Braking System

“Braking system is an arrangement of various linkages and components (brake lines or mechanical linkages, brake drum or brake disc , master cylinder or fulcrums etc.) that are arranged in such a fashion that it converts the vehicle’s kinetic energy into the heat energy which in turn stops or de accelerate the vehicle.”

The conversion of kinetic energy into heat energy is a function of frictional force generated by the frictional contact between brake shoes and moving drum or disc of a braking system.

Need of Braking System

In an automobile vehicle braking system is needed –

1. To stop the moving vehicle.
2. To de accelerate the moving vehicle.
3. For stable parking of a vehicle either on a flat surface or on a slope.
4. As a precaution for accidents.
5. To prevent the vehicle from any damage due to road conditions.

Classification of Braking System

1. On the Basis of Power Source

(i) Mechanical braking system
(ii) Hydraulic braking system
(iii) Air or pneumatic braking system
(iv) Vacuum braking system
(v) Electric braking system

2. On the Basis of Frictional Braking Contact

(i) Internal expanding brakes (e.g.- drum brakes)
(ii) External contracting brakes(e.g. disc brakes)

3. On the Basis of Application-

(i) Foot or service brakes
(ii) Hand or parking brakes

4. On the Basis of Brake Force Distribution

(i) Single acting brakes
(ii) Dual acting brakes

Mechanical Braking System

“The brakes which are operated mechanically by means of levers, linkages, pedals, cams, bell cranks etc. are known as Mechanical Brakes.” 

Mechanical brakes all act by generating frictional forces as two surfaces rub against each 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 mechanical brakes are generally Three Types:- 

1. Internal Expanding Brake (Drum Brake) 

2. External Expanding Brake (Disc Brake) 

3. Hand Brake (Parking Brake)

1. Internal Expanding Brake (Drum Brake) 

The whole assembly of the drum brake is fitted to the back plate of the wheel. The back plate remains stationary and it does not rotates with the wheel. 

1. Brake Drum: 

It is a round cast iron housing which is used to stop the vehicle with the help of brake shoe. The drum brake is bolted to the hub of the wheel. It rotates with the hub. 

2. Brake Shoe: 

It is the frictional part of the drum brake, without it the working of the brake is not possible. The brake shoe has brake lining at its outer curve. It is the brake lining which makes contact with brake drum during the stopping of the vehicle. 

It is of two types- 

1.Primary brake Shoe: The shoe having large lining material is called as primary shoe. 

2.Secondary brake shoe: The shoe with small lining material is called secondary shoe. 

3. Wheel Cylinder: 

It is used to force the brake shoe outward to apply the brake. The wheel cylinder is connected to the master cylinder. It contains piston which moves outward when brake is applied and forces the brake shoe towards inner surface of the drum. 

4. Return or Retracting Spring: 

It is used to retract the brake shoe after brake is applied. Two return springs are there in drum brake, one for the primary shoe and other one is for secondary shoe.

5. Self Adjuster: 

It maintain the minimum gap between the brake shoe and drum so that they do not contact each other when pedal is not pressed. In the case if the brake lining wear out, and gap increases in between the shoe and drum, It can be adjusted again to maintain the gap between shoe and drum inner surface. once it is adjusted it maintains the same gab during the brake working by itself.

Working of Internal Expanding Brake

• As the brake pedal is pressed, it compresses the fluid in the master cylinder and allows the piston of the wheel cylinder to expand outward. 
• The outward motion of the piston of wheel cylinder forces the brake shoe outward against the brake drum. 
• As the brake shoe lining touches the inner surface of the drum, and due to the friction generated in between the brake shoe and drum, the motion of the wheel reduces and vehicle stops.
• As the force is removed from the brake pedal, the retracting springs draws the brake shoe inward and the contact between the friction lining and drum ended. Now again the brake is ready to apply.
• A self adjusting screw is present at the bottom, which is used to maintain a minimum gap between the drum and brake shoe. When the lining of the brake shoe is wear out than the gap between the drum and brake shoe increases, at that time the adjuster is adjusted again to maintain the minimum gap.

Advantages of Internal Expanding Brake

1. They are self energizing braking system. It means they are designed to operate by itself. 2. It is cheaper than the disc braking system. 

Disadvantages of Internal Expanding Brake

1. Heating problem 

2. The drum brakes will not work properly if it gets wet in water.

2. External Expanding Brake (Disc Brake) 

1.Wheel Hub: 

The disc rotor is attached to the wheel hub and it rotates with it. The wheel of the vehicle is bolted to the wheel hub. 

2. Caliper Assembly: 

The caliper assembly consist of 

1. Brake pad: It makes contact with the rotor disc and due to the friction between the brake pad and rotor disc the vehicle speed reduces and it stops. 

2. Caliper bracket 

3. Caliper frame 

4. Piston: It applies the brake force on the brake pads when brake lever is pressed. 

3. Disc Rotor: It is the rotating part of disc brake. When brakes are applied, a lot of heat is generated which can decrease the braking efficiency, so the rotor has drilled vent holes on it which dissipates the heat.

Working of External Expanding Brake

• When brake pedal is pressed, the high pressure fluid from the master cylinder pushes the piston outward. 
• The piston pushes the brake pad against the rotating disc.
• As the inner brake pad touches rotor, the fluid pressure exerts further force and the caliper moves inward and pulls the outward brake pad towards the rotating disc and it touches the disc.
• Now both the brake pads are pushes the rotating disc, a large amount of friction is generated in between the pads and rotating disc and slows down the vehicle and finally let it stop.
• When brake pad is released, the piston moves inward, the brake pad away from the rotating disc. And the vehicle again starts to move.

Advantages of External Expanding Brake

1. It is lighter than drum brakes. 

2. It has better cooling (because the braking surface is directly exposed to the air). 

3. It offers better resistance to fade. 

4. It provides uniform pressure distribution 

5. Replacement of brake pads are easy. 

6. By design they are self-adjusting brakes. 

Disadvantages of External Expanding Brake

1. It is costlier than drum brakes. 

2. No servo action is present. 

3. It is difficult to attach a suitable parking attachment.

3. Hand Brake (Parking Brake)

 

Hand brake are usually the mechanical brakes. These brake independently of the foot brakes. These are used for parking on slopes & during emergency & also called secondary brakes. Hand brakes are generally located on the side of the driver’s seat. On most of the vehicles Hand brakes are applies on he rear wheels. In order to apply the brakes the ratchet is released first by pressing the ratchet release handle, which cause the pawl to move up, disengaging the ratchet. Then the brake lever pulled up, while further pulls the cable which in them operated the rear brakes mechanically through a linkage Operating on the piston of the rear wheel cylinder, which is two halves. The ratchet release handle which had been pressed so which had been pressed so far is released now, so that the pawl moves down the spring action & engages with the ratchet thus keeping the brakes applied.

Hydraulic Brake System

“Brakes which are operated by means of hydraulic pressure are known as Hydraulic brakes.” 

In hydraulic system when the brakes are applied, the pressure is increase sufficiently in the system to produce equal & uniform braking action on the all four wheels. The hydraulic brakes function based on the principle of Pascal’s law which state as follow:- 

“Pressure applied to a liquid is transmitted equally in all directions.”

Main parts of hydraulic brakes: 

1. Master cylinder: 

It is the main part is the whole assembly. It works as a hydraulic actuator which has a piston-cylinder arrangement. It is responsible for the conversion of mechanical force into the hydraulic force. As the brake pedal is pressed the fluid in the master cylinder compressed and exerts pressure which is transmitted to Brake assembly through the hydraulic lines. 

2. Brake pedal and mechanical linkage: 

Brake Pedal pressed manually when we have to stop or slow down the running body. It is further attached with little mechanical linkage such as spring which helps in retraction of the pedal further it connects to master cylinder. 

3. Hydraulic/brake fluid reservoir: 

It is kind of a small tank for the braking fluid. It is directly attached to the master cylinder. Sometimes due to small leakages the level of fluid goes down into the master cylinder so to maintain the proper amount of brake fluid in the working operation a reservoir is required. 

4. Hydraulic lines: 

Hydraulic lines are the connections between the various components of the braking system. Braking fluid travels through these lines from master cylinder to brake. These are the small diameter pipes which replace the different types of mechanical linkage in case of mechanical brakes.

5. Brake fluids: 

The common brake fluids which are used for the hydraulic brakes are DOT3, DOT4, DOT5, etc. For instance, DOT3 DOT4 and DOT5 are glycol ether based which generally means that they absorb moisture from the atmosphere.

Working of Hydraulic Brake

The brake pedal is connected to the master cylinder piston by means of a piston rod. When the brakes are applied or when the brake pedal is pressed, the piston is forced into the master cylinder, which increases the pressure of the fluid in the master cylinder and in the entire hydraulic system. This pressure is conducted instantaneously to the wheel cylinders on each of the four brakes, where it forces the wheel cylinder pistons outwards. These pistons, in turn, force the brake shoes out against the brake drums. Hence, brakes are applied When the brake pedal is released, the master cylinder piston returns to its original position due to the return spring pressure. The fluid pressure in the entire system drops to its original low value, which allows retracting springs on wheel brakes to pull the brake shoes out of contact with the brake drums into their original positions. This causes the wheel cylinder pistons also come back to their original inward position. Thus, the brakes are released.

Master Cylinder

In hydraulic braking system, master cylinder is a device that provides required amount of pressure or braking force to the final braking components after multiplication of the mechanical force applied by the driver through brake pedal or brake lever. 

Types of Master Cylinder 

1. Single Master Cylinder 

2. Tandem Master Cylinder or Dual Master Cylinder 

1. Single Master Cylinder:- 

It is the simple type of master cylinder just like a medical syringe, in this type of master cylinder single piston inside a cylinder is used to cause braking. Single master cylinder distributes equal force in all the wheels due to the use of single cylinder single piston or circuit. In single circuit master cylinder when brake pedal is not pressed i.e. non actuation position the piston remains at its original position which in turn closes the inlet valve of the reservoir due to which there is no incoming of brake fluid takes place between reservoir to compression chamber. When brake pedal is pressed i.e. actuated position, the piston which is connected to the brake pedal through connecting rod moves which in turn opens the inlet valve due to which incoming of brake fluid from reservoir to compression chamber takes place. This brake fluid inside the compression chamber is compressed due to the movement of piston inside the cylinder just like the medical syringe. After compression up to a certain pressure the outlet valve opens and this highly compressed brake fluid is further transferred to the brake lines for further brake actuation.

2. Tandem Master Cylinder or Dual Master Cylinder:- 

It is the modified type of master cylinder in which dual cylinder-dual piston or single cylinder dual piston along with dual circuit is used for independent braking between front and rear wheels. This type of master cylinder is used in almost all cars as it is more efficient than single circuit master cylinder.  When brake pedal is not actuated, the piston remains at their original place, closing the inlet valve of both the compression chambers, which in turn cuts the incoming of brake fluid between both the reservoir or both the reservoir chambers. When the brake pedal is actuated, at first the primary piston moves due to which opening of primary inlet valve takes place. Initially due to the movement of primary piston compression of the brake fluid inside primary chamber takes place. After completion of the compression in primary chamber primary outlet valve opens up and this compressed brake fluid is further sent to brake calipers through brake lines and actuation of the primary circuit brakes take place.

After the completion of the primary piston movement i.e. at its extreme end, the secondary piston starts moving because of the force applied by the primary piston’s spring which in turn opens the secondary valve and incoming of brake fluid from secondary reservoir to secondary compression chamber takes place. This brake fluid is then compressed and after complete compression secondary outlet opens up and this highly compressed fluid is sent to the brake calipers through brake lines and actuation of the secondary circuit brakes take place.

Advantages of Hydraulic Brake System

1. They transmit uniform pressure. (Due to hydrostatic pressure being equal in all directions, Pascal law). 

2. They help in multiplying the driver’s effort more times than that of Mechanical Brakes. (Hydraulic leverage ratio, hydraulic advantage). Higher mechanical advantage. 

3. The brake fluid also acts as a lubricant and reduce the frictional losses at high-speed braking. 

4. They are simpler in construction and lighter in weight. 

5. Thermal stresses generated are much lower in hydraulic brakes than Mechanical Brakes. 6. They are more wear resistant.

Disadvantages of Hydraulic Brake System

1. There is always a possibility of oil/fluid leakage which can render the system inoperative or compromise the friction surfaces. 

2. Extreme heat may cause the fluid to boil forming gas bubbles which compress and can’t transmit pressure effectively. 

3. However, Environmental factors such as moisture can deteriorate the hydraulic fluid over time and cause corrosion/failure of internal components.

Pneumatic Brake System

“Brakes which are operated by means of air pressure are known as air brakes.” 

Air brakes are also known as pneumatic brakes. The first air brake was invented by George Westinghouse, he introduced this type of brake for the use in trains. Air brakes are widely used in heavy vehicles like trucks and buses because they are heavy in weight and they need more effort on brake pedal to stop them, and for comfortably braking them air brake is good as it has high potential energy and does not requires much effort to push the brake pedal.

Parts of Pneumatic Brake System

The main components of Air brakes are as follows: 

1. Filter: 

It is a filter which filters the air by removing or blocking any dust particles and allow clean air to the system. The filtered air is sent to the air compressor. 

2. Compressor: 

It takes air through filter. It then compresses air. 

3. Reservoir: 

It stores compressed air which is used for the braking system. 

4. Unloader valve: 

It is situated at compressor. It opens when the compressor pressure switch trips to OFF position. 

5. Brake valve: 

It opens when the brakes are applied by extending lines of tubing.

Working of Pneumatic Brake System

Firstly, the compressor takes air from the atmosphere through a filter. Then air filter, filters the air sends it to the compressor where it gets compressed. Then this compressed air is sent to the reservoir through the unloader valve, which opens itself at a predefined reservoir pressure and are connected to the brake valve. The lines of tubing from the brake valve extend to the front and rear brake chambers. The air is supplied to brake chambers placed at each wheels, through the brake valve. This brake valve is controlled by the driver who can control the intensity of braking according to the requirement.

When the brake pedal is pressed, pressure in the reservoir drops which then pushes the brake pad against the brake drum and the braking action occurs and the vehicle slows down or stops according to the pressure applied. When the brake pedal is released the unloader valve gets closed and there is no pressure on brake pads. Additionally, the compressed air available on the vehicle is also used for the operation of additional assemblies of the vehicle like horn, windshield wipers, etc. 

Advantages of Pneumatic Brake System

1. The air braking system is cleaner. 

2. Air is freely available so no cost for air. 

3. Ease of use and maintenance. 

4. Safe and explosion proof. 

5. Reserved compressed air can be stored for afterwards usage. 

Disadvantages of Pneumatic Brake System

1. The air can leak very easily. 

2. When the air brakes are applied there is some kind of noise produced due to air. The noise is also produced while changing pressure from the compressor. 

3. It does not work underwater and under extreme temperature.

Vacuum Brake System

“Brakes which are operated by means of Vacuum are known as Vacuum brakes.” 

Vacuum brake refers to the braking system that utilize suction from engine inlet manifold for brake application. The braking force are provided by the pressure difference that exits on the opposite side of a piston or diaphragm that operated in cylinder. 

Types of Vacuum Brake System

The vacuum brake are generally two types:- 

1. Atmospheric suspended vacuum brake 

2. Vacuum suspended vacuum brake

1. Atmospheric suspended vacuum brake

Its consists of a piston cylinder arrangement in which the piston of master cylinder communicates with one side of the cylinder piston whose other side is connected to the brake pedal. There is a vacuum control valve that admitted vacuum to one side of the cylinder piston with atmospheric pressure prevailing on its side connected to brake pedal. Thus a pressure differential exits between the two sides & that pushes the piston to the vacuum side. This piston movement is communicated to the linkage mechanism that makes contact between brake shoes & the drum. 

2. Vacuum suspended vacuum brake 

Its consists of:- 

1. Control unit provided with a piston & two valves. 

2. Vacuum reservoir that connected with the engine inlet manifold. 

3. Servo cylinder, one side of which is connected to the vacuum reservoir through control unit while other side is connected to the inlet manifold. 

When the brakes are in released position the valve V1 is closed & Valve V2 is open. Apparently vacuum acts on both side of the piston in servo cylinder. when the brakes are applied the piston of control unit is pushed up due to force exerted by the pressure of brake fluid. That results into closing of valve V2 & opening of valve V1. the left side of the piston in the servo cylinder than open to atmospheric pressure, while vacuum acting on the right side. The piston of the servo cylinder moves under the pressure differential. Through  suitable linkage, the brake lining come in the contact with the drum causing brake action. With vacuum brakes, the driver’s fatigue is considerably reduced as the whole of braking effort is practically supplied by the engine vacuum.

Electric Brake System

“Brakes which are operated by means of Electric power are known as Electric brakes.” 

Electric brakes are devices that use an electrical current or magnetic actuating force to slow or stop the motion of a rotating component. 

Types of Electric Brake 

There are two main types of electric brakes

1. Magnetic Brakes 

2. Electrically Actuated friction Brakes 

Magnetic brakes are non-contact brakes that use magnetic fields to actuate the braking components. It is further divided into four types

1. Permanent Magnet Brakes 

2. Electromagnetic Brakes 

3. Eddy Current Brakes 

4. Hysteresis Powered Brakes 

Although many electric brakes use mechanical methods for actuation, others rely upon friction. It is also divided into four types

1. Band Brakes 

2. Drum Brakes 

3. Disc Brakes 

4. Cone Brakes 

These brakes require an electric brake controller. The brakes themselves are electromagnets inside the brake hubs that when energized will move with the brake drum and actuate the brake shoes providing friction to slow the trailer. The higher the voltage the more braking force is created. The brake controller is generally mounted in the driver’s area (some are fitted to the trailer). These receive an electrical brake signal when you apply the brakes and send out a specific voltage to your trailer brakes. Some cheaper units provide voltage that is manually set by the driver and the higher end units use a proportional braking system that will regulate the braking force depending on what the vehicle is doing. i.e. the harder you brake the harder the trailer will brake.

Advantages of Electric Brake System

1. Simple in design & installation 

2. Simplified operating linkage (only one cable for each drum) 

3. Much better control over braking effort 

4. Absence of grab 

5. No adjustment during its lining life.

Factor Controlling the stop an Automobile

1. Speed & Load 

2. Road Surface 

3. Tyre Thread 

4. Gradient 

5. Number of wheel braking 

6. Coefficient of friction of braking surface 

7. Braking force of engine 

8. Pressure applied through energization 

9. Weight transfer