04-04-2011, 03:41 PM
presented By
Shane Dunlevy
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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.
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
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
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
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
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
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
• Tandem Master Cylinder
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
• Diagonally Split System
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.
• Power Booster in closed position
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
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
• Typical 3 channel system
• 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.
