The Hydraulic brake system is a braking system which uses brake
fluid usually includes ethylene glycol, to transmit pressure from
the controlling unit, which is usually near the driver, to the
actual brake mechanism, which is near the wheel of the vehicle.
The most common arrangement of hydraulic brakes for passenger
vehicles, motorcycles, scooters, and mopeds, consists of the following
- Brake pedal or Brake lever
- Pushrod, also called an actuating rod
- Reinforced hydraulic lines
- Rotor or a brake disc or a drum attached to a wheel
- Master cylinder assembly includes:
Piston assembly is made up of one or two pistons,
a return spring, a series of gaskets or O-rings.
Fluid reservoir
- Brake caliper assembly usually includes:
One or two hollow aluminum or chrome-plated steel
pistons called caliper pistons.
Set of thermally conductive brake pads.
A glycol-ether based brake fluid regularly loads the system or
some other fluids are also used to control the transfer of force
or power between the brake lever and the wheel.
The automobiles generally use disc brakes on the front wheels
and drum brakes on the rear wheels. The disc brakes have good
stopping performance and are usually safer and more efficient
than drum brakes. The four wheel disc brakes are more popular,
swapping drums on all but the most basic vehicles. Many two wheel
automobiles design uses a drum brake for the rear wheel.
Operation of Hydraulic Brake System
In Hydraulic brake system when the brake pedal or brake lever
is pressed, a pushrod applies force on the piston in the master
cylinder causing fluid from the brake fluid tank to run into a
pressure chamber through a balancing port which results in increase
in the pressure of whole hydraulic system. This forces fluid through
the hydraulic lines to one or more calipers where it works upon
one or two extra caliper pistons protected by one or more seated
O-rings which prevent the escape of any fluid from around the
piston.
The brake caliper piston then apply force to the brake pads.
This causes them to be pushed against the rotating rotor, and
the friction between pads and rotor causes a braking torque to
be generated, slowing the vehicle. Heat created from this friction
is dispersed through vents and channels in rotor and through the
pads themselves which are made of particular heat-tolerant materials
like kevlar, sintered glass, et al.
The consequent discharge of the brake pedal or brake lever lets
the spring(s) within the master cylinder assembly to return that
assembly piston(s) back into position. This reduces the hydraulic
pressure on the caliper lets the brake piston in the caliper assembly
to slide back into its lodging and the brake pads to discharge
the rotor. If there is any leak in the system, at no point does
any of the brake fluid enter or leave.
Components
In hydraulic brake the brake pedal is called as brake pedal or
brake lever. One end of the hydraulic brake is connected to the
frame of the vehicle, the other end is connected to the foot pad
of the lever and a pushrod extends from a point along its length.
The rod either widens to the master cylinder brakes or to the
power brakes.
The master cylinder is separated as two parts in cars, each of
which force a separate hydraulic circuit. Every part provides
force to one circuit. Passenger automobiles usually contain either
a front/back split brake system or a transverse split brake system.
A front/rear split brake system utilizes one master cylinder
part to pressure the front caliper pistons and the other part
to pressure the rear caliper pistons. A split circuit braking
system is now necessary by rules in many countries for security
purposes, if one of the circuit fails the other circuit can stop
the automobile.
The diameter and length of the master cylinder contains a major
outcome on the performance of the brake system. The bigger diameter
master cylinder delivers more hydraulic fluid to the caliper pistons,
yet requires more brake pedal force and less brake pedal stroke
to achieve a given deceleration. A smaller diameter master cylinder
has the opposite effect.
A master cylinder may also use dissimilar diameters among the
two sectors to let improved fluid volume to one set of caliper
pistons or the other.
Power Brakes in Hydraulic Brake System
The power brake or vacuum booster is used in current hydraulic
brake systems in cars and other automobiles. The power brake or
vacuum booster is connected among the master cylinder and the
brake pedal which increases the brake force applied by the driver.
These parts contain an empty housing with a changeable rubber
diaphragm across the middle, making two chambers.
When power brake is connected to the small pressure part of the
throttle body or intake manifold of the engine the pressure in
both parts of the unit is decreases. The stability created by
the low pressure in both chambers remains the diaphragm from moving
until the brake pedal is depressed. A return spring remains the
diaphragm in the initial position until the brake pedal is applied.
When brake is applied through the brake pedal, the movement open
an air valve which lets in atmospheric pressure air to one chamber
of the booster. The pressure becomes higher in one part, the diaphragm
goes to the lower pressure part with a force produced by the part
of diaphragm and differential pressure. This force, in addition
to the automobile driver foot force, pushes on the master cylinder
piston.
A moderately tiny diameter booster element is necessary for
a very traditional 50% various vacuum, a secondary force of about
1500 N or 150 kgf is created by a 20cm diaphragm with an area
of 0.03 square meters. The diaphragm will stop moving when the
forces on both sides of the part attain balance. This is caused
by the air valve closing which is due to the pedal apply stopping
or run out is attained. Run out arises when the pressure in one
part attains atmospheric pressure and no extra force is produced
by the currently inactive differential pressure. After the run
out point is attained, only the driver foot force is used to apply
the master cylinder piston.
The fluid pressure from the master cylinder moves through couple
of steel brake tubes to pressure differential valve called as
brake failure valve, which do two functions. It balances pressure
among the two systems, and it offers a caution if one system drops
pressure. The pressure differential valve has two chambers which
are connected to hydraulic lines through a piston among them.
When the pressure in either line is balanced, the piston does
not move. If the pressure on one side is misplaced, the pressure
from the other side moves the piston. When the piston creates
contact through a simple electrical probe in the center of the
unit, a circuit is completed, and the operator is warned of a
failure in the brake system.
The brake tubing takes the pressure to brake elements at the
wheels from the pressure differential valve. The wheels do not
uphold a permanent relation to the automobile, hydraulic brake
hose is used from the end of steel line on vehicle frame to the
caliper at wheel. When steel brake tubing is let to flex, it encourages
metal fatigue and finally the brake collapses. It is to replace
the typical rubber hoses with braided stainless-steel wires which
are outwardly reinforced, have slight increase under pressure
and provide a firmer sense to the brake pedal with less pedal
move for a known braking attempt.
See also
Air Brake
Antilock Brake System
Disc Brake
Drum Brake
