Automotive

If your focus area is Automotive, Sections I and II of your written paper are about the automotive industry: 10 multiple-choice marks and about 15 marks of short answers (roughly six items, at least one worth 4–6 marks), 25 of the 40 written marks. They test Industry Related Manufacturing Technology for automotive: the materials, components, systems, tools, processes, WHS and environmental practices of the vehicle manufacturing, servicing and repair industry.

• Engines: the four-stroke cycle, petrol and diesel, engine components, valve train, turbocharging.
• Engine systems: cooling, lubrication, fuel and engine management (sensors and the ECU), ignition, emissions control.
• Electrical: battery, charging (alternator) and starting systems, basic fault-finding.
• Drivetrain: clutch, gearbox, gear ratios, final drive and differential, CV joints.
• Chassis: suspension, steering, brakes (hydraulics, disc and drum, ABS), wheels, tyres and alignment.
• Body and materials: steels, aluminium alloys, polymers and composites; crumple zones and safety systems.
• Electric and hybrid vehicles: motors, high-voltage batteries, regenerative braking and high-voltage safety.
• WHS and environment: hoists and stands, exhaust fumes, chemicals, waste oil, batteries and refrigerants.

Section II often asks you to explain how a system works (name the parts and say what each does, in order), to identify a fault and describe how to find it, or to calculate (gear ratios, displacement, tyre sizes, hydraulic forces).

A four-stroke engine completes one cycle in four strokes, which take two crankshaft revolutions:

1. Intake: inlet valve open, piston moves down, air–fuel mixture drawn in.
2. Compression: both valves closed, piston moves up and compresses the mixture.
3. Power: the spark ignites the mixture near top dead centre; expanding gases push the piston down and turn the crankshaft.
4. Exhaust: exhaust valve open, piston moves up and pushes burnt gases out.

Because each valve opens once per cycle, the camshaft turns at half crankshaft speed, driven by a timing belt, chain or gears. Diesel engines are compression-ignition: they compress air alone at a high compression ratio (about 15–22 : 1), and fuel injected into the hot air ignites by itself. Glow plugs only help cold starts.

Key components: pistons with compression rings (seal combustion pressure) and an oil control ring (scrapes oil off the cylinder wall); connecting rods and gudgeon pins; the crankshaft and flywheel; and the cylinder head with valves, springs and camshaft(s). A small valve clearance allows parts to expand so the valves still close fully when hot. A turbocharger uses an exhaust-driven turbine to spin a compressor that forces more air in; a supercharger does the same job but is driven by the crankshaft.

Displacement and compression ratio

where $V_c$ is the clearance (combustion chamber) volume. Work in centimetres to get cm³ (1000 cm³ = 1 litre). Worked example: a single-cylinder engine with a 70 mm bore, a 60 mm stroke and a 25 cm³ clearance volume.

Cooling: the water pump circulates coolant (water with ethylene glycol, which lowers freezing point, raises boiling point and inhibits corrosion) through the engine's water jackets. The thermostat stays shut until the engine warms up, then a wax pellet expands at about 80–95 °C and opens it to send coolant to the radiator. The pressure cap keeps the system pressurised, which raises the coolant's boiling point; its vacuum valve lets coolant return from the overflow tank. Never open a hot cap.

Lubrication: a pump draws oil from the sump through a pick-up, pushes it through the oil filter and into galleries to the bearings, camshaft and valve train. Oil lubricates, cools, cleans, seals and protects. In a multigrade such as SAE 5W-30, '5W' (winter) rates cold flow and '30' rates viscosity at operating temperature.

Electronic fuel injection and engine management:

The ECU calculates the injector pulse width (opening time) and ignition timing. The oxygen sensor gives closed-loop feedback that keeps a petrol engine near the stoichiometric ratio of about 14.7 : 1 (air : fuel by mass). A three-way catalytic converter then converts CO, HC and NOx into CO₂, water and nitrogen. Diesels use particulate filters and, in many newer vehicles, urea injection (AdBlue) to reduce NOx. Faults are read with an OBD-II scan tool, but a code points to a circuit or system; the fault must still be confirmed by testing.

• Battery: a 12 V lead-acid battery has six cells of about 2.1 V; a fully charged battery reads about 12.6 V at rest.
• Charging: the alternator produces AC; a diode rectifier converts it to DC and a regulator holds about 13.5–14.5 V.
• Starting: the ignition switch energises the solenoid, which pushes the starter pinion into the flywheel ring gear and closes the heavy contacts to the motor.
• Fault-finding: work from simple to complex, such as battery, terminals, fuses and relays, switches, voltage drop on cables and earths, then the component. Use a multimeter; check against specifications.

The clutch connects the engine to a manual gearbox by friction; pressing the pedal makes the release bearing push the diaphragm spring so the pressure plate unclamps the friction disc. Automatics use a torque converter (a fluid coupling that can multiply torque) and planetary gear sets or a CVT.

Gear ratio = driven teeth ÷ driver teeth (or driver speed ÷ driven speed). Ratios in series multiply, so overall ratio = gearbox ratio × final drive ratio. A reduction (ratio above 1) lowers speed and increases torque.

Worked example: a 12-tooth gear drives a 30-tooth gear. The ratio is 30 ÷ 12 = 2.5 : 1, so an input of 2000 rpm gives 2000 ÷ 2.5 = 800 rpm.

The differential lets the driven wheels turn at different speeds when cornering (the outer wheel travels further) and gives the final drive reduction. CV joints carry drive to steered front wheels at constant speed through changing angles; a split boot lets grit in and causes clicking on turns.

• Suspension: springs (coil, leaf, torsion bar or air) carry the weight and absorb bumps; dampers (shock absorbers) control spring oscillation and keep tyres on the road. A MacPherson strut combines spring and damper and locates the wheel.
• Steering: rack and pinion converts rotation into linear motion; most new cars use electric power steering. Alignment angles: camber (wheel tilt seen from the front), toe (seen from above) and caster (steering axis tilt seen from the side).
• Brakes: hydraulic systems follow Pascal's principle: pressure from the master cylinder is the same everywhere in the fluid, so force at a piston = pressure × its area. Disc brakes cool better and resist fade; drum brakes are cheaper, self-energising and make a simple handbrake. Glycol brake fluid absorbs water, which lowers its boiling point, so it is replaced every few years. ABS stops wheels locking so the driver can still steer; ESC brakes individual wheels to correct a skid.
• Tyres: in 215/60R17, 215 = width (mm), 60 = sidewall height as a percentage of width, R = radial, 17 = rim diameter (inches). Overall diameter = rim diameter + 2 × sidewall height.

Worked example (hydraulics): a 20 mm master cylinder piston pushed with 1000 N.

Passive safety reduces injury in a crash: crumple zones (deform to absorb energy and lengthen stopping time), a rigid safety cell, seatbelts with pretensioners and load limiters, and airbags. Active safety helps avoid crashes: ABS, ESC, autonomous emergency braking (AEB), lane-keeping and blind-spot systems.

A battery electric vehicle uses a high-voltage lithium-ion battery (several hundred volts), an inverter and electric motor(s). Hybrids combine an engine with a motor and battery. Regenerative braking makes the motor act as a generator, recharging the battery and saving brake wear.

High-voltage cables are usually orange. Only trained technicians work on them: isolate using the service disconnect, wait for capacitors to discharge, test to prove zero voltage, use insulated gloves and tools, and lock out and tag the vehicle. EVs are silent in 'ready' mode, heavier (more tyre wear), and damaged batteries can enter thermal runaway, so they need quarantine and a fire plan.

• Lifting: never work under a car held only by a jack; use rated axle stands at the correct support points and chock the wheels. Hoists need trained operators, correct lift points and safety locks.
• Exhaust: carbon monoxide is colourless and odourless; run engines only with exhaust extraction.
• Chemicals: fuels, solvents, brake fluid and coolant each have a Safety Data Sheet. Brake and clutch parts on older vehicles may contain asbestos (banned in Australia since 31 December 2003): never blow dust out with compressed air.
• Waste: used oil goes to a licensed recycler; lead-acid batteries are recycled (lead, acid and plastic are recovered); tyres go to tyre recyclers.
• Refrigerants: car air-conditioning (R134a in older cars, R1234yf in most newer ones) needs a refrigerant handling licence from the Australian Refrigeration Council, so refrigerant is recovered, not vented.
• Noise, manual handling and hot parts: hearing protection for air tools, lifting aids for gearboxes and batteries, and letting exhausts and engines cool.

• Saying the camshaft turns at crankshaft speed, or that a four-stroke cycle takes one revolution.
• Using the whole engine's displacement in a compression ratio (it is per cylinder), or mixing mm and cm.
• Adding gear ratios instead of multiplying them; or multiplying instead of dividing when finding output speed.
• Reading the tyre aspect ratio as a height in millimetres.
• Saying the thermostat 'cools' the engine or the radiator cap 'stops leaks'.
• Confusing ABS (prevents wheel lock) with ESC (corrects a skid) and AEB (brakes automatically).
• Giving only PPE as the control for every hazard.

• Explain how a system works: name the components in the order the energy, fluid or signal passes through them, and say what each one does.
• Fault-finding: start with the simplest, most likely cause and test before replacing anything.
• In calculations, write the formula, substitute with units, keep unrounded values until the end, and state the unit asked for.
• Use precise terms ('compression ignition', 'pulse width', 'stoichiometric', 'regenerative braking'), which markers reward.

• Industry Study (Section III): use automotive examples such as the shift to electric vehicles and the high-voltage skills it needs, OBD diagnostics and connected cars, apprenticeships (Certificate III in Light Vehicle Mechanical Technology, AUR30620, or its current equivalent), waste-oil and battery recycling, and WHS hazards such as hoists, exhaust fumes and asbestos.
• Major Project: if your project is automotive, the same systems knowledge, WHS procedures and costing apply to your folio.