BREAK SYSTEM

BREAK SYSTEM

                                                          

1. INTRODUCTION

            In running and control of vehicle the breaking system plays very important & essential role.  In order to bring vehicle to rest of slow down in a shortest possible time or slow down running speed in emergencies.  The rate of slowing down is governed by speed of conversion of energy form to another form.  Kinetic energy of vehicle converted into heat or heat energy given to air through breaking system.

            For realizing full potential of engine & road holding is safety.  It is necessary to bring the car or vehicle rapidly to rest from any speed by some mean.  The means of slowing down to rest a moving vehicle in shortest possible distance is called break.

            In early day vehicle with single shoe breaks were used.  They based on generated due to friction between wheel & shoe is proportional to force pushing shoe into contact. The greater force applied to shoe quicker is stop of vehicle. Now a days mechanically or powered breaks used on vehicle.        

2. PRINCIPLE OF BREAKING: -

           

Breaks applied during accelerating vehicle.  In accelerating heat energy of fuel is converted into power of kinetic energy of vehicle. In breaking this kinetic energy converted into heat energy by means of friction developed between two mating surfaces of break drum similar to tractive effort produced at peripheries of driving wheel by torque of engine. During the motor vehicle, the braking torque introduced at brake drum due to application braking produced a retarding effort or negative tractive effort. Which is by adhesion available between the brake lining & brake drum similar to adhesion between wheel and Retarding force created between brake lining & brake depend on pressure exerted on shoe by retarding mechanism & co-efficient of friction for two materials.

3. FUNCTION OF BRAKES: - 

            1. To stop or slow down vehicle in shorts possible distance in emergencies.

            2. To control vehicle to retained when descending a hill.

4. REQUIRES OF GOOD BRAKING SYSTEMS: -

             The brake should be stopping the vehicle in shortest possible distance & time. There are following number of requirements in braking system

            1. It should have less wearing parts.

            2. It should require less maintain.

            3. It should work equally well in all seasons.

            4. Brake should work equally good fair bad roads.

            5. Pedal effort applied by driver should not be more so as to not to strain driver.

            6. Brakes when applied should not disturb steering geometry.

            7. Brakes when applied should not pull vehicle to one side.

            8. There should be minimum possible sound when brake applied.

            9. An independent brake system available in case of emergency.

5. CLASSIFICATION OF BRAKES: -

                 The brakes are classified as,

           

            A: - With respect to application: -

            a) Foot brakes.

            b) Hand brakes.

           

B: - With respect to number of wheels: -

            a) Two brakes.

            b) Four-wheel brakes.

            C: - With respect to method of braking contact: -

            a) Internal expanding brakes.

            b) External expanding brakes.

            D: - With respect to number & method of applying braking force:-

            a) Single acting brake.

            b) Double acting brake.

            E: - With respect to brake gear: -

            a) Mechanical brake

             I  Hand brake

            II Foot brake

           

b) Power Brake

            I  Booster brake

           II Non-Booster brake.

           

F: - With respect to nature of power employed:-

            a) Vacuum brake

            b) Air brake

            c) Hydraulic brake

            d) Electric brakes

            e) Hydrostatic Brake.

G: - With respect to power transmission:-

            a) Direct acting brakes

            b) Geared brakes.

H: - With respect to power unit: -

            a) Cylinder brake

            b) Diaphragm brake.

6. TYPES OF BRAKES: -

           

1. Mechanical brake system

            2. Drum Brakes.

            3. Disc Brakes.

            4. Parking Brakes & emergency brakes.

            5. Air Breaks

            6. Vacuum Breaks

            7. Hydraulic Breaks

8. Electric Brakes

1. MECHANICAL BRAKES: -

           

These brakes are not used widely for braking of stopping of vehicle.  These brakes incorporating cables which link the brake pedal with the brake shoe operation device are now mainly used for parking brake & EMERGENCY BRAKE OF THE MOTOR CARS.  In these brakes units, rods & shaft or cable & many linkages are used to transmit pressure from the brake pedal to the wheel brake.  When the brake pedal is pressed the cum turns by means of brake linkage when the cum turns the shoes expands

outwards against the drum.  A toggle lever is also used for the same purpose.  The brake linkage rubs against the drum & thus stops its motion.

2. DRUM BRAKE:-

           

In this type of brake drum is attached to the wheel where as on the axle casting is mounted on the back plate.  Two brake shoes are anchored on the back plate fiction lining are mounted on the brake shoes.  On or two vetractor springs are used which serve to keep the brake shoe away from the drum when the brakes are not applied.  The broken shoes are anchored at one end.  Where as other end is forced if towards the brake drum by some external force the brake shoe against the revolving brake drum there by applying the brakes.

3. PARKING BRAKE AND EMERGENCY BRAKE: -

                       

As the name suggests this brakes is usually used while parking a vehicle out can also in the used while parking a vehicle but cum also be used in case of emergency when the foot brake system has failed according to motor vehicle Act all motor vehicles must have parking brakes.  Parking brake is generally of three types: -

           

A) Constructing type brake.

            B) Expanding type brake.

            C) Disc type brake.

            All these type of brakes operate to lock the transmission main or the propeller shaft, when the mechanical brake is applied.  As the rear wheel is connected to the propeller shaft through the axle shaft different & universal joint the rear wheel are prevented from running when the propeller shaft is locked.

           

4. HYDRAULIC BRAKE: -

           

The liquid pressure applies hydraulic brake.  This system is based upon Pascal s principles, which started that “The confined liquid transmits pressure without loss equally in all direction.”  The liquid is known as “Brake fluid “in this system when the brake pedal is pressed it presses the piston of the master cylinder & by compressing the brake fluid in compression chamber built up pressure.  Then this pressurized brake fluid or oil is goes to the wheel cylinder through pipes where forces out the piston of the wheel cylinder & which expands the brake shoes from it s rest positions towards the brake drum & by means of brake liner friction is made or create their which results the stopping is made or create their which results the stopping is made or create their which results the stopping of rolling of wheels on the road.  Thus the vehicle is stopped.

            5. POWER ASSOCIATED BRAKE: -

           

A great braking force is to be needed to apply the brakes incase of motor vehicle lifted with disc brakes as well as for heavy commercial vehicles power assisted brakes are used to equate the limited strength of the driver with the grate manifold vacuum is used by power assisted system.  Therefore they are also known as vacuums brake.

            In this system by using master cylinder control, servo cylinder & boost cylinder brakes are applied.  The vacuum is used to operate this brake by these units the vacuum pressure is increased & grate effort is developed to push the diaphragm in the boost cylinder and there by with grate effort the brakes are applied.

            6. VACCUM SERVO ASSISTED BRAKE: -

           

In this system the partial vacuum existing in the inlet manifold.  When the engine is running provides to power to operate the brakes.  The effort provides by the servo system is proportional to the applied power & it is usually in the ratio 4:1.

            In this brake the servo unit is used when used the vacuum of engine & by pressing with piston it passes to the lender master cylinder which increase the brake fluid pressure.  Then this pressurized fluid is passed to the wheel cylinder & by expending brake shoe thus the brake is worked.

            7. AIR BRAKE: -

           

Air brake are widely used in heavy vehicle like bases & trucks with requires a heavier braking effort that can be applied by the drivers foot.  The pressure of compressed air, instead of foot pressure, applies air brake acting against flexible diaphragm in brake chamber.  The diaphragm is connected to the brake & rods, which

connect to break operating cams, are controlled through a hand or foot operated valve.  The brake valve controls brakes operation by direction the flow of air from a reservoir against diaphragm in the brake chamber when the brakes are applied & from brake chambers to the atmosphere when the brakes are released.

            The air brakes are much powerful than the ordinary any mechanical or by hydraulic brakes & hence they are widely used in heavy vehicle.

 

            8. ELECTRIC BRAKE: -

            Electric brake are also used in some motor vehicle s although these one not very popular  “Worker electric brakes”  is one of the examples of such brakes an electric brakes essentially consists of an electric magneto within the brake drum.  When the current from the battery is utilized to energize the Electro magneto, which actuates the mechanism to expand the brake, shoes against the brake drum thus applying the brake.  The severity of braking is controlled by means of a rheostat, which is operated by the driver through the foot paddle.

            Electric brakes are much simple.  This brake does not required complicated operating linkages only cable is required to take current from the battery to the electromagnet.  Also there are very quick in action as compared to other types of brakes.

            9.  EXHAUST BRAKE: -

            This system consist by butterfly valve is used to limit the escape of gases from engine manifold.  The engine act s as a compressor driver by the read wheels when the exhaust brake is operated on conjunction with a fuel cutoff device.  The build up pressure in the exhaust system acting provides the rear filling effect against the engine piston.  The butterfly valve should be placed as close possible to the manifold to achieve  a high degree of containing a butterfly valve, which is bolted to a strengthened exhaust piece & placed close to the manifold.  Flanges the exhaust is cut off by the move of driver control valve.

           

                                   

 

7. HYDRAULIC BRAKE SYSTEM:-

           

In this brake system the pedal force transmitted to brake shoe through a fluid called brake fluid.  The fluid pressure acting upon wheel causes brake shoe to expand in this system force transmission based on Pascal s law (confined liquid transmission pressure without loss equality in all direction) which helps to multiply & transmit force applied on pedal to brake shoes.

           

The hydraulic braking system is fully pen sated due to use of hydraulic fluids the transmitting medium because presser is transmitted to position of each wheel cylinder with equal and same force resulting in pressure applied to brake shoe to be identical.  A hydraulic braking system consist of

           

                        1.         A fluid supplies tank.

                        2.         Master Cylinder

                        3.         Wheel Cylinder

                        4.         Pipe lines

           

The main difference between the hydraulic and mechanical brake is that instead of transmitting pedal pressure to brake by means of rod & joints or by means of pull cables, head of fluid in pipes is utilized for transmitting the pedal pressure of brake in case of hydraulic brake complete bleeding of brake line & brake cylinder is necessary for UN objectionable performance.

CONSTRUCTION: -

           

A cylindrical brake drum mounted on the inner side of wheel revolving with wheel brake as well as two wheel brake shoes mounted inside brake drum but without rotating are providing with each wheel brake in outer surface if the brake shoe is fitted on heat wear resisting brake using by means of piston rod, brake pedal is attached to master cylinder piston, wheel cylinder ion each of four wheel brake get this pressure to force there piston outward.  Hence brake shoe will be forced out against brake drum by there piston in turn now the brake pedal is released by driver hence brake shoes will be pulled out of contact with brake drum in to three original position by retracting springs on the wheel brake it is due to return of piston & brake pedal to their original position caused by pressure returning to piston & brake pedal to that their original position.  Further wheel position are forced back of their original inward position by these retracting springs on wheel brake causing fluid to return to the master cylinder with help of the reservoir master cylinder is kept fitted with liquid.

WORKING: -

           

When brakes are to be applied the driver depresses the pedal.  The piston is forced into master cylinder this increasing pressure of fluid in master cylinder & in the entire hydraulic system this pressure is conducted instantly to wheel it forces the wheel cylinder piston outward these pistons is turn forces the brake shoes out against brake drum thus brake are applied.

            When the driver releases brake pedal the master cylinder returns to its original position due to return spring pressure & thus fluid pressure is entire system drop to the original low valve which follows retracting spring on wheel brake to pull brake shoe out of contact with brake drum to original position. These causes-wheel cylinder positions also to come back to their original hard position thus brakes are released.

ADVANTAGES OF HYDRAULIC BRAKES: -

            1.         Simple in construction

            2.         Braking fluid exert equal braking pressure

            3.         It provides increased braking effect

            4.         Wear rate is low because system is self lubricated

            5.         Self compensated system.

            6.         They provide high mechanical advantage with use of long levers.

DISADVANTAGES OF HYDRAULIC BRAKES: -

1.         Complete braking system is liable to affect if any fault casing pressure loss or breakage or pipe to one wheel occurs.

            2.         The brake shoes are liable to get ruined if the brake fluid leaks out.

MASTER CYLINDER

            It is the central unit in hydraulic braking system master cylinder is generally made of cast iron & contains bracket & holes for mounting.  The hydraulic pressure required to operate the system is produced here.

The pressure of the driver s foot on break paddle through different linkage attachment is transmitted to the master cylinder piston.  It can be considered as heart of the hydraulic braking system.

The purpose served by Amstar cylinder is as under: -

            a) The hydraulic pressure required to operate the system is built up.

b) Due to the reservoir provided with it.  It serves to maintain a constant volume of fluid in the system.

            c) To bleed or force air out of the brake line & wheel cylinder, it acts as pump.

           

OPERATION OF MASTER CYLINDER: -

            When the brake pedal is pressed it forces the push rod towards, forcing the piston deeper into the cylinder the compensating part is sealed off by the primary cap.  When the piston starts moving inwards.  The fluid flows through the intake or breather art to keep the center of the piston filled up.

            The fluid trapped by the piston a head of it due to the closure of the compensating port.  The pressure created in the cylinder by the fluid pepping forces the check valve inner rubber flap to open & pass the fluid in to the lines.  With the piston moving inwards the wheel cylinder piston shoes to hold tightly against the spraining drum.  The brake shoes with remain pressed against the drum as long as the pressure in maintained on the brake pedal.

            When the pressure on the brake pedal is released the released position operation of the master cylinder the brake shoes return spring pill the shoes press to drum to cumbers the wheel cylinder piston.  The primary cap becomes free of the compensating part.  The breather or intake part is opened to the central section of the piston within the cylinder there is no pressure.

            In creation vehicles the master cylinder is rigidly fastened to the car frame.  It is linked to the service brake foot pedal by means of pedal rod.  The outlet of the brake lines is connected to the wheel cylinder.  Master cylinder is bolted to the engine side of the fire will through the wall is linked to through the brake lines when suspended brake pedal connected in to spool shaped piston is depressed.  The brake fluid is forced into the brake lines by the most of the piston towards the brake line exist.

WHEEL CYLINDER: -

            Wheel cylinder is the second IMP component of the hydraulic break system.  It consists of two pistons, which can move, in apposite directions by the fluid pressure.  It is rigidly mount on brake shield for backing plate.  The boots protect the cylinder from foreign substance.  Bleeder valves are provided in the cylinder to permit air & liquid to bee pumped out of the system during the bleeding operation.

Piston cap fits tightly in the cylinder against each piston & seals the mechanism against leakage of the brake fluid.  A spring services to hold the caps against the piston when the press is decreased.

When the brakes are applied the brake fluid entraps the cylinder from a brake line connection inlet between the two pistons.  It causes to force out of the two piston is opposite direction.  This motion is transmitted to the brake shoes directly or through links forces them against the brake drum, thus applying the brake.

           

The copper-coated tin-plated annealed steel tabbing & flexible hoses are used to connect the master cylinder to the wheel cylinder.  The hoses are used to connect the lines of the front wheel; to be turned.  Rear wheel cylinders are generally connected directly to a line fastened to the rear axle housing.  The brake line is attached directly or by means pf bracket is to the frame or axle housings.

8. AIR BRAKES: -

            The complete layout circuit is shown in fig. 9.60.  The compressor takes air from the atmosphere through the fitter & the compressed air is sent to the reservoir through the unloaded valve which gets lifted at a predator mined reservoir pressure & relieves the compressor of load.  From the reservoir the air goes to various accessories & also to the brake chambers all 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.

UNLOADED VALVE: -

            The unloaded valve in the braking system serves to regulate the line pressure.  When the specified air pressure has been attained, the unloaded valve relieves compressor.  Similarly when the line pressure decreases below the required limit, it re-establishes the compression.  It consists mainly of a governor valve, an unloaded plunger and a non-return valve.

           

As the reservoir pressure increases, pressure also builds up in the hollow plunger, the end of which is sealed by the spring-loaded inlet-exhaust valve. With build up of pressure, the diaphragm assembly lifts against the pressure-setting spring.  When the preset compressor cut-out point is reached, the inlet exhaust valve closes the exhaust passage.  Air pressure also acts upward on the underside of the governor plunger, thus fully opening the inlet valve, when air pressure moves the unloaded plunger against the force of its spring and unseats the unloaded valve allowing air from the compressor to pass through the exhaust check valve.

Necessary for the application for brakes.  The diaphragm receives compressed air form the service brake valve, while the secondary brakes are controlled by hand control valve and are affected by the power spring.

           

During all service brake applications, the power spring is held compressed and does not effect the brake operation.  However, when hand control valve lever is brought to “Park” position, compressed air is exhausted from the piston chamber and the power spring fully applies the brakes.  When the hand control valve lever is brought to “Release” or “Off” piston to release the brakes, the compressed air passed to the piston chamber builds up pressure against the piston and releases the brakes.  When hand control valve is operated to apply secondary brakes, compressed air opposing the piston is released to atmosphere.

BRAKE VALVE

          Brake valve or application valve is meant to control the intensity of braking gin an air pressure system fig. Shows the construction of such valve. It consists of spring loaded hollow piston, with inlet and exhaust valve, an air bleed hole and exhaust port. The compressed air from reservoir inters the brake valve through the inlet valve and goes to the stop light switch on one side and to the brake chamber at each wheel on the other side as shown.

           

Brake valve is operated either by a foot paddle or by push rod operated linkage or by means of salve cylinder supply with hydraulic pressure from a remote master cylinder.

ADVANTAGES OF AIR BRAKES: -

1. Air brakes are much more powerful than the ordinary mechanical or hydraulic brakes and that is the reason they arte exclusively used in heavy vehicles.

2. The air brake simplifies the chassis design, as it does not matter where the components of the system arte located on the chassis so long as a pipe line interconnects them.

3. A part form braking, the compressed air from the reservoir can be used for type inflation, windscreen wipers, horns and many other accessories.

9. DISC BRAKES: -

            The motor vehicle are now being fitted with disc brakes which are conventional type drum brakes which are generally used on some “AMERICAN” cars, Disc brakes consist of a rotating disc & two-friction pad s which four hydraulic wheel pistons contained in two halves of an assembly called a caliper attach.  The caliper

           

Assembly is secured to steering knuckle in a front wheel brake & to the axle housing in a rear wheel brake.

           

The chief advantage of the disc brake is their resistance to leading since the disc remains cool under appeared several brake applications.

10. MAIN COMPONENT OF BRAKES: -

BRAKE LINING: -

                        The brake lining is either of solid movement type of molded type.  The asbestos base nonmetallic linings have a verge coefficient of friction at 0.4. upto about 260⁰ c. There maximum temperature resistance is about 350 zinc wire linings have better resistance to wear than the non metallic type.  Molded type linings are prepared directly from the maximum, which contains asbestos.  Fiber together with resin powders and fillers.  These lining have a good wear resistance.  Their maximum temp.  Resistance is about 450⁰ c.  The average coefficient of friction is 0.4.

           

            The brake linings are attached with the brake shoes either by flavoring or by synthetic reason adhesives.  The second method is preferable, due to the absence of negative holes, more contact surface, free from scoring action and more effective wearing thickness.

Material for brake lining: -

            Requirement of material for brake lining: -

·         It should have high coefficient of friction should remain constant with change in temperature.

·         It should have low wear rate.

·         It should have high wear resistance

·         It should have high heat dissipation capacity.

·         It should not affect by moisture oil.

·         It should have good mechanical strength.

Material for brake Lining: -

Material	Coefficient of Friction (U)	Allowable Pr. (PN/mm2)
Cast Iron on Cast Iron	0.50-0.2	1-1.75
Bronze on C.I	0.50-0.1	0.56-0.84
Steel on C.I.	0.06-0.30	0.8 4-1.4
Wood on C.I.	0.08-0.35	0.40-0.62
Fiber on metal	0.1-0.2	0.07-0.28
Lather on metal	0.15-0.5	1.4-2.1
Asbestos on metal	0.20-0.25	1.4-2.1
Metal on C.I.	0.05-0.1	1.4-2.1
Wire Asbestos on metal	0.20-0.5	0.20-0.50

ADVANTAGES AND DISADVANTAGES:-

           

1. Simple in construction.

            2. Equal braking effort to all the four wheels.

            3. Increased braking effort.

            4. Self compensating system.

            5. Low wears rate.

            6. Flexibility in braking lines.

            7. High mechanical advantage.

            8. These brakes can also provide differential.

9. In this braking system, all the wheel brakes are forced to act together without       any consideration to their individual adjustment.  Braking action between the front and rear brake by using the wheel cylinder of different size for the front and rear wheels.

DISADVANTAGES: -

           

Complete the braking system is liable to be affecting dif. Any, fault causing pressure loss or the breakage of a pipe to one wheel occurs.