Secrets of the Sequel
By Bill Moore
When GM unveiled the Autonomy concept vehicle at the 2002 North American International Auto Show, it was, in Chris Borroni-Bird's own words, "a vision of the future in 2020". It was a car straight off the stylist's drawing board; a combination jet fighter and Formula One racer.
But it didn't actually work.
In contrast, the new Sequel fuel cell concept car GM rolled out this month at the 2005 show is -- or more accurately, will be -- again in Borroni-Bird's words, a "real car".
And how 'real' is a car powered by fuel cells, 10,000 psi storage tanks and drive-by-wire technology housed in a foot-thick "skateboard"?
That's what I was about to find out as I spoke, one-on-one, with the imaginative and engaging director of GM's Design and Technology Fusion Center.
The last time we spoke was just days after the premier of the Autonomy, a truly ground-breaking concept in automotive design where all the drive system and controls are located in a "skateboard" chassis, leaving the rest of the cabin completely free for whatever purpose designers wish to give it. So, my first question to Borroni-Bird was what has he learned since the debut of the Autonomy?
He began by describing how the concepts featured in the Autonomy were initially expressed in the Hy-Wire, a drivable version of fuel cell skateboard idea built largely, as he put it, with "off-the-shelf" components. It was this vehicle that GM has showcased around the globe over the past two years, even though it was limited to a top speed of 40 miles per hour and lacked many of the components envisioned by the Autonomy, such as all-wheel electric hub motors.
"It was very much a 'Let's take whatever's on the shelf and been proven to a certain level and combine it' ", he told me.
"When we started talking about the Sequel when the Hy-Wire was finishing, we did two things that were different, we drove significant performance improvements into the vehicle versus the Hy-Wire. So, it is a far-more capable vehicle. We call it a 'real vehicle'.
"Secondly, it's far more advanced technologically. We're not just using 'off-the-shelf' technology. Technology is being developed in parallel with the program; so this vehicle will have the latest and greatest technology, which will enable the vehicle to have far superior performance to any fuel cell vehicle developed. And more to the point, it will be the first fuel cell vehicle that will be truly competitive with a regular gasoline engine vehicle."
Borroni-Bird's team developed the innovative "skateboard" platform as an extension of the capabilities uniquely offered by fuel cell drive systems. As fuel cell stacks grew increasingly smaller and more powerful, they could be packaged into ever-smaller volumes of space. This lead to them be tucked under the cabin section of SUVs like the Toyota Highlander and DaimlerChrysler NECAR/FCell demonstration vehicles. The introduction of "x-wire" technology similar to the "fly-by-wire" systems found in modern jet aircraft made it possible to eliminate all mechanical linkage between the cabin and the drive system, as well as the control system. Steering, braking and acceleration could now all be handled by wires, instead of hydraulic lines, cables and steel linkage. The fusion of these two systems led to the breakthrough concept of putting all the drive system, fueling system and controls into a narrow wedge on top of which any body style you could imagine could be mounted or dismounted at whim.
Besides all of its other promising attributes, Borroni-Bird's skateboard all offers significant handling advances including lowering the center of gravity of the vehicle and making possible nearly perfect 50/50 weight distribution.
"There are some fundamental benefits to the vehicle from this architecture; and it also allows for a lot more design freedom," he said, adding that there are three things the Sequel and its successors will provide.
"We're really taking advantage of the fuel cell to produce three things. One is provide an environmentally better vehicle, which is always the case with a fuel cell. But more than that, it's really designing the vehicle around the fuel cell to provide additional design freedom, so the vehicle looks nicer, and styling sells. The third benefit is the electricity the fuel cell provides, we're taking full advantage of that to electrify the system to provide much better ride and handling and stability than is normally the case.
"So this vehicle will not only be a zero-emission vehicle, like any other hydrogen fuel cell vehicle, but because we have a skateboard, we're able to package a lot more hydrogen storage into the vehicle to get 300 miles range. And we've allow ourselves the opportunity to electrify chassis systems with all of the hardware that it currently requires in terms of redundancy in braking and steering. The package flexibility is a tremendous benefit with the skateboard. It allows us to pack a lot more hardware into the vehicle, which from a customer stand-point means the vehicle performs a lot better."
H2 Storage No Mean Feat
In order to get 300 miles range, GM's team turned to its partner Quantum for a trio of 10,000 psi storage tanks. Borroni-Bird pointed out to me that eight kilograms of hydrogen is double the amount available in any other fuel cell vehicle, including GM's. The Hy-Wire's three tanks held only 2 kg at 5,000 psi.
As the above see-thru illustration shows, the Sequel's three carbon fiber-wound tanks are place longitudinally in the skateboard, as opposed to the initial vision of the Autonomy, which had them originally placed perpendicular to the axis of the chassis. This enabled the Sequel team to use longer tanks with greater volume, as well. Borroni-Bird noted that there is also a safety benefit in placing the tanks in the center of the vehicle away from the primary crash zones, although because of the place of the center tank, there will be noticeable hump down the centerline of the skateboard.
Borroni-Bird sees 10,000 psi tanks as a necessary interim step in the development of a practical hydrogen fuel cell car and he, like everyone else, is hoping for a storage breakthrough that will eliminate the need for bulky, high pressure tanks. Towards this end, he told EV World that GM has research efforts going on around the globe to come up with a solution, though he hesitated to say which technology he thought showed the most promise.
2010 Target Date
Now that fuel cells have proven that they can be packaged into a competitive vehicle, at least in terms of consumer performance expectations, I asked Borroni-Bird if he was satisfied with the progress being made in fuel cell cost reduction and improved durability or reliability.
He replied that GM continues to adhere to its goal of manufacturing an affordable, durable fuel cell stack by 2010.
"Cost and durability are the two main areas of development now," he told me. "We set ourselves the target that by 2010, we expect the fuel cell to be affordable and durable. And if that's the case, when you combine it with a vehicle like the Sequel, which has compelling benefits for the drive with no compromises or trade-offs, we think that yes, you can build a real strong business case for production. You need both. You need it to be affordable, but you also need it to be acceptable to the customer. It can't just be a limited range, limited performance vehicle that's affordable, because that won't sell in large numbers.
"We could really, effectively have a 300 mile range, zero emission vehicle that holds five people, has lots of trunk space, great ride and handling, great noise (reduction), a lot of storage in the instrument panel that currently is not available, great thermal and HVAC performance, very good stability,excellent launch because of the wheel motors, faster stopping distance because of the the brake-by-wire, speed sensitive steering... I could go on and on. The benefits that this vehicle has will really make it compelling vehicle for the general public, and there is not outstanding compromise that anybody has to have to drive this vehicle."
A Whopping 65 KW Disappointment
One of the surprises I found in the specs of the Sequel was the description of a whopping 65 kilowatts worth of lithium ion battery packs. Visions of a 50-mile range, grid-rechargeable fuel cell "plug-in" hybrid suddenly began to dance in my head. That 65kW pack is nearly triple that of the original, two-place battery electric GM EV1 of the late 1990s.
But Borroni-Bird cut short my revelry by pointing out that this is 65kW of power not energy. Where the batteries for an all-electric car like the EV1 were formulated with "energy" storage in mind, hybrids and fuel cells need packs that are built to handle "power". The difference is how the battery chemically handles the flow of electrons. An "energy" battery slowly, steadily allows the electrons to flow, while a "power" battery can be rapidly charged and discharged, essentially for improved acceleration and to accept huge amounts of power when the vehicle goes into regenerative braking mode.
This is why the Sequel has 65kW of Saft lithium ion batteries. It's to give the car sub-ten second acceleration, where most other fuel cell prototypes are in the 14-to-15 second zero-to-sixty acceleration range. Borroni-Bird commented that his team is also looking at ultracapacitors to accomplish the same purpose, as well as a third, unidentified technology (flywheel or hydraulic hybrid-assist?). Ultracaps can accept huge voltage spikes and discharges over tens of thousands of cycles, making them ideal for this particular application.
Over time, he believes a combination of increased fuel cell power output and kinetic energy storage, will enable GM to reduce the size and therefore cost of the fuel cell, as well as that of the kinetic energy storage system, be it battery, ultracapacitor or something else entirely.
Hub Motor "Baby Steps"
The original Autonomy concept vehicle envisioned all four wheels of the skateboard being driven by electric wheel or hub motors. This has the primary advantage of freeing up even more space in the skateboard, along with other promised benefits like improved traction control, braking, etc. (See also "Wavecrest's Electric Pacemaker).
The Hy-Wire had to make due with a single electric motor mounted in the front of the skateboard driving a pair of half-shafts.
When it's completed at the end of 2005, the Sequel will take what Borroni-Bird calls a "baby step' towards realizing GM's vision by using two 25kW Italian-made wheel motors to drive the rear wheels, while the front wheels are driven by the same half-shaft E-motor arrangement found in the Hy-Wire. As he pointed out to me, the size of the fuel cell stack is really limited by the amount of power the electric motors can actually accept.
"Rather than putting all four wheel motors on like the Autonomy vision, we decide to take a baby step, which was to put the wheel motors on the rear. It would be challenge putting them on all four wheels. We still get the experience and learnings (sic) from the wheel motors to help push the technology along and to promote the technology development, but we're not risking too much in terms of the total vehicle performance at this point."
The wheel motors that will help propel the Sequel are built by Lucchi R. Elettromeccanica Srl, in Rimini, Italy, with the controls and integration done by GM's Advanced Technology Center in Torrance, California.
The challenge of using hub motors on any motor vehicle is how to manage the control and stability issues that immediately arise when placing relatively large masses like electric motors on the "unsprung" part of the wheel, where springs and/or shock absorbers can't do their job to dampen vibrations and bounces. This isn't all that critical a problem with small motors and limited speeds, but it can be a real headache when trying to power a hydrogen fuel cell crossover sport 'Ute at 80 mph.
"We certainly recognize that [unsprung mass] is a challenge," he acknowledged, "and that is one reason why we just wanted to put them on the rear wheels where we think the unsprung mass is less of an issue than on the front wheels.
"We also feel that with the wheel motors we have, we don't expect it to be a show-stopper in terms of unsprung mass. Clearly, it's not desirable to have unsprung mass and what we can do to minimize that going forward will be to specify the wheel motors to be optimized for the particular vehicle, and also to have improvements in the material. So, I would say for the Sequel, we expect the wheel motors to be acceptable, not ideal, but acceptable; and we think that going forward, they will become much better".
He added the caveat that the wheel motors on the Sequel were not designed specifically for it. He explained that you need much more than the 25kW the current Italian motors were designed for for high speed acceleration on the freeway, but that 25kW is much more than is needed for just tooling around the subdivision. Here you typically only need 5-10kW of power.
The ideal wheel motor in Borroni-Bird's view is one that can handle both of these situations, but so far that goal has eluded everyone involved in hub motor research.
"I think the main challenge will come down to cost," he stated. "Having two motors and two controllers is inherently more expensive than one electric motor and one control, which is also probably much more expensive than a conventional, mechanical all-wheel drive system."
So why bother with hub motors at all, was my next question?
"It does provide some packaging benefits having wheel motors," he responded, adding that they might also find application in a conventional hybrid-electric vehicle. But as he conceded and as the Hy-Wire demonstrated, the success of the skateboard concept does not rest on solving the unsprung mass problem. Certainly, inboard electric motors would take up more room in the skateboard chassis, impacting, for example the amount of hydrogen that could be stored and thus influencing range, but they would insure that the program continues to move forward.
Drive-By-Wire In Retrograde
One of the less noticed, but very important changes introduced in the Sequel is the return of the steering wheel and foot pedals. Where the Hy-Wire showed that it was possible to operate the vehicle without them, using just hand controls, practical experience over the last two years, has shown that dividing vehicle control tasks between hands and feet has very real value, especially after Alan Alda nearly dinged the Hy-Wire during the filming of his Scientific America Frontier's episode in 2003.
"We decided that the steering wheels and foot pedals have a lot going for them in terms of... obviously people are use to them. Even if they weren't used to them, the idea of splitting up the work load between the feet and the hands has merit, because you don't want to overload the hands with doing too many tasks," Borroni-Bird confided, adding that the Hy-Wire system has obvious advantages for the disabled.
"So, we decided to that to make this vehicle look truly relevant and credible, let's use a conventional steering wheel and foot pedals, but still operate them by-wire, which means that when you turn the steering wheel or press the brake or accelerator pedal, there are electrical signals going to the wheels and those signals are far faster than the conventional hydraulic or mechanical signal."
This translates into shorter stopping distances. Borroni-Bird estimates that a panic stop from 60 mph will let the Sequel stop from one to two car lengths less than a conventional vehicle using hydraulic brakes.
The combination of light-speed drive-by-wire and electric motors means that the car not only accelerates faster, it feels like it as well, he explained.
I asked if he was concerned about the safety of operating at 10,000 psi and what precautions, if any, were GM engineers taking when working at that level. He first noted that the new, longer, wider tanks give the vehicle four times the amount of hydrogen that was available in the Hy-Wire and five times the range.
"We have to be very careful and take a lot of precautions," he stated, adding the proviso that while this is a technology demonstrator and not a vehicle destined for production, people will be driving it.
"We take a lot of precautions, not just with the hydrogen storage system, but with the by-wire system and overall vehicle safety.
"This vehicle is meant to be driven at high-speed and not limited to 40 miles per hour like the Hy-Wire was. So, yes, we take a very strong look at the safety and we think we're addressing it in three ways. One is the location of the tanks makes for a very safe design. Secondly, the tanks themselves are extremely strong. These carbon fiber tanks have half-an-inch to three-quarters-of-an-inch thick walls. These tanks are tested to a safety factor of at least two or three. So, if they are rated at 10,000 psi, they've been tested to withstand 20,000 psi or higher. So, they are very strong tanks. It takes a lot more to damage one of these tanks than it would a gasoline tank.
"The third element is the hydrogen fuel itself. What if it did escape? Well, we believe that hydrogen, like any fuel, has to be treated with a lot of care and attention, but we don't feel its a more dangerous fuel than gasoline. It's different. It has different characteristics than gasoline. In many respects, it's a safer fuel than gasoline.
"My concern is primarily the cost of the tanks; and that if we really want this system affordable by 2010, we can't just look at the fuel cell costs; we have to look at the hydrogen storage costs as well. That's one reason why we're looking at alternative forms of hydrogen storage".
Surprisingly, Borroni-Bird estimates that it will take five minutes or less to refuel the Sequel. While this places refueling time within the same time,frame as a gasoline vehicle, one problem that consumers might not expect is the high temperature created when hydrogen is compressed to 10,000 psi. The gas has to be cooled as the vehicle is refueling, a task that is accomplished by the refueling unit itself and not on board the Sequel.
300 Mile Milestone
For Borroni-Bird, the single biggest achievement of the Sequel program is reaching the 300 mile range target in a "credible", five-passenger motor vehicle, as opposed to a super-light weight solar-type car carrying a single driver.
"I am not aware of any vehicle that has been able to demonstrate 300 miles range, zero emissions before, because I think battery technology has never allowed that to be the case. And even [with] a hydrogen fuel cell in a conventional vehicle architecture, you're limited by the amount of hydrogen storage you can carry on board the vehicle.
"I believe this vehicle is unprecedented in being able to do it and we plan to demonstrate that... Our mission is we want this vehicle to be a safe drive, first and foremost, and then we also want to be able to convince people that we truly have built a vehicle that is as good as we say it is."