Machine Characteristics, Energy Sources and Engine Mechanics

Main Characteristics of Machines

Power operation. All machines are supplied with an energy source to function, either by connection to the electric current, battery, combustion of fuel, or using air pressure. Machines transform and transmit energy through mechanisms and internal circuits; apparatuses transform the transmitted or received energy to produce effects. Machines are recognized by the effects of their operation: movement, heat, delivery of images, etc.

Parts of a Machine

Structure. The structure is constituted by the fixed parts of machines; it is the framework on which the rest of the pieces are based.

Mechanisms. Mechanisms are the mobile parts of machines such as toothed wheels, levers, pulleys, rollers, and similar elements.

Circuits. Circuits control the flow of electric power or fluid pressure. Types of circuits include electrical, electronic, and fluid systems.

Structural Joints and Housing

Housing or frame (chassis). The housing or frame constitutes the main support that the other parts rely on and provides the arrangement for the entire machine.

Guides and bearings. Guides and bearings define the paths of arms and moving parts, allowing them to slide or rotate.

Absorbers. Absorbers damp or absorb vibration and sudden movements to protect components and improve operation.

Types of Energy for Machines

• Electrical. Electrical energy can be obtained from the power grid, batteries, or voltaic cells.
• Thermochemical (chemical combustion). Chemical energy released by burning fuel produces thermal energy used in boilers, stoves, and heating applications.
• Fluid pressure. Compressed air or pressurized liquids provide power for compressors, pneumatic tools, and hydraulic pumps.
• Mechanical. Mechanical energy produced by forces, including human or animal muscle power, is useful to power tools, bicycles, tricycles, and simple machines.

Two Types of Engines

Electric engines (motors). These obtain mechanical energy from an electrical current. Direct current engines can be fed by batteries and are useful for portable appliances. Alternating current motors are connected to the electricity grid and used in industry and household appliances.

Combustion engines. These make use of the combustion of fuels to obtain energy.

• External combustion engines (steam engines). Combustion occurs outside the machine to heat a fluid such as water; the resulting steam moves mechanisms.
• Internal combustion engines. These use fossil fuels such as gasoline or diesel; combustion occurs inside the engine's combustion chamber. There are simple, low-power units found in motorcycles and small equipment, and others that develop great power, such as gas turbines in aircraft.

Four-Stroke Internal Combustion Engine

The four-stroke internal combustion engine is widely used in large ships, vehicles, and many other applications. It is formed by a structure or block containing one or more cylinders. Inside each cylinder a piston moves; through a connecting rod and crankshaft this motion rotates the engine shaft.

Fuel reacts with air (oxygen) inside each cylinder, producing an explosion and gas expansion that forces the piston downward. In each cylinder this sequence forms a four-stroke cycle. Intake and exhaust of gases are controlled by synchronized gas valves timed with the crankshaft motion.