HYDRAULIC BRAKE SYSTEM

What does a Brake system do?• A brake system is one of the most important parts of a

vehicle.• The main function of the brake system is to decelerate or

decrease the speed of a vehicle. • By stepping on the brake pedal, the brake pads press

against the rotor attached to the wheel, which then forces the vehicle to slow down due to friction.

• A brake system absorbs the kinetic energy of the vehicle mechanically or electrically in order to decrease its speed. In mechanical brakes, friction converts the kinetic energy into heat. In electric brakes, an electric current forces a magnet to apply the brakes.

Types of Braking systems used in vehicles

• Classification 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 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 Action on Front or Rear Wheels (a) Front-wheel brakes (b) Rear-wheel brakes.

Hydraulic Brake system• Although, there are a variety of brake systems

in use, the most commonly used system is the HYDRAULIC BRAKE SYSTEM which is reliable, easy to use and maintain in vehicles.

• Over 90% of all passenger cars use Hydraulic Brake systems

• Let us now discuss and describe this Hydraulic brake system

Working Principle

• Hydraulic brakes work on the principle of Pascal’s law which states that “pressure at a point in a fluid is equal in all directions in space”.

• The hydraulic principles that permit a brake system to function were discovered by a French physicist, Blaise Pascal (1632–1662).

• Pascal’s Law states that “when force is applied to a liquid confined in a container or an enclosure, the pressure is transmitted equal and undiminished in every direction.” So uniform braking action is applied on all four wheels.

Working principle illustrations

Applied pressure Is exerted equally in all directions.

Transmission of equal pressures to equal areas.

Working principle illustrations

Equal pressure transmitted by fluid(brake fluid) to larger area. (Increasing the Intensity of the

pressure)

Multiple units transmitting pressure from a single source of power

(pressure)

How do you apply the principles to design of Hydraulic system

Pascals lawTransmission of force from pedal to wheel

Intensification of force

How do Hydraulic brakes work

HYDRAULIC BRAKES:

The hydraulic brake is an arrangement of braking mechanism which uses brake fluid(liquid), 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.

HISTORY:

In 1918 Malcolm Lockheed developed a hydraulic brake system,

At that time the mechanised vehicles were just being introduced in the market for use as means of transport.

Hydraulic braking system diagram

Automobile Braking system

Hydraulic Brake system in Automobiles

Automobile hydraulic-brake system.1) Brake pedal; 2) piston; 3) master cylinder; 4) hydraulic line; 5) brake

cylinder; 6) brake piston; 7) brake band; 8) wheel; 9) return spring.

Components of the Hydraulic Brake system

• Brake pedal or lever• Connecting pushrod• A master cylinder assembly with a piston assembly• Hydraulic pipe lines• Wheel Brake assemblies at all four wheels

consisting of – steel pistons (called calliper pistons) in cylinder– a set of brake pads and a brake disc or drum attached to

an axle.• The system is usually filled with a glycol-ether based

brake fluid(liquid)

Increasing Intensity in Force at Pedal

• The distance from the pedal to the pivot is 4 times the distance from the cylinder to the pivot

• The force at the pedal will be increased by a factor of four before it is transmitted to the cylinder (Leverage principle)

• The diameter of the master cylinder is 3 times the diameter of the pedal cylinder. This further multiplies the force by nine(square of diameter)The above steps improve the mechanical advantage thus enabling comfortable

braking

Master cylinder Operation• The master cylinder is the

heart of the brake's hydraulic system.

• It converts the manual force exerted on the brake pedal into hydraulic pressure to apply the brakes.

• Depressing the brake pedal moves the push rod in the master cylinder.

• Mounted on the push rod are a pair of pistons that exert force against the fluid(liquid) in the master cylinder.

Liquid linkage in brakes

• The pressure created moves the fluid through the pipelines to each of the wheels.

• Since brake fluid is incompressible it acts like a liquid linkage between the master cylinder's pistons and wheel cylinders.

Wheel Cylinder Operation• A wheel cylinder is a

component in a drum brake system. It is located in each wheel and 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 with friction. FIGURE 10–8 The pushrods are held in place by the

rubber dust boots. As the wheel cylinder pistons move outward, the pushrods transfer the movement to the brake shoes.

Wheel hub with brake assembly

Friction use for the braking• Friction is a measure of how hard it is to slide

one object over another• Even though the metal or brake surfaces look

smooth to the naked eye they are actually quite rough at the microscopic level

• The little peaks and valley get squished together when brakes are applied to cause braking action to stop the car

• The tires made of rubber also grip the road surfaces and stop during the braking

Brake Pads/drums

Working Principle• Brake pads convert the kinetic energy of the car to thermal

energy by means of friction.Operation• When the brakes are hydraulically applied, the caliper clamps

or squeezes the two pads together into the spinning rotor to slow/stop the vehicle.

• When a brake pad is heated by contact with a rotor, it transfers small amounts of friction material to the disc, turning it dull gray.

• The brake pad and disc (both now with friction material), then "stick" to each other, providing the friction that stops the vehicle.

Brake pads/shoes for acting on wheels

FIGURE 10–9 Steelbrake shoes are made from two stampings welded together—the web and the lining table.

BRAKE FLUID & HOSES• Brake fluids are used to transfer force into pressure.

It works because fluids are incompressible• Since oils damage rubber seals and hoses in the

braking system, brake fluids are not petroleum-based.

• Most brake fluids used today are glycol-ether based, but mineral oil and silicone based fluids are also available.

• The connections between the master cylinder and wheel cylinders are made of copper coated ,tin plated, annealed, steel tubings and flexible hoses.

 

ADVANTAGES OF HYDRAULIC BRAKES

Hydraulic Brake system are very popular compared to the others owing to the following advantages

a) 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.

Disadvantages

However these systems suffer from the following disadvantages which must be overcome for safety in driving an automobile

a) Whole braking system fails due to leakage of fluid from brake linings.

b) Presence of air inside the tubings ruins the whole system.