Fundamentals of Automobiles

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This section covers the history, scope and future of automobiles, the classification and specification of motor vehicles, the major components of an automobile, the chassis layout and types of frames, the drive layouts (front, rear and all-wheel drive) and the main vehicle design considerations.

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Development History Year Milestone 1769 Nicolas-Joseph Cugnot — steam-powered tractor (first self-propelled road vehicle) 1876 Nikolaus Otto — four-stroke gas engine 1885–86 Karl Benz — Motorwagen, first practical petrol-engined car (patent 1886);

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Gottlieb Daimler and Wilhelm Maybach — high-speed petrol engine 1888 J.

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Dunlop — practical pneumatic tyre 1892–97 Rudolf Diesel — compression-ignition engine 1908–13 Henry Ford — Model T and moving assembly line (mass production) 1930s–60s Synchromesh, automatic transmissions, independent suspension, radial tyres, disc brakes 1970s–90s Electronic fuel injection, catalytic converters, ABS, airbags, OBD 1997 onwards Mass-produced hybrids (Toyota Prius), modern battery EVs (2008+), ADAS and connected, autonomous vehicles Scope and Future of Automobiles • Road transport carries most passengers and freight in Nepal (a largely mountainous country with limited rail), so automobile engineers work in vehicle import and dealership service, workshops, public transport operation, fleet management, the Department of Transport Management (vehicle registration and fitness testing), body building, and EV infrastructure. • Trends: electrification (BEV, HEV, PHEV, FCEV), lightweight materials, downsized turbocharged engines, stricter emission norms (Euro/Bharat stage), ADAS (adaptive cruise, lane keeping, automatic emergency braking), connected vehicles and autonomous driving, shared mobility.

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Classification of Motor Vehicles Basis Classes Purpose / use Passenger vehicles (cars, buses), goods vehicles (trucks, tippers, tankers), special-purpose (ambulance, fire engine, cranes), off-road/agricultural (tractors, earth movers) Load capacity Light motor vehicle (LMV), medium (MMV) and heavy motor vehicles (HMV) / heavy goods vehicles (HGV) Number of wheels / axles Two-, three-, four-, six-wheelers; multi-axle vehicles, articulated vehicles (tractor + semi-trailer) Fuel / power source Petrol, diesel, CNG/LPG, electric (BEV), hybrid, hydrogen fuel cell Drive Front-wheel drive, rear-wheel drive, four-wheel / all-wheel drive (4×2, 4×4, 6×4…) Engine position Front, mid, rear engine; transverse or longitudinal Body style Sedan, hatchback, coupe, convertible, SUV, MPV/van, pick-up, bus, truck Steering side Right-hand drive (Nepal, India, UK — traffic keeps left) / left-hand drive • Wheel notation 4×2 means 4 wheel positions of which 2 are driven;

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6×4 = 3 axles with two driven rear axles (heavy trucks).

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Vehicle Specifications • Dimensions: overall length, width, height, wheelbase (distance between front and rear axle centres), track (distance between centres of left and right wheels on one axle), ground clearance, front/rear overhang, turning circle radius, approach/departure angles. • Weights: kerb weight (unladen, with fuel and fluids), payload, gross vehicle weight (GVW) = kerb weight + payload + occupants, axle load limits. • Engine: type, number of cylinders, bore × stroke, displacement (cc), compression ratio, maximum power (kW @ rpm), maximum torque (N·m @ rpm). • Transmission, gear ratios, final-drive ratio, tyre size, brakes, suspension, steering type, fuel tank capacity, top speed, fuel economy (km/L), emission standard.

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Major Components of an Automobile System Main components Power unit Engine with fuel, ignition, cooling, lubrication, intake and exhaust systems (or electric motor + battery) Transmission (power train) Clutch / torque converter, gearbox, propeller shaft with universal joints, final drive, differential, axle shafts Chassis / running gear Frame, suspension, steering, wheels and tyres, brakes Body (superstructure) Passenger compartment or load body, doors, bonnet, bumpers Auxiliaries / controls Electrical system (battery, starter, alternator, lighting), instruments, HVAC, safety systems Chassis Layout and Frames • Chassis = vehicle without the body: frame + engine + transmission + suspension + steering + wheels + brakes.

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A 'rolling chassis' is common for buses and trucks, on which bodies are built locally (much bus body-building is done in Nepal and India). • Functions of a frame: carry the weight of body, passengers and payload; withstand engine and transmission torque, braking and acceleration forces, shocks from road, and cornering forces; provide mounting points.

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Frame type Description / use Conventional (ladder) frame Two long side members (channel, box or tubular) joined by cross-members; the body is bolted on (body-on-frame) — trucks, buses, pick-ups, rugged SUVs; heavy but easy to repair and modify Integral (unitised / monocoque) body No separate frame — the pressed-steel body shell itself carries the loads; light, stiff and cheap in mass production, better crash energy management — most modern cars Semi-integral Body with sub-frames that carry engine and suspension, attached through rubber mountings Backbone / tubular frame Central tubular backbone (e.g., Tatra, some sports cars) or space frame of welded tubes (racing cars) X-frame, perimeter frame Variations for torsional stiffness or lower floor • Frame sections: channel (C-section, most common and cheap), box (stiffer in torsion), tubular (light, stiff).

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Frame materials: pressed low-carbon or high-strength steel; aluminium in some cars. • Side members are often kicked up (swept up) at the rear for axle movement and narrowed at the front for wheel lock clearance.

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Drive Layouts (Vehicle Operation) Layout Features / merits Demerits Front engine, rear-wheel drive (FR) Good weight distribution; better traction when loaded or accelerating (load shifts rearward); simpler front end; trucks, buses, some cars Propeller shaft tunnel, more weight, oversteer tendency on slippery roads Front engine, front-wheel drive (FF) Compact transverse power pack, no propeller shaft, more cabin space, good straight-line stability and traction on slippery roads (engine weight over driven wheels) — most small cars Torque steer, CV joints wear, understeer, front tyres wear faster, lower traction uphill Rear/mid engine, rear drive (RR/MR) Excellent traction and braking balance; sports cars, many buses (rear engine) Little luggage space, oversteer, cooling difficulties Four-wheel / all-wheel drive (4WD/AWD) Drive to all wheels — best traction on hills, mud, snow;

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4WD with transfer case (part-time, low range) for off-road;

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AWD with centre differential/coupling (full-time) for on-road safety Heavier, costly, more fuel consumption, complex Vehicle Design Considerations • Performance (power-to-weight ratio, gradeability — important on Nepal's hill roads, top speed, acceleration); fuel economy and emissions; safety (active: brakes, stability, visibility; passive: crumple zones, airbags, seat belts); comfort and ergonomics (ride, noise, vibration and harshness — NVH, HVAC); handling and stability (low CG, weight distribution, suspension geometry); reliability, durability and serviceability; aerodynamics; cost; legal regulations (dimensions, axle loads, lighting, emission and safety standards); ground clearance and approach angle for poor roads; styling and aesthetics; recyclability.

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This section covers the clutch and fluid coupling, manual and automatic gearboxes (sliding-mesh, constant-mesh, synchromesh, epicyclic), DCT and CVT, overdrive and transfer case, universal joints and propeller shafts, the final drive and differential, four-wheel drive, limited-slip differential, and common troubles.

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Functions of the Transmission System • Connect/disconnect engine and wheels; provide torque multiplication and a range of speeds (engine torque is limited and occurs only within a speed band); provide reverse and neutral; turn the drive through 90° and give a final gear reduction; allow the driving wheels to rotate at different speeds on curves; allow for changes in propeller-shaft angle and length as the suspension moves.

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Clutch • Purpose: to engage and disengage the engine from the transmission smoothly — for starting, gear changing and stopping without stalling.

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Requirements: transmit maximum torque without slip, engage gradually, dissipate heat, small inertia of driven parts (for easy gear change), minimum pedal effort, balanced. • Torque capacity of a friction clutch (uniform wear):

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T = μ·W·Rm·n, Rm = (r1 + r2)/2, n = number of friction surfaces (2 for single plate).

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Type Description Single-plate dry clutch (coil-spring) Clutch plate (friction linings on both sides, torsional damper springs, splined hub) clamped between flywheel and pressure plate by coil springs; release levers, release (throw-out) bearing, fork — most common Diaphragm-spring clutch A conical diaphragm (Belleville) spring replaces coil springs and release levers — compact, uniform pressure, lower pedal effort, load does not fall as lining wears; modern cars Multi-plate clutch Several plates — higher torque in smaller diameter; wet (oil-immersed) in motorcycles and automatic transmissions Centrifugal clutch Engages automatically as speed rises (weights move outward) — mopeds, scooters (CVT), chain saws Cone clutch Conical friction surfaces — used in synchronisers Semi-centrifugal, electromagnetic, vacuum/hydraulic operated Special applications;

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A/C compressor uses an electromagnetic clutch • Fluid coupling: impeller (pump) on the engine side, runner (turbine) on the gearbox side in an oil-filled housing — transmits torque smoothly through oil with 2–3% slip at speed; no torque multiplication; engine cannot stall; replaced by the torque converter (impeller + turbine + stator on one-way clutch) which multiplies torque ≈ 2–2.5 times at stall. • Clutch operation: mechanical (cable/linkage) or hydraulic (master and slave cylinders).

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Clutch trouble Likely causes Slipping (engine speed rises, vehicle does not accelerate) Worn or oil-soaked linings, weak pressure springs, no pedal free play (release bearing always pressing), binding linkage Dragging / not disengaging (hard gear change) Excessive pedal free play, warped plate, air in hydraulic system, sticking hub on splines, broken diaphragm fingers Grabbing / judder Oil or grease on linings, worn splines, loose engine mountings, glazed linings, warped pressure plate Noise Worn release bearing (noise when pedal pressed), worn pilot bearing, broken damper springs Clutch pedal stiff / vibrating Dry linkage, uneven release levers Gearboxes (Manual) • Gear ratio = speed of input (engine) ÷ speed of output = product of (driven teeth/driver teeth) of the meshing pairs.

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Low gear → high ratio → high torque, low speed.

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Overall ratio = gearbox ratio × final-drive ratio. • Typical car ratios:

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1st ≈ 3.5, 2nd ≈ 2.0, 3rd ≈ 1.3, 4th = 1.0 (direct), 5th ≈ 0.8 (overdrive); reverse uses an idler gear to reverse rotation.

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Type Working Remarks Sliding-mesh Gears on the main shaft are slid along splines to mesh with countershaft gears Oldest; noisy, gear clashing, needs double declutching; spur gears Constant-mesh All gears always in mesh; main-shaft gears free on the shaft; dog clutches slide to lock the chosen gear Helical gears — quieter; dog clutches easier to engage; still needs double declutching; motorcycles Synchromesh Constant mesh plus synchronisers — a cone clutch (baulk ring) brings the gear and shaft to equal speed before the dog teeth (sleeve) engage Smooth, clash-free change without double declutching — all modern manual cars Epicyclic (planetary) Sun gear, planet gears on a carrier, ring (annulus) gear; holding one member by brake bands/clutches gives different ratios Used in automatic transmissions, overdrives, hybrid power-split units Automatic Transmissions, DCT and CVT • Conventional automatic (AT): torque converter + epicyclic gear sets controlled by multi-plate clutches and brake bands; hydraulic valve body and (now) electronic TCU choose shifts according to speed, throttle and load; positions P-R-N-D-L; lock-up clutch removes converter slip at cruise. • Epicyclic ratios (Willis): with ring fixed, sun driving and carrier output: ratio = 1 + TR/TS (maximum reduction).

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Locking any two members together gives direct drive (1 :

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1); holding the carrier gives reverse. • Dual-Clutch Transmission (DCT/DSG): two automated clutches — one for odd gears (1, 3, 5, 7) and one for even gears (2, 4, 6, R) on two concentric input shafts; the next gear is pre-selected and shifting simply swaps clutches → very fast shifts without interruption of torque, good efficiency.

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Demerits: cost, complexity, low-speed jerkiness, dry-clutch overheating in traffic. • Continuously Variable Transmission (CVT): two variable-diameter (V-groove) pulleys connected by a steel push belt or chain; hydraulic control changes effective diameters → infinite ratios within a range; engine kept at its most efficient or most powerful speed.

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Rubber-belt CVTs with centrifugal pulley in scooters; toroidal CVTs; hybrid e-CVT uses a planetary set. • AMT (automated manual): a normal manual gearbox with electro-hydraulic actuators for clutch and shift — low cost.

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Overdrive and Transfer Case • Overdrive: a gear ratio less than 1 (output faster than input), either an extra top gear in the gearbox or a separate epicyclic unit behind it.

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Allows lower engine speed at cruising → better fuel economy, less wear and noise.

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Troubles: not engaging (solenoid/switch/hydraulic fault, low oil), slipping, noise. • Transfer case (4WD): mounted behind the gearbox; divides drive between front and rear propeller shafts; provides 2H, 4H, 4L (low range) and neutral; may contain a centre differential or viscous coupling (full-time).

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Troubles: jumping out of gear, noise, leaks, difficulty shifting into 4WD, 'wind-up' of drive line when part-time 4WD is used on dry pavement (no centre differential).

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Universal Joints and Propeller Shafts • Propeller shaft transmits drive from gearbox to final drive in FR vehicles; usually a hollow steel tube, dynamically balanced; long shafts are split into two with a centre bearing (to raise whirling speed); a slip joint (splines) permits change of length as the rear axle moves up and down. • Universal joints permit transmission of power between shafts at an angle that changes with suspension movement.

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Joint Features Hooke's (cross/spider) joint Two yokes and a cross with needle bearings; output speed fluctuates twice per revolution when shafts are at an angle; cancelled by two joints with yokes in the same plane and equal angles Flexible (rubber doughnut / fabric) joint Small angles; absorbs vibration; no lubrication Constant-velocity (CV) joints Uniform output speed at large angles — Rzeppa (ball-type) at the wheel end of FWD drive shafts, tripod (plunging) at the gearbox end;

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Tracta, double-Cardan (Weiss) • Troubles: vibration (unbalance, bent shaft, worn U-joints, incorrect phasing), clunk when taking up drive (worn splines/U-joints), squeak (dry needle bearings), clicking noise on turns in FWD cars = worn outer CV joint (often torn boot).

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Final Drive and Differential • Final drive: gives a permanent speed reduction (≈ 3–6 :

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1 in cars, up to ≈ 7–9 :

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1 in trucks) and turns the drive through 90°.

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Types: straight bevel (noisy), spiral bevel (smooth, strong), hypoid (pinion axis offset below the crown-wheel centre — lowers the propeller shaft and floor, more teeth in contact, quiet; needs extreme-pressure (EP) hypoid oil due to sliding), worm and worm wheel (large reduction — some heavy vehicles), double-reduction for trucks. • Main parts of rear axle: crown wheel and pinion, differential case, two sun (side) gears splined to the half-shafts, two or four planet (pinion) gears on a cross-pin, bearings, axle casing. • Differential function: on a curve the outer wheel travels farther, so it must rotate faster; the differential lets the half-shafts turn at different speeds while dividing torque equally.

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Nleft + Nright = 2 × Ncrown wheel.

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If one wheel is held, the other turns at twice crown-wheel speed. • Drawback of an open differential: since torque is equal on both sides, if one wheel is on ice/mud (low traction), the other gets only the same small torque → vehicle gets stuck. • Limited-slip differential (LSD): clutch-pack (plate) type, viscous coupling, or torque-sensing (Torsen, helical gear) types limit speed difference and send more torque to the wheel with grip.

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Differential lock (off-road vehicles, tractors) locks the two sides together. • Four-wheel drive: front and rear axles driven through transfer case; front axle has a differential and CV/steering joints; full-time 4WD needs a centre differential to avoid wind-up; free-wheeling hubs disconnect the front wheels in 2WD. • Rear axle types by load: semi-floating (half-shaft carries torque + vehicle weight + bending — cars), three-quarter floating, full-floating (half-shaft carries only torque — trucks).

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Final drive / differential trouble Likely cause Noise on drive (acceleration) Incorrect crown-wheel/pinion mesh (heel contact), worn pinion bearings Noise on coast (deceleration) Incorrect mesh (toe contact), loose pinion bearing preload Noise only on turns Worn differential planet/sun gears or cross-pin Oil leakage Worn pinion oil seal, blocked breather, over-filling Clunk on take-up Excess backlash, worn splines

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This section covers the objectives, types, parts and troubleshooting of suspension systems; steering system types, gearboxes, power steering, steering geometry and wheel alignment; and wheel and tyre types, dimensions, nomenclature, tyre life, inflation pressure and tyre rotation.

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Suspension — Objectives and Parts • Objectives: isolate the body from road shocks and vibrations (ride comfort); keep tyres in contact with the road (road holding, braking and steering control); support the vehicle weight; maintain correct wheel alignment; resist roll, pitch (squat and dive); transmit driving and braking forces. • Main parts: springs (store energy from bumps), dampers (shock absorbers) (dissipate spring energy and stop oscillation), linkages/arms, anti-roll (stabiliser) bar, bushes, ball joints, bump stops. • Sprung mass = parts supported by springs (body, frame, engine); unsprung mass = parts not supported (wheels, tyres, brakes, axles) — low unsprung mass improves ride and road holding.

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Spring type Features Leaf spring (laminated, semi-elliptic) Leaves of graduated length clamped with centre bolt and U-bolts; shackle at one end allows length change; can locate the axle itself; inter-leaf friction gives some damping — trucks, buses, pick-ups Coil spring Stores more energy per unit weight, no friction damping, needs links to locate the axle — cars (independent and rigid) Torsion bar Steel bar twisted by a lever — compact, adjustable ride height Air suspension Rubber air bellows with compressor and levelling valves — constant height at any load; buses, luxury cars, trailers Rubber / hydro-pneumatic / hydrolastic Rubber blocks;

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Citroën hydro-pneumatic spheres (gas + fluid) • Shock absorbers: telescopic hydraulic (twin-tube or mono-tube gas-charged) — oil forced through small valves converts motion energy to heat; damping stronger on rebound than on compression. • Rigid (dependent) axle suspension: both wheels on one beam — strong, simple, constant track and camber (trucks, rear of many vehicles).

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Independent suspension: each wheel moves independently — better ride and handling, lower unsprung mass:

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MacPherson strut (most common front suspension in cars — strut combines spring and damper and acts as king pin), double wishbone (upper and lower A-arms), multi-link, trailing arm, swing axle.

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Semi-independent: twist-beam (torsion-beam) rear axle in FWD cars. • Anti-roll (stabiliser) bar: a torsion bar linking left and right suspensions — resists body roll on corners.

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Suspension trouble Likely cause Vehicle bounces repeatedly after a bump Worn shock absorbers Sagging on one side / low ride height Weak or broken spring Knocking noise over bumps Worn bushes, ball joints, loose U-bolts, worn shock mountings Excessive body roll Broken anti-roll bar or its links, weak springs Uneven tyre wear, pulling Bent arms, worn joints → wrong alignment Steering System • Functions: to turn the front wheels (direction control) with a small effort, provide self-centring (returnability) after a turn, absorb road shocks, give a feel of the road, and give correct rolling of all wheels (no side slip). • Layout: steering wheel → steering column (collapsible for safety) → steering gearbox → drop arm (pitman arm) → drag link → steering arm → stub axle; tie rod connects both steering arms; rack-and-pinion replaces drop arm and drag link. • Ackermann principle: all wheels roll about a common centre on the rear-axle line; the inner wheel turns more than the outer; condition cot φ − cot θ = c/b (φ outer, θ inner, c = distance between king-pin centres, b = wheelbase).

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Davis steering (sliding pairs) satisfies it exactly but wears;

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Ackermann linkage (turning pairs) is used in practice. • Steering ratio = angle turned by steering wheel ÷ angle turned by the road wheels (≈ 12–20 :

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1 cars, higher for trucks).

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Steering gearbox Features Rack and pinion Pinion on the column meshes a rack connected to tie rods — simple, light, precise, direct feel — most cars Recirculating ball Worm and nut with balls circulating between them; nut moves a sector — low friction, robust; trucks, SUVs Worm and sector / worm and roller Older designs; worm drives a sector or roller Cam and lever, worm and nut Older/heavy vehicles • Power steering: reduces driver effort (heavy vehicles, wide tyres, FWD cars).

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Hydraulic power steering (HPS): engine-driven vane pump, rotary control valve (torsion bar), power cylinder on rack; electro-hydraulic (EHPS): electric motor drives pump; electric power steering (EPS): electric motor on column/pinion/rack controlled by torque sensor and ECU — no pump, saves fuel, speed-sensitive assistance, enables lane-keeping and park assist. • Steering troubles: hard steering (low tyre pressure, lack of lubrication, power-steering fault, wrong alignment), excessive free play (worn gear, ball joints, tie-rod ends), wheel shimmy (unbalanced wheels, worn joints, low caster), wandering, pulling to one side (unequal tyre pressure, unequal camber/caster, brake drag).

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Steering Geometry and Wheel Alignment Angle Definition Purpose / typical value Camber Tilt of the wheel from the vertical seen from the front; positive if top leans outward Reduces steering effort, compensates load deflection; ≈ 0° to +1° (negative camber for sports cars — better cornering grip); excess → wear on one shoulder of tyre Caster Tilt of the king-pin (steering axis) from the vertical seen from the side; positive if the top tilts rearward Gives directional stability and self-centring; ≈ +2° to +8°; too much → heavy steering; unequal → pull King-pin (steering-axis) inclination (KPI/SAI) Inward tilt of the king-pin from the vertical seen from the front ≈ 7–13°; reduces scrub radius and steering effort, gives self-centring (vehicle is lifted when wheels are turned) Scrub radius Distance on the ground between the steering-axis line and tyre centre-line Small or negative (with diagonal split brakes) for stability Toe-in / toe-out Front of wheels closer together (toe-in) or farther apart (toe-out) than the rear, seen from above RWD cars ≈ 1–3 mm toe-in (wheels tend to toe-out under rolling resistance);

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FWD often slight toe-out/zero; wrong toe → feather-edge wear Toe-out on turns Inner wheel turns more than outer (Ackermann) True rolling without side slip Included angle Camber + KPI Constant; checks bent stub axles • Wheel alignment is checked and adjusted with optical/laser/3-D computer aligners; toe adjusted by tie-rod length; camber/caster by eccentric bolts, shims or strut top mounts.

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Also thrust angle (rear-wheel alignment) and four-wheel alignment. • Wheel balancing: static (weight evenly distributed about the axis — prevents wheel hop/tramp) and dynamic (no couple about the vertical axis — prevents shimmy/wobble) — corrected with lead/zinc weights on a balancing machine.

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Wheels and Tyres • Wheels: pressed-steel disc wheel (cheap, strong — most common), light-alloy (aluminium/magnesium) cast or forged wheels (light, better heat dissipation from brakes, stylish), wire-spoke wheels (motorcycles, vintage cars).

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Rim types: drop-centre (well-base) rim for tyre fitting in cars; flat-base/multi-piece rims for trucks. • Wheel dimensions: rim diameter (inches), rim width, offset (distance from rim centre-line to mounting face), PCD (pitch-circle diameter of stud holes) and number of studs, centre bore. • Tyre functions: support load, cushion shocks, transmit traction, braking and cornering forces, provide steering response and low rolling resistance. • Tyre construction: tread, sidewall, bead (steel wire), carcass plies, belts, inner liner.

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Cross-ply (bias): plies at ≈ 30–40° crossing each other — stiff sidewall, rough ride, more heat and rolling resistance; still used in some heavy/off-road.

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Radial-ply: plies at 90° (bead to bead) plus steel belts under the tread — flexible sidewall, stable footprint, longer life, better grip, lower rolling resistance and fuel consumption — nearly all cars.

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Tubeless tyres: inner liner seals against the rim — deflate slowly when punctured, run cooler, easy repair. • Tyre properties: cushioning, non-skidding (tread pattern), uniform wear, load-carrying capacity, low rolling resistance, low noise, heat dissipation, balance, puncture resistance.

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Tyre marking example:

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195/65 R15 91H Meaning 195 Section width in mm 65 Aspect ratio = section height ÷ width × 100 (%) R Radial construction (D or '-' = diagonal/bias) 15 Rim diameter in inches 91 Load index (91 = 615 kg per tyre) H Speed rating (H = 210 km/h;

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T = 190, V = 240, W = 270) Other markings DOT date code (week/year, e.g., 2325 = 23rd week of 2025), tread-wear indicator (TWI, 1.6 mm legal minimum in many countries), ply rating, 'Tubeless', max pressure, M+S • Overall diameter = rim diameter × 25.4 + 2 × (width × aspect ratio/100) mm — e.g., 195/65 R15 → 381 + 2 × 126.75 ≈ 634.5 mm. • Tyre pressure effects: under-inflation → both shoulders wear, heavy steering, higher rolling resistance and fuel consumption, overheating, sidewall damage; over-inflation → centre wear, hard ride, less grip, more impact damage.

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Check cold, as recommended on door-pillar placard. • Factors affecting tyre life: inflation pressure, overloading, speed, wheel alignment and balance, driving habits (hard braking, fast cornering), road surface, climate, worn suspension/brakes, tyre mixing. • Tyre rotation every ≈ 8 000–10 000 km for even wear: radial tyres — front-to-rear on the same side (or cross pattern as per maker); include spare in five-wheel rotation where recommended; directional tyres keep the same side. • Changing tyres: loosen nuts on ground, jack at jacking points, tighten nuts in a star (criss-cross) pattern to specified torque, re-check after ≈ 50–100 km; balance new tyres; replace in axle pairs.

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This section covers the objectives of brakes, stopping and braking distance, main parts of brakes, the types of service brakes (mechanical, hydraulic, pneumatic and power-assisted), brake adjustment and bleeding, construction of drums and calipers, shoe and lining materials, and the working of the anti-lock braking system (ABS).

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Objectives and Requirements • Brakes slow down or stop the vehicle in the shortest distance, hold it on a slope (parking brake) and control speed on long descents — by converting kinetic energy into heat through friction (or into electricity in regenerative braking). • Requirements: stop within the minimum distance; equal braking on both wheels of an axle (no pull); correct front/rear distribution; low pedal effort; good anti-fade (heat dissipation); reliability and a second (emergency) system; low wear and easy adjustment.

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Stopping Distance and Braking Distance • Reaction (perception-reaction) time ≈ 0.75–1.5 s — the vehicle travels reaction distance = v·tr before the brakes act. • Braking distance = distance travelled from when brakes are applied to stopping = v²/(2a); at the adhesion limit a = μg → s = v²/(2μg). • Stopping distance = reaction distance + braking distance.

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E.g., 72 km/h (20 m/s), tr = 1 s, μ = 0.8, g = 10 → 20 + 400/16 = 20 + 25 = 45 m. • Braking efficiency = (actual deceleration/g) × 100%.

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Braking distance ∝ v² — doubling speed quadruples braking distance. • Factors: speed, road surface and μ (wet, gravel, ice), tyre condition, brake condition, load, gradient, driver alertness.

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Main Parts and Classification • Main parts: brake pedal, master cylinder (or brake valve), lines, wheel cylinders/calipers, drums/discs, shoes/pads with linings, return springs, adjuster, parking-brake lever and cables, booster. • Classification: by purpose — service (foot) brake and parking (hand) brake, emergency brake, retarders; by construction — drum and disc; by actuation — mechanical, hydraulic, pneumatic (air), vacuum/power-assisted, electric; by location — wheel brakes, transmission brakes.

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Actuation type Working Use / features Mechanical Rods, levers and cables operate cams or levers to expand the shoes Parking brakes, old/small vehicles, motorcycles; hard to equalise, low efficiency Hydraulic Pedal pushes a piston in the master cylinder; pressure transmitted equally (Pascal's law) through lines to wheel cylinders/caliper pistons; force multiplied by area ratio Cars, light vehicles — equal braking, smooth, efficient; tandem (dual-circuit) master cylinder for safety (front/rear or diagonal split) Pneumatic (air) Engine-driven compressor → reservoir (≈ 7–8 bar) → brake valve (treadle) → brake chambers → push rods rotate S-cams to expand shoes Heavy trucks, buses, trailers — very high force, trailer connection; air leaks do not stop the system instantly; spring brakes apply automatically on air loss (parking/emergency) Power-assisted (servo) Vacuum booster (servo) uses manifold (or vacuum-pump) vacuum on one side and atmosphere on the other side of a diaphragm to add force to the master cylinder push rod; air-over-hydraulic systems for medium vehicles Cars, light trucks — low pedal effort Exhaust brake / retarders Exhaust valve closes to create back pressure; hydraulic or electromagnetic retarders Heavy vehicles on long mountain descents (reduce fade) Drum and Disc Brakes • Drum brake: cast-iron drum rotates with the wheel; two shoes with linings on a back plate are expanded by a wheel cylinder (or S-cam).

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Leading shoe (self-energising — drum rotation helps apply it) and trailing shoe; two-leading-shoe and duo-servo designs increase braking.

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Merits: self-energising, cheap, good parking brake, protected from dirt.

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Demerits: poor heat dissipation → brake fade, water fade, needs adjustment. • Disc brake: cast-iron disc (rotor, often ventilated) rotates with the wheel; a caliper with pistons squeezes friction pads on both sides.

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Fixed caliper (pistons on both sides) or floating/sliding caliper (piston on one side; caliper slides on pins).

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Merits: better cooling, resistant to fade, self-cleaning (water thrown off), self-adjusting (piston seal retraction), easy pad inspection.

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Demerits: not self-energising (needs higher pressure/booster), parking brake more complex. • Common arrangement: disc brakes at front (front carries more load during braking due to weight transfer), drum or disc at rear. • Brake drum materials: grey cast iron (good wear resistance, heat capacity, damping); discs: grey cast iron, carbon-ceramic in high-performance cars.

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Brake Shoe and Lining Materials • Requirements: high and stable coefficient of friction (μ ≈ 0.3–0.45) over temperature range, wear resistance, heat resistance and conductivity, not affected by water/oil much, low noise, no damage to drum/disc. • Types: asbestos-based (now banned — health hazard, asbestosis), non-asbestos organic (NAO) — fibres (glass, aramid/Kevlar), resins, fillers; semi-metallic (steel fibres — good heat resistance, noisier); low-metallic; ceramic pads (quiet, low dust); sintered metal (heavy-duty, racing).

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Linings are bonded or riveted to steel shoes/backing plates.

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Brake Adjustment and Bleeding • Adjustment: drum brakes need periodic adjustment of shoe-to-drum clearance as linings wear (star-wheel/screw adjusters, automatic self-adjusters; slack adjusters on air-brake S-cams); pedal free play and parking-brake cable adjustment.

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Disc brakes are self-adjusting. • Bleeding: removing air from the hydraulic system (air is compressible → spongy pedal).

18

Procedure: fill reservoir with recommended fluid (DOT 3/4/5.1); start from the wheel farthest from the master cylinder and work towards the nearest (or follow the maker's sequence for dual-circuit/ABS systems); attach tube from bleed screw into a jar of fluid; pump pedal and hold, open screw, close before releasing pedal; repeat until no bubbles; keep reservoir topped up.

19

Pressure bleeders and ABS scan-tool routines are also used. • Brake fluid is hygroscopic (absorbs water, lowering boiling point → vapour lock); replace every ≈ 2 years; never use mineral oil in glycol systems (swells rubber seals).

20

Brake trouble Likely cause Spongy pedal Air in lines, low fluid Pedal goes to floor / sinks Fluid leak, worn master-cylinder cups Vehicle pulls to one side Unequal adjustment, oil on lining, seized caliper, unequal tyre pressure Brake fade (less effect after repeated use) Overheating of linings/drums (long descents), wrong lining material, boiling fluid Squeal / grinding Worn pads (wear indicator), glazed linings, scored disc Brakes drag / binding No pedal free play, seized piston, weak return springs, blocked compensating port Hard pedal Faulty vacuum booster or vacuum hose Anti-lock Braking System (ABS) • Purpose: prevent wheels from locking during hard braking so that the driver keeps steering control and directional stability, and the stopping distance is usually shortened (maximum friction occurs at ≈ 10–30% wheel slip, not at 100% lock — a locked wheel has only sliding friction and no lateral grip). • Components: wheel-speed sensors (inductive or Hall/active) with toothed tone rings at each wheel;

21

ABS ECU; hydraulic modulator with inlet and outlet solenoid valves for each channel, return pump and accumulator; warning lamp. • Working: the ECU compares each wheel's speed and deceleration with vehicle reference speed; if a wheel is about to lock (slip too high), it goes through pressure hold → pressure release (dump) → pressure re-apply cycles, about 10–15 times per second (driver feels pedal pulsation).

22

4-channel/4-sensor (best), 3-channel, 1-channel (rear-only). • Related systems built on ABS hardware:

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EBD (electronic brake-force distribution), TCS (traction control — brakes spinning wheel/cuts torque), ESC/ESP (electronic stability control — brakes individual wheels to correct over/understeer), brake assist, hill-hold.

1

This section covers the vehicle lighting and wiring system, the starting system, the charging system, electrical and electronic instruments, and modern accessories related to safety and anti-theft.

2

Wiring System • Most vehicles use a 12 V system (24 V for heavy trucks and buses;

3

48 V mild hybrids; high-voltage 300–800 V in EVs).

4

Single-wire (earth-return) system: the vehicle body/frame acts as the return conductor — negative earth is standard. • Wiring harness: colour-coded copper cables (PVC insulated) grouped and taped/sleeved; cable size chosen for current and voltage drop; connectors, terminals and grommets. • Circuit protection: fuses (blade type, rated in A — melt on overload/short), fusible links, circuit breakers; relays let a small switch current control a large load current (headlamps, horn, starter, fans). • Wiring diagrams use standard symbols; faults: open circuit, short circuit (to earth), high resistance (corroded connections, poor earth) — found with test lamp, multimeter (voltage drop test).

5

Lighting System Lamp Function / notes Headlamps High beam (main) and low (dipped) beam; types: sealed-beam, halogen (tungsten filament in halogen gas — H4 twin-filament), HID/xenon (arc discharge, needs ballast, ≈ 25 kV ignition), LED and matrix/adaptive LED, laser.

6

Headlamp aiming must be checked Side/parking and tail lamps Show vehicle width and presence Stop (brake) lamps Operated by brake-pedal switch; high-mounted stop lamp Direction indicators and hazard lamps Flasher unit (thermal or electronic) ≈ 60–120 flashes/min Reverse, fog, number-plate, interior, instrument lamps Reversing and fog lamps, courtesy lamps with door switches Starting System • Components: battery, ignition/start switch, starter relay / solenoid, starter motor, heavy battery cables, and (in automatics) a neutral safety switch; clutch switch in manuals. • Starter motor: a DC series-wound motor (or permanent-magnet with gear reduction) because it gives very high starting torque at low speed; draws ≈ 100–300 A (petrol) and more for diesels.

7

Cranking speed ≈ 100–200 rpm (petrol), higher for diesel. • Starter drives:

8

Bendix (inertia) drive — pinion moves along a helical sleeve into mesh with the flywheel ring gear by inertia and is thrown out when the engine starts; pre-engaged (solenoid-shift) drive — the solenoid first pushes the pinion into mesh via a shift lever and then closes the main contacts; an overrunning (roller) clutch prevents the engine from driving the motor at high speed — used in all modern vehicles; gear-reduction starters.

9

Pinion : ring gear ratio ≈ 1 :

10

20. • Starting troubles: no cranking (flat battery, loose/corroded terminals, faulty solenoid, open circuit), slow cranking (weak battery, high resistance cables, thick oil, worn bushes), clicking only (low battery voltage, solenoid contacts), starter spins but engine does not turn (drive/overrunning clutch failure), grinding noise (worn pinion/ring gear).

11

Charging System • Purpose: recharge the battery and supply the electrical loads when the engine runs.

12

Components: alternator, voltage regulator, battery, charge warning lamp, drive belt. • Alternator (AC generator): the rotor (field winding on claw poles, fed through slip rings and brushes) rotates inside a three-phase stator winding;

13

AC output is converted to DC by a rectifier bridge of 6 (or more) diodes; diodes also prevent battery discharge through the alternator when the engine is off (no cut-out needed). • Alternator advantages over the older DC dynamo: charges even at idle (higher pulley ratio), lighter and smaller for the same output, higher output, brushes carry only small field current, no commutator, less maintenance. • Voltage regulator (electronic, usually built in): controls field current to keep output ≈ 13.8–14.4 V regardless of speed and load (temperature compensated); modern ECUs control 'smart charging'.

14

Alternator is self-limiting in current. • Charging troubles: warning lamp on (broken belt, faulty diode/regulator, open field), overcharging (faulty regulator — battery gassing, bulbs blowing), undercharging (slipping belt, worn brushes, faulty diode, high-resistance connections), noisy alternator (bearings, shorted diode whine).

15

Electrical and Electronic Instruments • Speedometer and odometer (earlier cable-driven magnetic/eddy-current type; now electronic from vehicle-speed sensor/ABS via CAN), tachometer (engine rpm), fuel gauge (float and variable resistor sender + thermal/magnetic gauge), temperature gauge (NTC thermistor sender), oil-pressure warning lamp (pressure switch), charge (battery) warning lamp, ammeter/voltmeter. • Modern digital instrument clusters (LCD/TFT displays), trip computer (fuel economy, range), warning lamps (MIL, ABS, airbag, seat-belt, TPMS), head-up display (HUD), multi-information displays; a voltage stabiliser is used for bimetal-type gauges.

16

Safety and Anti-theft Accessories Accessory Function Airbags (SRS) Crash sensors/accelerometer → airbag control unit → igniter/inflator fills bag with nitrogen gas in ≈ 30–50 ms; front, side, curtain and knee airbags; clock spring in steering column; works with seat belts Seat belts with pretensioner and load limiter Pretensioner tightens belt at crash; load limiter reduces chest force; seat-belt reminder ADAS Reversing camera and parking sensors (ultrasonic), blind-spot monitor, lane-departure warning/keeping, adaptive cruise control (radar), automatic emergency braking, driver-drowsiness alert TPMS Tyre-pressure monitoring — direct (sensor in each wheel) or indirect (via ABS wheel speeds) Wipers, washers, horns, defoggers, power windows, central locking Convenience and visibility; rain and light sensors Engine immobiliser Transponder chip in the key;

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ECM allows fuel/ignition only if the code matches — main anti-theft device Alarm systems and central locking Door, bonnet, tilt and ultrasonic intrusion sensors, siren; remote keyless entry (RKE), passive keyless entry and push-button start GPS tracking / telematics Locates stolen vehicles, remote immobilisation, eCall

1

This section covers the forces acting on a vehicle, tyre forces and moments, traction characteristics, vehicle aerodynamics, dynamic characteristics (handling), braking dynamics and stability, and suspension dynamics (ride).

2

Forces Acting on a Vehicle • Vehicle axes (SAE): x longitudinal (forward) — motion surge, rotation roll; y lateral — sway, rotation pitch; z vertical — bounce/heave, rotation yaw. • Forces: weight (through CG), normal reactions at tyres, tractive or braking forces, rolling resistance, aerodynamic drag, lift and side force, gradient resistance, inertia force during acceleration, centrifugal force on curves, side wind.

3

Resistance Formula Notes Rolling resistance Rr = fr·W fr ≈ 0.01–0.015 (car tyres on asphalt), higher on gravel/soft soil or under-inflation; due to tyre hysteresis Air (aerodynamic) resistance Ra = ½ρCDAV² Dominant at high speed; power ∝ V³ Gradient resistance Rg = W sin θ ≈ W × (G%/100) Large on hill roads Inertia (acceleration) resistance Ri = (m + mr)·a mr = equivalent mass of rotating parts (larger in low gears) • Total tractive resistance R = Rr + Ra + Rg (+ Ri).

4

Power required = R·V/ηt. • Tractive effort available at driving wheels:

5

Excess of Ft over R is available for acceleration (a = (Ft − R)/meff) and climbing; gradeability is the maximum slope climbable in a given gear. • Road speed V = 2πr·Ne/(60·ig·io) m/s.

6

Tyre Forces and Moments • Tyre forces: longitudinal force Fx (traction/braking), lateral (cornering) force Fy, normal force Fz.

7

Moments: overturning moment (about x), rolling-resistance moment (about y), self-aligning (aligning) torque (about z — tends to straighten the wheel; due to pneumatic trail). • Longitudinal slip s = (ωr − V)/V (traction) or (V − ωr)/V (braking).

8

Force rises almost linearly with slip, peaks at ≈ 10–20% slip (peak μ), then falls towards the sliding value at 100% slip (locked or spinning wheel). • Slip angle α: angle between the wheel plane and its direction of travel; cornering force Fy ≈ Cα·α at small angles (Cα = cornering stiffness); saturates at large slip angles.

9

Cornering stiffness increases with load (less than proportionally), lower aspect ratio and correct inflation. • Camber thrust: lateral force from wheel camber (important for motorcycles). • Friction circle (ellipse): the resultant of longitudinal and lateral forces cannot exceed μFz — heavy braking while cornering reduces lateral grip.

10

Traction Characteristics • Adhesion limit: maximum tractive force = μ × normal load on driving wheels (μ ≈ 0.7–0.9 dry asphalt, 0.4–0.6 wet, 0.1–0.2 ice).

11

Beyond this the wheels spin. • Load on axles during acceleration on level road: rear axle load increases by ΔW = m·a·h/L (h = CG height, L = wheelbase) — so rear-wheel drive gives better traction during acceleration and climbing; on gradients the load also shifts to the rear axle. • Traction diagram (performance chart): tractive effort in each gear vs road speed superimposed on the resistance curve — intersection gives maximum speed; vertical gap gives acceleration/gradeability reserve.

12

Ideal tractive-effort curve is a hyperbola (constant power) — gear ratios are chosen to approximate it (usually a geometric progression). • Maximum tractive effort (RWD, level):

13

Fmax = μ W af/(L − μh) where af = distance of CG from front axle;

14

(FWD) Fmax = μ W b/(L + μh) with b = CG distance from rear axle.

15

Aerodynamics of the Vehicle • Drag force FD = ½ρCDAV²; drag power = FDV ∝ V³.

16

Components: form (pressure) drag ≈ 55–65% — due to flow separation at the rear; interference drag (mirrors, wheels), internal (cooling) flow drag, skin friction, induced drag. • Typical CD: modern car ≈ 0.25–0.35;

17

SUV ≈ 0.35–0.45; bus/truck ≈ 0.6–0.9; best production EVs ≈ 0.20–0.23. • Aerodynamic lift reduces tyre load and stability at high speed; spoilers, air dams and diffusers reduce lift (or create downforce in racing cars).

18

Side-wind force and yaw moment affect directional stability — high-sided buses and trucks are sensitive to side winds. • Drag reduction: rounded front, raked windscreen, tapered rear (Kamm tail), smooth underbody, flush glass and handles, wheel covers, cab deflectors on trucks, controlled cooling-air flow.

19

Dynamic (Handling) Characteristics • Understeer: the front slip angles exceed the rear — vehicle turns less than intended (runs wide); driver must steer more; stable — preferred for ordinary cars (FWD cars tend to understeer).

20

Oversteer: rear slip angles exceed front — vehicle turns more than intended (tail slides out); can become unstable above a critical speed.

21

Neutral steer: equal slip angles. • Understeer gradient K = Wf/Cαf − Wr/Cαr;

22

K > 0 understeer, K < 0 oversteer, K = 0 neutral.

23

Steady-state steer angle δ = L/R + K·V²/(gR). • Factors: weight distribution, tyre pressures and sizes, roll stiffness distribution (stiffer front anti-roll bar → more understeer), suspension geometry, drive type. • Cornering: centripetal force mv²/R must be provided by tyre lateral forces.

24

Skidding limit v = √(μgR); overturning limit v = √(gRt/(2h)) (t = track, h = CG height) — a vehicle should skid before it overturns, so t/(2h) > μ is desirable (low CG, wide track).

25

On banked roads tan θ = v²/(gR) for no side friction. • Load transfer in cornering: outer wheels gain load ΔW = mv²h/(Rt).

26

Braking Dynamics and Stability • During braking, load transfers to the front: ΔW = m·a·h/L.

27

Front axle load Wf' = Wf + ΔW, rear Wr' = Wr − ΔW. • Ideal brake-force distribution is proportional to the dynamic axle loads — so front brakes are larger (≈ 60–80% of braking).

28

Proportioning valves, load-sensing valves and EBD reduce rear pressure to avoid rear lock. • Wheel-lock consequences: front wheels locked → loss of steering (vehicle goes straight, but stable); rear wheels locked → vehicle becomes directionally unstable and may spin (yaw) — most dangerous;

29

ABS prevents both. • Maximum deceleration with all wheels at the adhesion limit a = μg; braking efficiency and stopping distance as in 8.4. • Stability on gradient and braking on curves: combined braking and cornering limited by the friction circle;

30

ESC brakes individual wheels to create correcting yaw moments.

31

Suspension Dynamics (Ride) • Quarter-car model: sprung mass ms on suspension spring ks and damper cs, unsprung mass mu on tyre stiffness kt — two natural frequencies. • Body (sprung-mass) natural frequency f = (1/2π)√(k/m) ≈ 1–1.5 Hz for good ride comfort (human body is sensitive to ≈ 4–8 Hz vertical vibration); wheel-hop (unsprung) frequency ≈ 10–15 Hz. • Static deflection δ = mg/k gives f ≈ 0.5/√δ (δ in m) — soft springs (large deflection) give low frequency and good ride, but more roll and pitch. • Damping ratio ζ ≈ 0.2–0.4 for passenger cars (compromise between ride comfort and road holding); over-damped → harsh; under-damped → floaty, poor control. • Pitch and bounce: front and rear frequencies should be close, with the front slightly lower (Olley's criteria) so the car bounces rather than pitches.

32

Roll: controlled by spring stiffness, anti-roll bars and roll-centre height. • Active and semi-active suspensions (adaptive dampers, magnetorheological dampers, air suspension) adjust characteristics in real time.