Introduction To Chassis Design

The automotive chassis is tasked with holding all the components together while driving,and transfering vertical and lateral loads, caused by accelerations, on the chassis through the suspension and two the wheels. Most engineering students will have an understanding of forces and torques long before they read this. It is suggested that the reader has a good understanding of the concepts of axial forces, shear forces, bending, torsion, angular and normal deflections, and finally mass moment of inertia. The key to good chassis design is that the further mass is away from the neutral axis the more ridgid it will be.
This one sentence is the basis of automotive chassis design. Some people stress full triangulation and material choice but once you are into these specifics some critical understanding is missed. People familar with space frames may be thinking that full triangulation is the key to a good space frame. While this will make the design better it can still benefit from this more general design principles. The design section of the book will talk more about these items in relation to the types of chassis but the first part is the theory.
The perfect chassis is a large diameter thin walled tube. In order to understand this you should have a solid grasp of statics and deflection. The Automotive chassis has two main goals.
• Hold the weight of the components
• To ridgidly fix the suspension components together when moving
The first item is an easy design solution and is also the basis of the original chassis designs that were taken from horse drawn carriages. One of the most effective shapes for supporting point loads fixed at two ends is an I-Beam, a box tube, or a C-Beam. One beam on either side so that a floor could be attached and even the smallest of I or C beams can hold tremendous weight. Truck frames stil use this construction as it is an easy and effective method of supporting heavy loads.
It didn’t take long to find out that once these carriage chassis’s has been adapted and speeds increase they would no longer be sufficient to couple suspension components. It was a long time before body on chassis was elimnated in everyday vehicles and happened because of desire to reduce cost and weight in production cars. Long before that the spaceframe was born to fix the problems associated with this type of frame for higher performance vehicles. Space frames did not lend itself to mass production and stayed only in race cars and high performance sports cars.

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