Adams Assignments – Problem 5 – Compliance
Initially, the suspension assembly is created from the rear multilink template available in the acar_shared folder and loaded onto the Adams standard interface (shown in image 1).
Step 1:
The Brake steer and Longitudinal wheel recession under braking come under one baseline simulation. So under Simulate > Suspension analysis > Static loads option, the upper limit and lower limit of each tire are given 3000 N and -3000 N (braking forces) respectively, and the simulation was started.
Results:
Brake steer: 0.1641 deg/mm = 164.1 deg/m (shown in image 2). The suspension toes in during braking as the toe value is positive.
Longitudinal wheel centre recession: -5.2241E-04 = -0.0005 mm/N = -0.5 mm/KN (shown in image 3)
Step 2:
The Traction steer and Longitudinal wheel recession under Traction come under one baseline simulation. So under Simulate > Suspension analysis > Static loads option, the upper limit and lower limit of each tire are given 3000 N and -3000 N (Traction forces) respectively, and the simulation was started.
Results:
Traction steer: 0.0165 deg/mm = 16.5 deg/m (shown in image 4). The suspension toes in during traction as the toe value is positive.
Longitudinal wheel centre recession: -0.001 mm/N = -1 mm/KN (shown in image 5)
Step 3:
The Lateral force compliance steer and Lateral force compliance camber come under one baseline simulation. So under Simulate > Suspension analysis > Static loads option, the upper limit and lower limit of each tire are given 3000 N and -3000 N (Lateral forces) respectively, and the simulation was started.
Results:
Lateral force compliance steer: -0.000168 deg/N = -0.168 deg/KN (shown in image 6). Under the action of lateral force, the wheel toes out, deflecting away from the turn, resulting in an oversteer condition.
Lateral force compliance camber: -0.000405 deg/N = -0.405 deg/KN (shown in image 7). Under the action of lateral force, the wheel tilts away, giving a positive camber on loaded tires. Any contact patch reduction in rear tires results in oversteer condition.
Step 4:
The bump steer simulation is done, Simulate > Suspension Analysis > Parallel wheel travel with 100 and -100 as bump and rebound travel, respectively.
Results:
Bump Steer: -0.0024 deg/mm = -2.4 deg/m (shown in image 8). As the value of the slope is negative and there's a toe out condition during the bump. This will give an oversteer condition to the car.
Part 2: Tuning:
From the literature, the bump steer generally happens because the track rod does not point to the front view Instant Centre of the control arms or has a different length compared to the control arm. If I take the first scenario, modifying the z-coordinate of the track rod (shown in image 9) might point to the instant centre of the control arms.
Step 1:
After performing 9 iterations, the bump steer is optimised to +2.6 deg/m. As the value of the toe angle is positive, this means it's a toe-in setup, which gives an understeer condition to the vehicle.
Result:
Bump Steer: 0.0026 deg/mm = 2.6 deg/m (shown in image 10)
Optimising traction wheel centre recession stiffness:
To optimise the wheel centre recession, we have to change the stiffness of the trailing arm bushing (shown in image 11). Currently, the bushing has a stiffness of 4500 N/mm (shown in image 12). The current traction wheel centre recession stiffness is 953.8 N/mm (shown in image 13).
Target:
Traction wheel centre recession stiffness: 500 N/mm
Step 1:
First, the bushing stiffness is optimised to 200 N/mm after 4 iterations (shown in image 14). The wheel centre recession of 500.93 N/mm is achieved(shown in image 15).
Optimising Lateral force Camber Compliance:
Currently, with baseline bushing stiffness, we have a camber compliance of -0.405 deg/KN but we have to set it up to -0.45 deg/KN. As the upper control arm bushing is connected to the knuckle, it has higher camber control.
Currently, the bushing stiffness is 4500 N/mm (shown in image 16). The bushing stiffness was changed to 2300 N/mm (shown in image 17)
Results:
Lateral force Camber Compliance: -0.00046 deg/N = -0.46 deg/KN (shown in image 18).
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