CN109404242B - A double swash plate three oil port axial distribution plunger type variable pump - Google Patents

Abstract

The invention belongs to the technical field of axial plunger type hydraulic pumps, and discloses a double-swash-plate three-oil-port axial flow distribution plunger type variable pump. The variable pump comprises a rotor, a cylinder body, a plurality of plungers, a swash plate component, a flow distribution device, a left end cover and a right end cover, wherein the left end cover and the right end cover are arranged on the left side and the right side of the cylinder body, the plungers are symmetrically distributed on the left side and the right side of the cylinder body respectively, a plurality of plunger cavities and a plurality of oil suction and discharge ports communicated with the plunger cavities are arranged inside the cylinder body, the flow distribution device comprises a flow distribution shaft, a first partition plate and a second partition plate which are arranged inside the flow distribution shaft, and two kidney-shaped flow distribution windows are respectively arranged on the front side wall and the rear side wall of the flow distribution shaft. The variable pump is suitable for the asymmetric flow of the working oil port of the single-piston rod hydraulic cylinder, so as to realize a closed loop of servo control of the single-piston rod hydraulic cylinder, and can meet the requirements of small volume and large discharge capacity.

Description

A double swash plate three oil port axial distribution plunger type variable pump

Technical field

The invention belongs to the technical field of axial piston hydraulic pumps, and more specifically, relates to a double swash plate and three oil ports axial distribution piston variable pump.

Background technique

Piston pump/motor is one of the most important power components in the hydraulic field and is widely used in ships, aerospace, automobiles and other fields. The traditional axial variable pump/motor consists of a variable pump with a tilt swash plate and a variable adjustment mechanism. Most of the variable mechanisms adopt the structure of a single plunger cylinder, and control the plunger by changing the swing angle of the swash plate. Change in pump/motor output displacement. As a key power component in the hydraulic system, the hydraulic motor plunger pump has the characteristics of high pressure, wide speed range, and easy modification of the flow distribution structure. It can adapt to the development requirements of simplified circuits, energy conservation and environmental protection of the hydraulic system. Using a hydraulic pump to directly control the movement of a hydraulic cylinder is the most direct way to improve the energy efficiency of electro-hydraulic technology. It is an international research hotspot in this field. Many research works have been carried out in this area at home and abroad.

Chinese patent CN102135082A discloses a double swash plate hydraulic motor plunger pump, which includes a casing, a stator, a rotor, a cylinder, a plurality of plungers, two swash plate assemblies and a flow distribution device. There are multiple swashplates on the left and right sides of the cylinder. The suction and discharge port communicates with the plunger cavity, and the flow distribution device is in clearance fit with the cylinder. When the rotor spindle drives the cylinder to rotate, the swash plate assembly causes the plunger to make reciprocating linear motion in the plunger cavity. The flow distribution device is in contact with the cylinder body. The oil suction and discharge ports are periodically connected to realize the flow distribution of the motor plunger pump. The flow distribution device does not rotate with the main shaft, and the flow distribution device is a flow distribution shaft. The flow distribution device used in this invention effectively simplifies the overall structure of the pump, reduces the dead volume of the pump, and improves the volumetric efficiency of the motor plunger pump. Compared with the existing valve flow distribution plunger pump, it makes the inlet and outlet of the working medium in the pump cavity The flow rate is no longer limited by the size of the valve port, the flow is smoother, and there is no valve opening and closing lag caused by valve flow distribution.

In the prior art, some effective simplified flow distribution methods have been proposed for plunger pumps. For example, the flow distribution shaft device is periodically connected to the suction and discharge port of the cylinder to realize the flow distribution of the motor plunger pump. The flow distribution device does not rotate with the main shaft. . However, further research shows that the above-mentioned existing equipment still has the following defects or shortcomings: firstly, from the perspective of energy saving, it is difficult for the hydraulic system to automatically adjust the displacement and then realize servo control of the single-piston rod hydraulic cylinder; on the other hand, Currently, the process of adjusting the displacement requires the mutual cooperation of multiple valves. The equipment is numerous and the control is complex, which is not conducive to actual production.

Contents of the invention

In view of the above defects or improvement needs of the prior art, the present invention provides a double swash plate and three oil ports axial flow plunger type variable pump, which further improves and designs the structure of the variable pump, especially for the variable pump. The flow distribution mechanism of the hydraulic system has been organically improved. For example, the traditional two-port variable pump is set to a three-port variable pump. At the same time, a hydrostatic balancing tank is equipped on the distribution axis to adjust and balance the radial pressure for further cooperation. The mechanism of the swash plate inclination angle can be changed according to the work requirements, so that the variable pump can realize the variable adjustment mode through real-time discharge and compensation of oil volume during the work process, thereby adapting to the asymmetry of the working oil port of the single piston rod hydraulic cylinder. flow to realize the servo-controlled closed loop of the single-piston rod hydraulic cylinder, which can effectively reduce mechanical friction and meet the needs of small volume and large displacement. At the same time, this variable pump also has the characteristics of energy saving, low pollution, long service life, and preparation It is simple and suitable for mass production.

In order to achieve the above object, the present invention provides a double swash plate and three oil ports axial flow distribution plunger type variable pump, including a rotor, a cylinder, a plunger, a swash plate assembly, a flow distribution device and a flow distribution device disposed on the left and right sides of the cylinder. The left end cover and the right end cover, in which the rotor and the cylinder are an integrated structure, and a plurality of corresponding plunger chambers are arranged at both ends of the cylinder, and plungers are provided in the plunger chamber. The plungers at each end correspond to each other to form a plurality of plunger pairs. Each plunger is connected to a swash plate assembly. When the rotor drives the cylinder to rotate, the swash plate assembly causes the plunger to move in the plunger cavity. Reciprocating linear motion is characterized by:

The flow distribution device includes a cylindrical flow distribution shaft, and a first partition and a second partition provided inside the flow distribution shaft. The first partition is arranged along the axial direction of the flow distribution shaft, and the flow distribution shaft is The interior is divided into a first flow channel and a second flow channel arranged up and down, and a second partition is provided inside the first flow channel along the radial direction of the flow distribution axis, and the second partition divides the first flow channel into two parts. It is a left flow channel and a right flow channel arranged left and right, and the left flow channel serves as the first oil port of the variable pump, the right flow channel serves as the second oil port of the variable pump, and the second flow channel channel serves as the third oil port of the variable pump, and

Two waist-shaped flow distribution windows are respectively provided on the front and rear side walls of the flow distribution shaft, and the two flow distribution windows on one side connect the first flow channel to the plunger cavity, and the two flow distribution windows are The second partition is separated; two flow distribution windows on the other side connect the second flow channel and the plunger chamber;

In this way, during the oil suction and discharge process of the variable pump, the oil volume compensation and discharge are realized in real time through the cooperation of the three oil ports.

Further, the variable pump also includes a single piston rod hydraulic cylinder and a low-pressure oil tank, wherein the single piston rod hydraulic cylinder includes a rodless chamber and a rod chamber, and the rodless chamber and the rod chamber are located in a The push rods in the rod cavity are separated, and the push rod can move back and forth in the single piston rod hydraulic cylinder; the second flow channel is connected to the rodless cavity, and the right flow channel is connected to the rodless cavity. The rod cavity is connected, and the left flow channel is connected with the low-pressure oil tank.

Further, a hydrostatic balance groove is provided on the front and rear side walls of the flow distribution shaft, and the total area of the hydrostatic balance groove on each side is equal to the sum of the areas of the two flow distribution windows on each side.

Further, a one-way control valve is provided between the low-pressure oil tank and the single-piston rod hydraulic cylinder.

Further, the cylinder has an axially symmetrical structure, and has a central hole in the axial direction. The cylinder is supported on the left end cover and the right end cover respectively by cylindrical roller bearings.

Further, the swash plate assembly includes a left swash plate fixedly arranged on the left end cover and a right swash plate rotatably arranged on the right end cover, wherein the right swash plate can rotate around the cylinder. The central axis swings, and the relative phase relationship between the right swash plate and the left swash plate is changed by rotating the right swash plate, thereby changing the displacement of the variable pump.

Further, the swash plate assembly also includes a sliding shoe, a return plate and a central ball hinge, wherein one end of the sliding shoe is embedded in the chute of the swash plate, and the other end is hinged with the plunger through a central spherical hinge. The return disk is clamped between the sliding shoe and the chute.

Further, the central axis of the flow distribution shaft coincides with the central axis of the cylinder, and the connection between the two is rotatably sealed using a Stereo sealing ring.

Further, the displacement formula of the variable pump is:

Among them, V is the displacement of the variable pump, d is the diameter of the plunger, z is the number of plungers, D is the diameter of the distribution circle of the plunger hole in the cylinder, and θ is the upper and lower dead center connection of the left swash plate working surface. The angle between the line and the straight line projected on the projection circle from the line connecting the top and bottom dead centers of the working surface of the right swash plate, γ is the inclination angle of the left swash plate.

Generally speaking, compared with the existing technology, the above technical solution conceived by the present invention mainly has the following technical advantages:

1. The variable pump of the present invention further improves and designs the structure of the variable pump, especially the flow distribution mechanism of the hydraulic system of the variable pump, such as setting the traditional two-oil port variable pump to a three-oil pump. The variable pump is equipped with a hydrostatic balance tank on the distribution shaft to adjust and balance the radial pressure. Further cooperation can change the mechanism of the swash plate inclination angle according to the work requirements, so that the variable pump can pass through the valve during operation. The real-time discharge and compensation of oil volume realizes a variable adjustment method, which can adapt to the asymmetric flow of the single-piston rod hydraulic cylinder's working oil port to realize a closed loop of servo control of the single-piston rod hydraulic cylinder, which can effectively reduce mechanical friction, It meets the needs of small size and large displacement. At the same time, this variable pump also has the advantages of energy saving, low pollution, long service life, simple preparation and suitable for large-scale production.

2. The variable pump of the present invention adopts a three-port flow distribution shaft. Only one pump can adapt to the asymmetric flow of the two working oil ports of a single piston rod hydraulic cylinder. No auxiliary oil supply device is needed to achieve single-piston control. The control of the piston hydraulic cylinder avoids the flow loss caused by the use of valve control technology and improves the energy efficiency of the system.

3. In the variable pump of the present invention, the distribution shaft adopts a static pressure balance structure, which greatly reduces the unbalanced radial force on the distribution shaft and can effectively reduce friction and wear.

4. The variable pump of the present invention drives the right swash plate to rotate, thereby changing the relative phase relationship between the right swash plate and the left swash plate, thereby changing the amount of change in the volume of the plunger cavity between each pair of plungers in one working cycle. , so the present invention can easily adjust the displacement.

Description of drawings

Figure 1 is a front view of a double swash plate three oil port axial distribution plunger type variable displacement pump related to the present invention;

Figure 2 is a three-dimensional cross-sectional view I of the three-oil port distribution shaft device according to the present invention;

Figure 3 is a three-dimensional cross-sectional view II of the three-oil port distribution shaft device according to the present invention;

Figure 4 is a positional relationship diagram of the two swash plates and the three-oil port distribution shaft device involved in the present invention;

Figure 5 is a schematic two-dimensional structural diagram of the three-oil port distribution shaft device involved in the present invention;

Figure 6 is a schematic diagram of the hydrostatic balancing tank of the three-oil distribution shaft involved in the present invention;

Figure 7 is a schematic diagram of the oil suction flow distribution of the double swash plate three oil port axial flow distribution plunger type variable pump involved in the present invention;

Figure 8 is a schematic diagram of the oil discharge flow distribution of the double swash plate three oil port axial flow distribution plunger type variable pump according to the present invention;

Figure 9 is a working principle diagram of the double swash plate three oil port axial distribution plunger type variable pump involved in the present invention;

Figure 10 is the positional relationship and projection view of the two swash plates in the present invention;

Figure 11 is the positional relationship and projection view of the two swash plates when the displacement is maximum in the present invention;

Figure 12 is the positional relationship and projection view of the two swash plates when the displacement is minimum in the present invention;

Figure 13 shows the movement speed v of the plunger and the rotation angle of the pump in the present invention. relationship diagram.

In all drawings, the same reference numbers represent the same technical features, specifically: 1-casing, 2-stator core, 3-motor winding, 4-rotor, 5-locating pin, 6-cylindrical roller bearing, 7-cylinder block, 8-left bearing pressure plate, 9-left end cover, 10-left swash plate, 11-left return plate, 12-sliding shoe, 13-center ball joint, 14-left plunger, 15-distribution shaft, 16-Steel sealing ring, 17-right plunger, 18-right return plate, 19-right end cover, 20-oil outlet housing, 21-right swash plate, 22-circumferential positioning pin, 23-right bearing pressure plate , 24-positioning pin, 25-return spring member.

Detailed ways

In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

Referring to Figure 1, a double swash plate and three oil ports axial flow distribution plunger type variable pump includes a rotor 4, a cylinder 7, a plunger, a swash plate assembly, a flow distribution device and a left end provided on the left and right sides of the cylinder 7 Cover 9 and right end cover 19, in which the rotor 4 and the cylinder 7 are of an integrated structure. A plurality of corresponding plunger chambers are arranged at both ends of the cylinder 7, and plungers are provided in the plunger chambers. The plungers at both ends of the cylinder 7 correspond to each other to form a plurality of plunger pairs. Each plunger is connected to a swash plate assembly. When the rotor 4 drives the cylinder 7 to rotate, the swash plate assembly causes the plunger to rotate. Makes reciprocating linear motion in the plunger cavity. Specifically, the rotatable cylinder 7 is an axially symmetrical structure with a central hole in the axial direction. The cylinder 7 is supported by cylindrical roller bearings 6 on the left end cover 9 and the right end cover 19 respectively. The sub-bearing 6 is axially positioned by the cylinder 7 and the bearing pressure plate 8 against the inner and outer rings of the bearing. A plurality of plungers are symmetrically distributed on both sides of the cylinder 7: a left plunger 14 and a right plunger 17. The left plunger 14 and its corresponding symmetrical right plunger 17 form multiple plunger pairs. Each plunger is attached to the swash plate through the sliding shoe 12, the return plate and the central ball hinge 13. The central ball hinge 13 resists the return plate under the force of the return spring member 25. Among them, the left swash plate 10 is moved in the circumferential direction by the positioning pin 5 to prevent the swash plate from rotating in the circumferential direction. The positioning pin is sleeved on the outside of the circumferential positioning pin 22 . The flow distribution shaft 15 is installed in the center hole of the cylinder 7 and is rotatably sealed using a Ster seal ring 16. There is a truncated cone protrusion at the right end of the distribution shaft 15, which is fixed to the right bearing pressure plate 23 through a circumferential positioning pin. superior.

Referring to Figures 2-4, the structure of the internal distribution shaft 15 of a double swash plate three oil port axis distribution plunger type variable pump of the present invention is shown in the figure. The hydraulic pump has three oil ports, namely the first oil port. , the second oil port and the third oil port, wherein the third oil port is arranged along the axial direction of the flow distribution shaft 15 and penetrates the cylinder of the flow distribution shaft 15 .

Wherein, the flow distribution device includes a flow distribution shaft 15, and a first partition and a second partition provided inside the flow distribution shaft 15. The flow distribution shaft 15 is cylindrical, and the first partition is along the The axial arrangement of the flow distribution shaft 15 divides the flow distribution shaft 15 into a first flow channel and a second flow channel arranged up and down, and a second partition is provided inside the first flow channel along the radial direction of the flow distribution shaft 15 , the second partition divides the first flow channel into a left flow channel and a right flow channel arranged left and right; the first partition is arranged along the axial direction of the flow distribution shaft 15, dividing the interior of the flow distribution shaft 15 into The first flow channel and the second flow channel are arranged up and down, and a second partition is provided inside the first flow channel along the radial direction of the distribution axis 15. The second partition divides the first flow channel into left and right layouts. The left flow channel and the right flow channel, and then the left flow channel forms the first oil port of the variable pump, the right flow channel forms the second oil port of the variable pump, and the second flow channel forms the The third oil port of the variable pump is used in this way to achieve real-time compensation and discharge of oil through the mutual cooperation of the three oil ports during the process of oil suction and oil discharge by the variable pump.

When the three-port variable pump is used to control a single-piston rod hydraulic cylinder, the second flow channel is connected to the rodless cavity of the hydraulic cylinder, the right flow channel is connected to the rod cavity of the hydraulic cylinder, and the left flow channel is connected to the low-pressure oil tank of the system. Connected. When the right flow channel and the left flow channel absorb oil at the same time, the second flow channel is supplied to press oil to the system, and the pressure oil of the second flow channel drives the movable rod of the hydraulic cylinder to extend; otherwise, the second flow channel absorbs oil, and the right flow channel and the left flow channel The flow channel presses oil into the system, but the right flow channel enters the rod chamber, and the left flow channel discharges excess oil to the low-pressure tank. The ratio of the area of the rod cavity and the rodless cavity of the oil cylinder determines the flow ratio of the right flow channel and the left flow channel. Generally speaking, if the area of the rod cavity is 1/2 of the area of the rodless cavity, then the right flow channel It is equal to the flow rate of the left flow channel.

Referring to Figures 5 and 6, the second oil port is a bidirectional oil port, which can both absorb oil and press oil. The window of the flow distribution shaft 15 connects the corresponding flow channel with the plunger chamber through the radial through hole in a time-sharing manner within one cycle to achieve oil suction and oil pressure.

Referring to Figure 6, when the three-oil port pump is used to control a single-piston rod hydraulic cylinder, the third oil port is connected to the rodless chamber of the hydraulic cylinder, the second oil port is connected to the rodless chamber of the hydraulic cylinder, and the first oil port is connected to the rodless chamber of the hydraulic cylinder. Connected to the low pressure tank of the system. When the first oil port and the second oil port absorb oil at the same time, the third oil port is supplied to press oil to the system, and the second flow channel pressure oil drives the hydraulic cylinder movable rod to extend; otherwise, the third oil port absorbs oil, and the first oil The first oil port and the second oil port press oil to the system, but the second oil port enters the rod cavity, and the first oil port discharges excess oil to the low-pressure oil tank. The area ratio of the rod cavity and the rodless cavity of the oil cylinder determines the flow rate of the right flow channel and the left flow channel. Generally speaking, if the area of the rod cavity is 1/2 of the area of the rodless cavity, then the right flow channel and The flow rate of the left flow channel is equal, that is to say, the total number of plungers and the plunger cavity are divided into two equal groups, which are connected to the first oil port and the second oil port respectively.

Hydrostatic balance grooves are provided on the front and rear side walls of the flow distribution shaft 15, and the total area of the hydrostatic balance groove on each side is equal to the sum of the areas of the two flow distribution windows on each side. In this way, the flow distribution shaft is reduced. 15 unbalanced radial force. in particular:

Hydrostatic balancing grooves are provided on both sides of the outer circumference of the flow distribution shaft 15 correspondingly. The total area of the balancing tank on each side is equal to the area of the corresponding flow distribution window. For example: the high-pressure oil entering through the window on one side of the distribution shaft 15 enters the plunger cavity on the one hand, and on the other hand enters the balance groove on the other side of the distribution shaft 15 through the annular gap. Since the total area of the balance groove on one side is equal to the balance groove on the opposite side, Therefore, the unbalanced radial force on the flow distribution shaft 15 is greatly reduced. In the same way, the high-pressure oil coming in from the second oil port and the third oil port can also enter the balance tank to reduce the unbalanced radial force.

Further, the swash plate assembly includes a left swash plate 10 fixedly provided on the left end cover 9 and a right swash plate 21 rotatably disposed on the right end cover 19 , wherein the right swash plate 21 can rotate around The central axis of the cylinder 7 swings, and the relative phase relationship between the right swash plate 21 and the left swash plate 9 is changed by rotating the right swash plate 21 to change the displacement of the variable displacement pump.

Referring to Figures 5 to 13, the principle of realizing displacement change of the three-port variable pump is described in detail.

A one-way control valve is provided between the low-pressure oil tank and the single-piston rod hydraulic cylinder to control the flow direction and flow rate of discharge or compensation liquid from the left flow channel. Among them, the motion trajectory of the center of the bottom surface of the sliding shoe 12 is an ellipse on the working surface of the left swash plate 10, and its two intersection points with the vertical center line of the working surface of the left swash plate 10 are respectively the bottom dead points, which are recorded as " BDC _left ", and top dead center, recorded as "TDC _left "; the movement track of the center of the bottom surface of the sliding shoe 12 is also an ellipse on the right swash plate 21, which is in line with the two vertical center lines of the working surface of the right swash plate 21. The intersection points are respectively their bottom dead center, marked as "BDC _right ", and top dead center, marked as "TDC _right ". When the positions of the two swash plates are in any state, "BDC _left '" is the projection of "BDC _left " on the projection circle, "TDC _left '" is the projection of "TDC _left " on the projection circle, "BDC _right "'" is the projection of "BDC _right " on the projection circle, and "TDC _right '" is the projection of "TDC _right " on the projection circle. The relative position of the two swash plates at this time is defined by the relationship between the two projection straight lines on the projection circle. represented by the angle θ.

When θ=0°, in a working cycle, the plunger sucks (discharges) the largest volume of liquid from the first and second oil ports, and the largest liquid volume is discharged (sucked) from the third oil port. At this time, the variable pump The displacement is the largest; when θ is between 0° and 180°, as the angle θ becomes larger, the volume of liquid sucked (discharged) by the first oil port and the second oil port becomes smaller, and the third oil port discharges The (suction) liquid volume becomes smaller, the liquid passing through the distribution axis decreases, and the displacement V of the pump becomes smaller as the angle θ becomes larger; when θ = 180°, refer to Figure 12, the diameter of the plunger cavity between the plungers The volume changes to 0 in a working cycle. At this time, no liquid passes through the distribution shaft. The plunger discharges the smallest volume of liquid in a working cycle. At this time, the displacement of the variable pump is smallest and is 0.

The displacement formula of this variable pump is:

In the formula: V is the displacement of the variable pump; d is the diameter of the plunger; z is the number of plungers; D is the diameter of the distribution circle of the plunger hole in the cylinder; θ is the upper and lower stops of the left swash plate working surface. The angle between the line connecting the points and the line connecting the top and bottom dead centers of the right swash plate working surface on the projection circle; γ is the inclination angle of the left swash plate.

It is easy for those skilled in the art to understand that the above descriptions are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements, etc., made within the spirit and principles of the present invention, All should be included in the protection scope of the present invention.

Claims (8)

1. A double swash plate and three oil ports axial flow distribution plunger type variable pump, including a rotor (4), a cylinder (7), a plunger, a swash plate assembly, a flow distribution device and a flow distribution device arranged around the cylinder (7) The left end cover (9) and the right end cover (19) on both sides, in which the rotor (4) and the cylinder (7) are an integral structure, and a plurality of corresponding plunger chambers are arranged at both ends of the cylinder (7). , there is a plunger in the plunger cavity, and the plungers at both ends of the cylinder (7) correspond to each other to form a plurality of plunger pairs, and each plunger is connected to the swash plate assembly. In the rotor (7) 4) When the cylinder (7) is driven to rotate, the swash plate assembly causes the plunger to make reciprocating linear motion in the plunger cavity, which is characterized by: The flow distribution device includes a cylindrical flow distribution shaft (15), and a first partition and a second partition provided inside the flow distribution shaft (15). The first partition is along the flow distribution axis (15). ), the inside of the distribution shaft (15) is divided into a first flow channel and a second flow channel arranged up and down, and the inside of the first flow channel is provided with a second flow channel along the radial direction of the flow distribution shaft (15). The second partition divides the first flow channel into a left flow channel and a right flow channel arranged on the left and right, and the left flow channel serves as the first oil port of the variable pump, and the right flow channel serves as the first oil port of the variable pump. The second oil port of the variable displacement pump, the second flow channel serves as the third oil port of the variable displacement pump, and Two waist-shaped flow distribution windows are respectively provided on the front and rear side walls of the flow distribution shaft (15), and the two flow distribution windows on one side connect the first flow channel to the plunger cavity, and the two flow distribution windows The flow distribution window is separated by the second partition; the two flow distribution windows on the other side connect the second flow channel with the plunger chamber; In this way, during the oil suction and discharge process of the variable pump, the oil volume is compensated and discharged in real time through the cooperation of the three oil ports; The variable pump also includes a single piston rod hydraulic cylinder and a low-pressure oil tank, wherein the single piston rod hydraulic cylinder includes a rodless chamber and a rod chamber, and the rodless chamber and the rod chamber are located in the rod chamber. The push rods are separated, and the push rod can move back and forth in the single piston rod hydraulic cylinder; the second flow channel is connected to the rodless cavity, and the right flow channel is connected to the rod cavity , the left flow channel is connected to the low-pressure fuel tank; The swash plate assembly includes a left swash plate (10) fixedly arranged on the left end cover (9) and a right swash plate (21) rotatably arranged on the right end cover (19), wherein the The right swash plate (21) can swing around the central axis of the cylinder (7). By rotating the right swash plate (21), the relative position between the right swash plate (21) and the left swash plate (10) is changed. Phase relationship to achieve changing the displacement of the variable pump. 2. The variable pump according to claim 1, characterized in that hydrostatic balancing grooves are provided on the front and rear side walls of the flow distribution shaft (15), and the total area of the hydrostatic balancing grooves on each side is equal to the total area of the hydrostatic balancing grooves on each side. The sum of the areas of the two distribution windows is equal. 3. The variable pump according to claim 2, wherein a one-way control valve is provided between the low-pressure oil tank and the single-piston rod hydraulic cylinder. 4. The variable pump according to any one of claims 1 to 3, characterized in that the cylinder (7) has an axially symmetrical structure, and the cylinder (7) has a central hole in the axial direction. The body (7) is supported on the left end cover (9) and the right end cover (19) respectively by cylindrical roller bearings. 5. The variable pump according to any one of claims 1 to 3, wherein the swash plate assembly further includes a sliding shoe, a return plate and a central ball joint, wherein one end of the sliding shoe is embedded in the swash plate In the chute, the other end is hinged with the plunger through a central spherical hinge, and the return disk is clamped between the sliding shoe and the chute. 6. The variable pump according to claim 4, wherein the swash plate assembly further includes a sliding shoe, a return plate and a central ball joint, wherein one end of the sliding shoe is embedded in the chute of the swash plate, The other end is hingedly connected to the plunger through a central spherical hinge, and the return disk is clamped between the sliding shoe and the chute. 7. The variable pump according to any one of claims 1 to 3, characterized in that the central axis of the flow distribution shaft (15) coincides with the central axis of the cylinder (7), and the connection between the two Use the Ster seal ring (16) for rotational sealing. 8. The variable pump according to any one of claims 1 to 3, characterized in that the displacement formula of the variable pump is: in, is the displacement of the variable pump, d is the plunger diameter, z is the number of plungers, D is the diameter of the distribution circle of the plunger holes in the cylinder,/> Is the angle between the line connecting the upper and lower dead centers of the working surface of the left swash plate (10) and the straight line projected on the projection circle by the line connecting the upper and lower dead centers of the working surface of the right swash plate (21),/> is the inclination angle of the left swash plate (10).