LANCER EVOLUTION X - Body, chassis

Mitsubishi Motors’ corporate philosophy is encapsulated in the following motto:
“We are committed to providing the utmost driving pleasure and safety for our valued customers and our community. On these commitments we will never compromise. This is the Mitsubishi Motors Way.” 

Key words: Driving Pleasure, Vehicle Dynamics, 4WD System 

Body, chassis, evaluation and analysis

 Indeed, weight reduction, a low center of gravity and a low moment of inertia are all essential for enhanced dynamic performance of a vehicle. However, simply using aluminum materials causes problems with the rigidity of the body, which has a predominant influence on the vehicle’s dynamic performance. We had to work hard to ensure full rigidity of the body in develop- ing the LANCER EVOLUTION X.

As generally stated, the Young’s modulus and specific gravity of aluminum are both one third those of steel, which means that its specific rigidity (ratio of stiffness to weight) is also one third that of steel. If aluminum material were simply applied to the body framework for reduced weight, the body would be less rigid. An aluminum space frame structure uses extruded aluminum materials for the main structural members, taking advantage of the material’s characteristics to overcome such issues that are characteristic to steel monocoque body structures, such as a loss of rigidity at joints and spot welds. In addition to a low moment of inertia due to reduced weight, the aluminum space frame body provides the type of ride that is not possible with a steel monocoque structure. 

Increasing the number of spot welds is a widely known method of increasing rigidity. At MMC, this method was first employed for the LANCER EVOLUTION IV, followed by the FTO, PAJERO, COLT and other ranges. Today, continuous joining methods such as laser welding are drawing increasing attention as substitutes for spot welding. Furthermore, an increasing number of automaker’s are positive about using adhesives in combination with welding. 

Unlike tires and suspensions, it is difficult to logically express the impact of body characteristics on a vehicle’s dynamic performance by using mathematical formulae. In actual testing scenarios, staff traditionally use their senses to identify the vehicle’s dynamic performance.

It is simple to say “the rigidity of suspension mounts”, but it is not simple to define what the phrase means. To begin with, where is the reference point in the coordinates we should use? 

Flexural stiffness and torsional stiffness are typical values that represent the body’s rigidity, but they do not represent everything regarding rigidity. Rigidity is really difficult to express.

Rigidity of the vehicle’s body is difficult to measure. To measure rigidity, the vehicle’s body must be fixed in place, but the measurement results obtained from an improperly fixed body may not be what we need. These may represent other things, and you will not understand exactly what you are measur- ing. We require a method of presenting the force of inertia.

It is important to visually confirm the defor- mation on an actual vehicle body.

In addition to deformation measurement on a body in white (BIW), we used to reproduce the BIW faithfully by using plastic models of individual body parts to see how they deformed. Now, we generally do the same thing on computer screens using CAE technology visu- ally, but the BIW tests were useful to me because I could confirm how those plastic models deformed by physi- cally touching them. It was easy to cause poor structur- al components to deform by applying a force to them (laughter).