JPH1077953A - Axial plunger pump - Google Patents

Abstract

PROBLEM TO BE SOLVED: To discharge an air stored in a pump quickly. SOLUTION: The upper part of the dischrge side annular groove 24 in a pump is communicated with a drain passage 28 through a return passage consisting of an air introduction hole 41, through holes 38, 39, an air discharge orifice 42 and a return hole 37. A spool 40 for opening/closing the air discharge orifice 42 is interposed in the through holes 38, 39. A spool 40 is energized in the direction of a swash plate 14 by the force of a spring 49 and the pressure of an intake passage 5 acting on a first pressure receiving part 51. Second/third pressure receiving parts 52, 53 are installed on the spool 40 and the pressure of the annular groove 24 is made to act on the area difference corresponding part. The spool 40 opens/closes an orifice 42 by following to the swash plate 14 and the air in the annular groove 24 is discharged to the drain passage 28, in the term until the pressure of the annular groove 24 reaches a set pressure at the pump start time. When the pressure of the annular groove 24 is more than a set pressure, the spool 40 closes the orifice 42 by the pressure of the groove 24 and the leak of a fuel is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an axial plunger pump used for a fuel pressurizing pump or the like of a fuel injection device of an automobile, and more particularly to an axial plunger pump having a discharge passage improved for discharging air.

[0002]

2. Description of the Related Art As an axial plunger pump, a pump as disclosed in Japanese Utility Model Laid-Open No. 2-92073 has been proposed. In this axial plunger pump, a swash plate is integrally provided at an end of the drive shaft, while a plurality of plungers are disposed at positions corresponding to the swash plate in the housing so as to be able to advance and retreat, so that the rotation of the drive shaft is achieved. When the swash plate swings and rotates, a plurality of plungers are sequentially pressed by the swash plate to continuously perform a pumping operation.
The hydraulic fluid discharged from each plunger is merged after passing through a discharge check valve corresponding to each plunger, and is sent out therefrom to an external device via a discharge passage.

[0003]

However, the above-mentioned conventional axial plunger pump does not have a special structure for discharging air to a discharge passage in the pump, and therefore, when the pump is stopped for a long time at a high temperature. And, above all,
When a pump is used for pressurizing the fuel, a large amount of air (vapor) may be generated in the pump due to the characteristics of the fuel. This tends to cause a decrease, variation, etc. in the discharge flow rate.

[0004] Therefore, an object of the present invention is to provide an axial plunger pump that can rapidly discharge air remaining inside the pump and always obtain stable pump performance.

[0005]

As a means for solving the above-mentioned problems, according to the first aspect of the present invention, a plunger is provided so as to be able to advance and retreat in opposition to a swash plate which rotates integrally with a drive shaft. In an axial plunger pump in which a plunger is pressed by a swash plate and repeatedly protrudes and retreats in a cylinder to discharge pressurized hydraulic fluid to an external device, a return passage communicating with the storage passage in the discharge passage in the pump. And a spool that opens and closes the return passage in accordance with the advancing / retracting position is disposed to face the swash plate, and the spool is urged in the swash plate direction by an urging means. A pressure receiving portion for generating a thrust in a direction opposite to the swash plate direction is provided, pressure of the discharge passage is introduced to the pressure receiving portion, and when the spool moves in the swash plate direction, the return passage opens, It said return passage and moves the plate direction in the opposite direction to close as. At the moment when the pump is started, the spool is pressed in the direction of the swash plate by the force of the urging means because the pressure in the discharge passage is low, and the spool repeatedly moves forward and backward following the movement of the swash plate. Here, at the moment when the spool follows the swash plate and moves in the swash plate direction, the return passage opens, and the air remaining in the discharge passage is discharged to the storage tank via the return passage. Further, when the spool follows the swash plate and moves in the direction opposite to the swash plate direction, the return passage closes. Therefore, no matter how large the return passage opened and closed by the spool is formed so that air can easily escape, there is no phenomenon that the hydraulic fluid in the discharge passage entirely enters the return passage and the pressure of the discharge hydraulic fluid does not rise forever.
Further, when the pressure in the discharge passage becomes equal to or higher than the set pressure after the pump is started, the force acting on the pressure receiving surface of the spool overcomes the force of the urging means, and the spool moves in the direction opposite to the swash plate direction. And stops following the movement of the swash plate.
Therefore, the spool remains in the state moved in the direction opposite to the swash plate direction, and the return passage is closed. Therefore, when the normal operation of the pump is started, the hydraulic fluid does not leak from the return passage.

According to a second aspect of the present invention, the pressure of fuel sent from a supply pump driven by a motor is regulated by a low-pressure regulator provided in a suction passage, and the fuel is rotated integrally with a drive shaft driven by the engine. An axial plunger pump, which is arranged so as to face a swash plate to be pressed by the swash plate and repeatedly presses out and retreats in the cylinder to pressurize and discharge to a fuel injection device of an engine through a discharge passage. A return passage communicating with a drain passage of the low-pressure regulator is formed in the discharge passage in the pump, and a spool that opens and closes the return passage in accordance with the advance / retreat position is disposed facing the swash plate. While biasing the spool in the swash plate direction by the biasing means,
The spool is provided with a pressure receiving portion for generating a thrust in a direction opposite to the swash plate direction, pressure of the discharge passage is introduced to the pressure receiving portion, and when the spool moves in the swash plate direction, the return passage opens, and the swash plate direction is opened. When moved in the opposite direction, the return passage is closed. At the moment of starting the pump, the spool is pressed against the swash plate by the force of the urging means because the pressure in the discharge passage is low, and the spool repeats the forward and backward movements following the movement of the swash plate. Here, at the moment when the spool follows the swash plate and moves in the swash plate direction, the return passage opens, and the air remaining in the discharge passage is discharged to the drain passage via the return passage. In particular, when the supply pump is started when the engine is started, fuel at a predetermined pressure regulated by the low-pressure regulator is sent to the discharge passage, and the air in the discharge passage is positively discharged to the drain passage by the fuel pressure. Further, when the spool follows the swash plate and moves in the direction opposite to the swash plate direction, the return passage closes. Therefore, no matter how large the return passage opened and closed by the spool is formed so that air can easily escape, there is no phenomenon that the fuel in the discharge passage all passes through the return passage and the pressure of the discharged fuel does not rise forever. Further, when the pressure in the discharge passage becomes equal to or higher than the set pressure after the pump is started, the force acting on the pressure receiving surface of the spool overcomes the force of the urging means, and the spool moves in the direction opposite to the swash plate direction. And stops following the movement of the swash plate. Therefore, the spool remains in the state moved in the direction opposite to the swash plate direction, and the return passage is closed. Therefore, when normal operation of the pump is started,
No fuel leaks from the return passage.

Further, according to the invention of claim 3, according to claims 1 and 2,
Is constituted by a spring.

Further, in the invention according to claim 4, the urging means according to claim 2 is provided with a pressure receiving portion for generating an opening thrust on the spool, and the pressure receiving portion is provided downstream of the low pressure regulator. The pressure in the suction passage on the side is introduced. Normally, the pressure in the suction passage downstream of the low-pressure regulator is higher than the pressure in the discharge passage at the moment of engine start. For this reason, at this time, the spool opens the return passage and discharges the air in the discharge passage to the drain passage. Further, when the engine is started and pressurization by the pump is started, the pressure in the discharge passage becomes higher than the pressure in the suction passage, and the spool closes the return passage.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of the present invention will be described with reference to FIGS.
A description will be given based on FIG.

In this embodiment, an axial plunger pump 1 according to the present invention is applied to a fuel pressurizing pump of a fuel injection device of an automobile, and a supply pump 2 driven by a motor M is provided as shown in FIG. Such as gasoline (hydraulic fluid) supplied from the fuel tank 3 (storage tank) via the
Is pressurized to a predetermined pressure by the axial plunger pump 1 and supplied to the injector 4, the fuel is injected into the cylinder (not shown) of the engine by the injector 4, and excess fuel is injected from the injector 4 into the pump 1. It returns to the suction passage 5.

The axial plunger pump 1 comprises a housing body 7 in which a pump housing 6 has a recess, and a front cover 8 attached to a front end thereof.
The valve block 9 and the cylinder block 10 are connected to each other in the recess of the housing body 7 by bolts 11 in a superposed state. A drive shaft 12 is supported on the front cover 8 via radial bearings 13a and 13b formed of a needle bearing and a metal bearing. An end of the drive shaft 12 on the side facing the inside of the pump housing 6 has: A swash plate 14 having an end surface inclined at a predetermined angle with respect to the axis is integrally formed, and an end protruding outside the pump housing 6 is connected to a camshaft (not shown) of the engine. Is provided.

The cylinder block 10 has a plurality of cylinder holes 16 formed in the axial direction at equal intervals in the circumferential direction. Each of the cylinder holes 16 has a plunger 17 spring-biased in the direction of the swash plate 14. Are housed so as to be able to advance and retreat. Each of the plungers 17 has a hemispherical concave portion formed on the top surface thereof, and a shoe 18 is slidably fitted and held in the concave portion.

The valve block 9 at the back of the cylinder block 10 is provided with a plurality of suction ports 19 and discharge ports 20 communicating with the respective cylinder holes 16 of the cylinder block 10. Is provided with a suction check valve 21, and each discharge port 20 is provided with a discharge check valve 22. The suction port 19 is formed from the corresponding cylinder hole 16 along the axial direction of the valve block 9, and communicates with the suction side annular groove 23 formed on the inner surface of the bottom wall of the housing body 7 at the back of the valve block 9. Then, it communicates with the suction passage 5 of the housing body 7 through the annular groove 23. On the other hand, the discharge port 20 is formed radially outward from the corresponding cylinder hole 16 in the radial direction of the valve block 9,
Discharge side annular groove 2 formed on the outer peripheral surface of valve block 9
4 and through this annular groove 24 the housing body 7
Is connected to the discharge path 25. Therefore, when each plunger 17 moves forward and backward in the cylinder hole 16, fuel is sucked into each cylinder hole 16 via the suction side annular groove 23, and the fuel is discharged through the discharge side annular groove 24 through the discharge side annular groove 24. Will be sent to In this embodiment, the discharge-side annular groove 24 and the discharge passage 25 constitute a discharge passage in the present invention.

The suction passage 5 of the housing body 7 is connected to the suction pipe connection port 2 connected to the supply pump 2 by a pipe.
6 (see FIG. 2) and the suction side annular groove 23 (see FIG. 1). A low pressure for regulating the fuel sent from the supply pump 2 to a predetermined low pressure is provided in the middle of the passage. A regulator 27 is interposed. The low-pressure regulator 27 is mounted on the uppermost part of the housing body 7 and, when the pressure in the suction passage 5 becomes equal to or higher than a set pressure, discharges excess fuel to the drain passage 28 and discharges remaining fuel to the rear of the suction passage 5. It flows to the flow side (the annular groove 23 side).

On the other hand, a bottomed cylindrical auxiliary plate 29 is attached to the end surface of the swash plate 14 formed on the drive shaft 12 so as to be relatively rotatable. The auxiliary plate 29 has a boss 30 protruding from the center of the end face on the swash plate 14 side.
1 is fitted so as to be relatively rotatable. An annular thrust plate 32 having a high hardness and a small coefficient of friction is coupled to an end face of the auxiliary plate 29 on the cylinder block 10 side. The shoe fitted and held to the plunger 17 is attached to the thrust plate 32. 18 is slidably contacted. Since each plunger 17 is spring-biased in the direction of the swash plate 14 as described above,
Each shoe 18 is constantly pressed against the thrust plate 32 under the urging force of the plunger 17. Also,
Thrust bearings 33a and 33b are interposed between the front cover 8 and the swash plate 14, and between the swash plate 14 and the auxiliary plate 29, respectively.

Further, between the auxiliary plate 29 and the thrust plate 32, an inner peripheral edge of an annular resin diaphragm 34 is sandwiched in a sealed state. The outer peripheral edge of the diaphragm 34 is hermetically sandwiched between the joint between the housing body 7 and the front cover 8.
The inside of the pump is separated by a diaphragm 34 into a working fluid chamber 35 on the cylinder block 10 side and a lubricating fluid chamber 36 on the drive shaft 12 side. The working fluid chamber 35 is filled with fuel leaked from the cylinder block 10, and the lubricating fluid chamber 36 is filled with lubricating fluid for lubricating the bearings 33 a and 33 b around the drive shaft 12. It is enclosed.

Reference numeral 37 in the figure denotes a return hole for returning the fuel leaked into the hydraulic fluid chamber 35 to the fuel tank 3. The return hole 37 is a low-pressure regulator located above the hydraulic fluid chamber 35 and located above it. The vapor (air) generated in the hydraulic fluid chamber 35 is formed toward the drain passage 28 and can be discharged to the drain passage 28 together with the leaked fuel.

In the upper part of the outer peripheral edge of the cylinder block 10 and the valve block 9, through-holes 38, 39 extending in the axial direction are continuously formed on the same line, and these through-holes 38, 39 are formed. Has a spool 4 described later
0 is housed slidably and astride both.
The through hole 39 on the valve block 9 side is formed to be larger by a predetermined diameter than the through hole 38 on the cylinder block 10 side. In the through hole 39 on the valve block 9 side,
An air introduction hole 41 whose one end is open at an upper position of the discharge side annular groove 24 is formed, and one end is opened in the through hole 38 on the cylinder block 10 side at a position directly below the return hole 37 in the hydraulic fluid chamber 35. An air discharge orifice 42 is formed. In this embodiment, the air introduction hole 41, the through holes 39 and 38, and the air discharge orifice 4
2 together with the return hole 37 constitutes a return passage in the present invention.

The spool 40 is a small-diameter spool 43 fitted in the through hole 38 on the cylinder block 10 side.
And a large-diameter spool 44 fitted into the through-hole 39 on the valve block 9 side. The small-diameter spool 43 and the large-diameter spool 44 connect the rod portion 45 protruded from the small-diameter spool 43 to the large-diameter spool 44. The pins 46 are connected by engagement. The connection structure will be described in more detail. A receiving hole 47 having a diameter slightly larger than the diameter of the rod portion 45 is formed in the large diameter spool 44. The large-diameter spool 44 and the rod portion 45 are connected by a pin 46 which penetrates in the radial direction in a state of being inserted into the spool. That is, the small diameter spool 43 and the large diameter spool 44
A slight radial movement along the axis is possible. This is to allow a slight displacement of the center between the through hole 38 on the cylinder block 10 side and the through hole 39 on the valve block 9 side, and the spool 40 is inserted into the through holes 38 and 39 of the cylinder block 10 and the valve block 9. At the time of insertion, the small-diameter spool 43
And the large-diameter spool 44 is adjusted to be shifted in the radial direction. Therefore, even if the center of both through holes 38 and 39 is slightly shifted, smooth sliding of the spool 40 is ensured by this structure.

Here, the spool 40 is mounted on the rod 4
5 and the air introducing holes 41 by the gaps between the through holes 39 and 38.
And the air discharge orifice 42 communicates with each other. When the small-diameter spool 43 moves forward toward the hydraulic fluid chamber 35, the small-diameter spool 43 opens the air discharge orifice 42. The small diameter spool 43 closes the air discharge orifice 42. Further, the working fluid chamber 35 of the small-diameter spool 43 is provided.
Is formed in a spherical shape, and when the spool 40 projects to the hydraulic fluid chamber 35 side, the small-diameter spool 43 is closed.
Has a spherical surface in contact with the end surface of the thrust plate 32.

On the other hand, a concave portion 48 is provided on the end surface of the large diameter spool 44 on the bottom surface side of the housing body 7, and a coil spring 49 is interposed between the concave portion 48 and the bottom surface of the housing body 7. . The space in which the coil spring 49 is housed communicates with the suction passage 5 through the orifice 50, and the end surface of the large-diameter spool 44 on the bottom side of the housing body 7 receives the pressure in the suction passage 5. It has become. The first pressure receiving portion 51 generates a thrust in a direction for moving the spool 40 forward (a direction for opening the air discharge orifice 42) by receiving the pressure of the suction passage 5, and together with the coil spring 49, the urging means in the present invention. Is composed. Opposite end faces of the large-diameter spool 44 and the small-diameter spool 43 are respectively connected to the second pressure receiving portion 52 and the third pressure receiving portion 53 which receive the pressure of the discharge side annular groove 24.
The second pressure receiving portion 52 and the third pressure receiving portion 5
The thrust in the direction of retracting the spool 40 (the direction of closing the air discharge orifice 42) is generated by the pressure of the discharge side annular groove 24 received at the area corresponding to the area difference of No. 3. Therefore, the spool 40 is provided with the discharge side annular groove 24.
Is low, the force of the coil spring 49 and the first
Although the air discharge orifice 42 is displaced in the opening direction by the thrust generated in the pressure receiving portion 51, when the pressure of the discharge side annular groove 24 exceeds the set pressure, the area difference between the second pressure receiving portion 52 and the third pressure receiving portion 53. The thrust generated in the corresponding portion overcomes the force of the coil spring 49 and the thrust generated in the first pressure receiving portion 51, and is displaced in a direction to close the air discharge orifice.

In the above configuration, when the drive shaft 12 rotates with the start of the engine, the swash plate 14 integral with the drive shaft 12 rotates, whereby the auxiliary plate 29 is moved to the swash plate 1.
4 and swings (swings) integrally with the swash plate 14 while rotating relative to the swash plate 14. When the auxiliary plate 29 swings in this way, the plunger 17 on the cylinder block 10 sequentially repeats the forward and backward movements via the thrust plate 32 and the shoes 18 slidingly in contact with the thrust plate 32, whereby the pump action is continuously performed. At this time, the fuel supplied from the fuel tank 3 to the suction passage 5 via the supply pump 2 is adjusted to a set low pressure by the low pressure regulator 27, and then the suction side annular groove 23, the suction port 19, the suction check valve 21 Are sequentially sucked into the cylinder hole 16 and pressurized by the plunger 17, and then sequentially pass through the cylinder 16 from the discharge check valve 22, the discharge port 20, the discharge-side annular groove 24, and the discharge path 25. Supplied to
Excess fuel used in the injector 4 is returned to the suction passage 5.

By the way, when the driver operates the ignition key switch to the ON position when starting the engine,
Before the operation of the axial plunger pump 1 is started, the driving motor M of the supply pump 2 is started, whereby fuel of a predetermined pressure is introduced into the axial plunger pump 1. This fuel passes through the suction passage 5 after being regulated by the low-pressure regulator 27,
At this time, since each plunger 17 is not performing a pump operation, the pressure in the discharge-side annular groove 24 is lower than the pressure in the suction passage 5, so that the spool 40 The thrust plate 32 is pressed against the thrust plate 32 by the force and the thrust generated by the first pressure receiving portion 51.

At this time, if the spool contact portion of the thrust plate 32 is inclined toward the drive shaft 12, the spool 4
0 moves forward as shown in FIG.
Is open, and if it is inclined toward the cylinder block 10, it retreats as shown in FIG. 1 to close the air discharge orifice 42. When the air discharge orifice 42 is open as shown in FIG.
The air stagnating in the air inlet hole 4 together with some fuel
1, through holes 39, 38, air discharge orifice, return hole 3
7 are sequentially discharged to the drain passage 28.

Further, when the engine is started from such a state and the operation of the axial plunger pump 1 is started, the spool 40 is moved to the thrust plate 32 until the pressure of the discharge side annular groove 24 reaches the set pressure. The thrust plate 32 swings while being pressed against
Accordingly, the spool 40 is slidably moved back and forth in the through holes 39 and 38. When the spool 40 moves back and forth in this way, the spool 40 opens and closes the air discharge orifice 42 and forcibly sends out the staying air in the annular groove 24 in the direction of the air discharge orifice 42. The air collected in the upper part of the groove 24 is efficiently discharged to the drain passage 28 through the air discharge orifice 42.

No matter how large the air discharge orifice 42, which is opened and closed by the spool 40, is formed so that air can escape easily, the air in the discharge side annular groove 24 cannot be opened because the air discharge orifice 42 does not remain open. There is no phenomenon that all the fuel discharged through the air discharge orifice 42 is not boosted forever.

As described above, when the air inside the axial plunger pump 1 is efficiently discharged to the outside, the discharge side annular groove 24 and the discharge path 25 are rapidly pressurized, and as a result, the discharge side annular groove 24 The pressure immediately reaches the set pressure. When the pressure in the discharge side annular groove 24 reaches the set pressure, the thrust generated in the area corresponding to the area difference between the second pressure receiving portion 52 and the third pressure receiving portion 53 of the spool 40 is equal to the force of the coil spring 49 and the first pressure receiving portion. As a result, the spool 40 retreats and the air discharge orifice 42 is kept closed as shown in FIG. Therefore, thereafter, the air discharge orifice 42 is closed by the spool 40 during the operation of the pump, and the fuel does not leak from the air discharge orifice 42.

Even when the engine is stopped, if the spool contact portion of the thrust plate 32 is inclined toward the drive shaft 12, the spool 40 moves forward as shown in FIG. 3 to open the air discharge orifice 42. As a result, the air in the discharge-side annular groove 24 is discharged to the drain passage 28 in the meantime.

The embodiment of the present invention is not limited to the above-described one. For example, the urging means of the spool 40 may be only a spring such as the coil spring 49. The pressure of the suction passage 5 may be simply introduced into the pressure receiving portion 51. in this way,
When the spring is eliminated, there is an advantage that the number of parts is reduced.

[0030]

As described above, according to the present invention, the plunger is disposed so as to be able to advance and retreat in opposition to the swash plate which rotates integrally with the drive shaft, and this plunger is pressed by the swash plate to protrude and retract in the cylinder. In the axial plunger pump that discharges the pressurized hydraulic fluid to the external device by repeating the above, a return passage communicating with the storage tank is formed in the discharge passage in the pump, and the return passage is formed according to the advance / retreat position. A spool that opens and closes the swash plate is disposed to face the swash plate, and while the biasing unit biases the spool in the swash plate direction, a pressure receiving unit that generates a thrust in the spool in a direction opposite to the swash plate direction The return passage opens when the spool moves in the swash plate direction, and closes when the spool moves in the direction opposite to the swash plate direction. Therefore, when the pump follows the swash plate and moves in the direction opposite to the swash plate when the pump is started, the return passage is closed, so that the return passage opened and closed by the spool is formed as large as possible so that air can easily escape. There is no phenomenon that the hydraulic fluid in the discharge passage all passes through the return passage and the pressure of the discharge hydraulic fluid does not rise forever. Further, when the pressure in the discharge passage becomes equal to or higher than the set pressure after the pump is started, the force acting on the pressure receiving surface of the spool overcomes the force of the urging means, and the spool moves in the direction opposite to the swash plate direction. And stops following the movement of the swash plate. Therefore, the spool remains in the state moved in the direction opposite to the swash plate direction, and the return passage is closed. Therefore, when the normal operation of the pump is started, the hydraulic fluid does not leak from the return passage. Therefore, according to the present invention, by quickly discharging air from the inside of the pump, it is possible to eliminate a pressure rise delay at the time of starting the pump and to stabilize the discharge flow rate.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention.

FIG. 2 is a sectional view of the embodiment, taken along line AA of FIG. 1;

FIG. 3 is an enlarged sectional view of a main part showing the embodiment.

FIG. 4 is an enlarged sectional view of a main part showing the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Axial plunger pump, 2 ... Supply pump, 3 ... Fuel tank (storage tank), 5 ... Suction passage, 12 ... Drive shaft, 14 ... Swash plate, 24 ... Discharge side annular groove (discharge passage), 25 ... Discharge passage (Discharge passage), 27: Low pressure regulator, 28: Drain passage, 37: Return hole (return passage), 38, 39: Through hole (return passage), 41: Air introduction hole (return passage), 42: Air discharge orifice (Return passage), 40: spool, 49: coil spring (biasing unit), 51: first pressure receiving unit (biasing unit), 52: second pressure receiving unit (pressure receiving unit).

Claims (4)

[Claims] A plunger is provided so as to be able to advance and retreat in opposition to a swash plate that rotates integrally with a drive shaft, and the plunger is pressed by the swash plate and repeatedly pressurized and retracted in a cylinder. In an axial plunger pump that discharges hydraulic fluid to an external device, a return passage communicating with a storage tank is formed in the discharge passage in the pump, and a spool that opens and closes the return passage in accordance with an advancing / retracting position is provided on the swash plate. The spool is urged in the direction of the swash plate by the urging means, and a pressure receiving portion that generates a thrust in the direction opposite to the direction of the swash plate is provided on the spool.
The pressure of the discharge passage is introduced into the pressure receiving portion, and the return passage opens when the spool moves in the swash plate direction, and the return passage closes when the spool moves in the direction opposite to the swash plate direction. Axial plunger pump. 2. A fuel supplied from a motor-driven supply pump is regulated by a low-pressure regulator interposed in an intake passage, and the fuel is opposed to a swash plate that rotates integrally with a drive shaft driven by the engine. An axial plunger pump, which is pressed by a swash plate and repeatedly presses out and retreats in a cylinder to discharge pressure to a fuel injection device of an engine through a discharge passage. In the passage, a return passage communicating with the drain passage of the low-pressure regulator is formed in a branch, and a spool that opens and closes the return passage in accordance with the advance / retreat position is disposed to face the swash plate, and the spool is biased by biasing means. The spool is provided with a pressure receiving portion for generating a thrust in a direction opposite to the swash plate direction while being urged in the swash plate direction by the swash plate direction. An axial plunger pump wherein pressure in a passage is introduced to open the return passage when the spool moves in the swash plate direction, and closes the return passage when the spool moves in a direction opposite to the swash plate direction. 3. The axial plunger pump according to claim 1, wherein said urging means is constituted by a spring. 4. The urging means has a structure in which a pressure receiving portion for generating an opening thrust is provided on the spool, and the pressure of the suction passage downstream of the low pressure regulator is introduced into the pressure receiving portion. The axial plunger pump according to claim 2, characterized in that: