Ford Electro-Hydraulic Braking and Regenerative Systems

System Architecture and Electro-Hydraulic Braking (EHB)

In modern Ford electrified vehicle platforms, including the Mustang Mach-E and F-150 Lightning, the conventional vacuum-assisted power brake system has been superseded by Electro-Hydraulic Braking (EHB). This architecture is defined by the mechanical decoupling of the brake pedal from the hydraulic calipers during standard operation.

• Pedal Simulator: To maintain driver confidence, a spring-and-damper pedal simulator is integrated into the assembly. This component generates a synthetic tactile response and resistance curve that mimics traditional hydraulic pressure.
• Pressure Generation: Hydraulic force is no longer dependent on engine vacuum. Instead, a high-pressure electric pump or a brushless DC (BLDC) motor-driven plunger provides the necessary displacement to actuate the calipers.
• Active Braking Integration: The Brake Control Module (BCM) manages "active braking" events. This allows the vehicle to initiate hydraulic pressure for Automatic Emergency Braking (AEB) or Adaptive Cruise Control (ACC) without driver pedal interaction.

Control Logic: Total Torque Request and Blending

The EHB system functions on a 'Total Torque Request' logic. The Brake Control Module processes inputs from the Brake Pedal Position (BPP) sensor and dual travel sensors to calculate the exact Newton-meters of deceleration torque required.

1. Regenerative Priority: The system first queries the Powertrain Control Module (PCM) to determine the available negative torque from the electric drive motors (MG1/MG2). If the battery State of Charge (SOC) and temperature allow, the motors perform the bulk of the deceleration.
2. Friction Supplement: If the torque request exceeds the regenerative limits—such as during high-G deceleration or when the battery is at maximum capacity—the EHB unit energizes linear solenoid valves to introduce hydraulic pressure to the calipers.
3. Pulse Width Modulation (PWM) Blending: To prevent the driver from sensing the hand-off between regenerative and friction braking, the BCM uses PWM to modulate hydraulic solenoids. This ensures a seamless transition and prevents 'pedal drop' sensations during high-speed to low-speed transitions.

Failure Analysis and Redundancy Protocols

Engineering safety into a brake-by-wire system requires robust hardware and software redundancy to handle electronic failures.

• Hydraulic Fall-back (Manual Tick-over): In the event of a total 12V power loss or a critical BCM software hang, a fail-safe valve (normally open) defaults to a bypass position. This establishes a direct mechanical-hydraulic link between the master cylinder and the front brake circuits. Technicians should note that this mode results in significantly higher pedal effort and increased travel.
• Triple Redundant Sensing: The system utilizes three independent data points (two travel sensors and one pressure transducer).
• Sensor Divergence Logic: If a variance of greater than 10 percent is detected between these sensors, the BCM triggers a 'Limited Performance Mode.' Regenerative blending is disabled, and the system reverts to a consistent friction-only hydraulic map to ensure predictable stopping distances.

Advanced Diagnostics and Service Requirements

EHB systems are sensitive to air entrainment and electrical resistance. Traditional maintenance methods are often insufficient for these high-voltage/high-pressure systems.

• Brake Maintenance Mode: Before performing mechanical work such as pad or rotor replacement, the system must be placed in 'Brake Maintenance Mode' via the Ford Diagnostic and Repair System (FDRS). This command retracts the Electric Parking Brake (EPB) motors and depressurizes the EHB accumulator.
• FDRS Secondary Bleed: Air trapped within the internal solenoid blocks cannot be removed by gravity or pressure bleeding. A 'Secondary Bleed Procedure' must be initiated to cycle the BLDC motor and internal valves, purging air into the main lines for removal.

Diagnostic Troubleshooting Steps

Technicians should utilize the following protocol when diagnosing electronic braking faults:

• Verify Network Integrity: Conduct a High-Speed Controller Area Network (HS-CAN) test to ensure the BCM, PCM, and ABS modules are communicating. Latency in torque request signals can cause 'jerky' braking.
• Monitor PID Data: Use a datalogger to compare BRAKE_REL_POS (Pedal Position) against MCYL_PRES (Master Cylinder Pressure). In a functional EHB system, MCYL_PRES should remain near zero during light braking while regeneration is active.
• Analyze High-Amperage Circuits: The EHB high-pressure pump can pull between 40 and 60 amps. Perform a voltage drop test on the 12V supply and ground. High resistance often triggers 'Under-Voltage' DTCs and forces the system into manual fall-back.
• Calibrate Stroke Sensors: Following any component replacement or front-end alignment, perform the 'Brake Pedal Position Sensor Calibration.' Failure to zero these sensors leads to 'dragging' or 'grinding' sensations as the system miscalculates the pad-to-rotor air gap.