Automobile module v
- 1. Electrical systems Anoop P Asst. Professor Department of Mechanical Engineering
- 2. Introduction • Automobile electrical system includes starting system, charging system, ignition system and lighting system and some accessories. • The accessories include cigarette lighter, horn and mobile charging system, etc. Department of Mechanical Engineering, MITS Puthencruz 2
- 3. Major Components • Ignition System – Spark plugs (for petrol vehicle) – Distributor – Ignition coil – Ignition switch, etc. • Charging System – Alternator – Regulator, etc. • Starting System – Battery Department of Mechanical Engineering, MITS Puthencruz 3
- 4. Ignition System • In spark ignition engines, a device is required to ignite the compressed air- fuel mixture at the end of compression stroke. Ignition system fulfills this requirement. • It is a part of electrical system which carries the electric current at required voltage to the spark plug which generates spark at correct time. • It consists of a battery, switch, distributor ignition coil, spark plugs and necessary wiring. • A compression ignition engine, i.e. a diesel engine does not require any ignition system. • Because, self ignition of fuel air mixture takes place when diesel is injected in the compressed air at high temperature at the end of compression stroke. Department of Mechanical Engineering, MITS Puthencruz 4
- 5. Requirements • The ignition system should be capable of producing high voltage current, as high as 25000 volts, so that spark plug can produce spark across its electrode gap. • It should produce spark for sufficient duration so that mixture can be ignited at all operating speeds of automobile. • Ignition system should function satisfactory at all engine speeds. • Longer life of contact points and spark plug. • Spark must generate at correct time at the end of compression stroke in every cycle of engine operation. • The system must be easy to maintain, light in weight and compact in size. • There should be provision of spark advance with speed and load. • It should be able to function smoothly even when the spark plug electrodes are deposited with carbon lead or oil. Department of Mechanical Engineering, MITS Puthencruz 5
- 6. Types of Ignition Systems There are three types of ignition systems which are used in petrol engines. • Battery ignition system or coil ignition system. • Magneto ignition system. • Electronic ignition system. • In battery ignition system, the current in the primary winding is supplied by a battery whereas it is supplied by a magneto in magneto ignition system. • Battery ignition system is used in cars and light truck. • Magneto ignition system is used in some scooters. • Both the systems work on the principle of mutual electromagnetic induction. • Electronic ignition systems use solid state devices such as transistors and capacitors. Department of Mechanical Engineering, MITS Puthencruz 6
- 7. Battery ignition system Department of Mechanical Engineering, MITS Puthencruz 7
- 8. Advantages • Low initial cost. • Better spark at low speeds and better starting than magneto system. • Reliable system. • No problems due to adjustment of spark timings. • Simpler than magneto system. Disadvantages • Battery requires periodical maintenance. • In case of battery malfunction, engine cannot be started. Department of Mechanical Engineering, MITS Puthencruz 8
- 9. Magneto Ignition System Department of Mechanical Engineering, MITS Puthencruz 9
- 10. Advantages • Better reliability due to absence of battery and low maintenance. • Better suited for medium and high speed engines. • Modern magneto systems are more compact, therefore require less space. Disadvantages • Adjustment of spark timings adversely affects the voltage. • Burning of electrodes is possible at high engine speeds due to high voltage. • Cost is more than that of magneto ignition systems. Department of Mechanical Engineering, MITS Puthencruz 10
- 11. COMPARISON Battery ignition 1. It offers better spark at low speeds, starting and for cranking purpose 2. Initial cost is high 3. Reliable system, need periodic maintenance 4. High sped engine drive is usually simpler 5. With increasing speed, sparking voltage drops 6. Because of battery bulk of the system is high Department of Mechanical Engineering, MITS Puthencruz 11 Magneto ignition 1. More reliable as there is no battery and cable connections 2. More suitable for medium and very high speed engines 3. Less space is required 4. At low speed voltage is low. So not good in slow speed case. 5. The power sparks at high engine speeds cause burning of the electrodes
- 12. Electronic Ignition System Department of Mechanical Engineering, MITS Puthencruz 12
- 13. Why Electronic Ignition? • The disadvantage of the mechanical ignition system is that it requires regular adjustment to compensate for wear and the opening of the contact breakers, which is responsible for spark timing, is subject to mechanical variations. • In addition the spark voltage is also dependent on contact effectiveness and poor sparking may lower the engine efficiency. • Electronic ignition has solved these problems Department of Mechanical Engineering, MITS Puthencruz 13
- 14. Ignition Timing • Ignition timing is the correct instant of generating spark just before the completion of compression stroke. • Correct ignition timing is necessary to maximize power output of an engine. Department of Mechanical Engineering, MITS Puthencruz 14
- 15. Ignition Advance • Ignition advance is the condition when ignition of fuel occurs earlier than the correct ignition timing. • Ignition of mixture takes place near the end of compression stroke. • If the ignition is advanced it means fuel-air mixture will burn too early before the end of compression stroke. • In this case, the crank and connecting rod will have to push the piston in order to compress the gases (for completing the compression stroke). • In this situation, the force applied on piston by the connecting rod in upward direction may not be able to overcome the downward force acting on piston. • This downward force acting on the piston is due to enormous pressure generated by the combustion of fuel. • Under this condition, the engine may stop or stall. • Spark advance may also cause the fuel to explode suddenly under certain operating conditions. Department of Mechanical Engineering, MITS Puthencruz 15
- 16. Ignition Retard • Ignition retard means the condition when ignition occurs after the correct ignition timing. • It is known that after ignition burning (combustion) of fuel takes place. • If ignition is retarded too much then the combustion of fuel-air mixture (charge) will continue during power stroke (expansion stroke). • Therefore, peak pressures will not be developed. • Consequently work output of the engine will decrease. • In this case, burnt gases will leave the engine cylinder at higher temperature which will overheat the exhaust valve. • It results in loss of power, overheating and sometimes burning of exhaust valve, and excessive carbon deposits. Department of Mechanical Engineering, MITS Puthencruz 16
- 17. Need of Spark Advance/Retard Mechanism • Correct/Proper ignition timing is necessary to maximize the performance of the engine. • Correct ignition timing depends upon several factors. • These are compression ratio, diameter (bore) of cylinder, composition of mixture, engine speed and load, engine temperature and quality of fuel used. • Except first two factors other factors keep on changing. • Therefore, there must be an automatic mechanism of adjust the ignition timing of engine. • Sometimes the spark is to be advanced and sometimes it is required to be retarded. Department of Mechanical Engineering, MITS Puthencruz 17
- 18. Centrifugal Spark Advance Mechanism Department of Mechanical Engineering, MITS Puthencruz 18
- 19. • This mechanism consists of two fly weights, a base plate, cam and a spring. • Fly weights are also called advance weights. • The base plate is fixed to the drive shaft. • The fly weights are rotated by distributor drive shaft through the base plate. • The weights are pivoted on the base plate and also attached to the cam with the help of springs. • The cam is also joined with the distributor shaft through springs, flywheel and plate. • If engine speed increases, the fly weights are displaced out radially due to centrifugal force acting on it. • Movement of weights causes the ignition advance (spark advance). • At low speeds there is no advance while it is full advance of very high speeds Department of Mechanical Engineering, MITS Puthencruz 19
- 20. Vacuum Advance Mechanism Department of Mechanical Engineering, MITS Puthencruz 20
- 21. • Vacuum advance mechanism consists of a diaphragm whose movement automatically advances and retards the ignition depending upon engine speed and other operating conditions. • One side of diaphragm is connected to the induction manifold and other side is connected to atmosphere. (Induction manifold is at lower pressure than atmospheric and this pressure depends upon engine speed). • The diaphragm is connected to the distributor through a linkage. • As engine speed increases the pressure on one side of diaphragm decreases. • This change in pressure controls the movement of diaphragm which ultimately controls the ignition timings. • At normal position of diaphragm the ignition timing is set at fully retarded position. • As engine speed increases the ignition timings are advanced. • Vacuum advance mechanism takes more care of engine load and less of speed where as centrifugal advance mechanism takes more care of engine speed and less of load. Department of Mechanical Engineering, MITS Puthencruz 21
- 22. Standard Bendix Drive Department of Mechanical Engineering, MITS Puthencruz 22
- 23. Bendix Drive with Compression Spring Department of Mechanical Engineering, MITS Puthencruz 23
- 24. Folo-thru Starting Drive Department of Mechanical Engineering, MITS Puthencruz 24
- 25. Over Running Clutch Drive Department of Mechanical Engineering, MITS Puthencruz 25
- 26. Wiring Circuit for Cutout Relay Department of Mechanical Engineering, MITS Puthencruz 26
- 27. Wiring Circuit for 3 Unit Regulator Department of Mechanical Engineering, MITS Puthencruz 27
- 28. Spark Plug Department of Mechanical Engineering, MITS Puthencruz 28
- 29. Hot and Cold Spark Plugs Department of Mechanical Engineering, MITS Puthencruz 29
- 30. Capacitive Discharge Ignition Department of Mechanical Engineering, MITS Puthencruz 30
- 31. Head Lamp Department of Mechanical Engineering, MITS Puthencruz 31
- 32. Horn Circuit Department of Mechanical Engineering, MITS Puthencruz 32
- 33. Horn Circuit with Relay Department of Mechanical Engineering, MITS Puthencruz 33
- 34. Wind Screen Wiper Department of Mechanical Engineering, MITS Puthencruz 34
- 35. Fuel Gauge Department of Mechanical Engineering, MITS Puthencruz 35
- 36. Temperature Gauge Department of Mechanical Engineering, MITS Puthencruz 36
- 37. Automotive Air Conditioning System Department of Mechanical Engineering, MITS Puthencruz 37
- 38. Battery Department of Mechanical Engineering, MITS Puthencruz 38
- 39. Functions The battery performs the following functions: • To supply the heavy current required by the starter motor for starting the engine. • To supply the current to lamps, radio and other accessories when the engine is not running. • To act as a stabilizer to the voltage in the electrical system. Department of Mechanical Engineering, MITS Puthencruz 39
- 40. Battery Types Department of Mechanical Engineering, MITS Puthencruz 40
- 41. Dry Cell • Uses an electrolytic paste. • The electrolytic paste reacts with the electrodes to produce a negative charge on one electrode and a positive charge on the other. • The difference of potential between the two electrodes is the output voltage. Department of Mechanical Engineering, MITS Puthencruz 41
- 42. Lead Acid Cell • Anode: Lead-dioxide • Cathode: Porous lead • Electrolyte: Sulfuric acid • During Discharging Department of Mechanical Engineering, MITS Puthencruz 42
- 43. Effect of charging • When the battery is charged by passing an electric current in the opposite direction from an external source, the electrical energy is absorbed in the form of chemical energy. • The following reactions occur during charging. At Anode (+ve plate): • PbSO4 + 2H2O+SO4 → PbO2 + 2H2SO4 At Cathode (-ve plate) : • PbSO4 + H2 → Pb + H2SO4 Department of Mechanical Engineering, MITS Puthencruz 43
- 44. • Advantages: – Batteries of all shapes and sizes, available in – Maintenance-free products and mass-produced – Best value for power and energy per kilowatt-hour – Have the longest life cycle and a large environmental advantage – Ninety-seven percent of the lead is recycled and reused in new batteries • Disadvantages: – Lead is heavier compared to alternative elements – Certain efficiencies in current conductors and other advances continue to improve on the power density of a lead-acid battery's design Department of Mechanical Engineering, MITS Puthencruz 44
- 45. Battery capacity • The amount of electricity of battery will deliver within a certain time limit is known as its capacity or ampere-hour capacity. • The amount of current furnished by the battery depends upon the following factors: • Number of plates of battery. • Area of plate surface in contact with the electrolyte (sulphuric acid) • Quality of electrolyte • Temperature. • The battery capacity is greatly reduced by low temperature which retard the electro-chemical action in the cells. • Hence capacity will decrease with the decrease in temperature Department of Mechanical Engineering, MITS Puthencruz 45
- 46. Battery Ratings Department of Mechanical Engineering, MITS Puthencruz 46
- 47. Checking of Batteries for Voltage and Specific gravity • Specific gravity test (Hydrometer Test) • High rate discharge test. • Open circuit voltage test • Cadmium test. Department of Mechanical Engineering, MITS Puthencruz 47
- 48. Causes of Battery Failure • Electrolyte level • Under charging • Over charging • Temperature • Corrosion • Cycling • Vibration Department of Mechanical Engineering, MITS Puthencruz 48