Tamil Nadu HSE Second Year Basic Automobile Engineering flashcards

32 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: CR = (Vs + Vc)/Vc. Petrol engines run about 8:1 to 12:1, diesels about 14:1 to 23:1.

Four-stroke cycle

Sequence of intake, compression, power and exhaust strokes. The crankshaft turns twice per cycle, so a power stroke occurs every 720 degrees of crank rotation.

Volumetric efficiency

Ratio of actual air mass inducted to the theoretical swept volume of the cylinder. It falls at high engine speed because of flow losses in ports and valves.

Firing order

Sequence in which cylinders receive their power strokes, chosen to smooth torque and balance loads. Common inline-four orders are 1-3-4-2 and 1-2-4-3.

Stoichiometric air-fuel ratio

Mass ratio of air to fuel for complete combustion. For petrol it is about 14.7:1; richer mixtures give more power and leaner mixtures give better economy.

Lambda sensor

Oxygen sensor in the exhaust that reports whether the mixture is rich or lean. The ECU uses its signal to adjust injection pulse width and hold stoichiometric operation.

Ignition timing advance

Crank angle before top dead centre at which the spark occurs. Too much advance causes knocking; too little causes overheating, poor power and higher exhaust temperature.

Multigrade oil SAE 20W-50

Oil whose low-temperature viscosity behaves like grade 20 in winter and whose high-temperature viscosity behaves like grade 50 at operating temperature, giving easier cold starting.

Clutch free play

Clearance between release bearing and pressure plate before disengagement begins. Too little causes slip; too much causes incomplete disengagement and gear crunch.

Synchromesh

Cone-shaped baulk ring that uses friction to bring the gear and shaft to matching speed before dog teeth engage, preventing gear clash during shifting.

Torque converter

Fluid coupling with impeller, turbine and stator. The stator multiplies torque at stall, and a lock-up clutch bypasses slip at cruising speed for efficiency.

Differential

Gear set that transmits drive to both wheels while allowing inner and outer wheels to rotate at different speeds during a turn, reducing tyre scrub.

Ackermann steering geometry

Layout in which the inner front wheel turns through a larger angle than the outer, so all wheels roll about a common centre and tyre scrub is minimised.

Caster angle

Tilt of the steering axis from vertical in side view. Positive caster gives self-centring and directional stability, increasing steering effort slightly.

Brake fade

Loss of braking force caused by heat reducing friction, common in drum brakes. Disc brakes resist fade better because they are exposed to cooling air.

Anti-lock braking system

System using wheel-speed sensors to modulate brake pressure and prevent wheel lock, so the driver keeps steering control during hard braking.

Lead-acid battery cell voltage

Each cell produces about 2.1 volts, so a 12-volt battery has six cells in series. Capacity is rated in ampere-hours at a stated discharge rate.

Alternator

Belt-driven generator producing alternating current that is rectified by a diode bridge. A regulator holds charging voltage near 13.8 to 14.5 volts.

Series-wound DC motor

Motor whose field and armature windings are in series, giving very high starting torque. This characteristic makes it suitable for engine starter motors.

CAN bus

Twisted-pair network that lets electronic control units share sensor and status data. An open or shorted bus stops communication and sets multiple fault codes.

Tyre size marking

Code such as 185/65 R15 88H: 185 mm section width, 65 percent aspect ratio, radial construction, 15 inch rim, 88 load index, H speed rating.

Wheel balancing

Adding weights to the rim to correct mass imbalance. Static imbalance causes bouncing, while dynamic imbalance causes shimmy at speed.

Monocoque body

Construction in which the body shell carries structural loads. Crumple zones absorb collision energy while the passenger cell stays rigid.

Vernier calliper least count

Smallest measurement the instrument can read, commonly 0.02 mm. It equals the difference between one main scale division and one vernier scale division.

Blue exhaust smoke

Smoke caused by burning lubricating oil, usually from worn piston rings or valve guides. It indicates engine wear rather than a fuel mixture problem.

Spongy brake pedal

Pedal that feels soft and travels far, caused by air in the hydraulic circuit. Air is compressible, so the system must be bled.

Engine knock

Metallic pinging from uncontrolled combustion. Causes include over-advanced ignition timing, low-octane fuel, carbon deposits and overheating.

Regenerative braking

Electric vehicle system in which the traction motor acts as a generator during deceleration, converting kinetic energy back to battery charge.

Battery management system

Electronic unit monitoring cell voltage, current and temperature in a traction pack, balancing cells and protecting against overcharge and overheating.

Series hybrid

Hybrid layout in which the engine drives only a generator, and the electric motor alone drives the wheels, so engine speed is independent of road speed.

BS-VI emission norms

Indian emission standards limiting pollutants such as NOx and particulate matter. Diesel vehicles use particulate filters and selective catalytic reduction with AdBlue urea solution.

OBD-II diagnostic connector

Standard 16-pin socket under the dashboard that gives access to emission-related data and stored diagnostic trouble codes for fault finding.