| 1. Definition | 2. Functional Requirements | 3. Syntax | 4. Semantics |
1 Definition
Brake States define the set of operational conditions that a Brake, acting as a ProcessorInstance, may report to the Motion Actuation Subsystem (MAS) of a Connected Autonomous Vehicle (CAV). Brake States represent real, physical braking behavior derived from actuator feedback, hydraulic/electric control units, and supervisory systems such as ESC and ABS.
They enable MAS to interpret braking performance, diagnose abnormal conditions, and ensure safe autonomous vehicle operation under both nominal and degraded scenarios.
Brake States shall enable the CAV’s Motion Actuation Subsystem (MAS) to:
- Interpret the brake’s current physical behavior, including braking, holding, releasing, and full wheel‑stop conditions.
- Monitor advanced brake control behaviors, such as Anti‑lock Braking (ABS), Traction Control (TCS), and Regenerative Braking.
- Detect thermal, wear‑related, and functional degradation, supporting safe planning and fallback decisions.
- Identify emergency‑related braking behavior, including emergency braking triggered by AEB or collision‑mitigation logic.
- Detect fault conditions requiring degraded operation, fallback strategies, or safe stops.
3 Syntax
https://schemas.mpai.community/CAV2/V1.1/data/WheelStates.json
4 Semantics
| Label | Description |
|---|---|
| Header | Brake Command Header – Standard CAV‑BRS‑Vx.y. |
| Normal | Brake system is functioning normally with no active braking or special condition. |
| WheelStopped | Wheel rotational velocity is zero; wheel is fully stopped. |
| Braking | Brake is actively applying force or pressure; deceleration is occurring. Modern brake systems expose this state via pressure or actuator feedback. |
| Released | Brake is not applying any force; actuator fully disengaged. |
| Hold | Brake is maintaining constant force (e.g., at standstill, hill‑hold mode). |
| EmergencyBraking | Brake is executing an emergency braking action, typically triggered by AEB or collision‑mitigation logic. Supported by contemporary ESC modules in many vehicles. |
| ABSActive | Anti‑lock Braking System is modulating pressure. ABS activation state is reported by all modern ESC systems. |
| TractionControlActive | Traction Control System is intervening to prevent wheel slip during braking; a standard output of ESC systems. |
| RegenerativeBraking | A portion of braking torque is being supplied by the electric motor(s). Reported in EVs and hybrids; regenerative blending is ESC‑supervised. |
| Overheated | Brake disc or pad temperature has exceeded operational limits. Sensors capable of monitoring this exist in modern systems (>600 °C). |
| Degraded | Brake function is reduced due to wear, insufficient pressure, degraded sensors, or actuator limitations; used in diagnostic‑capable brake systems. |
| Fault | Fault preventing normal braking: actuator malfunction, hydraulic fault, control‑module error, or sensor failure. Exposed by ESC/EMB diagnostics. |
| Unavailable | Brake subsystem is initializing, offline, or not ready to accept commands (e.g., during ECU boot or communication failure). |
| DataXMData | Information about this Wheel State Instance. |
| DescrMetadata | Optional human‑readable descriptive metadata. |
