FBIS3-40368
"jpest004___94035"
JPRS-EST-94-004
Document Type:JPRS
Document Title:Science & Technology
Europe/International
4 February 1994
WEST EUROPE
AUTOMOTIVE INDUSTRY
France: Renault Tests Active Suspension Prototype
94WS0094A Paris INDUSTRIES ET TECHNIQUES in French 8 Oct 93
p 35
94WS0094A
Paris INDUSTRIES ET TECHNIQUES
Language: French
Article Type:CSO
[Article by Thierry Mahe: "Renault's Laboratory On Wheels,
Pasha"; first paragraph is INDUSTRIES ET TECHNIQUES introduction]
[Text] Engineers at the Aubevoye test center in Eure are
validating active suspension technology by mounting each wheel
on a computer-controlled hydraulic jack.
There are no highway signs to guide you to Renault's test
center in Aubevoye (Eure), where the manufacturer guards its
secrets carefully behind high hedges. The center is where
Renault tests the road handling of its prototypes. It also
validates there--with the agreement of the Rueil research
center--the new "skid resistance" technologies (suspension,
steering, braking, etc.) that will be standard on mass-produced
cars within 10 years. The suspension system of the Safrane (AMV)
passed its final examination at Aubevoye. The center will also
produce Renault's first "real" active suspension system. Nicolas
Varlot, the head of test systems development, explains.
"Renault's Safrane or Citroen's Xantia do not, strictly
speaking, have active suspension systems. Their shock absorbers
have simply been altered, without any addition of energy.
Outside of the Formula 1, the only example of active suspension
is Nissan's Infinity." Aubevoye has some strange-looking mutants
on its roads, including an R25 with an oddly upswept front hood
and a license plate that reads "Pasha", for "Active Hydraulic
Suspension Automobile Prototype." Each of Pasha's wheels has a
computer-driven hydraulic jack, and its rear trunk contains a
powerful (32 Mips) computer and an array of electronic boards.
Under the vehicle's front hood snakes a mass of hydraulic
circuits, and each suspension jack features three sensors to
monitor distance traveled, speed, and effort. Computations
consume a total of 32 input parameters. Pasha is a real
laboratory on wheels, designed to simulate all types of
suspension. Its has a steering counterpart, called Dirac. Says
Nicolas Varlot, "We have been testing Pasha since the beginning
of the year. By mid-1994, we will have worked up a
specifications sheet, and by late 1994, we will have preliminary
vehicles." Safrane's replacement may sport an active suspension
system...
Two parameters can be used to synthesize suspension
behavior:
wheel wobble, a safety factor; and autobody cycling, which is
linked to comfort (cycling = the oscillations to which the body
is subjected). Pasha can modulate these two parameters over a
very broad range. Depending on adjustments, passengers can feel
they are riding in a 2 hp, or a luxury limousine! Renault
engineers are experimenting with 16 types of servocontrol, one
of which will be selected as offering the best tradeoff between
comfort and safety. Assessing those two variables still provides
a great deal of food for thought. Francois Hebert, head of the
electronics/data-processing lab, stresses, "With Pasha, we can
even induce a counter-rolling motion. When the vehicle turns, it
leans in the opposite direction to that of most cars! Is this
good? Reducing or reversing rolling motion may be a good idea to
help cars grip the road, but the change skews the perception of
the driver. The same goes for the ABS, which makes people safer
and encourages them to drive faster. It's dangerous, especially
when the driver switches back to a regular model!"
The Aubevoye center is involved in every step of creating a
vehicle, starting from the very basic research level, during the
technology scouting stage. It remains active during the
pre-project phase "before the vehicle even gets to the drawing
board", and again during development of the prototypes. "Our job
is to work up the specifications sheet and check that the
prototype is valid. One of our suppliers (Valeo, Bendix, etc.)
then makes it. In return, we inspect the equipment," says
Nicolas Varlot.
One of the peculiar features of electronic equipment is that
it tends to break down. Annoying when the automatic window
controls are involved, failures are catastrophic if they affect
the steering, braking, or suspension systems! "Hence the
importance of strategies involving graceful degradation, which
occupies between 60 and 80 percent of the computer's memory.
Engineers must, for example, anticipate one of the suspensions
being knocked out--and design the other three to adjust
accordingly!" adds Nicolas Varlot.
Will numerical simulation of vehicle behavior make certain
road tests obsolete? "It's an old question.... We thought
structural computations were going to eliminate crash
studies--but they didn't at all. The more you refine a
simulation, the more new parameters pop up! At best, road
handling simulators will eliminate certain standard tests."
Concludes Varlot, "A problem solved raises other that need
solving. When the ocean recedes, it exposes new shoals!"
Boxed Material: Using Electronics in Testing
Francois Hebert's electronics lab has a staff of six and two
electronics CAD stations that run the Cadence program. Cadence
can be used to design and simulate digital/analog boards. Says
Francois Hebert, "One of the product's great features is its
behavioral simulation module, which enables us to close the
simulation loop." Indeed, the sim module can be used to model a
mechanical device--jack, steering column--governed by linear or
non-linear laws. The laboratory designs between 15 and 20 boards
a year, each of which requires about three months of study. "By
extending the limits of electronic board simulation, we have
reduced the number of touchups per board from 4 or 5 to 1.2 or
1.4. With each touchup costing 30,000 or 40,000 French francs,
CAD quickly pays for itself."
Boxed Material: Two Facilities for Torturing Prototypes
Renault has two facilities for prototype testing. The first,
at Lardy (Essonne), specializes in engines, while the second, in
Aubevoye (Eure), focuses on skid resistance (chassis,
suspension, brake system, etc.) and vehicle dynamics. Aubevoye
was created in 1982 and employs about 300 people. It boasts 21
kilometers of roadways to test speed, road handling, skid
resistance, comfort, and endurance. The test roads recreate
pothole conditions, high-speed national highways, city streets,
and mountain roads. The center has an acoustical bench and a
climate wind tunnel.