Cycle and Strokes

Engines can be either two-stroke cycle or four-stroke cycle. The complete cycle requires four piston strokes (intake, compression, power and exhaust).

Study the illustration below. In the two-stroke cycle or two-cycle engine, the intake and compression strokes and the power and exhaust strokes are combined. This condition permits the engine to produce a power stroke every two piston strokes, or every crankshaft rotation.

The actions in a cylinder can be divided into four stages, or "strokes." A stroke is the movement of the piston from the top position to the bottom position or freom the bottom position to the top position. The top position, or upper limit of piston movement, is called top dead center (TDC). The bottom position, or lower limit of piston movement, is called bottom dead center (BDC). A piston stroke or piston movement is either TDC to BDC or BDC to TDC.

The four strokes are called the intake stroke, the compression stroke, the power intake stroke and exhaust stroke. These four strokes make up the complete cycle of events in the cylinder. An engine that runs on this four-stroke cycle principle is called a four-stroke cycle engine, often shortened to four-cycle engine. The term Ott cycle is also applied to this type of engine.

Engine Parts

In the automobile, the engine is a source of power. It converts chemical energy of fuel into mechanical energy in the form of a rotative force to propel the qutomobile. Without the engine, the automobile will not operate; that is, it cannot move from one place to another.

The automotive engine can be divided into two major parts, the stationary parts and the moving jparts. The stationary parts are those that are fixed in a certain position. They do not move or change their position during engine operation. Moving parts are those that move or change their position during operation.

I. Engine Stationary Parts.

a. The cylinder head. The cylinder head covers the cylinders and is held to the cylinder block by bolts or nuts. It is cast from iron which is alloyed with other metals or cast from aluminum alloy. It contains the combustion chambers, water jackets on water cooled engines, cylinder head boltholes or stud holes, and the spark plug holes on gasoline engines or nozzle mounting holes on the diesel engines. It also contains some other parts such as the valve ports, valve seats, etc.

b. The cylinder head gasket. A water-tight and gas-tight seal beween the cylinder head and cylinder block is maintained through the use of a cylinder head gasket. This gasket may be in the form of a metal sheet, soft enough to be formed as required. In some cases, the cylinder head gasket is made from two thin plates of soft metals such as copper, with re-enforced asbestos filling beween. This gasket is provided with holes for the cylinder head bolts or studs and for the combustion spaces.

c. The combustion chambers. These are hollowed spaces within the cylinder head or above the pistons where the fuel charge is burned. They are made in different shapes designed to provide a more uniform and better mixture of air and fuel in order to obtain maximum combustion of the fuel.

d. The cylinder block. The cylinder block forms the main body or is referred to as the framework of the engine. It is cast from gray iron or iron alloyed with other metals like nickel and chromium or cast from aluminum. It contains the cylinders and the water jacket for the cooling water. In some types, the cylinder block also contains the valve ports, valve seats and valve mechanisms. In front are the water pump and the timing gear cover and at the rear is the bell housing or clutch housing. At the side of the block are the manifolds, fuel pump, distributor, etc.

e. The cylinders. The cylinders are cylindrical openings in the cylinder block where the pistons move up and down. They are usually provided with the cylinder liners or sleeves which are made from special types of metals, such as cast iron or steel. In some cases, the cylinders are not provided with sleeves; instead, they are parts integral with the cylinder block, and are plated with chromium to reduce wear and to lengthen their lives.

f. The crankcase. The crankcase is located at the bottom portion of the cylinder block and supports the crankshaft and camshaft by means of bearings. It contains the drilled oil passages for the lubricating oil and the oil pump.

g. The oil pan. Attached to the lower part of the crankcase is the oil pan. It encloses the lower portion of the engine and holds the lubricating oil. Without he oil pan, there is no means of storing the lubricating oil of the engine. The oil pan is provided with a drain plug to facilitate the drainage of lubricating oil when the lubricaing oil of the engine is changed

h. The manifolds. There are two kinds of manifolds used in the engine, the intake manifold and exhaust manifold.

The intake manifold provides a passage for the air-fuel mixture from the carburetor into the intake valve ports of the engine and also provides passage for the intake air for the diesel engine.

The exhaust manifold provides a passage for the burned gases coming out from the cylinders.

II. Engine Moving Parts

a. Pistons. Are the movable cylinder metal plugs. They are closed at the top and open at their bottom and are provided with grooves near their closed ends to accommodate the piston rings. They receive the force of explosion and transmit that force to the crankshaft through the connecting rod.

b. Piston rings. Are expanding ring placed in the piston grooves to provide a complete seal beween the piston and the cylinder wall. They prevent the leakage of fuel charge or explosion in the combustion chamber into the crankcase and control the lubricating oil from reaching the combustion chamber. In addition, they permit the proper lubrication of the cylinder and assist in cooling the piston.

c. Connecting rod. changes the reciprocating motion of the piston into a rotary motion. It is connected to the piston by a piston pin and to the crankshaft journal by a connecting rod cap and connecting rod bearings.

d. Crankshaft. is a cast of heat-treated alloy steel strong enough to withstand the downward thrust of the pistons cause by the force of explosion. It is provided with counterweights and drilled oil passages. The rear end is provided with a flange for the flywheel, and the front end carries the crankshaft gear of sprocket, vibration damper and fan belt pulley.

e. Flywheel. is a heavy wheel provided with a ring gear for starting and cranking. It provides for smooth rotations of the crankshaft even during non-power strokes and serves as the driving member of the clutch assembly.

f. Valves. allow the opening and closing of the ports while the engine is in operation. The inlet port has the intake valve to close it during the rest of the cycle and open it when the fuel is needed to enter the cylinder. The exhaust port has the exhaust valve to open the port when the burned gases go out from the combustion chamber.

g. Camshaft. is a straight shaft provided with cams to change rotary motion into a straight line motion. The cams of the camshaft cause the valves to open.

Engine Classification

There are two major classifications of engines: the internal and the external combustion engines. The engine that burns fuel inside its combustion chamber is called the internal combustion engine, while the engine that burns its fuel outside is called external combustion engine.

All automobile engines are of the internal combustion type, and they are also classified as follows:

According to Cylinder Arrangement

1. Vertical In-line. This is the simplest form of cylinder arrangements. The cylinders are arranged in-line in a vertical position.

2. Slanted In-line. The cylinders are still in-line but slightly slanted to one side. This car body style requires a lower engine hood. This slanted in-line design is made for stability.

3. V-Type. The main advantage of the V-type over the in-line is that the form is shorter and, therefore, needs a smaller engine room.

4. Horizontally Opposed. This engine has its cylinders arranged in two flat banks with the crankshaft between them. It provides a better mechanical balance and suited to the car with very limited space.

According to Valve Arrangement

The development of high-performance engines led to the variations in valve arrangements. The early mobile which were of the low compression designs were the F-type and L-type. Nowadays, most engines have their valves in the cylinder head, and modifications in the camshaft mountings have been introduced.

The intake and exhaust valves can be arranged in various ways in the engine cylinder head or block.

a. I-head Engine. In the I-head or overhead valve engine, the valves are in the cylinder head. In inline engines, the valves are usually in a single row.

b. V-8 Engines, I Head. The valves may be in a single row in each bank or in a double row in each bank. Either way, single camshaft operates all valves. The valve lifters, push rods, and rocker arms carry the motion from the cams to the valves.

c. L-Head Engine. In the L-head arrangement, the combustion chamber and the cylinder form an inverted L. The intake and exhaust valves are located side by side. All the valves for the engines are set in one line (except that V-8 L-head engines are in two lines). This way, a single camshaft can be used to operate all valves.)

d. V-8 Engines, L-Head. The intake and exhaust valves are arranged in two lines in the cylinder block.

e. Overhead camshafts. The I-head engine used push rods and rocket arms to operate the valves. This design is often called a push-rod engine. The push rods and rocker arms impose some inertia that affet valve action. The push rods and rocker arms flex or base slightly before they open the valve.

f. F-Head Engines. The intake valve are in a single row in the cylinder head while the exhaust are arranged in one row in the cylinder block.

Piping and Tubing

A complete refrigeration unit is composed of several parts that function to vaporize and condense the refigerant as it circulates through the system. Refrigerator parts are placed at a distance far from each other so it is necessary to have a good piping system to have the refrigerant travel. This is made possible with the use of piping that is only a hollow bar to transfer liquids and vapors from one part of the system to another.
Piping is ordinarily understood to have walls of considerable thickness, while tubing has comparatively thin walls.

Automotive Components

Engine. It is the power plant of the car. When fuel is burned inside the engine, the power produced drives the wheels and makes the car move.

Clutch. It connects and disconnects the power from the engine to the transmission.

Transmission. It rotates the engine torque, transmits the engine power from the clutch, and provides a means by which the driver can select the appropriate speed that will match the engine power.

Propeller Shaft. It transmits the power from the transmission to the differential at varying angles.

Differential. It enables the rear wheels to be driven at different speeds when the vehicle is making a turn.

Suspension System. It absorbs road surface irregularities and converts them into controlled vertical movements. Road shocks, impact sways and other unpleasant movement of the car are controlled by the suspension system, thereby providing a comfortable ride for the passengers.

Brake System. It stops or slows down the vehicle.

Steering System. It provides control of the car by the driver for maneuvering in the desired direction.

Electrical System. It provides electricity for the operation of the starter, ignition, lighting, signal, and other electrical accessories.