Hydraulic cylinders are becoming more and more widespread in our lives now, but we don't know much about their working principles and their classification. We need to understand their basic knowledge first, in order to better grasp the use method. The following editor will give you the details. Let's take a look at the classification and working principle of hydraulic cylinders.
First, the classification of hydraulic cylinders
There are various structural forms of hydraulic cylinders, and there are many classification methods: according to the movement mode, it can be divided into linear reciprocating motion type and rotary swing type; according to the hydraulic pressure, it can be divided into single-acting type and double-acting type; The form can be divided into piston type, plunger type, multi-stage telescopic sleeve type, rack and pinion type, etc.; according to the installation form, it can be divided into tie rod, earring, foot, hinge shaft, etc.; according to the pressure level, it can be divided into 16Mpa, 25Mpa , 31.5Mpa, etc.
1. Piston
Single-rod hydraulic cylinders only have a piston rod at one end. As shown in the picture is a single-piston hydraulic cylinder. Both the inlet and outlet ports A and B at both ends can pass pressure oil or return oil to achieve bidirectional movement, so it is called a double-acting cylinder.
The piston can only move in one direction, and the movement in the opposite direction needs to be done by external force. However, its stroke is generally larger than that of a piston hydraulic cylinder.
Piston hydraulic cylinders can be divided into two types: single rod type and double rod type. The fixing methods are fixed by the cylinder body and fixed by the piston rod. According to the effect of hydraulic pressure, there are single-acting type and double-acting type. In a single-acting hydraulic cylinder, the pressure oil is only supplied to one cavity of the hydraulic cylinder, and the hydraulic pressure makes the cylinder move in one direction, and the opposite direction movement is realized by external force (such as spring force, self-weight or external load, etc.); The movement of the piston in the two directions of the action hydraulic cylinder is completed by the action of hydraulic pressure through the alternate oil intake of the two cavities.
Schematic diagram of a single-rod double-acting piston hydraulic cylinder. It is only provided with a piston rod on one side of the piston, so the effective working areas of the two chambers are different. When the oil supply amount is the same, different cavities enter oil, and the movement speed of the piston is different; when the load force to be overcome is the same, different cavities enter oil, and the required oil supply pressure is different, or after the system pressure is set, the sanitation The load force that can be overcome by the hydraulic cylinder of the garbage truck in two directions is different.
2. Plunger
(1) The plunger hydraulic cylinder is a single-acting hydraulic cylinder, which can only move in one direction by hydraulic pressure, and the return stroke of the plunger depends on other external forces or the self-weight of the plunger;
(2) The plunger is only supported by the cylinder liner without contacting the cylinder liner, so the cylinder liner is very easy to process, so it is suitable for long-stroke hydraulic cylinders;
(3) The plunger is always under pressure during operation, so it must have sufficient rigidity;
(4) The weight of the plunger is often large, and it is easy to sag due to its own weight when placed horizontally, causing the wear of the seal and the guide unilateral, so it is more advantageous to use it vertically.
telescopic
The telescopic hydraulic cylinder has two or more stages of pistons. The order of the extension of the piston in the telescopic hydraulic cylinder is from large to small, while the order of no-load retraction is generally from small to large. The telescopic cylinder can achieve a longer stroke, while the retracted length is shorter and the structure is more compact. Such hydraulic cylinders are often used in construction machinery and agricultural machinery. There are multiple pistons that move at one time. When each piston moves successively, its output speed and output force change.
Double acting single piston rod hydraulic cylinder
3. Swing
The oscillating hydraulic cylinder is an executive element that outputs torque and realizes reciprocating motion. There are several forms such as single blade, double blade and spiral swing. Vane type: The stator block is fixed on the cylinder, and the vane and the rotor are connected together. According to the oil inlet direction, the vanes will drive the rotor to swing back and forth. The helical swing type is divided into two types: single helix swing and double helix. Now the double helix is more commonly used. The linear motion of the piston in the hydraulic cylinder of the two helical pairs is converted into a compound motion of linear motion and self-rotation motion, thereby realizing the swing motion.
Second, the working principle of hydraulic cylinder
Hydraulic cylinder is the actuator in the hydraulic transmission system, which is an energy conversion device that converts hydraulic energy into mechanical energy. The hydraulic motor realizes the continuous rotary motion, while the hydraulic cylinder realizes the reciprocating motion. There are three types of hydraulic cylinders: piston cylinder, plunger cylinder and swing cylinder. Piston cylinder and plunger cylinder realize reciprocating linear motion, output speed and thrust, and swing cylinder realizes reciprocating swing, output angular velocity (rotation speed) and torque. In addition to being used singly, hydraulic cylinders can also be used in combination of two or more or in combination with other mechanisms. to perform 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.
