CHASSIS OVERVIEW
Quick handling response, nimble performance, high dynamic capabilities, outstanding ride comfort, safety features and a fun-to-drive character aptly describe the 2011 Acura RL chassis. The RL features a highly rigid unit body that teams 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, 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 2011, and it retains its quick response and accurate torque distribution.
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 overall quality.
The RL's unit body design with a fully-independent suspension, Advanced Compatibility Engineering™ (ACE™) body structure and a SH-AWD™ system 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 RL's front suspension is a double-wishbone design with a large subframe mount and a special compliance bushing. The coil spring rates, dampers and stabilizer bar have been designed to reduce chassis attitude changes to ensure a flat ride during acceleration, cornering and hard braking.
Specific performance goals for the RL suspension included good response over rough roads while maintaining excellent steering feel. 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 large subframe mount and a long upper control arm. As a result, the vehicle roll center is optimized for good turning response, excellent 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.
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 high side loads that SH-AWD™, large 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 a traditional 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 stiff 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 Michelin Pilot HX MXM4 P245/45R18 M+S all-season tires that deliver outstanding handling and a compliant ride.
Within the trunk of the 2011 RL is a temporary-use Bridgestone T155/70D17 tire mounted on a 17x4-inch 12-spoke aluminum wheel.
WHEELS
To provide excellent handling and improved looks, new 18x8-inch diameter 15-spoke aluminum wheels are matched with performance-minded Michelin Pilot all-season tires. While the new wheels add a look of visual sophistication, they also deliver mechanical sophistication thanks to the first-ever use of resonator wheel technology.
In an effort to quell road noise transmitted to the RL's cabin, the new noise reducing wheel uses a polypropylene Helmholtz resonator that encircles the center portion of the inside of the wheel. Such resonator wheel technology significantly lowers middle frequency noise (between 100 and 500 hertz). Combined with the added use of insulation material on the floorboard areas of the RL, there is a 1.3 dB reduction in interior noise— which translates to a 15-percent improvement.
ELECTRONICALLY CONTROLLED, SPEED-SENSING, VARIABLE POWER ASSIST RACK-AND-PINION STEERING
Precise steering performance is an essential facet of the 2011 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 engine 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."
Vehicle Stability AssistTM with traction control
Vehicle Stability Assist™ (VSA®) is standard equipment on the 2011 RL. VSA® uses electronic traction control and ABS functions, combined with yaw and lateral acceleration sensors to detect if the RL is experiencing understeer or oversteer. If so, VSA® 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 engineers designed the 4-wheel disc brakes to create a true high-performance system. Engineers 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 based on 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.
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®).
BRAKE ASSIST
Brake Assist helps drivers apply full braking pressure during a collision 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. Brake Assist is only activated when the microprocessor detects that certain brake pedal speed and pressure thresholds are reached. 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 RL driver when the air pressure significantly decreases 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 traction 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 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.
If a tire's pressure drops significantly below the proper pressure specification, a "check tire pressure" alert appears on the MID screen mounted in the dashboard. The TPMS system can simultaneously display the air pressure in each of the vehicle's four tires via the MID, making it simple to identify an under inflated or over inflated tire. Regardless whether a driver chooses to monitor tire pressure, a warning will be given if a tire's pressure drops below a critical level.