Fuel Injection System

 

BRAKING SYSTEM

 

Braking System An automotive braking system is a group of mechanical, electronic and hydraulically activated which usecomponents friction / heat to stop a moving vehicle.

 

Principle of Braking 

Common principles on which a braking system depends when stopping a car is friction Bywheel, applying resistance, or friction,and to aheat. turning a vehicle's brakes cause the wheel to slow down and eventually stop, creating heat as a byproduct. The rate at which a wheel can be slowed depends on several factors including vehicle weight, braking force and total braking surface area.

 

Energy Conversion

The brake system converts the kinetic energy of vehicle motion into

heat 

 

Overview 



Brakes convert kinetic energy into heat by creating friction System must have very high reliability

 



Brake system is actually an energy conversion device that converts kinetic energy (car in motion possessing momentum) to potential energy (car stopping) through dissipating heat and noise to the surrounding air. The friction surfaces the brake a disc brake, the brakeofshoes on a pads drum on brake convert theor forward motion of the vehicle into heat. Heat is what causes the friction surfaces

 

Requirement of Braking System Requirement 



Most engines generate a large amount of power to get the car up to speed quickly To stop the car, an equal amount of power must be expended expended to stop the car. car.



Brakes to heat. turn the power of the rolling wheel  The quicker you stop, the more power is required, the more heat is generated

 

Requirement of brakes: The function of brakes is to stop the vehicle within the required time. The brake of the vehicle absorbs all the energy given by the engine plus that due to the momentum of the vehicle. This energy must then be dissipated. In most of the vehicles, the energy is absorbed by the brakes in the form of heat and dissipated into the stream of air passing around the vehicle.  Apart from stopping stopping the vehicle the brake brakes s should perform the others function too like the vehicle should stop without any jerk and the retardation should be smooth. Also Also the rate of retardation should be equal to the pedal effort and the effort applied by the driver to stop the vehicle should not be excessive. The rate of wear should also be low. The brake system should a not be low affected by water,and heat, and dust etc. It should require very maintenance durable.

 

Factors Governing Braking 

Pressure 



The amount of friction generated between moving surfaces contacting one another depends in part on the pressure exerted on the surfaces.

Coefficient of friction 

The amount of friction between 2 surfaces (pads and

rotors or shoes and drums)  Determined by dividing the force required to pull an object across a surface by the weight of the object

 

Friction

 

Factors Governing Braking 

Frictional Contact Surface The amount of surface surface,, or area, that is in contact. co ntact.  Simply put, bigger brakes brakes stop a car more quickly than smaller brakes used on the same car. 



Heat Dissipation 

The tremendous heat created by the rubbing brake surfaces must be conducted away away from the pad and rotor (or shoe and drum) and be absorbed by by the air.

 

Importance of Brakes Loss of brakes can cause accidents, death, and injury  When working on brakes, keep in mind that peoples lives are at stake 



If in doubt, seek help

 

Brake rules The car must have four wheel brakes operated by a single control. 

It must have two independent hydraulic circuits with independent fluid reserves. 

The brake system must be capable of locking all four (4) wheels, and stopping the vehicle in a straight line. 

The braking systems must be protected with scatter shields from failure of the drive train )  A brake pedal over-travel switch must be inst installed. alled.  This switch must kill the ignition and cut the power to any electrical fuel pumps.





Theilluminates car must be equipped with a redare brake light that when ever the brakes applied

 

rakk ing s ys tem work ? How does a bra 

When the brake pedal is depressed, the pressure on the brake pedal moves a piston in the master cylinder, cylinder, forcing the brake fluid from the master cylinder through the brake lines and flexible hoses to the calipers and wheel cylinders. The force applied to the brake pedal produces a proportional force on each of the pistons.

 

continued 

The calipers and wheel cylinders contain pistons, which are connected to a disc brake pad or brake shoe. Each output piston pushes the attached friction material against the surface of the rotor or wall of the brake drum, thus slowing thepedal rotation of the wheel. When pressuredown on the is released, the pads and shoes return to their released positions. This action forces the brake fluid back through the flexible hose and tubing to the master cylinder.

 

Classification of brakes

In automobile generally two types of brakes are used : Mechanical brakes   Air brakes & vaccum vaccum brakes

 

 Mec  Mech hani c al B r ak es 



Mechanical brakes all act by generating frictional forces as two surfaces rub against each other. other. The stopping power or capacity of a brake depends largely on the surface area of frictional surfaces as well as on the actuation force applied. The friction and wear encountered by the working surfaces are severe. Thus, the durability of a brake or service life between maintenance depends heavily on the type of material used to line the shoe or pad.

 

Air Brakes 

The compressed air is used for obtaining brake application. The brake pipe and feed pipe run throughout the length of the coach. Brake pipe and feed pipe on consecutive coaches in the train are coupled to one another by means of respective hose couplings to form a continuous air passage from the locomotive to the rear end of the train. The compressed air is supplied to the brake pipe and feed pipe from the locomotive. The magnitude of braking force increases in steps with the corresponding reduction in brake pipe pressure and vice-versa.

 

Air Brakes

 

Vacuum Brakes 

The vacuum brake system derives its brake force from the atmospheric pressure acting on the lower side of the piston in the vacuum brake cylinder while a vacuum is maintained above the piston. The train pipe runs throughout the length of the coach and connected with consecutive coaches by hose coupling. The vacuum is created in the train pipe and the vacuum cylinder by the ejector or exhauster



mounted on the locomotive.

 

Vacuum Brakes

 

Vacuum Brake Boosters

 

Types of Braking System 

Hydraulic System 

Master Cylinder 



Brake Line  Wheel Cylinders or Calipers 

Foundation Brakes 

Brake Linings or Pads  Brake Drums or Rotors

Parking Brake System  Brake Assist Assist Units 

 

Reason for Hydraulics   



 Air can be compressed Fluid cannot be compressed Fluid pressure in one place will be felt with the same strength everywhere the fluid goes When you press the brake pedal, the force is transmitted to the foundation brakes on each wheel

 

Hydraulic Principles An example of how hydraulics can increase output force

 

Basic Hydraulic System 

When the brake pedal is pressed, the piston forces fluid out through the brake lines to the wheel cylinders (or calipers)

 

Hydrau Hydr auli lic c Sy Syst stem em Co Con nfigurations There are two layouts of hydraulic brake systems used in cars and light trucks. Front/Rear hydraulic split:  Also called axle by axle, vertical, and some times “black and white” white”.. Diagonal Split:  Also called criss-cross. criss-cross.

The type of split is only significant in the event

of a hydraulic system failure.  

Front/rear Hydraulic Split Primary System

Front Axle Rear Axle

Secondary System

 

D i ag ona nall S pli t S ys tem 

In a diagonal split system, one brake line is run to each rear brake and one to each

front brake.  The connections are such that the left front and the right rear brake are on one circuit and the right front and left rear are on the other circuit

 

Typical Diagonal Split System

Right front left rear 

Left front right rear 

 

Brake Component Function Four Sub-systems    

 Actuation sub-system Foundation sub-system Parking brake sub-system  ABS & ESP (electronic stability

program) sub-system

 

Actuation Sub-system 

Brake Pedal



Master Cylinder 



Proportioning Proportionin g Valves



Brake Lines

 

The Brake Pedal Output to master cylinder

Hydraulic actuation allows

400 N and 36 mm

5:1 Nominal Pedal Ratio

multiplication of pedal force. In this system, a

10lb force on the Driv Dr iver er In Inpu putt pedal produces 360 lbs of force at the friction

100 N and 144 mm  

Master Cylinder  

Contains a reservoir of brake fluid



 A small piston piston is connected to the brake pedal



When the pedal is pushed, it builds pressure on the fluid (up to 10,000 PSI)

surface

 

Master Cylinder  



Provides a reservoir for brake fluid and contains the driving pistons in the hydraulic circuit 2 Types Frontt - Re Fron Rear ar sp splilitt -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

 

Master Cylinder 

 

How the Master Cylinder Works  A pushrod connects connects the brake pedal to tthe he master cylinder piston.  When the pedal is pressed, the piston is pushed forward and the fluid in front of the piston is displaced into the brake system moving the pads and shoes into contact with the drums and rotors.  As more force force is placed placed on the brake pedal, the fluid transmits force throughout the system. 

 

Master Cylinder Operation 

At rest:

Fluid in the reservoir can flow the area ahead of into the piston through the compensating port.



This keeps the system full and prevents pressure build-up during temperature changes

 

Master Cylinder Operation 

Applied:

The piston is moved forward blocking the compensating compensatin g port forming a sealed pump Cham

 

Master Cylinder Operation 

Brake release When the pedal is released the piston return springs force the piston back.  The piston cup seal 

collapses fluid flows pastand to allow speedy piston return and pressure decrease

 

Master Cylinder Components

 

Brake System Valves 

Metering valve 



Proportioning valve 



Reduces the hydraulic pressure to the rear drum brakes to balance braking.

Pressure differential valve 



Delays application of front disc brakes until pressure builds to rear drum brakes.

Used to operate a warning light switch.

Combination valve 

Combines several functions in one valve.

 

A Proportioning Valve

 

Pressure Differenti Pressure Differential al Valve Valve

 

Combination Valve

 

Brake Linings 

Brake linings are composed of a relatively soft but tough and heat-resistant material with a high coefficient of dynamic friction (and ideally an identical coefficient of static friction) typically mounted to a solid metal backing using hightemperature adhesives or rivets. The complete assembly (including lining and backing) is then often called a brake pad or brake shoe. shoe . The dynamic friction coefficient fortomost standard brake pads is usually in the range of "µ" 0.35 0.42. This means that a force of 1000 kg (or pounds) on the pad will give a resulting brake force force close to 400 kg (or pounds). pou nds). There are some racing pads that have a very high µ of 0.55 to 0.62

with excellent high temperature behavior.  

Brake Lining Materials 

Fully metallic 

Lining is made of sintered iron and has been used for years in heavy-duty and racing applications because they have great fade resistance.



They require very high pedal pressure and tend to quickly wear out drums and rotors.

 

Brake Lining Materials 

Semi-metallic 

Made of iron fibres moulded with an adhesive

matrix.  Offers excellent fade resistance with good frictional characteristics so only a moderate amount of application pressure is needed. 

Semi-metallic pads and shoes do not cause excessive wear on rotor or drum surfaces.

 

Brake Lining Materials 

Organic (non-metallic) For many decades, asbestos was the standard brake lining material.  It offers good friction qualities, long wear, wear, and low noise.  New materials, such as composite/organic, ceramics, and carbon fibres, are being used because of the health hazards of breathing asbestos dust. 

 

Brake Lining Material 

Synthetic 

Non-asbesto Non-a sbestos s lining materia materials ls made made of synthetic synthetic

substances are now available.  The major brake lining manufacturers are constantly experimenting with new materials that meet all established criteria for long life, friction characteristics, drum and rotor wear, wear, and heat dissipation.

 

Foundation Sub-System Types of Foundation Brakes Brakes 

Drum Older style used mainly on the rear brakes  Lots of moving parts 



Disc 

Newer style used on front brakes



Some cars may have 4 wheel brakes

 

Drum Brakes 

With drum brakes, brakes, fluid is forced into the wheel cylinder cylinder, , which the brake shoespushes out so that the friction linings are pressed against the drum, which is attached to the wheel, causing the wheel to stop.

 

Drum Brake Parts   





  

Brake Shoes (5, 12) Backing Plate (14) Return Springs (3, 13) Hold Down Springs (11) Self Adjusting Parts (4, 7, 8, 10) Wheel Cylinder  Parking Brake (6, 9) Drums

 

PARTS OF DRUM BRAKING SYSTEM 



Brake Shoes Like the disk pads, brake shoes consist of a steel shoe with the friction material or lining riveted or bonded bon dedally toy iit. t.ear Als Also o llike ike dis disk k pa pads, thelaced. lin lining ings s If tthe eve eventu ntuall w wear out and mus must t ds, be rep replac ed. he linings are allowed to wear through to the bare metal shoe, they will cause severe damage to the brake drum. Backing Plate The backing plate is what holds everything togethe tog etherr. It a attac ttaches hes to th the e ax axle le a and nd fo forms rms a sol solid id surface for the wheel cylinder cylinder,, brake shoes and assort ass orted ed hard hardwar ware. e. It rrarel arely yc caus auses es any pro proble blems ms..

 

CONTINUED



Brake Drum Brake drums are made of iron and a nd have a machined surface on the inside where the shoes make cont co ntac act. t. Ju Just st as w wit ith h di disk sk ro roto tors, rs, br brak ake e dr drum ums s wi willll sh show ow signs of wear as the brake linings seat themselves against agai nst the mac machin hined ed sur surfac face eo off th the e dr drum. um. Whe When n ne new w shoes are installed, the brake drum should be machined smooth. Brake drums have a maximum diameter specification that is stamped on the outside of the drum. When a drum is machined, it must never exceed that measurement. If the surface cannot be machined within

that limit, the drum must be replaced.  

Wheel Cylinder  

The wheel cylinder consists of a cylinder that has two pistons, one on each side. piston has a rubber rubb seal and a Each shaft that connects the er piston with a brake shoe. When br ake ake pressure is applied, the pistons are  are  forced out pushing the shoes into contac con tactt with with the dr drum. um. Whe Wheel el cy cylin linder ders s must be rebuilt or replaced if they show signs of leaking.

 

Drum Brake Operation 

The wheel cylinder forces the brake shoes apart

The shoes are forced against a drum  The friction changes rotary energy into heat energy which slows the car  



The harder the shoes are forced apart, the faster the car stops

 

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

 

Drum Brak Brakes es

 

Disc Brake Parts 

Calipers (4)



Brake Pads



Rotors (3)

 

Construction 







Disc brakes use a cast iron rotor,, inboard of the vehicle rotor wheel. Both sides of the rotor are machined smooth for the brake pads to rub against. Usually the 2 surfaces are separated a finned centre section for by better cooling (ventilated rotors). The pads are attached to metal shoes, which are actuated by pistons housed in

the brake calliper.  

Disc Brake Operation 

 A piston inside the caliper pushes the brake pads toward each other 





The rotor is located between the pads The squeezing effect causes friction which slows the car 

 

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 

 

Disc Brake Material A disc brake usually made of cast iron or ceramic composites (including carbon,

Kevlar and silica).  

DESIGN The design of the disc varies somewhat. Some are simply solid iron, but others are hollowed cast iron, out with fins or vanes joining together the disc's two contact surfaces. This "ventilated" disc design helps to dissipate the generated heat and is commonly used on the more-heavily-loaded front discs. Many higher performance brakes

have holes drilled through them. This is known as cross-drilling

A cross-drilled disc on a modern motorcycle

 

A railroad bogie and disc brakes  

Parking Brake Sub-System Parking Brakes 

Can be foot operated or console mounted



Both use a cable attached to the rear brakes





 As the cable is pulled, a lever forces the brake shoes apart This mechanically locks the brakes for parking

 

Parking Brake 

The parking brake is a mechanical brake operated through a separate hand lever or pedal; it applies parking-brake mechanisms usually at the two rear wheels. Most automotive vehicles have power-assisted braking, where a hydraulic or vacuum booster increases the force applied by the driver to the service-brake pedal.

 

Parking Brake for Rear Wheels

 

 Adjusting the Parking Brake 

Usually not necessary unless the shoes are worn

Some parking brakes are self adjusting  Locate the adjusting nut (under the lever or under the car) and tighten until you have sufficient parking brake 

 

Power brake systems 



Power brake systems on your vehicle are what help you easily press your brakes when needed. These systems are usually a simple vacuum booster attached to your brake pedal, but in can also be powered steering system a hydro boost setup,byoryour be apower fully electronic brake system. Most vehicles use the vacuum booster to assist your brakes. This is a simple system containing a brake booster and a vacuum check valve. Some cars also require a vacuum pump to assure there is enough vacuum to operate the brakes. This system only works when the car is running otherwise there will not be any

vacuum to operate the brakes.

 

Power-assisted Braking 

Power-assisted braking is provided by a hydraulic or vacuum booster. booster. As the brake pedal is depressed, the booster furnishes most of the force to push a pushrod into the master cylinder. by cylinder. The piston in the powerhydraulic booster is operated oilpower pressure from steering pump or from a separate pump driven by an electric motor. In the vacuum booster, a diaphragm usually is suspended in a vacuum supplied from the engine intake manifold ormotor. from .aDepressing vacuum pump by theallows engine or an electric motor the driven brake pedal atmospheric pressure to act against one side of the diaphragm. The resulting pressure differential moves the diaphragm and power piston, which forces the pushrod

into the master cylinder.  

Power Assist Units 



 

Some hydraulic brake systems have no power assistance The pressure applied is dependant on how much pressure you can apply Many systems use power assist units Can be vacuum, electrical, or hydraulic powered

 

Power Assistance 







Power booster reduces pedal force required to stop vehicle Engine is used to actuate vacuum a large diaphragm When the pedal is depressed, vacuum is applied to only one side of the diaphragm and force is applied to the master cylinder push rod Booster stores sufficient

vacuum for several brake applications if the engine fails.  

Power Booster in closed position

 

Vacuu acuum m Ass Assist ist Unit Units s 

Uses engine vacuum to add to the force of you foot when applying brakes



Leaking seals can cause lose of assist (hard brakes) or

lose of brake fluid  

Electric Assist Brakes Uses on newer cars  Not user serviceable 



Some cars use an electronic brake system. This system has an electric motor, motor, a hydraulic pump and an accumulator as well as a computer system to assist your brakes. These systems are very complex and require many special tools to repair.. It is also the more expensive system of repair the three to repair.

 

 ABS sub-system  

Anti-lock brake systems  Anti-lock brake systems are designed to minimize and and control wheel lock up during braking. lock, alsoon known as wheel slippage, can have aWheel dramatic affect the control of the vehicle during braking. Wheels that are locked up, with the tires sliding across the road surface, cannot be controlled by the vehicle operator. operator. The driver is  just along for the ride until wheel slippage is reduced to a point where vehicle control is regained. Braking performance is also affected by wheel slippage. The

effectiveness of the automotive braking system depends on the ability of the tires to grip the road surface.

 

Components of ABS  

 ABS CONTROL MODULE WHEEL SPEED SENSORS

HYDRAULIC MODULATOR   ABS WARNING WARNING LIGHT 

 

CONTROL MODULE  ABS CONTROL 

The ABS control module mod ule is a microprocessor mi croprocessor that is used to manage the operation of the ABS system. The ABS control module modu le monitors and processes information from various sensors, modulates pressure to the brake system and carries out selfdiagnostic tasks. Some of the inputs to the ABS module are thelight, wheel speedbrake sensors, brake switch, brake warning parking switch, pressure modulation devices and ignition and power feeds. The output controls consist of brake pressure

modulation components and the anti-lock brake lamp.  

WHEEL SPEED SENSORS SENSORS 

Wheel speed sensors sen sors are used by the ABS control module to monitor wheel lock up. Wheel speed sensors consist of a toothed wheel, mounted on the wheel hub or axle shaft, so as to rotate when wh en the wheel whee l is in motion. A magnetic sensor is placed at a fixed location, a calibrated distance the toothed wheel. air gap between thefrom toothed wheel and the The magnetic sensor is usually around .040 to .060 in

 

HYDRAULIC MODULA ATOR HYDRAULIC MODUL 

Brake lock up control is accomplished by rapidly applying and releasing the brakes of the affected wheel. To To achieve achi eve this, the ABS control modul module e is able to modulate brake hydraulic pressure to individual wheels. Brake pressure modulation is attained through several different methods. Design of the pressure modulation system varies according to vehicle design. One type of brake pressure modulator system uses solenoid

operated valves to control brake pressure to individual wheels.  

warning light  ABS warning The ABS warning light operation is managed by the  ABS control module. It is located in or near the instrument cluster and is used to warn the vehicle operator of a malfunction in the ABS system. In the event of a failure in tthe he ABS system, the ABS warning lamp is illuminated to warn the driver. Some systems will inhibit i nhibit ABS operation whe when n the ABS lamp is illuminated. Refer to a manufacturer's manual covering your particular year/make/model automobile for the diagnostic and troubleshooting

details before embarking involving the ABS system.on an auto repair project  

Brake Fluid 

Brake fluid is a type of hydraulic fluid used in brake applications for automobiles and light trucks. It is used to transfer force under pressure from where it is created through hydraulic lines to the braking mechanism near the wheels. Braking applications produce a lot of heat so brake fluid must have a high boiling point to remain effective and must not freeze under operating conditions. Brake fluid is also designed to protect against corrosion of the system materials it contacts, however those corrosion

inhibitors deplete over time. Excessive moisture is also an issue.  

Brake Bleeding 

Brake bleeding is the procedure performed on hydraulic brake systems whereby the brake lines (the pipes and hoses containing the brake fluid) are purged of any air bubbles. This is necessary because, while the brake fluid is an incompressible liquid, bubbles are in the compressible gas and air their presence brake system greatly reduces the hydraulic pressure that can be developed within the

system.  

Procedure of Brake Bleeding 

The process is performed by forcing clean, bubblefree brake fluid through the entire system, usually from the master cylinder (s) (s) to the calipers of disc brakes (or the wheel cylinders of brakes), but in certain drum brakes), cases in the opposite direction. A brake bleed screw is normally mounted

at the highest point on each cylinder or caliper.

disk brake bleed screw  

Methods of Brake Bleeding There are four main methods of bleeding:  

Pump & Hold (2 variations)



Vacuum Pressure



Reversed Pressure Pump & Hold generally requires two people, the other methods can be done by a single person.

 

Pump and Hold Method 

One person pumps the brake pedal to compress the air, air, then holds pressure pressure on it. The other person opens the bleeder valve to let out fluid and air, air, then closes the valveairafter thesucked pedal has (to prevent being backlanded in through the valve on the upstroke).

 

Vacuu acuum m Meth Method od 

The master cylinder is topped off and the cover left loose. A specialized specialized vacuum pump is valve, attached to the bleeder which is opened and fluid extracted with the pump until it runs clear of bubbles. Once again, the master cylinder reservoir level must be maintained. The vacuum method can also draw in air

via bleeder so . the the bubbles willthreads, never clear clear. Vacuum bleeding a disk brake caliper  

Pressure Method 

 A specialized pressure pump, is attached to the master cylinder and filled with fluid. Thethe pump is used to pressurize system to about 10psi, and the bleeder valves are opened one at a time until the fluid is clear of air.. One advantage to this air system is that the pump reservoir usually holds enough fluid that running dry

is not likely. is the method mostThis professional shops use.

Pressure bleeding a brake system

 

Reverse Pressure Method 

In this method, a pump is used to force fluid through the bleeder valve to the master cylinder. cylinder. This method may have advantages in some cases, however it is not in common usage.

 

Diagnosing Brake Problems 

Noisy brakes 

Worn linings

Low lining warning  Glazed linings 



Low brake pedal Broken line  Low brake fluid 



Worn linings

 

Diagnosing Brake Problems 

Spongy pedal  Air in the brake lines



Damaged foundation brakes  Leaking master cylinder 





Brake pull Wheel cylinder stuck  Brake fluid or oil leak 



Bad or loose suspension parts

 

Diagnosing Brake Problems 

Brake vibration 

Warped rotors



Out of balance tires