Basic Automobile interview questions

150 questions with answers (AUT-001 to AUT-150). Try each one aloud before reading the answer.

Engine Fundamentals

AUT-001 · What are the four strokes of a four-stroke engine?

Intake, compression, power (expansion) and exhaust. The crankshaft turns twice (720°) per cycle, and each cylinder fires once every two revolutions.

AUT-002 · What is the difference between an SI and a CI engine?

An SI engine uses a spark plug to ignite a premixed petrol–air charge at a lower compression ratio (about 8–12). A CI engine ignites diesel injected into hot compressed air at a higher compression ratio (about 14–22).

AUT-003 · What is the function of a radiator?

It removes engine heat from the coolant by passing it through thin tubes and fins, where air flowing past (ram air or fan) carries the heat away before the coolant returns to the engine.

AUT-004 · What is compression ratio?

The ratio of total cylinder volume at BDC to clearance volume at TDC: CR = (Vs + Vc)/Vc. Higher CR raises thermal efficiency but increases knock tendency in SI engines.

AUT-005 · What is engine displacement (swept volume)?

The volume swept by all pistons in one stroke. Per cylinder Vs = (π/4)·D²·L, multiplied by the number of cylinders. A 4-cylinder engine of 80 mm bore and 80 mm stroke displaces about 1.61 L.

AUT-006 · How does a two-stroke engine differ from a four-stroke engine?

A two-stroke completes the cycle in one crank revolution using ports for scavenging, so it fires every revolution and has high power-to-weight. It suffers from charge short-circuiting, higher HC emissions and total-loss lubrication.

AUT-007 · What are TDC and BDC?

Top dead centre and bottom dead centre: the piston positions farthest from and nearest to the crankshaft, where piston velocity is momentarily zero. The distance between them is the stroke.

AUT-008 · What is the function of a flywheel?

It stores rotational kinetic energy to smooth out torque fluctuations between power strokes, helps the engine idle steadily, carries the starter ring gear and provides the friction face for the clutch.

AUT-009 · What does a camshaft do?

It opens and closes the intake and exhaust valves via lobes at the right crank angles. In a four-stroke engine it rotates at half crankshaft speed, driven by a belt, chain or gears.

AUT-010 · What is valve overlap?

The period around TDC at the end of exhaust and start of intake when both valves are open. It uses exhaust momentum to scavenge the cylinder and improve breathing at high speed.

AUT-011 · What is the function of piston rings?

Compression rings seal combustion gas and transfer heat from the piston to the cylinder wall. The oil control ring scrapes excess oil from the bore to limit oil consumption.

AUT-012 · Why does an engine need lubrication?

To reduce friction and wear between moving parts, carry away heat, seal piston rings, clean deposits, prevent corrosion and cushion bearing loads with a hydrodynamic oil film.

AUT-013 · What does a thermostat do in the cooling system?

It blocks coolant flow to the radiator until the engine reaches operating temperature, then opens progressively to hold temperature steady. This speeds warm-up and reduces wear and emissions.

Fuel Systems & Combustion

AUT-014 · What is the octane number of a fuel?

A measure of a petrol's resistance to knock, defined as the percentage of iso-octane in an iso-octane/n-heptane blend that knocks equally in a test engine. Higher octane allows higher compression or more spark advance.

AUT-015 · What is the cetane number of a fuel?

A measure of a diesel fuel's ignition quality, based on cetane (100) and a low-ignitability reference fuel. Higher cetane means shorter ignition delay, smoother combustion and easier cold starts.

AUT-016 · What is the stoichiometric air–fuel ratio for petrol?

About 14.7:1 by mass: the exact air needed to burn all the fuel completely to CO₂ and H₂O. Diesel is close at about 14.5:1.

AUT-017 · What is a carburettor?

A device that meters fuel into the intake air using the pressure drop at a venturi. It has been replaced by electronic fuel injection, which meters fuel more precisely for emissions control.

AUT-018 · What is MPFI?

Multi-point fuel injection: one injector per cylinder sprays petrol into the intake port just upstream of the intake valve, with timing and quantity controlled by the ECU.

AUT-019 · What is gasoline direct injection (GDI)?

Petrol is injected at high pressure directly into the combustion chamber. Charge cooling allows higher compression and better efficiency, but GDI tends to produce more particulates than port injection.

AUT-020 · What is a CRDi system?

Common Rail Direct Injection: a high-pressure pump keeps diesel in a shared rail, and ECU-controlled injectors fire it into each cylinder. Injection pressure is independent of engine speed and allows multiple injections per cycle.

AUT-021 · What is knock in an SI engine?

Auto-ignition of the unburnt end gas ahead of the flame front, causing sharp pressure waves and a metallic pinging sound. Severe knock can damage pistons and head gaskets.

AUT-022 · What does a fuel injector do?

It is a solenoid- or piezo-actuated valve that sprays a metered quantity of atomised fuel. The ECU controls fuel quantity through the injector's opening duration (pulse width).

AUT-023 · What is lambda (λ)?

The ratio of actual air–fuel ratio to stoichiometric air–fuel ratio. λ = 1 is stoichiometric, λ > 1 is lean and λ < 1 is rich.

AUT-024 · What does the fuel pump do?

It delivers fuel from the tank to the injection system at the required pressure. Modern petrol cars use an electric pump in the tank; diesel common-rail systems add an engine-driven high-pressure pump.

AUT-025 · What is the function of a spark plug?

It produces an electric arc across its electrode gap, using a high voltage from the ignition coil, to ignite the air–fuel mixture near the end of the compression stroke.

AUT-026 · What are lean and rich mixtures?

A lean mixture has more air than stoichiometric (λ > 1). A rich mixture has excess fuel (λ < 1). Rich mixtures give more power and cooling but raise CO and HC; lean mixtures save fuel but can raise NOx and misfire.

Clutch, Gearbox & Transmission

AUT-027 · What is a clutch?

A device that engages and disengages engine power from the transmission, allowing smooth starts, gear changes and stopping without stalling the engine.

AUT-028 · What are the main parts of a single-plate dry clutch?

Flywheel, clutch (friction) plate on the splined input shaft, pressure plate, diaphragm or coil springs, clutch cover and release (throw-out) bearing operated by a cable or hydraulic actuator.

AUT-029 · Why does a vehicle need a gearbox?

An engine gives useful torque only over a narrow speed range. The gearbox provides several ratios so the vehicle gets high tractive effort at low speed and efficient cruising at high speed, plus reverse and neutral.

AUT-030 · What is a gear ratio?

The ratio of driven gear teeth to driver gear teeth, equal to input speed divided by output speed. A ratio above 1 reduces speed and multiplies torque by the same factor (ignoring losses).

AUT-031 · What is a synchromesh gearbox?

A constant-mesh gearbox with synchroniser cones and blocker rings that match the speeds of the gear and shaft by friction before the dog teeth engage, giving quiet, clash-free shifts.

AUT-032 · What is the difference between a manual and an automatic transmission?

In a manual the driver operates the clutch and selects gears. An automatic selects ratios itself, usually with a torque converter and planetary gear sets controlled hydraulically or electronically.

AUT-033 · What is a torque converter?

A fluid coupling with an impeller, turbine and stator that transmits engine torque through oil. The stator redirects flow so torque is multiplied at low speed ratio, typically about 2:1 at stall.

AUT-034 · What is a CVT?

A continuously variable transmission that gives infinitely many ratios between limits, usually with a steel belt or chain running between two variable-diameter pulleys. It keeps the engine at its most efficient speed.

AUT-035 · What is an AMT?

An automated manual transmission: a conventional manual gearbox and dry clutch whose clutch and gear shifts are operated by electro-hydraulic or electric actuators under control of a transmission ECU.

AUT-036 · What is a dual-clutch transmission (DCT)?

A gearbox with two clutches, one for odd and one for even gears, on concentric shafts. The next gear is pre-selected, so shifts happen by swapping clutches with almost no torque interruption.

AUT-037 · What is overdrive?

A gear ratio below 1:1, where the output shaft turns faster than the engine. It lowers engine rpm at cruising speed for better fuel economy and less noise.

AUT-038 · How is reverse gear achieved in a manual gearbox?

An idler gear is placed between the countershaft and the main shaft gears. The extra mesh reverses the direction of rotation of the output shaft.

AUT-039 · What is clutch slip?

A condition where the clutch plate does not lock fully to the flywheel under load, so engine speed rises without matching road speed. Causes include worn linings, oil contamination or weak springs.

Driveline & Differential

AUT-040 · What does a differential do?

It lets the left and right drive wheels rotate at different speeds while cornering, while still delivering drive torque to both. The outer wheel travels farther than the inner wheel in a turn.

AUT-041 · What is a propeller shaft?

A tubular shaft that transmits torque from the gearbox to the rear axle in front-engine rear-wheel-drive vehicles. It has universal joints at its ends and a slip joint to allow for length change.

AUT-042 · What is a universal joint?

A Hooke's (cross-type) joint that connects two shafts at an angle to transmit rotation. A single joint gives non-uniform output speed, so two joints are usually used in phase to cancel the fluctuation.

AUT-043 · What is a CV joint?

A constant-velocity joint (Rzeppa ball type or tripod type) that transmits uniform angular speed at large and varying angles. It is used in front-wheel-drive half shafts where the wheels also steer.

AUT-044 · What is a final drive?

The last gear reduction between the gearbox and the driven wheels, usually a crown wheel and pinion with a ratio of about 3–4.5 in cars. It also turns the drive through 90° in RWD layouts.

AUT-045 · What is the difference between FWD and RWD?

In FWD the front wheels both drive and steer, which is compact and cheaper. In RWD the rear wheels drive, giving better weight distribution, traction under acceleration and handling balance.

AUT-046 · What is the difference between AWD and 4WD?

AWD drives all wheels continuously or on demand, using a centre differential or coupling for on-road use. Traditional 4WD uses a transfer case, often with a low range and locking, for off-road use.

AUT-047 · What is a slip joint in a propeller shaft?

A splined sliding coupling that lets the propeller shaft length change as the rear axle moves up and down on the suspension.

AUT-048 · What is a limited-slip differential (LSD)?

A differential that limits the speed difference between the two wheels using clutch packs, gears (Torsen) or viscous couplings. It sends more torque to the wheel with more grip when one wheel spins.

AUT-049 · What is a half shaft?

A drive shaft that carries torque from the differential to a single wheel. In FWD cars it has an inner plunging CV joint and an outer fixed CV joint.

AUT-050 · What is the difference between a live axle and a dead axle?

A live axle transmits drive torque to the wheels as well as carrying load. A dead axle only supports the vehicle weight and does not transmit drive.

AUT-051 · What is a transfer case?

A gearbox in 4WD vehicles that splits drive between the front and rear axles, and often provides a low-range reduction for off-road use.

Suspension

AUT-052 · What is the purpose of a suspension system?

It isolates the body from road irregularities, keeps tyres in contact with the road for grip, controls body motions (roll, pitch, bounce) and supports the vehicle weight.

AUT-053 · What is a leaf spring?

A spring made of curved steel strips (leaves) clamped together, which flexes under load. It can also locate the axle, so it is common on trucks and rigid rear axles.

AUT-054 · What is a coil spring?

A helical steel spring that stores energy in torsion of the wire. It is compact and light, but cannot locate the wheel, so it needs links or a strut.

AUT-055 · What is a shock absorber?

A damper that converts the kinetic energy of suspension motion into heat by forcing oil through orifices and valves. It controls spring oscillation; it does not carry the vehicle weight.

AUT-056 · What are sprung and unsprung mass?

Sprung mass is supported by the springs (body, engine, occupants). Unsprung mass is not (wheels, tyres, brakes, hubs, part of the links). Lower unsprung mass improves ride and road holding.

AUT-057 · What is an anti-roll bar?

A torsion bar linking the left and right suspension. When one wheel rises relative to the other it twists and resists body roll in corners, without affecting equal bump on both sides.

AUT-058 · What is a torsion bar spring?

A straight steel bar that is twisted by a lever arm as the wheel moves. Its torsional stiffness provides the spring force, and it is often used in trucks and older cars.

AUT-059 · What is air suspension?

A suspension that uses rubber air bellows filled with compressed air as springs. It allows height adjustment and load levelling and gives a soft ride, at higher cost and complexity.

AUT-060 · What do bump and rebound mean in suspension?

Bump (jounce) is upward wheel travel compressing the spring. Rebound is downward wheel travel extending it. Dampers usually have different damping in each direction.

AUT-061 · What is ground clearance?

The minimum distance between the lowest part of the vehicle (excluding tyres) and the road. Higher clearance helps on rough roads but raises the centre of gravity.

AUT-062 · What is the role of bushings in a suspension?

Rubber or polyurethane bushes at link pivots allow controlled movement, isolate noise and vibration, and add compliance. Softer bushes improve comfort; stiffer bushes improve precision.

AUT-063 · What is the difference between a strut and a shock absorber?

A strut is a structural member that carries the spring, supports vehicle load and locates the wheel, with a damper inside. A shock absorber only damps motion and carries no structural load.

Steering & Wheel Alignment

AUT-064 · What is the function of a steering system?

It converts the driver's rotation of the steering wheel into angular movement of the road wheels, giving directional control with a suitable mechanical advantage and road feel.

AUT-065 · What is rack-and-pinion steering?

A pinion on the steering column meshes with a toothed rack connected to tie rods. Rotating the pinion moves the rack sideways and steers the wheels. It is simple, precise and common in cars.

AUT-066 · What is recirculating ball steering?

A steering box where a worm drives a nut through a chain of recirculating steel balls, reducing friction. The nut moves a sector gear and Pitman arm. It is used in heavy vehicles.

AUT-067 · What is power steering?

A system that assists the driver's steering effort, either hydraulically with an engine-driven pump or electrically (EPS) with a motor on the column or rack. EPS uses energy only when steering.

AUT-068 · What is camber?

The inward or outward tilt of the wheel seen from the front. Negative camber (top inward) improves cornering grip; excessive camber causes uneven tyre wear on one shoulder.

AUT-069 · What is caster?

The fore-aft tilt of the steering axis seen from the side. Positive caster (top tilted rearward) gives self-centring and straight-line stability, but increases steering effort.

AUT-070 · What are toe-in and toe-out?

Toe-in means the front edges of the wheels on an axle point toward each other; toe-out means they point apart. Toe settings affect straight-line stability, turn-in response and tyre wear.

AUT-071 · What is king-pin inclination (KPI)?

The inward tilt of the steering axis seen from the front, also called steering axis inclination. It reduces scrub radius, lowers steering effort and helps self-centring.

AUT-072 · What is steering ratio?

The ratio of steering wheel angle to the resulting road wheel angle. Cars typically use about 12:1 to 20:1; a lower ratio gives quicker steering but higher effort.

AUT-073 · What is turning radius?

The radius of the circle traced by the outer front wheel (or the vehicle's outermost point) during the tightest possible turn. It depends on wheelbase and maximum steering angle.

AUT-074 · What is wheel alignment?

Adjustment of the wheel angles (camber, caster, toe) to manufacturer specification so the vehicle tracks straight, steers predictably and wears tyres evenly.

AUT-075 · What is wheel balancing?

Adding small weights to the rim so the mass of the wheel and tyre is evenly distributed around the axis. It prevents vibration and steering shimmy at speed.

Braking Systems

AUT-076 · What is the function of brakes in a vehicle?

To slow or stop the vehicle, or hold it stationary, by converting kinetic energy into heat through friction between rotating discs or drums and stationary pads or shoes.

AUT-077 · What is the difference between disc and drum brakes?

Disc brakes clamp pads onto an exposed rotor, giving better cooling, fade resistance and water clearing. Drum brakes press shoes outward inside a drum; they are cheaper, self-energising and suit parking brakes.

AUT-078 · What is a master cylinder?

The hydraulic cylinder operated by the brake pedal. Its piston pressurises brake fluid, which transmits force through pipes to the wheel cylinders or calipers.

AUT-079 · What is brake fade?

A loss of braking effectiveness after repeated or prolonged braking. It is caused by overheated friction material losing friction coefficient, or by brake fluid boiling and forming vapour.

AUT-080 · What is a vacuum brake booster?

A diaphragm servo between the pedal and the master cylinder. Engine intake vacuum on one side and atmospheric pressure on the other multiply the driver's pedal force.

AUT-081 · What is a parking brake?

A mechanically or electrically applied brake, usually on the rear wheels, that holds the vehicle stationary and is independent of the service brake hydraulics.

AUT-082 · What is brake fluid and why is it hygroscopic?

A hydraulic fluid with a high boiling point; DOT 3, 4 and 5.1 are glycol-based and absorb moisture from air. Absorbed water lowers the boiling point, so the fluid must be replaced periodically.

AUT-083 · What is a brake caliper?

The housing that holds the brake pads and hydraulic pistons around a disc. Fixed calipers have pistons on both sides; floating (sliding) calipers have pistons on one side and slide to clamp the disc.

AUT-084 · What is the difference between brake pads and brake shoes?

Pads are flat friction blocks used in disc brakes. Shoes are curved friction linings used in drum brakes.

AUT-085 · What is a tandem master cylinder?

A master cylinder with two pistons feeding two independent hydraulic circuits, often split diagonally. If one circuit leaks, the other still brakes the vehicle.

AUT-086 · What is an air brake system?

A system used in heavy vehicles where compressed air from an engine-driven compressor applies the brakes via chambers. Spring brakes apply automatically if air pressure is lost.

AUT-087 · What is engine braking?

Retardation of the vehicle by engine pumping and friction losses when the throttle is closed and a gear is engaged. It reduces load on the friction brakes on long descents.

AUT-088 · What is a brake proportioning valve?

A valve that limits rear brake pressure relative to front pressure, so the rear wheels do not lock first as weight shifts forward. Electronic brake-force distribution (EBD) now does this through ABS.

Chassis, Body & Tyres

AUT-089 · What is a vehicle chassis?

The load-bearing framework that supports the engine, driveline, suspension, steering and body. The term often means the frame plus running gear without the body.

AUT-090 · What is the difference between a ladder frame and a monocoque body?

A ladder frame has two longitudinal rails with cross members, and a separate body is bolted on; it is rugged and used in trucks and SUVs. A monocoque uses the body shell itself as the structure, which is lighter and stiffer.

AUT-091 · What is a crumple zone?

A region at the front or rear of the body designed to deform progressively in a crash. It absorbs energy and lengthens deceleration time, reducing the forces on occupants.

AUT-092 · What does the tyre marking 205/55 R16 91V mean?

205 mm section width, aspect ratio 55% (sidewall height/width), R for radial construction, 16-inch rim diameter, load index 91 (615 kg per tyre) and speed rating V (240 km/h).

AUT-093 · What is the difference between radial and bias-ply tyres?

Radial tyres have body cords at 90° to the direction of travel, with belts under the tread, giving lower rolling resistance and better grip. Bias-ply tyres have criss-crossed cords at an angle, giving stiffer sidewalls but more heat build-up.

AUT-094 · What is a tubeless tyre?

A tyre that holds air without an inner tube, sealed by an airtight inner liner and the bead against the rim. It deflates slowly when punctured and runs cooler.

AUT-095 · What is the purpose of tyre tread?

The grooves channel water away from the contact patch to prevent aquaplaning, and the tread blocks provide grip on wet, loose or snowy surfaces.

AUT-096 · What are wheelbase and track width?

Wheelbase is the distance between the front and rear axle centres. Track width is the distance between the centres of the left and right tyre contact patches on the same axle.

AUT-097 · What is a space frame chassis?

A three-dimensional truss of tubes welded together, with body panels that carry no structural load. It is used in race cars and low-volume sports cars.

AUT-098 · What is a subframe?

A separate structural frame bolted to a monocoque that carries the engine, suspension or steering. It simplifies assembly and isolates noise and vibration through mounts.

AUT-099 · Why is correct tyre inflation pressure important?

Under-inflation increases rolling resistance, heat, sidewall flex and shoulder wear. Over-inflation reduces the contact patch, grip and comfort and causes centre wear.

AUT-100 · What is a body-in-white (BIW)?

The welded sheet-metal body structure before painting, trim, glass, moving parts and the powertrain are added.

AUT-101 · Why are alloy wheels used?

Aluminium or magnesium alloy wheels are lighter than steel wheels, which reduces unsprung mass. They also dissipate brake heat better and allow more styling freedom.

Vehicle Dynamics

AUT-102 · What is vehicle dynamics?

The study of vehicle motion in response to driver inputs, road inputs and aerodynamic forces. It covers longitudinal (acceleration and braking), lateral (handling) and vertical (ride) behaviour.

AUT-103 · What is understeer?

A handling condition where the front tyres reach their grip limit first, so the vehicle turns less than the steering input requests and runs wide in a corner.

AUT-104 · What is oversteer?

A handling condition where the rear tyres lose grip first, so the vehicle turns more sharply than intended and the rear slides outward.

AUT-105 · Why is centre of gravity height important?

A higher CG increases load transfer during braking, acceleration and cornering. This raises body roll and pitch and the risk of rollover, and reduces the usable tyre grip.

AUT-106 · What is rolling resistance?

The force opposing a rolling tyre, mainly from hysteresis loss as the rubber deforms. Fr = Crr·m·g, where Crr is about 0.007–0.015 for car tyres on asphalt.

AUT-107 · What is aerodynamic drag force?

Fd = ½·ρ·Cd·A·v², where ρ is air density, Cd the drag coefficient, A the frontal area and v the speed. Drag power grows with v³, so it dominates at highway speeds.

AUT-108 · What is tractive effort?

The driving force at the tyre contact patch: F = T·i·η/r, where T is engine torque, i the total gear ratio, η the driveline efficiency and r the wheel radius.

AUT-109 · What is gradient resistance?

The component of vehicle weight acting along an incline: Fg = m·g·sin θ. For small angles it is roughly m·g × (grade %/100).

AUT-110 · What is load transfer?

The shift of vertical tyre load between axles or sides during acceleration, braking or cornering, caused by inertial forces acting at the CG above ground level. The total load stays the same.

AUT-111 · What are yaw, pitch and roll?

Rotations of the vehicle body about its vertical axis (yaw), lateral axis (pitch, as in braking dive) and longitudinal axis (roll, as in cornering).

AUT-112 · What is tyre slip angle?

The angle between the direction the wheel is pointing and the direction it actually travels. Lateral tyre force builds up with slip angle as the tread deforms in the contact patch.

AUT-113 · What is the drag coefficient (Cd)?

A dimensionless number for how aerodynamically efficient a body shape is. Modern passenger cars typically have Cd around 0.25–0.35; trucks and boxy SUVs are higher.

Automotive Electronics & ECUs

AUT-114 · What is an ECU?

An electronic control unit: a microcontroller-based module that reads sensors, runs control algorithms and drives actuators for a subsystem, such as the engine, transmission, ABS or airbags.

AUT-115 · What is OBD-II?

On-board diagnostics, second generation: a standard self-diagnostic system that monitors emissions-related components, stores fault codes and gives access through a standard 16-pin connector.

AUT-116 · What is a diagnostic trouble code (DTC)?

A standard alphanumeric code stored by an ECU when it detects a fault. In OBD-II, the first letter gives the system: P (powertrain), C (chassis), B (body) or U (network), for example P0300 for random misfire.

AUT-117 · Which in-vehicle networks are commonly used?

CAN for most ECUs, LIN for low-cost body devices, FlexRay for deterministic high-speed control, MOST for older infotainment systems, and Automotive Ethernet for cameras, ADAS and high-bandwidth backbones.

AUT-118 · What is the LIN bus?

Local Interconnect Network: a low-cost single-wire serial bus (up to about 20 kbit/s) with one master and several slaves. It is used for windows, mirrors, seats and sensors.

AUT-119 · What does an oxygen (lambda) sensor do?

It sits in the exhaust and measures residual oxygen, so the ECU can keep the air–fuel ratio near stoichiometric in closed loop. Narrow-band sensors switch around λ = 1; wide-band sensors measure λ continuously.

AUT-120 · What is a MAP sensor?

A manifold absolute pressure sensor that measures intake manifold pressure. The ECU uses it with engine speed and air temperature to estimate air mass (speed-density method) and engine load.

AUT-121 · What is a MAF sensor?

A mass airflow sensor, usually hot-film type, that directly measures the mass of air entering the engine. The ECU uses this to calculate fuel quantity.

AUT-122 · What does the crankshaft position sensor do?

It reads a toothed reluctor wheel (often 60-2 teeth) with an inductive or Hall sensor. The ECU uses it to find engine speed and crank angle for injection and ignition timing.

AUT-123 · What is drive-by-wire throttle?

An electronic throttle in which an accelerator pedal position sensor sends a signal to the ECU, which drives a motorised throttle body. A throttle position sensor confirms the throttle opening, and there is no cable.

AUT-124 · What is a knock sensor?

A piezoelectric accelerometer on the engine block that detects knock-frequency vibrations. The ECU retards ignition timing on the knocking cylinder in response.

AUT-125 · What is the function of an alternator?

It is belt-driven by the engine and generates three-phase AC, which is rectified to DC by diodes and voltage-regulated (about 13.5–14.5 V in 12 V systems) to charge the battery and power the electrical loads.

AUT-126 · What does a starter motor do?

It is a high-torque DC motor that engages a pinion with the flywheel ring gear through a solenoid, cranking the engine until it fires.

Electric & Hybrid Vehicles

AUT-127 · What is a battery electric vehicle (BEV)?

A vehicle powered only by electric motors drawing energy from a rechargeable traction battery charged from the grid. It has no engine and produces no tailpipe emissions.

AUT-128 · What is the difference between an HEV, a PHEV and a BEV?

An HEV combines an engine and a motor with a small battery charged only on board. A PHEV has a larger battery that can be charged from the grid for electric-only range. A BEV relies only on the battery.

AUT-129 · What is state of charge (SOC)?

The remaining usable charge of a battery as a percentage of its full capacity, like a fuel gauge. It is estimated by coulomb counting, voltage models and Kalman filters.

AUT-130 · What are the main components of an electric vehicle powertrain?

Traction battery with BMS, inverter, traction motor, single-speed reduction gear and differential, on-board charger, DC–DC converter for the 12 V system, and thermal management.

AUT-131 · Why are lithium-ion batteries used in EVs?

They have high specific energy (about 150–270 Wh/kg at cell level), high efficiency, long cycle life and low self-discharge compared with lead-acid or NiMH batteries.

AUT-132 · What does the inverter do in an EV?

It converts DC battery power into variable-frequency, variable-voltage three-phase AC to drive the traction motor. During regeneration it rectifies the motor's AC back to DC.

AUT-133 · What is the difference between kW and kWh in an EV?

kW is power: the rate of energy flow, such as motor output or charging rate. kWh is energy: battery capacity. A 50 kWh battery charged at 50 kW takes about 1 hour in theory.

AUT-134 · What is the difference between AC charging and DC fast charging?

In AC charging, the vehicle's on-board charger converts grid AC to DC, which limits power. In DC fast charging, the off-board charger supplies DC directly to the battery at much higher power.

AUT-135 · What motors are used in EVs?

Mainly permanent magnet synchronous motors (PMSM) for high efficiency and power density. Induction motors avoid rare-earth magnets, and some vehicles use wound-rotor synchronous or switched reluctance motors.

AUT-136 · What is range anxiety?

A driver's worry that the EV's battery will run out before reaching a destination or charger. It is reduced by larger batteries, accurate range estimation and charging infrastructure.

AUT-137 · What is a mild hybrid?

A vehicle with a small motor-generator (often a 48 V belt starter-generator) that provides start-stop, torque assist and regeneration, but cannot drive the car on electric power alone for any useful distance.

AUT-138 · What is a fuel cell electric vehicle (FCEV)?

An EV that generates electricity on board in a hydrogen fuel cell (usually PEM type), where hydrogen and oxygen combine to produce power and water. A small buffer battery handles peaks and regeneration.

Emissions, Regulations & Vehicle Safety

AUT-139 · What are the main pollutants from vehicle exhaust?

Carbon monoxide (CO), unburnt hydrocarbons (HC), nitrogen oxides (NOx) and particulate matter (PM). CO₂ is also emitted as a greenhouse gas.

AUT-140 · What is a three-way catalytic converter?

A converter with a ceramic or metal substrate coated with Pt, Pd and Rh. It oxidises CO and HC and reduces NOx at the same time, but only works efficiently in a narrow window near λ = 1.

AUT-141 · What is EGR?

Exhaust gas recirculation: routing part of the exhaust back into the intake. The inert gas dilutes the charge and lowers peak combustion temperature, which reduces NOx formation.

AUT-142 · What is a diesel particulate filter (DPF)?

A wall-flow ceramic filter in the diesel exhaust that traps soot particles. It is periodically regenerated by burning off the soot at high temperature.

AUT-143 · What is ADAS?

Advanced driver assistance systems: features that use sensors such as camera, radar, ultrasonic and lidar to help the driver. Examples are adaptive cruise control, automatic emergency braking, lane keeping and blind-spot monitoring.

AUT-144 · What is NCAP?

New Car Assessment Programme: an independent crash-test and safety rating scheme (such as Euro NCAP, Global NCAP or Bharat NCAP). It rates cars with stars for adult and child occupant protection and safety assist.

AUT-145 · What is the function of an airbag?

It inflates within milliseconds of a crash, triggered by crash sensors and a pyrotechnic inflator. It cushions the occupant and spreads the load, working together with the seat belt.

AUT-146 · What is a seat belt pretensioner?

A pyrotechnic or mechanical device that pulls in belt slack at the start of a crash, coupling the occupant to the seat early. A load limiter then lets out webbing to cap chest force.

AUT-147 · What is electronic stability control (ESC)?

A system that compares the driver's intended path (steering angle) with actual yaw rate and lateral acceleration. It brakes individual wheels and reduces engine torque to correct understeer or oversteer.

AUT-148 · What is PCV?

Positive crankcase ventilation: blow-by gases from the crankcase are drawn into the intake through a valve and burnt in the engine instead of being vented to the atmosphere.

AUT-149 · What is an evaporative emission (EVAP) control system?

A system that captures fuel vapour from the tank in a charcoal canister and later purges it into the intake to be burnt, preventing HC escaping to the atmosphere.

AUT-150 · What is ISOFIX?

An international standard system for attaching child seats directly to rigid anchor points on the vehicle body, usually with a top tether or support leg. It reduces installation errors.

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