Attachment_0061_Tracked_Vehicle_Dynamics_Datasheet.xlsx

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Narrative

VEHICLE DATA PACKAGE FOR DYNAMIC MODELING AND SIMULATION

1.0 INTRODUCTION

This package describes the parametric data requirements for high resolution vehicle dynamic analysis using methodologies such as Dynamic Analysis and Design System (DADS). The nature of these methodologies is such that detailed vehicle data are necessary to formulate the models for the simulation to be performed. In order to facilitate the development of dynamic models of modern military vehicle systems, an attempt has been made here to provide generic data sheets to define the system parameters necessary to conduct any desired simulations. These sheets include the minimal requirements necessary to conduct simulations. Special vehicle features or performance characteristics which are not covered by the data sheets need to be described and parameters provided in sufficient detail for high resolution dynamic simulations.

2.0 OBJECTIVES

The purpose of this package is to: 1) define in detail the parameters, drawings, and descriptions that are necessary to perform high resolution vehicle dynamic simulation and 2) provide standardized work sheets which will facilitate wheeled vehicle system description and model development.

3.0 RECOMMENDATIONS

It should be noted that the data defined in this package has a direct effect on the dynamic response of the vehicle. However the parameter values are generally quite difficult to determine. As the model can only be as accurate as the data provided, consideration should be given to collecting accurate and precise data to be used in the modeling process. When accurate data are used correctly in a vehicle dynamic simulation, accurate results can be produced and decisions can be made based on predicted vehicle performance.

As the government deems it necessary, this package will be updated to add data requirements as modeling methodologies and simulation technologies grow.

4.0 DATA SHEETS

In order to determine the dynamic response of military vehicles, parametric data that describes the main subsystems of the vehicle must be known. The following data sheets are included to capture that data:

1. Sprung vehicle data

2. Power train data

3. Tracked vehicle:

A. Track data B. Track Suspension data

Models will be developed from each subsystem's parametric data and the models will be combined to create the vehicle model. The level of detail used to describe each subsystem and the accuracy of the parametric data will determine how well the model reflects the true system response.

4.2 Vehicle Mass and Inertia Properties

For the level of detail required for most analyses, it is sufficient to treat the vehicle sprung mass (chassis) as a single rigid body. However, if the first few mode shapes are known, provide the output from the finite element eigenvalue analysis from ANSYS, MSC/NASTRAN, or COSMIC/NASTRAN. This data can be incorporated into the dynamic model to provide additional accuracy. All spinning components of the wheel such as the wheel hub and tire assembly should be combined into one. If the axle is not composed of a single rigid body then its configuration should be depicted in additional drawings and the mass/inertia properties given for each major component. All center-of-gravity location should be given relative to a point located on the ground below the center of the front axle.

4.3 Wheeled Axle Data

For the most part, all of the data asked for on this sheet is self explanatory. The collection of this particular data gives us some background on what kind of tires will be used on the vehicle, how many wheels there are per axle and whether the axles are steered, powered, or braked. Operating load under the axle is important in helping us debug the model and would be useful at not only vehicle curb weight, but also at the various off-road and on-road loading conditions.

4.4 Tire Data (vertical and lateral force)

This section of data helps us in accurately characterizing the tire mechanical properties. It is important for us to get tire data for a range of tire inflation pressures that envelope the operating ranges that will be used during vehicle operation. This covers both on-road and off-road tire inflation pressures for a variety of gross vehicle weights. Tire vertical force data should reflect non-linear force/deflection up to the point of the tire bottoming out on the rim. Tire lateral force data should cover not only a range of tire inflation pressures but also a range of slip angles and tire vertical forces.

4.5 Suspension Characteristics and Data

Because of the wide variety of suspension systems in existence today, it is difficult to be explicit when specifying data requirements for a given vehicle suspension. It is important to emphasize that suspension systems significantly affect vehicle dynamic performance while negotiating terrain and obstacles, so they must be adequately modeled. Detailed drawings defining all suspension kinematics, joint locations, and attachment points of springs, shocks, and bump stops must be provided. All dimensions should be relative to a well-defined location on the vehicle such as a point on the ground located below the center of the front axle.

When providing suspension data for the vehicle it is important to cover the entire range of operation and include enough points to depict non-linearities in the suspension . This should include jounce and rebound characteristics as well. Tabulated data is required for force-deflection relationships, but including a plot of the data showing jounce, rebound and static equilibrium is desired. For independent suspensions, it should be stated whether the suspension force-deflection data is at the spring or the wheel, and if at the wheel, what the ratio is between the two.

4.6 Supplemental Data

Additional data will be required to set up an accurate model of the vehicle system. This section covers data that would come in the form of engineering drawings. In particular, any drawings that depict the steering kinematics of the vehicle and supplemental drawings of the suspension showing damper and spring attachment points, axle attachment points, and bump stop locations. There should also be top level drawings of the vehicle including the system center-of-gravity location and overall vehicle dimensions.

4.7 Track (See the "Track Data Sheet")

Track-soil dynamics are the most difficult part of tracked vehicle modeling. Driving and braking forces are transmitted between drive train and the ground via the track. Roadwheels are isolated from terrain irregularities by the bridging of the track. Rolling resistance between wheels and track, ground deformation under the track, and track vibrations account for a significant amount of energy dissipation.

The dimensions and mass of a track segment should be given. Track pad dimensions and material properties can be used for determining displacement between roadwheel, track, and ground. The stiffness and the damping characteristics of the rubber or other material in the roadwheels and track should be provided.

If track tension is dynamically adjusted, the necessary models and parametric data should be supplied in order to include these effects in the track model.

4.8 Suspension (See the "Suspension Data Sheet")

Suspension stiffness can be characterized in a number of ways. For example, torsion bar suspensions can be represented by describing torque versus relative angle position between the hull and roadarm, torsional friction versus relative angular velocity, and torsional damping versus relative angular velocity. It is sufficient to provide this data as a table of test points. The data should also characterize jounce and rebound stops, if they exist. If the suspension force data differs between suspension units due to different torsion bar characteristics, indexing, roadarm lengths, etc., separate data for each suspension unit should be provided. Also, provide the index angle for torsion bars and the static position at the nominal vehicle configuration.

If hydro-pneumatic suspension systems are employed, and if they are adjustable, a family of suspension curves or analytical models should be provided. If active suspension compensation devices are employed and if it is expected that they will significantly affect vehicle performance, these systems should be identified and data provided to fully model their performance. Include block diagrams with all parameters listed and defined. If the system is mechanical, the linkage dimensions, geometry, attachment points, etc. should be provided. All dimensions should be provided relative to a well-defined point on the hull such as the center of the sprocket, and for attachment points on the roadarm, with respect to the radar attachment point. If electrohydraulic-mechanical suspension systems are employed, a detailed description of the system, including block diagrams with all parameters defined in sufficient detail to establish a dynamic model, should be provided.

Suspension damping forces also play an important role in dynamic simulation. Force or torque versus relative position and velocity data are required for each damper in the suspension system.

If the suspension system interacts directly with braking, steering, or the drive train, and if these interactions will significantly alter vehicle performance, adequate data to perform detailed simulations of this interaction should be provided.

4.9 Power train

Vehicle model performance on irregular terrain and over obstacles is highly dependent upon the power train model. Power train models should be capable of dynamically adjusting to varying terrain-induced loads and throttle settings for realistic transient analysis. As in other subsystems, it is difficult to be explicit about all model requirements until the system configuration is known.

As a minimum, curves of maximum torque available at the sprocket versus sprocket speed over the nominal speed range of the vehicle should be provided. Rotational inertia of the drive train, from powerpack to the output sprocket in each gear, should also be provided. Transmission and final drive schematics, with all gear ratios, gear efficiencies and automatic transmission shifting characteristics defined, would make the model even more accurate. Other factors peculiar to a given system, which may substantially affect vehicle performance, should be provided.

Associated with the power train is the vehicle steering system. Tracked vehicles steer by braking or by positive control of differential sprocket speeds. Provide a steering schematic and describe any properties of the steering system such as response time, inefficiencies, etc.

1. Sprung Vehicle Data

SPRUNG MASS DATA (at Curb and GVW condition w/o turret and weapon)

Chassis mass (sprung mass, excluding turret, gun, and other bodies described below) lbf-sec2/in *

TURRET DATA

Turret mass lbf-sec2/in

WEAPON DATA

Provide finite element model and analysis data for each body that should be considered a compliant structure.

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2. Power Train Data Power Train Data

Property Comment

% Drive torque distribution to all axles (under various operating conditions)

Time to achieve 0 to 40 mph (under full throttle) on highway under operating load, seconds

Engine maximum power (hp)

Curve data of net engine torque (in-lbf) vs. speed (rpm)

Specify gear ratios and efficiencies of the power train

For tracked vehicles, reflected rotational inertia at sprocket (lbf-in-s2) Inertia (lbf-in-sec2) = Inertia (lbm-in2) / 386.088

Engine/Transmission mass (lbf-s2/in) Mass (lbf-sec2/in) = Mass (lbm) / 386.088

Engine/Transmission center-of-mass location (CG) Provide x,y,z coordinates (in); specify coordinate system

Engine/Transmission mount locations Provide x,y,z coordinates of each mount (in); specify coordinate system

Engine Torque (ft-lbf) verus Engine RPM and Throttle Opening (%) Torque versus RPM for full range of Percent Throttle Openings

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3A. Track Data

Ver 1.0 (Original, Unmodified)

Dynamics & Structures Team

3B. Track Suspension Data

Roadwheels are numbered from the idler (if present) to the sprocket

Ver 1.0 (Original, Unmodified)

Dynamics & Structures Team

3C. Susp Spring-Damper Data Suspension Spring/Damper/Bump-Stop Data (COPY and PASTE Table for each roadwheel station)

Index angle (free angle) deg Roadwheel angle when contacting bump stop: (deg) Roadwheel angle when contacting rebound stop: (deg)

Spring Displacement to Wheel Center Displacement Ratio (in/in) Damper Displacement to Wheel Center Displacement Ratio (in/in) Jounce Bumper Displacement to Wheel Center Displacement Ratio (in/in)

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3H. Vehicle Geometry Data Vehicle Geometry Data

(1) Provide a table of (x,y,z location) in a clearly defined reference frame. Also, provide the dimensioned drawings showing position*, geometry, connectivity, and layout of the following:

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