AUTOMOTIVE BRAKING SYSTEMS

Figure 1http://www.autonest.org/wp-content/uploads/2011/08/TiresStopFeaturedImage.jpg

Donald E Maurer

Overview

Your driving a car or truck. You press on the brake pedal, what happens?

A vehicle car goes through a process that multiplies the force you apply to the brake pedal with your foot and leg to stop the car.

This force is transmitted to the road through a series of parts using fluid pressure in most of today’s vehicles.

Brake components and their functions

THE BRAKE PEDAL

There are two or three pedals in today’s vehicles.

The pedal in the middle, or the pedal that is immediately left of the gas pedal is the brake pedal.

The main purpose of the brake pedal is to multiply the force that is exerted by the driver to slow and stop the vehicle.

BRAKE BOOSTER

Brake boosters are only used with power braking systems. This is standard on today’s vehicles.

The booster is used to provide more braking power while reducing the required effort from the driver.

Booster’s usually operate by using the vacuum from the vehicle engine.

Not all vehicles have this type of booster. Some provide assistance electrically.

Not all vehicles will have a booster. Some will be direct pressure from the driver.

Brake Booster

Figure 2http://t0.gstatic.com/images?

q=tbn:ANd9GcTC93pTwXrSYaFoEjNwglWalDE8p83QqGmGhyjxN-0yZAZEB487

MASTER CYLINDER

A master cylinder is provided to convert force from the booster into hydraulic pressure. If the vehicle does not

have a booster the pressure is converted from the brake pedal.

It is easier to transfer hydraulic pressure than mechanical pressure to the brakes.

Figure 3http://www.aa1car.com/library/brake_master_cylinder.gif

BRAKE FLUID, LINES, AND HOSES

Fluid pressure travels from the master cylinder through the brake lines to the brakes at each wheel of the vehicle.

Brake lines are rigid except at the wheels where it is necessary to provide flexibility because of the movement of the suspension.

The rigid lines are either steel or a composite material that can withstand the corrosive environment under the vehicle.

Part of the line is steel while a short flexible material (reinforced rubber) is used to connect it to the moving parts.

Brake fluid must withstand extreme pressure and temperature changes. It’s VERY important that the fluid:

Cannot be compressed Has a very high boiling point and flash

point Will not cause corrosion on the inside of

brake lines Can withstand extreme cold without

thickening

Hydraulic Disk Brake Diagram

Figure 4http://upload.wikimedia.org/wikipedia/commons/thumb/7/76/

Hydraylic_disc_brake_diagram.jpg/619px-Hydraylic_disc_brake_diagram.jpg

BRAKE CALIPERS

Fluid must be converted from hydraulic pressure to mechanical pressure.

Calipers contain a piston/s that convert hydraulic fluid pressure back to mechanical pressure.

A bigger piston or multiple pistons will produce more force. Racing or high performance applications

will use 4 or even 6 pistons in the caliper. Calipers are used with disk brake

systems.

BRAKE PADS

Brake pads are forced against the rotor by pressure applied from the caliper.

Friction from the contact between the pad and rotor slows the speed of the rotor.

This friction produces heat.

BRAKE ROTORS

The rotor is acted upon by the brake pads.

The friction produced is converted into torque at the wheel.

Rotors must be able to dissipate heat. Many rotors are made with cooling fins

that help to quickly dissipate heat. Rule of thumb – the bigger the rotor is, the

better it is at reducing heat, the better the stopping power of the brakes.

Brake Rotors, Calipers, Pads

Figure 5http://t1.gstatic.com/images?q=tbn:ANd9GcRD-

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WHEELS AND TIRES

The wheels and tires provide the contact between the vehicle and the road.

The primary function is to provide traction.

Traction works three ways: Increased acceleration. Shortened stopping distance. Increased cornering or handling.

Wheels and Tires

Figure 6http://t3.gstatic.com/images?q=tbn:ANd9GcQE5qr5y0F-

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In Summary

The brake system is designed to increase the pressure you apply to the brake pedal.

The increased pressure is applied to the calipers through hydraulics.

The calipers convert the hydraulic pressure back to mechanical force against the rotors.

The rotors apply torque to the wheels. The wheels and tires provide traction to

stop the vehicle.

Reference Erjavec, J (2010).Automotive Technology: A Systems

Approach. Clifton Park, NY: Delmar, Cengage Learning. (p1424-1456)Inline Citation -- (Erjavec, 2010)

Figures1. From autonest.org:

http://www.autonest.org/wp-content/uploads/2011/08/TiresStopFeaturedImage.jpg

2. From seecharanautospares.com:http://t0.gstatic.com/images?q=tbn:ANd9GcTC93pTwXrSYaFoEjNwglWalDE8p83QqGmGhyjxN-0yZAZEB487

3. From aa1car.com:http://www.aa1car.com/library/brake_master_cylinder.gif

4. From upload.wikimedia.org:http://upload.wikimedia.org/wikipedia/commons/thumb/7/76/Hydraylic_disc_brake_diagram.jpg/619px-Hydraylic_disc_brake_diagram.jpg

5. From truckinweb.com: http://t1.gstatic.com/images?q=tbn:ANd9GcRD-YK0vb_4ZOrSo2R_vkda2J9mAFy1LdlXZLzaotm8_o6QOvvuJg

6. From forums.tdiclub.comhttp://t3.gstatic.com/images?q=tbn:ANd9GcQE5qr5y0F-xlR5Jew6lFRqjjj1OIIKeiL6AImSn3GXldjLlHGd