The Disc Brake System - Coursework Example

?Product Innovation Disc type brakes are widely employed in vehicles around the world. These systems are commonly available and are simple to dismount, disassemble, service and reinstall. A few basic components make up the entire system. Certain dimensions are critical to ensure that the disc brake system performs flawlessly. Product Market Dick brakes are utilised on nearly all modern vehicles of all sizes. The list of disk brake installations is huge including bicycles, motorcycles, cars, minivans, vans, trucks, jeeps, trains etc. Moreover disc brakes are also utilised on stationary applications such as gantry cranes, pulley based braking systems and the like. (Ganaway, 2002) Disc brakes utilised on these different kinds of systems vary in form and design significantly but not in principle. The basic principle remains fixed at using a disc mounted to a vehicle hub. During braking, the brake disc is jammed by using a calliper that is often triggered hydraulically on cars, jeeps, trucks, trains and a majority of motorcycles. (Popular Science, 1964) However, disk brake installations on bicycles are actuated by wire based systems. Previously drum brakes were widely utilised on all forms of vehicles especially in the earlier years of automobiles. However, the advent of disk brakes changed this forever. Disk brakes are far more convenient to install and maintain and produce greater braking loads in comparison to regular drum brakes. Consequently, certain vehicles have begun to utilise disk brakes on all wheels especially racing cars. Passenger vehicles however are often designed to use disk brakes on the front wheels while drum brakes are used on the rear wheels. This comes about as the load on the front wheels in often greater due to the weight of the engine. The particular disk brake being analysed here is a Ford Cortina disc brake which was installed on these vehicles between 1970 and 1982. Three versions of vehicles were installed with these particular disk brakes which were the Ford Cortina Mark III, IV and V ranging from 1970-76, 1976-79 and 1979-82 respectively. (Octane, 2011) There were only minor variations in these disc brake assemblies with only a few minor changes to the material of the discs. Otherwise a disk brake assembly from any of these three versions of vehicle can be fitted to a Ford Cortina belonging to this range. Product Specification The disk brakes on the Ford Cortina range began to appear in 1964. (Autocar, 1969) The current disk brakes being analysed come from a scrapped 1980 Ford Cortina. The Ford Cortina disk brakes being offered online (as replacement spares) are different from the original configuration whose specifications are outlined below. The disk brakes are non-ventilated in the Ford Cortina. There is only a simple straight disk that is mounted on the hub of the vehicle. If the disk brake had been ventilated, there would have been two parallel disks with involutes in between but this is not the case. The disc brakes are solid one piece and seem to be cast after which the circular faces have been machined to ensure smooth braking. The brake disc is raised from the centre like all other disc brakes so as to create installation clearance from the hub (also known as the spindle). The height of this raised feature is just over one inch. The disc is held in place by four metric bolts with a PCD (pitch circle diameter) of 3.64 inches. The outer diameter of the disc is around 9.61 inches while its nominal thickness is some 0.5 inches. The minimum thickness of the disc is around 0.45 inches. The other important component of the disc brake is the calliper which effectively stops the disc from spinning. The calliper is cast after which it has been machined. This is in contrast to most modern brake callipers that are forged. There are two brake pads that cover each side of the disc for braking. The brake pads are both numbered BPS1674 while the calliper bears a Lucas Girling manufacturing mark. The calliper is actuated hydraulically and the piston installed for this purpose has a diameter of 2.125 inches. Analysis of Functions and System Disc brake assemblies are composed of the disc, the calliper (including brake pads) and the master cylinder along with the servo. When the driver depresses the brake pedal, a piston in the master cylinder causes hydraulic brake fluid to be pushed out of the cylinder thus turning mechanical force into hydraulic force. The hydraulic oil displaced from the cylinder is moved over to the servo that effectively amplifies the braking signal. This hydraulic signal is moved over to the callipers that effectively clamp down onto the disc. In this process the brake pads installed within the brake callipers contact the disc and cause it to stop given the friction between both parts. A return spring is included in the master cylinder so that the brake pedal returns to its normal position as soon as it is released. When compared with drum brakes, disc brakes offer better braking force values for an installation nearly the same in size. Moreover, disc brakes are composed of a lower number of components and hence tend to have lower threats of failure associated with them. There is also a dire need to service drum brakes on and off in order to ensure that they keep performing smoothly. However, there are no such compulsions for a disc brake. The disc is fully exposed to environmental variables such as dust, grit, water and the like. The action of the brake pads of the callipers ensures that the disc is cleaned up efficiently. This ensures that the disc need not be serviced time and again as it is self cleaning. Product Illustration (Complete and Stripped) Brake Disc Brake Disc and Callipers Hub and Brake Callipers Controlled Dimensional Requirements Like any other mechanical part, there are certain constraints that apply to dimensions in disc brake systems. One of the most critical dimensions at work is the diameter of the disc itself. If the diameter of the disc rises above a specified value then there are chances that the disc will not fit into the assembly while if the diameter falls below a certain level then the brake pad may not fully engage with the disc. This may cause a decrease in the braking force and may cause uneven wear of the disc and the brake pads. The other critical dimension is the surface finish of the brake disc. If the surface finish is above tolerable levels then the brake disc will not provide required contact that will end up lowering the brake force produced. Moreover, the disc will also be threatened with excessive vibration and heating which may result in warping of the disc brake. (Anderson, 1990) The disc also lies in danger of pulverisation at the surface if the disc’s surface is under surface finish levels. The third critical dimension within the disc is the thickness of the disc itself. In case that the disc’s thickness is too much, there is a strict chance that the brake pads may seize with the disc. On the other hand, if the thickness of the disc is too low then the brake callipers may have to travel excessively in order to produce effective braking force. In case that the disc’s thickness is too low the callipers may not be able to interact with the disc altogether. Furthermore, the disc may also face structural and thermal problems if its thickness is reduced too much. Similarly, the diameter and the surface finish of the master cylinder are critical to ensuring that the piston can move the right amount of hydraulic fluid each time without any leakage. Materials and Required Properties The brake disc is supposed to endure large stresses especially around its periphery. Moreover, the heat generated through braking tends to create thermal stresses within the brake disc. Therefore, the brake disc will be subject to structural and thermal stresses at the same time. This means that the material used to create a brake disc must have a high coefficient of thermal conductivity as well as a good tensile strength and toughness. Moreover, the brake disc must possess an acceptable surface finish. This ensures that the brake disc is smooth under all circumstances for braking. It is all the more better if the brake disc wears evenly which will ensure that the calliper’s brake pads engage smoothly all the time. In view of these considerations, the material used for disc brakes originally included cast iron that met these properties satisfactorily. However, there were chances for cast iron to warp if temperatures exceeded certain limits. With the passage of time, brake disc materials were changed to ceramics that performed better, had longer lives and did not warp at high temperatures. However, the current brake disc assembly for the Ford Cortina being analysed is made out of cast iron because it is one of the earliest brake disc designs. The other important component is the brake calliper that needs to possess high tensile strength to ensure that it does not break or deform under the high stresses that will be generated as a result of braking. Similarly, the piston of the brake assembly needs to possess good tensile strength as well as impeccable surface finish. The brake calliper and piston are both furnished out of steel to ensure their tensile strength. Current designs commonly use aluminium for the master cylinder piston. Design Improvements A number of improvements are possible over the existing design both in terms of feature and the materials used. The brake disc being analysed in composed of a single piece which is crafted out of cast iron. During very hard braking there are a lot of chances that the brake may warp as the heat transfer would not be sufficient. This can be improved by introducing two parallel discs with involutes in between them. The rotation of the disc ensures that the disc remains well ventilated as air rushes through the involutes to cool the disc surface down. In addition to adding involutes to act as cooling buffers, the material should also be changed to decrease the need for excessive disc cooling. The other major improvement that can be offered is lowering the mass of the disc which is apparent on almost all recently manufactured vehicles. This mass reduction aids in lowering the overall mass of the vehicle and thus promotes better fuel mileage. Moreover, reduction in the mass of the disc ensures that the un-damped mass remains low in comparison to the damped mass which would help to improve suspension performance. This can be done by crafting the disc out of new and innovative materials such as ceramics. The added advantage of ceramics will be resistance to warping and excessive wear under extreme braking loads. Another design improvement can be brought about in the material of the master cylinder and its piston that are manufactured out of steel. Newer designs are being created out of aluminium which offers better coefficients of frication as well as reduced weight. Similarly the material of the brake pads should be composites that incorporate ceramics and metals together to offer better coefficients of friction as well as longer life cycles. Bibliography Anderson, E., 1990. Hot spotting in automotive friction systems. Wear, 135, p.319–337. Autocar, 1969. Used Car Test: 1962 Ford Cortina. Autocar, 130(3804), pp.22-23. Ganaway, G., 2002. Air Disc Brake Production, Use & Performance. In NDIA Tactical Wheeled Vehicles Conference. Monterey, 2002. Octane, 2011. 1979-1982 Ford Cortina '80. [Online] Available at: HYPERLINK "http://www.classicandperformancecar.com/front_website/octane_interact/carspecs.php?see=4030" http://www.classicandperformancecar.com/front_website/octane_interact/carspecs.php?see=4030 [Accessed 3 August 2011]. Popular Science, 1964. What's new at American Motors. Popular Science, 185(4), pp.90-91. Read More