Brake Control Unit (BCU) 

The BCU is a typical standalone Brake Control Unit for a two channel inboard/outboard hydraulic Brake-by-Wire System of a medium sized turboprop Part-25 aircraft.

BCU Functions

 Control Functions

• Normal Brake Control
• Autobrake
• De-spin
• Antiskid Functions
• • Touch Down protection
• • Locked wheel protection 
• • Skid control 
• Ground spoiler deployment 
  

Monitoring Functions 

• Brake temperature monitoring
• Built-in-Test
• Uncommanded brake monitoring
  

Top Level Architecture

The BCU consists of two completely independant and segregated channels controlling the inboard and outboard wheels respectively. The two channels are separated by a solid aluminum sheet to prevent propagation electrical faults.

Each channel provides two lanes, the COMmand lane and the MONitor lane. The COM lane acquires and validates the pilot commands (via pedals, autobrake selector, etc.), and controls the brakes via Brake Control Servo Valve. It performs autobrake, de-spin braking as well as antiskid functions. 
The MON lane is protecting against uncommanding braking at high speed.  (the only catastrophic failure condition needing dissimilar monitoring).

The COM Lane consist of a microcontroller implementing the higher level functions, an FPGA implementing the I/O functions, signal conditioning and power conversion. The MON lane consist of an FPGA, signal condioning and power conversion. The FPGA is implementing I/O as well as the uncommanded braking monitoring functions.

The FPGAs COM and MON lanes as well as all other circuits which can lead to erroneous behavior are dissimilar.

The top level COM / MON architecture for one channel is shown below:

Environmental Qualification

The BCU is built into a 3MCU ARINC600 Housing. All sides of the housing are manufactured milled aluminum sheet, optimized for low weight at sufficient stiffness.  

BCU is qualified according to RTCA / DO 160G.