Chapter 11 — Vehicle Model Definition (Part A: Sprung Mass)

The HVE Vehicle Editor displays the current vehicle in the Vehicle Viewer. The HVE Vehicle Model is a general purpose physical/mathematical model of a vehicle developed by EDC. The HVE Vehicle Model applies to any type of vehicle having left-side and right-side wheels, including passenger cars, pickups, vans, sport-utility vehicles, trucks, trailers, dollies and barriers.

The Vehicle Editor allows editing of the parameters which define the HVE Vehicle Model. The general categories for these parameters are:

• Sprung Mass — Clicking on the CG allows the user to edit the sprung mass parameter groups: Inertias, Move CG, Color, Geometry File, Contact Surfaces, Inter-vehicle Connections, Belt Restraints, Airbag Restraints, Aerodynamic Drag, Body Torsion (this part).
• Unsprung Masses — Clicking on a wheel allows the user to edit the unsprung mass parameter groups at the selected wheel location: Suspension, Tire, Brake, Wheel x,y,z Coordinates (see Part C — Suspension and Part D — Brakes, Tires and Wheels).
• Exterior — Clicking on the exterior spheres allows the user to edit the exterior dimensions and structural stiffness (see Part B — Exterior).
• Brake Master Cylinder — Clicking on the brake master cylinder allows the user to edit the master cylinder or brake system compressor properties; also used for activating the ABS system and editing the ABS system properties (see Part E).
• Steering Wheel — Clicking on the steering wheel allows the user to edit the steering system properties (see Part E).
• Drivetrain — Clicking on the engine allows the user to edit the drivetrain properties: Engine, Transmission, Differential (see Part E).

These categories and their associated parameters are described in this chapter.

Figure 11-1: Vehicle Editor, Sprung Mass Data pop-up menu.

Inertial Properties

The inertial properties of the vehicle are displayed and edited using the Inertial Properties dialog. Two versions of the Inertias dialog are available: Basic and Complex (updated: the legacy manual called the expanded version "Detailed"; the current dialog's toggle buttons are labeled Basic... and Complex...). The Basic version of the Inertias dialog displays only the sprung-mass properties in a narrowed dialog; the Complex version displays paired Total (i.e., sprung + unsprung) and Sprung columns side by side. (updated: editing a value in one column automatically recalculates the corresponding value in the other column using the vehicle's unsprung masses and their locations. The last-used Basic/Complex state is remembered between sessions.)

NOTE: Typically, 2-D models use total vehicle inertial properties; 3-D models use the sprung mass properties. Why? The unsprung masses (i.e., wheels and axles) have their own independent equations of motion.

The Inertial Properties dialog also includes a feature that automatically updates the rotational inertias when the weight is changed.

NOTE: The updated rotational inertias assume the mass distribution is unchanged by the weight change. The effect of this assumption is that the updated rotational inertia is directly proportional to the weight change.

Figure 11-2: Vehicle Inertias dialog, Basic and Complex versions.

See also the code-verified reference page, Vehicle Inertia dialog.

The Inertial Properties dialog performs a number of calculations, depending on which values the user edits.

If the sprung weight, W_S, is edited, the total weight, W_T, is updated:

W_T = W_S + Σ(n=1..NumAxles) W_U

where W_U = unsprung weight of each wheel (plus axle for solid axle suspensions).

If the total weight, W_T, is edited, the sprung weight, W_S, is updated:

W_S = W_T − Σ(n=1..NumAxles) W_U

If the sprung rotational inertia, I_Sx, I_Sy or I_Sz (roll, pitch or yaw, respectively), is edited, the total rotational inertia, I_Tx, I_Ty or I_Tz, is updated using the parallel axis theorem:

I_T = I_S + Σ(n=1..NumAxles) (I_U + m_U * r_U²)

where

• I_U = rotational inertia of each wheel (and axle for solid axle suspensions) about its own x, y or z axis
• m_U = mass of each wheel (plus axle for solid axle suspensions)
• r_U = orthogonal distance from vehicle sprung mass CG to unsprung mass CG.

Similarly, if the total rotational inertia, I_Tx, I_Ty or I_Tz (roll, pitch or yaw, respectively), is edited, the sprung rotational inertia, I_Sx, I_Sy or I_Sz, is updated using the parallel axis theorem:

I_S = I_T − Σ(n=1..NumAxles) (I_U + m_U * r_U²)

If the Auto Update When Weight Changes checkbox is checked, the rotational inertias are updated as follows:

a) If the sprung weight is edited, the updated sprung rotational inertias are:

I_S = I_S0 * (W_S / W_S0)

where

• I_S0 = sprung rotational inertia before editing sprung weight
• W_S0 = sprung weight before editing

The total rotational inertias, I_T, are then calculated using the parallel axis theorem, as shown above.

b) If the total weight is edited, the updated total rotational inertias are:

I_T = I_T0 * (W_T / W_T0)

The sprung rotational inertias, I_S, are then calculated using the parallel axis theorem, as shown above.

To display or edit the current vehicle's inertial properties, perform the following steps:

1. In the Vehicle Viewer, click on the CG sphere. The Sprung Mass options for the current vehicle will be displayed.
2. Choose Inertias from the Sprung Mass option list. The Inertial Properties dialog will be displayed.

NOTE: Either the Basic or the Complex version of the dialog will be displayed, depending on its state during your last visit to the Inertial Properties dialog.

1. View and/or edit the desired properties. The other properties will be updated and displayed as described above.
2. Press OK to accept the changes.

The Inertial Properties are described below.

• Weight — Vehicle total and sprung weight.

NOTE: The Vehicle Editor actually divides your entered value by the current gravitational constant (see Environment Editor) and stores the resultant mass. That way, if you take the vehicle to the moon, it will behave correctly!

• Mass (entered as weight) — Vehicle total and sprung mass (weight/g), actually stored by the Vehicle Editor (see above note). This value is not user editable.
• Roll, Pitch and Yaw Rotational Inertias — Vehicle total and sprung mass rotational inertias.
• x-z Product of Inertia — Product of inertia about the y axis. This value represents the fact that the x-z plane is not a plane of symmetry for the vehicle sprung mass. (updated: entered in the Sprung column only.)

NOTE: For all practical purposes, a vehicle is symmetrical in the x-y plane (i.e., about the z axis) and in the y-z plane (i.e., about the x axis). Therefore, these inertial products are zero.

(updated: in HVE-2D, the Roll, Pitch and XZ Product fields are read-only, the Total column and the Basic/Complex button are hidden, and only the Yaw inertia may be edited.)

Table 11-1: Inertial Properties

Parameter	Unit Name	Description
Weight	UtVehForce	Vehicle total and sprung weight (HVE calculates and stores the mass by dividing the entered weight by the current acceleration of gravity)
Rotational Inertias	UtVehInertia	Vehicle total and sprung rotational inertias about the vehicle x, y and z (roll, pitch and yaw) axes
x-z Product of Inertia	UtVehInertia	Inertial product about the y axis

Move CG

The default CG (center of gravity) location of the vehicle sprung mass is determined from raw data (e.g., measured or table values). The user may choose to edit the CG location using the Move CG dialog. See also the code-verified reference page, Move CG dialog.

NOTE: The default location of the CG is determined by the wheel locations (which are defined relative to the CG). Refer to the Wheel Location parameters for more information.

NOTE: Changing wheel z coordinates or tire radii for any wheel location will change the calculated CG height.

Figure 11-3: Move CG dialog.

To display or edit the current vehicle's CG location (relative to the default location), perform the following steps:

1. In the Vehicle Viewer, click on the CG sphere. The Sprung Mass options for the current vehicle will be displayed.
2. Choose Move CG from the Sprung Mass option list. The Move CG dialog will be displayed.
3. View and/or edit the desired properties.
4. Press OK to accept the changes.

The Move CG parameters are described below.

• dx — Moves the CG in the +x or −x direction, relative to the vehicle-fixed coordinate system (+x is forward in all coordinate systems).
• dy — Moves the CG in the +y or −y direction, relative to the vehicle-fixed coordinate system (+y is to the right in the SAE coordinate system).
• dz — Moves the CG in the +z or −z direction, relative to the vehicle-fixed coordinate system (+z is down in the SAE coordinate system).

Table 11-2: Move CG Parameters

Parameter	Unit Name	Description
dx, dy, dz	UtVehDispLength	Adjustment of the default CG (center of gravity) location relative to the vehicle-fixed coordinate system
CG Height	UtVehDispLength	Approximate CG height, calculated from vehicle wheel positions and tire radius. Tire deflection is ignored.

Color

The color of the vehicle is obvious from looking at it. The color may be edited using the Color dialog.

Figure 11-4: Color Editor dialog.

To display or edit the current vehicle's color properties, perform the following steps:

1. In the Vehicle Viewer, click on the CG sphere. The Sprung Mass options for the current vehicle will be displayed.
2. Choose Color from the Sprung Mass option list. The Vehicle Color dialog will be displayed.
3. View and/or edit the color RGB value and intensity.
4. When finished, click on the Close button on the upper right corner of the dialog.

The Color Properties are described below.

• RGB Color Wheel — A small circle (hot spot) in the color wheel that determines the current color values. Move the hot spot to the desired color; towards the center of the color wheel creates neutral (gray) colors.
• Color Intensity — A slider ranging from 0 to 1 that determines the darkness or lightness of the color. Move the slider towards 0 to darken the vehicle.

NOTE: Do not use a Color Intensity of 1.0 if you plan to produce a video! Saturated colors (especially red) look bad on video tape. See the Video Output section.

Geometry File

The current vehicle may be visualized using a simplified vehicle shape or an actual 3-D geometry file created by digitizing the vehicle. If a 3-D geometry file is available for the current vehicle, it may be selected using the Geometry File dialog.

Figure 11-5: Geometry File dialog.

Mechanical Properties

The 3-D geometry file is not only used to visualize the vehicle, it is also used to define the mechanical/structural properties of the vehicle exterior. Each vertex includes a complete material specification. These material properties are:

• x,y,z coordinates — Vehicle-fixed coordinates for each vertex (a typical mesh includes approximately 2500 to 5000 vertices, not including the wheels).
• Force Constant — K₀, the force required to initiate vertex deformation.
• Linear Stiffness — F₁, the linear force-deflection constant for the vertex.
• Quadratic Stiffness — F₂, the 2nd-order force-deflection constant for the vertex.
• Cubic Stiffness — F₃, the 3rd-order force-deflection constant for the vertex.
• Damping Constant — The velocity-dependent force constant for the vertex.
• Friction Constant — The friction multiplier for the vertex.
• Maximum Force — Yield force for the vertex.
• Maximum Deflection — Yield at failure for the vertex.
• Unloading Slope — Linear force-deflection relationship during unloading.

Figure 11-6: View of 3-D geometry file (mesh). The mesh provides visual properties, as well as mechanical properties that may be used by collision algorithms.

These material properties are available for collision algorithms to simulate collision forces and moments, as well as to visualize the resulting deformation to the vehicle exterior.

NOTE: For more information regarding these parameters and how they are used, refer to the User's Manual for the particular simulation model being used.

Table 11-3: Vehicle 3-D Geometry Mechanical Parameters

Parameter	Unit Name	Description
x,y,z coords	UtVehDispLength	Vehicle-fixed vertex coordinates
Material Name	UtNone	Material name
Constant	UtVehForce	Force required to initiate deflection
Linear Stiffness	UtVehMatLinear	Linear material deformation coefficient
Quadratic Stiffness	UtVehMatQuad	Quadratic material deformation coefficient
Cubic Stiffness	UtVehMatCubic	Cubic material deformation coefficient
Damping Constant	UtVehMatDamp	Material velocity-dependent deformation constant
Friction Constant	UtNone	Friction coefficient
Maximum Force	UtVehForce	Force at which 3rd-order force-deflection relationship is abandoned
Maximum Deflection	UtVehDispLinear	Deflection at which 3rd-order force-deflection relationship is abandoned
Unloading Slope	UtVehMatLinear	Linear unloading slope beginning at max deflection

Geometry File Options

When Geometry File is selected from the Sprung Mass option list, HVE displays a cascade menu containing more options: New, Open and Save-As.

NOTE: HVE requires a unique file format for geometry.

NOTE: If you wish to use your own vehicle geometry file, you must place it in the ...images/vehicles subdirectory for vehicle geometry files. That's the place HVE expects to find all vehicle 3-D geometry files.

New

The New option removes the existing 3-D geometry file (if any) and replaces it with the simple vehicle shape.

NOTE: Choose this option if you accidentally select the wrong 3-D geometry file and you need to remove it.

To remove the existing 3-D geometry file, perform the following steps:

1. In the Vehicle Viewer, click on the CG sphere. The Sprung Mass options for the current vehicle will be displayed.
2. Choose Geometry File from the Sprung Mass option list. The 3-D Geometry File Selection dialog will be displayed.
3. Choose New.

The 3-D geometry is removed from the current vehicle.

Open

The Open option displays the Vehicle Geometry File Selection dialog and allows the user to assign a digitized 3-D geometry file for the vehicle. To open a new 3-D geometry file and assign it to the current vehicle, perform the following steps:

1. In the Vehicle Viewer, click on the CG sphere. The Sprung Mass options for the current vehicle will be displayed.
2. Choose Geometry File from the Sprung Mass option list. The 3-D Geometry File Selection dialog will be displayed.
3. Click on the Format option list to select the file format of the desired 3-D geometry file.
4. Select a 3-D geometry file from the list.
5. Press OK.

The selected 3-D geometry file is displayed on the current vehicle.

Save-As

The Save-As option displays the Vehicle Geometry File Selection dialog and allows the user to save the current 3-D geometry file using a new file format and file name. To save the current 3-D geometry file as a new file, perform the following steps:

1. In the Vehicle Viewer, click on the CG sphere. The Sprung Mass options for the current vehicle will be displayed.
2. Choose Geometry File from the Sprung Mass option list. The 3-D Geometry File Selection dialog will be displayed.
3. Click on the Format option list to select the file format you wish to save the current 3-D geometry file as.
4. Enter a filename or select a filename from the list.
5. Press OK.

The selected 3-D geometry file is saved in the images/vehicles subdirectory according to the selected file format and filename.

Contact Surfaces

The current vehicle may include contact surfaces used for simulating interaction forces between the vehicle and its occupants or pedestrians.

Contact Surfaces are planes defined by 3 corners (the fourth corner is automatically assigned by assuming a parallelogram). Contact surfaces are created using the Contact Surfaces dialog.

Figure 11-7: Vehicle contact surfaces — both interior and exterior contact surfaces are permissible.

Figure 11-8: Contact Surfaces dialog.

To display or edit the current vehicle's contact surfaces properties, perform the following steps:

1. In the Vehicle Viewer, click on the CG sphere. The Sprung Mass options for the current vehicle will be displayed.
2. Choose Contacts from the Sprung Mass option list. The Contact Surfaces dialog will be displayed.
3. To add a new contact surface, click on Add and enter a name for the contact surface, followed by OK.

NOTE: If a name already exists in the text field, editing the existing name creates a new surface having the new name. The original name and surface still exist as well.

1. Click the appropriate Bind Material To option (Vertex or Face) to define whether the contact material attribute is attached to the vertex or face.
2. Click on the Interior or Exterior radio button to identify the contact as an interior or exterior surface.

NOTE: The simulation may use this information to reduce the number of contacts for which it must calculate forces, based on whether the human is an occupant or pedestrian. For example, it is unnecessary to calculate the force between a pedestrian and seat cushion, since none will occur. (See Event Editor, Contacts Dialog, for more information.)

1. Enter the desired x,y,z (vehicle-fixed) coordinates for three corners of the contact surface. Be sure to choose three consecutive corners.

NOTE: The "right hand rule" is used to determine the positive side of the contact surface; the positive side of the surface is light-colored, while the opposite side is black. Force on the contact surface is only calculated if it is struck on the positive side!

NOTE: The fourth corner is created automatically assuming a parallelogram.

Figure 11-9: Convention for contact surfaces — three consecutive corners are selected; the right hand rule determines the positive side.

1. Choose Material to display the Contact Surface Properties dialog.
2. Click on the Current Material option button and choose the desired material from the materials option list. The properties of the selected material will be displayed.
3. If desired, edit the default material properties for the current surface.

NOTE: Any editing applies only to the current contact surface and does not affect the Materials Database.

1. Press OK to accept the current material properties.
2. Press OK again to update the vehicle's contact surfaces.

It is important to confirm the contact surfaces are correctly positioned and facing the right direction within the vehicle. Carefully view each surface to ensure its correct position and orientation.

NOTE: If the contact surfaces are not displayed, click on Options (main menu bar) and choose Show Contacts.

To edit an existing contact surface, perform the following steps:

1. If necessary, click on the vehicle CG and choose Contacts to display the Contact Surface dialog.
2. Click on the Contact Surface Name combo box button to display the list of contact surfaces.
3. Click on the desired name to make it the current surface. Its coordinates will be displayed.
4. If desired, edit the coordinates.
5. If desired, click on Material to display and edit the material properties or select a different material.
6. Click OK to update the list of contact surfaces for the current vehicle.

NOTE: No changes take effect until you press OK.

The Contact Surface parameters are described below.

• Bind Material To — Assigns an attribute, either Vertex or Face (polygon); the simulation uses this attribute to determine whether the material is associated with the vertex or polygonal area.
• Location — Assigns an attribute, either Interior or Exterior, available for use by the simulation model to distinguish between surfaces on the vehicle's interior and exterior.
• Material Name — Assigns a user-editable name to the material; not used in calculations.
• x,y,z — Assigns the vehicle-fixed x,y,z coordinates for the three corners of the contact surface (the fourth is assigned by assuming a parallelogram).
• Linear Stiffness — The first-order force vs deflection constant for the current contact surface.
• Quadratic Stiffness — The second-order force vs deflection constant for the current contact surface.
• Cubic Stiffness — The third-order force vs deflection constant for the current contact surface.
• Damping Constant — The velocity-dependent force contribution for the current contact surface.
• Friction Constant — Assigns friction characteristics to the surface; normally the friction between two surfaces is the arithmetic average of their individual friction coefficients.
• Maximum Force — The maximum force resisted by the contact surface; if exceeded, force remains constant until the Maximum Deformation is reached.
• Maximum Deflection — The maximum allowable material deformation.
• Unloading Slope — A value used to assign hysteresis. The unloading slope defines the force vs deflection relationship during unloading.

NOTE: The unloading slope should be steeper than the loading slope!

Figure 11-10: Contact Surfaces Materials dialog.

Figure 11-11: Typical force vs deflection curve for a contact surface. The loading slope (which occurs during penetration) may be defined by a 3rd-order polynomial: F = ad + bd² + cd³, where a = Linear Stiffness, b = Quadratic Stiffness, c = Cubic Stiffness. During unloading the slope is assumed linear: F = u(d_max − d), where u = Unloading Slope.

Table 11-4: Vehicle Contact Surface Parameters

Parameter	Unit Name	Description
Bind To	UtNone	Flag indicating whether material attributes are attached to each vertex or each face
Location	UtNone	Flag indicating whether the surface is an interior or exterior surface
x,y,z coords	UtVehDispLength	Vehicle-fixed vertex coordinates for each of 3 corners
Material Name	UtNone	Material name
Constant	UtVehForce	Force required to initiate deflection
Linear Stiffness	UtVehMatLinear	Linear material deformation coefficient
Quadratic Stiffness	UtVehMatQuad	Quadratic material deformation coefficient
Cubic Stiffness	UtVehMatCubic	Cubic material deformation coefficient
Damping Constant	UtVehMatDamp	Material velocity-dependent deformation constant
Friction Constant	UtNone	Friction coefficient
Maximum Force	UtVehForce	Force at which 3rd-order force-deflection relationship is abandoned
Maximum Deflection	UtVehDispLinear	Deflection at which 3rd-order force-deflection relationship is abandoned
Unloading Slope	UtVehMatLinear	Linear unloading slope beginning at max deflection

Belt Restraints

The belt restraint systems of the vehicle are displayed and edited using the Belt Restraints dialog.

Figure 11-12: Belt Restraints dialog.

To display or edit the current vehicle's belt properties, perform the following steps:

1. In the Vehicle Viewer, click on the CG sphere. The Sprung Mass options for the current vehicle will be displayed.
2. Choose Belts from the Sprung Mass option list. The Belt Restraints properties dialog will be displayed.
3. Click on the Seat Position option list and choose the desired seat position within the vehicle.
4. Click on the Belt Section option list and choose the desired belt section (Torso or Lap).
5. Click on the Device Installed checkbox to indicate a selected restraint system is installed at the selected seat location. The default belt properties for the right and left belt sections will become available for editing.
6. View and/or edit the desired properties for the current belt location and section.
7. Repeat the above steps for each seat location and belt section.
8. Press OK to accept the changes.

The Belt Restraint Properties are described below.

• Seat Location — A position index used to determine the location of the current belt restraint system.

NOTE: When the human is created using the Human Editor, it is assigned a position (Right Front, Left Front, ..., Pedestrian). If the vehicle does not have a belt restraint system at a location that matches the occupant position, you will not be able to set up a restraint system during event mode!

• Belt Section — A position index used to determine the section (torso or lap) of the current belt restraint system.
• Device Installed — A check box to indicate the vehicle has a belt system at the current location and section.

The following belt restraint material properties may be assigned for the left and right belt sections:

• x,y,z Anchor Points — Assigns the vehicle-fixed x,y,z coordinates where the belt is attached to the vehicle.
• Linear Stiffness — The first-order force vs deflection constant for the belt section.
• Quadratic Stiffness — The second-order force vs deflection constant for the belt section.
• Cubic Stiffness — The third-order force vs deflection constant for the belt section.
• Damping Constant — The velocity-dependent contribution to stiffness for the current belt section.
• Maximum Force — The breaking strength of the belt. If exceeded, belt force becomes zero.
• Unloading Slope — A value used to assign hysteresis. The unloading slope defines the force vs deflection relationship during unloading.

NOTE: The unloading slope should be steeper than the loading slope!

Table 11-5: Belt Restraint System Parameters

Parameter	Unit Name	Description
Location	n/a	Location index (Right Front, Left Front, ..., Left Back) used to assign the location of the current belt section
Section	n/a	Torso or Lap belt section
Device Installed	BOOLEAN (True or False)	Switch that determines that a restraint is installed at the selected location and section
x,y,z	UtVehDispLength	Vehicle-fixed x,y,z coordinates for the anchor point of the belt
Linear Stiffness	UtVehMatStiffLinear	First-order force vs deflection constant
Quadratic Stiffness	UtVehMatStiffQuad	Second-order force vs deflection constant
Cubic Stiffness	UtVehMatStiffCubic	Third-order force vs deflection constant
Damping Constant	UtVehMatDamp	Velocity-dependent force contribution
Max Force	UtVehForce	Maximum allowable force
Unloading Slope	UtVehMatStiffLinear	Force vs deflection constant during unloading

Airbag Restraints

The airbag restraint systems of the vehicle are displayed and edited using the Airbag Restraints dialog.

Figure 11-13: Airbag Restraints dialog.

Figure 11-14: Airbag x,y,z deployment coordinates and deployment (column) angle.

To display or edit the current vehicle's airbag properties, perform the following steps:

1. In the Vehicle Viewer, click on the CG sphere. The Sprung Mass options for the current vehicle will be displayed.
2. Choose Airbags from the Sprung Mass option list. The Airbag Restraints properties dialog will be displayed.
3. Click on the Seat Position option list and choose the desired seat position within the vehicle.
4. Click on the Device Installed checkbox to indicate the selected restraint system is installed at the selected seat location. The default airbag properties for the selected airbag location will become available for editing.
5. View and/or edit the desired properties for the selected airbag.
6. Repeat the above steps for each seat location.
7. Press OK to accept the changes.

The Airbag Restraint Properties are described below.

• Seat Location — A position index used to determine the location of the current airbag restraint system.

NOTE: When the human is created using the Human Editor, he/she is assigned a position (Front Right, Front Center, Front Left, ..., Pedestrian). If this vehicle does not have an airbag restraint system at a location that matches the occupant position, you will not be able to set up a restraint system during event mode!

• Device Installed — A checkbox to indicate the vehicle has an airbag system at the current location.
• x,y,z Deployment Coordinates — Assigns the vehicle-fixed x,y,z coordinates where the airbag is installed and deployed.
• Initial Bag Radius — Assigns the initial radius for the airbag.
• Passenger Airbag Length — Assigns the length for non-driver-side airbags.

NOTE: The driver's position is defined in the Vehicle Information dialog.

• Initial Pressure — Assigns the initial pressure for the airbag.
• Bag Membrane Thickness — Assigns the material thickness for the airbag.
• Bag Full Inflation Volume — Assigns the volume inside the airbag when fully inflated.
• Vent Discharge Coefficient — Assigns the thermodynamic discharge coefficient for the airbag vent hole.
• Vent Discharge Area Coefficient — Assigns the area of the airbag vent hole.
• Pressure To Open Vent Hole — Assigns the airbag pressure required to cause the vent hole to open.
• Force Convergence — Assigns the permissible force imbalance between the airbag and contact surfaces.
• Maximum Penetration — Assigns the penetration required before any force is computed.
• Bag Elastic Modulus — Assigns the elastic modulus for the airbag material during airbag filling.
• Bag Rebound Modulus — Assigns the elastic modulus for the airbag material during rebound.
• Bag Bottom-out Modulus — Assigns the elastic modulus for the airbag material after it has bottomed out.
• Gas Density — Assigns the gas density for the airbag filling agent.
• Gas Mass Flow Rate — Assigns the mass flow rate for the airbag filling rate.
• Gas Specific Heat — Assigns the specific heat (ratio) for the airbag filling agent.
• Maximum Column Collapse Distance — Assigns the maximum distance the steering column is allowed to collapse (applies to driver-side airbags only).
• Column Collapse Load — Assigns the axial load on the steering column required to begin collapsing the column (applies to driver-side airbags only).
• Column Angle — Assigns the steering column angle, about the vehicle's pitch axis (normally a negative angle).
• Backside Contact Surface — An option list containing all the vehicle interior contact surfaces. The selected surface is used to assign the material properties for the contact surface supporting the airbag.

NOTE: An airbag must be supported on the backside. Otherwise, the bag would simply bounce away from the occupant.

NOTE: This list of backside contact surfaces comes from the vehicle's interior contact surfaces.

Table 11-6: Airbag Restraint System Parameters

Parameter	Unit Name	Description
Location	n/a	Location index (Right Front, Left Front, ..., Left Back) used to assign the location of the airbag
Device Installed	BOOLEAN (True or False)	Switch that determines that an airbag restraint is installed at the selected location
Deploy x,y,z	UtVehDispLength	Vehicle-fixed x,y,z coordinates for the airbag deployment location
Initial Bag Radius	UtVehDispLength	Radius of the (spherical) airbag at the start of filling
Passenger Bag Length	UtVehDispLength	Length of the (cylindrical) airbag used for passenger-side airbag systems
Initial Bag Pressure	UtVehDispPress	Airbag pressure at the start of filling
Membrane Thickness	UtVehDispLength	Thickness of the airbag material
Full Inflation Vol	UtVehVolume	Volume of the airbag at full inflation
Discharge Coef	UtNone	Thermodynamic discharge coefficient of the airbag vent
Discharge Area	UtVehArea	Area of the airbag vent
Vent Opening Pressure	UtVehPress	Pressure required to open the vent
Bag Penetration for Force	UtVehDispLength	Minimum deflection of an ellipsoid into the airbag required to produce a force
Force Convergence Criterion	UtVehForce	Allowable difference between force on the airbag and force on the human
Bag Elastic Modulus	UtVehMatStiffQuad	Elastic modulus of the airbag membrane material during force application
Bag Elastic Modulus on Rebound	UtVehMatStiffQuad	Elastic modulus of the airbag membrane material during unloading
Bag Elastic Modulus When Bottomed Out	UtVehMatStiffQuad	Elastic modulus of the airbag membrane material at maximum penetration
Gas Density	UtVehDensity	Density of the airbag filling agent
Max Column Collapse	UtVehDispLength	Maximum column stroke before it bottoms out
Column Collapse Load	UtVehForce	Force required to initiate column collapse
Column Angle	UtVehDispAngle	Deployment (pitch) angle
Backside Contact	n/a	The name of the contact surface supporting the airbag (no force can exist between the human and airbag unless the airbag is supported on a contact surface that provides a reaction force)

(Note: the legacy table listed the Full Inflation Vol unit as UtVehForce; this is a typo — the quantity is a volume.)

Inter-vehicle Connections

The connections between tow vehicles and trailers are displayed and edited using the Inter-vehicle Connections dialog.

The available inter-vehicle connections are:

• Ball/Hitch
• Fifth Wheel/King Pin
• Pintle Hook/Eye (drawbars may be Fixed or Hinged)

Figure 11-15: Inter-vehicle Connections dialog.

Figure 11-16: Converter (hinged fifth wheel) and Fixed (hinged drawbar) dollies.

To display or edit the current vehicle's connection properties, perform the following steps:

1. In the Vehicle Viewer, click on the CG sphere. The Sprung Mass options for the current vehicle will be displayed.
2. Choose Connections from the Sprung Mass option list. The Inter-vehicle Connections Properties dialog will be displayed.
3. To put a connection on the front of a towed vehicle (e.g., a trailer), click on the Front Connections option button and select a connection type (None, Hitch, King Pin or Pintle Eye). Then enter the vehicle-fixed x,y,z coordinates for the connection.
4. To put a connection on the rear of a tow vehicle (e.g., a passenger car or truck tractor), click on the Rear Connections option button and select a connection type (None, Ball, Fifth Wheel or Pintle Hook). Then enter the vehicle-fixed x,y,z coordinates for the connection, friction and friction radius and maximum articulation angle.
5. Press OK to accept the changes.

The Inter-vehicle Connection Properties are described below.

• Front Connection Type — The type of connection on the front of the current vehicle. The allowable types are None, Hitch, King Pin and Pintle Eye.
• Front Connection Coords — The vehicle-fixed x,y,z coordinates of the front connection.
• Rear Connection Type — The type of connection on the rear of the current vehicle. The allowable types are None, Ball, Fifth Wheel and Pintle Hook.

NOTE: During Event Mode, the simulation model normally checks to see the user has selected vehicles with compatible connections: a Hitch on the trailer must be connected to a Ball on the tow vehicle; a King Pin on the trailer must be connected to a Fifth Wheel on the tow vehicle; a Pintle Eye on the trailer must be connected to a Pintle Hook on the tow vehicle. Otherwise, the simulation model should issue a message: Incompatible Connections.

• Rear Connection Coords — The vehicle-fixed x,y,z coordinates of the rear connection.

NOTE: The earth-fixed elevation of the connection above ground should be approximately equal on the rear connection of the tow vehicle and the front connection of the trailer. Otherwise, the trailer will be pitched up or down as necessary to make the connection. This can cause some physics models to compute an acceleration. For this reason, the physics model may terminate with an error message.

• Friction — The friction coefficient at the connection between the tow vehicle and trailer.
• Friction Radius — The moment arm at which the frictional torque acts at the connection between the tow vehicle and trailer.
• Maximum Articulation Angle — The maximum articulation angle allowable between the tow vehicle and trailer.

Table 11-7: Inter-vehicle Connection Parameters

Parameter	Unit Name	Description
Front Connection Type	n/a	Type of front connection (None, Hitch, King Pin or Pintle Eye)
Front Connection Coordinates	UtVehDispLength	Vehicle-fixed coordinates of the front connection
Rear Connection Type	n/a	Type of rear connection (None, Ball, Fifth Wheel or Pintle Hook)
Rear Connection Coordinates	UtVehDispLength	Vehicle-fixed coordinates of the rear connection
Connection Friction	n/a	Friction coefficient at the connection
Connection Friction Radius	UtVehDispLength	Frictional moment arm
Maximum Articulation Angle	UtVehDispAngle	Maximum articulation angle between the tow vehicle and trailer

Aerodynamic Drag

The vehicle drag associated with aerodynamic pressure. The Aerodynamic Drag dialog allows the user to view or edit these properties. See also the code-verified reference page, Aerodynamic Drag dialog.

Figure 11-17: Vehicle Aerodynamic Drag dialog.

To display or edit the current vehicle's drag factors, perform the following steps:

1. In the Vehicle Viewer, click on the CG sphere. The Sprung Mass options for the current vehicle will be displayed.
2. Choose Aerodynamic Drag from the Sprung Mass option list. The Aerodynamic Drag dialog will be displayed.
3. Select a surface (by default, the front surface has already been assigned those properties associated with velocity-dependent air drag; however, data for seven additional surfaces, including wings, air dams and spoilers, may also be assigned).
4. View and/or edit the desired properties.
5. Press OK to accept the changes.

The Aerodynamic Drag parameters are described below.

• Surface Option List — Assigns the selected surface. Available surface options are: Front, Right, Back, Left, Top, Bottom, Front Device, Back Device.
• Device Installed — Switch that activates the selected surface.
• Drag Coefficient — Assigns the properties resisting motion due to dynamic air pressure acting on the selected surface in the direction of the vehicle's total velocity vector. The force associated with this pressure is proportional to the velocity squared.
• Lift Coefficient — Assigns the properties resisting motion due to dynamic air pressure acting on the selected surface in the direction normal to the vehicle's total velocity vector.
• Projected Surface Area — Assigns the projected area parallel to the selected surface.
• Center of Pressure — Vehicle-fixed coordinates where the effective force from aerodynamic pressure is applied.

Table 11-8: Vehicle Aerodynamic Drag Parameters

Parameter	Unit Name	Description
Surface Name	n/a	Name of selected aerodynamic surface
Device Installed	n/a	Flag indicating device is installed and is capable of producing aerodynamic force on the vehicle
Drag Coefficient	UtVehDragQuad	Coefficient of aerodynamic drag acting on surface
Lift Coefficient	UtVehDragQuad	Coefficient of aerodynamic lift acting on surface
Projected Surface Area	UtVehArea	Projected surface area parallel to selected surface
Center of Pressure	UtVehDispLength	Vehicle-fixed coordinates where the aerodynamic force is applied

Body Torsion

The HVE Vehicle Model includes the capability to model torsional distortion of the body. By default, the body is assumed to be rigid. However, the user may wish to edit these default parameters, if the actual torsional stiffness of the body is known, to study the effect of torsional distortion on vehicle handling. The Body Torsion dialog is used to edit these properties. See also the code-verified reference page, Body Torsion dialog.

Figure 11-18: Body Torsion dialog.

To display or edit the vehicle's torsional data, perform the following steps:

1. In the Vehicle Viewer, click on the CG sphere. The Sprung Mass options for the current vehicle will be displayed.
2. Choose Body Torsion from the Sprung Mass option list. The Body Torsion dialog will be displayed.
3. Edit the torsional stiffness and torsional roll axis location (distance from the CG to the torsion axis).
4. Press OK to accept the changes.

Table 11-9: Vehicle Body Torsion Parameters

Parameter	Unit Name	Description
Axis Location	UtVehDispLength	Vehicle-fixed z-distance from the CG to the torsional roll axis
Body Stiffness	UtVehTorque	Torsional stiffness of the body

---

Source: HVE User's Manual (Version 5, Seventh Edition, Jan 2006), Chapter 11, pages 11-1..11-35 — updated against source code (HVEINV-64, Physics) 2026-07-05.

---

← Previous: Chapter 10 — Creating & Editing Vehicles | Index | Next: Chapter 11 — Vehicle Model Definition (Part B: Exterior) →