Step Steer

The steering input is a rotational motion or torque at the steering wheel or the input shaft to the steering gear. The standard output requests are included to measure vehicle response. Tire requests are included to understand tire forces during the event. The Altair Driver model maintains constant speed during the event.

A series of step steer tests (in both the left and right turn direction) at increasing steer angles can be used to characterize the vehicle understeer and lateral response.

The Step steer event is supported by the Cars & Small Trucks, Heavy Trucks, and Two-Wheeler vehicle libraries. Automated output reports are available to plot the results.

The Step steer event follows the +7401-2003 - Road vehicles - Lateral transient response test methods - Open-loop test methods.

Parameters


Parameter Name	Description
Units	Describes the Length, Velocity, and Acceleration units. Length (Model, m, ft) Velocity (Model, m/s, km/h, mph). Acceleration (Model, m/s², g’s).
Velocity	Velocity of the vehicle during the event.
Steer input start time*	Initial Steer start time (absolute time in seconds).
Lean input start time**	Initial Lean start time (absolute time in seconds).
Steer input end time*	Ending time for application of the step steer in seconds (absolute time).
Lean input end time**	Ending time for application of the step lean in seconds (absolute time).
Maximum steer	Maximum Steering input value.
Function type	Sine, step or ramp function (used to transition from 0 degrees steer to the maximum steer value).
End time	Absolute end time of the event, in seconds.

*Applicable only for Cars/Trucks i.e., Non-leaning events.

**Applicable only for Two-wheeler i.e., Leaning events.

Controller Settings

Non-leaning events (Cars/Trucks)

LONGITUDINAL – TRACTION CONTROLLER SETTINGS

Use additional control: Enables the additional feedback control for the traction control. The gains for the controller can be edited by toggling this check box.


Kp	Proportional gain for the feedback PID controller
Ki	Integral gain for the feedback PID controller
Kd	Derivative gain for the feedback PID controller

LATERAL – STEERING CONTROLLER SETTINGS

Altair Driver uses Feedforward steering controller for non-leaning vehicles like Cars and Trucks. The following settings can be edited by the user.


Look ahead time	Look ahead time for the feedforward model to evaluate future states of the vehicle
Prediction step size	Maximum step size, used by the Driver feedforward steering model

For more information see the Altair Driver Mathematical Methods topic.

Leaning events (Two-wheelers)

LONGITUDINAL – TRACTION CONTROLLER SETTINGS

Use additional control: Enables the additional feedback control for the traction control. The gains for the controller can be edited by toggling this check box.


Kp	Proportional gain for the feedback PID controller
Ki	Integral gain for the feedback PID controller
Kd	Derivative gain for the feedback PID controller

LATERAL – STEERING CONTROLLER SETTINGS

The Lean PID and Lateral Error PID controllers only apply to leaning vehicles (for example, motorcycles and scooters).

Steer control: Control mode for steering can be switched between ‘MOTION’ and ‘TORQUE’

Lean control

The Lean PID takes as input a demand lean angle and outputs front fork (steering) angle. For open loop events the lean angle demand is a function of time. For closed loop path following events the demand lean angle is computed based on the vehicle speed and the path curvature with a correction for lateral path error.


Kp	Proportional gain for the lean controller
Ki	Integral gain for the lean controller
Kd	Derivative gain for the lean controller

Lateral error control

The Lateral Error PID takes as input the predicted lateral path error and outputs an increment to the demanded lean angle. The lateral error is computed by predicting the vehicle’s lateral position relative to the path by the look ahead time in the future. The Lateral Error PID acts to lean the vehicle toward the path.


Look ahead time	Look ahead time for the feedforward model to evaluate future states of the vehicle
Kp	Proportional gain for the lateral error controller
Ki	Integral gain for the lateral error controller
Kd	Derivative gain for the lateral error controller

For more information see the Leaning Two and Three Wheeler Vehicles and Gain Tuning for Leaning Two and Three Wheeler Vehicles topics.

Signal Settings

Use the signal settings to set minimum, maximum, smooth frequency and initial values for Steering, Throttle, Brake, Gear, and Clutch signals output by the driver.

The smoothing frequency is used to control how fast the Driver changes signals. Only closed loop control signals from the Driver are smoothed. Open loop signals are not smoothed.

Road Settings

Three options are available to specify the road in the event, Flat Event, Road File, and Tires.

Flat Road

Uses a flat smooth road for the event with no required road file.

When the Flat Road is selected, the Graphics Setting option is available with the following parameters:

View path centerline: Enables the visualization of the event path.
- This check box is disabled for open loop events without a path.

View grid graphics: Enables the visualization of the road grid graphics.

When view grid graphics check box is toggled, road grid parameters can be edited in the Grid Settings tab.


Grid length	Defines the length of the road. Enter a positive value in the model units.
Grid Width	Defines the width of the road. Enter a positive value in the model units.
Grid X offset	Gives a distance offset to the road graphics in the longitudinal direction. Enter a positive value in the model units.
Grid Y offset	Gives a distance offset to the road graphics in the lateral direction. Enter a positive value in the model units.

Road File: The road file option enables the selection of a road file to be used in the event. Using this option, all tires in the model consider the event specified road file instead of the file included in the tire entities.
Tires: Using Tire as road selection option, the road file specified in the tire entity is used in the events simulation.

Automated Output Report

The list of outputs present in Step steer event report are as follows:


Report Name	Report Signals
Steering Input and Acceleration	Steering Wheel Angle vs. Time Steering Wheel Torque vs. Time Lateral Acceleration vs. Time Longitudinal Acceleration vs. Time
Vehicle Slip Angles	Front Sideslip Angle vs. Time Rear Sideslip Angle vs. Time CG Sideslip Angle vs. Time
Vertical Tire Forces	Left Front Tire Vertical Force vs. Time Right Front Tire Vertical Force vs. Time Left Rear Tire Vertical Force vs. Time Right Rear Tire Vertical Force vs. Time
Lateral Tire Forces	Left Front Tire Lateral Force vs. Time Right Front Tire Lateral Force vs. Time Left Rear Tire Lateral Force vs. Time Right Rear Tire Lateral Force vs. Time
Longitudinal Tire Forces	Left Front Tire Longitudinal Force vs. Time Right Front Tire Longitudinal Force vs. Time Left Rear Tire Longitudinal Force vs. Time Right Rear Tire Longitudinal Force vs. Time
Vertical Tire Forces vs. Lateral Acceleration	Left Front Tire Vertical Force vs. Lateral Acceleration Right Front Tire Vertical Force vs. Lateral Acceleration Left Rear Tire Vertical Force vs. Lateral Acceleration Right Rear Tire Vertical Force vs. Lateral Acceleration
Steering Wheel, Torque and Roll	Steering Wheel Angle vs. Lateral Acceleration Steering Wheel Torque vs. Lateral Acceleration Roll Angle vs. Lateral Acceleration Yaw Rate vs. Lateral Acceleration Understeer vs. Lateral Acceleration
Vehicle Slip vs. Acceleration	Front Axle Sideslip vs. Lateral Acceleration Rear Axle Sideslip vs. Lateral Acceleration CG Sideslip Angle vs. Lateral Acceleration
Lateral Load Transfer	Front Load Transfer vs. Lateral Acceleration Rear Load Transfer vs. Lateral Acceleration