ANTILOCK BRAKINH SYSTEM, LE THANH PHUC

ANTILOCK BRAKING SYSTEM Le Thanh Phuc Faculty of Automotive Engineering University of Technical Education Ho Chi Minh City Email: phuclt@hcmute.edu.vn Introduction • ABS is a safety-related feature that assists the driver in deceleration of the vehicle in poor or marginal braking conditions (e.g wet or icy roads) • In ABS-equipped cars, the wheel is prevented from locking by a mechanism that automatically regulates the force applied to the wheels by the brakes to an optimum for any given low-friction condition Introduction ABS system diagram Fundamental ABS system Wheel Speed Sensor A wheel speed sensor is mounted at each wheel and sends a wheel rotation signal to the ABS ECU Deceleration Sensor The deceleration sensor is used on some systems to provide input to the ABS ECU about the vehicle's rate of deceleration to improve braking performance Actuator • The actuator controls hydraulic brake pressure to each disc brake caliper or wheel cylinder based on input from the system sensors, thereby controlling wheel speed Pressure Holding Valve (2-position valve) The pressure holding valve controls (opens and closes) the circuit between the brake master cylinder and the wheel cylinder The valve is spring loaded to the open position (normally open) Pressure Reduction Valve (2-position valve) The pressure reduction valve controls (opens and closes) the circuit between the wheel cylinder and the actuator reservoir The valve is spring loaded in the closed position (normally closed) 10 Normal Braking Mode (2-position valve) 11 Pressure Holding Mode (2-position valve) 12 Pressure Reduction Mode (2-position valve) 13 Pressure Increase Mode (2-position valve) 14 15 16 17 18 ABS wiring diagram The ECU judges the slip condition between the wheels and the road surface by monitoring the change in the wheel's rotational speed during braking The ECU controls the ABS actuator to deliver the optimum hydraulic pressure to the brake cylinder to precisely control the speed of the wheels, maintaining maximum brake force with a 10 to 30% slip ratio 19 Wheel speed control The ECU continuously receives wheel speed signals from the speed sensors and deceleration sensor By calculating the speed and deceleration of each wheel, the ECU estimates the vehicle speed 20 21 Slip ratio • The car is traveling at a speed U and the wheels are rotating at an angular speed ωw where and where RPMw is the RPM of the wheel in revolutions per minute When the wheel is rolling (no applied brakes) where rw is the tire effective radius 22 [...]... maximum brake force with a 10 to 30% slip ratio 19 Wheel speed control The ECU continuously receives wheel speed signals from the speed sensors and deceleration sensor By calculating the speed and deceleration of each wheel, the ECU estimates the vehicle speed 20 21 Slip ratio • The car is traveling at a speed U and the wheels are rotating at an angular speed ωw where and where RPMw is the RPM of the