Odisha CHSE +2 Vocational Automobile Technology flashcards

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

Compression ratio

Ratio of total cylinder volume to clearance volume. Petrol engines run about 8:1 to 12:1; diesel engines run higher, typically 16:1 to 22:1, to achieve ignition by heat of compression.

Four-stroke cycle

Intake, compression, power and exhaust strokes, requiring two crankshaft revolutions per cycle. The power stroke produces work; the other three consume energy from the flywheel.

Mechanical efficiency

Brake power divided by indicated power, expressed as a percentage. It represents how much of the power developed in the cylinders reaches the crankshaft after friction losses.

Firing order

The sequence in which cylinders receive their power strokes. Common inline-four orders are 1-3-4-2 and 1-2-4-3; it balances load on the crankshaft and reduces vibration.

Torque wrench

A wrench that indicates or limits the applied torque so fasteners can be tightened to a specified value in N·m. Cylinder heads and wheel nuts need staged, diagonal tightening.

Valve clearance

The small gap between the valve stem tip and the rocker or cam follower, measured with a feeler gauge. Too little clearance prevents full valve seating and burns valves.

Cylinder bore taper

The difference in cylinder diameter between top and bottom of the bore, measured with a bore gauge. Excessive taper means reboring or replacement is needed during overhaul.

Piston ring end gap

The gap between the two ends of a ring when fitted squarely in its bore. Too small a gap closes up when hot and can break the ring.

Cylinder head warpage

Distortion of the head sealing face, checked with a straight edge and feeler gauge. If it exceeds the maker's limit, the head is resurfaced or replaced.

Blue exhaust smoke

Grey-blue smoke shows the engine is burning lubricating oil. Typical causes are worn piston rings, worn valve guides or failed turbo seals.

Clutch free play

The clearance at the clutch pedal before the release bearing acts, commonly 10 to 25 mm. Correct free play prevents slip and allows full engagement.

Clutch slipping

A fault where engine speed rises without a matching increase in vehicle speed. Causes include worn friction lining, weak pressure spring, oil contamination or no pedal free play.

Gear ratio

Driven gear teeth divided by driving gear teeth. A lower numerical ratio gives higher road speed; overall ratio equals gearbox ratio multiplied by final drive ratio.

Synchromesh

A device in a manual gearbox using a cone and baulk ring to bring the gear and shaft speeds together before the dog clutch engages, preventing gear clash.

Differential function

A gear set that lets the driven wheels rotate at different speeds on turns while still transmitting torque. The crown wheel and pinion set the final drive ratio.

Pascal's law in brakes

Pressure applied to a confined fluid is transmitted equally in all directions. Force at each wheel cylinder equals hydraulic pressure multiplied by piston area.

Brake fade

Loss of braking force caused by overheating of the friction material or fluid. It may also result from vapour lock when brake fluid boils.

Ackermann principle

On a turn the inner steered wheel follows a smaller radius and turns through a larger angle than the outer wheel. This reduces tyre scrub and steering resistance.

Camber angle

The tilt of a wheel from vertical when viewed from the front. Incorrect camber causes uneven tyre wear on the inner or outer shoulder.

Shock absorber

A hydraulic damper that controls spring oscillation after a bump. It converts suspension movement into heat and does not itself carry the vehicle load.

Ohm's law

Voltage equals current multiplied by resistance. Electrical power equals voltage times current, and also current squared times resistance.

Battery specific gravity

The density of battery electrolyte compared with water. A fully charged lead-acid cell reads about 1.260; a discharged cell reads about 1.120.

Alternator rectifier

A diode bridge that converts the alternator's three-phase AC output into DC for charging the battery and running vehicle loads. A failed diode causes poor charging.

Ignition coil

A step-up transformer with primary and secondary windings. It raises battery voltage to 15 to 30 kV to jump the spark plug gap.

Stoichiometric ratio

The chemically correct air-fuel mass ratio for complete combustion, about 14.7:1 for petrol. Richer mixtures give more power; leaner mixtures give better economy.

SAE oil grade 10W-40

A multigrade oil grade. The 10W number indicates cold-flow performance in winter, while 40 indicates viscosity at operating temperature.

Thermostat

A temperature-controlled valve in the cooling circuit that stays closed while the engine warms and opens near 80 to 90 degrees Celsius to allow radiator circulation.

Oil pressure warning lamp

A dashboard lamp that lights when lubrication pressure falls below a safe value. It warns of low oil level, a failed pump or a blocked filter.

OBD-II trouble code

A standard diagnostic code read from the engine control unit. The prefix letter identifies the system, such as P for powertrain or B for body.

Wet compression test

A compression test repeated after adding a little oil to the cylinder. If the reading rises, the fault is worn rings rather than leaking valves.

Micrometer least count

The smallest value a micrometer can read, usually 0.01 mm. It is calculated from the pitch of the spindle screw divided by the number of thimble divisions.

Plastigauge

A plastic strip placed across a bearing journal to measure oil clearance. After tightening, the crushed width is compared with a scale to give the clearance.

Bharat Stage VI norms

Indian emission standards limiting carbon monoxide, hydrocarbons, nitrogen oxides and particulate matter. BS-VI requires ultra-low-sulphur fuel and advanced after-treatment such as DPF and SCR.