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Key points of radial piston pump

Key points of radial piston pump (l) As mentioned above, radial piston pump has a small application range, and in the ordinary hydraulic system with mineral based hydraulic oil as working medium, radial piston pump with clearance sealing port pair is more and more replaced by axial piston pump (swash plate or swash shaft type). The scope of application of the two is roughly the same, and the oil absorption performance of the radial pump is generally better. The radial piston pump is one of the smallest and largest two-way variable displacement pumps in the hydrostatic driving device of walking machinery for continuous operation. The former is used for garden mower with power less than 3KW, while the latter is used for armored combat vehicle with power up to 500kW. The common characteristics of these two kinds of radial pumps are that they both use steel ball piston, both are axial flow distribution, and both are "back-to-back" assembled together with a quantitative motor with similar structure to form an integral hydraulic transmission. The traditional application field of valve distribution type radial piston pump is a variety of high-pressure and ultra-high-pressure hydraulic tools, such as various presses, material testing machines, steel pre-stressed tensioning machines, jacks, riveters, cutting tongs and various mechanical or manual hydraulic tools. Another important use of them is in mining, metallurgy, chemical industry and other equipment that need to use Refractory working fluid. In recent years, this kind of pump has been widely used in automobile hydraulic power steering system and hydraulic suspension system of some agricultural tractors, many of which can achieve variable special performance by controlling oil absorption. The axial flow radial piston pump is mainly used in the hydraulic system of some heavy machine tools. (2) Parameter selection and selection can refer to the method of axial piston pump. (3) Precautions radial piston pump use precautions are basically the same as the axial piston pump. In use, the relevant terms of the product manual should be carefully studied and installed and operated according to its requirements. For example, some pumps must be deflated before they are first used, so as to avoid damaging the pump. If the pump does not discharge foam oil after running 20s, the hydraulic system must be inspected. After the pump reaches the prescribed operation data, the pipeline should be checked whether the leakage is over, and the oil temperature is exceed the standard. . 5.1.7 troubleshooting The common faults of radial piston pump in use include no oil delivery or insufficient oil quantity, pressure can not rise or insufficient pressure, abnormal flow and pressure, excessive noise, abnormal heating and leakage, etc. the general methods of fault diagnosis and troubleshooting can refer to the axial piston pump for troubleshooting.

Gear motor

Gear motor 2.2.1 type characteristics (l) Classified gear motor is a hydraulic motor based on meshing principle, which belongs to high-speed hydraulic motor. It is the simplest structure of various hydraulic motors. Its detailed classification is shown in Figure y. Among them, the two gear type involute external gear motor is most widely used. (2) The characteristics are shown in the table below.   Characteristics of gear motor type Main advantage Main Disadvantages Involute external gear motor ①Simple structure and good processability ①The starting torque is relatively small; Large output torque ripple ②Small size, light weight ②inefficient ③Strong anti pollution ability ③Poor low-speed stability ④Impact resistant, low inertia ④High noise level Cycloid internal meshing gear motor ①Small size, light weight, high power to weight ratio complex structure ②High output torque ③Wide speed range ④Low price     2.2.2 working principle (l) Working principle of two gear type involute external gear motor and some problems needing attention ① The working principle diagram Z shows the working principle of two gear type involute external meshing gear motor. The centers of two meshing gears I and II are O1 and O2 respectively, and the radius of meshing point is R1 and R2 respectively. Gear I is an output shaft with a load. When the high pressure oil P1 (P2 is the return oil pressure) enters the oil inlet chamber of the gear motor, which is composed of the surfaces of teeth 1 ', 2', 3 'and 1', 2 ', 3', 4 'and the relevant inner surfaces of the shell and the end cover, because the radius of the meshing point is less than the radius of the addendum circle, the unbalanced oil pressure as shown by the arrow will be generated on the tooth surfaces of teeth 1' and 2 '. The hydraulic pressure generates torque for axes 01 and 02. Under the action of the torque, the gear motor rotates continuously in the direction shown in the figure. With the rotation of the gear, the oil is taken to the oil return chamber and discharged. As long as the pressure oil is continuously supplied to the gear motor, the motor will rotate continuously and output torque and speed. In the process of gear motor rotation, the output torque of the motor is pulsating because the meshing point constantly changes position. ② Compared with gear pump, gear motor has the following problems. a. The gear motor has the requirement of forward and reverse rotation, so the internal structure and oil passage are symmetrical. b. The oil in the low-pressure cavity of the motor is squeezed out by the gear, so the pressure in the low-pressure cavity is slightly higher than the atmospheric pressure, so the motor will not produce cavitation phenomenon because of the high suction flow rate like the gear pump. c. Due to the back pressure of the oil return from the motor, in order to prevent the shaft end seal from being damaged during the forward and reverse rotation of the motor, a separate oil leakage port is set on the gear motor housing, so as to lead the leakage oil of the bearing part to the oil tank outside the housing, instead of leading the leakage oil to the low pressure chamber as the gear pump does. d. Gear pump provides pressure and flow, emphasizing the volumetric efficiency, while gear motor produces output torque, emphasizing the mechanical efficiency, and trying to have good starting performance and low minimum stable speed. In order to improve the starting performance, it is necessary to reduce the friction torque, the starting pressure and the dead zone (see figure a). To reduce the minimum stable speed is to make the motor run stably at a very low speed without crawling. Therefore, the following measures are usually taken. i. Needle bearings are often used to reduce the starting friction torque of the motor. II. Improve the lubrication and cooling conditions of bearings, especially ensure good lubrication at the moment of starting. III. reduce the radial force to reduce the load on the bearing, so as to reduce the friction torque. IV. the compression coefficient of the clearance compensation device should be reduced as far as possible, so that the compensation device only slightly contacts with the gear with a weak tightening force, so as to reduce the friction torque. 5. The number of teeth of gear motor is generally more than that of gear pump, so as to reduce the fluctuation of torque, reduce the minimum stable speed, improve the low-speed stability and improve the starting performance. In addition, increasing the number of teeth is also beneficial to reduce vibration and noise. The number of teeth Z1 of the gear connected with the output shaft of the motor is greater than or equal to 14. The number of teeth of high pressure gear pump is generally z = 6 ~ 14 (in order to prevent undercutting and weaken the root strength, the tooth profile should be modified).

Classification and expression of hydraulic pump and motor

Classification and expression of hydraulic pump and motor   1.3.1 classification (1) There are many types of hydraulic pumps and motors, and the classification methods and names vary with the focus. It can be divided into gear type, vane type, plunger type and screw type According to the periodic change of the working chamber, the volume of liquid entering and discharging can be adjusted, which can be divided into quantitative type and variable type. In addition, according to its speed and torque, hydraulic motors are traditionally divided into three types: high-speed small torque type and low-speed large torque type, and swing motor which can only realize limited angle rotation. Generally, the motor with rated speed higher than 500 R / min is called high-speed motor, while the motor with rated speed lower than 500 R / min is called low-speed motor. The basic forms of high-speed hydraulic motors include gear type, screw type, vane type and axial piston type. Their structures are similar to those of the same type of hydraulic pumps, and their working principles are reversible. However, due to their different purposes of use, there are many differences in their structures, which generally can not be directly reversed. High speed hydraulic motor has the advantages of high speed, small moment of inertia, easy to start and brake, high sensitivity of adjustment and commutation, but the output torque is small (only tens to hundreds of n · m). When driving low-speed load, acceleration and deceleration device is needed. The basic form of low-speed motor is plunger type, including single acting and multi acting. Low speed hydraulic motor has the advantages of large displacement, low speed, large output torque (up to thousands to tens of thousands of n · m), and can be directly connected with its working mechanism without deceleration device, but its volume is large. Swing hydraulic motor can be divided into piston type and vane type, and vane type is mostly used. The structure of the swing hydraulic motor is simpler than that of the continuous rotary hydraulic motor. The outstanding advantage of the swing hydraulic motor is that the output shaft directly drives the load to swing, without any speed change mechanism, the output torque can reach tens of thousands of n · m, and the minimum stable speed can reach 0.001 rad / s. (2) The detailed classification of hydraulic pump and hydraulic motor is shown in Figure B and figure C. A 1.3.2 graphic symbols (1) The graphic symbols of common hydraulic pumps and motors and their significance the schematic diagrams of hydraulic components and systems including hydraulic pumps and motors are generally drawn with standard graphic symbols. As the graphic symbols only represent the function, operation (control) method and external connection of hydraulic components, but not the specific structure, performance parameters, actual position of connection and installation position of components, they are used to express the functions of various components in the system and the composition, oil circuit connection and working principle of the whole system. They are simple and clear, and convenient for drawing and technical exchange . In 1965, 1976, 1993 and 2009, China promulgated the hydraulic graphic symbol standards. The current standard is GB / T 786.1-2009 fluid power systems and components - Graphical symbols and circuit diagrams - Part 1: Graphical symbols for general use and data processing. The standard establishes the basic elements of various symbols (including line, connection and pipe joint, flow path and direction indication, basic mechanical elements, control mechanism elements, regulation elements, etc.), and formulates the design and application rules of hydraulic and pneumatic components (hydraulic: valve, pump and motor, cylinder, accessories; pneumatic: valve, air compressor and motor, cylinder, accessories) and symbols in circuit diagram (including The CAD symbols are introduced in the form of informative appendix. The graphic symbols of common hydraulic pumps and motors drawn in GB / T 786.1-2009 are shown in the table below, and the meaning of the graphic symbols is as follows. A ④ The graphic symbol of hydraulic pump is represented by a circle plus a solid equilateral triangle or two solid equilateral triangles. The outward arrow of equilateral triangle indicates the direction of pressure oil. A solid triangle for one-way pump, two solid triangle for two-way pump. The upper and lower vertical line segments of the circle represent the oil drain and oil suction pipes (oil ports) respectively. No arrow for quantitative pump, arrow for variable pump. The double line and arc arrows on the side of the circle represent the pump drive shaft and the rotary motion respectively. ② The graphic symbol of hydraulic motor is represented by a circle plus a solid equilateral triangle or two solid equilateral triangles. The inward arrow of equilateral triangle indicates the direction of pressure oil. One solid equilateral triangle represents unidirectional motor, and two solid equilateral triangles represent bidirectional motor. The upper and lower vertical line segments of the circle represent the oil inlet and oil outlet respectively. The motor without arrow is quantitative motor, and the motor with arrow is variable motor. The double horizontal and arc arrows on the side of the circle indicate the motor drive shaft and the rotary motion respectively. (2) Precautions for the use of graphic symbols the following precautions should be paid attention to when using GB / T 786.1-2009 to draw the schematic diagram of hydraulic components and systems. ① According to the size and needs of the drawing, the size of the graphic symbols of the components can be changed according to the appropriate proportion to draw, based on the principle of clear and beautiful. ② The components and circuit diagrams are generally drawn in the non working state without excitation (such as the working position of electromagnetic directional valve after power failure). ③ On the premise of not changing the meaning of the initial state defined in the standard, the direction of the component can be drawn according to the specific situation of horizontal turnover or 90 ° rotation, but the hydraulic tank must be drawn horizontally and the opening upward.

Working principle of axial piston motor

Working principle of axial piston motor (1) Type axial piston motor and axial piston pump are opposite in principle, so the structure of axial piston motor is basically the same as that of axial piston pump. However, in order to meet the requirements of forward and reverse rotation of the hydraulic motor, the structure of the valve plate and the size and shape of the oil inlet and outlet channels are generally completely symmetrical. At present, there are two basic types of axial distribution mechanism (axial distribution valve) and swash plate piston motor. (2) The main advantages of axial piston motor are compact structure, high power density, high working pressure, easy to realize variable, rich variable mode and high efficiency. The disadvantages are complex structure, high price, poor anti pollution ability and high maintenance requirements. working principle Take the straight axis (swash plate) axial piston motor shown in Figure r as an example to illustrate the working principle of the axial piston motor. When the pressure oil enters into the oil inlet chamber of the motor, the slipper will be pressed against the swashplate by the force. The axial component FX (parallel to the axis of the plunger) of the reaction force n is balanced with the hydraulic pressure on the plunger. The vertical component FY of the reaction force n (perpendicular to the axis of the plunger) generates torque on the cylinder and motor axis, driving the hydraulic motor to rotate and deliver oil It can generate mechanical energy. The speed and rotation direction of the motor can be changed by changing the size and direction of the swash plate angle. Most axial piston motors with straight shaft (swash plate) end face distribution and axial piston pumps with the same structure can be used against each other. The variable of axial piston high-speed hydraulic motor is similar to that of axial piston pump, which is realized by changing the angle of swash plate or swash shaft. The method of electro-hydraulic control is often used. The speed sensor or pressure sensor feeds back the changing speed or pressure to the electro-hydraulic proportional valve or servo valve with electricity to control the movement of the variable piston of the motor and realize the constant speed or pressure control of the hydraulic motor. This kind of control is easy to carry out the dynamic correction of the regulation process, and the best control can be achieved with the help of microcomputer. In order to make full use of the power of prime mover in the variable process of high-speed small torque and low-speed large torque, constant power variable motor can be used. In the constant current source system (that is, the flow of the pump source is basically constant), as long as the pressure difference between the inlet and outlet of the motor remains unchanged, the constant power control of the motor can be achieved approximately. Figure s shows the principle of constant power variable of axial piston motor. The variable piston of bidirectional variable displacement motor 2 is controlled by constant pressure control valve 5. If the load torque of the motor increases for some reason, in the constant current source system, when the motor displacement has not changed, its inlet pressure will increase. This pressure acts on the end of the spool of the constant pressure control valve 5, overcomes the spring force to move the spool to the left, and the piston of the variable cylinder l moves to the left, which increases the displacement of the motor, so the inlet pressure of the motor decreases. At the end of the adjustment process of the variable control system, when the variable piston stops, the valve core of the constant pressure control valve must be in the middle position, that is, the hydraulic pressure at the right end of the valve core is balanced with the spring preload at the left end. This means that regardless of the system load, the inlet pressure of the variable displacement motor remains constant throughout the adjustable range of the variable displacement motor. Since the oil source is a constant flow system, the constant power control of the motor is maintained by keeping the inlet pressure of the motor unchanged. When the load of the motor increases, the motor runs at a relatively large displacement, the speed decreases and the output torque increases, and the power basically remains constant. The control of the motor is a closed loop control system. In order to make the system stable and get higher response speed, it is necessary to set the gain and damping of the system properly. Throttle valve 4 is used to adjust the damping of the system, so that the system can get the fastest response speed under the premise of stability.

Troubleshooting of Gear Pump

Troubleshooting of Gear Pump Troubleshooting The following table is gear pump in the use of some common fault phenomena and troubleshooting.   Gear pump in the use of some common fault phenomena and troubleshooting Fault phenomenon Cause analysis Exclusion method 1. There is no oil or pressure in the pump (1) The rotation direction of prime mover and pump is inconsistent (1) Correct the rotation direction of prime mover (2) Pump drive key off (2) Re install the drive key (3) The oil inlet and outlet are connected reversely (3) Select the correct connection method according to the instruction manual (4) The oil level in the oil tank is too low, and the liquid level of the suction pipe is exposed (4) Replenish the oil above the minimum level line (5) Too low speed and insufficient suction (5) Increase the speed above the minimum speed of the pump (6) Oil viscosity too high or too low (6) Select the working oil with recommended viscosity (7) Blockage of suction pipe or filter device results in poor oil absorption (7) Choose the right filter according to the pump and instruction (8) Poor oil absorption due to high suction pipe or filtration accuracy (8) Choose the right filter according to the sample and instruction (9) Air leakage in suction pipe (9) Check the joints of pipes, seal and fasten them 2. The flow is not enough to reach the rated value (1) The speed is too low to reach the rated speed (1) Select the prime mover speed according to the rated speed specified in the product sample or instruction manual (2) There is a leak in the system (2) Check the system and repair the dew point (3) Because the pump works for a long time and vibrates, the connecting screw of the pump cover is loose (3) Tighten the screws properly (4) Same as table 1. (9) (4) Same as table 1. (9) (5) Insufficient oil absorption: ① Same as table 1. (9) ② The inlet filter is blocked or the flow rate is too small ③ The suction pipe is blocked or the diameter is small ④Improper viscosity of the medium (5) Solution to insufficient oil absorption: ① Same as Table 1. (9) ② Clean the filter or choose a filter with a flow rate that is more than twice the pump flow rate ③ Clean the pipeline and select a suction pipe with a diameter not less than the pump inlet diameter ④ Choose the recommended viscosity working medium 3.The pressure cannot rise (1)The pump cannot pump oil or the flow rate is insufficient (1)Same as Table 1. (2)The set pressure of the relief valve in the hydraulic system is too low or there is a malfunction (2)Reset the pressure of the overflow valve or repair the overflow valve (3)Same as Table 2.(2) (3)Same as Table 2.(2) (4)Same as Table 2.(3) (4)Same as Table 2.(3) (5)Same as Table 1.(9) (5)Same as Table 1.(9) (6)Same as Table 2.(5) (6)Same as Table 2.(5)    

Working principle of single acting radial piston motor

Working principle of single acting radial piston motor As there are two main types of radial piston motors, namely single acting and multi acting, their working principles are introduced in the following. (1) Working principle of single acting radial piston motor As shown in Figure o, five (or seven) cylinders are radially and evenly arranged along the circumference of the housing 1. The plunger 2 in the cylinder is connected with the connecting rod 3 through the ball hinge, and the end of the connecting rod contacts with the eccentric wheel of the crankshaft 4 (the center of the eccentric wheel is O1, the rotation center of the crankshaft is O, and the eccentricity of the two is e). One end of the crankshaft is the output shaft, and the other end is through the cross The coupling is connected with the valve distribution shaft 5. Two sides of the partition wall on the valve distribution shaft are oil inlet chamber and oil discharge chamber respectively. After the high-pressure oil from the oil source enters into the oil inlet chamber of the motor, it is introduced into the corresponding piston cylinder (1), cylinder (2) and cylinder (3) through the slots (1), cylinder (2) and cylinder (3) of the housing. The hydraulic force P produced by the high pressure oil acts on the top of the plunger and is transmitted to the eccentric of the crankshaft through the connecting rod. For example, the force acting on the eccentric by the piston cylinder ② is n, and the direction of the force is along the center line of the connecting rod and points to the center O1 of the eccentric. The force n can be divided into normal force FF (the line of action coincides with the connecting line 001) and tangential force F. The tangential force F produces a torque to the rotation center 0 of the crankshaft, which makes the crankshaft rotate counterclockwise around the center line 0. The piston cylinder (1) and (3) are similar to this, except that their position relative to the spindle is different, so the torque generated is different from that of cylinder (2). The total torque of crankshaft rotation is equal to the sum of the torque generated by the piston cylinder connected with the high-pressure chamber (①, ② and ③ in the case of figure o). When the crankshaft rotates, the volumes of cylinders ①, ② and ③ increase, while the volumes of cylinders ④ and ⑤ decrease, and the oil is discharged through the oil passage of the shell ④ and ⑤ through the oil discharge chamber of the port shaft 5. When the valve distribution shaft and crankshaft rotate synchronously for an angle, the "partition wall" of the valve distribution shaft closes the oil passage (3). At this time, the cylinder (3) is not connected with the high and low pressure chambers. Cylinders (1) and (2) are supplied with high pressure oil, which makes the motor produce torque, and cylinders (4) and (5) discharge oil. As the valve distribution shaft rotates with the crankshaft, the oil inlet chamber and the oil discharge chamber are respectively connected with each plunger in turn, so as to ensure the continuous rotation of the crankshaft. In one revolution, each plunger reciprocates the oil in and out once. The working principle of other single acting motors is similar to this. The working principle of single acting radial piston motor should pay attention to the following points. ① The motor can be reversed by changing the inlet and outlet of the motor. If the eccentric ring is separated from the output shaft of the motor and measures are taken to make the eccentric distance adjustable, the purpose of changing the displacement of the motor can be achieved, and the variable displacement motor is made. ② The motor shown in Figure o is shell fixed, so it is also called shaft motor; if the crankshaft is fixed, it can be made into shell motor. The shell motor is especially suitable for installation in the winch drum or on the wheel hub of the vehicle to directly drive the wheel and become the wheel motor. ③ The motor shown in Figure o of distribution pair is axial distribution. Because one side of the valve shaft is a high-pressure cavity and the other side is a low-pressure cavity, the working process of the valve shaft is subject to a large radial force, which pushes the valve shaft to one side and increases the gap on the other side, resulting in the wear of the sliding surface and the increase of leakage, resulting in the decrease of efficiency. For this reason, it is often adopted to set up a symmetrical balancing oil groove to balance the radial force. As shown in Figure P, the static pressure balance valve distribution shaft is sealed by a sealing ring. The central C-C window hole is the valve distribution window hole, the annular grooves on B-B and D-D are the oil inlet and oil return window holes respectively, and A-A and E-E are the static pressure balance semicircular annular grooves. It is assumed that the sealing rings are respectively placed in the center of the sealing belt. If the direction of oil inlet and outlet is as shown by the arrow in Figure P, the holes marked with the symbol P are high-pressure chambers, and the holes marked with the symbol T are low-pressure chambers. It can be seen that the circumferential pressures of B-B and D-D are the same, and there is no radial force; the upper chamber of C-C window hole section is connected with the oil inlet, which is the high pressure side, and the lower chamber is connected with the oil return port, which is the low pressure side, so the valve distribution shaft is subject to great radial force. In order to balance the radial force, semicircular annular balancing oil grooves A-A and E-E are set at both ends of the valve distribution shaft to make the upper cavity filled with high pressure oil. In order to reduce leakage, sealing rings are set between the cavities. In order to ensure the static pressure balance of the upper and lower sides, the relevant dimensions of the oil distribution window and the balance oil groove should meet the following equation: a+e=2(b+c) (5-4) Where a -- width of flow distribution window; B -- width of sealing belt of balance oil tank; C -- width of balance oil tank; E -- the width of the sealing belt of the flow distribution window. Because the radial force is balanced, the friction force is very small, which improves the mechanical efficiency. At the same time, the radial clearance between the valve shaft and the valve sleeve is reduced, the leakage is reduced, and the volumetric efficiency is improved. In the normal working range, the total efficiency is between 85% and 90%. Figure Q shows the end face flow distribution structure of the crankshaft connecting rod hydraulic motor. The crankshaft 13 drives the port plate 4 and the pressure plate 2 to rotate synchronously through the square head 12, and the port is realized during the rotation. During start-up or no-load operation, the backup spring (disc spring) 3 makes the valve plate and pressure plate close to the cylinder block 11 and the end cover. The design ensures that the close force is greater than the separation force between the valve plate and the cylinder block, and the hydraulic pressure realizes the close force during operation. However, due to the non coincidence of separation force and sticking force, the valve plate has tilting moment. By using the static pressure balance structure design, the end face port pair can achieve complete balance in theory. It should be pointed out that in order to improve the reliability and performance of the hydraulic motor and make its structure more compact, one of the development trends at home and abroad is to use the end port pair. ④ In addition to the port pair, the performance of the crankshaft connecting rod hydraulic motor largely depends on the connecting rod motion pair. The typical structure of connecting rod ball joint pair is shown in Figure R. It consists of two pairs of friction pairs, the ball head of connecting rod 4 and the ball socket of plunger 2, the bottom of connecting rod slider 5 and crankshaft (eccentric wheel) 6. The metal contact between the bottom of the connecting rod slider and the crankshaft (eccentric wheel) was in the early stage, and the wear-resistant alloy was cast at the bottom of the slider to reduce the friction. Some motor crankshafts (eccentric wheels) are equipped with roller bearings, which use rolling friction to replace the sliding friction between the bottom of the slider and the eccentric wheel; at present, most motors are designed as hydrostatic balance or hydrostatic support. An oil chamber is set at the bottom of the slider, and the pressure oil enters the bottom oil chamber through the damper in the center of the connecting rod. The sliding block doesn't float during the operation, the liquid pressure in the oil chamber balances most of the plunger thrust, and the friction pair is well lubricated.

Variable mechanism of axial piston pump

Variable mechanism of axial piston pump The type and characteristics of variable mechanism axial piston pump is easy to adjust the output flow under the condition of constant pump speed by adjusting the displacement, so as to adapt to the different flow requirements of the hydraulic system, and achieve significant energy saving effect, which is one of the advantages of piston pump compared with gear pump and vane pump. The mechanism to adjust the parameters is called variable mechanism. When the hydraulic pump works under a certain pressure, there should be force to push the variable mechanism. This force is called external control when it is supplied by external energy, and internal control when it is generated by the hydraulic pressure of pump or motor itself. The external control variable displacement pump usually uses a set of control oil source to provide the hydraulic pressure of the variable displacement mechanism. The control oil source is not affected by the load and pressure fluctuation of the pump itself, so it is relatively stable and can realize two-way variable displacement. Internal control variable displacement pump does not need any additional pump source, but because the pump is in the zero displacement condition, there is no flow output, so the variable mechanism can not continue to move, so that the pump displacement is reversed, so that the pump will stay in the zero displacement position, that is, it can not achieve two-way variable displacement. No matter external control or internal control, the variable mechanism of axial piston pump has many kinds of classification: according to the way of control force, it can be divided into manual control, mobile control, electric control, hydraulic control and electro-hydraulic control; according to the purpose of control regulation, it can be divided into pressure control, flow control and power control; according to the control information, it can be divided into load sensing, speed sensing and pressure sensing. In this paper, the characteristics and application fields of manual, mobile, electric, hydraulic and electro-hydraulic control variable mechanisms are briefly introduced from the angle of control force. a. Manual variable mechanism, which is the simplest variable mechanism, usually uses the hand wheel to adjust the swash plate angle through the screw mechanism. For example, A4VSO series Ma controlled plunger pump. When adjusting, manpower must overcome all kinds of resistance of variable mechanism, and the adjusting speed is low. Because the hand control force is not big enough, it is mostly used for the load adjustment of small displacement light series pumps and the no-load adjustment of large displacement pumps. In addition, manual variable mechanism can not realize remote control. In order to adjust the displacement in operation, manual servo control can be used. The servo valve is operated by hand. Through hydraulic amplification, the variable piston drives the variable mechanism to act. A certain position of the control handle corresponds to a certain displacement of the pump. Manual servo control reduces the manual control force, but it still can not achieve remote control. b. Motorized or electronically controlled variable mechanism variable mechanism can also be driven by other mechanisms (i.e. motorized control) or controlled by servo motor, stepping motor and other control motors (i.e. electronically controlled). For example, A4VSO series EO controlled piston pump. For the electric control form, if the output parameters of the pump (flow, pressure or motor torque, speed, etc.) are changed into electricity by sensors, the output can be fed back to form a closed-loop control. Electronic control can also realize remote control. Motorized or electronically controlled variable mechanism is suitable for fixed equipment. c. Hydraulic control variable mechanism if the variable mechanism is driven by the controlled oil pressure through the hydraulic cylinder, it is the hydraulic control variable, which is a variable mechanism used by most straight axis swash plate pumps. For example, A4VSO series HD controlled plunger pump. There are several common arrangements of hydraulic control variable displacement mechanism: single double acting variable displacement cylinder parallel to or slightly inclined to the transmission shaft of the pump in longitudinal centralized arrangement (for medium and light series pumps); two or four smaller single acting variable displacement cylinders parallel to or slightly inclined to the transmission shaft of the pump in longitudinal decentralized arrangement (for heavy series pumps) to make full use of the space in the pump shell; transverse arrangement In the end cover (mostly used for non through shaft pump) or side cover, etc. Simple hydraulic control can only be open-loop control, through a variety of control valves and hydraulic circuits can form a closed-loop control, forming a variety of variable displacement pumps with different functions. d. The movement of the piston of the variable displacement mechanism is controlled by the electro-hydraulic servo valve or the electro-hydraulic proportional valve, which becomes the electro-hydraulic variable displacement pump. A4VSO series DFE controlled plunger pump. The variable mechanism of electro-hydraulic control has good controllability and can form different forms of feedback, but its structure is complex. The electro-hydraulic servo control can achieve a higher working frequency, but the variable mechanism of the hydraulic pump has large inertia and low structure frequency, so the electro-hydraulic servo valve can not fully play its role, the anti pollution ability is poor, and the price is expensive. The frequency response of variable mechanism controlled by electro-hydraulic proportional valve is enough. Because the proportional valve is cheap and not as sensitive to oil pollution as servo valve, its application is gradually increasing.

Function and basic principle of hydraulic pump and motor

Function and basic principle of hydraulic pump and motor   1.1 working principle and composition of hydraulic system Hydraulic technology is a kind of technology which takes liquid as working medium and uses the static pressure of liquid in closed system to realize the transmission of information, motion and power and engineering control. A complete hydraulic system is composed of four types of hydraulic components and working media: energy components (hydraulic pump), executive components (hydraulic cylinder, hydraulic motor and swing hydraulic motor), control components (various hydraulic control valves) and auxiliary components (oil tank, filter and pipe fittings). When the mechanical equipment or device of hydraulic transmission and control works, its hydraulic system takes the hydraulic oil with continuous flow as the working medium. Through the hydraulic pump, the mechanical energy of the prime mover (motor or internal combustion engine) driving the pump is converted into the pressure energy of the liquid, and then through the closed pipeline and control valve, it is sent to the actuator, which is converted into mechanical energy to drive the load and realize the work Make the required movement of the mechanism. 1.2 function and basic principle of hydraulic pump and motor 1.2.1 function and importance Hydraulic pump is an indispensable energy component of any hydraulic mechanical equipment, whose function is to convert the mechanical energy of prime mover into hydraulic energy, that is, to provide the hydraulic system with a certain pressure and flow of liquid; and hydraulic motor is any hydraulic mechanical equipment or working mechanism that needs rotary movement (such as various industrial production machinery, military equipment rotary working mechanism and various vehicles) The function of the actuator is to convert the hydraulic energy into mechanical energy, and drive the working mechanism connected with it to do work in the form of torque and speed. The function principle of hydraulic pump and hydraulic motor is opposite to each other, but the structure is similar, and both of them occupy a considerable proportion in hydraulic technology. In the development of all kinds of hydraulic equipment and the design and use of hydraulic system, the correct and reasonable selection, use and maintenance of hydraulic pump and hydraulic motor is of great significance to improve the working quality and reliability of hydraulic system and even the whole hydraulic equipment. Therefore, the design and manufacture personnel, installation and debugging personnel and on-site use and maintenance personnel of hydraulic technology must master the working principle, type structure, technical characteristics and use and maintenance methods of hydraulic pump and hydraulic motor. 1.2.2 basic principle In the hydraulic system, there are many types of hydraulic pumps and motors (such as gear type, vane type, plunger type, etc.) with different structures, but they are all volumetric, that is, they all work based on the change of one or several seal volumes. Figure a shows a reversible hydraulic device: it can be used as both a hydraulic pump and a hydraulic motor. Its structure is described as follows: the eccentricity of eccentric cam 1 and 3 is e, and the eccentricity of eccentric cam 2 is e. The rotation centers 01, 02 and 03 of the three cams are connected and driven by the same transmission shaft 4 (rotor). Cams 1 and 3 control the opening or closing of check valves 5 and 7; cam 2 keeps contact with plunger 6 (squeezer), and the three cams are guaranteed to contact with parts 5, 6 and 7 by corresponding springs. The plunger can move back and forth in the hole of the cylinder block (stator) 8, and a sealing working cavity 12 with variable volume is formed between the cylinder block and the plunger. Now take figure a as an example to analyze and discuss the basic working principle of hydraulic pump and hydraulic motor. (1) Basic principle of hydraulic pump When the device shown in Fig. A is used as a hydraulic pump, the prime mover drives the transmission shaft 4 (rotor) to rotate clockwise as shown in the figure, then the three cams rotate along with the transmission shaft in a clockwise direction. Suppose the pump starts to rotate from the position shown in Fig. a (a), then the plunger 6 moves down, the volume of the sealing working chamber 12 increases, and a vacuum is generated; at the same time, the cam 3 opens the oil suction check valve 7 (instead of the piston) The cam 1 just closes the drain check valve 5). Under the action of atmospheric pressure, the oil in the open oil tank (not shown in the figure) is sucked into the sealing working chamber 12 through the oil inlet a, the oil suction check valve 7 and the oil passage B, which is the oil suction process. When the rotor continues to rotate to the position shown in Fig. a (b), the plunger 6 is compressed and moved upward by the cam 2, the volume of the seal working cavity 12 decreases, and the oil absorbed in the cavity is compressed and the pressure increases to discharge the oil; at the same time, the cam 1 just opens the oil discharge check valve 5 (while the cam 3 just closes the oil suction check valve 7), and the oil is transported through the oil passage C, the oil discharge check valve 5 and the oil discharge port D The oil is discharged to the system. The transmission shaft rotates for one circle, pumping and discharging oil once respectively. When the prime mover drives the transmission shaft to rotate continuously, the hydraulic pump continuously absorbs oil from the oil inlet a and discharges oil to the system from the oil outlet D. If the prime mover drives the transmission shaft or rotor to rotate counterclockwise, the oil flow will be reversed, that is, the pump will absorb oil through port D and discharge oil to the system through port a. The single plunger hydraulic pump has the basic structural principle characteristics of the displacement hydraulic pump. ① There are three parts called stator, rotor and squeezer, which vary with the structure of hydraulic pump. ② There are several sealed spaces which can change periodically. This space is called working cavity. It is generally composed of stator, rotor and squeezer. The working cavity is called oil suction cavity when it has oil suction function and oil discharge cavity when it has oil pressure function. The transition zone between oil suction cavity and oil discharge cavity is sealed by the surface of relevant parts. In order to change the volume of the working cavity, there must be a relative moving squeezer in the parts of the working cavity. The squeezer can make the volume of the working cavity periodically from small to large and continuously absorb the liquid; it can make the volume of the working cavity periodically from large to small and continuously discharge the liquid. ③ The utility model has an oil suction port and an oil discharge port. The two oil ports are respectively connected with the oil suction cavity and the oil discharge cavity. The flow area of the oil suction port of the hydraulic pump should be large enough to avoid cavitation and cavitation due to the high flow rate of the oil in it; the flow rate of the oil discharge port of the pump can be large enough to reduce the size and weight of the pipeline. ④ The input parameters of hydraulic pump are mechanical parameters (torque and speed), and the output parameters are hydraulic parameters (pressure and flow). The pressure of the oil suction chamber of the hydraulic pump depends on the oil suction height and the pressure loss caused by the resistance of the oil suction pipeline; the pressure of the oil discharge chamber depends on the pressure loss caused by the load and the resistance of the oil discharge pipeline. The theoretical oil displacement of the hydraulic pump is directly proportional to the volume change (or geometric dimension) of the working chamber and the number of changes (or rotational speed) per unit time, but has nothing to do with the oil displacement pressure and other factors. If the theoretical displacement of the pump can not be changed, it is a constant displacement pump, otherwise it is a variable displacement pump. ⑤ It has a valve mechanism (also known as a valve). The conversion of hydraulic pump from oil suction to oil discharge or from oil discharge to oil suction is called valve distribution. In order to ensure that the hydraulic pump regularly sucks and discharges the liquid, it should have the corresponding flow distribution mechanism to separate the oil suction cavity from the oil discharge cavity, so as to ensure that the pump regularly sucks and discharges the liquid. According to the different structure of the hydraulic pump, there are two kinds of flow distribution: the deterministic flow distribution relies on the hole or groove in the proper position of a part of the pump to realize the flow distribution. Most hydraulic pumps adopt this flow distribution mode, which generally has the reversibility as a hydraulic motor; the valve type flow distribution relies on the check valve to realize the flow distribution (the oil suction and discharge valves are in logic) It is often used in ultra-high pressure piston pump. Because the flow direction of this kind of pump can not be changed sometimes, it loses its reversibility as a hydraulic motor. For example, as shown in figure a, the flow distribution mode of single plunger hydraulic pump is valve type with check valve (suction valve 7 and pressure valve 5). ⑥ The absolute pressure of the liquid in the tank must be equal to or greater than the atmospheric pressure. In order to ensure the normal oil absorption of the pump, the oil tank must be connected with the atmosphere or use a closed gas filled oil tank. (2) Basic principle of hydraulic motor when the device shown in figure a is used as hydraulic motor, the transmission shaft is no longer driven by prime mover, but connected with the working mechanism. The pressure oil is input from the oil inlet a as shown in Fig. a (a). The pressure oil enters into the working chamber 12 of the motor through the oil inlet check valve 7 and the flow channel B, and generates a hydraulic force on the upper end of the plunger 6 to push the plunger. Due to the existence of the eccentricity e of the cam 2, the force will form a torque on the rotation center 02 of the cam 2, making the cams and the transmission shaft 4 rotate clockwise, After the cam 2 rotates to the position shown in Fig. a (b), it still rotates clockwise to make the plunger 6 move up, and the oil that has been done in the working chamber 12 is discharged to the oil tank (not shown in the figure) through the flow channel C, one-way oil drain valve 5 and oil drain port D. due to the proper phase of cam 1 and 3, the oil drain valve 5 of the hydraulic pressure motor is closed when the oil is fed, and the oil inlet valve 7 is closed when the oil is drained, so as to realize the oil distribution Flow. If the pressure oil is continuously input from the oil inlet a of the hydraulic motor, the motor can drive the working mechanism connected with its transmission shaft to realize continuous clockwise rotary movement, and the used oil is continuously discharged from the oil drain valve 5. Similar to the situation of hydraulic pump, if the direction of the input oil is reversed, that is, the oil is fed from port D and discharged from port a, then the rotation direction of the transmission shaft or rotor will also be reversed, that is, it will rotate counterclockwise. The plunger type hydraulic motor has the basic structural principle characteristics of the displacement type hydraulic motor. ① Like the hydraulic pump, it also has three parts called stator, rotor and squeezer, which vary with the structure of the hydraulic motor. ② Like the hydraulic pump, it also has several sealed and periodically changeable working cavities, which are generally composed of stator, rotor and squeezer. The working cavity connected with the high-pressure oil is called oil inlet cavity or high-pressure cavity, and the working cavity leading to the oil tank is called oil discharge cavity or low-pressure cavity. The transition area between the oil suction cavity and the oil discharge cavity is sealed by the surface of the relevant parts. In order to change the volume of the working cavity, there must be a relative moving squeezer in the parts of the working cavity. Under the action of pressure oil, the extruder stretches out so that the volume of the working chamber changes from small to large periodically. Under the action of swashplate and other parts, the extruder retracts so that the volume of the working chamber changes from large to small periodically and the low-pressure liquid is discharged continuously. ③ Like the hydraulic pump, the hydraulic motor also has oil inlet and oil outlet, but the oil inlet and oil outlet of the motor are respectively connected with the high pressure chamber and the low pressure chamber. Because the pressure of the low pressure chamber of the hydraulic motor is slightly higher than the atmospheric pressure, different from the hydraulic pump, the size of the oil inlet and the oil outlet of the motor can be the same. The rotation direction of the hydraulic motor can be changed by changing or exchanging the oil inlet and outlet of the hydraulic motor. ④ The input parameters of hydraulic motor are hydraulic parameters (pressure and flow), and the output parameters are mechanical parameters (torque and speed). The pressure of the oil inlet chamber of the hydraulic motor depends on the pressure loss caused by the input oil pressure and the resistance of the oil inlet pipe, while the pressure of the oil outlet chamber depends on the pressure loss caused by the resistance of the oil outlet pipe. The theoretical oil displacement of the hydraulic motor is related to the volume change (or geometric dimension) of the working chamber, but not to the oil inlet pressure and other factors. If the theoretical oil displacement of the motor can not be changed, it is a quantitative motor, otherwise it is a variable motor. The output speed of the hydraulic motor depends on the input flow and displacement of the motor; the output torque depends on the displacement of the motor and the pressure difference between the inlet and outlet. ⑤ Like the hydraulic pump, the hydraulic motor also has a flow distribution mechanism, and its function is basically the same as that of the hydraulic pump. But because the motor needs to rotate forward and backward, the structure of the flow distribution mechanism of the hydraulic motor should be symmetrical. The flow distribution mode of hydraulic motor varies with the structure of the motor. Generally, there are two kinds of flow distribution mode: definite type and valve type. For example, as shown in figure a, the flow distribution mode of plunger type hydraulic motor is valve type with one-way valve. To sum up, the hydraulic pump and the hydraulic motor are two different energy conversion devices. In principle, the positive displacement hydraulic pump can be used as the hydraulic motor, that is, to input pressure oil into the hydraulic pump and force its transmission shaft to rotate, it becomes the hydraulic motor. But in fact, although the same type of pump and motor are similar in structure, many types of hydraulic pump and motor can not be used in reverse in practice due to the differences in use purpose, performance requirements and structural symmetry.
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