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 Newton’s 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 it’s 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 SUV’s • 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.