Class 11 Basic Automobile Engineering — Exercise Solutions
Key Concepts Quick Recap
| System | Function | Key Components |
|---|
| Engine | Converts fuel to mechanical energy | Cylinder, piston, crankshaft, valves |
| Fuel system | Stores and delivers fuel | Tank, pump, carburettor/injectors |
| Cooling | Prevents overheating | Radiator, water pump, thermostat, coolant |
| Lubrication | Reduces friction/wear | Oil pump, oil filter, sump |
| Transmission | Transfers power to wheels | Clutch, gearbox, driveshaft, differential |
| Braking | Slows/stops vehicle | Disc/drum brakes, ABS |
| Suspension | Absorbs shocks; handling | Springs, shock absorbers, wishbones |
I. Choose the Best Answer (MCQs)
1. In a four-stroke petrol engine, how many strokes complete one power cycle? (a) One (b) Two (c) Three (d) Four
Answer(d) Four Four strokes: 1. Suction (induction): piston moves down, inlet valve open, fuel-air mixture drawn in. 2. Compression: both valves closed, piston moves up, mixture compressed. 3. Power (combustion): spark plug fires, mixture ignites, expanding gases push piston down. 4. Exhaust: exhaust valve opens, piston moves up, burnt gases expelled. Two crankshaft revolutions per power stroke.
2. The function of the cooling system in an engine is to: (a) Lubricate moving parts (b) Remove excess heat to prevent engine damage and overheating (c) Filter impurities from fuel (d) Regulate fuel injection
Answer(b) Remove excess heat to prevent engine damage and overheating Engine cooling: only ~30% of fuel energy becomes useful work; ~35% is wasted as heat to coolant; ~35% as exhaust. Water cooling: coolant (water + antifreeze) circulates through engine block → radiator (dissipates heat) → water pump (circulates) → thermostat (regulates temperature). Air cooling: fins on cylinder; used in motorcycles and small engines.
3. The differential in an automobile allows: (a) The engine to vary its speed (b) Both drive wheels to rotate at the same speed always (c) The left and right drive wheels to rotate at different speeds when cornering (d) The gearbox to change gears automatically
Answer(c) The left and right drive wheels to rotate at different speeds when cornering Differential: allows inside and outside wheels to rotate at different speeds when turning. When cornering, the outer wheel travels a longer path → needs to rotate faster. Without differential → tyre scrub and understeer. Types: open differential, limited-slip differential (LSD), electronic differential.
4. The purpose of the clutch in a vehicle is: (a) Change wheel direction (b) Disconnect and reconnect engine power to the gearbox (c) Slow down the vehicle (d) Filter impurities from engine oil
Answer(b) Disconnect and reconnect engine power to the gearbox Clutch: friction device that allows smooth engagement and disengagement of engine from drivetrain. Needed for: starting from rest, changing gears, stopping without stalling engine. Types: single plate dry friction clutch (most cars), multi-plate wet clutch (motorcycles), centrifugal clutch (scooters), torque converter (automatic cars).
5. Tyre pressure is measured in: (a) Nm (Newton-metres) (b) kPa or PSI (pounds per square inch) (c) RPM (d) kW
Answer(b) kPa or PSI (pounds per square inch) Tyre pressure: standard passenger car: 28-36 PSI (193-248 kPa) — check vehicle door sticker for specific values. Under-inflation: increased rolling resistance (poor fuel economy), overheating, blowout risk, uneven wear. Over-inflation: reduced contact patch (poor grip), harsh ride, centre tread wear.
6. The function of a shock absorber in a vehicle is: (a) To absorb fuel vibrations (b) To store potential energy like a spring (c) To dampen spring oscillations and improve ride comfort and handling (d) To connect the engine to the gearbox
Answer(c) To dampen spring oscillations and improve ride comfort and handling Shock absorbers (dampers): piston moving through oil-filled cylinder; converts kinetic energy of bounce to heat. Works with spring (which absorbs road shock) to control body motion. Without shock absorbers: car would continue bouncing after every bump. Types: telescopic (monotube, twin-tube), McPherson strut (combines spring and shock absorber).
7. Which type of brake is most commonly used on front wheels of modern cars for better stopping power? (a) Drum brakes (b) Disc brakes (c) Band brakes (d) Block brakes
Answer(b) Disc brakes Disc brakes: brake caliper squeezes brake pads against rotating disc (rotor) → friction → stops wheel. Advantages: better heat dissipation (open disc), consistent performance (no brake fade), easy inspection, better wet performance. Drum brakes: cheaper, provide better parking brake, still used on rear wheels of economical cars.
II. Short Answer Questions
Q1. Describe the lubrication system of an engine and its importance.
Answer
Engine lubrication system ensures oil reaches all moving parts to reduce friction and wear.
Functions of engine oil: 1. Lubrication: forms film between metal surfaces → reduces friction and wear. 2. Cooling: carries heat away from hot surfaces (piston, bearings) to oil sump. 3. Cleaning: carries contaminants to oil filter → keeps engine clean. 4. Sealing: helps pistons seal against cylinder walls. 5. Corrosion protection: chemical additives protect metal surfaces from oxidation.
Lubrication system components:
- Oil sump (pan): reservoir storing engine oil.
- Oil pump: driven by crankshaft or camshaft; forces oil under pressure to all parts.
- Oil filter: removes particles and contaminants from oil.
- Oil pressure gauge/warning light: monitors oil pressure.
- Oil galleries: drilled passages in engine block and head distributing oil.
Oil change interval: typically every 5,000-10,000 km (conventional oil) or 10,000-15,000 km (synthetic oil).
Q2. Explain the types of transmission systems in automobiles.
Answer
Manual transmission (MT):
- Driver manually selects gears using gear lever + clutch pedal.
- Direct mechanical connection → efficient; better driver control.
- Types: sliding mesh (old), synchromesh (modern — grinds don't occur).
- Common in India (economical, fuel efficient, preferred in traffic).
Automatic transmission (AT):
- No clutch pedal; gears change automatically via hydraulic torque converter.
- More comfortable in heavy traffic. Higher cost, slightly less fuel efficient.
- Types: traditional hydraulic AT, CVT (continuously variable), DCT (dual-clutch).
CVT (Continuously Variable Transmission):
- No fixed gear ratios; infinite ratio range via belt/pulley system.
- Smooth, fuel-efficient; feels like one continuous gear.
- Popular in scooters and some sedans (Honda City CVT, Maruti Baleno).
AMT (Automated Manual Transmission):
- Standard manual gearbox with automated clutch actuator.
- Budget friendly; common in small Indian cars (Maruti Celerio, Alto).
Exam Checklist
- 4-stroke: Suction → Compression → Power → Exhaust (2 crank revolutions).
- 2-stroke: power every revolution; simpler; more polluting.
- Cooling: radiator + water pump + thermostat.
- Clutch: disconnects engine from gearbox for gear changes.
- Differential: allows wheels to rotate at different speeds when cornering.
- Disc brakes: front wheels; better heat dissipation; preferred.
- Tyre pressure: 28-36 PSI for passenger cars.
- Lubrication: sump → oil pump → filter → galleries → back to sump.
- Manual: clutch + gear lever. Automatic: torque converter. CVT: infinite ratios.
