This paper describes a modelling method to investigate the dynamic behaviour of 4WD vehicle under a severe

driving condition, where the driver applies a rapid tip-in on the accelerator pedal in 2nd gear to achieve maximum

engine torque. This is followed by a tip-out event by releasing the accelerator quickly.

The Tip-In/Tip-Out events are one of important elements to assess the vehicle driveability. During these test

events, the vehicle is expected to generate low frequency vibration between 2 Hz and 10 Hz and gives discomfort

feelings induced by resonance effects on sensitive human organs. The aim of this paper is to develop a 4WD

vehicle model in a modern object-oriented multi-body simulation tool and study its driveability

Bin Raja Ahsan Shah, Raja Mazuir

Cheng, Caizhen

Jones, R. Peter

Pawar, Jasjit

English

Warwick Research Archives Portal Repository

http://go.warwick.ac.uk/lib-publications          Original citation: Bin Raja Ahsan Shah, Raja Mazuir, Cheng, Caizhen, Jones, R. Peter and Pawar, Jasjit (2011) Modelling of 4WD vehicle driveability during tip-in/tip-out events. In: 22nd International Symposium on Dynamics of Vehicle on Road and Tracks (IAVSD), Manchester, UK, 14-19 Aug 2011. Published in: IAVSD 2011 : 22nd International Symposium on Dynamics of Vehicles on Roads and Tracks : 14-19 August 2011 (No.0085). pp. 1-6. Permanent WRAP url: http://wrap.warwick.ac.uk/51652   Copyright and reuse: The Warwick Research Archive Portal (WRAP) makes the work of researchers of the University of Warwick available open access under the following conditions.  Copyright © and all moral rights to the version of the paper presented here belong to the individual author(s) and/or other copyright owners.  To the extent reasonable and practicable the material made available in WRAP has been checked for eligibility before being made available.  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For more information, please contact the WRAP Team at: wrap@warwick.ac.uk  1MODELLING OF 4WD VEHICLE DRIVEABILITY DURING TIP-IN/TIP-OUT EVENTSRaja Mazuir Raja Ahsan Shah1, Caizhen Cheng1, R.Peter Jones1, Jasjit Pawar21School of Engineering, University of Warwick, Coventry, United Kingdom2 Jaguar Land Rover, United Kingdome-mail: esriau@warwick.ac.ukAbstractThis paper describes a modelling method to investigate the dynamic behaviour of 4WD vehicle under a severedriving condition, where the driver applies a rapid tip-in on the accelerator pedal in 2nd gear to achieve maximumengine torque. This is followed by a tip-out event by releasing the accelerator quickly.The Tip-In/Tip-Out events are one of important elements to assess the vehicle driveability. During these testevents, the vehicle is expected to generate low frequency vibration between 2 Hz and 10 Hz and gives discomfortfeelings induced by resonance effects on sensitive human organs. The aim of this paper is to develop a 4WDvehicle model in a modern object-oriented multi-body simulation tool and study its driveability.1. INTRODUCTIONNot many evidences have been seen on the research carried out to examine the eminence of the vibrationresponse in 4WD vehicle system predominantly in the Tip-In/Tip-Out events. The basic test method is to studythe interaction between the driver and vehicle in terms of driveability at low speed events. The results can beanalysed to identify the root cause of the low frequency responses. From the past investigation [1] , the exposureof low frequencies to the driver leads to a sense of discomfort induced by resonance effects on different humanorgans such as upper torso, lower abdomen and shoulders.The previous effort [2] that influenced this work has resulted in the development of a single Torsional Model,a single Fore-Aft Model using the ADAMS modelling environment to study the above behaviours. Both modelshave been correlated with the ADAMS full nonlinear model as a reference model and the vehicle testing data. Thedevelopment of these single models was due to the long computation time of the ADAMS full nonlinear model.Furthermore, it was not possible to use the full nonlinear model for a real time application due to the complexity of itsarchitecture, which consisted of more than 550 Degree of Freedom (DoF). One aim of the work was to acceleratethe process of tuning the properties of the system components to improve the vehicle driveability. However, thesetwo models were not connected to represent the actual physical behavior of the vehicle system due to the lack oftyre model. Hence, it did not demonstrate the actual interaction between these two sub systems. In addition, therewere limitations to the development of control strategies in real time using ADAMS. This is due to longcomputation time and the ability to host the model in a real time platform.Considering the above factors, Dymola modelling platform [3] has been selected to develop the model ofvehicle system based on the open-source Modelica language. For this research, the vehicle model was constructedfrom standard and extended Modelica libraries by setting up the vehicle parameters. The model was alsointegrated in a MATLAB/Simulink environment and implemented in the real time platform, which allows thedevelopment of control strategies.From this experimental result, the vehicle model characteristics at low frequencies have been derived to givethe prediction of the vehicle driveability behavior. In the remaining of this paper, the modelling methods andmodelling details are presented in the next topics, which explained the results of simulation in Dymola, real timesimulation and conclusion of this research.2. MODELLINGThe architecture of the vehicle model was based on a 4x4 platform with 2.2L Diesel engine mounted in East-Westorientation. It consists of all drive-train subsystems and the chassis components acting on longitudinal direction.The physical characteristics of the components were represented by combining the torsional and fore-aftelements with the correct mechanical properties. The interaction of the drive-train and chassis systems wascaptured by a nonlinear tyre model in longitudinal direction, which was derived from simulation data to give atrue behavior of the tractive force on different road surfaces.2In order to build the complete reduced order architecture of the vehicle system, the Dymola single models werecorrelated with ADAMS single models by using the same inputs, which were extracted from vehicle measurement.The models then were coupled after the results have satisfied the specific output characteristics i.e. crank speed andseat acceleration. This Coupled model then has been correlated with the ADAMS full nonlinear model. Figure 1shows the architecture of the single Torsional Model and single Fore-Aft Model.a) Torsional Model b) Fore-Aft ModelFigure 1: 4WD Single Dymola Vehicle System Architecture2.1 Single Torsional ModelWith the adopted approach, the torsional system of engine and drive subsystem components had been simulatedto determine the transient response when subjected to the torque signal from the driver. The number of DoF hasbeen reduced to less than 20 to reduce the computation time [2, 4]. All sub systems were linear except the DualMass Flywheel (DMF), where two stages of stiffness properties (Figure 2) were applied to capture shufflefrequency as a function of angular displacement and angular speed. The vehicle inertias were attached to each ofwheel inertias to imitate the friction load acting on the system. The torsional system of a 4WD vehicle (Figure 1a)comprises of two drive system, namely a FWD system and a RWD system. 4WD is engaged by connecting theFWD system through the power take-off unit, and linked to the rear differential unit with propeller shaft andtraction control unit.Figure 2: DMF Characteristic2.2 Single Fore-Aft ModelThe chassis sub-system was represented by the Fore-Aft model as shown in Figure 1(b). It consists of highlevel components, which have the dominant effect on the system i.e. vehicle body, front and rear wheels,power-unit, front and rear sub-frames. Each of the components was connected through nonlinear compliances,and its displacement has been fixed on longitudinal direction except the mass carrier compliances. Both of themass carrier compliances (right hand and left hand side) have 3 DoF to perceive the effect of the power-unit’s1st Stage2nd StageAngular DisplacementTorqueAngular SpeedDriveReverse3pitch and yaw to the vehicle system dynamics. Similarly to Torsional Model, no tyre model has been includedto represent dynamics characteristics of the wheels, i.e. tractive force, slip ratio. The characteristics have beenreplaced by the forces taken from vehicle test data and used as the inputs to the front and rear wheels to excitethe system.2.3 Coupled ModelThe architecture of the Coupled Model consists of 40 DoF from 4 sub-systems and driver environment, . Eachcomponent of the sub-systems has the combination of torsional elements, masses, inertias and mechanicalproperties. From Figure 3, the engine is mounted to the transmission bell housing and the energy from thecombustion is transferred to input shaft via DMF. The integrated front differential inside the transmission splitsthe torque to the front half-shafts and Power Take Off (PTO) unit. The rear differential then divides the torqueto right and left side of the rear half-shafts. Both of the front and rear half-shafts are connected to the tyremodel to provide the longitudinal force as a function of vertical load and wheel slip ratio. The longitudinalforce drives the chassis sub-system where each of the chassis components is inter-connected by the nonlinearcompliances.Figure 3: Coupled Model of 4WD Vehicle SystemA generic tyre model has been developed based on the standard tyre parameters fitted on this particularvehicle. Car Maker software [5] was used to generate the 3 dimensional data, on tarmac surface with surfacecoefficient,  = 0.85. Fundamentally, the road surface coefficient is reduced as a function of vehicle speed; hencereduce the tractive force further. But this effect has been neglected in this analytical model. The input torque iscontrolled by the driver environment block to represent the combustion process to induce the crank trainsystem. The gear ratio is fixed at 2nd Gear with the assumption that no mechanical losses in the gearing system.By coupling the two single models as discussed earlier, the vehicle model was expected to be more robustand produce true physical representation of the sub-system behaviour. The common root causes of vehicledriveability were always associated with the rise rate of the torque demand as well as the overshoot of theoscillation, which can be sensed by most drivers [6, 7]. The explanation for this occurrence was due to therapid excitation of torque demand to the driveline system and its compliances. With this Coupled Model, it hasallowed more accurate study on driveability and to understand the energy flow from throttle demand to the seatrail via contact patch of the wheels.To validate the accuracy and robustness of the Dymola Coupled Model, a correlation was carried out with anADAMS full nonlinear model and had been verified with vehicle measurement data. The simulation parameterswere set-up to be the same as the ADAMS full nonlinear model.3. SIMULATIONDrivelinePower UnitDriver EnvironmentTransmissionChassis43.1 Off-line SimulationThe standard practices of the Tip-In/Tip-Out tests are to accelerate the vehicle up to 45 kilometer per hour (kph) andcoast down to 30 kph. An abrupt torque then applied within 0.12 seconds to excite the torsional system until it reachedmaximum torque. And finally the torque will be removed instantaneously from the crank train system. For thesimulation set-up, the model was run up to 17 seconds to replicate the test condition above, with fixed step integratorof 0.001 seconds. The Euler solver was used together with Implicit Euler as the inline integration for real time solver.Based on the single Dymola sub-systems simulation, the correlation results show a good agreement withthe single ADAMS models in terms of crank speed and seat acceleration as presented in Figure 4 and Figure5. These results verified that the single Dymola Torsional Model and Fore-Aft Model can be used to form theCoupled Model. For the Coupled Model, the computation time against the ADAMS full nonlinear system hasimproved significantly from 9 hours 30 minutes to only 10.5 seconds. In Figure 6, the crank speed is having thesame behavior as full nonlinear model but the oscillation is seen been phased in 2nd to 4th orders. However, thesediscrepancies can be neglected as the occurrence was due to the effect of the generic tyre model properties. Thecorrelation result demonstrates that the Coupled Model has performed the same manner as the ADAMS fullnonlinear model.Figure 4: Correlation results against single ADAMS Torsional Model without tyre modelFigure 5: Correlation results against single ADAMS Fore-Aft Model without tyre model9.5 10 10.5 11 11.5 12 12.5 13-2-101234Time [sec]SeatAcceleration[m/s2 ]Single ADAMS Torsional ModelSingle Dymola Torsional Model9.5 10 10.5 11 11.5 12 12.5 1316001800200022002400260028003000320034003600Time [sec]CrankSpeed[rpm]Single ADAMS Torsional ModelSingle Dymola Torsional Model5The next stage of the simulation for the Coupled Model was to conduct the Tip-In/Tip-Out events andobserved the response of the system based on 70% throttle position at 2nd Gear. Figure 7 shows that the systemgenerates shuffle frequencies of 3.42 Hz during Tip-In and 3.14 Hz during Tip-Out with exposure time of 2seconds measuring at the seat rail. As discussed earlier, these frequencies range (2 Hz - 10 Hz) will stimulate thehuman organs that can cause the motion sickness. These shuffle frequencies were dominated by the half-shafts[4] and can be tuned by changing its mechanical properties. The overshoots of the shuffle frequencies, whichattributes to the customer perception of vehicle driveability, exceed more than 85% for both events as shown inTable 1.From the graph, the rise rates have also been calculated during Tip-In and Tip-Out to characterize the vehicledriveability. The Tip-In event has generated higher value of rise rate at 3.62 g/s as the result of the suddenexcitation of the driveline system from steady state condition. When torque is removed instantaneously from thesystem, the rise rate on the seat acceleration is reduced by 30% compare to Tip-In event due to the nonlinearityand asymmetric of the system compliances. With these two outputs, it is possible to develop the driveabilitymatrix in the next phase of the research to assess the vehicle behaviour acting on the transient torque response aswell as developing the control strategies to damp the shuffle frequencies.Figure 6: Correlation between Dymola Coupled Model and ADAMS full nonlinear model with Throttle Input100% at 2nd Gear, surface coefficient,  =0.85Figure 7: Tip-In/Tip-Out with Throttle Position 70% at 2 nd Gear,  =0.859.5 10 10.5 11 11.5050100ThrottlePosition[%]9.5 10 10.5 11 11.5-2024SeatAcceleration[m/s2 ]Time [sec]9 9.5 10 10.5 11 11.5 12050100ThrottlePosition[%]9 9.5 10 10.5 11 11.5 1215002000250030003500CrankSpeed[rpm]9 9.5 10 10.5 11 11.5 12-20246Time [sec]SeatAcceleration[m/s2 ]ADAMS full nonlinear modelDymola coupled modelDecayPhase 2nd, 3rd and 4th Order13.5 14 14.5 15 15.5050100ThrottlePosition[%]13.5 14 14.5 15 15.5-4-202SeatAcceleration[m/s2 ]Time [sec]DecayTip-OutTip-In6Tip-In Event Tip-Out EventDamping Ratio,  0.0366 0.0393Natural Frequency, Hz 3.42 3.14Overshoot, % 89.1 88.4Rise rate, g/s 3.62 -2.36Table 1: Overshoot and Rise Rate during Tip-In/ Tip-Out with Throttle Position 70% at 2 nd Gear,  =0.853.2 Real Time SimulationFor the future control strategies development, it is essential to see how the vehicle reacts in real time and tovalidate the response of the vehicle sub-system as close as the actual condition. From the real time simulation, themodel has performed the same behaviour as the Dymola Coupled Model. The computation time for this model is0.5 milliseconds to process every 1 millisecond of sampling time with no overrun. It indicates that the coupledvehicle model can be used in real time simulation for the control development.4. CONCLUSIONSThe Coupled Model of 4WD vehicle system built in Dymola has performed equally as good as the ADAMS fullnonlinear system. The model has produced frequencies that can affect the human organs during Tip-In/Tip-Outevents. The oscillation is mainly dominated by the half shafts, where these frequencies can be shifted by tuningthe properties of stiffness and damping. The simulation time has also reduced from 9 hours 30 minutes with anADAMS full nonlinear model to 10.5 seconds with the Coupled Model with equally valid outputs. The CoupledModel also performs well in a real time test environment as seen by the measurement of the computation time togive a prediction of the vehicle behaviour during torque transient mode.ACKNOWLEGEMENTThe authors would like to thank Jaguar Land Rover and Warwick Manufacturing Group (WMG) for providing usthe support and information in this research project.REFERENCES[1] Atsumi, B., Tokunaga, H., Kanamori, H., Sugawara, T., Yasuda, E., and Inagaki, H., Evaluation of vehiclemotion sickness due to vehicle vibration, JSAE Review, Vol. 23(3), 2002, pp. 341 - 346.[2] Pawar, J., Low Frequency Powertrain and Vehicle System Dynamic, Eng.D Theses, University ofWarwick, Coventry, 2009.[3] Dymola, “Multi-Engineering Modeling and Simulation”http://www.3ds.com/products/catia/portfolio/dymola, [retrieved in July 2011][4] Shah, R.M.R.A., Dhadyalla, G., Jones, P., Pawar, J., Biggs, S., and Cheng, C., A Low Fidelity Non LinearModel of 4WD Torsional Stiffness at Tip-In/Tip-out Events,FISITA 2010 World Automotive Congress Proceedings, 2010, F2010C137[5] CarMaker 3.0 - Shift the test drive into simulation! http://www.ipg.de/CarMaker.609.0.html, [retrieved inJuly 2011][6] List, H.O. and Schoeggl, P., Objective Evaluation of Vehicle Driveability,International Congress &Exposition. 1998, SAE Paper No. 980204[7] Dorey, R.E. and Holmes, C.B., Vehicle Driveability - Its Characterisation and Measurement, InternationalCongress & Exposition. 1999, SAE Paper No. 2004-01-1338

A Low Fidelity Non Linear Model of 4WD Torsional Stiffness at Tip-In/Tip-out Events, FISITA

Evaluation of vehicle motion sickness due to vehicle vibration,

Low Frequency Powertrain and Vehicle System Dynamic, Eng.D Theses,

Multi-Engineering Modeling and Simulation”

Objective Evaluation of Vehicle Driveability,International Congress & Exposition.

Shift the test drive into simulation!

Vehicle Driveability - Its Characterisation and

Modelling of 4WD vehicle driveability during tip-in/tip-out events

http://wrap.warwick.ac.uk/51652/1/WRAP_Shah_IAVSD_0085_MODELLING%20OF%204WD%20VEHICLE%20DRIVEABILITY%20DURING%20TIP_IN%20TIP_OUT%20EVENTS.pdf

Modelling of 4WD vehicle driveability during tip-in/tip-out events

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