Body Engineering, Aerodynamics, Thermal Management and NVH

Introduction

Automobile engineering is concerned not only with propulsion and control, but also with how a vehicle carries occupants, protects them, moves through air, maintains acceptable temperatures, and provides a quiet and comfortable environment. Body engineering integrates structural design, materials, manufacturing, safety, styling, ergonomics, and serviceability. Aerodynamics influences fuel consumption, high-speed stability, cooling, wind noise, and lift. Thermal management controls the temperatures of the engine, transmission, battery, electric motor, cabin, and emissions systems. Noise, vibration and harshness (NVH) engineering converts dynamic disturbances into acceptable ride and acoustic quality.

These disciplines are strongly coupled. A grille opening may improve cooling but increase drag. A lighter body may reduce energy consumption but require careful control of crash deformation and vibration. A stiffer body can reduce structure-borne noise, but may transmit more road excitation unless mounts and suspension are redesigned.

Learning objectives

After completing this chapter, the student should be able to:

1. Explain body structures, load paths, materials, and crashworthiness principles.
2. Evaluate basic aerodynamic forces and identify methods of drag and lift reduction.
3. Describe vehicle heating, air-conditioning, engine cooling, and electric-vehicle thermal systems.
4. Explain the sources, transmission paths, measurement, and control of NVH.
5. Apply basic equations to preliminary design calculations.
6. Analyse the interactions among safety, mass, comfort, cost, efficiency, and sustainability.

1. Body engineering and vehicle structures

1.1 Body functions and architecture

The vehicle body must provide a passenger cell, support doors and glazing, carry powertrain and suspension loads, protect occupants in collisions, control noise and vibration, resist corrosion, and present an acceptable appearance. Principal architectures include:

• Body-on-frame: a separate frame carries major loads while the body is mounted on it. It is robust and suitable for heavy-duty vehicles, but usually has greater mass and a higher centre of gravity.
• Unitized or monocoque construction: body panels, pillars, rails, floor, roof and closures form an integrated load-bearing structure. It provides good mass efficiency and is common in passenger cars.
• Space-frame construction: a three-dimensional frame carries loads, with non-structural outer panels. It permits design flexibility but may be expensive to manufacture.
• Mixed-material structures: steel, aluminium, magnesium, plastics and fibre-reinforced composites are combined according to local requirements.

A modern passenger vehicle generally separates the structure into a relatively rigid safety cell and controlled deformation zones at the front and rear. The cell preserves occupant survival space, while crush zones absorb collision energy progressively.

1.2 Loads and load paths

A body experiences static loads from its own mass and payload, dynamic loads from acceleration and braking, lateral loads during cornering, road-induced cyclic loads, powertrain reactions, aerodynamic forces, and crash loads. Efficient design provides continuous load paths from the load application point to the structure and finally to the tyres and road.

Common structural members include longitudinal rails, cross-members, rockers or sills, pillars, roof rails, tunnel sections, suspension towers, subframes and bulkheads. Local reinforcements are used around hinges, seat-belt anchors, steering-column mounts and suspension attachments.

The basic normal stress relation is:

where σ is average normal stress in pascals, F is axial force in newtons, and A is the load-bearing area in square metres. This relation assumes a uniformly distributed axial stress and is not sufficient by itself for members subjected to bending, buckling, joints, stress concentration or plastic deformation.

For bending, the elastic flexural stress is:

where M is bending moment, y is distance from the neutral axis, and I is the second moment of area. The equation applies to linear-elastic beam behaviour with a suitable beam idealisation.

Body stiffness is commonly assessed using torsional and bending tests. Torsional stiffness may be expressed as:

where kₜ is torsional stiffness, T is applied torque, and θ is angular twist in radians. Higher stiffness generally improves alignment control, squeak-and-rattle performance and subjective solidity, but it can increase mass and manufacturing cost.

1.3 Materials and manufacturing

High-strength and advanced high-strength steels offer excellent energy absorption, weldability and cost effectiveness. Aluminium reduces mass but generally requires different joining methods and careful management of galvanic corrosion. Polymers are valuable for bumpers, trim and energy absorbers. Carbon-fibre composites provide high specific stiffness and strength but remain costly and demanding to repair and recycle.

Material selection should consider:

• yield and ultimate strength;
• ductility and strain-rate sensitivity;
• density and specific energy absorption;
• fatigue and corrosion resistance;
• joining, forming and repair processes;
• cost, recycling and embodied energy.

Manufacturing methods include stamping, hydroforming, roll forming, casting, extrusion, adhesive bonding, resistance spot welding, laser welding, riveting and hybrid joining. Joining design must accommodate thermal expansion, load transfer, fatigue, corrosion protection and inspection access.

2. Crashworthiness and occupant protection

2.1 Energy absorption

In a collision, vehicle kinetic energy must be dissipated through controlled deformation, friction, tyre-road interaction, restraint systems and, undesirably, injury-producing deformation. The translational kinetic energy before impact is:

where m is vehicle mass in kilograms and v is speed in metres per second. Because energy varies with the square of speed, a moderate increase in speed produces a disproportionately large increase in energy.

The average impact force over a deformation distance s can be estimated from work-energy principles:

This is a simplified estimate. Real crashes involve both vehicles, changing crush forces, rotation, restitution, structural failure and restraint-system energy absorption.

A desirable crash pulse has controlled acceleration rather than an abrupt peak. Front and rear crumple zones use triggers, tailored thicknesses, progressive folds and crush initiators. The passenger compartment uses strong pillars, roof rails, sills and cross-members to resist intrusion.

2.2 Restraints and compatibility

Seat belts are the primary occupant restraint. Pretensioners remove slack early in a crash, while load limiters control belt force. Airbags distribute loads and reduce contact with the steering wheel, instrument panel and side structure. Child restraints must be compatible with anchorage systems and occupant size.

Crash compatibility concerns the interaction of different vehicles. A tall, heavy vehicle can override or underride a smaller vehicle, reducing the effectiveness of deformation zones. Bumper height, stiffness distribution and load paths should therefore be designed to engage structures appropriately.

Crashworthiness is evaluated through regulatory tests and consumer-rating protocols, including frontal, side, rear and pedestrian-impact assessments. Compliance is necessary but does not guarantee optimum real-world protection; crash diversity, occupant position and restraint use remain important.

3. Ergonomics and human-centred body design

Ergonomics applies knowledge of human dimensions, biomechanics, perception and behaviour to vehicle design. Important features include seat adjustability, steering-wheel reach, pedal spacing, visibility, ingress and egress, control effort, mirror fields, head clearance and luggage access.

A seating package should accommodate a specified percentile range of occupants rather than an average person alone. The design process considers hip point, eye point, knee clearance, shoulder room, headroom and reach envelopes. Poor ergonomic design can cause fatigue, reduced visibility, unsafe posture and distraction.

Controls should be grouped by function, distinguishable by touch where possible, and located so that critical driving information is available with minimal glance time. Touchscreens can increase flexibility but may increase visual distraction when replacing tactile controls. Human-machine interfaces should therefore be tested in realistic driving conditions.

4. Vehicle aerodynamics

4.1 Fundamental forces

Aerodynamic resistance is governed by air density, speed, reference area and body shape. Drag is estimated by:

where Fᴅ is drag force in newtons, ρ is air density in kilograms per cubic metre, v is vehicle speed in metres per second, Cᴅ is the dimensionless drag coefficient, and A is frontal area in square metres. The equation assumes a defined reference area and steady external flow; actual road vehicles also experience wind, turbulence, rotating wheels, underbody flow and transient effects.

The aerodynamic power required to overcome drag is:

Thus, at constant Cᴅ and area, drag force varies with v² and drag power with v³. Rolling resistance, gradient resistance and acceleration resistance must also be included in a complete road-load model.

Lift is represented similarly:

where Cᴸ is the lift coefficient, using the sign convention selected by the analyst. Positive lift reduces normal tyre load; negative lift is downforce. Excessive lift can impair stability, while excessive downforce increases tyre load and usually drag.

4.2 Flow features and design methods

The main aerodynamic regions are the front stagnation zone, bonnet and roof flow, windscreen transition, rear separation region, underbody, wheels and cooling openings. Design methods include rounded leading edges, controlled roof curvature, tapered rear geometry, sealed underbodies, wheel deflectors, aerodynamic wheels, spoilers and active grille shutters.

A long, smoothly tapered rear may reduce separation, but styling, luggage volume and manufacturing constraints limit ideal forms. Wheel houses are particularly difficult because rotating wheels generate turbulence. Underbody panels can reduce drag but must tolerate impact, heat and service requirements.

Aerodynamics also affects cooling. Air entering the grille experiences pressure losses through the radiator, condenser and ducting. A well-designed system seals the high-pressure side to the heat exchanger and provides a low-resistance exit path. Cooling air should not be admitted unnecessarily because open grilles increase drag.

Worked example: highway aerodynamic power

A vehicle has Cᴅ = 0.30, frontal area A = 2.2 m², speed v = 30 m/s, and air density ρ = 1.20 kg/m³. The drag force is:

Fᴅ = ½(1.20)(30²)(0.30)(2.2) = 356.4 N.

The corresponding aerodynamic power is:

Pᴅ = 356.4 × 30 = 10,692 W ≈ 10.7 kW.

This is only the power overcoming aerodynamic drag. Driveline losses, rolling resistance, road gradient and auxiliary loads require additional power. If speed is doubled while conditions remain comparable, aerodynamic power theoretically increases by a factor of eight.

5. Heating, ventilation and air-conditioning

5.1 Cabin thermal comfort

Cabin comfort depends on air temperature, humidity, air velocity, radiant temperature, clothing, metabolic rate and occupant preference. Uniform temperature is not always desirable: solar radiation, glazing and local drafts create spatial differences. Defogging and demisting are safety functions, not merely comfort functions.

The cabin heating load can be estimated by an energy balance:

where Q̇ₕ is required heating rate, Q̇ₜᵣ is transmission heat loss through panels and glazing, Q̇ᵥ is ventilation or infiltration loss, Q̇ₛ is solar-related loss or gain according to the sign convention, Q̇ₒ is occupant and equipment load, and Q̇ᵢ is available internal heat. For cooling calculations, internal and solar gains generally become positive cooling loads. A detailed calculation requires transient heat transfer and spatial modelling.

Ventilation systems must supply fresh air, filter contaminants, distribute air effectively and avoid excessive noise. Recirculation reduces heating or cooling load but must be balanced against air quality and carbon-dioxide accumulation.

5.2 Refrigeration cycle

Automotive air-conditioning commonly uses a vapour-compression cycle consisting of compressor, condenser, expansion device and evaporator. Refrigerant vapour is compressed, rejects heat in the condenser, expands with a pressure drop, and absorbs cabin heat in the evaporator.

The coefficient of performance for cooling is:

where Q̇ₗ is heat removed from the low-temperature space and Ẇ is compressor power. COP is dimensionless when both quantities use the same power unit. It varies with temperatures, pressure ratios, refrigerant, compressor efficiency and heat-exchanger performance.

Refrigerant selection is governed by thermodynamic performance, flammability, toxicity, global-warming potential, service practice and regulation. Leakage prevention and recovery are essential environmental responsibilities.

5.3 Electric and hybrid vehicles

Internal-combustion vehicles can use waste engine heat for cabin heating. Electric vehicles have less readily available waste heat and therefore may use positive-temperature-coefficient heaters, heat pumps, or recovered heat from the motor, inverter and battery. A heat pump can reduce heating energy consumption, but performance declines at low ambient temperatures and during defrost operation.

6. Vehicle thermal management

6.1 Engine and power-electronics cooling

Thermal management maintains components within safe temperature limits while minimizing parasitic energy, warm-up time and emissions. An engine system may include coolant pump, thermostat, radiator, expansion tank, hoses, oil cooler, charge-air cooler and controlled fan.

The sensible heat transported by a coolant is:

where Q̇ is heat-transfer rate in watts, ṁ is mass flow rate in kilograms per second, cₚ is specific heat capacity in joules per kilogram-kelvin, and ∆T is coolant temperature rise in kelvins. The expression assumes single-phase flow with approximately constant specific heat and negligible kinetic and potential energy changes.

Heat transfer across a surface may be approximated by:

where U is overall heat-transfer coefficient, A is heat-transfer area, and ∆Tₗₘ is the appropriate logarithmic mean temperature difference for the exchanger arrangement. This relation is a design approximation; fouling, transient operation, non-uniform flow and phase change may require more detailed analysis.

A thermostat accelerates warm-up by restricting radiator flow until the engine reaches a target temperature. Fans and pumps may be speed-controlled to match demand. Excessive cooling increases warm-up time and friction, whereas insufficient cooling causes oil degradation, knock, component distortion and failure.

6.2 Battery thermal management

Lithium-ion batteries require control of temperature uniformity as well as average temperature. High temperature accelerates ageing and may increase safety risk; low temperature reduces power capability and charging acceptance. Liquid cooling plates, refrigerant-cooled systems, air cooling, heat pipes and phase-change materials are possible solutions.

Thermal management must coordinate charging, regenerative braking, propulsion, cabin comfort and preconditioning. Battery models and sensors estimate temperature and state of charge, while supervisory controllers allocate cooling or heating capacity.

Worked example: coolant flow rate

A cooling circuit must reject 20 kW. Coolant specific heat is 3.8 kJ/(kg·K), and the permitted coolant temperature rise is 10 K. From Q̇ = ṁcₚ∆T:

ṁ = 20,000 ÷ (3,800 × 10) = 0.526 kg/s.

If coolant density is approximately 1,050 kg/m³, the volume flow rate is:

V̇ = ṁ/ρ = 0.526 ÷ 1,050 = 0.000501 m³/s,

or approximately 30.1 L/min. Pump selection must then account for pressure losses, cavitation margin, control range and transient conditions.

7. Noise, vibration and harshness

7.1 Sources and transmission paths

Noise is unwanted airborne pressure fluctuation; vibration is mechanical oscillation; harshness is the subjective perception of unpleasantness, often involving transient shocks and low-frequency body motion. Sources include combustion pressure, gear meshing, imbalance, tyre-road interaction, wind, electric-machine electromagnetic forces, cooling fans and pumps.

Transmission paths are classified as:

• Structure-borne: forces pass through mounts, subframes, suspension, body panels and fasteners.
• Airborne: sound travels through the air from the source or through leaks and panels.
• Fluid-borne: pressure pulsations travel through exhaust, intake, hydraulic or coolant systems.

Effective NVH design identifies source, path and receiver. Treating only the receiver with insulation may add mass without eliminating the cause.

7.2 Fundamental vibration model

A single-degree-of-freedom system is represented by mass m, stiffness k and damping c. Its undamped natural angular frequency is:

and its natural frequency in hertz is:

The damping ratio is:

These equations assume linear stiffness and damping, small displacement, and a single dominant mode. Real vehicle structures have many coupled modes and nonlinear interfaces.

Resonance occurs when excitation frequency approaches a natural frequency. Control methods include shifting natural frequencies by changing mass or stiffness, adding damping, isolating sources with tuned mounts, balancing rotating parts, improving gear accuracy, and using absorbers or active control.

7.3 Sound measurement and human perception

Sound pressure level is expressed in decibels:

where p is measured root-mean-square sound pressure and p₀ is the reference pressure, conventionally 20 µPa in air. Decibels are logarithmic; they should not be added arithmetically. For independent, incoherent sources, sound levels are combined using energy ratios:

where Lᵢ are individual levels. Frequency weighting, especially A-weighting, approximates human hearing sensitivity but does not replace engineering analysis.

7.4 NVH treatments

Typical measures include engine and motor mounts, tuned mass dampers, constrained-layer damping, acoustic absorbers, barriers, seals, laminated glazing, low-noise tyres, gear-mesh optimisation, active noise cancellation and isolation bushings. Each treatment has trade-offs. Soft mounts improve isolation at some frequencies but may permit excessive displacement during torque reactions. Thick barriers reduce noise but increase mass. Active systems require sensors, actuators, reliable control algorithms and fail-safe behaviour.

8. Integrated design and professional practice

Body, aerodynamic, thermal and NVH decisions should be evaluated together. A design review should consider structural safety, mass, manufacturability, repairability, recyclability, cost, energy consumption, thermal robustness, acoustic quality and regulatory compliance.

Computer-aided engineering supports this process through finite-element crash and stiffness analysis, computational fluid dynamics, computational aeroacoustics, one-dimensional thermal networks, multibody dynamics and model-based control. Simulation must be correlated with instrumented tests. Mesh refinement, boundary conditions, material data and sensor placement can strongly influence results.

Data-driven and AI methods can assist surrogate modelling, design-space exploration, defect detection and predictive maintenance. They do not remove the need for physical validation, explainability, cybersecurity, protection of test data and engineering responsibility. Safety-critical decisions require traceable requirements, verified models and human approval.

Applied case: integrated cooling and aeroacoustic redesign

Background

The following is an illustrative engineering case. A compact hybrid vehicle meets its powertrain temperature requirement, but customers report high fan noise during hot-weather urban driving. Fuel consumption is also higher than the target during highway operation.

Problem analysis

Testing shows that the radiator requires a large airflow rate because of restricted ducting and a partially blocked exit path. The electric fan therefore operates at high speed. CFD indicates unnecessary leakage around the heat exchanger, while wind-tunnel testing identifies wheel-wake turbulence and an exposed underbody region. NVH testing finds a fan blade-passing tone transmitted through the front module and a resonance near the fan operating range.

Approach

Engineers seal the radiator duct, enlarge the low-pressure exit path, and introduce a controlled grille shutter. The fan is redesigned for improved aerodynamic efficiency and mounted on isolating bushings. A structural modal analysis shifts the front-module resonance away from the dominant excitation. Underbody panels and wheel deflectors reduce turbulence, while control software uses coolant temperature, ambient temperature and vehicle speed to schedule fan operation.

Outcome

The redesign reduces the required fan speed at cruise and lowers aerodynamic drag. During hot urban operation, cooling capacity remains adequate, but the fan operates for shorter intervals and the dominant tonal noise is reduced. Validation includes thermal soak tests, towing and hill climbs, hot-weather air-conditioning operation, water ingress checks, crash compatibility, durability, wind-tunnel measurements and subjective listening assessments.

Learning points

1. Improving heat-exchanger airflow can reduce both auxiliary power and noise.
2. Aerodynamic shutters must fail safely and tolerate contamination.
3. A source-path-receiver analysis is more effective than adding insulation alone.
4. Simulation results require correlation with physical tests.
5. Thermal, aerodynamic, structural and NVH requirements must be managed as a coupled system.

Challenges, regulation and sustainability

Vehicle bodies and systems must satisfy regulations governing crash protection, lighting, glazing, pedestrian protection, emissions, refrigerants, electromagnetic compatibility and exterior noise. Requirements vary by jurisdiction and vehicle category, so engineers must consult current standards rather than rely on historical limits.

Sustainability requires life-cycle thinking. Lightweighting can reduce use-phase energy but may increase manufacturing energy or complicate recycling. Multi-material bodies require separation strategies. Refrigerant leakage, battery thermal events, collision repair, end-of-life recovery and responsible sourcing of materials are important governance issues. Design for disassembly, clear service procedures and safe isolation of high-voltage systems support both environmental and occupational safety.

Best-practice design workflow

1. Establish measurable requirements for safety, mass, drag, thermal limits, noise and durability.
2. Define operating scenarios, boundary conditions and regulatory obligations.
3. Select architecture and load paths before detailed styling optimisation.
4. Use first-principles calculations for sizing and simulation for interaction effects.
5. Design source, path and receiver together for NVH.
6. Validate thermal and aerodynamic performance under worst credible conditions.
7. Correlate models with controlled tests and quantify uncertainty.
8. Review manufacturing, repair, recycling and high-voltage safety early.
9. Document assumptions, data sources, model versions and acceptance criteria.
10. Apply change control throughout the product life cycle.

Chapter Summary

Body engineering creates a safe, stiff, durable and ergonomic passenger structure through appropriate architecture, load paths, materials and manufacturing. Crashworthiness separates a protected occupant cell from controlled deformation zones and uses restraints to manage occupant loads. Aerodynamic drag depends primarily on air density, speed squared, drag coefficient and frontal area; the associated power rises approximately with speed cubed. Aerodynamic design must be coordinated with cooling and stability.

Heating, ventilation and air-conditioning maintain comfort, visibility and air quality. Thermal management transfers heat using coolant, air, refrigerant and controlled devices while protecting engines, batteries, motors and power electronics. NVH engineering identifies sources, paths and receivers and applies stiffness, damping, isolation, absorption, balancing and active control. Since these domains interact, professional vehicle development requires system-level trade-offs, simulation, testing, regulatory awareness and life-cycle responsibility.

Key Terms

Body-on-frame: Vehicle architecture with a separate load-carrying frame and body.

Unitized body: Integrated body structure in which panels and members jointly carry loads.

Safety cell: Strong occupant compartment intended to preserve survival space.

Crumple zone: Controlled deformation region that absorbs collision energy.

Crashworthiness: Ability of a vehicle to protect occupants during a crash.

Load path: Structural route by which forces travel through a vehicle.

Drag coefficient: Dimensionless measure of aerodynamic resistance for a specified reference area.

Frontal area: Projected vehicle area normal to the direction of motion.

Lift coefficient: Dimensionless coefficient describing aerodynamic lift or downforce.

Thermal management: Control of component and cabin temperatures within required limits.

Coefficient of performance: Ratio of useful refrigeration effect to compressor power.

Heat exchanger: Device transferring heat between fluids or between a fluid and a solid.

NVH: Noise, vibration and harshness engineering.

Structure-borne noise: Noise transmitted through solid structural paths.

Natural frequency: Frequency at which a system tends to oscillate freely.

Damping ratio: Dimensionless measure of damping relative to critical damping.

Resonance: Large response produced when excitation approaches a natural frequency.

Sound pressure level: Logarithmic measure of sound pressure relative to a reference pressure.

Review Questions

Short Answer Questions

1. Distinguish body-on-frame and unitized body construction.
2. Why are crumple zones and safety cells designed with different stiffness characteristics?
3. Define drag coefficient and frontal area.
4. What is the function of a thermostat in an engine cooling system?
5. Distinguish structure-borne noise from airborne noise.

Long Answer Questions

1. Explain the principal load paths and structural members of a unitized passenger-car body.
2. Describe crash-energy management, occupant restraints and crash compatibility.
3. Explain how vehicle shape, wheels, underbody flow and cooling openings affect aerodynamic performance.
4. Describe the vapour-compression air-conditioning cycle and compare cabin heating strategies in combustion and electric vehicles.
5. Explain the source-path-receiver approach to NVH control, including the role of damping and isolation.

Analytical / Application Questions

1. A vehicle has Cᴅ = 0.28, frontal area 2.0 m², air density 1.2 kg/m³ and speed 25 m/s. Calculate aerodynamic drag force and power. State the assumptions.
2. A cooling loop must reject 15 kW using coolant with cₚ = 4.0 kJ/(kg·K) and an allowable temperature rise of 8 K. Determine the required mass flow rate and explain two practical pump-selection considerations.
3. A structure has effective mass 250 kg and stiffness 100,000 N/m. Calculate its undamped natural frequency and explain two design changes that could reduce resonance response.

Multiple Choice Questions with Answers

Question 1

Which body region is primarily intended to preserve occupant survival space during a crash?

A. Safety cell

B. Front bumper cover

C. Radiator grille

D. Rear spoiler

Correct Answer: A. Safety cell

Question 2

If vehicle speed is doubled while other aerodynamic variables remain constant, aerodynamic drag force ideally becomes:

A. Half as large

B. Twice as large

C. Four times as large

D. Eight times as large

Correct Answer: C. Four times as large

Question 3

Which equation estimates aerodynamic drag force?

A. F_D = m a

B. F_D = ½ρv² C_D A

C. F_D = m c_p ΔT

D. F_D = kx

Correct Answer: B. F_D = ½ρv² C_D A

Question 4

What is the principal purpose of a thermostat in a conventional engine cooling circuit?

A. To increase tyre pressure

B. To control coolant flow and accelerate warm-up

C. To reduce refrigerant humidity

D. To balance rotating components

Correct Answer: B. To control coolant flow and accelerate warm-up

Question 5

A cooling system rejects 12 kW using coolant with cₚ = 4 kJ/(kg·K) and a 6 K temperature rise. What mass flow rate is required?

A. 0.25 kg/s

B. 0.50 kg/s

C. 2.00 kg/s

D. 8.00 kg/s

Correct Answer: B. 0.50 kg/s

Question 6

Which component absorbs cabin heat in a vapour-compression air-conditioning system?

A. Condenser

B. Compressor

C. Evaporator

D. Expansion tank

Correct Answer: C. Evaporator

Question 7

For a linear single-degree-of-freedom system, increasing stiffness while keeping mass constant generally causes natural frequency to:

A. Decrease

B. Remain unchanged

C. Increase

D. Become zero

Correct Answer: C. Increase

Question 8

Which is an example of structure-borne NVH transmission?

A. Sound travelling through open atmosphere only

B. A force transmitted through an engine mount into the body

C. Solar radiation entering glazing

D. Air entering the radiator

Correct Answer: B. A force transmitted through an engine mount into the body

Question 9

Sound pressure level is expressed using which type of scale?

A. Linear pressure scale only

B. Logarithmic decibel scale

C. Mass fraction scale

D. Absolute temperature scale

Correct Answer: B. Logarithmic decibel scale

Question 10

Why can a controlled grille shutter improve vehicle efficiency?

A. It increases unnecessary cooling airflow at all times

B. It eliminates the need for crash structures

C. It reduces airflow and drag when maximum cooling is unnecessary

D. It increases tyre-road friction

Correct Answer: C. It reduces airflow and drag when maximum cooling is unnecessary