Issue: Feb 2005

Staying the Course

The Sequel crossover concept moves GM’s “skateboard” fuel cell platform another generation toward reality.

by John Peter

In the movie business, sequels often pale in comparison to the original. General Motors hopes that a similar fate doesn’t meet the latest iteration of the Autonomy “skateboard” fuel cell car that debuted at the 2001 North American International Auto Show.





Autonomy promised to reinvent the way automobile’s were designed and manufactured as hydrogen fuel cell vehicles become a reality.

GM followed Autonomy with a driveable version called HyWire, later that year. While HyWire came up short on a lot of the advanced technology promised by the theoretical Autonomy, the intent was to build a vehicle that remained as close as possible to the original vision while using available parts and technologies.

Larry Burns, vice president of research and development and planning, says that Sequel represents a “real car” and while it’s not yet affordable, it is doable. Like HyWire, Burns promises a drivable version of Sequel before the end of 2005.

Burns says that Sequel is more than just a fuel cell vehicle. It’s the merging of four advanced technologies: advanced propulsion, vehicle electronics, controls and software, telematics and advanced materials.

Sequel is similar in size to a Cadillac SRX at 196.6 in. long and 66.8 in. wide sitting on a 119.7-in. wheelbase and weighs about 200 pounds more than the Cadillac crossover, or about 4,650 pounds.

Sequel’s chassis carries on the “skateboard” theme. All of the vehicle’s components fit within the 11-in. thick all-aluminum chassis. The fuel cell stack is mounted under the floor between the front seats and the Quantum gaseous hydrogen storage system takes up most of the space under the rest of the vehicle’s floor. The high-voltage lithium ion battery sits between the two rear wheels, which are powered by electric wheel-hub motors. A cooling module for the battery sits right behind it. Bywire control modules for the braking, steering and chassis control systems are mounted on top of the frame rails on either side of the hydrogen storage system. An electric traction motor is mounted up front underneath the HVAC control unit, driving the front wheels.


Sequel is powered by GM’s newest generation fuel cell stack developed by GM engineers in Honeoye Falls, N.Y. The 73 kW (97 hp) stack is made up of 372 cells and boasts an improved power density of 1.6 kW per liter with a maximum output of 110 kW.

The new stack is smaller than the stack found in HyWire but pumps out 25 percent more power. Technological improvements have allowed GM to eliminate a lot of the hanging-on technology by up-integrating some of those functions into the stack. The new power module contains the stack, hydrogen and air processing subsystems, cooling system and high-voltage distribution system. The new stack also uses a new air intake system that is lighter, quieter and more efficient than the previous system.

GM switched out the screw-type compressor for a patented, aerospace-influenced jet turbine design. The new compressor offers a more dynamic airflow and is lighter, smaller and costs less than the part it replaces. Dan O’Connell, head of GM fuel cell production engineering Honeoye Falls, N.Y., says that the smaller stack can operate over a wider range and needs less “care and feeding” than the previous generation.

“As the stacks become more robust they need fewer ancillary components,” O’Connell adds, “This not only makes them less complex, but the stacks produce more power out of the same size.”

Burns says that the improvements in stack technology have come quite fast. “We’ve had a power density increase of a factor of seven times in the last six years,” Burns says. “And significant improvements in durability, reliability and cold-start capability.” Burns says that cold-start isn’t a question of whether you can do it or not, but whether or not you can do it over and over again throughout the life of the automobile.

“So that becomes the important challenge,” Burns adds, “and we’re making good progress there.”

Burns says that GM has made rapid progress in reducing cost through material development and design improvements and systems and components simplifications, adding that the number of parts has been reduced by a factor of three in the last three years. The latest stack has one-tenth the moving parts of a conventional internal combustion propulsion system.

The three lightweight carbon-composite tanks (a large one in the middle and two smaller ones on each side) are a patented GM design and hold 8 kg (17.6 lb.) of gaseous hydrogen stored at 10,000 psi (compared to 5,000 psi in HyWire). This gives Sequel a range of 300 miles (450 to 500 miles if liquid hydrogen is used).

The carbon-fiber material, supplied by Toray Industries of Tokyo, Japan, provides for a storage tank that is lighter than comparable metal tanks while remaining close to the same size. Burns says that the high cost of the tanks is still one of the major hurdles to get over on the way to commercialization. The tank systems also take quite a bit more time to manufacture and cost quite a bit more than a standard plastic blow-molded gasoline tank.

Sequel has an independent double A-arm suspension with controlled damping up front (above left) and an independent double A-arm suspension linkage attached to the wheel motors out back (above right). The rear uses shock absorbers with controlled damping rate and air leveling capabilities. Both front and rear suspensions use a transverse-mounted fiberglass leaf spring. The rear wheels are powered by two 25 kW electric wheel motors developed by General Motors Advanced Technology Center in Torrence, Calif. The rear end also features electric steering similar to the Delphi-supplied Quadrasteer available on GM full-size pickups.
Sequel’s unique propulsion system powers the SUV from 0 to 60 mph in less than 10 seconds reaching a governed top speed of 90 mph. The powertrain, which makes 42 percent more torque than a conventional vehicle, uses a 60kw electric traction motor to drive the front wheels and two 25 kW wheel hub motors to power the rear wheels. The rear wheel hub motors, including the two inverters and the power inverter module for the front electric motor, are the work of GM’s Advanced Technology Center in Torrence, Calif. Burns says that while Sequel represents a “real world” fuel cell crossover, several different propulsion scenarios will probably pan out. A low-end vehicle might get the front motor only and a high-end vehicle may get wheel motors on all four corners.

Electricity stored in a lithium ion battery, supplied by Saft, of Bagnolet, France, offers 65 kW of peak power and weighs 143 pounds. Burns says that lithium ion was chosen for its improved performance, but it also gives engineers the opportunity to learn more about the technology in general and about the integration of key technologies that will drive the industry going forward.

As one of the byproducts of fuel cells is heat, thermal management becomes a priority. “When you’re designing a vehicle of this type from the ground up,” Burns says, “you can consider thermal management up front.”

Sequel uses three cooling modules mounted up front (one behind the grille and two behind vents underneath the headlamps) to keep the stack cool and a module in the rear to cool the battery and wheel hub motors.

Sequel uses the first application of GM’s advanced electrical architecture. Besides the high-voltage system needed to run the fuel cell, a conventional 14-volt system runs the standard accessories and a 42-volt system powers all of the by-wire controls. Sequel features by-wire braking, steering and chassis control. The steerby- wire system uses two motors up front and one in the rear to steer the rear wheels, similar to the Quadrasteer system designed by Delphi for GM’s pickup trucks and full-size SUVs. The rear-steer capability reduces the vehicle’s turning radius from 42 ft. to 37 ft. And can also play a role in improving handling. There is also a back-up mechanical steering system on the vehicle that Burns says will be in place until GM is confident that it is no longer needed. Sequel has an independent double A-arm suspension with controlled damping up front and an independent double A-arm suspension linkage attached to the wheel motors out back. The rear uses shock absorbers with controlled damping rate and air leveling capabilities. Both front and rear suspensions use a transversemounted fiberglass leaf spring.

The interior seats four and features a moving center console that runs on tracks making it accessible from either row of seats. It also features a passenger seat that rotates 180 degrees.
Sequel is the first GM vehicle to use Flexray — a universal electronic architecture developed by a consortium of OEMs and manufacturers. GM says that Sequel’s state-of-the-art bywire systems will offer better control, better maneuverability and more responsiveness. For example, the by-wire braking system will slow the vehicle from 60 mph to 0 mph in one car length (about 5 meters) shorter stopping distance than conventional hydraulic brakes. Sequel uses the first application of Stabilitrak 3.0 which integrates the by-wire systems via a supervisor control system, also an application first for GM.

OnStar is integrated into the vehicle’s electronic systems allowing GM engineers to monitor the vehicle’s vital signs 24-7 and collect real-time data.

Sequel features an extensive use of aluminum. The all-aluminum space frame is made of stampings, castings and extrusions and is welded to the aluminum chassis. Sequel also features cast-aluminum front and rear cradles and ETS mounts; extruded front bumper bar, HVAC mounting bracket and fuel cell shield and mounting brackets and a tank carrier made up of castings and tubular extrusions. Sequel is not a totally hand-built concept. Burns says that production tools were developed to give engineers some learning experience in manufacturing the body as the project moved forward.

While the show car is a one-off creation, the drivable version, coming later this year will utilize the seats, steering wheel and column and some door and structural components from GM’s large SUVs.

The center console folds forward to reveal the navigation and entertainment screen.
Ed Welburn, GM vice president of design, says that the crossover design was chosen because the layout of the chassis and fuel cell system required a vehicle with an SUV-like stance. Welburn also added that contemporary crossover-type vehicles appeal to drivers because of their combination of car and SUV attributes. The vehicle’s front fascia was designed to integrate into the vehicle’s thermal management system, with a large grill and two large vents underneath the headlights that provide cooling air to the fuel cell stack, power electronics and electric motor. A vent at the rear of the vehicle’s hood directs air to the HVAC system.

Two vents in the rear, situated just under the tail lamps, cool the battery and wheel motors. Robert Boniface, GM director of advanced design says that while these vents are typically found on the side of the vehicle just in front of the rear wheel wells, the design team asked if they could be moved for aesthetic reasons. “After some careful studies of airflow, Boniface says, “we learned the Sequel’s thermodynamics actually improved with the vents under the taillights.”

Sequel has LED head lamps and tail lamps. LEDs require less energy and create less heat than conventional lamps. Sequel also has a full-length sunroof that folds back in separate sections. Unlike HyWire, Sequel has brake and accelerator pedals and a traditional-looking steering wheel protruding out of a pod that houses the instruments. The pod is mounted to a “floating” IP that flows into the door panels. The controls for the HVAC system (which is mounted under the hood) are on the door panels, eliminating the need for a center stack. To keep the IP simple, air is vented out from behind the instrument panel using a highvolume, low-pressure HVAC system similar to those found on airliners. A multi-purpose center console slides on a track, providing access to the vehicle’s audio/DVD/navigation system to either front or rear seat passengers. The console also has Bluetooth USB docking points and storage compartments for DVDs and video game controllers.

The rear seats fold down to create extra cargo space.

A sunroof runs the full length of the roof and opens with a series of folding glass panels similar to the sunroof in the Pontiac G6.
Sequel’s flexible interior seats five with a passenger seat that can rotate 180 degrees and rear seats feature seat-back reclining and seat bottoms that fold up to provide a flat load floor between the rear doors.

Interior designers used a translucent silicone– rubber material for the armrests and load-floor strips that can be backlit, creating an ambient glow. The same lighting theme is continued up front with LED-lit trenches in the instrument panel.

Burns says that Sequel’s goal is to be much more than GM’s next generation fuel cell vehicle. This advanced technology platform will prove out a lot of technologies that will eventually find their way onto conventional GM automobiles. 

Suppliers to Sequel

Wheel motors, DC-DC converter: GM Advanced Tech Center
Fault-tolerant electrical system for by-wire: GH Hughes Research Lab
Hydrogen tanks: Quantum Technologies
Aluminum structure: Alcoa
Steer-by-wire: Visteon
42-volt electrical system: Lear
Interior, exterior body closures: Roush
Adaptive suspension: Sachs
Front electric drive motor: Siemens
Lithium ion battery: Saft
Air compressor: Liebherr
Power distribution and controls unit: Brusa
Brake-by-wire: PGT - Pacifica Group Ltd.
Carbon fiber for hydrogen tanks: Toray
HVAC and radiators: Mitsubishi Heavy Industries

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