Question 1

Hydraulic power steering — pump drive source In a conventional hydraulic power steering system, the power steering pump is driven by a:

Accepted Answer

Introduction / Context: Hydraulic power steering uses an engine-driven pump to generate fluid pressure for steering assist. Identifying the correct drive source helps with belt routing, noise diagnosis, and accessory layout understanding. Given Data / Assumptions: Traditional hydraulic assist (not electric power steering). Accessory belt system on the front of the engine. Pump is mounted with a pulley. Concept / Approach: The engine crankshaft pulley drives accessory belts that power the alternator, water pump, air conditioning compressor, and power steering pump. Direct camshaft or driveshaft drives are not used for this accessory, and timing chains are internal and not used to run external pumps. Step-by-Step Solution: Locate the crankshaft pulley at the front of the engine.Follow the serpentine or V-belt routing to the power steering pump pulley.Confirm mechanical drive by belt from the crankshaft. Verification / Alternative check: Service diagrams and belt replacement procedures show tensioner adjustments for a belt that includes the power steering pump and the crankshaft pulley. Why Other Options Are Wrong: A camshaft belt drive would vary with valvetrain layouts and is not used for this pump. A chain from the crankshaft is internal for timing, not for accessories. The driveshaft is part of the drivetrain, far from the engine bay. Common Pitfalls: Confusing hydraulic with electric power steering, where an electric motor replaces the belt-driven pump. Final Answer: belt from the crankshaft pulley

Question 2

Automotive batteries — electrolyte identification In conventional lead–acid starting batteries used in automobiles, the electrolyte is a water solution of which acid?

Accepted Answer

Introduction / Context: Lead–acid batteries dominate automotive cranking applications because of low cost and high surge current capability. The electrolyte chemistry determines performance, safety, and service procedures. Correctly identifying the acid ensures proper handling and maintenance. Given Data / Assumptions: Typical 12 V flooded or absorbent glass mat lead–acid battery. Electrodes are lead dioxide (positive) and sponge lead (negative). Electrolyte is an aqueous acid solution. Concept / Approach: Lead–acid cells use sulphuric acid in water. During discharge, lead and lead dioxide react with sulphuric acid to form lead sulfate and water, lowering electrolyte specific gravity. During charge, the reaction reverses. Other strong acids listed are not used and would severely attack materials or be unsafe in this context. Step-by-Step Solution: Identify battery type: lead–acid.Recall chemistry: sulphuric acid electrolyte participates in reversible reactions.Select sulphuric acid as the correct electrolyte. Verification / Alternative check: Service tools such as hydrometers measure electrolyte specific gravity, a direct indicator of sulphuric acid concentration and state of charge. Why Other Options Are Wrong: Hydrochloric, nitric, and hydrofluoric acids are incompatible and unsafe for this electrochemical system, offering no performance advantage and significant hazards. Common Pitfalls: Adding acid to raise specific gravity as a substitute for charging; correct practice is to add distilled water to restore level and charge the battery properly. Final Answer: sulphuric acid

Question 3

Spark-Ignition (Petrol) Engines — When does the spark occur? In an SI engine, ignition is initiated relative to the piston’s movement near top dead centre (T.D.C.) on the compression stroke. Identify the most accurate description.

Accepted Answer

Introduction / Context: This question checks understanding of ignition timing in spark-ignition (petrol) engines. Because combustion takes a finite time, the spark cannot be triggered exactly at top dead centre (T.D.C.); it is advanced so that peak pressure occurs slightly after T.D.C. for best torque and efficiency. Given Data / Assumptions: Conventional four-stroke spark-ignition engine. Normal gasoline fuel and typical flame speeds. No abnormal conditions such as knock control retarding timing. Concept / Approach: Flame propagation across the combustion chamber requires milliseconds, which correspond to several crank degrees at typical engine speeds. To align maximum cylinder pressure just after T.D.C. (often 10–20 crank degrees ATDC depending on design), the spark must be fired before T.D.C. while the piston is approaching T.D.C. on the compression stroke. This is called spark advance and is adjusted with speed and load. Step-by-Step Solution: Goal: achieve peak pressure slightly after T.D.C. for best leverage on the crank.Constraint: combustion duration is not instantaneous.Action: trigger spark BTDC (before T.D.C.) as piston approaches T.D.C. on compression.Therefore, the correct description is “approaching T.D.C. on the compression stroke.” Verification / Alternative check: Service data and timing marks show positive BTDC values at idle and greater advance at higher speeds, confirming that ignition occurs before T.D.C., not at or after it. Why Other Options Are Wrong: Exactly at T.D.C.: too late for optimal pressure phasing.Leaving T.D.C.: much too late; power and efficiency fall.Exhaust stroke: wrong stroke altogether.Mid-stroke: far too early; would cause severe knock. Common Pitfalls: Confusing spark timing (BTDC) with the crank angle of maximum pressure (typically ATDC). Final Answer: approaching the T.D.C. position on its compression stroke

Question 4

Engine Materials — What are common cylinder block materials? Select the most typical material combination used for engine cylinder blocks in automobiles.

Accepted Answer

Introduction / Context: Cylinder blocks must provide strength, wear resistance, and good thermal behavior. Historically, cast iron dominated due to strength, machinability, and bore durability; many modern engines use aluminium alloy blocks for mass reduction and faster warm-up, often with liners or coatings. Given Data / Assumptions: Mainstream passenger and light-commercial engines. Blocks may be grey cast iron or aluminium alloy (with liners or surface treatments). Focus on the block material, not heads or liners alone. Concept / Approach: Cast iron blocks offer rigidity and excellent wear; aluminium blocks reduce mass and improve vehicle dynamics and fuel economy. Both are widely used. Steel and brass are not typical block materials; steel is difficult for economical casting/machining in this application, while brass lacks high-temperature strength and is costly. Step-by-Step Solution: Identify mainstream choices: cast iron (grey or CGI) and aluminium alloy.Reject atypical combinations (steel, brass, magnesium for blocks).Thus the correct pair is cast iron and aluminium alloy. Verification / Alternative check: Survey of OEM engines shows extensive use of both materials; aluminium blocks often have cast-in iron liners or plasma-sprayed bores to ensure wear resistance. Why Other Options Are Wrong: Cast iron and steel: steel not typical for full blocks.Steel and aluminium alloy: again, steel blocks are rare and impractical.Brass and steel; magnesium and wrought iron: unsuitable for cost, strength, and thermal reasons. Common Pitfalls: Assuming aluminium always saves weight without trade-offs; it may need liners or special coatings. Final Answer: cast iron and aluminium alloy

Question 5

Exhaust Emissions — When is carbon monoxide (CO) highest? Identify the engine operating condition most likely to produce large quantities of CO in the exhaust.

Accepted Answer

Introduction / Context: Carbon monoxide (CO) is a primary pollutant from spark-ignition engines. It forms when carbon in fuel is not fully oxidized to carbon dioxide (CO2). Understanding mixture effects on CO formation is fundamental to emissions control and closed-loop fuel management. Given Data / Assumptions: SI engine without or before catalytic converter conversion. Comparison of rich vs. lean and temperature effects. Normal engine temperature, no severe misfire scenario. Concept / Approach: CO increases sharply with rich mixtures (lambda less than 1) because there is insufficient oxygen to fully oxidize carbon to CO2. Lean mixtures provide excess oxygen, typically reducing CO dramatically, though they may increase NOx if temperature is high. Extremely low temperature can increase unburned hydrocarbons (HC), but the dominant factor for CO is oxygen deficiency. Step-by-Step Solution: Relate CO formation to equivalence ratio: rich → high CO due to oxygen shortfall.Lean conditions → more O2 available → lower CO.Therefore, “insufficient air during combustion” (rich) yields high CO. Verification / Alternative check: Engine maps show CO rising rapidly at equivalence ratios above 1.0 and dropping as mixtures approach stoichiometric or lean. Why Other Options Are Wrong: Insufficient fuel (lean): tends to reduce CO but may increase NOx if hot.Low temperature combustion: affects HC more than CO.High temperature alone does not cause high CO if air is sufficient.Lean misfire: CO not dominant; HC spikes due to misfire. Common Pitfalls: Confusing CO (partial oxidation) with HC (unburned fuel) and NOx (temperature/oxygen dependent). Final Answer: insufficient air during combustion

Question 6

Engine Cycles — Which thermodynamic cycle models a Diesel engine? Select the idealized thermodynamic cycle that represents the working of a compression-ignition (Diesel) engine.

Accepted Answer

Introduction / Context: Ideal cycles provide simplified models for heat-engine behavior. While real engines deviate, identifying the appropriate ideal cycle helps predict trends and compare efficiencies. Given Data / Assumptions: Compression-ignition engine (Diesel). Air-standard assumptions for ideal cycles. Comparison against Otto, Rankine, and Carnot cycles. Concept / Approach: The ideal Diesel cycle features heat addition at constant pressure, representing fuel injection over a portion of the expansion after high compression of air alone. The Otto cycle models spark-ignition engines with constant-volume heat addition. The Rankine cycle describes vapor power (steam) plants, not internal combustion. Carnot is an unattainable ideal with isothermal and adiabatic processes, not a practical engine model. Step-by-Step Solution: Identify CI trait: air is compressed; fuel is injected and burns while the piston moves — approximated as constant-pressure heat addition.Match to cycle: Diesel cycle fits this description.Therefore, select “Diesel cycle.” Verification / Alternative check: Textbook p-v diagrams show the Diesel cycle with a horizontal (constant-pressure) heat-addition line versus the vertical (constant-volume) line of Otto. Why Other Options Are Wrong: Otto: constant-volume heat addition (SI engines).Carnot: reversible ideal benchmark, not engine-specific.Rankine: external-combustion steam cycle.Dual cycle: closer to real Diesels but not the canonical “Diesel cycle” asked here. Common Pitfalls: Assuming real Diesels match constant-pressure perfectly; many are better approximated by the dual cycle, but the standard answer remains “Diesel cycle.” Final Answer: Diesel cycle

Question 7

Tyres — Bias-ply versus radial: one practical advantage of bias-ply Compared with a radial tyre, which benefit is commonly associated with bias-ply construction under low-speed conditions?

Accepted Answer

Introduction / Context: Tyre construction affects ride, handling, wear, and efficiency. Radials dominate modern road use, but bias-ply tyres have certain characteristics that can be advantageous in specific conditions. Given Data / Assumptions: Standard passenger-car tyres for road use. Comparison focuses on general behavior, not specialty tyres. Concept / Approach: Bias-ply tyres have cords laid diagonally and criss-crossed, which gives a more compliant, flexible sidewall at low speeds on rough surfaces, often perceived as a cushier ride. Radials, with belts under the tread and radial sidewalls, deliver lower rolling resistance, better heat dissipation, longer tread life, and superior high-speed stability, but the ride can be firmer. Step-by-Step Solution: Identify bias-ply traits: flexible carcass and sidewalls → cushioned low-speed ride.Identify radial traits: lower rolling resistance, longer life, better heat management.Thus, the notable bias-ply advantage is smoother low-speed ride. Verification / Alternative check: Historic use on older vehicles and some off-road/trailer applications reflects the comfort and robustness bias-plies can offer at modest speeds. Why Other Options Are Wrong: Longer life and lower rolling resistance are radial strengths, not bias-ply.High-speed heat resistance favors radials due to internal heat paths.“None of these” ignores the real comfort advantage. Common Pitfalls: Assuming “better” means “for all metrics”; tyre design involves trade-offs. Final Answer: smoother ride at low speeds

Question 8

Batteries — How is capacity specified? Choose the standard unit used to express the capacity of an automotive storage battery.

Accepted Answer

Introduction / Context: Battery capacity quantifies how much charge a battery can deliver over time at a specified rate and temperature. This is crucial for sizing batteries for cranking performance and auxiliary loads in vehicles. Given Data / Assumptions: Lead-acid starter battery. Standard discharge rate (often 20-hour rate) and rated temperature. Concept / Approach: Capacity is expressed in ampere-hours (Ah), meaning the product of current and time that the battery can supply before reaching a cutoff voltage. Voltage (volts) indicates nominal electrical potential, not storage capacity. Amperes is instantaneous current, not duration. Weight is irrelevant to electrical capacity, and watt-seconds describe energy but are not the conventional capacity rating for starter batteries. Step-by-Step Solution: Define capacity: Ah = current (A) * time (h) to a specified end voltage.Identify the industry convention: automotive batteries are rated in Ah (and CCA for cranking).Select “ampere-hours.” Verification / Alternative check: Battery labels and datasheets list Ah and CCA; this aligns with service manuals. Why Other Options Are Wrong: Volts: nominal system voltage (e.g., 12 V), not capacity.Amperes: instantaneous current only.Weight: unrelated to electrical rating.Watt-seconds: energy unit; rarely used for automotive capacity ratings. Common Pitfalls: Confusing capacity (Ah) with cold-cranking amps (CCA); both are important but different metrics. Final Answer: ampere-hours

Question 9

Ignition Timing and Engine Speed — Does timing advance with rpm? As engine speed rises in an SI engine, should ignition timing be advanced to maintain optimal combustion phasing?

Accepted Answer

Introduction / Context: Ignition timing determines when the spark occurs relative to piston position. Because flame propagation time is roughly fixed in milliseconds, crankshaft degrees per millisecond increase with rpm, requiring timing changes to keep peak pressure properly phased after T.D.C. Given Data / Assumptions: Spark-ignition engine with mechanical, vacuum, or electronic control. Normal operation without knock events forcing retard. Concept / Approach: At higher rpm, the piston moves faster and the time available per cycle shrinks. To maintain the target crank angle of peak pressure (often around 10–20 degrees ATDC), the spark must be issued earlier in crank degrees, i.e., more BTDC advance. Load, swirl/tumble, mixture, and EGR also influence the optimal advance, which modern ECUs manage via ignition maps and knock sensors. Step-by-Step Solution: Recognize finite flame speed: milliseconds do not change much with rpm.Convert time to crank angle: higher rpm → more degrees per ms.Advance timing with rpm to keep peak pressure after T.D.C. Verification / Alternative check: Timing curves (mechanical/vacuum advance) and ECU spark maps show increasing advance with rpm up to knock or MBT (minimum spark for best torque) limits. Why Other Options Are Wrong: “No” or limited-case answers ignore the fundamental time-to-angle relationship. Common Pitfalls: Assuming advance is monotonic at all loads; near WOT and high load, knock limits may reduce advance relative to part-load. Final Answer: Yes

Question 10

Engine Geometry — What do we call the small volume at T.D.C.? When the piston is at top dead centre, the volume remaining above the piston within the combustion chamber is termed as:

Accepted Answer

Introduction / Context: Compression ratio and combustion characteristics depend on the relationship between the swept volume (displacement) and the small residual volume at top dead centre. Correct terminology is key to engine thermodynamics. Given Data / Assumptions: Piston at T.D.C. Four-stroke engine, simple chamber shape. Concept / Approach: The total cylinder volume at bottom dead centre equals swept volume + clearance volume. At top dead centre, only the clearance volume remains. Compression ratio CR is defined as (swept + clearance) / clearance. The clearance volume affects turbulence, flame travel, and detonation resistance. Step-by-Step Solution: At T.D.C.: piston occupies the swept space.Remaining gas space = clearance volume.Therefore, the correct term is “clearance volume.” Verification / Alternative check: Engine design texts consistently define CR using clearance volume Vc and swept volume Vs. Why Other Options Are Wrong: Cylinder volume: ambiguous; often refers to total or swept volume.Exhaust volume: not a standard term in this context.Swept volume: the displacement moved by the piston from T.D.C. to B.D.C., not the residual space at T.D.C. Common Pitfalls: Confusing total cylinder volume with swept volume; total at B.D.C. includes clearance volume. Final Answer: clearance volume

Question 11

Engine Mechanisms — Primary function of the connecting rod In a reciprocating engine, what is the principal function of the connecting rod?

Accepted Answer

Introduction / Context: The slider-crank mechanism converts linear motion of the piston into rotary motion at the crankshaft. The connecting rod is the vital link between piston pin (gudgeon pin) and crank pin. Given Data / Assumptions: Piston, connecting rod, and crankshaft form a classic slider-crank. Four-stroke cycle assumed. Concept / Approach: The connecting rod transmits force and motion bidirectionally: expanding gases push the piston, forces travel through the rod to the crank, producing torque; during other strokes, the crank pulls/pushes the piston through the rod. It must resist compressive and tensile loads, bending due to side thrust, and fatigue over millions of cycles. Step-by-Step Solution: Identify kinematic role: link between piston and crank.Identify load path: gas pressure → piston → pin → rod → crank pin → crankshaft.Therefore choose “transmit motion of the piston to the crankshaft.” Verification / Alternative check: Free-body diagrams show axial forces in the rod and torque at the crank proportional to gas pressure and geometry. Why Other Options Are Wrong: Turning the flywheel: done by the crankshaft with torque delivered through the rod, but not the rod’s independent function.Driving a drive plate or fuel pump: ancillary tasks via other mechanisms.Synchronizing valve timing: handled by the timing drive and camshaft, not the rod. Common Pitfalls: Attributing accessory functions to the connecting rod; its core role is motion/force transmission. Final Answer: to transmit motion of the piston to the crankshaft

Question 12

Piston Thermal Loading — Where is temperature highest? Within a running engine, which part of the piston generally reaches the highest temperature under normal operation?

Accepted Answer

Introduction / Context: Piston temperature distribution affects material selection, clearances, lubrication, and durability. Recognizing the hottest region helps explain design features such as crown thickness, oil cooling galleries, and ring land geometry. Given Data / Assumptions: Four-stroke engine with conventional cooling and oil jets (if fitted). Steady operating conditions without abnormal detonation. Concept / Approach: The piston crown faces the combustion chamber and absorbs intense thermal flux from burning gases. It experiences peak gas temperatures and pressures near T.D.C. on the power stroke. Heat then conducts through the crown to the ring belt and skirt, and is removed by oil cooling, ring contact with the bore, and convection. Thus the crown temperature is highest, decreasing toward skirt and pin bosses. Step-by-Step Solution: Identify heat source: combustion hot gases impinge on the crown.Establish heat flow paths: crown → ring belt → rings/cylinder → oil jets and splash.Conclude hottest zone: piston crown. Verification / Alternative check: Measured thermal maps and finite-element analyses show maximum temperature at or near the crown center or bowl lip (Diesel), validating the choice. Why Other Options Are Wrong: Skirt and walls are cooled by contact with cylinder and oil; temperatures are lower.Rings run cooler due to direct heat sink into the bore and active cooling by oil.Gudgeon pin receives heat via conduction but is not the hottest region. Common Pitfalls: Assuming rings are hottest because they are near combustion; they are effective heat paths to the cooled cylinder. Final Answer: crown of the piston

Question 13

Automotive differentials — bevel-gear (open) differential construction and gear meshing Which statement correctly describes how a bevel-gear type differential is built and how its gears mesh?

Accepted Answer

Introduction / Context: A bevel-gear (open) differential allows the left and right drive wheels to rotate at different speeds while still delivering torque. This is essential when cornering, since the outer wheel must travel a longer path than the inner wheel. Given Data / Assumptions: Conventional rear- or front-drive open differential. Input torque enters the differential carrier via the ring gear. Axle shafts connect to side gears through splines. Concept / Approach: The differential consists of a carrier (case) that holds the internal bevel gearset. Inside are two axle side gears splined to the axle shafts and two (sometimes four) small bevel pinion gears, often called spider gears, mounted on a cross-shaft fixed to the carrier. The spider gears mesh with both side gears at the same time. Step-by-Step Solution: Input torque turns the carrier through the ring gear.If both wheels have equal resistance, spider gears do not spin on their own axis; carrier simply drives both side gears together.When wheels need different speeds (cornering), spider gears rotate on their own axes and walk around the side gears, allowing differential action.Side gears are splined to axle shafts, so their speeds directly set wheel speeds. Verification / Alternative check: Exploded diagrams and service manuals show spider gears in constant mesh with both side gears and supported in the carrier on a cross pin. Why Other Options Are Wrong: Side gears splined to carrier (A/E): incorrect; side gears spline to axles, not to the case. Left side gear locked to carrier (B): defeats differential action. Carrier contains only side gears (D): incorrect; carrier houses both spiders and side gears. Common Pitfalls: Assuming each spider meshes with only one side gear; in reality, each spider simultaneously meshes with both side gears. Final Answer: The carrier (case) houses bevel pinion (spider) gears and two side gears; each spider gear simultaneously meshes with both side gears, which are splined to the axle shafts.

Question 14

Lead–acid starter battery basics How many series-connected cells are used to make a nominal 12 V automobile battery?

Accepted Answer

Introduction / Context: Automotive starter batteries are lead–acid types made by connecting multiple electrochemical cells in series to achieve the desired nominal voltage for vehicle electrical systems. Given Data / Assumptions: A single lead–acid cell has an open-circuit voltage of about 2.1 V when fully charged. The common vehicle system voltage is called “12 V.” Concept / Approach: To reach approximately 12–12.6 V at rest, cells are connected in series so that voltages add. The number of cells n is chosen so that n * 2.1 V ≈ 12.6 V (fully charged). Step-by-Step Solution: Voltage per cell (charged) ≈ 2.1 V.Target pack voltage ≈ 12.6 V.Compute n = 12.6 / 2.1 = 6.Therefore, a 12 V battery uses 6 cells in series. Verification / Alternative check: Battery casing often shows six filler caps on older designs, corresponding to six cells; modern MF batteries still contain six internal cells. Why Other Options Are Wrong: 2 or 4 cells: would yield about 4.2–8.4 V, insufficient. 8 or 12 cells: would produce about 16.8–25.2 V, not a 12 V system. Common Pitfalls: Confusing nominal 12 V with exactly 12.0 V; actual voltages vary with state of charge and temperature. Final Answer: 6

Question 15

Diesel engine intake process During the suction (intake) stroke of a compression-ignition (Diesel) engine, what is drawn into the cylinder?

Accepted Answer

Introduction / Context: Diesel (compression-ignition) engines differ from spark-ignition engines in when and how fuel is introduced. Understanding the correct intake charge is fundamental to diagnosing smoke, misfire, and starting issues. Given Data / Assumptions: No external mixture formation device (no carburettor). Fuel is injected directly (or into a pre-combustion chamber) near the end of the compression stroke. Concept / Approach: In a Diesel engine, the intake stroke draws in clean air only. This air is then compressed to a high pressure and temperature. Near the end of compression, fuel is injected and auto-ignites due to the hot air, starting combustion. Step-by-Step Solution: Intake stroke: intake valve opens; piston moves down; only air is inducted.Compression stroke: both valves close; air is compressed, raising temperature sharply.Injection: fuel is sprayed near top dead center into the hot air.Combustion: auto-ignition occurs without a spark plug. Verification / Alternative check: Component layout confirms no carburettor in Diesels; fuel system comprises high-pressure pump, injectors, and lines. Why Other Options Are Wrong: Air and fuel premixed or carburetted air–fuel (A/E): that is spark-ignition practice. Only fuel (B): intake cannot draw only fuel; airflow is required. Exhaust–air mixture (D): not normal; residuals may remain but intake is intended to be fresh air. Common Pitfalls: Assuming visible black smoke means fuel is drawn during intake; in reality, smoke is a combustion quality issue, not intake composition. Final Answer: Only air

Question 16

Tyre size nomenclature For a tyre designated 175/65 R14 82 S, what is the aspect ratio (section height as a percentage of section width)?

Accepted Answer

Introduction / Context: Tyre markings encode key parameters that affect ride, handling, and speed capability. The aspect ratio tells how tall the sidewall is relative to the tread width. Given Data / Assumptions: Example marking: 175/65 R14 82 S. Conventional passenger tyre notation: width/aspect construction rim load index speed symbol. Concept / Approach: In the code 175/65 R14 82 S: 175 = section width in mm; 65 = aspect ratio (%); R = radial construction; 14 = rim diameter in inches; 82 = load index; S = speed rating. Step-by-Step Solution: Identify aspect ratio position after the slash.In 175/65 R14 82 S, the number after the slash is 65.Therefore, aspect ratio = 65% (sidewall height is 0.65 * 175 mm). Verification / Alternative check: Any tyre data sheet or sidewall legend uses this standard notation across brands. Why Other Options Are Wrong: 175: section width in mm. 14: rim diameter in inches. 82: load index (maximum load capacity code). S: speed symbol, not a dimension. Common Pitfalls: Confusing load index and speed symbol with dimensional parameters; forgetting that aspect ratio is a percent, not millimetres. Final Answer: 65

Question 17

Tyre wear diagnosis An over-inflated tyre usually wears the tread most near the __________.

Accepted Answer

Introduction / Context: Interpreting tyre wear patterns helps diagnose inflation, alignment, and suspension issues. Over- and under-inflation produce characteristic patterns on the tread surface. Given Data / Assumptions: Radial passenger car tyre, typical load conditions. No severe alignment faults assumed (camber/toe). Concept / Approach: Inflation pressure changes the contact patch shape. Over-inflation bulges the center of the tread outward, concentrating load and friction there. Under-inflation lets the shoulders carry more load, wearing edges faster. Step-by-Step Solution: Consider how pressure affects contact patch curvature.Over-inflated: crown rides high → center wear accelerates.Under-inflated: shoulders bear load → edge wear pattern. Verification / Alternative check: Tyre service manuals show cross-sectional load distribution diagrams correlating pressure with wear patterns. Why Other Options Are Wrong: Edges/corners: typical of under-inflation or excessive camber. Random wear: indicates other faults such as shocks or balance, not classic pressure effect. Common Pitfalls: Misdiagnosing center wear as camber issue; ignoring that temperature and speed exacerbate pressure-related wear. Final Answer: centre

Question 18

ABS pedal feel characteristics During anti-lock braking system (ABS) operation, what typical sensation does the brake pedal transmit to the driver?

Accepted Answer

Introduction / Context: ABS prevents wheel lock by rapidly modulating brake pressure via solenoid valves. Understanding normal ABS pedal feedback reassures drivers and aids technicians in differentiating faults from normal operation. Given Data / Assumptions: Hydraulic ABS with modulator, pump, and solenoid valves. Firm brake application on a low-μ surface triggers ABS. Concept / Approach: When ABS activates, inlet and outlet valves cycle many times per second, and the pump returns fluid to maintain pressure. These hydraulic pressure fluctuations are transmitted back through the pedal as a rapid pulsation or light kickback. Step-by-Step Solution: Wheel speed sensor detects impending lock.ECU commands valves to dump/hold/apply pressure.Pump cycles to maintain system pressure and pedal feedback.Driver feels characteristic pulsation; should maintain firm pressure. Verification / Alternative check: OEM owner’s manuals explicitly describe pedal pulsation during ABS as normal; road tests on wet or gravel surfaces confirm the sensation. Why Other Options Are Wrong: Forced upward lock (A) or sinking to floor (E): indicative of faults, not normal ABS action. Always dramatically longer stroke (B): stroke may change slightly, but not a reliable hallmark. No change (D): most systems produce perceptible pulsation. Common Pitfalls: Pumping the pedal during ABS reduces effectiveness; the correct action is steady, hard pressure while steering. Final Answer: Slight pulsation or kickback is felt in the driver's foot as the valves modulate pressure.

Question 19

Automotive speed control — role of a governor In an automobile, what is the primary function of a governor mechanism?

Accepted Answer

Introduction / Context: Many vehicles use mechanical or electronic governors (speed limiters) to prevent overspeed that can damage the engine or drivetrain, or exceed regulatory limits for certain applications. Given Data / Assumptions: Governor acts on fuel or throttle command. Goal is to cap maximum speed rather than finely regulate all speeds. Concept / Approach: A governor senses engine or vehicle speed and reduces fuel delivery or throttle opening when a preset limit is reached. This prevents overspeed without attempting to hold a constant rpm at every load, which would be impractical in a road vehicle. Step-by-Step Solution: Measure speed via sensor or centrifugal weights.Compare with set limit (calibration).Actuate control (fuel rack, throttle plate, ECU torque request) to reduce power.Maintain speed at or below limit. Verification / Alternative check: Manufacturer data for heavy trucks and some passenger cars list governed top speed or governed engine rpm. Why Other Options Are Wrong: Constant speed under all loads (C): that is a stationary engine governor task, not typical driving. Limit power (A) or maximise economy (D): not direct functions; they may be side effects at the limit. Tailpipe control (E): handled by aftertreatment and engine management, not a governor. Common Pitfalls: Confusing cruise control (maintains set road speed) with a governor (caps maximum speed). Final Answer: Limit the vehicle speed (or maximum engine speed) to a safe value.

Question 20

Fuel knock tolerance — Highest Useful Compression Ratio (HUCR) HUCR is defined as the highest compression ratio at which the __________.

Accepted Answer

Introduction / Context: Knock resistance of spark-ignition fuels is characterized by octane rating and also by Highest Useful Compression Ratio (HUCR), a concept used in standardized knock testing. Given Data / Assumptions: Standardized CFR (Cooperative Fuel Research) test engine conditions. Focus on spark-ignition knock, not diesel auto-ignition quality. Concept / Approach: HUCR is the maximum compression ratio at which a fuel can operate in the test engine without audible knock under specified operating settings. It is a practical measure of a fuel’s anti-knock quality. Step-by-Step Solution: Operate CFR engine with the test fuel.Increase compression ratio gradually while monitoring knock.Record the highest ratio at which knock is not observed.Define that value as HUCR for the fuel under test conditions. Verification / Alternative check: Correlation exists between higher octane numbers and higher HUCR values, consistent with anti-knock performance. Why Other Options Are Wrong: Maximum output or peak efficiency (B/C): not the definition of HUCR. Simple continuous running (A): too vague. Perfect combustion and zero emissions (E): unrealistic and unrelated to HUCR. Common Pitfalls: Confusing HUCR with mechanical compression ratio limits of a particular production engine; HUCR is a test-fuel property under standardized conditions. Final Answer: fuel can be used in a standard test engine without knocking under specified conditions

Automobile Engineering Questions