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.