JPH11201046A - Bellows pump - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent over-elongation of bellows caused by excessive supply of hydraulic fluid (secondary fluid) to an auxiliary actuation chamber. SOLUTION: A main actuation chamber 22 where fuel (primary fluid) is enclosed and an auxiliary actuation chamber 24 where hydraulic fluid is enclosed are parted by a bellows 20 capable of elongation and contraction. By moving a piston 18 faced with the auxiliary actuation chamber 24 at one end 18a forward/backward, pump actuation of fuel is conducted by hydraulic fluid in the auxiliary chamber 24 and the bellows 20. Hydraulic fluid is supplied to the auxiliary actuation chamber 24 through a diametric passage 62 (secondary fluid passage 56) communicated with the auxiliary actuation chamber 24. An opening part 64 of the diametric passage 62 faced with a cylinder chamber 16 of the auxiliary chamber 24 is set at a position to be opened/closed by the piston 18 moving forward and backward.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a bellows pump suitably used for increasing the pressure of fuel of an internal combustion engine.

[0002]

2. Description of the Related Art Conventionally, a main working chamber in which a primary fluid is sealed and a sub-working chamber in which a secondary fluid is sealed are liquid-tightly separated by an expandable bellows. A bellows pump is known which pumps a primary fluid through a secondary fluid and a bellows in a sub-operation chamber by moving a piston facing forward and backward.
One example is disclosed in Japanese Patent Publication No. 099981.

[0003] In such a bellows pump, the bellows can isolate the primary fluid, which is pressurized by the pump action, from the sub-operating chamber in which the piston sliding portion which is liable to leak is provided. Such a fluid having a low viscosity and easily causing liquid leakage is particularly suitably used in a direct injection gasoline engine or the like in which a primary fluid to be pressurized is used.

[0004] Since a small amount of liquid leaks from the sliding portion between the piston and the sub-operation chamber, it has been conventionally possible to replenish the secondary fluid from the outside through a secondary fluid passage communicating with the sub-operation chamber. Is configured.

[0005]

However, in such a bellows pump, since a secondary fluid is interposed between the piston and the bellows, the phase of the bellows expands and contracts slightly with respect to the displacement of the piston. It causes a delay. For this reason, for example, for a predetermined period after the piston starts retreating with respect to the sub-working chamber, the volume reduction in the sub-working chamber cannot be followed, and the pressure in the sub-working chamber temporarily decreases. The secondary working fluid is excessively replenished to the sub-working chamber via the secondary working chamber. As a result, the bellows may be excessively elongated, and desired characteristics may not be obtained, and the durability of the bellows may be reduced.

In the bellows pump described in Japanese Patent Application Laid-Open No. Hei 4-209998, a check hole is provided in addition to a suction hole for supplying a secondary fluid into a sub-working chamber (outer compartment). And a secondary working fluid can be discharged from the subsidiary working chamber through the discharge hole. However, with such a configuration, it is necessary to connect two fluid passages (suction hole and discharge hole) to the sub-operation chamber, so that the structure becomes complicated and the device itself becomes large.

[0007]

A bellows pump according to the present invention comprises a main working chamber filled with a primary fluid, a sub working chamber filled with a secondary fluid, and the main working chamber and the sub working chamber. Having an expandable and contractible bellows and a piston having one end facing the sub-operation chamber, and performing a pump operation of the primary fluid via the secondary fluid and the bellows by moving the piston forward and backward. The secondary fluid is replenished to the sub-operation chamber via a secondary fluid passage communicating with the sub-operation chamber.

According to a first aspect of the present invention, one end of the secondary fluid passage is opened in a cylinder chamber which communicates with the auxiliary working chamber and slidably accommodates the piston. The opening to the cylinder chamber is set at a position opened and closed by the piston.

That is, during the period when the opening is closed by the piston, the secondary fluid is not replenished to the sub-operation chamber through the secondary fluid passage.

Further, the invention of claim 2 is characterized in that it has a shutoff means for shutting off the secondary fluid passage for a predetermined period at least after the piston starts to retreat with respect to the sub-operation chamber.

That is, the secondary fluid is not replenished to the sub-operation chamber via the secondary fluid passage at least for a predetermined period after the piston starts to retract with respect to the sub-operation chamber.

According to the third aspect of the present invention, the shutoff means is provided in the middle of the secondary fluid passage and opens and closes the secondary fluid passage, and a piston displacement detector for detecting the displacement of the piston. And a control unit for controlling the drive of the solenoid valve in accordance with a signal from the piston displacement detection unit.

According to a fourth aspect of the present invention, there is further provided an internal pressure detecting section for detecting the internal pressure of the sub-working chamber, wherein the internal pressure in the sub-working chamber is maintained during a period in which the secondary fluid is being replenished to the sub-working chamber. The opening degree of the solenoid valve is adjusted by the control unit so that does not exceed a predetermined value.

According to a fifth aspect of the present invention, there is provided an electromagnetic valve provided in the middle of the secondary fluid passage for opening and closing the secondary fluid passage, a bellows displacement detector for detecting the displacement of the bellows, and the displacement of the bellows. If the specified maximum allowable displacement is exceeded,
And a control unit for controlling the opening of the electromagnetic valve.

According to a sixth aspect of the present invention, there is provided a solenoid valve provided in the middle of the secondary fluid passage for opening and closing the secondary fluid passage.
A bellows displacement detector for detecting the displacement of the bellows,
A control unit that controls opening of the solenoid valve when the bellows is located at a minimum displacement point and the displacement of the bellows is larger than a predetermined reference minimum displacement.

[0016]

According to the present invention, it is possible to effectively avoid a state where the secondary fluid is excessively replenished into the sub-working chamber and the bellows is excessively extended. It is possible to suppress the decrease and the decrease in the durability of the bellows.

In addition, according to the first aspect of the present invention, the period during which the secondary fluid is replenished to the sub-operation chamber via the secondary fluid passage can be limited with a very simple structure.

Further, according to the second to fourth aspects of the present invention, for a predetermined period after the piston starts retreating with respect to the auxiliary working chamber,
That is, the secondary fluid passage is blocked during the predetermined period in which the volume in the sub-working chamber temporarily increases. Therefore, it is possible to reliably prevent the secondary working fluid from being excessively replenished into the sub working chamber during such a predetermined period.

Further, according to the fourth aspect of the invention, while the secondary working chamber is being replenished with the secondary fluid, the opening of the solenoid valve is adjusted so that the internal pressure of the secondary working chamber does not exceed a predetermined value. Therefore, abnormal displacement of the bellows can be more reliably prevented.

According to the fifth and sixth aspects of the present invention, since the solenoid valve is opened when the bellows is excessively displaced, an excess amount of the secondary fluid in the sub-working chamber passes through the secondary fluid passage. And is quickly discharged. Therefore, an abnormal state in which the bellows is excessively displaced can be corrected reliably and quickly.

[0021]

Preferred embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a sectional view showing a first embodiment of a bellows pump according to the present invention. This bellows pump boosts gasoline fuel of, for example, a direct injection internal combustion engine, and has a mounting hole 10a of an upper housing 10.
A cylindrical cylinder housing 14 extending over the mounting recess 12a of the lower housing 12 and a cylinder chamber 16 formed through the cylinder housing 14
A piston 18 is slidably inserted from one end 14a of the cylinder housing 14, and a bellows 20 surrounds the other end 14b of the cylinder housing 14 in a liquid-tight manner. A main working chamber 22 in which gasoline fuel as a fluid is sealed and a sub working chamber 24 in which working oil as a secondary fluid is sealed are liquid-tightly separated.

The cylinder housing 14 is formed with a radial passage 62 to be described later, and
Communication passage 2 that communicates the one region 24a with the cylinder chamber 16
6 are formed. A stopper 28 and a C-ring 30 for supporting the stopper 28 are provided in the cylinder chamber 16.
Is provided, and a return spring 32 is interposed between the stopper 28 and one end 18a of the piston 18.

A bottomed cylindrical cam follower 34 is attached to the other end of the piston 18, and an end face of the cam follower 34 is attached to a mounting hole 10 a of the upper housing 10.
One end faces the camshaft insertion hole 36 which is open. A camshaft 38, which is rotationally driven by a crankshaft of the engine, extends in the camshaft insertion hole 36 in a direction orthogonal to the piston 18. The end surface of the cam follower 34 is always in contact with the cam surface 38 a of the cam shaft 38 by the spring force of the return spring 32. Accordingly, the camshaft 38 and the piston 18 advance and retreat together with the rotation of the camshaft 38.

The bellows 20 is mainly composed of a bellows main body 40 having a bellows cylindrical shape. A substantially disk-shaped lid member 42 is fixed to one end of the bellows main body 40 via a collar 43 and the other end thereof. A tubular mounting bracket 44 is fixed.

The bellows body 40 has a bellows shape which can be easily expanded and contracted in the bellows axial direction. The outer surface of the bellows body 40 faces the main working chamber 22 and the inner surface thereof is the sub working chamber 24.
I'm facing inside. In this embodiment, the bellows body 40 is made of a metal that can withstand high pressure, but an elastic member such as rubber can also be used.

The mounting bracket 44 is screwed into the mounting hole 10 a of the upper housing 10 in a state fitted to the outer peripheral step of the cylinder housing 14. Thereby, the cylinder housing 14 and the bellows 20 are fixed to the upper housing 10.

The main working chamber 22 is separated by an outer surface of the bellows 20, an inner wall surface of the mounting recess 12a of the lower housing 12, and an end surface of the upper housing 10. In the main working chamber 22, one end of a fuel suction passage 46 formed in the lower housing 12 is opened, and one end of a fuel discharge passage 48 formed in the upper housing 10 is opened. A seal member 50 is interposed between the upper housing 10 and the mounting bracket 44 so that the fuel in the main working chamber 22 does not leak to the outside. An O-ring 52 is interposed therebetween, and an O-ring 54 is interposed between the mounting hole 10a of the upper housing 10 and the outer peripheral surface of the cylinder housing 14.

The sub working chamber 24 is separated by the inner surface of the bellows 20 and the inner and outer surfaces of the cylinder housing 14 and includes the cylinder chamber 16 and the communication passage 26.

The operation of the bellows pump will be briefly described. When the piston 18 advances and retreats due to the rotation of the camshaft 38, the bellows 2 moves through the working oil in the sub-operation chamber 24.
0 is expanded and contracted mainly in the cylinder axis direction. As a result, the volume in the main working chamber 22 increases and decreases, and the fuel pump operation is performed. That is, fuel is sucked in from the fuel suction passage 46, or high-pressure fuel is discharged from the fuel discharge passage 48. The high-pressure fuel discharged from the fuel discharge passage 48 is finally pressure-fed to a fuel injection valve (not shown). Although not shown here, the fuel suction passage 46 and the fuel discharge passage 4
In the middle of 8, there are provided appropriate check valves for preventing backflow of fuel.

By the way, the working oil sealed in the sub-working chamber 24 slightly leaks through the sliding surface between the piston 18 and the cylinder chamber 16, so that the working oil passes through the secondary fluid passage 56 described below. For example, lubricating oil for lubricating various parts of the engine is refilled into the sub-operation chamber 24 as hydraulic oil.

The secondary fluid passage 56 is formed in the upper housing 10 to supply lubricating oil at a predetermined feed pressure by a feed pump (not shown), and an upper passage through which the introduction passage 58 is opened. An oil reservoir 60 formed between the wall surface of the mounting hole 10a of the housing 10 and the outer peripheral surface of the cylinder housing 14;
And a radial passage 62 formed in the cylinder housing 14 so as to communicate the cylinder chamber 16 with the cylinder chamber 16.

Although not shown here, a suitable check valve is provided in the middle of the introduction passage 58 to prevent the backflow of the hydraulic oil from the auxiliary working chamber 24 toward the introduction passage 58. .

Here, in this embodiment, the opening 64 of the radial passage 62 facing the cylinder chamber 16 is set at an appropriate position that can be opened and closed by the outer peripheral surface of the piston 18. Specifically, when the piston 18 is located near the top dead center (the state shown in FIG. 1), the opening 64
Open to. Therefore, the hydraulic oil can be replenished from the radial passage 62 to the cylinder chamber 16. On the other hand, when the piston 18 advances downward from the state shown in FIG. 1, the opening 64 is closed by the outer peripheral surface of the piston 18 halfway. That is, the radial passage 62 is shut off from the cylinder chamber 16, and the radial passage 62 is
4) Hydraulic oil cannot be replenished. In FIG. 1, the configuration of each part is exaggerated and the piston 18
Although the opening 64 does not appear to be closed even when the vehicle advances, it is actually completely closed.

FIG. 2 is a timing chart showing the relationship between the working oil pressure of the sub-working chamber 24 and the opening area of the opening 64 with respect to the displacement of the piston 18.

When the piston 18 starts to retreat upward from FIG. 1 from the bottom dead center position shown at the left end of FIG. 2, the operating oil pressure in the sub-operating chamber 24 is reduced for a very short time Δt1. When the pressure is reduced only to reach a predetermined pressure Pmin (pressure 0 in this embodiment), the pressure is no longer reduced. Then, the bellows 20 is displaced in the contracting direction so as to follow the displacement of the piston 18 in accordance with the pressure difference between the sub working chamber 24 and the main working chamber 22.
As a result, the volume of the main working chamber 22 increases, and the main working chamber 2
The internal pressure of the fuel cell 2 decreases, and fuel is sucked from the fuel suction passage 46.

On the other hand, when the piston 18 reaches the top dead center and starts to advance from the state of the top dead center (the state shown in FIG. 1) with respect to the sub-working chamber 24, the inside of the sub-working chamber 24 The operating oil pressure is increased for a short period Δt2, and a predetermined pressure Pm
When the pressure reaches ax, the pressure is no longer increased. Then, according to the pressure difference between the sub working chamber 24 and the main working chamber 22, the bellows 2
0 is displaced in the extension direction so as to follow the displacement of the piston 18. Thus, the volume of the main working chamber 22 is reduced, the pressure in the main working chamber 22 is increased, and high-pressure fuel is discharged from the fuel discharge passage 48.

Here, the bellows 20 correspond to the periods Δt1 and Δt2 during which the pressure in the sub-operation chamber 24 is changing.
The expansion / contraction displacement causes a phase lag with respect to the displacement of the piston 18. In particular, as the cycle of the piston 18 becomes shorter, the phase lag becomes significant.

For this reason, the volume in the auxiliary working chamber 24 temporarily increases during a predetermined period after the piston 18 starts to retreat. If the working oil is replenished to the sub-working chamber 24 through the secondary fluid passage 56 during such a predetermined period, the working oil in the sub-working chamber 24 becomes excessive, and the bellows 20 is excessively extended. As a result, desired characteristics cannot be obtained, and the durability of the bellows 20 may be reduced.

In this embodiment, as is apparent from FIG.
The opening 64 is securely closed by the piston 18 for at least a predetermined period after the piston 18 starts to retreat from the bottom dead center. In other words, only in the short period T1 when the piston 18 is located near the top dead center, the opening 64 is opened, and the radial passage 62 and the cylinder chamber 16 communicate with each other.
Therefore, the working oil is not replenished to the sub-operation chamber 24 during the above-mentioned predetermined period in which the volume of the sub-operation chamber 24 temporarily increases. As a result, it is possible to effectively suppress excessive replenishment of the working oil into the sub-working chamber 24, and as a result,
Deterioration of characteristics due to excessive extension of the bellows 20 and reduction in durability of the bellows 20 can be suppressed.

Particularly, in this embodiment, since the opening portion 64 is opened and closed by the piston 18, an electromagnetic valve is provided in the middle of the secondary fluid passage 56 as in Examples 2 to 4 described later. The structure and control are simpler than when opening and closing control is performed, and the utility is extremely high.

FIGS. 3 and 4 show a bellows pump according to a second embodiment of the present invention. The same parts as those in the first embodiment are denoted by the same reference numerals, and redundant description will be omitted.

In the second embodiment, the opening 64 of the radial passage 62 facing the cylinder chamber 16 is set at a position where the opening 64 is not opened or closed by the piston 18, so that the cylinder chamber always moves regardless of the position of the piston 18 moving forward and backward. It opens to 16. In the middle of the introduction passage 58, an electromagnetic valve 70 for opening and closing the introduction passage 58 is provided instead of the check valve of the first embodiment. The solenoid valve 70 is connected to a control unit 72 such as a microcomputer.
Reference numeral 2 denotes an internal pressure detector 74 for detecting the internal pressure of the sub-operation chamber 24 and a cam angle of the camshaft 38 (displacement of the piston 18).
Angle detection unit (piston displacement detection unit) 76 for detecting
The opening degree of the solenoid valve 70 is adjusted based on the detection signal from.

More specifically, as shown in FIG. 4, the solenoid valve 70 is kept closed for a predetermined period T2 after the piston 18 starts retreating from the bottom dead center, and the solenoid valve 70 is closed after the predetermined period T2 has elapsed. Fully open. Further, during a period T3 from the elapse of the predetermined period T2 to the time when the piston 18 reaches the top dead center, the internal pressure in the sub-operation chamber 24 does not exceed the predetermined value P1.
The opening of the solenoid valve 70 is adjusted by the control unit 72. Specifically, the opening is gradually reduced as the piston 18 approaches the top dead center.

According to the second embodiment, as in the first embodiment, hydraulic oil is replenished to the sub-operation chamber 24 during the predetermined period T2 when the volume in the sub-operation chamber 24 temporarily increases. As a result, deterioration of characteristics due to excessive replenishment of hydraulic oil and reduction in durability of the bellows 20 can be effectively suppressed.

Further, in the second embodiment, during the period T3 during which the solenoid valve 70 is opened and the working oil is replenished to the working sub-chamber 24, the internal pressure of the working sub-chamber 24 does not exceed the predetermined value P1. Since the opening of the solenoid valve 70 is adjusted, abnormal displacement of the bellows 20 can be more reliably prevented.

In the third embodiment described below, a bellows displacement detector for detecting the expansion and contraction displacement of the bellows 20 is connected to the controller 72 instead of the internal pressure detector 74 and the cam angle detector 76 shown in FIG. Only in that it is different from the configuration of the second embodiment.

FIG. 5 is a flowchart executed by the control unit 72 of the bellows pump according to the third embodiment.
First, in step S10, the rotation speed Np of the feed pump that supplies the working oil to the introduction passage 58 is read. In the following step S12, the displacement x of the bellows 20 is set in advance,
It is determined whether or not the stored maximum allowable displacement X1 of the bellows 20 has been exceeded. In this step S12,
If it is determined that the displacement x of the bellows 20 has exceeded the maximum allowable displacement X1, the process proceeds to step S14, and a timer is started. Next, in step S16, the opening of the solenoid valve 70 is controlled. If it is determined in step S18 that the elapsed time t of the timer has exceeded a predetermined value Np · b proportional to the pump speed Np, the process proceeds to step S20, in which the solenoid valve 70 is controlled to be closed.

As described above, in the third embodiment, the bellows 20
When the displacement x exceeds the maximum allowable displacement X1, that is, when the bellows 20 is abnormally extended, the solenoid valve 70 is immediately opened for a predetermined time Np · b, and the sub-operation chamber 24 is opened.
The surplus hydraulic oil inside is discharged to the outside through the secondary fluid passage 56 as appropriate. Therefore, the state in which the bellows 20 is excessively extended can be reliably and promptly corrected, and a decrease in characteristics and a decrease in durability due to abnormal displacement of the bellows 20 can be reliably suppressed.

In the fourth embodiment described below, a cam angle detector 76 as shown in FIG. 3 is connected to the controller 72 in addition to the configuration of the third embodiment.

FIG. 6 is a flowchart executed by the control unit 72 of the bellows pump according to the fourth embodiment. First, in step S30, a cam angle detected by the cam angle detection unit 76 is read. Subsequent step S
At 32, based on the cam angle, the bellows 20
It is determined whether or not the bellows displacement is located at the top dead center where the bellows displacement is the shortest. In other words, the piston 18
Is calculated, and the bellows displacement is calculated from the displacement of the piston 18 to determine whether or not the bellows 20 is at the top dead center. In the following step S34, it is determined whether or not the displacement x of the bellows 20 has exceeded a preset and stored reference minimum displacement X2. That is, when it is determined that the displacement x of the bellows 20 at the top dead center is larger than the reference minimum displacement X2, the process proceeds to step S36 via steps S32 and S34, and the opening of the solenoid valve 70 is controlled. In the following step S38, a timer is started. If it is determined in step S40 that the elapsed time t of the timer has exceeded a predetermined time t1, which is set and stored in advance, the solenoid valve 70 is controlled to be closed in step S42.

As described above, in the fourth embodiment, whether the bellows 20 is located at the top dead center is calculated based on the cam angle, and the displacement x of the bellows 20 at the top dead center is larger than the predetermined reference minimum displacement X2. For example, the solenoid valve 70 is opened so that the bellows displacement x is equal to or less than the reference minimum displacement X2. As a result, the surplus hydraulic oil in the sub-operation chamber 24 is quickly discharged to the outside via the introduction passage 58. Therefore, similarly to the third embodiment, the state where the bellows 20 is excessively extended can be reliably and quickly corrected, and the characteristic deterioration and the durability decrease due to the abnormal displacement of the bellows can be reliably prevented.

[Brief description of the drawings]

FIG. 1 is a sectional view of a bellows pump according to a first embodiment of the present invention.

FIG. 2 is a timing chart showing the operation of the bellows pump according to the first embodiment.

FIG. 3 is a sectional view of a bellows pump according to a second embodiment of the present invention.

FIG. 4 is a timing chart showing the operation of the bellows pump according to the second embodiment.

FIG. 5 is a flowchart executed by a control unit of a bellows pump according to a third embodiment of the present invention.

FIG. 6 is a flowchart executed by a control unit of a bellows pump according to a fourth embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 16 ... Cylinder chamber 18 ... Piston 20 ... Bellows 22 ... Main working chamber 24 ... Sub working chamber 56 ... Secondary fluid passage 58 ... Introduction passage 62 ... Radial passage 70 ... Electromagnetic valve 72 ... Control unit 74 ... Internal pressure detection unit 76 ... Cam angle detector (piston displacement detector)

Claims (6)

[Claims] 1. A main working chamber filled with a primary fluid, a sub working chamber filled with a secondary fluid, a telescopic bellows separating the main working chamber and the sub working chamber, and a sub working. A piston having one end facing the chamber, and performing a pump operation of the primary fluid via the secondary fluid and the bellows by moving the piston forward and backward, and a secondary fluid passage communicating with the sub-operation chamber. A bellows pump that replenishes the secondary working chamber with the secondary fluid through the opening of one end of the secondary fluid passage in a cylinder chamber that communicates with the secondary working chamber and slidably accommodates the piston. Open the secondary fluid passage to the cylinder chamber,
A bellows pump characterized by being set at a position opened and closed by the piston. 2. A main working chamber filled with a primary fluid, a sub working chamber filled with a secondary fluid, a telescopic bellows separating the main working chamber and the sub working chamber, and the sub working. A piston having one end facing the chamber, and performing a pump operation of the primary fluid via the secondary fluid and the bellows by moving the piston forward and backward, and a secondary fluid passage communicating with the sub-operation chamber. A bellows pump for replenishing the secondary working chamber with the secondary fluid via the sub-working chamber, characterized in that the bellows pump has a shut-off means for shutting off the secondary fluid passage at least for a predetermined period after the piston starts to retract with respect to the sub-working chamber. And bellows pump. 3. An electromagnetic valve provided in the middle of the secondary fluid passage for opening and closing the secondary fluid passage;
A piston displacement detector that detects the displacement of the piston,
The bellows pump according to claim 2, further comprising: a control unit that drives and controls the solenoid valve according to a signal from the piston displacement detection unit. 4. An internal pressure detector for detecting an internal pressure of the sub-operation chamber, wherein the internal pressure in the sub-operation chamber exceeds a predetermined value during a period in which the secondary fluid is being replenished to the sub-operation chamber. 4. The bellows pump according to claim 3, wherein the opening of the solenoid valve is adjusted by the control unit so as not to occur. 5. 5. A main working chamber filled with a primary fluid, a sub working chamber filled with a secondary fluid, a telescopic bellows separating the main working chamber and the sub working chamber, and the sub working. A piston having one end facing the chamber, and performing a pump operation of the primary fluid via the secondary fluid and the bellows by moving the piston forward and backward, and a secondary fluid passage communicating with the sub-operation chamber. A bellows pump for replenishing the secondary working chamber with the secondary fluid through the solenoid valve, which is provided in the middle of the secondary fluid passage and opens and closes the secondary fluid passage, and a bellows displacement detection for detecting the displacement of the bellows A bellows pump comprising: a control unit that controls opening of the solenoid valve when the displacement of the bellows exceeds a predetermined maximum allowable displacement. 6. A main working chamber filled with a primary fluid, a sub-working chamber filled with a secondary fluid, a telescopic bellows separating the main working chamber and the sub-working chamber, and a sub-working. A piston having one end facing the chamber, and performing a pump operation of the primary fluid via the secondary fluid and the bellows by moving the piston forward and backward, and a secondary fluid passage communicating with the sub-operation chamber. A bellows pump that replenishes the secondary working chamber with the secondary fluid through the solenoid valve, which is provided in the middle of the secondary fluid passage and opens and closes the secondary fluid passage, and a bellows displacement detector that detects the displacement of the bellows A bellows pump comprising: a control unit that controls opening of the solenoid valve when the bellows is located at a minimum displacement point and the displacement of the bellows is greater than a predetermined reference minimum displacement.