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Triangulation of the front face of the suspension box





 
 

 

 


Fig. 49

 

Table 19

 

This modification shows that even with the previous stiffening of the suspension box the lack of lateral triangulation in this section was still paramount. It is believed that the stiffening of the suspension box has enhanced the effect the previous modifications will have on the torsional stiffness. This now provides triangulation to every face of the suspension box effectively turning it into a closed torsion box. With none of the beams in this section now placed in bending it shows a 60% increase in torsional stiffness over the previous model and a 205% increase over the original. This is reflected in the increase in efficiency of 56% over the previous model. Further triangulation for this area was considered however, the radiator is mounted to the front face of the suspension box and as much airflow is required through this face as possible. This prevented any further triangulation being added. The beam is 1” x 1” 16-gauge mild steel RHS.

 

Y-brace conversion of lower engine beam

 
 

 


Fig. 50

 

Table 20

 

To optimise the efficiency of the outer rails, which, from analysis of the stress plots of the deformed model, were not highly stressed, the lower engine support beam was modified. This involved splitting the load paths from channelling the loads only into the transmission tunnel to channelling them into the outer rails as well. This was accomplished by changing the rear section of the engine support beam to a Y-brace. From the results in Table 20 where an increase in torsional stiffness and efficiency of 6% is shown over the previous model it can be seen that this modification is viable.

 

 

Conversion of 8mm flat bar to 2” x 1” RHS

 
 

 


Fig. 51

 

Table 21

 

The upper triangulation on the rear firewall frame is of 8mm thick mild steel solid bar. This is approximately three times the mass of an equivalent section of 1” x 1” 16-gauge mild steel RHS and displays less torsional stiffness. Changing this to 2” x 1” 16-gauge mild steel RHS will not only reduce the mass but will also increase the torsional stiffness. This drop in mass and increase in torsional stiffness will inevitably lead to an increase in efficiency.

 

With an overall increase in torsional stiffness of 213% and an overall increase in efficiency of 197%, it is clear that the inclusion of all these modifications is viable.

 

Stage 3-Identical Modifications to Fully Panelled Chassis

 

The modifications as performed in 8.2 were performed on the fully panelled chassis to show the contribution to torsional stiffness provided by the shear panels. This also allowed an optimisation for mass as the panels could be changed from mild steel to aluminium and the effect on the stiffness of the modified chassis noted.

 

 

 
 

 


Fig. 52

 

Due to the panels partially obscuring the modifications (Fig.52) and their presence in 8.2, these results will be in a tabular form with no pictures of the chassis. The modifications were performed in the same order and are denoted by the notation 8.3.*.

 

Table 22

 

 

As can be seen in Table 22 when the modifications are performed on the fully panelled chassis from 8.1.9 the increase in torsional stiffness is almost 1000Nm/deg more than the sum of the individual improvements. This is due to the stiffening of the most flexible spring allowing a much greater improvement in the effectiveness of the stiffening of the passenger compartment. With an overall increase in torsional stiffness of 377% over the original chassis, these modifications show major improvement in the performance of the chassis. With an overall increase in efficiency of 286% over the original chassis, it can be assumed that more of the chassis is being used effectively to resist torsional loading

 

 

Stage 4-Optimisation Study

 

Now that a significant increase in torsional stiffness has been achieved, an optimisation study can be performed. This involves keeping the stiffness as high as possible but removing as much mass as possible. This can be achieved by conversion of mild steel panels to aluminium, by reduction in section size of beams that are not highly stressed or conversely increasing the section size of highly stressed beams. The optimisation has been aimed at achieving a minimum of 6000Nm/deg torsional stiffness with the minimum mass. It should be remembered at this stage that the baseline validation model was measured by the software as being 8Kg heavier than the original chassis. This means that the efficiency of the chassis will be even higher than the results suggest if a physical chassis with these modifications were to be constructed and it matched the predicted stiffness values. This is unlikely however and the efficiency is more likely to be as predicted due to the drop in mass and torsional stiffness that a physical chassis would have.

 







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