Brakes Introduction to Brakes Defination A brake is

Brakes

Introduction to Brakes: Defination “A brake is a device by means of which an artificial resistance is applied to a moving body in order to retard or stop the motion of body. ” The brake is a friction device for converting the power of momentum or kinetic energy of the moving vehicle into heat by means of friction.

Types of Brakes: �Main types of brakes are: 1. 2. 3. 4. 5. 6. Mechanical brakes Hydraulic brakes Disc brakes Pneumatic brakes Vacuum brakes Electric brakes

I. Mechanical Brakes: 1. Block or shoe brakes: This brakes consist of blocks which are pressed against the surface of a rotating drum. 2. Band brakes: This brakes consists of rope, belt or flexible steel band lined with frictional material which is wrapped partly round the drum. 3. Band block brakes: A band block brake consist of number of wooden blocks fixed inside a flexible steel band. 4. Internal expanding brakes: They consist of two semicircular shoes pivoted at the fixed fulcrum respectively.

Block and shoe brake: q Single block brake: (2Θ<60) Single block or shoe brake consists of block or shoe which is pressed against a rotating drum by means of a lever as shown in figure. Here, as the angle of contact is less than 60° it is assumed that normal pressure between the block and drum wheel is uniform

Block and shoe brake: q Pivoted block brake: If the angle of contact between block or shoe brake drum is more than 60° then pressure at the ends than the centre. In this case it is assumed that wear is not uniform. To get uniform wear in direction of applied force , block or shoe is pivoted to the lever instead of being rigidly attached as in figure.

Block and shoe brake: q Double block brake: When a single block brake is pressed against the rotating drum , an unbalanced load on the bearing of the shaft supporting the drum will act due to normal reaction , this unbalanced load produces bending of shaft. It is prevented by using a double block brake having two blocks on the two sides of the drum. Upper ends of brake arms are held together using spring.

Band Brakes: q They consists of a rope , belt or flexible steel band lined with frictional material which is wrapped party round the drum. q When band is pressed against the external surface of drum , the frictional force between drum and band will induce braking torque on the drum. 1. Simple band brake. 2. Differential band brake.

Band Brakes: q Simple band brake: A simple band brake is shown in figure. in this one end of the band is attached at the fulcrum of the lever while the other end is at some distance from the fulcrum.

Band Brakes: q Differential band brake: In a differential band brake , neither end of the band is attached to the fulcrum of the lever. The two ends of band are attached to the two points on opposite side of the fulcrum as in figure.

Band Block brake: q A band block consist of number of wooden blocks fixed inside a flexible steel band. When the brake is applied, the blocks are pressed against the drum. The friction between block and drum provides the braking action. q The advantage of providing wooden blocks is that it provides a higher coefficient of frictional and they can be easily replaced after being worn out , because of higher coefficient of friction of wooden block, effectiveness of this brake increases.

Internal expanding brake: q Internal expanding shoe brake consist of two semicircular shoes pivoted at the fixed fulcrum respectively as in figure. One end of the shoe is pivoted at fulcrum while the other end is subjected to the actuating force. Internal expanding shoe brake is used in motor cars and light trucks

Hydraulic Brakes: � Main components of a hydraulic brake system are as under: 1. 2. 3. 4. Brake pedal. Fluid reservoir. Master cylinder. Wheel cylinder.

Working principle: To bring vehicles to stop , its kinetic energy must be changed in to heat energy. The amount of pedal pressure is approximately 20 to 40 kg. to transmit the pedal pressure equally to each wheel, pascal’s law is applied. When the brakes are to be applied, the driver depresses the pedal , the piston is forced into the master cylinder , this increasing the pressure equally to each hydraulic system. The pressure is conducted instantaneously to the wheel cylinders on each of the four brakes , where it forces the wheel cylinder pistons outwards. The piston in turn, force the brake shoe out against the brake drums. Thus, the brakes are applied.

Disc Brakes: In a disc brake system, as the brake pedal is pressed or brake lever is squeezed, a pushrod exerts force on the piston in the master cylinder causing fluid from the brake fluid reservoir to flow into a pressure chamber through a compensating port which results in an increase in the pressure of the entire hydraulic system. This forces fluid through the hydraulic lines toward one or more callipers where it acts upon one or two additional calliper pistons secured by one or more seated O-rings which prevent the escape of any fluid from around the piston. The brale calliper piston 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, slowling the vehicle.

Disc Brakes:

Disc brakes: Subsequent release of the brake pedal or lever allows the spring within the master cylinder assembly to return that assembly’s piston back into position. This relives the hydraulic pressure on the calliper allowing the brake piston in the calliper assembly to slide back into its housing and the brake pads to release the rotor.

Pneumatic air brakes: in this type of braking system, the air pressure is converted into hydraulic pressure. Here, the air power cylinder is combined with the hydraulic master cylinder and the reservoir. The conventional type hydraulic brakes are actuated by the air power with the help of this unit. The bore of the power cylinder is generally kept four times that of the master cylinder. The ratio between hydraulic pressure and air pressure is generally maintained at 15: 1. In india , the commercial vehicles manufactured by m/s. Tata engg. And Locomotive Co. , have air hydraulic brakes.

Pneumatic air brakes:

Pneumatic air brakes: �Working Principle: The compressor takes air from the atmosphere through the filter and the compressed air is sent to the reservoir through the non-return valve, which gets lifted at a predetermined reservoir pressure and relives the compressor or load. From the reservoir the 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 the brake valve is with the driver who can control the intensity of braking according to the requirements. When the brakes are applied , the air pressure in the reservoir decreases. When the pressure drops to approximately 700 kpa; the governor again cuts in the compressor to raise system pressure.

Vacuum Brakes: In the vacuum brake system, the force of brake application is because of the difference of pressures on the opposite sides of the diaphragm. One side of the piston or diaphragm is exposed to the higher pressure, while the other to the atmosphere pressure. Hence, it is the potential difference which is utilized to create the braking effect. Similar type of effect can be obtained, if one side of the piston or diaphragm is exposed to the atmospheric pressure, while the other side to a pressure below the atmospheric pressure. The pressure below the atmospheric pressure is obtained by exhausting air from it. This is the “ Principle of Vacuum Brakes. ”

Vacuum Brakes: The system is classified into atmospheric suspended system and vacuum suspended system. If both the ends of the power cylinder are manifold, the system is said to be atmospheric suspended. If both ends of the power cylinder are normally in communication with the inlet manifold and the time of brake application. , one of them is connected to atmosphere, the system is said to be vacuum suspended. Nowadays, vacuum suspended type of brakes are predominantly used. In vacuum suspended servo, the air is first exhausted from both sides of the piston in a large cylinder and during application of the brake, the air is then admitted from the atmosphere to one side of the piston. The tank and the servo are protected with the help of non-return valves, in order to enable them to hold vacuum, ehich can be utilized for making number of stops in quick succession.

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