Air antilock brake systems Flashcards
will conventional braking continue if a portion or the entire ABS system failed
yes they would operate normally
what is the basic purpose of ABS
to monitor individual wheel speeds , compare them and moderate braking application pressure to prevent a lock up
how fast can ABS modulate braking force to each wheel
up to 100 times per second
can the ABS system provide extra braking force
no . it will only attempt to prevent wheel lock up
when did all on-highway heavy duty trucks and trailers equipped with air brakes become mandatory to have ABS
march 1 1998
what type of system is the minimum requirement on a tandem axle trailer
2S/1M system ( two sensors one modulator )
what type of system would provide the maximum protection from flat spotting due to tire skidding on a three axle configuration
6S/6M system ( six sensors six modulators )
how would a 2S/1M system modulate air pressure to a tandem axle trailer
it would modulate all four wheels at the same time
what are (channels) when referring to ABS
the number of circuits that are being modulated ( 2S/1M = one channel or 6S/6M = six channels
what is the purpose of the tone ring
spins at wheel speed and works with a speed sensor to generate a electrical pulsed signal that is sent to the ECU
typically how many teeth will tone rings have
80 to 120
can tone rings be an integral part of a wheel hub assembly
yes
what is a speed sensor
a permanent magnet wrapped in fine copper wire
it is a voltage generating sensor
what allows the speed sensor to be held and adjusted in place
a spring clip
what are the two components that make up an Ac signal
. voltage , measured in amplitude
. frequency, measured in hertz
how is the distance between the tone ring and the speed sensor set
by pushing the speed sensor until the face of the sensor contacts the tone ring . once the wheel rotates the sensor will slide back slightly and have the proper running clearance
what is an air brake modulator valve
an electro pneumatic output device
where is the air brake modulator vale located on the rear of the vehicle
between the relay valve and the airbrake chamber
where is the air brake modulator valve located on the front of the vehicle
between the quick release ( ratio valve ) and the brake chamber
how dose the air brake modulator valve work
it is a passive open valve that is controlled by the ECU that can exhaust . hold . or reapply air pressure to the brake chamber it is controlling
during normal braking application ( non - ABS operated ) what is happening to the solenoids
they are inactive or de-energized
what closes the exhaust port during normal braking operation in the ABS modulator valve
supply air pressure flowing past the exhaust solenoid working with spring pressure to close the exhaust diaphragm
what happens first when the ECU sees the wheel going into a lock
both solenoids are energized . this will allow air to enter the supply diaphragm control camber to close the supply diaphragm . preventing any more air to enter the chamber . then air pressure from the brake chamber flows back into the delivery port and unseats the exhaust diaphragm .releasing air pressure from the chamber
what happens when the ABS valve is in a holding position
when enough air has been released through the exhaust port to stop a wheel lockup . the exhaust solenoid is deenergized so supply air can close the exhaust diaphragm and stop air from leaving the chamber . the supply solenoid stays energized keeping the supply diaphragm closed not allowing more air pressure to enter the brake chamber
on trucks motor coaches and commercial buses when did the ABS light on the dash become mandatory
march 1 2001
what is the case when the ABS ight comes on but then goes off when vehicle speed reaches above 6km/h
self test has been completed and the system is ok
what is the one condition that might INCREASE the stopping distance when ABS is used
off road because during a lock up loose dirt/rocks form a wedge under tier assisting in stopping
what is the minimum ABS configuration a truck can have before it can be equipped with a traction control valve
4S/4M
who with the ATC reduce the amount of wheel spin
braking a specific wheel or reducing the amount of torque delivered to the drive wheels
where is the ATC valve located
between the treadle valve and the service brake relay
where are the three air line connections into the ATC connected to
treadle valve . brake service relay port . primary air tank
what is an advantage to the deep snow and mud option in a ATC system
allows the wheels to spin slightly faster to throw off mud and snow caught in the tire treads
why is it important to disconnect the ATC system when testing the vehicle on a chassis dynamometer
because the ATC will try to control the wheel spin and you wont be able to obtain a true torque and horsepower reading
what type of vehicle would be especially helpful to have a RSC system
a straight bodied truck with a high center of gravity
where is the RSC valve located
in the secondary air system between the treadle valve and the tractor protection valve
what responses would the RSC valve have to prevent a rollover
. reduce engine torque
. Engauge engine /driveline retarders
. Apply brake pressure to the drive axle brakes
. Modulate brake pressure to the trailer brakes
what dose a ESC module use to prevent a jackknife or spinout
a yaw sensor and accelerometer - both located inside the module
what would the yaw sensor measure
rotational forces in order to prevent a spinout or jackknife
what is the accelerometer used fore in the ESC module
to detect lateral acceleration during a corner to prevent rollovers
what is the steering angle sensor for
provides an input to tell the ABS ECU where the operator intends to steer
