Independent suspensions

Technique: Independent suspensions

Reusability	Reversible
Designers:	XYZ Cargo
Tools:	Wrenches
Parts:	Frames, Bolts, Nuts, End caps, Spindles
Techniques:	Bolting, Clevis fasteners, Tri joints, Live hinges, Steering knuckles

Introduction

Independent suspension is any automobile suspension system that allows each wheel on the same axle to move vertically (i.e. reacting to a bump on the road) independently of the others. This is contrasted with a beam axle or deDion axle system in which the wheels are linked – movement on one side does not affect the wheel on the other side. "Independent" refers to the motion or path of movement of the wheels or suspension. It is common for the left and right sides of the suspension to be connected with anti-roll bars or other such mechanisms. The anti-roll bar ties the left and right suspension spring rates together but does not tie their motion together.

Challenges

Because the wheels are not constrained to remain perpendicular to a flat road surface in turning, braking, and varying load conditions, control of the wheel camber is an important issue. Swinging-arm was common in small cars that were sprung softly, and could carry large loads, because the camber is independent of load. Some active and semi-active suspensions maintain ride height, and therefore the camber, independent of load. In sports cars, optimal camber change when turning, is more important.

Approaches

• Swing axle
• Sliding pillar
• MacPherson strut/Chapman strut
• Upper and lower A-arm (double wishbone)
• Multi-link suspension
• Semi-trailing arm suspension
• Swinging arm
  • Transverse leaf springs when used as a suspension link, or four-quarter elliptics on one end of a car are similar to wishbones in geometry, but are more compliant. Examples are the front of the original Fiat 500, then Panhard Dyna Z, and the early examples of Peugeot 403, and the backs of AC Ace and AC Aceca.

Wishbone and multi-link allow the engineer more control over the geometry, to arrive at the best compromise, than swing axle, MacPherson strut, or swinging arm do; however, the cost and space requirements may be greater.

Semi-trailing arm is in between, being a variable compromise between the geometries of swinging arm and swing axle.

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References

• Wikipedia: Independent suspension
• Wikipedia: Car suspension