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Braking System Operation

Braking System Operation. Roger Bortignon. Slideshow Contents. Part 1: base braking system slides 1-21 Part 2: anti-lock braking systems slides 22-31. Weight Distribution During Braking…. braking force is not 50% front & 50% rear front brakes can apply up to 80 % of the braking power

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Braking System Operation

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  1. Braking System Operation Roger Bortignon

  2. Slideshow Contents • Part 1: base braking system • slides 1-21 • Part 2: anti-lock braking systems • slides 22-31

  3. Weight Distribution During Braking… • braking force is not 50% front & 50% rear • front brakes can apply up to 80% of the braking power • this depends partly on whether vehicle is front or rear drive (weight distribution) • this is why front brakes may have to be replaced 4 or 5 times before the rear brakes need replacement

  4. Weight Distribution During Braking…

  5. Braking System Components

  6. Master Cylinder • converts pedal movement to hydraulic pressure

  7. Master Cylinder Action • applied position (pushing on brake pedal)…

  8. Master Cylinder Operation • brakes being applied • brake pedal released

  9. Caliper Designs • fixed caliper • pistons on both sides of the brake disc • caliper can have 2 or 4 pistons • there are some 8 piston versions for race applications

  10. Caliper Design • floating caliper • uses 1 or 2 pistons on one side of the caliper • caliper body slides (in reaction to the piston movement) • outer brake pad rubs on the outside of the disc

  11. Brake Pad Retraction • flexing of the caliper’s square cut o-ring causes piston to retract when the brake pedal is released • no return springs required

  12. Drum Brakes

  13. Self Energized, Non-Servo (Leading-Trailing) Drum Brakes • bottom of the brake shoes mount to a solid anchor • leading (front) brake shoe is self-energized • drum rotation increases braking force • front (leading) brake shoe is wedged tightly against the drum • brake shoes are equal length • front (leading) brake shoe may be thicker than the rear (trailing) • used on the rear of many front wheel drive vehicles

  14. Self Energized, “Dual-Servo” Drum Brakes • one shoe “serves” the other to increase application force • note how the bottom of the brake shoes are not mounted on a fixed anchor • the brake shoes can pivot or rotate with the drum • front (primary) shoe helps increase pressure on rear (secondary) shoe • this is referred to as servo action • brake shoes are different lengths (longer on back side {secondary shoe}) • drum rotation energizes both brake shoes • used on many rear wheel drive vehicles

  15. Hydraulic Line Connections • single piston master cylinder • used until 1967 • tandem split (fig. 11a) • used on rear drive vehicles • diagonal split (fig. 11b) • used on front drive vehicles Fig 11b Fig. 11a

  16. Brake Hydraulic Control Valves • metering valve: delays front brake application until rear brakes have overcome spring tension • used on disc/drum system only • used mainly on rear wheel drive vehicles

  17. Brake Hydraulic Control Valves • proportioning valve: limits hydraulic pressure to rear brakes under hard braking to prevent wheel lock-up • has no effect during light to moderate stops

  18. Proportioning Valve Operation • heavy braking: • pressure on large area of piston forces piston to left • this blocks pressure to rear brakes • piston will cycle back and forth only allowing a percentage of front brake pressure to the rear • lightto moderate braking: • master cylinder pressure acts on both sides of the green piston • pressure to front & rear brakes is equal

  19. Brake Hydraulic Control Valves Pressure Differential switch turns on a warning light if hydraulic pressure in one circuit is lost due to a leak...

  20. Parking Brakes with Rear Drums • mechanical cable actuates the brake shoes (on rear wheels)

  21. Parking Brakes on Rear Discs • 2 methods of applying the e-brake on vehicles that use rear disc brakes… 1) cable moves caliper piston out 2) cable pushes out mini brake shoes against the inside of the brake rotor

  22. Anti-lock Brake SystemsABS

  23. ABS • designed to prevent wheel lock-up to minimize stopping distance & help maintain steering control • by preventing wheel lock-up, tires will maintain traction with road surface • can also used on motorcycles and even trucks & buses with air brakes

  24. ABS Components

  25. How Many Channels? • a channel describes a hydraulic brake line that is capable of being controlled by the ABS module

  26. 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

  27. AC voltage ripple frequency will change with wheel speed changes

  28. Modulating Brake Fluid Pressure • Electronic Brake Control Modulator EBCM • EBCM-activated solenoids modulate brake fluid pressure • the solenoid valves can (while driver is stepping on pedal) either… • hold (maintain) pressure • dump (release) pressure • increase pressure • these solenoids can cycle the brakes 15 times/second Hold Pressure Dump Pressure Increase Pressure proportioning valve is no longer needed!

  29. ABS Modulator • may be attached to the master cylinder • integral ABS • may be mounted separate from the master cylinder • non-integral ABS

  30. schematic of brake lines and ABS components…

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