October
5, 1998 Design News
ANNUAL AUTO ISSUE
Body Stiffness
Alero 'stiffs' imports
At 25-Hz resonance frequency--along
with European luxury-car ride and handling--the new
Olds will give imports a run for their money
Charles J. Murray, Senior Regional
Editor
Four years ago, GM's Oldsmobile division was fighting
for its life. Five of its models--the 88, 98, Ciera,
Achieva, and Cutlass Supreme--were running out of gas.
All would eventually be slated for extinction. Worse,
within GM, Oldsmobile was seen as a parasite--a division
that siphoned off sales, not from competitors, but from
other GM divisions.
That gloom may soon be history. The cause for hope:
the new Alero, a mid-size import buster hitting showrooms
now. Olds executives are betting it will reverse their
fortunes and bring in a new class of buyers for the
division.
Change the target. The Alero is the
product of Oldsmobile's soul searching on what its target
market should be. In 1995, the division made a radical
move: Instead of battling Pontiac or Buick for customers,
the division would compete directly against imports.
"When you have Buick and Oldsmobile appealing to
the same customer, and that customer is in a segment
that's shrinking, it makes no sense," says General
Manager Darwin Clark. "It made more sense for Oldsmobile
to look for a market that was continuing to grow."
The import market, however, would be no easy conquest,
and they knew it. Many import buyers were unhappy former
GM customers. Worse, the vehicles they'd turned to,
such as the Toyota Camry and Honda Accord, were world-class
cars.
The Alero was one of the first projects to get the
green light after this change in strategy. Oldsmobile
began by researching import vehicles and their customers.
They learned what import buyers liked, then they benchmarked
such features as leg room, head room, instrument-panel
configuration, entrance, egress, ride, and handling.
"We were amazed how articulate and knowledgeable
import buyers are," says Kip Wasenko, chief designer
of the Alero. "They may tell you that their car
is for transportation, but they have tremendous knowledge
of the market segments."
Wasenko, who was tapped by Oldsmobile for his experience
as chief designer on the import-busting Saturns, already
understood the look that appealed to import buyers.
To those buyers, he says, fit and finish are critical.
They also like refined, understated, uncluttered designs.
"What we kept hearing was, 'Less is more,'"
he recalls. "Import buyers don't like cladding
or add-ons. They want the body sides to be very clean."
After taking Oldsmobile's assignment to design a "small
mid-size" vehicle, Wasenko began a design odyssey
that took him through 22 different themes, varying from
very conservative to very expressive. At first, the
designs were air-brush paintings, then scale models,
then full-size clay versions. With each successive design,
he honed in on the look that Oldsmobile's prospective
customers wanted.
Body stiffness. As Wasenko closed
in on the exterior and interior designs, engineers at
General Motors Technical Center in Warren, MI, began
the task of meeting the body, ride, and handling criteria.
From the outset, the team decided that the new car
would need world-class ride and handling. That meant
that the new vehicle's body would need to be stiff--much
stiffer than preceding GM vehicles. "Within GM,
the realization has been growing that body stiffness
is very important," says Mike Danek, chief engineer
for the Alero program. "Stiffness is the basis
for a great car. There are some aspects you can do without,
but stiffness is not one of them."
The reason for the new premium on stiffness is simple.
Without it, the vehicle's body bends. As it does, it
absorbs the impact from bumps and hard stops. As a result,
the suspension isn't permitted to do its job. And for
good ride and handling, the suspension--not the body--should
absorb impact. When it doesn't, ride and handling are
compromised. "Ideally, you want a good balance
between ride, handling, and steering," Danek says.
"You want responsive handling, but you don't want
a punishing ride."
To achieve that, engineers modeled the vehicle on computers.
Their goal: a body with a resonant frequency of 23 Hz
in bending.
The 23-Hz frequency was a daunting goal. Many vehicles
on the road today are closer to 18 Hz in longitudinal
bending, say team engineers. Some of the best European
luxury sedans hover around 22 Hz. "It seemed like
an aggressive goal at the time," says Gene Stefanyshyn,
GM vehicle line executive in charge of the Alero. "The
old Pontiac Grand Am was only about 19 Hz."
Still, GM engineers believed they couldn't achieve
the ride and handling they wanted without that bending
frequency, so they moved ahead. To accomplish it, they
employed a plan of integrated structural design, which
had only been used a handful of times prior to the Alero
program. In the integrated approach, a structural systems
manager acts as a director, or traffic cop, for the
rest of the design team. Engineers configuring the engine
cradle, suspension, exhaust system, or any of a hundred
other items all report to the structural systems manager.
That way, he can ensure that the original design specifications--including
stiffness--aren't lost in the process.
To meet the program's goals, Structural Systems Manager
Jim Blenman worked with team members to optimize placement
of mass. Using finite element analysis, he stiffened
the area around the vehicle's A pillars and rockers.
To enhance torsional rigidity, he and other team members
placed a cross-car beam between the rockers, behind
the rear pass-through area. They also placed additional
reinforcement beneath the so-called rear kick-up area
(where backseat riders put their feet), thus adding
even more torsional rigidity.
Using such techniques, the team ended up exceeding
its 23-Hz goal, ultimately reaching 25 Hz. Danek credits
the integrated structural design approach for enabling
them to achieve it. "With this method, you don't
have people working independently, not knowing what
the team's goals are," he says. "You have
one person who leads the whole organization, and body
structure is very important to him."
World-class handling. Stiffness, however,
was only one major focus of the program. The others--steering
and suspension--were critical if the Alero was to meet
its ride and handling goals.
From the beginning, the Alero brand team had said that
it wanted to reach a balance between low effort in tight
corners and proper feel at higher speeds. "The
people who planned the program felt that it was important
to give a solid, steady feel on the highway and agility
around town," Danek says.
Accomplishing that meant the team would need to employ
a speed-sensitive variable-effort steering system. Borrowing
from a patented system employed on earlier Cadillacs,
they designed a unit that would provide a nimble feel
without transmitting a lot of road harshness. They achieved
their goal by using a pre-load that let them tailor
the steering for so-called on-center feel. During higher-speed
operation, the pre-load valve provides a force that
must be overcome before the system provides additional
boost. That way, the design ensures that the larger
boosts are reserved for lower-speed, high-turning-effort
situations.
Engineers also designed the steering rack to provide
more isolation from road surfaces. To do that, they
mounted the rack to the vehicle's cradle instead of
its front dash surface to reduce the direct path that
disturbances can travel. Result: less noise and vibration.
To further enhance ride and handling, they also gave
the car a fully independent rear suspension. Partnering
with GM's Delphi Chassis Div., engineers employed a
"tri-link" independent rear suspension normally
used in higher-priced automobiles. The critical advantage
of the system is that it isolates bumps on one side
of the vehicle from the other side, especially during
turning. By using the tri-link, they eliminated potential
handling disturbances. "For a car that is supposed
to offer great ride and handling, independent rear suspension
is too important to pass up," Danek says. "It's
basic to the function of the vehicle."
Equally basic in the minds of Alero's design team was
a feature that too many compacts pass up: good seating.
For Alero, Oldsmobile employed a seating team composed
of 15 people of different heights, weights, and ages.
The team, determined to match the seating to the vehicle's
structure, "re-tuned" the seats every time
the suspension was changed. That meant softening or
stiffening the springs and foam, altering the mounting
techniques, and changing such things as the lumbar supports.
To maintain seating integrity, executives and designers
from outside the team were discouraged from making detailed
inputs. That way, the team could maintain a coherent
seat design without worrying that their effort would
be compromised by an inconsistent idea. Their "team
rule" served as a sharp contrast to years past,
when god-like executives and designers could change
major features on a whim. "People were invited
to offer their ideas," Danek says. "But if
they wanted to make any serious changes, they had to
join the team and go on the rides."
Winning customers. With the car now
arriving in showrooms, Oldsmobile executives know they
face a daunting challenge. Alero must go head to head
against the likes of the Honda Accord, Mitsubishi Eclipse,
Nissan Altima, Toyota Camry, and other successful imports.
The vehicle's features, however, should make it competitive.
Also helping make the Alero competitive is its relatively
low cost, achieved in part by sharing its architecture
with Pontiac's Grand Am. Unlike so many past efforts
in which GM employed a common architecture, however,
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