Suspension Design: Double Wishbone
In part II we briefly analyze the first type of suspension: trailing arm. Now let’s take a look at the second major type: double wishbone suspension.
This type of suspension uses two “A” shape arms, one place on the top and the other in the bottom. Because each A arm can limit 2 degrees of freedom, so the two A arms together limits 4 out of the total 6 degrees of freedom. Therefore we still need one more restriction to make the whole system to be 1 degree of freedom.
For front wheels, the extra restriction is the steering arm; for rear wheels, car designers usually use a toe angle control arm.
In the below chart, the one labeled with “Variation 1” is the high mounted double wishbone suspension, commonly used in front suspension. The upper arm is mounted at the strut tower, which saves space, good for engine/transmission packaging.
For rear suspensions, more evolution can be made to the upper/lower A arms. For example the one labeled as “Variation 2”, is decomposing the lower A arm into two separate control arms. This variation can be seen on the Nissan GT-R and Cadillac CTS; some cars may decompose the upper A arm, for example the Porsche Panamera.
What about decomposing both the upper and lower A arms? – You can do that, actually many auto makers do that too, and it has a name you must be very familiar to: multi-link suspension (or “5-link” for short), labeled as “Multi-link” in the above chart. So for now you should understand: the 5-link or multi-link suspension, it is in fact a variant of the double wishbone system.
In part IV, I will analyze the third type of suspension: the McPherson suspension.
Index:
Automobile Suspension Design 101 (Part I): What Is A Suspension?
Automobile Suspension Design 101 (Part II): Trailing Arm Suspension
Automobile Suspension Design 101 (Part III): Double Wishbone Suspension
Automobile Suspension Design 101 (Part IV): MacPherson Strut Suspension
Automobile Suspension Design 101 (Part V): H-Arm Suspension
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