In order to analyze a vehicle or half-suspension model with SVC, an Adams dataset must be created. This model must include certain statements necessary for SVC. SVC is designed to work with Adams vehicle models that have been developed for general use, such as transient handling simulations. It does, however, require that the user follow a few modeling guidelines and add some SVC-specific data to your dataset.
Note: | SVC Event creates all the necessary dataset statements needed for your model, no additional statements are needed. The following description is provided for informational purposes only. |
Modeling
The following conventions must be employed when building a vehicle or half suspension model. Orient the vehicle with the global Z axis upward, the global X axis rearward, and the global Y axis pointing out the right side of the vehicle. The vehicle may be positioned at any X or Z position, but the user must select the Y position in such a way that the XZ plane falls somewhere inside the vehicle track (between the left and right wheels).
Model Type
A full vehicle model should be supported only by tire forces applied to the spindles or wheels. There must be no other constraints or attachments to ground. If only the front or rear suspension is to be analyzed, the user must fix the body rigidly to ground. In this case, tire forces are optional. If it is desired not to model the tire forces, the suspension must be kept at the desired position during static equilibrium, by adjusting spring free lengths or by applying a constant vertical force to the spindles, for instance.
Steering Systems
A few of the SVCs rely on the pitman arm or the steering rack to transmit steering motion. For these to be computed properly, the pitman arm or rack must have some compliance relative to the body. If the pitman arm or rack is locked to the body (by a MOTION, for instance) there will be no compliance. This will make it impossible to compute the steer ratio and steering compliance. In addition, the reported Ackerman error will be incorrect. See the descriptions of these quantities for more details. SVC will issue a warning if this situation occurs. In a ball-nut steering system, a torsional spring between the pitman arm and the body is the simplest way of providing this compliance. In a rack and pinion steering system, compliance between the pinion and body will suffice.
If there is a desire to control the steering for a transient simulation, a steering wheel can be connected to the pitman arm or pinion by a torsional spring. The user may then rotate the steering wheel with a MOTION to control the vehicle, while leaving some compliance in the actual arm. This spring should be very stiff, since compliance at the pitman arm leads to compliance at the spindle. If the pitman arm were completely free to turn, for instance, the fore-aft compliance at the spindles would be very large.
SVC Data in the Data Set
SVC requires certain data about the vehicle's suspension. The user must pass this data to SVC via ARRAY and STRING statements in the dataset. Below is a description of the ARRAY and STRING statements used. Not all the statements are required, some statements have defaults, and other statements are not needed for some of the analysis options.
The following ARRAY statements contain data for computing a vehicle mass properties. These statements are only required for the full-vehicle analysis, since the half-vehicle analysis option does not compute overall vehicle mass properties.
Front_part_id_array:
ARRAY/9901, NUM=id_1, id_2, id_3, ..... id_n
List of fFront suspension part Adams IDs
Front_susp_mass_dist_array:
ARRAY/9902 NUM=ps_1, ps_2,ps_3, .....ps_n
% sprung (0-100) for each part above
Rear_part_id_array:
ARRAY/9903 rear suspension part IDs
Rear_susp_mass_dist_array:
ARRAY/9904 % sprung for each part in ARRAY/9903
Each part referenced must have non-zero mass and inertia. Further, each part must have a corresponding percent sprung value between 0 and 100. Any part not listed as part of the "front" or "rear"suspension is assumed to be 100% sprung.
Front_tire_ids:
ARRAY/9905, NUM=id_1, id_2
List of front tire force Adams IDs (only used in Adams Car)
Rear_tire_ids:
ARRAY/9906, NUM=id_1, id_2... id_n
List of rear tire force Adams IDs (only used in Adams Car)
ARRAY statement 9907 identifies MARKER statements that describe the front suspension geometry. ARRAY/9907 is not required for a rear suspension half-vehicle analysis.
ARRAY/9907, NUM= idwcfl, idwcfr, idksil, idksir, id-flspsu, id-flspby
, idfrspsu, id-frspby, id-flsksu, id-flskby, id-frsksu, id-frskby, idsfbl, idsfel,
, idsfbr, idsfer, id-str, faxlr, sratio
where:
idwcfl identifier of a MARKER statement located at the left front wheel center on the spindle part. The Y axis of the MARKER must lie along the spindle axis and point toward the passenger (right) side of the vehicle. Further, if the front suspension is supported by tires, the tire forces for the left front wheel must be applied to this MARKER.
idwcfr identifier of a MARKER statement located at the right front wheel center on the spindle part. The Y axis of the MARKER must lie along the spindle axis and point toward the passenger (right) side of the vehicle. Further, if the front suspension is supported by tires, the tire forces for the right front wheel must be applied to this MARKER.
idksil identifier of a MARKER statement located at the left front kingpin-spindle intersection on the steering knuckle. The Z axis of the MARKER must directed upward along the kingpin axis. If the kingpin axis and spindle axis do not intersect, the MARKER can be located any place along the kingpin axis.
idksir identifier of a MARKER statement located at the right front kingpin-spindle intersection on the steering knuckle. The Z axis of the MARKER must directed upward along the kingpin axis. If the kingpin axis and spindle axis do not intersect, the MARKER can be located any place along the kingpin axis.
■Rear Spring Statements
■Rear Shock Absorbers Statements
■Rear Stabilizer Statements
Front Spring Statements
id-flspsu identifier of a MARKER statement located at the front left spring seat on the axle. This MARKER is used to compute the front left wheel spring ratio.
Note: | If above marker is not present (leafspring), then create output communicator 'col_spring_marker_lower' of type marker on axle part. |
id-flspby identifier of a MARKER statement located at the front left spring seat on the body. This MARKER is used to compute the front left wheel spring ratio.
Note: | If above marker is not present (leafspring), then create output communicator 'col_spring_marker_upper' of type marker on body. |
id-frspsu identifier of a MARKER statement located at the front right spring seat on the axle. This MARKER is used to compute the front right wheel spring ratio.
Note: | If above marker is not present (leafspring), then create output communicator 'col_spring_marker_lower' of type marker on axle part. |
id-frspby identifier of a MARKER statement located at the front right spring seat on the body. This MARKER is used to compute the front right wheel spring ratio.
Note: | If above marker is not present (leafspring), then create output communicator 'cor_spring_marker_upper' of type marker on body. |
Front Shock Absorber Statements
id-flsksu identifier of a MARKER statement located at the front left shock absorber attachment point on the axle. This MARKER is used to compute the front left wheel shock ratio.
id-flskby identifier of a MARKER statement located at the front left shock absorber attachment point on the body. This MARKER is used to compute the front left wheel shock ratio.
id-frsksu dentifier of a MARKER statement located at the front right shock absorber attachment point on the axle. This MARKER is used to compute the front right wheel shock ratio.
id-frskby identifier of a MARKER statement located at the front right shock absorber attachment point on the body. This MARKER is used to compute the front right wheel shock ratio.
Front Stabilizer Bar Statements (not used)
idsfbl identifier of a MARKER statement located at the front left stabilizer-bar attachment point on the stabilizer-bar. This MARKER is used to compute the front left wheel stabilizer-bar ratio.
idsfel identifier of a MARKER statement located at the left end of the front stabilizer-bar. This MARKER is used to compute the front left wheel stabilizer-bar ratio.
idsfbr identifier of a MARKER statement located at the front right stabilizer-bar attachment point on the stabilizer-bar. This MARKER is used to compute the front right wheel stabilizer-bar ratio.
idsfer identifier of a MARKER statement located at the right end of the front stabilizer-bar. This MARKER is used to compute the front right wheel stabilizer-bar ratio.
id-str identifier of a MARKER statement located at the tip of the pitman arm in a Haltenburger steering system or at the center of steering rack in rack and pinion steering systems. A force in the global Y direction applied to this MARKER must steer the front wheels (see modeling conventions in the previous section)
faxlr front axle final drive ratio ( 0.0 if rear-wheel drive )
sratio the steering gear ratio. For a Haltenburger steering system the degrees of steering wheel rotation per degree of pitman arm rotation. For a rack and pinion steering system, the degrees of steering wheel rotation per unit of rack travel.
ARRAY/9908 identifies the MARKER statements that describe the rear suspension geometry. ARRAY/9908 is not required when analyzing a front suspension only.
ARRAY/9908, NUM = idwcrl, idwcrr, id-rlssu, id-rlsby, id-rrssu, id-rrsby,
, id-rlsksu, id-rlskby, id-rrsksu, id-rrskby, idsrbl, idsrel, idsrbr, idsrer,
, raxlr, idaxcm
where:
idwcrl identifier of a MARKER statement located at the left rear wheel center on the spindle part. The Y axis of the MARKER must lie along the spindle axis and point toward the passenger (right) side of the vehicle. Further, if the front suspension is supported by tires, the tire forces for the left rear wheel must be applied to this MARKER.
idwcrr identifier of a MARKER statement located at the right rear rbr identifier of a MARKER statement located at the rear right stabilizer-bar attachment point on the stabilizer-bar. This MARKER is used to compute the rear right wheel stabilizer-bar ratio.
Id-rlssu, id-rlsby, id-rrssu, id-rrsby spring MARKER identifiers in the rear suspension
Id-rlsksu, id-rlskby, id-rrsksu, id-rrskby damper MARKER identifiers in the rear suspension
Idsrbl, idsrel, idsrbr, idsrer identifier of a MARKER statements located at the right end of the rear stabilizer-bar. This MARKER is used to compute the rear right wheel stabilizer-bar ratio. (Not used)
raxlr rear axle final drive ratio (0.0 for front-wheel drive).
idraxcm identifier of a MARKER statement located at the C.G of the rear axle. This MARKER is used to compute the wheel hop and tramp natural frequencies for a solid axle suspension.
ARRAY/9909 contains information on the overall vehicle. It is not required for a half-vehicle analysis.
ARRAY/9909, NUM = idbcm, idbwfl, idbwfr, idbwrl, idbwrr, fdrat
, fbrat, idhpt
where:
idbcm identifier of a MARKER statement located at the body center of mass.
idbwfl identifier of a MARKER statement on the body part located at the design position of the front left wheel center. This MARKER statement is used to calculate the wheel center rise.
idbwfr identifier of a MARKER statement on the body part located at the design position of the front right wheel center.
idbwrl identifier of a MARKER statement on the body part located at the design position of the rear left wheel center.
idbwrr identifier of a MARKER statement on the body part located at the design position of the rear right wheel center.
fdrat front drive torque ratio. The portion of drive torque sent to the front wheels (e.g. 1.0 for front-wheel drive, 0.0 for rear-wheel drive, 0.5 (for instance) for four-wheel drive).
fbrat front braking ratio. The fraction of vehicle braking done by front brakes (should be between 0 and 1).
idhpt H-point marker of driver's hip.
ARRAY/9910 contains information about the ground plane. It is required for all analysis options.
ARRAY/9910, NUM = gblm, ght
where:
gblm identifier of a MARKER statement on ground giving the global reference frame. If tire forces are used to support a vehicle, this MARKER must also be the J marker for the vertical tire forces.
ght The height of the ground plane above the location of the gblm.
SVC uses the ground marker in several ways. It should be parallel to the global axes, because it is the reference frame used to compute many characteristics. It should also be the J marker on the vertical tire SFORCEs, otherwise the INFO calls to retrieve ground reaction forces will fail. The ground height defines the point on the marker Z axis that corresponds to ground level. This is used to compute various heights above ground.
Optional Array and String Statements
ARRAY/9911 contains the tire-to-ground stiffnesses at static equilibrium. These must include any temporary springs added by the tire model and nonlinearities in the vertical force.
ARRAY/9911 is optional for full-vehicle analyses. In this case SVC will accurately approximate the vertical tire stiffnesses. If a half-vehicle analysis is being performed, the user must always provide ARRAY/9911, even if there are no tires in the model (see next section).
ARRAY/9911, NUM = k1,k2, .... k24
where:
k1-k6 Left front tire X, Y, Z, AX, AY, and AZ stiffnesses
k7-k12 Right front tire X, Y, Z, AX, AY, and AZ stiffnesses
k13-k18 Left rear tire X, Y, Z, AX, AY, and AZ, stiffnesses
k19-k24 Right rear tire X, Y, Z, AX, AY, and AZ stiffnesses
ARRAY/9912 contains the conversion factors needed to convert forces, masses, lengths, speeds, and inertias from the units used in the Adams data-set to the units desired for output from SVC. ARRAY/9912 is optional, but if included at least fcf, mcf, and lcf must be given. If ARRAY/9912 is not included, SVC will use the same units for converted output as were used in the Adams data-set. The units conversion occurs only if you set "cflag" to 1 or 2 when invoking SVC with the CONTROL command. (See Executing SVC for more about the CONTROL command.)
ARRAY/9912, NUM = fcf, mcf, lcf, scf, icf
where:
fcf Force conversion factor (Output units force = Input units force * FCF)
mcf Mass conversion factor (Output units mass = Input units mass * MCF)
lcf Length conversion factor (Output units length = Input units length * LCF)
scf Speed conversion factor (Output units speed = Input units speed * SCF)
icf Inertia conversion factor (Output units inertia = Input units inertia * ICF)
STRING statements 1-3 contain text for the units used in the Adams data-set. These have no effect on the calculations, they are only used for labeling. Each string has a default value that is used if you do not provide one.
STRING/1,STRING=Force units used in the data-set(defaults to 'Newtons')
STRING/2, STRING= Mass units used in the data-set ( defaults to 'kg' )
STRING/3, STRING= Length units used in the data-set(defaults to 'mm' )
STRING statements 4 and 5 inform SVC whether the front and rear suspensions are independent or dependent. The STRINGs may be either 'INDEPENDENT' or 'DEPENDENT'.
STRING/4, STRING= Front suspension ( defaults to 'INDEPENDENT' )
STRING/5, STRING= Rear suspension ( defaults to 'DEPENDENT' )
STRING statements 6 and 7 are optional strings in which the user can input a one line description for the front and rear suspensions.
STRING/6, STRING= Front description string
STRING/7, STRING= Rear description string
STRING statements 11-15 contain text for the units used in the SVC output files. If a label is included the appropriate conversion factor must also be included in ARRAY/9912.
STRING/11,STRING=Force units to use during output(defaults to STRING/1)
STRING/12, STRING= Mass units to use during output (defaults to STRING/2 )
STRING/13, STRING= Length units to use during output (defaults to STRING/3)
STRING/14, STRING= Speed units to use during output (defaults to STRING/3 ¸ sec)
STRING/15, STRING= Inertia units to use during output
(defaults to STRING/1 * (STRING/3)2)
SVC handles tire stiffnesses differently depending on the analysis option and whether you provide ARRAY/9911. Some background on SVC and tire models is needed in order to explain when the user should and should not supply ARRAY/9911. SVC uses tire stiffnesses in two ways. First, if the model contains tire forces, the stiffnesses are used to remove tire effects on suspension compliance. Second, the vertical tire stiffnesses are explicitly used in the calculations of some SVCs, whether there are tire forces in the data set or not. In all cases, then, SVC uses at least the vertical stiffnesses.
Determining tire stiffnesses is complicated by two factors. Temporary springs are added during static equilibrium. This generally helps convergence to static equilibrium, but the tire can no longer be treated as a simple vertical spring. It is then necessary to supply the non-vertical terms to SVC as well. In addition, the vertical tire force is usually non-linear. The stiffness depends upon the vertical deflection, making it difficult to compute ahead of time for a particular model.
In the full-vehicle case, SVC can approximate the vertical tire stiffnesses from the compliance matrix. The other terms can be assumed from knowledge of the tire model. The Adams Car model, for instance, uses stiffnesses of 100 laterally and longitudinally on the left front tire and 100 laterally on the left rear tire. Adams TIRE uses stiffnesses of 1 on all translational and rotational degrees of freedom. If the user does not supply ARRAY/9911 in a full-vehicle analysis, SVC approximates the vertical stiffnesses and supplies the others.
In a half-vehicle analysis, the user must always supply ARRAY/9911, because SVC cannot approximate the vertical stiffnesses. Normally, you would not be modeling tires at all, in which case SVC does not need to modify the compliance matrix and will use only the vertical stiffnesses provided in computing a few of the characteristics.
ARRAY/9913 contains parameters needed to determine dive and pitch characteristics for half vehicle analysis. ARRAY/9913 is not required for full vehicle analysis.
ARRAY/9913, NUM = tcgh, wb, rlf, rlr
where:
■tcgh = Vehicle CG height with respect to ground
■wb = Vehicle wheel base
■rlf = Left tire rolling radius
■rlr = Rfile:///C:/Users/karthikeyan.subraman/AppData/Local/Microsoft/Teams/current/resources/app.asar/assets/teams_welcomescreen_v2.svgight tire rolling radius
Notes: | To run SVC Event on the user customized full-vehicle testrig in Adams Car and Adams Driveline, user need to add following input communicators: ci[lr]_front_suspension_mount ci[lr]_rear_suspension_mount ci[lr]_tire_force_front ci[lr]_tire_force_rear cis_diff_ratio (optional) cis_drive_torque_bias_front (optional) Optionally user can define variable pvs_brake_ratio in there testrig. If optional communicators or variables are not defined then the default values are considered. For dependent suspensions, the wheel hop and tramp frequencies can be calculated only if the center of the axle is provided by the cos_axle_cm communicator. |