402D: Air Antilock Brake Systems Flashcards
Will conventional braking continue if a portion of the ABS system fails?
Yes
402D
What is the basic purpose of ABS?
Monitors wheel speeds and modulates brake application to:
- Maintain control of vehicle
- Reduce stopping distance
- Reduce tire flat spotting
402D
How fast can ABS modulate brake application to each wheel?
Up to 100 times per second
402D
Can an ABS system provide extra braking force?
No
402D
When did ABS become mandatory on all on-highway heavy duty trucks and trailers equipped with air brakes?
March 1, 1998
402D
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?
Front axle
402D
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?
Rear axle
402D
What type of ABS system is the minimum requirement on a trailer?
2S/1M
402D
What type of ABS system would provide the maximum protection from flat spotting due to tire skidding on a three axle configuration?
6S/6M
402D
What is the common ABS configuration on a tandem axle tractor?
4S/4M
402D
What do channels refer to in an ABS system?
The number of modulators
402D
What is the purpose of the tone ring in an ABS system?
Works with the wheel speed sensor to generate an AC signal corresponing to wheel speed.
402D
How many teeth does a tone ring typically have?
80 to 120
402D
What is a wheel speed sensor?
A permanent magnet wrapped in fine copper wire that generates the AC signal corresponding to the wheel speed
402D
What allows the speed sensor to be held in place and adjusted?
Spring clip
402D
What are the two components to an AC signal?
Voltage - Will decrease as gap between sensor and tone ring increases
Freequency - Measured in hertz. Will increase with increased wheel speed
402D
How is the distance between the tone ring and speed sensor set?
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.
402D
Where in the air brake system is the air brake modulator valve located?
Drive Axles: Between the relay valve and air brake chamber
Steer Axle: Between the quick release valve and brake chamber
402D
What are the three stages of an ABS modulator valve as it modulates air brake application pressure?
Exhaust
Hold
Reapply
402D
During a normal brake application, what position are the ABS modulator valves in?
Supply Solenoid: De-energized
Exhaust Solenoid: De-energized
402D
During the first stage of an ABS event, what position are the ABS modulator valves in?
Stage: Exhaust
Supply Solenoid: Energized
Exhaust Solenoid: Energized
402D
During the second stage of an ABS event, what position are the ABS modulator valves in?
Stage: Holding
Supply Solenoid: Energized
Exhaust Solenoid: De-energized
402D
During the final stage of an ABS event, what position are the ABS modulator valves in?
Stage: Reapply
Supply Solenoid: De-energized
Exhaust Solenoid: De-energized
402D
On trucks, motor coaches, and commercial buses, when did the ABS light on the dash become mandatory?
March 1, 2001
402D
Where is the ABS indicator/warning light located on trailers built after March 1, 1998?
Left rear corner, facing outward
402D
What is the minimum ABS configuration a truck must have before it can be equipped with a traction control valve?
4S/4M
402D
As of March 1, 1998, the trailer antilock ECU receives its power through what pin in the trailer connector?
Auxillary/centre pin
402D
What are two methods that an ATC system can use to reduce the amount of wheel spin on slippery roads?
At speeds less than 40km/h
- Differential Braking
- Torque Reduction
At speeds greater than 40km/h
- Torque Reduction only
402D
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?
- 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
402D
Where in the air brake system is the ATC valve located?
Between the treadle valve and service brake relay valve
402D
What are the three airline connections into an ATC valve?
- Treadle valve
- Service relay valve
- Primary air tank
And an electrical connection to the ECU
402D
What is an advantage of 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
402D
Why is it important to disconnect the ATC system when testing a vehicle on a chassis dynamometer?
The ATC will try to control the wheel spin and you wont be able to obtain a true torque and horsepower reading
402D
Where is the RSC (Roll Stability Control) valve located?
In the secondary air system between the treadle valve and the tractor protection valve
402D
What system helps provide protection to a tractor or tractor trailer combo from loss of stability and rollover?
Roll Stability Control (RSC)
- Monitors wheel speed sensors and lateral acceleration
402D
What responses can the RSC valve do to prevent a rollover?
. Reduce engine torque
. Engage engine /driveline retarders
. Apply brake pressure to the drive axle brakes
. Modulate brake pressure to the trailer brakes
402D
What sensors do ESC modules use to prevent a jackknife or spinout?
- Yaw sensor
- Accelerometer (to mesaure lateral acceleration)
402D
If the governor fails, is there another valve to limit air pressure on an air brake system?
Safety valve
