Automotive Braking, Ignition, and Battery Systems

Q4 A) Working of Disc and Drum Brakes

Disc Brake Components and Operation

A disc brake consists of a brake disc, a caliper, and brake pads. When the brake pedal is pressed, hydraulic pressure pushes the pads against the rotating disc. The friction between the disc and pads slows down the wheel. Disc brakes provide better heat dissipation and performance at high speeds.

Drum Brake Components and Operation

A drum brake consists of a brake drum, brake shoes, a wheel cylinder, and return springs. Hydraulic pressure pushes the brake shoes outward against the inner surface of the rotating drum. Friction slows the wheel and stops the vehicle. Drum brakes are cheaper and mostly used on rear wheels.

Ignition System Construction and Working (6 Marks)

With a neat sketch, explain the construction and working of the ignition system. An ignition system is used in petrol engines to ignite the air-fuel mixture by producing a high-voltage spark at the spark plug.

Ignition System Components

• Battery: Supplies low-voltage electrical energy.
• Ignition Switch: Controls the ON/OFF state of the system.
• Ignition Coil: A step-up transformer which converts 12V to about 20,000–30,000V.
• Contact Breaker / Electronic Control Unit (ECU): Helps in timing the spark.
• Distributor: Sends high-voltage to each spark plug in the correct firing order.
• Spark Plug: Produces a spark in the combustion chamber.
• Condenser: Reduces arcing at breaker points in older systems.

Ignition System Operation

When the ignition switch is turned ON, the battery supplies current to the primary winding of the ignition coil. As the engine rotates, the contact breaker opens and closes. When it opens, the magnetic field in the coil collapses suddenly.

Q6 B) Lead-Acid Battery Construction and Working

A lead-acid battery is the most commonly used rechargeable battery in automobiles.

Lead-Acid Battery Construction

• Positive plates: Lead peroxide (PbO₂)
• Negative plates: Spongy lead (Pb)
• Electrolyte: Diluted sulphuric acid
• Separators: Placed between plates
• Container: Battery container and terminals

Lead-Acid Battery Working Principle

During discharging, a chemical reaction occurs between lead, lead peroxide, and sulphuric acid, producing an electric current at the terminals. During charging, an external current reverses the reaction and restores the sulphuric acid concentration. This battery supplies the required power for starting the engine, lighting, and the ignition system.