Tamil Nadu HSE First Year Basic Automobile Engineering flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Class B fire

A fire involving flammable liquids such as petrol, diesel, oil or paint. Extinguish with foam, carbon dioxide or dry powder; never direct a water jet at it, because water spreads the burning liquid.

Ring spanner advantage

A ring spanner grips the nut or bolt head on all six flats, so it is far less likely to slip or round off the corners than an open-ended spanner, particularly on tight or damaged fasteners.

Torque formula

Torque in newton-metres equals the applied force in newtons multiplied by the perpendicular distance in metres from the pivot. A longer wrench with the same hand force therefore produces greater tightening torque.

Wheelbase

The horizontal distance between the centre of the front axle and the centre of the rear axle. It influences passenger space, weight distribution, straight-line stability and the turning circle.

Monocoque chassis

A unitised form of construction in which the floor and body panels form the load-bearing structure. It is lighter and stiffer than a separate ladder frame and is used in most modern cars.

FR layout

Front engine, rear-wheel drive. The engine drives through the clutch, gearbox and propeller shaft to a rear differential, giving balanced weight distribution and separating steering from the driving wheels.

Compression ratio

The ratio of the total cylinder volume above the piston at bottom dead centre to the clearance volume at top dead centre, calculated as (swept volume plus clearance volume) divided by clearance volume.

Firing order

The sequence in which the cylinders are fired so that loads on the crankshaft stay balanced. A common four-cylinder order is 1-3-4-2, which gives an even firing interval of 180 degrees.

Top dead centre

The position of the piston at the highest point of its travel in the cylinder, where the crankshaft throw and connecting rod lie in a straight line. Valve timing and ignition timing are referenced to it.

Stoichiometric air-fuel ratio

The chemically ideal air-to-fuel mass ratio for petrol, about 14.7 to 1, at which the fuel burns completely with neither excess air nor unburnt fuel remaining in the exhaust.

Venturi

A narrowed throat in a carburettor or throttle body. Air speeds up as it passes through and its pressure falls, so atmospheric pressure in the float chamber pushes fuel out through the jet into the airstream.

Octane number

A scale expressing petrol's resistance to knock, with iso-octane rated 100 and n-heptane rated 0. A higher octane number allows a higher compression ratio without detonation.

Thermostat

A temperature-operated valve in the coolant outlet that stays closed while the engine warms up and opens near 80 to 90 degrees Celsius to allow coolant to circulate through the radiator.

Pressure radiator cap

A spring-loaded cap that holds the cooling system at about 0.9 to 1 bar. This raises the boiling point of the coolant to roughly 120 degrees Celsius and reduces loss by evaporation.

Oil relief valve

A spring-loaded valve in the lubrication circuit that opens when oil pressure exceeds a set value, bypassing surplus oil back to the sump to protect seals, gaskets and oil pipes.

Clutch function

To connect and disconnect the engine from the transmission smoothly, transmit full engine torque without slipping when engaged, and absorb shock loads in the driveline during gear changes.

Gear ratio

The number of teeth on the driven gear divided by the number of teeth on the driving gear. A ratio above one reduces output speed and multiplies torque by the same amount.

Differential

A gear train that divides drive between the two wheels and allows them to rotate at different speeds when cornering, while still transmitting torque to both driving wheels.

Caster angle

The fore-and-aft tilt of the steering axis from the vertical, viewed from the side of the vehicle. Positive caster makes the steering self-centring and improves stability at speed.

Toe-in

The amount by which the front edges of the front wheels are closer together than their rear edges, typically two to six millimetres, to offset running splay and reduce tyre scrub.

Tyre aspect ratio

The sidewall height of a tyre expressed as a percentage of its section width. On a 165/80 R14 tyre the sidewall height is 80 per cent of 165 millimetres.

Pascal's law

Pressure applied to a confined fluid is transmitted undiminished in all directions and acts at right angles to the containing surfaces, which is why a small master-cylinder piston can operate larger wheel cylinders.

Brake fade

The loss of braking force when friction surfaces overheat, causing the coefficient of friction of the lining to fall. It commonly follows repeated or prolonged braking, such as on a long descent.

Anti-lock braking system

A system in which wheel-speed sensors detect impending lock-up and a hydraulic modulator releases and reapplies brake pressure rapidly, keeping the wheels rolling so the driver retains steering control.

Battery electrolyte specific gravity

The density of the battery acid compared with water. A fully charged lead-acid cell reads about 1.260 to 1.280, and a discharged cell falls towards 1.120; a hydrometer is used to check it.

Alternator

A belt-driven three-phase generator that produces alternating current, which diode rectifiers convert to direct current. It recharges the battery and supplies the vehicle's electrical loads while the engine runs.

Starter solenoid

An electromagnetic switch that, when the ignition key is turned, pulls the starter pinion into mesh with the flywheel ring gear and then closes the heavy-current contacts feeding the starter motor.

Cold cranking amps

The current a battery can deliver at minus 18 degrees Celsius for 30 seconds while keeping its terminal voltage at or above 7.2 volts, indicating its ability to crank a cold engine.

Vernier least count

The smallest value a vernier caliper can read, equal to one main-scale division minus one vernier-scale division. A common metric least count is 0.02 millimetres.

Feeler gauge

A set of thin steel blades of marked thickness used to check small gaps such as valve clearances, spark plug gaps and contact-breaker points by finding the blade that just fits.

Compression test

A test in which a gauge is screwed into the spark plug or injector hole and the engine is cranked. A low reading that rises when oil is added indicates worn piston rings.

Daily preventive checks

The routine checks made before a journey: engine oil level, coolant level, tyre pressure and condition, lamp operation, and warning lamps on the dashboard, with any defect corrected before use.