1999 Acura TL Chassis
Design goals for the TL chassis centered on enhancing its sporting performance while preserving its luxury feel. These seemingly contradictory needs required a clean sheet apporach 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 TL is 30 mm longer overall and larger inside by every significant measure than the car it replaces.
Chassis architecture of the 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 newly designed double wishbone suspension has geometry refinements that significantly improve the TL's response to steering input, and its ultimate handling limits. Engineered to deliver a reduction in understeer at the limit of adhesion, the new chassis rewards the enthusiast driver with a more neutral, responsive sporting platfonn. Cornering grip is enhanced as well, with larger diameter 16-inch wheels that are stopped by a newly 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 and braking feel, and maximum cornering grip. The New 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 1999 TL chassis:
Ride and handling
- Refined geometry double-wishbone front suspension
- New 5-link double-wishbone rear suspension with refined geometry
- 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
- Enlarged front discs along with a drum-in-disc rear design allow separation of service and parking brake systems for superior linearity of brake action
- Vehicle-speed sensitive power steering with improved feel
- Rubber coupling in steering column improves shock isolation and maintains linearity
- Standard traction control
- Standard anti-lock disc brakes
- Improved steering linearity
- Improved maximum lateral cornering adhesion
All Acura passenger cars employ double wishbone suspension for the precise
control of wheel motion it affords. For the new TL, Acura engineers have redrafted
the layout ofthe front suspension to take advantage of the
stiffness of the new front subframe. The repositioned suspension anns 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 more responsive handling and improved 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.
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 trunk space, Acura designers completely redesigned the car's rear suspension.The new five-link system is much more compact, a factor that accounts for a significant amount of the TL's newfound 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. The new geometry also provides a much straighter toe curve, meaning that during suspension motion, there's 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 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 new 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 new rear subframe forms a large perimeter frame and is made up of large cross section members and smaller stringerswhich 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 new 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.
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-sensitive 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.
Upgraded ABS Braking System
With the upgrade to 16-inch wheels, the TL has also received larger-diameter ventilated front disc brakes. Measuring out at 11.8 inch (300 mm), the new discs make a significant improvement in braking power and fade resistance. New front calipers are 15% more rigid than their predecessors, resulting in a marked imrpovement in braking crispness and pedal feel. With system-wide tuning of the brake components, the new TL has significantly more linear brake pedal action, with a more predictable effort gradient as the pedal is applied.
By separating the service and parking brakes on the rear wheels, further improvements in brake performance were realized. The new drum-in-disc brake dsign 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 now operated with a push on/off type floor pedal.
Wheels and Tires
Given the new TL's enhanced sporting side, upgraded wheels and tires are a natural advancement. Though tire width has remained constant at 205 mm, tire aspect ratio has been reduced to 60%, while tire and wheel diameter has been increased to 16 inches. The width of the cast aluminum wheels remains 6.5 inches, though the wheel styling has been changed to a new seven spoke dsign. The new tire and wheel fittment, combined with the far reaching benefits of the TL's new platform and suspension have increased maximum skid-pad adhesion substantially, from 0.72 to 0.77 lateral g.