh vibrations from engine-vehicle and vehicle-road interactions. They can also be formed into a variety of shapes. With the ever-shrinking size of the engine compartment this is very important.

Radiator System There are several applications that have gone from metal to a polymer in the radiator with considerable reduction in vehicle mass. These applications include SMC and glass-filled PP supports, nylon and PP fans and fan shrouds, nylon end tanks, PE overflow, and nylon and polyphenylene sulfide (PPS) water pumps. The nylon end tanks have been studied for recycling at end of life. The radiators along with the end tanks are removed from the vehicle for recycling. This eliminates the cost of dismantling the end tanks from the radiation during recycling of the nylon. A part in the radiator that contains recycled material is the seal. It is generally made from a PP modified with recycled rubber.

Intake Manifold Nylon has been extensively used in the intake manifold. The applications include the 1993 4.0-liter V-8, 3800 engine in the Aurora, the 1994 Dodge Neon, the 1995 GM Quad IV, and the 1996 4.6-liter Mustang.

Engine Throttle Body Nylon has also found its way into an engine throttle body application. The 2000 Dodge Neon provides an example of this application. The nylon part was 60% lighter than aluminum [3], and the machining generally required with aluminum was eliminated with the nylon part. Thus the scrap, and energy used in manufacturing the part were reduced.

Battery Case and Tray The automotive battery is a great recycling success story. Today, about 99% of automobile batteries are collected for recycling. The lead and acid as well as the PP cases are recovered. The recycled PP from the case can then be used in other cases or used to produce the battery tray. Approximately 40% of the recycled case material is used in manufacturing cases [3]. An example of a unique battery tray is seen in the GM EV1 electric vehicle with a particularly large set of batteries. The batteries in the EV1 weigh over 500 kg. The structural load requirements included 5 G vertical load when bouncing over potholes, 25 G in a frontal collision, and 18 G in side and rear impact deceleration. The original design in aluminum had 16 parts and weighed 22.7 kg (50 lb). To minimize mass

Figure 17.8. EV1 glass-reinforced PP battery tray.

in this electric vehicle, plastics were considered for the tray application. The material chosen was a long glass-fiber random-reinforced polypropylene sheet. The final design was a single part that weighed only 15 kg (33 lb) (shown in Figure 17.8).

Fender Liner and Splash Shields PP is also the material of choice for fender liners and splash shields. The material is light weight and can be molded into a variety of shapes in different colors. Recycled PP can be used in many of these applications.

Fluid Reservoirs Newer vehicles are being continuously studied for mass savings opportunities. Some of the mass savings initiatives along with other design parameters have caused the engine compartment to become progressively smaller. Therefore, packaging the components within them has become increasingly difficult. Polymers enable packaging of fluid reservoirs in tight spaces. Power steering and brake fluid reservoirs are generally made from nylon. Coolant and windshield washer fluid reservoirs are made from PE and PP, respectively. Some pressurized coolant reservoirs, however, are made from nylon.

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