1. Firma convenzione
Politecnico di Milano e Veneranda Fabbrica
del Duomo di Milano
Aula Magna – Rettorato
Mercoledì 27 maggio 2015
Multi‐body Dynamics:
Improvement of the designed active rollover
control air Suspension with active
differential braking using nonlinear multi‐
body vehicle model
Alireza Izadi
Professors:
Federico Cheli and Pierangelo Masarati

2. Alireza Izadi, Multi-body Dynamics 2/15
Contents
Discussion includes:
1. Introduction
• Problems and solutions
2. Methodological approach
3. Vehicle model
4. Controller design
5. Estimator design
6. Results
7. Conclusion

3. Alireza Izadi, Multi-body Dynamics 3/15
Introduction:
Problem and solutions (SATA and my PhD thesis)
A problem of heavy vehicles:
• Considerable amount of fatal accidents (35%)
• Rollover causes 38% of fatal accidents in HVs
and it is the most horrible accident.
Preventability of rollover accidents:
• 50% are impossible to control even with
professional drivers.
Rollover reasons:
• High center of gravity and lower rollover
threshold
• Lack of lateral stability
Solutions:
1. Active roll controller
• Active anti‐roll bars
• Active air suspension
2. Active braking
3. Active steering
Figure 1 . Preventability of rollover accidents by driver.
3.3
38.4
49.7
8.6
0
10
20
30
40
50
60
Possible Maybe Impossible unknown
Figure 2 . Bendix ABS‐6 advanced with ESP.

4. Alireza Izadi, Multi-body Dynamics 4/15
Introduction:
Active air suspension (the first solution)
Our proposed solution:
• Using direct control of suspension roll
angle by implementing the existing air
springs.
Acheievements:
Figure 3 . Active air suspension operation in a turn.
Rollover improvement (%) 8
Maximum speed in DLC (km/h) 112
Extra required parts Control Valve
Costs Very low
More improvements needed:
• To increase the efficiency of active air
suspension,
• To deal with different active combinations
which are useless in previous control
strategy.

5. Alireza Izadi, Multi-body Dynamics 5/15
Introduction:
Active differential braking (the second solution)
Figure 4 . Passive braking system.
Figure 5 . Active braking system is stretching vehicle by engaging the brakes.

6. Alireza Izadi, Multi-body Dynamics 6/15
Vehicle Model:
Multibody Model of tractor semitrailer
• TruckSim delivers the most accurate, detailed, and efficient methods for simulating the
performance of multi-axle commercial and military vehicles. The tractor Semitrailer
model is described
• mathematically by 192 ordinary differential equations that describe its kinematical and
dynamical behavior.
• 76 bodies,
• 30 multibody degrees of freedom,
• 73 multibody coordinates,
• 82 auxiliary coordinates,
• 30 multibody speeds,
• 7 auxiliary speeds,
• 263 active forces,
• 135 active moments.
• Co-simulation with Simulink, LabVIEW, ETAS ASCET, Custom C/C++ programs,
Visual Basic, etc
Figure 6. 30‐dof model of TruckSim

7. Alireza Izadi, Multi-body Dynamics 7/15
Integration of active controllers
Co‐simulation of MathWorks and TruckSim
Minimum order
controller
Air springs and their PID
controllers
NLT estimator
PID
controller
Braking
system
‐+
,
,
,
Direct Active Roll Controller
Active differential braking Controller
1. Active roll controller
2. Active braking controller
Figure 7. Integration of active roll controller and active braking system.

8. Alireza Izadi, Multi-body Dynamics 8/15
Active braking controller
NLT estimator
PID
controller
Braking
system
,
,
Active differential braking Controller
Controller details
1. PID controller
2. NLT estimator
3. ABS braking system
Figure 8. Active braking controller with ABS braking system.

9. Alireza Izadi, Multi-body Dynamics 9/15
Proportional Integral Derivative controller and the weighting law
,
,
Equation 1
0 ,
2
,
2 ,
Equation 2
Control objective:
To minimize the NLT of each axle when axle is close to lift‐off.
Control law:
Weighting law:
• The closer is to 1, the later the controller will be activated.
• parameter shows how fast the controller should focus on minimizing the NLT.
• The smaller the difference between and is, the more quickly the performance weight
punishes the normalized load transfer.

10. Alireza Izadi, Multi-body Dynamics 10/15
Normalized load transfer estimator
, ,
, ,
Equation 3
measurements:
∆ ,
where
, , =
∅ Equation 4
and
∅
∆ ∆
2
Equation 6
And vertical equilibrium on axle gives:
, , , , 0 Equation 6
∅
,
,
,
,
And the air spring forces are calculated by by , , , .
Figure 9. Forces and moments on axle.

11. Alireza Izadi, Multi-body Dynamics 11/15
Roll angle estimations
Roll angle of axles estimated as well as normalized load transfer.
Figure 10. Active air springs in step maneuver. Estimations of axles roll angle on steer axle, drive axle, trailer axle.
Estimation error of steer axle, drive axle and trailer axle.
The error vector is asymptotically stable, adequately fast, robust to center of payload gravity
position and robust to 15 percent of velocity.

12. Alireza Izadi, Multi-body Dynamics 12/15
Normalized load transfer estimation
Figure 11. Estimations of normalized load transfer on steer axle, drive axle, trailer axle.
The error is converging to zero by imposing step steering input to vehicle model and in double
lane change the error is low and the estimations and measurements are in agreement.

13. Alireza Izadi, Multi-body Dynamics 13/15
Results
Double lane change simulation and maximum speed
Passive Active air suspension s Active air springs + Active braking
Speed (km/h) 98 112 112 120
Final speed at t = 12 [sec] ‐ 112 98.8 114.2
Speed drop (%) ‐ 0.54 11.77 4.83
Figure 12. Normalized load transfer (a), speed reduction of different controllers (b) and brake pressure (c).
Table 1. maximum speed of tractor semitrailer in a severe double lane change steering.
The severe maneuverability is improved 14.3 percent by active air suspension or active braking
while the improvement is 22.45 % for active air suspension and active braking.

14. Alireza Izadi, Multi-body Dynamics 14/15
Results
Active trailer and active tractor
Table 2. Maximum speed of tractor semitrailer in a severe double lane change steering for active tractor and trailer.
Combining two controllers causes maneuverability improvement for tractor and semitrailer
evenif only one of the units has active braking.
The response of controllers when only tractor is active or trailer is active is improving by
using active braking and active air suspension together.
Fully active air suspension 112
Fully active braking 112
Fully active air suspension & braking 120
Active air tractor 90
Active air trailer 98
Active braking tractor 98
Active braking trailer 98
Active air tractor & braking trailer 116
Activtractor braking & active air trailer 116

15. Alireza Izadi, Multi-body Dynamics 15/15
Conclusion remarks
Integration of two controllers
Considering the combination of actuators:
• The vehicle severe maneuverability is increased while the speed drop is less
than the only active braking controller implementation, thus this
combination is proper to be used for reducing the rollover risk in high
speeds and severe maneuvers while the .
Considering active tractor and active trailer:
• Applying this integration improves the manoeuvrability of active air tractor
and active air trailer in combination with active braking and vice versa.