Hyundai Tech: Sonatas of Two Different Flavors

Hyundai is expanding its Sonata lineup seemingly with something for everyone. In honoring this South Korean company’s press embargo, I cannot share driving impressions just yet, but I can spill the technical beans. And there are lots of them.

The 2.0T Sonata, as its name suggests, is powered by a turbocharged 2.0-liter engine. Hyundai avoided the GDI moniker that could have legitimately been attached, as this inline-4 also features direct injection of its gasoline. Now I admit there’s nothing particular novel about having a turbo-enhanced direct-injected engine of small displacement do the job of a traditional—and more fuel-consumptive—V-6. But Hyundai engineers have been busy in perfecting this concept in several distinctly innovative ways.

For one, the turbo’s compressor housing is actually part of the engine’s exhaust manifold. What’s more, the casting that integrates these two elements is of austenite stainless steel. It’s quite a technical achievement to use this material, but it’s ideal for this application because of its thermal properties of getting exhaust heat efficiently to the turbo’s compressor. And, of course, having the two components integrated into one only enhances this.

Factoid: It’s both the kinetic energy of exhaust flow as well as the thermal energy of its expanding gases that drive the turbo’s compressor and its attached forced-induction-producing impeller. Hyundai’s integrated design enhances both aspects.

The Sonata’s turbo is a twin-scroll type as well. That is, its porting and vanes are designed to exploit two separate paths of exhaust flow, from cylinders 1 and 4 and from cylinders 2 and 3. This way, pulses during inherent four-stroke operation don’t trip over each other. This twin-scroll idea isn’t unique to Hyundai (the 2.0-liter Buick Regal uses it as well). But the Sonata’s 274 bhp versus the Regal’s 220 suggests the other wizardry involved.

Hyundai engineers figure that optimized forced induction plus direct injection are worth around a 22-percent kick in torque, from 220 to 269 lb.-ft. over a broad rpm range, with the twin scrolls accounting for perhaps half this. There’s lots of synergy involved here as well: Direct injection provides a cooler charge of fuel; optimized intercooling does its magic as well with the forced induction of air. They combine to produce the 2.0T’s 137 bhp/liter, a figure that’s quite amazing in a car in the $24K-$29K range. More details on this and my driving impressions once the embargo has lifted.

The Sonata Hybrid also carries some very neat tech, specifically in its parallel-hybrid drivetrain, lithium-polymer battery pack and optimized thermal management. Hyundai engineers also pointedly used the term “fun to drive” in describing their hybrid design and development.

Its 2.4-liter gasoline engine operates on an Atkinson Cycle; more correctly, like other hybrids, on a innovatively valve-timed simulation of this short-compression/long-expansion concept. A clutch separates this powerplant from a 41-hp electric motor which resides directly ahead of a 6-speed automatic transmission eventually sending twist to the car’s front wheels.

Note the difference between Hyundai’s hybrid layout and those of Toyota Camry, Ford Fusion or Nissan Altima (these three, certainly technical siblings in more ways than one). The Hyundai’s 6-speed automatic is in marked contrast to the other’s CVTs, one claimed benefit being enhanced highway performance. What’s more, as its operation is integrated with the electric motor’s, this automatic has no need for an energy-sapping torque converter.

Unlike these other cars’ nickel/metal hydride battery technology, the Sonata Hybrid’s is lithium-polymer. Newer technology, it offers improvements in everything from power and energy density to weight to volume to cycle life to characteristics of state of charge.

This last one, SOC, for short, is particularly interesting in Hyundai’s optimization of hybrid operation. For reasons of durability, any battery profits from gentle chemical action—not being discharged too deeply, not being charged to its full capacity, with SOC being a measure of this. Typical nickel/metal hydride batteries owe their life-of-the-car longevity to an SOC window as narrow as 15 percent; e.g., operating no less than 50 percent SOC, no more than 65 percent SOC. Hyundai engineers say lithium technology can accept a wider range, say 50 to 75 SOC, with no degradation of battery durability.

What’s more, innovative thermal management stretches this further: In cold weather, for example, the Sonata Hybrid’s SOC window can expand to as wide as 45 percent, from 45 to 90 SOC. One benefit of this is balancing the inherent loss of battery performance concomitant with lower ambient temperatures. Despite these exemplary SOC characteristics, Hyundai engineers expect to confirm battery longevity on the order of 250,000 miles or more.

A last example of Hyundai’s thermal management and efficiency. Compared with other Sonatas, the Hybrid has a larger air intake; this, to handle hybrid powertrain cooling in extremes such as Death Valley at summer’s peak. On the other hand, such a gaping snout is detrimental to aerodynamics. To optimize matters, the Sonata Hybrid has what engineers term an Active Air Flap. As its name suggests, this gizmo automatically adjusts the airflow. It’s wide open at low vehicle speed and high coolant temperature; it closes as speeds increase or coolant temperature drops. Engineers figure there’s a 10-percent reduction in CD with this, all the more impressive when you hear that the car’s inherent drag is an already low 0.25.

My driving impressions of the Sonata Hybrid can appear on October 18 (one day before my birthday—please, no presents).