Brakes

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Brakes

  1. 1. Automotive Braking Systems
  2. 2. Overview <ul><li>Brakes convert kinetic energy into heat by creating friction </li></ul><ul><li>System must have very high reliability </li></ul><ul><li>Types of brakes: </li></ul><ul><li>- Disk </li></ul><ul><li>- Drum </li></ul>
  3. 3. System Basics <ul><li>Hydraulic actuation allows multiplication of pedal force. </li></ul><ul><li>In this system, a 10lb force on the pedal produces 360 lbs of force at the friction surface. </li></ul>
  4. 4. Braking Dynamics <ul><li>Dynamic weight transfer caused by braking shifts the weight balance towards the front of the car </li></ul><ul><li>Dynamic weight for the front and rear can be found using Newton’s Law </li></ul>
  5. 5. Braking Dynamics <ul><li>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 </li></ul><ul><li>Also, the system must be designed to distribute the application of force between front and rear </li></ul>
  6. 6. Disk Brakes <ul><li>Caliper squeezes pads to create force on the surfaces of the rotor. </li></ul><ul><li>Used in most automotive applications. </li></ul><ul><li>Benefits: </li></ul><ul><ul><li>Simple design </li></ul></ul><ul><ul><li>Self adjusting </li></ul></ul><ul><ul><li>Rotor venting allows faster heat dissipation </li></ul></ul>
  7. 7. 2 Types of disk brake calipers <ul><li>Floating caliper </li></ul><ul><ul><li>Piston pushes pad against the inner rotor surface, reaction force causes the caliper to slide and contact the outer surface </li></ul></ul>
  8. 8. 2 Types of disk brake calipers <ul><li>Fixed caliper has at least one piston on each side </li></ul><ul><li>Each piston drives it’s corresponding pad into contact with the rotor </li></ul>
  9. 9. Drum Brakes <ul><li>Expanding shoes create force on the inner surface of the drum </li></ul><ul><li>Used on the rear of some trucks and SUV’s </li></ul><ul><li>Self-energizing design requires less activation force </li></ul><ul><li>Require periodic adjustment </li></ul>
  10. 10. Tandem Master Cylinder
  11. 11. Master Cylinder <ul><li>Provides a reservoir for brake fluid and contains the driving pistons in the hydraulic circuit </li></ul><ul><li>2 Types </li></ul><ul><li>Front - Rear split </li></ul><ul><li>-One piston for front brakes and one for rear </li></ul><ul><li>-If a leak occurs you could lose front brakes </li></ul><ul><li>Diagonally split </li></ul><ul><li>-One piston drives one front wheel and one rear wheel </li></ul><ul><li>-Diagonal layout allows you to maintain directional control if a leak occurs </li></ul>
  12. 12. Diagonally Split System
  13. 13. Power Assistance <ul><li>Power booster reduces pedal force required to stop vehicle </li></ul><ul><li>Engine vacuum is used to actuate a large diaphragm </li></ul><ul><li>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 </li></ul><ul><li>Booster stores sufficient vacuum for several brake applications if the engine fails. </li></ul>
  14. 14. Power Booster in closed position
  15. 15. Anti-Lock Brakes <ul><li>A locked (sliding) wheel offers less braking force than a decelerating rolling wheel </li></ul><ul><li>The locked wheel also produces little lateral force, preventing steering control </li></ul><ul><li>Anti-Lock systems (ABS) monitor wheel lock-up and modulate brake pressure to provide controlled braking under most circumstances </li></ul>
  16. 16. Anti-Lock Brakes <ul><li>System can have 2, 3 or 4 channels </li></ul><ul><li>Trucks typically use 3 channel with only one sensor for the rear axle </li></ul><ul><li>Most modern cars use 4 channel system </li></ul><ul><li>Wheel speed sensors monitor each wheel speed </li></ul><ul><li>ABS controller and high-pressure pump increase or reduce pressure to wheels in order to maintain consistent wheel speeds </li></ul>
  17. 17. Typical 3 channel system
  18. 18. Valves and Switches <ul><li>Pressure Differential Switch </li></ul><ul><ul><li>-Senses a pressure differential between the two master cylinder stages and warns the driver that the system has a leak </li></ul></ul><ul><ul><li>Metering Valve </li></ul></ul><ul><ul><li>-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) </li></ul></ul><ul><ul><li>Proportioning Valve </li></ul></ul><ul><ul><li>-Reduces the pressure to the rear wheels to balance the effect of weight transfer to the front wheels. </li></ul></ul>

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