MODULE 2: BRAKES
Learning Outcomes
• Function of brakes
• Types of brakes and their advantages and disadvantages
• Braking units advantages and disadvantages
Function of Brakes
• Brakes take kinetic energy from a moving vehicle and transfer it to heat energy
through friction to make the car stop or slow down.
• Friction is the resistance to motion. Kinetic energy of a rotating wheel is
converted to heat energy as friction slows the wheel.
• Brakes are used to slow down or stop a machine by means of applying friction
onto the wheel.
• Stop machine within a certain time or distance
• Stop machine in emergencies
• Keep machine stationary on a slope
• Slow the speed of the machine down
Braking System Components
Component Description Figure
Drum Brakes • Drum is attached to the inside of
the wheel and inside there are
two heat resistant pads.
• When the pedal is pressed, pads
push outwards and squeeze the
drum which stops the wheel
Disc Brakes • Linked to the wheel or wheel
axle. To stop rotation, friction
material in the form of brake pads
is forced against the both sides of
disc. Friction thus stops the
wheel.
Brake Pads • Main component contained in the
drum or disc.
• Referred to as the “shoe”
• Used to create friction.
Types of Braking Systems
• Electromagnetic Braking System
• Hydraulic Braking System
• Pneumatic/Air Braking System
• Mechanical Braking System
Electromagnetic Braking System
Electromagnetic brakes use electro-magnets to apply a braking force.
• When an electric current flows; electromagnets are drawn towards
each other, a spring that is connected to the drum is compressed
and brake shoes are kept off the shaft allowing it to rotate.
• Conversely, as soon as the electric current stops flowing, the
solenoid loses its magnetic force. The spring is released and pulls
the brake shoes against the shaft.
Hydraulic Braking System
• Hydraulic fluid used to transmit braking force. Universally used and
preferred braking system.
• Driver pushes down on the brake pedal, brake pedal pushes down a
piston in the master cylinder. The pressure from the master cylinder
is transferred to the slave cylinders through the brake fluid. The
force on the cylinders cause the brake pads against the brake drum
or brake disc
Air Braking System
• Use compressed air to apply the braking force.
• By operating the brake lever, pressure is applied to the brake chamber causing the
brake shoe to push outwards against the drum causing friction and slowing down the
wheel. When the brake is applied the control valve opens and allows air to move into
the cylinder and pushes the piston down.
• On release of the brakes, the control valve closes cutting off air supply to the reservoir.
Air then travels through the pipes as the air piston moves upward releasing the brakes.
Excess air is allowed to escape through the exhaust pipe through the release valve.
Mechanical Brake System
• Through the use of rods or cables, the brake lever is connected with
the brake shoe. When pressure is applied on the pedal, the lever
forces the brake shoe outward resulting in the application of brakes.
Buckle adjusters are used to adjust the length of the rods/cables. A
hand brake is an example.
Brake Units
Disc Brake Systems – braking force • Easily cooled • Wear easily
applied parallel to the wheel rotation • Replacement quick and easily • Can be noisy
onto a disc. • Efficient under various conditions • Require higher operating force
Internal Drum and Shoe Brakes – • Adjustment foe lining wear is • Difficult to cool
braking force applied radially automatic • Friction tends to cause wear
outward. • Compact • Heat can cause the drum to
expand
External drum and band brakes – • Easily inspected and maintained • Unsafe
Brake force applied to the outside of • Easy to cool • Brake drums are large making
the brake drum. them difficult to handle
Cone Brakes – Friction brakes with • Less force needed due to cone • Grease or oil on the braking
cone-shaped rubbing parts shape. surfaces can cause brakes to fail
