Honda Car Forum


Go Back   Honda Car Forum - Accord Parts Civic Tuning Acura Racing > Acura Car > Acura MDX

LinkBack Thread Tools Display Modes
  #1 (permalink)  
Old 15 Aug 2008, 09:50 pm
Join Date: Aug 2007
Posts: 109,855
Default 2009 Acura MDX - Chassis

Torrance, Calif. - Aug 15 —


From its inception the MDX targeted the dynamics and driving feel of its strongest
European competitors. The essential elements of this engineering goal included
steering, suspension, braking and overall dynamic performance, as well as noise,
vibration and harshness (NVH) control.

At the beginning of MDX development, engineers tested European luxury SUV
competitors including the BMW X5, Mercedes-Benz ML350, Porsche Cayenne and Volvo
XC90. These experiences provided real-world understanding of how these luxury
SUVs functioned in everyday driving on their "home turf." Although
later development testing was conducted in the United States, the DNA of the
MDX was largely formed in Europe.

One essential tool that Acura used was the famed Nürburgring Nördschleife
road circuit in Germany. This 13-mile course contains over 170 corners, numerous
altitude changes and is considered the toughest natural road course in the world.
Engineers used the Nürburgring as a "weakness finder" because
it quickly exposes problems with a vehicle's dynamics, making them easier
to identify and fix.

In order to build in a combination of increased handling agility, increased
stability and comfort, the current MDX's wheelbase, tread width, and suspension
technology were changed from the first-generation MDX. Engineers changed the
lift and squat characteristics of the suspension to provide a flatter takeoff.
Thanks to its extended wheelbase together with SH-AWD®, the 2009 MDX offers
both exceptional high-speed stability and responsive handling.


The entire front chassis area was tuned to provide the best balance of handling
precision, road isolation, and impact after-shake damping. MacPherson struts
with inversely wound coil-over springs and forged-aluminum lower control arms
reduce unsprung weight, while the front subframe "floats" on rubber
mounts to provide road and engine isolation. The front suspension also uses
newly developed hydro-compliance bushings to provide superior ride isolation
as well as chassis vibration control. Suspension and engine mounts are specifically
tuned to provide minimum vibration transfer to the occupants, and the front
struts employ internal rebound springs to improve ride and handling. Anti-dive
properties were revised to improve impact harshness and ride comfort.


The MDX's rear suspension is a multi-link design mounted on a separate
steel subframe. Squeeze-cast aluminum uprights (or "knuckles") reduce
unsprung weight for improved response, while revised trailing-arm mounting points
(compared to the previous MDX) reduce body squat during acceleration. Coil springs,
dampers and an anti-roll bar are tuned for the optimum combination of ride and

Rear subframe mounts and lateral control link bushing rates were significantly
revised to create a discrete level of lateral force steer at the rear axle.
Since the SH-AWD® system constantly varies drive torque at the rear axle,
the longitudinal and lateral force steer properties were carefully developed
for optimum response, stability and consistency.


Included with the optional Sport Package, the Active Damper System gives the
MDX an elevated level of handling precision designed to satisfy the most discriminating
drivers, while maintaining a smooth and controlled ride. Acura considered all
of the available technologies before choosing electronically controlled, fast-acting
Magneto-Rheological fluid dampers as the ideal technology to maximize ride comfort
and handling in one integrated system.

The overall goal of the Active Damper System is to achieve outstanding levels
of handling response while maintaining refined levels of ride comfort. This
allows the driver intuitive vehicle control in a relaxed environment -
free from neck straining head toss and other sudden vehicle motions. This is
made possible by the quick response of the dampers and by the computer algorithms
that keep the dampers a step ahead of the actual body movements.

Advantages of the Active Damper System include:

  • Flat cornering feel with minimal body roll or pitch -- even during spirited

  • Responsive, precise and secure steering feel

  • Elimination of unwanted under-damped body heave, roll and pitch motions

  • Improved tire adhesion, vehicle stability and road isolation

Real-Time Damper Control

The secret to the MDX's Active Damper System is its fast-acting shock
absorbers. These dampers are built and tuned specifically for the MDX and offer
the ability to individually adjust from minimum to maximum damping force in
as little as five milliseconds (0.005 seconds). This ability hinges on the principle
of electromagnetic induction. Each damper carries a unique coil that generates
an electromagnetic field when current is passed through it. Proprietary damper
fluid contains microscopic (on the order of 10 microns in diameter) ferric spheres
that align when surrounded by the electromagnetic field, dramatically and instantly
changing the effective fluid viscosity. Not only is the overall range of damping
force available significantly more than that of a conventional damper, but there
are hundreds of damping steps within that range.

The current that passes through the field coils is controlled by an electronic
control unit (ECU) that uses special algorithms to determine the best damper
setting for the road conditions. This, combined with nearly instantaneous reaction
time of the dampers, allows damping control to occur before the vehicle's
tires or body are allowed to have any extraneous motion.

The Active Damper System will operate with low damping when the road is smooth
and level and the vehicle is being driven at a constant speed. Such limited
damping further reduces the amount of vibration and harshness that passes from
the suspension to the body thus quieting and improving the vehicle's ride

Using the dampers' 5-millisecond response time, the Active Damper System
reacts to sudden changes in driver or road inputs. The high damping force achieved
in this short time allows the dampers to aid the springs and stabilizer bars
in roll and pitch control, greatly improving the handling of the MDX.

The result of the improved transient handling, road isolation, and body control
is that the MDX with the Active Damping System noticeably reduces the driver's
workload when compared to other performance-oriented SUVs. The system is able
to achieve the benefits of a sporty suspension without the traditional ride
comfort tradeoffs. The overall benefit is more enjoyment, better control and
less fatigue over the long haul.

Sport or Comfort Mode

The Active Damper System provides two driver-selectable settings - Sport
and Comfort. Sport mode prioritizes handling response, vehicle body control
and tire adhesion to allow for spirited driving with high levels of precision
and composure. Comfort mode allows for a more relaxed driving experience by
prioritizing road isolation and reduced passenger fatigue caused by road inputs.
Either Sport or Comfort mode can be used in any type of operating conditions
as preferred by the driver.

The Active Damper system maintains the same quality, durability and performance
as all other Acura components, does not require any special maintenance and
has no scheduled replacement interval.


Of the luxury SUVs that Acura targeted in developing the MDX, the BMW X5 3.0i
offered the best steering quality. Acura set out to exceed the BMW's combination
of linearity, precise feel and security at high speed with using torque-sensing,
variable power-assist rack-and-pinion steering.

Acura engineers spent considerable energy studying steering "on-center"
feel in an effort to elevate the quality of steering feedback the driver receives.
Beyond offering the correct steering effort level, the MDX provides subtle transient
steering feedback that is an integral part of its subjective handling quality.
Notable geometry changes include increasing the rake and trail over the previous
MDX to provide a stronger steering feel.


The 2009 Acura MDX has standard 18x8-inch 5-spoke aluminum wheels with P255/55R18
104H M+S all-season tires. The tires were specially developed for the MDX by
Bridgestone and Michelin and offer a significant traction improvement in dry
and wet conditions, while maintaining the previous MDX's level of snow/ice
traction. Michelin P275/45R19 summer tires are also available with the Acura
accessory 19-inch aluminum alloy wheels.

Acura designers purposefully moved the wheels and tires to the high end of
the competitive set. In 2009, the MDX has larger tires than all of its base-level
AWD/4WD competitors and it is the only vehicle in the group with standard 18-inch


The 4-wheel disc brakes on the 2009 MDX are the largest brake system ever
featured on a production Acura vehicle. The brake system is engineered to provide
best-in-class braking capability in dry conditions, as well as while driving
in rain, snow or icy conditions.

Engineers benchmarked the existing MDX as well as the top competitors including
BMW X5 and Porsche Cayenne for braking performance and pedal feel. The 2009
model has short pedal travel and firm pedal feel, in keeping with the direct
feel that enthusiast drivers want. The ventilated front brake rotors are 13-inches
in diameter with a thickness of 1.1-inches, while the solid rear rotors are
13.2-inch diameter units with a thickness of 0.43-inches. Dual-piston cast iron
brake rotors are used in front and single-piston cast iron calipers are fit
in back.

The MDX brake design is validated by a severe fade test utilized by the German
enthusiast magazine Auto Motor und Sport and by rigorous testing at
the Nürburgring.


Vehicle Stability Assist™ (VSA®) is included as standard equipment.
By continually monitoring the vehicle's operating parameters (such as
road speed, throttle position, steering wheel position along with acceleration,
braking and cornering loads), VSA® anticipates if the MDX is approaching
oversteer or understeer. To help correct either of these situations, VSA®
first acts to transfer torque bias to the axle with the most traction. This
preventative measure significantly reduces the number of brake and throttle
interventions. The response is so quick that the instability may be corrected
even before the driver knows it is occurring. Traction Control is integrated
into the VSA®, and it helps the MDX accelerate smoothly on slippery surfaces.
In addition, the VSA® can request the SH-AWD® to adjust its torque level
- thus allowing direct yaw control of the MDX to maximize stability under
most all driving conditions.


An onboard Tire Pressure Monitoring System (TPMS) warns the driver if the
air pressure decreases significantly in any tire. The system helps reduce the
chance of damaging a tire or losing control of the vehicle due to low air pressure.
This is important because a slow leak, such as one that might be caused by a
nail or road debris, might not be easily detectable but could cause loss of
grip and potentially, a blowout.

TPMS uses a sensor mounted on each wheel that continually monitors tire pressure
and sends a coded signal to the TPMS electronic control unit (ECU). The process
begins with a signal initiator located inboard of each tire on the chassis.
The initiator sends a unique signal for each TPMS sensor. Then the TPMS sensor
sends tire pressure data to the TPMS ECU, which compares the values for each
tire's pressure against an acceptable range of pressures.

When a tire's pressure drops significantly below the proper level, a
"check tire pressure" alert will appear on the Multi-Information
Display (MID) alert screen. The system can display the air pressure in all four
tires simultaneously via the MID, making it simple to locate a low-pressure

At the driver's preference, the MID can continually show the air pressure
in all four tires. Regardless of whether the driver chooses to monitor the pressures,
a warning will still occur if a tire drops below specification.


Acura took thorough measures to ensure that off-road enthusiasts would be
satisfied with the MDX. The vehicle meets design criteria developed for the
original MDX, which was based on research at different off-road areas across
the country. This research was the foundation for specific minimum performance
criteria for the new MDX, including travel through standing water nearly 19-inches
deep, steep approach and departure angles (28-degrees front and 23-degrees rear),
rocks, off road and paved grades up to 60-percent. Components located underneath
the vehicle are tucked away to avoid damage in off-highway driving and the evaporative
canister is protected by a high-strength steel guard.

The high-torque V-6 engine, SH-AWD® system with hill logic and computer-controlled
traction capabilities help the MDX meet typical off-road challenges without
the need for low-range gears. The MDX outperforms its predecessor without the
need for a driver-selected 4WD "lock" mode.


The same technologies that make the MDX capable off-road also enhance its
performance in snow and ice. The SH-AWD® system with grade logic and computer-controlled
traction capabilities work together with the standard M+S tires to maximize
grip and driver control during winter driving conditions.


The MDX uses an array of technologies to reduce noise, vibration and harshness
(NVH) in the passenger cabin. Acura began by attacking vibration in the body
during the engineering phase instead of simply adding materials to the body
to damp it out later. Two examples of this process are new rear suspension mounting
points, which are now attached to the unit body for greater rigidity and reduced
vibration, and the stiffening of the front and rear subframes, which allowed
the mounting bushings to be made softer.

Engineers paid strict attention to addressing two specific issues - concrete
road noise and drumming - neither of which is acceptable to luxury customers.
By nature SUVs are susceptible to drumming noises in the cabin interior because
of their large open area. Where necessary, meltsheets are used in critical areas
on the front bulkhead and floor, and lighter insulators are used on the bodysides,
doors and roof. A new hybrid carpet and padding system further reduces noise
intrusion by balancing the transmission loss and absorption properties of the

To verify that the results were on target, engineers dynamically shook the
MDX body and measured vibration by scanning with lasers the floor to find the
"hot spots". This provided exact information on where to focus efforts.
As a result, the MDX is 20-percent stiffer and quieter than the previous version,
registering just 64 dBA at 60 mph.


With a towing capacity of 5,000 pounds the MDX can tow a boat or camper trailer
with equal confidence. Standard towing equipment includes a high-capacity radiator
with twin 160-watt fans, an automatic transmission fluid cooler, a heavy-duty
power-steering cooler and pre-wiring for an electric brake controller. A Towing
Package is available as dealer-installed accessory and includes a hitch, receiver,
ball and wiring harness.

One of Acura's durability tests was towing a 5,000-pound trailer in
Death Valley National Park during summer, including climbs up steep Townes Pass
and Daylight Pass with outside air temperatures between 113º and 120º F. Testers
also targeted the toughest boat ramp they could find - at Shasta Lake
in Northern California. The ramp is extremely steep, and its length varies depending
on the lake level. They also proved the MDX trailer-pulling skills elsewhere
in California as well as in Kentucky and West Virginia.


Every 2009 MDX comes with standard Vehicle Stability Assist™ (VSA®)
that includes special Trailer Stability Assist algorithms. Trailer Stability
Assist interprets oscillation (or wag) in the vehicle/trailer combination while
driving. This may occur if the trailer is not loaded correctly, or under certain
speed and road conditions. Using a combination of torque reduction and individual
brake application, Trailer Stability Assist activates to stabilize the vehicle
after sensing oscillations of the vehicle and trailer system.

Reply With Quote

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On

Similar Threads
Thread Thread Starter Forum Replies Last Post
2009 Acura RDX - Chassis skylight Acura RDX 0 13 Jun 2008 03:11 am
2009 Honda Pilot: Chassis skylight Honda Pilot 0 15 Apr 2008 02:10 am
2009 Acura TSX - Chassis skylight Acura TSX 0 19 Mar 2008 02:00 pm
2009 Acura RL - Chassis skylight Acura RL 0 06 Feb 2008 05:30 pm
what Honda Chasis is the Acura RL's chassis based on (similiar to the Acura TL being Yanai Acura Technical 3 26 Dec 2007 08:31 pm

All times are GMT -5. The time now is 07:59 pm.

Honda News | Autoblog
Powered by Yahoo Answers

Powered by vBulletin®
Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.
LinkBacks Enabled by vBSEO 3.6.0 PL2 © 2011, Crawlability, Inc. is not affiliated with Honda Motor Company in any way. Honda Motor Company does not sponsor, support, or endorse in any way. Copyright/trademark/sales mark infringements are not intended or implied.