- Car Safety & Safe Driving
brake system (an efficient lightweight brake)
Overview brake System
Brakes are most important safety parts in the vehicles. Generally all of the vehicles have their own safety devices to stop their car. Brakes function to slow and stop the rotation of the wheel. To stop the wheel, braking pads are forced mechanically against the rotor disc on both surfaces. They are compulsory for all of the modern vehicles and the safe operation of vehicles. In short, brakes transform the kinetic energy of the car into heat energy, thus slowing its speed.
Brakes have been retuned and improved ever since their invention. The increases in travelling speeds as well as the growing weights of cars have made these improvements essential. The faster a car goes and the heavier it is, the harder it is to stop. An effective braking system is needed to accomplish this task with challenging term where material need to be lighter than before and performance of the brakes must be improved. Today's cars often use a combination of disc brakes and drum brakes. For normal sedan car, normally disc brakes are located on the front two wheels and drum brakes on the back two wheels. Clearly shows that, together with the steering components and tires represent the most important accident avoidance systems present on a motor vehicle which must reliably operate under various conditions. However, the effectiveness of braking system depends on the design itself and also the right selection of material. It is important to do some analysis on a disc brake rotor which has been designed to predict the behavior of the systems than follow with some improvements. In order to understand the behaviors of braking system, there are three functions that must be complied for all the time (Smith, 2002);
a) The braking system must be decelerate a vehicle in a controlled and repeatable fashion and when appropriate cause the vehicle to stop.
b) The braking should permit the vehicle to maintain a constant speed when traveling downhill.
c) The braking system must hold the vehicle stationary when on the flat or on a gradient.
Nowadays, there are lot of software has been developed in order to cater the modeling and the finite element analysis on the vehicle component such as MSC.ADAMS (Automatic Dynamic of Mechanical Systems), CATIA, MSC PATRAN/NASTRAN, ANSYS, DYNA and ABAQUS. There is an advantage of using that powerful computational analysis software where by using those would make it easier, less cost, better accuracy and less computing time. Most of the software is used in the wide range of industries such as automotive, oil and gas, aerospace, marine, heavy duty engineering, construction, electro-mechanical and general mechanical industries. In this project, design package CATIA and finite element package ABAQUS and MSC PATRANNASTRAN will be used to generate model and run analysis on the chosen component.
Main problems to solve
A single seated race car needs an efficient brake system. An efficient brake system requires minimum stopping distance and minimum reaction time. In motorsports arena, the car weight plays very important roles in designing the race vehicle part. Minimum weight contributes to maximum power. Each part is custom made according to the vehicle specifications.
In the current design models for Formula Varsity and EIMA Race vehicle uses the brake system for motorcycle and a 850cc car model. Motorcycle brake system which also includes its disc is only suitable for that particular model. The same goes to a passenger vehicle brake system. Therefore, there is need to design a new brake disc which is more suitable for the single seated race vehicle that equipped with the 135cc engine and below. The brake disc should be lighter in weight but yet efficient.
If looking on the overall automotive parts, besides engines, there are more crucial parts that engineers need to look into consideration. Suspension, brake, electrical, hydraulic and gear are all the crucial systems in the automotive areas. Each of all system has their own functionality which brings life to the automation industries. Brakes is such a crucial system in stopping the vehicle on all moving stages including braking during high speed, sharp cornering, traffic jam and downhill. All of those braking moments give a different value of temperature distribution and thermal stress. Good performance of disc brake rotor comes from good material with better mechanical and thermal properties. Good designs of disc brake rotor are varying across the range of the vehicles. There are different design and performance of disc brake rotor if compared between passenger, commercial and heavy duty vehicle. There are also other constraints such as cost, weight, manufacturing capability, robustness and reliability, packaging, maintenance and servicing. For example, heavy duty vehicle need large size of disc brake rotor if compared to passenger vehicle. Due to that, it will increased total weight of vehicle as well as fuel consumption and reduces performances of the vehicle. Moreover, high weight of vehicle induces to high temperature increased during braking where the higher value of temperature during braking could lead to braking failure and cracking of disc brake rotor.
This main concern is the temperature distribution and constraint of the disc brake. Most of the passenger cars today have disc brake rotors that are made of grey cast iron (Mackin, 2002). Grey cast iron is chosen for its relatively high thermal conductivity, high thermal diffusivity and low cost (Mackin, 2002). In this project, the author will investigate on the thermal issues of single seated race vehicle disc brake , where the investigation are to determine the temperature behavior of the disc brake rotor due to severe braking of the disc brake rotor by using Finite Element Analysis (FEA).
According to (Valvano and Lee, 2000), braking performance of a vehicle can be significantly affected by the temperature rise in the brake components. High temperature during braking will caused to:
· Brake fade
· Premature wear
· Brake fluid vaporization
· Bearing failure
· Thermal cracks
· Thermally-excited vibration
Therefore, it is important to study and predict the temperature rise of a given brake component and assess its thermal performance in the early design stage. Finite element analysis (FEA) has been preferred and chosen method to investigate some of the above concerns such as disc brake rotor temperature rise and thermal cracks (Valvano and Lee, 2000). Finite element analysis for transient analysis will canny out through ABAQUS which applied heat transfer analysis where the 3D model imported from design tools CATIA, while the steady state analysis will be done by ABAQUS and MSC PATRAN / NASTRAN.
Research and Development
A lot of paper and journal has been read up and a part of it has been considered in this project. Meanwhile, the previous real brake disc dimension has been measured. CMM has been used in order to get accurate dimension of disc brake rotor. Later, the precise dimensions have been used to translate in 2D and 3D drawing by using CATIA.
Next, the fractional 3D model of disc brake rotor has been transfer to finite element software which is ANSYS / ABAQUS software. Thermal analysis will be done on steady state and transient responses. Assigning material properties, load and meshing of the model will be done in PSM2. Then, four type of material will be compare according to thermal analysis in the software to observe which one is the best thermal efficient. The materials selected are molded asbestos, chrome, cast iron and carbon composite. Finally an expected result of thermal analysis will be obtained.For the first step, I have to design the specific dimension of the disc according to the factor safety value that is 1.5. That is, I reduce the diameter of the disc brake to decrease the weight of the disc. The efficiency of the brake will be determined on the thermal elongation and the thermal analysis. So that from the result, we can decide which one is most efficient according to the thermal analysis.