The proper selection of aluminum alloy materials in heavy truck engines can reduce weight and improve fuel economy.
There is a growing demand for lightweight vehicles such as heavy trucks. This year, new commercial trucks must meet greenhouse gas emission (GHG) emission regulations and fuel economy standards, and these standards will be more stringent by 2018.
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In order to meet the diesel emission requirements, diesel truck particulate filter (diesel particulate filter (DPF) and selective catalytic reduction (SCR) systems added by truck manufacturers resulted in an increase of hundreds of pounds in vehicle weight. In order to meet regulatory requirements for reducing braking distance, manufacturers have to increase the size of the brake drum, which in turn leads to an increase in weight. Fueled by fuel economy and GHG emissions standards, the vehicle's aerodynamic system has been improved to improve vehicle efficiency, but these components often weigh hundreds of pounds.
The idling speed plan promotes the adoption of auxiliary power units (APUs), but the battery unit and the diesel drive will cause the truck to increase its weight by 500 pounds. Conversion to natural gas can achieve a return on investment in just two years, but the related attachments will result in trucks weighing 2,000 pounds.
On the other hand, the advanced interiors used to attract drivers have resulted in trucks gaining at least 100 pounds, which is exactly what the team is concerned about. In summary, the high-end "energy-efficient" truck weighs 2,390 pounds more than a standard truck.
Therefore, there will be a lot of room for weight reduction, most of which can be achieved by replacing steel and other materials. Wrought aluminum wheels can replace steel wheels, and iron wheels can be replaced by cast aluminum wheels. In addition, forged aluminum spare wheels and moulded composite body panels can be used with a 6x2 drive. The 6x2 has only one drive axle and can weigh 400 pounds.
In addition, the use of the latest metal materials and processing technology is also expected to achieve engine weight loss.
Aluminum has been used for a long time in the manufacture of diesel engines, but it is not as common as it is in gasoline engines. DeltaHawk, a manufacturer of diesel aero engines, has more than a decade of experience in producing cast aluminum engine blocks and cylinder heads. Mercedes-Benz began using cast aluminum cylinders in diesel engines in 2005. The 2014 Sprinter commercial vehicle's engine uses cast aluminum cylinder heads and cylinders with vermicular cast iron cylinder liners.
Recently, the new Cummins 5 litre ISV 5.0 diesel engine uses an aluminum intake manifold, an aluminum piston, and a high-strength aluminum alloy cylinder head (see "Diesel Engine Progress" March 2014).
Aluminum has a lower density of 0.1 pounds per cubic inch compared to standard cast iron materials and gray cast iron is 0.26 pounds per cubic inch. Aluminum is corrosion-resistant, its heat dissipation capacity is three times that of iron, and it is easy to machine and can be recycled. From a manufacturing point of view, aluminum makes it easier to cast complex cooling water jackets.
The disadvantage of aluminum is low hardness, poor wear resistance and vibration damping, and aluminum is not as resistant to high temperatures as compared to cast iron.
However, an article of the American Foundry Association entitled "Development Status of Cast Aluminum Alloys at High Temperatures of 250 Degrees Celsius," by DJ Weiss, GAGegeland K.S. Sadayappan, believes that the addition of niobium to aluminum can improve its high temperature performance. The aluminum-antimony alloy exhibits mechanical properties at 250 degrees Celsius (482 degrees Fahrenheit) that are 3.6 times higher than the wrought aluminum alloy 2618 and 2.1 times higher than the cast aluminum alloy 354.
By changing the content of the components in the metal alloy, its performance can be better improved. The silicon content in the aluminum alloy A356 decreased from the conventional 7% to 4%, at which time the strength did not change, but the elongation increased from 75% to 100%. This indicates that the alloy can extend the life of the intake manifold and cylinder head.
The 200 series aluminum alloys improve performance by adding copper and other elements, of which titanium is added to 206; silver is added to 201; titanium, zirconium, and vanadium are added to 224; titanium, nickel, and chromium are added to 242. The high temperature properties of these alloys are superior to common aluminum-silicon alloys. In addition, the key design parameters in the engine design, low-cycle fatigue characteristics, have been significantly improved in the A206 alloy.
The use of steel or iron liners in cylinders is common, and Eck Industries has been developing liners made of aluminum composites (silicon carbide and graphite in the aluminum matrix). Silicon carbide provides hardness and wear resistance, graphite provides lubrication, thereby minimizing the amount of oil and avoiding oil helium. Tests were conducted on cast aluminum compressors equipped with iron cylinder liners and cylinder liners with aluminum composites. The results showed that the temperature of the cylinders fell by 60 to 80 degrees Fahrenheit due to the better conductivity of the aluminum composite cylinder liners than the iron cylinder liners. After replacing iron with aluminum, the weight is also reduced.
Aluminum silicon carbide composites, a metal matrix composite (MMC), have also been applied to the main bearing caps of aluminum cylinders. Compared with aluminum, metal matrix composites have a 20% to 50% higher hardness and a lower coefficient of thermal expansion.
Cast aluminum technology has also made considerable progress, and it is expected to further realize the lightweighting of diesel engines. Diesel engine modeling and simulation technologies have become increasingly sophisticated. The 3D printing technology not only helps engineers visually express new designs, but also significantly shortens the production prototype time. In the field of casting, simulation tools for simulating metal flow have also been greatly improved. Analysts can accurately predict area porosity, high-speed fillers, temperatures, and the mechanical properties of certain alloys. A natural simulation model may be based on a conceptually designed CAD model to show the presence of relevant areas of stomata.
When simulation analysis begins, the foundry engineers work with the design engineers to grasp the areas that require optimal material characteristics, as well as the area between the feed and refill pipe locations. This cooperative relationship in the simulation phase can effectively improve the casting performance, as well as the repeatability and reliability of the manufacturing process.
Metal flow simulation software companies work with foundries to ensure that their models can realistically simulate real-world problems. Not all materials have the same fluidity, especially aluminum-silicon alloys and aluminum-copper alloys. Aluminium-copper alloy A206, for example, has high strength, fatigue, and high temperature properties, but because it contains no silicon, its fluidity and solidification are very different from those of the common cast aluminum alloy A356.
With the increase of simulation technology, engineers can use simulation to predict the metal characteristics of the casting process.
With the increasing demand for product performance, fuel economy and emission reduction, manufacturers will continue to think about ways to reduce weight for their products. Together with foundry engineers, design engineers can effectively promote the development of lightweight diesel engines and continuously realize technological innovation in diesel engines.
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