JPH08319976A - Oil-cooled air compressor - Google Patents

Abstract

(57) [Summary] [Structure] Air reaches the suction port 11 of the compressor body 1 from the air purifier 63 and the suction throttle valve 6, and after compression, from the discharge port 12 to the oil separator 3, the compressed air cooler 4, and the discharge. Delivered through valve 41. The oil enters the compressor body 1 through the oil supply port 13 and exchanges heat with the air, is separated by the oil separator 3, is cooled by the oil cooler 5, and is supplied again. The oil supply temperature is kept constant by controlling the amount by which the oil cooler 4 is bypassed by the oil temperature adjusting valve 51. Immediately before stopping, the bypass amount is reduced for a certain period of time to raise the oil temperature, vaporize the drain in the pipe, and place it on compressed air for discharge. [Effect] Even if the temperature drops after the operation is stopped, the amount of water remaining inside is small and the generation of drain can be suppressed. Therefore,
Corrosion inside the compressor and deterioration of oil are prevented, and it is possible to reliably start even after long-term operation stop.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an oil-cooled air compressor.

[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, send it out to the pipe outside the compressor after compression,
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, it is accompanied by several auxiliary machines in addition to the compressor body, and is put into practical use under the name of the air compressor. There is.

Although there are various types of compressor accessories, the main components are an air purifier, a suction throttle valve, a compressed air cooler, a compressed air dryer, and a power source such as an electric motor. The air purifier, as an air purifying means, removes dust contained in the sucked air and prevents foreign matter from entering the compressor body. 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. Then, it has a function of increasing / decreasing the amount of air to be discharged in accordance with a change in the amount of compressed air used and maintaining the discharge pressure within a certain range. The compressed air cooler serves as compressed air cooling means and cools the air that has become high in temperature due to the heat of compression. The compressed air drier removes moisture and water vapor contained in compressed air as a compressed air drying means. As the water vapor contained in the air becomes higher in pressure, it becomes easier for dew to condense inside the compressed air pipe, and problems such as corrosion easily occur. Therefore, the compressed air dryer is an indispensable auxiliary machine of the air compressor in the operation in the high temperature and high humidity environment. The electric motor or the internal combustion engine supplies power to the compressor body directly as a drive means of the compressor body or through a power transmission means such as a belt or a gear.

[0004] In an oil-cooled compressor in which the compressor body performs compression while injecting oil into the compression chamber, the compressor body needs to have an oil injection function, and some oil-related auxiliary machines are required. As an example, an oil separator as an oil separation means for separating the oil mixed in the air from the air after being compressed in the compression chamber, or the oil that has become hot due to the heat absorption from the air due to the compression is cooled and prepared for re-lubrication. Examples include oil coolers and oil purifiers that remove solid impurities in oil. Further, the oil itself circulating in the compression chamber of the compressor body, the oil separator, and the oil cooler is also an important factor related to the performance and reliability of the compressor.

One of the problems for maintaining high reliability of an air compressor and compressed air is a countermeasure against drainage. Drain is water formed by condensing water vapor contained in the sucked air. Since the dew point of air is higher under high pressure than under atmospheric pressure, when high-humidity air is cooled to the outside temperature after being compressed, it will be below the dew point and cause dew condensation to form a drain. Since the discharge air of the air compressor is at a high temperature during steady operation, it is rare that the steam passes through the compressor body and liquefies before the compressed air cooler even if steam remains dissolved in the compressed air.

[0006] Inside the compressed air cooler and downstream thereof, the temperature of the compressed air may drop to below the dew point, and drainage may occur. Depending on the user
In some cases, compressed air that does not have a compressed air dryer is used in order to send air to a drain-acceptable application or facility and compressed air is used. However, many users are equipped with a compressed air dryer to dry the compressed air before it is sent to the piping. The dried compressed air has a sufficiently low dew point so that drainage is unlikely to occur.

Drainage is often generated in the main body of the air compressor, which is unlikely to cause drainage due to high temperature during steady operation, after the stoppage for the following reason. After the stop, the temperature of the air remaining in the compressor body, piping, and inside gradually decreases due to heat radiation, and the temperature of the residual air falls below the dew point. The water vapor that had been dissolved in the air until then condenses to water, or drain.

The drain promotes rusting and corrodes the inside of the pipe,
Inside the compressor body, the sliding parts are fused and the surface roughness is deteriorated. As a result, when left unoperated for a long period of time, particularly when operated for a long time after operating in a high-humidity environment, the sliding part adheres and does not move, which may make the next operation difficult. Alternatively, if corrosion progresses in the piping portion, the wall pressure locally decreases and the strength decreases, so compressed air leaks, and there is a risk of rupture or the like if the situation is bad. Further, in the oil-cooled compressor, the drain is generated at a position where it comes into direct contact with the oil, which may cause another problem such as promoting deterioration of the oil or staying at the bottom of the oil separator.

In the prior art, in order to avoid the problem due to drainage, measures are taken such as using a material that is unlikely to corrode or coating the portion where drainage is expected to occur. Even when the compressor does not need to be operated for a long period of time, it is recommended that the user take operational measures such as performing warm-up operation about once a week.

Several methods have been proposed in which water vapor in the air sucked by the compressor main body is removed in advance and dry air is sucked in to fundamentally prevent the generation of drainage. For example, Japanese Unexamined Patent Publication No. 4-203384 proposes a method of dehumidifying with a honeycomb type dehumidifier, and Japanese Unexamined Patent Publication No. 4-325796 proposes a method of dehumidifying with a cooling type dehumidifier. Further, Japanese Patent Application Laid-Open No. 5-141350 proposes a method in which dried compressed air is returned to the suction side, the inside of the compressor main body is dried, and then stopped.

[0011]

At present, it cannot be said that the countermeasures by adopting the non-corrosive material or coating are sufficient. Non-corrosive materials and coatings are expensive and often have poor workability, so they are not suitable for compressors with many parts having complicated shapes. Therefore, there is a problem that the application of the non-corrosive material or the coating is limited to a particularly corrosive portion, a damage caused by the corrosion, and a portion having a simple shape. Further, in the oil-cooled screw compressor, the rotation transmission from the male rotor to the female rotor is made by the contact meshing of the rotor, so that it is difficult to use the covering material on the sliding portion such as the tooth portion of the screw rotor.

[0012] The warm-up operation of about once a week not only imposes a burden on the user, but also when the compressor is moved, a long-term operation suspension is inevitable and the warm-up operation may not be possible. Therefore, this method is only a temporary measure against drainage.

The effect of dehumidifying the inhaled air can be expected by the means disclosed in these Japanese Patent Laid-Open Publications. However, in order to implement all of them, it is necessary to add new members such as a dehumidifier, which inevitably leads to an increase in price, a complicated mechanism, and an increase in size of the entire air compressor. It is desirable that an air compressor should be low-priced, have a simple structure, and be downsized, and it is difficult to realize an air compressor using these means.
Further, dehumidification under atmospheric pressure has a low dew point as compared with dehumidification after compression, and thus has low efficiency.

By the means disclosed in JP-A-5-141350, an effect can be expected in an oil-free (aka dry) compressor. However, it cannot be said that the oil-cooled compressor has a sufficient effect because it does not sufficiently remove water contained in the oil circuit.

The object of the present invention is to prevent drainage after stopping the air compressor, suppress rusting and oil deterioration without adding a new large member, and to operate after a long stop. It is to provide a highly reliable air compressor that can be eliminated.

[0016]

In order to achieve the above object, the present invention uses the following first means.

An oil separator is provided on the downstream side of the discharge port of the compressor body, and the oil separator has one inlet from the compressor body and two outlets for air and oil. An oil cooler as an oil cooling means is connected downstream of the oil outlet. The cooling capacity of this oil cooler is variable, and in particular, it has a function of suppressing the cooling capacity in response to a command from the control device. As the function suppressing means, there are methods such as bypassing by a bypass flow path of the heat exchanger and adjustment of cooling air to be passed through the heat exchanger. The oiling pipe continuing from the outlet of the oil cooler reaches the compressor body and communicates with the air compression chamber. Also, since the pressure applied to the oil in the oil separator is higher than the oil pressure in the compressor body, differential pressure lubrication in which the oil circulates due to this differential pressure is common, but an oil pump must be installed in the middle of the oil circuit. There is also a method of forced refueling.

In order to more fully achieve the above object, the present invention uses the following second means in addition to the first means.

It is necessary to provide a compressed air dryer as a compressed air drying means downstream of the air outlet of the oil separator. The compressed air dryer is generally of a freezing type in which the dew point of air is lowered by cooling to condense steam, or an adsorption type in which steam is chemically trapped. The present compressed air dryer is not newly provided for the purpose of the present invention, but is used for drying the compressed air delivered in the normal operation.

The second means for achieving the object of the present invention is to newly branch from the downstream pipe of the compressed air dryer and communicate with the suction side of the compressor main body, and also to form a ring flow path having an on-off valve in the middle. Prepare The open / close valve is a controllable valve such as a solenoid valve or a pneumatic valve, and opens / closes according to an instruction from the control device. The intake amount limiting means upstream of the intake port of the main body also has a function of limiting the inflow of air according to a command from the control device.

[0021]

The air compressor according to the first means operates as described below.

To stop the air compressor, the user operates the stop button or, if the air compressor is under the control of the host controller as part of the plant, it receives a command to stop the host controller. As a result, the control device recognizes the stop and is started.

The control device instructs the oil cooling means to suppress the cooling capacity, the oil supply temperature rises even in the normal operation, and is controlled to a high temperature. The temperature of the circulating oil repeatedly rises due to absorption of the compression heat of air inside the compressor body and decreases due to heat dissipation from the oil cooler. If the temperature of the oil is too low, there is an increase in mechanical loss due to an increase in viscosity, and if it is too high, insufficient lubrication due to a decrease in viscosity, insufficient cooling of air, and accelerated deterioration of oil are not preferable. Therefore, during normal operation, the oil cooler capacity is adjusted to control the oil supply temperature within the optimum temperature range. Since the increase in oil temperature immediately before the stop does not require the discharge of air, throttling of the air reduces the power, and there is no problem of deterioration of lubrication and cooling capacity. In addition, because of the short time, deterioration of oil does not accelerate so much that it becomes a problem.

Since the oil is higher than in the normal operation, the water contained in the oil and the water remaining in the lowermost part of the oil separator or the oil cooler evaporate and are carried away together with the compressed air.

The water content in the inside decreases, and after a certain period of time, the control device instructs the compressor main body to stop, and the compressor main body stops by a method such as shutting off power to the electric motor of the power source. The oil circulation also stops with the stop of the compressor body. Since the moisture remaining in the compressor body and the oil circuit is reduced, even if time elapses after the stop and the temperature drops, condensation does not easily occur inside, and the occurrence of drainage and the resulting rust and corrosion are prevented.

The air compressor according to the second means for solving the problems of the present invention performs the following operation in addition to the operation by the first means.

When the control device recognizes the stop, at the same time as suppressing the cooling capacity of the oil cooler, the on-off valve in the middle of the return passage which has been closed during the normal operation is opened and the suction throttle valve which is the suction flow rate limiting means is closed. Then, the compressed air dried through the compressed air dryer flows into the suction side and circulates through the compressor body, the oil separator, and the compressed air dryer. Since this state lasts for a certain period of time, since the air passes through the compressed air dryer many times, the moisture contained in the circulating air is gradually removed.
At the same time, the temperature of the oil rises, so the residual water content in the compressor body and in the oil and air passages is very low.

After a lapse of a certain time, the operation of the compressor main body is stopped according to an instruction from the control device, and then the compressed air dryer is also stopped. Although the temperature of each part of the compressor gradually decreases, the amount of water remaining inside is small and the dew point is sufficiently lower than the outside air temperature, so that dew condensation and drainage do not occur.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The construction and operation of an air compressor according to a first embodiment of the present invention will be described below with reference to FIG. FIG. 1 is a schematic system diagram of the air compressor of this embodiment centering around the main air and oil flows.

The compressor body 1 is a screw type compressor. Its structure and function are as follows. Two screw rotors (hereinafter abbreviated as rotors), which are male and female, are meshed with two bores, which partially overlap each other provided in the casing, and are rotatably housed. When the male rotor rotates, the female rotor also rotates through the contact of the tooth surfaces, and the air accumulated in the compression chamber formed by closing the tooth groove of each rotor by the bore wall is transferred in the axial direction, while sucking, compressing, Discharge. The type of screw compressor in this embodiment is called an oil-cooled type,
Since the rotors come into contact with each other, it is necessary to lubricate the bore for lubrication. In addition to lubrication, oil seals the clearance between compression chambers to reduce air leakage and absorbs the compression heat of air to improve compression efficiency.

Power input to the compressor body 1 is performed by connecting a power transmission shaft 21 directly connected to the male rotor to the electric motor 2. The compressor body 1 has a suction port 11 and a discharge port 12, to which a suction flow passage 9 and a discharge flow passage 31 are connected, respectively. The oil-cooled compressor has a filler opening 13 in the compressor body 1,
It communicates with the internal compression chamber.

An induction motor is generally used as the electric motor 2, but other types such as a synchronous electric motor and a DC electric motor are not relevant to the present invention. Electric power is supplied to the electric motor 2 from a commercial AC power source 23 via an electromagnetic switch 22. The power connection between the electric motor 2 and the compressor main body 1 may be either direct drive by direct connection of a rotating shaft or drive via a transmission mechanism such as a gear, a belt or a coupling.

An air purifier 63 and a suction throttle valve 6 are provided on the upstream side of the suction port 11. The air purifier 3 has a structure in which a filter paper 64 that allows air to pass but does not easily pass dust blocks an air intake passage. The suction throttle valve 6 is a kind of on-off valve and has a function of limiting the flow rate so that the discharge pressure does not become excessive when the amount of compressed air used is small. Valve plate 62
The operation is usually performed by feeding back the discharge pressure to the piston 65, and the opening is automatically controlled in the direction to keep the discharge pressure constant. However, in the present invention, the valve plate 62 may be driven by any method such as air pressure or electromagnetic force. Even when the discharge pressure is low at the time of starting the air compressor or unloading air, it is necessary to limit the suction amount, so that it also has a function of forcibly closing the valve plate 62 by a command or operation from the outside. .

Here, the discharge unloading means that the suction amount is throttled while the operation of the compressor body 1 is continued, and at the same time, the compressed air remaining in the discharge passage is discharged to lower the discharge pressure. . Since the compressor main body 1 hardly performs the compression work in the state where the air is discharged, the power required is small and the electric power is saved. Therefore, the discharge unloading can be said to be a standby state in which rotation is continued without discharging compressed air, which is suitable for a relatively large air compressor in which it is difficult to frequently start and stop the electric motor.

An oil separator 3 is provided downstream of the compressor main body 1, and a discharge flow passage 31 continuing from the discharge port 12 is directly connected to an inlet 32 of the oil separator 3. The oil separator 3 has a function of separating the compressed air and the oil sent together, and after the separation, the compressed air is discharged from the upper air outlet 33 and the oil is discharged from the lower oil outlet 34. The bottom of the oil separator 43 also serves as an oil sump, and the oil level is within a certain range both when stopped and during operation.

The pipe drawn from the air outlet 33 is guided to the outside through the compressed air cooler 4 and the discharge valve 41, and the pipe is extended to the place where the compressed air is used. The discharge valve 41 has both the function of a check valve and the function of a pressure regulating valve that opens when the upstream side exceeds a certain pressure.

The oil supply pipe 53 drawn out from the oil outlet 34 enters the oil temperature adjusting valve 51. The temperature adjusting valve 51 and the oil cooler 5 are connected by a forward cooling pipe 54 and a returning cooling return pipe 55. An oil supply pipe 53 is connected to the oil supply port 13 of the compressor body 1 at the outlet of the oil temperature adjusting valve 51. The oil temperature adjustment valve 51 is a bypass valve that controls the oil supply temperature within a certain range, and the set temperature that is the control target follows the instruction of the control device 7. Oil temperature control valve 5
The structure and principle of 1 are not limited, but it is shown that there are the following methods, for example. A method in which a solenoid valve is provided in parallel with the bypass path and the solenoid valve is opened when a command from the control device 7 is transmitted by voltage to increase the bypass amount.
Alternatively, the flow of the oil temperature sensing portion such as bimetal is replaced with the flow to the oil supply pipe 56 at the normal time, and is switched to the flow of the cooling return pipe 55 having a lower temperature than that. Alternatively, the refueling pipe 56
A method that changes the control target value when electronic control is performed by sensing the internal oil temperature and controlling the bypass amount with a solenoid valve.

The oil cooler 5 is a heat exchanger, in which oil passes inside the pipe and cooling air flows outside the pipe to exchange heat. Cooling air is sent by the fan 52 to both the oil cooler 5 and the compressed air cooler 4. These two coolers may be an integral structure.

The control device 7 has a function of giving an instruction to the electromagnetic switch 22 and the temperature control valve 51, and is constituted by an electric circuit. Also, it is connected to the stop button 71 by electric wiring.

Each device constituting the air compressor is mounted on the same base (not shown), covered with a package (not shown) for the purpose of safety, soundproofing and aesthetics, and is used as a unit.

The air compressor in this embodiment operates as follows. During steady operation, the compressor body 1 receives rotational power from the electric motor 2 and performs a compression operation. The air passes through the air purifier 63, and the mixed dust is removed. Further, the air passes through the suction throttle valve 6, enters the compressor body 1 through the suction port 11, and is compressed. When the amount of compressed air used is large, the suction throttle valve 6 is open and the flow rate is not limited.

Inside the compressor body 1, the air is heated because it is compressed in a short time, and the temperature of the air when it comes out from the discharge port 12 rises with the pressure. Refueling port 13 during compression
The oil put in the compression chamber receives heat from the heat-generating air, and the temperature rises with the air. The compressed air and the oil are mixed together, pass through the discharge passage 12 through the discharge passage 31, and enter the oil separator 3 through the inlet 32.

The oil separator 3 separates the sent oil and air from each other by utilizing the difference in specific gravity and viscosity between them. The separated air is discharged from the upper air outlet 33, and the oil outlet is discharged from the lower oil outlet.

The compressed air discharged from the oil separator 3 passes through the compressed air cooler 4. High-temperature compressed air passes through the inside of the pipe, and low-temperature cooling air is sent by the fan 52 to exchange heat through the pipe wall. As a result, the compressed air is cooled. In addition,
Depending on the internal configuration of the air compressor and the environment in which it is used, even if a dedicated compressed air cooler is not provided, the piping from the discharge port 12 acts as a heat exchanger, and compressed air is sufficient while passing through the inside. It may be cooled to. In that case, the pipe serves as the compressed air cooling means. The air that has passed through the compressed air cooler 4 is sent out of the compressor via the discharge valve 41. The discharge valve 41 stops the discharge of the compressed air and at the same time prevents the backflow from the external pipe when the discharge pressure is not ensured at the time of starting or discharging the air.

The oil separated by the oil separator 3 passes through the oil feed pipe 53 and enters the oil temperature adjusting valve 51. Part of the oil is the cooling pipe 5
4 is sent to the oil cooler 5, is cooled by exchanging heat with the cooling air by the fan 52, and is returned to the oil temperature adjusting valve 51 through the cooling return pipe 55. The returned oil is the oil temperature adjusting valve 51.
By short-circuiting the inside and bypassing the oil cooler 5, the oil is merged with the uncooled oil, and both pass through the oil supply pipe 56 and are sent to the oil supply port 13. The ratio of the cooled oil and the bypassed oil is automatically determined by the oil temperature adjusting valve 51. When the oil temperature is low, the bypass amount is increased to suppress the cooling, and when the oil temperature is high, the bypass amount is increased to accelerate the cooling. This action keeps the oil temperature almost constant. The temperature set value of the oil temperature adjusting valve 51 can be changed by an instruction from the control device 7, but is maintained at the optimum temperature described later during normal operation.
Since the oil flow is generated by the difference between the internal pressure of the oil separator 3 and the oil supply pressure at the oil supply port 13, an oil pump for oil supply is not required.

The oil temperature greatly affects the performance, life and reliability of the oil-cooled compressor. For example, if the oil temperature is too low,
Since the viscosity is high, the agitation loss in the compression chamber and the bearing is large and the compression performance is reduced. On the other hand, if the oil temperature is too high, the cooling effect of the compression heat may decrease, and the bearing life may be shortened or the oil may be deteriorated due to oxidation. Therefore, it is desirable that the oil temperature be maintained near the optimum temperature that is determined by the type of oil and the configuration of the compressor, so an oil temperature adjustment valve is provided.

In this embodiment, the oil temperature is controlled by changing the cooling capacity of the oil cooling system depending on the amount of oil bypass, but it is also possible to control the oil temperature by the amount of cooling air which changes the rotational speed of the fan 52 and the pressure loss of the duct. A water-cooled type in which the compressed air cooler 4 and the oil cooler 5 are heat exchangers for cooling water is also possible.

When the air compressor according to the present embodiment is about to be stopped, the above operation is utilized and the effect of the present invention is realized by the following operation.

First, when the user presses the stop button 71, the control device 7 recognizes that it should stop, and immediately starts the stop operation. First, the control device 7 operates the oil temperature adjusting valve 5
Instruct 1 to raise the set temperature. Oil temperature adjustment valve 51
Raises the temperature of the oil by increasing the proportion of the oil to be bypassed and suppressing cooling, and raises it to a high set temperature limited during the stop operation. Drain is often accumulated at the bottom of the oil separator 3 and the bottom of the pipe, and thus the problem described in the problem is likely to occur. By increasing the oil temperature, the temperature of the entire compressor rises, centering on the compressor body 1 and the piping system, and the drainage is gradually evaporated and discharged to the outside through the discharge valve 41 together with the flow of compressed air.

Although it is possible to prevent the occurrence of drainage by raising the oil temperature during normal operation, the oil temperature is set too high unnecessarily for the reasons such as the cooling effect reduction, bearing life shortening, and oil deterioration promotion described above. You cannot do it. In this embodiment, the oil temperature is raised only for a short time immediately before the stop, so the influence on these problems is negligible.

After a sufficient time has passed to remove the water, the water accumulated inside the compressor body 1 and the bottom of the oil separator 43 is removed. The control device 7 instructs the electromagnetic switch 22 to cut off the current, and the electric motor 2 and the compressor body 1 stop. Subsequently, the fan 13 also stops. Further, the air remaining inside is discharged to atmospheric pressure, and the stopping operation is completed.

When the compressor is operated for a long time in a hot and humid environment, the oil separator 3 can be operated only by raising the oil temperature during the stop operation.
It may not be possible to completely remove the drain accumulated at the bottom of the. In that case, it is also possible to remove the drain by raising the oil temperature for a short period of time according to the judgment of the control device 7 every fixed time or each time the drain sensor newly provided in the oil separator 3 detects the drain.

According to this embodiment, the controller 7 and the oil temperature adjusting valve 5 are used in the oil-cooled air compressor which is widely used at present.
The effect of the present invention can be realized and the air compressor in which drainage is unlikely to occur can be realized by only adding one simple function.

The configuration and operation of the air compressor according to the second embodiment of the present invention will be described below with reference to FIG. FIG. 2 is a systematic diagram schematically showing the main air flow of the air compressor of this embodiment. It should be noted that the description of the configuration, operation, and effect overlapping with those of the first embodiment will be omitted.

A compressed air dryer 8 is provided downstream of the compressed air cooler 4. As a type of the compressed air dryer 8, a cooling type,
A membrane type, an adsorption type, etc. are generally used, and any of them does not affect the essence of the present invention. In this embodiment, a cooling type compressed air dryer is adopted. Cooled compressed air dryer 8
The principle of is explained. The compressed air that has been sent is once cooled and has its dew point lowered by heat exchange with the refrigerant cycle provided inside the compressed air dryer 8, and the moisture contained therein is condensed and removed. The compressed air is then reheated to reduce the relative humidity. The condensed water is intermittently discharged by the attached drain trap 82. The operation of the compressed air dryer 8 follows the control device 7.

An electromagnetic three-way valve 8 is provided downstream of the compressed air dryer 8.
The piping is guided to the outside of the air compressor through 1 and the discharge valve 41. The electromagnetic three-way valve 81 normally communicates with the inlet on the upper side and the discharge outlet on the right side in the figure, and is switched only when electric power is sent from the control device 7 and is instructed to communicate with the inlet and the reflux outlet on the left side. have. A return passage 83 is connected to the return outlet of the electromagnetic three-way valve 81, and reaches the suction throttle valve 6 via a silencer 84 on the way. In addition to the function of the first embodiment, the suction throttle valve 6 has a function of communicating the flow from the ring flow passage 83 with the suction passage 61 when the suction from the atmosphere is restricted by the valve plate 62.

The control device 7 has an instruction function for the suction throttle valve 6, an instruction function for the compressed air dryer 8 in addition to the first embodiment.
Equipped with an instruction function for an electromagnetic three-way valve. Further, in place of the stop button, a communication function with the host controller 72 outside the air compressor is provided. It is assumed that the air compressor of this embodiment is incorporated in a part of the plant and is under the instruction of the external upper controller 72 through the communication function.

The air compressor of this embodiment operates as follows.

During steady operation, the compressed air is cooled by the compressed air cooler 4 and then dehumidified by the compressed air dryer 8 and then sent out through the electromagnetic three-way valve 81 and the discharge valve 41. The operation of the compressed air dryer 8 is started prior to the operation of the compressor body 1 according to an instruction from the control device 7, and the compressed air sent first is sufficiently dehumidified.
Further, the electromagnetic three-way valve 81 maintains the communication between the inlet and the discharge outlet, and is closed to the annular flow passage 83.

The stop of the oil-cooled air compressor of the present embodiment is started by the upper control device 72 sending a stop signal and the control device 7 receiving it through the communication function.

The control device 7 first switches the electromagnetic three-way valve 81 so that the inlet and the reflux outlet are in communication with each other, and the compressed air after drying is flown into the circulation passage 83. Almost at the same time, the valve plate 6 of the intake throttle valve 6
2 is moved to the right end to restrict the suction of atmospheric air and introduce the dry air from the circulation channel 83 into the suction channel 61. In this state, the compressor does not suck in the atmosphere, does not output the compressed air to the outside, and only circulates the air remaining inside. Since the internal pressure of the annular flow path 83 is high and the pressure in the suction flow path 61 is almost atmospheric pressure, the direct blowout of the circulating air may cause noise due to a rapid pressure drop. In this embodiment, a silencer 84 is provided near the end of the ring flow passage 83, and the pressure is gradually reduced while passing through the silencer 84, so that noise generation is suppressed.

Before and after the switching of the electromagnetic three-way valve 81, the first
The controller 7 instructs the oil temperature adjusting valve 51 to raise the oil temperature, as in the above embodiment.

As the oil temperature rises, the temperature of the entire compressor rises, centering on the compressor body 1 and the piping system, and the same air continues to circulate and continue to be compressed and dried. Then, the drain accumulated inside the pipe evaporates, and at the same time, the circulating air is gradually dehumidified. As a result, the humidity of the air mixed as bubbles in the oil and the water dissolved in the oil are gradually dehumidified, and the water is removed from the inside of the compressor. The removed water is discharged to the outside from the drain trap 82 of the compressed air dryer 8.

After the time when the inside of the compressor is dried and the dew point thereof is sufficiently lowered, the compressor body 1 and the compressed air dryer 6 are stopped under the instruction of the controller 7. Sufficiently dried air remains inside the compressor body 1 and inside the pipe. Therefore, even if time elapses after the operation is stopped and the temperature of each device decreases, there is a margin up to the dew point of the internal residual air, and dew condensation does not occur. Therefore,
Even after a long time has passed thereafter, internal corrosion and oil deterioration caused by drainage are prevented.

According to this embodiment, since the air circulation flow path is a closed loop, the air can be dried reliably. Further, it is also possible to automatically remove the drain accumulated on the bottom of the oil separator 3. In that case, there is no fear of increasing power consumption during operation or shortening the bearing life or oil life. Further, it is possible to prevent fluid noise caused by air circulation during the stop operation.

When the emergency stop or the stop period is relatively short, it is not always necessary to perform the series of operations associated with the stop, and the operation of the compressor body 1 may simply be stopped.

[0067]

EFFECTS OF THE INVENTION In the air compressor, the water vapor contained in the sucked air is condensed after the compressor is stopped and becomes drain, which corrodes the inside and deteriorates the oil. In the oil-cooled air compressor according to the present invention, drainage does not occur inside the compressor even after operating in a high humidity environment, and rusting, corrosion and oil deterioration can be prevented. Therefore, it is possible to reliably start the air compressor even after the operation is stopped for a long time.

When the second means for solving the problem is implemented, it is possible to dry the air and oil remaining inside the compressor body, the oil separator and the piping system after the stop as much as possible. .

[Brief description of drawings]

FIG. 1 is a system diagram of an air compressor according to a first embodiment of the present invention.

FIG. 2 is a system diagram of an air compressor according to a second embodiment of the present invention.

[Explanation of symbols]

1 ... Compressor body, 3 ... Oil separator, 4 ... Compressed air cooler,
6 ... Suction throttle valve, 11 ... Suction port, 12 ... Discharge port, 13 ...
Oil filler port, 41 ... Discharge valve, 51 ... Oil temperature adjusting valve, 63 ... Air purifier.

Front page continuation (72) Inventor Yukazu Aoki 390 Muramatsu, Shimizu City, Shizuoka Prefecture Hitachi Ltd. Air Conditioning Systems Division

Claims (2)

[Claims] 1. A rotary positive displacement compressor body such as a screw type or a scroll type, an air cleaning means and an intake amount limiting means connected upstream of an inlet of the compressor body, and inside the compressor body. Lubrication means for the compression chamber,
Oil separating means connected to the downstream side of the discharge port of the compressor body, oiling pipe connecting the oil outlet of the oil separating means and the oiling means, oil cooling means in the middle of the oiling pipe, and driving of the compressor body In an oil-cooled air compressor provided with a motor as a means, the oil cooling means has a variable cooling capacity, and when the air compressor is stopped, the oil cooling means is cooled for a certain period of time before the operation is stopped. An oil-cooled air compressor, which has a function of suppressing the capacity and increasing the temperature of circulating oil as compared with that during normal operation. 2. The compressed air drying device according to claim 1, further comprising a compressed air drying device downstream of the air outlet of the oil separating device, branching from a downstream pipe of the compressed air drying device and communicating with a suction side of the compressor body, Provided with an annular flow path having an on-off valve in the middle, when the air compressor is stopped, only for a certain time before the operation stop,
An oil-cooled air compressor having the function of restricting the inflow of air from the outside into the compressor body by the suction amount restriction means at the same time when the on-off valve on the return path is opened.