The engine in the HX is the first E85-capable version of GM's "high-feature" V-6 and it's a configuration that's likely to appear in other vehicles in the coming years. The HX engine is based on the newly introduced direct injected engine that's available in the Cadillac CTS and STS. The direct injected engine bumps the power output from 263hp to 304hp while maintaining almost the same fuel economy.

Thanks to the direct injection system, GM has been able to increase the compression ratio of the engine to 11.3:1 without getting into problems with pre-ignition when running on gasoline. This will provide a performance and efficiency advantage when the engine runs on ethanol. As a normally-aspirated engine, the 3.6L will still be able to get some advantage from the high octane (104 RON) of E85.

The HX itself is the smallest HUMMER yet with length that conveniently falls in between the two and four door versions of the latest Jeep Wrangler. The HX concept has been created by a trio of young designers who were hired by the HUMMER design studio upon graduation from Detroit's College for Creative Studies in 2006. The three were tasked with designing a new generation of HUMMER and they each came up with a design.

The final vehicle is a collaboration among the three, David Rojas, Min Young Kang and Robert Jablonski based on Rojas' design. The HX takes all the expected HUMMER design cues like the low roof line, vertical windshield, round headlights and seven slot grille and applies them to a vehicle clearly targeted at the Wrangler. Elements of other HUMMERs like the high ground clearance and short overhangs are maintained as well. However the HX features removable roof panels above the front seats as well as a removable rear roof section. Different rear roof sections are available including a slant back and a square back.

Off-roading is facilitated by the removable fenders. The fenders are held in place by quick release fasteners so that they can be left behind when you challenge the Jeeps on the Rubicon Trail. Of course it will be a while before anyone can try it with the HX. Something like the HX will probably turn up in HUMMER showrooms as the H4 in a few years. Hopefully by that time it will also have the option of the 2.9L diesel V-6 that GM has developed for the Euro-market Cadillac CTS.

HX CONCEPT PROVIDES VISION OF A RUGGED, OPEN-AIR HUMMER

• Youthful, open-air entry-level-size HUMMER
• Designed by a trio of young designers
• Convertible body with removable roof panels and modular rear roof assembly
• Easily removable fender flares and doors
• Full-time 4WD with front and rear locking differentials
• Aeronautically inspired interior with functional, lightweight design elements
• Reconfigurable instruments for highway and off-road driving
• 3.6L SIDI V-6 E85 FlexFuel engine with six-speed automatic transmission

DETROIT – With its unmistakable HUMMER design and a compact, go-anywhere driving ethic, the HUMMER HX concept challenges the hierarchy of the trail. HUMMER displayed the nimble, reconfigurable off-roader at the 2008 North American International Auto Show.

More compact than a HUMMER H3 – 81 inches (2,057 mm) wide, with a 103-inch wheelbase (2,616-mm) – the HX concept is an open-air, two-door off-road vehicle that packs the off-road acumen for which HUMMER has become legendary, along with an easily convertible body that acclimates to varied trail conditions, cargo needs or passenger whims. Its design is based on the ideas developed by a trio of young designers who are new to the HUMMER studio.

"The HX is HUMMER's vision of an agile, trail-ready, open-air vehicle that fits the lifestyles of everyone who needs or wants to drive off road," said Martin Walsh, HUMMER general manager. "Of course, it carries exceptional off-road capability and the distinctive styling for which all HUMMERs are known."

The HX offers an open-air driving experience via a pair of removable roof panels above the driver and front passenger, and a modular, removable rear roof assembly. With the roof panels and roof assembly removed, the HX is transformed into a true convertible.

Easy removal of the roof panels and rear-roof assembly enables quick conversion from a closed vehicle to an open one. The HX also was designed with several roof assemblies, allowing this versatile vehicle to be configured as an SUT (with the roof assembly removed), a stylish slant-back or a traditional, wagon-like design that offers a bit more cargo space.

The HX was shown with a slant-back configuration, wearing a desert-inspired matte olive paint scheme, at the North American International Auto Show. Additional convertible features include:

• Removable doors – easily removable pins in the exposed hinges allow the doors to be removed quickly – an appreciated feature of many serious off-roaders
• Removable fender flares – attached with quarter-turn quick-release fasteners, the composite fender flares can be quickly removed for additional trail/rock clearance, or if the flare is damaged during off-road driving

"The modular design of the roof and removable body panels mark an evolution of HUMMER's design aesthetic," said Carl Zipfel, director of design. "These features demonstrate a deeper understanding of enthusiast desires when it comes to off-road driving – and the slant-back design gives the HX a look all its own."

Purposeful exterior

The design of the HX was driven by input from three young designers who were new to GM and the HUMMER design studio. As part of their "initiation," they were charged with developing concept drawings for a smaller, youthful HUMMER and the HX is a direct result of their creativity. The HX concept is based on one of the designers' original illustrations, but incorporates the best ideas and elements from the other designs.

"HUMMER appeals to young people globally and served as a perfect first assignment for our newest talent," said Ed Welburn, vice president, Global Design. "Today's graduates from top design schools are ready to hit the ground running. The HUMMER design challenge gave our newest designers an opportunity to sprint."

Inside and out, the HX carries a purposeful aesthetic that, from initial sketches to finalized clay models, was refined in only six months.

"This is the HUMMER design language stripped down to its essence," said David Rojas, creative designer. "The HX has an aggressive appearance and great proportions, with beauty lying in its functional austerity."

On the exterior, the lightweight theme is evidenced in the appearance of exposed, billet aluminum suspension components that feature CNC-machined lightening relieves, as well as clean, unadorned bodywork and minimal trim. The lightweight theme is taken to its extreme when the roof panels, roof assembly, fender flares and doors are removed.

Classic HUMMER design cues make the HX instantly recognizable, including the round headlamps located in square housings, an upright windshield profile, minimal overhangs, hood vents and prominent air intakes. The air intakes are functional and feed a V-6 engine beneath the hood, while the hood vents are active – they articulate to allow hot underhood air to escape.

And while the headlamps and grille are clearly HUMMER cues, they've evolved on the HX with a "chopped circle" motif. The grille slots and headlamps, as well as elements on the interior, have the appearance of circles or ovals that have been clipped at the top and bottom, creating a unique appearance that speaks to the vehicle's purposeful aesthetic.

"The 'cut-off' circles suggest larger, heavy-duty components that were trimmed to fit the compact HX," said Rojas.

And while it is unadorned by extraneous embellishments, the HX's exterior is nonetheless outfitted with features that speak to HUMMER's legacy of technology and innovation, including HID headlamps with focusing rings that adjust automatically when they're turned on – much like the lens of an auto-focus SLR-type camera. LED technology is used for the front turn signal lamps and taillamps.

Aeronautically inspired interior

From aircraft-inspired seats to integrated, off-road-ready tools, the HUMMER HX's interior has a beauty that lies in its purposeful intent. It was inspired by the functional and lightweight elements found in aircraft.

"Aeronautical parts are designed to be both lightweight and strong, and that is the feeling exuded by the HX's cabin," said Stuart Norris, interior design manager. "There isn't superfluous trim or decoration – it is a purposeful design that conveys beauty through strength."

Reinforcing the stripped-to-the-essence feel, the exterior's matte olive color carries over onto the interior's largely sheet metal-covered panels. The color is accented with pressed or extruded aluminum components, such as the handles, switches and other necessary parts.

Furthering the aeronautical influence is the instrument panel, which uses an exposed, extruded aluminum cross-vehicle beam as its foundation. On the beam, the instrument cluster and other vital controls are mounted; and it also features a unique, removal top cover that provides significant storage capability.

"The instrument panel is a styling element of the HX, and the removal of the top cover reveals a secondary design that enhances the vehicle's core design ethic," said Norris. "With the top cover removed, the interior conveys even more of a basic essence – and the structure beneath the cover is beautiful to those who appreciate finely crafted metal."

A rubberized floor and ballistic nylon-material covering on the instrument panel and other interior components reinforces the functional aesthetic.

Seating and console details

Like aircraft seats, the HX's seats are constructed on a lightweight framework with minimal components that feature lightening holes and strength-enhancing cross braces or triangulations. They are mounted on exposed, aircraft-style tracks and trimmed with a weather-resistant neoprene material.

The HX seats four, with a pair of bucket-type seats in the second row. The rear seats mimic the front seats' design and can be removed to generate more cargo room. All the seats feature a four-point, racing-style safety harness.

The inner seat track on both front seats is located beneath the outer edges of a prominent center console. The console offers exceptional storage capability and houses a unique shifter that mounts low and out of the way when the vehicle is parked – also hiding from sight the engine starter button. It has a spring-loaded cover that pops up when the driver is ready to select a gear.

The console also houses a resting place for phones, MP3 player and iPods or iPhones. In fact, there is no conventional radio in the HX, only integrated speakers. Passengers plug in an iPod, or similar device, to a USB connector to play music in the HX.

"From the console to the cargo area behind the seats, there are simply untold storage possibilities within the HX," said Norris. "It's like a four-wheel backpack that's already fitted with the necessities."

Gauges and tools

The "cut-off circles" motif of the exterior is seen even more so on the HX's interior, as the gauge cluster, instrument panel vents and even the steering wheel carry the design element.

A three-element gauge cluster – each of the three instrument "pods" carries the cut-off circle design – delivers crucial driver information in either a highway or off-road mode. This conceptual reconfigurable gauge layout uses LCD screens with multiple layouts, including a navigation system. The nav system features GPS and compass information; and is designed to upload trail information before setting off on an excursion.

The center gauge pod houses a speedometer and tachometer, but changes to a wheel angle indicator when the transmission is in the low position. This off-road mode changeover from the highway mode gives the driver information that is more pertinent to the driver conditions. The trail view of a camera mounted in the rear-view mirror can be displayed on the instrument panel, too.

The off-road mode features of the instrument panel comprise the virtual tools of the HX, while others are mounted for physical use, including a folding shovel, flashlight and first-aid kit. They all carry the "clipped circle" design motif found throughout the vehicle.

Ready for rocks, trails and more

With its compact dimensions, almost no overhangs and grippy 35-inch tires, the HX is ready for all terrains. Like all HUMMER production models, the HX has sturdy, body-on-frame construction, onto which is mounted front and rear independent suspensions.

The front suspension features an electronic-disconnecting stabilizer bar for enhanced maneuverability when driving off road, and the rear suspension is located with Computer Numerical Controlled (CNC)-machined, billet trailing arms. Heavy-duty shocks with piggyback reservoirs were custom-made for the HX by renowned racing shock manufacturer Fox; one is mounted at each wheel position.

A full-time 4WD system pulls the HX over, through and around off-road obstacles. It transfers torque to the front and rear axles, each of which is equipped with a locking differential. The torque meets the trail via custom 35-inch-tall off-road tires that are mounted on a set of custom, bead-lock-style wheels that have a two-tone appearance; dark-painted wheel centers complemented by silver-anodized outer rims.

A complete underbody armor kit, including a front skid plate, powetrain protection and more, protects the HX from wayward rocks and other potentially damaging objects. A power-operated winch is located in the front bumper, and the HX has recovery hooks mounted on the front and rear bumpers, just in case its help is required for wrangling others out of unfortunate off-road situations.

Motivation for the HX comes from an E85 FlexFuel 3.6L SIDI V-6 that is backed by a six-speed automatic transmission. The transmission is teamed with the 4WD system to offer exceptional low-speed traction and crawling capability. Four-wheel-disc brakes provide confident stopping power.

SPECIFICATIONS

Model:	HUMMER HX Concept
Body style / driveline:	two-door, four-seat open-top, four wheel-drive
Construction:	welded steel frame, electro galvanized steel
Engine type:	3.6L V-6 VVT (variable valve timing) with spark-ignition, direct injection
Displacement (cu in / cc):	217 / 3564
Bore & stroke (in / mm):	3.70 x 3.37 / 94 x 85.6
Block material:	sand-cast aluminum with cast-in bore liners
Cylinder head material:	cast aluminum
Valvetrain:	DOHC, 4 valves per cylinder, variable valve timing (VVT)
Fuel delivery:	direct high-pressure fuel injection
Compression ratio:	11.3:1
Horsepower (hp / kW @ rpm):	304 / 227 @ 6300 rpm (est)
Torque (lb.-ft. / Nm @ rpm):	273 / 370 @ 5200 rpm (est)
Fuel Type:	unleaded regular or E85 ethanol
Transmission:	Hydra-Matic 6L50 six-speed electronically control automatic transmission
Suspension:	front: independent SLA, custom Fox Racing coil-over shocks; 2-in shocks, 2.5-in springs rear: semi-trailing link, custom Fox Racing coil-over shocks; 2-in shocks, 2.5-in springs
Wheel travel (in / mm):	front: 9 / 228 rear: 11/ 279
Brakes	four-wheel disc; Brembo 6-piston calipers (front); Brembo 4-piston calipers (rear)
Rotor diameter x thickness (in / mm):	15 x 1.25 / 381 x 31.75
Wheel size & type:	20-inch x 9-inch
Tires:	35-inch custom Bridgestone Dueler
Wheelbase (in / mm):	103 / 2616
Overall length:	171 / 4343
Overall width (in / mm):	81 / 2057
Overall height (in / mm):	72 / 1829
Track (in / mm):	67 / 1702 (front); 68 / 1727 (rear)
Minimum ground clearance front (in / mm):	13 / 320
Approach angle (degrees):	56
Departure angle (degrees):	51
Breakover angle (degrees):	25
Grade capability (percent):	60
Side slope capability (percent):	40
Water fording capability (in / mm):	24 / 610 (at 5 mph)
Seating capacity:	4