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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).
They describe real, physical brake behaviour that MAS needs to interpret braking performance, diagnose issues, and ensure safe autonomous‑vehicle operation.

2       Functional Requirements

Brake States shall enable the CAV’s Motion Actuation Subsystem (MAS) to:

  1. Interpret the brake’s current physical behaviour, including braking, holding, releasing, and wheel‑stop conditions.
  2. Monitor advanced brake control behaviours, such as ABS, traction control, and regenerative braking.
  3. Detect thermal, wear‑related, and functional degradation, supporting safe decision‑making.
  4. Identify emergency‑related behaviour, e.g., emergency braking triggered by AEB logic.
  5. Detect fault states to trigger fallback behaviour and safe stops.
  6. Remain compatible with the minimal V1.0 state set (Normal, WheelStopped) for backward compatibility.

3       Syntax

https://schemas.mpai.community/CAV2/V1.1/data/BrakeStates.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. (Original CAV‑TEC V1.0 state)
WheelStopped Wheel rotational velocity is zero; wheel is fully stopped. (Original CAV‑TEC V1.0 state)
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).
DataExchangeMetadata
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Trace Provenance trace providing Source and Time per AIF rules.
DescrMetadata Optional human‑readable descriptive metadata.