Ready for Review ► Electronic brake control systems integrate computer controls to prevent wheel lock-up, shorten panic stop distances, help drivers maintain steering control, and improve vehicle stability.
► Basic anti-lock brake systems control hydraulic pressure hold and release via solenoid valves, but cannot function independently of the driver’s applied brake pressure.
► Traction control systems minimize wheel slip by automatically applying brake pressure to a slipping wheel’s brake unit and reducing engine output.
► Electronic stability control systems use steering wheel position sensors, yaw sensors, and wheel speed sensors to independently monitor vehicle stability and apply brakes as necessary.
► Primary components of an anti-lock braking system are: ABS master cylinder, electronic brake control module/electronic control unit, hydraulic control unit/modulator, power booster, wheel speed sensor, and brake switch.
► Braking force and wheel lock-up are affected by friction of road surface and type, condition, and loading of each tire.
► Maximum traction occurs with 10–20% tire slip.
► Wheel speed sensors signal the EBCM, which sends current to the solenoid valve, which then holds or releases hydraulic braking pressure.
► ABS master cylinders are integral (mainly in older vehicles) or nonintegral with the HCU.
► Solenoid valves provide three operating conditions: apply, hold, and release.
► The hydraulic control unit executes the commands of the ABS control module.
► Hydraulic control units differ by number of channels (one, two, three, or four), number of solenoid valves (single or dual), and type of accumulator (low or high pressure).
► Wheel speed sensors send electric signals to the EBCM to determine speed and rate of deceleration for each wheel.