Rugged, Yet Refined
"The all-new block for our 5.4-liter TritonTM V-8 is designed to provide the best balance of power, smoothness and quietness. We tested competitive engines side-by-side, and our 5.4 is quieter than any of them. Our powertrain also remains the most durable in the class."
Kevin Layden, powertrain manager
Rugged 2003 Ford Expedition Delivers Refined Power
Refinement was the watchword for the 2003 Expedition's powertrain engineers. The two available V-8 powertrains offer improved dynamic balance for reduced vibration and noise. Still, the engineers kept Expedition true to its mission to be rugged and powerful, with a class-leading tow rating. Powertrain highlights include:
- The 5.4-liter TritonTM V-8 uses an all-new cast iron engine block, with numerous computer-designed refinements to reduce vibration. The result is a modern, single-overhead cam engine that is quietest in its class - and quieter than engines in higher-priced luxury sport utilities.
- Expedition's 4.6-liter uses an all-new cast aluminum engine block which is optimized for weight reduction and NVH improvements.
- Torque curves show that both the 5.4-liter and 4.6-liter TritonTM V-8 engines have more usable power in the form of added torque at low engine speeds. Peak horsepower remains unchanged.
- Hydraulic engine mounts make the engine into a "tuned mass damper" to reduce not only powertrain vibrations, but suspension vibration as well, providing a smooth ride in adverse conditions.
- The Expedition differentials are the most durable in the class. The 4.6-liter engine uses an 8.8 inch rear axle gear, which is larger than the comparable axles in competitive full-size SUVs. The 5.4-liter engine upgrades to a 9.75 inch axle, which is largest in the class - compared with typical 8.6- or 8.8-inch competitors - yet delivers efficiency comparable to smaller differentials.
- The combination of powerful engines and robust axles contribute to Expedition's class-leading tow rating of up to 8,900 pounds.
- The 2003 Expedition is the cleanest-running full-size SUV based on California Cleanest Vehicle methodology and publicly available competitive information.
Balance is the Key
Vibration is the enemy of powertrain refinement, and to combat it, powertrain manager Kevin Layden began by seeking balance.
"We strove to balance every moving part in the drivetrain - the engine, transmission, driveshaft, differential, transfer case - stressing a total system approach," Layden says. "Then we used the engine mass to balance vibrations from the chassis. Finally, we balanced the intake and exhaust systems to tune the precise sound we wanted - the sound of confident power.
In an example of the engineering team's pursuit of driveline balance, the driveshaft is a seamless tube, with yokes at each end that are friction-welded in place. Friction welding, a relatively new technology, produces a weld line that is absolutely consistent throughout. Normal variations in the previous welding process could produce a slight floorpan vibration that the Expedition team found unacceptable for the 2003 model.
The Expedition's 5.4-liter engine block has been redesigned for 2003, with computer-designed ribbing and bracing, along with thicker side skirts and reinforcement at the oil pan flange. This reduces vibration and noise, for more refined performance.
The 5.4-liter TritonTM V-8 engine is by far the most popular powerplant choice for Expedition owners, and the team was determined to make it the best V-8 available in any full-size sport utility. While the main architecture - bore, stroke and overhead cam design - was already a five-time member of Ward's Automotive magazine's "Ten Best Engines" list, Ford's extensive computer engineering capability allowed powertrain engineers to fine-tune the design of the cast iron engine block, sculpting block wall thickness and locating cast-in-place ribs to reduce minute resonant vibrations in the block itself.
Other actions to reduce 'point sources" of noise include stiffening the exhaust manifolds to reduce mechanical noise and complement the exhaust tuning.
The design was optimized for installation into a robust, rigid new hydroformed frame. New hydraulic engine mounts prevent the powertrain from inducing vibrations into the chassis. Instead, the engines play an important role in absorbing chassis vibrations.
Because the engines are different - the 5.4-liter uses a cast-iron block, the 4.6-liter is aluminum - the mounts are optimized for each engine. For example, the 4.6-liter has a hydraulic mount on the left paired with a conventional solid rubber mount on the right. The 5.4-liter, on the other hand, has hydraulic mounts on both sides.
By optimizing these engine mounts, engineers were able to make the engine blocks into tuned mass dampers - the vibration equivalent of "heat sinks," absorbing chassis resonance and improving ride comfort, particularly over rough roadways or uneven highway pavement.
Other innovative solutions contribute to the new Expedition's quiet ride.
For example, the new differential carrier is made of cast aluminum with a machined gasket surface, not the typical stamped steel, and it is ribbed for structural strength and reduced vibration. It serves as a stressed member, mounting the axle assembly to the frame.
The exhaust system is attached to the engine manifold through a flex coupling that decouples it from powertrain vibrations. This transmits 40 percent less side forces to the exhaust hangers, blocking noises and vibrations from entering the passenger compartment through the exhaust system. Hanger locations are computer-optimized at resonance "dead zones," so vibrations aren't transmitted to the cabin.
Select engine heat shields are now made of a new space-age aluminized ceramic material that doesn't make a "tink" sound as it cools after the engine is shut off.
The driveline is oriented to take full advantage of the new chassis architecture. Independent rear suspension allows a more precise driveline angle, which improves interior space by almost eliminating the floor "hump," and reduces flex through the drive components.
The system is aligned within one-half of a degree, to minimize binding and vibration. The alignment is so precise that engineers had to build in one degree of purposeful flex to "exercise" the flex couplings on the drive shaft, keeping them limber in all directions.
Half-shafts are designed with helical splines at the constant-velocity joints, for reduced driveline slack, or free play, compared with straight splines. This design reduces noise and harshness when shifting into gear at rest as the driveline loads up.
Powertrain Tuned for Satisfying Sound
Both the 4.6- and 5.4-liter engines in the 2003 Expedition are tuned to provide linear response - both in acceleration and in audio feedback. Sound increases in direct proportion to the acceleration rate, meeting driver expectations.
In most everyday driving situations, the engines remain unobtrusive, acting confidently and quietly behind the scenes.
But when more power is summoned - such as for quick acceleration up a steep freeway ramp or a gnarly sand hill - the engine provides a confident answer.
Powertrain sound is tuned mainly through the induction system to provide just enough fourth-order resonant frequencies to generate the "sound of power" during acceleration. This sound level rises steadily in both tone and volume until the demand is met.
A touch of two-and-a-half order sounds is tuned in for just a hint of "rumble" in the background that maintains the engine's all-American character. The exhaust system is isolated from powertrain vibration, and is tuned for quiet operation with a second resonator whose location was identified using computer optimization.
Other than the desired resonances, other sounds are tuned out. For example, a new acoustic engine cover helps to eliminate high-frequency valve gear and induction sounds. A new metal-and-plastic laminated oil pan damps mid- and high-frequency vibrations at the bottom of the engine.
Driveline Adds Refinement, Capability
The new Expedition uses a rugged combination of components that have proven their durability both in Ford's renowned test facilities and in the field, and are further refined for 2003.
For example, the Expedition's transmission uses computer logic to provide smooth, quiet operation as well as a tailored response to heavy demands such as towing and off-roading.
The powertrain controller uses a logic circuit to select the gear that is best suited to the particular driving situation, helping to prevent "hunting" between gears. It recognizes the difference between full-throttle acceleration on flat pavement and full-throttle application to maintain speed while towing up a hill.
By predicting whether or not the transmission will be able to "carry" the next gear, this Ford-patented computer logic provides a more sophisticated solution to heavy demands than a simple shift delay switch, such as the one-size-fits-all "towing mode" some competitors use.
"This offers a dynamic response to determine shift points based on actual need," Layden says.
Expedition's 4R70W transmission is rated to handle up to 506 foot-pounds of torque, which provides a large performance cushion beyond the peak torque rating of Expedition's largest available engine.
The Expedition differentials also are the most durable in the class. The 4.6-liter engine uses an 8.8-inch rear axle gear, which is larger than the axle on Chevrolet's 5.3-liter engine.
The 5.4-liter Expedition engine delivers power through a 9.75-inch axle, which is largest in the class - compared with typical 8.6- or 8.8-inch competitors.
This is especially important in towing or off-road applications, such as driving in deep sand. An undersized axle gear can overheat and fail under such conditions, leaving a costly repair and stranded passengers.
With the 5.4-liter engine and two-wheel drive, the 2003 Expedition is rated to tow up to 8,900 pounds, properly equipped. Expedition can tow up to 6,050 pounds on the 4.6-liter V-8 with four-wheel drive.
The rear differential uses a cast iron housing for durability and NVH characteristics. Internally, lash, or clearance between moving parts, has been reduced to lower operating noise. The rear cover is structural aluminum, with cast-in-place ribs that serve to reduce vibration and enhance strength. A structural-foam-filled torque arm extending from the differential to a frame cross-member isolates driveline forces, improves shift feel, and enhances ride quality.
Key features of the engines also have been designed for durability and consistent operation. For example, the pistons are made of a hypereutectic alloy that is lighter than steel, yet expands 15 percent less than aluminum and resists heat transfer for better power and durability.
On both engines, the piston skirts are coated with a Teflon-based friction-reducing material and fitted with low-tension, low oil-consumption rings - and full-floating wrist pins on the 5.4-liter engine - to enhance both fuel economy and engine life.
The piston connecting rods are made of powdered metal and their mating surfaces are "cracked" apart during the production process to ensure a perfect fit when they're bolted together around the rod bearings.
Expedition's cooling system is designed to maintain ideal engine temperature even when subjected to a long 15 percent grade on a 115 degree day. Other tests include hours-long idle at low speeds.
A fail-safe cooling mode provides protection even in the case of a catastrophic coolant loss - such as a punctured radiator. In such a case, the electronic engine controller shuts off fuel to alternate cylinders to reduce the risk of engine damage from overheating. The valves continue to operate, in order to pump cooling air through the cylinders.
Body Boasts New Sound-Deadening Techniques
A new metal-and-plastic laminated material, like that used on the oil pan, is used in the dash panel, sandwiched with yet another metal panel and acoustic sealer. This so-called "dash doubler" design dramatically reduces engine- and road-noise through body panels.
Engineers relied heavily on computers to eliminate road noise sources early in development. Noises were identified by analyzing the vehicle in different configurations and on varying surfaces with CAE tools and laboratory tests. Sound levels were recorded at the tire patches and at the driver's location to simulate how much road noise reaches the driver.
Structural foam (blue areas) stiffens body and reduces NVH.
This testing revealed the new 2003 Expedition achieved best-in-class noise levels with a 4-decibel reduction over current models thanks to early design strategies and the application of various sound-deadening techniques and materials. For example, double seals along the door bottoms were used to reduce road noise.
Undesirable road and engine noises also are filtered by the interior acoustics of the vehicle through damping materials in the trim panels. A new material, called Versamat, was used on the backing of the trim panels because it absorbs high-frequency sounds better and also is lighter weight. The material is used in the door panels, carpet, headliner and cargo trim.
The new Expedition uses the most ambitious application of structural foam in the industry. Expedition's structural foam application, in the upper B-pillars, upper and lower D-pillars and floor pan, was computer optimized to eliminate body structure movement contributing to low-frequency noise and vibration.
In practice, it reduces interior noise across the frequency spectrum - including the key frequencies of human conversation. Unlike other competitive applications, structural foam was an important part of Expedition's design process from the beginning, rather than being applied as a bandage later.
This foam reduced road-induced interior sound by 2 decibels and provided a 42-percent increase in torsional stiffness, which reduces squeaks and rattles while benefiting handling. This lightweight material, injected into sheet metal cavities during assembly, completely fills the void and hardens in place, bonding to the steel. This provides added strength without encroaching on interior space the way structural bracing might.
In addition to strengthening key joints to improve body stiffness for driving dynamics, the structural foam helps adjacent body panels to resist vibration. This application addresses low-frequency "booming" that can be a major component of interior noise. Even subsonic low-frequency pressure waves - below the range of human hearing - can contribute to passenger unease, such as motion sickness.
Reducing Wind Noise
Wind noise also can be a major contributor to unpleasant sounds in the cabin. The passenger cabin is better sealed than before, in a campaign to cut wind noise reaching the occupants. For example, wind noise measured at 80 mph has been reduced from 35 sones to a world-class level of 29 sones.
Decibels Versus Sones
Correlation of NVH metrics to customer perception is always a tricky business. Ten years of listening to the customer, and sound analysis of over 100 vehicles has led to use of a new unit of loudness, called a sone, that better describes how people hear wind noise, which is dominated by high-frequency sounds. Decibels are a good measure for low-frequency sounds. The complex sone filtering formula better represents how the customer hears wind noise and is used for measurement and design performance. How do they compare: a 30 sones wind noise measurement would equate to a 71.2 dBA interior loudness.
A major contributor to this improvement is a new windshield that was thickened by 15 percent to reduce wind noise by 2.1 sones. NVH engineers also worked with designers early in the process to make sure the exterior was as aerodynamically slippery as possible to help reduce noise. The new Expedition's coefficient of drag was reduced from 0.44 to 0.41 as a result of this effort.
Body leakage, a measure of how much air leaks out of the cabin, has been reduced by 56 percent. These leaks translate into wind noise sources in driving conditions. Engineers accomplished this by pressurizing the cabin and then determining where air was escaping.
When leaks were identified, they were corrected with a variety of tools like expandable foam, patches or heavier sealing. For example, new gaskets seal the door handles better to reduce both wind and road noise.
The weather strips in the glass runs, the area where the glass moves within the casing, also were redesigned to further reduce noise. The window glass runs were sealed tighter to prevent noise from entering. These glass runs have a 100-percent deeper trough to ensure that no wind gets between them and the interior. The gaps between the doors and body panels were completely sealed off so there is no air leakage into the cabin.
The liftgate hinges in the rear were designed to minimize any airflow blocking or grabbing that could result in wind noise. The side mirrors were improved in several areas because of their important role. They were designed to be significantly larger, improving rearward visibility while reducing the width and placing them at a sharper angle to reduce airflow disturbances.
The mirror is fitted to the door very tightly so the wind cannot get into voids and create whistles. Wind that comes into the mirror from behind the glass is blocked using a molded foam gasket that separates the mirror from the door. The power mirror wiring was redesigned to fit tighter to the gasket to prevent air leakage and wind noise transmission.
The NVH team took extra steps to ensure manufacturing consistency to eliminate variances that negate sound-control measures. For example, two beads of sealant, instead of one, are applied to various exterior components like windows. This added layer reduces the chance of air bubbles creating inconsistent finishes that could host wind intrusion. This added step reduced the chances for sealant noise disturbances from 15 percent to less than 0.5 percent.
Body Mounts Isolate Passenger Compartment
The strategy of eliminating unpleasant noises and vibrations inside and outside the new Expedition was similar to refining the engine - design it right from the start. Expedition NVH engineers were involved early in the program to address issues on computer models so squeaks and rattles didn't creep up later on prototypes.
The chassis and frame were the first targets. The team focused on rough or coarse road surfaces since the new independent rear suspension can absorb and isolate larger undulations. Through extensive computer modeling, two types of mounts were used to isolate different irregularities that were moving through vehicle components.
These mounts - 10 in all - serve to isolate the passenger compartment from vibrations that reach the body. The front and rear mounts on both sides of the main passenger cabin are built with a "shear" design. The basic concept is that of two concentric tubes, one bolted to the frame, the other bolted to the body structure. Rubber is bonded between the two tubes.
By surrounding the rubber bushings entirely with metal, these shear-style body mounts spread forces across the entire bushing surface, contributing to more consistent long-term performance by the rubber and protecting it from deterioration. This design reduced the new mounts' degradation to 5 percent, compared to 75 percent for some current mounts, over the life of the vehicle.
"My goal was to make sure body mount response remained consistent over the entire life of the vehicle," says chassis supervisor Matt Howard, who patented the unique mounting system that makes the rear body mount possible.
The metal tubes also serve a crucial function in improving crash performance by limiting fore and aft movement of the passenger compartment.
The two center body mounts on each side of the passenger compartment were built with a new "cup" style design that is similar to the shear mounts in that it surrounds the rubber bushing material with a metal ring to protect it and better distribute forces. Unlike the front and rear "shear" mounts, the two center mounts are designed exclusively to isolate the passenger compartment from both vertical and lateral vibrations.
The final two body mounts are located on either side of the radiator housing. They are a more conventional solid rubber design, due to the less stringent demands placed on them.
Body and engine mount designs were computer designed, but then subjected to repeated evaluation to make sure they achieved the team's goal - a quiet cabin.
The science involved in crafting a quiet ride relies in part on precise measurements of sound at the "driver's ear" using sensitive microphones. But it also involves three-axis micro-accelerometers attached to the driver's seat track - literally an electronic "seat of the pants" measurement - that monitor vibrations transmitted through the seat to the driver.
Computer tools include three-dimensional representations of the frame, powertrain, suspension and body, which can be run through deflection simulations that exaggerate actual movements by a factor of 50, to reveal areas that may need attention.
"We were evaluating a great many options at a time," Howard says. "The only way to do this is with CAE - computer-aided engineering. It allowed us to weigh all the options before we actually built the designs and subjected them to instrumented testing."
Fuel Economy, Emissions
The 2003 Expedition is the cleanest-running full-size SUV, based on California Cleanest Vehicle methodology and publicly available competitive information. Expedition qualifies as an Ultra Low Emission Vehicle (ULEV) under California rules and is being certified to EPA's stringent Tier II rules one year earlier than required.
The engine's returnless fuel supply helps to reduce evaporative emissions by providing consistent pressure to the fuel injectors through a high-pressure pump. This system eliminates the return fuel line which, in traditional pumps at idle, sends back unused fuel that splashes into the tank and creates more evaporation.
The 2003 Expedition's fuel economy is among the class leaders, at an estimated 19 miles per gallon highway and 15 mpg city for the 4.6-liter two-wheel-drive model, based on preliminary internal testing. The 5.4-liter four-wheel-drive model is projected to improve to 14 city and 17 highway from 12/16 mpg today.