Transcript Anti-lock Brake Systems ABS

Anti-lock Brake Systems
ABS
R. Bortignon
1
ABS
• designed to control wheel lock-up to minimize stopping
distance & help maintain steering control
• is also used on vehicles with air brakes
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ABS Components
3
How Many Channels?
• a channel describes a brake hydraulic line that is capable
of being controlled by the ABS
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Wheel Speed Sensor
• wheel speed sensor is a magnetic impulse sensor
 works like a crankshaft position sensor
• creates an AC voltage signal as the tone ring rotates with
the wheel
• the AC voltage signal frequency changes as the wheel
speed changes
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Modulating Brake Fluid Pressure
• EBCM activated solenoids modulate brake fluid pressure
• these solenoid valves can either…
 hold (maintain) pressure
 dump (release) pressure
 increase pressure
 these solenoids can cycle the brakes 15 times/second
Hold Pressure
Dump Pressure
Increase Pressure
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Electronic Brake Control Module (EBCM)
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ABS “Electro-Hydraulic” Modulator
• may be attached to the master cylinder
 integral ABS
• may be mounted separate from the master cylinder
 non-integral ABS
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Servicing Precautions
• Bleeding
 may be done exactly the same as a non-ABS equipped vehicle
 or may have specific bleeding procedures
• when disconnecting brake lines, accumulator pressure may have
to be relieved – can be up to 2800 PSI!
• read manufacturer's instructions carefully before beginning
repairs!
• ABS problem: always begin with a thorough inspection of the base
brake system (non-ABS portion) first
• brake warning light indicates a problem in the base braking
system – not the ABS
• ABS warning lamp indicates a problem within the ABS
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Warning Lights
• both brake warning lights should come on when the
ignition is turned on
 this confirms that the warning circuit is operational
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Service Tips
• check wheel speed sensors for debris
build-up
• check tone rings for damage/debris
• check sensor wiring & connectors
• mismatched tire sizes confuses EBCM
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Service Tips
• do NOT push caliper pistons in without loosening bleeder
screw
 this prevents dirt from being pushed out of the caliper
& into the modulator
• regular brake fluid flushes (every 2 years) minimize
modulator & solenoid problems & extends their life span
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