Tamil Nadu HSE First Year Basic Automobile Engineering key terms

Personal protective equipment (PPE): gloves, goggles, boots, helmet and ear protection worn in the workshop to reduce injury from sharp edges, sparks, chemicals, noise and heavy lifting.

Portable cylinder that discharges water, foam, dry powder or carbon dioxide to put out a small fire; the type must suit the burning material and be inspected regularly.

Clamping device bolted to a workbench, with two jaws closed by a screw, that holds metal or wood firmly while it is sawed, filed, drilled or chiselled.

Hand tool that measures the turning force applied to a nut or bolt and signals or limits it at a preset value, preventing overtightening and ensuring joints are tightened to specification.

The complete underframe of a vehicle, including the frame, suspension, steering, brakes, wheels and drivetrain, to which the body and engine assemblies are mounted.

The strong metal structure of beams or box sections that supports the engine, transmission, suspension and body, keeping major components in correct alignment and carrying road loads.

The horizontal distance between the centres of the front and rear wheel contact patches; it influences interior space, weight transfer, turning circle and straight-line stability.

Top dead centre (TDC): the piston position at the very top of its travel, where it is farthest from the crankshaft axis; ignition and valve timing are often stated relative to this point.

Bottom dead centre (BDC): the piston position at the bottom of its travel, closest to the crankshaft axis; the distance from TDC to BDC is the stroke.

The distance the piston moves from TDC to BDC, or one complete upward or downward piston movement during the engine cycle.

The total cylinder volume above the piston at BDC divided by the clearance volume left at TDC; it shows how strongly the charge is squeezed before combustion.

The operating sequence of intake, compression, power and exhaust strokes, completed in two crankshaft revolutions, used by most petrol and diesel engines.

A device that mixes petrol with air for a spark-ignition engine by using the low pressure in a venturi to draw fuel through a metering jet.

A narrowed section in the carburettor throat where air speeds up and its pressure drops, creating the suction that lifts fuel from the float chamber into the airstream.

The mass of air entering an engine divided by the mass of fuel; for petrol about 14.7 to 1 is chemically correct, while richer or leaner mixtures alter power and emissions.

Abnormal, very rapid burning of the end gas in a cylinder that produces a sharp metallic knock and can damage pistons and bearings; high compression and overheating make it worse.

A heat exchanger at the front of the vehicle that passes hot coolant through tubes and fins, so airflow removes heat before the coolant returns to the engine.

A temperature-operated valve that blocks coolant flow through the radiator while the engine warms up and then opens to keep the engine near its designed operating temperature.

The lubricating fluid that forms a film between moving engine parts to reduce friction and wear, while also helping to cool, clean and seal internal components.

A fluid's resistance to flow; engine oil must be thin enough to circulate quickly when cold yet thick enough to protect bearings when hot.

A friction assembly between the engine flywheel and gearbox that can engage or disengage drive smoothly, letting the vehicle start from rest and gears be changed.

A set of gears and shafts that changes the ratio between engine speed and road-wheel speed, providing torque multiplication for starting and hill climbing and lower engine speed for cruising.

A rotating tube that carries power from the gearbox or transfer case to the final drive, usually fitted with universal joints to allow for suspension movement and alignment changes.

A gear assembly that divides drive between the two wheels and allows them to rotate at different speeds in a turn while still transmitting torque from the propeller shaft.

The number of degrees the steering wheel must turn to make the road wheels turn one degree; a larger ratio reduces effort but slows response.

The tilt of the top of a wheel away from vertical, seen from the front; too much positive or negative camber causes uneven tyre wear and affects cornering grip.

The setting in which the front edges of the two front wheels are closer together than their rear edges, used to offset the tendency of wheels to splay outward while rolling.

The springs, dampers, arms and linkages that connect the wheels to the chassis, absorbing road shocks while keeping the tyres in contact with the road.

A braking system in which fluid pressurised by the master cylinder forces pistons in wheel cylinders or calipers to apply friction linings to the drum or disc.

The pedal-operated pump that pressurises brake fluid and sends it through pipes to the wheel brakes, with a reservoir that compensates for fluid loss and pad wear.

The temporary loss of braking force when friction linings or brake fluid become too hot, reducing friction; it can occur after repeated hard braking on a long descent.

Anti-lock braking system (ABS): an electronic system that senses a wheel about to lock and rapidly releases and reapplies brake pressure, helping the driver retain steering control during hard braking.

An electrochemical storage device that supplies current for cranking, lighting and accessories and is recharged by the alternator; a lead-acid battery uses lead plates and dilute sulphuric acid.

An engine-driven generator that produces alternating current, rectifies it to direct current and charges the battery while supplying the vehicle's electrical loads.

A heavy-duty electric motor whose pinion engages the flywheel ring gear to crank the engine, drawing a large current from the battery for a short time.

A device screwed into the combustion chamber that receives a high-voltage pulse and produces an electric spark to ignite the compressed air-fuel mixture.

A measuring tool with a fixed main scale and a sliding vernier scale that reads outside diameter, inside diameter and depth, commonly to 0.02 mm.

A precision instrument with a screw-driven spindle and a calibrated thimble, used to measure small outside dimensions and thicknesses to hundredths of a millimetre.

A set of thin metal blades of known thickness used to check small gaps, such as valve clearance or spark plug gap, by finding the blade that just fits.

Scheduled cleaning, inspection, lubrication, adjustment and replacement of parts before they fail, intended to keep a vehicle safe, reliable and economical.