Author: Andrew Halonen, Mayflower Consulting Co., Ltd. (also published in the Light Metal Times)
Whether the vehicle is equipped with an electric engine or an internal combustion engine (ICE), there will be many factors in its design that affect fuel efficiency and cruising range. There are many forms of efficiency loss, but it is usually affected by factors such as aerodynamics, rolling resistance, friction loss, and weight. Aerodynamics may be the greatest lever to control fuel efficiency, but it is limited by vehicle features and design aesthetics. The rolling resistance is mainly related to the impact of the wheels, and the durability and traction of the wheels must be balanced. The friction loss is related to the function of the engine. The vehicle weight is the sum of the body and the system, plus the recommended payload for passengers, cargo, and towing. The weight can be optimized through a combination of design and material selection, which is the focus of this article.
In order to consider the influence of weight on EV efficiency and cruising range, it is best to understand the baseline by comparing the ICE vehicle structure and the EV structure. For the purpose of this comparison, the curb weight (weight of the vehicle without personnel or cargo) will be considered. In ICE vehicles, the weight distribution of ordinary cars is usually as follows: 1 Body structure (25%), power system (25%), chassis and suspension (21%), interior (14%), closures (8%) , And glass, electrical and fluid (7%). Combined with the body and closures, the metal plate accounts for about one-third of the vehicle's weight. For the four-door Ford Fusion, the overall curb weight is approximately 3,600 pounds (1,633 kg). At the same time, in electric vehicles, the weight distribution has changed. For example, for Tesla Model S2 with a curb weight of 4,600 lbs (2,087 kg), the weight distribution is as follows: 2 batteries (29%); motors, power trains, brakes and suspensions (23%); frames (17%); indoors (14%); off (4%); electrical (4%); and other components (9%). Automotive engineers often point out that "electric cars add 1,000 pounds of weight to the vehicle", as the comparison between the Ford Fusion and Tesla Model S just discussed illustrates this point. Usually the battery pack is the culprit for the increase in weight. For example, the Tesla Model S battery pack weighs approximately 1,323 pounds (600 kilograms). In another comparison, the proposed Rivian EV pickup truck is expected to weigh an average of 800 pounds (363 kg) than the average weight of the three major Detroit pickup trucks (Ford F-150, Chevrolet Silverado, and Dodge Ram). Lux Research created a model to compare the range of electric vehicles with vehicle quality and battery size. 3 In this relationship, the cruising range of an electric vehicle is expanded by reducing the mass of the vehicle or by improving the efficiency of the battery to reduce its size. Of course, these choices involve a significant cost factor, because electric vehicles need to become affordable to gain widespread acceptance by customers. Lux predicts, "In the next ten years, the energy density of battery packs will increase by about 15%. This increased energy density can be used to expand the range of vehicles by keeping the battery size unchanged, or to reduce costs by reducing the size of the battery pack. They also predict that by 2030, the cost value of electric vehicles for weight reduction will be about US$5/kg, which is roughly the same as today’s internal combustion engine vehicles.
When discussing the weight reduction of vehicles, people can't help but wonder about the various factors involved in making many decisions. Does the vehicle need to be reduced in weight, and if so, where is the most valuable in terms of reducing the weight of certain aspects of the vehicle, or, as the Americans say, "excellent value for money"? Certain systems in the vehicle cannot or are difficult to change, such as the engine, battery pack, or electric motor. These systems are designed by original equipment manufacturers and are considered "black boxes" or systems that have been locked by car manufacturers. People can still recommend an optimized material for these areas, but it will be a tough sale. However, when considering the rest of the vehicle, the material selection decision matrix provides more options. Over the years, the Lightweight Expo has demonstrated a large number of lightweight solutions for vehicle parts-from glass to polycarbonate windows (40% weight reduction); from steel to extruded aluminum beams; replacing a bumper Into another; wait. Lightweight improvements are maturing regularly. Chassis and suspension: One of the lesser-known areas of lightweighting is under the vehicle. In the chassis, suspension and braking system, there are many components that need to be considered for lightweight optimization. In each system, there are multiple options in terms of weight and cost. Generally speaking, molten steel is heavier and has the lowest cost. However, the aluminum industry should not be complacent, assuming that the material is always lighter than steel. After the Ford F-150 switched to an aluminum body structure, the steel industry made a lot of innovations in materials and processing. Today, automakers can purchase formable ultra-high-strength steel with a strength of approximately 1,500-2,000 MPa. For example, Mayflower Consulting predicts that the steel industry will soon be able to provide suspension arms as a one-piece stamping part, thereby further reducing weight and costs. For OEMs, this competitive landscape provides a better choice for the development of profitable cars. However, for material suppliers, it forces them to innovate in order to survive. As full-scale material manufacturers continue to innovate, it is a challenge for OEMs to choose between all available options. For suspension components, there are many options for the production of the front lower control arm, including forged aluminum, cast aluminum and welded steel. 4 There are also options for stamped steel and ductile iron, providing OEMs with five options-only for the lower control arm. Forgings are common on ICE and EV vehicles, and are usually used in the suspension systems of steering knuckles, control arms, and connecting rods. When asked why aluminum forgings are a good choice for front-end EV suspensions, Kerry Kubatzke, sales manager of Anchor Harvey Components, commented that EVs need a long control arm with sturdy end fittings, and the forgings can be designed to be sturdy, which is very suitable Design the required rigid components. A good example of this implementation is the new Ford Mustang Mach-E electric car, which shows one of these long forged aluminum lower control arms (Figure 1). For many reasons, the use of forgings in the electric vehicle market may increase. First, the vehicle is heavier. Second, the electric car sports suit requires higher performance (for example, the ridiculous mode of the Tesla Model S). Finally, the EV's center of gravity moves back and down, which puts more load on the suspension components. Forgings solve these problems by demonstrating the efficiency of design and packaging. Braking system: In terms of lightweight, automakers first focus on easy-to-achieve goals, which are defined as easily replaceable bolt-fixed parts because they require less integration. There are many such components in the entire body of a vehicle. The heavier parts include the subframe and suspension arms, while the smaller parts include the brakes and brake calipers. Brake calipers are non-sprung masses (including suspensions, wheels and other components directly connected to them) and usually have a higher value. When someone claims that every gram is important, the first thing to ask is what material did they choose for the brake calipers? Ford Explorer opted for cast aluminum calipers at the front, while Chevrolet Blazers opted for cast iron calipers. The difference between the two is that the weight on the front axle is 2,900 grams. However, a recent market study by Mayflower Consulting found that most of the brake calipers on the market are still made of iron. This raises the question, why don’t automakers seem to think these extra grams are important? Where else can automakers lose 2.9 kg, and how much effort and investment are needed? Mayflower is continuing to investigate the casting and machining costs of cast iron and aluminum to better understand OEM's preference for heavier brake calipers.
Most cars use a one-piece structure, which is built into the body instead of a body frame structure, which is popular in large vehicles such as pickup trucks. Without frame rails, the larger chassis subsystem includes a sub-frame, called an engine mount or K-frame. The materials that can be used for the subframe include aluminum extrusions, extrusions with cast aluminum corners, aluminum or magnesium castings or steel weldments. Electric vehicles use a mix of these options. For example, the Tesla Model S has an aluminum subframe, which is considered a hybrid car because it is formed by connecting extrusions and corner castings. 5 These are two different EV models (2019 Tesla Model 3 to the new 2021 Ford Mustang Mach-E (Figure 2). Model 3 uses a welded steel subframe weighing 24 kg (53 lb). Steel structure The advantages of the design are compact packaging and lower cost, but the disadvantages are increased weight and lower corrosion resistance. On the one hand, the use of welded steel for the rear subframe is not surprising, because the company turned most of it on the Model 3. Steel body (after the all-aluminum body away from Model S). On the other hand, on Model Y, Tesla took a different approach, converting many steel stampings in the vehicle floor structure into a single large aluminum casting. Known as "large castings".
At the same time, the Ford Mach-E uses a hollow cast aluminum subframe at the front and rear (the rear frame weighs only 18 kg, or about 40 pounds). This has reduced the weight of the vehicle by approximately 12 kg, which is an estimated 25% reduction. The hollow aluminum subframe is produced on a low-pressure casting machine, using a large sand core to make the hollow. Munro & Associates, a benchmarking and design company, expressed enthusiasm for Ford's engineering expertise in designing the new Mache-E subframe assembly. Another comparison can be made with Volkswagen’s new electric vehicle ID.4. Munro & Associates analyzed the vehicle system and pointed out that steel dominates the structure and suspension components. The subframe is welded steel, and the front suspension is a MacPherson strut design with steel lower control arms and cast aluminum steering knuckles. At the rear, steel is used for the subframe and lower control arm linkage. There are also two forged aluminum upper control arms and a cast aluminum rear steering knuckle. Take a look at the brake calipers, most of them in the industry are made of iron. However, in electric vehicles, the situation is just the opposite, most of which are made of aluminum. All Tesla models studied by Mayflower use aluminum calipers. At the same time, Mach-E has a large aluminum caliper at the front and a small iron caliper at the rear. Interestingly, the rear gray iron brake disc of the Mach-E is very thin, not as thick and ventilated as the Tesla Model 3 calipers. Using a thin and sturdy design instead of a thick ventilated design is nearly 5 kg, but compared to the aluminum version, using iron calipers adds some weight. This raises the question, why did these two vehicles of similar weight choose very different rear brake sizes? Maybe Ford is right because the rear EV brakes require lower performance. Figure 1. The aluminum front lower control arm on the 2021 Ford Mustang Mach-E. Figure 2. Comparison of rear subframe systems-The 2019 Tesla Model 3 system is made of welded steel and weighs 24 kg (53 lbs), while the 2021 Ford Mustang Mach-E system is made of hollow aluminum castings. 18 kg (40 lb). So it can be a thinner design. This theory can be proved by the evidence of Volkswagen ID.4, which follows a similar method and uses drum brakes.
Intuitively speaking, the lighter the weight of the vehicle, the longer it will travel on unit energy. Therefore, efficiency is always emphasized, but of course there are some limitations, such as available budget, packaging space suitable for lightweight components, and an available supply chain that provides reliable and competitively priced parts. In the analysis, Tesla 3 has a welded steel subframe very similar to the Volkswagen ID.4, so many weight reduction options such as hollow aluminum castings or extrusion-based designs were not selected. Is this because of cost, packaging, crash performance or vehicle dynamics? Is it because Model 3 will be produced on many continents and steel will be easier to purchase? However, the front of Tesla 3 did choose aluminum calipers, which reduced the weight by nearly 3 kg. Is it necessary to reduce the unsprung mass at the front wheel end, or does it need to reduce the vehicle weight balance? In the reference study, most ICE vehicles use ductile iron brake calipers, while most electric vehicles use cast aluminum. Some people say that the premium multiplier for weight reduction is US$5/kg. Lux Research suggests that this will become an indicator in 2030, so the value of lightweight may not change. Ducker Research refers to the suspension and braking components as "pendulum components," which means that the materials change back and forth depending on the person making the decision. In the late 1990s, a Detroit OEM's brake calipers were almost entirely made of aluminum, and now they are mostly made of iron. Maybe the same is true for the control arm, steering knuckle and subframe? You can bet that every time the chief engineer and the vehicle team are faced with the challenge of meeting weight, cost, range, and performance goals, there will be a heated debate. What we can do is keep innovating!
1. AluMag, North American Lightweight Procurement Seminar, November 2015. 2. "Tesla Model S Weight Distribution", Teslaati, July 19, 2013, www.teslarati.com/tesla-model-s-weight. 3. By 2030, pure electric vehicles will reduce their reliance on lightweight," Lux Research, November 12, 2020, www.luxresearchinc.com/press-releases/by-2030-battery-electric-vehicles-will- be-less-according to Lux research, it relies on lightweight. 4. Halonen, Andrew, "Automotive suspension components bring opportunities for aluminum forgings", Light Metal Times, December 2020, pp. 30-34. 5. "Vice Frame and engine bracket", Aluminum Extruder Council (AEC), www.aec.org/page/subframes-enginecradles# tesla. 6. "2021 Ford Mustang Mach-E: E3-Hoist Evaluation | Front Suspension" , Video, Munro & Associates, April 28, 2021, www.youtube.com/watch?v=sq_cQWYMoC8&t=303s. 7. "2021 Volkswagen ID.4: E3-Hoist review, front and rear suspension", video, Munro & Associates, April 12, 2021, www.youtube.com/watch?v=HkJXkWC9G_0.n
Andrew Halonen is the President of Mayflower Consulting, LLC, a lightweight consulting company that provides strategic marketing, market research and business development for high-tech clients. Halonen is engaged in the development of castings, extrusions, brakes and new materials. Contact him: www.lightweighting.co.