Firma convenzione Politecnico di Milano e Veneranda Fabbrica

del Duomo di MilanoAula 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

Alireza Izadi, Multi-body Dynamics 2/15

Contents

Discussion includes:

1. Introduction• Problems and solutions

2. Methodological approach3. Vehicle model4. Controller design5. Estimator design6. Results7. Conclusion

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 stabilitySolutions:1. Active roll controller

• Active anti‐roll bars• Active air suspension

2. Active braking3. 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.  

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.

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.

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 

Alireza Izadi, Multi-body Dynamics 7/15

Integration of active controllersCo‐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 controller2. Active braking controller

Figure 7. Integration of active roll controller and active braking system.

Alireza Izadi, Multi-body Dynamics 8/15

Active braking controller

NLT estimator PID controller

Braking system

,

,

Active differential braking Controller

Controller details1. PID controller2. NLT estimator3. ABS braking system

Figure 8. Active braking controller with ABS braking system.

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.

Alireza Izadi, Multi-body Dynamics 10/15

Normalized load transfer estimator

, ,

, ,Equation 3

measurements:∆ ,

where

, , = ∅ Equation 4

and

∅∆ ∆

2Equation 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.

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  15percent of velocity. 

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.

Alireza Izadi, Multi-body Dynamics 13/15

ResultsDouble 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 brakingwhile the improvement is 22.45 % for active air suspension and active braking.

Alireza Izadi, Multi-body Dynamics 14/15

ResultsActive 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 semitrailerevenif 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

Alireza Izadi, Multi-body Dynamics 15/15

Conclusion remarksIntegration 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 thiscombination is proper to be used for reducing the rollover risk in highspeeds 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.