Variable displacement control piston pump

Abstract

To provide a variable displacement control piston pump with reduced noise.SOLUTION: A stopper 23 is arranged rearward in a rocking direction of a swash plate 7 by a spring 21. A maximum tilt angle of the swash plate 7 can be regulated by the stopper 23. The stopper 23 in the piston pump 1 is stored in a cylinder 29 formed in a housing 3. A hydraulic circuit 27 is connected to the cylinder 29, and a constant hydraulic pressure is applied thereto. The stopper 23 receives force in a direction of being pushed out from the cylinder 29 by the hydraulic pressure. Accordingly, the stopper 23 is always pressed against the swash plate 7 with constant pressing force and a contact state is maintained.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a constant horsepower control type variable displacement control piston pump. [Background technology]

[0002] For example, in hydraulic pumps for construction machinery, etc., constant horsepower control type variable displacement control piston pumps are widely used to make effective use of engine output. Variable displacement piston pumps achieve constant horsepower control by balancing the moment due to spring load and the moment due to discharge pressure, so that when the discharge pressure increases, the swash plate tilts and the discharge flow rate decreases.

[0003] One example of such a variable displacement piston pump is a constant horsepower control piston pump (Patent Document 1), in which the center of oscillation of the swash plate and its oscillation central axis are positioned away from the resultant force central axis that presses the swash plate axially when the pistons are operating. In Patent Document 1, when one end of the swash plate presses a spring to reduce the tilt angle of the swash plate, the length of the resultant force arm from the piston relative to the oscillation center decreases. This allows for more ideal constant horsepower control characteristics. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Utility Model Application Publication No. 4-6775 Summary of the Invention [Problem to be solved by the invention]

[0005] 5 and 6 are diagrams showing a conventional piston pump 100. FIG. 5 shows a state in which the swash plate 107 is at its maximum angle and has a maximum discharge volume, and FIG. 6 shows a state in which the swash plate 107 has swung and the inclination angle of the swash plate 107 has become smaller.

[0006] The shaft 105 and the cylinder barrel 109 are rotatable around the shaft 105. A plurality of cylinders 111 are arranged in the cylinder barrel 109, and a piston 113 is provided in each cylinder 111. The end of each piston 113 abuts against the swash plate 107 via a shoe 117. The shoe 117 is slidable along the surface of the swash plate 107.

[0007] The swash plate 107 can swing around a swing center 119 with a rotation axis perpendicular to the axial direction of the shaft 105 (perpendicular to the plane of the drawing). That is, the angle of the swash plate 107 relative to the shaft 105 is variable. One end of the swash plate 107 is in contact with the tip of a spring holder 122 fitted into a spring 121, and the swash plate 107 is pressed by the spring 121. That is, a moment Ms due to the pressing force from the spring 121 is applied to the swash plate 107.

[0008] When the shaft 105 is rotated, the cylinder barrel 109 rotates, causing the piston 113 to move along the swash plate 107. At this time, because the swash plate 107 is tilted, the piston 113 reciprocates relative to the cylinder 111 according to the distance between the swash plate 107 and the cylinder barrel 109. At this time, oil is sucked in and discharged in accordance with the reciprocating movement of the piston 113.

[0009] Here, the swash plate 107 receives the resultant force from all the pistons 113. Therefore, a moment Mp due to the pressing forces from all the pistons 113 is applied to the swash plate 107. That is, the swash plate 107 is maintained at an angle where the moment Ms due to the springs 121 and the moment Mp due to the pistons 113 are balanced.

[0010] 7(a) is an enlarged view of the vicinity of the stopper 123 in FIG. 5. As described above, when Ms > Mp, the swash plate 107 swings counterclockwise in the figure due to the pressing force of the spring 121 and remains in contact with the stopper 123. That is, the stopper 123 is fixed to the housing and limits the maximum inclination angle of the swash plate 107. Meanwhile, from this state, Mp gradually increases, and when Mp exceeds Ms, the swash plate 107 begins to swing. FIG. 7(b) shows the state immediately after the swash plate 107 starts to swing and separates from the stopper 123.

[0011] The internal pressure of the cylinders 111 alternates between suction pressure and discharge pressure during one rotation of the shaft 105, causing the resultant piston force acting on the swash plate 107 to fluctuate, resulting in vibrations that cause the swash plate 107 to oscillate. This vibration causes a problem of a knocking noise due to contact and separation between the stopper 123 and the swash plate 107 near the cutoff point where the swash plate starts to oscillate from the maximum inclination angle. That is, when the difference between Mp and Ms is small, a small gap may form between the swash plate 107 and the stopper 123 (part X in the figure). This pulsation causes the states shown in Figures 7(a) and 7(b) to alternate, resulting in a knocking noise.

[0012] The present invention has been made in view of the above problems, and has as its object to provide a variable displacement control piston pump that produces less noise. [Means for solving the problem]

[0013] In order to achieve the above-mentioned object, the present invention provides a variable displacement control piston pump comprising: a cylinder barrel rotatable around a shaft within a housing; a plurality of cylinders in the cylinder barrel arranged at predetermined intervals circumferentially around the shaft; pistons capable of reciprocating relative to the cylinders in the axial direction of the shaft; a swash plate that can swing around a support portion so that its angle relative to the pistons is variable; a spring that can press against a portion of the swash plate to increase the inclination angle of the swash plate; and a stopper that limits the maximum inclination angle of the swash plate, wherein an end of the piston can slide along the swash plate, and the stopper has a pressing means that can press against the swash plate, and the stopper is maintained in a state where it is pressed against the swash plate with a predetermined force within the range of swash plate oscillation.

[0014] It is desirable that the pressing means be a hydraulic piston, and that the hydraulic piston be pressed against the swash plate with a constant force.

[0015] A spring may be disposed on the back of the hydraulic piston, and the spring may press the hydraulic piston in the pressing direction of the hydraulic piston.

[0016] The stopper may be disposed at a position facing the spring across the swash plate.

[0017] The stopper may be disposed on the opposite side of the support portion from the spring.

[0018] According to the first aspect of the present invention, a pressing means is provided behind the stopper to press the stopper against the swash plate, so that when the angle of the swash plate changes, the stopper follows the swash plate and maintains a predetermined pressing force against it, preventing the stopper from separating from the swash plate and suppressing the occurrence of knocking noise.

[0019] In particular, if the pressing means is a hydraulic piston, the stopper can be pressed against the swash plate with a constant force relative to the stroke length of the hydraulic piston, so that the stopper can be reliably pressed against the swash plate regardless of the inclination angle of the swash plate.

[0020] Furthermore, by placing a spring behind the hydraulic piston and using the spring to press the hydraulic piston in the direction of the pressure, the hydraulic piston can be pushed out smoothly immediately after the swash plate starts to oscillate. In other words, immediately after the swash plate starts to oscillate from the maximum discharge state, friction between the hydraulic piston and the cylinder can cause the piston to start moving unstably, but this type of delay in the hydraulic piston movement can be suppressed, and the piston can be pressed against the swash plate more reliably.

[0021] The stopper may be located opposite the spring across the swash plate, or on the opposite side of the support of the swash plate from the spring. In either case, the stopper limits the maximum inclination angle of the swash plate and suppresses the generation of knocking noise when the swash plate swings. [Effects of the Invention]

[0022] According to the present invention, it is possible to provide a variable displacement control piston pump that produces little noise. [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 2 is a diagram showing the piston pump 1 in a state of maximum discharge amount. [Figure 2] FIG. 2 is a diagram showing the piston pump 1 in a state in which the swash plate 7 is oscillating. [Figure 3] 1A is an enlarged view of the vicinity of the stopper 23 in the state where the discharge amount is maximum, and FIG. 1B is an enlarged view of the vicinity of the stopper 23 in the state where the swash plate 7 is oscillating. [Figure 4] FIG. 2 is a diagram showing a piston pump 1a in a state of maximum discharge amount. [Figure 5] FIG. 2 is a diagram showing the piston pump 100 in a state of maximum discharge amount. [Figure 6] FIG. 2 is a diagram showing the piston pump 100 in a state in which the swash plate 107 is oscillating. [Figure 7] 1A is an enlarged view of the vicinity of the stopper 123 in the state where the discharge amount is maximum, and FIG. 1B is an enlarged view of the vicinity of the stopper 123 in the state where the swash plate 7 starts to swing. DETAILED DESCRIPTION OF THE INVENTION

[0024] A piston pump according to an embodiment of the present invention will be described below. Fig. 1 shows the piston pump 1 in a state where the discharge amount is maximum, and Fig. 2 shows the piston pump 1 in a state where the swash plate 7 is oscillating. The piston pump of this embodiment is a constant horsepower variable displacement control type piston pump.

[0025] The piston pump 1 is mainly composed of a shaft 5, a swash plate 7, a cylinder barrel 9, a valve plate 15, a spring 21, etc. The shaft 5, the swash plate 7, the cylinder barrel 9, the valve plate 15, the spring 21, etc. are accommodated inside a housing 3.

[0026] The shaft 5 is rotatably attached to the housing 3. A cylinder barrel 9 is also connected to the shaft 5. That is, the cylinder barrel 9 is rotatable together with the shaft 5, with the shaft 5 as its axis. The cylinder barrel 9 has a plurality of cylinders 11 arranged at predetermined intervals in the circumferential direction around the shaft 5. Each cylinder 11 has a piston 13 arranged therein that is capable of reciprocating in the axial direction of the shaft 5.

[0027] An end of each piston 13 is brought into contact with the swash plate 7 via a shoe 17. The shoe 17 is slidable along the surface of the swash plate 7. That is, the end of the piston 13 moves circumferentially around the shaft 5 along the surface of the swash plate 7.

[0028] The swash plate 7 can swing around a support part (swing center 19) with a rotation axis perpendicular to the axial direction of the shaft 5 (direction perpendicular to the paper surface). That is, the angle of the swash plate 7 is variable with respect to the shaft 5. However, unlike the cylinder barrel 9, the swash plate 7 does not rotate around the shaft 5 as a rotation axis.

[0029] An arm is provided at one end (upper in the drawing) of the swash plate 7, and the tip of a spring 21 at the arm contacts the swash plate 7 via a spring holder 22, and the spring 21 presses the swash plate 7 so as to increase the inclination angle with respect to the shaft 5. That is, a moment Ms due to the pressing force of the spring 21 is applied to the swash plate 7 with respect to the oscillation center 19 as the reference. The moment Ms due to the force of the spring 21 causes the swash plate 7 to tilt counterclockwise in the drawing from the oscillation center 19 as the starting point.

[0030] A stopper 23 is disposed behind the swash plate 7 in the direction of oscillation caused by the spring 21. That is, the stopper 23 is disposed in a position facing the spring 21 across the swash plate 7. In the state shown in FIG. 1, the swash plate 7 is at its maximum inclination angle, and in this state, the stopper 23 prevents the swash plate 7 from further oscillating. That is, the stopper 23 can restrict the maximum inclination angle of the swash plate 7. The function of the stopper 23 will be described in detail later.

[0031] As described above, when the shaft 5 is rotated, the cylinder barrel 9 rotates together with the shaft 5. As a result, the cylinder 11 and the piston 13 provided in the cylinder barrel 9 move around the shaft 5. Also, as described above, the end of the piston 13 can move along the surface of the swash plate 7.

[0032] At this time, since the swash plate 7 is inclined, the piston 13 reciprocates with respect to the cylinder 11 according to the distance between the swash plate 7 and the cylinder barrel 9. For example, in FIG. 1, the piston 13 shown above the shaft 5 is in the state of being most withdrawn from the cylinder 11, and the piston 13 shown below the shaft 5 is in the state of being most pushed into the cylinder 11.

[0033] Holes are formed in the valve plate 15 at predetermined positions. Therefore, when the piston 13 moves from the pushed-in state to the pulled-out state, oil is sucked into the cylinder 11 through the holes in the valve plate 15. Also, when the piston 13 moves from the pulled-out state to the pushed-in state, oil is discharged through the holes in the valve plate 15. That is, as shown in FIG. 1, when the inclination angle of the swash plate 7 is maximum, the oil discharge amount is the largest, and as shown in FIG. 2, when the inclination angle of the swash plate 7 decreases, the oil discharge amount decreases.

[0034] Here, as described above, the swash plate 7 receives the combined force from all the pistons 13. That is, a moment Mp due to the pressing force from all the pistons 13 is applied to the swash plate 7. For this reason, when Ms > Mp, the swash plate 7 inclines in the direction in which the inclination angle increases (counterclockwise in the figure), and when Ms < Mp, the swash plate 7 inclines in the direction in which the inclination angle decreases (clockwise in the figure) against the moment Ms by the spring 21. At this time, when the inclination angle of the swash plate 7 decreases, the pressing force of the spring 21 increases, so the swash plate 7 is held at an angle where Ms and Mp are balanced. That is, when the hydraulic pressure of the piston pump 1 increases, the discharge amount is decreased and constant horsepower control is performed.

[0035] Next, the function of the stopper 23 in the piston pump 1 will be described in detail. FIG. 3(a) is an enlarged view of the vicinity of the stopper 23 in FIG. 1, and FIG. 3(b) is a state in which the swash plate 7 swings in the direction in which the inclination angle of the swash plate 7 decreases from the state of FIG. 3(a), and is an enlarged view of the vicinity of the stopper 23 in FIG. 2.

[0036] In the piston pump 1, the stopper 23 is housed in a cylinder portion 29 formed in the housing 3. A hydraulic circuit 27 is connected to the cylinder portion 29, and a constant hydraulic pressure (P in the figure) is applied to the cylinder portion 29. Note that the flow paths and various valves that make up the hydraulic circuit 27 may be disposed outside the housing 3 or may be housed within the housing 3.

[0037] The stopper 23 receives a hydraulic force in a direction pushing it out from the cylinder portion 29. Therefore, the stopper 23 can press the swash plate 7 with a constant force. In other words, the stopper 23 is a hydraulic piston and functions as a pressing means that presses the stopper 23 against the swash plate 7 with a predetermined force.

[0038] As described above, the inclination angle of the swash plate 7 is maintained in a state where the moment Ms acting on the swash plate 7 due to the pressing force of the spring 21 and the reverse moment Mp acting on the swash plate 7 due to the resultant force of the pistons 13 are balanced. For this reason, the spring force of the spring 21 is set in advance taking into account the pressing force of the stopper 23.

[0039] In this way, when the pressing force of the stopper 23 is sufficiently smaller than the pressing force of the spring 21 and the moment Ms of the spring 21 is larger than the moment Mp of the hydraulic pressure from the piston 13, the stopper 23 is pushed to its limit against the cylinder portion 29 by the pressing force of the spring 21 via the swash plate 7, as shown in FIG. 1.

[0040] Here, the state where the stopper 23 is completely pushed into the cylinder portion 29 means that the stopper 23 cannot move rearward any further. Therefore, the stopper 23 has the function of restricting the maximum inclination angle of the swash plate 7.

[0041] On the other hand, when Mp becomes larger than Ms, the swash plate 7 swings in a direction that decreases the inclination angle. At this time, a pressing force is applied to the stopper 23 from behind, so the stopper 23 follows the swash plate 7 and maintains contact with it. The stroke length of the stopper 23 is set to be equal to or greater than the displacement of the swash plate 7 within its swingable range (the maximum displacement of the spring 21). In other words, the stopper 23 has a movable range that can follow the swingable range of the swash plate 7 set in the piston pump 1 (i.e., the range from the state shown in FIG. 1 to the state where the spring 21 is most compressed within the operating range).

[0042] Therefore, as shown in Figure 3(b), even when the inclination angle of the swash plate 7 is at its minimum within the set range, the stopper 23 remains pressed against the swash plate 7 with a predetermined pressure. That is, the stopper 23 is constantly pressed against the swash plate 7 with a constant pressure and maintained in contact with the swash plate 7. Therefore, even if the swash plate 7 vibrates due to the repeated oil intake and discharge of the pistons 13, as described above, the stopper 23 follows the vibration and remains in constant contact with the swash plate 7. This suppresses the occurrence of so-called knocking noise.

[0043] A pin 31 having a diameter smaller than that of the main body of the stopper 23 is provided behind the stopper 23. A hole 33 is formed in the housing 3 behind the cylinder portion 29, and the pin 31 is received in the hole 33. A disc spring 25 having a diameter larger than that of the hole 33 is disposed behind the stopper 23 within the cylinder portion 29. The disc spring 25 can press the stopper 23 from the rear toward the swash plate 7. A hole is formed in the disc spring 25, and the pin 31 is inserted into the hole of the disc spring 25. As described above, when the stopper 23 is fully pressed into the cylinder portion 29, the disc spring 25 is in a crushed state.

[0044] When the stopper 23 is a hydraulic piston, as shown in Fig. 3(a), the operation of the stopper 23 may become unstable immediately after the swash plate 7 starts to oscillate from the state where the swash plate 7 is pressed by the spring 21 at the maximum inclination angle. For example, when the stopper 23 is completely pressed into the cylinder 29 by the force of the swash plate 7 and the swash plate 7 oscillates slightly, there may be a momentary delay in the stopper 23's response to the swash plate 7's oscillation due to the influence of friction between the stopper 23 and the cylinder 29.

[0045] In contrast, the disc spring 25 assists the operation of the stopper 23 immediately after the swash plate 7 starts to move. Therefore, the stopper 23 can stably maintain a state of pressing against the swash plate 7 from the initial stage of operation.

[0046] The length of pin 31 is set to be equal to or greater than the stroke length of stopper 23. Therefore, pin 31 does not come out of hole 33 within the movable range of stopper 23. Therefore, disc spring 25 does not come out of pin 31, and disc spring 25 is always held on the outer periphery of pin 31 (rear of stopper 23).

[0047] In the piston pump 1 shown in Figure 1 etc., the stopper 23 is arranged to face the opposite side of the spring 21 across the swash plate 7, but the arrangement of the stopper 23 is not limited to this. Figure 4 is a diagram showing a piston pump 1a according to another embodiment. In the mechanism of the piston pump 1a, components that perform the same functions as those in the piston pump 1 are assigned the same reference numerals as in Figure 1 etc., and redundant explanations will be omitted.

[0048] The piston pump 1a has a structure similar to that of the piston pump 1, but differs in the arrangement of the stopper 23. In the piston pump 1a, the stopper 23 is arranged on the opposite side of the support portion (oscillating center 19) of the swash plate 7 from the spring 21. In other words, the direction in which the spring 21 presses the swash plate 7 and the direction in which the stopper 23 presses the swash plate 7 are the same (toward the left in the figure).

[0049] In this embodiment, the stopper 23 is a hydraulic piston with a stroke length that can follow the swing range of the swash plate 7. That is, the stopper 23 follows the swing of the swash plate 7 and is always maintained in contact with the swash plate 7. In addition, since the stopper 23 has a limit to how far it can be pushed into the cylinder portion 29, it can also function as a stopper that prevents the swash plate 7 from tilting any further.

[0050] As described above, according to this embodiment, the stopper 23, which limits the maximum inclination angle of the swash plate 7, can move in accordance with the swing of the swash plate 7. Furthermore, since the stroke length of the stopper 23 can cover the swingable range of the swash plate 7, the tip of the stopper 23 does not separate from the swash plate 7. This prevents the occurrence of so-called knocking noise caused by the swash plate 7 and the stopper 23.

[0051] For example, even if the stopper 23 is movable and can follow the oscillation of the swash plate 7, if the stroke length is insufficient, the stopper 23 and the swash plate 7 may separate at any tilt angle of the swash plate 7, which may result in a knocking noise. In contrast, in the piston pump of this embodiment, the stroke length of the stopper 23 is sufficient to cover the range of oscillation of the swash plate 7, so that the generation of the knocking noise can always be suppressed regardless of the pressure (or the tilt angle of the swash plate 7).

[0052] Furthermore, by using a hydraulic piston as the stopper 23, the stopper 23 can be continuously pressed against the swash plate 7 with a constant force.

[0053] Furthermore, by disposing the disc spring 25 on the back of the stopper 23, the movement of the stopper 23 at the initial stage of operation is assisted, and the stopper 23 can be reliably pressed against the swash plate 7.

[0054] The arrangement of the stopper 23 is not limited to the above-described embodiment. The pressing means for pressing the stopper 23 from behind may be a method other than hydraulic pressure, and is not particularly limited. Furthermore, it is not necessarily required that a member be arranged behind the stopper 23, and other elastic members may be used instead of the disc spring 25. [Example]

[0055] Noise was evaluated using a piston pump having a conventional fixed stopper and a piston pump having a swash plate follow-up type stopper according to this embodiment. -1 The evaluation was performed at a pressure of -5 MPa, which is the cut point (the pressure at which the swash plate starts to swing).

[0056] As a result, the conventional pump produced a banging noise with a maximum noise level of 89.6 dB, whereas the pump according to this embodiment produced no banging noise and reduced noise to a maximum noise level of 80.9 dB.

[0057] Although the embodiments of the present invention have been described above with reference to the accompanying drawings, the technical scope of the present invention is not limited to the above-described embodiments. It is clear that those skilled in the art can conceive of various modifications and alterations within the scope of the technical ideas described in the claims, and it is understood that these modifications and alterations also fall within the technical scope of the present invention. [Explanation of symbols]

[0058] 1, 1a... Piston pump 3. Housing 5... Shaft 7……Swash plate 9...Cylinder barrel 11...Cylinder 13...Piston 15...Valve plate 17...Shoo 19....Swing center 21...Spring 22...Spring holder 23...Stopper 25...Disc spring 27...Hydraulic circuit 29...Cylinder section 31...pin 33……hole 100...Piston pump 105... Shaft 107……Swash plate 109...Cylinder barrel 111...Cylinder 113... Piston 117...Shoo 119....Swing center 121...Spring 122...Spring holder 123...Stopper

Claims

1. A variable displacement control piston pump, Within the housing, a cylinder barrel rotatable around a shaft; In the cylinder barrel, a plurality of cylinders are arranged at predetermined intervals in a circumferential direction around the shaft; a piston reciprocating relative to the cylinder in the axial direction of the shaft; a swash plate that can swing around a support portion so that the angle with respect to the piston can be changed; a spring that presses against a portion of the swash plate so as to increase the inclination angle of the swash plate; a stopper that limits the maximum inclination angle of the swash plate; Equipped with The end of the piston is movable along the surface of the swash plate, The stopper has a pressing means that can press against the swash plate, and the stopper is maintained in a state where it is pressed against the swash plate with a predetermined force within the swingable range of the swash plate.

2. 2. A variable displacement control piston pump according to claim 1, wherein said pressing means is a hydraulic piston, and said hydraulic piston is pressed against said swash plate with a constant force.

3. 3. The variable displacement control piston pump according to claim 2, wherein a spring is disposed on the back of the hydraulic piston, and the spring presses the hydraulic piston in the pressing direction of the hydraulic piston.

4. 2. The variable displacement control piston pump according to claim 1, wherein the stopper is disposed at a position facing the spring across the swash plate.

5. 2. The variable displacement control piston pump according to claim 1, wherein the stopper is disposed on an opposite side of the support portion from the spring.

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