21st Century - Engines

Detail Level 1

The engine is where chemical energy in the gasoline is burned (combusted) into gases that drive the piston.   These many small explosions occuring at high temperatures and pressures over long periods of timet heat the engine and subject it to high internal stresses.   Therefore, the engine and its parts must be must be strong enough to withstand this environment.

Engine location in the car engine compartment varies with the make and model. ^{Erjavec 188}

1. Front engine - longitudinal: Engine, transmission, front suspension and steering systems are installed in the front of the car over the axle with the engine facing forward (longitudinal), while the differential and rear suspension are located in the rear of the car.   This configuration is usually found in rear-wheel drive (RWD) and 4-wheel drive (4WD) cars.   Vehicle weight is evenly distributed between the front and rear wheels, which reduces the sterering force and equalizes the braking load on the wheels.   Relatively large engine compartments are required and the need for a rear-drive propeller shaft and differential reduces the passenger space.

2. Front engine - transverse: Same as above except that the engine is mounted transversely (sideways).   A A traqnsaxle is used, which combines a transmission and differential gearing fastened to the engine.   This arrangement reduces the size of the engine compartment and reduces the overall weight of the car.   Also, the elimination of the drive train increases the interior space by eliminating "hump" in the car associated with the long drive train.   Traction on the front drive wheels is increased for better braking.

3. Mid-Engine - transverse: Engine and drive train are located between the the passenger compartment and the rear axle.   Center of gradvity is now near the center of the vehicle, which improves steering and handling.   Because the engine is not under the hood, it can be sloped downward, thus improving aerodynamic flow of air around the car and the driver's field of vision.   However, engine access by the mechanic and cooling efficiency are reduced.   A barrier is required to reduce engine noise, heat, and vibration in the passenger compartment.   This arrangement is used in smaller, rear-wheel drive, high performance sports cars.

Engine parts are the following:

1.   Cylinder block
2.   Cylinder head
3.   Head gasket
4.   Pistons
5.   Piston rings
6.   Supercharger/Turbocharger
7.   Connecting rods, pins and bearings
8.   Crankshaft
9.   Flywheel
10. Balance shafts
11. Valve Train
12. Camshafts
13. Manifolds

Cylinder block (engine block) contains the cylinders, which are hollow tubes into which are fitted the pistons and connecting rods.   Because the block is subjected to high pressures and temperatures, it usually is made of cast iron or cast aluminum alloys.   The cylinder block also has several passageways for lubricating oil and coolant.

Cylinder head fits on top of the cylinder block to close off the combustion chambers, which are the spaces between the top of the cylinder head cavities to the top of the piston located in the cylinder.   The head has one or more intake ports for air and gasoline intake, and one or more ports for the exhaust gases (carbon dioxide, carbon monoxide, water vapor, and nitrogen oxides).   Like the cylinder block, the cylinder head must be made of cast iron or cast aluminum alloys to withstand high temperatures and pressures.

Head gasket is a seal between the cylinder block and cylinder head that prevents the air and gasoline mixture and the exhaust gases from escaping from the engine.   The head gasket is made of ......

Pistons are the parts that move down in the cylinder under the pressure of combustion expanding gases.   These gases press against the top of the piston to force it down.   Because the firing cycle is staggered, at any one time some pistons are moving down to power the crankshaft while others are powered by other pistons to move up under the crankshaft motion to compress the air/gas mixture.

Piston rings

Supercharger or turbocharger

Connecting rods are connected at one end to the pistons and at the other end to the crankshaft.   They transmit the linear up and down motion of the piston to the crankshaft, thus causing it to rotate.   The upper end that is connected to the piston moves up and down while the lower end that is connected to the crankshaft moves in a circle.   A pin connects the rod with the piston.   The rod has top and bottom bearings to absorb the wear from the rod motion against the pin and crankshaft.

Crankshaft, which is connected to the transmission gears, rotates and transmits this rotary motion to the drive train gears, thus causing them and the wheels to rotate.   The crankshaft is rotated by the downward (power) stroke of each piston.   Since there are 4 or more pistons synchronized to force the crankshaft to turn, the crankshaft is continually forced to rotate while the engine is running.

Flywheel is attached to the rear end of the crankshaft to smooth out the rotational motion of the crankshaft.

Balance shafts

Valve train is a group of parts that open and close the intake and exhaust ports located in the cylinder head.   The valve train is moved up and down by the camshaft through linkages.   This train motion causes the valves to open and close.   The valve train contains the following parts:

1. Valves open and close the cylinder head ports to allow air & gas mixtures to enter and exhaust gases to exit.   Usually, there is 1 intake valve and 1 exhaust valve per cylinder.   Some cars with more powerful engines have 2 intake and 2 exhaust valves that allow more air and gas into the cylinders.   There are 2 valve and camshaft placement configurations: (1) Overhead Valve (OHV) and (2) Overhead Cam (OHC).   In OHV, the intake and exhaust valves are mounted in the cylinder head.   This arrangement uses valve lifters, pushrods, and rocker arms to transfer camshaft rotation into valve movement.   It also eliminates the need for long valve timing belts or chains.   The intake and exhaust valves may operate from 1 or 2 camshafts.   This arrangement allows for variable intake operation.   In OHC, the cam is located in the cylinder head along with the valves.   The valves are moved by cam followers or tappets.   This arrangement also can have single or dual camshafts (DOHC).
2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.

Camshaft causes the intake and exhaust valves to open and close in a timed sequence consistent with the ignition of the air/fuel (oxygen/gasoline) mixture.   Cams are raised sections of the camshaft with high spots called lobes.   As the camshaft rotates, the lobes also rotate to lift the valve open and then continues to move as the valve spring lowers and closes the valve.   There may be 1, 2 or 4 camshafts depending on the engine configuration.

1. Overhead camshaft (OHC)
2. In-block overhead valve camshaft (OHV)
3. Duel overhead camshaft (DOHC)

Intake and exhaust manifolds are passageways the conduct the air and gas into the cylinder from the air intake and conduct the exhaust gases out of the cylinder and exhaust pipe.   They are attached to the cylinder head.

Operation of the engine firing cycle consists of 4 strokes:

1. Intake ("intake stroke") of air as the piston moves downward from top-dead-center (TDC).   This creates a partial vacuum in the cylinder that sucks in the air and gasoline into it through the intake port.   When the piston reached bottom-dead-center (BDC), the suction ceases, but the air/fuel mixture continues to enter the cylinder under its own weight.   The intake valve (and port) is open and the exhaust valve (and port) are closed during this stroke.
2. Compression ("compression stroke") of air occurs when the piston moves upward from BDC under the force of the rotating crankshaft that continues to be powered by other firing cylinders.   The intake and exhaust valves are both closed during this stroke.   This upward movement compresses the air/fuel mixture and heats it up.   (The volume of the cylinder at BDC divided by its volume at TDC is called the compression ratio.   It is a measure of the engine's power.).
3. Expansion ("power stroke") of combustion gases drives the piston downward after an electric spark ignites the gasoline and oxygen (in the air) mixture.   Both valves are closed during this stroke.   This downward stroke is the (only) one of the four that powers the crankshaft.
4. Exhaust ("exhaust stroke") occurs as the piston is moved upward from BDC under the force of the rotating crankshaft.   This movement, plus the existing pressure in the cylinder, pushes the combustion gases out of the open exhaust port as its valve is opened.   The intake valve is closed.
      (See illustration below.)

Note that only one of the 4 strokes, expansion, produces power.   However, car engines contain at least 4 cylinders with combustion occurring sequentially, so power is produced continuously.   This method of engine operation, called the Otto cycle after its inventor, Nicolaus Otto, has been used continuously in cars since their invention in the late 19th century.

 

Detail Level - 2 provides more detailed information.