402D: Air Antilock Brake Systems

Question 1

Will conventional braking continue if a portion of the ABS system fails?

Answer 1

Yes

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Question 2

What is the basic purpose of ABS?

Answer 2

Monitors wheel speeds and modulates brake application to:
- Maintain control of vehicle
- Reduce stopping distance
- Reduce tire flat spotting

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Question 3

How fast can ABS modulate brake application to each wheel?

Answer 3

Up to 100 times per second

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Question 4

Can an ABS system provide extra braking force?

Answer 4

No

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Question 5

When did ABS become mandatory on all on-highway heavy duty trucks and trailers equipped with air brakes?

Answer 5

March 1, 1998

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Question 6

To eliminate the need for extra components while still providing adequate braking, on what axle would the ABS wheel speed sensors be located in a tandem axle assembly with spring suspension?

Answer 6

Front axle

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Question 7

To eliminate the need for extra components while still providing adequate braking, on what axle would the ABS wheel speed sensors be located in a tandem axle assembly with air suspension?

Answer 7

Rear axle

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Question 8

What type of ABS system is the minimum requirement on a trailer?

Answer 8

2S/1M

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Question 9

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

Answer 9

6S/6M

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Question 10

What is the common ABS configuration on a tandem axle tractor?

Answer 10

4S/4M

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Question 11

What do channels refer to in an ABS system?

Answer 11

The number of modulators

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Question 12

What is the purpose of the tone ring in an ABS system?

Answer 12

Works with the wheel speed sensor to generate an AC signal corresponing to wheel speed.

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Question 13

How many teeth does a tone ring typically have?

Answer 13

80 to 120

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Question 14

What is a wheel speed sensor?

Answer 14

A permanent magnet wrapped in fine copper wire that generates the AC signal corresponding to the wheel speed

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Question 15

What allows the speed sensor to be held in place and adjusted?

Answer 15

Spring clip

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Question 16

What are the two components to an AC signal?

Answer 16

Voltage - Will decrease as gap between sensor and tone ring increases
Freequency - Measured in hertz. Will increase with increased wheel speed

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Question 17

How is the distance between the tone ring and speed sensor set?

Answer 17

Push 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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Question 18

Where in the air brake system is the air brake modulator valve located?

Answer 18

Drive Axles: Between the relay valve and air brake chamber

Steer Axle: Between the quick release valve and brake chamber

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Question 19

What are the three stages of an ABS modulator valve as it modulates air brake application pressure?

Answer 19

Exhaust
Hold
Reapply

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Question 20

During a normal brake application, what position are the ABS modulator valves in?

Answer 20

Supply Solenoid: De-energized
Exhaust Solenoid: De-energized

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Question 21

During the first stage of an ABS event, what position are the ABS modulator valves in?

Answer 21

Stage: Exhaust

Supply Solenoid: Energized
Exhaust Solenoid: Energized

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Question 22

During the second stage of an ABS event, what position are the ABS modulator valves in?

Answer 22

Stage: Holding

Supply Solenoid: Energized
Exhaust Solenoid: De-energized

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Question 23

During the final stage of an ABS event, what position are the ABS modulator valves in?

Answer 23

Stage: Reapply

Supply Solenoid: De-energized
Exhaust Solenoid: De-energized

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Question 24

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

Answer 24

March 1, 2001

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Question 25

Where is the ABS indicator/warning light located on trailers built after March 1, 1998?

Answer 25

Left rear corner, facing outward ## Footnote 402D

Question 26

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

Answer 26

4S/4M ## Footnote 402D

Question 27

As of March 1, 1998, the trailer antilock ECU receives its power through what pin in the trailer connector?

Answer 27

Auxillary/centre pin ## Footnote 402D

Question 28

What are two methods that an ATC system can use to reduce the amount of wheel spin on slippery roads?

Answer 28

At speeds less than 40km/h - Differential Braking - Torque Reduction At speeds greater than 40km/h - Torque Reduction only ## Footnote 402D

Question 29

Durring a wheel spin condition on a vehicle equiped with ATC and differential braking, how does the ECU control the transfer of torque from the spinning wheel to the stationary wheel?

Answer 29

- ATC valve sends air the service relay valve - ABS modulator valve blocks the air on the side with the stationary wheel - ABS modulator valve applies enough braking pressure to the spinning wheel to slow it down, which also transfers torque through the differential to the other wheel ## Footnote 402D

Question 30

Where in the air brake system is the ATC valve located?

Answer 30

Between the treadle valve and service brake relay valve ## Footnote 402D

Question 31

What are the three airline connections into an ATC valve?

Answer 31

- Treadle valve - Service relay valve - Primary air tank | And an electrical connection to the ECU ## Footnote 402D

Question 32

What is an advantage of the deep snow and mud option in a ATC system?

Answer 32

Allows the wheels to spin slightly faster to throw off mud and snow caught in the tire treads ## Footnote 402D

Question 33

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

Answer 33

The ATC will try to control the wheel spin and you wont be able to obtain a true torque and horsepower reading ## Footnote 402D

Question 34

Where is the RSC (Roll Stability Control) valve located?

Answer 34

In the secondary air system between the treadle valve and the tractor protection valve ## Footnote 402D

Question 35

What system helps provide protection to a tractor or tractor trailer combo from loss of stability and rollover?

Answer 35

Roll Stability Control (RSC) - Monitors wheel speed sensors and lateral acceleration ## Footnote 402D

Question 36

What responses can the RSC valve do to prevent a rollover?

Answer 36

. Reduce engine torque . Engage engine /driveline retarders . Apply brake pressure to the drive axle brakes . Modulate brake pressure to the trailer brakes ## Footnote 402D

Question 37

What sensors do ESC modules use to prevent a jackknife or spinout?

Answer 37

- Yaw sensor - Accelerometer (to mesaure lateral acceleration) ## Footnote 402D

Question 38

If the governor fails, is there another valve to limit air pressure on an air brake system?

Answer 38

Safety valve