Detroit--How do you improve on the nation's best-selling car? And even if you could, why would you want to? "It was time for a big step forward," says Keith McGee, vice president at Ford and general manager of Lincoln-Mercury. Thus began the redesign of the Ford Taurus.
The top-selling midsize for three years running, Taurus has a faithful following among car buyers. A Design News survey shows that engineers chose the Taurus as "the car I would buy today" for the tenth consecutive year, and ranked it as the "best-engineered American car" for the fourth year in a row. But the popularity of the vehicle had Ford engineers dreaming of the chance to improve on a good thing.
A ground-up redesign might look like double-jeopardy to the casual observer, but Ford didn't leave the direction of design changes to chance. "Our plan called for two sessions of market research," remembers Dick Landgraff, Ford's large-front-wheel-drive segment director. "We did four iterations of our clay models before we were convinced that we had the designs right."
Saws and supercomputers. Stiffness was the hallmark of the redesign. Body stiffness contributes to crash-worthiness, responsive handling, and noise control. Engine stiffness boosts efficiency and cuts vibration. And the '96 Taurus' stiffness--a whopping 87% improvement in torsional rigidity over the previous model--is evident in its every move.
The challenge for engineers was to stiffen the chassis without adding weight. To boot, Ford decided to do an integrated launch--that is, keep building the old model while changing to new production tools. The tooling restriction meant engineers were limited in where they could locate welds.
The stiffness quest began with extensive body-torsion analyses of the original Taurus and competitive vehicles. Engineers hunted vibration and body flex with a vengeance. In fact, they disassembled 14 competitive vehicles in search of ideal joints. "We went in with saws and torches and removed every one of the joints we thought was critical to making a good car," explains engineer Andy Benedict, who headed the body-structure development team.
After mounting and restraining each joint in three directions, engineers load-tested them and gathered deflection data. The information helped the team create targets for the CAE analysis that would direct the design of the new body. "That way, we could take the best properties of every joint from every car we tested and could build a car from those data," says Benedict.
Engineers in the Advanced Vehicle Engineering group designed CAE experiments and identified more than 100 noise, vibration, and harshness (NVH) items on the original design that could be improved. Using joint and section data gathered by the Body group, they created an optimized 2,000-finite-element model that would lay the groundwork for the redesign. In its final configuration, the model would have some 40,000 elements.
"In effect, we were working from the critical joints outward to other critical joints," recalls body-team member Ed Kuczera. The most critical joint in the project was the rear-suspension attachment to the underbody--a potential source of rear-seat noise and an unpleasant resonance engineers call "body boom."
To their displeasure, engineers discovered that the initial model's suspension bushing stiffness rate was the same as the body stiffness rate. "The sheet metal is supposed to be five times the rate of the suspension bushings, as a rule of thumb," says Kuczera. The group's charter: increase torsional stiffness in that area--without a lot of new tooling or weight.
With the help of in-house software and two Cray supercomputers, engineers studied material thickness, weld location, and cross-sectional shape. "The strategy allowed us to get the stiffness and improvements in structure without just adding on a lot of pieces," recalls chief designer George Bell. At one point, one of the Crays crunched numbers for 12 consecutive hours. When it was done, it had pulled 17 pounds of sheet metal out of the car without diminishing strength, rigidity, or safety.
Of course, the computer didn't do any of the design innovation. When all was said and done, engineers had completely redesigned the body shell, and had redone the rear cross-section where it bolts to the rear suspension, adding a cross-member in the underbody for strength. They also came up with new beading techniques in the floor pans and other major panels to improve their performance, says body structure engineer Steve Kozak. The team wasn't surprised to find that stiffness contributed to safety. "In almost all cases, if you target the NVH performance, the crash performance comes along almost for free," observes Kozak. Adding a small door bracket put the car beyond 1997 side-impact standards.
The Taurus uses a four-speed automatic transaxle, modified for non-synchronous shifting. The non-synchronous feature allows independent movement of two gear sets at a time, and smooths torque demand and coasting downshifts, say engineers. A fifth-generation engine controller, Ford's EEC-V, boasts 112 kbytes of memory--twice that of the previous module.
Beefed-up brakes, optional ABS, and, you guessed it: a stiffer suspension contribute to improved handling. Veteran racer Jackie Stuart describes the '96 Taurus as "very sure-footed."
The car has 28% more glass and a 10% lower drag coefficient than the outgoing model, putting it at "best in segment," claims Ford. To hush wind noise, Ford tested several car shapes at half-scale in a Lockheed wind tunnel at 110 mph. Engineers opted for a triple-sealed inset-door design, despite the inherent manufacturing challenge of a smooth fit on all four sides. "The previous Taurus door had a couple of overlap surfaces," says Bell. "That door is more forgiving in assembly, but you've got a margin out in the airstream."
To measure interior noise, engineers used the "Aachen Head," a mannequin-like simulation tool with microphones where the ears would be. Engineers eliminated noise in the frequency range that's important for speech intelligibility, among other targets. The result? Vastly improved back-seat sound conditions, say engineers. "Compare it with any car in the segment," boasts Bell. "We'll take on the competition on a number of fronts, and this is one of 'em."
New engine offerings. Of course, a rattle-and-squeak-free body and low wind noise don't do much good if the engine roars. In the pursuit of stiffness, engineers refined the Vulcan engine that will power the majority of new Tauruses. Like the body structure, this 3.0-l V6 went through FEA to strengthen the block by redistributing weight. Engineers added thickness to the block walls and main bearing areas, and removed material where it didn't contribute to strength. They also got rid of unused bosses from the block's exterior and altered the casting process to simplify manufacturing.
The engine team made a collection of modifications aimed at quiet, durable, efficient operation. For example, the steel camshaft is hollow to save weight, as are the intake valves. Lightweight valve springs and retainers reduce engine noise at high rpms. Roller-tipped camshaft followers reduce friction, as do cast-aluminum pistons with an exaggerated barrel shape. These changes also contribute to a 10-20% reduction in hydrocarbon emissions, say engineers. Likewise, new low-tension piston rings and tighter-sealing valve-stem seals boost oil economy.
The top-of-the-line Taurus LX offers a new engine option: The 3.0-l 24-valve V6 Duratec. Based on the DOHC V6 in the Contour and Mystique, the new engine uses wider intake and exhaust valves and a slightly wider cylinder bore to deliver 200 hp at 5,750 rpm. Like its 2.5-l predecessor, this engine boasts a 100,000-mile maintenance interval and uses a reinforced aluminum block and structural aluminum oil pan.
To fit it to the engine bay, engineers moved the water pump from the rear to the front of the engine--so that all engine-driven accessories are at one end--and added a bearing to the accessory-drive pulley to counteract crankshaft bending loads. The engine's high-silicon molybdenum cast-iron exhaust manifolds heat up promptly upon engine start-up. This feature trims emissions during cold operation, and allowed engineers to leave out light-off catalytic converters.
Innovative molding. Even if Taurus owners never peek under the hood, some design changes will be readily apparent. If ever there was a kinder, gentler dashboard, this is it. The integrated control panel (ICP), like just about everything else on the Taurus, is elliptical ˆ la the Ford logo.
Inspired by sophisticated consumer electronics, Ford engineers created an ambitious prototype ICP. "We brought suppliers in very early on," recalls design engineer Mark Jarvis. "If we hadn't, we might have had to back off on the design." In its final configuration, the ICP called for a team effort on the part of film, resin, and mold suppliers. "When we saw the styling themes, we were very concerned," recalls ICP module supervisor John Germaine. "Given the radical surfaces, we didn't know if we would have a decorating process to provide the appearance."
To get sharp graphics and incorporate several colors in the display without raised "witness lines" and surface defects typical of painted or laser-etched parts, engineers turned to a technique called in-mold decorating.
The process starts with a very thin sheet of polyester film supplied by Nissha Printing Co., Kyoto, Japan, that's coated with 12 layers of ink. The film is registered with respect to the mold, then warmed and vacuum-drawn into the mold cavity. The heat and pressure of injection-molding the module's polycarbonate substrate causes the inks to transfer to the part.
With the help of Southern Plastics Molding, Anaheim, CA, and Parametric Technology's Pro/ENGINEER 3D solid-modeling software, engineers created a textured tool for the ICP. The mold's carefully textured finish creates adjacent clear lens surfaces and opaque bezel in one shot, says design engineer Tom Jean. "In-mold decorating allowed us to have a one-piece assembly with a vacuum-fluorescent display built right in, rather than a separate display lens--a first," comments Jarvis. To illuminate the display, engineers chose electro-luminescent lighting for its even, cool illumination and ability to withstand the temperature and humidity extremes typical of car interiors.
To thwart thieves and conserve space in the high-demand area near the driver, engineers relocated some components of the climate controls and audio equipment. The ICP houses the tape-deck and display electronics. The radio tuner and amplifier are mounted in the trunk of the sedan and in the side-panel of the wagon. A new audio communications protocol communicates through a multiplex wiring network to link the systems.
Concurrent engineering. Ford credits the platform's 38-month development program to a dedicated, co-located team of design and manufacturing engineers. "We had manufacturing with us every step of the way. Every day, all day long," says Bell. "It just doesn't work any other way."
Some changes involved building sub-assemblies outside of the main plants in Chicago and Atlanta. For example, Ford used to build seats on the main assembly line, but found that the amount of storage and floor space needed was "enormous," says Bell. Now, supplier Lear Seating Corp., Detroit, MI, builds seats in adjacent factories, using the same build-order as the main factories. Likewise, modular front cooling components such as the radiator, hoses, and coolers for transmission and power steering are supplied by Toledo Molding and Die Corp., Toledo, to Ford pre-assembled.
"Modular assembly gives us access to connections that we wouldn't have on the line," says Bell. Rather than require extra design, the technique accommodates more automation and favors quality control, he adds.
Future releases. Ford plans to release a Taurus and Sable wagon, as well as the super-high-output "SHO" Taurus for '96. The company is exploring aluminum, composites, and magnesium for future Taurus components, says James Donaldson, vice president of the Large Front-Wheel-Drive Vehicle Center, "but we'll walk before we run on these material changes."
The company isn't saying how much the new platform cost, but the '96 Taurus GL will start at $19,390--only about 6% more than the previous model.
This Taurus is not fuel-finicky
Two flexible-fuel (FFV) Taurus models for '96 operate on unleaded gas and ethanol or methanol, respectively. Both engines are based on the Vulcan V6, and both use a sensor to detect the percentage of alcohol in the fuel and adjust flow and spark timing accordingly. To manage the corrosive nature of alcohols, all components in the FFVs that come in contact with fuel are stainless steel or nylon.
Wear problems make material selection especially critical in flexible-fuel vehicles. By volume, flexible-fuel engines use more fuel, so more lubricant is washed away from the cylinder bores and valve guides. Therefore, the Taurus FFV engine block is made from a tailored cast iron, and piston rings feature steel tops and a hard-particle chrome coating on wear surfaces.
At high speeds and high loads, alcohol fuels are prone to pre-ignition. "Uncontrolled combustion or pre-ignition can destroy an engine and do it silently and without warning," cautions Taurus FFV design engineer Rob Seiter. "We got down to some basic combustion research using a piston with fiber-optic windows to show us the combustion cycle."
Engineers found four or five sites that were occasionally pre-igniting, including the spark plug. To correct the situation, they changed the shape and contour of the combustion chamber, which altered the compression ratio. They also changed the angle of the spark plug and created larger water jackets around it to carry away heat. The methanol Taurus meets California low-emission vehicle (LEV) requirements.