Post: Automotive Suspension Technology

The process includes: Choose the system architecture / Choose the location of the “hard point”, or theoretical center of each ball joint or bushing / Choose the rate of the bushing / Analyze the loads in the suspension / Design the spring rate / Design the shock absorber characteristics
Design the structure of each component to make it strong, stiff, light and cheap / Analyze the vehicle dynamics of the final design.
Vehicle-level goals: Maximum steady-state lateral acceleration (in understeer mode) / Roll stiffness (degrees of lateral acceleration per gram) / Ride frequency / Percent lateral load transfer distributed front to rear / Front to rear roll moment distribution / Ride height at different load conditions / Understeer gradient / Turning radius / Ackerman / Bump travel / Bounce travel / Once the overall vehicle goals are determined, they can be used to set goals for the two suspensions. For example, the overall understeer goal can be decomposed into contributions from both ends using a Bundorf analysis.
System Architecture: Typically, vehicle designers work within a set of constraints. The suspension structure selected for each end of the vehicle must comply with these constraints. For both ends of the car, this will include spring type, spring location, and shock absorber location.
For the front suspension, the following points need to be considered:
Suspension type (MacPherson strut or double wishbone suspension) / Steering actuator type (rack and pinion or recirculating ball) / Steering actuator located in front of or behind the wheel center / In reality, there are more possible suspension types for the rear suspension.
Mount points: Hard points control the static settings and kinematics of the suspension.
Static settings are: Toe / Camber / Caster / Roll center height at design load / Mechanical (or caster) track / Anti-dive and anti-squat / Kingpin inclination / Friction radius / Spring and damper kinematic ratios
Kinematics describe the changes in important characteristics of the suspension when it moves, usually roll or steer.
They include: Bump steer / Roll steer / Traction steer / Braking steer / Camber gain in roll / Kingpin gain in roll / Roll center height gain / Ackerman change with steering angle / Roll track gain / Analysis of these parameters can be done graphically, through CAD or using kinematic software.
Compliance analysis: The compliance of bushings, body and other components can change the behavior of the suspension. Generally it is difficult to improve the kinematics of a suspension using bushings, but one method that does work is the toe control bushings used in torsion beam rear suspensions. More commonly, modern car suspensions include noise, vibration and harshness (NVH) bushings. These are designed to be the main path for vibrations and forces that cause road and impact noise, and should be adjustable without affecting the kinematics too much.
Loads: Once the basic geometry has been determined, the loads on each suspension component can be estimated. This can be as simple as determining the maximum load case possible for the contact patch and then plotting a free body diagram for each component to calculate the forces, or as complex as simulating the behavior of the suspension over a rough road and calculating the loads induced. Loads measured on a similar suspension are often used – this is the most reliable method.
Detailed design of the arm: The cantilever arms and spindles are then designed based on the loads and geometry. Inevitably, problems are discovered during this process that force compromises in the basic geometry of the suspension.