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.