30-03-2010, 08:02 PM
Hydraulic Brake System
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.
System Operation
Within a hydraulic brake system, as the brake pedal is pressed/ brake lever is squeezed, 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 which results in an increase in the pressure of the entire hydraulic system. This forces fluid through the hydraulic lines toward one or more calipers where it acts upon one or two additional caliper pistons secured by one or more seated O-rings which prevent the escape of any fluid from around the piston.
The brake caliper piston(s) then apply force to the brake pads. This causes them to be pushed 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 from this friction is often dissipated through vents and channels in the rotor and through the pads themselves which are made of specialized heat-tolerant materials
Subsequent release of the brake pedal/ lever allows the spring(s) within the master cylinder assembly to return that assembly's piston(s) back into position. This relieves the hydraulic pressure on the caliper allowing the brake piston in the caliper assembly to slide back into its housing and the brake pads to release the rotor. Unless there is a leak somewhere in the system, at no point does any of the brake fluid enter or leave.
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.
