Definition
Functional Requirements
Syntax
Semantics
Conformance Testing
Performance Assessment
1 Definition
Brake States define the set of operational conditions that a Brake may report to the Motion Actuation Subsystem (MAS). They describe real, physical brake behaviour that the 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:
- Interpret the brake’s current physical behaviour — including braking, holding, releasing, and wheel‑stop conditions.
- Monitor advanced brake control behaviours — such as ABS, traction control, and regenerative braking.
- Detect thermal, wear‑related, and functional degradation — supporting safe decision‑making.
- Identify emergency‑related behaviour — e.g., emergency braking triggered by AEB logic.
- Detect fault states — to trigger fallback behaviour and safe stops.
- Remain compatible with the minimal V1.0 state set — Normal and WheelStopped — for backward compatibility.
3 Syntax
https://schemas.mpai.community/CAV2/V1.1/data/BrakeStates.json
4 Semantics
Brake States is a string enumeration. Table 1 gives the set of valid values and their descriptions.
| Normal | System nominal; braking components responding within expected tolerances. |
| WheelStopped | Wheel speed indicates complete stop. |
| Braking | Brake system applying commanded braking torque/pressure; deceleration is occurring. |
| Released | Brake released; no pressure/torque applied; actuator fully disengaged. |
| Hold | Brake maintaining constant force (e.g., hill-hold or standstill stabilisation). |
| EmergencyBraking | High-priority braking event initiated by AEB or collision‑mitigation logic. |
| ABSActive | ABS modulating pressure to prevent wheel lock. |
| TractionControlActive | Brake system applying targeted braking to mitigate wheel slip. |
| RegenerativeBraking | Braking torque generated via electric motor rather than hydraulic system. |
| Overheated | Brake temperature exceeds thermal thresholds; performance derated. |
| Degraded | Brake system operating with reduced capability due to wear, pressure, or sensor issues. |
| Fault | Fault condition detected in hydraulic, electronic, or mechanical subsystems. |
| Unavailable | Brake system unavailable due to fault, maintenance, or power state. |
| PreCharge | System pre-charging hydraulic or electronic actuation circuits. |
| PressureBuildUp | Brake pressure increasing toward commanded level. |
| PressureDecay | Brake pressure intentionally decreasing. |
| HydraulicSaturation | System cannot increase hydraulic pressure further. |
| LowBrakeFluid | Low brake fluid detected; operational limits affected. |
| PadWearLimit | Pad wear sensor indicates end-of-life threshold reached. |
| CaliperStuck | Caliper not moving freely; may cause drag or reduced braking force. |
| LinePressureAnomaly | Unexpected hydraulic/pressure behaviour indicating leak or blockage. |
| ElectronicActuatorFault | Fault in electronic brake actuator or EMB motor system. |
| SelfTest | System performing internal diagnostics. |
| ServiceMode | System placed into maintenance or workshop mode; altered behaviour allowed. |
5 Conformance Testing
A Data instance conforms with Brake States (CAV‑BRS) if:
- The Data validates against the Brake States’ JSON Schema.
- The value is one of the strings defined in the Brake States enumeration.
6 Performance Assessment
Not part of this specification.
