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OFF ROAD DRIVE OF WHEELED VEHICLES IN DYNAMIC REALTIME SIMULATION

Carsten Harnisch, Björn Lach

Institut für Kraftfahrwesen und Kolbenmaschinen (IKK)

Universität der Bundeswehr Hamburg Holstenhofweg 85,

22043 Hamburg Germany

1. SUMMARY The paper presents the simulation program ORSIS (Off Road Systems Interactive Simulation) as one of the leading tools for the realtime simulation of multiaxle off road vehicles in terrain. After a short introduction the programs philosophy, the history and the program structure will be presented. The main submodels of the program, like the vehicle model, the terrain model and the tire-soil model will be discussed. Some examples of simulation results will be given, where different multiaxle-driveline concepts as well as tire inflation pressure strategies are compared. One focal point will be the discussion of the different fields of application, which are vehicle development and testing, driver training under off road conditions and mission planning in unknown terrain. In connection with the vehicle testing also the example of a HIL (Hardware in the Loop) application of ORSIS – the realtime coupling with a power test stand – will be described. Moreover the usage of ORSIS with the driving simulator MARS (Mobile Automotive Research Simulator) will be shown. The paper will be completed by a short outlook on the future development of ORSIS. 2. INTRODUCTION

Vehicles operating in terrain have to meet quite special requirements due to the uneven and deformable ground. Therefore it is important to know and to regard these effects, when developing off road vehicles. Unfortunately the real testing in terrain is expensive and often leads to unsatisfying results because the terrain properties are characterised by a considerable statistical scattering. Moreover the terrain properties change by deforming and compaction of the soil while driving through. For this reasons real testing often is not reproducible.

A solution could be the simulation, which has become an unrenounceable tool of the automotive industry through the last years. But even though there are a lot of established commercial tools for vehicle design on solid road there is a lack of tools for the off road driving. One reason is, that the simulation in terrain is very complex because of the manifolded effects of tire-soil interaction, such as sinkage, multipass, slip, slip-sinkage, etc. Models to describe these processes analytically, correlating the vehicle characteristics and soil data and the relevant mobility factors, are available. However, the different processes of wheel-soil interaction, superposing each other, make conclusions for the vehicle design and layout on base of these separate models difficult. In addition, the different load on each one of the vehicle wheels and the varying soil conditions under the wheels extend the problem, so that there is the need of simulation of the over-all-system.

A simulation tool that was specially developed for simulating all essential effects in off road locomotion of wheeled vehicles, is the simulation program ORSIS (Off Road Systems Interactive Simulation), developed at the Institute of Automotive Engineering of the University of Federal Armed Forces Hamburg.

In the following, the program with its actual state of development will be presented. The programs philosophy, the structure, the most important submodels and some examples of simulation results will be given. Attention will be drawn to the manifolded possibilities of application of ORSIS as a tool for vehicle layout, optimal adaption of components, hardware in the loop integration in combination with teststands, evaluation of competing vehicles and mission planning.

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3. PROGRAM HISTORY – GENERAL INFORMATION The development of ORSIS started in the early 90’s on the basis of a new tire-soil model which was elaborated at the IKK. With a steadily further development, using the latest findings in scientific research also with the FEM method, ORSIS could be established as one of the best simulation programs for the simulation of wheeled vehicles under off road conditions. Presentations on national and international conferences as well as numerous inquiries from industry are a proof for the outstanding results that have been archived. Today ORSIS represents more than ten years of continuos development and research at the IKK.

ORSIS is written in C++ programming language and has a modular structure, which allows easy and fast adaptations. It can be run on different computer platforms. The basic platform are SGI Unix-Systems and lately – almost more important - PC systems under the operation system LinuX (even on actual Laptops). 4. THE SIMULATION CONCEPT OF ORSIS The ORSIS simulation (Fig. 1) includes all three parts of the terrain driving system: The driver, the vehicle and the terrain.

O R SI S

ff oad ystems nteractive imulation

Terrain

Driver

Cardan shafts

Engine

Flywheel

Torque converter with bridgingclutch and shifting clutch

Gearbox

ShaftIntermediate shaft

Wheel planetary gears

Distribution gear

Axle differentials

Vehicle

Fig. 1: Simulation Concept of ORSIS

One of the main features of ORSIS is its realtime capability. This allows to integrate the human being into the simulation (man in the loop) as the driver of the car. The simulation can be driven by graphical elements on the computer screen that represents the single handling elements (steering wheel, acceleration and braking pedals, switches for differential lock etc.). For a more realistic simulation the whole vehicle can be controlled by a driving cabin with the original operating elements. 5. PROGRAM STRUCTURE The ORSIS program structure is depicted in Fig. 2. The essence of ORSIS consists of three main modules describing the vehicle, the terrain and the wheel-soil interaction. It is of great importance, that the functions of the vehicle components are physically modelled and all the parameters of influence on mobility, especially the characteristics and data of the vehicle, are integrated into the program. These can easily be varied in order to

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adapt to existing vehicles or to any virtual vehicle. As the program-structure is modular, vehicle components can be exchanged easily. This includes special functions, such as tire pressure control, propulsion slip control, manual or automatic addition of axle-drives, manual or automatic differential locking or coupling, which are already part of the program. Due to this structure it is also possible to consider new developments like active suspension systems in the future. 6. VEHICLE MODEL

TERRAINMODEL

3D-VISUALISATION

VEHICLE MODEL

Steering modelLongitudinally

Slip

TIRE-SOILMODEL

Laterally Slip

Dynamic model

Soil PropertiesAltitude

NormalsPrecompaction

Driveline model

Vehicle movementsSteering angle of wheelsWheel revolutions

PositionVelocityDirection

TopographieSoil type(Build up areas)

MAIN MODELS ADDITIONAL MODELS

HANDLINGELEMENTS

Steering angle

Steering angle,Accel., Brake,Gear

Accelerator, Brake,Gearstick, Differential Lock

Speedometer,Revolution counter

AUTOPILOT

Fig. 2: Program structure of ORSIS

As to be seen in Fig. 2 the vehicle model consists of the driveline, the steering model and the vehicle dynamics. All three modules are based on detailed physical modelling. DRIVELINE MODEL

Engine with flywheel

Torque converter withbridging clutch andshifting clutch

Gearbox

Shaft

Central distribution gear

Axle differentials

Axle differentialAxle differential

Distribution gear

Distribution gear Cardan shaft

Cardan shaft

Cardan shafts

Wheel planetary gears Wheel planetary gears

Fig. 3: Scheme of an 8x8 driveline

Multi axled vehicles often are equipped with a multi-axle-drive-system [5]. At off road vehicles generally all wheels are driven, Fig. 3. In addition to the diesel engine, the torque converter, the clutch, and the automatic shifting gear box, the driveline includes distri-bution gears with differentials, providing a certain torque distribution rate to the axles. Furthermore devices for engaging or bridging the differentials, the axle gears with lockable differentials and sometimes additional gears in the driven wheels are part of the driveline. In ORSIS an adequate configuration, adaptable to a 4x4, a 6x6 or a 8x8 truck, is implemented. Thereon it is

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possible to vary the torque distribution rate at the central distribution gearbox. Furthermore the differential locks on each one of the differentials can be activated at the users interface on the computer.

The latest version of ORSIS allows to create individual drivelines for very different types of vehicle (e.g. I or H configuration). It is also possible to simulate electrical drivelines with a central engine or individual engines for every single wheel. STEERING MODEL

Fig. 4: Graphical interface to change the steering configuration

The steering model is based on geometrical considerations according to ACKERMANN. A graphical interface allows to change the steering configuration right during the simulation process. As to be seen in Fig. 4 the user can interactively move the intersection point of the turning circle diameters of the single axles parallel to the vehicles longitudinal axis. By changing the steering abilities of the axles (+), nearly every imaginable steering configuration can be simulated. The only restriction is, that the turning circle diameters of the steerable axles have to intersect in one point, which is approximately true for almost every steering configuration. VEHICLE DYNAMICS The vehicle dynamics are very important for off road driving simulation mainly for two reason: At first, the (dynamic) wheel loads lead to a sinkage of the tires into the soft soil. This sinkage and the resulting rolling resistance, induced by soil compaction work, is an important limiting factor of the vehicles mobility in terrain. The other aspect are the accelerations of the vehicle effecting on the driver. In terrain driving high vertical oscillations can be observed, which are often a more limiting factor on the vehicle speed than the traction between the tires and the ground.

Fig. 5: Screenshot of the multibody-model of a military vehicle in ORSIS

In the actual version of ORSIS a dynamic multibody vehicle model is implemented, which allows to simulate the dynamic wheel loads but also the accelerations at the driver seat. The vehicle body and the individual axles are represented by single rigid bodies. The suspension arms are modelled by means of very stiff force elements without an individual mass. With this proceeding the kinematics and the dynamic of the axles can be simulated in a proper way without affecting the realtime capabilities of the program. Fig. 5 shows the multibody-model of an armoured 8x8 wheeled military vehicle with a single-wheel suspension.

It should be pointed out, that the multibody model allows to simulate the longitudinal, the vertical but also the lateral dynamics of terrain vehicles. So it is possible to simulate effects of lateral-slipping when driving at hillsides. Another interesting application is the simulation of skid-steering on soft grounds.

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7. TERRAIN MODEL ORSIS uses a high detailed terrain model which contains all information necessary for terrain driving. The terrain model is visualised by means of a graphical terrain map, shown in Fig. 6. As to be seen, different types of soil are indicated by using different colours. The dark colours stand for heavy loam soils, the lighter colours for firm sand. In addition the lines of equal height, streets and vegetation zones are depicted. The position and driving direction of the car is indicated by a red arrow. The shown terrain map represents a real terrain in the north of germany with a size of 2 km by 2 km which was modelled on bases of digital data from the local authority.

Beyond the visual properties the terrain model contains some interesting features, which should be mentioned in the following. Most important is the simulation of statistical distributed terrain properties, namely the statistical soil strength and the roughness of the surface.

Fig. 6: Terrain map of ORSIS (Screenshot) showing an real terrain in the north of Germany, the vehicle position and driving direction

is indicated by a red arrow.

ORSIS uses a special developed algorithm to generate a scattering of the strength-values as it can be observed in real measurements. The strength values, once assigned to a certain point, will permanently be true for this point, so that in case of reproduction of a simulated test, at any local point of the terrain the vehicle wheels will pass soil with equal strength as in former tests.

A similar procedure is used to create irregularities of the terrain surface. The roughness, super-imposing the triangular mask of the altitudes, is created on bases of a given power spectral density (PSP). Like the soil strength properties, the local height is fixed during the simulation run, so that reproducible results can be achieved.

It should be mentioned that the deformation of the irregularities of the terrain surface by the dynamic wheel-loads is also regarded. The latter are induced by the irregularities and influence the amplitudes of these irregularities, so that there is a mutual effect.

It is generally known, that the soil strength depends on water content, which especially is a result of the weather. In order to consider this influence, a physical model was developed at the IKK, which describes the dependence of the water content of the soil from rainfall, temperature and moisture of the air and of the level of ground water. With an additional empirical model, describing the dependence of soil strength from water content for the different soil types, which was found by experiments, conclusions on the actual soil strength can be drawn.

This model was implemented in ORSIS in a way, that the soil strength changes according to the weather history or – if desired - to a weather forecast. As a result it is now possible to calculate the expected trafficability with ORSIS regarding the weather data.

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8. TIRE-SOIL INTERACTION Without a doubt the most important part of an off road simulation tool is the interaction-model between the tire and the soft soil. ORSIS uses a further developed version of the traditional analytical method, which is based on the principles introduced by M.G. BEKKER [2]. Thereby the deformations of the ground with the stress in the ground under a wheel are considered as two independent effects, one in vertical and the other in horizontal (longitudinal) direction, neglecting the interdependence of the two considered effects. Accordingly, strength of soil is implemented by means of two different characteristics: - pressure-sinkage relation

- shear-tension-displacement relation

These soil characteristics, measured with special devices, can be modelled analytically. They are considered to be true also under a wheel, and are applied for the interaction of tire and ground. Such soil strength - characteristics have been measured in numerous experimental investigations and were evaluated with regard to different influences, for example the soil-type, the water content or the deformation speed.

These measured characteristics can be used in physical models of the tire-soil interaction. A first approach was to use a rigid wheel instead of an elastic tire, which is a good approximation in soft soils without a pre-compaction (without multipass effect). A significant improvement was the so-called parabolic model, developed by SCHMID [3], regarding the elastic tire. This model is comparably easy to handle and leads to good results and was therefore used with ORSIS for a long time.

According to the latest findings and using the calculation power of actual computer hardware a further developed model could be established. This model, still based on the former approaches, uses a substitute circle for the deflected tire according to Fig. 7. In comparison to the previous parabolic model it regards the elastic soil behaviour, which - among other things – are important for the calculation of the multipass effect. Another improvement is the integration of a model for the lateral forces on soft soils.

The new model allows to calculate all essential effects in interaction between the soft soil and the elastic tire. These are in detail:

zel,aus

zel,ein z0,1

z0,2

zSp,1zSp,2

D*

D

P0

P3P1

v

P2

f0Fig. 7: Analytical model (Substitute circle) for the

interaction between the elastic tire and the soft ground including elastic soil behaviour (case: multipass).

- sinkage and rolling resistance of the elastic wheel

- wheel-slip: longitudinal and lateral

- circumferential force

- lateral force

- deflection of the elastic tire

- influences of tire inflation pressure

- combined longitudinal and lateral forces

- slip-sinkage effect

- multipass effect, also in curves

Due to the limited space in this paper it is not possible to give a detailed description of the tire-ground model. More information can be found in [1-4][7].

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9. VISUALISATION The visualisation of simulation results is an essential part of every modern simulation. ORSIS offers different possibilities to give the users an idea of the actual action in the simulation.

The most intuitive way is to observe the vehicle motions in form of a realistic view on the car, as it is to be seen in Fig. 8 a. The driver’s view in the same situation is shown in Fig. 8 b. With this driver perspective it is possible to operate the vehicle similar to the real terrain driving. This viewpoint could be used in combination with a driving simulator.

Fig. 8: OpenGL visualisation from different viewing points (LinuX Screenshots)

b. Driver’s view

a. View from outside

A more technical point of view is offered by different bars, charts and indicators which are depicted during the simulation run. One example are the tire windows, which show essential results for every single tire. Here the forces, the slip and the sinkage/deflection/slip-sinkage of the wheel are shown. Another example is the forces window, that shows all the forces reacting on the vehicle body like air-resistance, rolling-resistance, slope-resistance and resulting traction force (Fig. 9 a). Fig. 9 b finally shows the indicator-window for the fuel consumption.

Moreover it is possible to analyse the results of a simulation by means of the powerful graphical evaluation tool xmgrace, which, as a freeware program is part of most LinuX distributions but also available for SGI systems. All simulation results - more than 200 single values for every time-step - are stored in a binary file. Stopping the simulation the user can choose, which values he want to look at and then start the graphical evaluation or safe the data in ASCII format.

a. Fuel consumption b. Forces on vehicle body

Fig. 9: Online visualisation of simulation results

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10. EXAMPLES OF SIMULATION RESULTS As explained before, ORSIS is a valuable tool for nearly all kinds of investigations concerning vehicle mobility under off road conditions. It is generally known, that in real terrain the soil properties often change locally within a few meters and are furthermore dependent on weather and daytime. Another problem of real testing is that the terrain is changed by every passing, so that one will never find identical conditions in experiments. Even though it is clear that experiments are still necessary, it is obvious, that the simulation can be a solution for a reproducible and fair comparison of different vehicle concepts under exact equal conditions.

In the following some simulation results will be shown that try to give an idea of the possible investigations. Due to the limited space within this paper, it is necessary to confine to a few examples. More information can be found in [1][4-7]. NUMBER AND POSITION OF DRIVEN AXLES An interesting question when building multiaxle off road vehicles is the conception of the driveline. It is well known that an all-wheel-drive is the best solution for off road conditions. On the other hand it should be regarded that such complex driveline leads to higher costs in building and service. In order to find the best solution for a certain vehicle ORSIS allows an objective comparison of different driveline variants.

Ndr

awba

r pul

l / k

driven axles ( )

Fig. 10: Comparison of different driveline concepts

20

40

60

80sand loam I loam II

The simulation run depicted in Fig. 10 shows a comparison of different three axle driveline concepts regarding the drawbar pull. It was performed with an equal wheel load distribution of 25 kN on three different soft soils. It is clearly that the all-driven variant has the highest drawbar pull. More interesting is the result, that a clear influence of the position of the driven axles can be observed. Here, in the case of only one driven axle, the usage of the first axle leads to a significant higher drawbar pull than the usage of the middle axle. DISTRIBUTION OF WHEEL LOAD As shown in Fig. 11 for the case of a 4x4 truck, there is a certain influence of the weight-distribution to the different axles, and it should be noted, that minimum rolling resistance does not coincide exactly with equal load distribution. A similar observation can be obtained for the circumferential force. This result indicates, that load-shifting because of drawbar-pull, acceleration or slopage will also cause changes of rolling resistance and circumferential forces and therefore influence the drawbar-pull. It is to be emphasised, however, that these mentioned effects - not shown here -, normally are simulated with ORSIS.

rollin

g re

sist

ance

/ kN

0

4

8

12

16

loam II

load to backload to front

FR

FRB

FRRFRB,front

FRB,rear

20

50 7040 60

distribution of axle load to rear axle / %

Fig. 11: Distribution of the wheel load on axles

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INFLUENCE OF TIRE INFLATION PRESSURE It is well known, that a lower tire inflation pressure leads to a lower sinkage and rolling resistance due to the lower pressure between tire and ground. At the same time, the size of the contact area is enlarged, so that higher circumferential forces can be transmitted. Another positive effect is the softer springrate of the inflated tire, which may lead to better ride qualities on rough terrain surface. All in all tire pressure control is an effective possibility to improve the vehicle mobility in terrain.

For a two axle vehicle the effects of tire inflation pressure are easily to understand. Looking at multiaxle vehicles things are much more complicated. There are nonlinear dependencies between the different axles due to the soil compaction caused by first axles and the changing of the distribution of the wheel load when reducing the tire inflation pressure of the tires of a single axle.

4,5 bar4,5 bar1,5 bar

1,5 bar1,5 bar

4,5 bar

draw

bar p

ull /

kN

rollin

gre

sist

ance

/ kN

-40

-20

0

20

40

60

80

100

Fig. 12: Influence of the tire inflation pressure for different vehicle concepts on soft loam (mass 14 t)

Fig. 12 gives examples of results and shows the effect on the traction, on the rolling resistance and on the resulting drawbar-pull for a 4x4 truck, a 6x6 truck and a 8x8 truck, all having same over-all-weight, but different wheel loads, according to the number of axles. It is evident that the lower the tire inflation pressure is, the better is the drawbar-pull on soft soils. The increased drawbar-pull due to higher axle number and due to lower inflation pressure is mainly caused by a reduction of the rolling resistance.

draw

bar p

ull /

kN

rollin

gre

sist

ance

/ kN

-40

-20

0

20

40

60

80

100

4,5 1,5 1,5 1,54,5bar barbarbar

4,5 4,5 1,54,5 4,5 4,5 1,54,5 4,5 1,5 1,5

loam I loam II firm sand

Fig. 13: Tire inflation pressure control on all axles and on

front axle(s) only (mass: 14 t)

A low tire inflation pressure unfortunately involves some disadvantages, especially a reduction of tire life cycle. Therefore it might be of interest, to reduce tire inflation pressure no more than necessary in the actual service, or to reduce the inflation pressure only on selected axles and not on all axles. The latter possibility would also reduce the expense for control-devices and the speed for filling in compressed air.

The simulation results in Fig. 13 show that - as expected - the best effect is reached, if for all tires the inflation pressure is reduced. However, in case of the 8x8 truck the reduction of inflation pressure on the first axle is the most effective, as a considerable improvement would be already acquainted by tire inflation pressure reduction on the first axle only. If the tire inflation pressure is reduced on the first and on the second axle, but not on the third and forth axle, the effect on rolling resistance and drawbar pull would be nearly equal to the case, where on all four axles the tire inflation pressure is reduced. As a consequence an economical solution for a 8x8 truck could be made by applying inflation pressure control only on first and second axle. For a 4x4 truck inflation pressure control on the first axle may be sufficient.

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11. FIELDS OF APPLICATION Due to the realtime capabilities, ORSIS has a wide field of application. As to be seen in Fig. 14 they can be divided in three main fields.

The first and so far most important field is the virtual vehicle development and testing. As explained before, ORSIS allows – in contrast to real testing – a reproducible and fair comparison of competiting vehicle designs. Moreover a reliable prediction of vehicle performance can be given. This includes the mobility on soft soils, the maximum driving speed concerning the acceleration at the driver seat, the maximum slope climbing capability but also details about the forces and torques in the driveline or the fuel consumption. In this connection also the combination with real test stands is of general interest. These, so called hardware in the loop applications allow to test real parts of the vehicle in combination with a virtual environment. Later in this paper there will be an example for this configuration.

The second application to be mentioned is the driver training in terrain. Using a driving simulator with original handling elements a realistic training can be realised. In comparison to other off road simulations ORSIS provides a extremely realistic driving feeling which allows an effective training of the off road driving. Here it is possible to train dangerous driving situations in heavy terrain - also under combat conditions - without any risk for mens health or the danger of damaging expensive material.

Driver Training in Terraintraining of dangerous situationstraining in heavy terraindriving with special equipmentdriving with special vehiclestactical driving in out of area missions

Development and Testingcomparison of alternative vehicle concepts in an early stage of development

test of vehicle components (hardware in the loop)

of torques and loadsprediction of vehicle performance dataprediction

reproducable vehicle testing vehicle optimization

prediction of mobiltiy and driving speed with regard to

- topographie- soil properties- weather

route planningvehicle choice for mission

Fig. 14: Fields of application of the ORSIS simulation

Due to the physical modelling it is even possible to practice with new vehicles that are still in development. Moreover vehicles in an unusual configuration can be simulated, for example special loadings with a high position of the centre of gravity.

The third field of application is the virtual mission planning by means of the simulation. ORSIS allows to give a prediction of the mobility for a certain terrain including important weather influences. Here it is possible to utilise weather information from the past or even a weather forecast to calculate the water content of the soil and to make correlation to the soil strength parameters. In addition comparisons between different vehicles, loadings and routes can be performed to find the best solution for a certain mission.

This also includes a prediction of the fuel consumption and the probable driving speed. Nevertheless it is possible to combine the planning of operations with the usage of a driving simulator. This may help to prepare drivers for their mission in unknown areas.

With these features ORSIS could be a worthy tool for the operation of wheeled vehicles in out of area missions.

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12. HARDWARE IN THE LOOP EXAMPLE

DCGen. 1

Engine PAISI ORSIS

I1

I2

M1,ist

M2,ist

n1 n1

n2n2

M1,soll

M2,soll

Test standcontrol

DCGen. 2

Cabin

δ

Brak

e

Dis

play

sys

tem

Stee

ring

angl

e

Vehicle Test stand Simulation

Drive line

Fig. 15: Scheme of the hardware in the loop (HIL) simulation using ORSIS and PAISI (Power and Inertia Simulator)

The combination of real test-stands with realtime simulations has become more and more important. One example for this was realised at the IKK with an combination of ORSIS and the power and inertia simulator PAISI. In this application the complete driveline of an 4x4 off road truck was used as hardware whereas the rest of the vehicle and the environment was contributed by the ORSIS-simulation (Fig. 15).

As an interesting feature the vehicle was driven from the real driver cabin including steering, gearshifting, accelerating, braking in combination with a virtual outside view generated by the simulation.

In this configuration the driving resistances in terrain were simulated by ORSIS and effected on the real driveline by means of electrical machines. These machines allow a dynamic operation over four quadrants, which is necessary to simulate all interesting manoeuvres of off road driving. The test-stand is to be seen in Fig. 16.

As a result it was possible to use the real driveline to drive interactively along a complex course though the virtual terrain. In addition it was also a good approach to validate the model of the driveline with the real counterpart.

Beyond this application it could be interesting to combine actual controllers with ORSIS, like ABS or ESP systems.

Fig. 16: Power and Intertia Simulator PAISI of the IKK

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13. DRIVING SIMULATOR As mentioned before the coupling of ORSIS with a driving simulator allows a lot of interesting investigations including the driver training. With the IKK driving simulator MARS (Modular Automotive Research Simulator) a system was established, which allows to use ORSIS for an realistic driving simulation in terrain (Fig. 17). The main feature of the simulator MARS is the 7 DOF Motion System (6 DOF by moving platform + one DOF by lateral motion). This allows to reproduce accelerations but also positions in space, which are important for off road driving. Actually it is planned to use a linear electrical engine for lateral motion and to enlarge the visualisation system by means of a multichannel projection system. 14. OUTLOOK ORSIS has reached a state of development, which pushes the program to the worldwide leading simulation tools for wheeled off road vehicles.

Fig. 17: Driving Simulator MARS (Modular Automobile Research Simulator) of the IKK

Nevertheless there is a lot to do and there are a lot of projects in progress to press ahead the programs functionality. One project is to improve ORSIS’ capabilities for driving on solid roads. Even though it is already possible, the used models are comparably simple. Here it is planned to implement the Delft magic formula model as the actual industrial standard to calculate the tire forces on rigid road. One objective is to simulate accidents where the vehicle passes from the firm road to soft soil. In this connection a more precise look will be spend on the modelling of actual suspension systems. Another project is to improve the 3D-graphics and to build up a cluster of LinuX PC’s to realise a cheap and powerful multichannel visualisation system based on highend consumer graphic boards. Actual information about the program and a free demo version for download can be found on the internet at http://www.orsis.de. REFERENCES [1] Ruff, K.: Fahrzeugbewegung im Gelände mit dem Simulationssystem ORIS, Dissertation 1997,

Universität der Bundeswehr Hamburg [2] Bekker, M.G.: Introduction to Terrain Vehicle Systems, Ann Arbor, The University of Michigan Press,

1969 [3] Schmid, I.C. and Aubel, Th.: Der elastische Reifen auf nachgiebiger Fahrbahn - Rechenmodell im

Hinblick auf Reifendruckregelung, VDI-Berichte Nr. 916, 1991 [4] Schmid, I.C.: Interactions of Vehicle and Terrain - Results from 10 Years Research at IKK, Journal of

Terramechanics, Vol. 32, No. 1, 1995 [5] Harnisch, C.: Drive line Concepts for Multi-Axle-Off road Vehicles, Simulation with ORIS, Proceed. 7th

European Conference ISTVS, Ferrara 1997 [6] Lach, B.: Strategies for Automatic Tire Inflation Pressure Control, Proceed. 7th European Conference

ISTVS, Ferrara 1997 [7] Harnisch, C.: Dynamische Echtzeitsimulation der Geländefahrt mehrachsiger Radfahrzeuge, Dissertation

2001, Universität der Bundeswehr Hamburg