The 1999+ Concorde/Intrepid Body

Information courtesy of Chrysler. We are not responsible for any errors or changes.

Beyond The 25-Hertz Body

By Chrysler Corporation PR

The 25 Hz (Hertz or cycles per second) body referred to in competitive advertising is one measure of dynamic body structural stiffness. This measurement identifies the first mode, or lowest, natural (resonant) frequency of the full body structure. If the body is vibrated at its first mode frequency, it will resonate (vibrate in harmony) with that input. In general, the higher this minimum frequency, the stiffer the body structure. The stiffer the body structure, the more solid and vibration free the ride. Increased stiffness also improves handling characteristics while reducing BSR's and other noise conditions.

Auto companies have used this measurement for about 10 years as a starting point for targeting body structure characteristics. However, developing a quiet, good-riding and vibration-free vehicle, one that is light for good fuel economy, and gives the customer ample interior room is a significantly more complex challenge. One problem is the passenger feels and hears inputs from vibration and noise sources that range from 1 to 20,000 Hz. Fortunately, the most dominant of inputs are in the first 500 Hz. However, there are still over 100 natural (resonant) frequencies in that range, only one of which is the first mode.

Most in the industry agree that 25 Hz is a good target. However, its acceptance is primarily based on simplicity, and until recent years, limited computer capacity to solve the more complex question, "What does the driver perceive?" We now know that there is little correlation between the first mode of the full body structure and good ride or vibration-free subjective perceptions. It is true that increasing the first mode frequency of a particular vehicle design by stiffening its structure may result in a better ride and lower noise, vibration, and harshness. However, another vehicle of a different basic design may have a lower frequency and be better in these attributes. In fact, the first mode frequencies of many of today's vehicles are lower than 25 Hz, yet they are subjectively as good or better than the "25 Hz" vehicles. The other significant issue with the 25 Hz goal is that in order to meet it, other desirable features such as weight, cost, and interior room may have to be compromised.

Over the past few years, Chrysler engineers have expanded their structural objectives to address these more complex issues using newer supercomputers. We still have targets for the first body mode, but they are no longer emphasized. Instead, we are concentrating on what the driver feels and hears, which is the vehicle's response in terms of force and sound pressure (noise) amplitude. Simply put, a larger force at the driver's seat or steering wheel, or a higher sound pressure causes a poorer subjective impression.

These vehicle response amplitudes can be predicted using Forced Response Dynamic Analysis, which the aerospace industry has used for years. Chrysler now uses this type of analysis as part of its design process. The analysis simulates road inputs and vehicle responses. Through design iterations, the responses are optimized. For ride and vibration, we measure amplitude at the seat track or steering column. These are the prime targets-locations where subjective-to-objective correlation has been developed for optimization.

Similarly, noise amplitude is minimized. During structure design we set impedance goals for all of the suspension and power train attachments to the body structure. (Impedance is a measure of the structure's ability to oppose energy flow-potentially audible vibration-from the source to the passenger compartment.) Together with acoustic transfer functions and other tactile response goals, there are about 100 structural performance objectives for each vehicle.

In conclusion, the reason why we do not emphasize the 25 Hz goal in structural design is that we have developed other goals that correlate better to subjective impressions. These more refined targets allow greater freedom in design decision making and are particularly useful in total vehicle design that includes weight, cost, and interior roominess considerations.

Body Shell

Beyond housing passengers and supporting the vehicle's functional systems, the body shell as a structure supports the suspension, attenuates noise, controls shakes, and manages energy a crash. Only recently has it become possible to address all of these issues through computer simulation during vehicle design. Structural analysis, as done today, requires CATIA's mathematical data base and supercomputers capable of handling the enormous amounts of data used in structural Finite Element Analysis (FEA). DMA (Digital Model Assembly) facilitated computer simulation by accurately locating all attachment points.

The number of detail features fine-tuning the Intrepid/Concorde's performance is a direct result of the iterative process of analysis and optimization made possible by computer simulation.

Suspension Support

Structural stiffness adds a solid feeling to the ride and helps make handling precise by allowing the suspension to work without deflecting the body. In the new Concorde and Intrepid Unibody shells, torsional stiffness is 37 percent greater and bending stiffness is 46 percent greater than the prior body, which was best-in-class when introduced.

Noise Attenuation

Noise attenuation through localized stiffening has been the major focus for structural analysis and development on the new Concorde and Intrepid. The iterative refinement and analysis process tunes the stiffness of structural paths from external noise sources, such as the engine and suspension system, to the passenger compartment, preventing the noise from being audible. Structural refinement is especially important because a large portion of structure-borne noise occurs at frequencies below 400 Hertz (cycles per second), which are hard to filter. It also reduces the need for added pads to control higher-frequency noise.

A new technique, P/A analysis, helps engineers predict the intensity of structure-borne noise that vehicle occupants will hear. P/A is the term for the partial pressure (noise level) received at the occupant's ears per unit of structural acceleration occurring at the point of attachment for a noise source. The acceleration is the result of a force applied to the structure by the power train, suspension, etc., due to hitting a bump, engine vibration, etc. The structure transmits noise by deflecting in the vicinity of the noise source. Stiffening the structure in these locations reduces deflection and noise transmission. The P/A analysis helps engineers understand the interactions between structural elements and noise inputs and the contribution that each input makes to the overall noise level. P/A analysis uses a combination of computational and experimental measurements to determine the effect of structural changes on audible noise. Finite Element Analysis (FEA) modeling, which determines the acceleration at each attachment point, is coupled with mathematically represented experimental audio data measured in the NVH laboratory. P/A analysis computed noise level transmitted to occupants as follows:

From 11 different noise-source attaching points on the body structure
For noise levels in three different frequency ranges between 50 to 300 Hz
For seven different operating conditions that created various combinations of input force and up to three directions through the attaching points

The results, expressed as total noise level for each set of test conditions, were reported in a chart to facilitate analysis. Frequently, a structural change in one area affected the response in another area, necessitating multiple iterations to obtain optimum results.

Shake Control

Shake is a low-frequency vibration characteristic that is visible in the seats, instrument panel and steering wheel, or felt in the seats and steering wheel. Using FEA, body structure engineers predict the response characteristics of these masses across the spectrum of vibration frequencies that tend to excite a shake response. Structural refinement minimized the level of vibration input at the mounting points for these masses.

Impact Energy Management

Impact energy management requirements are mutually exclusive with those of suspension support, noise attenuation, and shake control. Their integration through the SST (Synthesis of Simulation Technologies) process facilitates the best possible combination of capabilities.

Structural Features

The following features contribute to structural stiffness:

At the forward front suspension cradle attachments and at all four rear suspension cross member attachments, the body structure includes double-shear mounts. Mounting bolts for these components attach to body structural beams through surface mounting holes and sleeves welded inside the beams. The sleeves stiffen the beams at the attachment point, suppressing inputs to the passenger compartment.
A tubular cross beam bolted to the cowl sides beneath the instrument panel increases body torsional rigidity and enhances steering column stiffness. The beam is straight to provide maximum contribution to stiffness with a minimum of added weight. This beam also enhances instrument panel stability.
A bolt-in structural beam connecting the tops of the front suspension strut towers and stiffening of the tower structures enhances torsional stiffness of the new Concorde and Intrepid relative to the 1997 models.
To increase torsional stiffness at the rear of the structure, a transverse beam is welded to the top of the rear strut towers. This compact beam fits neatly under the shelf panel, leaving a large pass-though area for use with folding rear seats. These beams also contribute to noise attenuation and reduce the potential for BSRs (buzzes, squeaks and rattles)
High overall bending stiffness also reduces the potential for BSRs (buzzes, squeaks and rattles) from secondary components such as the instrument panel and steering column, because the structure does not transmit their natural frequencies
Structural sill construction, having no styled surface, contributes to a stiffer structure by allowing more overlap between center pillar and sill than is possible when the sill structure is also the styled surface
Laser-welded, front longitudinal rails with differential thickness sections provide needed stiffness more efficiently than single-thickness parts with added reinforcements
Stiffer suspension attachment points
Stiffer front strut towers include a cap reinforcement
Three-piece rear strut tower and wheelhouse assemblies reduce deflection. Low-contour areas include stamped beads to increase local stiffness
An extensive system of beads stamped into all low-contour floor pan areas increases local stiffness

Exterior Body Panel Accuracy

The 1998 Concorde and Intrepid have "two millimeter" bodies, meaning that all measured characteristics are maintained within two millimeters of the designed position. An accurate body shell contributes to the customer perception of good workmanship by providing flush body panels with tight and uniform gaps and by making trim and other mating parts fit well. Furthermore, it means that doors fit properly, reducing potential for wind noise and water leaks.

Shell Construction

To provide car line differentiation, Concorde and Intrepid have different body-in-white (BIW) assemblies. Each BIW has unique front fenders, hoods, roofs, quarter panels, and trunk lids. The Concorde has the first high-volume aluminum body panel (hood) ever used on a Chrysler vehicle.

The door panels have one-piece construction for dimensional control and high quality fit and finish (including door sealing). One-piece aperture panels also reduce the number of major stampings in the body side from 15 to 10, reducing cost while increasing body stiffness.

Throughout the body, part consolidation has reduced the number of stampings. A typical example is the quarter inner panel construction where one stamping replaces three on the prior body. In another area, the center pillar overlaps the sill, eliminating three additional stampings previously used. Dimensional accuracy is enhanced by reducing the number of pieces because additive tolerances associated with multiple parts and their respective welding operations do not exist.

Weight Reduction

One objective for the 1998 Concorde and Intrepid was to eliminate weight wherever possible. The new Concorde and Intrepid body shells are stronger, stiffer, and provide more features than their predecessors, including double-shear suspension mounts and integrated side impact protection, but weighs little more than its predecessor. This results from the use of lightweight materials and from optimizing the structure consistent with the added requirements. Extensive use of high-strength steels for the front and rear longitudinal rails, center pillars, and other areas affected by impact requirement reduced body shell weight by an estimated 40 pounds (18 kg) compared to mild steel.

Hood Construction

The aluminum hood on Concorde reduces weight by 19 pounds (8.5 kg) and makes the Concorde body shell equivalent in weight to that of the smaller Intrepid. Intrepid's steel hood was also lightened by optimizing the inner panel structure.

Hoods have single-pivot rear hinges, which are adjustable for accurate hood fit and gas prop counterbalance supports. Latches are placed at the leading edges of the hoods to permit the hoods to fit closely around the headlights without the possibility of contact if the hood is slammed shut. The secondary release mechanism is readily accessible and has a yellow handle for visibility.

Trunk Lid And Mechanism

New four-bar trunk lid hinges with gas prop counterbalancing increase usable trunk volume and improve trunk lid-to-body fit. Computer-designed hinge and prop geometry makes opening the lid easy. Lifting the lid a nominal amount brings the counterbalance forces into effect. Reaching the full-open position from there requires little or no effort. The hinges and props mount completely outside the trunk opening to avoid intruding on luggage capacity when closed-a major improvement over prior models. Four-bar linkage-two pivoting links on each side of the trunk opening connecting the lid to the body-is more compact than the former goose neck hinges, while guiding the lid away from the body and providing ample room for loading. This hinge system is also strong and stable, providing long-term alignment accuracy and durability. The trunk is sealed by a full-perimeter tubular weatherstrip attached to a raised flange surrounding the opening. The raised flange prevents water from running into the opening when the lid is open.

Full-Coverage Wheelhouse Liners

Full coverage, molded-plastic front and rear wheelhouse liners protect the body structure from potentially corrosive road splash, and prevent noise due to stone impingement on the body shell.

Exterior Ornamentation

Sill Cladding

High-impact, molded-plastic sill cladding resists chipping better than painted sheet metal and does not rust if chipped. The Intrepid cladding aft of the front wheels is shaped as a stone chip protector. The cladding also covers the sill area in the door openings outboard of the body-mounted seals, carrying the line of the cladding into the door opening. Sill cladding is used in conjunction with sill construction having no appearance surface, thus providing maximum model differentiation flexibility at less cost than full sheet metal sills with add-on cladding.

Side Window Opening Moldings

One-piece, die-cast zinc side window opening moldings have better dimensional control than multi-piece stampings. One-piece construction provides a smooth appearance free of joint lines and ensures consistent gloss and color. Moldings are flush with the outer surfaces of the doors and form the outer half of the glass channel, allowing the glass to more closely approach the surrounding sheet metal for a smooth, aerodynamic appearance and reduced wind noise. Using die-cast zinc, which is stronger than aluminum, provides the shallowest possible moldings and a high-quality surface finish. Side window opening moldings have a black, powder-coat paint finish with a satin finish. To prevent wind and other noises, a polyethylene foam backing is placed between the moldings and the door outer panels. "Flags" incorporated into each rear door molding aft of the window provides a smoothly curved continuation of the window opening.

Body Side Moldings

Body-side moldings protect against parking lot damage. New injection-molded construction includes preformed ends for a neat appearance. Inert-gas injection in the molding process provides a uniform outer surface and thin-wall construction that reduces weight compared to solidly molded parts. All moldings are painted body color.

Glass

Solar Control Glass is used for the windshields and rear windows to reduce the transmission of infrared and ultraviolet energy, to minimize interior heating and damage to organic materials from solar radiation.

The rear window molding is injection molded onto the glass, rather than being manually attached. It is dimensionally accurate and seam-free to provide a close fit to the body opening and a neat appearance. The molding includes mounting clips and positioning spacers to ensure easier assembly and accurate alignment of the window on the body.

Bumpers, Fascias And Grilles

Front and rear bumper and fascia systems fit close to adjacent body panels while providing low-speed impact protection for safety-related equipment. The bumper systems exceed the Canadian regulation for protection up to 5 mph (8 km/hr). Fascias are molded of either TPO (thermo-plastic olefin) or RRIM (reaction-injection molded urethane). Both materials are reformulated to increase abrasion resistance relative to their predecessors. New processes reduce fascia weight approximately 3 pounds (1.4 kg) per car compared to 1997.

New bumper systems continue to use a combination of high-density molded polypropylene-bead foam energy-absorbing material and light-weight, ultra-high-strength steel beams bolted to the body structure. The energy-absorbing foam conforms to both the interior shape of the fascia and the bumper beam. It cushions low-speed impacts and restores to near its original shape after a low-speed impact to help maintain fascia appearance. Engineers used computer FEA models to design deeply curved bumper systems fulfilling appearance requirements that the paradigms of bumper design practice said were not feasible. New, denser foam enhances the energy absorbing capabilities of the bumper systems. Shorter beams than in past practice terminate in lightweight, high-impact molded plastic inserts. These inserts also contribute to high-speed barrier impact energy management by extending the load path from the longitudinal rails of the body structure to the front of the bumper face bar. A patent is pending on this aspect of the bumper system.

Exterior Lighting

Headlamps

New headlamps provide a broader and longer beam pattern on the road. Separate high- and low-beam units ensure optimum performance of each function. In high-beam mode, all four units are lit. The new high-beam units produce double the light output of their predecessors and reach 65 percent farther down the road. Low beams produce 50 percent more light. Computer-designed reflectors focus the light. Using the same bulbs as their predecessors, these reflectors are twice as efficient at projecting light down the road.

Headlamp units are mounted to the body structure, allowing body panels to fit closely around them. Aiming is done by moving the reflector within the lamp assembly. Each lamp includes a bubble level and readily accessible adjustment screws for re-aiming the headlamps, if necessary. Because of their visual prominence, the headlamps include design features-decorated lenses, serrated textures on the outboard edges of the lenses, bright bezels beneath the lenses and styled interior surfaces that help integrate them with the adjacent body panels.

Fog Lamps

New, more powerful fog lamps are integrated with the front fascias on Intrepid ES. Circular, computer-designed reflectors project light on the road through clear, stone-chip resistant lenses. To increase their effectiveness as fog lamps, new switch logic allows them to operate with parking lamps, but without headlamps. They turn off automatically when high beam headlamps are switched on.

Door Systems, Rearview Mirrors & Weather Stripping

Front doors use seven parts compared to 11 in 1997. Rear door part count is reduced even more, from 13 to six. Reducing the number of parts allows a corresponding reduction in welding operations and the potential for variations resulting from each operation. Door inner panels are stamped from dual-thickness, laser-welded sheet metal to increase accuracy of the doors. Laser-welded inner panels eliminate the need for a separate welded-in reinforcement, the single largest cause of variation in door assembly. Instead of adding a reinforcement, the forward portion of the panel, to which the hinges are bolted, is nearly three times as thick as the remainder of the panel. The added thickness provides hinge mounting stability and contributes to a solid door closing sound. Furthermore, this inner panel construction is also lighter than a single-thickness panel with a welded reinforcement. To form the inner panel, sheets of dissimilar thickness steel are butted together and weld by a laser beam. The resulting weld joint is smooth and unobtrusive. Locating points in the inner panel stamping presses ensure that the weld seam is accurately aligned for proper sealing of the door in the door opening. One-piece aperture panels in the body sides facing the doors contribute to consistency of door fit.

Door hinge design and mounting provide more accurate door placement than the prior configuration. Hinge inner and outer halves are permanently assembled, reducing clearance required by the prior replaceable pivot pin system. Hinge attachment to the doors and pillars is controlled by alignment fixtures, eliminating the need for manual adjustment and its potential errors.

Door latches provide smoother and quieter operation. The new design provides 100 percent isolation against metal to metal contact between the latch pawl and the striker for quietness. Plastic and plastic-encapsulated steel components ensure quiet operation. Solid steel components are used only where required to assure strength and durability.

New 'door ajar' switches are integral with the door latch assembly. They operate both courtesy lamps and the door ajar indicator in the instrument cluster. This construction is more reliable and durable than previous stand-alone switches while being less susceptible to door adjustments, freezing, contamination and corrosion. New power lock motors are now virtually inaudible.

Weather Stripping

A body-mounted tubular weatherstrip encircles each door opening to provide primary sealing against wind noise and water leaks. A second body-mounted weatherstrip running up the windshield pillar and across the tops of the doors incorporates a trough to channel water away from the door opening. This sealing system prevents rain water from running into the passenger compartment when the doors are opened. A tubular-type weatherstrip attached to the leading edge of each rear door above the belt line prevents wind noise and acts as a sight shield. A tubular weatherstrip attached to the back of each door between the sill and the belt line also handles wind noise. Lip-type weatherstrips attached to the sill cladding seal the gap between doors and sills to keep road splash and dust out of the door openings and block wind and road noise more effectively than door-mounted weatherstrips. These weather strips snap into the sill cladding and also cover the cladding attachments.

Door Glass

Front door glass is cylindrical for fit and finish accuracy and easy window operation. Rear door glass is barrel shaped to conform to the compound curvature of the doors. As in the past, the rear windows lower only partially dropping 9.4 inches (240 mm) into the doors. This permits wider door openings than would have been possible with windows that drop completely.

Power Sunroof

A vent-and-slide power sunroof is optional. It blocks out ultraviolet light and up to 81 percent of visible light, to minimize interior heating and damage to organic materials from solar radiation. The unit is thin- at least 0.25 in. (6 mm) thinner than competitive units-to minimize passenger compartment intrusion. An opening 33.2 in. (844 mm) wide provides the driver and front passenger with clear upward views.

Soft-touch switches labeled 'VENT, OPEN, and CLOSE' are placed between the courtesy lights in the overhead console. A rocker switch provides vent and slide functions. A push button closes the sunroof in either mode. Operation continues only as long as a switch is pressed to allow adjustment of panel position in vent and close modes. In vent mode, panel movement is slow for precise positioning. The new Concorde and Intrepid sunroof includes an "express" open feature in the open mode. Pressing the 'OPEN' rocker switch causes the panel to move immediately to the full-travel position. Pressing the switch again before the panel reaches the full-open position stops movement. An electronic control system uses Hall-effect sensors rather than mechanical switches at the limits of panel movement.

The interior roof panel and headliner conform to the sunroof opening for a finished appearance without an add-on welt or molding common to some competitive applications. A laminated plastic sunshade is covered with foam-backed headliner fabric. It slides manually using a recessed handle molded into the surface or slides back automatically when the sunroof slides back.

To minimize wind noise and buffeting, a curved air deflector pops up at the front of the roof opening and the panel stops short of the full-open position. The height of the air deflector and the open-position stopping point were optimized in proving grounds tests. Positive sealing is ensured by a cam system that moves the panel into the closed position from the top down. A compact electric motor at the rear of the structure moves the panel with cables that are enclosed for smooth and quiet operation. Tempered glass protects the occupants from injury in the event of breakage. When broken, it crumbles into small pieces without sharp edges. Urethane encapsulation of theglass provides a neat installation. The structure is aluminum and molded plastic for light weight and corrosion resistance.

Windshield Wiper & Washer System

Cross-functional coordination produced a windshield curvature and wiper blade design to facilitate uniform wiper blade pressure. Computer modeling of the wiper linkage determined appropriate wiper pivot locations and helped determine the windshield configuration required to maintain blade pressure. The computer models also aided in designing linkage with low load variation for quiet operation. Aerodynamic design of the hood and cowl screen smoothes air flow, helping to hold the wiper blades on the glass at the vehicles' highest attainable speeds without resorting to add-on air foils. This air flow pattern also causes water pushed down by the wipers to flow to the sides rather than running back up the glass. Aerodynamic design of the windshield pillar shape and molding guides water swept aside by the wipers upward, keeping the lower portions the side windows clear. Cold-weather wiper performance is enhanced by a new defroster system that effectively clears frost from the glass and melts snow pushed down the base of the windshield by the wipers.

New wiper control logic in the BCM (Body Control Module) returns the blades to their parked position when the ignition is turned off, if the wipers were operating at that time. Continuing on the new Concorde and Intrepid is control logic that doubles the intermittent wipe delay time when the car is moving less than 10 mph (16 km/hr).

New wiper blades are three times as strong as current blades and provide more uniform pressure distribution. Aerodynamic configuration of the new wiper blades also helps hold them firmly on the glass at high speeds better than the added airfoils used previously. Bolt-on wiper arms are simpler to manufacture and more robust than the "latchlock" arms used previously.

A new, 30 psi (207 kPa) high-output windshield washer pump supplies two hood-mounted washer nozzle assemblies. Each nozzle assembly has three jets providing a triangular spray pattern that effectively covers the wiped area of the windshield. The spray nozzle design, pattern and pump pressure requirement were developed through extensive aerodynamic testing, which showed the individual jets to be more effective across the full vehicle speed range than other washer systems. A new washer fluid level sensor in the 110-ounce (3.25-liter) reservoir provides a more accurate indication of low fluid.