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Modelling and analysis of suspension systems 243
the reaction force at C can be determined the suspension does not move
despite a considerable vertical load being applied at the tyre contact patch.
In reality the damper has a sliding degree of freedom that allows the length
C–I to shorten until the additional compression of the spring produces the
force required for the suspension system to be in static equilibrium. This
mechanism is the key behind the iterations described in Chapter 3 that take
place during a solution step at a given point in time. In effect all the preceding
vector analysis can be considered typical of the computations during
one of many analysis iterations at a given point in time.
To demonstrate the final phase in this process a vector analysis will now be
performed to determine the new position of the movable points throughout
the suspension system due to a deflection in the suspension spring unit. In
this case we will shorten the line C–I by 100 mm taking this to be representative
of the movement for this suspension with typical spring and
damper properties. We can consider that we are looking here at the suspension
moving between the defined or model input position, to the full bump
position. During a typical analysis iteration the movement would in fact be
far less than this but the following calculations will illustrate the process
and complete our treatment of vector analysis in this chapter.
Before proceeding with the analysis Figure 4.79 is provided to remind us
of the suspension configuration, the point labelling system and to illustrate
the shortening of the damper unit.
In order to establish the position of any point that has moved in the suspension
system we must work from three points for which the co-ordinates
I
J
Shorten C–I
by 100 mm
C
B
H
A
C
D
Z 1
Y
X 1
1
O 1
E
F
G
K
L
P
Fig. 4.79 Shortening of damper unit for double wishbone suspension
geometry analysis