2002 Acura 3.2 CL -- Chassis
The CL is engineered to provide extraordinary performance. The engineering goals for the second-generation CL chassis have been achieved by enhancing sporty performance while preserving luxury feel. These seemingly contradictory requirements are embodied by the Global Mid-Size Platform. This front-drive platform combines the packaging efficiency and performance of a transversely mounted front-drive powertrain with Acura's latest thinking on suspension and chassis architecture.
Like the chassis of the Acura TL luxury performance sedan, the new generation CL's chassis further combines advanced performance dynamics with grand touring refinement. The CL chassis rewards the enthusiast driver with more neutral handling characteristics by employing isolated front and rear subframes and carries its engine on vacuum-controlled front and rear hydraulic mounts. The CL's double-wishbone suspension provides outstanding ride and handling characteristics and the rack-and-pinion steering responds immediately to input. An ABS-equipped disc brake system with large front and rear discs and rigid front and rear calipers is fitted to the CL along with all-season high performance tires on 16-inch alloy wheels on the CL and 17-inch wheels on the CL Type-S.
The Type-S suspension has been tuned to offer an even greater level of performance handling through a larger diameter rear stabilizer bar, stiffer front and rear springs, increased compression and rebound damping, along with longer front bump stops.
These chassis elements combine to create a high performance coupe that accelerates, steers, corners and brakes aggressively yet predictably.
The CL employs a double-wishbone suspension to provide precise control of wheel motion. The layout of the front suspension is designed to take advantage of the stiffness of the car's front subframe. A strut tower bar helps maintain precise suspension geometry positioning during cornering. Suspension arms enhance the car's responsive handling. The CL front suspension utilizes firm coil springs, gas-pressurized, hydraulic dampers and a large stabilizer bar to provide a confident driving feel and precise handling.
Additional tuning to the CL Type-S front suspension above and beyond the that of the CL includes stiffer springs, increased compression and rebound damping, along with longer bump stops for more sporty handling. These suspension enhancements allow the Type-S to corner confidently and maintain an optimum body stance for maximum performance.
The CL's rear suspension is designed to provide sporty handling and a smooth ride without intruding on interior or trunk space.
The compact, high-tension steel suspension links reduce weight and carry the rear wheels through a wheel path that is angled rearward to improve bump compliance and limit bump steer. This geometry also provides a more linear toe-in curve, meaning that during suspension motion, there is controlled rear-wheel-steer taking place. Pillow joints are also applied to better control side-force steer while reducing component friction to improve ride comfort. As in the front suspension, rear spring and damping rates have been chosen to provide sporty handling and a compliant ride.
The Type-S rear suspension, like the front, benefits from stiffer springs, higher compression and rebound damping and receives a larger diameter rear stabilizer bar to further reduce body roll during cornering.
FRONT AND REAR SUBFRAMES
The CL's chassis rigidity and NVH benefit from its robust front and rear subframes. In front, a perimeter frame consisting of a front member, side members and a rear bulkhead beam contributes to overall chassis stiffness and frontal and offset frontal impact resistance.
Like the front subframe, the rear subframe forms a large, rectangular-shaped perimeter frame and is made up of large cross section members and smaller stringers that locate the rear suspension and house the fuel tank. Both subframes are mounted to the body with rubber isolators that dampen vibration in the low- and mid-frequency ranges.
LOW ROLL CENTER
To help ensure precise and stable handling, the CL has been designed with a low roll center in its suspension geometry. The roll center of the front suspension is 57 mm above ground level while the roll center of the rear suspension is 116 mm above ground level.
HYDRAULIC ENGINE MOUNTS
To further isolate the cabin from vibration, the CL's 3.2-liter engine mounts to the subframe with two electronically controlled, hydraulic engine mounts and a side stopper mount. The hydraulic mounts are tuned to minimize vibration by transfer of fluid between two hydraulic chambers in the mount, thereby changing the damping frequency of the mount to help counter engine vibration.
The CL's power steering strikes a balance between the isolation expected of a premium coupe and the immediate response of a pure sports car. With the assist modulation based on engine speed, steering is light during low speed maneuvering and gets progressively heavier as engine speed increases for better road feel. A quick steering ratio delivers more responsive steering.
To insulate the driver from road harshness without degrading steering precision and feel, a rubber coupling is positioned in the bottom end of the steering column.
The CL is equipped with large diameter 11.8 in (300 mm) ventilated front disc brakes with rotor thickness of 1.1 in (28 mm) to provide confident braking with minimal fade. In addition, the CL has a short ratio brake pedal to provide immediate, consistent and predictable braking feel under all driving conditions.
Separating the service and parking brakes in the rear wheels and increasing rotor diameter to 11.1 in (282 mm), achieved further enhancements in brake performance. The drum-in-disc brake design employs the disc portion of the unit for dynamic braking, while the drum is used only for the parking brake function. The parking brake is operated with a push on/off type floor pedal, maximizing center console space between the driver and passenger seats.
ANTI-LOCK BRAKING SYSTEM (ABS)
The CL's standard 4-wheel ABS enhances steering control during hard braking. Speed sensors at each wheel send signals to the ABS control module. When the system detects 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.
While the CL features a three-channel ABS system, the Type-S is fitted with a special four-channel system that works in conjunction with the Vehicle Stability Assist (VSA) system. Both ABS systems operate in three-channel mode during straight-line braking, apportioning braking power to the front wheels independently and the rear wheels in tandem. This enhances the driver's ability to maintain steering control during hard stops on slick road surfaces.
The Type-S model's ABS system automatically switches to four-channel mode when the 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 enhanced braking performance.
TRACTION CONTROL SYSTEM (TCS)
The standard equipment Traction Control system (TCS) on the CL coupe detects wheel slip under acceleration and coordinates use of braking and ignition retard to regain traction. For the CL Type-S, TCS functions are incorporated into the VSA system.
In situations where the front drive wheels are on surfaces with different levels of traction, such as when one drive wheel is on wet pavement 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, the system also reduces total engine power output to minimize wheelspin.
VEHICLE STABILITY ASSIST (VSA)
First offered in 2000 on the Acura 3.5 RL flagship sedan, the VSA system is standard equipment on the CL Type-S model. Like the 3.5 RL system, the CL's system orchestrates the throttle and brakes to seamlessly integrate TCS, ABS and VSA processes. This innovation is designed to assist the driver in maintaining control during cornering, acceleration and sudden collision-avoidance maneuvers by applying brake force to the right or left front wheel as necessary and managing the throttle and ignition systems.
By monitoring input from eight vehicle sensors, the VSA system 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 the predicted response range, as when cornering forces exceed the tires performance, VSA automatically intervenes with corrective action. In the case of oversteer (which may lead to spin), VSA applies braking to the outside front wheel to counter the unintended yawing tendency. On the other hand, if understeer is detected, VSA applies braking to the inside front wheel and reduces engine power to turn the car back on to the intended course.
Unlike some vehicle stability systems, which can seem intrusive to enthusiast drivers, the CL's VSA is calibrated to add to stability and predictability, without stifling the driving enjoyment of the CL's carefully engineered chassis and double wishbone suspension. An indicator light flashes on the instrument panel while the system is actively enhancing the stability of the vehicle. A cockpit switch is provided to disable the VSA and TCS while leaving the ABS fully functional.
WHEELS AND TIRES
Because the CL is a performance vehicle, tire and wheel sizes were chosen to accommodate the additional demands of aggressive driving. The CL benefits from 6.5-inch wide x 16.0-inch diameter aluminum alloy wheels with 205/60R16 Michelin MXV4-Plus all-season tires. The CL incorporates a seven-spoke wheel design with a five-bolt lug configuration.
The CL Type-S sports aggressive 7.0-inch wide x 17.0-inch diameter, 5-spoke aluminum alloy wheels. The 5-spoke design incorporates a lipless outer rim design to achieve a seamless contour from the center of the wheel all the way out to the tire for an aggressive, sporty appearance. Large openings in the wheel ensure proper ventilation of the brakes. The Type-S model's wheels wear 215/50R17 V-rated, all-season, high-performance Michelin MXM4 tires for excellent all-around performance.