Oral Session 09

Ackermann Testing

CSU 203

Start Date

10-4-2018 1:05 PM

End Date

10-4-2018 2:05 PM

Student's Major

Automotive and Manufacturing Engineering Technology

Student's College

Science, Engineering and Technology

Mentor's Department

Automotive and Manufacturing Engineering Technology

Mentor's College

Science, Engineering and Technology

Description

Ackermann geometry is designed into the steering system of a vehicle to turn the wheels at slightly different rates. In a typical passenger vehicle the Ackermann is designed to turn the inner wheel on a corner more than the outer wheel so that the difference in turning radiuses are accommodated for and producing a common center of rotation. The idea behind this setup is to reduce the binding and scrubbing of tires that occurs when they do not have a common center of rotation. Reduction of the binding will save the tires from prematurely wearing and reduce rolling resistance. In race car applications the vehicles Ackermann geometry would need to be set up differently and can be often overlooked for performance benefits. The reasoning behind this difference comes from a tire and rubber polymer characteristic known as slip angle. Slip angle is the angle between the direction the wheel and tire are pointed verses the actual direction of travel. The slip angle is created when lateral force is applied to a tire, a distortion of the tire is caused differing the trajectory of the wheel and effective footprint of the tire on the ground. Slip angle varies with tire type, tire size, rubber compound, inflation pressure, and tire temperature and is actively affected by lateral force and vertical load from the result of turning force and vehicle weight transfer. When a vehicle experiences a cornering force, there is weight transfer from the inside tire to the outside tire. This will cause two different vertical loads between tires resulting in each tire having different slip angles. For effective cornering the trajectory of the tires effective footprints still need to have a common center of rotation, but with the addition of slip angle, the wheel and tire trajectories will differ even have varying angles throughout load ranges. Those differences have to be accommodated for with a change in Ackermann geometry from that of a typical passenger vehicle. The amount of Ackermann for each race car’s application will vary due to multiple variables affecting the slip angles. With the aid of specific tire data, testing of Ackermann variations is required to find the proper geometry for the application that the race car will be subject to. With the proper testing data, changes in geometry can be implemented for different events or tracks to obtain the maximum potential grip in corners. For testing, five different sets of tie rods and toe pick up points were made that set Ackermann geometry in five intervals within range specified range. Each set was tested and timed in a skid pad test along with a slalom section. The results were then compared to each other to see how each Ackerman settings worked in both test setups.

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Apr 10th, 1:05 PM Apr 10th, 2:05 PM

Ackermann Testing

CSU 203

Ackermann geometry is designed into the steering system of a vehicle to turn the wheels at slightly different rates. In a typical passenger vehicle the Ackermann is designed to turn the inner wheel on a corner more than the outer wheel so that the difference in turning radiuses are accommodated for and producing a common center of rotation. The idea behind this setup is to reduce the binding and scrubbing of tires that occurs when they do not have a common center of rotation. Reduction of the binding will save the tires from prematurely wearing and reduce rolling resistance. In race car applications the vehicles Ackermann geometry would need to be set up differently and can be often overlooked for performance benefits. The reasoning behind this difference comes from a tire and rubber polymer characteristic known as slip angle. Slip angle is the angle between the direction the wheel and tire are pointed verses the actual direction of travel. The slip angle is created when lateral force is applied to a tire, a distortion of the tire is caused differing the trajectory of the wheel and effective footprint of the tire on the ground. Slip angle varies with tire type, tire size, rubber compound, inflation pressure, and tire temperature and is actively affected by lateral force and vertical load from the result of turning force and vehicle weight transfer. When a vehicle experiences a cornering force, there is weight transfer from the inside tire to the outside tire. This will cause two different vertical loads between tires resulting in each tire having different slip angles. For effective cornering the trajectory of the tires effective footprints still need to have a common center of rotation, but with the addition of slip angle, the wheel and tire trajectories will differ even have varying angles throughout load ranges. Those differences have to be accommodated for with a change in Ackermann geometry from that of a typical passenger vehicle. The amount of Ackermann for each race car’s application will vary due to multiple variables affecting the slip angles. With the aid of specific tire data, testing of Ackermann variations is required to find the proper geometry for the application that the race car will be subject to. With the proper testing data, changes in geometry can be implemented for different events or tracks to obtain the maximum potential grip in corners. For testing, five different sets of tie rods and toe pick up points were made that set Ackermann geometry in five intervals within range specified range. Each set was tested and timed in a skid pad test along with a slalom section. The results were then compared to each other to see how each Ackerman settings worked in both test setups.

Recommended Citation

Harteau, Christopher. "Ackermann Testing." Undergraduate Research Symposium, Mankato, MN, April 10, 2018.
https://cornerstone.lib.mnsu.edu/urs/2018/oral-session-09/3