Air and Hydraulic Antilock Brake Systems Flashcards
How are all current anti-lock braked systems (ABS) managed?
All current anti-lock brake systems are electronically managed.
A typical ABS system adapts a standard air or hydraulic system for electronic management.
In the event of an electrical or electronic malfunction, what are all current systems designed to do?
All current systems are designed to default to non-managed operation in the even of an electrical or electronic malfunction.
What is now mandatory for new trucks?
New trucks are equipped with ABS brakes as these are now mandatory on FMVSS 121 compliant vehicles.
What does and ABS system consist of?
ABS system consists of:
1. a means of monitoring the speed of each wheel
2. an electronic control unit (ECU) or ABS module to manage the system
3 and a modulator assembly to manage the outcomes of the ECU logic processing by modulating the service application braking pressure to each wheel.
What are ABS brakes especially effective at?
ABS brakes are especially effective at managing split coefficient braking conditions.
Split coefficient braking occurs when road surface conditions (icy, wet, gravel, dry, etc.) differ from one wheel to another.
Where is the ABS warning light mounted?
The ABS warning light is mounted in the instrument panel.
The light indicates if the ABS is normal or if a defect is present.
What should the ABS warning light do when the ignition is turned on?
When the ignition switch is turned on the ABS warning light should be illuminated for a few seconds and then go off.
Some will come on again and stay on until the vehicle speed reaches 6 mph (10 km/h).
The ABS ;warning light goes off and remains off as long as the engine is running if the ABS operation is normal.
This light remains off even even when the vehicle speed reaches 6 mph.
What happens if the ABS warning light is on after the vehicle speed reaches 6 mph (10 km/h)?
If the ABS warning light is on after the vehicle speed reaches 6 mph (10 km/h), an electrical defect is present in the ABS.
The operation of the ABS warning light may vary depending on the truck manufacturer. Always consult the truck manufacturer’s service manual.
When the vehicle is first started, what is happening with the ABS system?
It is normal for the hydraulic brake system to make a noise when the vehicle is first started. This is the system doing a self check.
What channel ABS system is commonly used today?
Although ABS systems are available in two, four, or six-channel designs, the four channel system is commonly used today in tandem drive axle trucks.
Describe a 4 channel ABS system.
The 4 channel system has a sensor on each of the steer-axle wheels, and on two of the four rear wheel, both on the same axle.
The sensors input wheel speed data to the ABS module.
The ABS outputs an electrical signal to the four modulator valves.
Two modulator valves control each heel on the steer axle.
The other two control service braking on each side of the tandem drive axles; one for the right side service chambers, the other for the left side.
What does the ABS wheel sensors use to send a small AC electrical signal to the ABS module?
The ABS wheel sensors use a reluctor wheel (100 serrations on a disc or the brake drum) and pickup to send a small AC electrical signal to the ABS module.
the frequency of the AC voltage increases proportionally with wheel speed.
In this way, a lockup condition can be sensed by the ABS module.
What controls the system modulator valves?
The ABS module controls the system modulator valves.
What does the modulator valves control?
The modulator valves control the service application pressures to each of the front wheels and to each side of the tandem drive assembly.
What happens when a lockup condition is sensed by the ABS module?
When a lockup condition is sensed by the ABS module, the air to the service chamber(s) controlled by the modulator can momentarily relieved or pulsed.
