Sequel's Lessons for GM, Suppliers

The electronics inside the Chevrolet Sequel hydrogen fuel-cell vehicle ultimately may find their way into mainstream cars and trucks well before the dawn of the hydrogen economy.

The Sequel is the third in a trilogy of hydrogen-powered concepts from General Motors Corp. It incorporates the AUTOnomy platform, the fuel cell-dedicated architecture GM premiered in 2001, and the drive-by-wire technology showcased two years later in the Hy-Wire concept.

GM assembled just two models, the Sequel 1 and Sequel 2, in January at its Warren, MI, Technical Center and began road testing them in April. The two will be used as test vehicles, not show cars, GM stresses.

The AUTOnomy skateboard platform allows the Sequel to maintain a low center of gravity but offer a ride height and commanding view of the road similar to that of a Buick Rendezvous midsize CUV.

The drive-by-wire system replaces traditional hydraulic steering and braking with electric motors, actuators and a host of sensors and control devices.

By-wire technologies represent the “future of steering and braking,” Thomas Zebehazy, GM senior manager-global advanced technology development for chassis and powertrain integration says during a Sequel drive event at Camp Pendleton, CA. “You could potentially have different, personalized steering or braking feels.”

Tuning the by-wire systems for different vehicles and different driving conditions requires only a modest software reconfiguration, Zebehazy says.

One electric motor drives the front wheels, and two separate motors propel the rear. Because there is no transmission, torque is delivered directly to the wheels.

On paper, the Sequel kicks out 2,920 lb.-ft. (3,959 Nm) of torque, but that's with all three electric motors running at full capacity. Clearly, the Sequel isn't a rocket ship, reaching 60 mph (97 km/h) from a standstill in about 10 seconds.

GM says the Sequel's brake-by-wire system could make its way into mainstream vehicles sooner than its fuel-cell powertrain. PBR International of Australia developed the braking system for the Sequel.

With the exception of the humming fan supporting the air conditioning, the Sequel is as quiet as any electric vehicle.

But during a drive at the military base here, the Sequel “failed” several times, shifting into a limp-along mode that allowed only low-speed travel. Turning the key off then on, much like rebooting a computer, returned the vehicle to full power.

After it slid into the low mode several times, GM pulled out the second Sequel, which performed well, with no power faults on the remaining five miles (8 km) of the 25-mile (40-km) course. Later, a technician tells Ward's the first vehicle was suffering from a loose battery connection.

The lithium-ion battery pack is essentially the same as that found in laptop computers. The PC batteries have been known to overheat and even catch fire, prompting recent recalls.

The Sequel incorporates regenerative braking to recharge the battery and provide a power burst at critical times, such as when passing another vehicle.