2007 Acura TSX - Chassis
The Acura TSX is more than Acura's entry sedan. It is a responsive, balanced, sharp-handling sports sedan that is designed to compete on equal terms with Europe's best -whether front-drive, rear-drive or all-wheel drive. This capability begins with impressive unit body stiffness, which allows the precise tuning of the double-wishbone front and multi-link rear suspension systems for maximum responsiveness, flat cornering, and high-speed stability.
GOALS AND BENCHMARKS
The ride, handling and stability targets for the Acura TSX were to be better than the most respected compact sport sedans of Europe. As explained in the previous body section, this high performance level required an especially stiff unit body structure to enhance ride and handling precision as well as crash safety. This robust structure makes it possible to tune the suspension for a responsive, satisfying sport driving experience-not to compensate for body flex and resonance.
In today's sophisticated sport sedan market, one of the greatest challenges is in finding a balance that offers sports-car like handling, reassuring high-speed stability and abundant comfort for passengers at all times. To accomplish this, Acura chose independent multi-link front and rear suspension with a combination of steel and aluminum components and specific geometry designed to control lift, dive and body roll. The result is exceptional dynamic performance and stability at all speeds, a very comfortable ride, and greater confidence and enjoyment for the driver and passengers. Even as it approaches its high ultimate cornering limits, the TSX responds accurately to steering and throttle inputs.
The TSX front suspension is a double-wishbone system with sport-tuned shock absorbers and stabilizer, and a shock-tower bar. This set up provides quick response and precise suspension geometry control throughout its range of travel. This is evident when the TSX is driven hard through uneven or undulating corners. The car remains balanced and composed in an environment where even some premium European products become unsettled.
Computer-developed front suspension geometry allowed TSX designers to build in subtle handling enhancements. The TSX has pronounced steering self-centering to improve high-speed stability and lane control. There is also an anti-dive aspect to the geometry to keep the TSX from pitching forward excessively during hard braking, so the car feels more composed. Anti-lift aspects minimize excessive front end lift during hard acceleration. Subtle changes to front wheel toe control while cornering and braking simultaneously further improve vehicle stability. A special compliance bushing located at the front of the front suspension subframe allows controlled fore-aft compliance under rough road conditions, netting superior ride quality.
Both front and rear suspension systems use coil-over shock absorbers that offer quick response and particularly high rebound damping rates, coupled with relatively firm springs. As the stiffer springs compress, this stronger rebound damping is required to control the spring energy as it is released. Extensive on-road and racetrack testing in Europe, America and Japan was used to find the ideal suspension tuning balance between sporting performance and ride comfort.
In keeping with the goals of sporty handling for TSX, a 5-link rear suspension design is employed. The system utilizes an aluminum knuckle and double tubular wishbones. The light aluminum knuckle yields a weight reduction of 13.2 lbs. while providing 50 percent greater rigidity over iron. One benefit of the lighter knuckle is better ride quality. Because it has less "unsprung" weight, the suspension is more responsive to road roughness.
Like the front suspension, the system uses anti-dive geometry that helps keep the TSX stable-and the passengers more comfortable-during hard braking. Built-in toe control geometry helps optimize vehicle stability during corner turn-in, while a high level of roll stiffness, provided by a stabilizer bar, also helps the TSX remain stable during hard cornering by minimizing body roll.
Acura engineers adjusted the rear suspension "roll center" (the theoretical axis around which the car "rolls" or leans while cornering) to be as close as practical to its center of gravity (the height at which the vehicle's weight is effectively centered). This enhances the responsiveness and helps the TSX body to remain flat during sharp maneuvering.
POWER RACK-AND-PINION STEERING
The TSX quick-ratio power rack-and-pinion steering system was designed to reduce resistance in the system, improve linearity of steering response, and reduce steering-wheel kickback on rough roads. Here's how these objectives were accomplished.
- A light feel was obtained by tightening the tolerances in the rack-and-pinion assembly and adopting a steering damper with a variable-damping feature.
- Improving the stiffness of the steering mounting bushing and subframe yielded a more linear steering response on-center by reducing variance in the mounting assembly.
- To reduce kickback, a special variable hydraulic valve was incorporated into the steering gearbox valve housing. The valve works to absorb sudden shock in the steering system such as caused by potholes. It markedly reduces the kickback torque to the steering wheel in such instances.
The power steering gear box preload has been optimized to help provide a more linear steering feel.
The standard P215/50R17 93V MXM4 M+S all-season high-performance tires on the TSX provide an impressive combination of ride and handling. Jointly developed by Acura and Michelin, these tires also promote fuel efficiency through reduced rolling resistance. The tires mount on nine-spoke 17x7-inch aluminum wheels to visually fill the wheel arches, giving the TSX a more aggressive, muscular appearance.
The TSX has 4-wheel disc brakes with large 11.8-inch ventilated front rotors and 10.2-inch solid rear rotors designed to provide exceptional braking feel. A 4-channel anti-lock braking system is standard.
To achieve a solid brake pedal feel, engineers used three main strategies:
- A low 2.6:1 pedal ratio is used, together with a small 20.6 mm master cylinder piston. This reduces pedal travel and provides better brake "feel."
- A lighter and more powerful single (instead of tandem) master power vacuum unit improves stopping power.
- Ultra-stiff front brake calipers that reduce flex and require 8-percent less pedal stroke.
These components provide the TSX with a state-of-the-art braking system that delivers in a firm, confidence inspiring pedal feel with excellent braking effect, even in severe conditions.
ELECTRONIC BRAKE ASSIST
The TSX features Electronic Brake Assist, which helps drivers apply full braking pressure during an accident 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, Electronic Brake Assist brings the system to full ABS activation to help stop the vehicle in the shortest distance possible. It is only activated when the microprocessor detects that certain brake pedal speed and pressure thresholds are reached.
Importantly, Electronic Brake Assist assists the driver in obtaining full braking performance in an emergency. The Electronic Brake Assist system deactivates when the driver releases pressure on the brake pedal.
VEHICLE STABILITY ASSIST
Vehicle Stability Assist (VSA) is standard on every Acura TSX. It uses anti-lock braking system (ABS) technology, together with lateral acceleration sensors, wheel-speed sensors, steering position sensors and a dedicated microprocessor to detect wheel slip (understeer or oversteer). This helps the driver control the vehicle through a nearly instantaneous reduction in engine output (through the drive-by-wire throttle control) or the rapid pulsing application of one or more brakes as appropriate.
For example, if the driver enters a corner too quickly and the vehicle's front wheels begin to slip (understeer), VSA almost instantly detects the situation and interprets it as understeer. VSA then reduces engine torque and selectively applies the brake on the inner front and rear wheels to help counter the understeer and enhance the driver's control. The correction happens so quickly and so seamlessly that the situation is often resolved before the driver is even aware of it.
Another potential scenario involves a traction loss at the rear wheels, such as might be encountered when cornering on a dirty road or when encountering black ice. VSA detects the rear tires beginning to slip and quickly applies the outer front and rear brakes to counter the unwanted yawing motion and help restore control to the driver.
VSA is armed automatically when the TSX starts. Any time the system is triggered, an instrument-panel-warning lamp alerts the driver that VSA is operating. The system can be switched off completely via an instrument-panel-mounted switch.
The VSA system also handles traction control functions, enabling the vehicle to start and climb hills on low-friction surfaces with much greater ability and controllability. It utilizes ABS technology to sense wheel spin on the front (drive) wheels, and then implements individual brake application and drive-by-wire throttle control to restore traction. The benefit is greater security and active safety during winter snow driving or on other slippery surfaces including sand or water.