Automotive Systems: Suspension, Ignition, Batteries & Drivetrain

Posted on Jan 27, 2026 in Mechanical Engineering

Telescopic Shock Absorber

Construction

Cylinder (Outer Tube)

Main body filled with oil. Houses the piston rod and piston.

Piston Rod (Inner Tube)

Moves up and down inside the cylinder. Connected to the vehicle frame.

Piston

Has small orifices and valves for oil flow. Controls damping force.

Oil Reservoir

Space containing hydraulic oil. Provides resistance to piston movement.

Spring

Coil spring mounted around the shock absorber. Supports vehicle load and absorbs shocks.

Base Valve

Located at the bottom of the cylinder. Controls oil flow during compression.

Dust Cover and Seal

Prevents dirt entry and protects the rod surface.

Working of Telescopic Shock Absorber

Compression Stroke (Wheel Moves Up)

Piston moves downward. Oil flows through piston orifices and the base valve. Resistance to oil flow creates damping force and the shock is absorbed.

Rebound Stroke (Wheel Moves Down)

Piston moves upward. Oil flows back through rebound valves and orifices, controlling the return movement of the spring and preventing vehicle oscillation.

Damping Action

Oil flow through small openings creates hydraulic resistance. Kinetic energy of vibration is converted into heat, reducing vibration amplitude.

Battery Ignition System

Primary Circuit (Low Voltage)

When the ignition switch is ON, current flows from the battery to the ignition coil primary winding, then to the contact breaker and to ground. The coil stores magnetic energy in its soft iron core.

Contact Breaker Operation

The cam on the distributor shaft rotates with the engine. When the cam opens the contact breaker points, the primary circuit is suddenly broken, causing the magnetic field in the ignition coil to collapse.

Role of Condenser

The condenser absorbs the voltage surge produced during opening of the contact breaker, preventing sparking at the breaker points and ensuring rapid collapse of the magnetic field to help produce a stronger spark.

Secondary Circuit (High Voltage)

Rapid collapse of the magnetic field induces very high voltage (20,000–30,000 V) in the secondary winding of the ignition coil. This high voltage is supplied to the distributor rotor.

Distributor Function

The distributor rotor sends the high voltage to the correct spark plug according to the firing order.

Spark Plug

High voltage jumps across the spark plug gap and produces a strong spark, which ignites the air–fuel mixture in the engine cylinder.

Electronic Ignition System

Engine Position Sensing

A sensor mounted on the camshaft or crankshaft detects engine position and speed. It sends electrical signals (pulses) to the ECU or ignition module. These sensors replace mechanical contact breaker points.

Signal Processing by ECU

The ECU receives sensor signals and decides when to switch the primary current on and when to cut it off for exact ignition timing. The ECU uses engine load, speed, temperature and throttle position in advanced systems.

Primary Circuit Control (Transistor Switching)

The ECU uses a power transistor as an electronic switch. When the transistor is ON, the primary coil gets current and builds a magnetic field. When the ECU turns the transistor OFF, the magnetic field collapses rapidly.

High Voltage Induction in Secondary Coil

Rapid collapse of the magnetic field induces high voltage (up to 40,000 V) in the secondary winding of the ignition coil.

Distribution of High Voltage

In older electronic systems, high voltage goes to the distributor, then to spark plugs. In modern distributor-less ignition systems and coil-on-plug designs, each spark plug has its own coil and no distributor is needed.

Spark Plug Operation

High voltage jumps across the spark plug gap producing a strong and reliable spark even at high engine speeds.

Lead Acid Battery — Construction and Working

Construction

Container

Made of hard rubber or plastic. Acid-resistant and leak-proof.

Plates

Positive plates: lead peroxide (PbO2) coated on a grid.

Separators

Porous insulating materials (PVC, wood, fiber) placed between positive and negative plates to prevent short circuits.

Electrolyte

Dilute sulfuric acid (H2SO4) mixed with water.

Cell Cover and Vent Plug

Each cell has a cover with a vent plug for releasing gases (H2, O2) during charging.

Cell Connectors

Lead connectors join multiple cells in series. Each cell gives about 2.1 V, so a 12 V battery has six cells.

Terminals

Positive terminal (+) and negative terminal (−).

Working

Discharging (Supplying Current)

When the battery supplies electricity: the positive plate (PbO2) reacts with sulfuric acid and the negative plate (Pb) also reacts with sulfuric acid. Both plates convert to lead sulfate (PbSO4). Water is formed, so acid concentration reduces and specific gravity drops. Voltage per cell decreases from about 2.1 V to ~1.8 V.

Chemical reactions during discharge:
PbO2 + SO4²− + 4H⁺ + 2e⁻ → PbSO4 + 2H2O
Pb + SO4²− → PbSO4 + 2e⁻

Charging (Using an External DC Supply)

When connected to a charger, external current reverses the chemical reactions. Lead sulfate on both plates converts back to:
Positive: PbO2
Negative: Pb
Water breaks down and sulfuric acid concentration increases. Specific gravity rises back to about 1.26–1.28 and voltage per cell increases to 2.2–2.4 V.

Indications of full charge: gassing or bubbling, constant voltage, and stable specific gravity.

Functions of Tyres

• Support Vehicle Load
  • Tyres carry the entire weight of the vehicle along with passengers and cargo.
• Provide Cushioning and Shock Absorption
  • Tyres absorb road shocks and vibrations for a smooth, comfortable ride.
• Transmit Driving and Braking Forces
  • Tyres transfer engine power to the road (tractive effort) and transmit braking forces to stop the vehicle.
• Provide Steering Control
  • Front tyres help change direction and ensure accurate steering response.
• Maintain Road Grip and Traction
  • Tyres provide necessary friction to prevent slipping during acceleration, braking, and cornering.
• Reduce Road Noise and Vibrations
  • Tyres dampen vibration and sound, improving ride comfort.
• Provide Stability and Handling
  • Tyres ensure vehicle stability during turns, at high speeds, and on uneven roads.
• Protect Wheel Rim
  • The tyre forms a protective layer around the rim and prevents damage from impacts.
• Maintain Fuel Efficiency
  • Properly inflated tyres reduce rolling resistance, improving fuel economy.
• Ensure Safety
  • Good-quality tyres prevent skidding, hydroplaning, and improve overall driving safety.

AWD vs 4WD Comparison

Tubed Tyre vs Tubeless Tyre

Differential

A differential is a mechanical device used in the drivetrain of vehicles to allow the left and right wheels to rotate at different speeds, especially while turning.

Significance

1. Allows wheels to rotate at different speeds
   • During a turn, the outer wheel travels a longer path than the inner wheel.
   • The differential allows the speed difference between wheels to avoid skidding.
2. Improves handling and stability
   • Smooth turning without tyre wear or hopping.
3. Prevents tyre wear
   • If wheels were forced to rotate at the same speed, tyres would drag and wear quickly.
4. Efficient power transmission
   • Even while wheels rotate at different speeds, power from the engine is transmitted effectively.
5. Ensures safety during cornering
   • Prevents loss of control due to wheel slip.

Construction of Differential

A typical final drive differential consists of:

1. Bevel pinion gear
   • Driven by the propeller shaft.
2. Crown wheel (ring gear)
   • Meshed with the pinion; rotates the differential case.
3. Differential case / cage
   • Holds the spider gears and side gears.
4. Spider gears (2 or 4)
   • Small bevel gears mounted on a cross shaft in the differential case.
5. Side gears (sun gears)
   • Connected to the left and right axle shafts.
6. Axle shafts
   • Transmit power to the wheels.

Working of Differential

Vehicle Moving Straight

Both wheels travel the same distance. The pinion gear drives the crown wheel which rotates the differential case. Spider gears do not rotate on their axis; they move as a unit. Both side gears rotate at equal speed, transmitting equal torque.

Vehicle Taking a Turn

The inner and outer wheels must rotate at different speeds. The differential case rotates due to driving force from the pinion. Spider gears rotate on their own axis and rotate the side gears at different speeds: the outer wheel rotates faster and the inner wheel rotates slower.

How speed difference is achieved:
Speed of left wheel = Case speed + spider gear rotation.
Speed of right wheel = Case speed − spider gear rotation.

Thus, both wheels get the required speed difference automatically.

V2V vs V2I Communication

Oversteering vs Understeering

Constant Mesh Gearbox — Construction and Working

A constant mesh gearbox is a type of manual transmission where all gears are constantly meshed with mating gears on the countershaft. Only the dog clutches are engaged to select the desired gear. Used in motorcycles, light vehicles, older cars and tractors.

Construction

Main Shaft

Carries gears that rotate freely on the shaft.

Counter Shaft (Layshaft)

Parallel to the main shaft; carries gears that are fixed to it.

Gears

All gears on the main shaft are in constant mesh with corresponding gears on the layshaft. Spur or helical gears are used for smooth operation.

Dog Clutches (Dog Collars)

Sliding collars with dog teeth engage freely rotating gears to the main shaft for power transmission.

Gear Selector Forks and Lever

Move the dog clutches sideways to engage the required gear.

Clutch Shaft / Input Shaft

Driven by the engine through the vehicle clutch.

Working

All gear pairs (1st, 2nd, 3rd, 4th, reverse) are always in mesh. Only dog clutches slide to connect the required gear to the main shaft.

Neutral Position

Dog clutches are not engaged with any gear. Main shaft rotates freely and no power is transmitted to the output.

Engaging 1st Gear (Low Speed — High Torque)

1. Engine drives the clutch shaft so gears on the layshaft rotate.
2. 1st gear pair is already in mesh.
3. Operator moves the gear lever and the selector fork slides the dog clutch.
4. Dog clutch locks the 1st gear to the main shaft.
5. Power flows: Clutch shaft → layshaft → 1st gear pair → main shaft → wheels.

Engaging 2nd and 3rd Gears

Similar to 1st gear. Corresponding dog clutch slides and connects 2nd or 3rd gear to the main shaft. Gear ratio changes, giving higher speed and less torque.

Engaging Top Gear (Direct Drive)

Often a 1:1 ratio (input and output rotate at the same speed). The dog clutch locks the main shaft directly to the input/clutch shaft to give maximum speed and minimum power loss.

Reverse Gear

Uses an idler gear between the layshaft and main shaft gear to reverse the direction of rotation. Dog clutch engages reverse gear to the main shaft.

Advantages

Strong, reliable and durable. Less gear wear since gears are always meshed. Less noise than a sliding mesh gearbox.

Disadvantages

Dog clutch operation requires skill. Slightly noisier compared to a synchromesh gearbox and not suitable for high-speed modern cars.

Disc Brake vs Drum Brake

Synchromesh Gearbox — Construction and Working

A synchromesh gearbox is an improved form of the constant-mesh gearbox where synchronizers are used to match gear speeds before engagement. This allows smooth gear shifting without noise or grinding and is used in all modern cars.

Construction

Main Shaft

Carries gears that rotate freely until they are locked by synchronizers.

Counter Shaft (Layshaft)

Runs parallel to the main shaft. All gears on the layshaft are fixed to it.

Gears (Constant Mesh)

All gears on the main shaft are always meshed with the corresponding gears on the layshaft.

Synchronizer Unit

The key component of a synchromesh gearbox. A synchronizer has a hub fixed to the main shaft, a sleeve/sliding collar that slides over the hub, a baulk ring (blocking ring) which is a cone-shaped ring that matches gear speeds, and cones on gears which act as frictional surfaces for speed matching.

Selector Fork and Gear Lever

Move the synchronizer sleeve to engage the required gear.

Working

Initial Position (Neutral)

Gears rotate freely and the synchronizer sleeve is not engaged with any gear. No power flows to the output.

Selecting a Gear (Synchronizing Action)

1. Selector fork pushes the synchronizer sleeve toward the desired gear.
2. The baulk ring contacts the cone clutch surface on the gear.
3. Friction makes the gear and synchronizer rotate at the same speed.
4. This eliminates speed difference and prevents gear teeth clash.

Overdrive Gearbox

An overdrive is a supplementary gearbox fitted between the main gearbox and the propeller shaft. It provides a gear ratio greater than 1:1, meaning the output shaft rotates faster than the input shaft. Used in cars, jeeps and light commercial vehicles for better fuel economy and quiet high-speed cruising.

Construction

Sun Gear

Mounted on the input shaft from the main gearbox.

Planet Carrier

Holds several planet gears and drives the output shaft connected to the propeller shaft.

Planet Gears

Small gears that rotate around the sun gear.

Ring Gear (Internal Gear)

Encircles the planet gears and can be locked or released by a clutch or brake.

Overrunning Clutch / One-way Clutch

Allows automatic disengagement when required and prevents shock loads.

Overdrive Clutch / Solenoid

Used to engage and disengage overdrive, operated manually or automatically by a controller.

Lubrication Pump

Ensures oil flow for smooth functioning.

Working

Normal Drive (Overdrive OFF)

Overdrive clutch remains disengaged. Sun gear, planet carrier and ring gear rotate as a single unit. Gear ratio is 1:1 and output speed equals input speed; used for city or low-speed driving.

Overdrive Mode (Overdrive ON)

Driver switches ON overdrive (or ECU activates it). Solenoid pushes the overdrive clutch to lock the sun gear. The ring gear is driven by the input shaft, planet gears rotate around the stationary sun gear, and the planet carrier (connected to the output shaft) rotates faster than the input.

Automatic Disengagement

The overrunning clutch automatically disengages overdrive during sudden acceleration, hill climbing or low speed to prevent damage and provide normal torque.

Lithium-Ion Battery — Construction and Working

Lithium-ion (Li-ion) batteries are rechargeable batteries widely used in mobile phones, laptops, electric vehicles, drones and modern energy storage systems. They offer high energy density, low weight and long life.

Construction

Anode (Negative Electrode)

Usually made of graphite. Stores lithium ions during charging. Coated on a copper foil.

Cathode (Positive Electrode)

Made of lithium metal oxide such as LiCoO2, LiFePO4 or NMC (LiNiMnCoO2). Coated on an aluminum foil.

Electrolyte

A lithium salt (usually LiPF6) dissolved in organic solvents that allows movement of Li+ ions between the electrodes.

Separator

A thin porous plastic membrane that prevents physical contact between anode and cathode while allowing Li+ ions to pass.

Current Collectors

Copper foil for the anode and aluminum foil for the cathode. They carry electrons to the external circuit.

Battery Case / Pouch

Protects the cell and includes a safety vent and thermal protection.

Working

Discharging (Supplying Power)

When the battery is in use, lithium ions (Li+) move from the anode to the cathode through the electrolyte. Electrons (e−) flow from the anode through the external circuit to the cathode, powering the device.

Charging (Using External Power)

When plugged in, the external charger forces electrons from cathode to anode. Lithium ions move through the electrolyte from cathode to anode and get stored in the graphite layers of the anode.

Semi-Floating Axle — Construction and Working

A semi-floating axle is a rear axle type used mainly in light commercial vehicles, cars and SUVs. It supports both vehicle load and driving torque and is therefore called semi-floating.

Construction

Axle Shaft

The axle shaft itself carries part of the vehicle weight and transmits driving torque. The outer end of the axle is directly connected to the wheel hub.

Wheel Hub

Fitted on the outer end of the axle. The wheel bolts directly to the hub.

Bearing (Single Bearing Type)

A single ball or roller bearing is fitted between the axle shaft and the axle casing at the outer end. It supports the shaft and allows smooth rotation.

Axle Casing / Housing

Rigid housing that supports the bearing and holds lubrication. It is attached to the vehicle frame.

Retaining Plate / Collar

Bolts the axle shaft and bearing assembly firmly to the axle housing.

Differential Side Gear Connection

The inner end of the axle shaft is splined and fits into the side gear of the differential.

Working

Transmission of Torque

Power from the differential is transmitted through the side gear to the axle shaft, wheel hub and wheels. The axle shaft rotates along with the wheel.

Support of Vehicle Load

The axle shaft carries part of the vehicle’s weight while the bearing supports the rest. Because the shaft supports both weight and torque, it must be thicker than full-floating axle shafts.

Wheel Mounting

The wheel is directly bolted to the hub on the axle shaft, making the axle semi-floating because the shaft also acts as a support member.

Bearing Action

The single bearing helps the axle shaft rotate smoothly inside the axle housing and absorbs radial loads from the wheel.

Aerodynamic Drag

Aerodynamic drag is the resistive force acting opposite to the direction of motion of a body moving through air.

Cause

Drag occurs due to air friction on the body surface (skin friction drag), difference in pressure at the front and rear (pressure drag), and the shape of the body (form drag).

Effect

Drag reduces vehicle speed, increases fuel consumption and requires more engine power to overcome resistance.

Formula

D = 1/2 ρ V² A Cd where ρ = air density, V = speed, A = frontal area, Cd = drag coefficient.

Aerodynamic Lift

Lift is the vertical aerodynamic force acting on a moving vehicle due to pressure differences between the top and bottom surfaces.

Cause

If air pressure on the top surface is lower than on the bottom → positive lift (vehicle becomes lighter). If pressure on top is higher → negative lift or downforce.

Effect in Vehicles

Positive lift reduces tyre grip and is unsafe at high speeds. Negative lift (downforce) improves stability, cornering and braking. Sports cars use spoilers, diffusers and wings to generate downforce.

Pitching Moment

Pitching moment is the aerodynamic torque causing the vehicle to rotate about its lateral axis, resulting in nose-up or nose-down movement.

Cause

Uneven distribution of aerodynamic forces (drag and lift). Airflow differences over the front and rear parts of the vehicle cause pitching moments.

Effects

Nose-up moment at high speed reduces front wheel grip and can make the vehicle unstable. Nose-down moment improves front traction but may reduce rear stability.

Example

If more lift acts on the rear side, the nose dips down (negative pitch). If more lift acts on the front, the nose rises (positive pitch).

Double Wishbone Suspension System

A double wishbone suspension (also called double A-arm suspension) is an independent suspension system commonly used in cars, SUVs and performance vehicles. It provides excellent wheel control, good handling and better stability compared to simpler suspension systems.

Construction

It consists of two A-shaped arms.

Upper Control Arm (Upper Wishbone)

A-shaped arm mounted to the vehicle frame/body. Connected to the top of the steering knuckle using a ball joint.

Lower Control Arm (Lower Wishbone)

Larger A-shaped arm mounted to the chassis. Supports heavier loads and is connected to the bottom of the steering knuckle using a ball joint.

Steering Knuckle / Upright

Holds the wheel hub and brake assembly. Connected to upper and lower wishbones by ball joints.

Shock Absorber and Coil Spring

Usually mounted on the lower control arm. Can also be attached between the upper arm and chassis in some designs.

Bushings

Rubber or polyurethane bushings used at arm pivots for smooth movement and noise reduction.

Ball Joints

Provide rotational and angular movement and allow the wheel to steer and move vertically.

Stabilizer (Anti-roll) Bar

Connects left and right sides to reduce body roll during cornering.

Working

Vertical Wheel Movement

When the wheel hits a bump, both wishbones move up and down independently. The shock absorber and coil spring compress to absorb the shock.

Controlled Wheel Alignment

Wishbones keep the wheel nearly vertical throughout suspension travel, maintaining camber, caster and toe angles to ensure good tyre contact with the road.

Handling and Stability

The upper arm is usually shorter, causing negative camber gain during compression, which gives better grip during cornering and high-speed stability.

Steering Movement

Ball joints allow the wheel to turn left or right and steering forces are smoothly transmitted through the knuckle to the control arms.

Load Transfer

Vehicle weight is transferred mainly through the lower control arm and suspension geometry helps distribute forces efficiently.

Radial Ply Tyre vs Cross Ply Tyre