Braking system.pptx....Braking system.pptx

Braking system.pptx

1. Braking Systems Mr.Bidve M.A.

2. Brake The device used to stop any vehicle by applying frictional forces. One of most important control components of vehicle. They are required to stop vehicle within smallest possible distance. This is done by converting kinetic energy of vehicle into heat energy which is dissipated into atmosphere.

3. Functions of Brake It is used as emergency to avoid accident. It holds vehicle stationary on slope or steep road for parking. It control the vehicle to be retained when descending a hill. To retard or stop the vehicle within minimum possible distance, in consistent with safety and without wheel skidding.

4. Braking Requirements Brakes must be strong enough to stop vehicle with in a minimum distance in an emergency. Brakes must have good antifade characterstics i.e. their effectiveness should not decrease with prolonged application. This requirement demands cooling of brakes should be very efficient. The brake must operate with minimum effort of the driver. It should not cause wheel skidding. The brake must strong enough to sustain sudden large braking force.

5. Basic terms related to braking. 1.Brake Torque Brake torque  is the force applied at the brake wheel to stop the motion of the moving vehicle. It is twisting or torsional action caused by the disc or drum on the brake shoes during application of brake. 2.Brake Fade: Vehicle braking system  fade , or  brake fade , is the reduction in stopping power that can occur after repeated or sustained application of the brakes, especially in high load or high speed conditions. After prolong application of brake the coefficient of friction reduces which causes less braking effect.

6. 3.Stoppping distance: It depend upon 1.Tyre deflection. 2.Air resistance. 3.Inertia force. The distance required to stop the vehicle is proportional to the square of the speed at which the brakes are applied. It is inversely proportional to braking efficiency. It is defined as the distance between point of application of brake and to the point where vehicle comes to the rest. Stopping distance=V 2 /2a Meters. V-Velocity in M/Sec a- De acceleration in M/Sec

7. Stopping time Stopping time : It is the duration required between the brake application and when the vehicle comes to rest. It is inversely proportional to brake efficiency and proportional to the speed. Stopping Time= V/a Braking Efficiency: It is the ratio of Maximum retarding force applied at the wheel to the weight of the vehicle. When retarding force is equal to the weight of the vehicle and =1 then the retardation is 9.81 m/ S 2 and the braking efficiency is 100%.

8. Principle of Braking. The brake works on the principle of conversion of energy. It converts kinetic energy of wheels into heat energy by means of friction between two moving surfaces of brake drum. The brake torque applied at the wheels produces a retarding effort by the adhesion available between brake lining and brake drum. The heat generated at contact surfaces depends upon the intensity of force and coefficient of friction of two materials. F B=  B* W B W B –Normal force on the brake shoes.

9. Classification of brake The brakes of an automobile are classified according to as :- Purpose Location Construction Method of actuation Extra braking effort Application

10. Purpose:- From this point of view Brakes are classified as service or primary and parking or secondary brakes. Location:- From this point of view brakes are located at wheels(2 or 4) or at transmission. Construction:- From this point of brakes are drum brakes and disc brakes. Method of actuation:- This criterion gives following brake type : Mechanical Brakes Hydraulic Brakes Electric Brakes Vacuum Brakes Air Brakes By-wire Brakes

11. According to extra braking effort: 1) servo brake or power assisted brake 2) Power brakes or power operated brakes. According to application 1) Foot brake 2) Hand Brake

12. DRUM BRAKE or Internal expanding brake

13. https://youtu.be/ApuBEn2zct8

14. Working The drum encloses the complete brake mechanism and protect it from dust and moisture. The backing plate holds the all braking assembly. The backing plate is attached to the vehicle axle housing and act as base or frame for fastening the brake shoe and the operating cam mechanism with linkages. The brake shoe are hinged to back plate at one end by an anchor pin and other end rest on the cam or toggle. As the Brake pedal is pressed the cam turn by expanding brake shoes outward against the retractor spring force. The brake lining comes in contact with brake drum causes friction between them. This force of friction opposes the direction of rotation and reduce speed or stop the vehicle. When brake pedal is released the retractor spring pulls the brake shoe inward and brake are released. Drum brakes have more parts than disc brakes and are harder to service, but they are less expensive to manufacture .

15. Disc Brakes A disc brake consists of a cast iron disc bolted to wheel hub and stationary housing called caliper. Caliper having a piston and friction pad is connected to some stationary part of vehicle like axle. When brakes are applied, piston move friction pads into contact with disc, applying equal and opposite force on disc. On releasing brakes, the rubber sealing rings act as return springs and retract piston and friction pads away from disc .

16. Disc Brakes

17. Working of a disc brakes

18. Mechanical Brakes Mechanical brakes are assemblies consisting of mechanical elements for the slowing or stopping of vehicle. They use levers or linkages to transmit force from one point to another. There are several types of mechanical brakes. Band brakes, the simplest brake configuration, have a metal band lined with heat and wear resistant friction material. Drum brakes, which are commonly used on automobile rear wheels work when shoes press against a spinning surface called a drum. Disc breaks are constructed of brake pads, a caliper, and a rotor. During operation, the brake pads are squeezed against the rotor. Cone brakes are made with a cup and a cone, which is lined with heat and wear resistant material.  During actuation, the cone is pressed against the mating cup surface.

19. Band Brakes The principle is that a band is wrapped part round a rotating drum.  Tension can be applied to the band using a lever.    The restraining torque results from the difference in tension between the two ends of the belt.

20. Hydraullic Brakes The hydraulic brake is an arrangement of  braking  mechanism which uses  brake fluid specialy ehtylene glycol to transfer pressure from the controlling unit to the actual brake mechanism of the vehicle. Parts of hydaullic brakes:- Brake Pedal Push rod Master cylinder assembly Brake calliper assembly

21. Layout of Hyd. braking

22. Cont….

23. Hydraulic disc brake

24. Hydraulic drum brake

25. System Operation as the brake pedal is pressed, a pushrod exerts force on the piston(s) in the master cylinder.  This forces fluid through the hydraulic lines toward calipers. The brake caliper piston(s) then apply force to the brake pads. This causes them to be pushed against the spinning rotor, and the friction between the pads and the rotor causes a braking  torque  to be generated, slowing the vehicle.

26. In a hydraulic brake system, when the brake pedal is pressed, a pushrod exerts force on the piston(s) in the master cylinder, causing fluid from the brake fluid reservoir to flow into a pressure chamber through a compensating port. This results in an increase in the pressure of the entire hydraulic system, forcing fluid through the hydraulic lines toward one or more calipers where it acts upon one or more caliper pistons sealed by one or more seated O-rings (which prevent leakage of the fluid). Alternatively, in a  drum brake , the fluid enters a  wheel cylinder  and presses one or two  brake shoes  against the inside of the spinning drum. The brake shoes use a similar heat-tolerant friction material to the pads used in disc brakes. Subsequent release of the brake pedal/lever allows the spring(s) in the master cylinder assembly to return the master piston(s) back into position. This action first relieves the hydraulic pressure on the caliper, then applies suction to the brake piston in the caliper assembly, moving it back into its housing and allowing the brake pads to release the rotor.

27. Master Cylinder

28. There are two main chambers i.e fluid reservoir and compression chamber in which piston operates .The fluid in the reservoir compensates for any change in the fluid volume in the pipelines due to temperature variation and due to leakage. Towards brake line side of the compressor ,there is fcv with rubber cup inside .it serves to retain the residual pressure in the brake line even when the brakes are released. There are number of holes in the piston heads on the primary high pressure side. Two holes connect at the fluid reservoir to the compression chamber .the smaller one out of these is abut 0.7 mm dia and is called bypass or compensation port.

29. The second hole is called intake port. Besides there is vane in the cap ,to keep the brake fluid at atmospheric pressure . The push rod is operated with foot brake pedal through linkage. As the pedal is pressed, push rod moves to the left against the force of spring, till it cover bypass port. Further movement of the push rod causes building up of pressure in the compression chamber finally when sufficient pressure has built up, inner rubber cup of fluid check valve is deflected, forcing the fluid under pressure in the lines. This fluid enters wheel cylinder or the caliper and moves the piston thereby applying the brakes. When the brake pedal is release ,the spring pressure the master cylinder moves the piston to the right extreme position. The same force of spring keeps the fluid check valve pressed on its seat for sometime and thereby delays return of fluid from the lines into the compression chamber again.

30. Power Brakes These are the brakes in which power of engine or battery is used to enhance the braking effort. These are of four types:- Vaccum Brakes, Air Brakes, Hydraulic Booster Brake and Electro-Hydraulic Booster brake. Vaccum Brakes:- Vacuum brake system is controlled through a brake pipe connecting a brake valve in the driver's cab with braking equipment on every vehicle.  The operation of the brake equipment on each vehicle depends on the condition of a vacuum created in the pipe by an ejector or exhauster.

31. 2. Air Brakes:- The operatiom of air brakes is similar to hydraulic brake except that compressed air is used to apply brakes instead of hydraulic pressure. Air brake are commonly used on heavy vehicles like trucks, buses etc

32. Air brakes layout

33. Working The compressor takes air from the atmosphere through the filter and the compressed air is sent to the reservoir through the unloader valve, which gets lifted at a predetermined pressure and relieves the compressor of load. From the reservoir air goes to various accessories and also to the brake chambers also called the diaphragm units at each wheel ,through the brake valve. The control of brake valve is with the driver who can control the intensity of braking according to the requirements.

34. 3. Antilock Brake System (ABS):- Due to excessive braking brakes are locked which causes skidding. Skidding is avoided by releasing braking pressure just before wheels are lock up and then reapplying same. This process is calles pressure modulation. A modern ABS consists of an electronic control unit (ECU)., one sensor on each wheel,an electrically driven hydraullic pump and pressure accumlator . Accumlator is used to store hydraulic fluid to maintain high pressure in braking system. It is charged with nitrogrn gas. ECU monitors and controls the antilock function when required.

35. Thank You