Variable displacement swash plate type hydraulic pump and construction machine equipped with same

Abstract

To provide a variable displacement swash plate hydraulic pump that can improve tilt responsiveness, and has high reliability, without causing an increase in size, an increase in weight, and an increase in cost of the hydraulic pump, and without increasing vibration and noise.SOLUTION: First auxiliary pockets 36at and 36bt are set so as to be housed in cylindrical concave surface parts 32a and 32b when the tilt angle of a swash plate 31 is equal to or smaller than a predetermined angle, and so as to partially protrude from the cylindrical concave surface parts 32a and 32b when the tilt angle of the swash plate 31 exceeds the predetermined angle.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a variable displacement swash plate type hydraulic pump suitable for driving hydraulic motors for traveling and turning in construction machines such as wheel loaders, hydraulic excavators, and hydraulic cranes, and to a construction machine equipped with the same. [Background technology]

[0002] A variable displacement swash plate type hydraulic pump used in construction machines such as wheel loaders, as described in the following Patent Documents 1, 2, 3, etc., basically comprises a casing having a hollow portion, a rotating shaft rotatably provided in the casing, a cylinder block provided in the casing so as to rotate integrally with the rotating shaft, a plurality of cylinders (holes) (usually an odd number, for example, 9) extending in the axial direction and spaced apart in the circumferential direction of the cylinder block (formed in the cylinder block at predetermined angular intervals around the rotating shaft and parallel to the rotating shaft), pistons inserted in each of these cylinders so as to be capable of reciprocating motion, one axial end of each of the pistons protruding from the cylinder, shoes swingably attached to the protruding ends of each of the pistons via a spherical joint or the like, and a surface side of the pistons. The pump comprises a swash plate having a smooth sliding surface for guiding each shoe and a pair of left and right cylindrical convex portions on the back side for tilting, a cradle provided at one end of the casing and provided with a pair of left and right cylindrical concave portions into which the pair of left and right cylindrical convex portions slide in order to support the swash plate so that it can be tilted, a tilt actuator for tilting the swash plate, and a valve plate provided on the opposite side of the swash plate in the casing and having a pair of left and right supply and discharge ports formed of arc-shaped elongated holes (holes that are long in the circumferential direction) sandwiched between a pair of switching lands so as to intermittently communicate with each cylinder. By changing the tilt angle of the swash plate relative to the cradle using the tilt actuator, the amount of piston stroke can be varied, i.e., the pump capacity can be controlled.

[0003] A wheel loader, which is one type of construction machine that uses the above-mentioned variable displacement swash plate hydraulic pump, has hydraulic cylinders that drive a lift arm and bucket as a front attachment, and hydraulic actuators such as a hydraulic motor for traveling, and performs tasks such as excavating and moving earth and sand by appropriately operating these. This wheel loader has a directional control valve that controls the drive speed and direction of the front cylinder with pressure oil discharged from an open circuit hydraulic pump driven by an engine. The directional control valve is controlled in response to an input from an operating lever by the operator, and is switched so that pressure oil from the hydraulic pump is supplied to each cylinder.

[0004] On the other hand, the hydraulic pump that drives the travel motor is configured in a closed circuit, and forward / rearward switching and speed adjustment are performed by tilt control of the hydraulic pump. In this case, the responsiveness of the hydraulic pump is a very important performance because it affects the acceleration and deceleration performance of the vehicle. In particular, delays in the tilt response of the closed circuit hydraulic pump used for vehicle travel lead to delays until the vehicle stops, so it is desirable to keep it as small as possible. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5777411 [Patent Document 2] JP 2005-35140 A [Patent Document 3] Japanese Patent Application Publication No. 7-103134 Summary of the Invention [Problem to be solved by the invention]

[0006] In the above-mentioned variable displacement swash plate hydraulic pump, when the swash plate receives the load of the piston connected to the high pressure port, the resultant force of the piston load (hereinafter referred to as the point of application) acts on the swash plate shifted toward the top dead center (TDC). As mentioned above, a cylindrical convex surface is formed on the back side of the swash plate, and the center of the cylindrical convex surface is located perpendicular to the rotation axis. As a result, the piston resultant force acts in a direction that reduces the inclination angle of the swash plate. Hereinafter, this is called the tilt moment.

[0007] Due to the influence of this tilting moment, the swash plate type hydraulic pump tends to be slow in increasing the capacity and quick in decreasing the capacity.

[0008] However, when the hydraulic pump and the hydraulic motor for traveling form a closed circuit, the hydraulic pump may rotate, i.e., act as a motor, when going downhill. In this case, the tilt moment caused by the resultant force of the piston load acts on the side that increases the tilt angle. Therefore, when trying to stop traveling, the tilt moment acts on the side that prevents the tilt from decreasing, so there is a problem that the stopping of traveling is delayed. In this way, when the hydraulic pump and the hydraulic motor for traveling form a closed circuit, this leads to a delay in stopping traveling on a downhill slope, so there is a demand for an improvement in the pump tilt response when the hydraulic pump acts as a motor.

[0009] One approach to solving this problem of tilt response is to use a tilt actuator with a larger output. However, this approach would naturally require the tilt actuator to be larger, which in turn would result in the hydraulic pump becoming larger, heavier, and more expensive, making it difficult to adopt.

[0010] Furthermore, if the pressure inside the cylinder is suddenly changed in order to improve rotation response, the discharge pressure pulsation becomes large, causing problems such as increased vibration and noise.

[0011] The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a highly reliable variable displacement swash plate type hydraulic pump that can improve rotation response without increasing the size, weight, or cost of the hydraulic pump, and without increasing vibration and noise.

[0012] Another object is to provide a construction machine equipped with a variable displacement swash plate type hydraulic pump according to the present invention, which can improve tilt response when going down a slope, etc., thereby providing a construction machine with high operability and safety. [Means for solving the problem]

[0013] In order to achieve the above object, the variable displacement swash plate type hydraulic pump according to the present invention basically comprises a casing, a rotary shaft rotatably provided in the casing, a cylinder block provided within the casing so as to rotate integrally with the rotary shaft, a plurality of cylinders spaced apart in the circumferential direction of the cylinder block and extending in the axial direction, pistons reciprocally inserted within the cylinders, one axial end of each of which protrudes from the cylinder, shoes attached to the protruding ends of the pistons, and a swash plate side cylindrical surface portion for tilting the pistons, the front side of which is a smooth sliding surface for guiding the shoes and the back side of which is a swash plate side cylindrical surface portion for tilting the pistons. a cradle provided at one end of the casing and provided with a cradle-side cylindrical surface portion into which the swash-plate-side cylindrical surface portion slides to support the swash-plate so as to be tiltable; a tilt actuator for tilting the swash-plate; and a valve plate provided on the axially opposite side of the swash-plate in the casing, the valve plate having a pair of supply and discharge ports intermittently communicating with each of the cylinders, the pair of supply and discharge ports being formed across a pair of switching lands, the inside of the cylinder and the portion between the shoe and the sliding surface being communicated with each other via an oil passage formed in the piston and the shoe. A pressure pocket is provided on the swash-plate-side cylindrical surface portion to lubricate the area between the swash-plate-side cylindrical surface portion and the cradle-side cylindrical surface portion, and a pressure pocket is provided on the swash-plate-side cylindrical surface portion on the top dead center side of the orbit of the shoe on the sliding surface of the swash-plate. Second 1 communication hole of One end is open, One end of a second communication hole opens toward the bottom dead center of the orbit of the shoe on the sliding surface of the swash plate,A portion of the cylindrical surface portion of the swash plate on the top dead center side of the pressure pocket Second 1 secondary pocket but It is provided, a second sub-pocket is provided at a portion of the swash plate-side cylindrical surface portion closer to the bottom dead center than the pressure pocket; The other end of the first communicating hole is connected to the second sub-pocket, and the other end of the second communicating hole is connected to the first sub-pocket, and the first sub-pocket is configured to fit within the cradle side cylindrical surface portion when the tilt angle of the swash plate is equal to or less than a predetermined specified angle, and to have a portion of it protrude from the cradle side cylindrical surface portion when the tilt angle of the swash plate exceeds the predetermined angle. Effect of the Invention

[0014] The variable displacement swash plate type hydraulic pump according to the present invention can reduce the tilt moment at a specific time without increasing the size, weight, or cost of the hydraulic pump, and without increasing vibration and noise, thereby improving the tilt response and reliability.

[0015] Furthermore, in a construction machine equipped with the variable displacement swash plate type hydraulic pump according to the present invention, the tilt response when going downhill, for example, can be improved, thereby improving driving operability and improving safety.

[0016] Problems, configurations and effects other than those described above will become apparent from the following description of the embodiments. [Brief description of the drawings]

[0017] [Figure 1] 1 is a hydraulic circuit diagram of an example of a wheel loader, which is one type of construction machine to which an embodiment of a variable displacement swash plate type hydraulic pump according to the present invention is applied. [Diagram 2] 1 is an overall cross-sectional view of an embodiment of a variable displacement swash plate type hydraulic pump according to the present invention; [Diagram 3] FIG. 3 is a schematic diagram illustrating a configuration around a swash plate of the hydraulic pump shown in FIG. 2 . [Figure 4]4A is a schematic diagram illustrating the position and size of the sub-pocket (first sub-pocket) shown in FIG. 3, in which (a) shows the state when the inclination of the swash plate is neutral, (b) shows the state when the inclination of the swash plate is at a predetermined angle (minimum tilt angle), and (c) shows the state when the inclination of the swash plate exceeds the predetermined angle (minimum tilt angle). [Diagram 5] 4 is a schematic view of the swash plate shown in FIGS. 2 and 3 as viewed from the sliding surface side. FIG. [Figure 6] FIG. 3 is a schematic diagram illustrating the configuration of a valve plate shown in FIG. 2 . [Figure 7] FIG. 11 is a schematic view showing another example of a sub-pocket as viewed from the rear surface side of the swash plate. [Figure 8] FIG. 11 is a schematic view showing yet another example of a sub-pocket as viewed from the rear surface side of the swash plate. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0019] 1 is a hydraulic circuit diagram of an example of a wheel loader, which is one type of construction machine to which an embodiment of a variable displacement swash plate type hydraulic pump according to the present invention is applied. First, a wheel loader 50 will be described below.

[0020] In FIG. 1, a wheel loader 50 is equipped with an engine 1 as a power source, and this engine 1 drives a hydraulic pump 2. The hydraulic pump 2 draws up hydraulic oil stored in a tank 5 and discharges pressurized oil. The hydraulic pump 2 is connected to a hydraulic cylinder 4, which is an actuator, via a directional control valve 3. A main relief valve 6 shown in the figure is provided to limit the maximum pressure of the hydraulic pump 2. A pilot pump 7 is connected to the shaft of the hydraulic pump 2, and the discharged oil of the pilot pump 7 is supplied to an operating lever 8 and a pump regulator 9. A pressure reducing valve is built into the operating lever 8, and a secondary pressure proportional to the amount of operation in each operating direction is generated. This secondary pressure is supplied to pilot ports 3a and 3b of the directional control valve 3, and the opening of the directional control valve 3 is controlled by this secondary pressure. The above hydraulic circuit is an open circuit system in which the hydraulic pump 2 draws up oil from the tank 5, and the discharged oil passes through the directional control valve 3, returns to the tank 5 from the hydraulic cylinder 4 or the center bypass. Open circuit systems are primarily used for the circuits that drive the front actuators.

[0021] Meanwhile, the engine 1 drives the variable displacement swash plate type hydraulic (piston) pump 10 of this embodiment via gears etc., simultaneously with the hydraulic pump 2 of the open circuit system. The hydraulic pump 10 forms a closed circuit with a traveling hydraulic motor 11. By forming the hydraulic pump 10 and the traveling hydraulic motor 11 into a closed circuit configuration in this way, the forward and reverse (front-rear travel) and speed of the vehicle body 12 of the wheel loader 50 can be controlled by the tilt angle of the swash plate of the hydraulic pump 10, thereby simplifying the device configuration and improving energy efficiency, etc.

[0022] The closed circuit hydraulic pump 10 includes a pump casing (also simply referred to as a casing) 20 consisting of a hollow cylindrical front casing 21 with a bottom and a bottom-lid-like rear casing 22, as shown in Fig. 2. A rotating shaft 25 is rotatably supported near both ends by bearings 21A, 22A provided at both ends of the pump casing 20, and a splined shaft portion 25a provided at one end (front side) of the rotating shaft 25 is adapted to be connected to a power source. A thick-walled short cylindrical cylinder block 23 is fitted and fixed to an intermediate splined shaft portion 25b of the rotating shaft 25, so that the rotating shaft 25 and the cylinder block 23 rotate integrally.

[0023] In the cylinder block 23, a plurality of cylinders (holes) 24 (usually an odd number, for example, nine) are formed concentrically about the rotation axis O of the rotary shaft 25 (in other words, spaced apart in the circumferential direction of the cylinder block 23) at predetermined angular intervals and parallel to the rotary shaft 25 (in other words, extending in the axial direction). A cylindrical piston 27 with a bottom and an opening on the rear side is inserted into each cylinder 24 so as to be able to slide back and forth.

[0024] The tip of the piston 27 (front end in the axial direction) protrudes from the cylinder 24, and a shoe 28 with a spherical joint is swingably connected to the tip of the piston 27 (the end protruding from the cylinder 24). The spherical joint may be provided on the piston 27 side. The bushing 29 presses the shoe 28 against the smooth sliding surface 31c on the flat surface of the swash plate 31 via the retainer 30 by a spring. On the back side of the sliding surface 31c of the swash plate 31, cylindrical convex surface portions 31a, 31b (see FIG. 3) for tilting, which are formed of convex cylindrical surfaces, are formed on both sides (a pair of left and right surfaces) of the rotation axis O. A cradle 32 having cylindrical concave surface portions 32a, 32b (see FIG. 3) formed of concave cylindrical surfaces to match the cylindrical convex surface portions 31a, 31b, is attached to the front casing 21 (i.e., the front side of the casing 20). The cylindrical convex surface portions 31a, 31b and the cylindrical concave surface portions 32a, 32b are slidably fitted together, whereby the cradle 32 supports the swash plate 31 so as to be tiltable. The shapes of the cylindrical convex surface portions 31a, 31b and the cylindrical concave surface portions 32a, 32b may be reversed, that is, the back surface of the swash plate 31 may be configured as a concave cylindrical surface, and the front surface of the cradle 32 may be configured as a convex cylindrical surface, and fitted together. The inside of the cylinder 24 is connected to the portion between the shoe 28 and the sliding surface 31c of the swash plate 31 via an oil passage 39 formed in the center of the piston 27 and the spherical joint shoe 28.

[0025] The tilt angle of the swash plate 31 is controlled by pushing and pulling the swash plate 31 with a servo piston (not shown) that serves as a tilt actuator. By changing the tilt angle of the swash plate 31, the stroke amount of the piston 27 can be varied, that is, the pump capacity can be controlled. An oval cylinder port 24b is formed on the rear side (opposite the piston 27 side) of each cylinder 24, and oil is discharged and sucked through the cylinder port 24b as the piston 27 slides back and forth within the cylinder 24.

[0026] A valve plate 34, with which the rear surface of the cylinder block 23 slides, is fixed to the rear casing 22 (the rear side of the casing 20, the axial opposite side of the swash plate 31 across the cylinder block 23). As can be seen clearly from FIG. 6, the valve plate 34 is formed with a supply / discharge A port 34a and a supply / discharge B port 34b, which are a pair of left and right arc-shaped elongated holes (holes that are long in the circumferential direction), sandwiching a pair of switching lands 34td, 34bd. The rear casing 22 is also provided with a supply / discharge A passage 22a connected to the A port (supply / discharge port) 34a of the valve plate 34, and a supply / discharge B passage 22b connected to the B port (supply / discharge port) 34b of the valve plate 34. Here, the A port 34a and the A passage 22a discharge oil to the side in which the vehicle body 12 moves forward, and the B port 34b and the B passage 22b discharge oil to the side in which the vehicle body 12 moves backward. The top dead center of the piston when the A port 34a and the A passage 22a discharge oil will be called TDC and the bottom dead center will be called BDC (see FIG. 6).

[0027] Next, the configuration around the swash plate 31 will be described with reference to Fig. 3. Relatively long rectangular pressure pockets 35a, 35b are formed in the centers of the two cylindrical convex surfaces 31a, 31b of the swash plate 31. On the A port 34a side, a sub-pocket 36at is provided on the side of the piston top dead center TDC when the piston is discharged from the A port, and a sub-pocket 36ab is provided on the side of the bottom dead center BDC of the pressure pocket 35a. Similarly, on the B port 34b side, a sub-pocket 36bt is provided on the side of the piston top dead center TDC, and a sub-pocket 36bb is provided on the side of the piston bottom dead center BDC of the pressure pocket 35b. The four sub-pockets 36at, 36ab, 36bt, 36bb are small rectangular pockets with the same width and depth as the pressure pockets 35a, 35b, but are shorter in length.

[0028] Here, the positions, sizes, etc. of the four sub-pockets 36at, 36ab, 36bt, 36bb are set as follows: That is, as shown in Fig. 4(a), when the tilt of the swash plate 31 is neutral (tilt angle 0 degrees), and as shown in Fig. 4(b), at a predetermined angle (minimum tilt angle), the sub-pockets 36at, 36ab, and the sub-pockets 36bt, 36bb are contained within the cylindrical concave portions 32a, 32b of the cradle 32, but when the predetermined angle is exceeded, at least a part of the sub-pockets 36at, 36bt on the top dead center TDC side protrudes from the cylindrical concave portions 32a, 32b, and when the tilt angle reaches a certain angle or more, the sub-pockets 36at, 36bt on the top dead center TDC side protrude completely from the cylindrical concave portions 32a, 32b and are removed, as shown in Fig. 4(c).

[0029] Pressure oil from port A 34a is guided to pressure pocket 35a via supply and discharge passage 37A and fixed throttle 37a formed in pump casing 20. Similarly, pressure oil from port B 34b is guided to pressure pocket 35b via supply and discharge passage 37B and fixed throttle 37b formed in pump casing 20. This provides lubrication between cylindrical convex surfaces 31a, 31b on the swash plate 31 side and cylindrical concave surfaces 32a, 32b on the cradle 32 side.

[0030] 5, on the sliding surface 31c side that guides the shoe 28 of the swash plate 31, one end of a communication hole 38t opens on the top dead center TDC side (corresponding to the switching land 34td of the valve plate 34 in FIG. 6) of the orbit along which the shoe 28 slides, and one end of a communication hole 38b opens on the bottom dead center BDC side (corresponding to the switching land 34bd of the valve plate 34 in FIG. 6). The other end of the communication hole 38t communicates with the secondary pockets 36ab, 36bb, and the other end of the communication hole 38b communicates with the secondary pockets 36at, 36bt, respectively.

[0031] In other words, the communication hole 38t provided in the swash plate 31 communicates between the vicinity of top dead center TDC on the orbit along which the shoe 28 (its central portion) slides on the sliding surface 31c and the sub-pockets 36ab, 36bb (on both the left and right) on the bottom dead center BDC side, and the communication hole 38b provided in the swash plate 31 communicates between the vicinity of bottom dead center BDC on the orbit along which the shoe 28 (its central portion) slides on the sliding surface 31c and the sub-pockets 36at, 36bt (on both the left and right) on the top dead center TDC side.

[0032] Next, the operation will be described. Here, it is assumed that the vehicle body 12 is moving forward, the tilt angle of the swash plate 31 is set to a predetermined angle or more, and the sub-pockets 36at, 36bt on the top dead center (TDC) side are completely outside the cylindrical concave portions 32a, 32b as shown in Fig. 3 and Fig. 4(c).

[0033] First, a description will be given of the case where the A port 34a is pumping at a higher pressure than the B port 34b (when the A port 34a is the discharge port) in the hydraulic pump 10. When the A port 34a is discharging, the piston 27 on the A port 34a side is displaced in a direction to push out the oil in the cylinder 24 formed in the cylinder block 23. Conversely, on the B port 34b side, the piston 27 is displaced in a direction to suck in the oil.

[0034] In this way, the valve plate 34 switches between letting oil in and out, and this switching occurs near TDC and BDC of the piston 27. The pressure inside the cylinder 24 suddenly switches from low to high at BDC, and from high to low at TDC. Here, in this embodiment, one end of communication hole 38t opens near TDC, and one end of communication hole 38b opens near BDC, and the shoe 28 (its center portion) slides over the openings of these communication holes 38t, 38b.

[0035] Meanwhile, the oil in the cylinder 24 is guided through an oil passage 39 formed in the center of the piston 27 and the shoe 28 to the area between the shoe 28 and the sliding surface 31c of the swash plate 31. Therefore, the oil in the cylinder 24 is not only guided from the cylinder port 24b to the A port 34a and B port 34b of the valve plate 34, but also from the shoe 28 (and the sliding surface 31c of the swash plate 31) to the communication holes 38t and 38b.

[0036] As a result, when the pressure inside the cylinder 24 switches from high to low on the TDC side, the cylinder 24 communicates with the sub-pockets 36ab, 36bb on the BDC side via the communication hole 38t. As a result, pressure is generated in the sub-pockets 36ab, 36bb, and the portions of the cylindrical sliding surfaces (cylindrical convex surface portions 31a, 31b and cylindrical concave surface portions 32a, 32b) near the ends where there are no pressure pockets can be lubricated, and a sudden change in the internal pressure of the cylinder 24 is alleviated.

[0037] In addition, when the pressure is switched from low to high on the BDC side, the inside of the cylinder 24 communicates with the sub-pockets 36at, 36bt on the TDC side through the communication hole 38b. However, the sub-pockets 36at, 36bt are out of the cylindrical concave portions 32a, 32b, and the inside of the low-pressure cylinder 24 only communicates with the casing drain and does not operate. As described above, the pump operation can lubricate the cylindrical sliding surfaces of the swash plate 31 and the cradle 32 near the ends where there are no pressure pockets, thereby reducing the risk of the sliding surfaces seizing and improving the reliability of the pump.

[0038] Next, a case will be described where the hydraulic pump 10 discharges from the A port 34a, but the B port 34b is at a higher pressure than the A port 34a and is acting as a motor, such as when going downhill. When the hydraulic pump 10 is acting as a motor, the suction side is at a higher pressure than the discharge side, so the pressure relationship is reversed from when the pump is acting as a motor. Therefore, at the TDC side, the pressure inside the cylinder 24 switches from low to high. The communication hole 38t communicates with the sub-pockets 36ab and 36bb. However, since this communication is at a low pressure, no operation occurs.

[0039] On the BDC side, the communication hole 38b communicates with the secondary pockets 36at, 36bt, but since the secondary pockets 36at, 36bt are outside the cylindrical concave portions 32a, 32b, the internal pressure of the cylinder 24 can be released from the secondary pockets 36at, 36bt to the casing drain.

[0040] During motor operation, the BDC side switches from high pressure to low pressure, so the switch needs to be performed when the volume inside the cylinder 24 is at its maximum. Therefore, it takes longer for the pressure inside the cylinder 24 to switch from high pressure to low pressure than during pump operation. However, as described above, the pressure inside the cylinder 24 can be released from the communication hole 38b through the sub-pockets 36at and 36bt, so the switch can be performed earlier than when only the valve plate 34 is switched. As a result, the movement of the application point of the piston resultant force during motor operation can be reduced, so the tilt moment can be reduced. As a result, the tilt response of the swash plate 31 can be improved, and the operability and safety of the vehicle body 12 can be improved.

[0041] 3 and other figures, in the variable displacement swash plate type hydraulic pump 10 of this embodiment, two cylindrical convex surfaces 31a, 31b are present on the swash plate 31, and pressure pockets 35a, 35b are formed. On the A port 34a side, a sub-pocket 36at is provided on the side of the piston top dead center TDC at the time of delivery from the A port, and a sub-pocket 36ab is provided on the side of the bottom dead center BDC with respect to the pressure pocket 35a. Similarly, on the B port 34b side, a sub-pocket 36bt is provided on the side of the piston top dead center TDC, and a sub-pocket 36bb is provided on the side of the piston bottom dead center BDC with respect to the pressure pocket 35b. The positions, sizes, etc. of the sub-pockets 36at, 36ab, 36bt, 36bb are set so that when the tilt of the swash plate 31 is neutral, the sub-pockets 36at, 36ab, the sub-pockets 36bt, 36bb are contained within the cylindrical concave portions 32a, 32b of the cradle 32, but when the tilt angle is equal to or greater than a preset predetermined angle (minimum tilt angle), at least a part of the sub-pockets 36at, 36bt on the top dead center (TDC) side protrudes from the cylindrical concave portions 32a, 32b and is out of the cylindrical concave portions 32a, 32b. Pressure oil from the A port 34a is introduced to the pressure pocket 35a via a supply and discharge passage 37A and a fixed throttle 37a provided in the pump casing 20. Similarly, pressure oil from the B port 34b is introduced to the pressure pocket 35b via a supply and discharge passage 37B and a fixed throttle 37b provided in the pump casing 20. One end of a communication hole 38t opens at the top dead center (TDC) side of the trajectory along which the shoe 28 slides, and one end of a communication hole 38b opens at the bottom dead center (BDC) side of the sliding surface 31c that guides the shoe 28 of the swash plate 31. The other end of the communication hole 38t communicates with the sub-pockets 36ab, 36bb, and the other end of the communication hole 38b communicates with the sub-pockets 36at, 36bt.

[0042] According to the variable displacement swash plate type hydraulic pump 10 of this embodiment having the above configuration, the tilt actuator and the like can be used as they are, so there is no increase in size, weight, or cost of the hydraulic pump, and there is no increase in vibration and noise, and the tilt moment can be reduced at specific times. As a result, the tilt responsiveness can be improved, and the reliability can be improved.

[0043] Furthermore, in the wheel loader 50 equipped with the variable displacement swash plate type hydraulic pump 10 of this embodiment, tilt response when going downhill, for example, can be improved, thereby improving driving operability and also improving safety.

[0044] In the above embodiment, the sub-pockets are rectangular, but the shape is not limited thereto. For example, as shown in Fig. 7, the sub-pockets may be triangular or trapezoidal, narrowing toward the circumferential ends. This allows the overlap amount between the sub-pockets 36at, 36bt and the cylindrical concave surfaces 32a, 32b, i.e., the amount of pressure released from the cylinder 24, to be changed according to the inclination angle of the swash plate 31. Furthermore, as shown in Fig. 8, the sub-pockets may be composed of a plurality of small pockets, so that the overlap amount between the sub-pockets 36at, 36bt and the cylindrical concave surfaces 32a, 32b, i.e., the amount of pressure released from the cylinder 24, can be changed according to the inclination angle of the swash plate 31.

[0045] In the above embodiment, the hydraulic pump is applied to a hydraulic circuit for traveling in a construction machine such as a wheel loader, and a closed circuit is formed with a hydraulic motor for traveling. However, the present invention is not limited to this, and the hydraulic pump may be applied to a hydraulic circuit for turning, and a closed circuit may be formed with a hydraulic motor for turning. In this case, the turning and speed of the vehicle body are controlled by the tilt angle of the swash plate of the hydraulic pump.

[0046] In the above-described embodiment, the hydraulic pump is applied to a wheel loader as an example. However, the present invention is not limited to this, and the hydraulic pump may be applied to construction machines other than wheel loaders, such as hydraulic cranes and hydraulic excavators.

[0047] The present invention is not limited to the above-described embodiment, and includes various modified forms. For example, the above-described embodiment has been described in detail to clearly explain the present invention, and is not necessarily limited to those including all of the configurations described. In addition, it is possible to replace a part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. In addition, it is possible to add, delete, or replace a part of the configuration of each embodiment with another configuration. [Explanation of symbols]

[0048] 1: Engine 2: Hydraulic pump 3: Directional valve 4: Hydraulic cylinder 5: Tank 6: Main relief valve 7: Pilot pump 8: Control lever 9: Pump regulator 10: Variable displacement swash plate type hydraulic pump 11: Hydraulic motor 12: Body 20: Pump casing 21: Front casing 22: Rear casing 22a:A passage (supply / discharge passage) 22b: B passage (supply / discharge passage) 23: Cylinder block 24: Cylinder (hole) 24b: Cylinder port 25: Rotation axis 27: Piston 28: Shoe 29: Bushing 30: Retainer 31: Swash plate 31a, 31b: Cylindrical convex surface part (swash plate side cylindrical surface part) 31c: Sliding surface 32: Cradle 32a, 32b: Cylindrical concave surface portion (cradle side cylindrical surface portion) 34: Valve plate 34a: A port (supply / exhaust port) 34b: B port (supply / exhaust port) 34td, 34bd: Switching Land 35a, 35b: Pressure pockets 36at, 36bt: Secondary pocket (first secondary pocket) 36ab, 36bb: Secondary pocket (secondary pocket) 37A, 37B: Supply / discharge path 37a, 37b: Fixed aperture 38t: Communication hole (1st communication hole) 38b: Communication hole (second communication hole) 39: Oil road 50: Wheel loader (construction machinery)

Claims

1. A casing, a rotating shaft rotatably provided in the casing, a cylinder block provided in the casing so as to rotate integrally with the rotating shaft, a plurality of cylinders extending in the axial direction at a distance from the circumferential direction of the cylinder block, a piston inserted into the cylinder so as to be capable of reciprocating and having one end side in the axial direction protruding from the cylinder, a shoe attached to the protruding end of the piston, a swash plate having a front side that is a smooth sliding surface for guiding the shoe and a swash plate side cylindrical surface portion for tilting provided on the back side, a cradle provided on one end side of the casing and having a cradle side cylindrical surface portion into which the swash plate side cylindrical surface portion slides to support the swash plate so as to be tiltable, a tilt actuator for tilting the swash plate, and a valve plate provided on the axial opposite side of the swash plate in the casing, and a pair of supply and discharge ports intermittently communicating with each cylinder are formed across a pair of switching lands, the inside of the cylinder communicates with a portion between the shoe and the sliding surface via an oil passage formed in the piston and the shoe, A pressure pocket is provided on the swash plate side cylindrical surface portion to lubricate between the swash plate side cylindrical surface portion and the cradle side cylindrical surface portion, and one end of a first communication hole opens to the top dead center side on the orbit of the shoe on the sliding surface of the swash plate, and one end of a second communication hole opens to the bottom dead center side on the orbit of the shoe on the sliding surface of the swash plate, and a first sub-pocket is provided at a portion on the top dead center side of the pressure pocket on the swash plate side cylindrical surface portion, and a second sub-pocket is provided at a portion on the bottom dead center side of the pressure pocket on the swash plate side cylindrical surface portion, and the other end of the first communication hole communicates with the second sub-pocket, and the other end of the second communication hole communicates with the first sub-pocket, The first sub-pocket is configured to fit within the cradle side cylindrical surface portion when the tilt angle of the swash plate is equal to or less than a predetermined angle, and to protrude from the cradle side cylindrical surface portion when the tilt angle of the swash plate exceeds the predetermined angle. A variable displacement swash plate type hydraulic pump.

2. 2. The variable displacement swash plate type hydraulic pump according to claim 1, A variable displacement swash plate type hydraulic pump, characterized in that a pair of left and right swash plate side cylindrical surface portions are provided on the swash plate, a pair of left and right cradle side cylindrical surface portions are provided on the cradle, the first sub-pocket and the second sub-pocket are provided on each of the pair of left and right swash plate side cylindrical surface portions, the other end of the first communication hole is connected to both the left and right second sub-pockets, and the other end of the second communication hole is connected to both the left and right first sub-pockets.

3. 2. The variable displacement swash plate type hydraulic pump according to claim 1, At least one of the first sub-pocket and the second sub-pocket is formed in a shape that narrows toward a circumferential end thereof.

4. 2. The variable displacement swash plate type hydraulic pump according to claim 1, 2. A variable displacement swash plate type hydraulic pump, comprising: a first sub-pocket and a second sub-pocket, the first sub-pocket and the second sub-pocket being configured with a plurality of small pockets.

5. 1. A construction machine comprising: a hydraulic motor for traveling or turning; and the variable displacement swash plate type hydraulic pump according to claim 1 which drives the hydraulic motor; the hydraulic pump and the hydraulic motor form a closed circuit; and the forward / rearward traveling and speed of the vehicle body or the turning and speed are controlled by the tilt angle of the swash plate of the hydraulic pump.