Plunger and hydraulic pump

Abstract

The invention discloses a plunger. The plunger comprises a plunger base; a plunger body having a cylindrical shape and connected to the plunger base, in which the plunger body includes an outer peripheral wall and a cavity provided inside the outer peripheral wall; the end cover is connected to the plunger body; the fluid channel penetrates through the plunger base part and the plunger body; the peripheral wall comprises a first end connected to the plunger base part and a second end connected to the end cover in the central axis direction of the peripheral wall; the plunger is characterized in that one or more through holes for communicating the cavity with external fluid of the plunger body are formed in the end cover. The invention further discloses a hydraulic pump. The hydraulic pump comprises a cylinder body; a connecting rod; and the plunger located in the cylinder and rotatably connected to the connecting rod.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of hydraulic machinery, and more particularly, to a plunger and a hydraulic pump comprising the plunger. BACKGROUND

[0002] Hydraulic pumps include plungers to draw and deliver fluid. The plungers are mounted in a plunger rod for delivering fluid in the hydraulic pump. When the plungers are pulled back, fluid is drawn into the plunger rod from an inlet pipe. When the plungers are pushed forward, the fluid in the plunger rod is squeezed and delivered out from an outlet pipe. The plungers continuously reciprocate in the plunger rod, and fluid is continuously delivered to the target mechanism.

[0003] The degree of fluctuation of fluid pressure in the hydraulic pump is closely related to the noise problem. The fluctuation of fluid pressure can cause pressure pulsation in the hydraulic system, which can cause vibration of the hydraulic pump and the pipeline, thus generating noise. The main causes of noise include poor manufacturing quality of the hydraulic pump, poor precision, large fluctuation of pressure and flow, poor elimination of trapped oil phenomenon, poor sealing, and poor bearing quality, etc. In use, noise can also be caused by wear and tear of the hydraulic pump parts, excessive clearance, insufficient flow, and easy fluctuation of pressure.

[0004] In addition, cavitation phenomenon in the hydraulic system is also one of the main causes of noise. When the plunger of the hydraulic pump is on the suction (low pressure) side, due to the high speed of the plunger and the low suction pressure, the air in the fluid can be separated to form cavitation. When the plunger is on the discharge (high pressure) side, the cavitation can be broken by the high pressure fluid, generating a strong shock wave (also known as cavitation phenomenon). The cavitation repeatedly generated and eliminated beside the surface of the parts (such as the shoe and the plunger) of the hydraulic pump can generate additional noise and cyclic stress, which can form metal fatigue on the surface of these parts, eventually leading to damage of these parts. SUMMARY

[0005] The present application aims to solve or at least alleviate the problems existing in the prior art, i.e., to eliminate or reduce the noise and cavitation generated in the hydraulic pump.

[0006] In one aspect, the present application provides a plunger, comprising: a plunger base; a plunger body having a cylindrical shape and connected to the plunger base, wherein the plunger body comprises an outer peripheral wall and a cavity arranged inside the outer peripheral wall; an end cover connected to the plunger body; a fluid passage passing through the plunger base and the plunger body; wherein the outer peripheral wall comprises a first end connected to the plunger base and a second end connected to the end cover along a central axis direction thereof; characterized in that the end cover is provided with one or more through holes for fluid communication between the cavity and the outside of the plunger body.

[0007] In another aspect, the present application provides a hydraulic pump, characterized in that the hydraulic pump comprises: a cylinder; a connecting rod; and a plunger located in the cylinder and rotatably connected to the connecting rod. The plunger comprises: a plunger base; a plunger body having a cylindrical shape and connected to the plunger base, wherein the plunger body comprises an outer peripheral wall and a cavity arranged inside the outer peripheral wall; an end cover connected to the plunger body; a fluid passage passing through the plunger base and the plunger body; wherein the outer peripheral wall comprises a first end connected to the plunger base and a second end connected to the end cover along a central axis direction of the plunger body; and characterized in that one or more through holes are arranged on the end cover to fluidly connect the cavity with an outside of the plunger body.

[0008] In order to eliminate or reduce noise and cavitation, the plunger according to the present application is additionally provided with through holes at the end. In this way, when the plunger is pushed, the liquid outside the end cover will enter the cavity through the through holes. When the plunger is pulled, the liquid pressure in the cavity becomes higher than the liquid pressure outside the end cover, so the liquid in the cavity will flow back to the outside of the end cover through the through holes, so that the liquid pressure outside the end cover increases, preventing or reducing air separation therefrom. In this way, the pressure pulsation outside the end cover and in the fluid passage can be significantly reduced, thereby reducing the noise and cavitation generated by the pressure pulsation. BRIEF DESCRIPTION OF DRAWINGS

[0009] The disclosure of the present application will become more apparent from the following description in conjunction with the accompanying drawings. It is readily understood by those skilled in the art that the drawings are merely intended to illustrate the present application and are not intended to limit the scope of protection of the present application. In addition, similar numbers in the drawings are used to represent similar components, wherein:

[0010] Figure 1 is a cross-sectional view of a plunger according to a first embodiment of the present application;

[0011] Figure 2 is a cross-sectional view of a plunger according to a second embodiment of the present application;

[0012] Figure 3 is a cross-sectional view of a plunger according to a third embodiment of the present application;

[0013] Figure 4 is a cross-sectional view of a plunger according to a fourth embodiment of the present application;

[0014] Figure 5 is a graph of the liquid pressure outside the end cover collected when the plunger according to the present application is in operation. DETAILED DESCRIPTION

[0015] Exemplary embodiments of the present application will be described below in greater detail with reference to the accompanying drawings. While exemplary embodiments of the present application are shown in the drawings, it is to be understood that the present application can be embodied in various forms without being limited by the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present application to those skilled in the art.

[0016] Figure 1 A cross-sectional view of a plunger according to a first embodiment of the present application. The plunger comprises a plunger base 1, a plunger body 2, and an end cap 3. The plunger body 2 has a cylindrical shape and is connected to the plunger base 1, comprising an outer peripheral wall 21 and a cavity S provided inside the outer peripheral wall 21. The end cap 3 is connected to the plunger body 2, and comprises an inner recess 33 which is recessed towards the inside of the plunger body 2. The inner recess 33 is provided with an external thread on the outside of its side wall. The outer peripheral wall 21 is provided with an internal thread on the inside of the second end 212, corresponding to the external thread. The cavity S helps to reduce the weight of the plunger, so that the plunger has a higher efficiency.

[0017] The outer peripheral wall 21 comprises a first end 211 connected to the plunger base 1 and a second end 212 connected to the end cap 3, along the direction of its central axis. The end cap 3 is provided with a through hole 31 for fluid communication between the cavity S and the outside of the plunger body 2. In this way, when the plunger is pushed (to the right in the figure), liquid will enter the cavity S through the through hole 31. When the plunger is pulled (to the left in the figure), the liquid pressure in the cavity S is higher than the liquid pressure outside the end cap 3, so the liquid that previously entered the cavity S will flow back to the outside of the end cap 3 through the through hole 31, so that the liquid pressure outside the end cap 3 increases, reducing the pressure pulsation outside the end cap, thereby reducing the noise generated by the pressure pulsation and preventing or reducing air separation from the liquid, i.e. reducing cavitation on the surface of the various components of the plunger.

[0018] The end cap 3 is fixed in the plunger body 2 by screw connection, so that when it is necessary to replace the end cap 3 (for example due to wear), it is possible to simply unscrew the old end cap 3 and screw in a new one, without the need to re-manufacture the entire plunger. This can greatly reduce the maintenance costs of the plunger and the hydraulic pump.

[0019] The connecting rod 5 that drives the plunger is connected to the plunger base 1. In order to provide a degree of freedom with respect to the connecting rod 5, the connecting rod 5 comprises a sliding shoe 51 with a recess, while the plunger base 1 comprises a plunger connection 14 which is spherical in shape, corresponding to the shape of the sliding shoe 51.

[0020] The plunger connection portion 14 has a tip 13 on the side away from the outer peripheral wall 21. The tip 13 has a tapered hole that tapers from the outside of the plunger base 1 toward the inside of the plunger base 1. The plunger base 1 defines a first portion 41 of the fluid passage. The first portion 41 extends to the tip 13 and is connected to the tip of the tapered hole to be in fluid communication with the outside of the plunger body 2 so as to deliver part of the fluid between the plunger base 1 and the shoe 51 to form a liquid film, such as an oil film, to act as a lubricant. The connecting rod 5 includes a fluid receiving passage 52 provided in the shoe 51. The fluid receiving passage 52 is connected to the fluid passage 4 to direct fluid to the friction face of the shoe 51 to form a lubricating layer.

[0021] In Figure 1 the first embodiment shown, the cavity S serves as a second portion 42 of the fluid passage 4 in fluid communication with the first portion 41. The inner diameter of the second portion 42, i.e. the cavity S, is greater than the inner diameter of the first portion 41.

[0022] Figure 2 is a cross-sectional view of a plunger according to a second embodiment of the application. Compared to the first embodiment of Figure 1 the second embodiment of Figure 2 the second embodiment of the plunger, the end cap 3 includes a fluid hole 32 and a first inner peripheral wall 34 extending around the fluid hole 32 toward the first end 211 of the outer peripheral wall 21 of the plunger body 2. The first inner peripheral wall 34 is sealed to the end wall of the cavity S by means of a sealing ring to define a second portion 42 and a third portion 43 of the fluid passage 4 in the cavity S. The second portion 42 is in fluid communication with the first portion 41 and with the outside of the plunger body 2 through the fluid hole 32. The third portion 43 is in fluid communication with the outside of the plunger body 2 through the through hole 31. The inner diameter of the second portion 42 is equal to the inner diameter of the first portion 41. In other words, the first inner peripheral wall 34 surrounds the second portion 42 and the third portion 43 is formed between the outer peripheral wall 12 and the first inner peripheral wall 34. The third portion 43 and the first inner peripheral wall 34 maintain the strength of the plunger while reducing the weight of the plunger, so that the plunger has a higher efficiency. When the plunger is pushed (to the right in the figure), liquid enters the third portion 43 through the through hole 31. When the plunger is pulled (to the left in the figure), the liquid pressure in the third portion 43 is higher than the liquid pressure outside the end cap 3, so the liquid that previously entered the third portion 43 will flow back to the outside of the end cap 3 through the through hole 31, so that the liquid pressure outside the end cap 3 increases, reducing the pressure pulsation outside the end cap, thereby reducing the noise generated by the pressure pulsation.

[0023] In Figure 2 the second embodiment shown, the end cap 3 includes a plurality of through holes 31. In order to have the same effect of reducing the pressure pulsation as the first embodiment including a single through hole 31, the sum of the cross-sectional areas of the plurality of through holes 31 is equal to the cross-sectional area of the single through hole 31 in the case where the end cap 3 includes a single through hole 31, as inFigure 1 The cross-sectional area of the single through hole 31 is shown. The position of the plurality of through holes 31 on the end cap 3 can be arbitrarily set, as long as each through hole 31 is connected to the third portion 43.

[0024] Figure 3 A cross-sectional view of a plunger according to a third embodiment of the present application. Unlike the first embodiment shown, Figure 1 In the third embodiment shown, the end cap 3 is connected to the outer peripheral wall 21 by friction welding. The cavity S helps to reduce the weight of the plunger, so that the plunger has higher efficiency. Figure 3 The outer peripheral wall 21 includes a first end 211 connected to the plunger base 1 and a second end 212 connected to the end cap 3 in the direction of its central axis. The end cap 3 is provided with a through hole 31 that fluidly communicates the cavity S with the outside of the plunger body 2. In this way, when the plunger is pushed (to the right in the figure), liquid enters the cavity S through the through hole 31. When the plunger is pulled (to the left in the figure), the liquid pressure in the cavity S is higher than the liquid pressure outside the end cap 3, so the liquid that previously entered the cavity S will flow back through the through hole 31 to the outside of the end cap 3, so that the liquid pressure outside the end cap 3 increases, reducing the pressure pulsations outside the end cap, thus reducing the noise generated by the pressure pulsations and preventing or reducing the separation of air from the liquid, i.e., reducing cavitation on the surfaces of the various components of the plunger.

[0025] The connecting rod 5 that drives the plunger is connected to the plunger base 1. To provide freedom of movement with respect to the connecting rod 5, the connecting rod 5 includes a sliding shoe 51 with a recess, while the plunger base 1 includes a plunger connection 14 that is spherical in shape, corresponding to the shape of the sliding shoe 51.

[0026] The plunger connection 14 has a tip 13 on the side facing away from the outer peripheral wall 21. The tip 13 has a conical hole that tapers from the outside of the plunger base 1 towards the inside of the plunger base 1. The plunger base 1 defines a first portion 41 of the fluid channel. The first portion 41 extends to the tip 13 and is connected to the tip of the conical hole to fluidly communicate with the outside of the plunger body 2, so as to deliver part of the fluid between the plunger base 1 and the sliding shoe 51 to form a liquid film, such as an oil film, thus acting as a lubricant. The connecting rod 5 includes a fluid receiving channel 52 provided in the sliding shoe 51. The fluid receiving channel 52 is connected to the fluid channel 4 to direct the fluid to the friction face of the sliding shoe 51, forming a lubricating layer.

[0027] In the third embodiment shown,

[0028] The cavity S acts as a second portion 42 of the fluid channel 4, in fluid communication with the first portion 41, in the third embodiment shown. The inner diameter of the second portion 42 (i.e., the cavity S) is greater than the inner diameter of the first portion 41. Figure 3

[0029] Figure 4 ​: is a cross-sectional view of a plunger according to a fourth embodiment of the present application. Figure 3 The third embodiment is different in that Figure 4 In the fourth embodiment, in addition to the outer peripheral wall 21, the plunger body 2 also includes a second inner peripheral wall 22 arranged inside the outer peripheral wall 21. The second inner peripheral wall 22 defines a second portion 42 and a third portion 43 of the fluid channel 4. The second portion 42 is in fluid communication with the first portion 41 and is in fluid communication with the external fluid of the plunger body 2 through the fluid hole 32, and the third portion 43 is in fluid communication with the external fluid of the plunger body 2 through the through hole 31. The inner diameter of the second portion 42 is equal to the inner diameter of the first portion 41. In other words, the second inner peripheral wall 22 surrounds the second portion 42, and the third portion 43 is formed between the outer peripheral wall 12 and the second inner peripheral wall 22. The third portion 43 and the second inner peripheral wall 22 maintain the strength of the plunger while reducing the weight of the plunger, so that the plunger has higher efficiency. When the plunger is pushed (to the right in the figure), the liquid enters the third portion 43 through the through hole 31. When the plunger is pulled (to the left in the figure), the liquid pressure in the third part 43 is higher than the liquid pressure on the outside of the end cover 3. Therefore, the liquid that previously entered the third part 43 will flow back to the outside of the end cover 3 through the through hole 31, so that the liquid pressure on the outside of the end cover 3 increases, reducing the pressure pulsation on the outside of the end cover, and thus reducing the noise generated by the pressure pulsation.

[0030] exist Figure 4 In the fourth embodiment shown, the end cap 3 includes a plurality of through holes 31. In order to achieve the same pressure pulsation reduction effect as the third embodiment including a single through hole 31, the sum of the cross-sectional areas of the plurality of through holes 31 is equal to the sum of the cross-sectional areas of the end cap 3 including a single through hole 31 (e.g., Figure 3 The cross-sectional area of ​​the single through hole 31 is shown. The positions of the plurality of through holes 31 on the end cover 3 can be set arbitrarily, as long as each through hole 31 is connected to the third portion 43.

[0031] On the other hand, the present application further provides a hydraulic pump, which includes a cylinder (not shown), a connecting rod 5 , and a plunger located in the cylinder and rotatably connected to the connecting rod 5 .

[0032] Figure 5 FIG. 1 is a graph showing the liquid pressure outside the end cap collected when the plunger according to the present application is in operation. Figure 5In the figure, curve C1 represents the change of the liquid pressure outside the end cover over time when the end cover 3 of the plunger does not include the through hole 31. Curve C2 represents the change of the liquid pressure outside the end cover over time when the end cover 3 of the plunger includes a through hole 31 and the inner diameter of the through hole 31 is 0.6%-1.2% of the inner diameter of the plunger body 2 (or the cross-sectional area of ​​the through hole 31 is 0.0036%-0.0144% of the cross-sectional area of ​​the plunger body 2). Curve C3 represents the change of the liquid pressure outside the end cover over time when the end cover 3 of the plunger includes a through hole 31 and the inner diameter of the through hole 31 is greater than 1.2% of the inner diameter of the plunger body 2 (or the cross-sectional area of ​​the through hole 31 is greater than 0.0144% of the cross-sectional area of ​​the plunger body 2). From Figure 5 It can be seen that when the inner diameter of the through hole 31 is 0.6%-1.2% of the inner diameter of the plunger body 2 (or the cross-sectional area of ​​the through hole 31 is 0.0036%-0.0144% of the cross-sectional area of ​​the plunger body 2), the liquid pressure outside the end cover has a relatively low pulse. When the inner diameter (or cross-sectional area) of the through hole 31 is further increased, the liquid pressure outside the end cover cannot be increased to a sufficient level within the specified time, thereby affecting the efficiency of the hydraulic pump. In addition, when the end cover 3 of the plunger includes multiple through holes 31, the sum of the cross-sectional areas of the multiple through holes 31 is equal to the cross-sectional area of ​​the single through hole 31 when the end cover 3 includes a single through hole 31. Therefore, the sum of the cross-sectional areas of the multiple through holes 31 should be 0.0036%-0.0144% of the cross-sectional area of ​​the plunger body 2.

[0033] The above specific embodiments are merely intended to more clearly illustrate the principles of the present application. The various components are clearly shown or described to facilitate understanding of the principles of the present application. Those skilled in the art may readily make various modifications or variations to the present application without departing from the scope of the present application. It should be understood that such modifications or variations are intended to be encompassed within the scope of patent protection of the present application.

Claims

1. A plunger comprising: a plunger base (1); a plunger body (2) having a cylindrical shape and connected to the plunger base (1), wherein the plunger body (2) comprises an outer peripheral wall (21) and a cavity (S) disposed inside the outer peripheral wall (21); an end cap (3) connected to the plunger body (2); a fluid passage (4) passing through the plunger base (1) and plunger body (2); wherein, the outer peripheral wall (21) comprises a first end (211) connected to the plunger base (1) and a second end (212) connected to the end cap (3) in a direction of a central axis thereof; characterized in that, the end cap (3) is provided with one or more through holes (31) that fluidly communicate the cavity (S) with an outside of the plunger body (2).

2. The plunger according to claim 1, wherein, the end cap (3) is connected to the outer peripheral wall (21) by means of a threaded connection or friction welding; the plunger base (1) defines a first portion (41) of the fluid passage (4) and comprises a spherical plunger connection portion (14); the plunger connection portion (14) has a tip (13) on a side distal to the outer peripheral wall (21); the tip (13) has a conical hole tapering from an outside of the plunger base (1) towards an inside of the plunger base (1); the first portion (41) is connected to a tip of the conical hole to fluidly communicate with the outside of the plunger body (2).

3. The plunger according to claim 2, wherein, the cavity (S) fluidly communicates with the first portion (41) as a second portion (42) of the fluid passage (4).

4. The plunger according to claim 3, wherein, the end cap (3) comprises a fluid hole (32) for fluidly communicating the fluid passage (4) with the outside of the plunger body (2).

5. The plunger according to claim 4, wherein, the end cap (3) is provided with external threads; the outer peripheral wall (21) is provided with internal threads corresponding to the external threads inside the second end (212).

6. The plunger according to claim 5, wherein, the end cap (3) comprises a first inner peripheral wall (34) extending towards the first end (211) around the fluid hole (32); the first inner peripheral wall (34) abuts against an end of the cavity (S) to define a second portion (42) and a third portion (43) of the fluid passage (4) in the cavity (S); the second portion (42) fluidly communicates with the first portion (41) and with the outside of the plunger body (2) through the fluid hole (32); the third portion (43) fluidly communicates with the outside of the plunger body (2) through the through holes (31).

7. The plunger according to claim 4, wherein, the plunger body (2) comprises a second inner peripheral wall (22) disposed inside the outer peripheral wall (21). The second inner peripheral wall (22) defines, in the cavity (S), a second portion (42) and a third portion (43) of the fluid passage (4); The second portion (42) is in fluid communication with the first portion (41); The third portion (43) is in fluid communication with the outside of the plunger body (2) through the fluid hole (32).

8. The plunger according to any one of claims 1-7, wherein, In the case where the through hole (31) is provided on the end cap (3): The inner diameter of the through hole (31) is 0.6-1.2% of the inner diameter of the plunger body (2), or the cross-sectional area of the through hole (31) is 0.0036-0.0144% of the cross-sectional area of the plunger body (2).

9. The plunger according to any one of claims 1-7, wherein, In the case where a plurality of through holes (31) are provided on the end cap (3), the sum of the cross-sectional areas of the plurality of through holes (31) is 0.0036-0.0144% of the cross-sectional area of the plunger body (2).

10. A hydraulic pump characterized by, The hydraulic pump comprises: a cylinder; a connecting rod; and the plunger according to any one of claims 1-9, which is located in the cylinder and is rotatably connected to the connecting rod.

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