A cylindrical metal part that guides the piston to do linear reciprocating motion in it. The working medium expands in the engine cylinder to convert thermal energy into mechanical energy; The gas is compressed by the piston in the compressor cylinder to increase the pressure. The casing of a turbine, rotary piston engine, etc. Also commonly referred to as "cylinder".

A cylindrical chamber in an engine, the piston is driven by the pressure or expansion force of the working fluid, which is similar but not cylindrical in some special engines.

Generally speaking, under the same displacement, the more valves, the better the intake and exhaust efficiency, just like a person running, when he is exhausted, he needs to breathe with his mouth wide open. Traditional engines usually have an intake valve and an exhaust valve per cylinder. This dual-valve valve mechanism is relatively simple, low in manufacturing cost and relatively easy to maintain. For ordinary engines with low output power requirements, two valves can obtain satisfactory engine output power and torque performance.

The engine with large displacement and high power should adopt multi-valve technology. The simplest multi-valve technology is the three-valve structure, that is, an intake valve is added on the basis of the one-in-one-row two-valve structure. In recent years, most of the newly developed cars of major automobile companies in the world adopt four-valve structure. In the four-valve valve mechanism, each cylinder has two intake valves and two exhaust valves.

The four-valve structure can greatly improve the intake and exhaust efficiency of the engine, and most new cars adopt the four-valve technology. Of course, Volkswagen mostly adopts five-valve technology, such as the 20V engine of the old Jetta King, and the Bora 1.8T engine is also five-valve.

However, reaching or exceeding six valves not only makes the valve train structure too complicated and shortens the life of the engine, but also reduces the space curtain area (valve circumference and valve lift) for valve opening, which reduces the efficiency. Therefore, the four-valve technology is the most widely used at present.

Data expansion

The cylinder consists of a cylinder, an end cover, a piston, a piston rod and a seal.

1) cylinder barrel

The inner diameter of the cylinder represents the output force of the cylinder. The piston should be able to slide back and forth smoothly in the cylinder, and the surface roughness of the inner surface of the cylinder should reach Ra0.8um. For the steel tube cylinder, the inner surface should also be plated with hard chromium to reduce friction and wear and prevent corrosion. In addition to high carbon steel pipes, there are also high-strength aluminum alloys and brass. Small steel cylinders use stainless steel tubes. Gas cylinders with magnetic switches or used in corrosion-resistant environments shall be made of stainless steel, aluminum alloy or brass.

The piston of SMC CM2 cylinder adopts combined sealing ring to realize bidirectional sealing, and the piston is riveted to the piston rod without nut.

2) End cover

The end covers are provided with air inlets and air outlets, and some end covers are also provided with buffer mechanisms. The end cover on the rod side is provided with a sealing ring and a dustproof ring to prevent air from leaking from the piston rod and prevent external dust from mixing into the cylinder. The guide sleeve is arranged on the rod side end cover to improve the guiding accuracy of the cylinder, bear a small amount of lateral load of the piston rod, reduce the downward bending of the piston rod when it is extended, and prolong the service life of the cylinder.

Guide sleeves are usually made of sintered oil-bearing alloy and inclined copper castings. Malleable cast iron was commonly used in the end cover. Now, in order to reduce the weight and prevent rust, aluminum alloy die casting is often used, and the miniature cylinder is made of brass.

3) Piston

The piston is the compressed part in the cylinder. In order to prevent the left cavity and the right cavity of the piston from forming a channel with each other, a piston sealing ring is provided. The wear ring on the piston can improve the guiding performance of the cylinder, reduce the wear of the piston sealing ring and reduce the friction resistance. Wear-resistant ring length is made of polyurethane, PTFE, synthetic resin tape, etc. The width of the piston is determined by the size of the sealing ring and the necessary length of the sliding part.

The sliding part is too short, which is easy to cause early wear and seizure. The piston is usually made of aluminum alloy and cast iron, and the piston of small cylinder is made of brass.

4) Piston rod

The piston rod is the most important mechanical part in the cylinder. High carbon steel is usually used, and the surface is plated with hard chromium, or stainless steel is used to prevent corrosion and improve the wear resistance of the sealing ring.

5) Sealing ring

The component seal at the rotating or reciprocating position is called dynamic seal, and the seal at the static part is called static seal.

The connection modes between the cylinder and the end cover mainly include the following:

Integral type, riveted type, threaded connection type, flange type and pull rod type.

6) When the cylinder is working, the piston should be lubricated by oil mist in compressed air. There are also a few unlubricated cylinders.