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SPECIAL

Ford Territory

SPECIAL

Ford Territory

A Quieter Cabin Environment

Staff, Wednesday October 31, 2001.

Page 1 of 1

The goal was to create one of the quietest cabins available in a 4WD through an intense focus by engineers on reducing road, wind and powertrain noise.

Noise, Vibration and Harshness

The design team identified more than 1,000 NVH targets in three main categories: road noise, wind noise and powertrain noise. No area of the vehicle was left unscruitinised.

One area the Explorer team focused on particularly is the Articulation Index, which is a scientific measurement of the ability of people to understand sounds or speech within the cabin.

Engineers placed artificial human heads, equipped with microphone ?ears?, in the front and rear seating positions to measure the kinds of sounds that would interfere with occupants' ability to hold a conversation.

Named after a research center in Aachen, Germany, that developed the technology, the ?Aachen head? was used to measure and then generate a speech intelligibility rating, expressed as a percentage.

For example, a speech intelligibility rating of 85 would mean you could expect to hear and understand 85 per cent of what someone else in the vehicle is saying to you.

Measured at the driver's ears, the Explorer is rated at roughly 85 per cent - which compares with a rating in the upper 70s for competitive and even luxury models.

Cutting the clatter

To a driver and passengers, noise is subjective. It might be loud, annoying or even pleasant. However, an engineer needs a more objective way of looking at noise in order to reduce it.

The solution is the colour spectragraph. It's a relatively new and sophisticated tool that sound engineers use to quantify their work. The three-dimensional graph uses colour and brightness to fill in some of the noise picture that would be difficult to analyse on a traditional two-dimensional chart.

When sound is tuned properly, the spectragraph shows brighter, straight lines rising at a constant rate as engine RPM increases. Using this tool, engineers can look at lines or dots of light and often tell what sounds they represent, and whether they will be objectionable to Explorer passengers.

Optimising NVH levels requires rigorous attention to details - and a good ear.

For example, road noise analysis of an early Explorer prototype turned up a low frequency ?boom? at 37 Hz and 49 Hz, which was traced to the rear roof panel, the rear frame rail and minute vibrations by the liftgate glass, door panels and windshield at speed.

As a result, the team recommended revised body mounts, rear frame tuning and new rear roof adhesives.

The revised body mounts alone reduced noise by 3.6 decibels on average. Combining all three modifications further reduced interior sound by another 3 decibels.

In the science of sound measurements, a 6-decibel increase represents a doubling of overall pressure in the logarithmic scale used to measure sound. Even a single 3-decibel reduction is a noticeable improvement.

Powertrain NVH

The vehicle's powertrain also came under scrutiny. Even when the vehicle is stopped at a traffic light, the engine is moving, generating potential noise. Usually, the bigger the engine, the more noise it makes.

The Explorer team were able to match competitors' 3.0 litre engines with the Explorer?s 4.0 litre powerplant in industry-standard engine sound measurements.

Engine sound is, perhaps, the most subjective of all vehicle noises. Some people love the sound of a hearty V-8 engine while others have different ideas of what constitutes a pleasing engine sound.

Explorer's NVH team addressed this by making both the 4.0 litre V6 and 4.6 litre V-8 engines as quiet as possible at idle. Then, to satisfy the different types of customers, the 4.6-litre V-8 was tuned for a sportier, more powerful sound under spirited acceleration. Conversely, the 4.0 litre V6 remains quiet and refined under pressure.

Sound design

Making real improvements in sound quality and NVH works best when both are taken into account from the beginning of a vehicle's design work. Explorer's NVH reduction targets were identified early and plotted on computer - even as the body, chassis and powertrain were being ?assembled? electronically.

To achieve the aggressive targets, Explorer's body was sculpted for less wind resistance.

To further reduce wind noise, the vehicle's glass and door edges were shifted out of the airflow. Micro-cellular body mounts also were used to better isolate vibration from the frame to the body. The new mounts are more effective in reducing NVH than the rubber mounts they replace.

The engine's intake system also was retuned. The engine's composite intake is stiffer and tuned for engine performance, as well as sound reduction. The engine, transmission and exhaust system mounts also were redesigned, using advanced computer modelling techniques. By optimizing angles, rates and locations of the Explorer mounts, engineers were able to deliver a focalised mount system. Many mounting points that formerly were bolted to the frame now are welded in place, to eliminate potential rattles.

Under the vehicle, engineers used computer modelling to locate the optimum nodal point or ?dead spot? on the exhaust system to ensure exhaust hangers were placed in an area that wouldn't transfer noise and vibration into the body structure.

Packaging enhancements allowed use of a new muffler that better reduces exhaust noise.

Other enhancements include new dual door seals that reduce air leakage by 50 per cent and additional sound insulation in the hood, wheel wells, fenders, pillars and driveshaft tunnel to prevent drivetrain noise from entering the passenger area.

Engineers also developed a new, lightweight magnesium transfer case that joins directly to the transmission. In the past, a 12.5cm aluminium adapter was used to attach the heavy transfer case, which invited unwanted vibration.

Non-noise vibrations came under scrutiny, as well. For example, the new Explorer's steering wheel vibrates less than its predecessor's.

Similarly, the development team addressed a buzz in the accelerator pedal by using a longer cable and stiffer bracket.

Body stiffness

A key to the improved sound quality is Explorer's new, fully boxed frame, which provides a stiffer platform for the vehicle's chassis and dynamics improvements - and also improves NVH levels. Explorer is 350 per cent torsionally stiffer and 26 per cent improved in vertical and lateral bending - which contribute to the improved NVH.

In addition to a stiffer frame, the bodyshell of the new Explorer is torsionally 31 per cent stiffer than the previous model, providing further refinement in NVH levels. The body also exhibits a 61 per cent improvement in lateral bending mode frequency. Inside, Explorer features a laminated steel dash and a magnesium cross beam. To further isolate vibration, a combination of urethane and rubber body mounts are employed to attach the body to the frame.

NVH CHANGES AT A GLANCE

• Improved rigidity via a fully boxed frame with a 350 per cent increase in torsional stiffness and 26 per cent reduction in bending.

• Body sculpted for less wind resistance with glass and door edges shifted out of the airflow.

• Improved inherent powertrain NVH, as well as revised engine, transmission and exhaust mounts.

• Additional and improved sound controls, including micro-cellular body mounts, more isolated muffler, new dual door seals, better sound insulation in the hood, wheel wells, fenders, pillars and driveshaft tunnel.

For further information, please contact
Ford Australia Communications
Phone: 03-9359 8491

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