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HET4 > Air antilock brake systems > Flashcards

Air antilock brake systems Flashcards

1
Q

will conventional braking continue if a portion or the entire ABS system failed

A

yes they would operate normally

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2
Q

what is the basic purpose of ABS

A

to monitor individual wheel speeds , compare them and moderate braking application pressure to prevent a lock up

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3
Q

how fast can ABS modulate braking force to each wheel

A

up to 100 times per second

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4
Q

can the ABS system provide extra braking force

A

no . it will only attempt to prevent wheel lock up

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5
Q

when did all on-highway heavy duty trucks and trailers equipped with air brakes become mandatory to have ABS

A

march 1 1998

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6
Q

what type of system is the minimum requirement on a tandem axle trailer

A

2S/1M system ( two sensors one modulator )

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7
Q

what type of system would provide the maximum protection from flat spotting due to tire skidding on a three axle configuration

A

6S/6M system ( six sensors six modulators )

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8
Q

how would a 2S/1M system modulate air pressure to a tandem axle trailer

A

it would modulate all four wheels at the same time

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9
Q

what are (channels) when referring to ABS

A

the number of circuits that are being modulated ( 2S/1M = one channel or 6S/6M = six channels

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10
Q

what is the purpose of the tone ring

A

spins at wheel speed and works with a speed sensor to generate a electrical pulsed signal that is sent to the ECU

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11
Q

typically how many teeth will tone rings have

A

80 to 120

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12
Q

can tone rings be an integral part of a wheel hub assembly

A

yes

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13
Q

what is a speed sensor

A

a permanent magnet wrapped in fine copper wire

it is a voltage generating sensor

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14
Q

what allows the speed sensor to be held and adjusted in place

A

a spring clip

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15
Q

what are the two components that make up an Ac signal

A

. voltage , measured in amplitude

. frequency, measured in hertz

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16
Q

how is the distance between the tone ring and the speed sensor set

A

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

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17
Q

what is an air brake modulator valve

A

an electro pneumatic output device

18
Q

where is the air brake modulator vale located on the rear of the vehicle

A

between the relay valve and the airbrake chamber

19
Q

where is the air brake modulator valve located on the front of the vehicle

A

between the quick release ( ratio valve ) and the brake chamber

20
Q

how dose the air brake modulator valve work

A

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

21
Q

during normal braking application ( non - ABS operated ) what is happening to the solenoids

A

they are inactive or de-energized

22
Q

what closes the exhaust port during normal braking operation in the ABS modulator valve

A

supply air pressure flowing past the exhaust solenoid working with spring pressure to close the exhaust diaphragm

23
Q

what happens first when the ECU sees the wheel going into a lock

A

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

24
Q

what happens when the ABS valve is in a holding position

A

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

25
Q

on trucks motor coaches and commercial buses when did the ABS light on the dash become mandatory

A

march 1 2001

26
Q

what is the case when the ABS ight comes on but then goes off when vehicle speed reaches above 6km/h

A

self test has been completed and the system is ok

27
Q

what is the one condition that might INCREASE the stopping distance when ABS is used

A

off road because during a lock up loose dirt/rocks form a wedge under tier assisting in stopping

28
Q

what is the minimum ABS configuration a truck can have before it can be equipped with a traction control valve

A

4S/4M

29
Q

who with the ATC reduce the amount of wheel spin

A

braking a specific wheel or reducing the amount of torque delivered to the drive wheels

30
Q

where is the ATC valve located

A

between the treadle valve and the service brake relay

31
Q

where are the three air line connections into the ATC connected to

A

treadle valve . brake service relay port . primary air tank

32
Q

what is an advantage to the deep snow and mud option in a ATC system

A

allows the wheels to spin slightly faster to throw off mud and snow caught in the tire treads

33
Q

why is it important to disconnect the ATC system when testing the vehicle on a chassis dynamometer

A

because the ATC will try to control the wheel spin and you wont be able to obtain a true torque and horsepower reading

34
Q

what type of vehicle would be especially helpful to have a RSC system

A

a straight bodied truck with a high center of gravity

35
Q

where is the RSC valve located

A

in the secondary air system between the treadle valve and the tractor protection valve

36
Q

what responses would the RSC valve have to prevent a rollover

A

. reduce engine torque
. Engauge engine /driveline retarders
. Apply brake pressure to the drive axle brakes
. Modulate brake pressure to the trailer brakes

37
Q

what dose a ESC module use to prevent a jackknife or spinout

A

a yaw sensor and accelerometer - both located inside the module

38
Q

what would the yaw sensor measure

A

rotational forces in order to prevent a spinout or jackknife

39
Q

what is the accelerometer used fore in the ESC module

A

to detect lateral acceleration during a corner to prevent rollovers

40
Q

what is the steering angle sensor for

A

provides an input to tell the ABS ECU where the operator intends to steer

HET4 (43 decks)

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