Bundorf analysis
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A Bundorf analysis is a measure of the characteristics of a vehicle that govern its understeer balance. The understeer is measured in units of degrees of additional yaw per g of lateral acceleration.
An imaginary example
[edit]| Front | Rear | |
|---|---|---|
| deg/g | deg/g | |
| Load transfer effect and cornering stiffness of tire | 8.0 | 7.0 |
| Aligning torque | 0.2 | -0.2 |
| Roll camber | 1.2 | 0.0 |
| Roll steer | 0.6 | -0.4 |
| Fy Compliance steer | 0.3 | -0.1 |
| SAT compliance steer | 0.7 | 0.6 |
| Total Axle Cornering compliance | 11.0 | 6.9 |
Hence the total under-steer is 11.0 deg/g minus 6.9 deg/g, or 4.1 deg/g.
Negative values are over-steering, positive values are under-steering, for that axle. If the under-steer contribution of the rear axle is greater than that of the front axle you get negative under-steer, which is known as oversteer. The analysis is only applicable while the parameters remain constant, and thus only up to about 0.4 g.
Explanation of terms
[edit]Load transfer effect and cornering stiffness of tire. As load transfers across the vehicle the tire's ability to provide cornering force for a given slip angle changes. The latter is known as the cornering stiffness of the tire. See also Tire load sensitivity
Aligning torque. The tire does not just generate a lateral force, it generates a torque as well. This tends to rotate the vehicle as a whole.
Roll camber. As the vehicle rolls the kinematics of the suspension provide a change in the camber of the tire. This generates a force known as camber thrust.
Roll steer. As the vehicle rolls the kinematics of the suspension provide a change in the steer angle of the tire. This generates a cornering force in the normal way.
Fy compliance steer. The lateral force at the contact patch causes the wheel to rotate about the steer axis, generating a steer angle.
SAT compliance steer. The aligning torque directly twists the wheel on the compliances in the suspension, generating a steer angle.
Under-steer. In this case, the tendency for an axle or vehicle to turn outwards from a corner.
See also
[edit]References
[edit]Bundorf, R.T. and Leffert, R.L. (1976) 'Cornering compliance concept for description of vehicle. directional control properties', SAE paper 760713