The 1999-2003 Chrysler Concorde/Dodge Intrepid Noise Control

Courtesy Chrysler. We are not responsible for errors or changes.

Improvements in all areas of the Concorde and Intrepid provided a quieter, more comfortable ride for all occupants, particularly those in the rear seat. Interior noise level of the new Concorde and Intrepid was reduced by a substantial 3 dB (decibels) compared to their predecessors. The following subjective improvements accompanied this measured reduction:

  • Power train sound quality
  • Smoother, quieter ride
  • Reduced harshness
  • Less intrusion of exterior noise
  • Less wind noise

Power train

Both new Concorde and Intrepid engines were engineered to minimize noise generation, leaving less to be dealt with externally. Engine sound remained clearly perceptible, especially under hard acceleration, but the sound was smooth and suggested power.

A major portion of objectionable engine noise was caused by deflection and resonance in structural and dynamic components. To minimize this, components were stiffened and, in some cases, made lighter to impose less force, thereby reducing noise. Power train improvements provided the following noise-reducing increases in stiffness relative to the 1993-97 3.5-liter V-6 power train, which at its introduction in 1993, had the lowest radiated (structural) noise level of any engine ever tested by Chrysler:

  • A structural oil pan combined with a structural engine-to-transmission collar provided a 41 percent stiffer connection. Rather than just being containers, die-cast aluminum oil pans added stiffness to the cylinder block. They also included attachments for engine-to-transmission collars that stiffen the entire power train assembly
  • The transmission case was 14 percent stiffer than in 1997. Increased structural ribbing provides added stiffness
  • The transmission-to-cradle mount was stiffened by increasing structural ribbing and revising mount attachments

Both the new Concorde and Intrepid shared the following additional power train quietness features:

  • Select-fit engine main bearings reduced operating clearance
  • Cylinder blocked water flow passages designed using CFD help maintain uniform temperatures during warm-up, keeping cylinders round for quiet operation
  • Refined dual, hydro-elastic power train mounts, which used a combination of soft rubber elements and hydraulic damping, made the engine mass a ride damper, contributing to a solid ride
  • Lower alternator operating speeds and revised alternator fan geometry reduced high speed fan noise
  • Stiffer alternator housings minimized low speed magnetic noise
  • A refined air induction system produced 15 percent less noise at the air inlet with a more pleasant sound than the prior system. Components were larger and located more appropriately for proper tuning than their predecessors. Major elements included:
    An opening that smoothed entering airflow-outside the engine compartment between the right front fender and wheelhouse liner
    A Helmholtz resonator attached to the side of the inlet air duct that was tuned to damp out objectionable noise in a narrow frequency range
    An in-line resonator to control noise across the full spectrum intake air frequencies

2.7-Liter Engine

Vibration was reduced by making structures stiffer and moving parts stiffer and lighter. Noise transmission was avoided by preventing outer surfaces from resonating with noises inside the engine-valve train, camshaft drive chains, oil and water pumps, etc.

The 2.7-liter engine provided the following noise reduction features and their associated benefits compared to the former (214-hp) 3.5-liter engine:

  • The forged steel crankshaft had 26 percent greater torsional stiffness-the stiffest crankshaft Chrysler had ever analyzed. Within the parameters of required power output and the displacement required to produce it, computer analysis using possible bore and stroke combinations established parameters for the crankshaft, which was the first element to be designed. For the same stiffness, a forged steel crankshaft was smaller and lighter than a cast iron one. Bearing sizes were thereby also smaller, reducing internal friction
  • The cast aluminum cylinder block provided 28 percent greater torsional stiffness. The cylinder block was designed around the crankshaft. Beyond designing for stiffness, an aluminum block, though inherently less stiff due to basic material properties, was desired for light weight, making the task more challenging. The block included the following features:
    Extensive ribbing
    Six-bolt main bearing caps-four vertical, two transverse
    For quietness, the natural frequency of the bearing caps exceeded the firing frequency of the engine.
    Stiff bearing caps also reduced the potential for wear caused by deflection under load.
    Structural-beam windage tray
    By providing added support to the main bearing caps, it helped increase overall stiffness.
  • Rigid accessory drive mounting
    On the 2.7-liter engine, the air conditioning compressor and alternator mounted directly to the block and structural oil pan, rather than on brackets. This prevented these heavy items from vibrating independent of the engine, adding input to the power train mounts
  • Nominal engine unbalance: 27 percent less
    Measured at the crankshaft, imbalance met the objective of less than 1 ounce-inch at the accessory drive pulley and 2 ounce-inches at the torque converter drive plate. Contributing a major portion of the lower imbalance, the 2.7-liter engine pistons were 14 percent lighter relative to their bore size, than those of the 1997 3.5-liter engine
  • Low-rumble intake manifold
    The new design had the three tuned intake runners from each bank of cylinders connected to its plenum chamber in a cluster or focal point. In conventional manifolds, the runners were equally spaced lengthwise along the plenum
  • Ribbed block sides
    While providing overall stiffness to the block, ribs broke up flat surfaces into small sections that were too stiff to resonate with engine internal noises
  • Isolated composite valve covers
    Mounting of the cylinder head covers was completely isolated to prevent them from vibrating in resonance with the internal noise in the head. The covers were made of composite material that had inherent damping characteristics to further resist noise transmission

3.2-Liter Engine

  • The cylinder block had 11 percent greater torsional stiffness than the less-powerful 3.5 it replaces. High torsional frequency, torsional bending stiffness and lateral bending stiffness were engineered into the block using FEA. This was accomplished while keeping weight low, and in spite of the inherently lower stiffness compared to cast iron. The following features contributed to the block's stiffness:
    The casting included extensive ribbing
    Six-bolt main bearing caps-four vertical, two transverse-replace four-bolt caps used previously. They constrained the crankshaft to reduce deflection
    A structural-beam windage tray replaced a non-structural tray. By providing added support to the main bearing caps, it helped increase overall stiffness
  • The air conditioning compressor and alternator mounted directly to the block and structural oil pan, rather than on brackets. This prevented these heavy items from vibrating independent of the engine, adding input to the power train mounts. Only the power steering pump, which was the lightest of the accessories, still mounts on a bracket, and was more compact and stiffer than the previous brackets
  • Nominal engine unbalance was reduced 13 percent on the 3.2-liter engine. Measured at the crankshaft, imbalance met the same objective as the 2.7-liter engine: less than 1 ounce-inch at the accessory drive pulley and 2 ounce-inches at the torque converter drive plate. Contributing a major portion of the lower imbalance, the 3.2-liter engine pistons were 15 percent lighter, relative to their bore size, than those of the 1997 3.5-liter engine
  • Cast-aluminum cylinder head covers, which provided inherent noise damping, were completely isolated to prevent noise in the head from being transferred to the covers and radiating to the passenger compartment

Chassis

Both Concorde and Intrepid shared the following chassis systems quietness features:

An all-new power train/front suspension cradle helped reduce transmission of noise and vibration from the tires, suspension, and power train to the passenger compartment. Like its predecessor, the power train/front suspension cradle mounted to the body structure through four isolators. New, three-piece isolator construction-body, jounce plate, and rebound plate-allows fine-tuning of isolator performance.

Low-friction rubber front stabilizer bar mounts provided smooth, quiet operation throughout the life of the vehicle. Microcellular urethane jounce bumpers and urethane cushions at the top and bottom of each spring reduced harshness and helped minimize noise transmission to the body structure. They were also used in 1997.

A rubber-isolated rear suspension cross member helped reduce transmission of noise and vibration from the tires and suspension. Four tuned isolators block transmission of noise from the transverse suspension control arms, significantly improving rear seat quietness compared to the former structure-mounted control arms. Microcellular urethane jounce bumpers and urethane cushions at the top and bottom of each spring reduce harshness and helped minimize noise transmission to the body structure. They were also used in 1997.

Brakes

All disc brake rotors cast from damped iron, an alloy metallurgically formulated to ring less than conventional cast iron, reducing the potential for high speed brake squeal that can occur under some operating conditions.

ABS operation was less obtrusive because the new ICU (integrated control unit), which produced a pulsating noise during ABS action and also included a pump, was double-isolated. The ICU attached to its mounting bracket through rubber isolators. The bracket then attached to the power train/front suspension cradle, which was also rubber-isolated from the passenger compartment. Noise transmission was further reduced because the hydraulic unit was farther from the passenger compartment than on prior models.

Exhaust System

DMA (digital model assembly) found room for added muffler volume, a major factor in reducing exhaust noise. Conventional rolled construction further reduced noise because the outer shell had less tendency to resonate than did the previous stamped construction. To prevent exhaust noise from being transferred to the passenger compartment, hangers that support the muffler attached to the rubber isolated rear suspension cross member, providing a second level of isolation compared to the previous body mounts in these location. Hangers had improved isolation characteristics.

Two resonators were used with all power trains. A computer program was used to design the muffler and resonators silencing systems and position them at their most effective locations. One resonator was located under the floor and the other just forward of the tailpipe outlet. The muffler was placed transversely beneath the rear suspension cross member-a location proven to be highly effective for noise reduction. The exhaust system for each engine was also individually tuned for quietness while providing a pleasantly perceptible sound under medium to hard acceleration.

Body

Body Seam Sealing

To prevent high-frequency noise from entering the passenger compartment through small, frequently invisible openings in the body, lightweight, expandable body sealer was robotically applied after the bodies are primed. This was Chrysler's first use of 100 percent robotic body seam sealing. The sealer expanded to fill the openings when heated in the paint ovens. Robotic sealing was both accurate and easily adaptable to the unique features of all three body shells. It also applied the precise amount of sealer needed for a neat appearance with no clean-up required. Bodies were designed with the vast majority of openings no larger than 0.08 inches (2 mm) to assure long term sealing effectiveness. Openings over 0.08 inch (2 mm) were covered with foam tape that also expanded in the paint oven, rather than manually applied bulk sealer used previously, which was hard to apply consistently, and may fall out in time.

HVAC System

Air conditioning compressor quietness resulted from the findings of a 2-1/2 year benchmarking study and functional redesign. Reducing internal compressor tolerances and adding anti-friction coatings to various components reduced noise generation. To reduce noise transmission, refrigerant lines were carefully designed and mounted.

Cooling System

Transmission of noise from the cooling module to the body structure had been reduced through the use of a new integrated elastomer isolation and mounting system. Fan shrouds were also stiffer to avoid resonance in the system. Dual fans of different sizes operated at different speeds to avoid beat frequencies.

Quietness Package

The following add-on silencing devices and treatments were used on Concorde and Intrepid:

  • A molded fiber silencer attached to the underside of the carpet quieted the interior by increasing the area of contact between silencer and floor pan. The carpet and fiber pad were molded as a unit to conform to the floor pan, cut to fit, then adhered as a unit.
  • A layer of dense micro-cellular foam (massback) molded to the underside of the floor carpet blocked the transmission of sound from the floor pan
  • A molded foam dash liner w/EVA barrier (ethylene vinyl acetate) wrapped around the sides of the footwell, providing continuous coverage from door to door. Steel grommets inserted into its attachment holes improve performance of the dash liner. Mounting screws through the grommets hold the liner firmly in place without compressing the material nor pulling free to leave a hole.
  • Patch Constrained Layer (PCL) treatment applied to the dash panel and plenum chamber upper and lower panels dampens resonance with engine noise, road noise, and other vibrations. PCL used a layer of visco-elastic material bonded to a thin-gauge sheet metal "patch". The sheet metal patch was spot welded to the body panel where damping was required. During paint oven baking, the visco-elastic material expanded bonding the constraining patch to the body panel.
  • PUR® (expandable polyurethane) foam provided a major interior quietness improvement. Injected into seven body panel cavities in the sill, door opening, and shelf panel areas, the foam prevented these cavities from acting as conduits for noise. The new Concorde and Intrepid bodies were the first at Chrysler designed with openings to facilitate injection of PUR foam for this purpose. PUR used a two-part chemical formulation that expands within seconds of injection to fill the cavities. For consistency, the dispensing equipment checked to be sure the cavity was filled and directs the operator to repeat the process if necessary
  • Molded barrier door silencers provided a highly effective barrier against airborne noise emanating from inside the door cavities and seal out water, air and dust. They were thicker and more dense than previous liners and were adhesive sealed to the perimeter of the door inner panel. To assure effective sealing, holes required for wiring and door latch operating links were of minimum size and the only openings provided
  • The structural headliner was made of Acousticor® sound absorbing material
  • A molded fiberglass silencer was applied to the engine side of the dash panel
  • A molded fiberglass liner was applied to the underside of the hood
  • An extruded rubber lip w/die cut foam ends sealed the hood-to-plenum gap
  • A molded foam silencer was applied to the air intake plenum chamber
  • A silencer pad was applied to the rear roof pillar trim panel
  • Rear wheel houses were covered by a molded pad that included an EVA barrier
  • A molded silencer pad with EVA barrier installed under the rear package shelf
  • Molded pad w/EVA barrier bulkhead silencer
  • An EVA sound barrier and insulation pad assembly was attached to the back of each rear seat, preventing airborne noises from entering the passenger compartment from the trunk

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