1991 Acura Legend Chassis
With the existing Legend already suspended by four wheel double wishbone suspension and an anti-lock braking system standard on L and LS models, Honda R&D planners and engineers aimed at evolutionary improvements to all elements of the new model's chassis. Specific objectives called for more active, driver oriented handling characteristics, reduced noise and vibration, and improved braking feel.
A fundamental factor contributing to the 1991 Legend's excellent handling is its new weight distribution, which has gone from 65 percent front/35 percent rear for the previous Sedan models to 60/40. Honda R&D chassis engineers consider this the ideal distribution for a front drive automobile with sporting aspirations.
Part of the new drivetrain layout is a unique aluminum front subframe. This is not only lighter, but more rigid compared to the previous steel subframe. It is mounted to the main structure at eight optimum points with specifically tuned bushings designed to isolate vibration and distribute loads throughout the structure.
While similar to the previous layout in concept - double wishbone geometry - the front suspension is an all new design. New L-shaped lower arms (along with the new large-angle CV joints) take advantage of the longitudinal engine's smaller lateral space requirement to allow a 2.3-ft. reduction in turning circle.Steering offset at the tire/road interface is zero; center offset has been trimmed from 55 to 35mm, which reduces sensitivity to wheel-tire imbalance and transmission of road shocks through the steering. Increased caster, which increases camber by 40' when the wheels are steered 20, improves on-center steering feel, straight line stability and cornering capability. And the entire suspension system is able to operate more precisely thanks to the stronger subframe.
The rear suspension is also all new, featuring reduced unsprung weight and helping refine the Legend's ride and handling. The single upper and dual lower lateral arms are carried on a steel subframe. Two tubular trailing arm elements, bolted together into a unit, perform the function of fore-aft location and countering of braking torque. The hub carrier is now a separate forging.
A principal advantage of this construction is that it has allowed moving the rear wheels' "kingpin axis" - the line between the upper and lower points where the lateral arms meet the hub carrier - considerably outboard; this is now only 0.94 in. (24 mm) inboard from the wheel's vertical center plane, compared to 3.54 in. (90 mm) before. The axis is thus inside the wheel, so the suspension system is called an "in-wheel" type.
The practical result is reduced toe-out, hence excellent stability, during braking. In turn, this better control of geometry during braking has allowed a softening of the trailing arms' compliance bushings, which improves ride comfort. This new system reduces unsprung weight by almost 20 lbs. and it is also more rigid overall.
SPRINGING, SHOCK ABSORBERS AND STABILIZER BARS
Improved control of geometry,as just described for the front and rear suspension, has allowed reduction of the wheel rates through softer springs:
|1990 Legend||160Ib./in.(2.85kg/mm)||127Ib./in.(227kg/mm)||4.92 in./2.95 in.(125mm/75 mm)||5.51 in./2.95 in.(140mm/75mm)|
Together with smoother bump-stop characteristics, all this adds up to impressive riding comfort, particularly on poor road surfaces.
Innovative new shock absorbers also contribute to the Legend's riding comfort and handling. As before, they are of the gas pressure type, but they incorporate an exclusive new valve mechanism. Called the Honda Progressive Valve (HPV),the valving opens and closes progressively, rather than being simply open or closed. This improves the shock absorbers' response to quick wheel movements and results in better rebound control as well; in both cases tire to road adhesion is enhanced.
The new shock absorbers are also larger; with their cylinder diameter increased from 1.18 to 1.42in. (30 to 36mm) front and 0.98to 1.18in. (25 to 30 mm) rear with correspondingly larger oil passages. These larger passages greatly reduce fluid friction and combine with the HPV to produce more consistent damping action under a wide variety of conditions.
Stabilizer bar diameters have been matched to the new suspension geometry, springing and shock absorbers. The tubular front bar is now 1.13in. (28.6mm) in diameter, up from 1.04(26.4).The rear bar, formerly solid and 0.47 in. (12.0 mm) in diameter, is now a tubular one of 0.75 in. (19.1 mm) diameter. Wall thickness for the bars is 0.14 in. (3.5 mm) front, 0.12 in. (3.0 mm) rear.
Taken as a whole, this new suspension system enabled the Legend developers to realize the dream of any serious chassis engineer: to improve handling and riding comfort at the same time.
The 1991Legend has rack and pinion steering with a new speed-sensitive variable power assist system. For improved steering feel,the variation in power assist is now more linear. The system's vane type assist pump has high capacity for accurate response to quick steering wheel motions, and operates very quietly.
The new four wheel disc brakes match the new Legend's higher performance and 60/40 weight distribution. Its ventilated front discs are 11.1in. (282mm) in diameter and 0.91in. (23mm) thick, up from 0.83in. (21mm). At the rear, the solid discs are now 11.1in. in diameter, up from 10.2in. (258mm).A new drumin- disc parking brake, replaces the former mechanical actuation of the rear calipers. Not only does this result a more powerful parking brake, but reduced clearance between pads and rotor improves brake pedal feel and allows shorter pedal travel.
Standard in all models is the Honda R&D developed anti-lock braking system, which has four wheel speed sensors and three channels; previously this was standard in only L and LS models.
WHEELS AND TIRES
The new Legend's simply styled, sporty radial spoke cast alloy wheels are now wider:6.5 J x I5, versus 5.5 JJ x 15. The P205/60R-1590V V-rated tires are upgraded from their previous H speed rating. The spare tire and wheel are of compact, temporary use type. Thanks to a new exhaust system layout and more compact muffler, the spare well is large enough that a road wheel and tire can be stowed there when the spare is installed.