The term ‘lightweight’ seems to have become ubiquitous in the recent discussions about automobiles. Just as people focus on diverse methods for dieting, the car manufacturers are focusing their R&D efforts on producing as light cars as possible. It is easy to see why the technology is being seen as crucial: being lightweight improves not only fuel efficiency and eco-friendliness but also the very power of the car.
If the weight of a 1,500 kg midsize sedan were to be reduced by 5% (75kg), fuel efficiency and engine performance will improve by 1.5% and 4.5% respectively. The lighter body will also reduce collision energy by 4.5%, thus reducing the likelihood of body deformation and passenger injury. At the same time, greater agility results in improved acceleration, better cornering, and reduced braking distance.
From the environmental perspective, the exhaust gas is reduced as well—the lighter car will be less of a burden to the engine. Because environmental regulations on automobile exhaust will become stricter in North America and Europe in 2020, automotive lightweight technology is increasingly becoming a requirement for the manufacturers, not an option.
The general trend for EV/hybrid vehicles and the increasing demand for safety and convenience features is another context for the importance of lightweight technology. Hybrid cars come with an additional battery and electric motor in addition to the engine, so they are naturally heavier. The addition of safety and convenience features like ADAS (Advanced Driver Assistance Systems), head-up display, panoramic sunroof, and cooling seats are further increasing vehicles’ curb weight.
If costs were not a concern, then becoming lightweight could be achieved overnight by simply choosing the most lightweight material available. But realistically, doing so is not an option. Lightweight yet durable materials are typically very expensive. Particularly, CFRP(carbon-fiber-reinforced plastic) can halve the vehicle weight but is whopping 10 times as expensive as steel.
This material was notably used by Porsche in constructing wheels, which successfully reduced 8.5 kg in weight—but at the cost of around $20,000 per wheel. As such, the application of CFRP into mass-produced vehicles is merely an ideal, not a general possibility. Aluminum is a more viable alternative, reducing weight by 20 to 30%, but it also comes at double the price.
Indeed, utilizing readily available lightweight materials inevitably leads to rising costs. But developing the technology for a sturdy, safe, and yet economical material that is also lightweight is an enormous challenge as well. Since a few years ago, Hyundai/Kia Motors have been focusing their R&D efforts on automotive lightweight technology for all facets of the car, including platform, chassis, and powertrain. Some recent models are bearing out the success of such efforts. Of course, collision safety has also been improved.
Being lightweight and sturdy are inversely proportional—but technology can solve this dilemma.
In the past, Hyundai/Kia’s priorities lay in performance and safety. The 7th generation LF Sonata from Hyundai, released in 2014, was heavier than the previous 6th-gen YF by 45 kg. But it received good marks in various collision tests and addressed Sonata’s prior reputation for having a weak body, not to mention achieving greater stability at high speed and improved handling. NVH (noise, vibration, and harshness) marks were improved as well. Indeed, the general feedback on the 7th-gen Sonata was that “it rides well, turns well, and stops well,” and on-road performance tests substantiated that it achieved marked improvements from the previous generation across the board.
Having achieved body rigidity, Hyundai/Kia moved onto the next step: reduction in weight while ensuring safety. Without resorting to expensive materials, the manufacturers attempted to simultaneously catch the two rabbits of ‘weight reduction’ and ‘affordability.’ The technological challenge ahead of them was, of course, massive.
Light yet sturdy: the new Sonata’s secrets lie in structural optimization
The fruits of Hyundai/Kia’s efforts can be found in the new 8th-generation Sonata released this March. True to the design concept of ‘smart device,’ the new Sonata came with the added weight of various advanced electronic devices. Nonetheless, the goal was to still achieve lower curb weight and better collision safety than the previous generation.
A look into the departments in the companies’ R&D facilities then would have revealed the intense pressure under which the researchers toiled. Even the diminutive weight of a single screw or a cable was subjected to review. From the planning stage, all systems of the car—platform, interior/exterior, chassis, electronic devices—underwent the application of cutting-edge lightweight technologies. In the end, the new generation’s curb weight came 59 kg under the previous generation’s (North American release; domestic Korean release had a 65 kg decrease). Given that there was a 27 kg increase in added safety and convenience mechanisms, the reduced weight from structural optimization amounted to 86 kg (92 kg domestic).
To fulfill the two objectives from the planning stage, sturdiness and weight reduction, the new Sonata underwent optimization processes throughout. The relative lack of rigidity in the car’s underbody was resolved by utilizing the TRB/TWB (tailor rolled blanking/tailor welded blanking) method, whereby ultra-high-strength steel sheets are welded at different thicknesses for each body part as needed. Parts with hot stamping were increased from 16 to 21. And the body controller’s functions were integrated, reducing the number of parts.
As a result of such efforts, the new Sonata (North American release) comes at 1,415 kg in weight, lighter than that of the global competitors’ comparable models (most at nearly 1,500 kg). Compared to its popular competitor models Toyota Camry and the Honda Accord, it still boasts an advantage in being lightweight. Surprisingly, even with this significant weight loss, the Sonata showed improvements in collision safety.
Comparing the same models in the Korean release highlights the Sonata’s advantage further. Though a bit of difference admittedly exists in engine specs, the new Sonata (Smartstream 2.0ℓ) checks in at 1,405 kg, far lighter the Toyota Camry (2.5ℓ) at 1,580 kg and the Honda Accord (2.0ℓ Turbo) at 1,550kg.
This is not all—as mentioned, adding a hybrid drivetrain to an internal combustion engine car results in signification weight gain. A good example would be the 7th-gen Sonata Hybrid was heavier than the 2.0ℓ gasoline version by 125 kg. But the new Sonata Hybrid saw much innovation in the drivetrain’s system structure, reducing weight by 90 kg and increasing fuel efficiency compared to the LF Sonata Hybrid.
The new Sonata Hybrid increased battery power density while decreasing the battery’s size. Specifically, power density was increased by 21% while the volume fell by 16% (7.1ℓ), making the battery system lighter by 16 kg. The compact battery was placed under the rear seat in the low-middle part of the car body, an arrangement that improved driving performance. The newly developed HPCU (Hybrid Power Control Unit) also had its volume fall by 9.5% (7.6ℓ) and weight by 9 kg compared to the previous generation.
Lightweight Materials and Engine Downsizing
Lightweight materials and engine downsizing too are mainstays of automotive lightweight technology. The most prominent material for this purpose is aluminum; the next-gen Genesis will, for example, see an increased use of aluminum in addition to other lightweight technologies to achieve a lower weight.
Powertrain downsizing, which in the main uses turbo technology to reduce displacement and increase engine horsepower and torque, is an important factor of lightweight technology as well. The new Sonata Turbo, planned for release in the latter half of the year, is to be equipped with the Smartstream G1.6 T-Gdi engine, which is widely expected to show high performance despite having lighter weight.
Hyundai/Kia’s Hidden Tech for Weight Reduction
Hyundai/Kia’s lightweight technology can also be found in more subtle aspects of the car. One evidence of such is an ultra-low specific gravity sealer (ultralight adhesive) developed and mass-produced by the collaboration of the materials and production engineering departments. Sealers are adhesives applied between the panels to prevent rust and ensure water-tightness. In general, Approximately 6~8 kg is used for every car produced, which would amount to 150~170 m in length if placed in a horizontal line.
The crux of the new ultra-low specific gravity sealer is in the replacement of the filler material (50% of the sealer content) from calcium carbonate (specific gravity 2.9) to the cutting-edge lightweight material ‘glass bubble’ (specific gravity 0.38). Contrary to calcium carbonate composed mainly of stone powder, the glass bubble is a hollow ultralight material with a glass exterior layer and a vacuum interior. It is currently being used as a high-quality insulation filler material for fields such as construction and aircraft building.
Thanks to the introduction of the glass bubble, sealer weight could be reduced by 37%, or 3 kg. This technology is being expanded to various Hyundai and Kia models.
‘So much commotion for a mere 3 kg,’ one might think. But automotive weight reduction does not happen dramatically in a single part; it is the small contributions from every individual part that culminate in the lightweight vehicle.
Hyundai/Kia’s Weight Reduction Road Map
The ultra-low specific gravity sealer is but one example of many lightweight technologies used by Hyundai/Kia. The manufacturers have yet again set a goal of a 5% weight reduction in its next-generation models by utilizing cutting-edge technologies on new powertrains and platforms. To this end, the company’s vehicle analysis team has drawn up a mid-to-long-term “weight reduction road map” whereby new technologies will be researched and new materials and methods will be developed for mass production. Such efforts will encompass all areas of automotive development, including the body, moving, interior/exterior, platform, chassis, electronics, and eco-friendly tech.
In addition to the aforementioned CFRP, cutting-edge convergence materials such as magnesium and titanium alloy are also being researched. For components requiring high rigidity, such as chassis and body, strong metals like high-strength steel are the focus of development; for the interior, roofs, and bonnets, new polymer materials are the targets. Preparing for the era of the electric car, the company is also investing resources in developing an aluminum platform for EVs as well as a battery-body integrated structure. As for electronics, efforts are underway to combine the functions of multiple parts into a single integrated part, which would contribute to weight reduction.
Just as people find it difficult to lose weight, cars cannot shed weight overnight either. But Hyundai/Kia is valiantly meeting the weight loss objectives, not with a single task force but with the combined efforts of the entire organization. Beyond just the new Sonata, the upcoming Hyundai and Kia models are sure to please the drivers with their new lightweight, nimble selves.