COURSE LEARNING OUTCOMES No. Course Learning Outcome 1. 2. Compare working principle and identify advantages/disadvantages between the disc and drum brake systems used in passenger vehicles Analyze deceleration behaviour of a road passenger vehicle Weightage (%) 10 25 Assessment Methods Test Final Exam Test Final Exam Test 3. Analyze thermal performance in the disc and drum brake systems 25 Final Exam Assignment 1 4. Differentiate the use of Anti-lock brake system in the hydraulic and air brake systems 10 Assignment 2 Final Exam 5. Evaluate performance of the disc/drum brake using commercial finite element software and write a technical report. 30 Project report
GRADING Assessment Name Assessment Type Criteria/Description Total Date Project Group Computer simulation & writing technical report 30% Week 15 Assignment 1 Assignment 2 Individual Theoretical analysis 5% Week 6 Individual Article review 5% Week 13 Test Individual Lecture on week 1 week 7 20% Week 7 Final Exam Individual Lecture on week 1 week 15 40% Week 16-18 Total 100
REFERENCES : 1. Braking of Road Vehicles, AJ Day, University of Bradford, UK, 2014. 2. Rudolf Limpert, Brake Design and Safety, 2 nd Edition, Society of Automotive Engineers, Inc., Warrandale, USA, 1999. 3. An Introduction to Modern Vehicle Design, Edited by Julian HappianSmith, Butterworth Heinemann, Oxford, UK, 2001.
Introduction Nowadays, the design of braking system of a modern road vehicle involves with three distinct scientific and engineering disciplines: 1. Materials science and engineering. Advanced friction couples provide reliable, durable and consistent friction forces under the most arduous conditions of mechanical and thermal loading in operating environments. 2. Advanced mechanical engineering design. Enabled high-strength braking system components to be optimised to deliver consistent and controllable braking torques and forces over a huge range of operational and environmental conditions. This can be done by the use of computer-aided design and analysis methods. 3. Close and accurate control of braking systems and components. Electronics and software engineering has moved braking firmly into the area of active vehicle safety. Antilock Braking Systems (ABS) demonstrated the safety benefits of maintaining directional control while braking under high deceleration and/or low adhesion conditions.
Function of a Braking System A braking system must provide: 1. Decelerate a vehicle including stopping. It involves the change of the kinetic and potential energy into thermal energy. Important factors that must be considered including braking stability, brake force distribution, tyre/road friction utilization, stopping distance, brake fade and brake wear. 2. Maintain vehicle speed during downhill operation. It involves the transfer of potential into thermal energy. Important considerations are brake temperatures, lining fade and brake fluid vaporization. 3. Hold a vehicle stationary on a slope. It is activated by a parking brake. Since the parking brake may be used for vehicle deceleration during an emergency case, both thermal and vehicle dynamic factors must be considered.
The brake systems should work in diverse conditions: -Slippery, wet and dry roads -Rough or smooth road -Split friction surfaces -Straight line braking or when braking on a curve -Wet or dry brakes -New or worn linings -Laden or unladenvehicle -Vehicle pulling a trailer or caravan -Frequent or infrequent applications of short or lengthy duration -High or low rates of deceleration -Skilled or unskilled drivers
Brake System Components All hydraulic brake systems can be divided into four (4) basic subsystems: 1. Energy source. This includes the components of a brake system that produce, store or release and make available the energy required for braking. Eg. Muscular pedal effort in combination with a vacuum boost system. 2. Apply/Modulation system. All components that are used to modulate the level of braking. Eg. The driver, pressure limiting/modulating values, ABS (if fitted) 3. Energy transmission system. All components through which the energy required for applying the brakes travel from the apply system to the wheels. Eg. Accumulators, brake lines, brake hoses. 4. Foundation brakes. These disc/drum assemblies generate forces that oppose the motion of the vehicle.
Main components in a brake system
Brake System Configurations. Can be divided into two groups: Single-Circuit Systems - use only one circuit to transmit braking energy to the wheels. No braking is provided in the event of a circuit failure. FMVSS had prohibited this type of circuit since 1968 for all passenger cars and trucks. Dual- Circuit Systems - Required to all trucks with hydraulic brakes since 1983. - use two or more circuits to transmit braking energy to the wheels. In the event of a circuit failure, partial braking effectiveness is provided.
The foundation brakes convert the kinetic energy into heat. The process of energy conversion is achieved through frictional heating generated at the interface between the disc/drum and pads/shoes. Type of Friction Brake It can be grouped into two classes: Drum brakes: Disc brakes.
Type of drum brake:
Type of drum brake: Simplex & S-cam
Type of disc brake: Fixed caliper Sliding caliper
Disc versus Drum Advantages of Disc Brake: 1.disc brake requires less effort(brake torque) to stop the vehicle compare to drum brake. 2.It generates less heat compare to drum brake for the same brake torque. 3.Ease of maintenance as disc brake is outside the wheel rim. 4.It cools down faster compare to drum brake. 5.Ifwornoutbrakeshoesarenotchangedatpropertimeitcancutthebrakedrumindrumbrake.disc brake does not have such problem. 6.Itislesslikelytoskidcomparetodrumbrakeinwetcondition. 7.Itismuchsaferthandrumbrakeinhardbrakingcondition.Undersuchconditiondrumbrakecanlock uptherearwheel. 8.Ithasbrakepadwearindicatorwhichisnotthereindrumbrake. Disadvantages of Disc Brake: 1.It is expensive compare to drum brake. 2.More skills require to operate disc brake compare to drum brake that s the reason why some people are not comfortable with disc brake 3.Ifanyairremainsindiscbrakesystem,itcancauseaccidentasthebrakewillnotworkeffectively. 4.disc brake assembly has more moving parts and much complex than drum brake. 5.It requires lot of effort at maintenance front like brake fluid(bleeding), change of brake pads etc compare to drum brake.
Working principle
Friction materials There are many different types of friction materials in use today. 1. Carbon fibre composites: Aircraft and Formula 1 racing cars. 2. Sintered metal friction materials: Rally cars and motorcycles. 3. Resin-bonded composite friction materials: majority of modern road vehicles. For road vehicles the functional requirements of a modern friction material include: To provide a consistent and reliable frictional force. To be durable. To be mechanically and thermally strong enough to withstand the loads applied during use. To be tribologically compatible with the other part of the friction pair. To minimise or preferably avoid frictionally initiated instabilities or vibrations in the brake, suspension or vehicle system. To be environmentally acceptable in use: no emission of hazardous fumes, debris or waste. To be cost-effective in design, manufacture and use.
Modern resin-bonded composite friction materials are specially formulated to give good friction and wear performance under the sliding contact conditions of braking. The basis of such formulations is usually a polymeric binder (resin) and a fibrous matrix that provides most of the mechanical strength necessary to withstand the generated frictional forces. Fillers, friction modifiers, lubricants are included to tailor the mechanical, thermal, friction and wear properties, The binder is a thermoset polymer most commonly based upon a phenolic resin, and may include other related organic compounds to achieve the desired chemical, processing and thermophysical properties.
There are generally considered to be three classes within resin-bonded composite FM, namely non-asbestos organic (NAO), low steel and semi-metallic. NAO friction materials are usually the most expensive. They tend to have lower mu/cof levels (typically 0.3e0.4), and have superior wear characteristics up to around 220C, although wear can increase dramatically at higher m levels and higher duty. They tend not to use significant quantities of iron or steel in the formulation, are relatively clean in operation, and have low noise propensity in terms of avoiding brake squeal, Low steel friction materialsuse iron and/or steel in the formulation. They have higher mu/coflevels than NAO materials (typically 0.35e0.5) and are considered to provide good pedal feel. They have good fade and high-speed/duty performance, but noise propensity tends to be higher. Wear characteristics may not be as good as for NAO materials and they are not so clean in operation.
Semi-metallic friction materials tend to be simpler formulations compared with NAO and low steel materials, and have a ferrous metal content of up to 40% by weight. These friction materials are the lowest cost of the three classes and tend to have low m levels (typically 0.25e0.35). High wear can be experienced with these materials at high speed and low temperatures, but wear and fade performance are better at higher temperatures. They tend to be prone to noise and judder compared to NAO materials and, because of the high metallic content, heat transfer through the disc brake pad can affect the actuation system, e.g. by causing high brake fluid temperatures in a hydraulic system.
Exercises Q1. List and briefly describe types of disc and drum brakes. Q2. Explain the main function of braking system. Q3. What are the advantages and disadvantages of the disc and drum brakes? Q4. Describe the working principle of the disc and drum brake systems. Q5. Give three typical friction materials used in a modern vehicle. Q6. List five (5) functional requirements for a modern friction material. Q7. Briefly describe characteristics of three classes friction materials within resin-bonded composite.