Open center constant pressure and constant power variable hydraulic pump

Abstract

The application discloses an open type constant pressure and constant power variable hydraulic pump and belongs to the technical field of hydraulic pumps. The open type constant pressure and constant power variable hydraulic pump comprises a shell, a pump cover arranged on the shell, a power valve and a control valve installed on the shell, a transmission shaft rotationally connected to the shell, a cylinder body spline-connected to the transmission shaft, an oil distribution disc installed in the pump cover, an inclined disc arranged in the shell, a limiting bolt installed on the shell, a return disc rotationally connected to the inclined disc, a plurality of sliding shoes arranged in the return disc, a connecting rod ball-jointed to the sliding shoes, a plunger slidingly connected to the connecting rod and a piston cavity arranged on the cylinder body. When the piston cavity on the cylinder body passes through a transition zone on the oil distribution disc, the relative movement between the connecting rod and the plunger reduces the change amount of the volume of the corresponding piston cavity on the cylinder body, thereby reducing the degree of change of the hydraulic oil pressure in the piston cavity on the cylinder body and improving the stability of the hydraulic oil state.

Description

Technical Field

[0001] This invention relates to the field of hydraulic pump technology, and in particular to an open-type constant pressure and constant power variable hydraulic pump. Background Technology

[0002] Hydraulic pumps are mainly divided into vane pumps, gear pumps, piston pumps, and screw pumps. Among them, axial piston pumps are characterized by their compact structure, stable average output flow, and high pressure. They are widely used in hydraulic systems requiring high pressure, such as engineering machinery, metallurgical equipment, and ships. Their working principle is that the piston reciprocates in the cylinder bore, causing a change in the volume of the piston chamber, thereby drawing oil from the suction area and discharging it to the pressure area. Axial hydraulic pump systems are divided into open and closed types. Open hydraulic pumps require drawing hydraulic oil from the tank to inject into the actuator, while closed hydraulic pumps form a circulation system with the actuator and do not require drawing hydraulic oil from an external tank.

[0003] Because the oil pressure in the pressure zone is much higher than that in the suction zone, a transition zone of a certain width is set between the suction and pressure windows on the distributor plate to prevent high-pressure oil from directly flowing into the suction zone. However, when the plunger cavity rotates with the cylinder block and passes through the transition zone of the distributor plate, the plunger is still constrained by the swashplate and continues to move, causing the volume of the plunger cavity to increase or decrease during this process. At the same time, the plunger cavity is sealed off by the transition zone of the distributor plate, meaning it is not connected to either the suction window or the pressure window. This contradictory state of "volume change" and "cavity closure" causes the oil inside the cavity to be drastically compressed or expanded. The compression of the oil causes an abnormal increase in the pressure inside the cavity, while the expansion of the oil causes dissolved air to be released or the oil to vaporize, resulting in cavitation. These severe pressure fluctuations and cavitation impacts will act on key components such as the plunger, cylinder bore, slipper, and distributor plate. Repeated pressure impacts and cavitation corrosion will significantly aggravate the wear of related moving parts, generate noise and vibration, and in severe cases, even damage parts, ultimately leading to a decrease in the working efficiency, reduced reliability, and shortened service life of the hydraulic pump. Summary of the Invention

[0004] This invention provides an open-type constant pressure and constant power variable hydraulic pump to solve the problems mentioned in the background above.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: an open-type constant pressure constant power variable hydraulic pump, comprising a housing, a pump cover provided on the housing, an oil suction area and an oil pressure area provided inside the pump cover, a power valve and a control valve installed on the housing, a drive shaft rotatably connected to the housing, a cylinder body splinedly connected to the drive shaft, an oil distribution plate installed inside the pump cover, the oil distribution plate being used to separate the oil suction area and the oil pressure area on the pump cover, the oil distribution plate contacting the cylinder body, the oil distribution plate being provided with a feed area, a discharge area and two symmetrically distributed transition areas, a swashplate ball-jointed with the cylinder body provided inside the housing, a limiting bolt ball-jointed with the swashplate installed on the housing, a return plate rotatably connected to the swashplate, a plurality of slippers provided inside the return plate, the slippers contacting the swashplate, a connecting rod ball-jointed to the slippers, a plunger slidably connected to the connecting rod, and piston chambers the same number as the number of plungers provided on the cylinder body, the plungers sliding within the piston chambers corresponding to those on the cylinder body.

[0006] More preferably, the plunger has a sliding cavity near the end of the connecting rod, the connecting rod slides within the sliding cavity, a guide tube is installed in the sliding cavity of the plunger, the guide tube is slidably connected to the connecting rod, and the length of the guide tube is greater than the length of the sliding cavity on the plunger.

[0007] More preferably, both the connecting rod and the plunger are hinged to a limiting bracket, and the limiting brackets on the connecting rod and the adjacent plunger are located on the same side. A limiting ring is provided inside the housing, which is used to limit the maximum distance between two corresponding limiting brackets. The limiting ring is provided with symmetrically distributed limiting rods, and the housing is provided with symmetrically distributed limiting holes. The limiting rods limit the position of the limiting ring through the limiting holes on the housing.

[0008] More preferably, a blocking ring is fixedly connected inside the limiting ring, and a guide surface is provided on the side of the blocking ring near the plunger. The guide surface is used to guide the limiting frame on the plunger. A notch is provided on the limiting ring away from the guide surface. The notch is used to release the limiting ring from limiting the limiting frame on the plunger.

[0009] More preferably, the central angle of the arc corresponding to the notch and the central angle of the arc corresponding to the guide surface are both smaller than the central angle of the arc corresponding to the transition area on the oil distribution plate.

[0010] More preferably, the limiting frame is slidably and rotatably connected to a sliding sleeve, which slides along the limiting ring and the blocking ring.

[0011] More preferably, a guide plate is provided on the limiting ring near the notch, and the guide plate is only used to guide the corresponding sliding sleeve on the plunger into the space between the limiting ring and the blocking ring.

[0012] More preferably, the limiting rod is slidably connected to the limiting ring, the end of the limiting rod away from the limiting ring is hemispherical, and the depth of the upper limiting hole in the housing is greater than the diameter of the hemisphere of the limiting rod.

[0013] More preferably, the swash plate and the limiting ring are ball-connected with transmission rods arranged in a rectangular pattern.

[0014] More preferably, a connecting plate is fixedly connected to the limiting rod, the connecting plate is slidably connected to the limiting ring, and a spring is fixedly connected between the limiting rod and the limiting ring.

[0015] The present invention has the following advantages: 1. When the piston chamber on the cylinder passes through the transition zone on the distribution plate, the relative movement between the connecting rod and the plunger reduces the change in volume of the corresponding piston chamber on the cylinder, thereby reducing the degree of change in hydraulic oil pressure in the piston chamber on the cylinder and improving the stability of the hydraulic oil state.

[0016] 2. The present invention limits the position of the limiting frame by limiting ring and blocking ring, so that the relative position of the connecting rod and the plunger remains stable, ensuring that the volume of hydraulic oil drawn by the plunger into the piston chamber of the cylinder is the same each time, thereby increasing the stability of the hydraulic oil delivery process.

[0017] 3. In the process of swashplate rotation, the swashplate drives the limiting ring to rotate synchronously through the transmission rod, so that the limiting ring always remains parallel to the swashplate, thereby adapting to the changes in the moving distance of the connecting rod and the plunger at different angles. Attached Figure Description

[0018] Figure 1 This is a three-dimensional structural diagram of the present invention; Figure 2 This is a three-dimensional bottom view of the power valve, control valve, and limit bolt of the present invention; Figure 3 This is a three-dimensional structural diagram of the limiting ring and transmission rod of the present invention; Figure 4 This is a three-dimensional structural diagram of the cylinder block, swashplate, and return plate of the present invention; Figure 5 For the present invention Figure 4 Enlarged view of the 3D structure at point A; Figure 6 This is a three-dimensional structural diagram of the drive shaft, cylinder block, and swashplate of the present invention; Figure 7 This is a three-dimensional structural diagram of the slipper, connecting rod, and plunger of the present invention; Figure 8 This is a three-dimensional structural cross-sectional view of the guide tube, limiting frame, and sliding sleeve of the present invention; Figure 9 This is an exploded three-dimensional view of the connecting plate, spring, and guide plate of the present invention.

[0019] The meanings of the reference numerals in the figure are as follows: 1-Housing, 2-Pump cover, 3-Power valve, 4-Control valve, 5-Drive shaft, 6-Cylinder block, 601-Distributor plate, 7-Swashplate, 8-Limit bolt, 9-Return plate, 10-Slipper, 11-Connecting rod, 12-Plunger, 13-Guide pipe, 14-Limit bracket, 15-Limit ring, 16-Limit rod, 17-Drive rod, 18-Barrier ring, 19-Notch, 20-Sliding sleeve, 21-Connecting plate, 22-Spring, 23-Guide plate, 24-Guide surface. Detailed Implementation

[0020] References to embodiments herein mean that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0021] Example: Open-type constant pressure and constant power variable hydraulic pump, such as Figures 1-9 As shown, the system includes a housing 1, a pump cover 2 on the housing 1, an oil suction zone and an oil pressure zone inside the pump cover 2, a power valve 3 and a control valve 4 mounted on the housing 1, a drive shaft 5 rotatably connected to the housing 1, and a cylinder block 6 splinedly connected to the drive shaft 5. An oil distribution plate 601 is installed inside the pump cover 2, which separates the oil suction zone and the oil pressure zone on the pump cover 2. The oil distribution plate 601 contacts the cylinder block 6 and has a feed zone, a discharge zone, and symmetrically distributed feed valves. Two transition zones are provided. Inside the housing 1, there is a swashplate 7 that is ball-joined with the cylinder 6. A limiting bolt 8 that is ball-joined with the swashplate 7 is installed on the housing 1. The swashplate 7 is rotatably connected to a return plate 9. Multiple slippers 10 are provided inside the return plate 9. The slippers 10 are in contact with the swashplate 7. A connecting rod 11 is ball-jointed to the slipper 10. The connecting rod 11 is slidably connected to a plunger 12. The cylinder 6 is provided with the same number of piston chambers as the plungers 12. The plungers 12 slide in the piston chambers corresponding to those on the cylinder 6.

[0022] Furthermore, such as Figure 8 and Figure 9 As shown, a sliding cavity is provided at one end of the plunger 12 near the corresponding connecting rod 11. The connecting rod 11 slides within the sliding cavity. A guide tube 13 is installed inside the sliding cavity of the plunger 12. The guide tube 13 is slidably connected to the connecting rod 11. The length of the guide tube 13 is greater than the length of the sliding cavity on the plunger 12.

[0023] The above solution provides a way to reduce the pressure change in the piston chamber of cylinder 6 during the transition zone of the oil distribution plate 601; the pump cover 2 is located on the right side of the housing 1, and the two are connected by bolts. The oil suction area of ​​the pump cover 2 is located below the oil pressure area on it. The shape of the oil suction area and the oil pressure area on the pump cover 2 can be adjusted according to the actual situation. In use, the oil suction area of ​​the pump cover 2 is connected to the external oil tank, and the oil pressure area of ​​the pump cover 2 is connected to the external actuator. The power valve 3 and the control valve 4 are both located on the right side of the front of the housing 1. The power valve 3 and the control valve 4 are existing devices, and their specific structure, function and usage will not be described in detail. A motor is externally connected to the left side of the drive shaft 5. The output shaft of the motor drives the drive shaft 5 to rotate counterclockwise. Figure 3 (Viewed from right to left) In this embodiment, the number of piston chambers on the cylinder 6 is nine. The specific number of piston chambers can be adjusted according to the actual situation during use. The oil distribution plate 601 is located on the left side of the pump cover 2. The oil distribution plate 601, swash plate 7, limit bolt 8 and return plate 9 are all existing parts. Their specific shapes and functions of each area will not be described in detail. The swash plate 7 is located on the left side inside the housing 1. A bearing is provided between the swash plate 7 and the housing 1 to reduce the friction during the relative rotation of the swash plate 7 and the housing 1.

[0024] The limiting bolt 8 is located at the rear of the housing 1. Initially, the right side of the swashplate 7 is perpendicular to the axis of the drive shaft 5, and the slipper 10 will not move left or right when moving along the right side of the swashplate 7. The left end of the limiting bolt 8 is ball-jointed with the rear of the swashplate 7. In use, by rotating the limiting bolt 8, the rear of the swashplate 7 is tilted to the left, thereby changing the distance the slipper 10 moves left or right along the right side of the swashplate 7. There are nine slippers 10. The left side of the slipper 10 is always in contact with the swashplate 7. The left end of the connecting rod 11 is ball-jointed with the slipper 10. The left end of the plunger 12 is provided with a sliding cavity. Initially, the connecting rod 11 is located in the middle of the sliding cavity of the plunger 12, allowing the connecting rod 11 to move left and right relative to the plunger 12. The guide pipe 13 is used to prevent the hydraulic oil in the piston cavity of the cylinder 6 from entering the sliding cavity of the plunger 12 and affecting the stability of the hydraulic oil pressure. The slipper 10, the connecting rod 11, and the plunger 12 are all provided with through holes. The through holes of the plunger 12, the guide pipe 13, the connecting rod 11, and the slipper 10 are connected in sequence to allow the hydraulic oil in the piston cavity of the cylinder 6 to flow between the slipper 10 and the swashplate 7, reducing wear during their relative movement.

[0025] The drive shaft 5 drives the parts on it to rotate counterclockwise. Figure 3(Viewed from right to left), the drive shaft 5 drives the cylinder 6 and its parts to rotate synchronously. During the transition zone of the front (rear) side of the oil distribution plate 601 in one piston chamber of the cylinder 6, the slipper 10 moves to the right (left) along the right side of the swashplate 7. The slipper 10 drives the connecting rod 11 to move synchronously. The connecting rod 11 moves to the right (left) along the sliding chamber of the plunger 12, so that the plunger 12 does not move to the right (left), thereby reducing the change of the piston chamber and improving the stability of the hydraulic oil pressure. After the piston chamber and the axis of the swashplate 7 are on the same horizontal plane, the slipper 10 moves to the rightmost (leftmost) part of the right side of the swashplate 7, and the relative movement distance between the connecting rod 11 and the plunger 12 reaches the maximum. Then the connecting rod 11 moves in the opposite direction relative to the plunger 12 to reset.

[0026] Furthermore, such as Figure 5 and Figures 7-9 As shown, both the connecting rod 11 and the plunger 12 are hinged to limit frames 14, and the limit frames 14 on the connecting rod 11 and the adjacent plunger 12 are located on the same side. A limit ring 15 is provided inside the housing 1. The limit ring 15 is used to limit the maximum distance between the two corresponding limit frames 14. The limit ring 15 is provided with symmetrically distributed limit rods 16, and the housing 1 is provided with symmetrically distributed limit holes. The limit rods 16 limit the position of the limit ring 15 through the limit holes on the housing 1.

[0027] Furthermore, such as Figure 5 and Figure 9 As shown, a blocking ring 18 is fixedly connected inside the limiting ring 15. A guide surface 24 is provided on the side of the blocking ring 18 near the plunger 12. The guide surface 24 is used to guide the limiting frame 14 on the plunger 12. A notch 19 is provided on the limiting ring 15 away from the guide surface 24. The notch 19 is used to release the limiting ring 15 from limiting the upper limit frame 14 of the plunger 12.

[0028] Furthermore, such as Figure 3 and Figure 9 As shown, the central angle of the arc corresponding to the notch 19 and the central angle of the arc corresponding to the guide surface 24 are both smaller than the central angle of the arc corresponding to the transition area on the oil distribution plate 601.

[0029] The above solution provides a method to restrict the relative movement of the connecting rod 11 and the plunger 12 during the oil extraction (discharge) process in the piston chamber of the cylinder 6. The limiting frame 14 is composed of an arc-shaped plate and a round rod. The round rod of the limiting frame 14 points to the side of the connecting rod 11 and the plunger 12 away from the axis of the transmission shaft 5. Initially, the center line of the circle where the arc-shaped plate of the limiting frame 14 is located coincides with the center line of the connecting rod 11 and the plunger 12. The limiting ring 15 and the blocking ring 18 together form two "slides". The limiting frame 14 slides in the corresponding "slides", so that the two limiting frames 14 remain relatively stationary when sliding in the two "slides". A notch 19 is provided on the right rear side of the limiting ring 15. The position of the notch 19 corresponds to the transition area on the rear side of the oil distribution plate 601. The guide surface 24 of the blocking ring 18 corresponds to the transition area on the front side of the oil distribution plate 601. The guide surface 24 is composed of upper and lower parts, wherein... The depth is greatest at the junction of the upper and lower parts of the guide surface 24, and the central angle of the corresponding circle on the upper part of the guide surface 24 is not less than the central angle of the corresponding circle on the lower part. After the upper limit bracket 14 of the plunger 12 moves to the notch 19, the limit ring 15 releases the limit on the upper limit bracket 14 of the plunger 12, allowing the connecting rod 11 and the plunger 12 to move relative to each other. After the upper limit bracket 14 of the plunger 12 moves to the guide surface 24 of the blocking ring 18, the connecting rod 11 and the plunger 12 can move relative to each other. The ratio of the central angle of the guide surface 24 of the notch 19 and the blocking ring 18 to the central angle of the transition area on the oil distribution plate 601 is used to ensure that when the connecting rod 11 and the plunger 12 slide relative to each other, the piston chamber on the cylinder 6 is located in the transition area on the oil distribution plate 601 and is in a sealed state, which does not affect the normal extraction and delivery of hydraulic oil by the piston chamber on the cylinder 6 in the feed area and discharge area on the oil distribution plate 601.

[0030] Furthermore, such as Figure 5 and Figures 7-9 As shown, the limiting frame 14 is slidably and rotatably connected to the sliding sleeve 20, which slides along the limiting ring 15 and the blocking ring 18.

[0031] Furthermore, such as Figure 6 and Figure 9 As shown, a guide plate 23 is provided on the limiting ring 15 near the notch 19. The guide plate 23 is only used to guide the corresponding sliding sleeve 20 on the plunger 12 into the space between the limiting ring 15 and the barrier ring 18.

[0032] The above solution provides a method for guiding the movement and reset of the limiting frame 14; during the process of the connecting rod 11 (plunger 12) driving the limiting frame 14 to rotate, the sliding sleeve 20 is always in contact with the inner side of the limiting ring 15 under the action of centrifugal force, ensuring the contact area between the sliding sleeve 20 and the limiting ring 15 and the barrier ring 18; the guide plate 23 is located at the notch 19 on the limiting ring 15, and the guide plate 23 is composed of an arc plate and an inclined plate. The diameter of the inner side of the arc plate on the guide plate 23 is the same as the diameter of the inner side of the limiting ring 15, which is used to ensure that the outermost part of the sliding sleeve 20 is always in contact with the inner side of the limiting ring 15. The inner circle facilitates the subsequent movement and reset of the sliding sleeve 20. The inclined plate of the guide plate 23 is used to guide the limit bracket 14 on the plunger 12 to move to the left and reset. During the process of the plunger 12 at the corresponding position of the piston chamber on the cylinder 6 passing through the area of ​​the notch 19, the sliding shoe 10 drives the parts on it to move to the left. The volume of hydraulic oil in the corresponding piston chamber on the cylinder 6 remains unchanged, and the plunger 12 does not move to the left. That is, the plunger 12 drives the parts on it to move to the right relative to the connecting rod 11 and separate from its corresponding "slide". Until the sliding sleeve 20 corresponding to the plunger 12 contacts the guide plate 23, the guide plate 23 guides it to move into the corresponding "slide" and reset.

[0033] Furthermore, such as Figure 5 and Figure 9 As shown, the limiting rod 16 is slidably connected to the limiting ring 15. The end of the limiting rod 16 away from the limiting ring 15 is hemispherical, and the depth of the limiting hole in the housing 1 is greater than the diameter of the hemisphere of the limiting rod 16.

[0034] Furthermore, such as Figures 2-4 As shown, the swash plate 7 and the limiting ring 15 are connected together by a rectangularly distributed transmission rod 17.

[0035] Furthermore, such as Figure 5 and Figure 9 As shown, a connecting plate 21 is fixedly connected to the limiting rod 16, the connecting plate 21 is slidably connected to the limiting ring 15, and a spring 22 is fixedly connected between the limiting rod 16 and the limiting ring 15.

[0036] The above solution provides a method for adjusting the angle of the limiting ring 15; two symmetrically distributed truncated cones are provided inside the housing 1, and the two limiting holes of the housing 1 are located in the two truncated cones respectively, and their axes coincide. When the worker places the limiting ring 15, the truncated cones on the housing 1 can retract the limiting rod 16 into the limiting ring 15 by pressing the limiting rod 16. After placement, the truncated cones on the housing 1 contact the limiting ring 15. Figure 5As shown, the depth of the upper limit hole of the housing 1 is used to increase the stability of the position of the limit rod 16, ensuring that the limit rod 16 is always within the limit hole of the housing 1 after installation. There are four transmission rods 17, which are used to increase the stability of the connection between the limit ring 15 and the swashplate 7. When the swashplate 7 rotates, the swashplate 7 squeezes the limit ring 15 through the transmission rods 17, so that the limit ring 15 rotates synchronously. The right side of the swashplate 7 passes through its rotation center line to ensure the stability of the relative position of the swashplate 7 and the limit ring 15 during rotation. The connecting plate 21 is located on the right side of the limit rod 16. When the limit ring 15 needs to be replaced or cleaned, the two connecting plates 21 are pushed in opposite directions. The connecting plates 21 drive the limit rod 16 to move synchronously, so that the limit rod 16 is separated from the limit hole of the housing 1, thereby facilitating the disassembly and replacement of the limit ring 15. The spring 22 is always in a charged state to push the limit rod 16 towards the adjacent inner wall of the housing 1, so that the position of the limit rod 16 remains stable.

[0037] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An open-type constant pressure and constant power variable hydraulic pump, characterized by: The system includes a housing (1), on which a pump cover (2) is provided. The pump cover (2) contains an oil suction zone and an oil pressure zone. A power valve (3) and a control valve (4) are installed on the housing (1). A drive shaft (5) is rotatably connected to the housing (1). The drive shaft (5) is splinedly connected to a cylinder body (6). An oil distribution plate (601) is installed inside the pump cover (2). The oil distribution plate (601) separates the oil suction zone and the oil pressure zone on the pump cover (2). The oil distribution plate (601) contacts the cylinder body (6). The oil distribution plate (601) has a feed zone, a discharge zone, and two symmetrically distributed transition zones. The housing (1) is provided with a swashplate (7) that is ball-joined with the cylinder (6). The housing (1) is provided with a limiting bolt (8) that is ball-joined with the swashplate (7). The swashplate (7) is rotatably connected to a return plate (9). The return plate (9) is provided with a plurality of slippers (10). The slippers (10) are in contact with the swashplate (7). The slippers (10) are ball-jointed with a connecting rod (11). The connecting rod (11) is slidably connected to a plunger (12). The cylinder (6) is provided with a number of piston chambers equal to the number of plungers (12). The plungers (12) slide in the piston chambers corresponding to those on the cylinder (6). Both the connecting rod (11) and the plunger (12) are hinged to limit frames (14), and the limit frames (14) on the connecting rod (11) and the adjacent plunger (12) are located on the same side. A limit ring (15) is provided inside the housing (1). The limit ring (15) is used to limit the maximum distance between two corresponding limit frames (14). The limit ring (15) is provided with symmetrically distributed limit rods (16). The housing (1) is provided with symmetrically distributed limit holes. The limit rods (16) limit the position of the limit ring (15) through the limit holes on the housing (1). A blocking ring (18) is fixed inside the limiting ring (15). A guide surface (24) is provided on the side of the blocking ring (18) near the plunger (12). The guide surface (24) is used to guide the limiting frame (14) on the plunger (12). A notch (19) is provided on the limiting ring (15) away from the guide surface (24). The notch (19) is used to release the limiting ring (15) from limiting the limiting frame (14) on the plunger (12).

2. The open-type constant pressure constant power variable hydraulic pump according to claim 1, characterized in that: The plunger (12) has a sliding cavity at one end near the corresponding connecting rod (11), and the connecting rod (11) slides within the sliding cavity. A guide tube (13) is installed in the sliding cavity of the plunger (12), and the guide tube (13) is slidably connected to the connecting rod (11). The length of the guide tube (13) is greater than the length of the sliding cavity on the plunger (12).

3. The open-type constant pressure constant power variable hydraulic pump according to claim 2, characterized in that: The central angle of the arc corresponding to the notch (19) and the central angle of the arc corresponding to the guide surface (24) are both smaller than the central angle of the arc corresponding to the transition area on the oil distribution plate (601).

4. The open-type constant pressure constant power variable hydraulic pump according to claim 3, characterized in that: The limiting frame (14) is slidably and rotatably connected to a sliding sleeve (20), which slides along the limiting ring (15) and the blocking ring (18).

5. The open-type constant pressure constant power variable hydraulic pump according to claim 4, characterized in that: A guide plate (23) is provided on the limiting ring (15) near the notch (19). The guide plate (23) is only used to guide the plunger (12) corresponding to the sliding sleeve (20) into the space between the limiting ring (15) and the barrier ring (18).

6. The open-type constant pressure constant power variable hydraulic pump according to claim 5, characterized in that: The limiting rod (16) is slidably connected to the limiting ring (15). The end of the limiting rod (16) away from the limiting ring (15) is hemispherical. The depth of the limiting hole in the housing (1) is greater than the diameter of the hemisphere of the limiting rod (16).

7. The open-type constant pressure constant power variable hydraulic pump according to claim 6, characterized in that: The swash plate (7) and the limiting ring (15) are ball-connected with a transmission rod (17) arranged in a rectangular pattern.

8. The open-type constant pressure constant power variable hydraulic pump according to claim 7, characterized in that: A connecting plate (21) is fixedly connected to the limiting rod (16), the connecting plate (21) is slidably connected to the limiting ring (15), and a spring (22) is fixedly connected between the limiting rod (16) and the limiting ring (15).

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