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Pistons are said to be crucial engine parts, but what is piston and how does it work? Find the answer to that question here in this article. We included information about piston meaning, piston working principle, and piston purpose in a vehicle. The article also looks at the automotive piston design as well as its location in an engine.

If you are a car owner, automotive pistons supplier, or automobile parts enthusiast, read on to the end. The information contained here is aimed at making you more knowledgeable about this important vehicle part.

To start us off, a look at what is piston and where the component is used.


Piston Definition

A piston is a cylinder-shaped component that moves up and down a pressure-tight chamber or tube. The piston movement pressurizes a fluid, either liquid or gas, to create or transfer motion. To illustrate the piston mechanism, think about the usual syringe used by doctors. The part inside the syringe is the piston, and the handle the rod to operate it.

Piston diagram
Source: http://motorsportengineering.blogspot.com

Piston diagram showing the parts that make a typical engine piston.

The Piston Engine

A piston engine is named so for using pistons. The automotive piston assembly is much more complex than a syringe, of course. It consists of several components and works in a tougher environment. It is also larger and made of metal. The piston on car engine is made of materials that can withstand pressure, extreme heat, and several other conditions.

Piston uses in a vehicle is not confined to the engine only. The component is also found in a piston brake, particularly fixed and floating brake calipers. The piston caliper can house one or more pistons, depending on the type of brake or required braking force.

A floating caliper uses one piston and is called a 1 piston caliper. It is usually used in small cars. A 2 piston brake caliper comprises a piston on either side, while a 4 piston caliper contains two pistons on each side of the rotor.

Many trucks use a 6 piston caliper, some 8 piston calipers. Some performance cars will have 6 piston brake or even 8 and provide incredible stoppage. Most passenger vehicles do not need powerful braking, and a 1 or 2 piston caliper is often adequate.

Drum brakes also use pistons to move the brake shoes towards the drum. A typical drum brake, unlike a disc brake, will only have two pistons. Let us now have a detailed look and the use of a piston in automotive engines.

What is a Piston in a Car Engine?

As mentioned earlier, a piston engine relies on pistons to produce movement. Looking at the piston engine diagram above, you will clearly see the piston set arrangement. Configurations or piston arrangements vary across engines. However, the design does not. Pistons also operate same way on different engines.

Piston in a car engine
Source: http://www.youtube.com

The piston in a car engine is a cylindrical plug moving up and down the engine cylinder. It transforms the force of expanding gases in the cylinder into rotation, helping to move a vehicle. The pistons in a car connect to the crankshaft. Together, the piston and crankshaft make the main moving parts of an engine.

What is piston working mechanism that makes it such an important part of a vehicle? The automotive piston, as we have seen, is a simple vehicle component. Its operation is also a straightforward mechanism. Next, let us see how a piston on a car works.


Automotive Piston Working Principle

Automotive piston working principle
Source: http://filamatic.com

The operation of the piston is divided into phases called strokes. A piston stroke is indicated by the piston position, which ranges from the top, middle, and bottom parts of the cylinder. Regardless of the piston engine fuel system, the sequence fuel delivery and piston position is a perfectly timed process.

The combustion cycle or stroke starts with the piston on the upper part of the cylinder. During this time, the intake and exhaust valves are closed. The piston then begins a downward movement, creating a partial vacuum in the space above. Air then enters the cylinder.

Fuel also enters the cylinder at the same time, and the intake valves close. At this stage, the piston has begun moving upwards. Because all the valves are closed, the piston motion compresses the air/fuel mixture, creating a highly pressurized space between it and the cylinder head. The fuel/air mixture ignites, pushing the piston downwards.

The exhaust valves then open to allow the products of combustion to escape. This happens just as the piston starts the upward travel. The moving piston forces the exhaust gases out. Meanwhile, the intake valves open, fuel and air enter the cylinder, and the cycle repeats. 

The piston assembly consists of two distinct sections: the upper part that consists of the crown or the head of the piston and rings that provide an almost airtight seal. The piston and ring arrangement also helps to scrape oil from the cylinder walls and returns it to the oil sump.

Other than the piston and cylinder, there is also the section that consists of a connecting rod. This is the part that transfers the back and forth motion of the piston to the crankshaft The piston and connecting rod are joined by a shaft called a wrist pin.


Piston Material: What are Pistons Made of?

A piston in car takes in a lot of thermal and mechanical stress. It must, therefore, be made from a material that can stand up to high temperatures, pressures, mechanical impacts, and several other situations.

But the piston must also be lightweight, which means piston material should balance between mass and other qualities. The piston of engine types used in performance are usually made of aluminum alloys.

Initially, iron was used due to its excellent resistance to wear, good thermal conductivity, and other benefits. But iron produced heavy pistons. A piston for car use should not be heavy, or it will reduce the engine’s efficiency. Aluminum was an option, but not as effective when it came to resisting wear and heat.

Technological developments led to the production of aluminum alloys with superior characteristics, though. As a result, pistons made of aluminum dominate the automotive piston market today. The modern piston of diesel engine, petrol engine and virtually every internal combustion engine most likely be aluminum.

materials used for piston
Source: http://www.trucktrend.com

Pistons made from different materials

Aluminum alloy pistons have the following qualities that make them better than those made from iron.

  • Lightweight for higher engine RPM (a third of the weight of iron)
  • Ability to withstand high temperatures
  • Excellent structural integrity
  • Better thermal conductivity (three times higher)
  • Recyclable
  • Better finish

Pistons can be forged or cast from molten metal.

Piston diagram compairing grain structure
Source: http://www.examhill.com

Forging involves using a press to shape a heated chunk of metal into a piston. This method results in a product with superior qualities. A piston forged the right way is high-strength, reliable, and durable. Last-minute alterations are possible during manufacture.

Casting means pouring molten metal into molds then cooling it rapidly. The material then hardens in the shape of a piston. The piston is then machined to the required specifications.

Because casting involves fewer machines, it is cheaper and reduces piston price. But the process produces pistons of lesser quality in terms of strength, thermal expansion rates, and more. To improve the piston strength and other properties, automotive piston manufacturers usually use the hypereutectic method. It is still a casting method but which involves adding silicon to the aluminum.

Pistons produced the hypereutectic way are sturdier than those without silicon. They also have a lower thermal conductivity, which creates a better piston-cylinder seal. This reduces emissions significantly, plus it helps prevent piston seizures.

What type of piston material should one choose?

If piston price is a concern, those made using the casting method are a good option. Heypereutectic pistons would also be a good choice, especially if looking for better engine performance and durability.

If your engine has a turbo or supercharger, requires higher RPM, or operates in demanding conditions, forged pistons would be the way to go. You can use them in other engines, of course, but that would be unnecessary. In short, forged pistons are best used in high-performance engines due to their superior qualities and high price.


How Many Pistons are there in a Car Engine?

A piston moves inside a cylinder. That means pistons in an engine will, most of the time, be as many as the number of cylinders. Now, different engines use different cylinder configurations ranging from one to as many as ten or even more.

A 1 piston engine has one cylinder. Examples of its applications include the engines of some motorcycles, lawnmowers, and chainsaws. The piston of a motorcycle that uses one cylinder provides more torque at higher RPM. The same case applies to the lawnmower and other power tools with a similar engine.

1 cylinder engines

1 cylinder engines are simple machines whose fuel consumption is very low. Other common engine arrangements are 4 piston engine, 6 piston engine, and 8 piston engine designs. Most cars and SUVs use these types of engines, with the 4-cylinder or piston design being the most popular.  

An engine that uses 6 pistons and cylinders is commonly known as a V6 engine, and the type that uses 8 cylinders a V8. A 3 piston engine is also possible. The same with a 7 piston engine. However, these are not common, and most auto manufacturers do not use them in their automobiles.

A 2 pistons per cylinder engine does not need a cylinder head. Valves are replaced by openings on the cylinder, which provides an efficient flow of gases and reduces weight. These types of engines were mostly used in factory machines, military vehicles such as tanks, and large engines of ships.


Opposed Piston Engines

opposing piston engine

Although no longer popular, there is a variation of the piston engine worth mentioning. Known as the opposing piston engine, this one uses two pistons in each cylinder. The pistons move in opposite directions with each stroke.


Piston Function in an Engine

What is piston purpose in a car engine, and why is it such an essential auto part? As we have seen, pistons convert the heat energy of combustion into linear motion. The components transfer the energy to the crankshaft through the connecting rod. In most engines, a series of rods and pistons work together to rotate a crankshaft.

piston function in an engine
Source: http://www.hardwarezone.com.sg

Other functions that make these components important piston engine parts include:

  • Sealing the combustion chamber to facilitate compression and combustion in an airtight environment
  • Dissipating heat caused by combustion in the cylinder
  • Facilitating the entry and exit of gases by moving back and forth in the cylinder
  • Providing a supporting surface (the crown) for the air/fuel mixture
  • Guiding the connecting rod
  • Housing the rings that provide a seal to prevent leaks and the entry of oil into the combustion chamber

These are the functions that a piston serves in an engine. But the piston wears out over time, leading to a malfunctioning engine. When that finally happens, you may need to purchase what is called a piston kit. It contains various components to replace the damaged parts.

Piston kit price depends on your type of vehicle and can vary between $200 to $500 or more. When buying your replacement parts, it is advisable to check the automotive pistons catalog provided by manufacturers. That way, you will avoid buying the wrong type of piston for your vehicle.


Conclusion

Pistons move to rotate the crankshaft. This makes them essential auto parts, without which the heat energy from the combusting fuel/air mixture would not convert into motion. In this article, we looked at what is piston, its working mechanism, and the purpose it serves in an IC engine. Our next article looks at piston parts and functions. Check it out to understand the function of every component that makes the automotive piston.