2009 Acura RL - Chassis

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CHASSIS OVERVIEW

Quick handling response, nimble performance, high dynamic capabilities, outstanding ride comfort, safety features and a fun-to-drive character aptly describe the 2009 Acura RL chassis. The RL features a highly rigid unit body teamed with an Advanced Compatibility Engineering™ (ACE™) front frame structure to provide an excellent platform for the four-wheel independent suspension. The independent front double-wishbone and independent multi-link rear suspension incorporate numerous aluminum components that reduce unsprung weight to provide better handling, more consistent traction, improved suspension response, and a more supple ride-even on rough roads. Acura's technologically advanced Super Handling All-Wheel Drive™ (SH-AWD™) system returns for 2009, and it has been upgraded with numerous improvements that deliver quicker response, more accurate torque distribution, and new control parameters for the Active Torque Transfer System (ATTS).

For 2009, the new RL has further optimized chassis and suspension in the form of an upgraded electric assist power steering assembly, improved steering rack components, a new compact noise isolation (CNI) steering joint, stiffer subframe mount bushings, more performance minded coil springs, revised dampers, larger rear stabilizer bar, larger diameter aluminum wheels, and more advanced tires. As always, ride quality and road noise isolation were also the focus of substantial engineering effort, so even with its elevated sporting performance, the RL remains quiet and composed.

CHASSIS CONCEPT

The RL was designed to compete squarely with the best luxury sedans from Germany and Japan in dynamic performance, interior luxury appointments, features and quality.

The new RL's unit body design with a fully-independent suspension, Advanced Compatibility Engineering™ (ACE™) front frame structure, and a SH-AWD™ system to provide superb handling precision teamed with outstanding safety. The suspension's optimized geometry provides linear cornering feel, outstanding dry and wet weather cornering capabilities, a flat ride, and a high level of controllability at all times. It also results in an increased feeling of precision and security for the driver and passengers alike.

FRONT DOUBLE-WISHBONE SUSPENSION

The front suspension is a double-wishbone design with a large subframe mount and a special compliance bushing. In addition, the coil spring rate has increased (by 6-percent front and 10.5-percent rear), the dampers have been recalibrated for improved performance, and the rear stabilizer bar increases in diameter by 11-percent. These upgrades combine to reduce chassis attitude changes to ensure a flat ride during acceleration, cornering, and hard braking.

Specific performance goals for the RL suspension included better response over rough roads, improved steering feel, optimized geometry, and overall component ruggedness. The steering knuckles, upper control arms, lower control arms and subframe assembly are all constructed of lightweight aluminum.

REAR MULTI-LINK SUSPENSION

The rear suspension is a multi-link design with a new enlarged subframe mount and a longer upper control arm. As a result, the vehicle roll center is optimized for better turning response, improved cornering stability and more control in extreme conditions.

The optimized geometry results in more linear toe and camber changes during suspension travel. Improved roll stiffness also enhances the RL's cornering capabilities. The suspension design also has anti-lift characteristics to reduce the pitching motion of the body during hard braking.

As a result of the new compliance bushing and the specially designed suspension, harshness and road noise are significantly reduced while ride comfort is measurably improved.

In an effort for weight savings, lightweight aluminum is used in the construction of the control arms and subframe. The components are also stiffer to withstand the higher side loads that improved SH-AWD, the larger 18-inch diameter tires and the stiff unit body design create.

ALUMINUM HYBRID SUBFRAMES

The RL employs front and rear aluminum subframes made by unique high temperature bulge-forming and high vacuum die casting methods. Both manufacturing techniques result in significantly lighter units than would be possible with traditional aluminum hydroform or steel hydroform processes.

To bulge-form these components, within a specially shaped die an aluminum tube is heated and pressurized with air. The ability to shape a component under heat and pressure means that less material can be used thus lowering the overall weight of the finished component.

The aluminum hybrid subframes on the RL save more than 40 lbs compared to comparable steel hydroformed subframes.The subframes are connected to the RL's body using new, stiffer subframe mount bushings that help deter body roll during aggressive cornering.

TIRES

Buyers of premium luxury performance sedans expect a vehicle that delivers superior cornering precision while simultaneously providing a pleasing ride. Since tires directly affect cornering ability, the RL is equipped with the largest tires ever offered on a production Acura sedan. Standard equipment are Michelin Pilot HX MXM4 P245/45R18 M+S all-season tires that deliver outstanding cornering and a compliant ride.

The new 18-inch diameter Michelin Pilot tires were specifically designed for the 2009 RL. Despite a larger wheel diameter with a shorter sidewall aspect ratio, the tires deliver better ride comfort and lower noise while simultaneously improving overall handling. Moreover, the new tire has an improved sidewall appearance compared to the previous RL's 17-inch tire.

Within the trunk of the 2009 RL is a temporary-use Bridgestone T155/70D17 spare tire mounted on a 17x4-inch 12-spoke aluminum wheel.

WHEELS

The 2009 RL features all-new 7-spoke aluminum alloy 18x8-inch wheels. The satin silver wheels not only offer more aesthetic flair versus the previous 17-inch 5-spoke wheels, but they better fill the RL body's wheel openings to generate a lowered ride height appearance. In addition, the new wheels feature a concave, back-cut spoke design (applied to the back sides of the spokes) that reduces the amount of build material used thus reducing unsprung weight for improved performance and better fuel economy.

ELECTRONICALLY CONTROLLED, SPEED-SENSING, VARIABLE POWER ASSIST RACK-AND-PINION STEERING

Precise steering performance is an essential facet of the 2009 RL. The goals were to combine a light effort, yet linear steering feel at low speeds with a heavier and more solid steering feel at higher speeds. Such a request is beyond the range of traditional steering systems, thus the RL uses a unique electronically-controlled, speed-sensing, variable power assist rack and pinion steering system. Together with SH-AWD™ and the neutral handling characteristics of the chassis, the RL is engineered to feel like a smaller car than it actually is.

Compared to traditional mechanically controlled hydraulic power steering, the RL's speed-sensing steering assist unit is controlled electronically. Not only does the system free up additional power, but the electronically controlled assist provides a very linear and direct steering feel regardless of vehicle speed. In particular, the on-center feel is very precise and linear, with no discernible "dead spot."

To further improve the RL's steering feel and accuracy, engineers changed the diameter of the steering valves, improved the design of the steering rack guide, and incorporated an all-new CNI steering joint. The previous design was constructed of a soft rubber-to-rubber coupling. On the 2009 RL, the new CNI joint has higher rigidity due to being made of steel matched higher durometer rubber. The result is better steering accuracy with more linear response. In addition, engineers developed revised electronic control parameters for the steering system.

VEHICLE STABILITY ASSISTTM WITH TRACTION CONTROL

Vehicle Stability Assist™ (VSA®) is standard equipment on the RL. VSA® uses electronic traction control and ABS functions, combined with yaw and longitudinal/lateral acceleration sensors to detect if the RL is about to understeer or oversteer. VSA® then reduces engine output and applies one or more individual brakes to help stabilize the vehicle-often done before the driver is even aware of the handling instability.

4-WHEEL VENTILATED DISC BRAKES WITH ABS AND ELECTRONIC BRAKE DISTRIBUTION (EBD)

In keeping with the athletic capabilities of the RL, Acura designers upgraded the 4-wheel disc brakes to create a true high-performance system. They targeted the braking performance of top-level competitors from Audi, BMW and Mercedes-Benz as the benchmark to meet or exceed.

Up front, 12.6-inch diameter cast-iron ventilated rotors team with 4-piston aluminum brake calipers. The multi-piston calipers are extremely rigid and are derived from racing applications. In back, 12.2-inch diameter cast-iron ventilated rotors (attached to their hub via lightweight aluminum collets) are gripped by single-piston aluminum brake calipers. For 2009, the RL receives new rear brake pads that improve performance while simultaneously reducing NVH.

The RL includes Electronic Brake Force Distribution (EBD) that automatically adjusts the front/rear brake pressure to suit conditions, while an anti-lock braking system (ABS) helps the driver retain steering control during hard braking situations. Also affecting braking performance is the RL's 4-channel Vehicle Stability Assist™ (VSA®). The combined attributes of EBD, ABS, VSA®, improved brake pads and the RL's new shocks and springs all team to deliver more reliable, better braking.

BRAKE ASSIST

Brake Assist helps drivers apply full braking pressure in an accident avoidance situation. To do so, a microprocessor continually analyzes and "learns" the driver's normal braking habits- monitoring both the rate of pressure applied and the total pressure that the driver normally applies to the brake system.

If the driver suddenly applies the brakes, Brake Assist brings the system to full ABS activation to help stop the vehicle in the shortest distance possible. It is only activated when the microprocessor detects that certain brake pedal speed and pressure thresholds are reached.

Importantly, Brake Assist helps the driver obtain full braking performance in an emergency. The Brake Assist system deactivates when the driver releases pressure on the brake pedal.

TIRE PRESSURE MONITORING SYSTEM (TPMS)

The onboard Tire Pressure Monitoring System (TPMS) with specific location and pressure indicators warns the driver when the air pressure raises/lowers in any tire. This early notification helps reduce the chance of losing control of the vehicle due to improper tire pressure. Continually monitoring pressure levels is important because a slow leak might not be detectable immediately, but over time could cause significant air loss leading to reduced tire grip or the potential of a blowout.

A sensor mounted on each wheel continually monitors tire pressure and sends a coded signal to an initiator located inboard of the tire on the chassis. The information is then sent to an electronic control unit that compares the values of each tire against an acceptable set of pressure parameters.

When a tire's pressure drops significantly below the proper specification, a "CHECK TIRE PRESSURE" alert appears on the dashboard mounted MID alert screen. The TPMS system can simultaneously display the specific air pressure in all four tires via the MID, making it simple to specifically identify a low tire.

At the driver's preference the display 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 a critical level.

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