Mitsubishi Eclipse. Technical Information Manual (1994) - part 57

DRIVE-CONTROL COMPONENTS   Front Suspension

Double Wishbone Suspension

Double Wishbone Suspension

OPTIMIZED VIRTUAL KINGPIN AXIS POSITIONING
In a double-wishbone type suspension, the lower point the
kingpin axis passes through is the joint between knuckle and

lower arm (point A in the illustration at the left). If the double-
wishbone type suspension has a high-mounted upper arm,

therefore, the extension of the kingpin axis will meet the ground
at a point inside the center of the ground contacting area of
the tire as shown in the illustration (positive offset).

In the case of the multi-link suspension, a virtual
kingpin axis is formed in such a way that its lower

section passes through the intersection (point A’
as illustrated below) of the lateral lower arm and
compression lower arm extensions. This makes it
possible for the virtual kingpin axis ground meeting

Multi-Link Suspension

Rear View

‘Virtual kingpin axis

Poin

Negative offset

point to be located outside the center point where

the tire contacts the ground surface (negative offset).

In addition, the offset between the wheel center
(point C in the illustration) and the kingpin axis can
be made smaller than that in a strut type or double-

wishbone type suspension.

Plan View

Front of vehicle

Upper arm

Point 

Point

  I , , ,  

12x0093

 

   Front Suspension

Vehicle moving direction

The direction
toward which
the wheels
tend to pull

The direction

   

, 

Large; road
surface
resistance

I

Effects of Negative Offset Geometry
(1) When the brake pedal is depressed on a running vehicle

with one wheel on a slippery surface, a force is produced
which causes the vehicle to pull toward the side with larger

road surface resistance (to the right in the case illustrated
at the left).

(2) Because of the dynamics resulting from the negative offset,

moments 

 and 

 are generated in both wheels around

point A (the point where the kingpin axis meets the ground).
Since the magnitude of these moments is proportional

to the road surface resistance, a pull force is produced

in the wheels to turn them toward the side with either

the 

 or 

 moment whichever is greater (to the left

in the illustrated case).

(3) This means that the wheels pivot toward the direction in

which the vehicle’s pull force resulting from the difference

in road surface resistance is compensated for, thus main-

taining the vehicle’s straight-line movement.

 

   Front Suspension

Effects of Reduced Wheel Center to Kingpin Axis Offset
(1) When the vehicle is accelerated or decelerated,

(3) In the multi-link suspension, the offset is as

or when it goes over a projection on road without

small as about a third of that in a strut type

braking, the traction acting on the wheel center

suspension and about one half of that in a

generates a moment around the kingpin axis

double-wishbone suspension. The reduced 

that would cause the toe angle to change.

set, therefore, assures by far better directional

(2) Since the moment is 

 to the 

stability when the vehicle is accelerated or 

tude of offset between the ‘wheel center and

 or when it goes over a projection on

the kingpin axis, the smaller the offset, the less

road.

the change in toe angle, and the better the direc-
tional stability.

<Multi-Link Suspension>

<Double-Wishbone Type Suspension>

 Type Suspension>

 

 axis

 

   

 

HIGH-MOUNTED UPPER ARM

When a side force or any other force acts on the

it receives smaller camber affecting force as

tire in a way to change its camber angle, the degree

compared to the case with a low-mounted upper

of the rigidity that supports the tire depends on the

arm (see the illustrations below), and enough wheel

hardness of the upper and lower arm rubber bushing.

supporting 

 is ensured even with a softer

If the hardness of the bushings is increased, 

bushing. The high-mounted upper arm and softer

er, a larger friction will result during up-and-down

bushing combination, therefore, provides a 

motion of the suspension, leading to a poorer ride.

ful compromise between soft ride and outstanding

The high-mounted upper arm has made it possible

directional stability.

to use a softer bushing because the bushing on

Comparison of Forces Acting on Upper Arm Bushing between High-Mounted and Low-Mounted

 Arms

<Low-Mounted Upper Arm>

<High-Mounted Upper Arm>

Upper arm

 A

,

F: Lateral force acting on tire

 Lateral force caused to act on upper arm by force F

FL: Lateral force caused to act on lower arm by force F

When the equilibrium of moments established at point A in
the illustration is considered, the following formulas hold true.

 . 

   F . 

 

F . 

Also, when the equilibrium of moments established at point

B is considered, the following formulas hold true.

 . 

 

 . 

   

   F . 

   

Assume that   

 in the case of the low-mounted upper

arm and that   

 in the case of the high-mounted upper

arm. Then the 

 and FL are expressed as follows:

Low-Mounted Upper Arm

 

F . 

 

F . 

 2F

High-Mounted Upper Arm

 

F . 

 

   F . 

 

In the case of the high-mounted upper arm, as evident from

the above, smaller camber affecting forces are input in both

upper and lower arms.