Q.. Discuss the design considerations regarding the discs and friction pads of disc brakes.


Design Considerations of Discs of Disc Brake System

Initially discs were made of cast steel because cast steel has higher co-efficient of friction and wear is less. The disc was
not widely used because of uniform frictional property is very low. Later on, grey cast iron discs are produced as the material
is cheap and has good-anti wear properties but not comparatively better than cast steel. In latest advancements, discs are
manufactured with materials like ceramics and carbon fibres. These type of discs are mostly used in sports and racing cars
These materials are lighter in weight than any of the previous material used for disease. It reduces the overall weight of th
vehicle which in turn improves the steering system and dynamics of the vehicle.

The other considerations are,
1. High wear-resistant materials to be used for discs.
2. For different purposes, different types of disc rotors are used.

They are classified into four types as follows:

(a) Solid type disc                                                                                  (b) Ventilated type disc)
(c) Solid type with drum                                                                        (d) Spiral fin type disc.

Design Considerations for Brake Pads of Disc Brakes

Different brake design applications demand different brake friction pads. Some of the design considerations are a

1.Brake pad should withstand highest temperature without fading.
2.It should not wear out rapidly and should not wear the disc rotor.
3.The coefficient of friction should be constant for wide range of temperatures                                                                                        4.It should not produce noise.
5. It should resist the highest torque produced.                                    6.The material used for brake pads should have good bonding and adhesive properties.
7.Brake pads should be considerably thick, for a given initial cost, so that more wear can take place before they replaced.


Q.. Explain clearly the working of the grilling mechanical brakes.


Grilling Mechanical Brakes

The essential units of the grilling mechanical brakes are expander unit, adjuster unit and a compensator. In this type of
braking system, the braking pedal is connected to the shoe assemblies by a system of high tensile rods and levers. These rods
are maintained in tension at all time by a plunger, which is spring loaded and the levers are combined with compensatory. This
rod operates the expander which forces the shoes to contact the inner surface of a brake drum attached to the hub of each road
wheel. A central compensator is used to divide the available pedal force between the front and rear axles. Basically, grilling
mechanical brakes employ a wedge movement for expanding the brake shoes. Moreover, in these brakes, all the brake rods ar
in tension. They are lightly loaded. With the help of these brakes, the effort on the pedal applied by driver is multiplied to abou
six times. One of the important feature of grilling brake mechanism is that there is no need to jack the vehicle while carryin
brake adjustment.


Q.. Describe the mechanical brake system with
the help of a neat sketch.


Describe any one type of mechanical brake
with the help of a neat sketch.


Mechanical Brake System

The mechanical brake system contains,
1. A brake drum or auxiliary wheel
2. Pair of brake shoes with brake linings
3.A cam to expand the shoes
4. Brake shoes return spring
5. Anchor pins                                                                                        6. Linkages.


The brake drum on which the automobile wheel is
mounted or attached houses a pair of brake shoes. These
brake shoes are generally mounted to rub against the inner
surface of the brake drum, which is operated by a cam. Little
clearance is maintained between the inner surface of the brake
drum and the shoe in normal position or when the system is
not operated. The wheel attaching bolts on the drum are used
to connect wheel and drum. Entire mechanism is enclosed
inside the brake drum. The enclosure of the system is
completed by a braking plate which bolds the assembly to the
vehicle axle. This also acts as the base for fastening the brake
shoes and operating mechanism.

Each brake shoe is pivoted on an anchor pin on the
brake backing plate at one end. The other end of the anchor
pin in the shoe rests on a cam. Each brake shoe has brake
lining fastened or riveted on the outer surface.


When the driver presses the brake pedal, the cam on
the brake backing plate is operated through linkages and
expands the brake shoes. The action causes the brake shoe
lining to rub against the rotating brake drum. Since, the force
of friction is opposite to the direction of drum rotation, the
friction between the drum surface and the shoe linings serve
to slow down or stop the rotation of the drum, causing the
vehicle to stop. When the effort on the brake pedal is released,
the brake shoe return spring against its tension where the
brake shoe linings are expanded, and will be drawn back to its original position or released position.this system is also called internal expanding brake system.
In another system, where the brake shoe linings are placed on the outerside of a drum and operated to bring the vehicle
to halt is known as “external-contracting brakes”. Normally, these brakes are used in parking and emergency brake”.




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