Transport Braking Systems (Engineering)

Abstract This engineering report is about transport braking systems and how they operate. Information has been gathered from numerous online sources (refer to bibliography) and also from class information booklets.   Introduction Transport Brakes have become such an integral part of our society that if they didn’t exist, many of the machines on which we rely could not work. For example, if brakes didn’t exist, then the motor car wouldn’t be a feasible idea as it would not be able to stop, so it would be uncontrollable and unsafe. Brakes operate by utilising the friction created when two objects rub together. Friction is the resistance encountered when one body is moved in contact with another. This force transforms energy, such as kinetic energy (movement), into another form, usually heat or light energy thus slowing and ultimately stopping the object. There are many types of brake such as the ‘air brakes’ used on trains and planes and ‘disc brakes’ used on road vehicles. In this report I will be focusing on brakes used mainly in cars and other road vehicles. 1. Briefly discuss the history of transport braking systems from horse drawn vehicles to modern vehicles.

Horse drawn vehicles had braking apparatus that were controlled by the driver and consisted of the brake (a piece of wood) that he used to press to the wheel. This type of brake was called a ‘Shoe Brake’. Shoe brakes operated by pressing against the wheel causing friction between the two surfaces. This caused the kinetic energy of the wheel to be transformed into heat energy, therefore decreasing the vehicle’s speed.

The next major brake design was the ‘Band Brake’ which appeared in the late 1890s. These were developed because the ‘Shoe brake’ could not operate with motor cars fitted with pneumatic tyres. They worked by squeezing the wheel axle with a band to transform the kinetic energy into heat by using friction. However, this type of brake was quickly replaced by the ‘Drum brake’ as it suffered from wear, build up of dirt, and a lack of reverse functionality. The ‘Drum Brake’ was first used by Louis Renault in 1902. It operates by wedging the ‘shoes’ into the drum when a pedal is pressed and using its springs to pull the ‘shoes’ back once the pedal is released. As the moving parts would severely wear, maintenance had to be performed regularly and they had to be carefully calibrated to give equal performance on all wheels. As they were enclosed they were protected from weather but this also caused heat to build up quickly. The next major development for braking systems was the use of disc brakes. Although they were originally used in the early 1900s, for motor cycles, they only received true recognition in 1951 at the London Motor Show. Previously, they had not been used in cars but they quickly grew in popularity and by the 1960s they were used in most European cars. It operates by pressing the brake pads to the rotor which then transfers the friction to the wheel. This type of brake is commonly used in partnership with hydraulic systems to increase their effect.

2. Why have braking systems needed to improve in effectiveness over the last 100 years?

In the last one-hundred years braking systems have needed to improve to accommodate the newer, heavier and faster cars. As cars have become heavier and faster, they now can carry more kinetic energy therefore, the brakes need to be improved to better deal with this kinetic energy.

3. With the use of diagrams describe the operation of conventional drum and disc braking systems.

→Drum-Brakes work by wedging the ‘shoes’ into the drum when a pedal is pressed and then using its springs to pull the ‘shoes’ back once the pedal is released.

←Disc brakes operate by pressing the brake pads to the rotor which then transfers the friction to the wheel through hydraulics to increase the effect.

4. Describe how the braking hydraulics system found within a car works. How does this system improve braking efficiency?

The use of hydraulics in a car braking system work to increase the force that the brakes can apply to the wheel. Force that is applied at one point is transmitted to another point using an incompressible fluid (usually oil).

In a car, this force is multiplied by using different sized pistons at either end. For example, a small piston at the start of the system will, when compressed, add pressure to the fluid. This pressure pushes against a large piston at the end of the system with a force relative to the piston’s area. This increased force is then used to operate the brakes. The driver needs to apply significantly less strength to the brake pedal to stop the vehicle.

As this method transforms little force into a greater force, it greatly improves braking efficiency.

5. Select a car braking system and list;

a) Major individual parts and materials used

b) Manufacturing properties required

c) Service Properties required

The major components of a disc brake are 1. The Brake Pads; 2. The Calliper; 3. The Piston and 4. The Rotor.

1. The Brake Pads are made of a ceramic or similar material so that they have high resistance to heat and shear forces and they create friction. It is also made out of this material as that it can be easily shaped.

2. The Calliper is commonly made out of steel so that it can resist most types of impact and so that it can be easily cast into the necessary shape.

3. The Piston is usually made out of aluminium so that it is easily wrapped into the correct shape, can operate in high temperatures, provides smooth movement and it’s hardness is adequate for it’s function.

4. The Rotor is made out of cast iron or a ceramic so that it can resist heat, torsional forces and frictional forces and so that it can be easily shaped to fit within a wheel.

6. Heat is created within braking system by friction. Describe how frictional heat is reduced in a conventional automotive braking system.

In most modern braking systems, the heat created by friction is reduced through lubrication. Too much lubrication, however, can reduce the effectiveness of the brake. Most brake systems are designed to avoid heat build up by using specifically designed ventilation in the casing to disperse heat.

7. ABS braking systems have improved braking efficiency and safety. Describe how ABS brakes operate and list the advantages compared to conventional braking systems.

Anti-Lock Braking System (ABS) operates by monitoring speed sensors mounted on the wheels at all times. When a wheel is about to lock-up (cease spinning), it will rapidly decelerate. The ABS senses this and speeds the wheel up by reducing the brake pressure so that the wheel doesn’t lockup and keeps rotating in time with the car.

Advantages of ABS include the ability to slow down more quickly and the ability to continue to steer while braking. Conventional systems did not allow for this which meant the car would not respond once the wheels were locked, the driver would not be able to steer or correct his direction which would result in accidents causing damage to vehicles and lives.

8. How has the development of new materials assisted in the effectiveness of braking systems?

The development of new materials has greatly enhanced the effectiveness of brakes by increasing longevity, efficiency and functionality. After much research and testing, many of these new materials were created using a composite of multiple materials designed to maximise the advantages of the items used while cancelling out their negatives. An example of these polymers is Kevlar. It is five times stronger than steel (of equal weight), this means that it can resist much more pressure and abrasion than previously used materials. It achieves this by utilising the compression strength of glass and the wear resistance of nylon-like polymers to make a material resistant to all forces that may affect it.

Conclusion

Although, the basic concept of brakes remains the same (pressing an object to the wheel to convert kinetic energy to heat with friction) the materials and design have progressed hugely. In conclusion, transport braking systems have advanced greatly from early shoe brakes to powerful, computer controlled, easy to use, precision machines that are more reliable and thus safer than ever before.

Bibliography:       -www.howstuffworks.com

                             -www.carbibles.com (diagrams)

                             -Class Information Booklets