Computes instantaneous steering sensitivity, roll gradient, sideslip gradient, understeer from steering wheel angle, and understeer from just the slip angles at each time step. This routine is also used to input the maximum allowable roll angle the model can experience in a simulation. This parameter is useful in halting rollover simulations. The roll couple distribution is also calculated.
Input:
REQ/id, FUNCTION = USER (1119,bcg,grnd,ibdy,int_branch,swm,swrm,lfw,rfwm,rlw,rrw,lfwc,rfwc, lrwc,rrwc,oratio,proll)
where:
| | Description |
|---|
bcg | = | test equipment MARKER id |
grnd | = | ground reference MARKER id. For models created in a coordinate system other than Standard Adams Car, the origo MARKER id should be passed as grnd (origo marker represents a marker on ground in whose coordinate system the vehicle is built) |
ibdy | = | body cm MARKER id |
int_branch | = | internal branch id to specify correction to lateral acceleration. For standard Adams Car models the interal branch id used for vehicle statics request (ID = 1090) will be used for this request also.
1 - As original, uncorrected to gravity, vehicle roll and pitch
2 - Lateral acceleration corrected gravity, vehicle roll and pitch |
swm | = | steering wheel MARKER id |
swrm | = | steering wheel reference MARKER id on body |
lfw | = | wheel number of left front wheel |
rfw | = | wheel number of right front wheel |
lrw | = | wheel number of left rear wheel |
rrw | = | wheel number of right rear wheel |
lfwc | = | left front wheel center MARKER id |
rfwc | = | right front wheel center MARKER id |
lrwc | = | left rear wheel center MARKER id |
rrwc | = | right rear wheel center MARKER id |
oratio | = | overall steering system ratio. This is computed by dividing the steering wheel angle by the average front toe angle for a 90 degree steering wheel angle input at zero vehicle velocity |
proll | = | maximum allowable body roll angle in a simulation in degrees |
Request File Output
Column Number Output:
1. Vehicle understeer (slip angles) (deg/g)
2. Vehicle roll gradient (deg/g)
3. Vehicle sideslip gradient (deg/g)
4. Steering sensitivity (g/100 deg SWA)
5. Understeer computed from steering (deg/g) wheel angle
6. Roll couple distribution
Notes on Input and Output:
The test equipment MARKER and the ground MARKERs must have the same initial orientation as the global reference frame. The test equipment MARKER should also be located on the vehicle sprung mass and located at the same point the lateral accelerometer is typically mounted for actual vehicle testing. The steering wheel and steering wheel reference MARKERs must be oriented such the their Z axis lie along the axis of rotation. All wheel center MARKERs must lie on their appropriate wheel parts with their orientation in the global reference frame.
The roll and sideslip gradients are computed as follows:
Roll gradient = body roll angle / lateral acceleration in g's (instantatious)
Sideslip gradient = sideslip angle / lateral acceleration in g's (instantatious)
The steering sensitivity is computed by:
Steering sensitivity = 100.0 * lateral acceleration / steer angle (instantanious)
The understeer is computed in two ways:
The first uses the actual slip angles at all four wheels:
Understeer = (fwslip - rwslip) / latacc (instantanious)
where:
fwslip = (left front slip angle + right front slip angle)/2
rwslip = (left rear slip angle + right rear slip angle)/2
latacc = vehicle lateral acceleration in g's
The second uses the formula that understeer is the excess steering wheel angle required to make a maneuver than would be required at zero speed. The equation is as follows:
Understeer = (angact - angin) / lateral acceleration (instantanious)
where:
angact = steering wheel angle / overall steering system ratio
angin = wheelbase * lateral accel. / longitudinal velocity**2
The roll couple distribution is calculated from the vertical forces on the tires as follows:
Roll Couple = Front Load Transfer / Rear Load Transfer
where:
Front Roll Moment = ABS( LFVF - RFVF )
Rear Roll Moment = ABS( LRVF - RRVF )
and:
LFVF = Left front vertical tire load - static tire load
RFVF = Right front vertical tire load - static tire load
LRVF = Left rear vertical tire load - static tire load
RRVF = Right rear vertical tire load - static tire load