JP7766567B2 - Liquid-feed screw compressor - Google Patents

Description

The present invention relates to a liquid feed screw compressor.

Some screw compressors are of the liquid-supply type, which supplies liquid into the working chamber during the compression stroke for purposes such as sealing internal gaps between the screw rotor and casing, cooling the compressed gas, and lubricating sliding parts. The liquid used is often lubricating oil, for example. In such oil-supply screw compressors, lubricating oil is mixed into the compressed gas being discharged, so a separator is used to separate the lubricating oil from the compressed gas. The lubricating oil separated by the separator is self-circulated by utilizing the pressure difference between the discharge pressure generated by the compressor itself and the pressure within the working space of the compressor body, and is then supplied back to the compressor body (see, for example, Patent Document 1).

A typical screw compressor is connected to customer equipment that uses compressed air via an air tank and various filters. In such cases, the pressure in the air tank fluctuates depending on the amount of air used, so it is common for the screw compressor to be controlled to switch between loaded and unloaded operation, or to stop, depending on information obtained from a pressure detection device attached to the compressor.

For example, in the case of capacity control for a constant-speed machine in which the rotational speed of the motor that drives the compressor body is constant, the air tank is filled with compressed air and the pressure is maintained based on the pressure at which operation switches from loaded to unloaded (hereinafter referred to as the upper limit pressure) and the pressure at which operation switches from unloaded to loaded (hereinafter referred to as the return pressure).

In the case of capacity control of a variable speed machine, where the rotational speed of the motor that drives the compressor body is variable, the rotational speed of the motor is changed to maintain a preset pressure (hereinafter referred to as the control pressure), and compressed air is filled into the air tank, thereby controlling the pressure to be maintained.

These upper limit pressure, return pressure, control pressure, etc. can be changed from the factory settings (hereinafter referred to as the rated state) to suit the customer's equipment. Therefore, in an oil-lubricated screw compressor that is lubricated by differential pressure, the amount of lubricating oil supplied to the compressor body will vary depending on these settings. In other words, the optimal lubricating position when the customer is using the compressor may be different from the lubricating position set to maximize efficiency in the rated state.

Patent Document 1 discloses a method for an oil-lubricated screw compressor, in which the compressor has a normal oil supply line in the main body and a separate oil supply line equipped with an oil supply valve. The oil supply takes into account rated conditions to reduce power loss and suppress water condensation by taking water condensation into account. Patent Document 1 measures the temperature of the lubricating oil in the oil tank, and if the temperature is higher than a predetermined temperature, oil is supplied from both the oil supply line located in the low-pressure working space of the compressor main body and the oil supply line located in the high-pressure working space via the oil supply valve. On the other hand, if the temperature of the lubricating oil in the oil tank is lower than a predetermined temperature, the oil supply valve is closed and oil is supplied only through the oil supply line located in the low-pressure working space of the compressor main body, thereby reducing power loss and suppressing water condensation by taking water condensation into account when supplying oil.

Patent No. 6843033

However, while Patent Document 1 discloses adjusting the amount of oil supplied to the compressor body under rated conditions to reduce power loss, it does not disclose a method for adjusting the amount of oil supplied to the compressor body that takes into account the customer's usage conditions.

A liquid feed screw compressor according to an aspect of the present invention includes a compressor body accommodating a screw rotor, and a coolant path for separating coolant from a discharge gas discharged from the compressor body and returning the coolant to the compressor body, and the liquid feed screw compressor supplies coolant using a differential pressure between a working space pressure in the compressor body and a coolant pressure in the coolant path. The liquid feed screw compressor has a first supply passage for supplying coolant from the coolant path to a first working space where the working space pressure is a first pressure, a second supply passage for supplying coolant from the coolant path to a second working space where the working space pressure is a second pressure lower than the first pressure, a third supply passage for supplying coolant from the coolant path to a third working space where the working space pressure is higher than the second pressure and lower than the first pressure, a first valve body position for opening the first supply passage and closing the second supply passage, a second valve body position for opening the first supply passage and the second supply passage, and a second valve body position for closing the first supply passage and closing the second supply passage. and a drive mechanism that slides and drives the valve body by a first biasing force in a direction from the first valve body position to the third valve body position due to the elastic force of an elastic body and a second biasing force in a direction from the third valve body position to the first valve body position due to the discharge pressure of the discharge gas, wherein the drive mechanism slides and drives the valve body to the third valve body position when the discharge pressure is equal to or less than a first discharge pressure at which the coolant pressure becomes the first pressure and is greater than a second discharge pressure at which the coolant pressure becomes the second pressure, slides and drives the valve body to the second valve body position when the discharge pressure is greater than the first discharge pressure and is less than a predetermined pressure greater than the first discharge pressure, and slides and drives the valve body to the first valve body position when the discharge pressure is equal to or greater than the predetermined pressure , and the third supply path always supplies coolant regardless of the valve body position of the valve body .
According to another aspect of the present invention, there is provided a liquid feed screw compressor comprising: a compressor body accommodating a screw rotor; and a coolant path for separating coolant from a discharge gas discharged from the compressor body and returning the coolant to the compressor body, the liquid feed screw compressor supplying liquid based on a differential pressure between a working space pressure of the compressor body and a coolant pressure of the coolant path, the liquid feed screw compressor including: a pressure detection device for detecting the pressure of the discharge gas; a first supply passage for supplying coolant from the coolant path to a first working space whose working space pressure is a first pressure; a second supply passage for supplying coolant from the coolant path to a second working space whose working space pressure is a second pressure lower than the first pressure; and a third working space whose working space pressure is higher than the second pressure but lower than the first pressure. The cooling system includes a third supply path that supplies coolant to the coolant path, a valve body that is movable between a first valve body position that opens the first supply path and closes the second supply path and a second valve body position that closes the first supply path and opens the second supply path, a drive device that moves the valve body, and a control device that controls the movement of the valve body by the drive device based on a pressure detection value of the pressure detection device, wherein the control device moves the valve body to the first valve body position when the coolant pressure based on the pressure detection value is greater than the first pressure, and moves the valve body to the second valve body position when the coolant pressure based on the pressure detection value is equal to or less than the first pressure and greater than a second pressure , and the third supply path always supplies coolant regardless of the valve body position of the valve body .

This invention makes it possible to appropriately adjust the amount of oil supplied to the compressor body regardless of the customer's operating pressure, thereby improving the reliability of the compressor body.

FIG. 1 is a diagram showing an example of a system diagram of a liquid feed screw compressor according to the first embodiment. FIG. 2 is a diagram showing a switching device for lubricating oil circulated and supplied to the compressor body. FIG. 3 is a PV diagram illustrating the suction process, compression process, and discharge process of the compressor body. FIG. 4 is an enlarged view of the area in which the switching device of FIG. 2 is provided. FIG. 5 is a diagram showing the slide position of the oil supply switching valve when the discharge pressure is lower than the discharge pressure upper limit value. FIG. 6 is a diagram showing a second embodiment of a liquid-feed screw compressor according to the present invention.

The following describes an embodiment of the present invention with reference to the drawings. The following description and drawings are examples for explaining the present invention, and have been omitted or simplified as appropriate for clarity of explanation. Furthermore, in the following description, identical or similar elements and processes are given the same reference numerals, and duplicate explanations may be omitted. Note that the content described below is merely an example of an embodiment of the present invention, and the present invention is not limited to the embodiment described below, and can be implemented in various other forms.

(First embodiment)
1 is a diagram showing an example of a system diagram of a liquid feed type screw compressor 100 according to a first embodiment. In a liquid feed type screw compressor, water, oil, or the like is used as the liquid to be supplied, but the following description will be given taking as an example a case where lubricating oil is used as the coolant. Note that, hereinafter, the liquid feed type screw compressor 100 will be simply referred to as the compressor 100.

Although not shown, the compressor 100 is equipped with a housing that reduces noise generated by the compressor main body 3. Intake gas (e.g., air) is drawn into the compressor main body 3 through an opening in the housing, passing through an intake filter 1 and an intake throttle valve 2, where it is compressed to a predetermined pressure by the compressor main body 3. The compressor main body 3 is driven to rotate by a main motor 4. Power is supplied to the main motor 4 from a control device 9 mounted on a compressor control board.

The compressed gas (e.g., compressed air) compressed by the compressor main body 3 has the lubricating oil contained in the compressed gas separated in the oil separator 5, and after passing through the pressure regulating check valve 6, aftercooler 7, and a dryer (not shown), the gas is stored in the storage tank 10 installed downstream of the compressor. The pressure value of the compressed gas supplied from the compressor 100 is detected by the pressure detection device 11 and displayed on a display unit (not shown) provided on the control device 9. The compressed gas stored in the storage tank 10 is used as a gas source for the customer's equipment.

The pressure value detected by the pressure detection device 11 is lower than the discharge pressure of the compressor main body 3 due to pressure loss when the compressed gas passes through the oil separator 5 and aftercooler 7. Operation of the screw compressor is controlled based on the pressure value obtained by the pressure detection device 11. In the example shown in Figure 1, the pressure detection device 11 is installed between the aftercooler 7 and the storage tank 10, but the installation location is not limited to this and it can be installed anywhere from the compressor main body 3 to the storage tank 10.

Meanwhile, the lubricating oil separated in the oil separator 5 is sent to the oil cooler 8 via the temperature control valve 12 and cooled. After passing through an oil filter (not shown), the oil is returned to the compressor body 3 via the return pipe 13 of the lubricating oil path and supplied to the rotor, bearings, etc. housed inside the compressor body 3. The temperature control valve 12 controls the amount of lubricating oil that bypasses the oil cooler 8, thereby maintaining a constant temperature for the lubricating oil supplied to the compressor body 3. In this way, the lubricating oil circulates through the lubricating oil path of the compressor 100.

Generally, there are two main types of control methods for the compressor 100. The first is constant speed control, in which the rotational speed of the main motor 4 is kept constant, and the second is variable speed control, in which the rotational speed of the main motor 4 is varied. Constant speed control is a control method that maintains pressure by opening and closing the suction throttle valve 2 so that the pressure measurement value obtained from the pressure detection device 11 falls within a preset upper limit pressure and return pressure range, and by repeating loaded and unloaded operation. On the other hand, variable speed control is a control method that adjusts the rotational speed of the main motor 4 connected to the control device 9 so that the pressure measurement value obtained from the pressure detection device 11 becomes the preset control pressure.

The compressor 100 also has a design point called the rated state. The rated state is a state in which the compressor body 3 discharges a specified amount of gas at a specified pressure. Furthermore, the lubricating oil supply position a in the compressor body 3 for the lubricating oil that returns to the compressor body 3 through the lubricating oil path is predetermined to be the most efficient position in the rated state.

Figure 2 shows a switching device 40 for lubricating oil circulated and supplied to the compressor main body 3. In this embodiment, the switching device 40 is integrally provided in the casing of the compressor main body 3. The compressor 100 of this embodiment is a twin-shaft screw rotor compressor, and a pair of screw rotors consisting of a female rotor 31 with multiple spiral grooves and a male rotor (not shown) are provided within the rotor casing 30. In Figure 2, the pair of screw rotors are arranged along the front-to-back direction of the page. The female rotor 31 is rotatably supported by bearings 33 and 34 provided in the bearing casing 32 and a bearing 35 provided in the rotor casing 30. The female rotor 31 is driven to rotate by the main motor 4 shown in Figure 1.

A suction port 300 is formed at the top of the rotor casing 30 in the illustration, and a discharge port 301 is formed in the bearing casing 32. In the compressor 100, a closed working space is formed by the combination of the meshing female rotor 31 and male rotor and the rotor casing 30, and as the rotor rotates, the working space moves from the suction side (right side in the illustration) to the discharge side (left side in the illustration). During the movement process, there is a period when it is connected only to the suction port 300 (suction process), a period when it is not connected to either the suction port 300 or the discharge port 301 and the working space volume decreases (compression process), and a period when it is connected only to the discharge port 301 (discharge process), and the processes of suction, compression, and discharge of gas such as air are continuously performed.

A portion of the lubricating oil returning through the return pipe 13 shown in Figure 1 is supplied into the rotor casing 30 via the switching device 40. In this embodiment, the switching device 40 is formed integrally with the rotor casing 30, but it may be formed separately. The switching device 40 has a valve body chamber 41. The valve body chamber 41 is provided with an oil supply switching valve 42 that slides left and right within the valve body chamber 41 as shown. The valve body chamber 41 is divided into an elastic body chamber 411, an oil passage chamber 412, and a control chamber 413 by the oil supply switching valve 42. An elastic body 43 such as a spring is disposed in the elastic body chamber 411. Return lubricating oil is supplied to the oil passage chamber 412 via the return pipe 13. Discharge gas from the discharge port 301 is supplied to the control chamber 413 via a piping path 46. In this embodiment, the piping path 46 connects the control chamber 413 to the discharge port 301 of the compressor body 3, but it may be connected anywhere between the compressor body 3 and the pressure regulating check valve 6.

The elastic body chamber 411 is connected to the surrounding outside air, and its internal pressure is maintained at atmospheric pressure. The oil supply switching valve 42 is biased to the right in the figure by the elastic force of the elastic body 43, and to the left in the figure by the pressure of the discharge gas from the control chamber 413. Therefore, the oil supply switching valve 42 slides left and right depending on the magnitude of the discharge gas pressure. Three working space oil supply paths 45a, 45b, and 45c are formed in the valve body chamber 41, which communicate with different working spaces within the rotor casing 30. In order of decreasing working space pressure, the working space oil supply path 45a, working space oil supply path 45b, and working space oil supply path 45c are provided.

Figure 3 is a PV diagram illustrating the suction process, compression process, and discharge process of the compressor main body 3, with the horizontal axis representing the working space volume V and the vertical axis representing the working space pressure P. In Figure 3, curve L (ABC1) represents the PV diagram in the rated state, and curve L (ABD1) represents the PV diagram when the set pressure is lower than the rated state. C1 is the set pressure in the rated state, and the discharge pressure is controlled to be C1. D1 is the set pressure when the set pressure is lower than the rated state. In the following description, the compressor 100 is set between set pressure C1 and set pressure D1. Therefore, pressures C1 and D1 are sometimes referred to as the upper discharge pressure limit C1 and the lower discharge pressure limit D1.

Oil-lubricated screw compressors, which use differential pressure lubrication, utilize the pressure difference between the discharge pressure of the compressor body 3 and the pressure in the working space that supplies oil to the compressor body 3 for self-circulation lubrication. The pressure of the return lubricating oil at the oil supply port a in Figure 1 (hereinafter referred to as the oil supply pressure) decreases due to pressure loss ΔP as the lubricating oil passes through the oil separator 5, oil cooler 8, oil filter (not shown), etc., resulting in pressure values C2 and D2 lower than the discharge pressures C1 and D1. Therefore, when the pressure in the working space to be lubricated is equal to the oil supply pressures C2 and D2, no differential pressure for oil supply occurs, and C2 and D2 represent the oil supply limit pressures. Working space volumes E and F correspond to the oil supply pressures C2 and D2 and indicate the oil supply limit positions. When the set pressure is set to the upper discharge pressure limit C1, the oil supply range of the working space volume at rated operation is section BE. When the set pressure is set to the lower discharge pressure limit D1, the oil supply range is section BF. In the following, the fuel supply pressure C2 at the discharge pressure upper limit C1 may be referred to as the fuel supply pressure upper limit, and the fuel supply pressure D2 at the discharge pressure lower limit D1 may be referred to as the fuel supply pressure lower limit.

However, when the set pressure is set to the lower limit of discharge pressure D1, the oil supply pressure becomes the lower limit of oil supply pressure D2. Therefore, if the oil supply position is set near the oil supply limit position at point E, considering that the highest efficiency is achieved under rated conditions, oil will not be able to be supplied to the working space within section EF, reducing rotor reliability. Conversely, if the oil supply position is set within section BF, considering that the set pressure is lower than the rated condition, the amount of lubricating oil supplied will be excessive under the rated conditions of discharge pressure C1 and oil supply pressure D1, resulting in power loss and reduced performance.

In contrast, this embodiment is provided with a switching device 40 as shown in Figure 2, thereby preventing the occurrence of the above-mentioned problems. Figure 4 is an enlarged view of the area in Figure 2 where the switching device 40 is provided. Note that in Figure 4, the female rotor 31 is shown schematically with the working space instead of the rotor tooth shape shown in Figure 2. The band-shaped areas indicated by reference numerals 311, 312, and 313 represent the working spaces. Working space oil supply paths 45a, 45b, and 45c are connected to different working spaces 313, 312, and 311, respectively. The pressure of working space 311 is P1, and the volume is V1. Similarly, the pressure of working space 312 is P2, the volume is V2, and the pressure of working space 313 is P3, and the volume is V3.

A number of working spaces are formed according to the number of spiral grooves in the screw rotor, and as mentioned above, the working spaces move from the right to the left as the rotor rotates. Figure 4 shows the position of each working space at a given moment, and as the female rotor 31 rotates over time, working spaces 311, 312, and 313 move leftward as shown. In other words, the hatched area marked G indicates gas trapped in the working space, and the working space in which this gas G is trapped moves leftward as the rotor rotates.

When the working space containing gas G moves to the position indicated by the reference symbol 311 where it communicates with the working space oil supply path 45c, the gas G reaches a pressure of P1 and a volume of V1. The term working space 311 refers to the working space that has moved to a position where it communicates with the working space oil supply path 45c. Similarly, when the working space containing gas G moves to a position called working space 312, the gas G reaches a pressure of P2 and a volume of V2, and it communicates with the working space oil supply path 45b. Furthermore, when the working space containing gas G moves to a position called working space 313, the gas G reaches a pressure of P3 and a volume of V3, and it communicates with the working space oil supply path 45a. Points H1, H2, and H3 on the PV diagram shown in Figure 3 correspond to each state.

As shown in Figure 3, the pressure P3 in the working space 313 is greater than the oil supply pressure D2 when the discharge pressure lower limit D1 is reached, and the pressures P1 and P2 in the working spaces 311 and 312 are lower than the oil supply pressure D2. In other words, the working space oil supply paths 45b and 45c are configured to communicate with the working spaces 312 and 311 in the oil supply range BF when the set pressure is set to the discharge pressure lower limit D1 and the oil supply pressure lower limit D2.

When the valve disc diameters of the oil supply switching valve 42 that divide the valve disc chamber 41 are the same, a rightward force FR is applied to the oil supply switching valve 42 of the switching device 40 by the elastic body 43, and a leftward force FL is applied to the oil supply switching valve 42 by the gas pressure in the control chamber 413. The gas pressure in the control chamber 413 is the discharge pressure of the compressor body 3. The oil supply switching valve 42 then slides to a position where the forces FR and FL are balanced. Note that the leftward movement of the oil supply switching valve 42 is limited by the locking portion 44a shown in Figure 4, and the rightward movement is limited by the locking portion 44b shown in Figure 4. Therefore, the range of movement of the oil supply switching valve 42 is from the locking portion 44a to the locking portion 44b. The spring constant of the elastic body 43 is set so that FR(44a) < FL(C1) is satisfied when the fuel supply switching valve 42 is in contact with the locking portion 44a, and FR(44b) > FL(D1) is satisfied when the fuel supply switching valve 42 is in contact with the locking portion 44b. In other words, the spring constant of the elastic body 43 is set so that FL(C1) > FR(44a) > FR(44b) > FL(D1).

Next, the operation of the switching device 40, i.e., the relationship between the gas pressure in the control chamber 413 (i.e., the discharge pressure of the compressor main body 3) and the slide position of the oil supply switching valve 42, will be explained with reference to Figures 3 to 5. Figure 4 shows the slide position of the oil supply switching valve 42 when the discharge pressure of the compressor main body 3 is at the discharge pressure upper limit C1. Figure 5 also shows the slide position of the oil supply switching valve 42 when the discharge pressure is lower than the discharge pressure upper limit C1.

First, when the discharge pressure of the compressor body 3 is at the discharge pressure upper limit C1, compressed gas at pressure C1 is supplied to the control chamber 413, and the oil supply switching valve 42 abuts against the locking portion 44a, as shown in Figure 4. That is, in the rated state, the working space oil supply path 45c is blocked by the oil supply switching valve 42, and the working space oil supply paths 45a and 45b are open. As shown in Figure 3, when the discharge pressure is at the discharge pressure upper limit C1, the pressure in the oil passage chamber 412, i.e., the return lubricant oil supply pressure C2, is in the following order relative to the pressures P1, P2, and P3 in the working spaces 311, 312, and 313: C2 > P3 > P2 > P1. Therefore, the lubricant oil in the oil passage chamber 412 flows into the working spaces 313 and 312 via the working space oil supply paths 45a and 45b.

Next, consider the case where the discharge pressure drops from the discharge pressure upper limit C1 to pressure J1. In this case, as shown in the upper part of Figure 5, the oil supply selector valve 42 is in a state where the working space oil supply passage 45c is about to switch from a closed state to a state where it begins to open, as shown in the upper part of Figure 5. When the discharge pressure is lower than J1 but higher than K1, the working space oil supply passages 45a, 45b, and 45c are open, as shown in the middle part of Figure 5. Then, when the discharge pressure drops further to K1, the working space oil supply passage 45a is closed by the oil supply selector valve 42, and the working space oil supply passages 45b and 45c are open, as shown in the lower part of Figure 5. Although not shown, if the discharge pressure drops further, the oil supply selector valve 42 moves further to the right in the figure while the working space oil supply passages 45b and 45c remain open, and becomes engaged with the engaging portion 44b. Therefore, when the discharge pressure lower limit value D1 becomes the fuel supply pressure lower limit value D2, the fuel supply switching valve 42 is locked by the locking portion 44b.

When the discharge pressure is J1, the oil supply pressure is J2; when the discharge pressure is K1, the oil supply pressure is K2; and when the discharge pressure is lower limit D1, the oil supply pressure is lower limit D2. The pressure in the working space 313 is pressure P3 in state H3 in Figure 3. When C1 ≧ discharge pressure > K1, the oil supply pressure is C2 ≧ oil supply pressure > K2 > P3, ensuring a stable differential pressure (= oil supply pressure - P3) for supplying lubricating oil to the working space 313. On the other hand, when K1 ≧ discharge pressure ≧ D1, the oil supply pressure is K2 ≧ oil supply pressure ≧ D2. However, because the working space oil supply path 45a that supplies lubricating oil to the working space 313 is blocked by the oil supply switching valve 42, compressed gas in the working space 313 will not flow back into the oil passage chamber 412, even if the oil supply pressure falls below the working space 313 pressure P3.

In this embodiment of the compressor 100, which supplies oil using the differential pressure between the working space pressure in the compressor body 3 and the oil supply pressure, the state in which return lubricating oil is supplied from the working space oil supply paths 45a, 45b to the working spaces 313, 312 is configured to achieve an optimal oil supply state under rated conditions (discharge pressure C1). When the discharge pressure is lower than the upper discharge pressure limit C1, the oil supply switching valve 42 is slidably driven in accordance with the discharge pressure to switch the working space to which lubricating oil is supplied between (working spaces 312, 313) and (working spaces 311, 312, 313) and (working spaces 311, 312), as shown in Figure 5, thereby ensuring an appropriate supply of lubricating oil according to the discharge pressure.

For example, consider a configuration that does not include the switching device 40 and supplies lubricating oil to the working spaces 312 and 313 regardless of the magnitude of the discharge pressure. If the user changes the set pressure from the upper discharge pressure limit C1 to the lower discharge pressure limit D1, the oil supply pressure D2 will be lower than the pressure P3 in the working space 313. As a result, a problem occurs in which the lubricating oil cannot be supplied appropriately. On the other hand, in this embodiment, when the discharge pressure reaches the lower discharge pressure limit D1, the switching device 40 closes the working space oil supply path 45a and opens the working space oil supply path 45c, stopping the supply of lubricating oil to the working space 313 and supplying lubricating oil to the new working space 311, which has a lower pressure. As a result, it is possible to maintain an appropriate supply of lubricating oil due to the pressure difference, thereby improving the reliability of the compressor main body 3.

As described above, in the liquid-supply screw compressor of this embodiment, the oil supply switching valve 42 can be slid in accordance with the discharge pressure of the compressor main body 3, regardless of the customer's usage conditions, to adjust the amount of oil supplied to the compressor main body 3. This makes it possible to provide an oil-supply screw compressor with improved reliability for the compressor main body 3.

Second Embodiment
6 is a diagram showing a second embodiment of a liquid feed screw compressor according to the present invention. A compressor body 3B of the second embodiment is compared with the compressor body 3 described above in that the oil supply switching valve 42 in the switching device 40B is driven in a different manner, with the oil supply switching valve 42 being slidably driven by a driving device 18 such as a motor. The driving device 18 is controlled by a control device 9 based on a pressure value relating to the discharge pressure detected by a pressure detection device 11. Other configurations are the same as those of the first embodiment described above.

Similar to the first embodiment described above, the valve body chamber 41 is divided into an elastic body chamber 411B, an oil passage chamber 412, and a control chamber 413B by the oil supply switching valve 42. However, the piping path 46 shown in Figure 2 has been eliminated. The elastic body chamber 411B and the control chamber 413B are connected to the oil passage chamber 412, and the elastic body chamber 411B, the oil passage chamber 412, and the control chamber 413B are all at the same pressure. The rest of the configuration is the same as in the first embodiment, so a description will be omitted. Note that the locking portions 44a and 44b may or may not be provided.

Next, the switching operation by the oil supply switching valve 42 will be described. As mentioned above, the pressure detection device 11 is provided to detect the pressure of the compressed gas discharged from the compressor main body 3B, and detects a pressure value that is lower than the discharge pressure at the discharge port 301 of the compressor main body 3B by the amount of pressure loss in the path up to the pressure detection device 11. The control device 9 calculates the discharge pressure by adding the pressure loss to the detected pressure value, and controls the sliding drive of the oil supply switching valve 42 by the drive device 18 based on the calculated discharge pressure.

When the discharge pressure satisfies the condition "Pressure C1 ≥ (Discharge Pressure) ≥ J1," the control device 9 positions the oil supply switching valve 42 to the position shown in Figure 4. When the discharge pressure is "J1 > (Discharge Pressure) > K1," the control device 9 slides the oil supply switching valve 42 from the position shown in Figure 4 to the right in the figure in response to a pressure drop. In this case, when the discharge pressure = J1, the position is as shown in Figure 4, and when the discharge pressure = K1, the position is as shown in the lower part of Figure 5. Furthermore, when the discharge pressure becomes < K1, the control device 9 slides the oil supply switching valve 42 to a position where the working space oil supply path 45a is completely closed and the working space oil supply path 45c is completely open.

In the second embodiment, too, the oil supply switching valve 42 is moved according to the magnitude of the discharge pressure, switching the working space to which oil is supplied so that the differential pressure for oil supply does not fall below zero. As a result, it is possible to maintain an appropriate state of lubricating oil supply due to the differential pressure, thereby improving the reliability of the compressor main body 3B.

When using the drive device 18 to slide the oil supply switching valve 42, it is also possible to rapidly change the open/closed state of the working space oil supply paths 45a, 45b, 45c in a stepwise manner from (open, open, closed) to (closed, open, open) when the discharge pressure is within the range of "pressure C1 ≧ (discharge pressure) ≧ J1." However, if the state is changed in a stepwise manner, the amount of oil supplied may change suddenly, causing a sudden change in the load. Therefore, it is preferable to gradually change from the (open, open, closed) state to the (closed, open, open) state in accordance with the change in discharge pressure as described above, which can prevent a sudden change in the amount of oil supplied.

As another operating method, the oil supply switching valve 42 may be positioned to a position corresponding to the set pressure based on the set pressure set by the user. The user inputs set pressure information into the control device 9. The relationship between the set pressure in the control device 9 and the position of the oil supply switching valve 42 may be the same as the relationship between the discharge pressure and the slide position described above, or the open/closed states of the working space oil supply paths 45a, 45b, 45c may be (open, open, closed) when the set pressure is "C1 ≧ set pressure ≧ predetermined value," and the open/closed states of the working space oil supply paths 45a, 45b, 45c may be (closed, open, open) when the set pressure is "predetermined value ≧ set pressure ≧ D1."

In the first and second embodiments described above, oil is used as the liquid to be supplied, but other liquids (for example, water) may also be used. Furthermore, while the valve body diameters of the oil supply switching valve 42 are the same on the left and right, they may be configured to have different diameters. In the first and second embodiments, the oil supply path 45b is configured to always communicate with the operating space 312 and supply oil, but this may not be necessary if the amount of oil supplied is sufficient.

In the first and second embodiments described above, return lubricating oil is supplied to the female rotor 31 of a twin-screw compressor having male and female screw rotors via the switching devices 40 and 40B, but the present invention can also be applied to a configuration in which oil is supplied to the male rotor. Furthermore, the present invention is not limited to twin-screw configurations, and can also be applied to liquid-feed screw compressors with a single-screw configuration.

In the first and second embodiments described above, the oil supply switching valve 42 is used to switch between opening and closing the working space oil supply path 45a and the working space oil supply path 45c, which communicate with two working spaces with different pressures. However, it may also be possible to switch between opening and closing three or more working space oil supply paths. Furthermore, while the switching devices 40 and 40B use a switching valve with a sliding valve body, various configurations are possible, not limited to the sliding type.

The first and second embodiments of the present invention described above provide the following advantages:

(C1) As shown in Figures 1 to 5, the liquid feed screw compressor 100 comprises a compressor body 3 housing a screw rotor, and a return pipe 13 that separates lubricating oil from the discharge gas discharged from the compressor body 3 and returns the lubricating oil to the compressor body 3, and supplies oil by the differential pressure between the working space pressure of the compressor body 3 and the oil supply pressure. The liquid feed screw compressor 100 has a working space oil supply path 45a that supplies lubricating oil from the return pipe 13 to the working space 313 where the working space pressure is pressure P3, a working space oil supply path 45c that supplies lubricating oil from the return pipe 13 to the working space 311 where the working space pressure is pressure P1 lower than pressure P3, and a first valve body position shown in the upper part of Figure 5 that opens the working space oil supply path 45a and closes the working space oil supply path 45c, and a second valve body position shown in the middle part of Figure 5 that opens the working space oil supply path 45a and closes the working space oil supply path 45c. The oil supply switching valve 42 is slidable sequentially to a second valve body position that opens the working space oil supply path 45c and a third valve body position shown in the lower part of Figure 5 that closes the working space oil supply path 45a and opens the working space oil supply path 45c, and a valve body chamber 41 that constitutes a drive mechanism that slides and drives the oil supply switching valve 42 by a first biasing force FR in the direction from the first valve body position to the third valve body position due to the elastic force of the elastic body 43 and a second biasing force FL in the direction from the third valve body position to the first valve body position due to the discharge pressure. If the discharge pressure of the discharge gas is equal to or less than the discharge pressure K1 at which the feed oil pressure becomes pressure P3 and is greater than the discharge pressure P0 at which the feed oil pressure becomes pressure P1, the fuel supply switching valve 42 is slidably driven to the third valve body position (see the bottom row of Figure 5); if the discharge pressure is greater than the discharge pressure K1 and less than a predetermined pressure J1 that is greater than the discharge pressure K1, the fuel supply switching valve 42 is slidably driven to the second valve body position (see the middle row of Figure 5); and if the discharge pressure is equal to or greater than the predetermined pressure J1, the fuel supply switching valve 42 is slidably driven to the first valve body position (see the top row of Figure 5).

As described above, in the liquid feed screw compressor 100, which supplies liquid using the pressure difference between the working space pressure in the compressor main body 3 and the oil supply pressure, the oil supply switching valve 42 is slidably driven in accordance with the magnitude of the discharge pressure to switch the working space to which lubricating oil is supplied from (working spaces 312, 313) ←→ (working spaces 311, 312, 313) ←→ (working spaces 311, 312) as shown in Figure 5. This makes it possible to maintain an appropriate supply of lubricating oil using the pressure difference, thereby improving the reliability of the compressor main body 3.

(C2) As shown in Figures 1, 3 to 6, the liquid feed screw compressor 100 includes a compressor main body 3B housing a screw rotor, and a return pipe 13 that separates lubricating oil from the discharge gas discharged from the compressor main body 3B and returns the lubricating oil to the compressor main body 3B, and supplies oil using the differential pressure between the working space pressure of the compressor main body 3B and the oil supply pressure of the return pipe 13. It also includes a pressure detection device 11 that detects the pressure of the discharge gas, a working space oil supply path 45a that supplies lubricating oil from the return pipe 13 to the working space 313 where the working space pressure is pressure P3, a working space oil supply path 45c that supplies lubricating oil from the return pipe 13 to the working space 311 where the working space pressure is pressure P1 lower than pressure P3, a first valve body position that opens the working space oil supply path 45a and closes the working space oil supply path 45c shown in the upper part of Figure 5, and a second valve body position that closes the working space oil supply path 45a and closes the working space oil supply path 45c shown in the lower part of Figure 5. a fuel supply switching valve 42 that can move between a first valve body position that opens valve P1 and a second valve body position that opens valve P2; a drive device 18 that moves the fuel supply switching valve 42; and a control device 9 that controls the movement of the fuel supply switching valve 42 by the drive device 18 based on the pressure detection value of the pressure detection device 11. The control device 9 moves the fuel supply switching valve 42 to the first valve body position when the feed oil pressure based on the pressure detection value is greater than pressure P3, and moves the fuel supply switching valve 42 to the second valve body position when the feed oil pressure based on the pressure detection value is equal to or less than pressure P3 but greater than pressure P1.

As described above, by moving the oil supply switching valve 42 to the first valve element position or the second valve element position depending on the magnitude of the discharge pressure, the working space to which oil is supplied is switched so that the differential pressure for oil supply does not fall below zero. As a result, it is possible to maintain an appropriate state of lubricating oil supply due to the differential pressure, thereby improving the reliability of the compressor main body 3B.

(C3) In (C2) above, as shown in Figures 1, 3 to 6, when the oil supply pressure based on the pressure detection value is greater than pressure P3 and less than a predetermined oil supply pressure J2 greater than pressure P3, the control device 9 moves the oil supply switching valve 42 to the third valve body position (see the middle part of Figure 5) which opens the working space oil supply path 45a and the working space oil supply path 45c. In the configuration of (C2) above, by providing a third valve body position between the first valve body position and the second valve body position which opens the working space oil supply path 45a and the working space oil supply path 45c, it is possible to suppress sudden changes in the amount of lubricating oil supplied.

(C4) In the liquid feed screw compressor described in any one of (C1) to (C3) above, as shown in FIG. 2, a working space oil supply path 45b is further provided to supply lubricating oil from the return pipe 13 to the working space 312 where the working space pressure is greater than pressure P1 and less than pressure P3, and lubricating oil is always supplied via the working space oil supply path 45b regardless of the valve position of the oil supply switching valve 42. By providing the working space oil supply path 45b, it is also possible to accommodate cases where a larger amount of oil is required.

The above-described embodiments and various modifications are merely examples, and the present invention is not limited to these details as long as the features of the invention are not impaired. Furthermore, while various embodiments and modifications have been described above, the present invention is not limited to these details. Other aspects that can be considered within the technical scope of the present invention are also included within the scope of the present invention.

1...suction filter, 2...suction throttle valve, 3, 3B...compressor body, 4...main motor, 5...oil separator, 6...pressure regulating check valve, 7...aftercooler, 8...oil cooler, 9...control device, 10...storage tank, 11...pressure detection device, 12...temperature control valve, 13...return pipe, 18...drive device, 30...rotor casing, 31...female rotor, 32...bearing casing, 33-35...bearings 40, 40B...switching device, 41...valve body chamber, 42...oil supply switching valve, 43...elastic body, 44a, 44b...locking portion, 45a, 45b, 45c...working space oil supply path, 46...piping path, 100...liquid-feed screw compressor, 300...suction port, 301...discharge port, 311-313...working space, 411, 411B...elastic body chamber, 412...oil passage chamber, 413, 413B...control chamber

Claims (3)

A liquid feed screw compressor includes a compressor body containing a screw rotor, and a coolant path that separates coolant from discharge gas discharged from the compressor body and returns the coolant to the compressor body, and supplies liquid using a differential pressure between a working space pressure in the compressor body and a coolant pressure in the coolant path,
a first supply passage for supplying the coolant from the coolant path to a first working space having a working space pressure of a first pressure;
a second supply passage for supplying the coolant from the coolant path to a second working space, the working space pressure of which is a second pressure lower than the first pressure;
a third supply passage that supplies the coolant from the coolant path to a third working space, the working space pressure of which is greater than the second pressure and less than the first pressure;
a valve body that is slidably movable in order between a first valve body position that opens the first supply path and closes the second supply path, a second valve body position that opens the first supply path and the second supply path, and a third valve body position that closes the first supply path and opens the second supply path;
a drive mechanism that slides and drives the valve body by a first biasing force in a direction from the first valve body position to the third valve body position due to an elastic force of an elastic body, and a second biasing force in a direction from the third valve body position to the first valve body position due to a discharge pressure of the discharge gas,
The drive mechanism includes:
When the discharge pressure is equal to or lower than a first discharge pressure at which the cooling liquid pressure becomes the first pressure and is higher than a second discharge pressure at which the cooling liquid pressure becomes the second pressure, the valve body is slidably driven to the third valve body position,
When the discharge pressure is greater than the first discharge pressure and less than a predetermined pressure greater than the first discharge pressure, the valve body is slidably driven to the second valve body position,
When the discharge pressure is equal to or greater than the predetermined pressure, the valve body is slidably driven to the first valve body position ,
The third supply passage constantly supplies the coolant regardless of the position of the valve body of the liquid feed screw compressor. A liquid feed screw compressor includes a compressor body containing a screw rotor, and a coolant path that separates coolant from discharge gas discharged from the compressor body and returns the coolant to the compressor body, and supplies liquid using a differential pressure between a working space pressure in the compressor body and a coolant pressure in the coolant path,
a pressure detection device for detecting the pressure of the discharge gas;
a first supply passage for supplying the coolant from the coolant path to a first working space having a working space pressure of a first pressure;
a second supply passage for supplying the coolant from the coolant path to a second working space, the working space pressure of which is a second pressure lower than the first pressure;
a third supply passage that supplies the coolant from the coolant path to a third working space, the working space pressure of which is greater than the second pressure and less than the first pressure;
a valve body that is movable between a first valve body position that opens the first supply path and closes the second supply path and a second valve body position that closes the first supply path and opens the second supply path;
a drive device that moves the valve body;
a control device that controls movement of the valve element by the drive device based on a pressure detection value of the pressure detection device,
The control device
When the coolant pressure based on the pressure detection value is greater than the first pressure, the valve body is moved to the first valve body position;
When the coolant pressure based on the pressure detection value is equal to or less than the first pressure and is greater than the second pressure, the valve element is moved to the second valve element position ;
The third supply passage constantly supplies the coolant regardless of the position of the valve body of the liquid feed screw compressor. 3. The liquid feed screw compressor according to claim 2,
the control device, when the coolant pressure based on the pressure detection value is higher than the first pressure and lower than a predetermined coolant pressure that is higher than the first pressure, slides the valve element to a third valve element position to open the first supply path and the second supply path.