Suspension Modes
A 4-wheel vehicle can be understood as a 4-freedom degrees system defined by the independent movement of each wheel.If we combine these movements conveniently we can come with the so called "suspension modes", this is combined movements such as:
- Body Vertical movement
- Body Pitch movement
- Body Roll movement
- Axle crossing
The first approximation to these body/vehicle movements can be modeled with simple linear math analysis. If we consider every wheel position measured in respect to the vehicle body we have four values named x0, x1, x2 and x3. In each wheel we also have a tire load, this is, a force between the tire and the vehicle body that we can name f0, f1, f2 and f3. The next step is to define the relationship between such forces and position values to characterize the suspension system.
The next step is to depart from individual forces and movements and be able to define the forces and the wheel positions in an integrated relationship. This can be followed in depth in our paper SAE 2002-01-3105 (screen).pdf that describes this relationship as
Where
the resiliencies matrix defines all the suspension spring rates for every
body movement.
This math is particularly useful to model interconnected suspension systems, as it can perfectly separate the spring rates of every suspension mode.
