Antilock Braking System Dr. Khisbullah Hudha
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Transcript of Antilock Braking System Dr. Khisbullah Hudha
Antilock Braking System Dr. Khisbullah Hudha
Chapter 3 Antilock Braking System Dr. Khisbullah Hudha WHEN THE
WHEEL IS SAID TO BE LOCKED WHILE BRAKING?
Wheel locking is occurred when the wheel has no rotational speed,
but still displace either longitudinally or laterally. WHY DOES THE
BRAKE LOCK WHILE BRAKING? Ideal Brake Torque Ideal brake torque
should be able to maintain s=0.2 during braking (deceleration)
Ideal brake torque should be able to maintain Vw as close as
possible to Vv PROBLEMS WITH WHEEL-LOCK IN BRAKING
Purely Skidding Occurred in a condition where both brake torques
and road roughness are distributed uniformly in all four wheels.
Combination of Skidding and unwanted yaw motion Occurred in a
condition where either brake torques or road roughness are not
distributed uniformly in all four wheels. Skidding and unwanted yaw
may cause the driver lose control of the vehicle and may lead to a
road accident. ANTILOCK BRAKING SYSTEM
The ABS is a four-wheel system that prevents wheel lock-up by
automatically modulating the brake pressure during an emergency
stop. By preventing the wheels from locking, it enables the driver
to maintain steering control and to stop in the shortest possible
distance under most conditions. During normal braking, the ABS and
non-ABS brake pedal feel will be the same. During ABS operation, a
pulsation can be felt in the brake pedal, accompanied by a fall and
then rise in brake pedal height and a clicking sound. STRUCTURE OF
ABS MAIN COMPONENTS OF ABS There are four main components to an ABS
system: Speed Sensors The anti-lock braking system needs some way
of knowing when a wheel is about to lock up. The speed sensors,
which are located at each wheel, or in some cases in the
differential, provide this information. Valves There is a valve in
the brake line of each brake controlled by the ABS. On some
systems, the valve has three positions: - In position one, the
valve is open; pressure from the master cylinder is passed right
through to the brake. - In position two, the valve blocks the line,
isolating that brake from the master cylinder. This prevents the
pressure from rising further should the driver push the brake pedal
harder. - In position three, the valve releases some of the
pressure from the brake. Pump Since the valve is able to release
pressure from the brakes, there has to be some way to put that
pressure back. That is what the pump does; when a valve reduces the
pressure in a line, the pump is there to get the pressure back up.
Controller The controller is a computer in the car. It watches the
speed sensors and controls the valves. ABS Hardware Vehicle speed
sensor Pump & valve modulator
Wheel speed sensor DAQ & Controller MODELING, SIMULATION AND
CONTROL OF ANTILOCK BRAKING SYSTEM Equations of Motion Longitudinal
slip
Tt = Tire torque; Tb = brake torque; Iw = wheel inertia & w =
wheel angular acceleration Ft = Long force acting on tire = coef.
of friction Coef. Of friction as the function of long slip av=
vehicle long speed Hydraulic Brake Modeling Hydraulic Brake Model
Control Structure of ABS