Car Engine Mechanism

Engine Fundamentals

• An engine provides rotating power to drive the wheels through the transmission and driving axles.

Internal Combustion Engines

• Classified as internal combustion because the combustion or burning of fuel takes place inside the engine.
• Engines, both gasoline and diesel, require construction to withstand high temperatures and pressures created by burning vaporized fuel mixed with air.

Combustion Chamber

• The space between the piston at the top of its travel and the cylinder head.
• An enclosed area where the air/fuel mixture is burned.

Complete Combustion

• Requires the right amount of fuel mixed with the right amount of air.
• Mixture must be compressed in a sealed container, then ignited by the right amount of heat at the right time.
• Nearly all fuel that enters a cylinder is burned when these conditions exist.

Engine Efficiency

• About 30 percent of released energy is converted to useful power that moves the vehicle.
• Automotive engines have more than one cylinder to increase power.

Cylinder Requirements

• Each cylinder should receive the same amount of air, fuel, and heat for efficient engine operation.
• Cylinders require a way to allow heat, fuel, and air in and burnt air/fuel mixture out.

Valves

• Fitted to engines to meet cylinder requirements.
• At least two valves at the top of each cylinder: intake valve and exhaust valve.
• Valves are accurately machined plugs that fit into machined openings.
• Valve is said to be seated or closed when it rests in its opening or seat.
• Valve opens when pushed off its seat.

Camshaft Operation

• Rotating camshaft, driven by the crankshaft, opens and closes intake and exhaust valves.
• Cams are raised sections of a shaft with high spots called lobes.
• Cam lobes are oval shaped.
• Lobe placement on the shaft determines when the valve will open.
• Height and shape of the lobe determines how far the valve will open and how long it will remain open in relation to piston movement.