Honda Accord -- Chassis

9/15/2000 9:27:52 PM

OVERVIEW
Performance goals for the Accord chassis focused on improving its ride and handling characteristics, and reducing chassis-related NVI-1 (Noise, usually road noise; Vibration, both suspension- and engine-induced; and Harshness, usually low-frequency suspension impact-related). In addition, the chassis/frame is a major element in helping the new Accord meet all applicable safety regulations. Finally, manufacturing convenience, especially in terms of platform commonality, was a key factor in its design.

To meet these chassis goals, Honda engineers designed a new unit-body structure using front and rear subframes. Together the body and its subframes form a rigid unit that functions as an excellent platform for the Accord's new suspension system.

The design boasts enhanced capabilities in the areas of stability, handling and control, and ride smoothness.

The subframe assemblies and suspension system also have been engineered to help reduce vibration and noise transmission to the passenger compartment.

The braking system on the Accord has been designed to offer even better feel and response when braking.

The follwoing list highlights the Accord Chassis:

RIDE, HANDLING AND STABILITY

  • 5-link double wishbone rear suspension with refined geometry, broader-based subframe mounting points and greater compliance
  • Double wishbone front suspension with lowered roll center enhances handling linearity
  • Low spring rates for better ride
  • Large tire and wheel sizes on DX and LX Sedan and all Coupe models provides better ride and handling

NVH

  • Inertial axis 4-cylinder engine mounts minimize engine vibration
  • V-6 engine uses a rubber-mounted, floating subframe
  • Redesigned exhaust system with large mid-silencer (plus dual silencers for the V-6) is quieter and reduces NVH
  • Two electronically controlled (active) engine mounts and a side stopper mount with a (passive) hydraulic bushing help minimize engine vibration on V-6 models

BRAKING

  • New ABS has even better response and control. In addition, size and weight of the system have been reduced
  • ABS is available as an option on LX and DX models and is standard on all EX models
  • Master cylinder design adds more braking power and response. Combined with an altered pedal ratio, the result is even greater brake-pedal sensitivity, feel and control

STEERING

  • Rubber coupling in steering shaft reduces vibration and improves steering feel

SAFETY

  • Front subframe design helps Accord meet frontal-impact regulations

SUSPENSION SUBFRAMES

  • Help to increase overall structural rigidity
  • Quicker and easier installation
  • Greater packaging efficiency yields rear seat and trunk space

INDEPENDENT SUSPENSION
The Accord chassis uses an advanced version of Honda's 4-wheel double wishbone suspension. The front suspension is a complete redesign and takes advantage of the added rigidity and space efficiency of the Accord's front subframe design. The rear suspension is a 5-link double wishbone system. The suspension-system design meets Honda's goals for enhancing the Accord's traditional balance of agile handling, stability and ride comfort.

SUBFRAME-MOUNTED 5-LINK DOUBLE WISHBONE REAR SUSPENSION
The Accord's subframe-mounted 5-link double wishbone rear suspension offers more precise camber and toe control, greater ride compliance and better space efficiency than its predecessor. The 5-link system consists of one upper lateral link, one lower lateral link and a third lateral toe-control link located behind these two links and attached to the back edge of the upright. The upper and lower links control camber when cornering, so that the tire-contact patch remains flat (the optimum position for maximum adhesion) throughout the wheel's range of movement.

The lateral toe-control link compensates for the inherent toe deviation of independent rear suspensions, which tends to steer the car as it corners (roll steer). As a result, the Accord tracks accurately around curves with no noticeable roll-steer effect.

The rubber bushings used in the anchor points of the lateral links have a high spring rate that minimizes any deflection or deviation from the designed camber geometry.

While the previous Accord used a trailing arm (longitudinal link) for fore-aft wheel location, the new system uses a Watt linkage described by the two diagonal links -- one leading and one trailing. When viewed from the side, the diagonal (trailing) link attaches to the wheel upright below the axle, while the rear diagonal (leading) link attaches above the axle. Together they control the upward movement of the wheel so that it does not interfere with the rear bulk-head of the passenger compartment. Compliance is supplied by the trans-verse links. Soft rubber used in the bushings of the links' anchor points acts as compliance bushings and helps to absorb impacts to the sus-pension; for example, from changes in pavement height.

The 5-link double wishbone rear suspension is also more space-efficient than its predecessor, which helps create more rear-seat and trunk space. The inner and outer suspension attachment points are clustered close to the centerline of the axle and anchored to the new subframe below the inner wall of the body instead of on it.

The spring and shock absorber now occupy the space previously occupied by the long, curving upright and upper lateral link of the older system. This additional space allows the use of larger diameter, lower-rate springs, which yield a more comfortable, compliant ride.

In addition, since the upper attachment point is no longer on the body of the Accord, but on the separate subframe, the rear suspension can be attached in one operation. The rear subframe also allowed Honda engineers to spread the inner attachment points of the suspension over a broader area for better load distribution.

DOUBLE WISHBONE FRONT SUSPENSION
The Accord's double wishbone front suspension benefits from a large cross-section frame-rail design that adds even more strength and rigidity to the system. Like the rear suspension, the front design allows the spring-mounting points to be raised higher on the spring/shock absorber assembly, thereby allowing the use of larger diameter, lower-rate springs, resulting in a softer, more compliant ride without sacrificing handling.

The front suspension roll-center height has been lowered by 57 mm. As a result, the jacking effect of the suspension arms when cornering is reduced, yielding a more linear, less understeering behavior and even more precise handling.

FLOATING FRONT AND REAR SUBFRAMES
The Accord's chassis rigidity benefits from its front and rear subframes. In front, a perimeter frame consisting of a front member, side members and a rear bulkhead beam, all of a larger cross-section, replaces the previous Accord's H-pattern. The additional members form a very strong structure that contributes greatly to overall chassis stiffness and frontal-impact crush resistance. The new subframe design can carry either a V-6 or 4-cylinder engine.

Like the front subframe, the Accord's rear subframe forms a large perimeter frame and is made up of large cross-section members. A cross-member and smaller stringers com-plete the structure, which also' houses the fuel tank as well as the rear suspension pickup points.

The V-6 engine's front and rear sub-frames are both mounted to the body with rubber isolators that help damp-en vibration by as much as 5 dB in the low- and mid-frequency ranges. The V-6 engine is mounted to its subframe with two electronically controlled hydraulic engine mounts (one fore and one aft) and a side stopper mount with a passive-type hydraulic bushing.

The 4-cylinder engine subframe is rigidly mounted. The automatic-transmission version uses one electronically controlled hydraulic mount, one passive-type hydraulic bushing and two conventional engine mounts. The manual-transmis-sion version uses two passive-type hydraulic bushings and two conventional engine mounts.

The subframes also provide additional manufacturing benefits by making it possible to lift the front engine and suspension into the body as a unit. The rear subframe also allows the rear suspension and fuel tank to be installed in one operation.

STEERING SYSTEM
The Accord uses a power-assisted rack-and-pinion steering system. Power assist is steering-torque sensitive, meaning that hydraulic boost is applied to the system in direct proportion to the amount of force (torque) created between the tire and the road as the wheel is steered. As the force increases, the system increases the amount of power assist accordingly. Regardless of speed, an increase in effort (for example, if the wheels encounter a rough surface with a greater coefficient of friction) will be countered by an increase in boost.

Steering torque is sensed by a torsion bar-controlled rotary valve. One end of the bar is connected to the steering box, the other to the steering column. As the torsion bar twists in proportion to steering effort, it progressively opens larger orifices in the valve. As the orifice size increases, so does the amount of hydraulic fluid pumped, and therefore torque increases.

The power-steering pump is a large-capacity vane type that operates quietly and responds quickly to movements of the steering wheel. The vanes create a smaller pressure fluctuation and the pump body incorporates a flow-control valve that supplies optimum pressure. The system has two relief valves: one valve maintains a constant return pressure from the pump, while the other responds to pressure fluctuations from the steering system itself. The result is fast response (or boost) to steering loads, quieter operation and less kickback.

The Accord's roller bearing-equipped constant velocity joints (tripod joints) permit a larger steering angle and smaller turning diameter. The turning diameter is 36.4 feet (11.1 meters) curb to curb for the Sedan and 36.1 feet (11.0 meters) for the Coupe.

A special rubber coupling used in the steering column reduces vibration and shimmy while also improving steering feel.

REVISED BRAKING SYSTEM
The Accord uses 260 mm (10.2 in.) x 23 mm (0.9 in.)-thick ventilated front disc brakes. The rear brakes are 220-mm (8.6 in.) drums.

ABS is standard on all EX and V-6 LX models and is available as an option on 4-cylinder LX and DX models. It is a four-sensor, three-channel system with a speed sensor located at each wheel. When the driver applies maximum brake pressure and impending wheel lockup is detected, the sensors send a signal to an electronic control unit (ECU). The ECU processes the information, then tells the ABS to momentarily reduce and then reapply brake pressure at the appropriate wheel(s). If impending wheel lockup occurs when brake pressure is reapplied, the cycle is repeated. This allows the tires to maintain maximum braking traction.

There is a separate channel for each front wheel and the rear wheels share a common third channel. This is a "select-low" system, meaning the system con-trols both rear-wheel slave cylinders together when it senses incipient wheel lockup in either wheel.

WHEELS AND TIRES
Accord EX models have 15-inch alloy wheels. The Accord EX V-6 Coupe has 16-inch alloy wheels. Accord LX models have 15-inch steel wheels with full wheel covers. Accord DX models have 14-inch steel wheels with full wheel covers.

WHEELS AND TIRES

Accord EX
V-6 Sedan

Accord LX
V-6 Sedan

Accord EX
4-Cyl Sedan

Accord LX
4-Cyl Sedan

Accord DX
4-Cyl Sedan

Wheels

15 x 6 1/2 jj

15 x 6 1/2 jj

15 x 6 jj

l5 x 6 jj

14 x 5 1/2 jj

Aluminum

Steel w/Full

Aluminum

Steel w/Full

Steel w/Full

Alloy

Wheel Covers

Alloy

Wheel Covers

Wheel Covers

Tires

P205/65 R15

P205/65 R15

P195/65 R15

P195/65 R15

P195/70 R14

WHEELS AND TIRES

Accord EX
V-6 Coupe

Accord LX
V-6 Coupe

Accord EX
4-Cyl Coupe

Accord LX
4-Cyl Coupe

Wheels

16 x 6 1/2 jj

15 x 6 1/2 jj

l5 x 6 jj

15 x 6 j

Aluminum

Steel w/Full

Aluminum

Steel w/Full

Alloy

Wheel Covers

Alloy

Wheel Covers

Tires

P205/60 R16

P205/65 R15

P195/65 R15

P195/65 R15