Hydraulic brake system Thehydraulic brakeis an arrangement ofbrakingmechanism which usesbrake fluid, to transfer pressure from the controlling unit, which is usually near the operator of the vehicle, to the actual brake mechanism, which is usually at or near the wheel of the vehicle.CLASSIFICATION OF BRAKES On the Basis of Method of Actuation (a) Foot brake (also called service brake) operated by foot pedal. (b) Hand brake it is also called parking brake operated by hand. On the Basis of Mode of Operation (a) Mechanical brakes (b) Hydraulic brakes (c) Air brakes (d) Vacuum brakes (e) Electric brakes. On the Basis of Action on Front or Rear Wheels (a) Front-wheel brakes (b) Rear-wheel brakes. On the Basis of Method of Application of Braking Contact (a) Internally expanding brakes (b) Externally contracting brakes.

PRINCIPLES OF HYDRAULIC BRAKING Hydraulic brakes work on the principle of Pascals law which states that pressure at a point in a fluid is equal in all directions in space. According to this law when pressure is applied on a fluid it travels equally in all directions so that uniform braking action is applied on all four wheels

CONSTRUCTION

Brake pedalor lever A pushrod Amaster cylinder assemblycontaining apistonassembly Reinforced hydraulic lines Brake calliper assemblyusually consisting of one or two hollow aluminium or chrome-plated steel pistons (calledcalliper pistons), a set of thermally conductivebrake padsand arotor(also called a brake disc) ordrumattached to an axle. The system is usually filled with aglycol-etherbased brake fluid

A) MASTER CYLINDER

Themastercylinderis the heart of the brake's hydraulic system. It converts the force exerted on the brake pedal into hydraulic pressure to apply thebrakes. Depressing the brake pedal moves a push rod in the mastercylinder. Mounted on the push rod are a pair of pistons (primary and secondary) in tandem (one after the other) that exert force against the fluid in the master cylinder bore. The pressure created displaces fluid through the various brake circuits and lines to each of the wheels and applies the brakes. Since brake fluid is incompressible it acts like a liquid linkage between the master cylinder's pistons and the calipers and wheel cylinders.

Tandem master cylinder

if a leak develops in the front brake system:a) Piston 1 will move forward until it contacts Piston 2. Force from the brake pedal will be transmitted mechanically through Piston 1 to Piston 2.b) Although overall braking performance will be severely compromised, the rear brakes will still be functional provided sufficient pedal travel is available. The pedal will need to travel further than normal to fully engage the rear brakes. Also, it should be appreciated that trying to stop quickly with just the rear brakes is very tricky because the rear tires will easily reach the point of lock-up

If a leak develops in the rear brake system,a) Piston 2 will move forward until it contacts the closed end of the master cylinder housing. b) Once Piston 2 becomes stationary, pressurization of fluid between the two pistons will apply the front brakes. c) Although overall braking performance will be significantly compromised, the front brakes will still be functional provided sufficient pedal travel is available. The pedal will need to travel further than normal to fully engage the front brakes.

B) WHEEL CYLINDER Awheel cylinderis a component in adrum brakesystem. It is located in eachwheeland is usually at the top, above the shoes. Its responsibility is to exert force onto the shoes so they can contact the drum and stop the vehicle withfriction. The wheel cylinder consists of a cylinder that has two pistons, one on each side. Each piston has a rubber seal and a shaft that connects the piston with a brake shoe. When brake pressure is applied, the pistons are forced out pushing the shoes into contact with the drumC) BRAKE SHOES Brake shoes are made of two pieces of sheet steel welded together. The friction material is attached to the Lining table either by adhesive bonding or riveting. The crescent shaped piece is called the Web and contains holes and slots in different shapes for return springs. All the application force of the wheel cylinder is applied through the web to the lining table and brake lining. Each brake assembly has two shoes, a primary and secondary. The primary shoe is located toward the front of the vehicle and has the lining positioned differently than the secondary shoe

D) BRAKE DRUM The brake drum is generally made of a special type of cast iron. It is positioned very close to the brake shoe without actually touching it, and rotates with the wheel and axle. As the lining is pushed against the inner surface of the drum, friction heat can reach as high as600 F(316C). The brake drum must be:a) Accurately balanced.b) Sufficiently rigid.c) Resistant against wear.d) Highly heat-conductive.e) Lightweight.

E) BRAKE FLUID Brake fluids are used to transfer force into pressure. It works becauseliquidsareincompressible. Since oils damage rubber seals and hoses in the braking system, brake fluids are not petroleum-based. Most brake fluids used today are glycol-etherbased, but mineral oil and silicone (DOT 5) based fluids are also available. Boiling point: a) Brake fluid is subjected to very high temperatures, especially in the wheel cylinders of drum brakes and disk brake calipers.b) It must have a high boiling point to avoid vaporizing in the lines. This vaporization is a problem because vapor is compressible and negates hydraulic fluid transfer of braking force. Viscositya) For reliable, consistent brake system operation, brake fluid must maintain a constant viscosity under a wide range of temperatures, including extreme cold. This is especially important in systems with ananti-lock braking system(ABS), traction control, and stability control (ESP). Corrosion a) Brakes fluids must not corrode the metals used inside components such as calipers, master cylinders, etc. Compressibilitya) Brake fluids must maintain a low level of compressibility that remains low, even with varying temperatures.

F) BRAKE LINES AND HOSES The connections between the master cylinder and wheel cylinders are made of copper coated, tin plated, annealed, steel tubings and flexible hoses. A flexible hose is made up of alternate layers of rubber and fabric sheets wound over each other. These are used to connect the steering front wheels.OPERATION OF A HYDRAULIC BRAKE SYSTEMa) as the brake pedal is pressed,i. 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 which results in an increase in the pressureii. This forces fluid through the hydraulic lines toward calipers where it acts upon one or two caliper pistons iii. 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 brakingtorqueto be generated, slowing the vehicle.

ADVANTAGES AND DISADVANTAGES OF HYDRAULIC BRAKESa) Equal braking action on all wheels.b) Increased braking force.c) Simple in construction.d) Low wear rate of brake linings.e) Flexibility of brake linings.f) Increased mechanical advantage.