HEADLINES

2001 Acura 3.2 TL -- Chassis

OVERVIEW
Design goals for the second-generation TL chassis centered on enhancing its sporty performance while preserving its luxury feel. These seemingly contradictory needs required a clean sheet approach to design, embodied by the Acura/Honda Midsize Global Platform. This new-generation 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. Built on a unique underbody assembly 95 mm shorter than that of the previous TL, the new 3.2 TL is 30 mm longer overall and larger inside by almost every significant measure than the car it replaced.

Chassis architecture of the 3.2 TL reflects the pursuit of further luxury refinement while simultaneously advancing handling characteristics. The TL employs isolated front and rear subframes and carries its engine on vacuum-controlled front and rear hydraulic mounts. The double-wishbone suspension has geometric refinements that significantly improve the TL's response to steering input and its ultimate handling limits relative to its predecessor. Engineered to deliver a reduction in understeer at the limit of adhesion, the chassis rewards the enthusiast driver with a more neutral, responsive sporting platform. Cornering grip is enhanced as well, with larger diameter 16-inch wheels that are stopped by an upgraded ABS disc brake system with larger front discs and more rigid front calipers.

The net effect of these far-reaching changes is a substantial improvement in the car's handling precision and braking feel and maximum cornering grip relative to the previous generation TL. This latest TL delivers a more spirited driving experience and has higher ultimate limits than the car it replaces.

Here are the key areas of advancement to the new generation TL chassis:

Ride and handling

  • Refined double-wishbone front suspension
  • New multi-link double-wishbone rear suspension
  • Straightened rear suspension toe curve
  • Tire and wheel diameter increased from 15 to 16 inches
  • Rear suspension pillow joints added for better control of side-force steer (stability) and smoothness (ride comfort)
  • Lower roll center geometry and steering enhancements improve linearity of steering feel
  • Rubber-bushing isolated box-section front subframe
  • Rubber-bushing isolated rear subframe
  • Vacuum-controlled hydraulic front and rear engine mounts

Braking

  • Enlarged front and rear discs along with a drum-in-disc rear design allow separation of service and parking brake systems for superior linearity of brake action

Steering

  • Vehicle-speed sensing power steering with improved feel
  • Rubber coupling in steering column improves shock isolation and maintains linearity

Safety

  • Standard traction control
  • Standard anti-lock disc brakes
  • Excellent steering linearity
  • Excellent maximum lateral cornering adhesion

FRONT SUSPENSION
All Acura passenger cars employ double-wishbone suspension for the precise control of wheel motion it affords. For the new generation TL, Acura engineers redrafted the layout of the front suspension to take advantage of the stiffness of the new front subframe. The repositioned suspension arms deliver altered suspension geometry; the TL's roll center has been lowered by 36 mm to 57 mm, a contributing factor to the car's responsive handling and handling linearity. A strut tower bar also helps maintain precise suspension geometry during cornering. Relative to the previous generation TL, the new car rides on firmer coil springs and retuned dampers with higher compression and rebound damping rates.

REAR SUSPENSION
To satisfy the conflicting demands placed on the TL's rear suspension, which includes offering sporty handling yet a smooth ride without intruding on interior or trunk space, Acura designers completely redesigned the new generation car's rear suspension. The multi-link system is very compact, a factor that accounts for a significant amount of the TL's spacious interior and trunk space.

The compact high-tension steel suspension links reduce weight and carry the rear wheels through a wheel path that's angled rearward to improve bump compliance. This geometry also provides a much straighter toe curve, meaning that during suspension motion, there is controlled "rear steer" taking place. Pillow joints are also applied to better control side-force steer while reducing component friction to improve ride comfort. The rear suspension's roll center has also been lowered slightly relative to the previous generation TL. As in the front suspension, rear spring rates have been increased and dampers recalibrated to improve the TL's handling during aggressive maneuvering.

FRONT AND REAR SUBFRAMES
The TL's chassis rigidity and NVH benefits from its robust front and rear subframes. In front, a perimeter frame consisting of a front member, side members and a rear bulkhead beam is used to form a very strong structure that contributes greatly to overall chassis stiffness and frontal impact crush resistance.

Like the front subframe, the rear subframe forms a large perimeter frame and is made up of large cross section members and smaller stringers that locate the rear suspension and also house the fuel tank. Both subframes are mounted to the body with rubber isolators that help dampen vibration by as much as 5 db in the low- and mid-frequency ranges.

HYDRAULIC ENGINE MOUNT
To further isolate the cabin from vibration, the 3.2 liter engine is mounted to the subframe with two electronically controlled, hydraulic engine mounts and a side stopper mount. The hydraulic mounts are tuned to help minimize vibration throughout the operating range by controlling fluid transfer between two hydraulic chambers in the mount, thereby changing the damping frequency of the mount to help counter any engine vibration.

STEERING
Given the TL's lofty design goals, its steering must strike a balance between the isolation expected of a fine luxury car and the immediate, intuitive response of an accomplished sports sedan. Both ends are served by the TL's speed-sensing power steering. With the assist modulation based on vehicle speed, the effort is light during low speed maneuvering then gets progressively heavier as speed builds to foster a feeling of accuracy and security.

To insulate the driver from road harshness without degrading steering precision, a rubber coupling is positioned in the bottom end of the steering column.

BRAKING SYSTEM
At 11.8 in (300 mm), the new-generation TL's large diameter ventilated front brake discs offer significant braking power and fade resistance. The front calipers are 15 percent more rigid than their predecessors, resulting in a marked improvement in braking crispness and pedal feel. With system-wide tuning of the brake components, the TL has linear brake pedal action, with a predictable effort gradient as the pedal is applied.

By separating the service and parking brakes on the rear wheels and increasing rotor diameter to 11.1 in (282 mm), further enhancements in brake performance were realized. The new drum-in-disc brake design employs the disc portion of the unit for braking while underway, while the drum is used only for the parking brake function. The parking brake is operated with a push on/off type floor pedal.

ANTI-LOCK BRAKING SYSTEM (ABS)
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.

WHEELS AND TIRES
Given the new TL's pronounced sporting side, upgraded wheels and tires were a natural advancement for its current design iteration. Though tire width remained constant at 205 mm, tire aspect ratio was reduced to 60 percent, while tire and wheel diameter was increased to 16 in. The width of the cast aluminum wheels remained at 6.5 in, though the wheel styling was changed to a new seven-spoke design. The revised tire and wheel fitment, combined with the far-reaching benefits of the TL's new platform and suspension, have increased maximum skid-pad adhesion substantially compared to its predecessor, from 0.72 to 0.77 lateral g. To help provide sure-footed power handling in all weather conditions, Michelin all-season high performance V-rated radial tires are fitted to the TL.

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