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Automotive Braking Systems

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Trucks typically use 3 channel with only one sensor for the rear axle. Most modern cars use 4 channel system. Wheel speed sensors monitor each wheel speed ... – PowerPoint PPT presentation

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Title: Automotive Braking Systems


1
Automotive Braking Systems
By Shane Dunlevy
2
Overview
  • Brakes convert kinetic energy into heat by
    creating friction
  • System must have very high reliability
  • Types of brakes
  • - Disk
  • - Drum

3
System Basics
  • Hydraulic actuation allows multiplication of
    pedal force.
  • In this system, a 10lb force on the pedal
    produces 360 lbs of force at the friction surface.

4
Braking Dynamics
  • Dynamic weight transfer caused by braking shifts
    the weight balance towards the front of the car
  • Dynamic weight for the front and rear can be
    found using Newtons Law

5
Braking Dynamics
  • Because the maximum braking force is equal to the
    coefficient of friction times the normal force,
    the front wheels will have an increased capacity
    to provide braking force
  • Also, the system must be designed to distribute
    the application of force between front and rear

6
Disk Brakes
  • Caliper squeezes pads to create force on the
    surfaces of the rotor.
  • Used in most automotive applications.
  • Benefits
  • Simple design
  • Self adjusting
  • Rotor venting allows faster heat dissipation

7
2 Types of disk brake calipers
  • Floating caliper
  • Piston pushes pad against the inner rotor
    surface, reaction force causes the caliper to
    slide and contact the outer surface

8
2 Types of disk brake calipers
  • Fixed caliper has at least one piston on each
    side
  • Each piston drives its corresponding pad into
    contact with the rotor

9
Drum Brakes
  • Expanding shoes create force on the inner surface
    of the drum
  • Used on the rear of some trucks and SUVs
  • Self-energizing design requires less activation
    force
  • Require periodic adjustment

10
Tandem Master Cylinder
11
Master Cylinder
  • Provides a reservoir for brake fluid and contains
    the driving pistons in the hydraulic circuit
  • 2 Types
  • Front - Rear split
  • -One piston for front brakes and one for rear
  • -If a leak occurs you could lose front brakes
  • Diagonally split
  • -One piston drives one front wheel and one rear
    wheel
  • -Diagonal layout allows you to maintain
    directional control if a leak occurs

12
Diagonally Split System
13
Power Assistance
  • Power booster reduces pedal force required to
    stop vehicle
  • Engine vacuum is used to actuate a large
    diaphragm
  • When the pedal is depressed, vacuum is applied to
    only one side of the diaphragm and force is
    appled to the master cylinder push rod
  • Booster stores sufficient vacuum for several
    brake applications if the engine fails.

14
Power Booster in closed position
15
Anti-Lock Brakes
  • A locked (sliding) wheel offers less braking
    force than a decelerating rolling wheel
  • The locked wheel also produces little lateral
    force, preventing steering control
  • Anti-Lock systems (ABS) monitor wheel lock-up and
    modulate brake pressure to provide controlled
    braking under most circumstances

16
Anti-Lock Brakes
  • System can have 2, 3 or 4 channels
  • Trucks typically use 3 channel with only one
    sensor for the rear axle
  • Most modern cars use 4 channel system
  • Wheel speed sensors monitor each wheel speed
  • ABS controller and high-pressure pump increase or
    reduce pressure to wheels in order to maintain
    consistent wheel speeds

17
Typical 3 channel system
18
Valves and Switches
  • Pressure Differential Switch
  • -Senses a pressure differential between the two
    master cylinder stages and warns the driver that
    the system has a leak
  • Metering Valve
  • -Prevents the front brakes from engaging until
    the rear drums have enough pressure to overcome
    the shoe return springs (Front disk-Rear drum
    systems only)
  • Proportioning Valve
  • -Reduces the pressure to the rear wheels to
    balance the effect of weight transfer to the
    front wheels.
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