Tamil Nadu HSE First Year Basic Automobile Engineering cheat sheet

Fire classes: A = solid combustibles (wood, paper, cloth), B = flammable liquids (petrol, diesel, paint), C = electrical, D = combustible metals. Use CO₂ or dry powder on electrical and petrol fires; a water jet spreads burning liquid and conducts electricity.

Jacking rule: raise the vehicle with a hydraulic jack, then lower it onto rated axle stands placed under a strong chassis or suspension point. A jack alone can creep or fail and must never carry the load while anyone is underneath.

Ring and box spanners enclose the nut on all six flats and resist slipping far better than open-ended spanners; open-end jaws are set at 15° to the handle so they can be used where swing space is limited.

Torque T = F × r, measured in N·m; tighten cylinder-head bolts, wheel nuts and other critical fasteners to the manufacturer's figure with a calibrated torque wrench, working in the specified sequence.

Hacksaw blade selection: 18 teeth per inch (coarse) for thick soft metal, 24–32 TPI (fine) for thin tube, sheet and hard metal. Cut on the forward stroke with light, even pressure and keep at least three teeth in contact with the work.

Cold-chisel point angle: about 60° for general work on mild steel, 70° for hard metal, 40–50° for soft metals such as aluminium. Wear goggles, cut away from the body and use a chipping screen.

Files cut only on the forward stroke; never use a file without a handle, clean it with a file card, and do not use a file as a lever or a hammer.

Fuel and battery areas are explosion hazards: petrol vapour and the hydrogen given off during charging ignite from a single spark. No naked flame or smoking, ventilate the area, earth fuel containers and connect or disconnect battery leads with the charger switched off.

An automobile is chassis plus body. The chassis - frame with running gear - carries the payload, mounts the power unit and transmission, and resists road shock, bending and twisting.

Frame types: ladder frame (two channel-section side members with cross members), X-frame, backbone (central tubular spine), and integral or unitised construction in which the body shell itself is the load-bearing structure.

Drivetrain layout codes: FR (front engine, rear drive), FF (front engine, front drive), RR, MR and 4WD/AWD. FF removes the long propeller shaft and floor tunnel but loads the front tyres with both steering and driving.

Wheelbase = distance between front and rear axle centres. Track = distance between the centre lines of the two tyres on one axle. A shorter wheelbase gives a smaller turning circle; a wider track gives better cornering stability.

Running gear comprises the frame, suspension, steering, wheels and tyres and the brakes; the power train comprises engine, clutch, gearbox, propeller shaft, differential and half shafts.

Vehicle systems to know: engine, fuel supply and carburetion, cooling, lubrication, transmission, steering, suspension, braking, and the electrical system including the battery.

Load distribution affects handling: a heavy front bias encourages understeer and light steering; a near 50:50 front-to-rear split improves balance and braking stability.

Body construction: separate body-on-frame gives strength and easy repair for commercial vehicles; monocoque (stressed skin) is lighter and stiffer and uses crumple zones to absorb impact energy.

Four-stroke cycle: suction, compression, power, exhaust. One complete cycle needs two crankshaft revolutions (720°) but only one camshaft revolution, so the camshaft turns at half crankshaft speed via gears, chain or toothed belt.

Compression ratio = (swept volume + clearance volume) ÷ clearance volume. Petrol engines run roughly 8:1 to 12:1; diesel engines run 16:1 to 22:1 because ignition depends on the heat of compression.

Swept volume of one cylinder = (π/4) × bore² × stroke. Engine capacity (cc) = swept volume of one cylinder × number of cylinders.

Firing interval = 720° ÷ number of cylinders, so a four-cylinder engine fires every 180°. Typical firing orders: four-cylinder 1-3-4-2 or 1-2-4-3; six-cylinder 1-5-3-6-2-4.

Valve timing: inlet valve opens before TDC and closes after BDC; exhaust valve opens before BDC and closes after TDC. The overlap period near TDC uses inlet and exhaust gas inertia to scavenge the cylinder and improve filling.

Spark-ignition (petrol) engines ignite a pre-mixed charge with a spark plug; compression-ignition (diesel) engines inject fuel into air heated by compression, so the fuel ignites spontaneously.

Piston rings: two or three compression rings seal combustion pressure and transfer heat to the cylinder wall; one or two oil-control rings scrape surplus oil back to the sump and prevent it burning.

Valve (tappet) clearance, commonly 0.2–0.3 mm, is set with the engine cold on most designs; it allows for thermal expansion so the valve still seats fully when hot.

Main components: cylinder block and liner, cylinder head, piston and rings, gudgeon pin, connecting rod, crankshaft, flywheel, camshaft, valves and springs, and the timing drive.

Stoichiometric air-fuel ratio for petrol is about 14.7:1 by mass. Rich mixtures (about 12:1) give maximum power and cooler combustion; lean mixtures (about 16:1) give better economy but raise combustion temperature and risk misfire.

The carburettor works on the venturi (Bernoulli) principle: air accelerating through the narrowed throat loses pressure, so atmospheric pressure in the float chamber pushes fuel out through the main jet into the airstream.

Carburettor circuits: float chamber (constant fuel level), idle or pilot circuit, main metering circuit, accelerator pump (extra fuel on sudden throttle opening), choke (cold-start enrichment) and power/economy device.

Diesel fuel system: tank → pre-filter → filter → injection pump → high-pressure pipes → injectors. Injection pressure is far higher than in petrol injection, and injection timing directly controls combustion and emissions.

Stages of spark-ignition combustion: ignition lag (delay before pressure rise), flame propagation across the chamber, and afterburning. Abnormal combustion appears as detonation (knock) or pre-ignition.

Detonation causes: low-octane fuel, excessive compression ratio, over-advanced ignition timing, overheating, heavy carbon deposits and a weak mixture at high load. Remedies include retarding timing, using the specified fuel and removing deposits.

Octane number rates petrol anti-knock quality (iso-octane = 100, n-heptane = 0); higher octane permits higher compression. Cetane number rates diesel ignition quality - a higher cetane number gives a shorter ignition delay and easier cold starting.

Air cleaners: oil-bath type (older engines) and dry paper-element type. A choked filter enriches the mixture, raises fuel consumption and increases exhaust smoke, so it must be cleaned or replaced at the specified interval.

Heat balance: roughly 25–30% of fuel energy becomes useful work, about 30% leaves in the exhaust and about 30% passes to the coolant. Cooling holds metal temperatures low enough to preserve strength, oil film and clearances.

Water-cooling circuit: water jacket → thermostat → radiator → water pump (centrifugal) → back to the jacket, with a fan and shroud moving air through the radiator core.

The thermostat opens near 80–90 °C and regulates coolant flow so the engine reaches and holds its normal operating temperature quickly; a stuck-open thermostat causes overcooling and poor heater output.

A pressure cap keeps the system at about 0.9–1 bar, raising the coolant boiling point to roughly 120 °C and suppressing cavitation and evaporation. Never open a hot radiator: releasing pressure makes the coolant flash to steam.

Coolant is water plus ethylene-glycol antifreeze, commonly 50:50, which lowers the freezing point, raises the boiling point and adds corrosion inhibitors; the correct strength should be checked with a hydrometer or refractometer.

Air cooling: fins on the cylinder barrel and head increase surface area, and a fan or blower forces air across them. There is no radiator, coolant or water pump, so fin cleanliness and fan-belt condition are critical.

Lubrication methods: splash (dipper or scoop), pressure (forced by pump), combined splash-and-pressure, dry-sump (oil carried in a separate tank) and mist lubrication for two-strokes, where oil is mixed with the petrol.

Oil pump types: gear, rotor (gerotor), vane and plunger. A spring-loaded relief valve bypasses surplus oil back to the sump to limit maximum pressure and protect seals and pipes.

Lubricant duties: reduce friction and wear, carry heat away from bearings, seal piston rings, suspend and remove contaminants, and protect surfaces from corrosion. SAE 15W-40 means it meets a cold (W, winter) grade of 15 and a hot grade of 40.

Clutch duties: connect and disconnect engine and gearbox smoothly, transmit full engine torque without slip when engaged, and absorb driveline shock. Cars normally use a single dry-plate friction clutch.

Clutch components: flywheel, friction (driven) disc, pressure plate and springs, release bearing, release fork and cable or hydraulic linkage. Pedal free play is typically 20–30 mm; too little causes slip, too much causes incomplete disengagement and gear crash.

Gear ratio = teeth on driven gear ÷ teeth on driving gear. Overall ratio = gearbox ratio × final drive ratio, and torque multiplication equals the overall ratio while speed is reduced in the same proportion.

Gearbox types: sliding-mesh (gears moved into mesh), constant-mesh (gears always in mesh, engaged by dog clutches) and synchromesh (cone clutch equalises speeds before engagement). Reverse is normally sliding-mesh with no synchroniser.

Direct drive is a 1:1 ratio; overdrive has a ratio below 1, so the output turns faster than the input and engine speed falls for the same road speed.

The propeller shaft carries torque from the gearbox output to the final drive. Hooke's-type universal joints allow for suspension movement and angle changes; the slip (sliding) joint allows the shaft length to change.

The differential lets the outer wheel turn faster than the inner wheel in a turn while still dividing torque to both. Final drive ratio = crown-wheel teeth ÷ pinion teeth; hypoid bevel gears are common because they are quiet and allow a low floor line.

A limited-slip differential restricts speed difference between wheels to maintain traction; a transfer case provides high and low ranges plus front-axle drive on four-wheel-drive vehicles.

Front-wheel-drive vehicles use constant-velocity (CV) joints on the drive shafts instead of a single propeller shaft, because the shaft must transmit drive through large steering angles.

Steering path: steering wheel → column and universal joints → steering gear (rack-and-pinion or recirculating ball) → tie rods and steering arms → road wheels.

Ackermann principle: on a turn the inner wheel is steered through a larger angle than the outer wheel, so all four wheels roll about a common centre and tyre scrub is minimised.

Wheel alignment angles: camber (inward or outward tilt of the wheel top in front view), caster (fore-and-aft tilt of the steering axis, giving self-centring), king-pin inclination, and toe-in or toe-out, usually 2–6 mm of toe-in.

Steering ratio = steering wheel angle ÷ road wheel angle. A higher (slower) ratio reduces driver effort but needs more turns lock-to-lock; a lower ratio gives quicker response but heavier steering.

Suspension duties: support the vehicle weight, absorb road shocks, keep the wheels in correct geometry, and transmit driving, braking and cornering forces to the frame.

Spring types: leaf (multi-leaf, often with helper leaves), coil, torsion bar, air and rubber. The shock absorber is a damper that converts suspension movement into heat and controls spring oscillation - it does not carry weight.

Independent suspension, such as the MacPherson strut, lets each wheel move without affecting the other side, improving ride comfort, road holding and tyre contact on uneven surfaces.

Tyre size marking 165/80 R14: 165 = section width in mm, 80 = aspect ratio (sidewall height as a percentage of width), R = radial construction, 14 = rim diameter in inches.

Wheel balancing: static balancing corrects a heavy spot in one plane; dynamic balancing corrects imbalance across the wheel width. Imbalance shows as vibration through the steering or floor and causes uneven tyre wear.

Hydraulic brakes apply Pascal's law: pressure applied to a confined liquid is transmitted equally in all directions, so a small master-cylinder piston operated through a pedal lever produces high pressure at the larger wheel cylinders.

Brake fluid must be incompressible, lubricate seals and resist boiling. DOT 3 and DOT 4 are glycol-based and absorb moisture from the air; DOT 5 is silicone-based and must not be mixed with glycol fluid.

Drum brake: a wheel cylinder pushes the shoes outward against the drum. The leading shoe is self-energising in forward motion, giving strong braking for low pedal effort but poorer heat dissipation and fade resistance.

Disc brake: a caliper squeezes friction pads onto a rotating disc. There is no self-energising effect, so pedal effort is higher and a servo is normally used, but cooling, water recovery and fade resistance are better.

Air brakes are used on heavy commercial vehicles: an engine-driven compressor charges reservoirs, and a foot valve meters compressed air to brake chambers through a relay valve.

The parking or emergency brake is operated mechanically by cable or linkage, usually acts on the rear wheels, and is independent of the hydraulic circuit so it can hold a vehicle with a hydraulic failure.

ABS uses wheel-speed sensors and a hydraulic modulator to release and reapply pressure many times a second, preventing wheel lock so the driver keeps steering control during emergency braking.

Bleeding removes air from the hydraulic circuit. Air is compressible and produces a spongy, low pedal, so the system is bled in the prescribed sequence starting at the wheel farthest from the master cylinder.

Brake fade is the loss of friction when linings or discs overheat, or when linings are wet or contaminated with oil; it is managed by engine braking on long descents and by correct lining material and clearance.

The vehicle supply is nominally 12 V (24 V on many heavy vehicles). A 12 V lead-acid battery has six cells of about 2.1 V each, giving about 12.6 V at rest when fully charged.

Battery construction: positive plates of lead dioxide, negative plates of sponge lead, insulating separators, dilute sulphuric acid electrolyte, plate straps and terminal posts in a polypropylene case.

Electrolyte specific gravity is about 1.260–1.280 when fully charged and falls to about 1.120 when discharged; correct the hydrometer reading for temperature before judging state of charge.

Battery ratings: capacity in ampere-hours (Ah) at the 20-hour rate, and cold-cranking amps (CCA) - the current delivered at −18 °C for 30 s while staying above 7.2 V.

The alternator is a belt-driven three-phase AC generator; a diode rectifier converts the output to DC for charging and for the vehicle loads. The regulator holds charging voltage around 13.8–14.4 V.

The starter motor is a series-wound DC motor chosen for very high starting torque at low speed; a solenoid engages the pinion with the flywheel ring gear and closes the heavy-current motor contacts.

Conventional ignition: battery → ignition switch → ignition coil → distributor → spark plugs, with contact-breaker or electronic triggering. Spark plug gap is typically 0.6–0.9 mm and the coil generates the high voltage.

Lighting and accessories: headlamps on main and dip beam, tail, brake, reversing and indicator lamps, a flasher unit giving about 60–120 flashes per minute, horn, wipers and instruments.

Fuses and relays protect circuits. A blown fuse means an overload or short circuit; replace it only with one of the same rating, never with wire or foil, or the wiring harness can be damaged.

Vernier caliper least count = one main-scale division − one vernier-scale division; a common metric value is 0.02 mm. Reading = main-scale reading + (coinciding vernier division × least count).

Micrometer least count = screw pitch ÷ number of thimble divisions; a 0.5 mm pitch with a 50-division thimble gives 0.01 mm. Reading = barrel (sleeve) reading + thimble reading.

Special gauges: bore gauge or telescopic gauge for cylinder bore, taper and ovality; dial test indicator for run-out and end float; feeler gauge for valve clearance and plug gap; Plastigauge for bearing oil clearance.

Torque wrench readings are in N·m, kgf·m or lbf·ft. Torque = force × lever length; use the wrench only for tightening, store it at its lowest setting and recalibrate periodically.

Cylinder wear check: measure the bore at top, middle and bottom in two directions at right angles. Taper and ovality beyond the maker's limit require reboring or a new liner/block.

Preventive maintenance: daily checks of engine oil level, coolant level, tyre pressure and condition, lights and warning lamps; then periodic services at the specified time or kilometre interval for oil, filters, belts and adjustments.

Tyre pressures are set cold. Under-inflation increases rolling resistance, heat build-up and shoulder wear; over-inflation reduces the contact patch and wears the centre tread.

A compression test diagnoses piston rings, valves and head gasket: a low reading that rises when oil is added points to worn rings, while a low reading unchanged by oil points to valve leakage or a blown gasket.

Multimeter use: volts measured in parallel across a load, amps in series with the circuit, ohms across an isolated component with the supply switched off; never measure resistance on a live circuit.