Automobile engineering

1. BRAKING SYSTEM

2. INTRODUCTION
 The device used to stop any vehicle by applying frictional forces.
 One of most important control components of vehicle.
 They are required to stop vehicle within smallest possible distance.
 This is done by converting kinetic energy of vehicle into heat energy which is
dissipated into atmosphere.

3. BRAKING REQUIREMENTS
1. Brakes must be strong enough to stop vehicle with in a minimum distance in
an emergency.
2. Brakes must have good anti-fade characteristics i.e. their effectiveness
should not decrease with prolonged application. This requirement demands
cooling of brakes should be very efficient.

4. CLASSIFICATION OF BRAKES
Brakes
Application
Foot brake
Hand Brake
No. of wheels
2-wheel
brakes
4-wheel
brakes
Braking
contact
Internal
Expanding
External
contracting
Application of
Braking Force
Single Acting
Double acting
Brake Gear
Mechanical
Brakes
Power Brakes
Nature of
power
Vacuum
Brakes
Air Brakes
Hydraulic
Brakes
Hydrostatic
Brakes
Electric
Brakes
Power
transmission
Direct Acting
Geared Brakes
Power unit
Cylinder
Brakes
Diaphragm
Brakes

5. Mechanical Brakes
• Shoes press against a spinning surface.
In this system, that surface is called a
drum.
• Drum brakes have more parts than disc
brakes and are harder to service, but
they are less expensive to manufacture.

6. DISC BRAKES
• A disc brake consists of a cast
iron disc bolted to wheel hub
and stationary housing called
caliper. Caliper is connected to
some stationary part of vehicle
like axle.
• When brakes are applied, piston
move friction pads into contact
with disc, applying equal and
opposite force on disc. On
releasing brakes, the rubber
sealing rings act as return
springs and retract piston and
friction pads away from disc.

7. PARKING BRAKES
■ A parking brake (also known as an emergency) is part of the vehicle’s braking system. Another term that
is also used to describe the system is a handbrake.
■ The parking brake is connected to the rear brakes, which do not exert as much force in braking as the
front brakes and will do little to stop a vehicle moving at high speeds.
■ When engaged, it locks the wheels in place and works with the parking pawl to ensure that the vehicle
doesn’t roll away. While a parking brake isn’t required to be engaged for the vehicle to stay stopped, it
works to prevent your vehicle from rolling, especially on steep inclines, and to reduce stress on the
transmission.
■ When a vehicle’s gear shift is put into Park position, a parking pawl is engaged in the transmission. This
is a pin that locks the gears into place to prevent them from rotating.

8. PARKING BRAKES
Parking Brakes
(in case of
transmission or
propeller shafts)
External contracting
Brakes
Internal Expanding
Brakes
Disc type

9. HYDRAULIC BRAKES
• The hydraulic brake is an arrangement
of braking mechanism which
uses brake fluid especially, ethylene
glycol to transfer pressure from the
controlling unit to the actual brake
mechanism of the vehicle.
• Parts of hydraulic brakes:-
 Brake Pedal
 Push rod
 Master cylinder assembly
 Brake caliper assembly

10. MASTER CYLINDER

11. MASTER CYLINDER
■ The master cylinder is the heart of the brake's hydraulic system.
■ It converts the force exerted on the brake pedal into hydraulic pressure to apply the brakes.
■ Depressing the brake pedal moves a push rod in the master cylinder. Mounted on the push
rod are a pair of pistons (primary and secondary) in tandem (one after the other) that exert
force against the fluid in the master cylinder bore.
■ The pressure created displaces fluid through the various brake circuits and lines to each of
the wheels and applies the brakes.
■ Since brake fluid is incompressible it acts like a liquid linkage between the master cylinder's
pistons and the callipers and wheel cylinders.

12. MASTER CYLINDER
Tandem Master Cylinder

13. MASTER CYLINDER
Tandem Master Cylinder
If a leak develops in the front brake system:
a) Piston 1 will move forward until it contacts Piston 2. Force from the brake pedal will be transmitted
mechanically through Piston 1 to Piston 2.
b) Although overall braking performance will be severely compromised, the rear brakes will still be
functional provided sufficient pedal travel is available.
c) The pedal will need to travel further than normal to fully engage the rear brakes. Also, it should be
appreciated that trying to stop quickly with just the rear brakes is very tricky because the rear tires will
easily reach the point of lock-up

14. MASTER CYLINDER
Tandem Master Cylinder
If a leak develops in the rear brake system,
a) Piston 2 will move forward until it contacts
the closed end of the master cylinder
housing.
b) Once Piston 2 becomes stationary,
pressurization of fluid between the two
pistons will apply the front brakes.
c) Although overall braking performance will
be significantly compromised, the front
brakes will still be functional provided
sufficient pedal travel is available. The
pedal will need to travel further than
normal to fully engage the front brakes.

15. WHEEL CYLINDER
 A wheel cylinder is a component in
a drum brake system. It is located in
each wheel and is usually at the top,
above the shoes.
 Its responsibility is to exert force
onto the shoes so they can contact
the drum and stop the vehicle
with friction.
 The wheel cylinder consists of a
cylinder that has two pistons, one on
each side.
 Each piston has a rubber seal and a
shaft that connects the piston with a
brake shoe.
 When brake pressure is applied, the
pistons are forced out pushing the
shoes into contact with the drum

16. SELF ENERGIZING BRAKES
■ The hydraulic wheel brakes of drum type are
provided with a self-energizing or servo feature.
■ The force of the rotating drum is utilized to
increase the brake pressure.
■ When the vehicle is moving forward, the drum is
rotating in anti-clockwise direction.
■ When the brakes are applied, the primary shoe at
the left, tends to move in direction of drum’s
rotation due to the friction of the rotating drum.
■ Because the primary shoe is linked to the
secondary shoe at the bottom, the secondary shoe
is forced against the anchor pin at the top.
■ This action causes to force both the shoes in
tighter contact with the drum and the braking
pressure is uniformly applied.

17. FLOATING PISTON BRAKES
■ The caliper assembly consists of two
piece bridge construction fastened
together by tie bolts. Each half of the
caliper carries a piston.
■ The cylinders are connected by drilled
passages which are provided in the
castings.
■ The halves of the callipers are cast out
of malleable cast iron having high
ductility and fatigue strength.
■ The open end of the piston contacts the
back plate of the pads. The leakage of
fluid past the piston is prevented by the
square seal fitted in an annular groove
near the mouth of the calliper bore.

18. FLOATING PISTON BRAKES
■ The seal also maintains constant
clearance between the pad and the
disc. When the driver depresses the
pedal, the fluid pressure causes the
seal to deflect elastically.
■ The friction pad assembly is retained
within the calliper with the help of
retaining pins which pass through holes
in the calliper and the back plates.
■ The bellows types seal protects the
piston and bore of calliper and back
plates. The bellows type seals protects
the piston and the bore of calliper from
moisture and dirt.
■ In this case, the oil pressure generated
in the cylinder causes the pads against

19. FLOATING CALLIPER BRAKES

20. Servo Brake System
■ A servomechanism,
or servo, is an automatic
device that uses error-
sensing negative
feedback to correct the
performance of a
mechanism. It applies
only to systems where
the feedback or error-
correction signals help
control mechanical
position, speed or other
parameters.
■ It is an electronically
controlled mechanical or
hydraulic device
permitting a large action
or strong forces to be
controlled by a small
electrical signal.

21. POWER BRAKES
■ These are the brakes in which power of engine or battery is used to enhance the
braking effort.
Power Brakes
Air Brakes
Air Hydraulic
Brakes
Vacuum
Brakes
Electric
Brakes

22. POWER BRAKES
Air Brakes: The operation of air brakes is similar to hydraulic brake except that
compressed air is used to apply brakes instead of hydraulic pressure. Air brakes
are commonly used on heavy vehicles like trucks, buses etc.

23. POWER BRAKES
Air Hydraulic Brakes: The air pressure is converted into hydraulic pressure. Here the air
power cylinder is combined with the master cylinder and the
reservoir. The conventional type hydraulic brakes are actuated by the
air power with the help of this unit.

24. POWER BRAKES
Vacuum Brakes: Vacuum brake system is controlled through a brake pipe connecting a
brake valve in the driver's cab with braking equipment on every
vehicle. The operation of the brake equipment on each vehicle depends
on the condition of a vacuum created in the pipe by an ejector or
exhauster.

25. ELECTRICAL BRAKES
■ Electric brakes are actuator devices that use an electrical current or magnetic
actuating force to slow or stop the motion of a rotating vehicle.
■ There are two main types of electric brakes: magnetic and friction.
■ Magnetic brakes are non-contact brakes that use magnetic fields to actuate the
braking components.
■ Types of Electrical Brakes
 Permanent magnetic brake
 Electromagnetic brake
 Eddy current brakes
 Hysteresis powered brakes

26. Permanent Magnetic
Brake
1. Applications: Electric motors, Robotics
2. Advantages: High and accurate Torque, long life, unaffected
by power supply, safe and easy to use
3. Disadvantages: Require a constant current control to offset the
permanent magnetic field.

27. Electromagnetic brake
1. Applications: Copy machines, conveyor drives, packaging machinery,
printing machinery, food processing machinery and factory automation.
2. Advantages: Fast response time, smooth, reliable, and backlash free
operation, produce high torque, automatic air gap available.
3. Disadvantages: Braking force diminishes as speed diminishes, load cannot
be held at a standstill causing safety concern.

28. Eddy current brakes
1. Applications: Train and roller coaster brakes.
2. Advantages: Noncontact, Frictionless, resettable, light weight, few moving
parts.
3. Disadvantages: Unusable at low speeds, generates heat.

29. Hysteresis powered brakes
1. Applications: Food and drug packaging operations, clean rooms, environmental
test chambers, load simulation for life testing on rotating devices, capping,
bolting and other screwing applications.
2. Advantages: Long, maintenance-free life, cost effective, operational,
smoothness, torque repeatability, broad speed range, environmental stability,
high-dissipation capability. The torque remains constant and smooth and
responds with increases and decreases in current.
3. Disadvantages: Experience a salient-pole phenomenon called "cogging", an
undesirable, pulsating output torque which prevents smooth and efficient
operation of these systems

30. Anti-lock Braking System 1
The theory behind anti-lock brakes is simple. A skidding wheel (where the tire contact patch is sliding
relative to the road) has less traction than a non-skidding wheel. If you have been stuck on ice, you know
that if your wheels are spinning you have no traction. This is because the contact patch is sliding relative
to the ice. By keeping the wheels from skidding while you slow down, anti-lock brakes benefit you in two
ways: You'll stop faster, and you'll be able to steer while you stop.
There are four main components to an ABS system:
•Speed sensors
•Pump
•Valves
•Controller

31. ABS 2
Speed Sensors
The anti-lock braking system needs some way of knowing when a wheel is about to lock up. The speed
sensors, which are located at each wheel, or in some cases in the differential, provide this information.
Valves
There is a valve in the brake line of each brake controlled by the ABS. On some systems, the valve has three
positions:
•In position one, the valve is open; pressure from the master cylinder is passed right through to the brake.
•In position two, the valve blocks the line, isolating that brake from the master cylinder. This prevents the
pressure from rising further should the driver push the brake pedal harder.
•In position three, the valve releases some of the pressure from the brake.
Pump
Since the valve is able to release pressure from the brakes, there has to be some way to put that pressure
back. That is what the pump does; when a valve reduces the pressure in a line, the pump is there to get the
pressure back up.
Controller
The controller is a computer in the car. It watches the speed sensors and controls the valves.
Anti-lock Braking System 1

32. ABS 3
ABS at Work
The controller monitors the speed sensors at all times. It is looking for decelerations in the wheel
that are out of the ordinary. Right before a wheel locks up, it will experience a rapid deceleration. If
left unchecked, the wheel would stop much more quickly than any car could. It might take a car five
seconds to stop from 60 mph (96.6 kph) under ideal conditions, but a wheel that locks up could stop
spinning in less than a second.
The ABS controller knows that such a rapid deceleration is impossible, so it reduces the pressure to
that brake until it sees an acceleration, then it increases the pressure until it sees the deceleration
again. It can do this very quickly, before the tire can actually significantly change speed. The result is
that the tire slows down at the same rate as the car, with the brakes keeping the tires very near the
point at which they will start to lock up. This gives the system maximum braking power.
When the ABS system is in operation you will feel a pulsing in the brake pedal; this comes from the
rapid opening and closing of the valves. Some ABS systems can cycle up to 15 times per second.
Anti-lock Braking System 1