Method and system for simulating vehicle and roadway interaction

The present invention is directed to a system and method for simulating the interaction of a simulated vehicle with one or more simulated road surfaces. A computer modelling program is used to create a computer-based road surface model and a computer-based vehicle model. The computer-based vehicle model may include a body model, a chassis model, a suspension model, a wheel model and a tire model. A computer simulation engine program is operative with the computer-based road surface and vehicle models to selectively simulate the interaction therebetween and provide simulation data relative thereto. The simulation data may be used to identify high stress areas or low durability areas of the vehicle or to compute vehicle suspension parameters.

REFERENCE TO PRIOR APPLICATIONS 
This application claims the benefit of a U.S. Provisional Application No. 
60/003,303, filed Sep. 6, 1995. 
FIELD OF THE INVENTION 
The invention is an improved system and method for simulating the 
interaction of a motor vehicle and a road surface, and specifically, 
pertains to a system and method of using computer models of a vehicle's 
wheels and tires to evaluate vehicle performance in relation to a computer 
model of a roadway. 
BACKGROUND 
Systems for the simulation of vehicle operation are well known. Among these 
systems are vehicle operating simulators, which can be operated by a 
driver manipulating conventional controls and producing visual, aural and 
tactile feedback, such as those taught by Briggs, et al, in U.S. Pat. No. 
4,952,152 and DeGroat, et al, U.S. Pat. No. 5,277,584. 
Systems for the analysis of the forces imposed on a motor vehicle during 
operation are also well known. Using traditional finite element analysis 
(FEA) techniques, it is possible to construct so-called FEA models of 
vehicles and their component parts utilizing a computer, and further, to 
use the computer to simulate forces acting upon the vehicle computer model 
to determine and predict stress, strain, durability and fatigue of vehicle 
components. 
Our own finite element model builder system is an example of the current 
state of the art in the creation of finite element models using finite 
element analysis. With these systems, the structure of a motor vehicle 
body, chassis, drive train, suspension and other component parts can be 
created as a computer model. Manipulation of this model can then be 
performed in a variety of ways to assist the vehicle designer. The model 
can be viewed on a typical video display device, which allows the designer 
and engineer to rotate the view of the model, manipulate the components of 
the model and test the results of said manipulation or modification of the 
model. 
Our software also interfaces with a wide variety of other computer 
programs, for example, computer programs which assist in the designing of 
production tools. 
It is also known to utilize FEA models in a dynamic simulation environment. 
For example, a motor vehicle suspension model can be subjected to a 
repetitive computer-simulated force comparable to that force imposed on an 
actual motor vehicle suspension, e.g., the vehicle's encounter with a 
roadway pothole. By repeating this simulation, repetitive stresses on 
suspension components can be effectively evaluated, without the need to 
actually subject the physical component to the physical roadway 
conditions, in a much shorter time at less expense than that required by 
actual operation of a vehicle in the proving ground environment. 
An underlying problem with prior simulation methods and systems is the 
imprecision of the inherent estimations which are required to run the 
simulations. For example, in prior art "pothole" simulations, the systems 
assumed that the forces transmitted by the impact of the motor vehicle 
tire with a pothole would result in an isolated vertical force being 
applied to the vehicle's suspension and body. In reality, the pothole also 
results in a rearward force on the vehicle's suspension when the vehicle 
tire strikes the vertical surface of the pothole as the vehicle travels 
forward. Further, prior simulation techniques largely ignored the size, 
shape, mass, geometry and dynamics of the wheel/tire combination, and 
treated forces applied to the motor vehicle suspension and vehicle body as 
essentially point source forces at particular points in the vehicle 
suspension. Such assumptions have been shown to provide largely inaccurate 
simulation data. 
The present invention allows for the modeling and simulation of all vehicle 
components in the proving ground environment. Previous systems have been 
limited to the simulation of various vehicle sub-systems, but not the 
vehicle as a whole. The present invention also provides better consistency 
between successive tests and better consistency within specific model 
configurations. By providing an accurate model of both the vehicle and the 
road surface, any change in the individual model elements (e.g., the tire 
model) will isolate the effects of substitution of different elements 
under consideration, provided all other vehicle components and models 
remain unchanged. 
SUMMARY OF THE INVENTION 
Utilizing the system and method of the present invention, a computer-based 
model of a motor vehicle is created. Thereafter, additional computer 
models of various vehicle components, including the suspension, wheels and 
tires are created. Finally, a computer model of a typical test roadway 
surface is created. Once all required computer models have been generated, 
the vehicular components are combined into a virtual vehicle for computer 
analysis. The virtual vehicle is placed on a virtual roadway derived from 
the roadway model, digitized from the proving ground test track surface 
profile for example, and the elements of the vehicle and roadway are 
manipulated by computer analysis software which simulates the interaction 
between the virtual vehicle and the virtual roadway under various 
conditions of vehicle load, highway speed and maneuvering of the virtual 
vehicle in relation to the virtual highway. The stresses due to the forces 
imposed on the virtual vehicle during this analysis may be collected and 
analyzed by, among other means, computer-based fatigue analysis 
techniques. The data so obtained and analyzed can be displayed in the form 
of raw data, or in the form of graphic computer models which isolate and 
identify data of interest to vehicle designers and engineers, such as 
areas of high stress or low durability. The data may also be used to 
calculate and plot suspension parameters over the duration of the 
simulated interaction between the virtual vehicle and the virtual roadway. 
Such suspension parameters are valuable to suspension designers, 
development engineers, etc. in evaluating the effects of camber or toe 
change, caster, steer axis inclination, vehicle roll center, roll 
stiffness, anti-dive and anti-lift characteristics, and may be used to 
modify the vehicle suspension to achieve desired handling characteristics.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The system for simulating the vehicle/roadway interaction of the present 
invention comprises a computer having at least one input device, 
preferably at least one video display device, at least one hard copy 
output device such as a printer, at least one storage device, such as a 
disk drive having either removable or non-removable media, a computer 
program in the form of a finite element modelling program, and a second 
computer program in the form of a dynamic non-linear real-time simulation 
analysis module. 
The finite element modelling system is preferably of the type which we have 
authored, entitled "Finite Element Model Builder", and sold under the 
trademark "FEMB". This type of software accepts data regarding the 
dimensions, design, structure and mass of a physical component, such as a 
motor vehicle body, and creates a computer-based model of such a 
component. Models so created may be viewed as either solid or 
semi-transparent "wire mesh" images on a computer screen or output device. 
These models can be easily manipulated by the computer operator, e.g., the 
models can be rotated in three dimensions to permit the view of any 
surface. The models can be viewed in any of the classic engineering 
drawing views, as well as in any cross-section in any such view. Elements 
may be added to or removed from the model. Simulated forces can be imposed 
upon the model, and elements of the model can be deformed. These 
capabilities make it simple for the user of such computer programs to 
evaluate the integrity of the model without the necessity for actually 
constructing a physical object conforming to the model. While traditional 
CAD software is generally used to create the basic structures which are 
then converted to FEA models, software such as that described above has 
the capability of including its own integrated CAD generator. 
The preliminary step in the preferred embodiment of the invention is the 
selection of basic vehicle parameters 10 as shown in FIG. 1. While a 
detailed vehicle model may be utilized as explained herein, a preliminary 
evaluation of the suspension system and suspension/roadway interaction may 
be accomplished utilizing a simple vehicle wire model having a fixed mass. 
The next step 12 in the inventive method is the creation of a vehicle 
suspension model utilizing the same techniques above-described. In the 
first embodiment of the invention herein described, the vehicle suspension 
model is created without concern for the detailed specific physical 
structure of the vehicle, and instead of the creation of a detailed 
computer vehicle model, the suspension model is created in relation to a 
simplified vehicle body and chassis model, which comprises only a single 
element having a prescribed mass, but no particular physical structure. 
There are many benefits of this method. By reducing the number of vehicle 
components which are modelled and simulated, the calculations required 
during the analysis steps are drastically reduced. A full vehicle model, 
including tires, wheels, suspension, body, seats, engine, transmission and 
other components can consume several days of simulation computations. A 
simple suspension model, without a vehicle body and other vehicle 
components in detail, will enable the simulation to be completed much 
faster. 
After the creation of the suspension model, the method contemplates the 
creation of a detailed wheel/tire model. First, an initial computer model 
of a tire having a certain size, weight and other specifications is 
developed 14 using conventional finite element modelling techniques. A 
dynamic analysis of the performance of this tire is then performed, again 
using standard dynamic non-linear real time simulation techniques. The 
results of this computer analysis are compared to the performance of the 
actual tire under actual operating conditions. The variation between the 
performance of the actual tire and computer model is recorded, and the 
computer model is then revised. This process is repeated until the 
computer model of the tire conforms to the actual performance of the tire 
under operating conditions. Once this series of revisions has been 
completed, a computer model of the subject wheel is created, and combined 
with the computer model of the tire to create a computer model of the 
known wheel/tire combination. The tire model is then combined 16 with the 
suspension model, as shown in FIG. 1. 
The next modelling step comprises creation 15 of the computer model of the 
test roadway. Motor vehicle proving grounds have evolved to incorporate a 
variety of topological configurations, all of which may be created for use 
in the present inventive methodology. These configurations, known as road 
profiles, may include a pothole track to simulate a vertical loading 
conditions, a body twist track to simulate torsional loading conditions, a 
forward panic braking surface to simulate longitudinal loading conditions, 
a FIG. 8 or cornering track, which simulates maximum lateral loading 
conditions, a washboard surface which simulates a high frequency/low 
amplitude loading condition, and a chatter strip track, which simulates a 
high frequency/low amplitude vertical loading condition. These road 
profiles are designed to create harsh road conditions which make it 
possible to simulate the day to day conditions encountered by a wide 
variety of motorists, and to facilitate repetitive testing of vehicle 
durability and handling in a relatively short period of time. 
Again, using finite element modelling techniques, one or more computer 
models of the road surface is created 15. In the preferred embodiment, the 
road surface is modelled as a strictly rigid and non-deformable surface. 
After the creation of each of the above-described models, each computer 
model of a road surface may be stored in computer memory or computer 
storage device. The road models are preferably constructed using drawings 
of proving ground surfaces and produce a cross-section of the road surface 
using CAD data in 3-dimensions. The model is then "positioned" 18 on the 
simulated roadway. 
Thereafter, utilizing a simulation engine in the form of dynamic analysis 
software, such as LS/DYNA3D (commercially available from Livermore 
Software Technology Corporation), dynamic non-linear real-time simulation 
20 of the vehicle is performed. This initial simulation constitutes a 
validation step to confirm validity of the suspension/tire model. 
Initial velocity parameters of a full vehicle model are programmed into the 
vehicle model using the finite element modelling software. A 
pre-determined friction parameter between the tire model and the road 
surface model is input into the LS/DYNA3D program. The operator of the 
LS/DYNA3D program can select a duration of simulation for stand alone 
analysis. Further, the system operator may start and stop the simulation 
manually during the simulation process. 
It is important to note that an initial time must be provided for the tire 
models to "settle". Initially, the tire models are placed between the road 
model surface so that there is no vehicle weight applied to the tire 
model. At the beginning of the simulation, the tires are compressed as the 
vehicle model "falls" onto the road as shown in FIG. 1, flow chart 
operation 24. Therefore, a certain amount of time is required to permit 
the tires to "settle" and reach their normalized compression. The model is 
initially positioned behind any intended obstacle thereby giving the tire 
models time to settle by the time the first obstacle model is encountered. 
During the final simulation 26, the dynamic analysis software generates 
output files at various pre-determined times or positions. The suspension 
model provides a continuous data stream for identifying upper and lower 
limits of suspension movement during the simulation. This continuous data 
stream permits the operator to concentrate attention on particular areas 
of maximum stress on the vehicle. 
The data generated by the analysis program can be further analyzed 28 by a 
fatigue analysis program, such as the ETAFAT program. The fatigue analysis 
program analyzes the data generated by the dynamic analysis program, and 
permits prediction of component life. Data generated by the analysis 
program may also be used to analyze and predict noise and vibration levels 
resulting from vehicle operation. 
Data generated during the simulation may also be used to calculate and plot 
suspension parameters over the duration of the simulated interaction 
between the vehicle model and the road surface model. Such suspension 
parameters are useful to suspension designers and development engineers in 
studying the effects of camber, toe change, caster, steer axis 
inclination, vehicle roll center, roll stiffness, anti-dive and anti-lift 
characteristics, and may be used to modify the vehicle's suspension 
mounting locations, compliance, etc., in order to achieve desired vehicle 
handling characteristics. 
A second embodiment of the method of the invention is diagramed in FIG. 1. 
In the first embodiment above, a preliminary evaluation of the performance 
of the vehicle suspension system in relation to the roadway can be 
obtained, utilizing only the most fundamental information regarding the 
motor vehicle under test. Utilizing advanced FEA modelling techniques, 
however, the alternative inventive method herein described contemplates 
the creation of FEA models of the desired motor vehicle. Construction of 
this model may include incorporation of vehicle accessories, prescribed 
vehicle loading, and even the presence of occupants within the vehicle. 
The computer model of the vehicle so created is stored, on an interim 
basis, in the computer's memory or storage device for subsequent 
manipulation as herein described. In the second embodiment, however, in 
addition to the steps above-outlined, a full vehicle model is constructed 
30, to include the addition 32 of trimmed body masses in the steps in the 
inventive method. Thereafter, the alternate embodiment of the inventive 
method contemplates the merger 22 with the body model and suspension 
models prior to performing the final simulation 26. The second embodiment 
provides a much more accurate representation of the displacement, 
stresses, dynamic responses and fatigue life imposed on the motor vehicle. 
The elements of the system are diagrammed in FIG. 2. Basic input devices 40 
utilized for the finite element modelling program include conventional 
keyboards, digital tablets, computer mouse and the like. These input 
devices are utilized to provide all necessary data to the finite element 
model program 42. Program 42 communicates, in the usual fashion, with 
storage device 44, video display device 52 and output device 50, 
preferably in the form of a printer. Finite element modelling program 42 
further cooperates with the simulation analysis program 46 of the type 
commonly known as the LS/DYNA3D program above-described. The same analysis 
program cooperates with fatigue analysis software such as ETAFAT, also 
above-described. 
The simulation can be repeated as needed, by substituting new road profile 
models, and by changing the various tire, wheel, suspension, vehicle and 
vehicle component models. For example, seats may be added or removed from 
the model, different door configurations may be selected for analysis, and 
computer models of occupants may be added to the computer model of the 
vehicle. Even minor changes to the parameters may be introduced, such as 
slight reductions in tire pressure or tire tread design. 
While we have described this invention with reference to the above 
embodiments, it will be obvious to those skilled in the art that various 
modifications combinations of the above embodiments, as well as other 
embodiments of the invention may be easily made, without departing from 
the true scope of the invention.