Sharper Focus for the Hyundai Sonata

The last-generation Hyundai Sonata changed the midsize segment through its design. So what does the company do for an encore?

“Every car company has its own areas of focus for improvement,” says Mike O’Brien, vice president, Corporate & Product Planning, Hyundai Motor America, “some are very predictable. 

However, it used to be easier to predict where the competition was going to be before the explosion of interest in the midsize segment.”

Historically, Hyundai concentrated on three major areas for improvement: 

NVH, getting the highest structural rigidity at the lowest weight, and offering a superior value proposition in terms of features per dollar. And while these continue to guide the company’s efforts, they are no longer sufficient. “Nowadays, you have to look at the changes taking place in the segment, as well as what’s going on in the segment above,” says O’Brien. “Then you have to combine this with what the customer wants/will want, and where you expect the competition to improve. It’s not an easy task.”

This is why the seventh generation LF Sonata is less brashly bold and more sophisticated than its YF predecessor.

And why it is the only competitor in the segment to be classified as a large car by the EPA. It’s also the reasoning behind the increased focus on vehicle dynamics, on improving ride and handling, steering and braking feel. It is also why they increased structural rigidity to provide a stiff platform for the steering, suspension and brakes, and create a strong safety cage.

Advanced high-strength steel (>60 kg/mm2) use has increased from 21% to 51% of the body-in-white. Structural adhesive use also jumped from 11 meters of bond area on the 2014 Sonata to 119 meters on the 2015 model. 

The B-pillars are hot stamped and are part of a multi-strength tailored blank that makes up the inner body side ring. Not surprisingly, torsional rigidity is up 41%, and bending rigidity increased 31%. According to Hyundai, the competitor that comes closest in these measures is VW’s U.S.-built Passat. Despite being in the LF Sonata’s secondary competitive set (the Chevy Malibu, Ford Fusion, Honda Accord, Nissan Altima and Toyota Camry make up the primary set of competitors), the Passat was studied for its combination of solidity and premium feel.

The suspension story is one of—you guessed it—refinement. MacPherson struts remain up front, though the geometry was revised and bearing stiffness increased. The independent rear suspension is again a four-link design, but with a new dual lower arm replacing the single lower arm used previously. Combined with the 1.3-in. longer wheelbase—now at 110.3 in., the same as the VW Passat—it provides improved vehicle stability and more stable high-speed turn-in without adversely affecting ride quality.

Surprisingly, Hyundai opted for two different electric power steering (EPS) systems on the 2015 Sonata. “We knew the steering wasn’t good enough on the YF Sonata due to the tolerance stack-up in the column-mount design,” says O’Brien. This compelled the development team to specify a dual-pinion rack-mount EPS with a stiffer rack for improved responsiveness. 

However, development continued on the column-mount design, and the engineers working on that system increased the rigidity of both the column shaft and rack, and moved from a 16-bit to 32-bit controller. “The gains the team made surprised everyone,” says O’Brien, “but we continued the two-track approach, placing the rack-mount unit in the Sport model exclusively due to its slightly better on-center response and feel despite its higher cost.”

Most Sonatas are powered by a 2.4-liter inline four. Sport models get a 2.0-liter turbo. Both direct-injection engines are from Hyundai’s Theta II family, and are beneficiaries of many improvements. 

On the 2.4-liter, for example, inlet valve opening/closing is controlled by the DCmotor-driven continuous variable valve timing. This brings a 2% increase in fuel economy by allowing for late intake valve closing, improved drivability from the system’s faster response time, and lower emissions levels at low coolant temperatures. Engineers also increased the flow rate and velocity of engine coolant near the exhaust port to improve fuel efficiency at high rpms. Meanwhile, the 2.0-liter turbo gets motor-driven flaps in the intake manifold and asymmetrical port plates to enhance tumble and swirl flow when the flap is closed, and increase flow rate when it’s open. Optimizing the flow path of the twin-scroll turbocharger brought a 20% improvement in low-end torque, while switching to an electronic wastegate actuator improves boost control. Both engines are mated to a six-speed automatic, though the Sport model adds steering wheel mounted paddle shifters.

The naturally aspirated 2.4-liter engine produces 185 hp at 6,000 rpm and 178 lb-ft of torque at 4,000. For the turbo-charged unit these numbers increase to 245 hp at 6,000 and 260 lb-ft from 1,350-4,000 rpm. However, Hyundai has another powertrain combination in its lineup, a 1.6-liter twin-scroll, turbo-charged, direct injection engine mated to the company’s first dry dual-clutch automatic transmission (DCT). It produces 177 hp at 5,500 rpm, and 195 lb-ft from 1,500-4,500. Estimated fuel economy is 28 city/38 highway/32 combined, and it will be the most fuel-efficient model until the Hybrid arrives in 2015.

According to Hyundai, the DCT improves fuel economy by 6%-7% and acceleration from 0-60 mph by 3%-7%.