Hydraulic cylinder It is a hydraulic actuator that converts hydraulic energy into mechanical energy and performs linear reciprocating motion (or swing motion). It is simple in structure and reliable in operation. When it is used to realize reciprocating movement, the reducer can be avoided, and there is no transmission clearance, and the movement is stable, so it is widely used in various mechanical hydraulic systems. Output force of the hydraulic cylinder is proportional to effective area of the piston and pressure difference on both sides; The hydraulic cylinder is basically composed of cylinder barrel and cylinder head, piston and piston rod, sealing device, buffer device and exhaust device. The buffer device and exhaust device depend on the specific application, and other devices are indispensable.

I Hydraulic cylinder Classification of

Hydraulic cylinders have various structural forms, and their classification methods are also various: according to the motion mode, they can be divided into linear reciprocating motion type and rotary swing type; According to the action of hydraulic pressure, it can be divided into single action type and double action type; According to the structure, it can be divided into piston type, plunger type, multi-stage telescopic sleeve type, gear rack type, etc; According to the installation form, it can be divided into pull rod, earring, foot, hinge shaft, etc; According to the pressure grade, it can be divided into 16Mpa, 25Mpa, 31.5Mpa, etc.

1. Piston type

The single piston rod hydraulic cylinder only has a piston rod at one end. As shown in the figure, it is a single piston hydraulic cylinder. Both the inlet and outlet oil ports A and B at both ends can be supplied with pressure oil or return oil to realize two-way movement, so it is called double acting cylinder.

The piston can only move in one direction, and its reverse movement needs to be completed by external force. However, its stroke is generally larger than that of the piston type hydraulic cylinder.

The piston type hydraulic cylinder can be divided into single rod type and double rod type structures. Its fixing mode is fixed by the cylinder block and the piston rod. According to the action of hydraulic pressure, there are single acting type and double acting type. In the single acting hydraulic cylinder, the pressure oil is only used for one cavity of the hydraulic cylinder. The hydraulic pressure enables the cylinder to move in one direction, while the reverse movement is achieved by external forces (such as spring force, dead weight or external load); The movement of the piston in both directions of the double acting hydraulic cylinder is completed by the action of hydraulic pressure by alternately feeding oil into the two chambers.

The single rod double acting piston hydraulic cylinder is only equipped with a piston rod at one side of the piston, so the effective area of the two chambers is different. When the oil supply is the same, the movement speed of the piston is different with the oil inlet from different chambers; When the load force to be overcome is the same, the oil supply pressure required by different cavities is different, or after the system pressure is set, the load force that can be overcome by the hydraulic cylinder of the sanitation garbage truck moving in two directions is different.

2. Plunger type

(1) The plunger type hydraulic cylinder is a single acting hydraulic cylinder, which can only achieve movement in one direction by hydraulic pressure, and the return stroke of the plunger depends on other external forces or the weight of the plunger;

(2) The plunger is only supported by the cylinder liner and does not contact the cylinder liner, so the cylinder liner is very easy to process, so it is suitable for long stroke hydraulic cylinder;

(3) When working, the plunger is always under pressure, so it must have sufficient rigidity;

(4) The weight of plunger is often large, and it is easy to sag due to its own weight when it is placed horizontally, resulting in unilateral wear of seals and guides, so its vertical use is more favorable.

3. Telescopic

The telescopic hydraulic cylinder has two-stage or multi-stage pistons. The sequence of piston extension in the telescopic hydraulic cylinder is from large to small, while the sequence of no-load retraction is generally from small to large. The telescopic cylinder can achieve a longer stroke, while the length is shorter when retracted, and the structure is more compact. This kind of hydraulic cylinder is commonly used in construction machinery and agricultural machinery. There are multiple pistons moving at one time. When each piston moves step by step, its output speed and output force change.

4. Swinging type

Swinging hydraulic cylinder is an executive element that outputs torque and realizes reciprocating movement. It has several forms, such as single blade, double blade, spiral swing, etc. Vane type: the stator block is fixed on the cylinder block, while the blade and rotor are connected together. According to the oil inlet direction, the blade will drive the rotor to reciprocate. The spiral swing type can be divided into single spiral swing and double spiral swing. Now double spiral is more commonly used. The swing movement is realized by changing the linear movement of the piston in the hydraulic cylinder of the two screw pairs into the combined movement of linear movement and rotation movement.

2、 Working principle of hydraulic cylinder

The hydraulic cylinder is the actuating element in the hydraulic transmission system, which is an energy conversion device that converts hydraulic energy into mechanical energy. The hydraulic motor realizes continuous rotary motion, while the hydraulic cylinder realizes reciprocating motion. The structural types of hydraulic cylinders include piston cylinder, plunger cylinder and swing cylinder. The piston cylinder and plunger cylinder realize reciprocating linear movement, output speed and thrust, swing cylinder realizes reciprocating swing, output angular speed (speed) and torque. In addition to single use, hydraulic cylinders can also be used in combination with two or more or with other mechanisms. To accomplish special functions. The hydraulic cylinder is simple in structure and reliable in operation, and has been widely used in the hydraulic system of machine tools.