‘A deeply rooted tree survives droughts of all kinds,’ says one Korean proverb. The idea applies as well to car platforms, which could be considered the root of a car. Platforms are increasingly considered as more important in the fast-changing automobile industry: ‘a well-constructed platform can feed an entire car manufacturer,’ the saying goes. Indeed, the value of platforms in the modern auto industry is nothing short of crucial.
A good example of the role and the effect of a good platform can be found in Kia’s 3rd-generation K5. The various charms of the 3rd-gen K5 have resulted in an impact that transcends that of the 1st-gen K5 a decade ago. Intense visuals and bold stylings, dynamic driving performance, reduced weight and the resulting increase in efficiency, and improved safety features culminate in a vehicle that is sure to attract the modern consumer.
The sporty design has always been the K5’s identity through its three generations, but the 3rd-gen has further emphasized this distinction. A fastback style without the divide between the roofline and the trunk lid maximizes the image of a sleek sedan. But the fastback style is not alone in creating this effect: the 3rd-gen K5 offers a wide, stable, and yet sporty proportions that were made possible by having the 3rd-gen platform as its basis.
The 3rd-gen K5’s side profile is so dynamic as to create an illusion of movement even at a standstill. Particularly noticeable are the manufacturer’s efforts to break out of the conventional proportions of the front-wheel-drive sedan. To achieve its aggressive proportions, the K5 pushed back the point at which the windshield begins and reduced the front overhang by 20mm. Simultaneously, the wheelbase was increased by 45mm from the previous generation’s, and the height of the car body was lowered by 30mm, improving visual stability. Such changes, of course, were made possible by the 3rd-generation platform.
The 3rd-gen K5 feels more fluid and stable than its predecessors in driving. Such counter-intuitive improvements are the result of the car body’s lower center of gravity—all thanks to the 3rd-generation platform’s low-floor design. The platform has the engine, drivetrain, and other heavy parts on the bottom part of the car body, lowering the vehicle’s center of gravity. The resulting flat, low underbody of the K5 also results in reduced air resistance in the lower half of the car. On the whole, the car body, placed 30mm lower than the 2nd-gen’s, provides a much more stable driving performance for the driver.
Stable curving is influenced not only by the center of gravity but also by the weight distribution. Particularly, front-wheel-drive cars with heavy engines and drivetrains in the front of the car are susceptible to weight distribution problems. The 3rd-gen K5 has taken advantage of the package optimization technology of the 3rd-gen platform to overcome such issues.
For example, the platform moved the engine and the transmission—two of the heaviest car parts—further inside to center the distribution of weight. The hybrid model, too, had its 40kg high-voltage battery move from the bottom of the trunk to the bottom of the rear seat, achieving a similar centering of weight distribution.
Consequently, the K5’s movement feels lighter than its 1,400kg bulk would seem to suggest. Its driveability thus fits the image of its dynamic, sporty exterior.
The 3rd-gen K5 also comes with a redesigned suspension to improve driving performance. The suspension’ s placement and structure result in significant changes in comfortability and curving performance, making it one of the more difficult parts to calibrate.
The K5, however, has seen noticeable improvements in driving performance thanks to the dynamic yet stable new suspension from the 3rd-generation platform. Front-wheel suspension structure was amended to reduce the instances of understeering. Caster trail (the degree to which the rotational axis inclines toward the front or the rear of the vehicle) was increased to improve stability at high speeds. Lateral rigidity of the rear suspension was increased to improve the responsiveness of the rear wheels while cornering, and the control arm was repositioned as well. Finally, the damper, which had been on a slight incline in the previous generations, was installed upright to improve the comfortability in the rear seat.
Improvements in the chassis did not end with the suspension. The 3rd-gen platform comes with a new subframe with the shape of a sharp (#). Compared with the H-shaped subframe of the previous generations, the new subframe allows for a better distribution of load across the front and rear joints, achieving greater flexibility in load management, not to mention the improvements in durability and noise/vibration absorption.
Many other various adjustments were made to improve upon the general driving performance. The parts that are particularly susceptible to conveying noise and vibration were reinforced with sound-absorbing material to improve the vehicle’s NVH performance. Moreover, the car body’s lateral rigidity was generally increased, and the steering rack center was moved closer to the wheel center, resulting in improved handling.
Consumer expectations on vehicle safety grow year after year. Global institutions that conduct crash tests for new cars have also been tightening their safety standards annually, reminding the manufacturers to create as safe cars as possible. To that end, car body reinforcement seems to be the obvious solution—but reinforcements often lead to weight increase, harming the equally important goal of high fuel efficiency. The consumers’ demand, then, seems to embody two contradictory goals: a safe and lightweight car.
But the 3rd-gen platform has somehow delivered on those paradoxical goals, creating a lightweight but strong-bodied car. The 3rd-gen platform underwent an intricate redesign and repositioning of the body structures with higher rigidity and lower weight in mind. For example, high-strength steel and hot stamping were applied to many major parts. Parts receiving hot stamping increased to 21 from the previous generation’s 16, resulting in the average tensile strength of 70.9 kgf/㎟, an increase of 3.1kgf/㎟ from the previous generation. The “safety zone,” the area directly around the passengers, was particularly minded for high rigidity, ensuring the highest crash safety performance.
As shown, the 3rd-gen platform delivered on both goals of safety and reduced weight. The 3rd-gen K5 is lighter by 20 kg than the previous generation and lighter by 40kg in tolerance weight than competing models from the other manufacturers.
The 3rd-gen platform also shines in the small overlap frontal test, which is increasingly being seen as one of the more important facets of car crash testing. The multi-skeleton engine room is designed to effectively distribute collision energy in the event of an accident, minimizing the force delivered to the passengers. In the event of a car-to-car collision, the structure reduces the impact energy on the other car, minimizing the degree of injury to others as well.
The small overlap crash, where only the frontal 25% of the car body comes into contact, often results in violent rotation of the car body as it is pushed aside. In such a case, the driver may be thrust beyond the range of airbag protection. There is also the contingency of the second crash caused by the car in the rear.
The 3rd-generation platform prepares for these contingencies by applying the new “mobility control technology,” which causes the impacted wheels to disengage from the car body in the event of a small overlap crash. Thanks to this technology, the K5 does not violently rotate during small overlap crashes; upon coming into contact, it continues to move forward at an angle, which both reduces the likelihood of injury and prevents the occurrence of subsequent crashes.
Hyundai and Kia’s platforms have for long undergone gradual developments to culminate in the current masterpiece. From the earliest stages of development, the new platform was designed with eyes on meeting multiple, sometimes even contradictory, goals: design, driving performance, safety, and weight reduction. The superb quality of this platform is embodied in the new K5. Thanks to the contributions of the 3rd-gen platform, the 3rd-gen K5 could be sleek in design, agile in driving, and safe and lightweight all at the same time.
HMG Journal Operation Teamgroup@hyundai.com
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