Automotive suspension design is an aspect of automotive engineering, concerned with designing the suspension for cars and trucks. Suspension design for other vehicles is similar, though the process may not be as well established.
The process entails
Since the 1990s the use of multibody simulation and finite element software has made this series of tasks more straightforward.
A partial list would include:
Once the overall vehicle targets have been identified they can be used to set targets for the two suspensions. For instance, the overall understeer target can be broken down into contributions from each end using a Bundorf analysis.
Typically a vehicle designer is operating within a set of constraints. The suspension architecture selected for each end of the vehicle will have to obey those constraints. For both ends of the car this would include the type of spring, location of the spring, and location of the shock absorbers.
For the front suspension the following need to be considered
For the rear suspension there are many more possible suspension types, in practice.
The hardpoints control the static settings and the kinematics of the suspension.
The static settings are
The kinematics describe how important characteristics change as the suspension moves, typically in roll or steer. They include
The analysis for these parameters can be done graphically, or by CAD, or by the use of kinematics software.
The compliance of the bushings, the body, and other parts modify the behaviour of the suspension. In general it is difficult to improve the kinematics of a suspension using the bushings, but one example where it does work is the toe control bush used in Twist-beam rear suspensions. More generally, modern cars suspensions include a Noise, vibration, and harshness (NVH) bush. This is designed as the main path for the vibrations and forces that cause road noise and impact noise, and is supposed to be tunable without affecting the kinematics too much.
In racing cars, bushings tend to be made of harder materials for good handling such as brass or delrin.In Passenger cars, bushings tend to be made of softer material for added comfort.In general physical terms, the mass and mechanical hysteresis (damping effect) of solid parts should be accounted for in a dynamic analysis, as well as their elasticity.
Once the basic geometry is established the loads in each suspension part can be estimated. This can be as simple as deciding what a likely maximum load case is at the contact patch, and then drawing a Free body diagram of each part to work out the forces, or as complex as simulating the behaviour of the suspension over a rough road, and calculating the loads caused. Often loads that have been measured on a similar suspension are used instead - this is the most reliable method.
The loads and geometry are then used to design the arms and spindle. Inevitably some problems will be found in the course of this that force compromises to be made with the basic geometry of the suspension.
Simulation and direct equations:Abramov, S., Mannan, S., & Durieux, O. (2009)'Semi-Active Suspension System Simulation Using SIMULINK'. International Journalof Engineering Systems Modelling and Simulation, 1(2/3), 101 - 114 http://collections.crest.ac.uk/232/1/fulltext.pdf