Automotive Systems: Engine, Fuel, and Transmission Mechanics

Fuel Injection Systems

Continued and Timed Injection Systems

• Continued Injection: Delivers fuel continuously into the intake manifold, regardless of the engine cycle.
• Timed Injection: Synchronizes fuel delivery with the intake stroke of each cylinder for better efficiency and combustion control.

Piston Ring Functions

Primary Roles of Piston Rings

1. Seal the combustion chamber to prevent gas leakage.
2. Control oil consumption by scraping excess oil from the cylinder walls.
3. Transfer heat from the piston to the cylinder wall.

Racing Engine Preference

Petrol engines are favored in racing because they are lighter, provide a higher power-to-weight ratio, and offer faster throttle response, which is ideal for high-speed performance.

Single Plate Clutch Torque Parameters

Factors Affecting Clutch Torque

• Coefficient of friction between the clutch surfaces.
• Axial force applied by the pressure plate.
• Effective radius of the friction surface.

Gearbox Functions

Essential Roles of a Gearbox

1. Varies the torque and speed from the engine to suit driving conditions.
2. Allows the vehicle to move in reverse.
3. Enables the engine to run within its optimal speed range.

Overdrive Function

Overdrive reduces engine RPM at high speeds by providing a gear ratio less than 1:1, improving fuel efficiency and reducing engine wear.

Engine Testing Measurements

Important Quantities During Engine Testing

• Brake power
• Fuel consumption
• Exhaust emissions
• Cooling water and lubricating oil temperatures
• Engine speed and torque

CNG vs. Diesel: Pollution Viewpoint

CNG burns cleaner than diesel, producing lower levels of NOx, particulate matter, and CO2, making it more environmentally friendly.

Ignition System Components

Functions of Coil, Breaker, and Distributor

• Ignition Coil: Steps up battery voltage to create a spark.
• Contact Breaker: Interrupts current to the coil to induce high voltage.
• Distributor: Directs the high voltage to the correct spark plug at the right time.

Differential Necessity

Yes, in rear-wheel and four-wheel drive vehicles, the differential is essential to allow wheels to rotate at different speeds while turning, improving handling and reducing tire wear.

Vehicle Structure and Fuel Comparison

Chassis Versus Superstructure

• Chassis: The vehicle’s structural frame that supports the engine, wheels, suspension, and drivetrain.
• Superstructure: Refers to the body of the vehicle mounted on the chassis, like the cabin or load-carrying body.

CNG Preference Over LPG

CNG (Compressed Natural Gas) is preferred over LPG as automobile fuel because it is cleaner, safer, and more environmentally friendly due to lower emissions and a higher ignition temperature.

Shackle Function in Suspension

A shackle allows the leaf spring to change length as it flexes, ensuring smooth suspension movement and maintaining wheel alignment.

Clutch Role in Transmission

The clutch disconnects the engine from the transmission temporarily, allowing smooth gear changes and stopping the vehicle without stalling the engine.

Turbo Charger Definition

A turbocharger is a device that uses exhaust gases to drive a turbine, which compresses the intake air, increasing engine power and efficiency.

Adaptive Cruise Control and Braking

Adaptive cruise control automatically adjusts the vehicle’s speed to maintain a safe distance from vehicles ahead, and the braking system slows or stops the car accordingly.

Cut-Out Function in Charging

The cut-out regulates the battery charging by disconnecting the generator when the battery is fully charged to prevent overcharging.

MPFI vs. GDI Systems

• MPFI (Multi-Point Fuel Injection): Fuel is injected into the intake manifold near each cylinder.
• GDI (Gasoline Direct Injection): Fuel is injected directly into the combustion chamber, allowing better efficiency and performance.

Thermostat in Cooling System

The thermostat regulates the engine temperature by controlling coolant flow, ensuring the engine warms up quickly and maintains optimal operating temperature.

Diesel Fuel Injection Requirements

A diesel fuel injection system must meter the right amount of fuel, maintain high pressure, atomize fuel properly, and inject it at the right time for efficient combustion.

Automobile Starting Motor Drives

Types of Starting Motor Drives

Starting Motor Drive Variations

• Direct Drive
• Bendix Drive
• Inertia Drive
• Pre-engaged Drive (Most widely used)
• Gear Reduction Drive
• Folo-Thru Drive
• Overrunning Clutch Drive

Most Used Drive for Diesel Engines

Pre-engaged Drive

Pre-engaged Drive Description

The pre-engaged starter drive is commonly used in diesel engines due to its reliability and robust engagement mechanism. In this system, the pinion gear is engaged with the flywheel ring gear before the motor starts rotating, hence the name “pre-engaged”.

Components of Pre-engaged Drive

• A solenoid that pushes the pinion gear into engagement.
• An overrunning clutch that prevents the motor from being driven by the engine once it starts.
• A return spring that retracts the pinion gear after starting.

Working Principle

1. When the ignition switch is turned on, the solenoid pushes the pinion gear forward to mesh with the flywheel.
2. After engagement, the motor rotates the flywheel to start the engine.
3. Once the engine fires, the overrunning clutch disengages the pinion to prevent damage.