AUTOTECH Kerala

BALLAST RESISTOR A ballast resistor is defined as a resistor inserted into a circuit to minimize current. Ballast resistors also help to avoid over-current faults in a circuit. An “electric ballast” is a more general term used to refer to an electrical device used to maintain a circuit’s stability by limiting the value of current and voltage. Electric ballasts can be resistors, capacitors, inductors, or a combination of these. Ballast resistors are able to change resistance with the current. If the current flowing through the resistor increases above the threshold value, the resistance increases. The resistance can then correspondingly decrease as the current decreases. In this way, the ballast resistor tries to maintain a constant current flowing through a circuit. The ballast resistor is different from the load resistor. As it acts like a variable load connected with the system. But in the case of load resistor, resistance remains constant with different values of current...

FUSE If a circuit is closed but no resistor is in the circuit, a heavy or high current will flow and produce large amounts of heat in the wire and draw large quantities of power from the battery. The result is that the wire becomes very hot and in many cases burns. This is called a short circuit and is the cause of many fires. It may result in an electrical appliance becoming inoperative. To prevent this happening, each normal circuit is protected by a fuse which is device that holds a piece of thin wire and is placed in the circuit. If the heat in the wire should rise above an acceptable level, the wire in the fuse will heat and melt and open the circuit. No damage will be done to any device or wire and when the cause of the heating is fixed and the fuse replaced, the circuit is ready for use again. Fuse wires are bare wires made of easily melting materials having high specific resistance. Usually standard alloy (63% tin and 37% lead) fuse wires are used for small currents, say up to ...

WORK : Work is said to be done by force F when the point of its application moves Mathematically, through a distance S. Work = force x distance            = F x S an acceleration of one The unit force in the mks system is newton (N). defined as the force acting on one kilogram mass of a body for one second which gives metre per second. If in the above equation, . force = 1 N and distance = 1 m, then Work done = 1 N-m or joule (J) In the mks system of units, work done is given in joules. It is defined as the work done by a force of one newton when the point of its application moves through a distance of one metre in the direction of the force. Therefore 1 J = 1 N-m POWER :  Power may be defined as the rate of doing work. Mathematically, work done Power time Note : Work done or energy expanded = power x time. If in time t sec, a quantity of electricity Q is transferred between the ends of a conductor when a potential difference is V, then...

AMMETER An ammeter is required to measure the current. Therefore, it must be connected in series to the load of which the current is to be measured. As it is connected in series, it must have low resistance, otherwise the resistance of the instrument will appreciably change the current through the load. For connecting it in series with the load, open the circuit at one place and connect the meter in the circuit as shown in Figure. Note : An ammeter should never be connected in parallel with the load otherwise it can get damaged. VOLTMETER A voltmeter is used to measure the potential difference. Therefore it must be connected in parallel to the circuit of which the potential difference is to be measured. A voltmeter must have high resistance otherwise it will take heavy current. When a voltmeter is connected in series, it measures the voltage drop across its own terminals. For connecting the voltmeter in parallel to the circuit, the meter should be connected across the load ...

CONNECTING ELECTRICAL CIRCUITS When electrical components are connected, they may be placed either end on end (called series circuit) or side by side (called parallel circuit). SERIES CIRCUITS : When circuit components are connected with only one conducting path they are said to be connected in series. The same current is in all components. When batteries are connected in series, (the voltage obtained in the circuit will be a total of the voltage in the batteries. This principle is used in car batteries and many radio batteries, where voltages larger than 1.5 or 2 volts are required. In these cases the cells are joined together in series. If resistors are connected in series the resistance in the circuit will be equal to the sum of all resistors. i.e.  R = R1 + R2 + R3 + R4 PARALLEL CIRCUITS : When circuit components are connected with several conducting paths between the sources of e.m.f. they are said to be connected in parallel. When batteries are connected in parall...

ELECTRICAL CURRENT The movements of electrons along the conductor in a particular direction produce an electric current. The more electrons which move the greater the current. AMPERE : The amount of electron flow is the current and the current is measured in amperes. One ampere of current is said to flow when 6.28 x 10^18 electrons pass a given point in the conductor during a period of one second. The electric current or amperes (abbreviated amps) is measured by an ammeter.   DIRECT AND ALTERNATING CURRENT :  If the electrons flow continuously in one direction along the conductor, the current is said to be direct current (abbreviated d.c.). This is the type of current produced by a battery or a d.c. generator. If the electrons flow in one direction and then flow back again and continue this back and forth motion, the current is said to be alternating current (abbreviated a.c.). This is the type of current produced by an alternator or a.c. generator and is the type of electric...

.  BATTERY COIL IGNITION SYSTEM The above figure shows the diagram of a battery coil ignition system. It contains two circuits like primary and secondary circuits. The primary circuit have a battery, Ignition switch, primary coil, CB point, and condenser. The secondary circuit having secondary coil, HT cable, distributor, rotor and spark plug. When the driver turn on the Ignition switch, a low voltage current from the battery is passes through the primary circuit. At the same time the cam starts to rotates it cut off the current flow through it. So the current transmits the primary winding to secondary winding. It also helps to increases current low voltage to high voltage. This high voltage current flows to the distributor and spark plug through High Tension cable.

IGNITION SYSTEM FUNCTION The function of the ignition system is to produce a spark in the engine cylinder towards the end of the compression stroke. In a four-stroke engine, a spark should occur in each cylinder after two revolutions of the crankshaft, whereas in a two-stroke engine a spark in each cylinder is required every revolution of the crankshaft. Thus, for instance, in a 6-cylinder 4 stroke engine running at 5000 r.p.m., the number of sparks required per minute will be 15000 and these have to be timed very accurately. REQUIREMENTS OF AN IGNITION SYSTEM 1. Spark at the plug electrodes must be regular and synchronously timed with respect to the cylinder-piston position at all speeds and loads on the engine. 2. The spark should be sufficiently strong so as to start ignition of the charge. Since lean air fuel mixtures are less conductive, they require higher ignition voltages. Thus on modem emission-controlled engines that use lean-mixtures, higher-voltage ignition system is requir...

VALVES :  Inlet and exhaust valves are fitted to each cylinder of the four-stroke engine; the inlet valve admits the petrol/ air mixture, and the exhaust valve releases the combustion products, which are vented via the exhaust. A typical poppet valve is shown in Figure. VALVE TIMING :  The opening and closing of the valves in an engine in relation to the movement of the piston and flywheel is called valve timing. Very old, slow speed engines had the following valve timing: Inlet valve – opens at t.d.c. and closes at b.d.c. Exhaust valve - opens at b.d.c. and closes at t.d.c. Modern engines operate at high speeds, so to allow for this the valve timing is modified to : Inlet valve — opens just before t.d.c. and closes well past b.d.c. Exhaust valve — opens well before b.d.c. and closes just after t.d.c. VALVE OPERATING MECHANISMS : Two types of valve operating mechanisms are used in engines : SIDE VALVE MECHANISM : A cam mounted on a rot...

ENGINE COMPONENTS 1. CYLINDER BLOCK      The cylinder block is the main body of the engine. Cylinder head is mounted on the cylinder block. It houses iniet and exhaus valves. Crank case is attached to the bottom of the cylinder block. Crank case supports the crank shaft. Oil pan is attached to the bottom of the crank case. Cylinder block contains large cylindrical holes called cylinder bore. The cylinders are accurately finished to accommodate pistons. The space above the piston inside the cylinder at TDC called the combustion chamber. Combustion of fuel inside this space, high pressure and temperature will be developed inside the cylinder. Therefore, it should be made of material which can resist high pressure and temperature (2800°C). In water jackets has around the cylinders for the circulation cooling water to absorb the temperature while running of an engine. 2. CYLINDER HEAD Cylinder head is a separate casting placed on top of the cylinder block by studs and nuts. I...

AIM :  TO MAKE A STEP - JOINT TOOLS REQUIRED 1. STEEL RULE & SCRIBER 2. TRY SQUARE & DOT PUNCH 3. 8" BASTARD FLAT FILE 4. 6" SMOOTH FLAT FILE 5. 6" SMOOTH TRIANGULAR FILE 6. SAFE EDGE FILE 7. HACK SAW BLADE & FRAME 8. BALL PEEN HAMMER MATERIALS REQUIRED 1. 62 x 50 x 5 mm M. S. FLAT (2Nos.) 2. MARKING BLUE 3. COTTON WASTE PROCEDURE 1. CUT OFF THE WORK PIECES FROM THE GIVEN RAW MATERIAL BY USING A HACK SAW BLADE AND FRAME. ALSO MARK THE RAW MATERIAL AS THE DIMENSION OF 62mm. LENGTH. 2. THEN FILE ANY TWO MUTUAL SIDES PERPENDICULAR TO EACH OTHER BY USING A 12" BASTARD FLAT FILE. 3. THE PERPENDICULARITY IS CHECKED BY USING A TRY SQUARE. 4. AFTER FILING THE DATUM SIDES MARK THE WORK PIECES AS PER THE GIVEN DRAWING BY USING A VERNIER HEIGHT GAUGE. ALSO APPLY THE MARKING BLUE IN TO THE SURFACE OF WORK PIECE FOR BETTER CLARITY. 5. THEN PUNCH THE MARKED LINES WITH THE HELP OF A PRICK PUNCH AND BALL PEEN HAMMER. 6. THEN REMOVE THE UNWANTED AREA OF WORK ...

Engine : It acts as the power unit. The internal combustion engine is the most commonly used in automobiles. It is of two types ; (i) Spark ignition (ii) Compression ignition.         Both engines are called heat engines. A steam engine is an external combustion engine because the fuel is burned outside the engine. The principle of working of an external combustion engine is shown in the figure below. COMPARISON BETWEEN INTERNAL AND EXTERNAL COMBUSTION ENGINES      The internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber. In an internal combustion engine the expansion of the high temperature and pressure gases, which are produced by the combustion, directly applies force to a movable component of the engine, such as the pistons and by moving it over a distance, generate useful mechanical energy.          The internal combustion engine...

AUTOMOBILES        An automobile is a self-propelled vehicle, which is used for the transportation of passengers and goods. A selfpropelled vehicle is that in which power required for propulsion is produced from within. Car, bus, truck, jeep, tractor, scooter, motorcycle are the examples of automobiles. CLASSIFICATION OF AUTOMOBILES Capacity : (i) Light motor vehicles – Car, Motorcycle, Scooter (ii) Heavy motor vehicles – Bus, Coach, Tractor Fuel used: (i) Petrol vehicles – Car, Jeep, Motorcycle, Scooter (ii) Diesel vehicles – Truck, Bus, Tractor, Bulldozer (iii) Electric cabs - Battery truck, Fork lift (iv) Steam carriages – Steam road rollers Number of wheels :  (i) Two-wheeler (ii) Three-wheeler (iii) Four-wheeler (iv) Six-wheeler Purpose : (i) Passenger vehicles – Car, Jeep, Bus (ii) Goods vehicles – Truck Drive of the vehicles : (i) Single-wheel drive vehicle  (ii) Two-wheel drive vehicle (iii) Four-wheel drive vehicle (iv) Six-wheel drive...

AIM :  TO MAKE A SQUARE TOOLS REQUIRED: 1. STEEL RULE 2. SCRIBER, DOT PUNCH 3. HACK SAW BLADE AND FRAME 4. BALL PEEN HAMMER 5. TRY SQUARE 6. 12" BASTARD FLAT FILE 7. 6" SMOOTH FLAT FILE MATERIALS REQUIRED 1. 50 x 50 x 6 M. S. FLAT 2. MARKING BLUE 3. CLEANING BRUSH PROCEDURE: 1. INITIALLY CUT OFF THE WORK PIECE FROM RAW MATERIAL BY USING A HACK SAW FRAME AND A BLADE. THE MARKING IS DONE BY A SCRIBER AND STEEL RULE. 2. THEN DEBURR ALL THE EDGES BY USING A FILE. 3. AFTER DEBURRING HOLD THE JOB ON THE BENCH VICE TIGHTLY. 4. THEN FILE ANY ONE EDGE TO BECOME FLAT. IT IS CHEECKED BY USING A TRY SQUARE. ALSO THE FILING IS DONE BY BOTH 6" AND 12" FLAT FILES. 5. THEN FILE THE ADJACENT SIDE MUTUALLY PERPENDICULAR TO EACH OTHER BY USING 12" BASTARD FLAT FILE. THE PERPENDICULARITY WAS CHECKED BY A TRY SQUARE. 6. AFTER COMPLETING THE DATUM SIDES, MARK THE LENGTH AND HEIGHT OF 45mm. BY USING A VERNIER HEIGHT GAUGE. ALSO APPLY THE MARKING BLUE INTO THE SURFACES OF ...

  AIM :  CUTTING PRACTICE. TOOLS REQUIRED :                                                                      1. STEEL RULE       2. SCRIBER       3. PRICK PUNCH       4. TRY SQUARE     5. HACK SAW BLADE AND FRAME     6. 12'' BASTARD FLAT FILE     7. 6'' SMOOTH FLAT FILE     8. BALL PEEN HAMMER MATERIALS REQUIRED  1. 52 X 48 X 6 M.S. FLAT  2. MARKING BLUE  3. CLEANING BRUSH PROCEDURE :     1. CUT THE WORK PIECE FROM GIVEN RAW MATERIAL AS PER THE SIZE OF 52 x 48 x 6mm.     2. FILE ANY TWO ADJACENT SIDES MUTUALLY PERPENDICULAR TO EACH OTHER, BY USING A 12'' BASTARD FLAT FILE. ALSO CHECK THE PERPENDICULARITY BY USING A TRY SQUARE.     3. THEN MARK...

AIM:    TO MAKE A 'V' - JOINT AT THE ANGLE OF 90° TOOLS REQUIRED 1. HACK SAW BLADE & FRAME 2. TRY SQUARE & STEEL RULE 3. DOT PUNCH & BALL PEEN HAMMER 4. SAFE EDGE FILE 5. 10" SECOND CUT FLAT FILE 6. 6" SMOOTH FLAT FILE 7. 6" SMOOTH TRIANGLE FILE MATERIALS REQUIRED 1. 50 x 50 x 5 M.S. FLAT - 02 Nos. 2. MARKING BLUE 3. CLEANING BRUSH PROCEDURE 1. CUT OFF THE JOB FROM THE GIVEN RAW MATERIAL AS THE SIZE OF 50mm SQUARE (2 Nos.) BY USING A HACK SAW BLADE AND FRAME. THE MARKING IS DONE BY A STEEL RULE AND SCRIBER. 2. HOLD THE WORK PIECE TIGHTLY INTO THE BENCH VICE 3. INITIALLY FILE THE DATUM SIDES OF BOTH WORK PIECES WITH THE HELP OF 10" SECOND CUT FLAT FILE. 4. THEN MARK THE HEIGHT AND LENGTH OF 45mm BY USING A VERNIER HEIGHT GAUGE. THEN PUNCH THE MARKED LINES WITH THE HELP OF A PRICK PUNCH AND HAMMER. 5. AFTER MARKING, FILE THE WORK PIECE TO A SQARE OF 45mm SIDE. MAKE SURE THAT ALL THE SIDES ARE MUTUALLY PERPENDICULAR TO EACH OTHER. 6. AFT...

FOUR STROKE PETROL ENGINE MAIN PARTS 1. PISTON 2. CYLINDER 3. CONNECTING ROD 4. INLET VALVE 5. EXHAUST VALVE 6. SPARK PLUG 7. CRANK SHAFT 8. FLY WHEEL 9. CAM SHAFT CONSTRUCTION A four stroke petrol engine have a piston, connecting rod, crank shaft, inlet valve, exhaust valve and a spark plug. The connecting rod is used to connect the piston and crank shaft. The spark plug and valves are mounted in the cylinder head. Also the valves are operated by cam shaft which is connected to the crank. In this type of engines, there would be a power stroke for every two rotations of crank shaft. It is also known as otto cycle. Each full rotation of crank having two strokes. So one stroke is  180° rotation of flywheel. A four stroke petrol engine having the following strokes. WORKING Induction stroke : The crankshaft moves the piston downwards (TDC to BDC). The inlet valve is open and a mixture of fuel and air is sucked into the combustion chamber. It is also known suction stroke. In this strok...