Palli Goutham Reddy 17BME0720: Hydraulic Brakes

PALLI GOUTHAM REDDY
17BME0720
Hydraulic Brakes
A hydraulic brake is an arrangement of braking mechanism which uses brake fluid, typically
containing glycol ethers or diethylene glycol, to transfer pressure from the controlling mechanism to
the braking mechanism.
The most common arrangement of hydraulic brakes for passenger vehicles, motorcycles, scooters,
and mopeds, consists of the following:
Brake pedal or lever

A pushrod (also called an actuating rod)
A master cylinder assembly containing a piston assembly (made up of either one or two pistons, a
return spring, a series of gaskets/ O-rings and a fluid reservoir)
Reinforced hydraulic lines
Brake caliper assembly usually consisting of one or two hollow aluminum or chrome-plated steel
pistons (called caliper pistons), a set of thermally conductive brake pads and a rotor (also called a
brake disc) or drum attached to an axle.
The system is usually filled with a glycol-ether based brake fluid (other fluids may also be used).
At one time, passenger vehicles commonly employed drum brakes on all four wheels. Later, disc
brakes were used for the front and drum brakes for the rear. However disc brakes have shown better
heat dissipation and greater resistance to 'fading' and are therefore generally safer than drum brakes.
So four-wheel disc brakes have become increasingly popular, replacing drums on all but the most
basic vehicles. Many two-wheel vehicle designs, however, continue to employ a drum brake for the
rear wheel.
The following description uses the terminology for / and configuration of a simple disc brake.
System operationU.S. Army training film: Hydraulic Brake Operations (circa 1983) Play
media
In a hydraulic brake system, when the brake pedal is pressed, a pushrod exerts force on the piston(s)
in the master cylinder, causing fluid from the brake fluid reservoir to flow into a pressure chamber
through a compensating port. This results in an increase in the pressure of the entire hydraulic system,
forcing fluid through the hydraulic lines toward one or more calipers where it acts upon one or more
caliper pistons sealed by one or more seated O-rings (which prevent leakage of the fluid).
The brake caliper pistons then apply force to the brake pads, pushing them against the spinning rotor,
and the friction between the pads and the rotor causes a braking torque to be generated, slowing the
vehicle. Heat generated by this friction is either dissipated through vents and channels in
the rotor or is conducted through the pads, which are made of specialized heat-tolerant materials
such as kevlar or sintered glass.
Alternatively, in a drum brake, the fluid enters a wheel cylinder and presses one or two brake shoes
against the inside of the spinning drum. The brake shoes use a similar heat-tolerant friction material
to the pads used in disc brakes.
Subsequent release of the brake pedal/lever allows the spring(s) in the master cylinder assembly to
return the master piston(s) back into position. This action first relieves the hydraulic pressure on the
caliper, then applies suction to the brake piston in the caliper assembly, moving it back into its
housing and allowing the brake pads to release the rotor.The hydraulic braking system is designed as
a closed system: unless there is a leak in the system, none of the brake fluid enters or leaves it, nor
does the fluid get consumed through use. Leakage may happen, however, from cracks in the O-rings
or from a puncture in the brake line. Cracks can form if two types of brake fluid are mixed or if the
brake fluid becomes contaminated with water, alcohol, antifreeze, or any number of other liquids.
Pneumatic
Brakes
An air brake or, more formally, a compressed air brake system, is a type of friction brake for vehicles
in which compressed air pressing on a piston is used to apply the pressure to the brake pad needed to
stop the vehicle. Air brakes are used in large heavy vehicles, particularly those having multiple
trailers which must be linked into the brake system, such as trucks, buses, trailers, and semi-trailers,
in addition to their use in railroad trains. George Westinghouse first developed air brakes for use in
railway service.[1] He patented a safer air brake on March 5, 1872.[2][3] Westinghouse made
numerous alterations to improve his air pressured brake invention, which led to various forms of the
automatic brake. In the early 20th century, after its advantages were proven in railway use, it was
adopted by manufacturers of trucks and heavy road vehicles.
Design and function
Air brake systems are typically used on heavy trucks and buses. The system consists of service
brakes, parking brakes, a control pedal, and an air storage tank. For the parking brake, there is a disc
or drum arrangement which is designed to be held in the 'applied' position by spring pressure. Air
pressure must be produced to release these "spring brake" parking brakes. For the service brakes (the
ones used while driving for slowing or stopping) to be applied, the brake pedal is pushed, routing the
air under pressure (approx 100–120 psi or 690–830 kPa or 6.89–8.27 bar) to the brake chamber,
causing the brake to be engaged. Most types of truck air brakes are drum brakes, though there is an
increasing trend towards the use of disc brakes. The air compressor draws filtered air from the
atmosphere and forces it into high-pressure reservoirs at around 120 psi (830 kPa; 8.3 bar). Most
heavy vehicles have a gauge within the driver's view, indicating the availability of air pressure for
safe vehicle operation, often including warning tones or lights. A mechanical "wig wag" that
automatically drops down into the driver's field of vision when the pressure drops below a certain
point is also common. Setting of the parking/emergency brake releases the pressurized air in the lines
between the compressed air storage tank and the brakes, thus allowing the spring actuated parking
brake to engage. A sudden loss of air pressure would result in full spring brake pressure immediately.
A compressed air brake system is divided into a supply system and a control system. The supply
system compresses, stores and supplies high-pressure air to the control system as well as to
additional air operated auxiliary truck systems (gearbox shift control, clutch pedal air assistance
servo, etc.).

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Brake pedal or lever

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