JPH0979166A - Air compressor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce pressure adjusting parts and kinds of piping, simplify a capacity control system, reduce a load at starting time, control a delivery air quantity, and cope with many load conditions such as blowoff air unloading time. SOLUTION: In a suction throttle valve 5, a moving body 61 is fitted to an outer cylinder 71 arranged in a valve case 51, and a piston 58 is fitted to an inner cylinder 62, and a valve plate 55 is attached to it. The valve plate 55 reciprocatively operates, and comes into close contact with a valve seat 56, and blocks up an intake air passage 53, and stops intake air of an air compressor. Compression springs are provided in chambers on the valve plate 55 side of respective cylinders, and in the opposite side chambers, internal pressure of an air tank is communicated with an outside main chamber 72 through a solenoid valve 31, and the internal pressure is directly communicated with an inside main chamber 63. At starting time and blowoff air unloading time, the solenoid valve 31 is opened, and the valve plate 55 is closed by comparatively weak pressure applied to the outside main chamber 7, and at unloading time, the valve plate is opened and closed by comparatively strong pressure applied to the inside main chamber 63, and an intake air quantity is controlled.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to air compressors.

[0002]

2. Description of the Related Art Air compressors are widely used mainly for general industries. The basic operation is to take in air from the atmosphere and send it out to an external pipe after compression, and the sent compressed air is used as a power source or an injection medium. Since the air compressor is easy for the user to use and requires safe and reliable operation, the air compressor is put into practical use as an integral unit together with the compressor body and some auxiliary machines.

There are various types of compressor accessories, but the main ones are an air purifier, a suction throttle valve, a compressed air cooler, an air tank, and an electric motor or an internal combustion engine as a power source. The air purifier removes dust contained in the sucked air as an air purifying means. The suction throttle valve has a function of limiting the amount of air to be sucked in, or stopping the suction as a suction amount limiting means. The compressed air cooler serves as compressed air cooling means and cools the compressed air that has become high temperature. The air tank temporarily stores compressed air and suppresses fluctuations in discharge pressure.

When the compressor main body is an oil-cooled compressor that compresses while supplying oil to the compression chamber, the compressor main body has an oil supply function to enable continuous oil supply to the compression chamber.
Some oil related accessories are needed. As an example, an oil separator as an oil separation means that separates the oil mixed in the air from the air after compression, an oil cooler that absorbs heat from the air generated by compression and cools the oil whose temperature has risen, and prepares for re-lubrication, etc. Is. In addition, the compression chamber of the compressor body, the oil separator,
The oil circulating in the oil cooler is also an important factor related to the performance and reliability of the compressor.

One of the important functions required of the air compressor is the control of the discharge pressure. For the user, it is desirable that the discharge pressure be constant. However, the amount of air used by the user is often not constant. If the amount of air used decreases while the air compressor is operating at a constant capacity, the discharge pressure rises due to the surplus compressed air, and conversely, if the amount of air used increases, the discharge pressure drops. Therefore, the air compressor is usually provided with a capacity control function to control the discharge amount according to the amount of air used and maintain the discharge pressure within a certain range.

Several types of air compressor capacity control methods have been put into practical use. In a small compressor, on / off control is generally performed by repeatedly starting and stopping the electric motor depending on the pressure in the air tank. Since it is difficult to start and stop the electric motor frequently with medium-sized or larger compressors, and it takes time to restart the electric motor, the suction throttle restricts the suction amount of the compressor body with the suction throttle valve while continuing the rotation of the electric motor. Expression capacity control (also known as suction unloading) is widely used. In addition, a method in which the compressor body is driven at a variable speed by an inverter to control the capacity has been put into practical use.

When the amount of air used is extremely small or when the compressor is operated in cooperation with another compressor, it may not be necessary to discharge compressed air for a certain period of time. In that case, close the intake almost completely and at the same time release the compressed air in the air tank,
Lower the discharge pressure. Then, while the rotation of the electric motor continues, the torque required to rotate the compressor body is reduced, and the power consumption is saved. This state is called bleed unloading, and is widely used in medium-sized and larger air compressors.

In a medium-sized or larger air compressor, the starting method should be considered together with the capacity control. In order to easily start the electric motor of medium size or more, it is necessary to reduce the torque required for the rotation of the compressor to be smaller than that during normal operation immediately after the power is turned on. Therefore, the suction amount is limited by the suction throttle valve, and the suction pressure of the compressor body and the air tank internal pressure that is the discharge pressure are kept low. This is a state close to the previous unloading unloading, but since the suction is throttled before the internal pressure of the air tank rises, the air tank pressure is kept low compared to the unloading unloading.

A structure for controlling a plurality of suction pressure and discharge pressure states and a discharge amount for realizing the states is disclosed in Japanese Patent Laid-Open No. 60-2565.
No. 91 publication. In the known example, a plurality of solenoid valves and valves for pressure adjustment are required, and the piping system connecting them is complicated.

An example of a conventional capacity control device will be described with reference to FIGS. 2, 3, and 4. FIG. 2 is a system diagram of an oil-cooled air compressor provided with a mechanism for carrying out capacity control. It should be noted that parts that are not directly involved in the present invention are omitted. FIG. 3 shows an example of changes in the internal pressure of the air tank during the operation of the compressor over time, and the vertical axis shows absolute pressure with the atmospheric pressure as 1 atm. FIG. 4 is a graph showing the input / output pressure characteristics of the pressure regulating valve used in this mechanism.

During steady operation, air is taken in from the atmosphere and, after removing dust by the air purifier 14, passes through the suction throttle valve 2 and the suction passage 19. Subsequently, the air is sucked into the compressor body 1 through the suction port 11 and, after being compressed, the discharge port 12
Is discharged from. In the compression process, the oil continuously supplied from the oil supply port 13 is mixed into the air, and the oil functions as a lubricating, cooling and sealing material. The compressed air and the oil enter the oil separator 15 in a mixed state, and after the separation, the compressed air is guided to the outside through the discharge valve 16. The discharge valve 16 is composed of a check valve and a pressure regulating valve which are arranged in series, and prevents backflow and at the same time closes the pressure in the downstream when the pressure is extremely low to maintain the internal pressure of the air tank above a certain pressure. On the other hand, the oil discharged from the oil separator 15 is the oil cooler 1
After 7, the oil is again injected into the compressor body from the oil filler port 13. In the oil cooler 17, the cooling air sent by the fan 18 exchanges heat with the oil temperature.

The oil separator 15 has a sufficient volume inside, and the separated oil collects in the lower part, and the remaining upper space is filled with compressed air although some oil mist floats. Therefore, the oil separator 15 has not only the function of separating compressed air and oil, but also the functions of an air tank and an oil sump. Therefore, the upper part of the oil separator is handled as the air tank 20.

The intake throttle valve 2 includes a valve case 21, a valve plate 22,
A piston 23 and a rod 24 connecting them are built in. A part of the valve case 21 is a cylinder 2 in which a piston 23 reciprocates.
5 forming a valve plate 22 separated by a piston 23
The side will be called the sub chamber 27, and the opposite side will be called the main chamber 26. A compression spring 28 is provided in the sub chamber 26.

A compressed air discharge pipe 3 downstream of the oil separator 15.
From 3, the two valves, the solenoid valve 31 and the pressure regulating valve 32, branch in parallel and both communicate with the discharge passage 34. Solenoid valve 3
1 has a function of being closed when energized and fully opened when no voltage is applied. One end of the discharge passage 34 is connected to the main chamber 26 of the intake throttle valve 2.
And the other end reaches the end silencer 36 through the discharge throttle 35 and is opened to the atmosphere.

For the pressure regulating valve 32, the air tank 2 on the upstream side
The internal pressure of 0 is the input pressure, and the internal pressure of the discharge passage 34 and the main chamber 26 on the downstream side is the output pressure. As shown in FIG. 4, the pressure regulating valve 32 remains closed until the input pressure exceeds the set pressure (7 atmospheric pressure is assumed in FIG. 4). It has a function to output the pressure exceeding the set pressure, that is, the differential pressure obtained by subtracting the set pressure from the input pressure, for the input pressure higher than the set pressure. However, the actual pressure regulating valve exhibits a characteristic slightly deviating from the line shown in FIG. 4, and the path of the input / output characteristic may have different hysteresis in the process of pressure increase and decrease, but this is not an amount related to the essence. Further, the set pressure can be changed by an adjusting handle attached to the pressure adjusting valve 32.

A flow path communicating with the sub chamber 27 of the suction throttle valve 2 reaches a common port of the electromagnetic three-way valve 37. The electromagnetic three-way valve 37 has a function of connecting the common port to the suction passage 19 side when energized and connecting the common port to the atmosphere side at other times.

The electric motor 3 that drives the compressor body 1 is an induction motor, and commercial AC power 42 is sent through a starter board 41 to rotate. The starter board 41 has a function of switching a power supply circuit and performing star delta start-up in order to suppress an excessive current that is seen at the time of start-up.

The control device 4 is composed of an electronic circuit centered on a microcomputer, and has a function of issuing a command to the electromagnetic valve 31, the electromagnetic three-way valve 39, and the starter board 41. Further, it has a function of receiving information from the pressure sensor 44 provided downstream of the switch 43 and the discharge valve 16.

An example of the general operation of the air compressor is shown along the time axis of FIG. Air tank 2 before starting the air compressor
The 0 internal pressure is equal to 1 atmospheric pressure, which is the atmospheric pressure. At time A, the user turns on the switch 43. The controller 4 recognizes it,
The starter board 41 is instructed to drive the star circuit. At the same time, the electromagnetic valve 31 is instructed to open, and the electromagnetic three-way valve 37 is instructed to communicate the sub chamber 27 with the suction passage 19.

The electric motor 4 gradually accelerates from the stopped state, and the compressor body 1 also starts to compress the air, and the air is sent to the air tank 20 so that the internal pressure gradually rises. During this time,
Since the internal pressure of the air tank 20 does not reach the specified value, the discharge valve 16 is not opened. The compressed air slightly accumulated in the air tank 20 is guided to the main chamber 26 via the opened solenoid valve 31. Since the internal pressure of the air tank 20 does not reach the set pressure, the pressure adjusting valve 32
Remains closed. The compressed air in which the internal pressure of the air chamber 20 is applied to the main chamber 26 passes through the discharge throttle 35, and after the pressure is reduced, it is discharged from the silencer 36 to the atmosphere. Therefore, the internal pressure of the main chamber 26 is determined by the flow path resistance of the solenoid valve 31 and the conduit in the middle and the flow path resistance of the air discharge throttle 35, and is between the internal pressure of the air tank 20 and the atmospheric pressure. Normally, since the flow passage resistance of the discharge throttle 35 is increased, the internal pressure of the main chamber 26 is close to the internal pressure of the air tank 20.

Since the sub chamber 27 communicates with the suction passage 19, the sub chamber 27 is sucked by the compressor body 1 and the internal pressure becomes a negative pressure below atmospheric pressure.
The piston 23 moves leftward in the figure due to the pressure difference between the main chamber 26 and the sub chamber 27, and finally the valve plate 22 completely closes the flow path. Since air is not sent to the compressor body 1 in this state, the internal pressure of the air tank 20 rises by about 0.5 atm from the atmospheric pressure and remains almost constant, during which the drive torque of the compressor body 1 is increased. Becomes smaller. Since the required torque is small, the electric motor 4 is easily accelerated and the starting current is suppressed.

When the rotation speeds of the electric motor 4 and the compressor body 1 reach a sufficient value at time B, the starter board 41 switches the circuit from the star circuit to the drive by the delta circuit according to a command from the control circuit 4. Subsequently, the control device 4 controls the solenoid valve 3
1 is closed and the electromagnetic three-way valve 37 is switched to switch the sub chamber 27.
To communicate with the atmosphere side 38.

Since the supply of the compressed air from the air tank 20 is stopped, the air inside the main chamber 26 and the air discharge passage 34 is discharged from the silencer 3.
It runs out from 6, and the internal pressure drops to atmospheric pressure. On the other hand, since the sub chamber 27 also communicates with the atmosphere side 38 via the electromagnetic three-way valve 37, the internal pressure becomes atmospheric pressure. Since the pressure on both sides becomes equal to the piston 23, the gas pressure in the direction of closing the valve plate 22 does not work,
The valve plate 2 is caused by the reaction force of the compression spring 28 and the pressure difference between the two surfaces of the valve plate 22.
2 is open until it is fully opened.

The suction throttle valve 2 is fully opened, and the compressor body 1
Since the rotation speed is also in normal operation, the compressed air is sent into the air tank 20 at the maximum capacity. The internal pressure of the air tank 20 gradually increases and reaches 7 atm at time C. The discharge valve 16 is also opened after the specified pressure is exceeded, and compressed air is sent to the outside, and the normal operating state is achieved.

During normal operation, the internal pressure of the air tank 20 changes according to the amount of compressed air used, but suction restriction control is performed to maintain the discharge pressure between 7 and 8 atmospheres. The operation of this mechanism will be described. The internal pressure of the air tank 20 always acts on the input side of the pressure adjusting valve 32, but the pressure adjusting valve 32 is not opened until the internal pressure reaches the set pressure of 7 atm. When the internal pressure of the air tank 20 increases and reaches the set pressure, the pressure regulating valve 32 is automatically opened, and the compressed air flows out through the valve. This time,
The pressure of the air after passing through the valve is automatically controlled by the pressure adjusting valve 32 to a value obtained by subtracting the set pressure from the internal pressure of the air tank 20 which is the input.

The air that has passed through the pressure regulating valve 32 flows into the main chamber 26 of the suction throttle valve 2, pushes the piston, and the valve plate 2
Close 2 When the valve plate 22 is closed, the pressure loss of the intake air increases and the intake amount decreases, so that the internal pressure of the air tank 20 decreases. With the above functions, the discharge pressure is automatically controlled,
The pressure does not become excessive and is suppressed to 8 atm at maximum. At this time, 1 atm obtained by subtracting the set pressure of 7 atm acts on the piston to fully close the suction throttle valve. During the suction throttle, some air is discharged through the discharge throttle 35 and the silencer 36.

When the controller 4 senses with the pressure sensor 44 that the discharge pressure does not decrease because the air is not consumed for a certain period of time, it is determined that the discharge unloading state is entered to save power. The release operation is switched to the unloading unloading by the following operation. At time D, the control device 4 commands the solenoid valve 31 to open. The compressed air in the air tank 20 is a solenoid valve 31.
, Enters the main chamber 26, and is discharged through the discharge throttle 35 and the silencer 36. Since the internal pressure of the main chamber 26 rises,
The piston 23 pushes the rod 24 to fully close the valve plate 22. Since the air is discharged at the same time as the intake is stopped, the internal pressure of the air tank 20 gradually decreases and gradually approaches 3 atmospheric pressure. When the pressure is lower than this pressure, the intake throttle valve 2 is opened to allow air to flow in, and when the pressure is higher than this pressure, the air is discharged without being sucked.
It becomes stable at atmospheric pressure. If the stabilizing pressure is higher than this, the power consumption will be large and the effect of power saving will be small, and if the stabilizing pressure is lower than this, the air mixed in the oil will expand and cause a foaming phenomenon. There is.

The reason why the stable pressure of the internal pressure of the air tank due to the discharge unloading is higher than the stable pressure at the time of startup is that the internal pressure of the sub-chamber 27, which was a negative pressure at the time of startup, is as high as atmospheric pressure. This is because it is necessary to increase the pressure applied to the main chamber 26 in order to shut off.

During the discharge unloading, the internal pressure of the air tank 20 becomes lower than that of the downstream side external pipe, but the discharge valve 16 prevents the backflow of the compressed air.

When the use of compressed air is resumed at time E in the discharge unloading state, the discharge pressure drops. When the control device 4 detects this by the pressure sensor 44, the energization of the solenoid valve 31 is stopped and the closing is commanded. Since the supply of compressed air is stopped, the internal pressure of the main chamber 26 drops to atmospheric pressure, suction and compression of air are restarted, and the internal pressure of the air tank 20 rises.

When the user turns off the switch 43 at time F,
The control device 4 commands the starter board 41 to shut off the current and the solenoid valve 31 to open. The compressor body 1 is stopped, and the compressed air remaining in the air tank 20 is discharged through the solenoid valve 31, the discharge throttle 35, and the silencer 36. In the process, suction throttle valve 2
Is fully closed to prevent backflow from the compressor body 1 through the suction passage 19. Due to the air release, the internal pressure of the air tank 20 gradually decreases until time G when the atmospheric pressure is reached. Further, even during a power failure, the operation is stopped and the air is discharged by the same operation as when stopped.

The pressure value used in this embodiment is a tentative value for the purpose of explanation, and actually varies slightly depending on the usage conditions and purpose of use of the compressor.

[0033]

The air compressor having the capacity control mechanism according to the conventional example functionally satisfies the requirements and is widely used. However, since it corresponds to capacity control of start-up unloading, discharge unloading, suction throttle type, and prevents backflow of suction flow path after stop and discharges residual air, the control system is complicated and many parts are required. . Therefore, parts purchase and production,
There is a problem in that much cost, labor and time are required for assembly and adjustment, and the cost of the compressor as a whole becomes high. Further, for the same reason, there is a problem that it takes time and effort to maintain and maintain the reliability of the entire compressor.

It is an object of the present invention to provide an air compressor which realizes a capacity control device which enables the same function with a simple structure and a small number of parts.

[0035]

In order to achieve the above object of the present invention, the following first means is used.

The suction throttle valve, which is the suction amount limiting means, is mainly composed of a case in which the suction passage connecting the air purifier and the suction port of the compressor body and the outer cylinder are formed, and other members are combined. A valve plate provided in the middle of the suction passage is movably supported, and the valve plate has a function of partially or completely closing the suction passage depending on its position. The suction throttle valve is provided with an inside of a piston connected to a valve plate by a rod which is a connecting member, and the piston is fitted in an inner cylinder so as to be capable of reciprocating motion. The inner cylinder is divided into a plurality of chambers by a piston. The inner cylinder is formed inside a moving body that is a moving member, and the moving body is reciprocally incorporated in an outer cylinder provided in the case. The moving body divides the outer cylinder into a plurality of chambers. Further, the moving direction of the piston and the moving direction of the moving body coincide with each other, and means for limiting the moving range may be provided as needed.

In order to achieve the above object of the present invention more efficiently, the following second means is used in addition to the above first means.

Of the chamber formed by dividing the inner cylinder by the piston, the chamber located on the opposite side of the valve plate (referred to as the inner main chamber) is made to communicate with the flow path from the air tank downstream of the compressor discharge port. One of the chambers formed by dividing the outer cylinder by the moving body is communicated with the air tank through the opening / closing means. Here, the opening / closing means is a valve whose opening / closing can be controlled by remote control via an electric wire according to a command from a control device represented by a solenoid valve.

Further, a compression spring, or
Equipped with a tension spring in the inner main chamber, by adjusting the spring constant,
The discharge pressure set value of the compressor can be selected.

Both the first and second means do not require a passage communicating with the sub chamber including the electromagnetic three-way valve described in the conventional example, and the chamber on the valve plate side of the inner cylinder of the suction throttle valve is not required. It only needs to be in communication with the inhalation passage or the atmosphere. The pressure regulating valve described in the conventional example and the flow passages before and after it are also unnecessary.

[0041]

The suction throttle valve according to the means for solving the above-mentioned problems and the air compressor constructed using the suction throttle valve operate as follows. The outer cylinder chamber, through which the air tank internal pressure communicates via the opening / closing means, will be described as a chamber on the opposite side of the valve plate partitioned by the moving body. In the case of the chamber on the valve plate side, if the opening / closing of the opening / closing means is considered in reverse, the same operation is performed.

When the air compressor is started, the opening / closing means is opened,
Compressed air is sent from the air tank to the outer main chamber. Since the cross-sectional area of the outer cylinder is relatively large, even if the internal pressure of the air tank is less than the discharge pressure, for example, about 2 atm, the value is sufficient to push the moving body corresponding to the piston fitted in the outer cylinder. When the moving body moves toward the valve plate, the piston inside the moving body also moves integrally, closing the valve plate and closing the suction passage. At this time, the pressure in the inner main chamber does not reach a pressure sufficient to move the piston, and the piston does not move inside the inner cylinder and is integrated. Since the suction passage is blocked, the suction pressure becomes lower than the atmospheric pressure, and the discharge pressure is sufficiently lower than that during normal operation. Therefore, the torque required to move the compressor body is small, and the start-up becomes easy for the electric motor.

When the electric motor and the compressor body are accelerated to the rotational speed of normal operation, the start-up circuit becomes a delta circuit according to a command from the control device, and the opening / closing means is closed. Since the outer main chamber is separated from the working chamber, the supply of high-pressure air is interrupted, the internal pressure drops, the moving body retreats to the outer main chamber side, and the valve plate opens. At this time, since the pressure in the working chamber is still low, the valve plate and the piston remain integrated with the moving body. Since the valve plate is opened, the air flows into the compressor body, and the normal operation of compressing and discharging the air is started.

In a normal operating condition, the suction throttle type capacity control is performed as shown below. If the amount of compressed air used is less than the compression function, the air tank internal pressure will rise. Since the inner main chamber communicates with the air tank, the internal pressure gradually rises,
Finally, the set pressure is exceeded. Then, the force of the inner main chamber pressure pushing the piston toward the valve plate exceeds the reaction force of the spring provided in the inner cylinder, and the piston starts to move. The higher the inner main chamber pressure,
The force is large, causing the spring to deform more and closing the valve plate.
The position of the piston is determined by the balance between the differential pressure on both sides of the piston, the spring constant, the differential pressure on both sides of the valve plate, and some frictional force.
Normally, when the internal pressure of the air tank rises from the set pressure to a pressure higher by about 1 atm, the valve plate is completely closed. At this time, since the pressure in the outer main chamber is as low as atmospheric pressure, the moving body remains stationary on the outer main chamber side and does not move.

When it is judged that the discharge unloading operation is to be carried out under the condition that the amount of compressed air used is none or extremely small, the control device supports the opening / closing means to open. Since the air tank internal pressure passes through the opening / closing means and is applied to the outer main chamber, the moving body starts to move toward the valve plate. Even when the piston is at the end of the inner sub-chamber and the valve plate is closed at the time of shifting to the discharge unloading, only the moving body moves in the valve plate direction with the valve plate being closed, so the suction passage is It will never be opened. Also, even if the air tank internal pressure decreases due to air release and the internal main chamber pressure becomes insufficient to push the piston, the piston and valve plate are pushed together with the moving body by the external main chamber pressure to maintain the valve plate fully closed. .

The return from the discharge unloading to the normal operation is performed by closing the opening / closing means, and the same operation as at the time of starting is performed, and the increase of the air tank internal pressure and the subsequent restart of discharge are executed.

When the compressor is stopped, the opening / closing means is opened to close the valve plate, and subsequently the operation of the compressor main body is stopped. By closing the valve plate, air from the compressor body and backflow of oil in the working chamber of the oil-cooled compressor are prevented. Further, the air tank internal pressure is released through the opening / closing means, and the inside of the compressor also becomes atmospheric pressure. Therefore, ensure safety during maintenance and disassembly adjustment,
Alternatively, obstacles such as oil leakage are prevented.

[0048]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The construction and operation of the oil-cooled air compressor of the first embodiment will be described below with reference to FIGS. 1, 5, 6, and 7. FIG. 1 is a cross-sectional view of an intake throttle valve used in the air compressor of this embodiment, showing a state of full opening during full load operation. FIG. 5 is a system diagram of the air compressor of this embodiment. FIG. 6 is a cross-sectional view of a state in which the suction throttle valve used in the air compressor of this embodiment is fully closed at the time of starting or unloading air. FIG. 7 is a cross-sectional view at the time of fully closed unloading in which the amount of compressed air used by the same discharge throttle valve is extremely small and the suction is almost completely throttled.

The structure of the suction throttle valve 5 used in the air compressor of this embodiment will be described with reference to FIG. The suction throttle valve 5 is configured by incorporating suction passages 53 and 54 and various members described later in a valve case 51. In the figure, the left direction is expressed as the front side and the right direction is expressed as the back side. The intake path is considered such that the upstream side is divided into the upper intake path 53 and the downstream side is divided into the lower intake path 54 with the surface of the valve plate 55 pressed against the valve seat 56 closing the intake path as a boundary. The upper suction passage 53 communicates with the air purifier 14, and the lower suction passage 54 communicates with the suction port 11 of the compressor body 1.

The surface packing 94, which is the portion of the valve plate 55 that abuts on the valve seat 56, is made of an elastic material such as rubber having a close contact and airtightness. A rod 57 extends on the back side of the valve plate 55,
The piston 58 is fixed at the tip thereof. The valve plate 55, the rod 57, and the piston 58 integrally reciprocate. The piston 58 fits into an inner cylinder 62 that is a smooth cylindrical hole formed on the inner surface of the moving body 61. Therefore, reciprocating motion and rotation are allowed, but other degrees of freedom are restricted. Further, since the piston 58 comes into contact with a convex portion or a step formed on the end portion of the inner cylinder 62,
The reciprocating motion is also limited to a certain range. The outer periphery of the piston 58 and the inner surface of the inner cylinder 62 are not in contact with each other, a slight clearance is maintained, and a ring-shaped inner packing 59 that closes the outer clearance is fitted in a groove formed on the outer periphery of the piston 58. Inner packing 5
While 9 and other packings have elasticity and adhere to both sides of the clearance, a material having a small frictional force, a sectional shape and a surface treatment are selected. The inner cylinder 62 is divided into two chambers by a piston 58, of which the rear chamber is the inner main chamber 63,
The room on the front side is called an inner sub-chamber 64.

A compression spring 65 is provided in the inner sub chamber 64,
A force is applied in a direction in which the piston 58 is separated from the inner wall of the moving body 61, which is the front end surface of the inner sub chamber 64. The free length of the spring is longer than when the two are farthest apart, and therefore even when the two are farthest apart, a certain amount of initial force is exerted.
The magnitude of this force determines the set pressure for the compressor discharge.

The moving body 61 itself serves as a piston,
It fits into an outer cylinder 71 built in the valve case 51 and can reciprocate in the same direction as the piston 58. The moving body 61 having a substantially cylindrical shape is long in the axial direction, and ring-shaped outer packing 60 that closes the outer peripheral clearance is fitted in each outer peripheral groove provided near both ends thereof. The outer cylinder 71 is divided into three chambers with the two outer packings 60 of the moving body 61 as boundaries. The room on the back side is the outer main room 72, the room on the front side is the outer sub-chamber 73, and the outer circumference of the movable body 61 sandwiched between the two outer packings 60 is the outer room 74.

A compression spring 75 is provided in the outer auxiliary chamber 73,
A force is applied in a direction in which the front end surface of the outer auxiliary chamber 73 and the moving body 61 are separated from each other. The free length of the spring is longer than when the two are farthest apart. Therefore, even when the two are farthest apart, a certain amount of initial force is exerted. The compression spring 75 has a smaller spring constant than the compression spring 65 in the inner sub chamber 64, and is set to have a small initial force.

A communication hole 66 connecting the inner sub-chamber 64 and the outer sub-chamber 73 is made to penetrate through the front end surface of the moving body 61. Further, the valve case 51 has a communication hole 7 connecting the outer sub chamber 73 and the lower suction passage 54.
6 are provided. Therefore, the internal pressures of the inner sub-chamber 64 and the outer sub-chamber 73 communicating with each other follow the inner pressure of the lower suction passage 54. Since the chambers on both sides have almost the same pressure in the hole formed in the valve case 51 and the moving body 61 through which the rod 57 passes, a shaft seal is not required. However, slidability is required to ensure smooth movement. The moving body 61 is also provided with a communication passage 67 connecting the inner main chamber 63 and the outer chamber 74 on the side surface.

An inner main chamber 63 is provided at the center of the rear end surface of the moving body 61.
And the outer main chamber 72 are connected to each other. An overpressure air release valve 68 is provided. The overpressure air release valve 68 is formed by assembling a valve ball 69 and a valve spring 70 in a through hole opened on the end face of the moving body 61 and having a diameter changed in the middle. To do. When the internal pressure of the outer main chamber 72 is higher than the internal pressure of the inner main chamber 63, the valve ball 69 is pushed by the differential pressure to close the hole, and the overpressure relief valve 68 is closed. On the contrary, when the inner pressure of the inner main chamber 63 is higher than the inner pressure of the outer main chamber 72, the valve ball 69 is pushed by the force of the valve spring 70 until the pressure difference reaches a certain value, and the hole is blocked, and the pressure difference is not less than the pressure difference. In this case, the valve ball 69 is moved to the back side, a clearance is generated, and the overpressure release valve 68 is released.
Opens. Overpressure release valve 6 when the internal pressure of the outer main chamber 72 is atmospheric pressure
The internal pressure of the inner main chamber 63 when 8 is opened will be called overpressure,
Usually, it is set higher than the set value of the discharge pressure by about 1 atm.
Although the overpressure relief valve 68 is provided at the rear end of the moving body 61 in this embodiment, it maintains the relationship that the input communicates with the discharge pressure pipe 77 and the output communicates with the control pressure pipe 78, and has the same function. Position and structure.

In addition to the upper suction passage 53 and the lower suction passage 54, two pipes for control are connected to the main suction throttle valve 5 from the outside. One is a discharge pressure pipe 77 branched from the discharge passage 33,
The outer chamber 74 penetrates the valve case 51 and communicates therewith. The penetration position is a position that communicates with the outer chamber 74 regardless of the position of the moving body 61 in the operating range. The other is a control pressure pipe 78 that communicates with the outer main chamber 72 from the discharge pressure pipe 77 via the solenoid valve 31. The air discharge passage 34 branched from the control pressure pipe 78 communicates with the outside air via an air discharge throttle 35 and a silencer 36.

The valve case 51 of the intake throttle valve 5, the valve plate 55,
The structures such as the rod 57, the piston 58, and the moving body 61 do not have to be a single member, and may be an assembly of a plurality of members. In that case, the division position of the structure,
The arrangement of packings and seals for sealing does not matter to the essence of the present invention.

The structure of the air compressor having the intake throttle valve 5 will be described with reference to FIG. 5 in comparison with FIG. 2 which is a conventional example.

Of the two paths connecting the discharge path 33 and the discharge path 34, the line passing through the pressure adjusting valve 32 is the pressure adjusting valve 3.
It becomes unnecessary with 2. Although a new discharge pressure pipe 77 is required, the number of parts does not increase by integrating the solenoid valve 31 on the suction throttle valve 5 and replacing the piping with the hole formed in the valve case 51. In addition, the devices described above can be compactly configured.

The electromagnetic three-way valve 37 and the three pipes extending from the electromagnetic three-way valve 37, which are provided in the conventional example, are unnecessary. Further, the output function of the control device 4 to the electromagnetic three-way valve 37 is also unnecessary.

The air compressor according to this embodiment operates as follows.

Before starting the compressor, the internal pressure of the air tank 20 and other equipment and pipes are all atmospheric pressure. Suction throttle valve 5
There is no pressure difference between the inner chambers, and the valve plate 55 is at the back side position due to the spring force and is in the fully open state.

When the user's instruction to start driving is sensed by the switch 43, the controller 4 instructs the starter board 41 to start by the star circuit while keeping the opening / closing means 31 open.
Electric power is sent from the starter board 41 to the electric motor 3, and the compressor body 1
Is driven to start operation. Intake throttle valve 5 with air fully open
Is sucked into the compressor body 1 through the suction port 11, compressed, and sent to the air tank 20. Until this time, the internal pressure of each of the inner and outer cylinder chambers of the intake throttle valve 5 is substantially atmospheric pressure, and the valve plate 55 is fully opened by the reaction force of the compression springs 65 and 75.
Therefore, the compression of the air is carried out without hindrance. Also,
Since the internal pressure of the air tank 20 is also low, the driving torque is also small, and the startup is smoothly performed.

When the internal pressure of the air tank 20 slightly rises due to the short-time operation immediately after the start-up as described above, the compressed air acts on the outer main chamber 72 through the electromagnetic valve 31 and the control pressure pipe 78. The compression spring 75 of the outer cylinder 71 is relatively soft, and the moving body 6
Since the front area of No. 1 is relatively large, the moving body 61 pushed by a pressure slightly higher than the atmospheric pressure starts to move in the front direction. Since the internal pressure of the outer sub chamber 73 is a negative pressure lower than the atmospheric pressure due to the suction of the compressor body 1, the movement of the moving body 61 is assisted.

In this starting process, the internal pressure of the inner main chamber 63 is also the same as that of the outer main chamber 72, but the reaction force of the compression spring 65 is large, and the cross-sectional area of the piston 58 is larger than that of the moving body 61. Since it is small, no gas force is generated that exceeds the reaction force of the spring. Therefore, the piston 58 remains pressed against the rear end of the inner cylinder 62 by the compression spring 65. Therefore, the piston 58 including the rod 57 and the valve plate 55 is integrated with the moving body 61, and the movement of the moving body 61 in the front direction is the movement of the valve plate 55.

When the period elapses and the internal pressure of the air tank 20 further rises, the valve plate 55 finally comes into close contact with the valve seat 56, the suction passage is closed, and suction is stopped. This state is shown in FIG. At this time, the internal pressure of the air tank 29 is at most about 1.5 to 2 atmospheres, which is sufficiently lower than the discharge pressure in normal operation. Since the suction is blocked, the suction pressure is also low at negative pressure, and the compressor body 1
The torque for starting and accelerating the engine is suppressed, and starting and acceleration of the rotation speed are facilitated.

In the above-mentioned start-up state, the compressed air in the air tank 20 is continuously discharged from the discharge passage 34 to the atmosphere through the discharge throttle 35 and the silencer 36. Since the discharge is limited by the discharge throttle 35 and is small in quantity but continues, the internal pressure of the outer main chamber 72 gradually becomes insufficient in conjunction with the internal pressure of the air tank 20. Outside main room 7
2 Due to the decrease in the internal pressure, the moving body 61 is pushed back by the compression spring 75 and retracts in the rearward direction. The valve plate 5 that is interlocked with the moving body 61
5 also retracts slightly, and a gap is created between the valve plate 55 and the valve seat 56. Air is sucked in through the gap, and the air tank 20
The internal pressure rises again. With this series of operations, the internal pressure of the air tank 20 at the time of startup is automatically controlled to be substantially constant. Further, instead of the clearance formed between the valve plate 55 and the valve seat 56, an intentional leak flow path (purge flow path) that is not blocked by the valve plate 55 is provided in parallel with the suction path of the suction throttle valve 5. It is also possible to set it. In that case, it is necessary to provide a check valve in the leak passage to prevent backflow immediately after the compressor is stopped.

When the rotational speeds of the electric motor 3 and the compressor main body 1 reach the normal operating rotational speed, the control device 4 judges that
The starter board 41 is switched to the delta circuit, and subsequently the solenoid valve 31 is closed. The supply of compressed air to the air discharge passage 34 downstream of the solenoid valve 31 and the inside of the outer main chamber 72 is cut off, so the silencer 36 is exhausted and the inner pressure of the outer main chamber 72 decreases to atmospheric pressure. The rearward force acting on the moving body 61 due to the differential pressure on both sides of the valve plate 55 and the reaction force of the compression spring 75 causes the frontward force due to the differential pressure between the outer main chamber 72 at atmospheric pressure and the outer subchamber 73 at negative pressure. Surpass. The moving body 61 moves in the rearward direction to the movement limit together with the valve plate 55, and the suction throttle valve 5 is in the fully open state shown in FIG.

Since the electric motor is fed by the delta circuit in normal operation and the intake throttle valve 5 is fully opened, the compressor is in full load operation, and the compression and discharge amounts of air are maximized. The internal pressure of the air tank 20 rises, and the compressed air exceeding the specified pressure is sent to the outside through the discharge valve 16 and used.

When the amount of compressed air used is smaller than the discharge capacity of the compressor during normal operation, the compressed air becomes excessive, so the internal pressure of the air tank 20 gradually rises and exceeds the set value.
The inner pressure of the air tank 20 always acts on the inner main chamber 63 via the discharge pressure pipe 77, the outer chamber 74, and the communication passage 67. Therefore, if the internal pressure of the air tank 20 exceeds the set value, the piston 58
The force in the front direction due to the pressure difference on both sides exceeds the initial force of the compression spring 65, and moves the piston 58 in the front direction. Compression spring 6
Since the reaction force of 5 increases in proportion to the moving amount of the piston 58, the moving amount increases as the differential pressure increases. The movement of the piston 58 results in the movement of the valve plate 55 which is integrated, and gradually closes the suction passage to limit the suction amount. The limitation of the suction amount is the limitation of the discharge amount of the compressed air, and has the action of reducing the internal pressure of the air tank 20. Therefore, the piston 58 stabilizes at a position where the amount of compressed air used and the amount of discharge are balanced, and the discharge pressure is maintained at a set value or a value slightly higher than that. The above control is called intake throttle control, and that state is called unloading.

Air tank 20 with extremely small amount of compressed air used
When the internal pressure rises to a certain value (usually about 1 atmosphere higher than the discharge pressure set value), the valve plate 55 moves until it comes into contact with the valve seat 56, the suction throttle valve 5 is fully closed, and the compressed air is discharged. Is interrupted. This state shown in FIG. 7 is called full-closed unload.

In the unloading or fully-closed unloading state, the internal pressure of the outer main chamber 72 is atmospheric pressure, and the outer sub-chamber 73 is a negative pressure. The differential pressure produces a force in the front direction, but the pressure in the rear direction of the compression spring 75. The initial force prevails, and the moving body 61 remains pressed against the rear end of the inner cylinder 71. Therefore, the moving body 61 does not move while being integrated with the valve case 51.

Face packing 94 due to secular change and assembly error
Due to the leakage from the slight gap between the valve plate 55 and the valve seat 56 caused by the deterioration of the intake air, and the intentional purging of the intake air, a small amount of air is sucked even during the fully closed unloading. May pass through. The air is compressed and sent to the air tank 20. Since the compressed air is not used and there is no destination, the internal pressure of the air tank 20 continues to rise while exceeding the normal discharge pressure. Since excessive pressure is dangerous, the function of excessive pressure release described below operates to ensure safety.

The pressure on both sides of the overpressure relief valve 68 is set to the inner main chamber 6
3 is the internal pressure of the air tank 20, the external main chamber 72 is the atmospheric pressure, and the differential pressure is determined by the internal pressure of the air tank 20. When the internal pressure of the air tank 20 reaches an overpressure set to a certain value, the overpressure release valve 6
8 opens. The compressed air accumulated in the air tank 20 is discharged into the discharge pressure pipe 7
7 through the communication passage 67, the excessive pressure release valve 68,
It is discharged to the atmosphere through the control pressure pipe 78 and the silencer 36. When the internal pressure of the air tank 20 falls below the excessive pressure due to the release of air,
The overpressure relief valve 68 is closed to prevent a meaningless pressure drop. The above operation does not cause unlimited pressure increase or pressure decrease. In addition, in case the internal pressure of the air layer 20 exceeds the excessive pressure due to a failure of this mechanism or other unexpected situations, the air tank 20 is equipped with a safety valve. Can be lowered.

In some cases, when compressed air is not used or when a plurality of air compressors are operated in concert, the amount of compressed air used is small and one or more units can be stopped. These situations are detected from conditions such as a fully closed unloading state that lasts for a long time, and it is necessary to shift to air release unloading.
The control device 4 determines. The solenoid valve 31 is instructed by the control device 4.
Is released and the transition to the air release unloading begins.

The compressed air in the air tank 20 is introduced from the opened solenoid valve 31 into the outer main chamber 72 via the control pressure pipe 78. The internal pressure of the outer main chamber 72 becomes sufficiently high, and the gas force moves the moving body 61 in the front direction. At this time, the valve plate 55 remains in close contact with the valve seat 56, the relative positions of the valve plate 55 and the piston 58 with the valve case 51 remain unchanged, and only the moving body 61 moves in the front direction. When the moving body 61 starts moving, the solenoid valve 3
1, the compressed air in the air tank 20 is gradually discharged from the discharge passage 34 through the discharge throttle 35 and the silencer 36.

When the air release progresses and the internal pressure of the air tank 20 decreases, the internal pressure of the inner main chamber 63 causes the force for pushing the piston 58 in the front direction to become insufficient. However, the piston 58
Comes into contact with the rear end of the inner cylinder 62, and the contact force pushes the piston 58 in the front direction to move the moving body 61 together with the outer main chamber 6
With the pressure of 3, the valve plate 55 is pressed against the valve seat 56. Therefore, the closing of the suction throttle valve 5 is maintained during the transition process to the discharge unloading and after the transition is completed. The suction throttle valve 5 at the time of completion of the discharge is in the same state as that at the time of starting unloading shown in FIG.

When the discharge of air is completed and the internal pressure of the air tank 20 drops to the steady value in the discharge unloading state, the same stable state as the starting unloading state is reached. When it is necessary to make the internal pressure of the air tank 20 higher than that at the time of starting unloading, the following means are used. As an example, the opening degree of the solenoid valve 31 is made different between the start unload and the discharge unload.
Alternatively, the solenoid valve 31 or the control pressure pipe 78 is inserted with a member that changes the flow path resistance by starting unloading and air release unloading.
Alternatively, the size of the throttle of the air discharge throttle 35 is changed by starting unloading and air discharge unloading.

When the discharge air is unloaded, the pressure sensor 44 detects the decrease in the downstream pressure due to the restart of use of the compressed air.
When the control device 4 senses, the control device 4 determines to return to the normal operation, and gives an instruction to close the solenoid valve 31. Due to the closing of the solenoid valve 31, the pressure applied to the outer main chamber 72 is reduced to the atmospheric pressure, the same operation as the transition from the starting unload to the normal operation is performed, and the suction throttle valve 5 is opened. Since the rotation of the electric motor 3 is maintained even during the air discharge and unloading, it is possible to instantly return to the normal operation.

The switch 4 is used to stop the operation of the compressor.
The user presses 3, and the control device 4 that senses it instructs opening of the solenoid valve 31 and interruption of current to the electric motor 3 by the starter board 41. The compressed air that has passed through the solenoid valve 31 is controlled by the control pressure pipe 7.
From 8 to the outer main chamber 72, the moving body 61 is pushed in the front direction to push the valve plate 55 against the valve seat 56. At this time, the same operation is performed even if the compressor is in normal operation and the valve plate 55 is open, or if the valve plate 55 is already closed in the fully-closed unloading state or the discharge unloading state. Since the suction passage is closed, backflow of air and oil from the suction port 11 can be prevented even if the compressor body 1 stops. Further, due to the temporary rise in the internal pressure of the lower intake passage 54 that is about to flow backward, the pressure difference between the two sides of the valve plate 55 increases, and the force for closing the valve plate 55 increases.

Simultaneously with the above-described suction passage closing operation, the discharge passage 34
The compressed air remaining inside the air tank 20 is discharged through the discharge throttle 35 and the silencer 36. Degassing is an oil separator 1
Since it is air that has passed through 5, there is very little mixing of oil, and there is no problem in releasing it to the atmosphere. Since high-pressure air does not remain inside the compressor, maintenance such as inspection of the compressor and replenishment of oil can be safely performed after the operation stop is completed. In addition, since there is no residual pressure even when restarting, the above-described starting operation can be reliably executed.

In the present embodiment, the present invention can be implemented without making major design changes to the conventional oil-cooled air compressor. Although the intake throttle valve 5 of the present embodiment has some additional members as compared with the conventional intake throttle valve,
It has a simple structure and can be inexpensive and highly reliable.

The construction and operation of the air compressor of the second embodiment will be described below with reference to FIGS. 8, 9 and 5. FIG.
FIG. 4 is a sectional view of an intake throttle valve used in this embodiment. FIG. 9 is a sectional view of the intake throttle valve of the present embodiment during operation during an emergency stop. The air compressor in this embodiment is different from the first embodiment only in the structure of the suction throttle valve, and the piping system is common to the first embodiment shown in FIG. 5, so a new system diagram is not shown. This will be described using 5.

The intake throttle valve 6 has a basic structure when it is close to the intake throttle valve 5 in the first embodiment, but there are some differences described below.

The valve chamber 51 has an outer auxiliary chamber 73 and a lower suction passage 54.
No communication passage is provided to connect the
Seal with 1 to prevent air leakage. The movable body 61 is also not provided with a communication passage connecting the inner sub chamber 64 and the outer sub chamber 73, and the periphery of the rod 57 is sealed with a packing 81. Outer cylinder 7
The compression spring 79 provided inside 1 is provided not in the outer sub chamber 73 but in the outer main chamber 72. The free length of the compression spring 79 is set longer than the length of the compression spring 79 when the moving body 61 is located on the most front side, and is set so as to exert some initial force.

The conduit 83, which branches from the discharge pipe 33 and communicates with the air tank 20, is connected to the back side of the case 51. The end of the pipe 83 is branched inside the valve case 51, one of which is connected to the outer sub chamber 73 as a discharge pressure pipe 84, and the other is connected to the control pressure pipe 85 and the discharge passage 86 via the electromagnetic valve 31. The control pressure pipe 85 communicates with the outer main chamber 72, and the discharge passage 86 is opened to the atmosphere via the discharge throttle 87 and the silencer 36. The discharge pressure pipe 84, the control pressure pipe 85, and the air discharge passage 86 are holes formed in the valve case 51 and do not require a pipe material or a pipe connection component, so that the structure is simple. The exhaust throttle 87 is also not a dedicated part, and is realized by making the hole diameter smaller than other parts.

The movable body 61 includes an inner main chamber 63 to an outer sub chamber 73.
A communication passage 88 that is connected to In this embodiment, the communication passage 88
Is set to be long inside the side wall of the movable body 61 in the axial direction, but the discharge pressure pipe 84 does not pass through the outer sub chamber 73 but the discharge pressure pipe 84 passes through the outer chamber 74 as in the first embodiment, and is communicated. May be.

An overpressure discharge groove 93 having a length in the axial direction is provided near the front of the inner surface of the inner cylinder 62. The position of the inner packing 59 when the movable body 61 is on the rearmost side and the valve plate 55 contacts the valve seat 56 is the rear side end of the overpressure discharge groove 93. The axial length of the excessive pressure air discharge groove 93 is made longer than the axial width of the packing 59.

An atmosphere communication passage 89 is provided which passes from the center of the front side of the valve plate 55 to the center of the inside of the rod 57, opens to the side surface near the rear end of the rod 57 and communicates with the inner sub chamber 64. The valve plate 55 and the rod 57 are integral members, but the piston 58 is a separate member. The rear end of the rod 57 is fitted into a recess provided in the center of the front side of the piston 58, and usually the rod 57 and the piston 58 are integrated. Piston 5
An emergency air discharge passage 90 is opened at the bottom of the recess of 8 so as to connect the inner main chamber 63 and the inner sub chamber 64, but normally the rear end face of the rod 64 closes the mouth on the inner sub chamber 64 side. .

The valve case 51 is provided with a purge flow passage 91 extending from the upper suction passage 53 to the lower suction passage 54. Purge channel 91
Is not blocked by the valve plate 55, but has a small flow passage cross-sectional area and a large resistance, so only a small flow rate flows. Further, a check valve 92 is provided on the way, so that the check valve 92 can flow only in the forward direction toward the compressor body 1. A portion of the main passage of the intake passage of the intake throttle valve 6 that is closed by the close contact between the valve plate 55 and the valve seat 56 regardless of the purge passage 91 is referred to as a main valve.

The present embodiment operates as follows.

Before the compressor is activated, the internal pressures of the suction throttle valve 6 are all atmospheric pressure, and only the initial force of the compression springs 65 and 79 is applied. Therefore, the piston 88 is located at the rear end of the inner cylinder 62, and the moving body 61 pushes in the front direction of the outer cylinder 71 to push the valve plate 55 against the valve seat 56. Therefore, the main valve of the suction throttle valve 6 is closed.

The controller 4 senses that the user has pressed the switch 43, and the starting operation is started. The control device 4 closes the solenoid valve 31, and at the same time, the starter board 41 sends electric power to the electric motor 3 to start and accelerate the compressor body 1. Compressor body 1
During operation, the inside of the lower suction passage 54 becomes negative pressure, and the purge passage 91
A small amount of air drawn in via is compressed. Since the compression is performed little by little, the increase in the internal pressure of the air tank 20 is slow, and the acceleration of the rotation speed is completed before the driving torque of the compressor body 1 increases.

The inner pressure of the air tank 20 is constantly acting on the outer sub chamber 73 through the discharge pressure pipe 84, and after the acceleration is completed, the moving body 61 is moved to the back side by the gradually rising pressure. Since the solenoid valve 31 is closed and the air discharge passage 86 communicating with the outer main chamber 72 communicates with the atmosphere via the discharge throttle 87 and the silencer 36, the inner pressure of the outer main chamber 72 remains the atmospheric pressure. It does not hinder the movement of the moving body 61. When the main valve is slightly opened by the movement of the moving body 61, the intake amount of air further increases, whereby the increase in the internal pressure of the air tank 20 is accelerated, and the moving body 61 further moves. By this series of actions, the main valve is opened at a stroke and the normal operating state is entered.

Although the internal pressure of the air tank 20 is constantly applied to the inner main chamber 63, the cross-sectional area of the inner cylinder 62 is relatively small and the reaction force of the compression spring 65 is strong. It remains pressed against the rear end face. Therefore, at the time of start-up, the valve plate 55 remains integrated with the piston 58 and the moving body 61.

When the amount of compressed air used is less than the discharge capacity of the present compressor under normal operating conditions, the surplus compressed air is accumulated in the air tank 20 and the internal pressure gradually rises. The pressure reaches the communicating inner main chamber 63, and when it exceeds the discharge set pressure, the piston 58 starts to move. The inner pressure of the inner sub-chamber 64 is maintained at almost atmospheric pressure by the action of the atmosphere communication passage 89.
The gas force due to the differential pressure on both sides of the piston 58 causes the compression spring 65
The internal pressure of the inner main chamber 63 when the initial pressure is equal to is the set pressure.

Since the piston 58 is moved in the front direction, the interlocking valve plate 55 moves in the closing direction, and the unloading state that restricts the intake amount is established. Due to the limitation of the suction amount, the discharge amount of the compressed air is reduced, which acts to lower the internal pressure of the air tank 20. With the above-described function of controlling the discharge air amount, the valve plate 55 is stabilized at the position where the discharge amount is equal to the compressed air usage amount, and the discharge pressure is maintained at the set pressure or slightly higher than it.

The discharge pressure at the time of unloading is the air tank 2 at the time of startup.
Since the pressure in the outer sub-chamber 73 is still pressed against the rear side end portion because it is sufficiently higher than the zero internal pressure, the movable body 61 can be considered to be integral with the valve case 51.

When the amount of compressed air used is zero, the valve plate 55 is in close contact with the valve seat 56 and is fully closed. Even during the fully-closed unload, there is a slight suction through the purge passage 91, and the compressed air is sent to the air tank 20. No compressed air is used, the destination of the compressed air is lost, and the internal pressure of the air tank 20 continues to rise while exceeding the normal discharge pressure. Since excessive pressure is dangerous, the overpressure release described below operates to ensure safety.

When the internal pressure of the air tank 20 reaches an excessive pressure, the gas force applied to the inner main chamber 63 pushes the piston 58 and the valve plate 5
5 is strongly pressed against the valve seat 56. The face packing 94 is elastically deformed, and the piston 58 moves in the front direction more than when the piston 58 is fully closed and unloaded, and the packing 59 causes the overpressure discharge groove 93.
Come to the position where you cross. Then, a communication passage is formed from the inner main chamber 63 to the inner sub chamber 64 through the overpressure air release groove 93. The compressed air of excessive pressure passes through that path, and is further discharged from the atmosphere communication path 89 to the upper suction path 53 that communicates with the atmosphere. This air release prevents the internal pressure of the air tank 20 from dangerously increasing.

When it is sensed that the fully-closed unload state continues for a long time such as no use of compressed air, the control device 4 judges that the discharge unload should be started. The solenoid valve 31 is opened according to an instruction from the control device 4, and the shift to the discharge unloading is started.

At the same time as the compressed air flows into the outer main chamber 63 from the solenoid valve 31, it is discharged from the discharge passage 86 to the atmosphere through the discharge throttle 87 and the silencer 36. The moving chamber 61 moves in the front direction by the force of the compression spring 79 because the pressures on both sides become equal, but the closure of the main valve is maintained during the transition process to the discharge unloading and after the transition is completed. The positional relationship of each member inside the intake throttle valve 6 at the time of completion of the air release is almost the same as that immediately after the start of activation, but the pressure on both sides of the moving body 61 becomes higher than the atmospheric pressure level.

Although there is an inflow from the purge passage 91 even during the discharge unloading, it is balanced with the discharge amount, and the suction pressure and the discharge pressure of the compressor body 1 are kept low. Further, the pressure of each part at that time depends on the flow passage resistance of the purge flow passage 91 and the flow passage resistance of the discharge system by the discharge throttle 87, and can be selected within a certain range.

When it is judged that the discharge unloading is returned to the normal operation, the controller 4 closes the solenoid valve 31. The internal pressure of the outer main chamber 72 is reduced to the atmospheric pressure, and the discharge is restarted by the same action as the startup unload. Since the internal pressure of the outer main chamber 72 is decreased and the internal pressure of the outer sub chamber 73 is increased, the moving speed of the moving chamber 61 until the discharge is restarted is faster than that at the time of startup, and the return to the normal operation is quick.

When the compressor is stopped, the solenoid valve 31 is closed, and the same operation as the transition to the discharge unloading is performed. The main valve is closed and the air tank 20 is discharged at the same time. Since the purge passage 91 also has the check valve 92, the backflow immediately after the stop is prevented.

A belt is often used as a mechanical element for transmitting the rotation from the electric motor 3 to the compressor main body 1, but it may be broken due to its life or the like. Due to the belt breakage, the electric motor 3 continues to idle, and the compressor body 1 stops. In this case, unless the suction throttle valve 6 is urgently closed and the internal pressure of the air tank 20 is not released, a trouble occurs such that oil mixed in the compressed air flows backward from the suction port 11 by the same action as immediately after the stop. There is also a method in which a belt break is detected by a change in the current consumption of the electric motor 3 and the control device 4 opens the solenoid valve 31 to bring it into the same state as a normal stop, but there is a problem such as a slow response and cost. Therefore, it is desirable that the suction throttle valve 6 itself has a function of preventing backflow from the main valve when the belt is broken and a function of discharging the compressed air remaining in the air tank 20.

When the compressor body 1 suddenly stops, the compressed air containing oil that has accumulated on the discharge side flows backward to the suction side where the pressure is low. Since the internal pressure of the lower suction passage 54 becomes higher than the internal pressure of the upper suction passage 53, the valve plate 55 receives a force in the front direction. The rod 57, which is integral with the valve plate 55, is withdrawn from the recess of the piston 58, closing the valve plate 55 and preventing backflow. The emergency air discharge passage 90 closed by the end portion of the rod 57 is opened, and the inner main chamber 63 and the inner sub chamber 64 communicate with each other. This state is shown in FIG. The compressed air remaining in the air tank 20 is discharged to the atmosphere from the upper discharge passage 53 through the discharge pressure pipe 84, the outer auxiliary chamber 73, the communication passage 88, the inner main chamber 63, the inner auxiliary chamber 64, and the atmosphere communication passage 89. To be done. Since the air released through this path is the air that has passed through the oil separator 15, the oil contained in the air released is extremely small and does not pose a problem.

When the discharge of air is completed and the internal pressure of each chamber reaches the atmospheric pressure, the moving body 61 having the piston 88 built therein is compressed by the compression spring 71.
It is pushed in the front direction and moves to the end. The end of the rod 87 is re-fitted into the recess of the piston 88, and can be started as usual at the start of the next operation after the belt replacement.

According to this embodiment, the internal pressure of the air tank 20 at the time of starting unloading and the air unloading can be set separately by setting each flow path resistance. In addition, it is possible to realize an air compressor that quickly returns from the discharge unload to the normal discharge operation and has good responsiveness. Further, it is possible to simultaneously prevent backflow and release air even when the compressor main body is stopped due to breakage of the belt which is a power transmission member.

[0110]

By applying the suction throttle valve according to the present invention to an air compressor, a member such as an attached pressure control valve or electromagnetic three-way valve or piping for connecting them is unnecessary, and the suction throttle valve has a simple structure. A capacity control system can be realized. Since the control system is simplified, high reliability can be realized at low cost. This control system not only controls the discharge pressure according to the amount of compressed air used, but also performs torque reduction at start-up, intake blockage and air release operation at the time of air discharge and unloading, and even when stopped, the air compressor Satisfy all driving situations.

[Brief description of drawings]

FIG. 1 is a sectional view of a suction throttle valve used in the first embodiment when it is fully opened by full load.

FIG. 2 is a system diagram of a conventional oil-cooled air compressor.

FIG. 3 is an explanatory diagram showing an example of a temporal change in discharge pressure of the air compressor.

FIG. 4 is an input / output pressure characteristic diagram of a pressure control valve used in a conventional example.

FIG. 5 is a system diagram of the air compressor according to the first embodiment.

FIG. 6 is a cross-sectional view of the intake throttle valve used in the first embodiment when the intake throttle valve is started or when air is discharged.

FIG. 7 is a cross-sectional view of the suction throttle valve used in the first embodiment when it is fully closed and unloaded.

FIG. 8 is a sectional view of an intake throttle valve used in the second embodiment.

FIG. 9 is a sectional view of the suction throttle valve used in the second embodiment during an emergency operation.

[Explanation of symbols]

5 ... suction throttle valve, 51 ... valve case, 53 ... upper suction passage, 5
5 ... Valve plate, 56 ... Valve seat, 57 ... Rod, 58 ... Piston, 59 ... Inner packing, 60 ... Outer packing, 61 ... Moving body, 62 ... Inner cylinder, 63 ... Inner main chamber, 64 ... Inner auxiliary chamber,
65,75,79 ... Compression spring, 66,67,76 ... Communication passage, 68 ... Excessive pressure air release valve, 69 ... Valve ball, 70 ... Valve spring,
71 ... Outer cylinder, 72 ... Outer main chamber, 73 ... Outer auxiliary chamber, 74
Outer chamber, 77 ... Discharge pressure tube, 78 ... Control pressure tube.

Claims (2)

[Claims] 1. A rotary positive displacement compressor such as a screw type or scroll type, a suction amount limiting means connected to an upstream side of an intake port of the compressor body, and a downstream side of a discharge port of the compressor. In an air compressor including an air tank, a control device that manages the operation of the compressor, and an electric motor that is a driving unit of the compressor, the suction amount limiting unit has an intake passage and an outer cylinder formed therein. A valve case, a valve plate having a function of closing the suction passage, a piston coupled to the valve plate by a connecting member, and a piston that is reciprocally fitted while being divided into a plurality of chambers by the piston. A moving member having an inner cylinder formed therein, wherein the moving member is built in the outer cylinder so as to be reciprocally movable, and divides the outer cylinder into a plurality of chambers to reciprocate the piston. An air compressor in which the direction and the direction of the reciprocating motion of the moving member are matched. 2. The flow passage from the air tank to the chamber located on the side opposite to the valve plate among the chambers formed by dividing the inner cylinder, and the outer cylinder being divided. A flow path that communicates with one of the stored chambers from the air tank through the opening / closing means, and the opening / closing means has a function capable of opening / closing operation according to a command from the control device represented by a solenoid valve. air compressor.