JP7637554B2 - Variable displacement swash plate type hydraulic pump and construction machine equipped with same - Google Patents

Description

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

As described in the following Patent Documents 1, 2, 3, etc., a variable displacement swash plate type hydraulic pump used in construction machinery such as wheel loaders basically comprises a casing having a hollow portion, a rotating shaft rotatably mounted in the casing, a cylinder block mounted within the casing so as to rotate integrally with the rotating shaft, a plurality of cylinders (holes) (usually an odd number, for example, nine) extending in the axial direction and spaced apart from one another 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, with one axial end protruding from the cylinder, shoes swingably mounted to the protruding ends of each of these pistons via a spherical joint or the like, and a surface side The device is equipped with a swash plate having a pair of left and right cylindrical convex portions for tilting on the back side thereof, which is a smooth sliding surface that guides each shoe, 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 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 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 stroke amount of the piston can be changed, i.e., 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, has hydraulic cylinders that drive the 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 pressurized oil discharged from the open circuit hydraulic pump driven by the engine. The directional control valve is controlled in response to the operator's input using an operating lever, and is switched so that pressurized oil from the hydraulic pump is supplied to each cylinder.

Meanwhile, the hydraulic pump that drives the travel motor is configured as 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 to drive the vehicle lead to delays until the vehicle stops, so it is desirable to keep this as small as possible.

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

In the above-mentioned variable displacement swash plate hydraulic pump, the swash plate receives the load of the piston connected to the high pressure port, and 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 this cylindrical convex surface is located perpendicular to the rotation axis. As a result, the piston resultant force acts in a direction that reduces the tilt angle of the swash plate. Hereinafter, this is referred to as the tilt moment.

Due to the effect of this tilting moment, swash plate type hydraulic pumps tend to be slower when increasing capacity and faster when decreasing capacity.

However, when the hydraulic pump and the hydraulic motor for traveling form a closed circuit, the hydraulic pump may rotate, acting 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, resulting in a problem that stopping traveling is delayed. When the hydraulic pump and the hydraulic motor for traveling form a closed circuit like this, this leads to a delay until traveling stops on downhill slopes, so there is a demand for improving the pump tilt response when the hydraulic pump acts as a motor.

One way to solve this problem with tilt response is to use a tilt actuator with a higher output, but this would naturally require the tilt actuator to be larger, which would in turn lead to larger hydraulic pumps, increased weight and increased costs, making it difficult to adopt.

In addition, if the pressure inside the cylinder is suddenly changed to improve rotation response, the discharge pressure pulsation becomes large, causing problems such as increased vibration and noise.

The present invention was made in consideration of these circumstances, and its purpose 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.

Another object is to provide a construction machine equipped with the variable displacement swash plate type hydraulic pump of the present invention that can improve tilt response when going downhill, etc., and thus provides a construction machine that is easy to operate and safe.

In order to achieve the above object, the variable displacement swash plate 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 piston protruding 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 each of which is a smooth sliding surface for guiding the shoes, and the rear side of each of which is a swash plate-side cylindrical surface portion for tilting the pistons. the swash plate having a cradle side cylindrical surface portion into which the swash plate side cylindrical surface portion slides and fits so as to support the swash plate so that it can be tilted; a tilting 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 formed between a pair of switching lands and intermittently communicating with each of the cylinders, and the inside of the cylinder and the portion between the shoe and the sliding surface are connected 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, one end of a first communication hole opens on the top dead center side of the orbit of the shoe on the sliding surface of the swash plate, one end of a second communication hole opens on the bottom dead center side of the orbit of the shoe on the sliding surface of the swash plate, a first sub- pocket is provided on the swash plate side cylindrical surface portion at a position on the top dead center side of the pressure pocket, and a second sub-pocket is provided on the swash plate side cylindrical surface portion at a position on the bottom dead center side of the pressure pocket, 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, and the first sub-pocket is set 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 a part of the first sub-pocket protrudes from the cradle side cylindrical surface portion when the tilt angle of the swash plate exceeds the predetermined angle.

The variable displacement swash plate type hydraulic pump of the present invention can reduce the tilt moment at specific times without increasing the size, weight, or cost of the hydraulic pump, and without increasing vibration and noise. This can improve tilt responsiveness and reliability.

In addition, in construction machinery equipped with the variable displacement swash plate type hydraulic pump of the present invention, tilt response can be improved when going downhill, etc., improving driving operability and improving safety.

Issues, configurations, and advantages other than those described above will become clear from the description of the embodiments below.

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. 1 is an overall cross-sectional view of an embodiment of a variable displacement swash plate type hydraulic pump according to the present invention; FIG. 3 is a schematic diagram illustrating a configuration around a swash plate of the hydraulic pump shown in FIG. 2 . 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). FIG. 4 is a schematic view of the swash plate shown in FIGS. 2 and 3 as viewed from a sliding surface side. FIG. 3 is a schematic diagram illustrating the configuration of the valve plate shown in FIG. 2 . FIG. 11 is a schematic view showing another example of a sub-pocket as viewed from the rear surface side of the swash plate. 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.

The following describes an embodiment of the present invention with reference to the drawings.

Figure 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, the wheel loader 50 will be described below.

In FIG. 1, the 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. 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 discharged oil of the pilot pump 7 is supplied to an operating lever 8 and a pump regulator 9. The operating lever 8 has a built-in pressure reducing valve, which generates 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 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 and returns to the tank 5 from the hydraulic cylinder 4 or center bypass. Open circuit systems are primarily used for circuits that drive front actuators.

Meanwhile, the engine 1 drives the variable displacement swash plate type hydraulic (piston) pump 10 of this embodiment via gears and the like, simultaneously with the hydraulic pump 2 of the open circuit system. The hydraulic pump 10 forms a closed circuit with the hydraulic motor 11 for traveling. By forming the hydraulic pump 10 and the hydraulic motor 11 for traveling in this closed circuit configuration, the forward and backward (forward and backward traveling) 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, simplifying the device configuration and improving energy efficiency, etc.

As shown in FIG. 2, the closed circuit hydraulic pump 10 is equipped with a pump casing (also simply called the casing) 20 consisting of a hollow, bottomed cylindrical front casing 21 and a bottom-lid-shaped rear casing 22. A rotating shaft 25 is rotatably supported near both ends by bearings 21A and 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 connected to a power source. A thick-walled, short cylindrical cylinder block 23 is fitted and fixed to the middle splined shaft portion 25b of the rotating shaft 25, so that the rotating shaft 25 and the cylinder block 23 rotate together.

In the cylinder block 23, a plurality of cylinders (holes) 24 (usually an odd number, for example, nine) are formed on a concentric circle (in other words, spaced apart in the circumferential direction of the cylinder block 23) centered on the rotation axis O of the rotary shaft 25 and parallel to the rotary shaft 25 at predetermined angular intervals (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 that it can slide back and forth.

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 surface side of the swash plate 31, which is a flat surface, 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 composed of convex cylindrical surfaces, are formed on both sides (left and right pair) of the rotation axis O. A cradle 32 having cylindrical concave surface portions 32a, 32b (see FIG. 3) composed 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, so that the cradle 32 supports the swash plate 31 so that it can tilt. 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 then they may be 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.

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 acts as a tilt actuator. By changing the tilt angle of the swash plate 31, the stroke amount of the piston 27 can be varied, i.e., the pump capacity can be controlled. An oval cylinder port 24b is formed on the rear side of each cylinder 24 (the opposite side to the piston 27 side), and oil is discharged and sucked through the cylinder port 24b as the piston 27 slides back and forth within the cylinder 24.

A valve plate 34 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), with which the rear surface of the cylinder block 23 slides. As can be seen from FIG. 6, the valve plate 34 has a pair of arc-shaped long holes (long holes in the circumferential direction) for supply and discharge, A port 34a and B port 34b, which are formed on either side of a pair of switching lands 34td and 34bd. The rear casing 22 also has a supply and discharge A passage 22a connected to the A port (supply and discharge port) 34a of the valve plate 34, and a supply and discharge B passage 22b connected to the B port (supply and discharge port) 34b of the valve plate 34. Here, the A port 34a and the A passage 22a discharge oil to the side where the vehicle body 12 moves forward, and the B port 34b and the B passage 22b discharge oil to the side where 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 is called TDC, and the bottom dead center is called BDC (see Figure 6).

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 center of the two cylindrical convex surfaces 31a, 31b of the swash plate 31. On the A port 34a side, sub-pocket 36at is provided on the side of the piston top dead center TDC when the piston is discharged from port A, and sub-pocket 36ab is provided on the side of bottom dead center BDC with respect to pressure pocket 35a. Similarly, on the B port 34b side, sub-pocket 36bt is provided on the side of top dead center TDC with respect to pressure pocket 35b, and sub-pocket 36bb is provided on the side of bottom dead center BDC with respect to pressure pocket 35b. Here, the four sub-pockets 36at, 36ab, 36bt, 36bb are small rectangular pockets that are the same width and depth as pressure pockets 35a, 35b, but are 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. 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. However, when the predetermined angle is exceeded, at least a portion of the sub-pockets 36at, 36bt on the top dead center TDC side protrudes from the cylindrical concave portions 32a, 32b. When the tilt angle exceeds a certain angle, as shown in FIG. 4(c), the sub-pockets 36at, 36bt on the top dead center TDC side completely protrude from the cylindrical concave portions 32a, 32b. The positions, sizes, etc. of the sub-pockets 36at, 36bt on the top dead center TDC side are set so that they are out of the cylindrical concave portions 32a, 32b.

The pressure oil at 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, the pressure oil at 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 lubricates the area between cylindrical convex surfaces 31a, 31b on the swash plate 31 side and cylindrical concave surfaces 32a, 32b on the cradle 32 side.

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

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

Next, the operation will be described. 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 Figures 3 and 4(c), the sub-pockets 36at and 36bt on the top dead center (TDC) side are completely protruding from the cylindrical concave portions 32a and 32b.

First, we will explain the case when the A port 34a of the hydraulic pump 10 is pumping at a higher pressure than the B port 34b (when the A port 34a is the discharge port). 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.

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

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.

As a result, when the pressure inside the cylinder 24 switches from high to low on the TDC side, it communicates with the secondary pockets 36ab, 36bb on the BDC side via the communication hole 38t. As a result, pressure is generated in the secondary pockets 36ab, 36bb, which lubricates the areas of the cylindrical sliding surfaces (cylindrical convex portions 31a, 31b, cylindrical concave portions 32a, 32b) near the ends where there are no pressure pockets, and furthermore, sudden changes in the pressure inside the cylinder 24 are mitigated.

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

Next, we will explain the case when the hydraulic pump 10 discharges from port A 34a, but port B 34b is at a higher pressure than port A 34a and is acting as a motor, such as when going downhill. When the motor is acting, 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 described above. Therefore, at the TDC side, the pressure inside the cylinder 24 switches from low to high. The communication hole 38t communicates with the secondary pockets 36ab and 36bb. However, since this communication is at a low pressure, nothing happens.

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

When the motor is in operation, the BDC side switches from high pressure to low pressure, so the switch needs to be made 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 when the pump is in 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 this can be made faster compared to switching only the valve plate 34. As a result, the movement of the application point of the piston resultant force when the motor is in operation can be reduced, and the tilt moment can be reduced. As a result, the tilt responsiveness of the swash plate 31 can be improved, and the operability and safety of the vehicle body 12 can be improved.

In this manner, in the variable displacement swash plate type hydraulic pump 10 of this embodiment, as shown in Figure 3, the swash plate 31 has two cylindrical convex surfaces 31a, 31b, and pressure pockets 35a, 35b are formed. On the A port 34a side, a sub-pocket 36at is provided on the piston top dead center TDC side when the piston is discharged from the A port, and a sub-pocket 36ab is provided on the bottom dead center BDC side with respect to the pressure pocket 35a. Similarly, on the B port 34b side, a sub-pocket 36bt is provided on the top dead center TDC side with respect to the pressure pocket 35b, and a sub-pocket 36bb is provided on the bottom dead center BDC side 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 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 at a preset angle (minimum tilt angle) or more. 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. In addition, on the sliding surface 31c side that guides the shoe 28 of the swash plate 31, one end of the communication hole 38t opens on the top dead center (TDC) side of the orbit along which the shoe 28 slides, and one end of the communication hole 38b opens on the bottom dead center (BDC) side. The other end of the communication hole 38t communicates with the sub-pockets 36ab and 36bb, and the other end of the communication hole 38b communicates with the sub-pockets 36at and 36bt.

The variable displacement swash plate type hydraulic pump 10 of this embodiment having the above configuration can use the existing tilt actuator, etc., so there is no need to increase the size, weight, or cost of the hydraulic pump, and there is no increase in vibration or noise, and the tilt moment can be reduced at specific times. This allows for improved tilt responsiveness and improved reliability.

In addition, in a wheel loader 50 equipped with the variable displacement swash plate type hydraulic pump 10 of this embodiment, tilt response can be improved when going downhill, etc., improving driving operability and improving safety.

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 amount of overlap between the sub-pockets 36at, 36bt and the cylindrical concave portions 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 made up of a number of small pockets, which allows the amount of overlap between the sub-pockets 36at, 36bt and the cylindrical concave portions 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.

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 of the vehicle body and its speed are controlled by the tilt angle of the swash plate of the hydraulic pump.

In the above embodiment, the hydraulic pump is applied to a wheel loader, but the invention is not limited to this and may be applied to construction machines other than wheel loaders, such as hydraulic cranes and hydraulic excavators.

The present invention is not limited to the above-described embodiments, but includes various modified forms. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and are not necessarily limited to those having all of the configurations described. It is also possible to replace 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. It is also possible to add, delete, or replace part of the configuration of each embodiment with other configurations.

1: Engine 2: Hydraulic pump 3: Directional switching 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: Vehicle body 20: Pump casing 21: Front casing 22: Rear casing 22a: Passage A (supply and exhaust passage)
22b: B passage (supply/discharge 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/exhaust port)
34b: B port (supply/exhaust port)
34td, 34bd: switching lands 35a, 35b: pressure pockets 36at, 36bt: secondary pockets (first secondary pockets)
36ab, 36bb: Secondary pocket (secondary pocket)
37A, 37B: supply and discharge passages 37a, 37b: fixed throttle 38t: communication hole (first communication hole)
38b: Communication hole (second communication hole)
39: Oil passage 50: Wheel loader (construction machinery)

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

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