BRAKING UNIT

Brakes

• A brake is a mechanical device which is used to slow down or stop a moving vehicle.

• Types - 1. Friction Brake – a) Drum Brake b) Disc Brake 2. Magnetic Brake 3. Vacuum Brake

• Friction brake - A friction brake is a type of automotive brake that slows or stops a vehicle by converting kinetic energy into heat energy, via friction. The heat energy is then dissipated into the atmosphere.

Drum brake - A drum brake is a vehicle brake in which the friction is caused by a set of brake shoes that press against the inner surface of a rotating drum. The drum is connected to the rotating roadwheel hub.

• Types of Drum brakes - 1. Non-servo brakes.2. Servo brakes.

3. Non-servo brakes – each brake shoe is applied individually and the action of one shoe has no effect on the action of the other.

• It uses self-energizing action to improve braking performance.

2. Servo brakes – It is the most common drum design . It gets its name from the fact that one shoe “serves” the other to increase application force .

• Used primarily on trucks and provide additional stopping power in the forward direction only .

Disc brake - A brake disc is connected to the wheel or the axle. To stop the wheel, friction material in the form of brake pads (mounted in a device called a brake caliper) is forced mechanically, hydraulically, pneumatically or electromagnetically against both sides of the disc.

Disc Brake

8

Front Disc Brake

• Electromagnetic brake - Electromagnetic brakes slow an object through electromagnetic induction, which creates resistance and in turn either heat or electricity.

• Vacuum brake - The vacuum brake was originally devised for use on trains. These types of brakes works by creating air pressure changes in a compartment called the brake cylinder.

Brake actuators

The method by which the force from your hand or foot reaches the brake itself.

• Cable-operated -

• Solid bar connection -

Disadvantage - it needs hinge and pivot points. If they're not present, going over a bump could put the brakes on as the suspension moves relative to the lever.

• Single-circuit hydraulic -

• Dual-circuit hydraulic -

• Brake-by-wire -

• Power brakes - Power brakes are a system of hydraulics. It uses a combination of mechanical component to multiply the force applied to the brake pedal into enough force to actuate the brakes and stop a vehicle that can weigh several tons.

• Components – Vacuum Booster Master Cylinder Brake Calipers Drum Brakes

• The brake pedal is connected to the Vacuum booster. The booster passes the force to the Master Cylinder which compresses a liquid and forces it through the brake lines to the brakes themselves.

• The liquid that is pushed into the brakes activates the Brake Calipers which in the case of Disc Brakes, push against the brake rotor causing friction that slows and eventually stops the rotation of the vehicles wheels.

• Vacuum Booster - The vacuum booster was invented in 1927 in order to provide a shorter stopping distance. Vacuum boosters provide brake assist for the driver by multiplying the force out of the booster creating more than the force that was used to push on the brake pedal.

• Master cylinder – It is a control device that converts non-hydraulic pressure (commonly from a driver's foot) into hydraulic pressure. This device controls slave cylinders located at the other end of the hydraulic system.

• Electromagnetic brake - Electromagnetic brakes slow an object through electromagnetic induction, which creates resistance and in turn either heat or electricity.

• Vacuum brake - The vacuum brake was originally devised for use on trains. These types of brakes works by creating air pressure changes in a compartment called the brake cylinder.

Power Brake

Vacuum brake

Anti lock Braking Systems – ABS

It is an automobile safety system that allows the wheels on a motor vehicle to maintain tractive contact with the road surface according to driver inputs while braking, preventing the wheels from locking up (ceasing rotation) and avoiding uncontrolled skidding.

• Four-channel, four-sensor ABS - There is a speed sensor on all four wheels and a separate valve for all four wheels. With this setup, the controller monitors each wheel individually to make sure it is achieving maximum braking force.

• Three-channel, three-sensor ABS – It has a speed sensor and a valve for each of the front wheels, with one valve and one sensor for both rear wheels. This system provides individual control of the front wheels, so they can both achieve maximum braking force.

• One-channel, one-sensor ABS – It has one valve, which controls both rear wheels, and one speed sensor, located in the rear axle. This system operates the same as the rear end of a three-channel system.

Brake Fluid

• Brake fluid is a type of hydraulic fluid used in hydraulic brake and hydraulic clutch.Applications- automobiles, motorcycles, light trucks, and some bicycles.

It is used to transfer force into pressure, and to amplify braking force. It works because liquids are not appreciably compressible — in their natural state the component molecules do not have internal voids and the molecules pack together well, so bulk forces are directly transferred to compress the fluid's chemical bonds.

26

Brake LiningsBrake linings are probably the most mis-understood part of a brake system.

The output of any brake is directly related to the coefficient of friction (µ) between the lining and the disc or drum.

The challenge is knowing what the instantaneous value of µ is during any given stop.

Any design calculations you do, go right out the window if the lining you use does not have the µ value you assumed.

Brake Linings• These are the friction materials that a vehicle uses.• They can be bonded (glued), riveted, and injection

molded to the backing pad or shoes.

Types of Linings• Asbestos- these have phased out, very hazardous

to breath the dust.• Organic- mixture of asbestos and organic materials

with a resin binder• Semi-metallic- organic mixed with metal shavings,

last longer and very good at dissipating heat.• Ceramic – low dust output, provide exceptional

braking performance • Carbon/Kevlar- Motor sports application, not used

on road vehicles because of cost and they take time to warm up.

• This is why we don’t use a bow gun to clean brakes or brake parts (asbestos is hazardous in the airborne form)

Actuation Sub-system

• Brake Pedal

• Master Cylinder

• Proportioning Valves

• Brake Lines

The Brake Pedal

Driver Input

Output to master cylinder

100 N and 144 mm

400 N and 36 mm4:1 NominalPedal Ratio

Both Front Wheels Locked

Not good if you are on a curved road

You can’t steer

OK, if you must hit something

The vehicle goes straight

Both Rear Wheels Locked: The front wheels track straight ahead

Then the rear wheels deviate to the side Until the vehicle can’t track straight any longer

and the rear starts to spin around the front

Front LockIf there is more front brake torque than dynamic front weight

The front wheels will lock up before the rears

20%80% 40% 60%

Brake torquedistribution

Dynamic weight distribution

Rear LockIf there is more rear brake torque than dynamic rear weight;

The rear wheels will lock up before the fronts

40% 60% 20% 80%

Brake torquedistribution

Dynamic weight distribution

Optimum BrakingOptimum braking is achieved when brake torque distribution matches dynamic weight distribution

Weight Distribution

No Braking Hard Braking

40% 60% 20% 80%

Brake Fade

Brake fade is the loss of performance resulting from the lining friction decreasing as the lining and rotor

or drum rises in temperature

Formula SAE• Absolute reliability• High Speeds• Maximum possible decel without locking• Consistent balance with changing temperatures

Mini Baja• Absolute reliability• Low Speeds• Very hostile environment• Brake must work when wet and muddy

THANK YOU