OVERVIEW
The 3.5RL is equipped with four-wheel independent double-wishbone
suspension with coil springs, four-wheel disc brakes with ventilated
front rotors, an Acura-designed Antilock Braking System (ABS) and
stabilizer bars in both front and rear. The goals in developing the
RL chassis were to increase overall cornering ability and make the
response of the chassis to driver input as linear and predictable as
possible while at the same time achieving a smooth, well-controlled
ride-and reducing noise, vibration and harshness to a remarkable
degree.
Like all Acura models, the RL is designed as a true driver's car, and revised suspension tuning in '99 gave the car more nimble and sporty handling while maintaining excellent ride comfort. For 2000, a highly sophisticated Vehicle Stability Assist (VSA) system joins the RL's roster of control enhancing standard attributes.
LOW-FRICTION DOUBLE-WISHBONE SUSPENSION
The double-wishbone suspension layout of the RL (and all other Acura
automobiles) allows precise control of wheel movement while isolating
the damper units from the side-loading and resulting friction
inherent in the less-advanced McPherson strut design used on some
other luxury sedans. The front suspension uses unequal-length upper
and lower control arms and a tubular stabilizer bar, while the rear
suspension is a combination of a longitudinal trailing arm, three
lateral links and a tubular stabilizer. For excellent stability and
improved ride quality, added anti-squat and anti-dive geometries were
built into the RL suspension. To achieve a compliant ride without
compromising handling response or cornering capability, the RL
suspension also uses a number of innovations to reduce friction
throughout suspension travel. The stabilizer bars use highly
efficient ball joints at either end, as well as self-lubricating
bushings at the sub-frame mounts. The upper arms of both the front
and rear suspension have low-friction ball-joint bushings where they
attach to the main structure, reducing overall friction while
enhancing rigidity of the suspension assembly. The dampers of the RL
have an advanced Progressive Valve design for increased damping
control at low damper speeds while retaining quick, fluid response to
large impacts. Special redesigned Teflon seals within all four damper
units reduce friction even further for improved ride quality.
For the '99 RL, engineers worked to further optimize the suspension to provide a sportier handling feel while maintaining luxury-class ride comfort. Changes included new front and rear spring rates, modified front and rear control arm bushings and front dampers.
LOW ROLL CENTER
To give the RL a stable, predictable feel during hard cornering,
while improving overall lateral-acceleration capability, the
suspension geometry was designed with lower roll centers than
previous Acura luxury sedans. The roll center of the front suspension
is
59 mm above ground level and 70 mm above ground level at the rear. This has resulted in increased cornering performance, from 0.77 g to 0.80 g, as well as more predictable response at the limits of adhesion.
LIQUID-FILLED REAR TRAILING ARM BUSHING
To reduce road noise and harshness, the bushing at the front of the
rear-trailing arms is a liquid-filled design, instead of the more
conventional rubber-damped bushing.
NEW VEHICLE STABILITY ASSIST (VSA) SYSTEM
Building on Acura's long history of advancing the science of
automotive handling stability and control, the 2000 3.5RL now comes
standard with a state-of-the-art Vehicle Stability Assist (VSA)
system. Developed in cooperation with Bosch, this four-channel system
orchestrates the throttle and each of the RL's four disc brakes
independently to seamlessly integrate traction control, anti-lock
braking and stability enhancement processes under widely divergent
road and driving conditions.
By monitoring input from six vehicle sensors, the VSA can calculate a predicted range of vehicle response while constantly monitoring the vehicle's actual response and the driver's control inputs. If the actual response is outside of the predicted response range-as when cornering forces exceed the tire's performance, for example, VSA automatically intervenes with corrective action. In the case of oversteer during hard cornering (which might lead to spin), VSA applies braking to the outside front wheel to counter the unintended yawing tendency. On the other hand, if understeer becomes pronounced, VSA applies braking to the inside front wheel to turn the RL back onto the intended course.
Unlike some vehicle stability systems which can seem intrusive to enthusiast drivers, the Acura VSA is calibrated to add to stability and predictability, without stifling the driving enjoyment of the RL's carefully engineered chassis and double wishbone suspension. An indicator light flashes on the instrument panel while the system is actively stabilizing the vehicle. A cockpit switch is provided to disable the vehicle stability and traction control aspects of the system while leaving the antilock braking system fully functional.
BRAKING SYSTEM
Power-assisted four-wheel disc brakes are standard, with ventilated
rotors in front for minimal fade and excellent heat dissipation. For
1999, the RL benefited from larger diameter front-brake discs (up 20
mm to 300 mm) and thicker front and rear rotors (up 5 mm and 3 mm,
respectively) for reduced fade and braking performance. By
fine-tuning the leverage ratio of the brake pedal and the response
characteristics of the power-brake vacuum diaphragm, the RL
engineering team achieved reduced stopping distances while making
brake response more linear and intuitive. Combined with the
"low-creep" torque converter, these refinements also help make it
easier to hold the RL at a stop.
ANTILOCK BRAKING SYSTEM
The 2000 3.5RL has a revised four-wheel Antilock Braking System (ABS)
that is integrated into the new Vehicle Stability Assist (VSA)
system. The new ABS system operates in three-channel mode during
straight-line braking (apportioning braking power to the front wheels
independently and the rear wheels in tandem), and then automatically
switches to four-channel mode when the VSA system senses high
cornering forces. This allows the ABS system to take advantage of
weight transfer to the outside of the turn during cornering and apply
higher brake pressure to the outer rear wheel for braking
performance.
The ABS enhances steering control during hard braking. Speed sensors at each wheel send signals to the ABS control module; if the system detects impending wheel lockup, it first holds, then reduces hydraulic pressure to the affected wheel, letting it regain traction before full braking resumes. The ABS function is also highly effective on split-friction surfaces, in which one side of the vehicle has significantly less traction than the other.
In the highly unlikely event of an ABS failure, a warning light is illuminated on the instrument panel. In such a case, the control module cancels the ABS function, allowing the standard braking system to operate normally. The system used in the RL is a design that weighs 1.3 kg less than the previous-generation ABS system.
TRACTION CONTROL SYSTEM
The traction control aspect of the Vehicle Stability Assist (VSA)
system works just as seamlessly. When wheel slip is detected under
acceleration, differential braking and engine controls are called
into play to modulate the amount of power put to the ground. In
situations where the drive wheels are on surfaces with different
friction properties, such as when one drive wheel is in water while
the other is on dry pavement, the system applies braking action to
the wheel that's slipping, allowing the tire with better grip to move
the vehicle. In addition to independent control of the front wheel
brake, the system can also reduce total engine power output to keep
wheelspin in check.
ROTARY-VALVE, VARIABLE POWER-ASSISTED, RACK-AND-PINION POWER
STEERING
The speed-sensitive variable power-assisted rack-and-pinion steering
uses a rotary valve that senses torque applied to the steering wheel
and a vehicle speed sensor to vary power assist accordingly. The
system adjusts steering assist for easy steering in parking-lot
conditions and quick, precise steering feel at speed. The RL utilizes
a magnesium-cast steering wheel for lighter steering feel, and a
dynamic damper in the steering shaft for reduced wheel vibration.
WHEELS AND TIRES
The RL is equipped with P215/60R16 MXV4 Plus Michelin tires on 7.0 JJ
x 16 cast-aluminum alloy wheels to maximize handling while minimizing
road noise. The tires of the RL are of a special
low-rolling-resistance design, which yields outstanding ride
characteristics and improved fuel mileage while achieving excellent
handling response and overall grip. The tires are an All-Season
design, for enhanced traction on wet roads as well as on dry
pavement.