| 1. Definition | 2. Functional Requirements | 3. Syntax | 4. Semantics |
1 Definition
A Brake Command is issued by the Motion Actuation Subsystem (MAS) to a Brake of the physical vehicle. It expresses:
- The desired target velocity after a specified time, as defined by the MPAI‑CAV standard, and
- Additional actuator‑level command parameters needed by autonomous‑vehicle braking systems, such as brake pressure targets, brake force/torque targets, ABS‑related constraints, and emergency‑braking flags.
2 Functional Requirements
Brake Command shall enable the MAS to:
2.1 Specify the braking objective
- Provide the target velocity to reach after a specified time.
- Designate which BrakeID should execute the command.
2.2 Control actuator characteristics (extended for AVs)
Modern braking systems (hydraulic, electro‑hydraulic, and electromechanical) support additional controllable parameters:
- BrakePressureTarget
- BrakeForceTarget
- BrakeTorqueTarget
- DecelerationTarget
2.3 Support complex AV braking modes
- EmergencyBrakeFlag
- RegenerativeBrakeFraction (EVs)
- ABSAllow / ABSConstraint
2.4 Improve MAS planning and explainability
- Provide optional confidence, constraints, priority, and ramp‑time fields.
- Integrate MPAI‑AIF Trace for provenance and timing.
2.5 Support future and hybrid brake‑by‑wire systems
The Command shall be compatible with EMB, hydraulic, and hybrid brake systems.
3 Syntax
https://schemas.mpai.community/CAV2/V1.1/data/BrakeCommand.json
4 Semantics
| Label | Description |
|---|---|
| Header | Brake Command Header – Standard “CAV‑BRC‑Vx.y”. |
| BrakeCommandID | Identifier of the Brake Command instance. |
| BrakeID | Identifier of the Brake to which the command is addressed. |
| BrakeCommand | Container holding the command parameters. |
| – TargetVelocity | Target velocity expected at the end of BrakeCommandTime. Original MPAI field. |
| – BrakeCommandTime | Duration (seconds or ms) after which the target velocity must be reached. Original MPAI field. |
| BrakePressureTarget | Target hydraulic/actuator pressure. Present in modern ABS/ESC and electro‑hydraulic brakes. |
| BrakeForceTarget | Target brake force applied by caliper/EMB actuator. Used in electromechanical brakes. |
| BrakeTorqueTarget | Target brake torque (often derived from EMB motor current). |
| DecelerationTarget | Requested deceleration (m/s²). Enables MAS control loops. |
| RegenerativeBrakeFraction | Fraction of braking to be achieved by regenerative braking (EVs). |
| ABSAllow | Whether ABS may intervene. |
| EmergencyBrakeFlag | Indicates autonomous emergency braking (AEB) mode. |
| RampTime | Time needed to ramp from zero to full braking. |
| DataExchangeMetadata |
Specific DataExchangeMetadata may be used, but not all DEM fields are required.
|
| Trace | Provenance trace providing Source and Time per AIF rules. |
| DescrMetadata | Optional human‑readable descriptive metadata. |
