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Braking Test

This reference application represents a full vehicle dynamics model undergoing a braking test, including a split-mu test. You can create your own versions, establishing a framework to test that your vehicle meets the design requirements under normal and extreme driving conditions. Use this reference application in ride and handling studies and chassis controls development to characterize the vehicle dynamics during a braking test. For information about this and similar maneuvers, see standards SAE J299_2009014 and ISO 21994:20075.

To test advanced driver assistance systems (ADAS) and automated driving (AD) perception, planning, and control software, you can run the maneuver in a 3D environment. For the 3D visualization engine platform requirements and hardware recommendations, see 3D Visualization Engine Requirements and Limitations.

To create and open a working copy of the constant radius reference application, enter

This table summarizes the blocks and subsystems in the reference application. Some subsystems contain variants.

Reference Application ElementDescriptionVariants

Straight Maneuver Reference Generator

Generates accelerator and brake commands to conduct a straight line maneuver. The acceleration begins at the specified rate until the vehicle achieves the longitudinal velocity setpoint. The vehicle controller maintains the longitudinal velocity setpoint for the specified time or distance. The controller then decelerates the vehicle.

Optionally, specify fault conditions before braking during a split-mu test. If the vehicle speed, steering angle, or yaw rate is not within the allowable range before braking, the block sets a fault condition. The default values represent compliance with ISO 145126.

Driver Commands

Implements the driver model that the reference application uses to generate acceleration, braking, gear, and steering commands.

By default, Driver Commands subsystem variant is the Predictive Driver block.

Environment

Implements wind and road forces, including a constant or split friction coefficient scaling factor.

Controllers

Implements controllers for engine control units (ECUs), transmissions, anti-lock braking systems (ABS), and active differentials.

Passenger Vehicle

Implements the:

  • Body, suspension, and wheels

  • Engine

  • Steering, transmission, driveline, and brakes

Visualization

Provides the vehicle trajectory, driver response, and 3D visualization.

To enable 3D visualization, set the 3D Engine block parameter 3D Engine parameter to Enabled.

For the minimum 3D visualization environment hardware requirements, see 3D Visualization Engine Requirements and Limitations.

To override the default variant, on the Modeling tab, in the Design section, click the drop-down. In the General section, select Variant Manager. In the Variant Manager, navigate to the variant that you want to use. Right-click and select Override using this Choice.

Straight Maneuver Reference Generator

The Straight Maneuver Reference Generator block generates accelerator and brake commands to conduct a straight line maneuver. The acceleration begins at the specified rate until the vehicle achieves the longitudinal velocity setpoint. The vehicle controller maintains the longitudinal velocity setpoint for the specified time or distance. The controller then decelerates the vehicle.

Use the Maneuver Parameters to specify the maneuver start time, velocity setpoint, acceleration, and deceleration.

Optionally, on the Tracking Parameters tab, select Enable fault tracking before braking. Use the parameters to specify fault conditions before braking during a split-mu test. If the vehicle speed, steering angle, or yaw rate is not within the allowable range before braking, the block sets a fault condition. The default values represent compliance with ISO 145126.

For more information, see Straight Maneuver Reference Generator.

Driver Commands

The Driver Commands block implements the driver model that the reference application uses to generate acceleration, braking, gear, and steering commands. By default, if you select the Reference Generator block parameter Use maneuver-specific driver, initial position, and scene, the reference application selects the driver for the maneuver that you specified.

Vehicle Command Mode Setting

Implementation

Longitudinal Driver

Longitudinal Driver block — Longitudinal speed-tracking controller. Based on reference and feedback velocities, the block generates normalized acceleration and braking commands that can vary from 0 through 1. Use the block to model the dynamic response of a driver or to generate the commands necessary to track a longitudinal drive cycle.

Predictive Driver

Predictive Driver block — Controller that generates normalized steering, acceleration, and braking commands to track longitudinal velocity and a lateral reference displacement. The normalized commands can vary between -1 to 1. The controller uses a single-track (bicycle) model for optimal single-point preview control.

Open Loop

Implements an open-loop system so that you can configure the reference application for constant or signal-based steering, acceleration, braking, and gear command input.

Environment

The Environment subsystem implements wind and road forces, including a constant or split friction coefficient scaling factor.

Use the Road Track Friction block Type of surface parameter to specify the friction coefficient scaling factor:

  • Constant friction coefficient scaling factor — Constant surface friction during the maneuver

  • Split friction coefficient scaling factor — Two friction coefficients

    Select this option to specify the friction scaling coefficients for a split-mu braking test. Use the enabled parameters to set the ground friction and rectangular surface friction coefficient scaling factors.

For more information, see Road Track Friction.

The reference application has these ground feedback variants.

EnvironmentVariantDescription

Ground Feedback

3D Engine

Uses Vehicle Terrain Sensor block to implement ray tracing in 3D environment.

Constant (default)

Implements a constant or split friction coefficient scaling factor based on the Road Track Friction block output.

Controllers

The Controllers subsystem generates engine torque, transmission gear, brake pressure, and differential pressure commands.

ECU

The ECU controller generates the engine torque command. The controller prevents over-revving the engine by limiting the engine torque command to the value specified by model workspace variable EngRevLim. By default, the value is 7000 rpm. If the differential torque command exceeds the limited engine torque command, the ECU sets the engine torque command to the commanded differential torque.

Transmission Control

The Transmission Controller subsystem generates the transmission gear command. The controller includes these variants.

VariantDescription

Transmission Controller

Implements a transmission control module (TCM) that uses Stateflow® logic to generate the gear command based on the vehicle acceleration, wheel speed, and engine speed.

Driver - No Clutch

Open loop transmission control. The controller sets the gear command to the gear request.

PRNDL Controller (default)

Implements a transmission control module (TCM) that uses Stateflow logic to generate the gear command based on the vehicle acceleration, brake command, wheel speed, engine speed, and gear request.

Paddles

Implements a paddle controller that uses the vehicle acceleration and engine speed to generate the gear command.

Brake Pressure Control

The Brake Controller subsystem implements a Brake Pressure Control subsystem to generate the brake pressure command. The Brake Pressure Control subsystem has these variants.

VariantDescription

Bang Bang ABS

Implements an ABS feedback controller that switches between two states to regulate wheel slip. The bang-bang control minimizes the error between the actual slip and desired slip. For the desired slip, the controller uses the slip value at which the mu-slip curve reaches a peak value. This desired slip value is optimal for minimum braking distance.

Open Loop (default)

Open loop brake control. The controller sets the brake pressure command to a reference brake pressure based on the brake command.

Five-State ABS

Five-state ABS control when you simulate the maneuver.1,2,3 The five-state ABS controller uses logic-switching based on wheel deceleration and vehicle acceleration to control the braking pressure at each wheel.

Consider using five-state ABS control to prevent wheel lock-up, decrease braking distance, or maintain yaw stability during the maneuver.

The default ABS parameters are set to work on roads that have either:

  • Constant friction coefficient scaling factor of 0.6.

  • Split friction coefficient scaling factors of 0.6 and 0.8.

To specify the road surface, see Environment.

Active Differential Control

The Active Differential Control subsystem generates the differential pressure command. To calculate the command, the subsystem has these variants.

VariantDescription

Rear Diff Controller

Implements a controller that generates the differential pressure command based on the:

  • Steer angle

  • Vehicle pitch, yaw, and roll

  • Brake command

  • Wheel speed

  • Gear

  • Vehicle acceleration

No Control (default)

Does not implement a controller. Sets the differential pressure command to 0.

Passenger Vehicle

The Passenger Vehicle subsystem has an engine, controllers, and a vehicle body with four wheels. Specifically, the vehicle contains these subsystems.

Body, Suspension, Wheels SubsystemVariantDescription

PassVeh7DOF

PassVeh7DOF

Vehicle with four wheels:

  • Vehicle body has three degrees-of-freedom (DOFs) — Longitudinal, lateral, and yaw

  • Each wheel has one DOF — Rolling

PassVeh14DOF

PassVeh14DOF (default)

Vehicle with four wheels.

  • Vehicle body has six DOFs — Longitudinal, lateral, vertical and pitch, yaw, and roll

  • Each wheel has two DOFs — Vertical and rolling

Engine SubsystemVariantDescription

Mapped Engine

SiMappedEngine (default)

Mapped spark-ignition (SI) engine

Steering, Transmission, Driveline, and Brakes Subsystem

VariantDescription

Driveline Ideal Fixed Gear

Driveline model

All Wheel Drive

Configure the driveline for all-wheel, front-wheel, rear-wheel, or rear-wheel active differential drive and specify the type of torque coupling.

Front Wheel Drive

Rear Wheel Drive

Rear Wheel Drive Active Differential (default)

Transmission

Ideal (default)

Implements an ideal fixed gear transmission.

Brake Hydraulics

NA

Implements the heuristic response of a hydraulic system when the controller applies a brake command to a cylinder. Includes front and rear wheel bias coefficients. The subsystem converts the applied pressure to a cylinder spool position. To generate the brake pressure, the spool applies a flow downstream to the cylinders.

Visualization

When you run the simulation, the Visualization subsystem provides driver, vehicle, and response information. The reference application logs vehicle signals during the maneuver, including steering, vehicle and engine speed, and lateral acceleration. You can use the Simulation Data Inspector to import the logged signals and examine the data.

ElementDescription

Driver Commands

Driver commands:

  • Handwheel angle

  • Acceleration command

  • Brake command

Vehicle Response

Vehicle response:

  • Engine speed

  • Vehicle speed

  • Lateral acceleration

  • ABS indicator

  • Electronic stability program (ESP) indicator – Indicates when traction control system (TCS) is active

Steer, Velocity, Lat Accel Scope block

  • SteerAngle — Steering angle versus time

  • <xdot> — Longitudinal vehicle velocity versus time

  • <ay> — Lateral acceleration versus time

Vehicle XY Plotter

Vehicle longitudinal versus lateral distance

ISO 15037-1:2006 block

Display ISO standard measurement signals in the Simulation Data Inspector, including steering wheel angle and torque, longitudinal and lateral velocity, and sideslip angle

If you enable 3D visualization on the Reference Generator block 3D Engine tab by selecting Enabled, you can view the vehicle response in the AutoVrtlEnv window.

To smoothly change the camera views, use these key commands.

KeyCamera View

1

Back left

Image showing key commands and corresponding camera view

 View Animated GIF

2

Back

3

Back right

4

Left

5

Internal

6

Right

7

Front left

8

Front

9

Front right

0

Overhead

For additional camera controls, use these key commands.

KeyCamera Control
Tab

Cycle the view between all vehicles in the scene.

 View Animated GIF

Mouse scroll wheel

Control the camera distance from the vehicle.

 View Animated GIF

L

Toggle a camera lag effect on or off. When you enable the lag effect, the camera view includes:

  • Position lag, based on the vehicle translational acceleration

  • Rotation lag, based on the vehicle rotational velocity

This lag enables improved visualization of overall vehicle acceleration and rotation.

 View Animated GIF

F

Toggle the free camera mode on or off. When you enable the free camera mode, you can use the mouse to change the pitch and yaw of the camera. This mode enables you to orbit the camera around the vehicle.

 View Animated GIF

References

[1] Pasillas-Lépine, William. "Hybrid modeling and limit cycle analysis for a class of five-phase anti-lock brake algorithms." Vehicle System Dynamics 44, no. 2 (2006): 173-188.

[2] Gerard, Mathieu, William Pasillas-Lépine, Edwin De Vries, and Michel Verhaegen. "Improvements to a five-phase ABS algorithm for experimental validation." Vehicle System Dynamics 50, no. 10 (2012): 1585-1611.

[3] Bosch, R. "Bosch Automotive Handbook." 10th ed. Warrendale, PA: SAE International, 2018.

[4] J299_200901. Stopping Distance Test Procedure. Warrendale, PA: SAE International, 2009.

[5] ISO 21994:2007. Passenger cars — Stopping distance at straight-line braking with ABS — Open-loop test method. Geneva: ISO, 2007.

[6] ISO 14512:1999. Passenger cars — Straight-ahead braking on surfaces with split coefficient of friction -- Open-loop test procedure. Geneva: ISO, 2007.

See Also

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