Q.. Briefly describe construction and working of disc brakes. Compare them with the conventional
drum type brakes.
Disc brakes are very much familiar now-a-days because of their application not only in cars but also in bikes. Most of
the bikes with capacity of 125 CC or more are switching for disc brakes rather than conventional drum type brakes.
Construction of Disc Brakes
Disc brake system consists of cast iron disc, friction pad and a housing termed as caliper. The disc is fixed to wheel hub,
which rotates along with wheel caliper attached to a stationary part such as stub axle or axle casing. It has two compartments,
each compartment consists of a piston, which is connected to friction pad by means of retaining pins, spring plates and rubber
sealing ring between the cylinder and piston. These compartments are provided with a passage for entry and exit of fluid. Also
these are connected to each other for bleeding as shown in figure.
When the force is exerted on the brakes, the piston is activated hydraulically due to which both the friction pads mo
towards the disc. The friction pads stop the revolving disc(in turn stops the vehicle). When the brake is released, the pa
move away from the disc due to rubber sealing ring which acts as return spring.
Comparison of Disc Brakes and Drum Brakes
1. Disc brake consists of a revolving circular disc
and a caliper with a pair of friction pads,
2.It has better cooling effect because friction
surface is exposed to air.
3.Higher brake efficiency is obtained.
4.Overall weight of disc brake is lesser than
conventional drum brakes.
5.It offers better resistance to fade.
6.Simple in design and less number parts to
7.Initial cost is more.
8.Easier to replace friction pads.
1.Drum brake consists of a revolving drum with a
pair of brake shoes inside it.
2.Friction occurs on the internal surface, so heat is
transferred only when it is conducted to drum.
3.Brake efficiency is lower than disc brakes.
4.Heavier due to more number of components. 5.Anti-fade characteristics are low. 6. Design is complex than disc type with more components are subjected to wear.
7. Less expensive than disc brakes.
8 Difficult to replace because brake lining is either revetted or fixed with adhesives to brake shoe.
Q.. Describe with a neat sketch, the working of floating caliper type disc brake.
Floating Caliper Type Disc Brake
A typical floating caliper type has only a single piston that is located on the inboard side of the disc.
*The caliper floats (or) moves on rubber bushings on one/two steel guide pins.
* When the brakes are applied, the bushings allow the caliper to move slightly. *Some floating calipers have two pistons located on the inboard side of the disc.
* On applying the brakes, it causes the brake fluid to flow into the caliper. *This pushes the piston outward, due to which the inboard shoe is forced against the disc.
*At the same time, the pressure pushes against the caliper with an opposite and equal force. *The reaction causes the caliper to move on the bushings slightly, thereby bringing the outboard shoe into contact with the disc.
*Hence, the braking action is produced when the two pads clamp the disc.
Q.. Discuss clearly how the air brakes are adjusted with the help of a slack adjuster.
Air brakes are used to apply brakes by using compressed air from the reservoir. Firstly, air is taken from atmosphere
through filters to compressor pay an unloaded valve compressed air is transferred to reservoir.
Slack adjuster in air brake system is used to adjust the clearance between brake shoe and drum. It is easy and qu
method. It consists of a forged steel body, worm, worm wheel, adjusting nut and worm shaft. Adjusting nut mounted on
through worm which is in mesh with worm wheel.
When adjusting nut turns, the worm rotates the cam through worm wheel in between a pair of rollers, which cause
movement of brake shoe against the drum. The locking of worm shaft can be achieved by using a spring loaded loc
hexagonal head of shaft. Lock itself is prevented from rotating by a pin fixed to body.
The slack adjuster and push rod from brake chain should make an angle greater than 90°. For its preventive maintens
it should be lubricated with good grade of chasis grease after every six months or 16000 km.
Q.. Explain the working of wheel cylinder.
The function of wheel cylinder is to convert the hydraulic pressure from the master cylinder into mechanical movement
When the driver presses the brake pedal, brake fluid flows from a pressure chamber in the master cylinder through brake line
to the wheel cylinder. It has two pistons, with seals or cups, and a spring in between them. As the pressure increases, the pisto
overcome the tension of the brake shoe return spring and pushes the shoes outward. This motion is transmitted to the brake
shoes directly or through links, which force them against the brake drum, thus applying the brake. Wheel cylinder is also known as slave cylinder. It is fitted next to the master cylinder in the hydraulic brake system.
The front wheel cylinders are larger sometimes because, when the brakes are applied, the forward momentum of vehicle throws more weight on the front wheels. To have stronger braking effort, the wheel cylinders are larger at front.