JP2022158355A - Variable displacement swash plate hydraulic pump and construction machine comprising the same - Google Patents

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

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable displacement swash plate hydraulic pump suitable for driving hydraulic motors for traveling and turning in construction machines such as wheel loaders, hydraulic excavators, and hydraulic cranes, and construction machines equipped with the same.

A variable displacement swash plate type hydraulic pump used in construction machinery such as a wheel loader basically comprises a casing having a hollow portion and a rotating a rotating shaft that can be provided; a cylinder block that is provided in the casing so as to rotate integrally with the rotating shaft; A plurality of (usually an odd number, for example, nine) cylinders (holes) formed parallel to the rotation axis at predetermined angular intervals around the rotation axis, and reciprocatingly inserted into each of these cylinders. A piston having one axial end protruding from the cylinder, a shoe attached to the protruding end of each of these pistons through a spherical joint or the like so as to be able to swing, and a smooth sliding surface guiding each shoe. A swash plate provided with a pair of left and right cylindrical convex portions for tilting on the back side and a pair of left and right cylindrical convex portions provided on one end side of the casing to support the swash plate so as to be tiltable. A cradle provided with a pair of left and right cylindrical concave portions that are slidably fitted, a tilting actuator for tilting the swash plate, and intermittently connected to each cylinder provided on the opposite side of the swash plate in the casing. a valve plate in which a pair of left and right supply/discharge ports consisting of arcuate slots (long holes in the circumferential direction) are formed across a pair of switching lands so as to communicate with the cradle by a tilting actuator; By changing the tilting angle of the swash plate, the stroke amount of the piston can be varied, that is, the pump capacity can be controlled.

A wheel loader, which is one type of construction machinery that uses a variable displacement swash plate hydraulic pump as described above, includes hydraulic cylinders for driving a lift arm and a bucket as front attachments, and hydraulic actuators such as a hydraulic motor for traveling. , and by appropriately operating them, work such as excavating and moving earth and sand is performed. This wheel loader has a directional switching valve that controls the driving speed and direction of the front cylinder for pressurized oil discharged from an open-circuit hydraulic pump driven by the engine. The directional switching valve is controlled according to the operation lever input by the operator, and is switched to supply pressure oil from the hydraulic pump to each cylinder.

On the other hand, the hydraulic pump that drives the travel motor is configured in a closed circuit, and switching between forward and backward travel and speed adjustment are performed by tilting control of the hydraulic pump. In this case, the responsiveness of the hydraulic pump is very important because it affects the acceleration and deceleration performance of traveling. In particular, a delay in tilting response of a closed-circuit hydraulic pump used for running the vehicle leads to a delay until the vehicle stops running, so it is desirable to minimize it as much as possible.

Japanese Patent No. 5777411 JP-A-2005-35140 JP-A-7-103134

In the variable displacement swash plate type hydraulic pump described above, by receiving the load of the piston communicating with the high pressure port, the resultant force of the piston load (hereinafter referred to as the point of action) is applied to the swash plate at the top dead center (TDC). Acts sideways. As described above, a cylindrical convex surface is formed on the back side of the swash plate, and the center of the cylindrical convex surface is positioned perpendicular to the rotation axis. As a result, the piston resultant force acts in a direction to reduce the tilt angle of the swash plate. Hereinafter, this is called a tilting moment.

Due to the influence of this tilting moment, the swash plate type hydraulic pump tends to be slow to increase the displacement and fast to reduce the displacement.

However, when the hydraulic pump forms a closed circuit with the hydraulic motor for traveling, the hydraulic pump may be rotated when going down a slope, or act as a motor. In this case, the tilting moment due to the resultant force of the piston load acts to increase the tilting angle. Therefore, when an attempt is made to stop the vehicle, the tilting moment acts on the side of hindering the tilting from being lowered, resulting in a problem of delay in stopping the vehicle. When the hydraulic pump forms a closed circuit with the hydraulic motor for running in this way, it leads to a delay until the vehicle stops running on a downhill. ing.

As one measure for solving the problem of tilting responsiveness, it is conceivable to use a tilting actuator with a larger output. As a result, the size of the hydraulic pump increases, the weight increases, the cost increases, etc., making it difficult to adopt.

Further, if the pressure in the cylinder is rapidly switched in order to improve tilting responsiveness, the discharge pressure pulsation increases, causing a problem of increased vibration and noise.

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and aims to provide a hydraulic pump that does not increase in size, weight, or cost, and does not increase vibration and noise. To provide a highly reliable variable displacement swash plate type hydraulic pump capable of improving tilting responsiveness.

Another object of the present invention is to improve operability and safety in a construction machine equipped with a variable displacement swash plate hydraulic pump according to the present invention, in which tilting responsiveness when descending a slope can be improved. to provide construction machinery with high

In order to achieve the above object, a variable displacement swash plate hydraulic pump according to the present invention basically comprises a casing, a rotating shaft rotatably provided in the casing, and a rotating shaft rotating integrally with the rotating shaft. a cylinder block provided in the casing; a plurality of cylinders spaced apart in the circumferential direction of the cylinder block and extending in the axial direction; A piston protruding from a cylinder, a shoe attached to the protruding end of the piston, and a slanted surface provided with a smooth sliding surface for guiding the shoe on the front side and a swash plate side cylindrical surface portion for tilting on the back side. a plate, a cradle provided with a cradle-side cylindrical surface portion which is provided at one end of the casing and into which the swash plate-side cylindrical surface portion is slidably fitted to support the swash plate so that the swash plate can be tilted; and a pair of supply/discharge ports provided on opposite sides in the axial direction of the swash plate in the casing and intermittently communicating with the respective cylinders, with a pair of switching lands interposed therebetween. The inside of the cylinder and the portion between the shoe and the sliding surface communicate with each other through oil passages 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 a pressure pocket is provided on the swash plate side cylindrical surface portion on the track of the shoe on the sliding surface of the swash plate. One ends of the first communication hole and the second communication hole are opened on the dead center side and the bottom dead center side, respectively, and the pressure pocket on the swash plate side cylindrical surface portion is located on the top dead center side and the bottom dead center side. A first sub-pocket and a second sub-pocket are provided, respectively, 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 accommodated in the cradle-side cylindrical surface portion when the tilting angle of the swash plate is equal to or less than a predetermined angle; is set so as to protrude from the cradle-side cylindrical surface portion.

According to the variable displacement swash plate hydraulic pump according to the present invention, the tilting moment can be reduced at a specific time without increasing the size, weight, or cost of the hydraulic pump, and without increasing vibration and noise. can be reduced. Therefore, tilting responsiveness can be enhanced, and reliability can be improved.

Further, in the construction machine equipped with the variable displacement swash plate hydraulic pump according to the present invention, it is possible to improve the tilting responsiveness when going down a slope. Improvements can also be made.

Problems, configurations, and effects other than those described above will be clarified by the following description of the embodiments.

1 is a hydraulic circuit diagram of an example of a wheel loader, which is one of construction machines, to which an embodiment of a variable displacement swash plate hydraulic pump according to the present invention is applied; FIG. 1 is an overall sectional view of an embodiment of a variable displacement swash plate hydraulic pump according to the present invention; FIG. FIG. 3 is a schematic diagram for explaining the configuration around the swash plate of the hydraulic pump shown in FIG. 2; 4A and 4B are schematic diagrams for explaining the position and size of the sub-pocket (first sub-pocket) shown in FIG. When the tilt is at a predetermined angle (minimum tilt angle), (c) is a diagram showing when the tilt of the swash plate exceeds the predetermined angle (minimum tilt angle). FIG. 4 is a schematic view of the swash plate shown in FIGS. 2 and 3 as viewed from the sliding surface side; FIG. 3 is a schematic diagram for explaining the configuration of the valve plate shown in FIG. 2; Schematic view seen from the back side of the swash plate showing another example of the sub-pocket. Schematic view seen from the back side of the swash plate showing still another example of the sub-pocket.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

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

In FIG. 1, a wheel loader 50 has an engine 1 as a power source, and the engine 1 drives a hydraulic pump 2 . The hydraulic pump 2 sucks up hydraulic oil stored in a tank 5 and discharges pressure oil. The hydraulic pump 2 is connected via a direction switching valve 3 to a hydraulic cylinder 4 which is an actuator. The illustrated main relief valve 6 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 oil discharged from the pilot pump 7 is supplied to an operating lever 8 and a pump regulator 9 . A pressure reducing valve is incorporated in the operating lever 8 to generate a secondary pressure proportional to the amount of operation in each operating direction. This secondary pressure is supplied to the pilot ports 3a and 3b of the direction switching valve 3, and the degree of opening of the direction switching valve 3 is controlled by this secondary pressure. The hydraulic circuit described above is an open circuit system in which the hydraulic pump 2 sucks up oil from the tank 5 and the discharged oil is returned to the tank 5 via the directional control valve 3 via the hydraulic cylinder 4 or the center bypass. Open circuit systems are primarily used in circuits that drive front actuators.

On the other hand, the engine 1 drives a variable displacement swash plate type hydraulic (piston) pump 10 of the present embodiment via gears or the like at the same time as the hydraulic pump 2 of the open circuit system. The hydraulic pump 10 forms a closed circuit with a hydraulic motor 11 for running. By forming the hydraulic pump 10 and the hydraulic motor 11 for traveling in a closed circuit configuration as described above, the vehicle body 12 of the wheel loader 50 moves forward and backward (traveling in the front-rear direction) and its speed is controlled by the swash plate of the hydraulic pump 10. It can be controlled by the tilting angle, and it is possible to simplify the device configuration and improve the energy efficiency.

As shown in FIG. 2, the closed-circuit hydraulic pump 10 includes a pump casing (also simply referred to as a casing) 20 comprising a bottomed cylindrical front casing 21 with a hollow interior and a bottom lid-shaped rear casing 22 . Prepare. Near both ends of a rotating shaft 25 are rotatably supported by bearings 21A and 22A provided at both ends of the pump casing 20, and a spline shaft portion 25a provided at one end (front side) of the rotating shaft 25 serves as a power source. It is designed to be connected to A thick short cylindrical cylinder block 23 is fitted around the middle spline shaft portion 25b of the rotating shaft 25, and the rotating shaft 25 and the cylinder block 23 rotate integrally.

The cylinder block 23 has a plurality of (usually an odd number, for example, nine) cylinders concentrically around the rotation axis O of the rotation shaft 25 (in other words, spaced apart in the circumferential direction of the cylinder block 23). The (holes) 24 are formed parallel to the rotating shaft 25 (in other words, extending in the axial direction) at predetermined angular intervals. A bottomed cylindrical piston 27 having an opening on the rear side is fitted in each cylinder 24 so as to be reciprocally slidable.

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 oscillatably connected to the tip of the piston 27 (the protruding end from the cylinder 24). there is Note that the spherical joint may be provided on the piston 27 side. The bushing 29 presses the shoe 28 against the smooth sliding surface 31c of the swash plate 31 via the retainer 30 by means of a spring. On the back side of the sliding surface 31c of the swash plate 31, tilting cylindrical convex surface portions 31a and 31b (see FIG. 3) composed of convex cylindrical surfaces are formed on both sides (a pair of left and right) with the rotation axis O interposed therebetween. It is A cradle 32 having cylindrical concave surface portions 32a and 32b (see FIG. 3) formed of concave cylindrical surfaces so as to match the cylindrical convex surface portions 31a and 31b is attached to the front casing 21 (that is, the front side of the casing 20). ing. The cylindrical convex portions 31a, 31b and the cylindrical concave portions 32a, 32b are slidably fitted, whereby the cradle 32 supports the swash plate 31 so as to be tiltable. The cylindrical convex portions 31a, 31b and the cylindrical concave portions 32a, 32b have opposite shapes, that is, the back surface of the swash plate 31 is configured with a concave cylindrical surface, and the front surface of the cradle 32 is configured with a convex cylindrical surface. It may be mated. The inside of the cylinder 24 communicates with 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 shoe 28 with a spherical joint.

The tilt angle of the swash plate 31 is controlled by pushing and pulling the swash plate 31 with a servo piston (not shown) as a tilt actuator. By changing the tilting 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 of each cylinder 24 (on the side opposite to the piston 27 side). is performed.

A valve plate 34 is fixed to the rear casing 22 (on the rear side of the casing 20 and axially opposite to the swash plate 31 with the cylinder block 23 interposed therebetween). ing. As can be seen from FIG. 6, the valve plate 34 has an A port 34a and a B port 34b for supply and discharge, which are formed by a pair of left and right arcuate elongated holes (holes elongated in the circumferential direction). It is formed on both sides of the lands 34td and 34bd. Further, the rear casing 22 has an A passage 22a for supply/discharge connected to an A port (supply/discharge port) 34a of the valve plate 34, and a B port (supply/discharge port) 34b for supply/discharge connected to a B port (supply/discharge port) 34b of the valve plate 34. A passage 22b is provided. Here, the A port 34a and the A passage 22a discharge oil to the side on which the vehicle body 12 moves forward, and the B port 34b and the B passage 22b discharge oil to the side on which the vehicle body 12 moves backward. 34a, the piston top dead center at the time of discharge of the A passage 22a is called TDC, and the bottom dead center is called BDC (see FIG. 6).

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

Here, the positions, sizes, etc. of the four sub-pockets 36at, 36ab, 36bt, and 36bb are set as follows. That is, as shown in FIG. 4A, when the tilt of the swash plate 31 is neutral (tilt angle of 0 degrees), and as shown in FIG. The sub-pockets 36at, 36ab, and sub-pockets 36bt, 36bb are accommodated within the cylindrical concave surface portions 32a, 32b of the cradle 32 at the tilt angle). 36bt protrudes at least partially from the cylindrical concave surface portions 32a and 32b, and when the tilt angle reaches a certain angle or more, as shown in FIG. The positions, sizes, etc. of the sub-pockets 36at, 36bt on the top dead center TDC side are set so that they completely protrude from the portions 32a, 32b.

The pressure oil of the A port 34a is led to the pressure pocket 35a through a supply/discharge path 37A formed in the pump casing 20 and a fixed throttle 37a. Similarly, pressure oil from the B port 34b is led to the pressure pocket 35b through a supply/discharge path 37B formed in the pump casing 20 and a fixed throttle 37b. This lubricates between the cylindrical convex surfaces 31a and 31b on the swash plate 31 side and the cylindrical concave surfaces 32a and 32b on the cradle 32 side.

5, the sliding surface 31c of the swash plate 31 that guides the shoes 28 is located on the side of the top dead center TDC (the valve plate 34 in FIG. 6) on the track along which the shoes 28 slide. ), and one end of the communication hole 38b opens to 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 communicating hole 38t communicates with the sub-pockets 36ab and 36bb, and the other end of the communicating hole 38b communicates with the sub-pockets 36at and 36bt.

In other words, the communication hole 38t provided in the swash plate 31 is located near the top dead center TDC and on the side of the bottom dead center BDC (both left and right) on the track along which the shoe 28 slides on the sliding surface 31c. ) The communication hole 38b provided in the swash plate 31 communicates with the sub-pockets 36ab and 36bb, and is located near the bottom dead center BDC and the top dead center on the track on which (the central portion of) the shoe 28 slides on the sliding surface 31c. It communicates with the sub-pockets 36at, 36bt (on both the left and right sides) on the side of the point TDC.

Next, the operation will be explained. Here, when the vehicle body 12 moves forward, the tilt angle of the swash plate 31 is set to a predetermined angle or more, and as shown in FIGS. It is assumed that they are completely out of the cylindrical concave portions 32a and 32b.

First, the case where the A port 34a in the hydraulic pump 10 is pumping at a higher pressure than the B port 34b (when the A port 34a is a discharge port) will be described. When the A port 34a is discharged, the piston 27 is displaced in the direction in which the oil in the cylinder 24 formed in the cylinder block 23 is pushed out on the A port 34a side. On the other hand, on the B port 34b side, the piston 27 is displaced in the oil sucking direction.

In this manner, the valve plate 34 switches the oil in and out, and the switching is performed near the TDC and BDC of the piston 27 . The pressure in the cylinder 24 abruptly switches from low pressure to high pressure at BDC and from high pressure to low pressure at TDC. Here, in the present embodiment, one end of the communication hole 38t opens near TDC, and one end of the communication hole 38b opens near BDC. part) slides.

On the other hand, the oil in the cylinder 24 is led to the portion between the shoe 28 and the sliding surface 31c of the swash plate 31 through an oil passage 39 formed in the center of the piston 27 and the shoe 28. As shown in FIG. Therefore, the oil in the cylinder 24 is not only guided from the cylinder port 24b to the A port 34a and the B port 34b of the valve plate 34, but also from the shoe 28 (between the sliding surface 31c of the swash plate 31) and the communication hole. 38t and the communication hole 38b.

As a result, the interior of the cylinder 24 communicates with the secondary pockets 36ab and 36bb on the BDC side through the communication hole 38t when the pressure on the TDC side is switched from high pressure to low pressure. As a result, pressure is generated in the sub-pockets 36ab and 36bb to lubricate the portions near the ends of the cylindrical sliding surfaces (cylindrical convex surface portions 31a and 31b and cylindrical concave surface portions 32a and 32b) having no pressure pockets. Furthermore, rapid changes in the internal pressure of the cylinder 24 are mitigated.

Further, the inside of the cylinder 24 communicates with the secondary pockets 36at and 36bt on the TDC side through the communication hole 38b when switching from low pressure to high pressure on the BDC side. However, the sub-pockets 36at, 36bt are separated from the cylindrical concave portions 32a, 32b, and the inside of the low-pressure cylinder 24 only communicates with the casing drain and does nothing. As described above, the pump operation can lubricate the ends of the cylindrical sliding surfaces of the swash plate 31 and the cradle 32 where there are no pressure pockets, thereby reducing the risk of seizure of the sliding surfaces. , the effect of improving the reliability of the pump can be obtained.

Next, a description will be given of a case where the hydraulic pump 10 discharges from the A port 34a and the B port 34b is acting as a motor at a higher pressure than the A port 34a, such as when going down a slope. During the motor action, the pressure on the suction side is higher than that on the discharge side, so the pressure relationship is opposite to that during the pump action. Therefore, on the TDC side, the inside of the cylinder 24 is switched from low pressure to high pressure. The communication hole 38t communicates with the sub-pockets 36ab and 36bb. However, nothing works because it communicates in a low pressure state.

On the BDC side, the communication hole 38b communicates with the sub-pockets 36at, 36bt, but since the sub-pockets 36at, 36bt are separated from the cylindrical concave portions 32a, 32b, the internal pressure of the cylinder 24 is released from the sub-pockets 36at, 36bt to the casing drain. be able to.

Since it is the BDC side that switches from high pressure to low pressure during motor operation, it is necessary to switch when the volume in the cylinder 24 is at its maximum. Therefore, when the pressure inside the cylinder 24 is switched from high pressure to low pressure, it takes a longer time than when the pump operates. However, as described above, the internal pressure of the cylinder 24 can be released from the communication hole 38b via the sub-pockets 36at, 36bt, so that switching can be quicker than switching of the valve plate 34 alone. As a result, it is possible to reduce the movement of the point of application of the resultant force of the piston when the motor operates, so that the tilting moment can be reduced. As a result, the tilting responsiveness of the swash plate 31 can be enhanced, and the effect of improving the operability and safety of the vehicle body 12 can be obtained.

As described above, in the variable displacement swash plate type hydraulic pump 10 of the present embodiment, as shown in FIG. . On the A port 34a side, the pressure pocket 35a is provided with a sub-pocket 36at on the piston top dead center TDC side and a sub-pocket 36ab on the bottom dead center BDC side. A secondary pocket 36bt is provided on the top dead center TDC side of the pocket 35b, and a secondary pocket 36bb is provided on the bottom dead center BDC side. The positions and sizes of the sub-pockets 36at, 36ab, 36bt, and 36bb are such that when the tilting of the swash plate 31 is neutral, the sub-pockets 36at, 36ab, and sub-pockets 36bt, and 36bb correspond to the cylindrical concave portions 32a and 32b of the cradle 32. However, at a preset predetermined angle (minimum tilt angle) or more, the sub-pockets 36at, 36bt on the top dead center TDC side are set so that at least a portion thereof protrudes from the cylindrical concave portions 32a, 32b. be done. The pressure oil of the A port 34a is led to the pressure pocket 35a through a supply/discharge path 37A provided in the pump casing 20 and a fixed throttle 37a. Similarly, pressure oil from the B port 34b is led to the pressure pocket 35b through a supply/discharge passage 37B provided in the pump casing 20 and a fixed throttle 37b. On the side of the sliding surface 31c of the swash plate 31 that guides the shoe 28, one end of the communication hole 38t opens on the top dead center TDC side of the track along which the shoe 28 slides, and the communication hole 38t opens on the bottom dead center BDC side. One end of 38b is open. The other end of the communicating hole 38t communicates with the sub-pockets 36ab and 36bb, and the other end of the communicating hole 38b communicates with the sub-pockets 36at and 36bt.

According to the variable displacement swash plate hydraulic pump 10 of the present embodiment having the above-described configuration, the tilting actuator and the like can be used as before, so that the size, weight and cost of the hydraulic pump are not increased. , the tilting moment can be reduced at specific times without increasing vibration and noise. Therefore, tilting responsiveness can be enhanced, and reliability can be improved.

In addition, in the wheel loader 50 equipped with the variable displacement swash plate hydraulic pump 10 of the present embodiment, the tilting responsiveness when descending a slope can be improved, so that the traveling operability is improved and the safety is improved. It is also possible to improve performance.

In the above embodiment, the sub-pocket is formed in a rectangular shape, but it is not limited to this. For example, as shown in FIG. can be formed to As a result, the amount of overlap between the sub-pockets 36at, 36bt and the cylindrical concave portions 32a, 32b, that is, the release amount of the internal pressure of the cylinder 24 can be changed according to the inclination angle of the swash plate 31 . Further, as shown in FIG. 8, for example, the sub-pockets are composed of a plurality of small pockets, whereby the sub-pockets 36at, 36bt and the cylindrical concave portions 32a, 32b overlap according to the inclination angle of the swash plate 31. The amount, that is, the release amount of the internal pressure of the cylinder 24 may be changed.

In the above-described embodiment, the case where the hydraulic pump is applied to the hydraulic circuit for traveling in construction machinery such as a wheel loader, and a closed circuit is configured with the hydraulic motor for traveling has been described as an example. It may be applied to a turning hydraulic circuit, and a closed circuit may be formed with the turning hydraulic motor. In that case, the turning of the vehicle body and its speed are controlled by the tilting angle of the swash plate of the hydraulic pump.

In the above-described embodiment, the case where the hydraulic pump is applied to a wheel loader has been described as an example, but it is not limited to this, and may be applied to construction machines other than wheel loaders such as hydraulic cranes and hydraulic excavators. .

In addition, the present invention is not limited to the above-described embodiments, and includes various modifications. For example, the above-described embodiments have been described in detail in order to explain the present invention in an easy-to-understand manner, and are not necessarily limited to those having all the configurations described. Also, part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Moreover, it is possible to add, delete, or replace part of the configuration of each embodiment with another configuration.

1: Engine 2: Hydraulic Pump 3: Direction Switching Valve 4: Hydraulic Cylinder 5: Tank 6: Main Relief Valve 7: Pilot Pump 8: Operation Lever 9: Pump Regulator 10: Variable Displacement Type Swash Plate Type Hydraulic Pump 11: Hydraulic Motor 12 : Vehicle body 20: Pump casing 21: Front casing 22: Rear casing 22a: A passage (supply/exhaust passage)
22b: B passage (supply/exhaust passage)
23: Cylinder block 24: Cylinder (hole)
24b: cylinder port 25: rotating shaft 27: piston 28: shoe 29: bushing 30: retainer 31: swash plate 31a, 31b: cylindrical convex surface portion (swash plate side cylindrical surface portion)
31c: sliding surface 32: cradle 32a, 32b: cylindrical concave surface portion (cradle side cylindrical surface portion)
34: Valve plate 34a: A port (supply/discharge port)
34b: B port (supply/discharge port)
34td, 34bd: switching lands 35a, 35b: pressure pockets 36at, 36bt: secondary pockets (first secondary pockets)
36ab, 36bb: secondary pocket (second secondary pocket)
37A, 37B: supply/discharge paths 37a, 37b: fixed throttle 38t: communication hole (first communication hole)
38b: communication hole (second communication hole)
39: oil passage 50: wheel loader (construction machine)

Claims (5)

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, and spaced apart in the circumferential direction of the cylinder block in the axial direction. a plurality of extending cylinders; a piston reciprocatingly inserted into the cylinder and projecting from the cylinder at one end in the axial direction; a shoe attached to the projecting end of the piston; a swash plate having a smooth sliding surface for guiding and having a swash plate side cylindrical surface portion for tilting on the back side; A cradle provided with a cradle-side cylindrical surface portion with which the side cylindrical surface portion is slidably fitted, a tilting actuator for tilting the swash plate, and the swash plate in the casing are provided on opposite sides in the axial direction. a valve plate in which a pair of supply/discharge ports intermittently communicating with the cylinders are formed with a pair of switching lands interposed therebetween;
The inside of the cylinder and the portion between the shoe and the sliding surface communicate with each other through oil passages 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. One ends of the first communication hole and the second communication hole are opened on the side and the bottom dead center side, respectively, and the second communication hole is formed at a portion on the top dead center side and a portion on the bottom dead center side of the pressure pocket on the swash plate side cylindrical surface portion, respectively. A first sub-pocket and a second sub-pocket are provided, 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 accommodated in the cradle-side cylindrical surface portion when the tilt angle of the swash plate is equal to or less than a predetermined angle, and is partially accommodated when the tilt angle of the swash plate exceeds the predetermined angle. is set so as to protrude from the cradle-side cylindrical surface portion. In the variable displacement swash plate hydraulic pump according to claim 1,
The swash plate is provided with a pair of left and right swash plate side cylindrical surface portions, and the cradle is provided with a pair of left and right swash plate side cylindrical surface portions. and the second sub-pocket is provided, and the other end of the first communication hole communicates with the left and right second sub-pockets, and the other end of the second communication hole communicates with the left and right first sub-pockets. A variable displacement swash plate type hydraulic pump characterized by being in communication with each other. In the variable displacement swash plate hydraulic pump according to claim 1,
A variable displacement swash plate hydraulic pump, wherein at least one of the first sub-pocket and the second sub-pocket is formed in a shape that narrows toward the circumferential end. In the variable displacement swash plate hydraulic pump according to claim 1,
A variable displacement swash plate hydraulic pump, wherein at least one of the first sub-pocket and the second sub-pocket is composed of a plurality of small pockets. A hydraulic motor for running or turning and a variable displacement swash plate type hydraulic pump according to claim 1 for driving the hydraulic motor are mounted, and the hydraulic pump forms a closed circuit with the hydraulic motor. 1. A construction machine characterized in that the traveling and speed of a vehicle body in the longitudinal direction or the turning and speed thereof are controlled by the tilting angle of said swash plate of said hydraulic pump.

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