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 provide a quieter, more comfortable ride for all occupants, particularly those in the rear seat. Interior noise level of the new Concorde and Intrepid is reduced by a substantial 3 dB (decibels) compared to their predecessors. The following subjective improvements accompany 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 are engineered to minimize noise generation, leaving lessto be dealt with externally. Engine sound remains clearly perceptible, especially under hard acceleration, but the sound is smooth and suggests power.

A major portion of objectionable engine noise is caused by deflection and resonance in structural and dynamic components. To minimize this, components are stiffened and, in some cases, made lighter to impose less force, thereby reducing noise. Power train improvements provide 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 provides a 41 percent stiffer connection. Rather than just being containers, die-cast aluminum oil pans add stiffness to the cylinder block. They also include attachments for engine-to-transmission collars that stiffen the entire power train assembly
The transmission case is 14 percent stiffer than in 1997. Increased structural ribbing provides added stiffness
The transmission-to-cradle mount is stiffened by increasing structural ribbing and revising mount attachments

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

Select-fit engine main bearings reduce operating clearance
Cylinder block 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 use a combination of soft rubber elements and hydraulic damping, make the engine mass a ride damper, contributing to a solid ride
Lower alternator operating speeds and revised alternator fan geometry reduce high speed fan noise
Stiffer alternator housings minimize low speed magnetic noise
A refined air induction system produces 15 percent less noise at the air inlet with a more pleasant sound than the prior system. Components are larger and located more appropriately for proper tuning than their predecessors. Major elements include:
An opening that smoothes 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 is 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 is reduced by making structures stiffer and moving parts stiffer and lighter. Noise transmission is 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 provides the following noise reduction features and their associated benefits compared to the former (214-hp) 3.5-liter engine:

The forged steel crankshaft has 26 percent greater torsional stiffness-the stiffest crankshaft Chrysler has 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 is the first element to be designed. For the same stiffness, a forged steel crankshaft is smaller and lighter than a cast iron one. Bearing sizes are thereby also smaller, reducing internal friction
The cast aluminum cylinder block provides 28 percent greater torsional stiffness. The cylinder block is 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 includes the following features:
Extensive ribbing
Six-bolt main bearing caps-four vertical, two transverse
For quietness, the natural frequency of the bearing caps exceeds the firing frequency of the engine.
Stiff bearing caps also reduce the potential for wear caused by deflection under load.
Structural-beam windage tray
By providing added support to the main bearing caps, it helps increase overall stiffness.
Rigid accessory drive mounting
On the 2.7-liter engine, the air conditioning compressor and alternator mount directly to the block and structural oil pan, rather than on brackets. This prevents 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 meets 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 are 14 percent lighter relative to their bore size, than those of the 1997 3.5-liter engine
Low-rumble intake manifold
The new design has 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 are equally spaced lengthwise along the plenum
Ribbed block sides
While providing overall stiffness to the block, ribs break up flat surfaces into small sections that are too stiff to resonate with engine internal noises
Isolated composite valve covers
Mounting of the cylinder head covers is completely isolated to prevent them from vibrating in resonance with the internal noise in the head. The covers are made of composite material that has inherent damping characteristics to further resist noise transmission

3.2-Liter Engine

The cylinder block has 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 includes extensive ribbing
Six-bolt main bearing caps-four vertical, two transverse-replace four-bolt caps used previously. They constrain the crankshaft to reduce deflection
A structural-beam windage tray replaces a non-structural tray. By providing added support to the main bearing caps, it helps increase overall stiffness
The air conditioning compressor and alternator mount directly to the block and structural oil pan, rather than on brackets. This prevents these heavy items from vibrating independent of the engine, adding input to the power train mounts. Only the power steering pump, which is the lightest of the accessories, still mounts on a bracket, and is more compact and stiffer than the previous brackets
Nominal engine unbalance is reduced 13 percent on the 3.2-liter engine. Measured at the crankshaft, imbalance meets 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 are 15 percent lighter, relative to their bore size, than those of the 1997 3.5-liter engine
Cast-aluminum cylinder head covers, which provide inherent noise damping, are 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 share the following chassis systems quietness features:

An all-new power train/front suspension cradle helps 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 mounts 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 provide smooth, quiet operation throughout the life of the vehicle. Microcellular urethane jounce bumpers and urethane cushions at the top and bottom of each spring reduce harshness and help minimize noise transmission to the body structure. They were also used in 1997.

A rubber-isolated rear suspension cross member helps 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 help 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 is less obtrusive because the new ICU (integrated control unit), which produces a pulsating noise during ABS action and also includes a pump, is double-isolated. The ICU attaches to its mounting bracket through rubber isolators. The bracket then attaches to the power train/front suspension cradle, which is also rubber-isolated from the passenger compartment. Noise transmission is further reduced because the hydraulic unit is 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 reduces noise because the outer shell has 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 attach to the rubber isolated rear suspension cross member, providing a second level of isolation compared to the previous body mounts in these location. Hangers have improved isolation characteristics.

Two resonators are 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 is located under the floor and the other just forward of the tailpipe outlet. The muffler is placed transversely beneath the rear suspension cross member-a location proven to be highly effective for noise reduction. The exhaust system for each engine is 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 is robotically applied after the bodies are primed. This is Chrysler's first use of 100 percent robotic body seam sealing. The sealer expands to fill the openings when heated in the paint ovens. Robotic sealing is both accurate and easily adaptable to the unique features of all three body shells. It also applies the precise amount of sealer needed for a neat appearance with no clean-up required. Bodies are 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) are covered with foam tape that also expands in the paint oven, rather than manually applied bulk sealer used previously, which is hard to apply consistently, and may fall out in time.

HVAC System

Air conditioning compressor quietness results 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 reduces noise generation. To reduce noise transmission, refrigerant lines are carefully designed and mounted.

Cooling System

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

Quietness Package

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

A molded fiber silencer attached to the underside of the carpet quiets the interior by increasing the area of contact between silencer and floor pan. The carpet and fiber pad are 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 blocks the transmission of sound from the floor pan
A molded foam dash liner w/EVA barrier (ethylene vinyl acetate) wraps 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 uses a layer of visco-elastic material bonded to a thin-gauge sheet metal "patch". The sheet metal patch is spot welded to the body panel where damping is required. During paint oven baking, the visco-elastic material expands bonding the constraining patch to the body panel.
PUR® (expandable polyurethane) foam provides a major interior quietness improvement. Injected into seven body panel cavities in the sill, door opening, and shelf panel areas, the foam prevent these cavities from acting as conduits for noise. The new Concorde and Intrepid bodies are the first at Chrysler designed with openings to facilitate injection of PUR foam for this purpose. PUR uses a two-part chemical formulation that expands within seconds of injection to fill the cavities. For consistency, the dispensing equipment checks to be sure the cavity is filled and directs the operator to repeat the process if necessary
Molded barrier door silencers provide a highly effective barrier against airborne noise emanating from inside the door cavities and seal out water, air and dust. They are thicker and more dense than previous liners and are adhesive sealed to the perimeter of the door inner panel. To assure effective sealing, holes required for wiring and door latch operating links are of minimum size and the only openings provided
The structural headliner is made of Acousticor® sound absorbing material
A molded fiberglass silencer is applied to the engine side of the dash panel
A molded fiberglass liner is applied to the underside of the hood
An extruded rubber lip w/die cut foam ends seals the hood-to-plenum gap
A molded foam silencer is applied to the air intake plenum chamber
A silencer pad is applied to the rear roof pillar trim panel
Rear wheel houses are covered by a molded pad that includes an EVA barrier
A molded silencer pad with EVA barrier installs under the rear package shelf
Molded pad w/EVA barrier bulkhead silencer
An EVA sound barrier and insulation pad assembly is attached to the back of each rear seat, preventing airborne noises from entering the passenger compartment from the trunk