Brake-by-Wire is a braking system that transmits braking commands via electronic signals, replacing traditional mechanical/hydraulic connections. The core concept is the elimination of the direct physical connection between the brake pedal and the brake actuators. Instead, sensors capture pedal input, which is processed by the Electronic Control Unit (ECU) to directly control the actuators that generate hydraulic or mechanical braking force. Brake-by-wire systems offer fast response, precise control, flexible spatial layout, and enable support for autonomous driving. These systems are increasingly being adopted in various vehicle models. Based on actuator type, brake-by-wire systems can be divided into:
Electro-Hydraulic Brake (EHB): This system
retains the hydraulic brake circuit but replaces the traditional vacuum booster
or mechanical hydraulic valves with motors or pumps to control hydraulic force
via electrical signals. It offers high compatibility and is applicable to
traditional internal combustion engine vehicles, hybrids, and electric
vehicles, making it a mainstream technology today.
The Two-box brake architecture is currently the mainstream implementation of EHB. It consists of:
A Booster (electronic brake booster, or
eBooster)
An ESC (Electronic Stability Control
system)
In addition to providing basic brake assist
and stability control, it also coordinates regenerative braking, ensuring
consistent pedal feel during the transition between electric and hydraulic
braking.
Through the division of labor between the
eBooster and ESC, the Two-box solution achieves breakthroughs in performance
dimensions such as dynamic response, energy recovery, and redundancy safety—surpassing traditional braking systems.
eBooster: Acts as the primary actuator,
converting the driver’s brake input into hydraulic
pressure. It senses the pedal stroke and speed using sensors, then drives a
piston in the master cylinder via an electric motor to rapidly generate
hydraulic braking force. Compared to traditional vacuum boosters, the eBooster
offers faster response and software-tunable pedal feel, allowing for adaptable
driving styles.
ESC: Primarily responsible for vehicle
stability, integrating functions like: ABS (Anti-lock Braking System), TCS
(Traction Control System), VDC (Vehicle Dynamics Control). It coordinates the
distribution between hydraulic and electric motor braking, ensuring a balance
between energy recovery and stability. It also offers safety redundancy—if the eBooster fails, the ESC can use HBC (Hydraulic Brake
Compensation) to independently build pressure and take over brake assist to
meet regulatory emergency braking requirements.
Two-box Braking Mechanism and
Coordination
Hydraulic System Coordination:
The eBooster and ESC share a unified
hydraulic system (including brake fluid reservoir, master cylinder, and
pipelines). Under normal conditions, the eBooster drives the master cylinder
piston, and brake fluid flows through ESC valves to the wheel cylinders to
generate braking force. If the eBooster is inactive, the ESC can still control
brake fluid flow independently. The eBooster offers faster pressure build-up
and better NVH (noise, vibration, and harshness) performance, making it the
primary actuator. The ESC intervenes only during faults or special conditions.
Energy Recovery and Pedal Feel Consistency:
In new energy vehicles, the drive motor
provides electric regenerative braking. The ESC uses an accumulator to
temporarily store brake fluid from the master cylinder to prevent abrupt pedal
feel changes caused by overlapping hydraulic and electric braking. The eBooster’s PFC (Pedal Force Compensation) module dynamically adjusts braking
assist to maintain constant pedal feedback during transitions between electric
and hydraulic braking—ensuring a consistent driver
experience.
External ECU Interactions:
Braking commands from ADAS (Advanced
Driver-Assistance Systems) or automated parking systems are first sent to the
ESC, which processes and forwards them to the eBooster. This design reduces the
active pressure-building workload on the ESC, prolonging its service life.
The Two-box brake architecture is a key
transitional technology toward fully brake-by-wire systems. Its “dual-box separation, dual-mode collaboration” design balances safety, compatibility, and intelligence. It’s especially well-suited for today’s diverse
powertrain market. As electric vehicles demand higher energy recovery
efficiency and braking precision for autonomous driving, the Two-box
architecture will continue to evolve through integration with DCDC converters,
VCUs, and other systems for further performance optimization.
HOLS Automation has years of deep expertise in smart manufacturing and offers extensive experience in intelligent chassis automation solutions for the automotive industry. We provide smart production lines for brake-by-wire, steer-by-wire, suspension systems, and more. Inquiries are welcome.