Automotive Braking Systems

By –Tapan sen biswalReg.no- 0921216018

Overview

• Brakes convert kinetic energy into heat by creating friction

• System must have very high reliability

• Types of brakes:

- Disk

- Drum

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

• 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

Master Cylinder

• Provides a reservoir for brake fluid and contains the driving pistons in the hydraulic circuit

• 2 TypesFront - Rear split -One piston for front brakes and one for rear-If a leak occurs you could lose front brakesDiagonally split -One piston drives one front wheel and one rear wheel-Diagonal layout allows you to maintain directional control if a leak occurs

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

Regenerative brakes..

• Utilizes the energy wasted while applying brakes in form of heat.

• A motor driven wheel is used which changes its function to as a generator and charges the dc battery.

Regenerative braking 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.

Advantages• Drum brakes allow simple incorporation of a parking

brake.

• In hybrid vehicle applications, wear on braking systems is greatly reduced by energy recovering motor-generators.

• Disc brakes rely on pliability of caliper seals and slight run out to release pads, leading to drag and fuel mileage loss.

• Drum brake return springs give more positive action and, adjusted correctly, often have less drag when released.

Limitation• The regenerative braking effect drops off at lower

speeds; therefore the friction brake is still required in order to bring the vehicle to a complete halt. Physical locking of the rotor is also required to prevent vehicles from rolling down hills.

• The friction brake is a necessary back-up in the event of failure of the regenerative brake.

• Most road vehicles with regenerative braking only have power on some wheels (as in a two-wheel drive car) and regenerative braking power only applies to such wheels, so in order to provide controlled .

Conclusion

• The use of fuzzy logic controller gives a smooth braking system. Developing and testing a prototype model of fuzzy logic controller can further prove the accuracy of the system for braking in subway trains. For a future development of this project, the Fuzzy Logic Controller designed can be enhanced by applying more rules. By then, it can produce better response. The response should be better and can be applied to a real hardware model to observe the real response and yet can improve the system.

…..Any questions….????

Thank you…