Tamil Nadu HSE Second Year Basic Automobile Engineering cheat sheet

Four-stroke cycle order: intake, compression, power (expansion), exhaust; the crankshaft completes two revolutions per cycle, so one power stroke occurs every 720° of crank rotation.

Compression ratio CR = (swept volume + clearance volume) / clearance volume = (Vs + Vc) / Vc; petrol engines typically run 8:1 to 12:1, diesels 14:1 to 23:1.

Swept volume of one cylinder Vs = (π/4) × bore² × stroke; total engine capacity = Vs × number of cylinders.

Mean effective pressure relates to torque by BMEP = (2π × n × T) / Vs for a four-stroke, where n = 1 for a single-cylinder four-stroke per cycle count and T is torque.

Indicated power IP = (Pmi × L × A × N × k) / 60 for appropriate units; brake power BP = 2πNT/60 with T in N·m and N in rev/min.

Mechanical efficiency = BP / IP; volumetric efficiency = actual air inducted / theoretical swept volume, and it falls as engine speed rises beyond the torque peak.

Firing order spreads power strokes to smooth torque: common inline-four orders are 1-3-4-2 and 1-2-4-3; inline-six commonly 1-5-3-6-2-4.

Valve timing events (lead, lag, overlap) are measured in crank degrees; valve overlap improves scavenging but excessive overlap causes poor idling and backfire.

Diesel cycle heat addition is at constant pressure; Otto cycle heat addition is at constant volume - this explains the higher diesel compression ratio and thermal efficiency.

Stoichiometric air–fuel ratio is about 14.7:1 by mass for petrol; rich mixtures (e.g. 12:1) give maximum power, lean mixtures (e.g. 16:1) give best economy.

Carburettor circuits: float chamber, main metering jet, idle and progression ports, accelerator pump, choke, and power/economy enrichment valve.

MPFI injects fuel near each inlet port; the ECU computes injection pulse width from mass air flow, engine speed, coolant temperature and lambda (O2) sensor feedback.

Ignition coil steps battery voltage up to 15–30 kV; spark plug gap is typically 0.6–1.1 mm depending on ignition type, and a wider gap needs higher breakdown voltage.

Ignition timing advance is measured in crank degrees before top dead centre; excessive advance causes knocking, retarded timing causes overheating and power loss.

Cooling system: thermostat opens around 80–90 °C; a 50:50 glycol–water coolant raises boiling point and lowers freezing point; the radiator cap pressurises the system to raise boiling point.

Lubrication functions: reduce friction and wear, cool, clean, seal, and cushion shock loads; SAE 20W-50 means multigrade oil whose low-temperature viscosity is grade 20 and high-temperature viscosity grade 50.

Oil pump types include gear, rotor and vane; the pressure relief valve limits maximum oil pressure, and full-flow filters are fitted in the main gallery circuit.

Air cooling relies on fins and a fan; overheating causes are typically blocked fins, incorrect ignition timing, a stuck thermostat, a slipping belt or a failed water pump.

Clutch operation: the release bearing pushes the diaphragm spring, the pressure plate lifts, and the friction disc separates from the flywheel to break drive.

Clutch free play is measured at the pedal; too little free play causes clutch slip, too much causes incomplete disengagement (gear crunch).

Manual gearbox ratios: overall ratio = gearbox ratio × final drive ratio; engine speed = road speed × overall ratio × 60 / (2π × rolling radius) using consistent units.

Synchromesh uses a baulk ring whose cone friction matches gear speeds before the dog teeth engage, preventing gear clash.

Torque converter: impeller (pump) drives fluid into the turbine, stator redirects flow to multiply torque at stall; a lock-up clutch bypasses slip at cruising speed.

Differential function: allows outer and inner wheels to turn at different speeds during a turn while transmitting torque; bevel gear differential divides torque equally (ignoring friction).

Final drive ratio = number of crown wheel teeth / number of pinion teeth; a numerically higher ratio gives better acceleration and lower top speed.

Live axle transmits drive and carries vehicle load; independent suspension uses half-shafts with constant-velocity (CV) joints at each end.

Overdrive and fifth/sixth gears are ratio steps below 1:1 overall for economy; reverse gear uses an idler gear to reverse output direction.

Ackermann steering geometry: inner wheel turns through a larger angle than the outer wheel so all wheels roll about a common instantaneous centre.

Steering ratio = steering wheel rotation / road wheel rotation; higher ratio reduces effort but slows response; turning circle radius depends on wheelbase and maximum steer angle.

Caster angle gives self-centring and directional stability; camber is wheel tilt from vertical; toe-in/out is the difference in front and rear track measured at wheel height.

Suspension types: MacPherson strut, double wishbone, trailing arm, leaf spring (live axle); coil springs store energy, dampers (shock absorbers) dissipate it as heat.

Spring rate k = force / deflection (N/mm); natural frequency of a suspension is proportional to √(k/m), so stiffer springs raise ride frequency.

Hydraulic brake principle: pedal force × pedal ratio creates hydraulic pressure P = F/A; larger wheel-cylinder area gives more force but longer pedal travel.

Brake fade is loss of friction from heat; disc brakes resist fade better than drum brakes because they cool in open air.

ABS prevents wheel lock by modulating brake pressure using wheel-speed sensors; it preserves steering control during hard braking.

Parking brake acts mechanically on rear wheels; bleeding removes air from the hydraulic circuit because air is compressible and causes a spongy pedal.

Ohm's law V = I × R; power P = V × I = I²R. A 12 V system drawing 60 W takes 5 A.

Lead-acid battery: each cell gives about 2.1 V, so a 12 V battery has six cells in series; capacity is rated in ampere-hours (Ah) at a stated discharge rate.

Specific gravity of battery electrolyte indicates state of charge; a fully charged cell reads about 1.26–1.28, discharged near 1.10–1.15.

Alternator generates AC rectified by a diode bridge; the voltage regulator holds about 13.8–14.5 V charging voltage on a 12 V system.

Starter motor draws very high current (hundreds of amperes); the solenoid engages the pinion with the flywheel ring gear and switches the heavy current.

Series-wound DC motors give high starting torque, which is why they are used as starter motors.

Fuses protect circuits by melting at rated current; a relay uses a small control current to switch a large load current.

Electronic control unit inputs include sensors (MAP, TPS, coolant temperature, oxygen); outputs drive injectors, ignition coils and idle actuators.

CAN bus allows ECUs to share data on a twisted pair; a shorted or open bus halts communication and triggers multiple fault codes.

Tyre marking 185/65 R15 88H: 185 mm section width, 65% aspect ratio, radial construction, 15 inch rim, 88 load index, H speed rating.

Rolling circumference = π × (rim diameter in mm + 2 × section height); section height = section width × aspect ratio.

Wheel alignment angles: camber, caster, toe, and steering axis inclination; incorrect toe causes rapid, feathered tyre wear.

Under-inflation causes shoulder wear and heat build-up; over-inflation causes centre-tread wear and reduced grip.

Wheel balancing corrects dynamic imbalance with weights on the rim; static imbalance causes bounce, dynamic imbalance causes shimmy.

Torque wrench use: tighten wheel nuts in a star sequence to the manufacturer's torque to avoid disc distortion.

Measuring tools: vernier calliper (0.02 mm least count typical), micrometer (0.01 mm), feeler gauge for valve clearances, dial gauge for runout.

Body construction: monocoque (stressed body shell) versus body-on-frame; crumple zones absorb energy in a collision while the passenger cell stays rigid.

Workshop safety: chock wheels before jacking, use axle stands, disconnect the battery negative terminal first, and never work under a vehicle held only by a jack.

Periodic service items: engine oil and filter, air filter, fuel filter, coolant, brake fluid, spark plugs, belts, and tyre rotation.

Engine won't start - check sequence: battery charge and terminals, starter operation, fuel delivery, ignition spark, then compression.

Blue exhaust smoke indicates oil burning (worn rings or valve guides); black smoke indicates rich mixture or incomplete combustion; white smoke indicates coolant burning or condensation.

Overheating diagnosis order: coolant level, fan and belt, thermostat, radiator blockage, water pump, ignition timing, head gasket.

Brake pedal spongy = air in the hydraulic system; pedal sinks slowly under steady pressure = internal master cylinder leak.

Vibration at a specific road speed usually indicates wheel imbalance or a bent rim; vibration under braking indicates warped discs.

Engine knock (pinging) causes: over-advanced ignition timing, low-octane fuel, carbon deposits, or overheating.

Oil pressure warning light on: check oil level, oil pump, relief valve, and the pressure switch before running the engine further.

Tyre rotation extends tread life; check tread depth (minimum legal limit commonly 1.6 mm) and inspect for uneven wear patterns.

Electric vehicle traction battery packs commonly use lithium-ion cells; nominal cell voltage is about 3.6–3.7 V, and packs are series–parallel combinations with a battery management system (BMS).

EV range depends on battery energy (kWh) divided by consumption (Wh/km); regenerative braking recovers kinetic energy back to the battery.

Electric motor torque is maximum from zero speed, so EVs need no clutch or multi-speed gearbox in most designs.

Hybrid types: series (engine drives generator only), parallel (engine and motor both drive wheels), and series–parallel (power-split).

Battery electric vs fuel cell: fuel cell vehicles convert hydrogen and oxygen to electricity, emitting water vapour only.

Biofuels: ethanol blended with petrol (E10, E20), biodiesel blended with diesel (B5, B20); higher blends affect fuel system materials and combustion.

CNG and LPG are stored under pressure; CNG gives lower running cost but reduces luggage space and power output.

BS-VI emission norms limit particulate matter and NOx with diesel particulate filters and selective catalytic reduction (SCR) using AdBlue (urea solution).

OBD-II monitors emission-related components and stores diagnostic trouble codes read through a standard 16-pin connector.

Four-stroke cycle: intake, compression, power, exhaust; crankshaft makes two revolutions per cycle, one power stroke every 720° of crank rotation.

Compression ratio CR = (swept volume + clearance volume) / clearance volume; typical petrol 8:1–12:1, diesel 14:1–23:1.

Swept volume per cylinder Vs = (π/4) × bore² × stroke; engine capacity = Vs × number of cylinders.

Brake power BP = 2πNT/60 with T in N·m and N in rev/min; mechanical efficiency = BP / IP.

Volumetric efficiency = actual air inducted / theoretical swept volume; falls as speed rises beyond the torque peak.

Firing order spreads power strokes: common inline-four orders are 1-3-4-2 and 1-2-4-3.

Valve overlap improves scavenging but excessive overlap causes poor idling and backfire.

Diesel cycle adds heat at constant pressure; Otto cycle adds heat at constant volume, explaining the higher diesel compression ratio.

Stoichiometric petrol air–fuel ratio is about 14.7:1; rich (12:1) gives maximum power, lean (16:1) gives best economy.

Carburettor circuits: float chamber, main metering jet, idle and progression ports, accelerator pump, choke, power enrichment valve.

MPFI ECU sets injection pulse width from mass air flow, engine speed, coolant temperature and lambda sensor feedback.

Ignition coil produces 15–30 kV; spark plug gap typically 0.6–1.1 mm; excessive advance causes knock, retarded timing causes overheating.

Thermostat opens around 80–90 °C; 50:50 glycol–water coolant raises boiling point and lowers freezing point.

SAE 20W-50 is multigrade: grade 20 low-temperature viscosity, grade 50 high-temperature viscosity.

Lubrication functions: reduce friction and wear, cool, clean, seal, and cushion shock loads.

Overheating causes include blocked fins, incorrect ignition timing, stuck thermostat, slipping belt, failed water pump.

Clutch: release bearing pushes diaphragm spring, pressure plate lifts, friction disc separates from flywheel to break drive.

Too little clutch pedal free play causes slip; too much causes incomplete disengagement and gear crunch.

Overall ratio = gearbox ratio × final drive ratio; engine speed relates to road speed through overall ratio and rolling radius.

Synchromesh baulk ring uses cone friction to match gear speeds before dog teeth engage, preventing clash.

Torque converter: impeller drives fluid into turbine, stator multiplies torque at stall, lock-up clutch bypasses slip at cruise.

Differential allows inner and outer wheels to turn at different speeds in a turn while transmitting torque.

Final drive ratio = crown wheel teeth / pinion teeth; numerically higher ratio gives better acceleration, lower top speed.

Live axle carries load and drive; independent suspension uses half-shafts with CV joints.

Reverse gear uses an idler gear to reverse output direction.

Ackermann geometry: inner wheel turns more than outer so all wheels roll about a common instantaneous centre.

Steering ratio = steering wheel rotation / road wheel rotation; higher ratio reduces effort but slows response.

Caster gives self-centring; camber is wheel tilt from vertical; toe is difference in track at wheel height.

Spring rate k = force / deflection (N/mm); stiffer springs raise natural frequency proportional to √(k/m).

Dampers dissipate spring energy as heat; MacPherson strut, double wishbone and leaf spring are common layouts.

Hydraulic brake pressure P = F/A; larger wheel-cylinder area gives more force but longer pedal travel.

Disc brakes resist fade better than drum brakes because they cool in open air.

ABS modulates brake pressure using wheel-speed sensors to prevent lock and preserve steering control.

Spongy pedal indicates air in the hydraulic circuit; bleeding removes it.

Ohm's law V = I × R; power P = V × I = I²R; a 12 V system drawing 60 W takes 5 A.

Lead-acid cell gives about 2.1 V; a 12 V battery has six cells in series; capacity rated in Ah.

Electrolyte specific gravity about 1.26–1.28 fully charged, 1.10–1.15 discharged.

Alternator output is rectified AC; voltage regulator holds about 13.8–14.5 V charging on a 12 V system.

Series-wound DC motor gives high starting torque, used as starter motor; solenoid engages pinion with flywheel ring gear.

Fuses melt at rated current to protect circuits; relays switch large load current with small control current.

ECU inputs are sensors (MAP, TPS, coolant temperature, oxygen); outputs drive injectors, coils and idle actuators.

CAN bus shares data between ECUs on a twisted pair; open or shorted bus halts communication and sets multiple fault codes.

Tyre marking 185/65 R15 88H: 185 mm width, 65% aspect ratio, radial, 15 inch rim, 88 load index, H speed rating.

Section height = section width × aspect ratio; rolling circumference = π × (rim diameter in mm + 2 × section height).

Alignment angles: camber, caster, toe, steering axis inclination; incorrect toe causes feathered tyre wear.

Under-inflation causes shoulder wear; over-inflation causes centre-tread wear and reduced grip.

Static imbalance causes bounce; dynamic imbalance causes shimmy; corrected with rim weights.

Tighten wheel nuts in a star sequence to the specified torque to avoid disc distortion.

Vernier calliper least count typically 0.02 mm; micrometer 0.01 mm; feeler gauge for valve clearance; dial gauge for runout.

Monocoque body is a stressed shell; crumple zones absorb collision energy while the passenger cell stays rigid.

Jacking safety: chock wheels, use axle stands, disconnect battery negative first, never work under a vehicle held only by a jack.

Periodic service items: engine oil and filter, air filter, fuel filter, coolant, brake fluid, spark plugs, belts, tyre rotation.

No-start check order: battery charge and terminals, starter operation, fuel delivery, ignition spark, then compression.

Blue smoke = oil burning; black smoke = rich mixture or incomplete combustion; white smoke = coolant burning or condensation.

Overheating diagnosis order: coolant level, fan and belt, thermostat, radiator blockage, water pump, ignition timing, head gasket.

Spongy pedal = air in hydraulics; pedal sinking slowly under steady pressure = internal master cylinder leak.

Vibration at a road speed indicates wheel imbalance or bent rim; vibration under braking indicates warped discs.

Knock causes: over-advanced timing, low-octane fuel, carbon deposits, overheating.

Oil pressure warning on: check oil level, pump, relief valve and pressure switch before running the engine further.

Minimum tread depth commonly 1.6 mm; inspect for uneven wear patterns and rotate tyres to extend life.

Lithium-ion cell nominal voltage about 3.6–3.7 V; packs are series–parallel combinations managed by a battery management system (BMS).

EV energy use: range = battery energy (kWh) / consumption (Wh/km); regenerative braking recovers kinetic energy to the battery.

Electric motor gives maximum torque from zero speed, so most EVs need no clutch or multi-speed gearbox.

Hybrid types: series (engine drives generator only), parallel (engine and motor both drive wheels), series–parallel (power-split).

Fuel cell vehicles convert hydrogen and oxygen to electricity, emitting water vapour only.

Biofuel blends: ethanol in petrol (E10, E20), biodiesel in diesel (B5, B20); higher blends affect fuel system materials.

CNG and LPG are stored under pressure; CNG lowers running cost but reduces luggage space and power.

BS-VI norms limit particulate matter and NOx using diesel particulate filters and SCR with AdBlue urea solution.

OBD-II monitors emission components and stores diagnostic trouble codes read through a standard 16-pin connector.

Four-stroke cycle order: intake, compression, power, exhaust; two crankshaft revolutions per cycle, one power stroke per 720° crank rotation.

Compression ratio CR = (swept volume + clearance volume) / clearance volume; petrol 8:1–12:1, diesel 14:1–23:1.

Swept volume per cylinder Vs = (π/4) × bore² × stroke; total capacity = Vs × number of cylinders.

Brake power BP = 2πNT/60 (T in N·m, N in rev/min); mechanical efficiency = BP / IP.

Volumetric efficiency = actual air inducted / theoretical swept volume; falls as speed rises beyond the torque peak.

Firing order spreads power strokes; common inline-four orders are 1-3-4-2 and 1-2-4-3.

Valve overlap improves scavenging but excessive overlap causes poor idling and backfire.

Diesel cycle heat addition is at constant pressure; Otto cycle at constant volume, explaining the higher diesel compression ratio.

Stoichiometric petrol air–fuel ratio about 14.7:1; rich (12:1) gives maximum power, lean (16:1) gives best economy.

Carburettor circuits: float chamber, main metering jet, idle and progression ports, accelerator pump, choke, power enrichment valve.

MPFI ECU computes injection pulse width from mass air flow, engine speed, coolant temperature and lambda sensor feedback.

Ignition coil steps voltage to 15–30 kV; spark plug gap typically 0.6–1.1 mm; excessive advance causes knock, retarded timing causes overheating.

Thermostat opens around 80–90 °C; 50:50 glycol–water coolant raises boiling point and lowers freezing point.

SAE 20W-50 multigrade: grade 20 low-temperature viscosity, grade 50 high-temperature viscosity.

Lubrication functions: reduce friction and wear, cool, clean, seal, cushion shock loads.

Overheating causes: blocked fins, incorrect ignition timing, stuck thermostat, slipping belt, failed water pump.

Clutch: release bearing pushes diaphragm spring, pressure plate lifts, friction disc separates from flywheel.

Too little clutch free play causes slip; too much causes incomplete disengagement and gear crunch.

Overall ratio = gearbox ratio × final drive ratio; engine speed depends on road speed, overall ratio and rolling radius.

Synchromesh baulk ring uses cone friction to match gear speeds before dog teeth engage, preventing clash.

Torque converter: impeller drives fluid into turbine; stator multiplies torque at stall; lock-up clutch bypasses slip at cruise.

Differential allows inner and outer wheels to turn at different speeds in a turn while transmitting torque.

Final drive ratio = crown wheel teeth / pinion teeth; numerically higher ratio gives better acceleration, lower top speed.

Live axle carries load and drive; independent suspension uses half-shafts with CV joints.

Reverse gear uses an idler gear to reverse output direction.

Ackermann geometry: inner wheel turns more than outer so all wheels roll about a common instantaneous centre.

Steering ratio = steering wheel rotation / road wheel rotation; higher ratio reduces effort but slows response.

Caster gives self-centring; camber is wheel tilt from vertical; toe is difference in track at wheel height.

Spring rate k = force / deflection (N/mm); natural frequency proportional to √(k/m).

Dampers dissipate spring energy as heat; MacPherson strut, double wishbone and leaf spring are common layouts.

Hydraulic brake pressure P = F/A; larger wheel-cylinder area gives more force but longer pedal travel.

Disc brakes resist fade better than drum brakes because they cool in open air.

ABS modulates brake pressure using wheel-speed sensors to prevent lock and preserve steering control.

Spongy pedal indicates air in the hydraulic circuit; bleeding removes it.

Ohm's law V = I × R; power P = V × I = I²R; a 12 V system drawing 60 W takes 5 A.

Lead-acid cell about 2.1 V; 12 V battery has six cells in series; capacity rated in Ah.

Electrolyte specific gravity about 1.26–1.28 fully charged, 1.10–1.15 discharged.

Alternator output is rectified AC; voltage regulator holds about 13.8–14.5 V charging on a 12 V system.

Series-wound DC motor gives high starting torque, used as starter motor; solenoid engages pinion with flywheel ring gear.

Fuses melt at rated current to protect circuits; relays switch large load current with small control current.

ECU inputs are sensors (MAP, TPS, coolant temperature, oxygen); outputs drive injectors, coils and idle actuators.

CAN bus shares data between ECUs on a twisted pair; open or shorted bus halts communication and sets multiple fault codes.

Tyre marking 185/65 R15 88H: 185 mm width, 65% aspect ratio, radial, 15 inch rim, 88 load index, H speed rating.

Section height = section width × aspect ratio; rolling circumference = π × (rim diameter in mm + 2 × section height).

Alignment angles: camber, caster, toe, steering axis inclination; incorrect toe causes feathered tyre wear.

Under-inflation causes shoulder wear; over-inflation causes centre-tread wear and reduced grip.

Static imbalance causes bounce; dynamic imbalance causes shimmy; corrected with rim weights.

Tighten wheel nuts in a star sequence to the specified torque to avoid disc distortion.

Vernier calliper least count typically 0.02 mm; micrometer 0.01 mm; feeler gauge for valve clearance; dial gauge for runout.

Monocoque body is a stressed shell; crumple zones absorb collision energy while the passenger cell stays rigid.

Jacking safety: chock wheels, use axle stands, disconnect battery negative first, never work under a vehicle held only by a jack.

Periodic service items: engine oil and filter, air filter, fuel filter, coolant, brake fluid, spark plugs, belts, tyre rotation.

No-start check order: battery charge and terminals, starter operation, fuel delivery, ignition spark, then compression.

Blue smoke = oil burning; black smoke = rich mixture or incomplete combustion; white smoke = coolant burning or condensation.

Overheating diagnosis order: coolant level, fan and belt, thermostat, radiator blockage, water pump, ignition timing, head gasket.

Spongy pedal = air in hydraulics; pedal sinking slowly under steady pressure = internal master cylinder leak.

Vibration at a road speed indicates wheel imbalance or bent rim; vibration under braking indicates warped discs.

Knock causes: over-advanced timing, low-octane fuel, carbon deposits, overheating.

Oil pressure warning on: check oil level, pump, relief valve and pressure switch before running the engine further.

Minimum tread depth commonly 1.6 mm; inspect for uneven wear patterns and rotate tyres to extend life.

Lithium-ion cell nominal voltage about 3.6–3.7 V; packs are series–parallel combinations managed by a battery management system (BMS).

EV range = battery energy (kWh) / consumption (Wh/km); regenerative braking recovers kinetic energy to the battery.

Electric motor gives maximum torque from zero speed, so most EVs need no clutch or multi-speed gearbox.

Hybrid types: series (engine drives generator only), parallel (engine and motor both drive wheels), series–parallel (power-split).

Fuel cell vehicles convert hydrogen and oxygen to electricity, emitting water vapour only.

Biofuel blends: ethanol in petrol (E10, E20), biodiesel in diesel (B5, B20); higher blends affect fuel system materials.

CNG and LPG are stored under pressure; CNG lowers running cost but reduces luggage space and power.

BS-VI norms limit particulate matter and NOx using diesel particulate filters and SCR with AdBlue urea solution.

OBD-II monitors emission components and stores diagnostic trouble codes read through a standard 16-pin connector.

Four-stroke cycle order: intake, compression, power, exhaust; two crankshaft revolutions per cycle, one power stroke per 720° crank rotation.

Compression ratio CR = (swept volume + clearance volume) / clearance volume; petrol 8:1–12:1, diesel 14:1–23:1.

Swept volume per cylinder Vs = (π/4) × bore² × stroke; total capacity = Vs × number of cylinders.

Brake power BP = 2πNT/60 (T in N·m, N in rev/min); mechanical efficiency = BP / IP.

Volumetric efficiency = actual air inducted / theoretical swept volume; falls as speed rises beyond the torque peak.

Firing order spreads power strokes; common inline-four orders are 1-3-4-2 and 1-2-4-3.

Valve overlap improves scavenging but excessive overlap causes poor idling and backfire.

Diesel cycle heat addition is at constant pressure; Otto cycle at constant volume, explaining the higher diesel compression ratio.

Stoichiometric petrol air–fuel ratio about 14.7:1; rich (12:1) gives maximum power, lean (16:1) gives best economy.

Carburettor circuits: float chamber, main metering jet, idle and progression ports, accelerator pump, choke, power enrichment valve.

MPFI ECU computes injection pulse width from mass air flow, engine speed, coolant temperature and lambda sensor feedback.

Ignition coil steps voltage to 15–30 kV; spark plug gap typically 0.6–1.1 mm; excessive advance causes knock, retarded timing causes overheating.

Thermostat opens around 80–90 °C; 50:50 glycol–water coolant raises boiling point and lowers freezing point.

SAE 20W-50 multigrade: grade 20 low-temperature viscosity, grade 50 high-temperature viscosity.

Lubrication functions: reduce friction and wear, cool, clean, seal, cushion shock loads.

Overheating causes: blocked fins, incorrect ignition timing, stuck thermostat, slipping belt, failed water pump.

Clutch: release bearing pushes diaphragm spring, pressure plate lifts, friction disc separates from flywheel.

Too little clutch free play causes slip; too much causes incomplete disengagement and gear crunch.

Overall ratio = gearbox ratio × final drive ratio; engine speed depends on road speed, overall ratio and rolling radius.

Synchromesh baulk ring uses cone friction to match gear speeds before dog teeth engage, preventing clash.

Torque converter: impeller drives fluid into turbine; stator multiplies torque at stall; lock-up clutch bypasses slip at cruise.

Differential allows inner and outer wheels to turn at different speeds in a turn while transmitting torque.

Final drive ratio = crown wheel teeth / pinion teeth; numerically higher ratio gives better acceleration, lower top speed.

Live axle carries load and drive; independent suspension uses half-shafts with CV joints.

Reverse gear uses an idler gear to reverse output direction.

Ackermann geometry: inner wheel turns more than outer so all wheels roll about a common instantaneous centre.

Steering ratio = steering wheel rotation / road wheel rotation; higher ratio reduces effort but slows response.

Caster gives self-centring; camber is wheel tilt from vertical; toe is difference in track at wheel height.

Spring rate k = force / deflection (N/mm); natural frequency proportional to √(k/m).

Dampers dissipate spring energy as heat; MacPherson strut, double wishbone and leaf spring are common layouts.

Hydraulic brake pressure P = F/A; larger wheel-cylinder area gives more force but longer pedal travel.

Disc brakes resist fade better than drum brakes because they cool in open air.

ABS modulates brake pressure using wheel-speed sensors to prevent lock and preserve steering control.

Spongy pedal indicates air in the hydraulic circuit; bleeding removes it.

Ohm's law V = I × R; power P = V × I = I²R; a 12 V system drawing 60 W takes 5 A.

Lead-acid cell about 2.1 V; 12 V battery has six cells in series; capacity rated in Ah.

Electrolyte specific gravity about 1.26–1.28 fully charged, 1.10–1.15 discharged.

Alternator output is rectified AC; voltage regulator holds about 13.8–14.5 V charging on a 12 V system.

Series-wound DC motor gives high starting torque, used as starter motor; solenoid engages pinion with flywheel ring gear.

Fuses melt at rated current to protect circuits; relays switch large load current with small control current.

ECU inputs are sensors (MAP, TPS, coolant temperature, oxygen); outputs drive injectors, coils and idle actuators.

CAN bus shares data between ECUs on a twisted pair; open or shorted bus halts communication and sets multiple fault codes.

Tyre marking 185/65 R15 88H: 185 mm width, 65% aspect ratio, radial, 15 inch rim, 88 load index, H speed rating.

Section height = section width × aspect ratio; rolling circumference = π × (rim diameter in mm + 2 × section height).

Alignment angles: camber, caster, toe, steering axis inclination; incorrect toe causes feathered tyre wear.

Under-inflation causes shoulder wear; over-inflation causes centre-tread wear and reduced grip.

Static imbalance causes bounce; dynamic imbalance causes shimmy; corrected with rim weights.

Tighten wheel nuts in a star sequence to the specified torque to avoid disc distortion.

Vernier calliper least count typically 0.02 mm; micrometer 0.01 mm; feeler gauge for valve clearance; dial gauge for runout.

Monocoque body is a stressed shell; crumple zones absorb collision energy while the passenger cell stays rigid.

Jacking safety: chock wheels, use axle stands, disconnect battery negative first, never work under a vehicle held only by a jack.

Periodic service items: engine oil and filter, air filter, fuel filter, coolant, brake fluid, spark plugs, belts, tyre rotation.

No-start check order: battery charge and terminals, starter operation, fuel delivery, ignition spark, then compression.

Blue smoke = oil burning; black smoke = rich mixture or incomplete combustion; white smoke = coolant burning or condensation.

Overheating diagnosis order: coolant level, fan and belt, thermostat, radiator blockage, water pump, ignition timing, head gasket.

Spongy pedal = air in hydraulics; pedal sinking slowly under steady pressure = internal master cylinder leak.

Vibration at a road speed indicates wheel imbalance or bent rim; vibration under braking indicates warped discs.

Knock causes: over-advanced timing, low-octane fuel, carbon deposits, overheating.

Oil pressure warning on: check oil level, pump, relief valve and pressure switch before running the engine further.

Minimum tread depth commonly 1.6 mm; inspect for uneven wear patterns and rotate tyres to extend life.

Lithium-ion cell nominal voltage about 3.6–3.7 V; packs are series–parallel combinations managed by a battery management system (BMS).

EV range = battery energy (kWh) / consumption (Wh/km); regenerative braking recovers kinetic energy to the battery.

Electric motor gives maximum torque from zero speed, so most EVs need no clutch or multi-speed gearbox.

Hybrid types: series (engine drives generator only), parallel (engine and motor both drive wheels), series–parallel (power-split).

Fuel cell vehicles convert hydrogen and oxygen to electricity, emitting water vapour only.

Biofuel blends: ethanol in petrol (E10, E20), biodiesel in diesel (B5, B20); higher blends affect fuel system materials.

CNG and LPG are stored under pressure; CNG lowers running cost but reduces luggage space and power.

BS-VI norms limit particulate matter and NOx using diesel particulate filters and SCR with AdBlue urea solution.

OBD-II monitors emission components and stores diagnostic trouble codes read through a standard 16-pin connector.